Preparation And Electrochemical Behaviours Of MoSe₂-based Composite Materials

Layered-structured nanomaterials possess the merits of short Na-ion diffusion length and large pathway,which have been considered as the next-generation anode materials for sodium ion batteries（SIBs）.Molybdenum diselenide（MoSe₂）,a wider interlayer distance semiconductor,promises the most potential sodium-ion-storage capabilities among the layered-materials family.However,the poor cycling stability caused by irreversibility and low electronic/ionic conductivity hindered its further applications in SIBs.In this thesis,several MoSe₂ based nanocomposites complexing with metallic MoO₂ nanoparticles and reduced graphene oxide（rGO）were constructed.The preparation,microstructure and electrochemical behaviors,as well as mechanism/kinetics of electrochemical reactions were investigated.MoSe₂ nanoflowers and MoO₂ nanoparticles were prepared by a hydrothermal and a solvothermal reaction,respectively.Influences of parameters（i.e.time,temperature ect.）during chemical reactions on the structure and morphology have been investigated to show the possible formation mechanism.MoSe₂ nanoflowers and MoO₂ nanoparticles have a large specific capacity and outstanding rate performance due to the large specific area and short ionic diffusion pathway,respectively.MoO₂ decorated MoSe₂ nanocomposites（MoO₂/MoSe₂）were synthesized using hydrothermal and solvothermal reactions as an anode for SIBs.Ex-situ XRD results showed that the sodium-ion-storage processes were highly reversible in MoO₂/MoSe₂ nanocomposites,which resulted from the chemical adsorbed of Na₂Se on discharged MoO₂ via Na-O bond according to ex-situ XPS test.It displays superior cycling stabilities at a current density of 1.0 A g^-1 for 100 cycles with a retention rate of⁸0%(vs 1^st cycle).A hybrid composed of MoSe₂ and reduced graphene oxide（rGO）was prepared via an optimized hydrothermal reaction（rGO/MoSe₂）.Among them,the electron mobility of rGO_⊥/MoSe₂ nanocomposites was enhanced by high-conductivity of graphene and Mo-C chemical bond at MoSe₂-rGO interface.The Na-ion diffusion was improved via vertical arrangements and（002）facets exposure.rGO_⊥/MoSe₂exhibits an excellent rate capacity retention of 76%from 0.1 A g^-1 to 3.2 A g^-1.MoO₂ and rGO co-modified MoSe₂ was prepared through a solvothermal route,denoting as（MoO₂,rGO_⊥）/MoSe₂ thereafter.The reversibility,electronic conductivity and ionic transportation properties were optimized synergisticly,leading to an extra stable cycling stability and excellent rate performance.As-prepared（MoO₂,rGO_⊥）/MoSe₂ possess a capacity retention of over 98%after50 cycles at a current density of 0.4 A g^-1.The rate capacity retention was calculated as 81%when current density rising 0.1 A g^-1 to 3.2 A g^-1.A hybrid sodium capacitor（SIC）was designed and assembled using（MoO₂,rGO_⊥）/MoSe₂ as an anode and activated carbon（AC）as a cathode,delivering a maximum energy density and power output of 93.06 W h kg^-11 and 7920 W kg^-1,respectively.