Are we all getting GRADE B cells??

[toms]

Cells are not money, more does not mean better.

The most important thing in a battery is the consistency of many cells.

If a battery has 4 cells, 3 cells have 285Ah, and 1 cell has 290Ah, all other parameters are the same. Then which cell is better?

Compare cell by cell, you may think 290Ah cell is better.

But, cells don't work alone, you have to put them in series or parallel.

In the above battery, the 290Ah cell is the bad one, this cell makes the battery unbalanced.

So much wrong with your post above that o don’t have time to correct it all.

I’ll just respond to this part.

When you build a battery, it is always capacity limited by the weakest cell.

The cells with higher capacity are better cells, the capacity isn’t what makes for s quality battery, it is the composition.

In a group of cells that are all exactly 280ah, except for one 290ah, the 290ah is the best cell.

You cannot easily judge the quality of a cell when it is in a pack.

The lowest “quality” cell is the one that fails first. Putting a higher capacity cell in a pack doesn’t mean that cell will fail first, and being over capacity doesn’t effect the pack performance at all.

 

[Don B. Cilly]

Well, I did get a definition from the (supposedly reputable) vendor.
Grade A- : Its internal resistance and voltage are matched, the capacity is not. We tested the real capacity of some cells,at 275-284AH.

So, capacity.

Cells are not money, more does not mean better.

I did not say that. I said:

I mean, almost half price, for the difference, I can assemble another battery, I'm almost certain to gain in capacity, am I not?

Meaning, say my A- cells turn out to have less capacity than nominal. Probably some 1-2%, but even if it's 20%, and I pay 80% less, I still "gain", don't I? And, what if the cells are slightly out of balance (which seems pretty much inevitable even with the best of them)? I'm powering a little house in the middle of a field, not a mission-critical space station.
-

 

[lfpinside]

So much wrong with your post above that o don’t have time to correct it all.

I’ll just respond to this part.

When you build a battery, it is always capacity limited by the weakest cell.

The cells with higher capacity are better cells, the capacity isn’t what makes for s quality battery, it is the composition.

In a group of cells that are all exactly 280ah, except for one 290ah, the 290ah is the best cell.

You cannot easily judge the quality of a cell when it is in a pack.

The lowest “quality” cell is the one that fails first. Putting a higher capacity cell in a pack doesn’t mean that cell will fail first, and being over capacity doesn’t effect the pack performance at all.

For this specific battery, if there is another 280Ah cell on hand, it is better or not to replace the 290Ah one?

 

[lfpinside]

Well, I did get a definition from the (supposedly reputable) vendor.
Grade A- : Its internal resistance and voltage are matched, the capacity is not. We tested the real capacity of some cells,at 275-284AH.

So, capacity.


I did not say that. I said:

Meaning, say my A- cells turn out to have less capacity than nominal. Probably some 1-2%, but even if it's 20%, and I pay 80% less, I still "gain", don't I? And, what if the cells are slightly out of balance (which seems pretty much inevitable even with the best of them)? I'm powering a little house in the middle of a field, not a mission-critical space station.
-

Sorry, I mean parameters of cells are not money, such as capacity is not money, more capacity does not mean better in a group.

 

[Alkaline]

Cells are not money, more does not mean better.

The most important thing in a battery is the consistency of many cells.

If a battery has 4 cells, 3 cells have 285Ah, and 1 cell has 290Ah, all other parameters are the same. Then which cell is better?

Compare cell by cell, you may think 290Ah cell is better.

But, cells don't work alone, you have to put them in series or parallel.

In the above battery, the 290Ah cell is the bad one, this cell makes the battery unbalanced.



What is Grade A+, Grade A Grade A-, or Grade B? No agreed definition at all. Ambiguous definition causes meaningless debate.

Cells are not clothes, they are not made in bulk and go to a warehouse and sold to different customers.

Cells are made on-demand. According to the CATL datasheet, when a downstream company put an order to CATL, they should tell CATL the project design and BMS parameters, CATL will make cells according to these parameters. Then cells are sorted according to a standard, some cells which do not meet standards will be left. The downstream company is not allowed to modify project design or BMS after cells are made, otherwise, CATL will not provide any warranty. These are "Grade A" cells if we insist to give cells a grade.

Then what about the cells left. Are they bad cells? The answer is Yes and No.

