3D urchin-shaped Ni3(VO4)2 hollow nanospheres for high-performance asymmetric supercapacitor applications

3D urchin-shaped Ni-3(VO4)(2) hollow nanospheres were synthesized by a facile, template free, hydrothermal method. The size of the urchin-shaped Ni-3(VO4)(2) hollow nanospheres was similar to 500 nm and they were composed of similar to 10 nm thick sheet-like building block units. The morphological evolution was sensitive to alkaline media and similar to 50 nm nanoparticles were formed when liquid ammonia was replaced by sodium hydroxide. The formation of [Ni(NH3)(6)](2+) complex ions (hexaamminenickel(II) ions) and subsequent slow release of nickel ions to the growing crystal seem to have resulted in the formation of hollow urchin-shaped nanostructures. The electrochemical supercapacitor properties of these two nanostructures were investigated and it was found that the urchin-shaped nanospheres exhibited better performance than the nanoparticles in all respects. The as-fabricated porous urchin-shaped Ni-3(VO4)(2) nanosphere electrode exhibited a specific capacity of 402.8 C g(-1) at 1 A g(-1) with enhanced rate capability and an excellent capacity retention of 88% after 1000 cycles. An asymmetric supercapacitor was fabricated using Ni-3(VO4)(2) nanospheres as the cathode and activated carbon (AC) as the anode and the electrochemical properties were studied at various scan rates in the potential range of 0.0-1.6 V. The as-fabricated asymmetric supercapacitor (Ni-3(VO4)(2)//AC) achieved a high specific capacity (114 C g(-1)), energy density (25.3 W h kg(-1)) and power density (240 W kg(-1)). Moreover, this asymmetric supercapacitor displayed an excellent life cycle with 92% specific capacity retention after 1000 consecutive charge-discharge cycles. The impressive electrochemical performance of the Ni-3(VO4)(2) nanospheres, owing to their large surface area, pore volume and 3D structure, makes them a promising candidate for the future high energy storage systems.