Barry on Batteries: 11 Essential Steps in Lithium-Ion Battery Cell Manufacturing

As any process engineer knows, synthesizing an active pharmaceutical ingredient (API) or specialty chemical involves numerous reaction steps. Consider that a peptide API may require up to 36 steps. Even a supposedly "simple" specialty chemical demands as many as 15 steps — each with its distinct chemical combinations, process parameters and byproducts. 

If we look at the lithium-ion battery cell manufacturing market, the complexity of manufacturing is equal to that of APIs. Synthesizing the cathode active material along with the anode material, separators and electrolytes is very complex. The actual assembly of the cell battery is overly complex, with 11 different steps and many sub-steps. The following is a breakdown of each step in the cell production process and the critical materials involved, demonstrating why precise control and expertise are essential at every stage of production to ensure battery performance, safety and reliability. 

1.    Slurry Mixing 

In the first step, manufacturers combine various solids and liquids to form the cathode and anode slurry. For the cathode material, they blend conductive material with the binder and solvent. The anode material contains graphite mixed with the wetting-agent and its binder.

2.    Coating

The cell manufacturer layers the cathode slurry onto carbon-coated aluminum foil and applies the anode material onto copper foil. These foils serve as current collectors.

3.    Drying

The foils contain a solvent that manufacturers must remove through a drying process. They typically achieve this by subjecting the coated foils to high temperatures in convection steam-heated roller-ovens, resulting is solvent evaporation. They also can use infrared systems to enhance the drying speed.

4.    Calendaring

Calendaring involves passing the anode and cathode electrode sheets through rollers to compress and densify the material and to ensure a consistent thickness.  

5.    Slitting and notching

The electrode is a large sheet, and slitting is required to size it properly for the cell. Slitting of the electrode involves precise cutting into multiple rectangular strips. This two-step process begins with vertically slitting the electrode and removing dust and iron. The second cut is a V-shaped notch and tabs to form positive and negative terminals. The use of infrared edge positioning and laser notching help ensure correct sizing.

6.    Stacking and winding

The electrode stacking and winding process is where the cell starts to come together by layering the cathode foils,  anode foils and separator layer. All three must be perfectly aligned to make the cell. Included in this step are alignment detectors, adhesive units and hot-pressing units.

7.    Cell assembly

The cell assembly process has approximately seven sub-steps before manufacturers can add the electrolyte. They must first collect data, such as raw materials used, manufacturing history, quality, and manufacturing date, to ensure they can identify each cell later on, if necessary.  Following this is welding, positioning, stacking, cutting and several measurement steps to ensure prefect alignment, as well as thickness measurements. The components are then welded into “cans,” which are leak-tested and baked together in an oven for about eight hours.    

8.    Electrolyte filling 

The filling step is critical for ensuring complete wetting of the positive and negative electrodes. This may take up to several hours. Manufacturers must tailor the process to the cell design. They must weigh the cells before and after filling them as a final quality control test. Additional quality control tests include pressure measurements and “soaking” time, both required before the cells can be certified. 

9.    Formation and aging

In this step, forming refers to the electrochemical activation that results in the solid electrolyte interface (SEI) on the anode electrode of the battery. The step also involves charging and discharging, removal of gases that are generated during the process and resealing of the battery.  The aging process is simply a storage time on shelves to stabilize the SEI and then additional testing to ensure the cells meet the quality for capacity, voltage and cycle life.  

10.    Final testing and film wrapping

Now that the cells are completed, there is one more final check. This includes cell weighing, cell size inspection—both manual and automatic—insulation testing and then, once again, data traceability and cell certification.  

11.    Module assembly

The completed cells are assembled into the modules for shipping to the automotive companies that assemble the modules into packs for their electric vehicles (EV).   

Given the complexity of the processes involved, the manufacturing of lithium-ion batteries mirrors the precision of a high-stakes chemical plant, where every step is critical to the end product’s performance and safety — ensuring that, just like in pharmaceuticals, quality control at every stage is non-negotiable.

In my next column, I will expand on some of these points by exploring quality testing in cell manufacturing.