硫基复合材料的分子界面自组装及其储锂/钠机理研究

Lithium/Sodium–sulfur batteries are among the most promising power sources for energy storage because of their low cost,long life and high energy density. However, two major challenges hinder their practical application. One is the low electrical conductivity of sulfur and the intermediate polysulfides, which will dramatically reduce the electrochemical reactivity and decrease the rate capability . The other is the dissolution of various aforementioned polysulfides in electrolyte, leading to the irreversible loss of active materials and severe decay of battery capacity. Therefore, the key issue for the success of lithium/Sodium sulphur battery is the development of sulphur-based cathode materials with high energy density and cycling stability. To address these issue, most researchers mixed graphene, porous carbon, or conducting polymer with sulphur to prepare sulphur based composite. But in the composite, sulphur particles could not be strictly covered, which cause the disolution of polysulfides in the electrolyte and then the diffusion to the counter electrode. Here we propose to design graphene and polymer double- encapsulated nano sulfur particle composite cathode materials that are able to deliver electrons efficiently to the active materials as well as to trap the soluble polysulfides. The following aspects will be involved. Firstly, graphene and polymer encapsulated nano sulfur composite cathode materials will be prepared by molecular interface self-assembly reaction method. Secondly, the relationships between the composition, structure and electrochemical properties of the as-prepared cathode materials during charge-discharge cycles will be investigated. Finally, the structure-performance relationships and lithium/Sodium storage mechanism of the cathode materials will be set up. The expected research outputs will certainly provide both theoretical and practical guiding for the preparation of cathode material and the assembling of lithium/Sodium sulfur battery with high cycling stability and specific capacity.

具有低成本、长循环寿命和高能量密度的锂/钠硫电池被认为是储能电池领域的研究热点。目前该类电池存在以下两个主要问题：第一，硫及其放电产物的导电性差而导致硫的利用率低；第二，放电中间产物多硫化物穿过隔膜与锂负极反应而导致电池循环容量衰减过快。因此高能量密度和高循环稳定性的硫基复合正极材料的研发是高性能锂/钠硫电池成功的关键。目前研究人员主要采用多孔碳、导电聚合物和石墨烯等具有较高导电率的材料与硫复合的方法制备硫基正极材料，因为没有严格控制合成过程导致部分硫仍然裸露在复合材料表面而与电解液接触，不能阻止反应中间产物多硫化物的溶解和穿梭效应。本项目基于分子界面自组装制备石墨烯和聚合物双层紧密包覆纳米硫复合材料，研究其界面自组装机理和充放电过程中材料结构和电化学性能的演变规律，阐明其构效关系和储锂机理，为获得具有高能量密度、长循环寿命的锂/钠硫电池正极材料奠定科学基础。

锂/钠硫电池是一种非常有希望走未来产业化应用的储能器件。但是锂硫电池中硫正极的低电导率、高溶解性、体积膨胀、多硫化物的穿梭效应等缺点限制了他的发展，需要得到解决。本项目主要研究纳米硫复合正极材料的新颖制备方法，研究其反应机理和充放电过程中材料结构和电化学性能的演变规律，阐明其构效关系和储锂机理，为获得具有高能量密度、长循环寿命的锂/钠硫电池正极材料奠定科学基础。项目按照研究计划制备了三维类石墨烯硫复合材料、石墨烯硫复合材料、柔性自支撑硫化聚丙烯腈薄膜正极等硫基正极材料，研究了其构效关系和储锂/储钠的反应机理，另外，根据锂硫电池的最新发展趋势，项目增加了对新型硫正极粘结剂和高效无枝晶的金属锂复合负极材料的制备及相关机理的研究。相关研究成果对高能量密度的锂硫电池的产业化开发具有重要的理论指导意义。