Abstracts - Symposium F: Mobile Energy


Mobile Energy

November 28 - December 1, 2011

Subodh Mhaisalkar
Energy Research Institute Dept. of Materials Science and Engineering
Nanyang Technological University
Nanyang Ave.
Singapore, Singapore
        Krishna Shenai
Dept. of Electrical Engineering and Computer Science
University of Toledo
Toledo, OH 43606-3390

Gehan Amaratunga
Dept. of Engineering
University of Cambridge
Trumpington St.
Cambridge, CB21PZ United Kingdom
        Arokia Nathan
London Centre for Nanotechnology
University College London
17-19 Gordon St.
London, WC1H 0AH United Kingdom

Proceedings to be published in both print and electronic formats (see MRS Online Proceedings Library at www.mrs.org/opl) as Volume 1388 of the Materials Research Society Symposium Proceedings Series.

* Invited paper

SESSION F1: New Energy Systems I
Chairs: Michael Dudley and Brian Morgan
Monday Morning, November 28, 2011
Back Bay C (Sheraton)

10:00 AM *F1.1
Solid State Paper Battery.Rodrigo F. Martins1,2, Elvira M. Fortunato1,2, José Inácio F. Martins3 and Isabel Maria M. Ferreira1,2; 1Materials science Department, FCTUNL, Caparica, Portugal; 2CEMOP, Uninova, Caparica, Portugal; 3Eng. Quimica, FEUP, Porto, Portugal.

R. Martins, E. Fortunato, B. Brás, J.I. Martins, I. Ferreira The possibility of producing flexible, recyclable, non-toxic, and light weight electronic devices made with and on paper is highly appealing. Furthermore, the low-cost production of these devices renders them economically feasible and, since cellulose is one of the most abundant biopolymers on Earth, they are also ecologically disposable. Powering, in an integrated manner paper electronic devices is a challenging goal. This demand could be fulfilled by producing thin film batteries into the same paper device substrate. By doing so, self-sustained and energetic autonomy is achieved while keeping it mobile, light and flexible. Although cellulose based batteries have been reported, the need of liquid electrolytes, impregnation of salt solutions or CNTs paper functionalization, limits its integration into the substrate of the paper transistors. In this work we produce dry paper batteries where papers is simultaneously used as electrolyte and membrane. Moreover, the paper battery is rechargeable by expositing it to water vapor. Likely in most batteries, in this dry battery the voltage is dependent on the chosen pair of metal electrodes, while the current density depends on the thickness of the paper electrolyte, its porosity, bulk contents, density and composition of fibers. Thereafter, by actuating in any of these characteristics, the output of the device can be optimized to a specific purpose. All solid state batteries with Al/paper/LiAlF4/WO3/V2O5/GZO (zinc oxide doped with gallium oxide) structure show a voltage of 1.4 V. Moreover, paper reached in P2O5, SiO2, Al2O3 and CaO components contain higher concentration of ions (Na+, Cl-, SO4 (-2), PO4 (-3) , and Ca2+) leading to higher current density.

10:30 AM F1.2
A Thin-Film Battery Architecture Generated by Rapid Layer-by-Layer Assembly.Forrest Gittleson, Gustave Macheras and Andre D. Taylor; Chemical and Environmental Engineering, Yale University, New Haven, Connecticut.

Lithium polymer technology represents the current energy density leader in commercially available lithium batteries. Despite the literal and figurative flexibility of this technology and its wide potential for application in cell phones, laptops, and other portable devices, the processes for design, assembly, and packaging of lithium-ion polymer cells are limited. We demonstrate a versatile technique for thin-film assembly that is used to produce layer-by-layer (LbL) films of active lithium battery materials. The spin-spray layer-by-layer (SSLbL) method allows rapid assembly of polymer-composite films with nano-level control and superior uniformity when compared to films produced by the common dip-coating method of LbL assembly. Thin films of several different polyelectrolyte systems with incorporated carbon nanotubes (CNT) were analyzed for charge/discharge capacity, cycling stability, ion conductivity, and electrical conductivity. We found that when the amount of active material (CNT) is controlled in these electrode films, the selection of the polymer matrix, as well as the LbL deposition parameters, has a significant effect on cycle stability and capacity. Tuning the ion conductivity of the polymer matrix by varying layer thickness and polymer blend content is an essential tool in optimizing electrode performance. Polymer electrolyte films were also assembled by the SSLbL method, demonstrating the effect of salt content, polymer choice, and polymer concentration on ion conductivity. These findings showcase a novel method of developing improved solid polymer electrolytes, which have been shown to exhibit a better safety profile than more common polymer-gel electrolytes. Patterning of functional battery materials using the SSLbL technique is also demonstrated and has particular relevance in the design of micro-scale or flexible batteries.

10:45 AM F1.3
Highly Flexible Printed Batteries: Properties, Processing and Performance.Abhinav M. Gaikwad and Daniel Steingart; CUNY Energy Institute, The City College of New York, New York, New York.

Direct write printing technologies can be used to print battery electrodes of desired capacity and form factor. Printed batteries have advantages such as low cost, substrate as packaging, and high material yield. Moreover the battery can be tailored specifically to niche device requirements in ways traditional battery cannot. However, even printed batteries, as they are now are not sufficient for fully flexible electronics. Existing battery electrodes, printed or otherwise, are formulated with stiff, non-compliant components and brittle composites, making these electrodes fundamentally at odds with the mechanical perturbations expected during the use cycle of a flexible device . Thus, a functional, flexible printed battery requires a wholesale reconsideration of the traditional components and optimization methods. To examine this coupling, we have studied the electrochemical and mechanical performance of a printed silver micro-battery in a microfluidic device. We observed that discharge of the battery decreased when the electrode was under a shear stress and different phases of silver oxide had different mechanical strength. We also demonstrated a technique to make highly flexible battery electrodes by embedded the electroactive material inside a mesh support. The mesh absorbed the stress during bending. In present work we extend these methods to secondary battery systems while also linking ink rheology and printing parameters to the final battery. From the rheological property of the ink and the desired electrode dimensions the necessary printing parameters are shown to be predictable through basic continuum fluid dynamics modeling. Beyond the mechanics of deposition, we examine the mechanical-electrochemical behavior of our composite through a combinatorial study of binder, solvent, and active materials. In this we relate the drop in discharge capacity of the battery during flexing with electrode cracking and also present techniques such as EIS to predict the drop in discharge capacity with bending radius.

11:00 AM F1.4
Reverse Electrowetting - A New Approach to High-Power Harvesting of Mechanical Energy.Tom Krupenkin, J. Ashley Taylor and Supone Manakasettharn; University of Wisconsin - Madison, Madison, Wisconsin.

Over the last decade electrical batteries have emerged as a critical bottleneck in portable electronics development. High-power mechanical energy harvesting can potentially provide a valuable alternative to the use of batteries, but until now, its adoption has been hampered by the lack of an efficient mechanical-to-electrical energy conversion technology. In this talk a novel mechanical-to-electrical energy conversion method is discussed. This method is uniquely suited for high-power energy harvesting from a wide variety of previously inaccessible environmental mechanical energy sources, including human locomotion. The method is based on reverse electrowetting (REWOD) - a novel microfluidic phenomenon. Electrical energy generation is achieved through the interaction of arrays of moving microscopic liquid droplets with novel nanometer-thick multilayer dielectric films. Advantages of this process include the production of very high power densities, up to 1 KW per sq. m; the ability to directly utilize a very broad range of mechanical forces and displacements; and the ability to directly output a broad range of currents and voltages, from several volts to tens of volts. We hope that the REWOD-based energy harvesting can provide a novel technology platform for a broad range of new electronic products and enable reduction of cost, pollution, and other problems associated with the wide-spread battery use.

11:15 AM F1.5
Stretchable Electrochemical Capacitors: Power for Stretchable Electronics.Pritesh Hiralal1,2, Darryl Cotton2, Yinglin Liu2, Piers Andrew2 and Gehan A. Amaratunga1; 1Engineering, University of Cambridge, Cambridge, United Kingdom; 2Nokia Research Center, Nokia, Cambridge, United Kingdom.

Stretchable electronics allows a number of uses and tolerances which are not possible with rigid or even flexible electronics (flexible electronics or printed circuit boards). Whereas application of flexible electronics is limited to flat substrates, stretchable electronics can cover moving parts, such as joints in robotic elements, and also curved substrates or unusual materials such as silk, paper, leather etc. However, under stretch conditions, materials face large strains and changes in shape. Components need to be fabricated which can tolerate and function under these conditions. Substrate and interconnects should be made stretchable rather than flexible or rigid. Extensive efforts to advance stretchable electronics, including the integration of active components like diodes, transistors and integrated circuits, as well as sensors and actuators have been made. Here we demonstrate a power source, electrochemical capacitors, constructed onto copper substrates patterned on an elastomer, which withstand stretch ratios up to 100% before failure and deliver capacitances of 150mF/cm2. The fabrication process allows for mass production with roll-to-roll techniques based on printing and laminating. With stretchable interconnects, the electrochemical capacitors allow the construction of self-powered stretchable electronic devices.

11:30 AM *F1.6
Low Voltage and Flexible Electronics Based on Graphene.Manish Chhowalla, Rutgers University, Highland Park, New Jersey.

Graphene and its derivatives possess unique properties that make them attractive for both nano- and macro-electronics. Gaphene holds tremendous promise for large area electronics where the research is motivated by enabling low cost and flexible devices. Flexible displays, radio-frequency identification tags and large-surface sensor networks are examples of some macro-electronic devices that would benefit from the use of high mobility graphene as the channel material. Although the use of lightweight substrates and flexible active materials are useful towards making large area electronics technology portable, it is also necessary to develop devices that provide minimal power dissipation that can be powered by small batteries or by near-field radio-frequency coupling. In this presentation, I will present results of our work demonstrating how graphene can be an extremely useful for low power, flexible electronics. Specifically, I will present our work on developing a simplified photolithographic method, which effectively allows building complex high performance device architectures by means of fast and cost effective sheet-to-sheet solution processing. I will describe the versatility of symmetric reduced graphene source - drain (S-D) electrodes in organic electronics applications. In addition, I will describe discrete OFETs and graphene FETs based on a novel device architecture comprising a self-assembled monolayer (SAM) nanodielectrics. The latter is widely recognized as an elegant approach to reducing the operating voltage and power consumption in electronic devices.

SESSION F2: New Energy Systems II
Chairs: Manish Chhowalla and Rodrigo Martins
Monday Afternoon, November 28, 2011
Back Bay C (Sheraton)

1:30 PM *F2.1
GaN and SiC Materials Technology for Chipscale Mobile Power.Michael Dudley1 and Krishna Shenai2; 1Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York; 2Electrical Engineering and Computer Science Department, University of Toledo, Toledo, Ohio.

Both Silicon Carbide (SiC) and Gallium Nitride (GaN) have been touted to be the industry workhorses for 21st century energy-conversion power electronics, especially important for realizing the “smart grid” of tomorrow that must efficiently and reliably integrate distributed renewable energy sources in a cost-effective manner as well as for the demands of mobile electronic systems. However, their potential at present is significantly hampered because of large densities of material defects (100's to 1,000's per cm2 in SiC and 1,000,000’s per cm2 in GaN) which result in high manufacturing cost, limited voltage and current ratings, significant device de-rating, excessive power loss, and poor reliability. Experimental results accumulated over the past two decades by researchers around the world clearly suggest that, for the case of SiC, non-micropipe defects present in the bulk and epitaxial material cause severe degradation in power electronics device performance and reliability. The same crystal defects also limit the voltage and current ratings of devices, and severely hinder the development of cost-effective, efficient and reliable power electronics systems. Under high electric field and charge injection conditions, these crystal defect sites lead to enhanced generation of local microplasma and cause degradation in the forward current conduction and reverse voltage-blocking characteristics of high-voltage SiC Schottky barrier and PiN junction power diodes. More than a decade ago, a severe degradation in the diode breakdown voltage with increased diode area was demonstrated; this phenomenon was linked to the increased defect density in the SiC material . Early deployment of high-voltage SiC Schottky diodes in computer/telecom power supplies resulted in repeated field-returns. This type of device failure was attributed to dv/dt-related premature breakdown caused by excessive charge generation in the space charge region of a reverse-biased high-voltage SiC Schottky barrier diode with a high density of dislocations. The problem becomes particularly acute with increased dv/dt stress and at elevated temperatures. Subsequently, the basal plane dislocations (whose density has been tied to screw dislocations) were shown to cause forward voltage increase in PiN diodes when stressed at constant current that eventually led to thermal runaway and device destruction. This phenomenon has been attributed to defect movement and generation activated by the energy released from minority carrier recombination in a wide bandgap semiconductor operating under high-level charge injection condition. Similar susceptibility to material defects is expected in GaN power devices. In this paper we assess the influence of defects on the performance of power devices fabricated from both SiC and GaN and discuss potential paths forward.

2:00 PM F2.2
Thin Film Coil Design Consideration for Wireless Power Transfer Flat Panel Display.Jun Yu, Sungsik Lee, Arman Ahnood and Arokia Nathan; London Centre for Nanotechnology, University College London, London, United Kingdom.

Wireless power transfer has been an interesting and challenging topic since early 20th century when engineer Nikola Tesla first proposed this idea. Based on this, some recent research has been carried out on strongly coupled magnetic resonance theory. However, the receiver coils reported were relatively large-sized and non-thin-film based, and as such they are not applicable to displays or small mobile devices. In this work, we present a wireless power receiver system based on thin-film technology, and it could be integrated with thin-film display panel to produce a low cost system and a high throughput. In addition, the thin-film power receiver could be scaled down using metallisation during the process of making display, and suggests a possibility to be used for smaller mobile devices. A thin film based wireless power transfer circuit via strong magnetic resonance coupling is introduced. In particular, wireless power transfer through thin film technology is examined by transmission between an AC power transmitter and two receiver coils. Receiver thin film coils are the vital parts of the transmission, and planar spiral coils are used because of the ease of fabrication and reduction of metal layers. The optimal coil parameters are chosen according to the thin film fabrication limitations in order to obtain the maximum transfer efficiency. We fabricated the first receiver coil on the glass substrate and then deposited dielectric for isolation. The second receiver coil is placed on top of the dielectric layer. For fixed system parameters, the variation of transfer efficiency depending upon transfer distance is analysed. A comparison is made between theoretical and experimental results which show a good agreement. It is suggested that the thin film based wireless power transfer technology can be an integral part of the display system. Design Improvements as well as direction for further investigation will also be discussed.

2:15 PM *F2.3
Power Passives for Chipscale Power Management.Brian Morgan1, Sarah Bedair1, Christopher Meyer1,2, Lin Xue2, Christopher Dougherty2, Rizwan Bashirullah2 and David Arnold2; 1Army Research Lab, Adelphi, Maryland; 2Univ. of Florida, Gainesville, Florida.

We present research focused on developing mm-scale power converters for power management of emerging microsystem applications, such as sensor nodes or micro-autonomous robotics. High frequency (~100MHz) CMOS boost converter architectures have been developed to drive the needs for inductance, capacitance and efficiency of miniature power passives, targeting the <1W power level. Therefore, this talk will highlight progress in high voltage CMOS converter topologies, high performance air-core MEMS inductors, and novel work on nanoparticle-based passives (capacitors & inductors) using a fluidic self assembly delivery system.

SESSION F3: Mobile Systems and Solid State Ionics
Chairs: Manish Chhowalla and Michael Dudley
Monday Afternoon, November 28, 2011
Back Bay C (Sheraton)

3:15 PM *F3.1
Towards Self-Sustaining Energy Usage for Mobile Devices.Arman Ahnood1, Jacqueline Edge2, Arokia Nathan1, Shahin Ashtiani5, Arun Madan4, Pritesh Hiralal3 and Gehan Amaratunga3; 1London Center for Nanotechnology, University College London, London, United Kingdom; 2Dept of Physics and Astronomy, University College London, London, United Kingdom; 3Electrical and Computer Engineering, University of Cambridge, Cambridge, United Kingdom; 4MVSystems Inc., Golden, Colorado; 5School of Electrical & Computer Engineering, University of Tehran, Tehran, Iran, Islamic Republic of.

Long battery life is an important requirement for mobile devices and has often been satisfied by either improving energy efficiency of the device or increasing its battery’s energy density. An alternative to these approaches is for handheld devices to recycle some of their own energy consumed or harvest part of their energy from ambient sources. Displays are ideal for implentation of this approach due to their relatively high power consumption, large external surface area and the use of transparent substrates (glass or plastic). This talk discusses the design and implementation of a mobile energy system in mobile systems. As an example we conceder devices with flat panel displays including AMOLD and LCD. It starts by considering the key requirements for successful integration of photovoltaic energy system. The gain from energy recycling and harvesting from a display module are analysed and discussed. In addition to electrical energy generation, mobile energy systems store the generated energy in a suitable energy storage device and therefore require charging circuits. Various options for charging circuits and energy storage devices are reviewed, and a suitable circuit based on thin film transistors (TFTs) is discussed. Based on this an energy harvesting system, using amorphous silicon (a-Si:H) photovoltaic array, a-Si:H TFT charging circuit and thin film supercapacitor is proposed and fabricated. The general system performance is analysed and potential improvement methods are identified. The application of thin film technology, and low fabrication temperature opens the possibility of seamlessly integrating the energy system with display panels on rigid or flexible substrates.

3:45 PM *F3.2
Polymeric Membranes for Lithium Batteries.Stefan Manuel and N. Angulakshmi; Electrochemical Power Systems Division, Central Electrochemical Research Institute (CSIR-CECRI), Karaikudi, India.

Energy consumption relying on fossil fuels is forecasted to cause a severe problem in the world economics and ecology mainly because of depleting resources and increasing environmental concerns. Developing alternative energy storage or conversion devices with high power and energy densities is under serious consideration as a viable alternative. Lithium-ion batteries, fuel cells, and supercapacitors (SCs) are considered strongly as major contenders for power source applications. The state-of -art employ different cell components and chemistries. The commercialized lithium -ion batteries use a graphite carbon anode, a lithium intercalated transition metal oxide cathode separated by a liquid electrolyte comprised of lithium salts dissolved in organic solvents. On the other hand, lithium polymer battery has several advantages over its liquid counter part which include no- leakage of electrolyte, high energy density and flexible geometry. The development of polymeric membranes for lithium batteries has gone through three stages namely (i) dry solid (ii) gel polymer and (iii) nanocomposite polymer electrolytes. The present talk focuses the development of novel nanocomposite polymer electrolytes (NCPE) with different lithium salts and inert fillers and the cycling profile of Li/NCPE/LiFePO4 cells at 70°C. The significance of ionic liquid based gel polymer electrolytes will be discussed. The polymeric membranes prepared by electrospinning for applications in lithium batteries will also be presented. References 1. M. Armand, J.-M. Tarascon, Nature 451 (2008) 652-657. 2. A. Manuel Stephan, T.P.Kumar, N. Angulakshmi, J. Phys.Chem. B. 113 (2009) 1962-1972. 3. A. Manuel Stephan Eur.Polym.J, 42 (2006) 21-42.

4:15 PM F3.3
Chemical, Thermal and Interfacial Characterization of B2O3 Doped Glass Ceramic Electrolytes for Rechargeable Lithium Batteries.Nutan Gupta, Rachid Yazami and Madhavi Srinivasan; School of Material Science and Engineering, Nanyang Technological University, Nanyang Avenue, Jurong West-05, Singapore, Singapore.

Abstract The state-of-art Li-metal batteries using organic liquid electrolytes are plagued with issues associated with their limiting performance, thermal instability, flammability and corrosiveness with lithium metal. The phosphate-based glass ceramic electrolytes provide protective layers in the solid state that conduct lithium ions at ambient temperature but are electronically insulating has been proposed as a possible solution in future rechargeable lithium batteries. This work focuses on the production of glass and glass-ceramics of the LiO-Al2O3-SiO2-TiO2-P2O5 (LASTP) system obtained by melting and quenching followed by crystallization of a precursor glass, which shows a tendency for homogeneous nucleation. The electrochemical stability of the prepared glass-ceramic phases against lithium was studied in Li-Li symmetric cells with well-sintered LASTP pellets with B2O3 (1-10 mol.%) as electrolyte. The symmetric cell was heated at 60°C for 4 hours to improve the interfacial contact between lithium and solid electrolyte and after heating, the contact resistance was optimized for the symmetric cell study. Additional confirmative insight on the electrochemical stability of the phases was obtained from Li/liquid electrolyte/LASTP/Li cells. These results are necessary for understanding of origins of interfacial resistance in Lithium batteries and suggest pathways for material optimization. Keywords: Glass ceramic; rechargeable; lithium batteries; solid electrolytes; symmetric cell. *Email: Madhavi@ntu.edu.sg

SESSION F4: Poster Session: Energy Conversion and Storage for Mobile Energy Systems I
Chairs: Subodh Mhaisalkar and Denis Yu
Monday Evening, November 28, 2011
8:00 PM
Exhibition Hall D (Hynes)

Finite Element Simulations on Scaling Effects of Thermoelectric Generators.Nicholas E. Williams, Ali Gokirmak and Helena Silva; Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut.

In order for extensive adoption of thermoelectric generators (TEGs) into power generation, considerable improvements must be realized in the efficiency of thermal-electric direct energy conversion. Small-scale structures have been proposed for potential improvements in efficiency. In this study, two dimensional finite element simulations using Synposys Sentaurus TCAD software are employed for silicon based TEGs to examine the effects of scaling from mm to sub-µm range on device performance in a wide temperature range. <p>For these simulations, the geometry is composed of a single TEG that is sandwiched between two, 170 µm thick thermal contacts emulating the sheet metal encasing. Simulated TEG structures consist of a p-type and a n-type crystalline silicon columns which are electrically connected by a top copper contact where each leg has a separate bottom metal contact. The TEG is electrically isolated from the 170 µm thermal contacts by a 20 nm thick layer of SiO2. The n and p-legs are completely encapsulated by SiO2. Temperature dependent material parameters for electrical resistivity, thermal conductivity, Seebeck coefficient, and heat capacity are included in the model. <p>A heat source is applied to the top surface of the top metal contact while the bottom of the bottom contact is held at 300 K. Short circuit current, open circuit voltage, resistance, and power density are extracted for temperature gradients from 50 to 1350 K. Simulation results show that the optimum column height scales down for higher temperature gradients.

Electrical Characterisation, Analysis and Peformance Evaluation of Flexible Supercapacitor for Wearable Sensing Devices.Yen Kheng Tan, Wee Song Koh and Tsyh Ying Grace Wee; Energy Research Institute @ NTU, Singapore, Singapore.

During the past few years, impressive examples of wearable computing have been demonstrated within the scientific community and also developed into commercial products. These wearable devices impose major challenges to microelectronic packaging and power supply technologies, not only their systems have to become much smaller in size, packages must also become mechanically flexible and water-resistant (washable computing) and they have to be fabricated at low cost. Energy storage, as a significant source of size, weight and inconvenience to present-day systems, has provoked recent efforts to focus on the development of charge storage devices that possess large energy and power densities, i.e. carbon nanotube (CNT) supercapacitors, which allow better performance for more demanding applications. Numerous scientific research works have been hovering around the charge storage research, devoting effort towards improving on the performance of supercapacitors, however mainly from the material science perspective. In this paper, another perspective, from the electrical aspect, is employed to characterise, analyse and evaluate the performance a flexible supercapacitor. Experimental results obtained from the electrical approach are compared with those results obtained from the material science perspective to achieve a better electrochemical understanding of the supercapacitor. With this electrochemical understanding, the supercapacitor is designed to power a wearable sensing device for use in a body area network (BAN) application. For a wearable device, burst power is required for its onboard communication module to send data back to its base station, hence supercapacitor is much preferred over battery. Having said that, the design of the supercapacior, being stacked in parallel or series in a single package, is discussed and evaluated in this paper.

Abstract Withdrawn

Current Collector Design for High Temperature Batteries.Brian Oldfield, Paul Burke, Brice Chung and Donald Sadoway; Materials Science and Engineering, MIT, Cambridge, Massachusetts.

In high temperature battery systems with liquid components, the design of current collectors which are in contact with liquids is important to optimize performance. Key aspects of the design are chemical compatibility of the current collector in the battery, and wettability of the liquid components on the collector. The present work will focus on testing candidate collector materials and assess their suitability in different battery chemistries. Chemical compatibility will be characterized using optical microscopy and SEM/EDS . Measurements of the contact angle of the liquid on the candidate materials will be completed to characterize wetting properties.

P-Type a-SiC:H for a-Si:H p-i-n Solar Cells Deposited at 150°C.Arman Ahnood1, Arokia Nathan1, Jian Hu2 and Arun Madan2; 1London Center for Nanotechnology, University College London, London, United Kingdom; 2MVSystems Inc., Golden, Colorado.

Boron doped amorphous silicon carbide (a-SiC:H) has been widely used as the p-type window layer in the superstrate p-i-n amorphous silicon (a-Si:H) solar cell structure. Two of the most critical requirements of this material are wide a optical bandgap and high electrical conductivity. The former helps in improving the efficiency of the solar cell by minimising optical absorption in the p-layer. A high electrical conductivity implies low activation energy of holes and high density of free carriers, which in turn affects the solar cell efficiency by influencing its open circuit voltage (VOC). Much of the research in p-type a-SiC:H has focused on its optimisation for the conventional solar cell which is typically deposited at 250°C-350°C temperatures. At this temperature range minimising the dopant diffusion into the i-layer is critical in fabrication of high performance devices. This serves to limit the boron content in the p-layer. However, a low boron content in the p-layer inevitably requires a thicker p-layer (typically ~20nm) in order to avoid the p-layer depletion and to maximise VOC of the device. Furthermore given that the conductivity of p-type a-SiC:H drops substantially with increase in the bandgap, a lower boron content limits the ability to maximise the bandgap of a-SiC:H.

Abstract Withdrawn

Can Vanadium Be Substituted into LiFePO4?Fredrick Omenya1, Natasha Chernova1, Shailesh Upreti1, Peter Y. Zavalij2, Kyung-Wan Nam3, Xiao-Qing Yang3 and Stanley M. Whittingham1; 1Chemistry and Materials, Binghamton University, Vestal, New York; 2Chemistry and Biochemistry, University of Maryland, College Park, Maryland; 3Chemistry, Brookhaven National Laboratory, Upton, New York.

It has become generally accepted that the use of vanadium in the synthesis of LiFePO4 either as a dopant or as a composite compound results into improved rate capabilities. However, there has been a controversy on whether vanadium can be substituted into LiFePO4 and, if substituted, which site it will occupy, and/or whether it forms a separate phase. In this work we show that up to at least 10 mol. % of vanadium can be incorporated at the iron site of the LiFePO4 structure without any observable impurity using solid-state synthesis at 550 °C. High-resolution synchrotron X-ray diffraction (XRD) data indicates a single phase for vanadium content from 0 to 10 mol. %. The a and b lattice parameters and the unit cell volume decrease linearly with increase in the vanadium content, while the c lattice parameter slightly increases. Such linear relation is a strong indication for vanadium ion incorporation into the olivine structure. X-ray absorption spectroscopy indicates V3+ oxidation state, also confirmed by the magnetic properties. Rietveld refinement of the site occupancies suggests LiFe1-3y/2VyPO4 solid solution, where the V3+ charge is compensated by vacancies on the Fe site. The electrochemical performance is improved by the vanadium substitution, especially at high rates. Raising the sintering temperature to 700 °C leads to the separation of an olivine phase and a Li3V2(PO4)3 -type phase. The phase separation is observed for vanadium content as low as 5 mol. % as evidenced from the XRD data and CV curve which reveals redox peaks at 3.6, 3.7 and 4.1 V typical of Li3V2(PO4)3. The 700 °C synthesis also results in the formation of the Fe2P phase, as evidenced by the magnetic properties. Coexistence of Li3V2(PO4)3 and formation of Fe2P phases enhances both the electrochemical capacity and rate capability. Thus, we have shown that the solubility of vanadium in LiFePO4 is a function of temperature, which explains the contradictory results reported in the literature. This work was supported as part of NECCES (the Northeastern Center for Chemical Energy Storage), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001294.

