新型纳微多孔碳/硫复合正极材料的制备及其性能研究

High theoretical energy density, low cost and environmental friendliness make lithium-sulfur batteries very promising for large scale energy storage. However, issues of poor cycling stability and low Columbic efficiency caused by dissolution of soluble polysulfides in organic electrolytes and huge volume change during charge/discharge processes of sulfur cathodes as well as the insulating property of sulfur and insoluble short chain polysulfides have hindered its practical application. Although the use of microporous carbon/sulfur composites significantly improves the cycling performance and Columbic efficiency of sulfur cathodes, capacity is too low. To solve these problems, in this project, we will design and develop hierarchically nano/mesoporous carbon/sulfur composites, in which nanopores will be introduced into the microporous carbon matrix to increase the porosity. The effects of the micropore size and sulfur loading content on the structure damage caused by the volume change during charge/discharge processes and on the cycling stability will be investigated. The relationship between the architecture of the hierarchically porous carbon/sulfur composites and its conductivity/kinetics will be explored. In combination of the improvement in cycling performance and Coulombic efficiency by the blocking effects of microporous carbon to liquid electrolytes and soluble polysulfides, the pore size and porosity of the hierarchically porous carbon will be adjusted to increase the sulfur loading content (≥65%) and thus capacity. We aim at developing high performance sulfur electrodes with capacity of >1000 mAh/g and cycling stability of >3000 times.

硫正极材料具有理论比容量高、成本低、环保等优点，但由于充放电过程中生成易扩散的可溶性多硫化物、硫的体积变化大以及硫和所生成的不溶低硫化物导电性差等问题，硫正极材料的循环性能很差，库仑效率也很低。将硫负载在微孔碳中，可以极大改善循环稳定性和提高库仑效率，但导致比容量下降。针对上述问题，本项目拟在微孔碳基体中引入纳米孔，设计与合成纳微多孔碳/硫复合正极材料，探索纳米孔尺寸以及硫的负载量对由于硫体积膨胀/收缩造成的电极结构破坏程度和电极循环稳定性的影响，建立纳微多孔碳/硫复合材料的结构和组成与其导电性和金属离子扩散动力学之间的关系。在利用微孔碳对电解质和可溶性多硫化物扩散的阻隔作用、提高硫正极循环性能和库仑效率的同时，调节纳米孔尺寸和密度，通过增加硫的负载量（≥65%）提高比容量，力争获得比容量＞1000 mAh/g和循环次数＞3000次的硫正极材料。

针对硫电极充放电过程中生成易扩散的可溶性多硫化物、硫的体积变化大以及硫和所生成的不溶低硫化物导电性差等问题，开展了系统研究：采用模板自组装方法制备了具有形貌和孔结构可以精确调控的多孔碳，且揭示了自组装行为的机制；研究了极性表面对硫及多硫化锂的吸附固定的影响，明确了极性表面多孔基体高效载硫的作用，获得了硫含量超过75%的复合硫电极材料；利用天然聚合物具有丰富的极性基团的特点，制备了碳纤维/天然聚合物复合阻隔膜，有效阻挡了可溶性多硫化锂的穿梭，使硫正极的比容量超过1300 mAh/g，且能稳定循环，同时阐明了多硫化锂与天然聚合物中含氧基团之间的作用机理；研究了微孔碳/硫复合材料的结构性质及对不同离子的反应机理。结果将为设计发展高性能锂硫电池提供参考。