Sodium ion capacitors (SICs) are designed to deliver both high energy and power densities at low cost. Electric double-layer capacitive cathodes are typically used in these devices, but they lead to very limited capacity. Herein, we apply a pseudocapacitive layered ferric vanadate (Fe-V-O) as cathode to construct non-aqueous SICs with both high energy and power densities. The Fe-V-O nanosheets cathode displays remarkable rate capability and cycling stability. The pseudocapacitive sodium storage mechanism of Fe-V-O, with over 83% of total capacity from capacitive contribution, is confirmed by kinetics analysis and ex situ characterizations. The capacitive-adsorption mechanism of hard carbon (HC) anode is demonstrated, and it delivers excellent rate capability. Based on as-synthesized materials, the assembled HC//Fe-V-O SIC delivers a maximum energy density of 194 Wh kg −1 and power density of 3,942 W kg −1. Our work highlights the advantages of pseudocapacitive cathodes for achieving both high energy and power densities in sodium storage devices.
Pseudocapacitive cathode is applied to construct a high-energy sodium ion capacitor
Layered ferric vanadate cathode displays pseudocapacitive sodium storage behavior
Ferric vanadate cathode delivers remarkable rate capability and cycling stability
Hard carbon anode exhibits capacitive adsorption mechanism and high-rate performance
Electrochemical Energy Storage; Energy Materials; Nanoelectrochemistry