JP2017188299A - Nonaqueous secondary battery, and nonaqueous electrolyte used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery including acetonitrile superior in the balance between a viscosity and a relative dielectric constant, and a fluorine-containing inorganic lithium salt, which is arranged to be able to suppress the production of a complex cations formed from a transition metal and the acetonitrile, to exhibit superior load characteristics, and to suppress the self discharge when being stored at a high temperature.SOLUTION: A nonaqueous secondary battery comprises: a positive electrode having a positive electrode active material layer on one or each of opposing faces of a positive electrode current collector, provided that the active material layer includes at least one transition metal element selected from Ni, Mn and Co; a negative electrode having a negative electrode active material layer on one or each of opposing faces of a negative electrode current collector; and a nonaqueous electrolyte. The nonaqueous electrolyte includes a nonaqueous solvent containing 30-100 vol.% of acetonitrile, and a fluorine-containing inorganic lithium salt. In the nonaqueous secondary battery, there is a polymer having a pyridine ring.SELECTED DRAWING: Figure 1

Description

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

  Non-aqueous secondary batteries such as lithium ion secondary batteries are characterized by 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 used as industrial batteries typified 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 gaining attention in the field of power storage such as residential power storage systems.

  The electrolytic solution of the room temperature operation type lithium ion secondary battery preferably has a high relative dielectric constant and a low viscosity. However, when it has a high dielectric constant, the viscosity tends to increase. Therefore, it is necessary to mix a solvent having a high dielectric constant and a high viscosity with another low viscosity solvent to reduce the viscosity of the electrolytic solution. For example, cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) have a high dielectric constant but a high viscosity, so they are mixed with a low-viscosity solvent such as a lower chain carbonate to form an electrolytic solution. It is common. These high dielectric constant solvents have a high melting point, and can cause deterioration in load characteristics (output characteristics) and low-temperature characteristics of the non-aqueous electrolyte depending on the type of electrolyte salt used in the non-aqueous electrolyte.

As one of the solvents for overcoming such problems, a nitrile solvent excellent in the balance between viscosity and relative dielectric constant has been proposed. Among them, acetonitrile has a high potential as a solvent used for an electrolyte solution of a lithium ion secondary battery. However, since acetonitrile has a fatal defect of electrochemically reducing and decomposing at the negative electrode, practical performance could not be exhibited. Several improvements have been proposed for this problem.
The main improvement measures proposed so far are classified into the following three.

(1) Method for protecting negative electrode by combination with specific electrolyte salt, additive, etc. and suppressing reductive decomposition of acetonitrile For example, Patent Documents 1 and 2 include acetonitrile as a solvent as a specific electrolyte salt and an additive. There has been reported an electrolyte solution that reduces the influence of reductive decomposition of acetonitrile by combining with the above. In the early days of lithium ion secondary batteries, as disclosed in Patent Document 3, an electrolytic solution containing a solvent obtained by simply diluting acetonitrile with propylene carbonate and ethylene carbonate has been reported. However, in Patent Document 3, since the high-temperature durability performance is determined by evaluating only the internal resistance and battery thickness after high-temperature storage, 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 with ethylene carbonate and propylene carbonate. As a method for suppressing reductive decomposition of a 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 reductive decomposition of acetonitrile by using a negative electrode active material that occludes lithium ions at a potential nobler than the reduction potential of acetonitrile. For example, Patent Document 4 uses a specific metal compound for the negative electrode. Thus, it is reported that a battery avoiding reductive decomposition of acetonitrile can be obtained. However, in applications where the energy density of the lithium ion secondary battery is important, it is overwhelmingly advantageous to use a negative electrode active material that occludes lithium ions at a lower potential than the reduction potential of acetonitrile from the viewpoint of potential difference. Therefore, when the improvement measure of Patent Document 4 is applied in such an application, the range of usable voltages becomes narrow, which is disadvantageous.

(3) Method for maintaining a stable liquid state by dissolving a high concentration electrolyte salt in acetonitrile For example, Patent Document 5 discloses a lithium bis (trifluoromethanesulfonyl) imide (concentration of 4.2 mol / L). It is described that reversible lithium insertion / extraction from a graphite electrode is possible by using an electrolytic solution in which LiN (SO ₂ CF ₃ ) ₂ ) is dissolved in acetonitrile. Patent Document 6 discloses 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 is 4.5 mol / L. As a result of charge / discharge measurement, Li ⁺ insertion / extraction reaction to 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 JP-A-4-351860 JP 2009-21134 A International Publication No. 2013/146714 JP 2014-241198 A

  However, lithium ion secondary batteries using an electrolytic solution containing acetonitrile are inferior in high-temperature durability performance compared to existing lithium ion secondary batteries using an electrolytic solution containing a carbonate solvent. Has not yet reached full-scale practical use.

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

  In a high temperature environment, the fluorine-containing inorganic lithium salt decomposes while extracting hydrogen from the methyl group of acetonitrile, and the decomposition product promotes elution of the positive electrode transition metal. The complex cation in which acetonitrile is coordinated to the eluted metal is chemically stable, and the redox reaction of the stable complex cation may cause self-discharge. These phenomena supported by the results of the disassembly analysis are problems newly found 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 suppresses the generation of complex cations composed of transition metals and acetonitrile in a non-aqueous secondary battery using acetonitrile with an excellent balance between viscosity and relative dielectric constant, and exhibits excellent load characteristics. It aims at providing the non-aqueous secondary battery which can suppress the self-discharge at the time of high temperature storage.

