WO2017038628A1

WO2017038628A1 - Nonaqueous secondary battery and method for manufacturing same

Info

Publication number: WO2017038628A1
Application number: PCT/JP2016/074829
Authority: WO
Inventors: 映理児島; 丈主加味根; 上田　篤司
Original assignee: 日立マクセル株式会社
Priority date: 2015-08-28
Filing date: 2016-08-25
Publication date: 2017-03-09

Abstract

Provided are: a nonaqueous secondary battery having excellent charge and discharge characteristics with a large current; and a method for manufacturing this nonaqueous secondary battery. A nonaqueous secondary battery according to the present invention is characterized by being provided with: a positive electrode that has a positive electrode mixture layer, which contains a positive electrode active material, a binder and a conductive assistant, on one surface or both surfaces of a collector; a negative electrode that has a negative electrode mixture layer, which contains a negative electrode active material and a binder, on one surface or both surfaces of a collector; a separator; and a nonaqueous electrolyte solution that contains a lithium salt and an organic solvent. This nonaqueous secondary battery is also characterized in that the positive electrode mixture layer contains an olivine-type compound as the positive electrode active material, while containing, as the binder, a polymer (A) that has a unit represented by general formula (1) in each molecule. (In general formula (1), R¹ represents H or a methyl group; and R² represents an alkyl group having 1-18 carbon atoms.)

Description

Non-aqueous secondary battery and manufacturing method thereof

The present invention relates to a non-aqueous secondary battery excellent in charge / discharge characteristics at a large current and a method for producing the same.

Non-aqueous secondary batteries such as lithium ion secondary batteries are widely used as power sources for various portable devices because of their high voltage and high capacity. In recent years, the use of medium-sized and large-sized tools such as power tools such as electric tools, electric vehicles, and electric bicycles has been spreading.

Non-aqueous secondary batteries are first widespread for consumer use, and at present, they are spreading for in-vehicle and industrial use. Under these circumstances, non-aqueous secondary batteries are desired to improve various battery characteristics.

In improving the characteristics of the non-aqueous secondary battery, attempts have been made to improve various elements constituting the battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.

For example, Patent Document 1 uses a positive electrode using a specific lithium iron phosphate as a positive electrode active material and a negative electrode using amorphous carbon (amorphous carbon) such as soft carbon as a negative electrode active material. A lithium ion secondary battery has been proposed that has secured characteristics suitable for in-vehicle use.

In the case of non-aqueous secondary batteries, in particular, considering application to in-vehicle and industrial applications, for example, it is required to have battery characteristics (high output characteristics) that can function well even when discharged with a large current. is assumed.

The positive electrode for a non-aqueous secondary battery was prepared by collecting a composition for forming a positive electrode mixture layer (a positive electrode mixture-containing composition) prepared by dispersing a positive electrode active material, a binder, a conductive additive and the like in a solvent. In general, it is manufactured by a method of forming a positive electrode mixture layer on the surface of the current collector through a process of applying the surface of the electric body and removing the solvent by drying. A fluorine resin such as polyvinylidene fluoride is generally used for the binder for the positive electrode mixture layer.

However, lithium-containing composite oxides such as lithium iron phosphate, which are widely used as positive electrode active materials for non-aqueous secondary batteries, contain alkaline impurities because of their manufacturing method. For this reason, when such a positive electrode active material is formulated using a solvent containing water, the alkaline component of the impurity is easily eluted in the solvent, and a fluorine resin such as polyvinylidene fluoride as a binder is crosslinked. Cause. Further, even when an organic solvent is used for compounding, when a solvent that easily mixes water such as N-methyl-2-pyrrolidone is used, water contained as an impurity in the solvent, Causes that the alkaline component of the impurities is eluted in the solvent by the water mixed in the solvent at the time of compounding, and similarly causes a crosslinking reaction of the fluororesin. It becomes.

Thus, when the binder in the positive electrode mixture-containing composition is cross-linked, the composition becomes a gel and loses fluidity, so that application to the current collector becomes difficult or impossible. Therefore, the positive electrode mixture-containing composition using a fluorine resin such as polyvinylidene fluoride as the binder must be used for forming the positive electrode mixture layer in a short time until the binder is crosslinked after the preparation. This tends to impair the productivity of the positive electrode for a non-aqueous secondary battery.

On the other hand, a technique for solving the problem caused by the crosslinking of the binder by the alkali component in the positive electrode active material has been studied. For example, in Patent Document 2, the chemical formula LiMn _x M _1-x PO ₄ (0.3 ≦ x ≦ 1, M is selected from Li, Fe, Ni, Co, Ti, Cu, Zn, Mg, and Zr) As a binder of a positive electrode containing an olivine type lithium phosphate represented by one or more elements), acrylonitrile or methacrylonitrile and a chemical formula CH ₂ ═CR ₁ —CO—O—R ₂ (R ₁ is By using a copolymer with a monomer containing an ester group represented by H or CH ₃ , R ₂ is an arbitrary alkyl group), the gelation of the positive electrode mixture-containing composition is suppressed, rate characteristics and cycle A technique for forming a positive electrode for a lithium secondary battery having an excellent lifetime has been proposed.

However, the positive electrode active material having a high content of alkaline impurities tends to have a high water content, and in particular, when the surface is coated with a carbon material in order to improve the conductivity of the material, the water is adsorbed. It becomes easier and the water content is further increased. Therefore, when a positive electrode is produced using such a positive electrode active material and used as it is for producing a battery, a large amount of moisture is brought into the battery. In that case, the moisture contained in the positive electrode mixture reacts with a fluorine-containing inorganic lithium salt such as LiPF ₆ used as the electrolyte of the non-aqueous electrolyte solution to generate hydrogen fluoride. For this reason, in a situation where the battery is left in a high temperature environment for a long time, the constituent materials of the electrode are deteriorated, and problems such as a decrease in capacity are likely to occur.

For this reason, in order to prevent the above-mentioned problem due to the water content brought into the battery by the positive electrode mixture, it is necessary to sufficiently perform a dehydration process such as drying the positive electrode in a vacuum before assembling the battery. It is easy to contribute to the damage.

In order to solve the problem of storage deterioration, Patent Document 3 discloses that a phosphoric acid compound having a specific structure is added to the non-aqueous electrolyte, thereby suppressing the influence of moisture brought into the battery, load characteristics and high temperature. It has been proposed to improve the load characteristics after storage.

