JPH02105855A - Ionically conductive composition - Google Patents

Abstract

PURPOSE:To obtain an ionically conductive composition having a high ionic conductivity and excellent in film forming properties and processability by mixing at least an electrolyte with a polymer matrix which has a crosslinked structure formed by light irradiation and at least a half of which comprises a specified block copolymer. CONSTITUTION:The title ionically conductive composition comprises at least an electrolyte (e.g., LiClO4) and a polymer matrix having a crosslinked structure formed by light irradiation, wherein at least 50wt.% of the polymer matrix comprises a block copolymer of polyethylene oxide with polypropylene oxide. The composition of the above structure has a high ionic conductivity and excellent film forming properties and moldability, and it is useful by itself as a solid-state polyelectrolyte in various uses such as a battery, a capacitor, an EC element and a sensor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an ion-conductive composition useful for batteries, capacitors, EC elements, sensors, etc., which has particularly high ionic conductivity and is easy to form and process. This invention relates to an improved solid polymer electrolyte.

[Prior Art] Conventionally, electrochemical elements such as batteries, capacitors, and sensors use electrolytes, which has caused problems in terms of leakage, device mounting, and processability, and solidification is being considered. Among these, solid polymer electrolytes are attracting attention because they are lighter, more flexible, and have better moldability than inorganic solid electrolytes.

Among solid polymer electrolytes, polyethylene oxide (PE)
O) is reported to be a lithium ion conductor with a high ionic conductivity of ~to-' 87 cm at 100 °C [PolyIler, 14.588 (1
973)], at room temperature, the ionic conductivity decreased significantly due to crystallization of the PEO chains, making it difficult to apply to devices.

As one means of suppressing PEO crystallization and obtaining a material with high strength, a method of crosslinking the PEO chain ends has been attempted [PolymerJ, +8 (11)]
, 809 (198B)]. However, even with crosslinking, crystallization was not completely suppressed, and the problem of decreased ionic conductivity due to crystal portions remaining in the film was not solved.

Furthermore, in order to solve the above problem, attempts have been made to introduce polypropylene oxide (PPO), an amorphous polymer, into the crosslinked product by randomly copolymerizing it with PEO to suppress crystallization. (Unexamined Japanese Patent Publication No. 62-24
9361), thereby suppressing the crystallization of PEO chains and improving ionic conductivity at room temperature.

Furthermore, the present inventors used a PE0-PPO block copolymer as the polymer matrix of the polymer solid electrolyte, and by incorporating an ion dissociation unit in which three or more blocks of PEO were introduced into the polymer chain. proposed a solid electrolyte whose ionic conductivity is less dependent on salt concentration. In particular, when the polymer chains form a crosslinked structure, the mechanical strength is improved (Japanese Patent Application No. 63-228545).

However, in order to apply a solid electrolyte made of the crosslinked body to an element, even higher ionic conductivity is required. In addition, since the crosslinked product is insoluble and infusible, it is necessary to form a film at the same time as the reaction, but methods of crosslinking the ends of ion dissociative group molecules with urethane bonds, ester bonds, etc. are difficult to control the reaction, and film formation and processability are difficult. There was a problem. Generally, these reactions are accelerated by heating, but this method is difficult to apply to solid electrolytes containing thermally unstable electrolyte salts, and its use is greatly limited.

Furthermore, the crosslinking method according to this method has the disadvantage that if unreacted functional groups remain in the system, deterioration, alteration, etc. are significant, and therefore the crosslinking rate and the structure of the polymer matrix are restricted.

[Problems to be Solved by the Invention] In view of these circumstances, the present invention provides an ion-conducting composition that has high ionic conductivity, has excellent film formation and processability, and allows the crosslinking rate to be appropriately selected. The purpose is to

[Means for Solving the Problems] The present invention provides an ion conductive composition comprising at least an electrolyte salt and a polymer matrix having a crosslinked structure formed by light irradiation, in which 50% by weight or more of the polymer matrix is This is an ion conductive composition characterized by being a block copolymer of polyethylene oxide and polypropylene oxide.

Furthermore, in the present invention, especially when the polymer matrix is
The PE0-PPO block copolymer is formed by crosslinking a functional or higher functional PE0-PPO block copolymer with a bifunctional or higher functional PEO or PPO, and or the former PE0-PPO block copolymer is composed of three or more ethylene oxide-propylene oxide copolymers with different lengths. High ionic conductivity was obtained for those composed of polymer chains. Furthermore, the polymer matrix has three or more block copolymers of polyethylene oxide and polypropylene oxide that have three or more functional groups that form a cross-linked structure, and two polyether chains that have functional groups that form a cross-linked structure. and three or more polyethers having at least one type of polyether chain having no functional group were crosslinked.

