Research On The Preparation And Performances Of SiO/C With High Capacity For Li-ion Battery Anode

The development of anode materials with high capacity,long cycle life and high rate is an important research direction of lithi?m ion batteries.Amorphous SiO has a high theoretical specific capacity of 2400 mAh/g,and is a promising candidate of high-capacity anode material for lithi?m ion battery.However,SiO is unable to meet the other requirements of commercial applications in the cyclic and rate performances because of poor electrical conductivity and high volume change in litiation and delithiation reaction.To overcome these problems,this thesis used ball milling-spray drying-pyrolysis process,pre-disproportionation treatment to prepare the SiO/C composite materials from the raw microsized SiO.XRD,SEM-EDS,TEM,TG,XPS,FTIR,cyclic charge-discharge tests and electrochemical impedance spectroscopy were used to characterize microstructure and electrochemical properties of the SiO/C composites.The influences of ball milling,pyrolysis,carbon sources and disproportionation conditions on micro-structure and electrochemical performances were investgated.The main conclusions have been drawn as following:Firstly,using ball milling-spray drying-pyrolysis process to prepare the SiO/C composite materials,the optimized milling time for the SiO is 4 h.At the charge and discharge current density of 100 m A/g,the SiO/C composite prepared with the carbon source of sucrose,pyrolysis condition of 900 ? and for 3 h,exhibits a first discharge capacity of 1679.1 mAh/g and initial coulombic efficiency of 60.6%,the 100th-cycle capacity is 468.1 mAh/g,corresponding to the capacity retention of 43.3%.The electrochemical performance has been greatly improved compared with the pristine SiO.Also,the SiO/C composites were prepared from the carbon sources of asphalt,phenolic resin,citric acid and glucose.At 100 mA/g,the SiO/C composite prepared from asphalt has the best electrochemical performance with the first discharge capacity of 1296.9 mAh/g,and the initial coulombic efficiency of 62.7%.The 100th-cycle capacity is 661.7 mAh/g,corresponding to the capacity retention of 73.6%.Secondly,mixing the SiO/C composite precursor by asphalt with graphite(G)to prepare the SiO/C/G composites by using spray drying-pyrolysis process.The addition of graphite could further improve the cycle performance of the composite.At 100 mA/g,the SiO/C/G composite,which was prepared by pyrolysis condition of 900 ? for 3 h,has the best electrochemical performance,with the first discharge capacity of 1508.7 mAh/g,and the initial coulombic efficiency of 62.5%.The 100th-cycle capacity of 949.7 mAh/g,corresponding to the capacity retention of 87.8%.Meanwhile,the SiO/C/G composite showes excellent rate performance,at 400 mA/g and 1000 mA/g,the initial discharge capacity is 901.1 mAh/g and 714.2 mAh/g,respectively.The improvement of cyclic performance and rate performance is due to enhanced conductivity and effective buffering of vol?me expansion by graphite on the SiO.Finally,using ball mill-spray drying process to prepare the SiO/Graphene composites from the SiO by disproportionation process and grapheme.The SiO /Graphene composite,which was prepared by disproportionation temperature of 1050 ? and milling time of 4 h has the best comprehensive electrochemical performances,with the initial discharge capacity of 1786.3 mAh/g at 100 m A/g.The 100th-cycle capacity is 655.8 mAh/g at 200 mA/g.On this basis,the SiO/Graphene composites and electrode preparation technique were optimized.Using the optimized SiO/Graphene composite,305# as electrolyte and composite binder(50 wt.% CMC + 50 wt.% SBR)were used to prepare the electrode.The obtained electrode exhibits the optimal electrochemical performance.At 100 mA/g,the initial discharge capacity and initial coulombic efficiency are 1807.7 mAh/g and 67.3%,respectively.While at 200 mA/g,the 100th-cycle capacity is 1358.2 mAh/g,corresponding to the capacity retention of 92%.The improvement of cyclic capacity is due to the amorphous carbon formed by the pyrolysis of SBR,which are tightly coated on the SiO and graphene.