Graphitization as a Universal Tool to Tailor the Potential‐Dependent Capacitance of Carbon Supercapacitors

Abstract

Most efforts to improve the energy density of supercapacitors are currently dedicated to optimized porosity or hybrid devices employing pseudocapacitive elements. Little attention has been given to the effects of the low charge carrier density of carbon on the total material capacitance. To study the effect of graphitization on the differential capacitance, carbon onion (also known as onion‐like carbon) supercapacitors are chosen. The increase in density of states (DOS) related to the low density of charge carriers in carbon materials is an important effect that leads to a substantial increase in capacitance as the electrode potential is increased. Using carbon onions as a model, it is shown that this phenomenon cannot be related only to geometric aspects but must be the result of varying graphitization. This provides a new tool to significantly improve carbon supercapacitor performance, in addition to having significant consequences for the modeling community where carbons usually are approximated to be ideal metallic conductors. Data on the structure, composition, and phase content of carbon onions are presented and the correlation between electrochemical performance and electrical resistance and graphitization is shown. Highly graphitic carbons show a stronger degree of electrochemical doping, making them very attractive for enhancing the capacitance.

Transparent and flexible high-performance supercapacitors based on single-walled carbon nanotube films

“…This is likely due to the high surface area and graphitization of the SWCNTs (Fig. 2a) [33]. In Fig.…”

Quinone‐Decorated Onion‐Like Carbon/Carbon Fiber Hybrid Electrodes for High‐Rate Supercapacitor Applications

“…[17,22,47] The carbonized PANf ibers show as urface area of less than 50 m 2 g À1 ,w hich www.chemelectrochem.org prohibits their use for supercapacitors (at least withouta dditional physicalo rchemical activation). With an increasing amount of OLCs in the hybridmat electrode, the surfacea rea continuously increases for CF500 to maximum values of 313 m 2 g À1 (BET) and 291 m 2 g À1 (DFT).…”

“…We also noteapronounced butterfly shapeo fC Vs for all samples as ar esult of the nonconstant differential capacitance. [47,48] In detail, applying ah igher potentiali ntroduces additional states,i ncreases the electricalc onductivity of the carbon,a nd improves the ability to screen ionic charges. This phenomenon is known as electrochemicald oping and has been described in the literaturef or graphite, ACs, carbon nanotubes, and OLCs.…”

“…In the organic system, CVs at different scan rates from 1mVs À1 to 2Vs À1 between À1a nd + 1V versus AC were conducted in ah alf cell. [47,55] Each voltage was applied three times and the capacitance at 1V for each scan rate was calculated by using Equation (2): [56] C ¼…”

Synthesis of hollow-structured electrode material for energy storage

“…This incomplete charge screening generated by space constriction greatly limits the gravimetric capacitance of microporous carbons. [158] Moreover, microporous dominated carbon particles also suffer from the electrochemical accessibility problem in the electrolyte solution, which dramatically decreases the rate capacitance of electrode materials. [15] Due to aforementioned reasons, the high capacitive properties of microporous carbons are notably restricted.…”