The inventors of the present invention have made extensive studies to solve the above-described problems. As a result, the presence of a polymer having a pyridine ring structure in the non-aqueous secondary battery and contact with a non-aqueous electrolyte containing acetonitrile suppresses the formation of complex cations composed of transition metals and acetonitrile. The present inventors have found that it is possible to exhibit excellent load characteristics and suppress self-discharge during high-temperature storage, and have completed the present invention.
That is, the present invention is as follows.
[1]
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 surfaces of the positive electrode current collector;
A negative electrode having a negative electrode active material layer on one or both sides of a negative electrode current collector;
A non-aqueous electrolyte,
A non-aqueous secondary battery comprising:
The non-aqueous electrolyte contains a non-aqueous solvent containing 30 to 100% by volume of acetonitrile and a fluorine-containing inorganic lithium salt, and a polymer having a pyridine ring is present inside the non-aqueous secondary battery.
The non-aqueous secondary battery.
[2]
The nonaqueous secondary battery according to [1], wherein the fluorine-containing inorganic lithium salt contains LiPF ₆ .
[3]
The weight ratio of the N atom derived from the pyridine ring of the polymer is 0.002 to 2% by weight with respect to the total weight of the non-aqueous electrolyte present in the non-aqueous secondary battery, [1] Or the non-aqueous secondary battery as described in [2].
[4]
The non-aqueous secondary according to any one of [1] to [3], wherein the polymer is present on the surface or inside of the positive electrode or on the surface or inside of the negative electrode in the non-aqueous electrolyte. battery.
[5]
The nonaqueous secondary battery according to any one of [1] to [3], wherein the nonaqueous secondary battery further includes a separator, and the polymer is present on a surface or inside of the separator. .
[6]
The nonaqueous secondary battery according to [5], wherein the polymer is present on the surface of the separator on the positive electrode side.
[7]
The nonaqueous secondary battery according to [4], wherein the polymer is present on the surface or inside of the positive electrode.
[8]
The non-aqueous solvent containing 30 to 100% by volume of acetonitrile with respect to the total volume of the non-aqueous solvent;
LiPF ₆ as the fluorine-containing inorganic lithium salt;
0.01 to 10% by mass of a polymer having a pyridine ring with respect to the total mass of the nonaqueous electrolytic solution;
The non-aqueous electrolyte solution comprising:

  According to the present invention, in a secondary battery using an acetonitrile electrolyte having an excellent balance between viscosity and relative dielectric constant, generation of a complex cation composed of a transition metal and acetonitrile is suppressed, and excellent load characteristics are exhibited. In addition, it is possible to provide a non-aqueous secondary battery in which self-discharge during high-temperature storage is suppressed.

It is a top view which shows roughly an example of the non-aqueous secondary battery which concerns on this embodiment. It is the sectional view on the AA line of the non-aqueous secondary battery of FIG.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. In the present specification, numerical ranges described using “to” include numerical values described before and after.

<1. Overall configuration of non-aqueous secondary battery>
The non-aqueous secondary battery according to this embodiment is as follows:
A positive electrode containing a positive electrode material capable of inserting and extracting lithium ions as a positive electrode active material;
A negative electrode material capable of inserting and extracting lithium ions as a negative electrode active material, and a negative electrode containing one or more negative electrode materials selected from the group consisting of metallic lithium;
An electrolyte,
Is provided.

  Specifically, the non-aqueous secondary battery according to the present embodiment may be the non-aqueous secondary battery illustrated 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 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 with a separator 7 in a battery exterior 2 constituted by two aluminum laminate films 1, and a non-aqueous electrolyte solution ( (Not shown). The battery exterior 2 is sealed by heat-sealing the upper and lower aluminum laminate films 1 at the outer periphery thereof. The laminate in which the positive electrode 5, the separator 7, and the negative electrode 6 are sequentially laminated is impregnated with a nonaqueous electrolytic solution. In FIG. 2, each layer constituting the battery exterior 2 and each layer of the positive electrode 5 and the negative electrode 6 are not shown separately in order to avoid the drawing from being complicated.

The aluminum laminate film 1 constituting the battery casing 2 is preferably one in which both surfaces of an aluminum foil are coated with a polyolefin 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 8. Each of the positive electrode lead body 3 and the negative electrode lead body 4 is drawn out to the outside of the battery exterior 2 so that it can be connected to an external device or the like. It is heat-sealed together.

  In the non-aqueous secondary battery 8 shown in FIGS. 1 and 2, each of the positive electrode 5 and the negative electrode 6 has a single laminated electrode body. It can be increased as appropriate. In the case of a laminated electrode body having a plurality of positive electrodes 5 and negative electrodes 6, tabs having the same polarity may be joined 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 tab of the same polarity, an aspect constituted by an exposed portion of the current collector, an aspect constituted by welding a metal piece to the exposed portion of the current collector, and the like are possible.

  The positive electrode 5 includes a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The negative electrode 6 includes a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The positive electrode 5 and the negative electrode 6 are disposed so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator 7 interposed therebetween.

  Hereinafter, the term “electrode” is abbreviated as a generic term for the positive electrode and the negative electrode, the term “electrode active material layer” is a generic term for the positive electrode active material layer and the negative electrode active material layer, and the term “electrode mixture” is generically termed for the positive electrode mixture and the negative electrode mixture.

  As each of these members, a material provided in a conventional lithium ion secondary battery can be used as long as each requirement in the present embodiment is satisfied. For example, the following materials 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 includes a non-aqueous solvent (hereinafter also simply referred to as “solvent”) containing 30 to 100% by volume of acetonitrile and a fluorine-containing inorganic lithium salt. Although the fluorine-containing inorganic lithium salt is excellent in ionic conductivity, it does not have sufficient thermal stability, and is easily hydrolyzed by a trace amount of water in the solvent, and easily generates 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 is reduced, and the generated lithium fluoride and hydrogen fluoride corrode materials such as electrodes and current collectors. In some cases, the battery may have a fatal adverse effect such as decomposition of the solvent.

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

<2-1. Non-aqueous solvent>
Acetonitrile has high ion conductivity and can increase the diffusibility of lithium ions in the battery. Therefore, when the electrolytic solution contains acetonitrile, a collector in which lithium ions are difficult to reach at the time of discharge under a high load, particularly 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 diffused well to nearby regions. Therefore, a sufficient capacity can be extracted even during high-load discharge, and a non-aqueous secondary battery having excellent load characteristics can be obtained.

  In addition, by using acetonitrile as the non-aqueous solvent of the non-aqueous electrolyte solution, as described above, the ion conductivity of the non-aqueous electrolyte solution is improved, so that the quick charge characteristics of the non-aqueous secondary battery can be enhanced. 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 for the non-aqueous electrolyte, the CC chargeable area can be increased (the CC charge time can be increased), and the charging current can be increased, so charging of the non-aqueous secondary battery can be started. The time from full charge to full charge can be greatly reduced.

  The non-aqueous solvent is not particularly limited as long as it contains 30 to 100% by volume of acetonitrile with respect to the total volume of the non-aqueous solvent, and other non-aqueous solvents may or may not be contained.

  In the present embodiment, the “non-aqueous solvent” refers to a mixed liquid of acetonitrile, an organic solvent other than that, and a liquid electrode protecting additive, which will be described later, with the additive. . Therefore, a polymer containing a lithium salt and a pyridine ring which are solid contents does not correspond to a non-aqueous solvent.

  Examples of organic solvents used for non-aqueous solvents other than acetonitrile include alcohols such as methanol and ethanol; aprotic solvents and the like. Among these, an aprotic polar solvent is preferable.

