Renewable cellulose separator with good thermal stability prepared via phase inversion for high-performance supercapacitors

In this study, the regenerated porous cellulose films were properly prepared by dissolving different masses of cellulose (4%, 6%, 8%) in LiCl/DMAc solvent though a simple phase inversion process and as separator (CLD-4, CLD-6, CLD-8) for the assembled supercapacitors (ABSC-4, ABSC-6, ABSC-8). The investigation on the different masses of cellulose indicated that CLD-8 film showed a stronger hydrogen bond interaction, higher thermal stability and better tensile strength. In addition, CLD-8 has good lyophilicity (101.1°), high porosity (58.43%), and electrolyte absorption (329.30%). Furthermore, different cellulose films as separator were used for assembling supercapacitor. Compared with ABSC-4 and ABSC-6, ABSC-8 showed a lower equivalent series resistance of 0.37Ω, a higher charge-discharge efficiency of 98.87% at 1 A/g, and areal capacitance of 1.16 F/cm² at 5 mV/s. ABSC-8 also showed a superior capacity retention of 92.09% over 4000 cycles at 1 A/g. So, CLD-8 film has a potential to be used as separator for supercapacitor. Furthermore, the comparative analysis of supercapacitors assembled by CLD-8 separator and two commercial separators were conducted. The results show that ABSC-8 showed a higher value of 25.94 Wh/kg at 0.5 A/g with a powder density of 0.36 kW/kg, a lower voltage drops below 0.02 V at 1.0, and 3.0 A/g, a higher specific capacitance of 123 F/g at 0.5 A/g. Moreover, ABSC-8 maintained their quasi-rectangular and symmetrical triangular profiles of the CV and GCD curves in 0–1 and 0–1.5 V, respectively, suggesting the applicability of a wide working potential window. These results provide insights into the full use of natural and biodegradable cellulose film prepared by a simple phase inversion as separators for supercapacitors.