JP2001229967A - Gel-type electrolyte lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gel-type electrolyte that has high ion-conductivity and is stable with respect to lithium electrolyte containing fluorine atom, and to provide a battery without liquid leakages, that is superior in load characteristics, low-temperature characteristics and other battery characteristics. SOLUTION: This gel-type electrolyte comprises an electrolyte, nonaqueous organic solvent and particulate alumina, and the surface hydroxyl-radical number of this alumina is 0.003 (mmol/1) or lower. As the electrolyte, a lithium salt containing fluorine atoms or tetraalkyl ammonium salt and as the nonaqueous organic solvent, cyclo-carbonate and/or chain ester are desirable. Then the particulate alumina with methanol critical concentration of 20% or lower, specific surface area of 30 (m2/g) or more, and particle size of 50 nm or smaller is desirable. The inorganic-oxide particle are desirably mixed at 5-30 weight % in the gel-type electrolyte. The above-mentioned gel-type electrolyte is to be contained on a lithium battery, in particular in a lithium secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a gel electrolyte,
The present invention relates to a lithium battery using the gel electrolyte and, more particularly, to a gel electrolyte having high ionic conductivity and storage stability, and a lithium battery using the same.

[0002]

2. Description of the Related Art A battery using a non-aqueous electrolyte has a high voltage, a high energy density, and a high reliability at the time of storage. Therefore, it is widely used as a power source for consumer electronic devices. I have. One example is a non-aqueous electrolyte secondary battery,
Above all, lithium ion secondary batteries have become widespread.

The types of electrolyte materials used in the battery include a non-aqueous electrolyte in which the electrolyte is dissolved in a non-aqueous solvent, a polymer gel electrolyte comprising a non-aqueous electrolyte and a polymer matrix, and an electrolyte and a polymer compound. And inorganic ion conductive glass. The electrolyte material mainly used in commercially available lithium ion batteries is a non-aqueous electrolyte, and a fluorine-containing lithium salt such as LiPF ₆ is
A solution is used which is dissolved in a mixed solvent of a high dielectric constant carbonate compound solvent such as propylene carbonate and ethylene carbonate and a low viscosity solvent such as diethyl carbonate.

In recent years, lithium-ion batteries have been required to be thinner for the purpose of expanding their applications, and in response to this, there has been a movement to change the exterior material of the battery from a conventional metal to a laminated film of metal and resin. Is emerging. Examples of the electrolyte material mainly used for the battery include a polymer gel electrolyte, and specifically, a polymer matrix such as a polymer of an acrylic acid derivative, a vinylidene fluoride-hexafluoropropylene copolymer, and polyacrylonitrile. For example, a material obtained by impregnating the above-mentioned non-aqueous electrolyte solution and swelling a polymer matrix with the non-aqueous electrolyte solution is used.

[0005] By the way, as a problem relating to batteries in general, prevention of electrolyte leakage is cited. Even in the case of a battery using a metal outer can, there is a concern that in the unlikely event that the sealing portion is defectively crimped or a large amount of gas is generated in the battery, the electrolyte leaks and may lead to equipment failure. In a battery using a laminate film as an exterior material, if the strength of the laminate film is low, there is likely to be a risk of electrolyte leakage.

For this reason, the above-mentioned polymer gel electrolyte has been used as a measure for preventing the electrolyte solution from leaking out even if the exterior material should be damaged. However, in the polymer gel electrolyte, it is conceivable that the ionic conductivity of the electrolyte is reduced because the polymer matrix obstructs the conduction of lithium ions, and the load characteristics of the battery and the battery characteristics at low temperatures are reduced. Therefore, a gel electrolyte that has high ionic conductivity and does not cause liquid leakage even if the sealing of the battery is broken is demanded.

[0007] As a gel electrolyte material replacing the polymer gel electrolyte, Journal of Power Sources, 68 , 387
To 391 (1997) report the gelation of an electrolytic solution using ultrafine silica particles. Since a small amount of hydrophilic silica can be used to gel the electrolytic solution, a gel electrolyte having excellent conductivity can be obtained. It is stated that it will be. But,
It is also stated that hydrophobic silica cannot gel.

On the other hand, the electrolyte mainly used in lithium ion batteries is a lithium salt containing a fluorine atom such as LiPF ₄ or LiBF _4, and the electrolyte containing a fluorine atom reacts with hydrophilic silica. In order to generate hydrogen fluoride, it is difficult to apply this gel electrolyte as it is to a commercially available lithium ion battery.

Japanese Patent Application Laid-Open No. Hei 10-294016 describes an electrolytic solution to which ultrafine alumina particles are added for the purpose of removing impurities in the electrolytic solution. Occur, and the ionic conductivity is reduced. In this publication, the purpose is to obtain an electrolyte having a low viscosity, and there is no mention of a gel electrolyte.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gel electrolyte having high ionic conductivity and being chemically stable with respect to a lithium salt electrolyte containing a fluorine atom. Another object of the present invention is to provide a battery that prevents the electrolyte from leaking by using the gel electrolyte and has excellent performance in battery characteristics such as load characteristics and low-temperature characteristics.

[0011]

That is, the present invention relates to a gel electrolyte comprising an electrolyte, a non-aqueous organic solvent and particulate alumina, wherein the number of surface hydroxyl groups of the particulate alumina is 0.003 (mmol / m ² ) or less. It is. The electrolyte to be used is preferably a lithium salt or a tetraalkylammonium salt, particularly preferably a compound containing a fluorine atom in its molecule, particularly LiPF ₆ , LiB
At least one selected from the group consisting of F ₄ and a compound represented by the general formula Li ⁺ N ⁻ (SO ₂ R ¹¹ ) (SO ₂ R ¹² )
Species lithium salts are desirable. Where R ¹¹ and R
¹² represents a fluoroalkyl group having 2 to 6 carbon atoms.

