Study On Preparation And Performance Of Nitrogen-doped Graphene/nitrogen-doped Carbon/inorganic Nanoparticles Composites For Lithium-ion Batteries

The development of low cost,high capacity and high security of battery cathode material has become one of the key of lithium ion battery industry,so designing a new type composites used in lithium ion battery anode materials with some features such as simple process,low cost,environment friendly and high yield,have important theoretical and practical significance.In this work,a new nanocomposite of nitrogen doped graphene/silicon@nitrogen doped carbon?NG/Si@NC?was fabricated through facile and environmental solution-mixing and carbonization approach using glucosamine as the nitrogen-containing carbon source.We test the basic physical properties characterization of the nanocompisite and the electrochemical performance when it as lithium-ion batteries anode material,and the influence of silicon content on the microstructure and electrochemical performance was analyzed.Scanning electron microscope?SEM?and transmission electron microscope?TEM?images indicated that SiNPs were coated with a uniform shell of amorphous carbon?about 8 nm in thickness?and the Si@NC nanoparticles were evenly dispersed and fully encapsulated in NG nanosheets.X-ray photoelectron spectroscopy?XPS?and Raman results indicated the successful N-doping into graphene and carbon.Mapping revealed that N signals were evenly distributed as the same as carbon element.NG/Si@NC delivered an initial reversible capacity of 1142 mAh/g at a current density of 500 mA/g,and 82% retention after 100 cycles,graphene nanosheets and carbon layers played a dual protection role.What's more,the enhanced reversible capacity and rate capability of NG/Si@NC over G/Si@C can be attributed to the N-doping which improves the efficiency of electronic and Li transmission,and higher than the vast majority of similar composite materials reported in literatures.In addition,the NG/Si@NC nanocomposite can get different thickness of carbon layer and different electrochemical performance by changing the content of Si.When Si content is 57.5,70.3,83.9,and 89.2 wt%,the thickness of the carbon layer is 10,7,5,and 3 nm,respectively.When Si content is 70.3%,the electrode presented a stable cycle performance,relatively high reversible capacity and the optimal rate performance.In other words,the comprehensive electrochemical performance of NG/Si@NC is optimal when the Si content in the composite is 70.3%.Similarly,we also fabricated Fe₃O₄/nitrogen doped carbon/nitrogen doped graphene?Fe₃O₄/NC/NG?through hydrothermal and carbonization approach using glucosamine as the nitrogen-containing carbon source.Macrograph,SEM and BET results indicated that the Fe₃O₄/NC/NG nanocomposites had a 3D porous network structure with the excellent flexibility and structural stability.TEM images indicated that Fe₃O₄ nanoparticles embedd in the graphene-carbon layers,and the particle size is about 8 nm.The compression test showed that the Fe₃O₄/NC/NG had a certain compression elasticity,excellent flexibility and structural stability.The Fe₃O₄/NC/NG anode delivered a reversible capacity of 905 mAh/g at a current density of 200 mA/g after 100 cycles and delivered a reversible capacity of 628 mAh/g at a current density of 1 A/g.Compared with Fe₃O₄/C/G and Fe₃O₄/G,the cycling and rate performance of Fe₃O₄/NC/NG anode were improved significantly,and higher than the vast majority of similar composite materials reported in literatures.Fe₃O₄/NC/NG nanocomposites with 3D porous structure had excellent lithium-storage performance,and had great potential in the fields of lithium-ion battery anode materials used in wearable devices.