Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-12-01
2001-04-03
Nuzzolillo, Maria (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S231950
Reexamination Certificate
active
06210840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonaqueous electrolytic solution having high flame retardancy, and more particularly, to a flame-retardant electrolytic solution containing a phosphorus flame retardant having a specific structure and a nonaqueous secondary battery containing the flame-retardant electrolytic solution.
2. Description of the Related Art
In order to achieve size and weight reduction of portable equipment such as notebook computers, video cameras, and mobile phones, the need for secondary batteries having a higher energy density has been increasing. Further, development of batteries having a higher energy density than currently used lead batteries is also awaited for realizing practical use of electric automobiles which emit no air pollutant.
A lithium battery is known for its high energy density. A lithium battery usually contains a nonaqueous electrolytic solution of an electrolyte, such as LiBF
4
, LiPF
6
, LiClO
4
, LiAsF
6
, LiCF
3
SO
3
, LiAlCl
4
or LiSiF
6
, in a mixed solvent comprising a high-dielectric constant solvent, such as propylene carbonate, y-butyrolactone or sulfolane, and a low-viscosity solvent, such as dimethoxyethane, tetrahydrofuran or 1,3-dioxolane.
These solvents used in the nonaqueous electrolytic solution are combustible and incurs a danger of fire in case of a short circuit, etc. A countermeasure against fire is indispensable particularly in a high-energy density battery because the high energy would be released all at once in case of a short circuit.
While fire caused by an overcharge, an overdischarge or an external short circuit has been avoided by an external safety mechanism, such an external safety mechanism does not work on a short circuit inside a battery. It has thus been demanded to develop a battery with safety independent on an external safety mechanism.
To make the solvent flame retardant is known as a means for ensuring the safety independently of the external safety mechanism. Addition of flame-retardant compounds, such as phosphoric esters and halogen compounds, to an electrolytic solution has been proposed to data. For example, Japanese Patent Laid-Open Nos. 184870/92, 283205/94, and 22839/96 teach addition of phosphoric esters, e.g., trimethyl phosphate and tricresyl phosphate. However, these compounds have turned out to cause reduction in charge and discharge efficiency or dendritical precipitation of lithium at the time of charges, making the batteries unsatisfactory for practical use.
Japanese Patent Laid-Open No. 244565/90 proposes use of a small amount of a phosphorus compound, such as a phosphate and a phosphonate, for the purpose of improving the penetrability of an electrolytic solution into a separator, in which no reference is given to the effectiveness of a phosphoric ester compound in improving the flame retardancy of an electrolytic solution.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a flame-retardant electrolytic solution which exhibits excellent flame retardancy without adversely affecting the electrical characteristics.
Another object of the present invention is to provide a nonaqueous secondary battery containing the flame-retardant electrolytic solution.
As a result of extensive investigation, the inventors of the present invention have reached the findings that the above objects of the present invention are accomplished by adding a specific phosphorus compound to an electrolytic solution.
Completed based on the above findings, the present invention provides a flame-retardant electrolytic solution of an electrolyte salt in an organic solvent, wherein the organic solvent contains at least one phosphorus compound represented by formula (I):
wherein R
1
represents an alkyl group having 1 to 8 carbon atoms, a halogenated alkyl group, an aryl group, an alkylaryl group, an aralkyl group or —CH
2
—COOR
3
; R
2
represents a methyl group, an ethyl group or a halogenated alkyl group having 1 to 8 carbon atoms; R
3
represents an alkyl group having 1 to 8 carbon atoms or a halogenated alkyl group; and m and n each represents 1 or 2 and the sum of m and n is 3.
The present invention also provides a nonaqueous secondary battery containing the above-described flame-retardant electrolytic solution.
The flame-retardant electrolytic solution according to the present invention provides a nonaqueous battery with high flame retardancy without adversely affecting the battery performance.
The nonaqueous secondary battery according to the present invention exhibits high flame retardancy as well as excellent battery performance.
REFERENCES:
patent: 5580684 (1996-12-01), Yokoyama et al.
patent: 5972539 (1999-10-01), Hasegawa et al.
patent: 631 339 A2 (1994-12-01), None
patent: 02-244565 (1990-09-01), None
patent: 04-184870 (1992-07-01), None
patent: 10-223257 (1998-08-01), None
patent: WO 97/44842 (1997-11-01), None
Ito Miho
Kubota Naohiro
Mashimo Shinya
Usami Kyohei
Denso Corporation
Nuzzolillo Maria
Wills Monique
Young & Thompson
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