Fundamental understanding of ionic transport is critical to developing rechargeable batteries with high performance. While various techniques have been developed to characterize ionic transport in solid battery electrodes, little has been done to visualize ion movement in the liquid electrolyte, since it is difficult to realize high temporal, spatial and concentration resolutions simultaneously in liquids. Fluorescence imaging has the capability to detect ions in liquid with high resolution (< 1 s, < 300 nm and < 1 M), and it is widely used in biomedical studies. However, it has been rarely applied to battery studies. Here we show that using an ion indicator, the dissolution of trace amount of Mn from LiMn₂O₄, a common Li-ion battery cathode material, can be visualized under a fluorescence microscope. Moreover, important physical parameters, such as the dissolution rate and ionic diffusivity, can be extracted quantitatively from the fluorescence images. These results also show that nanoscale Al₂O₃ coating can effectively suppress Mn dissolution, which is consistent with past studies. This study demonstrates the capability of fluorescence-imaging based techniques for battery studies, which could help gain more insight on the behavior of ions in battery systems and develop better battery materials.

对离子传输的基本了解对于开发高性能的可充电电池至关重要。尽管已经开发出各种技术来表征固体电池电极中的离子迁移，但是几乎没有做任何工作来可视化液体电解质中的离子运动，因为很难同时在液体中实现高的时间，空间和浓度分辨率。荧光成像具有以高分辨率（<1 s，<300 nm和<1 M）检测液体中离子的能力，并且已广泛用于生物医学研究中。但是，它很少用于电池研究。在这里，我们表明使用离子指示剂可以从LiMn ₂ O _4中溶解痕量的Mn。常见的锂离子电池正极材料，可以在荧光显微镜下看到。而且，可以从荧光图像中定量提取重要的物理参数，例如溶解速率和离子扩散率。这些结果还表明，纳米级Al ₂ O ₃涂层可以有效地抑制Mn的溶解，这与以往的研究一致。这项研究证明了基于荧光成像技术的电池研究能力，可以帮助人们更深入地了解电池系统中离子的行为，并开发出更好的电池材料。