Electrode–Electrolyte Interface in Li-Ion Batteries: Current Understanding and New Insights

TLDR

Reactions at the electrode–electrolyte interface are critical for lithium‑battery cycle life and safety, yet the mechanisms of component formation and their influence on interphase properties remain poorly understood, especially for positive electrodes where Li‑rich layered oxides generate reactive species via oxygen redox. The study aims to use recent advances in in situ characterization of well‑defined electrode surfaces to gain mechanistic insights and develop strategies for tailoring EEI layer composition and properties. The authors review evidence supporting the mosaic structure model of the solid electrolyte interphase on negative electrodes such as lithium, graphite, tin, and silicon, and discuss how in situ characterization of well‑defined surfaces informs this model.

Abstract

Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. Despite research in the past four decades, there is still limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties. We review findings used to establish the well-known mosaic structure model for the EEI (often referred to as solid electrolyte interphase or SEI) on negative electrodes including lithium, graphite, tin, and silicon. Much less understanding exists for EEI layers for positive electrodes. High-capacity Li-rich layered oxides yLi2–xMnO3·(1–y)Li1–xMO2, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes. Recent advances in in situ characterization of well-defined electrode surfaces can provide mechanistic insights and strategies to tailor EEI layer composition and properties.