Continuous Flame Aerosol Synthesis of Carbon-Coated Nano-LiFePO4 for Li-Ion Batteries.Oliver Waser1, Robert Buchel1, Andreas Hintennach2, Petr Novak2 and Sotiris E. Pratsinis1; 1Particle Technology Laboratory, Department of Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland; 2Electrochemistry Laboratory, Department of General Energy, Paul Scherrer Institut, Villigen, Switzerland.

Non-toxic and safe energy storage devices are essential for use in todays electronics and increasingly in (hybrid) electric vehicles. LiFePO4 is promising as cathode material for its low cost, high stability and environmental friendliness. The low Li-ion and electronic conductivity of LiFePO4, however, requires the short diffusion paths of nanosized particles and an electrically conductive matrix. A core-shell structure of LiFePO4 coated with a carbon black shell offers an attractive electrical “wiring” of the electrochemically active LiFePO4 nanoparticles. Flame aerosol technology is an effective route for scalable synthesis of either cathode or anode materials [1] and is capable to produce, at least, up to 700 g/h of carbon-coated ceramic nanoparticles [2]. Core-shell, nanosized LiFePO4-carbon particles were made in one step by scalable flame aerosol technology in an enclosed unit. So core LiFePO4 particles were made by flame spray pyrolysis (FSP) and coated in-situ downstream by auto thermal carbonization (pyrolysis) of swirl-fed C2H2 in an O2-controlled atmosphere. The formation of acetylene carbon black (ACB) shell was investigated as a function of the process fuel-oxidant equivalence ratio (EQR). The core-shell morphology was obtained at slightly fuel-rich conditions (1.0 < EQR < 1.07) whereas segregated ACB and LiFePO4 particles were formed. Post-annealing of core-shell particles in reducing environment (5 vol% H2 in argon) at 700 °C for up to 4 hours established phase pure, monocrystalline LiFePO4 with a crystal size of 65 nm and 30 wt% ACB content. Uncoated LiFePO4 or segregated LiFePO4-ACB grew to 250 nm at these conditions. Annealing at 800 °C induced carbothermal reduction of LiFePO4 to Fe2P by ACB shell consumption that resulted in cavities between carbon shell and core LiFePO4 and even slight LiFePO4 crystal growth but better electrochemical performance. The present carbon-coated LiFePO4 showed superior cycle stability and higher rate capability than the benchmark, commercially available LiFePO4 [3]. [1] Ernst, F.O., Kammler, H.K., Rössler, A., Pratsinis, S.E., Stark, W.J., Ufheil, J., & Novák, P. (2007). Mater. Chem. Phys., 101, 372-378. [2] Kammler, H., Müller, R., Senn, O., & Pratsinis, S. E. (2001). AIChE J., 47, 1533-1543. [3] Waser, O., Büchel, R., Hintennach, A., Novák, P., & Pratsinis, S. E. (2011). J. Aerosol Sci., in press

Large Scale Synthesis and Characterization of Micro/Nano-Scale LiFePO4/C Composite Cathode Materials.Xiangcheng Sun1, Kai Sun2 and Bo Cui1; 1Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada; 2Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan.

Since the pioneering work of Goodenough in 1997 [1], because of its suitable operating voltage and high theoretical capacity (170 mAh/g) as well as its low cost, non-toxicity and safety properties, the olivine lithium iron phosphate (LiFePO4) has particularly become an attractive cathode material [2] for the design and fabrication of higher power lithium-ion batteries that especially used for hybrid and pure electric vehicles. In this study, the carbon-coated LiFePO4/C composite cathode materials were scale-up synthesized by larger volume solid state reaction method using the precursors of FeSO4, NH4H2PO4, Li2CO3 and conducting carbon source. The surface morphology and phase structures of those LiFePO4/C composite powders are fully investigated by the combinational techniques including scanning and transmission electron microscopy (SEM, HR-TEM), and electron diffraction (SAED), and high angle annular dark field (STEM-HAADF) image analysis on the nanometer scale. The homogenous features of graphitic carbon-coating layer are clearly revealed by X-ray photoelectron spectroscopy (XPS), it indicated that the as-synthesized composite powders had a carbon layer of about 8-10 nm. The valence state of Fe ions was also detected by high-resolution electron energy-loss spectroscopy (STEM-EELS). The revealed features of graphitic carbon-coating on those composite surfaces allows improving the electronic conductivity and reducing the diffusion path of the lithium ions, as evidenced from electrochemical test of charge-discharge cycling in LiFePO4/C composite samples. The LiFePO4/C composites delivered an initial discharge capacity of 157 mAh/g at a 0.2 C rate as the cathode. It also showed an excellent capacity retention ratio of 100% after the 50th charging/discharging cycle. References: [1] A. K. Padhi, K. S. Nanjundaswamy and J. B. Goodenough, Journal of Electrochemical Society 144, 1188 (1997) [2] B. Kang and G. Ceder, Nature, 458, 190 (2009) Acknowledgments: Research work support from the NSERC Postgraduate Scholarship (PGS) is greatly appreciated by Xiangcheng Sun

Optimization of the Cathode Material Li2MP2O7.Hui Zhou1, Shailesh Upreti1, Natasha A. Chernova1, M. Stanley Whittingham1 and Archit Lal2; 1Chemistry and Materials, State University of New York at Binghamton, Binghamton, New York; 2Primet Precision Materials Inc., Ithaca, New York.

We have recently reported a novel solid solution of Li2FeyMn1-yP2O7 (0 = y = 1) synthesized through a “wet” method. The initial electrochemical tests indicate that lithium can be reversibly inserted and extracted, and the compounds can work as cathode materials for lithium-ion batteries, especially the Li2FeP2O7. However, poor electronic conductivity and large particle size resulted in incomplete electrochemical performance of our initial samples. Here we report the results of the optimization of these series by nanosizing, carbon-coating and substitution. For the carbon-coated nano Li2FeP2O7 the initial charge capacity increases from 90 mAh/g to 155 mAh/g, and an improvement in the rate capability as well as cyclability is observed. Reversible capacity exceeding the theoretical for one lithium, 110 mAh/g, may point towards the oxidation of Fe beyond 3+. Changes in the structure and oxidation state of transition metals during lithium insertion/extraction are being studied by ex-situ and in-situ x-ray diffraction (XRD) and absorption (XAS). Ex-situ XRD with the GITT technique and in-situ XRD data are consistent with each other and reveal that the basic structural framework remains intact as we charge and discharge the material electrochemically. The intensity variations observed in x-ray reflections are currently understood in terms of iron migration between different sites of the crystal lattice during Li extraction/reinsertion. Specially designed cathode is being studied under synchrotron XRD to investigate this electrochemically driven topotactic, yet reversible, reaction. Detailed structural refinements, local structures from XAS and magnetic susceptibility data at different states of charge and discharge will be discussed. This work is supported by the US Department of Energy, Office of FreedomCAR and Fuel Partnership through the BATT program at Lawrence Berkeley National Laboratory.

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New Li2MnSiO4/C Nanocomposite Cathode Materials. Shu Zhang and Xiangwu Zhang; Fiber and Polymer Science, College of Textiles, North Carolina State University, Raleigh, North Carolina.

The ever-growing demand for compact, high-energy density electrochemical energy storage has led to the development of lithium-ion batteries. In order to meet high performance target, a new electrode materials- Li2MnSiO4 for lithium-ion battery has been studied. Theoretically, the exchange of two electros per reaction is available for this material with a theoretical capacity of 333 mAh/g, which is higher than the capacities of most current cathode materials. However, due to the intrinsic low electronic conductivity of Li2MnSiO4, less than one electron transfer has been practically realized. To overcome the major drawback of Li2MnSiO4, a novel approach to fabricate Li2MnSiO4/C nanocomposite was developed to improve the electronic conductivity by electrospinning and heat treatment. A precursor solution containing PAN as the carbon source, and lithium acetate, manganese acetate and tetraethyl orthosilicate as the Li2MnSiO4 precursor was first electrospun into nanofibers. Then, the fibrous mat was heat treated in a furnace at 700°C. Both Li2MnSiO4 and carbon nanofibers were formed simultaneously in this step. Cells using this material as the cathode showed a reversible discharge capacity of around 220 mAh/g, indicating more than one electron transfer reaction. However, more study is required to improve the cycling performance of this material.

LiCoO2 Core-Li3VO4 Shell Structure with Enhanced Cyclability as Cathode Materials in Li-Ion Batteries. Xiong Pu, Liang Yin and Choongho Yu; Department of Mechanical Engineering, Texas A & M University, College Station, Texas.

Core-shell structures are effective in improving the electrochemical properties of active electrode materials in Li-ion batteries. The surface modification may overcome some disadvantages of core materials, such as poor electrical conductivity (e.g. LiFePO4 with carbon shell), poor cyclability (e.g. Si with carbon shell) and structure instability (e.g. LiCoO2 with Al2O3 shell). LiCoO2 possesses a theoretical capacity as high as 275 mAh/g, but a half of its theoretical capacity is utilized because of the structural instability and dissolution of Co4+ that often happen when it is overcharged at a voltage higher than 4.2 V. Appropriate surface modifications with core-shell structures, however, may solve this problem and improve both capacity and cyclability of LiCoO2. Here, a novel LiCoO2-Li3VO4 core-shell nanostructure is presented. LiCoO2 nanoparticles have been synthesized by a hydrothermal method. Crystalline lithium vanadate (Li3VO4) coatings with different weight percentages on the LiCoO2 nanoparticles have been prepared by annealing them with NH4VO3. When charging/discharging between 2.4 and 4.4 V, both capacity and capacity retention after 50 cycles of the coated samples was improved as compared to those of pristine LiCoO2 nanoparticles. This is because that coating layer of crystalline Li3VO4 not only suppresses the reaction between LiCoO2 with an electrolyte but also contributes to energy storage in the charging/discharging window. This work suggests a novel promising approach compared to other core-shell structures with inactive materials (e.g., Al2O3) for the shell.

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Solvothermal Synthesis of LiMn2O4 Nanoparticles with Extremely High Rate Capability.Sanghan Lee and Jaephil Cho; UNIST, Ulsan, Korea, Republic of.

Rechargeable lithium-ion batteries have been intensively studied and have gained commercial success in portable electronic products segments such as cellular phones and laptop computers due to their high energy density and long cycle life. However, in terms of applying the technologies in electric vehicles (EVs) and hybrid electric vehicles (HEVs), we still suffer from the limitation of high-power requirements. LiMn2O4 spinel with a 3-demensional crystal structure has received a great deal of attention as the most promising cathode material for Li-ion battery in EVs and HEVs because of not only high rate performance but also abundance, low manufacturing cost, low toxicity and excellent voltage profile characteristics compare to layered LiCoO2 cathode materials. In the past decade, synthesis of nanostructured spinel LiMn2O4 with various morphologies have been intensively studied to enhance the rate capability. In this work, we found another simple method to synthesis of spinel Li1+xMn2-xO4 nanoparticles. 20nm-sized Li1+xMn2-xO4 particles were successfully synthesized via one-pot solvothermal method at 110'C for 12 hours. Despite soft synthetic conditions, this product exhibited the high crystallinity and very narrow size-distribution without any impurities. Galvanostatic test showed that the first discharge capacity of ~110mAh/g with the coulombic of >96% and extremely high rate discharge capability with 88% retention at 100C-rate, compare to initial discharge capacity at 1C, in the potential range of 4.3-3.0V. High rate charge capability also improved as 81% retention at 30C-rate and 73% retention at 50C-rate. Surprisingly, Li1+xMn2-xO4 - NPs were fully charged in 2 minutes by CC-CV(Constant Current, Constant Voltage) mode.

Next Generation Carbon Nanotube Lithium Ion Microbattery.Ankita Shah1, Cihan Yilmaz1, Christopher Allen2, Matthew Trahan2, Nagappan Ramaswamy2, Sivasubramanian Somu1, K. M. Abraham2, Sanjeev Mukerjee2 and Ahmed Busnaina1; 1Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts; 2Chemistry, Northeastern University, Boston, Massachusetts.

We combine the advantages of nanomaterials and directed assembly to develop a stacked two-dimensional lithium ion battery electrode. The stacked electrode architecture allows for an increase in power density by two orders of magnitude. In this structure, alternating layers of carbon nanotubes and active lithium nanoparticles are stacked together. The carbon nanotube layers create a highly porous and conductive scaffold to enhance electronic conduction and lithium ion diffusion through the layers of active electrode nanoparticles. The alternating layers of carbon nanotubes and active electrode nanoparticles are constructed via directed assembly, allowing for precise placement of nanomaterials at each layer. Directed assembly is a high-rate process that is conducted at room temperature and pressure. This technique ensures that each active lithium nanoparticle makes contact with the conductive carbon nanotube scaffold, minimizing diffusion limited losses. The cell voltage can also be tailored to a specific application as directed assembly can be implemented with any active lithium nanoparticles and battery capacity can be adjusted by controlling the number of layers that can be stacked. Lithium manganese oxide nanoparticles (LiMn2O4, 500nm) were used as a model active material while multi-walled carbon nanotubes (MWNT) were used as the scaffold. Governing parameters of the directed assembly process were studied to achieve uniform assembly of LiMn2O4 nanoparticles on MWNT. Potentiostatic and galvanostatic measurements were carried out on these assembled electrodes in a half cell configuration. We observed that the half cell capacity increased by a factor of four when the number of coupled layers (MWNT and LiMn2O4) was increased by one. The half cell also remained stable over 50 cycles when the experiment was stopped. Increasing the number of layers and the density of assembled LiMn2O4 nanoparticles within the same layer to further increase the capacity is ongoing. Galvanostatic cycling at high battery cycling rates (C-rates) will be performed over many cycles to determine the effect of multi-layers on the power density and cycle life of the cell.

Density Functional Theory Studies of Point Defects in LiNiO2.Hungru Chen, Colin L. Freeman, John H. Harding and Anthony R. West; Materials Science and Engineering, University of Sheffield, Sheffield, United Kingdom.

LiNiO2 is a potential material for rechargeable lithium ion batteries. Despite the enormous amount of effort directed towards this compound, the ground state properties and local structure of LiNiO2 remain unclear. It is well known that truly stoichiometric LiNiO2 has not yet been synthesised. There is always an excess amount of nickel ions sitting at Lithium sites, which gives the formula [Li1-xNix]NiO2 where x is usually greater than 0.02. In addition, this compound has been found to lose up to 5% oxygen under certain synthesis conditions. However it is not clear what defects exist to accommodate the oxygen non-stoichiometry. From our previous study on LiNiO2, we have found two possible ground states very close in lattice energy (<3meV/f.u.) with space groups P21/c and P2/c. In one of the cells (the one with P2/c symmetry), the charge disproportionation 2Ni3+ ? Ni2++Ni4+ occurs and in the other cell all nickel ions undergo Jahn-Teller distortion to lift the orbital degeneracy. In this study, based on the two possible ground state unit cells P21/c and P2/c, various point defects (eg. Li-Ni swap, Ni substitution on Li site, O vacancy) in LiNiO2 are investigated by performing density functional theory calculations using the VASP code. The DFT+U method is adopted with UNi=6.5 and UCo=4.9 in order to obtain better behaviour of transition metal oxides. The same types of defects in LiCoO2 and NaNiO2 have also been calculated to compare and contrast the behaviour of these three compounds. Table 1 shows the calculated defect formation energies. The Li-Ni swap is found to be the most likely defect in LiNiO2 followed by a defect where one extra Ni ion replaces one Li ion and the Ni charge states change to ensure overall neutrality. This result is consistent with the experimental difficulty to synthesise stoichiometric LiNiO2. The oxygen vacancy is the least likely point defect and the defect formation energy is ~0.6 eV higher than the Li-Ni swap defect which is not prohibitively high. Conversely, it is shown that the formation energy of an oxygen vacancy in LiCoO2 is about 1.5eV higher than in LiNiO2 (and hence the degree of non-stoichiometry is much less). This is possibly due to the strong stabilisation of d6 (t2g6eg0) electronic configuration of Co3+. It is harder to reduce Co3+ to Co2+ than Ni3+ to Ni2+, which is needed for the charge compensation for one oxygen vacancy. Also one Co3+ is left in an unfavourable fivefold coordination. The detailed local crystal structures and electronic structures of point defects are demonstrated and also the effect of the Co ions in LiNi1-xCoxO2 is discussed.

Interweaving Lithium Ion Battery Cathodes with Graphene by Genetic Engineering of M13 Virus.Dahyun Oh1,2, Xiangnan Dang1,2, Hyunjung Yi1,2, Mark A. Allen1,2, Kang Xu3, Yun Jung Lee4 and Angela M. Belcher1,2,5; 1Department of Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; 2The David H. Koch Institute for Integrative Cancer Research, cambridge, Massachusetts; 3Electrochemistry Branch, Power & Energy Division, Sensor and Electron Devices Directorate, U. S. Army Research Laboratory, Adelphi, Maryland; 4WCU Department of energy engineering, Hanyang University, Seoul, Korea, Republic of; 5Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Here, we report the nanocomposites fabrication of graphene and lithium ion battery cathode materials enabled by a genetically engineered M13 virus. To meet the demands for lithium ion battery cathodes with high energy density and high power density, we improved the electrochemical activity of conversion reaction materials, bismuth oxyfluoride, by incorporating the graphene. Although the composite formations of graphene and battery electrodes have been reported, they are limited to mechanical stirring or co-precipitation methods. By utilizing the materials specific interaction between graphene and the M13 virus, we broadened the stability windows of graphene and synthesized bismuth oxyfluoride nanoparticles while maintaining the homogeneous distribution of conducting networks in the battery electrode. The graphene-binding virus, p8cs#3, with an 8-mer peptide insert, was identified through a bio-panning method and it is regarded that hydrophobic moiety drives p-p and hydrophobic-hydrophobic interaction between virus and graphene. In addition, p8cs#3 was further changed to negatively charged glutamic acid (E), using a site-directed mutagenesis to catalyze the nucleation of bismuth oxyfluoride thus achieving a higher yield of products under ambient synthetic condition. The structural and chemical properties of virus-templated bismuth oxyfluoride were characterized by X-ray diffraction, high-resolution TEM and X-ray photoelectron spectroscopy elemental analysis giving cubic (Fm-3m) structure with lattice parameter of 5.8160 (1) Å and approximate chemical formula of BiO0.5F2. Building an efficient conducting framework of graphene with the M13 virus improved the electrochemical activity of bismuth oxyfluoride and the specific capacity increased to 210 mAh/g at a current density of 30 mA/g with only 3wt% addition of graphene. Furthermore, we achieved the power density of 711 W/kg (with 316 Wh/kg of energy density) of bismuth oxyfluoride supporting the enhanced conductivity of the electrodes. Using this genetically engineered M13 virus, we were able to compare the different effects of graphene and single-walled carbon nanotubes as a conducting agent in the bismuth oxyfluoride electrode system. The same amount of graphene and SWNT (0.5 wt%) were incorporated and the specific capacity has been increased from 128 mAh/g for SWNTs/bismuth oxyfluoride nanocomposites to 181 mAh/g for graphene/bismuth oxyfluoride nanocomposites at current density of 30 mA/g. This indicates that the graphene improves the kinetics of the conversion reaction better than the SWNTs do when small amounts of carbon are integrated. The conjugation of nanomaterials, graphene and M13 virus, was enabled by genetic engineering and we believe that our study could be applied to other high energy density battery electrodes for application to energy storage devices as well as fundamental studies of the electron transport and transfer in the system.

Synthesis of Carbon Nanomaterial for Air Cathode of Li/Air Battery by Solution Plasma.Jun Kang1, Nagahiro Saito1,2 and Osamu Takai1,2; 1Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Japan; 2EcoTopia Science Research Institute, Nagoya University, Nagoya, Japan.

Lithium-air battery technology looks to have a big future due to their high energy density, which could theoretically be equal to the energy density of gasoline. Substantial Li-air cell performance limitations are related to the air cathode, because the discharge products are deposited on the surfaces of carbon or catalyst in the air electrode, which blocks oxygen from diffusing to the reaction sites. Therefore, the real capacity that a Li/air battery can achieve is determined by the carbon air electrode, especially by the pore volume available for the deposition of discharge products. This study investigates about carbon nano material for lithium-air cathodes. The carbon nano ball (CNB) was synthesized by the solution plasma process(SPP) from toluene solution(40ml) without any catalysts and then annealed at low temperature. SPP is superior to other conventional methods, owing to its properties such as ease of handling, no need of pressure and temperature, short consumption time, and variation in a wide range of chemical use. The synthesized CNB have been systematically studied by scanning electron microscopy (SEM), transmission electron microscope (TEM) X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) method. The CNB was obtained 350mg (from toluene40 ml) and the diameters of CNB are in a range of 20 nm to 50nm. The SEM examination shows that these carbon spheres have a ball-like and chain-like morphology, and a quite uniform diameter. The BET surface area of CNB is 124 m2/g and the pore volume is 0.85 cm3/g, and the average pore size is 23nm indicating high surface areas and large pore volumes. And then these CNB were heated at low temperature (300~450’C) for 20 min under an atmosphere. The BET surface area of HCNB(heat treated CNB) 450~500 m2/g, and the pore volume is 1.56 cm3/g, and the average pore size is 15.6nm indicating very high surface areas and large pore volumes. The cell performance test was conducted to compare the discharge capacity with other carbon material such as Ketjen black, Vulcan XC-72r, Carbon sphere (made by CVD method). And we can find out that CNB showed a good discharge capacity compared to several commercial carbon material. This study may provide a new method to prepare air cathode for lithium/oxygen battery.

Nanoengineered Cathode Catalysts for Rechargeable Lithium-Air Batteries.Jun Yin, Bin Fang, Jin Luo, Bridgid Wanjala and Chuan-Jian Zhong; Department of Chemistry, State University of New York at Binghamton, Binghamton, New York.

The development of rechargeable lithium-air batteries represents an important pathway towards green energy. A key challenge for rechargeable lithium-air batteries is lack of fundamental understanding of the design of highly-effective catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the air cathode. One approach involves the design and synthesis of bifunctional or multifunctional catalysts for both ORR and OER. In this work, several types of gold-based bimetallic nanoparticles (e.g., AuCu, AuPt, AuAg etc) and other trimetallic nanoparticle catalysts prepared by nanoengineered synthesis and processing methods were examined as the cathode catalysts in single-cell measurements. Issues on how the bimetallic phase structures are operative for ORR and OER and how the catalytic intermediate deposition is manageable in connection with catalyst regeneration will be discussed. Results from the battery charging - discharging and cyclic voltammetric measurements in organic electrolytes will also be discussed to assess the mechanistic details for the formation of lithium peroxide or superoxide on the cathode catalyst materials, along with their implications to the design of highly-effective catalysts in the air cathode.

MnOx/Carbon Composite Nanofiber Cathodes for Rechargeable Li/Air Batteries.Guanjie Xu, Ying Li, Ozan Toprakci, Shu Zhang and Xiangwu Zhang; Textile engineering, chemistry and science, North Carolina State University, Raleigh, North Carolina.

The performance of Li-ion batteries has been improved significantly since the commercialization of Li-ion batteries by Sony in 1990; however, the energy density of current Li-ion batteries still cannot fulfill the needs in the modern market for energy storage. Li/air batteries, with the theoretical capacity of near 10 times greater than that of the current Li-ion batteries, are being developed. Li/air batteries are a new type of battery, which combines the advantages of Li-ion batteries and fuel cells. During discharge, the oxygen is fed continually to absorb electrons, while Li ions are transferred from anode to cathode through the electrolyte to react with O_2^(x-) to produce LiOx. However, there are several problems limiting the practical application of Li/air batteries. First of all, the discharging products are deposited on the electrode material surface and occupy large pore space, which reduce the electron conductivity of the electrode. Secondly, the slurry properties for both discharging and charging reactions broaden the gap between charging and discharging potentials, increase the polarization, and limit the reversible capacity and c-rate performance. To address these two problems, we prepared MnOx/carbon composite nanofiber cathodes, in which carbon nanofibers not only work as the electron source, but also as the porous matrix to hold the discharging products and to enable the oxygen permeation, while the MnOx acts as the catalyst to improve the electrode reaction kinetics. The electrospinning technique was used to produce MnOx/carbon composite nanofibers from a salt/polymer precusor mixture solution. The performances of the cathodes with different MnOx mount were tested in Swagelok cells. The presentation will discuss the structure and electrochemical performance of these new MnOx/carbon composite nanofiber cathodes.

Effect of Pd/Mn Substitution on Characteristics of Amorphous Zr-Ni-Ti-V Alloy Hydride Electrodes.Hiroshi Miyamura, Yoshihisa Fujita and Balachandran Jeyadevan; Materials Science, Univ. of Shiga Prerecture, Hikone city, Shiga Prefecture, Japan.

Hydrogenation properties of some amorphous Zr-Ni-Ti-V alloys were investigated. Pressure-composition(P-C) isotherms and hydrogen storage capacities at room temperatures were measured via an electrochemical method. Effect of elemental substitution of the components with Pd or Mn was studied. The alloy electrodes were prepared by use of amorphous (Zr-Ni-Ti-V)-(Pd,Mn) alloys prepared by the melt spinning method. The amorphous alloys in the electrode kept their amorphous structures during cycles of charge and discharge. The electrochemical hydrogen storage capacities were strongly affected by the substitution amounts of Pd or Mn. They changed both of the equilibrium dissociation pressure and the discharge kinetics. In the present study, the rechargeable capacity was optimized upto H/M=0.5 in the alloy electrode with the composition of (Ti25Zr45Ni30)-3at%Pd. The slope in the P-C isotherm suggested that the maximum H/M of the alloy would exceed 1.0 at higher hydrogen pressure than 1.0MPa, however, the wide distribution of site energy in the amorphous hydride resulted in extremely large slope in P-C isotherms, and consequently restricted the rechargeable capacities of the electrodes.

Production and Characterization of CaNi5 Compounds for Metal Hydride Batteries.Berke Oksuz and Kadri M. Aydinol; Metallurgical and Materials Engineering, Middle East Technical University, Ankara, Turkey.

NiMH batteries have superior properties which are long cycle life characteristics, low maintenance, high power, light weight, good thermal performance and configurable design. Hydrogen storage alloys play a dominant role in power service life of a NiMH battery and determining the electrochemical properties of the battery. In the negative electrode, compounds having high hydrogen storage capacity and fast hydrogen kinetics is an important issue. LaNi5, belonging to the CaCu5 crystal structure type, satisfy many of the properties. In this manner, CaNi5 gets more importance rather than LaNi5 due to its low cost, higher hydrogen storage capacity, good kinetic properties and much more discharge capacity. Nevertheless, the main restriction of usage CaNi5 is lower cycle life. Cycle life of CaNi5 can be improved by alloying additions. In this study, the effect of alloying additions (Si,Al,Zr) on the crystal structure and electrochemical properties were investigated. During the studies CaNi5 compounds were produced by vacuum casting method, pulverization with ball mill and homogenizing heat treatment under vacuum. After structural characterization, these anode materials were tested in a battery cell. Discharge capacity and cycleability of the developed alloys were determined. Some improvements in the cycle life of the battery have been observed.

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Cathode Materials for Fluoride Ion Batteries (FIB).Teng Yin Ting1, Denis Yu2,3, Steffen Hartung3, Rachid Yazami1,2,3, Andrew Soutar4, Harry Hoster3, Madhavi Srinivasan1,2,3, Subodh Mhaisalkar1,2,3; 1School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore; 2Energy Research Institute @ NTU, Singapore, Singapore; 3TUM CREATE Centre for Electromobility, Singapore Research Office, Singapore, Singapore; 4Surface Technology Group, Singapore Institute of Manufacturing Technology, Singapore, Singapore.

