Study On Synthesis And Performance Of LiCoPO₄ Cathode Materials For Lithium-ion Batteries

The main subject of this paper is to use wet-chemical method to produce LiCoPO4 and modified materials.Using Sol-gel method, single-factor experimental studies the factors influence product composition and electrochemical properties. The optimum process of synthesizing LiCoPO4 is listed as follows:roasted at 650℃for 8 h, and the molar ratio of n(Li):n(Co) was 1.5:1. The first discharge capacity of the cathode was 113.9mAh/g under 0.1 C rate. After charged/discharged at 0.1 C rate for 20 cycles, the discharge capacity was 70.4mAh/g. XRD and SEM analysis showed that the particles of synthetic samples are smaller, dispersing properties are very well.The compound of cathode materials doping with nonmetal (carbon) and rare earth elements(Y3+, La3+) were synthesized by sol-gel method. And their crystal structure charge-discharge properties and cycle performance were investigated.The composite materials LiCoPO4/C have better electrochemical performance than the pure LiCoPO4。Under 0.1C, the discharge of LiCoPO4/C up to 121.2mAh/g, and the pure LICoPO4 first discharge is 113.9mAh/g, the charge-discharge properties has greatly improved. The results show that carbon can improve the conductivity of the material, thereby enhancing the electrochemical properties of the material.The first discharge capacity of the cathode material Li0.99Y0.01CoPO4 reached 123.0mAh/g under 0.1 Crate, compared to the pure LiCoPO4 increased by 8%. After 20 cycles the discharge is 78.6mAh/g, the electrochemical performance of materials have much improvement.Under 0.1C rate, the first discharge capacity of the LiCo0.99La0.01PO4 isl33.6mAh/g, it is improved 13% compared to the pure LiCoPO4, after 20 cycles the capacity is 85.1mAh/g, so the circulation performance is greatly improved.Scanning electron microscope analysis of the composite and pure LiCoPO4, the results showed that the particle size of the modified materials was smaller than the pure materials, more homogeneous, and that could saw clear ellipsoidal structure.Using Microwave-sol-gel method, the appropriate process of synthesizing LiCoPO4 were determined by orthogonal test method to be:microwave power 700W, reaction time is 10min, the solution pH value of 7, as well as lithium-cobalt ratio of 1.5:1. The first discharge capacity is 110.1mAh/g under 0.1C; after20 cycles the discharge capacity is 71.2mAh/g.