Preparation Of Tin-Zinc Based/Carbon Composites And Its Application In Alkali Metal-ion Batteries

With the unprecedented improvement of modern science,technology and economy,human beings are paying more and more attention to energy and environmental issues.In recent years,electrochemical energy storage technology has been deeply applied in portable devices,large-scale power grids and microgrid systems due to its high cycle efficiency,long-term cycle life and low maintenance cost.Among them,lithium-ion batteries（LIBs）have played an important role due to their high operating voltage plateau and high energy density.However,commercial LIBs are increasingly difficult to meet the supply and demand of these energy and power electronics due to the lack of lithium resources,safety needs to be improved and high cost.To overcome these disadvantages of Li-ion batteries,rechargeable sodium-ion batteries（SIBs）and potassium-ion batteries（PIBs）have attracted much attention as alternatives to Li-ion batteries due to their elemental abundance in the earth’s crust and their low cost and high energy density.Negative electrode materials are a key part of the battery,yet their practical application is limited by several factors,such as undermining multiplicative performance,rapid capacity decay,sluggish charge transfer kinetics,and large volume changes during cycling.Studies have proven that heterogeneous composite electrodes composed of multiple active components designed to meet various electrochemical and structural requirements are essential to significantly improve the performance of batteries.More importantly,the heterojunction structure can combine the advantages of individual components while avoiding the disadvantages of each component to achieve a 1+1>2 effect and achieve kinetically fast conversion reactions,thus improving the electrochemical performance of the electrode,especially the multiplicity performance.In this paper,we focus on transition metal zinc and tin-based carbon composites to investigate the conformational relationship between the structure and performance of electrode materials,as follows:1.DH-Zn₂Sn O₄/Sn O₂@C composites with double-shell layer structure were prepared by a simple bilayer cladding treatment,high-temperature carbonization pyrolysis and alkali etching strategy using hollow ZnSn（OH）₆ as precursor,and their lithium storage performance as anode materials for lithium-ion batteries was investigated.The experimental results show that the double-shell layer structure enhances the composite pseudocapacitance contribution and accelerates the lithium-ion transport rate,thus improving the electrochemical kinetics as well as the pseudocapacitance contribution ratio.More importantly,the strong coupling between Zn₂Sn O₄,Sn O₂ and N-doped carbon matrix can effectively prevent the agglomeration of active materials,mitigate the volume change effect during the electrochemical reaction and keep the structure stable,so that DH-Zn₂Sn O₄/Sn O₂@C exhibits excellent electrochemical performance.Due to the unique structure of the composite,the prepared samples can provide ultra-high discharge specific capacities of 1085.2 and 469.3 mA h g^-1 at 0.1 and 5.0 A g^-1,respectively.The discharge specific capacity can still be maintained at 625 mA h g^-1after 900 cycles at a current density of 1.0 A g^-1.2.Still using hollow ZnSn（OH）₆ as a precursor,the bean pod-like carbon nanofiber composite Zn₂Sn O₄/Sn O₂@CNFs was successfully prepared by electrostatic spinning followed by high-temperature charcoal pyrolysis and applied to lithium-ion battery anode materials.The in situ pyrolysis of ZnSn（OH）₆ produces Zn₂Sn O₄ and Sn O₂,which were closely linked to form a heterojunction structure.The built-in electric field induced at the heterojunction interface promotes the rapid ion/electron transport.The hollow structure inside the composite increases the specific surface area to facilitate the penetration of the electrolyte,and the N-doped carbon nanofibers wrapped in the outer layer accelerate the electron transport process,while the introduction of N atoms provides more active sites in the composite,and the mesh structure of the carbon nanofibers effectively mitigates the volume expansion of the active material during the charging and discharging process.As expected,the composite exhibited excellent discharge specific capacity,reaching937 mA h g^-1 at a current density of 0.1 A g^-1;good multiplicative performance,419.2 mA h g^-1 at 5.0 A g^-1;and excellent long-cycle performance,with a discharge specific capacity of 293.5 mA h g^-1 even after 600 cycles at a current density of 5.0 A g^-1.3.Based on the previous work,a new ZnS/SnS₂ heterostructure with abundant phase boundaries was designed by electrostatic spinning and high-temperature vulcanization while encapsulated in nitrogen-containing carbon fibers to obtain hollow ZnS/SnS₂@CNFs heterostructured materials for alkali metal ion（Li⁺,Na⁺,K⁺）battery anode materials.It is shown that this network structure with hollow cubic ZnS/SnS₂ interconnected by carbon nanofibers to form a tandem network can effectively shorten the diffusion path of alkali metal ions and electrons,while the bimetallic sulfide has a high specific capacity.The built-in electric field induced at the electrode interface improves significantly the transport and diffusion of alkali metal ions during charging and discharging,while the large number of N heteroatoms in carbon nanofibers provides enough active sites to store alkali metal ions,leading to a storage mechanism with capacitance-controlled behavior.Therefore,the materials exhibit excellent electrochemical performance as anode for alkali metal ion batteries.As expected,the composite has a discharge specific capacity of 1437.5 mA h g^-1 as anode material for lithium-ion batteries,1321.2 mA h g^-1 as anode material for sodium-ion batteries,and 861.6 mA h g^-1 as anode material for potassium-ion batteries at 0.1 A g^-1,respectively.