纳米化锂电池正极材料磷酸铁锂的研究
发布时间：2019-06-10 22:26
【摘要】：正交橄榄石型LiFePO_4材料具有理论容量高(170 m Ahg-1),环境友好,热稳定性能好,循环性能高(超过2000次),原料丰富,成本低等优势,是具有极大应用前景的锂离子电池正极材料,已经得到了广泛的应用。但是LiFePO_4固有的缺陷是电子导电率和锂离子扩散速率都很低,严重影响材料实际容量及倍率性能的发挥。本论文采用廉价的工业原料合成纳米LiFePO_4,具体研究内容如下:首先以废铁水为铁源,磷酸氢二铵为磷源,柠檬酸作为表面活性剂,研究纳米Fe PO_4的制备。作为对比试验,将添加不同质量柠檬酸制备的Fe PO_4分别命名为FP-A(0 g柠檬酸),FP-B(0.2 g柠檬酸),FP-C(0.4 g柠檬酸)和FP-D(0.6 g柠檬酸)。用扫描电子显微镜(SEM)和傅里叶变换红外光谱(FTIR)分别研究了Fe PO_4的尺寸形貌和表面特性。测试表明,Fe PO_4尺寸随柠檬酸量的增加而减小。FP-D的尺寸分布在纳米级,团聚少;采用前驱体Fe PO_4,碳酸锂,蔗糖为原材料,通过碳热还原法合成LiFePO_4/C正极材料。作为对比试验,分别由FP-A,FP-B,FP-C和FP-D合成的LiFePO_4/C命名为LFP-A,LFP-B,LFP-C和LFP-D。用X射线衍射(XRD),SEM,电池恒流充放电分别研究了正极材料的结构,尺寸形貌及电化学性能。测试表明,Fe PO_4的尺寸形貌对LiFePO_4/C产生影响,Fe PO_4的尺寸越小、形貌越规则,LiFePO_4/C正极材料的尺寸就越小、团聚少。在0.1 C倍率下测试表明,柠檬酸的加入不利于LiFePO_4/C材料放电容量提高,但是会减小正极材料的极化和容量衰减,提高倍率循环性能。采用不同含量的金属Mn~(2+)离子(0%,5%,8%和10%)对LiFePO_4材料进行掺杂。用XRD,SEM,电池恒流充放电研究了不同含量金属掺杂正极材料的结构,尺寸形貌及电化学特性。测试表明,采用Mn~(2+)掺杂并不会影响正极材料的结构,当Mn~(2+)掺杂量为5%的Li Fe0.95Mn0.05PO_4正极材料在0.1 C倍率下首次放电容量最高。采用循环伏安(CV)法和电化学阻抗谱(EIS)研究了Mn~(2+)掺杂对正极材料电极动力学及锂离子传输的影响。
[Abstract]:Orthogonal olivine LiFePO_4 has the advantages of high theoretical capacity (170m Ahg-1), friendly environment, good thermal stability, high cycle performance (more than 2000 times), rich raw materials and low cost. It is a promising cathode material for lithium-ion batteries and has been widely used. However, the inherent defect of LiFePO_4 is that the electronic conductivity and lithium ion diffusion rate are very low, which seriously affects the actual capacity and rate performance of the material. In this paper, the synthesis of nano-LiFePO_4, from cheap industrial raw materials is as follows: firstly, the preparation of nano-FePO_4 was studied by using waste molten iron as Tie Yuan, diammonium hydrogen phosphate as phosphorus source and citric acid as surfactants. As a comparative experiment, the Fe PO_4 prepared by adding different mass citric acid was named FP-A (0 g citric acid) and FP-B (0.2 g citric acid), respectively. FP-C (0.4g citric acid) and FP-D (0.6g citric acid). The size, morphology and surface properties of Fe PO_4 were studied by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results show that the size of Fe PO_4 decreases with the increase of citric acid content. The size of FP-D is distributed in nanometer scale and the agglomeration is less. LiFePO_4/C cathode materials were synthesized by carbothermal reduction using precursor FePO_4, lithium carbonate and sucrose as raw materials. As a comparative experiment, the LiFePO_4/C synthesized by FP-A,FP-B,FP-C and FP-D is named LFP-A,LFP-B,LFP-C and LFP-D., respectively. The structure, size and electrochemical properties of cathode materials were studied by X-ray diffraction (XRD) (XRD), SEM, battery at constant current charge and discharge. The results show that the size and morphology of FePO_4 have an effect on LiFePO_4/C. The smaller the size of FePO_4, the more regular the morphology, the smaller the size of LiFePO_4/C cathode material and the less agglomeration. The test results at 0.1 C rate show that the addition of citric acid is not conducive to the increase of discharge capacity of LiFePO_4/C materials, but it can reduce the polarization and capacity attenuation of cathode materials and improve the rate cycle performance. Different contents of metal Mn~ (2) ions (0%, 5%, 8% and 10%) were used to doping LiFePO_4 materials. The structure, size, morphology and electrochemical characteristics of metal-doped cathode materials with different contents were studied by constant current charge-discharge of XRD,SEM, battery. The results show that the structure of the cathode material is not affected by Mn~ (2) doping, and the first discharge capacity of the Li Fe0.95Mn0.05PO_4 cathode material with Mn~ (2) doping content of 5% is the highest at 0.1 C rate. The effects of Mn~ (2) doping on electrode kinetics and lithium ion transport of cathode materials were studied by cyclic volt-ampere (CV) and electrochemical impedance spectroscopy (EIS).
