Preparation And Electrical Li ₃ V ₂ (PO ₄ ) ₃ / C Composite Cathode Material Of Sol-gel Method Chemical Properties

The monoclinic Li3V2(PO4)3with a NASICON-type structure is one of the most promising materials due to its good ion mobility, high lithium capacity, high operate voltage and stability structures. The reversible cycling of all three lithiums from Li3V2(PO4)3would correspond to a theoretical capacity of197mAh/g. However, the conductivity of this materials is low due to the VO6octahedron was segregated by PO4tetrahedron, and that has limited its development.In this paper, The lithium vanadium phosphate (Li3V2(PO4)3) was prepared by sol-gel method with NH4H2PO4, NH4VO3, and Li2CO3as the raw materials. The sugar was add to the mixed solution to form sugar crystal to control the growth of LVP/C. The effects of synthesis conditions,carbon content and sugar contents on the crystal structure, the lattice parameters and the average particle size and electrochemical properties of LVP/C were investigated.A series of LVP/C cathode materials were synthesized by control the different synthesis conditions and the content of citric acid of the content of carbon. The effects of synthesis conditions and carbon content on the crystal structure, the lattice parameters and the average particle size and electrochemical properties, especially the rate properties of LVP/C were investigated by TG-DTA, XRD, SEM and battery test system and other testing methods. It is found that different carbon content can change the crystal structure of the persours, but the synthesis conditions has s litter influent on the crystal structure. Also, the different synthesis conditions has a litter influent on the crystal structure of LVP/C. However, the average particle size of the Li3V2(PO4)3are reduced as the carbon content is increased, which indicating the amorphous carbon can restrain the growth of LVP/C. The average particle size of the Li3V2(PO4)3synthesized at strong synthesis conditions are smaller than that synthesized at weak synthesis conditions.In addition, the electrochemical performance of the Li3V2(PO4)3cathode materials was tested in CR2032button battery. When charged at3.0-4.3V at0.2C rate, the best one was expressed132.2mAh/g at first cycle and it emerge a good cycling performance at low rate. The capacity retention after50times reached98.7%. Compare to each other, the rate performance of LVP/C become worse due to the more coacervate, and the capacity also become lower. When add sugar to the mixed solution, the sugar crystal appeared when the solvent was volatilized and form many micro reaction zone, which can control the growth of LVP/C. The excrescent carbon can form many gas during calcination and form a loose structure. This materials has a better rate performance when charged at3.0-4.3. The best one can reached89.6mAh/g at5C, which is71.3%of its0.1C discharge capacity. It also has a good cycling performance.