MoS2纳米材料制备及其电化学性能研究
哈尔滨工业大学工学硕士学位论文
Abstract
Due to the large capacity, small size, safety, portability and non-pollution, Lithium-ion batteries have been developed into important energy storage devices in many fields such as electronic products, artificial satellites, military industries, and smart grids. However, graphite, which has been commercialized as an anode material for lithium ion batteries, has a low theoretical specific capacity value of 372 mAh/g cannot meet the increasing demand for lithium ion batteries. Therefore, exploration of new anode materials with high capacity value and long cycle stability is an important part in the development of lithium batteries.In recent years, molybdenum disulfide is expected to be a new generation of anode material with better performance due to its layered structure, similar to graphene, high capacity (670mAh/g) and low raw material cost. However, the molybdenum disulfide has large surface energy and is unstable and easy to stack; the insertion and extraction of lithium ions during charge and discharge will cause a large deformation, and the structure is easily broken; in addition, molybdenum disulfide, as a semiconductor material, has poor conductivity. Therefore, as a lithium battery anode material, molybdenum disulfide has great limitations in practical applications. This article aims at above issues, through the preparation of molybdenum disulfide nanocomposite electrode, cobalt doped molybdenum disulfide materials and other transition metal sulfide compounds—MoSe2research, preparing three anode materials with high specific capacitance, fast ion kinetics and long cycle life.
In order to improve the electrical conductivity and stability of the MoS2 electrode material, the MoS2is compounded with other more conductive sulfides. The MoS2/Co9S8composite electrode is prepared in situ on the carbon paper by the hydrothermal method, and thus improving the specific capacitance and conductivity of the material. The in-situ preparation of the composite structure on the conductive substrate can avoid the agglomeration and stacking of MoS2nanosheets and the synergistic effect of different material combination can improve the stability of the overall structure, and thus obtain a high-performance MoS2composite electrode material. Studies have shown that the optimal structure of the MoS2/Co9S8 composite electrode has a better specific capacitance and conductivity than the single MoS2 electrode material, and its specific capacity remains at 677 mAh/g after 100 cycles of charge and discharge, which is four times the specific capacitance value of the molybdenum disulfide electrode material alone.
哈尔滨工业大学工学硕士学位论文
In order to improve the performance of MoS2 material itself, cobalt-doped MoS2 electrode materials were prepared by hydrothermal method using different contents of cobalt nitrate, and the effects of doped cobalt on specific capacitance, conductivity, and cycle stability of MoS2 were studied. The results of experiments show that appropriate cobalt doping will not significantly change the morphology of MoS2 nanomaterials, but the cobalt atoms, doping into the MoS2 lattice will introduce extra vacancy defects into the (100) crystal plane, which promotes lithium ion in the electrolyte to enter the interior of the MoS2electrode material through these defect sites. In addition, cobalt doping can also improve the conductivity of the material. Therefore, the cobalt-doped MoS2 electrode material has better cycle stability than the pure MoS2 electrode, and the capacity is 426 mAh/g after 100 cycles of charge and discharge, which is maintained at 65% of the initial and better than original MoS2.
Finally, we extend our research ideas to MoSe2materials which has similar structure and properties of MoS2. The hydrothermal method is used to prepare the precursors on two-dimensional graphene nanosheets. Then, the precursors are selenized by a tube furnace to make the MoSe2nanosheets uniformly disperse on graphene nanosheets. The precursor is obtained under the condition of cobalt nitrate to finally obtain cobalt-doped MoSe2/graphene composite materials. The graphene allows the MoSe2 nanosheets to grow uniformly, avoiding their agglomeration and increasing the contact between the electrode material and the electrolyte. Cobalt atoms also introduce defects in the MoSe2 lattice, increase the reactive sites of the material, and accelerate the ion diffusion in the electrode material. For electrochemical performance test, the Co-MoSe2/G electrode material have a increasing capacity and activation process during the earlier stage of constant current charge-discharge process. After 100 weeks of charge and discharge, the capacity value can reach 492 mAh/g and the specific capacity after 200 cycle is about 320 mAh/g, which is 137% of the capacitance of the initial.
