Phase- and morphology-controlled MnO2: Its synthesis and influence on the electrochemical performance of spinel LiMn2O4 cathode materials

In this study, MnO₂ was synthesized via a hydrothermal method using four different oxidizing agents: KMnO₄, K₂S₂O₈, KClO₃, and (NH₄)₂S₂O₈. The KMnO₄ precursor led to the formation of aggregated α-MnO₂, while K₂S₂O₈ produced a mixed phase of α- and γ-MnO₂. (NH₄)₂S₂O₈ promoted the formation of γ-MnO₂ at lower temperatures and induced a structural transition to β-MnO₂ at elevated temperatures. Among the lithium precursors investigated, LiOH was found to be the most effective in preserving the spherical morphology of LiMn₂O₄ during synthesis. Electrochemical measurements revealed that the LiMn₂O₄ sample synthesized from γ-MnO₂ exhibited the highest charge capacity of 132.59 mAh∙g⁻¹, while the α-MnO₂-based LiMn₂O₄ demonstrated the best stability. These results indicate that the initial MnO₂ phase significantly influences the electrochemical performance of the resulting spinel cathode.