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 represent some of the best hopes for a safe, low-cost, efficient electric vehicle.
NiMH Batteries: Hybrids to EVs
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—a fact that's not going to change just by tweaking the nickel battery's chemistry.
Zinc-Air: From Hearing Aids to Cars
Michael Burz hopes the next big EV battery tech will be zinc-air, which his California-based company, , purchased from the U.S. Navy two years ago. With the zinc-air battery, Burz's team is looking to hit the electric vehicle trifecta: "High performance, safety, and low cost," he says. And he thinks they can do it by changing the way a battery is designed.
"People have been looking at the same kind of battery architectures for the past 100 years," Burz says. That architecture includes three elements: an anode, a cathode, and an electrolyte. The anode and cathode materials are chosen so that the anode donates electrons and the cathode accepts them. The anode and the cathode are separated by the electrolyte, which acts as a transport medium that lets ions flow freely.
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.
So, why aren't we using zinc-air batteries already? Because the ordinary version is not rechargeable. "That's been the big nut to crack," Burz says. Disposable zinc-air batteries have been around a long time and are used in hearing aids. To make this kind of battery rechargeable, EnZinc is developing a version in which the zinc anode regenerates as oxygen is released. The engineers have achieved this in the lab, and ARPA-E's funding gives them the opportunity to work on developing a prototype.
Sliming Down While Staying Safe
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, and his team at Oak Ridge National Laboratory in Tennessee are trying to cut the weight of the protective system around the battery.
Veith, a materials scientist, recalls standing around the hallway the day he and his colleagues came up with the idea for what became his proposal to ARPA-E: to develop an electrolyte material that would also function as part of the battery's safety system.
"In the event of an accident it would undergo a phase change and would become an impenetrable barrier," Veith says, hopefully preventing the kind of collision-related fires that have troubled Tesla recently. The challenge his team now faces is how to make the material respond quickly enough. "It wouldn't do us any good if it took 5 minutes for a phase change to occur," he says. "We want it to occur instantaneously."
Fill 'Er Up
Carlo Segre of the Illinois Institute of Technology wants to do away with the range anxiety that plagues today's EV drivers by making the recharging process more like a gas station fill-up. Segre's team is designing a battery that includes two liquid electrodes and an electrolyte of nanoparticles suspended in a liquid. Because the electrodes are fluid, it may be possible one day to replace the electrode the way you would fill up your car with gasoline.
"What you would do is just stop at the station and switch out the fluid," Segre says. "You can be on your way in a few minutes rather than taking however long it takes to charge the battery."
As with the other ARPA-E projects funded by, it will be at least three to five years before Segre knows whether his project will succeed. "That's the whole point of ARPA-E," he says. "[They] don't take things that are a sure thing."