The present invention will be explained in detail below.

The ion conductive composition of the present invention is composed of at least a polymer serving as a matrix and an electrolyte salt serving as a carrier. Ionic conduction is achieved when an electrolyte salt solvated into a polymer matrix dissociates and moves through the matrix by diffusion along an electric field.

The crosslinked polymer matrix used in the present invention has an ion-dissociable group having a structure in which PEO chains are alternately copolymerized. Since the polymer matrix dissociates the electrolyte salt and also plays the role of generating carrier ions, it is difficult to obtain high ionic conductivity unless the polymer matrix has a high dissociation ability. Further, since the carrier ions diffuse and move within the matrix due to the thermal movement of the polymer matrix, it is desirable that the polymer matrix is a mobile and crystalline molecule. Furthermore, the presence of crystalline portions within the molecules of the polymer matrix impedes ionic conduction and reduces electrical conductivity. In the present invention, in order to satisfy the above-mentioned characteristics, a material in which PEO, which promotes salt dissociation, and PEO chains, which reduce the crystallinity of the PEO chains, are alternately copolymerized was introduced. In the PE0-PPO block copolymer chain, PEO
The chain is introduced in the minimum amount necessary to keep the PEO chain in an amorphous state.

is preferable. If the PEO chain of the block copolymer chain is too short, the salt dissociation ability will be reduced, and if it is too long, crystallization will occur easily, resulting in low ionic conductivity. Therefore, an optimal number of repetitions is required.

That is, the PE0-PPO block copolymer chain has EO
For every 8 to 30 repeating units of PO, there are 1 to 5 repeating units.
It is particularly good to introduce 1 to 3. Furthermore, the PE0-
PPO block copolymerization unit and PEO unit are 3
more than one, i.e. [PEO+PP0-PEO+x] (X≧
2), the dependence of ionic conductivity on salt concentration was small, and there was almost no decrease in ionic conductivity due to the addition of a high concentration of salt.

When the PEo-PPO block copolymer chain described above is introduced into a polymer matrix, the content of the PEo-PPO block copolymer chain increases the ionic conductivity of the solid electrolyte (
Make it left and right. In the present invention, the polymer matrix 5
0% by weight or more, preferably 60% by weight or more is PE0-P
High ionic conductivity was obtained when it was a PO block copolymer chain. As described above, the polymer matrix used in the present invention is mainly composed of the above PE0-PPO block copolymer chains, but can contain other copolymer components in addition to these polymer chains. Other copolymerization components include, for example, polyethers such as polyethylene oxide, polypropylene oxide, and polybutylene oxide; polycarbonates such as polyethylene carbonate and polypropylene carbonate; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene;
In addition to polysiloxanes and polysiloxane derivatives such as polydimethylsiloxane, polyesters such as poly-β-propiolactone, polypeptides such as polyglutamic acid, polyphosphazene, polyvinylpyridine, polyacrylonitrile, acrylate resins, polyethyleneimine, polyethylene sulfide etc. and derivatives thereof, but are not limited thereto.

etc. can be mentioned.

Moreover, the polymer matrix used in the present invention is the above-mentioned P
It is preferable to form a three-dimensional network structure in which the terminals of the E0-PPO alternating block copolymer are crosslinked. The polymer matrix, which has become amorphous due to the introduction of PPO chains, becomes a self-supporting chain due to the intense thermal movement of the molecular chains. If this is applied alone to a device, conduction and breakage cannot be avoided.

In order to efficiently form a crosslinked structure, it is necessary to react a molecule with three or more functional groups that contribute to the crosslinking reaction with a molecule with two or more functional groups in one molecule. In the present invention, high ionic conductivity can be obtained in a composition in which a polymer matrix is a crosslinked product obtained by a crosslinking reaction between a trifunctional or higher functional PE0-PPO block copolymer and a difunctional or higher functional PE01 or PPO. In particular, if a crosslinked structure is formed by bonding the ends of two polyether chains that have ion dissociation ability, higher ionic conductivity can be obtained compared to conventional systems that use crosslinking agents that do not have ion dissociation ability. be able to. Furthermore, the PE0-PPO block copolymer is a branched molecule having three or more functionalities, and when the branched chains are PE0-PPO block copolymer chains with different lengths, high ionic conductivity can be obtained.

