Browsing by Author "Hong, S"

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    Critical role of Ti4+ in stabilizing high-voltage redox reactions in Li-rich layered material
    (Wiley, 2021-07-01) Cho, M; Song, SH; Hong, S; Kim, KS; Avdeev, M; Yoo, JG; Ko, KT; Hong, J; Kim, J; Lee, S; Kim, H
    Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+-substituted Li2IrO3 (Li2Ir0.75Ti0.25O3) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1′ upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2IrO3, thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.© 2021 Wiley-VCH GmbH
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    Enigmatic human remains from the Pleistocene-Holocene transition of southwest China and the complex evolutionary history of east Asians
    (Australian Geosciences Council, 2012-08-05) Curnoe, D; Ji, X; Herries, AIR; Bai, K; Taçon, PSC; Bao, Z; Fink, D; Zhu, Y; Hellstrom, JC; Luo, Y; Cassis, G; Su, B; Wroe, S; Hong, S; Parr, WCH; Huang, S; Rogers, N
    The Upper Pleistocene hominin fossil record of East Asia is poorly known due to a scarcity of well-described, reliably classified and accurately dated fossils. In 2008, we started a joint project involving six Chinese and five Australian institutions to examine the later Pleistocene human record from southwest China. The region has been identified from genetic research as a hotspot of human diversity, and has yielded a number of human remains thought to derive from Pleistocene deposits. We prepared, reconstructed, described and dated a new partial skeleton from a consolidated sediment block collected in 1979 from the site of Longlin Cave (Guangxi Province). We also undertook new excavations at Maludong (Yunnan Province) to clarify the stratigraphy and dating of a large sample of mostly undescribed human remains from the site. Both samples probably derive from the same population, exhibiting an unusual mixture of modern human traits, characters probably plesiomorphic for later Homo, and some unusual features. We dated charcoal with AMS radiocarbon dating and speleothem with the Uranium-series technique and the results show both samples to be from the Pleistocene-Holocene transition: ∼14.3–11.5 ka. At nearby sites, some modern humans had already begun the economic transition to agriculture by this time. We suggest the Longlin-Maludong humans represent either a late-surviving archaic population or a previously unknown modern human group who colonised East Asia probably without leaving descendants. The archaeological record of Maludong indicates these humans were engaging in complex behaviours, including ochring bones and shells and manufacturing containers from human skulls.
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    Rational design of Li off-stoichiometric Ni-rich layered cathode materials for Li-ion batteries
    (Elsevier, 2022-11) Song, SH; Hong, S; Cho, M; Yoo, JG; Jin, HM; Lee, SH; Avdeev, M; Ikeda, K; Kim, J; Nam, SC; Yu, SH; Park, I; Kim, H
    The electrification trend in the automotive industry is fueling research on Ni-rich layered NCM cathode materials with high specific capacities. The simplest way to maximize the electrochemical performance of Ni-rich NCM is to tune the crystal structure by controlling the Li content and synthesis temperature. Herein, we demonstrate the critical roles of the Li content and synthesis temperature in determining the crystal structure of Li-excess Ni-rich NCM with enhanced electrochemical performance. The crystal structure of Li-excess Ni-rich NCM was systemically investigated using X-ray diffraction, neutron diffraction, and X-ray absorption spectroscopy, revealing that excess Li can be accommodated in Ni-rich NCM as the synthesis temperature decreases, resulting in stable cycle performance at high working voltage. We believe that our findings provide a rational reason for the excess amount Li required for optimization of the synthesis of Ni-rich NCM and offer insight for the simplest design of Ni-rich cathode materials that are stable under high-voltage operation. © 2022 Elsevier B.V.
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    An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g(-1) Pb concentrations
    (Elsevier, 2009-02-23) Burn, LJ; Roseman, KJR; Candelone, JP; Vallelonga, P; Burton, GR; Smith, AM; Morgan, VI; Barbante, C; Hong, S; Boutron, CF
    Measurements of Pb isotope ratios in ice containing sub-pg g(-1) concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g-1 and fg g(-1) concentrations in Polar ice, were also measured. The final blank amounted to 0.2 +/- 0.2 pg of Pb with Pb-206/Pb-207 and Pb-208/Pb-207 ratios of 1.16 +/- 0.12 and 2.35 +/- 0.16, respectively, 1.5 +/- 0.4 pg of Ba and 0.6 +/- 2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only similar to 5%, similar to 14% and similar to 0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g(-1), 0.3 pg g(-1) and 2.3 fg g(-1). Uncertainties in the Pb isotopic ratio measurements were degraded by only similar to 0.2%. © 2009, Elsevier Ltd.