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Mechanistic Role of Li<sup>+</sup> Dissociation Level in Aprotic Li–O<sub>2</sub> Battery
Sharon, Daniel,Hirsberg, Daniel,Salama, Michael,Afri, Michal,Frimer, Aryeh A.,Noked, Malachi,Kwak, Wonjin,Sun, Yang-Kook,Aurbach, Doron American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.8
<P>The kinetics and thermodynamics of oxygen reduction reactions (ORR) in aprotic Li electrolyte were shown to be highly dependent on the surrounding chemical environment and electrochemical conditions. Numerous reports have demonstrated the importance of high donor number (DN) solvents for enhanced ORR, and attributed this phenomenon to the stabilizing interactions between the reduced oxygen species and the solvent molecules. We focus herein on the often overlooked effect of the Li salt used in the electrolyte solution. We show that the level of dissociation of the salt used plays a significant role in the ORR, even as important as the effect of the solvent DN. We clearly show that the salt used dictates the kinetics and thermodynamic of the ORR, and also enables control of the reduced Li2O2 morphology. By optimizing the salt composition, we have managed to demonstrate a superior ORR behavior in diglyme solutions, even when compared to the high DN DMSO solutions. Our work paves the way for optimization of various solvents with reasonable anodic and cathodic stabilities, which have so far been overlooked due to their relatively low DN.</P>
CHANDRA SPECTROSCOPY OF SUPERNOVA REMNANT 3C 391
CHEN YANG,SU YANG,SLANE PATRICK O.,WANG Q. DANIEL The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2
We performed a spatially resolved spectroscopic study of the thermal composite supernova remnant 3C 391 by the Chandra observation. Broad- and narrow-band X-ray images show a southeast-northwest elongated morphology and unveil a highly clumpy structure of the remnant. The spectral analysis for. the small-scale features indicates normal metal abundance and uniform temperature for the interior gas. The properties of the hot gas are largely in agreement with the cloudlet evaporation model as a main mechanism for the 'thermal composite' X-ray appearance, though radiative rim and thermal conduction may also be effective. An unresolved X-ray source, with a power-law spectrum, is observed on the northwest border. The equivalent width images reveal a faint finger-like protrusion in Si and S lines out of the southwest radio border.
Sharon, Daniel,Sharon, Pessia,Hirshberg, Daniel,Salama, Michael,Afri, Michal,Shimon, Linda J. W.,Kwak, Won-Jin,Sun, Yang-Kook,Frimer, Aryeh A.,Aurbach, Doron American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.34
<P>In this study, we present a new aprotic solvent, 2,4-dimethoxy-2,4-dimethylpentan-3-one (DMDMP), which is designed to resist nucleophilic attack and hydrogen abstraction by reduced oxygen species. Li-O-2 cells using DMDMP solutions were successfully cycled. By various analytical measurements, we showed that even after prolonged cycling only a negligible amount of DMDMP was degraded. We suggest that the observed capacity fading of the Li-O-2 DMDMP-based cells was due to instability of the lithium anode during cycling. The stability toward oxygen species makes DMDMP an excellent solvent candidate for many kinds of electrochemical systems which involve oxygen reduction and assorted evaluation reactions.</P>
Hirshberg, Daniel,Sharon, Daniel,Afri, Michal,Lavi, Ronit,Frimer, Aryeh A.,Metoki, Noa,Eliaz, Noam,Kwak, Won-jin,Sun, Yang-Kook,Aurbach, Doron American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.13
<P>Using UV-vis spectroscopy in conjunction with various electrochemical techniques, we have developed a new effective operando methodology for investigating the oxygen reduction reactions (ORRs) and their mechanisms in nonaqueous solutions. We can follow the in situ formation and presence of superoxide moieties during ORR as a function of solvent, cations, anions, and additives in the solution. Thus, using operando UV-vis spectroscopy, we found evidence for the formation of superoxide radical anions during oxygen reduction in LiTFSI/diglyme electrolyte solutions. Nitro blue tetrazolium (NBT) was used to indicate the presence of superoxide moieties based on its unique spectral response. Indeed, the spectral response of NBT containing solutions undergoing ORR could provide a direct indication for the level of association of the Li cations with the electrolyte anions.</P> [FIG OMISSION]</BR>
Feasibility of Full (Li-Ion)–O<sub>2</sub> Cells Comprised of Hard Carbon Anodes
Hirshberg, Daniel,Sharon, Daniel,De La Llave, Ezequiel,Afri, Michal,Frimer, Aryeh A.,Kwak, Won-Jin,Sun, Yang-Kook,Aurbach, Doron American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.5
<P>Aprotic Li-O-2 battery is an exciting concept. The enormous theoretical energy density and cell assembly simplicity make this technology very appealing. Nevertheless, the instability of the cell components, such as cathode, anode, and electrolyte solution during cycling, does not allow this technology to be fully commercialized. One of the intrinsic challenges facing researchers is the use of lithium metal as an anode in Li-O-2 cells. The high activity toward chemical moieties and lack of control of the dissolution/deposition processes of lithium metal makes this anode material unreliable. The safety issues accompanied by these processes intimidate battery manufacturers. The need for a reliable anode is crucial. In this work we have examined the replacement of metallic lithium anode in Li-O-2 cells with lithiated hard carbon (HC) electrodes. HC anodes have many benefits that are suitable for oxygen reduction in the presence of solvated lithium cations. In contrast to lithium metal, the insertion of lithium cations into the carbon host is much more systematic and safe. In addition, with HC anodes we can use aprotic solvents such as glymes that are suitable for oxygen reduction applications. By contrast, lithium cations fail to intercalate reversibly into ordered carbon such as graphite and soft carbons using ethereal electrolyte solutions, due to detrimental co-intercalation of solvent molecules with Li ions into ordered carbon structures. The hard carbon electrodes were prelithiated prior to being used as anodes in the Li-O-2 rechargeable battery systems. Full cells containing diglyme based solutions and a monolithic carbon cathode were measured by various electrochemical methods. To identify the products and surface films that were formed during cells operation, both the cathodes and anodes were examined ex situ by XRD, FTIR, and electron microscopy. The HC anodes were found to be a suitable material for (Li-ion) O-2 cell. Although there are still many challenges to tackle, this study offers a more practical direction for this promising battery technology and sets up a platform for further systematic optimization of its various components.</P>
Design and Self-Assembly of Amphiphilic Block Copolymers for Drug Delivery
Yi Yan Yang,Chuan Yang,Jeremy P. K. Tan,Nikken Wiradharma,Shrinivas Venkataraman,Amalina Bte Ebrahim Attia,Zhan Yuin Ong,Wei Cheng,Ashlynn Lee,Lin Kin Yong,Kazuki Fukushima,Sung Ho Kim,Daniel J. Coady 한국고분자학회 2011 한국고분자학회 학술대회 연구논문 초록집 Vol.2011 No.1