高性能锂离子电池层状富锂正极材料的制备及其改性研究

发布时间：2018-06-20 12:31

本文选题：层状富锂正极材料 + 表面修饰　；参考：《湘潭大学》2017年硕士论文

【摘要】：近年来,层状富锂正极材料xLi_2MnO_3·(1-x)LiMO_2(M=Ni,Co,Mn等过渡金属)因其具有高的放电比容量(250 mAh/g)和工作电压(4.6 V vs.Li/Li+),吸引了国内外研究人员的兴趣,并被视为最具前景的下一代高性能锂离子电池正极材料。尽管层状富锂正极材料拥有高放电比容量和能量密度,但是在其大规模商业化应用之前,层状富锂正极材料存在的几个固有缺陷必须要得到解决,如首次不可逆容量损失大以及差强人意的循环性能和倍率性能。针对以上问题,本文通过表面修饰,微纳结构设计以及形貌尺寸优化等策略,旨在改善层状富锂正极材料的电化学性能,主要研究内容如下:(1)首先采用共沉淀法及后续的高温固相反应合成了球形层状富锂正极材料Li1.5Ni_(0.25)Mn_(0.75)O_2+δ,然后用水热法在球形层状富锂正极材料的表面均匀地包覆了一层Li Ti_2(PO_4)_3(LTP)。系统地研究了不同量的LTP包覆材料物理及电化学性能之间的差异。结果表明,LTP主要是以纳米粒子的形式均匀地包覆在材料的表面,没有改变原材料的结构。另外,LTP包覆层不仅有效提高了富锂正极材料的首次库伦效率,其循环性能和倍率性能也得到了显著的改善。包覆量为3 wt%样品展示了最好的电化学性能,在0.5 C电流密度下,其首次可逆容量为232.8mAh/g,循环100次后容量保持率为95.9%,10 C大倍率下的放电容量高达103.2mAh/g。同时,LTP包覆层为无定形态的电化学活性材料,能够有效地抑制材料在循环过程中SEI膜的形成并降低了电荷转移阻抗,有助于锂离子和电子的传输。(2)采用简单而温和的共沉淀法通过自组装制备了一种新型的梭形多孔微纳结构富锂正极材料0.5Li_2MnO_3·0.5LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2。由纳米初级粒子堆积而成的微米材料能够稳定材料的结构,为材料的循环性能提供保障;多孔结构不仅可以显著地增大活性材料的比表面积,使其能与电解液更充分的接触,而且可以缩减Li+/电子的传输距离,显著改善材料的倍率特性。恒电流充放电测试表明该材料在0.1 C倍率,2.0~4.6 V条件下的初始可逆容量为294.8 mAh/g,0.5 C电流密度下循环200次后其容量依然保持在220.6 mAh/g,容量保持率高达87.1%。得益于这种独特的结构特征,该材料同样展示了卓越的倍率性能,在10 C大倍率下,其放电容量可高达139.5 mAh/g。(3)为了进一步提高层状富锂正极材料各方面的性能,设计并成功制备了一系列形貌和尺寸可控的微纳结构Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2正极材料。通过合理调节乙二醇在水/醇混合溶液中的体积比,在CTAB的辅助下,该材料的形貌可由棒状逐渐转变成橄榄状,继而演变成梭子状。研究结果表明,富锂正极材料的形貌和尺寸对它的电化学性能影响较大,相比于棒状和梭子状正极材料,橄榄状正极材料因其均一的形貌和合适的尺寸在首次可逆容量(0.1 C,297.0 mAh/g),循环性能(0.5 C循环100次,保持率为95.4%)以及倍率性能(10 C,142.8 mAh/g)等方面均显现出了更为优异的电化学性能。其卓越的电化学性能主要是得益于良好的形貌和适当的尺寸以及微纳结构之间的协同作用。
[Abstract]:In recent years, layered lithium rich cathode material xLi_2MnO_3 (1-x) LiMO_2 (M=Ni, Co, Mn and other transition metals) has attracted the interest of researchers both at home and abroad because of its high discharge specific capacity (250 mAh/g) and working voltage (4.6 V vs.Li/Li+), and is considered as the most promising next generation of high performance lithium ion battery positive electrode. The material has high discharge ratio and energy density, but before its large-scale commercial application, several inherent defects in the layered lithium rich cathode material must be solved, such as the first irreversible capacity loss and the poorly intended cycle performance and multiplying performance. In order to improve the electrochemical performance of layered lithium rich cathode materials, the main research contents are as follows: (1) first, spherical lamellar lithium rich cathode materials Li1.5Ni_ (0.25) Mn_ (0.75) O_2+ delta are synthesized by co precipitation method and subsequent high temperature solid state reaction, and then the hydrothermal method is used in spherical lithium rich cathode material A layer of Li Ti_2 (PO_4) _3 (LTP) was uniformly coated on the surface of the material. The differences between the physical and electrochemical properties of different amounts of LTP coated materials were systematically studied. The results showed that LTP was coated on the surface of the material evenly in the form of nanoparticles, and the structure of the raw material was not changed. In addition, the LTP coating not only