JP 2009-104983 A JP 2010-272272 A Japanese Patent Laid-Open No. 2001-319685

While the technique described in Patent Document 2 is effective in suppressing the cross-linking reaction of polyvinylidene fluoride that may be caused by an alkali component in the positive electrode active material and suppressing the gelation of the positive electrode mixture-containing composition, In order to improve rate characteristics and cycle characteristics using an active material with a specific surface area, the binder content is increased, and there is room for improvement in terms of improving charge / discharge characteristics at a large current.

In addition, in the technique described in Patent Document 3, in fact, as described in the examples, the sum of the amount of moisture brought into the battery with respect to the amount of the electrolyte by long-time vacuum drying of the electrode sheet or the separator. Is adjusted to be 30 to 800 ppm by weight so that the phosphoric acid compound functions effectively. Therefore, a problem remains in terms of battery productivity, and when the sum of the amount of moisture brought into the battery exceeds the above range, for example, the amount of moisture contained in the positive electrode mixture at the time of battery assembly exceeds 400 ppm. In such a case, there is still room for study on a method for effectively causing the phosphate compound to act.

An object of the present invention is to provide a non-aqueous secondary battery excellent in charge / discharge characteristics at a large current, and a method for producing the same, by preventing occurrence of problems associated with the positive electrode active material or moisture contained in the positive electrode.

One embodiment of the non-aqueous secondary battery of the present invention that can achieve the above object is a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a binder, and a conductive additive on one or both sides of a current collector, A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder on one side or both sides of a current collector, a separator, and a non-aqueous electrolyte containing a lithium salt and an organic solvent. And a positive electrode mixture layer containing a binder and a conductive additive on one or both sides of the current collector, the positive electrode mixture layer containing an olivine type compound as the positive electrode active material, and the following general formula The polymer (A) having a unit represented by (1) in the molecule is contained as the binder.

In the general formula (1), R ¹ represents H or a methyl group, and R ² represents an alkyl group having 1 to 18 carbon atoms.

The non-aqueous electrolyte in the non-aqueous secondary battery preferably includes a phosphoric acid compound having a group represented by the following general formula (2) in the molecule.

[In the general formula (2), X represents Si, Ge or Sn, and R ³ , R ⁴ and R ⁵ each independently represents an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms. Alternatively, it represents an aryl group having 6 to 10 carbon atoms, and part or all of the hydrogen atoms may be substituted with fluorine. ]

Further, the method for producing a non-aqueous secondary battery of the present invention capable of achieving the above object includes a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a binder and a conductive auxiliary agent on one side or both sides of a current collector, A nonaqueous secondary battery comprising a negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder on one or both sides of a current collector, a separator, and a nonaqueous electrolyte containing a lithium salt and an organic solvent In manufacturing, a positive electrode having a water content of 500 to 3000 ppm in the positive electrode mixture layer and a nonaqueous electrolytic solution containing a phosphate compound having a group represented by the general formula (2) in the molecule are packaged. It is sealed inside the body.

According to the present invention, it is possible to provide a non-aqueous secondary battery that is less prone to problems associated with moisture contained in the positive electrode active material or the positive electrode and has excellent charge / discharge characteristics at a large current, and a method for manufacturing the same.

It is a top view which represents typically an example of the non-aqueous secondary battery of this invention. It is the II sectional view taken on the line of FIG. It is a top view which represents typically an example of the positive electrode which concerns on the nonaqueous secondary battery of this invention. It is a top view which represents typically an example of the negative electrode which concerns on the nonaqueous secondary battery of this invention. It is a top view which represents typically the other example of the non-aqueous secondary battery of this invention. It is the II-II sectional view taken on the line of FIG.

The positive electrode (hereinafter simply referred to as “positive electrode”) according to the non-aqueous secondary battery of the present invention has a structure having a positive electrode mixture layer containing a positive electrode active material, a binder and a conductive additive on one side or both sides of a current collector. I have. And one example of the embodiment of the said positive electrode contains the polymer (A) which contains an olivine type compound as a positive electrode active material, and has the unit represented by the said General formula (1) in a molecule | numerator as a binder. ing.

The olivine type compound contains a lot of alkaline impurities as compared with a lithium-containing composite oxide such as lithium cobaltate. Therefore, when a composition (slurry) for forming a positive electrode mixture layer is prepared, Since the alkaline component of impurities elutes in the solvent (N-methyl-2-pyrrolidone, water, etc.) of the composition and crosslinks a fluororesin such as polyvinylidene fluoride (PVDF) as a binder, the composition over time The fluidity of the is reduced.

On the other hand, in the positive electrode of the above embodiment in the non-aqueous secondary battery of the present invention, the polymer (A) that hardly causes a crosslinking reaction due to an alkaline impurity in the olivine type compound is used instead of PVDF. As a result, even when using an olivine-type compound whose surface is coated with a carbon material, it becomes possible to prevent the composition from becoming a gel, improving the productivity of the non-aqueous secondary battery, Since it is possible to form a positive electrode mixture layer having a uniform and good property, it becomes possible to reduce the resistance value of the positive electrode and to constitute a battery having excellent charge / discharge characteristics at a large current.

In addition, when using a positive electrode active material that easily contains a lot of water due to the mixture of alkaline impurities such as lithium nickel composite oxide as well as olivine type compounds, especially when the surface is coated with a carbon material Depending on the conditions for assembling the battery, such as the conditions for drying the composition for forming the positive electrode mixture layer, a large amount of moisture is mainly brought into the battery through the positive electrode. It reacts with the electrolyte salt of the electrolytic solution (fluorine-containing inorganic lithium salt such as LiPF ₆ ) to generate hydrogen fluoride.

However, according to the method for producing a non-aqueous secondary battery of the present invention, the group represented by the general formula (2) is combined with a positive electrode having a positive electrode mixture layer containing a large amount of water of 500 to 3000 ppm. By enclosing the non-aqueous electrolyte containing the phosphoric acid compound contained in the exterior body, the battery of the battery accompanying the generation of hydrogen fluoride can be obtained without performing a special treatment to reduce the moisture content of the positive electrode. Characteristic deterioration can be suppressed.

By using a positive electrode including a positive electrode mixture layer that retains moisture at the above content, hydrogen fluoride serving as a trigger for forming a SEI (Solid Electrolyte Interface) film derived from the phosphoric acid compound, An amount necessary to efficiently form the SEI film on the surface of the positive electrode can be generated. On the other hand, the generated hydrogen fluoride is consumed by the formation reaction of the SEI film.

