Observing Dendrite Growth in Solid-State Sodium Batteries Using Fluorescence Tomography Technology

Abstract Dendrite growth in solid-state sodium batteries (SSBs) is one of the most concerned issues that critically affect the battery efficiency and cycling performance. Herein, a fluorescence tomography technology is developed to observe the sodium dendrite growth in SSBs by designing a fluorescent Eu3+-doped Na3Zr2Si2PO12 solid electrolyte (SE). Under the Eu3+-fluorescence contrast, three-dimensional optical images of the sodium dendrites are obtained by using a confocal laser scanning microscopy. In this way, in-depth sodium dendrite observation during charge/discharge cycles is performed, showing the dendrite initiating stage near the surface and subsequent propagation along the grain boundaries of the SE. Further, a grain-boundary-doping method is promoted and the corresponding Na//Na symmetric cell achieves a record-high cycling stability for more than 1 year (415 d, ongoing) at 25 ℃. This work demonstrates an optical tomography method observing dendrite growth in SSBs and provides an insightful guidance for the design of high-performance SEs.