Battery Performance

I want to get a electric vehicle and am doing research right now. The i-Miev is currently my first choice.

Unfortunately, in the US only limited technical data is available. You can't even ask someone (dealer, Mitsubishi), they just do not know. So I asked Japan, this data might help some, it sure helped me.

The technical information I received was already converted to US standards. This is for the traction battery.

- The battery can only operate at 100% at temperatures between 53.6 °F and 87.8 °F (between 12 °C and 31 °C).
- Temperatures > 87.8 °F (31 °C) can lead to performance degradation, temperatures > 122 °F (50 °C) destroy the battery cells.
- Temperatures < 53.6 °F (12 °C) cause performance limitations, but only slightly. The shelf life is not impaired.
- The charging behavior (curve in the upper half) is more limited by low temperatures as the discharge behavior (curve in the lower half).
- The traction battery can only develop full power in warm weather.
- If the battery temperature reaches 32 °F (0 °C), the battery can only be charged to about 60 %
- If the battery temperature is less than -4°F (-20 °C), it can no longer be charged. The segment display does not reflect this, but the range indicator does.
- Conversely, a fully charged battery is almost 100% efficient at -14 °F (-10 °C), at -4 °F (-20 °C) still more than 60%.

Operating the all-electric heater at maximum output (which draws 5 kW) consumes about as much energy as does cruising at 31.1 mph (50 km/h).

I also got all the details about the battery, technology, setup, weight, manufacturer. Lots to translate, I might do it later. If someone wants to know, let me know, and I can do it.

MIEV!

Empirical data gathered by hundreds of owners (much of it reported here) shows that the battery in the iMiEV is very robust, seldom prone to failure and delivers excellent performance in most 'normal' temperatures - Anything between about 15 degrees and 95F. While it's interesting to read what the factory claims, it's much better (IMO) to read real world performance - We all know that not everything 'claimed' is accurate

If you're thinking of buying an iMiEV, the battery won't be of big concern to you and you'd be taking much less risk than say you would buying a Leaf

Don

I beleive you should not be so affirmative about the robust ness of the I-miev basttery. Around here I know of 3 battery failure of I-Miev and around 200 sold. There is at least 6 times more Leaf sold and I didn't hear about one battery failure. The only ones I read about was in very hot climate.

Anyway, I love my I-miev, but we should not be so sure about the superiority of the I compare to the leaf. And comparing range with time. the Leaf shows the degradation of the battery pack on the instrument panel while the I-miev seems to mask degradation by extending the voltage range of the battery cells, with time until it is down to 2.75 volt and then will show rapid decrease in range.

IMO Pier

Hi RobertST,

I have been thinking about the imiev battery and temperature for along time now.

I have been driving my Imiev in Montreal for 3 years without any battery issues. I do keep my car in a garage at night to charge it. That saves it from the very cold winter temps and somewhat helps out in our brief high temp summers.

A couple of months ago I bought a second 2012 iMiev without quick charge (a great deal IMHO). This winter I will have to leave my first iMiev with quick charge out side and garage the "new" one. I'll report on how that experience goes for both cars.

In terms of real-world experience I would say as far as battery performance is concerned the iMiev battery is pretty good. Canion gives some visibility into the cell temps so you can adjust your driving to keep the battery from heating too much in the summer.

I think it's a topic of discussion to get to the bottom of what the actually cell core temp is and what the BMS is reporting to CANION. In the steady state CANION gives accurate battery temps and considering the dash has no battery temp information at all I would say CANION is a gold mine of information.

But I have to say that I'm not sure how much spending time (obsessing) thinking about the battery temp will make any difference. I guess it's kind of a peace of mind thing to see you battery sitting between 20 and 30 Deg C.

In general in the Winter I don't see any problem as long as you don't abandon the car and let it freeze solid to -30 Deg C or below. Driving the car on the highway increases the temp of the battery and recharging it maintains the temp or gradually increases it.

In the summer in hot weather it's more of a problem if you don't have a QC port. When it's 30 DEG c ambient temp and the car has been sitting at that temp for awhile then it's easy for the battery to start at 30 Deg C and climb up to 35 deg C or more as you drive. Then if you charge and drive more the temp will just contiue to climb. Driving fast on the highway just increases the slope of the temp climb. Perhaps this is the road to a cell death or battery degradation. It's kind of the corner case that you want to avoid if you can. I think only people that take the car out of it's normal urban environment and do a road trip with quick chargers (QC) bring the battery to this condition. Even then I remember a post where someone did a road trip and brought the cells up to 45 Deg C. Still below 50 Deg C. Maybe you can't get the cells to 50 Deg C at 30 Deg C ambient even if you drive on the highway. I never tried.


As far as the car limiting performance to protect the battery when it gets too hot or cold it's not really a big issue. Regen is dimished when it gets too cold and a QC is much slower when it's cold. A pain in the butt but not a show stopper.


