Nanoporous Carbon Supercapacitors in an Ionic Liquid: A Computer Simulation Study

Shim, Youngseon; Kim, Hyung J.

doi:10.1021/nn901916m

Cited by 275 publications

(319 citation statements)

References 53 publications

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“…Although it was observed from experiments and some simulations that the best performances were obtained for CDCs with an average pore size matching the size of the ions [24][25][26][27][28] , in a recent theoretical study, Kondrat et al 29 have shown that the best average pore size depends on the operating voltage. Nevertheless their model was based on a description of the porous carbon based on a distribution of slit-like pores; the present results show that it would be necessary to inject a more detailed adsorption model to fully address this point.…”

Section: Discussionmentioning

confidence: 99%

Highly confined ions store charge more efficiently in supercapacitors

et al. 2013

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Liquids exhibit specific properties when they are adsorbed in nanoporous structures. This is particularly true in the context of supercapacitors, for which an anomalous increase in performance has been observed for nanoporous electrodes. This enhancement has been traditionally attributed in experimental studies to the effect of confinement of the ions from the electrolyte inside sub-nanometre pores, which is accompanied by their partial desolvation. Here we perform molecular dynamics simulations of realistic supercapacitors and show that this picture is correct at the microscopic scale. We provide a detailed analysis of the various environments experienced by the ions. We pick out four different adsorption types, and we, respectively, label them as edge, planar, hollow and pocket sites upon increase of the coordination of the molecular species by carbon atoms from the electrode. We show that both the desolvation and the local charge stored on the electrode increase with the degree of confinement.

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Section: Discussionmentioning

confidence: 99%

Highly confined ions store charge more efficiently in supercapacitors

et al. 2013

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“…It is interesting to note that the PZC in our simulations corresponds to neither a minimum nor a maximum in DC. While simple EDL theories predict a minimum in DC at PZC, experimental measurements of DC 35,40 clearly show that the position of the minimum or maximum in DC depends upon the particular system and often does not correspond to PZC.…”

Section: B Capacitancementioning

confidence: 94%

Computer simulations of ionic liquids at electrochemical interfaces

Merlet¹,

Rotenberg²,

Madden³

et al. 2013

Phys. Chem. Chem. Phys.

155

188

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Ionic liquids are widely used as electrolytes in electrochemical devices. In this context, many experimental and theoretical approaches have been recently developed for characterizing their interface with electrodes. In this perspective article, we review the most recent advances in the field of computer simulations (mainly molecular dynamics). A methodology for simulating electrodes at constant electrical potential is presented. Several types of electrode geometries have been investigated by many groups, in order to model planar, corrugated and porous materials and we summarize the results obtained in terms of the structure of the liquids. This structure governs the quantity of charge which can be stored at the surface of the electrode for a given applied potential, which is the relevant quantity for the highly topical use of ionic liquids in supercapacitors (also known as electrochemical double-layer capacitors). A key feature, which was also shown by atomic force microscopy and surface force apparatus experiments, is the formation of a layered structure for all ionic liquids at the surface of planar electrodes. This organization cannot take place inside nanoporous electrodes, which results in a much better performance for the latter in supercapacitors. The agreement between simulations and electrochemical experiments remains qualitative only though, and we outline future directions which should enhance the predictive power of computer simulations. In the longer term, atomistic simulations will also be applied to the case of electron transfer reactions at the interface, enabling the application to a broader area of problems in electrochemistry, and the few recent works in this field are also commented upon.

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“…Previously, it was observed that the best performance of SCs can be realized when the average micropore size in nanostructured bulk electrodes (e.g., carbide-derived carbon) matches the size of the ions in the electrolyte [8][9][10][11][12][13][14][15] . It is expected that such a resonant effect is true even for defect-induced pores in quasi-two dimensional FLG substrates ( Figure 1a).…”

Section: Identification Of Best-suited Electrolytementioning

confidence: 99%

Defect‐Engineered Graphene for High‐Energy‐ and High‐Power‐Density Supercapacitor Devices

et al. 2016

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The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability.Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ionaccessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit.Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density. IntroductionSupercapacitors (SCs) are novel electrochemical devices that store energy through reversible adsorption of ionic species from an electrolyte on highly porous electrode surfaces. SCs are highly durable (lifetime >10,000 cycles) with power densities (10 kW/kg) that are an order of magnitude larger than batteries. But the low energy density (10 Wh/kg) of SCs 1 relative to batteries precludes their use in practical applications despite their ability to withstand >10,000 cycles. Graphene-based nanocarbons are ideal electrode materials for SCs due to their low cost, high stability, and high specific surface area. Indeed, an outstanding characteristic of single-layer graphene is its high specific surface area ~2675 m 2 /g, which sets an upper limit for electrical double layer capacitance (C dl ) ~21 µF/cm 2 (~550 F/g). 1-4 Notwithstanding this theoretical limit, there are two intrinsic bottlenecks that are impeding the emergence of high energy density SC devices:i) typically only 50-70% of the theoretical surface area is accessible to ionic species from the electrolyte, which limits the overall capacitance (10-15 µF/cm 2 ) and leads to low energy density, and ii) although the total energy that can be harnessed from a SC device depends predominantly on ion-accessible surface area, it is not the only factor. The presence of the so-called small quantum capacitance (C Q ) in series for nanocarbon electrodes, arising from their low electronic density of states at the Fermi level (DOS(E F )), overwhelms the high C dl further reducing the already limited capacitance and low energy density. 5-7While the efforts to increase energy density have been focused either on increasing the active surface area or the addition of pseudo-capacitance through redox active materials, there is a clear lack of methodologies to simultaneously address the inherent challenges described above. Here, we experimentally show that eng...

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Nanoporous Carbon Supercapacitors in an Ionic Liquid: A Computer Simulation Study

Cited by 275 publications

References 53 publications

Highly confined ions store charge more efficiently in supercapacitors

Highly confined ions store charge more efficiently in supercapacitors

Computer simulations of ionic liquids at electrochemical interfaces

Defect‐Engineered Graphene for High‐Energy‐ and High‐Power‐Density Supercapacitor Devices

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