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

China’s lithium iron phosphate battery cells and packs are mainly exported, and there are many scales and levels of manufacturers, resulting in great differences in quality standards, and the quality standards of different battery manufacturers are different. Each supplier claims that their battery cells are Class A batteries. So, what are the A-level and B-level, C-level battery cells?

How to Distinguish Grade A and Grade B LiFePO4 Prismatic battery Cell? How to Distinguish b cell battery ，b battery a and b batteries and are there b batteries?

The difference in price, the gap in quality and performance, as well as the safety hazards caused by improper procurement and application fields, force you to figure out A-class battery cells, B-class battery cells and C-class battery cells, and even recycling battery cells and dismantling battery cells. Definition of core and respectively.

The best way to know a cell is Grade A or Grade B is to check if the cell meets the manufacturers’ specifications.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.

This article will introduce the definitions of A-level cells, B-level cells, and C-level cells, and the difference between cell A, cell B, and cell. B-level cells are unavoidable problems in the manufacturing process, while B-level cells are unavoidable. Cells can only be used in areas that do not require high cell consistency. Remember not to use it in a power battery pack, otherwise the probability of accidents and spontaneous combustion will increase.

Battery Manufacturing and Cell Grades

What are battery cell grades?

cells are always categorized to be graded A, B and C but there is not a single manufacturing standard for categorizing cells; each manufacturing factory may have their own standard so thus cell grade categorization is not necessarily scientific.

How do manufacturers use cell grades in the manufacturing of batteries?

For example, Li-ion cell 053450, some companies may categorize the cell as follows

Grade A— capacity above 1000mAh, internal resistance below 60mΩ
Grade B—capacity 900 to 1000mAh, internal resistance 60mΩ to 80mΩ
Grade C—capacity below 900mAh, internal resistance above 80mΩ

But for some companies with better production lines and capability, they may have higher capacity cells so they may categorize cell 053450 as follows:

Grade A— capacity above 1100mAh, internal resistance below 60mΩ
Grade B—capacity 1000 to 1100mAh, internal resistance 60mΩ to 80mΩ
Grade C—capacity below 1000mAh, internal resistance above 80mΩ

One generally accepted conclusion can be drawn from these two examples and that is grade A cells have the longest runtime and cycle life, grade B has the second longest runtime and cycle life and grade C has the third longest runtime and cycle life.

Battery cell grades are a classification system that manufacturers use to distinguish the benefits of capacity and runtime.

Before I unpack that answer we need to understand that battery grades are not a measure of quality! Battery grades do not imply that one grade is “better” than another but a reflection of capacity and internal resistance at different price points.  Before I continue with cell grades it is important to understand capacity and internal resistance.

Battery capacity quantifies the total amount of energy stored within a battery. Battery capacity is rated in Ampere-hours (AH), which is the product of: AH= Current X Hours to Total Discharge. Battery capacity is measured in amperes, which is the volume of electrons passing through the batteries electrolyte per second. A milliAmp hour (mAh) is the most commonly used notation system for consumer electronic batteries. Note that 1000 mAh is the same as 1 Ah. (Just as 1000mm equals 1 meter). In essence more capacity equals longer runtime between battery charges.

Internal resistance, known as impedance, determines the performance and runtime of a battery. It is a measure of opposition to a sinusoidal electric current. A high internal resistance curtails the flow of energy from the battery to a device. Internal resistance is caused primarily from the opposition of current by the electrolyte that resides between a battery’s two electrodes.

Now battery cell grading is a process of categorizing cells into grades (Grade A, Grade B, and Grade C). Every grade is important to the manufacturer, meaning there is not one grade that is better than another. In fact every manufacturer wants to make and sell each cell grade because of the unique differences of each grade and because each cell grade has a specific market and device segment.

Performance of A Grade vs B Grade cells

Lithium-ion cells are known for their long-lasting life. The cells degrade and their energy holding capacity reduces over time but they last for a long time, unlike Lead Acid batteries which experience sudden death. B grade cells tend to experience sudden death failure after a certain number of cycles, especially when they are charged and discharged at higher C rates. This does not allow the B grade cells to be reused as second-life batteries and they directly end up at a recycling plant.

The cycle life of a lithium-ion cell is defined as the number of chargedischarge cycles at 80% Depth of Discharge (DoD) till the retention capacity of the cell comes down to 80% of its original capacity. If the capacity fade of a cell is higher, it tends to have a lower cycle life. B grade cells have a higher rate of capacity fade as compared to A grade cells.

Bulging of prismatic cells and swelling of pouch cells tend to happen in even A grade cells when they are overcharged, deep discharged or operated at very high temperatures. But the chances of bulging and swelling are higher in B grade cells because their cathode and anode stoichiometric ratio could be off and also due to B grade cells not undergoing proper formation in the first place.

