In-Situ Measurement and Modeling of Stress Evolution in Ge Electrode Due to Na/Na+ Redox Reactions

Abstract

Sodium-ion batteries are one of the promising alternatives to Li-ion batteries and experience similar capacity fade mechanisms due to volume expansion induced stresses. It is imperative to understand the stress evolution in Na-ion battery electrodes and how these stresses affect the electrode performance to be able to develop durable batteries. To this end, amorphous germanium (a-Ge) was selected as a model electrode material to understand the mechanics of Na-ion battery electrodes. Stress evolution in Ge thin film electrode was measured in-situ during electrochemical sodiation/desodiation cycling. It was observed that the Ge electrode sustains as high as 0.6 GPa of compressive stress during insertion of sodium and 0.75 GPa of tensile stress during extraction of sodium. In spite of no experimental evidence suggesting phase changes in Ge electrodes, the stress response during the initial sodiation reaction with pristine a-Ge was significantly different from that of subsequent sodiation/desodiation cycling. To further understand this interesting stress behavior, a diffusion-deformation theory was formulated and implemented in a finite element code to predict the mechanical and electrochemical response. In this talk, we will present our finite element results and explain the mechanism responsible for the interesting stress behavior observed in our experiments.