Excellent Li/Garnet Interface Wettability Achieved by Porous Hard Carbon Layer for Solid State Li Metal Battery

Abstract Garnet‐type Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) electrolyte is considered as a promising solid electrolyte because of its relatively high ionic conductivity and excellent electrochemical stability. The surface contamination layer and poor Li/LLZTO interface contact cause large interfacial resistance and quick Li dendrite growth. In this paper, a porous hard carbon layer is introduced by the carbonization of a mixed layer of phenolic resin and polyvinyl butyral on the LLZTO surface to improve Li/garnet interfacial wettability. The multi‐level pore structure of the hard carbon interlayer provides capillary force and large specific surface area, which, together with the chemical activity of the carbon material with Li, promote the molten Li infiltration with garnet electrolyte. The Li/LLZTO interface delivers a low interfacial resistance of 4.7 Ω∙cm 2 at 40 °C and a higher critical current density, which can achieve stable Li + conduction for over 800 h under current densities of 0.1 and 0.2 mA∙cm −2 . The solid‐state battery coupled with Li and LiFePO 4 exhibits excellent rate and cycling performance, demonstrating the application feasibility of the hard carbon interlayer for a solid state Li metal battery.