Improving electrochemical performance of Li-ion batteries based on a holistic binder concept for water-borne electrode slurries

电化学储能对于未来可靠的能源供应和个人移动性起着重要作用。今天，锂离子电池（LiB）主导着这一技术领域。电池效率在很大程度上取决于电极工程。在这里，我们希望开发一种粘合剂配方概念，为LiB电池提供具有改进的电化学性能、高循环稳定性和长电池寿命的电极层，利用基于技术规模浆料配方的活性材料的全部容量。这个概念是基于一个整体的方法，包括所有方面的活页夹功能。我们研究了在工业涂层工艺中实现浆料流动性能所需的粘合剂规格，从而获得均匀、无缺陷的电极层。然后，探索了对干电极层内的强内聚性和对集流体的强粘附性的要求，以避免在锂离子嵌入期间的机械故障，从而导致高循环稳定性和长电池寿命。除此之外，我们研究了粘合剂作为分散剂的作用，以控制电极层的微观结构，即活性材料和导电剂的空间分布和取向，以获得高电导率和Li离子迁移率。这显著影响电化学电池性能，尽管粘合剂不参与电化学过程。预计LiB的需求将强劲增长，我们专注于电极制造的水性浆料，包括最先进的活性材料和羧甲基纤维素（CMC）和丁苯橡胶（SBR）的组合作为粘合剂系统。我们系统地改变CMC分子量和取代度，并假设需要不同CMC类型的适当混合物以最小的粘合剂消耗来满足不同的、部分冲突的利益。具有有前途的粘合剂组合物的相应浆料用于制造用于电化学测试的电池，使我们能够验证并进一步改进粘合剂概念。使用具有定制的粘合剂组合物的浆料来制造分级电极，该分级电极由靠近集电器的包含SBR的薄层组成，从而提供强粘附性，并且由具有强内聚性和CMC控制的微结构的无SBR顶层组成，从而提供上级的电化学性能。在这种方法中，我们还希望利用我们实验室开发的毛细管力驱动的自组装过程，用于独立控制层孔隙率，旨在进一步改善电池性能。我们的基本方法专注于定制的粘合剂系统，以提高电池的电化学性能，在这里使用Li-NMC和石墨作为活性材料。该概念可以直接转移到包括不同活性材料或粘合剂的其他系统中，从而为电池浆料配方提供通用方法

Electrochemical energy storage plays an important role for reliable future energy supply and individual mobility. Today Li-ion batteries (LiB) dominate this technology field. Battery efficiency strongly depends on electrode engineering. Here we want to develop a binder formulation concept yielding electrode layers for LiB cells with improved electrochemical performance, high cyclic stability and long battery lifetime, exploiting the full capacity of the active material based on technical scale slurry formulations. The concept is based on a holistic approach including all aspects of binder functionality. We investigate binder specifications required to achieve slurry flow properties yielding uniform, defect-free electrode layers in industrial coating processes. Then, requirements for strong cohesion within the dry electrode layer and strong adhesion to the current collector are explored in order to avoid mechanical failure during Li-ion intercalation, resulting in high cyclic stability and long battery lifetime. Beyond that, we study the role of the binder as dispersing agent in order to control the microstructure of the electrode layer, i.e. the spatial distribution and orientation of active material and conductivity agent, to obtain high electrical conductivity and Li-ion mobility. This significantly affects the electrochemical cell performance although the binder is not involved in the electrochemical process. Anticipating a strongly growing demand of LiB we focus on waterborne slurries for electrode fabrication including state-of-the-art active materials and a combination of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binder system. We vary CMC molecular weight and degree of substitution systematically and hypothesize that an appropriate blend of different CMC types is needed to meet the diverse, partially conflicting interests at a minimum binder consumption. Corresponding slurries with promising binder composition are used to fabricate cells for electrochemical testing enabling us to validate and further improve the binder concept. Slurries with tailored binder composition are used to fabricate staged electrodes consisting of a thin layer including SBR next to the current collector thus providing strong adhesion and a SBR-free top layer with strong cohesion and CMC-controlled microstructure providing superior electrochemical properties. In this approach we also want to take advantage of a capillary force driven self-assembly process developed in our lab for an independent control of layer porosity aiming at a further improvement of cell performance. Our fundamental approach focusing on a tailored binder system to improve electrochemical performance of battery cells is demonstrated here using Li-NMC and graphite as active materials. The concept can be transferred to other systems including different active materials or binders in a straight forward manner, thus offering a generic approach for battery slurry formulation