39 Battery cell manufacturing | Tech focus batches while recording the material temperature and the torque applied to the rotors. The torque curves are very specific to the material composition and demonstrate high reproducibility. The torque rise corresponds to an increase in material resistance against deformation. In the cathode mixtures, torque rises when PTFE is sheared, forming fibrils and interconnecting the cathode active material particles. These interconnections lead to inner friction, resulting in a temperature increase, and the oscillation of the torque relates to material elasticity. After the fibrillation is complete and the maximum torque has been reached, the PTFE fibrils stretch and orient into the direction of the shear. This diminishes the inner friction, and the torque and material temperature decrease until a steady state is reached. A dry electrode process also requires novel processing solutions for compounding and coating the anode and cathode pastes. Twin-screw extruders achieve fine dispersion in high-viscous pastes through strong shear forces acting on the material. This alone reduces the solvent content by 50% in cathode pastes. PTFE forms fibrils under shear and it has been determined to be a suitable binder, fixing the electrode structure, and at the same time creating a pore network that ensures the diffusion of lithium ions. Compounding extrusion of active material with PTFE yields high-viscous electrode pastes with solvent contents below 5%. Extruders are successfully used in research projects for new approaches to electrode manufacturing. The highly viscous pastes are processed into pellets so they can be transported and stored easily without ageing. To form electrodes, the pellets can later be coated on collector foil and calendared in one step. This electrode-manufacturing route is scalable to mass production and uses about 60% less energy than conventional manufacturing. The technology is expected to be applicable to polymer electrolyte electrodes and, after minor adjustments, to solid-state electrodes. Depending on the availability of material, electrode pastes can be compounded with throughputs of between 200 g/hr and 30 kg/hr with 11 mm, 16 mm or 24 mm screw diameters. Identical geometry ratios enable easy scalability of the compounding process between the extruder sizes. 3D printing Another approach is to use additive manufacturing for electrode production. This process lays down layers of dry material to build up the electrodes to the required thickness in a highly controlled environment with constant monitoring. This fits into existing production lines with many different types of chemistry, but the real advantage is reducing waste and producing complex shapes. This allows battery cells with holes or indentations to be produced reliably and consistently without having to cut the electrodes. Validation Once assembled, the cell undergoes a conditioning phase. The formation, ageing and test phase is the critical time when the cell is initially charged, and it undergoes several tests to evaluate its characteristics and performance. The final sequence – of pre-charging, degassing, forming, high-temperature ageing – may differ in time, order and repetition, depending on the manufacturer. Also, depending on the validation protocol, the cells could spend weeks in this last phase. The equipment consists of a fully automated system filled with towers of channels resembling large, automated warehouses. The equipment required has a large impact on the final dimensions for the production plant due to the high volume of cells that are processed simultaneously. Machine learning and artificial intelligence are increasingly common, using the data from the process to provide continuous improvement. Solid state Existing lithium-ion batteries have the advantage of a liquid electrolyte, which makes it easier for ions to flow back and forth between the anode E-Mobility Engineering | January/February 2025 The ace 2 V a2A2448-120 cm CXP camera is well-suited to stacking. Its Sony IMX547 CMOS sensor delivers 122 fps at 5.1 MP resolution (Image courtesy of Basler)
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