Correlation between Pulse Charging, Volume Expansion and Structural Degradation in Silicon Electrodes for Li-Ion Batteries

Abstract

Silicon electrodes experience substantial volume expansion upon lithium insertion. The volume change is approximately linear with Li concentration which leads to a constant rate of expansion under galvanostatic charging. Interestingly, recent experiments have revealed that the rate of expansion (or contraction) spikes immediately following the application of a constant current, before converging to the lower, steady state value. This effect is seen throughout the entire range of charge and slowly fades away in the course of electrochemical cycles. The volumetric shock can have important implications on the structural stability of strain-rate sensitive materials during pulsed charging. In this work, we use operando nanoindentation to study the effect of the pulse frequency on the rate of expansion and structural evolution of silicon thin films. The electrode is subjected to intermittent step galvanostatic (dis)charge, and the volumetric response is recorded in the course of multiple cycles. The structural degradation is characterized via in-situ optical microscopy and possible mechanisms leading to experimental observations are discussed accordingly.