In situ cross-linked plastic crystal electrolytes toward superior lithium metal batteries

The low ionic conductivity and unstable electrolyte/electrode interface of solid-state electrolytes are the key issues hindering the progress of solid-state lithium batteries. Herein, a cross-linked succinonitrile (SN)-based solid-state electrolyte was synthesized by in situ thermal polymerization using polyethylene glycol diacrylate, vinyl carbonate, and SN. Vinyl carbonate and polyethylene glycol diacrylate are cross-linked to form a polymer network structure, which can immobilize SN and lithium difluoro(oxalato)borate in the electrolyte, thereby preventing the side reactions of SN and lithium metal. The as-prepared quasi-solid gel electrolyte exhibits a wide electrochemical window (5.3 V vs. Li+/Li), a high ionic conductivity (0.3 mS/cm), a good lithium-ion transfer number (0.58) at room temperature, and good interfacial stability between the electrodes and electrolyte. Therefore, cross-linked SN-based polymer electrolyte not only enables reversible lithium anode stripping/plating and impedes side reactions on the anode side but also accommodates high voltage cathode materials. The LiCoO2/Li cell shows a high specific capacity of 140 mAh/g, with a capacity retention rate of 87.2% after 350 cycles and a stable coulombic efficiency of about 99.5% at an operating voltage of 2.75∼4.3 V. This work paves a new path for designing high-safety electrolytes and facilitating the practical application of high-voltage lithium metal batteries.