For this reason, for example, even when the battery is placed in a charged state at a high temperature, there is a problem of decomposition of the non-aqueous electrolyte due to contact between the positive electrode and the non-aqueous electrolyte, and deterioration of battery characteristics due to the generated hydrogen fluoride. Therefore, it is possible to maintain good battery characteristics.

The phosphoric acid compound has a structure in which at least one of hydrogen atoms of phosphoric acid is substituted with a group represented by the general formula (2).

In the general formula (2), X is Si, Ge, or Sn. As the phosphoric acid compound, a phosphoric acid silyl ester in which X is Si is preferably used. In the general formula (2), R ³ , R ⁴ and R ⁵ each independently represents an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms. However, a methyl group or an ethyl group is more preferable. R ³ , R ^4, and R ⁵ may have some or all of their hydrogen atoms replaced with fluorine. The group represented by the general formula (2) is particularly preferably a trimethylsilyl group.

In the phosphoric acid compound, only one of the hydrogen atoms possessed by phosphoric acid may be substituted with the group represented by the general formula (2). Two of them may be substituted with a group represented by the general formula (2), and all three hydrogen atoms of phosphoric acid may be substituted with a group represented by the general formula (2). However, it is more preferable that all three hydrogen atoms of phosphoric acid are substituted with the group represented by the general formula (2).

As such a phosphoric acid compound, phosphoric acid (tris) trimethylsilyl is particularly preferable.

In the method for producing a non-aqueous secondary battery of the present invention, the moisture content of the positive electrode mixture layer is 500 ppm or more, preferably 1000 ppm or more, more preferably 1200 ppm or more, based on mass. Thereby, SEI film formation by the said phosphoric acid compound in a positive electrode can be advanced more efficiently, and the high temperature storage characteristic of a non-aqueous secondary battery can be improved. However, if the amount of water in the positive electrode mixture layer is too large, the amount of hydrogen fluoride generated becomes too large, and the battery characteristics may be deteriorated. For this reason, from the viewpoint of securing better battery characteristics, in the non-aqueous secondary battery manufacturing method of the present invention, the water content of the positive electrode mixture layer may be 3000 ppm or less and 2500 ppm or less on a mass basis. Preferably, it is more preferably 2000 ppm or less.

The water content of the positive electrode mixture layer as used in the present specification can be determined by, for example, the following method. A measurement sample (positive electrode) is put into a 150 ° C. heating furnace in which nitrogen gas is flowed, and held for 1 minute. Then, the flowd nitrogen gas is introduced into the measurement cell of the Karl Fischer moisture meter, and the moisture content is measured. The integrated value up to the end of titration is taken as the moisture content (the “moisture content” used as the standard for the calculation of “moisture content” described in the examples below) is a value determined by this method. A value obtained by dividing the water content by the mass of the positive electrode mixture layer is referred to as “moisture content of the positive electrode mixture layer” in the present specification. The moisture content is measured in a glove box having a dew point of −70 ° C.

In addition, although the moisture brought into the battery is mostly due to the positive electrode mixture layer, there are also those other than the positive electrode such as the negative electrode, the separator and the non-aqueous electrolyte, and these moisture are also contained in the non-aqueous electrolyte. The phosphoric acid compound can contribute to the formation of an SEI film.

Therefore, it is desirable to adjust the water content of the entire battery, including the moisture due to the configuration other than the positive electrode, to be within a preferable range for the SEI film formation by the phosphoric acid compound. Assuming that the water content of the entire battery is all contained in the non-aqueous electrolyte (hereinafter referred to simply as “the water content of the entire battery”), the SEI film of the phosphoric acid compound on the positive electrode is used. In order to promote the formation more efficiently, the total amount of the non-aqueous electrolyte is preferably about 1000 ppm or more, more preferably 1500 ppm or more, and particularly preferably 1700 ppm or more, based on mass.

On the other hand, in order to suppress deterioration of battery characteristics by forming the SEI film relatively thin, the water content of the entire battery is preferably 3500 ppm or less, more preferably 3000 ppm or less on a mass basis. It is especially preferable to set it as 2500 ppm or less.

The above-mentioned “moisture content of the entire battery” is the measurement of the moisture content in the measurement of the moisture content when determining the moisture content of the positive electrode mixture layer, with the measurement sample as all the constituent materials of the battery with the battery container opened. And this is calculated | required by dividing by the mass of the non-aqueous electrolyte which a battery contains.

The olivine type compound exemplified as the positive electrode active material in the non-aqueous secondary battery of the present invention is typically represented by a chemical formula of LiM ¹ PO ₄ (M ¹ : Co, Ni, Mn, Fe, etc.). However, it may contain one or more elements other than M ¹ such as Al and Y as additive elements. Moreover, the olivine type compound contained in the positive electrode mixture layer may be only one kind of those not containing the above-mentioned additive elements or one containing the above-mentioned additive elements, or two or more kinds. May be.

The average particle size of the olivine type compound particles is preferably 5 μm or more, more preferably 8 μm or more, and particularly preferably 10 μm or more. By setting the particle size, excellent binding properties can be maintained even when the content of the polymer (A) in the positive electrode mixture layer is reduced, and the charge / discharge characteristics can be further improved. it can.

On the other hand, if the average particle size of the olivine-type compound particles becomes too large, the conductivity of the positive electrode mixture layer decreases and the charge / discharge characteristics decrease, so the average particle size is preferably 20 μm or less, It is more preferably 17 μm or less, and particularly preferably 15 μm or less.

The olivine type compound particles may be composed of primary particles, but when the secondary particles are aggregated primary particles having a particle diameter of about 10 to 100 nm, or a granulated body obtained by granulating the primary particles, Compared with primary particles having the same particle size, charge / discharge characteristics can be further improved, which is preferable. The average particle size in this case may be calculated based on the particle size of the secondary particles or the granulated body.

In the present specification, the average particle diameter is a number average particle diameter measured using a laser scattering particle size distribution analyzer (for example, “LA-920” manufactured by Horiba, Ltd.).

In addition, in order to increase the conductivity of the particles of the olivine type compound having a low conductivity, it is desirable to provide a carbon coating layer on the particle surface, and thereby the conductivity in the positive electrode mixture layer becomes better.

