JP6767151B2 - Non-aqueous electrolyte and non-aqueous secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte solution and a non-aqueous secondary battery.

Non-aqueous secondary batteries such as lithium ion secondary batteries are characterized by their light weight, high energy, and long life, and are widely used as power sources for various portable electronic devices. In recent years, non-aqueous secondary batteries have been widely applied to industrial equipment represented by power tools such as electric tools; and as in-vehicle batteries in electric vehicles, electric bicycles, and the like. Furthermore, non-aqueous secondary batteries are also attracting attention in the field of electric power storage such as residential power storage systems.

From a practical point of view, it is desirable to use a non-aqueous electrolyte solution as the electrolytic solution of the room temperature operating lithium ion secondary battery. For example, a combination of a highly dielectric solvent such as a cyclic carbonate and a low-viscosity solvent such as a lower chain carbonate is exemplified as a general solvent. However, a normal high dielectric constant solvent has a high melting point and also causes deterioration of the load characteristics (output characteristics) and low temperature characteristics of the non-aqueous electrolyte solution depending on the type of electrolyte salt used in the non-aqueous electrolyte solution. obtain.

As one of the solvents for overcoming such a problem, a nitrile solvent having an excellent balance between viscosity and relative permittivity has been proposed. Among them, acetonitrile has a high potential as a solvent used in an electrolytic solution of a lithium ion secondary battery. However, acetonitrile has a fatal drawback of being electrochemically reduced and decomposed at the negative electrode, so that it has not been able to exhibit practical performance. Several remedies have been proposed for this problem.
The main improvement measures proposed so far are classified into the following three categories.

(1) A method of protecting the negative electrode by combining with a specific electrolyte salt, an additive, etc. and suppressing the reductive decomposition of acetonitrile For example, in Patent Documents 1 and 2, acetonitrile as a solvent is used as a specific electrolyte salt and an additive. An electrolytic solution in which the influence of the reductive decomposition of acetonitrile is reduced by combining with the above has been reported. In the early days of lithium-ion secondary batteries, an electrolytic solution containing a solvent obtained by simply diluting acetonitrile with propylene carbonate and ethylene carbonate has been reported as in Patent Document 3. However, in Patent Document 3, since the high temperature durability performance is determined only by the evaluation of the internal resistance after high temperature storage and the battery thickness, information on whether or not the battery actually operates when placed in a high temperature environment. Is not disclosed. In practice, it is extremely difficult to suppress the reductive decomposition of an electrolytic solution containing an acetonitrile-based solvent by simply diluting it with ethylene carbonate and propylene carbonate. As a method for suppressing the reductive decomposition of the solvent, a method of combining a plurality of electrolyte salts and additives as in Patent Documents 1 and 2 is realistic.

(2) A method of suppressing the reduction decomposition of acetonitrile by using a negative electrode active material that occludes lithium ions at a potential noble than the reduction potential of acetonitrile For example, Patent Document 4 uses a specific metal compound for the negative electrode. It has been reported that this makes it possible to obtain a battery in which the reductive decomposition of acetonitrile is avoided. However, in applications where the energy density of a lithium ion secondary battery is important, it is overwhelmingly advantageous to use a negative electrode active material that occludes lithium ions at a potential lower than the reduction potential of acetonitrile from the viewpoint of potential difference. Therefore, applying the improvement measures of Patent Document 4 in such an application is disadvantageous because the range of usable voltage is narrowed.

(3) Method of Dissolving High Concentration Electrolyte Salt in acetonitrile to Maintain a Stable Liquid State For example, Patent Document 5 states that lithium bis (trifluoromethanesulfonyl) imide (trifluoromethanesulfonyl) imide so as to have a concentration of 4.2 mol / L. It is described that reversible insertion and desorption of lithium into a graphite electrode is possible by using an electrolytic solution in which LiN (SO ₂ CF ₃ ) ₂ ) is dissolved in acetonitrile. Further, in Patent Document 6, for a cell using an electrolytic solution in which lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ ) is dissolved in acetonitrile so that the concentration becomes 4.5 mol / L. As a result of charge / discharge measurement, a Li ⁺ insertion / desorption reaction into graphite was observed, and it was reported that discharge was possible at a high rate.

International Publication No. 2012/057311 International Publication No. 2013/062056 Japanese Patent Application Laid-Open No. 4-351860 JP-A-2009-21134 International Publication No. 2013/146714 Japanese Unexamined Patent Publication No. 2014-241198

However, the lithium ion secondary battery using the electrolytic solution containing acetonitrile is inferior in high temperature durability performance to the existing lithium ion secondary battery using the electrolytic solution containing a carbonate solvent, and is at the level of a commercial product. Since it has not reached the limit, it has not yet reached full-scale commercialization.

From the results of various verification experiments, the reason why the acetonitrile-based lithium-ion secondary battery is inferior in high-temperature durability performance is considered as follows.

In a high temperature environment, the fluorine-containing inorganic lithium salt decomposes while abstracting hydrogen from the methyl group of acetonitrile, and the decomposition product promotes the elution of the positive electrode transition metal. The complex cation in which acetonitrile is coordinated to this elution metal is chemically stable. Therefore, when charging and discharging are repeated in a high temperature environment, the stable complex cation may be deposited on the electrode and cause an increase in internal resistance. In addition, the stable complex cation may adversely affect the protective film of the negative electrode that suppresses the reductive decomposition of acetonitrile. These phenomena, which are supported by the results of the disassembly analysis, are problems newly discovered by the present inventors and are not described at all in Patent Documents 1 to 6.

The present invention has been made in view of the above circumstances. Therefore, the present invention is excellent in suppressing the formation of a complex cation composed of a transition metal and acetonitrile in a non-aqueous electrolyte solution containing acetonitrile having an excellent balance between viscosity and relative permittivity and a fluorine-containing inorganic lithium salt. It is an object of the present invention to provide a non-aqueous electrolyte solution and a non-aqueous secondary battery capable of exhibiting a heavy load characteristic and suppressing an increase in internal resistance when a charge / discharge cycle is repeated.

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, even in a non-aqueous electrolyte solution containing acetonitrile as a non-aqueous solvent, when a specific nitrogen-containing cyclic compound is contained as an additive, the formation of a complex cation composed of a transition metal and acetonitrile is suppressed. However, they have found that they can exhibit excellent load characteristics and suppress an increase in internal resistance when the charge / discharge cycle is repeated, and have completed the present invention.
That is, the present invention is as follows.
[1]
With a non-aqueous solvent containing 20% to 100% by volume of acetonitrile;
With fluorine-containing inorganic lithium salt;
Below 1-6:
1. 1. It is a five-membered ring
2. Two or more N atoms are contained in the five-membered ring,
3. 3. Two or more double bonds are contained in the five-membered ring,
4. One or more of the double bonds are bonds with the N atom.
5. 6. No H atom is bonded to the N atom in the five-membered ring, and 6. With a compound having a structure satisfying that it does not have a cyclic structure that bonds with two or more atoms in the five-membered ring;
A non-aqueous electrolyte solution containing.
[2]
All C atoms contained in the five-membered ring of the compound have a double bond and
One of the N atoms in the five-membered ring is an alkyl group having 1 to 4 carbon atoms, an allyl group, a propargyl group, a phenyl group, a benzyl group, a pyridyl group, an amino group, a pyrrolidylmethyl group, a trimethylsilyl group, or a nitrile group. , Acetyl group, trifluoroacetyl group, chloromethyl group, methoxymethyl group, isocyanomethyl group, methylsulfonyl group, phenylsulfonyl group, azide sulfonyl group, pyridylsulfonyl group, or 2- (trimethylsilyl) ethoxycarbonyloxy group Combined with,
The non-aqueous electrolyte solution according to [1].
[3]
The non-aqueous electrolyte solution according to [2], wherein one of the N atoms in the five-membered ring is bonded to the alkyl group having 1 to 4 carbon atoms.
[4]
The non-aqueous electrolyte solution according to [3], wherein the alkyl group having 1 to 4 carbon atoms is a methyl group.
[5]
The non-aqueous electrolyte solution according to any one of [1] to [4], wherein the number of the N atoms contained in the five-membered ring of the compound is two or three.
[6]
The non-aqueous electrolyte solution according to any one of [1] to [5], wherein the five-membered ring structure of the compound is imidazole.
[7]
The non-aqueous electrolyte solution according to any one of [1] to [6], wherein the content of the compound is 0.01 parts by mass to 10 parts by mass with respect to 100 parts by mass of the non-aqueous electrolyte solution.
[8]
The non-aqueous electrolyte solution according to any one of [1] to [7], further containing vinylene carbonate and ethylene sulfate.
[9]
The non-aqueous electrolyte solution according to any one of [1] to [8], wherein the fluorine-containing inorganic lithium salt contains LiPF ₆ .
[10]
A positive electrode having a positive electrode active material layer containing at least one transition metal element selected from Ni, Mn, and Co on one or both sides of a positive electrode current collector;
The negative electrode having a negative electrode active material layer on one side or both sides of the negative electrode current collector; and the non-aqueous electrolyte solution according to any one of [1] to [9];
A non-aqueous secondary battery equipped with.

