ETH Zurich researchers have developed a new conductor material and a new electrode material that could make inexpensive batteries for the large-scale storage of renewable energy.

The potential of intermittent generating resources depends on technologies that allow the inexpensive temporary storage of electricity. A promising new candidate is aluminum batteries that are made from cheap and abundant raw materials.

Functional scheme of the aluminum batteries by the ETH Zurich and Empa researchers. Image Credit: Walter M et al. ETH Zurich. Click image for the largest view.

Maksym Kovalenko, Professor of Functional Inorganic Materials led a term of scientists from ETH Zurich and Empa involved in researching and developing batteries of this type. The researchers have now identified two new materials that could bring about key advances in the development of aluminum batteries.  The research results have been published in the journal Advanced Materials.

The first 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.

Because the electrolyte fluid in aluminum batteries is extremely aggressive and corrodes stainless steel, and even gold and platinum, scientists are searching for corrosion-resistant materials for the conductive parts of these batteries. Kovalenko and his colleagues have found what they are looking for in titanium nitride, a ceramic material that exhibits sufficiently high conductivity.

Kovalenko explained, “This compound is made up of the highly abundant elements titanium and nitrogen, and it’s easy to manufacture.”

The scientists have successfully made aluminum batteries with conductive parts made of titanium nitride in the laboratory. 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 aluminum 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,” said Kovalenko.

The second new material can be used for the positive electrode (pole) of aluminum batteries. The negative electrode in these batteries is made of aluminum, the positive electrode is usually made of graphite. Now, Kovalenko and his team have found a new material that rivals graphite in terms of the amount of energy a battery is able to store.

The material in question is polypyrene, a hydrocarbon with a chain-like (polymeric) molecular structure. In experiments, samples of the material – particularly those in which the molecular chains congregate in a disorderly manner – proved to be ideal. “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,” Kovalenko explained.

One of the advantages of electrodes containing polypyrene is that scientists are able to influence their properties, such as the porosity. The material can therefore be adapted perfectly to the specific application. “In contrast, the graphite used at present is a mineral. From a chemical engineering perspective, it cannot be modified,” said Kovalenko.

Because both titanium nitride and polypyrene are flexible materials, the researchers believe they are suitable for use in “pouch cells” (batteries enclosed in a flexible film).

An increasing amount of electricity is generated from solar and wind energy. But electricity is needed even when the sun is not shining and the wind is not blowing, thus new technologies will be needed, such as new types of batteries, to store this electricity in a cost-effective manner. Although existing lithium-ion batteries are ideal for electro mobility due to their low weight, they are also quite expensive and therefore unsuitable for economical large-scale, stationary power storage.

Aside from cost, lithium is a relatively rare metal and is hard to extract – unlike aluminum, magnesium or sodium. Batteries based on one of the latter three elements are thus seen as a promising option for stationary power storage in the future. So far such batteries are still at the research stage and have not yet entered industrial use.

Even with European high pressure for progress on the renewable resources the improvements come just as fast as innovation and creativity allow. Meanwhile, the cost benefit analysis is getting very hard to defend. Businesses that need steady reliable low cost electricity are leaving Germany in particular.

For all the wonder at the research results some cooler heads have noticed that energy isn’t the problem, its government and public policy dragging the economy down.

One has to wonder just what applicability might be beyond large scale storage. This looks tremendous progress focused on a small estimation of the potential. Kovalenko seems to sense this, perhaps taking the technology as far as possible and letting the market seek and choose will boost this along.


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