Why The 2010 Toyota Prius Doesn’t Have A Lithium-Ion BatteryWhy The 2010 Toyota Prius Doesn’t Have A Lithium-Ion Battery

Many reviewers lauded the new, third generation 2010 Toyota Prius hybrid when it launched last spring–but wondered why it didn’t use a lithium-ion battery, rather than 15-year-old nickel-metal-hydride technology.
Now we learn that the 2010 Prius was indeed supposed to have a new, more energy-dense lithium pack. But Toyota, by its own admission, chose the wrong lithium-ion chemistry for the cells, meaning they just couldn’t be produced economically.
2010 Toyota Prius high-voltage battery pack
Fallback to tried-and-true
Instead, Toyota fell back to the tried-and-true nickel-metal-hydride battery used in the 2004 to 2009 model. It was slightly redesigned, true, but that was about the extent of the changes.
In a lengthy technical presentation last month by Toyota’s managing officer Koei Saga, he revealed that the lithium cell that was to have been used in the 2010 Prius used a nickel-based chemistry.
2004-1009 Toyota Prius battery pack, second generation
(The term “lithium-ion” refers to a family of several different battery cell chemistries; the lithium ions move through the separator to generate electricity, but they may bond to molecules of different substances from one electrode.)
Expensive production
That nickel-based chemistry turned out to have low materials costs but a much more complicated production process, making its overall cost high.
As a result, Toyota concluded it had to switch its development efforts to a “tri-metal” electrode that combines cobalt, nickel, and manganese. That cell chemistry, Saga said, is less expensive to produce.
2010 Toyota Prius Plug-In Hybrid, 2009 Los Angeles Auto Show
Last year, Toyota established a new engineering group  solely to focus on battery production, one of very few automakers to do so.
Prius Plug-In for 2012
Toyota plans to start seeding test fleets with some of 600 Toyota Prius Plug-In Hybrids early this year. Set for a 2012 consumer roll-out, the Prius Plug-In will be Toyota’s first vehicle with a lithium-ion battery pack.
2010 Toyota Prius Plug-In Hybrid, 2009 Los Angeles Auto Show
It will likely be the only Toyota to use examples of the pricey lithium cells that Toyota has dropped. It takes several years to design, test, validate, and produce high-voltage battery packs, so to get the Prius Plug-In on the road required using the obsolete design.
Packs will coexist
While Saga said Toyota is devoting major effort to its lithium cell research, he noted the company believes it will be “quite far in the future” before today’s nickel-metal-hydride packs are entirely replaced by lithium for hybrid electric vehicles.
Nickel-metal-hydride cells, he said, have a 12-year track record, offer good life, and have proven “a very satisfactory technology.”
It all goes to show that even Toyota, whose Prius had seemed invincible until a recent accelerator-pedal recall and braking-feel problems, can stumble occasionally.  Just like all companies.
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