How to Distinguish Grade A and Grade B LiFePO4 Prismatic Cell?

We all know that Grade A cells are much more expensive than Grade B cells.So if you want to compare two products, you need to make sure that they are at the same level.

The best way to know a cell is Grade A or Grade B is to check if the cell meets the manufacturers' specifications.Today, we are going to talk about some important parameters listed on the datasheet.By compare the data with the specification to distinguish Grade A and Grade B cells.Let' s check.

1.Appearance

Each cell will be produced with an unique QR code as a proof of identity.Which make it more convenient to be recognized for the manufacturers when offering after-sale services.And as we mentioned in the last post, Grade B cells are categorized as unqualified ones, they usually do not offer warranty.Manufacturers will scrape off this QR code for distinguishing.So if you find a battery cell that with QR code concealed.Mostly it is Grade B cells.However, all Grade B cells will be covered with a new insulating sheet.So if there' s no obvious signs of QR code outside, you' Il need to tear off the insulating sheet.

• Tips: It does not mean that cells come with QR code are all Grade A cells.

2.Dimension & Weight

As dimension&weight will be slightly different at different SOC state, it would be necessary for you to confirm the testing SOC state with suppliers.Then measure the size at the same SOC conditions.And compare the results with listed on the date sheet.

So follow the datasheet SOC statement, and measure the dimension and weight of cells. If the size meets the datasheet, it is ok. If the size does not following the datasheet, then maybe problem or grade B cells.

3.Capacity

Capacity is usually tested at the temperature of 25°C, charging and discharging rate of 1C.Record the real tested capacity value.And compare the results with the specifications.

• Tips: Different temperature will affect the capacity of lifepo4 cells.?So some manufacturers will send you the cells that the capacity is a little bit higher than claimed.?If your testing results is a little bit higher than the datasheet. That will be alright.

4.Internal Resistance

First check the testing conditions on the datasheet, or confirm that with suppliers. That is the temperature and SOC state. Most manufacturers test AC internal resistance at 1000Hz. Other manufacturers, however, will test the DC internal resistance. Generally speaking, the DC internal resistance is more reliable.

• If your testing results meet the datasheet, It is Grade A cell.

5.Self-Discharging Rate

The self-discharging rate is calculted according to voltage decreasing. And at different SOC state, the self-discharging rate may be different. At the 100% SOC state, the voltage will decrease quicker than at 50% SOC state.So check the datasheet to make sure the testing SOC state fisrt.

Testing Methods

Solution 1: to test the voltage decreasing rate at room temperature of 25℃ by stocking for 28 days.

Solution 2: to test the voltage decreasing rate at higher temperature of 45℃ by stocking for 7 days.

If the self-discharging rate is 3%

For normal temperature, the self-discharging rate per day is 0.03/28=0.00107.then it's about 0.107%.

For high temperature, the self-discharging rate per day is 0.03/7=0.00428, then it's about 0.43%.

So we can stock the cells in the specified testing conditions, check and write down the voltage decreasing of the cell each day. Then, you can check each days' s self-discharging rate and the month/week's self-discharging rate as a double check.Generally speaking, solution 1 of stock for 28 days are more reliable.

6.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 datasheet.

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 test, 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 datasheet. It's Grade A quality cell.

Conclusion

What we are doing is to compare the testing data with specification of the cells. So we can trust the datasheet or supplier.After all the tests and comparison, if all the data meet the specification or datasheet, it is grade A cells. If not, it is grade B cells.

One more question:

If you've picked out several manufacturers who provides Grade A cells, which one you should choose? Just consider the price differences?