Some cells are indeed bad cells with defects, such as too high IR or self-discharging rate. These cells will not go to market usually.

Some cells are good cells, they just cannot be put into that big "Grade A" group according to that specific standard for that specific project. Sometimes because they are too good, such as capacity is too high. These are “grade A-” or “grade B” cells. They will be sold to the distributor in bulk. Manufacturers will not provide any warranty, this is why many CATL cells have scratched QR.

I have to lol at this post.

Now you sound exactly like a seller that just ended up with a big box of cells marked grade B by EVE. I have been learning many grade b sellers were shocked and dismayed about this because they had no idea EVE has started doing this.

 

[toms]

For this specific battery, if there is another 280Ah cell on hand, it is better or not to replace the 290Ah one?

It makes no difference.

In the factory, after cell construction and initial charge the cell will undergo spectroscopy to see the initial formation of the SEI (mainly to check for dendrite seeding). At this point a cell can be binned for selling to a wholesaler (ie no further responsibilities for manufacturer)

If the 290ah cell has inferior internal integrity then it is the weakest cell - regardless of capacity.

This is yet another reason why wholesale cells should never be parallel top balanced. The SEI is often incomplete, and low C rate / high voltage is the perfect breeding ground for dendrites.

This is why you see most wholesale cells fail before ten years. The initial capacity is virtually irrelevant.

 

[SparkyJJO]

So If you shouldn't top balance (which goes against what everyone has been saying and doing to fix imbalanced pack problems) - what SHOULD you do?

 

[John Frum]

This is yet another reason why wholesale cells should never be parallel top balanced. The SEI is often incomplete, and low C rate / high voltage is the perfect breeding ground for dendrites.

How should the SEI layer formation be completed for folks who have half-baked cells?

 

[toms]

So If you shouldn't top balance (which goes against what everyone has been saying and doing to fix imbalanced pack problems) - what SHOULD you do?

I didn’t say not to top balance. Just don’t leave a new cell at full voltage.

There are many ways to get a group of cells to the same SOC. Putting a group of mismatched SOC cells in parallel, applying a low C rate charge and letting them saturate is the worst way i can imagine.

My preferred depends on the BMS used, but in every instance i only assemble the cells once - in their final configuration.

If the cells have significant divergence, either apply a single cell charger to the lower cells, or a resistive load to the higher cells until the divergence is acceptable.

 

[Ampster]

In the factory, after cell construction and initial charge the cell will undergo spectroscopy to see the initial formation of the SEI (mainly to check for dendrite seeding). At this point a cell can be binned for selling to a wholesaler (ie no further responsibilities for manufacturer)

This is my belief as well and that is why I disagreed with that conclusion from the Seplos video that every cell goes through a 30 day formation process. The Seplos was linked in post #49 of this thread.

 

[toms]

How should the SEI layer formation be completed for folks who have half-baked cells?

Every manufacturer has their own method. The only one i know of has cells charged over 6 cycles, starting at 0.2C and ramping down to 0.05C.

Keep in mind that the charge method is to hold a constant current until 3.65V is reached and then immediately disconnect the charge source. 0.05C for a 280ah cell is 14amps.

If you start off at too low charge rate you risk dendrite seeding, if you run too many high C charge cycles early you risk a porous SEI layer.

 

[toms]

This is my belief as well and that is why I disagreed with that conclusion from the Seplos video that every cell goes through a 30 day formation process. The Seplos was linked in post #49 of this thread.

It may take 30 days for a batch to go from completed manufacturing to boxed for sale. The energy from charged cells is recycled which saves energy but takes time.

I doubt there are manufacturers putting 30 cycles into an SEI layer.

 

[lfpinside]

Here is an EVE patent: "Screening method for consistency of lithium-ion batteries".

https://patents.google.com/patent/CN111438083A/en

(1) pre-screening: carrying out a self-discharge test on n batteries with SOC larger than or equal to 30%, and selecting the battery with the battery voltage drop smaller than or equal to 10mV within the same time t, wherein n is larger than or equal to 3, and t is larger than or equal to 24 h;

(2) first sorting: carrying out one-time charging and discharging process on the batteries screened in the step (1), and selecting the batteries with a capacity difference of less than or equal to 30mAh and the alternating current internal resistance difference of less than or equal to 3m omega;

Cells within a limited capacity range are able to be grouped together, cell with capacity out of this range, even if it has a higher capacity, will be screened out. This is why I said more is not better. many patents have this step to limit the capacity variation range.

