On the Chemo-Mechanics of Advanced Electrode Materials Via Operando Acoustic Transmission

Abstract

Silicon anodes have emerged as a viable strategy for a negative material in solid-state batteries to balance their reactivity with high energy density. Compared to conventional graphite electrodes, silicon anodes have a large theoretical capacity of 3600 mAh/g compared to 372 mAh/g in graphite. This large capacity comes from the fact that lithiated silicon (Si4Li15) can accommodate 15 Li atoms per 4 Si atoms as opposed to LiC6. As a result, silicon anodes experience large volumetric expansions up to ~300% as Li ions alloy into the Si negative electrode. Acoustic transmission utilizes sound propagation to nondestructively probe electrode chemo-mechanics in operando.c = √(E/ρ)The speed of sound through a material is proportional to its Young’s modulus (E) and inversely proportional to density. Previous works have shown that acoustic transmission can detect gas formation and dewetting in commercial Li-ion cells and Li metal cells. There has also been a study showing acoustics can detect void formation during Li stripping in solid-state Li symmetric cells. To the best of our knowledge, there has not been an acoustic study of an all solid state Li full cell.This work intends to show that acoustic transmission can monitor Si expansion and contraction as a function of waveform damping and the Young’s modulus of the Si electrode. This works gives insight into the mechanical considerations and possible loss of contact as Si lithiates and delithiates repeatedly. The reliance of Si anodes on stack pressure is not well understood and is further elucidated in this work. We hope to give a better understanding of the intersection between the electrochemical reactions at the Si electrode and the mechanical stresses induced on the cell. Figure 1