At present, we can always see some large-capacity lipo batteries on the market, the small one is 20Ah, 50Ah, the big one is 200Ah or even 500Ah, 1000Ah. These large single-cell batteries are generally used for serial connection and parallel connection. To assemble large lithium battery packs for solar power projects, and electric vehicles, electric bus applications. So how is this design safety compare to the widely used 18650 lithium-ion battery cell solution?
big lithium polymer cell
I am afraid the answer is not optimistic, why?
- As we all know, the greater energy is in a system, the more dangerous it is. The lithium polymer battery is a typical example. Under the same materials and manufacturing processes, it is unrealistic to simultaneously increase the battery energy and reduce the risk.
- Due to the principle of current superposition, the vicinity of the pole of the lithium battery is a collection point of current superposition, which makes the current density of the large cell battery level plate uneven, and the local temperature is too high.
- When the battery is in operation, the temperature at the center position is very high. The larger the battery volume is, the larger the temperature gradient from inside to outside is, and the larger temperature difference between the internal and external is. Therefore, according to the second law of thermodynamics, the external battery temperature is the same. Next, the internal center temperature of the large-capacity polymer battery will be high.
- The change of the chemical reaction in the battery will cause the volume to change. The larger the battery is, the more the deformation of the plate is, causing the current variation uneven.
In summary, we can see that from the perspective of heat dissipation and structural stability, it is not safe to apply large-capacity polymer battery cells to battery pack assembly, and battery safety is reduced as the polymer cell capacity increases. . Therefore, the author appeals to the new energy peers of lithium batteries to pay enough attention to this, do not blindly pursue less cells series, and ignore the heat dissipation. If we lose sight of other vital factors, we ultimately may turn out resulting in greater mistakes. To ensure the safety of the entire battery pack, it is necessary to evaluate it from a comprehensive perspective, and put every influential factor into the basket to achieve real good results.