Resist Interface Delamination and Electrolyte Cracking in Cathodes of Solid-State Batteries by Compliant Electrolytes

Abstract

Interfacial debonding between active materials and solid electrolytes contributes to degrading interfacial kinetics of solid-state batteries. Fracture in electrolytes creates a barrier for the ionic conductivity. We apply a rigorous electro-chemo-mechanical fracture model of ionic conduction, electrochemical reaction, Li diffusion, mechanical stress and crack growth using a phase field method to investigate how to resist interface delamination and electrolyte cracking by optimizing the active material volume fraction and the electrolyte stiffness for cylindrical storage particles embedded in electrolytes. We find that more particle storage capacity can be utilized for higher active material volume fractions and softer electrolytes prior to unstable interface delamination during extraction, and delamination resistance can be improved by thinner and softer electrolytes, matching analytic considerations as well as experimental observations that sulfides are more suitable for electrolytes than oxides to avoid delamination. We further demonstrate more particle storage capacity can be utilized for lower active material volume fractions and softer electrolytes prior to unstable electrolyte breakage during insertion, and electrolyte cracking resistance can be improved by thicker and softer electrolytes, which aligns with analytic considerations and experimental observations. Finally, we provide guidelines for engineering the mechanical stability by designing solid-state cathodes with softer electrolytes and active material volume fractions of 50-60% to resist both interface delamination and electrolyte cracking.

Keywords: Interface delamination, Electrolyte cracking, Phase field model for fracture, Electrochemical reaction, Solid-state batteries