TW201308717A - Polymer electrolyte and lithium polymer battery - Google Patents

Abstract

A polymer electrolyte which comprises a hyper-branched polymer which is produced by polymerizing a monomer component comprising a monomer (A) having at least two radically polymerizable double bonds in the molecule in the presence of a polymerization initiator in an amount of 5-200 mol% relative to the amount of the monomer component and also comprises an electrolyte salt, wherein the monomer (A) is a compound having a vinyl group and/or a (meth)acryl group. Provided are: a polymer electrolyte which can exhibit good ion conductivity without the need of being impregnated with an electrolytic solution and has superior shape-retaining properties and mechanical strength compared with those of electrolytes each impregnated with a solvent; and a lithium polymer battery produced using the polymer electrolyte.

Description

Polymer electrolyte and lithium polymer battery

The present invention relates to a polymer electrolyte, and a solid lithium polymer battery provided with the electrolyte.

In recent years, lithium batteries using organic electrolytes have also been sold on the market, and their markets have grown rapidly.

Many proposals have been made for the battery constituting material and assembly. For example, it has been proposed to use LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , V ₆ O ₁₃ , TiS ₂ or the like as a positive electrode active material. A battery as a negative electrode active material such as lithium, lithium-aluminum alloy, carbon (hard carbon, natural graphite, mesocarbon microbeads, mesocarbon fiber).

In these lithium batteries, the electrolyte is generally used: a lithium salt such as LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , or LiN(CF ₃ SO ₂ ) _{2 is} dissolved in lithium ions. An electrolyte in an aprotic organic solvent such as propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane or diethyl carbonate.

However, since the aprotic solvent used in the electrolyte is flammable, there is a risk of ignition or explosion.

Further, when a lithium or lithium alloy negative electrode is used, there is a risk that a lithium dendrite formed on the negative electrode reaches the positive electrode to cause a short circuit.

In order to solve such problems, the development of a lithium polymer battery in which a polymer is colloidalized with a polymer is reported, and a high ion transmission is reported. A colloidal polymer type solid electrolyte (Patent Document 1).

However, there is still a problem that the volatilization of the solvent cannot be completely suppressed, the use conditions in a high-temperature environment cannot be withstood, and it is difficult to maintain shape retention and mechanical strength.

Therefore, research on solid lithium batteries using completely solid electrolyte polymers has been conducted in recent years.

Solid electrolytes are generally known as solid electrolytes of inorganic materials and solid electrolytes of polymer materials.

In the polymer solid electrolyte, since it is easy to process a large area, it is possible to achieve high capacitance quantification compared to an inorganic solid electrolyte produced by a vacuum process such as a sputtering method, and it is also expected to reduce the manufacturing cost. .

Further, the polymer solid electrolyte does not need to worry about liquid leakage and does not require a metal can, so it can be processed into various shapes such as a film, and has the advantages of being thinner and smaller in size.

Polymer solid electrolytes with such characteristics are widely discussed in various parts of the world.

For example, some people have actively studied polyethers such as polyethylene oxide as solid-state polymer solid electrolytes. It can be considered as: a mechanism in which lithium ions are caged by an ether functional group, lithium ions are highly dissociated, and ions are moved by block movement of a polymer chain (Non-Patent Literature) 1).

However, when polyether is used, the movement of the polymer chain block near the room temperature is limited, and the ion conduction energy is lacking. In fact, in a linear polyethylene oxide, the conductivity is about 10 ^-6 S/cm, and it is still not possible to greatly exceed this value (Patent Documents 2 and 3).

In order to enhance the block motion of the polymer chain, it is necessary to lower the molecular weight, but at this time, it is difficult to achieve good mechanical strength of the solid electrolyte, and crystallization or cracking of the film occurs, so that ion conduction energy is greatly reduced.

Further, when the electrolyte salt is added only to the polyether composed of polyethylene oxide, the mechanical strength is liable to lower, and when a large amount of the electrolyte salt is added, crystallization or cracking of the film occurs in the same manner. Therefore, it is impossible to produce a solid electrolyte containing an electrolyte salt at a high concentration, and the improvement in ion conductivity is limited.

[Previous Technical Literature] [Patent Document]

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 11-102613

Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-93382

Patent Document 3: Japanese Laid-Open Patent Publication No. 2009-104891

[Non-patent literature]

Non-Patent Document 1: J. Amer. Chem. Soc., 21, 648 (1988)

The present invention has been made in view of the above circumstances, and an object thereof is to provide a polymer which has good ion conduction energy even if it does not contain an immersion electrolyte solution, and which has good shape retention and mechanical strength as compared with an electrolyte impregnated with a solvent. An electrolyte, and a lithium polymer battery using the polymer electrolyte.