The concept of Fluoride Ion Batteries (FIB) is to use fluoride ions as the charge carrying species in a battery system, instead of Li ions in conventional Lithium Ion Batteries (LIB). Theoretical capacity of FIB is potentially larger than that of LIB, if more than one fluoride ion can be inserted and removed from the cathode and anode. The approach will be a first proof of concept for using anion-based batteries. In the search for suitable electrode materials, carbon has been demonstrated to accept fluoride ions, forming CFx, but the available capacity is low. In this presentation, we are exploring the use of metallic fluoride materials such as iron fluoride as a possible cathode in FIB. Electrochemical performance of the material will be shown during the meeting.

Determination of the Thermodynamic Properties of the Sr-Sb System by EMF Measurements with a SrF2 Electrolyte.Kavita Chandra, Sophie Poizeau and Donald R. Sadoway; MIT, Cambridge, Massachusetts.

Liquid metal batteries are under development for storage of electrical energy. Strontium and antimony are among the metals considered as candidate electrodes. To determine the theoretical discharge curve of such a battery, the thermodynamic properties of Sr-Sb are being evaluated by EMF measurements in a cell fitted with a solid electrolyte of strontium fluoride (SrF2) prepared by a process developed in house. The optimization of sintering parameters will be described. In addition, measured values will be reported of the activity of Sr in liquid Sr-Sb alloys for compositions exceeding 50% Sb over the temperature range spanning 600°C to 800°C.

Synthesis and Characterization of Thermoelectric LaNi0.05Co0.95O3 and La0.4Ca0.6MnO3 Thick Films for Mobile Energy Supply.Wenyan Jiang, Seung-Hyun Kim and Angus I. Kingon; School of Engineering, Brown University, Providence, Rhode Island.

Energy scavenging and efficient energy usage in electronic systems continues to be a focus of research activity for mobile devices. One attractive concept is to incorporate a micro-thermoelectric (TE) generator module into electronic systems to provide energy through waste heat conversion for mobile systems. Attractive characteristics of a TE generator include no moving parts, long lifetime and high reliability. A concern for micro TE generator performance is the power output and conversion efficiency, with both of the parameters strongly affected by the device geometry, including the thickness of the semiconductor TE legs in the classical vertical structure TE generators. Modeling demonstrates the tantalizing potential of low cost devices that are based on thin film oxides, but also emphasizes the importance of thermal contact resistance. As we discuss, very low thermal contact resistance would allow thin film thermoelectric devices, but more realistically achievable thermal contact resistances increase the required device (and thus film) thickness for optimum performance. This work focuses on achieving the best contact resistance, and then developing a process that yields thermoelectric films of optimum thickness. Experimental results indicate that film thicknesses (i.e. leg thicknesses) required are in the range 5-20 micron. To develop films of the required thicknesses, we developed a hybrid film preparation method. The method utilizes screen-printed film as the main body, and incorporates spin coating to infiltrate solution of the same composition into the porous screen-printed body. The film morphology and properties are compared with and without the infiltration process. Relatively dense thick films with tunable porosity (for controlling thermal conduction) have been prepared by this method. The infiltration process dramatically decreased film’s electrical resistivity. Thermoelectric characterization also showed film’s promising application as TE generator for mobile energy supply. For the final device improvement, the thermal boundary resistance between the electrode and the thermoelectric film has also been studied. Thermal boundary resistance is compared for different electrode materials, and implications for final device performance are discussed. This work is supported by NSF, ECS division under contract No. 0824212.

SESSION F5: Cathodes I
Chairs: Arman Ahnood and Denis Yu
Tuesday Morning, November 29, 2011
Back Bay C (Sheraton)

9:00 AM *F5.1
Benefit and Technical Challenges to Make C-LiMPO4 in Large Scale by Melt Casting.Guoxian Liang1, Jasmin Dufour1, Nathalie Ravet1, Christophe Michot1, Michel Gauthier1, Joesph Wontcheu2, Ruhul Amin2 and Dean Macneil2; 1Research and development, Phostech Lithium Inc.,, St-Bruno, Quebec, Canada; 2University of Montreal, Montreal, Quebec, Canada.

Interest is rapidly growing in using lithium iron phosphate as a cathode material in large size lithium ion batteries due to significant progress in the last few years on the manufacturing technologies of C-LiFePO4. High material purity, small particle size and carbon deposition on the surface of LiFePO4 particles have been the common strategy to improve electrochemical performance. Solid state reaction and hydrothermal syntheses are currently used in industry to manufacture this cathode material. In most cases, the phase purity, particle size control and carbon coating were performed in either a single or two steps, which make process control of the base material more difficult. Phostech Lithium has explored a melt casting process to make C-LiFePO4 and recently extended the activity to LiMnxFe1-xPO4 materials (1-3). The advantages of this synthetic process are the use of low cost precursors and individual steps for material synthesis, particle size control and carbon coating. This scheme may provide improved process and quality control to the final product. However, there are still many technical challenges in each step to be solved before commercial applications. In this presentation, we will discuss our latest results using melt casting, wet milling of LiMPO4 in solvent to nano size followed by carbon coating of LiMPO4 as well as the risk and potential of this process for large scale commercial application. The state of the art performance on LiMnxFe1-xPO4 achieved with the melt casting process will be also reported in comparison with those made by solid state and wet process. 1. M. Gauthier, C. Michot, N. Ravet, M. Duchesneau, J. Dufour, G. Liang, J. Wontcheu, L. Gauthier and D. D. MacNeil, J. Electrochem. Soc.,157 (4), A453, (2010). 2. D. D. MacNeil, L. Devigne, C. Michot, I. Rodrigues, G. Liang, and M. Gauthier, J. Electrochem. Soc.,157 (4), A463, (2010). 3. K. Zaghib, G. Liang, F. Labrecque, A. Mauget, C. Julien and M. Gauthier, abstract 582, 214th ESC meeting, the electrochemical society, Hawaii, 2008.

9:30 AM F5.2
Single Crystal Studies of Li Oxoanion Battery Systems - LiFePO4 and Beyond.Peter Khalifah1,2, Yuri Janssen1,2, Shouhang Bo1,2 and Clare Grey1,3; 1Stony Brook University, Stony Brook, New York; 2Brookhaven National Laboratory, Upton, New York; 3Cambridge University, Cambridge, United Kingdom.

Lithium ion batteries have helped enable the explosion of mobile electronic devices due to their high storage capacity and good rate performance. Among such systems, LiFePO4 has especially desirable characteristics due to its inexpensive and abundant components, as well the good safety performance associated with its particularly stable crystal structure. Large (mm- to cm-sized) single crystals of pristine and doped LiFePO4 have been prepared using newly-developed crystal growth routes, and are found to have very low defect concentrations. The growth and properties characterization of these crystals and of other promising oxoanion battery systems with even higher storage capacities with be described.

9:45 AM F5.3
Vacancy-Driven Anisotropic Defect Distribution in LiFePO4.Jaekwang Lee1,2, Wu Zhou1,2, Juan C. Idrobo1,2, Stephen J. Pennycook2 and Sokrates T. Pantelides1; 1Physics & Astronomy, Vanderbilt University, Nashville, Tennessee; 2Materials Science & Technology, Oak Ridge National Lab, Knoxville, Tennessee.

LiFePO4 is a promising new-generation cathode material for Li rechargeable batteries because of its high energy density, high safety, low cost, and environmental friendliness. The Li ion mobility is the key parameter for battery applications with high energy density. Computational and experimental studies of LiFePO4 indicate that Li+ ion migration occurs preferentially via one dimensional channels oriented along the [010] direction (b-axis). Such one-dimensional diffusion, however, is highly sensitive to the presence of immobile or low-mobility defects in the diffusion path. Even a single immobile defect in the path can block long-range diffusion. Recently, Chung et al. reported that iron antisite defects (FeLi) form preferentially in only a few channels along the b-axis instead of being homogeneously distributed in the lattice [1]. This kind of segregation is important because only a few diffusion channels are blocked, leaving most of them available for Li diffusion. The ability to control this segregation is, therefore, necessary in order to maximize the fraction of unblocked diffusion channels and optimize device performance. The cause of the FeLi segregation, however, remains unknown. We use first-principles calculations and statistical mechanics to show that the observed segregation of FeLi’s defects in selective b channels is the result of an unusual energy-lowering mechanism that is a feature of the one-dimensional nature of the Li diffusion path. VLi’s shuttle between FeLi’s defects and bind occasionally at the end-points along the b-channels. Segregation of FeLi’s in just a few channels results in shorter FeLi-FeLi separations, which induce longer binding times, lowering the system’s energy. Based on a one-dimensional random walk, we derive an analytical expression for the total energy lowering E(L, T) as a function of temperature, T, and the average distance, L, between neighboring FeLi’s. Through atomically-resolved EELS obtained with an aberration-corrected STEM, we show that FeLi in the b-axis channels has a slightly higher oxidation state relative to the nominal value of +2 for Fe in LiFePO4. This effect can be attributed to the formation of VLi-FeLi-VLi clusters, which is consistent with the energy-lowering mechanism proposed: a FeLi in a b-axis channel can bind a VLi on either side for a fraction of time as the VLi shuttle between end-point FeLi’s [2]. [1] S.-Y. Chung et al., Angew. Chem., Int. Ed. 48, 543 (2009). [2] J. Lee et al., submitted to Phys. Rev. Lett.. This research was partially supported by NSF Grant DMR-0938330 (J-CI, WZ), by ORNL’s SHaRE User Facility, which is sponsored by the DoE Office of Basic Energy Sciences (J-CI) and the DoE Office of Basic Energy Sciences (SJP, JL,STP), DOE grant DE-FG02-09ER46554 (STP), and by the McMinn Endowment (STP) at Vanderbilt University. Computations were done at the National Energy Research Scientific Computing Center, which is supported by the DoE Office of Science

10:30 AM F5.4
Atom by Atom Imaging of Defects in LiFePO4 with Olivine Structure.Xiang Yang Kong, shanghai Jiao tong University, Shanghai, China.

LiFePO4 has appeared as a promising cathode material for high-power rechargeable lithium-ion batteries, but much of its unusual phase behavior and transport properties remain to be understood. LiFePO4 performs the olivine structure with oxygen-anion scaffold-framework from corner-sharing FeO6 octahedral and PO4 tetrahedral anions. Olivine is regarded as a stable structure for Li-insertion/extraction and should have good cycling stability. However, little attention has been paid on the effects of defects in olivine structures on the electrochemical performance. In this talk, the LiFePO4 nanocrystals were observed using a 200 kV JEM-2100F (JEOL) microscope equipped with a spherical aberration corrector (CEOS). Lithium ions in LiFePO4 olivine structure were observed directly at atomic resolution by an aberration-corrected annular-bright-field scanning transmission electron microscopy technique. The probe-forming aperture semi-angle was 20 mrad. The annular dark field (ADF) detector spanned the range of 120 - 228 mrad and the ABF detector spanned the range of 6- 25 mrad. The atom by atom imaging of defects in LiFePO4 olivine structure was conducted by means of the STEM-ABF. The results show that the most favorable defect in LiFePO4 olivine structure is the Li-Fe “anti-site” pair in which an Li+ and an Fe2+ are interchanged. The anti-site cations on Li sites would impede Li diffusion or migration along [010] channels. Defect associated lattice distortion in olivine structure was also investigated.

10:45 AM F5.5
Structure, Defects, and Thermal Stability of Delithiated Olivine Phosphates.Gene Nolis, Fredrick Omenya, Natasha A. Chernova, Shailesh Upreti and M. Stanley Whittingham; Chemistry, SUNY at Binghamton, Binghamton, New York.

Commercialized electrode materials must demonstrate the ability to maintain their chemical structure over the course of hundreds of charge/discharge cycles and range of application conditions. Olivine phosphate, o-LiFe1-yMnyPO4, cathodes are candidates for high-power applications; however, the thermodynamics and stability data for their delithiated forms remain scarce and contradictory. We have previously reported o-FePO4, synthesized by Br2 delithiation of hydrothermally prepared LiFePO4, which transforms to trigonal, t-FePO4, phase at 580°C. Similar results were obtained by Masquelier’s group, using NO2BF4 delithiation of LiFePO4 synthesized by co-precipitation method, but the transition temperature was 620°C. Theoretical calculations by Ceder’s group suggest the existence of non-equilibrium decomposition route leading to iron reduction and oxygen release; and indeed, some papers report Fe7(PO4)6 and Fe2P2O7 among the o-FePO4 decomposition products. Various-temperature x-ray diffraction (XRD) of o-MnPO4 indicates decomposition to Mn2P2O7 with O2 evolution at temperatures above 210°C. The thermal stability and decomposition routes of intermediate o-Fe1-yMnyPO4 remain unclear. In this work, we have synthesized o-LiFe1-yMnyPO4 (y = 0, 0.2, 0.4, 0.6, 0.8, 0.9) by solid-state method from carbonaceous precursors. To obtain o-Fe1-yMnyPO4, chemical delithiation was performed using excess NO2BF4 in acetonitrile. XRD indicates pure phases with lattice parameters consistent with the reported ones, while the magnetic studies indicate presence of Fe2P in LiFe1-yMnyPO4 series and possible structural disorder of the delithiated products. Such o-FePO4 decomposes above 500°C to t-FePO4 and Fe7(PO4)6; suggesting that impurities, such as residual carbon, might drive reaction mechanism toward Fe3+ reduction. Differential scanning calorimetry and TGA data suggest that iron substitution, within o-Fe1-yMnyPO4, improves thermal stability as structural decomposition occurs at temperatures above 400°C; at least over 0 = y = 0.6 compositions. The reaction mechanism of decomposition is being investigated using various-temperature XRD. This work was supported as part of NECCES (the Northeastern Center for Chemical Energy Storage), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DESC0001294.

11:00 AM F5.6
Bilayer Conducting Olivine Nanoweb Cathodes for Lithium Ion Batteries.Yan Ling Cheah and Madhavi Srinivasan; School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.

Lithium transition metal phosphates (olivines) have attracted immense interest as storage cathodes for rechargeable lithium batteries because of their high energy density (150-170mAhg-1), low raw materials cost, environmental friendliness and safety. Other than the highly popular olivine phosphate LiFePO4, LiMnPO4 is also emerging as a promising cathode material due to its higher working potential (4.1V). However the low intrinsic electronic conducitivity (~10-15Scm-1) of LiMnPO4 has led to very low specific capacity and poor cycle performance, even at low current densities (low C rate). Attempts to enhance its electrochemical performance include carbon coatings and addition of conducting carbon, metal ion-doping and particle size-reduction to the nanometer range via ball-milling. Among various nanostructured architectures, the nanofibre morphology has been previously mentioned to be more electrochemically strain-resistant as compared to nanospheres, nanopowders and thin films. Electrospinning enables the formation of nanofibres from a polymer solution by application of a high accelerating voltage, which overcomes the surface tension of the solution. The resulting nanofibre mats have large surface area and small pore sizes, which facilitates lithium-ion transport by providing small electronic resistance and short diffusion pathways, and hence can deliver higher rate lithium-ion storage capability, faster charge-discharge kinetics, and better cyclic stability. In addition, the core-shell electrospinning technique enables the possibility of co-spinning different materials simultaneously. In this study, we have adopted a core-shell electrospinning techniques for fabricating bilayered composite nanoweb comprised of carbon and LiMnPO4. Previous studies has shown that addition of carbon fibres led to increased conductivity in olivine materials (LiFePO4). Nanocomposites of olivines with carbon-based materials (carbon fibres / nanotubes) that possess large surface area [~1000-1600m2g-1], excellent electrical conductivity [~103-104Scm-1]) will be studied in an effort to further improve the electronic conductivity and enhance capacity retention. Detailed fabrication procedures, characterization and electrochemical test results will be presented and discussed.

11:15 AM F5.7
Electrospun Nanofiber Networks as Electrode Materials for Li-Ion Batteries. Sanjay Mathur1, Robin von Hagen1, Ashish Lepcha1, Mehtap Bueyuekyazi1, Kai-Christian Moeller2, Henning Lorrmann2, Hanne Andersen2, Sonia Estrade3 and Juan Ramon Morante3; 1Department of Chemistry, University of Cologne, Cologne, Germany; 2Elektrochemische Energiespeicherung und -wandlung, Fraunhofer ISC, Wuerzburg, Germany; 3Electronics Department, University of Barcelona, Barcelona, Spain.

Due to their intrinsic properties nanostructured electrode materials are used to improve the performance of lithium ion batteries and gain high cycling stability and high rates as they are needed for 2nd generation applications such as electromobility. Therefore the low cost production and simple integration of these materials into the batteries are needed. The electrospinning method offers a great potential in the 1-D nanofiber design and production of anode/cathode materials with complex structure and composition with reliable control over morphology and no need of further work-up steps. By the judicious choice of precursor solutions in sol-gel type electrospinning and the calcination of the fiber networks under inert atmosphere, we were able to produce self-supporting electrodes of Sn/C (anode) and LiFe1-yMnyPO4/C, a-Li3V2(PO4)3/C (cathode) which showed superior electrochemical performance in terms of rate and stability. The free standing composite (active material/carbon) nanofiber networks could directly be used as electrode material without the need of further additives. The nanofibers further were characterized by SEM, BET, HR-TEM and XRD before and after the electrochemical cycling. A deeper investigation of lithiation and de-lithiation process of LiFe1-yMnyPO4 - with respect to the Mn-content - was done using EELS-TEM technique.

11:30 AM F5.8
Microwave-Assisted Solvothermal Synthesis and Electrochemical Properties of Various Polymorphs of LiVOPO4 Cathodes.Katharine L. Harrison and Arumugam Manthiram; Mechanical Engineering, University of Texas at Austin, Austin, Texas.

Cathodes containing polyanions offer the advantage of excellent thermal stability and safety characteristics. Although olivine LiFePO4 offers excellent electrochemical properties in lithium-ion cells, the lower operating voltage of 3.45 V limits its energy density. In this regard, LiVOPO4 is appealing as it operates at a higher voltage of ~ 4 V although it has a slightly lower theoretical capacity of 159 mAh/g. LiVOPO4 crystallizes in three polymorphic modifications. With an aim to access the various polymorphic modifications of LiVOPO4 at lower temperatures and assess their electrochemical properties, we present here the synthesis of LiVOPO4 by a microwave-assisted solvothermal method at around 200 oC within a short reaction time of 30 minutes in a mixed solvent (water and ethanol) environment. Microwave-assisted synthesis methods offer potential savings in energy and manufacturing cost by drastically reducing reaction temperatures and time relative to conventional solid state syntheses. Microwave methods also offer significant time savings relative to traditional hydrothermal and solvothermal methods. Additionally, microwave methods can sometimes allow tuning of particle size and morphology, which can have significant impacts on the electrochemical performances of battery electrode materials. Access to the various polymorphs of LiVOPO4 was limited with our microwave-assisted method in pure water medium and the precursors have limited solubility in ethanol, but we have been successful at accessing the three polymorphic modifications of LiVOPO4 (orthorhombic, tetragonal, and triclinic) by employing a water-ethanol mixed solvent reaction medium and altering the precursor ratios. Furthermore, since several reaction vessels can be used in one reaction and the reactions are fast, our microwave-assisted solvothermal method allowed us to quickly screen many different conditions to find the optimal solvent and precursor ratios for each phase. Particle morphology and electrochemical data for these three LiVOPO4 phases will be presented and compared.

11:45 AM F5.9
Effects of Post-Heat Treatment on the Spinel LiNi0.5Mn1.5O4.Jijun Feng, Natasha A. Chernova, Shailesh Upreti and M. Stanley Whittingham; Institute for Materials Research, State University of New York at Binghamton, Binghamton, New York.

The increasing demand on lithium-ion batteries with high energy and power density for electric vehicles and large scale energy storage requires the development of electrode materials providing either higher capacity or higher voltage. As a promising cathode material, spinel LiNi0.5Mn1.5O4 has received extensive attention for its high operating voltage (4.7 V vs. Li/Li+) and comparative electrochemical performance. One of the main issues with this high voltage material is the formation of undesirable impurities, such as NiO or LixNi1-xO during synthesis. The presence of impurities deteriorates the electrochemical performance of the spinel LiNi0.5Mn1.5O4 material. Many methods have been used to synthesize LiNi0.5Mn1.5O4, such as solid state method, sol-gel method, and hydrothermal method. It is obvious that different synthesis procedures have strong influences on the morphology and electrochemical performance of as-prepared materials. In this work, effects of different post treatment on the structure, phase purity, discharge profile and electrochemical performance were investigated. Mixture of stoichiometric LiAc, Ni(Ac)2?4H2O and Mn(Ac)2?4H2O were calcined at different temperature, 700 °C, 800 °C and 900 °C, followed by different treatment, including cooling down slowly, annealing and quenching. XRD patterns show that the LixNi1-xO impurities exist in all the three samples sintered at different temperatures followed by cooling down. The procedure of annealing at 700 °C results in an ordered structure, but the LixNi1-xO impurities still exist. It deserves special attention that the quenching process can effectively inhibit the formation of LixNi1-xO impurity. The sample synthesized at 800 °C has the best electrochemical performance in terms of both capacity and rate capability. Although the sample synthesized at 900 °C has a higher capacity than that of 700 °C, it is noteworthy that a higher portion of the capacity originated from the 4 V plateau related to the redox species of Mn3+/Mn4+.

SESSION F6: Cathodes II
Chairs: Guoxian Liang and Stefan Manuel
Tuesday Afternoon, November 29, 2011
Back Bay C (Sheraton)

1:30 PM *F6.1
Na-Ion Batteries: Materials and Interface.Shinichi Komaba and Naoaki Yabuuchi; Department of Applied Chemistry, Tokyo University of Science, Tokyo, Tokyo, Japan.

The demand for the lithium-ion batteries is continually growing, however, the cost of lithium resource is supposed to be drastically increased by commercialization of the large-scale lithium-ion accumulators. There are no doubts that sodium resource is inexhaustible everywhere. We have reported the reversible Na insertion of Fe2O3, NaNi0.5Mn0.5O2 and NaCrO2 for the positive electrodes, recently, we described that the hard carbon electrodes show the high capacity with excellent capacity retention whereas the graphite electrode is almost inactive [1]. Herein, we introduce our recent achievements on the battery materials of electrodes and electrolyte for the application to the Na-ion batteries. For the hard carbon electrodes, the reversible capacity was the highest in the PC and EC:DEC with the highest initial efficiency. By optimizing electrolyte solutions and additives such as fluorinated-EC, the highly reversible reaction of sodium insertion/extraction was achieved. In the range of 2.00 - 0.00 V, the highest reversible capacity of ca. 240 mAh g-1 was achieved, and a slight reduction in capacity to 220 mAh g-1 was observed during 100 cycles. Even though the initial reversible capacity slightly decreases to ca. 230 mAh g-1 in the limited domain of 2.00 - 0.01 V, degradation of the capacity was not observed over 120 cycles. When the reversible capacity was limited by restricting the voltage domains above 0.05, 0.10 and 0.20 V vs. Na, no capacity degradation was observed during 200 cycles. The improvement relates to the stability of the electrolyte solution at a lower potential from the results of FT-IR. We fabricated and tested the Na-ion batteries with hard carbon electrodes. The NaNi0.5Mn0.5O2/hard carbon full cell shows average voltage of ca. 3 V and enables the steady electrochemical charge-discharge cycling. From these results, we will discuss the materials science for the Na-ion battery as the alternative Li-ion battery. [1] S. Komaba, N. Yabuuchi et al., Adv. Funct. Mater., 2011, 10.1002/adfm.201100854

2:00 PM F6.2
High-Voltage, High-Energy Layered-Spinel Nanocomposite Cathodes with Superior Cycle Life for Lithium-Ion Batteries.Arumugam Manthiram and Eunsung Lee; Materials Science and Engineering, University of Texas at Austin, Austin, Texas.

Lithium-ion batteries have revolutionized the portable electronics industry, and they are being intensively pursued for vehicle applications. However, the energy density of the current lithium-ion technology is limited by the cathode capacity, and there is immense interest to develop new cathodes with higher capacity or higher operating voltages. One approach to realizing a combination of high energy and power density is to use a nanocomposite that consists of the high-capacity lithium-rich layered oxide Li[Li,Mn,Ni,Co]O2 and the high-voltage spinel oxide LiMn1.5Ni0.5O4. The cubic-close packed oxygen arrays in both the layered and spinel oxides are structurally compatible, facilitating the lithium-ion transfer smooth across the layered-spinel interface. However, little information is available on the structural and electrochemical characteristics during extended cycling of these composite cathodes. With an aim to develop a firm basic understanding of these layered-spinel composites, we present here a systematic characterization of the nanocomposite system xLi[Li0.2Mn0.6Ni0.17Co0.03]O2 - (1-x)Li[Mn1.5Ni0.425Co0.075]O4 (0 = x =1), consisting of the lithium-rich layered oxide Li[Li0.2Mn0.6Ni0.17Co0.03]O2 and the 5 V spinel oxide Li[Mn1.5Ni0.425Co0.075]O4. The unique structural characteristics of these layered-spinel nanocomposite cathodes and their effect on the electrochemical performances are investigated by ex-situ X-ray diffraction (XRD), neutron diffraction (ND), high-resolution transmission electron microscopy (HR-TEM), and electrochemical measurements. Certain compositions in these composite cathodes exhibit superior cycle life with capacities of ~ 250 mAh/g compared to the pure lithium-rich layered oxide cathodes. The observed electrochemical properties are explained based on the phase relationships identified by ex-situ XRD data collected during the charge-discharge process. In addition, approaches to minimize the irreversible capacity loss in the first cycle will be presented.

2:15 PM F6.3
Cationic Ratio Effects on the Peformance of Mn-Enriched Cathode Materials.Dapeng Wang1,2, Ilias Belharouak2, Guangwen Zhou1 and Khalil Amine2; 1Mechanical Engineering, State University of NewYork at Binghamton, Binghamton, New York; 2Argonne National Lab, Lemont, Illinois.

Layer structured lithium transition metal oxides including LiCoO2, LiMnO2, LiNiO2 and their derivations were widely studied as cathode materials for lithium ion batteries. Due to their low cost and high capacity, manganese enriched cathode materials with excess lithium have the potential to surmount the energy density shortfall of existing cathode materials, and thus are promising positive electrodes for vehicle applications. Compositions such as Li1.2Ni0.2Mn0.6O2 have specific capacity higher than 200mAh/g under low rates. However, small deviations in the cationic ratios can lead to dramatic decreases in the capacity the materials can deliver. We report a systematic study based on materials having different cationic ratios in order to establish the relation between compositions, structures, morphologies and electrochemical performances. Carbonate precursors with three different Mn/Ni ratios (7/3, 9/3, and 12/3) were synthesized via a co-precipitation method using a continuous stirred tank reactor (CSTR). For each precursor, three different lithium amounts were added during the lithiation process. X ray diffraction, scanning electron microscope, surface area analyzer, and electrochemical cycling were used to characterize the materials. Our results indicate that for each precursor there was an optimum lithium molar ratio for the best performance. It is shown that a little decrease in these ratios slightly decreased the capacity, while higher lithium ratios were detrimental and had led to an abrupt decrease in the capacity.

2:30 PM F6.4
A Computational Study on Structural Change and Cation Rearrangements during Li Deintercalation in Li[NixLi1/3-2x/3Mn2/3-x/3]O2.Bo Xu1, Christopher R. Fell2, Kyler Carroll1 and Ying S. Meng1,2; 1Department of NanoEngineering, University of California, San Diego, La Jolla, California; 2Department of Materials Science and Engineering, University of Florida, Gainesville, Florida.

