Visualizing Reaction Fronts and Transport Limitations in Solid‐State Li–S Batteries via Operando Neutron Imaging

• Published in: Advanced energy materials 2023-05, Vol.13 (17), p.n/a
• Main Authors: Bradbury, Robert, Dewald, Georg F., Kraft, Marvin A., Arlt, Tobias, Kardjilov, Nikolay, Janek, Jürgen, Manke, Ingo, Zeier, Wolfgang G., Ohno, Saneyuki
• Format: Article
• Language: English
• Subjects: Cathodes; composite electrodes; in situ neutron tomography; Ion currents; Ion transport; Lithium; Lithium sulfur batteries; Li–S batteries; operando neutron radiography; Product safety; solid‐state batteries; Spatial distribution; Storage batteries
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202203426

The exploitation of high‐capacity conversion‐type materials such as sulfur in solid‐state secondary batteries is a dream combination for achieving improved battery safety and high energy density in the push toward a sustainable future. However, the exact reason behind the low rate‐capability, bottlenecking further development of solid‐state lithium–sulfur batteries, has not yet been determined. Here, using neutron imaging, the spatial distribution of lithium during cell operation is directly visualized and it is shown that sluggish macroscopic ion transport within the composite cathode is rate‐limiting. Observing a reaction front propagating from the separator side toward the current collector confirms the detrimental influence of a low effective ionic conductivity. Furthermore, irreversibly concentrated lithium in the vicinity of the current collector, revealed via state‐of‐charge‐dependent tomography, highlights a hitherto‐overlooked loss mechanism triggered by sluggish effective ionic transport within a composite cathode. This discovery can be a cornerstone for future research on solid‐state batteries, irrespective of the type of active material. “Seeing is believing” holds true in the demonstration of lithium‐ion transport within composite cathodes for solid‐state batteries, as visualized with a neutron beam in an operando manner. The observation of a propagating reaction front and a nonuniform distribution of lost lithium upon cycling provides clear evidence of transport limitations within the composite cathode and uncovers the mechanism behind capacity loss.