Matrix-Free, Supramolecularly Assembled PANI/HEDP/Lignosulfonate Hydrogel Electrodes for Advanced Flexible Supercapacitors

Conductive polymer hydrogels for flexible supercapacitors usually contain nonconductive matrices (e.g., PVA, PAM), which hinder the electrochemical performance. This work presents a matrix-free strategy via supramolecular self-assembly, utilizing HEDP as a dual-functional dopant/cross-linker and lignosulfonate (LS) as a redox-active template. The incorporation of LS optimizes the nanostructure for faster ion transport while simultaneously contributing additional pseudocapacitance via quinone/hydroquinone redox couples. This supramolecularly assembled PANI/HEDP/LS (PHL) hydrogel demonstrates significant electrochemical advantages. At 0.5 A g–1, the PHL9 hydrogel electrode delivered a specific capacitance of 625 F g–1, exceeding that of the original PHL0 hydrogel without redox additives (419 F g–1). The PHL9 hydrogel electrode also exhibited an electrical conductivity of 86.51 S m–1, while maintaining stable cycling performance after 10,000 charge/discharge cycles (76.51% retention) and good flexibility, as 92.64% of the capacitance was still preserved after 200 bending cycles. All-hydrogel-state flexible supercapacitors (FSCs) constructed with PHL9 composite hydrogel electrodes delivered an energy density of 22.5 Wh kg–1 at a power density of 125 W kg–1, surpassing that of PHL0-based FSCs (16.2 Wh kg–1). Moreover, the device further maintained 80.75% of its initial capacitance after 10,000 charge/discharge cycles, indicating reliable long-term stability. Overall, these results indicate that the proposed strategy provides an effective route for developing high-performance composite hydrogel electrodes in wearable and flexible energy storage applications.