Li3V2(PO4)3 As a Positive Electrode Material for Rechargeable Lithium Batteries

Nowadays, demands lithium ion batteries which are mounted in portable devices increase day by day. As a result, research towards positive and negative electrode materials being intensively progressed.

 Most commonly used positive electrode is LiCoO₂ because it has good electrochemical property. However, Co is rare material and it is placed in limited area. Therefore, price of Co increases more and more. To substitute Co, plenty of transition metal material is studied such as Fe, Ni, Mn and V. Among them polyanion phosphate material such as LiMPO₄ (M = Fe, Co, Mn and etc) and Li₃V₂(PO₄)₃ are considered as possible candidate materials because of their structure, thermal stabilities and low price. However, those polyanion material, LiMPO₄ (M = Fe, Co, Mn) has low energy density, causing low energy density. Li₃V₂(PO₄)₃ has good safety as LiFePO₄ but higher energy density than LiFePO₄ because of its high redox potential, V^2+/5+. Also, Li₃V₂(PO₄)₃ has high reversible capacity and high theoretical capacity (197 mAh g^-1). In this paper, physical and electrochemical properties of Li₃V₂(PO₄)₃ is investigated.

Li₃V₂(PO₄)₃ is synthesized by solid state method. Stoichiometric amount of Li₂CO₃, NH₄H₂PO₄, and V₂O₅ powders were grind and mixed by ball mill. The mixed powders were calcined at 500 ^oC in air atmosphere. The calcined powders were pelletized and sintered at 800 ^oC for 5 h in reduction atmosphere again. The calcinations, heated pellets were grind in Ar filled glove box to avoid air exposure. The synthesized Li₃V₂(PO₄)₃ powders were identified by X-ray diffraction (XRD) with Cu Kα radiation and analyzed by Rietveld refinement. Electrochemical test were carried out in coin type cell. Galvanostatic electrochemical charge and discharge test were made between 3.0 V and 4.8 V at 10 mA g^-1 current at room temperature.

 The XRD pattern of the product shows single phase Li₃V₂(PO₄)₃ were obtained without impurity. The galvanostatic charge and discharge performances of Li₃V₂(PO₄)₃ as an positive electrode are tested in voltage range of 3.0 V and 4.8 V. Also to understand the mechanism during charge and discharge, ex-situ XRD, XPS and ToF-SIMS measurement were carried out at the first cycle. Furthermore to understand the affect the thermal stability high temperature XRD and TGA were carried out. Details will be discussed in the conference site.