A phase transformation route to porous 2D Mn₃O₄ nanosheets with promising anode performance for Li-ion batteries

A phase transformation route to porous 2D Mn₃O₄ nanosheets is developed by heat treatment of exfoliated layered MnO₂ nanosheets. The calcination of MnO₂ nanosheets at an elevated temperature of ≥ 500 °C in Ar atmosphere leads to the formation of porous 2D nanosheets as well as to reductive phase transition to low-valent Mn₃O₄. The formation of spinel-structured Mn₃O₄ phase with mixed tetrahedral and octahedral local symmetries is obviously evidenced by micro-Raman and X-ray absorption spectroscopies. An elevation of heating temperature enlarges the surface pore of 2D nanosheet and lowers the average oxidation state of Mn ion. In comparison with Mn₃O₄ crystal, the porous 2D Mn₃O₄ nanosheets show higher electrode activities for lithium ion batteries (LIBs) with larger discharge capacities, better rate characteristics, and excellent cyclabilities, emphasizing the advantage of porous 2D nanosheet morphology in optimizing the electrode functionality of metal oxide. The present study underscores the validity of the present phase transformation route in exploring novel high-performance metal oxide–based LIB electrode materials.