Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

TL;DR

This study uncovers the fracture mechanisms of single-crystal silicon electrodes in lithium-ion batteries, revealing how anisotropic lithiation causes cracks and proposing strategies to improve electrode durability.

Contribution

It provides a detailed physical understanding of crack initiation and growth in silicon electrodes, and suggests methods to enhance fracture resistance using electrolyte additives.

Findings

Cracks initiate perpendicular to the surface due to anisotropic lithiation.

Crack growth occurs through the electrode thickness, leading to delamination.

Electrolyte additives can heal cracks and improve fracture resistance.

Abstract

Long-term durability is a major obstacle limiting the widespread use of lithium ion batteries (LIBs) in heavy-duty applications and others demanding extended lifetime. As one of the root causes of degradation and failure of battery performance, the electrode failure mechanisms are still unknown. Here, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics, and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. Based on this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future LIBs from surface chemical, electrochemical, and material science perspectives.