Engineers at Toyota Motor Corp say they have tamed volatile lithium-ion battery technology, and can now safely pack more power at no significant extra cost, giving the Japanese automaker the option to enter the growing all-electric car market.

While rivals including Tesla Motors and Nissan Motor Co began adopting lithium-ion battery technology nearly a decade ago, Toyota has largely held back due to concerns over cost, size and safety.

Lithium-ion batteries can be unstable and have been blamed for incendiary Samsung smartphones and smoking Dreamliner airplanes.

Having Toyota endorse lithium-ion will be a fillip for the developing technology, and gives the automaker the option to produce for an all-electric passenger car market which it has avoided, preferring to put its heft behind hydrogen fuel-cell vehicles (FCVs).

Toyota says its Prius Prime, a soon-to-be-launched plug-in electric version of the world's top-selling gasoline hybrid, will use lithium-ion batteries, with enough energy to make the car go around 60 km when fully charged before the gasoline engine kicks in. Because of different methodology in measuring a car's electric mode range, the Prime's 60 km range will be listed in the US as around 40.2 kms.

Many lithium-ion car batteries use a chemical combination of nickel, cobalt and manganese. These store more energy, take a shorter time to charge, and are considered safer than other Li-ion technologies.

But they can still overheat and catch fire if not properly designed, manufactured and controlled.

“It's a tall order to develop a lithium-ion car battery which can perform reliably and safely for 10 years, or over hundreds of thousands of kilometres,” said Koji Toyoshima, the chief engineer for the Prius.

“We have double braced and triple braced our battery pack to make sure they're fail-safe ... It's all about safety, safety, safety,” he told Reuters.

Toyota has mainly used the more mature nickel-metal hydride batteries to power the motor in the conventional Prius, widely regarded as the forefather of the 'green' car, though it did use some lithium-ion batteries from 2009 in its first plug-in hybrid Prius, around the time the first all-electric cars powered by lithium-ion batteries - such as the Tesla Roadster and Nissan Leaf - came on to the mass market.

Working with battery supplier Panasonic Corp - which also produces Li-ion batteries for Tesla - Toyota has also improved the precision in battery cell assembly, ensuring battery chemistry is free of impurities.

The introduction of even microscopic metal particles or other impurities can trigger a short-circuit, overheating and potential explosion.

Battery experts say increasingly sophisticated systems that can track individual cell conditions are becoming closely-held trade secrets.

They say lithium-ion battery cell prices have fallen by about 60 per cent in five years to around $145 per kilowatt hour as larger-scale production has made them cheaper to make.

Falling battery prices have enabled Toyota to develop its more compact, efficient battery, while also adding more sophisticated controls into its battery pack, Toyoshima said. Toyota declined to say more on its costs.

While Toyota sees FCVs as the ultimate 'green' car, the US and China are encouraging automakers to make more all-electric battery cars as they push alternative energy strategies.

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