Sodium-ion breakthrough could lower environmental impact of batteries

A sodium-ion (Na-ion) battery that is claimed to be able to store as much energy as commonplace lithium-ion (Li-ion) batteries, but with a much-reduced environmental cost, has been developed by researchers.

A team from Washington State University (WSU) and Pacific Northwest National Laboratory (PNNL) reported one of the best results to date for a sodium-ion battery, with a design that holds more than 80 per cent of its charge after 1,000 cycles.

This is a key metric that makes it more appealing than other touted next-gen battery technologies, such as lithium-sulphur which starts to lose its capacity after just a few recharge cycles.

“This is a major development for sodium-ion batteries,” said Dr. Imre Gyuk, who works for the US Department of Energy. “There is great interest around the potential for replacing Li-ion batteries with Na-ion in many applications.”

Li-ion batteries have become the de facto choice for electronic gadgets, electric cars and even the mass storage of renewable electricity on the grid.

However, these batteries are made from materials such as cobalt and lithium that are rare, expensive and mostly found outside the US. In 2018, German researchers warned that shortages of these metals are expected by 2050, with demand expected to rise exponentially over the coming years.

Sodium-ion batteries could solve the issue as they are made from cheap, abundant and sustainable sodium from the earth’s oceans or crust. Up until now, this technology has been hampered by having a lower storage capacity and short lifespans.

A key problem for some of the most promising cathode materials is that a layer of inactive sodium crystals builds up at the surface of the cathode, stopping the flow of sodium ions and, consequently, killing the battery.

“The key challenge is for the battery to have both high energy density and a good cycle life,” said Junhua Song, lead author on the paper.

As part of the work, the research team created a layered metal oxide cathode and a liquid electrolyte that included extra sodium ions, creating a saltier soup that had a better interaction with their cathode. Their cathode design and electrolyte system allowed for continued movement of sodium ions, preventing inactive surface crystal build-up and allowing for unimpeded electricity generation.

“Our research revealed the essential correlation between cathode structure evolution and surface interaction with the electrolyte,” Lin said. “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.”

The researchers are now working to better understand the important interaction between their electrolyte and the cathode, so they can work with different materials for improved battery design. They also want to design a battery that doesn’t use cobalt, another relatively expensive and rare metal.

“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 said. “If we can find viable alternatives to both lithium and cobalt, the sodium-ion battery could truly be competitive with lithium-ion batteries”.

In April, a team claimed to have found a way to stabilise lithium-sulphur batteries which could bring them closer to commercial viability.

SOURCE

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