Carbonate‐Anion Engineering Enables Humidity‐Resistant Halide Solid Electrolytes with Superionic Conductivity

The commercialization of all‐solid‐state batteries (ASSBs) is hindered by the lack of a solid electrolyte (SE) that simultaneously delivers high ionic conductivity, resilience to humidity, and efficient low‐temperature operation. Herein, we propose to develop solid‐state electrolytes (SEs) by reacting Li 2 CO 3 with chloride frameworks. The CO 3 2− group serves a dual function: it forms a rigid, hydrolysis‐resistant scaffold via non‐hydrolysable metal‐carbonate bonds, while its high polarizability and charge delocalization soften local phonon modes, significantly reducing the activation energy for Li + migration. Ta‐based SE achieves an ionic conductivity of 7.1 mS cm −1 at 25°C, ranking among the highest for amorphous SEs; Zr‐based SE retains 80% of its conductivity after direct exposure to humid air (20% RH, 2 h), outperforming commercial sulfide and halide counterparts. ASSBs employing these SEs demonstrate ultralong cycling stability (>1000 cycles with 90% capacity retention at 25°C) and unprecedented low‐temperature performance, operating effectively down to −60°C. This work establishes a generalizable design principle for next‐generation SEs that unify high conductivity, stability, and practicality.