According to the present invention, since the crosslinked polymer matrix contains a polyester chain with one end unfixed,
Even better properties were obtained. This is thought to be because the polyether chain with one end unfixed has high mobility, allowing ions to move easily, resulting in high ionic conductivity.

The crosslinked structure in the present invention is a system formed by light irradiation, and good results were obtained. In particular, by selecting photocrosslinkable functional groups that do not cause deterioration or functional decline of the ion conductive composition even if they remain in the system, the reaction can proceed quickly at low temperatures, allowing for reaction control, film formation, and processing. succeeded in improving sex. Furthermore, since crosslinking by light does not require heating, it has become possible to use thermally unstable electrolyte salts.

Furthermore, by forming a crosslinked film through photoreaction, it has become possible to downsize manufacturing equipment.

Examples of photosensitive groups used for photocrosslinking in the present invention include -CO-C(CN) -Cl1- Cl1- co-(
◎, etc. Among these, particularly excellent effects were obtained with the cinnamoyl group and its derivatives.

Methods for introducing photosensitive groups into ionically dissociable polymer chains include, for example, esterification reactions, urethanization reactions, ureaization reactions, addition reactions from epoxy, etc., but are not particularly limited to these. It's not something you can do. In particular, a method in which COCl, -OH possessed by an ionically dissociable polymer or a compound having a photosensitive group is used and introduced by esterification has high reactivity and a high introduction rate.

The content of photosensitive groups is preferably 80% or more, preferably 80% or more.

Electrolyte salts that serve as carriers for polymer solid electrolytes include:
5CN-CI-"Br""I""BF4 P
F6- CF35O3SbF6- ASF&-
Examples include electrolyte salts consisting of an anion such as Cl04B(C6H5)4- CF3SO3- and a cation such as an alkali metal cation such as Li"Na"K+ or an organic cation such as (C4H9)4N"(C2H5)4N+.

To prepare a solid polymer electrolyte, that is, a composite of a polymer matrix and an electrolyte salt, a photo-crosslinked polymer matrix film is immersed in a solution in which the electrolyte salt is dissolved and the crosslinked polymer is insoluble. ; Examples include a method of forming a film from a solution of a polymer and an electrolyte salt by a casting method. In the present invention, the latter is preferable.

The method for forming a polymer solid electrolyte film is preferably carried out by the following steps: (1) casting a polymer by a melting method or solution method, and (2) irradiating it with light or energy rays. Here, the melting method is a method in which the polymer is directly applied to the substrate at a temperature higher than the melting point of the polymer. The solution method is a method in which a polymer is dissolved in an appropriate solvent, applied from the solution, and the solvent is removed by drying to obtain a film. Good results were obtained with both methods.

Since the polymer solid electrolyte before crosslinking has high viscosity in a molten state, it is preferable to cast it from a solution in order to obtain a uniform film. Examples of casting solvents used include alcohols such as ethanol, propatool and butanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as isopropyl acetate, and halogens such as dichloroethane. Uniform casting was achieved by using an applicator or by spin coating. The cast film was dried by heating below its melting point to remove the solvent.

The light sources that carry out the photocrosslinking reaction are visible light, ultraviolet light, X-rays, γ-rays,
An electron beam is used. The irradiation amount is 60% or more for the crosslinking reaction,
Preferably, the amount required is 80% or more. As a photoreaction sensitizer, for example, in the case of a polymer having a cinnamoyl group as a photosensitive group, a triple stack sensitizer was effective, and the photoreaction rate was doubled. As a sensitizer, one having absorption at a longer wavelength than the absorption wavelength of the photosensitive group or matching the maximum wavelength of the light source, such as 5-nitroacenaphthene, N
-Acetyl-4-nitro-1-naphthylamine and the like were effective.

The present invention will be explained in more detail with reference to Examples below.

Example 1 10 g of PE0-PPO block copolymer triol prepared by the above formula and 0.60 g of pyridine were mixed with 300 g of benzene.
1.03 g of cinnamic acid chloride dissolved in 20 cc of benzene was added dropwise at room temperature under an inert gas atmosphere, and the reaction was continued for 6 hours to obtain cinnamoylated PE0-PPO with a substitution rate of 95%. The obtained polymer was dissolved in methyl ethyl ketone to a concentration of 20%, and 0.04 mol of LiClO4 per ionically dissociated group (EO and po) and 5-nitroacenaphthene as a sensitizer were added to the cinnamoyl group. Dissolved 5 mol%, 50 μm
Casting was performed using an applicator. The cast film was dried at 30° C. for 20 minutes, and then irradiated with light at 10a+V/el12 for 10 minutes using a high-pressure mercury lamp to obtain a crosslinked product with a gelation rate of 85%.

