Salt Ice VI as Solid‐State Electrolytes

Abstract Solid‐state electrolytes (SSEs) are the decisive component of all‐solid‐state batteries (ASSBs), determining both safety and energy density. Instead of pursuing new SSEs via various synthetic methods and ever more complex chemical compositions, here a physical‐phase strategy is proposed: convert simple liquid electrolytes into high‐performance SSEs through pressure‐driven liquid‐solid transitions. Using lithium‐salt aqueous solutions as a model system, the pressure‐induced structural evolution is tracked in situ, and discovered that a conductive salt ice VI emerges reproducibly between 1.3 and 2.5 GPa. In situ high‐pressure electrochemical measurements reveal room‐temperature Li + conductivities of 10 −4 –10 −3 S cm −1 , an activation energy of 0.87 eV, and an electrochemical stability window widens to 3.8 V. Density‐functional calculations and a constructed pressure‐temperature phase diagram further elucidate the favorable migration pathways and robust phase stability of salt ice VI . These findings establish pressure‐phase engineering as a powerful, chemistry‐agnostic route for rapidly discovering next‐generation SSEs beyond traditional synthetic paradigms.