A 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 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-GF 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 endow the DESD-SIPN-GF with a voltage stability of up to 4.97 V. Accordingly, the LCO/DESD-SIPN-GF/Li cell stably cycles 500 times at 1 C and 4.6 V, and the NCM811/DESD-SIPN-GF/Li cell delivers a steady cycling performance at different cutoff voltages of 4.3 V, 4.5 V, and even 4.7 V.