A gloved hand holds a scorpion-shaped figure.

Smaller, safer batteries for superpowering robots

Robots are becoming increasingly prevalent in modern society. With that comes the search for more efficient and longer-lasting energy sources. Researchers at the University of Michigan are working on a type of battery that could provide 72 times more energy for robot devices. 

How it works

The rechargeable zinc battery integrates into the robot’s body. A critical battery component — the membrane — is made from a nanomaterial based on animals’ cartilage.

Hydroxide ions pass between a zinc electrode and the air side through an electrolyte membrane. The membrane is partially constructed from carbon nanofibers and a new water-based polymer gel. The nanofibers are recycled Kevlar, an extremely strong synthetic fiber found in bullet-proof vests.


The gel and nanofibers do not catch fire if the battery is damaged. That’s a huge safety gain over the electrolyte in traditional lithium-ion batteries that is flammable when the unit is even slightly damaged. 

Developing powerful, small batteries is important as robots shrink to sometimes microscopic scales that are too small for many existing batteries. 

“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,” Nicholas Kotov, an engineering professor at the University of Michigan, said in a news release. “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.”

The battery is considered more environmentally friendly because it is constructed from cheap, abundant materials that are mostly non-toxic. Using zinc also reduces reliance on lithium, an element in declining supply as demand increases.

Most zinc batteries only maintain a high operating capacity for about 100 cycles compared with the 500 cycles for lithium-ion batteries. Zinc batteries form spikes that eventually pierce the membrane and make the battery unusable. But the strong nanofibers used in this design are showing success in preventing the piercing that shortens battery life.

“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, recently a visiting researcher in Kotov’s lab.

What’s next

Kotov says the design could allow a shift from devices getting power from a single battery to using a distributed energy source. 

The scientists will continue to tweak the batteries and their components for use in many kinds of robots. The University of Michigan has applied for patent protection and is seeking commercial partners to bring the product to market.

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