MIT design new cathode-based battery

Nicola Brittain

Could cobalt-free batteries power cars of the future? A newly-developed battery cathode based on organic materials may hold the answer.

The majority of electric vehicles (EVs) are powered by lithium-ion batteries often comprised of a cobalt-containing cathode. While cobalt offers high stability and energy density, it is a metal that also carries high financial, environmental and social costs.

The material’s scarcity means its price can fluctuate dramatically, and much of the world’s cobalt deposits are located in politically unstable countries. Furthermore, cobalt extraction is fraught with hazardous working conditions, while the mining process itself generates toxic waste that contaminates the surrounding land, air and water.

“Cobalt batteries can store a lot of energy, and they have all of the features that people care about in terms of performance, but they have the issue of not being widely available, and the cost fluctuates broadly with commodity prices,” explains Mircea Dincă, W.M. Keck Professor of Energy at the Massachusetts Institute of Technology (MIT). “And as you transition to a much high proportion of electrified vehicles in the consumer market, it is certainly going to get more expensive.”

ORGANIC OPTIONS

Due to cobalt’s many drawbacks, extensive research into developing alternative battery materials has commenced, such as lithium-iron-phosphate (LFP). While some car manufacturers are beginning to use LFP in EVs, the material only has about half the energy density of cobalt and nickel batteries. Another potential option is organic materials, however so far many of these materials have not been able to match the conductivity, storage capacity and lifetime of their cobalt counterparts.

That is, until now. In a new study from MIT, researchers have successfully designed a new lithium-ion battery made up of a cathode based on organic materials which is capable of conducting electricity at similar rates as cobalt batteries. The new battery also has comparable storage capacity and can be charged up faster than cobalt batteries, the researchers claim.

“I think this material could have a big impact because it works really well,” Dincă explains. “It is already competitive with incumbent technologies, and it can save a lot of the cost and pain and environmental issues related to mining the metals that currently go into batteries.”

Six years in the making, the material consists of many layers of bis-tetraaminobenzoquinone (TAQ), an organic small module that contains three fused hexagonal rings. These layers can extend outward in every direction to form a structure similar to that of graphite. Within the molecules are chemical groups called quinones – the electron reservoirs – and amines, which help the material to form strong hydrogen bonds. These hydrogen bonds make the material highly stable and insoluble, preventing the material from dissolving into the battery electrolyte like some other organic battery materials do.

“One of the main methods of degradation for organic materials is that they simply dissolve into the battery electrolyte and cross over to the other side of the battery, essentially creating a short circuit,” Dincă says. “If you make the material completely insoluble, that process doesn’t happen, so we can go to over 2,000 charge cycles with minimal degradation.”

POWERFUL PERFORMANCE

According to the researchers’ tests, the material’s conductivity and storage capacity were comparable to that of traditional cobalt-containing batteries. The tests also show that batteries with a TAQ cathode can be charged and discharged faster than existing batteries, which could speed up the charging rate for future EVs.

The researchers added filler materials like cellulose and rubber to the organic material in order to increase its ability to adhere to the battery’s current collector. Making up just one-tenth of the cathode composite meant these materials did not significantly reduce the battery’s storage capacity and actually extended the lifetime of the battery cathode by preventing cracking during charging.

The primary materials to manufacturer the cathode – a quinone precursor and an amine precursor – are commercially available and produced in large quantities as commodity chemicals, meaning the material cost of assembling the organic battery could be less than half the cost of cobalt batteries.

With car manufacturer Lamborghini having licensed the patent on the technology, Dincă’s lab will continue to develop alternative battery materials and explore the replacement of lithium with cheaper and more abundant materials such as sodium or magnesium.

 

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