Preparation Of SiO_x/C Composite Anode Material For Lithium Ion Battery

In recent years,lithium ion batteries are widely used in portable electronic devices,electric vehicles and electronic storage systems,because of its high energy density and long cycle life.The commercial graphite anode material cannot meet the requirements of high energy lithium ion batteries because of its low theoretical capacity?372mAh/g?,the theoretical specific capacity of silicon materials?4200mAh/g?is much higher than that of graphite,so silicon materials are considered to be one of the most promising anode materials for lithium ion batteries.The volume expansion and low conductivity of the silicon material make them less effective,and the assembled battery shows a poor rate performance.The performance of silicon anode materials has been greatly improved by silicon nanocrystallization or silicon composite materials with other active/inert materials,but there is still a long way to go for its practical application.During the first embedding lithium-ion process of the silicon oxide materials,the active substance dispersed in lithium oxide and lithium silicate,alleviated the volume change which caused by the lithium silicon alloy,the cycle stability is better than pure silicon materials.But the low electrical conductivity of silicon oxide,the large initial irreversible capacity and poor cycle performance are main factors which limit its commercial application.To solve the above problems,based on the preparation of silicon monoxide by high temperature disproportionation,mechanical ball milling,spray drying and high temperature pyrolysis,we try to introduce organic carbon source and conductive materials to improve its electrochemical performance of silicon oxide.The main contents and conclusions are as follows:One,three kinds of composite negative electrode materials SiO_x/C,SiO_x/C/graphene and SiO_x/C/CNTs are prepared by high temperature disproportionation,mechanical ball milling,spray drying and high-temperature pyrolysis with the introduction of organic carbon source,graphene and carbon nanotubes,and analyzes its structure,morphology and electrochemical properties.The study shows that all composites we prepared show obvious diffraction peaks of SiO₂and Si.The morphology of the composites is near-spherical or spherical,and the amorphous carbon is uniformly coated on the surface of the silicon oxide particles.With the charge/discharge current density of 100mA/g,the initial charge and discharge specific capacity of three kinds of composite materials SiO_x/C,SiO_x/C/graphene and Si O_x/C/CNTs are 455.9mAh/g and 1458.2mAh/g,692.5mAh/g and 1656.3mAh/g,948.6mAh/g and 1847.3mAh/g.Among these,the charge and discharge specific capacity of SiO_x/C/CNTs composite is the highest,the initial coulomb efficiency is the highest?51.3%?.With the current density is 200mA/g,the first discharge specific capacity of SiO_x/C/CNTs composite material is 768.1mAh/g,which is higher than that of SiO_x/C/graphene?726.4mAh/g?and SiO_x/C?367.8mAh/g?.After 100 weeks of cycle,the discharge specific capacity of SiO_x/C/CNTs composite is still 448.4mAh/g,which is higher than SiO_x/C/graphene?391.9mAh/g?and SiO_x/C?164.8mAh/g?.These benefit from the hollow tubular structure,large surface area and a three-dimensional conductive network,which build"conductive bridge"for the dispersed silicon monoxide particles,and provide the release space required for the volume expansion,in favor of the capacity of active material and the improvement of cycle stability.Two,after determining to use organic carbon source coated and carbon nanotubes as high conductive materials to improve the low conductivity,large irreversible capacity and poor cycling performance of silicon oxide materials,by studying the addition of CNTs?2%,4%,6%?and the addition of organic carbon source?10%,15%,20%,30%?,we find that the electrochemical performance of SiO_x/C/CNTs composite negative electrode is the best when the addition of CNTs is 4%and the addition of organic carbon source is 20%.Under this condition,the first charge and discharge specific capacity of SiO_x/C/CNTs composite anode materials are1538.5mAh/g and 2176.8mAh/g,the initial columbic efficiency is 70.7%,and after100 cycles the discharge capacity is 1334.3mAh/g,the capacity retention rate is78.8%.Three,the SiO_x/C/CNTs composite and graphite are mixed in a certain proportion to receive SiO_x/graphite-420,SiO_x/graphite-450 and SiO_x/graphite-600composite anode material whose effective capacity are 420mAh/g,450mAh/g and600mAh/g.The first charge and discharge specific capacity of SiO_x/graphite-420composites is 446.1mAh/g and 541.1mAh/g.The initial columbic efficiency is 82.4%.After 280 cycles,the charge/discharge specific capacity is 428.6mAh/g and429.2mAh/g,the cycle performance of materials is excellent with a good application prospect.After 200 cycles,the effective capacity of SiO_x/graphite-450 and SiO_x/graphite-600 are only slightly below the designed effective capacity,the cycle performance is good,and they has some application prospects.