Li-excess layered oxide Li[NixLi1/3-2x/3Mn2/3-x/3]O2 (0 < x< 1/2) has gained much attention as a promising candidate of cathode materials for Li-ion battery. Comparing to conventional layered cathode such as LiCoO2, the material offers higher capacity (> 250mAh/g), costs less and is more environmental friendly. The “excess” Li ions are located in the transition metal (TM) layers forming an in-plane superlattice. During initial charging, a slopy region from the open circuit voltage to 4.4V appeared first, followed by a plateau region between 4.4V and 4.6V. This plateau region, however, never appeared in following cycles. Though it can be identified that the charge compensation of the slopy region originats from Ni2+/Ni4+ redox couple, the electrons sources of the plateau region are still under debate. Such anonymous first cycle irreversible capacity together with the material intrinsic inferior rate capability is hindering the materials from its commercial application. Previous work on this material showed that the Li superlattice in TM layer disappeared after cycling, and significant cation migrations near the electrode surface were observed. In this work, first-principles computation method is used to study from the atomic level the details of the Li deintercalation mechanism and accompanied cation rearrangements in compound Li[Ni1/4Li1/6Mn7/12]O2. Calculations based on Density Functional Theory (DFT) are performed with Vienna Ab Initio Simulation Package (VASP). Generalized Gradient Approximation (GGA) is applied and Hubbard U corrections are introduced to describe the effect of localized d electrons. Nudge Elastic Band (NEB) method is used to identify cation migration paths and barriers. The material phase stability is determined from the calculated formation enthalpy versus lithium concentration. Electronic calculations are performed to study the change of TM ion valences and oxygen charge distribution. Computation results suggest that tetrahedral cations are generated during de-lithiation and a new spinel-like phase may be formed. The possible formation of oxygen vacancies are also investigated in this work and its effect on the cation migrations are discussed.

SESSION F7: Advanced Batteries I
Chairs: Guoxian Liang and Krishna Shenai
Tuesday Afternoon, November 29, 2011
Back Bay C (Sheraton)

3:15 PM F7.1
Microstructural Evolution of Li(Ni,Co,Al)O2 and Li(Ni,Co,Mn)O2 Battery Cathode Material as a Function of Cycling Revealed by Electron Microscopy.Dean Miller1, Kayla Cooley1, Jianguo Wen1 and Daniel Abraham2; 1Materials Science Division and Electron Microscopy Center, Argonne National Laboratory, Argonne, Illinois; 2Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois.

The current generation of advanced Li-ion batteries shows impressive performance characteristics. However, capacity fade limits long term performance, and microstructural changes that take place during electrochemical cycling likely influence this behavior. In this work, we focused on the microstructure of Li(Ni,Co,Al)O2 and Li(Ni,Co,Mn)O2 cathode materials. As-prepared samples and samples that were subjected to long-term cycling were studied by post-test, ex situ characterization using FIB-SEM to reveal the nature and dynamics of microstructural changes. This microscopy and 3-dimensional reconstruction of the secondary particle microstructure revealed significant changes that could have a significant effect on long-term performance. These studies were complemented by in situ studies on single cathode particles. These in situ data revealed dramatic changes in secondary particle microstructure even during the very first charge cycle. Data from our experiments, and critical aspects of the electrochemical cycling process, will be discussed during our presentation. *Research sponsored by the U.S. DOE, Office of Science - Basic Energy Sciences and by U.S. DOE, EERE - Vehicle Technologies Program, under contract DE-AC02-06CH11357. The Electron Microscopy Center at Argonne is supported by the Office of Science.

3:15 PM F7.2
Study on the Electrochemical Insertion/Extrusion of Mg2+ into/from Electrodeposited Bi, Sb and Bi1-xSbx Anodes for Mg-Ion Batteries.Timothy S. Arthur and Masaki Matsui; Materials Research Department, Future Battery, Toyota Institute of North America, Ann Arbor, Michigan.

Magnesium (Mg) batteries have garnered interest as a possible alternative to Li-ion systems to meet the growing demand for rechargeable batteries. Currently, various groups have shown the long cycle-life of secondary batteries based on a magnesium metal anode and an organohaluminate electrolyte. Due to a Mg-ion blocking layer formed on the surface of magnesium metal, such battery systems only function when the electrolytes are dissolved in ether-based solvents, such as THF, and preclude the use of “typical” battery electrolytes i.e. Mg(TFSI)2 in carbonate solvents. Additionally, the best organohaluminate electrolytes only maintain oxidation stability up to ~3.0 V (vs Mg) which limits the choice of available high energy cathodes. One method to overcome the low oxidation stability of organohaluminate electrolytes is the use of alternative anodes which do not form a Mg-ion blocking surface layer with “typical” high-voltage battery electrolytes. Here, we report the our study on the electrochemical insertion/extrusion of Mg2+ into/from electrodeposited layers of Bi, Sb and Bi1-xSbx alloys. Electrochemical synthesis and cycling, XRD, and SEM/EDS analysis on electrodeposited thin-films will be presented, as well as our initial work into high-surface area electrodes. Electrodeposition is a solution-based electro-synthesis technique that directly places the anode material directly on the surface of a current collector and is a viable fabrication method towards anodes with high-surface area, three-dimensional structures. This is the first step towards long-cycle life, high voltage Mg-ion batteries.

3:45 PM F7.3
CuPt3 Bimetallic Nanoparticles Supported in Reduced Grapheme Oxide as Improved Catalyst for the Cathodic Reactions in Vanadium Redox Batteries.Javier Rubio-Garcia1, Cristina Flox1, Marcel Skoumal1, Raquel Nafria1, Teresa Andreu1, Andreu Cabot1, Marcel Boix2, Sergi Claramunt2 and Juan Ramon Morante1,2; 1IREC, San Adria del Besos, Barcelone, Spain; 2Departament Electronica, Universitat de Barcelona, Barcelona, Barcelona, Spain.

Flow batteries are one of the most promising solutions using liquid electrolyte for energy storage. Usually, they are using carbonaceous electrodes, such as graphite felts carbon nanotubes, carbon fibers or mesoporous carbon because they are relatively inexpensive, chemically stable and show good electrical conductivity. However, their kinetic reversibility is rather poor, which is especially critical at the cathode. This contribution, presents an advantageous alternative to improve the performance of the cathode applying bimetallic nanoparticles as catalyst. Our procedure is based on the decoration of ink-jet printed graphene oxide electrodes with bimetallic nanoparticles (CuPt3). We have also used metallic nanoparticles of Pt as reference. The oxygen-based groups of the graphene oxide layers facilitate the efficient attachment of the nanoparticles. Upon surface decoration, the electrodes show an improved kinetics of electrochemical reactions of the selected target redox couple. More precisely, a synergistic catalytic effect was evidenced for bimetallic nanoparticles obtained by colloidal synthesis which facilitates a significant amelioration of the electrode reversibility and contributing to a better battery cell performance.

4:00 PM F7.4
Modeling Coupled Charge/Ion/Thermal/Particle/Fluid Transport in Semi-Solid Flow Batteries with a Hybrid Lattice Boltzmann and Immersed Boundary Method.Miao Wang and Ying Sun; Mechanical Engineering and Mechanics, Drexel University, Philadelphia, Pennsylvania.

Semi-solid flow battery, where electrode slurries are composite of both electrolyte and electrode particles flowing through an electrochemical reaction zone [1], combines the best of both lithium-ion battery and redox flow battery. In Li-ion battery cells, additives that are used to boost electronic and ionic conductivities of the electrode materials comprise 30-40% of the battery volume, undermining both energy and power density of the cell and impairing the cycle life of the system. Redox flow batteries have shown great advantages especially their scale-up flexibility compatible with large-scale grid applications. However, limited by the solubility of metal ion redox couples in liquid solvents, the energy density is not very high. Semi-solid flow battery is designed so to have high energy and power density, and have the possibility to be scaled up. The major difference between a semi-solid flow battery and a static battery is that the electrode particles are moving with the flow, so charge and ion transport are solved with moving boundaries. When electrode particles interact and form a connected path to the current collector, electrochemical reactions will take place on the electrode-electrolyte active surface and release heat. In this paper, a novel modeling approach is proposed based upon the lattice Boltzmann method (LBM) for particle suspensions [2] integrated with the immersed boundary method (IBM) [3] for heat/charge/species transport to simulate transport phenomena in a semi-solid flow battery. Energy equation is first solved using the hybrid LBM-IBM and the result is compared with that from a full IBM model [4]. The hybrid model is then applied to solving for the species transport in both the electrolyte and particles inside electrode slurries. Furthermore, by integrating with a pore-scale electrochemical model previously developed by the authors [5], the performance of a semi-solid flow battery is studied as a function of the volume fraction and particle size of the electrode material. References: [1] Y-M. Chiang, W. C. Carter, B. Ho and M. Duduta, "High energy density redox flow device," U.S. Patent Application No. 20100047671 (2010). [2] A.S. Joshi and Y. Sun, "Multiphase lattice Boltzmann method for particle suspensions," Phys. Rev. E, 79, 066703 (2009). [3] C. S. Peskin, “The immersed boundary method,” ActaNumerica (2002) 479-517 [4] Z. G.Feng and E. E. Michaelides, “Heat transfer in particulate flows with Direct Numerical Simulation (DNS),” International Journal of Heat and Mass Transfer 52 (2009) 777-786. [5] A.S. Joshi, E.C. Kumbur, and Y. Sun, “Pore-scale modeling of transport phenomena in a vanadium redox battery using x-ray tomography and the lattice Boltzmann method,” the 63rd APS DFD Conference, Long Beach, CA, 2010.

SESSION F8: Anodes I
Chairs: Gehan Amaratunga, Prashant Kumta and J Pereira-Ramos
Wednesday Morning, November 30, 2011
Back Bay C (Sheraton)

8:30 AM *F8.1
Electrochemistry of Lithiated Metallic Nitrides with a 2D and 3D Structure as Negative Electrodes for Lithium-Ion Batteries.Jean-Pierre Pereira-Ramos1, Eddie Panabiere1, Nicolas Emery1, Stephane Bach1 and Patrick Willmann2; 1Institut de Chimie et Matériaux Paris Est, CNRS, Thiais, France; 2CNES, Centre National d'Etudes Spatiales, Toulouse, France.

In the present work, we report the structural features and the electrochemical properties of metallic layered nitrides containing cobalt, nickel and copper corresponding to the chemical compositions Li3-2xMxN (M = Co, Ni, Cu) in various potential ranges as a function of the metal content (0.1 < x < 0.6). Great attention is paid to the chemical reactivity of such compounds and their ageing in air and in electrolyte. We report the first example of an intercalation compound based on the nitrogen framework in which lithium can be intercalated and deintercalated. Results obtained herein suggest that Li insertion occurs in cationic vacancies located in Li2N layers while interlayer divalent cobalt or nickel cations are reduced to monovalent species. No structural strain is induced by the electrochemical insertion-extraction reaction which explains the high stability of the capacity. Indeed, attractive Li insertion reactions are responsible for the highly rechargeable behaviour of nitridocobaltates and nitridonickelates with stable capacities of 200 mAh/g, up to 400 mAh/g when the potential range is enlarged to 1.1V-0.02V. Conversion reactions also are investigated with larger initial capacity values but lower cycle life in more extended cycling limits. All the results are discussed in relation with structural data. In a second step, we investigate 3 D lithiated metallic nitrides with a cubic structure. In that case, various compounds Li7MnN4, Li6MoN4, Li6WN4 are synthesized and investigated as anode materials. The kinetic properties of Li7MnN4, are studied in details by ac impedance spectroscopy while an original rechargeable behaviour is found for Li6MoN4. The electrochemical mechanism responsible for this finding is discussed in this work.

9:00 AM F8.2
Recent Developments in Nanostructured Anode and Cathode Materials for Rechargeable Lithium-Ion Batteries.Mataz Alcoutlabi, Xiangwu Zhang, Liwen Ji, Ozan Toprakci and Ying Li; Fiber and Polymer Science Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, North Carolina.

We use electrospinning technology to process different materials aimed at preparing novel composite nanofibers which can be used as anodes and cathodes for lithium-ion batteries. We present the fabrication of silicon/carbon (Si/C) anode and LiFePO4/carbon (LiFePO4/C) cathode composite nanofibers and the integration of these nanofibers in lithium-ion batteries to achieve high system performance. The anodes that are made from Si/C nanofibers have the advantages of both carbon (long cycle life) and Si (high lithium-storage capacity). The cathode material, LiFePO4/C nanofibers, also shows good electrochemical performance, such as satisfactory cycling stability. The effect of the nanostructure on the electrochemical performance of these anodes and cathodes is presented. Their synthesis processes, electrochemical properties, and electrode reaction mechanisms are also discussed.

9:15 AM F8.3
High Power Nanostructured Anodes and Cathodes for Li-Ion Batteries.Hong-Li Zhang1,2,3, Jon Fold von Bulow2 and Daniel Morse1,2,3; 1Center for Energy Efficient Materials, University of California, Santa Barbara, Santa Barbara, California; 2Institute for Collaborative Biotechnologies, University of California, Santa Barbara, Santa Barbara, California; 3LifeCel Technology LLC, Santa Barbara, California.

Developing high-performance electrode (cathode and anode) materials is essential for next-generation high-power lithium-ion batteries and their applications (e.g. electric vehicles, storage of renewable energy, smart grids, etc.). The most widely used cathode (i.e. LiCO2) and anode (graphite) on the market, however, cannot meet the requirements for high power density. Using bio-inspired kinetically controlled catalytic synthesis, we developed a surface modified, Sn-based nanostructured composite anode (Sn@C) with super-high rate capability. Specifically, even at 50 C-rate (72 s discharge), this material retains a reversible capacity of 190 mAh/g (nearly half of the capacity at 0.1C), exhibiting a power density far greater than any commercial anode. Furthermore, this composite has very stable cyclic performance, overcoming the problem of poor cyclability exhibited by conventional Sn-based anodes due to the large volume changes and consequent pulverization of Sn during alloying/dealloying with lithium. To pair with this anode, we also developed a spinel-based nanocomposite cathode in which inexpensive carbon nanotubes are highly dispersed in situ to form a conductive network. Preliminary electrochemical measurements indicate that this novel nanocomposite cathode exhibits remarkably cyclic stability and an unsurpassed capacity retention upon cycling at high C-rates: ~96% retention of original capacity at 10 C and ~80% at 20 C.

9:30 AM F8.4
Nanosecond- and Picosecond-Laser Structuring of Electrode Materials for Lithium-Ion Batteries.Robert Kohler1, Johannes Proell1, Heino Besser1, Maika Torge1, Steffen Scholz2, Todor Dobrev2, Sven Ulrich1, Carlos Ziebert1 and Wilhelm Pfleging1; 1Institute for Applied Materials (IAM-AWP), Karlsruhe Institute of Technology, Karlsruhe, BW, Germany; 2Manufacturing Engineering Centre, Cardiff University, Cardiff, United Kingdom.

The development of high performance micro-batteries is of mayor importance for the ongoing miniaturization of mobile electronic devices. Lithium-ion batteries have shown great potential as light weight energy storage devices, due to their high energy density, power density and cycling stability. The modification and improvement of electrode materials play a dominant role in supplying decisive electrochemical properties. LiCoO2 is a frequently used cathode material for lithium ion batteries and is therefore well suited as model material for testing and evaluating new processing technologies which are investigated for an improvement of the battery performance. Therefore, thin films of LiCoO2 with a thickness of 3µm were deposited using radio frequency magnetron sputtering. SnOx (x˜2) thin films were investigated as anode materials exhibiting energy densities of up to 781mAh/g, which is significantly larger than the currently employed graphite anodes (372mAh/g). Yet, SnOx suffers from poor cyclability due to large volume changes of 359% and subsequent pulverization of the electrode material during lithium insertion. To overcome this disadvantage laser structuring processes were investigated, which formed free-standing structures to allow compensation of the volume expansion. Compared to SnOx, LiCoO2 exhibits minor changes in volume which are only in the range of a few percent. Even so, a large increase in active surface area by laser structuring may lead to an improved lithium diffusion rate which in turn can lead to higher discharge currents and an increased power density. A comparative study of thin film electrode laser structuring using ps- and ns-laser radiation was performed. The ps-laser radiation has a pulse width of 12ps and a wavelength of 355nm, while the applied ns-laser radiation has a pulse width of 4ns operating at a wavelength of 248nm. It could be shown that ps-laser ablation is more efficient in comparison to ns-laser ablation. Debris formation was observed by ps-laser ablation, while thermal impact was detectable when using ns-laser radiation. For LiCoO2 a subsequent annealing procedure was necessary to create an appropriate crystalline phase which is electrochemically active. This was verified using Raman-spectroscopy and X-ray diffraction analysis. Laser annealing using a high power diode laser with a wavelength of 940nm was used for this purpose. Electrochemical cycling using a conventional electrolyte was applied to study the influence of the laser processing procedures on battery performance. Laser surface modification creating free-standing structures could significantly improve the battery performance in terms of cycling stability for SnOx anodes and high rate capability for LiCoO2 cathodes.

9:45 AM F8.5
Atomic Layer Deposition of Protective Coatings on Lithium Ion Battery Anodes.David J. Comstock1,2 and Jeffrey W. Elam1,2; 1Energy Systems Division, Argonne National Laboratory, Argonne, Illinois; 2Center for Electrical Energy Storage, Argonne National Laboratory, Argonne, Illinois.

Protective coatings of metal oxides, fluorides, phosphates, and carbonates have all been shown to have beneficial effects on the performance of both lithium ion battery cathodes[1] and anodes.[2] These coatings are believed to improve performance via a number of mechanisms, including serving as a physical barrier to prevent electrode/electrolyte interactions, passivating surface defects, and gettering of corrosive hydrofluoric acid generated within the electrolyte. Typically, such coatings are deposited via sol-gel or colloidal processes; however, these deposition techniques suffer from limited conformality and thickness control. As a result, such coatings may be less effective as physical barriers or may significantly increase the electrode impedance. Alternatively, atomic layer deposition (ALD) is a technique that enables the deposition of highly conformal films with excellent thickness control. As a result, ALD is ideally-suited to the deposition of protective coatings on lithium ion battery electrode materials. ALD utilizes iterative, self-saturating surface reactions to deposit films in a monolayer-by-monolayer manner. The self-saturating nature of the surface reactions enables excellent conformality, even on highly complex, three-dimensional structures, while the monolayer growth mechanism enables precise control of both thickness and composition. Recently, thin ALD Al2O3 films have been demonstrated as effective electrode coatings for both LiCoO2 cathodes[3] and graphite anodes.[4] In particular, LiCoO2 cathodes exhibited improved capacity retention while graphite anodes exhibited both improved capacity retention and reduced irreversible capacity loss. In this work, we explore the effectiveness of ALD coatings on model anodes, including MnO and Sn. Both of these anode materials are known to form solid electrolyte interface (SEI) films, which result in significant irreversible capacity loss and performance degradation. Thin ALD coatings of differing compositions, such as Al2O3 and TiO2, and varied thicknesses are explored as a means to stabilize the electrode surface and minimize SEI formation. The effects of the ALD coatings are characterized by cyclic voltammetry and galvanostatic cycling. Preliminary results show reduced irreversible capacity loss due to SEI formation with the deposition of thin Al2O3 coatings. [1] Z. H. Chen, Y. Qin, K. Amine, and Y. K. Sun, J Mater Chem 20, 7606 (2010). [2] S. E. Lee, E. Kim, and J. P. Cho, Electrochem Solid St 10, A1 (2007). [3] Y. S. Jung, A. S. Cavanagh, A. C. Dillon, M. D. Groner, S. M. George, and S. H. Lee, J Electrochem Soc 157, A75 (2010). [4] Y. S. Jung, A. S. Cavanagh, L. A. Riley, S. H. Kang, A. C. Dillon, M. D. Groner, S. M. George, and S. H. Lee, Advanced Materials 22, 2172 (2010).

10:30 AM *F8.6
Nano-Scale Engineered Electrochemically Active Silicon Based Hetero-Structures.Prashant Kumta, Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania; Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania; Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania.

Nanotechnology is a revolutionary area that has impacted several areas of materials science and materials technology. The influence of reduction in grain sizes and structures has induced a remarkable impact on the electrochemical properties of materials for use as anodes in lithium-ion batteries, PEM fuel cell catalysts and catalyst supports, and supercapacitors. Since the discovery of tin oxide nanocomposites by Fuji as promising anode materials for lithium-ion batteries, there has been a resurgence of activities focused at identifying alternate materials to graphite, the current anode material of choice. Various strategies have been researched over the last few years comprising identifying new intermetallic anode systems, generation of a nanostructured disordered matrix containing the electrochemically active component upon electrochemical insertion of lithium as well as creation of nanowires and ‘core-shell’ structures. Our research over the years has been directed at synthesizing nanostructured composites comprising active and inactive phases generated directly ex-situ by exploiting novel low-cost synthetic approaches. The electrochemically inactive species comprising transition metal non-oxides, carbon and carbon nanotubes have been selected based on their thermodynamic and electrochemical stability towards lithium. The nanocomposites are fabricated by exploiting mechanochemical and high energy mechanical milling (HEMM)-based approaches as well as low temperature liquid injection chemical vapor deposition techniques (CVD). Initial results have shown that the resulting intra-type nanocomposites exhibit stable capacities as high as 1000 mAh/g while novel vertically aligned CNTs containing nanoscale Si clusters based hybrid heterostructures exhibit impressive capacities as high as ~3000 mAh/g. An intriguing aspect of the work is the Si-CNT interaction that serves to tether the amorphous/nanoscale Si clusters to the underlying CNT which results in the system exhibiting stable reversible capacities. Opportunities and challenges related to the synthesis and design of these nanostructured materials for next generation Li-ion batteries will be presented and discussed.

11:00 AM F8.7
Si-Based Materials for Li-Ion Batteries: Interplay between Electrochemistry, Crystal Structure and Stress.Sumohan Misra1, Nian Liu2, Johanna Nelson1, Seung Sae Hong4, Yi Cui3 and Michael F. Toney1; 1Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California; 2Department of Chemistry, Stanford University, Stanford, California; 3Department of Materials Science and Engineering, Stanford University, Stanford, California; 4Department of Applied Physics, Stanford University, Stanford, California.

Silicon is a promising anode material for Li-ion batteries. Its theoretical capacity, 4200 mAh/g, is the largest among available anode materials. However, the large capacity is accompanied by large volume expansion (ca. 400%) due to Li-ion insertion into Si. To address this volume change problem, we have developed Si nanowire (SiNW) assemblies as Li-ion anodes [1]. Due to their nanoscale diameter, SiNWs allow facile volume expansion while preventing cracking of the material and maintaining good electrical contact. To better understand these anode materials, we have studied the structural and morphological changes that SiNWs undergo during Li intercalation/deintercalation with in situ synchrotron X-ray diffraction (XRD) and transmission X-ray microscopy (TXM). As the Si-cells are cycled, the Si (111) and (220) diffraction intensities diminish and new diffraction peaks appear corresponding to three different crystal phases. Two sets of peaks (which we label Phase I & II) cannot be indexed to any materials and were not observed for cells without SiNWs. Hence these peaks correspond to new Li-Si phases (possibly metastable) that form during electrochemical cycling. The third set of peaks was indexed to Li15Si4 and observed only at low potentials (< 20 mV) during the Li-insertion cycle. We discuss the origin of these new peaks and their behavior during charge, discharge and relaxation cycles. Moreover to understand the interplay between stress (due to Li-insertion/extraction), electrochemistry and crystal structure, we have studied these SiNWs under various charge rates and studied different morphologies such as micron particles and nanoparticles. These have led us to formulate a phase diagram that depicts the evolution of these new phases as a function of potential and stress. [1] Chan, C. K., et al., Nat. Nanotechnol.2008, 3, 31.

11:15 AM F8.8
Real-Time Observations of Lithiation in Crystalline and Amorphous Si Nanorods.Hessam M. Ghassemi1, Reza Shahbazian Yassar1 and Ming Au2; 1Mechanical Eng. Department, Michigan Technological University, Houghton, Michigan; 2Savannah River National Lab, Aiken, South Carolina.

Abstract In-situ electrochemical lithiation processes inside a nano-battery consisting of an individual nanorod (NR), ionic liquid and cathode material were explored. Both, crystalline and amorphous Si NRs were used as anode and LiCoO2 was used as the cathode. Our results clearly showed that the Si structures expanded up to 270% in diameter as a result of Li+ intercalation into the anode. Electron diffraction pattern (EDP) along with the high-resolution images also confirmed the formation of LixSi particles/phases. In case of amorphous Si, it was found out that lithiation process is inhomogeneous and dominated by surface diffusion. This study showed that the volume expansion of Si NRs due to lithiation does not cause cracking in NRs as small in diameter as 26 nm, whereas cracks were observed during the lithiation of 55 nm Si NRs. Crystalline Si NRs showed preferred sites of nucleation during the early stage of the lithiation process. LixSi particles initially formed closer to the surface of the Si, confirming the surface dominant effect during diffusion of Li atoms into the anode. As lithiation process continued, more particles formed throughout the NR and the density of LixSi became more evenly distributed. EDPs of different stages of the lithiation process of crystalline Si were captured and the poly-crystallization of the single crystalline Si was observed. Real-time observation of the changes in the structure of NR as a result of Li+ intercalation and formation of LixSi phase were also detected.

11:30 AM F8.9
In Situ TEM Electrochemistry of Anode Materials in Lithium Ion Batteries.Jianyu Huang1, Xiaohua Liu1, Li Zhong2, Yang Liu1, Liqiang Zhang2, Akihiro Kushima3, Jiangwei Wang2, John Sullivan1, Scott Mao2, Ting Zhu4 and Ju Li3; 1Sandia National Laboratories, Albuqerque, New Mexico; 2University of Pittsburgh, Pittsburgh, Pennsylvania; 3University of Pennsylvania, Philadelphia, Pennsylvania; 4Georgia Institute of Technology, Atlanta, Georgia.

We created the first nano-battery inside a transmission electron microscope, allowing for real time atomic scale observations of battery charging and discharging processes. Two types of nano battery cells, one ionic liquid based, and the other all solid based, were created. The former consists of a single nanowire anode, an ionic liquid (IL) electrolyte and a bulk LiCoO2 cathode; the latter uses Li2O as a solid electrolyte and metal Li as anode. Some of the important latest results obtained by using the nano battery setup are summarized here: 1) Upon charging of SnO2 nanowires in an IL cell, a reaction front propagates progressively along the nanowire, causing the nanowire to swell, elongate, and spiral. The reaction front is a “Medusa zone” containing a high density of mobile dislocations, which are continuously nucleated at the moving front and absorbed from behind. This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically-driven solid-state amorphization. 2) In charging Si nanowires in both the IL cell and the solid electrolyte cell, the nanowires swell rather than elongate. We found unexpectly the highly anisotropic volume expansion in lithiated Si nanowires, resulting in a surprising dumbbell-shaped cross-section which developed due to plastic flow and necking instability. Driven by progressive charging, the stress concentration at the neck region led to cracking, eventually splitting the single nanowire into sub-wires. 3) Carbon coating not only increases rate performance but also alters the lithiation induced strain of SnO2 nanowires. The SnO2 nanowires coated with carbon can be charged about 10 times faster than the non-coated ones. Intriguingly, the radial expansion of the coated nanowires was completely suppressed, resulting in enormously reduced tensile stress at the reaction front, as evidenced by the lack of formation of dislocations. 4) The lithiation process of individual Si nanoparticles was observed in real time in a TEM. A strong size dependent fracture behavior was discovered, i.e., there exists a critical particle size with a diameter of ~ 150 nm, below which the particles neither cracked nor fractured upon lithiation, above which the particles first formed cracks and then fractured due to lithiation induced huge volume expansion. For very large particles with size over 900 nm, electrochemical lithiation induced explosion of Si particles was observed. This strong size-dependent fracture behavior is attributed to the competition between the stored mechanical energy and the crack propagation energy energy of the nanoparticles: smaller nanoparticles cannot store enough mechanical energy to drive a crack rpopogation. These results highlight the importance of in-situ TEM studies in understanding the fundamental sciences of lithium ion batteries, and the nano battery setup provides a unique test-bed for new battery materials.

11:45 AM F8.10
Direct Observation of Failure Modes in Silicon Nanowires for Li-Ion Batteries.Khim Karki1, Eric Epstein1, Jeong-Hyun Cho2, YuHuang Wang3, Chunsheng Wang4, Tom Picraux2 and John Cumings1; 1Material Science & Engineering, University of Maryland, College Park, Maryland; 2The Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico; 3Department of Chemistry & Biochemistry, University of Maryland, College Park, Maryland; 4Chemical & Biomolecular Engineering, University of Maryland, College Park, Maryland.

