Metal–organic Framework And Its Derivatives For Lithium Storage

Lithium ion batteries(LIBs) has been widely used in cell phones, laptop computer, and portable electronic devices because of high working voltage, long life and environmental friendly. However, with the rapid and large-scale applications of electric vehicles(EVs) and other high-power electric devices, at present, the commercial lithium ion battery has not yet able to meet the demand of EVs because of the challenges: the capacity, power density and rate performance is limited by its current primarily electrode materials. Thus, there is an urgent need to develop new electrode materials for the next generation of LIBs. Recently, a new type of porous materials, metal-organic frameworks(MOFs) and its derivatives have been successfully applied in LIBs, and have received wide attention.In this work, we first synthesized a metal-organic nanofiber from aspartic acid and copper nitrate(two environmental friendly materials with abundance). The nanofiber with small diameter reduces the Li-ion diffusion length, as anodic electrode materials the discharge capacity can retain a large value of 233 mAh/g at a current density of 50 mA/g. In addition, we synthesized MIL-88(Fe), which delivered a highly reversible capacity of 673.3 mAh/g at a current density of 200 mA/g after 500 cycles. By combining with other contrast experiments, the lithium ion store mechanism is preliminarily revealed. This part of work demonstrated that MOFs is a potential candidate as anode materials for LIBs.We successfully prepared CuO particles through direct thermal decomposition of Cu-based metal-organic nanofiber precursors under air atmosphere. When tested as an anode material for LIBs, a stable reversible capacity as high as ~680 m Ah/g up to 500 th cycle at 0.5C rate was obtained(theoretical capacity of 372 mAh/g). Similarly, we fabricated Fe3O4/C composites through heat treatment of MIL-88(Fe) in a tube furnace with argon atmosphere. When tested as an andoe material, the composites exhibited a highly reversible capacity of 927.4 mAh/g after 200 cycles at a rate of 0.5 C. The reason for the excellent electrochemical performance of this composite can be explained by the addition of the electrically conductive carbon, which reduces the internal resistance. Nevertheless, the addition of carbon also relieve the volume variation of the active material of the LIBs, thereby leading to high cyclability and rate capability.In addition, we obtained N-doped nanostructure carbons with N mass percentage up to 8.62% from thermal decomposition of Cu-MONFs under argon atmosphere. The nanostructure carbon electrode shown high discharge capacity of 853.1 mAh/g at a current density of 500 mA/g after 800 cycles. A discharge capacity of 440 mAh/g can be obtained after 1000 cycles at a high current density of 5000 mA/g, which is higher than the capacity of commercial graphite materials. To the best of our knowledge, the performance of this novel carbon electrode is significantly higher in comparison with the previously reported carbon materials. We suggested this excellent performance might be arises from its peculiar N-doped nanostructure.