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

A little bit ago, I was skeptical of an announcement by Hitachi about a 4,500W/kg battery they had planned to ship in the future. Well today Hitachi announced that battery will be sampling by the end of the year but still without a ship date. So its slowly inching closer, but a little bit of research shows that their third generation battery (more below) was announced in a research paper (abstract only) back in 2005, or a lead time of at least 5 years from research to production. So it seems likely that it might be another 3-5 years (given more interest in HEVs and other battery applications) before these batteries hit the market, maybe in time for the 1.5-gen PHEVs and BEVs.

Their third generation battery I mentioned above with a output of 3,000W/kg is set to enter mass production next year. However, I found a presentation for Pollutec 2008 by Hitachi, with cell specifics fairly close to this battery and the energy density was only 83Wh/kg. With a module rating of 75Wh/kg, it would increase the Volt’s battery from 180kg to 230kg (28% more) though you’d be able to go from 0-60 in no time flat – that many batteries would be able to source around 500kW, way more than is necessary for an electric H3, let alone a small car (670 hp).

Hitachi’s new batteries aren’t likely useful for PHEVs until the energy density ratio goes up, given the increased size and weight over batteries with a little less power density and higher energy density. They are more likely to end up in hybrids like the Prius rather than any BEVs or PHEVs. A small 3kWh pack could produce 100kW (133 hp), which is both smaller than the last-gen Prius battery (~4kWh), weighs less, and more powerful than the previous electric or gasoline engine. Fuel economy could be significantly boosted by this new application as the battery could drive for 5 miles in an electric only mode if plugged in.