JP2003257236A - Polymer solid electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer solid electrolyte that has a sufficient ion conductivity and mechanical property, and is flexible and superior in molding processing. <P>SOLUTION: This is a polymer solid electrolyte that contains a cross-linked substance (A) made by cross-linking an enclosure compound in which a linear macromolecule is enclosed by a cyclomolecule and which has a substitutional group at both ends of the linear macromlecule and an electrolyte salt compound (B). As the above cyclomolecule, cyclodextrin is desirable and as a liner macromolecule, polyethyleneglycol is desirable. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polymer solid electrolyte, and more particularly to a polymer solid electrolyte useful as an ion conductor of an electrochemical device such as a lithium ion secondary battery.

[0002]

2. Description of the Related Art Conventionally, solutions or pastes have been used as electrolytes that constitute electrochemical devices such as batteries, capacitors and sensors. Although these electrolytes have excellent ionic conductivity, they may cause damage to equipment due to liquid leakage, problems with device mounting and workability, and limitations on device miniaturization and thinning. Problems have been pointed out.

In contrast, inorganic crystalline substances, inorganic glass,
Solid electrolytes such as polymeric substances have been proposed. Among these, polymer materials are generally excellent in workability and moldability, the resulting solid electrolyte has flexibility and bendability,
From the viewpoint of increasing the degree of freedom in the design of applied devices, the development of polymer solid electrolytes is expected.

As such a polymer solid electrolyte, for example, an attempt has been already made to apply a specific alkali metal salt to a polyether polymer as an ionic conductor and apply it to an electrochemical device ( JP-A-61-83
249, JP-A-63-136407, JP-A-2-2
4975, JP-A-2-56870, etc.). However, it is difficult to say that the polymer solid electrolyte has satisfactory ionic conductivity and mechanical properties, and more excellent ones are required.

Further, in widely applying the polymer solid electrolyte to electrochemical devices, it is also desired to have sufficient flexibility. It is generally known that the addition of a plasticizer is advantageous for imparting flexibility to a polymer substance, but a polymer solid composed of a polyether polymer and an alkali metal salt as described above. When a plasticizer is added to the electrolyte, there is a problem that the ionic conductivity is significantly reduced.

[0006]

In view of the above-mentioned circumstances and problems of the prior art, an object of the present invention is to have sufficient ionic conductivity and mechanical properties, yet to be flexible and to have good moldability. Another object is to provide an excellent polymer solid electrolyte.

[0007]

Means for Solving the Problems The present inventor has been attracting attention as a compound in which a linear polymer is included in a skewered state in a cyclic molecule such as cyclodextrin, a so-called "rotaxane type structure" or "polyrotaxane" in recent years. The clathrate compound having a unique structure and its cross-linked product have been studied intensively for application to solid electrolytes and electrochemical devices.

As a result, a cross-linked product of the above-mentioned clathrate compound, in particular, a linear polymer constituting the cross-linked product is a polyether polymer having substituents at both ends, and an electrolyte salt compound are obtained. The inventors have found that a polymer solid electrolyte prepared in combination can solve the above-mentioned problems, and completed the present invention.

Thus, according to the present invention, a crosslinked product (A) in which a linear polymer is included in a cyclic molecule and an inclusion compound having a substituent at both ends of the linear polymer is crosslinked. )
And a polymer solid electrolyte containing the electrolyte salt compound (B). Cyclodextrin is preferred as the cyclic molecule. Further, polyethylene glycol is preferable as the linear polymer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The solid polymer electrolyte of the present invention comprises a cyclic molecule in which a linear polymer is clathrated, and a clathrate compound having a substituent at both ends of the linear polymer is crosslinked. And the electrolyte salt compound (B).

The inclusion compound is a rotor composed of a cyclic molecule and an axis composed of a linear polymer.
And a rotaxane type structure in which the shaft is end-capped so that the rotor cannot be detached from the shaft.

The rotor is not particularly limited as long as it is a cyclic molecule, and for example, α-cyclodextrin, β-
Cyclodextrins such as cyclodextrin and γ-cyclodextrin, and crown ethers can be mentioned. Of these, cyclodextrin is preferable, and α
-Cyclodextrin is more preferred.

