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drees
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 11:05 am

palmermd wrote:I agree that they could not change the chemistry at that time, but you can work to optimize what you have.

Given what we know about the LEAF batteries now, it appears to me that even thermal cooling would not have been enough to make the batteries last much longer than they do now for places like Los Angeles, unless they would be willing to sacrifice a large amount of efficiency (and range) to do so.

Look at the Volt TMS which uses a very similar battery as the LEAF and what maximum temperatures it aims for - it generally keeps the pack between 72-90F when the car is either on or charging. Even in Arizona, the Volt's battery appears to be holding up pretty well (hard to tell how much GM allows the SOC band to expand to compensate for capacity loss - don't know if people are able to monitor Volt battery pack voltages to get an idea or if they are able to sniff the CAN bus to find the data).

But LEAFs subjected to the same temperature band (like my San Diego LEAF which very rarely sees any battery temperatures over 85F) has still lost capacity at an alarming rate and TMS would not have helped my battery significantly.

It seems that GM got a battery from LG which has some "special sauce" which helps it's LiMn batteries last longer than the LEAF. And hopefully Nissan has their own "special sauce" ready to go soon.
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surfingslovak
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 11:37 am

drees wrote:
palmermd wrote:I agree that they could not change the chemistry at that time, but you can work to optimize what you have.

Given what we know about the LEAF batteries now, it appears to me that even thermal cooling would not have been enough to make the batteries last much longer than they do now for places like Los Angeles, unless they would be willing to sacrifice a large amount of efficiency (and range) to do so.

Look at the Volt TMS which uses a very similar battery as the LEAF and what maximum temperatures it aims for - it generally keeps the pack between 72-90F when the car is either on or charging. Even in Arizona, the Volt's battery appears to be holding up pretty well (hard to tell how much GM allows the SOC band to expand to compensate for capacity loss - don't know if people are able to monitor Volt battery pack voltages to get an idea or if they are able to sniff the CAN bus to find the data).

But LEAFs subjected to the same temperature band (like my San Diego LEAF which very rarely sees any battery temperatures over 85F) has still lost capacity at an alarming rate and TMS would not have helped my battery significantly.

It seems that GM got a battery from LG which has some "special sauce" which helps it's LiMn batteries last longer than the LEAF. And hopefully Nissan has their own "special sauce" ready to go soon.

Dave, please don't forget that it's time spent at temperature, and not just the band. I'm sure that you know this. If we shaved off the peaks over 70 F in San Diego, particularly during charging, I would think that there would be an improvement in pack longevity. Additionally, Volt's pack is thermally insulated, and ambient heat does not seep in as rapidly as with the LEAF. Insulation in turn necessitates active cooling to remove the heat energy creted during operation of the vehicle. These two factors could be significant, and combined with a more robust cell design, and potentially an expanding SOC range, could provide a good end-user experience.

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drees
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 11:50 am

surfingslovak wrote:Dave, please don't forget that it's time spent at temperature, and not just the band. I'm sure that you know this. If we shaved off the peaks over 70 F in San Diego, particularly during charging.

Oh, I'm not forgetting. 98% of my charging is in the middle of the night when the pack has already cooled down to 75F during the summer. The pack typically hits a peak of 80F at the end of the day during the summer months - not quite hot enough to trigger cooling. It takes a heat wave to get temps higher than that. It's just not that hot here.

Yeah, if TMS activated during driving and cooled the pack down to 75F while driving that might have a nominal effect on battery life. Maybe I'd only be down 14% instead of 18%. But it wouldn't be anywhere near the improvement Nissan needs to make where they should be aiming for 20% loss after 5 years. For Arizona owners? Yeah, they might get close to So Cal durability.

In the winter months the pack rarely gets above 70F, so TMS would almost never be activated then.
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RegGuheert
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 2:45 pm

drees wrote:The pack typically hits a peak of 80F at the end of the day during the summer months - not quite hot enough to trigger cooling. It takes a heat wave to get temps higher than that.
Please note that this is at the temperature sensors, which are attached to the ends of a few modules. The Volt flows coolant along the faces of each module, thereby keeping all of the modules in a condition where they are all nearly isothermal. In the LEAF, there is certainly a temperature rise from where the temperatures are sensed to where the heat is dissipated. The magnitude of that temperature rise is something only Nissan knows, but it I suspect it is non-trivial. The article on separators that Guy linked recently said that large-format cells often have a 10C temperature gradient across the cell under normal operating conditions. Perhaps the rise in the LEAF is more than that.

