新型多层次结构碳微球的制备及电化学性能研究

PREPARATION AND ELECTROCHEMICAL PROPERTIES OFHIERARCHICAL CARBON MICROSPHERES

张剑桥

11649189

硕士

材料工程

卢周广

2018-06-04

2018-07-04

哈尔滨工业大学

深圳

锂离子电池在消费电子和电动汽车领域的大规模应用使得锂矿石的价格不断飙升。为了缓解锂元素紧缺带来的压力，人们迫切的需要寻找能够代替锂离子电池的ᯠ型储能技术。同时，现有锂离子电池的能量密度随着这种需求的增加，其性能已经越来越显得“力不从心”。寻找能量密度更大，性能更加优越的电化学储能装置成为了人们关注的焦点。钾在地壳中储量巨大，同时与锂同属碱金属元素，现有锂离子电池的许多技术可以作为钾离子电池技术的参考，同时钾元素在地球上巨大的储量可以有效缓解锂离子电池中遇到的锂元素在地壳中丰度不足的问题。因此，在未来，钾离子是补充锂离子电池的理想装置。另一方面来讲，在动力电池领域，锂硫电池的正极具有高达 1672mAh/g 的理论容量，可以显著增加动力电池的续航能力，同时作为正极活性物质的单质硫环境友好，成本低廉，是非常理想的动力电池。因此，本文利用甲醛与尿素的缩聚反应，制备碳前驱体，设计合成了两种3D 多层次碳纳米碳球，并将其分别利用与锂硫电池正极与钾离子电池负极。主要内容和结果如下：（1）本文以脲醛树脂为前驱体，通过控制原料的比例，以及后续的碳化过程，合成了具有球中球结构的碳微球，其比表面积为 1250.52cm3/g。通过熔融扩散法将硫与碳微球复合用作锂硫电池正极材料，得到的复合材料的含硫量为 70wt%。由于球中球结构碳微球良好的导电性、结构稳定性，以及内部的空腔结构，使得该复合材料电极拥有良好的性能。有效地吸收了锂硫电池充放电过程中的体积膨胀，并抑制了穿梭效应，在 0.2C 的电流密度下，循环 100 圈后容量为 833.45mAh/g，依然保持了 80%以上的初始容量。（2）仍以上述脲醛树脂为前驱体，但通过在合成过程中加入十六烷基三甲基溴化铵（CTAB）作为添加剂。在该添加剂的作用下，使缩聚而成的脲醛树脂链排列为纳米片状结构，并聚集为球形，最终形成花状结构碳微球，其比表面积为1021.12cm3/g。将该碳微球应用于钾离子电池负极。由于该碳球的无定形碳的特征，以及由内向外的大量纳米片结构，使它可以在有效地储存钾离子的同时，保持结构的稳定性。在 1C 的电流密度下循环 900 圈后依然维持了 191.34mAh/g 的容量，显示了良好的循环稳定性实验结果表明脲醛树脂基碳微球对反应条件敏感，易于控制其形貌的变化。本文合成的两种碳微球均采用无加热、无模板的液相反应得到，制备方法简单，反应过程温和。分别应用于锂硫电池正极材料与钾离子电池负材料时展现出了良好的性能和稳定性。本文为制备多种形貌的碳材料ᨀ供了一种简便的方法，对改善碳材料的性能ᨀ供了一种思路。

The large-scale application of lithium-ion batteries in the field of consumer electronics and electric vehicles has led to soaring prices of lithium ores. In order to alleviate the pressure caused by the shortage of lithium, people urgently need to find a new energy storage technology that can replace lithium ion batteries. At the same time, the energy density of the existing lithium ion batteries increases with the increasing demand. It has become the focus of attention that searching for electrochemical energy storage devices with greater energy density and superior performance. Potassium is one of the most promising devices to supplement lithium ion batteries in the future, and lithium sulfur battery is one of the most promising solutions to increase the energy density of existing batteries, which is the ideal device to supplement lithium ion batteries in the future. Therefore, by using the condensation reaction of formaldehyde and urea to prepare carbon precursors, two kinds of 3D multilayer carbon nanospheres were designed and synthesized, and they were used respectively as anode of lithium sulfur battery and negative electrode of potassium ion battery. The main contents and results are as follows: (1) In this paper, using urea formaldehyde resin as precursor, by controlling the proportion of raw materials and subsequent carbonization, the carbon microspheres with ball in ball structure were synthesized. The specific surface area of the microspheres is 1250.52 cm3/g. Sulfur and carbon microspheres were used as cathode materials for lithium sulfur batteries by melting diffusion method. The sulfur content of the composites was 70wt%. Because of the good electrical conductivity, structural stability and internal cavity structure of the carbon spheres, the composite electrode has good performance. The volume expansion in the charge and discharge process of lithium sulfur batteries is effectively absorbed and the shuttle effect is suppressed. Under the current density of 0.2C, the capacity was 833.45mAh/g after 100 cycles, and the initial capacity remains above 80%.(2) Urea formaldehyde resin is still the precursor, but cetyltrimethyl ammonium bromide (CTAB) was added as an additive in the synthesis process. Under the action of this additive, the urea formaldehyde resin chain formed by the polycondensation was arranged into nanometallic structure and aggregated into spherical shape. Finally, the carbon microspheres with flower like structure are formed, and the specific surface area of the microspheres is 1021.12cm3/g. The carbon microspheres were applied to the anode of the potassium ion battery. Due to the amorphous carbon characteristics of the carbon sphere and a large number of nanoscale structures from inside to outside, it can keep the stability of the structure while storing potassium ions effectively. After 900 cycles of 1C current density, 191.34mAh/g capacity is maintained, showing good cycling stability.The experimental results show that urea formaldehyde resin based carbon microspheres are sensitive to reaction conditions and easy to control their morphologies. The two kinds of carbon microspheres synthesized in this paper are all prepared by liquid phase reaction without heating and template. The preparation method is simple and the reaction process is mild. Good performances and stability have been shown in the cathode materials of lithium sulfur batteries and negative materials of potassium ion batteries. This paper provides a simple method for preparing various morphologies of carbon materials, and provides a way to improve the properties of carbon materials

脲醛树脂 碳微球 钾离子电池 锂硫电池

urea-formaldehyde resin carbon nanosphere potassium ion batteries lithium-sulfur batteries

中文

联合培养

南方科技大学

张剑桥. 新型多层次结构碳微球的制备及电化学性能研究[D]. 深圳. 哈尔滨工业大学,2018.