Machine Design

Plug-in batteries come to hybrids

Watertown, Mass.-based startup A123Systems thinks it has solved the problem of overheating in lithium-ion batteries.

The new development could lead to use of lithium-ion cells in hybrid vehicles.

Lithium-ion cells have a high energy density, which makes them candidates for use in hybrids. But concern over batteries catching fire limits their use.

Fires typically happen when a manufacturing defect (possibly compounded by overcharging) lets oxygen escape the cathode in a heat-releasing oxidation reaction. An overheated cell triggers oxidation in neighboring cells through a process known as thermal runaway.

Batteries from A123 use cathodes from iron phosphate, which bonds to oxygen better than the cobalt dioxide in conventional lithium-ion batteries. This makes cells less prone to oxidation and thermal runaway. A nanopatterning design that boosts the conductivity of the iron phosphate helps overcome the material’s relatively low operating voltage, says the company.

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A123Systems, www.a123systems.com

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