【作者】 黄原君；

【导师】 苏光耀； 高德淑；

【作者基本信息】 湘潭大学 ， 物理化学， 2007， 硕士

【摘要】 目前,商业锂离子电池中主要采用LiCoO₂作正极材料,但由于价格和安全性的问题,LiCoO₂已不能满足锂离子电池发展的需要,因此,开发低成本,高性能的新型正极材料成为目前锂离子电池领域研究的热点。与LiCoO₂相比,Li(Ni_1/3Co_1/3Mn_1/3)O₂具有成本更低,安全性能更好等优点,不仅能取代LiCoO₂应用于小型锂离子电池,而且在动力电池等大功率锂离子电池中有着广阔的应用前景。本论文系统的研究了Li(Ni_1/3Co_1/3Mn_1/3)O₂的合成及其组成、结构、电化学性能之间的关系。深入研究了合成条件对材料性能的影响,并得到了优化的合成工艺。采用优化的工艺合成了LiNi_1/3Co_1/3Mn_1/3O₂,并采用SEM,XRD,恒电流充放电测试等方法对合成的LiNi1-x-yCoxMnyO₂系列化合物进行了表征测试。本文通过阴、阳离子复合掺杂改善LiNi_1/3Co_1/3Mn_1/3O₂材料的性能,获得电化学性能优良的阴、阳离子复合掺杂新型正极材料。研究了Si、F复合掺杂来改善Li(Ni_1/3Co_1/3Mn_1/3)O₂的电化学性能,结果表明Si、F复合掺杂能显著减少Li(Ni_1/3Co_1/3Mn_1/3)O₂层状结构中的阳离子混排效应,改善材料的倍率特性,尤其是提高了大电流放电情况下的放电平台保持率。Si-F复合掺杂结合了Si增加容量和F改善循环性能的特点,Li[Ni_1/3Co_1/3Mn_1/3]Si_0.04O_1.96F_0.04在2.8-4.3V电压范围内获得很高的初始容量（176.9 mAh·g-1）,第20个循环的容量保持率为92.1%,循环稳定性也得到了改善。由于Si-F复合掺杂效应,Li[Ni_1/3Co_1/3Mn_1/3]Si_0.04O_1.96F_0.04材料的电化学性能得到较大改善,交流阻抗谱图研究表明,Si、F复合掺杂能明显抑制Li(Ni_1/3Co_1/3Mn_1/3)O₂在大电流放电过程中电化学反应阻抗的增加。因此,Si-F复合掺杂是一种改进锂离子电池正极材料性能有效的方法。更多还原

【Abstract】 Today, the most widely used cathode material for commercial lithium ion batteries is LiCoO₂. Due to it’s relatively high cost and poor safety, LiCoO₂ is very difficult to meet the development demands of lithium ion battery in the future. Therefore, much more attempts are focused on developing new kinds of cathode materials with lower cost and higher performance which can substitute LiCoO₂ materials. Comparing with LiCoO₂, Li(Ni_1/3Co_1/3Mn_1/3)O₂ has lower cost and higher safety which can also be used in small-type lithium ion batteries. In this paper, we investigated the synthetic condition, structure, composition, and electrochemical performance of Li(Ni_1/3Co_1/3Mn_1/3)O₂. The effects of synthetic conditions on structure and electrochemical performance have been investigated and the optimum synthetic conditions were obtained. The obtained cathode materials were investigated by SEM, XRD, galavanostatic charge and discharge test, et al.In this paper, novel cathode materials with excellent electrochemical performance were prepared by anion-cation compound substitution at the base of Li(Ni_1/3Co_1/3Mn_1/3)O₂, which was attractive all around the world. Si and F elements were choosen as the co-doping agents to improve the electrochemical properties of Li(Ni_1/3Co_1/3Mn_1/3)O₂. The results indicated that Si, F co-doping can effectively steady the layered structure and improve rate-discharging capability of Li(Ni_1/3Co_1/3Mn_1/3)O₂ since Si-F substitution combined the increasing capacity of F-doping material with the good cyclability of Si-doping materials. In the range of 2.8-4.3 V, the Li[Ni_1/3Co_1/3Mn_1/3]Si_0.04O_1.96F_0.04 delivers an initial capacity of 176.9 mAh·g^-1 and its capacity retention is 92.1% after the 20th cycle. The conclusion could be drawn that Si-F compound substitution elevated the capacity and improved the cyclability. Study of AC impedance indicated that Si, F co-doping can obviously suppress the increase of electrochemical impedance in the course of discharging at larger rate current. Therefore, it is a promising method for Si-F compound substitution in this kind of cathode materials of Li-ion batteries.更多还原