Temperature-controlled in situ synthesized carbon nanotube-protected vanadium phosphate particle-anchored electrospun carbon nanofibers for high energy density symmetric supercapacitors.

Designing a novel composite material with hierarchical nanostructures as a negative electrode material with high capacitance and outstanding stability is challenging. To this end, we synthesized carbon nanotubes (CNTs)-protected vanadium phosphate (VPO) nanoparticles trapped within an electrospun carbon matrix (CNTs@VPO@CNFs) for potential use in energy storage applications. Temperature was found to be the major controlling factor for the fabrication of composites with CNT decoration. CNTs@VPO@CNFs exhibited the highest capacitance of 576.1F g-1 at a current density of 0.66 A g-1 among other corresponding electrode materials. Furthermore, this electrode exhibited outstanding stability of up to 99% after 5000 cycles, which was attributed to the coating of core-forming VPO@CNFs by the CNTs as the sheath material. Interestingly, the as-fabricated material worked in a wide potential range from -1.2 to 0.6, thereby providing the opportunity to assemble a symmetric supercapacitor device (SSCD). The SSCD showed an exceptionally high energy density of 69.1 W h kg-1 at a power density of 3.2 kW h and ~ 90% stability after 5000 cycles. Thus, this work presents a strategy for fabricating a new composite as a negative electrode material that can be used in a symmetrical supercapacitor device with an ultrahigh energy density.