Preparation Of Tin Disulfide-Based Composites And Application In Lithium-Sulfur Batteries

Promoting the high-quality development of new energy in the new era is an important foundation to ensure that China achieves the"double carbon"goal of carbon peaking and carbon neutrality as scheduled.At the same time,the more advanced electrochemical energy storage system is the fundamental guarantee of energy green and low-carbon transformation action.Lithium-sulfur（Li-S）batteries,with high theoretical energy density,environmentally friendly sulfur and abundant storage capacity,are regarded as the most promising high-performance energy storage devices in the new era.However,there are still many critical scientific issues in the development of Li-S batteries at this stage:poor electrical conductivity of sulfur and Li₂S₂/Li₂S;"shuttle effect"of soluble intermediate products lithium polysulfides（Li PSs）;slow conversion process between soluble and insoluble polysulfides.These problems seriously limit the industrial development of Li-S batteries.As an n-type semiconductor material with a CdI2 layered structure,tin disulfide is connected between its layers only by weak van der Waals forces,and this crystal structure facilitates the rapid transfer of Li⁺.In addition,tin disulfide has remarkable chemisorption and thiophilicity properties for Li PSs.Secondly,a variety of transition metal sulfides with efficient catalytic properties for Li PSs were combined to construct a heterojunction structure to fully synergize the properties of each component material.Finally,the heterogeneous interface-induced formation of the built-in electric field achieves rapid charge transfer and improves the comprehensive performance of the battery comprehensively.In this paper,nano-spherical SnS₂,hollow heterostructured Zn S/SnS₂and nitrogen-doped carbon nanofiber-encapsulated hollow heterostructured CoS₂/SnS₂materials were designed and prepared and applied to the separator modification and sulfur cathode modification of Li-S batteries,respectively,with a view to improving the electrochemical performance of the cell and actively exploring their reaction mechanisms.The specific studies are as follows:1.Flower spherical materials formed by self-assembled stacking of SnS₂nanosheets what were prepared by a one-step hydrothermal method and applied to a multifunctional modified separator for Li-S batteries.It was found that the nano-flower spherical SnS₂has an extremely high specific surface area,which increases the contact area with polysulfides.Secondly,it has excellent physical and chemical dual adsorption effect on polysulfides,which can play a role in blocking and inhibiting the shuttle behavior of Li PSs.Not only that,SnS₂has high electrochemical activity.The most of Li⁺will be inserted into SnS₂to form Lix SnS₂and provide additional specific capacity when the battery is discharged for the first time.This lithium-containing substance is able to form special Li⁺channels on the surface of the separator and significantly enhance the Li⁺transport efficiency.The results show that the SnS₂@PP-based cell exhibits thoroughly high initial discharge specific capacity(1477 m Ah g^-1at 0.1C)and high-Rate performance(631 m Ah g^-1at 5C).The cell exhibits excellent cycle stability（average decay rate of 0.06%per cycle）even after1000 cycles at 2C.2.Hollow heterostructured Zn S/SnS₂（ZSS）composites were prepared by co-precipitation and in-situ vulcanization methods and applied to the sulfur cathode of Li-S batteries.Firstly,the internal hollow structure effectively improves the sulfur loading and utilization.Secondly,the combination of Zn S and SnS₂to build the ZSS heterostructure exerts synergistic effect to further enhance the battery electrochemical performance.The three-level of adsorption-diffusion-conversion process with SnS₂as the adsorption site,heterogeneous interface as the diffusion center,and Zn S as the catalytic conversion core.Finally,the establishment of this multifunctional system can effectively anchor and release polysulfides to facilitate the diffusion of Li⁺.As well as lower the energy barrier for S reduction and Li₂S oxidation.As a result,the ZSS@S-based battery exhibits excellent rate performance and cycle stability,with an initial discharge specific capacity of 1252.8 m Ah g^-1at 0.1C and 635.7 m Ah g^-1at 5C.Also,the battery has high electrochemical reversibility,maintaining a low decay rate of 0.071%per cycle on average after 500 cycles at 2C.3.N-doped carbon nanofibers encapsulating CoS₂/SnS₂heterostructured materials CoS₂/SnS₂@CNFs what were prepared by electrostatic spinning technique and in situ vulcanization method.Specifically,hollow CoSn（OH）₆is used as the precursor,and polyacrylonitrile PAN and sulfur powder are used as raw materials.and applied to Li-S battery cathode.Firstly,the carbon nanofibers encapsulate hollow cubes,which not only improves the stability of the material structure but also serves as a framework for physically restricted polysulfides.Secondly,the doping of N atoms brings abundant active sites and improves the electrical conductivity of the material itself.In addition,the fibrous network structure facilitates the wetting of the electrolyte and shortens the ion transfer path.the CoS₂/SnS₂heterostructure has a better catalytic polysulfide conversion,and the rapid charge transfer is achieved by the built-in electric field induced by the heterogeneous interface.The results show that the CoS₂/SnS₂@CNFs@S-based cells exhibit excellent electrochemical performance.The initial discharge specific capacity was 1204.3 m Ah g^-1at 0.1C and615.2 m Ah g^-1at 4C.The long-term cycle performance showed that the cell only had an ultra-low average decay rate of 0.067%per cycle after 1000 cycles at 2C.When the sulfur loading is increased to 5.3 mg cm^-2and the electrolyte/sulfur（E/S）ratio is 6μL mg^-1,the cell still exhibits excellent cycle stability after 250 cycles at 0.2C.