Prolonging battery life, temperature, state-of-charge

[LEAFfan]

Full for the cell is about 4.2v, but the Leaf never goes higher than 4.1v. 80% is 4.05v so I don't know that 80% is vastly safer than 100% for a voltage to sit at for hours..

Interesting, my smartphone battery tops off at 4.218V. Unlike my earlier phone, this one stops charging when it reaches that level. I can't wait to get a gauge that will read the voltage for the LEAFs individual batteries.

 

[Deleted member 3391]

This is from a new article on the Toyota Prius PHEV, see it at http://www.greencarcongress.com/2011/09/toyota-introduces-2012-prius-plug-in-hybrid.html" onclick="window.open(this.href);return false; .

"A charge timer allows you to set charge start and finish time. (According to Toyota, one of the things they discovered during the demo program was that the battery packs responded better if they were allowed to rest prior to recharging.)"

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?)

Thanks

 

[TEG]

Unfortunately with public charging you tend to drive right up and start charging.
I have noticed a couple of times when I came off the freeway and plugged into a public charge point, then waited in the car, a faint sort of plastic smell that wasn't there when simply parked.
Maybe it is nothing, but I have this slight fear that it is the smell of the battery pack cooking itself.

 

[Herm]

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?)

No idea on the optimum rest time, but I know you should always allow rest time when cycling lithium-ion batteries continuously for life cycle testing. I believe it mostly allows the temperature of the cell to drop down to normal.

 

[TomT]

Considering the batteries appreciable thermal mass and the fact that the battery box is sealed, I doubt the temperature changes very fast at all...

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?)

 

[abasile]

Unfortunately with public charging you tend to drive right up and start charging.

I'd have a hard time believing that this is anything to worry about. After all, in typical non-freeway driving, you are using regenerative braking at regular intervals, which sends pretty substantial bursts of power to the battery. The battery has to be able to handle constantly alternating between charging and discharging. If I'm going to need the charge, I do not hesitate to plug in and start charging as soon as I pull up to a public charge point. Remember that standard L2 charging, at least at this time, is relatively slow and thus gentle on the battery.

That said, when charging at home, I use a timer to delay the start of charging. If you have time, it certainly doesn't hurt to let the battery cool down some, but perhaps more importantly, it is ideal for battery longevity if the time-averaged state of charge is closer to 40% or 50%, not 80% or above. However, as it's also less than ideal to leave the battery at low states of charge, I will generally put in some charge right away if the car has only one bar or less. Keep in mind that the majority of our driving is up and down on mountain roads, which is undoubtedly harder on the car than flatland driving, so I am trying to do whatever else I can, in a reasonably convenient manner, to optimize the life of the car.

 

[Volusiano]

All this discussion is interesting to have, but I'm beginning to wonder what the real ROI is in extending the battery life after we spend all this time micromanaging/over-managing the battery charging process. It's just too much to remember and to bother with waiting for the batter to cool down, fickle with the timer to set different charging scenarios to charge asap if SOC is too low, not charge too soon if SOC is high and battery is hot, not charge at all if SOC is 40-50%, etc.

After a while, you feel like you're serving the battery instead of the battery serving you.

Now, IF we have concrete data as to how much each of these micromanaging scenarios will give us in extra pro-longed battery life, that's another story, and we can decide which one is worth doing and which one is not.

If any of these scenarios are really worth doing, I think Nissan would have told us. The only thing Nissan told us so far is the 80% charging and not fast charging every day. Without Nissan telling us do to anything else differently, I'm just going to stick with these 2 advices and not bother with anything else.

 

[smkettner]

This is from a new article on the Toyota Prius PHEV, see it at http://www.greencarcongress.com/2011/09/toyota-introduces-2012-prius-plug-in-hybrid.html" onclick="window.open(this.href);return false; .

"A charge timer allows you to set charge start and finish time. (According to Toyota, one of the things they discovered during the demo program was that the battery packs responded better if they were allowed to rest prior to recharging.)"

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?)

Thanks

I agree Leaf does seem to charge better when there is a cooling off period.
I am just using L1 but I do seem to have more miles estimated in the morning if I use the end timer rather than the timer override.
Have not tracked it so it could just be in my head.

Seems like another reason to use L2.

 

[Stoaty]

If any of these scenarios are really worth doing, I think Nissan would have told us. The only thing Nissan told us so far is the 80% charging and not fast charging every day. Without Nissan telling us do to anything else differently, I'm just going to stick with these 2 advices and not bother with anything else.

