Preparation And Energy Storage Of Flexible Composite Electrode Based On Carbon Fiber/Carbon Nanotube

With the development of intelligent electronic products towards miniaturization,integration and wearability,flexible energy storage equipment that can match it is needed.The electrode material prepared by traditional process usually adopts metal collector to coat the electrode material,which is prone to stress concentration under various deformation,resulting in cracking and falling off of active substances,which affects the stability of energy storage performance.Carbon fiber（CF）has the advantages of high conductivity,good flexibility,strong mechanical properties and braidability.As the conductive skeleton of electrode,it has been widely used in flexible self-supporting electrode.However,when only CF is used as the collector,the utilization rate of active substances will decrease and the internal resistance will increase when the load of active substances reaches a certain degree.Carbon nanotubes（CNTs）are conductive nano materials commonly used in the field of electrodes with large aspect ratio and large specific surface area.Array carbon nanotubes（VACNTs）can also provide highly ordered conductive structure and improve the mechanical strength of electrodes.Electrode materials based on VACNTs have attracted extensive attention.At present,in the field of lithium-ion batteries,there is no literature report on using carbon fiber/carbon nanotubes（CF/VACNTs）hybrid materials as electrode skeleton and loading active substances as composite cathode and composite cathode of flexible lithium-ion batteries.Therefore,in this paper,VACNTs are grown in situ on CF as flexible self-supporting conductive skeleton to provide large specific surface area for the load of active substances and vertical transmission channel for lithium ions and electrolyte,Improve its energy storage performance.This paper carries out research from three aspects:（1）Controllable preparation of CF/VACNTs hybrid materials.In order to increase the loading efficiency of the catalyst on CF,the surface modification of Si O₂ coated thin layer was carried out on cf.the results showed that the Si O₂ coated thin layer was more uniform when the concentration in the precursor solution was 10 vol%in the hydrolysis/pyrolysis process.The effects of injection speed,catalyst concentration and gas flow rate on the growth orientation of CNT were further analyzed.The results showed that vacnts could be grown on CF when the injection speed was 15 m L/h,the catalyst concentration was 30 mg/m L and the gas flow rate was 300 sccm.In addition,the effect of growth time on the growth length of VACNTs was also studied.The results showed that the length of VACNTs increased with the growth time.When the growth time reached 25 min,its length could reach 15μm。（2）Preparation and energy storage properties of CF/VACNTs based composite electrodes.CF/VACNTs is used as flexible electrode framework,CF/VACNTs flexible composite cathode was prepared by hydrothermal method from its loaded negative active material Li₄Ti₅O₁₂（LTO）,and CF/VACNTs/LFP flexible composite cathode was prepared from loaded positive active material Li Fe PO₄（LFP）.By adjusting the concentration of precursor solution and hydrothermal reaction time in hydrothermal reaction,the active substances are uniformly loaded on the surface of CF/VACNTs hybrid materials.After hydrothermal reaction,LTO can form nano flake structure with size of100～200 nm on VACNTs,and LFP can form spherical particle structure with size of 30～40 nm on VACNTs.The composite positive electrode and composite negative electrode were assembled into button half cells respectively.The specific capacity of CF/VACNTs/LTO flexible composite negative electrode reached 166.7 m Ahg^-1,118 m Ahg^-1 at 10 C charge discharge rate,and the retention rate of specific capacity reached 94%after 100 cycles of charge and discharge.The specific capacity of CF/VACNTs/LFP flexible composite cathode reaches 161.8 m Ahg^-1,the specific capacity reaches119.1 m Ahg^-1 at 10 C charge discharge rate,and the retention rate of specific capacity reaches 97%after 100 cycles of charge discharge.（3）Assembly and energy storage performance of CF/VACNTs based lithium-ion batteries.In order to study the application performance of composite electrode based on CF/VACNTs conductive skeleton in the field of flexible lithium-ion battery,button type lithium-ion full battery and flexible soft package lithium-ion full battery were assembled with CF/VACNTs/LTO as negative electrode and CF/VACNTs/LFP as positive electrode.The specific capacity of button lithium-ion battery reaches 143.4 mAhg^-1,119.8 mAhg^-1 at 10 C charge discharge rate,and the retention rate reaches98.67%after 100 cycles of charge and discharge.The energy storage performance of flexible soft pack battery remains basically stable under different bending deformation.The specific capacity of battery reaches 142.9 m Ahg^-1,120.1 m Ahg^-1 at 10 C charge discharge rate,and the retention rate reaches 98.16%after 100 cycles of charge and discharge.In this paper,CF/VACNTs hybrid materials are used as the conductive skeleton of flexible electrode,which can significantly improve the specific capacity and magnification performance of the electrode,and show good bending deformation resistance.This research idea based on CF/VACNTs flexible conductive skeleton is also applicable to the preparation of flexible electrodes loaded with other electrode active substances,which provides a new breakthrough direction for the development of a new generation of flexible lithium-ion batteries.