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

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 NaV₃O₈ nanowires (NaNVO@C₁₀) 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@C₁₀/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@C₁₀/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.