Performance enhancement induced by electrospinning of polymer electrolytes based on poly(methyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium)

A series of novel fibrous polymer electrolytes with high ionic conductivity based on electrospun poly(methyl methacrylate-co-2-acrylamido-2-methylpropanesulfonic acid lithium) (P(MMA-co-AMPSLi)) membranes were prepared and characterized. P(MMA-co-AMPSLi) was synthesized by free radical copolymerization of MMA and AMPS, followed by ion exchange of the H⁺ with Li⁺. The fibrous polymer electrolytes were fabricated by immersing the electrospun P(MMA-co-AMPSLi) membranes into the liquid electrolyte. Fourier transform infrared spectroscopy and ¹H-nuclear magnetic resonance were used to characterize the structure of the copolymers. Thermogravimetric analysis was applied to investigate the thermal properties of the copolymers. Scanning electromicroscope was employed to observe the morphology of electrospun membranes before and after soaking the liquid electrolyte. AC impedance and linear sweep voltammetry were adopted to measure the electrochemical properties of the fibrous polymer electrolytes. The incorporation of the AMPSLi units effectively improved the electrospinnability of the copolymer, increased the dielectric constants of the electrospun membranes, and enhanced the dimensional stability by maintaining the pore structures even after the membranes absorbing large amounts of liquid electrolytes. As a result, the ionic conductivity of the polymer electrolytes increased with the increase in the molar ratio of AMPSLi units, and the highest ion conductivity was up to 4.12 × 10⁻³ S cm⁻¹ at room temperature. Meanwhile, the polymer electrolytes studied in this work exhibited a sufficient electrochemical stability (up to 5.0 V) that allows the safe operation in lithium-ion batteries.