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 Li2Zr0.625Ta0.3Cl4.2O0.9 halide electrolyte, synthesized via a non-equimolar cation-anion amorphous engineering strategy based on Li2ZrCl6, 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 LiNi0.88Mn0.06Co0.06O2 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. High-voltage solid-state batteries require conductive, stable electrolytes for fast charging. Here, authors show that an amorphous Zr-based oxyhalide electrolyte combines high ionic conductivity with self-passivating interphases, enabling sustained cycling at high voltages.