Smart construction of multifunctional Li_1.5Al_0.5Ge_1.5(PO₄)₃|Li intermediate interfaces for solid-state batteries

Due to high ionic conductivity, low cost and excellent air stability, NASICON-type Li_1.5Al_0.5Ge_1.5(PO)₄ (LAGP) electrolyte has been a promising candidate for high-performance solid-state batteries. Nevertheless, the poor interfacial compatibilities between LAGP and lithium (Li) metal (i.e., intrinsic instability of LAGP to metallic Li, growth of dendrite Li) retard its commercial application. Herein, a nano multifunctional LiF@Li-zinc (Zn) alloy layer consisting of electrically insulated but ionic conductive lithium fluoride (LiF) and Li-Zn alloy is introduced at the LAGP|Li interface (Z-LAGP) by in-situ conversion reactions. Such LiF@Li-Zn layer not only leads to stable and tight interface with low resistance and effective inhibition of side reactions, but also homogenizes the Li-ion flux with free of dendrite Li. Consequently, the Li|Z-LAGP|Li cells present the improved critical current density as high as 2.0 mA cm⁻², stable cycles with longer than 1000 h at 0.1 mA cm⁻², and as well as superior cycling performance from 0.1 to 0.5 mA cm⁻² with stable overpotential. What is more, the solid-state batteries of Li|Z-LAGP|LiFePO₄ show the good cycle stability with highly reversible capacity (>150 mA h g⁻¹) at 0.1 C under room temperature. This work highlights a rational design for the robust LAGP|Li interface and a novel strategy to optimizing interfacial compatibilities.