According to the present invention, the formation of a complex cation composed of a transition metal and acetonitrile is suppressed in a non-aqueous electrolyte solution containing acetonitrile having an excellent balance between viscosity and relative permittivity and a fluorine-containing inorganic lithium salt. It is possible to provide a non-aqueous electrolyte solution and a non-aqueous secondary battery having excellent cycle performance, which exhibit excellent load characteristics and suppress an increase in internal resistance when a charge / discharge cycle is repeated.

It is a top view which shows typically an example of the non-aqueous secondary battery of this embodiment. FIG. 5 is a cross-sectional view taken along the line AA of the non-aqueous secondary battery of FIG.

Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as “the present embodiment”) will be described in detail. The numerical range described by using "~" in the present specification includes the numerical values described before and after it.

<1. Overall configuration of non-aqueous secondary battery>
The electrolytic solution according to this embodiment can be used, for example, in a non-aqueous secondary battery. Examples of the non-aqueous secondary battery according to the present embodiment include the following:
A positive electrode containing a positive electrode material capable of occluding and releasing lithium ions as a positive electrode active material;
As the negative electrode active material, a negative electrode material capable of occluding and releasing lithium ions, and a negative electrode containing one or more negative electrode materials selected from the group consisting of metallic lithium;
With non-aqueous electrolyte;
A lithium ion secondary battery comprising the above is mentioned.

Specifically, the non-aqueous secondary battery according to the present embodiment may be the non-aqueous secondary battery shown in FIGS. 1 and 2. Here, FIG. 1 is a plan view schematically showing a non-aqueous secondary battery, and FIG. 2 is a cross-sectional view taken along the line AA of FIG.

The non-aqueous secondary battery 8 includes a laminated electrode body formed by laminating a positive electrode 5 and a negative electrode 6 via a separator 7 in a battery exterior 2 composed of two aluminum laminated films 1 and a non-aqueous electrolytic solution. (Not shown) and is housed. The outer peripheral portion of the battery 2 is sealed by heat-sealing the upper and lower aluminum laminate films 1. The laminated body in which the positive electrode 5, the separator 7, and the negative electrode 6 are laminated in this order is impregnated with a non-aqueous electrolytic solution. In FIG. 2, in order to avoid complicating the drawings, the layers constituting the battery exterior 2 and the layers of the positive electrode 5 and the negative electrode 6 are not shown separately.

The aluminum laminate film 1 constituting the battery exterior 2 is preferably formed by coating both sides of an aluminum foil with a polyolefin-based resin.
The positive electrode 5 is connected to the positive electrode lead body 3 in the battery. Although not shown, the negative electrode 6 is also connected to the negative electrode lead body 4 in the battery. One end of each of the positive electrode lead body 3 and the negative electrode lead body 4 is pulled out to the outside of the battery exterior 2 so that they can be connected to an external device or the like, and their ionomer portions are one side of the battery exterior 2. It is heat-sealed together with.

In the non-aqueous secondary battery 8 shown in FIGS. 1 and 2, the positive electrode 5 and the negative electrode 6 each have one laminated electrode body, but the number of laminated positive electrodes 5 and 6 is determined by the capacity design. It can be increased as appropriate. In the case of a laminated electrode body having a plurality of positive electrodes 5 and 6 negative electrodes, tabs of the same electrode may be joined to each other by welding or the like, and then joined to one lead body by welding or the like and taken out of the battery. As the tabs having the same pole, a mode in which the exposed portion of the current collector is formed, a mode in which a metal piece is welded to the exposed portion of the current collector, and the like are possible.

The positive electrode 5 is composed of a positive electrode active material layer prepared from a positive electrode mixture and a positive electrode current collector. The negative electrode 6 is composed of a negative electrode active material layer prepared from a negative electrode mixture and a negative electrode current collector. The positive electrode 5 and the negative electrode 6 are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other via the separator 7.

Hereinafter, the positive electrode and the negative electrode are collectively referred to as “electrode”, the positive electrode active material layer and the negative electrode active material layer are collectively referred to as “electrode active material layer”, and the positive electrode mixture and the negative electrode mixture are collectively referred to as “electrode mixture”.

As each of these members, as long as each requirement in the present embodiment is satisfied, a material provided in a conventional lithium ion secondary battery can be used, and for example, a material described later may be used. Hereinafter, each member of the non-aqueous secondary battery will be described in detail.

<2. Electrolyte>
The electrolytic solution in the present embodiment contains a non-aqueous solvent (hereinafter, also simply referred to as “solvent”), a fluorine-containing inorganic lithium salt, and a nitrogen-containing cyclic compound described in detail below. Although the fluorine-containing inorganic lithium salt is excellent in ionic conductivity, it has insufficient thermal stability, is easily hydrolyzed by a trace amount of water in the solvent, and has a property of easily generating lithium fluoride and hydrogen fluoride. When the fluorine-containing inorganic lithium salt is decomposed, the ionic conductivity of the electrolytic solution containing the fluorine-containing inorganic lithium salt decreases, and the generated lithium fluoride and hydrogen fluoride corrode materials such as electrodes and current collectors. Alternatively, it may have a fatal adverse effect on the battery, such as decomposing the solvent.

The electrolytic solution in the present embodiment preferably does not contain water, but may contain a very small amount of water as long as it does not hinder the solution of the problem of the present invention. The content of such water is preferably 0 to 100 ppm with respect to the total amount of the electrolytic solution.

<2-1. Non-aqueous solvent>
Acetonitrile has high ionic conductivity and can enhance the diffusivity of lithium ions in the battery. Therefore, when the electrolytic solution contains acetonitrile, a current collector in which lithium ions are difficult to reach during discharge under a high load, even in a positive electrode in which the positive electrode active material layer is thickened to increase the filling amount of the positive electrode active material. Lithium ions can be satisfactorily diffused to the nearby region. Therefore, it is possible to draw out a sufficient capacity even at the time of high load discharge, and it is possible to obtain a non-aqueous secondary battery having excellent load characteristics.

