Transcript
New research published in the journal Science Robotics, describes how a new kind of rechargeable zinc battery can be integrated into the body of a robot providing far more energy than traditional lithium-ion batteries. This approach to increasing capacity will be particularly important as robots shrink to the microscale at which point current stand-alone batteries become too big and inefficient.
According to the researchers, robot designs are restricted by the need for batteries that often occupy 20 percent or more of the available space inside the robot, and account for an even greater proportion of the robot’s weight.
Today, applications for mobile robots range from delivery drones to bike-lane take-out bots to robotic nurses to warehouse robots. On the micro-side, researchers are exploring swarm robots that can self-assemble into larger devices. For these applications, multifunctional structural batteries can potentially free up space and reduce weight, but until now they could only supplement the main battery.
But this breakthrough changes all that. The combination of energy density and inexpensive materials in these zinc batteries means that they may already double the range of delivery robots. And this is not the limit. The researchers 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.
The new battery works by passing hydroxide ions between a zinc electrode and the airside through an electrolyte membrane. That membrane is partly a network of carbon-based nanofibers 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 nanofibers will not catch fire if the battery is damaged, unlike the flammable electrolyte in lithium-ion batteries. And the nanofibers could be recycled from retired body armor, further reducing costs.
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.
As such, these batteries can do double duty: storing energy and protecting the robot’s internal components, such as processors and motors.
The downside of zinc batteries is that they only maintain high capacity for about 100 cycles, rather than the 500 or more cycles that we expect from lithium-ion batteries. This is because the zinc metal forms spikes that eventually pierce the membrane between the electrodes. But fortunately, the low-costs and recyclable nature of zinc batteries make them easy to replace, as needed.
Beyond the advantages of the battery’s chemistry, the design could enable a shift from a single battery to distributed energy storage. Distributed energy storage, avoids complex wiring and a single point of failure.
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