Conventionally known methods can be employed for coating the olivine type compound with a carbon material. Specifically, for example, a method of firing a mixture of an organic material that becomes a carbon precursor and an olivine type compound; a surface of an olivine type compound while decomposing a gas that becomes a carbon precursor by a vapor deposition (CVD) method And a general coating method such as:

The amount of carbon when the olivine type compound is coated with the carbon material is 1 mass per 100 parts by mass of the olivine type compound from the viewpoint of improving the conductivity of the positive electrode and enabling a more efficient charge / discharge reaction. Part or more. However, if the amount of carbon on the surface of the olivine type compound is too large, carbon may become a barrier during the lithium ion insertion / desorption reaction, which may cause a reduction in load characteristics of the non-aqueous secondary battery, for example. Therefore, the amount of carbon when the olivine type compound is coated with the carbon material is preferably 5 parts by mass or less with respect to 100 parts by mass of the olivine type compound.

The particle diameter in the case where a carbon coating layer is provided on the surface of the olivine-type compound particle may be regarded as the particle diameter of the olivine-type compound particle for the sake of simplicity. Good.

In order to further improve the charge / discharge characteristics of the battery, the content of the polymer (A) in the positive electrode mixture layer is reduced to, for example, 7% by mass or less, more preferably 5% by mass or less. However, in order to maintain excellent binding properties even when the binder content is reduced and prevent problems such as peeling of the positive electrode mixture layer, the BET specific surface area of the positive electrode active material is 25 m. ² / g or less is preferable, 15 m ² / g or less is more preferable, 13 m ² / g or less is particularly preferable, and 10 m ² / g or less is most preferable. On the other hand, in order to secure a reaction area of a certain level or more and improve charge / discharge characteristics at a large current, the BET specific surface area of the positive electrode active material is preferably 5 m ² / g or more, and 8 m ² / g or more. More preferably.

In the present specification, the BET specific surface area is a value obtained by analyzing a gas adsorption amount measured by a gas adsorption method using nitrogen gas using the BET method.

In addition, in the positive electrode of the above embodiment in which an olivine type compound is used as the positive electrode active material, other positive electrode active materials may be used together with the olivine type compound. Examples of such a positive electrode active material include various lithium-containing composite oxides (lithium-containing composite oxides other than olivine type compounds) used in non-aqueous secondary batteries such as lithium ion secondary batteries.

However, when a positive electrode active material other than the olivine type compound is used, the amount of the positive electrode active material other than the olivine type compound in the total amount of the positive electrode active material is preferably 30% by mass or less.

In addition to the olivine type compound, the positive electrode active material used in the positive electrode in which the positive electrode mixture layer has a water content of 500 to 3000 ppm includes lithium nickelate and a part of the nickel, other materials such as Co and Al. Lithium nickel composite oxides substituted with elements [Li _{1 + a} NiO ₂ , Li _{1 + a} Ni _1-x Co _x O ₂ , Li _{1 + a} Ni _1-xy Co _x Al _y O ₂ (−0.15 ≦ a ≦ 0. 1, x ≦ 0.4, x + y ≦ 0.4) and the like.

The content of the positive electrode active material in the positive electrode mixture layer is preferably 85 to 98% by mass.

In the polymer (A) used as the binder of the positive electrode mixture layer, the unit represented by the general formula (1) is a unit derived from an acrylic ester or a methacrylic ester [hereinafter referred to as acrylic acid and methacrylic ester. The acid may be collectively referred to as “(meth) acrylic acid”], and the polymer (A) is synthesized by polymerizing the (meth) acrylic acid ester.

Specific examples of the (meth) acrylate ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, (meth ) Isobutyl acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, amyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, ( Octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, (Meth) acrylic acid dodecyl, (meth) acrylic acid lauryl, (meta Stearyl acrylate, (meth) isostearyl acrylate, and the like, may be used only one of these may be used or two or more kinds.

In the polymerization of the (meth) acrylic acid ester, a monomer other than the (meth) acrylic acid ester may be used together with the (meth) acrylic acid ester. In this case, the polymer is a copolymer having in the molecule also units derived from monomers other than (meth) acrylic acid ester.

Monomers that are polymerized with the (meth) acrylic acid ester include cyano group-containing monomers; aromatic vinyl compounds (styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, divinylbenzene, vinyltoluene, etc.); conjugated dienes Compounds (butadiene, isoprene, chloroprene, 2-chloro-1,3-butadiene, etc.); unsaturated carboxylic acids; and the like.

Examples of the cyano group-containing monomer include unsaturated carboxylic acid nitriles such as acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, vinylidene cyanide; 2-cyanoethyl (meth) acrylate, 2-cyanopropyl (meth) acrylate, Cyanoalkyl esters of unsaturated carboxylic acid nitriles such as (meth) acrylic acid 3-cyanopropyl; and the like. Examples of the unsaturated carboxylic acid include unsaturated carboxylic acids such as (meth) acrylic acid and crotonic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, and mesaconic acid; Can be mentioned.

When (meth) acrylic acid ester and other monomer are copolymerized, the proportion of (meth) acrylic acid ester in all monomers is preferably 5% by mass or more, and more preferably 8% by mass or more. Preferably, it is 10 mass% or more.

In addition, when the cyano group-containing monomer is used, the ratio of the cyano group-containing monomer in all monomers is preferably 1 to 50% by mass, and more preferably 2 to 15% by mass. Further, when the above aromatic vinyl compound is used, the ratio of the aromatic vinyl compound in all monomers is preferably 20 to 50% by mass, and more preferably 30 to 45% by mass. When the conjugated diene compound is used, the ratio of the conjugated diene compound in all monomers is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. Further, when the above unsaturated carboxylic acid is used, the proportion of the unsaturated carboxylic acid in all monomers is preferably 1 to 10% by mass, and more preferably 2 to 7% by mass.

From the viewpoint of charge / discharge characteristics and binding power, the polymer (A) is derived from a cyano group-containing monomer, an aromatic vinyl compound, a conjugated diene compound and an unsaturated carboxylic acid together with a (meth) acrylic acid ester. It is preferable to have a structural unit.

The positive electrode mixture layer may contain a binder other than the polymer (A) having a unit represented by the general formula (1) in the molecule as a binder. In the case where the effect of gelation is difficult to occur, for example, in the case where the preparation of the composition to the assembly of the positive electrode are performed in a short time, only a resin such as PVDF that is easily gelled by an alkali component is used. It is also possible. Examples of the binder used in addition to the polymer (A) include polyvinylidene fluoride (PVDF), vinylidene fluoride copolymer (PVDF-HFP, etc.), polyimide, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC). And acrylic resin.

However, the proportion of the binder other than the polymer (A) having the unit represented by the general formula (1) in the molecule in the total binder contained in the positive electrode mixture layer may be 20% by mass or less. It is preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably only the polymer (A).