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 Cyclic carbonates represented by -2,3-pentylene carbonate and vinylene carbonate;
Cyclic fluorinated carbonates typified by fluoroethylene carbonate, 1,2-difluoroethylene carbonate, and trifluoromethylethylene carbonate;
Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;
Sulfur compounds represented by sulfolane, dimethyl sulfoxide, and ethylene glycol sulfite;
Cyclic ethers represented by tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;
A chain carbonate represented 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;
Linear fluorinated carbonates typified by trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethyl methyl carbonate;
Mononitriles represented by propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;
Alkoxy group substituted nitriles represented by methoxyacetonitrile and 3-methoxypropionitrile; malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1, 6-dicyanodecane and dinitriles represented by 2,4-dimethylglutaronitrile;
Cyclic nitriles represented by benzonitrile;
Chain esters typified by methyl propionate; chain ethers typified by dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;
A fluorinated ether represented by Rf-O-R (wherein Rf is an alkyl group containing fluorine and R is an organic group which may contain fluorine);
Ketones represented by acetone, methyl ethyl ketone, and methyl isobutyl ketone;
And the partial fluorination thing of these organic compounds, or a total fluorination thing is mentioned. These are used singly or in combination of two or more.

  Among these organic solvents, it is more preferable to use one or more of cyclic carbonate and chain carbonate together with acetonitrile. Here, only one of those exemplified above as the cyclic carbonate and the chain carbonate may be selected and used, or two or more (for example, two or more of the cyclic carbonates exemplified above, Two or more of the exemplified linear carbonates, or two or more of the exemplified cyclic carbonates and one or more of the exemplified linear carbonates) may be used. Among these, ethylene carbonate, propylene carbonate, vinylene carbonate, or fluoroethylene carbonate is more preferable as the cyclic carbonate, and ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate is more preferable as the chain carbonate. It is more preferable to use a cyclic carbonate.

  Acetonitrile is electrochemically susceptible to reductive decomposition. Therefore, it is preferable to mix acetonitrile with another organic solvent and / or to add an electrode protective additive for forming a protective film on the electrode to acetonitrile. Further, in order to increase the ionization degree of the lithium salt that contributes to charging / discharging of the non-aqueous secondary battery, the non-aqueous solvent used in this embodiment may contain one or more cyclic aprotic polar solvents. Preferably, it contains more than one cyclic carbonate.

  The content of acetonitrile is 30 to 100% by volume with respect to the total volume of the non-aqueous solvent, more preferably 35% by volume or more, and still 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 30% by volume or more, ionic conductivity tends to increase and high output characteristics tend to be exhibited, and further, dissolution of the lithium salt can be promoted. When the content of acetonitrile in the non-aqueous solvent is within the above range, the storage characteristics and other battery characteristics tend to be further improved while maintaining the excellent performance of acetonitrile.

<2-2. Lithium salt>
The lithium salt in this embodiment is characterized by containing a fluorine-containing inorganic lithium salt. Here, the “fluorine-containing inorganic lithium salt” refers to a lithium salt that 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” described later refers to a lithium salt that does not contain a carbon atom in an anion and is soluble in acetonitrile. The “organic lithium salt” contains a carbon atom in an anion and is soluble in acetonitrile. Lithium salt.

The fluorine-containing inorganic lithium salt in the present embodiment forms a passive film on the surface of the metal foil that is the positive electrode current collector, and suppresses corrosion of the positive electrode current collector. Fluorine-containing inorganic lithium salts are also excellent from the viewpoints of solubility, conductivity, and ionization degree. For this reason, 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 [wherein b is 0-3. An integer), LiN (SO ₂ F) _{2 and the} like.

These fluorine-containing inorganic lithium salts are used singly or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable. Among them, the use of a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it easily releases a free fluorine atom, LiPF ₆ is particularly preferred. Further, when a fluorine-containing inorganic lithium salt having a boron atom is used as the fluorine-containing inorganic lithium salt, it is preferable because an excessive free acid component that may cause battery deterioration is easily captured. From such a viewpoint, LiBF ₄ is particularly preferred.

  Although there is no restriction | limiting in particular about content of the fluorine-containing inorganic lithium salt in the electrolyte solution which concerns on this embodiment, It is preferable that it is 0.2 mol or more with respect to 1L of non-aqueous solvents, and it is 0.5 mol or more. More preferably, it is 0.8 mol or more. Further, the content of the fluorine-containing inorganic lithium salt is preferably 15 mol or less, more preferably 4 mol or less, and still more preferably 2.8 mol or less with respect to 1 L of the non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range, the ionic conductivity tends to increase and high output characteristics tend to be exhibited, while maintaining the excellent performance of acetonitrile, storage characteristics and other battery characteristics Tends to be even better.

In addition to the fluorine-containing inorganic lithium salt, a lithium salt generally used for a non-aqueous secondary battery may be supplementarily added as the lithium salt in the present embodiment.
Specific examples of other lithium salts include, for example:
An inorganic lithium salt containing no fluorine atom in the anion, such as LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiB ₁₀ Cl ₁₀ , chloroborane Li;
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 (where n ≧ 2), lower fat Organic lithium salts such as Lithium group carboxylic acid and Li tetraphenylborate;
Organic represented by LiN (SO ₂ C _m F _{2m + 1} ) ₂ such as LiN (SO ₂ CF ₃ ) ₂ or LiN (SO ₂ C ₂ F ₅ ) ₂ , wherein m is an integer of 1 to 8. Lithium salt;
LiPF ₅ (CF ₃₎ wherein, n is an integer of 1 to 5, and p is a integer of 1 to 8] _{LiPF n (C p F 2p +} 1) 6-n such as an organic lithium represented by salt;
LiBF _q (C _s F _{2s + 1} ) _4-q such as LiBF ₃ (CF ₃ ) _4-q [wherein q is an integer of 1 to 3 and s is an integer of 1 to 8] salt;
Lithium bis (oxalato) 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 ;
Organic lithium salts such as lithium tetrafluorooxalatophosphate represented by LiPF ₄ (C ₂ O ₄ ) and lithium difluorobis (oxalato) phosphate represented by LiPF ₂ (C ₂ O ₄ ) ₂ ;
A lithium salt combined with a polyvalent anion;
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)
{Wherein R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² may be the same as or different from each other, and represent a C 1-8 perfluoroalkyl group. Show. }, And one or more of them can be used together with the fluorine-containing inorganic lithium salt.

