Preparation And Electrochemical Performance Of Porous Silicon Carbon Composites Based On Si-Al Alloy Etching

The development of power batteries requires batteries with high energy density and high cyclability.The traditional graphite anode has been unable to meet the high capacity requirements of high energy density lithium ion batteries.However,silicon material has a wide source,low discharge potential and a high specific capacity of 4200 m Ah g^-1,which has great application prospect.However,its huge volume expansion in the process of delithium and lithium and low electronic conductivity limit its application.Numerous studies have been conducted by researchers.Preparation of nanoscale materials can effectively improve material properties,but nanoscale materials have high preparation cost,easy agglomeration,and low tab density,which limits its practical application.The design of porous structure can provide space to accommodate the expansion of silicon material,and the carbon shell can provide electronic conductive network and relieve material stress.In this paper,we choose silicon-aluminum alloy as silicon source and asphalt as carbon source.The porous silicon carbon composites were prepared by chemical dealloying and electrochemical dealloying respectively.In this paper,porous silicon carbon composites were prepared by the combination of pre-carbon coating method and chemical dealloying method.The carbon coating method was firstly followed by chemical dealloying,which effectively slowed down the rate of chemical dealloying and created mild dealloying conditions,so that the internal three-dimensional porous silicon structure could be maintained.The optimal carbon content and calcination conditions were found out through technological exploration.The prepared p-Si@C composite material has the best electrochemical performance.The first charging specific capacity is 1268 m Ah g^-1,and the specific capacity is 915 m Ah g^-1 after100 cycles at a 0.5 A g^-1 current which has a 72%capacity retention rate.When the rate from 5 A g^-1 returned to 0.1A g^-1,the capacity increased to 800 m Ah g^-1,showing good rate performance.In addition,silicon-aluminum alloy was coated with Ti O₂ by hydrothermal method and further improved by carbon coating to prepare p-Si@Ti O₂@C composite.And the capacity retention rate of p-Si@Ti O₂@C composites was 68.0%after100 cycles at 1 A g^-1.The chemical dealloying method has poor controllability and produces a large amount of waste water.Therefore,we proposed an innovative electrochemical dealloying method to prepare porous silicon.We combined the the electrolytic method with traditional paste method which is a method to prepare the anode by silicon-aluminum alloy powder to design the electrolytic cell.E-p-Si/C material was prepared by electrolysis method,which kept the porous silicon structure completely.In addition,a new type of binder,polyacrylonitrile,was proposed to prepare the anode of electrolytic cell.The in-situ carbon coating was formed by the cyclization of polyacrylonitrile calcined at 300?.The cycling performance of E-p-Si@C composites prepared by the new type binder were better than the E-p-Si/C prepared by traditional binder.E-p-Si/C@C composites were prepared by carbon coating with the optimized carbon content and temperature in chapter3.The first reversible specific capacity of E-p-Si/C@C was 1248 m Ah g^-1.And the capacity retention rate of E-p-Si/C@C composites was 84.5%after 100 cycles at 0.5 A g^-1.The capacity retention rate of 100 cycles was 78.1%at large rate of 1 A g^-1.In addition,When the current density changes from 5 A g^-1 to 0.1 A g^-1,its capacity changes from 498m Ah g^-1 to 1000 m Ah g^-1,showing excellent rate performance.