Sodium Storage Properties Of MoS₂-based Two-dimensional Nanocomposites For Sodium-ion Batteries

Sodium ion batteries?SIB?are attractive because of their many advantages,such as high natural reserves,wide distribution,and low cost.Sodium ion batteries?SIB?are also considered as a promising energy storage system.The key to affect the commercialization of sodium ion batteries is insufficient research on negative electrode materials.However,the structure of the negative electrode materials is seriously damaged during the insertion/extraction process owing to the larger radius of sodium ions,which will lead to a rapid reduction of the capacity retention rate of reversible capacity.Therefore,it is particularly important to find suitable active electrode materials for SIB.Typical layered transition metal chalcogenide materials,especially layered molybdenum disulfide?MoS₂?nanocomposites,have received much attention due to their large theoretical specific capacity and interlayer spacing,and are considered to be ideal anode materials for sodium ion batteries.Based on the above question,this paper chooses MoS₂ as subject to prepare two-dimensional IL-MoS₂/rGO and MoS₂/N-Ti₃C₂ nanocomposites,and also analyzes their physical and chemical characteristics and electrochemical characteristics.In addition,this paper also explores the pyrrolyl two-dimensional organic negative electrode material.The specific research contents and results are as follows:?1?Enhanced Sodium Storage in Strongly-Combined MoS₂/rGO Nanocomposite:Constructed by Ionic liquid Induced Layer-by-Layer Self-AssembleDuring the electrochemical process,MoS₂ anodes meet some disadvantages such as volume expansion and severe stacking,leading to a reduced cycle life and capacity reduction.In order to solve those issues,we propose an ionic liquid-induced layer-by-layer self-assembled method to construct a 2D well-anchored MoS₂/rGO composite.As a negative electrode material for sodium ion batteries,the prepared IL-MoS₂/rGO nanocomposites show excellent rate capability(364.3 mA h g^-1 at 6.4 A g^-1 and 309.2 mA h g^-1 at 12.8 A g^-1)and good long cycle life(263.2 mA h g^-1 after 300 cycles at 3 A g^-1).Excellent performance is due to the strongly-bonding two-dimensional nanosheet structure.The ionic liquid stabilizes the structure of GO and suppresses the serious stacking of MoS₂.At the same time,the enlarged interlayer space?increased from 0.62 nm to 0.66 nm?,is more suitable for the deintercalation of sodium ions.Moreover,graphene can improve the electrical conductivity of composite,release the large volume changes and enhance reaction kinetics.?2?Nitrogen-doped 2D MoS₂/N-Ti₃C₂ nanocomposites for enhanced sodium storageAs a new type of two-dimensional material,MXene is used as a negative electrode composite material for sodium ion batteries due to its unique sheet structure,excellent electronic and chemical properties.The electrostatic interaction can promote the mixing of MXene with other positively charged materials,and prevent MXene from spilling,which is helpful for forming a stable dispersion.In this part,two-dimensional layered composites?MoS₂/N-Ti₃C₂?with strong coupling of MoS₂ nanosheets and nitrogen-doped titanium carbide were prepared using dopamine,urea as nitrogen sources and water as solvents.The MoS₂/N-Ti₃C₂ two-dimensional layered material exhibits excellent electrochemical performance which delivers a reversible capacity of 119.4 mA h g^-1 at a high current density of 10 A g^-1.When tested at 0.1 A g^-1 for 100 cycles,the MoS₂/N-Ti₃C₂ negative electrode can still maintains a reversible capacity of 255.9 mA h g^-1,showing good cycling stability.The excellent sodium storage performance benefits from the uniform N-doped titanium carbide with a large number of active sites,which enhances the electrochemical performance.?3?Applying-exploration of pyrrolyl two-dimensional organic anode materials in sodium ion batteriesPolypyrrole has attracted wide attention because of its advantages such as low cost,excellent electrical conductivity,good redox reversibility,simple synthesis,and green safety.In this part,we use pyrrole as a raw material to synthesize two-dimensional 3,4-dibromopyrrole material through a mild deprotection method of substituted pyrrole sulfonamide,and explore3,4-positioned pyrrole as a negative electrode for sodium ion batteries.However,under the experimental conditions of high temperature and high pressure,we only obtain the debrominated pyrrole during the polymerization of 3,4-dibromopyrrole,and do not get the 3,4polymerized pyrrole we need,so we do not carry out morphology and electrochemical characterization.