Structural Design Of Metal Oxide@CNF Composites And Study On Their Lithium/Sodium Storage Properties

Lithium-ion batteries have the advantages of high energy density and long cycle life,and are widely used in mobile devices,new energy vehicles and other fields.However,due to the low theoretical capacity of traditional commercial graphite anodes,it is gradually unable to meet the battery’s requirements for high energy density.Therefore,the development of high-performance lithium-ion battery anode materials has important research value.The limitations and continuous consumption of lithium resources have led to an increase in the cost of lithium-ion batteries,limiting their long-term development.Sodium is rich in resources,and sodium and lithium have similar electrochemical properties,so sodium ion batteries have also received more and more attention.Metal oxides have the characteristics of high theoretical capacity,abundant resources,low price and easy preparation,and has become a hot spot in the research of lithium/sodium ion battery anode materials.This article mainly focuses on the disadvantages of large volume effect and poor conductivity of metal oxide anode materials during charge and discharge.Through electrospinning technology,a variety of metal oxide@CNF（CNF stands for carbon nanofiber）composite materials have been designed and prepared,and their electrochemical performance has been measured.The specific work is as follows:1.The one-dimensional CeO₂@NC（NC stands for nitrogen-doped carbon）composite was prepared for the first time through electrospinning technology and heat treatment process.The one-dimensional N-doped carbon matrix can effectively improve the electronic conductivity of the composite material,shorten the ion diffusion length,and accelerate the transfer of ions;at the same time,the CeO₂ nanoparticles have ultra-small size,which reduces the agglomeration effect of active materials and provides a large number of active sites.Therefore,CeO₂@NC shows excellent lithium storage performance.At a current density of 100 mA g^-1,CeO₂@NC releases a high reversible capacity of 724.8 mAh g^-1 after 100 cycles.2.Using electrospinning technology as the main material preparation method,one-dimensional SbO₂/Sb₂O₃@NC composite was prepared by the method of secondary oxidation.The micro-nano carbon fiber shell forms a good protection for SbO₂/Sb₂O₃nanoparticles,effectively inhibits the volume expansion of the active material,and improves the electrochemical stability of the composite material.When the current density is 100 mA g-1,the reversible lithium storage capacity of SbO₂/Sb₂O₃@NC is622 mAh g^-1,and the sodium storage reversible capacity is 307 mAh g^-1.3.Using solvothermal method,electrospinning method and subsequent high temperature sintering method,MoO₃ nanosheets were successfully encapsulated in one-dimensional carbon nanofiber matrix,and a self-supporting structure of MoO₂@CNF composite material was synthesized.The carbon shell provides a buffer space for the electrode material during charging and discharging,and reduces volume expansion.The three-dimensional network structure provides a channel for electronic transmission and improves the conductivity of MoO₂@CNF.The self-supporting structure avoids the adverse effects of the adhesive,promotes ion diffusion,and improves the performance of the material.Therefore,MoO₂@CNF shows excellent electrochemical performance.At 200 mA g^-1,MoO₂@CNF has a higher lithium storage reversible capacity(755.7mAh g^-1)after 100 cycles.When used as anode of sodium-ion batteries,at a current density of 100 mA g^-1,the reversible capacity of MoO₂@CNF remains at 233.6 mAh g^-1 after 100 cycles.