Two-step cold sintering of Li1.3Al0.3Ti1.7(PO4)3 composite solid electrolyte with non-equilibrium microstructures for enhanced electrochemical performance

Abstract

Due to the high ionic conductivity and low cost, Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) has emerged as a promising solid-state electrolyte for next-generation Li metal solid-state batteries. However, the susceptibility of LATP to side reactions with Li metal and the significant resistance at grain boundaries pose major challenges for the applications of all-solid-state batteries. In this work, the non-equilibrium microstructure at the interface of a LATP composite solid electrolyte (84 wt% LATP and 16 wt% LiTFSI) was adjusted by two-step cold sintering, reducing interfacial transport barriers for optimizing ionic transport paths and reducing sensitivity to Li metal anodes, thus increasing the ionic conductivity and interfacial stability of solid electrolytes. While preserving the original grain structure, the grain boundary resistance was significantly reduced, resulting in an impressive ionic conductivity of 7.3 × 10⁻⁴ S cm⁻¹. Additionally, the solid electrolyte had a high density of 97% and demonstrated excellent interfacial compatibility and electrochemical stability by maintaining stable cycling for 2300 h at 0.1 mA h cm⁻². This further demonstrates the favorable effect of the non-equilibrium microstructure on ion transport across grain boundaries and enhancing interfacial stability, which is crucial for achieving high performance. In conclusion, two-step cold sintering, with its unique process, offers significant advantages in modulating the interfacial microstructure and presents a novel solution for interfacial engineering.