高比能锂硫电池聚硫离子多重梯度抑制结构的平衡设计与固硫机制研究

Lithium sulfur battery, as one of the most promising candidates for the next generation of high energy density storage devices, is facing many challenging problems such as the low utilization of active materials, poor cyclability and serious self-discharge, which impede its commercial application. These problems are closely related to the dissolution, diffusion and shuttle effect of the polysulfides. In order to inhibit these behaviors of polysulfides, a kind of novel multilevel structure of Li-S battery for inhibiting polysulfide anion is designed in this project. This structure consists of three barriers : the first is the surface-modified coating with favorable conductivity, absorbability and flexibility binding on the surface of high sulfur loading cathode for the purpose of blocking the escape of polysulfides from the cathode and stabilizing the cathode structure; the functional electrolyte based on ionic liquid and organic fluorinated ether are regarded as the second barrier, in order to decrease the dissolution and diffusion of polysulfides in the electrolyte; and the last is the protective passivation film formed on the anode surface due to the contribution of electrolyte components, which is used for preventing the direct contact and reaction between polysulfides and Li anode. This project focuses on the study of formation and preparation mechanism of the coating and electrolyte in order to reveal the inhibition efficiency of different parts under variational conditions. By balancing design among three inhibiting barriers, the optimized multilevel gradient inhibition structure can be found for Li-S battery. Meanwhile, the basic running mechanism of the structure can be clarified, and the particular battery reaction model based on the structure can be build by the research in the project, which is expected to provide a valuable theory direction for constructing high performance Li-S battery with high energy density and long cycle life.

锂硫电池作为下一代高能量密度二次锂电池之一，其活性物质利用率低、循环寿命差，严重限制了商业化应用。这些问题与锂硫电池工作中聚硫锂的溶解、扩散和穿梭密切相关。为了有效抑制聚硫离子的上述行为，本项目设计了一种锂硫电池聚硫离子多重梯度抑制结构。该结构包含三重抑制层：第一层在传统硫正极片上涂覆具有导电性、吸附性和弹性的多功能涂层，用以阻挡聚硫离子，稳定电极结构；第二层基于离子液体和有机氟化醚配制新型电解液，用以降低聚硫锂的溶解和扩散；最后一层利用氟化醚在负极表面形成稳定的钝化保护膜，实现对聚硫离子的最后阻截。项目重点研究导电弹性涂层和新型电解液的成形和制备机理，揭示不同条件对各部分抑制层的阻截效果的影响规律；通过对各抑制层的联动平衡设计，探寻最优的锂硫电池多种梯度抑制结构；阐明多重梯度抑制结构的作用机制，建立新型电池反应模型，为获得高比能、长寿命的锂硫电池提供理论指导。

锂硫电池由于具有理论能量密度高、硫资源丰富、环境友好等优点有望成为下一代高能量密度的二次储能器件之一，但还存在硫及其放电产物的电导率低、中间产物多硫化锂溶于电解液中引起穿梭效应、锂负极腐蚀等问题阻碍其实用化。为解决这些问题，本项目从高性能硫-炭正极复合材料的设计、功能修饰涂层的构筑及多重梯度抑制结构的平衡设计、功能型电解液的开发及其多硫化锂穿梭抑制机理研究等方面入手，基于材料导电性与孔容的调控，设计并制备出高导电率、高孔容的层次孔石墨烯/介孔炭/导电炭黑（G/MPC/SP）材料、异原子掺杂钴-氮-碳多孔炭（Co-N-C）材料和MoS2/硫氮共掺杂多孔炭（MoS2@NSdC）材料，研究和阐明了材料特性对电池性能的影响机理；构筑并实现了硝酸氧锆功能修饰涂层、偏铝酸锂/掺氮空心碳球（LiAlO2/NHC）双层复合涂层以及电解液蓄留层的引入对多硫化锂的多重梯度抑制；开展了醚溶剂结构及组成、功能型电解液添加剂硝酸氧锆、硫代乙酰胺对锂硫电池电化学性能的影响及相关作用机理研究。构筑出性能优异的高比能锂硫电池；同时阐明其多重梯度抑制结构的作用机制，为获得高比能、长寿命的锂硫电池提供了理论指导。项目研究期间，所有工作均围绕上述研究目标而进行，并如期完成，共发表学术论文16篇，申请专利16项，培养博士研究生1名，硕士研究生2名，博士后1名。