Batteries that use a sodium-ion chemistry rather than the commonplace lithium-ion could offer a number of advantages, owing to the cheap and abundant nature of the element. Scientists at Washington State University, Pullman, Washington, have come up with a design billed as a potential game changer in this area – a sodium-ion battery offering a comparable energy capacity and cycling ability to some lithium-ion batteries already on the market.
In a way, sodium-ion batteries function just like lithium-ion batteries, generating power by bouncing ions between a pair of electrodes in a liquid electrolyte. One of the problems with them in their current form, however, is that while this is going on inactive sodium crystals tend to build up on the surface of the negatively-charged electrode, the cathode, which winds up killing the battery. Additionally, sodium-ion batteries don’t hold as much energy as their lithium-ion counterparts.
“The key challenge is for the battery to have both high energy density and a good cycle life,” says Washington State University’s Junhua Song, lead author on the paper. The research was published in the journal ACS Energy Letters.
Song and his team believe they may have come up with a solution to these shortcomings. Experimenting with the design of sodium-ion batteries led the team to produce a version with a cathode made of layered metal oxide and a liquid electrolyte with a higher concentration of sodium ions.
In testing, the team found that this led to a much smoother interaction between the electrolyte and the cathode, enabling the continuous movement of the sodium ions and avoiding the troublesome buildup of inactive crystals on the cathode surface. The upshot of that was battery offering capacity similar to some lithium-ion batteries and with an uninterrupted generation of electricity, maintaining 80 percent of its charge after 1,000 cycles.
“Our research revealed the essential correlation between cathode structure evolution and surface interaction with the electrolyte,” Lin says. “These are the best results ever reported for a sodium-ion battery with a layered cathode, showing that this is a viable technology that can be comparable to lithium-ion batteries.”
Enthused with the results, the team is now investigating how the electrolyte interacts with the cathode to better understand these interactions, with hopes of improving the design further, possibly even to avoid the use of other rare metals like cobalt.
“This work paves the way toward practical sodium-ion batteries, and the fundamental insights we gained about the cathode-electrolyte interaction shed light on how we might develop future cobalt-free or low cobalt cathode materials in sodium-ion batteries as well as in other types of battery chemistries,” Song says. “If we can find viable alternatives to both lithium and cobalt, the sodium-ion battery could truly be competitive with lithium-ion batteries. And, that would be a game changer.”