【作者】 张磊；

【导师】 单忠强；

【作者基本信息】 天津大学 ， 应用化学， 2007， 硕士

【摘要】 移动通讯电子设备和电动汽车的飞速发展,对锂离子蓄电池在高循环性能、高比能量方面提出了新的要求,因此以新能源和新材料技术为背景的锂离子蓄电池正极材料的研究也在不断开拓新的方向。对低成本、高比能量、环境友好、长寿命的新型正极材料的开发已经成为了主流的研究方向。LiFePO4正极材料以其高的理论比容量(170mAh/g),适中的工作电压(约3.5V),较好的常温和高温稳定性,低廉的成本和优良的环保性能,成为了下一代锂离子电池正极材料最有力的竞争者。但由于LiFePO4晶体结构的固有限制导致其电子导电率和锂离子扩散速度低,特别是大电流倍率放电性能强烈受制于其电子导电性能,因此提高LiFePO4粒子的电导率成为近来研究者关注的热点。目前改善LiFePO4导电性能的研究主要集中在碳包覆及金属掺杂两方面。本文主要采用高温固相法制备LiFePO4正极材料,通过掺杂金属离子以及碳包覆的方式对材料进行改性研究,采用XRD、SEM TEM、CV(循环伏安)等手段对材料进行表征,并在不同条件下测试了材料的电化学性能。在掺杂单一种类金属离子对材料进行改性的过程中,掺杂Zr和Nb离子制得的LiFePO4正极材料具有较好的电化学性能,0.1C电流密度下首次放电容量都达到110mAh/g以上,并具有高倍率条件下充放电性能。复合掺杂金属离子Mn、Zr、Ni对材料进行改性效果明显,0.1C电流密度下首次放电容量达到121.1mAh/g,高倍率条件下充放电性能良好。对上述单一以及复合掺杂金属离子的LiFePO4正极材料采取碳包覆的方法进行改性,碳包覆在材料原有基础上提高了比容量降低了极化度,进一步稳定了材料的电化学性能,大幅提升了材料的高倍率条件下的充放电性能。其中,对复合掺杂金属离子Mn、Zr、Ni的材料碳包覆效果最佳,0.1C条件下比容量达到159 mAh/g,高倍率0.5C条件下比容量仍能保持120 mAh/g。更多还原

【Abstract】 Because of the development of electronic equipment and electric mobile have new demands on lithium ion batteries for long cycling life and high theoretical capacity, depend on new energy resources and new material technology cathode material of lithium ion batteries continuously develops new direction.The developments of new cathode material with lower capital, high voltage, pollution-free and long cycling life already become primary research. LiFePO4 as the cathode material has the poformance of its high theoretical capacity (170mAh/g), appropriate voltage (about 3.5V), good stability both at room temperature and high temperature and being environmentally benign and inexpensive,that LiFePO4 has become the uppermost competitor at the cathode material. But the crystalloid configuration restricts LiFePO4 at low electronic conductivity and low lithium ion diffusivity, especially restricting its electrochemical reversibility, increasing the conductance of LiFePO4 is becoming the hotspot. In order to overcome these defaults, the researches focus the way both of carbon coating and ion doping.The cathode material LiFePO4 were obtained by solid-state reaction, and developing by ion doping and then coated carbon. LiFePO4 was characterized by XRD, SEM, TEM, CV analysis. We also studied the electrochemical properties of the product at different conditions.At the preparation by single species ion doping of LiFePO4, Zr ion and Nb ion dopants showed the best electrochemical properties. The both first discharge capacity of above-mentioned samples was over 120mAh/g with a current density of 0.1C.Excellent electrochemical reversibility and cycling stability have been achieved. Lithium iron phosphate contained diversified ion(Mn, Zr, Ni) dopants showed the best electrochemical properties. The first discharge capacity was 121.1mAh/g with a current density of 0.1C. The electrochemical reversibility and cycling stability were not bad.We used the carbon coating the ion doping samples for development which we mentioned. The carbon coating enhanced the discharge capacity, reduced the polarization of the material, tranquilized electrochemical properties and greatly increased the electrochemical properties of the cathode material.And the sample coated carbon which contained Mn, Zr, Ni ion had best performance .Its first discharge capacity was 159mAh/g with a current density of 0.1C. Its electrochemical reversibility was 120mAh/g with a current density of 0.5C.更多还原