The synthesis of the polymer (A), that is, the polymerization of the (meth) acrylic acid ester can be performed by an emulsion polymerization method. The conditions at that time are not particularly limited, and may be the same as those usually employed in the emulsion polymerization of (meth) acrylic acid ester. For example, emulsifiers (anionic surfactants, nonionic surfactants, amphoteric surfactants, etc.), polymerization initiators (persulfates such as ammonium persulfate, hydroperoxides such as cumene hydroperoxide, polymerization initiators and (Meth) acrylic acid ester and other monomers used as needed are added to water to which a redox polymerization initiator combined with a reducing agent, etc.) is added, and 1 at a temperature of about 30 to 90 ° C. Polymerization may be performed for about 30 hours.

In the case of using a copolymer of the (meth) acrylic acid ester and vinylidene fluoride or a mixture of the (meth) acrylic acid ester polymer and the vinylidene fluoride polymer (PVDF) as a binder. For example, a composite obtained by polymerizing a (meth) acrylic acid ester in the presence of a polymer of vinylidene fluoride can also be used. However, by this polymerization, the (meth) acrylic acid ester is bonded to the vinylidene fluoride polymer molecule, and the polymerization proceeds, so that the copolymer [consists of units represented by the general formula (1). A block copolymer having in its molecule a block composed of vinylidene fluoride-derived units; and a vinylidene fluoride polymer molecule as a main chain, represented by the general formula (1) Or the like, or a (meth) acrylic acid ester polymer is formed by the progress of homopolymerization of (meth) acrylic acid ester. Thus, it can be a mixture of this and the polymer of vinylidene fluoride, but it is not certain which form it will take.

The polymerization of (meth) acrylic acid ester in the presence of the polymer of vinylidene fluoride can also be performed by an emulsion polymerization method. The conditions at that time are not particularly limited, and for example, the synthesis conditions for the polymer (A) described above may be applied.

In addition, in order to prevent gelation by the alkali component of a positive electrode active material, when the unit which comprises a fluororesin is contained in a polymer (A) like the copolymer of (meth) acrylic acid ester and vinylidene fluoride The proportion of the polymer (A) is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less. Most preferably not.

In order to maintain excellent binding properties, the content of the polymer (A) in the positive electrode mixture layer is preferably 1% by mass or more, more preferably 1.5% by mass or more, and charging / discharging. In order to improve the characteristics, the content is preferably 7% by mass or less, more preferably 5% by mass or less, and particularly preferably 4% by mass or less.

The total content of all binders in the positive electrode mixture layer is also preferably 1% by mass or more, more preferably 1.5% by mass or more, and preferably 7% by mass or less. It is more preferably 5% by mass or less, and particularly preferably 4% by mass or less. Therefore, when using another binder with the said polymer (A) for the binder of a positive mix layer, the ratio of binders other than the said polymer (A) in all the binders in a positive mix layer is the said suitable value. It is preferable that the total content of all the binders in the positive electrode mixture layer is adjusted so as to be the above-mentioned preferable value while limiting to be.

Conductive aids for the positive electrode mixture layer include natural graphite (such as flake graphite) and artificial graphite (graphite carbon material); acetylene black; ketjen black, channel black, furnace black, lamp black, thermal Carbon materials such as carbon black such as carbon black; carbon fibers (including carbon nanofibers); carbon nanotubes;

Among these conductive aids, it is preferable to use at least one of carbon nanotubes and carbon nanofibers and at least one of acetylene black and carbon black. The olivine-type compound used as the positive electrode active material is a material having low conductivity. However, when the above-mentioned conductive auxiliary is used, in the place where the distance between the positive electrode active material particles is short, particulate acetylene black or carbon Conductivity is ensured by black. On the other hand, in places where the distance between the positive electrode active material particles is long enough to make it difficult to secure conductivity with acetylene black or carbon black, carbon nanotubes or carbon nanofibers having a fibrous form are used. Conductivity is ensured. Therefore, the conductivity in the positive electrode mixture layer can be better ensured by the combination of the conductive aids.

The average length of carbon nanotubes and carbon nanofibers is preferably 1 nm to 5 μm. The average diameter of the carbon nanotube or carbon nanofiber is preferably 1 nm to 2 μm.

The average length and average diameter of the carbon nanotubes and carbon nanofibers used in the present specification are determined by using a transmission electron microscope (TEM such as “JEM series” manufactured by JEOL Ltd., “H-700H” manufactured by Hitachi, Ltd.), etc. Is measured from a photographed TEM image at 100 or 200 kV. When viewing the average length, TEM images of 100 samples were taken at 20,000 to 40,000 magnification, and when viewing the average diameter at 200,000 to 400,000 magnification. The length and diameter are measured one by one with a metal scale certified as No. 1, and the average is taken as the average length and average diameter.

In addition, graphite (flaky graphite) also contributes to ensuring the conductivity between these particles at a location where the distance between the positive electrode active material particles is relatively long, as in the case of carbon nanotubes and carbon nanofibers. Therefore, it is also preferable to use graphite together with at least one of acetylene black and carbon black as a conductive additive for the positive electrode mixture layer.

When at least one of carbon nanotubes, carbon nanofibers and graphite and at least one of acetylene black and carbon black are used as a conductive additive, carbon nanotubes, carbon nanofibers and graphite in the positive electrode mixture layer are used. The total amount (when only one of them is used) is preferably 0.1 to 5% by mass. Further, when at least one of carbon nanotubes, carbon nanofibers and graphite and at least one of acetylene black and carbon black are used as a conductive additive, the total of acetylene black and carbon black in the positive electrode mixture layer The amount (when only one of them is used) is preferably 1 to 10% by mass.

The content of the conductive additive in the positive electrode mixture layer is preferably 1 to 10% by mass.

For the positive electrode, for example, a positive electrode active material, a binder, and a conductive auxiliary agent are dispersed in a solvent such as water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing composition (however, , The binder may be dissolved in a solvent), and this may be applied to one or both sides of the current collector (however, if a coat layer is formed on the surface of the current collector as described later, the surface of the coat layer) ) And a method of forming a positive electrode mixture layer through a step of drying, that is, the production method of the present invention. In preparing the positive electrode mixture-containing composition, in order to adjust the viscosity of the composition or increase the dispersibility of the composition, carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), etc. It can also be added as a thickener or dispersant.

Further, after the formation of the positive electrode mixture layer, for example, in order to adjust the density of the positive electrode mixture layer, a pressing process such as a calendar process may be performed.

