Crystal Structure, Electronic Structure and Electrode Performance of o-LiMn_1−xM_xO₂ (M=Mn, Co, Ni) as a Cathode Material for Li Secondary Battery

Abstract

We investigated the relationship between the electrode performance, crystal structure and electronic structure of LiMn_1−xM_xO₂ (M=Mn, Co, Ni, Zn). The discharge capacity of o-LiMn_1−xM_xO₂ decreased compared to that of LiMnO₂. On the other hand, the cycle fading decreased since the maximum capacity was improved by substitution with Co or Ni. The crystal structure analysis by neutron powder diffraction was examined for LiMn_1−yM_yO₂ (M=Co, Ni). The bond angle variances increased due to the Co or Ni substitution. The electron density distribution was obtained by XRD using the MEM/Rietveld method. The electron density distribution shows that the covalent bonding of (Mn,M)–O of LiMn_1−xM_xO₂ is stronger than that of o-LiMnO₂. Next, we calculated the net charge of each atom, the bond overlap population of Li–O, Mn–O, M–O, the density of states, and the electron density of o-LiMn_1−xM_xO₂ using first principles calculation by the DV-Xα method and FLAPW method. Based on the results, the Li ionicity always remained high and the covalent bonding of Mn–O and M–O of each o-LiMn_1−xM_xO₂ is stronger than that of o-LiMnO₂. As a result, the covalent binding of (Mn,M)–O is important for good cycle performance.