新型无机涂层锂离子电池隔膜的结构与性能的影响机制研究

As a critical component in liquid lithium-ion battery, separator performance has restricted its large-scale applications in large-sized batteries for electric vehicles and long-term energy storage devices.To enhance the heat resistance and integrated electrical properties of separator, coating solution consisted of functional polymer microspheres and zeolite particles with thermal and chemical stabilities as well as three-dimensional pore structure was coated on nonwoven substrate in this project.During hot rolling operation of the coated non-woven,organic microspheres will soften and melt to consolidate the zeolite coating,resulting in high performance separator.The proposed method can overcome a series of problems arising from traditional ceramic coating separator,such as the agglomeration of nano-particles in solution with adhesive,the filling of adhesive in the separator space and the cladding of adhesive around the ceramic particles leading to poor wettability and low porosity of separator.The porous structure of zeolite particles supply additional channels for ion diffusion,modifying ionic conductivity of the composite separator.The effect mechanism of organic microspheres in zeolite coating on microstructure of composite separator was revealed based on investigating on the interfacial interaction law between zeolite particles and organic microspheres.During hot rolling step the mechanism of microsphere structure evolution was studied.The difussion rule of solvation lithium ion through the internal and external channels of zeolite particles was also investigated.The universal rule between separator structure and battery performance was grasped through investigating on the influence of particle proportion relationship between zeolite particles and organic microspheres as well as hot rolling operation parameters.

作为关键组件，隔膜的性能制约着锂离子电池在电动汽车、化学储能等新能源领域的大规模应用。为提高锂电隔膜的耐热性能和电学性能，本项目利用有机微球的熔融粘性和沸石粒子发达的孔道结构及耐高温性，拟将有机微球与大孔沸石粒子的混合浆料涂覆无纺布底膜，经热辊压后，有机微球软化、熔融发挥粘合功能而制成高性能复合隔膜。相对于传统方法制备陶瓷涂层锂电隔膜，本方法的特点为：有机微球代替液态粘合剂，避免了传统方法中纳米粒子的团聚问题、粘合剂堵塞膜层空隙及包覆无机粒子的问题，有效提高了隔膜的孔隙率和电解液浸润性；多孔结构的沸石粒子代替陶瓷粒子，赋予锂离子额外的扩散通道，改善隔膜的离子电导率。本项目拟研究沸石粒子与有机微球的界面作用规律；制膜过程中有机微球的结构演变机制及其发挥粘合功能的机理；锂离子在沸石内部及外部的扩散规律；涂膜浆料中两种粒子的粒径、数量关系与热辊压操作参数等对隔膜结构特性及锂离子电池性能的影响。

随着锂离子电池在储能和动力等新能源领域应用的不断拓展，传统锂离子电池的性能以及安全性无法满足新兴领域的要求。隔膜是锂离子电池的关键部件，是电池容量、循环能力和安全性能的重要决定因素之一。由于产业化的聚烯烃隔膜存在耐温性差、亲液性差和孔隙率低等缺点，限制了其进一步应用。本项目针对常规陶瓷复合膜的不足，在此基础上进行新的结构设计及材料选择，制备高性能锂电隔膜。.首先引入PET无纺布代替聚烯烃隔膜作为陶瓷复合膜的衬底，详细比较了两种不同衬底制备的复合膜的隔膜结构、耐热性、亲液性、电化学特性以及电池性能。发现采用PET无纺布作为复合膜衬底可以明显改善复合膜的结构特性，提高孔隙率与透气性；明显提高隔膜的耐热性，降低热收缩率；显著提高隔膜电化学性能，降低阻抗；提高了电池的充放电性能及循环稳定性。.针对于常规陶瓷复合膜复合及粘合方式的缺点，引入了新型的溶剂蒸汽诱导的二元粒子涂覆的复合方法，将聚苯乙烯（PS）、聚甲基丙烯酸甲脂（PMMA）及聚偏氟乙烯（PVdF-HFP）等有机微球作为粘合剂，代替传统陶瓷复合膜中的连续相的聚合物粘合剂。在保持隔膜良好的耐热性的同时可以明显改善陶瓷复合膜的表面亲液特性及内部孔道结构，可以明显提升复合膜对锂离子传递能力（>50%），提升电池循环性能和倍率性能。另外引入了硅烷偶联剂改性的13X沸石作为无机粒子填料，得益于其独特的内部三维孔道结构及表面酸碱特性，制备的13X沸石-有机微球二元粒子复合膜表现出更优异的综合性能，是替代传统陶瓷粒子的最佳选择。.在二元粒子复合膜基础上，对13X沸石用硅烷偶联剂进行表面改性，同时合成了具有核壳结构的PS/PAA功能有机微球，利用PAA材料的在乙醇溶剂中的溶胀性，在维持复合膜优良性能的基础上实现了陶瓷复合膜涂覆浆料中有机-无机粒子的有效自组装，简化了隔膜制备过程，并优化了隔膜结构；同时通过改变涂覆浆料中有机微球的比例，赋予复合隔膜一定的热闭孔功能，有助于进一步提高电池的安全性。