| Lithium-ion batteries(LIBs)have been widely used in mobile phones,laptop computers,cameras and other portable electronic devices owing to their advantages of high open circuit voltage,high energy density,long service life,environmental friendliness,and low self-discharge.At present,the theoretical lithium storage capacity of commercial graphite electrodes is relatively low,only 372 mAh g-1,which can no longer meet the battery performance requirements of pure electric vehicles,hybrid electric vehicles and other new energy vehicles.Now,transition metal oxides show huge potential for lithium storage.However,their large volume changes and low electronic conductivity seriously hinder battery life.Because metal oxides have a relatively high theoretical capacity,they have been extensively explored and studied.Unfortunately,there is a serious volume effect during battery cycling.Metal electrodes usually exhibit poor rate performance and short cycle life.In order to improve the electrochemical performance of the material,we introduced nitrogen-doped hollow carbon spheres and compounded with metal oxides to prepare composite materials with excellent electrochemical performance.In this paper,MnO2@SnO2@NHCS,SnO2@NHCS,MnO2@NHCS and SnO2@NC composite materials have been successfully synthesized.The composite materials were characterized by SEM,TEM,XRD,XPS and other means,and electrochemical performance tests were carried out.The main contents are as follows:1.We have successfully synthesized SnO2@NHCS composite nanomaterials through a simple hydrothermal reaction.It is found that SnO2 is uniformly distributed on the surface of the nitrogen-doped hollow carbon spheres and the size of SnO2 nanoparticles is only 10nm by TEM.When SnO2@NHCS at a current density of 100 mA g-1 after 100 cycles,the reversible capacity of SnO2@NHCS is 308 mAh g-1.The MnO2@SnO2@NHCS multilayer hollow nanospheres have been controllably synthesized by a simple hydrothermal reflux method.The amorphous MnO2 nanosheets were uniformly fixed on the shell of the defective SnO2@NHCS template.The test results show that the electrode MnO2@SnO2@NHCS-5 has excellent electrochemical performance.After 100 cycles at a current density of 100 mA g-1,the reversible capacity of MnO2@SnO2@NHCS-5 remains at 1053.8 mAh g-1.MnO2@SnO2@NHCS-5 can still maintain a discharge capacity of 349.7 mAh g-1 at a super current density of 5 A g-1 after 1000 cycles.The reason for the excellent electrochemical performance of MnO2@SnO2@NHCS-5 is mainly due to the formation of amorphous MnO2 nanosheets on the shell of the defective SnO2@NHCS template,and they are tightly combined to inhibit the agglomeration of SnO2 crystals,To alleviate the volume effect of SnO2 crystals when releasing lithium,produce excellent ionic and electronic conductivity,and enhance the stability of the structure.2.Firstly we use glucose to prepare carbon spheres through hydrothermal reaction,and use it as a template to prepare SnO2 hollow spheres,and then synthesize SnO2@NC composites by deposition reaction.Finally,the SnO2@NC-3 electrode material was obtained.When tested at a current density of 400 mA g-1,SnO2@NC-3 can provide a high reversible capacity of 697.7 mAh g-1 after 270 cycles.Even at a high current density of 1000 mA g-1,the reversible capacity can still be maintained at 640.8 mAh g1 after 800 cycles.The reasons for the excellent electrochemical performance of the material are that the introduction of nitrogen atoms on the carbon can increase more defects and active sites of lithium ions,and the carbon doped with nitrogen coated on the surface of SnO2,which can devolve the volume effect.It is also conducive to Li+propagation and diffusion,coupled with nitrogen-doped carbon to stabilize the electrode structure,and at the same time improve the charge transfer ability of the material,so that the material exhibits better electrochemical performance. |
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