GM has tipped its hand about the type of battery materials it aims to use in the next generation of the Chevrolet Volt and other battery-powered cars. It has licensed battery-electrode materials developed at Argonne National Laboratory, a U.S. Department of Energy Lab. These materials, called mixed-metal oxides, could improve the safety and durability of car batteries and help double their energy-storage capacity, potentially leading to substantial costs savings by allowing GM to use a smaller battery pack.
Cost is the biggest problem with the wave of battery-powered vehicles that started to arrive on the market last month. GM’s Volt, an electric vehicle that goes 35 miles per charge and has a gasoline generator for longer trips, costs more than twice as much as a similar-sized conventional car, in large part because of the battery. Increasing the amount of energy that a battery stores allows an automaker to use a smaller battery pack, thereby reducing costs.
“The whole concept of improving energy density is the prize when it comes to these kinds of vehicles,” says Jon Lauckner, president of GM Ventures, GM’s venture-capital arm. He says it’s not clear yet how much money the new technology will save, but “suffice it to say, it is significant; it is not a single-digit percentage.”
The current model of the Volt uses lithium-ion batteries made with lithium-manganese spinel cathodes (“spinel” refers to the three-dimensional arrangement of atoms in the material). The Argonne patents that GM has licensed cover a cathode material that consists of lithium, nickel, manganese, and cobalt. The material has both active components, through which lithium ions move when the battery is charged or discharged, and inactive ones that help stabilize the active material and extend battery life. Longevity is essential for electric-car batteries, which are designed to last for a decade and have to survive harsh conditions on the road. The new material has such high energy density because it can operate at a higher voltage than current electrode materials and also store more lithium ions.
The patents cover a range of nickel-manganese-cobalt materials, including new variants that GM and Argonne are developing and some components of the current Volt battery electrodes, which is made by LG Chem, a Korean manufacturer. The company has been able to use the materials because the Argonne patents only apply in the United States. But now LG Chem is building a battery-manufacturing plant in Michigan and must license the intellectual property from Argonne for use in products made there. Other companies such as Sharp are also commercializing batteries with nickel-manganese-cobalt electrodes, but of types not covered by Argonne’s patents.
To increase storage capacity in future batteries, GM and Argonne (working separately) are modifying the nickel-manganese-cobalt material in a couple of ways, says Jeff Chamberlain, manager of Argonne’s battery program.
First, they are changing the relative proportions of the three metals, to create a material able to store more lithium ions. Second, they are “activating” some of the inactive components, by freeing lithium from the inactive material so that it can move between the cathode and the anode. Once the lithium ions are free, they move only in and out of the active material, and the inactive material continues to play its stabilizing role.
Much work remains before these materials can be used in cars. “It’s one thing to make powder in a reaction vessel here at Argonne; it’s a very different thing to make a battery pack,” Chamberlain says. “There is a lot of innovation on the engineering side in terms of turning these materials into batteries.”
Doubling the energy density of the cathode does not double the amount of energy the battery pack as a whole can store. The storage capacity of the anodes has to keep pace, and the electrolytes have to be modified to work at higher voltages. Also, all three of these main components of the battery have to be engineered to work well together—for example, in order to limit unwanted chemical reactions. Once engineers have successfully incorporated the electrodes and electrolytes into working battery cells, more engineering is needed to incorporate the cells into battery packs.
The stability of the new materials suggests a way to increase energy density at the pack level, Chamberlain says. The current Volt battery pack is designed with extra energy-storage capacity to ensure that the car’s performance doesn’t suffer much as the battery ages. He says if future batteries lasted without needing the extra capacity, this would decrease the cost of the pack.
“This is probably the most capable cathode material that we have seen out there, and that’s the reason that we think it’s really critical that we get started working on this material now, so that we can get it on the road,” Lauckner says. “It’s going to take some years to further develop it and validate it. The idea is we want to get this on the road for the next generation of battery packs that come out.”
Several other companies are working with Argonne’s technology, including one, Envia, that is working with Argonne to combine advanced nickel-manganese-cobalt electrode materials with advanced silicon anode materials. This project, which is being funded by the Department of Energy’s Advanced Research Projects Agency for Energy, aims to produce batteries that store three times as much energy as today’s lithium-ion car batteries.
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