【作者】 任亚琦；

【导师】 王殿龙；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2010， 硕士

【摘要】 锂离子电池正极材料磷酸亚铁锂以其具有无毒、充放电电压平稳、稳定性好、循环性能好以及成本低等优点受到广泛关注。流变相法和溶胶凝胶法制备过程原料混合均匀,制备材料尺寸小,利于充放电循环。以三价铁做铁源制备磷酸亚铁锂成本低、过程简单,所以本研究考虑以三价铁做铁源,用流变相法和溶胶凝胶法制备了纯相和金属离子掺杂的LiFePO4/C复合材料,并测试其室温下循环性能与倍率性能。通过X射线衍射(XRD)、扫描电镜(SEM)等表征手段分析所制备的LiFePO4/C复合材料的结构与形貌特点,并由循环伏安、电化学交流阻抗等电化学测试手段测试材料的循环可逆性和阻抗性能。利用溶胶凝胶法制备LiFePO4/C材料,考察了不同络合剂、预烧温度、锂盐和添加量、烧结温度、烧结时间对材料性能的影响,得出以硝酸铁：硝酸锂：磷酸二氢铵：柠檬酸=1：1.05：1：1,60mass%的蔗糖为原料,在260℃下预烧2h,650℃下烧结6h,所制备的材料0.2C放电下容量能够达到122mAh/g。以硝酸铁、磷酸二氢铵、氢氧化锂、蔗糖做为原料、以流变相法制备前驱体,通过高温烧结制备了LiFePO4/C正极材料,并且研究了不同金属离子的掺杂对材料性能的影响。结果表明,350℃预烧4h,650℃烧结18h制备的磷酸亚铁锂材料0.2C放电容量能够达到123mAh/g,0.5C放电下容量能够达到108mAh/g,1C放电下容量能够达到97mAh/g。对材料进行Zr4+、Al3+、Mg2+掺杂结果表明,掺杂Mg2+的材料性能最好,2%的Mg2+时,0.2C放电下能够达到140mAh/g,0.5C下放电容量为120mAh/g,1C放电容量为112mAh/g,且循环50次容量无衰减。用硝酸铁、磷酸二氢铵、硝酸锂、蔗糖做为原料,利用流变相法制备前驱体,通过高温烧结制备LiFePO4/C正极材料,考察了温度和时间对材料性能的影响。结果表明,260℃预烧2h,650℃烧结6h制备的磷酸亚铁锂材料,在0.2C充放电倍率下的质量比容量可达140mAh/g,0.5C为133mAh/g,1C为130mAh/g;对材料进行Mg2+掺杂研究表明,乙酸镁按化学计量比2%掺杂,合成样品在0.2C的放电容量保持在143mAh/g;在1C充电,1C、2C、5C、10C的放电倍率下放电容量保持在128mAh/g,109mAh/g,94mAh/g,84mAh/g,表现出良好的倍率性能,同时循环十次容量无衰减。更多还原

【Abstract】 Olivine LiFePO4 appears as an interesting positive electrode material for Li-ion batteries because of its low toxicity, good thermal stability, long cycle life and low cost. The rheological phase method and sol-gel method have the advantages of mixed well of the materials, small particle size which are good for the charge-discharge cycles. Ferric iron as the source to prepare LiFePO4 has the advantages of low cost and simple process, so in this study we chose ferric iron as Fe sources, with the rheological phase method and sol-gel to prepare pure phase and metal ions doped LiFePO4/C material, and test the cycling capability and rate performance at room temperature. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to character the structural and microscopy characteristics. Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) were used to character the cyclic reversibility and resistance of the materials.LiFePO4/C materials was prepared using sol-gel method and had been studied the influence of different complexing agents, calcining temperature, the lithium salt and content, sintering temperature, sintering time on the material properties had been studied. LiFePO4/C materials was prepared with precursors of ferric nitrate, ammonium dihydrogen phosphate, lithium, sucrose, citric acid, and the discharge capacity could reach to 122mAh/g at 0.2C, but Mg2+ and Al3+ doped materials using sol-gel method were not ideal.LiFePO4/C cathode material was prepared using rheological phase with the precursors of iron nitrate, ammonium dihydrogen phosphate, lithium hydroxide, and had been studied of different metal ions doping on the material properties. The results showed that after sintering 4h calcined at 350℃for the first process, and then sintering 18h calcined at 650℃, pure phase of lithium iron phosphate was prepared and its discharge capacity could reach to 123mAh/g at 0.2C. Doping Zr4+, Al3+, Mg2+ of LiFePO4/C material performance comparison showed that the material doped 2% Mg2+ showed the best performance, and the 0.2C,0.5C,1C discharge capacity reached to 140mAh/g,120mAh/g,112mAh/g, and the basic capacity after 50 cycles without degradation.LiFePO4/C cathode material was prepared using rheological phase with the precursors of iron nitrate, ammonium dihydrogen phosphate, lithium nitrate, sucrose. 0.2C discharge capacity of the LiFePO4/C cathode material could reach to 140mAh/g, 0.5C to 133mAh/g, 1C is 130mAh/g. Doping different content of Mg2+ of LiFePO4/C material performance comparison showed that the material doped 2% Mg2+ showed the best performance, and the 0.2C discharge capacity reached to 143mAh/g. At the same time high-rate performance of the material has been improved. When 2% doped samples charged at 1C rate, discharged at 1C,2C,5C,10C rate after 10 cycles, the discharge capacity could reached to 128mAh/g,109mAh/g,94mAh/g,84mAh/g.Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) were used to character the cyclic reversibility and resistance of the materials using different methods.更多还原