For some time now, scientists have eyed cheap and widely abundant salt as a potential replacement for lithium in batteries that power everything from laptops to cars. While these experimental sodium-ion batteries continue to show promise, there are a few kinks to be ironed out before we see them become commonplace. Researchers at Purdue University are claiming to have overcome one important shortcoming by first reducing the sodium to a powder form.
The urge to come up with alternatives to the ubiquitous lithium-ion battery are driven by the fact that lithium is rare and expensive to mine. Plentiful sodium, meanwhile, has it covered on a few fronts, with scientists eyeing low-cost and large-scale solar and wind storage facilities as applications with particular potential.
Like a lithium-ion battery, a sodium-ion battery generates power by having sodium ions travel from one electrode to the other through a liquid electrolye, at least in theory. The trouble is, sodium-ion batteries have a few operational issues in their current form.
One of these is a short life due to the congregation of sodium ions at the electrode made from carbon, called the anode, during the first few charging cycles. Here they build up and form what is known as a solid electrolyte interface, which hungrily eats up the sodium ions and before long, leaves a busted battery.
"The bigger problem is limited capacity of cathode comprising sodium," Vilas Pol, Purdue associate professor of chemical engineering, explains to New Atlas. "If most of that capacity is consumed by anode during solid electrolyte interface formation then there is limited amount of sodium to shuttle, limiting battery life."
So Pol and his team looked to make some tweaks. Using standard ultrasound technology, they melted chunks of sodium down into a milky purple liquid, which they in turn cooled into a powder and suspended in hexane solution, leaving an even spread of powder particles.
Adding just a few drops of this powder material during fabrication of both the anode and cathode electrodes brought much better results. Pol tells us they observed much longer charging and discharging cycles, along with better coulombic efficiency (the efficiency of charge transfer).
The team has filed a patent for the technology, and Pol says they are now working to optimize the fabrication of the powder process and the batteries that incorporate the material. Overall, the team hopes its sodium powder can be the missing ingredient needed to bring sodium-ion batteries to industry.
The research has been published in the Journal of Power Sources.
Source: Purdue University
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