Further, by using acetonitrile as the non-aqueous solvent of the non-aqueous electrolyte solution, as described above, the ionic conductivity of the non-aqueous electrolyte solution is improved, so that the quick charging characteristics of the non-aqueous secondary battery can be improved. In constant current (CC) -constant voltage (CV) charging of a non-aqueous secondary battery, the capacity per unit time in the CC charging period is larger than the charging capacity per unit time in the CV charging period. When acetonitrile is used as the non-aqueous solvent of the non-aqueous electrolyte solution, the CC charging area can be increased (the CC charging time can be lengthened), and the charging current can be increased. Therefore, charging of the non-aqueous secondary battery is started. The time from to full charge can be greatly reduced.

The non-aqueous solvent is not particularly limited as long as acetonitrile is contained in an amount of 20 to 100% by volume based on the total volume of the non-aqueous solvent, and other non-aqueous solvents may or may not be contained.

The "non-aqueous solvent" in the present embodiment means an element obtained by removing the lithium salt and the nitrogen-containing cyclic compound from the electrolytic solution. That is, when the electrolytic solution contains the solvent, the lithium salt, and the nitrogen-containing cyclic compound together with the electrode protection additive described later, the solvent and the electrode protection additive are collectively referred to as "non-aqueous solvent". .. The lithium salt and nitrogen-containing cyclic compound described later are not contained in the non-aqueous solvent.

Examples of non-aqueous solvents other than acetonitrile include alcohols such as methanol and ethanol; aprotic solvents and the like. Of these, aprotic polar solvents are preferred.

Specific examples of aprotic solvents include:
Ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis -2,3-Pentylene carbonate and cyclic carbonate typified by vinylene carbonate;
Cyclic fluorinated carbonates typified by fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and trifluoromethylethylene carbonate;
Lactones typified by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;
Sulfur compounds typified by sulfolanes, dimethyl sulfoxide, and ethylene glycol sulfite;
Cyclic ethers typified by tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;
Chain carbonates typified by ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and methyl trifluoroethyl carbonate;
Chain fluorinated carbonates typified by trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethyl methyl carbonate;
Mononitrile represented by propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;
Alkoxy group-substituted nitriles typified by methoxynitrile and 3-methoxypropionitrile; malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane , 1,7-Dicyanoheptan, 2,6-dicyanoheptan, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1, Dinitriles typified by 6-dicyanodecane and 2,4-dimethylglutaronitrile;
Cyclic nitrile represented by benzonitrile;
Chain ester represented by methyl propionate;
Chain ethers typified by dimethoxyethane, diethyl ether, 1,3-dioxolane, diglime, triglime, and tetraglime;
A fluorinated ether typified by Rf ^4- OR ⁵ (in the formula, Rf ⁴ is an alkyl group containing a fluorine atom and R ⁵ is an organic group which may contain a fluorine atom);
Ketones typified by acetone, methyl ethyl ketone, and methyl isobutyl ketone; and halides typified by these fluorides. These may be used alone or in combination of two or more.

Among these non-aqueous solvents, it is more preferable to use one or more of cyclic carbonate and chain carbonate together with acetonitrile. Here, as the cyclic carbonate and the chain carbonate, only one of the above-exemplified ones may be selected and used, and two or more kinds (for example, two or more kinds of the above-exemplified cyclic carbonates, the above-mentioned embodiment) may be selected and used. Two or more of the chain carbonates, or one or more of the above-exemplified cyclic carbonates and one or more of the above-exemplified chain carbonates) may be used. Among these, ethylene carbonate, propylene carbonate, vinylene carbonate, or fluoroethylene carbonate is more preferable as the cyclic carbonate, and ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate is more preferable as the chain carbonate. And it is more preferable to use a cyclic carbonate.

Acetonitrile is easily electrochemically reduced and decomposed. Therefore, it is preferable to mix acetonitrile with another solvent and / or add an electrode protection additive to acetonitrile for forming a protective film on the electrode. Further, in order to increase the degree of ionization of the lithium salt that contributes to the charging and discharging of the non-aqueous secondary battery, the non-aqueous solvent preferably contains one or more cyclic aprotic polar solvents, and one or more cyclic carbonates. It is more preferable to include it.

The content of acetonitrile is 20 to 100% by volume based on the total volume of the non-aqueous solvent. More preferably, it is 30% by volume or more, and more preferably 40% by volume or more. Further, the content of acetonitrile is more preferably 85% by volume or less, and further preferably 66% by volume or less. When the content of acetonitrile is 20% by volume or more with respect to the total volume of the non-aqueous solvent, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, and further, the dissolution of the lithium salt can be promoted. it can. Since the nitrogen-containing cyclic compound described below suppresses an increase in the internal resistance of the battery, when the content of acetonitrile in the non-aqueous solvent is within the above range, the high temperature cycle characteristics and high temperature cycle characteristics are maintained while maintaining the excellent performance of acetonitrile. There is a tendency that other battery characteristics can be further improved.

<2-2. Lithium salt>
The lithium salt in the present embodiment is characterized by containing a fluorine-containing inorganic lithium salt. Here, the "fluorine-containing inorganic lithium salt" refers to a lithium salt which does not contain a carbon atom in an anion but contains a fluorine atom in an anion and is soluble in acetonitrile. The "inorganic lithium salt" is a lithium salt that does not contain a carbon atom in an anion and is soluble in acetonitrile, and the "organic lithium salt" is a lithium salt that contains a carbon atom in an anion and is soluble in acetonitrile. To say.

The fluorine-containing inorganic lithium salt in the present embodiment forms a passivation film on the surface of the metal foil which is the positive electrode current collector, and suppresses corrosion of the positive electrode current collector. In addition, the fluorine-containing inorganic lithium salt is excellent in terms of solubility, conductivity, and ionization. Therefore, the fluorine-containing inorganic lithium salt must be added as a lithium salt. Specific examples of the fluorine-containing inorganic lithium salt include, for example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiSbF ₆ , Li ₂ B ₁₂ F _b H _12-b [in the formula, b is 0 to 3 It is an integer], LiN (SO ₂ F) _{2, and the} like.

These fluorine-containing inorganic lithium salts may be used alone or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound which is a double salt of LiF and Lewis acid is desirable, and among them, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it facilitates the release of free fluorine atoms. LiPF ₆ is particularly preferred. Further, it is preferable to use a fluorine-containing inorganic lithium salt having a boron atom as the fluorine-containing inorganic lithium salt because it is easy to capture an excess free acid component which may cause deterioration of the battery. From such a viewpoint, LiBF is preferable. ₄ is particularly preferable.

The content of the fluorine-containing inorganic lithium salt in the electrolytic solution according to the present embodiment is not particularly limited, but is preferably 0.2 mol or more, preferably 0.5 mol or more, with respect to 1 L of the non-aqueous solvent. More preferably, it is more preferably 0.8 mol or more. The content of the fluorine-containing inorganic lithium salt is preferably 15 mol or less, more preferably 4 mol or less, and further preferably 2.8 mol or less with respect to 1 L of the non-aqueous solvent. When the content of the fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, and while maintaining the excellent performance of acetonitrile, the high temperature cycle characteristics and other batteries There is a tendency for the properties to be even better.