In general, highly branched polymers have a large number of voids inside, and when compared with a linear polymer, ions which are extremely small like lithium ions are allowed to enter most. Due to this effect, when a high-branched polymer is used as an electrolyte such as a lithium ion battery or a lithium battery, an effect of suppressing internal resistance of the battery due to an increase in carrier density can be expected.

From the above viewpoints, the present inventors have conducted intensive studies and found that a predetermined high-branched polymer is used as a matrix polymer of an electrolyte salt, so that good ion conduction energy can be obtained even without using an organic solvent. The polymer electrolyte having good shape retention and mechanical strength thus completed the present invention.

That is, the present invention provides: 1. A polymer electrolyte comprising: a monomer component containing a monomer A having two or more radical polymerizable double bonds in a molecule, relative to the single a high-branched polymer obtained by polymerizing in the presence of a polymerization initiator of 5 to 200 mol%, and an electrolyte salt; the monomer A described above having a vinyl group and a (meth) acrylonitrile group A compound of either or both, 2. The polymer electrolyte of 1, wherein the monomer A is a divinyl compound or a di(meth) acrylate compound, 3. The polymer electrolyte of 1, wherein the monomer A is a combination of a di(meth)acrylate compound and a compound having both a vinyl group and a (meth)acrylonitrile group, 4. A polymer electrolyte such as 1 or 2, wherein the aforementioned monomer A is di(methyl) The polymer electrolyte according to any one of 1 to 4, wherein the monomer component contains: a monomer having a fluoroalkyl group and at least one radical polymerizable double bond in the molecule B. 6. The polymer electrolyte of 5, wherein the monomer B is 1 mol relative to the monomer A. a polymer electrolyte containing 0.05 to 3 mol, 7. 5 or 6, wherein the monomer B is a compound having a vinyl group or a (meth) acrylonitrile group, 8. a polymer electrolyte such as 7, wherein the monomer B Is a compound represented by the following formula (1);

(wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents a fluoroalkyl group having 2 to 12 carbon atoms which may be substituted by a hydroxyl group), and 9. The polymer electrolyte of 8, wherein the aforementioned monomer B is represented by the following formula: (2) a compound represented;

(wherein, X represents a hydrogen atom or a fluorine atom, m represents 1 or 2, n represents an integer of 0 to 5; R ¹ is the same as defined above), 10. The polymer electrolyte according to any one of 1 to 9, wherein the aforementioned The monomer component contains: a monomer C having a substituent containing an ether bond in the molecule and having at least one radically polymerizable double bond, 11. The polymer electrolyte according to any one of 1 to 10, wherein the aforementioned The polymerization initiator is an azo polymerization initiator, 12. The polymer electrolyte according to 11, wherein the polymerization initiator is selected from the group consisting of dimethyl 2,2'-azobisisobutyrate and 2,2' A polymer electrolyte according to any one of 1 to 12, wherein the electrolyte salt is selected from the group consisting of LiPF ₆ and LiBF ₄ An inorganic lithium salt of the group consisting of LiClO ₄ and LiAsF ₆ and the derivative thereof, and selected from the group consisting of LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN ( An organic lithium salt of the group consisting of SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ) and at least one of the derivatives, 14. The polymer electrolyte of 13, wherein the electrolyte salt is LiN (SO ₂ CF) _{3) 2} or LiBF _4, 15. A polymer electric The precursor solution is a single monomer containing a monomer A having two or more radical polymerizable double bonds in the molecule and having either or both of a vinyl group and a (meth) acryl group. a high-branched polymer obtained by polymerizing in the presence of a polymerization initiator of 5 to 200 mol% based on the monomer component, and an electrolyte salt dissolved in a solvent, 16. a polymer electrolyte precursor solution, wherein the solvent is selected from the group consisting of benzene, toluene, xylene, ethylbenzene, tetrahydronaphthalene, n-hexane, n-heptane, mineral spirits, cyclohexane, methyl chloride, methyl bromide, methyl iodide , dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, perfluoroethylene, o-dichlorobenzene, ethyl acetate, butyl acetate, methoxybutyl acetate, 2-methoxyethyl acetate, acetic acid 2-ethoxyethyl ester, propylene glycol monomethyl ether acetate, diethyl ether, tetrahydrofuran, 1,4-dioxane, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, propylene glycol monomethyl ether , acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-butanone, cyclohexanone, methanol, ethanol, n-propanol, isopropanol, n-butanol , isobutanol, tertiary butanol, 2-ethylhexanol, benzyl alcohol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl azine, and N - at least one of methyl-2-pyrrolidone, 17. The polymer electrolyte precursor solution of 16, wherein the organic solvent is at least one selected from the group consisting of methyl isobutyl ketone and tetrahydrofuran, 18. a polymer An electrolyte obtained by removing the solvent from the polymer electrolyte precursor solution according to any one of 15 to 17.

In the polymer electrolyte of the present invention, since a predetermined high-branched polymer is used, excellent ion conductivity of, for example, more than 1.0 × 10 ^-5 S/cm can be exhibited at room temperature. Therefore, by using the polymer electrolyte in an electrolyte portion of a lithium battery or the like, an all-solid battery having a low internal resistance can be provided.