The axis is not particularly limited as long as it is a linear polymer. For example, polyethers such as polyethylene glycol, polypropylene glycol and polytetrahydrofuran; polyolefins such as polyethylene and polypropylene; carboxymethyl cellulose and hydroxyethyl cellulose. , Celluloses such as hydroxypropyl cellulose; Among them, polyethers are preferable, and polyethylene glycol is more preferable.

The clathrate compound used in the present invention is a compound in which a linear polymer is included in the cyclic molecule in a skewered manner. There is no particular limitation on the method of including the linear polymer in the skewered state in the cyclic molecule, and a known method can be applied. When α-, β- or γ-cyclodextrin is used as the cyclic molecule and polyethers are used as the linear polymer, both components are stirred and mixed in an aqueous medium to obtain a reaction. Especially when polypropylene glycol is used as the linear polymer, it may be in a dispersed state.
Ultrasonic agitation is preferred.

The reaction temperature in the above reaction is not particularly limited and is usually 0 ° C to 100 ° C, preferably 10 ° C to 80 ° C. The reaction time is not particularly limited, usually 1 second to 10 days,
It is preferably 10 seconds to 1 day. The reaction product (inclusion compound) can be isolated by reprecipitation, filtration, centrifugation, membrane separation using an ultrafiltration membrane or the like.

In the clathrate compound used in the present invention, it is necessary that the cyclic molecule serves as a cross-linking point to form a network between the clathrate compounds, while the cyclic molecule can move freely on the linear polymer. . Therefore, the linear polymer needs to have a high molecular weight to some extent, and it is preferable that the cyclic molecules are loosely included, that is, the linear polymer is in a bare state to some extent. The number average molecular weight of the linear polymer is preferably 1,000 to 1,000,000, more preferably 5,000 to 500,000, and particularly preferably 10,000 to 300,000.

The ratio of the linear polymer to the cyclic molecule in the clathrate compound is a ratio of (the number of moles of monomer units constituting the linear polymer) :( the number of cyclic molecules), preferably 100: 1.
-100: 50, more preferably 100: 2-100:
40, particularly preferably 100: 3 to 100: 30.

If the ratio of the number of cyclic molecules is too small, the crosslinking may be insufficient, the shape retention may be deteriorated, and the liquid may be easily liquefied at a high temperature. On the other hand, if the proportion of cyclic molecules is too high, the movement of the cyclic molecules on the linear polymer is hindered, so that cross-linking becomes non-uniform and the mechanical strength may decrease. The ratio of the linear polymer to the cyclic molecule can be measured by ¹ H- and ¹³ C-NMR spectra, light absorption, elemental analysis and the like.

The inclusion compound used in the present invention has a substituent at both ends of the linear polymer. The substituent is preferably bulky. Preventing the cyclic molecule from being eliminated from the linear polymer by enclosing the linear polymer in the cyclic molecule as described above and then substituting both ends of the linear polymer with bulky substituents. be able to.

The bulky substituent is appropriately selected depending on the size of the opening of the cyclic molecule. Specifically, for example, 2, 4
-Dinitrophenyl group, 3,5-dinitrophenyl group,
Examples thereof include nitrophenyl groups such as 2,4,6-trinitrophenyl group; trimethylphenyl group (trityl group) and dansyl group represented by the chemical formula of "Chemical Formula 1" below.

[0021]

[Chemical 1]

The method of substituting both ends of the linear polymer with bulky substituents is not particularly limited. For example, polyethylene glycol bisamine having amino groups at both ends of polyethylene glycol is used as a linear polymer, and the amino groups at both ends are further reacted with 2,4-dinitrophenyl fluoride to obtain the bulky blocking group. The terminal can be substituted with a 2,4-dinitrophenyl group as. Further, if trityl bromide, dansyl chloride, 2,4,6-trinitrophenyl fluoride, or the like is used instead of the above 2,4-dinitrophenyl fluoride, a trityl group, a dansyl group, or 2,
The ends can be replaced with 4,6-trinitrophenyl groups.

Crosslinked product (A) of the clathrate compound used in the present invention
Can be obtained by crosslinking using the cyclic molecule in the clathrate compound as a crosslinking point. The cross-linking agent is not particularly limited, and known ones can be used. Specific examples thereof include cyanuric chloride, trimesic acid chloride, terephthalic acid chloride, epichlorohydrin, dibromobenzene, glutaraldehyde, phenylene diisocyanate, tolylene diisocyanate, 1,1′-carbonyldiimidazole, divinyl sulfone, tetramethoxy. Examples thereof include silane and tetraethoxysilane.

