Constructing a Uniform and Stable Mixed Conductive Layer to Stabilize the Solid‐State Electrolyte/Li Interface by Cold Bonding at Mild Conditions

Abstract Garnet‐type Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZ) electrolyte is a promising candidate for high‐performance solid‐state batteries, while its applications are hindered by interfacial problems. Although the utilization of functional coatings and molten lithium (Li) effectively solves the LLZ interfacial compatibility problem with Li metal, it poses problems such as high cost, high danger, and structural damage. Herein, a mixed conductive layer (MCL) is introduced at the LLZ/Li interface (RT‐MCL) via an in situ cold bonding process at room temperature. Such a stable and compact RT‐MCL can effectively suppress side reactions and protect the crystal structure of LLZ, and it also inhibits growth of Li dendrites and promotes uniform Li deposition. The critical current density (CCD) of the Li symmetric cell composed of RT‐MCL‐LLZ is increased to 1.8 mA cm^‐2 and provides stable cycling performance over 2000 h under 0.5 mA cm^‐2. Additionally, this in situ cold bonding treatment can significantly reduce cost and eliminate potential safety issues caused by the high‐temperature processing of Li metal. This work highlights tremendous potential of this cold bonding technique in the reasonable design and optimization of the LLZ/Li interface.