Preparation and electrochemical Li storage performance of MnO@C nanorods consisting of ultra small MnO nanocrystals

MnO, with low operation potential and cost, is very attractive among transition metal oxides as an anode material for Li ion batteries. In this work, hierarchical MnO@C nanorods, in which ultra-small MnO nanocrystals (generally <5 nm) were homogeneously dispersed in a carbon matrix and further coated with a well-proportioned carbon shell, were prepared through a two-step hydrothermal treatment and subsequent sintering at 600 °C, with a slow heating rate of 5 °C min−1. In contrast, when sintered at a higher temperature (800 °C) and a faster heating rate (10 °C min−1), the ultra-small MnO nanocrystals agglomerated into nanoparticles (30–80 nm) and partially lost the contact with the outer carbon shell. Profiting from the highly-dispersed ultra-small nanocrystals in the carbon matrix and the well-proportioned carbon shell, the carbon-coated MnO nanocrystals exhibited a reversible capacity of 481 mA h g−1 after 50 cycles at a current density of 200 mA g−1, which is higher than that of carbon-coated MnO nanoparticles. The results disclose the important roles of small particles and carbon shells in developing advanced anode materials for Li ion batteries.