"Biomorphic" Zinc-Air Batteries Could Boost Robots' Energy Storage by Up to 72 Times

Researchers led by the University of Michigan claim that they can boost the battery life of a given robot up to 72 times, by replacing its exterior structure with zinc-based "biomorphic batteries."

"Robot designs are restricted by the need for batteries that often occupy 20 percent or more of the available space inside a robot," explains Professor Nicholas Kotov of the research, "or account for a similar proportion of the robot's weight."

The solution: "structural batteries," which replace parts of the robot's structure while simultaneously storing energy. The only trouble is, structural batteries tend to be too weak to be a robot's sole power source and are typically only used as supplements to a primary lithium-ion or lithium-polymer battery.

The University's work, however, could solve that problem, thanks to breakthroughs in the science of zinc-based structural batteries. "No other structural battery reported is comparable, in terms of energy density, to today's state-of-the-art advanced lithium batteries," Kotov says. "We improved our prior version of structural zinc batteries on 10 different measures, some of which are 100 times better, to make it happen."

These improved batteries, the team claims, could already boost the range of a delivery robot twofold — but have the potential to go still further. "This is not the limit, however," notes first author Mingqiang Wang. "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."

The team's novel batteries are built of a network of aramid nanofibers — the same technology that goes into making Kevlar vests — with a new water-based polymer gel, alongside a zinc electrode. All the material used are low in cost, readily available, and largely non-toxic — meaning the resulting battery is, they claim, environmentally friendly. More importantly, it's safe: If a lithium battery is punctured, it tends to catch fire; the zinc battery, by contrast, will simply leak non-toxic material.

The inspiration for the concept: The animal world, as indicated by the prototype robots being in the shapes of worms and scorpions. "Batteries that can do double duty — to store charge and protect the robot's 'organs' — replicate the multifunctionality of fat tissues serving to store energy in living creatures," explains co-author Ahmet Emre.

"We don't have a single sac of fat, which would be bulky and require a lot of costly energy transfer," adds Kotov. "Distributed energy storage, which is the biological way, is the way to go for highly efficient biomorphic devices."

The team's work has been published under closed-access terms in the journal Science Robotics. The core technology, meanwhile, is being patented for commercial exploitation by the University of Michigan.