Preparation And Electrochemical Properties Of Nano-silicon-based Anode Materials For Lithium-ion Batteries

Silicon-based anode materials are considered to be one of the most promising anode materials for lithium-ion batteries due to their high theoretical specific capacity,low discharge potential and abundant reserves,but their low conductivity and volume up to 300%.Expansion limits the development of silicon-based anode materials.In view of the above problems,this paper prepares the nano-silicon-based material of hollow tubular structure to alleviate its volume expansion effect and improve its electrochemical performance.The main research contents and conclusions are as follows:?1?Firstly,a simple one-pot method was used to prepare SiO₂ nanotubes with controlled aspect ratio.The microstructure of SiO₂ nanotubes under different raw material ratios and reaction time was systematically investigated.The results show that the length-to-diameter ratio of SiO₂ nanotubes increases with the increase of TEOS before the addition of TEOS.With the increase of nickel chloride addition,the aspect ratio of SiO₂ nanotubes increases first and then decreases.The SiO₂ nanotubes were used as the anode materials of lithium ion batteries under different raw material ratios and reaction time,and their electrochemical properties were investigated.The results show that the micro-morphology of SiO₂ nanotubes affects the electrochemical properties of the SiO₂ nanotubes in terms of aspect ratio,uniformity and dispersion.The uniform aspect ratio determines the discharge specific capacity of SiO₂ nanotubes,and good dispersion.And the stable structure directly affects the rate performance of the material.The N₂H₄·H₂O/NiCl₂ is 5.75:1,and the SiO₂ nanotubes have uniform morphology at 6 h.As the anode material of lithium ion battery,the first charge capacity is 625.5 mAh/g.After 100 cycles,the capacity remains at 232.5 mAh/g.The capacity cycle retention rate relative to the second cycle was 75.7%.Combining the rate performance test and the impedance test results,it is found that the electrochemical performance of the SiO₂ nanotube material is much better than that of the commercial SiO₂ nanosphere,which shows a good structural advantage.?2?Carbon-coated SiO₂ nanotubes are modified to improve their electrochemical performance.The SiO₂ nanotubes were coated with carbon layers of different thicknesses by using formaldehyde and resorcinol as carbon sources.The results of constant current charge and discharge test show that the electrochemical performance of SiO₂ nanotubes coated with a small amount of carbon is obviously improved.The introduction of carbon not only improves the cycle performance of the material,but also promotes the release of specific capacity.The first discharge specific capacity of the carbon-coated SiO₂ nanotubes was 705.3 mAh/g,and the 100 cycles capacity was still maintained at 284.7 mAh/g.?3?Finally,the prepared SiO₂ nanotubes were used as raw materials,and Si nanotubes were prepared by magnesium thermal reduction process.The process conditions of magnesium thermal reduction were systematically studied.The optimum process conditions for the experiment were as follows:the mixing method of magnesium powder and silicon was manually ground for 30 min,the graphite boat was used as the reaction vessel,the heating rate was 5°C/min,and the material after magnesium thermal reduction was washed with 1 mol/L HCl for 12 h.The Si nanotubes prepared by this process condition have significantly improved cycle performance compared with commercial Si nanospheres.At a current density of 100mA/g,the material cycle performance is significantly improved,and the specific capacity after 300 cycles is 300 mAh/g.