"This is not the limit, however. We estimate that robots could have 72 times more power capacity if their exteriors were replaced with zinc batteries, compared to having a single lithium ion battery," said Mingqiang Wang, first author and recently a visiting researcher to Kotov's lab.To demonstrate their batteries, the researchers experimented with regular-sized and miniaturized toy robots in the shape of a worm and a scorpion. The team replaced their original batteries with zinc-air cells. They 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 Ahmet Emre, a doctoral student in biomedical engineering in Kotov's lab.
The downside of zinc batteries is that they maintain high capacity for about 100 cycles, rather than the 500 or more from lithium ion batteries. This is because the zinc metal forms spikes that eventually pierce the membrane between the electrodes. The strong aramid nanofiber network between the electrodes is the key to the relatively long cycle life for a zinc battery and the inexpensive and recyclable materials make the batteries easy to replace.
Beyond the advantages of the battery's chemistry, Kotov says that the design could enable a shift from a single battery to distributed energy storage, using graph theory approach developed at U-M.
A paper on this research is to be published in Science Robotics, titled, "Biomorphic structural batteries for robotics."
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