The powerful lithium-based batteries used in electric vehicle systems, laptops and cell phones are prone to overheating and even blowing up, but adding less than a gram of a new substance could keep both temperatures and costs down, federal researchers say.
The molecule, developed by researchers Khalil Amine and Zonghai Chen at Argonne National Laboratory, is being tested as an additive in the electrolyte of lithium batteries to keep cell voltage from going too high.
The batteries used in hybrid and electric vehicles typically consist of 200 to 400 small cells, strung together into one powerful whole. Individual cells sometimes overcharge, emitting heat when they reach too high a voltage and pushing neighboring cells past the breaking point to set off a runaway thermal reaction.
Because electric and hybrid vehicles are constantly discharging and recharging during normal driving, overcharging problems are not confined to the garage but pose a real operational hazard.
In the lab, Amine and Chen discovered they could make a molecule based on boron and fluorine and add a tiny amount of it to each cell to control charging. When the cell exceeds the safe voltage level, Amine explained, the molecule picks up electrons and keeps the cell charge from going up.
Currently, expensive electronic controls are used to regulate each individual cell in a battery and shut it down if the voltage gets too high. But the control systems are expensive, making up as much as 20 percent of a battery's cost, and the electronics are prone to failing.
Amine said the new approach offers several advantages over current technologies. In addition to the lower cost, the molecule is more reliable, he said. Other systems that use some kind of molecule in a similar way cannot control more than one overheating cycle, he said, while his molecule will soak up extra voltage through 500 or more cycles.
The material is not easy to make, but only a small amount is needed -- 2 to 3 percent of the electrolyte by weight. Today, it costs about $1,000 per kilogram, but Amine said battery company EnerDel is leasing the technology and using an Energy Department grant to scale up the fabrication process. He believes that making large batches should bring the cost down to about $100 per kilogram.
The molecule could save $100 to $200 per battery, Amine said. Battery makers today are targeting a total price of $500 to $1,000 per battery.
One more advantage of the new molecule is that unlike the sophisticated electronic control systems, adding a new chemical to the battery pack is quick and easy. "The electrolyte is the last thing you fill in, so it's an immediate adaptation. Just add this 2 percent and you're ready to go," Amine said.
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