JP2008112617A - Nonaqueous electrolyte solution for battery and nonaqueous electrolyte solution battery equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte solution for a battery with excellent safety and yet capable of improving battery performance. <P>SOLUTION: The nonaqueous electrolyte solution for a battery contains ionic liquid having a phosphorus-nitrogen double bond, an anhydrous dicarboxylic acid compound having a cyclic structure, and supporting salt. Further, 5-norbornene-2,3-dicarboxylic anhydride, 1,2,3,6-tetrahydro phthalic anhydride, and bicyclo [2.2.2] octo-5-ene-2,3-dicarboxylic anhydride are preferred as the anhydrous dicarboxylic acid compound having the cyclic structure, and a content of the anhydrous dicarboxylic acid compound having the cyclic structure is preferred to be in the range of 0.1 to 3.0% by mass of the total nonaqueous electrolyte solution for the battery. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a battery non-aqueous electrolyte and a non-aqueous electrolyte battery including the same, and in particular, contains a specific ionic liquid and dicarboxylic anhydride and has excellent safety and battery performance. It is about.

  In recent years, there has been a demand for lightweight, long-life, high-energy-density batteries as main power sources or auxiliary power sources for electric vehicles and fuel cell vehicles, or as power sources for small electronic devices. In contrast, a non-aqueous electrolyte battery using lithium as a negative electrode active material is known as one of batteries having a high energy density because the electrode potential of lithium is the lowest among metals and the electric capacity per unit volume is large. Many types of batteries, whether primary batteries or secondary batteries, have been actively researched, and some have been put into practical use and supplied to the market. For example, non-aqueous electrolyte primary batteries are used as power sources for cameras, electronic watches, and various memory backups. In addition, non-aqueous electrolyte secondary batteries are used as drive power sources for notebook computers and mobile phones, and are also being considered for use as main power sources or auxiliary power sources for electric vehicles and fuel cell vehicles. .

  In these non-aqueous electrolyte batteries, lithium as the negative electrode active material reacts violently with compounds having active protons such as water and alcohol, so that the electrolyte used in the batteries is non-ester compounds and ether compounds. Limited to protic organic solvents. However, although the aprotic organic solvent has low reactivity with the lithium of the negative electrode active material, for example, when a battery is short-circuited, a large current flows suddenly, and when the battery abnormally generates heat, it is vaporized and decomposed. Therefore, there is a high risk of generating gas, causing the battery to rupture or ignite due to the generated gas and heat, and sparks generated during a short circuit.

  To solve this problem, methods for making non-aqueous electrolytes flame-retardant have been studied. For example, phosphoric acid esters such as trimethyl phosphate are used for non-aqueous electrolytes, or phosphoric acid is used for aprotic organic solvents. Methods for adding esters have been proposed (see Patent Documents 1 to 3). However, these phosphate esters have a problem in that they are gradually reduced and decomposed at the negative electrode by repeating charge and discharge, and battery characteristics such as charge and discharge efficiency and cycle characteristics are greatly deteriorated.

  On the other hand, since the report of Wilkes et al. In 1992, an ionic liquid has attracted attention as a substance that is liquid at room temperature and has excellent ionic conductivity. In the ionic liquid, the cation and the anion are combined by electrostatic attraction, the number of ion carriers is very large, and the viscosity is relatively low, so that the ion mobility is high even at room temperature. It has the characteristic that the property is very high. In addition, since the ionic liquid is composed only of cations and anions, the boiling point is high and the temperature range in which the liquid state can be maintained is very wide. Furthermore, since the ionic liquid has almost no vapor pressure, it has low flammability and excellent thermal stability (see Non-Patent Documents 1 and 2). Due to these various advantages, application of the ionic liquid to the electrolyte of a non-aqueous electrolyte secondary battery has recently been studied (see Patent Documents 4 and 5). However, these conventional ionic liquids usually contain organic groups because they are liquid at room temperature. Therefore, these conventional ionic liquids have a risk of combustion, and even if the conventional ionic liquid is added, the risk of ignition / flammability of the non-aqueous electrolyte cannot be sufficiently reduced.

JP-A-4-184870 JP-A-8-22839 JP 2000-182669 A JP 2004-111294 A JP 2004-146346 A J. Electrochem. Soc., 144 (1997) 3881 “Functional creation and application of ionic liquids”, NTS, (2004)

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte for a battery that solves the above-described problems of the prior art, has excellent safety, and can improve battery performance. Another object of the present invention is to provide a non-aqueous electrolyte battery comprising such an electrolyte and having excellent safety and battery performance.

  As a result of intensive studies to achieve the above object, the present inventors have found that a non-aqueous electrolyte containing an ionic liquid having a phosphorus-nitrogen double bond and a dicarboxylic anhydride compound having a cyclic structure has high safety. Moreover, it has been found that the battery performance of the nonaqueous electrolyte battery can be significantly improved by applying the electrolyte to a nonaqueous electrolyte battery, and the present invention has been completed.

That is, the non-aqueous electrolyte for a battery of the present invention is
An ionic liquid having a phosphorus-nitrogen double bond;
A dicarboxylic anhydride compound having a cyclic structure;
And a supporting salt.

