High-Energy and High-Power Pseudocapacitor–Battery Hybrid Sodium-Ion Capacitor with Na~+ Intercalation Pseudocapacitance Anode

High-performance and low-cost sodium-ion capacitors(SICs) show tremendous potential applications in public transport and grid energy storage. However, conventional SICs are limited by the low specific capac-ity, poor rate capability, and low initial coulombic efficiency(ICE) of anode materials. Herein, we report layered iron vanadate(Fe5V15O39(OH)9·9 H2O) ultrathin nanosheets with a thickness of ～ 2.2 nm(FeVO UNSs) as a novel anode for rapid and reversible sodium-ion storage. According to in situ syn-chrotron X-ray diffractions and electrochemical analysis, the storage mechanism of FeVO UNSs anode is Na~+ intercalation pseudocapacitance under a safe potential window. The FeVO UNSs anode delivers high ICE(93.86%), high reversible capacity(292 mAh g-1), excellent cycling stability, and remarkable rate capability. Furthermore, a pseudocapacitor–battery hybrid SIC(PBH-SIC)consisting of pseudocapacitor-type FeVO UNSs anode and battery-type Na3(VO)2(PO4)2F cathode is assembled with the elimination of presodiation treatments. The PBH-SIC involves faradaic reaction on both cathode and anode materials, delivering a high energy density of 126 Wh kg-1at 91 W kg-1, a high power density of 7.6 kW kg-1with an energy density of 43 Wh kg-1, and 9000 stable cycles. The tunable vanadate materials with high-performance Na~+ intercalation pseudocapacitance provide affdirection for developing next-generation high-energy capacitors.