Study On Synthesis And Lithium Storage Property Of Carbon And Carbon/Silicon Composites Anode Materials

With the increasing emphasis on energy and environmental issues,lithium-ion batteries have received widespread attention as one of the most attractive energy storage devices owing to their high energy density and long cycling life.However,with the dramatically growing requirement for high-property of electric vehicles,portable electronic devices,and energy storage,it has become more and more urgent to develop novel electrode materials with higher specific capacity and greater rate performance.The porous carbon materials have a large specific surface area and good electrical conductivity,and its application to a lithium ion battery may effectively improve the electrochemical performance of the battery.The silicon?Si?anode materials have a good application prospect because of its unparalleled theoretical capacity of about 4000 mAh g^-1,which is far more than the conventional graphite anodes.Therefore,this paper studies the electrochemical performance of porous carbon and carbon/silicon composites materials as anode for lithium-ion batteries.The research was summarized as follows:?1?First of all,the nickel-based metal organic framework material?Ni-ZIF?was prepared by a facile hydrothermal method,and then carbonized at high temperature to obtain the Ni/C composites in which ultrafine Ni nanoparticles were uniformly embedded inside carbon microspheres.Finally,the N-doped porous carbon material was obtained by etching the Ni nanoparticles with HCl.As an electrode material for LIBs,it deliver an initial discharge/charge capacities of1497/725 mAh g^-1 at the current density of 100 mA g^-1.After 100 cycles,the electrode shows a reversible capacity of 585 mAh g^-1 with a capacity retention ratio of 80.7%.The N-doped porous carbon material has large specific surface area and abundant void structure,which beneficial to improve the penetration of the electrolyte into the electrode material and provide highways for lithium-ion transport.In addition,nitrogen doping can not only improve the electrical conductivity of carbon layers,but also introduce large number of defects to providing more active sites for lithium-ion storage,finally improving the electrochemical performance of electrode.?2?Inspired by the outstanding characteristics of film-forming and gelling of konjac glucomannan,we synthesized the Si/SiO_x/N-C composite by a scalable sol-gel process,using the natural polymer of konjac flour as carbon source and the polyvinylpyrrolidone as nitrogen source.The preparation process was simple and the Si nanoparticles were well embedded into the nitrogen-doped carbon layers.The nitrogen-doped carbon layers not only provided the fast lithiumion diffusion and electron transportation pathways but also supplied a robust mechanical support to alleviate the volume change of Si during the cycling process.Additionally,the SiO_x buffer layers with lower activity can effectively mitigate the volume change of Si.With the outstanding preponderances in structure,the Si/SiO_x/N-C electrode achieves superior electrochemical performance for lithium ion storage.The electrode delivers excellent cycling stability after 100 cycles with a higher capacity retention ratio of 91.7%at the current density of 200 mA g^-1,and shows a high reversible capacity of 952 mAh g^-1.?3?Sodium carboxymethyl cellulose was used as a carbon source and ammonium chloride was used as a nitrogen source.The nitrogen-doped 3D porous carbon/silicon composite was prepared by in-situ formation of sodium chloride crystals as a template by a heat treatment process.The obtained material has a 3D porous structure,which beneficial to improve the penetration of the electrolyte into the electrode material and facilitate the lithium-ion transport and electronic transfer.In addition,the Si nanoparticles were well embedded into the nitrogen-doped 3D porous carbon,which could effectively alleviate the volume change of Si during the cycling process,thereby improving the structural stability of the composite material.As an electrode material for LIBs,it deliver an initial discharge/charge capacities of1867/1325 mAh g^-1 with an initial coulomb efficiency of 71.0%at the current density of 200 mA g^-1.After 100 cycles,the electrode shows a reversible capacity of798 mAh g^-1.