The Synthesis And Electrochemical Performance Of A Novel LiCoPO₄ Cathode Materials

The lithium ion battery is one of the newest energy sources which has been developed recently, and it has an extensive application prospect. For the development of the lithium ion batteries, cathode materials play an important role. Therefore, the investigation of high performance cathode has become the central issue in now days. The discharge plateau of LiCoPO4 is 4.8V, which could enhance the energy density of novel cathode. However, the lower electric conductivity and diffusion speed of LiCoPOP4 lead to the reduction of cycle performance of high rate performance.LiCoPO4 powders were prepared through a spray drying method, with a subsequent calcination process. The effects of calcination temperatures, coating electrical carbon and ion-doping were investigated employing XRD, SEM and electrochemical test. The results indicated that calcination temperature is the key factor that determines the final phase composition of the powders, and pure phase LiCoPO4 powder was obtained at temperature over 650℃. SEM observation indicated that the LiCoPO4 microstructure is porous spheres, and the single crystalline with the sizes less than 200nm. Although the electrochemical performance of as prepared powder is not satisfying, it was magnificently enhanced by doping Fe ions into LiCoPO4 lattice, showing great potential for rechargeable batteries. The first discharge capacity of the cathode was 143.3mAh/g under 0.1C rate. After charge/discharge at 0.1C rate for 10 cycles, the discharge capacity samples are 90.9mAh/g, circulating rate was63.4%.LiCo1-xFexPO4/C powders were prepared through a Nano-ball mill method. Study the Fe content influence product phase and electrochemical properties. Under 0.1C, the discharge capacity of LiCo0.8Fe0.2PO4/C up to 160.8 mAh/g, the discharge energy is 690.9 Wh/Kg and the pure LiCoPO4/C first discharge is 125 mAh/g, the charge-discharge properties has greatly improved. After 20 cycles, the circulating rate was 67.2%. Although the electrochemical impedance spectroscopic (EIS) analysis, LiCo0.8Fe0.2PO4/C specific capacity and energy attributed to the of Li+ diffusions.Using Nano-ball mill method, study the sucrose or caramel and composition influence microstructure and electrochemical properties. Scanning electron microscope analysis of the LiNiaMnbFecCodPO4/sucrose and LiNiaMnbFecCodPO4/caramel, the results shows that the sucrose comes the massive electrical carbon, and the caramel comes reticular electrical carbon Moreover the electrochemical test shows LiNiaMnbFecCodPO4/caramel has the best electrochemical performance, under 0.1C, the discharge capacity of LiNiaMnbFecCodPO4/caramel is 144.9 mAh/g, after 20 cycles, the discharge capacity samples are 130.6mAh/g and the circulating rate was 90.1%. in particular, the average discharge energy density is 543.85 Wh/Kg. LiNiaMnbFecCodPO4/caramel is a potential cathode material for Li-ion battery.