摘要
随着科学技术的不断进步，人们对未来锂电提出了更高的要求，尤其是更高的比容量密度与安全性的要求。在现有正极材料比容量逐渐接近其理论极限值的情况下，开发具有超高比容量密度的负极材料是进一步提高电池比容量密度最为有效的方法之一。其中，锂金属负极（3860 mAh g−1）与硅负极（4200 mAh g−1）被人们寄予厚望。然而，这两种负极材料在充放电过程中均存在严重的循环体积效应，巨大的体积变化不仅会影响电池的比容量，还会带来一定的安全隐患。循环体积效应的存在极大地限制了锂金属负极与硅负极的应用，是未来锂电发展道路上必须要解决的问题。因此，本论文分别针对锂金属负极与硅负极进行了复合结构设计，以起到有效缓解二者的循环体积效应，达到比容量与安全性兼顾的效果。
为了有效缓解锂金属的循环体积效应，本文提出了一种工艺简单、可大规模化制备具有3D骨架的复合锂金属负极的方法。通过高温处理静电纺丝所得的碳纤维结构，使得普通碳基体转化为具有良好Li亲和力的表面石墨化碳支架，将该支架浸入熔融锂中，可利用骨架微纳孔洞的毛细作用将熔融锂吸附进3D碳骨架内部，从而获得具有3D骨架的复合锂金属负极。3D碳骨架的存在极大地增加了负极的活化比表面积，形核位置大大增加，同时电极的有效电流密度降低，有利于锂离子进行均匀沉积，使得锂金属负极的循环体积效应可以得到有效缓解。因此，相较于裸锂负极，3D复合锂金属负极拥有更加稳定的锂离子沉积-溶解行为，更低的形核势垒，更高的离子迁移效率，从而拥有更高的循环比容量与更好的倍率性能。
为了有效缓解硅负极的循环体积效应，本文提出了一种兼具三明治结构与柔性结构优点的复合结构设计。利用磁控溅射技术在隔膜上依次溅射氮化磷酸锂（lithium phosphorus oxynitride，LiPON）、Si、Cu薄膜，获得具有三明治复合结构的柔性硅负极材料。在LiPON薄膜的保护下，复合结构负极具有更加稳定的SEI 膜，同时借助隔膜柔性衬底的弹性形变，复合结构的硅负极能有效避免应力集中的问题，即便经过1000次循环，电极形貌依然可以保持完整、稳定。在LiPON薄膜与柔性隔膜的协同作用下，硅负极的循环体积效应可以得到有效缓解，电池也表现出较高的可逆容量，优异的循环稳定性和良好的倍率性能。
路西弗关键词：负极材料；循环体积效应；复合结构；锂金属负极；硅负极
Abstract
With the development of science and technology, people have t much higher requirements for lithium battery system in the future, especially higher specific capacity density and safety requirements. In the ca where the specific capacity of the existing positive electrode material gradually approaches its theoretical limit value, developing a new type anode material with high specific capacity density is one of the most effective methods for further increasing the specific capacity density of the battery. Among them, the lithium metal negative electrode (3860 mAh g−1) an
d the silicon negative electrode (4200 mAh g−1) are highly expected by people. However, the two kinds of negative electrode materials have rious circulation volume effect during charging and discharging process. The huge volume change will not only affect the specific capacity, but also bring some safety risks. The existence of the circulation volume effect greatly limits the application of lithium metal negative electrodes and silicon negative electrodes, and is an obstacle that must be overcomed for further development of lithium batteries. Therefore, this thesis propo a composite structure design for lithium metal negative electrode and silicon negative electrode respectively, expecting that the effect of the circulation volume can be effectively alleviated, and both the high specific capacity and high safety can be achieved.
In order to effectively reduce the circulation volume effect of lithium metal, this paper prents a simple method that can be ud to prepare a complex lithium metal negative electrode with a 3D framework inside it. By processing the carbon fiber structure obtained by electrospinning at a high temperature, the ordinary carbon matrix is converted into a surface graphitized carbon stent which has a good Li affinity. Then the stent is immerd in the molten lithium, and the molten lithium can be adsorbed easily into the stent under the capillary effect. Finally, a composite lithium metal negative electrode having a 3D skeleton inside is obtained. The existence of the 3D carbon skeleton greatly in
creas the electroactive surface area of the negative electrode, so that the nucleation sites can be incread a lot, and the effective current density of the electrode can be decread. It is conducive to the uniform deposition of lithium ions, and the circulation volume effect of the lithium metal negative electrode can be effectively alleviated.
Compared with the bare lithium negative electrode, the 3D lithium composite negative electrode has more stable lithium ion deposition-dissolution behavior, lower nucleation barrier, higher ion migration efficiency, and thus has higher cycle capacity and much better rate performance.
