WO2011077939A1

WO2011077939A1 - Secondary battery having ion fluid

Info

Publication number: WO2011077939A1
Application number: PCT/JP2010/071877
Authority: WO
Inventors: 晃純木村
Original assignee: コニカミノルタホールディングス株式会社
Priority date: 2009-12-24
Filing date: 2010-12-07
Publication date: 2011-06-30
Also published as: JPWO2011077939A1

Abstract

Disclosed is a secondary battery which has: a cathode, an anode having a carbon material, and an electrolyte. The secondary battery is characterized in that: the electrolyte has a one type of supporting electrolyte salt and two types of ion fluid, but the anions in the supporting electrolyte salt and the two types of ion fluid are different; and at least one the of types of anion is an anion which forms a passive film on a collector. Furthermore, the secondary battery is characterized by at least one of the anion types which differ from the anion which forms the passive film on the collector being an anion which forms an SEI film on the carbon material on the anode.

Description

Secondary battery containing ionic liquid

The present invention relates to a secondary battery containing an ionic liquid.

Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, have high voltage and high energy density, and have recently been widely used in applications such as portable electronic devices and personal computers. In the future, it is also expected to be adapted for large-scale use such as stationary applications at home and automobiles, but it is important to further improve cycle characteristics, particularly to suppress deterioration of cycle characteristics in a high-temperature environment. It has become an issue.

By adding vinylene carbonate to the electrolyte for a non-aqueous electrolyte secondary battery, a part of vinylene carbonate is decomposed to form an SEI film on the negative electrode, and the film suppresses further oxidative decomposition, It is known that cycle characteristics can be improved.

For example, a secondary battery containing 0.1 to 10% by volume of vinylene carbonate in an electrolyte is disclosed (for example, see Patent Document 1). Thus, it is described that an SEI film can be formed on the graphite intercalation compound and the cycle characteristics can be improved.

Further, as an example of forming an SEI film on an electrode using a chemical species other than vinylene carbonate for the purpose of improving cycle characteristics, a secondary battery using an electrolyte containing a cyclic sulfonate ester is disclosed. . Thereby, it is disclosed that an SEI film is formed on the surface of the positive electrode by sulfur atoms, thereby improving charge / discharge characteristics and storage characteristics (see, for example, Patent Documents 2 and 3).

JP 2005-149750 A JP 2005-251677 A International Publication No. 2004/034491

However, the electrolyte for non-aqueous electrolyte secondary batteries using flammable vinylene carbonate does not have sufficient cycle characteristics, and further improvements are desired. In addition, the electrolyte for non-aqueous electrolyte secondary batteries using vinylene carbonate may cause deformation or ignition of the secondary battery cells during abnormal heating of the secondary battery, and further improvement is desired from the viewpoint of safety. It is rare. Since there is no risk of ignition and safety is high, it may be possible to add a little vinylene carbonate to the electrolyte using a flame-retardant ionic liquid, but the SEI film with vinylene carbonate is an electrolyte cycle using an ionic liquid. The characteristics could not be improved greatly.

Also, the secondary battery containing a cyclic sulfonate ester in the electrolyte has not enough SEI film formed by the cyclic sulfonate ester, and there is still room for improvement in cycle characteristics.

The present invention has been made in view of the above problems, and an object thereof is to provide a secondary battery using an ionic liquid having high safety and cycle characteristics. A further object of the present invention is to provide a secondary battery having high safety and cycle characteristics.

As a result of inventor's sincere examination in view of the above-mentioned problems, at least one supporting electrolyte salt in which each anion is different and an electrolyte containing two ionic liquids, the first anion is formed on the current collector on the current collector. It was found that the above problem can be solved by using an electrolyte containing an anion that can form an SEI film on the active material made of the carbon material.

That is, the configuration of the present invention is as follows. In a secondary battery having a positive electrode, a negative electrode having a carbon material, and an electrolyte, the electrolyte has one type of supporting electrolyte salt and two types of ionic liquids, and the supporting electrolyte salt and the two types of ionic liquids Each anion is different, and at least one of the anions is an anion that forms a passive film on the current collector, and an anion that forms a passive film on the current collector; Among the different anions, at least one is an anion that forms an SEI film on the carbon material on the negative electrode.

2. 2. The secondary battery as described in 1 above, wherein the electrolyte contains an anion that does not form a passive film or SEI film on an active material comprising a current collector and a carbon material.

3. 3. The secondary battery as described in 1 or 2 above, wherein the anion capable of forming a nonconductive state on the current collector is an anion selected from the following general formula (1) and general formula (2).

