Block Copolymer Solid Electrolytes Based on Comb‐Like Poly(ethylene glycol) Plasticized Poly(ionic liquid)s for Lithium‐Ion Batteries^†

Abstract

Comprehensive SummaryElectrolytes based on poly(ionic liquid)s (PILs) have attracted great attention in the fields of next‐generation solid lithium‐ion batteries. However, the low ionic conductivity prevents their practical applications. Herein, we report novel solid electrolytes based on block copolymers composed of PILs and comb‐like poly(ethylene glycol) (PEG), which were synthesized via ring‐opening metathesis polymerization of 3‐(2‐(bicyclo[2.2.1]hept‐5‐en‐2‐yl)ethyl)‐1‐butyl‐1H‐imidazol‐3‐ium bis((trifluoromethyl)sulfonyl) amide and poly(ethylene glycol monomethyl ether) bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate. Comb‐like PEG acts as plasticizers in block copolymers dominated by PILs to promote the mobility of PILs segments. Effects of the copolymer composition and length of the comb‐like PEG chain on ionic conductivity were investigated. The optimized electrolyte delivers the highest ionic conductivity of 1.5 × 10–5 S·cm–1 at 30 °C, and robust electrochemical stability up to 4.6 V. A solid‐state Li/LiFePO4 cell using the optimized electrolyte demonstrates good cycle performance at 0.2 C with high capacity retention of 92% after 70 cycles at 50 °C.

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“…The decrease in Young's modulus is likely due to the plasticizing effect of PEG, which has been shown to improve the chain mobility of polymerized ionic liquid networks. 36,57,58 For 7.5–7.5-BVIM gels, the Young's modulus was 235.7 ± 25.3 kPa and the strain at break was 898.0 ± 30.2% (Fig. 2a).…”