The manufacturing process of lithium battery pack cells mainly consists of three stages: the preparation of the front-end electrode sheets, the assembly of the mid-stage cells, and the formation and packaging of the back-end cells. Each stage involves multiple key process steps. The following is a detailed introduction:

Preparation of the front-end electrode sheet

Ingredients: The cathode material is composed of active material, conductive agent and binder. The conductive agent needs to be baked at approximately 120℃ for 8 hours, the binder PVDF needs to be baked at approximately 80℃ for 8 hours, and whether the active material needs to be baked or not depends on the state of the incoming material and the process. The negative electrode system is mostly aqueous mixture, with deionized water as the solvent. The incoming material does not need to be dried, but the conductivity of the deionized water is required to be ≤1us/cm.

Pulping: Mix the positive and negative electrode active substances, conductive agents, binders, etc. with the solvent in proportion and stir them into a paste in a vacuum mixer. When making slurry for the positive electrode, attention should be paid to the feeding sequence (add the active material and conductive agent first and stir slowly to mix, then add the slurry), the feeding time and proportion. It is also necessary to strictly control the parameters such as the revolution and rotation speed of the equipment, the vacuum degree of stirring, and the temperature. In addition, the particle size and viscosity of the slurry should be regularly tested. The pulping process of the negative electrode is similar, but an additional dispersant needs to be added, and the stirring parameters are different.

Coating: The positive and negative electrode pastes are evenly coated on the surfaces of the aluminum foil (positive electrode) and copper foil (negative electrode) current collectors respectively through a coating machine.

Coating: The positive and negative electrode pastes are evenly coated on the surfaces of the aluminum foil (positive electrode) and copper foil (negative electrode) current collectors respectively. After coating, they are heated in a drying tunnel to remove the solvent, forming positive and negative electrode sheets. The single-sided density of the positive electrode coating is approximately 20-40 mg/cm². The temperature of the coating oven is typically 4-8 sections or more, and the baking temperature of each section is 95-120 ℃. The single-sided density of the negative electrode coating is approximately 10-15 mg/cm², and the baking temperature of each section is 80-105 ℃.

Rolling: Use a rolling press to compact the coated electrode sheets, adjust parameters such as the gap between the rolls, the position of winding and unwinding, and tension, to make the electrode sheets reach the designed thickness, increase the density and strength of the electrode sheets, and enhance the adhesion between the active material and the current collector.

Slitting: Use a slitting machine to cut the wider electrode sheets into narrow strips of the required width for a single battery cell. During slitting, pay attention to the burrs on the electrode sheets. All burrs in the X and Y directions of the electrode sheets should be inspected. The length of the longitudinal burrs is strictly limited by the process.

Slide preparation or film development: Slide preparation involves welding tabs on a slide preparation machine, attaching insulating glue to the TAB positions, and covering the exposed current collector and tabs. The blanking process involves using a blanking machine to cut the slitted electrode sheet rolls into the actual dimensions of the positive and negative electrode sheets required by the battery.

Assembly of midsection battery cells

Winding or lamination: The winding process involves rolling the strip-shaped positive and negative electrode sheets and the separator into cylindrical or square cores through a winding machine. It is required that the negative electrode sheet completely covers the positive electrode sheet, and the separator completely covers the negative electrode sheet. The laminating process involves alternately stacking multiple layers of positive and negative electrode sheets and separators through a laminating machine to form battery cells.

Shell insertion or packaging: For cylindrical batteries and square hard-shell batteries, the wound or stacked cores are placed in the corresponding steel or aluminum shells. For pouch batteries, insert the electrode core into the aluminum-plastic film that has already been punched with pits, and perform top sealing and side sealing, reserving the liquid injection port.

Bottom welding or TAB welding: For cylindrical batteries and square hard-shell batteries, the negative TAB needs to be welded to the bottom of the battery casing to make the battery casing the negative electrode. Soft-pack batteries are connected to external circuits by welding the tabs of the stacked cells with dedicated welding equipment.

Grooving or gluing: After the cylindrical battery is welded to the bottom of the shell, the core coil inside the steel shell is fixed through the grooving process. After the core of a pouch cell is assembled, it usually requires a gluing operation to fix and insulate the tabs and other parts.

Baking: Place the battery cells that have been shell-packed or packaged in an oven for baking to remove the moisture in the cells and ensure that the moisture content meets the standard requirements.

Liquid injection: The electrolyte is injected into the battery cells that have passed the moisture content test after baking through a liquid injection machine. The amount of liquid injection and the injection environment must be strictly controlled.

Welding and sealing: Weld the cover plate to the positive electrode TAB to make the cover plate the positive electrode of the battery, and then seal the battery case and the cover plate to keep the battery cell in a completely sealed state. After the soft-pack battery is injected with liquid, it undergoes a secondary seal, the internal gas is extracted, the airbag is punctured and cut off, and finally the edge is folded and formed.

The later stage is transformed into encapsulation

Formation: Perform the first charge on the battery cell to activate it and form a stable solid electrolyte phase interface (SEI) film on the surface of the negative electrode, reflecting the true electrical performance of the battery.

Aging: After formation, the battery cells in a certain state of charge are left in a certain temperature environment for a period of time. The voltage of the battery before and after being left is tested. Based on the voltage drop, the cells are screened and classified, and those with large or abnormal voltage drops are eliminated.

Sorting: According to the size of the AC internal resistance of the battery cells, sort out the battery cells of different internal resistance grades, and remove the battery cells with abnormal internal resistance.

Capacity separation: Conduct charge and discharge tests on the battery cells, classify the batteries by capacity, and determine the actual capacity and other electrical performance parameters of the batteries.

OCV test: It tests the open-circuit voltage, internal resistance and K value of the battery and other standards to evaluate the overall quality of the battery and select qualified products.