Characterizing the Li-Solid-Electrolyte Interface Dynamics as a Function of Stack Pressure and Current Density

The replacement of conventional liquid electrolytes with solid electrolytes has the potential to safely enable energy-dense Li-metal anodes. Because of the challenges surrounding solid-solid interfaces, it is crucial to better understand the Li-metal-solid-electrolyte interface. This work utilizes stack pressure to correlate mechanics with the electrochemical behavior of Li-electrolyte cells during galvanostatic cycling. Symmetric cells are constructed using Li7La3Zr2O12 and tested using AC and DC techniques under dynamic stack pressure conditions. It is demonstrated that significant polarization occurs during galvanostatic cycling at a current-dependent “critical stack pressure.” Using reference electrodes, this effect is isolated to the Li stripping electrode. This suggests that at low pressures, the Li stripping rate exceeds the rate at which mechanical deformation replenishes the interface, inducing the formation of voids and ultimately increasing resistance. This analysis not only motivates the need for further understanding of the Li-metal-solid-electrolyte interface but also provides guidelines for the future design of all-solid-state batteries.