Preparation And Modification Of High-performance SiO_x Anode Materials For Lithium Ion Batteries

With the rapid development of electric vehicles and large energy storage facilities,higher requirements are placed on the energy density of lithium-ion batteries.However,the current commercial anode is dominated by graphite,and its limited theoretical specific capacity(372 m Ah·g^-1)has been unable to meet the needs of high energy density of lithium ion batteries.With much higher specific capacity(～2000 m Ah·g^-1)and lower cost,SiO_xis considered to be one of the most promising electrode materials to replace graphite anode.However,the volume change of SiO_xduring the cycle process is large,which will lead to particle pulverization,the separation of active material and current collector,and the rapid attenuation of capacity.At the same time,its poor conductivity is not conducive to the transmission of Li⁺and electrons,and its practical application suffer form great challenges.In this paper,SiO_x-based composites were prepared by compounding,carbon coating or element doping with carbon materials with excellent conductivity,and their lithium storage properties were studied.The main research contents and results are as follows:（1）C,N and P co-doped SiO_xcomposites were prepared by ball milling,liquid phase coating and high temperature calcination.The effects of phytic acid（P source）addition on the electrochemical properties of SiO_x/G@CNP composites were studied.Appropriate P doping can not only improve the conductivity of the material,but also increase the content of pyridine N in the material,thereby improving the electrochemical performances of the material.When the addition amount of phytic acid was 20 wt%of SiO_x/G,the charge specific capacity of the prepared SiO_x/G@CNP-2 composite was370 m Ah·g^-1at a high current density of 5 A·g^-1,and the reversible specific capacity was 751.7 m Ah·g^-1after 150 cycles at 0.2 A·g^-1.（2）SiO_x,flake graphite and melamine were mixed and calcined,and then compounded with graphene oxide and carbon nanotubes.Finally,the compact N-SiO_x/C@C composites were prepared by asphalt coating.Multi-component carbon materials are beneficial to overcome the shortcomings of SiO_x-based anodes,especially to form a stable solid electrolyte interface,maintain the structural integrity of the electrode material,and enhance the conductivity of the electrode.The obtained N-SiO_x/C@C anode exhibits a high reversible capacity(980.2 m Ah·g^-1),an excellent cycle stability(capacity retention of about 70%after 500 cycles at 0.5 A·g^-1)and excellent rate performance(high specific capacity of 491.9 m Ah·g^-1at a high rate of 5 A·g^-1).（3）After SiO_xwas compounded with ECP-600JD with high conductivity,a rigid carbon coating was prepared with asphalt,and then a highly conductive flexible coating layer（PVA/PEI/CNTs）was formed on the surface of SiO_x/E@C by polyvinyl alcohol（PVA）,polyethyleneimine（PEI）and carbon nanotubes（CNTs）.The PVA/PEI/CNTs interface not only maintains the structural stability of the particles during cycling,but also enhances the electrical contact between the particles and enhances the transport capacity of Li⁺and electrons.Compared with SiO_x/E@C without flexible coating,After 700cycles at 0.5 A·g^-1,the capacity retention rate of the composite is 64.23%,which is increased by 16.37%,and the capacity of 407.1 m Ah·g^-1can be obtained at a current density of 5 A·g^-1.