Hydrothermal synthesis of vanadium dioxides/carbon composites and their transformation to surface-uneven V2O5 nanoparticles with high electrochemical properties

Vanadium dioxides/carbon composites composed of vanadium dioxides@carbon core-shell structures and amorphous carbon spheres were successfully synthesized using glucose as the carbon sources by a facile one-step hydrothermal route. Then vanadium dioxides/carbon composites were converted to surface-uneven V2O5 nanoparticles by the calcination in air atmospheres. The amorphous carbon reacting with O-2 in the air to release gas results in remaining V2O5 nanoparticles possessing broken, rough and poral structures. The electrochemical properties of surface-uneven V2O5 nanoparticles as supercapacitor electrodes were measured by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) both in the aqueous and organic electrolyte. Surface-uneven V2O5 nanoparticles exhibit the specific capacitance of 406 F g(-1) at the current density of 0.2 A g(-1) and retain 246 F g(-1) even at high current density of 10 A g(-1). The influence of the calcined temperature and time on the specific capacitance, phase and morphology of the products were discussed in detail. The results revealed that the calcination at 400 degrees C for 4 h with comparatively low ratio of V5+/V4+ are favorable for surface-uneven V2O5 nanoparticles with the high electrochemical property. During the cycle performance, the specific capacitances of V2O5 nanoparticles after 100 cycles are 13.8% and 98.5% of the initial discharge capacity in the aqueous and organic electrolyte, respectively, indicating the cycle performance is significantly improved in organic electrolyte. It turns out that surface-uneven V2O5 nanoparticles are an ideal material for supercapacitor electrode in the present work.