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

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.