Cold Sintering Halide-in-Oxide\nComposite Solid-State\nElectrolytes with Enhanced Ionic Conductivity

All-solid-state batteries (ASSBs) have attracted increasing\nattention\nfor next-generation electrochemical energy storage due to their high\nenergy density and enhanced safety, achieved through the use of nonflammable\nsolid-state electrolytes (SSEs). Oxide-based SSEs, such as Li<sub>1.3</sub>Al<sub>0.3</sub>Ti<sub>1.7</sub>(PO<sub>4</sub>)<sub>3</sub> (LATP), are notable for their high ionic conductivity and excellent\nchemical and electrochemical oxidation stability. Nevertheless, their\nbrittle mechanical properties and poor interface contact with electrode\nmaterials necessitate high-temperature and long-duration sintering\nor postcalcination processes, limiting their processability for real-world\napplications. Additionally, the formation of secondary phases can\ndetrimentally affect the ionic conductivity of LATP electrolytes.\nEmerging halide-based SSEs offer reliable deformation for practical\nprocessing while maintaining high ionic conductivity. In this work,\nwe report a transient liquid-assisted cold sintering process to integrate\noxide-based LATP as the matrix and halide-based Li<sub>3</sub>InCl<sub>6</sub> as the conductive boundary phase into a halide-in-oxide ceramic\ncomposite electrolyte at a low processing temperature of 150 °C.\nThis composite structure significantly reduces interface resistance,\neffectively addressing ion-transport depletion across the boundaries\nbetween LATP particles. Consequently, the cosintered LATP-Li<sub>3</sub>InCl<sub>6</sub> composite SSE exhibits a high ionic conductivity\nof 1.4 × 10<sup>–4</sup> S cm<sup>–1</sup> at ambient\ntemperature. Furthermore, the symmetric Li|LATP-Li<sub>3</sub>InCl<sub>6</sub>·<i>n</i>DMF|Li cell demonstrates stable stripping\nand plating processes for 1600 h at 55 °C (0.1 mA cm<sup>–2</sup>) and 1200 h at 100 °C (1 mA cm<sup>–2</sup>). This work\nrepresents the first demonstration of halide–oxide ceramic\ncomposite SSEs that combine the advantages of oxides and halides for\nhigh-performance SSBs.