In order to improve load characteristics and charge / discharge cycle characteristics of the non-aqueous secondary battery, it is preferable to supplementarily add an organic lithium salt having an oxalic acid group, and LiB (C ₂ O ₄ ) ₂ , LiBF ₂ ( It is particularly preferable to add one or more 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 contained in the negative electrode (negative electrode active material layer) in addition to being added to the non-aqueous electrolyte.

  The addition amount of the organic lithium salt having an oxalic acid group to the non-aqueous electrolyte is 0.005 mol as the amount per 1 L of the non-aqueous solvent of the non-aqueous electrolyte from the viewpoint of better securing the effect of its use. Preferably, it is 0.02 mol or more, and more preferably 0.05 mol or more. However, if the amount of the organic lithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, it may be precipitated. Therefore, the amount of the organic lithium salt having an oxalic acid group added to the non-aqueous electrolyte is preferably less than 1.0 mol in terms of the amount of the non-aqueous electrolyte per 1 L of the non-aqueous solvent. More preferably, it is more preferably less than 0.2 mol.

<2-3. Electrode protective additive>
The electrolytic solution in the present embodiment may contain an additive for protecting the electrode. In addition, as described above, when the electrolytic solution contains an electrode protecting additive, the electrode protecting additive is contained in a non-aqueous solvent. Therefore, the electrolytic solution contains a non-aqueous solvent containing an electrode protecting additive. 30-100 volume% acetonitrile should just be contained with respect to a solvent (total volume of the above-mentioned non-aqueous solvent and the electrode protection additive).

  The electrode protecting additive is not particularly limited as long as it does not hinder the problem solving according to the present invention. You may substantially overlap with the substance which plays the role as a solvent which melt | dissolves lithium salt (namely, the above-mentioned non-aqueous solvent). The electrode protecting additive is preferably a substance that contributes to improving the performance of the electrolytic solution and the non-aqueous secondary battery in this embodiment, but also includes substances that are not directly involved in the electrochemical reaction.

Specific examples of the electrode protecting additive include, for example:
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- Dioxolan-2-one and fluoroethylene carbonate represented by 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one;
An unsaturated bond-containing cyclic carbonate represented by vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate;
Lactones represented by γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;
Cyclic ethers represented by 1,4-dioxane;
Cyclic sulfur compounds represented by ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-methylsulfolane, 1,3-propane sultone, 1,4-butane sultone, and tetramethylene sulfoxide;
Is mentioned. These are used singly or in combination of two or more.

  Since acetonitrile, which is a component of a non-aqueous solvent, is easily electrochemically reduced and decomposed, a non-aqueous solvent containing acetonitrile is a cyclic aprotic polar solvent as an additive for forming a protective film on the negative electrode. It is preferable to include the above, and it is more preferable to include one or more unsaturated bond-containing cyclic carbonates.

  Although there is no restriction | limiting in particular about content of the electrode protection additive in the electrolyte solution in this embodiment, As content of the electrode protection additive with respect to the whole volume of a non-aqueous solvent, it is 0.1-30 volume%. Preferably, it is 2 to 20% by volume, more preferably 5 to 15% by volume.

  In this embodiment, the higher the content of the electrode protection additive, the more the deterioration of the electrolyte solution is suppressed. However, the lower the content of the electrode protection additive, the higher the output characteristics of the nonaqueous secondary battery in a low temperature environment. Will be improved. Therefore, by adjusting the content of the electrode protecting additive within the above-mentioned 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. There is a tendency to make the most of it. By preparing the electrolytic solution with such a composition, all of the cycle performance of the non-aqueous secondary battery, the high output performance in a low temperature environment, and other battery characteristics tend to be further improved.

<2-4. Other optional additives>
In the present embodiment, for the purpose of improving the charge / discharge cycle characteristics of the non-aqueous secondary battery, high-temperature storage property, improving safety (for example, preventing overcharge, etc.), the non-aqueous electrolyte solution includes, for example:
Anhydride, sulfonate ester, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene;
Phosphoric acid esters [ethyl diethylphosphonoacetate _{(EDPA) :( C 2 H 5} O) 2 (P = O) -CH 2 (C = O) OC 2 H 5; phosphate, tris (trifluoroethyl) (TFEP) : (CF ₃ CH ₂ O) ₃ P═O, triphenyl phosphate (TPP): (C ₆ H ₅ O) ₃ P═O, etc.], etc .; and any derivatives selected from these compounds Additives can be included as appropriate. In particular, phosphate esters are effective because they have the effect of suppressing side reactions during storage.

<3. Positive electrode>
As shown in FIG. 2, the positive electrode 5 includes a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode 5 is not particularly limited as long as it functions 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 additive and a binder.

  The positive electrode active material layer preferably contains a material capable of inserting and extracting lithium ions as the positive electrode active material. It is preferable that a positive electrode active material layer contains a conductive support agent and a binder as needed with a positive electrode active material. The use of such a material is preferable because a high voltage and a high energy density tend to be obtained.

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 of 0 to 1.1, and y represents a number of 0 to 2. }, A lithium-containing compound represented by each of the above and other lithium-containing compounds.

Examples of the lithium-containing compound represented by each of the general formulas (3a) and (3b) include:
Lithium cobalt oxide typified by LiCoO ₂ ;
Lithium manganese oxides typified by LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ Mn ₂ O ₄ ;
Lithium nickel oxide typified by LiNiO ₂ ;
Li _z MO ₂ (wherein M includes 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) And a lithium-containing composite metal oxide represented by z is a number greater 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 containing lithium, a metal phosphate compound containing lithium and a transition metal element, and lithium and a transition metal element. [For example, Li _t M _u SiO ₄ {wherein M is as defined in general formula (3a), t is a number from 0 to 1, and u is a number from 0 to 2] Show. } Etc.].

From the standpoint of obtaining a higher voltage, lithium-containing compounds are particularly:
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,
The composite oxide containing and a metal phosphate compound are preferable.

More specifically, the lithium-containing compound is more preferably a composite oxide containing lithium and a transition metal element or a metal chalcogenide having lithium and a transition metal element, and a metal phosphate compound having lithium, for example, following general formula (4a) and ^{_{(4b): Li v M I}} D 2 (4a)
Li _w M ^II PO ₄ (4b)
{Wherein D represents oxygen or a chalcogen element, M ^I and M ^II each represent one or more transition metal elements, and the values of v and w differ depending on the charge / discharge state of the battery, and v is 0.05 The number of ~ 1.10 is shown, w shows the number of 0.05-1.10. }, Compounds represented by each of the above.

