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 a novel strategy of incorporating CO₃²⁻ into halide-based electrolytes, effectively decoupling the inherent trade-off between ionic transport and environmental stability. The CO₃²⁻ 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 (>1,000 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.