Cold Sintering of Halide-in-Oxide Composite Solid-State Electrolytes

All-solid-state batteries (ASSBs) have attracted increasing attention for next-generation electrochemical energy storage owing to their high energy density and enhanced safety, achieved through the use of non-flammable solid-state electrolytes (SSEs). Oxide-based SSEs, such as Li1.3Al0.3Ti1.7(PO4)3 (LATP), are notable for their high ionic conductivity and excellent chemical and electrochemical oxidation stability. Nevertheless, their brittle mechanical properties and poor interface contact with electrode materials necessitate high-temperature and long-duration sintering or post calcination processes, limiting their processability for real-world applications. Additionally, the formation of secondary phases can detrimentally affect the ionic conductivity of LATP electrolytes. Emerging halide-based SSEs offer reliable deformation for practical processing while maintaining high ionic conductivity. In this work, we report a transient liquid-assisted cold sintering process to integrate oxide-based LATP as the matrix and halide-based Li3InCl6 as the conductive boundary phase into a halide-in-oxide ceramic composite electrolyte at a low processing temperature of 150 ℃. This composite structure significantly reduces interface resistance, effectively addressing ion transport depletion across the boundaries between LATP particles. Consequently, the co-sintered LATP-Li3InCl6 composite SSE exhibits high ionic conductivity of 1.4x10-4 S cm-1 at ambient temperature. Furthermore, the symmetric Li|LATP-Li3InCl6∙nDMF|Li cell demonstrates stable stripping and plating processes for 1600 hours at 55 ℃ (0.1 mA cm-2) and 1200 hours at 100 ℃ (1 mA cm-2). This work represents the first demonstration of ceramic-in-ceramic SSEs that combine the advantages of oxides and halides for high-performance SSBs.