锰系锂离子电池正极材料的制备及电化学性能研究

发布时间：2018-08-06 13:50

【摘要】：随着化石燃料资源的短缺和环境污染的加剧,二次电池作为清洁类能源和电子设备能量存储的媒介,近年来引起了人们越来越多的关注。其中锂离子电池因其性能优异,循环寿命长和环境友好等优点,被人们寄予厚望。然而,现有商业化的锂离子电池在能量密度方面仍不能满足日益增长的使用需求,因此,开发具有高能量密度的电池材料具有重要意义。以磷酸锰锂为代表的锰系锂离子电池正极材料,具有平台电压高,能量密度大,资源丰富,环境污染小,生产成本低等优点,被认为是最有潜力的动力电池材料之一。本论文主要探究了尖晶石锰酸锂、层状锰酸锂和橄榄石型磷酸锰锂的控制合成,并研究了不同形貌或构型与材料电化学性能间的关系。本论文的工作主要包括三个部分:1.多孔洋葱状LiMn_2O_4的控制合成与性能研究。通过固相法批量合成了多孔洋葱状锰酸锂,并结合共沉淀制备前驱体时溶液的电离平衡和各晶面的优势生长,研究其形貌产生的机理。进而使用相同的方法,通过调控pH合成了多孔球状和多孔立方状锰酸锂。电化学测试结果表明,洋葱状锰酸锂具有最高的能量密度,在0.2 C时能量密度达到了530 Wh Kg~(-1),这是由洋葱状锰酸锂层状的结构和丰富的孔洞所贡献的优异性能。2.不同锂含量对层状锰酸锂构型转化的影响及性能研究。使用固相法合成了不同锂含量的层状锰酸锂Li_(1±x)MnO_2,并探究了Li含量对层状锰酸锂结构转化时构型稳定性的影响。其中,Li/Mn比为0.75的材料的循环稳定性要强于Li/Mn比为1的层状锰酸锂。这是由于缺锂而出现了除层状锰酸锂相以外的尖晶石类的Mn_3O_4,由于Mn_3O_4的构型同转化产物尖晶石锰酸锂接近,因而在材料中起到了稳定结构的作用。另外,为了提升LiMnO_2的性能,掺杂了Al离子,掺杂后的材料极化较小,倍率性能也得到了较大的提升。3.橄榄石型磷酸锰锂LiMnPO_4的制备及性能研究。以蔗糖为导电碳源,采用溶剂热和固相结合的方法合成了碳包覆的磷酸锰锂,测试结果表明适量的蔗糖加入能显著地提升磷酸锰锂的导电性,其中,复合50wt%蔗糖的磷酸锰锂展现了更好的倍率性能和更小的阻抗。此外,探究了以工业用镍粉作为导电骨架,采用溶剂热法制得了复合镍的磷酸锰锂,镍粉作为电子传递的导体,较大地提升了磷酸锰锂的导电性能。
[Abstract]:With the shortage of fossil fuel resources and the aggravation of environmental pollution, secondary batteries have attracted more and more attention in recent years as a medium for energy storage of clean energy and electronic equipment. Lithium-ion batteries are expected for their excellent performance, long cycle life and environmental friendliness. However, the existing commercial lithium-ion batteries can not meet the increasing demand for energy density. Therefore, it is of great significance to develop battery materials with high energy density. The manganese-series lithium ion battery cathode material represented by lithium phosphate has the advantages of high platform voltage, high energy density, rich resources, low environmental pollution and low production cost, etc. It is considered as one of the most potential power battery materials. In this paper, the controlled synthesis of spinel lithium manganese oxide, layered lithium manganese oxide and olivine type manganese phosphate was studied, and the relationship between the morphology and electrochemical properties of the materials was studied. The work of this thesis mainly includes three parts: 1. Controlled Synthesis and Properties of porous Onion-like LiMn_2O_4. Porous Onion-like lithium permanganate was synthesized by solid state method. The ionization equilibrium of the solution and the growth of the crystal planes were studied in combination with the coprecipitation to prepare the precursor. The mechanism of the formation of the morphology of the precursor was studied. Furthermore, porous spherical and porous cubic lithium permanganate were synthesized by adjusting pH by the same method. The electrochemical results show that Onion-like lithium permanganate has the highest energy density, and the energy density reaches 530 Wh Kg-1 at 0.2 C. this is the excellent performance of Onion-like LiMnO _ 4 layered structure and abundant pores. The effect of different lithium content on the configuration conversion of layered lithium manganese oxide and its properties were studied. Layered lithium manganese oxide (Li _ (1 卤x) MNO _ 2) with different lithium content was synthesized by solid phase method, and the effect of Li content on the configuration stability of layered lithium manganese oxide was investigated. The cyclic stability of the material with Li / mn ratio of 0.75 is better than that of layered lithium manganese with Li/Mn ratio of 1. This is due to the lack of lithium and the appearance of spinel Mn3O _ 4 in addition to layered lithium manganate. Because the configuration of Mn_3O_4 is close to that of the transformed product, lithium manganate, it plays a role in stabilizing the structure of the material. In addition, in order to improve the performance of LiMnO_2, Al ion was doped, the polarization of doped material was small, and the ratio performance was also improved. 3. Preparation and properties of olivine type lithium manganese phosphate LiMnPO_4. Carbon coated lithium manganese phosphate was synthesized by solvothermal and solid-phase bonding with sucrose as conductive carbon source. The results showed that proper amount of sucrose could significantly improve the conductivity of lithium manganese phosphate. Manganese phosphate lithium phosphate with 50 wt% sucrose showed better performance and smaller impedance. In addition, the conductive properties of lithium manganese phosphate and nickel powder were investigated by using industrial nickel powder as conductive skeleton and solvothermal method.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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