High Capacity Silicon Carbon Negative Electrode Materials For Lithium Ion Batteries And Their Electrochemical Properties

Silicon material Which own the largest theoretical specific capacity(4200 mAh/g),is safe and non-toxic,and has abundant reserves in nature.It is an ideal anode material for next generation lithium ion batteries.However,its volume expansion of up to 400% has been restricting the commercial application of silicon in lithium-ion batteries.In this paper,a Si/MWCNTs/cellulose composite flexible lithium-ion battery anode was prepared.A porous flexible conductive paper was used instead of a hollow silicon ball loaded on copper foil collector to prepare lithium-ion battery.The performance of lithium-ion battery was enhanced by physical coating of nano-silicon with fluoride CNT.The electrochemical properties were studied by means of morphology observation,phase analysis and electrochemical performance test.The main research results are as follows:(1)The nano-silicon of Si/MWCNTs/cellulose composite flexible lithium-ion battery anode is evenly embedded in the pore of the three-dimensional conductive network constructed by MWCNTs.The nano-silicon has good contact with the conductive carrier,which greatly reduces the interface resistance.At the same time,nano-silicon has enough expansion space in the process of battery charging and discharging,which ensures the structural stability and chemical stability of the material.The electrochemical detection showed that the first discharge capacity was 2024mAh/g,and the specific capacity was maintained at 850 mAh/g after 50 cycles,showing good cycle stability.In addition,with the continuous cycle process,the battery capacity is slightly increased,indicating that this electrode structure will accompany the charge-discharge cycle more compact,increase the rate.(2)Lithium ion batteries were prepared by using porous flexible conductive paper instead of copper foil collector loaded hollow silicon balls.SEM showed that the active substances were evenly distributed in the pore of the three-dimensional conductive network constructed by MWCNTs,thus ensuring the structural and chemical stability of the materials.The battery has good electrochemical performance,high specific capacity and reversibility.At the current density of 80 mA/g,the specific capacity stabilized at 1 400mAh/g after 50 cycles.At the high current density of 12.6A/g,the capacity can remain stable at 330mAh/g.After the current density of 1A/g was restored,the capacity of the battery was restored to 1150mAh/g.(3)Fluorinated CNT/Si composite lithium-ion batteries were prepared by physical coating of nano-silicon with fluorinated carbon nanotubes.The specific capacity fluctuation was faster and cycle performance was excellent.The crystal structure of the material during charging and discharging can be stabilized by F,the polarization of the material during charging and discharging can be reduced by F,and help to improve the performance of the battery.At 100mAh/g current density,the first discharge specific capacity was 1376mAh/g.After the third charge and discharge,the battery became stable,and after 30 cycles,it was stable at 830mAh/g.