Unlocking Solid-State Sodium-Metal Batteries at -15 °C by Electrolyte Optimization and Interface Regulation.

Beta-AlO-based solid-state sodium metal batteries are some of the best options for large-scale energy storage systems because of their high energy density, high-level safety, and low cost. Nevertheless, their room-/low-temperature operation remains challenging due to low ionic conductivity of Beta-AlO electrolyte and weak solid-solid contact of the Na/Beta-AlO interface. Herein, an integrated strategy was developed via electrolyte optimization and interface regulation, in which Cu as a stabilizing agent was incorporated into Beta-AlO to improve density and ionic conductivity and the InS interface layer was introduced between the Na anode and solid electrolyte to induce the in situ formation of a mixed conductive layer (Na-In alloy and NaS). The integrated strategy bolstered the interfacial electrochemical stability and promoted fluent Na transport, allowing the symmetric battery to cycle steadily for more than 2670 h at room temperature with a current density of 0.2 mA cm. Impressively, it demonstrated remarkable endurance, cycling at 0.025 mA cm for more than 3315 h at -15 °C. The NaV(PO)|Beta-AlO-0.5 .% Cu@InS|Na full battery demonstrated outstanding cyclic stability and rate performance at -15 °C and room temperature, underscoring its potential for low-temperature solid-state sodium-metal batteries.