  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 obtained by substituting a part of the transition metal element with Al, Mg, or other transition metal elements for the purpose of stabilizing the structure, and include these metal elements in the grain boundaries. It is also possible that the oxygen atom is partially substituted with a fluorine atom or the like, or at least a part of the surface of the positive electrode active material is coated with another positive electrode active material.

As the positive electrode active material in the present embodiment, only the lithium-containing compound as described above may be used, or another positive electrode active material 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; a conductive polymer. Examples of the metal oxide or metal chalcogenide 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. And oxides, sulfides, selenides, and the like of metals other than lithium. Examples of the conductive polymer include conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole.

  Other positive electrode active materials are used alone or in combination of two or more, and are not particularly limited. However, in the present embodiment, lithium ions can be occluded and released reversibly and stably, and a high energy density can be achieved. Therefore, the positive electrode active material layer is at least selected from Ni, Mn, and Co. Contains one 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 usage ratio of both is preferably 80% by mass or more as the usage ratio of the lithium-containing compound with respect to the total mass of the positive electrode active material, 85 The mass% or more is more preferable.

  Examples of the conductive aid include carbon black typified by graphite, acetylene black, and ketjen black, and carbon fiber. The content ratio of the conductive assistant is preferably 10 parts by mass or less, 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 fluorine rubber. The content ratio of the binder is preferably 6 parts by mass or less, more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the positive electrode active material.

  The positive electrode active material layer is formed by applying 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 additive and a binder in a solvent, is applied to a positive electrode current collector and dried (solvent removal) And is formed by pressing as necessary. There is no restriction | limiting in particular as such a solvent, A conventionally well-known thing can be used, For example, N-methyl- 2-pyrrolidone, a dimethylformamide, a dimethylacetamide, water etc. are mentioned. The positive electrode active material layer is formed on one side or both sides of the positive electrode current collector.

  The positive electrode current collector is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode current collector may have a surface coated with a carbon coat 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 still more preferably 9 to 30 μm.

<4. Negative electrode>
As shown in FIG. 2, the negative electrode 6 includes 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 functions as a negative electrode of a non-aqueous secondary battery, and may be a known one.

From the viewpoint that the negative electrode active material layer can increase the battery voltage, lithium ion as a negative electrode active material is 0.4 V vs. It is preferable to contain a material that can be occluded at a lower potential than Li / Li ⁺ . It is preferable that a negative electrode active material layer contains a conductive support agent and a binder as needed with a negative electrode active material.

  Examples of the negative electrode active material include amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, glassy carbon, organic polymer compound fired body, mesocarbon microbeads, carbon fiber, activated carbon In addition to carbon materials such as carbon colloid and carbon black, metal lithium, metal oxide, metal nitride, lithium alloy, tin alloy, silicon alloy, intermetallic compound, organic compound, inorganic compound, metal complex, organic Examples thereof include polymer compounds.

  A negative electrode active material is used individually by 1 type or in combination of 2 or more types.

  Examples of the conductive aid include carbon black typified by graphite, acetylene black, and ketjen black, and carbon fiber. The content ratio of the conductive assistant is preferably 20 parts by mass or less, 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 fluorine rubber. The content ratio of the binder is preferably 10 parts by mass or less, more preferably 0.5 to 6 parts by mass with respect to 100 parts by mass of the negative electrode active material.

  The negative electrode active material layer is coated with 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 additive and a binder is dispersed in a solvent, and dried (solvent removal). And it forms by pressing as needed. There is no restriction | limiting in particular as such a solvent, A conventionally well-known thing can be used, For example, N-methyl- 2-pyrrolidone, a dimethylformamide, a dimethylacetamide, water etc. are mentioned. The negative electrode active material layer is formed on one side or both sides of the negative electrode current collector.

  The negative electrode current collector is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. The negative electrode current collector may have a carbon coating on the 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 still more preferably 7 to 30 μm.

<5. Separator>
As shown in FIG. 2, the non-aqueous secondary battery 8 according to this embodiment includes a separator between the positive electrode 5 and the negative electrode 6 from the viewpoint of providing safety such as prevention of short circuit between the positive electrode 5 and the negative electrode 6 and shutdown. 7 is preferably provided. The separator 7 may be the same as that provided in a known non-aqueous secondary battery, and is preferably an insulating thin film having high ion permeability and excellent mechanical strength. Examples of the separator 7 include a woven fabric, a nonwoven fabric, and a synthetic resin microporous membrane. Among these, a synthetic resin microporous membrane is preferable.

  As the synthetic resin microporous membrane, for example, a polyolefin microporous membrane such as a microporous membrane containing polyethylene or polypropylene as a main component, or a microporous membrane containing both of these polyolefins is suitably used. Examples of the nonwoven 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 configuration in which one type of microporous membrane is laminated or a plurality of microporous membranes may be laminated, or two or more types of microporous membranes may be laminated. The separator 7 may be configured to be laminated in a single layer or a plurality of layers using a mixed resin material obtained by melting and kneading two or more kinds of resin materials.

<6. Battery exterior>
In FIG. 2, the battery casing 2 is composed of two aluminum laminate films 1. However, the configuration of the battery casing of the nonaqueous secondary battery according to this embodiment is not particularly limited. For example, a battery can and a laminate film Any battery exterior of the exterior body can be used. As the battery can, for example, a metal can made of steel or aluminum can be used. As the laminate film outer package, for example, a laminate film having a three-layer structure of hot melt resin / metal film / resin can be used.

  Laminate film exterior is in a state where two sheets are stacked with the hot-melt resin side facing inward, or folded so that the hot-melt resin side faces inward, and the end is sealed by heat sealing It can be used as an exterior body. When using a laminate film exterior body, a positive electrode lead body (or a lead tab connected to the positive electrode terminal and the positive electrode terminal) is connected to the positive electrode current collector, and a negative electrode lead body (or the negative electrode terminal and the negative electrode terminal) is connected to the negative electrode current collector. Lead tab) may be connected. In this case, the laminate film exterior body may be sealed with the ends of the positive electrode lead body and the negative electrode lead body (or the lead tab connected to each of the positive electrode terminal and the negative electrode terminal) pulled out of the exterior body. .

<7. Polymer having pyridine ring>
The non-aqueous secondary battery according to this embodiment is characterized in that a polymer having a pyridine ring is present inside the battery. The polymer having a pyridine ring is a structure represented by the following general formula (1).

