High-Power and Long-Life Na₃V₂O₂(PO₄)₂F–Na₃V₂(PO₄)₃@C/AC Bimaterial Electrodes for Hybrid Battery–Capacitor Energy Storage Devices

In this work, we have reported sol–gel synthesized in situ carbon-coated Na3V2O2(PO4)2F–Na3V2(PO4)3 (NVOPF–NVP@C) composites as excellent cathode materials for hybrid Li-ion batteries (HLIBs). The structure of as-synthesized material enhances the electrochemical performances by reducing the diffusion distance and improving the electrical conductivity and structural stability. In addition, to further improve the rate performance and cycleability, hybridization between NVOPF–NVP@C and supercapacitor-type activated carbon (AC) has been persuaded, and the concept of double hybridization has been introduced. Thus, NVOPF–NVP@C/AC bimaterials demonstrate excellent performances in hybrid battery–capacitor (bat–cap) devices. For example, NVOPF–NVP@C/AC50 can retain 75.2% of its initial capacity with ∼100% Coulombic efficiency at a current density of 1000 mA g–1 even after 2000 repeated charge–discharge cycles. The excellent electrochemical performances of the bimaterial electrodes are mainly attributed to the synergistic interaction between NVOPF–NVP@C and AC, which correlates well with the improvement of electronic conductivity and ionic diffusivity in the electrodes. Thus, these electrodes, thanks to their high capacities and capacity retentions at higher current densities, can play a significant role in the development of high-energy and high-power hybrid bat–cap devices with improved safety and stability.