As the positive electrode current collector, the same one as used for the positive electrode of a conventionally known non-aqueous secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

The positive electrode current collector is preferably a metal foil (such as an aluminum foil) having a plurality of through holes. By using such a metal foil for the positive electrode current collector, the adhesion between the positive electrode mixture layer and the current collector is improved, and even if the battery is repeatedly charged and discharged, the positive electrode mixture layer and the current collector Since peeling becomes difficult to occur, the charge / discharge cycle characteristics of the battery are enhanced, and the conductivity in the positive electrode mixture layer is also improved.

When a metal foil having a plurality of through holes is used for the positive electrode current collector, the metal foil is partially bonded to the main body of the metal foil without removing the metal in the part forming the through holes. It is more preferable to have a protrusion that is bent and raised from the flat surface of the metal foil. When a metal foil having such protrusions is used as a positive electrode current collector, the protrusion penetrates into the positive electrode mixture layer, and thus the adhesion between the positive electrode mixture layer and the current collector and the positive electrode mixture layer The conductivity of the is further improved.

In a positive electrode current collector made of a metal foil having a plurality of through holes, the number of holes is preferably 5 to 30 per 1 cm ^{2 in} a plan view of the current collector. Therefore, in the case of a positive electrode current collector made of a metal foil having a plurality of through-holes and the protrusions, the number of protrusions should be 5 to 30 per 1 cm ^{2 in} plan view of the current collector. preferable. In addition, the height of the protrusion is preferably ½ or less of the thickness of the positive electrode mixture layer formed on the side where the protrusion is provided.

In the positive electrode current collector, the through holes and the protrusions may be regularly arranged or irregularly arranged, but are more preferably regularly arranged.

The positive electrode current collector is also preferably a metal foil (such as an aluminum foil) having a coating layer containing a carbon material on the surface. Also in this case, the adhesion between the positive electrode mixture layer and the positive electrode current collector is improved, and peeling of the positive electrode mixture layer and the current collector hardly occurs even when the battery is repeatedly charged and discharged. The charge / discharge cycle characteristics are enhanced, and the conductivity in the positive electrode mixture layer is also improved.

Examples of the carbon material contained in the coating layer include graphite (graphite carbon material) such as natural graphite (scaly graphite), artificial graphite; acetylene black; ketjen black, channel black, furnace black, lamp black, thermal black. Carbon black such as activated carbon; activated carbon; etc., and only one of these may be used, or two or more may be used in combination. Among these, activated carbon is more preferable because it can contribute to the capacity increase of the positive electrode.

The coat layer may contain a binder together with the carbon material. Examples of such a binder include various binders including a fluororesin such as PVDF and the polymer (A) exemplified above as a binder for a positive electrode mixture layer.

As the composition of the coating layer, the carbon material content is preferably 40 to 95% by mass, and the binder content is preferably 5 to 60% by mass. The thickness of the coat layer (the thickness per one side of the current collector) is preferably 0.1 to 5 μm.

The coating layer is a method in which a coating material containing a coating material prepared by dispersing and dissolving a carbon material and a binder in an organic solvent such as NMP or water is applied to the surface of a metal foil serving as a positive electrode current collector and dried. Etc. can be formed.

The thickness of the positive electrode mixture layer (when the positive electrode mixture layer is provided on both sides of the current collector, the thickness per side) is preferably 3 to 100 μm.

A lead body for electrical connection with other members in the battery may be formed on the positive electrode according to a conventional method.

The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution containing a lithium salt and an organic solvent, and the positive electrode may be the positive electrode of the above embodiment. There is no restriction | limiting in particular about a structure, The various structure and structure employ | adopted by the conventionally known nonaqueous secondary battery are applicable.

For the negative electrode of the nonaqueous secondary battery, for example, a negative electrode mixture layer containing a negative electrode active material and a binder can be used on one or both sides of the current collector.

As the negative electrode active material, a conventionally known negative electrode active material used for the negative electrode of a non-aqueous secondary battery, that is, an active material capable of occluding and releasing lithium ions can be used. Specific examples of such a negative electrode active material include, for example, graphite (natural graphite; artificial graphite obtained by graphitizing graphitized carbon such as pyrolytic carbons, mesophase carbon microbeads, and carbon fibers at 2800 ° C. or higher; ), Graphitizable carbon, non-graphitizable carbon, pyrolytic carbons, cokes, glassy carbons, organic polymer compound fired bodies, mesophase carbon microbeads, carbon fibers, activated carbon and other carbon materials; lithium and alloys Examples of such particles include metals that can be converted (Si, Sn, etc.) and materials containing these metals (alloys, oxides, etc.). In the negative electrode, only one type of the above illustrated negative electrode active materials may be used, or two or more types may be used in combination.

Among these negative electrode active materials, it is preferable to use at least one of graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon).

Examples of the soft carbon include coke obtained by firing a pitch. Further, examples of the hard carbon include amorphous carbon obtained by low-temperature firing of furfuryl alcohol resin (PFA), polyparaphenylene (PPP), and phenol resin. Such a carbon material has a d ₀₀₂ obtained by, for example, X-ray diffraction measurement of more than 0.340 nm (preferably 0.370 nm or more), preferably 0.400 nm or less. Compared to graphite, which is widely used as negative electrode active materials for batteries, the lithium ion accepting speed is faster, so by making these batteries with negative electrodes using negative electrode active materials, they are charged with a large current and per hour. Even if the amount of lithium ions released from the positive electrode increases, it is possible to suppress the precipitation of lithium dendrite by suppressing the stagnation of lithium ions in the vicinity of the negative electrode. Is possible. In addition, in the case of a negative electrode using soft carbon or hard carbon as a negative electrode active material, the release of lithium ions from the negative electrode during battery discharge proceeds smoothly. Therefore, by using these for the negative electrode active material, the charge / discharge characteristics at a large current of the nonaqueous secondary battery can be further enhanced.

When soft carbon or hard carbon and another negative electrode active material (for example, those exemplified above) are used together as the negative electrode active material, the amount of negative electrode active material other than soft carbon and hard carbon in the total amount of the negative electrode active material Is preferably 30% by weight or less. That is, the amount of soft carbon and hard carbon in the total amount of the negative electrode active material (when only one of them is used, it is the amount thereof, and when both are used together, it is the total amount thereof. The same applies hereinafter). Is preferably 70% by mass or more, and since only one of soft carbon and hard carbon may be used for the negative electrode active material, soft carbon and hard carbon in the total amount of the negative electrode active material The preferred upper limit of the amount is 100% by mass.

The negative electrode mixture layer contains a binder. Examples of the binder related to the negative electrode mixture layer include fluororesins such as PVDF, SBR, CMC, and acrylic resins.

