Researchers at the University of Michigan have developed a rechargeable zinc battery that integrates into the structure of a robot to provide much more energy.
The 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 nanofibres -- 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 nontoxic materials, the battery is more environmentally friendly than those currently in use. The gel and aramid nanofibers will not catch fire if the battery is damaged, unlike the flammable electrolyte in lithium ion batteries. The aramid nanofibers could be upcycled from retired body armor.
This approach to increasing capacity 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 percent 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. The university has applied for a patent on the technology.
Applications for mobile robots are exploding, from delivery drones and bike-lane take-out bots to robotic nurses and warehouse robots. On the micro side, researchers are exploring swarm robots that can self-assemble into larger devices. Multifunctional structural batteries can potentially free up space and reduce weight, but until now they could only supplement the main battery.
"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," said Kotov.
The combination of energy density and inexpensive