In Situ Construction of a Lithiophilic and Electronically Insulating Multifunctional Hybrid Layer Based on the Principle of Hydrolysis for a Stable Garnet/Li Interface

Abstract Adapting solid‐state Li‐metal batteries is an attractive way to pursue higher energy density and safety compared to liquid‐based ones. With high ionic conductivity and excellent stability with Li, Ta‐doped Li₇La₃Zr₂O₁₂ (LLZTO) is an effective option. However, the poor solid–solid interface contact induced by the lithiophobic Li₂CO₃ layer hinder its practical application. Herein, a versatile strategy is proposed based on the hydrolysis of sodium tetrafluoroborate (NaBF₄), aiming to convert the Li₂CO₃ into multifunctional hybrid layer containing LiF, LiBO₂, and NaF. Among them, LiF and LiBO₂ serve as the primary Li ion conductors, the introduction of NaF with high surface energy not only enhances the interface wettability, but also further elevates the critical dendrite strength against Li dendrites. All three components serve as excellent electronic insulators, suppressing electron invasion at the interface and preventing Li dendrite growth in the solid electrolyte. As expected, the interfacial impedance of the NaBF₄ treated symmetric cell is reduced to 6.0 Ω cm², the critical current density (CCD) comes to 2.0 mA cm⁻², and cycles over 3000 h at 0.3 mA cm⁻² and 1500 h at 0.5 mA cm⁻² respectively. Besides, the modified SSBs matched with LiFePO₄ or LiNi_0.6Co_0.2Mn_0.2O₂ cathode show great long‐term cycling and rate performance.