Construction And Performance Study Of Root-like CNTs-CNFs Anode For Lithium-ion Batteries

At present,lithium-ion batteries(LIBs)are generally considered the main energy storage devices.However,due to the limited capacity(372 m Ah g^-1),commercial LIBs graphite anode cannot meet the requirements of the next-generation energy storage system.Carbon nanomaterials are considered as the next generation of LIBs due to their high specific surface area,good contact with the electrolyte,and fast electrochemical power.Carbon nanofibers(CNFs)and carbon nanotubes(CNTs)are one-dimensional nanomaterials,which are widely concerned in the field of energy storage due to their high specific surface area and good mechanical properties.Electrospinning technology combined with carbonization technology has been widely studied in the preparation of CNFs.However,when CNFs are directly used in LIBs electrode,there are some disadvantages,such as slow rate and low coulomb efficiency,which can be solved by combining CNFs with CNTs.At present,the existing technology combining CNFs with CNTs has the problems of the complex preparation process and poor material properties.Coaxial electrospinning technology is widely used in the preparation of various functional nanofibers because of its simple equipment,easy operation,and strong scalability.Nickel(Ni)precursor fibers were prepared by coaxial electrospinning using polyacrylonitrile(PAN)mixed with nickel nitrate(Ni(NO₃)₂)as the spinning solution.Then CNFs loaded with Ni catalysts were prepared by carbonization.Finally,chemical vapor deposition(CVD)was used as a carbon source CNTs were grown on the surface of nanofibers by a deposition CVD technique,and root-whisker structured 3D carbon nanotubes-carbon nanofibers(CNTs-CNFs)nanocomposite fiber films were prepared.At the same time,its structure and electrochemical performance as LIBS self-supporting anode were studied.The main research contents are as follows(1)CNFs-Ni nanocomposite fiber network was prepared by electrospinning and high-temperature carbonization annealing.Then,the CNTs were grown vertically on the surface of CNFs by coaxial electrospinning and CVD,and a root-whisker structured 3D CNTs-CNFs anode was prepared.This method greatly simplifies the preparation process of CNTs-CNFs and reduces the cost of material preparation.(2)The structure and electrochemical properties of CNFs-Ni were characterized.The results show that the conductivity of CNFs-Ni is increased from 1.25 S m^-1 to34.48 S m^-1,and the specific capacity of CNFs-Ni is good(405 m Ah g^-1 is obtained after 100 cycles at 100 m A g^-1current density).However,the materials also show the disadvantages of poor cycle stability and low-capacity retention.(3)The structure and electrochemical properties of CNTs-CNFs were characterized.The results show that the specific surface area of CNTs-CNFs is320.161 m² g^-1 and the conductivity is 769.2 S m^-1.When applied to the anode material of LIBs,it shows excellent cycle stability and high specific capacity(564.48m Ah g^-1 for 100 cycles at 100 m A g^-1,and the capacity retention rate is more than 99%after ten cycles).At the same time,the material also shows stable rate performance(306.72 m Ah g^-1 at 1 A g^-1)and good long cycle stability(316.8 m Ah g^-1 after 1000cycles at 1 A g^-1 current density).