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

TL;DR

This paper re-examines the two-electron reduction mechanisms of ethylene carbonate in lithium-ion batteries using quantum chemistry, highlighting the importance of these pathways in understanding SEI formation.

Contribution

It provides a quantum chemistry analysis of two-electron reduction pathways of ethylene carbonate, clarifying their role in electrolyte decomposition and SEI formation.

Findings

Two-electron reduction pathways are viable and significant.

Excess electrons attack EC in the order: broken EC^- > intact EC^- > EC.

The study estimates the crossover point between one- and two-electron regimes.

Abstract

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. An estimate of the crossover between one- and two-electron regimes under a homogeneous reaction zone approximation is proposed.