Sonic boom. New light weight anode material for Li-ion battery

The discovery of new, functional materials is all about manipulating the elements to form compounds as needed. This, in turn, often involves breaking the bonds.

Sonochemistry, or using high-frequency sound waves, way above human hearing range, is one of the techniques for breaking the bonds. When high-intensity sound waves slither through a watery medium, they create extremely tiny bubbles that form and collapse rapidly. This process produces extremely high temperatures and pressures.

Sonochemistry is not something new. It has been long known to scientists but seems to be making a come back for newer applications today.

Prof Kothandaraman Ramanujam of the Department of Chemistry, IIT Madras, has synthesised a new material called ‘hydride-stabilised boron nanosheets’ (H-BNS) through this technique. There are many applications of this material, but the notable three include its use as — anode material for Li-ion batteries, reducing agent for organic reactions and a medium for storing hydrogen.

Their experiments have been published in a paper in the journal ChemComm.

Making of H-BNS

Kothandaraman and his students, Swati and Dr Anand, fired sonic waves into the water that had boron, after which they allowed time for unreacted boron particles to settle down—which were removed by a centrifuge. Then the supernatant solution was centrifuged at much higher speeds and longer to collect the ‘hydride-stabilised boron nanosheets’.

What happens is, the sonic waves break the bonds between hydrogen and oxygen in water molecules simultaneously boron-boron bonds freeing boron atoms to form 2D materials. Some of the nascent hydrogen atoms pick up an extra electron from 2D boron sheets and become ‘hydrides’. These hydrides go and ‘sit’ on the boron slabs (or ‘borophites’, which are multiple layers of borophene sheets). “Sonication helps in breaking boron-boron bonds and production of hydrides,” explains Kothandaraman. The hydride settles down on the boron nanosheets, forming H-BNS.

The team measured the thickness of H-BNS using ‘atomic force microscopy’ and found it to be ~ 20 nm thick. This indicates the formation of borophites (a one-atom thick, 2-dimensional sheet of boron).

Now, if you ‘intercalate’ (or insert) lithium into H-BNS, you have yourself a potential anode material for a lithium-ion battery. Boron is lighter than carbon (graphite) and hence these batteries could have higher energy densities if optimised. And, boron is plentifully available in nature. “The potential use of H-BNS for lithium-ion battery applications was successfully demonstrated in half-cell mode,” says Kothandaraman.

Furthermore, the use of H-BNS as a reducing agent has also been studied and confirmed. Since H-BNS has hydride, it is a potential hydrogen storage material, useful for fuel cells.

COMMENT NOW