锂硫电池用新型聚合物纳米复合纤维Janus隔膜的可控制备及其性能研究

Lithium-sulfur batteries have attracted increasing attentions due to their high specific capacity and energy density. Unfortunately, the severe dissolution of polysulfides from S cathode and their migration to Li anode through the separator in practical applications lead to low energy density and poor cycle life of lithium-sulfur batteries. Therefore, electrospun polymer nanofiber membranes with controllable porosity, pore size distribution and ion conductivity are proposed to be used as the substrate separator instead of the commercial polyolefin separator in this proposal. Furthermore, polymer nanofiber composites with Janus structures will be constructed through the uniform and ordered immobilization of carbon-based nanoparticles on the surface of the polymer nanofiber membrane template, which can effectively overcome the polysulfide dissolution issues as well as provide highly conductive pathways for fast lithium ion transfer. In addition, the relationship between the structure/morphology, surface/interface properties of the as-prepared polymer nanofiber composite separators and the sulfur rejection efficiency, lithium ion conductivity and electrochemical performance of the lithium-sulfur batteries will be thoroughly explored. Through the implementation of this project, it is expected to provide a new strategy and useful reference for the design and development of subtly structured separators in high-performance lithium-sulfur battery applications.

锂硫电池具有高理论容量和能量密度优势，但多硫化物的溶解和扩散引起的“穿梭效应”已成为严重制约其高能量密度和良好循环性能的瓶颈问题。本课题拟从锂硫电池隔膜材料出发，采用静电纺聚合物纳米纤维膜代替传统聚烯烃类多孔膜作为隔膜基体，利用静电纺纳米纤维结构可调控性强等特点，实现对纤维隔膜基体的孔隙率、孔径分布和离子电导率的有效调控；通过多种复合方式调控和优化功能性碳纳米材料修饰层在静电纺纤维膜表面的均匀有序负载，实现聚合物纳米复合纤维隔膜Janus结构的可控构筑，进而获得高效锂离子迁移和显著抑制“穿梭效应”的双重功能，为新型锂硫电池用隔膜材料的设计和开发提供新思路；系统研究复合纤维Janus隔膜的结构/形态、表/界面性质对多硫化物的截留性能、锂离子迁移效率及锂硫电池性能的影响，揭示复合纤维隔膜结构与锂硫电池性能之间的内在关系规律，为兼具高能量密度和长循环寿命的锂硫电池系统的研发和应用提供有益借鉴。

锂硫电池具有高理论容量和能量密度优势，但多硫化物的溶解和扩散引起的“穿梭效应”已成为严重制约其高能量密度和良好循环性能的瓶颈问题。本课题从锂硫电池隔膜材料出发，采用静电纺聚合物纳米纤维膜代替传统聚烯烃类多孔膜作为隔膜基体，利用静电纺纳米纤维结构可调控性强等特点，实现了对纤维隔膜基体的孔隙率、孔径分布和离子电导率的有效调控；进一步通过不同复合方式调控和优化了功能性碳纳米材料修饰层在静电纺纤维膜表面的均匀有序负载，实现了聚合物纳米复合纤维隔膜Janus结构的可控构筑，进而获得高效锂离子迁移和显著抑制“穿梭效应”的双重功能，为新型锂硫电池用隔膜材料的设计和开发提供理论与实验基础。主要研究成果如下：（1）发展了锂硫电池隔膜孔径与电负性可控调节的新策略，创新性地采用具有阳离子选择性的聚酰胺酸、聚丙烯酸等聚合物纳米纤维膜替代传统聚烯烃隔膜，通过阳离子选择性基团（如-COOH）的引入、以及隔膜孔径的可控调节，实现了对带正电荷锂离子的高效迁移，并通过同性电荷相斥原理有效抑制了多硫化锂在正负极之间的穿梭，分别获得了高倍率稳定和具有长循环寿命的聚酰胺酸、聚丙烯腈/聚丙烯酸复合纳米纤维隔膜；（2）提出了杂原子掺杂以及原位锂化聚合物纳米纤维隔膜的功能化新思路，通过引入强电负性的C-F键和-COO-Li，在实现对多硫化锂的高效吸附/屏蔽截留作用的同时显著提高了Li+迁移效率，从分子结构设计角度发展了高性能锂硫电池隔膜的功能化新策略；（3）构筑了具有Janus结构的新型无机纳米粒子修饰聚合物复合纤维隔膜，利用真空抽滤、界面聚合、以及静电纺-喷相结合等方法实现了厚度可控的氧化石墨烯、金属有机框架、聚酰胺薄层等无机或有机组分在纤维膜表面的均匀有序负载，揭示和建立了复合纤维膜的双层非对称结构、表/界面性质与其电化学性能之间的关系规律。