Polarization-induced distortion of ions in the pores of carbon electrodes for electrochemical capacitors

Ania, Conchi O.; Pernak, Juliusz; Stefaniak, Filip; Raymundo-Piñero, E.; Béguin, François

doi:10.1016/j.carbon.2009.06.054

Cited by 87 publications

(54 citation statements)

References 29 publications

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“…As expected from experimental studies 17,18 , the adsorption of ions in confined environments leads to their partial desolvation. This is clearly visible on the distributions of the ACN solvent molecule coordination number around each ion, as shown in Fig.…”

Section: Supercapacitors Simulationssupporting

confidence: 53%

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: Supercapacitors Simulationssupporting

confidence: 53%

Highly confined ions store charge more efficiently in supercapacitors

et al. 2013

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Section: Resultsmentioning

confidence: 99%

“…In comparison, PAN-derived CNFs showed a broader distribution of micropore size with an average value of 1.4 nm. Therefore, PAN/pitch-derived CNFs are theoretically more suitable as electrode materials in an aqueous medium, because the ultramicropores in the carbon structure match well with the size of solvated ions (less than 1.0 nm) [13].STM provides information on the domain size and micro-structure of the domains of CNFs. As the pitch concentration increased, the shape of the surface changed from small particle-like to flat plate-like to large particle-like (Fig.…”

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confidence: 99%

Solvent-induced porosity control of carbon nanofiber webs for supercapacitor

Kim

Yang

Kim

et al. 2011

Journal of Power Sources

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A simple and scalable method is reported for fabricating a porosity-controlled carbon nanofibers with a skin-core texture by electrospinning a selected blend of polymer solutions. Simple thermal treatment of the electrospun nanofibers from solution blends of various compositions creates suitable ultramicropores on the surface of carbon nanofibers that can accommodate many ions, removing the need for an activation step. The intrinsic properties of the electrode (e.g., nanometre-size diameter, high specific surface area, narrow pore size distribution, tuneable porosity, shallow pore depth, and good ionic accessibility) enable construction of supercapacitors with large specific capacitance (130.7 Fg -1 ), high power (100 kWkg -1 ), and energy density (15.0 Whkg -1 ).Keywords: Porosity, Skin-core, Electrospinning, Pore size distribution, Supercapacitor 3 1. Introduction Due to their high power density and long life-time, electrochemical capacitors are promising power sources for portable electronic systems and automotive applications [1][2][3]. To improve the performance of these capacitors, several approaches have been investigated (e.g., controlling the pore size distribution, introducing electroactive metallic particles or electron conducting polymers, and fabricating hybrid-type cells) [4][5][6]. Among the many types of active materials, carbon nanofibers (CNFs) are of great practical importance due to their flexibility and high aspect ratio (above 10 6 ). Moreover, to improve the energy density and ion transport within electrode materials, thin films consisting of carbon nanotubes and CNFs have been suggested as promising flexible electrodes for supercapacitors [7][8][9]. In this work, we investigated this approach for improving energy storage efficiency by narrow distribution of pore sizes, which can enhance the ionic accessibility into the pores polyacrylonitrile(PAN)/pitch-based CNFs having a skin-core structure. Further, the size of pores formed in the surface of the fiber can be controlled to an appropriate degree. Experimental FabricationThe pitch provided through condensation of the pyrolized fuel oil (PFO) with Cl 2 by Hanwha Chemical Co. Korea. The PFO used as the raw material is a heavy residual oil as by-product from naphtha cracking. The properties of the pitch used are summarized in Table 1. The concentration of pitch in THF was varied between 50 and 20 wt. %. A solution of PAN in DMF was added to pitch in THF solution achieve a PAN/pitch weight ratio of 7/3 wt.%. To produce a web, a voltage of 20 kV was applied to the positively charged capillary, and a tip-to-collector distance of 25 cm was maintained during the electrospinning process. The nanofibers were stabilized in air and carbonized at 1000 °C in a horizontal furnace under a flow of nitrogen.2.2.Characterization The CNFs were characterized by SEM (Hitachi, S-4700, Japan), TEM (using JEOL JEM-2010 FEF), and nitrogen adsorption-desorption isotherms (ASAP2010, Micromeritics Instruments Co.). The full range of pore sizes over a continuo...

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“…26 Note that the present calorimeter was configured for two electrode configuration and could not provide the potential evolution across each electrode separately. However, Ania et al 69 showed that, at low cell potential (i.e., ψ s ≤ 1 V), the potential difference was identical across the positive and negative electrodes of a symmetric EDLC cell in organic electrolyte.…”

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confidence: 99%

Effects of Constituent Materials on Heat Generation in Individual EDLC Electrodes

Munteshari

Lau

Ashby

et al. 2018

J. Electrochem. Soc.

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This study aims to investigate the effect of electrode composition on heat generation in electric double layer capacitor (EDLC) electrodes under galvanostatic cycling. EDLCs consist of two identical electrodes usually made of a mixture of (i) carbon-based material, (ii) binder, and (iii) other conductive additives. These constituents were found to influence the capacitance and internal resistance of the device and the heat generation rate in the positive and negative electrodes. Indeed, the heat generation rate was measured using an isothermal calorimeter in both electrodes of five EDLC devices with different electrode compositions but the same electrolyte consisting of 1 M LiPF 6 in EC:DMC. The reversible heat generation rates at the positive and negative electrodes were nearly identical in absence of CMC. However, in devices containing CMC, the reversible heat generation rate in the positive electrode was significantly larger than that in the negative electrode. Such asymmetric heating was attributed to asymmetry in the charging mechanism due to the overscreening effect caused by interactions between the anionic functional groups of CMC and the cations at the negative electrode. Electric double layer capacitors (EDLCs) have received significant attention in recent years for electrical energy storage applications in particular those requiring rapid charging/discharging, such as regenerative braking in electric vehicles, 1 smart grids, 2 and renewable energy harvesting systems.3-5 Indeed, EDLCs can provide higher power density, higher cycle efficiency, and longer lifetime than batteries. 4,6 EDLC devices consist typically of two carbon-based electrodes partitioned by a separator immersed in aqueous or organic electrolytes. EDLCs store electrical energy in the electrical double layer of ions forming at electrode/electrolyte interface.Heat generation in EDLC is a major concern since these devices are usually cycled under high current density resulting in excessive temperature rise.7 This, in turn, can lead to (i) accelerated cell aging, [8][9][10] (ii) increased self-discharge rates, 9,11 and possibly (iii) electrolyte decomposition and evaporation. 9,12 Heat generation in EDLCs can be classified into irreversible and reversible heat generation rates. 7,[13][14][15][16][17] Irreversible heat generation has been attributed, both theoretically and experimentally, to Joule heating. 7,9,11,[13][14][15][16][17][18][19][20] It is constant throughout the EDLC cell and equal to the product of the EDLC internal resistance and the square of the imposed current. 7,[14][15][16] On the other hand, reversible heat generation rate in the entire device was theoretically and experimentally found to be exothermic during charging and endothermic during discharging.7,14-16 The time-averaged reversible heat generation over a charging step was shown to be proportional to the imposed current under galvanostatic cycling.7,14-16 Experimentally, reversible heat generation has been assumed to be identical in both the positive and negative e...

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Polarization-induced distortion of ions in the pores of carbon electrodes for electrochemical capacitors

Cited by 87 publications

References 29 publications

Highly confined ions store charge more efficiently in supercapacitors

Highly confined ions store charge more efficiently in supercapacitors

Solvent-induced porosity control of carbon nanofiber webs for supercapacitor

Effects of Constituent Materials on Heat Generation in Individual EDLC Electrodes

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