General formula (1)
P (R) _X F _6-X
General formula (2)
B (R) _Y F _4-Y
(In the above general formulas (1) and (2), R represents an alkyl group, cycloalkyl group, aryl group, hydroxyl group, carboxyl group, nitro group, trifluoromethyl group, amide group, carbamoyl group, ester group, carbonyloxy Group, cyano group, halogen atom, alkoxy group, aryloxy group, sulfonyl group, alkylthio group, arylthio group, sulfonamido group, sulfamoyl group, amino group, alkylamino group and arylamino group. X represents an integer from 1 to 5, and Y represents an integer from 1 to 3.)

By adopting the above configuration, it was possible to provide a secondary battery that has high cycle characteristics and can be preferably applied to an ionic liquid. Conventionally known vinylene carbonates and cyclic sulfonates have a low ability to form an SEI film in an ionic liquid, so it is estimated that decomposition of the ionic liquid electrolyte cannot be prevented and sufficient cycle characteristics have not been improved. . In addition, since vinylene carbonate and cyclic sulfonic acid esters are flammable, there is a risk of deformation or ignition of the secondary battery cell during abnormal heating of the secondary battery, but the electrolyte of the present invention does not necessarily require an organic solvent. Therefore, it is advantageous from the viewpoint of safety.

Furthermore, the present invention has found that in an electrolyte containing an ionic liquid, the decomposition of the ionic liquid on the current collector as well as the decomposition of the ionic liquid on the current collector is a cause of poor cycle performance. By allowing the anion forming the passive film to coexist, it was possible to impart high cycle characteristics to the electrolyte having the ionic liquid.

Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

(SEI film)
The SEI film (SEI: solid electrolyte interface) in the present invention will be described. Means have been proposed for forming a SEI film (solid electrolyte interface) on the surface of the carbon material on the negative electrode so that the carbon material on the negative electrode does not react directly with an organic solvent. (Hiroyoshi Nakamura et al. “Decompression suppression of electrolyte for lithium battery using electrolyte containing acetate”, Electrochemistry and Industrial Physical Chemistry, Vol. 73, No. 6. pp 429-434 (June 2005)) The film needs to be a film that can transmit lithium ions and has low electron conductivity.

(Passive membrane)
The passive film in the present invention will be described. It is a dense and strong film formed on a current collector metal and generated by an anion containing fluorine. This passive film suppresses corrosion of the current collector and decomposition of the electrolyte, which are causes of deterioration of battery performance.

The electrolyte of the present invention contains at least one lithium salt and two ionic liquids, and as a combination of anions,
(1) When the two anions of the ionic liquid are an anion that can form a passive film on the current collector and an anion that can form an SEI film on the active material (2) The anion of the supporting electrolyte salt is the current collector When an anion capable of forming a passive film on the body and one anion of the ionic liquid is an anion capable of forming an SEI film on the active material (3) The anion of the supporting electrolyte salt is an SEI film on the active material There are three possible cases in which one anion of the ionic liquid is an anion that can form a passive film on the current collector. Also good.

The remaining one anion may be an anion that can form a passive film on the current collector, an anion that can form an SEI film on the active material, or an anion that does not form a passive film. By using an anion that does not form a dynamic membrane and an SEI coating, it can be preferably used because it can be an electrolyte having high decomposition stability and high cycleability.

The blending amount of the supporting electrolyte salt in the electrolyte having an anion capable of forming a passive film on the current collector or an anion capable of forming a SEI film on the active material is preferably 5 to 40% by mass, particularly The content is preferably 10 to 30% by mass. The total amount of the supporting electrolyte salt in the electrolyte of the ionic liquid having an anion capable of forming a passive film on the current collector or an anion capable of forming a SEI film on the active material is 10% by mass to 60% by mass. In particular, 15% by mass to 30% by mass is preferable.

[Secondary battery]
The secondary battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and a separator as necessary. If the electrolyte is sufficiently elastic and there is no fear that the electrodes will contact each other, such as when a solid electrolyte is used, the separator can be omitted.

The electrolyte according to the present invention contains at least one supporting electrolyte salt having different anions and two ionic liquids, an anion that can form a passive film on the current collector, and an anion that forms the passive film. Contains an anion capable of forming an SEI film on an active material made of different carbon materials.

Hereinafter, the steps of the present invention will be described, but the present invention is not limited to the following steps.

[Electrolytes]
The electrolyte according to the present invention contains at least one supporting electrolyte salt having different anions and two ionic liquids, and the anion can form a passive film on the current collector, and carbon on the negative electrode. The material contains an anion capable of forming an SEI film. In the present invention, an anion that forms a passive film, an anion that forms a SEI film, or both anions can be present in the electrolyte as an ionic liquid. When an anion is introduced as an ionic liquid, the amount of anion introduced is not limited because there is no salt precipitation at a low temperature as expected when a solid salt such as a Li salt is contained. Therefore, according to the present invention, an anion capable of forming a passive film, and an anion capable of forming a SEI film in the carbon material on the negative electrode can be contained in the electrolyte in an arbitrary amount. In addition, it is possible to produce an electrolyte for forming an SEI film.

