Can lithium ion / lithium poly "recover" after getting weak? - Page 1
Forum section: electronics / general

author: SilverSolder
author_rank: Super Contributor
timestamp: May 22, 2020, 09:07:44 pm
content: I have an ancient Lithium Ion power bank here, the USB type you might use to charge a phone. It is optimistically rated at 20,000mAh new.It had been "misplaced" in my cave, for several years. I found it with minimal remaining charge, but not stone dead. When I then recharged it the first time, it would only accept about 1,000mAh. So I thought great, it's almost dead, it might work to power an Arduino or something like that... so that's what I put it to use for. The use case means it gets drained until it shuts down, every time, before getting recharged.Except... it has powered the Arduino longer and longer... every time I recharge it, it seems to accept more and more juice. With the last recharge, it accepted 10,397mAh... which is probably getting close to whatever real capacity it had in the first place...I knew that new Li-Ion batteries have to go through a few cycles to build up to full capacity... but I didn't think this was something the battery could "forget" again?Is it expected that Li-Ion can "recover" some capability after standing around, with a bit of "massage" like this?

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 22, 2020, 09:30:48 pm
content: Most likely the SOC estimation is way off and it's slowly correcting itself each cycle.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 23, 2020, 12:35:24 pm
content: Some management chip doing some random things, nothing to do with the cells.

author: Peabody
author_rank: Super Contributor
timestamp: May 23, 2020, 02:34:55 pm
content: I don't think new lithium batteries need to be cycled to reach full potential. But the algorithm that many lithium chargers follow for a deeply discharged battery is to only apply 1/10 of the full charging current until the cell is back above 3V. That might explain your initial low charge rate. But I don't have an explanation for any gradual increase after that.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 23, 2020, 07:00:10 pm
content: I agree with the other posters that the management chip is relearning the actual capacity of the cells. I'm a bit surprised that it's taking multiple cycles.You should monitor that pack very carefully. AFAIK, this is the scenario that causes Lithium batteries to burst into flames. The battery discharges further than is safe and is damaged in the process. Then a charger that isn't as smart as it should be comes along and tries to recharge the damaged battery. The result is smoke, flames and shattered nerves!

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 23, 2020, 09:58:58 pm
content: Quote from: edpalmer42 on May 23, 2020, 07:00:10 pmDebunked by Big Clive - only a concern with multiple cells in series.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 24, 2020, 04:11:26 am
content: BigClive is good, but he's not an expert. He refers to a single study that came out in 2016 that says it's okay to recharge a Li-Ion cell that's been deeply discharged.I looked around to see what Li-Ion manufacturers have to say. Many manufacturers didn't mention it, but I did find the following:Samsung SDIAfter extended periods of storage, always check the voltage of the batteries or battery pack prior to charging. NEVER use or charge batteries or battery packs if the voltage is less than 2.5 V/cell.GNB Industrial PowerDo not deep discharge batteries; this leads to permanent damage. Deep-discharged lithium batteries are no longer permitted to be charged or operated.Both of these were recent documents (2019) or current web sites.Some Lithium technologies are more forgiving regarding abuse, e.g. LiFePO4. Regardless, caution is advised.

author: SilverSolder
author_rank: Super Contributor
timestamp: May 24, 2020, 11:46:14 am
content: So the management chip actually "learns" the size of the battery - it doesn't just stop at some preset voltage (and other criteria)?It kind of makes sense. I put a larger battery in an old Samsung S5. Now it gets >10 days battery life, LOL... but it took a couple of recharges to get there. And the prediction algorithm still doesn't believe it's true.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 24, 2020, 12:28:10 pm
content: Yes, do not charge overdischarged (below about 2.5V) li-ion cells unless you really know what you are doing (and how you are doing it).During overdischarge, copper dissolution in the electrolyte happens, increasing leakage current and the risk of internal shorting due to dendrites.There are procedures to charge slightly overdischarged cells at very low currents while monitoring the result by confirming low leakage current before deciding between ditch / go for full current. These procedures are not that important, because safe and well-performing cells that are not abused by overdischarge, do not randomly overdischarge. Hence, an overdischarged cell is always a sign there has been a problem which needs to be solved instead of trying to "repair" the result.By ignoring this advice, failure isn't guaranteed to happen, but this does not mean it's safe to do so. As always, there are layers of safety and not all forms of abuse are as dangerous as others. You can abuse 100 cells in a certain way and only 1 blows up."Debunking" this would require extraordinary evidence because the phenomenon is widely known and understood by the academy and industry.

