芯壳结构PEI/PVDF电纺纤维薄膜的构筑及其载流子输运机制

In this project, the coaxial electrospinning technology is used to solve the critical problem in the field of polymer electrolytes—the mismatch between ionic conductivity and mechanical properties. Polyetherimide (PEI), which is not gelled in liquid electrolytes, is introduced into electrospinning fibers as a core to provide an excellent mechanical support for polymer electrolytes. PVDF, which is readily gelled in liquid electrolytes, is used as a shell of the fibers to ensure good affinity with the liquid electrolyte for fibrous membranes. On this basis,inorganic oxides nanoparticles are introduced into shell structure to improve the dissociation and transmission capabilities of lithium ions. PVDF polymer electrolytes with excellent comprehensive performance will be obtained under the synergy of the elements described above. This project will develop an effective fabrication method for coaxial electrospinning fibrous membranes. Membranes with controllable coaxial fibrous structure will be achieved by controlling the factors such as diameters of the internal and external capillaries, solvents of spinning solutions, and fluid velocity. The relationship will be made clear between the structures of the fibers such as thickness and interface characteristics of core and shell parts and the dispersion of nanoparticles, and the properties such as thermal stability, ionic conductivity and mechanical strength. The effect laws of pore structures and crystallinity of membranes on the electrolyte absorbency and electrolyte retention will be revealed. The carrier transmission mechanism of polymer elctrolytes with coaxial fiber structure will be clarified. This project provides an effective solution to resolve the mismatch problem between the mechanical and electrical properties of the polymer electrolyte, and provides a theoretical and experimental basis for exploring the relationship between structure and properties of coaxial fiber polymer electrolytes.

本项目针对聚合物电解质薄膜亟待解决的离子电导率和力学性能不匹配问题，采用同轴静电纺丝法对纤维薄膜进行结构设计。以在电解液中不发生凝胶化的聚醚酰亚胺（PEI）为芯结构，提供力学支撑；以PVDF为壳结构，保持对电解液的亲和性；在此基础上，在壳层结构中引入无机氧化物纳米颗粒，提高锂离子的离解和传输能力，制备综合性能优良的纤维聚合物电解质薄膜。本项目将研究同轴纤维结构的有效实现方法，通过控制内外毛细管直径，纺丝液特性，流体流速等因素，获得结构可控的同轴电纺纤维薄膜。明确纤维芯/壳层厚度、界面特征以及纳米颗粒的分散性与薄膜热稳定性、离子电导率和力学强度之间的关联性，揭示薄膜孔结构和结晶度对电解液吸收和保持能力的影响规律，阐明同轴纤维结构聚合物电解质的载流子传输机制。为实现聚合物电解质力学和电化学性能的同步提升提供有效的解决方法，并为探索同轴纤维聚合物电解质结构与性能的关联性提供理论依据和实验基础。

随着锂离子电池的应用领域从移动数码产品拓展到电动汽车和间歇性能源储能系统，聚烯烃隔膜已无法满足高能量密度锂离子电池的需求。人们非常需要具有更加优异的热稳定性和高电化学性能的隔膜，以保证电池的使用安全。为解决这一问题，本项目以不同材料间相互协同发挥作用的思想为出发点、借助于同轴静电纺丝、无机粉体纤维表面原位生长、聚合物材料共混纺丝等方法，构筑新型同轴结构纤维基有机/有机，有机/无机聚合物电解质隔膜，在保证薄膜良好热尺寸稳定性的同时使其具备优良的电解液亲和性，为锂离子电池提供了性能更加优异的隔膜材料。本项目采用具有优良的力学特性、热稳定性以及电化学稳定性的聚醚酰亚胺（PEI）和聚醚砜（PES）作为芯层材料，将电解液亲和性优良的聚偏氟乙烯（PVDF）作为壳层材料，制备了新型同轴电纺纤维膜。研究发现调整喷丝头内外针头推进速率比，内外针头直径比，可有效控制同轴纤维的芯壳层厚度。皮层厚度越薄，越容易出现偏心情况，但薄膜仍具有较好的性能。同轴纤维膜表现出超高的电解液吸收能力，用其组装的电池显示了良好的循环性能和倍率性能。采用原位生长法可以得到有机无机同轴纤维薄膜，无机壳层以纤维为轴绕轴生长，在纤维表面形成均匀的纳米颗粒包裹层。无机壳层有效提高薄膜的热尺寸稳定性和阻燃性。在PVDF的熔点附近对同轴薄膜进行热压处理，借助皮层的微熔融，在搭接点处纤维相互粘结，形成网状结构，有效提升同轴电纺膜的力学特性。通过对压力、温度、时间的控制，找到了提高力学性能确保良好的电解液吸收能力的最佳参数。本项目揭示了纺丝条件对同轴薄膜热稳定性、电解液吸收能力的影响规律，实现了对芯皮层厚度的有效控制，探索了有机无机同轴结构的复合效果，为我国开发具有自主知识产权的电纺纤维电池隔膜制备技术提供理论基础和技术支撑，对推动我国锂电池隔膜的先进制造具有重要的意义。