Preparation And Modification Of Cathode Material Li₃ V₂ (PO₄)₃ For Lithium-Ion Batteries

In this paper, solid state reaction method and sol-gel method were employed to prepare Li3V2(PO4)3 as cathode materials for lithium ion batteries. In addition, Li3V2(PO4)3 is doped with different elements. The prepared samples were characterized by XRD, SEM, cyclic voltammetry, electrochemical charge-discharge cycling and so on. The structure and electrochemical properties of the samples prepared by different synthesis methods, different temperatures, doping and doping amount of different elements were investigated.LiOH-H2O, NH4VO3, NH4H2PO4 and oxalic acid were used as starting materials. Thereamong, oxalic acid was used as a reducing agent. Carbon coating was subsequently conducted to prepare Li3V2(PO4)3/C. The prepared Li3V2(PO4)3 and Li3V2(PO4)3/C samples were characterized by XRD, cyclic voltammetry and galvanostatic charge-discharge cycling. The results indicated that Li3V2(PO4)3/C had better electrochemical properties than pure 3. The initial charge and discharge capacity of the Li3V2(PO4)3/C sample at a current density of 0.1 C was 119.7 and 106.7 mAh·g-1, respectively. Moreover, a discharge capacity of 105 mAh·g-1 was retained after 20 charge-discharge cycles.3 material was synthesized by sol-gel method using LiOH·H2O2, NH4VO3, NH4H2PO4 and citric acid. The effect of different synthesis temperatures, doping and doping amount of different elements on the structure and electrochemical performance of Li3V2(PO4)3 material were studied. The results indicate that the first discharge capacity of the cathode was 119.26 mAh·g-1 at a current density of 0.1 C. A series of Cr3+ doped Li3V2-xCrx(PO4)3 (x= 0,0.1,0.25 and 0.5) samples were prepared by a sol-gel method. The effects of Cr3+ doping on the physical and chemical characteristics of Li3V2(PO4)3 were investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr3+ doped samples have no extra reflections, which indicates that Cr3+ enters the structure of 3. As indicated by the charge-discharge measurements, the Cr3+ doped 3 (x=0.1,0.25 and 0.5) exhibited lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g.1 C and 2 C) were enhanced by proper amount of Cr3+ doping (x= 0.1). The highest discharge capacity and capacity retention at the rates of 1 C and 2 C were obtained for Li3V19Cr0.1(PO4)3. The improvement of electrochemical performance could be attributed to the higher crystal stability and smaller particle size induced by Cr3+ doping. 3 (x= 0,1/12,1/6,1/3) displayed a more stable cycle performance when x equal to 1/12. The highest discharge capacity and capacity retention at the rates of 1 C and 2 C were obtained for Li3V1.8Mg0.1Ti0.1(PO4)3. The Ti4+ and Mn2+ doping could not improve the electrochemical performance of Li3V2 (PO4)3 sample.