Gel-form solid polymer electrolyte

Details Gel-form solid polymer electrolyte Gel-form solid polymer electrolyte

1998-07-29

2001-10-02

Gupta, Yogendra (Department: 1751)

Compositions

Electrically conductive or emissive compositions

C252S506000, C252S509000, C252S518100, C526S314000, C526S187000, C526S225000, C526S167000, C526S174000, C526S243000

Reexamination Certificate

active

06296783

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a polymeric gel electrolyte for use in, for example, a primary battery, a secondary battery or a capacitor.
BACKGROUND ART
It is common practice to use liquid electrolytes in electrochemical devices such as a primary battery, a secondary battery and a capacitor. However, the liquid electrolytes have a drawback in that they are likely to cause a liquid leakage to thereby render their long-term reliability unsatisfactory.
The use of a solid electrolyte is known as means for solving this problem. When the solid electrolyte is used in the above electrochemical device, not only can the liquid leakage be avoided to thereby provide a highly reliable device but also the device itself can be miniaturized with its weight reduced. In recent years, various polymeric solid electrolytes (solid polymer electrolytes) have been investigated as providing the above solid electrolyte. The polymeric solid electrolyte not only possesses such a flexibility that its versatile use can be effected irrespective of a volume change which occurs in the course of ion electron exchange reaction between an electrode and the polymeric solid electrolyte but also has the above characteristics of the solid electrolyte. A composite of a polyethylene oxide having a polyether structure and an alkali metal salt such as a lithium salt is known as providing an example of the above polymeric solid electrolyte. Further, Japanese Patent Laid-open Publication No. 5(1993)-25353 describes a polymeric solid electrolyte consisting mainly of a polyoxyalkylene diester compound, a polymethoxyoxyalkylene ester compound, a crosslinked resin of a copolymer with an oxy compound having a double bond and an inorganic salt. Still further, Japanese Patent Laid-open Publication No. 6(1994)-223842 describes a polymeric solid electrolyte composed of an organic polymer having carbonate groups as a functional group and a metal salt.
However, the ionic conductivity of the solid electrolyte is generally lower than that of the liquid electrolyte, so that it has been difficult to obtain primary and secondary batteries exhibiting excellent discharge characteristics from the solid electrolyte. In the above circumstances, there is a demand for the development of a polymeric solid electrolyte which can satisfy requirements for, for example, enhanced ionic conductivity and electrochemical stability.
OBJECT OF THE INVENTION
The present invention has been made in view of the above prior art, and it is an object of the present invention to provide a polymeric gel electrolyte which exhibits a high ionic conductivity and is chemically stable.
DISCLOSURE OF THE INVENTION
The polymeric gel electrolyte of the present invention comprises:
(a) an acrylic ester polymer matrix containing structural units derived from at least one acrylic ester selected from among acrylic esters represented by the general formulae (I) and (II):
wherein R
1
, R
2
and R
2′
are identical with or different from each other and represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R
3
represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 1 to 100, and
wherein R
4
to R
9
are identical with or different from each other and represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and p, q and r are identical with or different from each other and are an integer of 1 to 100;
(b) a nonaqueous solvent of a carbonic ester (carbonic acid ester); and
(c) a salt of a metal of Group Ia of the periodic table.
It is preferred that the acrylic ester polymer matrix be a homopolymer or copolymer of an acrylic ester selected from among acrylic esters represented by the general formulae (I) and (II).
It is also preferred that the acrylic ester polymer matrix be a copolymer of:
an acrylic ester represented by the general formula (I) or (II), and
a vinyl monomer, vinylidene monomer or vinylene monomer copolymerizable with the acrylic ester represented by the general formula (I) or (II).
The nonaqueous solvent is preferably at least one carbonic ester selected from among cyclic carbonic esters and chain carbonic esters.
The nonaqueous solvent may be a mixed solvent of a cyclic carbonic ester and a chain carbonic ester.
The salt of metal of Group Ia of the periodic table is preferably at least one lithium salt selected from among LiClO
4
, LiBF
4
, LiPF
6
, LiAsF
6
, LiCF
3
SO
3
, LiN(CF
3
SO
2
)
2
and LiC(CF
3
SO
2
)
3
.
The polymeric gel electrolyte of the present invention is preferably produced by performing a simultaneous polymerization of a solution containing the salt of metal of Group Ia of the periodic table, the nonaqueous solvent of carbonic ester and the acrylic ester represented by the general formula (I) or (II).
BEST MODE FOR CARRYING OUT THE INVENTION
The polymeric solid electrolyte of the present invention will be described in detail below.
The terminology “polymerization” used herein may mean both of homopolymerization and copolymerization without being limited to homopolymerization. The terminology “opolymer” used herein may mean both of homopolymer and copolymer without being limited to homopolymer. The terminology “acrylic ester” used herein means not only an ester of acrylic acid but also an ester of acrylic acid whose hydrogen atom has been substituted with an alkyl group, such as methacrylic acid.
[Acrylic Ester Polymer Matrix]
First, the acrylic ester polymer matrix for use in the present invention will be described.
The acrylic ester polymer matrix contains structural units derived from at least one acrylic ester selected from among acrylic esters represented by the general formulae (I) and (II).
Acrylic Esters Represented by the Formula (I)
In the formula, R
1
, R
2
and R
2′
are identical with or different from each other and represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably, a hydrogen atom or a methyl group.
R
3
represents an alkyl group having 1 to 4 carbon atoms, preferably, a methyl group, an ethyl group or a t-butyl group.
n is an integer of 1 to 100, preferably, 1 to 10.
Examples of the above acrylic esters represented by the general formula (I) include:
The acrylic ester represented by the above general formula (I) can be synthesized from, for example, the compound represented by the following general formula (i) and the compound represented by the following general formula (ii) in the following manner.
In the above formulae, R
1
, R
2
, R
2′
, R
3
and n are as defined with respect to the above formula (I).
In the above synthesis, the compound represented by the general formula (ii) is used in an amount of 0.5 to 5 mol per mol of the compound represented by the general formula (i). Further, for example, K
2
CO
3
, Na
2
CO
3
, Li
2
CO
3
and NaOCH
3
can be used as a catalyst in the above reaction. Such a catalyst is used in an amount of 1×10
−5
to 1×10
−2
mol per mol of the compound represented by the general formula (i).
The reaction of the compound represented by the general formula (i) and the compound represented by the general formula (ii) is generally conducted under agitation and under reflux while removing formed alcohol. The reaction temperature generally ranges from 40 to 140° C. and the reaction time generally ranges from 2 to 60 hr.
In the formula, R
4
to R
9
are identical with or different from each other and represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably, a hydrogen atom or a methyl group. p, q and r are identical with or different from each other and are an integer of 1 to 100, preferably, 1 to 10. Examples of the above acrylic esters represented by the general formula (II) include:
The acrylic ester represented by the above general formula (II) can be synthesized from, for example, the compound represented by the following general formula (iii) and the compound represented by the following general formula (iv) in the following manner.
In the above formula, R
4
to R
9
, and p, q and r are as defined with respect to

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