Does it make a big difference? Perhaps. Developing cells which have a long life even in high temperatures is what is needed for the EV industry long-term.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 4:25 pm

I think the ev industry needs to follow dysons lead. When the portable vac has below optimal power out just shuts down rather then giving a suboptimal experience. Likewise, the battery should have a buffer to the upside which initially allows a little less then full charge, but you'd that as the battery ages. Then one the battery goes to low, the maintenance light goes on, and signals it's time for a repair (under warranty for 3 years) the service shop can then restore our replace the battery. The user experience on range then status consistent. There is a cost, but overall satisfaction should justify that cost via higher sales and incremental sticker price.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 4:29 pm

DougWantsALeaf wrote:I think the ev industry needs to follow dysons lead. When the portable vac has below optimal power out just shuts down rather then giving a suboptimal experience. Likewise, the battery should have a buffer to the upside which initially allows a little less then full charge, but you'd that as the battery ages. Then one the battery goes to low, the maintenance light goes on, and signals it's time for a repair (under warranty for 3 years) the service shop can then restore our replace the battery. The user experience on range then status consistent. There is a cost, but overall satisfaction should justify that cost via higher sales and incremental sticker price.


Congratulations: you just tripled the cost of a Leaf and now I can't afford it!
I don't think people want their car "shutting down" on the highway @60mph :shock:
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surfingslovak
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 4:59 pm

Stanton wrote:I don't think people want their car "shutting down" on the highway @60mph :shock:

No, you definitely don't want that. I've been through this with another EV, where the engineers saw it fit to shut down the car when a battery sensor malfunctioned. I can confirm from my own experience that this is a horrible idea, and the other drivers who have been through this, concur!


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drees
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Re: Why do lithium batteries die and how to improve them?

Sat Feb 15, 2014 1:23 pm

DougWantsALeaf wrote:I think the ev industry needs to follow dysons lead. When the portable vac has below optimal power out just shuts down rather then giving a suboptimal experience. Likewise, the battery should have a buffer to the upside which initially allows a little less then full charge, but you'd that as the battery ages. Then one the battery goes to low, the maintenance light goes on, and signals it's time for a repair (under warranty for 3 years) the service shop can then restore our replace the battery. The user experience on range then status consistent. There is a cost, but overall satisfaction should justify that cost via higher sales and incremental sticker price.

No, it's simple. Just do these steps:

1. Give realistic expectations on how fast you might expect the battery to lose capacity based on use and climate. Provide an upper and lower bound that one might see based on various usage habits. Make sure the car tracks operating conditions accurately to help improve future expectations.
2. Give a max charge slider like Tesla and say how much using lower SOC will improve calender life.
3. User can slide the max charge slider up as capacity is lost to maintain a consistent range themselves.
4. Give a price for battery pack replacement once the pack drops below required capacity.

Really, all the magic is in #1. Provide realistic expectations and err on the side of under promising and over delivering.

Do that and people will be able to make their own educated decisions in terms of what is and is not acceptable.
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TimLee
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Re: Why do lithium batteries die and how to improve them?

Sat Feb 15, 2014 1:38 pm

drees wrote:No, it's simple. Just do these steps:

1. Give realistic expectations on how fast you might expect the battery to lose capacity based on use and climate. Provide an upper and lower bound that one might see based on various usage habits. Make sure the car tracks operating conditions accurately to help improve future expectations.

Really, all the magic is in #1. Provide realistic expectations and err on the side of under promising and over delivering.

Do that and people will be able to make their own educated decisions in terms of what is and is not acceptable.

+10,000
False marketing will accomplish nothing other than complete total destruction of your BRAND!!!!

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palmermd
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Re: Why do lithium batteries die and how to improve them?

Sat Feb 15, 2014 3:40 pm

drees wrote:Really, all the magic is in #1. Provide realistic expectations and err on the side of under promising and over delivering.

Do that and people will be able to make their own educated decisions in terms of what is and is not acceptable.


I like it. Keep things simple.
Michael

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