Anne Dillon National Renewable Energy Laboratory
Se-Hee Lee University of Colorado-Boulder
Ping Liu HRL Laboratories
Bruce Dunn University of California-Los Angeles
Yimei Zhu Brookhaven National Laboratory
M1: Li-ion Anodes I
Tuesday AM, April 26, 2011
Room 2009 (Moscone West)
9:00 AM - **M1.1
Nanostructured Materials for Anodes of Li-ion Batteries.
Ruigang Zhang 1 , M Stanley Whittingham 1 Show Abstract
1 Chemistry and Materials, SUNY, Binghamton, New York, United States
Carbon-based materials are the common anode materials used in Li-Ion batteries to day. However, their very low volumetric capacities and limited lithium-insertion rates demands that a replacement be found. Simple bulk metals, such as aluminum, tin and silicon have been found lacking because of the substantial expansion and contraction on reaction. This leads to a breakdown of the SEI layer and a continuous and exponentially increasing cell resistance. We have completed a study of the Sn-Co nano-amorphous compound, which convincingly shows that optimized nanostructures can be deep cycled without loss of capacity and have twice the volumetric capacity of carbon. The reaction mechanism of these compounds will be discussed. Other nanosized materials, such as manganese oxides, have also been found to cycle effectively. Thus, we believe that these reactions that undergo structural destruction and rebuilding, rather than only intercalation, can be used for anode reactions provided the material is nano-enough. This work was supported by US-DOE-BATT.
9:30 AM - M1.2
Inelastic Electrodes for High-capacity Lithium-ion Batteries.
Matt Pharr 1 , Kejie Zhao 1 , Zhigang Suo 1 Show Abstract
1 School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Silicon can host a large amount of lithium, making it a promising electrode for high-capacity lithium-ion batteries. Upon absorbing lithium, silicon swells to several times its original volume; this deformation often induces large stresses and pulverizes silicon. Existing models of lithiation-induced deformation and fracture have assumed that the electrodes are elastic. Recent experiments, however, indicate that under certain conditions lithiation causes inelastic deformation. Here, inelastic electrodes are modeled by considering diffusion, elastic-plastic deformation, and fracture. The model allows for simulation of the distribution of concentration and stress in the host during charge and discharge. It is found that fracture is averted for a small and soft host—an inelastic host of a small feature size and low yield strength.
9:45 AM - M1.3
Diffusion-deformation Coupling and Inelastic Flow in Li-Alloy-based Electrodes.
Yifan Gao 1 , Min Zhou 1 Show Abstract
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Lithium alloys with metallic or semi-metallic elements are attractive candidate materials for the next generation negative electrodes of lithium ion batteries due to their large specific and volumetric capacities. The key challenge with lithium alloy electrodes, especially Li/Si, has been their large volume changes during insertion and extraction of lithium. These volume changes can lead to pulverization and debonding. Recent efforts to improve the cyclability of Li-alloy based electrodes are highlighted by the utilization of nano-structured materials. It is widely accepted that nano-sized materials provide better accommodation for diffusion-induced stress (DIS) and thus improve a battery’s cyclability. In this work, diffusion-induced stress (DIS) development and stress-enhanced diffusion (SED) in amorphous lithium alloy nanowire battery electrodes are investigated using a finite deformation model, accounting for full two-way coupling between diffusion and stress evolution. The analyses reveal significant contributions to the driving force for diffusion by stress gradient, an effect much stronger than those seen in cathode lattices but so far has been neglected for alloy-based anodes. The contribution of stress to diffusion is small at low lithium concentrations, this lack of SED leads to significantly higher DIS levels in early stages of a charging cycle. As lithium concentration increases, SED becomes more pronounced, leading to lower DIS levels. The long-term DIS level in the material scales with charging rate, nanowire radius, and the mobility of Li ions as modulated by the effect of stress. The solutions obtained provide guidance for lowering stresses during charging. In particular, lower charging rates should be used during the initial stages of charging cycles. The formation of nano-voids in Li/Si NWs upon cycling is another issue affecting the cyclability. The underlying process is large inelastic deformations of the anode material. Recently, Sethuraman et al. measured the evolution of stress in silicon thin films during electrochemical cycling and showed that the flow stress of lithiated Si decreases as Li concentration increases. The finding suggests that plastic (or viscoplastic) flow is an important process that cannot be neglected. Here, a model for the nucleation of nano-voids is developed based on the balance of stress work rate and the rate of surface energy change. The theory is applied to anodes with core-shell structures to estimate the likelihood of void formation. A critical void size is identified. If the radius of a nucleated void is larger than the critical size, the void will grow into a nano-pore; otherwise, the void will shrink and may vanish. This critical radius depends on the yield strength and surface energy of the anode material and local stress triaxiality.V. A. Sethuraman, M. J. Chon, M. Shimshak, V. Srinivasan, and P. R. Guduru, Journal of Power Sources 195 (2010) 5062.
10:00 AM - M1.4
Silicon Nanowire Growth on Metal Substrates for a Lithium-ion Battery Anode.
Jeong-Hyun Cho 1 , Xianglong Li 1 , S. Tom Picraux 1 Show Abstract
1 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
A miniature rechargeable battery with maximized energy and power density is in high demand for portable electronic systems and hybrid electric vehicles. Among the many different kinds of rechargeable batteries, lithium-ion batteries are widely used in consumer electronics because of their relatively high energy and power density, no memory effect, and low self-discharge. However, the energy and power density is not high enough for long-term operations.Recently, in order to increase the energy and power density, silicon nanowires (SiNWs) have been explored as anode materials since SiNWs show excellent theoretical capacity (10 times higher than commercialized anodes), low discharge potential (0.5-1V), short lithium-ion diffusion time, and low pulverization. However, it is challenging to grow SiNWs on metal substrates (metal current collectors) due to wetting of the catalyst which limits NW nucleation and to competing metal silicide formation during the SiNW growth process. Although silicon shows the highest gravimetric capacity, the resulting reduced density of silicon nanowire on stainless steel and metal silicide formation on the substrates leads to reduced overall capacities. Moreover, for the overall capacity measurements, the competing metal silicide and silicon nanowire capacities do not allow accurate lithium-ion battery characterization. Here, we demonstrate high density, electrically contacted Si nanowire growth on stainless steel substrates (metal current collectors) with minimal unwanted substrate-silicide formation for high Li ion battery performance. In order to maximize the growth of SiNWs and minimize metal silicide reactions with the substrate, we have developed surface barriers which form a protective layer while maintaining electrical contact with a robust stainless steel current collector. Coated Ti barrier layers are shown to provide for much higher densities of SiNWs while reducing metal silicide formation from 80 down to 2 weight percent of the SiNW mass. Specific energy capacity and Li ion cycling results will be presented for Ti and TiN barrier layers to clarify these competing effects for SiNW half-cell batteries and to demonstrate the benefits of this approach.
10:15 AM - M1.5
Lithium-ion Insertion Studies of Mesoporous-ordered TiO2(B) Nanoparticles.
Anthony Dylla 1 , Keith Stevenson 1 Show Abstract
1 Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas, United States
TiO2(B) is the most recently discovered TiO2 polymorph and has shown enhanced Li+ insertion behavior as an anode material for rechargeable Li-ion batteries due to its unique open crystal structure that allows for facile insertion and extraction of Li+. Furthermore, enhancements in charge transport (i.e., electronic and ionic mobility) have been observed when metal oxides such as TiO2 are ordered into mesoporous structures by use of structure directing agents. One strategy to produce mesoporous electrode materials is to cast films of molecular Ti precursors mixed with structure directing agents such as block copolymers onto a conductive substrate followed by heat treatment to produce mesoporous TiO2 thin films. While this method can provide highly ordered and robust structures, it is often difficult to control the phase of the resultant TiO2 polymorph. To circumvent this problem we have adopted a nanoparticle building block approach. By using presynthesized small, phase-pure TiO2(B) as our TiO2 source we are able to produce mesoporous-ordered nanoparticle films with predominantly TiO2(B) phase present. Here we present the Li+ insertion behavior of mesoporous ordered TiO2(B) nanoparticles. Using presynthesized 5-8 nm TiO2(B) nanoparticles as building blocks and a common ethylene glycol propylene glycol block copolymer (P123) as a structure directing agent we are able to produce coral reef-like structures of phase pure TiO2(B) with mesopore channels ranging from 10 to 20 nm in diameter. We will present slow scan cyclic voltammetry studies that probe structural and interfacial chemistry of these nanostrucutured, mesoporous TiO2 architectures. These results will be compared to non-mesoporous-ordered TiO2(B) nanoparticles to gain better understanding of the enhanced mass and charge transport properties of mesoporous metal oxide materials.
M2: Li-ion Anodes II
Tuesday AM, April 26, 2011
Room 2009 (Moscone West)
11:00 AM - M2.1
Fabrication of Nanostructured Composite Anodes for Advanced Lithium Ion Batteries.
Liwen Ji 1 , Ariel Ismach 1 , Zhongkui Tan 1 , Yuegang Zhang 1 Show Abstract
1 , Lawrence Berkeley National Lab, Berkeley, California, United States
Si has the highest theoretical specific capacity among all known materials which is 4200mAh/g (Li4.4Si) when used as anodes for rechargeable lithium-ion batteries (LIBs). Nevertheless, the pure Si-based anodes suffer from huge volume changes upon repeated cycle, leading to severe capacity fading along with poor rate capability. To put the Si-based materials into carbon matrix in order to prepare carbon/Si composites is a promising way to decrease the large volume changes of pure Si so as to improve the final electrochemical performance. In the present research, we designed and fabricated a nanocomposite structure, and directly used it as anode for rechargable LIBs. We show that the materials can deliver a large charge and discharge capacities of about 2728, 2232 mAh g-1 at the first cycle, respectively, with a high coulombic efficiency of 82% at 50 mAg-1 current density. At the second cycle, the reversible capacity still can be preserved at around 2180 mAh g-1. At 30 cycles, the reversible capacity still can be as large as 1320 mAh g-1. It is believed that nanocomposite materials buffer the large volume changes of Si films and improve the electronic and ionic conductivities. As a result, excellent electrochemical performance, such as large reversible capacity, improve cycle life are obtained.
11:15 AM - **M2.2
High Energy and Low-cost Energy Storage with Nanostructures.
Yi Cui 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
The capability of synthesizing materials with nanometer size and shape control has enabled exciting opportunities to engineer materials for understanding and controlling electronic, ionic and mechanical processes, which are critical for advanced energy storage. In this talk I will show several examples on how to design nanostructured materials towards high energy density and novel paper and textile storage devices. In one example, a variety of silicon nanostructures including nanowires are exploited to maximize efficiency of simultaneous electron and ionic insertion with facile strain relaxation, which enable lithium ion battery anodes with 10 times higher specific charge storage capacity compared to current technology. Lithium sulfide cathode materials are embedded into conducting mesoporous carbon to overcome multiple fundamental challenging problems associated with sulfur compounds. Combining with silicon nanowire anodes, we can produce ultrahigh energy batteries. In another example, I will discuss how to combine state of the art nanotechnology with thousands year old paper and textile technologies as novel ways for energy storage devices and demonstrate high performance. General principles will be concluded on how nanoscale materials design can impact energy storage applications in a significant way.
11:45 AM - M2.3
Investigation of Tin Oxide/graphene Electrodes as Anode Materials for Li-ion Batteries.
Abirami Dhanabalan 1 , Xifei Li 2 , Chunlei Wang 1 Show Abstract
1 Department of Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States, 2 Department of Mechanical and Materials Engineering, The University of Western Ontario, London, Ontario, Canada
Graphite is generally used as an anode in commercial lithium ion batteries because it reacts with lithium-ions in the intercalation potentials with reasonable specific capacity of 372 mAhg-1. There is limited possibility to improve the cathode material because of issues such as high potential, structural stability due to the inclusion of lithium. On the other hand, there are a wide range of metals, metal oxides, alloys and composites that can be used as an anode. Tin oxide has emerged as a potential candidate among the other metal oxides because of its high theoretical capacity (786mAhg-1). However, tin oxide anodes undergo a large volume expansion (>300%) during cycling which leads to pulverization of the electrode, loss of electrical contact and rapid decay in the performance. To mitigate these problems carbonaceous materials with good ductility and high electrical conductivity can be used as a buffer matrix, conductive additive and an active electrode material. Among the carbonaceous materials, graphene is one of the promising contenders with high electrical conductivities, high surface area of over 2600 m2/g, chemical tolerance, and a broad electrochemical window that would be very advantageous for energy applications. In this work, we synthesized tin oxide/graphene composite electrode using electrostatic spray deposition. The morphology, crystal structure and vibrational modes of the composite anodes are analyzed using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Specific capacity, rate capability and cycle life of the anodes are obtained by galvanostatic cycling. All the electrochemical tests were carried out using a versatile multichannel potentiostat. The experimental results will be discussed in detail.
12:00 PM - M2.4
Nanostructured Metal Doped Graphite Nanoplatelets as Anode Material for Lithium Ion Battery.
Anchita Monga 1 , Lawrence Drzal 1 Show Abstract
1 Chemical Engineering & Materials Science, Michigan State University, East Lansing, Michigan, United States
The demand for high energy and high power batteries for hybrid and electric automotive vehicles has driven a lot of focus towards material selection, synthesis and assembly both for cathode and anode side. Nanographitic materials such as nanotubes and graphene nanosheets have gained considerable attention as potential anode materials, because of their enhanced mechanical, thermodynamic, transport and kinetic properties; however, they are restricted in terms of their performance for lithium storage. Other category of materials which are of prime significance are the metal nanostructures, which are capable of delivering high specific capacity by reversible alloying with lithium, but suffer from a big problem of rapid volume expansion and electrode disintegration. Our approach here is to integrate these two materials, focusing on incorporating the benefits from both the sides.The reference nanographitic material used for all the experiments is exfoliated graphite nanoplatelets (GnP), prepared by an acid intercalation technique, followed by thermal exfoliation. These nanoplatelets which are stack of very few grapheme sheets, can be produced in varying dimensions ranging from 50 microns to 0.1 microns in diameter and 20 nm to 3 nm thicknesses, and are relatively an inexpensive substitute to carbon nanotubes and single layered graphene. The studies on this graphitic material have shown an irreversible capacity of ~370mAh/g, which indicates complete utilization of its theoretical lithium storage potential.The underlying concept is based on developing a tailored nanographite assembly by using metal doped GnP platelets, where the addition of small nanoparticles of metal allows the potential for a tailorable architecture. The addition of these nanoscale metal particles created a pillared nanostructure by increasing interlayer spacing and thus facilitates lithium diffusion in and out of the anode, especially at faster charge rates. Furthermore, these metal dopants can play the role of a conducting additive and as inherent lithium storage material. Noble metal nanoparticles (Pt, Pd, Ru etc.) of controlled sizes, different morphologies and uniform distribution have been doped previously on GnP platelets by microwave assisted polyol process. GnP platelets doped with nickel nanoparticles of different sizes were prepared by the polyol methodology described above. Preliminary performance investigation showed good cycle life , with the capacity values around 370-400 mAh/g at C/5 and C/2, which maintains to be so even at faster charge rates, like C and 2C. Optimization of the size of nanoparticles and metal concentration is currently under progress and there is immense scope for performance improvement. Other metal dopants like Silicon and Tin are also under investigation. Results and interpretations of the role of metal dopants, and the dependence on the size and type of nanoparticles will be presented.
12:15 PM - M2.5
Novel Single-step Method for the Preparation of DopedLTO Nanoparticles for Li-ion Battery Applications.
T. Karhunen 1 , M. Karppinen 2 , A. Lahde 1 , E. Pohjalainen 2 , S. Rasanen 2 , U. Tapper 3 , J. Jokiniemi 1 3 Show Abstract
1 Fine Particle and Aerosol Technology Laboratory, University of Eastern Finland, Kuopio Finland, 2 Laboratory of Inorganic Chemistry, Aalto University, Espoo Finland, 3 Fine Particles, VTT Technical Research Centre of Finland, Espoo Finland
Li-ion secondary cells are one of the most advanced energy storage systems currently available as it provides one of the highest energy-to-weight ratios. Due to the high energy density of Li-ion batteries, they offer the best route for many advanced storage applications related to clean electricity.1 However,new commercial applications, such as hybrid and full electric vehicles, place increasing demands on specific capacity, power density, rate capacity and cycle life of the energy storage devices.2,3
Lithium titanium oxide (Li4Ti5O12, LTO) is recognized as a promising material for the negative electrode of Li-ion batteries as it is cheap and safe, and has an excellent cycle life.2,4 However, the major drawback of LTO is its low electronic conductivity. To overcome this problem the particle size can be reduced to the nanoscale increasing the specific surface area, and decreasing the diffusion lengths within particles and the local current density.5 For LTO an optimum size of about 17 nm has been reported.6 However, the current method of solid-state chemical reaction typically produces LTO particles with a diameter of the order of 1 μm. Another solution is to use metal dopants (e.g. Cu, Ag).7,8 Currently the doping is typically carried out in a separate process which increases the complexity and costs of the production.
