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Electro Energy’s Prototype Bi-Polar NiMH Battery Pack for Plug-in Hybrids

The EEI “silver bullet” PHEV prototype

There were two implementations of a plug-in Prius on Capitol Hill earlier in May in support of the testimony before the House on plug-in hybrids (earlier post): CalCars’ white Prius (flown in for the event) built by EnergyCS with Valence lithium-ion batteries—earlier post); and Connecticut battery-maker Electro Energy’s (EEI) “silver bullet” (built by EEI and CalCars with EEI bi-polar NiMH batteries).

CalCars announced last October that it was working with EEI on a custom prototype battery pack based on the company’s bi-polar NiMH batteries. Instead of using the conventional cylindrical coiled electrode or flat plate prismatic designs, the EEI design uses individual sealed flat rectangular wafer cells that are stacked on top of each other to create a series-connected battery. (Earlier post.)

This bi-polar design is more compact, exhibits higher power capability, and presumably will be lower in cost than the conventional cylindrical and prismatic designs of either NiMH or Li-ion chemistries. (EEI has begun developing a bi-polar lithium-ion design.)

The battery. The bipolar NiMH used in the EEI Prius is a first-generation, proof-of-concept application. It is rated at 28 Ah, 6.0 kWh (180 cells), with a battery-only weight—i.e., not including controls, etc.—of 300 lbs (44 Wh/kg), giving the vehicle a projected theoretical all-electric range (AER) of more than 20 miles.

Electro Energy points out that this prototype is a non-optimized battery used for integration and NiMH demonstration only. (In its conversion fact sheet, CalCars puts the realized performance at between 3 to 4 kWh.) EEI estimates that it will be able to deliver a final version of the PHEV Bi-polar NiMH battery rated at 30 Ah, 6.5 kWh (180 cells) also weighing 300 pounds (48 Wh/kg).

PHEV Battery Comparison Table
CalCars Rangea
EEI Data courtesy of Electro Energy Inc.
aCalCars assessment based on mixed-mode driving (50% EV) range at double normal Prius gasoline mileage
b The Energy CS implementation removes the OEM battery from the Prius (70 lbs) resulting in a net weight increase of 80 lbs over OEM level.
cTheoretical rating of 6.0 kWh.
d This application assumes the removal of the OEM battery from the Prius (70 lbs) resulting in a net weight increase of 230 lbs over OEM level.
Energy CS Valence Li-Ion 9.0 150b 132 50-60
EEI 1st-gen prototype (current demo) 6.0c
300 44 20-30
EEI Final version NiMH 6.5 300d 48 40-50

Unlike the Energy CS conversion, in which the OEM battery is removed and replaced with the Valence Li-ion pack, the first-generation EEI car adds the NiMH battery as a supplement to the OEM pack, connecting it in parallel and using a DC-DC converter/charger to integrate the two batteries. Hymotion also takes this approach. (Earlier post.)

James Landi, the Pilot Program Manager at EEI, thinks that the next version of the battery could be applied either as a replacement or as a supplement.

In terms of pricing, for a production-scale battery EEI targets between $500 to $600 per kWh. That would bring a 6.5 kWh NiMH system in at around $3,900—or, once balance of plant and integration costs are factored in, approximately half the current cost of the Li-ion system.




Hum, I wonder if these bi-polar NIMH will have a higher or lower recharge cycle life?


Why such a high all eclectic range. Generally you will want it use the ICE at speeds greater than 45 mph. It seems to me that a 10 mile range would be sufficient for now. Am I missing something?


BTW if the battery last 5 years the cost would be less than $800/year. Not too bad.

Joseph Willemssen

Probably not a good PR move to fly the car out there.


The reason for a high EV range for plug-in hybrids is that the average commuter drives 40miles/day.
Being able to drive most of your days on 100% electric would greatly reduce fuel consumption.

And while yes, this would shift the burden of power to the electric infrastructure, it is easier to use alternative fuels in infrastructure, because the weight and power density is not as important as in transportation.


Much easier to monitor one powerplant for adherence to and implementation of emissions controls as oppossed to a hundred thousand vehicles.

