Electronic Structure of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ Positive-electrode Materials for Lithium-ion Battery

The electronic structures of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ positive electrode materials were calculated by using the density functional theory based plane-wave pseudo-potential technique (DFT-PW-PS). The computational results show that trivalent manganese and tetravalent manganese are two existing states of the manganese in LiMn₂O₄, and the average magnetic moment is about 3.5 μ_b. A strong covalent bond is formed between the Mn3d orbital and O2p orbital, and ionic bond is mainly formed between lithium and oxygen. The strong interactions between manganese and oxygen is conducive to maintaining the lattice stability, which is beneficial for the reversible insertion and extraction of lithium ions. When the manganese is partially substituted by nickel, the redox center is translated to the nickel during the intercalation/deintercalation of lithium ions, and the doping of nickel suppresses the reduction of manganese and the dissolution of manganese of low valence states, improves the integrity of lattice. Hence, the doping of nickel is beneficial for improving the structural stability and electrochemical performance of the materials.