摘 要

钠离子电池已经逐渐成为大规模能源存储以及智能电网建立的最佳储能器件候选者之一。但是，对于进一步实现钠离子电池的商业化应用，高倍率、长寿命的负极材料开发是一个十分关键性的难题。为了寻求更高的负极容量，转化反应型和合金化反应型电极材料被认为是钠离子电池应用的潜在材料，并引起了广泛的研究。但是对于高倍率性能和长循环寿命的实现，它们还面临着本征导电性差、结构易破坏导致容量急剧衰减等一系列问题。针对于上述问题，本文结合了分级纳米结构构筑方法的优势，提出了由零维纳米颗粒嵌入到一维碳管，并进一步夹嵌于二维石墨烯层间的多级组装的纳米复合物。该结构兼具多种分级结构优势，极大地改善了电极材料的倍率性能及循环稳定性。主要研究结果如下：

(1) 利用简单普适的水热-电荷调控-冷冻干燥-还原煅烧法，制备了分级组装的纳米架构复合材料，其主要由零维的V₂O₃纳米颗粒嵌入到一维碳纳米管，继而夹嵌在二维层状还原氧化石墨烯中组成。

(2) 利用循环伏安法、恒电流充放电测试等对其进行了电化学性能测试。在20 A g^-1的电流密度下，其放电比容量仍可以达到165 mAh g^-1；在5 A g^-1的电流密度下，其首次容量可以达到237 mAh g^-1，循环15000次后，容量保持率为72%。并且在600-15000次循环间，容量无任何衰减。此结果验证了这种多级组装纳米架构复合物的结构有效性。

(3) 利用多种非原位测试技术，本文首次研究了三氧化二钒纳米颗粒的电化学储钠机制，发现其主要是发生一个逐步粉化的转化反应过程，并且具有十分良好的反应可逆性。

(4) 探究了这种零维、一维、二维多级组装的纳米复合物的电化学优化机制，阐述了其性能与结构的构效关系。提出了一种有效的“限制-缓冲”机制，一维碳管可以有效地抑制V₂O₃纳米颗粒的膨胀和粉化流失，同时，二维石墨烯结构可以作为缓冲层进一步缓解一维碳管的膨胀应力，实现整体结构的有效保持。此外，一维碳管还可以稳定SEI膜的存在，提高材料本征导电性，确保V₂O₃纳米颗粒高度可逆的电化学反应。

关键词：多级组装，缓冲效应，超长循环寿命，高倍率性能，储钠机制，三氧化二钒

Abstract

Sodium ion battery has gradually become one of the best candidates as energy supply for large-scale energy storage system and smart grid. However, the exploitation of high-rate and ultralong-life anode materials for sodium-ion battery is a key issue to commercial applications. In order to seek higher specific capacity, the conversion-type and alloying-type materials has been researched in the sodium-ion battery applications. But, for the realization of high-rate performance and long cycle life, they also faced with the poor intrinsic conductivity, quick capacity fading owing to structure damage and other issues. For the above problems, this paper combines the advantages of multidimensional nanostructures, constructing the 0D1D2D multistage-assembled nano-composites which are made out of 0D nanoparticles embedded in 1D carbon nanotubes sandwiched between 2D graphene layers. The multistage-assembled nanostructures with many structural advantages significantly improve the rate capability and cyclic stability of the electrode material. The main research results are as follows.

(1) Multidimensional assembled nano-composite structures are synthesized by the simple hydrothermal, charge controlling, freeze drying combining with calcining methods, which are made out of 0D V₂O₃ nanoparticles embedded in 1D carbon nanotubes sandwiched between 2D graphene layers.

(2) Electrochemical performance is tested by the cyclic voltammetry and galvanostatic charge-discharge testing. At a current density of 20 A g^-1, multidimensional assembled nano-composites still achieve a discharge capacity of 165 mAh g^-1. At a current density of 5 A g^-1, they deliver the initial capacity of 237 mAh g^-1. After 15000 cycles, the capacity retention of 72% is obtained. And between 600 and 15000 cycles, the capacity has no any capacity decay. These results suggest the effectiveness of the multidimensional assembled nano-composite structures.

(3) Using ex-situ testing techniques, this work firstly investigates the electrochemical sodium ion storage mechanism of V₂O₃ nanoparticles. The V₂O₃ nanoparticles primarily display a gradual pulverization and conversion reaction during discharge process. And the conversion reaction has a good reaction reversibility.

(4) Electrochemical optimization mechanism of 0D-1D-2D multidimensional assembled nano-composites is explored to explain the relationship of its structure and performance. An efficient "confined-buffered" mechanism is proposed, 1D carbon nanotube can effectively confine the expanding and loss of V₂O₃ nanoparticles, while the 2D graphene layer can be used as a buffer layer to further buffer the swelling stress of 1D carbon tube, and effectively maintain the whole structures. In addition, the 1D carbon tube can also stable SEI films, improve the intrinsic conductivity, and ensure highly reversible electrochemical reaction of V₂O₃ nanoparticles.

Keywords: multistage-assembling, buffered effect, ultralong cyclelife, high rate performance, sodium ion storage mechanism, vanadium trioxide

目录

摘要 I

Abstract II

第一章 绪 论 1

1.1 引言 1

1.2 高性能钠电负极材料的设计方法 3

1.2.1 碳包覆法 3

1.2.2 氧化层包覆法 6

1.2.3 石墨烯复合法 7

1.2.4 分级多孔结构设计 9

1.3 三氧化二钒作为钠电电极材料的研究现状 10

1.4本文研究内容及意义 11

第二章 多孔氮掺杂V₂O₃/C纳米管@rGO复合缓冲结构的制备与表征 13

2.1实验原料及仪器 13

2.1.1 实验原料 13

2.1.2 实验仪器 13

2.2实验方法 14

2.2.1 钒氧化物纳米管前躯体 14

2.2.2 多孔氮掺杂V₂O₃/C纳米管@rGO复合缓冲结构 14

2.3 结构与形貌表征 15

2.3.1表征设备 15

2.3.2 合成机制与结构表征 15

2.3.3 物相、价态及孔结构表征 19

第三章 多孔氮掺杂V₂O₃/C纳米管@rGO复合缓冲结构的电化学性能 22

3.1扣式钠离子电池的组装与测试方法 22

3.1.1 扣式电池的组装 22

3.1.2 电化学性能测试方法 22

3.2电化学性能表征 22

第四章 多孔氮掺杂V₂O₃/C纳米管@rGO复合缓冲结构的储钠与缓冲机制 26

4.1储钠机制研究 26

4.2缓冲机制研究 28

第五章 结论与展望 31

5.1结论 31

5.2展望 31

参考文献 33

致 谢 36

第一章 绪 论

1.1 引言

能源危机和环境污染已成为制约人类发展的关键性问题。据统计，2050年，世界人口将会超过80亿人，其能源需求量将达到现今社会需求量的两倍—28TW^[1]。这种经济的快速发展和人口的急剧膨胀会带来巨大的能源需求。因此，绿色、可持续清洁能源，如风能、太阳能、生物能等的开发和利用显得尤为重要。但是，此类能源存在着获取输出不稳定、地域分布广、难以并入电网等问题。所以，开发高效、智能、快捷的低成本能源储存技术，建立大规模智能电网，对可再生能源的储存和再分配十分关键 (图1.1)。在大规模储能技术中，电化学储能具有转换效率高、环境适应性强、持续性强，而被认为是一种非常具有应用前景的储能方式^[2]。