Solid crosslinked-polymer electrolyte and use thereof

Details Solid crosslinked-polymer electrolyte and use thereof Solid crosslinked-polymer electrolyte and use thereof

2000-12-15

2004-01-13

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S305000, C429S306000

Reexamination Certificate

active

06677084

ABSTRACT:

TECHNICAL FILED
The present invention relates to a composition for a solid polymer electrolyte and a crosslinked material thereof, and more particularly to a solid polymer electrolyte suitable for a material for an electrochemical device such as a battery, a capacitor, a photovoltaic conversion element and a sensor.
RELATED ART
Hitherto, in view of ionic conductivity, an electrolyte in the form of solution or paste has been used as an electrolyte constituting an electrochemical device such as a battery, a capacitor, a photovoltaic conversion element and a sensor. However, problems have been pointed out such as a fear of damage to apparatus by liquid leakage and a limitation to fabricating super-small or thin devices due to the need for a separator that is impregnated with an electrolytic solution. To solve these problems, solid electrolytes such as inorganic crystalline substances, inorganic glass, and organic polymeric substances are proposed. The organic polymeric substances are generally excellent in processability and moldability, and solid electrolytes obtained therefrom have good flexibility and bending processability to provide a high degree of freedom in the design of devices to which the electrolytes are applied, so that their development is highly expected. However, at the present time, the organic polymeric substances are inferior to other materials in view of ionic conductivity.
Due to the discovery of ionic conductivity in a system comprising a homopolymer of ethylene oxide and an alkali metal ion, the active researches of solid polymer electrolytes are now being made. Polyethers such as polyethylene oxide are considered as being the most promising polymer matrixes in view of high mobility and solubility of metal cation. Migration of ions are prospected to occur not in a crystal part but in an amorphous part of the polymer. Since then, the copolymerization with various epoxides have been carried out in order to reduce the crystallinity of polyethylene oxide. Japanese Patent Kokai Publication No. 62-249361 (1987) discloses a solid electrolyte comprising a copolymer of ethylene oxide and propylene oxide; and U.S Pat. No. 4,818,644 discloses a solid electrolyte comprising a copolymer of ethylene oxide and methyl glycidyl ether. However, none of these has a satisfactory ionic conductivity.
Further, Japanese Patent Kokai Publication No. 02-235957 (1990) including the present applicants proposes an attempt to allow a specific alkali metal salt to be contained in a mixture of an epichloro-hydrin/ethylene oxide copolymer and a low-molecular-weight polyethylene glycol derivative for application to a solid polymer electrolyte. However, a practically sufficient value of conductivity has not yet been obtained.
Recently, Japanese Patent Kokai Publication No.09-324114 (1997) including the present applicants discloses a copolymer of ethylene oxide and an oxirane compound having an ethylene oxide unit in a side chain, as a copolymer having a high ion-conductivity. However, because the copolymer is a non-crosslinked material, the copolymer involves a problem in shape stability, and in particular, the copolymer lacks in strength as a film at a high temperature, so that the copolymer cannot be used as a solid polymer electrolyte. Further, WO97/4225 1 including the present applicants discloses crosslink of this polymer, where copolymerization with a monomer having a reactive group as a third component is carried out for crosslink. However, introduction of the third component deteriorates the ionic conductivity of the copolymer to greatly reduce the properties for a solid polymer electrolyte. Furthermore, if the reactive group is an ethylenically unsaturated group such as an allyl group, the reactive group is unstable to heat or ultraviolet rays, whereby a gel compound insoluble in solvents is produced. Also, if the reactive group is a reactive silicon group, the reactive group reacts with moisture in ambient air, whereby also a gel compound insoluble in solvents is produced, so that the gel compound cannot be treated as a film.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a solid electrolyte excellent in mechanical properties and ionic conductivity.
The present invention provides a composition comprising:
(i) a polyether copolymer having a weight-average molecular weight within a range from 10
5
to 10
7
and comprising
(A) 5 to 95 mol % of repeating unit derived from a monomer represented by the formula (1):
 wherein R
1
, R
2
and R
3
each is a hydrogen atom or —CH
2
O(CH
2
CH
2
O)
n
R where n and R may be different among R
1
, R
2
and R
3
, provided that all of R
1
, R
2
and R
3
are not simultaneously a hydrogen atom; R is an alkyl group having 1 to 12 carbon atoms; and n is from 0 to 12, and
(B) 95 to 5 mol % of repeating unit derived from a monomer represented by the formula (2):
(ii) a crosslinking agent selected from an organic peroxide and/or an azo compound, and
(iii) a crosslinking aid which is an organic compound having a carbon-carbon double bond and an imide group.
In addition, the present invention provides a crosslinked material obtainable by crosslinking said composition.
Further, the present invention provides a solid polymer electrolyte comprising:
(1) said crosslinked material,
(II) an electrolyte salt compound, and
(III) an optionally present plasticizer selected from the group consisting of an aprotic organic solvent, a derivative and metal salt of linear or branched polyalkylene glycol having a number-average molecular weight of from 200 to 5,000, and a metal salt of the derivative.
Yet further, the present invention provides also a battery comprising said solid polymer electrolyte.
EXPLANATION OF THE PREFERRED EMBODIMENTS
When a plasticizer is incorporated into a solid polymer electrolyte, the ionic conductivity will be improved because the crystallization of the polymer is restrained to lower the glass transition temperature, and amorphous phase is formed in a large amount even at a low temperature. The inventors of the present invention also found out that the use of the solid polymer electrolyte of the present invention gives a highly efficient battery having a small internal resistance. The solid polymer electrolyte of the present invention may be in a gel form. Here, the gel refers to a polymer which is swollen by a solvent.
The copolymer of the present invention has
(A) repeating unit derived from the monomer of the formula (1):
 wherein R
1
, R
2
and R
3
each is a hydrogen atom or —CH
2
O(CH
2
CH
2
O)
n
R where n and R may be different among R
1
, R
2
and R
3
, provided that all of R
1
, R
2
and R
3
are not simultaneously a hydrogen atom; R is an alkyl group having 1 to 12 carbon atoms; and n is from 0 to 12, and
(B) repeating unit derived from the monomer of the formula (2):
&Parenopenst;CH
2
—CH
2
—O&Parenclosest;  (2′)
At least one group, i.e. one, two, or three groups among R
1
, R
2
and R
3
groups are —CH
2
O(CH
2
CH
2
O)
n
R. The number n may be from 1 to 12, for example, from 2 to 10. The repeating unit (A) in the copolymer of the present invention may be derived from at least two types of monomers.
The polymerization reaction can be carried out as follows. The polyether copolymer can be obtained by reaction of the monomers under stirring at a reaction temperature of from 10 to 80° C. in the presence or absence of a solvent with the use of a catalyst system based on organic aluminum, a catalyst system based on organic zinc, or an organic tin/phosphoric acid ester condensate catalyst system or the like as a catalyst for ring-opening polymerization. Among these, the organic tin/phosphoric acid ester catalyst system is preferable in view of the polymerization degree or the properties of the resultant copolymer.
In the polyether copolymer of the present invention, the molar ratio of the repeating unit (A) and the repeating unit (B) is so that the repeating (A) is from 5 to 95 mol %, preferably from 10 to 95 mol %, and the repeating unit (B) is from 5 to 95 mol %, preferably from 5 t

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