Ni nanoparticle doped porous VN nanoflakes assembled into hierarchical hollow microspheres with a structural inheritance from the Ni1-xVxO2 cathode material for high performance asymmetric supercapacitors

The binary transition metal oxide of a Ni1-xVxO2 cathode material with a 3D hierarchical hollow microsphere (HHMS) structure was designed in this study. The combination of two metal species and a 3D HHMS structure, providing sufficient active sites for electrochemical reactions and efficient ion transportation, endows this material with excellent electrochemical properties such as a high specific capacitance of 677.8 F g(-1) and an enhanced rate capability. The as-obtained Ni1-xVxO2 HHMS was also used as an original material to fabricate a Ni nanoparticle (NP) doped VN 3D HHMS hybrid anode material via an effective nitridation treatment. In this composite, the Ni NPs are well dispersed in the VN skeleton, which enables good electrical contact and transfer of the interface electrons. Based on the excellent performances of the two materials, a (-)Ni/VN//Ni1-xVxO2(+) asymmetric supercapacitor (ASC) was fabricated. The obtained ASC exhibits a high specific capacitance of 65.7 F g(-1) and a maximum energy density of 23.3 Wh kg(-1). Moreover, it also exhibits an excellent cycling stability, with 87% specific capacitance retention after 1000 cycles. These impressive results show great potential in the development of high-performance energy storage systems for practical applications.