Lithium-ion (Li-ion) batteries are everywhere these days: laptops, cars, power tools, and cellphones, including Samsung’s infamous smoldering Galaxy Note 7. Now, researchers have come up with a new way to prevent these rechargeables from going haywire—a zinc-nickel battery that provides nearly the same electrical jolt, but not the fire risk of Li-ion cells. The new batteries—still in development—could one day power devices as varied as consumer electronics and hybrid cars.
Zinc batteries are surprisingly old-school. Standard nonrechargeable alkaline batteries have one electrode of zinc and another of manganese dioxide. They’re safe because they contain a nonflammable, water-based electrolyte that helps ferry charges through the battery. Lithium cells instead require a flammable organic electrolyte to prevent side reactions that can kill the batteries. Scientists have come up with all sorts of schemes to stop those cells from catching fire, like adding flame retardants.
They’ve also searched for ways to make zinc-based batteries rechargeable. In addition to being safer, zinc is far more abundant, and thus cheaper, than lithium. But previous zinc-based rechargeables suffer from a major drawback: Repeated cycles of charging and discharging cause zinc atoms to pile up on one of the electrodes. That causes the growth of “dendrites,” tiny zinc spears that can pierce other parts of the battery, causing it to short-circuit and fail.
Getting rid of those battery-killing dendrites isn’t easy. To make a powerful battery, the negative zinc electrode, or anode, needs a large surface area for the chemical reactions that take place during charging and discharging. Scientists get that large area by making the electrode porous, starting with particles in a fine zinc powder that they press together and secure in place with chemical binders. The trouble is that the zinc in those electrodes winds up unevenly distributed. As a result, the electric field in the battery spikes at particular spots during charging, drawing zinc atoms to deposit at those sites. And once a dendrite is born, the problem only snowballs with each additional cycle.
To get around that issue, Debra Rolison, a chemist at the Naval Research Laboratory in Washington, D.C., led researchers in a project to make a 3D zinc sponge electrode. The scientists started with the same zinc powder, but they mixed it with a blend of water and oillike organic compounds, creating a gray slurry that they could pour into a mold of their choice. They then dried and heated their material, which solidifies into a uniform, porous zinc framework. When wired into a battery, the spongelike anode lacks hot spots thanks to its uniformity and thus prevents dendrites from forming.
Rolison and her colleagues are now doing extensive testing on their zinc rechargeables. In the new study, published today in Science, they find that the batteries can complete more than 100 charge and discharge cycles when designed to provide roughly the same amount of energy as Li-ion cells. In a separate design common in hybrid vehicles—in which a small amount of power is discharged and then instantly recharged—the researchers showed that their batteries could cycle up to 50,000 times with no dendrite formation.
“It’s an important development with tremendous potential,” says Héctor Abruña, a chemist at Cornell University who was not involved in the work. Not only would future zinc-based rechargeables be safer than their lithium counterparts, but the cheap cost of zinc could drive its use in many applications.
To speed up that process, Rolison and her colleagues have licensed their technology to EnZinc Inc., a startup in San Anselmo, California, that is developing batteries for hybrid cars, electric bikes, and wearable electronics. If the company succeeds, zinc rechargeables may soon set the battery world on fire—just not themselves.