Na metal is an attractive anode material for rechargeable Na ion batteries, however, the dendritic growth of Na can cause serious safety issues. Along with modifications of solid-electrolyte interphase (SEI), engineering the electrode has been reported to be effective in suppressing Na dendritic growth, likely by reducing localized current density accumulation. However, fundamental understanding of Na growth at the nanoscale is still limited. Here, we report an in-situ study of Na electrodeposition in electrochemical liquid cells with the electrodes in different surface roughness, e.g., flat or sharp curvature. Real time observation using transmission electron microscopy (TEM) reveals the Na electrodeposition with remarkable details. Relatively large Na grains (in the micrometer scale) are achieved on the flat electrode surface. The local SEI thickness variations impact the growth rate, thus the morphology of individual grains. In contrast, small Na grains (in tens of nanometers) grow explosively on the electrode at the point with sharp curvature. The newly formed Na grains preferentially deposit at the base of existing grains close to the electrode. Further studies using continuum-based computational modeling suggest that the growth mode of an alkali metal (e.g. Na) is strongly influenced by the transport properties of SEI. Our direct observation of Na deposition in combination with the theoretical modeling provides insights for comprehensive understanding of electrode roughness and SEI effects on Na electrochemical deposition.

钠金属是可充电钠离子电池有吸引力的阳极材料，但是，钠的树枝状生长会引起严重的安全问题。伴随着对固体电解质中间相（SEI）的修改，据报道，对电极进行工程设计可有效抑制Na树突状生长，这可能是通过减少局部电流密度累积来实现的。然而，对钠在纳米尺度上生长的基本了解仍然有限。在这里，我们报告一个原位电极在不同表面粗糙度（例如平坦或尖锐曲率）的电化学液体电池中进行钠电沉积的研究。使用透射电子显微镜（TEM）进行的实时观察揭示了钠电沉积的细节。在平坦的电极表面上可获得相对较大的Na晶粒（以微米为单位）。局部SEI厚度变化会影响生长速率，从而影响单个晶粒的形态。相反，小的Na晶粒（数十纳米）在具有急剧曲率的点上爆炸性地生长在电极上。新形成的钠晶粒优先沉积在靠近电极的现有晶粒的底部。使用基于连续谱的计算模型进行的进一步研究表明，碱金属的生长模式（例如 Na）受SEI传输特性的强烈影响。我们对钠沉积的直接观察与理论模型相结合，为全面了解电极粗糙度和SEI对钠电化学沉积的影响提供了见识。