Salt Ice VI as Solid-State Electrolytes

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.