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.

The problem is 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 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 said. "But too much of the interface consumes the sodium ions that we need for charging the battery."