Mechanically flexible V <sub>3</sub> S <sub>4</sub> @carbon composite fiber as a high‐capacity and fast‐charging anode for sodium‐ion capacitors
Zhifei Mao, Xiao‐Jun Shi, Taoqiu Zhang, Peng-Ju Liang, Rui Wang, Jun Jin, Beibei He, Yansheng Gong, Qiang Wang, Xili Tong, Huanwen Wang
Abstract
Abstract Hybrid Na‐ion capacitors (NICs) have received considerable interests owing to their low‐cost, high‐safety, and rapidly charging energy‐storage characteristics. The NICs are composed of a capacitor‐type cathode and a battery‐type anode. The major challenge for NICs is to search for suitable electrode materials to overcome the sluggish diffusion of Na + in the anode. Herein, ultrafine vanadium sulfide is encapsulated in carbon fiber (V 3 S 4 @CNF) as a self‐supported electrode by electrospinning and in situ sulfurization. The carbon cladding and one‐dimensional (1D) nanofiber network‐like structure could alleviate the volume expansion of V 3 S 4 during Na + de‐/intercalation process. Consequently, the V 3 S 4 @CNF anode exhibited a pseudocapacitive sodium storage in terms of large Na + ‐storage capacity (476 mAh·g −1 at 0.1 A·g −1 ), high‐rate capability (290 mAh·g −1 at 20.0 A·g −1 ) and excellent cycling stability (95% capacity retention for 1500 cycles at 2.0 A·g −1 ) in Na half‐cells. By employing V 3 S 4 @CNF as the anode and the activated carbon (AC) cathode, the as‐assembled NICs could deliver a high energy density of 110 Wh·kg −1 at a power density of 200 W·kg −1 . Even at a high power of 10,000 W·kg −1 , the specific energy is still up to 42 Wh·kg −1 .