As the lithium salt in the present embodiment, in addition to the fluorine-containing inorganic lithium salt, a lithium salt generally used for non-aqueous secondary batteries may be additionally added.
Specific examples of other lithium salts include:
Inorganic lithium salts that do not contain fluorine atoms such as LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , and chloroborane Li in anions;
LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (in the formula, n ≧ 2), lower fat Organic lithium salts such as Li group carboxylic acid and Li tetraphenylborate;
LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) _2, etc. LiN (SO ₂ C _m F _{2 m + 1} ) ₂ [In the formula, m is an integer of 1 to 8] Lithium salt; represented by LiPF _n (C _p F _{2p + 1} ) _6-n such as LiPF ₅ (CF ₃ ) [where n is an integer of 1 to 5 and p is an integer of 1 to 8]. Organolithium salt;
Organolithium represented by LiBF _q (C _s F _{2s + 1} ) _4-q [in the formula, q is an integer of 1-3 and s is an integer of 1-8] such as LiBF ₃ (CF ₃ ). salt;
Lithium bis (oxalate) borate (LiBOB) represented by LiB (C ₂ O ₄ ) ₂ ;
Halogenated LiBOB;
Lithium oxalatodifluoroborate (LiODFB) represented by LiBF ₂ (C ₂ O ₄ );
Lithium bis (malonate) borate (LiBMB) represented by LiB (C ₃ O ₄ H ₂ ) ₂ ;
Organolithium salts such as lithium tetrafluorooxalat oxalate represented by LiPF ₄ (C ₂ O ₄ ) and lithium difluorobis (oxalate) phosphate represented by LiPF ₂ (C ₂ O ₄ ) ₂ .
Lithium salts combined with multivalent anions;
The following general formulas (2a), (2b), and (2c):
LiC (SO ₂ R ⁶ ) (SO ₂ R ⁷ ) (SO ₂ R ⁸ ) (2a)
LiN (SO ₂ OR ⁹ ) (SO ₂ OR ¹⁰ ) (2b)
LiN (SO ₂ R ¹¹ ) (SO ₂ OR ¹² ) (2c)
{In the formula, R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² may be the same or different from each other, and may contain perfluoroalkyl groups having 1 to 8 carbon atoms. Shown. }, And one or more of these can be used together with the fluorine-containing inorganic lithium salt.

In order to improve the load characteristics and charge / discharge cycle characteristics of the non-aqueous secondary battery, it is preferable to supplementally add an organic lithium salt having an oxalic acid group, LiB (C ₂ O ₄ ) ₂ , LiBF ₂ ( It is particularly preferred to add at least one selected from the group consisting of C ₂ O ₄ ), LiPF ₄ (C ₂ O ₄ ), and LiPF ₂ (C ₂ O ₄ ) ₂ . The organic lithium salt having an oxalic acid group may be added to the non-aqueous electrolytic solution or contained in the negative electrode (negative electrode active material layer).

The amount of the organolithium salt having a oxalic acid group added to the non-aqueous electrolyte solution is 0.005 mol per 1 L of the non-aqueous solvent of the non-aqueous electrolyte solution from the viewpoint of ensuring a better effect by its use. The above is preferable, 0.02 mol or more is more preferable, and 0.05 mol or more is further preferable. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte solution is too large, it may precipitate. Therefore, the amount of the organolithium salt having a oxalic acid group added to the non-aqueous electrolyte solution is preferably less than 1.0 mol per 1 L of the non-aqueous electrolyte solution, preferably 0.5 mol. It is more preferably less than, and even more preferably less than 0.2 mol.

<2-3. Electrode protection additive>
In addition to the nitrogen-containing cyclic compound, the electrolytic solution in the present embodiment may contain an additive that protects the electrode. As described above, when the electrolytic solution contains an electrode protection additive, the electrode protection additive is contained in a non-aqueous solvent. Therefore, the electrolytic solution contains a non-aqueous electrode protection additive. Acetonitrile may be contained in the solvent (the total amount of the above-mentioned non-aqueous solvent and the electrode protection additive). Since the reduction decomposition of the nitrogen-containing cyclic compound is dramatically suppressed by the electrode protection additive, the effect is great from the viewpoint of long-term stability.

The electrode protection additive is not particularly limited as long as it does not hinder the solution of the problem according to the present invention. It may substantially overlap with a substance (ie, the non-aqueous solvent described above) that serves as a solvent for dissolving the lithium salt. The electrode protection additive is preferably a substance that contributes to improving the performance of the electrolytic solution and the non-aqueous secondary battery in the present embodiment, but also includes a substance that is not directly involved in the electrochemical reaction.

Specific examples of the electrode protection additive include:
4-Fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans- 4,5-Difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3- Fluoroethylene carbonate typified by dioxolane-2-one and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;
Unsaturated bond-containing cyclic carbonates typified by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;
Lactones typified by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;
Cyclic ether typified by 1,4-dioxane;
Cyclic sulfur compounds typified by ethylene sulfite, propylene sulfite, butylene sulfite, pentensulfite, sulfolane, 3-methylsulfolane, 1,3-propanesulton, 1,4-butanesulfone, and tetramethylene sulfoxide can be mentioned. .. These may be used alone or in combination of two or more. Ethylene sulfite is particularly preferably used.

Since acetonitrile, which is a component of a non-aqueous solvent, is easily chemically reduced and decomposed, the non-aqueous solvent containing acetonitrile uses a cyclic aprotic polar solvent as an additive for forming a protective film on the negative electrode. It is preferable to contain more than one kind, and more preferably to contain one or more kinds of unsaturated bond-containing cyclic carbonates. Among them, vinylene carbonate is preferably used. Furthermore, it is preferable to use vinylene carbonate in combination with ethylene sulfide.

The content of the electrode protection additive in the electrolytic solution in the present embodiment is not particularly limited, but the content of the electrode protection additive with respect to the total volume of the non-aqueous solvent is 0.1 to 30% by volume. It is preferably 2 to 20% by volume, more preferably 5 to 15% by volume.

In the present embodiment, the higher the content of the electrode protection additive, the more the deterioration of the electrolytic solution is suppressed, but the lower the content of the electrode protection additive, the higher the output characteristics of the non-aqueous secondary battery in a low temperature environment. Will be improved. Therefore, by adjusting the content of the electrode protection additive within the above range, excellent performance based on the high ionic conductivity of the electrolytic solution can be obtained without impairing the basic function as a non-aqueous secondary battery. It tends to be able to be maximized. By preparing the electrolytic solution with such a composition, it tends to be possible to further improve the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and other battery characteristics.

<2-4. Nitrogen-containing cyclic five-membered ring compound>
As described above, the electrolytic solution according to the present embodiment contains the following conditions 1 to 6: in addition to the non-aqueous solvent containing acetonitrile and the fluorine-containing inorganic lithium salt.
1. 1. It is a five-membered ring
2. Containing two or more N atoms in a five-membered ring,
3. 3. Contains two or more double bonds in a five-membered ring,
4. One or more of the double bonds are bonds with N atoms,
5. No H atom is bonded to the N atom in the five-membered ring, and 6. It contains a compound having a structure that does not have a cyclic structure that bonds with two or more atoms in the five-membered ring (hereinafter, also referred to as "nitrogen-containing cyclic five-membered ring compound").

｛式中、Ｒは、水素原子以外の置換基である。｝
で表される群から選択される少なくとも１つの五員環構造が挙げられる。 As a specific example of the structure satisfying the conditions 1 to 6, the following formula:

{In the formula, R is a substituent other than a hydrogen atom. }
There is at least one five-membered ring structure selected from the group represented by.

From the viewpoint of the stability of the nitrogen-containing cyclic five-membered ring compound, it is preferable that all the C atoms contained in the five-membered ring of the nitrogen-containing cyclic five-membered ring compound have a double bond.

The group R bonded to the N atom includes an alkyl group having 1 to 4 carbon atoms, an allyl group, a propagyl group, a phenyl group, a benzyl group, a pyridyl group, an amino group, a pyrrolidylmethyl group, a trimethylsilyl group, and a nitrile group. An acetyl group, a trifluoroacetyl group, a chloromethyl group, a methoxymethyl group, an isocyanomethyl group, a methylsulfonyl group, a phenylsulfonyl group, an azide sulfonyl group, a pyridylsulfonyl group, or a 2- (trimethylsilyl) ethoxycarbonyloxy group. preferable.
Among them, an alkyl group having 1 to 4 carbon atoms is more preferable, and a methyl group is further preferable.

