A team from HZB and the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden has gained new insights into lithium-sulphur pouch cells at the BAMline of BESSY II. Supplemented by analyses in the HZB imaging laboratory and further measurements, a new picture emerges of processes that limit the performance and lifespan of this industrially relevant battery type. The study has been published in the prestigious journal Advanced Energy Materials.
Lithium-sulphur batteries have a number of advantages over conventional lithium batteries: they use the abundant raw material sulphur, do not require the critical elements cobalt or nickel, and can achieve extremely high specific energy densities. Prototype cells are already achieving up to 500 Wh/kg, almost twice as much as current lithium-ion batteries.
Degradation processes examined
However, lithium-sulphur batteries have so far been much more susceptible to degradation processes: during charging and discharging, dissolved polysulphides and sulphur phases form on the lithium electrode, gradually reducing the performance and lifetime of the battery. ‘Our research aims to elucidate these processes in order to improve this type of battery,’ says HZB physicist Dr. Sebastian Risse, who leads a team at HZB working on operando analysis of batteries.
The pouch cell lab at HZB
He is focusing on pouch cells, a battery format widely used in industry. HZB’s Institute for Electrochemical Energy Storage (CE-IEES), headed by Prof. Yan Lu, has therefore set up a laboratory specialising in the production of lithium-sulphur batteries in the required pocket format. Here, scientists can produce and investigate a wide variety of lithium-sulphur pouch cells. As part of the BMBF-funded ‘SkaLiS’ project, coordinated by Sebastian Risse, a team from the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden has now published a comprehensive study of lithium-sulphur pouch cells in the prestigious journal Advanced Energy Materials.
Multimodal setup
The battery cells were studied in a setup developed at HZB using various methods such as impedance spectroscopy, temperature distribution, force measurement and X-ray imaging (synchrotron and laboratory source) during charging and discharging. For the first time, we were able to observe and document both the formation of lithium dendrites and the dissolution and formation of sulphur crystallites during multi-layer battery operation,’ says Dr Rafael Müller, HZB chemist and first author of the study.
Read more on HZB website
Image: Photomontage: the diagonal line divides the image into a photo of the lithium-sulfur pouch cell (left) and the corresponding X-ray image (right) during the multimodal measurement with force sensor (golden) and temperature sensors. The perforated honeycomb structure of the current collector can be clearly seen on the X-ray image. This new design approach reduces the weight of the cell without compromising performance.
Credit: R. Müller/ HZB