论文总字数：21518字

摘 要

经济的高速增长导致人们对能源的需求越加迫切。锂空气电池因其高达3500 Wh kg^-1的优秀理论比功率密度成为储能领域的研究焦点。目前对锂空气电池的研究处于探索阶段，离商业化目标还需攻克许多难题，提高电池倍率性能与循环效率、改良电解质与电极材料都是亟待解决的问题。其中，放电产物Li₂O₂难以分解导致充电过程电池极化大，大大降低了电池的循环性能，而且金属Li负极经空气中H₂O、CO₂的腐蚀会产生安全隐患。因此本实验选择以纯氧作为电池工作环境，即锂氧电池。本文通过对正极材料催化剂的研究，使锂氧电池循环性能大大提升。本文围绕高性能正极催化剂材料，创新地提出使用电化学沉积法直接在碳布上原位生长Co₃O₄纳米片，获得了自支撑的3D立体框架结构，并将其应用于锂氧电池正极材料。一般来说正极材料的设计需用到催化剂、导电剂、粘结剂和集流体碳纸，而具有自支撑的Co₃O₄纳米片结构的正极材料不需要添加导电剂、粘结剂以及集流体碳纸，一方面减少了电池充放电过程中导电剂和粘结剂可能带来的副反应；另一方面降低了正极材料制备过程中的繁琐程度，有益于商业化应用。

电沉积之后再经过煅烧，成功制备了以碳布为基底的Co₃O₄纳米片，经过SEM与XRD表征得出Co₃O₄以纳米结构均匀生长在碳布上。通过锂氧电池首圈充放电性能对比，Co₃O₄纳米片充放电极化较碳布很小，而碳布极化非常高，性能很差，说明Co₃O₄纳米片对放电产物Li₂O₂的分解具有良好的催化作用。在电池循环性能表征中，Co₃O₄纳米片也表现出了比碳布更为稳定的循环性能。

关键词：锂氧电池 正极 电沉积 纳米结构 钴基催化剂

ABSTRACT

The rapid economic growth has led to an increasing demand for energy. Lithium-air batteries have become the focus of research in the field of energy storage due to their excellent theoretical specific energy density of up to 3500 Wh kg^-1. At present, the research on lithium-air battery is in the exploratory stage. It is still necessary to overcome many problems from the commercialization goal. Improving battery rate performance and cycle efficiency, and improving electrolyte and electrode materials are all urgent problems to be solved. Among them, the discharge product Li₂O₂ is difficult to decompose, resulting in large polarization of the battery during charging, which greatly reduces the cycle performance of the battery, and the corrosion of the Li metal negative electrode through H₂O and CO₂ in the air will cause safety hazards. Herein, the lithium-oxygen batteries in this study were operated under pure oxygen working environment. It was found that the cycling performance of lithium-oxygen battery can be improved by optimizing the cathode catalyst.

In this work, we mainly focus on the fabrication of the high-performance cathode catalyst. For example, Co₃O₄ nanosheets were in situ grown on carbon cloth by electrochemical deposition. The self-supporting 3D stereo framework was obtained and applied as the oxygen cathode for lithium-oxygen battery. Generally, the oxygen cathode is composed of a catalyst, a conductive matrix, a polymer binder, and a current collector of carbon paper. Note that a binder-free and self-standing oxygen cathode was fabricated based on Co₃O₄ nanosheets and carbon cloth, which does not require the addition of conductive agent, binder, and current collector. In this case, the side reaction resulted from the conductive agent and the binder can be efficiently suppressed upon cycling. Meanwhile, the oxygen cathode prepared by electro-chemical deposition is simple and cost-competitive, which is beneficial to large scale commercial applications.