Nissan has a vested interest in making the Leaf easy for people to use. That may be in conflict with optimal battery life. If the battery capacity gets too low for someone to find it useful in 6 years instead of 7-8 years, Nissan may get to sell another EV. The fact that the life of Volt battery (a Lithium Manganese chemistry like the Leaf) has a strong temperature dependence even at 60% charge (5 years for 90 degrees, 8 years for 72 degrees) leads me to believe that minimizing exposure to high temperatures and keeping the SOC as low as reasonable are good strategies. It would be interesting to know what the life is for the Volt battery at 40% charge (where I plan to keep my Leaf most of the time when it isn't working) and various temperatures.

 

[Volusiano]

If any of these scenarios are really worth doing, I think Nissan would have told us. The only thing Nissan told us so far is the 80% charging and not fast charging every day. Without Nissan telling us do to anything else differently, I'm just going to stick with these 2 advices and not bother with anything else.

Nissan has a vested interest in making the Leaf easy for people to use. That may be in conflict with optimal battery life. If the battery capacity gets too low for someone to find it useful in 6 years instead of 7-8 years, Nissan may get to sell ano alther EV.

You do have a point. However, it's also in Nissan's best interest to make sure that their battery lasts long enough in the field, or else, no matter how easy it is to use, people aren't going to want to buy Nissan products again if their original product doesn't last long enough to people's expectation. So it's a fine line for them to walk and decide what to disclose and what not to disclose. The fact that the 80% charge disclosure is already a minus in terms of ease of use, yet Nissan chooses to disclose it anyway, shows that this one has a significant enough impact worthy of disclosing. Same with the daily fast charge. The other stuff, yes, maybe there is some benefit to doing them. But apparently not significant enough as deemed by Nissan that is worthy of disclosing.

Sure, if you're diligent enough to fickle more with the charging process, maybe you can get another year or two out of your battery. But in the grander scheme of things, 5 to 10 years from now, if battery technology has advanced enough and become more affordable with better range, people may want to trade in their old batteries for newer batteries sooner rather than later anyway, even before their old battery is truly out of life. So all that work to fickle with the battery process for all those years to squeeze out a little bit of extra life may become a moot point anyway.

To me, ease of use has high value, too, over battery life. So I'd be willing to trade off 10% of extra battery life for ease of use just so I can have my car always ready at 80% charge in case I need it. And I also don't have to keeping fussing about how I'm going to charge my battery differently every single time depending on the scenario of the day.

 

[LEAFfan]

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?) Thanks

I never wait after driving before I charge and it usually takes about 22 min. a bar to 80%.

 

[DaveEV]

Anyone have experience in optimum rest time for the Leaf batteries? Maybe 4-5 hours after the last drive before recharging? (Guess it's related to the temperature decreasing during the rest time improving the battery pack response during recharge?)

Not sure, but some papers I've read have shown that the cell's internal resistance is lower after letting the cell rest a bit after charging than with no rest. How this affects cycle life is hard to say.

I doubt it has to do with temperature, as usually lithium batteries's capacity goes up slightly with temperature indicating lower internal resistance.

At a minimum, allowing the pack to spend more time at a lower SOC should be beneficial to life. If you are just charging to 80%, I don't think I'd worry too much...

 

[TEG]

...After a while, you feel like you're serving the battery instead of the battery serving you...

Some of us are just a bit obsessive about this stuff. I agree that it may be way more care than necessary, but it is sort of a hobby to figure out the "best" way to coddle the battery pack.

 

[phxsmiley]

In the spirit of 'coddling' the battery, I have a box fan in my garage, and turn it on to blow across the underside of the car, from front to back. I can feel the air passing out underneath the rear of the car. I don't know if it helps the battery, but it makes me feel better about charging the car in our hot Phoenix garage.

 

[Volusiano]

...After a while, you feel like you're serving the battery instead of the battery serving you...

Some of us are just a bit obsessive about this stuff. I agree that it may be way more care than necessary, but it is sort of a hobby to figure out the "best" way to coddle the battery pack.

If you put it like that, sure, I can see the point in it. But for people who only think of it as maintenance work, then it becomes too much. Thanks for pointing that out.

 

[surfingslovak]

The fact that the life of Volt battery (a Lithium Manganese chemistry like the Leaf) has a strong temperature dependence even at 60% charge (5 years for 90 degrees, 8 years for 72 degrees) leads me to believe that minimizing exposure to high temperatures and keeping the SOC as low as reasonable are good strategies. It would be interesting to know what the life is for the Volt battery at 40% charge (where I plan to keep my Leaf most of the time when it isn't working) and various temperatures.