  In the non-aqueous electrolyte for a battery of the present invention, the dicarboxylic anhydride compound having a cyclic structure includes anhydrous 5-norbornene-2,3-dicarboxylic acid, anhydrous 1,2,3,6-tetrahydrophthalic acid and anhydrous bicyclo [2.2.2] Oct-5-ene-2,3-dicarboxylic acid is preferred.

  It is preferable that the nonaqueous electrolytic solution for a battery of the present invention further contains an aprotic organic solvent.

  In the suitable example of the non-aqueous electrolyte for batteries of this invention, content of the dicarboxylic anhydride compound which has the said cyclic structure is 0.1-3.0 mass% of the whole non-aqueous electrolyte for batteries.

In the non-aqueous electrolyte for a battery of the present invention, the ionic liquid includes the following general formula (I):
(NPR ¹ ₂ ) _n ... (I)
[Wherein R ¹ is independently a halogen element or a monovalent substituent, and at least one R ¹ is represented by the following general formula (II):
_{^{-N + R 2 3 X - ···}} (II)
Wherein R ² is each independently a monovalent substituent or hydrogen, provided that at least one R ² is not hydrogen and R ² may be bonded to each other to form a ring; X ⁻ represents a monovalent anion), and at least one R ¹ is fluorine; n is 3 or 4. An ionic liquid represented by

  Moreover, the non-aqueous electrolyte battery of the present invention comprises the above-described non-aqueous electrolyte for batteries, a positive electrode, and a negative electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte for batteries containing the ionic liquid which has a phosphorus-nitrogen double bond, and the dicarboxylic anhydride compound which has a cyclic structure is low, and the danger of combustion is low. be able to. Moreover, the non-aqueous electrolyte battery provided with this electrolyte solution and excellent in safety and battery performance can be provided.

<Non-aqueous electrolyte for batteries>
Below, the non-aqueous electrolyte for batteries of the present invention will be described in detail. The nonaqueous electrolytic solution for a battery of the present invention is characterized by containing an ionic liquid having a phosphorus-nitrogen double bond, a dicarboxylic anhydride compound having a cyclic structure, and a supporting salt.

  The ionic liquid contained in the battery non-aqueous electrolyte of the present invention is decomposed to generate nitrogen gas, phosphate ester, and the like. The risk of the electrolyte solution burning is reduced by the action of the generated nitrogen gas, and the chain decomposition of the polymer material constituting the battery is suppressed by the action of the generated phosphate ester, etc. The risk of ignition and ignition can be effectively reduced. When the ionic liquid contains a halogen, the halogen functions as an active radical scavenger in the unlikely event of combustion, reducing the risk of the electrolyte burning. Further, when the ionic liquid contains an organic substituent, it produces a carbide (char) on the separator at the time of combustion, and has an oxygen blocking effect. Moreover, although the reason is not necessarily clear, since the coating on the electrode surface produced by the ionic liquid and the dicarboxylic anhydride compound having the cyclic structure effectively suppresses decomposition of the electrolytic solution, stable charge / discharge characteristics are obtained. The battery performance such as cycle characteristics can be improved.

  The ionic liquid used for the non-aqueous electrolyte for a battery of the present invention has a melting point of 50 ° C. or lower and preferably a melting point of 20 ° C. or lower. The ionic liquid is composed of a cation part and an anion part, and the cation part and the anion part are bonded by electrostatic attraction. Here, the ionic liquid preferably has a phosphorus-nitrogen double bond in the cation part, and more preferably an ionic compound represented by the above general formula (I).

Since the compound of the above general formula (I) is a kind of cyclic phosphazene compound having a plurality of phosphorus-nitrogen double bonds, it has a high combustion suppression effect. In addition, since at least one of R ¹ in the formula (I) is an ionic substituent of the above formula (II), it has ionicity. Furthermore, since at least one of R ¹ in the formula (I) is fluorine, it has high nonflammability. From the viewpoint of nonflammability of the ionic compound, it is further preferred that at least one R ¹ in the formula (I) is an ionic substituent of the above formula (II) and all the others are fluorine. .

R ¹ in the general formula (I) is independently a halogen element or a monovalent substituent, provided that at least one R ¹ is an ionic substituent represented by the general formula (II). And at least one R ¹ is fluorine. Here, preferred examples of the halogen element in R ¹ include fluorine, chlorine, bromine and the like, and among these, fluorine is particularly preferred. Examples of the monovalent substituent in R ¹ include an alkoxy group, an alkyl group, an aryloxy group, an aryl group, a carboxyl group, and an acyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, a methoxyethoxy group, a propoxy group, an allyloxy group containing a double bond, a vinyloxy group, and the like, and an alkoxy-substituted alkoxy group such as a methoxyethoxy group and a methoxyethoxyethoxy group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the aryloxy group include a phenoxy group, a methylphenoxy group, and a methoxyphenoxy group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. Examples of the acyl group include a formyl group, an acetyl group, a propionyl group, a butyryl group, an isobutyryl group, and a valeryl group. Note that the hydrogen element in the monovalent substituent is preferably substituted with a halogen element, and preferred examples of the halogen element include fluorine, chlorine, bromine and the like.

