Study On Synthesis And Electrochemical Performance Of Metal Sulfide Materials As Anode Material For Sodium Ion Batteries

Metal sulfide has attracted people's attention as a negative electrode material for sodium ion batteries because of its advantages such as high theoretical capacity,good structural stability,large interlayer distance,and low environmental protection cost.Among them,MoS2 and VS4 have important application prospects in the fields of photoelectric conversion,photolysis of water,sensors and battery energy storage However,the development of metal sulfide as a new anode material for sodium ion battery is seriously limited by its disadvantages such as electronic,low ionic conductivity and serious volume expansion.At the same time,graphene is considered as one of the best choice of carbon composite materials.It has a layered structure,large specific surface area and good conductivity.It not only provides more adsorption sites for Na+,but also helps buffer the volume change caused by the insertion/extraction of sodium ions.In this paper,MoS2 and VS4 materials are the main research objects,and their electrochemical properties are studied by compounding them with graphene.The specific research content of the paper is as follows(1)By adding a proper amount of cetyltrimethylammonium bromide,the vertical nanowall MoS2/rGO composite electrode material was synthesized in situ by hydrothermal methodThe MoS2@rGO composite was prepared by a simple and easy-to-operate hydrothermal method.Cetyltrimethylammonium bromide(CTAB)was used to induce MoS2 on the surface of reduced graphene oxide(rGO)through electrostatic action.Vertical growth to form a nanowall structure.This unique nanowall has a large specific surface area,which can not only expose a large number of active sites,shorten the diffusion distance of Na+,but also improve electronic conductivity and structural stability.A detailed kinetic analysis was also performed to explain the storage behavior of Na+.Pseudocapacitor-based contributions ensure more stable and faster storage of Na+.Therefore,MoS2@rGO composites show excellent electrochemical performance.The results show that the capacity of the MoS2@rGO composite can still be maintained at 571.5 mA h g-1 after 100 cycles at 0.1 A g-1,retaining 94.1%.And after cycling 300 times at 1 A g-1,the capacity can still be maintained at 417.2 mA h g-1.It is impressive that MoS2@rGO still shows a considerable capacity of 124 mA h g-1 at an ultra-high current density of 40 A g-1.The excellent properties make the MoS2@rGO material an expected electrode for large SIBs(2)Nanorod VS4/P-rGO composite was prepared by compounding phosphorus-doped graphene with VS4 material to improve the electrochemical sodium storage performanceMoS2 materials have been researched extensively by many researchers,and the theoretical specific capacity of MoS2 itself is only 670 mA h g-1.Therefore,VS4 with a higher theoretical specific capacity(theoretical specific capacity is 1196 mA h g-1)is further considered as the research object of the anode material of sodium ion batteries.This material has attracted more and more attention of scientific researchers in recent years.Although the predecessors have done some preliminary work on VS4 materials,the problem of poor rate performance of VS4 materials has not been solved very well.In this paper,by introducing phytic acid,a simple hydrothermal method is used to synthesize phosphorus-doped graphene and VS4 composite material in one step After the optimization of the conditions,the VS4/P-rGO composite material increases the defects of graphene due to phosphorus doping,thereby reducing the Na+ diffusion resistance and thereby increasing the Na+ diffusion rate;at the same time,the small-sized particles of the nanorod VS4 have a larger specific surface area,which further increases the contact area between the electrode material and the electrolyte and shortens the ion diffusion path;the C-S bond between VS4 and rGO.The VS4 nanorods are firmly fixed on the surface of rGO,which not only greatly enhances the structural stability of the composite material,but also improves the electronic conductivity of the composite material.Due to the above structural characteristics,as the anode material of SIB,VS4/P-rGO has excellent rate performance and cycle performance.At an ultra-high current density of 10 A g-1,VS4/P-rGO still has an excellent reversible capacity of 378.7 mA h g-1.And under the high current density of 0.5 A g-1,VS4/P-rGO can still maintain a high reversible capacity of 485.4 mA h g-1 after 300 cycles.The nanorod VS4/P-rGO composite material makes VS4 one of the candidate anodes for high performance sodium ion battery due to its excellent electrochemical performance.