Advanced binder-free electrode based on core-shell nanostructures of mesoporous Co3V2O8-Ni3V2O8 thin layers@porous carbon nanofibers for high-performance and flexible all-solid-state supercapacitors

The development of thin layer structures on flexible current collectors has become as an effective strategy for preparing advanced portable and wearable power sources. Herein, a flexible and efficient electrode was fabricated based on electrospun porous carbon nanofibers (PCNFs) substrate with elaborately designed thin layer Co3V2O8-Ni3V2O8 core-shell nanostructures (Co3V2O8-Ni3V2O8 TLs@PCNFs). The resulting free-standing Co3V2O8-Ni3V2O8 TLs@PCNFs composite was used directly as a flexible electrode in three electrode system for supercapacitor studies without the need for utilization of either binder or metal-based current collector. The unique thin layer structure of Co3V2O8-Ni3V2O8 TLs@PCNFs fully enables utilization of the synergistic effects from both high electrochemical performance of cobalt, nickel, and vanadium and excellent conductivity, and flexibility of PCNFs. Benefiting from their intriguing structural features, the Co3V2O8-Ni3V2O8 TLs@PCNFs and PCNFs were used directly as a positive and a negative electrode, respectively, for fabrication of flexible all-solidstate asymmetric supercapacitors, which render superior flexibility and reliability, high energy density (59.7 Wh kg(-1) at 1.97 kW kg(-1)), high power density (13.4 kW kg(-1) at 40.6 Wh kg(-1)), and outstanding cycling stability (88.5% capacitance retention after 3000 cycles at 5.0 A g(-1)). This performance comparable to or higher than high-end commercially available supercapacitors and most of the previous reported asymmetric devices. Therefore, it is believed that this novel design shows a great potential in developing flexible energy storage devices with high energy and power densities in the future.