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

Abstract

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 °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.