过渡金属氧化物负极材料的制备与电化学行为表征

POLYDOPAMINE INCREASEING CAPACITY OF ALBUMIN NANOPARTICLES FOR PHOTOTHERMAL GENE SYNERGISTIC TUMOR THERAPY

金东

11849130

硕士

材料工程

谷猛

2020-05-30

2020-07-01

哈尔滨工业大学

深圳

过渡金属氧化物材料比容量高、资源丰富、经济成本低，十分有希望成为下一代高性能锂离子电池负极材料。然而，过渡金属负极材料的实际应用受到循环稳定性差和电子电导率低的限制。虽然研究者们已经采取了各种各样的方法来解决这一问题，但是过渡金属氧化物负极材料的真实电化学过程、电化学反应机制、容量衰减的原因和微结构的变化过程还需要深入研究。在众多的过渡金属氧化物中，Co3O4 拥有极高的理论容量和优异的物理性质。通过对 Co3O4 电极的研究，我们发现 Co3O4 电极在前几个循环中比容量极高，但是经过 30 次循环后比容量迅速下降，表明 Co3O4 电极循环性能较差。对比前人的研究可以知道，Co3O4 低的电导率和体积膨胀问题是导致循环性能差的主要原因。因此，本文以 ZIF-67 型金属有机骨架为前驱体制备了 Co3O4 多面体，其中金属有机框架可以有效抑制 Co3O4 的体积膨胀问题。同时，将导电性能优异的碳材料与 Co3O4 复合，以提高 Co3O4 的电导率。本文所获得的 C 包覆 Co3O4 和 CNTs/Co3O4 显示出独特的十二面体结构，具有三维孔隙结构，可有效改善 Co3O4 在充放电过程中的体积膨胀问题。基于碳纳米管（或导电碳涂层）和金属有机框架结构的协同作用，C 包覆 Co3O4 和CNTs/Co3O4 电极具有优异的电化学性能：在 1 C 的高电流密度下经过 500 次循环后，仍可实现 391.7 mAh g-1和 309.4 mAh g-1的可逆容量，库仑效率接近 100％。本文制备了不同形貌的 NiO 纳米结构，并利用原位透射电子显微镜技术观察了 NiO 在锂化过程中的微观形貌和相结构的动态演变过程，同时分析了 NiO的组分和价态变化。结果表明在首次充锂过程中，NiO 被还原成 Ni，并伴随着Li2O 的生成，得到了 NiO 的锂化反应。另外，在我们发现 NiO 在锂化过程中存在着巨大的体积膨胀，以及在充锂后部分锂离子不能从 NiO 电极中脱出，这些会导致 NiO 差的循环性能。我们以 NiO 纳米颗粒为工作电极，锂金属为对电极组装成半电池，研究了NiO 电极的电化学性能。我们在充放电循环曲线中发现，在前 25 个循环左右，NiO 电极的比容量高且稳定，在此之后，比容量迅速下降。结合原位透射显微镜表征结果，我们发现比容量的迅速下降正是归因于每次循环中都有部分锂离子因 Li2O 差的导电性而不能脱出，导致活性物质的损失。且 Li2O 在 NiO 电极上的不断积累，导致 NiO 电极的导电性越来越差，也会损失部分比容量。

The transition metal oxide material has high specific capacity, abundant resources, and low economic cost. So, it is very promising to become the nextgeneration high-performance lithium-ion battery anode material. However, the practical application of transition metal oxide anode materials is limited by poor cycle stability and low electronic conductivity. Researchers have adopted a variety of methods to solve this problem. However, the real electrochemical process, electrochemical reaction mechanism, cause of capacity decay and microstructure change process of transition metal oxide anode materials need to be further studied.Among the many transition metal oxides, Co3O4 has extremely high theoretical capacity and excellent physical properties. Through the study of Co3O4 electrode, we found that the specific capacity of Co3O4 electrode was very high in the first few cycles, but the specific capacity decreased rapidly after 30 cycles. The phenomenon indicated that the cycling performance of Co3O4 electrode was poor. Compared with previous studies, it can be known that the low conductivity and volume expansion of Co3O4 are the main reasons for poor cycling performance. Therefore, a Co3O4 polyhedron was prepared in this paper based on the ZIF-67 metal organic framework as the precursor system. The metal organic frame can effectively inhibit the volume expansion of Co3O4. At the same time, carbon materials with excellent conductivity were compounded with Co3O4 to improve the conductivity of Co3O4.The C coated Co3O4 and CNTs/Co3O4 obtained in this paper showed a unique dodecahedral structure. It has a three-dimensional pore structure, which can inhibit the volume expansion of Co3O4 in the charging and discharging process. Based onthe synergistic effect of carbon nanotubes (or conductive carbon coating) and metal organic framework structure, C coated Co3O4 and CNTs/Co3O4 electrodes show excellent electrochemical performance. After 500 cycles at a high current densityof 1 C, they maintained the reversible capacities of 391.7 and 309.4 mAh g-1, respectively, with an average coulomb efficiency of nearly 100%.We prepared NiO nanostructures with different morphologies in this paper. And the morphology evolution, phase transformation, electrochemical reaction and valence state changes of NiO during lithiation process have been probed in real timeby in situ TEM. The results show that NiO is reduced to Ni, and Li 2O is formed during the first lithium charging process. We found that NiO has a huge volume expansion during lithiation. In addition, some lithium ions cannot be extracted from the NiO electrode after lithium charging, which will lead to poor cycling performance of NiO.We assembled half-cell using metallic Li as anode and NiO nanoparticles as the working electrode. Studied the electrochemical performance of the NiO electrode. The results of the cyclic voltammetry curve showed that the discharge / charge reaction of the NiO electrode. The results confirm the conclusions obtained in the in-situ TEM. It is worth noting that that the specific capacity of the NiO electrode is high and stable around the 25 cycles. After that, the specific capacity quickly dropped. Combined with the in-situ TEM results, we believe that the rapid decrease in specific capacity is because of the loss of active material. Owing to the poor conductivity of Li2O, some lithium ions cannot be extracted. Moreover, the continuous accumulation of Li2O on the NiO electrode causes the conductivity of the NiO electrode to become worse and worse, and part of the specific capacity will also be lost.

锂离子电池 负极材料 过渡金属氧化物 原位透射电镜技术

lithium-ion battery anode material transition metal oxides in-situ transmission electron microscopy

中文

联合培养

南方科技大学

金东. 过渡金属氧化物负极材料的制备与电化学行为表征[D]. 深圳. 哈尔滨工业大学,2020.