Deep eutectic solvent-based semi-interpenetrating polymer electrolyte for high-voltage stable lithium-metal batteries

Although solid polymer electrolytes (SPEs) hold great promise for high-performance lithium metal batteries (LMBs), the low ionic conductivity and narrow electrochemical window limit their practical application. Herein, we report an ethyl cyanoacrylate (ECA) based semi-interpenetrating polymer network (SIPN) structured SPEs without a traditional solvent removal process. The fabricated deep eutectic solvent (DES) is utilized as both a plasticizer and initiator to trigger the anionic polymerization of ECA to form the linear PECA (DES-PECA). The polymer network formed by copolymerization of poly (ethylene glycol) dimethacrylate and methyl methacrylate is further incorporated to afford the SIPN-based SPEs with lithium difluoro(oxalato)borate as an additive (DESD-SIPN). Benefitting from the unique SIPN structure with a crosslinked polymer network affording mechanical robustness and linear polymer providing high mobility, the DESD-SIPN achieves a decent tensile strength of 1.3 MPa and a high ionic conductivity of 0.139 mS cm-1. The DES and PECA also enable the DESD-SIPN with a voltage stability of up to 4.97 V. Accordingly, the LCO/DESD-SIPN/Li cell stably cycles for 500 times at 1 C and 4.6 V, and the NCM811/DESD-SIPN/Li cell delivers a steady cycling performance at different cutoff voltages of 4.3 V, 4.5 V, and even 4.7 V.