The SIB development by Washington State University and (the likewise Washington-based) Pacific Northwest National Laboratory—led by WSU’s Professor Yuehe Lin and PNNL’s senior research scientist, Xiaolin Li—is the first one ever to show the extent to which sodium-ion (chemically known as Ni-ion) batteries can perform similarly to their LIB counterparts. The research findings have been published in ACS Energy Letters.
“These are the best results ever reported,” said Professor Lin from the School of Mechanical and Materials Engineering at WSU, “for a sodium-ion battery with a layered cathode, showing that this is a viable technology that can be comparable to lithium-ion batteries.”
As the research shows, however, neither SIBs nor LIBs are ideal energy storage technologies (due to, among other limitations, the former’s poor electrolytic and cathode efficiency and the latter’s resource-intensive manufacture), so the WSU and PNNL scientists had to attempt to circumvent the cons of both sodium and lithium-based batteries, and in turn, find a way to achieve the best of both worlds.
Attempting to Circumvent the Cons of Both SIBs and LIBs
To quote WSU’s news page, the researchers’ SIB was ultimately “able to … recharge successfully, keeping more than 80% of its charge after 1,000 cycles”. However, the scientists knew that a sodium-based energy storage chemistry would initially come with the challenge of its having a low capacity (at least when compared to LIBs, whose long-lasting nature has made them the leading choice for consumer technologies, such as smartphones).
The reason for the notable capacity fade in sodium-ion batteries is largely cited by WSU to be based on the poor performance in shuttling sodium ions from “[even] the most promising cathodes”, as WSU staff write. (The difficulty in finding an efficient cathode for battery chemistries is such, in fact, that it challenges LIB manufacturers, too, which has spurred some breakthrough R&D into how to optimise such a component.)
This is due to the fact that the surface of SIB cathodes are hindered by the buildup of sodium crystals that occurs in traditional sodium-based chemistries—and this ultimately leads to the battery’s failure, particularly given the proportions of the sodium ions. To quote PNNL’s ‘Available Technologies’ page, “a sodium-ion storage mechanism is scientifically challenging because sodium ions are about 70% larger in radius than that of lithium ions, [making] it difficult to find a suitable host material to accommodate the sodium ions and allow reversible and rapid ion insertion or extraction”.
PhD graduate Junhua Song and his colleagues have developed a sodium-ion battery that may rival lithium-ion battery chemistries. Pictured: Song holds up, front and centre, the coin-shaped battery development (labelled ‘Na-ion’). Image Credit: Washington State University.
On top of this, while Li-ion batteries may still lead the way in energy storage, their manufacture is also problematic, as it involves the (often controversial) mining of materials (such as cobalt and lithium) that are rare, expensive, and remote to most countries. As WSU staff write, with the demand for electrification (particularly in transport) rising ever higher, “these materials will become harder to get and possibly more expensive”. Accordingly, the Washington-based researchers collaborated to achieve the following solution.
Working to Achieve the Best of Both Worlds
Given the reasons above, the researchers had to act on the need for a battery chemistry that is based on one of the world’s most abundant and affordable materials, silicon (which makes up over a quarter of the earth’s crust)—while also securing the marked energy storage capacity of lithium.
Such a balancing act was ultimately achieved after the researchers took stock of the said sodium-ion buildup problem that occurs in SIB-based cathodes. The solution was the development of a layered metal oxide cathode alongside a liquid electrolyte that contained extra sodium ions.
The WSU news page explains that such an improved cathode-electrolyte interaction “creat[ed] a saltier soup [than that seen in traditional SIBs] that had a better interaction with their cathode”. WSU’s news staff link their enhanced SIB chemistry to the “continued movement of sodium ions, [which] prevent[ed] inactive sodium crystal buildup and allowed for unimped[ed] electricity generation” in their developed battery.
Overcoming the Future Demands of Energy Storage
All in all, the potential—to one day replace lithium-ion batteries with the less resource-intensive chemistry, sodium-ion—shows promise as a means to tackle our future demands on energy storage. As Junhua Song (pictured above), the lead author of the study and postdoctoral researcher explains:
“[T]he fundamental insights ... shed light on how we might develop future cobalt-free ... cathode materials in sodium-ion batteries, [alongside] other types of battery chemistries. If we can find viable alternatives to both lithium and cobalt, the sodium-ion battery could truly be competitive with lithium-ion batteries.”