The high-branched polymer contained in the polymer electrolyte of the present invention can form fine particles having a diameter of 1 μm or less by a homopolymer, and a linear polymer In contrast, the molecular chain is less entangled. Therefore, the viscosity of the polymer is low, and it is easy to increase the free energy of the added electrolyte ions, such as lithium ions. Further, since the entanglement of the molecular chains can be suppressed, a large amount of voids can be generated inside the polymer, and ion migration in the inside of the polymer can be easily performed.

Further, since the high-branched polymer used in the present invention contains a highly polar functional group such as an ester group or an ether group, it has high compatibility with a lithium salt used as an electrolyte salt, and can be uniformly mixed at a high concentration. The electrolyte salt, as a result, forms an electrolyte layer containing a high concentration of an electrolyte salt.

For example, when synthesizing the high-branched polymer used in the present invention, when ethylene glycol di(meth)acrylate is used as the monomer A, the -C(O)-O is constructed in the highly branched polymer. -CH ₂ CH ₂ -OC(O)- unit. In this unit, since the unpaired electrons on the ether oxygen atom are not localized, it is presumed to be a normal polyether unit (-CH ₂ CH ₂ -O-CH ₂ CH ₂ -O-CH ₂ CH ₂ -) The ratio is difficult to form with lithium ions, but the polymer electrolyte of the present invention exhibits excellent ion conductivity.

Further, when the high-branched polymer is synthesized, a high-branched polymer containing a fluorine functional group can be easily formed by using a monomer having a fluorine functional group, which is advantageous for improvement in withstand voltage characteristics and thickening of SEI. The suppression, the adhesion to the current collector, the dispersion of the electrode active material and the conductive auxiliary material, and the improvement of the flame retardancy.

Further, by using a monomer having an ether group or an oxirane group, the degree of dissociation of lithium ions can be increased, and ion conduction energy can be further enhanced.

In the high-branched polymer having an -O-CH ₂ CH ₂ -O- unit such as an ethylene oxide chain in the molecule, lithium ions may be formed in a similar manner as in the following formula (3). Thereby, even when the lithium salt is caged in the polymer, the ionization state can be maintained to achieve high lithium ion conductivity, and this effect can also be expected to suppress the internal resistance of the battery.

Further, the highly branched polymer used in the present invention can form a glassy polymer or a rubbery polymer having a low glass transition temperature and flexibility. Thereby, the block motion of the polymer chain can be improved, and the ion conduction energy is improved by the improvement of the ion conduction path, and the thickness of the electrode can be increased, the thickness is reduced, the contact resistance is increased, and the battery cycle is also beneficial. Improved features.

According to the above effects, when the electrolyte containing the highly branched polymer of the present invention is used as an electrolyte for a battery including a lithium ion secondary battery, it is possible to produce an electrolyte layer exhibiting high ionic conductivity and exhibit high rate characteristics. A battery that has high cycle characteristics and is safe without the doubt of solvent volatilization or ignition.

Further, in the polymer electrolyte of the present invention, since the film can be produced in a state in which the lithium salt is contained, it is not necessary to perform treatment such as impregnation of the electrolytic solution.

Since the polymer electrolyte of the present invention does not use an electrolytic solution, that is, does not contain an organic solvent, there is a problem that it is not necessary to worry about the volatilization of the solvent, and there is an advantage that the shape retainability and the mechanical strength are lowered due to the inclusion of the solvent.

The invention is further described in detail below.

The polymer electrolyte of the present invention is characterized in that the monomer component containing the monomer A having two or more radical polymerizable double bonds in the molecule is 5 to 200 m per mol of the monomer component. a high-branched polymer obtained by polymerization in the presence of a polymerization initiator of %, and an electrolyte salt; and monomer A is a compound having either or both of a vinyl group and a (meth) acrylonitrile group.

[Highly branched polymer]

Highly branched polymers, generally broadly distinguished as dendrimers and superbranched polymers, are highly branched polymers used in the present invention, preferably superbranched polymers.

The highly branched polymer used in the present invention is a so-called starter fragment-embedded high-branched polymer having a residue of a polymerization initiator used in polymerization at the terminal.

The monomer A is not particularly limited as long as it has either or both of a vinyl group and a (meth) acrylonitrile group, and is preferably a divinyl compound or a di(meth) acrylate compound.

Further, the monomer A may be used in combination of plural kinds, and for example, a combination of a di(meth) acrylate compound and a compound having both a vinyl group and a (meth) acrylonitrile group is also preferable.

The (meth) acrylate compound means both an acrylate compound and a methacrylate compound. For example, (meth)acrylic means Acrylic acid and methacrylic acid.

Specific examples of the monomer A include the following organic compounds represented by (A1) to (A8).

