The Research Of The Preparation And Electrochemical Performance Of Cathode Materials LiFePO₄/FeN

Olivine-LiFePO₄is acknowledged to be the most promising cathode material inHEV for its high theoretical capacity,brilliant cyele stability,cost effective raw materialsand non-toxicity. However, the poor electronic conductivity and small lithium iondiffusivity of LiFePO₄have limited its application in high-power-density batteries. If wemake N atoms combine with the Fe atoms which were belong to the olive structure ofthe LiFePO₄, and then a metal-property similar materials such as FeN will be formed forwhich will improve the low electronic conductivity of the LiFePO₄to some extent. Thus,an enhanced performance of this lithium battery is reasonable. On the base of reviewingthe development of lithium ion battery and its cathode materials in detail,olivineLiFePO₄were chosen as cathode material, their synthesis and modification werestudied.In this paper, LiFePO₄/FeN composite cathode materials was synthesized byreduction method using urea as a high temperature reducer and a nitrogen source.Thefact that no characteristic peaks of FeN could be detected in the XRD spectra, indicatethat FeN have no effect on the skeleton structure. The FeN was formed on the surface ofLiFePO₄sample, which was also proved by Raman spectroscopy. The existence of FeNhas positive impact on the electronic conductivity of LiFePO₄sample was also provedby EIS.The effects of calcination temperature、calcination time、and nitrogen content onstructure、 morphology and electrochemieal performance were systematicallyinvestigated. It was found that the sample calcined at650℃for9h presented the bestelectrochemical performance with129.6mAh/g initial discharge capacity at the currentdensity of0.1C.As-prepared nona Fe2O3was used to synthesize the target product as the raw materials instead of the normal industrial Fe2O3. The consequences showed that thegrain size was nano-scale, electronic microscope photograph displayed the sample wasgathered with LiFePO₄particles.Electrochemical performance results show that: thesample that was synthesized by this method has good discharge capacity.