多维硅酸亚铁锂纳米材料的调控合成及储锂性能

发布时间：2018-06-04 16:15

本文选题：纳米电极材料 + 硅酸亚铁锂　；参考：《武汉理工大学》2014年博士论文

【摘要】：基于化学能/电能储存与转化的新型电池及器件是当前科学研究的热点与重点。锂离子电池以其质量轻体积小、储存容量高、寿命长、安全性能高和环境友好等优点，在能量储存和转化领域具有广阔的应用前景。然而，受限于传统正极材料较低的能量密度和功率密度，锂离子电池还难以满足下一代高端的动力电池设备要求。新型的硅酸盐正极材料具有理论比容量高，资源丰富，价格便宜，以及安全性能高等特性。其中中Li2FeSiO4由于具有稳定的循环性能，越来越受到人们的青睐，具有广阔的应用前景。然而，Li2FeSiO4正极材料低的电导率和锂离子扩散动力学，，限制了其应用。本文针对Li2FeSiO4正极材料存在的问题，通过结构设计与调控，制备了多维的高比容量、长寿命、高倍率性能的纳米Li2FeSiO4锂离子电池电极材料，主要获得了以下创新性研究成果： 1.通过水热法和有机聚合法制备了零维(0D)Li2FeSiO4纳米晶/网络碳复合锂离子电池正极材料。得益于网络碳的优异导电性和纳米晶的锂离子快速传输，这种新颖的复合材料在0.1C的倍率下具有1.28个锂离子脱嵌的比容量，实现了从Fe2+到Fe3+，再到Fe4+的连续两部的氧化反应。在0.5，1，2，5和10C的不同倍率下，比容量分别达到189.8，175.6，148.9，125.7和106.6mAh/g；经过高倍率回到1C后，其比容量仍然达到175mAh/g。特别值得指出的是，在10C倍率下经1000次循环后，其比容量仍然高达90.9mAh/g，保持率为97.7%，具有优异的倍率循环性能。 2.采用一种更廉价的三价铁源水热还原制备了一维（1D）Li2FeSiO4纳米棒材料。研究发现，单一的Li2FeSiO4材料由于充放电过程中容易团聚，引起比容量的快速衰减。为此，实验采用了一种简单的PVP锚定法将纳米棒锚定于石墨烯片上，有效地抑制了活性材料的团聚。而且，其中的石墨烯还能起到电子传输和缓解应力作用。制备的纳米棒状Li2FeSiO4/石墨烯片复合材料具有优异的电化学性能：当作为锂离子电池正极材料在1.5-4.8V之间进行充放电时，在0.01A/g（1/16C）的电流密度下的放电比容量为298mAh/g，且具有高的倍率性能和长的循环寿命；当作为锂离子电池负极材料在0-3V之间进行充放电时，在0.02A/g（2/16C）的电流密度下的首次放电比容量为1530mAh/g，随后的可逆容量为1160mAh/g，倍率性能和循环稳定性能也非常突出。因此，采用石墨烯修饰纳米棒状Li2FeSiO4复合电极材料具有优异的电化学性能，完全适合下一代动力锂离子电池的需要。 3.通过乙二醇辅助的一步水热法制备了具有等级梭形结构的Li2FeSiO4材料。研究发现，梭形结构是由单晶的纳米片构筑而成。经电化学测试发现，在0.1C下，该材料的首次放电比容量为180.6mAh/g，库伦效率为97.5%；2C时，比容量为71.0mAh/g，性能与传统碳包覆Li2FeSiO4复合材料相当。高的倍率容量主要归因于Li2FeSiO4特殊的等级结构具有高的锂离子扩散动力学。 4.在等级梭形结构的基础之上，通过控制水热反应温度和溶剂比例，获得了一种新颖的、由单晶二维（2D）纳米花瓣组装而成的三维（3D）等级花形Li2FeSiO4材料。采用2-3nm厚度的石墨烯进行表面包覆和电化学活化后，该复合材料的比容量高达327.2mAh/g，已接近两个锂离子的脱嵌，对应的比能量为879Wh/kg，优于传统的Li2Mn2O4（487Wh/kg）和LiFePO4（500Wh/kg）材料。进一步的倍率测试显示，与目前报道的Li2FeSiO4材料性能相比，该复合材料在各个倍率下均具有较高的比容量。此外，经200次高倍率循环后，其比容量保持率为92%左右。突出的电化学性能主要归因于Li2FeSiO4次级单晶纳米花瓣在薄层方向上较短的锂离子传输路径，以及石墨烯包覆层的保护作用、锂离子和电子的双重输运作用等。
[Abstract]:New types of batteries and devices based on chemical energy / energy storage and conversion are the focus and focus of current scientific research. Lithium-ion batteries have the advantages of small mass, high storage capacity, long life, high safety performance and friendly environment. It has a wide application prospect in the field of energy storage and transformation. However, it is limited to traditional positive materials. Lower energy density and power density, lithium-ion batteries are difficult to meet the requirements of the next generation of high-end power battery equipment. The new type of silicate positive material has high theoretical ratio, rich resources, cheap price, and high safety performance. Among them, Li2FeSiO4 is getting more and more people because of its stable cycle performance. It has wide application prospects. However, the low conductivity and lithium ion diffusion kinetics of Li2FeSiO4 cathode materials limit its application.
In this paper, in view of the problems existing in the Li2FeSiO4 cathode material, through structural design and regulation, multi-dimensional nano Li2FeSiO4 lithium ion battery electrode materials with high specific capacity, long life and high ratio are prepared, and the following innovative research results are mainly obtained.
1. the zero dimension (0D) Li2FeSiO4 nanocrystalline / network carbon composite lithium ion battery cathode material was prepared by hydrothermal method and organic polymerization. Thanks to the excellent conductivity of the network carbon and the rapid transmission of nanocrystalline lithium ion, this novel composite material has 1.28 lithium ion inlaid specific capacity at the rate of 0.1C, which has realized from Fe2+ to Fe3+. The two continuous oxidation reactions to the Fe4+ have reached 189.8175.6148.9125.7 and 106.6mAh/g at the different ratios of 0.5,1,2,5 and 10C, and the specific capacity is still up to 175mAh/g. after a high rate of return to 1C, and the specific capacity is still up to 90.9mAh/g at the 10C ratio of 1000 times. The rate is 97.7%, with excellent multiplier cycle performance.
