Starfruit-like vanadium oxide with Co²⁺ pre-intercalation and amorphous carbon confinement as a superior cathode for supercapacitors

The vanadium dioxide (VO₂(D)), with ultra-high theoretical capacitance, has been considered as a boon for electrode materials of advanced supercapacitors (SCs). However, the VO₂ has a series of shortcomings such as poor electrical conductivity, severe structural damage, and rapid capacity fading during cycles, resulting in unsatisfactory electrochemical performance. Herein, the Co²⁺ pre-intercalation and amorphous carbon confined vanadium dioxide (CoxVO₂@C) with starfruit-like nanostructure is synthesized on a conductive Ni foam substrate via a versatile and cost-effective method. As a cathode for SCs, the obtained CoxVO₂@C not only enables a small amount of Co²⁺ pre-intercalation layer to offer faster ion diffusion kinetics for VO₂, but also utilizes a high-conductivity amorphous carbon to protect VO₂ from dissolution in an alkaline electrolyte, thereby exhibiting the ultrahigh specific capacitance up to 4440.0 mF cm⁻² at 5 mA cm⁻² (525.2 F g⁻¹ at 2 A g⁻¹) and the prominent long-term stability performance of the electrode. Benefited from these excellent characteristics, a high-performance CoxVO₂@C//V₂O₃ hybrid supercapacitor (HSC) device with an operating voltage of 1.7 V is further assembled. The HSC device delivers a superior energy density of 102.3 W h kg⁻¹ at a power density of 6.1 kW kg⁻¹, manifesting its practical feasibility.