JPH07331019A - Polymeric solid electrolyte - Google Patents

Abstract

PURPOSE:To obtain a polymeric solid electrolyte, comprising a specific polymer and an electrolyte, having a high oxidative decomposition potential, excellent ionic conductivity, solvent and shape retaining properties, moldability and mechanical strength and suitable as a material, etc., for electrochemical devices. CONSTITUTION:This polymeric solid electrolyte is obtained by blending (A) 100 pts.wt. polymer having >=20wt.% structural unit of formula I, preferably a copolymer having preferably 5-70wt.% structural unit of formula II or preferably 2-60wt.% structural unit of formula III in the molecule with (B) preferably 300-400 pts.wt. electrolyte such as LiClO4. Furthermore, the polymer molecules are preferably mutually cross-linked with an oligomer having the structural unit of formula I in the molecule as the state of the polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer solid electrolyte, and more particularly to a polymer solid electrolyte having excellent ionic conductivity and suitable as a material for various electrochemical devices such as thin batteries.

[0002]

2. Description of the Related Art As solid electrolytes, polymer solid electrolytes are known to exhibit extremely high ionic conductivity even at room temperature, and are regarded as promising materials for various electrochemical devices such as batteries operating at room temperature. ing.

Conventionally, a base polymer of a polymer solid electrolyte is a polymer chain having a coordination ability with respect to a cation, which is composed of pseudosolvation by a non-shared electron pair such as oxygen, nitrogen, sulfur and molecular chain motion. Research has been conducted from the viewpoint of efficiently carrying out the ion conductivity of the. From this point of view, as the base polymer, a polymer having a low Tg and a high amorphous property at room temperature, for example, a chain polyether and a crosslinked product thereof, and the compounding ratio of the polymer / electrolyte solution is 8/2
(Weight ratio) polyacrylonitrile (PAN) gel, polymer particles of styrene-butadiene rubber / nitrile-butadiene rubber (SBR / NBR) latex, etc. were preferably selected and used. The polymer solid electrolyte has been produced, for example, by mixing the above-mentioned polymer with the electrolyte and molding it into an arbitrary shape or size such as a sheet or a film, or by impregnating the molded product of the above-mentioned polymer with the electrolyte.

[0004]

However, since the conventional polymer solid electrolyte has the above-mentioned base polymer as the main composition, its ionic conductivity is 10 ^-4 S / S.
It was below cm. In addition, the PAN gel is a carcinogen and has a problem in its use, and also tends to undergo phase separation. Furthermore, the polymer solid electrolyte prepared from the PAN gel has low mechanical strength, and battery production is difficult. There was a problem above.
In addition, when a sheet-shaped solid electrolyte is molded using the SBR / NBR latex, for example, a sheet thickness of less than 100 μm is usually required in the production of a thin battery, but there is a problem that the thickness is 100 μm or more. . An object of the present invention is to solve the above problems and provide a polymer solid electrolyte having a high ionic conductivity, which is particularly suitable for producing a thin battery.

[0005]

Means and Actions for Solving the Problems
In order to solve the above problem, the amount of solvent held by the base polymer is increased, and Li ions are allowed to move in the solvent, thereby focusing on improving the ionic conductivity of the solid polymer electrolyte. Overlaid. As a result,
The solvent retention ability is affected by the polar strength of the polar group in the polymer molecule. For example, in the case of —O— group such as chain polyether, the polarity is too low and the solvent retention is insufficient, while the chain It has been found that the -OH group of the solid polyol has a solvent-holding ability, but has too strong a polarity to be dissolved in a limited liquid such as hot water, resulting in poor processability.

The present invention has been completed based on the above findings, and a polymer obtained by introducing a specific amount of a specific polar group having optimum polar strength for solvent retention into a molecule is prepared as a polymer solid electrolyte. It is characterized by being used as a base polymer. That is, the polymer solid electrolyte of the present invention comprises an electrolyte and a polymer containing at least 20% by weight of the structural unit represented by the formula (I) in the molecule.

