New method visualizes transport of lithium in batteries

The method employed in the experiments can be compared to billiards on atomic level. In the study lithium ions with MeV energies were directed on thin film battery systems. When the incident lithium ions hit another lithium nucleus in the sample, both ions can be simultaneously emitted in an angle of 90 degrees with respect to each other. The particles can be subsequently detected by two detectors in a narrow time interval on the nanosecond timescale. Due to this so-called coincidence-measurement with two detectors, the otherwise weak signal from lithium becomes clearly visible. This weak signal is otherwise masked by the background caused by the other species in the sample, which is a common problem in conventional approaches using only a single detector.

“The major novel aspect of the study is, that both the distribution and movement of lithium ions in a whole battery stack can be measured during operation, which means without destroying the battery during the investigation or limiting measurements to only part of the battery system”, mentions Daniel Primetzhofer, Associate professor at the Department of Physics and Astronomy.

This research is of importance as the method tested could be employed for further development of thin film batteries. These batteries are expected to become of particular importance for flexible electronics but also in medical implants where a liquid electrolyte, as used in conventional lithium ion batteries is undesired for safety reasons.

Daniel Primetzhofer has together with his colleagues Vairavel Mathayan and Marcos Moro from Uppsala University and researchers from Japan now shown that the approach they chose actually works. A next step will be to employ the method to address specific questions in battery research. As an example, it could be investigated which material composition and structure is beneficial for maximizing capacity and lithium transport. But also, under which conditions and why the transport of lithium is decreasing over time and the battery is aging can be investigated. Finally, the approach can be also used to address other research questions, where the mobility of lithium or other light chemical elements is of great relevance, such as for example within fusion research by using a helium beam to probe small amounts of tritium.

Article Reference

Mathayan, V. et al. In-operando observation of Li depth distribution and Li transport in thin film Li ion batteries, Applied Physical Letters 117, 023902 (2020), DOI: https://doi.org/10.1063/5.0014761

Camilla Thulin