Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B20: Focus Session: Physics of Energy Storage Materials II -- Anodes and Capacitors |
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Sponsoring Units: FIAP/DMP GERA/DCOMP Chair: Gholam?Abbas Nazri, General Motors Company Room: D168 |
Monday, March 21, 2011 11:15AM - 11:27AM |
B20.00001: Anode-electrolyte double-layer of Li-ion batteries: Structure and Li-ion intercalation David O. Wipf, Ibrahim Abou Hamad, Per Arne Rikvold, Mark A. Novotny The electrochemical double-layer structure plays an important role in Li-ion intercalation during charging of Li-ion batteries with a graphite anode. In our recent Molecular Dynamics studies of a proposed accelerated charging method [I. Abou Hamad~\textit{et al.}, Phys. Chem. Chem. Phys. {\bf 12}, 2740-2743 (2010)], we notice that ethylene carbonate and propylene carbonate molecules of the electrolyte assemble themselves in a preferred orientation at the electrode-electrolyte interface. On the other hand, they are randomly oriented in the bulk electrolyte. We show that the structure of the double layer is affected by the intercalating Li-ion: while the dipole moments of double-layer molecules far from the intercalating Li-ion point toward the graphite sheets of the anode, they point away from the intercalation site close to the intercalating Li-ion. This observation should contribute to a better understanding of the intercalation process. [Preview Abstract] |
Monday, March 21, 2011 11:27AM - 11:39AM |
B20.00002: High Throughput Computational Discovery of Intermetallic Anodes for Li Batteries Scott Kirklin, Chris Wolverton We have developed a framework to perform high-throughput computational screening of intermetallic compounds as candidates for Li battery anodes. We have used our method to calculate, from density functional theory (DFT), more than 5000 anode lithiation reactions, based on more than 100 intermetallic compounds. We have specifically focused on the 3d-transition metal silicides, nidtrides and phosphides. Given the set of DFT total energies for all compounds, the reaction path upon lithiation is predicted using the recently-developed grand canonical linear programming (GCLP) method. The anode performance is then characterized by the cell potential vs lithium metal, energy density and volume expansion. The accuracy of this approach is first validated for pure silicon, and then extended to binary intermetallic compounds. Based on the results of these calculations, future experimental study can be guided toward systems with promising thermodynamic properties. [Preview Abstract] |
Monday, March 21, 2011 11:39AM - 11:51AM |
B20.00003: Li and Si diffusion in Si anodes in Li-ion batteries: An \emph{ab-initio} molecular-dynamics-based study Priya Johari, Vivek B. Shenoy Several studies have been carried out in the past few years to understand the dynamics of Li diffusion in Si anodes of Li-ion batteries, however, most of these studies are restricted to the diffusion of a single Li atom in crystalline Si. While, it is well known that crystalline Si becomes amorphous on lithiation, this phenomenon has not been considered in previous computational work. Here, we report the results of molecular dynamics simulations that were carried out to study the diffusion of Li atoms in crystalline as well as amorphous Si for the LiSi phase. We have also analysed the dynamics of the Si atoms during lithiation to understand its role in stress generation/relaxation. We find that Li diffuses faster in amorphous Si as compared to crystalline Si, while the diffusivity of Si is around two orders of magnitude lesser than Li. [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:27PM |
B20.00004: Li-ion Battery Electrode Materials Design from First-Principles Calculations Invited Speaker: First-principles calculations can provide a powerful tool for investigating and optimizing electrode materials. While the strength of computations lies in the ability to control what is being calculated, the challenge is to ensure that the calculation is relevant for the physical processes that dominate the performance of the material. We will discuss this balance and show examples of how computations can aid in the design of current Li-ion rechargeable battery electrode materials by identifying and understanding the performance bottlenecks on the atomistic level. As the most commonly used anode in today's Li-ion batteries, graphite shows poor rate capability at lower temperatures, leading to over-potential and Li plating. Using first-principles calculations, coupled with a cluster expansion of Li interactions and kinetic Monte Carlo we were able to show that \textit{intrinsic} Li diffusion in graphite can be very fast, providing guidance towards designing higher-rate carbonaceous anode materials. On the cathode side, we have studied the layered Li(Ni$_{1/3}$,Mn$_{1/3}$,Co$_{1/3})$O$_{2}$ material, which is an interesting candidate if Co is partially substituted by the cheaper Al. Li migration in this material is influenced by several factors such as Li slab space, cation ordering and interlayer mixing. We present ab initio calculations of Li diffusivity as a function of Al content and slab spacing in the layered material, which elucidates the intrinsic rate performance effect of the Al substitution in the bulk material. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 12:39PM |
