The process of assembling a lithium battery cell into a group is called a Battery Pack. It can be a single battery or a series or parallel battery module. Under the background of the new national standards, the demand for lithium batteries is increasing, and many lead-acid battery companies have also launched lithium battery products. Actually, the lithium battery PACK process is not difficult.
The composition of the PACK
PACK consists of battery PACK, bus bar, soft connection, protective board, outer packing, output (including connector), highland barley paper, plastic support and other auxiliary materials.
The characteristics of the PACK
1.The battery PACK requires the battery to have high consistency (capacity, internal resistance, voltage, discharge curve, life).
- The cycle life of a battery PACK is lower than that of a single battery.
- Used under limited conditions (including charging, discharge current, charging mode, temperature, etc.).
- After the lithium battery PACK is formed, the battery voltage and capacity have been greatly improved, must be protected, to its charging balance, temperature, voltage and over current monitoring.
- The battery PACK must meet the voltage and capacity requirements required by the design.
The assembly methods of the PACK
1.Series and parallel assembly
A battery pack consists of a single cell connected in parallel or in series, which is produced by lithium battery manufacturer. For example, 3.6V/10Ah battery is composed of a single 18650/2AH through 5 cells in parallel connection.
Parallel connection 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, the failure of a single battery automatically exits, except for the reduction of capacity, does not affect the use of parallel, parallel process is strict. In parallel, when a unit battery shorts, the current of the parallel circuit is very large, which is usually avoided by using fuse protection technology.
Series connection before parallel connection: The whole battery capacity is first connected in series, such as 1/3 of the whole battery capacity, and then connected in parallel to reduce the failure probability of large-capacity battery.
According to their own design requirements to select the corresponding cell, parallel and series battery requirements of the same type, model, capacity, internal resistance, voltage difference is not more than 2%. In general, after the battery is combined in parallel series, the capacity loss is 2%-5%. The more batteries, the more capacity loss.
Whether it is a pouch pack battery or a cylindrical battery, multiple series combination is required. 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. High current discharge performance is required.
Motor starting current is 3 times of the normal working current, large current discharge can improve the motor dynamic performance. Require good heat dissipation of the battery. Due to the large number of batteries, the temperature rise of the battery inside the battery box is not easy to come out, resulting in uneven temperature between the batteries and different discharge characteristics, resulting in long-term degradation of battery performance. Production technology level is high. The battery should be able to withstand the shock of a bumpy road. High requirements on production technology, especially spot welding technology. After the completion of welding test to prevent false welding, off welding.
3.The process of the PACK
The battery PACK is realized in two ways. One is laser welding or ultrasonic welding or pulse welding, which is a common welding method. The advantage is better reliability, but it is not easy to replace. The second is through the elastic metal sheet contact, the advantage is no need for welding, battery replacement easy, the disadvantage is that may lead to poor contact.
Charge and discharge time
Charging time (hours) = (battery capacity Ah x charging coefficient)/charging current A
Discharge rate: the discharge rate of a battery is expressed in terms of discharge time or in terms of the hourly coefficient required to discharge the rated capacity of a certain discharge. Wherein, discharge ratio = rated capacity/discharge current
Assembly of bus bar and soft connection
In the process of PACK, such as nickel sheet, copper-aluminum composite bus bar, copper bus bar, total positive and negative bus bar, aluminum bus bar, as well as copper soft connection, aluminum soft connection, copper foil soft connection and so on will be used. The processing quality of bus bars and soft connections needs to be evaluated from these aspects：
- Whether the material composite requirements, bus bar material will increase the resistivity, especially the need to confirm whether composite ROHS requirements.
- key size processing is in place. Out-of-tolerance of key dimensions may lead to insufficient safety distance between high voltage devices during assembly and cause serious safety hazards.
- The binding force of the hard zone of soft connection and the stress absorption condition of the soft zone.
- The actual processing of soft connections and bus bars over the flow capacity to meet the design standards, insulation thermoplastic casing position whether there is damage.
The above is the introduction of lithium battery manufacturing process and PACK basic knowledge. Looking into the future, if lithium battery can be improved in terms of cost and performance, the application of lithium battery will be greatly expanded, enabling many new technologies to break through the bottleneck of energy storage.
SmartPropel Orignal Writer: Michelle