Research On Preparation And Properties Of Nano SnO₂ Anode Materials For Lithium-ion Batteries

Lithium-ion batteries（LIBs）have become the most widely used energy storage devices in various fields due to their higher energy density,lower pollution of the environment and safer working potential.With the large-scale popularization of high-power equipment,the demand for high energy density of LIBs gradually increases.However,currently commercial LIBs are limited by the low energy density of graphite anode,which is difficult to meet the needs of high-power equipment.Therefore,it is urgent to develop high performance anodes.SnO₂ is regarded as the most promising candidate for a new generation of anodes due to its impressive theoretical specific capacity.Nevertheless,SnO₂ anode is limited by its low conductivity and poor structural stability,which hinders its commercial development.In this paper,a modification idea for preparing carbon/SnO₂ composites is proposed in view of these problems of SnO₂ anode,and experiments are carried out to verify the effectiveness of the modification measures.Although the composite with traditional carbon-based materials could improve the poor conductivity of SnO₂ anode,the low capacitance of the latter still limits the capacity of the composite.Fluorinated carbon nanotubes（F-CNTs）with high energy density were introduced into the composite anode system to compensate for the loss of overall electrode capacity due to the low capacitance of carbon.In addition,F-CNTs were subjected to high-temperature defluorination treatment,and the application of defect engineering successfully constructed numerous structural defects in defluorinated carbon nanotubes（D-CNTs）,which provided additional lithium storage capacity for carbon materials.The phase and morphology of F-CNTs and D-CNTs before and after defluorination were analyzed by XRD,XPS,Raman,FTIR and AFM,and composite electrodes were prepared with SnO₂,respectively.Among them,D-CNTs@SnO₂ exhibited better electrochemical performance and maintained 465.19m Ah g^-1 reversible discharge capacity after 200 cycles at 0.1 A g^-1.Due to the volume effect of SnO₂,it was observed that the reversible capacity of D-CNTs@SnO₂ electrode decreased dramatically during the later cycle.To solve this problem,we design the structure of D-CNTs@SnO₂ electrode from the perspective of reserving buffer space,and successfully prepare the nano hollow-rod D-CNTs@SnO₂@nitrogen doped carbon（N-C）composite anode.The hollow structure can adapt to the volume change that occurs during Li-ion insertion/desorption.In addition,the detachment of F atoms and the insertion of N atoms,which are chemical processes that occur on the surface of carbon materials,promote an increase in surface porosity and defect density,thereby providing additional lithium storage sites.The double carbon effect caused by defect engineering provides a multidimensional transport path and rapid migration rate for Li-ions,which enables the electrode to display excellent electrochemical performance.A high reversible capacity of 1311.15m Ah g^-1 could be provided after 200 cycles at 0.1 A g^-1.The introduction of D-CNTs and the construction of hollow structures successfully improved the electrochemical performance of SnO₂ anode.However,we noticed that the application of defect engineering would disrupt the ordered arrangement of carbon ring atoms,thus limiting the rate capability of the composite anode.Therefore,aramid conductive fibers were prepared and loaded D-CNTs@SnO₂@N-C（D-AF）.The unique flexible skeleton in D-AF could realize the internal encapsulation of the active substances and adapt to the deformation of the electrode sheet under stress.The dense CNTs network promotes the improvement of the electrode conductivity.Aramid conductive fibers,as new flexible current collectors,provide D-CNTs@SnO₂@N-C with more stable service life and stronger rate capability.After 200 cycles at 1.0 A g^-1,D-AF still retains 647.74 m Ah g^-1 reversible capacity.