  N in the general formula (I) is 3 to 4, and 3 is particularly preferable from the viewpoint of easy availability of the raw material.

The substituent represented by the general formula (II) is formed by bonding —NR ² ₃ and X mainly by electrostatic attraction. Therefore, the compound of formula (I) having an ionic substituent of formula (II) has ionicity.

R ² in the above general formula (II) is each independently a monovalent substituent or hydrogen, provided that at least one R ² is not hydrogen and R ² is bonded to each other to form a ring. May be. Here, examples of the monovalent substituent in R ² include an alkyl group and an aryl group. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. Examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group. In addition, when a plurality of R ² are bonded to each other to form a ring, any two of the three R ² are bonded to form an aziridine ring, azetidine ring, pyrrolidine ring, piperidine ring or the like. Examples thereof include a cycloalkane ring and an azacycloalkanone ring having a structure in which a methylene group of the azacycloalkane ring is replaced with a carbonyl group. Examples of the ring formed by combining three R ² include a pyridine ring. It is done. Note that the hydrogen element in the monovalent substituent may be substituted with a halogen element or the like.

X ⁻ in the general formula (II) represents a monovalent anion. As the monovalent anion in X ⁻ of the formula (II), F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ⁻ , ( CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (C ₃ F ₇ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ) N ⁻ , (CF ₃ SO ₂ ) (C ₃ F ₇ SO ₂ ) N ⁻ , (C ₂ F ₅ SO ₂ ) (C ₃ F ₇ SO ₂ ) N ^{− and the} like.

The method for producing the ionic compound is not particularly limited. For example, the following general formula (III):
(NPR ³ ₂ ) _n ... (III)
[Wherein R ³ is each independently a halogen element or a monovalent substituent, at least one R ³ is chlorine, at least one R ³ is fluorine; n is 3 or 4] A cyclic phosphazene compound represented by the following general formula (IV):
NR ² ₃ ... (IV)
[In the formula, R ² is as defined above] By reacting with a primary, secondary or tertiary amine represented by the following general formula (V):
(NPR ⁴ ₂ ) _n ... (V)
[Wherein, R ⁴ is independently a halogen element or a monovalent substituent, and at least one R ⁴ is represented by the following general formula (VI):
_{^{-N + R 2 3 Cl - ···}} (VI)
Wherein R ² is as defined above and at least one R ⁴ is fluorine; n is as defined above] (ie And an ionic compound represented by the above general formula (I), wherein X ⁻ in the general formula (II) is Cl ⁻ .

Furthermore, the chlorine ion of the ionic compound represented by the general formula (V) can be appropriately substituted with another monovalent anion, for example, the ionic compound represented by the general formula (V) The following general formula (VII):
A ⁺ X ^- ··· (VII)
[Wherein A ⁺ represents a monovalent cation, and X ⁻ represents a monovalent anion] is reacted (ion exchange reaction) with a salt represented by the above general formula. An ionic compound represented by (I) can be produced.

  Note that the ionic compound represented by the general formula (V) can be produced simply by mixing the cyclic phosphazene compound represented by the general formula (III) and the amine represented by the general formula (IV). However, since the produced ionic compound of formula (V) may be unstable and difficult to isolate, a two-phase system composed of an aqueous phase and an organic phase is represented by the above general formula (III). It is preferable that the cyclic phosphazene compound and the amine represented by the general formula (IV) are added and reacted to produce the ionic compound represented by the general formula (V). In this method, the cyclic phosphazene compound of formula (III) and the amine of formula (IV) are mainly present in the organic phase, while the resulting compound of formula (V) is mainly present in the aqueous phase due to its ionic nature. Therefore, after separating the aqueous phase and the organic phase, the ionic compound of formula (V) can be isolated by drying the water of the aqueous phase by a known method, and the isolated formula (V The ionic compound of) exists stably even in the atmosphere.

In the general formula (III), each R ³ is independently a halogen element or a monovalent substituent, at least one R ³ is chlorine, and at least one R ³ is fluorine. Here, since the amine of the formula (IV) is added to the portion of the formula (III) where R ³ is chlorine, the number of chlorines bonded to the phosphorus of the skeleton of the cyclic phosphazene compound of the formula (III) as the starting material By adjusting, the number of introduced ionic substituents represented by the formula (VI) in the ionic compound of the formula (V) can be controlled.

In R ³ of the general formula (III), preferred examples of the halogen element include bromine and the like in addition to chlorine and fluorine. Among these, chlorine and fluorine are preferred. On the other hand, as the monovalent substituent in R ³ , those exemplified in the section of the monovalent substituent in R ¹ can be similarly exemplified. In the formula (III), n is 3 or 4, and 3 is preferable from the viewpoint of availability.

