Eiki Yasukawa

Characterization of Lithium Electrode in Lithium Imides/Ethylene Carbonate, and Cyclic Ether Electrolytes I. Surface Morphology and Lithium Cycling Efficiency

The surface and cross-sectional morphologies of deposited lithium on a nickel substrate in LiN(SO 2 C 2 F 5 ) 2 (LiBETI) electrolytes with ethylene carbonate (EC) + tetrahydropyran (THP), dimethoxyethane, dimethylcarbonate (DMC), propylenecarbonate (PC), γ-butyrolactone (GBL) (1:1) binary solvents were investigated by scanning electron microscopy observation. Dendritic morphology of deposited lithium was observed in DMC-, PC-, and GBL-containing solvents. However, deposited lithium in a EC + THP electrolyte exhibited a fine particle-like morphology and had a thinner surface film. The EC + THP electrolyte provided excellent performance based on the results of cycling characteristics using a Li/LiCoO 2 cell and Li/Ni cell. The morphology of deposited lithium in an EC + tetrahydrofuran electrolyte was strongly influenced by the kind of solutes. In LiBETI electrolyte, freshly deposited lithium exhibited uniform and fine particle-like morphology. In contrast, dendritic morphology was observed in LiN(SO 2 C 2 F 5 ) 2 (LiTFSI) electrolyte, resulting in a subsequent decrease in the lithium cycling efficiency. Electrolyte temperature was also an important factor influencing the lithium surface and efficiency. The use of LiTFSI electrolyte at elevated temperatures could suppress dendritic formation, resulting in excellent efficiency and cycling characteristics. We confirmed that the lithium surface morphology correlated well with the lithium cycling efficiency and the efficiency was strongly influenced by combinations of solvents and solutes.

Characterization of Lithium Electrode in Lithium Imides/Ethylene Carbonate and Cyclic Ether Electrolytes II. Surface Chemistry

Chemical components of surface films of deposited lithium on nickel substrates in electrolytes with LiN (SO 2 CF 3 ) 2 ) (LiTFSI), LiN (SO 2 C 2 F 5 ) 2 (LiBETI), LiPF 6 solutes, and tetrahydrofuran solvents were characterized by Fourier-transform infrared, two-dimensional nuclear magnetic resonance (2D NMR), X-ray photoelectron spectroscopy, evolved gas analysis, and ion chromatograph in order to understand the electrochemical performance of lithium imide/cyclic ether-based electrolytes. The top layers of the surface film were ROCO 2 Li, Li 2 CO 3 , polymer constituents, and LiF. The inner layers of the surface film consisted of Li 2 O and carbide species. In imide/cyclic ether-based electrolytes, Li 2 S 2 O 4 and Li 2 SO 3 as outer layers, and Li 2 S as the inner layer were formed on a nickel substrate as reductive constituents of imide solute. We found that organic surface layers consisted of lithium etoxides, lithium ethylene dicarbonate (CH 2 OCO 2 Li) 2 , polyethylene oxide, and lithium ethylene dicarbonate containing an oxyethylene unit by 1 H, 13 C, and 2D NMR. Li cycling efficiency affects not only the deposited lithium morphology but also chemical components.

Lithium Imide Electrolytes with Two‐Oxygen‐Atom‐Containing Cycloalkane Solvents for 4 V Lithium Metal Rechargeable Batteries

Lithium bisperfluoroethylsulfonyl imide (LiN(SO 2 C 2 F 5 ) 2 ) electrolytes with five-, six-, and seven-membered cycloalkane solvents containing two oxygen atoms were characterized in order to develop the organic electrolytes for 4 V lithium metal rechargeable batteries. Among the examined electrolytes, ethylene carbonate (EC) and 1,3-dioxane (DOX) mixed electrolyte (5:5) with I mol/dm 3 LiN(SO 2 C 2 F 5 ) 2 as solute were found to be the most advantageous, with high cycling efficiency (95.2%), good oxidation stability (>5 V), promising freezing point (-21°C), and high boiling point (105°C) of DOX solvent. Furthermore, only a slight decline in discharge capacity was observed for a Li/LiMn 2 O 4 coin cell with this electrolyte. Lithium cycling efficiency was also found to increase with decreasing deposition current density. Especially at deposition/dissolution current density of 0.3/0.6 mA/cm 2 , lithium cycling efficiency in 1 mol/dm 3 LiN(SO 2 C 2 F 5 ) 2 /EC + DOX (5:5) electrolyte achieved above 99%. Thermal tests disclosed that this mixed electrolyte showed good thermal stability even with the existence of lithium metal.

