I’ve covered the batteries in question before, I believe they are Hitachi cells specifically designed for hybrid vehicles. They have different characteristics than the LG Chem cells used in the Volt. For hybrid vehicles you carry a small amount of storage (2-3kWh) and pull energy out of the battery quickly to accelerate and to store it quickly when braking. The Volt needs a higher specific energy (storage) while these hybrid batteries need high specific power (horsepower).

The batteries that GM is likely to get have a specific power of around 2,250W/kg. The PDF I link in the above article shows a 3kWh Li-Ion pack, 47kg and 1.4 cubic ft. This would provide for a total power of 90kW (120HP) in an area 41″ x 12″ x 5″. Being able to accept and output that much power could allow the vehicle to drive up to speeds of 35MPH on electricity alone (depending on car weight and other factors). However it is unlikely that GM would use this configuration – their mild hybrid systems only provide 20HP. The minimum battery pack for this size would be about 500Wh (or 8 of the above cells), and a larger 1kWh pack would be able to provide twice that (28kW/40HP).

All other mainstream hybrid vehicles currently use NiMH batteries, which are not as capable of high power output as lithium-ion batteries are. The switch to Li-Ion batteries would not only increase power output (allowing higher all-electric mode speeds), but also a lighter, smaller package. The 3kWh module mentioned above could even power the vehicle at all electric speeds for a few miles (again, depending on vehicle weight, etc).

Cost could be an issue, as these batteries are more expensive than their NiMH counterparts. Lithium-ion batteries command a cost between $800-1000/kWh, while NiMH batteries cost around $200-300/kWh.

via GM-Volt

Word is that Hitachi has a new lithium-ion battery that has a high W/kg ratio and can last 10 years in EREV applications.

I’m tempted to not even write about it since such so little is known about the battery, other than percentage improvements. Thats not really a substantial yardstick to gauge how well the batteries would work in an automotive context (spec sheets are a little better, but sometimes lack necessary information as well).

They state that the batteries can produce 4,500W/kg, which is outstanding considering other batteries today have pulse power ratings around 1000-1500W/kg. But again, other batteries have about 6-7 years to catch up to this hypothetical future battery. For reference, a Volt’s motor would need 120kW peak, and that H3 Electric Hummer was 200kW, each necessitating only 27kg and 45kg of batteries. The problem wont be pulse power at this point, rather power density, volume and recharge cycles – but even at a futuristic sounding 250W/kg, for a 40 mile plug-in like the Volt, you’ll need 40kg at least for 10kWh of energy storage.