(A1) Vinyl hydrocarbons:

(A1-1) Aliphatic vinyl hydrocarbons; isoprene, butadiene, 3-methyl-1,2-butadiene, 2,3-dimethyl-1,3-butadiene, 1,2-polybutadiene, pentadiene, hexadiene, octadiene, etc.

(A1-2) alicyclic type vinyl hydrocarbons; cyclopentadiene, cyclohexadiene, cyclooctadiene, bicycloheptadiene, etc.

(A1-3) aromatic vinyl hydrocarbons; divinylbenzene, divinyltoluene, diethylenexylene, trivinylbenzene, divinylbiphenyl, divinylnaphthalene, divinylanthracene, divinylcarbazole, divinylpyridine Wait

(A2) vinyl ester, allyl ester, vinyl ether, allyl ether, ketene:

(A2-1) vinyl ester; divinyl adipate, divinyl maleate, divinyl phthalate, divinyl isophthalate, divinyl econate, (methyl) Vinyl acrylate, etc.

(A2-2) allyl ester; diallyl maleate, diallyl phthalate, diallyl iconate, diallyl adipate, allyl (meth)acrylate Ester

(A2-3) vinyl ether; divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, etc.

(A2-4) allyl ether; diallyl ether, diallyloxyethane, triallyloxyethane, tetraallyloxyethane, tetraallyloxypropane, tetraallyloxy Butane, tetramethylallyloxyethane, etc.

(A2-5) ketene; diketene, diene acetone, etc.

(A3) (meth) acrylate: ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, di(methyl) Pentaethylene glycol acrylate, propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(methyl)acrylate, glycerol tri(meth)acrylate, Pentaerythritol tetra(meth)acrylate, alkoxytitanate tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 2-methyl-1,di(meth)acrylate , 8-octyl glycol ester, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate Ester, dioxane di(meth)acrylate, 2-hydroxy-1-propenyloxy-3-methylpropenyloxypropane, 2-hydroxy-1,3-di(methyl)propene Alkoxypropane, 9,9-bis[4-(2-(methyl)propene oxiranyloxy)phenyl]anthracene, undecyloxyethylene di(meth)acrylate, vulcanization 4-(methyl)propene sulfonium thiophenyl], sulfurized bis[2-(methyl)propene sulfonium thioethyl], 1,3-adamantyl di(meth)acrylate, di(a) ) Acrylate, 1,3-adamantane dimethanol ester

(A4) A vinyl compound having a polyalkylene glycol chain: a di(meth)acrylic acid polyethylene glycol (molecular weight 300) ester, a di(meth)acrylic acid polypropylene glycol (molecular weight 500) ester, or the like

(A5) A nitrogen-containing vinyl compound: diallylamine, diallyl isocyanurate, diallyl cyanurate, methylenebis(meth)acrylamide, bismaleimide Wait

(A6) a vinyl compound containing ruthenium: dimethyldivinyl decane, two Methyl divinyl decane, divinyl methyl phenyl decane, diphenyl divinyl decane, 1,3-divinyl-1,1,3,3-tetramethyldioxane, 1,3-two Vinyl-1,1,3,3-tetraphenyldiazepine, diethoxydivinyl decane, etc.

(A7) fluorine-containing vinyl compound: 1,4-divinyl perfluorobutane, 1,6-divinyl perfluorohexane, 1,8-divinyl perfluorooctane, etc.

(A8) (meth) acrylate compound containing a vinyl ether group: 2-(2-vinyloxyethoxy)ethyl acrylate

Among these, the aromatic vinyl hydrocarbons of the above (A1-3) group, the vinyl esters, allyl esters, vinyl ethers, allyl ethers and ketenes of the group (A2), (A3) group ( a methyl acrylate, a vinyl compound having a polyalkylene glycol chain of the (A4) group, and a nitrogen-containing vinyl compound of the group (A5), particularly preferably a divinylbenzene of the group (A1-3), A2) Group of diallyl phthalate, (A3) group of ethylene glycol (meth)acrylate, tetraethylene glycol di(meth)acrylate, and hexaethylenedi(meth)acrylate An alcohol ester, 1,3-adamantane dimethanol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and methylene bis(meth) acrylamide belonging to the group (A5).

In particular, divinylbenzene, ethylene glycol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, and particularly preferably ethylene glycol di(meth)acrylate.

Further, a combination of each of the above compounds and 2-(2-vinyloxyethoxy)ethyl acrylate of the (A8) group is also preferred.

Further, the monomer component used in the synthesis of the high-branched polymer used in the present invention may be mixed in addition to the above monomer A: A monomer B having a fluoroalkyl group and at least one radical polymerizable double bond.

In this case, the monomer B preferably has at least one of a vinyl group and a (meth) propylene group.

The monomer B is preferably a compound represented by the following formula (1), and more preferably a compound represented by the following formula (2).

(wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a fluoroalkyl group having 2 to 12 carbon atoms which may be substituted by a hydroxyl group),

(wherein, X represents a hydrogen atom or a fluorine atom, m represents 1 or 2, and n represents an integer of 0 to 5; and R ¹ is the same as defined above).

Specific examples of the monomer B represented by the above formula (1) or (2) include 2,2,2-trifluoroethyl (meth)acrylate and 2,2,3 (meth)acrylate. 3,3-pentafluoropropyl ester, 2-(perfluorobutyl)ethyl (meth)acrylate, 2-(perfluorohexyl)ethyl (meth)acrylate, 2-(perfluoro) (meth)acrylate Octyl)ethyl ester, 2-(perfluorodecyl) (meth)acrylate Ethyl ester, 2-(perfluoro-3-methylbutyl)ethyl (meth)acrylate, 2-(perfluoro-5-methylhexyl)ethyl (meth)acrylate, (meth)acrylic acid 2 -(Perfluoro-7-methyloctyl)ethyl ester, (meth)acrylic acid 1H, 1H, 3H-tetrafluoropropyl ester, (meth)acrylic acid 1H, 1H, 5H-octafluoropentyl ester, (methyl )1H,1H,7H-dodecafluoroheptyl acrylate, 1H,1H,9H-hexadecafluorodecyl (meth)acrylate, 1H-1-(trifluoromethyl)trifluoroethyl (meth)acrylate , (meth)acrylic acid 1H, 1H, 3H-hexafluorobutyl ester, 3-perfluorobutyl-2-hydroxypropyl (meth)acrylate, 3-perfluorohexyl-2-hydroxypropyl (meth)acrylate Ester, 3-perfluorooctyl-2-hydroxypropyl (meth)acrylate, 3-(perfluoro-3-methylbutyl)-2-hydroxypropyl (meth)acrylate, (meth)acrylic acid 3-(perfluoro-5-methylhexyl)-2-hydroxypropyl ester, and 3-(perfluoro-7-methyloctyl)-2-hydroxypropyl (meth)acrylate.

When the monomer B is mixed in the monomer component used in the synthesis of the high-branched polymer used in the present invention, it is preferred that the monomer A is a di(meth)acrylate compound, and the monomer B is a monomer having a fluoroalkyl group and at least one radical polymerizable double bond in the molecule, and particularly preferably a monomer A is ethylene glycol di(meth)acrylate, and the monomer B is represented by the above formula (2) Expressed as a compound.

In the present invention, the ratio of the copolymerization of the monomer A and the monomer B is considered to be a reactivity, a surface modification effect, etc., and it is preferred that the monomer B contains 0.05 to 3.0 mol with respect to 1 mol of the monomer A, particularly Good is 0.1~1.5mol.

The monomer component used in the synthesis of the high-branched polymer used in the present invention may be mixed with the above-mentioned monomer A: a substituent having an ether bond in the molecule, and having at least one free Base polymerized double bond Monomer C.

The monomer C is preferably a compound having one of a vinyl group and a (meth) propylene group, or a maleimide compound.

Further, monomer C can be used for both monomer A and monomer B.

Examples of the substituent containing an ether bond include an ethylene oxide (-CH ₂ -CH ₂ -O-) group.

Specific examples of the monomer C include a vinyl ether group-containing (meth) acrylate compound such as 2-(2-vinyloxyethoxy)ethyl (meth)acrylate; glycidyl methacrylate; and the like. An alkoxyalkyl group-containing (meth) acrylate compound such as an epoxy group-containing (meth) acrylate compound; 3-methyl propylene oxypropyl triethoxy oxane; cyclohexylmaleimide; A maleic imine compound or the like of N-benzylmaleimide or the like.

In the present invention, the ratio of the copolymerization of the monomer C to the reactivity and the surface modification effect is preferably 0.05 to 3.0 mol, particularly preferably 0.1 to 1.5 mol, per mol of the monomer A.

The polymerization initiator used in the synthesis of the highly branched polymer is not particularly limited, and in the present invention, an azo polymerization initiator is preferred.

Examples of the azo-based polymerization initiators include the compounds represented by the following (1) to (5), and these may be used alone or in combination of two or more.

(1) Azoonitrile compounds: 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylisobutyronitrile), 2,2'-azobis (2,4 - dimethyl valeronitrile), 1,1'-azobis(1-cyclohexanecarbonitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile ), 2-(aminomethyl sulfhydrylazo) isobutyronitrile, etc.

