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Toyota Pushing Lithium-Ion Development

Kyodo. Toyota Motor is accelerating efforts to develop a practical lithium ion battery to power hybrid motor vehicles in a bid to reinforce its presence in the market for the environment-friendly cars.

The project will be led by Panasonic EV Energy, a joint venture between Toyota and Matsushita Electric Industrial, as part of Toyota’s program to develop a smaller, more powerful hybrid vehicle. (Earlier post.) Toyota recently increased its stake in Panasonic EV to 60%, making it a subsidiary. (Earlier post.)

Panasonic EV is the supplier of the nickel metal-hydride (NiMH) battery packs for Toyota’s hybrids, as well as for Honda Civic and Insight hybrids. The company currently offers only NiMH products.

Although it is far ahead of the competition in development and sales of hybrid vehicles, Toyota hopes to further strengthen its position by developing a practical lithium ion battery.

Lithium-ion batteries offer a higher power density than NiMH—up to 4 kW/kg, double that of the best NiMH levels of 2 kW/kg.



Not only can you get higher power density from lithium ion batteries (A123 systems offers batteries with 3 kW/Kg, a 50% increase) but you can get batteries that can be fully charged and discharged several thousands of times before capacity falls below 80%. Currently, the batteries in the Toyota Prius are charged to no more than 80% and discharged to no less than 60% (using only 20% of the battery capacity to extend battery life). Using only 20% capacity slashes the energy density of these NiMH batteries to 1/5 of the rated capacity (which is much lower than Lithium ion batteries to begin with). Both Toyota and Honda have engaged in a campain of misinformation marqueting the "No need to plug in" the hybrids they sell when in fact it is the only factor that keep the Prius mpg at 55 mpg (rated by EPA, actual mpg is lower) and the new Honda Civic mpg at 50 mpg.


Actually, I don't think they are trying to develop a smaller, more powerful vehicle, but a lighter, more powerful vehicle with a more powerful electric motor. Even without a more powerful elecric motor, they could increase gas mileage with a battery that was more dense and could be more fully discharged.

In any event, this is exciting news. Maybe this can be available by the 2008 model, at which time I will be ready to upgrade my current 2005 Prius.

Freddy. I must say your last sentence was confusing. What is the only factor that keeps the Prius mpg at 55mpg? The inability to plug it in?


By the way, the Prius uses 40% of the battery capacity for longevity, from 40% (empty) to 80% (full). The electric motor in the Prius is actually quite powerful (67hp) but the battery can only push about 25hp out, so the balance has to come from the gas engine via the generator. With a battery capable of better burst current you could program the car to use the gas motor less, although eventually all energy comes from the gasoline engine unless you can plug it in.


The Prius batteries are used for more then 20% of thier capacity. The batteries are charged to 80% as you say but are used down to 40%. So in reality they are used for 40% of thier capacity. LIon batteries are of course much better.

Bob H

What is the relationship between the current 'state of the art' battery and the maximum speed to run the car on battery only. Will a better, faster recharging battery change that equation ?


Schwa. The battery is also recharged through regenerative braking and coasting. You can see this happening on the multi-display screen while you're driving.


What is the battery capacity of a typical all electric car, and what the capacity of the Prius - anyone know?


Harvey D

Dave: The Prius NIMH battery capacity is about 1.3 KWh. To maintain a steady speed of 55-60 mph, a relatively light car like the Prius requires about 1/4 KWh per mile, or 1 Kwh for 4 miles or 10 KWh for 40 miles or 25 KWh for 100 miles etc. Considering that roads are not always level, stops or slowdowns are unavoidable and that NIMH rechargeable batteries are not normally fully charged or discharged (yet) to prolong their duration, you have to add about 40% to the battery capacity given above.


I want to purchase an electric car to travel to/from work ~7 miles one way. I live in PA suburbs of Philly.
Could you please suggest where to purchase one. All I've seen are in CA and aren't serviceable on the East Coast. Thanks, Wendy

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