My theory about battery longevity

[highend]

Hi, I live in Poland.. Drive leaf for more than year. Climate is ok. Should be perfect for leaf. Summer is warm and hot but hottest are 2-3 weeks and then is nice .
I use Leaf Spy pro to monitor capacity. Last year since April to December I've got SOH reading between 97-99% until December. This year since January I saw quite big drop and every day. How does it stand vs hot weather? It was winter, not summer... And capacity started to drop rapidly.
In march I had ahr readings around 62, got software update capacity upped to 64 AHr, but after one week it dropped again to 62 and were falling. In April lost over 1ahr and now it says 59.70Ahr.
Should it last for a few months after update ? It returned to its back state just after one week! And my leaf mileage is 11.000 miles only! And summer is coming. SOH is now 90%

But considering topic. Saw few leafs with mileage over 60.000miles. All got still 12 capacity bars, so SOH is bigger than 85%. Climate was moderate like mine. So my theory is that it not matters if you charge to 80 or 100%... It just matters when you charge and drive... Charge and drive.... Thus cycling keeps battery in good state and you can drive over 60.000miles with all capacity bars.

So things gets damaged when not used or used rarely. Keep your Leaf driving as much as possible and your battery will be ok. What you people think about that?

 

[LeftieBiker]

From what I've read here, it doesn't match up with what is being observed in the US. Here it appears to be heat, and sitting for long periods at 100% SOC. More charging cycles seem to make it worse, not better, all other things being equal.

 

[donald]

As far as I understand the current research (i.e put AFAIK before everything below!):

Battery temperature is by far the biggest killer for Li-ion. Keep it cool. When it is very cool the electrolyte is 'sluggish' and you will see a temporary apparent drop, which will recover.

High temperature kills because it accelerates the degradation of the electrolyte, which then coats and passivates the electrodes with crap.

The next killer is high and low voltages. This is because there are phase change behaviours in the electrodes of Li batteries which are relatively benign but the longer the battery spends in those states the less reversible the processes become (i.e. the electrodes start fragmenting at a nano-scale and lose electrical conductivity).

The 3rd rank of battery killer behaviour is frequent recharging to high SOC, which is therefore a variant of the previous issue. It is fine to 'flex' the battery every so often, but do it multiple times a day to high SOC and you'll kill it.

Summary:

Hot is very bad. Leaving fully charged is bad. Charging frequently to fully charged is problematic.

Cool is very good. Leaving 25% to 75% SOC is good. Charging often to 80% is no problem.

plus-

Very cold is problematic. If ambients are very low, IMHO try to charge immediately after using the battery rather than letting it cool down and then charging. You can discharge Li at lower temps than you can charge it (you may have noticed regen is limited when cold, for this reason), so charge to 80% day before, then draw power very gently the next day and slowly build up the battery temp through use. I see no issue with an 80% charge the day before, then a final top up in the morning which should help put a teeny bit of heat into the battery too before you start.

 

[AP1]

Nice summary, Donald, thanks. I was going to nail you for "passivate," but you got it right:

Oxford Dictionary:
"Make (a metal or other substance) unreactive by altering the surface layer or coating the surface with a thin inert layer."

 

[gbarry42]

Some of our members have worked out a model for battery aging (in particular, user Stoaty). In plain words, this is what it says:

• - Heat degrades the battery. Above a certain temperature, it will degrade so fast that the other factors have little effect.
  
  - If you keep the temperature down, then the degradation is due to cycle wear. This isn't the number of cycles, but rather the amount of energy that's been put in and removed. You can use miles driven, since everything you put in, you take out again, and even with efficiency considerations, it's still proportional to the total.
  
  - If you keep the battery cold, and don't drive the car much, then the aging factor will get you. The battery degrades over time just due to chemical factors.

So, there are multiple factors, and if you exaggerate one of them, then that one will have the most effect.

 

[highend]

- If you keep the temperature down, then the degradation is due to cycle wear. This isn't the number of cycles, but rather the amount of energy that's been put in and removed. You can use miles driven, since everything you put in, you take out again, and even with efficiency considerations, it's still proportional to the total.

