Rational design of MnO/carbon nanopeapods with internal void space for high-rate and long-life li-ion batteries

Searching the long-life MnO-based materials for lithium ion batteries (LIBs) is still a great challenge because of the issue related to the volumetric expansion of MnO nanoparticles (NPs) or nanowires (NWs) during lithiation. Herein, we demonstrate an unexpected result that a peapod-like MnO/C heterostructure with internal void space can be facilely prepared by annealing the MnO precursor (MnO-P) NW/polydopamine core/shell nanostructure in an inert gas, which is very different from the preparation of typical MnO/C core/shell NWs through annealing MnO NW/C precursor nanostructure. Such peapod-like MnO/C heterostructure with internal void space is highly particular for high-performance LIBs, which can address all the issues related to MnO dissolution, conversion, aggregation and volumetric expansion during the Li ⁺ insertion/extraction. They are highly stable anode material for LIBs with a very high reversible capacity (as high as 1119 mAh g^-1 at even 500 mA g^-1) and fast charge and discharge capability (463 mAh g^-1 at 5000 mA g^-1), which is much better than MnO NWs (38 mAh g^-1 at 5000 mA g^-1) and MnO/C core/shell NWs (289 mAh g^-1 at 5000 mA g^-1). Such nanopeapods also show excellent rate capability (charged to 91.6% in 10.6 min using the constant current mode). Most importantly, we found that MnO/C nanopeapods show no capacity fading even after 1000 cycles at a high current density of 2000 mA g^-1, and no morphology change. The present MnO/C nanopeapods are the most efficient MnO-based anode materials ever reported for LIBs.