The Morphology Of LiFePO₄Synthesized By Hydrothermal Method And Its Modification

Olivine LiFePO4cathode material has advantages of wide range of sources, good cycle performance, environmentally friendly and good security and so on, so it is concerned of the most promising lithium-ion battery cathode material by researchers. In this paper, LiFePO4cathode material was synthesized by hydrothermal method, and then the LiFePO4/C composite cathode material was synthesized by carbon-coated. XRD, SEM, Raman, Laser Particle Size Analyzer and constant current charge/discharge were used to characterize the structure, micro-morphology and electrochemical properties of LiFePO4cathode material.1. The orthogonal experiments indicated that the reaction time had largest impact on the purity quotient of the material, and the molar ratio of phosphoric acid and phosphates had the minimal, the molar ratio of lithium, reaction temperature ranked the second and third, respectively. Orthogonal experiments indicated that the reaction time had minimal impact on the tap density of the material, and the reaction temperature had the largest impact on the tap density of the material, the molar ratio of phosphoric acid and phosphate, the molar ratio of lithium ranked the second and third, respectively. The tap density of sample synthesized by using NH4H2PO4as phosphorus source was lower than the tap density of sample synthesized by using H3PO4as phosphorus source, but the former sample was more uniform and the particle size was smaller, and had better electrochemical performance.2. Comparing the samples synthesized by using the solvent as water, the mixed solvent of ethanol and water, acetone and water, we found that when using the mixed solvent of ethanol and water, the particles of the sample we obtained could be refined and less agglomeration, which can improve the electrochemical performance.3. The particle size of the sample decreased with the increasing of the concentration of NaHC03. And the sample we obtained was pure phase when we increased the concentration of NaHCO3.4. When using polyvinyl alcohol or phenolic resin as carbon source, the morphology and crystal structure of the samples did not change significantly, but carbon coated process could improve the electrochemical properties of the samples. When using polyvinyl alcohol as carbon resource, the carbon layer coated on the particles was more uniform, and the sample had better electrochemical performance.