It’s one of the weirder laws of nature: everything eventually ends up as crabs. And in this modern age, it seems nature is moving with the times – because the next thing to get crabby might just be your e-vehicle.
“Rechargeable aqueous Zn [zinc] metal battery is promising for grid energy storage needs, but its application is limited by issues such as Zn dendrite formation,” explains a new paper, published yesterday in the journal Matter. “In this work, we demonstrate a Zn-coordinated chitosan (chitosan-Zn) electrolyte for high-performance Zn-metal batteries.”
To understand what’s going on here, we need to know a little bit about how batteries work – and what the problem with the current (ha ha) models are. At its most basic, a battery consists of three things: an anode, a cathode, and an electrolyte layer connecting the two.
When a battery is discharging, what’s actually going on is a chemical process called an oxidation reaction: charged ions are released from the anode – the negative terminal of the battery, often made from zinc – through the electrolyte to the cathode, or positive terminal. All this happens while a stream of electrons moves through an external circuit, which balances the system and provides the electrical current that powers your flashlight, phone, or limited edition Nintendo Virtual Boy console.
But our sheer reliance on these tiny chemical reactors can have a profound effect on the planet. “Vast quantities of batteries are being produced and consumed, raising the possibility of environmental problems,” explained Liangbing Hu, director of the University of Maryland’s Center for Materials Innovation and lead author of the new paper, in a statement.
“For example, polypropylene and polycarbonate separators, which are widely used in Lithium-ion batteries, take hundreds or thousands of years to degrade and add to environmental burden.”
But as the climate apocalypse grows ever closer, we’re not likely to be giving batteries up any time soon – quite the opposite, in fact. Five years from now, it’ll be as cheap to buy an electric car as a gas-fueled one, and we can already fly in electric planes and race electric speedsters in the desert. So clearly, another solution is needed.
And Hu’s team think they have the answer: crabs. Or, more specifically, chitosan – a biological material that can serve as a fully biodegradable electrolyte.
“Chitosan is a derivative product of chitin,” said Hu. “Chitin has a lot of sources, including the cell walls of fungi… and squid pens.”
But “the most abundant source of chitosan is the exoskeletons of crustaceans,” he explained. That “includ[es] crabs, shrimps and lobsters, which can be easily obtained from seafood waste. You can find it on your table.”
As ecological innovations go, it sounds rather Monty Burns-esque – but it might just work. A chitosan electrolyte layer can be almost entirely broken down by microbes within just five months, leaving just the metal of the battery behind. Using zinc, rather than lithium or lead, means that metal is highly recyclable: “Zinc is more abundant in earth’s crust than lithium,” said Hu.
“Generally speaking, well-developed zinc batteries are cheaper and safer,” he added.
And not only is this zinc-chitosan battery more ecologically sound, it’s also just … better. Experiments found the prototype to have an energy efficiency of 99.7 percent after 1,000 battery cycles – quite an improvement on the 70-75 percent efficiency usually considered exceptional for zinc batteries.
That high efficiency also means the new battery is an option for storing energy generated by wind and solar for transfer to power grids, further improving its green credentials. But Hu isn’t done yet: he has designs to make the battery even more eco-friendly – from the manufacturing process up.
“In the future, I hope all components in batteries are biodegradable,” he said. “Not only the material itself but also the fabrication process of biomaterials.”