Kalapsazova M, Ivanova S, Kukeva R, Simova S, Wegner S, Zhecheva E, Stoyanova R
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria.
Phys Chem Chem Phys. 2017 Oct 11;19(39):27065-27073. doi: 10.1039/c7cp04849a.
Knowledge on the formation of mixed transition metal layers on lithium and sodium transition metal oxides, Li/Na(Co,Ni,Mn,)O, determines the ability to control their electrochemical properties as electrode materials in alkaline ion batteries. Taking this into account, herein we combine the EPR and Na MAS NMR spectroscopic techniques to gain insights into the structural peculiarities of the mixed cobalt-nickel-manganese layers of NaCoNiMnO with a three-layer stacking (P3-type) structure. Two types of compositions are examined where diamagnetic Co and paramagnetic Ni and Mn are stabilized: NaCoNiMnO and NaNiMnO. EPR spectroscopy operating in the X- and Q-band region is applied with an aim to improve the spectra resolution and, on the other hand, to provide straightforward information on the coordination of the transition metal ions inside the layers. The analysis of EPR spectra is based on the reference for the Mn and Ni ions occurring simultaneously in oxides with two layer stacking, P2-NaNiMnO. Complementary to EPR, Na MAS NMR spectroscopy at high spinning rates is undertaken to assess the local structure of the Na nucleus in the layered P3-NaCoNiMnO oxides. All results are discussed taking into account the EPR and NMR data for the well-known lithium analogues O3-LiCoNiMnO and O3-LiNiMnO. Finally, the structure peculiarities of the transition metal layers extracted from the EPR and NMR methods are demonstrated by electrochemical intercalation of Li ions into P3-NaCoNiMnO.
了解锂和钠过渡金属氧化物Li/Na(Co,Ni,Mn)O上混合过渡金属层的形成，对于控制其作为碱性离子电池电极材料的电化学性能至关重要。考虑到这一点，我们在此结合电子顺磁共振（EPR）和钠魔角旋转核磁共振（Na MAS NMR）光谱技术，以深入了解具有三层堆叠（P3型）结构的NaCoNiMnO混合钴-镍-锰层的结构特性。研究了两种类型的组成，其中抗磁性的Co以及顺磁性的Ni和Mn得以稳定：NaCoNiMnO和NaNiMnO。应用在X波段和Q波段区域操作的EPR光谱，目的是提高光谱分辨率，另一方面是提供有关层内过渡金属离子配位的直接信息。EPR光谱分析基于对具有两层堆叠的氧化物P2-NaNiMnO中同时出现的Mn和Ni离子的参考。作为EPR的补充，进行了高自旋速率下的Na MAS NMR光谱分析，以评估层状P3-NaCoNiMnO氧化物中Na核的局部结构。所有结果均结合了著名的锂类似物O3-LiCoNiMnO和O3-LiNiMnO的EPR和NMR数据进行讨论。最后，通过将锂离子电化学嵌入P3-NaCoNiMnO中，展示了从EPR和NMR方法中提取的过渡金属层的结构特性。