Silicon based anode material for lithium ion batteries has received enormous interests due to its high gravimetric energy density (3572 mAh/g vs. 372 mAh/g for existing graphite) and relatively low working potential (~ 0.5V vs. Li/Li+). However, the commercial realization is still far away because of the inapplicable measures of structural instability associated with huge volume changes of ~300% during subsequent cycles. While nanostructuring of materials such as nanowires tend to mitigate some of these effects, basic scientific understanding of failure modes that initiate at an atomic level is still unclear. With a specialized TEM nanomanipulation stage, we study direct lithiation/delithiation phenomena of silicon nanowires while being able to characterize structural and morphological changes in real time effectively. Thus, the mechanical robustness of pristine, lithiated, and delithiated nanowires will be presented. Results will be presented from systematic studies on various sizes and crystal orientation dependence of silicon nanowires to establish how these extrinsic parameters can alter the lithiation performance. This work is supported by the US Department of Energy, Office of Basic Energy Sciences as part of an Energy Frontier Research Center.

Chairs: Subodh Mhaisalkar and Arokia Nathan
Wednesday Afternoon, November 30, 2011
Back Bay C (Sheraton)

1:30 PM F9.1
Small and Soft Electrodes for High-Capacity Lithium-Ion Batteries.Matt Pharr, Zhao Kejie, Zhigang Suo and Joost Vlassak; School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.

Silicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries. Upon absorbing lithium, silicon swells to several times its original volume; this deformation often induces large stresses and pulverizes silicon. Existing models of lithiation-induced deformation and fracture have assumed that the electrodes are elastic. Recent experiments, however, indicate that under certain conditions lithiation causes inelastic deformation. Here, inelastic electrodes are modeled by considering diffusion, elastic-plastic deformation, and fracture. The model allows for simulation of the distribution of concentration and stress in the host during charge and discharge. It is found that fracture is averted for a small and soft host—an inelastic host of a small feature size and low yield strength. Recent experiments we have done will be shown as a demonstration of these principles.

1:45 PM F9.2
Carbon-Silicon Composite Nanofibers Prepared via Electrospinning as Anode Materials for Lithium Ion Batteries.Chunhui Chen, Majid Beidaghi, Tae-Kwon Kim and Chunlei Wang; MME, Florida International University, Miami, Florida.

Carbon and silicon are two attractive anode materials for lithium ion batteries, because of the long cycle life(C) and the high lithium-storage capacity(Si). The C/Si composite combines the advantages of both carbon and silicon. In our study, a film of carbon nanofibers that contain Si nanoparticles has been prepared by electrospinning technique, accompanying subsequent carbonization process. The composition and structures were characterized by Fourier transformation infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The PAN/Si (9/1, w/w) nanofiber exhibits high capacity up to 950 mAhg-1 for the first cycle and excellent capacity retention, up to 540 mAhg-1 in 100 cycles. The morphology change during discharge/charge was investgated via ex situ scanning electron microscopy, and the results show that abundant spaces between the fibers can effectively buffer the volume change and prevent the electrode from mechanical failure. These results demonstrate that such C/Si composite nanofiber can be an alternative anode material for lithium-ion batteries.

2:00 PM F9.3
Amorphous SnCo-C Anode: Understanding the Electrochemistry and Reaction Mechanism.Natasha A. Chernova1, Ruigang Zhang1, Shailesh Upreti1, Feng Wang2, Jason Graetz2, Lin-Shu Du3, Faisal Alamgir4, Cole Petersburg4, Elaine Lin4, Olaf Borkiewicz5, Karena Chapman5, Peter Chupas5, Clare P. Grey6 and M. Stanley Whittingham1,3; 1Binghamton University, Binghamton, New York; 2Brookhaven National Laboratory, Upton, New York; 3Stony Brook University, Stony Brook, New York; 4Georgia Institute of Technology, Atlanta, Georgia; 5Argonne National Laboratory, Argonne, Illinois; 6University of Cambridge, Cambridge, United Kingdom.

Amorphous SnCo-C anode demonstrating much higher volumetric capacity than traditionally used graphite has attracted much attention after its commercialization by SONY. This anode is comprised of 5 nm SnCo particles embedded in carbon matrix. X-ray diffraction (XRD) reveals only graphite peaks, indicating nano-amorphous nature of this alloy. Unlike crystalline tin, the nano-amorphous anode shows prolonged cycle life. However, the mechanisms of chemical transformations of this alloy upon lithium cycling remain unclear. We have employed a range of local and bulk characterization techniques, including 7Li MAS NMR, STEM, X-ray absorption spectroscopy (XAS), pair-distribution function analysis of x-ray scattering data (PDF), and magnetic studies. In-situ characterization is conducted whenever possible (XRD, XAS) and combined with the ex-situ experiments to assess crystallographic and morphological changes that occur in the amorphous SnCo locally, as well as in bulk. Local structural characterization techniques (XAS, PDF) do not reveal much of change upon lithiation and delithiation, indicating that local Sn and Co environments remain similar to that of SnCo alloy. NMR data suggests diamagnetic environment of Li up to 40% lithiation; upon further lithiation, a strong sideband manifold develops in NMR spectra, indicating a formation of magnetic phase in close proximity to Li-containing phase. Magnetic studies are consistent with NMR revealing no magnetization increase up to 40% lithiation followed by linear magnetization increase. Saturation magnetization is significantly lower than expected for the displacement of Co metal from the alloy, and no clear evidence of metallic Co is found in XAS and PDF data. We suggest that the lithiation reaction proceeds by the formation of diamagnetic LixSn and Sn1-yCo, which is ferromagnetic when Co-rich. STEM-EELS studies are in progress to investigate Co-containing phase in more detail, as are further NMR studies of the nano-LixSn phase. This research is supported as part of the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Basic Energy Sciences under Award Number DE-SC0001294 and at Georgia Institute of Technology - by the Creating Energy Options program.

2:15 PM F9.4
Tin Oxide/Carbon Nanotube Composite Electrode for High Energy Density Li-Ion Battery.Dongjoon Ahn1,2, Aiping Yu3, Zhongwei Chen3, Yawen Li4 and Xingcheng Xiao1; 1Chemical Science & Material System Lab., General Motors R&D, Warren, Michigan; 2Chemical & Material Engineering, University of Kentucky, Lexington, Kentucky; 3Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario, Canada; 4College of Engineering, Lawrence Technological University, Southfield, Michigan.

Tin oxide (SnO2) is one of the interesting negative electrodes for Li-ion batteries because of its high theoretical capacity (781 mAh/g). However, the huge volume expansion during the cycling leads to quick mechanical degradation and the associated short lifetime. In this work, SnO2 nanoparticles were deposited on the functionalized single wall carbon nanotubes (CNTs) which were not only used as the buffer to suppressing mechanical degradation of SnO2, but also as the conducting additives to enhance the electronic conductivity in the composite electrode. It has been shown that the reversible capacity of SnO2 coated CNT bundles was about 750 mAhg-1, comparing to the 200 mAhg-1 from the pristine SnO2 nanoparticle. The composite electrode also has much better cycling stability with the initial capacity of 750 mAhg-1 at first charge cycle and retained more than 90% of its initial capacity after 50th cycle, while the pristine SnO2 had low capacity at first charge and continuously decreased to 50 mAhg-1 after 10 cycles. The CNTs also improved the rate capability of the composite electrode. The impedance measurements showed the overall resistance of SnO2 coated CNT bundles was reduced through embedding CNT.

SESSION F10: Advanced Batteries II
Chairs: Subodh Mhaisalkar and Arokia Nathan
Wednesday Afternoon, November 30, 2011
Back Bay C (Sheraton)

3:00 PM *F10.1
Powering Mobile Micro- and Nano-Instruments.Vassili Karanassios, Chemistry, University of Waterloo, Waterloo, Ontario, Canada.

Over the last several years, a key trend toward miniaturization of chemical analysis instrumentation has emerged. Unlike their traditional, large-scale counterparts that are anchored to a lab and are tethered to a wall outlet, such micro- and nano-instruments can be used for measurements on-site (i.e., in the field). Mobile micro- and nano-instruments that are fast, cheap and under wireless control will cause a paradigm shift in classical chemical analysis by allowing practitioners to bring the lab (or part of the lab) to the sample. But how does one provide electrical power to such mobile instruments? In this presentation, mobile energy issues will be used to address this question. Particular emphasis will be paid to current, expected or required breakthroughs that may be crucial in powering mobile instruments.

3:30 PM F10.2
Reduced Graphene Oxide-Sulfur Nanocomposites for Advanced Lithium-Sulfur Batteries.Liwen Ji1, Mumin Rao2,3, Haimei Zheng4,5, Elton Cairns2,3, Vincent Battaglia2 and Yuegang Zhang1; 1The Molecular Foundry, Inorganic Nanostructures Facility, Lawrence Berkeley National Lab, Berkeley, California; 2Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California; 3Department of Chemical Engineering,, University of California, Berkeley, Berkeley, California; 4National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California; 5Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California.

Lithium-sulfur batteries have received more and more attention due to their both high theoretical specific capacity (about 1675 mAh g-1) and high theoretical specific energy (about 2600Wh.kg-1) along with some other unique merits. However, the development of Li-S batteries are still facing many challenges. The first one is its insulator nature of S. The second one is the formed Li polysulfides in discharge process is easy to dissolve in liquid electrolyte phase. To resolve these problems, we take an approach on incorporating nano-sulfur into reduced graphene oxides by chemical reaction. The reduced graphene oxide components with their large surface areas along with ubiquitous cavities can establish more efficient electronic contact and hold the electrochemical active sulfur. Their various kinds of functional groups can also absorb and anchor S atoms, effectively exclude the dissolution of polysulfides in the electrolyte. The role of reduced graphene oxides also include to provide a matrix that can buffer or absorb the massive volume expansion and contraction upon repeated insertion and extraction processes; Therefore, reduced graphene oxides-S composite cathodes may offer high Li-storage capacity, fast charge-discharge kinetics, improved capacity retention, and enhanced rate capability.

3:45 PM F10.3
N-Doped Carbon as a Bifunctional Electrocatalyst for Li-Air Batteries.Victor Roev, Jeong Kuk Shon, SangBok Ma, Dong Joon Lee, Young-Gyoon Ryu and Dongmin Im; Energy Lab, SAIT, Yongin-si, Korea, Republic of.

The lithium-ion batteries (LIB) is one of the most successful technologies developed in the past few decades, but their energy storage characteristics are too low for the electrification of the road transport. Recently, lithium-air batteries with organic electrolytes seem to be a great alternative to LIB, because of potentially large gravimetric energy density. In current Li-air cells the charging voltage is considerably higher than the discharge voltage. This corresponds to a low cycle electrical energy efficiency, currently on the order of 60-70% [1]. The aim of this work is to define the carbonaceous material, as potential electrocatalyst and/or support for air-electrode, having a maximum of round-trip efficiency in the comparative experiments. In-house doped carbons were prepared by combination of wet impregnation method with following pyrolysis and all cases finally an acidic rinse was applied for carbonaceous nanopowders purification. The resulting electrocatalysts were characterized by ICP, XRD, XPS, HR-SEM and N2 adsorption isotherms. The high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was confirmed by cycling Li-air cells under dry air conditions. It was shown, that nitrogen doping improved both ORR and OER activities in LiTFSI+PC electrolyes, that gives 74% of round-trip cycle efficiency. However, the addition of sulfur in the carbon was not efficient for activities improvement. The nature of active sites for ORR and OER is very important for new active electrode material development. Thus, XPS clearly show that pyridinic nitrogen functionality itself is not responsible for activities enhancement, but even 3.0at.% of quaternary nitrogen in the carbon demonstrates significant activity improvement. The experimental results concerning a Li-air battery performance will be presented and discussed. References 1.G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, and W. Wilcke J. Phys. Chem. Lett. 1 (2010) 2193.

4:00 PM F10.4
The Influence of Catalysts on Electro-Oxidation Activity of Lithium Peroxide/Oxide for Lithium-Air Batteries.Jonathon R. Harding1, Yi-Chun Lu2, Yasuhiro Tsukada3 and Yang Shao-Horn3,2; 1Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; 2Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; 3Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Lithium-air batteries have the potential to provide 4-6 times the energy density of current lithium-ion batteries.1 However, the round-trip efficiency of lithium-air batteries is very low, primarily due to the high overpotential of the oxygen evolution reaction (OER).2 Our previous work has shown that Pt and PtAu nanoparticles can considerably lower the charging voltage in comparison to Vulcan carbon, giving rise to one of the lowest reported charging voltages of Li-O2 cells to date.1, 2 As the charging voltage might be influenced by the composition of discharge products, we here examine the OER activity of Vulcan carbon, and supported Pt, Au, and other precious metal nanoparticles on Vulcan carbon toward electro-oxidation of Li2O2 and Li2O by potentiostatic measurements of composite M/C/Li2Ox electrodes. We discuss the activity trend of different metal nanoparticles for these two reactions, from which we gain insights into developing highly active OER catalysts for rechargeable Li-air batteries. References[1] Lu, Y.-C.; Gasteiger, H. A.; Parent, M. C.; Chiloyan, V.; Shao-Horn, Y. The Influence of Catalysts on Discharge and Charge Voltages of Rechargeable Li-Oxygen Batteries. Electrochemical and Solid-State Letters2010,13 (6), A69-A72. [2] Lu, Y.-C.; Xu, Z.; Gasteiger, H. A.; Chen, S.; Hamad-Schifferli, K.; Shao-Horn, Y. Platinum-gold nanoparticles: a highly active bifunctional electrocatalyst for rechargeable lithium-air batteries. Journal of the American Chemical Society2010,132 (35), 12170-12171.

4:15 PM F10.5
Morphological Evolution of Li2O2 Discharge Product in Aligned Carbon Nanofiber Electrodes for Li-Air Batteries.Robert R. Mitchell1, Betar M. Gallant2, Yang Shao-Horn2,1 and Carl V. Thompson1; 1Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; 2Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Lithium-Air batteries have received renewed attention in the last several years owing to an increasing need for high-density energy storage for electric vehicle applications.1, 2 In comparison with lithium-ion batteries, which are limited by the intrinsic performance of oxide or phosphate positive electrodes to gravimetric energies of ~600 Wh/kgelectrode and ~200 Wh/kgcell,3 lithium-air batteries are projected to achieve ~5 times higher gravimetric energies for the O2 electrode in the fully discharged state and ~3 times higher gravimetric energies at the packaged cell level. During discharge, Li+ reduces molecular O2 to form lithium peroxide (Li2O2) in the void volume of the air cathode and conversely during charge, the Li2O2 particles are dissolved and O2 is evolved. In our previous study4 we demonstrated that at low rates (< 100 mA/gC) Li2O2 particles appear to nucleate as small spheres on the sidewalls of the carbon nanofibers, before assuming a toroidal structure and growing as large as 1 µm in diameter before merging into a monolithic mass, which fills the volume between the aligned carbon nanofibers. Further we found that the unique structure of aligned carbon nanofiber electrodes enabled high gravimetric energy densities (up to 2500 Wh/kgelectrode). In this study we expand on our previous results by exploring the morphological evolution and dissolution of Li2O2 during charge using ex situ scanning electron microscopy. Additionally, transmission electron microscopy is used to investigate the structure and crystallinity of the particles at various depths-of-discharge and charge. Finally, the influence of rate on the shape and extent of Li2O2 discharge product will be addressed. References: (1) Y. C. Lu, H. A. Gasteiger, M. C. Parent, V. Chiloyan and Y. Shao-Horn, Electrochem. Solid-State Lett., 2010, 13, A69-A72. (2) T. Ogasawara, A. Debart, M. Holzapfel, P. Novak and P. G. Bruce, J. Am. Chem. Soc., 2006, 128, 1390-1393. (3) H. Chen, M. Armand, G. Demailly, F. Dolhem, P. Poizot and J.-M. Tarascon, ChemSusChem, 2008, 1, 348-355. (4) R. R. Mitchell, B. M. Gallant, C. V. Thompson and Y. Shao-Horn, Energy & Environmental Science, 2011, Accepted, DOI:10.1039/C1031EE01496J.

SESSION F11: Poster Session: Energy Conversion and Storage for Mobile Energy Systems II
Chairs: Harry Hoster and Denis Yu
Wednesday Evening, November 30, 2011
8:00 PM
Exhibition Hall D (Hynes)

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Electronically Conducting Polymers/Aligned Carbon Nanotubes Association as Nanostructurated Electrode for Supercapacitor Applications.Mathieu Pinault1, Sébastien Lagoutte2, Florent Tatard1, François Tran Van3, Martine Mayne-L'Hermite1, C. Sarrazin2, Claude Chevrot2 and Pierre-henri Aubert2; 1DSM/IRAMIS/SPAM, CEA Saclay-Laboratoire Francis Perrin, Gif sur Yvette Cedex, France; 2Laboratoire de Physico-Chimie des Polymères et des Interfaces, Université de Cergy-Pontoise, Cergy Pontoise, France; 32 Laboratoire de Chimie-physique des Matériaux et Biomolécules, Université de Tours, Tours, France.

Recently, with the development of supercapacitors, electronically conducting polymers (ECPs) have been suggested as promising materials for electrode elaboration due to their capacitance that can theoretically reach 200 to 1000F/g with polythiophene, polyaniline or polypyrroles derivatives.[1] Nevertheless, as most of the ECP, their low cyclability is still the limiting factor for a large development and their use for electrode elaboration often lead to an important decrease of electrode capacitance (80-100F/g). In order to solve this problem nanostructuration of the ECP could be considered as a promising way. In this study, we present the elaboration of nanocomposites made of poly(3-methylthiophene) (P3MT) as ECP electrodeposited onto nanostructured electrode made of aligned multiwalled carbon nanotubes (CNTs) obtained by aerosol-assisted CCVD [2]. We will present the optimization of the electropolymerization parameter leading to controlled thickness of the ECP on the CNT acting as a template electrode and to the homogeneity of the coating in the depth of the carpet (TEM, SEM), depending on several parameters (concentration, current density, galvanostatic profile…). Preliminary results concerning the elaboration and the performance of nanostructured ECP/aligned nanotubes will be presented, showing a significant increase of the specific capacitance Cm of the nanocomposite (180 F/g) and the possibility to obtain self-supported and flexible nanocomposite carpets. References: [1]C. Arbizzani, M. Mastragostino and L. Meneghello, Electrochimica. Acta, 41(1996)21; D. Bélanger, X. Ren, J. Davey, F. Uribe, S. Gottesfeld, J. Electrochem. Soc., 147 (2000) 2923; J. C. Carlberg, O. Inganäs, J. Electrochem. Soc., 144 (1997) 61; A. Laforgue, P. Simon, J. F. Fauvarque, Synth. Met., 123(2000)311 [2] M. Pinault, V. Pichot, H. Khodja, P. Launois, C. Reynaud and M. Mayne-L’Hermite, NanoLett. 2005, p. 2394

A Comparative Study on Substituted Polyanilines for Supercacitors.Punya A. Basnayaka1, Farah Alvi2, Manoj Ram3, Robert Tufts3 and Ashok Kumar1,3; 1Department of Mechanical Engineering, University of South Florida, Tampa, Florida; 2Department of Electrical Engineering, University of South Florida, Tampa, Florida; 3Nanotechnology Education and Research Center, University of South Florida, Tampa, Florida.

Supercapacitors provide higher power and durability for novel energy devices. They have been applied for mobile/portable energy storage and handling, including in micro-autonomous robots, hybrid vehicles and distributed sensors. There is an ongoing search for new and existing materials that meet the high power density and durability requirements of supercapacitor applications. The conducting polymer ‘Polyaniline’ (PANI) has been commonly applied in supercapacitor applications. Recently, derivatives of PANI have generated greater interest, because of their better procesibility in common organic solvents. In this study, we have evaluated the effect of two substituent groups (-OCH3 and -CH3) of monomers in polyanilines for supercapacitor applications. PANI, poly (o-anisidine) (POA with -OCH3) and poly (o-toluidine) (POT with -CH3) were synthesized by oxidative polymerization method, and characterized by Cyclic Voltammetry (CV), UV-visible spectroscopy, Raman spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) techniques. Due to electron localization of substituted groups, conductivity measured using four-probe technique was maximum for PANI and minimum for POT. Diffusion coefficients of PANI, POA, and POT were estimated by chronoamperometric measurement, and were found to vary as a function of substituent in aniline monomer. Specific capacitance, open circuit voltage, breakdown voltage, charging/discharging and electrochemical impedance characteristics of the supercapacitor cells fabricated with PANI, POA, and POT electrodes were evaluated in 2M H2SO4 and ionic electrolytic media. They exhibited specific capacitance levels of 400, 300 and 100 F/g in the respective order. It was observed that the specific capacitance of substituted polyanilines has the same trend as their conductivities and the diffusion coefficients. We believe that the successful facile synthesis of substituted polyanilines and their electrochemical stability and promising specific capacitance could pave the way in employing such materials for various energy storage applications.

Electrode Stabilization of Graphene-Polyaniline Based Nanocomposite Electrodes Using Barium Strontium Titanate.Supriya A. Ketkar1, Farha Alvi1, Manoj Kumar2, Ashok Kumar2,3, Thomas Weller1 and Andrew Hoff1; 1Electrical Engineering, University of South Florida, Tampa, Florida; 2Mechanical Engineering, University of South Florida, Tampa, Florida; 3Nanotechnology Research and Education Center, University of South Florida, Tampa, Florida.

Electrochemical supercapacitors are emerging as devices of crucial importance owing to their superior characteristics unmatched by any other charge storage device, like long cycle life and high power densities at relatively high energy densities. These properties are important for applications in power electronics, large scale transport systems, intermittent generators including windmills and smart grid. Carbon-material based electrodes are the most popular candidate for supercapacitor application because of their desirable physical and chemical properties. Recently, graphene has received a lot of attention from the scientific community with respect to supercapacitor application due to its high surface area, electronic and mechanical properties. There have been several attempts to incorporate graphene with other pusedocapacitance materials for use in supercapacitors. The graphene (G)-polyaniline (PANI) has been synthesized where graphene have been successfully applied with aniline monomer to produce highly conductive nanocomposite material. A leakage current hinders the application of supercapacitors in many low power electronics which is due to Faradic reactions at the surface of electrodes preventing the use the supercapacitor like battery applications. The coating the surface of the electrodes with a thin film of an dielectric material generates a potential barrier which reduces the reaction rate, with a slight drop in specific capacitance but increases the relative dielectric constant by increasing the capacitance of the supercapacitor. Keeping in view, we have deposited nm -thickness of high dielectric constant material using electrophoretic technique. The nm thick layers of Barium Strontium Titanate (BST) film was deposited on graphene-PANI nanocomposite electrodes. This will enhance the energy storage capability of the capacitor making it desirable for application in hybrid vehicle batteries. Electrochemical performance of the supercapacitor cells were tested using cyclic voltammetry (CV) and galvanostatic charge/discharge. In addition, the prepared electrodes were physically characterized using tools like XRD and SEM. The specific capacitance, charging -discharging and stability of electrodes estimated in 2M H2SO4 as electrolyte. The presence of dielectric layer in G-PANI electrode gives supercapacitor closer to the ideal situation of having a battery-like energy density while maintaining the high capacitor-like power density in the fabricated supercapacitor.

Polymer Nanocomposite Supercapacitors with Flame-Made Barium-Strontium Titanate Nanoparticles.Georgios A. Sotiriou and Sotiris E. Pratsinis; Particle Technology Laboratory, ETH Zurich, Zurich, Switzerland.

Supercapacitors play important role in the energy systems. In this work, barium strontium titanate nanoparticles were made by aerosol technology. A precise control over their size and the exact composition could be achieved. As prepared particles were characterized by X-ray diffraction, N2 adsorption. Their mixing with PMMA resulted in polymer nanocomposites and their dielectric properties were examined.

Nickel-Nickel Oxide Electrode: A Promising Energy Storage Candidate for Supercapacitor Applications.Anirudha Jena1, N. Munichandraiah2 and S. A. Shivashankar1,3; 1Materials Research Centre, Indian Institute of Science, Bangalore, KARNATAKA, India; 2Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, KARNATAKA, India; 3Centre for Nano Science and Engineering (CeNSE), Indian Institute of Science, Bangalore, KARNATAKA, India.

Electrochemical capacitors (supercapacitors) represent an emerging energy storage technology that offers high power density, long cycle life, quick charging and safety. Metal oxides show pseudocapacitive behaviour (i.e., redox capacitors), representing a class of capacitors with potential for high energy densities resulting from the fast and reversible redox reactions at/near the interface of the active storage material and electrolyte. In the present effort, a composite of metallic nickel embedded in its own oxide matrix has been synthesized via a novel microwave-assisted chemical route. A metalorganic complex of nickel, Ni(II) tertiarybutyl-3-oxobutanoate, synthesized in house, was used as precursor. A domestic microwave oven (2.45 GHz) was used for synthesis of the Ni/NiO nanostructures by subjecting a solution of the nickel complex in chloroform to irradiation for a few minutes, in the presence of a suitable reducing agent. The resulting powder was characterized by XRD, SEM, TEM, Raman spectroscopy, X-ray photoelectron spectroscopy, revealing that it comprises nanometric crystalline material of intimately mixed Ni and NiO. The deconvoluted core level spectrum confirms the presence of both Ni0 and Ni2+. Electrochemical measurements of such material are significant because of the Ni0/Ni+2 redox couples present within, which can enhance capacitance of the nanomaterial by adding a pseudocapacitive component. The Ni/NiO powder electrode material was pasted onto a stainless steel plate, using PVDF as binder. Cyclic voltamograms were recorded in 0.1M Na2SO4 electrolyte at different scan rates, providing substantially rectangular plots, when the potential range was 0 to -0.8 V. A linear behavior of cathodic current vs sweep rates indicates a charge-transfer process rather than a diffusion-controlled one. The electrodes were subjected to charge-discharge cycling at different current densities within the above potential range. The specific capacitance of the Ni/NiO electrode material was calculated from charge-discharge data to be 125 F/g, with excellent cyclability. The stability of the electrode was confirmed by subjecting it 1000 charge-discharge cycles. The resistivity of the metal-metal oxide electrode material, the resistivity of the electrolyte within the porous layer of the electrode, and the contact resistance between the electrode and the current collector were studied using electrochemical impedance spectroscopy at open circuit potential. It was found that the charge transfer resistance (Rct) and the diffusive resistance (Warburg impendence, W) of the Ni/NiO material are small. The electrode characteristics were also studied by systematically varying the nature (basic and neutral) concentration of the electrolyte. Optimization of the Ni/NiO composite is expected to yield higher specific capacitance, thus making it a promising electrode material.

Abstract Withdrawn

All Solid-State Batteries Utilizing Garnet-Structured Li7La3Zr2O12 Solid Electrolyte: Investigation of the Electrolyte/Electrode Interface.Ryan P. Maloney, Ezhiylmurugan Rangasamy, Isabel David and Jeffrey Sakamoto; Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan.

Current state of the art lithium ion battery designs utilize a liquid electrolyte, which necessitates extensive packaging and internal thermal safety mechanisms. This packaging takes up a significant portion of the battery’s total mass, and this portion increases as the battery’s size is scaled down, posing a challenge for many mobile applications. Additionally, both the flammability and the thermal stability of the organic electrolyte pose safety concerns, and necessitate the integration of cooling systems. This further reduces the total power and energy density of the energy storage system. These issues can be circumvented with the utilization of a solid electrolyte. Previous solid electrolytes have been met with limited success, due to either an unacceptably low ionic conductivity or poor chemical stability against lithium metal or air. However, the recently discovered solid electrolyte Li7La3Zr2O12 (LLZO) with a cubic garnet structure is both chemically stable and highly conductive, and can enable the next generation of solid-state lithium-ion batteries. For such a solid electrolyte to work, an interface must be formed between it and the solid active materials. To date, limited work has been published on this subject, focusing on either LiCoO2 (LCO) cathodes or lithium metal anodes. This work extends the investigation to Li4Ti5O12 (LTO) anodes, which, when paired with an LCO cathode, can enable an air-stable all solid-state battery. Preliminary findings have revealed that LLZO/LTO interface is much more readily formed than LLZO/LCO. In this work, these interfaces are extensively studied, with focus given both to the nature of the interface that forms and the application of the interface towards the creation of a solid-state battery. The thickness and composition of the interfaces are characterized as a function of sintering temperature and time, using SEM, EDS and XRD techniques. The effect of the interface on lithium transport is explored electrochemically in a half-cell with a lithium anode, using a combination of cyclic voltammetry, AC impedance and galvanostatic cycling. A prototypical full cell using solid-state anodes and cathodes is similarly characterized. This all solid-state, low cost, air-insensitive, inherently safe battery should push the design envelope of electrochemical energy storage far beyond current liquid-electrolyte based lithium ion cells.

