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Sun, Yang‐,Kook,Lee, Min‐,Joon,Yoon, Chong S.,Hassoun, Jusef,Amine, Khalil,Scrosati, Bruno WILEY‐VCH Verlag 2012 Advanced Materials Vol.24 No.9
<P>Y.‐K. Sun, C. S. Yoon, B. Scrosati and co‐workers report on page 1192 the role of an AlF3‐coating layer on Li‐enriched cathode materials, which not only improves electrochemical performances but also thermal stability. These improvements are attributed to the trans‐formation of the initial layer (Li<SUB>2</SUB>MnO<SUB>3</SUB>) to a spinel phase, induced by the Li chemical‐leaching effect of the AlF3 coating layer. The spinel phase transferred from the layer on the Li‐enriched electrodes is able to negate the previous shortcomings of these designs. </P>
Yoon, Sung-Jun,Park, Kang-Joon,Lim, Byung-Beom,Yoon, Chong S.,Sun, Yang-Kook The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.2
<P>Full concentration gradient (FCG) cathode material having nickel-rich core Li[Ni0.89Co0.01Mn0.10]O-2 and nickel-deficient outer layer Li[Ni0.61Co0.09Mn0.30]O-2 was synthesized via co-precipitation method. A smoothly varying concentration gradients for Ni, Co, and Mn extended from the core to the surface within a single cathode particle with an average composition of Li[Ni0.65Co0.08Mn0.27]O-2. Electrochemical and thermal properties of the FCG cathode were evaluated and compared to the conventional cathode (CC) material, Li[Ni0.65Co0.08Mn0.27]O-2 without the concentration gradient. The BET surface area measurement demonstrated the presence of densely agglomerated primary particles in the FCG cathode. Owing to the unique spatial distribution of the cations and particle morphology, the FCG cathode delivered higher discharge capacity, superior cycle stability and excellent thermal stability compared to the CC Li[Ni0.65Co0.08Mn0.27]O-2. (C) The Author(s) 2014. Published by ECS.</P>
Yoon, Chong S.,Ryu, Hoon-Hee,Park, Geon-Tae,Kim, Jae-Hyung,Kim, Kwang-Ho,Sun, Yang-Kook The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.9
<P>The electrochemical properties of Li[Ni0.95Co0.025Mn0.025]O2, the composition of which is similar to that of LiNiO2, were evaluated to test whether the beneficial effect of Co and Mn addition persists at this extremely Ni-rich layered Li[NixCoyMn1−x−y]O2(NCM) cathode. Despite their low concentrations, the presence of Co and Mn ions notably improved the cycling and thermal stability of Li[Ni0.95Co0.025Mn0.025]O2over that of LiNiO2(initial discharge capacity of 238 mA h g<SUP>−1</SUP>with 85% retention after 100 cycles when cycled at 4.3 V for Li[Ni0.95Co0.025Mn0.025]O2<I>vs.</I>248 mA h g<SUP>−1</SUP>but with 74% retention for LiNiO2). It was also shown that the capacity degradation of highly Ni-enriched NCM cathodes appears to arise from the anisotropic volume change during Li removal/insertion, which was aggravated by the formation of the H3 phase in the delithiated state. The particle core was especially susceptible to structural damage from the accumulation of the intrinsic internal strain, which led to the initiation and propagation of microcracks from the particle core. The microcracks subsequently exposed the particle core to electrolyte damage for a prolonged period in the delithiated state, leading to eventual disintegration of the secondary particles. It appears that protecting the particle core (or interparticle boundaries) may help in extending the cycling stability of Ni-rich NCM cathodes, especially for those with very high Ni compositions.</P>
Yoon, Chong S.,Park, Kang-Joon,Kim, Un-Hyuck,Kang, Ki H.,Ryu, Hoon-Hee,Sun, Yang-Kook American Chemical Society 2017 Chemistry of materials Vol.29 No.24
