锂离子电池正极材料磷酸铁锂的溶剂热合成及其改性
发布时间：2018-12-14 17:56
【摘要】：锂离子电池正极材料磷酸铁锂因其循环性能好、材料来源广泛、低毒、环境友好、理论比容量高、热稳定性高等优点而被认为是最有希望取代钴酸锂而成为电动车和混合动力车的电源。但是磷酸铁锂三个明显的缺点(电子电导率低、离子导电率低和振实密度低)阻碍了其市场大规模化应用。人们为了改善LiFePO4的电化学性能和提高振实密度做了大量的工作。本文针对以上的问题,开展了如下的工作： (1)采用溶剂热法合成锂离子电池正极材料LiFePO4,运用X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)、高分辨透射电镜(TEM)、选区电子衍射(SAED)和恒流充放电测试表征了产物的晶体结构,形貌、微观结构和电化学性能。结果表明,在200℃下,添加2ml乙二胺,溶剂热反应24h获得的材料具有片状结构,尺寸在0.5～1.5μm之间,厚度约为50nm、结晶度较高,片状结构有利于缩短锂离子的扩散距离,提高材料的电化学性能。我们还探讨了时间,温度以及乙二胺对产物结构及形貌的影响。通过不同时间下产物的XRD图和SEM简单阐述了片状结构LiFePO4的生长机理。电化学测试结果表明,材料在0.1C、0.2C和1C倍率下的放电比容量分别为120.6、104.9和68.8mAh·g-1。 (2)采用溶剂热法一步合成了振实密度达到了1.2g.cm3鸟巢状分级结构橄榄石型磷酸铁锂样品。该样品具有较高的结晶度,长5-11μm,直径3-7μm由厚度约为70nm,暴露(100)晶面的纳米片组成。该分级结构既能保持片状结构的优异电化学性能,又能保持类球形结构的高振实密度。N2吸附脱附测试结果表明材料的BET比表面积为6.8m2.g-1,平均孔径分布在20nm。这种结构有利于锂离子扩散和电解液的渗透。对比实验表明P123对材料的形貌有较大影响。通过不同时间下产物的XRD图和SEM简单阐述了鸟巢状分级LiFePO4的生长机理。电化学测试结果表明,加入P123制得的鸟巢状分级结构磷酸铁锂样品的电化学性能优于未加P123时制得的饼状结构。 (3)以葡萄糖为碳源对LiFePO4进行表面包覆。使用XRD、IR和TEM对LiFePO4/C进行表征。恒流充放电测试、循环伏安测试和交流阻抗法测试显示LiFePO4/C材料具有优异的的电化学性能。通过化学原位聚合氧化法制得LiFeP04/PPy复合材料,运用SEM和IR对材料进行表征。恒流充放电测试结果表明,LiFeP04/PPy复合材料在0.1C、0.2C、0.5C和1C倍率电流下充放电时的放电比容量为155、145、130.8和117.0mAh·g-1。
[Abstract]:Lithium iron phosphate, the cathode material of lithium ion battery, is characterized by its good cycling performance, wide source, low toxicity, friendly environment and high theoretical specific capacity. It is considered to be the most promising power source for electric vehicles and hybrid vehicles because of its high thermal stability. However, three obvious disadvantages of lithium iron phosphate (low electronic conductivity, low ionic conductivity and low vibrational density) hinder its large-scale application in the market. A great deal of work has been done to improve the electrochemical performance and the vibrational density of LiFePO4. In order to solve the above problems, the following work has been done: (1) Solvothermal synthesis of lithium ion battery cathode material LiFePO4, using X-ray diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), The crystal structure, morphology, microstructure and electrochemical properties of the products were characterized by high resolution transmission electron microscopy (TEM) (TEM), selective electron diffraction (SAED) and constant current charge-discharge measurements. The results show that at 200 鈩，
本文编号：2379063
[Abstract]:Lithium iron phosphate, the cathode material of lithium ion battery, is characterized by its good cycling performance, wide source, low toxicity, friendly environment and high theoretical specific capacity. It is considered to be the most promising power source for electric vehicles and hybrid vehicles because of its high thermal stability. However, three obvious disadvantages of lithium iron phosphate (low electronic conductivity, low ionic conductivity and low vibrational density) hinder its large-scale application in the market. A great deal of work has been done to improve the electrochemical performance and the vibrational density of LiFePO4. In order to solve the above problems, the following work has been done: (1) Solvothermal synthesis of lithium ion battery cathode material LiFePO4, using X-ray diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), The crystal structure, morphology, microstructure and electrochemical properties of the products were characterized by high resolution transmission electron microscopy (TEM) (TEM), selective electron diffraction (SAED) and constant current charge-discharge measurements. The results show that at 200 鈩，
本文编号：2379063
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