Living in a world with smartphones, laptops and cars powered by batteries means putting up with two things: waiting for a depleted battery to charge and charging it more frequently when its once-long life inevitably shortens. That’s why the supercapacitor is still in the game.
But as demand for energy storage grows, scientists and consumers are keeping up their search for alternatives to lithium-ion batteries. In a study this month in ‘Nature Materials’, researchers reported a new phenomenon that could potentially bring a supercapacitor’s energy storage capacity on par with lithium-ion batteries: by using a new class of electrolytes composed of ionic liquids, or salts that remain liquid at room temperature. The materials are abundant: The molecular components in this novel class of liquid salts are found in soaps, detergents and even stool softeners.
Xianwen Mao, lead author of the study, had been working in a research group to improve the surface of a supercapacitor’s electrodes .
When the ionic liquids were first tested in a prototype supercapacitor, Mao did not observe any significant improvement in energy storage capacity.
But he didn’t abandon the idea. Noticing that the liquids were quite viscous, he decided to heat up the experiment. At 130 0 C and above, the prototype’s energy storage capacity abruptly spiked.
The researchers looked at what was happening at the electrode-electrolyte interface. It turned out that the giant, negatively charged surfactant ions had corralled the small, positively charged ions into squeezing and huddling on the supercapacitor’s electrodes while their tails intertwined into a network.
Surfactants are known to self-assemble — like when a soap bubble forms. This phenomenon was observed for the first time at the electrode-electrolyte interfaces, Mao said. The high concentration of positively charged ions on the electrode means the supercapacitor packs more energy in less space. The researchers have applied for a patent to use the ionic liquids as supercapacitor electrolytes.