Zr-based oxyhalide superionic electrolyte with self-passivating interphase stabilisation for high-voltage and fast-charging all-solid-state lithium batteries

The pursuit of high-energy-density all-solid-state lithium batteries necessitates integration with next-generation high-voltage positive electrodes. However, a critical challenge lies in the intrinsic instability of most highly ionically conductive solid electrolytes, which decompose at potentials above 4.30 V vs Li + /Li, resulting in severe interfacial degradation and increased impedance. Here, we show that an amorphous Li 2 Zr 0.625 Ta 0.3 Cl 4.2 O 0.9 halide electrolyte, synthesized via a non-equimolar cation-anion amorphous engineering strategy based on Li 2 ZrCl 6 , effectively overcomes this limitation. With a high ionic conductivity of 4.11 mS cm −1 at 25 °C, it enables stable high-potential cycling through kinetically stabilized operation mediated by a self-passivating positive electrode–electrolyte interphase. When paired with LiNi 0.88 Mn 0.06 Co 0.06 O 2 positive electrode and a Li-In alloy negative electrode, the cells retain up to 81.2% of the initial capacity after 2,000 cycles at 10 C under cell cutoff voltages of 4.18 V (corresponding to 4.80 V vs Li⁺/Li). Overall, non-equimolar cation–anion amorphous engineering enables conductive, high-voltage-tolerant Zr-based halides for all-solid-state lithium batteries.