| As a kind of renewable clean energy,lithium ion batteries have attracted much concern with human beings,due to its many advantages,such as high working voltage,small self-discharge,long cycle life,easy to carry and so on.The key of improving electrochemical lithium storage performance is to use excellent anode materials.Carbon-based anode materials(commercial graphite,ordered mesoporous carbon,hollow carbon spheres,etc.)have a good conductivity and electrochemical stability,but its theoretical specific capacity is extremely limited(only 372 mAh/g),which can not meet the application requirements.SnO2 has many advantages of high theoretical specific capacity(782 mAh/g),environmental friendliness and abundant reserves as the anode material.However,its poor conductivity and severe volumetric strain on the process of discharge/charge limit its commercial application.Based on this,SnO2/C composites were prepared to improve the conductivity of SnO2 and the specific capacity of carbon materials,and slow down the volume change of SnO2 during the discharge/charge process.The main contents of this paper are as follows:(1)Using SnCl2·2H2O as tin source and commercial graphite as carbon source,respectively tin dioxide/commercial graphite(SnO2/CG)composites were prepared by simple sonochemical method,vacuum drying and annealing.As a result,the discharge specific capacities of pure SnO2 and CG electrodes are only 346.9 mAh/g and 200.2 mAh/g at the current density of 500 mA/g after 150 cycles,respectively.However,the SnO2/CG electrode can still provide a discharge specific capacity of 643.1 mAh/g at the current density of 500 mA/g after 150 cycles.Compared with pure SnO2 electrode and CG electrode,SnO2/CG electrode shows excellent electrochemical performance.(2)In order to improve the electrochemical properties of SnO2/C composites,SnO2/CMK-3 nanocomposites were synthesized by the same process.The results show that SnO2/CMK-3 electrode can still provide high discharge specific capacity of 1062.4 mAh/g,927.7 mAh/g,784.9 mAh/g,642.2 mAh/g and 522.4 mAh/g at the different current densities of 100 mA/g,200 mA/g,500 mA/g,1000 mA/g and 2000 mA/g after 10 cycles,respectively.And when the current density decreases to 100 mA/g,the discharge specific capacity of SnO2/CMK-3 electrode can still reach 1033.6 mAh/g after 30 cycles.At the same time,the discharge specific capacity of SnO2/CMK-3 electrode can still provide 898.8 mAh/g after 150 cycles at the current density of 500 mA/g.The reason is due to the synergistic effect of highly ordered mesoporous of CMK-3 and SnO2 particles(5 nm of particle size),which improves the electrochemical performance of SnO2/CMK-3 electrode.(3)SnO2/N-HCS composites were synthesized by adjusting the content of SnCl2·2H2O and using the same preparation process.SnO2/N-HCS has a novel morphology:ultrafine SnO2 nanoparticles are uniformly dispersed on the carbon skeleton of hollow N-HCS.In addition,Nitrogen-doped provides a large number of nucleation sites for SnO2,and inhibits the agglomeration and nuclear growth of SnO2.The results show that the SnO2/N-HCS 25 electrode can supply high discharge specific capacities of 1444.4 mAh/g,1252.9 mAh/g,1063.9 mAh/g,927.5 mAh/g,796.9 mAh/g and 608.3 mAh/g at the different current densities of 100 mA/g,200 mA/g,500 mA/g,1000 mA/g,2000 mA/g and 5000 mA/g after 5 cycles,respectively.When the current density goes back to 100 mA/g after 5 cycles,the SnO2/N-HCS 25 electrode can still provide a high discharge specific capacity of 1261.7 mAh/g.In addition,the discharge specific capacity of SnO2/N-HCS 25 electrode can still offer 1252.5 mAh/g at the current density of 500 mA/g after 80 cycles,which is much higher than other electrodes. |
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