The cyclic phosphazene compound represented by the general formula (III) is, for example, a commercially available phosphazene compound in which R ³ in the formula (III) is all chlorine as a starting material. Then, after introducing an alkoxy group, an amine group or the like into the target chlorine substitution site, chlorinating again with a chlorinating agent such as HCl or phosgene, or R ³ in the formula (III) to be used is It can be synthesized by a method of adding a necessary amount of a fluorinating agent after calculating the equivalent amount of fluorine to be introduced to commercially available phosphazene compounds which are all chlorine. Here, the number of chlorine in R ³ in the formula (III) can be controlled by changing the amount of chlorinating agent used in rechlorination, the amount of the fluorinating agent used in fluorination, and the reaction conditions.

In the general formula (IV), R ² is a R ² as defined in the above formula (II), are each independently a monovalent substituent or hydrogen, provided that at least one R ² is hydrogen And R ² may be bonded to each other to form a ring. Examples of the monovalent substituent in R ² of formula (IV), can similarly be illustrated those which have been exemplified in the section of the monovalent substituent in R ² of Formula (II), also, the formula (IV) any two of the three R ² as the ring ring and three R ² formed by the bonding formed by combining any two of the three R ² of formula (II) is formed by bonding What was illustrated by the term of the ring formed by combining a ring and three R < ² > can be mentioned similarly. Specific examples of the amine represented by the formula (IV) include aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, and tributylamine, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and the like. And cyclic tertiary amines, dialkyl-substituted anilines such as dimethylaniline, aromatic tertiary amines such as pyridine, and aromatic primary amines such as aniline. Among these, tertiary amines are preferred.

In the general formula (V), each R ⁴ is independently a halogen element or a monovalent substituent, and at least one R ⁴ is an ionic substituent represented by the general formula (VI), at least One R ⁴ is fluorine. Examples of the halogen element in R ⁴ include fluorine, chlorine, bromine and the like. In addition, a part of R ⁴ can be changed to chlorine by adjusting the amount of the amine of the formula (IV). On the other hand, as the monovalent substituent in R ⁴ , those exemplified in the section of the monovalent substituent in R ¹ can be similarly exemplified. Moreover, n in Formula (V) is 3 or 4, and 3 is preferable from a viewpoint of the availability of a raw material.

In the general formula (VI), R ² is, by R ² as defined in the above formula (II), are each independently a monovalent substituent or hydrogen, provided that at least one R ² is hydrogen And R ² may be bonded to each other to form a ring. Examples of the monovalent substituent in R ² of formula (VI), can similarly be illustrated those which have been exemplified in the section of the monovalent substituent in R ² of Formula (II), also, the formula (VI) any two of the three R ² as the ring ring and three R ² formed by the bonding formed by combining any two of the three R ² of formula (II) is formed by bonding What was illustrated by the term of the ring formed by combining a ring and three R < ² > can be mentioned similarly.

In the production of the ionic compound of the formula (V), the amount of the amine of the formula (IV) can be appropriately selected according to the amount of the amine introduced, for example, R in the cyclic phosphazene compound of the formula (III) The range of 1 to 2.4 mol per mol of chlorine in ³ is preferred.

  Further, the reaction temperature in the reaction of the cyclic phosphazene compound of the formula (III) and the amine of the formula (IV) is not particularly limited, but is preferably in the range of 20 ° C to 80 ° C, and the reaction is sufficiently performed even at room temperature. proceed. Further, the reaction pressure is not particularly limited, and the reaction can be performed under atmospheric pressure.

  In the two-phase system composed of the aqueous phase and the organic phase, the organic solvent used in the organic phase is not miscible with water and can dissolve the cyclic phosphazene compound of formula (III) and the amine of formula (IV). Those having low polarity such as chloroform and toluene are preferred. The amount of the aqueous phase and the organic phase used is not particularly limited, and the volume of the aqueous phase is preferably in the range of 0.2 to 5 mL with respect to 1 mL of the cyclic phosphazene compound of the formula (III). The volume is preferably in the range of 2 to 5 mL with respect to 1 mL of the cyclic phosphazene compound of the formula (III).

In the general formula (VII), A ⁺ represents a monovalent cation, and X ⁻ represents a monovalent anion. Examples of the monovalent cation in A ⁺ in the formula (VII) include Ag ⁺ and Li ⁺ . Further, as the monovalent anion in X ⁻ of the formula (VII), monovalent anions other than Cl ⁻ , specifically, BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , CF ₃ SO ₃ ^- _{other, (CF 3 SO 2) 2} N -, (C 2 F 5 SO 2) 2 N -, (C 3 F 7 SO 2) 2 N -, (CF 3 SO 2) (C 2 Examples thereof include imide ions such as F ₅ SO ₂ ) N ⁻ , (CF ₃ SO ₂ ) (C ₃ F ₇ SO ₂ ) N ⁻ and (C ₂ F ₅ SO ₂ ) (C ₃ F ₇ SO ₂ ) N ⁻ . Here, when A ⁺ is Li ⁺ , X ⁻ is preferably an imide ion. In contrast to Li ⁺ , which has a small ionic radius, the imide ion has a large ionic radius, so it reacts well due to the influence of the difference in ionic radius between cation and anion (soft / hard base / acid relationship). This is because the substitution reaction proceeds. On the other hand, when A ⁺ is Ag ⁺ , almost all anions can be used. When Ag ⁺ X ⁻ is used as the salt of the formula (VII), the impurities can be easily removed because AgCl is precipitated.