The C atom in the five-membered ring may be bonded to other atoms or substituents in addition to the H atom. Examples thereof include alkyl groups having 1 to 4 carbon atoms, fluorine-substituted alkyl groups having 1 to 4 carbon atoms, alkoxy groups having 1 to 4 carbon atoms, fluorine-substituted alkoxy groups having 1 to 4 carbon atoms, nitrile groups, and nitro groups. , Amino group, or halogen atom.

However, when a compound which is a double salt of LiF and Lewis acid is used as the fluorine-containing inorganic lithium salt, it is preferable that there is no steric hindrance around the N atom in the nitrogen-containing five-membered ring compound. Therefore, it is preferable that the C atom adjacent to the N atom has a structure having no substituent other than the hydrogen atom.

Among these nitrogen-containing five-membered ring compounds, those having a structure in which a substituent R is bonded to an N atom are preferable. The substituent R preferably used is an alkyl group, and a methyl group is particularly preferable.

Further, from the viewpoint of thermal stability, a compound having a small number of N atoms contained in the five-membered ring is preferably used. Specifically, it is preferably 2 to 3 atoms, and more preferably an imidazole ring having 2 N atoms.

The non-aqueous electrolyte solution of the present embodiment contains acetonitrile as an additive, which contains a nitrogen-containing cyclic compound satisfying conditions 1 to 6, and thus has an excellent balance between viscosity and relative permittivity, and a fluorine-containing inorganic lithium salt. In a non-aqueous electrolyte solution containing, suppresses the formation of a complex cation composed of a transition metal and acetonitrile, exhibits excellent load characteristics, and suppresses an increase in internal resistance when a charge / discharge cycle is repeated. Can be done.

The content of the nitrogen-containing cyclic compound in the electrolytic solution in the present embodiment is not particularly limited, but is preferably 0.01 to 10% by mass, preferably 0.02 to 100% by mass, based on the total mass of the electrolytic solution. It is more preferably 5% by mass, and even more preferably 0.05 to 3% by mass. In the present embodiment, the nitrogen-containing cyclic compound suppresses the formation of a complex cation composed of a transition metal and acetonitrile. Therefore, the non-aqueous secondary battery containing the nitrogen-containing cyclic compound exhibits excellent load characteristics, and the increase in internal resistance when the charge / discharge cycle is repeated is suppressed. However, the nitrogen-containing cyclic compound in the present embodiment is not necessarily highly soluble due to the influence of the π-conjugated plane. Therefore, by adjusting the content of the nitrogen-containing cyclic compound within the above range, the reaction of forming a complex cation on the electrode surface can be suppressed without impairing the basic function as a non-aqueous secondary battery. It is possible to reduce the increase in internal resistance due to charging and discharging. By preparing an electrolytic solution with such a composition, the cycle performance, high output performance in a low temperature environment, and other battery characteristics of the obtained non-aqueous secondary battery are all further improved. Tend to be able to.

<2-5. Other optional additives>
In the present embodiment, for the purpose of improving the charge / discharge cycle characteristics of the non-aqueous secondary battery, improving the high temperature storage property, improving the safety (for example, preventing overcharging, etc.), the non-aqueous electrolyte solution is used, for example:
Anhydrous acid, sulfonic acid ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene;
Phosphate Ester [Ethyl Diethylphosphonoacetate (EDPA): (C ₂ H ₅ O) ₂ (P = O) -CH ₂ (C = O) OC ₂ H ₅ , Tris (Trifluoroethyl) Phosphate (TFEP) : (CF ₃ CH ₂ O) ₃ P = O, triphenyl phosphate (TPP): (C ₆ H ₅ O) ₃ P = O, etc.], etc .; and any addition selected from derivatives of these compounds, etc. The agent can also be appropriately contained. In particular, the above-mentioned phosphoric acid ester has an effect of suppressing side reactions during storage and is effective.

<3. Positive electrode>
As shown in FIG. 2, the positive electrode 5 is composed of a positive electrode active material layer prepared from a positive electrode mixture and a positive electrode current collector. The positive electrode 5 is not particularly limited as long as it acts as a positive electrode of a non-aqueous secondary battery, and may be a known one.

The positive electrode active material layer contains a positive electrode active material, and optionally further contains a conductive auxiliary agent and a binder.

The positive electrode active material layer preferably contains a material capable of occluding and releasing lithium ions as the positive electrode active material. The positive electrode active material layer preferably contains a conductive auxiliary agent and a binder together with the positive electrode active material, if necessary. When such a material is used, it tends to be possible to obtain a high voltage and a high energy density, which is preferable.

Examples of the positive electrode active material include the following general formulas (3a) and (3b):
Li _x MO ₂ (3a)
Li _y M ₂ O ₄ (3b)
{In the formula, M represents one or more metal elements including at least one transition metal element, x represents a number from 0 to 1.1, and y represents a number from 0 to 2. }, Lithium-containing compounds represented by each, and other lithium-containing compounds can be mentioned.

Examples of the lithium-containing compound represented by each of the general formulas (3a) and (3b) include:
Lithium cobalt oxide represented by LiCoO ₂ ;
Lithium manganese oxides typified by LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ Mn ₂ O ₄ ;
Lithium nickel oxide represented by LiNiO ₂ ;
Li _z MO ₂ (In the formula, M contains at least one transition metal element selected from Ni, Mn, and Co, and two or more selected from the group consisting of Ni, Mn, Co, Al, and Mg. Lithium-containing composite metal oxides and the like represented by (z indicates a number of more than 0.9 and less than 1.2).

The lithium-containing compound other than the lithium-containing compound represented by each of the general formulas (3a) and (3b) is not particularly limited as long as it contains lithium. Examples of such a lithium-containing compound include a composite oxide containing lithium and a transition metal element, a metal chalcogenide having lithium, a metal phosphate compound containing lithium and a transition metal element, and lithium and a transition metal element. silicic acid metal compound [e.g. _containing, in Li _t M u SiO ₄ {wherein, M has the same meaning as the general formula (3a), t represents a number of 0 to 1, and u is the number of 0 to 2 Shown. } Etc.].

From the viewpoint of obtaining a higher voltage, as a lithium-containing compound, in particular:
With lithium
Selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), and titanium (Ti). At least one transition metal element
Composite oxides containing, and metal phosphate compounds are preferred.

More specifically, as the lithium-containing compound, a composite oxide containing lithium and a transition metal element, a metal chalcogenized product containing lithium and a transition metal element, and a metal phosphate compound having lithium are more preferable, for example, respectively. The following general formulas (4a) and (4b):
^{_{Li v M I D 2 (4a}} )
Li _w M ^II PO ₄ (4b)
{Wherein, D is an oxygen or chalcogen element, M ^I and M ^II is represents one or more transition metal elements each, the value of v and w vary according to the charge and discharge state of the battery, v 0.05 It indicates a number of ~ 1.10, and w indicates a number of 0.05 to 1.10. } Can be mentioned.

The lithium-containing compound represented by the general formula (4a) has a layered structure, and the compound represented by the general formula (4b) has an olivine structure. These lithium-containing compounds are those in which a part of the transition metal element is replaced with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, and these metal elements are included in the crystal grain boundary. It may be one in which a part of oxygen atoms is replaced with a fluorine atom or the like, one in which at least a part of the surface of the positive electrode active material is coated with another positive electrode active material, or the like.

As the positive electrode active material in the present embodiment, only the above-mentioned lithium-containing compound may be used, or other positive electrode active materials may be used in combination with the lithium-containing compound. Examples of other positive electrode active materials include metal oxides or metal chalcogenides having a tunnel structure and a layered structure; sulfur; conductive polymers, and the like. Examples of metal oxides or metal chalcogenides having a tunnel structure and a layered structure include MnO ₂ , FeO ₂ , FeS ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS ₂ , MoS ₂ , and NbSe _2. Examples thereof include oxides, sulfides, and serenes of metals other than lithium. Examples of the conductive polymer include conductive polymers typified by polyaniline, polythiophene, polyacetylene, and polypyrrole.

