Application of quaternary polymer electrolyte based on ionic liquid in LiFePO₄/Li, Li₄Ti₅O₁₂/Li and LiFePO₄/Li₄Ti₅O₁₂ batteries

Highlights: • Paper describes properties of polymer electrolyte based on IL for lithium-ion batteries. • LiNTf₂ + MePrPipNTf₂ + PVdF+ VC polymer electrolyte shows good compatibilities with LFP and LTO. • The full LFP/PE/LTO cell could deliver high specific capacities at moderate rates and displayed good cycling performances. - Abstract: In the present study, a type of polymer electrolyte (PE) based on a PVdF polymer network, MePrPipNTf₂ + LiNTf₂ ionic liquid (MePrPip: N-methyl-N-propylpiperidinium cation, NTf₂ is bis(trifluoromethanesulphonyl)imide anion) and vinylene carbonate (VC) as the SEI forming additive was prepared by the casting technique. The produced PE working together with the LiFePO₄ (LFP) and Li₄Ti₅O₁₂ (LTO) was characterized by thermal gravimetry (TG), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic sweep voltammetry (CV) and galvanostatic charging/discharging. PE had a high ionic conductivity of 4.4 mS cm⁻¹ at 25 °C with an activation energy of 12.4 kJ mol⁻¹. The membrane with IL showed a thermal decomposition temperature of 310 °C. The LiFePO₄ cathode showed good cyclability (161 mAh g⁻¹ after 40 cycles) and coulombic efficiency (99%). Charge/discharge tests of Li₄Ti₅O₁₂/PE/Li cells at different C rates exhibited a good specific capacity of 158 mAh g⁻¹ and 133 mAh g⁻¹ at C/5 and C/2, respectively. The efficiency of the full LFP/PE/LTO cell charging/discharging under study was high (ca. 151 mAh g⁻¹ after 40 cycles)