"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, researchers have been investigating sodium-ion batteries because they could store energy for large solar and wind power facilities at lower cost as sodium is cheap as a material.
The problem is that sodium ions stick to the carbon anode during the initial charging cycles and not travel over to the cathode, building 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," said Pol. "But too much of the interface consumes the sodium ions that we need for charging the battery."
The researchers proposed using sodium as a powder, which provides 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 the sodium's exposure to the moisture to stop it burning by making the sodium powder in a glovebox filled with the gas argon. To make the powder, they used ultrasound 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 allows a sodium-ion battery cell to charge and discharge with more stability and at higher capacity.