The manufacturing process of lithium-ion batteries consists largely of 4 big steps of electrode manufacturing, cell assembly, formation and pack production, in that order. Each step employs highly advanced technologies. Here is an image that shows how batteries are produced at a glance.
▶STEP 1. Electrode manufacturing – making the cathode and anode of a battery
① Mixing : Basic battery constituents, such as cathode and anode active materials and solvents, are mixed to make a slurry, an intermediate good. A binder is added for improving adhesion between the particles of the active materials. Also, conductive additives plug holes that can be created between the particles and can reduce the capacity.
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② Coating : The completed cathode and anode slurries are thinly coated onto aluminum and copper foils respectively. In this process, binders are evenly dispersed onto electrodes for higher performance and longer life of batteries. LG Energy Solution became the first in the industry to introduce the Double Layer Slot Die Coating (DLD) method of coating different electrode slurries onto the current collector at the same time.
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③ Roll pressing : When the coating is done, electrodes go through two big rolls and get evenly flattened. The electrode surface bonds to active materials better, allowing lithium ions travel more easily. As a result, the output and performance of the batteries improve.
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④ Slitting and notching : The flattened electrodes are cut into required sizes to fit for the battery. They are slit vertically in the slitting process and cut horizontally to get a V-shaped notch as well as cathode and anode tabs in the notching process.
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▶STEP 2. Cell assembly – forming the battery shape (pouch/ cylindrical batteries)
In the cell assembly process, batteries take the shapes as we know them. The order of manufacturing process differs depending on the shape (cylindrical, pouch, and prismatic types) and each battery maker employs different technology.
Pouch battery : First, a 7-layer pouch film is pressed to make a pouch case. In this step, an electrode pocket and an air pocket are produced. Battery ingredients (cathode, anode, separator, electrolyte) are placed in the former and electrolytes are injected and gas is stored in the latter. The ingredients are piled up in the electrode pocket using “lamination and stacking” method and electrolyte is injected into the air pocket to reach even pores in the electrode pocket.
* View more about cell assembly of pouch battery (Ep.1)
* View more about cell assembly of pouch battery (Ep.2)
Cylindrical battery : Cathode, anode, and separator are rolled up using the “winding” method. An aluminum tab is attached to the uncoated part of cathode and a copper tab on that of anode of the resulting “jelly roll.” Then, it is fixed in the cylindrical battery can. Electrolyte is injected. Lastly, after an insulated tube is put on the completed battery to separate the cathode and anode and prevent short circuits, then it has the shape of a cylindrical battery.
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▶STEP 3. Formation – activating a battery with electrical energy and stabilizing it
The next step is formation where batteries are activated with electric energy and their safety is checked. This process consists of repeated aging, charging, and discharging. First, the battery is put at room temperature so that electrolyte can permeate into the cathode and anode, which is called “aging.” When the electrolyte soaks into the inside of the battery and ions move smoothly between the cathode and anode, the battery is charged to a certain level.
(* The formation process differs by manufacturers.)
A pouch battery may form gas in it during the repeated aging, charging, and recharging. Then, the gas is removed through “degassing,” after which aging and charging is repeated to test the capacity and isolate substandard batteries.
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▶STEP 4. Pack process – forming a module to fit for the models
This process is about making modular batteries with manufactured battery cells and putting them into a pack. First, battery cells are fixed side by side in a module case. The cells are connected and when a cover is put on the case, a module is complete. Lastly, finished modules are placed in a battery pack and connected to each other, and a pack is complete.
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We have taken a look at battery manufacturing at a glance. Each step contains more detailed procedures. Next time, we will explore key processes of each step and specific technologies of the step with an infographic.