Self-discharge suppression by composite regenerated cellulose ion-selective separator for high-energy aqueous supercapacitors

Abstract

Aqueous supercapacitors exhibit the advantage of high cycling stability, inherent safety and appealing energy density, and thus have long been considered an exceptional technology for efficient energy storage. However, in the absence of an electric field, the spontaneous transmembrane diffusion of ions leads to self-discharge or energy decay of supercapacitors. Herein, we propose a phase transformation strategy to design a porous regenerated cellulose and polyvinylidene difluoride composite separator with ion selectivity by utilizing cellulose dissolution regeneration with PVDF enhancement. Specifically, the anion selective property of PVDF screens the transmembrane diffusion of electrolyte ions, thereby suppressing the self-discharge of supercapacitors. The in-depth characterization indicated that the RC@PVDF separator applied to aqueous supercapacitors demonstrated high performance by maintaining a capacitance of 173 F g−1 after 20,000 cycles. After 24 h of self-discharge, the supercapacitor retained 59 % of its energy. In addition, the cross-linked network of regenerated cellulose provides critical properties for the ion-selective separator, including strong mechanical stability, excellent thermal stability (220 °C) and uniform pore structure (31 nm). This work is anticipated to provide considerable insight into the creative design of self-discharge suppression separators for long-term energy storage supercapacitors.