Efficient Li ⁺ Transport through a Single-Ion-Conducting Protective Layer for Stable Lithium–Metal Batteries

The application of metallic Li anodes as high-capacity anodes is usually compromised by unstable solid electrolyte interphase, Li⁰ dendrites, and side reactions, which lead to diminished cycling performance and serious safety concerns. To mitigate these issues, a hybrid single-ion-conducting protective layer (i.e., SPL-20) is proposed to enhance both the cycling lifetime and the safety of Li-metal batteries. With single-ion-conducting properties, such a layer can effectively reduce the uneven distribution of surface reactions, as evidenced by both simulations and electrochemical measurements. Thus, SPL-20 possesses the advantages of suppressing Li⁰ dendrites, preventing rapid capacity decay, and operability at extreme conditions (e.g., -25 °C). Notable achievements include an anode-free battery (LiFePO₄/SPL-20@Cu cell) with a capacity retention of 59% at 0.5 mA cm⁻² after 50 cycles, a LiFePO₄/SPL-20@Li cell with a capacity of ∼110 mAh g⁻¹ at 2C, especially a full cell with high-voltage cathode and 20 μm thick Li anode (NCM811/SPL-20@Li cell) with specific capacity of 172 mAh g⁻¹ under 25 °C and 143.1 mAh g⁻¹ under -25 °C after 100 cycles. This modified anodic interface strategy provides promising solutions to conquer interface challenges in high-performance Li-metal batteries.