Batteries with conformal shape and multiple functionalities could provide new degrees of freedom in the design of robotic devices. However, the current stand-alone batteries are too large, often inefficient, and can add significant mass to any robot design.
Now, a group of researchers from the University of Michigan has demonstrated a new rechargeable zinc-air battery that integrates directly into the structure of a robot to provide much more energy than conventional lithium-ion batteries, in addition to reducing weight and occupy less space. The principle of energy storage in ‘biological fat reserves’ in animals was taken as a basis. As a result, a completely new type of battery was created that is capable of providing 72 times more energy.
“Robot designs are restricted by the need for batteries that often occupy 20% or more of the available space inside a robot, or account for a similar proportion of the robot’s weight,” said Nicholas Kotov, the Joseph B. and Florence V. Cejka Professor of Engineering, who led the research.
Previously, no other structural battery could match the energy density of today’s state-of-the-art advanced lithium batteries, Kotov said. To achieve this, scientists have improved the previous version of zinc batteries in 10 different parameters, some of which have improved their performance by a factor of 100 or more.
Made with cheap, environmentally friendly, abundant, and largely nontoxic materials, the new zinc battery works by passing hydroxide ions between a zinc electrode and the air side through an electrolyte membrane. The membrane is mainly composed of aramid nanofibers – the carbon-based fibers found in Kevlar vests – and a new water-based polymer gel, which helps transfer the hydroxide ions between the electrodes. The composites enable pliable zinc-air batteries with cyclic performance exceeding 100 hours that can also serve as protective covers in various robots, including soft and flexible miniaturized robots.
Unlike the flammable electrolyte in lithium-ion batteries, the gel and nanofibers will not catch fire if the battery is damaged. Mingqiang Wang, the first author of the research, estimates that the total capacity of these body-integrated structural batteries is 72 times greater compared with a stand-alone Li-ion battery with the same volume.
“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.
Researchers have already tested their creation on regular-sized and miniaturized toy robots in the shape of a worm and a scorpion. The new zinc batteries were attached to the motors and wrapped them around the outsides of the creepy crawlers, as a video from the University of Michigan shows.
The research suggests that biomorphic batteries could provide much more power to robots, making them more efficient and functional.
- Biomorphic structural batteries for robotics. DOI: 10.1126/scirobotics.aba1912