溶胶凝胶法制备磷酸铁锂复合材料及其微结构与磁性能研究

发布时间：2018-07-17 05:53

【摘要】：锂离子电池正极材料橄榄石型磷酸铁锂具有对环境无污染、价格低、原料来源丰富、比能量高和安全性能突出等特点,是最有潜力的锂离子电池正极材料中的一种。但是锂离子电池正极材料橄榄石型LiFePO4存在缺点,第一是它的堆积密度小,这样使得其体积比容量低,对应做出来的电池体积相对较大。第二是其离子扩散系数小及电导率低。而材料的电导率κ、磁性和空穴型极化子有关。橄榄石型磷酸铁锂中空穴的自旋与三价铁阳离子(Fe3+)的(tg↑)3(eg↑)2电子结构相关,与拥有(tgT)3(egT)2tg↓电子结构的二价铁阳离子(Fe2+)通过双交换机制发生铁磁耦合,所以失去电子就会引起极子型的畸变,这时会产生自旋极化电荷云。本文使用操作简单、合成条件易于控制、制备材料颗粒小等特点的溶胶凝胶法(sol-gel),通过一步法制备磷酸铁锂碳复合材料;通过两步法制备金属单质铜与磷酸铁锂碳复合材料;通过两步合成AxOy型金属氧化物(二氧化锰、三氧化二铝)与橄榄石型磷酸铁锂碳复合材料。并用TG、XRD、FTIR、SEM、VSM等方法对复合材料的合成过程样品热特性、物相结构、官能团及化学键、微观表面形貌和磁学特性等特征进行了研究。主要研究结果和创新点如下:1.研究了不同碳源对磷酸铁锂复合材料的影响,使用了五种不同的碳源(乙二醇、聚乙二醇4000、聚乙烯醇PVA-124、一水合柠檬酸和葡萄糖)通过溶胶凝胶法(sol-gel)合成LiFePO4/C复合材料。XRD研究表明样品均为橄榄石相磷酸铁锂。SEM测试表明以乙二醇为碳源的样品成多孔结构,而以葡萄糖为碳源的样品颗粒较大,大小为40微米。VSM研究表明:一方面以聚乙烯醇(PVA-124)为碳源的样品相对比饱和磁化强度最大,大小为2.01 emu/g,另一方面以乙二醇为碳源的样品矫顽力最大,其值为170.67 Oe。2.研究了铜(Cu)对磷酸铁锂复合材料的影响,通过两步法合成不同质量比的铜和磷酸铁锂复合材料,并用TG、XRD、FTIR、SEM和VSM等方法对铜和磷酸铁锂复合材料的合成过程样品热特性、物相结构、官能团及化学键、微观表面形貌和磁特性进行了研究。表明复合材料前驱体升温到大概400℃以后可能开始有复合材料合成。复合材料物相结构分析出现明显磷酸铁锂和铜单质的主要峰型,无杂质峰。微观形貌SEM分析表明复合材料颗粒性明显、分散性较好,颗粒大小主要为400 nm。室温下测试磁滞回线表明铜单质的引入使得复合材料的 Ms(emu/g)、Mr(emu/g)和 Area of hysteresis loop(kOe·emu/g)都有微小减小变化趋势。3.研究二氧化锰对磷酸铁锂复合材料的影响,通过两步法合成不同质量比的二氧化锰和磷酸铁锂复合材料,并用TG、XRD、FTIR、SEM和VSM等方法对二氧化锰和磷酸铁锂复合材料的合成过程样品热特性、物相结构、官能团及化学键、微观表面形貌和磁特性进行了研究。表明复合材料前驱体升温400℃以后可能开始有复合材料合成。复合材料物相结构分析出现明显磷酸铁锂和二氧化锰的主要峰型,无明显杂质峰型。微观形貌SEM分析表明复合材料颗粒性明显、分散性较好,颗粒大小主要为168 nm。室温下测试磁滞回线表明二氧化锰的引入使得复合材料的Ms(emu/g)、Mr(emu/g)和Area of hysteresis loop(kOe·emu/g)基本上是随着二氧化锰的增加而增加。4.研究三氧化二铝(A1203)对磷酸铁锂复合材料的影响,通过两步法合成不同质量比的A1203和磷酸铁锂复合材料,并用TG、XRD、FTIR、SEM和VSM等方法对Al203和磷酸铁锂复合材料的合成过程样品热特性、物相结构、官能团及化学键、微观表面形貌和磁特性进行了研究。表明复合材料前驱体升温450℃以后可能开始有复合材料合成。复合材料物相结构分析出现明显磷酸铁锂和Al2O3的主要峰型,没有出现杂质峰。微观形貌SEM分析表明复合材料颗粒性明显、分散性较好,颗粒大小主要为350 nm。室温下测试磁滞回线表明三氧化二铝的引入使得复合材料的Ms(emu/g)、Mr(emu/g)和Area of hysteresis loop(kOe·emu/g)都有微小变化。
[Abstract]:Lithium-ion battery cathode material olivine phosphate lithium-ion has the characteristics of no pollution to the environment, low price, rich source of raw materials, high specific energy and high safety performance. It is one of the most potential cathode materials for lithium ion batteries. However, the lithium ion battery positive material peridotite type LiFePO4 has shortcomings. The first is its accumulation density. In this way, the volume is lower than the capacity, and the volume of the battery is relatively large. Second is the ion diffusion coefficient and the low conductivity. The conductivity kappa of the material is related to the hole type polaron. The spin of the hole in the olivine type iron phosphate is related to the 2 electronic structure of the Fe3+ (TG) 3 (eg). The two valence iron cation (Fe2+), with the electronic structure of (tgT) 3 (egT) 2tg, produces ferromagnetic coupling through the double exchange mechanism, so the loss of electrons will cause the distortion of the polar subtype, and the spin polarized charge cloud will be produced. This paper uses the simple operation, the synthesis conditions easy to control, and the preparation of the sol-gel method (sol-gel), which is characterized by small particle size and so on. The lithium iron phosphate composite material was prepared by a step method, and the metal single copper and phosphite lithium carbon composites were prepared by two steps, and the AxOy metal oxides (manganese dioxide, three oxide two aluminum) and olivine type lithium carbon composites were synthesized by two steps and the synthesis process of the composites was heated by TG, XRD, FTIR, SEM, and VSM. Characteristics, phase structure, functional group and chemical bond, microsurface morphology and magnetic properties are studied. The main research results and innovation points are as follows: 1. the effects of different carbon sources on the lithium phosphate composites were studied, and five different carbon sources (ethylene glycol, polyethylene glycol 4000, polyvinyl alcohol PVA-124, monohydrate citric acid and Portuguese) were used. LiFePO4/C