One of the prioritized research topics in MoZEES is to develop high voltage battery materials in order to increase the energy density of heavy duty batteries. MoZEES PhD student Elise Ramleth Østli is currently spending 6 months at the Ångström Advanced Battery Center (ÅABC) in Uppsala to learn more about her cathode material's surface coating, and how shooting x-rays at it can be used to understand the coating’s effect.
The Ångström Advanced Battery Center (ÅABC) in Uppsala has a wide variety of ongoing battery research, ranging from Na-ion batteries to polymer electrolytes for Li-ion batteries. A popular characterization technique amongst the ÅABC researchers is X-ray photoelectron spectroscopy (XPS) which is a powerful technique to get information about surfaces. MoZEES PhD student Elise Ramleth Østli is spending 6 months at the ÅABC to learn more about how her surface coating of the cathode material LiNi0.5Mn1.5O4 (LNMO) can improve this material, and how XPS can be used to understand the coating’s effect.
LNMO is a promising cathode material first and foremost due to its high operating voltage which can increase the energy density of the battery. A higher voltage also means that you can reduce the number of batteries you need connected in series to achieve the wanted voltage for your application.
However, the high operating voltage also comes at a cost. At such high voltages, both the LNMO electrode and the electrolyte will be unstable, and this leads to unwanted side reactions that lowers the battery’s lifetime.
One of the consequences is Mn-ion dissolution. This means that Mn-ions dissolve from the LNMO cathode material during battery cycling and go into the electrolyte. Here they are quite mobile and can therefore easily travel over to the anode (negative electrode) where they cause problems. Elise is currently investigating how thin surface coatings can hinder the Mn-ions from escaping the cathode. To do this, accurate information about the surface of the electrodes is needed and XPS is an ideal tool for that.
The birthplace of XPS
The XPS technique was in fact developed in Uppsala, where the first high-energy-resolution specter was recorded in 1954. Since then, the technique has become well-established in several fields, and a huge number of XPS papers are published every year. The principle of XPS is in short to shoot X-rays at a surface and then measure the energy of the electrons that are emitted from it. This can give information about which chemical elements are present and which state they are in. This is very useful to understand more about the degradation mechanisms that occur inside a battery when it is being cycled.
Being both the birthplace of the XPS-technique and having a world leading research group on battery materials, Uppsala was the perfect place for me to go for exchange. I am very glad that I got to stay here as long as 6 months, as I am still learning new things every day after 3 months here, Elise says
Pouch cells
At the ÅABC Elise is making pouch-cell batteries with both the uncoated and coated LNMO cathode material and compare how the surfaces of the electrodes are after they have been cycled. There are films formed on the surface of the electrodes while the battery is being cycled, and by looking at the thickness of the films and the chemical composition of them one can get a good estimate of how well the coating is keeping the Mn-ions inside the cathode.
At the end of January 2020 Elise will return to Trondheim and NTNU, hopefully with exciting results that can shed light on how to solve the Mn-ion dissolution problem in LNMO cathodes. Elise thinks the research group has been very welcoming, and says that working in the lab is both very social and educational. It is really easy to get in contact with people, and we all work together to solve the issues that we face in the lab, she says.