author: SilverSolder
author_rank: Super Contributor
timestamp: May 24, 2020, 12:44:06 pm
content: Quote from: NiHaoMike on May 23, 2020, 09:58:58 pmThinking about it, my particular power bank did discharge "too quickly" initially, after the first charge - in other words, not only did it not accept a full charge (as measured with a USB coulomb counter), it also lost the puny 1,000mAh charge that it did accept far faster than an Arduino should be able to drain.I'm inclined to believe that something had happened to at least one of the cells inside the power bank (I am assuming 2 cells in a 5V pack) that caused the battery bank as a whole to have significantly increased self-discharge rate, which it then somehow recovered from.Recharging the bank a couple of times seems to have greatly improved the performance (both the quantity of charge, and the self discharge rate). Maybe there are several effects happening at the same time when you charge an old Li Ion battery a couple of times - management chips learning, battery chemistry "feeling better", cells getting "more balanced" with each other?I attached the research article found by Big Clive for reference.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 24, 2020, 04:37:03 pm
content: Quote from: SilverSolder on May 24, 2020, 12:44:06 pmIt's a very interesting paper but I really can't see how it supports a view that overdischarging only causes damage below 0V. I can see how someone who does not normally read scientific papers can make this wrong conclusion, though. (Didn't watch the Big Clive video, maybe he's not claiming that, but it seems he was being understood that way.)SEI destruction and release of gases alone is a huge issue.

author: ConKbot
author_rank: Super Contributor
timestamp: May 24, 2020, 06:45:25 pm
content: Sounds like the behavior of a severely imbalanced series pack that is slowly balancing itself at the top of charge. One cell is grossly over-discharged, the rest are ok. You charge it, it takes a little bit of charge, the full cells hit 4.2v, charge terminates. As it discharges, the low cell hits cutoff and it stops running. Balancing as maintenance only needs a few mA of current, so there isn't a point in a built-in balancer that can correct a severe imbalance in a few hours, so as it spends more and more hours at top of charge, the more time the balancers have to get everything in order.

author: ConKbot
author_rank: Super Contributor
timestamp: May 24, 2020, 07:00:49 pm
content: Quote from: Siwastaja on May 24, 2020, 04:37:03 pmPeople after cheap garbage love to hand-wave all sorts of danger. I've seen videos showing people how to reset the CID on the top of 18650s, or how to trick chargers into recharging 0V cells by paralleling them with a good cell in a cradle, just slam a 0V cell with a few amps to charge, sure, sounds like a fantastic idea. Stuff like this is why LG is flat out like 'don't use bare cells, its too dangerous for you smooth brains' there is danger associated with lithium ion batteries, but buried away in a pack its protected, but some people love to just forcibly align holes in the swiss-cheese model. Reset a CID on a cell that has experienced some serious overstress, put it in a cradle to charge at a few A from dead, solder on leads so they can put it in a pack of mismatched cells.Ok now here comes the anecdotes.

author: SilverSolder
author_rank: Super Contributor
timestamp: May 24, 2020, 08:45:36 pm
content: Quote from: Siwastaja on May 24, 2020, 04:37:03 pmIs this what causes some lithium ion batteries to swell up?

author: edpalmer42
author_rank: Super Contributor
timestamp: May 24, 2020, 10:15:13 pm
content: Quote from: SilverSolder on May 24, 2020, 11:46:14 amAFAIK, the charging circuit always includes a low-value shunt resistor. Measure the voltage across that and you've got the current, both charge and discharge. Measuring the voltage is easy. The chip has some kind of clock signal so that gives it time. Now it can measure energy, both charging and discharging. Itdoeshave voltage limits that it limits the battery to. But it likely doesn't know how big the battery is. That's why you run through a few charge/discharge cycles so it can learn the battery size. By measuring the number of AH in from the charger and out to the load, it gains an approximation of the battery's SOC (State of Charge).Over time, the battery degrades so it's important to occasionally run the battery down so the chip can learn the battery's current () condition.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 24, 2020, 10:27:37 pm
content: Cheap powerbanks don't usually have batteries in series. That would require some form of BMS to keep the cells balanced. It's more common to have them in parallel with a boost converter to get a 5V output.SilverSolder, in your case, the initial 1000 mah charge may have been due to the management chip deciding that only a small trickle charge was allowed. The low current caused the voltage as viewed outside the battery to climb quickly. The charger itself may have terminated the charge. After the first discharge, the cell voltage was still good and the chip allowed a more complete charge.Forgetting a device in a drawer for a long period of time is a common way that the batteries get overdischarged. The management chip itself needs power and, over time, discharges the batteries and then refuses to charge them back up! I have a lantern that was in that condition when I bought it used. The actual cell was just slightly below the cutoff voltage so just poking a bit of charge into it was enough to raise the voltage to the point that the management chip let it recharge.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 25, 2020, 08:58:54 am
content: Quote from: SilverSolder on May 24, 2020, 08:45:36 pmYes. Overdischarge isn't the only condition to cause it, though.