Symposium T: Mobile Energy

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Mobile Energy
December 1 - 3, 2008





Chairs  

Gehan Amaratunga
Dept. of Engineering
University of Cambridge
Trumpington St.
Cambridge, CB2 1PZ United Kingdom
44-1223-332-675

   

Arokia Nathan
London Centre for Nanotechnology
University College London
17-19 Gordon St.
London, WC1H 0AH United Kingdom
44-20-7679-2367

Munichandraiah Nookala
Dept. of Inorganic and Physical Chemistry
Indian Institute of Science
Bangalore, 560-012 India
91-80-2293-3183

 

Marshall C. Smart
Jet Propulsion Laboratory
California Institute of Technology
MS 277-207
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
818-354-9374

Proceedings to be published online
(see Proceedings Library at www.mrs.org/publications_library)
as volume 1127E
of the Materials Research Society
Symposium Proceedings Series.
 


* Invited paper
 

SESSION T1: Batteries I
Chair: Gehan Amaratunga
Monday Morning, December 1, 2008
Liberty (Sheraton)


8:30 AM T1.1
Fabrication of Nanoscale High-Order Hierarchical Sn/C Composites for Highly Reversible Li+ Ion Storage. Da Deng and Jim Yang Lee; Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore, Singapore.

The rapid progress in portable electronic devices in this information-rich era demands continuing improvement in the performance of the power sources, which are typically the lithium-ion batteries. One of general strategies is to reduce the active electrode materials to the nanoscale to increase the capacity and rate capability of the electrodes. This is a report of our recent studies on the fabrication of various high-order Sn-carbon composites as lithium-ion storage compounds for the anode of lithium-ion battery. They range from hollow core-shell mesospheres, to hierarchical Rambutan-like and chestnut-like nanostructures. The methods of preparation are remarkably simple, environment-friendly, low cost and easily scaled up for volume production. In particular, the chestnut-like nanocomposites fabricated directly on copper current collectors are binder-free and conducting-additive free. Their double roughness structure of nanohairs on mesospheres also impart to them superhydrophobic properties mimetic of the lotus effect. For the unique hierarchical Rambutan-like nanostructure, tin remains electrochemically active even after 200 cycles of charge and discharge, thereby allaying some of the previous concerns on the use of tin as a lithium storage compound. These high-order nanomaterials also show impressively high capacity, high rate capability, and high reversibility demonstrating their potential as carbon alternatives for the next generation lithium ion batteries. This presentation will focus on the synthesis methods and the possible mechanisms of the formation of these intriguing morphologies.


8:45 AM T1.2
Electrochemical Preparation of Nanostructured TiO2 as Anode Material for Li Ion Batteries. Huanan Duan1, Xiangping Chen2 and Jianyu Liang1; 1Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts; 2Material Science & Technology, South China University of Technology, Guangzhou, Guangdong, China.

TiO2 is an attractive anode material due to its high capacity, high mechanical stability during Li intercalation/deintercalation process, limited side reactions with the electrolyte, low cost, and environmental friendliness. In this study, TiO2 films on various copper substrates are prepared from acidic aqueous solutions of TiOSO4 and H2O2 by potentiostatic cathodic electrosynthesis. Different Cu substrates include planar Cu disc, mechanically polished planar Cu disc, and Cu nanorod arrays grown on Cu disc. Cyclic voltammetry (CV) has been employed to study the electrochemical redox reactions in this system. The CV scan results show a big and sole cathodic peak in the potential range of -700 ~ -850mV, corresponding to the formation of titanium hydroxide gel. The electrodeposited gel films are annealed at 400 oC in argon atmosphere to obtain crystalline TiO2 films. The morphology and microstructure of the TiO2 films are characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). SEM results show that the deposits on planar Cu surfaces have a macro-particulate structure and those on Cu nanorod arrays are composed of nanoparticles with particle size around 100 nm. The presence of Cu nanorod arrays clearly impact on the growth and resulted morphology of TiO2 deposits. The obtained nanostructured TiO2 materials are tested as anode materials for Li ion batteries by conventional charge/discharge tests. The influence of Cu nanorods - TiO2 nanopowder structures and interface between Cu nanorods and TiO2 nanoparticles on the electrode performance is discussed.


9:00 AM T1.3
Electrochemical Behavior of the Ce4+ / Ce3+ Couple in the Novel Ce - V Redox Flow Cell. Yang Liu, Department of Chemistry, University of Montreal, Montreal, Quebec, Canada; Institute of Applied Chemistry, Xinjiang University, Urumqi, Xinjiang, China.

A novel Ce-V redox flow cell has been investigated. It was composed of the Ce4+ / Ce3+ couple, which replaced the V5+ / V4+ couple of the all-vanadium redox flow cell, and the V2+ / V3+ couple. The normal potential and the kinetic parameters for anodic oxidation of Ce3+ and cathodic reduction of Ce4+ were measured. The results showed that the surface of platinum electrode was fully covered with type I oxide that inhibited the reduction of Ce4+. The reversibility of the Ce4+ / Ce3+ couple improved with the increase of H2SO4 concentration, but both higher energy efficiency and coulombic efficiency were observed in 0.5 mol/dm3 H2SO4 solution. Different electrochemically active substances were found to exist at various state of charge (SOC) and the reversibility of the Ce4+ / Ce3+ couple at the carbon electrode was found to be superior to platinum electrode. Periodic charge-discharge measurements were conducted under constant current and constant load with the proposed Ce-V redox flow cell. The results indicated that the coulombic efficiency remained around 90% and the discharge voltage stabilized between 1.5 and 1.2 V. But as the cycle numbers increased, the discharge capacity declined a bit and a better result might be expected by improving the separator materials. By comparison with the existing Fe-Cr, Fe-Ti and all-vanadium redox flow cell, the Ce-V system has a higher open-circuit voltage (OCV). And results from this preliminary study suggest that the novel Ce-V redox flow cell is a promising energy saving system and is worthy of further studies.


9:15 AM T1.4
Al-based Composite Material for Anode in Li-ion Batteries. Wenchao Zhou and M. Stanley Whittingham; Institute for Materials Research, SUNY-Binghamton, Binghamton, New York.

In the past few years there has been extensive research on Si and metal-based materials for anode in Li-ion batteries. In this work aluminum powder has been revisited as a candidate for anode material. It delivers a high capacity of about 1000 mAh/g but the cycling performance is poor in carbonate electrolytes. Also, the voltage delays during lithium insertions prevent it from high power application. A series of composite samples containing aluminum and graphite with different ratios were synthesized by the high energy ball-milling method. The samples were characterized by X-ray diffraction, scanning electron microscope, ac impedance spectroscopy and galvanostatic cycling. The composite material delivers a capacity of ~400 mAh/g after 10 cycles. It is found that graphite largely enhanced the contact between aluminum and carbonate electrolytes, thus very good rate capability is obtained. The voltage delay during lithium insertion is reduced. Very flat charge and discharge curves were observed. The lithium extraction reaction takes place at ~0.46 V vs. Li+/Li. This profile is superior to that of graphitic carbon anode while ameliorating the safety problems at high charge rates. 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.


9:30 AM T1.5
Fire-Retardant Phosphazenes for Lithium Battery Electrolyte Systems. Shih-To Fei and Harry R Allcock; Chemistry, Penn State University, University Park, Pennsylvania.

A lithium battery is an energy storage device with a wide range of applications. However, the current highly flammable designs lead to safety concerns. Although flame retardant additives are commercially available, they tend to decrease the overall efficiency of the battery. We report here a series of lithium battery additives based on nitrogen-phosphorous phosphazene oligomers and polymers, which can increase the fire resistance of the battery while retaining high energy efficiency. We have obtained conductivities in the range of 10-4 S/cm for self-extinguishing non-halogenated ion-conductive phosphazene oligomers. The addition of 25% wt phosphazene to traditional carbonate type electrolytes lowers the linear flame propagation rate significantly while maintaining good conductivity. Further research should lead to high-efficiency lithium batteries with good fire safety properties.


9:45 AM T1.6
Conjugated Microporous Polymers as Potential Components in Energy Storage Devices. Andrew Ian Cooper, Chemistry, University of Liverpool, Liverpool, United Kingdom; Centre for Materials Discovery, University of Liverpool, Liverpool, United Kingdom.

There is a continual need for the discovery of new organic materials as components in batteries, fuel cells, and capacitors. Recently, we have developed new synthetic routes to produce conjugated microporous polymer networks with high specific surface areas (BET > 1000 m2/g) [1]. Conjugated microporous polymers produced so far include poly(aryleneethynylene)s (PAEs) [1-3], poly(phenylenevinylene) (PPV) [4], and poly(phenylene)s [3], and it is likely that the methodology can be extended to a host of other conjugated materials [5]. These materials may be very interesting for energy applications for the following reasons; (i) they combine high surface areas with extended conjugation, and hence exhibit a large interface; (ii) some of the structures (for example, microporous PAEs [1-3]) have similarities with dendrimer materials which have been used previously for light harvesting; (iii) the substantial micropore volume in these materials might be post-filled with other molecules (e.g., donors, acceptors, other conjugated polymers or oligomers) in order to produce interesting composite materials with a highly dispersed molecular interface. In this presentation we will discuss the synthesis of these materials, methods for obtaining synthetic fine control over pore structure [2], and the broad potential for synthetic diversity and energy-related applications that these new approaches bring. REFERENCES: [1] Jiang JX, Su F, Trewin A, Wood CD, Campbell NL, Niu H, Dickinson C, Ganin AY, Rosseinsky MJ, Khimyak YZ, Cooper AI (2007) Angew Chem Int Ed Engl 46: 8574 [2] Jiang J-X, Su F, Trewin A, Wood CD, Niu H, Jones JTA, Khimyak YZ, Cooper AI (2008) J Am Chem Soc 130: 7710 [3] Weber J, Thomas A (2008) J Am Chem Soc 130: 6334 [4] Dawson R, Su FB, Niu HJ, Wood CD, Jones JTA, Khimyak YZ, Cooper AI (2008) Macromolecules 41: 1591 [5] Weder C (2008) Angew Chem Int Ed Engl 47: 448


10:30 AM *T1.7
High Energy Density Layered Oxide Cathodes for Next Generation Lithium Ion Batteries. Arumugam Manthiram, Materials Science and Engineering, University of Texas at Austin, Austin, Texas.

Lithium ion batteries have revolutionized the portable electronics market, but only 50 % of the theoretical capacity of the currently used layered LiCoO2 cathode can be utilized in practical cells due to the chemical and structural instabilities at deep charge. In this regard, complex layered oxide solutions between layered Li[Li1/3Mn2/3]O2 and Li[Ni1-y-zMnyCoz]O2 have become appealing recently as they exhibit two times higher capacity than layered LiCoO2. However, these layered oxide solid solutions exhibit an irreversible loss of oxygen from the lattice and a huge irreversible capacity loss (difference between first charge and discharge capacities) during first cycle, and the charge and discharge capacity values depend sensitively on the layered oxide compositions. This presentation will focus first on a systematic investigation of a number of such high energy density layered oxide solid solutions and the factors influencing their irreversible capacity loss and discharge capacity values. A careful analysis of the first charge and discharge capacity values of a number cathode compositions suggests that part of the oxide ion vacancies formed during the first charge are maintained in the layered lattice during the subsequent discharge-charge cycling in contrast to the idealized literature models involving the elimination of all the oxide ion vacancies from the layered lattice. The presentation will then focus on the surface modification of these layered oxide solid solutions with other oxides like alumina, zirconia, and aluminum phosphate to reduce the irreversible capacity loss and increase the discharge capacity. The reduction in irreversible capacity loss and the increase in discharge capacity on surface modification are due a retention of more number of oxide ion vacancies after the first charge compared to that in the unmodified pristine material. Some of the surface modified cathode compositions offer high capacities of around 300 mAh/g compared to the 140 mAh/g realized with the currently used layered oxide cathodes, making them appealing for next generation lithium ion batteries. However, the charge-discharge process of these layered oxides involve charging to higher cutoff voltages of around 4.8 V, and compatible electrolyte compositions that will be stable to 4.8 V need to be developed to realize the full potential of these new class of cathodes.


11:00 AM T1.8
Optimization of Block Copolymer Performance as a Dry Battery Electrolyte. Ayan Ghosh1 and Peter Kofinas2; 1Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland; 2Fischell Department of Bioengineering, University of Maryland, Collge Park, Maryland.

Solid polymer electrolytes are in general more electrode compliant than conventional inorganic and gel-type electrolytes, possessing a higher electrochemical stability window. The ease of processing of solid polymers would allow for the production of thin film nanoscale batteries that could be wound into coils or processed as sheets or coatings. Solid state polymer electrolytes could be used as light-weight, versatile alternative energy storage systems compared to commercial lithium batteries which require bulky protective enclosures. Over the years, the inherent insulating characteristics of polymers have been a challenge towards the development of a commercially viable solid state charge transfer medium. The semi-crystalline nature of Poly(ethylene oxide) (PEO), a widely researched polymer, has been a limiting factor in its performance as a battery electrolyte at room temperature. We have developed a PEO-based block copolymer dry electrolyte with lithium bis(oxalate) borate (LiBOB) as salt. The self assembly of block copolymers has been used as a template to create a tailored nanoarchitecture, to improve electrolyte performance. The polymer microstructure was studied using transmission electron microscopy (TEM). These salt-content optimized electrolyte films possess an average ionic conductivity of 1.26 × 10-5 Scm-1 at room temperature (21 °C). The block copolymer was also observed to have higher salt loading capability as compared to traditional PEO based polymers for peak performance. Differential scanning calorimetry (DSC) was used to compare the crystallinity and glass transition temperatures of the various electrolyte samples.


11:15 AM T1.9
All solid, flexible thin film batteries for portable applications Pritesh Hiralal, Husnu E Unalan and Gehan Amaratunga; Engineering, University of Cambridge, Cambridge, United Kingdom.

Zinc carbon or Leclanche batteries are widely used because of the inexpensive raw materials. The anode of these batteries consists of Zn, while the cathode consists of manganese dioxide. We retake this chemistry from the perspective of flexible, thin film solid state power sources required for many of todays applications. These flexible configurations are achieved by the use of a range of different nanomaterials; on one hand polymer electrolytes blended with ceramic nanoparticles and on the other electrodes based on different carbon nanotube and nanofibre configurations. Dry polymer electrolytes such as polyethene oxide (PEO) are candidates for use in batteries because of ease of fabrication, good electrochemical stability, low flammability and toxicity with the ability to form good interfacial contact with electrodes. Conductivity and mechanical properties of dry electrolytes, however, need to be improved. It has been shown that both these properties can be improved by using ceramic nanoparticles. We show the use nanoparticles (TiO2, ZnO) of various geometries (spheres, wires), leading to battery performances comparable to liquid electrolytes (~8mAh/mg MnO2). Arrhenius plots of conductivity are shown for different nanoparticle morphologies as well as battery performance in a number of configurations. As for the electrodes, a thin (0.1 mm) Zn foil is used as one of the anode. Flexibility in the cathode is achieved by the use of carbon nanomaterials in several configurations, onto which MnO2 particles are pasted. Porous mats of electrospun carbon fibres (0.6-1.3µm diameter) leading to flexible mats as well as thin conducting films of vacuum filtrated single-walled carbon nanotubes act as both electrode and current collectors, while dense forests of vertically aligned carbon nanotubes are grown directly on metal foils. All these configurations provide a very high surface area to carbon weight ratio. The above configuration is shown to have extended shelf life as well as excellent mechanical stability. Battery performance under mechanically stressed conditions is shown. Finally, we present recent progress in a novel battery concept in which the benefits of 1-D nanomaterials (high surface area, high aspect ratio, reduced material use) are exploited in every component of a rechargeable Zn-silver battery, opening the venue for printed batteries for printed electronics.


11:30 AM T1.10
Embedded 3-D microbatteries by laser direct-write processing. Thomas Yersak and Craig B. Arnold; Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey.

As electronic devices grow smaller and more portable, there exists a need for commensurate-sized power sources that can be integrated with the electronic components in order to reduce size and weight and increase the device functionality. In order to address this concern, we present laser manufacturing methods that enable the direct integration of embedded 3-d lithium-ion microbatteries and microultracapacitors for energy storage within the confines of standard integrated circuit packaging. Laser micromachining is used to produce a pocket in standard substrate materials as well as epoxy potting materials. This pocket is refilled by laser printing of electrodes, separators, and current collector components providing a completed Li-ion microbattery or a completed ruthenium oxide microultracapacitor. In this presentation, we will discuss the resulting electrochemical measurements of these devices as well as the details of the fabrication process.


11:45 AM T1.11
Structure and Electrochemistry of Carbon-Iodine Nanocomposite. Electrodes for Electrochemical Energy Storage Prabeer Barpanda1, Scott P Beckman2, David H Vanderbilt2 and Glenn G Amatucci1; 1Department of Materials Science and Engineering, Rutgers University, North Brunswick, New Jersey; 2Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey.

