锂硫电池用高选择性人工SEI保护锂金属负极研究

It is of great scientific and practical significance to design lithium-sulfur batteries with high specific energy, Coulomb efficiency, cycle stability and safety performance. Due to the outstanding performance of artificial SEI in the field of traditional lithium-ion battery, in order to solve the rapid degeneration of the capacity caused by the shuttle effect in the lithium-sulfur battery system, the present project uses sulfonated styrene butadiene rubber to bind the novel two-dimensional material fluorographene on the surface of the lithium metal anode, and builds artificial SEI protective film through the spontaneous passivation. The two-dimensional structure confers the excellent mechanical strength, flexibility and lithium ion conductivity of the layered lithium fluoride SEI, which encapsulates the inner electrode to prevent the interaction between the polysulfide and the lithium anode, and then forbids side reactions occurring during the discharge process effectively. Meanwhile, sulfonated styrene butadiene rubber containing pendant sulfonic acid groups, the membranes facilitate electrolyte wetting and Li+ ion transport, but are highly selective in preventing migration of negatively charged polysulfide species. The formation mechanism of artificial SEI in the passivation process will be further studied by in situ analysis technique, and the effect of the SEI on the growth of lithium dendrites and the shuttle effect of the lithium-sulfur battery will also be investigated, in order to construct the qualitative or quantitative relationship between the artificial SEI and the electrochemical performance, and provide a new way for the research of high performance lithium sulfur batteries.

设计制备高比能量、库伦效率、循环性能和安全性能的锂硫电池具有重要的科学和实践意义。基于人工固体电解质界面（SEI）在传统锂离子电池领域的突出表现，为了根本解决锂硫电池体系中穿梭效应引起的容量快速衰减，本项目利用磺化丁苯橡胶粘合新型二维材料氟化石墨烯形成复合薄膜，修饰于金属锂负极表面，通过自发钝化，构筑人工SEI保护膜。二维结构赋予了层状氟化锂SEI优异的机械强度、柔韧性和锂离子电导率，并对内层电极进行了限域和束缚，阻止硫化物和锂负极之间相互作用，有效缓解充放电过程中发生副反应。同时，磺化橡胶包含的磺酸基团可以促进电解质润湿和Li+传输，在防止带负电荷的多硫化物迁移方面具有高选择性。进一步通过原位分析技术研究人工SEI在钝化过程中的形成机制，并探究其在循环过程中对锂硫电池枝晶生长和穿梭效应的影响，尝试构建该类SEI与电池电化学性能之间的定性或定量关系，为高性能锂硫电池的研究提供新途径。

锂硫电池具有极高的理论容量，在电动汽车和大型储能系统中具有广阔的应用前景。然而，由于溶解性多硫化锂中间产物的穿梭效应导致锂硫电池的长期循环性能差，其市场化发展受到严重阻碍。本项目针对锂硫电池存在的关键性问题，为了根本解决锂硫电池体系中长链多硫化物溶解引起的穿梭效应及容量快速衰减，利用新型二维材料氟化石墨烯在锂金属负极表面自发钝化，人工构建了具有选择性功能的SEI保护层。所形成的层状SEI具有高机械强度、良好的柔韧性和高锂离子电导率。氟化锂SEI对内层电极进行了限域和束缚，阻止了硫化物和锂负极之间相互作用，有效缓解充放电过程中发生副反应，在防止溶解在液体电解质中带负电荷的多硫化物迁移方面具有高选择性，提高了电池的库伦效率和循环性能，在0.5C下可提供1092 mAh g-1的高放电容量，在1C下循环300次后的容量衰减率仅为0.022％。进一步通过原位分析技术研究了氟化石墨烯在锂负极表面自发钝化过程中人工SEI的形成机制，构建了该类选择性二维层状人工选择界面与电化学性能之间的定性或定量关系。通过原位紫外可见光分析、Li2S成核试验和渗透实验证实了选择性SEI对抑制多硫化物的“穿梭效应”和有效保护Li负极的重要意义。作为拓展研究内容，本项目还通过吐温聚合物与金属锂的自发反应，在传统的锂金属表面构筑了一层稳定的聚合物界面层，获得了单锂离子通道的吐温改性锂负极。该人工界面层显示出较高的离子电导率，并可以有效阻碍多硫化物靠近金属锂表面，从而抑制了多硫化物在锂金属表面的还原。