Surface enriched graphene hollow spheres towards building ultra-high power sodium-ion capacitor with long durability

We report the synthesis and fabrication of all carbonaceous electrode based high-energy and high-power- sodium-ion capacitors (NICs) which are anticipated to bridge the gap between rechargeable batteries and double layer capacitors. Unfortunately, the kinetic imbalance between battery type electrode and capacitive cathodes severely restricts the energy–power capabilities of NICs. To circumvent the kinetic mismatch and boost the efficiency of NICs, we are utilizing the rationally designed graphene hollow nanospheres (GHNS) as a bi-functional electrode in which nitrogen and sulfur atoms are infiltrated through the carbonaceous matrix. This eventually results in enhanced Na-ion storage capacity of GHNS which is paralleled by density functional theory calculations owing to the binding ability. All GHNS based NIC displays a high operating voltage, high energy density, and high power density, for example, the energy densities of 121 Wh kg⁻¹ at the power density of 100 W kg⁻¹. Further, the NIC can render remarkable cycling stability of ~85% retention after 10,000 cycles (~0.0015% energy decay per cycle) and emphasized to be used as a potential candidate for hybrid charge storage systems in the near future.