Furthermore, an organic solvent, inorganic fine particles, a polymer, and a polymerizable compound can be appropriately contained depending on the physical properties required for the electrolyte. In particular, it is also possible to form a solid electrolyte by containing inorganic fine particles and a polymer or inorganic fine particles and a polymerizable compound in the electrolyte. When a solid electrolyte is used for the secondary battery of the present invention, a separator is unnecessary, which is preferable.

(Anion capable of forming a passive film on the current collector and anion capable of forming a SEI film on the carbon material on the negative electrode)
The electrolyte according to the present invention is characterized by containing an anion capable of forming a passive film on the current collector and an anion capable of forming an SEI film on the carbon material on the negative electrode. As will be described later, since the current collector and the carbon material according to the present invention have different physical properties, it is difficult to form a passive film and an SEI film with the same anion. If either one of the passive film and the SEI film is not sufficiently formed, the electrolyte is electrolyzed from that portion, and therefore, it is considered that the electrolyte is deteriorated and the cycle characteristics are lowered. Therefore, in the present invention, by forming an SEI film on each of the current collector and the active material, it is possible to prevent the electrolyte from being electrolyzed to the minimum necessary and to prevent the deterioration of the electrolyte, thereby improving the cycle characteristics of the secondary battery. The present invention has been reached.

Tetrafluoroborate, hexafluorophosphate, and tris (pentafluoroethyl) trifluorophosphate can be used as the anion that can form a passive film on the current collector. The anion mentioned by (1) and General formula (2) can be used preferably.
General formula (1)
P (R) _X F _6-X
General formula (2)
B (R) _Y F _4-Y
In the above general formulas (1) and (2), R represents an alkyl group (methyl, ethyl, i-propyl, hydroxyethyl, stearyl, dodecyl, eicosyl, docosyl, oleyl, etc.), a cycloalkyl group (cyclopropyl, cyclohexyl). Etc.), aryl group (phenyl, p-tetradecanyloxyphenyl, o-octadecanylaminophenyl, naphthyl, hydroxyphenyl, etc.), hydroxyl group, carboxyl group, nitro group, trifluoromethyl group, amide group (acetamide, Benzamide etc.), carbamoyl group (methylcarbamoyl, butylcarbamoyl, phenylcarbamoyl etc.), ester group (ethyloxycarbonyl, i-propyloxycarbonyl, phenyloxycarbonyl etc.), carbonyloxy group (methylcarbonyloxy) , Propylcarbonyloxy, phenylcarbonyloxy, etc.), cyano group, halogen atom (chlorine, bromine, iodine, fluorine), alkoxy group (methoxy, ethoxy, butoxy, etc.), aryloxy group (phenoxy, naphthyloxy, etc.), sulfonyl group (Methanesulfonyl, p-toluenesulfonyl, etc.), alkylthio groups (methylthio, ethylthio, butylthio, etc.), arylthio (phenylthio, etc.), sulfonamide groups (methanesulfonamide, dodecylsulfonamide, p-toluenesulfonamide, etc.), sulfamoyl groups (Methylsulfamoyl, phenylsulfamoyl etc.), amino group, alkylamino group (ethylamino, dimethylamino, hydroxyamino etc.) and arylamino group (phenylamino, naphthylamino etc.) It represents a substituent. X represents an integer from 1 to 6, and Y represents an integer from 1 to 4. In addition, when it has several R in General formula (1) and General formula (2), each R may be the same or different.

Also, bisfluorosulfonylamide or fluorosulfonyl (trifluoromethylsulfonylamide) can be used as an anion that can form a SEI film on the active material.

There is no limitation on the cation which is a counter ion of the above anion.

The anion capable of forming a passive film on the current collector or the anion capable of forming an SEI film on the active material is not limited to a cation when it is an ionic liquid, but imidazolium (eg, 1-alkyl-3 -Methylimidazolium, 1-allyl-3-alkylimidazolium, 1-alkyl-2,3-dimethylimidazolium, etc.), pyridinium, ammonium, piperidinium, pyrrolidinium, pyrazolium, phosphonium, guanidinium can be used. Preferred cations include tetramethylammonium, ethyltrimethylammonium, n-propyltrimethylammonium, diethyldimethylammonium, di-n-propyldimethylammonium, triethylmethylammonium, n-butyldiethylmethylammonium, N, N-diethyl-N-methyl. -N- (2-methoxyethyl) ammonium, tetraethylammonium, tetra-n-propylammonium, tetra-n-butylammonium, tetra-n-pentylammonium, 5-azoniaspiro [4.4] nonane, dimethylimidazole, propylmethylimidazole, butyl Methylimidazole, N, N-dimethylpyrrolidinium, N-methyl-N-ethylpyrrolidinium, N-methyl-N-butylpyrrolidinium, N, -Dimethyl-piperidinium, N-methyl-N-ethyl-piperidinium, N-methyl-N-propyl-piperidinium, N-methyl-N-butyl-piperidinium, tetraethylphosphonium and 5-phosphonia spiro [4.4] nonane Can be preferably used.

