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5. Using chronoamperometry to rapidly measure and quantitatively analyse rate-performance in battery electrodes

Author

Tian, Ruiyuan, King, Paul J., Coelho, Joao, Park, Sang-Hoon, Horvath, Dominik V, Nicolosi, Valeria, ODwyer, Colm, and Coleman, Jonathan N

Subjects
Physics - Chemical Physics
Abstract

For battery electrodes, measured capacity decays as charge/discharge current is increased. Such rate-performance is important from a practical perspective and is usually characterised via galvanostatic charge-discharge measurements. However, such measurements are very slow, limiting the number of rate experiments which are practical in a given project. This is a particular problem during mechanistic studies where many rate measurements are needed. Here, building on work by Heubner at al., we demonstrate chronoamperometry (CA) as a relatively fast method for measuring capacity-rate curves with hundreds of data points down to C-rates below 0.01C. While Heubner et al. reported equations to convert current transients to capacity vs. C-rate curves, we modify these equations to give capacity as a function of charge/discharge rate, R. We show that such expressions can be combined with a basic model to obtain simple equations which can fit data for both capacity vs. C-rate and capacity vs. R. We demonstrate that these equations can accurately fit experimental data within normal experimental ranges of rate. However, we also observe that, at high rates, the curves obtained from CA deviate from the normal behaviour showing a new, previously unobserved, decay feature. We associate this feature with the very early part of the current transient where electronic motion dominates the current. Using a simple model, we show that the dependence of the high-rate time constant on electrode thickness can be linked to electrode conductivity.

Published
2019

8. Quantifying the factors limiting rate-performance in battery electrodes

Author

Tian, Ruiyuan, Park, Sang-Hoon, King, Paul J., Cunningham, Graeme, Coelho, Joao, Nicolosi, Valeria, and Coleman, Jonathan N

Subjects
Condensed Matter - Materials Science
Abstract

A significant problem associated with batteries is the rapid reduction of charge-storage capacity with increasing charge/discharge rate. For example, improving this rate-performance is required for fast-charging of car batteries. Rate-performance is related to the timescales associated with charge or ionic motion in both electrode and electrolyte. However, no quantitative model exists which can be used to fit experimental data to give insights into the dominant rate-limiting processes in a given electrode-electrolyte system. Here we develop an equation which can be used to fit capacity versus rate data, outputting three parameters which fully describe rate-performance. Most important is the characteristic time associated with charge/discharge which can be expressed by a simple equation with terms describing each rate-limiting process, thus linking rate-performance to measurable physical parameters. We have fitted these equations to ~200 data sets from ~50 papers, finding exceptional agreement, and allowing parameters such as diffusion coefficients or electrolyte conductivities to be extracted. By estimating relevant physical parameters, it is possible to show which rate-limiting processes are dominant in a given situation, facilitating rational design and cell optimization. In addition, this model predicts the upper speed limit for Li/Na ion batteries, in agreement with the fastest electrodes in the literature.

Published
2018
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9. Dynamics of liquid crystal on hexagonal lattice

Author

Shehzad, Muhammad Arslan, Lee, Junsu, Park, Sang Hoon, Akhtar, Imtisal, Khan, Muhammad Farooq, Hussain, Sajjad, Eom, Jonghwa, Jung, Jongwan, Kim, Gunn, Hwang, Chanyong, and Seo, Yongho

Subjects
Condensed Matter - Soft Condensed Matter, Physics - Optics
Abstract

Nematic liquid crystal (LC) molecules adsorbed on two dimensional materials are aligned along the crystal directions of the hexagonal lattice. It was demonstrated that short electric pulses can reorient the aligned LC molecules in the preferred armchair direction of hexagonal boron nitride (h-BN). Several states with a variety of colors were obtained by changing the direction and strength of the electric pulses. The ab initio calculations based on density functional theory was carried out to determine the favorable adsorption configurations of the LC molecules on the h-BN surface. A non-volatile display, in which pixel resolution can be determined by grains of hexagonal surface, is proposed, which can offer a pathway towards dynamic high-quality pixels with low power consumption, and could define a new paradigm for all non-volatile display applications.

Published
2018
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11. Foldable three dimensional neural electrode arrays for simultaneous brain interfacing of cortical surface and intracortical multilayers

Author

Lee, Ju Young, Park, Sang Hoon, Kim, Yujin, Cho, Young Uk, Park, Jaejin, Hong, Jung-Hoon, Kim, Kyubeen, Shin, Jongwoon, Ju, Jeong Eun, Min, In Sik, Sang, Mingyu, Shin, Hyogeun, Jeong, Ui-Jin, Gao, Yuyan, Li, Bowen, Zhumbayeva, Aizhan, Kim, Kyung Yeun, Hong, Eun-Bin, Nam, Min-Ho, Jeon, Hojeong, Jung, Youngmee, Cheng, Huanyu, Cho, Il-Joo, and Yu, Ki Jun

Published
2022
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17. Development of an evaluation indicator for highway climate change adaptation projects based on analytical hierarchy process in South Korea.

