Printable polymers for (future) biodegradable batteries

What if, instead of a rigid chunk of lithium-ion, your phone was charged by a flexible, printable battery? And what if, once it had seen out its lifespan, that battery were biodegradable?

According to a group of Australian and Chinese researchers, this is possible with technology they’re working on. Such batteries would probably only ever be powerful enough to charge small devices – they couldn’t compete with lithium-ion to run a car. But, at least in the lab, they’re rivalling lithium-ion already at the small scale.

The research revolves around organic radical batteries, or ORBs. These batteries rely on an organic (carbon-containing) polymer to store and transport electrons.

They don’t require any metals to make. So, while the battery materials aren’t currently biodegradable, it should be possible to create them from a biodegradable material. They can also bend and flex, unlike traditional brittle batteries, and can be made from liquids with a process that’s not unlike printing.

ORBs aren’t a new concept, but previously they’ve had several features that are inferior to commercial batteries, according to Dr Zhongfan Jia, a researcher in chemistry at Flinders University in Adelaide.

The first is the batteries’ voltage: the force with which they can discharge power.

“The higher the voltage, that means you can store a lot of energy,” says Jia.

“It’s like a water reservoir dam.”

If you’re using a dam to generate hydroelectricity, the higher the dam, the greater the pressure and thus the more electricity you can generate.

“The height of the dam is like our voltage,” says Jia.

The next problem is capacity – what we might think of as storage.

“The bigger your reservoir, it can last a longer time when you release the water to generate electricity,” explains Jia.

“Capacity is how much energy you can put in.”

The third issue is power density.

“If you think about a car – a general car maybe takes 30 or 40 seconds to accelerate from 0km/h to 100km/h. But if you have a fancy racing car, it might be accelerated from 0 to 100km/h within six or seven seconds. That difference is related to the power density,” says Jia.

Jia and colleagues have found a catalyst that that allows these batteries to compete with lithium-ion in both voltage and storage capacity.

“Catalysis has been widely used in lithium-based batteries such as lithium-oxygen batteries and lithium-sulphur batteries to improve their energy and power performance,” says Jia.

The researchers described a prototype battery with a voltage of 2.8 V, published in Chemical Engineering Journal. This is one of the highest voltages ever reported in an ORB.

And, over in ACS Energy Letters, they’ve explained how their catalyst nearly doubles the ORB’s capacity. This makes it comparable with commercial lithium-ion – although Jia cautions that it’s unwise to assume a lab prototype will be as good when made industrially.

“When you make something from the laboratory into a commercial product, the properties usually will reduce a little bit – because you are not dealing with small scale. You need the engineering to come in and make it industrial scale,” he says.

Nevertheless, the researchers are excited by their progress, and are seeking funding to take the project further.

“We will use this concept or this idea to make – to create – a polymer that can be biodegradable. And if the polymer can be degradable, then eventually the battery material can also be degradable. That’s the next stage,” says Jia.

If they can get funding, Jia believes they could develop a prototype biodegradable battery in one or two years.

“That battery may be not comparable to the lithium batteries, but it might be able to be used in certain scenarios that you don’t need that high capacity, and you just want to power some small devices, and then afterwards just discard it,” he says.

If there’s enough commercial interest, such a battery could be available in five to 10 years.

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