Production Process of Pouch - type Lithium - ion Batteries

　　The production of pouch - type lithium - ion batteries is a complex and highly - controlled process, involving multiple steps to ensure high - quality and reliable battery performance.

　　1. Electrode Preparation

　　The first step is the preparation of electrodes. For the positive electrode, a mixture of active materials such as lithium cobalt oxide (LiCoO₂), lithium nickel - manganese - cobalt oxide (NCM), or lithium iron phosphate (LiFePO₄) is blended with conductive agents like carbon black and binder materials such as polyvinylidene fluoride (PVDF). This mixture is then coated onto a thin metal foil, usually aluminum, using a doctor - blade or slot - die coating method. After coating, the electrode is dried in an oven at a specific temperature to remove the solvent. The negative electrode is prepared in a similar way. Graphite is the most commonly used active material for the negative electrode. It is mixed with a binder and coated onto a copper foil. The thickness and uniformity of the electrode coatings are crucial as they directly affect the battery's capacity and performance.

　　2. Cell Assembly

　　Once the electrodes are prepared, the cell assembly process begins. A separator, typically made of porous polypropylene or polyethylene, is placed between the positive and negative electrodes to prevent short - circuits while allowing the flow of lithium ions. The electrode - separator - electrode sandwich is then carefully rolled or stacked, depending on the design of the battery. In the case of a stacked design, multiple layers of electrodes and separators are precisely stacked on top of each other. After that, the assembly is inserted into a pouch - type packaging material, which is usually made of a multi - layer laminate film consisting of a metal layer (such as aluminum) for protection and two polymer layers for sealing.

　　3. Electrolyte Filling

　　The next step is electrolyte filling. The electrolyte, which is a solution of lithium salts (such as lithium hexafluorophosphate, LiPF₆) in organic solvents like ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), is carefully injected into the pouch through a small opening. The amount and quality of the electrolyte are critical. Too little electrolyte may lead to poor ion conductivity, while too much can cause swelling and leakage. After filling, the opening is sealed immediately to prevent moisture absorption, as moisture can react with the electrolyte and degrade the battery performance.

　　4. Activation and Aging

　　The assembled battery is then subjected to an activation process. This involves a series of charge - discharge cycles at a low current rate. During activation, the battery's electrochemical reactions start to occur, and the solid - electrolyte interphase (SEI) layer forms on the surface of the negative electrode. The SEI layer is essential for the long - term stability of the battery. After activation, the battery undergoes an aging process. It is stored at a specific temperature for a certain period to allow the internal components to stabilize and for any minor defects to manifest. This helps in improving the consistency and reliability of the battery performance.

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