Polyether copolymer, solid polymer electrolyte and battery

Details Polyether copolymer, solid polymer electrolyte and battery Polyether copolymer, solid polymer electrolyte and battery

1999-04-19

2001-03-13

Tucker, Philip (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S415000, C429S311000

Reexamination Certificate

active

06201071

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a polyether copolymer, a solid polymer electrolyte and a battery. More particularly, it relates to a solid polymer electrolyte which is suitable as a material for an electrochemical device such as a battery, a capacitor and a sensor.
RELATED ART
As an electrolyte constituting an electrochemical device such as a battery, a capacitor and a sensor, those in the form of a solution or a paste have hitherto been used in view of the ionic conductivity. However, the following problems are pointed out. That is, there is a fear of damage of an apparatus arising due to liquid leakage, and subminiaturization and thinning of the device are limited because a separator to be impregnated with an electrolyte solution is required. To the contrary, a solid electrolyte such as inorganic crystalline substance, inorganic glass and organic polymer substance is suggested. The organic polymer substance is generally superior in processability and moldability and the resulting solid electrolyte has good flexibility and bending processability and, furthermore, the design freedom of the device to be applied is high and, therefore, the development is expected. However, the organic polymer substance is inferior in ionic conductivity to other materials at present.
Extensive researches have been carried out on solid polymer electrolytes since the finding of ionic conductivity in a system of ethylene oxide homopolymer and alkali metal ions. As a result, polyethers such as polyethylene oxide are now considered to be most promising as polymer matrices in view of their high mobilities and solubilities of metal cations. It has been predicted that migration of ions occurs in amorphous regions rather than crystalline regions of such polymers. Since then, copolymerization of polyethylene oxide with various epoxides has been carried out in order to decrease the crystallinity of polyethylene oxide. Japanese Patent Kokoku Publication No. 249361/1987 discloses solid electrolytes comprising copolymers of ethylene oxide and propylene oxide, and U.S. Pat. No. 4,818,644 discloses solid electrolytes comprising copolymers of ethylene oxide and methyl glycidyl ether. Their ionic conductivities were not, however, entirely satisfactory in either case.
Although Japanese Patent Kokai Publication No. 235957/1990 filed by the present applicant proposes an attempt in which particular alkali metal salts are contained in mixtures of epichlorohydrin-ethylene oxide copolymers and low molecular weight polyethylene glycol derivatives to be used as solid polymer electrolytes, a practically adequate value of conductivity could not been achieved.
Furthermore, Japanese Patent Kokai Publication Nos. 223842/1994 and 295713/1996 describe solid electrolytes comprising copolymers having carbonate groups on the side chains. The backbone of these copolymers, however, does not have a polyether structure, but has a polyolefin structure which has a poor mobility and a low conductivity.
SUMMARY OF THE INVENTION
An object of the present invention provides a solid electrolyte which is superior mechanical properties and ionic conductivity.
The present invention provides a polyether copolymer having a weight-average molecular weight of 10
4
to 10
7
which may optionally be cross-linked and which comprises:
(A) 1 to 99% by mol of a repeating unit derived from a monomer represented by the formula (I):
 wherein R
1
represents a divalent organic group,
(B) 99 to 1% by mol of a repeating unit derived from a monomer represented by the formula (II):
 and
(C) 0 to 15% by mol of a repeating unit derived from a monomer having one epoxy group and at least one reactive functional group.
The present invention also provides a solid polymer electrolyte comprising:
(1) the above polyether copolymer,
(2) an electrolyte salt compound, and
(3) if necessary, a plasticizer selected from the group consisting of an aprotic organic solvent, and a derivative or metal salt of a linear or branched polyalkylene glycol having a number-average molecular weight of 200 to 5,000 or a metal salt of said derivative.
The present invention further provides a battery comprising the above solid polymer electrolyte.
A crosslinked material of the polyether copolymer is used when the shape stability at high temperature is required.
When the plasticizer is blended with the solid polymer electrolyte, the crystallization of the polymer is inhibited and the glass transition temperature is lowered and a large amount of an amorphous phase is formed even at low temperature and, therefore, the ionic conductivity is improved. It has been also found that, when the solid polymer electrolyte of the present invention is used, a high-performance battery having small internal resistance can be obtained. The solid polymer electrolyte of the present invention may be in the form of a gel. The term “gel” used herein means a polymer swollen with a solvent.
DETAILED DESCRIPTION OF THE INVENTION
The repeating unit (C) may be derived from a monomer of the formula (III):
wherein R
2
represents a reactive functional group-containing group.
The polyether polymer of the present invention comprises
(A) a repeating unit derived from a monomer (I):
wherein R
1
is a divalent group, and
(B) a repeating unit derived from a monomer (II):
 &Parenopenst;CH
2
—CH
2
—O&Parenclosest;  (II′)
In the polyether copolymer of the present invention, the divalent group of R
1
group in the formula (I) is preferably
—CH
2
—O—(CHA
1
—CHA
2
—O)
n
—CH
2
—,
—CH
2
—O—(CH
2
)
n
—,
—CH
2
—O—(O)C—(CH
2
)
n
—,
—(CH
2
)
m
—CO
2
—(CH
2
)
n
—, or
—(CH
2
)
m
—O—CO
2
—(CH
2
)
n
—
wherein each of A
1
and A
2
is hydrogen or a methyl group, n is the number of 0 to 12,
and m is the number of 0 to 6.
More preferably, the R
1
group is
—CH
2
—O—(CHA
1
—CHA
2
—O)
n
—CH
2
—,
—CH
2
—O—(CH
2
)
n
—, or
—CH
2
—O—(O)C—(CH
2
)
n
—
wherein each of A
1
and A
2
is hydrogen or a methyl group, and n is the number of 0 to 6.
The polyether copolymer optionally comprises (C) a repeating unit derived from a monomer having one epoxy group and at least one reactive functional group. A crosslinked material can be derived from the polyether copolymer having the repeating unit (C) by utilizing the reactivity of the reactive functional group.
The copolymer used in the present invention may be crosslinked or not crosslinked. Examples of a crosslinking agent for crosslinking a binary copolymer having the repeating unit (I′) and the repeating unit (II′) specifically include isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diphenylmethane diisocyanate and hexamethylene diisocyanate.
The repeating unit (C) derived from a monomer of the formula (III) is represented by the formula (III′):
wherein R
2
represent a reactive functional group-containing group.
The reactive functional group in the repeating unit (C) is preferably (a) a reactive silicon group, (b) an epoxy group, (c) an ethylenically unsaturated group, or (d) a halogen atom.
The polymerization method of the polyether copolymer, which may have a crosslinkable side chain, of the present invention is the polymerization method wherein a copolymer is obtained by a ring opening reaction of ethylene oxide portion and can be conducted in the same manner as that described in Japanese Patent Kokai Publication Nos. 154736/1988 and 169823/1987 filed by the present applicant.
The polymerization reaction can be conducted as follows. That is, the polyether copolymer can be obtained by reacting the respective monomers at the reaction temperature of 10 to 80° C. under stirring, using a catalyst mainly containing an organoaluminum, a catalyst mainly containing an organozinc, an organotin-phosphate ester condensate catalyst and the like as a ring opening polymerization catalyst in the presence or absence of a solvent. Among of them, the organotin-phosphate ester condensate catalyst is particularly preferable in view of the polymerization degree, or properties of the resulting copolymer and the like.

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