Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1995-11-17
1997-11-25
Bell, Bruce F.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429218, 429197, 429203, H01M 614
Patent
active
056910843
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application is a 371 of PCT/JP95/00464 filed Mar. 17, 1995.
The present invention relates to an organic electrolytic solution secondary cell. In particular, the present invention relates to a secondary cell comprising an organic electrolytic solution which has improved safety and shelf stability.
DESCRIPTION OF THE RELATED ART
An organic electrolyte solution secondary cell is a secondary cell in which an organic solvent is used as a solvent of an electrolytic solution. Such type of the secondary cell is increasingly used, since it has a large capacity, generates a high voltage and has a high energy density.
In such secondary cell, as a solvent of the electrolytic solution, an organic solvent such as 1,2-dimethoxyethane and propylene carbonate has been used. But, since 1,2-dimethoxyethane is included in the Dangerous Object, Class 4, list and has a low flash point so that it has large danger to ignite, in these days, the use of such solvent is undesirable in view of the safety from fire.
An ester of phosphoric acid is a desirable solvent for the organic electrolytic solution secondary cell, since it is incombustible or nonflammable (a flush point of above 100.degree. C.).
But, when lithium or its alloy is used as a negative electrode in relation to a positive electrode active material such as manganese oxide together with the electrolytic solution comprising the phosphoric acid ester, lithium in the negative electrode reacts with the solvent to increase an internal resistance greatly, whereby the cell properties are deteriorated and then the shelf stability is worsened.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an organic electrolytic solution secondary cell which solves the problems of the above conventional organic electrolytic solution secondary cell, has the improved safety and shelf stability, and is excellent in the cell properties.
According to the present invention, there is provided an organic electrolytic solution secondary cell comprising a positive electrode, a negative electrode and an organic electrolytic solution, wherein a solvent of said organic electrolytic solution contains a triester of phosphoric acid, and said negative electrode comprises a carbonaceous material.
In one preferred embodiment, a ratio of a peak intensity of carbon around 285 eV (I.sub.285) to a sum of peak intensities of carbon from around 284 eV to around 289 eV (I.sub.c) (I.sub.285 /I.sub.c) in an X-ray photoelectron spectroscopy on a surface of the negative electrode is not larger than 1.0.
In another preferred embodiment, a ratio of a peak intensity of phosphorus around 135 eV (I.sub.135) to a sum of peak intensities of carbon from around 284 eV to around 289 eV (I.sub.c) (I.sub.135 /I.sub.c) in an X-ray photoelectron spectroscopy on a surface of the negative electrode is at least 0.05, and this ratio on the surface is larger than a I.sub.135 /I.sub.c ratio of an inside of the negative electrode.
In another preferred embodiment, carbon dioxide is dissolved in the organic electrolytic solution.
The organic electrolytic solution secondary cell of the present invention is excellent in the cell properties such as a closed circuit voltage, a retention (a difference between a charge capacity and a discharge capacity), a discharge capacity, and so on.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a vertical cross sectional view of an example of the organic electrolytic solution secondary cell according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the triester of phosphoric acid is a compound of the formula: monovalent organic hydrocarbon group. A preferred example of the triester is a compound of the formula (I) in which R' is an alkyl group having 1 to 6 carbon atoms, that is, a trialkyl phosphate.
Hereinafter, the present invention will be explained by making reference to a cell using a trialkyl phosphate as a solvent of the organic electrolytic solution, but the scope of the present invention is not limited
REFERENCES:
patent: 4668595 (1987-05-01), Yoshino et al.
patent: 5455127 (1995-10-01), Olsen et al.
"Summaries of Lectures in Autumn Meeting of Electrochemistry in 1991"; Electrochemical Society; p. 132 (with abstract), no month available.
Higashiguchi Masaharu
Kawakami Akira
Kita Fusaji
Murakami Kouji
Bell Bruce F.
Hitachi Maxell, Ltd
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