Nitrogen-doped amorphous carbon coated mesocarbon microbeads as excellent high rate Li storage anode materials

A composite anode material consisting of a stable inner core of mesocarbon microbeads and a porous nitrogen-doped amorphous carbon shell active for lithium storage is prepared. The thin birnessite MnO 2 nanosheets hydrothermally deposited on mesocarbon microbeads are in situ replaced by polypyrrole , which is then transformed to nitrogen-doped amorphous carbon layer by calcination in nitrogen atmosphere. The surface modified mesocarbon microbeads exhibit average discharge capacities of 444 and 103 mA h g −1 at the current densities of 0.1 and 3 A g −1 , respectively, obvious higher than the corresponding values of the bare sample, 371 and 60 mA h g −1 . Moreover, the composite anode maintains a discharge capacity of 306 mA h g −1 after 500 cycles at 1 A g −1 , suggesting an excellent cycle stability. It is believed that the nitrogen-doped amorphous carbon layer has provided additional lithium storage capacity and stabilized the structure integrity of mesocarbon microbeads. This work demonstrates that the capacity and rate performance of commercial graphitic carbons can be much improved by simply introducing a nitrogen-doped carbon coating layer active for Li storage, making them attractive for high power Li-ion batteries.