The electrolyte fluid in aluminium batteries is extremely aggressive and corrodes stainless steel, and even gold and platinum, so finding a corrosion-resistant materials for the conductive parts of these batteries is essential. The first development is a corrosion-resistant material for the conductive parts of the battery; the second is a novel material for the battery’s positive pole that can be adapted to a wide range of technical requirements.
Maksym Kovalenko, Professor of Functional Inorganic Materials and his team at ETH found that titanium nitride, a ceramic material that exhibits sufficiently high conductivity. “This compound is made up of the highly abundant elements titanium and nitrogen, and it’s easy to manufacture,” said Kovalenko.
The team have successfully made aluminium batteries with conductive parts oated in titanium nitride in the lab. The material can easily be produced in the form of thin films, also as a coating over other materials such as polymer foils. Kovalenko believes it would also be possible to manufacture the conductors from a conventional metal and coat them with titanium nitride, or even to print conductive titanium nitride tracks on to plastic. “The potential applications of titanium nitride are not limited to aluminium batteries. The material could also be used in other types of batteries; for example, in those based on magnesium or sodium, or in high-voltage lithium-ion batteries,” he said.
The second new material can be used for the positive electrode of aluminium batteries. Whereas the negative electrode in these batteries is made of aluminium, the positive electrode is usually made of graphite. Kovalenko and his team used polypyrene, a hydrocarbon with a chain-like molecular structure instead, which is particularly effective when the molecular chains congregate in a disorderly manner. “A lot of space remains between the molecular chains. This allows the relatively large ions of the electrolyte fluid to penetrate and charge the electrode material easily,” said Kovalenko.
One of the advantages of using polypyrene is that the team could adjust properties such as porosity to adapt for particular application. “In contrast, the graphite used at present is a mineral. From a chemical engineering perspective, it cannot be modified,” said Kovalenko.
As both titanium nitride and polypyrene are flexible materials, the researchers believe they are suitable for use in traditional pouch cells.