Sol-Gel and Solid State Synthesis of LLZO Garnet Ceramic Electrolyte.Ezhiylmurugan Rangasamy1, Hyunjoong Kim1, Yunsung Kim3, Jeff Wolfenstine2 and Jeffrey Sakamoto1; 1Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan; 2Army Research Laboratory, Adelphi, Maryland; 3School of Advanced Materials Engineering, Kookmin University, Seoul, Korea, Republic of.

Current generation lithium ion batteries utilize a Lithium Hexafluorophosphate electrolyte in volatile organic solvents. This poses a safety risk due to the flammability of the organic solvents and the reactivity of electrolyte with moisture to form Hydrofluoric acid. The usage of ceramic electrolytes will mitigate these risks and aid in improving the safety. We are thereby proposing the development of Lithium Lanthanum Zirconium Oxide as an electrolyte for lithium ion batteries. Garnet structured Lithium Lanthanum Zirconium Oxide (LLZO) is a promising candidate for use as a solid state electrolyte in lithium based energy storage devices. LLZO exhibits the unique combination of high ionic conductivity, electrochemical and chemical stability. In this work we investigate the effects of synthesis methods, dopants and conditions that affect the phase purity and ionic conductivity of cubic LLZO. This is the first report of a non-Pechini sol-gel technique that can form the cubic phase garnet at 6000C. The ability to synthesize LLZO at lower temperatures is beneficial in that it can significantly reduce lithium loss prevalent during calcination. A direct comparison of the LLZO synthesized from sol-gel process and high temperature solid state synthesis process has been done. High relative density pellets (98%) were made using uni-axial hot press technique. These were then subjected to electrochemical cycling in a Lithium-Garnet-Lithium cell to assess the stability of Garnet with lithium. Electrochemical Impedance Spectroscopy was done as a function of temperature to analyze the change in charge transfer resistance at the garnet-lithium interface. Cycled pellets were observed under SEM and XRD to analyze the interface post-cycling. The effect of dopants and their concentrations were done to analyze their role in controlling defect concentrations along with stabilizing the cubic phase garnet. Our current efforts are focused on fundamental studies to understand the mechanisms that stabilize the cubic phase and enables fast ion conductivity.

Mussel-Inspired Polydopamine-Treated Coated Polyethylene Separators for Power Enhanced Li Ion Batteries.Myung-Hyun Ryou1, Yong Min Lee2, Jung-Ki Park1,3 and Jang Wook Choi3; 1Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea, Republic of; 2Department of Applied Chemistry, Hanbat National University, Daejeon, Korea, Republic of; 3Graduate School of EEWS (WCU), Korea Advanced Institute of Science and Technology, Daejeon, Korea, Republic of.

While the development of advanced electrode materials and structures is leading Li ion battery technology these days, separators, one of main component of the battery cell, should be also considered for better cell performance. In this work, we showed the development of outstanding separators also can improve the cell performance remarkably. Inspired by mussels’ exceptional adhesion capability onto versatile substrates, in this study, we treated polyethylene (PE) separators surfaces with mussel inspired polydopamine layers. By a simple dipping method, PE separators become much hydrophilic so that their wetting with polar electrolytes, usually used in commercial cells, gets significantly enhanced. The enhanced wetting properties improve the cell power capability significantly. The coating process does not sacrifice original advantages of PE separators including mechanical, thermal shutdown, and ionic conductivity properties. This study provides a lesson on how what we learn from nature can be applied to energy storage technology.

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New Li6CoO4 Cathode Additives for Controlling Irreversible Capacity Loss from Si-Based Anodes in Li-Ion Cells.Mijung Noh and Jeaphil Cho; Interdisciplinary School of Green Energy, UNIST, Ulsan Metropolitan City, Korea, Republic of.

The anti-fluorite type Li6CoO4 materials were investigated as cathode additives for compensating high irreversible capacity of Si-based anode materials in lithium-ion batteries. Li6CoO4 could deliver high charge capacity of 320mAh/g with a 96% irreversible ratio during the first cycle between 4.4 and 3V, and therefore the capacity loss from the LiCoO2 cathode to Si-based anodes could be compensated. When using pure LiCoO2 and Si-based anode with typical irreversible capacity ratio of 60% in a full cell between 4.3 and 3V, the first discharge capacity of LiCoO2 was 80 mAh/g. When using natural graphite instead of Si-based anode, however, the first discharge capacity of the LiCoO2 was 154 mAh/g. Upon optimization of additive content to 15wt% (85 wt% LiCoO2) in a full cell, the first discharge capacity of LiCoO2 was 160 mAh/g, which is identical to that obtained in the lithium half cell. In-situ XRD and TEM results were confirmed the loss of Li2O from the Li6CoO4 with a concomitant increasing formation of CoO, which led to main capacity loss according a following reaction: Li6CoO4 ? Li6-xCoO4 +Li+ ? yCoO + 2Li2O + 1-yLi6-xCoO4

In Situ TEM and Spectroscopy Study of Structural and Chemical Evolution of Electrode Materials in Lithium Ion Batteries.Chongmin Wang, Xiaolin Li, Wu Xu, Jun Liu, Jiguang Zhang, Libor Kovarik, Satyanarayana Kuchibhatla, Laxmikant V. Saraf, Bruce W. Arey, S. Thevuthasan and Donald R. Baer; Pacific Northwest National Lab, Richland, Washington.

Li-ion batteries, similar to many other electrochemical energy storage devices, are complex multi-component systems that incorporate widely dissimilar phases in physical and electrical contact. Repeated charging and discharging of the Li-ion batteries induces microstructural changes both at the interface between the electrolyte and the electrode and within the electrode. Although it has been established that this microstructural evolution is responsible for the failure of the battery, the mechanisms of microstructural change as a function of charging/discharging are not well understood. In this work, we review and discuss the fundamental designing concepts that enable in-situ TEM studies of lithium ion battery under the operating condition of the battery. In a specific example, we studied the structural evolution of SnO2 anode based on a configuration of a nanobattery using a single nanowire in a TEM column during the dynamic operation of the battery. The present model work can be applied in parallel to explore the dynamic microstructural and phase evolution of other battery systems. Furthmore, we also explored the possibility of integrating different instrumentations that provide complementary chemical and structural information with a range of temporal and spatial resolution, such as atom probe tomography(APT) and TEM. In perspective, in-situ TEM imaging and spectroscopy in combination with direct quantitative microstructural analysis and multiscale computational simulation will enable correlation of microstructural evolution features with mass and charge transport kinetics and mechanisms in a battery system, which provide vital information for design of a better battery.

Anisotropic Volume Expansion of Si Nanowires during Lithiation Revealed by In Situ Transmission Electron Microscopy.Xiaohua Liu1, He Zheng2, Li Zhong2, Shan Huang3, Khim Karki4, Li Qiang Zhang2, Yang Liu1, Akihiro Kushima5, Wen Tao Liang6, Jiang Wei Wang2, Jeong-Hyun Cho7, Eric Epstein4, Shadi A. Dayeh7, Tom Picraux7, Ting Zhu3, Ju Li5, John P. Sullivan1, John Cumings4, Chunsheng Wang4, Scott X. Mao2, Sulin Zhang6 and Jian Yu Huang1; 1Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico; 2University of Pittsburgh, Pittsburgh, Pennsylvania; 3Georgia Institute of Technology, Atlanta, Georgia; 4University of Maryland, College Park, Maryland; 5University of Pennsylvania, Philadelphia, Pennsylvania; 6Pennsylvania State University, University Park, Pennsylvania; 7Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico.

Atomic-scale deformation mechanism of Si during charging in a nano-battery revealed by advanced in situ TEM experiments will be presented. Si has attracted much interest because it has the highest theoretical capacity (4200 mAh/g for Li22Si5) among the anode materials for lithium ion batteries (LIBs). However, the large volume change during cycling causes pulverization of Si and loss of the electrical contact between Si and the electrode. Understanding the atomic scale mechanism of the lithiation behavior will help to develop strategies to mitigate these adverse effects. In situ transmission electron microscopy (TEM) enables real-time observations of microstructural evolution of the electrode materials during battery operation, providing important insight about the electrochemical reactions. We have constructed successfully two types of working nano-batteries inside the high vacuum of a TEM to test the lithiation behavior of individual Si nanowires, i.e. a solid cell and a liquid cell. The former consisted of a Si nanowire electrode, a solid-state Li2O electrolyte, and a Li metal electrode, while the latter used an ionic liquid electrolyte and a bulk LiCoO2 cathode. An unusual anisotropic swelling was observed. Upon lithiation of the <112>-oriented Si nanowires, the diameter expanded by 200% along the <110> directions but by less than 20% along the <111> directions, resulting in a unique dumbbell shaped cross section. The fully lithiated phase was Li15Si4 as identified by electron diffraction, corresponding to an achievable capacity of 3579 mAh/g. The results uncover previously unknown anisotropic deformation mechanism and highlight the critical role of plastic flow in the lithiation and fracture of Si nanostructures.

In Situ Neutron Reflectivity Measurements on the Lithiation/De-Lithiation of Amorphous Silicon Anode for Li-Ion Batteries.Bal Mukund Dhar1,2, Liwei Huang1, Kaikun Yang1, Steven C. Decaluwe2, Joseph A. Dura2, Yuping He3, Yiping Zhao3, Christopher L. Soles5, Alec A. Talin4 and Howard Wang1,2; 1Institute of Materials Research and Dept of Mechanical Engineering, State University of New York, Binghamton, Binghamton, New York; 2Center for Neutron Research, National Institute of Standards and Technology(NIST), Gaithersburg, Maryland; 3Department of Physics and Astronomy, University of Georgia, Athens, Georgia; 4Center for Nanoscale Science and Technology(CNST), National Institute of Standards and Technology(NIST), Gaithersburg, Maryland; 5Polymers Division, National Institute of Standards and Technology(NIST), Gaithersburg, Maryland.

In-situ neutron reflectivity has been used to measure the structural changes in the amorphous silicon anode of a lithium ion battery. A specially designed battery assembly contains with-beam evaporated 10 nm amorphous silicon films as the active electrode, Li metal as the counter electrode, and 1M LiPF6 in dimethyl carbonate and ethylene carbonate (1:1 ratio) as the electrolyte. Neutron reflectivity measurements were carried out on the batteries at various charge states over several cycles. The thickness of the thin film silicon anode increases to 15 nm upon lithiation at 13% of the theoretical capacity, and returns to ca. 12 nm after delithiation. The quantitative analysis agrees with the previously reported values of volume expansion of silicon anodes as a function of lithium concentration in the alloy.

Si/C Nanofiber Composite Anodes for New-Generation Rechargeable Lithium-Ion Batteries.Ying Li, Guanjie Xu, Ozan Toprakci, Shu Zhang and Xiangwu Zhang; North Carolina State University, Raleigh, North Carolina.

To reduce the gaseous emissions from the burning of fossil fuels and meet the ever-growing need for high energy and high power, rechargeable lithium-ion batteries have attracted more and more attention. Lithium-ion batteries are one of the most promising energy storage devices due to their high energy density, long cycle life, high voltage, and excellent rate capability. However, commercial lithium-ion batteries are using graphite as anodes, and graphite only has a theoretical capacity of 372 mAh/g. To increase energy density and performance of lithium-ion batteries, alternative anode materials with higher capacities are needed. Si is a promising anode material due to its extremely large theoretical capacity of 4200 mAh/g. However, the practical use of Si anodes is hindered by the structural failure of the material during charge/discharge cycling caused by the large volume changes. In our group, we have developed a new type of nanofiber composite anode formed by embedding Si nanoparticles in electrospun carbon nanofibers. Electrospinning is a convenient and low-cost technology to make nano-scale materials. Embedding Si nanoparticles in electrospun carbon nanofibers allow them to withstand large volume changes during cycling. This presentation discusses the structure and performance of these new Si/C nanofiber anodes.

Macroporous Si Spheres as Anode for Lithium-Ion Batteries.Wenchao Zhou1, Shailesh Upreti2 and M. Stanley Whittingham1,2; 1Materials Science, State University of New York at Binghamton, Binghamton, New York; 2Materials Research Institute, State University of New York at Binghamton, Binghamton, New York.

In the past several years metal-based (Si, Sn Al, etc.) materials have received a lot of research interest as candidates to replace the graphitic carbon anode for lithium-ion batteries. The significant volume change during lithium insertion/removal in these metals is a big problem that deteriorates their cycling performance. Recent work on porous Si materials indicated improved performance due to better accommodation of the volume expansion. In this work macroporous Si spheres were synthesized via etching a Si-containing alloy. XRD (X-ray diffraction) found crystalline Si after etching. SEM (Scanning Electronic Microscopy) indicated that the microstructure of Si was retained from the raw material. The Si particles were micron-sized spheres with abundant nano-sized pores inside. Electrochemical tests showed that the initial charge (lithium removal) capacity was more than 2100 mAh/g with around 1200 mAh/g retained after 50 cycles at 0.5 mA/cm2. On lithium removal more than 80% of the capacity was retained even at 8 mA/cm2 showing its high rate capability. This work is supported by Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under the Batteries for Advanced Transportation Technologies (BATT) Program.

Structural Analysis of Nano Si-C Composites Produced by Plasma Spray Evaporation for Lithium Ion Batteries.Tasuku Hideshima, Keiichiro Homma, Makoto Kambara and Toyonobu Yoshida; University of Tokyo, Tokyo, Japan.

Silicon is expected promisingly as negative electrodes for high density lithium ion battery. To make the best of its high Li storage capability, this material has to be designed to cope with its huge volume change during lithiation/delithiation. Several approaches based on nano-sized, porous composite structures are proposed [1,2]. Still, it is equally important that these structures are to be produced at the practical throughputs. With this in mind, we have attempted nano composite powder production by plasma spray (PS) evaporation. Uniqueness of this process includes the use of metallurgical grade Si powders and CH4 gas for Si and C sources, respectively [3], and also the simultaneous attainment of nano particle and Si-C composite formation. Preliminary batteries using PS powders exhibited fundamentally that increase in CH4 improves the cyclability but decreases the initial capacity significantly. However, the total capacity and cycle performance are maintained reasonably high when CH4 was introduced to C/Si~1. The objective of this work is, therefore, to identify the structural characteristics of the PS composites and understand the correlation with the cycle performance. XRD analysis identified the presence of c-Si and 3C-SiC phases in the pristine PS electrode. However, after the 1st cycle, Si peaks dramatically decreased while SiC peak remains unchanged retaining almost the initial intensity. This tendency is similarly observed for other C/Si powders. Therefore this suggests that c-Si is transformed to a-Si whereas SiC is intact during the electrochemical kinetics in the 1 st cycle. TEM observation identified for the pristine PS powders that Si particles are fundamentally single crystalline (~50 nm) and are coated by amorphous structure with the thickness of 2 ~ 3 nm. EDS analysis further revealed that the composition of such an amorphous layer is primarily Si and C. These amorphous Si-Cx coating is observed for all the specimens with different C/Si ratios, but there is no noticeable difference in its thickness between them. Furthermore, for all the half coin cells assembled with PS powders with different C/Si, a clear peak appears at around 0.1V in the differential capacity curve of the first cycle lithiation. The position of the peak however looks to shift to the lower voltages as the C/Si ratio increases. The peak at this potential can be associated with the transformation of c-Si to a-Si and the peak shift is considered as a result of the altered solid electrolyte interphase (SEI) characterisitcs with C/Si ratio, as have been reported for the c-Si coated by a-C [2]. In conclusion, the CH4 addition can alter the chemical characteristics of the a-Si-Cx shell, and its shell structure formed at higher CH4 is more favorable for improvement in the cycle performace. [1] A. Magasinski, et. al., Nature Mater, 9, 353(2010), [2]. S. Ng, et. al., J. Phys. Chem. C, 111, 11131(2007), [3] M. Kambara, et. al., 219th, ECS Meeting, #290, May 4 (2011)

Electrical Explosion Synthesis of Si/C Nanocomposites for Li Secondary Batteries.Yoon-Cheol Ha, Siyoung Choi, Chuhyun Cho and Chil-Hoon Doh; Korea Electrotechnology Research Institute, Changwon, Korea, Republic of.

Electrical explosion of silicon was successfully applied, for the first time, to the synthesis of nano-sized Si particles by using liquid media to suppress the detrimental plasma formation which had made it impossible to explode silicon in a gaseous atmosphere. The material properties of the products from different liquid media was analyzed by XRD, FE-SEM, HR-TEM and the effect of such products on the electrochemical performance of Si/C nanocomposite anode was analyzed by electrochemical charge/discharge experiments. Using hexane and ethanol, an instantaneous one-pot synthesis of Si/C nanocomposite was achieved with high content of carbon derived from the thermal decomposition of the solvents. The nanocomposites consisted mainly of Si-thick graphene carbon core-shell particles and SiC nanoparticles, which made detrimental effects on the electrochemical performance. In order to minimize the formation of the graphene-layered Si particles and the SiC phase, a 2-step process was developed based on wire explosion in methanol followed by pyrolysis of a carbon precursor. The Si/C nanocomposites synthesized by this method showed high capacities and excellent cycle performances depending on the carbon content and the pyrolysis temperature. The mechanism of the improved anode performance was characterized by various instrumental analyses, by which the optimal synthetic condition for Si/C nanocomposites was discussed.

Li and Si Diffusion in Si Anodes in Li-Ion Batteries: An Ab Initio Molecular-Dynamics Study.Priya Johari1, Yue Qi2 and Vivek Shenoy1; 1School of Engineering, Brown University, Providence, Rhode Island; 2General Motors Global R&D Center, Warren, Michigan.

Several studies have been carried out in the past few years to understand the dynamics of Li diffusion in Si anodes of Li-ion batteries . While, experiments provide a wide range of results for the diffusivity of Li into Si, most of the theoretical studies are restricted to the diffusion of a single Li atom in crystalline Si. Moreover, it is well known that crystalline Si becomes amorphous on lithiation, but the dynamics of this process has not been considered in previous computational work. We, therefore, in the current work, present the results of ab-initio molecular dynamics simulations that were carried out to study the diffusion of Li atoms in crystalline as well as amorphous Si during and after the formation of the LiSi phase. We have also analyzed the dynamics of the Si atoms during lithiation to understand its role in stress generation/relaxation. We find that Li diffuses faster in amorphous Si as compared to crystalline Si, while Si remains relatively immobile in both cases. The Si atoms, however, expand to accommodate Li. In order to further understand the mixing mechanism of Li into Si, we have examined the structural changes during lithiation by calculating the radial pair distribution function and have analyzed the evolution of Si-Si bonds leading to the formation of rings and other structures at different stages of the lithiation process. We find that Li atoms break the Si rings and chains and create ephemeral structures like stars and boomerangs, which eventually transform to Si-Si dumbbells and isolated Si atoms in the LiSi phase. However, we find that on further lithiation, Li even breaks the dumbbells and isolate Si atoms from each other. We show that our results are in agreement with the available experimental data.

SnO2-Graphene Sandwich Structures as Anode Material in Li-Ion Batteries.E. A. Anumol1, C. Nethravathi1, Konda Shiva2, Aninda J. Bhattacharyya2 and N. Ravishankar1; 1Materials Research Centre, Indian Institute of Science, Bangalore, India; 2Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India.

SnO2 is a potential candidate for Li-ion battery anode considering the high theoretical capacity but the volume change associated with the Li insertion causes the rupture of the lattice and thereby poor cyclability. SnO2-graphene composites are investigated as anodes as the high surface area of graphene can provide a percolating network throughout the electrode ensuring facile electron transport, the high mechanical flexibility of graphene helps to accommodate the volume change induced by SnLix and the Li2O matrix and the close contact between the SnO2 nanoparticles and graphene can minimize the electrical isolation of nanoparticles during battery cycles. We present a simple solvothermal method to synthesize SnO2 nanoparticles of varying sizes supported on reduced graphene oxide. Detailed characterization of the composite has been carried out using high resolution transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction. The effect of reaction temperature, solvent and precursor on the microstructure and property of the composite is studied. The structure and morphology change of the composite during cell cycling process is investigated using microscopy techniques. The composite shows high capacity and improved cyclability compared to SnO2 nanoparticles and mesoporous SnO2 aggregates.

Heat Treatment Effect of Anode Current Collectors in Lithium Ion Batteries. Tae Kwon Kim, Wei Chen and Chunlei Wang; Mechanical and Materials Engineering, FIU, Miami, Florida.

Materials of battery components are imperative to decide electrochemical performance in lithium ion batteries. Lithium ion batteries are mainly composed of electrode materials, electrolyte, separator and current collectors. Most of the recent lithium ion battery research focus is improving electrochemical performance of electrode materials which are critical to decide the cell performance, such as power density, energy capacity and electrochemical potential. However, to date, little research has been reported on the electrochemical behavior of current collectors in lithium ion batteries. Current collectors are key component that provide electronic conduction to the active electrode materials. They are typically electrochemically inactive in contact with cell components over the battery voltage window. However, it is questionable if they are thermally treated during battery assembly processes, since heat treatment is accompanied in active material fabrication processes to evaporate solvents or improve active material crystallinity. Therefore, it is important to understand how the heat treatment can affect the electrochemical behavior of current collectors in lithium ion batteries. In this study, anode current collectors, such as Ni foam, Cu foil and stainless steel foil, were chosen as examples, and the effect of thermal treatment on their electrochemical reaction and capacity contribution to the whole cell performance was investigated. The results demonstrate that the effect of heat treatment is non-negligible in the electrochemical performance and the capacity contribution of thermally treated current collectors is closely related to the heat treatment temperature.

SnO Nanobranches as an Anode of Lithium-Ion Battery.Jeong Ho Shin1,2, Jae Yong Song1,2, Young Heon Kim2, Seung Min Hyun3 and Hyun Min Park1,2; 1University of Science and Technology, Daejeon, Korea, Republic of; 2Korea Research Institute of Standards and Science, Daejeon, Korea, Republic of; 3Korea Institute of Machinery and Materials, Daejeon, Korea, Republic of.

Rechargeable lithium-ion batteries have been investigated as the most attractive power source for mobile electronic devices such as cellular phones, camcorders and lap-top computers, due to their high energy densities. Graphite has been widely used as an anode material for commercial lithium-ion batteries. However, graphite anode cannot meet the requirements for higher storage capacity because of its insufficient theoretical capacity of 372mAh/g. Nowadays, there have been studies of replacing the graphite with metals or metal oxides in order to obtain higher charge capacities. Sn-based materials have attracted much interest as an anode material because they can have much higher theoretical charge capacities, such as 994mAh/g for Sn, 875mAh/g for SnO, and 783mAh/g for SnO2. However, high charge capacities accompany huge volume expansion and shrinkage during the Li+ charge and discharge process. This huge volume changes result in the pulverization and cracking and lead to the failure of the contacts between anode material and current collector. Therefore, there have been some efforts of using nanostructured anodes in order to avoid the drawbacks related to the huge volume changes. In this work, we present the direct synthesis of SnO branched nanostructures with Sn nanoparticles on Cu collector without any binder. The SnO branched nanostructure were investigated as an anode for lithium-ion battery. The SnO nanobranches exhibited extraordinarily high discharge capacities more than 520mAh/g during 40 cycles and good coulombic efficiency. The microstructural changes of SnO nanobracnches before and after Li+ intercalation were studied and correlated to the enhanced cyclability.

Electrochemical Studies of the Effect of Thermal Reduction of Graphene Oxide.Chananate Uthaisar1, Valeri Petkov1,2, Veronica Barone1,2 and Bradley Fahlman1,3; 1Science of Advanced Materials Ph.D. program, Central Michgian University, Mount Pleasant, Michigan; 2Department of Physics, Central Michigan University, Mount Pleasant, Michigan; 3Department of Chemistry, Central Michigan University, Mount Pleasant, Michigan.

Graphene oxide (GO) was synthesized from expanded graphite (EG) by a modified Hummer’s method, and we are investigating the mechanism of GO reduction under various experimental conditions. GOs and reduced GOs were characterized by a variety of techniques such as FT-IR, Raman spectroscopy, TGA, SEM and TEM, XRD, etc. The FT-IR, and Raman confirm the successful synthesis of GOs. The Raman spectra and TGA results show the thermal stability of the reduced GOs and indicate a high purity and crystallinity at high temperatures. However, our results suggest that the reduction of GOs at high temperature (900 oC) may not entirely restore the lattice to a pristine graphitic state. At a temperature of 250 oC, we found that the reduced GO structures present signatures of amorphous structures combined with pristine graphene. The electrochemical Li intake capacity of reduced GOs at ambient temperature was improved up to ~2300 mAh/g (irreversible capacity) and ~1000 mAh/g (reversible capacity) for the first cycle. To elucidate these complex structures further, we have also utilized high-energy XRD and atomic pair distribution functions in lithiated and pristine graphene oxides.

Electrochemical-Active Transition Metal Sulfide/Graphene Nanocomposite Electrodes for High Performance Lithium-Ion Batteries.Liwen Ji1, Mumin Rao2,3, Elton Cairns2,3 and Yuegang Zhang1; 1The Molecular Foundry, Inorganic Nanostructures Facility, Lawrence Berkeley National Lab, Berkeley, California; 2Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California; 3Department of Chemical Engineering, University of California, Berkeley, Berkeley, California.

In order to meet the challenge of serious environmental pollution, global warming, and the impending exhaustion of fossil fuels, it is now essential to develop new, low-cost and environmentally friendly energy storage systems to harness and redistribute sustainable energy from sources, such as wind, solar, and nuclear, which have inconsistent power outputs. Lithium-ion battery is one of the most viable candidates for renewable storage devices. The developments of the rechargeable batteries with high energy/power density require the development of novel and multi-nanostructure electrodes to overcome the intrinsic limitations of their bulk counterparts and to display synergic properties by combining the merits of the single components as well. In the current study, a novel strategy was utilized to fabricate electrochemically-active metal sulfides nanoparticle-graphene nanocomposites and evaluate their electrochemical behaviors as high performance anodes for rechargeable lithium-ion batteries. It was demonstrated that these new nanocomposites have high Li storage capacity, improved capacity retention, and especially, excellent rate performance even at high current rates.

Incorporation of Phosphorous into the Surface of Natural Graphite Anode for Use in Lithium Ion Batteries.Min-Sik Park, Seung-Hyun Oh, Yong-Nam Jo, Jae-Hun Kim and Young-Jun Kim; Advanced Batteries Research Center, Korea Electronics Technology Institute, Seongnam, Korea, Republic of.

