lipo Battery Manufacturing Process

Soft-pouch lithium-ion batteries are widely used in portable electronic devices due to their high safety, energy density, and design flexibility. The manufacturing process involves several critical steps:

1. Material Preparation

The key materials required for battery production include:

• Cathode Materials: Such as lithium cobalt oxide (LiCoO₂), lithium iron phosphate (LiFePO₄), and other lithium compounds.
• Anode Materials: Typically graphite or other carbon-based materials.
• Separator: A thin, porous polymer membrane.
• Electrolyte: A lithium-ion conductive solution.

The choice of materials is crucial for the battery’s performance and safety.

2. Electrode Preparation

• Slurry Preparation: Active materials, conductive agents, and binders are evenly dispersed to create a uniform, stable slurry. The slurry’s consistency is vital for maintaining the battery’s uniformity during production.
• Coating: The cathode slurry is coated on aluminum foil, and the anode slurry is coated on copper foil. The thickness and drying temperature are strictly controlled to ensure quality and consistency.
• Rolling: The coated electrodes are compressed using rollers to improve their density and strength.
• Cutting and Drying: The rolled electrodes are cut into the required size and dried to remove solvents and moisture.

3. Separator Preparation

The separator is a critical component that allows lithium-ion movement while preventing electron flow. It must have enough mechanical strength and chemical stability to ensure the battery’s safety and performance.

4. Electrode Cutting and Stacking

The dry cathode and anode electrodes, along with the separator, are stacked in sequence to form the basic structure of the cell. Accurate alignment and positioning are essential for the battery’s structural integrity and performance.

5. Battery Assembly

• Cell Shaping: The cell’s dimensions are designed according to customer requirements, and the aluminum-plastic film is molded into shape.
• Top and Side Sealing: The wound cell is placed into a prepared mold, and the packaging film is folded over to seal the top and sides, securing the terminal leads.
• Liquid Injection and Pre-sealing: After sealing, the cell is inspected for alignment, and any moisture is removed before the electrolyte is injected and pre-sealed.

6. Formation and Activation

• Resting: The injected electrolyte is allowed to fully soak into the electrodes.
• Formation: The battery undergoes its first charge to activate the cell, forming a stable solid electrolyte interface (SEI) on the electrodes. Gas production occurs during this process, so some manufacturers use fixtures to channel gas into designated bags.
• Fixture Shaping: After formation, the electrode interfaces are optimized, and the fixture shaping ensures the battery retains its correct shape and dimensions.

7. Secondary Sealing and Shaping

• Secondary Sealing: A vacuum is used to remove any remaining gas from the bag and some of the electrolyte, followed by a second sealing process. The gas bag is then trimmed, and the cell takes its final shape.
• Edge Trimming and Folding: The edges of the first and second seals are trimmed to the correct width and folded to ensure the battery meets dimensional specifications.

8. Testing and Sorting

Each cell undergoes a series of tests, including capacity, internal resistance, and leakage current checks, to ensure they meet quality standards. Cells that do not meet the criteria are discarded to maintain the product’s quality and consistency.

9. Packaging and Final Testing

Qualified cells are packaged into their final form and undergo a final round of testing. This includes appearance inspection, voltage testing, and capacity checks to confirm that the product meets customer requirements.

Quality Standards for Soft-Pouch Lithium-Ion Batteries

1. Packaging and Labeling: The battery packaging should be intact, with no damage, and the printed information (brand, model, capacity, voltage, production date) should be accurate and clear. The seal should be tight, with no gaps.
2. Appearance Integrity: The surface of the battery should be free of scratches, dents, deformities, stains, or rust. The terminal leads should be flat, without bends, breaks, or oxidation. The aluminum-plastic film should be free of damage, wrinkles, or bubbling.
3. Capacity: The actual capacity should be close to the rated capacity, with a higher ratio indicating better performance.
4. Internal Resistance: A low internal resistance is crucial for ensuring minimal energy loss during charge/discharge cycles and high energy efficiency.
5. Charge and Discharge Performance: The battery should charge fully within a reasonable time, without abnormal heating, smoke, or swelling. During discharge, the voltage should not drop too quickly, and the current should be stable.
6. Cycle Life: After multiple charge/discharge cycles, the battery’s capacity retention and performance decay should remain within acceptable limits. For consumer batteries, the cycle life should be ≥800 cycles, with a capacity retention rate ≥80%.
7. Safety: The battery should feature effective overcharge protection, over-discharge protection, and short-circuit protection. It should remain stable at high temperatures without deformation or swelling.

The manufacturing process of soft-pouch lithium-ion batteries involves precise control at each step to ensure optimal performance, safety, and reliability.