Carbons form one of the most-widely used electrode materials, starting from anode of secondary batteries to electrochemical supercapacitors. Specially, activated carbons are prevalent in commercial supercapacitors, which store charge through a couple consisting of non-faradaic interfacial Helmholtz double layer and internal space charge formation. These activated carbons can be electrochemically improved by suitable physico-chemical modification. We have reported one such higher-capacity carbon electrode by nanoscale iodine-incorporation employing high-energy mechanochemistry techniques. Iodation process distinctly modifies the structure, morphology and electrochemistry of activated carbons. The current work illustrates the structure and electrochemistry of carbon-iodine nanocomposites system. Carbon-iodine interaction at nanoscale has been studied using in-situ/ ex-situ XRD, Raman, 2D-NMR, XPS and first-principle modeling. Activated carbons possess amorphous structure with embedded graphitic zones. When iodine is introduced into activated carbons, it destroys the graphitic domains. Raman spectroscopy and thermal analysis (DSC) reveals the formation of polyiodide compounds (triiodides, pentaiodides) and absence of any free iodine. This in turn suggests possible charge transfer reaction between highly-electronegative iodine with host carbon. The iodine-induced structural and chemical modification can affect the intrinsic DOS and electronic conductivity of precursor carbons. We will present the effect of iodation on the DOS and conductivity of activated carbons combining experiments and density-functional perturbation theory. Besides the structural modification, iodine notably modifies the carbon morphology by preferential filling of existing micropores (0-2 nm) with polyiodides and leaving majority of mesopores (2-50 nm) open. This morphological development has been studied using BET analysis and DFT calculation. Overall, iodation process results in lower BET area coupled with improved electrochemical capacity. The improvement in capacity arises mainly due to the evolution of large faradaic plateau at 3.1 V as a result of reversible conversion reaction between carbon polyiodides and lithium. Long run cycling proves complete reversibility of this faradaic reaction in iodated carbons. An extensive study of electrochemical properties of carbon-iodine nanocomposites will be presented using X-ray diffraction and fluorescence, TEM, galvanostatic and potentiodynamic tests. Using the non-faradaic and faradaic study, we will gauge the possible application of carbon-iodine nanocomposites in supercapacitors and low energy-density batteries.


 

SESSION T2: Cathodes and Anodes
Chair: Nookala Munichandraiah
Monday Afternoon, December 1, 2008
Liberty (Sheraton)


1:30 PM *T2.1
Metal Fluoride Nanocomposites; A Question of Transport. Fadwa Badway1, Nathalie Pereira1, Andrew Gmitter1, Adam Skrzypczak1, Irene Plitz1, Azzam Mansour2, Won-Sub Yoon3, Frederick Cosandey1 and Glenn G Amatucci1; 1Rutgers, The State University of New Jersey, North Brunswick, New Jersey; 2Naval Surface Warfare Center, West Bethesda, Maryland; 3Brookhaven National Laboratory, Upton, New York.

Electrochemical energy storage in the form of state of the art battery technologies such as the ubiquitous Li-ion battery is largely governed and limited by a myriad of charge transport issues. These challenges are manifested in both electronic and ionic aspects. Ionic transport includes diffusion between electrodes via liquid or solid state electrolytes, diffusion through interfaces / interphases which form on electrodes as byproducts of reactions with the electrolyte, and complex diffusion within and between the domains of the electroactive material. The latter can exist as distributed intercalation processes or through two phase boundaries which develop during the redox process. Electronic transport includes electronic conduction within the electrode material (which in many cases changes as a function of depth of discharge), tunneling relatively insulative solid state electrolyte interfaces to a conductive additive, and finally percolation of the electron through the porous electrode composite to the current collector which is often covered in a semiconducting or thin insulative oxide. Nanomaterials and nanocomposites have opened the door to the utilization of materials and more importantly energy storage mechanisms not deemed practical or even possible a decade ago. In almost all cases, this has been due to improved transport, either electronic or ionic. For four decades, metal fluorides, due to their theoretical high energy densities, have been seen as a path towards high energy density batteries. This goal was quite elusive due to the high bangdgap and low conductivity of these materials. During the past six years a number of metal fluorides have now been enabled at theoretical voltages through the use of nanocomposites. These have included homogeneous and also heterogenous metal fluorides. These metal fluorides operate on a reversible conversion mechanism enabling very high capacities in excess of 2X of today’s state of the art. Such processes open the door questions regarding the non intuitive transport processes which enable the conversion and more importantly the reconversion process. This paper will be an overview of the work our group has accomplished in this area specifically regarding the optimization of performance and interphases. The latter will be discussed relative to mixed conducting matrices, which enable both ion and electron transport to the individual metal fluoride nanodomains within a nanocomposite. New data regarding application of the reversible conversion mechanism to alternative metal fluorides will be shown. Specific information regarding the large number of challenges that still remain to be overcome before successful implementation of this technology will also be discussed.


2:00 PM T2.2
Synthesis, Characterization, and Electrochemical Testing of Olivine Structures with a Controlled Concentration of Lithium Vacancies. Joel K Miller, Natalya A Chernova, Shailesh Upreti and Stanley M. Whittingham; Chemistry and Materials, State University of New York at Binghamton, Binghamton, New York.

Knowledge of the effect of lithium vacancies on lithium mobility in the olivine-type phosphates could be useful in determining the optimum number of lithium vacancies for enhanced electrochemical performance. During the galvanic cycling of lithium iron phosphate, a lithium dilute (vacancy rich) phase and a lithium rich (vacancy dilute) phase are present. Since no phases with an intermediate concentration of lithium vacancies are normally present during cycling, the diffusion coefficient and activation barrier cannot be experimentally determined as a function of the vacancy concentration. In nature, there are olivine-type phosphates where the intermediate phases are stabilized by incorporating other cations (Mg2+, Ca2+, etc.) on the iron site in the structure. One example of such a mineral is simferite, Li0.5(Mg0.5Fe0.3Mn0.2)PO4. According to single crystal x-ray diffraction data, in simferite, an oxidized olivine structure, the Mg2+ creates randomly distributed lithium vacancies, which might lead to single phase lithium cycling.1 In this study, a series of simferite-related compounds with a controlled concentration of randomly distributed lithium vacancies were synthesized. The synthesis involves hydrothermal reaction to produce Li(Mg0.5Fe0.3Mn0.2)PO4 followed by chemical oxidation with bromine or nitronium tetrafluoroborate. Powder x-ray diffraction showed that our synthesis approach successfully produced a single olivine phase with lattice parameters similar to those predicted by Vegard’s law. DC-Plasma Emission Spectrometry confirmed that the ions are present in the desired ratio. Magnetic properties indicate that a small amount of Fe or Mn may be present in the lithium sites. The electrochemical properties and lithium diffusion as a function of lithium vacancies concentration 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. 1. O.V. Yakubovich, V.V. Bairakov, M.A. Simonov, Doklady Akademii Nauk SSSR, 307, 1119, 1989.


2:15 PM T2.3
Black Lithium Titanate Spinel as The Anode for Ultra-High Power Lithium Batteries. Jian Hong and Stanley M Whittingham; State University of New York at Binghamton, Binghamton, New York.

The advantages of lithium-titanate spinel Li4Ti5O12 as anode material for lithium ion battery have been known for many years. Yet, the high working potential (1.55 V vs. Li/Li+) makes it less promising than conventional carbonaceous anode materials. However, recent results showed that it could provide high power capability and stability if combined with lithium iron phosphate (LiFePO4), which makes this system a viable candidate to replace electrochemical super-capacitors and for the wide use in electrical vehicles. In this work a reduced Li4Ti5O12 spinel was synthesized in a high-energy milling machine followed by heat treatment in reductive He/H2 atmosphere with the goal to improve the electronic conductivity and to investigate how it affects the rate capability. The x-ray diffraction data indicates formation of a single-phase cubic spinel with a lattice parameter of 8.372(7) Å, which is noticeably larger than 8.368(3) Å observed for the conventional material synthesized in an oxidative atmosphere. The increase of the unit cell size and darker color of the samples are consistent with the reduction of some Ti4+ to Ti3+. The obtained powder consists of monodisperse particles of several hundred nanometers in diameter. It delivers 158 mAh/g (94% of the theoretical) capacity without noticeable fading for over 100 cycles when tested at current density of 0.5 mA/cm2. At a high discharge current of 8 mA/cm2 (~10C) the electrode still retains 80 mAh/g capacity. These results indicate that relatively large particles can work well at high currents. The effect of Ti reduction on the electronic conductivity and electrochemical properties 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.


2:30 PM T2.4
Harvesting Uncoupled Energy in Organic Light Emitting Diode Displays. Reza Chaji1, Arokia Nathan2 and Andrei Sazonov3; 1Ignis Innovation Inc., Kitchener, Ontario, Canada; 2London Centre for Nanotechnology, University College London, London, United Kingdom; 3Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada.

A considerable fraction of the useful display luminance emitted in organic light emitting diode (OLED) displays is lost in the substrate due to poor wave-guiding, which causes the emitted light to reflect away from the useful viewing plane of the display and out through the edges. This is undesirable as it reduces display luminous efficacy leading to increase in power consumption, thus lowering the battery life for hand-held devices. This paper will present preliminary results and address techniques for harvesting this uncoupled energy, by judiciously locating solar cells at the display periphery and edges, so as to charge the battery in a regenerative fashion. Since the flat panel display constitutes a considerable surface area of any hand-held device, there is a significant window to capture the uncoupled emitted or ambient light without altering the device’s form factor. Techniques for the seamless integration of the solar panels with thin batteries, and associated thin film battery charging circuits, on the same panel would also be discussed. Considering that the multimedia applications are continuously being added to hand-held devices, any savings in display power will result in significant overall power reduction, given that the display a typical hand-held device consumes 30%-50% of the total power consumption.


2:45 PM T2.5
Electrochemical Characterization of LiMn2-xCrxO4 Cathode Materials for High Energy Density Li Ion Rechargeable Batteries. Rahul Singhal1, Rajesh K Katiyar2, Ricky Valentín2 and Ram S Katiyar1; 1Physics, University of Puerto Rico, San-Juan, Puerto Rico; 2Mechanical Engineering, University of Puerto Rico, Mayaguez, Puerto Rico.

Rechargeable Li ion batteries are found to be suitable for portable electronics devices and electrical vehicle due to their lightweight and high energy density. From literature it is known that the charge-discharge characteristics and cycleability of LiMn2O4 can be improved by substituting Mn3+ ions with transition metals e.g. Al, Cr, Co, Fe, Ni, Cu, etc.[1-5]. In the present work, we will synthesize and characterize LiMn2-xCrxO4 cathode materials for high energy density Li ion rechargeable batteries. Stoichiometric compositions of lithium acetate, manganese (II) acetate, and chromium acetate were separately dissolved in 2-ethylhexanoicacid with continuous stirring and slow heating. After one hour, all solutions were mixed together followed by heating and continuous stirring upto boiling point for 1 hour. The solution was allowed to evaporate overnight at about 100oC, resulting in the formation of amorphous powders. The powder was again dried at 450oC for 4h. Finally, LiMn2-xCrxO4 phase was formed at a calcination temperature of 900oC for 24h. The resultant powders were structurally characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and micro Raman scattering. The cathodes and coin cells were prepared as reported earlier5. The coin cells were electrochemically characterized by cyclic voltammetry (CV) and charge-discharge characteristics. The XRD patterns of Cr doped LiMn2O4 cathode materials shows cubic spinel phase structure having Fd-3m space group, where Li+ ions occupy tetrahedral (8a) sites; Mn3+, Mn4+ and Cr+ ions occupy octahedral (16d) sites and O2- reside at (32e). The electrochemical performance of LiMn2-xCrxO4 has been studied and the results will be presented. Acknowledgements The above research work was supported by grant received from NASA (NNX 08AB12A). References: 1. Y. Ein-Eli, W. F. Howard, Jr., S. H. Lu, S. Mukerjee, J. McBreen, J. T. Vaughey, and M. M. Thackeray, J. Electrochem. Soc. 145, 1283 (1998) 2. M.C. Tucker, J.A. Reimer, E. J. Cairns, J. Electrochem. Soc., 149, A574 (2002) 3. R.I. Eglitis, G. Borstel, Phys. Stat Sol. (a) 202R13-R15 (2005). 4. S.B. Park, W.S. Eom, W. Il Cho and H. Jang, J. Power Sources, 159, 679 (2006) 5. R. Singhal, M.S. Tomar, S.R. Das, S.P. Singh, A. Kumar, R.S. Katiyar, Electrochemical and Solid-State Letters, 10(7) 2007, A163.


3:30 PM *T2.6
Effect graphite anode and electrolyte additives on the safety of lithium batteries Khalil Amine, Argonne National Laboratory, Argonne, Illinois.

One of the major barriers to enable lithium ion batteries in hybrid electric vehicle and plug in hybrid electric vehicle is the poor abuse tolerance of the battery when subjected to external heat or overcharge. In order to address these concerns, we investigated the role of each cell components on the safety of lithium batteries. It is well known that the cathode play a big role in the thermal run away of lithium batteries. The oxidation of the solvent from the oxygen released during the decomposition of the oxide cathode play a major role on battery safety. However, when cylindrical full cell containing the olivine LiFePO4 and graphite was studied by Accelerated rate calorimetry, the cell want on a thermal run away despite the fact that the cell contained the olivine that is believed to be one of the safest cathode. Therefore, we suspect that graphite anode can also play a key role on the overall safety of lithium batteries. Detail study on the carbon anode shows that the onset temperature of the breakdown of the SEI layer occurred at a temperature lower than 100oC, after which a significant amount of a continuous heat was observed because of the continuous breakdown and formation of the SEI at the surface of graphite up to 200oC. The amount of accumulated heat generated at temperature lower than 200oC is significant enough (507 J/g) to trigger a thermal runaway inside a cell regardless of the nature of the cathode, especially in large batteries with cells in series and parallels. This result clearly demonstrates that unlike what is speculated in the literature, the safety of Li-ion cells should be addressed at the level of both cathode and graphite anode. The heat generated at the carbon anode below 200oC is directly related to the breakdown and formation of the SEI which take place at the surface of carbon. Therefore, to improve the safety of carbon, it is necessary to select a carbon anode with low surface area. Since the onset temperature of the breakdown of the SEI is dependent on the stability of the SEI layer itself, selecting electrolyte additives that form stable SEI’s at the carbon anode can push the onset temperature higher and reduce the over all accumulated heat. To further improve the inherent thermal properties of graphite in the cell, the use of low surface area carbon combined with appropriate functional additives in electrolytes can significantly reduce the initial heat and possibly delay the onset temperature from which the SEI breakdown occur.


4:00 PM T2.7
Improved Cycleability of Zr-Substituted LiMn2O4 Thin Film Cathodes Prepared by Pulsed Laser Deposition. Dong Wook Shin1,2, Ji-Won Choi1, Yong Soo Cho2 and Seok-Jin Yoon1; 1Korea Institute of Science and Technology, Seoul, South Korea; 2Yonsei University, Seoul, South Korea.

Development of cathode materials for thin film lithium batteries with low price, environmental friendliness and high cycleability is important to meet the demands for microelectronic applications such as ubiquitous sensor networks and microelectromechanical systems. LiMn2O4 has been one of the most viable materials alternative to commercialized LiCoO2 due to its high operating voltage, low materials cost and non-toxicity. However, the gradual capacity loss of the pristine LiMn2O4 associated with manganese dissolution and the phase transition, caused by the Jahn-Teller distortion has inhibited its commercial use for the thin film batteries. In this study, Zr-substituted LiMn2O4 thin films, prepared on a Pt/Ti/SiO2/Si(100) substrate by pulsed laser deposition, were investigated to improve the cycleability of LiMn2O4 as a function of Zr content. The electrochemical measurements of the Zr-substituted thin films showed less distinct plateau in voltage-capacity profiles and higher cycleability than the pristine LiMn2O4 thin films. The role of Zr substitution into the spinel structure will be discussed with the other physical and electrochemical characteristics by XRD, AFM, SEM, electrochemical measurement system and so on.


4:15 PM T2.8
Transition Metal Ordering and Electrochemistry of Li(4-x)/3Mn(2-0.5x)/3(Ni0.4Co0.1)xO2 Cathode Materials for Li-ion Batteries. Natalya A. Chernova1, Jie Xiao1, Shailesh Upreti1, M. Stanley Whittingham1, Dongli Zeng2, Jordi Cabana2 and Clare P Grey2; 1Chemistry and Materials, SUNY Binghamton, Binghamton, New York; 2Department of Chemistry, SUNY Stony Brook, Stony Brook, New York.

