锂硫电池硫镍一体化正极的制备及电化学性能研究

发布时间：2018-05-10 17:51

本文选题：锂硫电池 + 正极材料　；参考：《湘潭大学》2014年硕士论文

【摘要】：锂硫电池被认为是最具开发潜力的电池体系之一，理论能量密度高达2600Wh/kg。单质硫是目前已知比容量最高的正极材料(理论比容量为1675mAh/g)，而且硫在自然界中储量丰富，成本低廉，同时具有低毒性，环境友好。但是硫正极在应用中存在着致命的缺点：单质硫不导电以及电化学反应过程中放电产物溶于电解液，导致活性物质利用率低、电极循环稳定性差，严重制约了锂硫电池的发展。本论文在充分调研的基础上，以具有高导电性、高比表面积的泡沫镍为基体与硫复合，对硫镍一体化正极的制备及性能的优化展开了系统的研究。本学位论文的创新性研究成果如下： (1)采用热蒸法将硫包覆到泡沫镍基体的多孔结构中，制备硫镍正极材料。通过SEM、XRD对材料进行结构及成分表征，通过模拟电池的组装进行电化学性能测试。结果表明，正极的三维网络结构保持良好，活性物质分布均匀，且以硫镍化合物的形式存在。在前20次循环内，电池内部电化学反应良好，但是随着循环次数的进一步增加，活性物质会从基体剥离，造成正极结构损伤，容量衰减，库伦效率偏低。 (2)为了稳固正极结构，并发挥单质硫理论比容量高的优势，采用化学法制备硫镍正极材料。结果表明，活性物质以单质硫的形式均匀包覆在泡沫镍骨架表面，且有少量大颗粒状硫附于表层。其首次放比电容量较高，具有典型的充放电平台，库伦效率接近100%，经100次循环后容量保持率为75%。但是表层大颗粒硫的脱落会造成循环使用过程中容量的波动，不利于实际应用。 (3)对化学法制备硫镍正极材料进行后续熔硫处理，目的在于消除表层大颗粒硫对循环性能的影响。结果表明，活性物质硫高度分散在基体的多孔结构中，增加了电化学反应过程中微反应场所，有效抑制放电产物溶解，，循环可逆性好。经不同的倍率充放电循环110次后容量保持率高达95%。而且随着循环的进行，电极的界面阻抗及锂离子扩散阻抗均明显下降。综上所述，本论文以传统集流体材料泡沫镍为基体制备的硫镍正极材料，即硫镍一体化正极，可以直接用于电池装配，无需添加粘结剂、导电剂和分散溶剂进行制浆、涂布，工艺简单。化学-熔硫法制备的一体化正极具有高比表面积的稳定结构，极大提高了活性物质的利用率，可以有效抑制多硫化物的溶解，电化学反应可逆性良好，为锂硫电池新型正极材料的设计提供了实验依据。
[Abstract]:Lithium-sulfur batteries are considered as one of the most promising battery systems with theoretical energy density as high as 2600Wh/ kg. Elemental sulfur is the most known cathode material with the highest specific capacity (theoretical specific capacity is 1675mAh/ g / g), and sulfur in nature is rich in reserves, low cost, low toxicity and environmentally friendly. However, sulfur positive electrode has some fatal disadvantages in application: simple sulfur nonconductivity and discharges dissolved in electrolyte during electrochemical reaction, which leads to low utilization of active substances and poor electrode cycle stability, which seriously restricts the development of lithium-sulfur batteries. On the basis of full investigation, the preparation and performance optimization of nickel foam with high conductivity and high specific surface area were studied systematically in this paper. The innovative research results of this dissertation are as follows: 1) the sulfur was coated into the porous structure of the foamed nickel matrix by thermal evaporation to prepare the nickel sulfide cathode material. The structure and composition of the materials were characterized by SEM XRD, and the electrochemical properties were tested by the assembly of simulated batteries. The results show that the positive electrode has a good three-dimensional network structure and a uniform distribution of active substances, and exists in the form of sulfur and nickel compounds. During the first 20 cycles, the electrochemical reaction in the battery was good, but with the further increase of the cycle times, the active substances would be stripped from the matrix, resulting in the damage of the structure of the positive electrode, the capacity attenuation, and the low efficiency of the Coulomb. In order to stabilize the structure of positive electrode and give full play to the advantage of high specific capacity of elemental sulfur theory, nickel sulphide cathode material was prepared by chemical method. The results showed that the active substances were uniformly coated on the surface of the foamed nickel skeleton in the form of elemental sulfur, and a small amount of large granular sulfur was attached to the surface layer. Its first discharge capacity is high, it has a typical charging and discharging platform, the Coulomb efficiency is close to 100, and the capacity retention rate is 75 after 100 cycles. However, the falling off of large particles of sulfur in the surface will cause the fluctuation of capacity in the process of recycling, which is not conducive to practical application. In order to eliminate the influence of large particles of sulfur on the cycling performance of nickel and sulfur cathode materials prepared by chemical method, the sulfur melting treatment is carried out. The results show that the active sulfur is highly dispersed in the porous structure of the matrix, which increases the micro-reaction sites in the electrochemical reaction process, effectively inhibits the dissolving of the discharge products, and has good circulation reversibility. After 110 cycles at different rates of charge and discharge, the capacity retention rate is as high as 95%. The interfacial impedance and lithium ion diffusion impedance of the electrode decreased with the cycle. To sum up, the traditional fluid-collecting material, nickel foam as the substrate, can be directly used in battery assembly without adding binder, conductive agent and dispersing solvent for pulping and coating, which is the integral positive electrode of sulfur and nickel, which can be used in battery assembly directly. The process is simple. The integrative positive electrode prepared by chemical-melting sulfur method has a stable structure with high specific surface area, which greatly improves the utilization ratio of active substances, effectively inhibits the dissolution of polysulfide, and has good reversibility in electrochemical reaction. It provides experimental basis for the design of new cathode materials for lithium-sulfur batteries.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

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