Engineers design tiny batteries to power cell-sized robots

A tiny battery designed by MIT engineers could enable the deployment of cell-sized autonomous robots to deliver drugs to the human body, as well as other applications such as locating leaks in gas pipelines.

The new battery, which is 0.1 millimeter long and 0.002 millimeter thick (about the thickness of a human hair), can capture 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 is going to be very beneficial for robotics,” says Michael Strano, a professor of chemical engineering at MIT and lead author of the study. “We’re building robotic functions on the battery and starting to assemble those components into devices.”

Ge Zhang, Ph.D., and Sungyun Yang, a graduate student at MIT, are the lead authors of the paper, which appears in Scientific robotics.

Powered by batteries

For several years, Strano’s lab has been working on tiny robots that can sense and react to stimuli in their environment. One of the main challenges in developing these small robots is ensuring that they have enough energy.

Other researchers have shown that they can power small devices with solar energy, but this approach is limited by the fact that the robots must be constantly pointed at them by a laser or other light source. These devices are called “puppets” because they are controlled by an external power source. Inserting a power source such as a battery inside these tiny devices could allow them to move much further.

“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 access spaces that you wouldn’t be able to access otherwise, it needs to have a greater level of autonomy. A battery is essential for something that’s not going to be tethered to the outside world.”

To create more autonomous robots, Strano’s lab decided to use a type of battery called a zinc-air battery. These batteries, which have a longer lifespan than many other types of batteries because of 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 polymer called SU-8, commonly used in microelectronics. When these electrodes interact with oxygen molecules in the air, the zinc oxidizes and releases electrons that flow to the platinum electrode, creating a current.

In this study, the researchers showed that this battery could provide enough energy to power an actuator, in this case a robotic arm that can be raised and lowered. The battery could 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 from atomically thin molybdenum disulfide and the other from carbon nanotubes.

“We make the building blocks to create functions at the cellular level,” Strano explains.

Robotic swarms

In this study, the researchers used a wire to connect their battery to an external device, but in future work, they plan to build robots in which the battery is integrated into a device.

“This will be the core of a lot of our robotics efforts,” Strano says. “You can build a robot around a power source, much like you can build an electric car around a battery.”

One such effort involves designing tiny robots that could be injected into the human body, where they could seek out a target site and then release a drug such as insulin. For use in the human body, researchers envision the devices being made from biocompatible materials that would break down once they were no longer needed.

Researchers are also working on increasing the battery voltage, which could enable additional applications.

This article is republished with kind permission from MIT News (web.mit.edu/newsoffice/), a popular site covering the latest research, innovation, and teaching at MIT.