核-壳型单离子导体修饰P(VDF-HFP)基聚合物电解质的结构设计与性能研究

Lithium ion batteries with polymer electrolytes can avoid explosion accidents resulting from the gas bulking and leakage of liquid electrolytes during the repeatedly charge-discharge cycling processes, which can be attributed to the polymer electrolytes without or with few liquid electrolytes. However, the polymer electrolytes are still kept away from the lithium ion battery area because of its lower ionic conductivity at room temperature and lithium ion transference number and worse mechanical property and interfacial stability. In this project, core-shell structural single ion conductor is firstly prepared by hydrolytic condensation, in-situ radical polymerization and ion exchange processes, and then the P(VDF-HFP)-based composite polymer electrolytes are obtained by modifing the as-prepared polymer electrolytes fabricated by casting and phase inversion methods with single ion conductor. Firstly, the interfacial stability and ionic conductivity at room temperature of the polymer electrolytes can be improved owing to the nanocrystallization of the single ion conductor and the interactions between the nano-single ion conductor and polymer matrix, respectively. Secondly, stabilized core structure of the single ion conductor will enhence the mechanical property of the as-prepared polymer electrolytes. Furthermore, the lithium ion transference number would be increased because more lithium ions can easily release from the shell of the single ion conductor. The study shows the influence law of the ionic conduction and interfacial property and mechanism of lithium ion migration in the composite polymer electrolytes doped with single ion conductor. These all can provide new ideas and theoretical guidance for the development and application of novel polymer electrolytes for lithium ion batteries.

聚合物电解质因其含微量或不含液态电解液，避免了所装配的锂离子电池在反复的充放电过程中因发生气胀或电解液泄漏而引发的爆炸等安全事故。但由于室温离子电导率低、机械性能差、界面稳定性差和锂离子迁移数低等缺点，制约了其在锂离子电池领域中的应用。本项目拟先通过水解-缩合、原位自由基聚合和离子交换制备核-壳结构的单离子导体，后将其用来修饰通过流延成膜-倒相法制备的电解质而得到P(VDF-HFP)基复合型聚合物电解质。利用纳米化的单离子导体和与聚合物基体的相互作用分别提高体系的界面稳定性和室温离子电导率；利用单离子导体稳定的内核结构改善所制备复合聚合物电解质的机械性能；利用单离子导体外壳易释放锂离子的特性提高体系中的锂离子迁移数。通过本项目的研究，揭示单离子导体修饰对复合聚合物电解质的离子传导机制、界面稳定特性及体系中的锂离子迁移途径的影响规律，为新型聚合物电解质的开发与应用提供新的思路和科学依据。

聚合物电解质因其含微量或不含液态电解液，避免了所装配的锂离子电池在反复的充放电循环中因发生气胀或电解液泄漏而引发的爆炸等安全事故。但由于其室温离子电导率低、机械性能差、界面稳定性差和锂离子迁移数低等缺点，严重制约了其在锂离子电池领域中的应用。本项目通过水解-缩合、原位自由基聚合和离子交换制备具有核-壳结构的单离子导体，后将其用来修饰制备P(VDF-HFP)基复合型聚合物电解质。研究结果表明，通过单离子导体与基体高分子长链间的Lewis酸碱作用，可以降低基体的结晶度来提高聚合物电解质体系的室温离子电导率；通过单离子导体稳定的内核结构可以改善其的机械性能；通过单离子导体纳米化结构独特的表面性能可以改善其界面性能；通过单离子导体外壳无定形结构的锂盐极易离解释放出自由移动的锂离子，可以增加载流子浓度来提高体系中的锂离子迁移数。通过工艺优化，使得制备的复合聚合物电解质的室温离子电导率高达3.9×10-3 S cm-1，锂离子迁移数达到0.48，且与钴酸锂正极和石墨负极材料间有较好的匹配性。Li/CPE/LiCoO2扣式电池在1 C和5 C的容量保持率经过200次循环后分别为97 %和96%；Li/CPEs/Graphite扣式电池在1 C下其放电比容量为288.5 mAh g-1，首次效率高达89.1 %。此外，本项目还制备并考察了Zr基有机-无机杂化材料掺杂制备复合聚合物电解质，其性能测试表明，有机-无机杂化Zr基材料掺杂制备的复合聚合物电解质具有优异的理化和电化学性能，基本上达到了项目的预期指标。通过本项目的研究，揭示了单离子导体修饰对复合聚合物电解质的离子传导机制、界面稳定特性及体系中的锂离子迁移途径的影响规律，为新型聚合物电解质的开发与应用提供了新的思路和科学依据。