High‐Performance Transparent Solid Polymer Electrolyte Based on Copolymer of Deep Eutectic Electrolyte and Methyl Methacrylate for Electrochemical Devices

ABSTRACT Polymerizable deep eutectic electrolytes (PDEEs) have emerged as next‐generation electrolytes for electrochemical devices, addressing the leakage risk of traditional DEEs and the safety concerns of flammable ionic liquid electrolytes. However, a significant challenge hindering further development is the scarcity of DEE‐based polymers capable of simultaneously balance the electrolyte conductivity, mechanical strength, and stability. Herein, a high‐performance poly(DEEs) was engineered by exploiting the synergistic effects of hydrogen bonding and ion‐dipole interactions via the incorporation of acrylamide (AM), succinonitrile, LiClO 4 , and methyl methacrylate (MMA). The solid polymer electrolytes were elaborately designed via in situ copolymerization, facilitating Li + transport through hydrogen bond interaction with NH 2 and C≡N groups, and utilizing the dual‐skeleton framework of AM and MMA to integrate electrochemical and mechanical properties. The optimized poly(DEE‐MMA) exhibits a high ionic conductivity of 1.43 mS cm −1 , a superior Li + transference number of 0.83, and excellent tensile strength of 17.8 MPa at 298 K, enabling the Li||LiFePO 4 battery to deliver an impressive lifespan of 120 cycles with 83% capacity retention and the electrochromic device sustains 2000 coloration‐bleaching cycles with retaining 80% of the initial optical modulation. These findings provide a novel strategy for high‐performance solid polymer electrolytes and demonstrate potential applications in electrochemical devices.