In-situX-ray absorption spectroscopy investigations of a layered LiNi0.65Co0.25Mn0.1O2 cathode material for rechargeable lithium batteries

Abstract

In-situ X-ray absorption spectroscopy investigations have been carried out to evaluate the oxidation states and the local structure at the Mn, Co and Ni K-edges for LiNi_0.65Co_0.25Mn_0.1O₂ during a charging and discharging process in this study. It was found that only the Ni atom in LiNi_0.65Co_0.25Mn_0.1O₂ is electroactive from the evolution of XANES spectra and the bond length variation of Ni–O. We observed that the Ni^II/Ni^IV and Ni^III/Ni^IV redox pairs exist and the oxidation states of Mn and Co remain as Mn^IV and Co^III, respectively, in LiNi_0.65Co_0.25Mn_0.1O₂ on a charge and discharge cycle. In addition, the irreversible capacity at the first cycle derives mainly from the appearance of inactive Ni during the first discharging, which is consistent with the energy shift E–E₀ of the absorption edge for the Ni absorber and the bond length change of Ni–O. A decrease/increase of Debye–Waller factor of the Ni–O contribution results from a decrease/increase of Jahn–Teller active Ni^III concentration on the charge and discharge cycle. The charge ordering between Ni^II and Mn^IV may take place in this compound, resulting from the significant difference of the bond length and the Debye–Waller factor for the second shell Mn–M and Ni–M contributions between the starting and fully charged states. A balance of the repulsive force and size effect in the layered compound plays an important role in the inhibition of structure distortion during the delithiation and lithiation cycle.