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basics of lithium battery PACK

Jul 25, 2018

China Energy Storage Network News:

The process of assembling lithium battery cells into groups is called PACK. It can be a single battery or a series or parallel battery module. Under the background of the new national standard, the demand for lithium batteries is increasing, and many lead-acid battery companies have also introduced lithium-ion products. In fact, the lithium-ion battery PACK process is not difficult. Mastering this technology can assemble batteries, instead of just acting as a manufacturer. The role of "battery porters", profits and after-sales are no longer subject to people; master a technology, there is "lithium" to travel all over the world.
PACK composition
PACK includes battery pack, bus bar, soft connection, protection board, outer packaging, output (including connector), auxiliary materials such as bark paper and plastic bracket to form PACK.

Lithium battery PACK instance
PACK features

1 Battery pack PACK requires a high degree of consistency (capacity, internal resistance, voltage, discharge curve, lifetime).
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, discharging current, charging method, temperature, etc.).
4 Lithium battery pack PACK molding battery voltage and capacity have been greatly improved, must be protected, charge balance, temperature, voltage and overcurrent monitoring.
5 Battery pack PACK must meet the voltage and capacity requirements required by the design.
PACK method
1 string and composed: The battery is made up of single cells and connected in series. The capacity is increased in parallel, the voltage is constant, the voltage is doubled after series connection, and the capacity is unchanged. For example, the 3.6V/10Ah battery is composed of a single N18650/2Ah through 5 and. First and last strings: Parallel due to the difference in internal resistance, uneven heat dissipation, etc. will affect the battery cycle life after paralleling. However, the single battery failure automatically exits, except that the capacity is reduced, and the parallel connection process is not affected. When a unit battery in a parallel is short-circuited, the parallel circuit current is very large, and the fuse protection technology is usually avoided. After the first string and then: according to the entire battery capacity first series, such as the entire group capacity 1/3, and finally parallel, reducing the probability of large-capacity battery pack failure.
2 battery core requirements: according to their own design requirements to select the corresponding battery, parallel and series of batteries require the same type, the same model, the difference in capacity, internal resistance, voltage value is not more than 2%. Under normal circumstances, after the battery is combined in parallel and in series, the capacity loss is 2%-5%, and the more the number of batteries, the more capacity loss. Whether it is a flexible package or a cylindrical battery, multiple combinations are required. If the consistency is poor and the battery capacity is affected, the battery with the lowest capacity in a group determines the capacity of the entire battery. Large current discharge performance is required. The motor starting current is three times the normal operating current, and high current discharge can improve the motor dynamic performance. The battery is required to dissipate heat well. The number of batteries is large, and the temperature rise of the battery inside the battery box is not easily dissipated, resulting in uneven temperature between the batteries, and the discharge characteristics are different, and the battery performance is degraded for a long time. The production process is high. The battery should be able to withstand the vibrational impact of bumpy roads. High requirements are imposed on the production process, especially the spot welding process. After welding, test to prevent cold welding and desoldering.
3PACK process: The PACK of the battery is realized by two methods. One is laser welding or ultrasonic welding or pulse welding. This is a common welding method. The advantage is that the reliability is good, but it is not easy to replace. The second is through the contact of the elastic metal sheet, the advantage is that no welding is required, the battery replacement is easy, and the disadvantage is that the contact may be poor.

Pack instance
Charge and discharge 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 hourly coefficient required to discharge the rated capacity with a certain discharge current. Among them, discharge rate = rated capacity / discharge current

Assembly of busbar soft connections
In the PACK process, such as nickel sheets, copper-aluminum composite busbars, copper busbars, total positive total negative busbars, and aluminum busbars, copper soft connections, aluminum soft connections, and copper foil soft connections are also used. The processing quality of busbars and soft connections needs to be evaluated from these aspects.
1 Whether the material of the material is compounded or not, the material of the bus bar will not increase the resistivity, especially the need to confirm the requirements of the composite ROHS.
2 key size processing is in place. The out of tolerance of critical dimensions may result in insufficient safety distance between high voltage devices during assembly and cause serious safety hazards.
3 The bonding strength of the hard-bonded hard zone and the stress absorption of the soft zone.
4 Whether the actual processing of the soft connection and the overcurrent capability of the bus bar meet the design standard, and whether the insulated thermoplastic casing part is damaged.