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Two-electron reduction of ethylene carbonate: A quantum chemistry re-examination of mechanisms

Chemical Physics Letters

Leung, Kevin

Passivating solid-electrolyte interphase (SEI) films arising from electrolyte decomposition on low-voltage lithium ion battery anode surfaces are critical for battery operations. We review the recent theoretical literature on electrolyte decomposition and emphasize the modeling work on two-electron reduction of ethylene carbonate (EC, a key battery organic solvent). One of the two-electron pathways, which releases CO gas, is re-examined using simple quantum chemistry calculations. Excess electrons are shown to preferentially attack EC in the order (broken EC-) > (intact EC-) > EC. This confirms the viability of two electron processes and emphasizes that they need to be considered when interpreting SEI experiments. A speculative estimate of the crossover between one- and two-electron regimes under a homogeneous reaction zone approximation is proposed. © 2013 Elsevier B.V. All rights reserved.

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TYPE Conference YEAR 2013
OSTIScopus

Hydration structures of U(III) and U(IV) ions from ab initio molecular dynamics simulations

Journal of Chemical Physics

Leung, Kevin; Nenoff, Tina M.

We apply DFTU-based ab initio molecular dynamics simulations to study the hydration structures of U(III) and U(IV) ions, pertinent to redox reactions associated with uranium salts in aqueous media. U(III) is predicted to be coordinated to 8 water molecules, while U(IV) has a hydration number between 7 and 8. At least one of the innershell water molecules of the hydrated U(IV) complex becomes spontaneously deprotonated. As a result, the U(IV)-O pair correlation function exhibits a satellite peak at 2.15 Å associated with the shorter U(IV)-(OH -) bond. This feature is not accounted for in analysis of extended x-ray absorption fine structure and x-ray adsorption near edge structure measurements, which yield higher estimates of U(IV) hydration numbers. This suggests that it may be useful to include the effect of possible hydrolysis in future interpretation of experiments, especially when the experimental pH is close to the reported hydrolysis equilibrium constant value. © 2012 American Institute of Physics.

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TYPE Journal Article YEAR 2012
DOIOSTIScopus

First-principles modeling of the initial stages of organic solvent decomposition on Li xMn 2O 4(100) surfaces

Journal of Physical Chemistry C

Leung, Kevin

Density functional theory and ab initio molecular dynamics simulations are applied to investigate the initial steps of ethylene carbonate (EC) decomposition on spinel Li 0.6Mn 2O 4(100) surfaces. EC is a key component of the electrolyte used in lithium ion batteries. We predict a slightly exothermic EC bond-breaking event on this oxide facet, which facilitates subsequent EC oxidation and proton transfer to the oxide surface. Both the proton and the partially decomposed EC fragment weaken the Mn-O ionic bonding network. Implications for an interfacial film made of decomposed electrolyte on cathode surfaces, and Li xMn 2O 4 dissolution during power cycling, are discussed. © 2012 American Chemical Society.

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TYPE Journal Article YEAR 2012
DOIOSTIScopus

Real-time Studies of Battery Electrochemical Reactions Inside a Transmission Electron Microscope

Sullivan, John P.; Huang, Jian Y.; Leung, Kevin; Shaw, Michael; Fan, Hongyou; Liu, Xiaohua L.; Liu, Yang; Hudak, Nicholas S.

We report the development of new experimental capabilities and ab initio modeling for real-time studies of Li-ion battery electrochemical reactions. We developed three capabilities for in-situ transmission electron microscopy (TEM) studies: a capability that uses a nanomanipulator inside the TEM to assemble electrochemical cells with ionic liquid or solid state electrolytes, a capability that uses on-chip assembly of battery components on to TEM-compatible multi-electrode arrays, and a capability that uses a TEM-compatible sealed electrochemical cell that we developed for performing in-situ TEM using volatile battery electrolytes. These capabilities were used to understand lithiation mechanisms in nanoscale battery materials, including SnO2, Si, Ge, Al, ZnO, and MnO2. The modeling approaches used ab initio molecular dynamics to understand early stages of ethylene carbonate reduction on lithiated-graphite and lithium surfaces and constrained density functional theory to understand ethylene carbonate reduction on passivated electrode surfaces.

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TYPE SAND Report YEAR 2011
DOIOSTI
Results 101–125 of 170
Results 101–125 of 170