论文总字数：34942字

摘 要

锂硫电池是以单质硫作为电池正极，金属锂作为负极的一种锂二次电池，目前尚处于研究阶段。硫正极材料比容量高达1675 mAh g^-1，是目前商业上广泛应用的钴酸锂正极材料比容量（lt;150 mAh g^-1）的五倍。而且，相对于价格高昂、污染严重的金属元素，硫对环境的污染较轻。因而锂硫电池是一种非常有前景的电化学储能系统。但是，目前的锂硫电池中的硫电极材料也存在下列问题：（1）硫是电子和离子绝缘体；（2）硫电极充放电过程中的中间产物易溶于有机电解液，造成活性物质的损失；（3）单质硫在充放电过程中伴随着78%左右的体积收缩或体积膨胀，导致正极材料微观形貌破坏。

为了克服上述锂硫电池存在的问题，本课题以蔗糖作为碳源制备纳米中空碳球，研究其微观形貌和孔结构差异，并与单质硫热处理形成硫碳复合材料。

所制备的中空碳球通过一系列表征来对其结构成分进行探究。通过对空心碳球的微观形貌发现十二胺改性后可以降低碳球（碳骨架）的分散程度，使得碳球相互接触形成一定的紧密堆积形式，最后形成三维碳骨架，对电子电导率和离子电导率有很大的提升；而未改性的空心碳球分散性比较好，使得碳球之间电子传输比较困难。通过XRD分析相结构的区别；再通过元素分析得到碳球的主要组成；最后通过XPS谱图分析碳骨架表面元素的存在形式。

负载50 wt%硫的复合材料，不同形貌的碳骨架对首次充放电比容量影响不大，两者在0.1 C电流密度下比容量均在1200 mAh g^-1左右。0.1-2 C的倍率性能测试中，两样品在低倍率相差很小，但是在电流密度达2 C时，碳骨架比容量达到了554 mAh g^-1，而空心碳球比容量仅为78 mAh g^-1。在0.5 C和1 C电流密度下循环300圈，改性前后容量相差也较为悬殊。为提高复合材料的体积密度，硫负载量提升至70%，与硫负载50%的复合材料相比，容量并没有太大下降，在1 C下经过300圈循环后比容量保持在480 mAh g^-1，2 C下100圈循环后比容量保持在545 mAh g^-1。在1 C下循环500圈，碳骨架比容量维持在431 mAh g^-1，平均每圈的容量衰减仅0.088%，以上均说明了碳骨架具有优异的循环和倍率性能。

关键词：电化学 锂硫电池 十二胺 碳骨架 空心碳球

Nano-Hierarchically Hollow Carbon Spheres for Lithium-Sulfur Battery Cathodes

Abstract

Lithium-sulfur battery is now still in the research stage. Lithium-sulfur battery consists of an elemental sulfur battery anode, a lithium metal anode and separator. With specific capacity of up to 1675 mAh g^-1, the capacity of Li-S batteries are much higher than the widely used commercial lithium cobalt oxide (lt;150 mAh g^-1). Furthermore, sulfur is an eco-friendly element with no environmental contamination. However, many problems are still unsolved in regard to the state-of-the-art sulfur cathode materials: (1) Elemental sulfur is both electronic and ionic insulator;(2) Polysulfide produced in charging and discharging process is soluble in organic electrolyte, resulting in loss of active material; (3) Volume variation of sulfur is ~78% during the cycling, which may cause the morphology collapse.

To overcome the above problems of the lithium-sulfur battery, Herein，we use sucrose as carbon source to prepare nano hollow carbon spheres (HCS) to study the morphology and structural differences hole, and heat treatment with elemental sulfur to form sulfur carbon composite material.

HCS-prepared through a series of characterization to investigate its structural and components. We found dodecylamine modified can reduce dispersion of HCS(we call it Carbon skeleton), so that the HCS contact closely with each other, and finally form a three dimensional Carbon skeleton, the electronic conductivity and ionic conductivity is greatly improved; However,the HCS is opposite.Then, we use XRD to analysis the phase structure of the two sample,and to determine main components by elemental analysis. Finally, the surface element of the carbon skeleton is determined by XPS spectra.

There is no obvious distinction between the two sample with low sulfur load for the first discharge performance , which is 1200 mAh g^-1 at 1/10 C current density approximately. The specific capacity of two samples at low current density is close from the rate capacities tests between 1/10 C-2 C. But with current density up to 2 C, the specific capacity of the carbon skeleton is 554 mAh g^-1, as compared to the HCS is only 78 mAh g^-1. At current density of 0.5 C and 1 C, the performance of carbon skeleton is much better than HCS after 300 cycles. In order to increase the volume density of sulfur-carbon composite material, the sulfur loads need increase to 70% . The results show that the capacity of carbon skeleton with high sulfur loads is close to low ,which can remain 480 mAh g^-1 at 1 C after 300 cycles and 545 mAh g^-1 at 2 C after 100 cycles. At last ,we give the cycle curve of carbon skeleton with high sulfur loads, which specific capacity can still maintained at 431 mAh g^-1 after 500 cycles at 1 C, the decrease of capacity is only 0.088% each cycle. Above all proved that carbon skeleton having excellent cycle performance and rate capacity.

Key Words: Electrochemistry; Lithium-Sulfur ; Dodecylamine; Carbon Skeleton; Hollow Carbon Spheres

目 录

摘 要 II

第一章 绪论 6

1.1前言 6

1.2 锂硫电池的工作原理及电池结构 6

1.2.1锂硫电池的工作原理 6

1.2.2锂硫电池的电池结构 7

1.2.3 锂硫存在的问题与解决途径 7

1.3 锂硫电池正极材料 8

1.3.1金属硫化物正极材料 9

1.3.2硫/金属氧化物复合正极材料 9

1.3.3硫/导电碳复合正极材料 10

1.3.4其他正极材料 14

1.4 本论文的研究目的和主要工作 14

1.5 本论文的创新点 15

第二章 实验与表征 16

2.1 实验试剂与仪器 16

2.2 材料的制备 17

2.2.1 硬模板富羟基硅球的制备 18

2.2.2 空心碳球的制备 18

2.2.3 硫/碳复合材料的制备 19

2.3 材料的基本表征 19

2.4 锂硫电池正极材料制备及电池组装 20

2.4.1 正极极片的制备 20

2.4.2 电池的组装 20

2.5 硫/碳复合材料正极的电化学测试 20

第三章 结果与讨论 22

3.1 硫/碳复合材料硫负载量 22

3.2材料的表征分析 22

3.2.1 中空碳球微观形貌表征 22

3.2.2 X射线衍射分析 24

3.2.3比表面积分析 26

3.2.4 HCS元素分析 27

3.2.5 XPS分析 28

3.3 硫/碳复合材料电化学性能测试及分析 29

3.3.1电化学过程的分析 29

3.3.2电化学循环及倍率性能分析 32

第四章 结论与展望 36

4.1 结论 36

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