<P>Electrochemical properties and structural and thermal stability of Li[Ni<SUB>0.65</SUB>Co<SUB>0.13</SUB>Mn<SUB>0.22</SUB>]O<SUB>2</SUB> (FCG65), Li[Ni<SUB>0.75</SUB>Co<SUB>0.08</SUB>Mn<SUB>0.17</SUB>]O<SUB>2</SUB> (TSFCG75), and Li[Ni<SUB>0.85</SUB>Co<SUB>0.05</SUB>Mn<SUB>0.10</SUB>]O<SUB>2</SUB> (TSFCG85) with concentration gradients of Ni and Mn were evaluated to comprehensively demonstrate the effectiveness of compositional gradation for a wide range of Ni-rich Li[Ni<SUB><I>x</I></SUB>Co<SUB><I>y</I></SUB>Mn<SUB>1–<I>x</I>–<I>y</I></SUB>]O<SUB>2</SUB> (NCM) cathodes. The discharge capacities of FCG65, TSFCG75, and TSFCG85 were 194.2, 206.8, and 222.2 mAh g<SUP>–1</SUP>, respectively with capacity retention of over 90% after 100 cycles. The high capacities and enhanced cycling stability relative to those of conventional Ni-rich NCM cathodes were attributed to the compositional partitioning, strong crystallographic texture, and unique particle morphology. In addition, the highly correlated particle orientation helped to reduce the anisotropic internal strain induced by Li removal/extraction from the Ni-rich NCM cathodes. The accelerated aging test (storing the delithiated cathodes in an electrolyte at elevated temperature) reconfirmed the superior stability of the TSFCG85 cathode compared to the commercial Li[Ni<SUB>0.82</SUB>Co<SUB>0.14</SUB>Al<SUB>0.04</SUB>]O<SUB>2</SUB> cathode, which exhibited fast structural degradation. Thus, NCM cathodes with concentration gradients represent a viable solution that simultaneously addresses the specific energy density, cycling and chemical stability, and safety issues of Ni-enriched NCM cathodes for general electromobility.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2017/cmatex.2017.29.issue-24/acs.chemmater.7b04047/production/images/medium/cm-2017-04047h_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm7b04047'>ACS Electronic Supporting Info</A></P>
Yoon, Chong S.,Choi, Moon Ho,Lim, Byung-Beom,Lee, Eung-Ju,Sun, Yang-Kook The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.14
<P>LiNiO2 with theoretical capacity of 275 mAh g(-1) is regarded as a promising cathode material for Li-ion batteries, but its potential capacity has not been fully realized due to the severe capacity loss in the first charge/discharge cycle. Via co-precipitation method, we synthesized Li[Ni0.90Co0.05Mn0.05]O-2, Li[Ni0.95Co0.025Mn0.025]O-2, and LiNiO2 which delivered 221, 230, and 240 mAh g(-1) respectively, when cycled from 2.7 to 4.3 V vs. Li-0/Li+ at 0.1 C and retained similar to 70% of the initial capacity after 100 cycles. To date, such high reversible capacities are not yet to be reported from the Ni-rich Li[Ni1-x-yCoxMny]O-2 cathodes. The observed high capacities were attributed to the presence of a rock salt phase from severe cation mixing and excess Li ions in the host structure. It is believed that the rock salt phase stabilized the host structure in the delithiated state while the excess Li allowed the Li ions percolated through the rock salt phase which would be electrochemically inactive otherwise. (C) 2015 The Electrochemical Society. All rights reserved.</P>
Cho, Chong Pyo,Jo, Sangpil,Kim, Ho Young,Yoon, Sam S. Taylor Francis 2007 NUMERICAL HEAT TRANSFER PART A-APPLICATIONS - Vol.52 No.12
<P> The two-dimensional laminar combustion characteristics of coal particles at various oxygen concentration levels of a surrounding gas have been numerically investigated. The numerical simulations, which use the two-step global reaction model to account for the surrounding gas effect, show the detailed interaction among the inter-spaced particles, undergoing devolatilization and subsequent char burning. Several parametric studies, which include the effects of gas temperature (1700 K), oxygen concentration, and variation in geometrical arrangement of the particles on the volatile release rate and the char burning rate, have been carried out. To address the change in the geometrical arrangement effect, multiple particles are located at various inter-spacings of 4-20 particle radii in both streamwise and spanwise directions. The results for the case of multiple particles are compared with those for the case of a single particle. The comparison indicates that the shift to the multiple particle arrangement resulted in the substantial change of the combustion characteristics and that the volatile release rate of the interacting coal particles exhibits a strong dependency on the particle spacing. The char combustion rate is controlled by the level of oxygen concentration and gas composition near particles during combustion. The char combustion rate is highly dependent on the particle spacing at all oxygen levels. The correlations of the volatile release rate and the change in total mass of particles are also found.</P>