Fast charging until 4.2 V and then cutting off

[twikis]

Hi everyone!

So it's well known that when you charge Li batteries to only 4.1 V, you round about double the cycle life at ~90 % capacity ...
Does anybody know (or has any experience) on how bad the effect on cycle life is when you instantly cut off at 4.2 V and do not charge until full saturation? That leaves a voltage between 4.0 to 4.1 V (depending on the battery and charge current...).
Because this way you could just charge until 4.2 V with "unthrottled" current and enjoy a fast charge + have a good cycle life.

Couldn't find anything about it, just wondering.

Regards!

PS: This is my first post on the on the official endless sphere forum, but I'm surfing around from time to time as I'm always interested in new EV tech and endless sphere is just great in this regard.

Some of you might know me from the endless sphere facebook group as Matthias Tau, where I'm quite active.

 

[redilast]

Li-ion charging uses a CC (constant current) + CV (constant voltage) charge method. You can absolutely just stop the charge cycle right at the end of the CC phase. There would be no downsides, only benefits to charging this way, as you would only be charging up the battery about 80% in most cases. And an 80% charge yields about 4x cycle life. The main problem though is how do you go about doing this? You can either just pull the cell/the pack off before the current starts tapering down by manually monitoring the charge process, or if you are using a hobby charger you can adjust the termination current to something very high so it basically does not do the CV phase at all. And another method that would mostly ignore the CV phase would be if you used a timer on your charger. So say for example you know your pack will take 3 hours to full charge using a standard CC/CV charge method, set a timer for 2 hours.

Welcome to the forums.

 

[twikis]

Ah yes right, short description would just be "stopping after the CC phase". (It's late here in Germany, having one of those sleepless nights....)

That's what I'm thinking too, would just like to get some background info about it as I read somewhere that batteries that aren't charged via CV at the end supposedly have a higher self-discharge.

Mainly I'm wondering though how much "damage" this short 4.2 V peak does to the battery.

Doing this is quite easy I'd say, you could do it with a microcontroller and a very simple program or just a simple analogue circuit, as in the end all that needs to happen is a shut down at a certain voltage.

Thanks red!

 

[999zip999]

Very little. It doesn't stay there for long. But over time you may end up with an unbalanced pack.Monitor.

 

[twikis]

Of course, cells need to be balanced.

Just wondering how many cycles (in percent) are lost when only doing CC to 4.2 V compared to doing traditional CC/CV (up to the same finish voltage)?

If it's just like 10-20 % percent I'm really wondering why e. g. Tesla isn't doing it

 

[Offroader]

Of course, cells need to be balanced.

Just wondering how many cycles (in percent) are lost when only doing CC to 4.2 V compared to doing traditional CC/CV (up to the same finish voltage)?

If it's just like 10-20 % percent I'm really wondering why e. g. Tesla isn't doing it

To be honest nobody has done any tests with newer cells and how well the handle 4.1 vs 4.2 volts. From some tests done on the forum it seems that there might not be as big of a difference as you think charging 4.1 vs 4.2 volts. There is probably much less of a difference if you charge right before you ride the bike and don't let the pack sit at 4.2 volts.

I just learned by accident that my cells can be charged easily to 4.3 volts and higher and the cells will hold a lot of extra capacity. 4.2 volts is by no means 100% capacity of the cell. They are even selling high voltage lithium ion that you can charge to 4.35 volts.

I believe what may be more damaging to the cells is running them to very low voltages.

You need to look at some of the cell tests done on this board. I also think there needs to be new tests done on the newer cells and lipo out now.

my point is I wouldn't take 100% true some of what you heard cycle life.

 

[e-beach]

Tesla owners are told to keep the charge under 90% for longevity. Keeping the SOC even lower may extend the batteries much longer. Ballance is an issue if you use a bms that won't balance until a full charge voltage is reached. So if you can balance without going full charge, or full discharge, or overheating your battery during usage then it will last a long time. How long? History has not yet let us use electric vehicles, or one ev battery chemestry long enough to have accurate data for all battery's yet. Over time that info will come out, but now it is all piece-meal information. However, this form a Tesla forum.

