Synthesis Of Porous Silicon And Its Application As Anode Material For Lithium-Ion Batteries

Lithium-ion batteries have been widely used in modern life due to their high capacity,reliability and convenience.In recent years,with the rapid development and popularization of electric vehicles and portable electronic devices,higher requirements have been placed on the energy density and cycle life of lithium ion batteries.As a traditional commercial anode material,graphite has become a major obstacle to the further performance improvement of lithium-ion batteries due to its low capacity density.Silicon has a high theoretical specific capacity and is considered to be an ideal next-generation anode material.However,in the process of deintercalating lithium,the problem of rapid capacity decay due to the large volume change of silicon has not been completely solved yet,which has also hindered the large-scale practical application of silicon anode materials.The porous structure of porous silicon provides space for the inward expansion of silicon,which not only effectively buffers the volume expansion effect,but also increases the contact area of the active material with the electrolyte.The network structure of silicon provides multiple channels for the transport of lithium ions and charges.The above advantages make porous silicon one of the focuses of research in the field of anode materials for lithium ion batteries.In this paper,porous silicon and porous silicon/carbon composite materials were prepared by using de-alloying,chemical etching and hydrothermal etching to explore the low-cost,simple and easy-to-scale industrialized porous silicon preparation technology.The electrical properties of the lithium ion battery devices based on porous silicon negative electrode were investigated,and the innovative results obtained were as follows:Porous silicon-carbon composite materials were prepared by silicon alloy etching.A new etching solution and related etching process are proposed,which improves the incomplete metal removal by traditional acid etching and the collapse of the porous structure caused by the intense exothermic reaction.Based on structurally stable,high silicon content porous silicon powders,the porous silicon/carbon microtube composites(PoSi/CMTs)were synthesized by introducing carbon using chemical vapor deposition.The method mainly comprises three steps:HCl and CuCl2 are combined to etch the Al-Si alloy,the C2H2 and Ar mixed gas is used for CVD treatment of the precursor,and HNO3 removes excess Cu and its oxide.This method can quickly and effectively remove aluminum in the aluminum-silicon alloy and use Cu to form carbon microtubes,which greatly shortens the reaction time and simplifies the process.The obtained PoSi/CMTs materials were used to prepare button lithium ion battery device in order to test electrical properties.The initial capacity was 2802 mAhg-1,the first coulombic efficiency was 83%,and after 100 cycles,the reversible capacity of the PoSi/CMTs electrode was maintained at 1563 mAhg-1.(2)The preparation of porous silicon powders by wet chemical etching often cause problems such as uneven corrosion and low yield due to the non-wetting of the silicon surface to water.The effects of surfactants,silicon powders types and etching parameters on porous silicon powders were investigated systematically.Furthermore,the composites of porous silicon powders and graphene are used as the anode material of lithium ion battery(Si/RGO).On the one hand,the excellent mechanical properties of graphene can be used to suppress the electrode crack caused by the volume expansion of the Si.On the other hand,the high conductivity of graphene improves the electron conduction capability of the negative electrode.The content of graphene in the Si/RGO composites was 12.38 wt%by thermogravimetric analysis.The reversible capacity of Si/RGO electrode was 1085.9 mAhg-1 after 100 cycles of current density of 200 mAg-1.(3)There are few reports on the preparation of porous silicon by hydrothermal etching method.The porous silicon structure has been successfully prepared only on silicon wafers so far.This method is used for the first time to prepare porous silicon powders in this paper.The BET test showed that the specific surface area of the porous silicon powder was 86.7 m2/g.The porous silicon electrode still has a capacity of 1150.8 mAhg-1 after circulating 40 times at a current density of 200 mAg-1.