Preparation And Application Of Carbon Silicon Composite Anode For Lithium Ion Battery

Nowadays,the demand for energy storage is increasing urgently.Lithium-ion batteries are widely used because of its advantages such as high energy storage density,long service life,and high rated voltage.The anode material is a key factor in determining the lithium capacity.At present,the negative electrode materials commonly used in commercial lithium-ion batteries are carbon-based materials such as graphite,but the specific capacity of carbon-based negative electrode materials is low,and it is difficult to meet people's requirements for high-energy lithium batteries.The silicon anode has high theoretical specific capacity,low deintercalated lithium voltage,and it is reserved in abundance,environmental protection,and is expected to become the next generation of high-energy lithium battery anode materials.However,the commercialization of silicon anodes still has the following challenges:(1)With the de-intercalation of lithium ions,the volume expansion of silicon can reach more than 420%,which causing the structure of the negative electrode active material to collapse,and the cycle performance of lithium batteries to decline;(2)The crushed silicon,electrolyte and lithium ions continue to form SEI films,which causing reduced capacity;(3)The conductivity of silicon is low,which causing greater resistance when lithium ions are de-intercalated.Micro-doped silicon,nano-doped silicon,and doped graphite were developed in this experiment in response to the problems.Different carbon-silicon composite materials were prepared by using high-temperature pyrolysis,ball milling,and cell pulverization methods.The following conclusions were obtained:(1)Compared with carbon/micron-level undoped silicon lithium batteries,the carbon/micron-type n-type and p-type doped silicon lithium internal resistances have decreased by 34 ? to 114 ?,and the first cycle discharge specific capacity capacity Increased from 136.6 mAh/g to 517.0 mAh/g;(2)The structure of carbon nanotubes/carbon-coated silicon can effectively improve the volume effect of the silicon negative electrode in the first charge and discharge,and the first charge and discharge efficiency of lithium batteries has been increased from less than 28.8% to 63%;(3)The negative electrode material prepared by combining carbon/carbon nanotube materials with nano-silicon prepared by the magnesium thermal method can greatly improve the cycle stability of lithium batteries.The first effect of the lithium battery with a carbon-to-silicon ratio of 1:1 is increased to more than 95%,but due to the low purity of silicon,the specific capacity of the lithium battery is only 442.4 mAh/g.After using commercial nano-silicon,the battery still has a specific capacity of 244.4 mAh/g to 836.9 mAh/g after ten cycles of charge and discharge cycles,and the charge and discharge efficiency are all over 95%;(4)Due to the self-limiting capacity of graphite,even using doped graphite/silicon anode materials can reduce the internal resistance of lithium batteries,and the specific capacity can only be increased from 17.5 mAh/g to 89.6 mAh/g.The lithium battery can still have a capacity residual ratio of 60.5% to 88.7% after five charge and discharge cycles.