(Supporting electrolyte salt)
The supporting electrolyte salt according to the electrolyte of the present invention is a salt that gives ions in the electrolyte composition for secondary batteries, and known supporting electrolyte salts used for batteries can be used. As the supporting electrolyte salt, a lithium salt can be preferably used.

Among the anions of metal ion salts, the anion that does not form a passive film and SEI film includes SCN ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ CF ₂ SO ₂ ). ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , CF ₃ SO ₃ ^{— and the} like can be mentioned. An anion capable of forming a passive film on the current collector and an SEI film can be formed on the active material. Any anion is preferably used.

(Ionic liquid)
The ionic liquid according to the electrolyte of the present invention is not particularly limited as long as it is a salt that is liquid at room temperature, and preferably has a melting point of 80 ° C. or lower, more preferably 60 ° C. or lower, more preferably 30 ° C. or lower. .

As such ionic liquids, alkyl ammonium salts, pyrrolidinium salts, piperidinium salts, imidazolium salts, pyridinium salts, sulfonium salts, phosphonium salts and the like can be used. An imidazolium salt represented by the following general formula (3) can also be preferably used.

In the general formula (3), R ¹ and R ³ represent a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and R ² , R ⁴ and R ⁵ represent a hydroxyl group, an amino group, respectively. A nitro group, a cyano group, a carboxyl group, an ether group, or a hydrocarbon group having 1 to 10 carbon atoms which may have an aldehyde group or a hydrogen atom, X represents a monovalent anion, Either an anion capable of forming a passive film on the current collector and an anion capable of forming a SEI film on the active material are preferably used, but an anion that does not form a passive film and SEI film may be used. Specifically, chlorine, bromine, iodine, NO ₃ ⁻ , CF ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (C ₂ F _{_{_{^{5 SO 2) 2 N -,}}}} AlC ₄ ^{^-,} _Al 2 Cl ₇ ^-, and the like.

Specific examples of the compound represented by the general formula (3) include, for example, ethylmethylimidazole-bisfluoromethylsulfonylamide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium-bisfluorosulfonyl Amide, ethylmethylimidazole-bistrifluorosulfonylamide, N-methyl-N-propylpyrrolidinium-bistrifluorosulfonylamide, 1-isopropyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt, 1-ethyl-2, 3-dimethylimidazolium bistrifluoromethanesulfonyl, 1-butyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl salt, 1-hexyl-2,3-dimethylimidazolium bistrifluoromethanesulfonyl 1-octyl-2,3-dimethyl-imidazolium bis trifluoromethanesulfonyl, and the ionic liquid or the like to the respective bis-fluorosulfonyl anion the bis trifluoromethanesulfonyl anion moieties.

In the present invention, it is preferable to use an ionic liquid that does not form a passive film or SEI film having a viscosity of 100 mPa · S or less. By using such an ionic liquid, sufficient ionic conductivity can be ensured even in an electrolyte that does not contain an organic solvent, and a secondary battery with higher safety can be manufactured. In addition, an electrolyte that does not contain an organic solvent is advantageous not only from the viewpoint of safety but also from the viewpoint of improving cycle characteristics because it does not have a volatile component in the electrolyte and can suppress an increase in internal pressure even at high temperatures. As ionic liquids having a viscosity of 100 mPa · S or less, ethylmethylimidazole-bisfluoromethylsulfonylamide, N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium-bisfluorosulfonylamide, ethylmethylimidazole- Examples include, but are not limited to, bistrifluorosulfonylamide, N-methyl-N-propylpyrrolidinium-bistrifluorosulfonylamide, or 1-ethyl-2,3-dimethylimidazolium bisfluorosulfonyl salt.

The content of the ionic liquid in the electrolyte is preferably 10% by mass to 90% by mass, and particularly preferably 40% by mass to 80% by mass.

(Organic solvent)
The electrolyte of the present invention contains a lithium salt and an ionic liquid, and an anion that can form a passive film. Therefore, an organic solvent containing vinylene carbonate that may impair flame retardancy is not necessary. However, it can also be contained within a range that does not hinder the effects of the present invention for the purpose of improving the conductivity of the electrolyte or reducing the viscosity.

Examples of the organic solvent applicable to the electrolyte of the present invention include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di Carbonates such as (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2- Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amide; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone, or those obtained by further introducing a fluorine substituent into the above organic solvent Can be used.

(Inorganic fine particles)
The electrolyte of the present invention can further contain inorganic fine particles, a polymerizable compound, and a polymer. It is also possible to obtain a solid electrolyte by containing a small amount or no use of the organic solvent and containing inorganic fine particles and a polymerizable compound or inorganic fine particles and a polymer in the electrolyte.

