| “Cabon peaking and carbon neutrality”goal has triggered a global consensus that the construction of a novel energy storage systerm is crucial for advancing the development of new energy industry in the world.Currently,lithium-ion batteries（LIBs）and sodium-ion batteries（SIBs）are the most important technologies to to promote the new energy-storage industry.Nowadays,LIBs have been widely used due to their high energy density and excellent cycle stability.However,the shortage of lithium resources and the rising cost of mining and have seriously hindered the long-life and large-scale application of LIBs.Compared with LIBs,SIBs have great advantages in terms of resources,cost and safety,and therefore,have attracted much attention in the new large-scale energy storage system in recent years.Since Na and graphite cannot form stable compounds like Li C6,the commercial anode material graphite for LIBs cannot be used for SIBs,which has stimulated the development of new anode nanomaterials for SIBs.Among various anode materials for SIBs,metal sulfides have been investigated widely as anode for SIBs,due to their good electrochemical performance and abundant redox reactions.However,metal sulfide electrodes have slow kinetics in practical applications,which seriously affects their capacity and rate performance improvement.Moreover,the problem of slow kinetics of metal sulfide materials is exacerbated by larger ionic radius of Na+than that of Li+.Therefore,it is urgent to solve the problem of slow kinetics of metal sulfide anode materials.This disertation aims to solve the problems of easy aggregation and large volume expansion of metal sulfides during the charging/discharging process.Four types of metal sulfides and r GO composite anode nanomaterials were prepared by using the characteristics of metal element lattice positioning effect and interlayer confinement of layered double hydroxide（LDH）precursors,as well as the structural design and interface effect,and their significantly improved sodium-storage performances were achieved.The four main research contents and results of the disertation are presented below.（1）Two-component MoS2/CoS2 synergistic effects improves sodium storage performanceUsing the interlayer confinement effect of LDHs,the precursor of Co（OH）2 interlayer intercalated phosphomolybdate was synthesized,followed by calcination and sulfidation to prepare a hierarchical Mo S2/Co S2 bimetallic sulfide composites.The prepared Mo S2/Co S2composites have three strong pointss:（1）Mo S2 nanosheets prepared by the interlayer confinement effect of LDHs are small and uniform in size,avoiding serious volume changes during the charging/discharging process;（2）The large interlayer spacing of layered Mo S2 could accelerates the diffusion kinetics of Na+;（3）Due to their unique hierarchical structure,the prepared Mo S2/Co S2 composites can reduce the sodium ion transport resistance,shorten the ion/electron diffusion path,expose the sodium storage active site,and improve the structural stability.Therefore,because of the synergistic effects of two-component metal sulfides and the uniform composite of Mo S2 and Co S2,the prepared Mo S2/Co S2 composites exhibit good rate and cycling stability performance(its capacity remains at 396.6m A h g-1 for 80 cycles at 0.1 Ag-1).The method to prepare metal sulfides by anion confinement effect of LDHs can provide a feasible strategy for the preparation of small-sized and uniformly dispersed anode materials for SIBs.（2）Dicationic vacancy Co9S8@MoS2 heterostructure improves sodium storage performanceHeterostructure construction is an effective method to enhance Na storage in transition metal sulfides.The spontaneously developed internal electric field strongly promotes charge transport and significantly reduces the activation energy.Co9S8@Mo S2/S-r GO composites were prepared,which simultaneously possessed abundant dication vacancies and heterostructures with unique electronic structures and abundant active sites.When used as an anode of SIBs,at a current density of 0.1 A g-1,the Co9S8@Mo S2/S-r GO composite could maintain 638.8 m A h g-1 after 100cycles.Theoretical calculations showed that the Co9S8@Mo S2/S-r GO heterojunction material could significantly enhance the electronic conductivity.（3）Ion/electron dual fast transport channel Ni-CoS2（?）CNTs/MoS2/r GO improves sodium storage performanceFirst,a NiCoMo ternary hydrotalcite was synthesized by a co-precipitation method.Then,using the confinement effect of hydrotalcite layer and the advantage that Ni and Co could catalyze dicyandiamide into tubes,double carbon confinement Ni-Co S2（?）CNTs/Mo S2/r GO composites were prepared after addition of dicyandiamide,calcination and vulcanization.Among them,few-layer disordered Mo S2 can provide more Na+adsorption sites to improve the Na+transport kinetic rate,and N-doped CNTs and r GO carbon substrate materials can improve the electronic conductivity of the composite.Through the combination of multi-component metal sulfides and the synergistic effect of N-doped CNTs and r GO carbon substrate materials,the composite material can improve the kinetics of Na-ion batteries from the two aspects of electrons and ions,which then enhances the performance of SIBs.The synthesized Ni-Co S2（?）CNTs/Mo S2/r GO composite exhibits excellent electrochemical performance,with a high reversible capacity of(592.6 m A h g-1 after 200cycles at 0.5 A g-1)and a good rate capability(486.2 m A hg-1 at 5.0 A g-1).The design of such homogeneous mixed metal sulfides with a two-carbon confinement structure can provide a general strategy to design other electrode materials for new energy storage devices.（4）Conversion/alloying dual mechanism combined with MoS2/SnS/Co S@r GO-S enhances sodium storage performanceUsing the confinement effect of the metal elements of LDHs,a CoMo Sn ternary LDH as the precursor was vulcanized and then coverted to a Mo S2/Sn S/Co S@r GO-S composite.The Sn S particles in the prepared Mo S2/Sn S/Co S@r GO-S composite were smaller,which could alleviate large-volume changes of the electrode material during the process of repeated charge and discharge.Moreover,the alloying process combined with the conversion reaction was used to improve the electrochemical performance.The Mo S2/Sn S/Co S@r GO-S electrode could be delicered a high reversible specific capacity(627.6 m A h g-1 after 100 cycles at 0.1 A g-1 and CE=～100%).The composite as an electrode showed excellent rate performance of 371.0 m A hg-1 at a big current density of 5.0 A g-1.The outstanding cycling performance and rate capability of the Mo S2/Sn S/Co S@r GO-S due to r GO conductive substrate and multicomponent metal sulfides.In addition,the small size of Sn S particles could speed up sodium-ion transport,thereby providing more channels for sodium intercalation.This work may provide a new strategy for preparing other composite materials that can be applied to novel rechargeable batteries. |
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