[0007]

[Chemical 5]

In the above polymer, the content of the structural unit (hereinafter sometimes referred to as acrylonitrile unit) in the molecule is at least 20% by weight,
Preferably 20-80% by weight, more preferably 40-6
About 0% by weight is suitable. When the amount of the acrylonitrile unit is less than 20% by weight, the amount of the solvent retained in the whole polymer becomes small, which is not preferable.

The molecular weight of the above polymer is usually 40,000.
0 to 140,000, preferably 60,000 to 12
30,000, particularly preferably 80,000 to 100,0
It is preferably about 00.

According to the above-mentioned polymer, since the specific polar group (--CN) is introduced into the molecular chain of the polymer, the interaction between the polymer and the solvent for the electrolyte is improved, so that the weight of the polymer is at least several times its own weight. The electrolyte can be retained. Further, since the binding energy of the CN portion that interacts with the electrolytic solution or the electrolyte salt is larger than the carbon-oxygen bond of the polar portion of the conventional electrolyte polymer, the oxidative decomposition potential can be increased. Therefore, Li ions of the electrolyte move through the solvent retained in the polymer in a large amount, so that the ion conductivity of the solid polymer electrolyte can be significantly improved.

According to the present invention, the polymer solid electrolyte has a moldability,
In order to impart shape retention, it is preferable to use, as the base polymer, a copolymer having the acrylonitrile unit and the structural unit represented by the formula (II) (hereinafter sometimes referred to as butadiene unit).

[0012]

[Chemical 6]

In the copolymer, the content of the butadiene unit in the molecule is usually 80% by weight or less, preferably about 5 to 70% by weight. When the content of the butadiene unit exceeds 80% by weight, the solvent retention tends to decrease, and when it is less than 5% by weight, the elongation of the material decreases.

Further, in the present invention, in order to impart mechanical strength to the solid polymer electrolyte, the base polymer may be of the formula (III) in addition to the acrylonitrile unit.
It is preferable to use a copolymer having a structural unit represented by (hereinafter sometimes referred to as a styrene unit).

[0015]

[Chemical 7]

In the copolymer, the content of the styrene unit in the molecule is usually 80% by weight or less,
About 20 to 60% by weight is preferable. If the styrene unit exceeds 80% by weight, the solvent retention tends to decrease, and if it is less than 20% by weight, the improvement in resistance to pulling, bending, twisting and the like is small.

In the solid polymer electrolyte of the present invention, when a copolymer having all of the above acrylonitrile unit, butadiene unit and styrene unit is used as the base polymer, solvent retention, moldability, shape retention of the polymer solid electrolyte, It is preferable because mechanical strength and the like are improved. In the copolymer, the content of each of the acrylonitrile unit, the butadiene unit and the styrene unit in the molecule is 20% by weight or more of acrylonitrile unit, preferably 20 to 80% by weight, and 80% by weight or less of butadiene unit, preferably Is 5 to 70% by weight, and the styrene unit is 80% by weight or less, preferably about 20 to 60% by weight.

Specific examples of the polymer having the above structural unit used in the present invention include acrylonitrile-butadiene copolymer (NBR), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile-styrene copolymer (AS). ), Acrylonitrile-acrylic rubber-styrene copolymer (AAS), acrylonitrile-chlorinated polyethylene-styrene copolymer (AC
S) and the like.

When the copolymer having the butadiene unit is treated with ozone, the double bond portion in the structural unit is cleaved and the cleaved terminal portion is converted into carbonyl as shown in the following formula. Thus, the polarity of the base polymer itself is increased, the solvent retention ability is improved, and the ionic conductivity can be further improved.

[0020]

[Chemical 8]

The ozone treatment is carried out by irradiating the base polymer with ozone generated by an ozone generator or the like for about 1 to 2 hours.

Further, in the solid polymer electrolyte of the present invention, the base polymer is such that the polymer state has a structural unit (acrylonitrile unit) represented by the formula (I) in the molecule between the polymers having the above structural unit. A crosslinked polymer obtained by crosslinking with an oligomer is preferably used.

