Standards of Lithium - Ion Battery Cell Production Process

The production process of lithium - ion battery cells is a complex and highly - standardized procedure that involves multiple steps, each of which is crucial for ensuring the quality, performance, and safety of the final product.

1. Raw Material Preparation

Negative Electrode Material: Graphite is the most widely used negative electrode material. It is processed to have a specific particle size distribution and surface properties. Artificial graphite is often produced by graphitizing petroleum coke or mesocarbon microbeads at extremely high temperatures (above 2500°C). The graphite should have a low sulfur content (less than 0.05%) to prevent corrosion of the battery components.

Electrolyte: The electrolyte is typically a solution of lithium salts (such as lithium hexafluorophosphate, \(LiPF_6\)) in organic solvents like ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The concentration of \(LiPF_6\) in the electrolyte is usually in the range of 1 - 1.2 mol/L. The water content in the electrolyte must be strictly controlled, generally below 20 ppm, as water can react with \(LiPF_6\) and degrade battery performance.

2. Electrode Coating

Positive Electrode Coating: The positive electrode material is mixed with a binder (such as polyvinylidene fluoride, PVDF) and a conductive agent (such as carbon black) in a suitable solvent (N - methyl - 2 - pyrrolidone, NMP). The slurry is then coated onto a current collector, usually aluminum foil, using techniques like doctor - blading or slot - die coating. The thickness of the positive electrode coating is precisely controlled, typically in the range of 80 - 120 μm, and the coating weight per unit area is carefully monitored to ensure consistent performance.

Negative Electrode Coating: Similarly, the negative electrode slurry, composed of graphite, binder (e.g., styrene - butadiene rubber, SBR), and thickener (e.g., carboxymethyl cellulose, CMC), is coated onto a copper foil current collector. The thickness of the negative electrode coating is generally 60 - 100 μm. After coating, the electrodes are dried in an oven at elevated temperatures (around 120 - 150°C) to remove the solvent completely.

3. Cell Assembly

Winding or Stacking: In the winding process, the positive electrode, separator (usually made of porous polyolefin such as polyethylene or polypropylene), and negative electrode are wound together in a spiral - like structure. For prismatic cells, the electrodes and separator are stacked layer - by - layer. The alignment of the electrodes and separator is critical; any misalignment can lead to short - circuits or non - uniform current distribution.

Cell Enclosure: The assembled electrode stack is placed into a battery case, which can be cylindrical (made of steel or aluminum), prismatic (aluminum alloy), or pouch - type (laminated aluminum - plastic composite film). The case is then sealed tightly, and the electrodes are connected to the terminals. In the case of pouch - type cells, the edges are heat - sealed to ensure a hermetic seal, and the sealing strength should be sufficient to withstand internal pressure changes during battery operation.

4. Activation and Aging

Activation: The newly assembled cells are subjected to an initial charge - discharge process called activation. This process forms a solid - electrolyte interphase (SEI) layer on the surface of the negative electrode, which is essential for the stable operation of the battery. The activation charge - discharge current is usually set at a low rate, such as C/10 (where C is the battery's rated capacity).

Aging: After activation, the cells are aged at a specific temperature (e.g., 45 - 55°C) for a certain period (usually 2 - 7 days). Aging helps to stabilize the battery's performance and improve its consistency. During aging, any internal chemical reactions that may affect long - term performance are allowed to occur in a controlled environment.

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