论文总字数：24066字

摘 要

为了加快经济的发展，人们大力开发与利用能源。传统能源，如石油、煤炭等，在全球的储量日渐减少，且其燃烧易造成环境的破坏。某些清洁能源，如太阳能、潮汐能等，缺乏稳定供能和持续供能的能力。如此，研发可存储的清洁能源显得尤为重要。其中，锂离子电池的高速发展和成功地商业化，向大众证明了二次电池的活力和潜力。但随着锂离子电池的应用推进，锂元素资源短缺的问题日益突显，人们开始尝试其他电池来代替锂离子电池。而钠离子电池由于与锂离子电池工作原理类似，且钠资源储量丰富，促使钠离子电池逐渐成为研究热点。

钠离子与锂离子电池虽然工作原理类似，但仍旧存在区别。钠离子由于其半径大于锂离子的半径，而加大了钠离子电池的正负极材料选择的难度。不同正负极材料对阳离子的接纳程度不同，进而会影响电池的可逆容量，所以现在有关钠离子电池的研究重点在于对其电极材料的合理改性，来提高钠离子电池各个方面的性能。磷酸氧钒原本作为锂离子电池的正极材料，在嵌锂和脱锂过程中都展示出其特殊层状结构的优势。但是，由于钒含有的毒性会对人体造成损害，该材料在实际生产应用中会受到一定限制。为了减少电池中钒的含量，本论文尝试通过掺杂铁离子取代部分的钒离子。同时，铁的化合物价格更加低廉，又可以降低材料制备的生产成本。本文围绕于VOPO₄（以下简称VOP）的改性展开，尝试通过在其结构中掺杂铁离子代替部分钒。

本文涉及两种材料制备。第一种是制备磷酸氧钒VOP材料，其目的是获取物化性能作为实验的对照组，用以判断掺杂前后对结构的影响。我们以五氧化二钒和磷酸分别作为钒源和磷源，在浓硝酸的催化作用下，通过加热回流制备磷酸氧钒材料。第二种是使用加热回流的方法制备掺杂铁离子的[Fe(H₂O)]_0.20(VO)_0.80PO₄·2H₂O（以下简称FeVOP）材料。我们采用九水合硝酸铁作为铁源，为VOP材料以1:0.3的Fe/V摩尔比掺杂铁离子。对制得VOP和FeVOP的进行形貌分析，我们发现改性前后材料依旧保持片层结构，但掺杂后的FeVOP结构更偏向碎片化，从而提高了电极材料的比表面积，提高了离子迁移率。将制得的FeVOP材料配制成正极浆液，干燥后组装为钠离子电池，再进行电化学测试。研究发现在充放电过程中，FeVOP材料的充电平台和放电平台分别在3.74V左右和3.30V左右。其充放电平台符合V⁴ /V⁵ 氧化还原对，说明了钠离子实现在FeVOP结构中的可逆脱嵌。该材料在50mA·g^-1的电流密度下，1.5~4.3V电压范围的首次充电比容量为102.6mAh·g^-1。其在0.2C、1C、2C和5C倍率下的可逆比容量分别为115.8mAh·g^-1、74.6mAh·g^-1、62.5mAh·g^-1和46.1mAh·g^-1。通过比较两种样品的形貌表征和电化学性能，我们发现掺杂铁离子后未对材料的晶型造成改变，仅缩小了晶格间距，但仍保持原本的倍率性能和循环性能。

关键词：钠离子电池 正极材料 铁离子掺杂 磷酸氧钒

Study on cathode material of sodium ion battery modified with vanadium phosphate

Abstract

In order to speed up economic development, people vigorously develop and use energy. The reserves of traditional energy, such as oil and coal, are decreasing all over the world, and their combustion is easy to cause environmental damage. Some clean energy sources, such as solar and tidal energy, lack the ability of stable and sustainable energy supply. In this way, it is very important to research and develop the storable clean energy. Among them, the rapid development and successful commercialization of lithium-ion batteries prove the vitality and potential of secondary batteries to the public. However, with the development of lithium-ion batteries, the shortage of lithium resources has become increasingly prominent. People began to try other batteries to replace lithium-ion batteries. Sodium ion battery has become a research hotspot because of its similar working principle and abundant sodium resources.