Examples of the acrylic resin include a copolymer of butyl acrylate and acrylic acid (a copolymer having a unit derived from butyl acrylate and a unit derived from acrylic acid in the molecule), and such a resin. Is more preferably used for the binder of the negative electrode mixture layer. By using such a binder, the heat resistance of the negative electrode can be improved, so that the storage characteristics of the battery in a high temperature environment can be further improved.

The negative electrode mixture layer may contain a conductive additive. The same thing as what was illustrated previously as a conductive support agent which concerns on a positive mix layer can be used for the conductive support agent which concerns on a negative mix layer.

The negative electrode is prepared by, for example, preparing a negative electrode mixture-containing composition by dispersing a negative electrode active material, a binder, and a conductive auxiliary agent used as necessary in a solvent such as water or an organic solvent such as NMP. The binder may be dissolved in a solvent), which can be produced by a method in which the binder is applied to one or both sides of the current collector and dried to form a negative electrode mixture layer. Further, after the formation of the negative electrode mixture layer, for example, in order to adjust the density of the negative electrode mixture layer, press treatment such as calendaring may be performed.

As the current collector for the negative electrode, copper or nickel foil, punching metal, mesh, expanded metal, or the like can be used, but copper foil is usually used. In the negative electrode current collector, when the entire negative electrode is thinned in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit of the thickness is 5 μm to ensure mechanical strength. Is desirable.

In the negative electrode mixture layer, the content of the negative electrode active material (the total amount when a plurality of types of negative electrode active materials are used) is preferably 90 to 98% by mass, and the binder content is 2 to 2%. It is preferable that it is 10 mass%. In addition, when the conductive additive is contained in the negative electrode mixture layer, the content of the conductive aid in the active material layer is preferably 2 to 10% by mass. Furthermore, the thickness of the negative electrode mixture layer (when the negative electrode mixture layer is provided on both sides of the current collector, the thickness per side) is preferably 20 to 100 μm.

In addition, the density of the negative electrode mixture layer is preferably 1.5 g / cm ³ or less from the viewpoint of further increasing the lithium ion receiving speed in the negative electrode, and the battery is provided with a certain amount of the negative electrode active material to secure the battery. From the viewpoint of increasing the capacity, it is preferably 0.9 g / cm ³ or more.

The density of the negative electrode mixture layer in the present specification is a value measured by the following method. The negative electrode is cut into a predetermined area, the mass is measured using an electronic balance having a minimum scale of 0.1 mg, and the mass of the negative electrode mixture layer is calculated by subtracting the mass of the current collector. On the other hand, the total thickness of the negative electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the negative electrode mixture layer was calculated from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. To do. Then, the density of the negative electrode mixture layer is calculated by dividing the mass of the negative electrode mixture layer by the volume.

In the negative electrode, a lead body for electrical connection with other members in the battery may be formed according to a conventional method.

In the non-aqueous secondary battery, the negative electrode and the positive electrode include, for example, a laminated body (laminated electrode body) stacked with a separator interposed therebetween, or a wound body obtained by further winding this laminated body in a spiral shape ( Used in the form of a wound electrode body).

The separator preferably has a property (that is, a shutdown function) that closes the pores at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). Separator used in non-aqueous secondary batteries, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. Moreover, you may use the nonwoven fabric made from a cellulose or a polyimide excellent in heat resistance (decomposition temperature 200 degreeC or more).

As the non-aqueous electrolyte solution related to the non-aqueous secondary battery, a solution containing a lithium salt and an organic solvent and dissolving the lithium salt in the organic solvent is used. Moreover, in the manufacturing method of the non-aqueous secondary battery of this invention, the electrolyte solution which further contains the phosphoric acid compound which has group represented by the said General formula (2) in a molecule | numerator is used.

The content of the phosphoric acid compound having in the molecule thereof the group represented by the general formula (2) in the non-aqueous electrolyte is 0.5 mass from the viewpoint of ensuring the above-mentioned effects better. % Or more, and more preferably 1% by mass or more. In addition, if the content is too large, the thickness of the SEI film that can be formed at the electrode interface increases, which may increase resistance and decrease load characteristics. Therefore, in the non-aqueous electrolyte, The content of the phosphoric acid compound having a group represented by the general formula (2) in the molecule is preferably 7% by mass or less, more preferably 5% by mass or less, and 3% by mass or less. More preferably.

Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ ; 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 (n ≧ 2), LiN (FSO ₂ ) ₂ [LiFSI], LiN (CF ₃ SO ₂ ) ₂ [LiTFSI], LiN (C ₂ F ₅ SO ₂ ) ₂ , or an organic lithium salt such as lithium bisoxalate borate (LiBOB);

When the phosphoric acid compound is contained in the non-aqueous electrolyte, a fluorine-containing inorganic lithium salt such as LiPF ₆ alone or another inorganic lithium salt such as LiClO ₄ or lithium bisoxalate is used as the lithium salt. By using a positive electrode with an organic lithium salt such as borate (LiBOB) and a positive electrode mixture layer containing a large amount of moisture, hydrogen fluoride is generated by reaction with the moisture of the positive electrode, and the phosphorus The formation of the SEI film derived from the acid compound can be efficiently advanced.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; γ-butyrolactone, α Cyclic esters such as lactones having a substituent at the position; chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; Nitriles such as acetonitrile, propionitrile, methoxypropionitrile; sulfites such as ethylene glycol sulfite; These can be used as a mixture of two or more. In order to obtain a battery having better characteristics, it is desirable to use a combination that can obtain a high conductivity, such as a mixed solvent of the above-mentioned cyclic carbonate and the above-mentioned chain carbonate.

It is also preferable to use lactones having a substituent at the α-position as the organic solvent. Since the lactone having a substituent at the α-position has a high boiling point of 150 ° C. or higher, it is difficult to volatilize even when the battery is placed in a high temperature environment, and the composition of the non-aqueous electrolyte changes and the outer body swells. Therefore, a battery having higher heat resistance and excellent storage characteristics at high temperatures can be configured.

In addition to lactones having a substituent at the α-position, high-boiling solvents having a boiling point of 150 ° C. or higher are known, but generally high-boiling solvents have low permeability to polyolefin separators, In order to increase the permeability of the non-aqueous electrolyte to the separator, it is necessary to use another solvent (generally having a low boiling point). On the other hand, since lactones having a substituent at the α-position have good permeability to polyolefin separators, by using a non-aqueous electrolyte using this, for example, without impairing the load characteristics of the battery, Heat resistance can be improved.

