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Title: Surface-Mediated Solvent Decomposition in Li–Air Batteries: Impact of Peroxide and Superoxide Surface Terminations

A viable Li/O2 battery will require the development of stable electrolytes that do not continuously decompose during cell operation. In some recent experiments it is suggested that reactions occurring at the interface between the liquid electrolyte and the solid lithium peroxide (Li2O2) discharge phase are a major contributor to these instabilities. To clarify the mechanisms associated with these reactions, a variety of atomistic simulation techniques, classical Monte Carlo, van der Waals-augmented density functional theory, ab initio molecular dynamics, and various solvation models, are used to study the initial decomposition of the common electrolyte solvent, dimethoxyethane (DME), on surfaces of Li2O2. Comparisons are made between the two predominant Li2O2 surface charge states by calculating decomposition pathways on peroxide-terminated (O22–) and superoxide-terminated (O21–) facets. For both terminations, DME decomposition proceeds exothermically via a two-step process comprised of hydrogen abstraction (H-abstraction) followed by nucleophilic attack. In the first step, abstracted H dissociates a surface O2 dimer, and combines with a dissociated oxygen to form a hydroxide ion (OH). In the remaining surface oxygen then attacks the DME, resulting in a DME fragment that is strongly bound to the Li2O2 surface. DME decomposition is predicted to be more exothermic on the peroxide facet; nevertheless,more » the rate of DME decomposition is faster on the superoxide termination. The impact of solvation (explicit vs implicit) and an applied electric field on the reaction energetics are investigated. Finally, our calculations suggest that surface-mediated electrolyte decomposition should out-pace liquid-phase processes such as solvent auto-oxidation by dissolved O2.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4]
  1. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering
  2. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Physics
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Mechanical Engineering and Applied Physics Program
Publication Date:
OSTI Identifier:
1325870
Report Number(s):
LLNL-JRNL--666496
Journal ID: ISSN 1932-7447
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 119; Journal Issue: 17; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 25 ENERGY STORAGE