As the conditions for the crosslinking reaction, known methods can be adopted. For example, when using α-cyclodextrin as the cyclic molecule and crosslinking the inclusion compound using polyethylene glycol whose both ends are substituted as the linear polymer, the inclusion compound is dissolved in an alkaline aqueous solution and The crosslinking reaction can be carried out by adding epichlorohydrin or cyanuric chloride and stirring at room temperature. Further, even when dimethyl sulfoxide is used as the solvent and 1,1′-carbonyldiimidazole or tolylene diisocyanate is used as the crosslinking agent, the crosslinking reaction can be similarly performed.

The crosslinked product (A) of the clathrate compound obtained by crosslinking in this manner can be directly used for the production of the solid polymer electrolyte, but the unreacted compound remaining in the crosslinked product by dialysis or the like. It is preferable to remove the cross-linking agent and by-products for purification. It is also preferable to remove the solvent used for the crosslinking reaction and purification by a known method such as drying under reduced pressure.
By thus purifying and drying the crosslinked product, the ion conductivity of the solid polymer electrolyte can be increased.

The electrolyte salt compound (B) used in the present invention is soluble in the crosslinked product (A) of the clathrate compound, and when combined with the crosslinked product (A),
The solid electrolyte is not particularly limited as long as it exhibits ionic conductivity.

Examples of such an electrolyte salt compound (B) include cations selected from metal cations, ammonium ions, amidinium ions and guanidinium ions, and chlorine ions, bromine ions, iodine ions and perchloric acid. Ion, thiocyanate ion, tetrafluoroborate ion, nitrate ion, AsF ₆ ⁻ , PF ₆ −, stearylsulfonate ion, octylsulfonate ion, dodecylbenzenesulfonate ion, naphthalenesulfonate ion, dodecylnaphthalenesulfonate ion, 7,
7,8,8-tetracyano-p-quinodimethane ion,
X ¹ SO ₃ ⁻ , [(X ¹ SO ₂ ) (X ² SO ₂ ).
N] ⁻ , [(X ¹ SO ₂ ) (X ² SO ₂ ) (X ³ S
O ₂ ) C] ⁻ , and [(X ¹ SO ₂ ) (X ² SO ₂ ).
YC] ⁻ and an anion selected from the above.

However, the above X¹, X^Two, X^ThreeAnd Y is
It is an electron-withdrawing group. Preferably X ¹, X^TwoAnd X^Three
Are each independently a perfluoroalkyl group having 1 to 6 carbon atoms.
Alkyl group or perfluoroaryl group, and Y is
Toro group, nitroso group, carbonyl group, carboxyl group,
Alternatively, it is a cyano group. X¹, X^TwoAnd X^ThreeIs it
They may be the same or different.

As the metal cation, for example, a cation of a transition metal can be used. Preferably M
It is a cation of a metal selected from n, Fe, Co, Ni, Cu, Zn and Ag. In addition, Li, Na, K, R
It is also recommended to use a cation of a metal selected from b, Cs, Mg, Ca and Ba, more preferably Li, N
It is a cation of a metal selected from a and K.

As the electrolyte salt compound (B), the compound consisting of the above-mentioned cation and anion may be used alone or in the form of 2
More than one kind can be used together. The amount of the electrolyte salt compound (B) used is usually 1 to 30% by weight, preferably 3 to 20% by weight, based on the crosslinked product (A) of the clathrate compound. If the amount of the electrolyte salt compound (B) used is too large, the processability, moldability or mechanical strength of the solid electrolyte may be impaired. In addition, the ionic conductivity may decrease.

In the solid electrolyte of the present invention, a plasticizer is preferably used in order to enhance the ionic conductivity and improve the flexibility. As such a plasticizer, known ones can be appropriately selected and used. For example, an aprotic organic solvent; a linear or branched polyalkylene glycol or a derivative thereof or a metal salt thereof; Is mentioned.

