锂离子电容器用预锂化硬炭负极的研究

发布时间：2018-05-08 14:58

本文选题：硬炭 + 活性炭　；参考：《天津大学》2014年硕士论文

【摘要】：随着电池和电容器应用范围的不断扩大，对于这些储能元件的能量密度、功率密度、循环寿命等性能的要求也越来越高。锂离子电容器（LIC）因兼具电化学电容器良好的功率特性和锂离子电池较高的能量密度而引起人们的关注。从锂离子电容器未来的产业化角度出发，炭材料因为廉价易得是锂离子电容器的首选材料。本论文以商品化的活性炭为正极、硬炭为负极，1M LiPF6/EC+DEC为电解液组装了锂离子电容器，考察了负极预锂化容量、预锂化工艺、正负极质量配比对锂离子电容器电化学性能的影响。将硬炭/Li半电池进行不同程度放电以获取不同预锂化容量的硬炭，并将得到的预锂化硬炭用于LIC。研究发现，当负极嵌锂容量小于200mAh/g时，LIC的首次效率很低，正极会发生高压极化，超出了活性炭的稳定电压区间；当嵌锂容量大于200mAh/g时，负极的不可逆容量因得到了充分补偿，LIC的效率在90%以上。随着嵌锂容量的增加，LIC的能量密度增加，然而当嵌锂容量超过400mAh/g时，负极会发生锂的沉积。在负极嵌锂容量不同的条件下，以嵌锂容量为400mAh/g的LIC综合性能最优，其具有最小的扩散电阻，最高能量密度和功率密度分别为76.5Wh/kg和5.1kW/kg，且循环1000次后，能量保持率仍高达92.0%。利用硬炭与锂源自放电这种简单方法对LIC负极进行了预锂化，结果表明该种方法能成功实现负极的预锂化。LIC的比容量随着预锂化时间的延长先增大后减小，其最佳预锂化时间为15h。经过15h预锂化的锂离子电容器最高能量密度可达97.2Wh/kg，即使在功率密度为5.4kW/kg的条件下，其依然具有45.1Wh/kg的能量密度，同时该电容器具有最小的阻抗和良好的循环性能（1A/g的电流密度下循环1000次后，能量保持率为91.2%）。通过改变正负极质量配比，对LIC的电化学性能进行进一步优化。结果表明，当正负极质量配比为2.2时，电容器具有最优的电化学性能。电流密度从1.2C增加到82C时，，电容器的能量密度由88.7Wh/kg衰减到48.7Wh/kg，能量保持率为57.0%。同时，电容器具有非常小的电荷转移内阻（10.4），最大能量密度和功率密度分别为88.7Wh/kg和12kW/kg。
[Abstract]:With the continuous expansion of battery and capacitor applications, the energy density, power density, cycle life and other performance requirements of these energy storage elements are becoming higher and higher. Lithium-ion capacitors (LICs) have attracted much attention because of their good power characteristics and high energy density of lithium-ion batteries. From the point of view of the future industrialization of lithium ion capacitors, carbon materials are the preferred materials for lithium ion capacitors because of their low cost. In this paper, the lithium ion capacitor was assembled with commercial activated carbon as positive electrode and hard carbon as negative electrode with 1m LiPF6/EC DEC as electrolyte. The effects of prelithiation capacity, prelithiation process and mass ratio of positive and negative electrode on electrochemical performance of lithium ion capacitor were investigated. The hard carbon with different prelithiation capacity was obtained by discharging the hard carbon / Li half-cell to different degree, and the obtained prelithiated hard carbon was used for LICs. It is found that when the lithium intercalation capacity of the negative electrode is less than 200mAh/g, the initial efficiency is very low, and the positive electrode will be polarized at high pressure, which exceeds the stable voltage range of the activated carbon, and when the lithium intercalation capacity is greater than 200mAh/g, The irreversible capacity of the negative electrode is more than 90% due to the efficiency of fully compensating the LIC. With the increase of the lithium intercalation capacity, the energy density of the LIC increases, but when the lithium intercalation capacity exceeds the 400mAh/g, the lithium deposition will occur in the negative electrode. Under the condition of different lithium intercalation capacity, the LIC with lithium intercalation capacity as 400mAh/g has the best comprehensive performance. It has the smallest diffusive resistance, the highest energy density and power density are 76.5Wh/kg and 5.1 kW / kg, respectively. After 1000 cycles, the energy retention rate is still up to 92. 0%. The simple method of self-discharge of hard carbon and lithium source is used to prelithiate the LIC anode. The results show that the specific capacity of prelithium. LIC of negative electrode increases first and then decreases with the prolongation of prelithiation time. The optimum prelithiation time is 15 h. The maximum energy density of the lithium-ion capacitor after 15 h pre-lithiation can reach 97.2Wh-1 / kg, even when the power density is 5.4kW/kg, it still has the energy density of 45.1Wh/kg. At the same time, the capacitor has the minimum impedance and good cycling performance. After 1000 cycles at 1 / g current density, the energy retention rate is 91.2%. The electrochemical performance of LIC was further optimized by changing the mass ratio of positive and negative electrodes. The results show that the capacitor has the best electrochemical performance when the mass ratio of positive and negative electrode is 2.2. When the current density is increased from 1.2C to 82C, the energy density of the capacitor attenuates from 88.7Wh/kg to 48.7 Wha / kg, and the energy retention rate is 57.0 / kg. At the same time, the capacitor has a very small charge transfer resistance of 10.4%, the maximum energy density and power density are 88.7Wh/kg and 12kW / KG, respectively.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM53

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