Effect Of Morphology Regulation And Composite Design Of Sn、Si Based Anode Materials On Electrochemical Performance For Lithium Ion Batterries

Lithium-ion batteries are not only widely used in military equipment such as chariots,fighter planes,satellites,and spaceships,but are also widely used in home electronics such as electric vehicles,notebook computers,video cameras,and mobile phones.The rapid development of microelectronics technology makes it more and more difficult for some commercial lithium-ion batteries to meet the requirements for use.Anode material,as an important part,shows an increasingly important role in the energy and cycle life of the lithium ion battery.At present,most commercial lithium-ion batteries use carbon-based materials as anode materials,which have problems such as low specific capacity,low first-time charge and discharge efficiency.The search for new anode materials with high specific capacity and good cycle stability has become one of the key issues in the development of lithium-ion batteries.Compared with traditional carbon-based anode materials,tin-based and silicon-based anode materials are favored by scientific researchers for their higher specific capacity and better safety performance.However,the low conductivity and unstable structure of tin-based and silicon-based anode materials make their electrochemical performance not ideal,which limits their practical application in lithium-ion batteries.Aiming at the above problems,this paper takes layered silicate,tin oxide and tin sulfide as the main research objects.With the main purpose of improving the electrochemical performance of lithium-ion battery anode materials,new types of lithium-ion battery anode materials were constructed through structure/morphology design and compounding.Explore the growth mechanism of materials,analyze the material’s lithium storage performance,lithium storage mechanism and its dynamic characteristics,and explore the effect of material micro-nano structure and functional composite design on the electrochemical performance of lithium ion battery anode materials.The main research work carried out in this paper is as follows:Ⅰ.The layered nickel silicate material has a stable structure,but it faces the problem of poor electronic conductivity.In order to enhance the conductivity of nickel silicate nanomaterials,introduce carbon-doped Co nanofibers into layered nickel silicate materials,and carbon doped Co nanofibers@nickel silicate nanosheet core-shell composites were prepared by hydrothermal methods combined with high temperature calcination process.XRD,SEM,TEM and other testing methods were used to characterize the material structure/morphology.Cycle performance and rate performance were studied by electrochemical testing methods,and its lithium storage mechanism and kinetic characteristics were analyzed.Except for the first cycle,the carbon doped Co nanofibers@nickel silicate nanosheet core-shell composite electrode has relatively excellent cycle stability.At a constant current density of 60 mA/g,after charging and discharging for 50 cycles,the reversible capacity was 432 mAh/g,which was significantly higher than that of the nickel silicate based electrode reported in the literatures.Ⅱ.Tin oxide Sn₃O₄ is composed of alternating layers of tin and oxygen atoms and a certain number of oxygen vacant sites.Using as anode material,few reports have been reported at home and abroad.Sn₃O₄ nanosheets were prepared by a hydrothermal method,and the synthesis mechanism and lithium deintercalation performance of the material were discussed.In order to enhance the conductivity of Sn₃O₄nanosheets,graphene-doped Sn₃O₄ nanosheet composites were prepared by a solution reduction method using graphene oxide as carrier.The effects of the introduction of graphene on the material capacity,rate performance,and cycle stability were studied.Compared with Sn₃O₄ nanosheet electrodes,graphene-doped Sn₃O₄ nanosheet composites show superior electrochemical performance.The conductive network structure of graphene offers opportune channels for lithium ion transmissionⅢ.Aiming at the problems of volume expansion and poor cycle stability of Sn₃O₄ anode materials,Sn₃O₄ materials were modified with porous TiO₂ nanobelts,and porous TiO₂nanoribbons were prepared by hydrothermal method,ion exchange method and high temperature calcination process.On the basis of this,a hydrothermal method was used to grow Sn₃O₄nanosheets on the surface of the porous TiO₂ nanobelts to prepare porous TiO₂ nanobelts@Sn₃O₄ nanosheet composites.The growth mechanism of composite materials was discussed,and the effects of the introduction of porous TiO₂ nanobelts on the rate performance and cycle performance of the materials were studied.The initial discharging/charging capacities of the porous TiO₂ nanobelts@Sn₃O₄ nanosheet composite electrodes were 1513.7 mAh/g and 1104.4mAh/g,respectively,and the corresponding initial coulombic efficiency was 72.96%.After charging and discharging for 50 cycles,the reversible capacity was 646.8 mAh/g,and the corresponding reversible capacity retention rate was 58.6%.The stable crystal structure,crystal plane parallel channels and porous structure are the important factors to improve the electrochemical performance of composite electrodes.Ⅳ.SnS₂ has a layered hexagonal crystal“sandwich”structure.The layered structure can reduce the volume change during charge and discharge in a certain range,but it also faces the problem of poor conductivity.In order to enhance the conductivity of SnS₂,Co metal complex nanofibers were prepared by hydrothermal method,and then the Co S₂ nanofiber@SnS₂nanosheet composites by hydrothermal method using thioacetamide as a sulfur source.While improving the conductivity of the material,the specific surface area of the material is increased,which provides favorable conditions for the transportation and storage of lithium ions.With a current density of 60mA/g,the first discharging/charging specific capacities were 1194.9mAh/g and 832mAh/g,the first coulombic efficiency was 69.7%,and the reversible capacity retention after 100 cycles was 66%,which was much higher than SnS₂ nanosheet electrode material.Ⅴ.Aiming at the problems of volume expansion and poor cycle stability of SnS₂ materials during charging and discharging,SnS₂ anode material was compounded with molybdenum oxide with relatively poor activity.while maintaining their respective advantages,exerting a synergistic effect between substances to improve material cycling performance and charge/discharge capacity.α-MoO₃ nanorods@SnS₂ nanosheet composites were synthesized using two-step hydrothermal method.The growth mechanism of the composites was discussed.The cycle performance,the mechanism of lithium deintercalation and the rate performance were investigated,and the relationship between the composite structure and its electrochemical performance was analyzed.Compared withα-MoO₃ nanorods and SnS₂ nanosheets,the synthesizedα-MoO₃ nanorods@SnS₂ nanosheet composite electrodes exhibit superior cycle performance and rate performance.The excellent electrochemical performance of theα-MoO₃nanorod@SnS₂ nanosheet composite electrode was attributed to special core-shell structure,large specific surface area and synergy of different electrode materials.Ⅵ.If the SnS₂ anode material is compounded with polypyrrole,the polypyrrole crosslinked conductive network structure can simultaneously improve the volume expansion and poor conductivity of the SnS₂ electrode material during charge and discharge.The pyrrole monomer was oxidized by chemical oxidative polymerization with FeCl₃ as oxidant in the presence of methyl orange.The carbonized PPy nanotubes were obtained by high temperature calcination under an inert atmosphere.Carbonized PPy nanotubes were used as templates to grow SnS₂nanosheets by a hydrothermal method to obtain carbonized PPy nanotubes@SnS₂ nanosheet composites and the growth mechanism of carbonized PPy nanotubes was discussed.The lithium storage performance,rate performance and dynamic characteristics of composite materials were analyzed.The structural changes and the composition of SEI film during the charge and discharge of the materials were discussed.The first discharging capacity of the carbonized PPy nanotubes@SnS₂ nanosheet composites was 1279 mAh/g,and the charging capacity was909.5mAh/g at a current density of 300 mA/g.The corresponding coulomb efficiency is 71.1%.The reversible charging specific capacity is 525.7 mAh/g after 100 cycles,and the corresponding capacity retention rate is 57.8%.