Synthesis And Electrochemical Lithium Storage Properties Of Novel Nanostructured Anode Materials Derived From MOFs And Their Composites

Transition metal oxides(TMOs)and silicon are considered to be potential alternatives to commercial anode graphite for lithium-ion batteries(LIBs)because of their higher theoretical capacity.However,both of them suffer huge volume changes during the lithization/de-lithization,resulting in poor structural stability and cycling performance.At the same time,due to their poor electronic conductivity and electrochemical kinetics,the rate performances of transition metal oxides and silicon materials still need to be promoted.At present,the most effective way to solve above issues is to synthesize nanostructures and combine with carbon.Metal-organic frameworks(MOFs)have been proved to be ideal precursors for the preparation of transition metal oxide/carbon composites due to their composition and structural characteristics.However,the preparation conditions of pure phase metal-organic frameworks are rather harsh,and their applications are limited.Furthermore,the in-situ coating methods of MOFs and the preparation of silicon-carbon composites with MOFs reported in the literature are scarce.Considering this,we have done some meaningful work as following:Co-MOF and Ni-MOF precursors were prepared by a simple solvothermal method.After subsequent heat treatment,urchin-like Co3O4/C microspheres and NiO@Graphene microflowers were obtained.The effect of different solvothermal conditions on the morphology of MOF precursor and the phase transformation of MOFs during heat treatment were studied.Their unique structure can provide numerous active sites for the electrochemical reaction.When evaluated as anode of LIBs,urchin-like Co3O4/C microspheres and NiO@Graphene microflowers show good lithium storage performance.Fe2O3/MIL-00(Fe)nanospheres were prepared by adjusting the solvothermal conditions.After annealing in air and Ar respectively,hollow Fe2O3 nanospheres and hierarchical Fe3O4@C nanospheres were prepared.The differences of their components and structure are analyzed.Meanwhile,the lithium storage performance of these two materials is compared in details.Due to its better electronic conductivity and electrochemical kinetics,hierarchical Fe3O4@C nanospheres exhibit better rate performance and cycling performance.After cycled 500 times at a current density of 500 mA g-1,Fe3O4@C exhibits a discharge capacity of 757.9 mAh g-1.SiAl@Al-MOF intermediate was prepared by in-situ coating method with SiAl alloy as the main raw material by self-corrosion reaction of Al with 1,4-naphthalene dicarboxylic acid under hydrothermal conditions.The core-shell porous Si microsphere@C(pSiMS@C)and Si nanoparticles@C(SiNPs@C)composites were fabricated by one-step and two-step annealing-etching processes respectively.The composition and structure of these two composites are characterized,and the reasons for the structural evolution are analyzed.Because the porous silicon microsphere(pSiMS)core composed of interconnected Si nanowires can provide more lithium storage sites,shorten the diffusion path of Li+ and relieve internal stress,pSiMS@C displays a better lithium storage performance.The revisable capacity of pSiMS@C after 500 cycles at 1 A g-1 is 1027.8 mAh g-1.SiAl@Ni-MOF intermediate was prepared by electroless Ni plating and self-corrosion reaction of metal Ni with pyromellitic acid under solvothermal condition.Then Si@Ni/Graphene microsphere composites were further synthesized by the self-catalysis of Ni-MOF pyrolysis.Because the Ni/Graphene coating on the surface of microsphere can effectively improve the electronic conductivity,maintain the integrity of the structure and prevent the material from breaking,the specific discharge capacity of the core-shell Si@Ni/Graphene microspheres can maintain 1697.3 mAh g-1 after 100 cycles at a current density of 200 mA g-1.