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 present novel solid magnesium electrolytes 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. By combining spectroscopic characterization and molecular dynamics simulations with a machine learning-based interatomic potential energy model, we identify that partial anion exchange between the precursors leads to the formation of GaCl 3 -like domains within the amorphous structure, which is responsible for the soft mechanical properties. This partial anion exchange creates undercoordinated magnesium ions in a chlorine-rich environment, 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.