Composition of lithium battery module

　　1. Series and parallel composition: the battery is composed of single batteries in series. The capacity will be increased in parallel with the same voltage. The voltage will be doubled after series connection with the same capacity. For example, the 3.6V/10Ah battery is composed of a single N18650/2Ah through 5. Parallel before series connection: the battery cycle life after parallel connection will be affected due to the difference of internal resistance and uneven heat dissipation. However, when a single battery fails, it will automatically exit. In addition to the reduction of capacity, it will not affect the use after parallel connection. The parallel connection process is strict. When a unit battery in parallel is short circuited, the current of the parallel circuit will be very large, which is usually avoided with fuse protection technology. Series first and then parallel: Series connection shall be carried out according to the capacity of the whole group of batteries, such as 1/3 of the capacity of the whole group, and then parallel connection shall be carried out, which reduces the failure probability of large capacity batteries.

　　2. Battery cell requirements: select corresponding battery cells according to their own design requirements. The batteries in parallel and in series shall be of the same type and model, and the difference in capacity, internal resistance and voltage shall not be greater than 2%. Generally, after the batteries are combined in parallel and in series, the capacity loss will be 2% - 5%. The more the batteries are, the more the capacity loss will be. Whether it is a flexible packaging battery or a cylindrical battery, it needs to be combined in multiple strings. If the consistency is poor, the battery capacity will be affected. The battery with the lowest capacity in a group determines the capacity of the whole group of batteries. High current discharge performance is required. The starting current of the motor is 3 times of the normal working current, and large current discharge can improve the dynamic performance of the motor. The battery shall have good heat dissipation. The number of batteries is large, and the temperature rise of the batteries inside the battery box is not easy to disperse, resulting in uneven temperature and different discharge characteristics among the batteries, which will lead to a long-term decline in battery performance. The production process level is high. The battery shall be able to withstand the vibration impact of bumpy road surface. High requirements for production process, especially spot welding process. The test shall be carried out after welding to prevent false welding and desoldering.

　　3. The process of lithium battery module: The lithium battery module is realized by two ways. One is laser welding, ultrasonic welding or pulse welding, which is a common welding method. It has the advantage of good reliability, but it is not easy to replace. Second, it is contacted by elastic metal sheet, which has the advantage of no welding, easy battery replacement, and the disadvantage of poor contact.

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