Cu-Lignin Enhanced Hydrogel Supercapacitor Simultaneously Achieves Ultrahigh Energy and Power Density via H+/Cu+ Cooperative Transport

Designing and fabricating hydrogel supercapacitors (SCs) with ultrahigh energy and power densities and multienvironmental adaptability remains challenging due to the inherent conflict between “ion transport kinetics” and “charge storage capacity.” Herein, a metal phenolic network was formed using lignin catalyzed by Cu2+ ions and reinforced with phytic acid (PA)-cross-linked poly(acrylic acid) to develop a hydrogel electrolyte with homogeneous ion diffusion channels. Then, a polyaniline (PANI) electrode layer was grown in situ on the surface of the electrolyte to construct an integrated hydrogel SC with ultrahigh energy and power densities (the maximum energy and power densities were 1027.91 μWh cm–2 and 3002.42 μW cm–2, respectively, at a current density of 2 mA cm–2, and the capacitance retention ratio was 95.6% after 5000 cycles). Phytate-chelated Cu2+ ions undergoes redox competition with lignin, producing Cu+ ions with low electrostatic binding. These ions can then act synergistically with H+ ions to magnify the system’s charge storage capacity. Additionally, abundant hydrogen bonding and electrostatic interactions provide the PANI conductive layer with more charge adsorption sites whereas the uniform network structure provides optimal ion diffusion channels. Furthermore, the capacitor exhibits favorable capacitance output across various temperatures and humidity levels. Notably, the pigskin covered by this SC exhibits excellent flame-retardant properties when exposed to a butane flame, with a surface temperature of 34.8 °C. This work advances the practical application of hydrogel SCs for flexible energy storage.