Preparation And Potassium Storage Properties Of Iron-based Sulfide Composite Carbon Nanofibers

Iron sulfides possess unique optoelectronic and chemical properties,which make them widely and deeply studied in the fields of condensed matter physics,energy storage and conversion,and nanoscience.In recent years,it has also become the focus of potassium-based energy storage due to its high theoretical specific capacity,abundant natural reserves,and higher electrical conductivity compared with oxides and phosphides.However,the capacity fading problem of metal sulfides due to the obvious volume effect during the charging and discharging process is the biggest problem that limits their application in the field of electrochemical energy storage.Therefore,it is necessary to improve their performance through corresponding effective means.In this paper,iron-based sulfides are chosen as the research object.In order to improve their potassium-ion storage stability in potassium-ion batteries（PIBs）and potassium-ion hybrid capacitors（PIHCs）,based on the nanostructure design and carbon composite modification strategy,electrospinning technology is optimized and graphene is introduced to rationally control the distribution of iron-based sulfide particles in electrospun fibers.The main research results obtained are as follows:（1）Nearly fully coated Fe₉S₁₀ particle composite carbon fibers are prepared for high stability potassium storage.For the problem that exposing a large number of particles on the surface of metal sulfide composite carbon fibers prepared by traditional electrospinning technology easily leads to poor energy storage stability,a strategy for the preparation of near-completely embedded composite fiber electrodes based on a new sulfur supply mode is proposed in Chapter 2.Adding sulfur powder to the electrospinning precursor solution to prepare nanocomposites(CNF@G-Fe₉S₁₀-1).As an anode for PIBs,CNF@G-Fe₉S₁₀-1 exhibits high capacity and stability(103.2 m Ah g^-1 after 892 cycles at a large current density of 1000 m A g^-1)and the PIHCs(CNF@G-Fe₉S₁₀-1//AC)also show better stability,which provides a new strategy for the design and synthesis of metal sulfides and their future electrochemical energy storage applications.（2）Nanocomposite fibers with Fe S particles fully encapsulated are designed for high stability potassium storage.In order to explore the effect of graphene on the morphology and properties of metal sulfides,nanocomposite fibers with fully embedded structure of Fe S particles（Fe S@CNF@G）are fabricated via an optimized electrospinning technique and one-step annealing in Chapter 3.The introduction of graphene reduces the size of Fe S particles and controls the distribution of Fe S particles in the fibers.Furthermore,graphene forms a double-layer protective layer with carbon fibers,which increases the structural stability of the electrode material during cycling.As an anode for PIBs,Fe S@CNF@G exhibits better potassium storage performance(the reversible capacity of 104.1 m Ah g^-1 at 1000 m A g^-1 after 645 cycles)than Fe S@CNF.As an anode for PIHCs,it still provides capacity of 102.3 m Ah g^-1 at 1000m A g^-1 after 1000 long cycles（capacity retention rate as high as 99.86%）,proving the extremely excellent potassium storage stability of Fe S@CNF@G.