Technology analysis and summary of lithium battery aging process
The production of lithium ion batteries is a process closely linked by various technological steps. Overall, the production of lithium batteries includes the electrode manufacturing process, battery assembly process and the final injection, sealing, formation, aging process. In these three stages of the process, each process can be divided into several key processes, each step will have a great impact on the final performance of the battery.
In the manufacturing process stage, it can be divided into five processes: slurry preparation, slurry coating, plate rolling, plate cutting, plate drying. In the battery assembly process, and according to the different battery specifications and models, roughly divided into winding, shell, welding and other processes. After the assembly is completed, the injection process includes injection and sealing. Finally, the three step process of battery formation, aging and split capacity. After the battery is manufactured, the battery needs to be pre-activated and stabilized for the first time, that is, the final formation-aging-capacity separation process.
The concept of Pre-formation is to charge and discharge lithium-ion batteries with a small current. After the lithium battery is finished, it needs to charge and discharge the battery in a small current. There are two main purposes for precharging:
1. After the battery is fabricated, the electrode material is not in the best applicable state, or the physical properties are not suitable (for example, the particles are too large, contact is not tight, etc.), or the phase itself is not correct (for example, some alloy mechanism of metal oxide anode), it needs to be activated by the first charge and discharge.
2. During the first charge of lithium batteries, Li+ is removed from the active material of the cathode and embedded into the graphite layer of the anode after passing through the electrolyte-diaphragm-electrolyte. In this process, electrons migrate from the positive electrode to the negative electrode along the peripheral circuit. At this point, because the potential of lithium ion embedded in graphite anode is lower, electrons will react with the electrolyte to form SEI film and some gases.
In this process, part of the gas will be produced and a small amount of electrolyte will be consumed. Some battery manufacturers will exhaust and recharge the battery after this process. Especially for LTO batteries, a large amount of gas will be produced, resulting in the bulge thickness of the battery more than 10%. For graphite anodes, less gas is produced and no exhaust operation is necessary because the SEI film generated during the first charge prevents further reactions between electrons and electrolytes, and no gas is produced. This is also the source of irreversible capacity of graphite batteries, although caused irreversible capacity loss, but also achieved the stability of the battery.
Aging generally refers to the placement of batteries after the first charge and formation after the completion of the assembly of liquid, there can be room temperature aging can also have high temperature aging, both of the role is to make the SEI film formed after the first charge and formation of more stable, to ensure the stability of the battery electrochemical performance. There are three main purposes of aging:
1. After the cell is pre-formed, a certain amount of SEI film will be formed on the graphite anode inside the cell. However, the membrane structure is compact and porous. Aging the cell at high temperature will help to restructure the SEI structure and form loose and porous membrane.
2. The voltage of the battery is in an unstable stage after being transformed, and the voltage is slightly higher than the real voltage. The purpose of aging is to make the voltage more accurate and stable.
3. Placing the battery at high temperature or room temperature for a period of time can ensure that the electrolyte can be fully infiltrated into the electrode, which is conducive to the stability of the battery performance.
The battery formation-aging process is indispensable. In actual production, the battery charging and discharging process is selected according to the material system and structure system of the battery, but the battery formation must be charged and discharged under the condition of small current. After these two key processes, and then stabilized the battery capacity, after packaging and other processes can be on the scene.
Source: lithium battery
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