The Zinc-Air battery is the power source for the Vancruiser, UBC’s Chem-E-Car. Zinc-air batteries are similar to conventional cells as they generate power from a chemical reaction. In the case of the Vancruiser, the Zinc-Air battery powers 2 DC motors of a rating of 12V each.
A zinc air battery comprises of a positively charged cathode and a negatively charged anode separated by an electrolytic medium of 6M KOH. Our previous battery was generic: it comprised of zinc gel at the anode, 6M KOH as the electrolyte and a gas diffusion layer as the air cathode. At the Chem-E-Car Regionals competition, we faced an issue with the battery drying out too quickly and not being able to power the motor. After research and troubleshooting, we discovered that the underlying issue with the battery’s poor performance was the composition of the electrolytic gel. Hence, we optimized our battery by slightly modifying its recipe. We now use an organic substance to bind the battery’s electrolyte together, which is our secret (or not so secret anymore) ingredient - Tapioca starch. The tapioca retains water and ensures that the battery does not run out of electrolytic juice. A major advantage is that it does not influence the chemical reaction of the zinc with hydroxyl while ensuring a functional and optimum battery.
The Vancruiser’s battery design and composition is visualized below in a Solidworks animation. This video entails the different components of the battery, and the chemical reaction behind its working.
The Zn-Air Battery system’s components. Each tall stack can hold upto 15 cells, and each cell has a voltage of 1.45V.
Oxygen molecules enter the cell through tiny pores in the top of the cell through a ‘Gas Diffusion Layer’ which has porous carbon fibres, gold-plated nickel current collector and silver catalyst. Theoretically, the Gas Diffusion Layer need not be present, however, as it is coated with a silver catalyst, the rate of the chemical reaction is increased. Water present in the pores of the electrode react with the oxygen to produce hydroxyl ions. These molecules migrate through the electrolytic medium of 6M KOH,water and tapioca paste to a negatively charged anode that consists of zinc gel. The hydroxyls bond to a zinc molecule to form a compound known as zincate - Zn(OH)42- , which immediately splits into two hydroxyls, a water molecule and zinc oxide, and releases two electrons that travel through a circuit to power a device-and in our case, our car’s motor. Vancruiser’s motors receive a voltage of 22V for 2 stacks of 12 cells each.
The Zinc-Air battery is a safe and environmental friendly technology. Zinc-air cells contain no toxic compounds and are neither highly reactive or flammable. They can be recycled, safely disposed of and in our case, recharged with a new zinc gel each trial we prepare the battery. Their only downside is that constant contact with ambient air can dry up the zinc gel, but has been solved by implementing the tapioca binder method. The other downside is that Zinc-Air batteries have a relatively limited output and short active life as compared to commercial favorites such as Lithium-Ion batteries and hence are not so common within industry.
Despite their minor shortcomings, zinc air batteries’ advantages prove that there is a scope for further development into a daily use battery.They are used commercially in hearing aid devices, transmitters and in railway track signals. Electric vehicle companies such as Electric Fuel are developing zinc-air battery technology for automobiles. Researchers are exploring this rechargeable and efficient technology to power the future.
The Vancruiser’s Zinc-Air battery promotes a renewable and alternative source of energy. It has simple modifications to pre-existing zinc-air technologies which make it a unique and viable battery. The Zinc-Air battery for our shoe-box size car stands as a bench-scale prototype for commercial cars and demonstrates the usage of alternative resources as fuel. The UBC Chem-E-Car team hopes the Vancruiser, powered by the Zinc Air battery, drives towards success at the upcoming AiChe Annual Chem-E-Car Competition.