Electrochemical Behavior of Lithium Imide/Cyclic Ether Electrolytes for 4 V Lithium Metal Rechargeable Batteries

To develop organic electrolytes for 4 V lithium metal rechargeable batteries, LiN(SO{sub 2}CF{sub 3}){sub 2} electrolytes with five-, six-, and seven-membered cyclic ether solvents were characterized. Among these examined electrolytes, LiN(SO{sub 2}CF{sub 3}){sub 2}/tetrahydropyran (THP) electrolyte was found to possess the most advantages, such as high cycling efficiency, good oxidation stability, and high boiling point. Furthermore, lithium cycling efficiency and conductivity were improved by mixing 50% ethylene carbonate (EC) in 1 mol/dm{sup 3} LiN(SO{sub 2}CF{sub 3}){sub 2}/THP electrolyte. By using LiN(SO{sub 2}C{sub 2}F{sub 5}){sub 2} solute as an alternative to LiN(SO{sub 2}CF{sub 3}){sub 2} in EC + THP (1:1) electrolyte, corrosion of the aluminum current collector was inhibited and therefore, excellent cycling performance of a Li/LiMn{sub 2}O{sub 4} coin cell was realized. It was also found that lithium cycling efficiency increased with decreasing deposition current density or increasing dissolution current density. Especially at deposition/dissolution current densities of 0.2/0.6 mA/cm{sup 2}, the observed lithium cycling efficiency in 1 mol/dm{sup 3} LiN(SO{sub 2}C{sub 2}F{sub 5}){sub 2}/EC + THP (1:1) electrolyte was above 99%. Thermal tests further disclosed that this mixed electrolyte has good thermal stability even in the presence of lithium metal or cathode materials.

Determination of glutamate-pyruvate transaminase activity in blood serum with a pyruvate oxidase/poly(vinyl chloride) membrane sensor

Abstract Pyruvate oxidase (E.C. 1.2.3.3.) is immobilized by adsorption on a wet PVC membrane. Glutamate-pyruvate transaminase activity (5–1600 IU l −1 ) in serum is determined by a pyruvate oxidase sensor consisting of the immobilized pyruvate oxidase coupled to a platinum electrode for measuring hydrogen peroxide, after an l -alanine—α-ketoglutarate reaction. The assay requires ⩽60 s, and has a precision of 2–3%. Endogenous pyruvate should not interfere if measurements are made > 30 s after starting the reaction.

Wet poly(vinyl chloride) membrane as a support: Sorption and transport of low-molecular-weight organic compounds and proteins

Abstract Characteristics of sorption and transport behavior of “wet” (PVC) membranes prepared by a poly(vinyl chloride) casting method were studied. It was found that wet PVC membranes adsorbed enzymes and proteins, whilst they did not adsorb low-molecular-weight compounds. The diffusivity of acetylcholine iodide as a penetrant through the wet PVC membrane was approximately 10 −7 cm 2 /sec, although it depended strongly on membrane thickness and slightly on PVC concentrations in the casting solution. Activation energy of acetylcholine iodide diffusivity was 2.6 kcal/mol. These results were explained by hydrophobic interaction and minute pore dimensions. Wet PVC membrane was suggested as a support for immobilization and was compared with collagen on the basis of transport behavior.

A new gelling agent and its application as a solid electrolyte for lithium batteries

Abstract A new gelling agent 1,3:2,4-di( p -methoxycarbonylbenzylidene)sorbitol was used to immobilize liquid electrolytes for lithium batteries. The liquid electrolytes were solidified without a significant decrease in conductivity. The mechanical strength of a gelled electrolyte comprising poly(ethylene oxide)-grafted poly(methacrylate) and the liquid electrolyte was remarkably enhanced without a conductivity decrease.