Preparation And Electrochemical Properties Of Metal Sulfide/Graphene Composites

With the booming development of power batteries and energy storage batteries,the development of materials with high energy density is increasingly pursued.However,due to the low theoretical specific capacity(372 m Ah g^-1),commercial graphite anodes can no longer meet the requirements of high energy density.Tin-based anode materials,such as tin dioxide（SnO₂）and tin disulfide（SnS₂）,have attracted more and more attention because of their high theoretical capacity,high natural abundance,and suitable working voltage.They are not only widely studied in the direction of lithium-ion batteries,but also show good potential in emerging batteries such as sodium ion and potassium ion.However,the single anode used for alkali metal ions has a large volume change and slow reaction kinetics,leading to serious structural degradation and capacity attenuation in the process of charging and discharging,which hinder its practical application.By combining graphene material with high conductivity and structural stability,the volume expansion of tin-based sulfide is inhibited,and its cycle stability for the negative electrode is improved,so that it can achieve a stable cycle in lithium-sodium-potassium ion batteries.In thesis,based on the basic properties of a single material,the structure of the composite material is regulated by a simple hydrothermal synthesis method,and the structure-activity relationship between the structure and performance of the electrode material is studied to make it suitable for a variety of alkali metal ion batteries.The composites of SnO₂,SnS₂ supported on graphene and three-dimensional composites of SnS₂,graphene,and carbon nanotubes with nanometer size were prepared.The electrochemical reaction mechanism of the composite was investigated by in situ and ex-situ characterization.The specific research contents are as follows:（1）SnS₂ and SnO₂ nanoparticles were grown on S-doped graphene aerogel by simple synthesis of a unique ternary hybrid structure by one-step hydrothermal method（SnO₂/SnS₂/SGA）.SnS₂/GA and SnO₂/GA were synthesized by the same method,and the cyclic stability of SnO₂/SnS₂/SGA was better than that of SnS₂/GA and SnO₂/GA.In this study,the structural morphology of the composite was compared in detail.The tight adhesion of SnO₂ and SnS₂ to graphene and their nanosize helped mitigate unnecessary damage to the electrode material due to volume expansion.In addition,SnO₂ and SnS₂ quantum dots anchored to graphene aerogel can undergo reversible transformation reactions through synergistic effects.The mechanism of SnO₂/SnS₂/SGA used in the negative electrode of lithium and sodium ion batteries was analyzed by ex-situ high-resolution transmission electron microscopy.（2）SnS₂/graphene/carbon nanotube（SnS₂/GA/CNTs）was simply synthesized by hydrothermal method.Fewer layers of SnS₂ grew parallel to graphene,and the carbon nanotube further connected the whole complex,which was conducive to the occurrence of conversion reaction and the insertion and removal of alkali metal ions,so that it has a high actual specific capacity and fast transport dynamics.Moreover,it can inhibit the aggregation and growth of SnS₂ nanosheets during the cycle process,and maintain a highly stable state to realize the cycle stability.The composite is suitable for alkali metal ion batteries.As a negative electrode at a current density of 0.1Ag^-1,the specific capacities of lithium,sodium and potassium ion batteries are still 1150,750 and 550m Ah g^-1 after 100 cycles.（3）Using SnS₂/GA/CNTs composite material to directly perform mechanical pressing to make a pole piece without copper foil support,which is used for the negative electrode of lithium-ion batteries.The steps of batching,ball milling,coating,and drying of the wet electrode are avoided,the time for making pole pieces is reduced,the production of high-quality loaded pole pieces is realized,and the area capacity is improved.In this composite material system,the loading capacity and area capacity of the wet electrode are limited,while the dry pressed electrode can control the quality of the pressing to achieve controllable area of the active material,and avoid the use of binders and solvents,which greatly reduces the time cost and material costs,and has broad prospects for development and commercialization.There are 50 figures,7 tables and 120 references in this dissertation.