缺陷调控金属氧化物对多硫化合物的化学吸附及其在Li-S电池中的应用

Although sulfur as the cathode electrode of lithium ion battery has high theoretical specific capacity, the solubility of the intermediate polysulfides induced “shuttle effect” severely limits its cycling performance. Different from the physical encapsulation of carbon materials, metal oxides has even stronger and better absorption effects for polysulfides. However, the conductivity of most of metal oxides is very poor, the absorbed polysulfides cannot be directly reduced on the surface of metal oxides. Moreover, stoichiometric metal oxides have saturated coordination environments and limited absorption sites, resulting in limited absorption capacity of metal oxides. While metal oxides with defects own better electrical conductivity and more absorption sites, the current understanding of the polysulfides absorption on defected metal oxides, especially absorption and modulation mechanism and surface reaction kinetics, is still not enough, which significantly hinders metal oxides as absorbents for polysulfides in Li-S batteries. In this proposal, we will employ synchrotron radiation X-ray photoelectron spectroscopy, X-ray absorption fine structure analysis spectroscopy, electrochemistry and electrical studies to establish the absorption model and elucidate the effects of defects on the chemical absorption and surface reaction kinetics of polysulfides.

硫作为锂电池的正极材料具有很高的理论比容量，但是中间产物多硫化合物的溶解引起的穿梭效应极大降低了其循环稳定性。不同于碳材料的物理吸附，金属氧化物对多硫化合物的化学吸附力更强，吸附效果更好；但是大部分金属氧化物的导电性非常差，导致化学吸附的Li2Sx很难直接在氧化物表面被还原。而且，化学计量比下的金属氧化物由于其饱和的配位环境和有限的吸附位点，对多硫化合物的吸附量也是有限的。缺陷金属氧化物拥有更好的导电性和更多的吸附位点，但是目前对缺陷调控多硫化合物的吸附方面，尤其是对吸附及调控机制和反应动力学的认识还有很多不足，很大程度的限制了金属氧化物作为吸附剂在Li-S电池中的应用。本项目拟利用同步辐射光电子能谱、X射线精细结构分析光谱以及电学，电化学分析手段，构建吸附模型，阐明缺陷对多硫化合物的化学吸附以及表面反应动力学的影响。

该项目针对Li-S电池中多硫化合物在正极添加剂表面吸附行为，界面电荷转移以及反应动力学调控认识不清楚的科学问题，利用同步辐射光电子能谱，X射线精细结构吸收谱，电化学分析以及第一性原理计算等手段，阐明多硫化锂的化学吸附和表面反应动力学的影响规律。研究成果如下：1. 揭示了多硫化物在钴基化合物和Ta基化合物表面的能带结构和d电子填充程度的调控规律。2. 借助元素掺杂改性S8分子极性，提升氧化还原反应动力学性质。3. 构建了多壳层Co9S8-CNTs复合结构，实现物理吸附，化学吸附以及催化转换的一体化设计。4. 发展了高性能的磷基复合负极材料，用于与S正极匹配，构建全电池。发表论文9篇，包括1篇Joule, 2篇Chem, 1篇ACS Energy Letters, 1篇Nanoscale Horizons, 1篇ChemsusChem, 1篇Chemical Research in Chinese Universities, 1篇Journal of Material Chemistry A, 1篇Frontiers in Energy Research, 其中发表在Joule上的研究论文被评为ESI高被引论文。