Examples of the inorganic fine particles related to the electrolyte of the present invention include iron oxide, zirconium oxide, niobium oxide, tantalum oxide, antimony oxide, clay, tin oxide, tungsten oxide, titanium oxide, aluminum phosphate, silicon oxide, zinc oxide, aluminum oxide, These composite oxides can be preferably used.

The average particle diameter of the inorganic fine particles is preferably 0.05 to 50 μm, more preferably 0.1 to 20 μm from the viewpoint of safety and voltage characteristics.

The average particle diameter is a volume average value of the diameter (sphere converted particle diameter) when each particle is converted into a sphere having the same volume, and this value can be evaluated from an electron micrograph. That is, by taking a transmission electron micrograph of the battery composition or particle powder, measuring 200 or more particles in a certain visual field range, obtaining a spherical equivalent particle diameter of each particle, and obtaining an average value thereof. Value.

The content of the inorganic fine particles is not particularly limited, but is preferably 0% by mass or more and 100% by mass or less with respect to 100% by mass of the ionic liquid. More preferably, it is 10 mass% or more and 70 mass% or less.

(Polymerizable compound)
As the polymerizable compound according to the electrolyte of the present invention, a polymerizable monomer that can be polymerized by polymerization or a polymerizable oligomer can be used.

Examples of the polymerizable monomer include radically polymerizable monomers and cationically polymerizable monomers. Although not particularly limited, ethylenically unsaturated monomers shown below are preferably used.

Examples of ethylenically unsaturated monomers include 2-vinylpyrrolidone, acryloylmorpholine, 2-hydroxybutyl vinyl ether, ethylethylene glycol mono (meth) acrylate, propylethylene glycol mono (meth) acrylate, and phenylethylene glycol mono (meth) acrylate. Monofunctional monomer, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polypropylene glycol di (meth) ) Acrylate, butylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, ethylene oxa Modified bisphenol A type di (meth) acrylate, propylene oxide modified bisphenol A type di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, glycerol di (meth) acrylate, pentaerythritol di (meth) acrylate, Bifunctional monomers such as ethylene glycol diglycidyl ether di (meth) acrylate, diethylene glycol diglycidyl ether di (meth) acrylate, phthalic acid diglycidyl ester di (meth) acrylate, hydroxypivalic acid modified neopentyl glycol di (meth) acrylate, Trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate , Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) acrylate, tri (meth) acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly (meth) acrylate, etc. Trifunctional or higher monomer, polyethylene glycol mono (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol-polypropylene glycol mono (meth) acrylate , Poly (ethylene glycol-tetramethylene glycol) mono (meth) acrylate, poly (propylene glycol-teto Ramethylene glycol) mono (meth) acrylate, methoxy polyethylene glycol mono (meth) acrylate, ethoxy polyethylene glycol mono (meth) acrylate, octoxy polyethylene glycol-polypropylene glycol mono (meth) acrylate, lauroxy polyethylene glycol mono (meth) acrylate And stearoxy polyethylene glycol mono (meth) acrylate. Of these, methoxypolyethylene glycol mono (meth) acrylate is preferably used.

Examples of the polymerizable oligomer include epoxy (meth) acrylate, polyester (meth) acrylate, and urethane (meth) acrylate compounds, and urethane (meth) acrylate compounds are preferably used. These polymerizable monomers and polymerizable oligomers can be used in combination.

Examples of the method for polymerizing the above monomers include methods using heat, X-rays, ultraviolet rays, visible rays, infrared rays, microwaves, and the like. In the case of the method using ultraviolet rays, a polymerization initiator that reacts with ultraviolet rays can be blended in the solid electrolyte composition in order to effectively advance the reaction. Examples of the ultraviolet polymerization initiator include benzoin, benzyl, acetophenone, benzophenone, Michler ketone, biacetyl, benzoyl peroxide and the like. These initiators can be used alone or in combination.

In the case of polymerization by heat, infrared rays, or microwaves, a thermal polymerization initiator can be used. As thermal polymerization initiators, 1,1-di (tertiarybutylperoxy) -3,3,5-trimethylcyclohexane, 2,2-bis- [4,4-di (tertiarybutylperoxycyclohexyl) propane ], 1,1-di (tertiarybutylperoxy) -cyclohexane, tertiarybutylperoxy-3,5,5-trimethylhexanonate, tertiarybutylperoxy-2-ethylhexanoate, benzoyl peroxide And dibenzoyl peroxide. These initiators can be used alone or in combination.

(High molecular)
The electrolyte according to the present invention can contain a polymer. When producing a solid electrolyte, a battery that can withstand repeated charge and discharge over a long period of time can be stably produced by using a solid electrolyte to which the above-described inorganic fine particles, polymerizable compound and polymer are added.