(2) Azoguanamine compound: 2,2'-azobis{2-methyl-N-[1,1- Bis(hydroxymethyl)-2-hydroxyethyl]propanamine}, 2,2'-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propanamine}, 2,2'-azobis[2-methyl-N-(2-methyl-N-(2-hydroxyethyl)propanamide], 2,2'-azobis[N-(2- Allyl)-2-methylpropionamide], 2,2'-azobis(N-butyl-2-methylpropionamide), 2,2'-azobis(N-cyclohexyl) -2-methylpropionamide)

(3) Cyclic azo hydrazine compound: 2,2'-azobis[2-(2-imidazolin-2-yl)propane dihydrochloride], 2,2'-azobis dihydrate dihydrate [2 -(2-imidazolin-2-yl)propane], 2,2'-azobis[2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane dihydrochloride], 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis(1-imino-1-pyrrolidinyl-2-yl dihydrochloride) Propane)

(4) Azo quinone compound: 2,2'-azobis(2-methylpropionamidine dihydrochloride), 2,2'-azobis[N-(2-carboxyethyl)-2-tetrahydrate Methyl propyl hydrazine]

(5) Others: 2,2'-dimethyl azobisisobutyrate, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis (2,4, 4-trimethylpentane), 1,1'-azobis(1-ethenyloxy-1-phenylethane), etc.

In the above azo polymerization initiator, the surface energy of the obtained high-branched polymer is considered, preferably having a relatively low polarity substituent, particularly preferably 2,2'-azobisisobutyric acid Methyl ester and / or 2,2 '-azobis (2,4,4-trimethylpentane).

The polymerization initiator is used in an amount of 5 to 200 mol% based on the number of moles of the monomer A in the monomer component. It is preferably 15 to 200 mol%, particularly preferably 15 to 170 mol%, more preferably 50 to 100 mol%.

Even when monomer B and monomer C are mixed with the aforementioned monomer A, The polymerization initiator is also used in the above ratio with respect to the molar number of the monomer A.

The synthesis of a specific high-branched polymer can be carried out in accordance with the method described in Japanese International Publication No. 2010/137724 or Macromol. Chem. Phys. 206, 860 (2005).

[electrolyte salt]

The electrolyte salt used in the polymer electrolyte of the present invention includes various conventional electrolyte salts which can be used in lithium ion batteries.

Specific examples of the electrolyte salt are preferably an inorganic lithium salt selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ and the derivative, and are selected from the group consisting of LiSO ₃ CF ₃ and LiN (SO ₂ CF _{3 ). 2} [LiTFSI], LiN(SO ₂ C ₂ F ₅ ) ₂ [LiBESI], LiN(SO ₂ CF ₃ )(SO ₂ C ₄ F ₉ ), and lithium bis(oxalate) borate [Li(BOB) )] The organic lithium salt and the derivative of the group consisting of at least one of them are preferably LiPF ₆ , LiBF ₄ , and LiTFSI in terms of versatility and conductivity, and in terms of conductivity , especially good for LiTFSI.

The amount of the above electrolyte salt added is preferably 0.5 to 5.0 mol, more preferably 1.0 to 4.0 mol, and most preferably 2.0 to 3.0 mol, based on 1 kg of the high-branched polymer.

[Polymer Electrolyte Precursor and Polymer Electrolyte]

When producing the polymer electrolyte of the present invention, it is preferred to use a solvent which can dissolve the above-mentioned high-branched polymer and electrolyte salt and does not react with the two components. .

By using such a solvent, a solution-like polymer electrolyte precursor is prepared, and the precursor solution is applied to a substrate such as metal or glass, and then heated at 30 to 200 ° C for 10 minutes to 6 hours, for example. The polymer electrolyte of the present invention can be produced by drying, but the method for producing the polymer electrolyte of the present invention is not limited thereto.

In the present invention, the solvent is removed by heating or the like at the time of formation of the polymer electrolyte. Therefore, the above solvent contains almost no polymer electrolyte.

The ratio of the solvent to be used in the preparation of the polymer electrolyte precursor is not particularly limited, and is preferably from 5 to 95% by mass, particularly preferably from 30 to 70% by mass, based on the total mass of the obtained polymer electrolyte. Good is 40~60% by mass.

The solvent used in the preparation of the polymer electrolyte precursor is not particularly limited as long as it can dissolve the high-branched polymer and the electrolyte salt and does not react with the two components.

Examples of the specific examples include aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, and tetrahydronaphthalene; and aliphatic or alicyclic rings such as n-hexane, n-heptane, mineral spirits, and cyclohexane. Type hydrocarbon solvent; halogenated solvent of methyl chloride, methyl bromide, methyl iodide, dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, perfluoroethylene, o-dichlorobenzene, etc.; ethyl acetate, butyl acetate An ester or ester ether solvent such as ester, methoxybutyl acetate, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, etc.; diethyl ether, tetrahydrofuran, 1,4- Dioxane, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, An ether solvent such as propylene glycol monomethyl ether; a ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-butyl ketone or cyclohexanone; methanol, ethanol, n-propanol, isopropanol, n-butanol An alcohol solvent such as isobutanol, tertiary butanol, 2-ethylhexanol or benzyl alcohol; a guanamine such as N,N-dimethylformamide or N,N-dimethylacetamide A solvent; a hydrazine solvent such as dimethyl hydrazine; a heterocyclic compound such as N-methyl-2-pyrrolidone; and a mixed solvent of two or more of these.

