Basic knowledge introduction about lithium battery pack

The process of assembling lithium battery cells into groups is called PACK, and 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 package, output (including connector), auxiliary materials such as bark paper and plastic bracket to form PACK.

Lithium battery PACK instance

PACK features

1 Battery pack requires a high degree of consistency (capacity, internal resistance, voltage, discharge curve, lifetime).

2 The cycle life of the battery pack is lower than the cycle life of a single battery.

3 To use under limited conditions (including charging, discharging current, charging method, temperature, etc.)

4 Lithium battery pack molding battery voltage and capacity have been greatly improved, must be protected, charge balance, temperature, voltage and over current monitoring.

5 Battery 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. Parallel increase capacity, voltage is unchanged, voltage is doubled after series connection, capacity is unchanged, such as 3.6V/10Ah battery is composed of 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 and 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 packaging battery 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 starting current of the motor is three times that of the normal operating current, and the high current discharge can improve the dynamic performance of the motor. 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.

3 PACK 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 the instance

Charge and discharge time

Charging time (hours) = (Ahx rechargeable battery capacity coefficient)/charging current A

Discharge rate: the discharge rate of the battery discharge time said or by a certain electric exile rated capacity coefficient of the required hours. Among them, the discharge ratio = rated capacity/discharge current

Bus-bar soft connection assembly

PACK will be used in the process of such as nickel, copper, aluminum composite bus bar, copper bus bar, the general is the general negative bus-bar, aluminum bus bar, also can use copper soft to connect, copper foil, aluminum soft connection, etc. Bus-bar and soft connection processing quality needs from the several aspects to evaluate.

(1) Whether the material compound requirements, bus-bar below-standard material will increase the rate of resistance, especially need to confirm whether composite ROHS requirements.

(2) The key size process is in place. Key size out-of-tolerance is likely to lead to high pressure device in the assembly process between the safe distance is not enough, and cause a serious security hidden danger.

(3) Soft connection soft hard the binding force and the stress absorption.

(4) The actual processing of the soft connection and bus-bar over-current ability whether meet the design standards, thermoplastic casing of the insulation parts whether there is any breakage.

The page contains the contents of the machine translation.