Impedance, also known as internal resistance, has an inverse relationship with cell performance. The lower the impedance, the better rate of charge and discharge the cells can go through. EVs demand fast charging and high power discharge, and hence EV Grade cells have lower impedance when compared to Energy Storage Grade cells.

As the cells are charged and discharged, their impedance increases. At some point, the impedance of the cell rises to a level that it becomes unusable for a particular application (such as EVs). At that point, it is disassembled and used as a part of a second-life battery to power applications (such as Energy Storage Systems) using a lower charge-discharge C rating. B grade cells experience a faster rise in the impedance level, and hence they become unusable much earlier compared to A grade cells.

Since B grade cells do not meet the performance parameters compared to A grade cells, it is not advisable to use B grade cells for fast charging and high power discharge applications such as EVs.

If B grade cells are made to perform at the level of A grade cells, especially in EV applications and combined with a mediocre BMS, consider it a recipe for disaster. It can cause internal cell short circuits due to dendrite formation and lead to thermal runaway. Thermal runaway from NMC chemistry cells can be extremely dangerous as NMC cells tend to catch intense fire, as seen in the cases reported from EV fires from across the globe.

Classifying the Lithium-ion cells

During the manufacturing of Lithium-ion cells, a very strict procedure is followed for grading them.Since no manufacturing process can produce 100% perfect yield, less than 10% of the produced cells do not meet the standards required to fall under A grade and hence they are classified as B grade cells. The reasons for rejection can be either the cells do not match up to the expected performance or a cosmetic defect or both. B grade cells also have a minimum performance expectation and if they don’t meet it, they are further classified as C grade cells. C grade cells are the lowest priced cells in the market and they can be used for single-cell portable applications operating at a very slow charge and slow discharge rate with lower expected battery life.

A technical way to know if the cell is B grade is to charge-discharge the cell for a suitable number of cycles depending on the cell capacity, chemistry, form factor and intended application of the battery pack and look at the data. If the capacity fade is higher than what is mentioned in the cell datasheet cycle life graph, it is a B grade cell. And, if the cycling data is true to the values mentioned in the datasheet, then it is an A grade cell.

A few OEMs and battery pack suppliers have experienced issues with using B grade cells because their batteries could not perform up to expectation even during the warranty period, and these companies are slowly shifting towards sourcing A grade cells. However, some new entrants in the battery pack assembly field seem unaware that there exist A grade and B grade cells in the market.

How to Distinguish Grade A and Grade B cell – Prismatic Cell

The best way to know a cell is Grade A or Grade B is to check if the cell meets the manufacturers’ specifications. This article will introduce some important specifications on a datasheet. By comparing those specifications with the testing data. We’ll know the differences between Grade A and Grade B 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 datasheet.

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.

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.

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 datasheet. If only there aren’t too many differences. That will be alright.

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.

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 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

datasheet. It’s Grade A quality cell.

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.

During the manufacturing of Lithium-ion cells, a very strict procedure is followed for grading them.Since no manufacturing process can produce 100% perfect yield, less than 10% of the produced cells do not meet the standards required to fall under A grade and hence they are classified as B grade cells. The reasons for rejection can be either the cells do not match up to the expected performance or a cosmetic defect or both. B grade cells also have a minimum performance expectation and if they don’t meet it, they are further classified as C grade cells. C grade cells are the lowest priced cells in the market and they can be used for single-cell portable applications operating at a very slow charge and slow discharge rate with lower expected battery life.

LiFePO4: A123 Systems ANR26650M1B Grade A vs Grade B – discharge capacity test

B-class cells are not necessarily lower than A-class cells, we explain through actual measurement, I have got 4 ANR26650 M1Bs – 2 of each grade and tested a pair by discharging at 0.5A (0.2C), 5A, 10A and 20A discharge rates. Then i tested the second pair at 20A and compared all 4 cells.

Note: ANR26650M1B cells now are being manufactured and sold under Lithium Werks brand. In March 2018 Lithium Werks acquired A123 Systems’ industrial business and manufacturing plants located in Changzhou, China. These plants were the first to introduce the revolutionary NanoPhosphate® technology in the form of cylindrical cells.

The cells were bought from Queen Battery. The first pair was bought 4 months ago and the second – a month ago.

As always, I’ve tested with ZKETECH EBC-A20 and a self-made battery holder. It’s a PC-connected battery tester supporting 4-wire measuring and discharging at up to 20A.

I’ve followed all the prescriptions of the IEC61960-2003 standard concerning battery’s capacity measurement. Before each discharging cycle each battery was charged at standard current (2.5A) mentioned in the ANR26650M1B datasheet (pdf) to 3.6V (cut-off at 0.1A, which is the lowest supported by EBC-A20). Before each discharging or charging i’ve held a 1-1.5hrs pause. The environment temperature was 20-25°C (23-25°C to be honest).

