Preparation Of Silicon/Carbon Anode Material And Its Electrochemical Performance Research Of Lithium Storage

Lithium-ion batteries have been widely used in micro-small mobile terminals such as mobile phone.However,for many fields,such as new energy vehicles,large-energy storage power stations,and air transportation,the existing lithium-ion batteries are difficult to be applied.In this thesis,in view of the fact that the existing portable lithium-ion battery materials cannot meet the requirements of working under a wide temperature operating window and high-power,an elastic carbon layer-coated silicon core composite material?Si@LTO@C?and a silicon particles embedded in porous carbon fiber composite material?Si@Si Ox@NCNFs?have been synthesized to solve the problem,and we have further studied its electrochemical performance and lithium storage mechanism.Si@LTO@C compound was synthesized by ball milling using micron silicon,multi-dimensional carbon materials?conductive carbon black,carbon nanotubes,expanded graphite?and lithium titanate as raw materials.At room temperature,working electrode can deliver capacity of 876 m Ah g^-1at 2 A g^-1 after 200 cycles,about three times of that of commercial graphite anode.After 1000 cycles under the test conditions of a test temperature of 80°C and a current density of 15A g^-1,a discharge specific capacity of working electrode of 848 m Ah g^-1can be achieved.Such excellent electrochemical performance is attributed to the contribution of the carefully designed elastic carbon coating and the pseudocapacitance.The good electrochemical performance under a wide operating temperature window makes Si@LTO@C a promising anode material for lithium ion batteries used in high temperature environments.Si@Si Ox@NCNFs compound was prepared by an electrostatic spinning process.Waste wool?main component is polyacrylonitrile polymer?was used as the organic carbon source,silica balls synthesized by the St?ber method were used as the silicon source,and methyl methacrylate?PMMA?was added as a pore-forming agent.When this material is used as an anode material of a lithium ion battery,at room temperature,working electrode can deliver capacity of 528 m Ah g^-1at 8 A g^-1 after 210 cycles,and it also has a discharge specific capacity of 1045 m Ah g^-1 after 500 cycles at a current density of 8A g^-1 and a test temperature of 80?.When this material is paired with commercial Li Fe PO₄ for full-cell testing,it can reach a specific capacity of 345Wh kg^-1 at 50?and 100m A g^-1.At the same time,by analyzing the ex-situ Raman spectrum,calculating the lithium ion diffusion coefficient,and calculating the contribution ratio of the pseudocapacitance to the total capacity,the kinetic lithium-storage mechanism of silicon-based anode materials at high temperature is deeply discussed.