Numerical values in the general formula (1) are integers of l ≧ 0, m ≧ 1, and n ≧ 1.
In the general formula (1), when l = 0, m ≠ 0, and n ≠ 0, a structure having a pyridine ring in the main chain is obtained.
As the structure X that bonds the pyridine rings, a bond state such as an alkyl chain, an ester structure, or a structure that includes both, or a single bond in which the pyridine rings are directly bonded to each other can be selected.
However, a structure in which the pyridine rings are directly bonded to each other is preferable because gas generation due to decomposition products hardly occurs when the bonding site is decomposed inside the battery. The pyridine ring skeleton may be a regular repeating structure, a block structure, or a random structure. The number of repeating units n and m of the polymer varies depending on the structure of the polymer (repeating / blocking / random), the molecular weight of the polymer, and the substituent.
When l ≠ 0 in the general formula (1), a polymer having a pyridine ring in the side chain is obtained. The structure Y of the repeating unit of the main chain is an alkyl chain and adjusts the introduction interval of the side chain. Y may have a crosslinked structure. The side chain repeating structure X can be selected from an alkyl chain, an ester structure, or a structure containing both, or a bonding state such as a single bond in which pyridine rings are directly bonded. The number of l, m and n will vary depending on the structure, molecular weight, or substituent of the polymer.

For example, if Y is CH ₂ , X is a single bond, m = n = 1, and the single bond X is formed at the 2-position of the pyridine ring, it becomes poly (2-vinylpyridine) 4 If it is a position, it becomes poly (4-vinylpyridine).

  In the pyridine ring in the polymer having the structure represented by the general formula (1), a part of H atoms present therein may be substituted. Examples of the substituent include an alkyl group, a cycloalkyl group, an alkyloxy group, an alkylamino group, a phenyl group, and a cyano group. As for carbon number of an alkyl group, 1-6 are preferable.

  Further, part or all of the H atoms of the pyridine ring and part or all of H of the substituent connected to the pyridine ring may be substituted with F, Br or the like. Further, part or all of the H atoms in the main chain alkyl skeleton may be substituted with F.

  When a compound that is a double salt of LiF and Lewis acid is used as the fluorine-containing inorganic lithium salt, it is desirable that there is no steric hindrance around the N atom of the pyridine ring. Therefore, a structure in which no substituent is present on the carbon atoms at the 2nd and 6th positions on both sides of the N atom is preferable. Moreover, it is preferable that the bonds in the polymer main chain or the bonds to the polymer side chain are also bonded at sites other than the 2 and 6 positions.

  When a polymer having a pyridine ring comes into contact with a non-aqueous electrolyte containing acetonitrile, it suppresses the formation of complex cations composed of transition metals and acetonitrile, exhibits excellent load characteristics, and self-discharge during high-temperature storage Can be suppressed.

  In the present embodiment, the polymer having a pyridine ring used in the battery may be dissolved in the non-aqueous electrolyte solution, or may be present as a coating layer in the battery. Moreover, it may be dispersed in the form of particles. Further, a plurality of these states may be used. The molecular weight of the polymer is a weight average molecular weight of 1,000 to 100,000. The number n of repeating units in the general formula (1) and the number m of repeating units in the side chain may be such that the molecular weight of the polymer falls within the above-mentioned range.

  If the polymer having a pyridine ring has a low molecular weight, the solubility in an organic solvent is increased. Therefore, the presence of the polymer in the electrolytic solution as a solution increases the effect of suppressing the formation of complex cations. On the other hand, high molecular weight polymers have low solubility and therefore low reactivity, but are less prone to degradation and are excellent in sustainability.

  In the battery of the present invention, the polymer having a pyridine ring is present inside the battery in a state where the polymer contained in the electrolytic solution and the polymer are in contact with each other, whereby complex formation can be suppressed. Therefore, it is preferable that the polymer is dissolved in the nonaqueous electrolytic solution. When dissolved in the electrolytic solution, the polymer having a pyridine ring is present almost throughout the battery. In the case of a polymer having low solubility, it is preferable that the polymer be present in any one or more of the surface or inside of the electrode (for example, positive electrode and / or negative electrode) and the surface or inside of the separator. If it is the surface of an electrode or a separator, a polymer solution may be applied. If it is inside the electrode, it is added to the active material mixture as a polymer solution or polymer particles when the active material is applied to the electrode. If it is inside the separator, there are means such as kneading with the separator material resin at the time of manufacturing the separator. In addition, there may be a plurality of states of the polymer described herein.

  Formation of a complex cation composed of a transition metal and acetonitrile occurs mainly on the positive electrode side. Therefore, when a polymer having a pyridine ring is present on the positive electrode side, the generation of complex cations can be effectively suppressed. Therefore, a form in which the polymer is applied or dispersed and fixed to the surface of the positive electrode, the inside of the positive electrode, and the positive electrode side surface of the separator is preferable. In particular, when the positive electrode active material particle surface is coated with a polymer having a pyridine ring, it is possible to suppress the complex formation reaction at a place where the complex formation on the positive electrode surface is most likely to occur.

  When the amount of the polymer having a pyridine ring present in the battery according to this embodiment is defined by the weight of N atoms derived from the pyridine ring structure contained in the polymer, the total weight of the electrolyte present in the battery is The weight of the N atom derived from the pyridine ring structure is preferably 0.002 to 2% by weight, more preferably 0.005 to 1% by weight, and still more preferably 0.01 to 1% by weight.

  From the viewpoint of suppressing the formation of complex cations in the battery, ensuring excellent load characteristics of the battery, and suppressing self-discharge during high-temperature storage, the non-aqueous electrolyte according to this embodiment has a pyridine ring. When the content of the polymer is defined as a ratio with respect to the total mass of the non-aqueous electrolyte solution, it is preferably 0.01 to 10% by mass.

  In the present embodiment, by adjusting the content of the polymer having a pyridine ring within the above range, the reaction on the electrode surface can be suppressed without impairing the basic function as a non-aqueous secondary battery. The increase in internal resistance accompanying charging / discharging can be reduced.

<8. Manufacturing method of battery>
As shown in FIG. 2, the non-aqueous secondary battery in this embodiment includes the above-described non-aqueous electrolyte, the positive electrode 5 having a positive electrode active material layer on one or both surfaces of the current collector, and one or both surfaces of the current collector. The negative electrode 6 having the negative electrode active material layer, the battery casing 2 and, if necessary, the separator 7 are used to produce the negative electrode active material layer.

First, the laminated body which consists of the positive electrode 5 and the positive electrode 6, and the separator 7 as needed is formed. For example, an aspect 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 laminate having a wound structure;
A mode of forming a laminate having a laminated structure in which a positive electrode sheet and a negative electrode sheet obtained by cutting the positive electrode 5 and the negative electrode 6 into a plurality of sheets having a certain area and shape are alternately laminated via a separator sheet. ;
A mode of forming a laminated body having a laminated structure in which long separators are folded in a zigzag manner, and positive electrode sheets and negative electrode sheets are alternately inserted between the zipped separators;
Etc. are possible.

