Synthesis of high-purity LiMn2O4 with enhanced electrical properties from electrolytic manganese dioxide treated by sulfuric acid-assisted hydrothermal method

Abstract

Using sulfuric acid-assisted hydrothermal treatment, β-MnO2 particles were obtained from the electrolytic manganese dioxide (EMD). Via high-temperature solid-phase reactions, spinel lithium manganese oxides (LiMn2O4) were produced using the obtained β-MnO2 particles as precursor mixed with LiOH·H2O for the lithium-ion battery cathodes. Atomic absorption (AAS) shows that after the hydrothermal treatment, the contents of impurity ions, such as Na+, K+, Ca2+, and Mg2+, caused by the limitation of preparation technology of EMD are greatly reduced. X-ray diffraction and scanning electron microscopy show that β-MnO2 is highly alloyed consisting of nano sticks. Spinel lithium manganese (LiMn2O4) synthesized by the β-MnO2 precursor has high crystallinity with a well 111 face grow and presents a regular and micron-sized octagonal crystal. When used as cathode materials for lithium-ion batteries, LiMn2O4 synthesized by the β-MnO2 precursor has greater discharge capacity, better cycle performance, and better high-rate capability when compared with LiMn2O4 synthesized by the EMD precursor. Cyclic voltammetry and electrochemical impedance spectroscopy indicate that LiMn2O4 synthesized by the β-MnO2 precursor has better electrochemical reaction reversibility, greater peak current, higher lithium-ion diffusion coefficient, and lower electrochemical impedance.