Study On SiO₂-based Carbon Nanofibers Flexible Free-standing Anode For Lithium-ion Storage Properties

With the speedy development of flexible electronic devices,flexible batteries have been widely concerned by researchers.The key to develop flexible batteries is to prepare flexible free-standing anode materials with outstanding electrochemical performance.Flexibility can ensure stable output of battery under mechanical deformation,free-standing can reduce the addition of inactive components,so as to advance the energy density and power density.Electrospinning combined with heat treatment has been widely used to prepare flexible free-standing anode materials.Silica/carbon nanofiber composite（Si O₂/CNF）has become a favorable competitor of the flexible free-standing anode due to its advantages of high theoretical capacity,appropriate voltage platform and abundant reserves.However,Si O₂/CNF have problems such as nanoparticle agglomeration,poor ionic diffusivity and unstable structure,leading to its rapid capacity decay.In this paper,the electrochemical properties of Si O₂/CNF are improved from interface modification and multilayer structure.The main research work is as follows:（1）Porous carbon nanofibers with Si O₂ nanoparticles uniformly embedded（PVP-g-Si O₂@CNF）as flexible free-standing lithium anode material for LIBs is prepared by PVP interface modification,electrospinning and heat treatment.PVP is grafted on the surface of Si O₂nanoparticles by grafting method.The PVP layer could adjust the interface between Si O₂nanoparticles and electrospinning solution to prevent agglomeration of Si O₂ nanoparticles and promote their uniform distribution in carbon nanofibers.Uniform nanofiber network structure can increase Li⁺storage sites,alleviate the volume expansion of Si O₂ during lithiation process,and enhance the reversible capacity and cyclic stability of the material.At the same time,PVP can generate thermal decomposition during heat treatment process,which can construct porous nanofiber network,promote ions and electrons transport,so as to improve the rate performance of the material.When used as flexible free-standing anode material for LIBs,PVP-g-Si O₂@CNF presents excellent cycle stability(440 m Ah g^-1 at 0.1 A g^-1 after 200 cycles)and rate performance.After bending deformation,the anode still has stable electrochemical performance,and the capacity retention rate is 89%of the original electrode.（2）Through TEOS in-situ generation,electrospinning,electrospray and heat treatment,carbon coated silica nanofiber composite carbon coated silica spheres（Si O₂-CNF@Si O₂-CS）flexible self-supporting lithium anode materials were prepared with small scale Si O₂nanoparticles evenly embedded and multilayer structure.TEOS is used to generate in-situ Si O₂nanoparticles to promote the uniform distribution of Si O₂ in the composite and increase the reaction sites of Si O₂ and Li⁺.Si O₂-CS spheres layer is prepared by electrospray with heat treatment to increase the content of Si O₂,the high specific capacity component of the composite,so as to improve the reversible capacity of the material.Si O₂-CNF nanofibers layer is prepared by electrospinning with heat treatment technology to provide flexible free-standing substrate for the composite.In order to increase the stability of composite structure,the multilayer structure with alternating nanofibers layer and spheres layer is prepared by alternating electrospinning and electrospray.When used as a flexible free-standing material for LIBs,Si O₂-CNF@Si O₂-CS shows high reversible capacity(633 m Ah g^-1 at 0.1 A g^-1 at 1^st cycle)and good cycle stability（stable capacity within 300～1000 cycles）.