Fabrication of hierarchical porous MnCo sub(2)O sub(4) and CoMn sub(2)O sub(4) microspheres composed of polyhedral nanoparticles as promising anodes for long-life LIBs

Uniform hierarchical porous MnCo sub(2)O sub(4) and CoMn sub(2)O sub(4) microspheres (3-6 mu m) were fabricated through a solvothermal process followed by a post-annealing treatment. Fascinatingly, these porous MnCo sub(2)O sub(4) and CoMn sub(2)O sub(4) microspheres are composed of numerous polyhedral nanoparticles with diameters in the range of 200-500 nm. The porous structure is believed to be beneficial for improving the lithium-storage performance of the products, which can effectively buffer the volume expansion during the Li super(+) insertion/extraction process and shorten the Li super(+) diffusion lengths. The polyhedral structure can enhance the electrolyte/electrode contact area and increase the number of Li super(+) insertion/extraction sites. When used as anode materials for lithium-ion batteries, the porous MnCo sub(2)O sub(4) and CoMn sub(2)O sub(4) microspheres exhibited excellent long-life cycling performance at high rate density. At a current density of 1000 mA g super(-1), the MnCo sub(2)O sub(4) and CoMn sub(2)O sub(4) exhibit an initial capacity of 1034 and 1107 mA h g super(-1) and the capacity is maintained at 740 and 420 mA h g super(-1) after 1000 cycles. Furthermore, the growth mechanism of porous microspheres is proposed based on many contrast experiments. The relationship between morphology evolution and annealing time is particularly investigated in detail. It is found that the annealing time plays an important role in obtaining products with different morphologies. Through the controlled annealing time, porous microspheres, yolk-shell microspheres and solid microspheres could be selectively obtained.