composite material.XRD study by sol-gel method (sol-gel) showed that the samples were all peridotite phase lithium iron phosphate.SEM test showed that the sample with ethylene glycol as carbon source was porous structure, and the sample particles with glucose as carbon source were larger, the size of 40 micron.VSM study showed that polyvinyl alcohol (PVA-124) as carbon on the one hand The relative saturation magnetization of the source samples is the largest, the size is 2.01 emu/g. On the other hand, the sample with ethylene glycol as carbon source has the greatest coercivity, and its value is 170.67 Oe.2. to study the effect of copper (Cu) on the lithium phosphate composite material. The two step method is used to synthesize copper and phosphate lithium phosphate composites with different mass ratio, and TG, XRD, FTIR, SEM and VSM are used. Methods the thermal properties, phase structure, functional group and chemical bond, micro surface morphology and magnetic properties of copper and lithium iron phosphate composites were studied. The results show that composite materials may begin to be synthesized after heating up to about 400 degrees C. The phase structure analysis of the composite material appears obvious lithium and copper phosphate. The micromorphology SEM analysis shows that the particle size of the composite is obvious and the dispersion is better. The particle size is mainly 400 nm. at room temperature and the hysteresis loop shows that the introduction of copper monomer makes the composite material Ms (emu/g), Mr (emu/g) and Area of hysteresis loop (kOe emu/g) have a slight decreasing trend. The effect of manganese dioxide on the lithium iron phosphate composite was studied. By two step method, the composite of manganese dioxide and lithium iron phosphate with different mass ratio was synthesized and the thermal properties, phase structure, functional group and chemical bond, micro surface morphology and surface morphology of manganese dioxide and lithium iron phosphate composites were prepared by means of TG, XRD, FTIR, SEM and VSM. The magnetic properties are studied. It is shown that composite materials may begin to be synthesized after heating up to 400 degrees C. The phase structure analysis of the composites appears to be the main peak type of lithium iron phosphate and manganese dioxide, and there is no obvious impurity peak type. Micromorphology SEM analysis shows that the composite has obvious particle size, good dispersibility and main particle size. To test the hysteresis loop at room temperature for 168 nm., the introduction of manganese dioxide makes the Ms (emu/g), Mr (emu/g) and Area of hysteresis loop (kOe. Emu/g) of the composite substantially increase with the increase of manganese dioxide and increase the effect of the three oxidation of two aluminum on the lithium phosphate composite material, and the synthesis of different mass ratios by the two step method. The thermal properties, phase structure, functional group and chemical bond, microsurface morphology and magnetic properties of the samples of Al203 and lithium iron phosphate composites are studied by means of A1203 and TG, XRD, FTIR, SEM and VSM. The results show that composite materials may begin to be synthesized after heating up to 450 degrees C. The main peak type of lithium iron phosphate and Al2O3 was found in the phase structure analysis of the composites, and no impurity peaks were found. Micromorphology SEM analysis showed that the composites were granular and dispersed well. The size of the particles was 350 nm. at room temperature and the hysteresis loop showed that the introduction of three oxidation two aluminum made the composite Ms (emu/g), Mr (emu/g) and the composite material. There are slight changes in Area of hysteresis loop (kOe. Emu/g).
【学位授予单位】：广西师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB33;TM912

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