Chemical Sciences and Engineering Division, ‡X-ray Sciences Division, and §Materials Science Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
ACS Appl Mater Interfaces. 2017 Nov 29;9(47):41291-41302. doi: 10.1021/acsami.7b13597. Epub 2017 Nov 14.
Surface alumina coatings have been shown to be an effective way to improve the stability and cyclability of cathode materials. However, a detailed understanding of the relationship between the surface coatings and the bulk layered oxides is needed to better define the critical cathode-electrolyte interface. In this paper, we systematically studied the effect of the composition of Ni-rich LiNiMnCoO (NMC) on the surface alumina coatings. Changing cathode composition from LiNiMnCoO (NMC532) to LiNiMnCoO (NMC622) and LiNiMnCoO (NMC811) was found to facilitate the diffusion of surface alumina into the bulk after high-temperature annealing. By use of a variety of spectroscopic techniques, Al was seen to have a high bulk compatibility with higher Ni/Co content, and low bulk compatibility was associated with Mn in the transition metal layer. It was also noted that the cathode composition affected the observed morphology and surface chemistry of the coated material, which has an effect on electrochemical cycling. The presence of a high surface Li concentration and strong alumina diffusion into the bulk led to a smoother surface coating on NMC811 with no excess alumina aggregated on the surface. Structural characterization of pristine NMC particles also suggests surface Co segregation, which may act to mediate the diffusion of the Al from the surface to the bulk. The diffusion of Al into the bulk was found to be detrimental to the protection function of surface coatings leading to poor overall cyclability, indicating the importance of compatibility between surface coatings and bulk oxides on the electrochemical performance of coated cathode materials. These results are important in developing a better coating method for synthesis of next-generation cathode materials for lithium-ion batteries.
氧化铝表面涂层已被证明是提高阴极材料稳定性和循环性能的有效方法。然而，为了更好地定义关键的阴极-电解质界面，需要深入了解表面涂层与体相层状氧化物之间的关系。在本文中，我们系统地研究了富镍 LiNiMnCoO（NMC）阴极组成对氧化铝表面涂层的影响。研究发现，改变阴极组成，从 LiNiMnCoO（NMC532）变为 LiNiMnCoO（NMC622）和 LiNiMnCoO（NMC811），在高温退火后，表面氧化铝更容易扩散到体相。通过使用多种光谱技术，发现 Al 与较高的 Ni/Co 含量具有较高的体相相容性，而与过渡金属层中的 Mn 则具有较低的体相相容性。还注意到，阴极组成会影响涂层材料的观察到的形貌和表面化学，从而对电化学循环产生影响。高表面 Li 浓度的存在和氧化铝强烈地扩散到体相，导致 NMC811 表面涂层更加光滑，表面没有多余的氧化铝聚集。原始 NMC 颗粒的结构表征也表明表面 Co 偏析，这可能有助于 Al 从表面向体相的扩散。Al 向体相的扩散被发现对表面涂层的保护功能有害，导致整体循环性能不佳，这表明表面涂层与体相氧化物之间的相容性对涂层阴极材料的电化学性能至关重要。这些结果对于开发下一代锂离子电池用阴极材料的更好合成涂层方法非常重要。
