Battery Degration 20.000km later

Hello!

Last year i did a trip around Neusiedlersee, Burgenland, Austria.

To get a feeling for battery degration, i did this trip today again. Battery temperature was today a little bit higher as last year (2014: 19,1°C -> 21,3°C, 2015: 23,4°C -> 25,8°C).

I discharged the battery from 100% to 2% Soc on this trip. This means 15.325Wh - 737Wh = 14.588Wh (98% DoD). So the useable battery capacity (100% DoD) is 14.885Wh. Last year this value was 14.865Wh.

So i can't talk about appreciable battery degration 20.000km later. Unknow to me is the impact of battery temperature: the battery was round 4°C warmer as last year.

caniOn ScreenShot 2014:



caniOn ScreenShots 2015:






























Martin

Martin, thank you for posting. I love it, your battery capacity has increased! :roll:
In addition to temperature, perhaps tire wear played a part? Edit: DUH, I just noticed the 145.9km vs. 145.3km
In any case, your battery is holding up extremely well.

Wow Martin, you are one disciplined driver- I only see three excursions beyond 40 amps in the entire trip, and within two minutes of your original 2 1/2 hour trip? I doubt I and my i would produce similar results....

jray3 said:

Wow Martin, you are one disciplined driver- I only see three excursions beyond 40 amps in the entire trip..

Click to expand...

+1, and to think Martin did exactly 100Wh/km (161Wh/mi) both times! In USA, using EPA's convoluted terminology, that means 209.3mpge. :mrgreen:

Like we keep saying, your mileage (thus range) is whatever it needs it to be - you just need to drive accordingly.

1km/100Wh * 1mi/1.61km * 33.7kWh/gal *1000Wh/kWh = 209.3mi/gal :ugeek:

Recharging tooks 17.500Wh, measured via dedicated Ferraris-counter. So with 14.588Wh used, i have 20% loose at charging or 83% efficiency for the whole batterysystem with charging-unit.

Regarding battery degration: it seems to me, that Mitsubishi follows the strategy to give us always the same battery capacity. You see this at the cell voltages at 2% SoC:

2014: 3,395V weakest cell, 3,505V strongest cell, average 3,457V.
2015: 3,235V weakest cell, 3,470V strongest cell, average 3,381V.

Difference weakest cell (#57): 160mV
Difference strongest cell (#48): 35mV
Difference average: 76mV

So the weakest cell is stressed mostly and degraded fastest. The batterysystem is as good as the weakest cell in this configuration with all cells in serial.

I had done another trip (another road) last year from 100% -> 2% SoC ... also using the heater:



If you look to my recording at http://www.spritmonitor.de/en/detail/532466.html you see my normal driving style. Most km are commuting 20km to the office and 20km back to home on country roads. These values are measured from wall. So the allover average from battery is 14.588Wh/17.500Wh*15,1kWh/100km = 12,6kWh/100km.


Martin

I believe that the i-MiEV only recalibrates the capacity after some time, and we could have to wait more then one year to see the new calibration. I think your car, didn´t make any calibration between the two trips, so it works as it have the same capacity. But that´s not true, there is some degradation, and i think we can see that by the voltage at the same 2% SoC. Now the voltage at 2% SoC is 298V, against 305V last time (not sure). In an year, maybe it will be 285V, and maybe it can't reach the 0,0% SoC (because one cell will be at 2,75V before the SoC goes to 0,0%), unless it recalculates the capacity in the next year.

And there is something that can make these conclusions wrong. 100% SoC isn´t allways the same energy. I see in my car, sometimes 100% SoC and 361V and other times 100% SoC and 359V. To take conclusions, we have to see if the 100% SoC in the two trips, are the same voltage.

But assuming that 100% SoC was the same voltage in the two trips, and see such a low difference, that´s definitively good news. Maybe 1/2% less capacity?

Quelle régularité ! What a constant way of driving comparing 2014 and 2015. Same Wh/km of 100.
Since the most important factor to monitor is the tension (volt) at the weakest cell, we can see that yours was 3.395 volt (2014) down to 3.235 volt (2015). As a comparaison, the weakest cell on my new pack is 3.600 volt at 4% soc, and 13970 Wh out compare to your 14588Wh out. Never went down to 2%.

As you say : « Regarding battery degration: it seems to me, that Mitsubishi follows the strategy to give us always the same battery capacity. ». So, battery capacity is and will be calculated from the weakest cell, always at a max volt of 4.1 down to a decreasing minimum with time down to 2.75 volt after «X» years. The degradation of cells still occured during that time, but is not seen in the available energy from the pack and the available range. It will be interesting to see what happens when reaching the min tension of 2.75 volt. Sure a real decrease in available energy and range.. We'll see.

Malm, it seems to me that the computer does a short time calibration of the soc every time we start it. Probably not the overall calibration you're talking about, on the entire range from 0% to 100%.

One real life example: Driving from 100% soc to 60%soc give a reading of 148 Wh for each 1%soc. I stop the car for 20 min. On restart canion gives 65% available soc on the increased of voltage at rest of course. For the rest of the trip down to 10% soc, the reading is 131 Wh for each 1%soc ( compare to 148Wh previously).

Also when no full recharge, let's say 95%soc, the Wh for each 1%soc is always lower than recharging to 100%. It could be as low as 120 Wh/1%soc.

Pier