Yolk-shell型硫—氧化石墨烯复合正极材料的制备与性能研究

发布时间：2018-06-03 09:41

  本文选题：锂硫电池 + 硫-氧化石墨烯复合材料　； 参考：《浙江大学》2015年硕士论文

【摘要】：锂硫电池被认为极有可能替代传统锂离子电池成为下一代被广泛应用的电池体系。为了解决锂硫电池存在的问题,研究者们提出了许多改进的方案,包括对正极材料的结构设计与性能优化等。其中,yolk-shell型复合材料制备作为一种很好的解决方案受到研究者们的关注,一些研究者合成了yolk-shell型TiO2-S或yolk-shell型聚合物-S等复合材料,用作锂硫电池正极材料。yolk-shell型结构由于壳层及空隙的存在,能够使内部的材料得到很好的保护作用。yolk-shell型锂硫电池复合正极材料通常的制备方法是,包覆硫之后通过将内部的硫部分溶出或者加热促使壳层内部产生空隙。这类方法需要将硫部分溶解或反应,容易破坏材料完整性,不利于对硫单质的保护,并且过程复杂,不易控制。本课题拟采用具有凹陷结构的硫颗粒,包裹氧化石墨烯后直接获得具有内部空隙的yolk-shell型S-GO复合材料。本文采用湿化学方法合成单质硫颗粒,研究了硫单质制备过程中工艺条件对所制得的硫颗粒的形貌产生的影响,实现了对硫颗粒形貌的调控,并最终获得了具有明显凹陷结构的均匀亚微米硫球。选取氧化石墨烯(GO)作为包覆材料,通过控制溶液的离子强度,在室温下完成了GO对硫单质的包覆,复合材料具有良好的电化学性能。具体研究内容及结果如下：(1)通过改变表面活性剂PVP的添加量,可以得到不同形貌的硫颗粒。PVP可以使合成的硫颗粒尺寸趋于均匀,随着PVP的增多,硫颗粒的表面会出现凹陷的结构,在一定范围内凹陷程度随PVP的增多而增大。反应成功制备出粒径500nm左右具有凹陷结构的均匀硫球。(2)反应物浓度、PVP的分子量、反应温度、盐酸的用量和酸的种类等条件的改变都会影响到硫颗粒的形貌。获得具有凹陷结构的硫球的具体实验条件为：在30℃以下,向100ml的0.04M的Na2S2O3溶液中,加入0.2g表面活性剂PVP,磁力搅拌下滴加0.67ml浓盐酸反应2小时,抽滤并洗涤。(3)GO包覆具有凹陷结构的硫球后直接形成yolk-shell型复合材料,材料在0.2A/g的电流密度下的首次放电比容量为575.98mAh/g,含有较多氧化石墨烯的样品在1A/g的大电流下循环100次后容量保留了61.9%,总体表现出了较好的倍率性能和循环稳定性。
[Abstract]:Lithium-sulfur battery is considered to be a promising alternative to the traditional lithium ion battery as the next generation of widely used battery systems. In order to solve the problems of lithium-sulfur batteries, researchers have proposed many improved schemes, including the structure design and performance optimization of cathode materials. Among them, the fabrication of yolk-shell composites as a good solution has attracted the attention of researchers. Some researchers have synthesized yolk-shell type TiO2-S or yolk-shell type polymer-S composites. The yolk-shell structure used as cathode material for lithium-sulfur batteries can be used to protect the inner materials well due to the existence of shells and voids. The usual preparation methods of the composite cathode materials for lithium-sulfur batteries are: After covering the sulfur, the inner sulfur part is dissolved or heated to cause the void in the shell. This kind of method needs to dissolve or react part of sulfur, it is easy to destroy the integrity of the material, is not conducive to the protection of sulfur, and the process is complex and difficult to control. In this paper, yolk-shell type S-GO composites with internal voids are obtained by using sulfur particles with hollow structure and encapsulating graphene oxide. In this paper, simple sulfur particles were synthesized by wet chemical method. The influence of technological conditions on the morphology of sulfur particles was studied, and the morphology of sulfur particles was regulated. Finally, a uniform submicron sulfur ball with obvious concave structure was obtained. By controlling the ionic strength of the solution, go was used as the coating material to coat the sulfur elements at room temperature. The composite has good electrochemical properties. The specific research contents and results are as follows: (1) by changing the amount of surfactant PVP, we can obtain different morphologies of sulfur particles. PVP can make the size of synthesized sulfur particles more uniform, and with the increase of PVP, The concave structure of sulfur particles will appear on the surface, and the degree of depression increases with the increase of PVP in a certain range. The molecular weight, reaction temperature, the amount of hydrochloric acid and the type of acid can affect the morphology of sulfur particles. The experimental conditions are as follows: below 30 鈩，

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