From raw materials to battery cells

Now that the raw materials have been extracted, what comes next? The supply chain continues as the raw materials are transported around the globe to locations for further purification, refinement, and chemical modification. Then, the cells are manufactured.

Below, explore the process of lithium-ion pouch cell production and the safety risks that manufacturers are on the lookout for.

Batteries and cells: what’s the difference?

 

Lithium-ion batteries consist of single or multiple lithium-ion cells along with a protective circuit board. They are referred to as “batteries” only when the cells — or cell — are installed inside a device with the protective circuit board.

There are many shapes (or “formats”) of lithium-ion cells and batteries for many types of products.

Remember, a battery is defined as one or more cells in an electrical circuit.

A mobile phone is often powered by a pouch cell, which helps make the slim shape of the phone possible and reduces the battery’s weight. The process of manufacturing a mobile phone pouch cell battery is closely controlled and monitored. Let’s take a look.

Let’s take a look.

1. Electrode slurry

Powders containing the active materials in electrodes are mixed in a big bowl with binding materials, which act like a glue to create what scientists call a slurry, or a paste.

In your mobile phone battery, the electrode active materials are likely lithium cobalt oxide and carbon at the cathode, and graphite at the anode.

Video provided courtesy of Pacific Northwest National Laboratory

2. Electrode coating

The slurry is then spread out onto a very long piece of foil, which slowly rolls through high heat. This heat (300° F, 149° C) bakes the electrode into a solid and sticks the paste to the foil. The foil becomes a current collector attached to the electrode paste.

In your mobile phone battery, the foil is made of aluminum at the cathode, and copper at the anode.

Video provided courtesy of Pacific Northwest National Laboratory

3.  Electrode stamping

The baked electrode roll is cut into smaller pieces, which are placed under a super-sharp, rectangular die. With a sudden movement, the die quickly pushes down on the electrode sheet and cuts out an individual electrode battery piece.

Video provided courtesy of Pacific Northwest National Laboratory

4. Electrode stacking

An automated machine uses suction to pick up and release sheets of cut-out electrode material and wrap an insulating layer in between each sheet. The components are laid flat to look like layers in a cake. These layers include the anode, separator, cathode, and another separator.

The result is a credit card-sized electrode stack, which is spit out of the machine with the turn of a metal arm.

Video provided courtesy of Pacific Northwest National Laboratory

5. Pouch making

A special plastic, moisture-resistant barrier material is pressed to create rectangular pouches. The electrode stack is inserted into the resulting pouch to create a pouch cell.

Video provided courtesy of Pacific Northwest National Laboratory

6. Electrolyte injection

Liquid electrolyte is injected into an open battery pouch. In your mobile phone battery, the electrolyte is made of organic carbonates and a salt.

Video provided courtesy of Pacific Northwest National Laboratory

7. Battery Sealing

The electrolyte-soaked battery pouch is heat-sealed and placed in a vacuum chamber, which removes gases from inside the pouch.

Video provided courtesy of Pacific Northwest National Laboratory

The manufacturing process is complete!

All cells must undergo a charge-cycling procedure. During the first instance a battery cell is charged and discharged, Li+ ions forge tiny pathways in the solidified paste of the electrode layers.

This process “trains” the cells to charge and discharge later on.

The next step is to test for safety and performance: Was the pouch cell manufactured without any defects, is it safe to transport, and is it safe to use?

Lithium-ion Cell Manufacturing

Most pouch cell batteries are produced in manufacturing locations in China, South Korea, and Japan.

What are the risks?

Lithium-ion technology is generally safe when quality battery manufacturers take exhaustive steps to minimize design flaws, vet material suppliers and control quality of production.

To prevent damage and ensuing fires or explosions, manufacturers take special precautions and follow exact procedures.

When making lithium-ion batteries, attention is focused on avoiding any hidden defects that could be formed in the cell during the manufacturing process. This hidden defect can gradually create an internal short circuit while the battery is in use. An internal short circuit can cause thermal runaway.

Defects of concern come from contaminants such as water, foreign objects such as dust, and metal particles such as iron. When something gets into or damages the pouch, that becomes a problem.

For instance, too much moisture in the room can allow water to enter the cell pouch. When water makes contact with the electrolyte, the chemical reaction will cause the battery pouch to swell and eventually fail.

If pouch cell components are cut with a dull knife, the electrodes will have jagged edges, called “burrs”; those burrs can puncture the separator and cause an exothermic reaction.

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