LAUSR

Lithium–solid electrolyte (SE) improper contact and morphological instabilities at the interface during Li plating and stripping are two critical problems that may hinder the realization of Li metal solid‐state batteries (SSBs). While the application of a substantial stack pressure during battery operation can potentially overcome these issues, its proper metering is challenging, especially, when Li metal is employed as the anode, as demonstrated here with Li6PS5Cl as the SE. The low yield strength of Li leads to its extrusion through the micropores of a considerably dense (≈92%) SE even under a moderate stack pressure, resulting in mechanically induced short circuit, which is expedited with decreasing SE thickness. This predicament is avoided at low stack pressures, but inhomogeneous Li plating/stripping triggers dendritic failure at higher currents. Besides highlighting the significance of assembly pressure on the Li‐SSB performance, a comprehensive understanding of the too much versus too little stack pressure dilemma is presented here, which can potentially guide the development of strategies to overcome the electrochemomechanical issues at the Li–SE interface.