Other positive electrode active materials may be used alone or in combination of two or more, and are not particularly limited. However, in the present embodiment, since lithium ions can be occluded and released in a reversible and stable manner and a high energy density can be achieved, at least the positive electrode active material layer is selected from Ni, Mn, and Co. It preferably contains one type of transition metal element.

When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of both to be used is preferably 80% by mass or more, preferably 85% by mass or more, as the ratio of the lithium-containing compound used to the total mass of the positive electrode active material. More preferably by mass% or more.

Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the positive electrode active material.

For the positive electrode active material layer, a positive electrode mixture-containing slurry in which a positive electrode mixture obtained by mixing a positive electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a positive electrode current collector and dried (solvent removal). ), And if necessary, it is formed by pressing. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned. The positive electrode active material layer can be formed on one side or both sides of the positive electrode current collector.

The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The surface of the positive electrode current collector may be coated with carbon, or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

<4. Negative electrode ＞
As shown in FIG. 2, the negative electrode 6 is composed of a negative electrode active material layer prepared from a negative electrode mixture and a negative electrode current collector. The negative electrode 6 is not particularly limited as long as it acts as a negative electrode of a non-aqueous secondary battery, and may be a known one.

The negative electrode active material layer contains lithium ions of 0.4 V vs. as the negative electrode active material from the viewpoint of increasing the battery voltage. It preferably contains a material that can be occluded at a lower potential than Li / Li ⁺ . The negative electrode active material layer preferably contains a conductive auxiliary agent and a binder together with the negative electrode active material, if necessary.

Examples of the negative electrode active material include amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, thermally decomposed carbon, coke, glassy carbon, fired organic polymer compound, mesocarbon microbeads, carbon fiber, and activated carbon. , Carbon colloid, and carbon materials such as carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetal compounds, organic compounds, inorganic compounds, metal complexes, organic Examples include high molecular compounds.

The negative electrode active material may be used alone or in combination of two or more.

Examples of the conductive auxiliary agent include graphite, acetylene black, carbon black typified by Ketjen black, and carbon fiber. The content ratio of the conductive auxiliary agent is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

Examples of the binder include PVDF, PTFE, polyacrylic acid, styrene-butadiene rubber, and fluororubber. The content ratio of the binder is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass with respect to 100 parts by mass of the negative electrode active material.

For the negative electrode active material layer, a negative electrode mixture-containing slurry in which a negative electrode mixture obtained by mixing a negative electrode active material and, if necessary, a conductive auxiliary agent and a binder is dispersed in a solvent is applied to a negative electrode current collector and dried (solvent removal). It is formed by pressing as needed. The solvent is not particularly limited, and conventionally known solvents can be used. For example, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, water and the like can be mentioned. The negative electrode active material layer can be formed on one side or both sides of the negative electrode current collector.

The negative electrode current collector is composed of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Further, the negative electrode current collector may have a carbon coat on its surface or may be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

<5. Separator>
As shown in FIG. 2, the non-aqueous secondary battery 8 in the present embodiment has a separator 7 between the positive electrode 5 and the negative electrode 6 from the viewpoint of preventing short circuits between the positive electrode 5 and the negative electrode 6 and imparting safety such as shutdown. It is preferable to provide. As the separator 7, the same one as that provided in a known non-aqueous secondary battery may be used, and an insulating thin film having high ion permeability and excellent mechanical strength is preferable. Examples of the separator 7 include woven fabrics, non-woven fabrics, and microporous membranes made of synthetic resin. Among these, microporous membranes made of synthetic resin are preferable.

As the microporous membrane made of synthetic resin, for example, a microporous membrane containing polyethylene or polypropylene as a main component, or a polyolefin-based microporous membrane such as a microporous membrane containing both of these polyolefins is preferably used. Examples of the non-woven fabric include a porous film made of a heat-resistant resin such as glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, and aramid.

The separator 7 may have a structure in which one type of microporous membrane is laminated in a single layer or a plurality of types, or may be a structure in which two or more types of microporous membranes are laminated. The separator 7 may have a configuration in which two or more kinds of resin materials are melt-kneaded and laminated in a single layer or a plurality of layers using a mixed resin material.

<6. Battery exterior ＞
In FIG. 2, the battery exterior 2 is composed of two aluminum laminated films 1, but the configuration of the battery exterior of the non-aqueous secondary battery according to the present embodiment is not particularly limited, and for example, a battery can and a laminated film. Any battery exterior of the exterior can be used. As the battery can, for example, a metal can made of steel or aluminum can be used. As the laminate film exterior body, for example, a laminate film having a three-layer structure of a heat-melted resin / metal film / resin can be used.

The laminated film exterior is in a state in which two sheets are stacked with the heat-melted resin side facing inward, or bent so that the heat-melted resin side faces inward, and the ends are sealed by heat sealing. Can be used as an exterior body. When the laminated film exterior body is used, the positive electrode lead body (or the lead tab connected to the positive electrode terminal and the positive electrode terminal) is connected to the positive electrode current collector, and the negative electrode lead body (or the negative electrode terminal and the negative electrode terminal) are connected to the negative electrode current collector. A lead tab) may be connected. In this case, the laminated film exterior body may be sealed with the ends of the positive electrode lead body and the negative electrode lead body (or the lead tabs connected to the positive electrode terminal and the negative electrode terminal respectively) pulled out to the outside of the exterior body. ..

<7. Battery manufacturing method>
As shown in FIG. 2, the non-aqueous secondary battery in the present embodiment includes the above-mentioned non-aqueous electrolyte solution, a positive electrode 5 having a positive electrode active material layer on one or both sides of a current collector, and one or both sides of a current collector. It is produced by a known method using a negative electrode 6 having a negative electrode active material layer, a battery exterior 2, and a separator 7 if necessary.

First, a laminate composed of the positive electrode 5 and the positive electrode 6 and, if necessary, the separator 7 is formed. For example, an embodiment in which a long positive electrode 5 and a negative electrode 6 are wound in a laminated state in which the long separator is interposed between the positive electrode 5 and the negative electrode 6 to form a laminated body having a wound structure;
An embodiment of forming a laminated body having a laminated structure in which a positive electrode sheet and a negative electrode sheet obtained by cutting a positive electrode 5 and a negative electrode 6 into a plurality of sheets having a certain area and a shape are alternately laminated via a separator sheet. ;
A mode in which a long separator is folded in a zigzag manner to form a laminated body having a laminated structure in which positive electrode body sheets and negative electrode body sheets are alternately inserted between the zigzag-folded separators.
Etc. are possible.

Next, the above-mentioned laminate is housed in the battery exterior 2 (battery case), the electrolytic solution according to the present embodiment is injected into the battery case, and the laminate is immersed in the electrolytic solution and sealed. The non-aqueous secondary battery according to the present embodiment can be manufactured.
Alternatively, a gel-like electrolyte membrane is prepared in advance by impregnating a base material made of a polymer material with an electrolytic solution, and a sheet-shaped positive electrode 5, negative electrode 6, and electrolyte membrane, and if necessary, are used. After forming a laminated body having a laminated structure using the separator 7, a non-aqueous secondary battery can be produced by accommodating the battery in the battery exterior 2.

The shape of the non-aqueous secondary battery in the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a square cylinder shape, a button shape, a coin shape, a flat shape, a laminated shape and the like are preferably adopted.

