论文总字数：33603字

摘 要

鉴于目前国际上石油天然气价格的上涨，新能源的研究正逐渐引起人们的重视。同时，随着近年来信息技术的飞速发展，对能源的要求也越来越高，以至于传统的锂离子电池无法满足当前的需求。而锂硫电池作为一种新型的高性能、大容量二次电池，则可以更好地满足当今社会的需求。锂硫电池的理论容量可达1675 mAh/g，其能量密度可达2500 Wh/kg。然而，锂硫电池也存在一些问题，导致其发展受到了阻碍。与此同时，MXene材料的问世也给电池行业带来了一场重大的革新，由MAX相腐蚀而来的MXene材料具有优异的导电性、倍率性能、较高的比表面积、优异的电磁屏蔽性能，且具有数量众多的表面基团，提供了大量活性点位。Fe₂O₃作为金属氧化物，可以通过吸附多硫化物来抑制锂硫电池的“穿梭效应”，因此可以将Fe₂O₃与MXene材料复合，利用MXene材料的表面活性点位将Fe₂O₃负载到其表面，制备出电化学性能优异且稳定的电极材料。本实验通过LiF/HCl腐蚀法将A层从MAX相中抽出，再进行超声剥离，成功制备出单层Ti₃C₂T_X纳米片的悬浮液，将其与Fe₂O₃与S复合，得到S-Fe₂O₃-Ti₃C₂T_X复合电极（S载量为70wt%，Fe₂O₃载量为30wt%），并从阻抗、循环伏安曲线（CV）、长循环以及倍率性能四个方面对制备出来的复合电极进行全面的评价。同时，本实验还利用得到的悬浮液分别制备了致密与多孔的柔性膜，并进行了电导率测试（致密膜电导率远高于多孔膜）。表征结果表明，S颗粒在Ti₃C₂T_X纳米片上分布均匀，但Fe₂O₃颗粒出现了明显团聚，分布不均匀。根据等电化学测试结果，此种复合电极材料的初始容量很高，达到1600 mAh/g，但是在长循环下有较为明显的容量衰减（循环200次后容量仅为200 mAh/g）。此外，其阻抗较小，CV曲线具有标准的锂硫电池特征峰，且其前两次循环十分稳定。倍率性能方面，该材料在0.05C下放电容量高，约为1550 mAh/g，在1C下时则为700 mAh/g，最后回到0.05C时，容量恢复到1400 mAh/g左右，可见其倍率性能良好。因此将Fe₂O₃引入锂硫电池正极材料中可以在一定程度上提高电池的性能。但是由于Fe₂O₃有团聚现象，分布不均匀，导致材料的电化学性能不稳定，需要进一步研究。

关键词：Ti₃C₂T_X MXene Fe₂O₃ 正极材料 锂硫电池 水热法 冷冻干燥 电化学性能

The preparation and electrochemical performance of Ti₃C₂T_X (MXene)-based composite cathode for Li-S battery

Abstract

Given the increasing price of oil and gas in the world, new energy research is getting a lot of attention. At the same time, with the rapid development of information technology in recent years, the demand for energy is also increasingly high. Therefore, the traditional lithium-ion battery cannot fulfill the current demand. As a new type of secondary battery with high performance and capacity, lithium-sulfur battery can meet the needs of today's society better. The theoretical capacity of a lithium-sulfur battery can reach 1675 mAh/g, and its energy density can reach 2,500 Wh/kg. However, there are still some problems with lithium-sulfur battery, which hinder its development. At the same time, the advent of MXene also brings a significant innovation to the battery industry. MXene, prepared by etching of MAX phase, has excellent conductivity, rate performance, high specific surface area and excellent electromagnetic shielding performance. As a metallic oxide, Fe₂O₃ can impede the "shuttle effect" of lithium-sulfur battery by adsorbing polysulfide. Therefore, in this experiment, it is compounded with MXene material to prepare an electrode material with excellent and stable electrochemical properties.In this experiment, Al layer was extracted from Ti₃AlC₂ by the LiF/HCl etching method. Then the ultrasonic treatment is applied to delaminate multi-layer Ti₃C₂T_X into single-layer Ti₃C₂T_X nanosheets. Finally, the Ti₃C₂T_X nanosheets are composited with Fe₂O₃ and S to prepare the S-Fe₂O₃-Ti₃C₂T_X composite cathode (the S load is 70wt% and the Fe₂O₃ load is 30wt%). The composite material was comprehensively evaluated by means of impedance, cyclic voltammetry (CV) curve, long cycle and rate performance. The results show that the initial capacity of the composite electrode material is very high, reaching 1600mAh/g, but it has an obvious decay under long cycle (the capacity is only 200mAh/g after 200 cycles). In addition, its impedance is small, and the CV curve has a standard characteristic peak of lithium-sulfur battery, with its first two cycles being very stable. In terms of rate performance, the material has a high power capacity under 0.05C, which is about 1550mAh/g, while under 1C, it is 700mAh/g. When it finally returns to 0.05C, the capacity is restored to about 1,400 mAh/g, indicating that its power efficiency performance is good. Therefore, the introduction of Fe₂O₃ into the anode material of lithium sulfur battery can improve the performance of the battery to a certain extent, but it is still a long way from commercialization. However, due to agglomeration, the distribution of Fe₂O₃ is not quite uniform, resulting in the unstable electrochemical performance of the material. Therefore, some further researches are eagerly needed.

Key Words: Ti₃C₂T_X MXene, Fe₂O₃, cathode material, lithium-sulfur battery, hydrothermal method, freeze drying, electrochemical performance

目 录

摘 要 I

ABSTRACT II

第一章 绪论 1

1.1 引言 1

1.2 锂硫电池简介 2

1.2.1 工作原理 2

1.2.2 存在的问题 3

1.3 锂硫电池正极材料研究现状 4

1.3.1 硫-碳型 4

1.3.2 硫-金属氧化物型 5

1.3.3 硫-导电聚合物型 6

1.4 二维过渡族金属碳（氮）化物 (MXene) 研究现状 7

1.4.1 MXene简介 7

1.4.2 制备方法 7

1.4.3 结构特点 8

1.4.4 性能 9

1.4.5 应用 10

1.5 课题的研究意义与研究内容 14

1.5.1 研究意义 14

1.5.2 研究内容 14

第二章 实验部分 15

2.1 实验原料 15

2.2 实验设备 16

2.3 材料制备 16

2.3.1 技术路线图 16

2.3.2 Ti₃C₂T_x MXene制备 17

2.3.3 S-Fe₂O₃-Ti₃C₂T_X复合正极材料的制备 17

2.3.4 电池组装 18

2.4 材料表征 18

2.4.1 XRD分析 18

2.4.2 SEM分析 19

2.4.3 电导率测试 19

2.4.4 电化学性能测试 19

第三章 结果与讨论 20

3.1 Ti₃C₂T_X MXene的表征 20

3.2 S-Ti₃C₂T_X -Fe₂O₃复合材料的表征 24

3.3 S-Ti₃C₂T_X -Fe₂O₃复合材料的电化学性能 27

第四章 结论与展望 31

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