Solvent-less processing of battery electrodes

目前锂离子电池（LIB）电极的制造是通过浆料铸造进行的，浆料铸造将电化学活性颗粒、碳颗粒和聚合物粘结剂悬浮在逸散性液体粘结剂中。对于活性正极材料，如广泛使用的基于Li(Co,Ni,Mn)O2的材料，溶剂是有机的，以避免与活性颗粒发生反应，并且还需要溶解聚合粘合剂（通常是PVDF）。一旦这种溶剂/悬浮液混合物被加工成具有所需流变性和其他特性的浆液，它就会作为薄层（~ 100微米）沉积或铸造到金属箔上，在金属箔上干燥形成多孔电极，用于植入LIB。该工艺已成功扩展到“超级工厂”规模，运行宽度可达2米，生产速度可达100米/分钟。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有用的作用，只是在制造过程中暂时存在，以溶解粘合剂和悬浮电化学活性和其他电极材料。这些溶剂，特别是用于阴极的溶剂，通常是有毒的，易燃的，购买和处理都很昂贵。此外，溶剂的受控干燥要求电极干燥线是能源密集型的，占用大量的工厂面积。无溶剂，或干法加工，是指一系列新的和新兴的工艺，其目的是将一小部分粘合剂完全分散在固态，同时确保其保留其关键的电极机械稳定性和粘附功能。无溶剂处理可以在提高快速增长的超级工厂电池制造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，而且许多基础的科学理解尚未发展。这项研究将建立在我们对无溶剂、变形处理锂离子电池电极的概念验证工作的基础上。我们将以科学为导向的方法来理解多材料混合物的剪切变形的基本原理，包括颗粒尺寸，表面能，粘合剂化学等的影响。关键目标是更好地定量描述促进关键粘结剂纤维化步骤的条件。在发生纤化的地方，前驱游标活性颗粒、碳添加剂和粘结剂混合物会自发地形成一个完整的复合预制体。在第二步中，复合预制体然后通过热压延形成面积达10 x 10厘米，厚度小于300微米的LIB电极。多孔结构的演变、与电流收集器的粘附以及随着温度的变化而发生的纤维化将是研究的重点领域。这些方面将使用数值模拟，关键阶段的中断处理和各种显微镜和x射线显微断层扫描的显微结构分析相结合进行研究。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，以及完整的电池，其性能将与传统处理的等同物进行比较和合理化。考虑到不同的粘结剂形态，关键问题将是长期的机械稳定性，以及了解从根本上不同的干法加工微观结构可能带来的好处。将产生的理解结合在一起，将考虑设计和实现大规模制造干法加工电极的方法。该项目属于EPSRC能源和脱碳研究领域。这是一项为期4年的法拉第研究所奖学金（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)