2. a one dimensional (1D) Li2FeSiO4 nanorod material was prepared by thermal reduction of a cheaper trivalent iron source. It was found that the single Li2FeSiO4 material was easily reunited in the process of charging and discharging, causing rapid attenuation of specific capacity. Therefore, a simple PVP anchoring method was used to anchor the nanorods on the graphene sheet and effectively suppress the nanorods. The reunion of active materials is made. Moreover, the graphene in it can also play an electronic transmission and relieve stress. The prepared nano rod like Li2FeSiO4/ graphene composite has excellent electrochemical properties: at the current density of 0.01A/g (1/16C) when the cathode material is charged between 1.5-4.8V as a lithium ion battery cathode material. The discharge specific capacity is 298mAh/g, and has high multiplier performance and long cycle life. When the anode material is charged and discharged between 0-3V as lithium ion battery, the initial discharge specific capacity at the current density of 0.02A/g (2/16C) is 1530mAh/g, the subsequent reversible capacity is 1160mAh/g, and the ratio performance and the cyclic stability performance are very sudden. Therefore, the use of graphene modified nano rod Li2FeSiO4 composite electrode material has excellent electrochemical performance, which is fully suitable for the needs of the next generation of power lithium ion batteries.
3. the Li2FeSiO4 material with a grade shuttle structure was prepared by the step hydrothermal method assisted by ethylene glycol. The study found that the spindle structure was made of single crystal nanoscale. The electrochemical test showed that the initial discharge ratio of the material was 180.6mAh/g and the efficiency of Kulun was 97.5% under 0.1C, and the specific capacity was 71.0mAh/g when 2C. Conventional carbon coated Li2FeSiO4 composites are equivalent. High rate capacity is mainly attributed to Li2FeSiO4 special hierarchical structure with high lithium ion diffusion kinetics.
4. on the basis of the grade shuttle structure, a novel, three dimensional (3D) grade Li2FeSiO4 material is obtained by controlling the temperature of the hydrothermal reaction and the proportion of solvent. The specific capacity of the composite is up to 327 after the surface coating and electrochemical activation of the 2-3nm thickness graphene. .2mAh/g, nearly two lithium ions have been deembedded, corresponding to the specific energy of 879Wh/kg, is better than the traditional Li2Mn2O4 (487Wh/kg) and LiFePO4 (500Wh/kg) materials. Further multiplier tests show that the composite has a higher specific capacity compared with the performance of the present reported Li2FeSiO4 materials at the rate of 200 times. After the ring, the specific capacity retention rate is about 92%. The outstanding electrochemical properties are mainly attributed to the short transport path of lithium ion in the thin layer of Li2FeSiO4 secondary single crystal, as well as the protective effect of the coating layer of graphene, the dual transport of lithium ion and electrons.
【学位授予单位】：武汉理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

【参考文献】