Eco-friendly and thermally stable cellulose film prepared by phase inversion as supercapacitor separator

The transparent and renewable porous cellulose separators (ACR-3, ACR-5, ACR-7, ACR-9) with different concentration of cellulose solution (3 wt%, 5 wt%, 7 wt%, 9 wt%) were prepared via a phase-inversion process with 1-allyl-3-methylimidazolium chloride (AMIM-Cl) as the solvent. Cellulose separators displayed high thermal stability, strong mechanical properties and excellent apparent properties. ACR-7 separator showed a higher porosity of 74.90% and electrolyte uptake of 323.68% with a smaller pore size and a more uniform pore structure compared with the other cellulose separators. The assembled supercapacitors (electrode/separator/electrode, SCD-7) showed good electrochemical performances in many aspects, including a lower equivalent series resistance of 0.5 Omega, a higher charge-discharge efficiency of 98.58% at 3 A/g and areal capacitance of 1.15 F cm(-2) at 5 mV/s than the SCD-3, SCD-5, SCD-9 and the assembled SCDs with two commercial separators (TF4040 for SCD-40 and MPF30AC for SCD-30). SCD-7 showed a high retention of 81.99% after 4000 charge-discharge tests at 1 A/g, showing a good charge-discharge cycle stability. Compared with SCD-40 and SCD-30, SCD-7 showed a lower voltage drop below 0.03 V, a higher specific capacitance of 130 F/g, energy density of 25.94 Wh/kg and power density of 0.36 kW/kg at 0.5 A/g. Overall, ACR-7 is expected to be applied as a separator in the field of supercapacitors.