“No other reported structural battery has been compared, in terms of energy density, with today’s modern advanced lithium batteries. We have improved our previous version of structural zinc batteries on 10 different measures, some of which are 100 times better, to make it happen, ‘he continued.
In a study published Wednesday in the journal Science Robotics Kotov points out that not only is the zinc-air battery chemistry that his team uses about three times as energy-dense as your standard Li-Ion brick, but by incorporating the battery into the body of the robot itself, they could 20 percent more space in the interior of the robot than if they had used a conventional power system.
“However, this is not the limit. We estimate that robots could have 72 times more power capacity if their exterior was replaced with zinc batteries, compared to having a single lithium-ion battery, ‘noted first author Mingqiang Wang.
What’s more, this battery design gets to see another tricky variation in other efforts to incorporate batteries into a machine structure: that between the amount of energy the battery can produce and its ability to sustain stress. Normally, electrochemical metal-air batteries use an aqueous solution to separate the cathode and anode. The U of Michigan battery consists of a zinc electrode and a cathode for ambient air separated by a layer of Kevlar fibers suspended in a water-based polymer gel that aids in the transfer of hydroxide ions between the electrodes. Since the separating layers are effectively a solid, they will not break or occur under stress like a liquid separator would. And even if it breaks, the solution is not toxic.
What’s more, the separation layer is so hard that it actually helps to prevent the formation of zinc dendrites, small outgrowths of metal between the electrodes made during the charge-discharge cycle that affect the performance of the battery and degrade life. Lithium-ion batteries can last for about 500 cycles without noticeably destroying, however zinc batteries start to decrease to just 100.
Kotov compares the battery system to fat of human body. Our fat not only stores energy for us, it also provides cushions for our joints and helps maintain body heat. As such, he expects the current single-battery design to eventually evolve into a distributed power storage system. “We do not have a single sarcastic fat that would be bulky and would require a lot of expensive energy transportation,” Kotov notes. “Distributed energy storage, which is the biological way, is the way to go for highly efficient biomorphic devices.”
Kotov hopes to have a commercial battery system ready within the next 3 to 5 years and expects the first buyers to become drone and robot manufacturers. “And it’s not just about the big Amazon robots, but also about very small ones,” Kotov said IEEE Spectrum. “Energy storage is a very important issue for small and flexible soft robots.”
