MANUFACTURING

Coating is also carried out in a cleanroom (to avoid impurities damaging electrochemical stability): the positive electrode material is coated on aluminum foil (aluminum resists the high potential of the positive electrode), and the negative electrode material is coated on copper foil (copper adapts to the low potential of the negative electrode). The coating thickness must be controlled within 1mm to ensure electrode uniformity and support cell energy density and cycle performance.

Calendering is a key process in pole piece preparation: in addition to making the positive and negative electrode materials firmly adhere to the aluminum/copper foil substrate, it is also necessary to precisely control the compaction density-both to increase the proportion of active materials per unit volume to optimize energy density and to avoid excessive rolling that damages the material structure.

Drying is a key process in pole piece preparation, which is carried out after coating and before calendering. It mainly removes moisture and residual solvents mixed in the stirred slurry to avoid internal side reactions of the cell. This not only ensures the purity of the electrode material but also stabilizes the pole piece compaction density, directly affecting the cell energy density and cycle stability.

Slitting is accurately carried out according to the shape requirements of the battery. The precision must be strictly controlled during the cutting process to avoid burrs on the pole pieces, which can prevent internal short circuits of the cell. The edges of the slit positive and negative pole pieces are neat, which can better adapt to the subsequent winding or lamination process, ensuring the assembly precision and operational safety of the finished battery.

The slit positive and negative pole pieces need to be welded with tabs, which is a key step for current extraction of the cell. The positive pole pieces are matched with aluminum tabs (resistant to high potential), and the negative pole pieces are matched with copper or nickel tabs (adapted to low potential). The welding must be firm without false welding, laying a solid foundation for the subsequent connection between the cell and external circuits.

The positive and negative electrode pieces separated by a diaphragm are closely attached and wound into a basic elliptical cylindrical cell; then, it is extruded and shaped according to the specifications of the finished battery, which not only ensures the compact and regular structure of the cell but also improves the energy density per unit volume.

In the assembly process, the wound and shaped cell is put into a specialized cell casing for basic packaging. This can isolate external impurities and moisture and avoid structural loosening of the cell.

The baking process is carried out on the packaged cells to completely remove trace moisture infiltrated during the packaging process. If moisture remains, it is prone to side reactions with the positive electrode material and damage the stability of the electrolyte. This measure can effectively avoid the risk of cell capacity degradation and ensure its energy density and cycle service life.

In the electrolyte injection process, electrolyte is injected into the dried cell through reserved air holes. The electrolyte will fully infiltrate the positive and negative electrode pieces and the diaphragm, activating the electrode active materials. This step can be called the "first heartb eat" of the battery, laying a key foundation for subsequent formation and capacity activation.

After electrolyte injection, the cell needs to undergo vacuum treatment to extract residual air and trace moisture inside. This can avoid side reactions between oxygen and moisture in the air and the active materials of the positive and negative electrodes, prevent cell capacity degradation and internal resistance increase, and lay a foundation for stable performance in the subsequent formation process.

The cells after vacuum sealing are subjected to charging and discharging treatment, which can not only activate the activity of lithium ions in the positive and negative electrode materials but also promote the formation of a dense and stable SEI (Solid Electrolyte Interface) film on the negative electrode surface, thereby locking the cycle life and capacity upper limit of the cell and laying a core foundation for the performance of the finished battery.