The non-aqueous secondary battery in the present embodiment can function as a battery by the initial charging, but is stabilized by decomposing a part of the electrolytic solution during the initial charging. The method of initial charging is not particularly limited, but the initial charging is preferably performed at 0.001 to 0.3C, more preferably 0.002 to 0.25C, and 0.003 to 0.2C. It is more preferable to be carried out in. It is also preferable that the initial charging is performed via constant voltage charging on the way. The constant current that discharges the rated capacity in 1 hour is 1C. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, SEI (Solid Electrolyte Interface) is formed on the electrode surface, and the effect of suppressing an increase in internal resistance including the positive electrode 5 is suppressed. In addition to the above, the reaction product is not firmly fixed only to the negative electrode 6, and somehow gives a good effect to members other than the negative electrode 6, such as the positive electrode 5 and the separator 7. Therefore, it is very effective to perform the initial charging in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte solution.

The non-aqueous secondary battery in the present embodiment can also be used as a battery pack in which a plurality of non-aqueous secondary batteries are connected in series or in parallel. From the viewpoint of controlling the charge / discharge state of the battery pack, the working voltage range per battery pack is preferably 2 to 5 V, more preferably 2.5 to 5 V, and preferably 2.75 V to 5 V. Especially preferable.

Although the embodiment for carrying out the present invention has been described above, the present invention is not limited to the above-described embodiment. The present invention can be modified in various ways without departing from the gist thereof.

Hereinafter, the present invention will be described in more detail by way of examples. Various evaluations were carried out as follows.

(1) Positive electrode immersion test The aluminum laminated bag was processed to 2.7 cm × 6 cm. A positive electrode described later was punched out to a size of 23 mm × 17 mm in this bag, and then 0.5 mL of the non-aqueous electrolyte solution prepared in each Example or Comparative Example was injected under an inert atmosphere. At this time, it was confirmed that the electrode surface was immersed in the electrolytic solution. After pouring the liquid, it was sealed, and the aluminum laminated bag was kept at 60 ° C. in a vertically leaning state and stored for 10 days. After storage, the internal electrolytic solution and the surface of the positive electrode were observed. The test result was "○ (good)" when no gel-like substance containing a salt of a complex cation composed of a transition metal and acetonitrile as a main component was observed in both the electrolytic solution and the surface of the positive electrode. When the gel-like substance was found on any of the surfaces, the test result was determined to be "x (defective)".

(2) Fabrication of battery (2-1) Fabrication of positive electrode (P1) As a positive electrode active material, a composite oxide of lithium, nickel, manganese, and cobalt having a number average particle diameter of 11 μm (LiNi _1/3 Mn _1/3 Co _{1 /) 3} O _2, and the density 4.70g / cm ^3), and acetylene black powder having an average particle diameter of 48nm as a conductive additive (density 1.95g / cm ^3), polyvinylidene fluoride (PVdF; density 1.75g / Cm ³ ) was mixed at a mass ratio of 93: 4: 3 to obtain a positive electrode mixture. N-Methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. This positive electrode mixture-containing slurry is applied to one side of an aluminum foil having a thickness of 20 μm and a width of 200 mm, which serves as a positive electrode current collector, by the doctor blade method while adjusting the basis weight to 22 mg / cm ² , and a solvent is applied. Removed by drying. Then, by rolling with a roll press so that the density of the positive electrode active material layer was 2.8 g / cm ³ , a positive electrode (P1) composed of the positive electrode active material layer and the positive electrode current collector was obtained.

(2-2) Preparation of negative electrode (N1) Graphite carbon powder with a number average particle diameter of 25 μm (trade name “MCMB25-28”, manufactured by Osaka Gas Chemical Co., Ltd.) as a negative electrode active material and number average particles as a conductive auxiliary agent. Acetylene black having a diameter of 48 nm and polyvinylidene fluoride (PVdF; density 1.75 g / cm ³ ) as a binder were mixed at a solid content mass ratio of 93: 2: 5. N-Methyl-2-pyrrolidone was added to the obtained mixture and further mixed to prepare a slurry containing a negative electrode mixture. This negative electrode mixture-containing slurry is applied to one side of a copper foil having a thickness of 10 μm and a width of 200 mm, which serves as a negative electrode current collector, by the doctor blade method while adjusting the basis weight to 12 mg / cm ² , and the solvent is removed by drying. did. Then, by rolling with a roll press so that the density of the negative electrode active material layer was 1.5 g / cm ³ , a negative electrode (N1) composed of the negative electrode active material layer and the negative electrode current collector was obtained.

(2-3) Preparation of single-layer laminated battery (for evaluation) Two laminated films (without drawing, thickness 120 μm, 31 mm × 37 mm) in which an aluminum layer and a resin layer are laminated are placed with the aluminum layer side facing outward. The three sides were sealed to prepare a laminated cell exterior. The positive electrode (P1) prepared as described above was punched to 14.0 mm × 20.0 mm, and the negative electrode (N1) prepared as described above was punched to 14.5 mm × 20.5 mm. Subsequently, a polyethylene microporous film (thickness 20 μm, 16 mm × 22 mm) was prepared as a separator, and a laminate in which a positive electrode (P1) and a negative electrode (N1) were laminated on both sides of the separator was formed on the above-mentioned laminate cell exterior. Placed inside. Next, the electrolytic solutions prepared in each Example and Comparative Example were injected into the cell exterior, and the laminate was immersed in the electrolytic solution. Then, the remaining side of the exterior of the laminated cell was sealed to produce a non-aqueous secondary battery (single-layer laminated battery, hereinafter also simply referred to as "battery"). This was held at 25 ° C. for 24 hours, and the electrolytic solution was sufficiently blended into the laminate to obtain a single-layer laminated battery having 1 C = 8.5 mA.

Here, 1C means a current value that is expected to end the discharge in 1 hour after discharging the fully charged battery with a constant current. The single-layer laminated battery produced above means a current value that is expected to discharge from a fully charged state of 4.2 V to 2.7 V at a constant current and complete the discharge in 1 hour.

(3) Battery Evaluation of Single-Layer Laminated Battery With respect to the battery obtained as described above, first, the initial charging process and the initial charge / discharge capacity measurement were performed according to the procedure of (3-1) below. Next, each battery was evaluated according to the following (3-2) and (3-3). Charging / discharging was performed using a charging / discharging device ACD-01 (trade name) manufactured by Asuka Electronics Co., Ltd. and a constant temperature bath PLM-63S (trade name) manufactured by Futaba Kagaku Co., Ltd.

(3-1) Initial charge / discharge characteristics of single-layer laminated battery The ambient temperature of the battery is set to 25 ° C, and the battery is charged with a constant current of 1.7 mA, which corresponds to 0.2 C, and the battery voltage reaches 4.2 V. After charging, the battery was charged at a constant voltage of 4.2 V for 8 hours. Then, it was discharged to 2.7 V with a constant current of 1.7 mA corresponding to 0.2 C. This series of charge / discharge operations is defined as one cycle, and the value obtained by dividing the discharge capacity at the nth cycle by the charge capacity at the nth cycle is defined as the initial charge / discharge efficiency.

