| As the world’s energy demand continues to increase,the application of renewable energy sources such as wind energy and solar energy is expanding.The efficient use of renewable energy is inseparable from high-performance energy storage devices.The sodium ion-based electrochemical energy storage device(sodium ion battery/capacitor)is considered to be an ideal choice for the next generation of large-scale energy storage devices due to its abundant sodium resources,and has received much attention in recent years.Among them,the development of suitable anode materials is one of the keys to obtain high-performance sodium ion batteries/capacitors.Due to the larger radius of sodium ions,it is more difficult for reversible deintercalation to occur in the electrode material,resulting in poor cycle performance and rate performance of sodium ion batteries/capacitors.The tin-based chalcogenide compound has a unique twodimensional crystal structure with a large interlayer distance.As a negative electrode material for sodium ion batteries,it exhibits a high reversible capacity.The nanostructured chalcogenide compound also has sodium ion pseudocapacitive storage characteristics.Therefore,it has huge application prospects as a negative electrode material for sodium ion capacitors.However,the tin-based chalcogenide compound still has the problems of poor conductivity and large volume expansion during the reaction,and the electrochemical performance is not ideal in the application of sodium ion batteries.To solve its volume expansion and improve the conductivity of the material is the key to improving the cycle life of tin-based chalcogenide compounds.Based on the above knowledge,this paper carried out the research of two tin-based chalcogenide compounds(stannous sulfide,stannous selenide)as negative electrode materials for sodium ion batteries/capacitors.Starting from improving its conductivity and easing its volume expansion,graphene was introduced as a carbon matrix to design and prepare two composite materials of stannous sulfide/graphene and amorphous stannous selenide/graphene.By constructing a nano-composite structure,the volume expansion and pulverization of pure phase stannous sulfide and stannous selenide are suppressed,and the problem of insufficient diffusion power of sodium ions in the bulk material is improved.As a negative electrode material for sodium ion batteries,stannous sulfide/graphene and amorphous stannous selenide/graphene have achieved significantly improved electrochemical performance.At the same time,combined with their high surface activity and high sodium ion pseudocapacitance storage capacity,we futher used them as negative electrode materials,activated carbon as positive electrode materials to assemble sodium ion capacitors,and investigated their electrochemical performance as sodium ion capacitor electrode materials.Studies have shown that stannous sulfide/graphene and amorphous stannous selenide/graphene also exhibit higher energy density,power density and cycle life in sodium ion capacitors.The specific research contents are summarized as follows:(1)Design and preparation of stannous sulfide/graphene and study on sodium storage properties.Layered stannous sulfide(SnS)is a promising anode material for sodium ion batteries,because it has a high specific theoretical capacity of sodium ion of 1020 mA h g-1,and a large interlayer spacing allows rapid sodium ion transmission.However,pure stannous sulfide has poor conductivity and a large volume expansion in the process of deintercalation of sodium,which is likely to cause agglomeration and powdering of electrode materials.Lead to poor electrochemical performance.In response to the above problems,we synthesized the directional growth of SnS nanosheets in graphene through electrostatic self-assembly and hydrothermal reaction.Research shows,SnS nanosheets growing along(100)and(010)directions are suppressed due to the confinement by graphene,which exhibit smaller thickness and particle size.Those nanostructure expose abundant open edge,which offers rich active sites and Na+ easy transport pathways.Vacancies formed at the edge due to the presence of Sn4+-O and S and N co-dopants in graphitic structure promoted Na+surface adsorption/desorption.Such nanocomposites with SnS nanosheets confined by N,S codoped graphene demonstrated significantly enhanced pseudocapacitance.The SICs delivered excellent energy densities of 113 and 54 Wh kg-1 at power densities of 101 and 11100 W kg-1,respectively,with 76%capacity retention after 2000 cycles at 1 A g-1.(2)Design and preparation of Stannous selenide/graphene and study on sodium storage properties.The theoretical capacity of stannous selenide is 780mA h g-1,which is lower than that of stannous sulfide.However,the electrical conductivity has been improved compared to stannous sulfide.It has a lamellar structure like stannous sulfide and has a similar energy storage mechanism.However,stannous selenide also has the problem of large volume expansion during the deintercalation of sodium,which is likely to cause the agglomeration and powdering of electrode materials.In response to the above problems,in this work,a-SnSe/rGO composites were synthesized by simple hydrothermal reaction design,and amorphous SnSe quantum dots(about 2 nm)were anchored in nitrogen-doped graphene(a-SnSe/rGO).Research shows,the amorphous SnSe structure largely suppresses the volume change comes from the tin alloying reaction process,decreasing the particle pulverization.Strong Sn-C,Sn-O-C,and Se-C chemical bonds are formed between a-SnSe and graphene,guaranteeing rapid electrical transport channels during the sodiation/de-sodiation process.As a result,it presents superior electrochemical reversibility of 397 mA h g-1 at 1 A g-1 after 1400 cycles with 0.014%capacity fading per cycle as sodium ion battery anode.The excellent rate performance and the high proportion of pseudocapacitance contribution for aSnSe/rGO also make it very suitable for the anode materials for sodium ion capacitor.It exhibits high energy density 58 Wh k g-1 after 5000 cycles at 1 A g-1 in optimized aSnSe/rGO‖AC sodium ion capacitor. |
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