  In the step of forming this laminate, a polymer having a pyridine ring may be applied or mixed on the surface and / or inside of the separator and / or the positive electrode.

Next, the above-described laminated body is accommodated in the battery exterior 2 (battery case), the electrolytic solution according to the present embodiment is injected into the battery case, and the laminated body is immersed in the electrolytic solution and sealed. A non-aqueous secondary battery according to this embodiment can be produced.
Alternatively, an electrolyte solution in a gel state is prepared in advance by impregnating a base material made of a polymer material with an electrolytic solution, and the sheet-like positive electrode 5, the negative electrode 6, the electrolyte membrane, and if necessary Then, after forming a laminated body having a laminated structure using the separator 7, the separator 7 can be housed in the battery casing 2 to produce a non-aqueous secondary battery.
In the step of manufacturing the non-aqueous secondary battery, a polymer having a pyridine ring may be dissolved in the electrolytic solution to be immersed.

  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 rectangular tube shape, a button shape, a coin shape, a flat shape, a laminated shape, and the like are suitably employed.

  The non-aqueous secondary battery in the present embodiment can function as a battery by the first charge, but is stabilized when a part of the electrolytic solution is decomposed during the first charge. Although there is no restriction | limiting in particular about the method of initial charge, It is preferable that initial charge is performed at 0.001-0.3C, It is more preferable to be performed at 0.002-0.25C, 0.003-0.2C More preferably, it is performed. It is also preferable that the initial charging is performed via a constant voltage charging in the middle. The constant current for discharging the rated capacity in 1 hour is 1C. By setting the voltage range in which the lithium salt is involved in the electrochemical reaction for a long time, SEI (Solid Electrolyte Interface: solid electrolyte interface) is formed on the electrode surface, and the effect of suppressing the increase in internal resistance including the positive electrode 5 In addition to the above, the reaction product is not firmly fixed only to the negative electrode 6, and in some form, a good effect is given to members other than the negative electrode 6 such as the positive electrode 5 and the separator 7. For this reason, it is very effective to perform the initial charge in consideration of the electrochemical reaction of the lithium salt dissolved in the non-aqueous electrolyte.

  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 managing the charge / discharge state of the battery pack, the operating voltage range per unit is preferably 2 to 5 V, more preferably 2.5 to 5 V, and 2.75 V to 5 V. Particularly preferred.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the above-mentioned embodiment. The present invention can be variously modified without departing from the gist thereof.

  Hereinafter, the present invention will be described in more detail with reference to examples. Various evaluations were performed as follows.

(1) Positive electrode immersion test After processing an aluminum laminated bag to 2.7 cm x 6 cm and enclosing a positive electrode described later punched to 23 mm x 17 mm, the non-aqueous system prepared in each example or comparative example in an inert atmosphere 0.5 mL of electrolyte solution was injected. At this time, it was confirmed that the electrode surface was immersed in the electrolytic solution. After injecting the solution, it was sealed and kept at 60 ° C. with the aluminum laminate bag leaning vertically and stored for 10 days. After storage, the internal electrolyte and the positive electrode surface were observed. “○” (good) when the formation of a gel-like substance composed mainly of a complex cation salt composed of a transition metal and acetonitrile is not recognized, and “×” when the formation of the gel-like substance is recognized (Defect) was determined.

(2) Battery production (2-1) Production of positive electrode (P1) Lithium, nickel, manganese and cobalt composite oxide 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 ) at a mass ratio of 93: 4: 3 to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as a solvent was added to the obtained positive electrode mixture and further mixed to prepare a positive electrode mixture-containing slurry. This positive electrode mixture-containing slurry was applied to one side of an aluminum foil having a thickness of 20 μm and a width of 200 mm to be a positive electrode current collector by a doctor blade method while adjusting the basis weight to 22 mg / cm ² , Removed dry. Then, the positive electrode (P1) which consists of a positive electrode active material layer and a positive electrode electrical power collector was obtained by rolling so that the density of a positive electrode active material layer might be 2.8 g / cm < ³ > with a roll press.

(2-2) Production of negative electrode (N1) Graphite carbon powder (trade name “MCMB25-28”, manufactured by Osaka Gas Chemical Co., Ltd.) having a number average particle diameter of 25 μm as a negative electrode active material, and number average particles as a conductive auxiliary 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 mass ratio of 93: 2: 5. N-methyl-2-pyrrolidone was added to the obtained mixture and further mixed to prepare a negative electrode mixture-containing slurry. The negative electrode mixture-containing slurry was applied to one side of a copper foil having a thickness of 10 μm and a width of 200 mm to be a negative electrode current collector by a doctor blade method while adjusting the basis weight to 12 mg / cm ² , and the solvent was dried. Removed. Then, the negative electrode (N1) which consists of a negative electrode active material layer and a negative electrode electrical power collector was obtained by rolling so that the density of a negative electrode active material layer might be set to 1.5 g / cm < ³ > with a roll press.

(2-3) Production of single-layer laminated battery (for evaluation) Two laminated films (no drawing, thickness 120 μm, 31 mm × 37 mm) in which an aluminum layer and a resin layer are laminated, with the aluminum layer side facing outward The three sides were sealed to produce a laminate cell exterior. The positive electrode (P1) produced as described above was punched into 14.0 mm × 20.0 mm, and the negative electrode (N1) produced as described above was punched into 14.5 mm × 20.5 mm. Subsequently, a polyethylene microporous membrane (film thickness 20 μm, 16 mm × 22 mm) is prepared as a separator, and a laminate in which the positive electrode (P1) and the negative electrode (N1) are overlapped on both sides of the separator is used as the laminate cell exterior. Placed in. Subsequently, the electrolyte solution prepared in each Example and Comparative Example was injected into the cell exterior, and the laminate was immersed in the electrolyte solution. Then, the remaining one side of the laminate cell exterior was sealed to produce a non-aqueous secondary battery (single-layer laminated battery; hereinafter, also simply referred to as “battery”). This was kept at 25 ° C. for 24 hours, and the laminate was sufficiently adapted to the electrolyte solution to obtain a single-layer laminate type battery with 1C = 8.5 mA.

  Here, 1C means a current value at which a fully charged battery is discharged with a constant current and expected to be discharged in 1 hour. The single layer laminate type battery produced above means a current value that is expected to be discharged from a fully charged state of 4.2 V to 2.7 V at a constant current and to be discharged in 1 hour.

