Solvent-less processing of battery electrodes

目前的Li离子电池（LIB）电极制造通过浆料浇铸进行，所述浆料浇铸将电化学活性颗粒、碳颗粒和聚合物粘合剂悬浮在短效液体粘合剂中。在活性阴极材料例如基于广泛使用的Li（Co，Ni，Mn）O2的那些的情况下，溶剂是有机的以避免与活性颗粒反应，并且还需要溶解聚合物粘合剂（通常是PVDF）。一旦将该溶剂/悬浮液混合物加工成具有所需流变学和其他性质的浆料，将其作为薄层（~ 100微米）沉积或浇铸到金属箔上，在金属箔处其干燥以形成用于并入到LIB中的多孔电极。该工艺已成功地扩大到“千兆工厂”规模，以高达2米的宽度和100米/分钟的生产速度运行。然而，形成浆料所需的有机溶剂在最终的锂离子电池中没有发挥有用的作用，并且仅在制造过程中暂时存在以溶解粘合剂并悬浮电化学活性材料和其他电极材料。这些溶剂，特别是用于阴极的溶剂，通常是有毒的、易燃的，并且购买和处理昂贵。此外，溶剂的受控干燥要求电极干燥线能耗高，并占用大量的工厂面积。无溶剂或干法加工是指一系列新兴工艺，其目的是将小部分粘合剂完全分散在固态中，同时确保其保持关键的电极机械稳定性和粘合功能。无溶剂加工可以在提高快速增长的电池生产的可持续性方面发挥非常重要的作用，但从实践的角度来看还不成熟，许多基础科学认识还有待发展。这项研究将建立在我们对锂离子电池电极的无溶剂变形加工的概念验证工作的基础上。我们将采取以科学为主导的方法来理解多材料混合物剪切变形的基本原理作为温度的函数，包括颗粒尺寸，表面能，粘合剂化学等的影响。一个关键目标是更好地定量描述促进关键粘合剂原纤化步骤的条件。在发生原纤化的情况下，前体活性颗粒、碳添加剂和粘合剂混合物自发地形成整体复合材料预成型件。在第二步骤中，然后通过热烧结将复合预成型件形成为面积高达10 × 10 - 3cm且厚度小于300微米的LIB电极。多孔微观结构的演变，与集流体的粘附性和作为温度函数的持续原纤化将是研究重点的关键领域。这些方面将使用数值模拟，中断处理的关键阶段和微观结构分析的各种显微镜和X射线显微断层扫描相结合的研究。将详细研究电极的电化学和循环行为。阳极和阴极都将被研究，沿着全电池，其性能将与常规处理的等效物进行比较并合理化。关键问题将是长期的机械稳定性，考虑到不同的粘结剂形态和理解从根本上不同的干加工微观结构可能提供的好处。将产生的理解放在一起，考虑设计和实施大规模生产干法加工电极的方法。该项目福尔斯EPSRC能源和脱碳研究领域。这是一个为期4年的法拉第研究所学生奖学金（部分课程费用由牛津材料基金支付）。

Current Li ion battery (LIB) electrode manufacture takes place by slurry casting that suspends electrochemically active particulates, carbon particulates and polymeric binder in a fugitive liquid binder. In the case of active cathode materials such as those based on widely used Li(Co,Ni,Mn)O2, the solvent is organic to avoid reaction with the active particles, and is also required to dissolve the polymeric binder (usually PVDF). Once this solvent/suspension mixture is processed into a slurry with the required rheological and other properties, it is deposited, or cast, as a thin layer (~ 100 microns) onto a metallic foil where it dries to form a porous electrode for incorporation into a LIB. The process has been successfully scaled to the "gigafactory" scale, operating at up to 2 m width and production speeds of 100 m/min. However, the organic solvent required to form the slurry plays no useful role in the final Li ion battery and is only present transitorily during manufacture to dissolve the binder and to suspend electrochemically active and other electrode materials. These solvents, especially for cathodes, are usually toxic, flammable and expensive to buy and handle. Further, the controlled drying of the solvent mandates electrode drying lines that are energy intensive and occupy significant factory area.Solvent-less, or dry processing, refers to a family of new and emerging processes with the objective of dispersing the small fraction of binder entirely in the solid state, while ensuring it retains its critical electrode mechanical stabilisation and adhesion function. Solvent-less processing could play a very significant role in increasing the sustainability of the fast-growing gigafactory manufacture of batteries, but is immature from a practical standpoint and much of the underpinning scientific understanding has yet to be developed.The research will build on our proof-of-concept work on solvent-free, deformation processing of Li ion battery electrodes. We will take a science-led approach to understanding the underlying principles of shear deformation of multi-material mixtures as a function of temperature, including the effect of particulate size, surface energy, binder chemistry, etc. A key target is a better quantitative description of the conditions that promote the critical binder fibrilisation step. Where fibrilisation occurs, the pre-cursor active particulate, carbon additive and binder mixture spontaneously forms an integral composite preform. In a second step, the composite preform is then formed by warm calendaring into a LIB electrode of area up to 10 x 10 cm and thickness less than 300 microns. The evolution of the porous microstructure, adhesion with the current collector and ongoing fibrilisation as a function of temperature will be key areas of research focus. These aspects will be studied using a combination of numerical simulation, interrupted processing at key stages and microstructural analysis by various microscopies and X-ray micro-tomography. The electrochemical and cycling behaviour of the electrodes will be studied in detail. Both anodes and cathodes will be studied, along with full cells whose performance will be compared with and rationalised in terms of conventionally processed equivalents. Key issues will be long term mechanical stability given the different binder morphologies and understanding what benefits the fundamentally different dry processed microstructures may offer. Drawing the generated understanding together, consideration will be given to the design and implementation of approaches large scale manufacture of dry processed electrodes.This project falls within the EPSRC energy and decarbonisation research areas.This is a 4-year Faraday Institution Studentship (part of the course fee paid from Oxford Materials funds)