Rechargeable lithium-ion batteries have one big problem that researchers are dedicating a lot of time to: their cathodes. Now, a team from the University of Maryland, the Brookhaven National Laboratory, and the U.S. Army Research Lab claims to have made a breakthrough in solving the problem.
Cathodes, unlike anodes, tend to have a very limited capacity. As one of the lead authors in the new research puts it, “Cathode materials are always the bottleneck for further improving the energy density of lithium-ion batteries.” So the team set out to improve the energy density of the cathode by using an unlikely material: iron.
They used a new form of iron trifluoride, which is cheap, easy to come by, and environmentally friendly. More importantly, iron trifluoride can transfer more than one electron when the battery discharges and charges, which makes such a battery theoretically much more efficient than comparable ones.
However, iron trifluoride doesn’t exactly have a good track record in batteries: it has low energy efficiency, slow reaction rate, and it also comes with side reactions that compromise the rechargeability of the battery it is used in.
To tackle these challenges and make iron trifluoride actually usable, they added oxygen and cobalt atoms to the cathode rods they worked with. Before adding them, the battery worked by converting lithium ions into iron and lithium fluoride in the cathode. The reverse reaction, however, was not possible. After adding the cobalt and the oxygen atoms, the reaction became reversible.
After this, the team did a lot of measurement and analysis work to confirm they had actually solved iron’s battery problem. It seems they have, but the applicability of this solution is yet to be determined. If iron trifluoride batteries become a mass thing, they could accelerate the adoption of grid-scale energy storage installations—these are urgently needed to eliminate the number-one problem of solar and wind energy: their intermittent nature.
Yet there have been so many breakthroughs in battery technology that it has been difficult to single out the ones that have the best chance of going mainstream. Lots of scientists are looking for cheaper, more efficient materials to use in lithium-ion batteries, and many are actually looking for substitutes to lithium-ion technology.
Australian researchers recently announced a battery that works with just water and carbon, breaking down the water into its constituent elements, with the hydrogen bonding with the carbon electrode during the charging phase. The discharge reverses the reaction, and the hydrogen leaves the carbon cathode to bind with oxygen and turn back into water.
Another recent announcement in the battery field also deals with hydrolysis, but with the addition of manganese to facilitate the reaction. The researchers behind this battery say it’s very energy dense, at 140 Wh/kg, durable, with a lifecycle of 10,000 charge-discharge cycles, and is easily scalable, which would make it perfect for energy storage systems at solar and wind farms.
Battery development is definitely a hot space right now, what with the great expectations about EVs and renewable energy. Yet most breakthroughs have only taken place in the lab. It will be some time before we know for sure which promising batteries actually live up to the promise.