Sodium-ion batteries offer multiple advantages over their lithium-ion cousins. Energy storage, however, isn't one of them. That might be set to change thanks to a new method of creating the batteries involving water-rich cathodes.

Currently, there's really no beating lithium-ion batteries in terms of energy density and light-weight form factors. That's why they've found their way into everything from electric cars to cell phones. But there are certainly issues with the technology, including the fact that lithium itself is difficult, expensive, and environmentally damaging to mine. Lithium batteries are also prone to overheating, can occasionally burst into flames, and don't perform well in very low temperatures.

That's why researchers have been giving a lot of attention to sodium-ion batteries. After all, sodium is extremely abundant, easy to mine, and doesn't come with the geopolitical complications involved with lithium mining. That said, sodium-ion batteries tend to be heavier and have a lower energy density than lithium-ion batteries, meaning you get less power out of a heavier material. Still, they are safer, cheaper to produce, and have pretty much zero supply-chain issues.

Now, by taking a unique approach to the cathode material in a sodium-ion battery, researchers from the University of Surrey in England have found a way to nearly double its energy storage capacity. The cathodes were created out of a compound that is continuously being explored for use in these types of batteries called nanostructured vanadate hydrate (NVOH). Typically, though, NVOH is used after being dehydrated. This time around the team took a different approach.

"Our results were completely unexpected," said study lead author Daniel Commandeur. "Sodium vanadium oxide has been around for years, and people usually heat-treat it to remove the water because it's thought to cause problems. We decided to challenge that assumption, and the outcome was far better than we anticipated. The material showed much stronger performance and stability than expected and could even create exciting new possibilities for how these batteries are used in the future."

NVOH was so effective in fact, that the researchers say it is now considered at the very top of cathode materials for sodium-ion batteries. The test batteries made with the material remained stable for over 400 charge cycles.

The study, which has been published in the Journal of Materials Chemistry A, says the reason for the boosted energy storage has to do with the fact that the extra water allowed the material's layers to spread out slightly, giving the sodium ions more room to move in and out and allowing the cathode to store more of them.

The team also tested out hydrated NVOH's performance as a potential desalinization medium and found that it did as well, if not better than, other common electrodes used for the process.

"Being able to use sodium vanadate hydrate in salt water is a really exciting discovery, as it shows sodium-ion batteries could do more than just store energy – they could also help remove salt from water," concluded Commandeur. "In the long term, that means we might be able to design systems that use seawater as a completely safe, free and abundant electrolyte, while also producing fresh water as part of the process."

Source: University of Surrey