The Study Of LiCoPO₄ Cathode Materials With High Energy Density

LiCoPO4, a potential cathode material with a theoretical discharge capacity of 167mAh/g,a high discharge platform around 4.8 V and a high energy density of 802Wh/Kg, is considered as one of the most promising material in the future battery system in the field of high energy application. But low Li+ diffusion coefficient and poor electronic conductivity of the present products result in poor electrochemical performance and prevented its further application in many fields. So, the research of LiCoPO4 is still in development stage before it can be practical employed.In this paper, we used a hydrothermal synthesis to prepare x%LiFePO4/LiCoPO4 cathode materials in which nano sized LiFePO4 crystals were employed as seeding templates. The effects of processing parameters on the structure and morphology of the prepared powders were investigated. By adjusting the key parameters such as the synthesis temperature, growth time and the amount of LiFePO4 seeds employed, x%LiFePO4/LiCoPO4 (x=5,10, 15)powders with high energy density were obtained. The phase purity, crystal morphology and electrochemical performance of the samples were characterized by X-ray diffraction (XRD)and scanning electron microscopy (SEM), charge-discharge and cyclic voltammetry experiments.It was found by the study that pure LiFePO4 with crystal size of 30?80nm can be prepared by solvent microwave mothed. The optimal synthesis process is 140? and 10min.The distribution curve of LiFePO4 particles is close to normally distributed, which shows that its particle size is uniform.Pure LiCoPO4 with crystal size of 0.2um?1.5um can be prepared by hydrothermal mothed at 220?and 12h, without LiFePO4 seeds. The electrochemical testing shows that LiCoPO4 with discharge capacity of 56.4mAh/g, energy density of 328.4Wh/Kg and capacity retain ratio of 44.6% after 50cycles at 0.1 C.The optimal synthesis process of x%LiFePO4/LiCoPO4(x=5,10,15) is 180? and 8h by hydrothermal mothed with LiFePO4 seeds. Nano-LiFePO4 seeds can reduce the required systhesis temperature and shorten growth time so as to promote the formation of x%LiFePO4/LiCoPO4(x=5,10,15) with crystal size of 0.7um?1.0um. Learning from the electrochemical experiments, 10%LiFePO4/LiCoPO4 composite has the best electrochemical performance, under 0.1C, the 10%LiFePO4/LiCoPO4 composite cathode material showed a specific capacity of 133.2mAh/g, a capacity retention of 82.7% after 50 cycles. In particular,the cathode material presented a discharge energy density of 628.4Wh/Kg, which was increased by 90% and 19% when compared to the values of the LCP sample obtianed by normal method and the commercial LFP product. Based on the above findings,the composite LCP material is expected to have great potential to be used in the field of power battery in the future.