Supercapacitors cost rapidly however retailer little vitality as a result of all of the motion takes place solely on the interface the place its strong elements — the electrodes — and its liquid part — the electrolyte — meet. In distinction, a battery brings its cost contained in the electrodes and thus makes use of the total quantity of the electrodes for storage.
“Think of an electrode as a sponge,” mentioned Dr. Schwartz, who was not concerned within the examine. “The battery soaks water up into all of the sponge, whereas the supercapacitor just has it on the surface of each pore.”
Xianwen Mao, a chemical engineer at Cornell University and the lead writer of the examine, had been working in a analysis group led by Alan Hatton on the Massachusetts Institute of Technology to enhance the floor of a supercapacitor’s electrodes. But then, a few years in the past, Paul Brown, a chemist who studied ionic liquids, labored with Dr. Mao to deal with creating new electrolytes as a substitute.
In the M.I.T. lab, Dr. Brown ready new ionic liquids from positively and negatively charged ions that have been considerably completely different in dimension. Crucially, the negatively charged ions have been additionally widespread surface-active brokers, or surfactants: large molecules carrying a lengthy, water-repelling tail whereas holding their destructive cost on their water-loving heads.
When the ionic liquids have been first examined in a prototype supercapacitor, Dr. Mao didn’t observe any vital enchancment in vitality storage capability. But he didn’t abandon the thought. Noticing that the liquids have been fairly viscous, he determined to warmth up the experiment. At 130 levels Celsius and above, the prototype’s vitality storage capability abruptly spiked.
To perceive this sudden enchancment in vitality storage capability, the researchers checked out what was taking place on the electrode-electrolyte interface. It turned out that the enormous, negatively charged surfactant ions had corralled the small, positively charged ions into squeezing and huddling on the supercapacitor’s electrodes whereas their tails intertwined into a community.
Surfactants are recognized to self-assemble — for instance, when a cleaning soap bubble kinds. This self-assembly phenomenon was noticed for the primary time on the electrode-electrolyte interfaces, Dr. Mao mentioned.