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The car-manufacturing giant found Aalto University and Maarit Karppinen’s research group on the basis of a recommendation.

‘They bought the reactor needed for atomic layer deposition from Picosun, a Finnish company that told them we would have the research expertise they needed,’ explains doctoral researcher Mikko Nisula, who works in Professor Karppinen’s group.

 ‘It’s great that an international car-manufacturing giant is capable in practice of utilizing the long-term basic research with ALD technology we’ve been doing. The cooperation has advanced quite smoothly,’ Professor Karppinen says.

Atomic layer precision

Atomic layer deposition (ALD) is a method patented in Finland with which it is possible to produce very thin films of excellent quality with up to atomic layer precision. In a joint project by Toyota and Aalto, ALD is being utilized in the manufacture of safer lithium-ion batteries. The goal is to be able to replace the liquid, combustion-sensitive electrolyte normally used with a solid-state electrolyte.

‘A battery is composed of three elements: a positive electrode, negative electrode and an electrolyte between them which is generally lithium salt dissolved in organic fluid. These solutions are quite inflammable – i.e. if something goes wrong, they can really burst into flames. In addition, ordinary liquid electrolytes disintegrate when using the battery, whereupon a passivating layer is formed on the surface of the electrodes which weakens battery operation and reduces its service life,’ relates Mikko Nisula.

A solid-state electrolyte is more stable, but there is a problem linked with its use as well. A passivating layer also forms with solid-state electrolytes, and the layer is often so thick that the battery can only be used with quite minimal power.

‘Our idea is to coat the positive electrode particles with a suitable material by utilizing the atomic layer deposition method, so that a protective layer of a couple of nanometres is formed on them which will prevent the reaction of the electrode with the electrolyte, but still allow the movement of lithium-ions,’ states Mikko Nisula, outlining the idea of the research project.

For a company like Toyota, safe and functional batteries are vital.

According to Mr Nisula, the most challenging aspect of the work is the production of a protective layer that is even in quality. The goal of the year-long project is to indicate that the idea works in practice. For a company like Toyota, safe and functional batteries are vital.

‘In a traffic accident, an easily ignited battery can pose a great risk,’ Mikko Nisula further points out.

‘Our idea also extends the service life of batteries in operation. In electric cars, the battery makes up a large part of the price, so a longer-lasting battery in such vehicles in particular would mean a great saving.’  

More information:

Doctoral candidate Mikko Nisula, Aalto University School of Chemical Technology, Department of Chemistry
mikko.nisula@aalto.fi

Professor Maarit Karppinen, Aalto University School of Chemical Technology, Department of Chemistry
maarit.karppinen@aalto.fi

Text Minna Hölttä, photos Mikko Raskinen