B20.00005: Crystalline-amorphous interfaces in Li-ion batteries Maria K. Chan, Jeffrey Greeley Amorphous and crystalline materials are associated with fast ionic transport and long term structural stability, respectively, both desirable properties in lithium ion battery materials. It is therefore no surprise that amorphous-crystalline interfaces are ubiquitous in Li-ion batteries. Using first principles density functional theory (DFT), and primarily Si as an example, we study models of crystalline-amorphous interfaces in Li-ion batteries. We will discuss the structure of such an interface and its energetic and mechanical effects on lithium insertion, as well as the kinetics of Li ion transport near and across the interface. The mechanism of solid state amorphization will also be discussed. [Preview Abstract] |
Monday, March 21, 2011 12:39PM - 12:51PM |
B20.00006: Li Diffusion Characteristics and Energetics in TiO$_{2}$ H. Yildirim, Subramanian Sankaranarayanan, Jeff Greeley We present the results of density functional theory-based calculations for the activation energies of Li diffusion in TiO$_{2}$ crystalline and amorphous structures. Additionally, molecular dynamics simulations using shell potential models are used to investigate the Li ion diffusion mechanisms for various titania morphology. The diffusion pathways and the corresponding energetics for each diffusion mechanism are further probed using the DFT-based Nudged Elastic Band Method. We will report the calculated diffusion energetics (MD and DFT) for each (Li-TiO$_{2})$ system and compare the atomic scale Li transport characteristics on crystalline and amorphous TiO$_{2}$ structures. We also discuss the effect of Li concentration on the diffusion energetics. [Preview Abstract] |
Monday, March 21, 2011 12:51PM - 1:03PM |
B20.00007: Composite MnO2-Carbon Electrodes for High Energy Density Storage Brad Corso, Israel Perez, Philip Collins The development of batteries with ever higher power densities is challenged by fundamental materials limitations that might be solved with hybrid combinations of materials. For example, metal oxides with high lithium ion capacities lack the conductivity to be good battery anodes, but composites that add graphitic carbon can achieve both capacity and conductivity. In this case, fast interfacial electron transfer between the materials is critical to achieving high performance. Here, we describe an electrochemical synthesis that achieves precise, conformal MnO2 films on graphitic surfaces. Furthermore, by using single-walled nanotubes as the carbon support, we can control defect densities with single defect resolution. Charge-discharge cycling of these electrodes, combined with control over point defects, directly distinguishes the enhanced charge transfer of defects and illuminates the structure-function relationship in interfacial electron transfer.~This research is supported by the NEES Energy Frontier Research Center of the U.S. DOE Office of Basic Energy Sciences ({\#}DESC0001160). [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:15PM |
B20.00008: Charge-Driven Structural Transformation and Valence Versatility of Boron Sheets in Magnesium Borides Yufeng Zhao, Chunmei Ban, Qiang Xu, Suhuai Wei, Anne C. Dillon We show here that boron sheets exhibit highly versatile valence and the layered boron materials may hold the promise for a high energy-density magnesium-ion battery. Practically, boron is superior to previously known multi-valence materials, especially transition metal compounds, which are heavy, expensive, and often not benign. Based on Density Functional Theory simulations, we have predicted a series of stable magnesium borides MgBx with a broad range of stoichiometries, 2 $<$ x $\le $ 16, by removing magnesium atoms from MgB2. The layered boron structures are preserved through an in-plane topological transformation between the hexagonal lattice domains and triangular domains. The process can be reversibly switched as the charge transfer changes with Mg insertion/extraction. The mechanism of such a charge-driven transformation originates from the versatile valence state of boron in its planar form. The discovery of these new physical phenomena suggests the design of a high-capacity magnesium-boron battery. [Preview Abstract] |
Monday, March 21, 2011 1:15PM - 1:27PM |
