Predicting the Voltage Dependence of Interfacial Electrochemical Processes at Lithium-Intercalated Graphite Edge Planes

TL;DR

This study develops a method to accurately predict the voltage dependence of interfacial electrochemical processes at lithium-intercalated graphite edges using ab initio molecular dynamics, revealing new insights into electron localization and electrolyte decomposition.

Contribution

It introduces a novel approach combining AIMD and free energy calculations to calibrate electrode potential in DFT simulations of lithium-ion battery interfaces.

Findings

PF6- decomposes electrochemically at low potentials.

Excess electrons localize in the gap states of the organic electrolyte.

The organic carbonate liquid is not semiconductor-like as previously assumed.

Abstract

The applied potential governs lithium-intercalation and electrode passivation reactions in lithium ion batteries, but are challenging to calibrate in condensed phase DFT calculations. In this work, the "anode potential" of charge-neutral lithium-intercalated graphite (LiC(6)) with oxidized edge planes is computed as a function of Li-content n(Li)) at edge planes, using ab initio molecular dynamics (AIMD), a previously introduced Li+ transfer free energy method, and the experimental Li+/Li(s) value as reference. The voltage assignments are corroborated using explicit electron transfer from fluoroethylene carbonate radical anion markers. PF6- is shown to decompose electrochemically (i.e., not just thermally) at low potentials imposed by our voltage calibration technique. We demonstrate that excess electrons reside in localized states-in-the-gap in the organic carbonate liquid region, which is not semiconductor-like (band-state-like) as widely assumed in the literature.