Surface Modification Of Carbon Materials Research Articles

Surface modification of carbonaceous materials for EDLCs application

In this study, carbonaceous materials such as activated carbon and activated carbon aerogel were chemically modified with a surfactant sodium oleate in order to improve their specific capacitance and energy storage in electrochemical double-layer capacitors (EDLCs). Optimal conditions for surface modification of activated carbon have been examined as a surfactant solution concentration of 0.25 wt.% together with a time of 24 h for treatment at 25 °C. Specific capacitance and energy density can be improved significantly by surface modification of carbon materials. The enhancement in specific capacitance and energy density is mainly attributable to improvement in wettability of carbon materials, which results in a higher usable surface area and a smaller internal resistance. The effects from surface modification become more marked at higher discharge rates, at which the internal resistance has a more important impact on the energy delivery. A two times energy density of the original carbon could be achieved for the modified carbon materials at a high discharge rate, which indicates that the modified carbons are more suitable in EDLCs for high current applications. In addition, the modified carbon materials possess excellent cycle stability (the capacity decay was only 4% after 20,000 cycles).

Surface fluorination and oxidation of carbon materials for negative electrode of lithium ion secondary battery

The effect of surface modification of carbon materials on their electrochemical behavior has been studied. Fluorination, ozonization and air-oxidation of carbon surfaces increased the charge-discharge capacities. The change in the d-spacings of carbon materials due to surface modification was negligibly small. XPS measurement indicated that surface oxygen contents slightly increased not only in oxidized samples but also in fluorinated one. XPS also revealed the existence of nearly ionic and semi-covalent fluorines at the surface of the fluorinated sample.

Surface Fluorination and Oxidation of Carbon Materials for Negative Electrode of Lithium Ion Secondary Battery

The effect of surface modification of carbon materials on their electrochemical behavior has been studied. Fluorination, ozonization and air-oxidation of carbon surfaces increased the charge-discharge capacities. The change in the d-spacings of carbon materials due to surface modification was negligibly small. XPS measurement indicated that surface oxygen contents slightly increased not only in oxidized samples but also in fluorinated one. XPS also revealed the existence of nearly ionic and semi-covalent fluorines at the surface of the fluorinated sample.

Effects of Plasma Composition Elements on the Surface Modification of Carbon Materials by Nitrogen Plasma.

This investigation was conducted on the surface modification of Glassy carbon(GC) material by R.F. glow discharge plasmas with the aim of investigating the surface nitriding for the GC materials with the nitrogen plasma. The contact angles for water to GC surface after the plasma treatment was measured. And their surfaces were analyzed by using Raman spectroscopy and ESCA. Nitrogen-plasma treatment makes the GC surface hydrophilic. The difference Δθ of the contact angles between those before the treatment (80°) and those at 30minutes after the treatment was investigated. Δθ is considered the effects of plasma treatment. As input power increased from 10W to 70W, the difference Δθ increased (on power electrode : from 46° to 63°, on earth electrode: from 32° to 58°). The composition ratios, O/C and N/C on the untreated GC surfaces were 0.0 and 0.0, respectively. Upon treatment with N2 plasma, this ratio increased to 0.12(O/C) and 0.18(N/C) for the GC surface. Nitrogen atoms and oxygen atoms, namely, were introduced to the GC surface. Introduction of nitrogen atoms was caused by the nitrogen radicals and nitrogen ions. The oxygen atoms were introduced by nitrogen ions. Nitrogen ions were accelerated by the sheath voltage and bombarded the GC surface at high energy. As the result, the active and long life-time radicals were generated. The reaction between these radicals and the oxygen in the air took place when they were taken out from the treatment chamber to the air after plasma treatment.The contact angle decreased by introducing the functional groups having nitrogen atoms and oxygen atoms onto the GC surface with nitrogen plasma. The surface nitriding of the carbon materials can be made easily with the short-time treatment of nitrogen plasma.