Engineers claim to have tamed volatile lithium-ion battery technology and can now safely pack more power at no significant extra cost.

This would give Toyota the option to enter the growing all-electric car market rather than relying solely on its hybrid and fuel cell technology. Lithium-ion batteries can be unstable and have been blamed for fires in Samsung smartphones and smoke alerts on Boeing Dreamliner aircraft.

Toyota said its Prius Prime, the plug-in electric version of its petrol hybrid, would use lithium-ion batteries with enough energy to give the car a range of 60km (37.3 miles) when fully charged before the petrol engine kicks in.

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 there remain the danger that they can overheat and catch fire if not properly designed, manufactured and controlled.

Prius chief engineer Koji Toyoshima told Reuters: "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. We have double braced and triple braced our battery pack to make sure they're fail-safe."

Toyota has mainly used nickel-metal hydride batteries in the Prius although it did use some lithium-ion batteries from 2009 in its first plug-in hybrid Prius.

Toyota's confidence in its battery's safety and stability comes from improved control technology that precisely monitors the temperature and condition of each of the 95 cells in its new battery pack. Working with Panasonic, 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.

Toyota has also reduced the size of each cell, closing the distance between the anode and cathode where active ions travel when charging and discharging. This has doubled battery capacity to around 8.8 kilowatt hours while only increasing the battery pack size by around two thirds and its weight by a half.

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.

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