Fabrication of hierarchical porous MnCo2O4 and CoMn2O4 microspheres composed of polyhedral nanoparticles as promising anodes for long-life LIBs

Abstract

Uniform hierarchical porous MnCo₂O₄ and CoMn₂O₄ microspheres (3–6 μm) were fabricated through a solvothermal process followed by a post-annealing treatment. Fascinatingly, these porous MnCo₂O₄ and CoMn₂O₄ 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⁺ insertion/extraction process and shorten the Li⁺ diffusion lengths. The polyhedral structure can enhance the electrolyte/electrode contact area and increase the number of Li⁺ insertion/extraction sites. When used as anode materials for lithium-ion batteries, the porous MnCo₂O₄ and CoMn₂O₄ microspheres exhibited excellent long-life cycling performance at high rate density. At a current density of 1000 mA g⁻¹, the MnCo₂O₄ and CoMn₂O₄ exhibit an initial capacity of 1034 and 1107 mA h g⁻¹ and the capacity is maintained at 740 and 420 mA h g⁻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.