How old are you, battery?

Battery capacity loss is among the biggest brakes in e-mobility and the industry. A research team from FRM II and other institutions is now validating a method that can be used to determine the distribution of elements in the anode of a battery and, thus, better understand aging.

The researchers determined the thickness of the lithium layer on the anode with high accuracy © Bernhard Ludewig, FRM II / TUM

The researchers determined the thickness of the lithium layer on the anode with high accuracy © Bernhard Ludewig, FRM II / TUM

It is a common experience that a new cell phone initially gets you through the day on a single charge. But after just a few months, you realize you should take a charging cable to be safe: the battery is aging. The reason for this is usually the loss of free lithium, which is increasingly and irreversibly deposited in a layer on the anode of the battery cell with each charging cycle.

Ivana Pivarníková testing a battery © Bernhard Ludewig, FRM II / TUM

Ivana Pivarníková testing a battery © Bernhard Ludewig, FRM II / TUM

A deep look into the anode
A precise understanding of these effects is crucial to minimize the influence of aging effects on future battery generations. This also includes characterizing the depth profile of a sample. In a recent article, researchers from the Heinz Maier-Leibnitz Zentrum (MLZ) and the Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg, among others, have now validated a method that promises to make such investigations more precise and faster to carry out.
For the first time, they compared the two established methods of Glow Discharge Optical Emission Spectroscopy (GD-OES) and Neutron Depth Profiling (NDP) when applied to the anodes of aged batteries.

Batteries age. This is usually due to the loss of free lithium, which is increasingly and irreversibly deposited in a layer on the anode of the battery cell with each charging cycle. © FRM II / TUM

Batteries age. This is usually due to the loss of free lithium, which is increasingly and irreversibly deposited in a layer on the anode of the battery cell with each charging cycle. © FRM II / TUM

Neutrons are non-destructive
“Neutron techniques can improve and validate these new methods.” says Ivana Pivarníková. She is a PhD student at the MLZ and co-first author of the article, along with Dr. Marius Flügel from the ZSW. She explains: “NDP has the advantage of a larger material surface area that can be examined in one measurement and that it is non-destructive to the sample.”
Although the classic calculation of the depth profile is based on samples with a homogeneous element distribution, the researchers improved the method by determining the thickness of the lithium layer on the anode with a high degree of accuracy. With these findings, the method can be regarded as complementary to NDP investigations.
This validation of the GD-OES method represents an important step that could make the development of new batteries less dependent on neutron testing in some areas without replacing it entirely.