Preparation And Lithium Storage Performance Of Tin-based Nanocomposite Materials

Currently,graphite is widely used as anode material for lithium ion batteries(LIBs)due to its good thermal,chemical,dimensional,and cycling stability.Nevertheless,graphite is still not applicable for the future electric vehicles for its relatively low theoretical capacity(372 mAh/g).As a novel anode material for lithium ion batteries,tin-based materials have attracted much attention owing to its high specific capacity and low lithium insertion potential.However,the large volume change during the charge-discharge process leads to severe irreversible capacity fading and poor cycling performance.Design of nanostructured tin-based materials and its composites has proved to be an effective way to solve this problem.In this work,we synthesized a series of tin based nanocomposites,especially Sn or SnO2 nanowire,nanoparticles and their composites with amorphous carbon.Furthermore,the electrochemical performance of the products was studied as anode materials for lithium ion batteries.The main research work is summarized as follows:1.Mesoporous carbon was synthesized by evaporation induced self-assembly,which was then used as hard template to allow the formation of SnO2 in the mesoporous channel.Carbon-supported SnO2 nanowire arrays were obtained by partial removal of the carbon.The materials were characterized by transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray diffraction(XRD),thermogravimetric analysis(TGA)and nitrogen adsorption/desorption.The resulting products possess a large specific surface area due to the free interspaces between the nanowire arrays.The obtained tetragonal structured SnO2 nanowires show an average diameter of 5 nm.The content of the tin dioxide in this sample is estimated to be around 92 wt% by thermogravimetric analysis.The as-obtained materials were also characterized by galvanostatic discharge-charge and cycling performance.A relatively high reversible capacity of 539 mAh/g can be retained after 100 cycles at a current density of 160 mA/g,which is 1.4 times higher than that of pure SnO2 nanowires.The carbon-supported SnO2 nanowires can deliver large reversible capabilities with excellent cycling performance on account of the mesoporous carbon matrix,which can be served as a buffering layer to relax the stress,reduce the volume variation,andprotect the SnO2 nanowires from severe structural degradation during the insertion-deinsertion process of lithium ions.2.Sn/carbon nanofibers with well dispersed Sn nanoparticles in carbon nanofibers were fabricated by electrospinning process using SnO2 sol and polyacrylonitrile as raw materials.The use of SnO2 sol as tin precursor can improve the compatibility of tin/carbon composites and prevent Sn nanoparticles from agglomeration upon thermal treatment.The nanofibers display a diameter of 300 nm consisting 61.3 wt% of tetragonal structured Sn nanoparticles.The materials were characterized by galvanostatic discharge-charge,CV test and electrochemical impedance.The Sn/carbon nanofibers possess a high reversible capacity of 583 mAh/g after 100 cycles with a Coulombic efficiency of 99%.The relatively good cycling performance is mainly ascribed to the advantages of well dispersed Sn nanoparticles and the presence of the carbon nanofibers,which provide a physical buffering layer to accommodate the volume change of Sn during the lithiation and de-lithiation process.3.Mesoporous phenolic resin was synthesized by hydrothermal technique using triblock copolymer F-127 as structure directing agent.Then mesoporous carbon was synthesized by calcination of the phenolic resin under Ar.SnO2/mesoporous carbon nanocomposites were synthesized by co-precipitation of the carbon and tin dioxide sol.The obtained SnO2 nanoparticles possess tetragonal cassiterite structure with a diameter of 3.5 nm.The content of the tin dioxide is estimated to be around 43 wt% by thermogravimetric analysis.Electrochemical characterization shows that a relatively low reversible capacity of 328 mAh/g can be retained after 100 cycles at a current density of 200 mA/g.This is probably resulted from the low content of SnO2 in the composites,which is partly deposited on the surface of the mesoporous carbon by co-precipitation.