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

(3-1) Initial charge / discharge characteristics of single-layer laminate type battery The battery temperature reaches 4.2V when the ambient temperature of the battery is set to 25 ° C. and the battery is charged with a constant current of 1.7 mA corresponding to 0.2C. Then, charging was performed at a constant voltage of 4.2 V for 8 hours. Thereafter, the battery was discharged to 2.7 V with a constant current of 1.7 mA corresponding to 0.2C. 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 that was first charged / discharged by the method described in (3-1) above, charging was performed at a constant current of 8.5 mA corresponding to 1C, and charging was performed until the battery voltage reached 4.2V. After that, the battery was charged at a constant voltage of 4.2 V for a total of 3 hours. Thereafter, the battery was discharged to a battery voltage of 2.7 V at a constant current of 8.5 mA corresponding to 1C. The discharge capacity at this time was A. Next, the battery was charged with a constant current of 8.5 mA corresponding to 1 C and charged until the battery voltage reached 4.2 V, and then charged with a constant voltage of 4.2 V for a total of 3 hours. Thereafter, the battery was discharged to a battery voltage of 2.7 V at a constant current of 42.5 mA corresponding to 5C. The discharge capacity at this time was B. The following values were calculated as output test measurement values.
Capacity maintenance rate = 100 × B / A [%]

[Example 1]
Under an inert atmosphere, a mixed solvent composed 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 poly (2-vinylpyridine) (manufactured by Aldrich, Mw = 5,000) as an additive was dissolved in 100 parts by mass of the mixed solvent to obtain an electrolytic solution. The weight ratio of N atoms derived from the pyridine ring present in the electrolytic solution is 0.13% by weight.

[Example 2]
Electrolysis was performed under the same conditions except that the additive used in Example 1 was 0.1 part by mass of poly (4-vinylpyridine) (manufactured by Aldrich, Mw = 60,000) with respect to 100 parts by mass of the mixed solvent. A liquid was obtained. The weight ratio of N atoms derived from the pyridine ring present in the electrolytic solution is 0.013% by weight.

[Comparative Example 1]
In the said Example 1, the electrolyte solution which does not put an additive with the same composition was produced.

[Positive electrode immersion test and first charge / discharge treatment of Examples 1 and 2 and Comparative Example 1]
When the positive electrode immersion test of (1) was performed on the electrolytic solutions having the compositions of Examples 1 and 2 and Comparative Example 1, a polymer having a pyridine ring in the electrolytic solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile. In Comparative Example 1 containing no brown, the formation of a brown gel was observed. The gel-like product was found to contain a complex cation composed of a transition metal and acetonitrile from the results of analysis by ¹ H-NMR, ¹⁹ F-NMR, and ICP. On the other hand, even in an electrolyte solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile, in Examples 1 and 2 containing a polymer having a pyridine ring, the formation of a brown gel was not observed.

  From these results, it was revealed that the addition of a polymer having a pyridine ring greatly contributed to high-temperature durability in an electrolytic solution containing a fluorine-containing inorganic lithium salt and a significant amount of acetonitrile.

  Next, the positive electrode (P1) and the negative electrode (N1) produced as described above were combined with the electrolyte solutions prepared in Examples 1 and 2 and Comparative Example 1, and the method described in (2-3) above was followed. A single layer laminate type non-aqueous secondary battery was produced. The battery was first charged / discharged 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 performance of the battery not containing, as Comparative Example 2, an electrolytic solution containing no acetonitrile was prepared. 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 batteries of Comparative Examples 1 and 2 were subjected to discharge capacity measurement by the method described in (3-2) above.

[Electrolyte compositions and evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2]
The electrolytic solution compositions of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1, and the battery evaluation results are shown in Table 2.

  Although the battery of Comparative Example 1 has an initial charge / discharge efficiency comparable to that of other batteries, gel generation occurs in the electrolytic solution due to storage, and then the battery characteristics deteriorate rapidly.

  Examples 1 and 2 and Comparative Example 1 are batteries containing acetonitrile in the electrolytic solution. For comparison with this, the battery of the electrolytic solution not containing acetonitrile of Comparative Example 2 was prepared and evaluated. Compared with a battery containing acetonitrile (Comparative Example 1), the capacity retention rate is extremely poor.

  From the above results, it was verified that the non-aqueous secondary battery using the electrolytic solution according to the present embodiment achieves high output characteristics while maintaining high temperature durability performance comparable to that of the existing electrolytic solution.

  The non-aqueous secondary battery of the present invention is, for example, a portable device such as a mobile phone, a portable audio device, a personal computer, an IC (Integrated Circuit) tag; a rechargeable battery for a vehicle such as a hybrid vehicle, a plug-in hybrid vehicle, and an electric vehicle; It can be applied to a residential power storage system.

DESCRIPTION OF SYMBOLS 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 (8)

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 surfaces of the positive electrode current collector;
A negative electrode having a negative electrode active material layer on one or both sides of a negative electrode current collector;
A non-aqueous electrolyte,
A non-aqueous secondary battery comprising:
The non-aqueous electrolyte contains a non-aqueous solvent containing 30 to 100% by volume of acetonitrile and a fluorine-containing inorganic lithium salt, and a polymer having a pyridine ring is present inside the non-aqueous secondary battery.
The non-aqueous secondary battery. The non-aqueous secondary battery according to claim 1, wherein the fluorine-containing inorganic lithium salt contains LiPF ₆ .   The weight ratio of the N atom derived from the pyridine ring of the polymer is 0.002 to 2% by weight with respect to the total weight of the non-aqueous electrolyte solution present in the non-aqueous secondary battery. Or the non-aqueous secondary battery of 2.   The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the polymer is present on the surface or inside of the positive electrode or on the surface or inside of the negative electrode in the non-aqueous electrolyte.   The nonaqueous secondary battery according to any one of claims 1 to 3, wherein the nonaqueous secondary battery further includes a separator, and the polymer is present on a surface or inside of the separator.   The non-aqueous secondary battery according to claim 5, wherein the polymer is present on a surface of the separator on the positive electrode side.   The non-aqueous secondary battery according to claim 4, wherein the polymer is present on the surface or inside of the positive electrode. The non-aqueous solvent containing 30 to 100% by volume of acetonitrile with respect to the total volume of the non-aqueous solvent;
LiPF ₆ as the fluorine-containing inorganic lithium salt;
0.01 to 10% by mass of a polymer having a pyridine ring with respect to the total mass of the nonaqueous electrolytic solution;
The non-aqueous electrolyte solution comprising:

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