  In the production of the ionic compound of the formula (I), the amount of the salt of the formula (VII) used can be appropriately selected according to the amount of chlorine ions of the ionic compound of the formula (V). The range of 1 to 1.5 mol is preferable per 1 mol of chloride ions of the ionic compound.

  The reaction temperature in the reaction of the ionic compound of formula (V) and the salt of formula (VII) is not particularly limited, but is preferably in the range of room temperature to 50 ° C., and the reaction proceeds sufficiently even at room temperature. To do. Further, the reaction pressure is not particularly limited, and the reaction can be performed under atmospheric pressure.

The reaction of the ionic compound of formula (V) with the salt of formula (VII) is preferably carried out in an aqueous phase. In the reaction of the ionic compound of the above formula (V) with the silver salt represented by the formula (VII) and A ⁺ is Ag ⁺ , silver chloride is produced as a by-product, Since the solubility in water is very low, by-products can be easily separated when the reaction is carried out in an aqueous phase. Isolation from the aqueous phase of the ionic compound of formula (I), which is the target substance, may be carried out by evaporating the water in the aqueous phase by a known method. The volume of the aqueous phase is not particularly limited, but is preferably in the range of 2 to 5 mL with respect to 1 mL of the ionic compound of the formula (V).

  In the non-aqueous electrolyte for a battery of the present invention, the content of the ionic liquid is preferably 1% by volume or more, and more preferably 5% by volume or more. By adding 1% by volume or more of ionic liquid, the effect of improving the wettability between the battery member and the electrolytic solution is suitably expressed, and by adding 5% by volume or more of ionic liquid, high flame retardancy is imparted to the electrolytic solution.

  The nonaqueous electrolytic solution for a battery according to the present invention further includes a dicarboxylic anhydride compound having a cyclic structure. Here, the dicarboxylic anhydride compound having a cyclic structure is an anhydride of dicarboxylic acid and has a cyclic structure in the molecule. Preferred examples of the dicarboxylic anhydride compound having a cyclic structure include anhydrous 5-norbornene-2,3-dicarboxylic acid, anhydrous 1,2,3,6-tetrahydrophthalic acid and anhydrous bicyclo [2.2.2]. Oct-5-ene-2,3-dicarboxylic acid. These dicarboxylic anhydride compounds having a cyclic structure may be used singly or in combination of two or more.

  The content of the dicarboxylic anhydride compound having the cyclic structure is preferably in the range of 0.1 to 3.0% by mass of the whole battery non-aqueous electrolyte from the viewpoint of balance of battery performance.

As the supporting salt used in the nonaqueous electrolytic solution for a battery of the present invention, a supporting salt serving as an ion source of lithium ions is preferable. The supporting salt is not particularly limited. For example, LiClO ₄ , LiBF ₄ , LiBC ₄ O ₈ , LiPF ₆ , LiCF ₃ SO ₃ , LiAsF ₆ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) Preferable examples include lithium salts such as ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used alone or in combination of two or more. The concentration of the supporting salt in the battery non-aqueous electrolyte of the present invention is preferably in the range of 0.2 to 1.5 mol / L (M), more preferably in the range of 0.5 to 1 mol / L. If the concentration of the supporting salt is less than 0.2 mol / L, the conductivity of the electrolyte cannot be sufficiently ensured, and the discharge characteristics and charging characteristics of the battery may be hindered. Since the viscosity of the electrolytic solution increases and the mobility of lithium ions cannot be ensured sufficiently, the conductivity of the electrolytic solution cannot be sufficiently ensured in the same manner as described above, which may hinder battery discharge characteristics and charge characteristics. .

  The nonaqueous electrolytic solution for a battery of the present invention preferably further contains an aprotic organic solvent, and the content thereof is preferably 95% by volume or less from the viewpoint of the safety of the electrolytic solution. Examples of the aprotic organic solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), diphenyl carbonate, ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), γ Preferred examples include esters such as valerolactone and methyl formate (MF), and ethers such as 1,2-dimethoxyethane (DME) and tetrahydrofuran (THF). Among these, propylene carbonate, 1,2-dimethoxyethane, and γ-butyrolactone are preferable as the aprotic organic solvent for the non-aqueous electrolyte of the primary battery, while for the non-aqueous electrolyte of the secondary battery. As the aprotic organic solvent, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate and methyl formate are preferable. Cyclic esters are preferred in that they have a high relative dielectric constant and excellent solubility of the supporting salt, while chain esters and chain ethers have low viscosity, so It is suitable in terms of lowering the viscosity. These aprotic organic solvents may be used alone or in combination of two or more.

<Nonaqueous electrolyte battery>
Next, the nonaqueous electrolyte battery of the present invention will be described in detail. The non-aqueous electrolyte battery of the present invention includes the above-described non-aqueous electrolyte for a battery, a positive electrode, and a negative electrode, and is usually used in the technical field of non-aqueous electrolyte batteries such as a separator as necessary. Other members may be provided, and the primary battery or the secondary battery may be used.

