Synthesis and Characterization of a Novel Hydrated Layered Vanadium(III) Phosphate Phase K<sub>3</sub>V<sub>3</sub>(PO<sub>4</sub>)<sub>4</sub>·H<sub>2</sub>O: A Functional Cathode Material for Potassium-Ion Batteries
T.R. Jenkins, José A. Alarco, Ian D.R. Mackinnon
Abstract
High Resolution Image Download MS PowerPoint Slide Hydrated vanadium(III) phosphate, K 3 V 3 (PO 4 ) 4 ·H 2 O, 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 VO 6 octahedra connected by corner and edge-sharing PO 4 tetrahedra with a hydrated K + ion interlayer. The unit cell is assigned to the orthorhombic system (space group Pnna ) with a = 10.7161(4) Å, b = 20.8498(10) Å, and c = 6.5316(2) Å. Earlier studies of this material report a K 3 V 2 (PO 4 ) 3 stoichiometry with a NASICON structure (space group R 3 ̅c ). Previously reported XRD and electrochemical data on K 3 V 2 (PO 4 ) 3 are critically evaluated and we suggest that they display mixed phase compositions of K 3 V 3 (PO 4 ) 4 ·H 2 O and known electrochemically active phases KVP 2 O 7 and K 3 V(PO 4 ) 2 . In the present study, the synthesis conditions, structural parameters, and electrochemical properties ( vs K/K + ) of K 3 V 3 (PO 4 ) 4 ·H 2 O 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).