Imaging Sodium Dendrite Growth in All‐Solid‐State Sodium Batteries Using (23)Na T (2)‐Weighted Magnetic Resonance Imaging

Two‐dimensional, Knight‐shifted, T (2)‐contrasted (23)Na magnetic resonance imaging (MRI) of an all‐solid‐state cell with a Na electrode and a ceramic electrolyte is employed to directly observe Na microstructural growth. A spalling dendritic morphology is observed and confirmed by more conventional post‐mortem analysis; X‐ray tomography and scanning electron microscopy. A significantly larger (23)Na T (2) for the dendritic growth, compared with the bulk metal electrode, is attributed to increased sodium ion mobility in the dendrite. (23)Na T (2)‐contrast MRI of metallic sodium offers a clear, routine method for observing and isolating microstructural growths and can supplement the current suite of techniques utilised to analyse dendritic growth in all‐solid‐state cells.