Here, pure and doped LTO nanoparticles are prepared in the gas phase with flame spray pyrolysis (FSP). It is a fast, dry, and single-stage process that enables the preparation of materials with high-purity.9 The precursor solution used for the studies contained lithium acetyl acetonate and titanium isopropoxide in mixture of toluene and 2-ethyl hexanoic acid (1:1). The silver and copper doping was performed by adding, respectively, silver and copper 2-ethyl hexanoic acid directly into the precursor solution.
The resulting particles were found to be high-purity (99%), single crystalline nanoparticles with a primary particle size of about 10 nm. A uniform dopant distribution was observed in the doped LTO nanoparticles. The silver dopant nucleated independently and deposited on the surface of the LTO particles. The copper doping, on the other hand, reacted chemically with the LTO forming a double spinel structure.7 This study will focus on the effects of the doping on the Li-ion battery performance.
1Hall and Bain, 2008. Energy Policy, 36, 4352-4355.
2Du Pasquier et al., 2003. J. Power Sources, 115, 171-178.
3Wen et al., 2008. Solid State Ionics, 179, 1800-1805.
4Ohzuku et al., 1995. J. Electrochem. Soc., 142 (5), 1431-1435.
5Arico et al., 2005. Nature Mater. 4, 366–377.
6Kavan et al., 2003. J. Electrochem. Soc., 150 (7), A1000-A1007.
7Wang et al., 2009. Electrochem. Commun., 11, 50-53.
8Huang et al., 2006. Solid State Ion., 177, 851-855.
9Mädler et al., 2002. Aerosol Science, 33, 369-389.
Anne Dillon National Renewable Energy Laboratory
Se-Hee Lee University of Colorado-Boulder
Ping Liu HRL Laboratories
Bruce Dunn University of California-Los Angeles
Yimei Zhu Brookhaven National Laboratory
M6: Poster Session: Li-ion Battery
Yoon Seok Jung
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
1:00 AM -
M6.22 Transferred To M4.12
M4: Enabling High Performance Li-ion Batteries
Wednesday AM, April 27, 2011
Room 2009 (Moscone West)
9:00 AM - **M4.1
The Interaction of Lithium with Anodic Reduced Metal Nanoparticles.
John Lemmon 1 , Jie Xiao 1 , Wiaojian Wang 2 , Xiao-Qing Yang 2 , Shidi Xun 3 , Gao Liu 3 , Jun Liu 1 Show Abstract
1 , Pacific Northwest National Laboratory, Richland, Washington, United States, 2 , Brookhaven National Laboratory, Upton, New York, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Li-ion batteries continue to attract a tremendous amount of interest around the world because they are the most promising candidate to power hybrid electric vehicles (HEV) or electric vehicles (EV) and stationary energy storage systems. New cathode and anode materials are being investigated extensively to identify a combination that can meet the goals set by the U.S. Advanced Battery Council (USABC). For graphite, which is the currently used anode, the low specific capacity (372 mAh/g) cannot fully meet the requirements for use in HEVs or EVs. Alternative materials such as silicon (Si) (4200 mAh/g) or tin (Sn) (994 mAh/g) also have been investigated as a replacements to the graphite anode and have shown significant improvement when the structures are in the nano-regime. Recent we have reported on the formation of nanocomposites comprised of layered metal sulfides with poly(ethylene oxide) and graphene that exhibit enhanced capacity and rate capability. The nanocomposites can be formed using facile synthesis methods and have high packing densities as electrodes. The nanocomposites were anodically reduced on the initial cycle with lithium in the range of 0.01-0.02V vs Li/Li+ and exhibit a significant increase in lithium capacity. During the initial cycle the nanocomposite material is irreversible transformed into Li2S and nanoparticles of the metal and capable of stable high capacity cycling in the range of 0.01-3.0 V vs Li/Li+ than is significantly enhanced with the addition of PEO. The interaction of lithium with the metal nanoparticle contributes to the increased capacity, however in bulk form the metals typically have low lithium solubility and the formation of alloys or intermetallics phases is absent. In this presentation we report on the lithium electro-interaction with different metal nanoparticles and our efforts to describe the interaction mechanism. Understanding such interactions could lead to the use of low cost metals as lithium anodes without alloy formation or volume expansion.
9:30 AM - M4.2
Silicon Coated Vertically Aligned Carbon Nanotubes as High Capacity Anodes for Lithium Ion Batteries.
Kara Evanoff 1 3 , Thomas Fuller 2 , W. Jud Ready 1 3 , Gleb Yushin 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , Georgia Tech Research Institute, Atlanta, Georgia, United States, 2 Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The development of thick, high specific capacity anodes with long cycle lifetime is an attractive route to increase the energy and power storage characteristics of Lithium ion (Li-ion) secondary batteries with reduced cost and weight for electrical and hybrid electrical vehicles (1, 2). Silicon (Si) has a theoretical capacity nearly ten times greater than graphite (372 mAh/g) and is sought as a graphite alternative. However, utilizing Si in a non-destructive manner is challenging due to the large volume changes that occur during Li (de)alloying (1-3). Without sufficient free space for Si volume expansion during alloy formation, significant stresses are generated, which commonly lead to anode mechanical degradation and the loss of electrical contact between particles and the current collector (2). In this study, we present a novel, robust, highly structured anode architecture consisting of vertically aligned carbon nanotubes (VACNTs) decorated with nano-coatings of silicon and carbon to achieve high-capacity, large thickness, and improved anode stability.A high yield, low-pressure chemical vapor deposition process (CVD) utilizing iron (II) chloride catalyst and acetylene gas produced VACNTs on quartz substrates with a measured growth rate of 100 μm/min. In contrast to other CNT synthesis methods, catalyst pre-deposition is not required. For this study, a constant growth time was used to synthesize VACNT films of approximately 500 μm in length. Low-pressure CVD utilizing a silane gas precursor produced amorphous nano-Si coatings with a “beaded necklace” morphology. With increasing deposition time, the Si coating thickness and Si anode composition increased. An ultra-thin C coating was deposited by the decomposition of propylene gas onto the Si-coated VACNTs at atmospheric pressure for very short times. High-rate performance, solid electrolyte interface (SEI) quality, and Coulombic efficiency are improved by the presence of the external C coating. The process of transferring the active materials to a thin metallic current collector will be discussed. The primary considerations for a well-developed interface include good electrical conductivity, adhesion, and stability during testing. Electrochemical cells were assembled as 2032-type coin cells with a Li foil reference electrode and a commercially blended LiPF6 electrolyte solution. Cell testing has demonstrated stable performance and reversible capacities greater than theoretical graphite by more than 2,000 mAh/g. Reductions in reversible capacity with increased cycling rates are observed and investigations of the effect of the electrode thickness, interface characteristics, and SEI formation are being conducted to enhance high-rate performance.1. B. Hertzberg, A. Alexeev, G. Yushin, Journal of the American Chemical Society 132, 8548-8549 (2010).2. A. Magasinski et al., Nature Materials 9, 353-358 (2010).3. A. M. Wilson, J. R. Dahn, J. Electrochem. Soc. 142, 326-332 (1995).
9:45 AM - M4.3
Co-axially Electrospun Si Core/C Shell Nanofibers for Li-ion Battery Application.
Byoung-Sun Lee 1 , Woong-Ryeol Yu 1 , Se-Hee Lee 1 , Kyu-Min Park 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of)
Secondary battery such as Li-ion cell is indispensible to small electronic devices such as mobile phone, laptop computer, camcorder, etc. Since multifunctional and high efficient elements have been introduced to those mobile devices, a demand on high capacity cells has been significantly increased. In addition, the development of electric vehicles has accelerated researches into electrode materials with high efficiency and long life cycles. Silicon has been recognized as a candidate material from long time ago that can meet these needs.Silicon is such an excellent anodic material that its theoretical efficiency reaches approximately 4200 mAh/g due to its high accommodation capacity (4.4 Li-ion per single atom). This capacity is nearly ten times higher than that of carbon anode (400 mAh/g, 1 Li-ion per single atom). On the other hand, silicon has a fatal demerit that it accompanies large volumetric change during lithiation and delithiation reaction, causing pulverization and destruction of Si crystal structure and electrical contact. As such many attempts have been made to develop silicon anodes free from or diminishing the problem, one of which is composite anode consisting carbon and silicon. Here the main idea is to both utilize high performance of Si and structural stability of carbon. Electrospinning and subsequent thermal treatment is a typical route to fabricate solid or hollow carbon nanofibers from polyacrylonitrile (PAN). In this study we manufactured Si/C core-shell nanofibers using co-axial electrospinning of Si precursor such as Si tetraacetate and SiO2 nanopowder in core and PAN in shell. A novel feature of this process may be a new composition of core and shell materials, i.e., styrene acrylonitrile (SAN) was introduced to both two materials, resulting in the stable formations of core-shell nanofibers and porous shell. Subsequent thermal treatment was employed to convert PAN and Si precursors to carbon and silicon crystal, respectively. Morphological and structural characterization was carried out to investigate the validity of current compositions and processes. Finally the electrochemical performance of prepared composite nanofibers was characterized using coin-cell test, demonstrating that the pulverization (thus losing electrical contact) can be reduced due to the carbon shell that can provide a conduit or buffer zone for Si during electrochemical reaction.
10:00 AM - M4.4
Improved Cycling Stability of Silicon Thin Film Electrodes through Patterning for High Energy Density Lithium Batteries.
Xingcheng Xiao 1 , Mark Verbrugge 1 , Ping Liu 2 , Hamed Haftbaradaran 3 , Huajian Gao 3 , Sumit Soni 3 , Brian Sheldon 3 Show Abstract
1 , General Motors Global R&D Center, Warren, Michigan, United States, 2 , HRL Laboratories, LLC, Malibu, California, United States, 3 , Brown University, Providence, Rhode Island, United States
The mechanical degradation of electrodes caused by lithiation and delithiation is one of the main factors responsible for the short cycle life of lithium-based batteries with high capacity electrodes. Silicon electrodes are particularly promising as next generation negative electrodes due to high Coulombic capacity and low cost, but they are limited by mechanical degradation associated with large volume variations during cycling. In this work, we employed a simple patterning approach to improve cycling stability of Si, based on the observation of a critical size for the distance between cracks in continuous films. An improvement in cycle life was noted when the pattern size was below a critical size (7 to 10 micron), in which case the Si electrode patches adhered well to the Cu substrate after many cycles. Also, in situ stress measurements show that the smaller pattern generated less stress in the film during cycling. By considering plastic deformation within both the Si thin film and the Cu substrate, we find that the calculated crack spacing is consistent with experimental observations. These theoretical considerations provide a rational explanation for the failure of the patterned Sielectrodes above the critical size. The results suggest a new approach for extending the cycle life of Si-based electrode materials by using size to control stress generation and relaxation due to lithiation and delithiation.
10:15 AM - M4.5
Copper Coated Amorphous Silicon Particles for Enhanced Lithium Insertion.
Sankaran Murugesan 1 , Keith Stevenson 1 , Justin Harris 2 , Brian Korgel 2 Show Abstract
1 Department of Chemistry & Biochemistry, The University of Texas Austin, Austin, Texas, United States, 2 Department of Chemical Engineering , The University of Texas Austin, Austin, Texas, United States
Silicon materials have drawn considerable interest in recent years for their electrochemical properties. Silicon’s ability to alloy with lithium at high lithium loading levels (Li4.4Si) produces a high charge storage capacity of 4200 mAh/g. However, the stability of silicon-based electrodes is not good over multiple cycles. This is due to a large volume expansion upon formation of the silicon-lithium alloy, causing pulverization of the electrode. In the context of cyclability, amorphous silicon has advantages over crystalline silicon through its homogeneous volume expansion. Unfortunately, amorphous silicon also has a lower conductivity and slower lithium insertion than its crystalline counterpart. To aid in conductivity and lithium insertion, a conductive metal, such as copper, can be coated over the amorphous silicon. This presentation introduces strategies for synthesizing and characterizing such copper coated amorphous silicon materials for cyclable lithium insertion. In particular, we will highlight enhanced lithium insertion in amorphous silicon particles through a polyol-mediated deposition of copper on pre-synthesized particles. The copper coated amorphous silicon particles exhibit nearly five-times enhanced charge storage capacity over pristine amorphous silicon particles when tested in a single electrode lithium coin cell, demonstrating the potential benefits of this approach.
11:00 AM - M4.6
Vertically Aligned Carbon Nanotube Templated Silicon as a High Capacity Electrode Material for Lithium Ion Batteries.
Jun Song 1 , Yin Zhang 2 , Amy Balls 2 , Richard Vanfleet 1 , John Harb 2 , Robert Davis 1 Show Abstract
1 Physics and Astronomy Department, Brigham Young University, Provo, Utah, United States, 2 Chemical Engineering Department, Brigham Young University, Provo, Utah, United States
Here we report synthesis and testing of high capacity silicon/carbon nanotube (CNT) composite electrodes fabricated directly on stainless steel substrates. The electrodes were synthesized by growing vertically aligned carbon nanotube (VACNT) forests on catalyst coated stainless steel foils, followed by infiltration of the forests with silicon to yield silicon coated nanotubes. The electrodes were assembled into cells and tested by cycling against a lithium counter electrode. Capacity measurements during cycling were performed for electrodes of various thicknesses (nanotube heights) and silicon content. This VACNT/Si system provides an effective test bed for studying the effects of geometry (e.g. electrode thickness, porosity, void fraction, and surface area) on capacity and cycling performance. Specific capacity ranged from 1500 to 3000 mAh/g (per gram of silicon) and was a strong function of charge/discharge rate and surface area. Electrodes 10 microns thick (nanotube forest height) with a 15 nm Si shell on the CNTs showed stable capacities greater than 2000 mAh/g at 0.6 C for 20 cycles. Areal capacities greater than 10 mAh/cm2 were observed, which are believed to be the highest areal capacities reported for silicon electrodes.
11:15 AM - **M4.7
Carbon Nanotube Functionalized Li-ion Electrodes for Enhanced Rate Capability and Durability.
Chunmei Ban 1 , Zhuangchun Wu 1 , Yoon Seok Jung 1 , Le Chen 1 , Yanfa Yan 1 , Anne Dillon 1 Show Abstract
1 Chemical & Materials Science, National Renewable Energy Laboratory, Golden, Colorado, United States
Improving Li-ion electrodes (e.g. capacity, rate-capability and cyclic life) is essential for integration of Li-ion batteries in road transportation and stabilization of power grid with renewable energy penetration. NREL research has resulted in greatly improved performance of various Li-ion electrodes by creating a new architecture that enables binder-free electrodes. The electronic conductivity and electrode integrity are profoundly improved by integrating small quantities of carbon single-wall nanotubes (SWNTs) during electrode fabrication. For example, an Fe3O4-SWNT anode was made with only 5 wt.% SWNTs and had a stable capacity of 1000 mAh g-1 (~2000 mAh cm-3) at C rate, 800 mAh g-1 at 5C and ~600 mAh g-1 at 10C for over 100 cycles. Also, LiNi0.4Mn0.4Co0.2O2 binder-free cathode shows a sustainable capacity of ~ 130 mAh g-1 at 5C and nearly 120 mAh g-1 at 10C, both for over 500 cycles, further confirming the advantages of this methodology. Morphology and structural analyses have been emphasized to understand how both the electrode architecture and ameliorated electronic conductivity lead to dramatically improved electrochemical performance. This talk will summarize our recent research and emphasize new mechanistic understanding. The U.S. Department of Energy provided funding under subcontract number DE-AC36-08GO28308 through: DOE Office of Energy Efficiency and Renewable Energy Office of the Vehicle Technologies Program. Ban, C. M.; Wu, Z. C.; Gillaspie, D. T.; Chen, L.; Yan, Y. F.; Blackburn, J. L.; Dillon, A. C. Advanced Materials 2010, 22, E145
11:45 AM - M4.8
Coating Electrode Materials by Atomic Layer Deposition for Li-ion Batteries.
Yoon Seok Jung 1 , Andrew Cavanagh 2 , Young Hee Lee 2 , Chunmei Ban 1 , Se-Hee Lee 2 , Steven George 2 , Arrelaine Dameron 1 , Robert Tenent 1 , Gi-Heon Kim 1 , Ahmad Pesaran 1 , Anne Dillon 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 , University of Colorado at Boulder, Boulder, Colorado, United States
Surface modification is one of the most effective ways to achieve a stable electrode-electrolyte interface that is critical for the durability and safety of lithium-ion batteries (LIBs). Atomic layer deposition (ALD) is a scalable coating technology based on sequential, self-limiting surface reactions. ALD has many advantages over wet-chemical methods (e.g., sol-gel) including: conformal coating, atomic thickness control, flexibility regardless of the substrate – either on powders or on as-fabricated composite electrodes. Ultrathin (~1 nm) ALD coatings on LiCoO2
, natural graphite, and nanosized MoO3
 have been demonstrated to significantly improve the performance of LIBs by our group. The previous results are based on Al2
ALD, which is one of the most robust chemistries.
