锂离子电池电化学循环过程中活性锂的消耗机制与抑制方法

The essence of charge-discharge cycle for lithium ion cells is the insertion and deinsertion of active lithium ion between cathode and anode. The cycleable lithium ion can be consumed through various side reactions at the electrode surfaces and this invariably leads to the capacity and life degradation of the cell. For more than 20 years, most researches regarding lithium-ion batteries have been focused on the preparation and optimization of the key materials. less attention has been paid to the key and common issue involved in the cell, i.e. lithium consumption, which is known as a major factor strongly affecting the storage and cycle life of lithium ion batteries. In this proposal, we plan to use some cathode and anode materials which are promising for electric transportation and energy storage applications. Full lithium ion batteries will be assembled with these materials. With the help of SEM, TEM, EDX, XRD, and FTIR spectroscopic techniques, and impedance and galvanostatic test, the mechanism of lithium consumption and its impact on the long-term cycling performance and on the storage properties will be discussed. The amount of the consumed lithium at the electrode surface will be determined through Inductive couple plasma (ICP) method and the quantitative relationship between the capacity loss of the cell and the consumed lithium will be developed. Internal and external factors affecting lithium consumption will also be discussed. Based on these results, we will try to explore different ways to suppress lithium consumption by proper surface coatings. This study will lay academic and technical foundation for making long-life lithium-ion batteries to meet the requirements of electric transportation and energy storage applications.

锂离子电池充放电循环的本质是活性锂离子在正极和负极之间嵌入和脱出，电极表面多种副反应都会消耗电池中有限的可循环锂离子，活性锂离子消耗直接造成电池容量损失和寿命下降。20多年来，人们对锂离子电池的研究一直集中在关键材料的制备和优化方面，而对影响锂离子电池容量和寿命的最基础和共性问题- - - - 活性锂消耗的机制研究很少。本研究拟以动力和储能领域有前景的锂离子电池系统为研究对象，借助SEM、TEM、EDX、XRD、FTIR等现代光谱学技术和阻抗、充放电等电化学技术，探讨整体锂离子电池在长期循环和存贮过程中的锂消耗机制及其对电池寿命等的影响，使用ICP方法测定不同循环和存贮条件下电池内部的活性锂消耗量，建立锂消耗与电池容量衰退间的定量关系，探讨影响电池锂消耗的内部和外部因素，寻找抑制电池循环过程中锂消耗的方法和途径，延长电池寿命，为满足动力和储能领域对锂离子电池的寿命要求奠定学术和技术基础。

高性能长寿命锂离子电池是当前动力和储能电池发展的重要方向，活性锂离子在电池循环过程中的消耗是影响锂离子电池寿命的最重要因素，也是锂离子电池系统中存在的基础和共性问题。在该项目的支持下，我们系统研究了磷酸铁锂(LFP)电池、三元NCM电池的容量衰退机理，证实了锂消耗对电池寿命的重要影响，计算了不同电池体系中锂消耗在电池容量损失中的占比，揭示了电池长期循环过程中电池内部锂消耗的微观机制，发现石墨颗粒的反复膨胀和收缩与石墨表面SEI膜的脆性破裂是SEI膜持续生长和电池锂消耗的根本。为了从根本上解决这一问题，需要在碳负极表面发展具有高弹性和韧性的SEI膜，我们创新性地提出了发展了抑制电池循环过程中的锂消耗，延长电池的寿命的几种方法，特别是首次提出了基于含有不饱和键的有机小分子模板包覆技术在石墨表面原位生长高弹性和韧性的有机质SEI膜，富C-F键的多功能添加剂改性SEI膜等，可以有效抑制由于石墨体积膨胀造成的SEI膜脆性破裂，抑制了SEI膜的持续生长和演变，实现了延长锂离子电池寿命1倍以上的研究目标，相关工作为发展高性能和长寿命锂离子电池奠定了很好的基础，也为锂离子电池产业的未来发展提供了可行的方案。