In-Situ X-ray Absorption Spectroscopic Study on Variation of Electronic Transitions and Local Structure of LiNi1/3Co1/3Mn1/3O₂ Cathode Material during Electrochemical Cycling

In-situ X-ray absorption spectroscopic investigations have been carried out to examine the changes of the electronic transitions and local structure at the Mn, Co, and Ni K-edge for the LiNi 1/3 Co 1/3 Mn 1/3 O 2 electrode during charging and discharging process in this study. It was found that only Ni atom in Li 1 - x Ni 1/3 Co 1/3 Mn 1/3 O 2 is electroactive from the evolution of the XANES spectra and the bond length variation of Ni−O. It was found that the redox pairs of Ni 2+ /Ni 3+ and Ni 3+ /Ni 4+ exist and the oxidation states of Mn and Co remain as Mn IV and Co III, respectively, in Li 1 - x Ni 1/3 Co 1/3 Mn 1/3 O 2 upon charge and discharge. The oxygen, rather than the transition-metal ions (Ni, Co, and Mn), functions as electron donor at the end of charge. In addition, the irreversible capacity at the first cycle derives mainly from the appearance of inactive Ni, which is evidenced by the energy shift E − E 0 of the absorption edge for the Ni absorber and the bond length change of the Ni−O. A decrease/increase of Debye−Waller factor of Ni−O contribution results from a decrease/increase of Jahn−Teller active Ni III concentration during cycling. The trends of the variations for the bond length and Debye−Waller factor for the second shell Mn−M and Ni−M contributions are significant and similar, suggesting the short-range ordering between Ni II and Mn IV may take place in this compound.