Aerobic electric cars

In contrast to conventional Li–ion batteries, metal–air batteries use oxygen from the surrounding air rather than that stored in chemicals in the battery itself. This decreases weight and mass and also increases energy density, or the energy delivered compared to the size of the battery. Despite their benefits, making rechargeable versions of metal–air batteries has been difficult and they are currently only available as primary units.

The EU-funded project 'New concept of metal-air battery for automotive application based on advanced nanomaterials' (NECOBAUT) is developing an iron–air battery exploiting low-cost nano-structured carbon electrode materials and a potassium hydroxide electrolyte. The main market sector is fully electric vehicles.

For the anode side, the team investigated various iron carbide nano-structured materials supported on high-surface carbon prepared by a project partner. Additives were included to minimise hydrogen evolution and enhance charging efficiency.

Several catalysts for the air side (cathode) were tested, including innovative perovskite materials developed in the project. These were evaluated on both commercial carbon supports and on project carbon. Perovskite supported on project carbon was the most promising catalyst.

Iron and air electrodes have been manufactured and assembled in a novel metal–air battery cell in which the electrolyte is circulated to dissipate heat and remove gases. A separator prevents internal short circuits and improves safety.

Preliminary tests demonstrate its potential to meet energy density goals so the team is now conducting studies to charge the cell at higher current densities. A cell model is aiding in optimisation of designs.

Optimisation of all materials and components under a number of operating conditions during the next period will facilitate design of the final prototype. It is planned to have higher electrode energy capacities and enhanced corrosion resistance, among other improvements. A low-cost and durable alternative to Li–ion batteries that can take all-electric cars farther before recharging will have major impact. Widespread market uptake of such vehicles will have important benefits for manufacturers, consumers and the environment.