Prolonging battery life, temperature, state-of-charge

[Herm]

This may be what the Volt's liquid cooling system is attempting to prevent.. if you park the car with a fully charged battery and the ambient temp is 140° F it will actively cool the pack down until (room temp 72° F) it discharges to 50%, then it shuts down the AC and stops further attempts to keep the battery cool. GM stated that once the pack was partially discharged then the high temp would not age the pack.

 

[Stoaty]

This may be what the Volt's liquid cooling system is attempting to prevent.. if you park the car with a fully charged battery and the ambient temp is 140° F it will actively cool the pack down until (room temp 72° F) it discharges to 50%, then it shuts down the AC and stops further attempts to keep the battery cool. GM stated that once the pack was partially discharged then the high temp would not age the pack.

I thought the Volt only discharged the battery to 75%, not 50% (from the quote on the gm-volt site) before stopping the cooling.

 

[surfingslovak]

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...

Tom, thanks for mentioning that. I think I found your post and referenced the SOC check sheet photo below. It says that 35% was the standard SOC for shipments out of Japan, and it's probably safe to assume that this is a conservative value for mid to long-term storage. The only remaining question, is Nissan referring to the real SOC or what's indicated on the battery gauge on the dash and in Carwings? I would think that it's the former.

The SOC check sheet itself shows that more than 3 bars are needed before Leafs are loaded onto a ship, but only two bars are needed when the cars arrive at the destination port. What's also interesting, your Leaf apparently was charged to 11 bars before it was shipped and it declined to 6 bars by the time it arrived in Long Beach? That would be fairly high rate of self-discharge, minus the driving they had to do when loading and unloading the car in port. Would you remember the initial mileage of your Leaf when it was delivered by your dealer?

 

[Herm]

I thought the Volt only discharged the battery to 75%, not 50% (from the quote on the gm-volt site) before stopping the cooling.

You could be right, its been a while.

 

[surfingslovak]

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.

Yes, if both effects are considered and we assume an unmodified LMO/C chemistry of the cell, then the best cycle life will likely be returned between 40 and 60% SOC. If our battery model is correct, this would correspond to cycling between 3 to 7 bars. The Leaf should not be stored or parked for extended period of time in either highly charged or discharged state. There are several other factors beside manganese dissolution and the Jahn-Teller spinel distortion, but these two could account for up to half of the capacity loss over time.

The graph from the Sony battery study we looked at earlier shows that about twice the amount of manganese was lost when bringing the cells up to 100% SOC versus cycling them only to 80%. The rate of manganese dissolution peaked at 80%, but it needs to be seen in relation to the full cycle. I believe that this also underscores the importance of limiting time spent at high SOC (above 60% or so).

 

[surfingslovak]

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.

Yes, if both effects are considered and we assume an unmodified LMO/C chemistry of the cell, then the best cycle life will likely be returned between 40 and 60% SOC.

I found another rather recent report to corroborate this further. According to the graph, the cycle life of LMO/C cells under test was dramatically improved when they were charged to 4.0V and discharged to 3.5V. I wish that they covered a wider range of charge protocols, but alas we only have this. And again, the basic chemistry is a match, but we don't know how Nissan and NEC customized the AESC battery to improve cell performance. Also worth noting is the dramatic effect of elevated ambient temps on cycle life.

 

[Stoaty]

According to the graph, the cycle life of LMO/C cells under test was dramatically improved when they were charged to 4.0V and discharged to 3.5V.

I believe that 3.6 volts is about 1 bar (post by GregH). How many bars does 4.0 volts correspond to for the Leaf?

 

[surfingslovak]

I believe that 3.6 volts is about 1 bar (post by GregH). How many bars does 4.0 volts correspond to for the Leaf?

4.0V should correspond to about eight bars.

 

[AndyH]

I believe that 3.6 volts is about 1 bar (post by GregH). How many bars does 4.0 volts correspond to for the Leaf?

4.0V should correspond to about eight bars.

Are you suggesting the fuel gauge bars display voltage?

 

[Stoaty]

Are you suggesting the fuel gauge bars display voltage?

I think he was suggesting that the cell voltage when 8 fuel bars are left is about 4.0 volts, but of course it isn't displayed anywhere. I think this info came from someone with an SOC meter, since firmware 1.08 can read total pack voltage, and dividing by 96 gives an approximation of individual cell voltage.