[0023]

[Chemical 9]

As the oligomer, acrylonitrile having a structural unit represented by the above formula (I) is prepared by a known method such as radical polymerization or anionic polymerization to obtain a polymerization degree of 10
-100, preferably 20-90, more preferably 25
What was polymerized to -50 is used. When the degree of polymerization is less than 10, since the chain of the molecular chains is too small, the solvent-holding ability of the crosslinked polymer is not sufficiently improved.
If it exceeds, the entanglement of the molecular chains becomes the main and the solvent holding space in the rope portion tends to be difficult to expand.

Since a molecular network is formed in this crosslinked polymer, the solvent retention ability is improved. Further, since the polar group --CN group is present in the crosslinked chain, the solvent retention ability is further improved, and the solvent can be retained by about 10 times the dead weight of the crosslinked polymer. Further, since the molecular network is large, the Li ions of the electrolyte can easily move through the gap, and the ionic conductivity can be greatly improved.

The crosslinked polymer crosslinked with the specific oligomer having the --CN group is produced, for example, by the following method. When a polymer having the above-mentioned structural unit having a carboxyl group introduced in its molecule, for example, NBR latex (particles) having a carboxyl group introduced on its surface is crosslinked with an acrylonitrile oligomer, the carboxyl group is reacted with thionyl chloride or the like to obtain an acid chloride. Turn into. On the other hand, the acrylonitrile oligomer is reduced with lithium aluminum hydride at room temperature to convert only the terminal nitrile group into an amino group. Crosslinked NBR latex by heating and refluxing the acid chloride-modified NBR latex (particles) and an acrylonitrile oligomer having terminal amino groups in an alkali dilute solution such as NaOH or KOH having a pH of 10 to 2 for 2 to 6 hours. (Particles) are obtained.

The above-mentioned example is an example, and in the present invention, any cross-linked polymer obtained by cross-linking between the polymers with the oligomer having the acrylonitrile unit may be produced by any method.

The solid polymer electrolyte of the present invention comprises the above-mentioned polymer (copolymer) or cross-linked polymer (copolymer) mixed with an electrolyte, and is molded into a desired shape. The electrolyte is not particularly limited, and generally, for example, cations such as Li ion, Na ion and K ion, and I ion, CF ₃ SO ₃ ion, BF ₄ ion, ClO ₄ ion, AlCl ₄ ion, PF ₆ An alkali metal salt or the like formed of a combination of an ion and an anion such as AsF ₆ ion is used. Specifically, for example, Li
ClO ₄ , LiI, LiBF ₄ , LiPF ₆ , LiAs
F _6, LiAlCl _4, LiCF ₃ metal salts of SO ₃ can be suitably used.

In the present invention, the above electrolyte is used as ethylene carbonate, propylene carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolane, 2-methyl. Used as an electrolyte dissolved in one or a mixture of two or more organic solvents such as tetrahydrofuran and diethyl ether. The electrolytic solution is usually prepared to have a concentration of 0.1 to 3 mol / liter.

The amount of the above-mentioned electrolyte compounded is appropriately determined depending on the ionic conductivity of the intended solid polymer electrolyte, etc., but is usually 100 to 500 parts by weight, preferably 100 to 500 parts by weight, based on 100 parts by weight of the base polymer. 300-400
It is compounded in parts by weight.

In the solid polymer electrolyte of the present invention, a base polymer is made into a suitable organic solvent solution such as dimethylformamide, if necessary, and the electrolytic solution is mixed, followed by a casting method, a pressing method, or a gelling agent. By a suitable molding method such as a sheet-like elastic body method by mixing,
It is manufactured into a desired shape and size such as a film or sheet. At this time, the base polymer may be appropriately crosslinked and then molded. Also, the base polymer is molded by the above method, and then the molded body is doped with an ion carrier by a known method such as immersing the molded body in an electrolytic solution.

When the solid electrolyte is in the form of a film or sheet, its thickness is usually 5 mm or less, preferably 10 mm.
It is set to μm to 1 mm.