- If you keep the battery cold, and don't drive the car much, then the aging factor will get you. The battery degrades over time just due to chemical factors.[/list]

To all - I know very well about heat issue. And I agree of course.
I just observed quite big capacity loss (1AHr every month) in normal climate (winter/spring) where heat is definitelly not an issue. My Leaf has only 11.000miles.
But observing high mileage Leafs - one famous member here (TaylorSFGuy - if correcttly remembered?) didn't lost any bar after 60.000 miles,
also recently saw Leaf in United Kingdom with 66.000 miles and all 12 capacity bars, my conclusion is that the more you use your leaf in not hot climate, the more the battery will last.

My leaf is used almost daily, but not always - and has 11.000miles, I drive about 600-700 miles every month, and it is 2012 january model with P3227 update done in march 2014. Currently it has 59.70AHr (according to Leaf Spy) and in December 2013 it was around 65AHr (like almost new Leaf). Started falling in January 2014 (from 64-65AHr to current 59.70Ahr in just five months = 1 AHr every month).
So I'm trying to find question why capacity is falling in not-so-hot climate. Also summer is coming...
I'm not worried - I have battery warranty till 01.2017

 

[linkim]

- If you keep the temperature down, then the degradation is due to cycle wear. This isn't the number of cycles, but rather the amount of energy that's been put in and removed. You can use miles driven, since everything you put in, you take out again, and even with efficiency considerations, it's still proportional to the total.

- If you keep the battery cold, and don't drive the car much, then the aging factor will get you. The battery degrades over time just due to chemical factors.[/list]

To all - I know very well about heat issue. And I agree of course.
I just observed quite big capacity loss (1AHr every month) in normal climate (winter/spring) where heat is definitelly not an issue. My Leaf has only 11.000miles.
But observing high mileage Leafs - one famous member here (TaylorSFGuy - if correcttly remembered?) didn't lost any bar after 60.000 miles,
also recently saw Leaf in United Kingdom with 66.000 miles and all 12 capacity bars, my conclusion is that the more you use your leaf in not hot climate, the more the battery will last.

My leaf is used almost daily, but not always - and has 11.000miles, I drive about 600-700 miles every month, and it is 2012 january model with P3227 update done in march 2014. Currently it has 59.70AHr (according to Leaf Spy) and in December 2013 it was around 65AHr (like almost new Leaf). Started falling in January 2014 (from 64-65AHr to current 59.70Ahr in just five months = 1 AHr every month).
So I'm trying to find question why capacity is falling in not-so-hot climate. Also summer is coming...
I'm not worried - I have battery warranty till 01.2017

I had the P3227 update done on my 2011 LEAF in early Oct. 2013. Initially the Ah capacity increased a bit then it dropped from about 61 to 56 in a matter of a few months. At present, I have about 20500 miles and the reading is near 56.5 Ah. The behavior you observed is similar to mine and others who have posted here.

 

[highend]

I had the P3227 update done on my 2011 LEAF in early Oct. 2012. Initially the Ah capacity increased a bit then it dropped from about 61 to 56 in a matter of a few months. At present, I have about 20500 miles and the reading is near 56.5 Ah. The behavior you observed is similar to mine and others who have posted here.

but my concerns have nothing to do with update.
Capacity falling started on january 2014 (1AHr by month), I got update on March 2014 (capacity upped by 3AHr to 64AHr - but quickly dropped - just after one week to 61AHr).... So it has nothing to do with P3227 update,

 

[linkim]

I had the P3227 update done on my 2011 LEAF in early Oct. 2013. Initially the Ah capacity increased a bit then it dropped from about 61 to 56 in a matter of a few months. At present, I have about 20500 miles and the reading is near 56.5 Ah. The behavior you observed is similar to mine and others who have posted here.

but my concerns have nothing to do with update.
Capacity falling started on january 2014 (1AHr by month), I got update on March 2014 (capacity upped by 3AHr to 64AHr - but quickly dropped - just after one week to 61AHr).... So it has nothing to do with P3227 update,

What I observed is that before the upgrade, the Ah capacity varied widely - changing by over 1 Ah up and down in a month or so. After the upgrade, there were still periodic changes but the variation was much smaller - < than 1 Ah. The major changes in Ah occurred last August-Sept. so I don't know if the temperature was important. However, since about March 1, 2014, the Ah capacity has been about 56.5 Ah. Let us know what your capacity is in a few months - hopefully it will settle to a constant value. If your readings follow the same trend as mine, it will start to settle down to a constant value, but much lower than before the upgrade.

