Wet Chemistry Route to Li3InCl6: Microstructural Control Render High Ionic Conductivity and Enhanced All-Solid-State Battery Performance.

Abstract

Thanks to superionic conductivity and compatibility with >4 V cathodes, halide solid electrolytes (SEs) have elicited tremendous interest for application in all-solid-state lithium batteries (ASSLBs). Many compositions based on groups 3, 13, and divalent metals, and substituted stoichiometries have been explored, some displaying requisite properties, but the Li⁺ conductivity still falls short of theoretical predictions and appealing sulfide-type SEs. While controlling microstructural characteristics, namely grain boundary effects and microstrain, can boost ionic conductivity, they have rarely been considered. Moving away from the standard solid-state route, here a scalable and facile wet chemical approach for obtaining highly conductive (>2 mS cm^-1) Li₃InCl₆ is presented, and it is shown that aprotic solvents can reduce grain boundaries and microstrain, leading to very high ionic conductivity of over 4 mS cm^-1 (at 22 °C). Minimized grain boundary area renders improved moisture stability and enhances solid-solid interfacial contact, leading to excellent LiNi_0.6Mn_0.2Co_0.2O₂-based full-cell performance, exemplified by stable room temperature (22 °C) cycling at a 0.2 C rate with 155 mAh g^-1 capacity and 85% retention after 1000 cycles at 60 °C with a high 99.75% Coulombic efficiency. The findings showcase the viability of the aprotic solvent-mediated route for producing high-quality Li₃InCl₆ for all-solid-state batteries.