Prussian blue-graphene oxide composite cathode for a sodium-ion capacitor with improved cyclic stability and energy density

For applications involving sodium-ion capacitor (SIC) with high energy and high power, it is necessary to develop cathode materials with high operating voltage, high capacity, and excellent cyclic stability. Prussian blue and its analogs are considered promising candidates for cathode materials owing to their high energy and high stability resulting from their open framework structure. We demonstrate that the Prussian blue-graphene oxide composite (PBGO) can be applied to SIC as a battery-type cathode. PBGO is synthesized by a single-step decomposition method and has a morphology in which graphene oxide covered Prussian blue, which has a uniform cubic structure. PBGO exhibit a high capacity of 165 mAh g−1 at 20 mA g−1, as well as 68 mAh g−1 at a high current density of 4 A g−1. The SIC is fabricated using PBGO as the cathode materials and activated carbon (AC) as a capacitor-type anode, and it exhibit a high specific energy density of 65.3 Wh kg−1 and a superior capacity retention of 78.8% after 10,000 cycles. The use of battery-type cathodes presents a promising strategy for developing SIC with high energy and long lifespan.