Exploration of Metal Alloys as Zero‐Resistance Interfacial Modification Layers for Garnet‐Type Solid Electrolytes

Abstract A solid‐state battery with a lithium‐metal anode and a garnet‐type solid electrolyte has been widely regarded as one of the most promising solutions to boost the safety and energy density of current lithium‐ion batteries. However, lithiophobic property of garnet‐type solid electrolytes hinders the establishment of a good physical contact with lithium metal, bringing about a large lithium/garnet interfacial resistance that has remained as the greatest issue facing their practical application in solid‐state batteries. Herein, a melt‐quenching approach is developed by which varieties of interfacial modification layers based on metal alloys can be coated uniformly on the surface of the garnet. It is demonstrated that with an ultrathin, lithiophilic AgSn_0.6Bi_0.4O_x coating the interfacial resistance can be eliminated, and a dendrite‐free lithium plating and stripping on the lithium/garnet interface can be achieved at a high current density of 20 mA cm⁻². The results reveal that the uniform coating on the garnet surface and the facile lithium diffusion through the coating layer are two major reasons for the excellent electrochemical performances. The all‐solid‐state full cell consisting of the surface modified garnet‐type solid electrolyte with a LiNi_0.8Mn_0.1Co_0.1O₂ cathode and a lithium–metal anode maintains 86% of its initial capacity after 1000 stable cycles at 1 C.