The ionic conductivity of the obtained ion conductive composition was determined by the complex impedance method by sandwiching the sample between platinum plates.

Example 2 A reaction was carried out in the same manner as in Example 1 using acrylic acid chloride instead of cinnamic acid chloride, and the acrylic ester of the PE0-PPO block co-polymerized polymer (esterification rate 9
0%) was obtained. The obtained polymer was dissolved in dichloroethane for 2
0.04 mol of LiCIO4 per ion dissociative group and 5-nitroacenaphthene, a sensitizer, were dissolved at 5 mo1% relative to the acrylic acid group, and a 50 μm applicator, a catalytic converter, etc. Casting was done using. The obtained membrane was dried at room temperature for 20 minutes, photo-crosslinked in the same manner as in Example 1, and the ionic conductivity was measured.

Example 3 10 g of PE0-PPO block copolymer triol prepared by the above formula and 0.68 g of pyridine were mixed with 300 g of benzene.
1.17 g of cinnamic acid chloride dissolved in 20 cc of benzene was added dropwise at room temperature under an inert gas atmosphere, and the mixture was allowed to react for 6 hours to obtain cinnamoylated PE0-PPO with a substitution rate of 90%.

On the other hand, formula 110(EO)+z 1(PO)3 (EO
)+2) PE0-PPO block copolymer diol represented by 20H was similarly cinnamoylated.

The obtained two types of polymers were added to the same amount of methyl ethyl ketone.
The ion dissociative group (E
0.04 mol of LiClO4 per O and PO) and 5-nitroacenaphthene, a sensitizer, were dissolved at 5 mol% relative to the cinnamoyl group, and cast using a 50 μm applicator. The cast membrane is 30
Dry at ℃ for 20 minutes, then use a high-pressure mercury lamp to
mW/ea+'``t'' 10 minutes of light irradiation, gelation rate 9
096 (7) A crosslinked product was obtained.

The ionic conductivity of the obtained ion conductive composition was measured by a complex impedance method using a sample sandwiched between platinum plates.

Example 4 CI+2 (EO)220+1 1Qg of polyethylene oxide triol (average molecular weight 3000) represented by the above formula and 1.16 g of pyridine were dissolved in 300 cc of benzene, and 1.96 g of cinnamic acid chloride dissolved in 20 cc of benzene was stirred at room temperature. It was added dropwise under an active gas atmosphere and reacted for 6 hours to obtain cinnamoylated PEO with a substitution rate of 85% [Polymer (1)]
].

On the other hand, as in Example 1, cinnamoylated PEo-pp
An o block copolymer was obtained [Polymer (2)].

These polymers (1) and (2) were dissolved in equal amounts in methyl ethyl ketone to give a concentration of 20 νt%, and 0.04 mol of LiCl per ethylene oxide unit was dissolved therein.
O4 and 5-nitroacenaphthene, a sensitizer, were dissolved at 5 mol % relative to the photosensitive group, and cast using a 50 .mu.m applicator. The cast film is 3
Dry at 0°C for 20 minutes, then use a high-pressure mercury lamp to
A crosslinked product was obtained by irradiating with light for 10 minutes at 0 mν/cII12.

The ionic conductivity of the obtained ion conductive composition was measured by a complex impedance method using a sample sandwiched between platinum plates.

Example 5 10 g of PE0-PPO block copolymer triol represented by the above formula and 0.68 g of pyridine were added to 300 cc of benzene.
1.17 g of cinnamic acid chloride dissolved in 20 cc of benzene was added dropwise at room temperature under an inert gas atmosphere, and the mixture was allowed to react for 6 hours to obtain a cinnamoylated PE0-PPO block conjugate with a substitution rate of 85%. Ta.

On the other hand, PEO diol having a molecular weight of about 340 was similarly cinnamoylated. The obtained two types of polymers were dissolved in the same amount of methyl ethyl ketone to a concentration of 20 wt%, and 0.04 mol of LiC per unit of ethylene oxide was dissolved therein.
1O4 and 5-nitroacenaphthene, a sensitizer, were dissolved at 5 mol% relative to the photosensitive group, and a 50 μm applicator was cast using a paper towel. The cast film was dried at 30° C. for 20 minutes, and then irradiated with light using a high-pressure mercury lamp at lOn+W/cm 2 for 10 minutes to obtain a crosslinked product.