Rafael Seidl

Well, there certainly has been a lot of progress on the battery front. $500-$600 per kWh is a fraction of what you had to pay just a few years ago. Of course, adding 250-300 lbs of weight for 40 miles range (at what speed?) will yield a very substatial performance penalty once you have to switch from (H)EV to ICE-only operation.

Would it not make more sense to use a 150 lb battery with a high power rating and pair it with a seriously downsized ICE and a dual clutch transmission in a regular parallel HEV? A cheap three-cylinder turbocharged unit rated at ~65kW (e.g. Opel family 0)would do. Turbo lag can be masked by the powerful electric motor.


$800 per yr isnt a very good deal for only 100 mpg.

At 15,000 mi per yr, 45 mpg for a stock prius, $3 per gallon, $800 per yr for battery, ignoring the cost of electricity you'd have to get at least 225 mpg to break even $ wise.

If you say but its cleaner ...
Then how come the 2001 rav 4 ev that is rated at 29 city and 37 hw (Kwh / 100 mi) is rated a 4.2 tons of GHG
and a stock 2006 prius (rated at 60/51 city hw mpg)
is rated at 3.4 tons of GHG per yr

The calcars link "assumption of 260 grid Wh/mi)"

If we pro rate the all electric GHG per mile by comparing this to the rav 4 EV that has a city consumption of 290 Wh/mi (260/290)*4.2 tons /yr @15,000 mi

We get 3.76 tons of GHG per yr if all the miles were plug in miles ... which is Higher than a stock 2006 prius.

though slightly better than a stock 2001 prius at 3.8 tons per yr.

It is interesting but how is this better?

Sam Syrac

$800 per year isn't a good deal assuming gas will be $3/gallon....

Right. Gas isn't going to be $3/gallon in a few years. In fact, gas isn't $3/gallon right now. How about promoting an infastructure that isn't entirely dependent upon the most unstable part of the world that also hates us?

I often see critiques like this on this site. "It's still not a good deal" or "it still emits some amount of CO2". Yes, and that's too bad. But am I the only one that thinks the most pressing issue in all of this is that our food system, medical system, school system, and pretty much our entire economy is based on a declining resource located in countries that openly pledge our destruction?

Is it perfect? No. But I highly doubt that a "wonderfuel" that's dirt cheap and has no emissions is going to come along. So in the meantime how about we stop putting off these very important advancements and get working with what we have.

Jeez! Sorry for the rant but my lord, let's get it started here people.


What unrealistic and naive dreaming!
Never ever such a vehicle will ever be sold in big numbers. There is just no market for such a cart. With an "engine" sounding like a vacuum cleaner providing only poor performance. Hey, nobody wants to buy such a car. That's a fact. And that's the reason, why for example the big 3 in USA, but also BMW are not interested in this technology.

Shaun Williams

Good to see some more competition in this very important technology.

These predictable and misguided comments by the vision impaired will be irrelevant in a few short years.


Jan, I could not disagree more. The plug-in hybrid market would be substantial if the price permits it. Personally, I'd pay for a vehicle like this if it is marketed correctly. Companies need to place this technology in low to mid range models (ie Ford Focus), not the upper end like the Tahoe or Lexus. This is certainly part of the answer to energy independence. If only battery research were funded as well as fuel cells.

J Padula

I drove a EV-1 and it would blow the doors off most cars of the era, it was designed in early 1990's. I witnessed the T Zero do 0-60 in about 3.5 secs two years ago. It has a range of over 200 miles on Battery (lithium).
Take these cars make the batteries smaller, reduce the range to 40 miles and use the saved Mass to add a Serial Hybrid arrangement. Turbo Engine runs at constant speed, narrow band load to optimise pollution. No turbo lag problems.
I also used a RAV-4 EV as a work car. It was wonderful.

