General synthesis of MFe2O4/carbon (M = Zn, Mn, Co, Ni) spindles from mixed metal organic frameworks as high performance anodes for lithium ion batteries

A general method has been developed for the synthesis of the spindle-like MFe2O4/C (M = Zn, Co, Ni, Mn). The synthetic procedure involves the preparation of mixed metal organic frameworks (i.e. Fe2M-MOFs) and their subsequent calcination. The obtained MFe2O4/C spindles show an intriguing structure, which consists of carbon coated secondary MFe2O4 nanoparticles with an interconnected carbon network. This makes them highly promising as the active materials for various applications with enhanced performance. For example, when used as the anode for lithium ion batteries (LIBs), the MFe2O4/C spindles exhibit higher reversible capacities and higher cycling stability in comparison to the MFe2O4 materials reported previously. Most interestingly, these MFe2O4/C spindles exhibit good morphology preservation during cycling. This shows that the volumetric expansion of MFe2O4 upon lithiation leads to the leaching of some active materials to the surface of the MFe2O4/C spindles along the percolation channels. This alleviates the volumetric expansion energy and prevents the structural destruction of MFe2O4/C spindles. The leached active materials do not detach from the MFe2O4/C spindles and participate in the lithiation/delithiation reactions throughout the whole cycling process, giving the MFe2O4/C spindles with high specific capacity and good durability. The approach reported here is highly versatile and might be applicable to the synthesis of other MFe2O4/C spindles for various applications.