Author

Song, Moon‐Soo, Yum, Sang‐Guk, Yun, Hong‐Sic, Park, Sang‐Hoon, Bae, Sang‐Won, and Lee, Jae‐Joon

Subjects
CLIMATE change adaptation, ANALYTIC hierarchy process, CLIMATE change, COST control, WEIGHING instruments, JOB creation, CLIMATE change & health
Abstract

Owing to climate change, abnormal climate phenomena occur frequently, damaging aging highway facilities. Therefore, it is necessary to develop adaptation projects for highway systems. Adaptation projects focus on mitigating the impact of climate change on highway facilities and enabling safe use. The present study aims to develop quantified evaluation indicators that are necessary for planning and selecting appropriate climate change adaptation projects. By analysing previous studies, the most important factors to be considered in the evaluation process of climate change adaptation projects were defined, and 20 preliminary evaluation indicators were divided into three layers. A feasibility study for each class was performed on the preliminary evaluation indicators by an expert panel; 16 evaluation indicators were selected through a feasibility study, and the weight of each indicator was calculated using the analytical hierarchy process (AHP) method. The priority of the evaluation indicators was service improvement through adaptation projects (weight 8.76), cost reduction and job creation (weight 8.46), and climate change impact reduction and vulnerability reduction (weight 8.31). These quantified evaluation indicators can help organizations that manage highways respond to climate change and establish adaptation projects. [ABSTRACT FROM AUTHOR]

Published
2024
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18. Influence of Unit Water Content Control on Concrete Performance in the Ready-Mixed Concrete Production Process.

Author

Park, Sang-Hoon, Ryu, Hwa-Sung, and Park, Won-Jun

Subjects
*MANUFACTURING processes, *CONCRETE, *CONCRETE mixing, *COMPRESSIVE strength, *CHLORIDE ions
Abstract

This study examined the effects of increasing concrete unit water content and artificially controlling water content on concrete performance in the production process of ready-mixed concrete. Results showed that changes in the unit water content of 20 concrete mix proportions without air-entraining significantly reduced concrete compressive strength, increased porosity, and in-creased occurrence of bleeding. A unit water content increase of 25 kg/m3 or more may reduce the compressive strength of concrete below the design standard and significantly affect the occurrence of bleeding water. Moreover, an extra unit water content of at least 25 kg/m3 could significantly affect the diffusion of chloride ions in the concrete. The carbonation depth of concrete was extremely high with the increase in unit water content and water addition. In the production of concrete requiring at least normal strength or durability, the extra water change to total unit water content should be maintained at 15 kg/m3 or less. And a water–cement ratio of 48% or less and a unit water content of 155 kg/m3 or less are considered effective for management of concrete quality. Considering the aggregate type, absorption rate, and moisture state, the management of unit water content error in concrete production processes requires greater. [ABSTRACT FROM AUTHOR]

Published
2024
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23. Facile Preparation of Petroleum Pitch-Based Activated Carbon with Open Macropore Walls for High Energy Density Supercapacitors.

Author

Jang, Suhyeon, Lee, Woo Cheol, Park, Sang-Hoon, Lim, Chang-Hun, Park, JaeHyun, Kang, Jin-kyun, Han, Yujin, Song, Byung Jin, and Kim, Hyun-Kyung

Subjects
ENERGY density, ACTIVATED carbon, CAPACITORS, SUPERCAPACITORS, ENERGY storage, SUPERCAPACITOR electrodes
Abstract

Electric double-layer capacitors have attracted considerable attention for energy storage because of their excellent power capability, high stability, and long cycle life. Activated carbon is the most widely employed electrode material for electric double-layer capacitors owing to its high specific surface area, hierarchical porous structure, and high electrical conductivity. However, to increase the energy density of the devices, new synthetic methods for enhancing their specific capacitances are required. We developed a facile preparation method for petroleum pitch-based activated carbon and investigated the optimal conditions to improve its electrochemical performance in terms of rate capability, specific capacitance, and cycle life. The obtained activated carbon exhibited a high specific capacitance (163.67 F/g at 0.1 A/g), which can be attributed to the efficient charge transport due to the micropores developed in the open macroporous walls of the carbon structure and the high electrical conductivity. Our approach provides an efficient strategy for synthesizing activated carbon with excellent properties. The results reveal a correlation between the physicochemical and electrochemical properties of activated carbon. [ABSTRACT FROM AUTHOR]

Published
2023
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42. Nonproliferation of Nuclear Weapons and the Nuclear Program of the DPRK

Author

Park Sang Hoon

Subjects
Договор о нераспространении ядерного оружия (ДНЯО), МАГАТЭ, Северная Корея, ядерная программа, ядерная проблема, Шестисторонние переговоры, International relations, JZ2-6530, Political science (General), JA1-92
Abstract

The article analyzes the contemporary aspects of the nuclear weapon nonproliferation issue as exemplified by the international approaches to the DPRK nuclear weapons program, as well as the international community efforts to resolve it, in particular via the Six-Party Talks.

Published
2012

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