Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y34: Focus Session: Materials for Electrochemical Energy Storage |
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Sponsoring Units: GERA DMP FIAP Room: 210A |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y34.00001: Advanced 3D Ni(OH)$_{2}$/CNT Gel Composite Electrodes for Supercapacitors Hanlin Cheng, Hai Minh Duong In order to enhance the performance of supercapacitors, advanced 3D Porous CNT/Ni(OH)$_{2}$ gel composite electrodes are developed in this work. Compared with previously reported graphene gel supercapacitors, our electrodes using 1D CNTs have smaller diffusion resistance due to a shorter ion transport path. The developed 3D xerogel composite electrodes demonstrate the success of a careful engineered guest/host materials interface. Initially, the CNT gels are coated on the nickel foam to form a 3D scaffold, which serves as a microscopic electrical conductive network. Then Ni(OH)$_{2}$ are incorporated using a traditional electrodeposition method. In this work, two types of the 3D CNT-coated nickel foams are investigated. The gels can be used directly as hydrogels or dried in air to form xerogels. Both hydrogels and xerogels present 3D tangled CNT networks. It shows that the hydrogel composite electrodes with unbundled CNTs, though presenting high capacitances of 1400 F/g at low discharge rate, possess lower capacitances at higher discharge rate and a poor cycling performance of less than 23{\%} retention. In contrast, the xerogel composite electrodes can overcome these limitations in terms of a satisfied discharge performance of 1200 F/g and a good cycling retention more than 85{\%} due to a stronger Ni(OH)$_{2}$/CNT interface. The CNT bundles in the xerogel electrodes formed during the drying process can give a flat surface with small curvature, which facilitate the Ni(OH)$_{2}$ nucleation and growth. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y34.00002: Energetic and solvation effects at photoanode-catalyst interfaces: IrO2/WO3 Yuan Ping, William Goddard III, Giulia Galli One key challenge in building photo-electrochemical cells to split water is to engineer interfaces between photo-electrodes and catalysts that are stable in harsh pH conditions and permit optimal charge transfer. Iridium oxide is the only known catalyst for oxygen evolution stable in acidic conditions and hence a good candidate to be interfaced with photo-anodes. Using ab initio calculations, we investigated the structural and electronic properties of tungsten trioxide surfaces interfaced with an iridium dioxide thin film. We built a microscopic model of the interface that exhibits a formation energy lower than the surface energy of the most stable IrO2 surface, in spite of a large lattice mismatch, and we found no impurity states pinning the Fermi level. Both within Density Functional and many body perturbation theory (GW), we found that the two oxides form undesirable Ohmic contacts, when an IrO2 thin film fully covers WO3. However, our calculations predicted that if the morphology of the catalyst allows for partial exposure of the two oxides to water, then Schottky barriers may be formed, which favor charge transfer and hence water splitting. This work suggests ways to optimize light-absorber-catalyst interfaces for optimal charge transport. [Preview Abstract] |
Friday, March 6, 2015 8:24AM - 9:00AM |
Y34.00003: Connecting the dynamic response of electrodes to their electronic structure Invited Speaker: Anton Van der Ven The electrodes of Li-ion batteries exhibit a wide range of intriguing electronic, thermodynamic and kinetic properties. Most electrode materials undergo a series of phase transformations as a result of drastic changes in Li concentration during each charge and discharge cycle. The mechanisms of these phase transformations remain poorly understood but usually involve a coupling between ionic diffusion, structural changes and interface migration. While phase transformations affect electrodes at the particle level, their mechanisms are ultimately determined by the electronic structure and crystallography of the electrode chemistry. Describing these phase transformations phenomenologically starting from first principles requires suitable coarse-graining strategies and a reliance on statistical mechanical approaches to account for the important role of temperature and entropy. This talk will describe how first-principles statistical mechanical approaches have provided insights about the mechanisms of kinetic processes in a variety of transition metal oxides and sulfides with widely differing crystal structures. [Preview Abstract] |
Friday, March 6, 2015 9:00AM - 9:12AM |