 

[40milecommuter]

Nissan now states charging to 100% is OK. They have seen no harm doing so and have eliminated the 80% charge option. The conspiracists here who think "Kennedy was killed by not one but two assassins" and "man never landed on the moon" will tell you Nissan eliminated the 80% charge option to boost the EPA rating. Believe what you want, but Nissan now states with the 2014 model that 100% charge is fine and it won't hurt your battery.

 

[cwerdna]

Nissan now states charging to 100% is OK. They have seen no harm doing so and have eliminated the 80% charge option. The conspiracists here who think "Kennedy was killed by not one but two assassins" and "man never landed on the moon" will tell you Nissan eliminated the 80% charge option to boost the EPA rating. Believe what you want, but Nissan now states with the 2014 model that 100% charge is fine and it won't hurt your battery.

I agree w/the bolded part and disagree w/your last statement due to ALL the statements/cautions from Nissan before, known information (unfortunately, usually on other li-ion chemistry variants) about degradation vs. SoC, and the practices of many of some other notable EV makers about this (e.g. Tesla and Toyota w/the the Tesla-powered Rav4 EV.)

Nissan made many claims about the Leaf early on, esp. degradation which turned out to be untrue. It was significantly worse than they claimed and w/caveats that didn't surface until the Phoenix degradation fiasco, where the rapid degradation was very surprising, in light of the original claims.

Seriously, go thru the ranges of all the BEVs at http://www.fueleconomy.gov/feg/evsbs.shtml" onclick="window.open(this.href);return false; that had known ranges before the '14 Leaf "new range" announcement and think about how the '13 rating of 75 miles would stack up against it to consumers who know nothing about the back story (http://insideevs.com/2014-nissan-leaf-mostly-unchanged-as-range-technically-moves-up-to-84-miles/" onclick="window.open(this.href);return false; and http://insideevs.com/2013-nissan-leaf-rated-at-75-miles-but-84-miles-using-the-old-system/" onclick="window.open(this.href);return false.

Here are some 4+ seater BEVs that consumers could lease/buy...
Rav4 EV: 103 miles
Fiat 500e: 87 miles
'14 Leaf: "84 miles"
Fit EV: 82 miles
Spark EV: 82 miles
Focus Electric: 76 miles
'13 Leaf: 75 miles
i-Miev: 62 miles

And now the BMW i3 is out w/82 miles...

 

[roperld]

My hypothesis is that charging or discharging causes some lithium ions to get trapped in the cathodes and anodes and heat increases the rate of trapping. As the number of charging cycles increases there are fewer interstices in the cathodes and anodes in which ions can get trapped. Therefore, capacity loss occurs faster when a battery is new and slower as a battery gets old. Nissan states that the average driver can expect ~20% capacity loss after 5 years and ~30% capacity loss after 10 years, which fits the idea that the capacity loss slows down with driving, i.e., charging cycles. See capacity-loss curves in http://electricvehiclewiki.com/Battery_Capacity_Loss#Battery_Aging_Model .

If this hypothesis is correct for the main cause of capacity loss, capacity loss should either reach an asymptote or decrease very slowly at long times. Perhaps other causes for losing capacity are in play, also.

 

[donald]

If this hypothesis is correct for the main cause of capacity loss, capacity loss should either reach an asymptote or decrease very slowly at long times. Perhaps other causes for losing capacity are in play, also.

Generally, it is not true.

The main degradation is electrolyte degradation. The rate of degradation wrt temperature is altered according to the electrolyte mix. Most battery manufacturers will add at least vinylene carbonate to their ethylene/propylene carbonate mixtures. This does not, so much, reduce the rate of oxidation of the electrolyte to crud that settles on the electrodes and degrades their performance but instead helps prevent the crud precipitating on the electrode. Most battery manufacturers add several additives to their electrolytes to control all of this, which affects its sensitivity to temperature and cycling.

Electrode degradation is 'secondary' insofar as you are more likely to experience temperature effects first. However, if you maintain a 'perfect' temperature, then yes it becomes the more important factor because lithium is stored by phase change processes which gradually damages the electrodes. In other words, this might well become the more important factor if the battery reaches 'old age', because by implication you are in a reasonable climate for temp if you have got your battery that far.

