Versatile Biomass Hydrogel Electrolyte for Supercapacitors: Exceptional Water Retention, Robust Adhesion, Subzero Self‐Healing, and All‐Climate Cycling Stability

Developing hydrogel electrolytes that simultaneously overcome the critical challenges of rapid dehydration, narrow operational temperature windows, poor interfacial adhesion, and irreparable mechanical damage remains an urgent need for reliable supercapacitors, since these challenges significantly compromise their cycling stability. Herein, a versatile biomass hydrogel electrolyte (PSBGD‐Li) is developed through dynamic borate ester crosslinking between peach gum polysaccharide and starch, integrating exceptional water retention (≥66 days, 92.01% retention), wide temperature adaptability (−30 °C to 50 °C), rapid subzero self‐healing (99.4% recovery in 5 min at −30 °C), high ionic conductivity (34.71 mS cm −1 at 25 °C; 9.22 mS cm −1 at −30 °C), and excellent mechanical robustness (>1600% strain without breakage, 30.7 kPa interfacial adhesion). Supercapacitors equipped with PSBGD‐Li exhibit superior all‐climate electrochemical cycling stability, delivering a high specific capacitance of 216 F g −1 at 25 °C with 98.6% capacitance retention after 15 000 cycles. Remarkably, they maintain outstanding temperature reliability, retaining 99.2% capacitance at −30 °C and 92.4% at 50 °C, while preserving >99% specific capacitance after sequential thermal cycling between −30 °C and 50 °C. Flexible supercapacitors also maintain stable electrochemical performance after repeated bending or cutting/healing cycles, highlighting significant potential for developing green, temperature‐tolerant, reliable flexible energy storage in extreme environments.