Hierarchical‐Heterogeneous Biogel Electrolytes Regulate Zinc Anode Interfacial Compatibility Towards Green and High‐Performance Solid‐State Hybrid Capacitors

Gel electrolytes are high-priority materials for solid-state Zn-ion hybrid capacitors, characterized by high ionic conductivity and intrinsic mechanical flexibility. However, because the existing gel electrolytes are relatively soft and do not contact intimately with rigid Zn anodes, they have inferior interfacial compatibility with Zn anodes, leading to device degradation. Here we develop a class of biogel electrolytes by in situ crystallizing gelatin triple helix units from the alginate polymer domain to form a unique hierarchical-heterogeneous structure. The biogel electrolyte demonstrates combined advantages of high toughness, temperature-triggered adhesion, high Zn²⁺ transference number and temperature-independent ionic conductivity. These notable features favor Zn²⁺ 3D diffusion and accommodate zinc anode volume changes, thus enabling the symmetric Zn||Zn cell to highlight a balance among high current density, high areal capacity and prolonged cycling life. Moreover, the assembled zinc||activated carbon hybrid capacitor performs exceptional capacitive behavior and stable operation across the temperature range from 25°C to -40°C, delivering competitive energy density of 125.5 Wh kg^-1 with high capacity retention of 97.1% over 10 000 cycles even at -40°C. Finally, system-level demonstration based on the resulting hybrid capacitors can power portable electronics in a power cable-free manner, validating applicability for green power sources in outdoor activities.