Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z4: Physics of Batteries, Supercapacitors and Fuel Cells |
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Sponsoring Units: GERA Room: Mayor Cockrell Room 004 |
Friday, March 6, 2015 11:15AM - 11:51AM |
Z4.00001: In-situ Studies of Structures and Processes at Model Battery Electrode/Electrolyte Interfaces Invited Speaker: Paul Fenter The ability to understand and control materials properties within electrochemical energy storage systems is a significant scientific and technical challenge. This is due, at least in part, to the extreme conditions present within these systems, and the significant structural and chemical changes that take place as lithium ions are incorporated in the active electrode material. In particular, the behavior of interfaces in such systems is poorly understood, notably the solid-liquid interface that separates the electrode and the liquid electrolyte. I will review our recent work in which we seek to isolate and understand the role of interfacial reactivity in these systems through in-situ, real-time, observations of electrochemically driven lithiation/delithation reactions. This is achieved by observing well-defined model electrode-electrolyte interfaces using X-ray reflectivity. These results reveal novel understandings of interfacial reactivity in conversion reactions (e.g., Si, Si$_{\mathrm{x}}$Cr, Ge, NiO) that can be used to control the complex reaction lithiation pathway through the use of thin-film and multilayer electrode structures. [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z4.00002: Hybrid Functional Calculations of Acceptor Doping in Protonic Conductor SrZrO$_3$ Leigh Weston, Anderson Janotti, Xiangyuan Cui, Catherine Stampfl, Chris Van de Walle Perovskite oxides such as SrZrO$_3$ (SZO), which exhibit high temperature proton conductivity, are promising electrolyte materials for use in solid oxide fuel cells (SOFCs). Proton conductivity in SZO is typically achieved via acceptor doping with trivalent cations substituting at the Zr site, where the formation of charge compensating oxygen vacancies facilitates proton solvation. We present a detailed study of Sc and Y dopants in SZO based on first-principles, hybrid density functional calculations. When substituting at the Zr site, both dopants form deep acceptors, where the neutral charge state forms a localized hole polaron state. Under certain growth conditions Sc and Y will form auto-compensating donor species by substituting at the Sr site, which would inhibit proton solubility. Moreover, the proton - dopant association was found to be strong, with proton binding energies of -0.41 eV and -0.31 eV for Sc$_{\mathrm{Zr}}^-$ and Y$_{\mathrm{Zr}}^-$ respectively, indicating that proton transport is limited by trapping. These new results will be useful in the development of zirconate based proton conducting electrolyte materials for solid oxide fuel cells. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z4.00003: Effect of Fe doping on O vacancy/interstitial formation and migration in PrBaCo2O5$+$d Omotayo Salawu, Liyong Gan, Udo Schwingenschlogl Oxygen vacancy formation and migration are key factors considered for the operation of cathodes in solid oxide fuel cell. First-principles calculations are used to investigate Fe doped PrBaCo2O5$+$d as cathode material for intermediate temperature solid oxide fuel cells. We discuss the electronic properties of the pristine system and the effect of Fe doping on the structural and electronic properties. Different concentrations of the dopants are calculated. We find that the volume of the unit cell and O vacancy formation energy increase linearly with the Fe content concentration. We also investigate the formation of oxygen interstitial as a function of Fe substitution and the possibility of anisotropic diffusion of the O ion was also studied. [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z4.00004: Short-lived K$_{2}$S Molecules in Superionic Potassium Sulfide Yusuke Okeya, Kazuo Tsumuraya The first principles molecular dynamics method allows us to elucidate the formation of short-lived K$_{2}$S molecular states in superionic potassium sulfide. The covalent and the Coulomb bonds exist between the ionized mobile potassiums and the ionized immobile sulfurs. Both the bonds induces indirect covalent and indirect Coulomb attractions between the di-interstitial potassiums on the mid-sulfurs, which forms the short-lived K$_{2}$S molecular states. The covalent electron density also exists between short-lived potassium dimers. The three attractions reduce Haven's ratios of the potassiums in the conductor. The molecule formation indicates the electronic state of the conductor is intermediate between the ionic and covalent crystals. The absence of the long-lived potassium dimers implies a failure of the caterpillar diffusion model or the Frenkel-Kontorova chain model for the superionic diffusion of the potassiums in the sulfide. The incompletely ionized cations and anions reduce the Coulomb attractions between them which induces the sublattice melting of smaller size of the potassiums than the sulfurs. [Preview Abstract] |
(Author Not Attending)