 

[yaq]

The matched and batched 280Ah cells from Shenzhen Luyuan are $190US now (what some would call the "best" china vendor reviewed here).

We don't really know the source of their cells. They could be automotive grade, but could also just be new cells that EVE rejected because they didn't meet the automotive grade spec. I believe the general consensus/belief in this thread, is that they are likely the latter, and that this is the case for most of the reputable sources ppl buy from on this forum. And the less reputable vendors try to even get away with selling used cells, or just plain junk (see the post where buddy found blocks of granite in the battery to make it weigh more).

If you look at sunfunkits site (people who made the video in the OP), they assert that they are buying the automotive grade cells from EVE and on their site they are $925US for four 280Ah cells, or ~$231US each. Whether they are worth an additional $40US/cell, is for anyone to decide on their own I guess. I am sure they are "better" cells but whether it matters in practice for non-automotive applications (solar = lower charge/discharge rates from automotive), I'm not sure.

For your information: AMY of Shenzhen Luyuan has just sent me the link of the EVE factory test for the 68 280Ah grade A cells that I ordered from him, the production dates oscillate between 24.04.22 and 27.04.22, the Ri of the three tests between 015 and 0.16 milliohms and the capacities between 286 and 287 Ah and the price, contrary to your assertions, is $148 per cell!
Good luck with that.

 

[Rossman]

the price, contrary to your assertions, is $148 per cell!

The price was ~$190/cell from Luyuan not that long ago (last month?), but apparently they were able to acquire additional volumes of the cells at a lower price because of how the lockdowns in China janked up the supply chains (factory were still making cells, but there was nowhere for them to go/no-one able to move them....so now have a glut they need to move quickly).

I would imagine this price ($148) will rise as things correct.

If you paid $148/cell you basically bought at the PERFECT time, you're getting deal just because of circumstances that are transient.

 

[RobertGreen]

For your information: AMY of Shenzhen Luyuan has just sent me the link of the EVE factory test for the 68 280Ah grade A cells that I ordered from him, the production dates oscillate between 24.04.22 and 27.04.22, the Ri of the three tests between 015 and 0.16 milliohms and the capacities between 286 and 287 Ah and the price, contrary to your assertions, is $148 per cell!
Good luck with that.

Are you saying that the price of the cells DDP is $148 each?

 

[Alkaline]

Last time I checked it was like 170 shipping for a 4 pack via sea, but then Alibaba screws you with sales tax + a transaction fee, I think it is about $189/cell shipped to TX.

 

[Rossman]

Are you saying that the price of the cells DDP is $148 each?

No, not DDP, before shipping, the raw cell price is $148 right now.

 

[yaq]

Are you saying that the price of the cells DDP is $148 each?

At AMY https://szluyuan.en.alibaba.com/ the price of a cell ( EV quality ) with double busbar and 0,5mm separation is 158$ pc for 68 cells in CIF in a free port in Switzerland, all insured until the destination.
For a security identical to Paypal but by credit card (less expensive) the trick is to indicate a deadline of delivery on the proforma invoice, because the credit card does not generally cover the transaction beyond one month! For my part, I have set it at November 1st, which gives me a sufficient buffer in case of dispute with the credit card.

 

[yaq]

It makes no difference.

In the factory, after cell construction and initial charge the cell will undergo spectroscopy to see the initial formation of the SEI (mainly to check for dendrite seeding). At this point a cell can be binned for selling to a wholesaler (ie no further responsibilities for manufacturer)

If the 290ah cell has inferior internal integrity then it is the weakest cell - regardless of capacity.

This is yet another reason why wholesale cells should never be parallel top balanced. The SEI is often incomplete, and low C rate / high voltage is the perfect breeding ground for dendrites.

This is why you see most wholesale cells fail before ten years. The initial capacity is virtually irrelevant.

You open balancing prospects that seem to me off the beaten track!
But with scientifically coherent beginnings which for my intuition seem important to me.
Basically if I follow you, the important thing for a good start of life of cells, is it a kind of "sowing" of balanced sei?
And the usual protocols of balancing at the beginning of life of a cell seem too extreme to you?
Which protocol do you employ and what are the advice you recommend?