All and all the iMiev is really great and blows away any other small car in an urban environment.

I'm curious how did you get information from Japan ? I would love to see all of it.


Don......

DonDakin said:

All and all the iMiev is really great and blows away any other small car in an urban environment.

I'm curious how did you get information from Japan ? I would love to see all of it.Don......

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I'll second that, I would love to see more too.

All of this battery data is held close to the vest by manufacturers. It only leaks out here or there. They have done the testing that answers some if not most of our questions.

Thanks RobertST for posting it. My experience (while more qualitative) fits that heat more than any other single factor is a problem for longevity. high C rates in or out are a close second. But they produce spot heat internally in the cells so perhaps that is heat degradation too? I'll definitely be sharing the AC with the battery box as much as possible this summer.

Aerowhatt

DonDakin said:

...
I'm curious how did you get information from Japan ? I would love to see all of it.


Don......

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Hello,

I am foreign, well educated, speak several languages and have worked worldwide. Major part was in the automotive industry. So I have a few contacts, or can ask around and hopefully get where I have to go to get information. If the source then reveals it, well, that is a different question. Yes, they do not want anybody to know. However, we buy competitor cars and take them apart, so it is really not a big deal. BM (Battery Management) is different, there are even measurements in place that, if you mess around with it, it will destroy itself.

Much information is available online, just watch out for the source. People like to talk/write. I am interested in an i-Miev. I don't go by the fake advertising or people talking and not knowing what they are talking about.

Unfortunately I can not attach a file here, I have reports, sheets, papers.

Here is the current (May 2015) battery detail. The paper is quite long, contains even the shareholder information about GS Yuasa, but of course is in Japan.

Battery:

Location: Floor
Weight: 200 kg
Internal: Contains 88 lithium-ion battery cells based on the cathode technology LiMn2O4.
Cells: 50 Ampere hours
Nominal cell voltage: 3.7 Volts
Total Voltage: 330 Volts (app.)
Cell blocks: LEV50-4
Supplier: GS Yuasa
Rating: 109 Wh/kg and 218 Wh indicated
Charging time: 6 hours (app.) at 230 Volts to full
Between 15 to 30 minutes (CHAdeMO Japan), DC with 62.5 kW to about 80%
Energy Content: 16kWh (nominal)
Usable capacity: Between 70 and 80% (11-13 kWh), limited by BMS

MIEV!

Hey Robertst,

Nihon jin desu ka ?

I spent a couple of years in Japan in the 90's.

Well your post is very informative. It kind of sucks that they have boobie trapped parts of the car. It that even legal ???

I know that in laptops the cells cannot be replaced. The bms ages the batteries and needs to be reprogrammed to reset the counter. If you put in new cell the battery still reports the old capacity. I imaging this is a protect your battery replacement market kind of thing. I guess you can do anything when you have a computer controling things. Hopefully mitsubishi is also ethical.....

Well as much of this information that you feel comfortable translating, i appreciate all of it. Alot of us have been living with this car for about 3 years now. We share information and try to understand how things work by observing the car externally. CANION has given us a lot of insight into the car but we dont have any information on the internals other then what we can observe. It makes for interesting discussions and puzzles to solve but anything else you can provide to enlighten us is great.


Thanks for putting the effort into this.

Don.....

日本 人 です 日 ?

いいえ、私はドイツ人です。

Luckily I am on a Linux computer, Windows acts up when using foreign characters. Watch out what you type, it might be not right!

I am currently working on the details about recharging, regenerative braking and when the car is not under load. It is a big 'thing', I am trying to come up with some number, like if the car is not under load from 35 mph to a full stop, how much electricity goes back into the battery? I am just a very curious person.

Legality is not an issue, besides, you can't sue someone to make something (what they call) temper-proof, after all, you tempered with it, didn't it say 'Do not open' or 'No warranty if seal is broken'?

I have a paper now which lists not only the type of battery used in the i-Miev, but every possible replacement battery. Quite interesting. Below is the original abstract. The rest is all Japanese, lots of charts etc. If you like to practice Japanese, send me a pm with an email and I can send it to you.

Miev!

Abstract

We have developed a new large-sized lithium-ion cell and its battery module for electric vehicle (EV)
applications. They are based on the advanced technologies inheriting basic features from "LIM series" of
large sized lithium ion batteries already manufactured so far;
therefore, the construction and electrode materials are similar to those of the latter series ones. These new cell and battery module have nominal capacity
of 50 Ah and the specific energy is 109 Wh kg-1
and 99 Wh kg-1 for cell and battery module, respectively.
This cell is capable to accept quick charge up to about 80% of state of charge
(SOC) within 30 minutes at 25 °C．The specific power of the cell is higher than or equal to 550 W kg-1
at 50% SOC at 25 °C．Furthermore, regarding
the calendar life, capacity retention of 65% is anticipated after 10 years storage at 25 °C from our life prediction
formula. The cycle life test at 25 °C after 1000 cycles showed capacity retention of 85%. These battery modules
will be mass-produced starting in 2009 by newly established joint venture "Lithium Energy Japan" through the stage of
in vehicle verification field tests in 2008.

