Co₃ O₄ Polyhedron@MnO₂ Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries

In this work, a novel lollipop nanostructure of Co₃ O₄ @MnO₂ composite is prepared as anode material in lithium-ion batteries (LIBs). Cobalt metal-organic framework (ZIF-67) is grown on the open end of MnO₂ nanotubes via a self-assembly process. The obtained ZIF-67@MnO₂ is then converted to Co₃ O₄ @MnO₂ by a simple annealing treatment in air. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction characterizations indicate that the prepared Co₃ O₄ @MnO₂ takes a lollipop nanostructure with a stick of ≈100 nm in diameter, consisting of MnO₂ nanotube, and a head part of ≈1 µm, consisting of Co₃ O₄ nanoparticles. The charge-discharge tests illustrate that this unique novel configuration endows the resulting Co₃ O₄ @MnO₂ with excellent electrochemical performances, delivering a capacity of 1080 mAh g^-1 at 300 mA g^-1 after 160 cycles, and 696 mAh g^-1 at 1 A g^-1 after 210 cycles, compared with 404 mAh g^-1 and 590 for pure Co₃ O₄ polyhedrons and pure MnO₂ nanotubes at 300 mA g^-1 after 160 cycles, respectively. The lollipop configuration consisting of porous Co₃ O₄ polyhedron and MnO₂ nanotube shows excellent structural stability and facilitates lithium insertion/extraction, leading to excellent cyclic stability and rate capacity of Co₃ O₄ @MnO₂ -based LIBs.