锂离子电池正极材料磷酸铁锂的制备和改性研究

发布时间：2018-04-11 13:59

  本文选题：锂离子电池 + 磷酸铁锂　； 参考：《郑州大学》2014年硕士论文

【摘要】：磷酸铁锂正极材料因具有铁、磷原料丰富，价格低廉，比容量大，高温性能优异，高功率输出，，循环寿命长，环境友好等优势成为电池行业的研究热点。磷酸铁锂电池有潜力大规模应用于纯电动汽车、储能装置等领域。然而磷酸铁锂存在锂离子扩散系数小、电子电导率低和振实密度低等缺点，削弱了它的大电流放电能力，阻碍了其工业化应用。 本文采用微波法和溶剂热两种方法制备磷酸铁锂。首先是以碳酸锂、磷酸铁为原料，葡萄糖作还原剂和碳源，乙酸锰、二氧化钛、氧化镁分别为掺杂的锰源、钛源和镁源，采用微波法制备了掺杂单一或混合金属阳离子的LiFePO4/C。研究了微波热处理温度和金属离子掺杂对材料结构和电化学性能的影响。其次，以乙二醇-水为体系，FeSO4·7H2O，H3PO4，LiOH·H2O为原料，抗坏血酸为还原剂，采用溶剂热法制备了特定形貌的纯相LiFePO4，研究了反应物摩尔比、溶剂热温度、反应时间、溶剂比例、表面活性剂对产物形貌和电化学性能的影响。主要结果如下： （1）微波热处理温度在650℃、700℃、750℃，保温时间25min时均能合成纯相的橄榄石结构LiFePO4/C。其中650℃合成的样品放电电压最高，容量最大，性能最好。 （2）无论单一还是混合掺杂金属离子（掺杂量≤1.5%）均不会改变LiFePO4的晶体结构。相比碳包覆的LiFePO4，单一或混合掺杂Ti4+、Mn2+、Mg2+后提高了LiFePO4的大电流放电性能和电化学反应的可逆性，且循环性能良好。其中掺杂锰、钛离子分别为0.5%、1%时电化学性能最佳，0.2C倍率放电比容量138mAh/g；0.5C倍率放电比容量116mAh/g；1C倍率放电比容量105mAh/g；1C倍率循环20次后容量保持率在96.5%。 （3）溶剂乙二醇/水为1：1，加入阳离子表面活性剂CTAB均有利于沿（010）面方向生长。且加入阳离子表面活性剂CTAB后，磷酸铁锂的粒径更小，分布更均匀，电化学性能有所提高。 （4）当摩尔比Li+：Fe2+：PO43-=2.5：1：1，乙二醇/水=1：1，180℃反应9h时合成纺锤体形状的磷酸铁锂，表面是沿（010）面呈片状生长。将LiFePO4与12wt%的葡萄糖进行碳包覆后，其0.1C倍率放电比容量为100.1mAh/g。
[Abstract]:Lithium iron phosphate cathode material has become a research hotspot in battery industry because of its advantages such as abundant iron, phosphorus, low cost, large specific capacity, excellent high temperature performance, high power output, long cycle life and environmental friendliness.Lithium iron phosphate batteries have the potential to be widely used in pure electric vehicles, energy storage devices and other fields.However, lithium iron phosphate has the disadvantages of low lithium ion diffusion coefficient, low electronic conductivity and low vibrational density, which weakens its high current discharge ability and hinders its industrial application.Lithium iron phosphate was prepared by microwave method and solvothermal method.Firstly, lithium carbonate and iron phosphate were used as raw materials, glucose as reducing agent and carbon source, manganese acetate, titanium dioxide and magnesium oxide as doped manganese source, titanium source and magnesium source respectively. LiFePO _ 4 / C doped with single or mixed metal cations was prepared by microwave method.The effects of microwave heat treatment temperature and metal ion doping on the structure and electrochemical properties of the materials were studied.Secondly, pure phase LiFePO _ 4 with specific morphology was prepared by solvothermal method with FeSO _ 4 _ 7H _ 2O H _ 3PO _ 4H _ 2O as raw material and ascorbic acid as reducing agent. The molar ratio of reactants, solvothermal temperature, reaction time and solvent ratio were studied.Effects of surfactants on the morphology and electrochemical properties of the products.The main results are as follows:1) the pure olivine structure LiFePO _ 4 / C can be synthesized by microwave heat treatment at 650 鈩

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