Layered oxides have attracted much attention as cathode materials for Li-ion batteries. LiCoO2 commercialized by SONY in 1991 is now being replaced by Li(NiyMnyCo1-2y)O2 compounds, which is caused by the limited capacity of LiCoO2, scarcity of Co sources and safety concerns. In an attempt to minimize Co and maximize Mn content, while maintaining layered structure and good electrochemical characteristics, we have synthesized Li(4-x)/3Mn(2-0.5x)/3(Ni0.4Co0.1)xO2 (0≤x≤1) solid solutions, characterized their structure using x-ray diffraction (XRD), Li MAS NMR and magnetic properties, and studied the effect of composition on the electrochemical performance in Li-cells. XRD patterns indicate the formation of a layered structure over the whole composition range. For x<0.5 superstructure peaks are observed, which are characteristic of honeycomb-type ordering. No Ni is found in the Li layer, while Li content in the TM layer determined from the NMR spectra deconvolution fits well to the values expected for the xLi[Ni0.4Mn0.5Co0.1]O2.(1-x)Li[Li1/3Mn2/3]O2 compositions. For x≥0.5 the diffraction patterns can be refined in the R3-m group. Both a and c lattice parameters increase linearly with x, while the amount of Ni in the transition metal layer remains constant at about 5%. Magnetic properties indicate a shift of the antiferromagnetic ordering transition observed at 36.5 K in Li[Li1/3Mn2/3]O2 (x=0) towards lower temperature when x increases to 0.3, spin-glass transition at 7 K for x=0.5 and progressive increase of ferrimagnetic cluster size with increasing x for x>0.5. Thus, we conclude that a solid solution based on the Li[Li1/3Mn2/3]O2 honeycomb structure exists for x up to 0.5, while for x>0.5 Ni/Li exchange occurs and a disordered flower structure, similar to that of LiNi0.5Mn0.5O2 is realized. The latter is evidenced by the similarity of the NMR spectra and magnetic properties. The best electrochemical performance is found for Li1.1Ni0.28Mn0.55Co0.07O2 (x=0.7) with the first-cycle charge and discharge capacities of 285 and 200 mAh/g, respectively, when cycled between 2.5 and 4.6 V at 0.5 mA/cm2. At 4.6 V a plateau is observed at the charge curve, which is related to the removal of Li2O from the compound. In situ XRD tests indicate a sharp decrease of the c-lattice parameter at 4.8 V consistent with the formation of a one-block structure. Because of these structural changes, an additional capacity obtained above 4.6 V is irreversible. 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. We appreciate the valuable collaboration with W.-S. Yoon, K.-W. Nam and X.-Q. Yang at Brookhaven National Laboratory for the in situ XRD data.


4:30 PM T2.9
Study of Sn-Co-Fe-C Alloys Prepared by Mechanical Attrition. Pierre Philippe Ferguson, Richard A Dunlap and Jeff Dahn; Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada.

Nanostructured tin-cobalt-carbon (Sn-Co-C) alloys are now being used as advanced negative electrode materials instead of graphite in Li-ion batteries. Sn-Co-C alloys have greater specific capacity and density than graphite, leading to Li-ion batteries with higher energy density. Sony recently commercialized the first Li-ion battery with such negative electrode materials in 2005 [1].<p> Amorphous and/or nanostructured materials appear to show the best charge/discharge cycle life of negative electrodes [2]. Sputtered samples of (Sn0.55Co0.45)1-yCy with y ≈ 0.4 are nanostructured and have a reversible capacity near the calculated theoretical estimate [2]. These sputtered samples are best described as nanometer scale amorphous Co-Sn grains dispersed in a carbon matrix [3].<p> An economical and industrially scaleable method to prepare electrode materials is mechanical attrition. A vertical-axis attritor (Union Process 01-HD) was used to prepare Sn-Co-C electrode materials. By varying milling conditions, such as milling time, it was possible to obtain nanostructured materials. Materials were characterized by X-ray diffraction (XRD) and electrochemically using coin cells. Sn30Co30C40 alloys prepared by mechanical attrition were shown to have a specific capacity of 500 mAh/g, a density of 6.7 g/cc and hence a volumetric capacity of over 3200 mAh/cc, more than four times that of graphite [4]. In addition, the material showed no capacity loss over the 150 charge-discharge cycles tested.<p> However, the rising cost of cobalt is a concern to the commercialisation of Sn-Co-C anodes and cobalt should be replaced. This is difficult because, of the 3d transition metals, only Co leads to the desired nanostructured materials. In this work, the replacement of cobalt with a cheaper transition metal, iron, will be studied.<p> Electrochemical studies of Sn-Fe and Sn-Fe-C systems were done previously [5, 6]. No nanostructured diffraction patterns were observed in those studies and capacity retention was poor. Even though Fe-carbides exist, Sn-Co-Fe-C alloys were prepared by mechanical attrition and studied primarily with an eye on cost reduction. XRD, electrochemical tests and Mössbauer effect spectroscopy were used to investigate the Sn-Fe-C and Sn-Co-Fe-C systems. Results of these systems will be presented and discussed.<p> [1] http://www.sony.net/SonyInfo/News/Press/200502/05-006E/<p> [2] J.R. Dahn, R.E. Mar and Alyaa Abouzeid, J. Electrochem. Soc. 153, A361 (2006).<p> [3] A.D.W. Todd, R.A. Dunlap and J.R. Dahn, J. Alloys and Compd. 443, 114 (2007).<p> [4] P.P. Ferguson, A.D.W. Todd and J.R. Dahn, Electrochem. Comm. 10, 25 (2008).<p> [5] A. D. W. Todd, R. E. Mar and J. R. Dahn, J. Electrochem. Soc. 153, A1998 (2006).<p> [6] O. Mao, R.L. Turner, I.A. Courtney, B.D. Fredericksen, M.I. Buckett, L.J. Krause and J.R. Dahn, Electrochem. and Solid-State Lett. 2, 3 (1999).<p>


4:45 PM T2.10
Combined Experimental and First Principles Studies on Factors Affecting Li Mobility in Spinel Lithium Transition Metal Oxides. Bo Xu, Ming-Che Yang and Ying Shirley Meng; Materials Science and Engineering, University of Florida, Gainesville, Florida.

Among possible high rate cathode materials, LiMn2O4 and related oxides have gained much attention because of their low cost, low toxicity, and relatively high energy density. Several research groups have reported new transition metal substituted spinel materials (LiMxMn2-xO4, M = Ni, Co, Cu, Cr, Fe, etc.) with high working voltages more than 4V[1]. Nevertheless, the rate capability and cycling ability of these new materials have not been optimized yet, partly due to the lack of systematic understanding of the effects of local environment and point defects on the lithium diffusion in the spinel framework. In close packed oxides with a spinel structure, it is believed that the tetrahedral Li ions diffuse by migrating through intermediate octahedral sites. The activation barrier for Li hopping may be affected by the size of the octahedral site and the electrostatic interaction between Li+ in that site and surround cations. The difference in size of the octahedral site and the electrostatic interaction will be demonstrated with various substituting metal M. The lithium diffusion barriers and electronic structures of spinel lithium transition metal oxides with different doping elements are investigated using first principles methods. The Generalized Gradient Approximation (GGA) method is used and the calculations are performed with Vienna Ab Initio Simulation Package (VASP). Hubbard U correction is introduced by the GGA+U method to describe the effect of localized d electrons on the diffusion activation barrier of Li in both lithium-rich and lithium-poor spinel. Trends in lattice parameters and redox potentials at different lithium concentration will be discussed. Conventional wisdom holds that Li mobility in the spinel crystal structures should be higher than that in layered crystal structures due to the three-dimesional lithium diffusion paths in the former. However, spinel crystal structures are more compactly packed and therefore could exhibit higher activation barriers for Li migration than layered crystal structures. By comparing two spinel materials LiMn2O4 and LiNi1/2Mn3/2O4 in details, we will discuss the relation between the crystal structure, electronic structure and lithium mobility.


 

SESSION T3: Batteries II
Chair: Marshall Smart
Tuesday Morning, December 2, 2008
Liberty (Sheraton)


8:30 AM T3.1
Lithium Difluoro(oxalato)borate as Additive to Improve the Thermal Stability of Lithiated Graphite. Zonghai Chen, Yan Qin, Jun Liu and Khalil Amine; Chemical Sciences and Engineering, Argonne National Lab, Argonne, Illinois.

Since the Sony Corporation first commercialized lithium-ion batteries, LiPF¬6 has been the dominant lithium salt for lithium-ion batteries. It is widely accepted that LiPF6 decomposes to LiF and PF5, and the latter readily hydrolyzes to form HF and PF3O. Both products of the hydrolysis reaction are highly reactive with both negative and positive electrodes and the detrimental impact of the byproducts has attracted more attention because of both the introduction of lithium manganese oxide spinel cathodes and the current high-power applications of lithium-ion batteries. Today, researchers are actively searching for additives to improve the thermal stability of cathodes and anodes in the electrolyte. In this paper, the effect of lithium difluoro(oxalato)borate (LiDFOB) as an electrolyte additive on the thermal stability of the lithiated graphite was investigated using differential scanning calorimetry (DSC). Without LiDFOB, the decomposition of the solid electrolyte interphase (SEI) took place at about 100oC and was followed by a continuous formation/decomposition of the SEI up to 250oC. Another two peaks were observed at temperatures above 250oC. These peaks were attributed to the major reaction of lithiated graphite with the nonaqueous electrolyte. With the addition of lithium difluoro(oxalato)borate as an electrolyte additive, the onset temperatures of the three peaks were pushed higher. By fitting the DSC data in the equation, we were able to extract the activation energy of the thermal decomposition reactions. It was found that the activation energy increased with the concentration of LiDFOB used, indicating the improve of the thermal stability. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.


8:45 AM T3.2
Production of Anode Materials using Aerosol through Plasma. Claudia C Luhrs1, Monique Richard2, Jonathan Phillips3,1 and Angela M Knapp2; 1Dept. Of Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico; 2Materials Research Department, Toyota Research Institute North America, Ann Arbor, Michigan; 3Los Alamos National Laboratory, Los Alamos, New Mexico.

Nanoparticle applications, for batteries, fuel cells, catalysts, specialty solid fuels, etc, require not simply nanoparticles, but highly engineered nanoparticles. For example, in applications ranging from batteries to catalysts, there is a need for nanoparticles with a ‘core’ to do the chemical work and a shell to prevent sintering. In our work we have produced a number of novel nano structured ceramic structures using a microwave generated atmospheric pressure plasma though which an aerosol containing precursor species is passed, a technique we call ‘Aerosol-through-plasma’ (A-T-P). The mechanism of particle formation using the A-T-P process appears to be unique, and once understood permits the creation of designed structures on the nanoscale. Specifically, we report on the design and generation of core-shell nanospheres for use as battery anode materials. We report on the logic of the particle design, the protocol engineered to create the selected design, the remarkable match of design and reality, and finally the electrochemical performance of this material and its derivatives.


9:00 AM T3.3
Morphology and Electrochemistry of Hydrothermally Prepared Limnpo4. Jan L. Allen, T. Richard Jow and Jeff Wolfenstine; Electrochemistry Branch, US Army Research Laboratory, Adelphi, Maryland.

Lithium metal phosphates have been under intense study as next generation positive electrode materials for use in lithium ion batteries. Their high safety, environmental friendliness and long cycle life all suggest that they may have potential application in hybrid electric vehicles. LiFePO4 materials are commercialized. There is an increased interest in LiMnPO4 which offers a higher voltage of intercalation, 4.1 V versus 3.4V in the iron analog, but few researchers have been able to achieve reasonable rate capability. One important issue for improved rate capability is the optimization of the synthesis to achieve small particle size and optimal particle morphology. Hydrothermal synthesis is a commercially viable method of synthesis that is particularly suitable for preparation of LiMnPO4 and through modification of key synthesis parameters particle characteristics may possibly be controlled. In this study we examined the hydrothermal synthesis of single-phase, small-particle-size LiMnPO4. Variation of the synthesis parameters such as pH, reactant choice and concentration and their effect on the particle morphology was explored. The small-particle-size LiMnPO4 was examined through x-ray diffraction, microscopy, surface area and electrochemical measurements.


9:15 AM T3.4
Structure and Electrochemistry of Novel Silver Metal Oxyfluoride Perovskites: Cathode Materials for High Volumetric Energy Storage. Wei Tong1, Won-Sub Yoon2 and Glenn Amatucci1; 1Dept. of Materials Science and Engineering, Rutgers, The State University of New Jersey, North Brunswick, New Jersey; 2Brookhaven National Laboratory, Upton, New York.

Cathode materials exhibiting a very high volumetric energy density and a good power need to be developed for an ever increasing demand of portable electronic devices in many fields including biomedical. Relative to other applications, material cost has a low priority in biomedical relative to its performance (high energy density, voltage > 3 V). Presently, these needs are being met by silver vanadium oxides (SVO), Li/CF1 and Li-I2 for a different rate application. Other than these, metal fluorides are electrochemically attractive due to their high theoretical output voltage and high energy density. However, they exhibited a very poor utilization due to their low intrinsic electronic conductivity. Recently, a new avenue has been presented through the fabrication of carbon metal fluoride nanocomposites (CMFNCS) or mixed conducting matrices (MCM), which successfully enabled the attractive electrochemical activity of these fluorides (FeF3, CuF2 and BiF3). Surpassing CuF2 and BiF3, silver fluoride is of interest due to its higher theoretical output voltage (4.46 V) and energy density (9.1 Wh/cc). In contrast to the aforementioned nanocomposite, we found the formation of a new nanocompound, silver metal oxyfluoride of perovskite structure. It can be easily synthesized through a mechanochemical process within 15 minutes. These new compounds exhibited a very good conductivity and successfully enabled the electrochemical activity of the unstable and insulating silver fluoride at 3.5V without the presence of the conductive carbon matrix. The perovskite structure of the mechanochemically fabricated silver metal oxyfluorides has been examined in detail utilizing X-ray powder diffraction combined with Raman spectroscopy. The electronic and structural modification of the silver metal oxyfluoride phases were studied by X-ray absorption spectroscopy (XAS and XANES). Rietveld refinement was performed to further confirm the structure determination of the silver metal oxyfluoride phases. In addition, the electrochemistry of the silver metal oxyfluoride was also investigated. Without the presence of the carbon black, both silver metal oxyfluorides exhibited a very good electrochemical performance with output voltage of ~3.5 V and volumetric capacity of ~1000 Ah/L at voltages > 2.5 V. Several tests through the addition of the conducting agents (carbon black and metallic Ag2F) were performed to improve the rate capability of the silver metal oxyfluorides for the practical use. Further, the lithium insertion process was investigated by in-situ XRD, in-situ Raman and ex-situ XANES, revealing the displacement or possible conversion reaction of silver metal oxyfluoride to Ag metal upon lithium insertion at the 1st plateau (> 3.1 V).


9:30 AM *T3.5
In situ and Ex situ Solid State NMR and Pair Distribution Function Analyses of Short Range Order in Silicon Anodes for Lithium-Ion Batteries. Baris Key1, Rangeet Bhattacharya1, Mathieu Morcrette2, Vincent Seznac2, Jean-Marie Tarascon2 and Clare P Grey1; 1Chemistry, Stony Brook University, Stony Brook, New York; 2LRCS, Universite de Picardie Jules Verne, Izumi, Japan.

Conventional diffraction techniques provide limited information for systems that involve structural changes in amorphous phases, such as those that occur during the electrochemical lithiation of crystalline silicon in a lithium-ion battery (LIB). Here, we demonstrate the use of a combination of local structure probes, such as Solid State NMR and X-ray PDF and analysis, to understand the structural changes that occur for bulk and nanoparticulate silicon anodes. In particular, we demonstrate that in-situ NMR studies of a working Li-Si working battery can be used to reveal processes that are not captured in the ex-situ study. Crystalline silicon undergoes a crystalline to amorphous phase transformation in the beginning of the first discharge when it is cycled versus Li metal. The long plateau at 0.09V vs. Li is associated with the formation of a lithiated amorphous (a)-LixSi. Larger particles then crystallize to form the metastable intermetallic Li15Si4 phase[1]. We investigated the lithiation of crystalline Si and the formation of the lithiated amorphous phase and the formation of the recrystallized intermetallic metastable phase Li15Si4 at the end of discharge, by ex-situ MAS-SSNMR. The discharged electrode spectra were compared with model intermetallic compounds in Li-Si system in order to provide 7Li and 29Si peak assignments. The data obtained was compared with the in-situ static SSNMR data of an actual working LIB, which allowed the local structures present in the the first amorphous phase to be determined and then the changes in local structure to be followed. Insitu methods revealed a new process that was not seen by ex-situ methods and demonstrated that the fully lithiated phase is not stable in the electrolyte over periods of a few hours. The combination of the two techniques was then used to investigate the processes that occur on subsequent charge and discharges. Ex-situ PDF analysis of model intermetallic compounds and Si electrodes stopped at various charged/discharged stages showed changes in Li-Li, Si-Si and Li-Si distances, and could be used to follow the transformation from crystalline to amorphous phases. By comparing the interatomic distances with those found in model intermetallic compounds, local structures for the amorphous phases could be proposed.


10:30 AM T3.6
Carbon Nanotube-Enhanced Lithium Ion Batteries. Brian Landi, Matthew Ganter, Christopher Schauerman, Tyler Kallen, Christopher Redino, Cory Cress and Ryne Raffaelle; RIT - NanoPower Research Labs, Rochester, New York.

