A team of researchers led by the University of Michigan has shown that a new rechargeable zinc battery can be integrated into the structure of a robot to provide much more energy. This biomorphic battery in robots will be just like energy-storing fat reserves in humans.
The Concept Explained
All the animals store energy in the form of fat in various parts of our body whereas robots typically have one battery where all the energy is stored. With the new zinc batteries, robots also can have energy stored in various parts of its body.
“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.
Today, there is a lot of demand for moving robots for a variety of applications right from delivery drones to warehouse robots. Thus we need new ways to improve the efficiency, battery life, size, and weight of the robot.
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,” Kotov said.
According to Kotov, the energy density and cheap material means that the battery may already double the range of delivery robots.
“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.
Working of the New Battery
It works by passing hydroxide ions between a zinc electrode and the airside through an electrolyte membrane.
The electrolyte membrane is made up of a network of aramid nanofibers (the carbon-based fibers found in Kevlar vests) and a new water-based polymer gel. The gel helps take the hydroxide ions between the electrodes.
This new battery has many advantages like
1. It is made of cheap materials.
2. It is made up of non-toxic and environmentally friendly materials.
3. It doesn’t catch fire like lithium batteries.
To demonstrate their batteries, the researchers experimented with 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 covered them around the outsides of the creepy crawlers.
“Batteries that can do double duty, one to store charge and second to 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.
As every coin has two sides, there are downsides of zinc batteries as well. One is that these batteries maintain high capacity for about 100 cycles, rather than the 500 or more that we expect from the lithium-ion batteries in our smartphones.
The low life is because the zinc metal forms spikes that eventually pierce the membrane between the electrodes. But researchers have tried to solve this problem to some extent. The strong aramid nanofiber network between the electrodes was added to relatively increase 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.
“We don’t have a single sac of fat, which would be bulky and require a lot of costly energy transfer,” Kotov said. “Distributed energy storage, which is the biological way, is the way to go for highly efficient biomorphic devices.”
Biomorphic structural batteries for robotics, Science Robotics (2020): robotics.sciencemag.org/content/5/45/eaba1912