Among them, an aromatic hydrocarbon solvent, a halogen solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, a guanamine solvent, or an anthraquinone solvent is preferred, and toluene, xylene, and o-di are preferred. Chlorobenzene, butyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, 1,4-dioxane, 2-methoxyethanol, methyl isobutyl ketone, N,N-dimethylformamide , N,N-dimethylacetamide.

Since the lithium polymer battery of the present invention is characterized in that the polymer electrolyte is used, other battery components can be used, and can be appropriately selected from conventionally known materials and components.

Example

The present invention will be more specifically described by the following examples and comparative examples, but the present invention is not limited to the following examples.

The molecular weight of the polymer is determined by the following method.

[GPC: Gel Permeation Chromatography]

Device: HLC-8220GPC manufactured by Tosoh Co., Ltd.

Column: Shodex KF-804L, KF-805L

Column temperature: 40 ° C

Solvent: tetrahydrofuran

Detector: RI

[1] Production of polymer electrolyte membrane [Example 1]

A fluorine-containing high-branched (super-branched) polymer (Mw 17,000, Mw/Mn = 2.2, hereinafter referred to as Compound 1) synthesized by the method described in Example 8 of Japanese International Publication No. 2010/137724 3.0 g and methyl isobutyl ketone (MIBK) 3.0 g were weighed in a sample bottle, and ultrasonic waves were irradiated for 60 minutes by an ultrasonic cleaner (FU-6H, manufactured by Tokyo Glass Machinery Co., Ltd.). MIBK solution of highly branched polymer. 2.6 g of LiTFSI (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the obtained solution, and the mixture was stirred for 60 minutes with a mixing rotor (MRC-5, manufactured by AZONE Co., Ltd.) to obtain a polymer electrolyte precursor solution. The obtained precursor solution was applied to an aluminum plate by a doctor blade method, heated at 60 ° C for 30 minutes, and further heated at 150 ° C for 30 minutes to prepare a polymer solid electrolyte membrane.

In this composition, the fluorine-containing high-branched polymer contained 3.0 mol of LiTFSI per 1 kg.

[Examples 2 to 6]

The other additives were added in the same manner as in Example 1 except that the respective additives or the amounts thereof were changed in accordance with the first table.

[Comparative Example 1]

PEG was prepared by the method of Example 1 using 0.5 g of polyethylene glycol (PEG, an average molecular weight of 20,000, manufactured by Junsei Chemical Co., Ltd.) in place of 3.0 g of the super-branched polymer, and the amount of MIBK was set to 0.5 g. MIBK solution with an average molecular weight of 20,000). 0.3 g of LiTFSI was added to the obtained solution, and after stirring by the mixing rotor, it was colloidalized in a stage of uniform dispersion (dissolution), and it was not possible to prepare a precursor solution which can be applied to the aluminum plate by a doctor blade method, and a film could not be produced. .

[Comparative Example 2]

PEG (average molecular weight of 6,000) was prepared by the method of Example 1, using 5.0 g of PEG (average molecular weight 6,000, manufactured by Junsei Chemical Co., Ltd.) to replace 3.0 g of the super-branched polymer, and the amount of MIBK was set to 5.0 g. The MIBK solution was then used in an amount of 2.9 g of LiTFSI to obtain a polymer electrolyte precursor solution by the method of Example 1. Using the obtained precursor solution, a polymer solid electrolyte membrane was attempted by the same method as in Example 1, but it was maintained in a liquid state after heating, and a film could not be produced.

[2] Determination of ionic conductivity [Examples 7-12]

The ionic conductivity of the polymer electrolyte produced in the above Examples 1 to 6 was measured by the following method. The results are shown in Table 2.

The coating surface of the obtained coating film was sandwiched so as to be in contact with each other, and measured by an AC impedance method (PARSTAT [registered trademark] 2273 Advanced Electrochemical System, manufactured by Princeton Applied Research) at room temperature (25 ° C). Ionic conductivity.

As shown in the second table, a film having an average molecular weight of 6,000 was used and a film was tried by the same method as in Example 1, but the film could not be obtained even if it was sintered. Further, using a PEG having an average molecular weight of 20,000 and attempting to produce a film by the same method as in Example 1, the solution was colloidally formed while stirring the MIBK solution and LiTFSI. From these results, it is explained that even if a low molecular weight polyether compound having an average molecular weight of 6,000 (PEG having an average molecular weight of 6,000) is used, the same polymer solid electrolyte membrane as in the case of using the compound 1 to 3 cannot be produced, and even if it is used, A high molecular weight polyether compound (PEG with an average molecular weight of 20,000) or a polyether compound (PEO) which is considered to be more colloidal than a PEG having a molecular weight of 20,000, and a polymer solid electrolyte which is the same as that of the compound 1 to 3 can not be produced. membrane.

