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

• 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.

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).