Visualization of ion transport in electrolyte provides fundamental understandings of electrolyte dynamics and electrolyte-electrode interaction, shedding light on material designs to enhance device performance, such as batteries and fuel cells. However, this task is extremely challenging for existing techniques due to their inability to capture the low ionic concentration (&lt;1 M) and the fast dynamics (1-10 s) of the electrolyte. Here we show that an emerging Stimulated Raman Scattering (SRS) microscopy offers the required spatial (sub-micrometer optical resolution), temporal (faster than 1 s per frame) and chemical (around mM) sensitivities to address this challenge. In Raman, [Li+] can be probed by either Li+-solvent interaction, or vibrational mode in the anion which has the same concentration as Li+ due to electroneutrality. Utilizing this technique, we examined and provided evidence for a long-lasting question: How does Li+ concentration correlate with and contribute to the uneven deposition of lithium metal? A three-stage lithium deposition process is uncovered, each corresponding to no-depletion, partial-depletion and full-depletion regime of Li+, respectively. Further analysis reveals a previously uncharacterized spatial heterogeneity of Li+concentration near lithium surface, and a positive feedback mechanism between the inhomogeneous growth of lithium and the local ionic concentration or flux. This study shows that SRS microscopy is a powerful technique for imaging ion transport and will open various applications in materials and energy fields.

Operando and three-dimensional visualization of ion depletion and lithium growth by stimulated raman scattering microscopy

2019 Fall National Meeting

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