O → Al-OH*
However, there is significant reason to further investigate other ALD coatings such as ZrO2
because sol-gel coatings of ZrO2
and various other metal oxides, metal phosphates etc. have been extensively explored. By exploring variations of these ALD coatings, it may be possible to further tune electrochemical stability, transport properties of Li+
ions, mechanical stresses and thermal stability.Here we compare the performance variations depending on the various ALD coating materials. For example, Al2
following 2 cycles of ALD retain 68% and 79% capacity after 15 charge-discharge cycles, respectively, when cycled between 3.3-4.8 V (vs.
) at 0.1 C-rate for the first two cycles and 1 C-rate for subsequent cycles. We also investigated the electrochemical performance after employing molecular layer deposition (MLD) to deposit thin fims on electrodes as follows:
+ HOR′OH → M-OR′OH*
→ R′O-MRx-1 *
+ RH Where M is the metal and R is an alkyl molecule. The results depending on variations of ALD and/or MLD processes will be discussed in detail with a major focus on stability and transport properties.
 Y. S. Jung et al., J. Electrochem. Soc. 157, A75 (2010).
 Y. S. Jung et al., Adv. Mater. 22, 2172 (2010).
 L. A. Riley et al., ChemPhysChem. 11, 2124 (2010).
 A. A. Dameron et al., Chem. Mater. 20, 3315 (2008).
12:00 PM - M4.9
Binder-free Li-ion Battery Electrodes with a Li+ Conductive Coating.
Zhuangchun Wu 1 , Chunmei Ban 1 , Dane Gillaspie 1 , Yanfa Yan 1 , YoonSeok Jung 1 , Anne Dillon 1 Show Abstract
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Saftey issues in Li-ion batteries are a major concern when a large charge/discharge current is needed for applications such as hybrid electric, plug-in hybrid electric and especially fully electric vehicles. Recent progress has been reported on coated electrodes with various protective materials via various techniques such as atomic layer deposition and sputtering. Improved lifetime has been demonstrated by using these coated electrodes. New biner-free electrodes fabricated in our group  by utilizing only 5 wt.% carbon single wall nanotubes (SWNTs) to replace traditional conductive additives and polymer binders (typically 20-30 wt.% of the electrode), have shown highly durable cycling performance, even at very high rate, 5C and10C. Here we will present new results on coating the whole SWNT binder-free electrode with a thin layer of a Li-ion conducting film, such as LiPO4 and LiAlF4 in order to increase both the the safety and performance of the novel electrodes. The coating layer will protect the active material from undesirable side reactions in the organic electrolyte, without sacrificing the Li-ion conductivity across the coated film.YoonSeok Jung et.al., Advanced Materials, 22 (2010) 2172-2176Chunmei Ban, et.al., Advanced Energy Materials 22 (2010) E145-E149
12:15 PM - M4.10
Rate and Stability Studies on the Effects of Ultrathin Al2O3 Coatings on Nano-LiCoO2 by Atomic Layer Deposition.
Isaac Scott 1 , Yoon Seok Jung 2 , Andrew Cavanagh 1 , Yanfa Yan 2 , Anne Dillon 2 , George Steven 1 , Se-Hee Lee 1 Show Abstract
1 , University of Colorado, Boulder, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Efficient and durable electrical energy storage with high rate performance is one of the major limiting factors for Li-ion batteries. Performance at high charge and discharge rates is critically dependent on the size and morphology of the particles used to prepare the electrodes where capacity fade can be contributed to electrolyte decomposition, lithium deposition, active material dissolution, phase transition inside the insertion electrode materials, and solid electrolyte interphase (SEI) formation - many of which can be suppressed by coating the particles with a suitable barrier . In addition, using nano over micron-sized particles dramatically decreases the length the Li+ must diffuse in the solid state and increases the high rate performance. Nanoparticle lithium cobalt oxide (LiCoO2) is synthesized using KNO3 as the high-temperature reaction media. This molten salt synthesis method has been reported to be one of the simplest means in preparing homogeneous LiCoO2 powder . The particle size is controlled by varying the flux (molar ratio of CoO:KNO3), the final heating temperature, and reaction dwell time. The synthesized nanoparticles act as the active material for “thick” composite cathodes, which are then coated with aluminum oxide (Al2O3) by atomic layer deposition. Charge-discharge experiments carried out at various c-rates along with electrochemical impedance spectroscopy (EIS) is used to evaluate the performance of the electrodes prepared using bare nanparticle LiCoO2 and bulk LiCoO2 to that of Al2O3 ALD-coated nanoparticle LiCoO2 electrodes that are prepared using 2 and 6 ALD cycles. These experiments and the cyclic voltammograms (CVs) show enhanced high-rate electrochemical properties in the Al2O3-coated LiCoO2 cathodes compared to both the uncoated and bulk. The improved rate behavior for the coated electrodes is caused by the suppression of cobalt dissolution from the LiCoO2 with the formation of an aluminum-oxide barrier residing between the LiCoO2 cathode and the liquid electrolyte and by decreasing the particles size from bulk material.
12:30 PM - M4.11
Vapor Solid Solid Growth of Germanium Nanowires on Copper Substrates for Battery Applications via In Situ Germane Production.
Hugh Geaney 1 , Christopher Barrett 1 , Edric Gill 1 , Robert Gunning 1 , Catriona O sullivan 1 , Ajay Singh 1 , Emma Mullane 1 , Dervla Kelly 1 , Kevin Ryan 1 Show Abstract
1 Materials and Surface Science Institute, University of Limerick, Limerick Ireland
Cu is an attractive material for Group IV NW catalysis due to its prevalence as an anode component in lithium ion batteries. As such, the growth of Ge NWs directly on Cu substrates offers potential for battery applications. The Ge/Cu eutectic temperature of 644 C means that only solid seeding growth may be possible at reduced temperatures. Previous solid seeding studies have highlighted a reduction of metal incorporation into the NWs which is beneficial for device applications. While Ge NW growth from evaporated and sputtered Cu layers has been achieved through the use of germane based CVD processes, simple routes allowing widespread growth on bulk substrates are lacking. Here we present the large scale growth of Cu catalyzed Ge NW from bulk, untreated Cu substrates. The synthesis is facilitated by a glassware based alternative to the typical CVD process where the thermolytic decomposition of diphenylgermane is used as an in situ source of germane gas. This gas is simultaneously decomposed in and transported to the growth substrate by the vapour phase of a high boiling point organic solvent. The NWs form dense mats over the substrate surface. TEM analysis of the NWs was conducted in order to probe the growth mechanism which was found to follow the vapour-solid-solid type model as illustrated by the appearance of Cu seeds on the NWs.
12:45 PM - M4.12
Highly Ordered Hierarchical Porosity of Lithium Titanate Electrodes for Zero-strain, High-power Lithium-ion Batteries.
Ryan Maloney 1 , Hyunjoong Kim 1 , Ezhiylmurugan Rangasamy 1 , Apoorv Shaligram 1 , Jeffrey Sakamoto 1 Show Abstract
1 Chemical Engineering & Materials Science, Michigan State University, East Lansing, Michigan, United States
As our society moves away from fossil fuels and towards renewable energy, it has become apparent that advances in energy storage are necessary. For electrical energy storage in particular, nanostructured materials have shown great promise in increasing the energy and power density of storage devices. However, while nanostructuring of cathode materials has shown great improvement in electrode performance, similar tailoring of anode materials has unique challenges that must be addressed. Electrodes may appear two dimensional on a macro scale, but nanoparticles behave as a three dimensional system and should be considered as such. By engineering large channels perpendicular to the current collector that connect to smaller pores in-plane, which then feed into the nanometer-scale porosity inherent in the electrode material, ionic transport within the electrode can be optimized. This highly ordered, hierarchical porosity enables detailed study of the transport properties of the electrode, especially as active material areal loadings increase in the push towards more energy-dense batteries.In this work, we present the fabrication and characterization of a sol-gel derived lithium titanate spinel anode with highly ordered hierarchical porosity. The nanometer-scale porosity of the sol-gel can be maintained through supercritical drying, forming a highly porous aerogel. The nanoparticles of the sol-gel eliminate solid-state lithium diffusion as the limiting factor in electrode kinetics. Further, because lithium titanate does not form a solid electrolyte interface (SEI) layer, it can be used as a model system to isolate the ionic conductivity through the pores of the electrode as the rate limiting step. Lithium titanate does have poor electrical conductivity, but the sol-gel process allows the incorporation of graphite nanoplatelets around which the spinel gel network may form. This creates an internally wired, electrically conductive network of interconnected particles, allowing for fast electron transport. Finally, meso- and macro-scale porosity can be engineered into the final electrode, allowing for a highly ordered hierarchical distribution of pores both in plane and perpendicular to the surface. The effect of this engineered porosity on the electrochemical performance of the electrode is explored, with special attention given to the rate capability of the material at higher electrode loadings.Through optimization of the porous network and utilization of a non-SEI forming anode material, ionic transport through nanostructured porous electrodes can be studied in detail. Further progress in this area will lead to electrodes that maintain excellent rate performance with increasing thickness, allowing for more energy- and power-dense storage devices.
M6: Poster Session: Li-ion Battery
Yoon Seok Jung
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
9:00 PM - M6.10
Diffusion of Lithium into Silicon and Silicon Nanoparticles.
Hatice Karacuban 1 2 , David Krix 1 2 , Hermann Nienhaus 1 2 , Hartmut Wiggers 3 , Helge Grimm 3 Show Abstract
1 Department of Physics, University of Duisburg-Essen, Duisburg Germany, 2 , CeNIDE Center for nanointegration Duisburg-Essen, Duisburg Germany, 3 Institute for Combustion and Gasdynamics, University of Duisburg-Essen, Duisburg Germany
Silicon is known to have a high storage capacity for lithium which greatly exceeds the storage capacity of commonly used graphite anodes in lithium-ion batteries. Therefore it is a promising candidate as a replacement material for lithium-ion batteries electrodes. Technological problems arise from the large density difference between elemental silicon and the silicide upon absorption of lithium. The resulting amorphization of the electrode material in turn leads to a shortened lifetime of the battery. Silicon based nanomaterials, i.e., nanoparticles, do not show amorphization caused by the adsorption of lithium. They thus combine the benefit of high storage capacity while promising longer life times for lithium-ion batteries. We present studies of the diffusion of lithium into silicon single crystals and silicon nanoparticles, and the effect of oxidation to the diffusion processes.The activation energy for the diffusion of lithium into silicon was studied by Auger-Electron spectroscopy under ultra high vacuum conditions. Thin layers of lithium were deposited in situ onto H-passivated p-type silicon (001)-wafers at low temperatures forming a metallic film on the surface. The film’s thickness was chosen such that the Auger electrons emitted from the silicon substrate could still be detected and thus could be used as a measure for the lithium thickness. We find that lithium silicide was formed at the interface of silicon and lithium. The intensity of the silicide signal was measured as a function of time. The diffusion of lithium into the bulk silicon means a smaller lithium coverage, thus leading to a higher silicide intensity. The same experiment was carried out for different temperatures between 160 K and 180 K. With increasing temperature the diffusion process becomes accelerated due to thermal activation. An activation energy of 0.49 eV was deduced from the experimental data, which is lower than values reported in the literature [1,2]. This diffusion behaviour was used as reference to get a better understanding of the diffusion of lithium into silicon nanoparticles. P-type silicon nanoparticles with a size of about 30 nm were deposited onto a glassy carbon substrate by spin coating followed by a treatment in HF. A thin layer of lithium was deposited in situ and the activation energy of the diffusion was determined. Furthermore the effect of oxidation of the silicon surfaces was studied. Oxide layers of different structure were produced on the silicon single crystals and the nanoparticles’ surfaces by chemical and thermal treatments and the activation energy was obtained. E.M. Pell, Phys. Rev. 119, (1960), 1222  A. Keffous, Vacuum 81, (2006), 417
9:00 PM - M6.13
Silicon Nanowires within a Carbon Nanotube Matrix as Anode Materials for Lithium Ion Batteries.
Xianglong Li 1 , Jeong-Hyun Cho 1 , Samuel Picraux 1 Show Abstract
1 MPA-CINT, Los Alamos National Lab, Los Alamos, New Mexico, United States
We report on the fabrication and cycling performance of hybrid silicon nanowire/ carbon nanotube matrix structures for improved Li ion anode performance. Advanced lithium ion batteries with high energy density, high-rate capability, and excellent cycling performance are critically important for various automobile and stationary energy storage applications such as electric vehicles, portable electronics, power tools, and energy storage for many types of renewable energy sources. From the materials point of view, silicon is one of the most promising candidates for anode materials of these lithium ion batteries owing to its abundance in nature, relatively low working potential, and the highest known theoretical charge capacity of 4200 mA h/g (eleven times higher than that of commercialized graphite). However, the dramatic volume change (> 300%) during lithium insertion and extraction processes causes capacity fading due to severe pulverization and electrical disconnection from the current collector, and thus hinders their practical implementation. In order to overcome these drawbacks, nanostructured silicon composite anodes with a well-designed layout are highly desirable. Here, we report a new silicon nanowire-based heterogeneous composite anode architecture, in which multi-walled carbon nanotubes are directly grown on conductive substrates followed by the gold catalytic seeding and vapor-liquid-solid growth of silicon nanowires. The carbon nanotubes within these hybrid structures function not only as buffering matrixes for accommodating the volumetric change of silicon nanowires, but also as robust electrically conductive networks to make long-term high-rate cycling be possible. The microstructure before and after cycling, specific energy capacity, and cycling performance improvements of these hybrid structures will be discussed.
9:00 PM - M6.14
Enhanced Electrochemical Properties and Structural Analysis of Lithium Vanadium Phosphate Cathode Materials for Lithium-ion Batteries.
A-Ra Jo 1 , Ji-Won Lee 1 , Chang-Geun Son 1 , Seo-Mi-Gon Yang 1 , Won-Sub Yoon 2 , Ki-Suk Kang 3 , Yun-Sung Lee 1 4 Show Abstract
1 Applied Chemical Engineering, Chonnam University, Gwangju Korea (the Republic of), 2 Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of), 3 Material Science and Engineering, KAIST, Daejeon Korea (the Republic of), 4 Chemistry, Brookhaven National Laboratory, Upton, New York, United States
Lithium vanadium phosphate, Li3V2(PO4)3 in a structure similar to the open framework NASICON. The poly-anion instead of the O2− ions helps to stabilize the structure and allows a faster ion migration. The reversible cycling of all three lithium ions from Li3V2(PO4)3 would corresponds to a theoretical capacity of 197 mAh/g in the voltage range of 3.0-4.8 V, which is the highest reported of the phosphates. However, the Li3V2(PO4)3 has lower electronic conductivity of about 2.3 x 10-8 S/cm at 300 K due to the polarization of V-O bond, which greatly restricts its practical application for lithium ion batteries. In this paper, we tried to improve the electrochemical performance of the Li3V2(PO4)3 cathode materials which have poor electronic conductivity by a carbon coating. The Li3V2(PO4)3 were prepared using conventional solid-state synthesis. Carbon-coated samples were prepared as follows: stoichiometric ratios of Li:V:P source materials with various molar ratios (0, 0.05, 0.1 and 0.15) of adipic acid to total metal ions were finely ground using mortar. And then precalcined at 300 oC for 4 h, the precursor was reground and pelletized, then heated at 900 oC for 8 h under Ar atmosphere in a tubular furnace. The electrochemical characterizations were performed using CR2032 coin-type cell. The electrolyte used was a mixture of 1M LiPF6-EC/DMC (1:1 by vol.). The charge/discharge current density was 0.1 mA/cm2 with a voltage of 3.0 - 4.8 V at room temperature. In order to study the phase transformation of lithium bi-metal phosphate during the lithiation /delithiation reaction. in-situ synchroton X-ray studies carried out in transmission mode at λ=0.99186 Å at the XRS KIST-PAL (XRD) 10B beamline of the Pohang Light Source(PLS), Pohang, Republic of Korea.The XRD pattern shows a well synthesized single phase Li3V2(PO4)3 with monoclinic structure. The charge/discharge tests were carried out between 3.0 - 4.8 V at 0.1 mA/cm2. The carbon coated Li3V2(PO4)3 sample exhibits highest initial discharge capacity of 171 mAh/g with 90 % capacity retention after 30 cycles. Carbon-coated samples show improved capacity and cycle performance compared to the pristine Li3V2(PO4)3. CV curves show four oxidation and three reduction peaks. The peak intensity value of the carbon coated sample is higher than parent one, which reveals that the carbon coating increases the conductivity as well as the reaction kinetics. From the in-situ XRD analysis, we can find phase transformation of samples during the lithiation /delithiation, which induces unique electrochemical characterization of Li/Li3V2(PO4)3 sample.Acknolwdgements This work was also supported by Energy Resources Technology R&D program (20092020100040) under the Ministry of Knowledge Economy, Republic of Korea.