The polymer in the present invention preferably has a polymerization unit (monomer) number average polymerization degree of 1000 or more. For example, polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, poly (meth) acrylate alkyl, Poly (meth) acrylate aryl, polyfluorene, polyamide, polyimide, polyester, polycarbonate, polyurethane and the like are preferably used. Of these, alkyl poly (meth) acrylate is preferably used.

The blending amount of the above-described polymerizable compound and polymer in the electrolyte is preferably 0 to 40% by mass. In particular, when a solid electrolyte is used, it is preferably contained in an amount of 10 to 30% by mass.

[electrode]
The electrode according to the secondary battery of the present invention includes a positive electrode in which a positive electrode active material is provided on a current collector, and a negative electrode in which a negative electrode active material is provided on a current collector.

(Positive electrode active material)
As the positive electrode active material according to the secondary battery of the present invention, a mixture of an inorganic active material, an organic active material, or both, and an electrode mixture can be used. The positive electrode active material preferably contains at least an inorganic active material because the energy density of the secondary battery can be increased.

As the inorganic active material, for example, Li _0.3 MnO ₂ , Li ₄ Mn ₅ O ₁₂ , V ₂ O ₅ , LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFePO ₄ LiCo _1/3 Ni _1/3 Mn _{1 / 3} O ₂ , Li _1.2 (Fe _0.5 Mn _0.5 ) _0.8 O ₂ , Li _1.2 (Fe _0.4 Mn _0.4 Ti _0.2 ) _0.8 O ₂ , Li _{1 + x} (Ni _0.5 Mn _0.5 ) _1-x O ₂ , LiNi _0.5 Mn _1.5 O ₄ , Li ₂ MnO ₃ , Li _0.76 Mn _0.51 Ti _0.49 O ₂ , LiNi _{0 .8} Co _0.15 Al _0.05 O ₂ , Fe ₂ O ₃ , etc., metal oxides, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li ₂ MPO ₄ F (M = Fe, Mn), LiMn _0.875 Fe _{0. _{_{_{25 PO 4, Li 2 FeSiO 4}}}} , Li 2-x MSi 1-x P x O 4 (M = Fe, Mn), LiMBO 3 (M = Fe, Mn) metal phosphate such as metal silicate oxides, Metal borate is raised. In these chemical formulas, x is preferably in the range of 0-1. Further, fluorine-based compounds such as FeF ₃ , Li ₃ FeF ₆ , and Li ₂ TiF ₆ , metal sulfides such as Li ₂ FeS ₂ , TiS ₂ , MoS ₂ , and FeS, and composite oxides of these compounds and lithium can be given.

Among these, metal oxides and metal phosphorous oxides are preferable, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ , Li ₂ MPO ₄ F, LiMn _0.875 Fe _0.125 PO ₄ are more preferable, and LiFePO ₄ is most preferable. .

Examples of the organic active material include conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyparaphenylene, organic disulfide compounds, organic sulfur compounds DMcT (2,5-dimercapto-1,3,4-thiadiazole). ), Benzoquinone compound PDBM (poly 2,5-dihydroxy-1,4-benzoquinone-3,6-methylene), carbon disulfide, sulfur-based positive electrode materials such as active sulfur, organic radical compounds, and the like.

In addition, it is preferable that the surface of the positive electrode active material is coated with an inorganic oxide from the viewpoint of extending the life of the battery. In coating the inorganic oxide, a method of coating the surface of the positive electrode active material is preferable, and examples of the coating method include a method of coating using a surface modifying apparatus such as a hybridizer.

Examples of inorganic oxides include oxides of group 2 to 16 elements such as magnesium oxide, silicon oxide, alumina, zirconia, and titanium oxide, barium titanate, calcium titanate, lead titanate, γ-LiAlO ₂ , LiTiO _3. In particular, silicon oxide is preferable.

(Negative electrode active material)
As the negative electrode active material according to the secondary battery of the present invention, a material obtained by applying a mixture of a carbon material and an electrode mixture onto a current collector and drying can be used. The negative electrode active material that has been applied and dried may be formed by pressing. Examples of carbon materials include graphite materials such as various natural graphites, synthetic graphites, and expanded graphites that have been appropriately pulverized, mesocarbon microbeads that have been carbonized, mesophase pitch carbon fibers, and vapor grown carbon. Carbon materials such as fibers, pyrolytic carbon, petroleum coke, pitch coke, and needle coke, and synthetic graphite materials obtained by subjecting these carbon materials to graphitization, or mixtures thereof.

(Electrode mixture)
The electrode mixture according to the secondary battery of the present invention contains a conductive agent and a binder. As other materials, fillers, lithium salts, aprotic organic solvents and the like may be added.

The conductive agent is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the configured secondary battery. Conductive materials include carbon materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and conductive materials such as metal powders such as copper, nickel, aluminum, and silver, metal fibers, and polyphenylene derivatives. Can be used as one or a mixture thereof. Among them, a mixture of graphite and acetylene black is particularly preferable.