The positive electrode active material of the non-aqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the positive electrode active material of the non-aqueous electrolyte primary battery, fluorinated graphite [(CF _x ) _n ], MnO ₂ (which may be electrochemical synthesis or chemical synthesis), V ₂ O ₅ , MoO ₃ , Ag ₂ CrO ₄ , CuO, CuS, FeS ₂ , SO ₂ , SOCl ₂ , TiS _2, etc. Among these, MnO ₂ and fluorinated graphite are preferable from the viewpoints of high capacity and high safety, and high discharge potential and excellent wettability of the electrolytic solution. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

On the other hand, as the positive electrode active material of the non-aqueous electrolyte secondary battery, metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , MnO ₃ , LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFeO _{2 are used.} Preferable examples include lithium-containing composite oxides such as LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. The lithium-containing composite oxide may be a composite oxide containing two or three transition metals selected from the group consisting of Fe, Mn, Co, Al, and Ni. In this case, the composite oxide LiMn _x Co _y Ni _(1-xy) O ₂ [where 0 ≦ x <1, 0 ≦ y <1, 0 <x + y ≦ 1], LiMn _x Ni _(1-x) O ₂ [wherein , 0 ≦ x <1], LiMn _x Co _(1-x) O ₂ [where 0 ≦ x <1], LiCo _x Ni _(1-x) O ₂ [where 0 ≦ x <1], LiCo _x Ni _y Al [wherein, 0 ≦ x <1,0 ≦ y <1,0 <x + y ≦ 1] (1-xy) O 2, LiFe x Co y Ni (1-xy) O 2 [ wherein , 0 ≦ x <1, 0 ≦ y <1, 0 <x + y ≦ 1], or LiMn _x Fe _y O _{2 -xy} . Among these, lithium-containing composite oxides are preferable in terms of high capacity, high safety, and stability at high voltages. These positive electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The negative electrode active material of the nonaqueous electrolyte battery of the present invention is partially different between the primary battery and the secondary battery. For example, as the negative electrode active material of the nonaqueous electrolyte primary battery, lithium metal itself, lithium alloy, etc. Is mentioned. Examples of the metal that forms an alloy with lithium include Sn, Pb, Al, Au, Pt, In, Zn, Cd, Ag, and Mg. Among these, Al, Zn, and Mg are preferable from the viewpoints of rich reserves and toxicity. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

On the other hand, as the negative electrode active material of the non-aqueous electrolyte secondary battery, lithium metal itself, an alloy of lithium and Al, In, Sn, Si, Pb or Zn, a carbon material such as graphite doped with lithium, TiO ₂ Preferred examples include metal oxides such as TiO ₂ —P ₂ O _{4 and the} like, and among these, the safety is higher and the wettability of the electrolyte is superior. Carbon materials are preferred, and graphite is particularly preferred. Here, examples of graphite include natural graphite, artificial graphite, mesophase carbon microbeads (MCMB), and the like, and widely include graphitizable carbon and non-graphitizable carbon. These negative electrode active materials may be used individually by 1 type, and may use 2 or more types together.

  The positive electrode and the negative electrode can be mixed with a conductive agent and a binder as necessary. Examples of the conductive agent include acetylene black. Examples of the binder include polyvinylidene fluoride (PVDF) and polytetrafluoro. Examples include ethylene (PTFE), styrene / butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. These additives can be used at a blending ratio similar to the conventional one.

  Moreover, there is no restriction | limiting in particular as a shape of the said positive electrode and a negative electrode, It can select suitably from well-known shapes as an electrode. For example, a sheet shape, a columnar shape, a plate shape, a spiral shape, and the like can be given.

  Other members that can be used in the non-aqueous electrolyte battery of the present invention include a separator that is interposed between positive and negative electrodes in a role of preventing current short-circuit due to contact between both electrodes. As the material of the separator, it is possible to reliably prevent contact between the two electrodes and to allow the electrolyte to pass through or to contain, for example, synthesis of polytetrafluoroethylene, polypropylene, polyethylene, cellulose, polybutylene terephthalate, polyethylene terephthalate, etc. Preferred examples include resin non-woven fabrics and thin layer films. Among these, a polypropylene or polyethylene microporous film having a thickness of about 20 to 50 μm, a film made of cellulose, polybutylene terephthalate, polyethylene terephthalate, or the like is particularly suitable. In the present invention, in addition to the separators described above, known members that are normally used in batteries can be suitably used.

