The interface between solid electrolytes and Li metal anode is a significant hurdle for the development of all-solid-state lithium metal batteries. Introducing a thin gel polymer electrolyte interlayer to conformally coat solid electrolytes can improve the interface wettability of Li metal anode and thus reduce the interfacial resistance. Here we used a plasticized poly(ethylene oxide)-based electrolyte with high concentrations of bis(trifluoromethane)sulfonamide lithium (LiTFSI) that show 100% amorphous character. These electrolytes show Li+ conductivity as high as σ = 2.9 × 10−4 S cm−1 at room temperature. We discovered by thermogravimetric analysis (TGA) with off-gas analysis in conjunction with nuclear magnetic resonance (NMR) spectroscopy that the electrolyte films had absorbed N-methyl-2-pyrrolidone (NMP) vapors to form a gel electrolyte. We incorporated the gel electrolyte as an interfacial modification layer between LLZO and Li metal electrodes and found a 58 times reduction in the area specific resistance (ASR) at room temperature.

Solid-state electrolytes are continually being explored for Li-ion batteries due to their enhanced safety and their enabling of high energy density active materials, particularly Li metal anodes. However, the interface between solid-state electrolytes and Li metal anodes are prone to high impedance due to poor contact, limiting their applicability. Introducing a thin gel polymer electrolyte interlayer to conformally coat solid electrolytes can improve the interfacial contact of Li metal anode and thus reduce the interfacial resistance. Here we used a plasticized poly(ethylene oxide)-based electrolyte with high concentrations of bis(trifluoromethane)sulfonamide lithium (LiTFSI) that show 100% amorphous character. These electrolytes show Li+ conductivity as high as σ = 2.9×10-4 S/cm at room temperature. We discovered by thermogravimetric analysis (TGA) with off-gas analysis in conjunction with nuclear magnetic resonance (NMR) spectroscopy that the electrolyte films had absorbed N-methyl-2-pyrrolidone (NMP) vapors to form a gel electrolyte. We incorporated the gel electrolyte as an interfacial modification layer between LLZO and Li metal electrodes and found a 58 times reduction in the area specific resistance (ASR) at room temperature.

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