Practical Implications of Using a Solid Electrolyte in Batteries with a Sodium Anode: A Combined X‐Ray Tomography and Model‐Based Study

The commercial use of metal anodes is difficult due to dendrite growth during battery charge, whereas solid electrolytes (SEs) can be applied as a protective layer to mitigate this issue. In this article, X‐ray tomography of cycled symmetric sodium (Na) cells with Na‐β‐alumina is used to validate the success of a protective layer. X‐ray imaging after cell failure reveals that the SE unexpectedly breaks apart alongside a crack. The crack may have acted as the nucleation site for Na dendrite growth, which ended in short‐circuiting and cell failure. Operando X‐ray radiography reveals that a tilted SE is even more likely to break. Simulations complement the experimental study and shed light on the current density distribution at the edges and smallest pinholes. The results obtained emphasize that during fabrication of a battery with a protective layer, particular care needs to be taken to align the metal electrodes as flat and planar as possible. To achieve the aim of fully utilizing a metal anode in the future battery technology, much effort has to be made to engineer a proper cell design by accounting for mechanical stress in the SE material.