A123 Systems ANR26650M1B has the following specs according to it’s datasheet:

Nominal capacity: 2.5Ah at 0.5C rate

Minimum capacity: 2.4Ah at 0.5C rate

Nominal voltage: 3.3V

Charge end voltage: 3.6V

Standard charge current: 2.5A (1C)

Fast charge current: 10A (4C)

Max continuous discharge current: 50A (20C)

Max pulse discharge current (10 sec): 120A (48C)

Discharge cut-off voltage: 2.0V

AC impedance at 1KHz: 6mΩ

Weight: 76g

The Grade A cell has more information on its wrapper than the Grade B one which only is marked “ANR26650”

and the Grade B’s negative pole has no stripes around the metal

The positive poles are identical

A123 Systems ANR26650M1B Grade A capacity test results:

A123 Systems ANR26650M1B Grade B capacity test results:

Surprisingly enough, the Grade B cell appears to be slightly better than the Grade A one. So let’s compare 2 Grade A cells with 2 Grade Bs at 20A to see if that’s a rule or exception

It seems that both of Grade Bs are better than the more expensive Grade As. Two pairs are not enough to conclude a rule, but at least we can see that the Bs are not worse than As, if not better. Maybe they have reduced cycle life or they are worse at higher discharge rates or some of them have scratches on the barrel – i don’t know.

B grade battery definition: made bad product, discarded, alas, of the batteries sold at a low price, the price is generally normal ryohin keikaku 1/10 of the batteries is even lower.

B grade lithium battery in the power battery

B grade battery definition: made bad product, discarded, alas, of the batteries sold at a low price, the price is generally normal ryohin keikaku 1/10 of the batteries is even lower.

B grade classification:

The appearance of B grade

basically, as long as no leakage, no serious damage will not scrap, will be sold as a B grade, detailed standards of each manufacturer will be a slight difference. Appearance grade B need to pay special attention to is bad bumps, protruding mark, because generally bumps, protruding mark is caused by internal impurities, power battery working current is bigger, bumps, convex marks will be current, the concentration of heat, heat shrinkage easily lead to isolation membrane, causing internal short circuit, even if did not cause short circuit, bumps, protruding mark inside the battery current caused by uneven, bumps, Convex mark parts of the current is larger, local polarization is serious, the failure in advance, and ultimately affect the service life of the battery pack.

Package B grade

for soft package of lithium electricity, encapsulation appears especially important (for metal shell of lithium electricity, should be welded encapsulates), generally there is no leakage, but there are risks encapsulation of battery will be sold as a B grade. Encapsulation B grade is sensitive to temperature, easy to open the leakage at high temperature sealing side, also easy in use for a long time there is water vapor infiltration, lead to battery bilge gas (if it is metal shell lithium electricity, it is the internal pressure is too high, instant relief when danger)

The performance grade B

mainly has low capacity, low pressure, high resistance, etc. All performance grade B use has a great influence on power battery. Performance grade B directly influence the consistency of the battery pack with is low capacity battery, also because of the low capacity reason, after the loop performance is not consistent, eventually caught the battery pack.

Main reason for the low capacity battery

there were (1) into reasons for the low capacity battery is not fully, the SEI film formation is bad, leading to an empty enough of the active material cannot play out capacity, key factors and SEI is to maintain the stability of the cycles, the battery cycle life will be much worse, and eventually drag down the rest of the battery pack. Excessive foreign matter in (2) internal excess levels (including water), consumption part of the active material, quality of active matter less, capacity of natural low, uneven impurities caused the current at the same time, serious local plan, will failure in advance, and ultimately affect the service life of the battery pack.

the main reason for the low voltage battery

low voltage battery internal micro short circuit, the main reason is that lead to self-discharge is big, in the use of power battery, the battery is safe problem in the first place, the internal micro short circuit in the large current under the action of continuous will deteriorate further, easy to eventually lead to serious internal short circuit, the end result is serious accidents such as fire; Followed by the performance problems, low voltage of battery capacity decline faster (because internal micro short-circuit consumed), tend to take the lead in no electricity, affects the whole battery pack.

The cause of the high internal resistance battery

the cause of the high internal resistance of batteries have poor isolation membrane, internal connection to crinkle, to turn into bad, electrolyte composition and dosage and long time storage, and so on. High resistance in the process of using power battery, battery first high internal resistance took a lot of energy, and the second is the high internal resistance of batteries are the ratio of performance to far worse, when with other battery using the same current loop performance will be worse, eventually caught the whole battery pack.

Because of the manufacturing technology level, B grade battery is inevitable, but it is strongly recommended that not to B grade battery on the power battery pack, because higher consistency requirements for battery power battery.