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 Nb 2 O 5 @Carbon core–shell nanoparticles (Nb 2 O 5 @C NPs) and reduced graphene oxide (rGO), and an analysis of their electrochemical performance with respect to various weight ratios of Nb 2 O 5 @C NPs to rGO (e.g., Nb 2 O 5 @C, Nb 2 O 5 @C/rGO‐70, ‐50, and ‐30). In a Na half‐cell configuration, the Nb 2 O 5 @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 Nb 2 O 5 @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.