Nano-MnO₂@TiO₂ microspheres: A novel structure and excellent performance as anode of lithium-ion batteries

A structurally hierarchical MnO₂/TiO₂ composite (Nano-MnO₂@TiO₂) is fabricated by calcining MnCO₃ microspheres and coating a thin layer of TiO₂ through the heat decomposition of tetrabutyl titanate, and evaluated as anode of gravimetrically and volumetrically high energy density lithium ion battery. The characterizations from FESEM, TEM, HRTEM and XRD, indicate that the resulting Nano-MnO₂@TiO₂ takes a spherical morphology with a core of about 2 μm in diameter, consisting of compact MnO₂ nanoparticles, and a shell of 60 nm thick, consisting of smaller TiO₂ nanoparticles. The charge/discharge tests demonstrate that Nano-MnO₂@TiO₂ exhibits excellent performance as anode of lithium ion battery, delivering a capacity of 938 mAh g⁻¹ at 300 mA g⁻¹ after 200 cycles, compared to the 103 mAh g⁻¹ of the uncoated sample. The microsphere consisting of compact nanoparticles provides Nano-MnO₂@TiO₂ with high specific gravity. The dimensionally and structurally stable TiO₂ maintains the integrity of MnO₂ microspheres and facilitates lithium insertion/extraction. This unique structure yields the excellent cyclic stability and rate capability of Nano-MnO₂@TiO₂.