Preparation And Properties Of Carbon Nanotubes / Silicon Substrate For Lithium Ion Batteries

The ever-increasing demands for higher energy density and higher power capacity of Li-ion secondary batteries have led to search for electrode materials whose capacities and performance are better than those available today.However, commercial graphite anode material, its theoretical capacity is only372mAhg-1, this has been unable to meet the requirements of a new generation of lithium-ion batteries. Silicon (Si) is one of the most attractive and the anode material has been extensively studied because of its high theoretical specific capacity (up4200mAhg-1). But, the silicon anode material will appear very large volume expansion during charging and discharging, resulting in a cracking and pulverization of electrodes,accelerating the invalid of the electrode, which greatly limits its commercial applications. Combination nano and composite of silicon material is the main research directions. Carbon nanotubes (CNTs) have excellent mechanical properties, good lithium storage performance, a large surface area and high electrical conductivity, and it is widely applied research in a lithium-ion battery electrode materials.This paper is based on the review of progress in carbon nanotube and composite materials in lithium ion battery cathode materials.CNTs and Si composite is prepared first, using a unique one-dimensional tubular structure of CNTs as a buffer matrix to buffer the volume expansion of the silicon during the cycle, using excellent electrical conductivity of CNTs to mprove performance of high-rate performance of the material;then prepared carbon coated CNTs/Si composite material, the core-shell structure is formed, the expansion of volume of silicon-based material is further buffered during cycle. Also discussed the impact on the electrochemical properties of the binder.Silicon/carbon nanotube/amorphous carbon (Si/CNTs/C) composites was prepared as anode material for lithium-ion batteries by ball milling and high temperature solid pyrolysis method,to improve and enhance the electrical chemical properties of activity silicon in composite material.By using a scanning electron microscope (SEM), X-ray diffraction(XRD), Raman spectroscopy instruments analysis the structural and morphology of Si/CNTs/C composites. Study the electrochemical properties of Si/CNTs/C composites by constant current charge-discharge, cyclic voltammetry, electrochemical impedance and other analysis methodsFirst, effect of different amount of carbon nanotubes for Si/CNTs/C composite electrochemical performance was reseached.The results show that10%CNTs of Si/CNTs/C composites (40/10/50) exhibited good electrochemical performance, when50mAhg-1current density (0.05C) charging and discharging,show the initial discharge capacity of2695.14mAhg-1, the reversible capacity of1561.16mAhg-1, coulombic efficiency of57.93%, the discharge capacity is still as high1882.69mAhg-1after10cycles, the capacity retention rate was97.83%.Second, performance of the cycle and rate of the Si/CNTs/C composite material (40/10/50) was studied when using different binder, in term of cycling performance, when using sodium alginate binder to50mAg-1current density (0.05C) during charging and discharging, Si/CNTs/C composites showed initial discharge capacity of3233.35mAhg-1, the reversible capacity of2202.65mAhg-1, coulombic efficiency of68.12%, significantly higher than when using the PVDF binder of the initial charge and discharge capacity and coulombic efficiency; in term of rate performance,when250mAg-1current density (0.25C) charging and discharging, Si/CNTs/C showed composites initial discharge capacity of1566.5mAhg-1, a reversible capacity of795.8mAhg-1,coulombic efficiency of50.8%, the discharge capacity of962.5mAhg-1after10cycles,the capacity retention rate of up to98.4%. This is significantly higher than the PVDF binder that showed an initial discharge capacity of808.33mAhg-1, coulombic efficiency of only43%, the capacity retention rate of96.93%after ten cycles. The above studies indicate that different electrode materials need match different binders to improve and enhance electrochemical performance.