42 July/August 2024 | E-Mobility Engineering Peter Donaldson looks at the myriad processes enabling more efficient manufacturing of lithium ion batteries Clever chemistry Manufacturing lithium-ion batteries for e-mobility applications is a complex, costly and capitalintensive undertaking, involving multiple processes and consuming large amounts of energy and time. The process involves several critical steps, each requiring precision and advanced technology to ensure a battery achieves its design performance, safety and longevity goals. Material preparation is the first stage and it starts with the procurement of essential raw materials, such as lithium, cobalt, nickel, manganese and graphite, from which cathode materials such as lithium nickel cobalt manganese oxide are synthesised, while the graphite is prepared for anode formation. In the next stage, electrode manufacturing, these substances are mixed with binders and liquid solvents to create slurries that will form the active components of each electrode – one for the cathode and the other for the anode. Each slurry is then applied to a metal foil (typically aluminium for the cathode and copper for the anode) using techniques such as slot-die coating. When the coating is complete, the foils are dried to remove solvents, resulting in solid, electrode layers. This is followed by calendaring, in which these layers are compressed to a specified thickness and density to optimise the electrode’s performance and consistency. The foils are then slit to the required width, and cut to the lengths and shapes required for assembly into cells, then the anode and cathode form the outer layers of a sandwich, with their active materials prevented from coming into contact by a separation layer, which prevents electron flow but allows ion flow between them. This layer is typically a coated polymer. For cylindrical cells, the electrode and separator layers are wound into a ‘jelly roll’ form, while they are stacked to make the cores of prismatic and pouch cells. The cell cores are then inserted into their containers, which are injected with electrolyte to enable ion transport between the electrodes before sealing. Pouch cells generally have polymer envelopes that are heat-sealed, while cylindrical and prismatic cells have metal cans that are sealed by welding. At this stage, sealing is not complete as a vent is left for the removal of gases during the formation and ageing processes that follow. Battery production is increasingly automated, with solutions such as this line assembling cylindrical cells into modules (Image courtesy of Dürr Systems)
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