Large‐Area,Uniform, Aligned Arrays of Na3(VO)2(PO4)2F on Carbon Nanofiber for Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors

Sodium–vanadium fluorophosphate (Na₃V₂O_2x(PO₄)₂F_3?2x, NVPF, 0 ≤ x ≤ 1) is considered to be a promising Na‐storage cathode material due to its high operation potentials (3.6–4 V) and minor volume variation (1.8%) during Na⁺‐intercalation. Research about NVPF is mainly focused on powder‐type samples, while its ordered array architecture is rarely reported. In this work, large‐area and uniform Na₃(VO)₂(PO₄)₂F cuboid arrays are vertically grown on carbon nanofiber (CNF) substrates for the first time. Owing to faster electron/ion transport and larger electrolyte–electrode contact area, the as‐prepared NVPF array electrode exhibits much improved Na‐storage properties compared to its powder counterpart. Importantly, a quasi‐solid‐state sodium‐ion hybrid capacitor (SIHC) is constructed based on the NVPF array as an intercalative battery cathode and porous CNF as a capacitive supercapacitor anode together with the P(VDF‐HFP)‐based polymer electrolyte. This novel hybrid system delivers an attractive energy density of ≈227 W h kg^?1 (based on total mass of two electrodes), and still remains as high as 107 Wh kg^?1 at a high specific power of 4936 W kg^?1, which pushes the energy output of sodium hybrid capacitors toward a new limit. In addition, the growth mechanism of NVPF arrays is investigated in detail.