高容量锂合金电极在原位聚合化电解质中的结构与界面稳定性研究

High capacity Li-alloy negative electrodes suffer from big volume changes during charge and discharge, leading to a loss of electronic contact and degradation of the cycling performance. Some reported nanostructured composite materials and electrodes, represented by silicon, demonstrate excellent cycling performances. However, most of them are difficult to be prepared in large-scale or low-cost, or it is valid only under a relatively low electrode loading. The practical application of the Li-alloy negative electrodes still meets the serious challenge. We propose this project, in which easily available Si- and Al-based Li-storage materials are adopted, and an integrative battery structure with the stable interface and high mechanical strength is formed by the electrochemical formation of a homogeneous solid electrolyte interphase (SEI) layer and the following in-situ polymerization of the liquid electrolytes. In addition, this approach will be compared with the direct in-situ polymerization of the liquid electrolyte. Close contact between the optimized SEI and solid polymer electrolyte will improve the interfacial stability under the volume change of the active phase, and avoid the constant permeation and decomposition of the liquid electrolytes and deactivation of the lithiated aluminum caused by its continuous reaction with the electrolyte solution. By this way, the problems of the relatively low cycle efficiency and the poor cycle stability could be fundamentally solved for the high loading alloy electrodes and the battery safety could be improved. This work will push the development of the next generation of Li-ion batteries with high energy density.

高容量锂合金负极在充放电过程中有大的体积变化，易造成电接触丧失和循环性能下降。已报道的以硅为代表的一些纳米结构的复合材料和电极表明优异的循环性能，但大多难以大规模或低成本制备，或仅仅是在较低电极载量条件下有效，锂合金负极的实际应用仍面临严峻挑战。我们提出本项目的研究，旨在采用易得的硅基和铝基储锂材料，通过预先电化学生成均匀的固体电解质界面相（SEI）膜再使液体电解质原位聚合,形成界面稳定且机械强度高的一体化电池结构，并与直接电解液原位聚合进行比较。优化的SEI与固化的聚合物电解质紧密接触有望改善活性相体积变化时界面的稳定性，并避免液体电解质不断渗入再分解以及锂化的铝与电解液不断反应造成失活，从而从根本上解决高载量合金电极循环效率偏低和稳定性差的问题，并改善电池安全性，推动下一代高能锂离子电池的实用化。

锂离子电池以其独特的优势已在电动车和消费电子领域得到广泛应用，但其更多的应用依赖于能量密度和安全性进一步提升，这就需要从电极和电解质材料取得新突破。以硅或金属锂代替石墨负极有望显著提高电池的能量密度，而采用无机或不燃的聚合物固态电解质是安全的重要保证。但高容量锂合金或金属锂负极在充放电时有大的体积变化，易造成界面SEI膜受损和电接触丧失，使渗入的电解液不断发生分解，导致电极容量快速下降。采用非流动聚合物电解质有望解决此问题，但其机械强度和锂离子导电性仍然不足，并且也存在易燃的问题。针对上述问题我们开展了下列研究: (1) 设计并合成了自愈合多功能的硅负极粘结剂，用于亚微米的硅或更大颗粒的氧化亚硅，在超过4mAh/cm2的载量下能稳定循环。开发了双组分电解质添加剂，改善了硅负极的高温性能。(2) 开发了新型电子/离子传导的三维锂金属复合负极，避免锂枝晶形成和充放电时体积变化。(3) 系统地研究了固态锂电池的电解质原位聚合化。与非原位工艺相比，原位聚合化可使电解质膜大幅减薄，也使界面接触更加完善，从而显著改善电池的功率特性。设计并合成了含磷聚合物单体，通过原位聚合制作本征阻燃和循环稳定的金属锂二次电池。首次引入纳米二氧化硅树脂同时作为无机填料和三官能团ETPTA交联剂，获得了高含量SiO2均匀分散的无机-有机复合固体电解质，其室温电导率达10-4 S/cm，锂离子迁移数高达0.63，杨氏模量大于6 GPa，原位聚合的Li/NCM523电池表现出好的循环性能。研究了硅基负极与原位聚合电解质的界面稳定机制，采用高柔性聚合物电解质能顺应硅负极的强体积变化，保持界面良好接触，显著提高循环稳定性。相关研究成果共发表SCI论文16篇，推动了高能和高安全的锂二次电池发展。