Hydrothermal Synthesis Of LiFePO₄ And LiCoPO₄ For Lithium Ion Batteries

Lithium ion battery is one of the newest energy sources which has 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 nowadays. In this paper, new cathode materials LiFePO₄ and LiCoPO₄ were prepared by hydrothermal method. The processing conditions which effected the powders crystallization were also discussed. The products were characterised by XRD, SEM, TEM, EDS and particle size and distribution. The major results are as follows.1. The results of the LiFePO₄ powders obtained by hydrothermal synthesisLiFePO₄ cathode material powders were successfully obtained by hydrothermal method. The preparation conditions were choosen from the different pH, temperature, holding time, and lithium resouce. After that, the particle size and distribution of LiFePO₄ as prepared in alcohol-water mixed solutions under the best conditions were discussed. The results are listed as follows.1) In single water system, the pure and well-crystallized LiFePO₄ powders were synthesized under conditions of pH=10.50 and held for 2h at 180℃. The better raw material for lithium was LiOH·H₂O and the molar ratio of the materials was n Li : nFe:nP=3:1:1. The morphology of products was short columnar, and perfect cleavage appeared in the products.2) The well-crystallized LiFePO₄ powders were also synthesized by changing the media of the solvents under the same conditions which were discussed in above. The pure and narrow size distribution LiFePO₄ powders were obtained when the volume ratio of isopropanol to water was 1:1, and the particle size was about 10-30nm.2. The results of the LiCoPO₄ powders obtained by hydrothermal method LiCoPO₄ cathode material powders were successfully obtained by hydrothermal method. The processing conditions which affect the final products crystallization and morphology were also investigated. The products were characterised by XRD, SEM, EDS. The results are as follows.The pure and well-crystallized LiFePO₄ powders were synthesized under conditions of pH=8.50 and held for 4h at 220℃. The better raw material for lithium was LiOH·H₂O and the molar ratio of the materials was n Li : nCo:nP=2:1:1. The products were orthorhombic prism-like, and perfect cleavage appeared in the products. The XRD and SEM results showed that the LiCoPO₄ crystal grains were recrystallized based on the dissolution of the intermediates in hexagonal and rhombohedral system, and the primary precusor was Co(OH)2.