Preparation Of Tin-based Oxide Composite And Its Applications In Lithium Ion Batteries

The invention of lithium-ion batteries has opened the process of electronic device portability,and even promoted the developments in the field of electric vehicles in recent years.Compared with other conventional secondary batteries,lithium-ion batteries are increasingly showing advantages,such as small size,light weight,long life span,high energy density and environmental friendliness.Owing to the above characteristics,lithium-ion batteries are widely applied in power tools,electric vehicles,military equipment,aerospace,and many other fields.Nevertheless,one of the major challenges that restrict its development is to seek alternative electrode materials with high specific capacity to replace the commercial graphite anodes.In recent years,great efforts have been devoted to build hybrid architectures using the materials with high specific capacity for lithium-ion batterie anode.As an alternative anode material,tin oxide with high theoretical capacity due to its lithium storage mechanism with conversion reaction and alloying reaction at the same time,has attracted many explorations.Based on this,through unique structure design,a variety of tin-based oxide anode materials with various microstructure have been synthesized.The electrochemical performance and the lithium storage mechanism of the composites as the anode of lithium-ion batteries have been studied,which provides a new strategy for the reasonable design of advanced anode materials with superior and reversible lithium storage capacity.The main research results and innovations are as follows.(1)A novel Sn/Sn O_x/Zn O@N-CNF composite has been successfully synthesized through electrospinning technology and a two-step calcination process.The effects of tin/zinc ratio on the electrochemical performance have been discovered,and the mechanism of lithium storage controlled by pseudocapacitance was obtained.The results show that the Sn O_x and Zn O was firmly wraped by the N-doped carbon nanofibers(N-CNF),which can limit the volume expansion of the oxides during the lithiation/delithiation reaction.The outermost layer is covered with a small amount of tin particles,which can improve the conductivity of the composite.The high theoretical capacity of Sn O_x,high Li ion diffusion coefficient of Zn O,as well as stable cycle performance and great conductivity of N-CNFs were integrated into the composite by the synergistic effect,which delivers a high reversible capacity of 588.7 m Ah/g after100 cycles at 0.5 A/g.In the case of great rate performance and cycle stability at high current densities,the Sn/Sn O_x/Zn O@N-CNF electrode is endowed with significantly improved initial coulombic efficiency and prominent advantage in electrical conductivity.(2)A sandwich-architecture Si-Sn O₂@G@C composite has been designed and prepared by a simple two-step hydrothermal method.The system analysis of the microstructure and growth mechanism were performed,and the excellent electrochemical performance of the composite as the anode material of lithium-ion battery was illustrated.It was found that silicon doping and carbon coating played an important role in the microtopography and electrochemical properties of the composites.Morphological and structural characterizations have confirmed that the Si-doped Sn O₂ nanoparticles on the surface of graphene were firmly wrapped in the C-coating and formed a porous sandwich structure,which can efficiently prevent the Sn nanoparticles from aggregation and provide more extra space for accommodating the volume variations and more active sites for reactions.The carbon layer can also block the immediate contact of the Sn O₂ nanorods with electrolyte and prevents the graphene nanosheets from the restacking.The doped Si not only improves the reversibility of lithiation/delithiation reactions but also accelerates the diffusion of Li⁺.As a consequence,the Si-Sn O₂@G@C nanocomposite electrode delivers great rate performance.The reversible specific capacity is 564 m Ah/g at the current density of 5A/g.Also,it can maintain a high capacity of 654 m Ah/g at 2 A/g even after 1200 cycles with negligible capacity loss and excellent reversibility with a Coulombic efficiency retention over 99%.(3)The Sn O_x/Si O₂@N-CNF composite material was successfully prepared by the combination of hydrothermal synthesis and electrostatic spinning technology.The morphology of the composites was systematically characterized,and the outstanding lithium storage performance was revealed.The synergistic effect of Sn O_x and Si O₂ made the composite electrode exhibit diffusion-controlled lithium storage reaction kinetics.The results show that the Sn O_x and Si O₂ nanoparticles are firmly encapsulated in the N-doped carbon nanofibers,which can efficiently prevent the volume expansion and the direct contact with electrolyte of Sn O_x and Si O₂,as well as shorten the diffusion distance of Li⁺to improve the conductivity.In addition,owing to the synergistic effect of Sn O_x and Si O₂,the diffusion of the lithium ions is improved,so the diffusion-controlled redox reaction dominates the charge transfer during charge-discharge process.The Sn O_x/Si O₂@N-CNF electrode exhibits not only excellent rate performance(434 m Ah/g at 2 A/g),but also remarkable long-term cycling performance(754 m Ah/g at 1 A/g after 1000 cycles)as the anode of LIBs.