Lithium Manganese Oxides with Spinel Structure and Their Cathode Properties for Lithium Ion Battery

抄録

Structural and electrochemical properties of lithium manganese spinels at 4 V and 5 V ranges were reviewed. To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4 V class lithium secondary batteries, the quaternary spinel solid solution phases LiM_yMn_2-yO₄ (M = Co,Cr,Ni,Al, y = 1/12,1/9,1/6,1/3)(Fd3m) were prepared and studied extensively. The partially substituted spinels showed better cycle performance than the parent LiMn₂O₄. The improvement in cycling seems to be attributed to the stabilization in the spinel structure by the doped metal cations. In order to make the existing issues clear, local structural studies of LiM_yMn_2-yO₄ were carried out by molecular dynamics (MD) and extended to the measurement of Extended X-ray Absorption Fine Structure (EXAFS). From the analysis of the site potential around the octahedral cation site from the MD simulation, it became clear that the substitution by selected metal ion M³⁺ or M²⁺ strengthens the bond between octahedral M and O atoms. As a possible candidate of 5 V class, stoichiometric LiNi_0.5Nn_1.5O₄ (ordered-type P4₃32) and nonstoichiometric LiNi_0.5Mn_1.5O_4-δ (disordered type Fd3m) were examined. The disordered-type phases showed higher rate properties than the ordered-type. From the Coulomb potential calculation of both structures, it was suggested that the diffusion of lithium in the disordered-type occurs more easily compared with that in the ordered-type. These results supported the observed charge-discharge behavior of the resulting cells.