Jeong-Ju Cho

Global physiological understanding and metabolic engineering of microorganisms based on omics studies

Through metabolic engineering, scientists seek to modify the metabolic pathways of living organisms to facilitate optimized, efficient production of target biomolecules. During the past decade, we have seen notable improvements in biotechnology, many of which have been based on metabolically engineered microorganisms. Recent developments in the fields of functional genomics, transcriptomics, proteomics, and metabolomics have changed metabolic engineering strategies from the local pathway level to the whole system level. This article focuses on recent advances in the field of metabolic engineering, which have been powered by the combined approaches of the various “omics” that allow us to understand the microbial metabolism at a global scale and to develop more effectively redesigned metabolic pathways for the enhanced production of target bioproducts.

Co-Use of Cyclohexyl Benzene and Biphenyl for Overcharge Protection of Lithium-Ion Batteries

Cyclohexyl benzene (CHB) is widely used as an electrolyte additive for overcharge protection of lithium-ion batteries. This study reports that CHB and biphenyl (BP) mixtures are much more effective than CHB. On the overcharging tests for graphite-LiCoO 2 cells with a nominal capacity of 760 mAh, CHB and BP mixtures expand the safety region up to 12 V/2 A where CHB alone without BP can never reach. Using the linear sweep voltammetry and the electrochemical quartz crystal microbalance, it was found that the CHB and BP mixture exhibits much bigger oxidation current and forms a larger amount of polymeric film than the numeric sum of each components response. The origin of the synergistic effects between CHB and BP has been speculated based on their different electrochemical characteristics.

Theoretical studies of the solvent decomposition by lithium atoms in lithium-ion battery electrolyte

Abstract We have carried out density functional and ab initio calculations on the structure and stability of MLi n ( n =0, 1, and 2) complexes, where the M=ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), ethylene sulfite (ES), and glycol sulfate (GS). Although the molecules are geometrically similar, it is found that the reactions with lithium atoms may provide various reaction products depending upon the structures and stabilities. Reductive decomposition by lithium atoms appears to be in order of the most energetically favorable, ES∼GS>EC∼PC>VC, and GS>PC∼EC∼VC>ES for the first and second lithium atom addition reactions to the molecules, respectively. The transition states are also determined and discussed for EC, VC, and ES.

Fluoropropane sultone as an SEI-forming additive that outperforms vinylene carbonate

Vinylene carbonate (VC) has been the best performing solid electrolyte interphase (SEI) additive for the current lithium-ion batteries (LIBs). However, it is also true that the current LIB technology is being stagnated by the limit set by VC. This study introduces 3-fluoro-1,3-propane sultone (FPS) as a novel SEI additive to replace VC and another popular SEI additive, 1,3-propane sultone (PS). Both density functional calculations and electrochemical experiments confirm that the presence of an electron withdrawing fluorine group is favourable in terms of anodic stability and SEI forming ability. In the cyclability of LiCoO2/graphite cells over a wide temperature range (25–60 °C), FPS exhibits remarkable enhancement compared with PS, and is even superior to VC. During elevated temperature (90 °C) storage of the cells, VC suffers from severe swelling, whereas FPS causes little thermal degradation. Considering the high anodic stability, the excellent cyclability, and the good thermal stability, FPS is an outstanding SEI additive that can expand the performance boundary of the current LIBs.

Comparison of Voltammetric Responses over the Cathodic Region in LiPF6 and LiBETI with and without HF

This study reports the effects of HF on the voltammetric responses below 3 V (vs. Li/Li + ) in LiPF 6 solutions being widely used in rechargeable lithium-ion batteries (LIBs). During the first cathodic scan on a Pt electrode, two reduction peaks are observed between 3.0 and 1.5 V in LiPF 6 solutions irrespective of the solvents used. The reduction reactions are absent in LiBETI solutions but present after the addition of trace amount of HF. Thus, the reduction reactions in LiPF 6 solutions are due to the HF, an inevitable impurity of LiPF 6 solutions. Based on the results of the rotating disk electrode and the rotating ring disk electrode experiments, two reduction peaks are assigned to the hydrogen underpotential deposition and the hydrogen evolution reaction, respectively. HF reduction reactions forms a surface layer of which the main constituent is LiF. The surface layer suppresses the other reduction reactions otherwise occurring below 3.0 V. For example, the electrodeposition of metallic Mn, which takes place below 1.0 V in LiBETI solutions, is severely hampered in LiPF 6 solutions. The passivity by HF reduction is observed not only for a Pt electrode but also for a glassy carbon electrode.

Determination of the oxidation potentials of organic benzene derivatives: theory and experiment

Abstract We have calculated the IP, Δ G e , and E ox values for 10 mono -substituted benzene molecules and compared them with experimental values obtained by linear sweep voltammetry. The E ox values were evaluated using the density functional method and thermodynamic cycles. The relative oxidation potentials are in close agreement with experimental values, while the UB3LYP/6-31+G(d) approach shows the absolute E ox values to be lower by about 0.9 V. Consideration of bulk solvent effects is important to fully describe the experimental variation in E ox . The HOMO, NBO, and Wiberg bond index were analyzed to investigate the changes when moving from neutral to cationic molecules.