The non-aqueous solvent is preferably an aprotic organic solvent, particularly preferably at least one solvent selected from the group consisting of the general formulas (1), (2) and (3).

[0013]

Embedded image

Here, R ^{1 to} R ⁶ and R ⁸ represent hydrogen, fluorine, a hydrocarbon group having 1 to 6 carbon atoms or a fluoroalkyl group, and R ⁷ represents hydrogen, 1 to 6 carbon atoms. A hydrocarbon group, a fluoroalkyl group, an alkoxy group, or a dialkylamino group having 1 to 12 carbon atoms;
Y, W, Z represents O, and CH ₂ or N-R ^9,, R
⁹ is a hydrocarbon group having 1 to 6 carbon atoms.

In particular, the aprotic organic solvent is ethylene carbonate or propylene carbonate,
If it is a mixed solvent with at least one chain ester selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl trifluoroethyl carbonate, an electrolyte having a high ionic conductivity and a stable gel state can be obtained. This is desirable.

On the other hand, the above-mentioned particulate alumina preferably has a methanol critical concentration of 20% by weight or more as measured by a methanol wet test. Having a degree of hydrophobicity represented by this methanol critical concentration,
It is desirable because the reactivity with the electrolyte containing a fluorine atom is reduced or suppressed, and the gel property is enhanced.

It is preferable that the above-mentioned fine particle alumina has a specific surface area of 30 (m ² / g) or more or a particle diameter of 50 nm or less, since the electrolyte becomes a stable gel state.

As such fine-particle alumina, fine-particle alumina obtained by a gas phase oxidation method in a flame is preferable, and the surface is treated with a hydrophobizing agent or a heat treatment method to impart the above-mentioned hydrophobicity. It is more desirable to make the particles fine. It is desirable that such fine-grained alumina be a good gel electrolyte when adjusted to account for 5 to 30% by weight of the entire gel electrolyte.

The present invention also provides the negative electrode, wherein the negative electrode is made of at least one material selected from the group consisting of lithium, a lithium alloy, carbon capable of inserting and extracting lithium ions, and a metal oxide capable of inserting and extracting lithium ions. Is composed of at least one material selected from the group consisting of a transition metal oxide, a transition metal sulfide, a composite oxide of lithium and a transition metal, a conductive polymer compound, and a disulfide compound. The present invention relates to a lithium battery composed of an electrolyte. This battery has a high ionic conductivity and is almost free from electrolyte leakage.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The gel electrolyte according to the present invention comprises:
A non-aqueous electrolyte comprising an electrolyte and a non-aqueous organic solvent to which particulate alumina is added, and the lithium battery according to the present invention is a battery using such a gel electrolyte, and The configuration will be described in detail.

The electrolytic membrane electrolyte used in the present invention is generally may be either inorganic or organic electrolytes are used as the non-aqueous electrolyte for the electrolyte. When producing a lithium battery having a high energy density, it is preferable to use an inorganic electrolyte, particularly a lithium salt, as the electrolyte. Specific examples of lithium salts include the following compounds, which may be used alone or as a mixture of two or more.

(1) LiPF ₆ , LiBF ₄ , LiClO
_{4, LiAsF 6, Li 2 SiF} 6, Li (C 4 F 9) S
_{O 3, Li (C 8 F} 17) SO 3 , etc. (2) Lithium salt LiO (SO ₂ R ^{1 0)} represented by the following general formula ^{_{LiN (SO 2 R 1 1)}} (SO 2 R 1 2) LiC ( ^{_{SO 2 R 1 3) (SO}} 2 R 1 4) (SO 2 R 1 5) LiN (SO 2 OR 1 6) (SO 2 OR 17) wherein, R ^{1 0} to R ¹⁷ are carbon atoms 1 to 6 And may be the same or different from each other.

Specific examples include the following compounds. LiO (SO ₂ CF ₃ ) LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ CF ₂ CF ₃ ) ₃ LiN (SO ₂ OCF) ₃ ) ₂ , LiN (SO ₂ OCF ₂ C
F ₃ ) ₂

Of these, LiPF₆, LiB
F_FourAnd LiN (SO_TwoCF_Three)_TwoAnd LiN (SO_TwoCF_Two
CF_Three)_TwoThe general formula LiN (SO_TwoR^{1 1}) (S
O_TwoR ^{1 Two}) Shows high ionic conductivity
It is preferable from the point of view.

Such a lithium salt is added to the non-aqueous organic solvent so as to have a concentration of usually 0.1 to 5 (mol / l), preferably 0.5 to 3 (mol / l). Is done.

When the electrolytic solution is used for an electric double layer capacitor or an aluminum electrolytic capacitor, a compound having an organic cation such as a tetraalkylammonium salt, a tetraalkylphosphonium salt or a pyridinium salt may be used as the electrolyte. it can. Specific examples thereof include the following compounds, which may be used alone or as a mixture of two or more. Among them, the use of a tetraalkylammonium salt is preferred.

(1) (C ₂ H ₅ ) ₄ NPF ₆ , (CH ₃ ) ₄ N
PF ₆ , (C ₂ H ₅ ) _n (CH ₃ ) _m NPF ₆ (n and m are integers, n + m = 4) (2) (C ₂ H ₅ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBF ₄ , C ₂
H ₅ ) _n (CH ₃ ) _m NBF ₄ (n and m are integers, n + m
= 4)

(3) (C ₂ H ₅ ) ₄ NN (SO ₂ R ¹⁸ ) (S
^{_{O 2 R 1 9), (}} CH 3) 4 NN (SO 2 R 18) (SO
^{_{2 R 1 9), (C}} 2 H 5) n (CH 3) m NN (SO 2 R 18)
^{_{(SO 2 R 1 9) (}} n and m are integers, n + m = 4) ( 4) (C 2 H 5) 4 NSO 3 CF 3, (CH 3) 4 NSO 3 C
F ₃ , (C ₂ H ₅ ) _n (CH ₃ ) _m NSO ₃ CF ₃ (n and m
Is an integer, n + m = 4) (5) Tetraethylammonium phthalate, triethylmethylammonium phthalate, etc.

