Study of a novel gel electrolyte based on poly-(methoxy/hexadecyl-poly(ethylene glycol) methacrylate) co-polymer plasticized with 1-butyl-3-methylimidazolium tetrafluoroborate

Abstract

Compared with traditional liquid electrolytes, solid polymer electrolytes possess higher reliability and safety but much lower ionic conductivity, which can be improved by incorporating plasticizers to form gel polymer electrolytes (GPEs). However, the commonly employed plasticizers are flammable organic solvents which may cause safety issues. Herein, ionic liquid 1-bultyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄) is selected as the plasticizer to fabricate inflammable GPE due to its non-volatility and inflammability. The solid matrix is co-polymerized from methoxy-poly(ethylene glycol) methacrylate (MPEGM) and hexadecyl-poly(ethylene glycol) methacrylate (HPEGM). The effect of the electrolyte composition on its properties is systematically studied. The synthesized GPEs possess excellent thermal stability and exhibit relatively high ionic conductivity, among which the one named as PMH₁₂-60, composed of 32 wt% MPEGM, 8 wt% HPEGM and 60 wt% [Bmim]BF₄, presents an ionic conductivity comparable to liquid electrolytes, up to 1.13 × 10⁻³ S cm⁻¹ at 30 °C. In addition, the GPE shows good compatibility with metallic lithium. Furthermore, the coin cell based on PMH₁₂-60, with a LiFePO₄ cathode and a lithium anode shows a discharge capacity as high as 145 mA h g⁻¹ and 158 mA h g⁻¹ when cycled at 30 °C and 50 °C, respectively, under the cycling rate of 0.1 C. Moreover, no obvious capacity loss is observed after 30 cycles at both temperatures.