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Effects of Solvent-Salt Charge-Transfer Complexes on Oxidative Stability of Li-Ion Battery Electrolytes

preprint
submitted on 20.08.2018 and posted on 21.08.2018 by Eric Fadel, Francesco Faglioni, Georgy Samsonidze, Nicola Molinari, Boris V. Merinov, William A. Goddard III, Jeffrey C. Grossman, Jonathan P. Mailoa, Boris Kozinsky
Electrochemical stability windows of electrolytes largely determine the limitations of operating regimes and energy density of Li-ion batteries but the controlling degradation mechanisms are difficult to characterize and remain poorly understood. We investigate the oxidative decomposition mechanisms governing high voltage stability of multi-component organic electrolytes using computational techniques of quantum chemistry. The intrinsic oxidation potential is modeled using vertical ionization potentials (IP) of ensembles of anion-solvent clusters generated using molecular dynamics. In some cases, the IP of the solvent-anion complex is significantly lower than that of each individual component. This effect is found to originate from the oxidation-driven charge transfer complex formation between the anion and the solvent. We propose a simple model to quantitatively understand this phenomenon and validate it for 16 combinations of common anions (4,5-dicyano-2-(trifluoromethyl)imidazolium, bis-(trifluoromethane solfonimmide), tetrafluroborate, hexafluorophosphate) and solvents (dimethyl sulfoxide, dimethoxyethane, propylene carbonate, acetonitrile). This new understanding of the microscopic details of oxidation allows us to interpret trends in published experimental and computational results and to formulate design rules for rapidly assessing stability of electrolyte compositions.

Funding

Robert Bosch LLC

History

Email Address of Submitting Author

nmolinari@seas.harvard.edu

Institution

Harvard University

Country

United States of America

ORCID For Submitting Author

0000-0002-2913-7030

Declaration of Conflict of Interest

There are no conflicts to declare.

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