Advanced Ti-based multi-electron pair electro-active solid halide electrolyte for all-solid-state lithium batteries

Abstract

The development of high-energy-density all-solid-state lithium batteries (ASSLBs) hinges critically on the design of advanced composite cathode components. While significant progress has been made in optimizing solid electrolytes as separators, the advancement of catholytes—particularly those combining multi-electron pair redox activity, high ionic conductivity, and mechanical compressibility—remains underexplored. A key challenge in current composite cathodes is the non-negligible high loading of electro-inactive electrolytes, which drastically reduces the energy density of the ASSLBs. To address this limitation, we propose an alternative strategy to improve the energy density by using Li_2.6Ti_0.6Zr_0.4Cl₆ as an electro-active catholyte with multi-electron pair. This material exhibits exceptional ionic conductivity (1.39 mS cm^–1 at 25°C) while simultaneously delivering a highly reversible specific capacity of approximately 90.62 mAh g^–1. Aliovalent Ti substitution enhances ionic conductivity through a structural transition from high-symmetry to low-symmetry space groups, coupled with a crystallinity strengthening effect. Moreover, the composite cathode of Li_2.6Ti_0.6Zr_0.4Cl₆ and LiFePO₄ reveals an impressive initial discharge capacity of 258.97 mAh g^–1_LFP. This work introduces a new type of functional electro-active catholyte, significantly enhancing the energy density and cost-effectiveness of ASSLBs, opening new avenues for the development of next-generation solid-state battery technologies.