| The recent development in high energy density lithium ion batteries and their cathode materials were reviewed in this paper. Based on the brief demonstration of the important applying field and the industry of spinel manganese oxide, the main research works were focused on the synthetic technology and surface grafting of the cathode materials and the applying in lithium ion rechargeable batteries. The LiMn204 is the most perspective material to substitute LiCo02 as the lithium ion battery positive materials. The influencing factors on the LiMn204 scale-up production were discussed and the MCCF was synthesized under these conditions; Surface grafting as an effective way to improve the elevated performance of positive materials was reported ; the paper has systematically discussed the lithium ion diffusion coefficients in solid materials. They are mainly given as follows.1) The LiMn204 samples synthesized by melt-impregnation method, using LiOH ?H20 and Mn304 as the lithium and manganese sources, calcining under 750~780癈 about 36 hours is confirmed to be best in view of storage and cycling performance. The results obtained from many control experiments show that the fresh air is needed in calcining because the deoxidized gas would be produce in the progress of calcining. Because of using different doping sources, the productions of LiMxMn2-xO4 M=(Cr,Co) show different PH value, which affect the capacity of the materials. Washing the production is a way to solve it. The experiments also show that controlling the molar ratio of Li to Mn2 is important and the suitable value is 1.03~ 1.04. The performance of the LiCrxCoyMn(2-x-y)04-zFz (MCCF) cathode materials obtained according to these results have discharge capacity above 120mAh.g-1.2) The lithium ion rechargeable batteries were constructed by the best MCCF as cathode materials and the Yt7-11 graphite as anode materials. The weight of MCCF in 063740 size lithium ion batteries was 4.95g. The design capacity was 500mAh. The discharge experiments were carried out at various current densities. The results show that when in 0. 5C discharge the initial discharge capacity was over 461.2mAh, the specific capacity was 94.34 mAh.g-1, cycling under 50 times the discharge capacity is 90.45%of the initial capacity. Because of the SEM (Solid Electrolyte Interface) , there are irreversible capacity in the first cycle. The results show that there are almost no different in the rate discharge feature and the rate of local action between the same type of lithium ion manganese rechargeable and lithium cobalt rechargeable. Factors that may cause capacity decrease of lithium ion battery during cycling are discussed in this paper.3) Surface grafting with silance coupling agent on the spinel LiCrxMn2-x04 was reported. The structure of the grafting and ungrafting LiCr,Mn2.x04 was characterized by EPX, SEM and XRD. The result show that after grafting, the silica enrichment on the surface of LiCrxMn2-x04 was found and the positive materials had increased stabilized cycling performance and reduce self-discharge. After 100 cycles, the grafting and ungrafting LiCrxMn2-x04/Li batteries discharge capacity is 89. 4 and 71. bof the initial capacity. That is to say surface grafting with silane coupling agent is an effective way to improve the elevated performance of positive materials.4) The charge/discharge rate has the same importance with the charge /discharge capacity, and the paper has systematically discussed the parameter, lithium ion diffusion coefficients in solid materials. The open circuit voltage for MCCF with the change of intercalation composition has beer, measured. The lithium ion diffusion coefficient has been obtained by EIS (A. C impedance) method and the results indicate that its values are change with the change of lithium ioa intercalation compositions. The lithium ion diffusion coefficient has the extremities at the point of solid phase structure changes happened during charge and discharge progress, which may be identified clearly from the maximum values in the dE/dx... |
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