A Flexible Na-Ion Supercapacitor/Battery Hybrid Device

A hybrid supercapacitor/battery device is proposed by integrating Na₃V₂(PO₄)₂F₃ and multi-walled carbon nanotubes as the battery electrode and carbon nanofiber as a supercapacitor electrode. The device made via the slurry casting of electrode material on foldable thin nickel foils leads to a robust, mechanically flexible sodium-ion capacitor/battery (supercapattery) as a hybrid energy storage system. The device exhibits a specific capacitance of 136 F g⁻¹ with a corresponding specific capacity of 95 C g⁻¹ at a potential scan rate of 1 mV s⁻¹, a maximum working voltage of 0.70 V, and a power density of 15 kW kg⁻¹ at 2.50 Wh kg⁻¹. Mechanical flexibility tests show practically unperturbed electrochemical properties at significant bending angles of up to 160°, indicating excellent robustness during large-scale device deformation. The current study offers new avenues to develop energy storage systems for next-generation portable and wearable energy storage devices that can be integrated into a variety of platforms.