多功能梯度化复合聚合物电解质的设计制备及其锂离子传导机制研究

In order to meet the technical requirements of next-generation lithium-ion batteries for high-performance and multi-functional electrolyte materials, the new type of poly(acrylic acid - six fluorine butyl acrylate) block polymers and high dielectric poly (vinylidene fluoride - hexafluoropropylene) copolymer will be used as raw material in this project, and the porous electrolyte skeleton materials containing BaTiO3 with a gradient change of content through electrospinning. And the porous polydopamine microspheres will also be incorporated into to the gradient skeleton materials. The quasi-solid composite polymer electrolyte can be prepared after gelation process of the gradient skeleton materials by using the solution consisting of low boiling point plasticizers and lithium salt with large anion groups and subsequent drying process. The conduction mechanism of lithium ion in multiphase system and multistage micro/nano structure will be analyzed, and the influence of quasi-solid electrolyte on the positive and negative electrode interface stabilization in the process of cell cycle, as well as the capture mechanism of dissolved metal ions from the anode material will be studied. The relationship between material composition, structure parameters of quasi-solid electrolyte and the electrochemical properties and battery cycle performance can be established. Through the optimization of composite electrolyte material composition, structure design and preparation process, the multi-function quasi-solid composite polymer electrolyte materials with high security, high ionic conductivity and electrochemical stability, good mechanical strength and improved stability of the positive and negative electrode interface will be obtained. It can provide technical foundation for design and development of polymer electrolyte with high efficiency and high safety.

为满足下一代锂电池对于高性能多功能电解质材料的技术要求，本项目采用新型聚丙烯酸-丙烯酸六氟丁酯嵌段聚合物和高介电聚偏氟乙烯-六氟丙烯共聚物为原料，通过静电纺丝法制备BaTiO3含量呈梯度变化的多孔电解质骨架材料，同时将多孔聚多巴胺微球复合到梯度化骨架中，经含有大负离子基团锂盐的低沸点增塑剂溶液的凝胶化及干燥处理得到准固态复合聚合物电解质。分析该电解质多相体系、多级微/纳米结构中锂离子的传导机制，研究准固态电解质在电池循环过程中对于正、负极界面稳定化的影响，以及对正极材料溶解的金属离子的捕获机制，建立多孔电解质材料组成、结构参数与电化学性能和电池循环性能之间的关联性。通过复合电解质材料组成、结构设计和制备工艺的优化，获得具有高安全性、高离子电导率、高电化学稳定性、良好机械强度和能够同时稳定正、负极电极界面的多功能准固态复合聚合物电解质材料，为高效、安全的聚合物电解质的设计和开发建立技术基础。

为满足下一代锂电池对于高性能多功能电解质材料的技术要求，本课题通过静电纺丝技术将纳米钛酸钡（BTO）和六方氮化硼纳米片（h-BNNS）引入到PVDF-HFP基体中，制备了梯度结构的纳米纤维膜，将其凝胶化得到非对称聚合物电解质，匹配三元高压正极可以实现界面的稳定，具有较高的电化学性能。以该电解质组装的Li/LiNi0.5Co0.2Mn0.3O2电池在0.5 C下循环的初始放电比容量为151 mAh g-1，进行170次循环后容量仍保持初始的80%。在此基础上，制备了聚多巴胺包覆的BTO（PDA@BTO），通过静电纺丝将其与BTO引入到PVDF-HFP基体中制得非对称聚合物电解质，其中掺杂PDA@BTO的一侧靠近锂金属负极，既可以避免钛离子与锂金属的副反应，又可以改善电极电解质的界面接触性能。该电解质的离子电导率高达5.36×10-3 S cm-1，使用该电解质组装的Li/LiNi0.8Co0.1Mn0.1O2电池在0.5 C下循环的初始放电比容量为197 mAh g-1，并且在10 C的大电流密度下放电比容量仍可保持在113 mAh g-1。此外，将RAFT乳液聚合合成的三嵌段聚合物PAA-b-PnBA-b-PAA和PAA-b-(PnBA-co-PHFBA)-b-PAA作为Li-S电池正极粘结剂，减缓了电池循环过程中造成的电极结构破坏，可增强与多硫化物的亲和性，抑制硫穿梭效应，改善Li-S电池的容量衰减率、库伦效率及电极结构稳定性。通过本项目的研究，得到了可配合商业三元正极和高容量金属锂负极，具有高安全性、高离子电导率、高电化学稳定性、良好机械强度，能够同时稳定正、负极电极界面的多功能准固态复合聚合物电解质材料，以及高性能Li-S电池正极粘结剂，为高效、安全的聚合物电解质及电池粘结剂的设计和开发建立了技术基础。