Ohnuma Toshiharu, Kobayashi Takeshi
Material Science Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI) 2-6-1 Nagasaka Yokosuka-shi Kanagawa-ken 240-0196 Japan
RSC Adv. 2019 Nov 4;9(61):35655-35661. doi: 10.1039/c9ra03606g. eCollection 2019 Oct 31.
Simulation of Ni K-edge X-ray absorption near edge structure (XANES) spectra in LiNiCoMnO (NCM523) was performed. The structure of NCM523 was optimized by first-principles calculation based on density functional theory and XANES spectrum simulation the finite difference method. The calculated Ni K-edge XANES spectra of NCM523 with Li amounts of 1.0 and 0.5 showed good agreement with the measured spectra. The bond length between Ni and O shortened as the valence of Ni increased. Distortion of the structure resulting from Jahn-Teller distortion was observed with Ni. The XANES spectra of the Ni K-edge of Ni, Ni, and Ni were calculated. In NCM523 with a Li amount of 1.0, the spectrum of Ni shifts towards the higher energy side compared to that of Ni; at a Li amount of 0.5 the absorption edge of Ni, Ni, and Ni shifts toward a higher energy as valence increases. Even at the same Ni valence number, the XANES spectra were different when the Li amounts were 1.0 and 0.5. Cation mixing of Li/Ni readily occurs at a Li amount of 1.0, more than that of 0.5 because of the super exchange interaction. The K-edge XANES spectrum of the Ni of the Li site did not change the position of the absorption edge of the Ni site Ni XANES spectrum; a difference in shape of the shoulder peak and the pre-edge peak appeared. From these results, the Ni valence, bonding state, and cation mixing effect of Li/Ni on the Ni K-edge XANES spectrum in NCM523 were clarified.
对LiNiCoMnO（NCM523）中的Ni K边X射线吸收近边结构（XANES）光谱进行了模拟。基于密度泛函理论的第一性原理计算对NCM523的结构进行了优化，并采用有限差分法进行了XANES光谱模拟。Li含量为1.0和0.5的NCM523的计算Ni K边XANES光谱与测量光谱显示出良好的一致性。随着Ni价态的增加，Ni与O之间的键长缩短。观察到Ni因 Jahn-Teller 畸变导致结构发生畸变。计算了Ni²⁺、Ni³⁺和Ni⁴⁺的Ni K边XANES光谱。在Li含量为1.0的NCM523中，与Ni²⁺相比，Ni³⁺的光谱向高能侧移动；在Li含量为0.5时，随着价态增加，Ni²⁺、Ni³⁺和Ni⁴⁺的吸收边向高能方向移动。即使在相同的Ni价态下，当Li含量为1.0和0.5时，XANES光谱也不同。由于超交换相互作用，Li/Ni的阳离子混合在Li含量为1.0时比0.5时更容易发生。Li位点的Ni的K边XANES光谱没有改变Ni位点Ni XANES光谱的吸收边位置；肩峰和预边峰的形状出现了差异。从这些结果中，阐明了NCM523中Ni价态、键合状态以及Li/Ni的阳离子混合效应对Ni K边XANES光谱的影响。
