Carbon-encapsulated niobium carbonitride with high volumetric capacitance and wide potential windows in aqueous pseudocapacitors

Electrochemical capacitors deliver high power and have long operational lives; however, their energy densities are limited. Compared to carbon-based electrical double-layer capacitors, pseudocapacitors with an aqueous electrolyte are predicated to provide both high gravimetric and volumetric capacitance while being cost-effective and eco-friendly. However, their narrow operational potential windows limit the practical delivery of energy. In this study, we synthesized novel NbCxN1-x nanoparticles encapsulated in a uniform carbon layer. This pseudocapacitive material exhibits a high volumetric capacitance, a wide potential window stability (∼345 F cm−3, 2.1 V, in 1 M of Li2SO4), and a long cycling life (>10 000 cycles). Moreover, the symmetric cells (2.2 V, in 1 M of Li2SO4) exhibit high energy density as well as excellent cyclability and rate performances. These findings provide new opportunities for the design of aqueous energy storage devices having a wide applied potential difference and excellent performance.