scottf200
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Re: Why do lithium batteries die and how to improve them?

Mon Feb 10, 2014 1:09 pm

TimLee wrote:The truly horrendous coulombic efficiency of the LiMn battery as used by the LEAF and Volt does raise interesting questions about why Nissan and GM went that way.
Looks like the TMS with 30C/86F is the key. From video where I added F temps in the red.
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Graphs from this Volt article.
http://gm-volt.com/2013/05/03/volt-batt ... izona-sun/
Image
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Last edited by scottf200 on Mon Feb 10, 2014 4:40 pm, edited 2 times in total.
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scottf200
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Re: Why do lithium batteries die and how to improve them?

Mon Feb 10, 2014 1:36 pm

The Volt apparently had chemistry changes in 2013.

2013 Chevrolet Volt Boosts EV Range to 38 Miles
Battery storage capacity increase and cell chemistry changes enable improved range
2012-06-07
http://media.gm.com/media/us/en/gm/news ... _volt.html
In addition, the total storage capacity of the Volt battery has been increased from 16 kWh of energy to 16.5 kWh, and engineers have expanded the state-of-charge window to use 10.8 kWh of the total battery energy – up from 10.3 kWh used in the 2012 model. The battery system maintains a buffer to ensure battery life, but that buffer has been reduced.
<snip>
Cells with improved chemistry have accumulated 150,000 test miles to date. The tests have revealed less battery degradation, the ability to withstand temperatures as low as -30 degrees Celsius and less impact by energy throughput.
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Re: Why do lithium batteries die and how to improve them?

Wed Feb 12, 2014 11:31 pm

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

Fri Feb 14, 2014 8:31 am

drees wrote:Ran across this great presentation from Professor Jeff Dahn (Dalhousie University) talking about various issues in engineering batteries for EVs (and other applications) that last a long time. Professor Dahn has been working with GM for a year or two now helping them in their battery testing lab.



Notes:
  • Coulombic efficiency is an easy way to compare cycle/calendar life of a lithium batteries without having to run very prolonged cycling tests - the better the efficiency, the more durable the battery.
  • Chemistry (and additives) are vital in determining cycle/calendar life of a lithium battery.
  • The colder the battery, the longer it will last (Arrhenius' equation).
  • The lower the SOC the battery is charged, the longer it will last (example was storing battery at ~20% or 3.5V resting voltage).
  • LiMn (as used in the LEAF/Volt) has horrendous cycle/calendar life at temperatures of 30C+ compared to say LiCo (as used by Tesla). LiCo is even better than LiFe (A123).
  • Additives can have a very strong effect on coulombic efficiency (and thus durability)

Too bad no one at Nissan ever watched this presentation.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 9:28 am

KJD wrote:Too bad no one at Nissan ever watched this presentation.


Pretty tough to watch a presentation given in 2013 when you're developing/testing a battery that went in a commercial production vehicle in 2010 :?
Having said that, the video/information is interesting and valuable, but we've debated ad nauseum (in other threads) the 1000's of decisions Nissan had to make in building the car. I also maintain that when battery capacities are on the order of a Tesla and beyond, losing some capacity--either temporarily due to cold temps, or permanently due to hot temps--won't be such a killer.
And don't start the "Tesla has a TMS so it must be better" argument, because they HAD to based on the battery chemistry type they chose, or they would be having even more fires than they already do (there was another reported a couple of days ago).
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 9:51 am

Stanton wrote:Pretty tough to watch a presentation given in 2013 when you're developing/testing a battery that went in a commercial production vehicle in 2010 :?
Having said that, the video/information is interesting and valuable, but we've debated ad nauseum (in other threads) the 1000's of decisions Nissan had to make in building the car. I also maintain that when battery capacities are on the order of a Tesla and beyond, losing some capacity--either temporarily due to cold temps, or permanently due to hot temps--won't be such a killer.
And don't start the "Tesla has a TMS so it must be better" argument, because they HAD to based on the battery chemistry type they chose, or they would be having even more fires than they already do (there was another reported a couple of days ago).


Well, if you look at the post before, you can see a report that the information was known in 2009.
with regard to the fire story released at 4pm yesterday, it was a 12v battery fire issue and the exact cause is not yet known. The vehicle was customized and perhaps the custom work is the source, but it also might be something in the Tesla 12v, either way it had nothing to do with the traction pack.
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drees
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 10:08 am

palmermd wrote:Well, if you look at the post before, you can see a report that the information was known in 2009.

2009 is too late for the current generation LEAF batteries. But it would not have been too late for the next generation LEAF batteries.

Presumably (or at least we can hope) they have learned similar lessons or are using similar techniques for their next generation of batteries due out soon.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 10:27 am

drees wrote:Presumably (or at least we can hope) they have learned similar lessons or are using similar techniques for their next generation of batteries due out soon.
Image

Indeed. I know for a fact that Nissan has worked with well-regarded battery experts, and they have certainly been active in this area for over a decade. I'm still a bit baffled how they could have released the 2011 LEAF, with all the marketing claims heaped on top of it. While it would be interesting, we may never learn what happened. If there was a breakdown in communication or inadequate testing, and where it might have occurred. I really hope that they will make this right by everyone affected, to the extent that's possible. Thanks for finding, and posting Prof. Dahn's lecture, Dave.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 10:28 am

drees wrote:
palmermd wrote:Well, if you look at the post before, you can see a report that the information was known in 2009.

2009 is too late for the current generation LEAF batteries. But it would not have been too late for the next generation LEAF batteries.


+1 You can't even design and build a dishwasher in 12 months let alone an automobile :roll:
Last edited by Stanton on Fri Feb 14, 2014 10:32 am, edited 1 time in total.
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Re: Why do lithium batteries die and how to improve them?

Fri Feb 14, 2014 10:31 am

drees wrote:
palmermd wrote:Well, if you look at the post before, you can see a report that the information was known in 2009.

2009 is too late for the current generation LEAF batteries. But it would not have been too late for the next generation LEAF batteries.

Presumably (or at least we can hope) they have learned similar lessons or are using similar techniques for their next generation of batteries due out soon.


It was not too late for them to have known that they needed to put at least some simple cooling mechanism. They even put a peltier cooler into the Renault Fluence pack, which is the exact same cells as we have in our Leaf's.

Image

There were plenty of people who knew before 2009 and were giving warnings to Nissan.

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