A novel type of graphene with a unique artificial nanostructure can make sodium-ion batteries as high-capacity as lithium-ion batteries, offering a more sustainable approach to energy storage. Researchers at the Chalmers University of Technology have engineered two-faced graphene sheets to store sodium, an abundant low-cost metal unlike lithium which is expensive and its mining isn't sustainable.
However, sodium-ion batteries currently can't compete with lithium-ion batteries in terms of capacity: the capacity of sodium intercalation-the insertion of a molecule or ion into a layered material-is less than one tenth of the capacity for lithium-ion intercalation in graphite. Sodium ions can't be efficiently stored in the graphite because they are larger than lithium ions.
Chalmers University scientists have come up with a solution to this problem in sodium-ion batteries: they created a two-faced graphene layer to provide an interaction point for the ions, which boosts capacity tenfold.
"We have added a molecule spacer on one side of the graphene layer. When the layers are stacked together, the molecule creates larger space between graphene sheets and provides an interaction point, which leads to a significantly higher capacity," said researcher Jinhua Sun at the Department of Industrial and Materials Science at Chalmers and first author of the scientific paper, published in Science Advances.
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"The research is still at an early stage, but the results are very promising. This shows that it's possible to design graphene layers in an ordered structure that suits sodium-ions, making it comparable to graphite," says Professor Aleksandar Matic at the Department of Physics at Chalmers.
The novel graphene design, also called Janus graphene after the two-faced god in Roman mythology, could one day help sodium-ion batteries give lithium-ion batteries a run for their money.
"Our Janus material is still far from industrial applications, but the new results show that we can engineer the ultrathin graphene sheets - and the tiny space in between them - for high-capacity energy storage. We are very happy to present a concept with cost-efficient, abundant and sustainable metals," said Vincenzo Palermo, Affiliated Professor at the Department of Industrial and Materials Science at Chalmers.
The adoption of electric vehicles and increased installation of energy storage have resulted in soaring demand for lithium, cobalt, and nickel. Analysts expect supply challenges for some of the energy transition metals, including lithium.
Demand for lithium is expected to rise the most, according to Wood Mackenzie. Lithium faces a six-fold increase from the battery sector by 2030, WoodMac analysts say.
That's why the race for efficient high-capacity battery designs is going full steam ahead.
Chinese battery manufacturer Contemporary Amperex Technology Co., Ltd. (CATL), which supplies Tesla and Volkswagen among others, unveiled last month its first-generation sodium-ion battery.
"CATL has applied Prussian white material with a higher specific capacity and redesigned the bulk structure of the material by rearranging the electrons, which solved the worldwide problem of rapid capacity fading upon material cycling," the battery maker said.
CATL also presented its AB battery pack solution, which is able to integrate sodium-ion cells and lithium-ion cells into one pack. The company plans to set up a basic industrial chain for sodium-ion batteries by 2023.
"Sodium-ion technology has long been touted for commercial battery use due to sodium's low cost and high abundance relative to lithium, and CATL producing large scale sodium-ion batteries shows the technology's appeal is coming to fruition sooner rather than later," Wood Mackenzie's research analyst Max Reid said.
"The lower energy of the sodium-ion cells suggests that the technology may be more suited for stationary energy storage applications which are less restrictive, while the unveiling of battery packs combining both sodium-ion and lithium-ion cells could point towards compromise in performance for low-cost electric vehicles, with the potential to disrupt the mass market," Reid noted.
By Tsvetana Paraskova for Oilprice.com
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