Examples of the aprotic organic solvent used as the plasticizer include propylene carbonate and γ-
Butyrolactone, butylene carbonate, 3-methyl-
2-oxazoline, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether and the like can be mentioned.

The linear or branched polyalkylene glycol has, for example, a weight average molecular weight of 200 to 200.
Examples thereof include polyethylene glycol or polypropylene glycol of 5000, and the derivatives thereof include ester derivatives or ether derivatives having an alkyl group having 1 to 8 carbon atoms or an alkenyl group having 3 to 8 carbon atoms, and its metal salt is sodium salt. , Lithium, dialkyl aluminum salts, and the like. Examples of the metal salt of the polyalkylene glycol derivative include polyethylene glycol monomethyl ether, polyethylene glycol monoethyl ether or polyethylene glycol monoallyl ether dioctylaluminum salt.

The mixing ratio of such a plasticizer can be appropriately selected, but is 0 to 2000 parts by weight, preferably 1 to 1000 parts by weight, relative to 100 parts by weight of the crosslinked product (A) of the clathrate compound.
It is more preferably 2 to 500 parts by weight.

When flame retardancy is required when using the solid electrolyte of the present invention, a commonly used flame retardant method can be adopted. For example, a brominated epoxy compound,
An effective amount of a known flame retardant such as tetrabromobisphenol A, chlorinated paraffin, antimony trioxide, antimony pentoxide, aluminum hydroxide, magnesium hydroxide, phosphoric acid ester, polyphosphate and zinc borate may be added.

The method for producing the solid electrolyte of the present invention is not particularly limited. For example, a method of mechanically mixing the crosslinked product (A) of the inclusion compound and the electrolyte salt compound (B); an electrolyte salt in a suitable solvent. A method of dissolving the compound (B) and immersing the crosslinked product (B) of the clathrate compound in the solution; dissolving the crosslinked product (A) of the clathrate compound and the electrolyte salt compound (B) in a solvent or And the like. After being suspended and mixed, the solvent is removed.

As means for mechanically mixing the crosslinked product (A) of the clathrate compound and the electrolyte salt compound (B), various kneaders, open rolls, extruders and the like can be arbitrarily used. Further, when the solid electrolyte of the present invention is produced using a solvent, various polar solvents such as tetrahydrofuran, acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide, dioxane, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol diethyl ether, etc. Can be used alone or as a mixture.

Since the solid polymer electrolyte of the present invention has high ionic conductivity, appropriate flexibility for adhering to electrodes, and moldable strength, it can be used in various applications such as thin batteries. It is also useful as a material for electrochemical devices such as electrochromic displays, electric double layer capacitors, and various sensors.

When the polymer solid electrolyte of the present invention is applied to a battery, the type of battery is not particularly limited, and examples thereof include alkali metal batteries such as lithium, potassium and sodium, zinc-silver chloride, magnesium-silver chloride, Examples thereof include halogen salt batteries such as magnesium-copper chloride, and proton-conducting batteries such as nickel-hydrogen batteries. Among these, the lithium battery is suitable because it has high voltage and high energy and the conductivity of lithium ion is high in the present solid electrolyte.

When a battery using the polymer solid electrolyte of the present invention is prepared, the positive electrode material is a lithium-manganese composite oxide, a lithium-vanadium composite oxide, lithium cobalt oxide, lithium nickel oxide, cobalt-substituted nickel. Lithium acid, polyacene, polypyrene, polyaniline, polyphenylene, polyphenylene sulfide, polyphenylene oxide, polypyrrole, polyfuran,
Polyazulene or the like is used.

Examples of the negative electrode material include an intercalation compound in which lithium is inserted between graphite or carbon layers, lithium metal, lithium-lead alloy, and the like. Further, by utilizing the high ionic conductivity of the present solid electrolyte, use of cations such as alkali metal ions, Cu ions, Ca ions and Mg ions as a diaphragm of the ion electrode can be considered.

[0042]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Parts and% in these examples are by weight unless otherwise specified.

The evaluation method of the polymer solid electrolyte is shown below. (1) Measurement of ionic conductivity Films vacuum dried at 30 ° C. and 0.1 kPa or less for 72 hours are sandwiched between platinum electrodes, voltage 0.5 V, frequency range 5
It was calculated by the complex impedance method using the alternating current method of Hz to 13 MHz. (2) Strength Measurement of Polymer Solid Electrolyte Film A film having a width of 7 mm and a length of 30 mm was gripped by both hands and pulled. The film strength was evaluated according to the following 3 grade criteria based on the breaking condition. ◯: Stretched well and did not break easily. Δ: Fractured relatively easily. X: Fractured with almost no elongation.

