Solid electrolyte and method for producing it

Details Solid electrolyte and method for producing it Solid electrolyte and method for producing it

1999-07-15

2001-12-11

Dunn, Tom (Department: 1725)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S189000

Reexamination Certificate

active

06329103

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a solid electrolyte usable in batteries, capacitors, electrochromic devices, sensors, etc.
Solid electrolytes are produced, for example, by mixing an acryloyl-modified polymer compound having an alkylene oxide polymer chain, an electrolytic salt and, optionally, a solvent, in which mixture the polymer compound is crosslinked.
For crosslinking the polymer compound, employable are any among the following: UV irradiation, electronic irradiation, thermal crosslinking and the like, which, however, have the following drawbacks.
In a cell system containing a solid electrolyte, the solid electrolyte acting as a binder shall be also in the positive electrode and the negative electrode, wherein active materials are employed. For the solid electrolyte in such a cell system, UV irradiation is often problematic in that UV rays cannot readily penetrate into the cell system because of the existence of active materials. As a result, the polymer compound constituting the solid electrolyte is often difficult to crosslink through such UV irradiation to a satisfactory degree.
Polymer crosslinking through electronic irradiation may be possible even in such a cell system, as the transmittance of electron rays through the system is high. However, satisfactory polymer crosslinking is difficult in thick cell systems even through electronic irradiation. In addition, another problem with electronic irradiation is that the apparatus for it is expensive.
Conventional thermal crosslinking requires heating at high temperatures of 90° C. or higher, and is therefore problematic in that it often causes degradation of electrolytic salts and much vaporization of solvents, if used.
In that situation, some improved methods for producing solid electrolytes have been proposed in JP-A 5-36305, 5-114419 and 5-151992, which, however, are still defective in the following points. In the method in JP-A 5-36305, a radical polymerization accelerator or retardant is used so as to control the curing rate of polymers, and the amount thereof to be added to the polymer system must be controlled extremely accurately. The method in JP-A 5-114419 and 5-151992 is characterized in that two solutions, either one of which contains an alkali metal salt, are mixed and cured in cells, and therefore the application range of the method is limited.
The invention has been made in consideration of the problems noted above. Namely, the object of the invention is to provide a solid electrolyte obtained by employing a specific crosslinking initiator in order to solve the above-identified problems.
SUMMARY OF THE INVENTION
The solid electrolyte of the invention comprises a crosslinked product of an alkylene oxide polymer having a polymerizable double bond at the terminal and/or in the side chain, and an electrolytic salt, in which the alkylene oxide polymer is thermally crosslinked in the presence of an organic peroxide initiator having an activation energy of at most 35 Kcal/mol and having a half-value period of 10 hours at a temperature not higher than 50° C.
Preferably, the alkylene oxide polymer is represented by the following chemical formula (1) or (2):
wherein Z represents a residue of an active hydrogen compound;
k represents an integer of from 1 to 6;
R
1
represents an alkyl group or —CH
2
—O—Re
1
—Re
2
;
Re
1
represents —(CH
2
CH
2
O)
p1
—, p1 represents 0 or any integer;
Re
2
represents an alkyl group;
Y
1
represents an acryloyl group or a methacryloyl group;
m represents an integer of from 0 to 460, and n represents an integer of from 0 to 350.
wherein Z represents a residue of an active hydrogen compound;
k represents an integer of from 1 to 6;
R
1
represents an alkyl group or —CH
2
—O—Re
1
—Re
2
;
R
2
represents —CH
2
—O—Re
1
—Re
3
;
Re
1
represents —(CH
2
CH
2
O)
p1
—, p1 represents 0 or an integer of 1 or more;
Re
2
represents an alkyl group;
Re
3
represents an alkenyl group;
Y
2
represents an alkyl group, an aralkyl group, an aryl group, an acryloyl group or a methacryloyl group;
q represents an integer of from 0 to 100,000, r represents an integer of from 0 to 50,000, and s represents an integer of from 1 to 22,000.
The solid electrolyte may optionally contain a low-molecular weight polar solvent.
One method for producing the solid electrolyte comprises preparing a precursor that contains an alkylene oxide polymer having a polymerizable double bond at the terminal and/or in the side chain, an electrolytic salt, and, optionally, a solvent, followed by thermally crosslinking the alkylene oxide polymer in the resulting precursor; which is characterized in that an organic peroxide initiator having an activation energy of at most 35 Kcal/mol and having a half-value period of 10 hours at a temperature not higher than 50° C. is added to the precursor being prepared, in an amount of from 0.05 to 5% by weight relative to the total weight of the alkylene oxide polymer, the electrolytic salt and the solvent, and that the alkylene oxide polymer in the resulting precursor is thermally crosslinked.
The polymer in the solid electrolyte of the invention is crosslinked in the presence of an organic peroxide initiator having specific physical properties, and its crosslinking can be attained at low temperatures not higher than 50° C., for example, even at room temperature. Crosslinking the polymer in the solid electrolyte of the invention does not require any expensive apparatus such as those for electron irradiation, and is free from the problem with conventional thermal crosslinking that causes degradation of electrolytic salts and vaporization of solvents.
Therefore, the solid electrolyte of the invention is extremely useful, as being able to be in any systems containing active materials, such as cells, etc.
DETAILED DESCRIPTION OF THE INVENTION
To produce the solid electrolyte of the invention, a precursor that comprises, as the indispensable components, an alkylene oxide polymer having a polymerizable double bond, for example, an acryloyl group, a methacryloyl group or the like, at the terminal and/or in the side chain, and an electrolytic salt, and optionally contains a low-molecular weight polar solvent (plasticizer), is prepared, and the alkylene oxide polymer in the precursor is thermally crosslinked in the presence of a specific organic peroxide initiator.
The components are mentioned in detail hereinunder.
1. Alkylene Oxide Polymer
The alkylene oxide polymer for use in the invention, which has a polymerizable double bond at the terminal and/or in the side chain is not specifically defined. Preferred is any one or a mixture of two having a structure of the following chemical formula (1) or (2). One or more of those alkylene oxide polymers may be employed herein either singly or as combined.
wherein Z represents a residue of an active hydrogen compound;
k represents an integer of from 1 to 6;
R
1
represents an alkyl group or —CH
2
—O—Re
1
—Re
2
;
Re
1
represents —(CH
2
CH
2
O)
p1
—, p1 represents 0 or an integer of 1 or more;
Re
2
represents an alkyl group;
Y
1
represents an acryloyl group or a methacryloyl group;
m represents an integer of from 0 to 460, and n represents an integer of from 0 to 350.
wherein Z represents a residue of an active hydrogen compound;
k represents an integer of from 1 to 6;
R
1
represents an alkyl group or —CH
2
—O—Re
1
—Re
2
;
R
2
represents —CH
2
—O—Re
1
—Re
3
;
Re
1
represents —(CH
2
CH
2
O)
p1
—, p1 represents 0 or an integer of 1 or more;
Re
2
represents an alkyl group;
Re
3
represents an alkenyl group;
Y
2
represents an alkyl group, an aralkyl group, an aryl group, an acryloyl group or a methacryloyl group;
q represents an integer of from 0 to 100,000, r represents an integer of from 0 to 50,000, and s represents an integer of from 1 to 22,000.
The alkylene oxide polymer may be prepared from a starting material of an active hydrogen compound, such as diglycerin, pentaerythritol or the like, for example, by adding a monomer of, for example, ethylene oxide, propylene oxide or the like to the starting compound, followed by e

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