Structural Characterization of Boron-doped Submicron Vapor-grown Carbon Fibers and Their Anode Performance

Abstract

Structural evolution of undoped and boron-doped submicron vapor-grown carbon fibers (S-VGCFs) was monitored as a function of heat-treatment temperature (HTT). Based on x-ray and Raman data, over the range of HTT from 1800 to 2600 °C, it was found that boron atoms act as catalysts to promote graphitization due to boron's higher diffusivity. For the range of HTT from 2600 to 2800 °C, the process of boron out-diffusion from the host material induces defects, such as tilt boundaries; this process would be related with the improved capacity and Coulombic efficiency of boron-doped S-VGCFs. When 10 wt% S-VGCFs was used as an additive to synthetic graphite, the cyclic efficiency of the capacities was improved to almost 100%.

Microstructure and Electrochemical Properties of Boron-Doped Mesocarbon Microbeads

“…As a result, previously diffused boron atoms in substitutional sites would, at high HTT (above 2500ЊC), diffuse out from the substitutional sites to form boron carbide, consistent with the synthesis temperature for boron carbide known to be at 2500ЊC. 16 These structural features with different morphologies found in borondoped MCMBs may degrade their electrical properties, because homogeneous morphology may be an important factor for producing high-performance anode materials.…”

Defect-Assisted Heavily and Substitutionally Boron-Doped Thin Multiwalled Carbon Nanotubes Using High-Temperature Thermal Diffusion

“…It is well-known that the high-temperature boron doping technique was highly efficient to jump up the electrical conductivity of carbon materials including carbon nanotubes. 20,21 Main advantages of high-temperature thermal diffusion over an aerosol CVD are as follows: (1) Highly crystalline MWNTs can be obtained because boron atoms act as graphitization accelerators around 2000°C. 21 (2) The relative amount of the substitutional boron atoms with regard to other types of boron species are quite high.…”

“…Furthermore, it has been reported that substitutionally introduced boron atoms allow multiwalled carbon nanotubes (MWNTs) to have a semimetallic character with a vanishing or narrow band gap. , Up to now, an aerosol CVD technique has been used to synthesize boron-doped MWNTs. − However, TEM images of the aerosol CVD-grown MWNTs exhibited highly disordered and undulated fringes and sometimes cone-stacked structures. − When considering the electrical conductivity of an individual MWNT, a nested MWNT with straight, long crystalline layers is highly desirable because the defects present in the tubes act as scattering centers in electron transport. It is well-known that the high-temperature boron doping technique was highly efficient to jump up the electrical conductivity of carbon materials including carbon nanotubes. , Main advantages of high-temperature thermal diffusion over an aerosol CVD are as follows: (1) Highly crystalline MWNTs can be obtained because boron atoms act as graphitization accelerators around 2000 °C . (2) The relative amount of the substitutional boron atoms with regard to other types of boron species are quite high.…”

High-Yield Synthesis of Helical Carbon Nanofibers Using Iron Oxide Fine Powder as a Catalyst

“…Among them, carbon nanomaterials have attracted considerable attention since the discovery of fullerene in 1985 [2]. Carbon nanotubes (CNTs) [3,4] and various types of carbon nanofibers (CNFs) [5] have also drawn increasing attraction.…”