Electro Energy’s Prototype Bi-Polar NiMH Battery Pack for Plug-in Hybrids
30 May 2006
|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|
|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
|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.
CalCars conversion fact sheet
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