Synthesis And Properties Of Silicon Based Materials As Anode For Lithium-Ion Batteries

Silicon has the advantages of ultra-high capacity,low operating voltage,and abundant reserves.It is one of the most promising next-generation lithium battery anode materials.However,the large volume expansion,unstable SEI film,and poor conductivity during the charge and discharge process of silicon anode prevent further practical application.In order to solve these problems,this paper mainly uses hydrochloric acid instead of hydrofluoric acid to selectively etch the template to engineer abundant void space to prepare a silicon-carbon composites with a porous structure,and through a series of physical and chemical tests to characterize its performance for silicon anode.The methods and conclusions are as follows:1. In order to reserve buffer space for the volume expansion of silicon,we use a combination of sacrificial layer template method,high-temperature calcination method and solvothermal method to prepare silicon-carbon composite materials to improve the performance of silicon anodes.A core-shell silicon-carbon composite?Si@void@C-Al?was prepared by using Al₂O₃ as a template and polydopamine as a carbon source.In a weakly acidic environment,aluminum sulfate is slowly hydrolyzed on the surface of silicon to form aluminum hydroxide,and then in the vacuum drying process,a?-type alumina is formed to cover the surface of the silicon core.The target product is obtained by dopamine coating,high-temperature calcination under N₂ atmosphere,and selective etching with hydrochloric acid.The charge and discharge test shows that the Si@void@C-Al composite material has better cycle stability.After cycling 100 times at a current density of 300 m A g^-1,there is still 926.2 m Ah g^-1.At the same time,the material also shows excellent rate performance,with a charging capacity of 1390.6 m Ah g^-1 at a current density of 2000 m A g^-1.The sufficient reserved space of the composite material greatly relieves the volume expansion of silicon during the charge and discharge process,improves the stability of the silicon negative electrode,and extends the cycle life of the active material.2. In order to improve the controllability of the reserved space,we used CaCO₃ as the template to prepare a Si@void@C-Ca composite with porous structure.The nano calcium carbonate template and silicon powder prepared are uniformly mixed and then coated with a phenolic resin.After high temperature calcination under N₂ atmosphere and etching with hydrochloric acid,the silicon nanoparticles are fully encapsulated into the mesoporous carbon matrix with abundant void space.The LIBs with the Si@void@C-Ca anode exhibits excellent specific capacity of 973.2 m Ah g^-1 and high capacity retention of 84.9%after 100 cycles at a current density of 300 m A g^-1.We have conducted the morphological studies on the volume changes for the various electrode.And the Si@void@C-Ca exhibited the smallest volume change of only 9.9%after 100 charge/discharge cycles.The abundant void space between Si core and outer carbon shell to accommodate the volume expansion of silicon and form a stable SEI layer during the cycling process.And,the outer pyrolytic carbon layer can significantly reduce the ohmic resistance to improve the conductivity of the electrode.3. In order to optimize the experimental process,an experimental scheme with simple steps and environmental protection is proposed.We choose nano-graphite as the conductive matrix,replace elemental oxide template with elemental sulfur with a low melting point,and use phenolic resin as a coating to prepare porous silicon-carbon composites?Si/NG@void@C?.The graphite/silicon mixture and sulfur powder mixed are thoroughly mixed at room temperature with carbon disulfide as a solvent,coated by phenolic resin,and then carbonized and desulfurized by high-temperature calcination in a N₂ atmosphere.The Si/NG@void@C composite material has a specific charge capacity of663 m Ah g^-1 after 100 cycles at a current density of 300 m A g^-1,and the cycle retention rate was 84.7%.The charge specific capacity after 500 cycles at a current density of 1 A g^-1was 328 m Ah g^-1,and the cycle retention rate was 52.6%.Compared with the currently commercialized materials,the cyclic stability of the materials has been significantly improved.