Study On The Structure Design And Sodium Storage Properties Of Two Dimensional Tin-Based Anode Materials

Sodium-ion batteries are expected to be widely used in energy storage and other fields due to their low cost and abundant reserves.Among them,tin-based materials are used as potential anode materials for sodium-ion batteries owe to their high theoretical capacity and low voltage platform（<0.5V）during the alloying process.However,their shortcomings such as large volume effect,poor electronic conductivity,and easy solubility of intermediate product limited its application.In this research,the two-dimensional tin-based material Sn X_n（X=S,Se,n=1,2）is taken as the research object,and the modification of the two-dimensional tin-based material is studied by means of structural design.In view of the above shortcomings,two-dimensional tin-based materials have been modified by means of particle nanoization,material compounding,surface coating and special morphology control,etc.,to improve the electrochemical activity and structural stability of tin-based materials as anode materials for high-performance sodium-ion batteries（1）SnSe-SnSe₂@PPy composites were prepared by low-energy solvothermal method,and the effects of SnSe and SnSe₂ ratio on the structure and electrochemical properties of the materials were studied.By comparing the differences in lithium storage and sodium storage properties of composite materials,ideas for the modification of materials are provided.The changes of morphology and structure of the composites with different ratios of SnSe and SnSe₂ were systematically studied.Combined with first-principles calculations,the generation mechanism of Se vacancies in the composites was obtained.The generation of Se vacancies originates from Sn²⁺occupying Sn⁴⁺sites,which makes the composites have lower formation energy.The existence of vacancies can provide more active sites for electron transfer and stabilize the structure of the material.The surface conductive polymer coating layer can promote electron conduction and stabilize the material structure.The recombination of materials can facilitate charge transfer and lower the reaction energy barrier.At the same time,by comparing the lithium storage and sodium storage performance differences of materials,it provides ideas for the structural design of anode materials for sodium-ion batteries with higher energy density.The reversible capacities of the as-prepared Sn₃Se₅@PPy as anode materials for sodium-ion batteries at 1 A g^-1 after 100 cycles are 295.5mAh g^-1.（2）To further improve the sodium storage performance of two-dimensional tin-based materials,sulfides with higher theoretical capacity were selected as the research objects.SnS@C@rGO composites were successfully prepared by solvothermal method and high-temperature sintering.And the effect of surface structure design on properties of materials was investigated.Using the three-dimensional conductive network constructed by organic cracked carbon and graphene as the coating layer can improve the electronic conductivity of the material and suppress the structural collapse caused by the volume expansion of the material.Moreover,the synergistic effect of organic cracked carbon and graphene enables better cross-linking of the composite carbon layer and the inner SnS active material,which can effectively improve the structural damage of the electrode material during cycling.Moreover,the double modification of carbon and graphene can improve the electrochemical activity of the material,reduce the charge transfer resistance and promote the transfer of electrons and ions.The SnS@C@rGO composites modified with carbon and graphene still exhibited a reversible capacity of 312.2 mAh g^-1 after 500 cycles at 5 A g^-1.Moreover,the reversible capacities at current densities of 10 and 15 A g^-1 are 245.6 and212.2 mAh g^-1,respectively.The composites modified by carbon and graphene synergistically exhibit excellent sodium storage properties.（3）The alloying reaction of 2D tin-based materials at low potential can provide high capacity for batteries,but the large volume change during this process lead to the capacity fading.To further improve the cycle stability of the material,combined with the previous methods of material compounding,surface coating and nano-design,ZnS and nano-tin-based materials were selected for compounding,and the sodium storage performance of the composite materials with different sodium deintercalation potentials was studied.The results show that ZnS has good cycling stability,but its capacity is low.As a contrast,SnS₂ has higher discharge capacity but fast capacity decay.The structural stability and electrochemical activity of the material can be effectively improved by combining the above two materials.Moreover,the composite material has a lower sodium ion migration energy barrier and a higher pseudocapacitance effect than the single-phase material,which can effectively improve the rate performance of the material.The first coulombic efficiency of ZnS-SnS₂@C composite at 0.1 A g^-1 is 82.45%,and it still maintains a reversible capacity of 234.4 mAh g^-1at 5 A g^-1after 500 cycles.（4）In order to prevent the large volume expansion of Sn-based materials during the cycle,and better encapsulate the active material inside the particles.Combined with the previous modification methods,the MoS₂/SnS@C material with a hollow hierarchical structure was designed and its formation mechanism and sodium storage properties were studied.The results show that the material exhibits a good layered structure due to the preferential growth of SnS.Among them,MoS₂,as the pillar of nanotubes,can stabilize the structure of the material,while the carbon in the surface layer and the SnS material in the middle layer have a tighter connection,which can effectively improve the electronic conductivity of the material.Through the design of the hollow structure,a huge space can be reserved in the interior to accommodate the huge volume expansion during the alloying process of Sn.At the same time,through the layered design,the Na₂S of the intermediate product can be better locked in the interior of the particles,reducing its dissolution.The as-prepared MoS₂/SnS@C material exhibited an average capacity decay of 0.02%at 5 A g^-1 for 2000 cycles,and still maintained a reversible capacity of 325mAh g^-1at 15 A g^-1.There are 62 figures,21 tables,and 167 references...