Lithium-ion batteries have taken us a long way in phones, tablets, and even cars over the years, but it’s not a perfect technology
— battery capacity holds us back. Scientists have been on the lookout for an alternative, but nothing has quite panned out yet. There’s been considerable interest around lithium-sulfur batteries in the last few years, and a breakthrough experiment from the Bourns College of Engineering at the University of California, Riverside could make these batteries the next big thing. All it takes is a little glass.
Traditional lithium-ion batteries have found their way into virtually all types of mobile technology, because they have significant energy density and relatively long life. You can charge a li-ion cell a few hundred times before it starts to fail, and there’s no memory effects as with older nickel cadmium and nickel-metal hydride rechargeables. This is where lithium-sulfur still falls short, but not because of the memory effect. They just get dirty.
A fresh, new lithium-sulfur battery can have energy density ten times that of a conventional lithium-ion battery. Imagine a large Android phone with 30,000mAh of juice instead of just 3,000mAh. How fantastic would that be? With current lithium-sulfur technology, that starts dropping off rather quickly as lithium and sulfur reaction products start clogging the works. These products, called lithium polysulfides, dissolve in the electrolyte solution and become stuck at the electrodes. This causes an overall decrease in capacity, and there’s no way to reverse it.
The UC Riverside team found they could prevent this “polysulfide shuttling” by using nano-scale sulfur beads in the battery’s cathode and coating them with SiO2, which you might know as glass. The thickness of this silica sheath is measured in tens of nanometers. It can’t be too thick or it would interfere with the battery’s function. However, it also can’t be too thin, or the glass layer could rupture and allow the formation of lithium polysulfides that damage the structure.
Just coating the sulfur in glass offered substantial improvements in durability, but the coating was still prone to rupture. That breakage issue had to be addressed. Researchers found that incorporating graphene oxide (mrGO) into the cathode added stability and made the nanoparticles less likely to rupture. These cells managed 50 discharge cycles without a substantial decrease in capacity.
Researchers are still falling short of developing the kind of stability you’d need to commercialize a lithium-sulfur battery for consumer technology. Batteries in phones and tablets are increasingly non-removable, so they need to last at least a few years or several hundred cycles. This experiment gets us closer to a battery revolution, but you might want to keep your charging cable handy for now.
