Preparation Of Graphene Based-Metal(Sn,Zn,Mo) Selenides Composites And Their Investigation Of Electrochemical Performance

The application of metal compounds-based anode materials in the field of lithium/sodium/potassium storage is limited by their poor cyclic stability and rate performance.In our work,Sn O₂,Zn Se and Mo Se₂ were selected as the research object.Through the controllable design for composition and microstructure,as well as the introduction of graphene（GN）or porous carbon,the electrochemical performance of the Sn O₂,Zn Se and Mo Se₂ based anodes can be significantly improved.Meanwhile,the characteristics and mechanism in energy storage were investigated by GITT and a series of ex-situ measurements in-depth.The main content of our research is displayed as bellow:1.A double shell micro-cube assembled by nanosized Co₃Sn₂/Sn O₂ heterostructures with amorphous carbon layers wrapped in three-dimensional graphene（GN）matrix（DS-Co₃Sn₂/Sn O₂@C@GN）is successfully synthesized via co-precipitation,hydrothermal reaction and annealing treatment.The heterojunction interfaces between Co₃Sn₂ and Sn O₂significantly accelerate transfer kinetic of ions and therefore enhance the dynamics of electrochemical reaction.The chemical bonds between Co₃Sn₂ and Sn O₂,as well as the double shell structure can effectively improve the structural stability of the anode material.Meanwhile,the“double-carbon”modification can enhance conductivity of the anode material.As an anode material for LIBs/SIBs,the DS-Co₃Sn₂/Sn O₂@C@GN electrode can deliver excellent electrochemical performance.2.A yolk-shell nitrogen-doped porous carbon polyhedron skeleton evenly embedded with Zn Se and Co Se₂ nanodots in the yolk and shell parts,respectively（Zn Se-NC@Co Se₂-NC）,is fabricated by the simultaneous carbonization/selenization process of the ZIF-8@ZIF-67precursor.The built-in electric field formed at the heterojunction interfaces between Zn Se and Co Se₂ can drive the ions transmission with high speed,contributing accelerated electrochemical reaction dynamics.The nitrogen doped porous carbon skeleton with yolk shell structure can shorten ions diffusion path,improve the structural stability and electrical conductivity of electrode materials.In LIBs/SIBs,the anode material can show excellent electrochemical performance than Zn Se-NC and Co Se₂-NC.The great performance of the electrode in lithium full battery shows its practical potential.3.Mo Se₂ nanosheets were successfully grown on GN substrate vertically with dispersed ultrasmall Sn Se nanodots（Sn Se/Mo Se₂@GN）via facile hydrothermal method combined with calcining process.The Sn originated from discharging product of Sn Se can exist in subsequent cycles and promote the conversion from Mo/Na₂Se（K₂Se）to Mo Se₂ during the charging process to improve reversible conversion efficiency of Mo Se₂.The introduction of GN substrate bonded with Mo Se₂ by Mo-C bond can effectively expose active sites of Mo Se₂,improve stability and electrical conductivity of the whole material.In SIB/PIB half-cell,the Sn Se/Mo Se₂@GN anode can deliver remarkable properties.Meanwhile,the excellent performance of the electrode in sodium/potassium full battery shows its practical potential.4.Through hydrothermal method combined with annealing process,Mo Se₂ nanosheets doped with different content of Sn were dispersed on GN surface uniformly in vertical direction（Sn-Mo Se₂@GN）.The uniformly dispersion of Sn in crystal structure of Mo Se₂can effectively facilitate reversible conversion of Mo Se₂ in storing Na-ions.Measurement results illustrate that the Sn with doping content of 9.6%（atomic fraction）in Mo Se₂@GN has the most defects,biggest specific surface and lattice spacing,which is beneficial to expose more active sites,improve the capture ability and capacity of Na⁺.Meanwhile,the cut-off voltage of discharging was enhanced to 0.2 V in electrochemical performance test,which could prevent completely structural damage of Mo Se₂ resulted from complete conversion to Na₂Se.As an anode material for sodium storage,the 9.6%Sn-Mo Se₂@GN electrode can exhibit excellent cycle stability and rate performance.