LiMn₂O₄ has been considered one of the most promising cathode materials for Li-ion batteries due to its thermal stability, abundance, environmental affinity, and the possibility to exchange Li-ions in three-dimensions. However, it still suffers from major problems, such as capacity fading and voltage decay, which has been associated to phase transformations and dissolution of transition metals. In this report, we use scanning transmission electron microscopy, coupled with differential phase contrast (DPC), to better understand the mechanisms behind the structural transformations occurring in LiMn₂O₄. We use the fact that DPC has the ability to observe simultaneously light and heavy elements, as well as measure projected electric fields and charge distribution at the atomic level. This approach allows us to monitor the migration of very low amounts of Mn to the Li atomic positions, at the surface and subsurface regions, which otherwise is very challenging to observe using other techniques such as HAADF and ABF. These observations not only provide a fundamental understanding of the structure of LiMn₂O₄ but also reveal DPC as a novel technique to determine local structural changes in materials consisting of heavy and light elements, as well as identify the location of light elements, monitor low concentrations of substitutional species and identify phase transformations.

LiMn ₂ O ₄由于其热稳定性，丰度，对环境的亲和力以及可以以三维交换锂离子的能力，被认为是锂离子电池最有希望的正极材料之一。然而，它仍然遭受诸如容量衰减和电压衰减之类的主要问题，这已经与相变和过渡金属的溶解有关。在本报告中，我们使用扫描透射电子显微镜以及微分相衬（DPC），以更好地了解LiMn ₂ O _4中发生的结构转变背后的机制。。我们利用DPC能够同时观察轻元素和重元素以及测量原子级上的投影电场和电荷分布这一事实。这种方法使我们能够监测非常少量的Mn迁移到表面和亚表面区域的Li原子位置，否则使用其他技术（例如HAADF和ABF）很难观察到这一点。这些观察结果不仅提供了对LiMn ₂ O ₄结构的基本了解，而且揭示了DPC是一种确定由重元素和轻元素组成的材料的局部结构变化以及识别轻元素的位置，监测低位的新技术。替代物种的浓度，并确定相变。