This from a Tesla forum:
https://forums.tesla.com/forum/forums/setting-charge-limit-below-90-improve-battery-life

DonPedro | May 24, 2013

Here is a quote from a talk Dave Duff from Tesla gave at Stanford (he has apparently not worked on the battery packs, only the connectors):

I've heard stories about the cycle life of these packs. If you treat them well, i you only charge them to 60-70% full - you don't charge them to max all the time, you don't take them down to the bottom all the time - they actually will take tens of thousands of charge cycles. It really this top to bottom cycling that beats the hell out of them.

I haven't gotten my car yet, but my plan will be to have the charge setting at 70% during periods where I know I will not be going on a long trip. If there is any chance at all of a long trip I'll do the 85% std. charge, and when I am actually going I won't hesitate to go to 100% every single time.

Edit: TwinMaTesla | June 27, 2015

A Tesla tech rep told me that after intense cycle testing, they were surprised to find no battery degradation with charges under 89% -- it was only higher charging that affected battery life. He added that, if you're going on vacation, it's best to store the battery at about 50%, and never let the car sit with a depleted battery for long. Based on his advice, and because the freedom to be spontaneous is valuable to me, we charge to 87%.

 

[Hillhater]

Search some of the cell testing threads (there are several/many)
From memory...yes keeping cells at max charge is bad for cycle life, but so is high charge rate (1C+), high discharge current, and low discharge voltage.
Also some evidence to indicate "resting" cells for a few weeks may restore some of the capacity loss ! (Tesla cells)

 

[Punx0r]

IME cutting off the charge before the CV stage has completed results in each cell showing a little less than 4.2V.

 

[999zip999]

It depends on the quality of cells and how well matched then throw in internal resistance. If well matched it should be fine. Monitor. Quality made cells should have a better chance. You now are the bms so sense wires and monitor . I have worn out three sets of sense wires by monitoring 930 cycles so far.

 

[Ykick]

Of course, cells need to be balanced.

Just wondering how many cycles (in percent) are lost when only doing CC to 4.2 V compared to doing traditional CC/CV (up to the same finish voltage)?

If it's just like 10-20 % percent I'm really wondering why e. g. Tesla isn't doing it

To be honest nobody has done any tests with newer cells and how well the handle 4.1 vs 4.2 volts. From some tests done on the forum it seems that there might not be as big of a difference as you think charging 4.1 vs 4.2 volts. There is probably much less of a difference if you charge right before you ride the bike and don't let the pack sit at 4.2 volts.

I just learned by accident that my cells can be charged easily to 4.3 volts and higher and the cells will hold a lot of extra capacity. 4.2 volts is by no means 100% capacity of the cell. They are even selling high voltage lithium ion that you can charge to 4.35 volts.

I believe what may be more damaging to the cells is running them to very low voltages.

You need to look at some of the cell tests done on this board. I also think there needs to be new tests done on the newer cells and lipo out now.

my point is I wouldn't take 100% true some of what you heard cycle life.

This is pretty much how I feel about the matter although I can only speak to RC Lipo experience.

Have found that allowing cells to sit around 4-4.1V/cell they’re going to last much longer than if they’re allowed to sit around 4.2V.

Notice I’m saying “allowed to sit”. They can be charged up to 4.2V or even a little above that as long as they’re soon discharged. The main thing seems to be don’t allow them to sit fully charged for days, weeks on end.

That’s the only practical advantage to “short charging” I’ve been able to witness/experience for about 7 years using RC Lipo.

I’m so convinced of this, when I fully charge my eBike but 'don’t ride it and I'll be going away for a few days? I take the time and go through the trouble to dig out the toaster oven load and burn off a couple 0.100V’s. Try to get ‘em around 4V.

And yes, over discharge is immediately more damaging so I prefer to take my chances with the other end of the voltage spectrum where the worst case I lose a "little" longevity.

And the other thing is? As long I'm seeing around 3-4 years battery service the replacement stuff is always better anyway. I'm a dinosaur from SLA era when it was nothing to replace 9Ah lead 2 or 3 times per year. Young'uns ain't got no idear how heavy, saggy and horrible that stuff was to haul around...