Preparetion And Properties Of Magnesium Thermal Silicon/Carbon Negative Material

Due to its high theoretical capacity(3579 mAh g^-1)and low lithium insertion potential,silicon has a very broad application prospect in the field of lithium ion batteries,but silicon anode materials have two fatal weaknesses:one is lithiation and desorption.The lithiation process will produce a huge volume expansion,resulting in electrode structure breakdown and capacity attenuation;second,the silicon material itself has low electronic conductivity,resulting in poor rate performance of the silicon anode material.Therefore,this paper starts from the exploration of simple and controllable preparation process of nanometer silicon powder,and at the same time,in order to solve the above two problems,the process optimization of magnesium thermal reduction method,and designs a new idea of magnesium thermal reduction to prepare nanometer silicon powder.Firstly,by introducing different inorganic molten salt systems such as CaCl₂,NaCl and KCl,nanometer silicon powder was prepared by magnesium thermal reduction.XRD test showed that nanometer silicon powder prepared under the inorganic molten salt system of CaCl₂ had few impurities and high purity..The nano-silicon powder prepared under the inorganic molten salt system of CaCl₂ has shown good performance after passing the performance test.The initial capacity can reach 2850 mAh g^-1,which is close to the specific capacity of actual theory of silicon.In order to further improve the cycling performance of nano-silicon powder and change the process conditions,CTAB organic molten salt medium is introduced.Nanometer Si spheres with particle size of about 150nm were successfully prepared by magnesium thermal reduction in CTAB organic molten salt medium.Nanometer Si spheres showed good cycling stability and could maintain a reversible capacity of 600 mAh g^-1 for 50 cycles at current density of 0.1A g^-1.In addition,carbon nanotubes can also improve the cycling performance of nanometer silicon powder.Si/CNTs composites with different CNTs content were prepared by magnesium thermal reduction.The prepared Si/CNTs also had good electrochemical performance.According to the cyclic performance test,0.2Si/CNTs showed the best cyclic performance.The reversible capacity of 330 mAh g^-1 could be maintained in 100 cycles at the current density of 0.5A g^-1,and the rate performance was also good.