Study On Lithium Battery Anode Materials Based On Carbon Shell Hollow Microspheres

Porous/hollow microspheres were widely used in catalysis,drug carriers,microreactors,supercapacitors and lithium-ion battery because of their large specific surface area and easy ion transport.Due to the emphasis on new energy sources,many researchers have conducted in-depth research on nanomaterials as electrodes.Their preparation methods mainly include hard and soft template method and no-template method.The hard template method is widely used because it can better control the morphology of the product.The purpose of this paper was to prepare porous/hollow nanospheres by aerosol method,and study their electrochemical properties as the anode for lithium-ion battery.Firstly,PS@SiO₂ microspheres were prepared by aerosol method,the p-SiO₂ porous spheres were obtained by calcining in air.And then,p-SiO₂@C hollow spheres were successfully prepared after coating the p-SiO₂ templates by the carbon layer from the carbonization of PDA.Finally,reducing with magnesium metal,p-Si@C were obtained.When being applied as the anode material for lithium-ion batteries,carbon package solid silicon particles?Si@C?deliver only 806 mAh/g during first five cycles at 100 mA/g.While p-Si@C shows the capacity about 1228 mAh/g.And at high current of 1000 mA/g,p-Si@C still exhibits a discharge capacity of up to 266 mAh/g after 600 cycles,and the Coulomb efficiency reaches 99.9%.It can be seen that the hollow structure has obvious contribution for improving the capacity and cycle stability.Secondly,C@SiO₂ hollow microspheres were prepared by aerosol method through adding sucrose to the precursor.SiO₂ nanoplates with opened macroporous structure on carbon layer?C@mSiO₂?have been obtained by dissolving and subsequent regrowing the outer solid SiO₂ layer of the aerosol-based C@SiO₂ double-shell hollow spheres.Subsequently,triple-shell C@mSiO₂@C hollow spheres were successfully prepared after coating the C-mSiO₂ templates by the carbon layer from the carbonization of sucrose.When C@mSiO₂@C hollow spheres were applied as the anode material for lithium-ion batteries,at a current density of 200 mA/g,the initial discharge capacity was 648.0 mAh/g and the charge capacity was 412.7 mAh/g,which coulomb efficiency was calculated to be 64.0%.And its capacity still maintained 501.5 mAh/g after 100 cycles.As for C@SiO₂@C,it delivered 375.7mAh/g after 100 cycles at 200 mA/g.Obviously,the unique structure of the outer and inner carbon layer which not only enhances electrical conductivity,structural stability,but buffers volume change of the intermediate SiO₂ layer during repeated charge–discharge processes.Finally,Fe₃O₄@C-SiO₂ core-shell materials containing Fe₃O₄ cores were prepared by aerosol method through adding Fe₃O₄ nanoparticles to the precursor solution.Then using Fe₃O₄@C-SiO₂ as template,Fe₃O₄@mC hollow microspheres were obtained through carbonization after self-assembly of resin,and treated with hot alkali to remove SiO₂.Fe₃O₄@mC showed a high capacity of 645 m Ah/g at 2.0 A/g even after 1000 cycles.Discovered through the rate performance test,it delivered 1110,829,780,646,451,335 and304 mAh/g respectively during the current density from 0.2 to 10.0 A/g.Importantly,the unique structure could prevent aggregating and spreading out from the carbon shell of the Fe₃O₄ nanoparticles during the expansion process due to cage confining effect of the macropores on the dispersed Fe₃O₄ nanoparticles.