In the molding of the above-mentioned solid polymer electrolyte, a hydrogel can be optionally used in combination with the base polymer when the electrolytic solution is blended. The combined use of this hydrogel is preferable because it improves the ionic conductivity of the solid polymer electrolyte.

Examples of the hydrogel include polyacrylic acid, saponified starch / acrylonitrile graft copolymer, starch / acrylic acid graft copolymer, carboxymethylcellulose / isobutylene / maleic acid copolymer, vinyl acetate / acrylic acid ester copolymer. A saponified polymer, polyvinyl alcohol, etc. can be used.

The amount of the hydrogel used is 1 to 100 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of the base polymer.

The polymer solid electrolyte of the present invention is 10 ^-3 S / when measured with an AC impedance analyzer.
Since it has a high ionic conductivity in the cm order, it is useful for various electrochemical devices such as thin film batteries, sensors, displays and capacitors.

[0037]

EXAMPLES Hereinafter, the present invention will be described more specifically by showing examples. Needless to say, the present invention is not limited to these examples. Example 1 Commercially available NBR (trade name N220S Japan Synthetic Rubber (JS
R) (manufactured by R): acrylonitrile amount 41% by weight) was purified by reprecipitation and dissolved in tetrahydrofuran (THF) to prepare a 10% by weight solution. 1 of the same amount as THF
A propylene carbonate solution of LiClO _{4 having} a molar concentration was added and sufficiently stirred. This mixed solution was transferred to a Teflon dish and heated at 100 ° C. for 120 minutes to remove THF to prepare a sheet having a thickness of about 100 μm.

Example 2 Acrylonitrile / butadiene 8/2 (weight ratio) copolymer synthesized by emulsion polymerization [acrylonitrile amount 50
% By weight] 100 parts by weight was dissolved in 1,4-dioxane to give a 20% by weight solution. A 1: 1 (weight ratio) mixed solution of ethylene carbonate / dimethyl carbonate of LiClO ₄ having the same amount as dioxane and a molar ratio of 1/1, and 10 parts by weight of dicumyl peroxide as a cross-linking agent were added thereto and stirred sufficiently. When this mixed solution was transferred to a Teflon dish and heated at 150 ° C. for 120 minutes to remove 1,4-dioxane, a sheet having a thickness of about 200 μm was obtained. This was further pressed and heat-molded by a pressing machine to prepare a crosslinked sheet having a thickness of about 100 μm.

Example 3 An ozone generator was applied to the sheet prepared in Example 1
Irradiated with ozone for hours. Use this sheet to add 1 molar L
When immersed in 200 parts by weight of a propylene carbonate solution of iClO ₄ and allowed to stand for a day and night, the electrolyte solution was further absorbed and retained.

Example 4 A commercially available ABS resin (trade name N220S manufactured by Nippon Synthetic Rubber Co., Ltd.) [acrylonitrile amount of 40% by weight] was swollen with dioxane and left for one day and one night.
A 1/1 (weight ratio) mixed solution of ethylene carbonate / dimethyl carbonate having a molar concentration of LiClO ₄ was added, and the mixture was sufficiently stirred. The obtained mixture was sandwiched between Teflon sheets and compressed by a hand press to prepare a sheet having a thickness of 100 μm.

Example 5 A commercially available NBR latex having a surface modified with a carboxyl group (manufactured by Zeon Corporation: acrylonitrile amount 40% by weight,
100 parts by weight of thionyl chloride was added to 100 parts by weight of the resin solid content (50% by weight) to convert the carboxyl group into an acid chloride. When 50 parts by weight of separately prepared acrylonitrile oligomer polymerized to a polymerization degree of 20 was reduced with lithium aluminum hydride at room temperature, only the terminal nitrile group could be converted to an amino group due to steric hindrance. Then, the acid chloride NBR latex and the terminal aminated acrylonitrile oligomer were reacted in a dilute solution of NaOH (pH 10) for 4 hours to obtain a crosslinked NBR (gel substance). After sufficiently swelling 10 parts by weight of the crosslinked NBR with 90 parts by weight of tetrahydrofuran, a propylene carbonate solution of 1 molar LiClO ₄ was added to the crosslinked NBR.
Four times the amount (weight) of BR (gel-like substance) was added, and the mixture was sufficiently stirred. The obtained mixture was sandwiched between Teflon sheets and compressed by a hand press to prepare a sheet having a thickness of 100 μm.

