Many electric cars are powered by batteries containing cobalt, a metal that carries high financial, environmental and social costs. With this in mind, researchers at the Massachusetts Institute of Technology (MIT) have now designed a battery material that could provide more sustainable power for electric vehicles. The new lithium-ion battery will include a cathode based on organic materials rather than cobalt or nickel.
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 battery also has comparable storage capacity and can be charged faster than cobalt batteries, the researchers report.
"I think this material could have a big impact because it works so well," said Mircea Dincǎ, a professor at MIT and senior author of the research paper. "It's already competitive with existing technologies, and it could save a lot of the cost, pain, and environmental concerns associated with mining metals currently used in batteries."
As we all know, most electric vehicles are powered by lithium-ion batteries, which are charged when lithium ions flow from the positive electrode (cathode) to the negative electrode (anode). In most lithium-ion batteries, the cathode contains cobalt, a metal that has high stability and energy density.
However, cobalt has significant disadvantages. As a scarce metal, the price of cobalt can fluctuate significantly, and most of the world's cobalt deposits are located in politically unstable countries. The mining of cobalt creates dangerous working conditions and produces toxic waste that pollutes the land, air and water surrounding the mines.
Because of this, a lot of research is trying to develop alternative battery materials. One such material is lithium iron phosphate (LFP), which some automakers are starting to use in electric vehicles. While LFP is certainly useful in practical applications, its energy density is only about half that of cobalt and nickel batteries.
organic materials
Another attractive option is organic materials, but so far, most have been unable to match the conductivity, storage capacity and longevity of cobalt-containing batteries. Because of their low electrical conductivity, these materials often need to be mixed with a binder such as a polymer to help them maintain a conductive network. These binders make up at least 50% of the total material, reducing the battery's storage capacity.
About six years ago, Dincǎ's lab began working on a project with funding from Lamborghini to develop an organic battery that could be used to power electric vehicles. While studying porous materials that are partly organic and partly inorganic, Dincǎ and his students realized that a 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 graphite-like structures. Within the molecule are chemical groups called quinones, which are electron reservoirs, and amines, which help the material form strong hydrogen bonds.
These hydrogen bonds make this material very stable and extremely poorly soluble. This insolubility is important because it prevents the material from dissolving into the battery electrolyte, as some organic battery materials do, thereby extending its service life.
"One of the main ways organic materials degrade is by simply dissolving them in the battery electrolyte and 'crossing over' to the other side of the battery, essentially creating a short circuit. If you make the material completely insoluble, this process does not occur, so we can perform over 2,000 charge cycles with minimal degradation," they said.
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 increase its ability to stick to the battery's current collector, which is 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 cathode composite, so they don't significantly reduce the battery's storage capacity.
These fillers also prevent the cathode from cracking when lithium ions flow into the cathode as the battery charges, extending the battery's life.
It is reported that the main materials required to make such cathodes are quinone precursors and amine precursors, which are already produced in large quantities as commercial chemicals. The researchers estimate that the materials cost of assembling these organic batteries could be one-third to half the cost of cobalt batteries.
In the future, they plan to continue developing alternative battery materials and are exploring the possibility of replacing lithium with sodium or magnesium, which are cheaper and more abundant than lithium.