Wan-Jin Lee

The Use of Carbon Nanofiber Electrodes Prepared by Electrospinning for Electrochemical Supercapacitors

Poly(acrylonitrile) (PAN) solutions in dimethylformamide (DMF) were electrospun into webs consisting of 300 nm ultrafine fibers. High-surface area carbon nanofiber webs were prepared by oxidatively stabilized electrospun PAN fibers, followed by activation at 800°C with steam for different times. The specific surface areas of samples ranged from 460 to 1160 m 2 /g. The specific capacitances from the samples ranged from 133 to 75 F/g, depending on the activation time. The results provided a simple and economical means that could substantially enhance the capacitance of the carbon materials.

Adsorption of toluene on carbon nanofibers prepared by electrospinning

This paper reports the novel results of activated carbon nanofibers (ACNF) used to improve the toluene adsorption capacity. The ACNF was prepared by stabilization, carbonization and activation after electrospinning the polymer solution of polyacrylonitrile (PAN) in N, N-dimethylformamide. The average diameter of the ACNF was approximately 300 nm, ranging from 200 to 500 nm. The toluene adsorption capacity of ACNF10 activated at 1000 degrees C increased to 65 g-toluene/100 g-ACNF. This was attributed to the high specific surface area (1403 m(2)/g), large micropore volume (0.505 cm(3)/g), and narrow average pore diameter (6.0 A). The oxygen to carbon ratio (O/C ratio) in ACNF10 was 1.8%. This O/C ratio appears to induce a higher toluene adsorption capacity, which originates from a non-polar interaction between the ACNF surface and toluene. In conclusion, the electrospun ACNF prepared in this study promotes the adsorption of toluene through the high specific surface area, large pore volume, narrow pore diameter and low O/C ratio.

A Hydrous Ruthenium Oxide-Carbon Nanofibers Composite Electrodes Prepared by Electrospinning

Ruthenium-embedded carbon nanofibers were prepared by the processes of stabilization, carbonation, and activation after electrospinning a composite solution of ruthenium(III) acetylacetonate and polyacrylonitrile in N,N-dimethylformamide. When Ru particles were embedded in the carbon nanofibers, the average pore diameter increased from 2.0 to 2.5 nm. The Ru particles were embedded randomly within the carbon fibers, and the size distribution of the Ru particles ranged from 2 to 15 nm. The specific capacitance of the carbon nanofiber without the Ru loading was 140 F/g, while that of 7.31 wt % Ru-carbon nanofibers increased to 280% as 391 F/g. This was attributed to the synergistic effect of electric double-layer capacitance as a result of the expansion of the average pore diameter as well as the pseudocapacitance by the well-dispersed Ru particles.

Supercapacitors Prepared from Carbon Nanofibers Electrospun from Polybenzimidazol

A new form of carbon nanofiber web was prepared that is considered to be a suitable material for the electrode of a supercapacitor exhibiting high capacitance. A polybenzimidazol/dimethyl acetamide solution was electrospun, and subsequently the web was steam activated at 700-900°C. The specific capacitance of the activated carbon nanofiber ranged from 125 to 178 F/g, depending on the activation temperature. The capacitance of the electrical double-layer capacitor was strongly dependent on the specific surface area, micropore volume, and resistivity of the samples. The results provide a simple and economical means that could substantially enhance the capacitance of carbon materials.

Hierarchically mesoporous CuO/carbon nanofiber coaxial shell-core nanowires for lithium ion batteries

Hierarchically mesoporous CuO/carbon nanofiber coaxial shell-core nanowires (CuO/CNF) as anodes for lithium ion batteries were prepared by coating the Cu2(NO3)(OH)3 on the surface of conductive and elastic CNF via electrophoretic deposition (EPD), followed by thermal treatment in air. The CuO shell stacked with nanoparticles grows radially toward the CNF core, which forms hierarchically mesoporous three-dimensional (3D) coaxial shell-core structure with abundant inner spaces in nanoparticle-stacked CuO shell. The CuO shells with abundant inner spaces on the surface of CNF and high conductivity of 1D CNF increase mainly electrochemical rate capability. The CNF core with elasticity plays an important role in strongly suppressing radial volume expansion by inelastic CuO shell by offering the buffering effect. The CuO/CNF nanowires deliver an initial capacity of 1150 mAh g−1 at 100 mA g−1 and maintain a high reversible capacity of 772 mAh g−1 without showing obvious decay after 50 cycles.

