微波固相法制备锂离子电池负极材料及其储锂特性研究

发布时间：2018-03-01 21:00

  本文关键词： 锂离子电池 负极材料 Li4Ti5O12 Nb ZnCo2O4 MWCNTs　出处：《华中科技大学》2014年硕士论文　论文类型：学位论文

【摘要】：当前商业化使用的锂离子电池负极材料主要是石墨类碳材料，然而不可逆容量大、倍率性能差等缺点制约了这类材料的进一步发展。锂离子电池负极要满足高容量、高能量密度、高倍率性能、高循环性能的未来需求就必须开发新的材料。 Li4Ti5O12是一种充放电过程中体积效应几乎为零的材料，循环寿命长、高稳定性高，是锂离子电池负极材料研究的热点。但是钛酸锂的电子导电率差，影响了它的电化学性能，需要进行改性来改善，特别是高倍率下的电化学性能。 ZnCo2O4是一种金属氧化物的衍生物。通过无毒性的Zn代替Co，不仅有金属氧化物理论比容量高的特点，而且降低了成本和环境的污染。但是需要改性提高它的首次库伦效率。 本文选用新型制备方法微波固相法得到了纳米尺度的锂离子电池负极材料Li4Ti5O12和ZnCo2O4，并分别进一步进行金属离子Nb5+掺杂和包覆多壁碳纳米管MWCNTs改性，提高了材料的电化学性能。与传统固相加热方式相比，微波辐射利用反应物分子和微波之间的相互作用让固相反应进行得更快，合成温度相对低、反应时间更短。现代微波控制系统可以精确地控制反应时间、温度，使得微波能够均匀快速的被反应物或者反应介质吸收从而将高温固相反应时间缩短至十几分钟，是一种很好的制备纳米材料的方法。Li4Ti5-xNbxO12(MW,0≤x≤0.1)的制备是采用Li2CO3、TiO2、Nb2O5为原料，利用微波固相法在750oC下保温20min得到了分布均匀的纳米尺度的钛酸锂材料，纳米颗粒尺寸大约在200 400nm。ZnCo2O4(MW,CNTs)复合材料的制备是采用Zn(NO3)22H2O、 Co(NO3)26H2O、多壁碳纳米管MWCNTs为原料，利用微波固相法在450oC保温20min制备了ZnCo2O4(MW, CNTs)复合材料。 研究结果表明微波固相法制备的Li4Ti5-xNbxO12(MW,0≤x≤0.1)性能优于传统固相法制备的LTO (T)。特别是当Nb掺杂量在0.03mol%时，表现出高容量、好的稳定性和好的倍率性能。在1C、5C、10C以及20C充放电循环200圈后，放电比容量分别保持了174.7、157.1、141.7和130.2mAh g1。这项研究提供了高性能钛酸锂工业化生产的新思路。相对于传统固相法制备的ZnCo2O4，ZnCo2O4(MW, CNTs)复合材料的电化学性能有了改善，，0.1C下首次库伦效率由22%提高到了77%，20圈后放电比容量还保持了700mAh g1。
[Abstract]:The current commercial cathode materials for lithium ion batteries are mainly graphite carbon materials. However, the disadvantages of large irreversible capacity and poor rate performance restrict the further development of these materials. The future demand of high energy density, high rate performance and high cycle performance requires the development of new materials. Li4Ti5O12 is a kind of material whose volume effect is almost zero in charge and discharge process. It has long cycle life and high stability, so it is a hotspot in the research of cathode materials for lithium ion batteries. However, the electronic conductivity of lithium titanate is poor, which affects its electrochemical performance. Modification is needed to improve electrochemical performance, especially at high rates. ZnCo2O4 is a derivative of metal oxides. It not only has the characteristics of high theoretical specific capacity of metal oxides, but also reduces the cost and environmental pollution, but it needs to be modified to improve its first Coulomb efficiency. In this paper, nanoscale cathode materials Li4Ti5O12 and ZnCo _ 2O _ 4 for lithium ion batteries were prepared by microwave solid-state method. Metal ion Nb5 doped and coated multi-walled carbon nanotubes (MCNTs) were further modified respectively. The electrochemical properties of the materials are improved. Compared with the conventional solid-state heating, microwave radiation uses the interaction between reactants and microwaves to make the solid-state reaction proceed faster and the synthesis temperature is relatively low. The modern microwave control system can accurately control the reaction time and temperature, so that the microwave can be absorbed uniformly and quickly by reactants or reaction media, thus shortening the reaction time of high temperature solid phase to 10 minutes. Li4Ti5-xNbxO12MW0 鈮

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