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锂离子电池LiNi1/3Co1/3Mn1/3O2正极材料的制备及低温性能的研究
谭双媛
学位类型硕士
导师徐金宝
2015-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料工程
关键词锂电池 低温性能 倍率性能 包覆改性 共沉淀法
摘要

锂离子二次电池具有高容量、无污染、无记忆效应、自放电小和较好的循环性能等优点,是性能优异的二次电池储能设备。锂离子电池在便携电子设备产业占有巨大的优势,未来在动力电池和大型储能领域有很好的发展前景。锂离子电池正极材料是制约锂电池容量和寿命的关键因素。在众多正极材料中,三元系正极材料LiNi1/3Co1/3Mn1/3O2由于比容量高、循环性能好、毒性低等特点,在动力电池市场占有较大份额,被认为是最有望取代LiCoO2的正极材料之一。动力电池的工作温度范围要求较宽,在特殊地区环境温度甚至能达到-40℃。在边防和航空领域,对储能电池的低温要求甚至达到-60℃。锂离子电池的传统工作温度范围在-20~55℃之间,在温度低于-20℃时,锂离子电池的性能受到限制。影响锂离子电池低温性能的因素很多,在正极活性物质方面,主要集中在低温时锂离子扩散率降低、电荷转移阻抗增加和电极极性增强。本论文首先采用高温固相法、Pechini法和草酸根共沉淀法制备三元正极材料LiNi1/3Co1/3Mn1/3O2,对比电性能以确定LiNi1/3Co1/3Mn1/3O2材料的制备工艺。通过XRD和电性能表征后发现,草酸根共沉淀制备的正极材料的Li+/Ni2+混排最小,并且具有较好的循环性能和倍率性能。为了改善LiNi1/3Co1/3Mn1/3O2材料的低温性能,使用液相法对草酸根共沉淀法制备的LiNi1/3Co1/3Mn1/3O2正极材料进行包覆改性。包覆材料为非晶态锂快离子导体Li2O-2B2O3(LBO)。与包覆前LiNi1/3Co1/3Mn1/3O2材料相比,改性后材料的低温电性能得到显著提高。在较严苛的-40℃时0.2 C倍率的放电比容量从37.2mAh g-1大幅提高到101.9 mAh g-1,比容量保有率为57.8%,是包覆前的约2.5倍。除此之外,包覆改性后LiNi1/3Co1/3-Mn1/3O2材料在-20℃具有更好的循环稳定性,在0.2 C倍率循环50次后,包覆材料的放电比容量保有率达到70.6%,远高于未包覆LiNi1/3Co1/3Mn1/3O2材料的28.8%。交流阻抗测试表明,LBO包覆能够降低材料在低温时的电荷转移阻抗,提高锂离子扩散率,从而有效改善LiNi1/3Co1/3Mn1/3O2的低温电化学性能。为了对LiNi1/3Co1/3Mn1/3O2的倍率性能做进一步改进,我们对材料的制备方法做出改进。采用碳酸根共沉淀法和水热法制备LiNi1/3Co1/3Mn1/3O2材料。通过扫描电镜表征发现,水热后的LiNi1/3Co1/3Mn1/3O2具有类球形多孔二次颗粒。电性能测试表明,水热合成的LiNi1/3Co1/3Mn1/3O2在10 C倍率充放电条件下最大放电比容量达到132.7 mAh g-1高于普通碳酸根共沉淀法样品的123.9mAh g-1。在-20℃时,2 C倍率的放电比容量为72.9 mAh g-1,高于共沉淀样品的46.0mAh g-1。通过水热法制备的LiNi1/3Co1/3Mn1/3O2正极材料由于具有类球状多孔隙二次颗粒,有效增加了正极活性物质的比表面积,增强了活性物质与电解液的接触,显著改善了LiNi1/3Co1/3Mn1/3O2正极材料的倍率性能。

其他摘要

Lithium ion batteries with high capacity, pollution-free, no memory effect, self-discharge less, good circulation performance, and many other advantages is considered to be excellent performance of a new generation of storage battery. Li-ion battery has held an enormous advantage in the portable electronic equipment, and in the future it will be applied widely in the fields of power battery and large energy storage. Cathode material is the key component which directly affect capacity and cycle life of lithium ion battery. Because LiNi1/3?Co1/3?Mn1/3O2 cathode material has many advantages, such as high capacity, good cycle performance and low toxicity, it is expected to be one of the best candidate materials for replaced LiCoO2 for the batteries. The power batteries must have wide range of working temperature. And in some special working areas the environmental temperature may reach -40 °C. In the field of border and aviation, the requirement of working temperature for batteries even reached to -60 °C. The range of working temperature for traditional Li-ion battery is between -20 °C to 55 °C. When at -20 °C, Li-ion battery usually has poor performance. The factors which influence low temperature performance of Li-ion batteries are low lithium ion diffusion rate, high charge-transfer resistance and high polarization. In this paper, we adopted three different methods which were solid state method, Pechini method and oxalate co-precipitation method to synthesize LiNi1/3?Co1/3?Mn1/3O2. In order to determine the best preparation, we compared performance of the samples. As it is shown in XRD patterns, the sample which is prepared by oxalate co-precipitation method has the minimum mixture of Li+/Ni2+. And it also has better cycle and rate performance. The effect of the lithium boron oxide glass coating on the low temperature electrochemical performance of LiNi1/3Co1/3Mn1/3O2 via solution method had been investigated. LBO-coated LiNi1/3Co1/3Mn1/3O2 has improved discharge capacity at low temperature. At -40 °C the discharge capacity of LBO-coated LiNi1/3Co1/3Mn1/3O2 increases from 37.2 mAh g-1 to 101.9 mAh g-1 and the discharge capacity retention is almost 2.5 times more than that of the bare one. LBO-coated LiNi1/3Co1/3Mn1/3O2 shows good cyclic performance at -20 °C. The capacity retention after 50 cycles increases from 28.8% to 70.6%. Electrochemical impedance spectroscopy shows that the decreased charge transfer resistance and the increased lithium ion diffusion coefficients are main factors that improve the low temperature discharge capacity obviously. In order to enhance the rate performance of LiNi1/3Co1/3Mn1/3O2, we made improvement of the synthesis method. The LiNi1/3Co1/3Mn1/3O2 material was synthesized by carbonate co-precipitation and hydrothermal method. As it is shown in SEM, LiNi1/3Co1/3Mn1/3O2 which is synthesized by hydrothermal method has kind of spherical porous secondary particles. At 10 C the discharge capacity of porous LiNi1/3Co1/3Mn1/3O2 is 132.7 mAh g-1 which is higher than that of the normal sample (123.9 mAh g-1). At -20 °C the discharge capacity at 2 C is improved from 46.0 mAh g-1 to 72.9 mAh g-1. The spherical porous secondary particles increases the specific surface area of the positive electrode active material, and enhances the contact with the electrolyte. So that, the porous LiNi1/3Co1/3Mn1/3O2 has improved rate performance.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4262
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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谭双媛. 锂离子电池LiNi1/3Co1/3Mn1/3O2正极材料的制备及低温性能的研究[D]. 北京. 中国科学院大学,2015.
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