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.’
Doctoral candidate Mikko Nisula, Aalto University School of Chemical Technology, Department of Chemistry
Professor Maarit Karppinen, Aalto University School of Chemical Technology, Department of Chemistry
Text Minna Hölttä, photos Mikko Raskinen