Comparative evaluation of performance reproducibility of all-solid-state lithium batteries

There are still no uniform standards for research into solid-state batteries, which will also be used in electromobility in the long term, even though billions are being invested in this field worldwide. Researchers at the University of Bayreuth have identified the reasons for this and presented them in the scientific journal Natural energy.

Solid-state or all-solid-state batteries (ASSB) promise a significant increase in energy density compared to conventional lithium-ion batteries. This is why they are considered the future energy storage system for electromobility. However, there is no standardized protocol for the validation of solid-state battery cells in battery research.

When publishing results, it is often uncertain whether they are comparable to those of other research groups. It is therefore necessary to create a starting point for the reproducibility and comparability of cell-based tests in order to be able to reliably evaluate innovations in this technology.

“At least once a week we hear about a new breakthrough in battery cell performance that will revolutionize electric mobility or energy storage in general. However, very few of these “highly publicized” reports find application outside the laboratory.

“In many cases, this is because it is impossible to reproduce them outside the original laboratory,” says Professor Nella M. Vargas-Barbosa, chair of electrochemistry at the Bavarian Center for Battery Technology (BayBatt) at the University of Bayreuth. She is the lead author of a recently published paper.

In this study, the researchers measured the extent to which the properties of single test cells varied de facto: 21 research groups with recognized research and industry expertise in the field of solid-state batteries were given the same battery materials and a predefined electrochemical test procedure, but each group used its own cell assembly method and individual, non-standardized measurement techniques.

“We now report the huge differences in how the battery cells were assembled and how they performed in comparison, including variations in the pressure applied and the composition of the negative electrode,” the researchers say.

“The dispersion of performance data between the different battery cells built was found to be immense. While this may be worrisome, it is a first step towards necessary improvement. The study identified some of the cell preparation conditions that can strongly influence battery performance, such as the amount of metallic lithium in the negative electrode.

“This study is unique because it involves many well-known international groups in the field of solid-state batteries. We all collectively recognize that we need to do more to improve the comparability and reproducibility of the work we report.”