Preparation And Electrochemical Properties Of Silicon-based Anode Materials For Lithium-Ion Batteries

Silicon-based materials are considered to be the most promising next-generation high-performance anode materials for lithium-ion batteries due to the advantages of high theoretical capacity,suitable lithium-intercalation potential and rich resources.However,silicon-based anode materials usually suffer from large volume change during the charge and discharge process,which easily leads to the pulverization of particle,the separation of active material from the current collector,and the damage to the SEI film,which causes the degradation of electrochemical performance.In addition,the silicon-based materials usually have poor conductivity and is poor to the transmission of Li+and electrons.As for the main problems of silicon-based anode materials,this work started from the structure and composition design of the materials,using nanometerization,hollowing,and composite technology to prepare a series of silicon-based anode composite materials,and further studied the lithium storage performance of the materials.The main results are as follows:1.Using ZIF-8@SiO2 as the precursor,the H-Si@C material with a hollow structure was prepared by acid etching,magnesium thermal reduction and carbon modification.The initial reversible capacity of the H-Si@C electrode is 2353 mAh g-1 at the current density of 0.1 A g-1.Another great feature of H-Si@C is the high capacity of 1500 mAh g-1after 200 cycles at the current density of 0.5 A g-1.2.The in situ exfoliation of graphite can be achieved by adding TiO2 during the ball milling process.The exfoliated multilayer graphene(MLG)can be evenly wrapped on the SiOx surface to form the SiOx/TiO2@MLG composite.The first coulombic efficiency is as high as 84.4%when the SiOx/TiO2@MLG composite is used for the negative electrode of lithium-ion batteries.After 1200 cycles at the high current density of 2 A g-1,it can release a specific capacity of 451 mAh g-1 with the capacity retention of 93%.In addition,it also shows good electrochemical performance in full lithium-ion batteries(vs.NCM622).3.The controllable growth of CNTs or graphene is achieved on the surface of SiOx particles through a simple in-situ self-catalytic method.When it is applied to the negative electrode of lithium-ion batteries,the capacity retention is as high as 89.1%after 500 cycles at the current density of 2.0 A g-1.Assembled it with NCM622 cathode material to form a full battery,it can cycle steady more than 150 cycles at the current density of 0.3 C.4.A highly conductive and elastic interface layer is formed on the surface of micro-sized particles SiOx/C particles by introducing PEI and CNTs(SiOx/C/P-CNTs).Compared with the unmodified SiOx/C,the first coulombic efficiency has increased by 2.6%when the SiOx/C/P-CNTs composite is used for the negative electrode of lithium-ion batteries.After 100 cycles at 0.5 C current density,the capacity retention rate has increased by 12%.In addition,when the SiOx/C/P-CNTs composite is mixed with artificial graphite in a certain proportion to serve as the composite negative electrode,its first coulombic efficiency is as high as 87%,and the reversible specific capacity can reach 641 mAh g-1.It can also cycle 130 cycles and maintain 541 mAh g-1 with the capacity retention of 91.8%at the current density of 0.5 C.5.The main reasons for the excellent electrochemical performance of the above silicon-based materials are:(a)The hollow nanostructure not only facilitates the infiltration of the electrolyte and the transport of Li+by increasing the electrode-electrolyte contact area,the large internal space can also effectively relieve the volume change during the charge and discharge processs;(b)The coating layer of graphene or in-situ constructed CNTs can improve the rate performance of the batteries by improving the conductivity of the material,and slow the decomposition of the electrolyte and effectively alleviate the volume effect;(c)The polymer coating layer avoids the direct contact between the materials and electrolyte and forms a thinner SEI film,which is beneficial to improve the coulombic efficiency of the batteries;(d)As an intermediate medium,TiO2 can not only improve the transfer speed of Li+,but also create the internal space to alleviate the volume effect of SiOx.