Interfacial Electron Transfer and Ion Solvation in the Solid Electrolyte Interphase

Abstract

As a chemically and structurally well-defined model for redox processes in the solid electrolyte interphase of battery electrodes, we investigate electron transfer (ET) to lithium ions at the interface between a platinum metal anode and a solid polymer electrolyte. Studied electrolytes include LiTFSI (lithium bis(trifluoromethane)sulfonimide) salts in polyethylene oxide and poly(diethylene oxide-alt-oxymethylene), as well as in the associated liquid electrolytes 1,2-dimethoxyethane and tetraglyme. Atomic-resolution simulations are performed with constant-potential polarizable electrodes to characterize interfacial ET kinetics, including lithium-ion solvation structures and solvent reorganization effects as a function of applied electrode potential. The linear-response assumptions of the Marcus theory for ET are found to be robust in these systems, yet ion-solvation behavior at the anode interface is strikingly dependent on chain connectivity, solvation environment, and the magnitude of the applied electrode potential, resulting in very different ET kinetics for lithium electroreduction.

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