Keywords: molybdenum disulfide, molybdenum selenide，lithium ion battery，cobalt doping，composite electrode material
哈尔滨工业大学工学硕士学位论文
目录
摘要 ............................................................................................................................... I Abstract ........................................................................................................................... III
第1章绪论 (1)
1.1 课题背景及研究意义 (1)
1.2 锂离子电池组成及工作原理 (2)
1.3 MoS2负极材料研究现状 (4)
1.3.1 MoS2电极材料结构及其优缺点 (4)
1.3.2 MoS2复合材料 (5)
1.3.3 掺杂改性MoS2材料 (8)
1.3.4 MoSe2电极材料 (9)
1.4 本文主要研究内容 (11)
第2章实验材料、设备及方法 (12)
2.1 实验材料和试剂 (12)
2.2 实验仪器设备 (12)
2.3 材料表征及测试方法 (13)
2.3.1 拉曼光谱分析(Raman) (13)
2.3.2 X射线光电子能谱分析(XPS) (13)
2.3.3 扫描电镜分析(SEM) (13)
2.3.4 透射电镜分析(TEM) (13)
2.3.5 X射线衍射分析(XRD) (14)
2.3.6 X射线荧光光谱分析(XRF) (14)
2.3.7 电极材料的制备及扣式电池的组装 (14)
2.3.8 电极材料的电化学性能测试 (15)
第3章高性能MoS2/Co9S8复合电极材料的研究 (16)
3.1 引言 (16)
3.2 碳纸上原位制备MoS2/Co9S8复合电极材料 (16)
3.3 MoS2/Co9S8复合电极材料的形貌和结构表征 (17)
3.3.1 Co(OH)2前驱体 (17)
3.3.2 MoS2/Co9S8复合电极材料 (18)
3.3.3 MoS2和Co9S8电极材料 (21)
哈尔滨工业大学工学硕士学位论文
3.4 MoS2/Co9S8复合电极材料电化学性能表征 (22)
3.4.1 恒流充放电和循环寿命测试分析 (22)
3.4.2 交流阻抗谱测试分析 (24)
3.5 本章小结 (25)
第4章钴掺杂MoS2电极材料的研究 (26)
4.1 引言 (26)
4.2 钴掺杂MoS2电极材料的制备 (26)
4.3 钴掺杂MoS2电极材料的形貌结构分析 (27)
4.3.1 SEM、TEM和BET表征分析 (27)
4.3.2 XRD、Raman和XRF表征分析 (31)
4.3.3 XPS表征分析 (32)
4.4 钴掺杂MoS2电极材料的电化学性能表征 (33)
4.4.1 循环伏安测试、恒流充放电及循环寿命测试分析 (33)
4.4.2 交流阻抗谱分析测试 (36)
4.5 本章小结 (37)
第5章钴掺杂MoSe2/石墨烯复合电极材料的研究 (39)
5.1 引言 (39)
5.2 钴掺杂MoSe2/石墨烯复合电极材料的制备 (39)
5.3 钴掺杂MoSe2/石墨烯复合电极材料的形貌结构分析 (40)
5.3.1 SEM和TEM分析 (40)
5.3.2 XRD、Raman和XRF表征分析 (43)
5.3.3 XPS表征分析 (44)
5.4 钴掺杂MoSe2/石墨烯复合电极材料的电化学性能表征 (46)
5.4.1 循环伏安测试、恒流充放电及循环寿命测试分析 (46)
5.4.2 交流阻抗分析测试 (48)
5.4.3 三种电极材料的锂电性能分析 (48)
5.5 本章小结 (49)
结论 (50)
参考文献 (51)
攻读硕士学位期间发表的论文及其它成果 (56)
哈尔滨工业大学学位论文原创性声明和使用权限 (57)
致谢 (58)