• Journal of Electrochemical Science and Technology
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• v.10 no.2
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• pp.196-205
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• 2019

Ni-rich layered oxides $Li(Ni_xCo_yMn_z)O_2$ (x + y + z = 1) have been extensively studied in recent times owing to their high capacity and low cost and can possibly replace $LiCoO_2$ in the near future. However, these layered oxides suffer from problems related to the capacity fading, thermal stability, and safety at high voltages. In this study, we use surface coating as a strategy to improve the thermal stability at higher voltages. The uniform and conformal $Al_2O_3$ coating on prefabricated electrodes using atomic layer deposition significantly prevented surface degradation over prolonged cycling. Initial capacity of 190, 199, 188 and $166mAh\;g^{-1}$ is obtained for pristine, 2, 5 and 10 cycles of ALD coated samples at 0.2C and maintains 145, 158, 151 and $130mAh\;g^{-1}$ for high current rate of 2C in room temperature. The two-cycle $Al_2O_3$ modified cathode retained 75% of its capacity after 500 cycles at 5C with 0.05% capacity decay per cycle, compared with 46.5% retention for a pristine electrode, at an elevated temperature. Despite the insulating nature of the $Al_2O_3$ coating, a thin layer is sufficient to improve the capacity retention at a high temperature. The $Al_2O_3$ coating can prevent the detrimental surface reactions at a high temperature. Thus, the morphology of the active material is well-maintained even after extensive cycling, whereas the bare electrode undergoes severe degradation.

• Journal of the Korean Electrochemical Society
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• v.22 no.2
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• pp.60-68
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• 2019

High-voltage operation of the lithium ion battery is one of the advantageous approaches to obtain high energy capacity without changing the conventional cell components and structure. However, operating at harsh condition inevitably results in severe side reactions at the electrode surface and structural disintegration of active material particles. Herein we coated layers composed of $Al_2O_3$ and ZnO on the electrode based on NCM using atomic layer deposition (ALD). Thicker layers of novel Al-doped ZnO (AZO) coating compared to conventional ALD coated layers are prepared. Cathode based on NCM with the varying AZO coating thickness are fabricated and used for coin cell assembly. Effect of ALD coating thickness on the charge-discharge cycle behavior obtained at high-voltage operation was investigated.

• Journal of Convergence for Information Technology
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• v.11 no.2
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• pp.117-123
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• 2021

The effects of electrolyte concentration on the electrochemical properties of Fe4[Fe(CN6)]3(FeHCF) as a novel active material for the electrode of aqueous zinc-ion batteries was investigated. The electrochemical reactions and structural stability of the FeHCF electrode were significantly affected by the electrolyte concentration. In the electrolyte solutions of 1.0-7.0 mol dm-3, the charge-discharge capacities increased with increasing electrolyte concentration, however gradually decreased as the cycle progressed. On the other hand, in the 9.0 mol dm-3 electrolyte solution, the initial capacity was relatively small, however showed good cyclability. Additionally, the FeHCF electrode after five cycles in the former electrolyte solutions, had a change in crystal structure, whereas there was no change in the latter electrolyte solution. This suggests that the performance of the FeHCF electrode is greatly influenced by the hydration structure of zinc ions present in electrolyte solutions.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.407-415
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• 2022

Surface coating of cathodes is an essential process for all-solid-state batteries (ASSBs) based on sulfide electrolytes as it efficiently suppresses interfacial reactions between oxide cathodes and sulfide electrolytes. Based on computational calculations, Li₃PO₄ has been suggested as a promising coating material because of its higher stability with sulfides and its optimal ionic conductivity. However, it has hardly been applied to the coating of ASSBs due to the absence of a suitable coating process, including the selection of source material that is compatible with ASSBs. In this study, polyphosphoric acid (PPA) and (NH₄)₂HPO₄ were used as source materials for preparing a Li₃PO₄ coating for ASSBs, and the properties of the coating layer and coated cathodes were compared. The Li₃PO₄ layer fabricated using the (NH₄)₂HPO₄ source was rough and inhomogeneous, which is not suitable for the protection of the cathodes. Moreover, the water-based coating solution with the (NH₄)₂HPO₄ source can deteriorate the electrochemical performance of high-Ni cathodes that are vulnerable to water. In contrast, when an alcohol-based solvent was used, the PPA source enabled the formation of a thin and homogeneous coating layer on the cathode surface. As a consequence, the ASSBs containing the Li₃PO₄-coated cathode prepared by the PPA source exhibited significantly enhanced discharge and rate capabilities compared to ASSBs containing a pristine cathode or Li₃PO₄-coated cathode prepared by the (NH₄)₂HPO₄ source.

• Journal of Electrochemical Science and Technology
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• v.13 no.1
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• pp.128-137
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• 2022

For this study, the sol gel method was used to synthesize the spinel LiNi_0.5Mn_1.5O₄ (LNMO) electrode material. Structural, morphological, electrochemical, and kinetic aspects of the LNMO have been characterized. The synthesized LNMO was indexed with the Fd3m cubic space group. The excellent capacity retention indicates that the spinel framework of LNMO has the ability to withstand high rate charge-discharge throughout long cycle tests. The Li diffusion coefficient (D_Li) changes non-monotonically across three orders of magnitude, from 10^-9 to 10^-12 cm² s^-1 determined from GITT method. The variation of D_Li seemed to be related to three oxidation reactions that happened throughout the charging process. A small dip in D_Li at the beginning stage of Li deintercalation is correlated with the oxidation of Mn³⁺ to Mn⁴⁺. While two pronounced D_Li minima at 4.7 V and 4.75 V are due to the oxidation of Ni²⁺/Ni³⁺ and Ni³⁺/Ni⁴⁺ respectively. The depletion of D_Li at the high voltage region is attributed to the occurrence of two successive phase transformation phenomena.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.4
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• pp.201-209
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• 2016