Y34.00004: Large modification of electrostatic fields in liquids between charged plates: Effects of the dielectric response of solvent molecules Hongbo Chen, Issei Nakamura We study the effects of dielectric inhomogeneity on the electrostatic properties of liquids between two charged plates, developing a modified Poisson-Boltzmann equation via the Booth theoryfor the dielectric response of solvents under external electrostatic fields. We show that variations in the capacitance for ion-containing solutions can be non-monotonic, whereas the conventional Poisson-Boltzmann theorypredicts monotonic behavior. Importantly, the effects of ions on the reorganization of solvent dipoles near electrodes significantly affect the capacitance. Furthermore, we show thatthe dielectric contrast in immiscible liquid mixturesunder external electrostatic fields may cause conceptually new phase behaviors between charged plates; interfaces between the liquidsperpendicular to an external fieldmay be energetically favored over parallel interfaces. [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y34.00005: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y34.00006: Extracting the Redox Orbitals in Li Battery Materials with High-Resolution X-Ray Compton Scattering Spectroscopy B. Barbiellini, K. Suzuki, Y. Orikasa, N. Go, H. Sakurai, S. Kaprzyk, M. Itou, K. Yamamoto, Y. Uchimoto, Yung Jui Wang, H. Hafiz, A. Bansil, Y. Sakurai We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution X-ray Compton scattering. Application of our method to spinel LixMn2O4 (a lithium ion battery cathode material) is discussed. The orbital involved in lithium insertion and extraction process is mainly the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of the lithium ion battery. Work supported in part by the US DOE. [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y34.00007: Electronic Structure at Electrode/Electrolyte Interfaces in Magnesium based Batteries Janakiraman Balachandran, Donald Siegel Magnesium is a promising multivalent element for use in next generation electrochemical energy storage systems. However, a wide range of challenges such as low coulombic efficiency, low/varying capacity and cyclability need to be resolved in order to realize Mg based batteries. Many of these issues can be related to interfacial phenomena between the Mg anode and common electrolytes. Ab-initio based computational models of these interfaces can provide insights on the interfacial interactions that can be difficult to probe experimentally. In this work we present ab-initio computations of common electrolyte solvents (THF, DME) in contact with two model electrode surfaces namely --- (i) an ``SEI-free'' electrode based on Mg metal and, (ii) a ``passivated'' electrode consisting of MgO. We perform GW calculations to predict the reorganization of the molecular orbitals (HOMO/LUMO) upon contact with the these surfaces and their alignment with respect to the Fermi energy of the electrodes. These computations are in turn compared with more efficient GGA (PBE) \& Hybrid (HSE) functional calculations. The results obtained from these computations enable us to qualitatively describe the stability of these solvent molecules at electrode-electrolyte interfaces [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y34.00008: Possible Mg intercalation mechanism at the Mo6S8 cathode surface proposed by first-principles methods Liwen Wan, David Prendergast In recent years, great attention has been paid to the development of divalent Mg-ion batteries, which can potentially double the energy density and volumetric capacity compared to monovalent Li-ion batteries. The prototype Mg-ion battery, comprising Mg(anode)/Mg(AlCl$_2$BuEt)$_2\cdot$THF(electrolyte)/Mo$_6$S$_8$(cathode), was established in 2000 by Aurbach et al. Despite the remarkable success of this prototype system, we still lack a clear understanding of the fundamental Mg intercalation/deposition mechanism at the electrolyte/electrode interfaces that perhaps results in the observed sluggish Mg transport process. Our previous work has shown that Mg-ions are strongly coordinated in the bulk electrolyte by a combination of counterion, Cl$^-$, and organic aprotic solvent, THF. In this work, we use first-principles methods to study Mg intercalation behavior at the Mo$_6$S$_8$ cathode surface with the presence of solvent molecules. It is found that the image charge, formed on this metallic cathode surface, can effectively weaken the solvent-surface interactions and facilitate Mg intercalation. A detailed Mg intercalation mechanism is proposed and the unique role of Mo$_6$S$_8$ as the cathode material is emphasized. