33 Battery cell manufacturing | Tech focus E-Mobility Engineering | January/February 2025 is challenging to scale up to a wellcontrolled, continuous process. Extruders also provide excellent capabilities for solid-state battery (SSB) development (see below). An understanding of the rheological properties of an electrode slurry is necessary for a precise printing process to obtain batteries with high capacity and a high number of charging cycles. Coating and drying Once the slurry is produced, it is pumped through a piping system to the coating area, where the mix is printed on a metal foil that is unrolled to the coating head. There, the slurry is deposited, and the coated foil continues its process through a drying oven, where the solvent evaporates, leaving the active material attached to the foil and evenly distributed. Gradual drying is key to obtain a good-quality electrode, which requires ovens as long as 80 m. This can also reduce the amount of solvent required, decreasing the energy required for drying the slurry by as much as 30% by producing almost-dry battery pastes. The coating, which is applied on both sides of the foil, can be intermittent or continuous, depending on the cell size and format to be produced. In general, the width of the printed strips on the roll limits the dimensions of the cell and therefore directly affects the production capacity of the line. Calendering The next step in the manufacturing process is calendering, which acts as the finishing process for the coated rolls. Like the previous step, it is a roll-to-roll process, where the coated rolls travel through two heated rollers to compress the material, and thus ensure constant thickness, density and better adherence. Slitting Slitting is the first cutting process used to limit the foil to the size of the individual electrodes that will be required for final assembly. The rolls coming from the calendering process go through a bank of blades, which cuts them into multiple, smaller (daughter) rolls to fit with the final design. Dry room assembly Once the electrode-manufacturing phase is complete, the process moves onto the second phase of assembling the cells. One of the most relevant aspects of this phase for lithium-ion and lithium sulfur batteries is that it must be carried out in a dry environment to avoid any humidity remaining in the electrode, which can lead to increased degradation and capacity loss. There are two types of equipment to produce the slurry: batch production (usually planetary mixers) or continuous production (which combines the basic dosing operations along the mixing chamber by means of automated, gravimetric feeding systems). During the multi-step process, from raw materials to the final battery cell, the use of a twin-screw extruder can improve the critical step of the slurry. Battery slurry production commonly uses a batch process to mix the active materials, carbon black, solvents, binders and additives in stirred vessels. This process is labour-intensive, bears the risk of batch-to-batch variations and requires production downtimes for cleaning. Twin-screw compounding offers a continuous production process with precisely controlled material shear, heat transfer, material throughput and residence time. The twinscrew extrusion process offers high reproducibility, less cleaning time and high material efficiency. The dispersive and distributive mixing of a twin-screw extruder enables a much more homogeneous cathode paste, compared with alternative batch-mixing in, for example, a dissolver. In return, this can lead to improved material properties. As a result, using twin-screw extrusion can help to improve the classic production of cathode and anode slurries by moving from a batch that Using a twin-screw extrusion can help to improve the classic production of cathode and anode slurries by moving to a well-controlled, continuous process The stages of battery cell manufacturing (Image courtesy of CIC energiGUNE)
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