Chemists developed ionic liquids similar to laxatives to enhance the performance of electrolytes used in today's supercapacitors.
While basically all salts melt, some have extremely high melting points. For instance, sodium chloride’s melting point is around 801 degrees Celsius. On the other hand, other organic salts have low melting points that they could melt even at room temperature, turning into liquids called ionic liquids.
Some could even melt at temperatures below 0 degrees Celsius. Usually, scientists take water’s boiling point (100 °C) as an arbitrary point of reference to restrict the term.
These salt-like materials have unique chemical and physical properties, allowing them to serve a wide range of chemical applications. These include solvents and lubricants, fuel cells, batteries, and heat storages, to name a few.
Another important potential use of ionic liquids is in supercapacitors.
Viscous Ionic Liquids, Better Electrolytes
Supercapacitors are energy storage devices that work on electrolytes which, naturally present in the human body, can be liquid or solid, or something in between. Electrolytes can also be viscous, as new research shows, along with other new and strange properties that could be harnessed for more efficient energy storage technologies.
An international team of chemists obtained highly viscous electrolyte material by adding a compound “similar to a surfactant, like those used to disperse oil spills.” According to the researchers, these surface-active ionic liquids (SAILs) outperform other known electrolytes and can turbocharge supercapacitors.
“It’s hard to imagine that this viscous liquid could be used for energy storage,” says MIT postdoctoral student Xianwen Mao, the lead author of the paper.
“But what we find is that once we raise the temperature, it can store more energy, and more than many other electrolytes.”
With current electrolyte materials, they lose their viscosity as temperature increases, but in this case, the viscosity and energy-storage capacity increase with increasing temperature.
The reason for the viscous ionic liquids to behave in this way is because of molecules that intrinsically assemble themselves in sandwich-like, double-layered structure.
“We engineered a new class of ionic liquids that can store energy more efficiently,” Mao says. “These detergent-like ionic liquids can self-assemble into sandwich-like bilayer structures on electrode surfaces. And that is the very reason why they give better energy storage performance.”
This highly ordered structure helps prevent “overscreening,” a phenomenon that naturally emerges in conventional electrolytes, causing ion scattering. In other words, less efficiency in energy storage.
These ionic liquids could be a better alternative to conventional electrolytes because they have high energy densities, safe (non-flammable), stable, and are more environmentally friendly.
Results show that supercapacitors running on SAILs could see their energy density increased by a factor of four or five. The researchers claim that SAIL-powered capacitors could potentially replace batteries in electronics, electric cars, and large-scale energy storage facilities in the future.
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