Improved electrochemical performance of lithium-sulfur batteries by crosslinked polymer layers

Battery Science and TechnologyLithium sulfur (Li-S) battery is new generation system. Sulfur is widely known as a high theoretical capacity (1672 mAh g-1) and high theoretical energy density (2600 Wh kg-1). The attractive features of sulfur are low cost, abundant resources and nontoxic. Sulfur (S) is utilized as a cathode material and Li metal is an anode in Li-S cells. Since Li metal has high theoretical capacity of about 3860 mAh g-1 and the most electropositive (-3.04V versus standard hydrogen electrode), a high energy density can be achieved. During the discharge process, elemental sulfur (S8) electrochemically reduces to soluble long-chain polysulfides and the resulting polysulfides can be dissolved into the electrolyte. Dissolved long-chain lithium polysulfide can diffuse to the Li anode and short-chain intermediate species (insoluble Li2S2 and Li2S) may deposit on the anode, leading to the formation of unstable and non-uniform solid electrolyte interphase (SEI) layer. It can cause considerable capacity fading and safety concern related to the dendritic Li generated by non-uniform current distribution of the Li anode. These are important issues about thermal stability in all battery systems. In this study, we aim to understand thermal properties of sulfur cathodes and improve electrochemical performance of Li-S cells. In chapter II, we investigate exothermic peaks for sulfur cathode according to different depth of discharge and fully charge step compared to delithiated lithium metal oxide cathode in a Li-ion battery by using the DSC technique. The exothermic peak of lithiated and delithiated sulfur cathode in the battery is considerably reduced at around 360 oC. Also surface changes of the sulfur cathode were clearly demonstrated by ex-situ XPS technique during the different depth of discharge and fully charge processes. The thermal reaction between lithium metal and sulfur generated catastrophic exothermic heat in the presence of the ether-based electrolyte, but, the mixture of Li metal and lithium sulfide (Li2S) showed greatly reduced exothermic peak. In chapter III, we demonstrate the positive impact of the protective film on electrochemical properties of lithium metal anode in Li-S cells. Li metal, which is very reactive anode material, readily undergoes the reactions with polysulfides dissolved from the sulfur cathode. It is expected that the introduction of a protection layer based on the crosslinked gel polymer (semi-IPN structure) prevents unwanted reactions with polysulfide. Li-S cells without the protection layer show significant overcharge behavior during 10cycles, while the cell with protection layer effectually mitigates the overcharging.ope

Bis(methanol-κO)bis­(quinoline-2-carboxyl­ato-κ2 N,O)nickel(II)

In the title complex, [Ni(C10H6NO2)2(CH3OH)2], the NiII ion lies on an inversion center and is coordinated by two quinoline-2-carboxyl­ate ligands in the equatorial sites and two axial methanol ligands, forming a distorted octa­hedral environment. In the crystal, mol­ecules are linked via O—H⋯O hydrogen bonds into a two-dimensional network parallel to (10)

Antifungal Activity and Action Mechanism of Histatin 5-Halocidin Hybrid Peptides against Candida ssp.

The candidacidal activity of histatin 5 is initiated through cell wall binding, followed by translocation and intracellular targeting, while the halocidin peptide exerts its activity by attacking the Candida cell membrane. To improve antimicrobial activities and to understand the killing mechanism of two peptides, six hybrid peptides were designed by conjugating histatin 5 and halocidin. A comparative approach was established to study the activity, salt tolerance, cell wall glucan binding assay, cytotoxicity, generation of ROS and killing kinetics. CD spectrometry was conducted to evaluate secondary structures of these hybrid peptides. Furthermore the cellular localization of hybrid peptides was investigated by confocal fluorescence microscopy. Of the six hybrid congeners, di-PH2, di-WP2 and HHP1 had stronger activities than other hybrid peptides against all tested Candida strains. The MIC values of these peptides were 1-2, 2-4 and 2-4 μg/ml, respectively. Moreover, none of the hybrid peptides was cytotoxic in the hemolytic assay and cell-based cytotoxicity assay. Confocal laser microscopy showed that di-PH2 and HHP1 were translocated into cytoplasm whereas di-WP2 was accumulated on surface of C. albicans to exert their candidacidal activity. All translocated peptides (Hst 5, P113, di-PH2) were capable of generating intracellular ROS except HHP1. Additionally, the KFH residues at C-terminal end of these peptides were assumed for core sequence for active translocation

Bifunctional Li4Ti5O12 coating layer for the enhanced kinetics and stability of carbon anode for lithium rechargeable batteries

We introduce an effective way to improve the electrochemical properties of graphite anodes by Li4Ti5O12 (LTO) coating for lithium rechargeable batteries. LTO coated graphite is prepared by a sol-gel method coupled with hydrothermal reaction. LTO coating renders the electrochemical performance of graphite to be significantly improved compared to pristine graphite. Moreover, LTO coating layers affect the stability of the solid electrolyte interphase (SEI) by making an even SEI film without further electrolyte decomposition and thus making it more stable. Also, LTO coating layers prevent the electrolyte decomposition species from going into the interior graphite, proving that LTO coating can contribute to not only the electrochemical properties of graphite but also its thermal stability.close0

Thermal Reactions of Lithiated and Delithiated Sulfur Electrodes in Lithium-Sulfur Batteries

The thermal reactions of lithiated and delithiated sulfur cathodes with 1.3M lithium bis(trifluoromethane sulfonyl)imide (LiTESI) in tetra(ethylene glycol)dimethyl ether (TEGDME) are investigated by differential scanning calorimetry (DSC). To understand the thermal reactions of cycled sulfur cathodes, the products formed during cycling are characterized by ex-situ X-ray photoelectron spectroscopy (XPS).close1

Killing kinetics of Hst5, P113, di-18Hc, hybrid peptides against <i>Candida albicans</i>.

<p>Killing kinetics of peptides against <i>C</i>. <i>albicans</i> was measured by colony count assay. Candida cells were treated with a different concentration of peptides at a determined time. 10 mM NaPB was used as a control. Killing percent was calculated with the following equation: Killing % = (number of control cell—number of treated cell)/control cell × 100.</p

Hemolytic activities of Hst5, P113, di-18Hc, Halocidin-P113 hybrid peptides and control peptide.

<p>1% of triton-X100 was used as the control for 100% hemolysis and 0.01% acetic acid was used as the peptide-free control. Percent hemolysis was calculated with the following equation: Hemolysis (%) = (A₅₄₀ of sample—A₅₄₀ of peptide-free control) / (A₅₄₀ of 100% control—A₅₄₀ of peptide-free control) × 100.</p

CD spectra of Hst5, P113, di-18Hc and hybrid peptides.

<p>This study was performed with one concentration (200 μg/ml) of each peptide in various buffers: 10 mM sodium phosphate buffer (Red line), 50% TFE in phosphate buffer (green line) and 20 mg of laminarin in phosphate buffer.</p

Effects of salt on MICs of Hst 5, P113, di-18Hc and hybrid peptides against Candida strains.

<p>Effects of salt on MICs of Hst 5, P113, di-18Hc and hybrid peptides against Candida strains.</p

Amino acid sequence of histatin 5, halocidin and hybrid peptides.

<p>Amino acid sequence of histatin 5, halocidin and hybrid peptides.</p