In-situ X-ray absorption spectroscopy investigations of a layered LiNi_(0.65)Co_(0.25)Mn_(0.1)O_2cathode material for rechargeable

摘要

In-situ X-ray absorption sepctroscopy investigations have been carried out to evaluate the oxidation states and the local structure at the Mn,Co and Ni K-edges for LiNi_(0.65)Co_(0.25)Mn_(0.1)O_2 during a charging and discharging process in this study.It was found that only the Ni atom in LiNi_(0.65)Co_(0.25)Mn_(0.1)O_2 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_(0.65)Co_(0.25)Mn_(0.1)O_2 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-E_0 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 form a decrease/increase of Jahn-Teller active Ni~III concentration on the charge and dischange cycle.The charge ordering between Ni~II and Mn~IV may take place in this compound,resulting form the significnat 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 in the inhibition of structure distortion during the delithiation and lithiation cycle.