Li-ion cell with poly(acrylonitrile-methyl methacrylate)-based gel polymer electrolyte

Poly(acrylonitrile-methyl methacrylate) (AMMA) plasticized with 1 m LiBF4 dissolved in γ-butyrolactone (GBL) liquid electrolyte was studied as a gel polymer electrolyte (GPE) of Li-ion cell. Typically, a GPE composed of 12 wt.% AMMA and 88 wt.% liquid electrolyte has an ionic conductivity of 3.9 mS/cm at 20 °C and 1.1 mS/cm at −30 °C. Results of cyclic voltammetry showed that such a GPE is electrochemically stable to withstand the normal operation of a Li-ion cell. With this GPE, Li/graphite and Li/cathode half-cells presented 89% and 80%, respectively, of Coulombic efficiency (CE), in the first cycle and approached to unity in the following cycles. For graphite/GPE/cathode Li-ion cell, its initial CE was 82%, being close to the lower one of either half-cell. Due partially to high ionic conductivity of the GPE, the Li-ion cell can be reversibly cycled in a wide temperature range. In particular, the Li-ion cell retained as high as 66% of discharge capacity even at −30 °C, as compared to that obtained at 20 °C, when it was cycled at 0.5 mA/cm2 (∼0.5 °C) between 2.5 and 4.2 V.