 

[LeafSwe]

My theory about rapid AHr loss in cold/normal climate was that p3227 reduced the AHr, but now i belive its more time related. When the battery gets about 24month old it starts to lose AHr rapidly. My car went from 66.5 to 59.5 in 8month. Hopefully the rapid loss will stop. Many cars are sold in Norway and is soon 2,5 years old without any bar loss, i think many cars there is about to soon loose the first capacity bar.

 

[highend]

My theory about rapid AHr loss in cold/normal climate was that p3227 reduced the AHr, but now i belive its more time related. When the battery gets about 24month old it starts to lose AHr rapidly. My car went from 66.5 to 59.5 in 8month. Hopefully the rapid loss will stop. Many cars are sold in Norway and is soon 2,5 years old without any bar loss, i think many cars there is about to soon loose the first capacity bar.

This could be answer to mine concerns. Same observed here. It has nothing to do with p3227 update.
Exactly when my battery was 2 years old it started to lose AHr rapidly. In cold. But my car went from 64 to 59.5 in 4 months. In cold/normal climate - driving about 600-700 miles monthly.

So I assume driving (using) car a lot in normal/cold climate don't affect battery so much (so there are over 60.000mile Leafs with 12 capacity bars).

Do we have then another (besides heat) capacity degradation model - AGING ?

 

[RegGuheert]

To all - I know very well about heat issue. And I agree of course.
I just observed quite big capacity loss (1AHr every month) in normal climate (winter/spring) where heat is definitelly not an issue. My Leaf has only 11.000miles.
But observing high mileage Leafs - one famous member here (TaylorSFGuy - if correcttly remembered?) didn't lost any bar after 60.000 miles,
also recently saw Leaf in United Kingdom with 66.000 miles and all 12 capacity bars, my conclusion is that the more you use your leaf in not hot climate, the more the battery will last.

I can only agree with this conclusion if you specify it to say: "The more you use your leaf in ANY climate, the more MILES the battery will last." Why would this be true? Calendar losses in the LEAF appear to be extremely high. Only in the coolest climates do they appear to come close to Nissan's predictions. As a result, the only way to get many miles out of the LEAF battery is to drive many, many miles. But driving many miles also degrades the battery, so it will shorten the TIME that the battery will last versus sitting.

My leaf is used almost daily, but not always - and has 11.000miles, I drive about 600-700 miles every month, and it is 2012 january model with P3227 update done in march 2014. Currently it has 59.70AHr (according to Leaf Spy) and in December 2013 it was around 65AHr (like almost new Leaf). Started falling in January 2014 (from 64-65AHr to current 59.70Ahr in just five months = 1 AHr every month).
So I'm trying to find question why capacity is falling in not-so-hot climate. Also summer is coming...
I'm not worried - I have battery warranty till 01.2017

I have pointed out many times on this forum that most of the published literature indicates that long-term Li-ion battery calendar losses tend to either be linear or accelerate with time. (For most Li-ion batteries, it is only at the very beginning of life, before linear or super-linear modes become dominant, that calendar losses appear exponential.) It is cycling losses (losses due to driving) that tend to decay exponentially over the life of the vehicle.

The good news is that Li-ion battery engineers and scientists are working to reduce the linear and super-linear calendar degradation modes to a very low level so that only the exponential decay modes will remain. Hopefully future EVs will have extremely low battery capacity losses, both in terms of calendar losses and cycling losses.

 

[kmp647]

im in northern Va also, 2012 leaf purchased 11/11/11

charge to 100% nightly currently at 40,000 miles all 12 cap bars

the only efforts made to protect battery are avoiding loitering at 100% for days(charge timer each night 12am to 5am)
I avoid letting car sit at high soc

range has dropped some, I have leaf spy lite only, I will try to look at AH

I agree best way to get life out of a Leaf is drive it alot ! letting it sit around just wastes pack life.

 

[kmp647]

Just lost my first bar today. 40,311 miles 31 months

Temps a have been warm lately and 6 bars on the temp gauge
Had a quick charge todaywiththe battery at 91f

One thing that did help my leaf , for the first year my evse was mounted outside my garage and I think the nighttime cooling during the summer , instead of cooking in the garage with the v8 ice!

Moved last year and mounted my evse in the garage , great for winter , but not so good for cooling the pack.

Range still works for my commute. 58 miles RT