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
本文编号：2496783
[Abstract]:Orthogonal olivine LiFePO_4 has the advantages of high theoretical capacity (170m Ahg-1), friendly environment, good thermal stability, high cycle performance (more than 2000 times), rich raw materials and low cost. It is a promising cathode material for lithium-ion batteries and has been widely used. However, the inherent defect of LiFePO_4 is that the electronic conductivity and lithium ion diffusion rate are very low, which seriously affects the actual capacity and rate performance of the material. In this paper, the synthesis of nano-LiFePO_4, from cheap industrial raw materials is as follows: firstly, the preparation of nano-FePO_4 was studied by using waste molten iron as Tie Yuan, diammonium hydrogen phosphate as phosphorus source and citric acid as surfactants. As a comparative experiment, the Fe PO_4 prepared by adding different mass citric acid was named FP-A (0 g citric acid) and FP-B (0.2 g citric acid), respectively. FP-C (0.4g citric acid) and FP-D (0.6g citric acid). The size, morphology and surface properties of Fe PO_4 were studied by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results show that the size of Fe PO_4 decreases with the increase of citric acid content. The size of FP-D is distributed in nanometer scale and the agglomeration is less. LiFePO_4/C cathode materials were synthesized by carbothermal reduction using precursor FePO_4, lithium carbonate and sucrose as raw materials. As a comparative experiment, the LiFePO_4/C synthesized by FP-A,FP-B,FP-C and FP-D is named LFP-A,LFP-B,LFP-C and LFP-D., respectively. The structure, size and electrochemical properties of cathode materials were studied by X-ray diffraction (XRD) (XRD), SEM, battery at constant current charge and discharge. The results show that the size and morphology of FePO_4 have an effect on LiFePO_4/C. The smaller the size of FePO_4, the more regular the morphology, the smaller the size of LiFePO_4/C cathode material and the less agglomeration. The test results at 0.1 C rate show that the addition of citric acid is not conducive to the increase of discharge capacity of LiFePO_4/C materials, but it can reduce the polarization and capacity attenuation of cathode materials and improve the rate cycle performance. Different contents of metal Mn~ (2) ions (0%, 5%, 8% and 10%) were used to doping LiFePO_4 materials. The structure, size, morphology and electrochemical characteristics of metal-doped cathode materials with different contents were studied by constant current charge-discharge of XRD,SEM, battery. The results show that the structure of the cathode material is not affected by Mn~ (2) doping, and the first discharge capacity of the Li Fe0.95Mn0.05PO_4 cathode material with Mn~ (2) doping content of 5% is the highest at 0.1 C rate. The effects of Mn~ (2) doping on electrode kinetics and lithium ion transport of cathode materials were studied by cyclic volt-ampere (CV) and electrochemical impedance spectroscopy (EIS).
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912
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