Design,Synthesis Of High Energy Tin/Vanadium Based Anode And Their Alkali Metal Ion Storage Performance

Based on the research ideas from material design,controllable preparation,structure characterization to electrochemical performance test,this doctoral dissertation mainly focuses on the development of advanced tin based and vanadium based negative electrode materials with enhanced energy density and prolonged cycling life for lithium/sodium ion batteries.In our work,porous Co V₂O₆ nanosheets,sulfur-deficient porous SnS_2-x nanoflowers,high-loading SnO₂ quantum dots@GO and SnO₂@P@GO were successfully designed and synthesized.In addition,material properties and electrochemical performances of all these samples were systematically characterized and analyzed.The results obtained are as follows:（1）In order to solve the problem that the capacity of vanadate decreases rapidly under high current density,porous Co V₂O₆nanosheets were prepared by co-precipitation method combined with calcination.It has been proved that acetylene black can be used as an external source to induce heterogeneous growth of uniform Co V₂O₆nanosheets and porous nanosheets structure can be formed due to the removal of crystallization water.The stable porous structure can effectively suppress large volume expansion/contraction,provides continuous electron path,promotes structural integrity and electron transport,and shortens lithium diffusion length.The macroporous Co V₂O₆ nanosheets exhibit greatly enhanced capacitance contribution and relatively lack of diffusion control,thereby significantly improving the cycle stability and rate performance(at 5000 m A g^-1,after 1000 cycles,the capacity is 307m A h g^-1,the average loss of capacity from 2 to 1000 cycles is only 0.027%).（2）In order to improve the elctron/ion conductivity of SnS₂ and provide space for volume expansion,we prepared the three-dimensional Sulfur-deficient porous SnS_2-xnanoflowers through a simple hydrothermal method and followed thermal treatment.The formation principle of three-dimensional porous structure and sulfur vacancies were studied.The porous SnS_2-x nanoflowers exhibit greatly enhanced capacitance contribution and relatively lack of diffusion control.As the anode for sodium ion battery,porous SnS_2-x nanoflowers exhibit a high reversible capacity of 522 m A h g^-1after 200 cycles at a high current density of 5000 m A g^-1,and the capacity retention rate is as high as 89.5%when compared with the third circle.（3）In order to improve the elctron/ion conductivity of SnO₂ and provide space for volume expansion,we prepared SnO₂ quantum dots@graphene oxide composite via a simple solvothermal method.The high mass loading of SnO₂ quantum dots were directly grown on GO nanosheets with the Sn²⁺ions in-situ oxidized by the oxidization groups of GO nanosheets.As the anode of lithium ion batteries,SnO₂ quantum dots@GO exhibits high capacity and excellent cycle stability(at high current density of2000 A g^-1,the capacity retained 477 m A h g^-1 after 2000 cycles,and the capacity retention rate is as high as 86%compared to the second cycle).The excellent electrochemical performance is mainly attributed to the following reasons:SnO₂quantum dots have high mass loading on GO;the gap between each quantum dot can provide space for volume expansion and inhibit aggregation of each particle;the conductive graphene oxide nanosheets support high electronic conductivity for each quantum dot.（4）In order to further improve the electrochemical performance of SnO₂,we prepared P-bridged SnO₂ quantum dots and GO（SnO₂@P@GO）composite material via a simple solvothermal method.In this unique structure,P serves as“bridge”to connect graphene and tin oxide through P-C and Sn-O-P bonds.During the electrochemical charging/discharging process,the covalent bonds can well buffer the expansion/contraction of SnO₂ and improve the structural integrity,thereby achieving cycling stability and excellent rate performance.When SnO₂@P@GO acted as as the anode of lithium ion battery,the structure of SnO₂ particles coated with GO were kept and no exposure to the electrolyte were found at 1000 m A g^-1 after 700 cycles,suggesting the excellent structure stability of SnO₂@P@GO.