Scientists make biodegradable batteries from crabs

There are those who say that ours is the age of the battery. New and improved batteries, perhaps more than anything else, have made possible a world of mobile phones, smart devices and burgeoning fleets of electric vehicles. Clean-energy power grids may soon depend on server farm-sized battery projects with massive storage capacity.

But our batteries aren’t perfect. Even if one day they are the foundation of a world that is sustainable, today they are made of materials that are not. They rely on heavy metals or inorganic polymers that can take hundreds of years to degrade. This is why battery disposal is such a difficult task.

Enter researchers at the University of Maryland and the University of Houston, who made a battery out of a promising alternative: crustacean shells. They’ve taken biological material, easily obtained from the same crabs and squid you can eat, and made it into a partially biodegradable battery. They published their results in the journal matter on September 1.

This is not the first time batteries have been made from this material. But what makes the researchers’ work new is the design, according to Liangbing Hu, a materials scientist at the University of Maryland and one of the paper’s authors.

A battery has three key components: two ends and a conductive filling called an electrolyte. In short, charged particles crossing the electrolyte discharge a steady stream of electric current. Without an electrolyte, a battery would just be a sitting shell of electrical charge.

Today’s batteries use a range of electrolytes, and there are few things you’d want to put in your mouth. A standard AA battery uses potassium hydroxide paste, a dangerously corrosive substance that makes throwing batteries in the trash a very bad idea.

[Related: This lithium-ion battery kept going (and going and going) in the extreme cold]

The rechargeable batteries in your phone are a completely different kind of battery: lithium-ion batteries. These batteries can be powered for many years and typically rely on plastic and polymer-based electrolytes that are not as toxic, but can still take centuries or even millennia to degrade.

Batteries themselves, filled with environmentally unfriendly materials, are not the most environmentally friendly. They are also rarely produced in a sustainable manner, relying on the extraction of rare earth elements. Even if batteries can withstand thousands of discharges and recharges, thousands more are thrown away every day.

So researchers are searching through oceans of materials for a better alternative. In doing so, they have begun digging up parts of crustaceans. From crabs, shrimps and lobsters, battery makers can extract a material called chitosan. It is a derivative of chitin, which also makes up the hardened exoskeletons of crustaceans and insects. There’s plenty of chitin to go around, and a relatively simple chemical process is all that’s needed to turn it into chitosan.

We already use chitosan for quite a few applications, most of which have little to do with batteries. Since the 1980s, farmers have been sprinkling their crops with chitosan. It can stimulate plant growth and strengthen their defenses against fungal attacks.

[Related: The race to close the EV battery recycling loop]

Away from the fields, chitosan can remove particles from liquids: treatment plants use it to remove sediment and impurities from drinking water, and alcohol producers use it to clarify their drink. Some dressings come with chitosan, which helps seal wounds.

You can also sculpt things from chitosan gel. Because chitosan is biodegradable and non-toxic, it is especially good for making things that need to enter the human body. It’s entirely possible that hospitals of the future will use specialized 3D printers to cut chitosan into tissues and organs for transplants.

Now researchers are looking to put chitosan into batteries whose ends are made of zinc. Largely experimental today, these rechargeable batteries could one day form the backbone of an energy storage system.

The Maryland and Houston researchers weren’t the first to think about turning chitosan into batteries. Scientists around the world, from China to Italy to Malaysia to Iraqi Kurdistan, have been playing with crabs for about a decade, unraveling them into a complex web that charged particles can traverse like adventurers.

The authors of the new work added zinc ions to this chitosan structure, which enhanced its physical strength. In combination with the zinc ends, the additive also increases the efficiency of the battery.

This design means that two-thirds of the battery is biodegradable; the researchers found that the electrolyte completely degraded in about five months. Compared to conventional electrolytes and their millennia-long landfill lifetimes, Hu says, they have a slight disadvantage.

And although this design was made for these experimental zinc batteries, Hu sees no reason why researchers can’t extend it to other types of batteries — including the one in your phone.

Hu and his colleagues are now continuing their work. One of their next steps, Hu says, is to expand their focus beyond the confines of the electrolyte to the other parts of the battery. “We will pay more attention to the design of a fully biodegradable battery,” he says.

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