| Olivine structured LiFePO4is considered as one of the most promising candidates fora new generation of lithium ion secondary battery cathode materials due to its170mAh/gtheoretical capacity, higher discharging voltage(3.4V vs.Li+/Li), good cycling performance,excellent high-temperature property and thermostability, non-toxic and low cost.Consequently, LiFePO4has been widely used in digital products, electric tools, lightelectric vehicle and energy storage equipment, and other fields. And it has become apreferred cathode material for large capacity, high power lithium ion battery.In this paper, a brief description on the development of lithium ion battery and theresearch progresses of cathode materials were given, and then the Li-insertion/extractionmechanisms and the main preparation methods for LiFePO4material were summarizedbased on the introduction of the structural feature of LiFePO4. The recent development onthe carbon coating, ion doping, decreasing the particle size and morphology controlling ofLiFePO4material were also summed up, and the main research contents and significancesof the paper were presented on the basis of the previous researches of the team work.Under laboratory conditions, the processes of micro-nano structure iron phosphateraw material prepared by the turbulent flow cycle method and LiFePO4/C compositeprepared by the carbon thermal reduction method were improved and optimized. And theperformance of the samples were characterized and tested. Then, the ultrafine lithiumphosphate powder was synthetized by the turbulent flow cycle method, and themodification effect on the electrochemical performance of LiFePO4/C material by usingthe ultrafine lithium phosphate was studied.Firstly, the iron phosphate powder material was controllably synthetized, the resultsshowed that iron phosphate prepared by the co-precipitation method in a turbulent flowcycle equipment was a pure phase, a small particle size and narrow distribution of mediandiameter D50=2.12μm, and a powder material with characteristic of micro-nano structure.This material had a high purity, main impurity ions in total was under50ppm. The moleratio of iron to phosphorus was0.998, which was consistent with the theoretical value. It was suitable as a raw material for the synthesis of LiFePO4.Secondly, using the synthetic iron phosphate as iron source and phosphorus source,lithium carbonate as lithium source and polymer sol as carbon source(coated with2~3%carbon), the LiFePO4/C composite synthetized in the air atmosphere furnace by a newcrucible system had a good crystallinity and a uniform distribution of spherical particles,the smallest particle size of which was under1μm. This material showed a goodelectrochemical performance, the initial discharge capacity of the material reached152.7mAh/g under0.1C rate when the battery was galvanostaticly charged and discharged overa volt of2.0~4.2V, and the discharge capacity held148.9mAh/g after30laps, thecapacity retention rate was97.5%. At high rates of1C,2C and3C, the discharge capacityretention rate was98.5%,100.7%and99.2%, respectively, which showed certain cyclestability.Finally, the lithium phosphate powder prepared by the co-precipitation method in aturbulent flow cycle equipment had a pure phase, a good thermal stability under750℃, anarrow particle size distribution of D50=3.25μm, and a specific BET surface of13.38m2/g.Put this material into the electrolyte of1mol/L LiPF6/(EC+DMC+MC), and the assembledlithium iron phosphate batteries in electrochemical performance test under differentvoltages, which showed a better electrochemical performance. |
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