The working principle of sodium ion and lithium ion battery exhibit similar, but they still exist differences. Because the radius of sodium ion is larger than that of lithium ion, it is more difficult to select the anode and cathode electrode materials of sodium ion battery. Different anode and cathode materials have different degrees of acceptance about cations, which will affect the reversible capacity of the battery. Therefore, the current research on sodium ion battery focuses on the reasonable modification of its electrode materials to improve the performance of various aspects of sodium ion battery. Vanadium oxyphosphate was originally used as the cathode material of lithium-ion batteries. It showed the advantages of special layered structure in the process of lithium intercalation and deintercalation. However, due to the toxicity of vanadium will cause damage to people, the material will be limited in practical production and application. In order to reduce the content of vanadium, this paper attempts to replace some vanadium ions by doping iron ions. At the same time, the compound of iron is cheaper, and the production cost of material preparation can be reduced. This paper focuses on the modification of VOPO₄ (hereinafter referred to as VOP), and tries to explore the change of material structure and properties by doping iron ions in its structure.

This paper dealt with two times of material preparation. The first one was the preparation of VOP material, which aimed to obtain the physical and chemical properties as the experimental control group to judge the influence of doping on the structure. Vanadium pentoxide and phosphoric acid were used as vanadium and phosphorus sources respectively. Under the catalysis of concentrated nitric acid, vanadium oxyphosphate materials were prepared by heating and reflux. The second was the Fe doping of VOP materials(hereinafter referred to as FeVOP) ,using the method of heating reflux.We used ferric nitrate nine hydrate as the iron source and doped iron ions with 1:0.3 Fe / V mole ratio as VOP material. Through the morphology analysis of VOP and FeVOP, we found that the structure of FeVOP remained the lamellar structure before and after the modification, but the FeVOP structure after doping was more fragmented, which improved the specific surface area of the electrode material and the ion mobility. The prepared FeVOP material was prepared into positive slurry, dried and assembled into sodium-ion battery, and then electrochemical test was carried out. It is found that the charging platform and discharge platform of FeVOP are about 3.74V and 3.30V respectively. The charging and discharging platform is in accordance with V⁴ /V⁵ redox pair, which shows that sodium ion could realize reversible deblocking in FeVOP structure. Under the current density of 50mA·g^-1, the first charge specific capacity of the material in the voltage range of 1.5 ~ 4.3V is 102.6mAh·g^-1. The reversible specific capacity at the rate of 0.2C,1C,2C and 5C are 115.8mAh·g^-1,74.6mAh·g^-1,62.5mAh·g^-1 and 46.1mAh·g^-1 respectively. By comparing the morphology and electrochemical properties of the two samples, we found that doping iron ions did not change the crystal form of the material, only reduing the lattice spacing, but still maintained the original rate performance and cycling performance.

Key Word: Sodium-ion battery; cathode material; Iron dope; VOPO₄·2H₂O

目 录

摘要 I

ABSTRACT III

第一章 绪论 1

1.1 引言 1

1.2 钠离子电池简介 2

1.2.1 发展历史 2

1.2.2 研究重点 2

1.3正极材料 3

1.3.1 聚阴离子化合物 3

1.3.2 过渡金属氧化物 4

1.3.3 普鲁士蓝类化合物 5

1.4 磷酸氧钒正极材料 6

1.4.1 磷酸氧钒的简介 6

1.4.2 磷酸氧钒的优缺点 7

1.4.3 磷酸氧钒的研究进展 7

1.5本课题的研究内容 7

第二章 实验部分 8

2.1实验药品和仪器 8

2.1.1 实验药品 8

2.1.2 实验仪器 8

2.2 实验部分 9

2.2.1 VOPO₄·2H₂O（以下简称VOP）的制备 9

2.2.2 [Fe(H₂O)]_0.20(VO)_0.80PO₄·2H₂O（以下简称FeVOP）的制备 9

2.3 材料表征方法 10

2.3.1 X射线衍射分析（XRD） 10

2.3.2 扫描电子显微镜（SEM） 10

2.4 电极制备与电池组装 10

2.4.1 电极制备 10

2.4.2 电池组装 10

2.5 电化学性能测试 11

2.5.1 循环性能测试 11

2.5.2 倍率性能测试 11

第三章 结果与讨论 12

3.1 引言 12

3.2 物理表征 12

3.2.1 材料形貌研究 12

3.2.2 晶体结构分析 13

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