Nonaqueous Organic Solvent The solvent used in the present invention may be any aprotic organic solvent that is stable to the electrolyte, has high solubility for the electrolyte, and is electrochemically stable. The following are specific examples of such solvents.

(1) Dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl allyl carbonate, methyl vinyl carbonate, divinyl carbonate, diallyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, propionic acid Methyl, ethyl propionate,
Chain esters such as methyl butyrate, methyl valerate, methyl acrylate, methyl methacrylate, vinyl acetate and vinyl pivalate

(2) Phosphates such as trimethyl phosphate and triethyl phosphate (3) 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether, etc. (4) 1,4-dioxane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran, 3
-Methyl-1,3-dioxolane, 2-methyl-1,3
-Cyclic ethers such as dioxolane

(5) Amides such as dimethylformamide (6) Chain carbamates such as methyl-N, N-dimethyl carbamate (7) Chain sulfones such as dimethyl sulfone, diethyl sulfone, divinyl sulfone, diallyl sulfone (8) ) Γ-butyrolactone, γ-valerolactone, 3-
Cyclic esters such as methyl-γ-butyrolactone and 2-methyl-γ-butyrolactone

(9) Cyclic sulfones such as sulfolane and sulfolene (10) Cyclic carbamates such as N-methyloxazolidinone (11) Cyclic amides such as N-methylpyrrolidone (12) N, N-dimethylimidazolidinone (13) Ethylene carbonate, propylene carbonate, 4,4-dimethyl-5-methyleneethylene carbonate, 4-methyl-4-ethyl-5-methyleneethylene carbonate, 4-methyl-4-propyl-5-methylene Ethylene carbonate, 4-methyl-4-butyl-5
-Methylene ethylene carbonate, 4,4-diethyl-
5-methylene ethylene carbonate, 4-ethyl-4-
Propyl-5-methyleneethylene carbonate, 4-ethyl-4-butyl-5-methyleneethylene carbonate, 4,4-dipropyl-5-methyleneethylene carbonate, 4-propyl-4-butyl-5-methyleneethylene carbonate, 4, 4-dibutyl-5-methyleneethylene carbonate,

4,4-dimethyl-5-ethylidene ethylene carbonate, 4-methyl-4-ethyl-5-ethylidene ethylene carbonate, 4-methyl-4-propyl-5-ethylidene ethylene carbonate, 4-methyl-
4-butyl-5-ethylidene ethylene carbonate,
4,4-diethyl-5-ethylidene ethylene carbonate, 4-ethyl-4-propyl-5-ethylidene ethylene carbonate, 4-ethyl-4-butyl-5-ethylidene ethylene carbonate, 4,4-dipropyl-5-
Ethylidene ethylene carbonate, 4-propyl-4-
Butyl-5-ethylidene ethylene carbonate, 4,4
-Dibutyl-5-ethylidene ethylene carbonate,

4-methyl-4-vinyl-5-methyleneethylene carbonate, 4-methyl-4-allyl-5-methyleneethylene carbonate, 4-methyl-4-methoxymethyl-5-methyleneethylene carbonate, 4-methyl- Cyclic carbonates such as 4-acryloxymethyl-5-methyleneethylene carbonate, 4-methyl-4-allyloxymethyl-5-methyleneethylene carbonate

(14) Vinylene carbonate derivatives such as vinylene carbonate, methylvinylene carbonate and dimethylvinylene carbonate (15) Vinyl ethylene such as 4-vinylethylene carbonate, 4,4-divinylethylene carbonate and 4,5-divinylethylene carbonate Carbonate derivatives (16) 4-vinyl-4-methylethylene carbonate, 4-vinyl-5-methylethylene carbonate,
-Vinyl-4,5-dimethylethylene carbonate, 4
-Vinyl-5,5-dimethylethylene carbonate, 4
-Alkyl-substituted vinyl ethylene carbonate derivatives such as -vinyl-4,5,5-trimethyl ethylene carbonate

(17) Allyloxymethylethylene carbonate derivatives such as 4-allyloxymethylethylene carbonate and 4,5-diallyloxymethylethylene carbonate (18) 4-methyl-4-allyloxymethylethylene carbonate, 4-methyl Alkyl-substituted allyloxymethylethylene carbonate derivatives such as -5-allyloxymethylethylene carbonate (19) acryloxymethylethylene carbonate derivatives such as 4-acryloxymethylethylene carbonate and 4,5-acryloxymethylethylene carbonate (20 ) Alkyl-substituted acryloxymethyl ethers such as 4-methyl-4-acryloxymethylethylene carbonate and 4-methyl-5-acryloxymethylethylene carbonate Ren carbonate derivatives

(21) Ethylene glycol, diethylene glycol, triethylene glycol, and compounds represented by the following general formulas: HO (CH ₂ CH ₂ O) _a H, HO ｛CH ₂ CH (CH ₃ )
O｝ _b H, CH ₃ O (CH ₂ CH ₂ O) _c H, CH ₃ O ｛CH
₂ CH (CH ₃ ) O｝ _d H, CH ₃ O (CH ₂ CH ₂ O) _e C
H ₃ , CH ₃ O {CH ₂ CH (CH ₃ ) O} _f CH ₃ , C ₉ H
₁₉ PhO (CH ₂ CH ₂ O) _g {CH (CH ₃ ) O} _h CH ₃
(Ph is a phenyl group), CH ₃ O ｛CH ₂ CH (CH ₃ )
O｝ _i CO ｛O (CH ₃ ) CHCH ₂ ｝ _j OCH ₃ (In the above formula, a to f are integers of 4 to 250, and g to j are 2 to 249.
5 ≦ g + h ≦ 250 and 5 ≦ i + j ≦ 250. )

When this gel electrolyte is applied to a lithium battery, the following general formula (1) or (2)
When at least one non-aqueous organic solvent selected from the group consisting of the cyclic compound represented by the general formula (3) and the chain ester represented by the general formula (3) is used, it is preferable because the electrochemical stability of the solvent is high. Battery can be obtained.

