X-ray absorption near edge structure simulation of LiNi0.5Co0.2Mn0.3O2via first-principles calculation

• Published in: RSC advances 2019-11, Vol.9 (61), p.35655-35661
• Main Authors: Ohnuma, Toshiharu, Kobayashi, Takeshi
• Format: Article
• Language: English
• Subjects: Cations; Chemistry; Density functional theory; Distortion; Finite difference method; First principles; Jahn-Teller effect; Mathematical analysis; Phosphates; Simulation; Spectra; X ray absorption
• ISSN: 2046-2069
• DOI: 10.1039/c9ra03606g

Simulation of Ni K-edge X-ray absorption near edge structure (XANES) spectra in LiNi0.5Co0.2Mn0.3O2 (NCM523) was performed. The structure of NCM523 was optimized by first-principles calculation based on density functional theory and XANES spectrum simulation via 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 Ni3+. The XANES spectra of the Ni K-edge of Ni2+, Ni3+, and Ni4+ were calculated. In NCM523 with a Li amount of 1.0, the spectrum of Ni3+ shifts towards the higher energy side compared to that of Ni2+; at a Li amount of 0.5 the absorption edge of Ni2+, Ni3+, and Ni4+ 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 Ni2+ 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.