I was going to follow up on our earlier conversation, and I apologize for not doing so. I've been busy and although these threads are both interesting and important, I believe that it would be in our common interest to come up with a set of simple agreed-upon rules and make them part of an FAQ. Any factual information we will be able to extract from Nissan or any 3rd party testing could help validate or refine these rules further. Obviously, it would be up to individual owners to decide if they wanted to adopt some of these practices or just drive the Leaf without giving it much thought.

I didn't have time to read the old thread you started in its entirety, but if I remember correctly, there was something in it about leaving the Leaf in a hot parking lot with one or two bars. I was going to advise against it on the grounds that it could leave you stranded, but I came across some additional information I wanted to share.

It might not be a good idea to store the Leaf or park it for extended period of time is a state of low charge. We know the basic chemistry of the AESC cells used in the Leaf, but we don't know how Nissan and NEC have customized their parameters and properties. It might be prudent to avoid assumptions and only make recommendations that are conservative and fairly generic. I found a report this weekend, which was measuring the capacity fade in cells with the same basic chemistry (LMO cathode, graphite anode with LiPF6 EC type electrolyte) at different SOC levels. The takeaway? The cells degraded the most at 20% state of charge at 60C ambient temperature due to the Jahn-Teller effect. We don't know if Nissan has done anything to neutralize this effect, and if this was applicable to the AESC cells at all. But in the light of this, it would be best to recommend keeping the pack close to 50% for storage or when parking the car on a hot parking lot for the entire day. This is a generic, middle-of-the-road rule. I would not feel comfortable recommending something more extreme, because it may or may not actually cause more damage to the battery. Of course, if Nissan unequivocally said that 80% was best for storage, whether it's hot or not, then that's what we should adopt.

 

[Stoaty]

I didn't have time to read the old thread you started in its entirety, but if I remember correctly, there was something in it about leaving the Leaf in a hot parking lot with one or two bars. I was going to advise against it on the grounds that it could leave you stranded, but I came across some additional information I wanted to share.

Actually, it was more like 4-7 bars (7 bars until recently, going to shoot for 5 bars, or about 50% SOC in future). Looks like I am right on track.

It might not be a good idea to store at Leaf or park it for extended period of time is a state of low charge. We know the basic chemistry of the AESC cells used in the Leaf, but we don't know how Nissan and NEC have customized their parameters. It might be prudent to avoid assumptions and only make recommendations that are conservative and fairly generic. I found a report this weekend, which was measuring the capacity fade in cells with the same basic chemistry (LMO cathode, graphite anode with LiPF6 EC type electrolyte) at different SOC levels. The takeaway? The cells degraded the most at 20% state of charge at 60C ambient temperature due to the Jahn-Teller effect. We don't know if Nissan has done anything to neutralize this effect, and if this was applicable to the AESC cells at all. But in the light of this, it would be best to recommend keeping the pack close to 50% for storage or when parking the car on a hot parking lot for the entire day.

Which curve in that graph is most closely related to the Leaf battery chemistry?

 

[surfingslovak]

Actually, it was more like 4-7 bars. Looks like I am right on track... Which curve in that graph is most closely related to the Leaf battery chemistry?

Oh good to hear. I think cell type A shares the same basic chemistry properties, it's the upper curve in the graph above. The differences are fairly marginal and we have no way of knowing what the actual behavior of AESC cells is until they have been tested or Nissan has disclosed this information.

I don't want to confuse things, but the same source is citing this report, which studied dissolution of manganese into the electrolyte and the measured something else altogether. Perhaps I'm not interpreting it right, but it underscores that we should be careful about what we do and recommend in the name of pack longevity

 

[Stoaty]

Perhaps I'm not interpreting it right, but it underscores that we should be careful about what we do and recommend in the name of pack longevity

So far, I haven't heard anyone say that the 40-50% range was bad, guess I will stick with that as a good "middle ground". 80% doesn't look too good on that graph.

 

[TomT]

My Leaf came with a shipping sheet from the production line that showed the range at which they required the battery to be for shipping from the factory. It also had places for checkoffs and initials along the way afterwards. I found it in the door pocket when I picked up the car. It's posted on the board here somewhere but if recall correctly, they wanted it between 35 percent and 80 percent, and required recharge when it dropped below 35 percent...

But in the light of this, it would be best to recommend keeping the pack close to 50% for storage or when parking the car on a hot parking lot for the entire day. This is a generic, middle-of-the-road rule. I would not feel comfortable recommending something more extreme, because it may or may not actually cause more damage to the battery.