Jun-Ichi Yamaki

Ethylene carbonate/ether mixed solvents electrolyte for lithium batteries

Conductivities and Li charge—discharge efficiencies for LiClO4ue5f8ethylene carbonate (EC)/ether mixed solvents systems were studied, compared with those for propylene carbonate (PC)/ether and EC/PC/ether mixed solvents electrolytes, for use in nonaqueous lithium secondary batteries. As the ethers, tetrahydrofuran (THF), 1,2-dimethoxyethane, diethoxyethane and 1,3-dioxolane were used. Conductivities for EC/ether mixed systems were higher than those for both EC/PC/ether and PC/ether mixed systems, due to the high dielectric constant for EC and low viscosity for ethers. Conductivities showed maximum values around EC/ether mixing volume ratio = 1/1 and at about 1 M solute. For example 1 M LiClO4ue5f8EC/THF (1/1) showed approximately 40% higher conductivity, 14 × 10−3 S cm−1, than for PC/THF. Li charge—discharge efficiencies for EC/ether mixed systems also increased more than those for EC/PC/ether and PC/ether. This seems to be due to adsorption of less Li reactive ether and EC than PC, around deposited Li. In the same solute—solvents systems, Li cycling efficiencies for EC/eether mixed systems tended to increase Li cycling efficiency of 92%. This value was approx. 10% higher than for PC/THF.

Application of the Kirkwood theory of transport in polymer solutions to rigid assemblies of beads

The Kirkwood general theory of irreversible processes in polymer solutions is reformulated to give correct translational and rotatory diffusion coefficients for highly symmetric, rigid molecules which may be represented by rigid assemblies of beads. This provides an elementary description of the physical meaning of the Kirkwood approximation, and gives simple criteria to judge whether Kirkwoods incorrect formulas are or are not exactly valid for a given system. Following the formulation presented here, translational and rotatory diffusion coefficients of rigid rods and rigid rings are also evaluated.

Translational Diffusion Coefficients of Plane‐Polygonal Polymers: Application of the Modified Oseen Tensor

The translational diffusion coefficient of a plane‐polygonal polymer is investigated in the Kirkwood‐Riseman scheme following the procedure of Paul and Mazo with the use of the modified Oseen tensor for the finite bead model. Required summations over indices are exactly carried out with the aid of a digital computer. It is pointed out that the mathematical singularities or zeroes can occur in both cases of the Oseen tensor and the modified Oseen tensor, but never appear within the physically possible range of the strength of the hydrodynamic interaction if the beads are assumed to obey Stokes law. The correct asymptotic solution is also obtained and the results are compared with those for a continuous rigid ring.

Ethylene carbonate/linear-structured solvent mixed electrolyte systems for high-rate secondary lithium batteries

Abstract Lithium (Li) cycling efficiency by Li half cell tests and conductivity dependency on temperature are examined for LiAsF 6 —ethylene carbonate (EC)/linear-structured solvent (LS) mixed solvent electrolytes, to obtain organic electrolyte systems with higher conductivity than EC/2-methyltetrahydrofuran (2MeTHF) and high Li cycling efficiency. Methyl formate, acetonitrile and methyl acetate are used as LSs. Conductivities for all the EC/LS mixed systems examined here are higher than EC/2MeTHF in the −30 to 25°C range. Although mixing of EC to LS was effective in the improvement of Li cycling efficiency for LS—single solvent electrolytes, there are no electrolyte systems having higher Li cycling efficiencies than EC/2MeTHF. Selection of organic electrolytes seems to depend largely on future application purposes and cathode compatibility.

Inhibiting effects of Al corrosion by polymer ammonium chlorides in alkaline electrolyte

Abstract To inhibit Al corrosion in primary cells with Al anodes and alkaline electrolyte, the inhibiting effects of polymers with ammonium cation were studied. Two polymers, polyvinylbenzyltrimethylammonium chloride (PVBA) and polydiallydimethylammonium chloride (PDDA), inhibited Al corrosion effectively. Corrosion current icorr of pure Al was 5.40 mA cm−2 in 1 N KOH with PVBA at 5 × 10−2 M and 4.03 mA cm−2 with PDDA at 3 × 10−1 M. It is noted that they inhibited cathodic predominantly, which was preferable to the Al anode, because Ecorr shifted more negative (−22.00 V vs sce). The cathodic inhibiting effect of polymer cation seems to be due to the thicker double layer of polymer cation which prevents H+ ions from approaching the Al surface. The results to double layer capacitance measurement support this assumption.

The Decomposition of Propylene Carbonate in a Lithium/Metal Phthalocyanine Cell

Experimental results from a study of the catalytic effect of metal phthalocyanine (MPc) on the gas evolution reaction in Li batteries are reported. The trials comprised galvanostatic discharge tests with a battery containing a Li anode, an MPc cathode and a reference electrode. A gas evolution curve was generated, and further tests were performed with a cell containing FePc to investigate the gas evolution reaction more quickly. The gas evolved was proportional to the discharge capacity and featured propylene as the chief component. The appearance of propylene was attributed to a reaction between Pc and the discharge product of phthalocyanine. 9 references.

In situ Zn/ZnO mapping elucidating for “shape change” of zinc electrode

For the use of the zinc anode in secondary batteries, it is necessary to solve the “shape change” deterioration issue in that zinc species agglomerate in the center of the electrode to fade the available capacity. The local chemical compositions of the zinc electrodes during “shape change” were precisely analyzed using the synchrotron X-ray diffraction mapping analysis of practical zinc-nickel cells in a non-destructive manner. The in situ Zn/ZnO mapping shows that metallic Zn deposition chiefly occurs in the periphery of ZnO while ZnO are left in the center of electrode like a hill on charging. On discharging, the ZnO hill grows to the perpendicular direction on the electrode while metallic zinc is oxidized and dissolved. These findings allow us to propose a mechanism for the shape change; thus dissolved zincate species are decomposed on the ZnO hill during discharging to be accumulated in the center of the electrode. It is suggested that suppressing zincate dissolution and non-uniform zinc deposition sl...

Positive Electrodes of Nano-Scale for Lithium-Ion Batteries (Focusing on Nano-Size Effects)

Lithium-ion batteries are used as a power source for portable electric devices all over the world for their high power density and high discharge voltage, and they have begun to be used as a power source with high power for large electric equipment.

Thermal Stability of Materials Used in Lithium-Ion Cells

Abstract Lithium-ion (Li-ion) cells may smoke when abused and can ignite when the abuse is extreme. Thermal stability is a basic problem as regards cell safety. Several exothermic reactions occur inside a cell as its temperature increases. It is generally considered that “thermal runaway” occurs if heat output exceeds thermal diffusion. Possible exothermic reactions are: (1) chemical reduction of the electrolyte by the anode, (2) thermal decomposition of the electrolyte and (3) oxidation of the electrolyte on the cathode. Thermal stability of graphite anode, silicon/Li alloy anode, LiPF 6 /Alkyl carbonate mixed-solvent electrolytes, LiPF 6 /methyl difluoroacetate electrolyte, LiCoO 2 cathode and FeF 3 cathode with 1xa0M LiPF 6 /ECxa0+xa0DMC were investigated using DSC. Charged graphite anode and silicon/Li alloy anode showed almost the same heat output based on the amount of Li in each anode. LiPF 6 /methyl difluoroacetate electrolyte and FeF 3 cathode showed a very small heat output.