  The form of the non-aqueous electrolyte battery of the present invention described above is not particularly limited, and various known forms such as a coin-type, button-type, paper-type, square-type or spiral-type cylindrical battery are suitable. Can be mentioned. In the case of the button type, a non-aqueous electrolyte battery can be produced by preparing a sheet-like positive electrode and negative electrode and sandwiching a separator between the positive electrode and the negative electrode. In the case of a spiral structure, for example, a non-aqueous electrolyte battery can be manufactured by preparing a sheet-like positive electrode, sandwiching a current collector, and stacking and winding a sheet-like negative electrode on the current collector. it can.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Ionic liquid synthesis example 1)
A two-phase system consisting of 15 mL of water and 15 mL of chloroform was prepared, and the two-phase system was represented by 5 mL of triethylamine, represented by the above general formula (III), where n was 3, and 1 of 6 R ³ 5 mL of a cyclic phosphazene compound, one of which is chlorine and five of which is fluorine, was successively added dropwise. Thereafter, when the two-phase system was stirred while cooling, white crystals were precipitated in the chloroform phase. When the mixture was returned to room temperature and stirred, the white crystals disappeared. The chloroform phase was colorless before the reaction, but became cloudy after the reaction. The aqueous phase was collected using a pipette, evaporated, and then water was distilled off using a vacuum pump to obtain 5.2 g of white crystals (yield 53%). Next, 2 g of the obtained white crystals and 2.2 g of AgPF ₆ were dissolved in 20 mL of water, and after stirring for 30 minutes, the aqueous phase was collected and the water was evaporated to leave a transparent liquid, which was further dried under reduced pressure. As a result, 1.8 g (yield 79%) of ionic liquid A was obtained. The obtained ionic liquid A was dissolved in heavy water and analyzed by ¹ H-NMR, and further dissolved in DMSO and analyzed by ³¹ P-NMR. The ionic liquid A was represented by the above general formula (I). It was confirmed that n in the formula was 3, 5 out of 6 R ¹ were fluorine, and ¹ was —N ⁺ (CH ₂ CH ₂ ) ₃ PF ₆ ^— . The result of ¹ H-NMR of the product is shown in FIG. 1, the result of ³¹ P-NMR is shown in FIG. 2, and the reaction scheme is shown below.

(Ionic liquid synthesis example 2)
A two-phase system consisting of 15 mL of water and 15 mL of chloroform was prepared, and the two-phase system was represented by 5 mL of aniline and the above general formula (III), where n was 3, and 1 of 6 R ³ 5 mL of a cyclic phosphazene compound, one of which is chlorine and five of which is fluorine, was successively added dropwise. Thereafter, when the two-phase system was stirred while cooling, white crystals were precipitated in the chloroform phase. When the mixture was returned to room temperature and stirred, the white crystals disappeared. The chloroform phase was colorless before the reaction, but became cloudy after the reaction. The aqueous phase was collected using a pipette and evaporated, and then water was distilled off using a vacuum pump to obtain 4.8 g of white crystals (yield 54%). Next, 2 g of the obtained white crystals and 2.3 g of AgPF ₆ were dissolved in 20 mL of water, and after stirring for 30 minutes, the aqueous phase was collected and evaporated to leave a transparent liquid, which was further dried under reduced pressure. As a result, 1.6 g (yield 72%) of ionic liquid B was obtained. When the obtained ionic liquid B was dissolved in heavy water and analyzed by ¹ H-NMR, and further dissolved in DMSO and analyzed by ³¹ P-NMR, the ionic liquid B was represented by the above general formula (I). In the formula, it was confirmed that n was 3, 5 out of 6 R ¹ were fluorine, and ¹ was —N ⁺ H ₂ C ₆ H ₅ PF ₆ ^— . The result of ¹ H-NMR of the product is shown in FIG. 3, the result of ³¹ P-NMR is shown in FIG. 4, and the reaction scheme is shown below.

(Example 1)
5% by volume of ionic liquid A obtained as described above and EC / PC / DMC [mixing containing ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) at a volume ratio of 1/3. Solvent] LiPF ₆ was dissolved in a mixed solvent consisting of 95% by volume so as to be 1 mol / L, and 0.1% by mass of anhydrous 5-norbornene-2,3-dicarboxylic acid (NDCA) was added thereto to add non-aqueous solution. An electrolyte solution was prepared. Next, the safety of the obtained nonaqueous electrolytic solution was evaluated by the following method, and the results shown in Table 1 were obtained.

(1) Electrolyte Safety The safety of the electrolyte was evaluated from the combustion behavior of flames ignited in an atmospheric environment by the method of arranging UL94HB method of UL (Underwriting Laboratory) standard. At that time, ignitability, combustibility, formation of carbides, and secondary ignition phenomena were also observed. Specifically, based on the UL test standard, a nonflammable quartz fiber was impregnated with 1.0 mL of an electrolytic solution, and a test piece of 127 mm × 12.7 mm was produced. Here, when the test flame does not ignite the test piece (combustion length: 0 mm), it is “non-flammable”, and when the ignited flame does not reach the 25 mm line and the fallen object is not ignited, “flame retardant” The case where the ignited flame was extinguished on the 25 to 100 mm line and the fallen object was not ignited was evaluated as “self-extinguishing”, and the case where the ignited flame exceeded the 100 mm line was evaluated as “combustible”.