Lithium ion batteries are receiving considerable attention for use in applications ranging from portable electronics to electric vehicles due to their superior energy density over other rechargeable battery technologies. Single wall carbon nanotubes (SWCNTs) are a candidate material for use in lithium ion batteries based upon their high aspect ratio, potential for lithium ion intercalation, and excellent conductivity (electrical and thermal). The prospect of incorporating SWCNTs on the anode side for lithium ion storage and on the cathode side for electrical conductivity enhancement has been investigated. The ability to fabricate stand-alone SWCNT papers eliminates the need for metal foil substrates; therefore increasing the useable anode specific capacity (mAh/g). The electrochemical cycling performance of high purity SWCNT paper electrodes has been measured vs. lithium metal for a series of electrolyte solvent compositions. The variations in capacity with galvanostatic charge rate and cycling temperature have been measured between 25 - 100 °C. The measured reversible lithium ion capacities for SWCNT anodes range from 600-800 mAh/g for a 1M LiPF6 electrolyte. The solid-electrolyte-interface (SEI) formation and first cycle charge loss, however, are shown to vary dramatically with carbonate solvent selection and illustrate the importance of solvent alkyl chain length and polarity on SWCNT capacity. SWCNT anodes have also been incorporated into full battery designs using LiCoO2 and LiNiCoO2 cathode composites with and without SWCNT additives. An electrochemical pre-lithiation sequence, prior to battery assembly, has been developed to mitigate the first cycle charge loss of SWCNT anodes. The pre-lithiated SWCNT anodes show reversible cycling at varying depths of discharge with each of the cathode systems. These battery results are complemented by a post-mortem analysis of the SWCNT electrodes after electrochemical cycling using scanning electron microscopy, x-ray diffraction, Raman and optical absorption spectroscopy. The summary of data shows that the structural integrity of individual SWCNTs is preserved after cycling, and that free-standing SWCNT paper electrodes represent an attractive material for lithium ion batteries.


10:45 AM T3.7
Electrochemical Properties of LiFePO4 Synthesis by Solid State Route. Arun Kumar, Physics, University of Puerto Rico, San Juan, Puerto Rico; physics, Institute for Functional Nanomaterials, University of Puerto Rico,, Mayaguez, Puerto Rico.

Lithium Olivine LiFePO4 has under intense investigation since its introduction in 1997 as a possible cathode material for Li-ion rechargeable batteries (1). This material has many advantages, it is environmentally benign, inexpensive and thermally stable in the charge state [2, ]..LiFePO4 based olivine cathode materials theoretically capacity of 170 mAh/g, good cycling stability and flat discharge potential of 3.4 V versus Li/Li+. These properties make it an attractive candidate as a the cathode material. The main problem with this material is poor rate capability, which is attributed to its low electronic conductivity and poor diffusion of lithium ions through LiFePO4/FePO4 interface seems to the cause of lower measured capacity. Stoichiometric amount of lithium carbonate, iron oxalate,ammonium dihydrogen phosphate were used as precursor material to prepare for carbon free LiFePO4 and LiFePO4: C composite cathode materials. The precursor materials were first milled in a high energy ball mill in acetone media for 4h. , ground in a mortar paste, and calcined at 400oC for 10h in nitrogen. The carbon mixed powder was calcined for the formation of orthorhombic olivine lithium iron phosphate particles. The phase formation behavior of the synthesized powder was investigated using X-ray diffraction, using Cu Kα radiation. The morphology of the synthesized powder was investigated using a scanning electron microscopy (SEM), and transmission electron microscopy (TEM, Carl Zeiss Leo Omega 922 at 200 KeV). The XRD pattern for carbon free and carbon coated. The XRD data was further analyzed using a Rietveld refinement program. In carbon free sample new diffraction peaks appeared for Li3PO4 and Fe2P. From the elemental analysis, the residual carbon (2-8 wt. %) was contained in carbon coated prepared sample. The Discharge curves of LiFePO4-C sample excellent discharge capacity (~163 mAhg-1) and cycleability (~ 96% retention after 50 cycles) at C/5 rate was attained in the synthesized carbon coated sample .


11:00 AM T3.8
Multicomponent 5V Cathodes for Li-ion Batteries. Malgorzata K Gulbinska1, Boris Ravdel1, Svetlana Trebukhova1, Sanjeev Mukerjee2 and Brian N Hult2; 1Yardney Technical Products, Inc., Pawcatuck, Connecticut; 2Chemistry and Chemical Biology, 317 Egan Research Center, Northeastern University, Boston, Massachusetts.

Lithium-ion batteries (LIB) have progressed technically and commercially since their first implementation more than a decade ago. Nowadays, rechargeable lithium-ion cells ranging from 2 to 200 mAh with specific energies of >200 Wh/kg are built and applied in a multitude of applications. However, non-incremental improvements, such as specific energies as high as 350 Wh/kg are required in order to meet the growing needs of the modern market. In order to achieve major advances in specific energy of LIB, novel concepts for lithium-ion battery chemistry and/or design, such as the multiphase electrodes, are highly desired. In former studies of the multicomponent cathodes such as LiMO2.Li2M’O3 (M=Co, Ni, Mn; M’=Ti, Zr, Mn), the addition of Li2M’O3 was found to enhance the stability of the positive-electrode material. The addition of the layered LiNi0.8Co0.2O2 material to lithium-manganese spinel Li1+xMn2-xO4 was found to inhibit the spinel dissolution in the electrolyte and reduce capacity losses during storage at elevated temperatures.1 Feasibility of preparation and possible advantages of manganese oxides-based composite cathodes were also discussed by Thackeray et al.2 Despite the challenges related to synthetic methods (obtaining the phase purity, etc.) the authors agreed that the composite electrode systems are worth exploring.1,2 In this study, the multicomponent electrode approach was used in an attempt to simultaneously improve the cell’s specific energy values by shifting the cathode’s voltage up to the 5V-region, combined with the increased specific capacity via addition of the second electrode component. The electrode materials were prepared by variety of synthetic methods (e.g. mechanical mixing, solid state, hydrothermal, etc.) and tested for lithium-ion intercalation properties. Structural properties and morphology of synthesized materials were characterized by X-ray diffraction (XRD) methods and Scanning Electron Microscopy (SEM), respectively. The prospective 5V cathode materials were investigated as cathodes in Li-ion cathode half-cells and full cells. 1Wu, Y. P., Rahm, E., Holze, R., Electrochimica Acta, 2002 , 47, 3491. 2Thackeray, M. M., Johnson, C. S., Vaughey, J. T., Li, N. S., Hackney, A., J. Mater. Chem., 2005 , 15, 2257.


11:15 AM T3.9
Highly Crystalline, Porous Transition Metal Oxides for Mobile Energy Applications. Mahendra Christopher Orilall1,2, Jinwoo Lee2, Francis J DiSalvo1 and Ulrich Wiesner2,1; 1Chemistry and Chemical Biology, Cornell University, Ithaca, New York; 2Materials Science and Engineering, Cornell University, Ithaca, New York.

Highly crystalline porous transition-metal oxides for potential use in mobile energy applications are synthesized from two different approaches. In the first approach, mesostructured TiO2 and Nb2O5 are structure directed using an amphiphilic block copolymer, poly(isoprene-b-ethylene oxide) (PI-b-PEO). High crystallinity without collapse of the mesostructure is achieved via a combined assembly of soft and hard (CASH) chemistries. To this end, the metal oxide-copolymer composite is heated to high temperatures under an inert environment for full conversion of the amorphous metal oxide to crystalline material. At the same time, the sp2 hybridized carbon atoms of the PI block are converted to a sturdy amorphous-graphitic like carbon material that acts as a scaffold to the mesostructure during crystallization. The carbon is subsequently oxidized away at lower temperatures in air leaving an ordered mesoporous solid with uniform pores behind. In the second approach, highly crystalline macroporous TiO2 and Nb2O5 thin films are prepared by a colloidal crystal templating technique. Here, polymer colloids from polymers such as polystyrene (PS), are deposited onto a substrate and the metal oxide solution is filled into the interstitial spaces to leave an organic-inorganic three-dimensionally ordered material. Using the CASH approach, the sp2 hybridized carbon atoms of the PS are subsequently converted to carbon material acting as a scaffold to the macrostructure during crystallization. In this way, highly crystalline ordered macroporous transition-metal oxides can be produced. Finally, strategies to deposit metal nanoparticles onto these porous supports for mobile energy applications are discussed and their electrochemical activity are characterized.


11:30 AM T3.10
Nanoscale Engineering of LiFePO4 Cathodes for Thin Film Lithium-ion Batteries. Zhiyong Xu and Howard Wang; Mechanical Engineering, Binghamton University, Binghamton, New York.

Multiple approaches in nanoscale engineering of LiFePO4 cathodes for thin film lithium-ion batteries have been carried out. At the synthesis stage, controlled hydrothermal reaction leads to enhanced homogeneous nucleation to yield sub-micron grains of high purity LiFePO4 crystals. The reaction products were further engineered to yield exfoliated nanocrystals, which were incorporated in hierarchically structured nanocomposites to achieve optimized electrical and ion conductivity, and cycling stability. Electrochemical performances of cathodes in functioning battery cells were correlated to their structure and dynamics.


11:45 AM T3.11
Reduction of bis(oxalato)Borate on a High Surface Area Carbon Electrode. John Flynn and Carl Schlaikjer; Tracer Technologies, Somerville, Massachusetts.

Lithium bis(oxalato)borate has gained widespread interest as an electrolyte salt for lithium ion batteries because of its high conductivity, low cost, thermal stability, and adequate solubility in many organic solvents(1). Cyclic voltammetric data(2) taken on low surface area electrodes indicate electrochemical stability over a wide potential range. We show that bis(oxalato)borate can be reduced at about 1.75 volts anodic to lithium, by discharging electrolytes at low current density (0.1 mA/cm2) on high surface area carbon electrodes containing a mixture of acetylene and Ketjen carbon blacks. The evidence includes discharge profiles and boron 11 NMR data. The behavior of discharge plateaus indicates that bis(oxalato)borate is reduced to a soluble species with electrolytic properties, and the appearance of a broad B11 NMR peak in the electrolyte indicates that the reduced species undergoes extensive exchange. 1. Ulrich Wietelmann, Uwe Lishka, Marion Wegner U.S Patent 6,506,516 2. Wu Xu and C. Austen Angell, Electrochem. Solid-State Lett., 4 (1) E1-E4 (2001)


 

SESSION T4: Novel Conversion and Storage Techniques
Chair: Arokia Nathan
Tuesday Afternoon, December 2, 2008
Liberty (Sheraton)


1:30 PM T4.1
Formation of GaN Nanocrystal on Si and Its Photoelectrochemical Application. Katsushi Fujii1, Takashi Kato1, Keiichi Sato1, In-Ho Im1, Ji-Ho Chang2 and Takafumi Yao1; 1Center for Interdisciplinary Research, Tohoku University, Sendai, Japan; 2Major of Semiconductor Physics, Korea Maritime University, Pusan, South Korea.

Photoelectrochemical water splitting is an important technique for hydrogen evolution. GaN is one of the suitable materials for the photo-illuminated working electrode considered from the band edge energy and the stability in solutions. We have used flat surface GaN layer because the crystals have been made by epitaxial technique. The larger area is expected to be the better efficiency from the chemical reaction point of view, but it is difficult to make the nano-structured GaN surface. Thus, we investigated the growth of the GaN nanostructure on Si substrate by molecular beam epitaxy (MBE), and evaluated the photoelectrochemical characteristics in this report. The GaN nanodots were made on n-type Si (111) substrates as follows. Firstly, the surface oxide layer of Si wafer was removed by NH4F solution. Secondly, the Si substrate was transferred into the MBE chamber and annealed for 10 min at 850 degC. Thirdly, Ga flux (beam equivalent pressure (BEP) : 0.1E-7, 0.5E-7, 1.0E-7, 2.0E-7 Torr for each sample) was exposed for 50 sec at 530 degC. Fourthly, nitrogen plasma (BEP : 1.6E-5 Torr) was exposed for 120 sec at 530 degC and annealed for 10 min at 900 degC. Finally, we got out the sample from the MBE chamber and dipped into HCl solution for 24 h to remove the residual Ga. The formation of nanodots was not sufficient at annealed under 850 degC. Thus, annealing process is probably the key for the formation of the GaN nanodots for this growth procedure. The obtained GaN nanodot diameter decreased from 130 nm to 22 nm with increasing Ga BEP from 0.1E-7 to 1.0E-7 Torr, however, the density increased from 7.4E8 to 1.0E11 cm-2. Continuous surface was obtained when the Ga BEP was 2.0E-7 Torr. Photocurrent densities of the samples were measured directly connected to a counterelectrode in 1.0 mol/L HCl under 350 mW/cm2 Xe lamp. The photocurrent densities were sub mA/cm2 order and increase with the order of the nanodot density. The current densities were quite low compared with typical density of the GaN layer on sapphire substrate grown by metal-organic vapor phase epitaxy (sub mA/cm2). This is probably because of the existence of Si-GaN hetero barrier and the quite thin photo absorption region (several ten nm) of nanodots. The maximum current density obtained from the maximum GaN nanodot density sample was higher than that with continuous surface. The nano structure is effective for the photocurrent density improvement from these results. This indicates the rate limiting process is not the light absorption but the electrochemical reaction at the surface as we expected.


1:45 PM T4.2
Sub 500 °C Vacuum Thermionic Energy Conversion based on Doped Diamond Thin Film Structures. Franz Alexander Koeck and Robert J Nemanich; Arizona State University, Tempe, Arizona.

This research presents a demonstration of vacuum thermionic energy conversion at temperatures less than 500 °C. Vacuum thermionic energy conversion is an efficient means of transforming heat directly into electricity where a thermionic emitter is separated from a cooled collector by a vacuum gap. The negative electron affinity of diamond is a crucial aspect of obtaining a low temperature thermionic electron emitter. In this research we have prepared nitrogen - doped and ultra - nanocrystalline (UNCD) diamond multilayered thin film emitter structures on metallic substrates by microwave plasma assisted CVD. Electron emission is described in terms of the Richardson - Dushman equation which is based on the work function φ and Richardson constant A. Our new film structure demonstrate significant improvements in the emission which is attributed to the low resistivity UNCD interface layer as well as selective metal substrates. Films are assembled into a thermionic converter configuration where the emitter was separated from a collector with similar properties. At increased emitter temperatures, while keeping a cooler collector, a self - generated voltage appears at the electrodes. Operating the converter at 500 °C resulted in an open source voltage of V0 ≈ 0.42 V. With an electrical load of variable resistance the output voltage of the converter was recorded. Maximum output power was achieved at a load voltage of ~ 0.1 V indicative of vacuum thermionic energy conversion at 500 °C. This research is supported through the Office and Naval Research TEC MURI.


2:00 PM *T4.3
Nano-structured Si-Ge Films Deposited by Low Frequency Plasma for Photovoltaic Application. Andrey Kosarev1, Alfonso Torres1, Carlos Zuniga1, Marco Adamo2 and Liborio Sanchez1; 1Electronics, Institute National for Astrophysics, Optics and Electronics, Puebla, Puebla, Mexico; 2"Lambda Energia", S.A. de S.V., Cuernavaca, Morelos, Mexico.

Narrow optical gap materials are required in order to collect charge carriers generated by low energy photons of solar spectrum. Attractive candidate is silicon-germanium alloy deposited by plasma (Si1-yGey1-yGey:H with y>0.5 films have not been reported. In this work we present the study of fabrication, Ge incorporation, structure and electronic properties of nano-structured Si1-yGey:H films with y>0.5 prepared by low frequency (LF) PECVD. Si1-yGey:H films were deposited by LF PECVD at a frequency f=110 kHz from SiH4+GeH4+H2 gas mixture. SiH4 and GeH4 flows were varied to fabricate the films in wide range of 0≤y≤1. Hydrogen dilution was varied in the range of R=20 to 80. Structure of the films was studied by AFM and SEM with consequent image processing to extract statistical parameters such as grain distribution and mean values. Composition of the films was characterized by SIMS and EDS. Electronic properties were characterized by temperature dependence of conductivity, spectral dependence of optical absorption. Sub-gap absorption was used to obtain Urbach energy, EU, and defect absorption, αD. We observed grain like nano-structure with Gauss distribution of grain diameters by both AFM and SEM measurements. The most interesting films had mean grain diameter <D>= 24.0±0.7 nm, dispersion ΔD=11.0±0.2 nm and fill factor FF=0.313, Ge content y=0.96-0.97(by SIMS and EDS). These films showed also the lowest values of EU=0.030 eV and αD = 5x102 cm-1 (hν = 1.04 eV) that indicates low density of localized states in mobility gap. p- and n-doped films have been also fabricated and studied. Finally we shall discuss application of the above films in photovoltaic devices.


2:30 PM *T4.4
Flexible Thin-Si Solar Cell Devices for Mobile Energy. Qi Wang, National Renewable Energy Laboratory, Golden, Colorado.

