Study On The Prepartion And Electrochemical Properties Metal Oxide/Sulfide Anode Materials

In recent years,lithium-ion battery technology has developed rapidly,and has been applied in many fields and gradually promoted to the energy system of electric vehicles,which also puts higher demands on the performance of the battery.The current commercial anode materials for lithium-ion batteries are mainly graphite,whose low theoretical capacity can no longer meet the growing demand for high power and energy density,so the search for better anode materials is urgent.At the same time,with the expansion of the lithium-ion battery market size,the problem of lithium resource shortage is highlighted.The metal sodium and lithium are in the same main group of elements and have similar chemical properties,which makes mature lithium-ion battery technology easy to transfer to sodium-ion batteries and reduce development costs.It is also rich in sodium and has a low price that can be exploited on a large scale.As a result,sodium-ion batteries are seen as an alternative to the next generation of lithium-ion batteries.Metal oxygen/sulfide has a high theoretical specific capacity as an anode material for the conversion reaction mechanism,and it can be used as a backup anode material for the new generation of lithium/sodium secondary batteries,which is very popular among researchers.However,poor electrical conductivity,large volume expansion during cycling,and complexity of the preparation process limit the development of metal oxygen/sulfide anode materials.Therefore,in this thesis,based on the above problems,a simple and easy experimental method was designed to synthesize a carbon composite metal oxygen/sulfide with a micro-nano structure and to study its lithium/sodium storage properties.The specific research is as follows:(1)Based on the special structure and porosity of metal-organic backbone(MOF),Ti-MOF was dispersed as a template agent in Fe Cl₃ solution,and the Fe-Ti-O@C composite was obtained by simple stirring at a certain temperature until high temperature calcination after solvent evaporation.Carbon loaded Fe-Ti-O composites were synthesized using MOF precursors,which not only combined the advantages of Fe Ti O₃ and Fe₃O₄ materials,but also the MOF in situ generated carbon material during the calcination process improved the electrical conductivity of the active material,making the material exhibit good electrochemical lithium storage properties.The material exhibits a capacity of 988 m Ah g^-1 after 160 cycles at a discharge magnification of 200 m A g^-1,and even at a current density of 1000 m A g^-1,the capacity remains at936 m Ah g-1 after 800 cycles.(2)A simple method for the preparation of metal sulphides was explored for the more cumbersome problems of metal sulphides preparation.Carbon loaded Fe₇S₈composites were synthesized in situ by a one-step calcination method using ferrocene and sublimated sulfur as raw materials.By regulating the ratio of ferrocene-sulfur powder,controlling the product shape,and exploring the optimal ratio of raw materials,we have obtained lithium/sodium anode materials with excellent electrochemical properties.In terms of lithium storage performance,the reversible capacity after 100cycles is 1042 m Ah g^-1 at a current density of 100 m A g^-1,and 584 m Ah g^-1 even at a current density of 5000 m A g^-1;in terms of sodium storage performance,the reversible capacity after 500 cycles can reach 370 m Ah g^-1 at a current density of 500 m A g^-1.Compared with other Fe₇S₈ anode materials,this method is a one-step synthesis without tedious steps,and the resulting materials show good cycling and multiplication performance.