Comparative Examples 1-2 Polyethylene oxide was used to cast a film having a thickness of 100 μm (Comparative Example 1) by the casting method, and similarly to Example 4 described above, a hand pressing method was used to obtain a thickness of 100 μm.
Press sheets (Comparative Example 2) were prepared. The above film and sheet were immersed in a 1 molar LiClO ₄ propylene carbonate solution for 12 hours to obtain L
A polymer solid electrolyte doped with i ions was prepared.

(Measurement of Electrolyte Retaining Ability) The weight of the raw material polymer and the weight of the obtained electrolyte sheet were measured and compared, and the electrolyte retaining capacity of each of the base polymers used in Examples 1 to 5 and Comparative Example was measured. Was measured and found to be as shown in Table 1. In addition, the amount of retained electrolyte is shown assuming that the polymer weight is 1.

(Measurement of Ionic Conductivity) Examples 1 to 5 above
The ionic conductivity of each of the polymer solid electrolytes prepared in Comparative Examples was measured with an AC impedance analyzer, and the results shown in Table 1 were obtained.

[0045]

[Table 1]

As is clear from Table 1 above, the polymer solid electrolytes obtained in the examples all have ionic conductivity
The value was on the order of 10 ⁻³ S / cm, which was a high value close to the ionic conductivity of the electrolyte solution shown in the reference.

Example 6 Lithium carbonate, basic cobalt carbonate and phosphorus content 85%
Lithium / cobalt / phosphorus composite oxide prepared by heating up to 900 ° C. in an electric furnace after weighing the phosphoric acid and the phosphoric acid in the atomic ratio of Li: Co: P = 2: 1: 1. Using the material Li as the negative electrode and the sheet prepared in Example 5 as the electrolyte, the oxidation-reduction reaction was monitored by cyclic voltammetry, but a peak showing decomposition appeared even when 6 V was applied between the electrodes. There wasn't.

[0048]

The polymer solid electrolyte of the present invention uses as a base polymer a polymer in which a specific amount of an acrylonitrile unit having a nitrile group having an excellent electrolyte retaining ability is introduced into the polymer molecule. It becomes possible to retain twice to ten times as much electrolytic solution, and shows an ionic conductivity of the order of 10 ⁻³ S / cm, which is the same level as the ionic conductivity of the electrolytic solution.

Further, a polymer solid electrolyte using a polymer in which a specific amount of an acrylonitrile unit having a nitrile group in the molecule is introduced into the polymer molecule has a higher oxidative decomposition potential, so that it is used in, for example, a battery. Thus, a high electromotive force type battery is obtained. Further, since the solid polymer electrolyte is excellent in moldability and a thin film such as a sheet or a film can be easily molded, a thin battery can be obtained by using this as a battery, for example.

As described above, the solid polymer electrolyte of the present invention has a high ionic conductivity, a high oxidative decomposition potential and an excellent moldability, and thus is particularly useful for producing a thin high electromotive force type battery. .

Claims (4)

[Claims] 1. A solid polymer electrolyte comprising a polymer containing at least 20% by weight of the structural unit represented by formula (I) in the molecule, and an electrolyte. [Chemical 1] 2. The polymer solid electrolyte according to claim 1, wherein the polymer is a copolymer having a structural unit represented by the formula (II). [Chemical 2] 3. The polymer according to claim 1, which is a copolymer having a structural unit represented by the formula (III).
The polymer solid electrolyte described. [Chemical 3] 4. The polymer solid electrolyte according to claim 1, wherein the state of the polymer is a crosslinked polymer obtained by crosslinking between the polymers with an oligomer having a structural unit represented by the formula (I) in the molecule. [Chemical 4]