Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-01-14
2001-01-16
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S309000, C429S003000, C429S003000, C429S321000, C429S322000, C429S324000, C252S062200, C528S272000
Reexamination Certificate
active
06174626
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyelectrolyte used in primary batteries, secondary batteries, electrochromic displays, electrochemical sensors, iontophoresis devices, capacitors, and other electrochemical devices. More particularly, the invention relates to a polyelectrolyte comprising a (meth)acrylic polymer as a main component, and also to sheets obtained by forming this in the form of a sheet, a tape, of the like.
BACKGROUND OF THE INVENTION
With the recent increasing demand for reduction in size and weight of electronic equipment, electrochemical devices have been attracting attention. Electrochemical devices are constituted of a variety of constituent materials, and improvement is shown in the respective constituent materials. Of those constituent materials, an electrolytic solution is one of the main materials making up lithium batteries. The electrolytic solution generally comprises an organic solvent, such as propylene carbonate or ethylene carbonate, and an ionic salt, such as lithium fluorophosphate, as a solute, while it depends on matching with positive and negative electrodes. Use of such an electrolytic solution, however, involves many problems in, for example, leakage of liquid, safety, and the like. A polymer having dispersed therein a compound whose ion is easily movable, and a polyelectrolyte layer comprising a crosslinked polymer comprising polyethylene oxide as a main component, have been proposed. However, their performance is insufficient as yet in terms of flexibility at low temperatures or stability. Thus, a satisfactory electrolyte is not yet obtained. It has therefore been demanded to develop an effective polyelectrolyte that overcomes the above problems and will contribute to further advancement of technology.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems in the prior art.
Accordingly, an object of the present invention is to provide an ion-conducting polyelectrolyte which is easily molded and has flexibility even at low temperatures.
As a result of extensive investigations, it has been found that a polyelectrolyte which is moldable and is also stable in the working temperature range can be obtained by using a (meth)acrylic polymer comprising a monomer having a specific structure as an ion-conducting functional component. The present invention has been completed based on this finding.
According to one embodiment of the present invention, there is provided a polyelectrolyte comprising a (meth)acrylic polymer and an ionic salt, the (meth)acrylic polymer comprising:
(A) 20 to 100 parts by weight of a (meth)acrylic monomer represented by the following formula (I):
CH
2
═C(R
1
)COO—R
2
—R
3
(I)
wherein R
1
represents a hydrogen atom or a methyl group; R
2
represents an alkyl chain having 3 to 12 carbon atoms; and R
3
represents (XR
4
)
n
XR
5
, wherein X represents —O— or —S—; R
4
represents an alkyl group having 1 to 4 carbon atoms; n represents 0 or an integer of 1 to 20; and R
5
represents a hydrogen atom, a methyl group or an ethyl group,
(B) 0 to 80 parts by weight of a (meth)acrylic monomer represented by the following formula (II):
CH
2
═C(R
1
)COO—R
6
(II)
wherein R
1
represents a hydrogen atom or a methyl group; and R
6
represents an alkyl group having 2 to 12 carbon atoms, and
(C) 0 to 30 parts by weight, per 100 parts by weight of the total amount of components (A) and (B), of a monomer copolymerizable with components (A) and (B).
According to another embodiment of the present invention, there is provided a polyelectrolyte comprising 100 parts by weight of the (meth)acrylic polymer comprising components (A), (B), and (C) and 400 parts by weight or less of an ionic salt solution.
According to further embodiment of the present invention, there is provided sheets, such as a film, a sheet, or a tape, comprising a substrate having provided on one or both sides thereof a layer formed of the above polyelectrolyte that is solid at room temperature.
DETAILED DESCRIPTION OF THE INVENTION
The (meth)acrylic monomer as component (A) has a structure having a relatively long alkyl chain (R
2
) as a side chain, as represented by the formula (I). R
2
in formula (I) includes tetramethylene (C
4
), hexamethylene (C
6
), and octamethylene (C
8
) groups. If the number of carbon atoms in R
2
is smaller than 3, in the (meth)acrylic polymer comprising an ester of acrylic acid or methacrylic acid having such a relatively long side chain (alkyl chain), a (thio)glycol moiety on the side chain which serves as a functional component with ion conductivity will greatly affect the main chain in the resulting (meth)acrylic polymer, for example, only to provide a (meth)acrylic polymer having an increased glass transition temperature and thereby lacking flexibility. On the other hand, if the number of carbon atoms in R
2
is greater than 12, the mutual influences among the side chains become conspicuous, resulting in an increase in glass transition temperature, too. Monomers containing a methyl group, an ethyl group, etc. as a branch of the alkyl side chain can also be used.
R
3
that is bonded to the end of the side chain is an ion-conducting functional component. R
3
includes a hydroxyl group, a methoxy group or an ethoxy group and their sulfur analogues; glycols (e.g., polymethylene glycol, polyethylene glycol, and polypropylene glycol) and/or sulfur analogues thereof (thioglycols); and these (thio)glycols with the end thereof methylated or ethylated.
If the number of carbon atoms in the (thio)glycol moiety represented by R
4
is greater than 4, the density of the functional component serving for ion conduction is too small for sufficient manifestation of ion conductivity. The number n of the repeating units is 20 or less. If it exceeds 20, this moiety exerts too much cohesive force, making it difficult to secure flexibility of the (meth)acrylic polymer.
Since the (meth)acrylic polymer has a relatively long alkyl chain, the (meth)acrylic polymer containing such component (A) has degree of freedom between the polymer main chain and the ion-conducting functional component. As a result, an increase in glass transition temperature is relaxed to secure flexibility, and the effect of the ion-conducting functional component on the polymer side chain can be enhanced markedly.
The (meth)acrylic monomer as component (A) is not limited by the process for preparation. For example, it is prepared by starting with a diol selected so as to give a desired side chain length. The diol is brominated with hydrogen bromide to obtain a dibromide having a desired side chain length. The dibromide is reacted with Cellosolve, Carbitol or a sulfur analogue thereof, etc. in the form of, e.g., a sodium salt to obtain a bromide having an ion-conducting functional group, which is then reacted with (meth)acrylic acid.
The (meth)acrylic monomer represented by the formula (II) as component (B) is a monomer effective in imparting flexibility to the resulting (meth)acrylic polymer. That is, the alkyl chain R
6
having 2 to 12 carbon atoms makes a contribution to the flexibility of the polymer similarly to R
2
of component (A).
Accordingly, it is preferred for R
6
in component (B) to have approximately the same number of carbon atoms as in R
2
of component (A). Examples of component (B) are ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, and dodecyl (meth)acrylate. In other words, component (B) cooperate with component (A) in securing flexibility of the (meth)acrylate polymer. Component (B) is particularly effective where the ion-conducting functional moiety on the side chain of component (A) is relatively large or where an ionic salt solution containing a relatively large amount of an organic solvent is used.
One or more than one (meth)acrylic monomers (I) can be used as component (A). Component (A) is used in a proportion of 20 to 100 parts by weight, and preferably 50 to 95 parts by weight, per 100 parts by
Kojima Makoto
Omata Tetsuo
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
Weiner Laura
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