A High Capacity and High-Rate Anode Material for Lithium-Ion Batteries Based on Bimetallic CoNi-MOFs

Metal-organic frameworks (MOFs) with a high porosity and high specific surface area are widely used as anode materials in Li-ions batteries. Herein, we synthesized bimetallic CoNi-MOFs with a general solvothermal method, and the obtained CoNi-MOFs show alamellar bulk structure. The CoNi-MOFs exhibit a remarkable electrochemical performance, with a high reversible capacity up to 1120 mAhg-1 after 200 cycles performed at a current density of 500 mA g-1 and an excellent rate performance, which is ascribed to the variable-valence metal ions and redox-active ligands. We employed a suite of measurements, including X-ray photoelectron spectroscopy (XPS), X-ray adsorption fine structure (XAFS) measurements, and scanning electron microscopy (SEM).The SEM images show that the morphology of the electrode changes as the electrode is charged and discharged during cycling.We found that the transition metals Co and Ni are in high valence states during charging. However, the XAS and XPS results suggest that Ni2+ and Co2+ are induced to Ni0 and Co0during discharging. This evidence is conducive to exploring the intrinsic mechanism of Li insertion/extraction and understanding the electrochemical behaviors. We optimized the material design and performed a more in-depth study of the mechanism used to make the MOF materials better to meet the high power/energy density requirement of lithium-ion batteries (LIBs).