Direct visualization of ion transport in electrolyte provides fundamental understanding of this process and electrolyte-electrode interaction, shedding light on material designs to enhance device performance, such as batteries, fuel cells and desalination. However, this task is extremely challenging, since electrolytes possess a much lower ionic concentration (~0.01-2 M) and a much higher diffusion coefficient (~10-6 cm2/s) than the solid phase (5-50 M, &lt;10-9 cm2/s). Therefore, chemical-specific imaging with superb sensitivity (&lt;10 mM), fine temporal (&lt;~1 s per frame) and spatial resolutions (&lt;1 μm) are required for characterizing the 3D ion transport in electrolyte. These requirements are beyond the capability of state-of-the-art tools, such as synchrotron-based techniques and MRI. Here we show that an emerging Stimulated Raman Scattering (SRS) microscopy offers unprecedented temporal and chemical resolution (&lt;1 s and &lt;1 mM) to solve this challenge1,2. Utilizing this technique, we examined and provided direct evidence for a long-lasting question: How does heterogeneity of Li+ concentration affect the uneven deposition of lithium metal? A three-stage lithium deposition model is uncovered, each corresponding to non-depletion, partial-depletion and full-depletion of Li+. Further analysis reveals a previously unproven spatial heterogeneity of Li+ concentration near lithium surface, and a positive feedback mechanism between the inhomogeneous growth of lithium and the local ionic concentration/flux. We then demonstrate that Li3PO4-based artificial solid electrolyte interface (SEI) is effective in homogenizing Li+ concentration near lithium surface and suppressing the dangerous dendritic growth of lithium in the second and third stages, which could help enhance the safety of lithium anode. This study shows that SRS microscopy is an exceptional technique for capture the dynamics of chemical species. It can potentially answer various key questions in materials and energy sciences, such as inhomogeneous ion transport/ intercalation, material separations, and products in catalytic processes.

In-operando mesoscale 3D visualization of ion transport in battery electrolyte

256th National Meeting (2018)

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