Preparation And Properties Study Of Metal Oxide-Modified Nano Si/C Composite Anode Materials

Lithium-ion battery,as a green secondary electrochemical power source with high energy density and long cycle life,has a wide application prospect and space in the fields of agricultural production,intelligent agriculture and energy storage in agricultural power grid.The anode material as ion acceptor is an important part of lithium-ion battery.But the theoretical specific capacity of the commercial graphite anode is only 372 mAh·g-1,which limits the further improvement of the energy density of lithium-ion battery.Silicon(Si)and Transition Metal Oxide(TMO,Transition Metal Oxide)anode materials are promising new anode materials with high lithium storage capacity and low cost,which have been widely attracted by domestic and foreign researchers.However,silicon and transition metal oxide anodes will have severe volume and shrinkage during lithium intercalation/delithium intercalation.It will lead to cracking,pulverization and shedding of active materials on the electrode surface,which will seriously affect the cycle life of the battery.At the same time,the lower intrinsic conductivity also limits its magnification performance.In order to solve the above problems,one-dimensional composite nonmaterial based on metal oxide-modified Si/C composite were prepared by electrospinning technology.In order to prolong the lifetime and improve the rate performance of the battery,we enhanced the conductivity and stability of the composite electrode through functional microstructure design.The main research contents of this paper are as follows:(1)The Fe2O3/Fe3O4/CNF composite was obtained by electrospinning method.It is clearly observed that a large number of hollow Fe2O3/Fe3O4 nanoparticles was developed and assembled on the surface of CNF.The results show that the Fe2O3/Fe3O4/CNF composite electrode has good electrochemical performance.After 200 cycles tests at 0.2 A·g-1,the reversible specific capacity of the Fe2O3/Fe3O4/CNF electrode remained higher than 900 mAh·g-1,With the good feature of rate performance,the reversible capacity can still reach 730 mAh·g-1 at a high current density of 3 A·g-1.CNF effectively inhibits the agglomeration of ferroxide nanoparticles and provides conductive network and structural support,which improves the electronic conductivity and structural stability of active materials.Hollow nanoparticles provide buffer Space for the volume caused by Li+ embedding in active materials,which improves the cycle characteristics of active materials.(2)The composite material with hierarchical nanostructure of Sn-doped CNF modified by Co3O4 nanosheets and Fe2O3 nanoparticles were synthesized by combining electrospinning technology and chemical precipitation method.The results show that the Co3O4/Fe2O3/Sn-CNF electrode has high capacity,excellent cycle stability and rate capacity.Co3O4/Fe2O3/Sn-CNF still has a high specific discharge capacity of 991 mAh·g-1 after 200 cycles at 0.2 A·g-1,and the specific discharge capacity can reach 686 mAh·g-1 when the current density increases to 2 A·g-1.Sn-doped CNF materials have good electronic transport properties and mechanical properties,which buffer the volume deformation of Co3O4 and Fe2O3 during the lithiation and delithiation process,and enhance its structural stability.The composite of Co3O4 and Fe2O3 loaded on CNF surface have good dispersion,which further enhances the specific capacity of the composites.In addition,the three-dimensional structure after double coating provides more reactive sites,shortens the transport path of Li+,and improves the charge-discharge capacity of active materials at high current density.(3)The Carbon-coated Si nanoparticles modified by Fe2O3,Co3O4 and SnO2 composite nanofibers were prepared by electrospinning method.The result shows that the Co3O4/C/Si composites have a high specific surface area and the lowest carbon content,abundant reactive sites,and provide high specific capacity and rate performance.The electrochemical tests results show that the initial discharge capacity of Co3O4/C/Si is 2799 mAh·g-1 and the specific capacity is 824 mAh·g-1 after 200 cycles at 0.5 A·g-1.With the good feature of rate performance,the specific discharge capacity of electrode is 729 mAh·g-1 at 1 A·g-1.Crosslinked network structure of carbon layers can prevent the direct contact between Si nanoparticles and electrolyte,reduce side reactions,limit the volumetric expansion of Si in lithification process,and improve the structural stability of the electrode.The metal oxide modification layer can improve the specific surface area and regulate the carbon contents in composites.(4)The C/LTO/Si composites of CNF-coated Li4Ti5O12(LTO)and Si nanoparticles were prepared by ball milling method and electrospinning technology.The results show that the C/LTO/Si composite anode material has high specific capacity,good cycle stability and rate characteristics.The specific discharge capacity of C/LTO/Si electrode is 1018 mAh·g-1 at 0.2 A·g-1 for 200 cycles.The specific discharge capacity of electrode is still up to 560 mAh·g-1 at a high current density of 3.2 A·g-1.The LTO nanoparticles uniformly coated on the surface of Si can effectively suppress the volume expansion of Si nanoparticles during the Li+insertion process and increased the area of C coating layer,which promoted the rapid diffusion of Li+.The network structure of the composites effectively improves the charge transport and diffusion characteristics of C/LTO/Si composites,and improves the structural stability and rate performance of active materials.And it also can reduce polarization effect.