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

Solid-state electrolytes (SSEs) have attracted increasing attention for next-generation electrochemical energy storage technologies due to their high energy-density, extended cycle life, and enhanced safety compared to conventional Li-ion batteries with organic liquid electrolytes. Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a widely used NASICON-typed solid electrolyte in all solid-state batteries (ASSBs) owing to its high ionic conductivity and excellent chemical and thermal stability. However, traditional densification of LATP requires a high-temperature and long-duration sintering process, which may lead to the loss of mobile cations and changes in stoichiometry. Herein, we report a cold sintering process for the densification of halide-in-LATP composite electrolyte at 150 ℃ using a transient liquid phase, N,N-dimethylformamide (DMF), as a sintering aid. This low-temperature co-sintering method enables the integration of LATP particles with Li3InCl6 halide as a boundary phase, improving the ionic conductivity of the co-sintered halide-in-oxide composite solid electrolytes. We studied various sintering conditions and effect of halide phase on the composition, microstructure, and electrochemical properties of sintered composite SSE. The result revealed that LATP with 20 wt% of Li3InCl6, sintered at 150 ℃ under 500 MPa pressure for 1 hour, exhibited the highest ionic conductivity (1.4x10-4 S cm-1 at room temperature). The symmetric Li|SSE|Li cell demonstrated a stable stripping and plating processes for 1700 hours at 55 ℃ (0.1 mA cm-2,), and 1200 hours at 100 ℃ (1 mA cm-2). This indicates that the halide boundary phase can bridge the LATP conducting phase with reduced interface resistance, resulting in fast, stable lithium-ion transport and high ionic conduction.