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The Battery Pack for Mitsubishi’s i MiEV

Imiev1
The battery pack of the i MIEV. Click to enlarge.

At the Advanced Automotive Battery Conference and Symposium 2008 in Tampa, Florida (12-16 May), Takuha Miyashita from Mitsubishi described the characteristics of the lithium-ion battery pack that Mitsubishi, in partnership with GS Yuasa, developed for the i MiEV (earlier post).

The i MiEV is powered by a compact 47 kW motor that develops 180 Nm (133 lb-ft) of torque and a 330V, 16 kWh lithium-ion battery pack. Top speed is 130 kph (81 mph), with a range of up to 160 km (100 miles) under Japanese 10-15 cycle driving conditions.

GS Yuasa Corporation, Mitsubishi Corporation (MC) and Mitsubishi Motors Corporation (MMC) launched a joint venture—Lithium Energy Japan—last December to manufacture large-capacity and high-performance lithium-ion batteries. (Earlier post.)

Battery-maker GS Yuasa is the majority shareholder with 51%; MC holds 34% and MMC holds the remaining 15%. Initial production is targeted at 200,000 cells in fiscal year 2009.

The 16 kWh i MiEV battery pack is installed under the base floor. The pack consists of 22 cell modules connected in series at the nominal voltage of 330 V—the high voltage helps deliver high power. There are two types of modules to enable efficient use of the limited space. Two 4-cell modules are vertically placed at the center of the pack and 10 8-cell modules are placed horizontally.

Specifications of the i MiEV Li-Ion Cell
Dimensions 43.8W x 113.5H x 171D [mm]
Weight 1.7 kg
Rated capacity 50 Ah
Nominal voltage 3.7V
Specific energy 109 Wh/kg
Energy density 218 Wh/L
Specific power
(60-sec pulse at 25°C and 50% SOC)
550 W/kg
Max output current @ 25°C 300A

Mitsubishi and GS Yuasa developed the cell for both high specific energy and high rate discharge. The newly developed prismatic cell used in the i MiEV pack has a specific energy of 109 Wh/kg and specific power of 550 W/kg. Energy density is 218 Wh/L. The entire pack has a specific energy of 80 Wh/kg.

The cell—and pack—feature high capacity retention at constant current discharges. Capacity at the high current of 200A is slightly less than at the lower rates (93.9% of capacity).

When discharged with an ambient temperature of 25° C, the pack is capable of delivering the maximum power from 80% DOD. Even at 0°C, the pack can deliver the maximum power from 70% DOD and enough power for propulsion from 90% DOD.

Imiev2 Imiev3
Pack capacities at 25°C. Click to enlarge. 60-sec pulse power of pack. Click to enlarge.

Mitsubishi tested the cycle life of the pack under standard (50 A) and quick charge (120 A) conditions using the JC08 driving pattern and found that the pack retained 84% of capacity with quick charging and 83% with standard charging after 1,000 cycles.

Development of the i MiEV EV concept began in 2005, and Mitsubishi is currently field testing units in Japan in cooperation with electric utilities, with market introduction slated for 2010. The company is also targeting market introduction in Europe and North America.

Comments

Herm

the market will allocate the distribution of batteries to hybrids and full blown BEVs, and it will do it most efficiently..

The best combination may be a short range BEV, lets say 20 miles, and an optional (hopefully removable) small generator... not the 50KVA monster that the Volt will use. Maybe 600cc like the original Mitsubishi car uses..or maybe smaller using a turbocharger. The important thing is that it must be optional, and while you are at it make the battery size optional also.. Versatility!

John Taylor

I like the layout of having the batteries under the floor. This low and center weight should bring the center of gravity to the bottom center of the car and really improve handling.

Also, it looks like they had the smarts to make the pack removable and easy to replace in the event that improvements in battery technology come to market.

I hope to see it available in my area soon.

drivin98

I love this car. I don't know if I can wait to buy it though. I might get a Triac instead. $20,000 and available in a couple months.

fred schumacher

For a small car with limited weight capacity, these batteries are disappointingly heavy, about 50% more than the Tesla's. Perhaps they're less expensive. Tesla's cost about $350 per Kwh storage.

If that cost were amortized over 100,000 miles (roughly 50 miles per day over six years), that would be a cost of about six cents per mile. The electricity would be two to three cents per mile, for a total "fuel" cost under 10 cents per mile, roughly the equivalent of 40 mpg at $4.00 per gallon. Drive less and your fuel cost goes up, since most of the cost is in the battery and not the electricity.

This doesn't count the cost of recycling. Modern day ICE drive trains are very reliable, and at the end of their life are easily recycled and are actually quite valuable as scrap. Batteries will be more problematic. There may be an end of life cost attached to a BEV.

