The most important two points of the lithium battery assembly process
Many people think that the lithium battery cell welded together is not a lithium battery? Isn't that easy to do? The lithium battery market is gradually becoming more and more widely used, and many businesses who are optimistic about the lithium battery industry have begun to purchase and sell, but in order to obtain more profit margins, the assembly of lithium batteries has become the best choice for major businesses. Lithium battery to put it together is very easy, but to do well, it is not as simple as friends imagine!
Because the lithium battery market belongs to the development period, the personal assembly and production technology can not be well improved, in order to safer production, systematic technical learning is essential. Two important points for assembling a lithium battery pack:the battery and spot welding.
These two points are not passed, either the battery life is very short, or the range attenuation is fast, and the consequences of virtual welding and missing welding are more serious. With three cells, assembly of batteries to fool people, to make only then can be used, even lead-acid batteries are dry but their so-called lithium batteries, if they use a good battery to do the battery is not as long as our general battery, they do not care whether you can use for a long time, fool you no discussion, really want to do a good job of lithium batteries, safe and stable, long life, slow attenuation, and do not use three cells, It's not so simple.
Before the lithium cell is assembled into a battery pack, it is often necessary to pass the accurate pairing of voltage/resistance/capacitance in order to play the maximum effect of each cell; The result of not pairing accurately is that the battery pack will output the worst cell (or string), yes, the barrel effect.
Many people think that the battery cell bought is a distributor (let's say some self-styled "manufacturers") good, they do not need to test, and they can be installed directly. Let's not say full inspection, at least you have to spot check, otherwise the mentality of quick success will only let you continue to do after-sales battery in the future.
Assemble any battery pack must not hold the mentality of cutting corners to do, the auxiliary materials must be used, and it must go through a series of steps such as subcapacitance, sorting, spot welding, detection, aging and so on.
The inconsistency of lithium battery parameters mainly refers to the inconsistency of capacity, internal resistance and open circuit voltage. Inconsistent battery strings and used together, the following problems will occur:
1) Capacity loss, the battery cell consists of a battery pack, and the capacity is in line with the "barrel principle", and the capacity of the worst battery cell determines the capacity of the entire battery pack.
In order to prevent the battery from overcharging and overdischarging, the logic of the battery management system is set as follows: when discharging, when the lowest single voltage reaches the discharge cutoff voltage, the entire battery pack stops discharging; When charging, stop charging when the highest cell voltage touches the charging cutoff voltage.
Take the example of two batteries in series. One battery has a capacity of C, and the other has a capacity of only 0.9C. In series, both cells pass the same amount of current.
When charging, the battery with a small capacity must be filled first, and the charging cutoff condition is reached, and the system no longer continues to charge. When discharging, the battery with a small capacity must also first emit all available energy, and the system immediately stops discharging.
In this way, the small capacity cell is always full, and the large capacity cell is always using part of the capacity. A portion of the capacity of the entire battery pack is always idle.
2) life loss, similarly, the life of the battery pack is determined by the cell with the shortest life. Most likely, the cell with the shortest lifespan is the one with the smallest capacity. Small capacity cell, every time is full of discharge, output is too strong, it is likely to reach the focus of life first. At the end of the life of the battery cell, a group of cells welded together will follow the end of life.
3) The internal resistance increases, different internal resistance, flow through the same current, the internal resistance of the large cell heat is relatively more. The battery temperature is too high, resulting in accelerated deterioration, and the internal resistance will further increase. The internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of the high internal resistance cell.
The above three parameters are not completely independent, and the internal resistance of the cell with a deep aging degree is relatively large, and the capacity attenuation is more. Separate explanation, just want to make clear their respective influence direction.