Low temperature hydrogenated amorphous Si based materials and solar cells on flexible substrate are good candidate for mobile energy applications. Hydrogenated amorphous Si solar cell is a semiconductor device that converts light into electricity. It consists of stack of many functional thin-layers with the thinnest layer can be in the order of a few nm over a larger area. The low temperature process makes it possible to use low cost and flexible substrate such as plastic and fabricate mobile energy devices. For example, portable battery chargers and solar powered tent are available on the limited market. This presentation will describe a-Si:H solar cells and mobile device manufacture using the industrial standard plasma enhanced chemical vapor deposition and address issues that associated with.


3:30 PM *T4.5
Mechanically Flexible Photovoltaic Devices for Distributed and Portable Energy Generation using Roll-to-Roll Processing. Andrei Sazonov, Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, Ontario, Canada.

To Be Determined


4:00 PM T4.6
Ink-jet Printed Carbon-based Micro-Supercapacitor for Integrated Energy Storage. Magali Brunet1, Pierre-Louis Taberna2, Patrice Simon2, Norbert Fabre1, Veronique Conedera1, Fabien Mesnilgrente1, Hugo Durou1 and Carole Rossi1; 1UPR 8001, LAAS-CNRS, University of Toulouse, Toulouse, France; 2UMR 5085, CIRIMAT- CNRS, University of Toulouse, Toulouse, France.

The actual need for self-powered modules, able to perform sensing, data processing and information wireless transmission raises the question of energy storage. In these applications, the remote locations of the modules in the environment or the necessity to implement them inside permanent structures such as aircraft structure for health monitoring for instance exclude the use of batteries as energy source because no replacement is allowed. In that context, one widely proposed solution is to harvest ambient energy (thermal, mechanical, solar). Batteries or supercapacitors can then be used as intermediate energy storage level between the power harvesting device and the load (sensors). The advantage of supercapacitors lies then in the fact that they can still provide an effective storage in harsh environment, especially at low temperature (down to -40°C) whereas batteries stop functioning below -20°C. The levels of power that can be harvested in the environment being fairly low (nW to a few 100s µW), the power dissipation in the circuitry and storage device should be kept to a minimum. It is then believed that integrating a supercapacitor together with the power harversting device and its conversion circuitry will present the optimum configuration for reducing the power losses through connections. Since low profile is essential to provide non invasive systems in self powered applications, the integration of the complete system will also allow size reduction. We propose a new technology to integrate on silicon a carbon based micro-supercapacitor. The developed micro-supercapacitor consists in two interdigited gold electrodes on oxidised 4" silicon wafer. On these electrodes, the active material (activated carbon + PTFE) is deposited by ink-jet with an ALTADrop® equipment. The structure is then ready for electrolyte impregnation and encapsulation. Through this simple technology, process steps are kept to a minimum. Careful functionalisation of the surfaces (silicon versus gold) had to be developed to achieve selective coverage of the gold electrodes by the active material. The resolution obtained was 40 µm. The fabricated prototypes had 20 interdigited electrodes fingers, 40 µm wide and 800 µm long, separated by 40 µm. After active material deposition (few µm thick), the prototypes were bonded and tested with propylene carbonate + Net4BF4 (1M) electrolyte through impedance spectroscopy and cycling voltammetry. A capacitance of 1 µF (700 nF/mm^2) was measured, which is 10 times higher than an interdigited structure without active material. Future developments will consist in depositing thicker active material, optimising the active material itself and provide full device encapsulation. This new technology could address the need for mobile integrated energy storage.


4:15 PM T4.7
Flexible, Light Weight Supercapacitors from Single-walled Carbon Nanotube Thin Films. Pritesh Hiralal1, Husnu E Unalan1, Di Wei2 and Gehan Amaratunga1; 1Engineering, University of Cambridge, Cambridge, United Kingdom; 2Nokia Reseach centre, University of Cambridge, Cambridge, United Kingdom.

Electrochemical capacitors or supercapacitors offer complementary charge storage capabilities to batteries. High charge and discharge rates without loss in performance (albeit lower energy density) are attractive for many applications. In fact, placed in parallel with the battery terminal, such a capacitor can provide in addition to significant storage capacity, a significant current boost on high load demands. This enhances the battery’s performance and prolongs runtime1. We present the fabrication of thin, flexible supercapacitors employing thin films of single-walled carbon nanotubes (SWNTs) as the sole electrode material. The thin films are deposited onto a PET sheet by a simple solution based vacuum filtration method. The SWNTs provide both electron conductivity and high surface area in contact with the electrolyte, while using an extremely low amount or carbon (~0.0024-0.01 mg/cm2). The resulting devices consist of porous carbon networks as electrode material with a nitrocellulose membrane wetted in 1M sulphuric acid as separator. This results in very high capacitances of ~60F/g active material (or ~0.15F/cm2), as revealed by cyclic voltammetry and charge-discharge curves. We report the behavior of different densities of SWNTs, as well as the performance this structure with both solid polymer electrolyte (polyethene oxide) and ionic liquids (RTIL) in order to improve the electrochemical windows. This technology leads to thin film supercapacitors fabricated at room conditions. With the use of ionic liquids or polymer electrolytes, devices show some degree of transparency. The process can be foreseen to be extended to roll-to-roll and inkjet processes. 1. Kaempgen et al, Appl. Phys. Lett, 90, 264104 (2007)


4:30 PM T4.8
Development of Ultrahigh Surface Area Porous Electrodes using Simultaneous and Sequential Meso- and Micro-structuring Methods. Franchessa Maddox1, Catherine Cook1, Brenda O'Neil1,2,3, Leigh McKenzie2,3, Elizabeth A Junkin1 and Martin Bakker1,2; 1Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama; 2Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama; 3Admiral Moorer Middle School, Eufala, Alabama.

Very high surface area nanostructured metal electrodes are of interest as efficient current collectors. For thin film devices, the nanostructured metal can be grown in place using electrodeposition or electroless deposition. For larger devices metal electrodes structure at more than one length scale is desirable. Self-assembling surfactant templates are a versatile method of generating a range of nanostructures. As we report here, electrodeposition of nickel, cobalt and copper from liquid crystalline solutions of Triton X-100 produces a number of nanostructures, with significant surface area increases. The nature of the nanostructure is impacted by the metal and by whether deposition is carried out on low area flat substrates or higher area 3-dimensional substrates. Electrodeposition into templates with microstructure has proven more demanding. Oil-in-water microemulsions of Tween surfactants and soy oil, produce micrometer scale structures, however surface area does not scale with sample thickness, suggesting that such samples are not bicontinuous. The method is also not robust, and was found to give microstructures only for nickel and cobalt. Preliminary results from other approaches, including wax beads and monolithic silica columns indicate that these methods do not appear to suffer from the same limitations, and will prove to be more robust microstructuring methods.


4:45 PM T4.9
Nanostructured Pt-Based Electrodes for the Enhanced Electrocatalytic Activities. Chunjoong Kim, Yejun Park, Changwoo Nahm and Byungwoo Park; Department of Materials Science and Engineering, Seoul National Univeristy, Seoul, South Korea.

Despite significant progress in proton-exchange fuel cell (PEMFC) and direct-methanol fuel cell (DMFC) research nowadays, there are still prohibitive issues for the wide-range commercialization, such as the low efficiency of electrodes, the loss of activity during the long-term operation, methanol crossover, easy poisoning, etc. To resolve these, nanostructured Pt-based electrodes have been investigated for the potential use as anodes and/or cathodes. In this study, the nanostructured Pt/metal-phosphate electrodes were synthesized, and their oxidation and reduction activities were examined. The nanostructured Pt electrodes exhibited the enhanced catalytic activities compared with the Pt thin films. These enhancements are attributed to the metal-phosphate-induced electronic/bifunctional effects. [1] C. Kim, B. Lee, Y. Park, B. Park, J. Lee, and H. Kim, Appl. Phys. Lett. 91 , 113101 (2007). [2] B. Lee, C. Kim, Y. Park, T.-G. Kim, and B. Park, Electrochem. Solid-State Lett.9 , E27 (2006). Corresponding Author: Byungwoo Park: byungwoo@snu.ac.kr


 

SESSION T5: Poster Session: Energy Storage Devices for Mobile Energy
Chair: Andrei Sazonov
Tuesday Evening, December 2, 2008
8:00 PM
Exhibition Hall D (Hynes)


T5.1
A Noble Process for Ink-jet Printable LiCoO2 Nanoparticles and its Application to Lithium Thin Film Battery Prepared by Ink-jet Printing. Jae-man Choi, Moon-seok Kwon, Hansu Kim and Seok-kwang Doo; Energy group, Samsung Advanced Institute of Technology, Younin-Si, Gyeonggi-Do, South Korea.

The rapid development of modern electronic technology has created a strong demand for thin film battery as a power source for the future electronic systems such as smart card, active radio-frequency identification tag, electronic papers and wearable electronic devices. Rechargeable lithium thin film battery fabricated using vacuum deposition processes showed promising performance, for instance, high volumetric energy density, good safety and long cycle life. However, high production cost should be addressed for commercialization. One of the effective ways to reduce cost is the replacement of vacuum deposition process by printing process. Printing has emerged as an attractive technique for the production of the electronic devices, because it has some advantages such as low cost, high production speed and high compatibility with roll-to-roll process. There have been recent research efforts to make conventional primary and rechargeable battery into thin and light-weight battery as a power source for the future electronics using low-cost printing process. In particular, ink-jet printing such as direct writing process and non-contact printing. In this work, we will demonstrate ink-jet printed LiCoO2 thin film electrode for rechargeable lithium thin film battery with DMP-2800 ink-jet printer(Dimatix, Inc.). Ink-jet printable LiCoO2 particles of about 100nm size were prepared by high energy mechanical milling combined with combustion synthetic route. The LiCoO2 ink was composed of LiCoO2 nanoparticles as an active material, carbon black(super P) as a conductive agent, polyvinylidene fluoride(PVdF) as a binder and N-methylpyrrolidone(NMP) as a solvent. Herein, we will present the electrochemical behaviors of ink-jet printed LiCoO2 thin film electrode as a cathode for rechargeable lithium thin film battery.


T5.2
Structure and Electrochemical Hydriding Properties of Pd/Mg/Pd Thin Films Prepared by Pulsed Laser Deposition. Said Bouhtiyya and Lionel Roue; INRS-EMT, Varennes, Quebec, Canada.

Magnesium is a very interesting hydrogen storage material because of its high hydrogen storage capacity (7.6 wt.% for MgH2), low density and low cost. However, its operation temperature is typically over 600 K. The reasons are the presence of a native surface oxide preventing the access to metallic magnesium, the high energy barrier for H2 dissociation on Mg and the slow hydrogen diffusion through the MgH2 phase. Moreover, the high thermodynamic stability of MgH2 (enthalpy of decomposition of about 70 kJ mol-1 H2) results in a low partial hydrogen pressure at ambient temperature. This strongly restricts the practical applicability of magnesium as H storage material for fuel cells or Ni-MH batteries. However, hydrogen uptake by Mg can occur at room temperature for Pd-capped Mg thin films helped by the high H2 dissociation rate and high hydrogen diffusivity of the Pd outermost layer. Unfortunately the saturation level of hydrogen in the Mg film is low and decreases with increasing H2 pressure. This is attributed to the formation of a Mg hydride layer at the Mg/Pd interface that blocks further hydrogen uptake due to the slow hydrogen diffusion in the magnesium hydride (β) phase. In the present work, it is shown that the pulsed laser deposition (PLD) is a suitable technique to elaborate nanostructured Pd/Mg/Pd thin films with variable microstructures depending of the deposition parameters. More particularly, it is demonstrated that the increase of the pressure of the background helium gas in the PLD chamber during Mg deposition increases the roughness of the Mg layer, which induces an extension of the Pd/Mg interface region. This extension has a strong positive influence on the electrochemical hydriding properties of the films.


T5.3
Thermodynamic Properties at the High Temperature of the Li-N-H Hydrogen Storage System. Toshihisa Izuhara, Hiroyuki T Takeshita and Keiko Kobayashi; Faculty of Chemistry, Materials and Bioengineering, Kanasi University, Suita-City, Osaka, Japan.

The mixture of LiH and LiNH2 has high hydrogen storage capacity of 6.5mass% by the following reversible reaction [1]. “LiH + LiNH2=Li2NH+H2” The mixture is promising material as an on-board hydrogen source. However, the hydrogen desorption of the mixture is very slow (For example, it takes 10 hours or longer to achieve complete hydrogen desorption at 473K). Kojima and Kawai were reported that the standard enthalpy and entropy change of the hydrogen desorption was -66.6 kJ/molH2 and -120J/molH2 K, respectively [2]. However, our previous study showed that the equilibrium pressure was lower than the calculated value from these thermodynamic parameters over the melting point of LiNH2 (about 640K). It is expected that the melting of LiNH2 causes decreasing of the absolute vale of the standard enthalpy change for the above-mentioned reaction. In the present study, thermodynamic properties around the temperature of the melting point of LiNH2 were investigated for the Li-N-H hydrogen storage system by the PCT measurement.LiNH2 was mixed with LiH in the molar ratio of LiH to LiNH2 in the range from 1:1 to 3:1 by mechanochemical method. Thermodynamic properties of the samples were measured by PCT method in the temperature range from 523K to 813K. The constituent phases of samples were identified by the XRD and FT-IR. It took more than ten hours to reach the equilibrium pressure of hydrogen desorption below the temperature of 640K, whereas it took less than five hours over the temperature of 640K. The standard enthalpy change of the hydrogen desorption at the temperature higher than the melting point of LiNH2 was calculated to be about -40kJ/molH2. [1] P. Chen et al., Nature, 420 (2002), 302-304. [2] Y. Kojima and Y. Kawai, J. Alloys Compd., 395(2005), 236-239.


T5.4
Amorphous Carbon Coated Counter Electrode for Electric Double Layer Capacitor. H. Ino, S. Ishigaki and Yoshiyuki Show; Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa, Japan.

Stainless steal is widely used for counter electrodes of coin type electric double layer capacitors (EDLCs), because of its high corrosion resistance. The passive film is existed on the stainless surface. This film increases the contact resistance between the polarizable electrode and stainless steal counter electrode in the EDLC. Therefore, the EDLC formed with the stainless steal counter electrodes generally shows high series resistance, which cause to low charge and discharge efficiency. In this paper, amorphous carbon film was coated on the stainless steal counter electrodes to prevent corrosion of its surface. The amorphous carbon coated counter electrodes were applied to EDLC in order to decrease series resistance. Stainless steal was used as the counter electrode. The amorphous carbon film was coated on the counter electrode by using RF plasma CVD equipment. Acetylene gas was used as source gas. Growth temperature was varied from room temperature to 600oC. Growth time was fixed at 1 hours. Activated carbon with a specific surface area of 2000m2/g was used as the base material for the polarizable electrode of the EDLCs. The EDLCs with use of the counter electrodes coated with amorphous carbon film at various temperature show 2F in capacitance. No dependence of coating temperature on the capacitance was observed. The EDLC with use of counter electrodes coated with amorphous carbon film at 500oC showed 15Ω in series resistance, which was lower than that of counter electrodes without the coating. The series resistance decreased up to 2Ω with an increase in the coating temperature 600oC. This value was as same as that of use of platinum counter electrodes. The passive film on the surface of stainless steal is removed by the coating of amorphous carbon film, because the surface was exposed to hydrocarbon plasma. Higher coating temperature coursed the conductivity of the amorphous carbon film to be lower. Therefore, series resistance of the EDLC was as low as 2Ω because the contact resistance between the counter electrode and the polarizable electrode was decreased. Above results indicates that the amorphous carbon coating to counter electrodes is useful technique to decrease the series resistance of the EDLC.


T5.5
The Synthesis of Complex Metal Hydrides via Surfactant Templating. Leo Seballos and Eric H Majzoub; Physics and Astronomy, University of Missouri, Saint Louis, St. Louis, Missouri.

Current hydrogen storage/delivery systems have yet to meet all of the requirements established by the U.S. Department of Energy for widespread application, and the search for material candidates continue. Complex metal hydrides have attracted considerable attention for their high gravimetric hydrogen densities, but many have decomposition enthalpies outside the desirable range of 20-40 kJ/mol H2. Recent theoretical and experimental work has suggested that deviations from bulk properties are possible in the Mg system. The synthesis of nanoscale materials presents a technique to modify bulk performance characteristics. The formation of nanoscale structures in microemulsions is a well established method for production of quantum dot semiconductors, and optical materials. A related surfactant templating method using non-aqueous microemulsions for reactive and oxygen sensitive complex hydride materials will be presented. Results on the synthesis of nanoparticles of complex metal hydrides such as NaBH4, NaAlH4 and LiAlH4 will be given. References: 1. R. W. P. Wagemans, J. H. van Lenthe, P. E. de Jongh, A. J. van Dillen, and K. P. de Jong. J. Amer. Chem. Soc., 127 (47), 16675, 2005. 2. K. F. Aguey-Zinsou, and J. R. Ares-Fernandez, Chem. Mater., 20, 376, 2008.