The addition amount of the conductive agent is preferably 1 to 50% by mass, and more preferably 2 to 30% by mass. When using a carbon material, 2 to 15% by mass is particularly preferable.

Examples of the binder used in the electrode mixture according to the present invention include polysaccharides, thermoplastic resins, and polymers having rubber elasticity. Specifically, starch, carboxymethyl cellulose, cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium alginate, polyacrylic acid, sodium polyacrylate, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylonitrile , Polyacrylamide, polyhydroxy (meth) acrylate, water-soluble polymers such as styrene-maleic acid copolymer, polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride -Tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, poly (Meth) acrylic acid ester copolymer containing (meth) acrylic acid ester such as propylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, polyvinyl acetal resin, methyl methacrylate, 2-ethylhexyl acrylate, (Meth) acrylic acid ester-acrylonitrile copolymer, polyvinyl ester copolymer containing vinyl ester such as vinyl acetate, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, polybutadiene, neoprene rubber, fluororubber, poly Emulsions such as ethylene oxide, polyester polyurethane resin, polyether polyurethane resin, polycarbonate polyurethane resin, polyester resin, phenol resin, epoxy resin Scan) or latex suspension and polyacrylate systems.

Among these, carboxymethylcellulose, polytetrafluoroethylene, and polyvinylidene fluoride are more preferable.

The binder can be used alone or in combination of two or more. When the amount of the binder added is small, the holding power and cohesive force of the electrode mixture are weakened. If the amount is too large, the electrode volume increases and the electrode unit volume or the capacity per unit mass decreases. For this reason, the addition amount of the binder is preferably 1 to 30% by mass, and more preferably 2 to 10% by mass.

The filler used in the electrode mixture according to the present invention can be any fibrous material that does not cause a chemical change in the secondary battery of the present invention. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. The amount of filler added is not particularly limited, but is preferably 0 to 30% by mass.

(Current collector)
As the current collector for the positive electrode and the negative electrode, an electron conductor that does not cause a chemical change is used.

As the current collector of the positive electrode, in addition to aluminum, stainless steel, nickel, titanium, etc., the surface of aluminum or stainless steel is preferably treated with carbon, nickel, titanium, or silver. Among them, aluminum and aluminum alloys are preferable. More preferred.

The negative electrode current collector is preferably copper, stainless steel, nickel, or titanium, and more preferably copper or a copper alloy.

As the shape of the current collector, a film sheet is usually used, but a porous body, a foam, a molded body of a fiber group, and the like can also be used. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm. Moreover, it is also preferable that the current collector surface is roughened by surface treatment.

[Electrode shape and electrode fabrication method]
The shape of the electrode and the method for producing the electrode according to the present invention will be described.

The shape of the secondary battery of the present invention can be applied to any shape such as a sheet type, a square type, and a cylinder type. The electrode is manufactured by applying a positive electrode active material or a mixture of a negative electrode active material and an electrode mixture on a current collector, drying and then pressing.

Examples of the application method of the positive electrode active material or the mixture of the negative electrode active material and the electrode mixture include, for example, a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, and a dip method. A squeeze method and the like are preferable. Of these, the blade method, knife method and extrusion method are preferred. The coating is preferably performed at a speed of 0.1 to 100 m / min. Under the present circumstances, the surface state of a favorable application layer can be obtained by selecting the said application | coating method according to the solution physical property and dryability of a mixture. Application may be performed one side at a time or both sides simultaneously.

Furthermore, the coating by the above method may be continuous, intermittent or striped. The thickness, length and width of the coating layer are determined by the shape and size of the battery. The thickness of the coating layer on one side is preferably 1 to 2000 μm in a compressed state after drying.

As a method for drying and dehydrating the electrode sheet coated product, a method in which hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air are used alone or in combination can be used. The drying temperature is preferably 80 to 350 ° C, more preferably 100 to 250 ° C. As a sheet pressing method, a generally adopted method can be used, but a calendar pressing method is particularly preferable. The pressing pressure is not particularly limited, but is preferably 20 to 300 MPa. The press speed of the calendar press method is preferably 0.1 to 50 m / min, and the press temperature is preferably room temperature to 200 ° C. The ratio of the negative electrode sheet width to the positive electrode sheet is preferably 0.9 to 1.1, particularly preferably 0.95 to 1.0. The content ratio of the positive electrode active material and the negative electrode active material varies depending on the compound type and the mixture formulation.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

[Production of Secondary Battery 1]
The secondary battery 1 was produced according to the following method.

(Manufacture of positive electrode)
Slurry positive electrode active material in which 90% by mass of lithium cobaltate, 6% by mass of graphite powder, 4% by mass of polyvinylidene fluoride copolymer and N-methylpyrrolidone are mixed on a 15 μm thick aluminum foil Was applied in a thickness of 200 μm. After drying with warm air at 130 ° C. for 5 minutes, a positive electrode was produced by roll pressing.

