Study On Selenide Anode Materials For Sodium Ion Batteries

Sodium ion batteries?SIBs?are rich in sodium sources and have attracted great attention.However,the anode of sodium ion battery has some limitations in practical application,including low Na storage capacity and slow kinetic performance,which is difficult to meet the needs of society.Therefore,the exploration of promising anode materials with excellent electrochemical properties has triggered a lot of exploration activities.The existing electrode mechanisms are divided into insertion type?e.g.,carbon,TiO₂,V₂O₅?,conversion type?e.g.,carbon,TiO₂,V₂O₅,CoO,FeS₂,NiSe₂?and alloy type?e.g.,Sn,Sb,Bi?.Among them,the materials based on the transformation reaction showed higher sodium storage capacity and smaller volume expansion.Transition metal chalcogenides?TMDCs?are considered major members of the transition pattern.However,the traditional metal oxides?MO?and metal sulfides?MS?are affected by the dense solid electrolyte phase?SEI?membrane which impedes ion transport and the"shuttle"effect of polysulfides,thus limiting the performance of the electrode,so it is necessary to study new electrode materials.Metal selenide based on electrochemical conversion reaction has the advantages of high electronic conductivity and low energy consumption,which makes metal selenide?MSe?have ultra-high service life,high reversible capacity and appropriate working potential,so it is considered as a potentially valuable SIBs anode material.In this paper,two kinds of selenides are mainly studied,including the experimental scheme of graphene-based carbon clad copper selenide and three-dimensional carbon composite CoSe2,and their structures and properties are studied and discussed.The main research contents are as follows:?1?Water and anhydrous ethanol were used as solvent to step simple solvent thermal response,using hydrazine hydrate as reducing agent,reduction of monolayer graphene oxide?rGO?as the carbon base,at the same time use the low temperature carbonization of glucose for soft template while coated copper selenide,compare copper selenide uniform load in the reduction of monolayer graphene oxide?rGO?.The various chemical properties of the electrode material in sodium ion battery were studied,and the excellent performance of sodium storage was demonstrated.In the long cycle performance,under the low current density of 0.2A/g,30 cycles were performed,showing 371 mAh/g with a retention rate of 83.7%.Under the condition of high current density of 3A/g,1400 cycles were performed,showing the specific capacity of 392mAh/g,and the capacity retention rate was as high as 90%.In the multiplier performance test,after the current density is increased from 0.1A/g to 5A/g,the specific capacity is about 400 mAh/g and the capacity retention rate is 92.1%.?2?A one-step solvothermal reaction is performed with water and cholesterol as solvents,in which citric acid is used as a complexing agent,and hydration is reduced to a reducing agent.The hydrothermally obtained product is then calcined at high temperature in a tube furnace in an Ar/H2?10%?atmosphere to further carbonize the citric acid to obtain a three-dimensional carbon composite CoSe₂.The performance of the samples synthesized in this experiment in the electrochemical test can reach a satisfactory level.In the long cycle performance,at a low current density of 0.2A/g,the initial discharge specific capacity is 550mAh/g,the initial charging specific capacity is 500.5mAh/g,the initial Coulomb efficiency?CE?is 90.1%,and the cycle is 30 cycles No obvious attenuation of the rear capacity can be maintained at 405.5mAh/g,which is higher than73.6%.After 5 cycles of activation at a current density of 0.1A/g,the current density is converted to a current density of 5A/g.The results show that After about 300 charge and discharge cycles,its reversible capacity can still be maintained at 346mAh/g,and the retention rate can reach 62.9%.