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New zinc batteries can serve as power storage and exterior shell for robots

Image credit: Dreamstime

Robots could store up to 72 times more energy if their exteriors were replaced with a new type of rechargeable battery made from zinc, University of Michigan researchers have said.

In a similar fashion to how biological fat reserves store energy in animals, the zinc batteries can serve as both the structure and the power supply for robots.

Such a system will be particularly important as robots shrink to the microscale and below – scales at which current stand-alone batteries are too big and inefficient.

“Robot designs are restricted by the need for batteries that often occupy 20 per cent or more of the available space inside a robot, or account for a similar proportion of the robot’s weight,” said Professor Nicholas Kotov, who led the research.

“No other structural battery reported is comparable, in terms of energy density, to today’s state-of-the-art advanced lithium batteries. We improved our prior version of structural zinc batteries on 10 different measures, some of which are 100 times better, to make it happen.”

He believes the combination of energy density and inexpensive materials means that the battery may already double the range of delivery robots for example.

The new battery works by passing hydroxide ions between a zinc electrode and the air side through an electrolyte membrane.

That membrane is partly a network of aramid nanofibers – the carbon-based fibres found in Kevlar vests – and a new water-based polymer gel. The gel helps shuttle the hydroxide ions between the electrodes.

Made with cheap, abundant and largely non-toxic materials, the battery is more environmentally friendly than those currently in use and the gel and aramid nanofibers will not catch fire if the battery is damaged, unlike the flammable electrolyte in lithium-ion batteries.

To demonstrate their batteries, the researchers experimented with regular-sized and miniaturised toy robots in the shape of a worm and a scorpion. The team replaced their original batteries with zinc-air cells then wired the cells into the motors and wrapped them around the outsides of the creepy crawlers.

“Batteries that can do double duty – to store charge and protect the robot’s ‘organs’ – replicate the multifunctionality of fat tissues serving to store energy in living creatures,” said doctoral student Ahmet Emre.

The researchers estimate that robots could hold 72 times more power if their exteriors were replaced with zinc batteries, instead of using a single lithium-ion battery.

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