Experimental Evaluation of Influence of Stress on Li Chemical Potential and Phase Equilibrium in Two-phase Battery Electrode Materials

We experimentally evaluated the influence of stress on the Li chemical potential (mu(Li)) and phase equilibrium in the two-phase battery electrode materials through the emf measurements while applying a mechanical load. In our measurements, we prepared an electrochemical cell by depositing a thin film of a two-phase electrode material (LiFePO4 or LiCoO2 in the two-phase region) on each of the solid electrolyte surfaces. Then we applied a mechanical load to the electrochemical cell through four-point bending, and the resulting mu(Li) variation in the electrode material was measured as the emf between the two thin films. Our results indicated that mu(Li) in the two-phase electrode materials immediately changed just after loading and then gradually changed while maintaining a constant mechanical load. Besides, the loading and unloading led to the mu(Li) variation in the opposite direction. Such characteristic mu(Li) variations could be explained by considering the change in the phase equilibrium between the two phases, which led to the Li content variation in the two phases and the stress relaxation due to the volume fraction variation of the two phases. Our results can provide valuable insights regarding the influence of stress on the performances of energy storage devices with two-phase electrode materials. (C) The Author(s) 2021. Published by ECSJ.

Automated summary

The experimental results show that the mu(Li) in two-phase electrode materials immediately changes after loading and then gradually changes while maintaining a constant mechanical load. Loading and unloading lead to mu(Li) variations in the opposite direction. This characteristic mu(Li) variations can be explained by considering the change in the phase equilibrium between the two phases.