[0040]

Embedded image

In the formula, R ^{1 to} R ⁶ and R ⁸ represent hydrogen, fluorine, a hydrocarbon group having 1 to 6 carbon atoms or a fluoroalkyl group, and R ⁷ represents hydrogen, 1 to 6 carbon atoms. Represents a hydrocarbon group, a fluoroalkyl group, or an alkoxy group, or a dialkylamino group having 1 to 12 carbon atoms.
X, Y, W, Z represents O or CH ₂ or N-R ^9,. R ⁹ is a hydrocarbon group having 1 to 6 carbon atoms.

In the above general formulas (1), (2) and (3), preferred examples of R ^{1 to} R ⁶ include hydrogen, methyl, ethyl, vinyl, propyl, isopropyl and fluoromethyl. , A difluoromethyl group, a trifluoromethyl group, and a pentafluoroethyl group. Preferred examples of R ⁸ include a methyl group, an ethyl group, a vinyl group, a propyl group, an isopropyl group, a trifluoroethyl group, and a pentafluoropropyl group. Also,
Preferred examples of R ⁷ include hydrogen, methyl, ethyl, propyl, isopropyl, methoxy, ethoxy,
Examples include a propoxy group, an isopropyloxy group, a dimethylamino group, a methylethylamino group, a diethylamino group, and a dipropylamino group.

Of the cyclic compounds represented by the above general formulas (1) and (2), a cyclic carbonate in which X, Y, W and Z are all oxygen is most desirable. Specific examples thereof include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate,
3-pentylene carbonate, vinylene carbonate,
Examples thereof include vinyl ethylene carbonate, divinyl ethylene carbonate, trifluoromethyl ethylene carbonate, and fluoroethylene carbonate. In particular,
It is preferable to use ethylene carbonate and propylene carbonate having a high dielectric constant and a small molecular size because a high ionic conductivity can be obtained.

When a carbon material having a (002) plane spacing (d002) of 0.340 nm or less measured by X-ray analysis is used as a negative electrode active material of a battery using a gel electrolyte, Use of ethylene carbonate is preferred, and ethylene carbonate and other cyclic carbonates may be used as a mixture of two or more.

Specific examples of the chain ester represented by the general formula (3) include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, methyl trifluoroethyl carbonate, and propion. Examples thereof include methyl acid, methyl pivalate, methyl formate, and methyl acetate. Among them, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl trifluoroethyl carbonate, which have high electrochemical stability, low viscosity and high ion conductivity, are preferably used. These chain esters may be used as a mixture of two or more.

When the cyclic ester represented by the general formula (1) or (2) is used, the dissociation of the electrolyte is promoted due to its high dielectric constant, and the chain ester represented by the general formula (3) is used. When is used, its viscosity is low, so that the ion mobility can be increased. When a non-aqueous solvent is formed by combining a cyclic ester and a chain ester, the viscosity is low, and a high ionic conductivity is obtained, so that the non-aqueous solvent is suitable as a non-aqueous solvent for an electrolyte. Thus, a gel electrolyte having excellent electric conductivity can be obtained, and a battery having excellent load characteristics and low-temperature characteristics can be obtained.

The non-aqueous organic solvent may be composed of a cyclic ester represented by the general formula (1) or (2) or a chain ester represented by the general formula (3) alone, or Both can be combined and used as a mixed solvent. In the case of using the latter mixed solvent, the mixing ratio (weight ratio) is expressed as cyclic ester: chain ester, 1:99 to 99: 1, preferably 5: 9.
5 to 80:20, more preferably 10:90 to 70:
30, particularly preferably 15:85 to 55:45.
When the content is within such a mixing range, the increase in the viscosity of the solvent can be suppressed and the degree of dissociation of the electrolyte can be increased, so that high ionic conductivity can be obtained, and the load characteristics and low-temperature characteristics of the battery can be improved. it can.

Fine- grained alumina Fine- grained alumina used in the present invention is added for the purpose of promoting the gelation of the electrolytic solution. At the same time, in order to suppress the reaction with the electrolytic solution, the surface hydroxyl group per unit surface area is reduced. The number is 0.003 (mmol / m ² ) or less, preferably 0.
002 (mmol / m ² ) or less, more preferably 0.
It is desirable that the particulate alumina is 001 (mmol / m ² ) or less. When the number of surface hydroxyl groups is within the above range, the reaction with the inorganic electrolyte is actually reduced or suppressed, and the generation of hydrogen fluoride can be almost prevented. Fine-particle alumina having such a number of surface hydroxyl groups can be obtained by subjecting ordinary fine-particle alumina to a surface treatment as described below, for example, to remove at least part, preferably most of the surface hydroxyl groups. it can.

The commonly used finely divided silica or titania is a so-called hydrophilic silica or titania having a large number of surface hydroxyl groups, so that it easily reacts with an electrolyte containing a fluorine atom, and hydrogen fluoride is used. Comes out. However, when the above-mentioned particulate alumina is used, the reaction with the electrolyte containing a fluorine atom is suppressed, so that an electrolyte having a high ionic conductivity itself such as LiPF ₆ or LiBF ₄ can be used. The ionic conductivity of the gel electrolyte can be increased.