Lithium-ion batteries have a number of important advantages over competing technologies because they are much lighter and could offer higher energy density. Recently, many researchers access to build advanced lithium ion batteries for entering new markets such as energy storage systems (ESS) and electric vehicles (EVs) in particular. Natural graphite is a long-standing anode material in application for lithium ion batteries thanks to its low reaction potential close to 0 V vs. Li/Li+ and high theoretical capacity of 372 mAh/g. In addition, it is much cheaper than other carbonaceous materials. However, the practical use of natural graphite is highly limited by its insufficient cyclic retention and rate-capability arising from the surface exfoliation and formation of unstable passive layer called solid electrolyte interphase (SEI) during cycles. A new chemical approach to guarantee efficient cyclic performance of natural graphite anode has been designed and introduced here. We have investigated the electrochemical properties of natural graphite after surface modification with ammonium hexafluoro-phosphate (NH4PF6) to elucidate a correlation between its surface chemistry and electrochemical performance. Figure 1 shows a comparison of electrochemical voltage spectroscopy (EVS) profiles before and after the surface modification. We found that more Li+ was consumed to form an SEI after the surface modification. It can support the incomplete formation mechanism of SEI on the surface of natural graphite. The excellent cyclic retention of 94.9% at the 50th cycle was obtained without the addition of functional additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC). Such improvement could be attributed to the formation of more stable SEI as a result of incorporation of phosphorous compounds on the surface of natural graphite. The electrochemical measurements combined with structural analyses indicate that the incorporation of foreign element could make its surface more stable and reinforce the SEI during cycles. Discussion in this study focused on identifying the influence of incorporation of phosphorus on the physicochemical properties of SEI is presented with an electrochemical point of view. Furthermore, we will provide a new insight to enhance the long-term stability of SEI.

Atomic Layer Deposition of Lithium-Containing Aluminum and Titanium Oxides for Lithium Ion Battery Applications.David J. Comstock1,2 and Jeffrey W. Elam1,2; 1Energy Systems Division, Argonne National Laboratory, Argonne, Illinois; 2Center for Electrical Energy Storage, Argonne National Laboratory, Argonne, Illinois.

The conformality and thickness control of atomic layer deposited (ALD) films is ideally-suited to a number of applications within lithium ion batteries (LIBs). For example, the deposition of thin electrode stabilization films by ALD has been shown to significantly improve the performance of both LIB anodes and cathodes.[1,2] While for all-solid-state LIBs, ALD enables the fabrication of batteries within high-surface area, three-dimensional architectures that provide greatly enhanced energy and power densities relative to more traditional planar architectures. Many of the desirable materials for LIB applications contain lithium as a component, and consequently, ALD processes for synthesizing lithium-containing materials must be developed. Recently, ALD using lithium t-butoxide (LiOtBu) and H2O was demonstrated.[3] However, this chemistry is less than ideal, as it results in LiOH deposition which is both hygroscopic and air-reactive. The hygroscopic nature of LiOH is particularly problematic in the growth of thicker films, as the growing film hydrates on exposure to the H2O precursor which complicates the necessary self-limiting surface reactions of ALD. However, these problems can be alleviated by combining the LiOtBu-H2O process with other ALD processes, such as Al2O3 or TiO2, to deposit mixed metal oxides. In this work, we focus on the ALD of lithium aluminum oxide (LiAlOx) as a potential interfacial stabilization layer and lithium titanium oxide (LiTiOx) as a potential interfacial stabilization layer and as a LIB anode material, such as Li4Ti5O12. For both materials, the ALD process is characterized by quartz crystal microbalance and film deposition studies. Film morphology is characterized by scanning electron microscopy and x-ray diffraction, while composition is characterized by x-ray photoelectron spectroscopy and inductively coupled plasma mass spectrometry. The LiAlOx films are deposited by varying the ratio of LiOtBu-H2O and TMA-H2O cycles. Relatively constant growth rates and uniform films are achieved for ALD using < 50% LiOtBu-H2O cycles. However, at LiOtBu-H2O rich compositions, the hygroscopic nature of the LiOH component inhibits uniform deposition over large surface areas. In the case of LiTiOx, both titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP) were evaluated in combination with LiOtBu-H2O. TTIP-H2O results in more uniform, reproducible films; however, uniform deposition occurs only at < 40% LiOtBu-H2O cycles. [1] Y. S. Jung, A. S. Cavanagh, L. A. Riley, S. H. Kang, A. C. Dillon, M. D. Groner, S. M. George, S. H. Lee, Adv. Mater., 22 (2010) 2172. [2] Y. S. Jung, A. S. Cavanagh, A. C. Dillon, M. D. Groner, S. M. George, S. H. Lee, J. Electrochem. Soc., 157 (2010) A75. [3] M. Putkonen, T. Aaltonen, M. Alnes, T. Sajavaara, O. Nilsen, H. Fjellvag, J. Mater. Chem., 19 (2009) 8767.

Zinc Oxide-Polyaniline Nanocomposite Films as an Anode for Efficient Lithium Ion Battery.Farah Alvi1, Manoj Kumar1,2,3 and Ashok Kumar1,2,3; 1electrical engineering, University of south florida, Tampa, Florida; 2Nanomaterials and Nanomanufacturing Research Center, university of south florida, Tampa, Florida; 3Nanomaterials and Nanomanufacturing Research Center, university of south florida, Tampa, Florida.

In recent years, there has been considerable interest amongst researchers to develop novel inorganic-organic hybrid materials with composition modulated on the nanoscale due to their wide potential applications in display technologies, microelectronics, catalysis, sensors and molecular electronics. The fabrication of nanocomposite films by wet chemical techniques has been proved as a simple and inexpensive strategy than technologically demanding physical methods. It is known that PANI is one of the widely studied materials due to its unique electrochemical, chemical and physical properties. In addition, PANI exhibits high electrical conductivity and good environmental stability in doped and pristine (undoped) states. On the other hand, zinc oxide (ZnO) is a multifunctional semiconducting material with a wide band (3.37 eV at 300 K) and large exciton binding energy (60 MeV). Recently, it has been shown to exhibit several promising prospects for nanoscale structures. Further, using nanocomposite polymer scaffold, it is also possible to increase the properties of PANI as well as ZnO nanomaterials. In this work, initially we have prepared ZnO-PANI nanocomposite films by wet polymerization method. Following this, we have then characterized the ZnO-PANI by UV-Vis, FTIR, cyclic voltammetry, impedance, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and electrical conductivity. We present here first time ZnO-PANI nanocomposite as electrodes material for lithium ion batteries. The electrochemical investigations revealed that the individual redox properties of ZnO and PANI can be maintained in ZnO-PANI system, results indicated that ZnO-PANI film has exhibited wide potential window. The electrochemical and charge/discharge characteristics of ZnO-PANI nanocomposites were investigated in different electrolytic media, and the specific discharge capacitance for Li-ion battery was estimated to be 150 mAh/gm. In this work we have explored the choice of ZnO-PANI nanocomposite as an anode for the use of rechargeable batteries. We believe that the successful facile synthesis of ZnO-PANI with excellent chemical and electrochemical stability, and promising specific capacitance could pave the way in employing ZnO-PANI for various energy storage applications.

Zinc Compounds as a Potential Anode Candidate of Lithium-Ion Secondary Batteries.Chil-Hoon Doh, Ju-Seok Kim and Min-Ji Hwang; Battery Research Center, Korea Electrotechnology Research Institute, Changwon, Gyungnam, Korea, Republic of.

Zinc is a potential material as the negative of alkaline primary battery and zinc-air primary battery using the electrochemical equilibrium reaction between metallic zinc and Zn2+ cation. The direct electrochemical redox reaction of zinc occurs in the aqueous medium to have the specific capacity of 820 mAh/g. The direct redox reaction of zinc is difficult in the organic medium compared to that of lithium. And zinc was known to be alloy with lithium. The highest lithium composition of zinc-lithium is Li1Zn1. In this study, lithium alloying properties of zinc compounds were studied. Zinc compounds were prepared using sol-gel method and heat treatment, prepared as the sheet electrode, and fabricated as the coin cell with metallic lithium counter electrode to evaluate the electrochemical characteristics. Zinc compounds were analyzed as ZnO phase mainly. The specific capacity of an electrode of Zn-In-Ni(90:7.5:2.5 atomic %, heat-treated at 550 deg. C) with conductive material (10%) and binder (10%) was 400 mAh/g with good cycle-ability and rate capability. Electrochemical properties of zinc-lithium alloy were studied based on thermodynamics using published results and ab initio calculation. Potential of Li1Zn1 was known as 0.18 V as the measured value, 0.238 V as the calculated value from thermodynamic result and 0.332-0.433 V as the calculated value from ab initio calculation.

Fabrication, Performance, and Characterization of Highly Textured Positive and Negative Thin Film Electrodes in Lithium-Ion Batteries.Martin Bettge1,2,3, Seung Yoon Ryu2, Steve Burdin2, Scott MacLaren2, Ivan Petrov2, Min-Feng Yu3, Ernie Sammann2 and Daniel P. Abraham1; 1Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois; 2Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois; 3Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois.

With the demand for energy density, power density, and cycle life exceeding what current battery materials can deliver, much attention is being paid to lithium-ion cells incorporating high surface area, high capacity electrodes. We present here a templating method which allows straightforward fabrication of highly textured thin film electrodes of virtually any material using standard deposition techniques. Tex-tured electrodes based on aligned, high aspect-ratio wire arrays can provide large interfacial-area-to-volume ratios improving charge transport and diffusion kinetics, and provide built-in voids allowing mechanical strain compensation, preventing structural failure. Our approach uses vertically aligned, chemically robust silicon oxide nanowires as templates and mechanical supports for electrochemically active core-shell wire arrays. With these templates, we can readily fabricate highly textured high-capacity electrodes of vastly different materials, such as silicon (Si), tin (Sn), and lithium manganese oxide (LiMn2O4) which then can be directly compared to planar films. The method is equally effective for positive and negative electrode mate-rials. Textured Si films show much improved capacity retention over planar ones with a capacity fade around 0.8% per cycle over 30 cycles. As cell diagnostics using electron microscopy, electro-chemical cycling, and impedance spectroscopy show, the continuous formation of a solid electrolyte interface (SEI) has a significant impact on cycling performance. However, while SEI formation traps significant charge throughout cycling, it also slows down the rate of capacity loss in the Si anode. Textured LiMn2O4 films maintain their unique texture after 30 cycles and show much re-duced diffusional impedance. Some capacity fade is observed, which is attributed to chemical dissolution of the oxide material. Overall, this work offers a method to determine the particular advantages and problems associated with highly textured electrodes formed from virtually any material.

Nanonet-Based Heteronanostructures for High-Performance Li-Ion Batteries.Jin Xie, Xiaogang Yang, Sa Zhou and Dunwei Wang; Chemistry, Boston College, Chestnut Hill, Massachusetts.

As an electrochemical energy storage technology, Li-ion battery’s performance is heavily influenced by the properties of its various components. High energy capacities and high power rates, for instance, can only be obtained on devices whose electrodes can be lithiated and delithiated at a fast rate. Materials of high surface area, good electrical conductivity, and excellent reactivity with Li ions are ideal for this purpose. Unfortunately, single-component compounds that satisfy all the property requirements simultaneously are rare. We show here that this deficiency may be corrected by a heteronanostructure design. At the core of our design is a unique two-dimensional material we call nanonets. This material is made of TiSi2, and is different from more commonly encountered nanostructures such as nanowires or nanoparticles in its webbed morphology where nanowire-shaped beams are seamlessly joined together to yield a structure with high surface area and excellent conductivity. When combined with silicon nanoparticles, the nanonets exhibited minimum interface resistance. Collectively, these unique properties contributed to the measured high energy density and high power rate that are usually difficult to obtain with Si-based electrodes. Cells cycled at 6A/g showed a capacity >2000mAh/g and capacity retention of 90% in 100 cycles. Using various electrochemical techniques, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittence titration technique (GITT), we were able to quantify the diffusion coefficient of Li ions in the nanonet-based electrodes as approximately 10-10 to 10-12 cm2/s. The enhanced performance compared to typical bulk silicon materials may benefit from the reduction of electrical polarization and the short diffusion distance, both enabled by our heteronanostructure design.

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Modeling the Temperature Dependence of the Performance of a Lithium-Ion Battery.Jaeshin Yi1, Ui Seong Kim1, Jeong Bin Lee1, Chee Burm Shin1, Taeyoung Han2 and Seongyoung Park3; 1Division of Energy Systems Research, Ajou university, Suwon, Korea, Republic of; 2Vehicle Development Research Laboratory, GM R&D Center, Warren, Michigan; 3Advanced Technology Team, GM Korea, Inchon, Korea, Republic of.

The lithium-ion battery (LIB) is one of the preferred energy sources for mobile electronic systems due to its outstanding characteristics such as high energy density, high voltage, and low self-discharge rate among others. Because of the inherent nature of the mobile energy, it is necessary to design a battery management system (BMS) that secures an optimum operation of the battery as a mobile energy source against all climates. In order to build an effective BMS in all climatic conditions, the accurate prediction of the dependence of the battery performance on ambient temperature is essential. In this work, a modeling is performed to predict the dependence of the performance of a LIB on the ambient temperature. The discharge characteristics such as discharge voltage and current are modeled at the discharge rates ranging from 0.5C to 5C under various ambient temperatures. Then, the heat generation rates as a function of the discharge time and the position on the electrodes are calculated to predict the temperature distributions of the LIB based on the modeling results of the discharge characteristics. The temperature distributions obtained from the modeling are in good agreement with the experimental IR images.

In Situ Small Angle Neutron Scattering Measurements of Lithiation and Fracturing of Graphite Particles.Kaikun Yang1,2, Liwei Huang1,2, Swastisharan Dey2, Jon Owejan3, Jeanette Owejan3, Jeffrey Gagliardo3, Stephen Harris3, Yiping Zhao4, Bo Yang5, Christopher Soles6, M. Stanley Whittingham1,7 and Howard Wang2,6,8; 1Institute for Material Research, State University of New York at Binghamton, Binghamton, New York; 2Department of Mechanical Engineering, State University of New York at Binghamton, Binghamton, New York; 3Electrochemical Energy Research Laboratory, General Motors Company, Honeoye Falls, New York; 4Department of Physics and Astronomy, and Nanoscale Science and Engineering Center, University of Georgia, Athens, Georgia; 5Department of Mechanical and Aerospace Engineering, Florida Institute of Technology, Melbourne, Florida; 6Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland; 7Department of Chemistry, State University of New York at Binghamton, Binghamton, New York; 8Department of Materials Science and Engineering, University of Maryland, College Park, Maryland.

In-situ small angle neutron scattering (SANS) has been used to study the compositional and structural variation of graphite particles in lithium-ion batteries (LIBs) during their lithiation/delithation cycles. In-situ SANS cells were fabricated with graphite composite films as the working electrode, lithium metal as the counter electrode, and EC/DMC/LiPF6 as electrolyte encapsulated between two quartz plates. SANS data show that the variation of scattering intensity fully synchronizes with the lithiation/delithation cycles, decreasing upon lithiation and increasing upon delithiation. The observation is consistent with the variation of the neutron scattering length density (SLD) of graphite due to Li intercalation hence the change the scattering contrast with the surroundings. At higher cycling rates, although the degree of Li intercalation decreases, the amplitude of SANS intensity variation increases, contradictory to the prediction by the single mechanism based on the contrast variation. A second mechanism contributing to the enhanced scattering is the creation of new surfaces due to stress-induced fracturing of graphite particles. The irreversible process is partly responsible for the permanent capacity loss of LIBs. Using Porod’s law, we have quantitatively analyzed the lithiation state and the total area of fracture surfaces of graphite particles. Experimental results are discussed in the context of systematic numerical simulations based on realistic materials parameters.

In Situ Neutron Depth Profiling Measurements of Lithium Ion Transport in Secondary Batteries.Liwei Huang1, Kaikun Yang1, Gregory Downing2, Jon Owejan3, Jeffrey Gagliardo3, Dmitry Ruzmetov4, Albert Talin4, Yuping He5, Yiping Zhao5, Christopher L. Soles2 and Howard Wang1,2,6; 1Institute for Material Research and Department of Mechanical Engineering, State University of New York, Binghamton, Binghamton, New York; 2Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland; 3Electrochemical Energy Research Laboratory, General Motors Company, Honeoye Falls, New York; 4Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland; 5Department of Physics and Astronomy, and Nanoscale Science and Engineering Center, University of Georgia, Athens, Georgia; 6Department of Materials Science and Engineering, University of Maryland, College Park, Maryland.

Time-resolved neutron depth profiling (TRNDP) has been applied to measure the Li concentration distribution in electrode layers of various secondary batteries during charge/discharge cycles. NDP uniquely measures Li profiles in a thickness range from hundreds of nanometers for solid state thin film batteries to tens of microns for conventional liquid-electrolyte-containing Li-ion batteries. TRNDP spectra have been quantitatively analyzed through model fitting, in which NDP data are compared with calculated energy-loss spectra for given Li concentration profiles through iterative nonlinear least-square minimization. Particularly, we have employed rigorous self-consistent fitting schemes as both the stopping power and the energy dispersion function vary with time and depth due to the transport and redistribution of Li in active electrode layers. TRNDP data demonstrate quantitatively that ionic transport in electrodes follows the electric current in the external circuits under normal charge/discharge conditions whereas deviates upon sudden structural changes. The discrepancy between the ionic and electric transport could be a powerful indicator of the onset of battery failure.

Effect of Helium Dilution on a-Si:H Deposited at 150°C for Photovoltaic Applications.Arman Ahnood1, Arokia Nathan1, Jian Hu2 and Arun Madan2; 1London Center for Nanotechnology, University College London, London, United Kingdom; 2MVSystems Inc., Golden, Colorado.

Intrinsic amorphous silicon (a-Si:H) has been widely used as the absorber layer in photo voltaic (PV) devices. The ability to deposit high quality a-Si:H at temperatures of around 150°C allows the possibility of directly fabricating PVs on plastic substrate, which offers advantages such as light weight, low cost, and mechanical flexibility. The effect of deposition temperature on a-Si:H has been well investigated, and it has been shown that low deposition temperatures leads to incorporation of di- and poly-hydrides in the a-Si:H, resulting in higher efects. As a solution the concept of soft helium ion bombardment has been proposed for low temperature deposition of a-Si:H. In this method the excess, weakly bonded hydrogen can be removed from the film during the deposition, by introducing helium in the PECVD chamber. In this work we apply the concept of soft helium ion bombardment to the deposition of a-Si:H. The optical and electrical properties of the a-Si:H as a function of helium dilution is systematically investigated. We show that while there is a need for helium dilution at 150 degrees celsius, excessive use of helium leads to creation of defects. Using the optimised a-Si:H film we fabricated a PV device. The performance of the device is presented and discussed.

Cross-Contamination in a-Si:H PVs Fabricated Using Two-Chamber PECVD System.Arman Ahnood1, Arokia Nathan1, Jian Hu2 and Arun Madan2; 1London Center for Nanotechnology, University College London, London, United Kingdom; 2MVSystems Inc., Golden, Colorado.

Conventional solar cell devices are fabricated in cluster tools with dedicated chambers for the deposition of p-, i- and n-layers. This is done to avoid contamination of the intrinsic layer with boron and phosphorus. Such deposition system typically requires at least three chambers and involves a complex design that leads to a higher cost of production tools. This has fuelled the interest in fabrication processes for single deposition chambers minimise the cross-contamination of the intrinsic layer. In this work we investigate the use of a two-chamber deposition system with a dedicated intrinsic chamber connected thorough a load lock to the doped chamber which is used for the deposition of both p- and n-layers. Two-chamber system can be fabricated with lower complexity and cost than three-chamber system. Furthermore comparing the cross-contamination in two-chamber with single-chamber systems provides an insight in the origin and the location of the contamination defect within the solar cell structure. The wavelength dependent collection efficiency can be used as a tool to probe the location of the defects in superstate a-Si:H p-i-n solar cells structures. Using this method we investigate the effect of the doping chamber wall’s plasma treatment duration using CF4 and O2. It is shown that that an additional post cleaning purge step using H2 and N2 is required to fully minimise effect of the cross contamination. The results of this work suggest that the presence of boron at the n-i interface can also results in recombination losses. Boron contamination can be eliminated by adopting suitable chamber conditioning steps. The possible mechanisms of this recombination loss are discussed.

SESSION F12: Characterization and Theory I
Chairs: Piers Andrew and Harry Hoster
Thursday Morning, December 1, 2011
Back Bay C (Sheraton)

8:30 AM F12.1
In Situ TXM and XRD on Li-S Batteries.Johanna Nelson1, Sumohan Misra1, Yuan Yang2, Ariel Jackson2, Yi Cui2, Joy C. Andrews1 and Michael F. Toney1; 1SLAC, Menlo Park, California; 2Materials Science and Engineering, Stanford University, Stanford, California.

Sulfur is an attractive Li-ion battery cathode material candidate because of its high specific energy (2600 Wh/kg); however, it is well known that Li-S batteries suffer from capacity loss or fading. It is generally accepted that this is due to the loss of active material and the formation of nonconducting Li2S as a thin film coating the electrode. Both phenomena stem from the dissolution of active sulfur particles in the non-aqueous electrolyte as soluble long chain polysulfides form during the early stages of cell discharge. By using both in situ transmission X-ray microscopy (TXM) and X-ray diffraction (XRD), we can characterize both the morphological changes as well as the changes in cathode crystallinity and crystal structure. The hard X-ray, full-field microscope at 6-2 allows up to 30 nm resolution 2D and 3D images without the need for highly specialized battery cell configurations. This permits the use of the same in situ cell configuration in both the TXM and XRD measurements. We can then correlate the data from the complementary methods to better understand the reduction of elemental sulfur and various adaptations employed to retain battery capacity over numerous cycles.

8:45 AM F12.2
Oxygen Evolution Reaction of Lithium Peroxide in the Lithium-Air Battery: A First Principles Study.Yifei Mo, Shyue Ping Ong and Gerbrand Ceder; Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

The Lithium-air battery is an interesting candidate for the next generation batteries with higher specific energy. However, the Li-air battery currently suffers from poor reversibility, low power density, and a high overpotential upon charging. The widespread commercial adoption of the Li-air battery is not possible until these substantial challenges are overcome. To facilitate the experimental efforts in improving the performance of the Li-air battery, it is essential to gain a better understanding of the fundamental mechanism of the cathode reactions, such as the oxygen reduction reaction (ORR) during discharging and the oxygen evolution reaction (OER) during charging. Using first principles calculations, we study the fundamental mechanism of OER processes during the discharging of the Li-air battery. Our first principles calculations identified the lowest energy surfaces and the Wulff shape of Li2O2. We determined the elementary reaction steps and the reaction energy profile of the OER on the low-index surfaces of Li2O2. In all the surfaces investigated, we found that the formation of lithium superoxide LiO2 is an intermediate step to decompose Li2O2 during discharging. Our first principles calculations have shown that the OER processes are kinetically limited by the high energy barrier of the evolution of oxygen molecules and the kinetic rate of OER is highly dependent on the surface orientation. The low power density and poor reversibility of the Li-air batteries is probably caused by the poor kinetics for the OER.

9:00 AM F12.3
In Situ Neutron Diagnosis of Lithium Ion Batteries.Howard Wang1,2,11, Kaikun Yang1, Liwei Huang1, Bal Mukund Dhar1,2, Lianfeng Zou1, R. Gregory Downing2, Christopher L. Soles2, Yuping He3, Yiping Zhao3, Dmitry Ruzmetov4, A. Alec Talin4, Steven DeCaluwe5, Joseph A. Dura5, Jon Owejan6, Jeanette Owejan6, Jeffrey J. Gagliardo6, Daniel S. Hussey7, M. Stanley Whittingham8, Jiguang Zhang9 and Bo Yang10; 1Institute for Materials Research and Department of Mechanical Engineering, State University of New York, Binghamton, Binghamton, New York; 2Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland; 3Department of Physics and Astronomy and Nanoscale Science and Engineering Center, University of Georgia, Athens, Georgia; 4Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland; 5NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; 6Electrochemical Energy Research Laboratory, General Motors Company, Honeoye Falls, New York; 7Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland; 8Institute for Material Research and Department of Chemistry, State University of New York, Binghamton, Binghamton, New York; 9Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington; 10Department of Mechanical and Aerospace Engineering, Florida Institute of Technology, Melbourne, Florida; 11Department of Materials Science and Engineering, University of Maryland, College Park, Maryland.

Rechargeable Li-ion batteries (LIB) are a promising technology for efficient energy storage. We have carried out critical in situ neutron measurements on Li distribution and transport to gain new insights in the function and failure of battery systems. Four neutron measurement techniques, neutron depth profiling (NDP), neutron reflectivity (NR), small angle neutron scattering (SANS), and neutron imaging (NI) have been used to quantify real-time information of the Li transport in electrode, sub-nanometer interfacial structures, and fracturing of electrode particles. NDP data show that the discrepancy between the ionic and electric transport could be a powerful indicator of the onset of battery failure. NR probes depth-dependent compositions and interfacial structures in buried thin films with sub-nanometer resolution and correlates the lithiation state with the integrity of electrode films. Quantitative analysis of in-situ SANS data yields the total area of fracture surfaces of graphite particles induced by lithiation/delithiation cycling. Real-time NI monitoring of the lithiation of highly-oriented pyrolitic graphite illustrates the existence of hot-spots near the surface, through which Li ions enter to intercalate the bulk of the graphite electrode. The findings demonstrate that in situ neutron diagnoses offer promising new opportunities for better understanding of rechargeable batteries.

9:15 AM F12.4
In Situ SEI Characterization through Neutron Reflectometry.Jeanette E. Owejan1, Joseph A. Dura2, Jon P. Owejan1 and Steven C. DeCaluwe2; 1EERL, General Motors, Honeoye Falls, New York; 2NIST-Center for Neutron Research, Gaithersburg, Maryland.

Decomposition of electrolyte components in lithium ion batteries form the solid electrolyte interphase (SEI). This passivation type layer has been studied extensively by various electrochemical and spectroscopic techniques for decades. Neutron reflectometry has been introduced to lithium battery diagnostic applications because of its high special resolution, in-situ capabilities, and neutron sensitivity to lithium and isotopes of hydrogen. In this study, neutron reflectometry is used for the first time in an operating cell to characterize formation, composition, and thickness of the SEI in situ on a non-intercalating electrode at the AND/R beam at the NIST reactor in Gaithersburg, MD. Furthermore, the possibility of preferential carbonate decomposition is explored through use of deuterated and protonated solvents. Complementary electrochemical data as well as ex-situ specular reflectance FTIR and high resolution XPS data have also been collected on the passivation films. Combination of all diagnostic results enables an improved understanding of SEI as a heterogeneous film.

9:30 AM F12.5
Mapping Irreversible Electrochemical Behavior on Li-Ion Conducting Glass Ceramic by Electrochemical Strain Microscopy.Thomas M. Arruda, Amit Kumar, Sergei V. Kalinin and Stephen Jesse; CNMS, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Electrochemical phenomena in solids including interfacial reactions and ionic transport underpin a broad range of energy technologies ranging from metal-ion and metal-air, batteries to fuel cells, all of which are considered leading candidates for electrical vehicle applications. Functionality of these systems is often enabled or controlled by the phenomena at solid-gas and solid-solid interfaces, with examples ranging from electrocatalysis at triple-phase junctions to grain-boundary and interface mediated phenomena that control ionic transport and local polarization. Electrochemical Strain Microscopy (ESM) was developed as a probe for detecting and mapping ionic currents in solids on the nanoscale. In ESM, a high frequency periodic bias is applied between the tip and an electrochemically active material surface (tip-electrode). The SPM tip acts as a probe of local periodic strains generated due to bias-induced ion redistribution and associated changes in molar volume of the material. The intrinsic high sensitivity of AFM to small (~2-5 pm level) oscillatory surface displacements combined with high (10-20 nm) lateral resolution allows Li-ion motion to be probed in ~ 10^6 smaller volumes than possible by current-based electrochemical methods. ESM has been successfully deployed to investigate Li-ion conduction in Li ion battery materials such as LiCoO2 cathodes and Si anodes. Here we will demonstrate that ESM is a useful tool to investigate Li-ion conduction in solid state electrolytes as well. Commercially available LISICON (product AG-01, Ohara Inc.) is an ideal candidate for ESM as it exhibits high Li-ion conductivity and is a polished glass ceramic consisting of three phases, all of which yield slightly different ESM signal, hence giving rise to spatial contrast. This talk will describe our ESM observations for various ESM imaging and spectroscopic modes including Band Excitation Piezoresponse Spectroscopy (BEPS), First Order Reversal Curves (FORC) and current measurements. These SPM modes produce nanoscale maps of Li-ion current and further the understanding of electrochemical processes (reversible and irreversible) on single particles. These results are necessary for understanding of origins of high charge-discharge hysteresis and polarization losses in Li-ion batteries and suggest pathways for material optimization. Acknowledgement Research was sponsored by the Laboratory Directed Research and Development Program and conducted at the Center for Nanophase Material Sciences of ORNL, managed by UT-Battelle, LLC, for the U.S. Department of Energy.