(Manufacture of negative electrode)
A slurry negative electrode active material in which 96% by mass of natural spherical graphite, 4% by mass of polyvinylidene fluoride copolymer and N-methylpyrrolidone are mixed is applied to a thickness of 200 μm on a copper foil having a thickness of 10 μm. did. After drying with hot air at 130 ° C. for 5 minutes, a negative electrode was produced by roll pressing.

(Manufacture of secondary battery 1)
In the glove box with a dew point of −60 ° C., a part of the positive electrode and the negative electrode prepared above is left as a tab, and is cut out to a size of 30 mm × 50 mm, and a separator Celgard 3501 of 32 mm × 52 mm (Celgard, manufactured by LLC) At the same time, it was inserted into a laminate film D-EL40H (Dai Nippon Printing Co., Ltd.). Thereafter, an electrolytic solution obtained by mixing 20 parts of 1-ethyl-3-methylimidazolium bisfluorosulfonylamide, 60 parts of 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonylamide and 20 parts of LiBF ₄ was poured into the laminate film. After the liquefaction, vacuum heat sealing was performed, and the secondary battery 1 was produced.

[Production of secondary batteries 2 to 14]
Secondary batteries 2 to 14 were produced in the same manner as in the production of the secondary battery 1 except that the electrolytic solution was changed to the ionic liquid and supporting electrolyte salt shown in Table 1.

[Evaluation of secondary battery]
The fabricated secondary batteries 1 to 14 were evaluated as follows. A battery charged at a voltage of 4.2 V and a charge rate of 0.125 C for 8 hours was discharged at a discharge rate of 0.125 C until the voltage of the secondary battery became 3 V, which was defined as one cycle. This cycle was repeated, and the number of times until the initial discharge capacity fell below 80% was measured.

Moreover, in Table 1, the abbreviation described in each ionic liquid and supporting electrolyte represents the following compounds.
EMIFSA: 1-ethyl-3-methylimidazolium bisfluorosulfonylamide EMITFSA: 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonylamide P13FSA: N-methyl-N-propylpyrrolidinium bisfluorosulfonylamide EMIBF ₃ ( CF ₂ CF ₃ ): 1-ethyl-3-methylimidazolium (pentafluoroethyl) trifluoroborate HNIPTP: 1-hexyl-3-methylimidazolium tris (pentafluoroethyl) trifluorophosphate EMIFTA: 1-ethyl- 3-Methylimidazolium fluorosulfonyl (trifluoromethylsulfonylamide)
EMIBF ₄ : 1-ethyl-3-methylimidazolium tetrafluoroborate P13TFSA: N-methyl-N-propylpyrrolidinium bistrifluoromethylsulfonylamide LiBF ₄ : lithium tetrafluoroborate LiTFSA: lithium bistrifluoromethylsulfonylamide LiFSA: lithium Bisfluorosulfonylamide Among these compounds, EMIFSA, P13FSA, EMIFTA, and LiFSA are compounds having an anion that forms an SEI film, and EMIBF ₃ (CF ₂ CF ₃ ), HNIPTP, EMIBF ₄ and LiBF ₄ are passive films. It is a compound which has an anion which forms. EMITFSA and P13TFSA are compounds having anions that do not form SEI films or passive films.

As is clear from Table 1, the secondary battery having an anion that forms a passive film on the current collector and an anion that forms an SEI film on the carbon material on the negative electrode has safety and cycle characteristics. Is apparently high.

Claims

In a secondary battery having a positive electrode, a negative electrode having a carbon material, and an electrolyte, the electrolyte has one type of supporting electrolyte salt and two types of ionic liquids, and the supporting electrolyte salt and the two types of ionic liquids Each anion is different, and at least one of the anions is an anion that forms a passive film on the current collector, and an anion that forms a passive film on the current collector; Among the different anions, at least one is an anion that forms an SEI film on the carbon material on the negative electrode.
The secondary battery according to claim 1, wherein the electrolyte contains an anion that does not form a passive film or SEI film on an active material made of a current collector and a carbon material.
The secondary battery according to claim 1 or 2, wherein the anion capable of forming a nonconductive state on the current collector is an anion selected from the following general formula (1) and general formula (2).
General formula (1)
P (R) X F 6-X
General formula (2)
B (R) Y F 4-Y
(In the above general formulas (1) and (2), R represents an alkyl group, cycloalkyl group, aryl group, hydroxyl group, carboxyl group, nitro group, trifluoromethyl group, amide group, carbamoyl group, ester group, carbonyloxy Group, cyano group, halogen atom, alkoxy group, aryloxy group, sulfonyl group, alkylthio group, arylthio group, sulfonamido group, sulfamoyl group, amino group, alkylamino group and arylamino group. X represents an integer from 1 to 5, and Y represents an integer from 1 to 3.)