Capacity Loss on 2011-2012 LEAFs

[TonyWilliams]

Does anyone have any links to official Nissan videos or documents like the one above. I'm trying to gather all the ammo I can for the battle.

Azdre and I captured these two videos, in case Nissan decides to pull them down some day...

http://www.youtube.com/watch?v=DShtvd5jJHQ" onclick="window.open(this.href);return false;

http://www.nissan-global.com/EN/REPORTS ... 10803.html" onclick="window.open(this.href);return false;

Interesting that Mark Perry says the frequently repeated 70-80% battery capacity in 10 years, "and that is gradual".

I'm glad he clarified that, because I wasn't sure a jury would know what gradual meant. Now they do. Thanks!



Keep in mind that Nissan has already "reset" at least one car's battery capacity gauge to read "like new", when it is probably about 25% reduced in capacity. So, I don't think Nissan will EVER have a reduced capacity battery, according to their twisted logic.

[opossum]

+1, however my initial reaction was to tell them to disclose or go to hell. The New Jersey in me always comes out in my initial reactions...

I'm right there with you, DesertDenizen. Well, not literally, as that would put me close to the UofA. But I share some of that NJ sentiment. The information sharing has been completely 1-sided. 4+ months of this headache. My wife almost can't make ONE trip to work in the car now. Roughly 10 trips to dealers and a test facility. Countless work hours and weekends lost. And all Nissan can share with us is that everything is "normal." Yeah, I'm very close to being done dealing directly with Nissan. My back side is really sore...

[Nubo]

If this is the case, then the "charge up and measure energy input" is not a good approach for capacity measurement.

I would stay away from battery measurements. Nissan can just reply to you (and a court with a team of engineers / scientists) that they measured the battery and "all was well". Just a software glitch.

The only issue the end user (us) is really concerned about is how far can it go. Even the dumbest juror will understand that when the car was new, it goes this far (then show 5 or 10 cars that were tested right out of the dealer's lot), and now these cars only go XX% of that number in the same conditions.

I like the wall-measurement approach. Unless we are talking about some significant decrease in energy efficiency being involved (and I haven't seen that proposed), then the energy storage capacity of the battery is what determines how far it can go under any given set of conditions. And measuring the watt-hours the battery will accept is much more repeatable and eliminates a lot of variables involved with trying perform multiple test cycles on public roads. Or at least it's a lot easier.

[palmermd]

And after reading 10 official definitions of the word gradual from well-respected ( and not so respected dictionaries) there is no way in hell that 0-10 percent in one year followed by 20-30% in 3 months can be gradual.

This is the first comment on "gradual" that I can fully agree with. Losing 30% in a year or two could be gradual, but 25% in the the first few months of the second year after 5% the entire first is not gradual, and this seems to be the pattern. Most people do not see any noticable loss in the first year and then suddenly (opposite of gradual) they lose a big chunk of capacity right after their anniversary.

[thankyouOB]

regarding the use of various adjectives -- some, many, most -- to describe the world of battery capacity-losing Leaf owners: i dont see any significant battery capacity degradation at 16 months and 16k miles.

I live in a moderate climate.
I still make my 50-mile, roundtrip to work on 8 bars.

[LEAFfan]

And after reading 10 official definitions of the word gradual from well-respected ( and not so respected dictionaries) there is no way in hell that 0-10 percent in one year followed by 20-30% in 3 months can be gradual.

+1!

[tbleakne]

It would not improve driving range, the purpose is to minimize battery degradation. The Volt consumes about 200Wh to keep the battery cool, even if its unplugged, a minimal use of energy. GM boasts that they are using "space age" insulation and apparently it is needed. Insulating the battery pack is crucial or you will quickly drain the battery in Phoenix.. you also want to prevent condensation from forming and that is a problem.
GM claims (and a recent study mentions it) that once the pack is discharged to 60% SOC it is fairly immune to heat degradation, thus at that point you can stop cooling the pack until it is plugged in again. True the its not exactly the same chemistry as the Leaf is using.

Sounds pretty feasible, at least energy-wise. I had assumed a larger cooling energy drain.

I agree active cooling in a hot parking lot for a work-day without plug-in should be feasible. Assumptions:
30 sq. ft of area of battery pack to insulate.
R6 insulation
40 deg F temperature gradient
8 hr work day

(30/6)*40 = 200 BTU/hr heat load
Typical room A/C delivers 8K BTU/hr using 1500W.
1500*(200/8000) ~= 40W.
40W*8hr = .3 kWh per work day

I also have also found some published data supporting the drop in degradation at 60% SOC. I will post that separately.

[tbleakne]

From pg 326:

I have updated the Wiki with surfingslovaks table of estimated relative rate of battery capacity loss based on Arrhenius equation for rate of chemical reactions that 10 degree Celsius increase in temperature doubles rate of battery capacity loss:

http://www.mynissanleaf.com/wiki/index. ... What_To_Do" onclick="window.open(this.href);return false;

Additions, corrections, etc. are welcome (especially from surfingslovak).

Arrhenius Factor: Exp(-(DeltaE)/kT) where
T is absolute temperature
DeltaE is activation energy.

I agree the Arrhenius factor is very relevant, but how fast it varies with temperature depends upon the activation energy of the chemical process that is causing our degradation. A higher activation energy reduces the absolute magnitude of the factor, but it increases the relative change in the factor for a given change in temperature. This makes sense, since we are dealing with a very slow chemical process.

60 F is 540 Rankin (absolute). A 40 F change in temperature (60 vs 100 F) represents only a 40/540 = 7% change in absolute temperature, yet we are seeing perhaps a 5 to 1 change in relative degradation rates for folks in different climates.

Your rule that "10 degree Celsius increase in temperature doubles rate of battery capacity loss" implies a certain activation energy. The wide disparity between degradation for folks on this forum suggests a higher activation energy might be closer.

The following published paper studies lithium-ion battery loss as a function of both temperature and SOC:
"Correlation of Arrhenius behaviors in power and capacity fades with cell impedance and heat generation in cylindrical lithium-ion cells"
from Sandia National Laboratories.

http://144.206.159.178/ft/641/92454/1607538.pdf

This 2003 paper is obviously not talking about the LEAF's particular Lithium chemistry, but I believe the behaviors it describes are typical. Capacity fade is discussed on pg 7, Fig 5, which I display below:


The chart shows that capacity fade slows for all temperatures as the SOC is reduced from 10% to 80% to 60% SOC. At high state of charge the Li-ions are concentrated on the graphite electrode. My understanding is that the primary loss process takes place at this electrode, so it seems reasonable that this process would slow as the SOC lowers.

[GeekEV]

The chart shows that capacity fade slows for all temperatures as the SOC is reduced from 100% [EDIT: I'm assuming you meant 100% here not 10%] to 80% to 60% SOC. At high state of charge the Li-ions are concentrated on the graphite electrode. My understanding is that the primary loss process takes place at this electrode, so it seems reasonable that this process would slow as the SOC lowers.

Except that graph seems to show that at 55C the 80% SOC level will fade MORE than the 100% SOC level. Does that suggest that at extreme temperatures you're better off charging to 100% SOC as often as possible?

[mwalsh]

Except that graph seems to show that at 55C the 80% SOC level will fade MORE than the 100% SOC level. Does that suggest that at extreme temperatures you're better off charging to 100% SOC as often as possible?

So it's not just me who saw that then? I just finished a couple of beers, and had already discounted it as an alcohol fueled delusion.