The ionic conductivity of the obtained ion conductive composition was measured by a complex impedance method using a sample sandwiched between platinum plates.

Example 6 The PE0-PPO block copolymerized triol log represented by the above formula and 0.88 g of pyridine were added to 300 cc of benzene.
1.17 g of cinnamic acid chloride dissolved in 20 cc of benzene was added dropwise at room temperature under an inert gas atmosphere, and the mixture was allowed to react for 6 hours to obtain a cinnamoylated PE0-PPO block Jljfff with a substitution rate of 85%. .

On the other hand, PPO diol having a molecular weight of about 440 was similarly cinnamoylated. The two types of polymers obtained are PE0-PP
O:PP0-6:4 was dissolved in methyl ethyl ketone to give a concentration of 20vt%, and 0.04 mol of LiClO4 per ethylene oxide unit and 5-nitroacenaphthene, a sensitizer, were added to the photosensitive group at a concentration of 5%. It was dissolved in mol% and cast using a 50μ applicator. The cast film was heated to 20°C at 30°C.
After drying for 1 minute, use a high-pressure mercury lamp to
A crosslinked product was obtained by irradiating with C112 for 10 minutes.

The ionic conductivity of the obtained ion conductive composition was measured by a complex impedance method using a sample sandwiched between platinum plates.

Example 7 In the PE0-PPO block copolymer triol used in Example 1, one branch chain was -(EO) + (PO
)(EO)+30i! Cinnamoylation was carried out in the same manner using Here, ion dissociative groups (EO, PO)
0.04 mol of LiC10+ and sensitizer per 5
- 5 mo of nitroacenaphthene to cinnamoyl group
It was dissolved at 1% and cast using a 50 μm applicator.

The cast film was dried at 30° C. for 20 minutes, and then irradiated with light at 1O*W/am 2 for 5 minutes using a high-pressure mercury lamp to obtain a crosslinked product.

The ionic conductivity of the obtained ion conductive composition was measured by a complex impedance method using a sample sandwiched between platinum plates.

Example 8 The PE0-PPO block copolymer triol used in Example 1 was similarly cinnamoylated using a diol in which the terminal of one branched chain was methoxylated. Here, an ionically dissociable group (EO) is added.

0.04 mol of LiClO4 per PO) and 5-nitroacenaphthene, a sensitizer, were dissolved in 1% 5IlIO with respect to the cinnamoyl group, and cast using a 50 μl applicator. The cast film is 3
After drying at 0°C for 20 minutes, I
A crosslinked product was obtained by irradiating with light at OmW/c+e' for 5 minutes.

The ionic conductivity of the obtained ion conductive composition was determined by ΔIII using a complex impedance method by sandwiching a sample between platinum plates.

Comparative Example 1 In Example 4, polymer (1) and polymer (2) were 3
A solid polymer electrolyte was prepared in the same manner except that the ratio was 72, and the ionic conductivity was determined by IIFJ.

Comparative Example 2 The cinnamoylated PEO [polymer (1)] prepared in Example 4 was dissolved in methyl ethyl ketone to a concentration of 20 vt%, and 0.04 mol of LiClO4 per ethylene oxide unit and 5-nitro sensitizer were added thereto. Acenaphthene is dissolved in 5 mol% based on the photosensitive group, and 50
Casting was performed using a μm applicator. The cast film was dried at 30° C. for 20 minutes, and then irradiated with light for 5 minutes using a high-pressure mercury lamp at 110 ml 1 x 112 to obtain a crosslinked product.

The ionic conductivity of the obtained ion conductive composition was measured by sandwiching the sample between platinum plates and using a multi-wire impedance method.

Comparative Example 3 10g of PEO triol used in Example 4)
0.85 g of 2,4-diisocyanate (0.01 g of dibutyltin dilaure) was dissolved in methyl ethyl ketone, and LiClO4 was added to give a concentration of 0.04 mol per ethylene oxide unit, followed by casting.
It was heated at 100°C for 20 minutes. Ionic conductivity was measured in the same manner as in Example 1.

The above measurement results are shown in the table below.

[Effects of the Invention] As explained above, the ion conductive composition according to the present invention has high ionic conductivity and excellent film forming and moldability, and can be used in various applications as a solid polymer electrolyte. It is useful for

Claims (1)

[Claims] In an ion-conducting composition comprising at least an electrolyte salt and a polymer matrix having a crosslinked structure formed by light irradiation, 50% by weight or more of the polymer matrix is a block copolymer of polyethylene oxide and polypropylene oxide. An ion conductive composition characterized by: