Fig. 4. Electrochemical window, Li⁺ transference number, ionic conductivity(σ) and Li symmetric cell cycling performance in IPEs.

a Cyclic voltammetry curves at a sweep rate of 10 mV s⁻¹ in IPEs developed with C₂mim TFO, C₂mim BF₄, C₂mim ES and Dems TFSI. Inset plots show the enlarged view of the cycles in high voltage range. b Steady-state current in symmetric Li||Li cell under 10 mV polarization. c The thickness of the IPEs (~50 μm) is characterized by SEM. The scale bar is 100 μm. d Arrhenius plots for σ of the 4 IPEs. e Cell voltage versus time for a symmetric Li||Li cell assembled with the 4 IPEs at current densities (J) from 1 to 6 mA·cm⁻² with changes in J every 10 cycles at 80 °C (each cycle lasts 1 h).