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Choi, Jaecheol,Son, Bongki,Ryou, Myung-Hyun,Kim, Sang Hern,Ko, Jang Myoun,Lee, Yong Min The Korean Electrochemical Society 2013 Journal of electrochemical science and technology Vol.4 No.1
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.
Choi, Jaecheol,Kim, Kyuman,Jeong, Jiseon,Cho, Kuk Young,Ryou, Myung-Hyun,Lee, Yong Min American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.27
<P>A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g<SUP>–1</SUP>), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g<SUP>–1</SUP> and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g<SUP>–1</SUP> after 300 cycles at 1.2 A g<SUP>–1</SUP> and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm<SUP>–2</SUP>, which is a commercially acceptable level, the Si anode could deliver 647 mAh g<SUP>–1</SUP> until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g<SUP>–1</SUP>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-27/acsami.5b03364/production/images/medium/am-2015-03364z_0014.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b03364'>ACS Electronic Supporting Info</A></P>
Measurement and Analysis of Adhesion Property of Lithium-Ion Battery Electrodes with SAICAS
Son, Bongki,Ryou, Myung-Hyun,Choi, Jaecheol,Lee, Taejoo,Yu, Hyung Kyun,Kim, Jong Hun,Lee, Yong Min American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.1
<P>The adhesion strength of lithium-ion battery (LIB) electrodes consisting of active material, a nanosized electric conductor, and a polymeric binder is measured with a new analysis tool, called the Surface and Interfacial Cutting Analysis System (SAICAS). Compared to the conventional peel test with the same electrode, SAICAS gives higher adhesion strength owing to its elaborate cutting-based measurement system. In addition, the effects on the adhesion property of the polymeric binder type and content, electrode density, and measuring point are also investigated to determine whether SAICAS provides reliable results. The findings confirm SAICAS as an effective and promising tool to measure and analyze the adhesion properties of LIB electrodes.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-1/am404580f/production/images/medium/am-2013-04580f_0014.gif'></P>
ID-based Sensor Node Authentication for Multi-Layer Sensor Networks
Sung, Soonhwa,Ryou, Jaecheol The Korea Institute of Information and Commucation 2014 Journal of communications and networks Vol.16 No.4
Despite several years of intense research, the security and cryptography in wireless sensor networks still have a number of ongoing problems. This paper describes how identification (ID)-based node authentication can be used to solve the key agreement problem in a three-layer interaction. The scheme uses a novel security mechanism that considers the characteristics, architecture, and vulnerability of the sensors, and provides an ID-based node authentication that does not require expensive certificates. The scheme describes the routing process using a simple ID suitable for low power and ID exposure, and proposes an ID-based node authentication. This method achieves low-cost communications with an efficient protocol. Results from this study demonstrates that it improves routing performance under different node densities, and reduces the computational cost of key encryption and decryption.
A Trusted Key Management Scheme for Digital Rights Management
정연정,윤기송,Jaecheol Ryou 한국전자통신연구원 2005 ETRI Journal Vol.27 No.1
In this paper, we propose a key management scheme which can provide delivery of the key used to encrypt a digital content from the package server to digital rights management (DRM) clients in a secure manner. The proposed scheme can protect digital content from attacks since an encrypted digital content is sent by a package server and only DRM clients can decrypt the encrypted digital content. It protects the key not only from purchasers but also among the other principals who manage the distribution and license servers.
Effect of cathode/anode area ratio on electrochemical performance of lithium-ion batteries
Son, Bongki,Ryou, Myung-Hyun,Choi, Jaecheol,Kim, Sang-Hern,Ko, Jang Myoun,Lee, Yong Min Elsevier 2013 Journal of Power Sources Vol.243 No.-
<P><B>Abstract</B></P> <P>The effects of cathode/anode area ratio on the electrochemical performance of lithium-ion batteries are investigated using 2032-type coin full cells. As the anode area is increased from 1.13 (ø12 mm) to 2.54 cm<SUP>2</SUP> (ø18 mm) while maintaining the cathode area as 1.13 cm<SUP>2</SUP> (ø12 mm), both coulombic efficiency and discharge capacity at the first formation step become increasingly worse, probably owing to greater formation of solid electrolyte interphase (SEI). Moreover, rate capability also declined with increased anode area, whereas discharge capacity retention behavior during 1C/1C charge/discharge cycling appeared similar except for a slightly decreased capacity of coin cells with larger anode areas. The findings indicate that cathode/anode area ratio should be carefully evaluated to achieve reliable data on electrochemical performance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Relatively larger anode causes low initial coulombic efficiency and discharge capacity. </LI> <LI> Rate capability and cycle life are also dependent on cathode/anode area ratio. </LI> <LI> Slightly larger anode area is recommended for better electrochemical properties. </LI> </UL> </P>
Method to Analyze Information Leakage Malware using SSL Communication in Android Platform
( Gilsu Cho ),( Sangwho Kim ),( Jaecheol Ryou ) 한국인터넷정보학회 2018 인터넷정보학회논문지 Vol.19 No.3
Widely used around the world, smartphones contain many features and can store content such as contacts, photos, and videos. Information that can be leaked in proportion to the information that the smartphone can store has also been increased. In recent years, accidents such as personal information leakage have occurred frequently. Personal information leakage is happening in the Android environment, which accounts for more than half of the smartphone operating system market share. Analyzing malicious apps that leak information can tell you how to prevent information leakage. Malicious apps that leak information will send importantinformation to the hacker's (C & C) server, which will use network communication. Malicious apps that are emerging nowadays encrypt and transmit important information through SSL communication. In this case, it is difficult to knowwhat kind of information is exposed to network. Therefore, we suggest a method to analyze malicious apps when leak important information through SSL communication. In this paper, we identify the way malicious apps leak information. And we propose a method for analyzing information leaked by SSL communication. Data before encryption was confirmed in the device through SSL hooking and SSL Strip method.