Preparation And Electrochemical Properties Of Nanocomposites Derived From Iron-based Metal Organic Framework

On account of reasonable cost,abundant resources,structural diversity and high specific area,iron-based metal-organic framework(FeMOF)was widely used in energy storage.More importantly,due to its very high theoretical capacity,Fe-MOF derivatives are favorable candidates for anode materials.However,significant volume expansion and inferior conducting power are the present situation for this type of material.Compositing these materials with graphene is an effective solution.In this context,different morphologies of Fe-MOF@GO were synthesized by introducing graphene oxide(GO)and controlling reaction conditions.Nanocomposites with different morphologies were prepared through using various derivation sources and methods.They were used as anode of lithium-ion battery and their electrochemical properties were tested.(1)Octahedral Fe-MOF@GO was synthesized by one-step solvothermal method,and octahedral Fe2P/C@rGO nanocomposites were prepared by one-step high temperature calcination using sodium hyphosphite as phosphorus source.Nanostructure can alleviate the internal stress to some extent,and shorten the transmission path of Li+.More importantly,P-doped reduced graphene oxide(rGO)and octahedral carbon skeleton form a good conductive network that further inhibiting the volume expansion of Fe2P nanoparticles.At the same time,the doped surface can provide more lithium storage sites.After 180 times at 0.1 A g-1,the reversible capacity of octahedral Fe2P/C@rGO reachs 983.1 mAh g-1.(2)In order to synthesizing materials with higher capacity,the flowerlike FeS/C@rGO nanocomposites were successfully prepared by one-step high temperature calcination using the octahedral Fe-MOF@GO as the precursor and thioacetamide(TAA)as the sulfur source.The flower-like structure is formed by self-assembly of FeS nanosheets after octahedral collapse,which enlarges the reachable zone between the electrode material and the electrolyte and improves the transmission efficiency of Li+.At the same time,rGO can effectively inhibit the volume expansion and agglomeration of FeS nanosheets.At 0.1 A g-1,the reversible capacity of flower-like FeS/C@rGO is 1428.2 mAh g-1 after 130 times.The pseudocapacitive behavior contributes the main capacity of the electrode material.(3)Spindle-like Fe-MOF@GO was synthesized by using glacial acetic acid and poly ether polyol(P-123)as molecular regulator through the first hydrothermal process,and Fe7S8/C@rGO nanocomposites were prepared by using TAA as sulfur source through the second hydrothermal process.Nano-sized Fe7S8 is very convenient for Li+and electron transport.S-doped rGO can maintain the stability of the spindle-like carbon skeleton,and further inhibit the agglomeration and volume expansion of Fe7S8 nanoparticles.It also can induce more electrons and lithium ions to transport.The reversible capacity of spindle-like Fe7S8/C@rGO is 1465.1 mAh g-1 after 150 times at 0.1 A g-1.