Browsing by Author "Hong, S"
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- ItemCritical 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, HLi-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
- ItemAn 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, CFMeasurements 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.