Structure Characteristic Evaluation of Triclinic and Orthorhombic LiVOPO4 of Cathode Materials in Lithium Ion Batteries

Abstract

LiVOPO4 has the stable structure result from stable PO4 unit, high potential of 4.0 V compare with LiFePO4 (3.5 V), and it has a theoretical capacity of 166 mAh g-1, which is slightly lower than LiFePO4 (170 mAh g-1). In addition to this, it appears the high theoretical energy density (664 Wh/kg) as against the 578 Wh/kg for LiFePO4. Based on the spatial arrangement of VO6 octahedral and PO4 tetrahedral units, which host the lithium ions in the interstitial sites of the framework, LiVOPO4 exists different crystallographic phases such as α-, β-. γ-. δ-. ε-, ω- LiVOPO4. Triclinic α-LiVOPO4 and orthorhombic β-LiVOPO4among them has magnificent electrochemical performance. VO6 octahedral was consisted of four oxygen atoms in the equatorial and two oxygen atoms at the axial vertices of the octahedron. The oxygen at the axial has different bond length. In this study, we compared the physical properties of triclinic α-LiVOPO4 and orthorhombic β-LiVOPO4., This materials were synthesized by the sol-gel method. The starting materials used vanadium oxide, lithium carbonate, ammonium dihydrogen phosphate. The used precursors measured the DSC (Differential Scanning Calorimeter) to confirm the phase transition temperature. And structure analysis of synthesized LiVOPO4 and impurities formation were confirmed through the XRD measurement. Also, SEM (Scanning Electron Microscopy) and EDS (Energy dispersive X-ray spectroscopy) measured to confirm the particle size of synthesized LiVOPO4 and distribution of atoms. And local structure such as bond length, oxidation state, and parameter of unit cell was confirmed by rietveld refinement and XAFS (X-ray Absorption Fine Structure). The Electrochemical Li ion intercalation performances such as EIS (Electrochemical Impedance spectroscopy), CV (Cyclic Voltammetry), CD (charge-discharge), rate capability also evaluated as the cathodes.