Facile Surface Modification Method to Achieve an Ultralow Interfacial Resistance in Garnet-Based Li Metal Batteries

Among various solid-state electrolytes (SSEs), the garnet type is currently the most promising one to realize Li metal-based batteries with a high energy density and improved safety. However, the huge interfacial resistance, resulting from the poor interface between the Li metal and the pellet, impedes its practical applications in Li metal-based batteries. In this work, we report a facile yet effective methodology to address the issue. The garnet pellet is modified by a thin perhydropolysilazane (PHPS) layer simply via spin coating, which then spontaneously converts into silica by reacting with water vapor and oxygen in air. After lithiation, this layer not only functions as a fast Li⁺ conductor but also dramatically improves the contact between lithium metal and garnet. As a result, the interfacial resistance is substantially reduced from 1046 to 49 ω cm², and a symmetric lithium cell can achieve an ultralow overpotential and stable plating/stripping cyclability without lithium dendrite growth. Furthermore, a full Li/LiFePO₄ battery with the silica modified garnet demonstrates a remarkably higher discharge capacity (>150 mAh g^-1 at 0.1 C), Coulombic efficiency (>99%), and cycling stability (>50 cycles) compared with its pristine counterpart.