Preparation Of Iron-Based MOF Derivatives And Their Application In Lithium/Sodium Secondary Batteries

Fe-based MOFs derivatives have many advantages to meet the use and development of secondary batteries and are a highly promising anode material.In this paper,we focus on iron-based MOFs derivatives as the central point to solve the problems of its volume expansion and short cycle life as a battery material and optimize the material performance to the maximum extent by phosphorylation or sulfidation of precursors.The relevant conclusions are as follows:（1）Fe₂P/C@r GO nanocomposites with three-dimensional multichannel structure were prepared by one-step hydrothermal and one-step calcination methods.The material exhibits an octahedral structure with the size of different octahedra in the range of 700-900 nm and graphene plays an important role in forming the three-dimensional spatial structure,which can better play the role of graphene conductive/supporting skeleton and facilitate ion-electron conduction,and slow down the volume expansion to a certain extent.The three-dimensional multichannel octahedral Fe₂P/C@r GO nanocomposites have a satisfactory capacity:the reversible capacity is maintained at 696.7m Ah g^-1after 500 charge/discharge cycles at a current density of 1.0 A g^-1.In the investigation of the effect of GO solution concentration variation on the material properties,it can be determined that when GO concentration is moderate,the prepared electrode material has the relatively most excellent performance.（2）Controlled self-assembled sheet crossed Fe S/C@r GO materials were effectively prepared by a convenient hydrothermal method and calcination process using Fe-MOFs as self-sacrificing templates.Under the high temperature atmosphere,the precursor structure is difficult to maintain and cleaves into nanoflakes,which subsequently self-assemble in situ to generate sheet crossed composites.The flakes vary in size,length,and thickness,although they are all related to the previous octahedral prismatic edges,and their overall size is about 800 nm.On the one hand,the nanosheet crossover structure can effectively slow down the volume increase and thus prevent the rupture of SEI during lithium embedding/delithiation;on the other hand,the nitrogen-doped structures with more tiny pores on the surface,which makes the electrochemical stability of the electrode material more excellent.Meanwhile,the addition of reduced graphene oxide improves the electrical conductivity of the material and effectively slows down the volume growth.The electrochemical performance of the material was tested as the anode material for lithium-ion batteries,and the reversible capacity of Fe S/C@r GO as the anode of lithium-ion batteries reached 1426.5m Ah g^-1,after 70 cycles.（3）The MIL-53@ZIF-8@RF precursor materials were obtained by synthesizing MIL-53 nanostructures by the solvothermal method,and then coating ZIF-8 and RF layers on the surface.The spindle-shaped Fe₇S₈/C@Zn S/N-C@C composites were successfully prepared by high-temperature vulcanization using sulfur powder as the sulfur source.The different spindle-shaped materials are about 700-900 nm long and about 350 nm wide.This core-double-shell structure material with layered active material distribution designed by MOF-on-MOF strategy was then used as the anode of sodium ion battery.The electrochemical results show that Fe₇S₈/C@Zn S/N-C@C has the best electrochemical reaction kinetics,and the reversible specific capacities of the materials are 646.3 m Ah g^-1（100 cycles）,482.4 m Ah g^-1（500 cycles）,401.7 m Ah g^-1（200 cycles）,and 468.7 m Ah g^-1when the current density distributions are 0.1,1.0,2.0,and 5.0 A g^-1,respectively.（200 cycles）,and 468.2m Ah g^-1（300 cycles）.The combination of bimetallic sulfide modification,carbon modification,and core-bishell structure nanostructure of the material gives the material satisfactory excellent electrical conductivity,interfacial sodium storage capacity,and structural stability.