(3-2) Measurement of discharge capacity at high output of single-layer laminated battery (output test)
Using the battery subjected to the initial charge / discharge treatment by the method described in (3-1) above, the battery is charged with a constant current of 8.5 mA corresponding to 1C and charged until the battery voltage reaches 4.2 V. After that, the battery was charged at a constant voltage of 4.2 V for a total of 3 hours. After that, the battery was discharged to a battery voltage of 2.7 V with a constant current of 8.5 mA corresponding to 1 C. The discharge capacity at this time was defined as A. Next, the battery was charged with a constant current of 8.5 mA, which corresponds to 1C, until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V for a total of 3 hours. After that, the battery was discharged to a battery voltage of 2.7 V with a constant current of 42.5 mA corresponding to 5 C. The discharge capacity at this time was defined as B. The following values were calculated as output test measured values.
Capacity retention rate = 100 x B / A [%]

(3-3) 50 ° C. Cycle Measurement of Single-Layer Laminated Battery The charge / discharge cycle characteristics at 50 ° C. were evaluated for the battery subjected to the initial charge / discharge treatment by the method described in (3-1) above.
First, the ambient temperature of the battery was set to 50 ° C. After charging with a constant current corresponding to 0.2C and reaching 4.2V, charging was performed at 4.2V for a total of 3 hours, and then discharged to 2.7V with a constant current corresponding to 0.2C. 50 cycles of charging and discharging were performed, with the above step of charging and discharging once as one cycle. The first, 25th, and 50th discharges were performed with a constant current corresponding to 0.5C instead of 0.2C, respectively.
At this time, the ratio of the discharge capacity of each cycle when the discharge capacity of the second cycle is 100% was defined as the discharge capacity retention rate.

(3-4) AC Impedance Measurement of Single-Layer Laminated Battery AC impedance is measured using a frequency response analyzer 1400 (trade name) manufactured by Solartron and Potency Galvanostat 1470E (trade name) manufactured by Solartron. went. As the non-aqueous secondary battery to be measured, the battery at the time of charging up to the first cycle and the 50th cycle when the 50 ° C. cycle measurement was performed by the method described in (3-3) above was used. Only one battery was used for this measurement, and after the measurement was performed after charging in each predetermined cycle, the 50 ° C. cycle measurement was continued and used for the next measurement.

As the measurement conditions, the amplitude was set to ± 5 mV and the frequency was set to 0.1 to 20 kHz, and the AC impedance values at 0.1 kHz and 20 kHz were obtained. The ambient temperature of the battery when measuring the AC impedance was 25 ° C.

[Example 1]
Under an inert atmosphere, a mixed solvent consisting of 830 mL of acetonitrile and 170 mL of vinylene carbonate was prepared as a non-aqueous solvent, and 1.3 mol of LiPF ₆ and 0.1 mol of LiBOB were dissolved in the mixed solvent. Next, 1 part by mass of 1-methylimidazole was dissolved as an additive in 100 parts by mass of the mixed solvent to obtain an electrolytic solution.

[Comparative Example 1]
In Example 1 above, an electrolytic solution having the same composition and containing no additive was prepared.

[Positive electrode immersion test of Reference Example 1, positive electrode immersion test of Example 1 and Comparative Example 1 and initial charge / discharge characteristics]
The electrolytic solution obtained as described above was subjected to a positive electrode immersion test by the method described in (1) above.
In Comparative Example 1 containing no nitrogen-containing cyclic compound in the electrolytic solution containing a fluorine-containing inorganic lithium salt and acetonitrile, the formation of a brown gel-like substance was observed. ^From the results of analysis by ¹ H-NMR, ¹⁹ F-NMR, and ICP, it was found that this brown gel-like substance contained a complex cation composed of a transition metal and acetonitrile. On the other hand, in the electrolytic solution containing the fluorine-containing inorganic lithium salt and acetonitrile, the formation of this brown gel-like substance was not observed in Example 1 containing the nitrogen-containing cyclic compound.

From these results, it was suggested that the nitrogen-containing cyclic compound contributes to the high temperature durability of the battery in the electrolytic solution containing the fluorine-containing inorganic lithium salt and acetonitrile.

In Reference Example 1 in which only an organic lithium salt (LiBOB 0.1 mol / L) was used as the lithium salt, the formation of a brown gel-like substance was not observed. From this, it was suggested that the formation of a brown gel-like substance is a problem peculiar to an electrolytic solution containing a fluorine-containing inorganic lithium salt and acetonitrile.

Next, the positive electrode (P1), the negative electrode (N1), and the electrolytic solutions of Example 1 and Comparative Example 1 were combined to prepare a single-layer laminated battery according to the method described in (2-3) above. The single-layer laminated battery was subjected to the initial charge / discharge treatment by the method described in (3-1) above.

[Comparative Example 2]
Moreover, in order to compare the performance of the battery of the electrolytic solution containing acetonitrile and the battery which does not contain acetonitrile, an electrolytic solution containing no acetonitrile was prepared as Comparative Example 2. That is, a battery was prepared using an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1.0 mol / L in a non-aqueous solvent mixed with ethylene carbonate / ethyl methyl carbonate = 30/70 (V / V). The discharge capacity of the batteries of Comparative Examples 1 and 2 was measured by the method described in (3-2) above.

[Electrolyte composition and evaluation results of Example 1, Comparative Examples 1 and 2, and Reference Example 1]
The electrolyte compositions of Example 1, Comparative Examples 1, 2 and Reference Example 1 are shown in Table 1, and the initial charge / discharge efficiency and capacity retention rate of each are shown in Table 2.

From the comparison between Comparative Example 1 and Comparative Example 2, when the electrolytic solution containing acetonitrile was used, the capacity retention rate in the output test was remarkably improved as compared with the case where the electrolytic solution not containing acetonitrile was used. Was confirmed.

Next, with respect to the single-layer laminated battery prepared according to the method described in (2-3) above using the electrolytic solutions of Example 1 and Comparative Example 1, the method described in (3-1) above The initial charge / discharge treatment was performed, and 50 ° C. cycle measurement and AC impedance measurement were performed by the methods described in (3-3) and (3-4) above. The evaluation results are shown in Table 3.

From the comparison between Example 1 and Comparative Example 1, the case where the electrolytic solution containing acetonitrile, the fluorine-containing inorganic lithium salt and the nitrogen-containing cyclic compound was used was compared with the case where the electrolytic solution containing no nitrogen-containing cyclic compound was used. It was confirmed that the decrease in capacity retention rate and the increase in internal resistance after 50 cycles of charge and discharge were suppressed at 50 ° C.

From the above results, it can be seen that the non-aqueous secondary battery using the electrolytic solution of the present embodiment realizes extremely high output characteristics while maintaining high temperature durability performance comparable to that of the existing electrolytic solution.

The non-aqueous secondary battery produced by using the non-aqueous electrolyte of the present invention is, for example, a rechargeable battery for mobile devices such as mobile phones, portable audio devices, personal computers, and IC (Integrated Circuit) tags; hybrid automobiles, Rechargeable batteries for automobiles such as plug-in hybrid automobiles and electric automobiles; expected to be used as residential power storage systems.

1 Aluminum laminated film 2 Battery exterior 3 Positive electrode lead body 4 Negative electrode lead body 5 Positive electrode 6 Negative electrode 7 Separator 8 Non-aqueous secondary battery

Claims (4)

With a non-aqueous solvent containing 20% to 100% by volume of acetonitrile;
With fluorine-containing inorganic lithium salt;
Possess an imidazole structure, a N atom in the imidazole structure and a compound which is bound to a methyl group;
A nonaqueous electrolyte containing the content of the compound is 0.0 5 parts by mass to 3 parts by mass with respect to the nonaqueous electrolyte solution 100 parts by mass, the non-aqueous electrolyte solution. The non-aqueous electrolyte solution according to claim 1, further containing vinylene carbonate and ethylene sulfite. The non-aqueous electrolyte solution according to claim 1 or 2 , wherein the fluorine-containing inorganic lithium salt contains LiPF ₆ . A positive electrode having a positive electrode active material layer containing at least one transition metal element selected from Ni, Mn, and Co on one or both sides of a positive electrode current collector;
The negative electrode having a negative electrode active material layer on one side or both sides of the negative electrode current collector; and the non-aqueous electrolyte solution according to any one of claims 1 to 3 ;
A non-aqueous secondary battery equipped with.

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