| Olivine LiFePO4cathode material, with many characters like wide range of sources, low cost, environmentally friendly, excellent safety performance, good cycle performance and so on, has become one of the most promising next-generation battery cathode materials. Ferrous oxalate dehydrate powders of fine particle size, different microstructure and dimensionality were prepared using simple chemical method. XRD, IR-spectroscopy, Laser Particle Size Analyzer and SEM were used to study the microstructure of prepared Ferrous oxalate dehydrate. The hydrothermal processing was adopted to synthesize LiFePO4cathode material. XRD, SEM, RAMAN and charge-discharge at constant current were used to characterize the structure, micro-morphology and electrochemical properties of LiFePO4cathode material.Ferrous oxalate dehydrate powders of fine particle size, different microstructure and dimensionality were prepared using H2CO4·2H2O and FeSO4·7H2O as starting materials. Pure α-ferrous oxalate dehydrate could be obtained when aged at90℃for7h. When aging temperature was below90℃or aging time was less than7h, pure β-ferrous oxalate dehydrate or the mixture of two phase was obtained. Adding FeSO4solution into H2CO4solution and the increasing of FeSO4concentration, stirring speed and dispersant amount all generate finer particle size. Crystalline of ferrous oxalate tends to be worse and particle size gets finer as pH value increases.Crystalline of LiFePO4prepared by a-ferrous oxalate dehydrate is better than that of β-ferrous oxalate dehydrate, and the latter is easier to appear phenomenon of disorder of Li and Fe atom. The particle size of LiFePO4decreases as the decline of that of ferrous oxalate dehydrate used in a certain range. According to the synthesis method in this paper, the morphology of LiFePO4is in agreement with that of ferrous oxalate dehydrate used in some way, but particle size is smaller than that of ferrous oxalate dehydrate.The hydrothermal processing method was used to synthesize the LiFePO4cathode material. The crystalline of LiFePO4get better and the particle size grow with the reaction temperature increasing and time extending. The pressure of hydrothermal processing system also had some effect on the microstructure and performance of LiFePO4. When the pressure increased from5Mpa to10Mpa, the crystalline of LiFePO4got better, and the particle size got smaller and more uniform. In addition, the shape of particle tended to become from bulks to flakes, and the electrochemical performance got better.Microstructure, morphology, particle size and electrochemical performance of LiFePO4synthesized by different Li amount were studied. The results of XRD showed that the number of diffraction peaks of LisPO4impurity increased and their intensity strengthed with the increasing of Li amount, but intensity of LiFePO4diffraction peaks decreased and their FWHM increased. The results of SEM and Laser Particle Size Analyzer showed that particle size of LiFePO4decreased with the increasing of Li amount. Raman diffraction peaks of LiFePO4became wider and shifted to low frequency direction as Li amount increased. The initial charge specific capacity rised and their initial charge/discharge efficiency decreased with the increasing of Li amount.LiFePO4/C was synthesized by carbon-coated. The results showed that the material after high-temperature treatment had a complete crystal structure, regular appearance, uniform particle size, and there was no significant grain growth. The conductive carbon network was formed by carbon-coated on the material. The electrochemical performance was greatly increased after the addition of carbon. The results of Raman showed that the extent of carbon graphitization was higher when PVA was adopted as carbon source than PF was adopted. The continuity of carbon fiber obtained from PVA was better and the breaking number of carbon fiber was fewer, so the electrochemical performance of LiFePO4/C using PVA as carbon source was much better. |
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