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Z4.00005: First principles calculations of stability and lithium intercalation potentials of ZnCo$_{2}$O$_{4}$ L.C. Yu, J. Wu, H. Liu, Y.N. Zhang Among the metal oxides, which are the most widely investigated alternative anodes for use in lithium ion batteries (LIBs), binary and ternary tin oxides have received special attention due to their high capacity values. ZnCo$_{2}$O$_{4}$ is a promising candidate as the anode material for LIB, and one can expect a total capacity corresponding to 7.0 - 8.33 mol of recyclable Li per mole of ZnCo$_{2}$O$_{4}$. Here we studied the structural stability, electronic properties, diffusion barrier and lithium intercalation potentials of ZnCo$_{2}$O$_{4}$ through density functional calculations. The calculated structural and energetic parameters are comparable with experiments. Our DFT studies provide insights in understanding the mechanism of lithium ion displacement reactions in this ternary metal oxide. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z4.00006: Density Functional Theory Study of the Conductivity of Manganese Dioxide Nanowires during Li$^{+}$ Insertion Ruqian Wu, Hui Wang, May Le Thai, Reginald M. Penner Manganese oxide ($\delta $-MnO$_{2})$ as a battery material has various advantages such as low cost, high earth abundance and environmentally safe, and it has large interlayer space for lithium ion insertion and migration. In this work, the system of 200 MnO$_{2}$ nanowire array is used to study the electrochemical changes through in situ conductivity measurements during the lithium ion insertion process. The result indicates that the conductivity of each MnO$_{2}$ nanowire array increases as the lithium ion concentrations increases corresponding to more negative insertion potential. We perform \textit{ab initio} molecular dynamic (AIMD) simulations and density functional theory (DFT) calculations with the van der Waals (vdW) correction to understand the fundamental electrochemical and structural properties of $\delta $-MnO$_{2}$ nanowires. We find that water molecules are important for the expansion of the interlayer distance of $\delta $-MnO$_{2}$, and reveal that the variation of conductivity of $\delta $-MnO$_{2}$ nanowires with different Li$^{+}$ concentrations stems from the Li-produced gap states. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z4.00007: \textit{In Situ} Correlation of Volummetric Expansion with Charge Storage in Nanostructured MnO$_{2}$ Tetyana Ignatova, Brad Corso, Deng Pan, O. Tolga Gul, Phillip G. Collins Pseudocapacitors aim to meet developing energy storage needs by combining the high energy density of batteries with the power performance of capacitors. However, degradation remains a critical issue for pseudocapacitor electrodes. After many cycles, nanostructured metal oxides like MnO$_{2}$ lose their capacity through mechanisms that remain poorly understood. In this work, we studied the volummetric changes that accompany charge storage in nanoscale MnO$_{2}$ electrodes by combining in-liquid atomic force microscopy (AFM) with 3-terminal electrochemical cycling. Typical samples consisted of thin films (100 to 400 nm) of porous, amorphous MnO$_{2}$ deposited onto 2 $\mu $m$^{2}$ Pt electrodes and then cycled in aqueous LiClO$_{4}$ electrolyte. \textit{In situ} measurements of film expansion during charge insertion observed 3.6{\%} volummetric expansion for partial charging of 0.1 electron per Mn atom over a wide range of scan rates and voltage windows, even though these parameters change the balance between fast, double-layer capacitance and bulk, redox pseudocapacitance mechanisms. In fact, volume expansion is universally attributed to bulk charging, so the invariance highlights an unexpected role for surface processes in nanostructured electrode materials. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z4.00008: Topological defect dynamics in \textit{operando} battery nanoparticles Andrew Ulvestad, Shirley Meng, Oleg Shpyrko Topological defects are ubiquitous in physics and manifest themselves as magnetic monopoles in quantum field theories and crystallographic imperfections in condensed matter systems. In the latter, the defect properties determine many of the material's properties and as such represent substantial novel opportunities for design and optimization of desired functionalities through deliberate defect engineering and manipulation. However, this approach of ``defect choreography'' currently suffers from the lack of suitable nanoscale probes to track buried single defects \textit{in-situ} and \textit{in-operando}. Here we report 3D imaging of single edge dislocations and their motion in an individual nanoparticle under \textit{operando} conditions in a Lithium ion battery. We further observe the dislocation act as a nucleation point during the structural phase transformation. We find that the region near the dislocation enters a negative Poisson's ratio, or auxetic, regime at high voltage. Dislocation imaging is thus a powerful nanotechnology and it opens a new, powerful avenue for facilitating improvement of nanostructured devices. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z4.00009: Structure and Stoichiometry in doped LLZO (Li$_7$La$_3$Zr$_2$O$_{12}$) Michelle Johannes, Noam Bernstein, Ashfia Huq, Saikat Mukhopadyay, Jeff Wolfenstine, Jan Allen, Travis Thompsen, Jeff Sakamoto, Derek Stewart LLZO has a tetragonal, Li-ordered phase with very low ionic conductivity and a cubic, Li-disordered phase with two orders of magnitude higher conductivity, relevant for solid electrolyte usage. The jump in conductivity can be correlated to dopant-induced Li vacancies that disorder the Li sublattice and cause the structural phase transition. In this work, we use extremely careful synthesis, neutron diffraction, synchrotron XRD, Raman scattering, and first principles techniques to show how both overall structure and selected local structural elements change as a function of dopant concentration. In particular, we examine how the local structure that defines the Li ion pathways changes with the lattice constant and how important microscopic quantities such as different Li site energies and hopping barriers change accordingly. Our work provides a link between the easily measurable lattice constant and extremely important but difficult to measure performance indicators such as exact Li vacancy concentration and hopping energy barriers. We hope that the ``map'' between structure and property provided here will speed optimization of the ionic conductivity via targeted doping strategies. [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z4.00010: Compressive Sensing Cluster Expansion Studies of Lithium Intercalation and Phase Transformation in MoS2 for Energy Storage Chi-Ping Liu, Fei Zhou, Vidvuds Ozolins Bulk molybdenum disulfide (MoS2) is a good electrode material candidate for energy storage applications, such as lithium ion batteries and supercapacitors due to its high theoretical energy and power density. First-principles density-functional theory (DFT) calculations combined with cluster expansion are an effective method to study thermodynamic and kinetic properties of electrode materials. In order to construct accurate models for cluster expansion, it is important to effectively choose clusters with significant contributions. In this work, we employ a compressive sensing based technique to select relevant clusters in order to build an accurate Hamiltonian for cluster expansion, enabling the study of Li intercalation in MoS2. We find that the 2H MoS2 structure is only stable at low Li content while 1T MoS2 is the preferred phase at high Li content. The results show that the 2H MoS2 phase transforms into the disordered 1T phase and the disordered 1T structure remains after the first Li insertion/deinsertion cycle suggesting that disordered 1T MoS2 is stable even at dilute Li content. This work also highlights that cluster expansion treated with compressive sensing is an effective and powerful tool for model construction and can be applied to advanced battery and supercapacitor electrode materials. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z4.00011: Binder-free Carbon Nanotube Flexible Solid State Supercapacitor Kofi Adu, Danhao Ma, Ramakrishnan Rajagopalan, Cheng-Yu Wang, Angela Lueking, Clive Randell We present a post synthesis self-assemble protocol that transforms the trillions of CNTs in powder form into densely packed flexible, robust and binder-free macroscopic membranes with hierarchical pore structure. The binder-free CNT membranes could be as thin as \textless 10$\mu $m with mass density greater than that of water (1.0g/cc). As the thickness of the CNT membrane is increased, we observed a gradual transition from high flexibility to buckling and brittleness in the flexural properties of the CNT membranes. We have demonstrated the use of the CNT membranes as electrode in two-electrode 1M H$_{2}$SO$_{4}$ aqueous double layer supercapacitor that shows very high power density $\sim$ 1040 kW/kg based on the mass of both electrodes and time constant of $\sim$ 15 ms with no degradation in performance even after 10,000 cycles. Furthermore, we will show the designing of flexible 3-stack bipolar solid-state ultracapacitor and present results on energy/power densities, voltage, cyclability, temperature stability in relation to flexibility and weight. Preliminary results indicate high temperature stability \textgreater 85$^{\circ}$C and CV voltage $\sim$ 3V with very low leakage current $\sim$ 10nA. [Preview Abstract] |
Friday, March 6, 2015 1:51PM - 2:03PM |
Z4.00012: X-ray absorption spectroscopy as a probe of dissolved polysulfides in lithium sulfur batteries Tod Pascal, David Prendergast There has been enormous interest lately in lithium sulfur batteries, since they have 5 times the theoretical capacity of lithium ion batteries. Large-scale adoption of this technology has been hampered by numerous shortcomings, chiefly the poor utilization of the active cathode material and rapid capacity fading during cycling. Overcoming these limitations requires methods capable of identifying and quantifying the products of the poorly understood electrochemical reactions. One recent advance has been the use of X-ray absorption spectroscopy (XAS), an element-specific probe of the unoccupied energy levels around an excited atom upon absorption of an X-ray photon, to identify the reaction products and intermediates. In this talk, we'll present first principles molecular dynamics and spectral simulations of dissolved lithium polysulfide species, showing how finite temperature dynamics, molecular geometry, molecular charge state and solvent environment conspire to determine the peak positions and intensity of the XAS. We'll present a spectral analysis of the radical (-1e charge) species, and reveal a unique low energy feature that can be used to identify these species from their more common dianion (-2e charge) counterparts. [Preview Abstract] |
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