摘 要

锂资源的短缺以及其昂贵的价格限制着锂离子电池在大规模能源存储中的应用，钠离子电池因其成本低等优势有望成为锂离子电池的替代品。然而，由于钠离子相对于锂离子具有较大的半径，这对电极材料提出了更高的要求。目前，最具应用潜力的钠离子正极材料Na₃V₂(PO₄)₃受限于其较低的比容量和不高的电压平台，能量密度难以满足应用的需求。因此，钠离子电池的发展迫切需要开发高能量密度的正极材料。

本文进行了对钠离子正极材料的探索，展开了对Li₃V₂(PO₄)₃作为钠离子电池正极材料的研究。并取得了以下成果：

（1）成功合成了Li₃V₂(PO₄)₃以及具有不同复合形式的Li₃V₂(PO₄)₃/石墨烯复合材料，构筑了三维石墨烯网络框架包裹Li₃V₂(PO₄)₃纳米颗粒的结构。

（2）通过电化学拓扑取代实现了钠离子在Li₃V₂(PO₄)₃中的可逆嵌入和脱出，并探究了Li₃V₂(PO₄)₃的储钠性能。优化后的Li₃V₂(PO₄)₃材料实现了501.2 Wh kg^-1的能量密度，高于绝大多数已报道的聚阴离子型钠离子电池正极材料。

（3）通过优化电压区间，Li₃V₂(PO₄)₃复合材料展现出优秀的倍率性能（1000 mA g^-1的电流密度下，仍然有66 mAh g^-1的放电容量）以及循环稳定性（500次充放电循环后，容量保持率为65.0%）。

（4）通过原位XRD等技术对Li₃V₂(PO₄)₃的储钠机制进行了初步研究。Li₃V₂(PO₄)₃作为钠离子电池正极材料的储钠过程可分为两个过程，首次充放电的电化学拓扑取代过程以及随后循环的钠离子可逆嵌入/脱出过程。

关键词：钠超离子导体；Li₃V₂(PO₄)₃；钠离子电池；机制

Abstract

The application of lithium-ion batteries (LIBs) in large-scale energy storage systems (ESSs) has been restrained by the limited reserve and exorbitant price of lithium. Sodium-ion batteries (SIBs) have been investigated as the replacement of LIBs due to their low cost. However, the radius of sodium-ions is larger than that of lithium-ions, putting forward the higher requirement for electrode materials. Recently, Na₃V₂(PO₄)₃ has been considered as the most promising cathode material for SIBs. However, it has been contained by its limited capacity and medium potential plateau, resulting in low energy density which is difficult to meet the needs of application in ESSs. Thus, the development of SIBs is urgent need to exploit high energy density cathode materials.

Herein, the research of cathode materials for SIBs has been carried out, and Li₃V₂(PO₄)₃ has been investigated as cathode materials for SIBs. The obtained results are as following:

(1) The Li₃V₂(PO₄)₃ and Li₃V₂(PO₄)₃/graphene composite with different composite type have been successfully synthesized and the structure of three-dimensional graphene framework wrapped Li₃V₂(PO₄)₃nanoparticles has been obtained.

(2) The reversible sodium-ion insertion/extraction in lithium ion sites of LVP has been realized via an electrochemical topotactic replacement method. Moreover, the electrochemical performance of Li₃V₂(PO₄)₃ as cathode materials for SIBs has been investigated for the first time. The modified Li₃V₂(PO₄)₃ achieved a high energy density of 501.2 Wh kg^-1, and higher than those of most polyanionic compound cathodes for SIBs.

(3) After optimizing the potential range, the modified Li₃V₂(PO₄)₃ exhibits excellent rate performance (66 mAh g^-1 at 1000 mA g^-1) and cycling stability (capacity retention of 65.0% after 500 cycles).

(4) Based on the in-situ XRD technology and so on, the sodium-storage mechanism of Li₃V₂(PO₄)₃ has been investigated systematically. The sodium-storage process of Li₃V₂(PO₄)₃ can be divided into two processes, the electrochemical topotactic replacement occurs in the first charge/discharge process and the reversible insertion/extraction of sodium-ions takes place in the subsequent cycling process.

Key Words: NASICON; Li₃V₂(PO₄)₃; sodium-ion battery; mechanism

目 录

摘要 I

Abstract II

第1章 绪论1

1.1 引言1

1.2 钠离子电池简介1

1.3.1 钠离子电池的结构及工作原理1

1.3.2 钠离子电池面临的挑战2

1.3 钠超离子导体结构M₃V₂(PO₄)₃ (M=Li, Na)3

1.3.1 钠超离子导体结构3

1.3.2 M₃V₂(PO₄)₃ (M=Li, Na)在钠离子电池中的应用4

1.4 本文研究内容及意义5

第2章 Li₃V₂(PO₄)₃及其复合材料的制备与形貌、结构表征6

2.1 实验原料及仪器6

2.1.1 实验原料6

2.1.2 实验仪器6

2.2 Li₃V₂(PO₄)₃及其复合材料的制备7

2.2.1 Li₃V₂(PO₄)₃的制备7

2.2.2 Li₃V₂(PO₄)₃/石墨烯复合材料的制备7

2.3 Li₃V₂(PO₄)₃及其复合材料的形貌与结构表征8

2.3.1 表征技术8

2.3.2 表征结果及分析9

2.4 本章小结13

第3章 Li₃V₂(PO₄)₃及其复合材料的储钠性能与机制14

3.1 扣式电池的组装与测试方法14

3.1.1 扣式电池的组装方法14

3.1.2 扣式电池的测试方法14

3.2 Li₃V₂(PO₄)₃及其复合材料的储钠性能14

3.2.1 较大电压区间的储钠性能14

3.2.2 电压区间优化后的储钠性能15

3.3 钠超离子导体结构的储钠机制17

3.4 钠超离子导体结构的结构性能相关性19

3.5 本章小结19

第4章 结论与展望21

4.1 结论21

4.2 展望21

参考文献22

致谢25

第1章 绪 论