Another problem to consider is that of running out of juice while far from home. It would only take a few powerless BEVs to totally block a freeway during rush hour. I would feel more comfortable with a built-in 5 Kw genset and two gallons of fuel for get-home power.

clett

@Fred,

Remember the deletion of the engine, coolant system, radiator, exhaust, emissions control systems, precious metal catalytic converter etc etc all offsets the "additional cost" of the battery, so it's not fair to look at the running cost of the battery alone. Rather you should look at the cost of the whole vehicle over 100,000 miles.

Also, remember that the servicing costs of an EV are going to be much lower than an ICE vehicle over 100,000 miles. That alone saves another 3 cents per mile for the EV.

Anne

@fred:

Another problem to consider is that of running out of juice while far from home. It would only take a few powerless BEVs to totally block a freeway during rush hour.

What utter nonsense! What about cars running out of gas? Is that a problem nowadays? Cars out of gas clogging highways? Don't you think electric cars will have a battery indicator? And an audible warning when the charge level gets low, WITH an indication of how many km's can be driven on the resting charge? The year is 2008, not 1908.

Ben

@ Fred: This pack is 200kg. Tesla's is 450kg. Perhaps you are speaking of per cell mass per unit storage. Remember also that Tesla uses 18650 sized cells (2-2.5Ah) and this is 50Ah, so at least 20X larger per cell. When you integrate many cells, it adds weight, volume, and cost. Another key issue is that the pack is only 16kWh, so these cells may have been designed with more of a power bent with thinner coating on the electrodes, giving away some of the possible energy.
I'm excited to see a large format lithium pack going into production. I think this will facilitate a large drop in battery system costs down the road.

me2

Where did you get the info that Tesla's pack is $350 per KWHR ?

Herm

Driving past the line of people at the gas station must be worth at least $0.25 a mile :)

T2

@FRED - know this
When a BEV runs low on 'gas' you park it. Half an hour later you get back in and drive off. A 16Kwhr Pb-acid battery may give you three or four miles before it becomes undriveable again.
T2

deden

You guys do not accept that the weakness of human spirit has caused the apocalypse that looms before us! Your electric cars will not help! Your bicylcists are insignificant, your FCL bulbs will make no difference! You all are F*&^ked!! Because you are arrogant. You think you should save the world when you cannot save yourselves. Fools!! Doom is upon you. Folly will reap cataclysm! And now...standby for a commercial break...

critta

Deden,

you don't seem to include yourself in the human race as you keep referring to humanity in the second person. Are you an alien or have you just evolved to a higher plane?

Peacefreak

Be careful, deden might be God. Filling stations will eventually become charging stations, quick charges will take maybe 10 minutes, even 20 minutes we can get used to. The important thing is get the ICE machines in the barn with the horse and buggy.

Henry Gibson

Electric cars must be forbidden by law. All electric motor driven cars should be plug-in-hybrid; then no one could complain about the limited range or the lack of cheap high range batteries. Very small engines with high power to weight have been built for model airpanes for years and modern technology could give them even higher speed and power. TZERO employed motorcycle engines for its plug-in-hybrid operation. You can buy a two horse-power engine at a local model airplane hobby shop. This it enough to move any automobile at ten to twenty miles an hour. There is no reason to fear being stuck on the road away from home. Yes the engines can be engineered to have higher horse-power, low emissions and high efficiency and also to run on any fuel. See OPOC or RCV. High efficiency single piston engines could have heavy flywheels for vibration control and peak energy storage. Electronic vibration and sound damping could make their operation unnoticable. In the future,perhaps, tiny efficient microturbines could be built. Most of these spare engines would not need to be run often, even with low capacity lead batteries.

Electric cars have been possible since the the lead-acid battery and automobiles were first put together a hundred years ago. ZEBRA batteries have allowed the existence of long distance electric cars for over ten years. Lithium batteries are not needed for electric cars. ..HG..

HHN

By the time your typical recharging station is installed,3 phase,oodles of amps capacity,don't be surprised in order for the filling station to recoup his investment and make a profit,he would probably have to charge at least 75 cent per KWH,and where does that put you trying to save on transportation cost?

ecojet

The batteries can be charged from a standard 15 A/200 V car charger in seven hours :

15x200 = 3000 watts for 7 hours : 3KWh

66% of us use fossil fuels to generate electricity.

Modern coal fired stations (not latest designs yet to be built) assume 1000g per KWh

So MiEV from coal fired Power Plant: 131 g/km CO2

Compare that to the 1999 Audi A2 1.2 TDI: 81g/km and 93mpg (uk). The latter can run on biofuel (GEN2 would be best).

Some 1.6 billion people, about one quarter of the world?s population,
have no access to electricity today.

Good effort from Mitsubishi but overall where's the progress?


darwin

1 Gallon of Gas = 125,000 BTUs
Source: US Department of Energy

3,400 BTUs = 1 KWH
Source: US Department of Energy, Bonneville Power Mgt.

so about 1 gallon of gas = 36 kwh

Seems to me that the limiting factor remains to be the battery technology. Need a battery that will not detoriate overtime, handle deep cycles without reducing its life, and lightweight. Thats where the research needs to be done.

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