Theoretical maximum methane yield of glucose at STP (1 atm, $0^{\circ}C$) is 0.35 L $CH_4/g$ COD. However, most researched actual methane yields of anaerobic digester (AD) on lab scale is lower than theoretical ones. A wide range of them have been reported according to experiments methods and types of organic matters. Recent year, a MET (Microbial electrochemical technology) is a promising technology for producing sustainable bio energies from AD via rapid degradation of high concentration organic wastes, VFAs (Volatile Fatty Acids), toxic materials and non-degradable organic matters with electrochemical reactions. In this study, methane yields of food waste leachate and sewage waste sludge were evaluated by using BMP (Biochemical Methane Potential) and continuous AD tests. As the results, methane production volume from the anaerobic digester equipped with MET (AD + MET) was higher than conventional AD in the ratio of 2 to 3 times. The actual methane yields from all experiments were lower than those of theoretical value of glucose. The methane yield, however, from the AD + MET occurred similar to the theoretical one. Moreover, biogas compositions of AD and AD + MET were similar. Consequently, methane production from anaerobic digester with MET increased from the result of higher organic removal efficiency, while, further researches should be required for investigating methane production mechanisms in the anaerobic digester with MET.

• Journal of the Korean Electrochemical Society
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• v.23 no.3
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• pp.66-72
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• 2020

In this study, the development of biosensors capable of bi-enzyme reactions by including Horseradish peroxidase and glucose oxidase was carried out for detection of glucose. The sensors were manufactured using electro deposition method to reduce production time, and screen printed electrodes (SPE) were used to produce economical sensors. To check the bienzyme effect, the sensor was compared and analyzed with single enzyme biosensor. The characteristics of the sensor were evaluated using scanning electron microscopy(SEM), cyclic voltammetry(CV), electrochemical impedance spectroscopy(EIS), chronoamperometry(CA), and flow injection analysis(FIA). Analysis results from SEM, CV and EIS confirmed that the enzymes are well fixed to the electrode surface. In addition, it was confirmed that bi-enzyme biosensors manufactured from the CA method improved signal performance by 200% compared to single enzyme biosensors. From this results, we were able to explain that HRP and GOD react catalyzed to each other. And the results of FIA showed that the intensity of each current signal was constant when the same concentration of glucose was injected four times. In addition, by analyzing the intensity of current signals for glucose concentrations, the biosensors manufactured in this study showed excellent trends in signal sensitivity, reproducibility and stability.

• Journal of Convergence for Information Technology
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• v.12 no.2
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• pp.134-141
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• 2022

To improve the performance of aluminum-air batteries, it is very important to understand the effect of electrolytes on the electrochemical properties of electrodes. In this study, the effects of electrolyte cations on the electrochemical redox reactions proceeding at the negative and positive electrodes were investigated using electrolytes having the same anion but different cations such as NaCl, LiCl, CaCl₂, and ZnCl₂. It was confirmed by discharge test, scanning electron microscopy and X-ray diffraction analysis that electrolyte cations affect the discharge potential and specific capacity of the electrode. Precipitates were formed on the surface of the positive electrode by Ca²⁺ and Zn²⁺ ions, resulting in degradation of the performance of the positive electrode. In addition, Ca²⁺ ions passivated the negative electrode and accelerated the performance degradation. This suggests that the positive ions of the electrolyte have different effects on the electrochemical performance of the positive and negative electrodes.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.167.1-167.1
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• 2016

The interaction between adsorbed water and hydrogen on metallic surfaces is important for fundamental understanding of heterogeneous catalysis and electrode surface reactions in acidic environment. Here, we explore a long-standing question of whether hydronium ion can exist or not on a Pt surface coadsorbed with atomic hydrogen and water. Studies based on mass spectrometry and infrared spectroscopy show clear evidence that hydrogen atoms are converted into hydrated protons on a Pt(111) surface. The preferential structures of hydrated protons are identified as multiply hydrated $H_5O_2{^+}$ and $H_7O_3{^+}$ species rather than as hydronium ions. The multiply hydrated protons may be regarded as two dimensional zundel ($H_5O_2{^+}$) and Eigen cation ($H_7O_3{^+}$) in water-metal interface. These surface-bound hydrated protons may be key surface intermediates of the electrochemical interconversion between adsorbed hydrogen atoms and solvated protons.

• Bulletin of the Korean Chemical Society
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• v.28 no.10
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• pp.1683-1688
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• 2007

This paper presents a novel simple method for introducing gold nanoparticles in a poly(4-vinylpyridine) (PVP) polymer layer over a glassy carbon (GC) electrode with the aim of forming a tunable electrochemical interface against a cationic ruthenium complex. Initially, AuCl4 ? ions were spontaneously incorporated into a polymer layer containing positively charged pyridine rings in an acidic media by ion exchange. A negative potential was then applied to electrochemically reduce the incorporated AuCl4 ? ions to gold nanoparticles, which was confirmed by the FE-SEM images. The PVP layer with an appropriate thickness over the electrode blocked electron transfer between the electrode and the solution phase for the redox reactions of the cationic Ru(NH3)6 2+ ions. However, the introduction of gold nanoparticles into the polymer layer recovered the electron transfer. In addition, the electron transfer rate between the two phases could be tuned by controlling the number density of gold nanoparticles.