9:45 AM F12.6
Abstract Withdrawn


10:30 AM *F12.7
Thermodynamics Study on Lithium Ion Battery Materials.Denis Yu1, Rachid Yazami1, Harry Hoster2 and Subodh Mhaisalkar1,3; 1Energy Research Institute, Nanyang Technological University, Singapore, Singapore; 2TUM-CREATE Centre of Electromobility, Singapore, Singapore; 3School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore.

The ability to monitor the status of a battery during charge and discharge is important to predict its performance and life. This is typically done by measuring the voltage and resistance across the terminals, or by external characterization methods such as X-ray diffraction and Raman spectroscopy. Thermodynamics measurements based on entropy and enthalpy provide another mean to “look inside” a battery, giving us more information to determine the state of health of the battery. In particular, entropy undergoes dramatic changes at boundaries of phase transitions taking place in each electrode material at defined states of charge (lithium stoichiometry). So the entropy profile of a full cell (anode + cathode) is specific to the battery chemistry. Recent work on thermodynamics study on lithium ion battery materials will be shown at the meeting.

11:00 AM F12.8
Solid Electrolyte Interfaces and Interphases in Lithium Batteries: In situ Studies Using Nonlinear Optical Probes. Prabuddha Mukherjee, Alexei Lagutchev and Dana D. Dlott; School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois.

Solid-electrolyte interphase (SEI) regions play a critical role in stabilizing lithium batteries, but little is known about the detailed mechanisms of their growth and formation. We have developed a novel method for in situ study of the growth of SEI layers. Our method uses a nonlinear vibrational spectroscopy method termed femtosecond broadband multiplex vibrational sum-frequency generation spectroscopy (SFG) and a lithium battery electrochemical cell with optical access. The SFG method has high sensitivity and high selectivity needed to study the molecular species created during SEI growth. In contrast to ordinary spectroscopic techniques which are most sensitive to bulk materials, SFG is most sensitive to interfacial regions. With SFG we can ignore the bulk electrolyte and focus directly on the solid-electrolyte interface region that is just a few molecules thick. We will present results obtained using a lithium battery and model materials relevant to such batteries, where during successive cycles of charge and discharge, we selectively probed the structure and material changes, via vibrational spectroscopy. Since there are two sides to every interface, we obtained spectra of both the SEI and the adjacent fluid electrolyte. This material is based upon work supported as part of the Center for Electrical Energy Storage - Tailored Interfaces, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number A2703 DOE ANL 9F-31921.

11:15 AM F12.9
In Situ TEM Observation of Pulverization of Aluminum Nanowires and Evolution of the Thin Surface Al2O3 Layers during Lithiation/Delithiation Cycles.Yang Liu, Nicholas S. Hudak and Jian Yu Huang; Center for Integrated Nanotechnologies (CINT), Sandia National Laboratories, Albuquerque, New Mexico.

Lithiation/delithiation cycles of individual aluminum nanowires (NWs) with naturally oxidized Al2O3 thin surface layers with a thickness about 4-5 nm were conducted in situ in a transmission electron microscope (TEM). Surprisingly, the lithiation was always initiated from the surface Al2O3 layer, forming a stable Li-Al-O glass tube with a thickness of about 6-10 nm wrapping around the Al nanowire core. After lithiation of the surface Al2O3 layer, lithiation of the inner Al core took place, which converted the single crystal Al to a poly-crystalline LiAl alloy, with a volume expansion about 100%. The Li-Al-O glass tube survived the 100% volume expansion, acting as a rubber with exceptional mechanical robustness. Voids were formed in the Al NWs at the first delithiation process and grew continuously at each following delithiation cycles, leading to pulverization of the Al NWs to isolated nanoparticles confined inside the Li-Al-O tube due to de-alloying of Li from the LiAl alloy. The results provide important insight into the degradation mechanism of metal electrodes and into the recent reports about the performance improvement of lithium ion batteries (LIBs) by atomic layer deposition of Al2O3 coating on the active materials or on the electrodes.

11:30 AM F12.10
Location- and Orientation-Dependent Progressive Crack Propagation in Cylindrical Graphite Electrode Particles.Rassin Grantab and Vivek B. Shenoy; Mechanics of Solids, Brown University, Providence, Rhode Island.

Crack propagation in graphite electrodes has been discovered to facilitate the growth of solid electrolyte interphases (SEI) that greatly affect the long-term capacity of lithium ion batteries. In order to maintain the charge capacity of these batteries over a number of years, crack propagation must be understood and minimized. Using cohesive zone models in finite element calculations, we have studied crack propagation in cylindrical graphite anodes by considering the progressive growth of preexisting defects during cyclic charging. We have found that for a defect to grow, it must be situated far from the center of the particle in order to be placed under high tensile stress, and it must also be closely aligned with the radial direction so the components of stress normal to the defect are high enough to cause crack propagation. Such defects begin to grow during the delithiation - not the lithiation - phase of the charging cycle due to the state of high tensile hoop stress that occurs in the outer region of the particle during lithium de-intercalation. Upon subsequent cycles, the cracks progressively grow further, until complete failure of the particle is observed. Our simulations show that for typical charging conditions, defects situated within 88% of the particle's radius from the center, and those mis-aligned from radial lines by more that 26 degrees, will not propagate. A failure diagram that demarcates safe and unsafe crack growth regimes is presented as a function of the location and orientation of defects. We also discuss the influence of particle size, crack microstructure, and charging rate on the failure map. The main results dealing with location-dependent failure are qualitatively the same when fully anisotropic material behavior is considered as opposed to an isotropic assumption. (Accepted for publication in the Journal of the Electrochemical Society, in press)

11:45 AM F12.11
Role of Applied Voltage on Damage of Graphite Electrodes Electrochemically Cycled vs. Li/Li+.Sandeep Bhattacharya, A. Reza Riahi and Ahmet T. Alpas; Mechanical, Automotive and Materials Engineering, University of Windsor, Windsor, Ontario, Canada.

Graphite electrode surface damage that occurs as a result of voltage applied during potentiostatic, cyclic (CV) and linear sweep (LSV) voltammetry tests (vs. Li/Li+, using 1 M LiClO4 in a 1:1 volumetric mixture of ethylene carbonate and 1,2-dimethoxy ethane) was observed using in-situ high magnification optical and cross-sectional transmission electron (TEM) microscopy methods. To observe the effect of voltage on damage, potentiostatic experiments were performed at constant values of voltage. Microscopical evidence revealed graphite damage in the form of particle removal. Ex-situ micro-Raman spectroscopy provided evidence for fracture and fragmentation of graphite particles. Surface changes on graphite electrodes were also observed (in-situ) during CV tests performed between 0.00?3.00 V at ambient and subzero temperatures (= -5oC). Under ambient temperature conditions, subsurface microstructures of graphite electrodes, prepared by FIB-milling, exhibited partial delamination of graphite layers adjacent to solid electrolyte (SEI)/graphite interface due to formation of interlayer cracks. Local compositional changes in graphite subsurface, investigated using high-resolution (HR)-TEM, included preferential deposition of lithium compounds (LiC6, Li2CO3 and Li2O) near the tip of these cracks. Deposited layers caused partial closure of propagating graphite cracks during electrochemical cycling possibly reducing the crack growth rate. Also, interconnecting graphite fibres bridged crack faces and retarded crack propagation. In another set of experiment (LSV), tests initiated from a peak voltage (3.00 V) promoted formation of SEI on graphite and reduced graphite degradation. In these experiments, the voltage was decreased using different sweep rates of 0.05-5.00 mV s-1 to a constant base potential (0.02 V). The effects of scan rate and temperature, on SEI formation and graphite damage mechanisms, will be discussed.

SESSION F13: Characterization and Theory II
Chairs: Vassili Karanassios and Denis Yu
Thursday Afternoon, December 1, 2011
Back Bay C (Sheraton)

1:30 PM *F13.1
Electrocatalysts for Oxygen Reduction - Exploring the Volcano in Model Studies. Otavio B. Alves2, R. Jürgen Behm2 and Harry E. Hoster1; 1TUM CREATE Centre for Electromobility Singapore, Technische Universität München, Singapore, Singapore; 2Institut für Oberflächenchemie und Katalyse, Universität Ulm, Ulm, Germany.

Oxygen reduction is a key process at the cathodes of fuel cells or Lithium-air batteries. According to the Sabatier principle, the chemical reactivity of electrocatalysts should be neither too high nor too low, which is usually visualized by the so-called volcano curve. For metal electrodes, the electrochemical reactivity can be tuned via alloying. An elegant way of exploring the attainable range of reactivities is the fabrication of model electrodes consisting of atomically thin metal layers vapour deposited onto single crystal surfaces. Structure and composition of these films can be precisely analyzed by imaging and spectroscopic methods and atomic scale surface imaging [1-3], whereas preparation parameters like deposition rate and sample temperature offer control of the microscopic structure [1]. Using Pt thin films [2] and PtRu surface alloys [1,3] supported on Ru(0001) as examples, it is shown that the electrochemical properties as observed by cyclic voltammetry in aqueous electrolyte can be predicted by DFT calculations. Moreover, the oxygen reduction performance can be tuned towards the same level as previously obtained for other Pt containing alloy single crystals and nanoparticles [4]. Our data demonstrate that the volcano curve for a given electrocatalytic process can not only be explored by the choice of metals used in the alloy [4], but in particular also by varying surface structure and composition for a given metal combination. From a technical point of view, however, the study also indicates that, even for chemically and structurally optimized alloy cathodes, sluggish oxygen reduction remains a bottleneck in electrochemical energy conversion. References: [1] T. Diemant et al., ChemPhysChem 11 (2010) 3123 [2] H.E. Hoster et al., ChemPhysChem 11 (2010) 1518 [3] H.E. Hoster et al., Physical Chemistry Chemical Physics 12 (2010) 10388 [4] J. Greeley et al., Nature Chemistry 1 (2009) 552

2:00 PM F13.2
Surface Reactions and Concomitant Stress Evolutions in Graphitic Thin Film Electrodes in Li-Ion Battery. Amartya Mukhopadhyay1, Anton Tokranov1, Fei Guo1, Xingcheng Xiao2, Robert H. Hurt1 and Brian Sheldon1; 1School of Engineering, Brown University, Providence, Rhode Island; 2R and D center, General Motors, Warren, Michigan.

Despite graphitic carbon being the most commonly used material for anodes in Li-ion batteries, plausible stress developments due to SEI layer formation/solvated Li-ion co-intercalation, in addition to actual Li-intercalation, as well as lithium self discharge, which contribute extensively towards limiting the performance of such electrode materials, are not yet fully understood. For aiding fundamental understanding of such phenomenon, our work focuses on model thin film systems of c-axis oriented graphitic carbon thin films, developed using chemical vapor deposition. Multibeam Optical Stress Sensor (MOSS) technique is used for in-situ quantitative determination of the stress developed in the thin film anode materials during charging and discharging cycles in a custom made Li-ion battery. Extremely low compressive stress (~ 0.25 GPa) gets developed parallel to the current collector/substrate during actual Li-intercalation to near theoretical capacity. However, an interesting observation has been the development of a net irreversible compressive stress of ~ 0.5 GPa for ~ 18 cycles, which correlates extremely well with the irreversible capacities observed for the same number of cycles and which is attributed to Li consumption for formation of SEI layer. On a different note, it has been reported that Li self discharge from the graphitic anode materials is one of the contributing factors towards the loss of capacity for Li-ion batteries. A distinct advantage of using in situ stress measurements with our thin, elastic electrodes is that the Li content in the film is directly related to the measured stress. Hence stress rise due to Li de-intercalation during self discharge (zero current hold) can be directly used for analysis of self discharge kinetics. In this regard we have used long zero current holds after fully charging the graphitic thin films with Li, when only self discharge leads to loss of Li with concomitant stress relief. Mathematical models have been developed to fit the self discharge steps, and also the lithiation/delithiation steps which will give an estimate of the self discharge kinetics and the mechanisms. In addition to the c-axis oriented CVD carbon thin films, chromonic liquid precursors have been used to develop a-axis oriented graphitic thin films (graphene planes perpendicular to substrate). These films have been observed to allow better capacity retention at high electrochemical cycling rates due to possibility of faster Li intercalation/de-intercalation kinetics. Study of SEI kinetics and self discharge in such films will also provide more insight into effects of graphitic orientation on such phenomenon.

2:15 PM F13.3
Growth and Characterization of Single and Multi-Layered Graphene for Li-Ion Anodes.Gouri Radhakrishnan, Joanna D. Cardema, Paul M. Adams, Brendan J. Foran and Hyun I. Kim; Materials Science Department, The Aerospace Corporation, Los Angeles, California.

There is a continued need for improvements in lithium ion technology for next-generation power systems that aim for higher energy density, higher rate capability and reduced battery weight. Nano-materials have yielded promise for meeting these goals. In particular, single and multi-layer graphene films on thin copper and nickel foils offer the potential for significant weight reduction in lithium ion batteries. Here we describe the growth of graphene films on 15 mm diameter copper and nickel foils for direct fabrication into anodes. The growth was achieved using a novel and inexpensive precursor. Unlike existing methods of graphene growth, our method does not employ hydrogen as a process gas. Eliminating H2 as a process gas offers increased safety and greatly facilitates fabrication scaling. Process pressures were tuned between low pressures and ambient pressure to optimize monolayer and multilayer graphene growth. Prior to the fabrication of anodes, the as-grown graphene films were characterized with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Both grain size and grain orientation of the graphene were established with transmission electron microscopy. Scanning electron microscopy and X-ray diffraction pole figures were used to evaluate substrate grain orientation before and after deposition. For purposes of establishing the electrochemical effects solely due to the graphene, anodes were assembled without the use of a binder. The graphene layer(s) were tested by cycling the graphene electrode versus lithium metal in a 2032 coin cell, with a 1 M LiPF6 in ethylene carbonate:diethyl carbonate 1:1 electrolyte. Galvanostatic cycling at a rate of 5 µA/cm2 indicated that the charge and discharge capacities for single and multilayer graphene were on the order of 0.04 mAh/cm2, which is comparable to previous reports of carbon-based thin film electrodes. For multilayer graphene, distinct peaks were observed in cyclic voltammograms, indicating intercalation of lithium into the graphene layers. Details of the growth process, characterization of the graphene films, and XPS analysis of the cells after cycling will be presented. The comparison between single and multilayer graphene anodes, as well as comparisons to well-ordered bulk graphite layers from highly oriented pyrolytic graphite cycled under the same conditions will be discussed.

SESSION F14: Electrochemical Capacitors
Chairs: Vassili Karanassios and Denis Yu
Thursday Afternoon, December 1, 2011
Back Bay C (Sheraton)

3:00 PM *F14.1
Nanostructure Enhanced Energy Storage.Piers Andrew1, Di Wei1, Pritesh Hiralal1, Yinglin Liu1, Chris Bower1, Markku Rouvala2, Haolan Wang3, Gehan Amaratunga3 and Li Niu4; 1Nokia Research Center, Cambridge, United Kingdom; 2Nokia Research Center, Helsinki, Finland; 3Department of Engineering, University of Cambridge, Cambridge, United Kingdom; 4Changchun Institute of Applied Chemistry, Changchun, China.

In this work we describe the performance enhancement of energy storage devices obtained through control of electrode nanostructure, focusing on nanocarbon-based supercapacitors and flexible Li secondary batteries with cathodes formed by the deposition of graphene-based inks. Supercapacitors are promising candidates to fulfil increasing power demands upon energy storage systems and in certain applications may complement or replace batteries, possessing advantages such as high power density, rapid charge/discharge, high cycle life, and improved safety characteristics (no heavy metals and reduced likelihood of catastrophic failure) [1]. Here, attention is given to decreasing device internal resistance which causes unacceptable power loss and voltage drop in key applications requiring high current bursts. We describe nanocarbon-based electrical double layer supercapacitors fabricated with a two step process to decrease their equivalent series resistance (ESR). First, a thin, conductive carbon layer coated on a copper current collector decreases the nanocarbon electrode/copper terminal contact resistance. The rough surface of the carbon layer increases both the contact area and adhesion between the electrode and the copper surface and furthermore prevents metal oxidation and corrosion, mitigating ESR increase upon cycling and prolonging the device life. Second, addition of multiwall carbon nanotubes (CNTs) further decreased the device ESR. CNTs have good electrical conductivity and scanning electron microscopy shows that CNTs cover the surface of the nanocarbon particles and bridge interparticle gaps. After surface treatment of the copper and CNT addition, our supercapacitors have significantly reduced ESR and highly enhanced capacitance as measured by voltammetry and charge/discharge measurements. In addition to satisfying the ever-increasing demand for increased energy density, batteries for future mobile devices should sustain flexure, allowing the use of new form factors, functionalities and user interactions. To address this, we have constructed and characterised flexible secondary Li batteries using cathodes deposited from graphene-containing inks and polymer gels which act as both electrolytes and separators. Here we describe how the energy density, open-circuit voltage and cyclability of such batteries can all be improved by a combination of chemical functionalization of the graphene platelets with anionic polymers, incorporation of titania nanoparticles and addition of lithium salts. Using such an optimised ink formulation we were able to achieve an open circuit voltage of ~3V and a first discharge capacity of 582 mAh/g, which decreased to ~250 mAh/g on the fourth cycle, thereafter remaining constant until at least the 100th cycle [2]. [1] Conway, B.E. “Electrochemical Supercapacitors” Kluwer Academic; New York (1999) [2] Di Wei et al; J. Mater. Chem., 2011, 21, 9762-9767

3:30 PM F14.2
Design of Flexible Supercapacitors Using Metal Oxide-Decorated Carbon Nanotube Sheet.Meredith C. Sellers1, Niels P. Zussblatt1,3, Andrew P. Friedl1, Scott M. Lux1, Justin R. Hesterberg1, Carl A. Feickert1, Sean Morefield1 and Charles P. Marsh1,2; 1US Army Engineer Research and Development Center, Construction Engineering Research Laboratory, Champaign, Illinois; 2Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois; 3Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Functional fabrics are designed with integrated, active capabilities that distinguish them from conventional textiles. These lightweight materials offer innovative possibilities for power generation and storage as well as human interface elements, environmental sensing devices, and radio frequency functionality. Their enhanced properties typically arise from the incorporation of conducting/semiconducting fibers or the modification of conventional fibers with nanoelectronics and chemical treatments. In particular, electrochemical capacitors, or supercapacitors, are promising energy storage solutions for incorporation into flexible, conductive textiles due to their high charging/discharging rates and small masses. They often contain composites of carbon nanotubes (CNTs), whose high specific surface area and electrical conductivity permit double-layer capacitance; and metal oxide particles, whose multiple valance states and reversible surface redox reactions result in pseudocapacitance. Because the synthesis and assembly of CNT-based supercapacitors comprising binder-enriched slurries of active material, resistance-lowering interlayers, and current collectors is often time-consuming, a simple route to the manufacture of sub-micron thin film electrodes and easily scalable devices is appealing. The present work involves the preparation of manganese oxide and ruthenium oxide-decorated CNT sheet electrodes via one-step redox and metal nitrate deposition methods. The effects of aqueous solution selection and treatment time on electrode morphology, metal oxide composition, and elemental chemical states were investigated by SEM/EDAX and XPS. XRD reveals information about metal oxide crystallinity and microstructure with and without post-deposition annealing. The nanostructured CNT-based electrodes were assembled into a two-electrode Swagelok cell that was optimized by judicious selection of aqueous and polymer hydrogel electrolytes. Supercapacitor cell performance was characterized using cyclic voltammetry, charge/discharge measurements, and electrochemical impedance spectroscopy. Charge storage capabilities have been correlated to factors such as metal oxide type, deposition route and associated physicochemical properties, choice of electrolyte, and overall cell configuration. Overall, this simplified approach holds promise for robust and cost-effective implementation of electrochemical capacitors in functional fabrics amenable to integration with a variety of platforms.

3:45 PM F14.3
Micro-Supercapacitors of Hybrid Graphene/CNT Electrodes.Majid Beidaghi, Sadeq Behdad and Chunlei Wang; Mechanical and Materials Engineering, Florida International University, Miami, Florida.

Recently, graphene has been introduced as a potential material to replace conventional carbon electrodes in high performance supercapacitors. With an intrinsic electric double layer capacitance of 21 µFcm-2, theoretically graphene is able to deliver a specific capacitance of 550 Fg-1 if its surface area is fully utilized. However, in practice agglomeration and restacking of single layer graphene sheets during electrode preparation limits their accessible surface area. Moreover, the conventional 2D stacking of the electrodes also limits the penetration of electrolyte ions between the graphene planes. In this work, we have tackled these issues by fabrication of supercapacitors with interdigital micro-electrodes of hybrid graphene/CNT electrodes. The addition of CNTs between the graphene layers minimizes the restacking of graphene sheets, thus providing a higher accessible surface area. Moreover, the interdigital in-plane design of the micro-electrodes provides a better pathway for penetration of ions between the graphene layers. The micro-device also takes advantage of high surface to volume ratio and binder free deposition technique of electrode without the use of polymer separators. Details of fabrication method and electrochemical performance of micro-supercapacitors will be presented.

4:00 PM F14.4
Direct Measurement of the Interfacial Capacitance of Graphene.Meryl Stoller, Yanwu Zhu, Carl Magnuson, Shanthi Murali, Ji Won Suk and Rodney Ruoff; Department of Mechanical Engineering and Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas.

A supercapacitor's energy density is primarily determined by the cell's electrode material and operating voltage. An electrode material’s storage capacity in turn is based on its interfacial double-layer capacitance (uF/cm2) and its surface area (m2/g). There is thus an interest in developing very high surface area electrode materials. Graphene has a theoretical surface area of 2630 m2/g and our group has previously reported on graphene derived materials for supercapacitor electrodes, specifically chemically reduced graphene oxide[1], graphene oxide reduced in propylene carbonate[2], microwave exfoliated graphite oxide[3], and a novel carbon produced by the chemical activation of graphene[4]. For very high surface area materials such as graphene, it is critical to understand the components that affect interfacial capacitance and the charge that can be stored. Indirect calculations of the interfacial capacitance of multilayer graphene[5] and the direct measurement of the interfacial capacitance on one side of single layer graphene supported by a SiO2 surface[6] have been reported. However, to fully utilize graphene’s available surface area in a supercapacitor electrode, the electrolyte should simultaneously access both sides of single atom thick sheets, and to our knowledge, interfacial capacitance measurements of graphene in this configuration have yet to be reported. In this study, we directly measured the interfacial capacitance of large area, single layer graphene with the electrolyte present on both sides of the graphene. The results show that the area normalized charge that can be stored simultaneously on both sides is significantly lower than could be stored on just one side of single layer graphene, consistent with charge storage being affected by factors such as quantum capacitance and charge screening. The results are also consistent with the specific capacitance of graphene materials as previously measured in two electrode ultracapacitor cells and provide a basis for the further understanding and development of graphene based materials for electrical energy storage. Details of this study will be presented here. References: [1] M. D. Stoller et al., Nano Lett. (2008). [2] Y. W. Zhu et al., Acs Nano 4, 1227 (2010). [3] Y. W. Zhu et al., Carbon 48, 2118 (2010). [4] Y. W. Zhu et al., Science 10.1126 (2011). [5] D. W. Wang et al., Electrochem Commun 11, 1729 (2009). [6] J. L. Xia et al., Nat Nanotechnol 4, 505 (2009).

4:15 PM F14.5
Synthesis and Characterization of a Graphene-Poly (o-anisidine) Hybrid Nanocomposite for Supercapacitor Applications.Punya A. Basnayaka1, Farah Alvi2, Manoj K. Ram3, Yusuf Emirov3 and Ashok Kumar1,3; 1Department of Mechanical Engineering, University of South Florida, Tampa, Florida; 2Department of Electrical Engineering, uth FloriUniversity of Soda, Tampa, Florida; 3Nanotechnology Education and Research Center, uth FloriUniversity of Soda, Tampa, Florida.

Electrochemical supercapacitors have high energy densities combined with excellent reversibility. They are operated at greater specific power than most rechargeable batteries. As a result, many researchers have focused on introducing novel materials and methods to enhance the operation of supercapacitors. Conducting polymers (CPs) such as polyaniline (PANI), polypyrrole (PPy) and poly (3, 4-ethylenedioxythiophene) (PEDOT) have drawn much attention in this regard, because of their promising electrochemical properties. However, CPs have poor stability compared to activated carbon and metal oxides (e.g. RuO2 and MnO2) used in industrial supercapacitors. Nanocomposites based on CPs (e.g. CP/carbon nanotubes, CP/carbon fibers and CP/Graphene) have been investigated by researchers to address some of the stability and capacitive behavior issues. Recently, we have studied graphene-polyaniline (G-PANI) nanocomposite electrodes for supercapacitor applications. Though G-PANI exhibits excellent environmental stability, controlled reversibility (due to oxidation and protonation) and high electrical conductivity, it suffers poor procesibility in most common organic solvents. In this context, we synthesized poly (o-anisidine) (POA) as well as graphene-poly (o-anisidine) (G-POA) nanocomposite at three different monomer (o-anisidine) to graphene weight ratios (90:10, 50:50 and 10:90), and characterized them using Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), UV-visible spectroscopy, Raman spectroscope, Fourier Transform Infrared Spectroscope (FTIR), X-Ray-Diffraction(XRD), Cyclic Voltammetry (CV), and conductivity measurement techniques. The G-POA nanocomposite showed high conductivity at all three monomer to graphene ratios. The supercapacitor study of G-POA electrodes was carried out with different electrolytes (2M H2SO4, 1M LiClO4 and the ionic liquid 1-butyl-3-methylimid-azolium hexafluorophosphate). The conductivity of G-POA was found to be higher than pristine POA due to the presence of graphene nanoparticles’ moieties. The G-POA nanocomposite has revealed superior electrochemical performance than pristine POA because of its synergistic effect. The G-POA synthesized at 50:50 weight ratio of monomer to graphene showed the highest specific capacitance of 380 F/g in 2M H2SO4. Interestingly, the potential window was observed to be 2.5 V in 1M LiClO4 and ionic liquid, whereas it was 1V in the 2M H2SO4. The scope of this work includes comparing the specific capacitance, stability and life cycle of the POA, G-PANI and G-POA materials for supercapacitor applications.

4:30 PM F14.6
Nickel-Cobalt Hydroxides/Graphene Ternary Nanocomposites for Ultrahigh Performance Supercapacitors.Xiang Sun, Gongkai Wang, Hongtao Sun and Jie Lian; Department of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York.

A Ni-Co double hydroxide with high specific surface area, and multi-valence states was first prepared with a low cost surfactant template process. The layered morphology and significant amount of meso-pores enable the materials with exceptional high capacitance. The significantly different electrochemical performance of the double hydroxide at different Ni to Co ratios (1:1, 1:2, 2:1) demonstrates the importance of controlling the stoichiometry of the compound. Moreover, upon the integration of graphene with the double hydroxide to form a ternary system via in-situ chemical reduction, the specific capacitance especially at high charge/discharge rates can be greatly improved due to the nature of the interconnected three dimensional conductive graphene channels. Detailed characterizations including BET, SEM, TEM, XRD, XPS and EIS have probed a complete understanding of the interplay among the crystallinity, crystal size, valence states, porosity, and conductivity, and their effects on the electrochemical properties. The integrated graphene/hydroxide ternary system exhibits superior performance. The successful design of the binary or ternary pseudocapactive materials based on graphene/metal hydroxide systems will impact significantly on the development of advanced materials to enhance the energy density of supercapacitors toward batteries.

4:45 PM F14.7
Abstract Withdrawn

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