Synthesis and properties of gel polymer electrolyte membranes based on novel comb-like methyl methacrylate copolymers

Based on the principle of molecular design, three comb-like methyl methacrylate copolymer matrixes for gel polymer electrolyte (GPE) were designed and synthesized by reacting methyl methacrylate-maleic anhydride copolymer (P(MMA-MAh)) with poly(ethylene glycol) monomethyl ether (PEGME) of different molecular weight (350, 600, and 750) respectively. The structures of comb-like polymers were characterized by Fourier transform infrared (FTIR) and ¹H-nuclear magnetic resonance (¹H NMR), and their thermal properties were investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The membranes of P(MMA-MAh) copolymer and comb-like copolymer based polymer electrolytes, plasticized with propylene carbonate (PC) and LiClO₄ as salt, have been prepared by solution casting technique respectively. And AC impedance was used to characterize the ion conductivity of GPE systems. Compared with P(MMA-MAh) copolymer, introducing the flexible ether chain segments can reduce the resistance of ion transport in polymer matrix and improve the mobility of electroactive ions in the GPE systems. With the increase in side chain length of copolymers, ionic conductivity of GPEs is improved dramatically. The highest conductivity observed in MMA/MAh-g-PEGME600 GPE system (matrix content: 45 wt%) is 1.22 × 10^-3 S/cm at 60 °C. And temperature dependence of GPE membranes could be described by Vogel-Tamman-Fulcher (VTF) behavior. TGA curves showed that these gel polymer electrolyte membranes possessed favorable thermal stability for lithium ion battery use.