The new battery, which is 0.1 millimeter long and 0.002 millimeters thick — about the width of a human hair — can pull oxygen from the air and use it to oxidize zinc, creating a current of up to 1 volt. That’s enough to power a small circuit, sensor or actuator, the researchers showed.

“We think this will be a big help for robotics,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT and the study’s lead author. “We’re building robotic functions on top of the battery and starting to assemble these components into devices.”

Ge Zhang PhD ’22 and Sungyun Yang, an MIT doctoral student, are the lead authors of the paper, which was published in Science Robotics.

Battery operated

For several years, Strano’s lab has been working on small robots that can sense and respond to stimuli in their environment. One of the biggest challenges in developing such small robots is making sure they have enough power.

Other researchers have shown that they can power microscopic devices using solar energy, but the limitation of that approach is that the robots must have a laser or other light source pointed at them at all times. Such devices are known as “marionettes” because they are powered by an external power source. By placing a power source such as a battery inside these tiny devices, they can roam much farther.

“The puppet systems don’t really need a battery, because they get all the power they need from outside,” Strano says. “But if you want a small robot to be able to go into spaces that you otherwise wouldn’t be able to get into, it needs to have a higher degree of autonomy. A battery is essential for something that’s not tethered to the outside world.”

To create robots that could become more autonomous, Strano’s lab decided to use a type of battery known as a zinc-air battery. These batteries, which have a longer lifespan than many other types of batteries due to their high energy density, are often used in hearing aids.

The battery they designed consists of a zinc electrode connected to a platinum electrode embedded in a strip of a polymer called SU-8, which is widely used in microelectronics. When these electrodes interact with oxygen molecules in the air, the zinc is oxidized and releases electrons that flow to the platinum electrode, creating a current.

In this study, the researchers showed that this battery can provide enough energy to power an actuator — in this case, a robotic arm that can be moved up and down. The battery can also power a memristor, an electrical component that can store memories of events by changing its electrical resistance, and a clock circuit, which allows robotic devices to keep track of time.

The battery also provides enough power to run two different types of sensors that change their electrical resistance when they encounter chemicals in the environment. One of the sensors is made of atomically thin molybdenum disulfide and the other of carbon nanotubes.

“We’re making the basic building blocks to build functions at the cellular level,” Strano says.

Robotic swarms

In this study, the researchers used a wire to connect the battery to an external device. In the future, however, they want to build robots where the battery is integrated into a device.

“This is going to be at the core of a lot of our robotics efforts,” Strano says. “You can build a robot around an energy source, just like you can build an electric car around a battery.”

One such effort involves designing small robots that can be injected into the human body, where they can seek out a target site and then release a drug such as insulin. For use in the human body, the researchers envision that the devices would be made of biocompatible materials that would break apart when no longer needed.

The researchers are also working on increasing the battery voltage, which could lead to even more applications.

The research was funded by the U.S. Army Research Office, the U.S. Department of Energy, the National Science Foundation, and a MathWorks Engineering Fellowship.