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Researchers Develop Stable Sodium Powder Version Of Lithium Batteries
Sep 21, 2018

Don't require the rare material being mined from the mountains of South America


Sodium normally explodes if exposed to water, but performs well in batteries as a powder, Purdue researchers discovered. Credit: Purdue University video/Vilas Pol.

Scientists have long warned that if the world depletes its source of lithium, mined to power modern devices, then battery production could stagnate.


However, researchers from Purdue University have made a sodium powder version of lithium batteries that don't require the rare material which is mostly mined from the mountains of South America.


It's no news that sodium is a very cheap and earth-abundant alternative to using lithium-ion batteries. The problem with sodium though is that it's known for turning purple and combusting if exposed to water, even just water in the air.


Worldwide efforts to make sodium-ion batteries just as functional as lithium-ion batteries have long since controlled sodium's tendency to explode, but not yet resolved how to prevent sodium-ions from "getting lost" during the first few times a battery charges and discharges


But the Purdue University researchers claimed to have fixed this problem with their latest sodium battery development, even stating that it can hold a charge properly.


"Adding fabricated sodium powder during electrode processing requires only slight modifications to the battery production process," said Vilas Pol, Purdue associate professor of chemical engineering.


"This is one potential way to progress sodium-ion battery technology to the industry."


Even though sodium-ion batteries would be physically heavier than lithium-ion technology, the researchers have been investigating sodium-ion batteries because they could store energy for large solar and wind power facilities at lower cost.


The problem was that sodium ions stick to the hard carbon end of a battery, called an anode, during the initial charging cycles and not travel over to the cathode end. The ions would build up into a structure called a "solid electrolyte interface."


"Normally the solid electrolyte interface is good because it protects carbon particles from a battery's acidic electrolyte, where electricity is conducted," Pol explained. "But too much of the interface consumes the sodium ions that we need for charging the battery."


Purdue researchers solved this by using sodium as a powder, which provided the required amount of sodium for the solid electrolyte interface to protect carbon, but doesn't build up in a way that it consumes sodium ions.


They minimised sodium's exposure to the moisture that would make it combust by making the sodium powder in a glove box filled with the gas argon. To make the powder, they used an ultrasound - the same tool used for monitoring the development of a foetus - to melt sodium chunks into a milky purple liquid. The liquid then cooled into a powder and was suspended in a hexane solution to evenly disperse the powder particles.


Just a few drops of the sodium suspension onto the anode or cathode electrodes during their fabrication allowed the sodium-ion battery cell to charge and discharge with more stability and at higher capacity, the "minimum requirements for a functional battery", the researchers said.