As a method for quantifying the number of surface hydroxyl groups, a lithium aluminum hydride method (Journal of Colloid and I
nterface Science, 125 , 61-68, (198
8) is desirable. This method uses a lithium aluminum hydride (Li
AlH ₄ ), and the number of surface hydroxyl groups is determined by measuring hydrogen generated by the following formula. In this formula, the compound having a hydroxyl group is represented by (-O
H). 4 (−OH) + LiAlH ₄ → (−O) Li +
(-O) ₃ Al + 4H ₂

The fine-particle alumina is added as a gelling agent for the electrolyte. The fine-particle alumina having a small number of surface hydroxyl groups, which has been described above, is prepared by a method of adjusting the number of hydroxyl groups by reaction with a hydrophobizing agent. When employed, the alumina substantially exhibits hydrophobicity, so that the electrolyte has a higher gelling effect than when the same weight of hydrophilic fine-particle alumina is used. Therefore, gelation of the electrolyte can be promoted with a small amount, and interference of ionic conduction can be suppressed by the reduced amount, so that ionic conductivity can be increased. For this reason, it is more desirable that the particulate alumina having a small number of surface hydroxyl groups simultaneously exhibit hydrophobicity.

The degree of hydrophobicity of the particulate alumina can be evaluated by the critical concentration of methanol. That is, the particulate alumina used in the present invention preferably has a critical concentration of methanol of 20% by weight or more, more preferably 30% by weight or more, in a methanol wet test. When the methanol critical concentration is in the above range, it is substantially hydrophobic, and can promote gelation with a small amount of addition. As the amount of added alumina is small,
The ionic conductivity of the electrolyte can be kept high.

The methanol wetness test is a test method for measuring the wettability of a powder with respect to a mixed solution of water and methanol. The specific test method is as follows. First, 100 g of a mixture of methanol and water having a predetermined concentration is put in a 200 ml capacity container that can be hermetically sealed, and then 1 g of powder is charged to seal the container. Mix vigorously for 1 minute,
Let stand for minutes. When the mixed liquid and the powder form a uniform single phase or when the powder precipitates in the liquid phase, it indicates that the powder is wet with the mixed liquid, and when the powder becomes two or more phases, The powder indicates that the mixture is not wet. The minimum amount (% by weight) of methanol in the mixture that is necessary for the powder to wet the mixture is referred to as the methanol critical concentration. The higher the critical concentration of methanol, the higher the hydrophobicity.

Further, the particulate alumina used in the present invention is composed of particles small enough to be expressed as ultrafine particles, and has a particle diameter of 50 nm or less, preferably 2 nm or less.
It is desirable that the thickness be 0 nm or less, more preferably less than 10 nm. The smaller the particle size, the higher the effect of enhancing the gel properties of the electrolyte.

Further, the particulate alumina has a specific surface area of 30 (m) measured by a general nitrogen adsorption method or the like.
² / g) or more, and more preferably 80 (m ² / g) or more. When the specific surface area is in the above range, gelation of the electrolyte can be sufficiently promoted.

The fine-particle alumina having such physical properties used in the present invention can be obtained by heat-treating the fine-particle alumina or subjecting the fine-particle alumina to a surface treatment by a reaction with a hydrophobizing agent. In the method by heat treatment, a dehydration reaction is caused between hydroxyl groups present on the alumina surface by heat treatment, so the higher the heat treatment at a higher temperature, the higher the dehydration effect. In some cases, the effect of gelling the electrolyte is reduced. Therefore, the heat treatment temperature is 150 to 1000
° C, preferably 250-600 ° C, more preferably 30 ° C.
0-500 degreeC is desirable.

The surface treatment with the hydrophobizing agent proceeds by a reaction between an alkylating agent, a silylating agent, an esterifying agent and the like and a hydroxyl group on the alumina surface. As the alkylating agent,
Alkyl sulfate, alkyl sulfonate, alkyl borate,
Examples thereof include alkyl phosphate and alkyl carbonate. As a silylating agent, chlorotrialkylsilane,
Examples thereof include alkyl trialkoxy silane, dialkyl dialkoxy silane, and trialkyl alkoxy silane. Various alcohols can be used as the esterifying agent. Alternatively, a reaction with a metal alkoxide such as trialkoxy aluminum or tetraalkoxy titanium may be used.

The surface treatment method may be any of the above-mentioned methods. However, when a treatment method using an alkylating agent or a silylating agent is selected, the type of the alkyl group provided to the surface can be appropriately selected. Thereby, the degree of hydrophobicity can be controlled, and the gel state of the electrolyte can be appropriately adjusted.

As a surface treatment method using a hydrophobizing agent, any of a gas phase method and a liquid phase method can be adopted. However, when the liquid phase method is used, particles are easily aggregated. The use of treated particulate alumina is preferred. As the treatment method, a fluidized bed system described in JP-B-41-17049, JP-B-61-50882 and the like can be used.

The hydrophobizing agent is not particularly limited as long as the effects of the present invention can be sufficiently obtained, and can be appropriately selected from the following specific compounds. One of those hydrophobizing agents may be used, or two or more thereof may be used in combination. Further, two or more kinds of hydrophobic fine-particle aluminas surface-treated with different hydrophobizing agents may be mixed and used.

(1) Alkylating agents such as alkyl halides, dialkyl sulfates, and alkyl sulfonates (where the alkyl group is ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, dodecyl, etc .; , Chlorine, bromine, etc.) (2) Chlorosilanes such as methylchlorosilane, ethylchlorosilane, propylchlorosilane, vinylchlorosilane and phenylchlorosilane (3) Polymerized silicon compounds such as dimethylpolysiloxane and silicone oil ( 4) methylmethoxysilane, methylethoxysilane,
Alkoxysilanes such as ethylmethoxysilane, vinylmethoxysilane, and phenylmethoxysilane (5) Fluorinating agents such as diethylaminotrimethylsilane, carbonyl fluoride, and hydrogen fluoride

In the present invention, it is particularly preferable to use fine-particle alumina obtained by a gas-phase oxidation method in a flame and hydrophobic fine-particle alumina whose surface is subjected to a hydrophobic treatment with a hydrophobizing agent.

