Fast Room-Temperature Mg-Ion Conduction in Clay-Like Solid Electrolytes

The discovery of mechanically soft solid-state materials with fast Mg-ion conduction is crucial for the development of solid-state magnesium batteries. Herein, we report a novel solid magnesium electrolyte that achieve high ionic conductivity of 0.47 mS/cm at room temperature. These Mg-ion conductors exhibit clay-like mechanical properties, enabling intimate contact at the electrode–electrolyte interface during battery cycling. With a combination of experimental and computational analysis, we identify that the soft-clay formation is induced by partial anion exchange. This partial anion exchange creates undercoordinated magnesium ions, yielding fast Mg-ion conduction. Our work demonstrates the potential of clay-like halide electrolytes for all-solid-state magnesium batteries, with possible further extension to other multivalent battery systems.