Query: Our LEV-50 battery density is 188 Wh/liter per http://atip.org/atip-publications/atip-news/2009/7804-gs-yuasas-commercial-lithium-ion-battery-for-ev.html

The Panasonic battery used (or used at one time) in the Tesla appears to be 675 Wh/liter per: http://news.panasonic.com/press/news/official.data/data.dir/en091218-2/en091218-2.html

These both appear to be 2009 articles and perhaps technology. So, is the Wh/liter the correct factor to compare when evaluating the possible range of a battery type?

If so, then is it fair to say that our iMiev battery, being of a lower density, will liter by liter, have a lower range?

Wh/kg

Phximiev said:

If so, then is it fair to say that our iMiev battery, being of a lower density, will liter by liter, have a lower range?

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Yes, BUT energy density is a compromise between volumetric energy density and energy density by weight (mass). From the same article, the Panasonic/TESLA cells calculate out to 236 Wh/kg. Our Yuasa LEV50 based-batteries are 109 Wh/kg. Of course, density for a finished battery will be less than naked cells, but surely TESLA came out on top. The other factors are power density by volume and weight (ampacity), and then we get to juggle temperature performance characteristics, cycle life at different DOD, form factor, etc. etc... It seems that TESLA's design came out on top in all regards. There's still one aspect where the Mitsu battery should be better, and that's the ability to repair or rebuild the pack. Replacing one of 88 large prismatic cells is pretty straightforward task, and for that matter, replacing one of the Nissan 'tuna can modules' can be done too. If too many of the little cells in a TESLA pack were to fail, you pretty much have to scrap the whole thing, tearing it apart to get to the cells.

Liter-by-liter density matters less to me than energy density and power by weight, but I'm not trying to create a voluminous cabin over a fairly flat battery, like both Mitsubishi and TESLA managed to do. Fail to manage battery volume and placement well, and you get a Ford Focus EV, Fusion PHEV or C-Max PHEV.....

Ok, that was an informative response and leads to more questions.

1. Has anyone heard whether GS Yuasa will increase the battery density such that we get a corresponding increase in range with no change the size of the cell (or pack)?

It would seem that this should be possible given the age of the technology and the comparison to the Panasonic battery even if the weight of the cells go up. Also, given the recent InsideEV LG articles about packs with greater range, I think they (GS Yuasa and Mitsubishi) should be in the process of doing this.

2. Has anyone tried replacing the LEV-50s with Panasonics in an iMiev? Obviously this would be a custom pack, but it would seem that one (a motivated one!) could achieve a range increase by trying this.

Phximiev said:

2. Has anyone tried replacing the LEV-50s with Panasonics in an iMiev? Obviously this would be a custom pack, but it would seem that one (a motivated one!) could achieve a range increase by trying this.

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Until a hack is developed for the i-MiEV's battery management system and the ability to integrate it with, or spoof, the existing digital interface, I think we have a problem. Pity, as the suggestion you've made could be implemented both mechanically and electrically.

The closest we've come is postulating the feasibility of adding an external dc-dc (like the Prius Enginer pack) or simply an additional external 360v pack to parallel our existing one. This should be feasible without affecting the car's existing BMS. Sadly, with saia47 leaving us as a resource, we'll now go a step backwards because he had successfully added a high-power direct dc charger to the i-MiEV and was already a step ahead of us in this arena.

Also, as far as increasing the pack capacity, I think the i-MiEV is not programmed to allow this. Evidence suggesting this:

1. The car will shut down at 0% SoC, with no apparent regard to cell voltages. Malm has shown us this before his car re-calibrated, it would hit low-voltage cutoff (LVC) before reaching 0%. After doing this a certain number of times, it re-calibrated to prevent that from happening and now reaches 0% SoC before the cells hit the LVC.
2. With a failing cell, SoC is calibrated to follow the voltage curve of the lowest cell. This is shown by the car stopping charge before reaching 16 bars.

The unknown is, how will the i-MiEV behave with reaching 100% SoC and the cells nowhere near the limit of 4.105 volts/cell?

Depending on how the situation with Bear turns out, or if I happen to find a wrecked/flooded i-MiEV with the electronics usable for a good price, I've spec'd cells with the same chemistry but higher energy density compared to the LEV50 cells. My original plan was to build a suitcase pack (actually two) to boost the range from 62 to 101 miles. I never did it, though, due to uncertainty with warranty and an explosion of CHAdeMO chargers in my area.

I would love for Mitsubishi to boost the capacity of the battery pack and the size of the on-board charger. That would make the i-MiEV much more appealing to buyers, not to mention a better trip car.