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y34.00009: Asymmetric Supercapacitors with Dominant Pseudocapacitance in Neutral Aqueous Electrolyte Yuanbing Mao, Qiang Li Electrochemical capacitors (ECs) are promising power sources for portable electronics and hybrid electric vehicles. To solve the poor ionic conductivity, intrinsic inflammability and toxicity issues of current ECs incorporating organic electrolytes, aqueous electrolyte-based asymmetric supercapacitors (ASCs) have been attracting intensive attention recently. In this presentation, prototype MnO$_{2}$-NFs//KCl//CNTs supercapacitor cells in neutral aqueous electrolyte allow rapid charge/discharge kinetics, fast ionic response, and evident pseudocapacitive dominance due to the unique MnO$_{2}$-NF architecture and novel ASC design. For the first time, the respective contributions of the pseudocapacitance and EDL capacitance to the overall electrochemical performance of ASCs were differentiated with a proof of pseudocapacitive dominance ($q_{\mathrm{pseudo}}$/$q_{\mathrm{dl}} = $ 2.5). To sum, this study provides a brilliant proof-of-concept design of novel supercapacitors with pseudocapacitive dominance to achieve ultimate energy storage applications with both high energy and power density. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y34.00010: Impact of strong electronic correlations on the phase stability of oxide and phosphate intercalation materials Eric Isaacs, Chris Marianetti Li intercalation in certain battery cathode materials such as Li$_x$FePO$_4$ (LFP) occurs via a two-phase (phase separated) process, which significantly impacts the voltage profile and charge/discharge kinetics. The phase separation in LFP is not predicted by density functional theory (DFT), but it is captured by DFT plus Hubbard $U$ (DFT+$U$) suggesting the significant role of electronic correlations in determining its thermodynamic properties [F. Zhou et al., Phys. Rev. B 69, 201101 (2004).]. In order to understand the impact of such correlations on the phase stability of transition metal oxide and phosphate intercalation materials, here we investigate the formation energies of phase separating LFP, phase stable Li$_x$CoO$_2$, and phase stable Sr$_x$La$_{1-x}$TiO$_3$ within DFT+$U$. We present the relationship between different formation energy contributions and the on-site Coulomb energy. Furthermore, we illustrate how band filling, $p$-$d$ hybridization, magnetism, and charge and orbital ordering can impact the phase stability of such systems. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y34.00011: Structure and interface properties of the electrolyte material Li$_4$P$_2$S$_6$ Zachary D. Hood, Cameron Kates, N. A. W. Holzwarth Li$_4$P$_2$S$_6$ has been identified in several high temperature preparations of lithium thiophosphate electrolytes as a synthesis or decomposition product. Its characteristic P$-$P bond may be partly responsible for its relative stability. Early structural analysis\footnote{R. Mercier {\em{et. al.}}, {\em{J. Solid State Chem.}} {\bf{43}} 151 (1982)} found the P sites to be disordered. Our previous simulations,\footnote{N. A. W. Holzwarth, {\em{J. Power Sources}} {\bf{196}} 6970 (2011) } found a related low energy structure with ordered P sites. We report here a re-examination of the simulation results and new $X$-ray measurements which indicate that the lowest energy structure of Li$_4$P$_2$S$_6$ is different from that determined in previous analysis. Ionic conductivity and thermal stability are also reported. In addition to examining the bulk electrolyte, we have simulated idealized interfaces of Li$_4$P$_2$S$_6$ and lithium metal representing an electrolyte/anode system. [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y34.00012: Modeling solid electrolyte/electrode interface stability using first principles calculations Nicholas Lepley, N. A. W. Holzwarth The formation of a stable interface between electrode and electrolyte materials is a necessary property for batteries in general and for Li-ion batteries in particular. We present a framework for understanding and predicting the electrochemical stability of electrode/electrolyte interfaces based on density functional theory calculations. Within this framework, we have extended our previous work\footnote{N.\ D.\ Lepley, N.\ A.\ W.\ Holzwarth, and Y.\ A.\ Du, Phys. Rev. B {\bf88}, 104103 (2013).} to include quantitative results for the solid-solid interface energy of the Li$_3$PS$_4$/Li, Li$_3$PO$_4$/Li, Li$_2$S/Li, Li$_2$O/Li, and Li$_3$PS$_4$/Li$_2$S interfaces. We show that under local equilibrium conditions the interface energy appears to be a good indicator of the stability of the interface. While the results we present are focused on the interface between Li-ion solid electrolytes and Li metal we expect the method to be applicable to other interface systems. [Preview Abstract] |
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