Imaging dendrite growth in solid-state sodium batteries using fluorescence tomography technology.

Dendrite growth in solid-state sodium batteries (SSBs) is one of the most concerned issues that critically affect the battery efficiency and cycling performance. Here, by designing a fluorescent Eu³⁺-doped Na₃Zr₂Si₂PO₁₂ solid electrolyte (SE) to facilitate three-dimensional (3D) optical imaging on a confocal laser scanning microscopy, a fluorescence tomography (FT) method is developed for observing the sodium dendrite growth during charge/discharge cycles of the SSBs in a 3D view. It is quantitatively revealed that small-size sodium islands appear after several cycles, and with the cycles increasing, large-size dendrites in tens of micrometers gradually form until a critical sodium dendrite volume arrives where a short circuit or severe performance deterioration occurs. Furthermore, by regulating the Eu³⁺ doping ratio, a record-high sodium plating/stripping cycling stability for more than 1 year (487.5 days) is achieved at 25°C. This work demonstrates an FT method observing sodium dendrite growth in SSBs and will promote the functional design of high-performance SEs.