In order to effectively reduce the circulation volume effect of the silicon negative electrode, this paper propos a composite structure design that combines the advantages of a sandwich structure and a flexible structure. To obtain a flexible silicon negative electrode material with a sandwich composite structure, lithium phosphorus oxynitride (LiPON), Si and Cu nano-films were sputtered on the parator in quence by magnetron sputtering technology, Under the protection of the LiPON film, the negative electrode has a more stable SEI film. Meanwhile, the silicon negative electrode can effectively avoid the problem of stress concentration due to the elastic deformation of the flexible substrate (parator), even after 1000 cycles, the electrode morphology still remains intact and stable. With the synergistic effect of the LiPON film and the flexible parator, the circulation volume
effect of the silicon negative electrode can be effectively alleviated, and the battery also exhibits high reversible capacity, excellent cycle stability, and good rate performance.relation是什么意思
Key words: negative electrode material; circulation volume effect; composite structure; lithium metal negative electrode; silicon negative electrode
目录
第1章引言 (1)
1.1 锂电池相关简介 (1)
1.1.1 锂电池的发展历程 (1)短篇英语故事
1.1.2 锂离子电池的组成 (2)
1.1.3 锂离子电池正极材料 (3)
1.1.4 锂离子电池负极材料 (3)
1.1.5 锂电未来发展方向：高比容量与安全性兼顾 (5)
1.2负极材料的循环体积效应 (7)
1.2.1 循环体积效应对比容量的影响 (8)
bra是什么1.2.2 循环体积效应对安全性的影响 (9)
1.3 锂金属负极循环体积效应及相关研究进展 (9)
1.3.1 锂金属负极的循环体积效应 (9)
1.3.2 锂金属负极循环体积效应相关研究进展 (10)
1.4 硅负极循环体积效应及相关研究进展 (13)
考研政治答题卡>amor什么意思1.4.1 硅负极的循环体积效应 (14)
1.4.2硅负极循环体积效应相关研究进展 (15)
1.5 关键研究问题与本文结构安排 (17)
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1.5.1 关键研究问题 (17)
1.5.2 本论文结构安排 (18)
第2章研究内容与方法 (19)
2.1 本文研究内容 (19)
2.2 实验试剂与仪器 (19)
2.2.1 锂金属负极实验所用试剂与仪器 (19)
2.2.2 硅负极实验所用试剂与仪器 (21)
2.3 材料表征方法 (22)
2.3.1 场发射扫描电子显微镜分析 (22)
2.3.2 能量色散X射线光谱分析 (22)
2.3.3 X射线光电子能谱分析 (23)
2.3.4 台阶仪分析 (23)
2.3.5 X射线衍射仪分析 (23)
2.3.6 透射电子显微镜分析 (23)
2.3.7 激光拉曼光谱仪分析 (24)
2.4 电化学性能测试方法 (24)
外教在线英语培训排名2.4.1 LiCoO2正极片的制备 (24)
2.4.2 扣式电池组装过程 (24)
2.4.3 恒流充放电循环测试 (25)
2.4.4 循环伏安曲线测试 (26)
四六级报考网站官方2.4.5 电化学交流阻抗测试 (26)
第3章表面石墨化3D碳骨架复合锂金属负极的设计制备及性能研究 .. 27
3.1 引言 (27)
3.2表面石墨化3D碳骨架复合锂金属负极实验设计思路 (28)
3.3 表面石墨化3D碳骨架复合锂金属负极的制备 (30)
3.4 高温处理对3D碳骨架形貌、物相与性能的影响分析 (31)
3.4.1 高温处理前后3D碳骨架的形貌观察与分析 (31)
3.4.2 高温处理前后3D碳骨架的物相变化 (32)
3.4.3 高温处理前后3D碳骨架对熔融锂浸润性的表征与分析 (34)
3.5 3D复合锂金属负极对锂循环体积效应的影响分析 (36)
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3.5.1 电池充放电循环测试分析锂沉积行为的稳定性 (36)
3.5.2 锂金属负极循环前后的形貌结构分析 (43)
3.6 本章小结 (44)
第4章LiPON保护下的三明治复合结构柔性硅负极的设计制备及性能研究 (45)
4.1 引言 (45)
4.2 三明治复合结构柔性硅负极材料实验设计思路 (45)
4.3不同结构硅负极材料的制备 (47)
4.4 电极材料的膜厚、形貌与结构分析 (48)
4.4.1 三明治复合结构柔性硅负极各层薄膜膜厚的测定 (48)
4.4.2 不同结构硅负极材料的形貌观察与分析 (49)
4.4.3 LiPON保护层的形貌与结构分析 (50)
4.5 三明治复合结构柔性硅负极对硅循环体积效应的影响分析 (53)
4.5.1 半电池充放电循环测试分析硅负极的循环稳定性 (53)