B20.00009: Nanostructured Mg Thin Film Electrodes for Mg-Air Batteries Taha Demirkan, Wisam Khudhayer, Fatih Cansizoglu, Tansel Karabacak Over the past decades, primary Mg-air batteries got the attention of several researchers due to their low cost, non-toxicity, and theoretically expected high terminal voltage and high specific capacity values. However, corrosion and formation of a passivation layer around the electrode have been among the major challenges resulting in low columbic efficiencies compared to theoretically expected values. In this study, we utilized a glancing angle deposition (GLAD) method for fabricating nanostructured Mg thin film electrodes with unique physical properties to overcome these problems. Electrodes were prepared using a thermal evaporation GLAD system. Magnesium coatings in various forms ranging from conventional dense thin films to highly porous nanoblades were prepared through the control of deposition angle from normal to oblique angles, respectively. We show that the properties of Mg-air batteries can be significantly improved using nanostructured Mg thin film electrodes and lead to enhanced terminal voltage and specific capacity values. [Preview Abstract] |
Monday, March 21, 2011 1:27PM - 1:39PM |
B20.00010: 1-pyrenecarboxylic acid Functionalization of Graphene: Effect on Capacitive Energy Storage Sujoy Ghosh, Rakesh Shah, Xiaohong An, Dinesh Rawat, Swastik Kar, Saikat Talapatra We will present a comparison of Electrolytic Double Layer Capacitance (EDLC) performance of membrane electrodes fabricated using pure and 1-pyrenecarboxylic acid (PCA)-functionalized graphene flakes. A significant increase in specific capacitance as well as energy and power density values in PCA graphene electrodes indicates that surface functionalization (that affects the hydrophilicity) of graphene-based materials is crucial for improving capacitive energy storage ability of these materials. [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 1:51PM |
B20.00011: Electrochemical Double Layer Capacitors Using Few Layers of Graphene Grown on Nickel Foil. R. Shah, U. Philipose, J.M. Perez, S. Talapatra We report on the properties of Electrochemical Double Layer Capacitors (EDLCs) fabricated using few layers of graphene synthesized on Nickel (Ni) foil by Chemical Vapor Deposition (CVD). The graphene films were characterized by Raman spectroscopy and showed that the film comprised more than one layers of graphene. The capacitive behavior of the fabricated EDLCs was examined using cyclic voltammetry, constant current charge/discharge, and impedance spectroscopy. These measurements show that the charge storage phenomenon is non-Faradic in nature. The capacitance of graphene on Ni electrodes was then compared to blank Ni foil electrodes and it was found that the capacitance of graphene on Ni foil is substantially higher than the blank Ni foil electrode. These results show that the few layers of graphene film grown on Ni foil could be promising material to function as electrodes for electrochemical energy storage device applications. [Preview Abstract] |
Monday, March 21, 2011 1:51PM - 2:03PM |
B20.00012: First-principles study of the structure of RuO$_{2} \cdot x$H$_{2}$O Fei Zhou, Yongduo Liu, Mark Asta, Vidvuds Ozolins Hydrous ruthenia, RuO$_{2} \cdot x$H$_{2}$O, is a high-performance electrode material for electrochemical supercapacitors. Two different structural models of hydrous ruthenia had been proposed. In one of them, hydrogen is incorporated in metal vacancies inside the oxide host ( (``bulk model''), while in the other model structural water associated with Ru-O occupies the region between rutile nanograins (``core + grain-boundary model''). We present a theoretical examination of the validity of the bulk model by optimizing hydrogen positions within RuO$_{2}$ with proton-compensated Ru vacancies using a combination of a systematic search algorithm based on electrostatics, database searching and density-functional theory calculations. We find that all the considered bulk model structures are unstable by $\sim 0.3 - 0.4$ eV per H$_{2}$O molecule with respect to phase separation into anhydrous RuO$_{2}$ and water. Structures with hydroxyl groups or aggregate H$_{2}$O are significantly lower in energy (though still unstable with respect to phase separation), demonstrating that the water prefers to agglomerate outside RuO$_{2}$. Our results strongly disfavor the bulk model with hydrogen inside RuO$_{2}$ and support the core+grain-boundary model of hydrous ruthenia. [Preview Abstract] |
Monday, March 21, 2011 2:03PM - 2:15PM |
B20.00013: Ab initio study of the charge storage mechanism of ruthenium dioxide as an electrochemical ultracapacitor Yongduo Liu, Fei Zhou, Vidvuds Ozolins The charge storage mechanisms of ruthenium dioxide were investigated by first principles calculations. Both H-injected bulk and H-adsorbed RuO2(110) surface have been studied in order to obtain a whole picture of the discharging process of ruthenium dioxide as a supercapacitor. We have predicted the crystal structure of ruthenium-oxy-hydroxide (ROOH). By ab-inito voltage calculations, we also found that the RuO2(110) surface is completely hydrated before the usual voltammagram measurements, which suggests that the redox reactions happen in deep layers and should be diffusion dominated processes. [Preview Abstract] |
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