(Example 1) The following crosslinked product of the clathrate compound was prepared according to the method described in WO01 / 83566. First, 0.9 part of polyethylene glycol bisamine having a number average molecular weight of 20,000 and 3.6 parts of α-cyclodextrin were added to 30 parts of water and heated to 80 ° C. to be dissolved. The solution was cooled and stood at 5 ° C. for 12 hours. The white paste-like precipitate generated is collected, dried,
The mixture was added to a mixed solution of 2.4 parts of 2,4-dinitrofluorobenzene and 10 parts of dimethylformamide and stirred at room temperature for 15 hours. Dimethylsulfoxide (D
MSO) (40 parts) was added and dissolved, and then the mixture was poured into 800 parts of a 0.1% concentration saline solution to separate the precipitate. 50 deposits
Redissolved in 800 parts of DMSO, then again 800 parts of 0.1%
The precipitate was collected by pouring into saline. The precipitate was washed with water and methanol three times each and then vacuum dried at 50 ° C. for 12 hours. In this way, 3 parts of an inclusion compound in which polyethylene glycol bisamine was included in α-cyclodextrin in a skewered form and 2,4-dinitrophenyl groups were bonded to both terminal amino groups was obtained. The composition ratio of the clathrate compound determined by ¹ H-NMR measurement is the ratio of the number of moles of ethylene oxide unit: the number of α-cyclodextrin molecules,
It was 100: 14.

1 part of this clathrate compound was dissolved in 5 parts of an aqueous solution of sodium hydroxide having a concentration of 1 mol / liter, and 0.35 part of cyanuric chloride (crosslinking agent) was added to 5 parts of an aqueous solution of sodium hydroxide having a concentration of 1 mol / l. After mixing with the dissolved solution,
The mixed solution was poured evenly on the nickel plate. After standing at room temperature for 10 hours, the thin film of the cross-linked product formed on the nickel plate was peeled off, sufficiently dialyzed in water and dried at 100 ° C. The thin film thus obtained was immersed in a 3% dimethylsulfoxide solution of LiBF ₄ for 8 hours under a dry argon gas atmosphere. Dimethyl sulfoxide was removed by evaporation from the taken-out thin film to obtain a sheet-like polymer solid electrolyte having a thickness of 0.1 mm. The ionic conductivity of the obtained polymer solid electrolyte was 6 × 10 ⁻⁵ (S / cm).
Further, the strength evaluation was good, and the balance between ionic conductivity and mechanical strength was excellent.

(Example 2) When the thin film of the crosslinked product obtained in the above Example 1 was dipped in a 3% dimethylsulfoxide solution of LiBF ₄ , polyethyleneethylene glycol having a molecular weight of 250 was used as a plasticizer in the solution. 1 for the weight of
The same operation as in Example 1 was performed except that 0% was added. The ionic conductivity of the obtained polymer solid electrolyte is 1.5 × 10.
^{It was -4} (S / cm). In addition, the strength evaluation was ◯, and by adding the plasticizer, a polymer solid electrolyte having improved ionic conductivity while maintaining strength was obtained.

[0047]

Industrial Applicability The polymer solid electrolyte of the present invention is excellent in ionic conductivity, mechanical strength and flexibility, and by utilizing these properties, a solid electrolyte in the form of a thin film having a large area can be easily obtained. The effect of being able to be played. Further, it is possible to sufficiently meet the demand for miniaturization of the electrochemical device.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 10/40 H01M 10/40 B

Claims (3)

[Claims] 1. A crosslinked product (A) in which a linear polymer is included in a cyclic molecule, and an inclusion compound having a substituent at both ends of the linear polymer is crosslinked, and an electrolyte salt. A polymer solid electrolyte containing the compound (B). 2. The solid polymer electrolyte according to claim 1, wherein the cyclic molecule is cyclodextrin. 3. The polymer solid electrolyte according to claim 1, wherein the linear polymer is polyethylene glycol.