Researchers at the University of California, Berkeley, have discovered a method that could see other metals used in place of cobalt in lithium-based batteries, as well as increasing their storage capacity.
The technology could see manganese used in place of cobalt, reducing the world’s dependency upon the mineral that is largely mined in the copper belt in the Democratic Republic of Congo (DRC), Central African Republic and Zambia—with the DRC alone accounting for more than 50% of world production.
Building on their 2014 discovery, which found cathodes can maintain a high energy density without the layering structure of cobalt, the team members have now shown that they can also increase battery storage capacity without cobalt. They believe that this could open up new possibilities for the design of cathodes.
“We’ve opened up a new chemical space for battery technology,” said senior author and professor in the Department of Materials Science and Engineering at Berkeley Gerbrand Ceder.
“For the first time we have a really cheap element that can do a lot of electron exchange in batteries.”
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In traditional lithium-based batteries, lithium ions are stored in cathodes, the negatively charged electrode. These cathodes are layered structures, with cobalt on of the few elements that won’t move during the charging process, making it critical to the battery industry.
In 2014, Ceder’s lab discovered that cathodes can maintain a high energy density without cobalt layers using a concept called disordered rock salts. The new study shows that manganese can work in this process, offering a more abundant and therefore cheaper alternative to cobalt.
“To deal with the resource issue of cobalt, you have to go away from this layeredness in cathodes,” said Ceder. “Disordering cathodes has allowed us to play with a lot more of the periodic table.”
Using a process called fluorine doping, the scientists were able to incorporate a large amount of manganese in the cathode. Having more manganese ions with the proper charge allows the cathodes to hold more lithium ions and increase the battery’s capacity.
The disordered manganese cathodes approached 1,000 watt-hours per kilogram, with typical lithium-ion cathodes in the range of 500-700 watt-hours per kilogram.
“In the world of batteries, this is a huge improvement over conventional cathodes,” said lead author Jinhyuk Lee, who was a postdoctoral fellow at Ceder’s lab during the study.
The team plans on scaling the technology up to test it in applications such as laptops or electric vehicles, but Ceder is confident that the discovery will provide freedom for further developments.
“You can pretty much use any element in the periodic table now because we’ve shown that cathodes don’t have to be layered,” said Ceder.
“Suddenly we have a lot more chemical freedom, and I think that’s where the real excitement is because now we can do exploration of new cathodes.”
The study, which will be published in the 12 April edition of the journal Nature, was a collaboration between scientists at UC Berkeley, Berkeley Lab, Argonne National Lab, MIT and UC Santa Cruz.