Preparation and Characterization of Ni-Sn/Carbon Nanofibers Composite Anode for Lithium Ion Battery

The Ni and Sn-embedded carbon nanofiber (Ni-Sn/CNF) nanocomposites as anode materials were prepared by using electrospinning technique and optimum thermal process. The fine structure of Ni-Sn/CNF was scrutinized by EXAFS. The nanocomposite prepared at 700°C had disordered Ni 3 Sn 2 , disordered NiO, amorphous SnO x and crystalline SnO 2 phases created as tiny particles in the carbon nanofibers (CNF). The 100th discharge capacity of Ni-Sn/CNFs were ranked as follows by their preparation temperature: 700°C (641 mAh g ―1 )>600°C (573 mAh g ―1 )>800°C (559 mAh g ―1 ), and their initial coulomb efficiencies were ranked by preparation temperature: 700°C (60%)>600°C (58%)>800°C (55%). The excellent specific discharge capacity and cycle retention of the sample prepared at 700°C were attributed to the formation of Ni 3 Sn 2 intermetallic compounds, the buffering role of the CNF, and the good distribution of active particles by electrospinning.

Electrospun Activated Carbon Nanofibers Electrodes Based on Polymer Blends

Activated carbon nanofibers (ACNFs) based on a polymer blend, which consists of polyacrilonitrile (PAN) and cellulose acetate (CA), were prepared by electrospinning and subsequent thermal treatment. The diameter of ACNF increased with increasing CA content. The electrical conductivity increased with the addition of CA due to a larger oxygen amount of CA molecules. The specific surface area and average pore diameter of CA-free ACNF (CP) were 742 m 2 /g and 2.0 nm, respectively, while those of 15 wt % CA-blended ACNF (15CP) increased to 1160 m 2 /g and 2.8 nm, respectively. The capacitance of CP was 141 F/g at 1 mA/cm 2 , whereas that of 15CP increased to 245 F/g. This is why the CP is predominated by small surface area with microporos- ity, whereas the 15CP is affected by higher surface area with better mesoporosity due to the combination of electrospinning based on polymer blends and thermal treatment.

Preparation and ionic conductivity of sulfonated-SEBS/SiO2/plasticizer composite polymer electrolyte for polymer battery

Abstract Sulfonated poly(styrene–ethylene–buthylene–styrene) (SSEBS) for a polymer electrolyte membrane was prepared according to the capacity of ion exchange. SSEBS was sufficient to utilize with the polymer electrolyte membrane from the viewpoint of appearance, tensile strength, and ionic conductivity. The SSEBS/SiO2/plasticizer composite polymer electrolyte for the polymer battery was fabricated with various silica contents. LiClO4 or LiCF3SO3 was used as a salt, EC/PC (1:1 vol.%) as solvents, SiO2 as a filler, and DBP as a plasticizer, respectively. The ionic conductivity was enhanced with increasing the degree of sulfonation. The ionic conductivity reached 2.6×10−3 S/cm when the content of silica was 12 wt.% at 1 M LiClO4 in EC/PC (1:1 vol.%) and 40 wt.% for plasticizers. However, if the content of silica was too excessive, the ionic conductivity was decreased due to restriction of ionic movement.

SYNTHESIS OF HIGHLY CRYSTALLINE OLIVINE-TYPE LiFePO4 NANOPARTICLES BY SOLUTION-BASED REACTIONS

LiFePO4 nanocrystals were synthesized in various polyol media without any further post-heat treatment. The LiFePO4 samples synthesized using three different polyol media namely, diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG), exhibited plate and rod-shaped structures with average sizes of 50–500 nm. The X-ray diffraction (XRD) patterns were indexed on the basis of an olivine structure (space group: Pnma). The samples prepared in DEG, TEG, and TTEG polyol media showed reversible capacities of 123, 155, and 166 mAh/g, respectively, at current density of 0.1 mA/cm2 with no capacity fading and exhibited excellent capacity retention up to the 50th cycle. In particular, the samples showed excellent performances at high rates of 30 and 60 C with high capacity retention. It is assumed that the nanometer size materials (~50 nm) possessing a highly crystalline nature may generate improved performance at high rate current densities.

Coaxial carbon nanofiber/NiO core–shell nanocables as anodes for lithium ion batteries

Hierarchically coaxial carbon nanofiber/NiO (CNF/NiO) core–shell nanocables for lithium ion batteries are prepared to coat α-Ni(OH)2 on the surface of electrospun carbon nanofibers (CNF) by electrophoretic deposition, followed by thermal processing in air. In the coaxial CNF/NiO nanocables, a NiO shell of about 20 nm thick is formed by coating with nano-furs outward on the surface of a CNF core of 200 nm in diameter, which is the main factor for providing a three-dimensional (3D) structure. The NiO shells, comprising of abundant inner spaces on the surface of CNF and high conductivity of 1D CNF, are deeply dependent on the enhancement of electrochemical rate capability. Abundant inner spaces in the NiO shell and the interconnected network between nanocables facilitate the mass transfer. The CNF core with the cushioning effect created through the elastic deformation provides electrochemical stability by protecting both radial compression and volume expansion originating from NiO shells radially. The CNF/NiO nanocables deliver a high reversible capacity of 825 mA h g−1 at 200 mA g−1 after 50 charge–discharge cycles without showing obvious decay. The coaxial CNF/NiO nanocables increase not only electrochemical capability but also electrochemical stability.