According to an analysis, China shares 73% of global lithium cell manufacturing capacity. Therefore, to know the Chinese battery market is a critical part for those who enrolled in this industry. There are many factories producing LiFePO4 battery cells in China. And the quality standards are different. And every supplier claimed that they sell Grade A cells. What exactly are Grade A and Grade B cells?
The best way to know a cell is Grade A or Grade B is to check if the cell meets the manufacturer's specifications. This article will introduce some important specifications on a data sheet. By comparing those specifications with the testing data. We’ll know the differences between Grade A and Grade B cells.
Appearance
The first thing we can do to check a cell is to check its appearance. Each cell was produced with a
unique QR code as a proof of identity. Which also makes it more convenient for the manufacturers to offer after-sale services. And as we mentioned in the last post, Grade B cells are categorized as unqualified ones, they usually do not offer a warranty. That’s why they will scrape off this QR code.
So if you find a battery cell with QR code concealed. Mostly it is Grade B battery cell. However, all Grade B cells will be covered with a new insulated sheet. So if there are no obvious signs of QR code outside, you’ll need to tear off the insulated sheet.
Tips: It does not mean that all battery cells with QR code are Grade A cells.
Dimension&Weight
As dimension&weight will be slightly different at different SOC percentage, it would be necessary for you to confirm with the supplier of their testing SOC percentage. Then measure the size at the same SOC percentage level. And compare the measured value with the one they offered on the data sheet.
Capacity
Capacity is usually tested at the temperature of 25℃, charging and discharging rate of 1C. Record the real tested capacity. And compare these two data.
Note: Different temperatures will affect the capacity of lifepo4 battery cells. So some manufacturers will send you the cell with its capacity a little bit higher than it should be. If your testing capacity is a little bit higher than the data sheet. If only there aren’t too many differences. That will be alright.
Internal Resistance
Firstly, confirm the testing environment with suppliers. Including temperature and SOC conditions.AC internal resistance is usually tested at the frequency of 1000HZ. An AC internal resistance meter will help you with the testing. For other manufacturers, they will provide DC internal resistance. Then you may need a multimeter. Compare the real tested data with the one offered in specifications.
Self-discharge Rate
The self-discharge rate differs at different SOC state. For example, the voltage decrease quicker at 100% SOC than at 50% SOC. So before testing the self-discharge rate, check the battery specification about the testing SOC state first.
Capacity Recovery
To test the capacity recovery rate, you just do a 100% DOD charging and discharging cycle. And check if the capacity recovery rate meets the data sheet.
For example, for a 3.2v 100ah battery cell, if the recovery rate is 95%. We have tested the capacity at the beginning. It is 100ah. Then after all the tests, we do a 100% DOD charging and discharging.Then the capacity should be more than 95ah. If yes, the battery capacity recovery rate meets the data sheet. It's Grade A quality cell.
Conclusion
What we are doing is to compare the testing data with the specification of the cells. So we can trust the data sheet or supplier. After all the tests and comparison, if all the data meet the specification or data sheet, it is Grade A cells. If not, it is grade B cells.
Ask your supplier for some samples. And test whether it is Grade A or Grade B cells?