• Journal of Electrochemical Science and Technology
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• v.4 no.1
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• pp.27-33
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• 2013

The consequences of electrode density and thickness for electrochemical performance of lithium-ion cells are investigated using 2032-type coin half cells. While the cathode composition is maintained by 90:5:5 (wt.%) with $LiCoO_2$ active material, Super-P electric conductor and polyvinylidene fluoride polymeric binder, its density and thickness are independently controlled to 20, 35, 50 um and 1.5, 2.0, 2.5, 3.0, 3.5 g $cm^{-3}$, respectively, which are based on commercial lithium-ion battery cathode system. As the cathode thickness is increased in all densities, the rate capability and cycle life of lithium-ion cells become significantly worse. On the other hand, even though the cathode density shows similar behavior, its effect is not as high as the thickness in our experimental range. This trend is also investigated by cross-sectional morphology, porosity and electric conductivity of cathodes with different densities and thicknesses. This work suggests that the electrode density and thickness should be chosen properly and mentioned in detail in any kinds of research works.

• Journal of Electrochemical Science and Technology
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• v.9 no.1
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• pp.9-19
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• 2018

The anodic behavior of aluminum (Al) foils with varying purity, capacitance, and withstand voltage in organic electrolytes was examined for EDLC. The results of cyclic voltammetry (CV) and chronoamperometry (CA) experiments showed that the electrochemical stability improves when Al foil has higher purity, lower capacitance, and higher withstand voltage. To improve the electrochemical stability of EDLC current collectors made of low-purity foil (99.4% Al foil), the foil was modified by chemical etching to reduce its capacitance to $60{\mu}F/cm^2$ and forming to have withstand a voltage of 3 Vf. EDLC cells using the modified Al foil as a current collector were made to 2.7 V with 360 F, and a constant voltage load test was subsequently performed for 2500 hours at high temperature under a rated voltage of 2.7 V. The reliability and stability of the EDLC cell improved when the modified Al foil was used as a current collector. To understand the deterioration process of the Al current collector, standard cells made of conventional Al foil under a constant voltage load test were disassembled, and the surface changes of the foil were measured every 500 hours. The Al foil became increasingly corroded, causing the adhesion between the AC coating layer and the Al foil to weaken, and it was confirmed that partial AC coating layer peeling occurred.

• Journal of Electrochemical Science and Technology
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• v.9 no.4
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• pp.330-338
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• 2018

The adhesion strength as well as the electrochemical properties of $LiNi_{0.4}Mn_{0.4}Co_{0.2}O_2$ electrodes containing various conductive carbons (CC) such as fiber-like carbon, vapor-grown carbon fiber, carbon nanotubes, particle-like carbon, Super P, and Ketjen black is compared. The morphological properties is investigated using scanning electron microscope to reveal the interaction between the different CC and the active material. The surface and interfacial cutting analysis system is also used to measure the adhesion strength between the aluminum current collector and the composite film, and the adhesion strength between the active material and the CC of the electrodes. The results obtained from the measured adhesion strength points to the fact that the structure and the particle size of CC additives have tremendous influence on the binding property of the composite electrodes, and this in turn affects the electrochemical property of the configured electrodes.

• Journal of Electrochemical Science and Technology
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• v.12 no.1
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• pp.1-20
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• 2021

In-depth knowledge of electrode processes is crucial for determining the electrochemical performance of lithium-ion batteries (LIBs). In particular, the conduction mechanisms of charged species in the electrodes, such as lithium ions (Li+) and electrons, are directly correlated with the performance of the battery because the overall reaction is dependent on the charge transport behavior in the electrodes. Therefore, it is necessary to understand the different electrochemical processes occurring in electrodes in order to elucidate the charge conduction phenomenon. Thus, it is essential to conduct fundamental studies on electrochemical processes to resolve the technical challenges and issues arising during the ionic and electronic conduction. Furthermore, it is also necessary to understand the transport of charged species as well as the predominant factors affecting their transport in electrodes. Based on such in-depth studies, potential approaches can be introduced to enhance the mobility of charged entities, thereby achieving superior battery performances. A clear understanding of the conduction mechanism inside electrodes can help overcome challenges associated with the rapid movement of charged species and provide a practical guideline for the development of advanced materials suitable for high-performance LIBs.

• Journal of Electrochemical Science and Technology
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• v.12 no.2
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• pp.188-203
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• 2021

The specific benefits of the modified films formed on preliminary anodized aluminum, including the versatility of their potential applications impose the need for evaluation of the exploitation reliability of these films. In this aspect, the durability of Cu and Ni modified anodized aluminum oxide (AAO) films on the low-doped AA1050 alloy was assessed through extended exposure to a 3.5% NaCl model corrosive medium. The electrochemical measurements by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) after 24 and 720 hours of exposure have revealed that the obtained films do not change their obvious barrier properties. In addition, supplemental analyses of the coatings were performed, in order to elucidate the impact of the AC-deposition of Cu and Ni inside the pores. The scanning electron microscopy (SEM) images have shown that the surface topology is not affected and resembles the typical surface of an etched metal. The subsequent energy dispersive X-ray spectroscopy (EDX) tests have revealed a predominance of Cu in the combined AAO-Cu/Ni layers, whereas additional X-ray photoelectron (XPS) analyses showed that both metals form oxides with different oxidation states due to alterations in the deposition conditions, promoted by the application of AC-polarization of the samples.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.415-423
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• 2021