(2) Production of Lithium Secondary Battery Next, lithium cobalt composite oxide (LiCoO ₂ ) is used as the positive electrode active material, the composite oxide, acetylene black as a conductive agent, and a fluororesin as a binder. Are mixed in a mass ratio of 90: 5: 5 and dispersed in N-methylpyrrolidone to form a slurry, which is applied to an aluminum foil as a positive electrode current collector and dried, and then a φ16 mm disc The positive electrode was produced by punching into a shape. On the other hand, the negative electrode was a lithium foil (thickness 0.5 mm) punched out to φ16 mm. Next, the positive electrode and the negative electrode are stacked and accommodated in a stainless steel case also serving as a positive electrode terminal via a separator (microporous film: made of polypropylene) impregnated with the electrolytic solution, and the negative electrode terminal is inserted through a polypropylene gasket. A CR2016 type coin-type battery (lithium secondary battery) with a capacity of 4 mAh was produced. The initial discharge capacity, discharge capacity after 50 cycles, and discharge capacity retention rate of the obtained battery were measured by the following methods, and the results shown in Table 1 were obtained.

(3) Discharge capacity at the initial stage and after 50 cycles
Under an environment of 20 ° C, charge and discharge are performed under the conditions of an upper limit voltage of 4.2 V, a lower limit voltage of 3.0 V, a discharge current of 50 mA, and a charge current of 50 mA, and the initial discharge capacity is obtained by dividing the discharge capacity at this time by the known electrode weight. (MAh / g) was determined. Moreover, charge / discharge was repeated up to 50 cycles under the same charge / discharge conditions, and the discharge capacity after 50 cycles was determined. Furthermore, the following formula:
Discharge capacity retention rate = discharge capacity after 50 cycles / initial discharge capacity × 100 (%)
The discharge capacity retention rate was calculated according to

(Examples 2 to 12)
In a mixed solvent having the composition shown in Tables 1 and 2, LiPF ₆ was dissolved at 1 mol / L, and the additives shown in Tables 1 and 2 were added to prepare a non-aqueous electrolyte. The safety was evaluated in the same manner. Moreover, the lithium secondary battery was produced similarly to Example 1, and battery performance was evaluated. The results are shown in Tables 1 and 2. In Tables 1 and 2, dicarboxylic anhydride C is anhydrous 5-norbornene-2,3-dicarboxylic acid (NDCA), dicarboxylic anhydride D is anhydrous 1,2,3,6-tetrahydrophthalic acid, EC / PC / DMC represents a mixed organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) at a volume ratio of 1/3.

(Comparative Examples 1-2)
LiPF ₆ was dissolved in a mixed solvent having the composition shown in Tables 1 and 2 so as to be 1 mol / L to prepare a nonaqueous electrolytic solution, and safety was evaluated in the same manner as in Example 1. Moreover, the lithium secondary battery was produced similarly to Example 1, and battery performance was evaluated. The results are shown in Tables 1 and 2.

  From Table 1 and 2, it turns out that the electrolyte solution containing the ionic liquid which has a phosphorus-nitrogen double bond, and the dicarboxylic anhydride compound which has a cyclic structure is excellent in safety | security and battery performance. From Examples 3, 6, 9 and 12, the electrolyte solution containing 5% by mass of the dicarboxylic anhydride compound having a cyclic structure has poor cycle characteristics. Therefore, the content of the dicarboxylic anhydride compound having a cyclic structure is It was confirmed that the range of 0.1 to 3.0% by mass of the whole liquid was preferable.

It is the result of ¹ H-NMR of the product obtained in the ionic liquid synthesis example 1. It is a ³¹ P-NMR result of the product obtained in the ionic liquid synthesis example 1. It is the result of ¹ H-NMR of the product obtained in the ionic liquid synthesis example 2. It is a ³¹ P-NMR result of the product obtained in the ionic liquid synthesis example 2.

Claims (6)

An ionic liquid having a phosphorus-nitrogen double bond;
A dicarboxylic anhydride compound having a cyclic structure;
A battery non-aqueous electrolyte containing a supporting salt.   The dicarboxylic anhydride compound having the above cyclic structure is anhydrous 5-norbornene-2,3-dicarboxylic acid, anhydrous 1,2,3,6-tetrahydrophthalic acid and bicyclo [2.2.2] oct-5-ene. The non-aqueous electrolyte for a battery according to claim 1, wherein the non-aqueous electrolyte for a battery is at least one selected from the group consisting of -2,3-dicarboxylic acid.   Furthermore, the non-aqueous electrolyte for batteries of Claim 1 containing an aprotic organic solvent.   2. The battery non-aqueous electrolyte according to claim 1, wherein a content of the cyclic dicarboxylic anhydride compound is 0.1 to 3.0% by mass of the whole battery non-aqueous electrolyte. The ionic liquid has the following general formula (I):
(NPR ¹ ₂ ) _n ... (I)
[Wherein R ¹ is independently a halogen element or a monovalent substituent, and at least one R ¹ is represented by the following general formula (II):
_{^{-N + R 2 3 X - ···}} (II)
Wherein R ² is each independently a monovalent substituent or hydrogen, provided that at least one R ² is not hydrogen and R ² may be bonded to each other to form a ring; X ⁻ represents a monovalent anion), and at least one R ¹ is fluorine; n is 3 or 4. Item 4. A nonaqueous electrolytic solution for a battery according to Item 1.   A nonaqueous electrolyte battery comprising the battery nonaqueous electrolyte solution according to claim 1, a positive electrode, and a negative electrode.

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