T5.6
Wireless Reactive Power Transfer through the Natural Media. Charles William Van Neste1,2,3, Satish Mahajan3 and Thomas Thundat1; 1Oak Ridge National Laboratory, Oak Ridge, Tennessee; 2Oak Ridge Associated Universities, Oak Ridge, Tennessee; 3Electrical Engineering, Tennessee Technological University, Cookeville, Tennessee.

We present a method of energy transfer originally developed by Nikola Tesla which may allow industrial levels of power to be transmitted wirelessly to both stationary and mobile apparatus at great distances. Conventional methods of power distribution rely on active power transfer. Transmitting wires are used to convey energy to a distance while the earth is used as the electrical return path. Great care is needed to maintain an in-phase voltage/current relationship for maximum power efficiency. In our method, real power is converted to reactive power before transmission. A single wire is used as both the transmitting and returning path. We replace the single wire with a ground connection, utilizing the earth as both a transmitting and returning path. The electrical oscillation expands outward, the distance dependent on the AC frequency used. At some distance, the electrical ground oscillations are used to drive a high Q coil into resonance. The power received by the resonating coil is inductively converted back into real power that can be used to power a load.


T5.7
Application of the Electric Double Layer Capacitors Formed with Carbon Nanotube to Secondary Power Source of Fuel Cell. H. Yoshida, H. Totani, T. Heishi and Yoshiyuki Show; Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa, Japan.

Electric double layer capacitors (EDLCs) using carbonaceous materials are an increasingly popular energy storage device with a high power density, high cycle-efficiency and long cycle life. One of the applications of EDLCs is as a secondary power source of fuel cells. The EDLC smoothes a load and stabilizes output voltage of the fuel cell. Therefore, the efficiency of fuel cell is improved by combining with the EDLC . For this application, EDLCs with low series resistance are required. In this study, carbon nanotube was added to the polarizable electrode of EDLC instead of the acetylene black as conducting material. The CNT addition leads series resistance of the EDLC to be low. Therefore this EDLC is useful for a secondary power source of fuel cell. Activated carbon with a specific surface area of 2000m2/g was used as the base material for the polarizable electrode. The CNT was added into the polarizable electrode at various concentration from 0 to 20%. The EDLC was assembled using the polarizable electrode added with the CNT. Direct methanol fuel cell was used as a primary source. The EDLC was connected to the fuel cell in parallel. The fuel cell supplied current with 10mA as a steady operation. The pulse current with a current of 80mA and width of 500mSec was flown into the load. The voltage change by flowing pulse current was measured. The EDLCs without and with addition of CNT show 2F in capacitance. No dependence of CNT on the capacitance was observed. The EDLC without addition of the CNT was 15Ω in the series resistance. The series resistance of the EDLC was decreased by addition of the CNT into the polarizable electrodes. An EDLC fabricated with a CNT concentration of 20% has a series resistance as low as 2.5Ω. The direct methanol fuel cell showed output voltage of 270mV at output current of 10mA. When the pulse load at the current of 80mA was applied to the fuel cell without connection of the EDLC, the output voltage decreased to 32mV. The voltage drop of 238mV was occurred by increased output current. When the EDLC was connected the fuel cell in parallel, the voltage drop was decreased. Moreover, the CNT addition into the polarizable electrodes of the EDLC prevented the voltage change, because of low series resistance of the EDLC. Above results indicate that the CNT is useful for decreasing series resistance of EDLC. Moreover, the EDLC with the CNT addition is suitable for a secondary power source of fuel cells.


T5.8
Continuous-flow, Vapor-phase Synthesis of Pt/Ru Nanoparticles in an Atmospheric-pressure Microplasma. Laurentiu Andrei Lita, Brian W Nelson and R. Mohan Sankaran; Chemical Engineering, Case Western Reserve University, Cleveland, Ohio.

Hydrogen- and methanol-based fuel cell devices are subject to gradual poisoning of the catalyst by CO. Improved catalysts are needed to remove the CO, which is present in reformate hydrogen and is also generated during methanol dehydrogenation. Recently, platinum-ruthenium (Pt/Ru) nanoparticle alloys have been found to be superior to other catalysts towards catalytic oxidation of CO [1]. Here, we present a new approach to the synthesis of tunable size and composition of Pt, Ru, and Pt/Ru nanoparticles. Nanoparticles are synthesized in the gas phase using a non-thermal DC microplasma discharge by electron impact disassociation of organometallic precursors typically used in chemical vapor deposition processes [2]. The short residence times available in the microplasma reactor allow the synthesis of narrow dispersions of nanometer-sized particles in a single step. The process is continuously operated at atmospheric pressure and integrated with real-time monitoring using aerosol size classification methods. Particle diameters below 3 nm were achieved to optimize the catalytic activity. As-grown nanoparticles are high-purity, non-agglomerated, and narrowly dispersed. We will discuss the physical properties of the nanoparticles, characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray energy dispersive spectrometry (XEDS), and X-ray photoelectron spectroscopy (XPS). [1] S. Alayoglu, A. U. Nilekar, M. Mavrikakis, and B. Eichhorn, Nat. Mat. 7, 333 (2007). [2] R. M. Sankaran, D. Holunga, R. C. Flagan, K. P. Giapis. Nano Lett. 5, 537, (2005).


T5.9
Synthetic Clay/PVA Nanocomposite Membrane for Direct Methanl Fuel Cell. Dharmaraj Raghavan1, Jason Ganley2, Nana KariKari1 and Sheriff Abudu1; 1Department of Chemistry, Howard University, Washington, District of Columbia; 2Department of Chemical Engineering, Howard University, Washington, District of Columbia.

Nafion®, the current state-of-the-art membrane material for polymer electrolyte membrane (PEM) fuel cells has several drawbacks that limit its performance and ultimate application in fuel cell systems, especially those involving the direct use of methanol as a fuel. Most notably, Nafion® exhibits unacceptably poor performance at temperatures exceeding 80°C and in low humidity conditions. In addition, the high crossover rate of methanol limits PEM fuel cells with Nafion® membranes to very low overall efficiencies. To overcome these limitations, we are developing novel nanocomposite synthetic clay membranes for alkaline direct methanol PEM fuel cells. We have designed a synthetic clay/polymer nanocomposite electrolyte membrane. The clay materials incorporated into polyvinyl alcohol films for the creation of a fuel cell membrane are layered double hydroxides (LDHs) based on the transition metal nickel. These new organic-inorganic hybrid clay nanocomposites are excellent candidates for a new class of proton electrolyte membranes due to their characteristic layered structure, high surface area, excellent mechanical properties, ion exchange capacity, and their polar, hydrophilic surface properties. In this work, we present results from experiments carried out to examine the effects of Ni-LDH nanocomposite PVA membranes in alkaline fuel cells. The data reported describe the cell performance of nanocomposite and LDH-free electrolyte support films using hydrogen and methanol fuels, comparing their performance across a range of temperature, relative humidity, and electrical load. Preliminary results indicate that Ni-LDH nanocomposite PVA membrane exhibit higher water retention and better fuel cell performance than the LDH-free PVA membrane.


T5.10
Computer Simulation of Structural Stability by Hydrogenation in Hydrogen Storage Materials. Masahiko Katagiri1, Hidehiro Onodera1 and Hiroshi Ogawa2; 1National Institute for Materials Science, Tsukuba, Ibaraki, Japan; 2National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.

Recently, energy problem is recognized as a very serious one. In such a situation an alternative energy resource is strongly desired. Hydrogen is one of the hopeful energy resources. One of the keys to realize the hydrogen-energy society is to store hydrogen effectively and safely. The intermetallic compound is a hopeful material. Several compounds have been developed. However, a break-through is desired to design the innovative storage materials. Then the basic study of hydrogen storage materials is needed. We focus on the problems of the lattice stability under hydrogenation and hydrogen diffusion. They are related to hydrogen amount and release temperature. Hydrogen-Induced Amorphization (HIA) is a phase transformation from crystalline to amorphous induced by hydrogenation. We report HIA and other stability and diffusion problems by hydrogenation. HIA was simulated by classical molecular dynamics (MD). We compared non-HIA and HIA materials, YAl2 and CeNi2, respectively. Elastic stability is discussed by calculating the elastic constants using the fluctuation formula as follows. We incorporated hydrogen into the systems. YAl2 did not show HIA. On the other hand, the amount of hydrogen exceeds a critical value, CeNi2 showed HIA. In YAl2, hydrogen simply increases volume and the bulk modulus is reduced because of the non-linearity of interatomic potentials. A similar reduction is observed under an isotropic tensile load. The main cause of the reduction is the potential term. On the other hand, in CeNi2, hydrogenation greatly reduces the bulk modulus. This reduction is mainly caused by the negative increase of the pressure-fluctuation term. As a result, hydrogenation leads to the amorphization at a much smaller volume than under a load. The increase of the pressure-fluctuation is the result of the atomic relaxation by hydrogenation. In CeNi2, the contraction and expansion are realized simultaneously, and relaxation can occur by hydrogenation. Even if the potential-energy change resulting from the relaxation is small, the change in pressure fluctuation is high. The role of the size effect is to allow the atomic relaxation by hydrogenation and to facilitate the elastic instability by the increase of pressure fluctuations. MD gives a good example to reveal the role of the size effect.


T5.11
First Principles Studies of Silicon as a Negative Electrode Material for Lithium-ion Batteries. Vincent L Chevrier1, Josef W Zwanziger2,1 and Jeff R Dahn1,2; 1Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada; 2Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada.

Silicon has emerged as an excellent candidate as a negative electrode material for Li-ion batteries over the last several years. It offers excellent specific capacity, volumetric energy density, and thermal stability compared to graphite, the common commercial negative electrode material. When Li is added to Si in an electrochemical cell at room temperature, the Si becomes amorphous a-LixSi and subsequently crystalline Li15Si4. When Li is removed from Li15Si4 the formed LixSi is amorphous again. [1, 2] However, if lithiation occurs in molten LiCl at 415 °C, the measured potential-composition profile displays plateaus at compositions matching each of the four binary phases of the Li-Si equilibrium phase diagram: Li12Si7, Li7Si3, Li13Si4, Li22Si5. [3] Density functional theory (DFT) total energy calculations, have been previously performed to accurately reproduce the potential-composition curve of Li/LixSi electrochemical cells at high temperature using the phases of the equilibrium phase diagram. A protocol is now proposed to extend the use of DFT to model the lithiation of Si at room temperature through incremental lithiation. Potential-composition curves obtained with this protocol are compared with experiment. Results show the impact of computational cell sizes on calculated potential-composition curves. Finally, an analysis of the variations in atomic order as a function of lithiation is presented. References [1] P. Limthongkul, Y.-I. Jang, N.J. Dudney, Y.-M. Chiang, Acta Mater. 51 1103 (2003). [2] M.N. Obrovac, L. Christensen, Electrochem. Solid-State Lett. 7 A93 (2004). [3] C.J. Wen, R.A. Huggins, J. Solid State Chem. 37 271 (1981).


T5.12
Abstract Withdrawn


 

SESSION T6/S7: Joint Session: Solid State Ionics for Mobile Energy
Chairs: Jennifer Rupp and Enrico Traversa
Wednesday Morning, December 3, 2008
Back Bay A (Sheraton)


8:30 AM *T6.1/S7.1
Functional Impact of Nafion-Metal Oxide Composite Membranes in Proton Exchange Membrane Fuel Cells: The Elevated Temperature Operating Window. Andrew B. Bocarsly1, Paul Majsztrik1 and Jay B Benziger2; 1Department of Chemistry, Princeton University, Princeton, New Jersey; 2Chemical Engineering, Princeton University, Princeton, New Jersey.

Present day proton exchange membrane (PEM) fuel cells (FC) are subject to poisoning by the presence of trace amounts of CO in the hydrogen fuel stream, water management limitations and difficulty in dumping waste heat. One solution to this problem is the implementation of a PEMFC that operates at an elevated temperature regime (i.e. from 120-150°C). However, Nafion®, the primary proton exchange membrane material available, undergoes changes above ~90°C that lead to extensive degradation of fuel cell output parameters. We have found however, that the use of a composite membrane formed from the addition of a metal oxide to a Nafion matrix allows for reproducible, stable cell operation up to ~145°C. Addition of a metal oxide component also provides improved performance under conditions of low humidity in the 60-80°C operation range. Metal oxide/Nafion composite membranes can be synthesized by the direct addition of metal oxide particles to a Nafion recasting suspension followed by solvent evaporation. Metal oxide content of 3-20% by weight leads to a mechanically and thermally robust composite membrane. The nature of the metal oxide and the recasting solvent is critical to the operation of the membrane. A model is put forward to account for the observed cell improvement involving a specific chemical interaction between the Nafion sulfonate groups and coordinately unsaturated sites on the metal oxide surface. Extensive interfacial interaction can lead to the leaching of metal ions from the oxide particle. This process degrades membrane performance in a fuel cell. On the other hand, if the interfacial interaction is extremely weak, no benefit is observed. Metal oxide-Nafion systems that show a catalytic chemical interaction using thermal gravimetric analysis are found to also provide a robust fuel cell response. Chemical modification of the metal oxide surface can be used to vary the polymer-inorganic interaction, thereby optimizing the observed PEM performance. Elevated temperature cells running above 135°C show enhanced carbon monoxide tolerance and good water management properties. An unexpected benefit of introducing a metal oxide phase is improved membrane mechanical parameters. The viscoelastic response of the PEM membrane is found to directly couple to the electrochemical output of the fuel cell. The composite membranes under consideration here have mechanical stability and improved elastic relaxation properties, providing an improved electrochemical response under conditions where the cell humidity, thermal content, or electrical power is varying.


9:00 AM T6.2/S7.2
Influence of Titania Morphology on the Electrochemical Properties of Composite Polymer Electrolyte Membranes. Debora Marani1,2, Chavalit Trakanprapai1, Silvia Licoccia1, Enrico Traversa1 and Masaru Miyayama2; 1NAST Center & Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma “Tor Vergata”, Roma, Italy; 2Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan.

One of the key topics in membrane electrolyte research is the need to develop inexpensive polymeric electrolyte membranes (PEMs) for operation under increased temperature (120-130 °C) and low humidity level (20-50 % of RH) with limited methanol permeability. An effective strategy to achieve high temperature and low humidity operation conditions deals with the development of electrolytes containing dispersed hygroscopic oxides. Several ceramic compounds, such as titania, silica, and zirconia, have been already evaluated, and encouraging results have been obtained. In this work, the influence of titania morphology on the electrochemical properties of 58% degree of sulfonation S-PEEK-based composites was investigated. Inorganic fillers were anatase powders having two different morphologies, mesoporous and nanometric. PEEK sulfonation reaction was carried out in concentrated H2SO4. The sulfonation degree was determined by titration and by H1 NMR, obtaining results in agreement. Mesoporous titania powders were obtained using a non-ionic surfactant assisted procedure: titanium alkoxide as metal precursor (Ti(OR)4) and non-ionic surfactant as templating agent (polyoxyethylene (18) tridecyl ether, C13EO18) were used. The obtained products were calcined at 350°C for 6 hours. Nanometric titania powders were synthesized using a sol-gel procedure, starting from Ti(OiPr)4. The obtained xerogels were calcined at 450°C for 4 hours. The powders were characterized using X-ray diffraction (XRD) analysis, specific surface area (B.E.T.) measurements, and scanning electron microscopy (SEM) observations. Composite membranes with different titania content, ranging from 1.33 up to 10 wt.%, were prepared by casting and characterized in terms of thermal stability, ion exchange, water uptake, and proton conductivity. The comparison between the two different morphologies showed significant differences in their effect both on water absorption and electrochemical properties. From the electrochemical characterization, the nanometric composites clearly showed a superior electrochemical performance, showing a higher enhancement in proton conductivity values. This observed effect could be associated to the larger number of water-adsorbing acidic sites on the nanometric surface, despite of its lower specific surface area (83 m2/g and 147 m2/g for nanometric and mesoporous titania powders, respectively). Further investigations to better understand this point are in progress.


9:15 AM T6.3/S7.3
Highly Conductive Polyelectrolyte Multilayers for Electrochemical Devices. Avni A. Argun, James N Ashcraft and Paula T Hammond; Department of Chemical Engineering, MIT, Cambridge, Massachusetts.

