A flexible and stable zinc-ion hybrid capacitor with polysaccharide-reinforced cross-linked hydrogel electrolyte and binder-free carbon cathode

Abstract

Aqueous zinc-ion hybrid capacitors (ZHCs) are receiving immense attention in view of their merits in energy/power density, water compatibility, and economy. However, achieving superior ZHCs is also extremely challenging due to the ineluctable dendrite and side reaction issues of Zn anodes and the unsatisfactory capacity of carbon cathodes. Herein, we report a molecular-level regulation strategy to eliminate the current barriers from Zn anodes by designing a polysaccharide-reinforced hydrogel electrolyte of polyacrylamide/carboxymethyl cellulose/xanthan gum/zinc trifluoromethanesulfonate (PAM/CMC/XG/Zn(CF₃SO₃)₂). The fabricated hydrogel electrolyte can efficiently prevent dendrite formation and protect Zn anodes from the water-caused corrosion and hydrogen evolution reaction to achieve an extended life of the Zn//Zn cell over 230 h and a high average coulombic efficiency of 99.3% in the Zn//Cu cell. Additionally, a carbon fabric (GCNF), with a large surface area, N-doped structure, and plentiful microcrystalline regions, was finely designed as a binder-free cathode for aqueous ZHCs, which has a fairly high capacity of 173.8 mA h g⁻¹ with excellent rate characteristics. And the quasi-solid-state ZHC composed of PAM/CMC/XG/Zn(CF₃SO₃)₂ and GCNF demonstrates a high capacity retention of 93.5% over 10 000 cycles and an impressive energy density of 113.2 W h kg⁻¹ at a power density of 206.2 W kg⁻¹. Notably, the device is highly flexible without distinct capacity attenuation under deformations. The dual strategy of engineering electrolytes and cathodes offers a good platform for improving Zn-ion storage capacity.