The Lithium-Ion Battery Manufacturing Process
The Lithium-Ion Battery Manufacturing Process
These steps include:
Lithium-ion batteries (LIBs) are a valuable power source for many types of components ranging from electric vehicles to portable electronics and much more. They not only exhibit high power and energy density but also deliver a long cycle life.
Lithium-ion battery manufacturers offer a range of cell design options, such as pouch, prismatic, and cylindrical. Regardless of which cell type is being produced, the manufacturing process itself remains somewhat similar.
At Optimation Technology, we can design and build efficient production lines that include customized automation solutions catered to your battery manufacturing needs.
We work with you to develop and implement robotics, material handling, conveyance, and other automated technologies needed to carry out each step in the battery production process.
Mixing
LiB manufacturing begins with an electrode slurry mixing process. Active material , binding material, and solvent are combined to form a uniform slurry. The mixing process must be performed thoroughly to ensure the slurry’s homogeneity.. There are several types of mixing that can be performed depending on the slurry’s material characteristics:
- Ball mixing: A commonly used method of combining dry powder and slurry
- Ultrasonic mixing: A method of mixing high concentration slurry
- Hydrodynamic shear mixing: A standard mixing technique that features a rotating impeller.
The measurable characteristics of this process, such as viscosity, solid content, and density, all have a direct effect on the end quality of the battery and the electrode’s uniformity. After the anode and cathode slurries are mixed, they are ready to be delivered to the coating machine for the next step in the process.
Coating and Drying
Coating and drying processes are essential for electrode fabrication and are typically connected by a roll-to-roll system. First, the slurry is pumped from the mixing area into a slot die.
The electrode slurry is then dispersed onto two sides of current collector foil.
Two types of foils are used: typically aluminum foil for cathode and copper foil for the anode. The next step is to deliver the components to drying equipment to evaporate the solvent.
Solvent Recovery
Since the organic solvent (NMP) used in cathode slurries is toxic, there are strict emission regulations that must be adhered to. For this reason, a solvent recovery process is performed during the drying period.
The recovered NMP is then reused in battery manufacturing with an average loss of 20% to 30%. For water-based anode slurries, the harmless vapor can be directly exhausted into the ambient environment.
Calendering
The next step is to compact and compress the newly coated electrode onto the current collector foil. This process, known as calendering, improves the electrode’s energy density and provides consistent thickness.
High calendering pressure creates an even thickness and slurry adhesion to the electrode sheet, which improves cell performance.
Slitting
The compressed electrode must be cut to the required size and further refined. To accomplish this, a slitting machine featuring a blade, chisel, or other device cuts the electrode into narrower widths according to the dimensions required by the cell’s design.
The cutting method used depends on a number of electrode and process details. Since any burring that occurs will pose a safety risk, achieving clean edges and eliminating imperfections is critical.
Laser Cutting
Compared to other cutting techniques, laser cutting creates clean edges with less deformation. The cutting efficiency is controlled by altering the laser’s power and scanning speed. Infrared fiber lasers can reach 30 m/min cutting speed, with only 54 W power on the anode and cathode.
Vacuum Drying
The electrodes are sent to the vacuum oven to remove excess moisture. The electrodes are dried using infrared heating in a continuous process. This time is also when solvents are recovered. Vacuum drying is a critical process and requires intense time and energy consumption. The reaction between the leftover moisture and Li salt can produce hydrogen fluoride (HF) gas, which can pose damage and safety threats. It can also lead to reduced electrochemistry performance in the battery.
Due to its residual moisture from the aqueous binder, the anode contains a much higher amount of moisture than the cathode. The drying technology creates a low-pressure environment for the electrodes, featuring 60 °C to 150 °C heating for over 12 hours, with the option of an inert gas supply.
Stacking / Winding
After the drying and slitting [BB3] process is completed, the electrodes and separators are ready to be shaped into their final cell design. They are either stacked layer by layer or winded to form a cell’s internal structure.
When creating pouch cells, stacking is typically performed. For cylindrical or prismatic cells, winding processes are used. Separators are placed in between cathodes and anodes to prevent short circuits and also to transport lithium ions.
Welding
After the cells have been stacked or winded into shape, copper and aluminum tabs are welded onto the anode and cathode current collectors. The type of welding method used is based on the cell packing technique.
Ultrasonic welding is commonly used for joining tabs to pouch cells, and in certain instances on cylindrical and prismatic cells as well. Typically, however, resistance spot welding is used for cylindrical and prismatic cell designs. Laser welding techniques are also sometimes used.
Enclosing / Filling
Before the final sealing and production completion, cell enclosures must be filled with electrolyte. Each manufacturer has their own preferred enclosure method. The filling and enclosure process is performed in a dry room, as moisture causes the electrolyte to decompose, creating toxic hydrogen fluoride (HF) gas.
A high-precision dosing needle is used to fill the electrolyte. By applying a pressure profile to the cell, a capillary effect is activated, wetting the separator.
Formation
The formation process takes up to 3 weeks to complete and involves soaking, pre-charging, formation cycles, aging, degasing and resealing. To begin, cells are placed in racks and held for a period of time to let the electrolyte fully soak the cell contents. Then cells are contacted by spring-loaded pins and given an electrical potential between tabs. This starts the solid electrolyte interface(SEI) layer activation to to enable operation stability. A stable layer of SEI prevents irreversible consumption of the electrolyte and protects the anode from further reduction.
After the aging process is completed, the cells are ready for testing and delivery to end-product manufacturers.
Final Testing Process
Finally, after the aging process is complete, the cells are transported to an end-of-line testing station. Here, they are discharged to the shipping state of charge, and pulse testing is performed.
In addition, internal resistance measurements, OCV tests, leakage tests, and optical inspections are performed.
After the tests have been successfully completed, the cells are ready to be assembled into battery packs as required by the end-use application.
Battery Manufacturing Solutions from Optimation Technology
Optimation Technology supports US-based battery manufacturing with cost-effective, high-quality solutions. Our production capabilities allow us to deliver battery pack assembly line solutions capable of carrying out tasks from material storage through final pack assembly. To learn more about how we can enhance the production and throughput of your lithium-ion battery manufacturing operations, reach out to our team today.
