【作者】 朱伟；

【导师】 潘复生；

【作者基本信息】 重庆大学 ， 材料学， 2004， 博士

【摘要】 锂离子二次电池是以嵌入锂化合物作为正、负极材料的最新一代高比能蓄电池。它具有电池电压高、比能量大、循环寿命长、自放电小以及有利于环保等优点。近年来，锂离子蓄电池在各方面均在不断改进。负极与电解质进步较快，但正极材料的发展较为缓慢。对正极材料应用和研究的主要材料有LiCoO2、LiNiO2、LiMn2O4、LiFePO4等。其中尖晶石LiMn2O4和橄榄石LiFePO4都具有价格低、无毒、理论比容量较高等优点。是下一代锂离子电池最有前途的正极材料。本文从降低锂离子电池的生产成本和提高材料的稳定性出发，主要研究尖晶石LiMn2O4和橄榄石LiFePO4的合成制备方法，以及掺杂提高电池材料的稳定性等问题。得到下述几方面的研究结果。本文首先针对固相法制备尖晶石LiMn2O4的合成制备时间长，电化学性能差，溶胶凝胶法的工序多，原料消耗大，成本高等缺点。用溶胶凝胶法改进了制备工艺，简化了制备步骤，这种工艺称为改进柠檬酸溶胶凝胶法。实验探索了最佳合成温度、柠檬酸的最佳比例，以及应用改进的溶胶凝胶法，进行了掺杂和表面包覆以改性LiMn2O4等内容。对尖晶石LiMn2O4材料改性主要选择了Li+、Al3+作为阳离子掺杂，选择Cl－作为阴离子掺杂。对溶胶凝胶法合成制备的尖晶石LiMn2O4材料，组成实验电池，用恒电流充放电进行电化学测试，实验表明掺杂Li+、Al3+、Cl－后的尖晶石LiMn2O4的充放电稳定性都有提高。还采用LiCoO2和Al2O3包覆处理LiMn2O4，也能提高LiMn2O4材料的稳定性。当掺Al量为LiAl0.2Mn1.8O4时，能获得较高的容量和很好的循环性能。运用改进的溶胶凝胶法，可制备初始容量大于130mAh/g的尖晶石LiMn2O4。改进溶胶凝胶法可以方便对其掺杂和包覆处理。在简化了以前溶胶凝胶法的合成步骤和减少柠檬酸原来用量的基础上，能合成性能较好LiMn2O4样品，说明该方法可行。针对合成橄榄石LiFePO4多用草酸亚铁和醋酸亚铁，我们率先改用Fe3+盐，选用溶胶凝胶法，以高温还原Fe3+合成出LiFePO4。运用溶胶凝胶，以Li2CO3、Fe（NO3）3·9H2O、NH4H2PO4为原料，在保护性气氛条件下，在650℃左右可以合成出电化学性能比较好的橄榄石型的LiFePO4，且粒度较均匀，放电比容量可达到140mAh/g以上。并对掺杂Ag、Cu、Mg等对材料性能的影响进行了实验探索。应用高温反应还原Fe3+制备LiFePO4的设想，进一步改用Fe2O3代替Fe（NO3）3·9H2O，并掺不同碳源作为还原剂，应用固相法进行了一系列合成试验。加乙炔黑作为还原剂，同时起到掺碳的作用，在高温下还原制备了橄榄石型的磷酸亚铁<WP=6>锂，放电的比容量可达到130mAh/g 。XRD证实了用乙炔黑能将Fe2O3还原成亚铁制备LiFePO4。在此基础上，本文进一步以蔗糖代替乙炔黑为还原剂，以蔗糖自身分解的产物作为碳源，用高温固相法合成LiFePO4，由于蔗糖在高温下的熔融作用，使参与反应的原料反应充分，以及糖炭化形成包覆和掺碳的作用，获得放电比容量150mAh/g以上的样品，采用廉价的Fe2O3和蔗糖合成出了放电比容量高、性能稳定的LiFePO4，这显示了该法的优越性。。其次还实验了大电流1～3mA/cm2充放电和充放电温度对材料性能的影响,显示温度升高,材料放电比容量增大。对上述大量实验结果，均用电化学测试方法对充放电容量、循环性能等进行了检测，对材料的合成温度、合成时间以及掺杂、包覆等对材料性能影响进行较系统的探索，用电镜等比较了这些方法所得样品的粒度分布，用X射线衍射方法对材料的晶型结构进行了测试，并对各种方法优劣进行评价。在原料方面采用廉价原料和减少药品用量比例等，使成本降低、工艺缩短是本研究的革新，目前正在用包覆的方法（已取得成功）取代使用保护气氛，更是本研究的创新。更多还原

【Abstract】 Up to now, people realized that the Li-ion battery is a new generation of high specific capacity battery with merits of high voltage and long life and a little self discharging etc. Recently, this battery is still under improving constantly. The investigation of negative and electrolytes have progress more quicker, while the studies on positive material is slower. The major positive material for studying containing LiCoO2, LiNiO2, LiMn2O4 and LiFePO4 etc. However, the spinel LiMn2O4 and olivine LiFePO4 are very hopeful material with low price and few toxic and higher specific capacity, etc. Based on decreasing the production cost and enhancing the stability of the material, this work will studying the preparation method of these material for enhancing their stability through using doping and choosing optimal technology.First of all, to counter the weak points of longer synthesis time, poor electrochemical behavior, long process of reaction and higher cost, etc., the auther created a modified sol-gel method with citric acid for shorten the preparing step, exploring optimal synthesizing temperature and technology, used the doping and covered some film on the product and so on.To improve the behavior of spinel LiMn2O4, We used the doping with the donor Li+, Al3+,and Cl-. The examination results of galvanostatic charge-discharge experiments shown that the stability of charge-discharge of Li+, Al3+,and Cl- doped spinel LiMn2O4 have enhanced. The LiMn2O4 coated with LiCoO2 and Al2O3 film were enhanced the stability.The experiments shown that the modified sol-gel method can prepare the spinel LiMn2O4 with original capacity higher than 130mAh/g and shorten the synthesizing step, decreasing the citric acid and so on.To counter the synthesis of olivine LiFePO4 with Fe(C2O4)2 and Fe(CH3COO)2 mostly , we are the first to used the sol-gel method with Fe3+ through high temperature to make LiFePO4. We prepared the olivine LiFePO4 with good electrochemical behavior and its discharge specific capacity as high as 140mAh/g.This work have explored the influence of Ag, Cu, Mg-doped LiFePO4 to the <WP=8>behavior of LiFePO4 through high temperature reaction for reducing Fe3+ and used Fe2O3 instead of Fe(NO3)3·9H2O. We also used the carbon from different source as a reducing reagent, prepared the olivine LiFePO4 through high temperature reduction, the prepared sample has the discharge specific capacity reached 130mAh/g. Based on this exploration to carry out experiment, the prepared sample get high discharge specific capacity to 150mAh/g and excellent behavior, we have discussed the mechanism briefly.The article have reported the examination of prepared sample through electrochemical method for their charge-discharge behavior, the XRD method for their crystalline structure, explored the influence of different experimental factor to the behavior of all sample.更多还原