9:00 PM - M6.15
Synthesis and Electrochemical Performance of LiMn1/3Co1/3V1/3PO4 as Cathode Materials for Lithium-ion Batteries.
Seo Mi Gon Yang 1 , A Ra Jo 1 , Ji Won Lee 1 , Chang Geun Son 1 , Karthikeyan Kaliyappan 1 , Amaresh SamuthiraPandian 1 , Yun Sung Lee 1 2 Show Abstract
1 Faculty of Applied Chemical Engineering, Chonnam National University , Gwangju Korea (the Republic of), 2 Department of Chemistry, Brookhaven National Laboratory, Upton, New York, United States
In recent years, research and development of phosphate materials have been attracting attention as cathode materials for lithium ion battery due to their high theoretical capacity, high operating voltage, good stability and a battery reversible capacity. However, these single-transition-metal phosphates suffer the disadvantage of low electrical conductivity. Recently, lithium multi-transition-metal phosphates such as LiFe1/3Mn1/3Co1/3PO4, LiFe1/4Mn1/4Co1/4Ni1/4PO4 have been studied for improved electrochemical performance. During charging/discharging, lithium multi-transition-metal phosphates having Nickel does not work well at 5 V region due to electrolyte decomposition at such a high voltage region.3-4 In case of monoclinic lithium vanadium phosphate Li3V2(PO4)3, having structure similar to the open framework NASICON has advantages of high reversible capacity, high operating voltage, good ion mobility and so on. Therefore, we used vanadium source instead of the transition metallic Ni as precursor for lithium multi-transition-metal phosphates. In this study, LiMn1/3Co1/3V1/3PO4 was prepared by two-step solid state route. For the bare-sample, stoichiometric amount of chemicals were ground using mortar for 30 min and first heated at 400 oC in a tubular furnace with a flowing Ar atmosphere for 3h. The resulted samples were reground, pelletized and sintered at 700 oC for 5h under Ar atmosphere. The LMCVP/C composites were synthesized by adding adipic acid(C6H10O4) as carbon source using the initial materials and the same procedure as described above. Different molar ratios of adipic acid to total metal ions (0~0.6) were studied. The electrochemical characterizations were performed using CR2032 coin-type cell. A 1M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate(DMC) (1:1, v/v, Techno Semichem Co., Ltd., Korea) mixture was used as electrolyte. The current density for charge/discharge test was 0.2 mA/cm2 with a cut-off voltage of 2.9–5.2 V at room temperature.Lithium multi-transition-metal phosphate LMCVP and LMCVP/C were synthesized at 400 oC for 3 h and then at 700 oC for 5 h in an Ar atmosphere using solid-state route. The materials showed well developed XRD pattern. LiMn1/3Co1/3V1/3PO4 exhibited initial discharge capacity of about 103 mAh/g. In case of LMCVP/C composite, it showed well developed XRD pattern without any impurity at various molar ratios of adipic acid(0~0.6) and its initial discharge capacity was observed to be about 121 mAh/g for the cell with a 0.5 molar ratio of aidpic acid. A detailed discussion about electrochemical properties of LMCVP materials will be reported in this meeting.Acknolwdgements This work was also supported by Energy Resources Technology R&D program (20092020100040) under the Ministry of Knowledge Economy, Republic of Korea.
9:00 PM - M6.16
Fabrication and Electrochemical Properties of Embossed Nanostructure LiMn2O4 Thin Films for Rechargeable Thin Film Batteries.
Woo Yeon Kong 1 2 , Haena Yim 1 , Hi Gyu Moon 1 , Ho Won Jang 1 , Seok-Jin Yoon 1 , Sahn Nahm 2 , Ji-Won Choi 1 Show Abstract
1 Electronic Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Electro Ceramics Laboratory, Korea University, Seoul Korea (the Republic of)
Lithium insertion compounds have been widely investigated in the search for electrode materials for use in high-voltage rechargeable batteries. LiCoO2, LiMn2O4, LiNiO2 and LiFePO4 have commonly been used as positive electrode materials. Especially, LiMn2O4 has much concerned owe to high electrochemical potential, high abundant, low cost, and environmental friendliness. In general, LiMn2O4 thin films have been fabricated to the two dimensional structure. However, two dimensional thin film batteries have low capacity and high internal resistance. To overcome these problems, three dimensional (3D) design with high active surface area should be required.In this study, we show the design and making of embossed 3D positive electrode for thin film lithium battery. LiMn2O4 cathode thin films were prepared by simple template method to obtain nanostructure.The poly-styrene (PS) template layer, was prepared on SiO2/Si(100) substrate by a spin-coating method. The platinum layer was deposited on the template-coated, followed by annealing the template at 500oC. When the templates were removed by annealing, embossing structure was formed. The LiMn2O4 layer was deposited by radio frequency (RF) sputtering. Controlled O2 plasma treatment on the close-packed monolayer makes to highly ordered nanostructures in the colloid templates. Embossed nanostructure thin film cathode will provide larger active area and enhanced lithium intercalation and deintercalation.The structural and electrochemical properties of embossed nanostructure thin films will be discussed in comparison with plain thin films.
9:00 PM - M6.18
Facile Synthesis and Electrochemical Characterization of Porous and Dense TiO2 Nanospheres for Lithium-ion Battery Applications.
Hong En Wang 1 , Hua Cheng 1 , Chaoping Liu 1 , Igor Bello 1 Show Abstract
1 Physics and Materials Science, City University of Hong Kong, Hong Kong China
We present a two-step method to optimize the nanoporous characteristics of TiO2 samples. Unlike compact TiO2, these nanoporous structures incorporated in lithium-ion batteries enable higher charge and discharge capacities as well as a better rate capability. We use a simple sol-gel process to fabricate spherical titanium glycolates precursors followed by subsequent hydrothermal or annealing treatments resulting, respectively, in highly porous or dense TiO2 nanospheres. These processes enable to control the crystal size and specific surface area (area per weight) of the TiO2. The fabricated TiO2 nanostructures were subsequently used to assemble the lithium-ion batteries. Galvanostatic discharge-charge tests indicate that the porous TiO2 nanospheres possess high and stable reversible capacity of 200, 133, and 56 mAh/g at discharge/charge rates of 10, 100 and 1000 mA/g, respectively; whereas the corresponding values for dense TiO2 nanospheres are 200, 45, and ~1 mAh/g. This considerable improvement of the electrochemical activity is believed to be caused by the porosity in TiO2 nanostructures, and consequential change in diffusion length. The developed technology thus enables to optimize the high rate capability in TiO2-based lithium-ion batteries.
9:00 PM - M6.19
High-performance Nanostructured Si Composite Anode for Ultra-high Energy Rechargeable (UHER) Lithium Batteries.
Carlos Poventud-Estrada 1 , Jose Lopez-Perez 1 , Javier Palomino 1 , Emmanuel Febus-Paris 1 , Carlos Martinez 1 , Gerardo Morell 1 Show Abstract
1 Physics, University of Puerto Rico - Rio Piedras, San Juan United States
Synthesis of novel silicon nanocomposites to achieve UHER with specific energy of 260Wh/kg at C/10 discharge rate and 0°C. The goal is the development of battery anodes made of silicon nanocomposites that can at least reach a specific energy of 1000mAh/g at C/10 and 0°C. The silicon nanostructured materials developed will be used as working electrodes in lithium based batteries such as C2032 coin cells. The proposed materials developed are designed to be mechanically robust, and both easy and inexpensive to produce. Furthermore, the proposed new Si composite materials are intended to be scalable to large areas by synthesis via Sol-Gel method.
9:00 PM - M6.2
Electrochemical Performance of Anodized TiO2 Nanotubes for Rechargeable Lithium Batteries.
Rayavarapu Prasada Rao 1 , Li Kangle 1 , Stefan Adams 1 , M. Venkataswamy Reddy 2 , Bobba V.R. Chowdari 2 Show Abstract
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore, 2 Physics, National University of Singapore, Singapore Singapore
Rechargeable lithium ion batteries are important energy storage devices; however, the limited reversible charge capacity of electrode materials, insufficient power performance, safety concerns and high cost of materials and processes limit the application range. TiO2 particles, nanowires and nanotubes, prepared by a molten salt, hydrothermal route and surfactant assisted methods etc. and studied the electrochemical properties of TiO2 in the voltage range, 1.0-3.0V vs. Li.Here, we have prepared vertical titania nanotube electrodes by anodization of titanium foils in an electrolyte containing ammonium fluoride (NH4F). Ti foils (99.7% Aldrich) were cleaned by ultrasonic cleaning for 10 min. in 0.5% Decon 90, acetone, ethanol and de-ionized (DI) water in sequence. The cleaned Ti foils were dried by a nitrogen stream and anodized under 50V for one hour with an initial voltage ramp rate of 0.25 V/s. The anodization electrolyte consists of 0.6wt% NH4F in ethylene glycol and DI water solution (vol. ratio 98:2). The as-anodized NT electrodes were treated by ultrasonication for 30 seconds in DI water containing Al2O2 powder (30nm in average) to remove the top debris. The as anodized foils were kept at 200°C for 15min., followed by annealing at 480°C for 60min to ensure the conversion of amorphous TiO2 into a 6-8 μm thick anatase nanotube array. Charge/discharge cycling and cyclic voltammtery studies are used to analayze electrochemical performance of these TiO2 nanotube. The samples are cycled in the range, 1.0-3.0V, at current rate of 0.5 C using a Li metal as counter and reference electrode and 1 M LiPF6 in EC + DMC (1:1) used as electrolyte. The cyclic voltammtery studies shows characteristic redox couple of 1.8/1.6V vs. Li. Initial discharge capacity (180 mAh g-1,Limax= 0.54) and, the reversible capacity of 150 mAh g-1 at the end of 20th cycle. The rate capabalites, long term cycling studies with different mass and thickness of TiO2 nanotube electrodes were discussed in detail. The reaction mechanisms, ¬phase changes, stress and morphology changes during the cycling are monitored by X-ray diffraction and complemented by computational studies on the Lithium redistribution. Investigation of TiO2 nano tubes in full cells with liquid and solid electrolytes will be presented at the conference.
9:00 PM - M6.20
Monolithic, Fused Silica Particles as Templates for the Synthesis of Hierarchically Porous Carbons and Their Performance as Anode Material in Lithium Ion Batteries.
Philipp Adelhelm 1 , Birte Jache 1 , Stefanie Diegelmann 1 , Laemthong Chuenchom 1 , Christian Neumann 2 , Joerg Becker 2 , Bernd Smarsly 1 , Juergen Janek 1 Show Abstract
1 Institute of Physical Chemistry, Justus-Liebig-University Giessen, Giessen Germany, 2 , Heraeus Quarzglas GmbH & Co. KG, Kleinostheim Germany
Nanostructuring and/or the introduction of tailored porosity have been shown to be powerful tools to improve the kinetics of lithium de- and insertion reactions in carbon anode materials. Hierarchical porous carbon materials with excellent rate capability and capacity have been prepared via the nanocasting route, for example. Here, we present the electrochemical characterization of novel porous carbon materials that have been prepared via the nanocasting route. For the first time, large silica monoliths that were prepared by flame hydrolysis (a method readily available on the industrial scale) were used as templates. Mesophase pitch was used as carbon precursor. The silica monoliths exhibit an anisotropic distribution of silica primary particles in a layer-like fashion. Particle size and porosity of the silica template can be tailored by variation of the synthesis conditions. Usually a broad pore size distribution is found with primary particles of defined, spherical shape in the range of 100-500 nm. Accordingly, the corresponding carbon replica exhibit broad pore size distributions with defined maxima in the macropore range. Additionally, some intrinsic microporosity arises from the carbon precursor. Whereas mesophase pitch as carbon precursor yields a carbon material with a well-developed graphene structure, sucrose as precursor yields a very disordered carbon structure.The electrochemical characterization of the templated carbon materials was performed between 0,01 and 2 V vs. metallic lithium in a 1M solution of LiPF6 in (1:1) EC/DMC. Graphite and non-templated carbon served as reference. The electrode preparation procedure was identical for all sample.High capacities and excellent rate capability were found for all templated carbon materials. Typically, capacities larger than 500 mAh/g (after 10 cycles, C/5) were observed, i.e. much larger than graphite reference and non-templated carbon (210 mAh/g). Tests on the rate capability showed superior behavior of the templated carbons compared to the references. No electrode degradation during cycling at C-Rates between 1 and 10 was observed for the templated carbons, whereas graphite and non-templated carbon showed capacity fading.The results demonstrate that monolithic silica materials, which can be produced at industrial scale, can be effectively used as templates to prepare porous carbon materials that exhibit high Li capacity and improved rate capability. The excellent performance probably results from the favorable combination of silica template and carbon precursor.Hu YS, Adelhelm P, Smarsly B, Hore S, Antonietti M, Maier J., Adv. Funct. Mater. 2007; 17, 1873
9:00 PM - M6.21
Three-dimensional Porous Core-shelled Sn@carbon Composite Anode for Lithium Ion Batteries Application.
Xifei Li 1 , Abirami Dhanabalan 1 , Chunlei Wang 1 Show Abstract
1 , Florida International University, Miami, Florida, United States
The commercialized graphite anode of lithium ion batteries has high initial efficiency and good cycle performance. However, its theoretical capacity is limited, 372 mAh g-1 to form LiC6 intercalation compound. It cannot meet the application of high capacity for lithium ion batteries. Indeed, many metals, for example, Sn, can electrochemically react with Li to form alloy with a large number of Li atoms for formula units, which provides the high capacity. And Sn anode with high theoretical capacity, 994 mAhg-1, has recently been extensively considered. Sn anode can alloy with Li up to about 4.4 Li per Sn with the huge volume change. During Li+ intercalation and de-intercalation, its huge volume expansion and shrinkage results in the pulverization and cracking of anode materials, and lose the contact between active materials and current collector. This drawback leads to the significant capacity fade, which limits its application as anode materials for lithium ion batteries.Electrostatic spray deposition (ESD) is a simple and versatile method for generating thin film. In this work, we used ESD method to prepare the porous Sn/C composite as anode material for lithium ion batteries. Firstly tin (IV) acetate was dissolved in the 80 vol% of butyl carbitol and 20 vol% of ethanol, and PVP was added to dissolve as the precursor solution. And then obtained precursor was used to deposit the thin film by means of ESD. The deposition was carried at 270 oC at a flow rate of 1.0 ml h-1. The as deposited thin films were heated at 900 degree in forming gas environment. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectra and Raman scattering. The SEM and HRTEM images clearly indicate that the porous core-shelled Sn@carbon was successfully prepared. The porous structure is very stable without any cracks although the films were heated at 900 oC. This stable structure is beneficial to resist the volume change during charge and discharge.In an argon-filled glove box the thin films were assembled as the electrochemical cells using lithium sheet as the counter electrode. The electrolyte was 1M lithium bis(perfluoroethylsulfonyl)imide dissolved in ethylene carbonate (EC): diethyl carbonate (DEC): ethyl methyl carbonate (EMC) in a 1:1:1 volume ratio. Celgard 2400 was used as the separator. Cyclic voltammetry tests were performed on Versatile Multichannel Potentiostat (VMP3) at a scan rate of 0.2 mV s -1 over a potential range of 0.02 and 3.00 V (vs. Li/Li+). All cells were galvanostatically cycled between 0.02 and 3.00 V (vs. Li/Li+) at room temperature by NEWARE BTS-610 battery tester. The experimental results will be discussed in detail. This work was supported by AFOSR (No. FA9550-05-1-0232), USA.
9:00 PM - M6.23
Capacity Contribution of the Interfacial Layer on Anode Current Collectors and Their Electrochemical Properties in Lithium Ion Batteries.
Tae Kwon Kim 1 , Wei Chen 1 , Chunlei Wang 1 Show Abstract
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Most of the recent research focus for the advanced rechargeable batteries is improving electrochemical performance of electrode materials which are significantly important to determine the energy capacity, power density and electrochemical potential. Current collectors are mainly used to give the electronic conduction through the active electrode materials to the external circuit in lithium ion batteries. Although current collectors may be considered to be electrochemically inactive in the cell, their electrochemical reactions can not be ignored in case an interfacial layer formed on the current collector once they are thermally treated with active electrode materials. In this work, typical anode current collectors such as Cu and Ni foam were investigated to understand their capacity contribution and electrochemical properties after heat treatment. Cu and Ni foam were heated at 5 different temperatures, 100°C, 200°C, 300°C, 400°C and 500°C, and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. For testing electrochemical performance of these heated current collectors, cyclic voltammetry (CV) and galvanostatic charge-discharge test were performed in half cells. It was found that the capacity contribution of the interfacial layer on current collectors has varied with heat treatment temperatures. The electrochemical performance delivered by the heated current collectors at different temperatures will be discussed in detail.
9:00 PM - M6.25
Single-crystalline TiO2 Nanowires on Titanium Foil for Lithium Ion Batteries.
