摘 要

目前的通信、各式电子仪器、电力汽车和空间科技等领域迅猛发展，对电池的性能要求越来越高。因此，发展高比容量、成本低和环保型的新锂离子电池具有重大意义。锂离子电池系统的各部份组成中，正极材料向来是影响电池发展的重要因素。传统的基于过渡金属氧化物的锂离子电池正极材料由于其理论的锂储存容量限制，难以取得快速进展。近来，可充电Li-S电池因其高理论比能量密度优势而受到极大的关注。Li-S电池作为下一代的能量存储系统，特别是适用于大规模应用。实现这种高能量密度的障碍主要包括正极材料硫的绝缘性，硫与电解液浸润性差和循环时的穿梭效应导致的快速容量衰减。

为了改善以上问题,本文设计了一步法合成微孔碳材料的方法。此碳基材料利用于锂硫电池的正极材料硫单质的载体物质，以达到增强正极材料中硫单质的导电性的目的。此外，我们通过利用磷酸氢氨作为掺杂源掺杂N,P元素引入极性化学键提高了上述碳材料表面的极性，以实现碳材料对电解液的更好浸润性。这种碳材料平均孔径只有0.41nm，这种微孔小尺寸（＜0.7nm），可产生物理限域效应，使得低于0.7nm的微孔能够抑制短链硫的转移，因此能够抑制“穿梭效应”。本文的另一个独特优势在于用一步法合成碳材料，合成方法简便，成本相对较低，便于工业化生产。为了验证该碳材料用于锂硫电池的性能优势，我们用该碳硫复合材料和纯硫材料分别组装成扣式电池并在进行了充放电测试。测试结果表明碳硫复合材料电池0.1C下首圈放电容量达1492mAh/g，0.5C下150圈后比容量剩余570mAh/g，库伦效率接近100％。而纯硫电池0.5C下首圈容量只有570 mAh/g，48圈后电池完全失效。

关键词：锂硫电池；微孔碳材料；氮磷掺杂

Abstract

Current communications, various electronic devices, electric vehicles and space technology are rapidly developed, and the requirements for high performance batteries are becoming more and more urgent. Thus it is of great significance to develop new lithium-ion batteries (LIBs) with high specific capacity, low cost and environmentally friendliness. In lithium-ion battery systems, cathode materials are always crucial to develop high performance LIBs. Due to their theoretical lithium storage capacity limitation, conventional transition metal oxide based cathode materials have made it difficult for applications in LIBs. Recently, rechargeable Li-S batteries have increasing attention due to their high theoretical specific energy density, which is three to five times higher than that of intercalation-based Li-ion batteries. Li-S batteries are promising for large scale used as next-generation energy storage systems. Obstacles to achieve this high energy density include high internal resistance, fast capacity decay due to shuttle effect during self-discharge and cycling.

In order to improve the above problems, in this thesis, we design a one-step synthesis of microporous carbon materials. The prepared carbon-based material is used for a carrier material of a single element of sulfur as a positive electrode material of a lithium-sulfur battery to enhance the conductivity of sulfur in the positive electrode material. In addition, N doping is performed by using ammonia hydrogen phosphate as a N source, and the introduction of polar chemical bonds by the P element increases the polarity of the surface of the above carbon material to achieve better wettability of the carbon material to the electrolyte. The average pore diameter of this carbon material is only 0.41 nm. The small size (lt;0.7 nm) of the micropores can produce a physical confinement effect, so that can inhibit the transfer of short-chain sulfur, thus inhibiting "shuttle effect". Another unique advantage of this work is the one-step synthesis of carbon materials, which is simple, relatively low cost, and convenient for industrial production. In order to verify the performance advantages of the carbon material for lithium-sulfur batteries, we further assemble the carbon-sulfur composite material and the pure sulfur material into button-type batteries, respectively, and tested them in charge and discharge processes. The results show that the carbon-sulfur composite battery has a discharge capacity of 1492 mAh/g in the first cycle at 0.1 C, a residual capacity of 570 mAh/g after 150 cycles at 0.5C, and the Coulomb efficiency is close to 100%. In contrast, the pure sulphur battery has a capacity of only 570 mAh/g at 0.5C, and completely fails after 48 cycles.

Key Words：Lithium-sulfur battery；Microporous carbon material; Nitrogen and phosphorus doping

目 录

第1章 绪论 1

1.1 引言 1

1.2 锂硫电池的现状及发展 1

1.2.1 锂硫电池的基本原理 1

1.2.2 硫正极容量损失及衰减机理 4

1.2.3 硫正极性能提高 5

1.3 锂硫电池负极和电解液的简单介绍 6

1.4 本文的研究目的与内容 6

第2章 氮磷掺杂微孔碳材料的制备及其表征 8

2.1 引言 8

2.2实验试剂与设备 8

2.3 氮磷掺杂微孔碳材料的制备 10

2.4 材料表征 10

2.5 结果与讨论 11

第3章 氮磷掺杂微孔碳材料在锂硫电池中的应用与性能分析 16

3.1 引言 16

3.2 电池组装与性能测试 16

3.2.1 碳/硫复合材料正极片的制备 16

3.2.2 扣式电池的组装 16

3.2.3 电化学性能测试 16

3.3 结果与讨论 17

第4章 总结 20

参考文献 21

致谢 24

附录1 25

附录2 26

第1章 绪论

1.1 引言

经过二十年的优化，锂离子电池（LIB）正在接近插层材料所允许的能量密度瓶颈，约为300 mAh g^-1。 目前，LIB不能为纯电动车辆（PEV）提供适当长的行驶里程（即gt; 300km），并且它用于插电式混合动力电动车辆（PHEV）也有限制。可再生能源的负载水平还需要提高，高能量密度和廉价的能量存储系统需要发展。我们正在寻找新一代电池系统，以实现更高的能量密度和更低的生产成本。毫无疑问，这些将超越嵌入化学进入“整合”化学领域，实现电极的放电/电荷与氧化还原过程中的共价键的裂解/形成以及形态/结构动力学相结合。实例包括为锂空气电池^[1] 和锂硫电池体系中正在发生的的电化学相关反应。

Herbet 和Ulam^[2]于1962年第一次提出了硫单质作为电池正极材料的概念。硫具有许多有价值的特性，如低当量，极低成本和环境友好。基于锂金属和硫的电池系统在20年以前已经被发明。由于只有低原子量的锂元素和硫元素，锂-硫电池系统是目前所知的化学可逆系统中具有最高能量密度的体系之一，锂硫体系理论能量密度为2600W·h·kg^-1和2800W·h·L^-1，平均电压2V，适用于低电压电子器件应用。