Preparation And Modification Of Boron-doped Carbon Nanotube Films And Their Electrochemical Properties

Compared with pristine carbon nanotubes(CNTs),the boron-doped carbon nanotubes(B-CNTs)have better conductivity and structural stability,well promising for the application in lithium-ion battery(LIB)anode materials.However,the relatively low Li storage capacity of B-CNTs has been the main factor limiting its development.In this work,continuous B-CNTs films have been successfully prepared by floating catalytic chemical vapor deposition(FCCVD)method,and the material with the best electrochemical performance was determined by adjusting the type and content of boron source,i.e.the B-CNTs-2 film obtained by adding 2 wt.%boric acid into the precursor.When used as the self-standing anode of LIB,B-CNTs-2 presented a capacity of 427 m Ah g^-1 at the current density of 0.05 A g^-1 with good cycling stability.In order to further improve the Li storage capacity and electrochemical performance of B-CNTs,three kinds of modification methods,heat treatment modification,atmosphere modification and Si O₂ coating,were adopted.Among these,when treated at 650°C,the B-CNTs-65 film possessed good structural uniformity as well as high graphitization degree,and exhibited a high specific capacity of 510.5 m Ah g^-1 at 0.1 A g^-1.Besides,after adding 4 wt.%pyridine into the precursor to adjust the growth atmosphere,some defects were introduced on the surface of py-B-CNTs-3while the original flat graphite structure maintained.After 300 cycles at the current density of 0.1 A g^-1,py-B-CNTs-3 still showed a high reversible capacity of 548 m Ah g^-1.In addition,py-B-CNTs-3 film also had excellent mechanical properties which could bear nearly 50%deformation before plastic fracture and had 50%tensile resilience after 10%strain,significantly higher than B-CNTs and CNTs films.Finally,the electrochemical performance of B-CNTs has been significantly improved by adding a small amount(0.5 wt.%)of TEOS into the precursor.Due to the combination of good conductivity of B-CNTs and high Li storage activity of well-crystallized Si O₂,Si O₂@B-CNTs-0.5 had a high specific capacity of 658.4 m Ah g^-1 at 0.05 A g^-1 and good rate performance as well as the excellent flexibility ensuring its effective application on the soft package of flexible LIBs.