Interface Engineering for Constructing Air-Stable and Lithiophilic Garnet-Type Solid Electrolytes

Garnet-type solid electrolytes (SEs) exhibit high ionic conductivity, a wide electrochemical window, and lithium stability, making them ideal for solid-state Li metal batteries. However, their air sensitivity leads to Li₂CO₃ formation, causing poor Li wettability, high interfacial resistance, and dendrite growth. To address this, Mg₃(PO₄)₂ is coated via a wet chemistry method, converting Li₂CO₃ into a Li₃PO₄/MgO composite upon heating. This composite prevents reactions with moisture and CO₂, ensuring air stability while enhancing Li wettability and reducing interfacial resistance. The Li⁺-conducting Li₃PO₄ and insulating MgO in the composite interface enable rapid Li⁺ diffusion while effectively suppressing electron penetration, resulting in a high critical current density of 1.1 mA·cm^–2, with stable cycling for over 1200 h at 0.4 mA·cm^–2. Furthermore, the modified SEs demonstrate excellent cycling stability in Li metal batteries with LiFePO₄ and LiCoO₂ cathodes, confirming the practical feasibility of this solid electrolyte interface modification strategy.