A Flexible Na‐Ion Supercapacitor/Battery Hybrid Device

A hybrid supercapacitor/battery device is proposed by integrating Na 3 V 2 (PO 4 ) 2 F 3 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.