Research On Binary Metal Chalcogenides As Anode Materials For Sodium Ion Batteries

As a promising class of anode materials for Na-ion batteries,binary metal chalcogenides have high electrical conductivity and theoretical specific capacity.Compared with monometallic chalcogenides,binary metal chalcogenides benefit from the synergistic effect of bimetals and can provide more active sites for redox reactions in reaction kinetics,exhibiting better rate performance and cycling stability.At the same time,binary metal chalcogenides also have the following shortcomings,first,such materials inevitably face the problem of volume expansion;second,the electrical conductivity of the material needs to be improved to improve high-rate performance;third,there is an urgent need for development and theoretical research combined general methods to guide the rational design and exploration of binary metal chalcogenide combinations as anodes for SIBs.In response to the above problems,this thesis successfully explored a series of new binary metal chalcogenides preparation methods by continuously improving the experimental scheme.These new binary metal chalcogenides were compounded to reduce graphene oxide and carbon nanofibers to improve electrical conductivity,and through a reasonable composite modification scheme to improve the cycle stability of the material.Moreover,the sodium storage mechanism of Cu Fe S₂ and Cu₃Sb S₄ was preliminarily studied by cyclic voltammetry scanning and ex-situ X-ray diffraction analysis,and it was revealed that the capacity of Cu Fe S₂ electrode material was mainly provided by the conversion reaction,while the capacity of Cu₃Sb S₄ electrode material was mainly provided by the conversion reaction,Alloying reactions are provided together.In order to improve the electrochemical performance of Cu Fe S₂ as a negative electrode material for sodium-ion batteries,it was anchored on reduced graphene oxide chemically modified with ethylenediamine by a polyol solvothermal method,and Cu Fe S₂/EN-r GO was used as a sodium-ion battery.The negative electrode material still has a discharge capacity of 247.8 m Ah g^-1 after 250 cycles at 1 A g^-1.Even at a high current density of 3.2 A g^-1,the discharge capacity can reach 296.4 m Ah g^-1,which is an improvement in performance.It is illustrated by the calculation of sodium ion rate diffusion coefficient and X-ray electron spectroscopy analysis.The results show that ethylenediamine-modified reduced graphene oxide can effectively improve the comprehensive electrochemical performance of Cu Fe S₂.The EN-r GO in the Cu Fe S₂/EN-r GO composite plays a dual role as a fast electronic conductor and a functional carbon matrix by chemically immobilizing the active material to maintain structural integrity.Secondly,Cu₃Sb S₄ was selected as the research object,and Cu₃Sb S₄/r GO was synthesized by solvothermal method and ball milling.In this chapter,reduced graphene oxide was also used as a carbon composite material,and it was found that the electrochemical performance was greatly improved.Under the condition of 1000 m A g^-1,the Cu₃Sb S₄/r GO electrode can still provide a discharge capacity of 366.6 m A g^-1 after 70cycles.Even at 9000 m A g^-1,Cu₃Sb S₄/r GO can provide a discharge capacity of 193.0 m Ah g^-1.The reduced graphene oxide effectively slows down the agglomeration of Cu₃Sb S₄particles and increases the electrical conductivity of Cu₃Sb S₄ during discharge/charge.Detailed electrochemical kinetic analysis shows that in Cu₃Sb S₄/r GO,Na ion storage is mainly controlled by the surface capacitive process,thus enhancing the material's rate capability.Finally,in order to improve the cycling stability and rate performance of Mn Se/Co_0.85Se,a modification strategy of composite carbon nanofibers was adopted.Mn Se and Co_0.85Se nanoparticles were embedded in one-dimensional carbon nanofibers,in which the N-doped carbon layer could As a buffer layer to slow down the volume change,to ensure the integrity of the material structure,so that the electrode material has excellent long-cycle performance,and the one-dimensional nanofibers are Mn Se and Co_0.85Se as a cross network of conduction electrons to ensure fast Electron transport capacity and Na⁺diffusion rate.Therefore,Mn Se/Co_0.85Se/N-CNFs exhibit improved electrochemical performance for sodium storage,with a high reversible discharge capacity of 350 m Ah g^-1at 0.1 A g^-1;considerable rate capability,discharging at 5 A g^-1 The capacity is 166.4 m Ah g^-1 and the ultra-long cycle stability,1 A g^-1 still has a discharge capacity of 262.3 m Ah g^-1after 700 cycles.The synergistic effect between manganese and cobalt in the Mn Se/Co_0.85Se/N-CNFs composite improves the reversible capacity of the anode material and enhances the rate capability of the material.