Engineering fibrous-interconnected potassium bis(dioxovanadium) phosphate frameworks for fast-charging and high-rate sodium-ion supercapacitors

Abstract

Flexible and high-performance sodium-ion storage systems are essential for next-generation energy technologies. Here, orthorhombic K(VO2)2(PO4) nanostructures were synthesized on carbon cloth through a controlled phosphorization process for 4 h (4KVOP-C). The 4KVOP-C electrode exhibited a fibrous network morphology, providing abundant active sites, short Na+ diffusion pathways, and strong contact with the conductive substrate. Moreover, its robust P-O bonds and open ion-diffusion channels enhanced its structural stability and charge transport. The 4KVOP-C electrode delivered outstanding electrochemical performance, with a high areal capacitance and excellent rate capability in a three-electrode configuration. The phosphate-stabilized vanadyl framework of KVOP enables delocalized charge redistribution across the V-O-P networks during Na adsorption, resulting in a higher quantum capacitance and density of states at the Fermi level. This electronic preconditioning underlies its superior areal capacitance, fast charge-discharge, and enhanced Na-ion accommodation compared with those of potassium-intercalated vanadium oxide. Moreover, a symmetric 4KVOP-C//4KVOP-C supercapacitor was assembled, which operated over a wide voltage window of 2.0 V, achieving an energy density of 50 & micro;W h cm-2 at a power density of 1980 & micro;W cm-2, along with excellent cycling stability. These results demonstrate that the fibrous K(VO2)2(PO4) nanostructures synthesized via optimized phosphorization exhibit excellent intrinsic electrochemical properties, making them potential electrode materials for flexible, high-energy-density and durable sodium-ion supercapacitors.