| The cathode material Li3V2(PO4)3/C for lithium-ion battery is prepared by sol-gel method in this paper, and modified by ion doping and metal oxide coating.The temperature for synthesization is determined according to TG-DTA curves of Li3V2(PO4)3/C precursor. The effect of Mn2+ and Y3+ doped on the structure and electrochemical performances of Li3V2(PO4)3/C is investigated by XRD and galvanostatic charge-discharge. The results show that doping small amount of Mn2+ and Y3+ ion does not affect the monoclinic structure of the material Li3V2(PO4)3/C, and doping the proper amount Mn2+ and Y3+ ion can improve cyclic stability and high-rate dischargeability of Li3V2(PO4)3/C.Li3V1.94Mn0.09(PO4)3/C is investigated by FE-SEM,XPS and electro -chemical impedance spectroscopy (EIS). The results show that the particles of Mn-doped sample are smaller than those of un-doped sample. XPS analysis shows that oxidation valences state of V and Mn in Li3V1.94Mn0.09(PO4)3/C is +3 and +2, respectively. EIS measurement indicates that doping Mn reduces the charge transfer resistance.Metal oxide coated Li3V2(PO4)3/C is investigated by XRD and FE-SEM. The results show that coating with a small amount of metal oxide does not affect the monoclinic structure of the material and the particles of metal oxide coated samples become bigger than those of non-coated sample.Effect of metal oxide coated on the electrochemical property of Li3V2(PO4)3/C is studied. For example, the maximum discharge capacity, cyclic stability and high-rate dischargeability of resultant materials are measured by galvanostatic charge-discharge. The results show that coating with proper amount of Al2O3 and MgO can improve cyclic stability and high-rate dischargeability of Li3V2(PO4)3/C. MgO-coating enhances the discharge capacity significantly and reduces the polarization of material and improves electrochemical properties of Li3V2(PO4)3/C material. The sample of coating amount of 4.5 mol% exhibits excellent electrochemical properties, and can deliver a reversible capacity as high as 195 mAh/g at a discharging rate 0.2C, which is close to its theoretical capacity of 197 mAh/g, and it is able to deliver a capacity of 174 mAh/g and 149 mAh/g at 0.5 C and 1 C, respectively.
|
PDF Full Text Request