Toward Higher Voltage Solid‐State Batteries by Metastability and Kinetic Stability Design

The energy density of battery systems is limited largely by the electrochemical window of the electrolyte. Herein, the combined thermodynamic and kinetic effects of mechanically induced metastability are shown to greatly widen the operational voltage window of solid‐state batteries based on ceramic‐sulfide electrolytes. Solid electrolyte voltage stability up to 10 V is achieved with minimal degradation, far beyond the capability of organic liquid electrolytes. Furthermore, combined experiment, ab initio computation, and theoretical modeling identify the nature of mechanically constrained Li₁₀GeP₂S₁₂ decomposition both within the bulk and at interfaces with cathode materials at very high voltages. Previously unclear kinetic processes are identified that, when properly implemented, can potentially allow solid‐state full cells with remarkably high operational voltages.