Preparation And Electrochemical Performance Of Metal Chalcogenides Anode Materials For Sodium Ion Batteries

Due to the advantages of light wight,high efficiency,enhanced energy density and long cycling life,lithium ion batteries（LIBs）have kept the majority market share of portable electronic devices,and gradually been applied in power source of electric vehicle.However,the limited lithium resources in the earth’s crust with the uneven distribution would be a critical issue for large-scale application,accompanied with the ever-increasing price of LIBs.Recently,sodium ion batteries（SIBs）have attracted considerable attentions and been regarded as the promising alternative to LIBs,owing to the nature abundance and low cost of sodium sources,as well as the SIBs sharing similar chemical working principle with LIBs.Unfortunately,the graphite,which is widely used in the commercial lithium ion batteries,exhibits the low Na⁺storage capacity and hardly satisfies the practical appliaction.Therefore,the searching for appropriate anode material is a hot topic and a vital matter for developing high performance SIBs.In this work,metal chalcogenides have been systematically investigated for exploring the novel anode materials for SIBs.It is expected to improve the energy density and cycling life of modified anode composites with a delicate architecture by novel approaches.The results are specifically illustrated as following aspects:Firstly,NbS₂ nanosheets have been fabricated by a facile solid-sulfidation and chemical exfoliation method and pioneeringly utilized as the anode material for SIBs.NbS₂ is classical two-dimensional（2D）layered structure,as their sandwiched framework stacked up together by van der Waals force can facilitate the electrons transportation and reversible Na⁺ions intercalation.The chemically exfoliated NbS₂（ce-NbS₂）nanosheets deliver a high reversible specific capacity of 205 mAh g^-1 at 100 mA g^-1,exhibit high rate performance and excellent cycling stability.In situ X-ray diffraction test demonstrates that ce-NbS₂ nanosheets will not suffer any unwanted phase transformation upon soidation/desodiation,which make them promising to construct high capacity and long cycle life anode materials for SIBs.Secondly,in order to explore the novel anode materials with high-performance,we report that monoclinic structured V₅S₈ nanosheets fabricated by a facile solid-sulfidation and chemical exfoliation method,when combined with graphite（ce-V₅S₈-C）,are a promising anode material for high-performance SIBs.The synthesized V₅S₈ possesses a unique crystal structure consisting of VS₂ monolayer building blocks,between which one-quarter of the available crystallographic sites are occupied by V atoms.Within each VS₂ monolayer,VS₆octahedra are face-shared with the adjacent VS₆ octahedra centered on the V atoms in the V-partially depleted interlayer.Such a unique structure gives an increased electronic/ionic conductivity,thus promoting a fast three-dimensional（3D）electron and Na⁺-diffusion transport for reversible charge/discharge cycles.Electrochemical performance results indeed suggest that the ce-V₅S₈-C hybrid is a promising anode material for SIBs with a good reversible capacity(682 mAh g^-1 at 0.1 A g^-1),cycling stability and rate capacity in the potential range of 0.01-3.0 V.Meanwhile,in situ XRD analysis reveal that the high capacity of V₅S₈-C hybrid is derived from the combined Na⁺intercalation and conversion reactions.Thirdly,owing to their high specific capacity,transition metal chalcogenides（TMCs）based materials attract enormous attentions for energy storage,yet the performance decay observed in TMCs anodes are strongly depended on the host material and working conditions.Here we report CoSe₂ nanorods as a promising alternative for sodium-ion batteries（SIBs）,which are fabricated by a facile hydrothermal strategy.At upper cut-off voltage of 0.4 V,the as-prepared sample can demonstrate improved sodiation capacity,rate capability,and cycling stability(a high capacity of 386 mAh g^-1 at 5000 mA g^-1 even after 2000 cycles).In situ XRD and ex situ TEM measurements are utilized to investigate the phase transition behavior of CoSe₂ under different cut-off voltage ranges.The results show that the deep conversion reaction below 0.4 V could easily induce the volume expansion and pulverization of CoSe₂.It convinces that applying suitable and optimal cut-off voltage is a useful approach to regulate the reactions progress for TMCs anode,improving their structure stability.Fourthly,reduced graphene oxide（rGO）homogenously wrapped nickel diselenide（NiSe₂/rGO）hybrid has been prepared by a facile one-spot hydrothermal method.When investigated as anode material for sodium ion batteries（SIBs）,NiSe₂/rGO hybrid delivers a high reversible capacity,superior rate performance and excellent cycling stability within the0.4-3.0 V voltage range.In situ XRD analysis and ex situ SEM/TEM measurement reveal that the high capacity of NiSe₂/rGO is originated from the combined Na⁺intercalation and conversion reactions.These results validate the impact of voltage range on electrochemical property,and provide a new route to enhance the conductive performance of NiSe₂ anode material.The facile synthesis and superior electrochemical performance of the NiSe₂/rGO hybrid render it a promising anode material for SIBs.Fifthly,to further improve the Na⁺storage by alloying reation,Sb₂Se₃ nanorods uniformly wrapped by reduced graphene oxide（rGO）as a promising anode material for SIBs are reported.The results show that such Sb₂Se₃/rGO hybrid anode yields a high reversible mass-specifc energy capacity,and sustains at least 500 stable cycles at a rate of 1000 mA g^-1with an average mass-specifc energy capacity of 417 mAh g^-1 and capacity retention of 90.2%.In situ X-ray diffraction study on a live SIB cell reveals that the observed high performance is a result of the combined Na⁺intercalation,conversion reaction between Na⁺and Se,and alloying reaction between Na⁺and Sb.The presence of rGO also plays a key role in achieving high rate capacity and cycle stability for Sb₂Se₃/rGO hybrid anode by providing good electrical conductivity,tolerant accommodation to volume change,and strong electron interactions to the base Sb₂Se₃ anode.In conclusion,metal chalcogenides have been successfully designed and synthesized as superior electrochemical performance anode materials for SIBs.Meanwhile,the structure evolution and reaction mechanisms of metal chalcogenides are thoroughly anaylized and discussed,demonstrating that metal chalcogenides are promising condidates for SIB anode materials with advanced energy density and long cycling life.Through the optimation the electrode and investigation of reaction mechanisms,it is beneficial for the designing and preparation of SIB anodes,which is of great significance for the development of sodium ion batteries.