Synthesis and Characterization of a Novel Hydrated Layered Vanadium(III) Phosphate Phase K3V3(PO4)4•H2O: A Functional Cathode Material for Potassium-Ion Batteries

Hydrated vanadium(III) phosphate, K3V3(PO4)(4)center dot H2O, has been synthesized by a facile aqueous hydrothermal reaction. The crystal structure of the compound is determined using X-ray diffraction (XRD) analysis aided by density functional theory (DFT) computational investigation. The structure contains layers of corner-sharing VO6 octahedra connected by corner and edge-sharing PO4 tetrahedra with a hydrated K+ ion interlayer. The unit cell is assigned to the orthorhombic system (space group Pnna) with a = 10.7161(4) angstrom, b = 20.8498(10) angstrom, and c = 6.5316(2) angstrom. Earlier studies of this material report a K3V2(PO4)(3) stoichiometry with a NASICON structure (space group R (3) over barc). Previously reported XRD and electrochemical data on K3V2 (PO4)(3) are critically evaluated and we suggest that they display mixed phase compositions of K3V3(PO4)(4 )+120 and known electrochemically active phases KVP2O7 and K3V(PO4)(2). In the present study, the synthesis conditions, structural parameters, and electrochemical properties (vs K/K+) of K3V3(PO4)4 center dot H2O are clarified along with further physical characterization by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray fluorescence (XRF), Raman spectroscopy, Fourier transform infrared (FT-IR), and thermogravimetric analysis (TGA).

Automated summary

Hydrated vanadium(III) phosphate, K3V3(PO4)(4)center dot H2O, was synthesized by aqueous hydrothermal reaction and its crystal structure was determined using XRD and DFT. Physical characterization was further carried out using SEM, EDX, XRF, Raman spectroscopy, FT-IR, and TGA.