In recent decades, tremendous attention has been paid to the development of new electrode materials with high capacitance to meet the requirements of electrode materials in supercapacitors. Among vanadium oxides, VO(A) has recently received increasing attention due to its unique layered structure, phase transformation and applications in Li-ion batteries. However, few studies have focused on the electrochemical properties of VO(A) as electrochemical capacitors. Herein, we develop a facile hydrothermal method to prepare VO(A)@C core-shell structured composites by carbonization of glucose in the presence of VO nanowires. The electrochemical properties of the VO(A)@C core-shell composites are investigated as a supercapacitor electrode material for the first time; the composites show excellent pseudocapacitive behavior and display a specific capacitance as high as 179 F g at 1 A g. A flexible asymmetric supercapacitor device is fabricated using VO(A)@C composites and activated carbon and delivers an excellent capacitance of 0.5 F cm at a scan rate of 5 mV s. Replacing the aqueous electrolyte with a LiCl/PVA gel electrolyte can efficiently improve the cycling performance to 85% retention after 1600 cycles. The good electrochemical performance of the composites indicates their high potential as electrode materials for supercapacitors.

Porous vanadium pentoxide (V2O5) microcrystals with different morphologies were synthesized through the decomposition of butterfly-like, rhombohedral, and flower-like ammonium metavanadate (NH4VO3) microcrystals, which were synthesized by the drowning-out crystallization of hydrothermal NH4VO3 aqueous solution using ethanol as both the antisolvent and the template for the self-assembly of vanadate ions. The effects of reaction conditions on the morphologies of products were characterized by scanning electron microscopy (SEM), and the possible growth mechanism was proposed. The electrochemical properties of the produced porous V2O5 with different morphologies were studied as battery-type electrodes for supercapacitors using 1 M LiClO4/propylene carbonate (PC) as the electrolyte. Rhombohedral V2O5 exhibited the highest initial specific capacitance of 641 F·g–1 at 0.5 A·g–1 among the three obtained morphologies, as well as an excellent rate capability and cycling stability, with a retention of over 119% after 2000 cycles, making it a promising electrode material for supercapacitors. The influences of morphologies on the capacitance and cycle performance are analyzed. The results indicate that the increasing complexity of the structure leads to lower specific capacitance because of the higher degree of electrode polarization and higher resistance, while the structure stability of the microcrystals is related to the rate capability as well as the cycling performance.

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