| Lithium-ion batteries（LIBs）have been widely used in intelligent electronic equipment,power vehicles and other fields due to their high energy density and power density,good cycle stability and long life.However,the limited reserves of lithium resources and high extraction costs limit the large-scale application and sustainable development of lithium-ion batteries.In contrast,sodium resources are very rich and the extraction cost is low.Sodium-ion battery（SIBs）is considered to be the most promising energy storage system to replace lithium-ion battery in the future.The performance of lithium/sodium-ion battery is closely related to the types,microstructures,physical and chemical properties of cathode materials and anode materials.The anode materials used in lithium-ion batteries are mainly graphite（including natural graphite and artificial graphite）.Graphite has the advantages of good charge discharge potential distribution,good electrochemical stability and low cost,but its low theoretical specific capacity(372 m A h g-1)and poor rate performance make it difficult to meet the application requirements of high-energy density lithium-ion batteries.Transition metal sulfide based anode materials have high theoretical specific capacity and low production cost,and are a kind of potential graphite substitute materials.However,the transition metal sulfide has the problems of large volume expansion and poor conductivity during charging and discharging,which lead to the material structure is easy to be damaged and the capacity decreases rapidly during charging and discharging.The main strategies to overcome this defect are structural design（morphology and particle size regulation）,multi-component hybridization and surface coating.In this paper,three kinds of composite anode materials with special morphology,namely iron based sulfide/carbon material,nickel based sulfide/carbon material and molybdenum based sulfide/carbon material,are constructed by in-situ vulcanization and hydrothermal method,respectively.The particle morphology,crystal phase,structural composition,synthesis mechanism,electrochemical performance and electrochemical process kinetics of the materials are analyzed.The results show that the as-synthesized anode materials have excellent lithium or sodium storage properties.The main research contents and results are as follows:（1）Fern leaf-like Fe S2@sulfur-doped carbon（SC）composites with core/shell structure are synthesized through an in-situ sulfuration process in argon atmosphere using fern leaf-likeγ-Fe2O3@C as the raw material.The structure of fern-like leaves in Fe S2 particle is conducive to the rapid diffusion of Li+ions along different vein directions.When doped with sulfur carbon（S,C）,the conductivity of the material is significantly enhanced.The volume expansion and dissolution of the material itself are restrained during the charging and discharging process,which promotes the electron transport in the composite.When Fe S2@SC composite serves as an anode material for LIBs in the potential range of 0.01–3.0V,it can deliver high specific capacity and good cycle stability.The discharge specific capacity is 848.9 m A h g-1 after 300 cycles at 1 A g-1,which corresponds to 89.14%of the 2nd discharge specific capacity.The kinetic analysis of lithium storage process confirms that the anode material has a pseudo capacitance mechanism for lithium storage.The full cells assembled with commercial Li Ni0.5Co0.2Mn0.3O2 cathode material also show good cycle stability and high discharge specific capacity.（2）Flower-like Ni S-Ni3S4/stereotaxically constructed graphene（Ni S-Ni3S4/SCG）composite is synthesized by one pot hydrothermal method.The petal in the composite is composed of flake Ni S-Ni3S4 nanoparticles.SCG adheres to the petal surface of Ni S-Ni3S4 particles to form an effective three-dimensional conductive network.The three-dimensional elastic matrix can buffer the material volume expansion.When evaluated as anode materials for SIBs,Ni S-Ni3S4/SCG composite shows excellent rate performance and cycle stability.The Ni S-Ni3S4/SCG composite can provide a discharge specific capacity of about 600 m A h g–1 after 50 cycles at 2 A g–1.When the current density is increased to 10 A g–1,the material still retains a discharge specific capacity of 322.9 m A h g–1 with a coulombic efficiency near 100%after 2000 cycles.In contrast,flower-like Ni S-Ni3S4 sample without SCG can only provide a discharge specific capacity of 230.3m A h g–1 after 1000 cycles at 10 A g–1,indicating that the doping of SCG effectively improves the sodium storage performance of the material.（3）Oxygen-incorporated Mo S2（OI-Mo S2）/reduced graphene oxide（OI-Mo S2/r GO）microspheres have been successfully fabricated using a PEG400-assisted one-pot hydrothermal method.OI-Mo S2 has ultra-thin curved nano sheet morphology,and the microspheres contain a large number of internal cavities with different sizes.It is demonstrated that the synergistic effect of oxygen incorporation and r GO addition plays a critical role in improving the cycling stability of Mo S2 as anode material for SIBs.The electrochemical analysis results show that the OI-Mo S2/L-r GO microspheres deliver a discharge specific capacity of 462 m A h g-1 during the 2nd cycle at 100 m A g-1,with significantly improved capacity retention compared to those of OI-Mo S2 and Mo S2/L-r GO in carbonate-based electrolyte.Based on the analysis of d Q/d V plots and XRD patterns,we conclude that the better cycling performance of OI-Mo S2/L-r GO can be attributed to reasonable adjustment for the depth of the conversion reaction at same voltage state,which avoids excessive structural damage and prevents the dissolution of polysulfides.The kinetics of sodium storage process is studied.It is confirmed that the OI-Mo S2/L-r GO microspheres has a pseudo capacitance mechanism to store sodium.The oxygen-incorporation strategy proposed in this study may open up a new pathway to prepare other transition metal sulfides with excellent sodium storage performance. |
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