Among the families of solid electrolytes, sulfides retain the highest ionic conductivity. [10][11][12][13][14] Sulfide glass solid electrolytes [15,16] and glass-ceramic solid electrolytes [17][18][19] have demonstrated ionic conductivities on the order of 0.1 − 1 mS cm −1 and above 1 mS cm −1 , respectively. The ceramic-sulfide electrolytes, most notably Li 10 GeP 2 S 12 (LGPS) and Li 10 SiP 2 S 12 (LSPS), are particularly promising as they maintain exceptionally high ionic conductivities.LGPS was one of the first solid electrolytes to reach ionic conductivities comparable with liquid electrolytes [20] at 12 mS cm −1 , only to then be displaced by LSPS [10] which achieved the highest reported ionic conductivity of 25 mS cm −1 . However, despite these superior ionic conductivities, the ceramicsulfide family has been plagued by reports of narrow electrochemical stability windows [11,13,21] and interfacial reactions with common electrode materials. [4,11,22] Moreover, the reported electrochemical stability windows of ceramic-sulfides suffer from substantial inconsistencies. Several works, both computational and experimental, have shown that the ceramic-sulfides are only stable in the narrow voltage window on the order of 1.7-2.1 V versus lithium, [11][12][13]21] which is the correct general thermodynamic prediction. Many others, however, have experimentally found that the upper voltage limit can reach in excess of 4-6 V versus lithium. [10,20,23,24] A consolidated understanding of these findings is needed in order to establish design principles for practical ceramic-sulfide batteries.In this work, we develop a generalized thermodynamic theory that unifies these disparate findings and, hence, provides the unique design principle through mechano-electrochemical effect for ceramic-sulfide-based solid-state batteries. Expanding upon our previous work, [25] in which core-shell morphologies were used to widen the voltage window of LSPS, we derive a generalized strain stabilization model that indicates at which voltages strain-induced stabilization can lead to metastability of the ceramic-sulfide phases. A mean-field solution to our generalized strain model recovers our previous model [25] and is shown to be a lower limit on the strain induced stability. The second solution we explore, a nucleation or inclusion decay, is shown to provide a greater capability for stabilization. Note that our current and previous [25] understanding forms a general theoretical framework for the design of ceramic electrolyte with widened voltage stability, which is not limited to any particular design strategy, such as the core-shell morphology of Ceramic-sulfide solid electrolytes are a promising material system for enabling solid-state batteries. However, one challenge that remains is the discrepancy in the reported electrochemical stability. Recent work has suggested that it may be due to the sensitivity of ceramic sulfides to mechanically induced stability. Small changes in ceramic-sulfide microstructure, for example, have been shown to c...
