Facile hydrothermal synthesis and electrochemical properties of orthorhombic LiMnO2 cathode materials for rechargeable lithium batteries

Pure-phase, LiMn2O4-mixed and aluminum-doped orthorhombic LiMnO2 (o-LiMnO2) cathode materials with high discharge capacity and excellent cyclic stability were prepared by one-step hydrothermal reaction of MnCl2, EDTA, LiOH, AlCl3 and NaClO solutions. Chemical composition and aluminum content were affected by temperature and the concentration of LiOH, NaClO and AlCl3. A mixed phase of Mn3O4 and o-LiMnO2, pure-phase o-LiMnO2, and a mixed phase of o-LiMnO2 and LiMn2O4 were formed with increasing the concentration of NaClO from 0.08 to 0.25 mol L-1 at 180 degrees C for 24 h. Adding EDTA and NaClO facilitated the formation of o-LiMnO2. Al/Mn molar percent ratios in doped o-LiMnO2 were 0.34, 0.58, 0.91, and 1.22 when Al/Mn molar ratios in hydrothermal system were controlled at 0.05, 0.10, 0.15, and 0.20, respectively. Mixing LiMn2O4 and doping Al improved the discharge capacity and cyclic stability of o-LiMnO2. o-LiMnO2, the mixture with an o-LiMnO2/LiMn2O4 mass ratio of 2.45, and doped o-LiMnO2 with an Al/Mn molar percent ratio of 0.58 exhibited initial discharge capacities of 76, 139, and 82 mA h g(-1), and cycling capacities of 124, 144, and 156 mA h g(-1) after 100 cycles, respectively. This work facilitates the preparation and electrochemical performance improvement of o-LiMnO2.