【作者】 杜国栋；

【导师】 努丽燕娜；

【作者基本信息】 上海交通大学 ， 化学工程， 2008， 硕士

【摘要】 近年来,随着能源环境问题的日益严重以及电子产品轻型化的要求,人们对锂离子二次电池的研究不断深入。商业化的锂离子电池正极材料LiCoO2由于价格高,有毒性,人们一直努力在寻找其替代品。锰酸锂由于价格低廉、无毒而倍受关注。而加入镍的LiNi0.5Mn1.5O4充放电平台在4.6~4.8V之间,是5V材料,理论容量可达到147mAh g-1,具有更高的能量密度,有希望作为动力电池得到应用。本文主要研究氟掺杂对LiNi0.5Mn1.5O4的影响。采用的溶胶凝胶方法合成的氟掺杂材料比球磨掺氟法效果好。用溶胶凝胶法制备时前驱体在450℃空气中使醋酸盐分解,轻微研磨后压片,在850℃氧气气氛中煅烧12h得到样品材料。通过XRD、SEM、BET表征材料结构形貌等物理特性,通过恒电流充放电、循环伏安、交流阻抗等手段对材料电化学稳定性进行测试。比较不同合成条件,不同掺氟量,以及高温条件下不同样品的性能。XRD结果表明得到的所有样品均为尖晶石结构,氟掺杂没有明显改变材料的结构。SEM显示随着氟含量的增加颗粒变大也更均匀。氟的加入量增多,材料初始容量降低,循环性能变好,综合考虑LiNi0.5Mn1.5O3.9F0.1效果最好。高温保存过程中,贫锂相的结构会随着锂离子的重新嵌入而发生自放电反应因而电压降低;高温条件下,氟的掺杂可以稳定样品的电化学性能,减小电极与电解液界面的阻抗;高温下,电解液会分解,并且影响电极表面SEI膜的形成而导致不能连续充放电,如果在常温下活化几次后则可以在高温下循环。最后对5V体系的电解液进行了初步探索,BMIBF4和PP14-TFSI离子液体均没达到理想效果,要开发与之相匹配的体系仍需要更多研究。更多还原

【Abstract】 In recent years, as the environmental problems go serious and the electronic products become more and more portable, the study of lithium secondary batteries goes further. Because of the high price and toxicity of the industrialized LiCoO2 cathode material, more attention has been paid to the substitutes for it. Lithium manganese oxide proves one of the most promising cathode materials since it is inexpensive and environmental friendly. LiNi0.5Mn1.5O4 is a 5V cathode material. The charge and discharge plateau is between 4.6 and 4.8V vs. Li/Li+, and the theoretical capacity is 147mAh g-1, so it possesses higher energy density and is promising to be used in Li-ion power sources for electrical vehicles.In the present work, fluorine doping in LiNi0.5Mn1.5O4 and the effect on the electrochemical performances are studied. The result shows that sol-gel method to dope fluorine was better than the planetary ball milling. The precursor was first heated to 450℃in air for 5h to make the acetates decompos fully, thereafter ground thoroughly and pressed into pills, and then calcinated in oxygen at 850℃for 12h.The samples were characterized by XRD、SEM and BET and the electrochemical performances were tested by constant-current charge and discharge, cyclic voltammograms, AC impedance to optimize the different synthesize conditions, and different fluorine doping amount,and then tested the performances at high temperature.XRD results indicate that all the samples belong to spinels phase and there is no obvious difference between different fluorine doping amount samples, and SEM photographs show that the particles become larger and uniform as the fluorine amount increases. At the same time, the initial discharge capacity declines and the cyclability becomes better. LiNi0.5Mn1.5O3.9F0.1 is the best material. At high temperature storage, the cell potentials decline because of self-discharge via the lithium ion intercalation into the poor lithium phase. Fluorine doping reduces the impedance between the electrode and the electrolyte and is beneficial to the electrochemical performance at high temperature. Under high temperature, the electrolyte will decompose and influences the SEI membrane forming on the surface of the electrode, resulting in the failure of continuous charge and discharge. If the sample is activated at room temperature by charge and discharge several times, then it can charge and discharge at high temperature.At last, efforts have further been made to explore new electrolytes for the 5V cathode material, but BMIBF4 and PP14-TFSI can not meet the requirements. More work will be done to reach this goal.更多还原