What Composed of A Lithium-ion Battery Pack?
What composed of a lithium-ion battery pack? When people talking about lithium batteries applied to concrete products, it refers to a battery pack rather than a single cell. Reach out Bonnen engineer below to see what is a battery pack? What should be noted when doing the assembling of it?
PACK includes battery case, bus bar, soft connection, protection board, external packaging, output (including connector), barley paper, plastic bracket, and other auxiliary materials together to form PACK.
Features of PACK
①Battery 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 is lower than that of a single battery cell.
③Used under limited conditions (including charging, discharging current, charging method, temperature, etc.)
④The battery voltage and capacity of the lithium battery pack are greatly improved after the molding of the lithium battery pack, which must be protected by charging balance, temperature, voltage, and Overcurrent monitoring.
⑤The battery pack must meet the voltage and capacity requirements of the design.
①Serial and parallel composition: Battery pack is formed by the parallel and series connection of single cells. Connecting in parallel increases the capacity and the voltage remains the same. After a series connection, the voltage doubles and the capacity remains the same.
Parallel first and then series: Due to the difference in internal resistance and uneven heat dissipation, the parallel connection will affect the battery cycle life after paralleling. However, the failure of a single cell will automatically exit. In addition to the reduction in capacity, it will not affect the use after parallel connection. The parallel process is stricter. When a unit battery is short-circuited in parallel, the current in the parallel circuit is very large, which is usually avoided by fuse protection technology.
First in series and then in parallel: According to the capacity of the whole group of batteries, it is connected in series first, such as the capacity of the whole group is 1/3, and finally connected in parallel, which reduces the failure probability of large-capacity battery packs.
②Cell requirements: According to your own design requirements, select the corresponding cells. The parallel and series batteries require the same type, and the difference in capacity, internal resistance, and the voltage value is not more than 2%. Whether it is a flexible package battery or a cylindrical battery, multiple strings are required. High current discharge performance is required, and good battery heat dissipation is required. With a high level of production technology, batteries must be able to withstand the vibration and impact of bumpy roads. High requirements for the production process, especially the spot welding process. Test after welding to prevent false welding and desoldering.
③The process of PACK: The PACK of the battery is realized in two ways. One is laser welding or ultrasonic welding or pulse welding. This is a commonly used welding method. The advantage is that it has good reliability, but it is not easy to replace. The second is the contact through the elastic metal sheet which call busbar. The advantage is that there is no need for welding and the battery is easy to replace. The disadvantage is that it may lead to poor contact.
Charge and discharge time
Charge time (hours) = (battery capacity Ah x charge factor) / charge 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 with a certain discharge current. Among them, discharge rate=rated capacity/discharge current.
Soft busbar connection
In the assembly PACK process of the such as nickel sheet, copper-aluminum composite bus, copper bus, totally positive and total negative bus, aluminum bus, copper flexible connection, aluminum flexible connection, copper Foil soft connection, and so on. The processing quality of busbars and flexible connections needs to be evaluated from these aspects.
①Whether the material meets the requirements, the busbar material will increase the resistivity if the material does not meet the standard. In particular, it is necessary to confirm whether the relevant ROHS requirements are met.
②Whether the processing of key dimensions is accurate. The over-tolerance of key dimensions may cause insufficient safety distance between high-voltage devices during the assembly process and cause serious safety hazards.
③The bonding force of the hard zone of the soft connection and the stress absorption condition of the soft zone.
④Whether the actual processed soft connection and the overcurrent capacity of the busbar meet the design standards, and whether the insulated thermoplastic sleeve is damaged.