The increasing focus on clean and sustainable energy sources has led to an interest in electrochemical energy devices such as batteries, fuel cells, and dye-sensitized solar cells. At the core of these devices is an electrolyte which facilitates charge transport between electrodes. Polymeric ionic conductors offer high mechanical strength and fabrication flexibility compared to traditional electrolytes, as well as better physical separation of electrodes. Although the desired properties of solid-state polymer electrolytes depend on the device application, fast ion conduction is essential to reduce electrical resistance and power losses. Furthermore, it would be desirable to utilize approaches that are cost effective and environmentally friendly. Layer-by-layer (LBL) assembly is a versatile thin-film fabrication technique which consists of the repeated, sequential immersion of a substrate into aqueous solutions of complementary functionalized materials.[1] This approach presents strong advantages as it allows the incorporation of many different functional materials within a single film at a full range of compositions with exceptional homogeneity. In one example, we have developed LBL films by pairing a sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (sPPO) with poly(diallyl dimethyl ammonium chloride) (PDAC) to obtain ionic conductivity values of 35.2 mS/cm at 25°C and 98% relative humidity. These multilayer films exhibit low liquid methanol permeability and have high chemical stability to provide a direct application as proton-exchange membranes in direct methanol fuel cells (DMFCs). We have demonstrated that simply coating traditional fuel cell membranes with 3 to 5 bilayers of these LBL films improves the power output of DMFCs by over 50% at 25°C.[2] We are currently developing standalone LBL films peeled off from a low surface energy template as a way of eliminating the need for a substrate. <p> [1] Lutkenhaus, J. L.; Hammond, P. T., Electrochemically Enabled Polyelectrolyte Multilayer Devices: From Fuel Cells to Sensors. Soft Matter 2007 , 3, 804-816.Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers. Advanced Materials 2008 , 20, 1539-1543.


9:30 AM T6.4/S7.4
Titanium Body-Centered-Cubic (BCC) Alloys as Anodes for Lithium Ion Batteries. Ruigang Zhang, Shailesh Upreti and M. Stanley Whittingham; Binghamton University, Binghamton, New York.

Titanium BCC alloys with many interstitial insertion sites are one of the state-of-the-art hydrogen storage materials and have been shown to react rapidly with large amounts of hydrogen. Their electrochemical discharge capacity can reach near 1000 mAh/g when using as nickel-hydrogen battery anode. Due to the similarity between hydrogen and lithium, it is interesting to study whether this kind of alloy can be used as the anode in lithium ion batteries. A series of titanium BCC alloys were prepared by arc melting method and their crystal structures were studied by powder X-ray diffraction. Before reaction with lithium, these alloys were treated by various processes including ball milling of various duration, with and without various coatings; annealing at different temperature, and applying hydrogen decrepitation reaction to produce alloy fine particles by reaction with hydrogen gas. Another alloy preparation method — high-energy mechanical ball milling — was also studied. All of the alloys produced by the above processes were tested electrochemically. Experimental results indicate that BCC alloys could improve their lithium intercalation-deintercalation capacity from zero to near 100 mAh/g after the hydrogen decrepitation process. From this initial study, we can conclude that titanium BCC hydrogen storage materials may be considered as lithium ion battery anode. Optimization of synthesis and hydrogen decrepitation conditions, detailed electrochemical studies and determination of structural changes after hosting lithium are underway. We thank Robert Huggins for some initial discussions on these alloys. 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.


9:45 AM T6.5/S7.5
Thermogalvanic Cells for Small-Scale Energy Harvesting and Storage. Nicholas Hudak and Glenn Amatucci; Department of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey.

For many applications, the nodes in a wireless sensor network must be cubic-millimeter sized and have a long lifetime. The amount of energy that can be stored in a sensor node is determined by its size. A cubic-millimeter-sized node with a battery as the sole power source has a severely limited lifetime. Alternatively, energy harvesting devices may be used to recharge the battery or to directly power the sensor and communication components, thus allowing for small nodes with unlimited lifetime. Small-scale energy harvesting devices based on thermoelectric, vibration, and radiofrequency power conversion have been considered for this purpose. An alternative type of thermal energy harvesting, based on thermogalvanic cells, accomplishes both energy harvesting and energy storage in the same device. This multi-functionality is an important space-saving advantage because it eliminates the need for an interface between the energy harvester and the battery. A thermogalvanic cell (or non-isothermal cell) is an electrochemical cell in which the two electrodes are at different temperatures. In symmetric thermogalvanic cells (those with compositionally identical electrodes), the temperature gradient produces a proportional voltage output. The dV/dT values of thermogalvanic cells are typically ~1 mV/K or higher, which is four to five times higher than those of the best thermoelectric materials. A cell with symmetric, single-phase intercalation electrodes can undergo a charge-discharge cycle when supplied with oscillating heat flow. We have demonstrated symmetric LixTiS2 cells operating near room temperature with a temperature difference between the electrodes ranging from 1 K to 10 K. The dV/dT values are dependent on electrode composition (x in LixTiS2) and are around 1 mV/K for 0.4 < x < 0.8. There is also a slight dependence on electrolyte concentration and electrolyte anion. Unlike thermoelectric Seebeck coefficients, these thermogalvanic dV/dT values are closely related to both the entropy of lithium intercalation into LixTiS2 and the thermal diffusion potential of the electrolyte solutions. The former is a function of many parameters including the site energy, related to the overall Madelung energy of the host. A greater understanding of these effects will aid in the selection of materials for battery-type thermogalvanic cells, and results for a range of electrode-electrolyte combinations will be presented.


10:30 AM T6.6/S7.6
Structural Optimization by TOhoku University Mixed-Basis Orbitals ab Initio Computation Method (TOMBO): Case Study of Hydrides and Molecules. Ryoji Sahara1, Masaya Iwamoto1, Osamu Kikegawa1, Bahramy Saeed1, Ryunosuke Note1, Hiroshi Mizuseki1, Marcel Sluiter2 and Yoshiyuki Kawazoe1; 1Institute for Materials Research, Sendai, Japan; 2Dept of MSE, 3ME, TU Delft, Delft, Netherlands.

To realize applicable hydrogen storage materials, fundamental understanding for hydrides is an important task. While, it is well-known that it is impossible to treat some properties such as XPS spectra and hyperfine structure within pseudopotential approaches. An all-electron method can overcome these limitations. It tends to be slower than a pseudopotential method which deals with valence eigenstates only. Mixed-basis method, in which the electronic eigenstates are expressed in terms of truncated atomic eigenfunctions augmented with plane waves, can be expected to be conceptually and computationally advantageous compared to other full-potential all-electron methods. Although the development of scheme has been attempted, it is not sufficient yet. Our laboratory has developed original program code TOMBO (TOhoku university Mixed-Basis Orbitals ab initio computation method) [2, 3]. In the present study, we deal, for the first time, with structural optimization for twenty molecules including hydrides by TOMBO to testify the effect of the method for light elements including hydrogen compared with “conventional” approaches. The bond lengths and bond angles are compared with the results obtained by VASP [3], Gaussian[4] and experimental values. Present results reproduce experimental values well. That is, the difference between the calculation and experimental data are within 1\% in the typical case. In our presentation, to introduce an advantage of mixed basis method, we also show the results for other molecules and discuss relationship between optimized structures and calculation condition, such as cut-off energy, unit cell and so on. [1] http://www-lab.imr.edu/~marcel/index.html [2] K. Ohno, K. Esfarjani, and Y. Kawazoe, Computational Materials Science, Solid State Sciences 129, (Springer Verlag, Berlin, 1999). [3] http://cms.mpi.univie.ac.at/vasp/vasp/vasp.html [4] Gaussian 03, Revision D.01, M. J. Frisch et al..


10:45 AM T6.7/S7.7
Synthesis of High Surface Area Pt-Ru Alloys for Electrocatalytic Oxidation of Methanol. A. Anumol, Aditi Halder and Ravishankar Narayanan; Materials Research Centre, Indian Institute of Science, Bangalore, India.

Pt alloys are attracting a considerable amount of attention for the last few years as anode catalysts for direct methanol fuel cells (DMFCs) and CO-tolerant proton exchange membrane (PEM) fuel cells. Bi-functional theory invoked for the methanol oxidation in fuel cell mainly rely on the fact that Pt activates the C-H bonds of methanol having the by-product Pt-CO while Ru activates water to produce hydroxyl ion at lower potential and accelerates oxidation of surface-adsorbed CO to CO2. We are reporting a new method of synthesis of Pt-Ru alloys in organic medium. The nanoalloys formed are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). Microstructural studies have been carried out using high resolution transmission electron microscopy (TEM). Cyclic voltammeter (CV) studies have been carried out to verify the electrocatalytic behaviour towards the methanol oxidation.


11:00 AM T6.8/S7.8
Self-Filling Small-Scale Electrochemical Cells by Dual Laser Beam Processing. John A Brehm1, Alberto Pique2 and Craig B. Arnold1; 1Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey; 2Naval Research Laboratory, Washington, District of Columbia.

The fabrication of small-scale energy storage components for microdevices is necessary to meet growing demands in these emerging technologies. Successful microbatteries and ultracapacitors electrodes have previously been fabricated, but the completed electrochemical cells typically require assembly or additional processing. One particular complication is the addition of a controlled amount of liquid electrolyte to activate the device. In this work, we present results on a dual-beam laser processing technique that is able to complete the required fabrication including forming electrodes and electrolyte filling in a single processing step. We focus on the system of hydrous ruthenium oxide electrode material with liquid sulfuric acid electrolyte. Electrode and electrolyte material is deposited by laser direct write and the cells are fabricated in a planar geometry. Results show high capacity (>200 mF/cm2) and material utilization with linear discharge behavior. The implications of this technique are discussed in the context of improving the efficiency of these small energy storage devices as well as enabling direct integration on existing microdevices.


11:15 AM T6.9/S7.9
Solid Oxide Fuel Cell System for Air-independent Applications. Louis G. Carreiro and Alan Burke; Code 8231, Naval Undersea Warfare Center, Newport, Rhode Island.

The U.S. Navy’s need for an unmanned undersea vehicle (UUV) power source with extended mission capability has prompted the development of a solid oxide fuel cell (SOFC) system designed for air-independent operation. To this end, a 30-cell SOFC stack with balance of plant (BoP) was tested under closed anode-loop operation using a high-temperature blower to recycle hot anode exhaust gases generated by the fuel cell. The exhaust was passed through a steam reformer, which converted S-8 (synthetic diesel fuel) to a hydrogen/methane-rich gas stream. A carbon dioxide sorbent bed was employed to prevent fuel dilution by accumulation of carbon dioxide, as well as to provide additional heating for the steam reformer. Over 1 kilowatt of power was generated by the stack with only S-8 and pure oxygen supplied to the stack. The following were achieved simultaneously: greater than 90% oxygen utilization, 75% S-8 utilization, water neutral operation and over 50% efficiency based on the electricity generated versus the lower heating value of S-8.


11:30 AM T6.10/S7.10
Modeling of the Cycle Life of a Lithium-polymer Battery. Chee Burm Shin, Ui Seong Kim and Won Jin Jeon; Chemical Engineering, Ajou University, Suwon, South Korea.

The lithium-polymer battery is one of the preferred energy sources for mobile electronic systems due to its outstanding characteristics such as high energy density, high voltage, low self-discharge rate, and good stability among others. Because one of the primary concerns in designing a lithium-polymer battery as a mobile energy source is reliability, the estimation of the remaining life of battery is important. In this work, a one-dimensional modeling is performed to calculate the capacity fade during cycling of a lithium-polymer battery comprising a LiMn2O4 cathode, a graphite anode, and a plasticized electrolyte. The model determines the capacity fade and the cycle life on the basis of the irreversible loss of active lithium ions due to solvent reduction reaction on the anode surface. The model has been validated by the comparison between the modeling results and the experimental measurements.


 

SESSION T7: Fuel Cells
Chair: Andrew Bocarsly
Wednesday Afternoon, December 3, 2008
Liberty (Sheraton)


1:30 PM T7.1
Nanosize PtRu Catalytic Activity Enhanced by Ligand Effect. Shuji Goto, Yuli Li, Yoshihiro Kudo, Akihiro Maesaka, Naomi Nagasawa, Tadashi Senoo and Tsuyonobu Hatazawa; Advanced Materials Laboratories, Sony Corporation, Atsugi-shi, Japan.

Direct methanol fuel cells (DMFCs) are a promising power source for portable applications owing to their system simplicity and high-energy-density fuel. High power density and cost reduction are necessary, however, to satisfy the requirements of the latest mobile electronics. In particular, a highly active methanol electro-oxidation catalyst using as little noble metal as possible is required. Platinum-ruthenium (PtRu) alloy nanoparticles are now widely used in the anodes of DMFCs. The catalytic activity of PtRu alloys for methanol electro-oxidation is generally attributed to the bifunctional mechanism. Ru promotes the oxidation of CO, which is formed by the dehydrogenation of methanol and is strongly bound to the adjacent Pt, by supplying an oxygen source (Ru-OH). The oxidation of adsorbed CO is thought to be the rate-determining step. PtRu random alloy structures should therefore have the most Pt-Ru pairs and high catalytic activity. The ligand effect, on the other hand, holds that heterometallic bonding between Pt and Ru modifies the Pt electronic structure so that the binding strength of adsorbed CO is weakened, thereby reducing the oxidation overpotential. The ligand effect allows us to use non-alloy PtRu structures in which only Pt is on the surface. We report here a new PtRu catalyst with a nanostructure which takes full advantage of the ligand effect. 1-2 Pt atomic layers formed on amorphous Ru nanoparticles showed high catalytic activity for methanol electro-oxidation. Carbon-supported Ru nanoparticles were prepared by chemical reduction of RuCl3 with sodium borohydride in a carbon-dispersed solution. The size of the Ru nanoparticles determined by TEM was 1.9 nm on average with a narrow size distribution. XRD, XPS and elemental analysis showed that the nanoparticles were amorphous pure Ru. The Ru nanoparticles were subsequently coated with Pt by reducing H2PtCl6 with sodium borohydride in the carbon-supported Ru nanoparticle-dispersed solution. The average particle size grew from 1.9 nm to 2.1-2.9 nm depending on the amount of platinum deposited. The synthesized carbon-supported PtRu catalysts were introduced in the anodes of DMFCs and their electrochemical performance was compared with that of commercial anode catalysts. A PtRu nanoparticle catalyst with an optimal Pt:Ru ratio of 7:3 exhibited as high a power density (90 mW/cm2) as a commercial PtRu catalyst having very high power density, in spite of 40% less Pt and 50% less Ru in the anode. EXAFS showed that crystalline Pt exists only on the amorphous Ru nanoparticles in the synthesized catalysts. Pt and Ru were not alloyed but segregated. The high catalytic activity of the synthesized catalyst is considered to be due to the ligand effect, not the bifunctional mechanism. This result indicates that DMFC performance can be further improved by changing the nanostructures of the most commonly used PtRu catalysts.


1:45 PM T7.2
Ultrathin Nanocrystalline Lanthanum Strontium Cobalt Ferrite Cathode for Low Temperature Micro Solid Oxide Fuel Cells. Bo-Kuai Lai, Hui Xiong, Alex C Johnson and Shriram Ramanathan; School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.

Solid oxide fuel cells (SOFCs) are electrochemical devices that convert chemical energy from hydrogen or hydrocarbon fuels directly into electrical energy at elevated temperatures. Because of its high energy efficiency, high power density, and clean emissions, SOFCs has been considered as a promising energy alternative for applications ranging from large scale power plants to smaller scale ones, such as portable electronics. In recent years, micro SOFCs (µSOFCs) particularly have stimulated considerable attention because they are potentially more scalable and can be integrated in small form factor. By taking advantage of well-established microfabrication techniques, they could possibly be mass-produced at low cost. To realize µSOFCs, it is important to develop suitable deposition and micromachining techniques to integrate multilayer (namely, cathode, electrolyte, and anode), functional ceramic thin films onto Si wafers and operate them at low temperatures with adequate power output. Cathodes need special attention because they are responsible for majority of voltage loss in SOFCs. To achieve low temperature operation, new cathode materials that can have significant catalytic activity to enable oxygen reduction at temperatures below 500 degree C need to be explored. Lanthanum Strontium Cobalt Ferrite (LSCF) has long been considered as one of the most promising cathode materials for the low temperature operation due to its high mixed ionic and electronic conductivities and high electrocatalytic activity of oxygen reduction reaction. In this work, we will report on our recent results that RF sputtering provides a low temperature and microfabrication compatible synthesis approach to realize nanocrystalline LSCF ultrathin films. Such ultrathin films exhibit high electrical conductivity that is comparable to LSCF bulk and thick films and absence of resistive interfacial reaction products with YSZ electrolytes. Approaches to optimize stresses, which are largely responsible for failure of micro-SOFC cathode-electrolyte-anode membranes, in thin film structures will be presented. Finally, performance of micromachined µSOFCs utilizing nanocrystalline LSCF ultrathin films will be demonstrated.


2:00 PM T7.3
Ab-initio Prediction of Platinum Nanoparticle Dissolution in an Acid Aqueous Environment. Byungchan Han, Kristin Persson and Gerbrand Ceder; Materials Science and Engineering, Massachusetts Institute of Technology, Cambrisdge, Massachusetts.

The high cost and short lifetime of Pt-based catalysts have been major challenges to the wide commercialization of low-temperature fuel cells. Recent experimental observations disclosed that main driving cause is dissolution of Pt nanoparticles to acid electrolyte(1). We developed an ab initio approach to predict the dissolution of atoms from nanoparticles in aqueous environment as function of pH and potential. Using information from direct ab initio calculations on nanoparticles we construct Pourbaix diagrams for both bulk and Pt nanoparticles with varying sizes (0.5, 1 and 2 nm). Our results show that the stability regions of Pt metal, surface oxides (PtOx) and hydroxide (Pt(OH)x) are strongly dependent on the particle size, applied potential and pH of the solution. We find the loss of cohesive energy in the nanoparticle leads directly to enhanced dissolution, compared to bulk Pt. The solid-aqueous phase boundaries shifts to lower potential as particle size decreases. Our results indicate that a vital step towards long-term functioning fuel cells is to increase the inherent stability of Pt nanoparticles against dissolution. (1)Y. Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, E.Holby, and D. Morgan, Topics in Catalysis, 46, 285, (2007).


