Oxidatively stable solid-state ionogels for high-voltage lithium metal batteries

Developing safe and high-performance electrolytes is essential for the advancement of next-generation lithium-ion batteries (LIBs), particularly those employing high-voltage cathodes. In this study, we systematically investigate an effective strategy to enhance the electrochemical stability of ionic liquid electrolytes by solidifying them within a 3D polymer network, forming a quasi-solid ionogel that mitigates oxidative degradation during high-voltage operation using LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cathodes. The polymer matrix, containing electron-withdrawing moieties and amorphous domains, enhances electrolyte confinement and oxidative stability. Compared to the liquid electrolyte, which decomposes at ~4 V (vs. Li/Li + ), the ionogel exhibits a wider electrochemical window, high ionic conductivity (8.3 mS cm −1 ), and a lithium-ion transference number of 0.53. Lithium stripping/plating tests confirm excellent interfacial stability and long-term cycling over 400 h. When applied in lithium metal cells with NCM811 cathodes, the ionogel achieves a discharge capacity of 160.9 mAh g −1 at 0.1C and maintains 124.6 mAh g −1 at 2C, with 94 % capacity retention after 100 cycles at 0.5C. Scanning and transmission electron microscopy (SEM and TEM) analyses reveal that the use of an ionogel electrolyte effectively suppresses oxidative electrolyte degradation and results in a cleaner cathode surface. These findings highlight the potential of quasi-solid-state ionogels as robust, safe, and high-voltage-compatible electrolytes for next-generation LIBs. • The polymer matrix suppresses oxidative decomposition of the ionic liquid electrolyte under high-voltage conditions. • Ionogel shows a wide electrochemical window (~5.5 V vs Li/Li + ), exceeding the neat ionic liquid. • Lithium stripping/plating remains stable for over 400 h with low polarization. • High ionic conductivity and a high lithium-ion transference number enable fast, selective ion transport.