Bin Liu 1 , Eray Aydil 1 Show Abstract
1 , University of Minnesota, Minneapolis, Minnesota, United States
Rechargeable lithium ion batteries (LIBs) are important for powering mobile or portable electronic devices and for storing energy in intermittent renewable power production systems that rely on the wind and the sun. During the charging and the discharging of an LIB, lithium ions insert the anode and the cathode materials, respectively. The ideal host electrode materials must have large surface-to-volume ratios and must be able to repeatedly accept and reject a large number of lithium ions without significant degradation after many charging-discharging cycles. In this presentation, we describe a simple and environmentally benign three-step hydrothermal method to grow oriented single-crystalline TiO2-B and/or anatase TiO2 nanowire arrays on titanium foil over large areas. The heterogeneous growth of TiO2-B and anatase TiO2 nanowires relies on the formation of sodium titanate nanowires on titanium foil followed by ion-exchange and calcination steps that transform them first into hydrogen titanate, and then into TiO2 nanowires. We show that these nanowire arrays are suitable for use as the anode in lithium-ion-batteries; they exhibit specific capacities ranging from 200-250 mAh/g at 0.3 C rate (here 1 C is defined based on the theoretical capacity of anatase 168 mAh/g). Batteries retain this capacity over as many as 200 charge-discharge cycles. Even at high charge-discharge rates of 0.9 C and 1.8 C, the specific capacities were 150 mAh/g and 120 mAh/g, respectively. These promising properties are attributed to both the nanometer size of the nanowires and their oriented alignment. The comparable electrochemical performance to existing technology, improved safety, and the ability to roll titanium foils into compact three-dimensional structures without additional substrates, binders or additives suggest that these TiO2 nanowires on titanium foil are promising anode materials for large scale energy storage.
9:00 PM - M6.26
Porous Iron Oxide-carbon Composite (Fe3O4-C): High-rate Anode Material for the Li-ion Battery.
Hiesang Sohn 1 , Yunfeng Lu 1 Show Abstract
1 Chemical and Biomolecular Engineering, UCLA, Los Angeles, California, United States
Due to increasing demand of high-power lithium-ion batteries (LIBs), novel electrode materials are required to enable fast insertion/extraction of lithium. Nano-sized electrode materials with short lithium ion and electron diffusion paths and a large surface area in contact with the electrolyte are recommended for high rate applications. Without using the nanosized architecture, the bulk electrode materials are easily disconnected from each other due to their severe volume expansion/shrinkage during cycling, resulting in fast capacity fading. In addition, they support only slow charge-discharge rates. Fe3O4 has advantages over other candidate materials for high-energy and high-power anode materials for LIBs due to high electronic conductivity, low cost, and environmental benignity. Carbon can act as conductive matrix to enhance the mechanical integrity in composite with high-volume change materials such as Si. In the present work, the porous iron oxide-carbon composite (Fe3O4-C) are prepared with aerosol assisted method and investigated with transmission electron microscopy, X-ray diffraction, N2 sorption analysis and tested as anode materials for LIBs. The porous iron oxide carbon composites are composed of iron oxide nanoparticles and carbon where nano-sized (~15 nm) primary iron oxide (Fe3O4) particles are connected with carbon scaffold forming bigger sized (~500 nm) porous iron oxide-carbon composite. The nano-sized iron oxide-carbon composite provides better interparticle contact than conventional iron oxide nanoparticles. The electrolyte can also flood the pores providing a high contact area owing to high surface area (64.6 m2/g) of the composite. In addition, judicious control of sintering process made carbon scaffold more conductive and act as buffer layer for drastic volume change of Fe3O4 during cycling. The porous iron oxide carbon composite significantly enhanced the cycle performance and the rate capability. It shows high reversible capacity (620 mAh/g) at the first cycle and 420 mAh/g after 80 cycles between 0.005-3.000 V (vs. Li/Li+) at 500 mA/g. The improvements can be mainly attributed to the unique porous structure of iron oxide-carbon composite. Especially, uniform and continuous carbon scaffold connecting iron oxide nanoparticle mostly contributes to the stability of the composite structure during cycling by maintaining the structural integrity of particles and enhancing the electronic conductivity.
9:00 PM - M6.27
Nano-sized LiCoO2-decorated Carbon Nanotubes as Cathode Materials for Lithium-ion Battery.
Xiong Pu 1 Show Abstract
1 , Texas A&M University, College Station, Texas, United States
Lithium cobalt oxide (LiCoO2) receives worldwide interest as active cathode materials for rechargeable Li-ion batteries, because of its high specific capacity and stable cycling performance. Nanostructuring the cathode by dispersing carbon nanotubes (CNTs) in active nanosized LiCoO2 results in a higher surface area, shorter Li-ion diffusion distance and higher electrical conductivity of the electrode. Decorating LiCoO2 on the surface of single-walled CNTs is realized by sonication of the mixture suspension of purified SWCNTs and nanosized LiCoO2 synthesized by hydrothermal method. XRD, SEM and TEM are carried out to investigate the structure and morphology of the active materials. Batteries with cathodes made of LiCoO2-decorated CNTs and LiCoO2 with dispersed CNTs are assembled respectively. Electrochemical analysis shows that decorating SWCNTs with nanosized LiCOO2 can effectively improve the high-rate capability of the battery.
9:00 PM - M6.28
Pre-lithiated Silicon Nanowires as Lithium Ion Battery Anodes.
Nian Liu 2 , Liangbing Hu 1 , Matthew McDowell 1 , Yi Cui 1 Show Abstract
2 Department of Chemistry, Stanford University, Stanford, California, United States, 1 Department of Materials Science and Engineering, Stanford University, Stanford, California, United States
Silicon nanowires are attractive for next-generation lithium-ion battery with high energy density. However, lithium must be available in the cathode for full cell applications, which limits the choice of cathode materials. In this work, we demonstrated that Si nanowires can be prelithiated with a simple diffusion process. Proof of concept is demonstrated, and a prethiation mechanism is proposed. Through the prelithiation time dependence study, we found that 30 minute allows 80% of prelithiation to its full capacity. TEM and SEM study clearly shows the change of morphology of the Si nanowires, similar to those through battery charge-discharge process. Full cell is demonstrated with sulfur cathodes, which have no lithium inside. This work is significant for practical use of Si nanowires to pair up with cathodes without free lithium for next generation high energy density Li-ion batteries.
9:00 PM - M6.32
Monodisperse Metallic and Semiconducting Single-walled Carbon Nanotubes in Lithium Ion Battery Anodes.
Laila Jaber Ansari 1 , Albert Lipson 1 , Mark Hersam 1 Show Abstract
1 Material Science and Eng., Northwestern University, Evanston, Illinois, United States
Single-walled carbon nanotube (SWCNT) thin films and nanocomposites are promising candidates for lithium ion battery anodes due to their high surface area, high conductivity, chemical stability, and mechanical resilience. While the properties of SWCNTs have been investigated previously as anodes in lithium ion batteries, these results have been difficult to interpret and the anode performance has likely not been optimized due to the polydispersity in structure and electronic properties of the as-synthesized SWCNT material. To address this limitation, we employ density gradient ultracentrifugation (DGU) to sort SWCNTs based on their electronic structure. In particular, fabrication of metallic and semiconducting SWCNT anodes with purities exceeding 99% is achieved with DGU. The cycling capacity is observed to improve by an order of magnitude as the metallic composition of SWCNTs in the anode is increased from 1 to 99%. In addition to lithium ion capacity measurements, these high purity SWCNT anodes are characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and X-ray photoelectron spectroscopy (XPS) in an effort to evaluate the anode material at different stages of lithium ion intercalation.
9:00 PM - M6.34
Carbon Coated Silicon Thin Film for Lithium-ion Battery Anode.
Chunhui Chen 1 , Wei Chen 1 , Chunlei Wang 1 Show Abstract
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Si-based materials have recently received great attention as potential anodes in Li-ion batteries for their high theoretical specific capacities, which are an order of magnitude over that of conventional graphite. However, the significant volume change during cycling results in poor cyclability because the mechanical failure and the loss of electrical contact in the electrode. The aggregation of silicon nanoparticles during the cycling is believed to be another reason for the poor cyclability. Many research works have shown that carbon coated Si powder can enhance the cyclability to some degree. In this work, carbon coated Si porous thin films were prepared by Electrostatic Spray Deposition (ESD). Si powders (<100 nm) were mixed with citric acid, a carbon precursor, in ethanol solution via ultrasonication. The resulting mixture was deposited on Ni foam by ESD. Depending on the deposition conditions used, different morphologies of the thin films were obtained. The variations in the morphologies lead to different electrochemical performances. In comparison with bare silicon anodes, the carbon coated silicon porous thin film showed superior and stable cycle performance which indicated the excellent potential use of such composite as alternative anodes materials for lithium-ion batteries.
9:00 PM - M6.35
A Hollow Sphere Secondary Structure of LiFePO4 Nanoparticles.
Myeong-Hee Lee 1 , Jin-Young Kim 1 , Guntae Kim 1 , Hyun-Kon Song 1 Show Abstract
1 , UNIST, Ulsan Korea (the Republic of)
A hollow sphere secondary structure of spherical nanoparticles was evolved by a solubilization-reprecipitation mechanism based on the difference of solubility products (Ksp) of two different precipitates. Carbon-coated nanoparticles of olivine structure LiFePO4 served as the primary nano-blocks to build the secondary nano-architecture. Li3PO4 and Fe3(PO4)2 were sequentially precipitated in presence of a carbon precursor. During the second precipitation step, phosphate was dissolved from the first precipitate Li3PO4 (with higher Ksp1) and re-utilized for formation of Fe3(PO4)2 (with lower Ksp2), producing hollow LiFePO4, a cathode material for lithium ion batteries. The hollow-sphere-secondary-structured LiFePO4 showed the superior performances at high power charge as well as discharge ( > 10C) especially with low plateau potential rise or drop.
9:00 PM - M6.37
Synthesis of Highly Ordered Vanadium Oxide Nanotubes via Anodization of Vanadium Foil.
Dominik Koll 1 , Daniel Jacobs 1 , Hannes Kerschbaumer 1 , Steffen Pfeiffer 1 , Alexander Birkel 1 , Stefan Frank 1 , Wolfgang Tremel 1 Show Abstract
1 , Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg - University of Mainz, Mainz, Rhineland Palatinate, Germany
During the last years one dimensional nanostructures, such as nanotubes or nanowires, were subject to extensive research due to their size dependent, tunable properties. Compared to nanowires, nanotubes offer the advantage of a higher accessible surface area, due to their external and internal surfaces. Nanotubes can be made from various materials, such as carbon, transition metal sulfides or transition metal oxides via different synthetic routes, including hydrothermal-, template assisted-, sol-gel-, and electrochemical synthesis. The electrochemical synthesis of transition metal oxide nanotubes yields highly ordered arrays of nanotubes with tunable dimensions in a self assembly process. While the most prominent example is the synthesis of TiO2-nanotube arrays via anodization of titanium metal foils , a number of other metals, such as tungsten , zirconium , niobium  or tantalum  can be treated in similar fashion to also yield oxidic nanotubes. In this work vanadium metal foils were anodized in organic solvents using different electrolytes. Through careful optimization of the anodization conditions, e.g. adjustment of the solvent or the electrolyte, a control of the nanostructure morphology is possible. As a result, a new synthetic pathway towards highly ordered vanadium oxide nanotubes was established and is reported here for the first time, to the authors’ best knowledge. Ordered vanadium oxide nanopores are potentially useful in various applications, such as optical and electrical switching devices, catalysis, energy storage or as material for Li-Ion batteries. Since these applications depend on the composition of the oxide (VO2 vs. V2O5), a careful determination of the composition of the obtained oxide is crucial. This was performed using x-ray diffraction and x-ray photoelectron spectroscopy.  Andrei Ghicov, Patrik Schmuki, Chem. Commun., 2009, 2791-2808
9:00 PM - M6.39
Copper Sulfate Based Cathode Materials for Rechargeable Lithium Batteries.
Jonathan Schwieger 1 , Yair Ein-Eli 1 Show Abstract
1 Materials Engineering, Technion-Israel Institute of Technology, Haifa Israel
In the realm of highly attractive polyanion-type structures as high-voltage cathode materials, the sulfate group possesses an acknowledged superiority over other contenders in terms of open circuit voltage arising from the inductive effect of strong covalent S-O bonds. In parallel, novel lithium insertion mechanisms are providing alternatives to traditional intercalation, enabling reversible multi-electron processes securing high capacities. Combining both of these advantageous features, the successful electrochemical reactivity of copper sulfate pentahydrate with respect to lithium insertion is reported here.The demonstrated two-electron displacement reaction entails the extrusion of metallic copper and is shown to respond to optimization techniques, namely reductions in particle size and electrode thickness. By galvanostatic cycling and cyclic voltammetry, lithium insertion is shown to progressively evolve from a single-step process along both discharge and charge, to a full two-step process, owing to the faster kinetics at the nanometer scale. In the fully optimized scenario, this process occurs at the dual voltage of 3.2 V and 2.7 V followed by the reversible extraction of Li at 3.5 V and 3.8 V. Structural considerations reveal the crucial nature of the hydration water in copper sulfate pentahydrate in relation to its electrochemical reactivity by improving ionic diffusion thanks to a larger unit cell volume. When dehydrated to both a monohydrate and anhydrous state, the performances of the electrodes are considerably decreased.
9:00 PM - M6.4
High-voltage of LiFexMn1-xPO4/C Cathode Materials Technology for Lithium-ion Battery.
Chia-Haw Hsu 1 , Sheng-Wen Hsu 2 , Shu-Ghun You 1 , Shih-Chieh Liao 1 , Jin-Ming Chen 1 , Tai-Hung Lin 2 Show Abstract
1 , ITRI, Hsinchu Taiwan, 2 , HIROSE, Taipei Taiwan
The olivine structure cathode materials have recently received great attention, as they offer safety, high-power capability and stable cycling life, but their major disadvantages include the intrinsic insulating material and low working voltage during Li ions insertion and extraction. This investigation developed the carbon-containing LiFexMn1-xPO4 powders. First, using dispersing agent and the sand-milling technology prepared the medium precursors and used spray dryer technology to micron powders contained in the nano porous of the structure. During the sintering process at high temperature, the LiFexMn1-xPO4 structure was formed and carbon source was carbonized to form the conductive amorphous carbon to improve the electric conductivity and the nano porosity of this structure to allow for fast transport of Li ions.The composite second particles of the LiFexMn1-xPO4 cathode materials with amorphous carbon obtained good electric conductivity because of 3D conductive nano-size carbon network technology and the higher average discharge voltage due to substitute transition metal. So far, this technology applied on olivine structure to produce LiFexMn1-xPO4/C cathode materials with the capacity of 148 mAh/g and the average work voltage of 3.76 V, which is attributed to the 3D conductive network of LiFexMn1-xPO4/C resulted in the conductivity from 10-9 S/cm (LiFexMn1-xPO4 powders without coating carbon) to 10-3 S/cm and due to the 3.9~4.0 V of Mn work voltage and the 3.4~3.5 V of Fe work voltage.
9:00 PM - M6.40
High Energy Supercapacitor Based on Carbon Electrodes Operating in Conjugated Redox Couples Solutions as Electrolyte.
Krzysztof Fic 1 , Grzegorz Lota 1 , Elzbieta Frackowiak 1 Show Abstract
1 , Poznan University of Technology, Poznan Poland
Energy storage phenomenon in supercapacitors (applied in high power demanding devices as Hybrid Electric Vehicles, lifts, cranes, etc.) is generally attributed to electrical double layer charging, formed on electrode/electrolyte interface. Carbon materials, due to their well developed surface area, seem to be most promissing materials for supercapacitor electrodes. Unfortunately, capacitance revealed by these materials is still relatively small. However, if apart from double layer charging/discharging, some additional charge from faradaic reactions will be provided, the capacitance increases rapidly. This kind of additional capacitance, called pseudocapacitance, might be provided by enriching carbon materials in heteroatoms or applying carbon-transition metal oxides composites as electrode materials and assembling supercapacitor in asymmetric system. This study follows the completely novel insight on pseudocapacitance phenomenon, because an additional charge comes from electrolyte solution, not from electrode bulk. First study reported by our team concerns alkali metal iodides aqueous solution. Carbon electrodes, operating in these solutions can even reach the values of 2272 F/g (for 1 mol/L RbI solution), but supercapacitor capacitance does not exceed the value of 220 F/g, due to poor capacitance of counter electrode which determines the total capacitance of supercapacitor. Hence, huge capacitance of positive electrode remains unexploited. This work, focused on carbon electrodes with pseudocapacitive phenomena, reveals intriguing behavior of iodide/vanadyl system. These redox couples, when applied in solution as supercapacitor electrolyte, allows to exploit capacitance of positive electrode (operating in iodide solution) and significantly improve the capacitance of negative one (operating in vanadyl solution). Full electrochemical characterisation of activated carbon as well as activated carbon/multiwalled carbon nanotubes electrodes operating in conjugated redox couples solutions (1 mol/L KI and 1 mol/L VOSO4) reveals unusual capacitance values, being about 650 F/g for total system. This value significantly improves the energy of supercapacior, even to the level of 20 Wh/kg, which is the highest reported value for aqueous medium. Galvanostatic charge/discharge investigation, performed in wide range of current density (0.2 – 20 A/g) proved a good electrochemical behaviour of this capacitor. Cyclic voltammetry performed in range of scan rates 1-20 mV/s, reveals faradaic character of capacitance. Electrochemical impedance spectroscopy (100 kHz – 1 mHz) confirmed good charge propagation and small charge transfer resistance. These advantages are followed by very stable cyclability (10% of capacitance decay after 5000 charge/discharge cycles), small self-discharge and low leakage currents. Additionally, aqueous medium is much more environmental friendly and significantly cheaper than organic one, usually applied for high energy supercapacitors.