The particulate alumina obtained by the gas phase oxidation method in a flame is generally known by the name of fumed alumina, and is generally available under the trade name Aerosil manufactured by Nippon Aerosil Co., Ltd. The production method thereof is described in JP-B-47-46274 and JP-A-58-91031.
No., etc. The raw material may be any compound having volatility and being hydrolyzable, such as aluminum halides such as trichloroaluminum, and alkoxyaluminums such as trimethoxyaluminum, triethoxyaluminum, triisopropoxyaluminum, and diethoxyaluminum hydride. , Aluminum alkyl such as triethyl aluminum

Gel Electrolyte The gel electrolyte according to the present invention was obtained by adding particulate alumina to an electrolyte and a non-aqueous organic solvent (hereinafter, the solution may be referred to as an electrolyte), and as a whole a gel was formed. An electrolyte is formed. The addition amount of the particulate alumina at this time is determined in consideration of the properties of the gelled electrolyte and the ionic conductivity, and is expressed as a ratio (weight ratio) of the particulate alumina to the electrolytic solution of 5:95. ~ 30: 70, more preferably 7: 93 ~ 25: 75, even more preferably 1
Desirably, it is in the range of 0:90 to 20:80.
Within this range, the electrolyte exhibits sufficient thixotropic properties,
Good gel state is maintained and high ionic conductivity is exhibited.

As described above, the gel electrolyte according to the present invention has performance such as high ionic conductivity comparable to the ionic conductivity of the electrolyte comprising the electrolyte and the non-aqueous organic solvent. When used as a battery, a battery with almost no liquid leakage can be obtained, and it can be used as an electrolyte for various electrochemical devices such as an electric double layer capacitor and an aluminum electrolytic capacitor.

Lithium Battery The lithium battery according to the present invention comprises a negative electrode, a positive electrode and the above-mentioned gel electrolyte, and this structure is particularly suitable for a lithium secondary battery.

As the negative electrode active material constituting the negative electrode, lithium metal, a lithium alloy, and a material capable of doping and dedoping lithium ions can be used. Such a material that can be doped or dedoped with lithium ions can be appropriately selected from carbon materials, titanium oxide, transition metal nitrides, tin oxide, silicon, and the like. Among them, a carbon material capable of doping and de-doping lithium metal, a lithium alloy, or lithium ion is preferable. In particular, a carbon material capable of doping and de-doping lithium ions is preferable, and such a carbon material may be graphite or amorphous carbon, and may be activated carbon, carbon fiber, carbon black, meso carbon. Carbon microbeads, natural graphite and the like can be used.

As the positive electrode active material constituting the positive electrode, Mo is used.
Transition metal oxide or transition metal sulfide such as S ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , L
Composite oxides composed of lithium and a transition metal such as iMn ₂ O ₄ , LiNiO ₂ , and LiNi _X Co _(1-X) O ₂ , polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline composite, etc. Examples include a conductive polymer compound and a disulfide compound. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable.

The gel electrolyte is used by filling the gap between the negative electrode and the positive electrode facing each other and the pores of the negative electrode and the positive electrode. Between the negative electrode and the positive electrode, a separator may be interposed to prevent electrical contact between the negative electrode and the positive electrode, and a microporous polyolefin film or a nonwoven fabric made of polyolefin or ceramic fiber is usually used as the separator. .

A lithium battery using such a gel electrolyte can be formed into a film shape, a cylindrical shape, a coin shape, a square shape, or any other shape. However, the basic structure of the battery is the same regardless of the shape as described above, and the design can be changed according to the purpose. In such a battery, there is almost no fear of electrolyte leakage.

For example, a method of manufacturing a film-shaped lithium secondary battery will be described. A negative electrode active material is applied to a negative electrode current collector such as a copper foil or a copper mesh to form a negative electrode, and a positive electrode current collector such as an aluminum foil or an aluminum mesh is formed. A multi-layer film in which a positive electrode active material is applied to a conductor to form a positive electrode, and then a negative electrode and a positive electrode are laminated via a polyolefin nonwoven fabric holding a gel electrolyte, while a film of polyolefin or polyester is laminated on an aluminum foil. Is prepared in advance, and the above-mentioned laminated body is stored in this multilayer film-made outer bag. Alternatively, it can also be manufactured by applying a gel electrolyte on the negative electrode and the positive electrode with a doctor blade or the like, stacking them via a separator, and then storing the above-mentioned laminate in an outer bag made of a multilayer film.

The filling of the gel electrolyte into the electrode is performed by applying pressure to the battery at a pressure higher than the gel electrolyte shows thixotropic to fluidity. At this time, the inside of the multi-layer film bag may be decompressed so that the gas in the electrode can be easily removed. The sealing of the bag made of the multilayer film can be performed by heat sealing the end of the bag.

As another method for manufacturing a battery, a battery is assembled by interposing fine-particle alumina between a positive electrode and a negative electrode in advance, and then an electrolyte is injected into the battery.
As a result, a method of forming a gel electrolyte composed of an electrolytic solution and hydrophobic fine-particle alumina may be employed.

[0074]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the examples unless it exceeds the gist.

