lithium 3400mah 3.7v 18650 battery PACK process flow and example analysis

Under the background of the new national standard, the demand for lithium batteries is increasing, and many lead-acid battery companies have also launched lithium battery products; in fact, the lithium battery PACK process is not difficult. Mastering this technology can assemble batteries by yourself, instead of just acting as a "battery porter" for the manufacturer, and profits and after-sales are no longer subject to others; mastering a technology, you can travel the world with "lithium". 1PACK composition PACK includes battery packs, busbars, soft connections, protection boards, outer packaging, output (including connectors), barley paper, plastic brackets and other auxiliary materials. These items together constitute PACK.

2PACK characteristics ① Battery pack PACK requires batteries to have a high degree of consistency (capacity, internal resistance, voltage, discharge curve, life). ② The cycle life of the battery pack PACK is lower than the cycle life of a single battery. ③ Use under limited conditions (including charging and discharging current, charging method, temperature, etc.) ④ After the lithium battery pack PACK is formed, the battery voltage and capacity are greatly improved, and it must be protected, and the charge balance, temperature, voltage and overcurrent monitoring are performed on it. ⑤The battery pack PACK must meet the voltage and capacity requirements required by the design.

3PACK method①Series-parallel composition: The battery is composed of single cells connected in series. Parallel connection increases capacity and the voltage remains unchanged. After series connection, the voltage doubles and the capacity remains unchanged. For example, a 3.6V/10Ah battery is composed of a single N18650/2Ah connected in parallel 5 times. Parallel first and then series: The difference in internal resistance and uneven heat dissipation in parallel will affect the battery cycle life after parallel connection. However, the failure of a single battery will automatically exit. In addition to the reduction in capacity, it does not affect the use after parallel connection. The parallel connection process is stricter. When a unit battery in parallel is short-circuited, the current of the parallel circuit is very large, which is usually avoided by adding fuse protection technology. Series first and then parallel: According to the capacity of the entire battery group, series connection is first carried out, such as 1/3 of the entire capacity, and then parallel connection is carried out, which reduces the probability of failure of large-capacity battery packs. ②Battery cell requirements: Select the corresponding battery cell according to your own design requirements. The batteries in parallel and series connection are required to be of the same type and model, and the difference in capacity, internal resistance and voltage value is not more than 2%. Generally speaking, after the battery is combined in parallel and series, the capacity loss is 2%-5%. The more batteries there are, the more capacity loss there is. Whether it is a soft-pack battery or a cylindrical battery, multiple strings are required. If the consistency is poor, the battery capacity is affected. The battery with the lowest capacity in a group determines the capacity of the entire group of batteries. High current discharge performance is required. The starting current of the motor is 3 times the normal working current. Only by high current discharge can the motor power performance be improved. The battery heat dissipation is required to be good. There are a large number of batteries, and the temperature rise of the batteries inside the battery box is not easy to dissipate, resulting in uneven temperature between the batteries, different discharge characteristics, and long-term battery performance degradation. The production process level is high. The battery must be able to withstand the vibration impact of bumpy roads. The production process, especially the spot welding process, is highly required. After welding, test to prevent false welding and desoldering. ③PACK process: The battery PACK is realized in two ways. One is through laser welding, ultrasonic welding or pulse welding. This is a commonly used welding method. The advantage is good reliability, but it is not easy to replace. The second is through elastic metal sheet contact. The advantage is that no welding is required and the battery is easy to replace. The disadvantage is that it may cause poor contact.

pack Example 4 Charging and discharging time Charging time (hours) = (battery capacity Ah x charging factor) / charging current A Discharge rate: The discharge rate of the battery is expressed by the discharge time or the hour factor required to discharge the rated capacity at a certain discharge current. Among them, discharge rate = rated capacity / discharge current

5 Assembly of bus soft connection In the PACK process, nickel sheets, copper-aluminum composite bus, copper bus, total positive and total negative bus, aluminum bus, copper soft connection, aluminum soft connection, copper foil soft connection, etc. will be used. The processing quality of bus and soft connection needs to be evaluated from these aspects. ① Whether the material meets the requirements. If the bus material does not meet the standards, the resistivity will increase. In particular, it is necessary to confirm whether it meets the relevant ROHS requirements. ② Whether the key dimensions are processed in place. The deviation of key dimensions may lead to insufficient safety distance between high-voltage devices during assembly and cause serious safety hazards. ③ The bonding strength of the hard area of the soft connection and the stress absorption of the soft area. ④ Whether the current carrying capacity of the actually processed flexible connector and bus meets the design standard, and whether there is any damage in the insulating thermoplastic sleeve.

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