Research On Synthesis And Performance Of Li₃V₂（PO₄）₃as Cathode Materials For Lithium Ion Batteries

Recently, Li3V2(PO4)3has attracted great attention due to its low cost, high potential, structure stability and large theoretical specific capacity (197mAh·g-1), expected it to replace the lithium cobalt oxide cathode materials. However, the poor electrical conductivity and low lithium ion diffusivity limite Li3V2(PO4)3to be put into use, therefore it is needed to do some modifications of this material. In this paper, the precursor was prepared by hydrothermal method. The effects of calcination temperature, calcination time, the quantity of carbon, the kinds of carbon resource, voltage region on the performance of material and the kinetics of the electrode were studied in detail, the best synthesis technics were optimized. The main contents are summarized as follows:Firstly, the influence of synthesis technics on performance of Li3V2(PO4)3was studied. The results showed that Li3V2(PO4)3/C precursor was synthesized using LiOH·H2O, NH4VO3, NH4H2PO4and maltose without further purification as starting materials by hydrothermal method method. The sample which was preparated at600℃for2h in Ar ambience had better crystallinity, uniform particle sizes and electrochemical performance. The highest initial discharge capacity of181.3mAh·g-1and at the40th cycle, the sample still kept159.2mAh·g1at0.1C in the voltage range of3.0～4.8V with2.24%carbon contents, and the capacity retention was87.81%; the highest initial discharge capacity of91.8mAh·g-1and at the40th cycle, the same sample still kept91.4mAh·g-1at1.0C in the voltage range of3.0～4.3V, and the capacity retention was99.56%。The Li3V2(PO4)3/C sample was investigated by cyclic voltammetry and three couples of oxidation peaks and reduction peaks were identified, which was in agreement with the charge-discharge curve.Secondly, the influence of carbon-coated on the performance of Li3V2(PO4)3was studied. Four Li3V2(PO4)3/C samples with different carbon content were synthesized by hydrothermal method with maltose by adjusting the content of maltose. XRD patterns could be indexed on the single-phase of monoclinic Li3V2(PO4)3with a space group P21/n. The highest initial discharge capacity of126.4mAh·g-1and at the40th cycle, the sample still kept121.8mAh·g-1at1.0C in the voltage range of3.0-4.3V with10.23%carbon contents, and the capacity retention was96.36%; its discharge capacity had only9.44%decrease from134.5mAh·g-1at0.1C to121.8mAh·g-1at 1C.Otherwise, the kinds of carbon resource on the performance of Li3V2(PO4)3/C were investigated. The Li3V2(PO4)3/C samples were synthesized by hydrothermal method with maltose, glucose and tartaric acid as carbon source, respectively. The results showed that the sample which was prepared with maltose as carbon source had the best electrochemical performance. The initial discharge capacity at0.1C was134.1mAh·g-1and the discharge capacity was132.6mAh·g-1after40cycles, the capacity retention rate was98.62%, It indicated that maltose was an ideal carbon source for Li3V2(PO4)3/C.