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

The vanadium dioxide (VO(D)), with ultra-high theoretical capacitance, has been considered as a boon for electrode materials of advanced supercapacitors (SCs). However, the VO 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 Co pre-intercalation and amorphous carbon confined vanadium dioxide (CoxVO@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 CoxVO@C not only enables a small amount of Co pre-intercalation layer to offer faster ion diffusion kinetics for VO, but also utilizes a high-conductivity amorphous carbon to protect VO from dissolution in an alkaline electrolyte, thereby exhibiting the ultrahigh specific capacitance up to 4440.0 mF cm at 5 mA cm (525.2 F g at 2 A g) and the prominent long-term stability performance of the electrode. Benefited from these excellent characteristics, a high-performance CoxVO@C//VO 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 at a power density of 6.1 kW kg, manifesting its practical feasibility.