Julian Zoller's 3D-Printed Electric Car Draws Its Power From a Homemade Zinc-Air Battery

Maker and chemical engineer Julian Zoller has been working on building his own 3D-printed zinc-air battery — and to prove it works has used the device to power a model car.

"The special thing [with a zinc-air cell] is that we have air as a reaction partner here," Zoller explains, in translation from the original German, of the battery chemistry picked for the project. "That means the cell is open to the ambient air. The cathode, in particular, is open to the ambient air and is made up of three layers or three components: a gas diffusion layer, through which air must pass to reach the active layer; then an electrical conductor, which can be a metal lattice, over which the electrons are conducted, thus establishing good contact with the actual reaction site, so that we have low electrical resistance for the conduction of the electrons; and finally, the active layer."

Most people's hands-on experience with zinc-air chemistry will likely be with tiny coin-cell batteries used for hearing aids and other compact devices, though the technology — which sits somewhere between a traditional chemical battery and a fuel cell — scales all the way up to powering electric vehicles. Zoller's implementation sits somewhere in the middle: it powers an electric vehicle, yes, but a small-scale model rather than something you can drive to the shops.

"Since we're building a battery ourselves," Zoller says in translation, "we have to assume that it might not perform quite as a well as a proper commercial battery. That means we have to expect that it won't deliver a lot of power. Nevertheless, the motor must be able to propel the car despite its low power output. That means we need a motor that operators at low power and still delivers high torque."

The car is propelled along by an N20 reduction-gear motor, which can run from just 40mA at 3V. "Even 3V is an achievable power output with a homemade battery," Zoller explains, again in translation, "when several cells are connected. To reach 3V, we need at least three cells connected in series. And for our 6V, we can have a maximum of five cells. I decided to connect as many cells as possible in series, so that we have a high voltage — simply because it's more efficient to connect more cells in series and you get significantly more power that way. I opted for 8cm² of electrode projection area, with five cells in series. For design reasons, I then reduced that a bit — that means in the end it's only 7.75cm² of electrode projection area."

Despite that reduction, the homemade battery does deliver: the boxy model car does indeed move under the power of the five-cell zinc-air battery, traveling at a speed of 4cm per second (around 1.6" per second) — dropping to a glacial 0.6cm per second (around 0.24" per second) if you connect only a single cell. "A rocket, right," Zoller jokes in translation. "But hey, now we've built a battery ourselves from basic materials available on Amazon, capable of powering a vehicle. That's something, isn't it?"

Zoller goes into considerably more detail in the German-language video embedded above and on his YouTube channel; he has has also released 3D print files for the car on Thingiverse under the reciprocal Creative Commons Attribution-ShareAlike license.