新型锂硫全电池的制备和电化学性能研究

Recently, there has been an increasing interest in the study of lithium/sulfur batteries, due to their high specific capacity, high energy density, environmental benign and low cost. However, most current studies on Li/S batteries are based on half cell in which lithium metal is chosen as anode, and there is few study on the preparation and electrochemical performance of Li/S full batteries. As is well known, lithium-metal anode usually suffers several safety problems such as dendrite growth, which impedes the widespread practical applications of rechargeable Li/S batteries. Herein, this proposed project is aiming to lithiate sulfur based cathode, and assemble with a lithium metal-free anode, forming the Li/S full cell with an excellent electrochemical performance. Base on the preliminary studies on sulfur based cathodes, in this proposed project, stabilized lithium metal powder (SLMP) is chosen to lithiate the sulfur cathode, and well-lithiated sulfur cathode will be obtained by optimizing the lithiation technology. Afterwards, the Li/S full cell will be assembled with graphite anode. The electrochemical performance of the Li/S full cell will be explored. The electrochemical behaviour mechanism will be further studied. The proposal will result in a high electrochemical performance Li/S full cell, which can lay a scientific material and technology foundation for the wide commercial application of Li/S batteries.

锂硫二次电池凭借其高容量、高能量密度、绿色环保和低成本等特点，一直是近些年来的研究热点。然而，目前的锂硫电池研究大多基于金属锂作为负极的半电池，很少涉及锂硫全电池的制备与性能考察。金属锂作为负极，存在枝晶生长等诸多不安全隐患，限制了锂硫电池的大规模实际应用。本项目旨在利用新颖的锂化工艺实现硫基正极由“贫锂”到“富锂”的转化，从而实现与非锂负极的成功匹配，制备高性能的锂硫全电池。基于前期锂硫正极材料的制备经验，本申请拟采用商用稳定化的金属锂粉末（SLMP）对硫基正极进行锂化，优化锂化工艺，得到锂化程度高的正极，并与石墨负极组装制备锂硫全电池。对锂硫全电池的电化学性能进行研究，同时深入分析其电化学行为机理，最终制备出高容量和高循环性能的锂硫全电池，为锂硫电池的大规模商业应用奠定理论和技术基础。

锂片作为负极和单质硫作为正极的锂硫电池通过化学转换可获得高达2600Wh kg-1的理论能量密度，成为备受世界各国研究工作者关注的下一代二次电池。而且，单质硫作为正极具有1672 mAh g-1的高理论容量，并且价格低廉，储量丰富，环境友好，是很有潜力的正极材料。然而，锂硫电池中采用金属锂作为负极材料时，由于锂枝晶的生长，可能会在实际应用中引起安全性问题。在我们目前的研究工作中，设计和开发了具有不同组分和结构的硫基复合材料用于锂硫电池的正极。在这些单质硫复合正极材料的候选者中，其中2个被选为作为构建锂硫电池全电池的高性能正极。此外，我们还合成了高性能负极材料，用于锂硫全电池。在全电池设计中，选用稳定的锂金属粉末（SLMP）来锂化硫正极，并通过优化锂化技术获得了锂化的硫正极。优化的锂化条件为：SLMP与硫的摩尔比为3：1，球磨速度为600rmp，球磨时间为6h，电解质添加量为80μL，锂化时间为16h。在此锂化条件下，我们设计并测试了不同的锂硫全电池。在锂化后的碳涂层S/PAN复合正极//石墨负极电池系统中，电池具有953 mAh g-1的高初始放电容量，经过100次循环后仍可保持810 mAh g-1。在锂化后的S/PAN/GO复合正极//硅负极电池系统中，初始放电容量为1015 mAh g-1，100次循环之后，仍保持830 mAh g-1。为了研究电化学行为机制，我们对锂硫电池的半电池和全电池进行了拆解电池的非原位实验，比较得出充放电循环后锂硫全电池中复合材料的形貌变化更为剧烈，这可能导致其应用于全电池时的电化学比其应用于半电池时性能不高。