9:00 PM - M6.41
Controlled Synthesis of Nano-textured Manganese Oxides for Lithium Battery Electrodes
David Portehault 1 , Sophie Cassaignon 1 , Emmanuel Baudrin 2 , Jean-Pierre Jolivet 1 Show Abstract
1 LCMCP, UPMC, Paris France, 2 LRCS, UPJV, Amiens France
During the last years, research on lithium batteries has evolved toward nanoscaled electrode materials. Among them different oxides were reported to present new reactivities and/or improved electrochemical behavior upon Li reaction in terms of rate capabilities and reversibility when the surface area is high and the crystallite size is sufficiently decreased.Within this context, manganese oxide nanomaterials are of particular interest from a fundamental point of view to investigate structure and size effect on the electrochemical behavior owing to the richness of this family. Nevertheless, tailoring the electrode materials structure/texture remains a significant challenge. Our group develops the synthesis of manganese oxide nanoparticles by precipitation in aqueous medium at low temperature. This soft chemistry route is well known to provide a versatile control of the solid formation.This presentation is focused on a low temperature aqueous route for precipitation of Mn(IV), Mn(III) or mixed valence Mn(III)-Mn(IV) manganese (oxyhydr)oxides using MnO4- and/or Mn2+ precursors. Soft conditions permit fine tuning of the reaction path and different pure phases are obtained depending on the synthesis conditions (i.e. acidity, oxidation state, temperature and aging). In particular, nanowires of cryptomelane K0.11MnO1.85(H2O)0.75, manganite γ-MnOOH and pyrolusite β-MnO2 are formed through self-assembly or topotactic processes, while γ-MnO2 hollow nanocones originate from heterogeneous oriented attachment. In parallel, heterogeneous nucleation or heteroepitaxy can be controlled in order to obtain hierarchical nanoheterostructures such as core-corona architectures of lamellar birnessite K0.19MnO1,77(H2O)0.30 or cryptomelane-birnessite nanocomposites. Soft chemistry is therefore a valuable tool to investigate and to control nucleation-growth processes, as well as the resulting morphological characteristics.Using these well-defined structures, shapes, sizes and hierarchical orders, some effects of the nanoscale on the electrochemical properties versus lithium are emphasized.
9:00 PM - M6.5
Electrochemical Performance of Li2MnSiO4/C Prepared by Microwave Assisted Sol-gel Process.
Won-Bin Im 1 2 , Won-Young Chang 1 , Byung-Won Cho 1 , Hee Rak Choi 2 , Hae Yong Jeong 2 , Kyung Yoon Chung 1 Show Abstract
1 Advanced Battery Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Division of Advanced Materials Science and Engineering, Pukyoung National University, Seoul Korea (the Republic of)
Recently, the application field of the lithium secondary batteries expanded rapidly to the various fields including portable electronic devices, electric vehicles, and energy storages. Those applications require the secondary batteries with better abuse tolerances and higher specific capacities. Currently, most of the commercialized lithium secondary batteries use cobalt based materials as a cathode material. However, alternative cathode material needs to be developed to meet the demands for the large scale batteries. Among the many candidates, silicate based materials are one of the very attractive cathode material candidate because their theoretical specific capacities are over 300 mAh/g and they are expected to be abuse tolerable. However, it suffers from very poor cycle performance and rate performance due to intrinsically very low electronic conductivity.In this study, we have synthesized the Li2MnSiO4 and tried to improve the electronic conductivity by means of using microwave assisted sol-gel process and in situ carbon coating using sucrose as a precursor. Their electrochemical performances and structural variations during charging and discharging will be presented. The details will be discussed at the meeting.
9:00 PM - M6.6
Atomic Layer Deposition (ALD) of V2O5 for Electrochemical Energy Storage in Nanostructures.
Xinyi Chen 1 2 , Parag Banerjee 1 2 , Keith Gregorczyk 1 2 , Laurent Henn-Lecordier 3 , Gary Rubloff 1 2 4 Show Abstract
1 Department of Material Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 , Institute for Systems Research, University of Maryland, College Park, Maryland, United States, 3 , Cambridge Nanotech Inc., Boston, Massachusetts, United States, 4 Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland, United States
Electrical energy storage devices are becoming increasingly smaller in order to take advantage of highly increased interfacial areas and shortened charge carrier transportation distances. The unprecedented capabilities of atomic layer deposition (ALD) in terms of uniformity and conformality offer new opportunities in engineering novel nanostructured devices. V2O5 thin films are of particular interest in electrochemical systems and were grown using ALD. The precursors used were vanadyl triisopropoxide (VTOP) and water which gave a growth rate ~0.28 A/cycle and excellent thickness uniformity (>95%) across 4” wafers. Their structural, chemical and electrochemical properties were studied. A low temperature deposition process (<150oC) was used and the as-deposited V2O5 films were amorphous as confirmed by x-ray diffraction and Raman spectroscopy. Rapid thermal annealing above 450oC in oxygen easily crystallizes the films to the orthorhombic phase, although different orientations are present depending on the substrate used i.e., ITO or Si. X-ray photoelectron spectroscopy (XPS) shows that the as-deposited films include ~10% V4+, while the annealed films only contain V5+. The as-deposited films and the annealed films demonstrate dramatically different electrochemical properties. Cyclic voltammograms show a distinct difference between the as-deposited and the annealed films. Specifically we find the as-deposited films show capacitor-like behavior with specific capacitance of 372F/g, while the annealed films show battery-like behavior, with two strong peaks indicating phase transitions. Furthermore, galvanostatic measurements show that the as-deposited films exhibit higher specific capacity (190 mAh/g) than the annealed films (50 mAh/g). Both the as-deposited films and the annealed films show fast lithiation rates and good cyclability. Finally, we have investigated the growth of ALD V2O5 in high aspect ratio porous anodic aluminum oxide membranes. Initial results show penetration of the ALD film to ~35 um into 200 nm diameter pores. Furthermore, conformality is improved using O3 as the oxidant, rather than water. Overall, these results indicate that the ALD V2O5 films are good candidates for use in electrochemical nanostructures for electrical energy storage, with the possibility of high power and high energy density.
9:00 PM - M6.7
LiFePO4 Cathodes for Rechargeable Li-ion Batteries by Plasma Spray Deposition.
Satish Chikkannanavar 1 , Nick Moroz 1 , Xuan Zhou 1 , Harishankar Umapathy 1 , Pravansu Mohanty 1 Show Abstract
1 Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, MI, Michigan, United States
Li based rechargeable batteries hold great potential for energy storage applications. Over recent years important advances have been reported on the synthesis, control of microstructure and electrochemical performance of the cathode materials based on LiFePO4. There is a need to further improve the process for electrode fabrication in terms of cutting down the ingredient sub-processes and also reduce the process cost. An approach which could afford simultaneous synthesis and deposition of cathodic films hold a great promise for industry. In this regard we have explored the solution plasma spray (SPS) deposition technique for synthesis of cathodic films of LiFePO4. We have successfully demonstrated the deposition of binderless LiFePO4 films using this approach. These films show the desired microstructure and electrochemical performance. The films consist of nanoparticles in the size range 50-80 nm and are uniformly coated with carbon. The cyclic voltammetry studies indicate the faster kinetics during Li insertion and extraction due to nanosized particles. The charge-discharge studies so far indicate that the films show capacity in the range of 60-70% of theoretical capacity. Considering the unique capabilities of SPS method, such as atmospheric environment, high throughput and large area deposition, it holds great potential for industrial applications.
9:00 PM - M6.8
Synthesis, Characterization, and Electrochemical Performance of Nanostructured TiO2 Battery Anode Material.
Kyung-Ho Lee 1 , Young-San Bae 1 , Seung-Wan Song 1 Show Abstract
1 , Chungnam National University, Daejeon Korea (the Republic of)
TiO2 is one of the attractive anode materials in rechargeable lithium batteries, which shows the plateau of lithium insertion and extraction near 1.8 V vs. Li/Li+ and stable electrochemical performance. The electrochemical performance of TiO2 tends to strongly depend on the crystal structure, nanostructure, particle size and shape. We synthesized nanostructured anatase TiO2 powders using a simple one-step hydrothermal method in aqueous solution without post-annealing, using minerallization agents and pH control. Scanning and transmission electron microscopic imaging revealed that rice shaped primary nanoparticles are oriented to the (101) plane, which appear to be favored for enlarged interfacial area with electrolyte and high structural stability upon extended or high-rate cycling, respectively. In this presentation, we report synthesis, structural characterization, and electrochemical performance of nanostructured TiO2 battery anode material in various electrolytes.
9:00 PM - M6.9
Synthesis of Nanocomposite Powders in Fe2O3-Mg, Ti System Induced by Mechanical Alloying.
Chung-Hyo Lee 1 , Kwang-Duk Kim 1 , Han-Woong Kim 1 Show Abstract
1 Mat.Sci. & Eng., Mokpo National University, Muan Korea (the Republic of)
Mechanical alloying(MA) has been recognized as a powerful method to prepare metastable crystalline, amorphous phases and nano-structured alloys through solid-state reaction under intense mechanical deformations. Also, it has been found that MA facilitates the formation of metal-metal oxide nanocomposites through solid-state reduction of metal oxide by a more reactive metal. In the present work, we report the magnetic nanocomposite formation by MA a mixture of Fe2O3-M (M=Mg, Ti) powders, where pure metals are used as reducing agents. The effects of different reducing agent on the solid-state reduction and the formation of nanocomposite powder have been investigated by structural analysis and magnetic measurements. Magnetic measurement supports the characterization of the solid-state reduction between metal and metal oxide due to MA process: it can be used to obtain the information on magnetic phase composition and microstructure of nanocomposite powders. Acknowledgements Following are results of a study on the "Human Resource Development Center for Economic Region Leading Industry" Project, supported by the Ministry of Education, Science & Technology(MEST) and the National Research Foundation of Korea(NRF).
Anne Dillon National Renewable Energy Laboratory
Se-Hee Lee University of Colorado-Boulder
Ping Liu HRL Laboratories
Bruce Dunn University of California-Los Angeles
Yimei Zhu Brookhaven National Laboratory
M10: Electrochemical Capacitors I
Friday AM, April 29, 2011
Room 2009 (Moscone West)
9:00 AM - **M10.1
High-performance Electrochemical Capacitors Enabled by Metal-oxide-decorated Carbon Nanoarchitectures.
Megan Sassin 1 , Jeffrey Long 1 , Azzam Mansour 2 , Steven Greenbaum 3 , Jean Marie Wallace 1 4 , Katherine Pettigrew 1 4 , Debra Rolison 1 Show Abstract
1 Code 6170, Surface Chemistry Branch, U.S. Naval Research Laboratory, Washington, District of Columbia, United States, 2 Systems and Materials for Power and Protection Branch, Naval Surface Warfare Center–Carderock Division, West Bethesda, Maryland, United States, 3 Department of Physics and Astronomy, Hunter College of the City University of New York, New York, New York, United States, 4 , Nova Research Inc., Alexandria, Virginia, United States
Carbon nanofoams are attractive plug-and-play electrode substrates for electrochemical capacitors and batteries due to such desirable properties as high specific surface area, electrical conductivity, and through-connected pore structure, but their reliance on double-layer capacitance for charge storage ultimately limits the energy density of the resulting devices. We have developed self-limiting deposition methods to incorporate conformal, nanoscale metal oxide (MnOx, LiMn2O4, TiO2, or FeOx) coatings throughout the macroscopic thickness (70–300 μm) of pre-formed carbon nanofoams as a means to substantially increase the charge–storage capacity through pseudocapacitance–based reactions, without significantly altering the high-rate capabilities of the carbon nanofoam. Incorporation of these nanoscale metal oxides increases the mass–, geometric–, and volume–normalized capacitance (2–to–10 fold) relative to the unmodified carbon, and the nanoscopic morphology of the oxide coating enables charge–storage capacities that exceed those typically observed in conventional powder-composite electrode structures. Prototype aqueous asymmetric electrochemical capacitors comprising a MnOx-carbon positive electrode and an FeOx-carbon negative electrode provide operating voltages approaching 2 V. The increased operating voltage and the 3D nanoarchitectural electrode design result in cell-level specific capacitance >30 Fg-1 and an energy density of 13.5 Whkg-1 that can be delivered within a <10–s charge–discharge timeframe, while also maintaining the cost and safety advantages associated with the use of a moderate-pH aqueous electrolyte. En route to high-performance electrochemical capacitors we also apply various spectroscopic tools to investigate the fundamental electrochemical charge-storage mechanisms of these nanostructured materials.
9:30 AM - M10.2
Effect of Electrodeposition Conditions on the Electrochemical Capacitive Behavior of Synthesized Manganese Oxide Electrodes.
Banafsheh Babakhani 1 , Douglas Ivey 1 Show Abstract
1 Cemical and Materials Eng., University of Alberta, Edmonton, Alberta, Canada
Electrochemical capacitors are currently receiving significant attention, since they are extremely useful as energy storage devices in systems requiring quick bursts of energy such as portable electronic devices. Manganese-based oxide electrodes store electrochemical energy by simultaneous injection of electrons and charge-compensating cations, as with other electroactive transition metal oxides. Therefore, they are potentially useful for charge storage applications such as electrochemical capacitors in aqueous electrolytes.In this study, the electrochemical capacitive behavior of nanocrystalline manganese oxide electrodes are investigated to determine the effect of morphology, chemistry and crystal structure on the corresponding electrochemical behavior of synthesized electrodes. Manganese oxide electrodes are synthesized by anodic deposition on Au coated Si substrates from acetate-containing aqueous solutions. By changing the deposition parameters including deposition current density, electrolyte composition and pH, deposition time and temperature, a series of nanocrystalline manganese oxide electrodes with various morphology (equiaxed and fibrous features, rod-like structures and interconnected rods) and different crystal structures is obtained. Detailed microstructural characterization of as-deposited and cycled electrodes is conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical behavior (specific capacitance and electrochemical cyclability) are investigated by cyclic voltammetry. The experimental results show that manganese oxide electrodes, with rod-like and interconnected structures, exhibit enhanced electrochemcial performance by improving manganese oxide utilization.
9:45 AM - M10.3
The Roles of Material Structure and Morphology on the Pseudocapacitance of Niobium Pentoxide.
Veronica Augustyn 1 , Jong Woung Kim 1 , Thomas Quickel 2 , Sarah Tolbert 2 , Bruce Dunn 1 Show Abstract
1 Materials Science & Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Chemistry & Biochemistry, University of California, Los Angeles, Los Angeles, California, United States
Fast, reversible energy storage can be accomplished through the use of pseudocapacitive materials, which, when coupled with an electrolyte, store energy through redox reactions that occur within a few layers of the electrode’s surface. Recently, films of well-ordered mesoporous niobium pentoxide have shown excellent capacitive storage behavior, demonstrating a further need to understand materials properties, beyond the well-known surface area effect, that influence the pseudocapacitive behavior . Through the synthesis of niobium pentoxide nanocrystals, aerogels, and mesoporous films, we have been able to investigate the relationships between pseudocapacitance and crystal phase, crystallite size, preferred orientation and porosity.In the research reported here, we characterized the kinetic behavior of the various forms of niobium pentoxide and determined the role of capacitive processes in the overall charge storage mechanism. These results have enabled us to better understand the nature of the redox reactions taking place. Cyclic voltammetry at various sweep rates is used to differentiate between capacitive and diffusion-controlled charging processes in an electrode material. The electrochemical behavior of crystalline niobium pentoxide is characterized by a large current response in the 1 to 2 V region (vs. Li/Li+). Differences arise in the number and shape of the redox peaks as well as the cyclability. These differences are related to both the original crystal structure, which dictates the types of sites available for redox reactions, as well as to the porosity, which determines the ability for the ions to access the sites. To understand further the redox mechanism, x-ray photoelectron spectroscopy was performed at various points during the charging and discharging process. In particular, the binding energy of the niobium 3d electrons was probed in order to determine the niobium oxidation state during electrochemical cycling. K. Brezesinski, J. Wang, J. Haetge, C. Reitz, S. O. Steinmueller, S. H. Tolbert, B. M. Smarsly, B. Dunn, and T. Brezesinski. J. Amer. Chem. Soc. 132 (2010) 6982.
