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- 저자 : Markovsky, Boris (검색결과 5 건)
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Erickson, Evan M.,Bouzaglo, Hana,Sclar, Hadar,Park, Kang-Joon,Lim, Byung-Beom,Schipper, Florian,Ghanty, Chandan,Grinblat, Judith,Markovsky, Boris,Sun, Yang-Kook,Aurbach, Doron The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.7
<P>In this work, nickel-rich, layered-structure LiNi0.65Co0.08Mn0.27O2 cathode materials were synthesized and compared with materials of the same overall composition, but with a concentration gradient throughout the particles: the Ni concentration is higher at the center of the particles and lower at surface, while the opposite is true for the Mn concentration. The co-precipitation synthesis parameters were optimized, with two different annealing protocols for the final products and the effect of chelating agent concentration during synthesis examined. The gradientmaterials provided superior capacity and rate capability than their respective non-gradient-materials, at normal operating potentials and temperatures, e.g. 30 degrees C up to 4.3 V vs. Li. The reasons for the improved discharge capacity of the gradient materials were explored through impedance spectroscopy and post-mortem characterization. The gradient structure evolution was examined via TEM and electron diffraction measurements of particle cross-sections. Prolonged cycling, even at elevated temperatures, did not change the initial concentration profiles determined by the synthesis. Additionally, long-term cycling experiments of the second-generation material electrodes vs. graphite electrodes in full cells were performed in order to explore the practical advantage of these novel materials. (C) 2016 The Electrochemical Society. All rights reserved.</P>
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Kumar Nayak, Prasant,Grinblat, Judith,Levi, Elena,Penki, Tirupathi Rao,Levi, Mikhael,Sun, Yang-Kook,Markovsky, Boris,Aurbach, Doron American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.5
<P>Li- and Mn-rich transition-metal oxides of layered structure are promising cathodes for Li-ion batteries because of their high capacity values, >= 250 mAh g(-1). These cathodes suffer from capacity fading and discharge voltage decay upon prolonged cycling to potential higher than 4.5 V. Most of these Li and Mn-rich cathodes contain Ni in a 2+ oxidation state. The fine details of the composition of these materials may be critically important in determining their performance. In the present study, we used Li1.2Ni0.13Mn0.54Co0.13O2 as the reference cathode composition in which Mn ions are substituted by Ni ions so that their average oxidation state in Li1.2Ni0.13Mn0.54Co0.13O2 could change from 2+ to 3+. Upon substitution of Mn with Ni, the specific capacity decreases but, in turn, an impressive stability was gained, about 95% capacity retention after 150 cycles, compared to 77% capacity retention for Li1.2Ni0.13Mn0.54Co0.13O2 cathodes when cycled at a C/5 rate. Also, a higher average discharge voltage of 3.7 V is obtained for Li1.2Ni0.13Mn0.54Co0.13O2 cathodes, which decreases to 3.5 V after 150 cycles, while the voltage fading of cathodes comprising the reference material is more pronounced. The Li1.2Ni0.13Mn0.54Co0.13O2 cathodes also demonstrate higher rate capability compared to the reference Li1.2Ni0.13Mn0.54Co0.13O2 cathodes. These results clearly indicate the importance of the fine composition of cathode materials containing the five elements Li, Mn, Ni, Co, and 0. The present study should encourage rigorous optimization efforts related to the fine composition of these cathode materials, before external means such as doping and coating are applied.</P>
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Nayak, Prasant Kumar,Grinblat, Judith,Levi, Mikhael D.,Haik, Ortal,Levi, Elena,Talianker, Michael,Markovsky, Boris,Sun, Yang-Kook,Aurbach, Doron American Chemical Society 2015 Chemistry of materials Vol.27 No.7
<P>Li[Ni<SUB>1/3</SUB>Mn<SUB>2/3</SUB>]O<SUB>2</SUB> was synthesized by a self-combustion reaction (SCR), characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy, and studied as a cathode material for Li-ion batteries at 30 °C and 45 °C. The structural studies by XRD and TEM confirmed monoclinic Li[Li<SUB>1/3</SUB>Mn<SUB>2/3</SUB>]O<SUB>2</SUB> phase as the major component, and rhombohedral (LiNiO<SUB>2</SUB>), spinel (LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB>), and rock salt Li<SUB>0.2</SUB>Mn<SUB>0.2</SUB>Ni<SUB>0.5</SUB>O as minor components. The content of the spinel phase increases upon cycling due to the layered-to-spinel phase transition occurring at high potentials. A high discharge capacity of about 220 mAh g<SUP>–1</SUP> is obtained at low rate (C/10) with good capacity retention upon cycling. However, LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> synthesized by SCR exhibits a discharge capacity of about 190 mAh g<SUP>–1</SUP> in the potential range of 2.4–4.9 V, which decreases to a value of 150 mAh g<SUP>–1</SUP> after 100 cycles. Because of the presence of the spinel component, Li[Ni<SUB>1/3</SUB>Mn<SUB>2/3</SUB>]O<SUB>2</SUB> cathode material exhibits part of its capacity at potentials around 4.7 V. Thus, it can be considered as an interesting high-capacity and high-voltage cathode material for high-energy-density Li-ion batteries. Also, the Li[Ni<SUB>1/3</SUB>Mn<SUB>2/3</SUB>]O<SUB>2</SUB> electrodes exhibit better electrochemical stability than spinel LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> electrodes when cycled at 45 °C.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-7/acs.chemmater.5b00405/production/images/medium/cm-2015-00405w_0020.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b00405'>ACS Electronic Supporting Info</A></P>
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CLASSIFICATION OF QUASIGROUPS BY RANDOM WALK ON TORUS
MARKOVSKI, SMILE,GLIGOROSKI, DANILO,MARKOVSKI, JASEN 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.19 No.1
Quasigroups are algebraic structures closely related to Latin squares which have many different applications. There are several classifications of quasigroups based on their algebraic properties. In this paper we propose another classification based on the properties of strings obtained by specific quasigroup transformations. More precisely, in our research we identified some quasigroup transformations which can be applied to arbitrary strings to produce pseudo random sequences. We performed tests for randomness of the obtained pseudo-random sequences by random walks on torus. The randomness tests provided an empirical classification of quasigroups.
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Classification of Quasigroups by Random Walk on Torus
Smile Markovski,Danilo Gligoroski,Jasen Markovski 한국전산응용수학회 2005 Journal of applied mathematics & informatics Vol.19 No.1-2
Quasigroups are algebraic structures closely related to Latin squares which have many different applications. There are several classificationsof quasigroups based on their algebraic properties. In this paperwe propose another classification based on the properties of strings obtained by specific quasigroup transformations. More precisely, in our research we identified some quasigroup transformations which can be applied to arbitrary strings to produce pseudo random sequences. Weperformed tests for randomnessof the obtained pseudo-random sequencesby randomwalks on torus. The randomness tests provided an empirical classification of quasi-groups.
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