improved the rich of the LTP coating effectively. The first Kulun efficiency of lithium-ion cathode material has been greatly improved for its cycle performance and multiplying performance. The coating volume of 3 wt% shows the best electrochemical performance. Under the 0.5 C current density, its first reversible capacity is 232.8mAh/g, the capacity retention rate is 95.9% after 100 cycles, and the discharge capacity of 10 C ratio is as high as 103.2mAh/g. At the same time, the LTP coating is an amorphous electrochemical active material, which can effectively inhibit the formation of the SEI film during the cycle process and reduce the charge transfer impedance, which is helpful for the transfer of lithium ions and electrons. (2) a new type of shuttle shaped porous micro nano structure is prepared by self assembly by a simple and mild coprecipitation method. Micron materials, 0.5Li_2MnO_3. 0.5LiNi_ (1/3) Co_ (1/3) Mn_ (1/3) O_2., which are deposited by nanometer primary particles, can stabilize the structure of materials and provide a guarantee for the cycling performance of the materials. The porous structure can not only significantly increase the specific surface area of the active material, make it contact more fully with the electrolyte, but also reduce the Li+/. The transmission distance of the electron significantly improves the ratio of the material. The constant current charge discharge test shows that the initial reversible capacity of the material at 0.1 C ratio and 2.0~4.6 V is 294.8 mAh/g, and the capacity remains 220.6 mAh/g after 200 cycles of 0.5 C current density, and the capacity retention rate is as high as 87.1%. benefits from this unique structural feature. The material also shows excellent multiplier performance. Under 10 C large ratio, the discharge capacity can be as high as 139.5 mAh/g. (3). In order to further improve the properties of layered lithium rich cathode materials, a series of morphology and size controlled micro nano structure Li_ (1.2) Ni_ (0.13) Co_ (0.13) Mn_ (0.54) O_2 positive electrode has been prepared and successfully prepared. By adjusting the volume ratio of ethylene glycol in water / alcohol mixed solution, with the aid of CTAB, the morphology of the material can be transformed from bar shape to olive shape and then into a shuttle shape. The results show that the morphology and size of the lithium rich cathode material have great influence on the electrochemical properties of the material, compared with the bar like and the shuttle shaped positive material, the olive shape. Due to its homogeneous morphology and suitable size, the cathode material has more excellent electrochemical properties, such as the first reversible capacity (0.1 C, 297 mAh/g), cycling performance (0.5 C cycle 100, retention rate 95.4%), and multiplying performance (10 C, 142.8 mAh/g). Its excellent electrochemical performance is mainly due to good morphology and adaptation. The synergy between the size and micro nano structure.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912;TQ131.11

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