High-Performance Sodium-Ion Hybrid Supercapacitor Based on Nb₂O₅@Carbon Core–Shell Nanoparticles and Reduced Graphene Oxide Nanocomposites

Sodium-ion hybrid supercapacitors (Na-HSCs) have potential for mid- to large-scale energy storage applications because of their high energy/power densities, long cycle life, and the low cost of sodium. However, one of the obstacles to developing Na-HSCs is the imbalance of kinetics from different charge storage mechanisms between the sluggish faradaic anode and the rapid non-faradaic capacitive cathode. Thus, to develop high-power Na-HSC anode materials, this paper presents the facile synthesis of nanocomposites comprising Nb₂O₅@Carbon core–shell nanoparticles (Nb₂O₅@C NPs) and reduced graphene oxide (rGO), and an analysis of their electrochemical performance with respect to various weight ratios of Nb₂O₅@C NPs to rGO (e.g., Nb₂O₅@C, Nb₂O₅@C/rGO-70, -50, and -30). In a Na half-cell configuration, the Nb₂O₅@C/rGO-50 shows highly reversible capacity of ≈285 mA h g⁻¹ at 0.025 A g⁻¹ in the potential range of 0.01–3.0 V (vs Na/Na⁺). In addition, the Na-HSC using the Nb₂O₅@C/rGO-50 anode and activated carbon (MSP-20) cathode delivers high energy/power densities (≈76 W h kg⁻¹ and ≈20 800 W kg⁻¹) with a stable cycle life in the potential range of 1.0–4.3 V. The energy and power densities of the Na-HSC developed in this study are higher than those of similar Li- and Na-HSCs previously reported.