Research On The Controlled Synthesis Of LiCoPO₄ Cathode Materials

Li-ion batteries have been successfully used in portable products,HEV,energy storage batteries.There are the commercialization of lithium-ion battery cathode materials at present and they are layered LiCoO2,pristine LiFePO4,Li-Ni-Co-Mn-O materials,but the materials that are mentioned have lower redox potential and it leads to the capacity density of whole material lower,it can not meet people's application in todays,people want urgently one of cathode materials,which has high redox potential and high capacity density.Pristine LiCoPO4 has redox potential of 4.8 V vs.Li+/Li and a theoretical capacity of 167 mAh/g,it will be new cathode material with high redox potential and high capacity density in future.However,due to the electronic conductivity and Li-ion diffusivity of LiCoPO4 material are lower,its lead to the poor electrochemical performance of LiCoPO4 material,that is to say,the first discharge capacity of LiCoPO4 material is lower and the cycle performance is worse.For the above problem,at first,LiCoPO4 and LiCoPO4/C samples are synthesized by the solid phase method in this article,the electrochemical performance of LiCoPO4 and LiCoPO4/C samples are studied by changing the temperature,the ways of sinter,protective atmosphere.From the XRD patterns,SEM,and the electrochemical performance,it is ease that the LiCoPO4 material is synthesized under the two-stage process and the protective atmosphere is Ar,and attained the well performance of LiCoPO4 material.The carbon is not effective modifier in LiCoPO4/C material,in terms of increasing the electrochemical performance of LiCoPO4 material,compared with the carbon-coated LiCoPO4 material,the particle size of LiCoPO4 material is more important.The smaller particle size of LiCoPO4 material is not helpful to attain well cycle performance.Secondly,when LiCoPO4 and LiCoPO4/C samples are synthesized by the solid phase method,it is easily that LiCoPO4 material will be reduced under the high-temperature heat-treatment and Ar protective atmosphere,and it can be occur the catalytic property Co2P.The catalytic property of Co2P in influencing the electrochemical performance of LiCoPO4 material is studied by changing the quality of Co2P and protective atmosphere.From the XRD patterns and the electrochemical performance,when the existence of Co2P in LiCoPO4 material,the electrolyte decomposition is serious at LiCoPO4 electrode surface,the charge capacity and the charge plateau of LiCoPO4 material added,the whole material's structure is destroyed,the discharge capacity decreased,and it lead to the coulombic efficiency of LiCoPO4 material declined.Therefore,the formation of Co2P should be precluded in the synthesis of LiCoPO4.When the catalyst Co2P lost the activity,the coulombic efficiency of LiCoPO4 material do not change nearly.At last,LiCoPO4 material is successfully synthesized by the comprehensive method,the electrochemical performance of LiCoPO4 samples are studied by changing the temperature and carbon coated.From the XRD patterns,SEM,and the electrochemical performance,it is first that LiCoPO4 material is attained at 500 ? and it have the electrochemical performance,the performance of sample is best at 600 ?.The NaCl material is fabricated and it successfully replaced the role of carbon in preventing the particle growth at lower temperature.