LiMn2O4 Cathode Materials with Excellent Performances by Synergistic Enhancement of Double-Cation (Na+, Mg2+) Doping and 3DG Coating for Power Lithium-Ion Batteries

LiMn2O4 is a very important cathode material in the field of plug-in hybrids. However, it has limited large-scale practical application because of its severe electrode polarization and rapid capacity decay. By means of synergistic enhancement of double-cation (Na+, Mg-2(+)) doping and three-dimensional graphene (3DG) coating, the Li0.94Na0.06Mg0.08Mn1.92O4/3DG composite cathode material was successfully synthesized via hydrothermal synthesis, high-temperature solid-phase sintering, and freeze-drying. Electrochemical test results display that the initial discharge specific capacity of the Li0.94Na0.06Mg0.08Mn1.92O4/3DG material reaches 146 mAh/g (137 mAh/g for LiMn2O4) at 0.5C, and the specific capacity remains at 130 mAh/g after 100 cycles (99 mAh/g for LiMn2O4). At 10C, the initial discharge specific capacity of the Li0.94Na0.06Mg0.08Mn1.92O4/3DG material is 90 mAh/g (69 mAh/g for Li0.94Na0.06Mg0.08Mn1.92O4 and 38 mAh/g for LiMn2O4), which should be resulted from the synergistic enhancement of double-cation (Na+, Mg2+) doping and 3DG coating. Na+, Mg2+ codoping effectively expands the Li+ diffusion path and the diffusion coefficient of Li0.94Na0.06Mg0.08Mn1.92O4/3DG, and inhibits the dissolution of Mn3+. 3DG coating effectively improves the conductivity and reduces electrode polarization during the charge and discharge course. In addition, 3DG coating also plays an important role in inhibiting the dissolution of Mn3+.