10:00 AM - M10.4
Nanocomposite Materials Based on Conducting Polymers and Carbon/Silicon Nanostructures for Ultracapacitor Applications.
Siu-Tung Yau 1 , Qiang Liu 1 , Osama Nayfeh 2 , Munir Nayfeh 3 Show Abstract
1 , Cleveland State University, Cleveland, Ohio, United States, 2 , US Army Research Laboratory, Adelphi, Maryland, United States, 3 , University of Illinois at Urbana-Champaignoratory, Urbana, Illinois, United States
Nano-composite materials formed by dispersing carbon- or silicon-based nanomaterials, including ultrasmall (2.8 nm) silicon nanoparticles, carbon nanotubes, and graphene, in polyaniline have been prepared and used as electrode materials for constructing ultracapacitors. Electrochemical characterization of electrodes made of the composite materials indicated that polyaniline produces pseudocapacitance while the nanomaterials give rise to double-layer capacitance. The composite materials showed significantly improved capacitance compared to that of pure polyaniline. The specific capacitances were found to be 85.07F/g and 409.27F/g for the polyaniline electrode and the composite electrode, respectively. Charging/discharging cycling measurements showed that the capacitor remained stable for at least 1000 cycles. We have constructed flexible ultracapacitors by painting sheets of flexible plastic electrolyte with the composite materials. We have observed the effects of the constituents of the composite materials on the performance of the capacitor. Charging/discharging measurements showed that the operating voltage of the supercapacitors can be increased with increasing amounts of carbon nanotubes in the composite material. Ragone plots were obtained to show the energy-storage and power capabilities of the capacitor sheets. Stacks of the capacitor sheets were used to light up a system of light-emitting diodes.  Q. Liu, M. H. Nayfeh and S.-T. Yau “Supercapacitor electrodes based on polyaniline–silicon nanoparticle composite” Journal of Power Sources 195, 3956-3959 (2010). Q. Liu, M. H. Nayfeh and S.-T. Yau, “Brushed-on flexible supercapacitor sheets using a nanocomposite of polyaniline and carbon nanotubes”, Journal of Power Sources 195, 7480–7483(2010)
10:15 AM - M10.5
High Performance Supercapacitors Based on Intertwined CNT/V2O5 Nanowire Nanocomposites.
Zheng Chen 1 , Veronica Augustyn 2 , Dunn Bruce 2 , Yunfeng Lu 1 Show Abstract
1 Department of Chemical and Biomolecular Engineering, University of California , Los Angeles, California, United States, 2 Department of Materials Science and Engineering, University of California , Los Angeles, California, United States
An ideal electrical energy storage device provides both high energy and power density. Supercapacitors exhibit significantly higher power densities compared to batteries and would be excellent candidates for numerous electronic devices and industrial applications if their energy density could be improved. The most commonly used electrode material (porous carbon) generally possesses double layer capacitances of around 100 F g-1, which can provide a specific energy density up to 25 Wh kg-1 in an organic-electrolyte based symmetric device. Somewhat greater energy densities can be reached as specific capacitances of up to 150 F g-1 with carbide-derived carbon have been reported. By comparison, transition-metal oxides possess significantly higher specific capacitance via pseudocapacitance. Thus, an asymmetric supercapacitor consisting of a carbon cathode and an oxide anode may provide a significantly higher energy density than symmetric capacitors based on carbon. Nevertheless, building such high-energy density asymmetric devices has been highly challenging, mainly due to the kinetics of the pseudocapacitive electrode. In order to minimize the kinetic limitations, most of the pseudocapacitive electrodes made today are limited to sub-micron thin films.[8,12-15] Since the electrochemically inert components of a supercapacitor, including the current collectors, separator, and packaging, account for a large fraction of the total weight of the device, the use of thin electrodes results in a significantly lower energy density than what could be attained using thicker electrodes. Therefore, the development of thick electrodes for supercapacitors presents an intrinsic advantage for making high-energy supercapacitors for practical applications. Herein, we report the fabrication of high energy-density asymmetric supercapacitors containing thick-film electrodes (over 100 μm thick) of our CNT/V2O5 nanowire composite. The excellent conductivity, high specific capacitance, and large voltage window of the CNT/V2O5 nanocomposite enable the fabrication of devices with an energy density as high as 40 Wh kg-1 at a power density of 210 W kg-1. Even at a high power density of 6300 W kg-1, the device possesses an energy density of 6.9 Wh kg-1. Moreover, the resulting devices exhibit excellent cycling stability. This work demonstrates that the nanowire composite approach is an effective strategy towards high-energy and high-power density supercapacitors.
11:00 AM - **M10.6
High-energy Density Microporous Carbons Film for Capacitive Storage Applications.
Patrice Simon 1 , P. Huang 1 2 , P. Taberna 1 , D. Pech 2 , M. Brunet 2 , M. Heon 3 , Y. Gogotsi 3 Show Abstract
1 , Paul Sabatier University, Toulouse France, 2 CNRS, LAAS, Universite de Toulouse, Toulouse France, 3 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Supercapacitors, also called electric double layer capacitors (EDLC), store energy in two closely spaced layers with opposing charges and offer fast charge/discharge rates and the ability to sustain millions of cycles. They can complement or even replace batteries in specific applications where high power and long cycle life are needed . This is also true in electronics and power electronics applications, where small-size devices are needed, and there are today numerous applications where high power delivery is needed at small scale (MEMS and sensors for instance) highlighting the need for developing micro-supercapacitor systems [2,3].In this paper, we report the recent results obtained about the development of high energy density films based on Carbide Derived Carbons. Metal carbide (TiC) films were sputtered onto various substrates, including Si wafer. After chlorination process to remove the Ti, bulk microporous films were obtained, with fine-tuned pore size and pore size distribution . Electrochemical characterizations of these films were achieved in aqueous and organic electrolytes and volumetric capacitance as high as 180 F.cm-3 could be obtained for thin-films (~1 µm). Optimization of the film synthesis conditions is expected to lead to further increase in capacitance and response rate, resulting in an increase in both, energy and power density. These results pave the way to the development of new, high energy density micro-supercapacitors that can be used for high power (discharge) and energy harvesting (charge) applications.References: Materials for Electrochemical Capacitors: Building a Battery of the FutureP. Simon and Y. Gogotsi, Nature Materials, 7 (2008) 845-854. Elaboration of a microstructured inkjet-printed carbon electrochemical capacitorD. Pech, M. Brunet, P.L. Taberna, P. Simon, N. Fabre, F. Mesnilgrente, V. Conédéra and H. Durou Journal of Power Sources 195 (2010) 1266-1269. Monolithic Carbide-Derived Carbon Films for Micro-SupercapacitorsJ. Chmiola, C. Largeot, P.-L. Taberna, P. Simon, Y. Gogotsi, Science 328 (2010) 380-383. Continuous carbide-derived carbon films with high volumetric capacitanceM. Heon, S. Lofland, J. Applegate, R.Nolte, E. Cortes, J. D. Hettinger, P.-L. Taberna, P. Simon, P. Huang, M. Brunet and Y. Gogotsi, Energy and Environmental Science (2010), in press.
11:30 AM - M10.7
Graphene Aerogels for Energy Storage.
Marcus Worsley 1 , Michael Stadermann 1 , Monika Biener 1 , Matthew Suss 1 3 , Klint Rose 1 , Tammy Olson 1 , Peter Pauzauskie 2 , Juergen Biener 1 , Joe Satcher 1 , Theodore Baumann 1 Show Abstract
1 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Department of Mechanical Engineering, Stanford University, Palo Alto, California, United States, 2 Department of Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Graphene has shown the potential to significantly impact a number of different technologies, including energy storage. Properties such as high surface areas and electrical conductivity make it a promising material for hydrogen storage, battery, and ultra capacitor applications. One route to realizing the full potential of graphene in energy storage applications is the assembly of three-dimensional macroscopic graphene networks that retain the properties of individual graphene sheets. Herein we present a class of graphene-based aerogels that represent significant step toward realizing the properties of individual graphene sheets in a macroscopic monolith. These graphene aerogels possess high electrical conductivities, and surface areas that approach the theoretical value expected for a single graphene sheet. In addition, the mesopore volumes observed are among some of the highest reported to date. The impact of these graphene-based aerogels on energy storage applications (e.g. electrical, hydrogen) will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the DOE Office of Energy Efficiency and Renewable Energy.
11:45 AM - M10.8
Graphene Based Materials for Ultracapacitors.
Yanwu Zhu 1 , S. Murali 1 , M. Stoller 1 , A. Velamakanni 1 , R. Piner 1 , D. Dreyer 2 , P. Valle-Vigon 3 , S. Park 1 , J. An 1 , D. Chen 1 , W. Cai 1 , C. Morales 1 , A. Fuertes 3 , C. Bielawski 1 , R. Ruoff 1 Show Abstract
1 Mechanical Engineering, UT Austin, Austin, Texas, United States, 2 Chemistry, UT Austin, Austin, Texas, United States, 3 , Instituto Nacional del Carbon, Oviedo Spain
With high pulse power and long cycle lifetimes, electrical double-layer capacitors (EDLC, also called ‘ultracapacitors’ or ‘supercapacitors’) are used for energy recapture, storage, and delivery. Graphene materials can have high surface area and electrical conductivity, making them candidates for use in energy storage applications, including ultracapacitors.1 Obtaining graphene-based materials from graphite oxide is one route to the potential large-scale production of electrode materials. A variety of methods have been developed in our group to obtain graphene-based materials. Chemically reduced graphene oxide was obtained by dispersing graphite oxide in water (thus generating dispersed graphene oxide platelets) followed by chemical reduction with hydrazine. When this carbon was used as electrode material, capacitance values of 135 and 99 F/g were obtained from KOH and organic electrolytes, respectively.2 By simply heating the graphene oxide dispersed in propylene carbonate at 150 oC, reduced graphene oxide with a powder conductivity value of 5230 S/m was obtained and this material yielded 120 F/g in organic electrolytes.3 By microwave irradiation of graphite oxide in a commercial microwave oven,4 we have obtain microwave exfoliated graphite oxide (MEGO) material composed of crumpled, few layer thick and conductive ‘graphitic’ sheets. Using MEGO as electrodes in ultracapacitor cells, high capacitances up to 190 F/g has been demonstrated in KOH electrolyte. In addition, we have investigated the ultracapacitor performance of some novel carbon materials in ionic liquids for the improved energy density. We found that a porous carbon capsule material with a high surface area (1500 m2/g), high conductivity (330 Sm-1), and high carbon purity (90 wt%) has good compatibility with several room-temperature ionic liquids.5 A high specific capacitance of up to 134 F/g working at 2.7 V has been obtained by charge-discharge measurement at a constant current of 1 A/g. Recently, by using a novel carbon derived from graphite, we have been able to further increase the BET surface area to ~2500 m2/g and maintain a reasonably high electrical conductivity in commercial ionic liquids, yielding both a high energy and power density.1.Zhu, Y.; Murali, S.; Cai, W.; Li, X.; Suk, J. W.; Potts, J. R.; Ruoff, R. S., Advanced Materials 2010, 22 (35), 3906-3924.2.Stoller, M. D.; Park, S. J.; Zhu, Y. W.; An, J. H.; Ruoff, R. S., Nano Letters 2008, 8 (10), 3498-3502.3.Zhu, Y.; Stoller, M. D.; Cai, W.; Velamakanni, A.; Piner, R. D.; Chen, D.; Ruoff, R. S., Acs Nano 2010, 4 (2), 1227-1233.4.Zhu, Y.; Murali, S.; Stoller, M. D.; Velamakanni, A.; Piner, R. D.; Ruoff, R. S., Carbon 2010, 48, 2118-2122.5.Murali, S.; Dreyer, D. R.; Valle-Vigón, P.; Stoller, M. D.; Zhu, Y.; Morales, C.; Fuertes, A. B.; Bielawski, C. W.; Ruoff, R. S., 2010, submitted to Energy and Environmental Science
12:00 PM - M10.9
Modeling of Nanocarbon Ultracapacitor.
Antonis Orphanou 1 , Toshishige Yamada 1 , Cary Yang 1 Show Abstract
1 Center for Nano-Structures, Santa Clara University, Santa Clara, California, United States
Until recently, efforts to enhance the energy storage capability of a capacitor have primarily focused on the increase in the capacitor’s surface area. By introducing a “forest” of nanotubes as an electrode, the capacitance can increase by as much as 50% compared to conventional technology . Adding an electrolyte solution will also increase the capacitance significantly . However, the nanotube forest and the electrolyte ions create a complicated electric field inside the capacitor, making it challenging to elucidate the resultant electrolyte ionic motion in the capacitor operation. To meet this challenge, we have successfully calculated the electric field in a nanocarbon ultracapacitor (NU) using the molecular-dynamic technique . Our approach requires placing the electrolyte ion charges around each nanocarbon electrode and letting them interact with one another and the electrode through the Coulomb force. Assuming the electrode surface is equipotential regardless of its shape, we have determined the minimum-energy configurations under various applied voltage conditions. We have further developed our software code to compute capacitance-voltage characteristics, which compare well with previously reported Nyquist plots for NUs . Our work represents the first application of a particle-motion-tracking simulation method to study ionic behavior in an electrolyte-electrode system. We will present results on the optimized nanotube density and length-diameter ratio determined by our simulation method. J. Schindalls, “The charge of ultracapacitors,” IEEE Spectrum, Nov (2007).T. Yamada and D. K. Ferry, Phys. Rev. B 47, 6416 (1993). E. Frackowiak, K. Metenier, V. Bertagna, and F. Beguin, Appl. Phys. Lett. 77, 2421 (2000).
12:15 PM - M10.10
VN Nanorods as a Promising Electrode Material for Electrochemical Supercapacitors.
Ying Chen 1 , Alexey Glushenkov 1 Show Abstract
1 Institute for Technology Research and Innovation, Deakin University, Waurn Ponds, Victoria, Australia
Nanocrystalline vanadium nitride (VN) has been proposed as a promising material for electrochemical supercapacitors. It could deliver a specific capacitance of 1340 F/g in 1M KOH aqueous electrolyte when a thin film of it (0.25 mg/cm2) was assessed by cyclic voltammetry at a scan rate of 2 mV/s. The impressive performance of the material has been attributed to the combination of high metallic electronic conductivity of vanadium nitride and redox reactions provided by few atomic layers of vanadium oxides or oxynitrides on the surface of the material. We have recently investigated the structure and capacitive properties of porous particles of VN synthesized by NH3 reduction of V2O5 powders. It has been observed that the VN particles produced from V2O5 possess capacitive properties and have an acceptable rate capability in three aqueous electrolytes - 1M H2SO4, 1M KOH, and 3M NaCl solutions. They demonstrate about 80 % of their maximal capacitance at the current rate of 1 A/g in galvanostatic charging/discharging experiments in all of the above electrolytes. The negative effect of material loading on the value of capacitance of VN is also suppressed: thick films of VN can retain high capacitances. The electrochemical properties of nanoporous VN nanorods produced by temperature-programmed NH3 reduction of V2O5 nanorods are assessed in the same three types of aqueous electrolytes. The performance of VN nanorods is compared with that of VN particles mentioned above. The use of VN nanorods in nanostructured binder-free electrodes of a special design is suggested as the most efficient way of applying this type of nanomaterials in electrochemical supercapacitors.
12:30 PM - M10.11
Molecular Simulations of Graphene-based Electric Double-layer Capacitors.
Raja Keerthi Kalluri 1 , Alberto Striolo 1 Show Abstract
1 School of Chemical, Biological and Materials Engineering, The University of Oklahoma, Norman, Oklahoma, United States
Towards deploying renewable energy sources (e.g., solar and wind) it is crucial to develop efficient and cost-effective technologies to store energy. Traditional batteries have been used successfully, but they are plagued by a number of practical problems that at present limit their widespread applicability. One possible solution is represented by electric double-layer capacitors (EDLCs), also known as super-capacitors.When compared to traditional batteries, EDLCs are typically characterized by unusually high energy density, but unfortunately are plagued by relatively low working voltage. It has been shown by careful experimental investigations that using an appropriate nanoporous material (typically activated carbons, although significant attention is being devoted to carbon nanotubes) it is possible to further improve the storage density. Because of large surface area and because they offer the possibility of controlled hierarchical three-dimensional structures, graphene sheets hold the promise of providing the core material for developing the next generation of EDLCs. The working voltage can be adjusted by appropriately selecting the charge-carrying fluid placed within the porous material (a considerable amount of research is considering ionic liquids for such purposes). However, the structure and dynamics of confined charged systems are not well understood, thus limiting the possibilities available to EDLCs.We present here our recent simulation results for the structure and dynamics of concentrated aqueous solutions of NaCl, CsCl, and NaI confined within charged graphene-based porous materials. We will discuss how the structure of confined aqueous mixtures, the salt concentration, the ions size, and the surface charge density, and the pore-network structure determine the accumulation of electrolytes within the porous network. Multi-scale simulations will be presented in an attempt to develop models for entire charge-discharge cycles. Our results are critical for relating macroscopic observations to molecular-level properties of the confined working fluids.