 

[JJnHAWAII]

It sounds like the jury is still out on waiting to charge after use. The battery should at least in theory last longer with a rest period before charging. Does it really matter that much though? I'm only using L1 and charge immediately upon returning home.

 

[surfingslovak]

It sounds like the jury is still out on waiting to charge after use.

Yes, I think your assessment is correct. We don't even have consensus on questions that should be more straightforward than this, such as charging to 80%. If you asked me, I would go with the conservative recommendation and say that it won't hurt to let the battery rest a bit before charging. I don't follow that approach personally though, and I'm not convinced that it would have any measurable benefit. In my experience, there is almost no discernible difference in pack temperature in day-to-day use.

 

[Stoaty]

We don't even have consensus on questions that should be more straightforward than this, such as charging to 80%. If you asked me, I would go with the conservative recommendation and say that it won't hurt to let the battery rest a bit before charging. I don't follow that approach personally though, and I'm not convinced that it would have any measurable benefit. In my experience, there is almost no discernible difference in pack temperature in day-to-day use.

As far as I can tell, the effects of ambient temperature on battery pack temperature are far greater than the effects of charging, at least when going to environments of 90 degrees F. or more with the Leaf parked in the sun.

 

[surfingslovak]

As far as I can tell, the effects of ambient temperature on battery pack temperature are far greater than the effects of charging, at least when going to environments of 90 degrees F. or more with the Leaf parked in the sun.

Yes, that seems to be a reasonable assumption. However, Nissan has gone on record saying that their batteries don't require a TMS. Well, at least not in the US market, and that they were considering active cooling for markets such as Dubai.

While it's reasonable to assume that it's safe to charge the Leaf to 100% each and every day and park it in an unshaded spot in a hot parking lot, Nissan does not tell us what a more careful approach would yield in relative terms. If an average pack degraded 20% after five years of careless use, and 15% after 60 months of babying, then perhaps the extra effort was not worth it. Obviously, it should be up to the owner to decide. And what if the difference was more significant? Unfortunately, Nissan is probably not going to tell us, and will continue to hide behind references to proprietary battery technology.

About the report we discussed earlier, I wanted to add that although the cells under test had the same basic chemistry, they were not optimized for EV use. I found a spec sheet for LG Chem's E1 cell. It's from 2004 and it's very likely that the cells they are using in the Volt have evolved quite a bit since then. Likewise, I imagine that the AESC cells the Leaf is using are similar in their characteristics. And again, we are only doing this comparison, because AESC does not tell us anything about cycle and calendar life of their cells.

The E1 cells have about ten times better cycle life than the ones we looked at earlier. They were cycled in a wider range too: 3.0 to 4.2V versus 3.4 to 4.2V. The capacity loss was about 15% after 500 cycles versus 15% after 60 cycles. Although LG Chem does not say anything about calendar life, it's likely that they optimized that characteristic too and E1 performed much better than the cells examined by the University of Michigan in their report.

I'm only saying this to underscore that anything we do, from charge protocols to storage temperature has only a relative effect on battery life and the pack has already been optimized for EV applications with everything that it entails.

 

[Stoaty]

Yes, that seems to be a reasonable assumption. However, Nissan has gone on record saying that their batteries don't require a TMS. Well, at least not in the US market, and that they were considering active cooling for markets such as Dubai.

While it's reasonable to assume that it's safe to charge the Leaf to 100% each and every day and park it in unshaded spot in a hot parking lot, Nissan does not tell us what a more careful approach would yield in relative terms. If an average pack degraded 20% after five years of careless use, and 15% after 60 months of babying, then perhaps the extra effort was probably not worth it. Obviously, it should be up to the owner to decide.

It might very well be worth it if the 4% a year vs. 3% a year was carried out to 10 years, though: 40% degradation vs. 30% degradation might very well be the difference between the car still being useful for a particular person or not.

 

[surfingslovak]

It might very well be worth it if the 4% a year vs. 3% a year was carried out to 10 years, though: 40% degradation vs. 30% degradation might very well be the difference between the car still being useful for a particular person or not.

Yes, of course, and the relative difference could be more significant too. Unfortunately, there are too many unknowns and Nissan does not make this easy, since they don't offer any battery capacity warranty. But even if they did, there could be owners interested in extending the useful life of their vehicles. I think those wanting to beat the metrics Nissan has used for their battery warranty, deserve answers and AESC is best qualified to provide them.

