Unveiling solid-solid contact states in all-solid-state lithium batteries: An electrochemical impedance spectroscopy viewpoint

All-solid-state lithium batteries (ASSLBs) are strongly considered as the next-generation energy storage devices for their high energy density and intrinsic safety. The solid-solid contact between lithium metal and solid electrolyte plays a vital role in the performance of working ASSLBs, which is challenging to investigate quantitatively by experimental approach. This work proposed a quantitative model based on the finite element method for electrochemical impedance spectroscopy simulation of different solid-solid contact states in ASSLBs. With the assistance of an equivalent circuit model and distribution of relaxation times, it is discovered that as the number of voids and the sharpness of cracks increase, the contact resistance R_c grows and ultimately dominates the battery impedance. Through accurate fitting, inverse proportional relations between contact resistance R_c and (1 − porosity) as well as crack angle was disclosed. This contribution affords a fresh insight into clarifying solid-solid contact states in ASSLBs.