1. Preparation of gel electrolyte and gel properties
The evaluation gel electrolyte was prepared by dissolving LiPF ₆ as an electrolyte to a concentration of 1 (mol / l) in a mixed solvent of ethylene carbonate and methyl ethyl carbonate (volume ratio of 1: 2) to obtain an electrolytic solution (hereinafter referred to as “electrolyte”). (Referred to as an electrolytic solution (A)), and then various inorganic oxide fine particles were mixed at the ratio shown in Table 1 to prepare.

[0076]

[Table 1]

(Note) (1) A product of Nippon Aerosil Co., Ltd. (fumed alumina; trade name: AEROSIL C) was heated at 500 ° C. (2) A product manufactured by Nippon Aerosil Co., Ltd. (fumed alumina; trade name: AEROSIL C) was treated with octadecyldimethylchlorosilane and then heated at 200 ° C. (3) Nippon Aerosil products (hydrophilic fumed silica; trade name AEROSIL 200) (4) Nippon Aerosil products (hydrophilic fumed titania; trade name AEROSIL P25) (5) Volume ratio of ethylene carbonate and methyl ethyl carbonate 1 (mol) of LiPF _{6 in} a 1: 2 mixed solvent
/ L) electrolytic solution dissolved at a concentration of

The properties of the oxide fine particles are as described in Table 2. The numbers in parentheses described in the type column correspond to the numbers described in the comment column.

[Table 2]

The thixotropic properties of the above-mentioned electrolytes were evaluated by the following method, and the results are shown in Table 3. Gel electrolyte 30 m in a container of 40 mm in diameter and 70 mm in height
m, and a rod having a diameter of 3.3 mm was pressed onto the gel electrolyte, and a load was gradually applied to the rod.
At this time, the load at which the rod sinks by 25 mm or more was named the flow load, and the thixotropic property was evaluated based on the value. The greater the flow load, the higher the thixotropy and the lower the fluidity of the liquid.

[0080]

[Table 3] (Note) It flowed under the load (3 g) of only the rod.

From the results shown in Table 3, the gel electrolytes of Examples 1 to 6 show thixotropic properties, and the electrolytes have almost no fluidity. On the other hand, in the system in which fumed alumina was not added (Comparative Example 1) and the system in which the amount of fumed alumina was small (Comparative Example 2), the flow load was small, and it was found that almost no gelation occurred. Further, from the comparison between Examples 2 and 3, it can be seen that the use of hydrophobized particulate alumina is more excellent in thixotropy.

[0082] 2. Evaluation of the thermal stability of the gel electrolyte The electrolyte obtained in the above Examples and Comparative Examples,
The thermal stability was evaluated. In the evaluation method, the gel electrolyte was stored in a thermostat at 80 ° C. for 24 hours, and judgment was made based on the presence or absence of gas generation.

[0083]

[Table 4]

From the results shown in Table 4, it can be seen that no gas was generated when the hydrophobic fine-particle alumina was used, and the reaction with LiPF ₆ was suppressed. On the other hand, when hydrophilic fumed silica and hydrophilic fumed titania were used, gas generation was clearly observed.

[0085] 3. Lithium ion using gel electrolyte
To prepare a lithium ion battery using the electrolyte obtained in Examples and Comparative Examples of the characteristics above down battery was evaluated for initial load characteristics and high temperature storage characteristics of the battery.

<Preparation of Negative Electrode> Natural graphite (L made by Chuetsu Graphite Co., Ltd.)
87 parts by weight of F-18A) and 13 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidinone as a solvent to prepare a natural graphite mixture slurry. Next, the negative electrode mixture slurry was applied to a 18 μm-thick negative electrode current collector made of a strip-shaped copper foil, dried, compression molded, and then punched into a disk shape having a diameter of 14 mm to obtain a coin-shaped natural graphite electrode. Was. The thickness of this natural graphite electrode mixture is 11
0 μm and the weight was 20 mg / Φ14 mm.

<Preparation of LiCoO ₂ Electrode>
₂ (HLC- manufactured by Honjo FMC Energy Systems Co., Ltd.
21) 90 parts by weight, 6 parts by weight of graphite as a conductive agent, 1 part by weight of acetylene black, and 3 parts by weight of polyvinylidene fluoride as a binder are mixed, dispersed in N-methylpyrrolidone as a solvent, and mixed with LiCoO _2. An agent slurry was prepared. This LiCoO ₂ mixture slurry was applied to a 20 μm-thick aluminum foil, dried, and then compression molded. This was punched out into a 13 mm-diameter disc to produce a LiCoO ₂ coin-type electrode. The thickness of this LiCoO ₂ mixture is 90
μm, and the weight was 35 mg / Φ13 mm.

<Preparation of Coin-Type Battery> A natural graphite electrode having a diameter of 14 mm, a LiCoO ₂ electrode having a diameter of 13 mm, and a microporous polypropylene film having a diameter of 16 mm and a thickness of 25 μm each coated with 50 mg of a gel electrolyte on both surfaces. A separator was prepared. In Comparative Example 5, an electrolytic solution was impregnated in a microporous polypropylene film having the same shape. Next, a natural graphite electrode, a separator, and LiCo are placed in a stainless steel 2032 size battery can.
The O ₂ electrode were laminated in this order. Then, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) was housed in the battery can, pressed, and excess gel electrolyte was removed by protruding from the electrode. Finally, the spring was housed, and the battery can lid was swaged via a gasket made of polypropylene. As a result, a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was obtained, and the airtightness in the battery was maintained.

<Measurement of Load Characteristics of Battery> Using the above-mentioned coin-type battery, the current value of the battery at a constant voltage of 4.2 V was 0 at a constant current of 0.5 mA and a constant voltage of 4.2 V. The battery was charged until the current reached 0.05 mA, and then 3.0 V from the battery under the conditions of a constant current of 1 mA and a constant voltage of 3.0 V.
It discharged until the current value at the time of a constant voltage became 0.05 mA. Next, the battery was charged to 3.9 V and charged at 60 ° C. for 1 hour.
After storage for 1 day, under the conditions of a constant current and a constant voltage of 1 mA, the termination condition was a current value of 0.05 mA at a constant voltage,
A charge / discharge of 4.2 V to 3.0 V was performed once, and a discharge capacity was measured (a low load discharge capacity).