 

[ElectricVehicle]

It might very well be worth it if the 4% a year vs. 3% a year was carried out to 10 years, though: 40% degradation vs. 30% degradation might very well be the difference between the car still being useful for a particular person or not.

Yes, of course, and the relative difference could be more significant too. Unfortunately, there are too many unknowns and Nissan does not make this make this easy, since they don't offer any battery capacity warranty. But even if they did, there could be owners interested in extending the useful life of their vehicles. I think those wanting to beat the metrics Nissan has used for their battery warranty, deserve answers and AESC is best qualified to provide them.

The SOC meters might help us to see some capacity effects in 2 to 3 years, but then we'll have to make assumptions about what that owner did that affected the capacity, assuming someone treats the batteries the consistently for 2 or 3 years!

We'll certainly want to hear from the first people that have the first one or two dots disappearing from the far right section (Capacity Level Gauge, Owner's Manual 2-10) of the battery gage which indicates the pack capacity relative to new. It looks like the Avalable Charge Gauge goes from 0-12 bars based on the battery's current capacity. So if the battery after many years degraded to 80 % of new capacity, and is fully charged, the Available Charge (pg 2-9) would show 12 bars, while the Capacity Level would show 10 instead of 12 rectangular dots.

 

[surfingslovak]

We'll certainly want to hear from the first people that have the first one or two dots disappearing from the far right section (Capacity Level Gauge, Owner's Manual 2-10) of the battery gage which indicates the pack capacity relative to new. It looks like the Avalable Charge Gauge goes from 0-12 bars based on the battery's current capacity. So if the battery after many years degraded to 80 % of new capacity, and is fully charged, the Available Charge (pg 2-9) would show 12 bars, while the Capacity Level would show 10 instead of 12 rectangular dots.

Right, that's a very good point. The two people I'm always keen to hear from are Jimmydreams and gudy. There is also a highly interesting and appropriately named thread: I want my 281. I have reviewed the relevant section of the owner's manual earlier today, and while Nissan is quite specific about what to do (practice moderation and avoid heat), they don't quantify the impact battery care can have on battery life. If our understanding of the capacity gauge is correct, then the first bar won't disappear until the pack has lost about 16% of its original capacity. This might not be practical for our needs, we would want to detect battery degradation earlier so that we can make adjustments and avoid some of the pitfalls.

 

[ElectricVehicle]

Right, that's a very good point. The two people I'm always keen to hear from are Jimmydreams and gudy. There is also a highly interesting and appropriately named thread: I want my 281. I have reviewed the relevant section of the owner's manual earlier today, and while Nissan is quite specific about what to do (practice moderation and avoid heat), they don't quantify the impact battery care can have on battery life. If our understanding of the capacity gauge is correct, then the first bar won't disappear until the pack has lost about 16% of its original capacity. This might not be practical for our needs, we would want to detect battery degradation earlier so that we can make adjustments and avoid some of the pitfalls.

Of course the various communtiy SOC meters for the LEAF will give us earlier insight and a more reliable base line than the gauge. I meant to mention in my earlier post that I know one person who uses LEAFs in his security patrol business just for the economics of saving gas money, and I expect some clients prefer his firm for the fleet of EVs and Prius he uses, way cool..! Back on topic, he's got 12,000 miles on one of his LEAFs already and he didn't mention any degradation yet. The warranty is 8 years / 100,000 miles, so he's already 12% into the warranty life. I think he's at a rate of 20,000+ miles / year.

I also started this thread Quick Charge to 60% - Better Battery Life? to discuss how we can get the most use out of Quick Charging (QC) with minimal impact to battery life to extend the tripops and utility of our LEAFs. While the Quick Charge itself may be expensive - $10? $20? since has high peak power and will likely be used on peak electricity, the far greater cost to me is any singnificant battery degradation it may cause, especially when you need 2 Quick Charges, or more, in one day to make a 150+ ile round trip.

 

[surfingslovak]

Back on topic, he's got 12,000 miles on one of his LEAFs already and he didn't mention any degradation yet. The warranty is 8 years / 100,000 miles, so he's already 12% into the warranty life. I think he's at a rate of 20,000+ miles / year.

Great, yes, it would be very interesting to get some data from his fleet vehicles. If he didn't have an SOC meter, perhaps a loaner could be found. Way to promote his business BTW, very clever. I believe that Jimmydreams was well over 10K miles as well. He is in SoCal though.