Friday, September 12, 2014


The Tesla Model S may be the darling of the EV world, but it's currently under investigation by federal auto-safety regulators after multiple fires involving the 60- or 85-kilowatt-hour lithium-ion battery pack that powers the car. 

The battery pack can send the S flying to 60 mph in just 4.4 seconds (in the top-of-the-line Performance variant) by taking advantage of the beneficial qualities of lithium, a relatively lightweight material that can release a lot of energy quickly. But because the material is so reactive, lithium-ion batteries need to be heavily protected to avoid explosions. That drives up the cost of manufacturing and adds around 500 pounds to the vehicle, reducing the number of miles it can travel between charges. And even then, the battery may still overheat and catch fire, which is why researchers are working fast and furiously on new electric-car-battery technology—with a little help from the U.S government. 

This past summer the U.S. Department of Energy's Advanced Research Projects Agency-Energy, or ARPA-E, awarded $36 million in funding to researchers across the country with proposals for redesigning EV batteries. The 22 funded projects represent some of the best hopes for a safe, low-cost, efficient electric vehicle. 

One of the people searching for a better alternative to the lithium-ion battery is Michael Fetcenko, a chemical engineer with BASF, the German corporation that owns the license to the technology behind nickel-metal hydride (NiMH) batteries. Those batteries are currently used in gas-electric hybrids, but Fetcenko and his team are using an ARPA-E grant to explore whether NiMH chemistry could be applied to purely electric vehicles as well. 

The key is to both lower the cost and increase the energy density of the NiMH battery. Right now, a NiMH battery has an energy density of 1 kilowatt-hour. But in order to be a viable replacement for lithium-ion batteries, BASF has to find a way to boost the energy density up to 30 to 50 kilowatt-hours. 

One way to do this would be to find a replacement for some of the battery's most important materials: rare earth elements. Rare earth elements are a set of 17 chemical elements in the periodic table, so named not because they are truly rare (one of them, cerium, is as abundant as copper) but because they are found in ores that are expensive to mine and process. Rare earth elements are "the workhorse" of the NiMH battery, supplying half of the reaction necessary for the battery to produce energy, Fetcenko says. But rare earths are limited in their ability to store energy, and because they have to be imported from China, their cost can be volatile and their supply uncertain. 

So, BASF is looking to develop metal hydride alloys using low-cost metals for use in the NiMH battery. Fetcenko thinks they can improve the NiMH-battery chemistry and make the new batteries cheaper and more efficient. But for a pure-EV battery, lithium still has the advantage over NiMH because it's considerably lighter.

In a lithium-ion battery, lithium ions travel from the lithium oxide anode to a carbon-based cathode through an organic electrolyte. But a zinc-air battery uses air as its cathode. This means EnZinc can pack more zinc anode material into the battery to achieve a greater energy density. Zinc is also a benign substance—its byproduct in a battery is zinc oxide, the main ingredient in sunscreen. Add in the fact that the U.S is the third largest producer of zinc in the world and you have the makings of a safe, low-cost, high-energy battery. 

Not everyone is looking for a replacement for the lithium-ion battery. Some researchers are approaching the challenge as if it were a giant jigsaw puzzle, focusing on improving just one aspect of the battery. For example, Gabriel Veith and his team at Oak Ridge National Laboratory in Tennessee are trying to cut the weight of the protective system around the battery. 

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