论文总字数：49905字

摘 要

锂硫（Li-S）电池因其极高的理论比容量与能量密度、低廉的制造成本和环境友好性而被人们所青睐。但因单质硫导电性差、活性物质多硫化锂的穿梭效应及体积膨胀现象，极大地削弱了锂硫电池的性能。MXene是一种新型二维材料，具有独特的结构、优异的导电性以及丰富的表面化学环境以及亲水性，因此有望有效缓解当前锂硫电池所面临的问题。此外，三维网络结构能提供较大的活性硫负载空间以及离子扩散通道，因此本研究考虑制备三维多孔Ti₃C₂T_x MXene泡沫作为硫载体，并使用Ti₃C₂T_x MXene对隔膜进行改性。

本文采用新型、安全、高效的HCl-LiF腐蚀剂腐蚀Ti₃AlC₂前驱体，一步插层、剥离后制备出Ti₃C₂T_x粘性墨汁。使用HCl诱导自组装-冷冻干燥处理后制备得到比表面积为42.8 m²/g的三维多孔Ti₃C₂T_x泡沫。以此为载体，采用液相滴注-熔融法载硫制得S/Ti₃C₂T_x复合正极材料。结果表明，下首次放电容量达，圈后容量为，单圈衰减率为，具有良好的可逆性、长循环性能和较低的阻抗。分析认为，发达的孔隙提供了硫单质的负载空间；丰富的表面官能团与Ti活性位点有效地吸附了硫颗粒；自支撑网络结构缓解了体积膨胀并为Li 的嵌入/脱嵌过程提供更多的通道，因此表现出优异的电化学性能。

使用Ti₃C₂T_x MXene进行隔膜改性与S-Ti₃C₂T_x制备正极，测试结果表明，下首次放电容量为，圈后比容量为，单圈衰减率为，具有良好的电化学性能。通过分析，Ti₃C₂T_x MXene改性隔膜层充当内部集流体并以物理、化学吸附方式显著地抑制了穿梭效应，因此显示出优异的电化学性能。

关键词：锂硫电池 Ti₃C₂T_x MXene 泡沫 隔膜改性 电化学性能

Fabrication and performance of composite cathode for lithium-sulfur battery based on Ti₃C₂T_x (MXene)

ABSTRACT

Lithium-sulfur (Li-S) batteries are preferable due to their high theoretical specific capacity and energy density, low cost and environmental-friendly characteristics. However, due to the near-insulation of elemental sulfur and the shuttle effect and volume expansion of the active material lithium polysulfide, the performance of the lithium-sulfur battery is greatly impaired. MXene is a new two-dimensional material with unique structure, excellent electrical conductivity, rich surface chemical environment and hydrophilicity, so it is expected to effectively alleviate the problems faced by current lithium-sulfur batteries. In addition, the three-dimensional network structure can provide a large active sulfur loading space and ion diffusion channels. Therefore, this study considers the preparation of three-dimensional porous Ti₃C₂T_x MXene foam as a sulfur carrier, and uses Ti₃C₂T_x MXene to modify the membrane.

In this paper, a new, safe and efficient HCl-LiF corrosion etchant is used to etch Ti₃AlC₂ precursor, and Ti₃C₂T_x concentrated ink is obtained by one-step intercalation and delamination. A three-dimensional porous Ti₃C₂T_x foam having a specific surface area of 42.8 m²/g was obtained by using HCl-induced self-assembly-freeze drying treatment. As a carrier, S/Ti₃C₂T_x composite cathode was obtained by liquid phase instillation-melting method. The results show that the initial discharge capacity at 1C is 1128 mAh/g. After 800 cycles, the specific capacity is maintained at 732 mAh/g, the capacity retention rate is 64.89%, and the single-circle attenuation rate is 0.054%, which has good reversibility, long cycle performance and low impedance. It is concluded that the developed pore provides the loading space for sulfur; the abundant surface functional groups and Ti active sites effectively adsorb sulfur particles; the self-supporting network structure alleviates the volume expansion and provides more channels for the Li embedding/de-embedding process, thus exhibiting excellent electrochemical performance.

Ti₃C₂T_x MXene was used for membrane modification and S-Ti₃C₂T_x was used to prepare the positive electrode. The test results showed that the initial discharge capacity was 1203 mAh/g at 1C, and the specific capacity was maintained at 1013 mAh/g after 400 cycles. The capacity retention rate was 84.27%. The single-circle attenuation rate is 0.043%, which has good electrochemical performance. Through analysis, Ti₃C₂T_x MXene modified diaphragm acts as internal collector and significantly inhibits shuttle effect by physical and chemical adsorption, thus showing excellent electrochemical performance.

KEYWORDS: Lithium-sulfur battery; Ti₃C₂T_x MXene; foam; membrane modification; 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 1

1.2.1 工作原理 1

1.2.2 存在的问题 2

1.3 锂硫电池正极材料研究进展 3

1.3.1 一维结构材料 3

1.3.2 二维结构材料 5

1.3.3 三维结构材料 7

1.4 锂硫电池隔膜研究进展 10

1.5 二维过渡族金属碳（氮）化物 (MXene) 研究现状 12

1.5.1 MXene的简介 12

1.5.2 MXene的制备 12

1.5.3 MXene的结构与性能 14

1.5.4 MXene的应用 15

1.6 课题的提出与研究内容 17

第二章 实验 18

2.1 实验原料 18

2.2 实验设备 18

2.3 材料制备过程 19

2.3.1 技术路线 19

2.3.2 少层/单层Ti₃C₂T_x MXene的制备 20

2.3.3 Ti₃C₂T_x泡沫的制备 20

2.3.4 S/Ti₃C₂T_x泡沫的制备 20

2.3.5 Ti₃C₂T_x MXene改性隔膜的制备 20

2.3.6 锂硫电池的组装与电化学性能测试 21

2.4 材料表征 21

2.4.1 X射线衍射表征 21

2.4.2 扫描电子显微表征 21

2.4.3 透射电子显微表征 22

2.4.4 原子力显微表征 22

2.4.5 比表面积表征 22

2.4.6 热重分析 22

2.4.7 Zeta电位表征 22

2.4.8 电导率测试 22

2.5 电化学性能测试 23

2.5.1 恒流充放电性能测试 23

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