锂硫电池硫基正极材料与隔膜改性研究

发布时间：2018-07-27 15:27

【摘要】：锂硫电池作为一种新型的能量储存系统,理论能量密度高达2600 Wh/kg,受到研究者的广泛关注,并且活性物质单质硫具有环境友好、价格低廉和资源丰富的特点。与传统的锂离子电池相比,锂硫电池优势明显。到目前为止,锂硫电池还处于实验室研发阶段,可实现的能量密度远低于理论值,并存在容量衰减快,循环寿命短等问题,限制了其大规模工业生产。从锂硫电池的结构和工作原理进行分析,活性物质单质硫为绝缘体,电子导电率不高和中间产物多硫化物易溶于电解液,引发的穿梭效应是主要原因。本论文针对锂硫电池存在的关键问题,从硫基正极和隔膜改性两方面开展研究。将镀镍碳纳米管作为硫的载体应用于正极改性;研究了氮化钛/硫复合正极的电化学性能;在商用隔膜表面涂覆导电氧化物Ti4O7,制备Ti4O7改性隔膜。具体研究内容如下:(1)通过加热熔融的方法使升华硫进入镀镍碳纳米管的孔隙,制得镀镍碳纳米管/硫复合正极材料。作为硫的载体,镀镍碳纳米管相互交错,构成了三维导电网络。其中碳纳米管具有中空结构,比表面积和孔隙率高,能对多硫化物产生物理吸附作用,并适应活性物质在充放电过程中的体积变化。镍颗粒均匀分布在碳纳米管的表面,缩短电子传输路径,增强了复合正极的电子电导;并在电化学反应中起到催化作用,有利于多硫化物向Li2S的转化。(2)采用二氧化钛碳热还原氮化的方法制备氮化钛颗粒,氮化钛导电性良好,与硫-胺化学方法制备的纳米硫进行复合,制备氮化钛/硫复合正极。氮化钛与多硫化物之间存在化学键合作用,减少多硫化物的穿梭效应。通过CV和阻抗分析可知,氮化钛能够降低电池的电荷转移电阻,促进电化学反应的进行,有利于提升电池的电化学性能。1 C下充放电循环200次,还保留602 mAh/g的可逆比容量。(3)通过高温碳热还原金红石二氧化钛的方法制备了Ti4O7粉体,均匀涂覆在Celgard 2400隔膜表面,涂层的厚度为5μm。作为物理阻挡层,可以抑制多硫化物向锂负极的扩散。Ti4O7涂层还具有二次集流体的作用,提高了硫的利用率,减少了容量的损失。与使用普通隔膜的电池相比,Ti4O7改性隔膜电池在循环和倍率性能方面有了大幅度的提升,在1 C下充放电循环600次,还保留565 mAh/g的可逆比容量;在大倍率4 C下,放电比容量达到528 mAh/g。
[Abstract]:As a new type of energy storage system, the theoretical energy density of lithium-sulfur battery is as high as 2600 Wha / kg, which has attracted extensive attention of researchers. The simple sulfur, an active substance, has the characteristics of environmental friendliness, low price and abundant resources. Compared with the traditional lithium ion battery, lithium sulfur battery has obvious advantages. Up to now, the lithium-sulfur battery is still in the stage of laboratory research and development, the energy density is far lower than the theoretical value, and there are some problems such as fast capacity attenuation, short cycle life and so on, which limits its large-scale industrial production. The structure and working principle of lithium-sulfur battery are analyzed. It is found that the simple sulfur is an insulator, the electronic conductivity is not high and the intermediate product polysulfide is easily dissolved in the electrolyte. The main reason is the shuttle effect. In this paper, the key problems of lithium-sulfur battery are studied from two aspects: sulfur positive electrode and membrane modification. Nickel coated carbon nanotubes were used as carrier of sulfur to modify positive electrode. Electrochemical properties of titanium nitride / sulfur composite positive electrode were studied. Conductive oxide Ti4O7 was coated on the surface of commercial diaphragm to prepare Ti4O7 modified diaphragm. The main contents are as follows: (1) by heating and melting, sublimated sulfur enters the pores of nickel coated carbon nanotubes, and the nickel coated carbon nanotubes / sulfur composite cathode materials are prepared. As the carrier of sulfur, nickel-coated carbon nanotubes intersect with each other to form a three-dimensional conductive network. Carbon nanotubes have hollow structure, high specific surface area and porosity, which can produce physical adsorption to polysulfide and adapt to the volume change of active substances during charge and discharge. Nickel particles distribute uniformly on the surface of carbon nanotubes, shorten the electron transport path, enhance the electronic conductivity of the composite positive electrode, and play a catalytic role in the electrochemical reaction. (2) Titanium nitride particles were prepared by carbothermal reduction and nitridation of titanium dioxide. Titanium nitride particles had good electrical conductivity. Titanium nitride / sulfur composite positive electrode was prepared by compounding with nano-sulfur prepared by sulfur-amine chemical method. There is a chemical bond cooperation between titanium nitride and polysulfide to reduce the shuttle effect of polysulfide. The results of CV and impedance analysis show that titanium nitride can reduce the charge transfer resistance of the battery, promote the electrochemical reaction, and improve the electrochemical performance of the battery. The reversible specific capacity of 602 mAh/g was also retained. (3) the Ti4O7 powder was prepared by carbothermal reduction of rutile TIO _ 2 at high temperature. The Ti4O7 powder was uniformly coated on the surface of the Celgard 2400 diaphragm. The thickness of the coating was 5 渭 m. As a physical barrier layer, the diffusion of polysulfide to lithium negative electrode can be inhibited. Ti4O7 coating also has the effect of secondary fluid collection, which improves the utilization rate of sulfur and reduces the loss of capacity. Compared with the battery with ordinary diaphragm, Ti4O7 modified membrane battery has a great improvement in cycle and rate performance. It has a reversible specific capacity of 565 mAh/g at 1 C for charge / discharge cycles, and at a large rate of 4 C, The specific discharge capacity is 528 mg / g.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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