Incorporating batteries into the structure of electric vehicles and drones has long been a goal of designers and engineers, as it has the potential to reduce weight and extend range. However, placing a battery into the bumper of a car or the wing of drone has obvious safety implications. Published in the journal ACS Nano, the research describes a rechargeable zinc battery with a cartilage-like solid electrolyte that is resistant to damage.
"A battery that is also a structural component has to be light, strong, safe and have high capacity,” said research lead Nicholas Kotov, a Professor of Chemical and Materials Science Engineering at Michigan. “Unfortunately, these requirements are often mutually exclusive."
Zinc is an established structural and battery material, but the rigid dendrites it forms on repeated recharge cycles have seen the metal largely confined to single-use batteries. To overcome the dendrite problem, Kotov’s team developed a solid electrolyte from a composite of branched aramid nanofibres (BANFs) and poly(ethyleneoxide). Based on the structure of cartilage, the BANFs mimic the tissue’s tough collagen and resist penetration from dendrites, while the poly(ethyleneoxide) replicates the cartilage’s softer components and allows zinc ions to flow between the battery’s two electrodes.
"Nature does not have zinc batteries, but it had to solve a similar problem," Kotov said. "Cartilage turned out to be a perfect prototype for an ion-transporting material in batteries. It has amazing mechanics, and it serves us for a very long time compared to how thin it is. The same qualities are needed from solid electrolytes separating cathodes and anodes in batteries."
According to the research, the prototype battery can run for more than 100 cycles at 90 per cent capacity. As secondary batteries on drones, the zinc cells can extend the flight time by 5 to 25 per cent, depending on the battery size, mass of the drone and flight conditions. After piercing the battery with a knife multiple times to demonstrate its durability, the team found it continued to discharge close to its design voltage. Kotov's team now intends to explore whether there is a better partner electrode that could improve the speed and longevity of the structural batteries.
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