锂离子电池用尖晶石锰酸锂正极材料的应用研究

【作者】 刘环敏；

【导师】 刘耘畦； 黄可龙；

【作者基本信息】 昆明理工大学 ， 应用化学， 2003， 硕士

【摘要】 本文详细评述了高性能锂离子电池及其正极材料的研究前沿和发展动态。主要研究了尖晶石型锰酸锂正极材料的制备与应用。锂离子二次电池的发展必然要求廉价、低污染的新型材料替代现有的昂贵的钴酸锂材料。尖晶石锰酸锂由于其更高的性能价格比成为最有希望替代钴酸锂的正极材料。本文在已有的实验基础上做锰酸锂材料的扩大化生产条件实验，并在实验的最佳条件下烧制多元复合掺杂锰酸锂材料；同时将该材料应用于工业生产中做成成品锰酸锂离子电池并测试其性能；针对锰酸锂材料的容量衰减问题尤其是高温下容衰减严重，首次用硅烷偶联剂对掺杂锰酸锂材料进行表面处理来改善其高温性能，并用交流阻抗法测试锂离子固相扩散系数。主要内容如下：1、 针对扩大化生产中经常出现的二次电池的容量偏低现象，采用溶盐-浸渍法制备尖晶石锰酸锂材料，研究不同的锂、锰原料、Li／Mn2配比、煅烧方式与温度、空气循环、洗涤等因素对材料的电化学性能的影响。结果表明采用LiOH·H2O和Mn3O4为主要锂、锰原料在750～780℃下烧36h获得的锰酸锂材料具有最好的电化学性能，比容量可达127mAH·g-1。烧制过程中产生的还原性气氛易导致低价锂锰氧化物的杂质生成，通过通入适量空气增加氧化性气氛有利于煅烧出高性能的LiMn2O4材料。由原料不同使材料呈碱性或酸性从而对产物的电化学性能有一定的影响。水洗是解决这个问题的一个办法。在以上研究的基础上制备了金属离子和F的共掺杂尖晶石锰酸锂LiMn2-(A+B)CoACrBO4-CF。(MCCF)，比容量为120 mAH·g-1，虽然较纯尖晶石锰酸锂的比容量有所降低，但具有优良的循环性能。2、 选用综合性能较好的复合掺杂尖晶石锰酸锂(MCCF)材料做成成品锰酸锂离子电池，并测试其电化学性能。做成063740型电池正极附料量为4． 95克，设计容量为500mAh，第一次循环的放电容量为461． 2 mAh，放电比容量为94． 34mAH．g-1。前几次放电过程中由于具有保护作用的钝化膜(SolidElectrolyte Interface，简称SEI膜)的形成产生了一定的不可逆容量损失。对电池进行充放电测试，0． 5C循环50次后容量保持率为90． 45％，充放电效率一直在99． 5％以上。以MCCF为正极材料的锰酸锂离子电池的循环性能和倍率放电特性、自放电率等与同种型号的钴酸锂离子电池相比几乎没有差别。对锂离子电池的容量损失原因进行了分析，认为电极过充、电解液的氧化分解、自放电、界面膜的形成、正极溶解和正极材料的相变都是产生锂离子电池容量损失的原因。3、 对尖晶石LiCrxMn2-xO4材料表面进行硅烷偶联剂处理，以形成一热稳定性昆明理工大学硕士研究生毕业论文摘要好的硅化物表面层来提高材料的电化学性能。用EPX、SEM和XRD等方法对处理前后的尖晶石LICrxMnZ一xo;正极材料进行了表征，结果表明经硅烷偶联剂处理后的LICrxMnZ一，04正极材料，在其表面形成了富硅层。电化学测试表明硅烷偶联剂表面处理的LICr、MnZ一xo。正极材料在高温下(55℃)100次循环后的容量保持率为89.4%，而未处理的LICrxMnZ一x0;材料的容量保持率为71.5%。因此，硅烷偶联剂表面处理是改善铿离子电池正极材料LICr:MnZ一，0。高温性能的有效途径。 4、将Li/MCCF半电池进行交流阻抗实验，由库仑滴定法做Li/MCCF的开路电压随组成变化曲线，求}dE/dx}，从而计算扩散系数。本实验求出的Li’扩散系数大小在10一sc，。2/S数量级。更多还原

【Abstract】 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更多还原