Preparation Of C/si Ox Lithium-ion Battery Anode Materials With High Initial Coulomb Efficiency By The Lithium Supplement Method

With the increase of fossil fuel consumption and environmental crisis,lithium-ion battery,as a kind of electric energy storage device,has attracted extensive attention because of its advantages of high energy density,long cycle life and low environmental pollution.For lithium-ion batteries,the cathode material is one of the key factors to determine their energy density.Carbon coated silicon oxide（C/SiO_x,0<x≤2）lithium-ion battery anode material,the carbon protective layer can buffer volume expansion,prevent agglomeration of active substances,and improve electrical conductivity.However,the low initial coulomb efficiency（ICE）is one of the main reasons why C/SiO_x anode materials can not be widely used at present.In this thesis,a variety of porous composites are prepared by one-step carbonization method using rice husk as carbon and silicon sources and doping metal salts or bases containing lithium.The effects of metal salts or bases containing lithium on electrochemical properties and ICE are investigated,which contributes to accelerating the industrial application of C/SiO_x anode materials.Using rice husk as a raw material and doping LiOH,LiOH-doped porous C/SiO₂composites are prepared by the one-step carbonization method.Due to the activation of LiOH,the porosity of all doped samples is increased obviously,and the Li₂O formed by the high temperature decomposition of LiOH effectively alleviates the volume expansion of the materials during charge and discharge,and the cycle stability,discharge specific capacity and rate performance of the composites are improved.The reversible capacity of the doped samples can reach 660 m Ah/g after 100 cycles at a current density of 0.1A/g,which is higher than that of undoped CRH.However,due to the high temperature decomposition of LiOH into irreversible substance Li₂O,some lithium ions will be consumed during the first discharge,but the ICE can reach about 60%,which is significantly higher than that of carbonized rice husks.Porous SiO_x@Li₂SiO₃/C composites are prepared by the one-step carbonization method using rice husk as a raw material and doping Li₂CO₃.Its graded porous structure promotes the transport of Li⁺and relieves the mechanical stress in the process of Li⁺intercalation/detachment.The resulting Li₂SiO₃ layer improves the electronic conductivity of SiO_x particles and obviously improves the ICE of porous C/SiO_x.As the negative electrode of the lithium-ion battery,the reversible specific capacity of SiO_x@Li₂SiO₃/C remains at 825 m Ah/g and ICE is about 80%after 100 cycles at the current density of 0.1A/g.Therefore,as a low-cost and environment-friendly anode material,SiO_x@Li₂SiO₃/C composite material has a broad application prospect in the field of high-performance lithium-ion battery.Li₃PO₄-doped porous C/SiO₂ composites are prepared by the one-step carbonization method using rice husk as a raw material and doping Li₃PO₄.The graded porous structure promotes the transport of Li⁺and reduces the mechanical stress in the process of Li⁺intercalation/detachment.In addition,Li₃PO₄ is uniformly dispersed on the surface and pore wall of porous C/SiO_x anode materials after the reaction,which can be used as a pre-formed solid electrolyte membrane（SEI）to inhibit electron transfer,to accelerate Li⁺transport,and to reduce Li⁺consumption effectively during the first discharge,and the ICE of the electrode is increased.In addition,the phosphate group and P-C bond will introduce more defects to the C matrix of Li₃PO₄-doped porous C/SiO₂ composites,which is helpful to improve the reversible specific capacity of the electrode.As the negative electrode of lithium-ion battery,the reversible capacity of the doped sample remains at 780 m Ah/g and ICE is about 77%after 100 cycles at the current density of 0.1A/g.Therefore,Li₃PO₄-doped porous C/SiO₂ composites are also green and environmentally friendly anode materials,which can promote the industrial application of C/SiO_x materials.