For a battery module where single cells are connected in series, the single cells should each have a similar state of charge (SOC) to prevent them from being exposed to an overcharge or over-discharge during charge-discharge cycling. To detect the existence of unbalanced SOC cells in a battery module, we propose a simple measurement method using a single-frequency response of electrochemical impedance spectroscopy (EIS). For a commercially available graphite/nickel-cobalt-aluminum-oxide lithium-ion cell, the cell impedance increases significantly below SOC20%, while the impedance in the medium SOC region (SOC20%-SOC80%) remains low with only minor changes. This impedance behavior is mostly due to the elementary processes of cathode reactions in the cell. Among the impedance values (Z, Z', Z"), the imaginary component of Z" regarding cathode reactions changes heavily as a function of SOC, in particular, when the EIS measurement is performed around 0.1 Hz. Thanks to the significant difference in the time constant of cathode reactions between ≤SOC10% and ≥SOC20%, a single-frequency EIS measurement enlarges the difference in impedance between balanced and unbalanced cells in the module and facilitates an ~80% improvement in the detection signal compared to results with conventional EIS measurements.

• Journal of Electrochemical Science and Technology
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• v.12 no.4
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• pp.424-430
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• 2021

The element iron (Fe) is affordable and abundantly available, and thus, it finds use in a wide range of applications. As regards its application in rechargeable lithium-ion batteries (LIBs), the electrochemical reactions of Fe must be clearly understood during battery charging and discharging with the LIB electrolyte. In this study, we conducted systematic electrochemical analyses under various voltage conditions to determine the voltage at which Fe corrosion begins in general lithium salts and organic solvents used in LIBs. During cyclic voltammetry (CV) experiments, we observed a large corrosion current above 4.0 V (vs. Li/Li⁺). When a constant voltage of 3.7 V (vs. Li/Li⁺), was applied, the current did not increase significantly at the beginning, similar to the CV scenario; on the other hand, at a voltage of 3.8 V (vs. Li/Li⁺), the current increased rapidly. The impact of this difference was visually confirmed via scanning electron microscopy and optical microscopy. Our X-ray photoelectron spectroscopy measurements showed that at 3.7 V, a thick organic solid electrolyte interphase (SEI) was formed atop a thin fluoride SEI, which means that at ≥3.8 V, the SEI cannot prevent Fe corrosion. This result confirms that Fe corrosion begins at 3.7 V, beyond which Fe is easily corrodible.

• Journal of the Korean Chemical Society
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• v.67 no.5
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• pp.339-347
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• 2023

In this study, a nanocomposite of multi-walled carbon nanotubes@poly(p-phenylenediamine)-Prussian blue (MWCNTs@PpPD-PB) was synthesized and employed for the electrochemical detection of hydrogen peroxide (H₂O₂). A straightforward approach was utilized to prepare an electrochemical H₂O₂ sensor using a MWCNTs@PpPD-PB modified glassy carbon electrode, and its electrochemical behavior was investigated through techniques such as electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The modified electrode displayed a favorable electrocatalytic response towards the reduction of H₂O₂ in an acidic solution. The developed sensor exhibited linearity in the concentration range of 0.005 mM to 2.225 mM for H₂O₂, with high sensitivity (583.6 ㎂ mM^-1cm^-2) and a low detection limit (0.95 ㎛, S/N = 3) at an applied potential of +0.15 V (vs. Ag/AgCl). Additionally, the sensor demonstrated excellent selectivity, reproducibility, and stability. Moreover, successful detection of H₂O₂ was achieved in real samples.

• Journal of Electrochemical Science and Technology
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• v.6 no.3
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• pp.88-94
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• 2015

In this study we investigated the electrocatalytic oxidation of saccharose on conductive polymer- Nickel oxide modified graphite electrodes based on the ability of anionic surfactants to form micelles in aqueous media. This NiO modified electrode showed higher electrocatalytic activity than Ni rode electrode in electrocatalytic oxidation of saccharose. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of saccharose was found in agreement with the values obtained from CV measurements.

• Korean Journal of Materials Research
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• v.12 no.2
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• pp.103-111
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• 2002

The thermally insulated underground pipelines have been used for district heating system. The sensor wire embedded in the insulation was used for monitoring the insulating resistance between the sensor wire and the pipe. The resistance measurement system detects corrosion of steel pipe under insulation. The corrosion and stress corrosion cracking(SCC) characteristics of sensor wire in synthetic ground water were investigated using the electrochemical methods and constant load SCC tests. The polarization tests were used to study the electrochemical behavior of sensor wire. The sensor wire was passivated at temperatures ranging from 25 to $95^{\circ}C$. However, the applied sensing current larger than passive current resulted in breakdown of passive film. The constant load SCC tests were performed to investigate the effects of applied current and load on the fracture behavior. Stress-corrosion cracks initiated at pits that were produced by sensing current. The growth of the pit involves a tunnelling mechanism, which leads to ductile fracture.