Flexible and Anti-freezing Cu@Fe3O4-PANI/Polyvinyl Alcohol/Phytic Acid/LiCl Hydrogel Electrolytes in High-Performance All-Solid-State Supercapacitors

Abstract The widespread adoption of flexible electronics has driven the development of all-solid-state energy storage materials. However, the limited single-functionality and unsatisfactory low-temperature tolerance of conventional hydrogel electrolytes remain critical challenges for wearable applications. Thus, a Cu@Fe3O4-PANI/PVA/PA/LiCl (CPPALi) hydrogel was fabricated via a freeze–thaw approach. Through hydrogen bonding, physical cross-linking, and electrostatic interactions, the one-pot incorporation of PA, Cu@Fe3O4-PANI (CFP) hybrids, and LiCl significantly enhanced the conductivity, water retention, and adhesion, and anti-freezing performance. The above as-obtained CPPALi0.6 hydrogel strain sensor exhibited linear strain sensing characteristics (GF = 1.95) for human motion monitoring with high conductivity (2.74 S m–1) and outstanding freeze resistance (–47 °C) and good water retention capacity. The all-solid-state CPPALi0.6 supercapacitor devices were assembled with CPPALi0.6 hydrogel as electrolyte and activated carbon as electrodes. Importantly, they delivered a specific capacitance of 310.8 mF cm–2 at 1 mA cm–2, achieved an energy density of 45.6 μWh cm–2 at a power density of 255.1 μW cm–2, and retained stable electrochemical stability even at –30 °C. Series-connected CPPALi0.6 supercapacitor devices could power a light bulb and drive a timer for 60 min. After 3000 charge–discharge cycles, the capacitance retention remained as high as 94.4%, and the performance remained stable after 21 days. Thus, this multifunctional hydrogel integrates structural stability, adhesion, anti-freezing, energy storage, and sensing functionalities, demonstrating significant potential in the field of wearable all-solid-state electronic devices.