静电纺丝技术优化锂离子电池正极材料 LiCoO2 电化学性能研究

近年来，锂离子电池的应用领域已经从传统的消费电子产品慢慢扩展到了具有重要战略意义的能源和动力领域，因此对其性能的要求也不断在提高。具有高能量密度、功率密度和高安全性的锂离子电池是当前能源和动力领域研究的重点，而正极材料是影响锂离子电池性能的关键。层状结构材料LiCoO2因为有较高的脱嵌锂电压和较高的可逆比容量，所以是最先被大规模使用的锂离子电池正极材料。LiCoO2的理论比容量在所有正极材料中处于一个较高的水平，可达到274 mAh g-1，但是在4.2 V截止电压下的实际比容量却只有140 mAh g-1。目前，经过对其改性，LiCoO2的充电截止电压已经提高到了4.35 V，相应的实际比容量为160 mAh g-1。如果想要继续进一步提高LiCoO2的可逆比容量，则需要提高其充电截止电压至4.5 V，但随之而来的问题如正极表面副反应、结构退化、钴的溶解、电解液分解等将严重影响电池的正常使用。本文采用了简单易行的静电纺丝技术对LiCoO2进行改性处理，不仅实现了对材料的纳米化处理，又实现了材料表面包覆改性，既提高了充放电容量，又提高了循环性能。

（一）采用单轴静电纺丝技术制备了LiCoO2纳米颗粒。首先通过单因素变量法和正交实验法得到了最优的单轴静电纺丝工艺参数配比；随后通过XRD、SEM等表征得到不同制备方法得到的LiCoO2形貌和结构的区别；最后对比三种制备方法得到的LiCoO2的电化学性能发现，采用单轴静电纺丝技术制备得到的LiCoO2起始放电比容量得到了极大提升，但是由于表面副反应的增多，其容量衰减速度也比其他制备方法的LiCoO2快。

（二）在上述研究的基础之上，采用了同轴静电纺丝技术对LiCoO2进行了TiO2包覆处理。首先研究了单轴电纺和同轴电纺对纤维形貌的影响；随后研究了不同包覆温度的LiCoO2@TiO2的形貌和结构区别，电化学性能测试结果显示，最佳的包覆温度为800 ℃，在此包覆温度下，循环性能得到了很大提升；最后对包覆温度对LiCoO2改性的影响进行了机理探索，发现在800 ℃下LiCoO2与TiO2发生了反应产生了Li2TiO3和Co3O4，附着在表面提高了电导率，从而使得LiCoO2电化学性能提高。

In recent years, the application field of lithium ion battery has gradually expanded from traditional consumer electronics to the field of energy and power with important strategic significance. Therefore, the requirements for its performance are also increasing. Lithium ion batteries with high energy density, power density and high safety are the focus of current research in the field of energy and power, and the cathode material is the key to affect the performance of lithium ion batteries. Layered structure material LiCoO₂ is the first commercial cathode material for lithium ion batteries because of its high de intercalation voltage and high energy density. The theoretical specific capacity of LiCoO₂ is much higher than that of other cathode materials, which can reach 274 mAh g^-1, but the actual specific capacity at 4.2 V cut-off voltage is only 140 mAh g^-1.At present, after its modification, the charging cut-off voltage of LiCoO₂ has been increased to 4.35 V, and the corresponding actual specific capacity is 160 mAh g^-1. If you want to further improve the specific capacity of LiCoO₂, you need to increase its charging cut-off voltage to 4.5 V. However, the following problems, such as side reaction on the positive surface, structural degradation, dissolution of cobalt, decomposition of electrolyte, will seriously affect the normal use of the battery. Aiming at the above series of problems, LiCoO₂ is modified by simple electrospinning technology, which not only realizes the nano treatment of the material, but also realizes the surface coating modification of the material, which not only improves the charge discharge capacity, but also improves the cycle performance.

（1）LiCoO₂ nanoparticles were prepared by uniaxial electrospinning. Firstly, the optimal ratio of uniaxial electrospinning process parameters was obtained by single factor variable method and orthogonal experiment method; Then, the morphology and structure of LiCoO₂ obtained by different preparation methods were characterized by XRD and SEM; Finally, comparing the electrochemical properties of LiCoO₂ obtained by the three preparation methods, it is found that the initial discharge specific capacity of LiCoO₂ prepared by uniaxial electrospinning technology has been greatly improved, but due to the increase of surface side reactions, its capacity decay rate is also faster than that of LiCoO₂ prepared by other preparation methods.

（2）Based on the above research, LiCoO₂ was coated with TiO₂ by coaxial electrospinning technology. Firstly, the effects of uniaxial electrospinning and coaxial electrospinning on fiber morphology were studied; Then the effects of different coating temperatures were studied LiCoO₂@TiO₂ The electrochemical performance test results show that the best coating temperature is 800 ℃, and the cycle performance is greatly improved at this coating temperature; Finally, the mechanism of the effect of coating temperature on the modification of LiCoO₂ was explored. It was found that LiCoO₂ reacted with TiO₂ at 800 ℃ to produce Li₂TiO₃and Co₃O₄, which attached to the surface and improved the conductivity, so as to improve the electrochemical performance of LiCoO₂.

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