Many electric vehicles are powered by batteries containing cobalt, a metal that carries high financial, environmental and social costs.
MIT researchers have now designed a battery material that could provide a more sustainable way to power electric vehicles. New lithium-ion batteries include cathodes based on organic materials instead of cobalt or nickel, another metal commonly used in lithium-ion batteries.
In a new study, researchers show that the material is much cheaper to produce than batteries containing cobalt and can conduct electricity at a similar rate to cobalt batteries. The new batteries also have comparable storage capacity to cobalt batteries and charge faster, the researchers report.
“I think this material could have a big impact because it works so well,” said Mircea Dincă, WM Keck Professor of Energy at MIT. “It’s already competitive with existing technologies and could save a lot of money compared to mining currently. The costs, pain and environmental concerns associated with metals used in batteries.”
Dinka is the senior author of the study, which is published today in the journal American Chemical Society Central Science Center. Tianyang Chen PhD ’23 and former MIT postdoc Harish Banda are the lead authors of the paper. Other authors include Jiande Wang, a postdoc at MIT; Julius Oppenheim, a graduate student at MIT; and Alessandro Franceschi, a researcher at the University of Bologna.
Cobalt alternatives
Most electric cars are powered by lithium-ion batteries, which are charged when lithium ions flow from a positively charged electrode, called the cathode, to a negatively charged electrode, called the anode. In most lithium-ion batteries, the cathode contains cobalt, a metal with high stability and energy density.
However, cobalt also has significant disadvantages. As a rare metal, its price can fluctuate widely, and most of the world’s cobalt deposits are located in politically unstable countries. Cobalt extraction creates hazardous working conditions and produces toxic waste that contaminates the land, air and water surrounding mines.
“Cobalt batteries can store a lot of energy and have all the features people care about in terms of performance, but they have the problem of not being widely available, and their costs fluctuate greatly with commodity prices. And when the proportion of electric vehicles in the consumer market increases significantly, , its price will definitely become higher,” Dinka said.
Because cobalt has many disadvantages, a lot of research has been done to try to develop alternative battery materials. One such material is lithium iron phosphate (LFP), which some automakers are starting to use in electric vehicles. While lithium iron phosphate still has practical uses, its energy density is only about half that of cobalt and nickel batteries.
Another attractive option is organic materials, but so far most of these materials have not been able to match the conductivity, storage capacity and longevity of cobalt-containing batteries. Because of their low electrical conductivity, such materials often need to be mixed with binders such as polymers to help them maintain a conductive network. These adhesives make up at least 50% of the overall material and reduce the battery’s storage capacity.
About six years ago, Dinka’s lab began working on a Lamborghini-funded project to develop an organic battery that could be used to power electric vehicles. While studying porous materials that are partly organic and partly inorganic, Dinka and his students realized that the fully organic material they had made seemed likely to be a strong conductor.
The material is composed of layers of TAQ (bis-tetraaminoquinone), a small organic molecule containing three fused hexagonal rings. These layers can extend outward in all directions, forming a graphite-like structure. There are chemical groups called quinones (electron pools) and amines within the molecule that help the material form strong hydrogen bonds.
These hydrogen bonds make the material highly stable and very insoluble. This insolubility is important because it prevents the material from dissolving into the battery electrolyte, as some organic battery materials do, extending its lifespan.
“One of the main ways organic materials degrade is that they simply dissolve into the battery electrolyte and travel across to the other side of the battery, essentially creating a short circuit. If you make the material completely insoluble, this process won’t happen, so we can More than 2,000 charging cycles with minimal degradation,” said Dincă.
Powerful performance
Tests of the material showed that its conductivity and storage capacity were comparable to conventional cobalt-containing batteries. In addition, batteries with TAQ cathodes can charge and discharge faster than existing batteries, which could speed up the charging of electric vehicles.
To stabilize the organic material and improve its ability to adhere to battery current collectors made of copper or aluminum, the researchers added filler materials such as cellulose and rubber. These fillers make up less than one-tenth of the entire cathode composite, so they do not significantly reduce the battery’s storage capacity.
These fillers also prevent cracking when lithium ions flow into the cathode while the battery is charging, extending the life of the battery cathode.
The main materials required to make this type of cathode are quinone precursors and amine precursors, which are already commercialized and produced in large quantities as commodity chemicals. The researchers estimate that the materials cost to assemble these organic batteries could be about one-third to one-half the cost of cobalt batteries.
Lamborghini has licensed the technology. Dinka’s lab plans to continue developing alternative battery materials and is exploring the possibility of replacing lithium with sodium or magnesium, which are cheaper and more abundant than lithium.