A Bipartite Synergistic Strategy for All‐Weather Sodium‐Ion Fiber Supercapacitor with Excellent Energy Density and Temperature Adaptability

Abstract Sodium‐ion fiber supercapacitor (AFSIC) are promising candidates for wearable devices. However, their practical implementation is hindered by the absence of cathodes with fast Na‐ion diffusion kinetics to match the anode and the poor temperature adaptability of conventional electrolytes. To address these challenges, a carbon‐coated NaV 3 O 8 nanowires (NaNVO@C 10 ) with low diffusion energy barriers of Na‐ion are designed, enabling rapid and reversible Na‐ion intercalation/de‐intercalation. By leveraging the liquid crystalline phase induced characteristic of graphene oxide (GO), NaNVO@C 10 /rGO fiber cathode is fabricated using wet spinning. This fiber achieves a large volume capacitive of 565 F cm −3 . In parallel, a novel dual co‐solvent electrolyte (SLPHNa) is developed by introducing sulfolane and ethylphosphate as co‐solvent. This electrolyte synergistically reshape the Na‐ion solvation sheath, thereby improving the cycle stability and enhancing temperature adaptability from −60 to 80 °C of AFSIC. The resulting NaNVO@C 10 /rGO//MXene AFSIC exhibits a remarkable energy density of 35 mWh cm −3 , and maintains 9.3 mWh cm −3 even at −60 °C, along with an ultra‐long lifespan of 10 000 cycles under all‐weather condition. Moreover, the device maintains 82% of its initial capacitance after 1000 bending cycles, showing excellent mechanical durability. This work offers new insights into the development of high performance all‐weather sodium‐ion fiber supercapacitors.