Next, the battery was charged to 4.2 V under the same conditions, and then discharged at a constant current of 10 mA and terminated when the battery voltage reached 3.0 V, and the discharge capacity was measured ( High load discharge capacity). The ratio of the high-load discharge capacity to the low-load discharge capacity at this time was determined as an initial load characteristic index, and the results are shown in Table 5.

Next, in order to examine the high temperature stability in the state of the battery, the high temperature storage characteristics were examined. The battery was charged under the conditions of a constant current of 1 mA and a constant voltage of 4.20 V until the current value at a constant voltage of 4.2 V became 0.05 mA. Thereafter, the battery was stored at a high temperature for 7 days in a thermostat at 60 ° C. Thereafter, the load characteristics were measured under the same conditions as the measurement of the initial load characteristic index, and determined as the post-storage load characteristic index. The results are shown in Table 5.

[0092]

[Table 5] (Note) (9) Indicates that charging / discharging could not be performed.

From the results shown in Table 5, it was found that the battery using the gel electrolyte containing the particulate alumina had battery characteristics equal to or better than the battery using the electrolyte. On the other hand, a battery using a gel electrolyte using fumed silica having surface hydroxyl groups and fumed titania could hardly be charged or discharged.

[0094]

Gel electrolyte according to the present invention is adapted to gel state electrolyte stable only by adding a small amount of particulate alumina, also lithium salt containing fluorine atom such as LiPF ₆ Even when is used as an electrolyte, almost no reaction occurs between them, and a high electrolyte is maintained and a stable electrolyte is formed.

The battery using the gel electrolyte having a high ionic conductivity and having a stable ionic conductivity has almost the same load characteristics and load characteristics as those of a conventional battery using an electrolyte composed of an electrolyte and a non-aqueous organic solvent. The battery exhibited high-temperature storage characteristics, and furthermore, had almost no fear of liquid leakage.

Claims (16)

[Claims] 1. A gel electrolyte comprising an electrolyte, a non-aqueous organic solvent, and particulate alumina, wherein the number of surface hydroxyl groups per unit surface area of the alumina is 0.003 (mmol / m ² ) or less. 2. The gel electrolyte according to claim 1, wherein said electrolyte is a lithium salt or a tetraalkylammonium salt. 3. The gel electrolyte according to claim 2, wherein said lithium salt or tetraalkylammonium salt contains a fluorine atom in its molecule. 4. The method according to claim 1, wherein the lithium salt is LiPF ₆ , LiB
At least one selected from the group consisting of F ₄ and a compound represented by the general formula Li ⁺ N ⁻ (SO ₂ R ¹¹ ) (SO ₂ R ¹² )
The gel electrolyte according to claim 3, which is a kind of lithium salt. (Where R ¹¹ and R ¹² represent a fluoroalkyl group having 2 to 6 carbon atoms) 5. The gel electrolyte according to claim 1, wherein said non-aqueous solvent is an aprotic organic solvent. 6. The organic solvent according to claim 5, wherein said aprotic organic solvent is at least one solvent selected from the group consisting of formulas (1), (2) and (3).
2. The gel electrolyte according to item 1. Embedded image (Here, R ^{1 to} R ⁶ and R ⁸ represent hydrogen, fluorine, a hydrocarbon group having 1 to 6 carbon atoms, or a fluoroalkyl group, and R ⁷ represents hydrogen, a carbon group having 1 to 6 carbon atoms. Hydrogen group,
A fluoroalkyl group, an alkoxy group, or a group having 1 carbon atom
X, Y, W, and Z represent a dialkylamino group of
Represents O, CH ₂ , or NR ⁹ , wherein R ⁹ is a hydrocarbon group having 1 to 6 carbon atoms. ) 7. The aprotic organic solvent is ethylene carbonate or propylene carbonate, and at least one chain ester selected from the group consisting of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and methyl trifluoroethyl carbonate. The gel electrolyte according to claim 5, which is a mixed solvent of the following. 8. The above-mentioned particulate alumina has a methanol critical concentration of 2 as measured by a methanol wet test.
The gel electrolyte according to any one of claims 1 to 7, wherein the content is 0% by weight or more. 9. The gel electrolyte according to claim 1, wherein the particulate alumina has a specific surface area of 30 (m ² / g) or more. 10. The gel electrolyte according to claim 1, wherein the fine particle alumina has a particle diameter of 50 nm or less. 11. The gel electrolyte according to claim 1, wherein the surface of the particulate alumina is subjected to a hydrophobic treatment with a hydrophobizing agent. 12. The gel electrolyte according to claim 11, wherein the hydrophobizing agent is an alkylating agent or a silylating agent. 13. The gel electrolyte according to claim 1, wherein the fine-particle alumina has a surface subjected to a hydrophobic treatment by heat treatment. 14. The gel electrolyte according to claim 1, wherein said particulate alumina is obtained by a gas phase oxidation method in a flame. 15. The gel electrolyte according to claim 1, wherein said particulate alumina occupies 5 to 30% by weight of the entire gel electrolyte. 16. The negative electrode is made of at least one material selected from the group consisting of lithium, a lithium alloy, carbon capable of storing and releasing lithium ions, and a metal oxide capable of storing and releasing lithium ions. An oxide, a transition metal sulfide, a composite oxide of lithium and a transition metal, a conductive polymer compound, and at least one material selected from the group consisting of a disulfide compound, and the electrolyte is any one of claims 1 to 15. A lithium battery comprising the gel electrolyte according to item 1.