After electrodeposition and calcination, Co₃O₄ nanosheets in situ grown on carbon cloth were successfully prepared. The SEM and XRD showed that Co₃O₄ was uniformly grown on carbon cloth with sheet-like nanostructure. Through the comparison of the charge and discharge performance of the first cycle of the lithium-oxygen battery, the charge and discharge polarization of the Co₃O₄ nanosheet are both smaller than that of the carbon cloth. The polarization of the carbon cloth is very high and the performance is very poor, indicating that the Co₃O₄ nanosheet has a good catalytic effect on the decomposition of the discharge product Li₂O₂. For battery cycling performance test, Co₃O₄-nanosheet deposited carbon cloth also showed more stable cycling stability than carbon cloth.

KEYWORDS: lithium-oxygen battery; positive electrode; electrodeposition; nanosheets; cobalt-based catalyst

目录

摘要 I

ABSTRACT II

第1章前言 1

1.1选题背景及研究意义 1

1.2锂氧电池概要 2

1.2.1锂氧电池发展历程 2

1.2.2锂氧电池的优势 2

1.2.3锂氧电池的工作原理 3

1.3锂氧电池存在的问题 6

1.4正极催化剂 7

1.4.1碳材料 7

1.4.2贵金属 8

1.4.3过渡金属氧化物 8

1.5本论文内容及研究意义 9

第2章实验部分 10

2.1实验试剂及实验设备 10

2.2正极材料制备与电池组装 11

2.2.1电化学沉积法制备Co₃O₄纳米片 11

2.2.2制备正极材料 12

2.2.3锂氧电池的组装 12

2.2.4锂氧电池的拆解 13

第3章实验结果与讨论分析 14

3.1催化剂需要的材料表征 14

3.1.1 X射线衍射测试（XRD） 14

3.1.2 扫描电子显微镜（SEM） 15

3.2锂氧电池电化学性能方法及测试 16

3.2.1恒电位沉积测试 16

3.2.2循环伏安法（Cyclic Voltammetry, CV） 16

3.2.3 锂氧电池首圈充放电性能测试 17

3.2.4锂氧电池在不同电流密度下首圈充放电性能测试 17

3.2.5锂氧电池在不同电流密度下倍率容量测试 19

3.2.6 电池放电产物XRD测试 19

3.2.7电池阻抗测试（Electrochemical Impedance Spectroscopy, EIS） 20

3.2.8锂氧电池充放电循环性能测试 21

3.3实验结论 22

3.4展望 22

参考文献 24

第1章前言

1.1选题背景及研究意义

当前经济高速发展使储能问题日益凸显。人口数量的爆炸增长和第三次工业革命的快速推进导致人们对能源的需求越来越迫切。预计2040年能耗量较现在将增长56%^[1]。在此背景下传统化石能源需求量连年增长，越来越多的可再生能源与核能也进入供能行列。发展可再生能源能大大降低温室气体的排放，有益经济的可持续发展，但同时也提高了对储能材料的要求。对比化石能源，大批量存储是对可再生能源使用的基本要求。电网供电大批量储能商业化还需要时间，但是运输领域的商业需求越来越迫切。电动汽车作为未来交通工具其发展瓶颈就在于低成本，高能量密度的储电装置。

锂离子电池因较高的能量密度成为过去二十年间电子设备的储能首选。但在漫长的发展历程中，锂离子电池的能量密度提升工作进展缓慢，离电动汽车商业化还有很长距离。电极材料是提升电池能量密度的重要因素。提升电池能量密度可以从正负极材料入手，设计具有高容量且低电压的负极材料和高电压的正极材料均能提高电池性能，而正极材料设计难度高，也是提升锂离子电池能量密度的关键。锂离子电池能量密度极限为250 Wh kg^-1[2],距700 Wh kg^-1内燃机要求相差甚远。在此现状下，电动汽车的商业化只能依赖对高功率密度新型电池的研究，例如锂氧电池和锌空电池。锌空电池充放电过程中存在过电压的问题，尽管其理论比能量密度高达1350 Wh kg^-1，但只有50%的能量效率制约了锌空电池的实际应用。

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