Phase transition of manganese (oxyhydr)oxides nanofibers and their applications to lithium ion batteries and separation membranes

Abstract

Mn₅O₈, MnO₂, Mn₂O₃ nanofibers were obtained by annealing β-MnOOH nanofibers. Through β-MnOOH treated under hydrothermal conditions γ-MnOOH nanowires that were 40–100 nm in diameter and a few micrometres in length were derived. High resolution transmission electron microscopy (HRTEM) revealed that synchronous “oriented attachment” and dissolution–recrystallization mechanisms were both involved in the transition between these two manganese oxyhydroxides. Lithium ion battery performance of Mn₅O₈ nanofibers is presented for the first time in this work. Manganese oxides showed a great improvement in lithium storage (almost four times) compared to their corresponding bulk counterparts. The differences in lithium ion battery performance of these oxides are discussed based on their crystal structures. We propose that the interplanar trigonal prisms in Mn₅O₈ might hinder the movement of lithium ions, while they could diffuse freely in the tunnels formed by MnO₆ octahedra in MnO₂. Fibrous membranes were prepared from γ-MnOOH nanowires. By a deep filter mechanism, the membrane had a 93% rejection for 100 nm particles and 70% for 30 nm particles at a flux of 11000 L m⁻² h⁻¹ bar⁻¹.