Massive lithium batteries may have a part to play in grid-scale storage of renewable energy, as we're seeing with the giant Tesla battery in South Australia. But they can also be mighty expensive to set up and carry the risk of fire, as we're seeing with the giant Tesla battery in South Australia. Zinc-based batteries are one of a number of more cost effective, and potentially safer alternatives, and a new breakthrough shows how crab shells might make them a whole lot more sustainable as well.

The demand for energy storage is only expected to grow as we lean more on renewables and electric vehicles for transport, and while the lithium-ion batteries in widespread use today serve us well, there are other architectures with more long-term promise. Mining lithium is expensive and comes with environmental costs, and the batteries that use them don't lend themselves too well to recycling processes.

"Vast quantities of batteries are being produced and consumed, raising the possibility of environmental problems," said lead author Liangbing Hu, director of the University of Maryland's Center for Materials Innovation. "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."

Scientists are exploring many possible alternatives to the tried and trusted lithium-ion architecture, and zinc-based batteries are an option that could be safer, more cost effective and friendlier to the environment. We've seen scientists demonstrate versions of these batteries that offer high power density and can be produced as cheaply as a lead-acid cary battery, for example.

"Zinc is more abundant in Earth's crust than lithium," said Hu. "Generally speaking, well-developed zinc batteries are cheaper and safer."

A major hurdle in this field, however, is the short lifespan suffered by zinc-based batteries, and scientists have placed a big emphasis on developing versions that can be recharged reliably. This might involve chemistry tweaks that prevent water damage, or new electrocatalysts that help maintain their efficiency across repeated cycling. Hu and his team have put another solution on the table which may address the rechargeability issue, and make the devices much more sustainable at the same time.

A zinc battery sends ions traveling back and forth between a zinc anode and cathode in an electrolyte solution as it cycled. Conventional electrolyte solutions in lithium batteries carry flammable and corrosive chemicals, but the authors of this new study developed a gel electrolyte for use with a zinc anode that is made from a natural material called chitosan.

"Chitosan is a derivative product of chitin," said Hu. "Chitin has a lot of sources, including the cell walls of fungi, the exoskeletons of crustaceans, and squid pens. The most abundant source of chitosan is the exoskeletons of crustaceans, including crabs, shrimps and lobsters, which can be easily obtained from seafood waste. You can find it on your table."

In their testing, the team showed a zinc battery using their new electrolyte performed impressively. It prevented the formation of tentacle-like growths that can hamper battery performance and demonstrated "exceptional cycling stability," maintaining an efficiency of 99.7% over 1,000 cycles when operating at a high current density of 50 mAh per square cm.

And because of its eco-friendly design, around two thirds of the battery can be broken down by microbes, while the chitosan electrolyte could be completely broken down within five months. The zinc that is left over can then be recycled.

"In the future, I hope all components in batteries are biodegradable," said Hu.

The research was published in the journal Matter.

Source: Cell Press via ScienceDaily