On the other hand, by using the compounds 1 to 3, a polymer solid electrolyte membrane can be produced, and the obtained film exhibits a high ionic conductivity of 1.0 × 10 ^-5 S/cm or more.

Claims (18)

A polymer electrolyte comprising a monomer component containing a monomer A having two or more radical polymerizable double bonds in a molecule, and is 5 to 200 mol% based on the monomer component. a high-branched polymer obtained by polymerization in the presence of a polymerization initiator, and an electrolyte salt; the monomer A is a compound having either or both of a vinyl group and a (meth) acrylonitrile group. The polymer electrolyte according to claim 1, wherein the monomer A is a divinyl compound or a di(meth) acrylate compound. The polymer electrolyte according to claim 1, wherein the monomer A is a combination of a di(meth)acrylate compound and a compound having both a vinyl group and a (meth)acrylonitrile group. The polymer electrolyte according to claim 1 or 2, wherein the monomer A is ethylene glycol di(meth)acrylate. The polymer electrolyte according to any one of claims 1 to 4, wherein the monomer component contains a monomer B having a fluoroalkyl group and at least one radical polymerizable double bond in the molecule. The polymer electrolyte according to claim 5, wherein the monomer B contains 0.05 to 3 mol based on 1 mol of the monomer A. The polymer electrolyte according to claim 5 or 6, wherein the monomer B is a compound having a vinyl group or a (meth) acrylonitrile group. . The polymer electrolyte according to claim 7, wherein the monomer B is a compound represented by the following formula (1); (wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents a fluoroalkyl group having 2 to 12 carbon atoms which may be substituted with a hydroxyl group). The polymer electrolyte according to claim 8, wherein the monomer B is a compound represented by the following formula (2); (wherein, X represents a hydrogen atom or a fluorine atom, m represents 1 or 2, and n represents an integer of 0 to 5; and R ¹ is the same as defined above). The polymer electrolyte according to any one of claims 1 to 9, wherein the monomer component contains: a substituent having an ether bond in a molecule and having at least one radical polymerizable double bond Body C. The polymer electrolyte according to any one of claims 1 to 10, wherein the polymerization initiator is an azo polymerization initiator. The polymer electrolyte of claim 11, wherein the polymerization initiator is selected from the group consisting of dimethyl 2,2'-azobisisobutyrate and 2,2'-azobis (2,4,4). At least one of -trimethylpentane). The polymer electrolyte according to any one of claims 1 to 12, wherein the electrolyte salt is an inorganic lithium salt selected from the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ and the derivative And selected from LiSO ₃ CF ₃ , LiC(SO ₃ CF ₃ ) ₂ , LiN(SO ₃ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ and LiN(SO ₂ CF ₃ ) (SO ₂ C _{4 )} F ₉ ) at least one of an organic lithium salt of the group consisting of and a derivative thereof. The polymer electrolyte according to claim 13, wherein the electrolyte salt is LiN(SO ₃ CF ₃ ) ₂ or LiBF ₄ . A polymer electrolyte precursor solution which comprises a monomer having two or more radical polymerizable double bonds in a molecule and having either or both of a vinyl group and a (meth) acryl fluorenyl group The monomer component of A is obtained by polymerizing a high-branched polymer obtained by polymerizing in the presence of a polymerization initiator of 5 to 200 mol% based on the monomer component, and an electrolyte salt, which is dissolved in a solvent. The polymer electrolyte precursor solution according to claim 15 , wherein the solvent is selected from the group consisting of benzene, toluene, xylene, ethylbenzene, tetrahydronaphthalene, n-hexane, n-heptane, mineral spirits, and cyclohexane. , methyl chloride, methyl bromide, methyl iodide, dichloromethane, chloroform, carbon tetrachloride, trichloroethylene, perfluoroethylene, o-dichlorobenzene, ethyl acetate, butyl acetate, methoxybutyl acetate, acetic acid 2-methoxyethyl ester, 2-ethoxyethyl acetate, propylene glycol monomethyl ether acetate, diethyl ether, tetrahydrofuran, 1,4-dioxane, 2-methoxyethanol , 2-ethoxyethanol, 2-butoxyethanol, propylene glycol monomethyl ether, acetone, methyl ethyl ketone, methyl isobutyl ketone, di-n-butanone, cyclohexanone, methanol, ethanol, n-propanol, isopropanol, n-Butanol, isobutanol, tertiary butanol, 2-ethylhexanol, benzyl alcohol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl alum And at least one of N-methyl-2-pyrrolidone. The polymer electrolyte precursor solution according to claim 16, wherein the organic solvent is at least one selected from the group consisting of methyl isobutyl ketone and tetrahydrofuran. A polymer electrolyte obtained by removing the solvent from the polymer electrolyte precursor solution according to any one of claims 15 to 17.