12:45 PM - M10.12
Templated Hybrid Nanostructures for Electrical Energy Storage.
Erik Spoerke 1 , Erica McCready 1 , David Wheeler 1 , Mark Roberts 1 , Michael Brumbach 1 , Bruce Bunker 1 2 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Center for Integrated Nanotechnologies, Albuquerque, New Mexico, United States
Resolving the growing disparity between materials capabilities and global electrical energy storage demands will require new materials solutions that integrate multimaterials across multiple length scales. We describe here the synthesis, characterization, and electrochemical performance of a series of hierarchically templated organic/metal oxide hybrids potentially applicable as electrodes in ultracapacitors or lithium ion batteries. Our synthetic strategy utilizes both functional organic and inorganic templates to create mesoporous electroactive nanocomposites exhibiting emergent electrochemical behaviors. More specifically, we have learned to make unique templated mixed transition metal oxides of ruthenium/niobium oxide and molybdenum/niobium oxide with porosity across multiple length scales. While amphiphilic organic templates provide mesoporous character in the oxides, inorganic templates, like zinc oxide, provide submicron porosity to the hybrid materials. Both levels of porosity are shown to enhance electrochemical behavior. In addition to introducing porosity in these materials, however, the templates themselves can be used to tailor composite properties such as electrical conductivity, ionic conductivity, or even redox activity. For example, by varying the chemistry of the organic amphiphiles or introducing secondary organic phases, such as conductive polymers, to these systems we find we can elicit enhanced, composite electrochemical performance from these hybrid materials. These types of materials, in which nanostructured morphology and multiple functional components are cooperatively integrated, may play key roles in the development of next generation energy storage systems. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
M11: Electrochemical Capacitors II
Friday PM, April 29, 2011
Room 2009 (Moscone West)
2:30 PM - **M11.1
Onion-like Carbon Electrodes for Electrochemical Capacitors.
Yury Gogotsi 1 , John McDonough 1 , Volker Presser 1 , Vadym Mochalin 1 , Pierre-Louis Taberna 2 , Patrice Simon 2 Show Abstract
1 Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 , Université Paul Sabatier, Toulouse France
Electrochemical capacitors, also called supercapacitors, are used to capture, store and deliver energy. Their electrostatic charge storage in a double-layer leads to fast charge/discharge rates and to the ability to sustain millions of cycles. It is frequently stated that supercapacitors bridge the gap between batteries and electrolytic (“conventional”) capacitors, but contemporary devices have a lower specific energy than Li-ion batteries and are much slower than electrolytic capacitors. It has been shown that nanostructured carbon onions of 6-7 nm in diameter exhibit a much higher volumetric capacitance and about the same specific power as electrolytic capacitors. Moreover, observed discharge rates up to 200 V/s are about three orders of magnitude higher than conventional supercapacitors. Carbon onion-based electrodes show time constants in the 10-20 ms range, compared to seconds for conventional supercapacitors. This breakthrough in terms of power densities emphasizes the synergetic benefit of integrating carbon nanoparticles in micro-devices characterized by a high surface to volume ratio without the use of organic binders and polymer separators. This approach holds the key to fundamental advances in electrical energy storage and to integration in harvesting systems. Electrochemical micro-capacitors with activated carbons exhibit an energy density of 10-2 Wh/cm3 (10 Wh/L), and with the use of OLC, a maximum power density 100 times higher, close to 1 kW/cm3. This paper will describe the structure and electrochemical properties of carbon onions as a function of the synthesis temperature. The results of testing in aqueous and organic electrolytes will be presented.
3:00 PM - M11.2
Dielectric Properties of 0-3 Metal or Ceramic-polypropylene Nanocomposites for Pulse-power Capacitor Applications.
Lisa Fredin 1 2 , Zhong Li 1 , Mark Ratner 1 2 , Tobin Marks 1 2 Show Abstract
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Materials Research Science and Engineering Center, Northwestern University, Evanston, Illinois, United States
Aluminum oxide encapsulated high dielectric constant (k) ceramic and metallic nanoparticles with chemisorped metallocene catalyst [rac-ethylenebisindenyl]zirconium dichlororide (EBIZrCl2) affords 0–3 particle-polypropylene nanocomposites via in situ polyermerization. The in situ polymerization yields homogeneous dispersed nanoparticles in the polyolefin matrix. Electrical measurements show that as the concentration of the filler nanoparticles increases the effective dielectric constant of the nanocomposites increases with k values reaching as high as 15.4. The effective permittivites of ceramic composites can be predicted by the Maxwell-Garnett formalism using effective medium theory for volume fractions (νf) of nanoparticles below 0.06; whereas, the high contrast in the dielectric constant of metal (k ~ ∞) or very high-k ceramic (k > 2000, like BaTiO3) particles and the polymer matrix (polypropylene k ~ 2.25) causes the composite to be percolative. Thus the dielectric constant of these composites is best described by the percolation law for two phase composites. These nanocomposites have leakage current densities of ~ 10-7–10-9 A/cm2 at electrical field of 105 V/cm, and very low dielectric loss in the frequency range of 100 Hz–1 MHz. These composites have energy storages up to ~ 7 J/cm3 with relatively low loss even at applied fields up to 1 MV/m.
3:15 PM - M11.3
High Capacity Supercapacitors Electrodes from Carbon Nanotubes - Vanadium Oxide Nanostructures by Supercritical Fluid Deposition.
Quyet Do 1 2 , Changchun Zeng 1 2 , Chuck Zhang 1 2 , Ben Wang 1 2 Show Abstract
1 High Performance Materials Institute, Florida State University, Tallahassee, Florida, United States, 2 Industrial & Manufacturing Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida, United States
Multi-walled carbon nanotubes – vanadium oxide nanostructures were fabricated by supercritical fluid deposition. Vanadium (III) acetylacetonate was dissolved in supercritical carbon dioxide and adsorbed on multiwall carbon nanotubes buckypaper. Subsequent oxidized in air leads to the formation of CNTs – vanadium oxide composite with a thickness of the oxide layer about a few atomic layers. The vanadium oxide shows amorphous structure with an excellent uniformity. The nanostructured electrodes exhibit high electrochemical performance. From cyclic voltametry measurement in KCl aqueous solution, constant pseudo-capacitance of more than 1000 F/g - active mass was observed for vanadium oxide loading up to 6.4 %, at a scan rate as high as 100 mV/s.
4:00 PM - M11.4
Electrical Energy Storage Performance of Poly(triarylamine-thiophene) Electrodes.
Mark Roberts 1 , David Wheeler 2 , Bruce Bunker 2 Show Abstract
1 Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Supercapacitors are electrical energy storage devices combining the high power, rapid switching, and exceptional cycle life of a capacitor with the high-energy density of a battery. Power sources based on supercapacitors are emerging as a preferred option for applications requiring short power pulses, particularly when combined with conventional batteries. In order to maximize capacitance, switching speed, and power, materials for supercapacitors need to incorporate conductive and redox-active materials into high surface area structures that are engineered to provide intimate contact between the redox sites and the electrolyte. Conducting polymer are well-suited to address these challenges owing to the myriad of synthetic and processing methods which result a in a variety of nanostructures and electrical behaviors.In this research, we evaluate the electrical energy storage performance of electrodes comprising polymers with varying compositions of triphenylamine and thiophene. The composition of the polymer electrodes are controlled by 1) synthesizing monomers with varying amounts of thiophene rings and 2) varying the concentration of thiophene and triphenylamine in solution. The electrodes were characterized structurally with scanning electron microscopy and electrochemically with cyclic voltammetry, charge-discharge and electrical impedance spectroscopy. Electrode structures fabricated with triarylamine-based conducting polymers exhibited a specific capacitance approaching 1000 F/g in 100 mM TBAF in acetonitrile with power and energy densities greater than 6 kW/kg and 25 W-hr/kg, respectively. The electrochemical properties of the electrodes are shown to depend on the amount of thiophene within the electrochemically synthesized co-polymer. Electrode performance metrics are presented for electrochemical half-cells for highly porous and nanotube electrodes, which are used to provide insight into the electrochemical storage mechanism.
4:15 PM - M11.5
C-MEMS/Manganese Oxide Composites as Electrodes for Micro-supercapacitors.
Majid Beidaghi 1 , Wang Chunlei 1 Show Abstract
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Supercapacitors, also called Electrochemical Capacitors (ECs), have higher power density and cycle lifetime compared to batteries and higher energy density compared to conventional electrolytic capacitors. Supercapacitors are used to power hybrid electric vehicles and portable electronic equipments and other devices. Miniaturized supercapacitors or micro-supercapacitors have attracted attention to provide power to small electronic devices. Previously, we have reported applications of carbon-microelectrochemical systems (C-MEMS) for the development of micro-electrodes for electric double layer capacitors (EDLCs). In this technique, patterned photoresist is carbonized to form micron-sized patterned carbon structures. Here, for the first time, we report the fabrication and evaluation of C-MEMS/Manganese Oxide composite electrodes for micro-supercapacitors. Two different methods were used to synthesize the composite electrodes: (1) addition of manganese oxide precursors to the photoresist before carbonization, and (2) the development of manganese oxide nanostructures on the carbonized photoresist. Detailed synthetic methods and electrochemical performance of composite electrodes will be presented at the meeting.
4:30 PM - M11.6
Binder–free Porous Network of Graphene/Manganese Oxide Composites as Electrodes for Electrochemical Capacitors.
Majid Beidaghi 1 , Chunlei Wang 1 Show Abstract
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Electrochemical capacitors (ECs) with high pulse power and long cycle lifetime have attracted a great deal of attention for use in electrical energy storage and delivery. Manganese oxides have been extensively studied as high performance electrode materials for ECs. However, Due to the poor electronic conductivity of manganese oxide films, the specific capacitance of thin film electrodes of manganese oxides are significantly lower than theoretical capacitance. To improve the performance of the nanostructure of manganese oxide electrodes, several studies on the synthesis of manganese oxide/carbon nanocomposites have been recently reported. Graphene nano sheets have received rapidly growing interest (especially in energy storage) due to their superb electronic, thermal, physical and chemical properties. In this work, electrostatic spray deposition (ESD) technique has been used to fabricate a binder-free porous network of graphene sheets to act as a highly conductive backbone for nanostructure manganese oxides. Graphene/manganese oxide nanocomposites show excellent electrochemical performance when compared to composites of manganese oxide with other carbon materials. A detail of synthetic methods and the electrochemical performance of nanocomposite electrodes will be presented at the meeting.
4:45 PM - M11.7
Effect of Surfactants on Capacitance Properties of Carbon Electrodes.
Krzysztof Fic 1 , Grzegorz Lota 1 , Elzbieta Frackowiak 1 Show Abstract
1 , Poznan University of Technology, Poznan Poland
Nowadays it is well known that supercapacitors (called also ultracapacitors or electric double layer capacitors) are very attractive devices for efficiently energy storage. Carbon materials, especially activated carbons, due to their electrochemical properties, seem to be a very interesting electrode materials. However, even activated carbons with large surface area (above 2000 m2/g) reveal relatively small capacitance. It may be caused by the hydrophobic character of the surface. Hence, use a small amount of surfactants (wetting agents) as a aqueous electrolyte additives, seems to be a very promising way to improve the capacitance.Two-electrode capacitors were assembled in a Swagelok system with pellets of comparable mass. The electrode was composed of 85 wt.% of carbon (SBET= 1901 m2/g, Smicro= 1327 m2 /g), 10 wt.% of polyvinylidene fluoride (PVDF Kynar Flex 2801) and 5 wt.% of acetylene black. Electrodes were prepared in the form of pressed pellets (7–10 mg) with a geometric surface area of 0.8 cm2 per electrode. The investigations were performed in acidic (1M H2SO4) and alkaline (6M KOH) solutions. As a electrolyte additives, three kind of surfactants were used: lithium and sodium dodecyl sulphate as a anionic surfactants, tetrapropylammonium bromide and iodide as a cationic surfactants and polymer of polyethylene glycol and p-t-octylophenol (called Triton X-100) as non-ionic surfactant. A glassy fibrous material played the role of separator. The capacitance properties of the composite materials (expressed per active mass of a single electrode) were studied by galvanostatic (1 A/g), potentiodynamic cycling at voltage scan rates from 5 to 100 mV/s using VMP2/Z Biologic, France. For non-ionic surfactant the shape of voltammetry curves for supercapacitor operating in elec-trolyte with surfactant are almost ideally rectangular. The capacitance changed from 151 F/g in electrolyte without surfactant to 167 F/g in electrolyte with non-ionic surfactant. For anio-nic surfactant the capacitance increased to 157 F/g. For cationic surfactant the increase of capacitance is not significant. It is noteworthy, that these values are kept after 5000 charge-discharge cycles. For acidic solutions obtained results are very similar. Almost ideal, rectangular shape of obtained voltammetry curves suggest that surfactants are electrochemically stable in applied potential window (0.8V) and improve the electrolyte penetration into pores. Hence, the effect of surfactants (especially non-ionic) on capacitance properties of carbon electrodes is positive and improved the capacitance.
5:00 PM - M11.8
Interesting Electrochemical Properties of Supercapacitor Carbon Electrodes Operating in Neutral Aqueous Electrolyte.
Krzysztof Fic 1 , Grzegorz Lota 1 , Elzbieta Frackowiak 1 Show Abstract
1 , Poznan University of Technology, Poznan Poland
Electrochemical double layer capacitors (EDLC or supercapacitors) are very attractive devices for efficient energy storage. The mechanism of this phenomena is based simply on the electrochemical double layer charging/ discharging and eventually on faradaic reactions which may occur on electrode/electrolyte interface. Contrary to conventional batteries, these devices can be charged and discharged in a few seconds, however, the energy densities are still significantly lower than for traditional energy/power sources. The main reason is electrochemical stability limitation of applied electrolytes. In aqueos medium, due to water decomposition, supercapacitor voltage is limited to 0.8-1V, whereas in organic medium this value reaches even 2.7 V for industrial capacitor. However, organic electrolytes have significantly lower conductivity and gives much lower capacitance values, they are environment unfriendly and make capacitor assembling much more complicated and expensive. From this point of view aqueous electrolytes, apart from their narrow operating voltage range, seem to be much more interesting for the further supercapacitor technological development.This study shows a new insight into symmetric (carbon-carbon electrodes) EDLCs operating in neutral aqueous medium (1 mol/L Li2SO4 solution). A detailed characterization of supercapacitor (galvanostatic charging/discharging, cyclic voltammetry, electrochemical impedance spectroscopy) in two- and three electrode configuration reveals exceptional capacitance dependencies. The results proved that this electrolyte is very promising and seems to be much more attractive than organic one. The values of cell voltage exceeded 2 V, capacitance over 100 F/g has been obtained at a high discharged current density of 5 A/g and energy densities of 21 Wh/kg have been achieved. It is noteworthy that during over 15 000 charge/discharge cycles at high regimes these values remained stable when optimal composition of electrolyte was selected. Advanced study has been performed in the wide range of Li2SO4 concentrations and for other alkali metals sulphates. For some electrolyte a well selected surfactant gave additional capacitor improvement. A mechanism of this exceptional performance has been suggested taking into account a possible solvation/desolvation of ions. The proposed mechanism was supported by ions molecular modeling.Additionally, the crucial point is that neutral medium is definitively less corrosive than typically used alkaline and acidic electrolytic solutions. Surely, it gives a better choice of current collectors for capacitor assembly.
5:15 PM - M11.9
Novel Synthesis Method of Aligned MnO2 Nanowires and Investigation of Their Physical and Electrochemical Properties.
Jay Simmons 1 , Pani (Chakrapani) Varanasi 2 , Jie Liu 1 Show Abstract
1 Chemistry, Duke University, Durham, North Carolina, United States, 2 Material Science Division (RDRL-ROE-M), U.S. Army Research Office, Research Triangle Park, North Carolina, United States
Manganese oxides (MnO2) are very important materials as they can be used to develop the next generation of supercapacitors, lithium batteries, gas sensors and others. As the search for the next generation of power devices continues, supercapacitors may be one of the most promising applications of MnO2. The promise of MnO2 lies in its high theoretical specific capacitance (1110F/g), low cost, environmental friendliness, and natural abundance. Although such high capacitance has not yet been achieved, MnO2 nanostructures, such as nanowires, have potential to reach this goal due to their high surface area. Here we report a novel method for synthesizing aligned MnO2 nanowires for energy storage applications. These nanowires were grown for the first time using a simple process based on high temperature oxidation. MnO2 nanowires with diameters ranging from 10 - 50 nanometers and lengths of 2 – 4 microns have been repeatedly formed using this method. The novel process presented here is simple and scalable for large area applications. Proce