Nickel-based layered rock-salt cathode materials for lithium-ion secondary batteries have drawn considerable attention due to their high energy capacity, lower cost, and better environmental compatibility than other current potential materials. As the nickel content increases, however, these materials suffer from significant capacity fading during charge-discharge cycles at elevated temperatures. While the capacity deterioration and poor cycling stability are mainly because of the formation of NiO-like rock-salt structures at the surface of active materials, the degradation mechanisms have not been fully investigated. In this study, to clarify the process of formation of inactive NiO-like structures, the degradation mechanism of a cathode-active material, namely, LiNi_0.80Co_0.15Al_0.05O₂ (NCA) is studied after a single charge–discharge cycle, by using site-selective energy-dispersive X-ray spectroscopy associated with transmission electron microscopy. It is confirmed that cation mixing occurs between the lithium- and transition metal-sites of the LiMO₂ (M = transition metals) layered rock-salt structures during the transition to partially ordered transition states and then to the final NiO-like disordered rock-salt structures. Further, the volume fractions of the partially/fully disordered phases in the NCA primary particles are quantitatively estimated.

用于锂离子二次电池的镍基层状岩盐阴极材料由于其高能量容量，较低的成本以及比其他当前潜在材料更好的环境相容性而备受关注。但是，随着镍含量的增加，这些材料在高温下的充放电循环过程中会遭受明显的容量衰减。尽管容量下降和循环稳定性差主要是由于在活性材料表面形成了类似NiO的岩盐结构，但其降解机理尚未得到充分研究。在这项研究中，为弄清无活性的NiO状结构的形成过程，正极活性材料LiNi _0.80 Co _0.15 Al的降解机理在单个充放电循环后，通过使用与透射电子显微镜相关的位点选择性能量色散X射线光谱学研究了_0.05 O ₂（NCA）。已经证实，在过渡到部分有序的过渡态，然后过渡到最终的类似NiO的无序岩石的过渡过程中，LiMO ₂（M =过渡金属）层状岩盐结构的锂和过渡金属位点之间发生了阳离子混合。盐结构。此外，对NCA一次粒子中的部分/完全无序相的体积分数进行定量估计。