摘 要

电极材料作为高能化学储能器件的核心部件，决定着电池的各项性能指标、成本及应用前景。因此，对电极材料的研究是提高高能化学储能器件性能的关键。V₂O₅作为传统锂离子电池的电极材料已经被广泛研究。近年来对V₂O₅电极材料性能的改进一直是锂离子电池领域研究的热点与前沿之一。本论文结合五氧化二钒的结构特点，采用溶胶凝胶法结合冷冻干燥法对五氧化二钒进行Mo掺杂制备Mo_xV_2-xO_{5 y}二维纳米材料，通过控制Mo的掺入量来控制Mo_xV_2-xO_{5 y}纳米材料的结构，进而调节该纳米材料的各项基本性能。并且对不同Mo掺入量的Mo_xV_2-xO_{5 y}纳米材料进行结果和性能的分析，以此确定Mo_xV_2-xO_{5 y}纳米材料的电化学性能以及形成机理。主要的研究内容与结果如下：

利用XRD、FESEM、TEM等测试方法对Mo_xV_2-xO_{5 y}纳米材料的微观结构、形貌进行表征。通过XRD表征发现掺杂后的V₂O₅样品中V₃O₇的存在。在样品的FESEM图像中可以清楚的看到大面积的二维薄片状结构，这种二维薄片结构的形成大大提高了V₂O₅的表面活性，使得锂离子更容易嵌入和脱出有利于充放电过程中锂离子的传输。对样品的TEM图像分析发现Mo_xV_2-xO_{5 y}晶体沿着多种不同的方向生长，这可能就是样品中大量二维薄片状结构产生的原因。另外还采用了XPS和FTIR对样品进行测试。分析纳米材料的界面价键状态及材料表面的原子分布状态，探讨MoO₃对材料结构所产生的影响。

利用循环伏安法（CV）和恒流充放电测试对样本的电化学性能进行了测试分析。研究发现相比于五氧化二钒Mo_0.04V_1.96O_{5 y}中锂离子嵌入/脱出的更快而且Li 扩散的量更大，而且结果还显示Mo_0.04V_1.96O_{5 y}具有更高的比容量。通过电化学测试，研究模拟电池在不同充放电倍率下的比容量和循环稳定性。在相同的循环次数下Mo_0.04V_1.96O_{5 y}具有高的可逆容量保持率以及更好的倍率性能。而且在循环充放电过程中Mo_0.04V_1.96O_{5 y}还显示出较好的稳定性。

关键词：冷冻干燥、五氧化二钒、电化学性能、掺杂

Abstract

Electrode material, as a core department of high-energy-saving equipment, decides various parameter of the equipment, such as experiment performance, electrochemical properties, the cost, and potential application. Therefore, studying Electrode material as well as overcome it’s limitation is the key to improve the performance of high-energy-saving equipment. As a traditional Electrode material for Lithium Ion Batteries (LIBs), V₂O₅ has been studied over decades. Recently, improving the performance of V₂O₅ Electrode material is a hot topic in the field of Lithium Ion Batteries (LIBs). In this work, combining of the structure of V₂O₅, we successfully synthesized the V₂O₅ nanosheets doped by MoO₃ (Mo_xV_2-xO_{5 y}) by using sol-gel method combined with freezing-drying process. In this synthesizing process, we control the structure of Mo_xV_2-xO_{5 y} two-dimension nanomaterial by changing the quality of Mo, and thus, change various basic properties of the nanomaterial. Meanwhile, we analyzed the experiment data of Mo_xV_2-xO_{5 y} nanomaterial with different quality of doped Mo. In this way, we can understand the electrochemical property and formation mechanism of Mo_xV_2-xO_{5 y} nanomaterial:

In our study, the micro-structures and morphology of Mo_xV_2-xO_{5 y} were characterized by XRD, TEM and FESEM analysis. As a result, by analyzing the XRD, the Mo_xV_2-xO_{5 y} can be indexed to an orthorhombic V₂O₅ phase. Besides that, we also fund the V₂O₇ phase in our doped V₂O₅ sample. The FESEM picture show a obvious two-dimensional layered structure, and this structure significant improve the surface activity of V₂O₅, and thus, make the transition of lithium ion in the charge/discharge process easier. The TEM picture show crystal Mo_xV_2-xO_{5 y} grow in different direction, which can explain a obvious two-dimensional layered structure of the Mo_xV_2-xO_{5 y} sample. In order to investigate the atom distribution of the nanomaterial’s surface, the doping of MoO₃ was also confirmed by the XPS and FTIR analysis. Based on the characterization we discuss above, we could study the influence on the structure of material resulted from doping MoO₃.

Furthermore, the electrochemical performance was characterized by the cyclic voltammetry (CV), and galvanostatic discharge/charge cycling analysis. Comparing with V₂O₅, the Li of Mo_0.04V_1.96O_{5 y} sample can insert and extract faster and also have better diffusible capacity. Moreover, the result shows that the Mo_0.04V_1.96O_{5 y} sample have higher specific capacity. The electrochemical test indicates the specific capacity and cycle stability of simulated battery at different current density. After the same cycle times, Mo_0.04V_1.96O_{5 y} possess higher the cycle reversible capacity retention rate and better rate capability. Moreover, during the charge-discharge process, Mo_0.04V_1.96O_{5 y} show excellent cycle stability.

Key words: freezing-drying, Mo_xV_2-xO_{5 y}, electrochemical performance, doping

目 录

第1章 绪论 1

1.1前言 1

1.2锂离子电池电极 2

1.2.1锂离子电池电极 2

1.2.2 锂离子电池正极材料 4

1.3 氧化钒电极材料 5

1.4本文研究的主要内容及可行性 8

1.4.1 本文研究的主要内容 8

1.4.2本研究的可行性 9

第2章 Mo_xV_2-xO_{5 y}纳米材料的制备 10

2.1 实验内容 10

2.2 实验原料及仪器 10

2.3 实验过程 10

2.4 结构及性能表征方法 11

2.4.1 结构分析 11

2.4.2 电化学性能测试 11

第3章 Mo_xV_2-xO_{5 y}纳米材料的结构及性能分析 12

第4章 结论 21

参考文献 22

致谢 25

第1章 绪论

1.1前言

为了满足社会的发展和进步，上世纪人类对传统能源（化石能源等）进行了破坏性的开采，使得人类早早的陷入了能源危机，传统能源的使用导致的温室效应以及空气污染已经严重的危及到了人类的生存。传统能源的枯竭问题以及日益严重的气候变暖问题也得到了世界各国人民的重视。进入21世纪以来能源问题和环境问题已经成为人类必选面对的两个最严峻的问题。煤炭、石油、天然气等传统的能源材料，具有污染大、不可重复利用、成本高、利用率低、有限性和生态破坏等缺点，已经不再适应当前社会发展的需要。人们不得不把目光集中于可再生和可持续的清洁能源的开发和使用。近些年来人类开始将目标转向可再生的能源如风能、太阳能以及地热能上，但是这三种能源的利用存在很大的局限性例如风能不能随时随地的为人们所使用，太阳能不能持续的供能，地热能又只能在特定的地方产生。要想很好的开发和利用这些能源我们必须设计一种满足需求的能量存储系统，将多余的能量储存起来，便于我们的使用。