2:15 PM T7.4
Reaction-Limited Aggregates of Nanoporous Pt with High Surface Area. B. Viswanath1, S. Patra2, N. Munichandraiah2 and Ravishankar Narayanan1; 1Materials Research Centre, Indian Institute of Science, Bangalore, India; 2Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India.

Porous structures with large surface areas are technologically important as supports for catalysts, as membranes, in scaffolding applications and as surface stress-based sensors. In particular, noble metals with high surface areas are routinely employed as catalysts in fuel cells, as substrates for surface-enhanced Raman spectroscopy and for sensor/actuator applications. Here, we present a general strategy to produce porous structures by controlled aggregation of sub-units and apply it for synthesizing nanoporous Pt. The nature of aggregate produced is controlled by tuning the electrostatic interaction between the sub-units in the solution phase. The catalyst, thus produced has an extremely high surface area (~ 39 m2/g) and exhibits high activity for methanol oxidation. The strategy can be extended to produce porous structures of other functional inorganics for a variety of applications.


2:30 PM *T7.5
Fabrication of Carbon Nitride Nanotubes for Hydrogen Storage. Jeung Ku Kang, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong Gu, Daejeon, South Korea.

Hydrogen is an attractive fuel alternative to conventional hydrocarbon fuels because water is the only product when hydrogen burns with oxygen in a fuel cell. On the other hand, one of the main issues for hydrogen economy is the development of a suitable hydrogen storage material that is small, light, and safe. In addition achieving at least the weight percent of 6.5 wt % is the goal of the US Department of Energy (DOE). Because of these requirements, early in the development of hydrogen storage materials various carbon materials were investigated. This is because carbon materials can give many different types of structures, which provide a variety of hydrogen storage sites. For example, the carbon nanotubes (CNTs) having high surface-to-volume ratios were suggested as ideal structures for fast kinetics because of their reversible characteristics during hydrogenation and dehydrogenation. Despite these advantages, recent studies have shown that the hydrogen stored on a pristine carbon nanotube (CNT) is less than 0.01 wt% at 1 bar condition and room temperature. On the other hand, here we present that nanopores with ~6 Å diameters on the stems of the nanotubes are capable of giving great potentials to reversible hydrogen storage sites. However, if carbon atoms bonded in the perimeter of carbon-based nanopores could be replaced with other elements such as nitrogen atoms (or hereafter called as the carbon nitride nanotube, the physical interaction diameters of N-doped nanopores for possible penetration of H2 could be reduced such that hydrogen could desorb at the temperatures ranging from room temperature to 80oC, which is the ideal condition for various applications. Here, we report that the carbon nitride nanotube having 6 Å pores is an ideal structure being capable of satisfying the required temperature condition. Our experiments also demonstrate that versatile 6 Å pores could be created on the stems of the multiwalled carbon nitride nanotubes with the uniform distribution.


3:30 PM T7.6
Development of Ni-based Metallic Glassy Bipolar Plate for PEMFC. Masanori Yokoyama1, Shin-ichi Yamaura2, Hisamichi Kimura2 and Akihisa Inoue2; 1Hirosaki University, Hirosaki city, Japan; 2Tohoku University, Sendai city, Japan.

The proton exchange membrane fuel cell (PEMFC) is a promising candidate as an electrical supply source for the future mainly in electric cars and cell-phone, owing to its advantageous characteristics such as clean driving power and low temperature operation. Bipolar plates are the important constituents of fuel cells in the viewpoints of weight, volume, performance and cost. Although carbon graphite has been conventionally used for bipolar plate applications, it is very expensive and brittle. So, carbon graphite bipolar plate may not be suitable for mass-production and widespread use of PEMFCs. In recent years, some research groups have studied the possibility of metallic glass as bipolar plate material. Since metallic glasses possess high corrosion resistance and high mechanical strength in general, it would be expected to reduce cost of bipolar plates by substituting the metallic glass for the carbon graphite. Therefore, the objective of this work is to develop a Ni-based metallic glass having high corrosion resistance and high mechanical strength and to produce metallic glassy bipolar plates. The Ni-Cr-P-B quaternary glassy alloys are known to have good corrosion resistance. Since high corrosion resistance is an essential factor for bipolar plate material, the Ni-Cr-P-B ally system was adopted and the most suitable composition was investigated in this alloy system in the viewpoint of high thermal stability. As the result, the Ni65Cr15P16B4 glassy alloy having a large supercooled liquid region of 43K was obtained. The corrosion test was also conducted by immersing the alloy in the 1mass% H2SO4 solution at 353K. As the result, it was shown that the Ni65Cr15P16B4 glassy alloy (6.94×10-3mm/year) had the higher corrosion resistance than SUS316L (1.48×10-2mm/year). Then the groove formability of the Ni65Cr15P16B4 glassy alloy was studied by hot-pressing with the dies with serpentine flow field grooves. It was found that a precise groove forming can be achieved by hot-pressing the alloy in a supercooled liquid state at Tg+20 K. Finally, a single cell of PEMFC was assembled with the Ni65Cr15P16B4 glassy bipolar plates and the power generation test was conducted. As the result, it was found that the I-V power generation characteristic of a single cell with the glassy bipolar plates are more excellent than one with bipolar plates made of high corrosion resistant stainless steal (SUS316).


3:45 PM T7.7
Metallographic and Numerical Characterization of MgH2-Mg System. Annalisa Aurora1, Massimo Celino1, Fabrizio Cleri2, Daniele Mirabile Gattia1, Simone Giusepponi1,3, Amelia Montone1 and Marco Vittori Antisari1; 1ENEA - CR Casaccia, S. Maria di Galeria (Rome), Italy; 2IEMN-CNRS, Université des Sciences et Technologies de Lille, Villeneuve d’Ascq Cedex, France; 3CASPUR, Rome, Italy.

The remarkable ability of magnesium to store significant quantities of hydrogen has fostered intense research efforts in the last years in view of its future applications where light and safe hydrogen-storage media are needed. Magnesium material, characterized by light weight and low cost of production, can reversibly store about 7.7 wt% hydrogen (MgH2). However, further research is needed since Mg has a high operation temperature and slow absorption kinetics that prevent for the moment the use in practical applications. For these reasons a detailed study of the interface between Mg and MgH2 is needed to characterize the dynamics during the desorption of the hydrogen. Further insights are gained by characterizing the Mg-MgH2 system from both the experimental and the numerical point of view. The study of the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information. A method for studying this phase transformation by cross sectional samples SEM observation of partially transformed material has been developed. This method exploits the peculiar features of this system where the MgH2 phase is insulating and the Mg is a metallic conducting phase. This difference can induce a contrast between the two phases owing to the different secondary emission yield. The contrast is particularly high at low voltage where the emissivity of the insulating phase is limited to the unity by the surface charging effect. Further insights are gained by characterizing and comparing Mg-MgH2 interfaces by means of accurate ab-initio molecular dynamics simulations based on the density-functional theory with norm-conserving pseudopotentials and plane-wave expansion (CPMD code). Extensive electronic structure calculations are used to characterize the equilibrium properties and the behavior of the surfaces in terms of total energy considerations and atomic diffusion.


4:00 PM T7.8
Durable Electrocatalysts based on Titanium Nitride Nanoparticles for Proton Exchange Membrane Fuel Cells. Bharat K Avasarala, Wenzhen Li and Pradeep Haldar; College of Nanoscale Science & Engineering, University at Albany, SUNY, Albany, New York.

Proton exchange membrane fuel cells (PEMFC) have become the focus of interest in recent years as a suitable power sources for stationary and automotive applications. However, the currently lifetime of a PEMFC is lower compared to a conventional system such as an IC engine. One of the main reasons for poor durability is the degradation of electrocatalyst, platinum on high surface area carbon (Pt/C), during extended operation and repeated cycling in the corrosive fuel cell operating conditions. During degradation, weight of carbon in Pt/C will gradually decrease over time due to which the Pt particles may agglomerate to form larger particles reducing active Pt surface area[1]. Therefore an important objective in the development of PEMFC will be to improve the durability of the electrocatalyst. In the present work, highly conductive titanium nitride (TiN) nanopowder is used as a support for Pt catalyst to obtain Pt/TiN that can act as highly durable electrocatalyst. Using commercially available TiN nanoparticles, Pt/TiN is prepared by polyol process[2] using ethylene glycol as a reducing agent and hexachloroplatinic acid as precursor. X-ray diffraction analysis and electron imaging of Pt/TiN showed the Pt particle size to be 4-6 nm. It is reported[3] that, repeated potentiodynamic cycling between hydrogen adsorption and oxide formation potentials can change the electrochemical surface area (ECSA) of Pt, thus indicating the degradation of the electrocatalyst. Potentiodynamic cycling was done on Pt/TiN and 20 wt% Pt/C (Pt particle size ~2-3nm) in a three-electrode cell set up with a Pt loading of 100μg/cm2. The electrode was cycled at 50 mV/s between 0-1.3V (RHE) in 0.1M HClO4 electrolyte at 60C. Active Pt surface area was measured from the charge under the hydrogen adsorption peaks. Initial degradation test results show that, after 1080 cycles, Pt/C has an ECSA loss of ~60% and Pt/TiN has an ECSA gain of ~60%. To some extent, it could be attributed to a ‘cleaning’ process involving surface impurity removal. Though showing improved durability, initial absolute ECSA of Pt/TiN is low compared to 20wt% Pt/C. XPS analysis indicated the presence of oxide and/or oxynitride layer on TiN nanoparticles and Pt/TiN based membrane electrode assembly showed high internal resistance. It is hypothesized that the oxide/oxynitride layer could be acting as an insulating layer preventing electron transfer from the catalytic reaction and thus leading to poor electrocatalyst performance. Further research is being conducted on using high purity TiN nanopowder, with measures to limit the oxide formation during polyol process and to study durable properties of Pt/TiN. References:[1]B.Merzougui and S.Swathirajan, Jour. of The Elec.chem. Soc.2006, 153 (12) A2220-A2226. [2]W. Li et al, J. Phys. Chem. B.2003, 107, 6292-6299 [3]T. Tada & T. Kikinzoku, in Handbook of Fuel Cells, Fundamentals, Technology and Applications.2003, Vol 3, Wiley, New York, pg 481.


4:15 PM T7.9
Intercalation of Quasi-liquid-cation and Solid-anion Phase in the Hydrogen Storage Material Li2NH. C. Moyses Araujo1, A. Blomqvist1, Ralph H Scheicher1, Ping Chen2 and Rajeev Ahuja1,3; 1Department of Physics and Materials Science, Uppsala University, Uppsala, Sweden; 2Department of Physics and Department of Chemistry, National University of Singapore, Singapore, Singapore; 3Department of Materials and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden.

The hydrogenation of Li3N has been demonstrated to represent a promising approach to achieve a suitable hydrogen storage material [1]. In this system, the hydrogen absorption and release processes take place in the following two-step reaction without the need for any catalyst: Li3N + 2H2 ↔ Li2NH + LiH + H2 ↔ LiNH2 + 2LiH. (1) The hydrogen is, thus, stored in the mixture of lithium amide (LiNH2) and lithium hydride (LiH) with a remarkable theoretical storage capacity of 10.5wt%. However, the involved thermodynamic and kinetic properties still require further improvement before this approach could be considered suitable for on-board applications. To design ways of overcoming these limitations it is necessary to understand the mechanisms of the reactions in (1) which require knowledge about the crystal structures of the various reactants and products. This is a challenging problem that has prompted a great deal of research. In particular, Li2NH undergoes a temperature-induced order-disorder structural phase transformation at about 385 K [2]. A conclusive picture of the mechanism of such a phase transition is still lacking and different proposals can be found for both the high- and low-temperature crystal structures. In this work, we have employed ab initio molecular dynamics simulations attempting to bring more insight into this problem. The inter-atomic forces are obtained from density functional theory calculations using generalized gradient approximation for the exchange-correlation functional and projected augmented wave method as implemented in VASP code [3]. The simulations were performed for temperatures in the interval 100-1200 K. We have found a structural phase transition in the temperature range 300-400 K in good agreement with the experimental finding. From the analysis of radial distribution functions and mean square displacements, we demonstrate that such transition is associated with a melting of the cation sub-lattice (Li+), which is accompanied by an order-disorder transition of the N-H bond orientation. The results obtained here contribute to a better understanding of the hydrogen storage reactions involved in this material. The surprising findings of our study may also apply to similar materials where cations and anions differ sufficiently in mass.


4:30 PM T7.10
Enhanced Hydrogen Storage Capabilities through Single Pd Atoms in Activated Carbon Fibers. Klaus van Benthem1, Stephen J Pennycook2, Cristian I Contescu2 and Nidia C Gallego2; 1Dept. for Chemical Engineering and Materials Science, University of California at Davis, Davis, California; 2Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

The use of hydrogen as an energy carrier is one of the main goals to overcome the future energy crisis. Promising candidates for hydrogen storage materials are carbon-based nanomaterials, such as nanotubes or nanofibers, for which significant increases in hydrogen uptake can be achieved by the addition of metal catalyst particles. Results have shown that a significant enhancement of H2 adsorption was obtained at room temperature for activated carbon fibers (ACF) modified with supported Pd catalyst particles. The additionally observed H2 uptake in the presence of Pd exceeds amounts expected due to hydride formation, hence supporting the so-called spillover effect. Aberration-corrected scanning transmission electron microscopy was used to investigate the carbon fibers microstructure in the presence of Pd catalyst nanoparticles to identify possible storage sites such as nanopores. High resolution annular dark field imaging revealed the presence of isolated Pd atoms embedded in the volume of the activated carbon fibers. Different thermal activation recipes not only revealed variations in the hydrogen uptake data, but also modified the dispersion of single Pd atoms. Based on electron back-donation, a single isolated Pd atom is theoretically able to bind 3 hydrogen molecules, i.e. six atoms. Palladium hydride, however, only contains 0.6 hydrogen atoms per metal atom. Results of the electron microscopy characterization will be reported and possible hydrogen storage mechanisms will be discussed during the presentation. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Division of Scientific User Facilities. KvB also acknowledges financial support by UC Davis start-up funds.


4:45 PM T7.11
Kinetics of Hydrogen Desorption in Pristine and Ti-doped NaAlH4 using Transition State Theory. Gopi Krishna Phani Dathara and Daniela S Mainardi; Institute for Micromanufacturing, Louisiana Tech Universtiy, Ruston, Louisiana.

Sodium aluminum hydride is first among the most researched complex metal hydrides suitable for solid state hydrogen storage. Though the weight percentage of hydrogen that can be retrieved from NaAlH4 is not in the limits proposed by US DOE, it is well suited for researching the underlying principles of hydrogen desorption in its pristine or transition metal doped state. Sodium aluminum hydride (NaAlH4) decomposes through a two step reaction to yield 5.6 wt% of hydrogen which results in Na3AlH6, Aluminum and NaH phases. Evaluation of formation of one of the phases would be able to provide information about the rate limiting steps in the hydrogen desorption. Addition of Ti dopants is known to improve thermodynamics and kinetics of hydrogen desorption. Formation of Ti-Al and Ti-Al-H phases are concluded to have a role in improved thermodynamics due to transition metal dopants. Most recent development in improved kinetics of hydrogen desorption from other studies suggest vacancy mediated diffusion of higher mass species containing aluminum rather than atomic hydrogen. Our previous studies include the determination of various suitable sites for titanium ion ad/absorption in NaAlH4 (001) surface and bulk, that has shown an almost equal probability of occupying the surface Na lattice site and on top of the interstitial site. Further studies include the diffusion of hydrogen and ionic/molecular species in pristine and Ti doped NaAlH4 simulated using Density Functional Theory Molecular Dynamics (DFT-MD). This study focuses on determining the kinetics of hydrogen desorption by determining the energy barriers for diffusion of vacancies, AlH3 species and transition from AlH63- ions from AlH4- in pristine and Ti doped NaAlH4 using Transition State Theory. All the calculations are done using DMoL3 module licensed by Accelrys Inc. Electronic energies of the reactants and products are calculated using Generalized Gradient Approximation (GGA) with PW91 correlation and DNP (double numerical plus polarization) basis set. For transition state calculations, Combined Linear Synchronous Transit (LST) and Quadratic Synchronous Transit (QST) Search is performed to bracket the maximum along the reaction path. First LST maximization is performed followed by optimization in directions conjugate to the reaction pathway. QST maximization is performed on the obtained structure and the cycle is repeated until the transition state is found. The obtained transition state is further optimized using transition state optimization subroutine to obtain a true transition state. Free energies of reactants, products and transition states are computed to calculate the energy barriers thereby calculating the rates of proposed reactions.

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