The MPG "equilivent" number you quote are based on "assuming" the mix in the grid for the US as a whole.
If you lived in Washington State, where hydro provides most of the electricity, they are non-polluting. If you charge from solar panels or windmills they are non polluting. When we lived in texas all our power was from windmills.
If a powerplant makes a mistake and puts out too much pollution, the CEM system lets them know immediately(and the State). In a car you could be out of tune for years before your next inspection. Should cars get the same fines industry does when it exceeds standards?
When you buy a ICE car the emmisions regulations freeze when you buy it. Powerplants upgrade constantly and the grid as a whole displaces older plants with newer technology. Would you like to Have to buy the Microsoft style "upgrade " to your 2008 when the emmision rules change.
Electric cars get cleaner every day as the grid does. With all the risk and regulation complience done by utilities.
The serial hybrid plug in electric car is the future. Initially with a Turbocharged engine, much later with fuel cells.
The options should be larger battery( more battery only range), larger engine smaller battery, better performance shorter electric range.
The largest mistake I see amoung posters on this board is the fail to take into account the externalities of air pollution.

Harvey D.

J Padula progressive approach + upgradable battery size options for PHEVs (now) leading to EVs when higher performance batteries are available make sense.

Why wait for the perfect ideal PHEVs or EVs. The ICE vehicles were upgraded many times during the last 100 years, so will the PHEVs and EVs. With time, larger 4 x 4 PHEVs and EVs will be produced to satisfy that on-going requirement.

There is enough clean wind and sun power potential in USA and Canada for 250+ million PHEVs and EVs. If done on a very large scale, it could be as cheap if not cheaper than ICE + gas at $5/gal while being much cleaner and the money + jobs would stay home.

Transition will be very slow as long as cheap gas in available. A new progressive-variable $2/gal tax is required to keep the price above or at $5/gal.


I just saw a story about Venezulas Orinoco region. Oil there was considered too thick and costly to refine at $20 a barrel, but at more than $50 a barrel it makes business sense, just like the Canadian oil sands.

T. Boone Pickens was quoted on 60 minutes saying about the Canadian oil sands that he is now invested in, "30 years ago we said oil would have to be over $5 a barrel to make that profitable"..

A veteran exporation executive from Shell said years ago "we will still be able to find oil, it will just cost a lot more."

Combine that with India and China using more oil and you have a probable outlook of higher oil prices going forward. This is a good case for developing any and every alternative that we can.

tony chilling

It's all about the battery.
There is no quick charging battery or energy storage unit that will provide 100kWh for comparable performance
and cost wth the fire breathing, but dying fossils we drive today.
We will be living with, and driving IC powered cars for at least the next 30 years.
Thaere's Oil in those sands!

Shaun Williams

"It's all about the battery"

Yes, precisely Tony...(sigh)...

And THAT is why PHEVs are the critical transition technology.

Got it?


The following text expains better than I can why $800.00 per year is not bad at all (though others are correct that it has no payback).
< In the short term, however, Takeshita's seemingly logical assumption about lower-cost hybrid cars might not be right. Scott Miller, CEO of the market-trend analysis company Synovate Motoresearch, in Royal Oak, MI, says a major reason consumers buy hybrids today is to have a "badge of honor" that shows their commitment to the environment or to curbing gasoline use. And it's an opinion shared by Toyota's Hermance. Part of this distinction, as Miller sees it, comes from having to pay a price premium for the vehicle. Hence, in the short term, he says, it might actually be wise for carmakers to leave hybrid prices higher.>

E. Hunter

Another advantage of increased battery capacity, and one which will be much appreciated by those living in mountainous areas, is that much of the energy which goes to waste on downgrades will be saved by the battery. In my situation, after reaching the summit of the Rocky Mountain region which I traverse weekly, the battery is discharged and then is fully recharged after only about 3-4 miles of downhill coasting. The potential energy of the remaining 6-7 miles of downgrade is wasted. The larger battery would store that otherwise wasted energy and would ultimately increase the MPGs.


Regenerative is a good way to reuse energy. Otis elevators has the GEN2 series which stores energy on the way down to be reused on the way up. Imagine 100,000 elevators worldwide using 40% less energy to do the same work. It is innovations like these that will have people saying "why didn't we do this long ago?"

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