The lactone having a substituent at the α-position is preferably, for example, a 5-membered ring (having 4 carbon atoms constituting the ring). The α-position substituent of the lactone may be one or two.

Examples of the substituent include a hydrocarbon group and a halogen group (fluoro group, chloro group, bromo group, iodo group) and the like. As a hydrocarbon group, an alkyl group, an aryl group, etc. are preferable, and it is preferable that the carbon number is 1 or more and 15 or less (more preferably 6 or less). When the substituent is a hydrocarbon group, a methyl group, an ethyl group, a propyl group, a butyl group, a phenyl group, and the like are more preferable.

Specific examples of lactones having a substituent at the α-position include α-methyl-γ-butyrolactone, α-ethyl-γ-butyrolactone, α-propyl-γ-butyrolactone, α-butyl-γ-butyrolactone, α-phenyl -Γ-butyrolactone, α-fluoro-γ-butyrolactone, α-chloro-γ-butyrolactone, α-bromo-γ-butyrolactone, α-iodo-γ-butyrolactone, α, α-dimethyl-γ-butyrolactone, α, α -Diethyl-γ-butyrolactone, α, α-diphenyl-γ-butyrolactone, α-ethyl-α-methyl-γ-butyrolactone, α-methyl-α-phenyl-γ-butyrolactone, α, α-difluoro-γ-butyrolactone , Α, α-dichloro-γ-butyrolactone, α, α-dibromo-γ-butyrolactone, α, α-diiodo-γ-butyrolactone Tons, and the like, it may be used only one of these may be used in combination of two or more. Among these, α-methyl-γ-butyrolactone is more preferable.

When lactones having a substituent at the α-position are used in the organic solvent, only lactones having a substituent at the α-position may be used, but when other organic solvents are used together, 150 ° C or higher It is preferable to use a high-boiling solvent having a boiling point (ethylene carbonate, propylene carbonate, γ-butyrolactone, sulfolane, trimethyl phosphate, triethyl phosphate, etc.).

When the lactone having a substituent at the α-position is used as the organic solvent, the ratio in the total organic solvent in the nonaqueous electrolytic solution is preferably 30 to 100% by volume.

The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.6 to 1.8 mol / L, and more preferably 0.9 to 1.6 mol / L.

In addition, for the purpose of improving characteristics such as battery safety, charge / discharge cycleability, and high-temperature storage stability, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, biphenyl, fluorobenzene are added to the non-aqueous electrolyte. Additives such as t-butylbenzene and halogen-substituted cyclic carbonates (4-fluoro-1,3-dioxolan-2-one etc.) can also be added as appropriate.

Furthermore, in the non-aqueous secondary battery of the present invention, a gel (gel electrolyte) obtained by adding a gelling agent such as a known polymer to the non-aqueous electrolyte may be used.

Examples of the form of the non-aqueous secondary battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can, or a coin shape. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Synthesis of binder for positive electrode mixture layer>
A latex in which PVDF is dispersed in water (the amount of PVDF is 40% by mass) is placed in a reaction vessel (the amount of PVDF is 20 parts by mass), and water: 150 parts by mass is added thereto, and the reaction vessel is filled with nitrogen. Replaced.

Water: 60 parts by mass, emulsifier (ether sulfate type emulsifier: dispersion having a solid content of 25% by mass): 2 parts by mass (as solid content), methyl methacrylate: 20 parts by mass, 2-ethylhexyl acrylate : 10 parts by mass, butyl acrylate: 25 parts by mass, acrylonitrile: 20 parts by mass, and acrylic acid: 5 parts by mass were put in another container and sufficiently stirred to prepare an emulsion containing the monomer. .

The temperature inside the reaction vessel was started, and when the internal temperature reached 50 ° C., 0.5 parts by mass of ammonium persulfate and 0.1 part by mass of sodium sulfite were added to the reaction vessel. Subsequently, when the temperature in the reaction vessel reaches 60 ° C., dropping of the emulsion into the reaction vessel is started, and the total amount of the emulsion is reduced to 2 while maintaining the temperature in the reaction vessel at 60 ° C. Added over time. Then, the binder for the positive electrode mixture layer containing the polymer (A) having the unit represented by the general formula (1) in the molecule by polymerizing for 2 hours while maintaining the inside of the reaction vessel at 60 ° C. (B1) was synthesized.

<Preparation of positive electrode>
As the positive electrode active material, olivine-type lithium iron phosphate (LiFePO ₄ , average particle diameter 13 μm, BET specific surface area: 9 m ² / g) whose surface is coated with a carbon material: 89 parts by mass, and acetylene black as a conductive auxiliary agent: 3.5 parts by mass and 1.5 parts by mass of graphite, binder B1: 3.3 parts by mass, polyvinylpyrrolidone (dispersing agent): 0.3 parts by mass, and CMC (thickening agent): 2.4 parts by mass And water were mixed to prepare a positive electrode mixture-containing composition. The olivine-type lithium iron phosphate whose surface is coated with a carbon material is obtained by mixing iron phosphate, lithium phosphate and sucrose, and firing at 800 ° C. in nitrogen gas. The amount of carbon covering the surface was 2.3 parts by mass with respect to 100 parts by mass of lithium iron phosphate.

This positive electrode mixture-containing composition was applied to one side of an aluminum foil (current collector) having a thickness of 15 μm and dried to obtain a positive electrode having a positive electrode mixture layer having a thickness of 5 μm on one side of the current collector. .

<Production of negative electrode>
The negative electrode active material-containing composition was prepared by mixing 96 parts by mass of soft carbon as the negative electrode active material, 2 parts by mass of SBR, 2 parts by mass of CMC, and water. This negative electrode mixture-containing composition was applied to one side of a 10 μm thick copper foil (current collector) and dried to obtain a negative electrode having a negative electrode mixture layer having a thickness of 6 μm on one side of the current collector. . The density of the negative electrode mixture layer was 1.0 g / cm ³ .

<Preparation of non-aqueous electrolyte>
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 2.

<Battery assembly>
The positive electrode and the negative electrode are overlapped via a separator (a separator made of microporous polyethylene film, thickness 16 μm, opening ratio 50%) to form a laminated electrode body, which is inserted into an aluminum laminate film exterior body, and this exterior After injecting the non-aqueous electrolyte into the body, the outer package was sealed to produce a laminated non-aqueous secondary battery having the cross-sectional structure shown in FIG. 2 with the appearance shown in FIG.

Here, FIG. 1 and FIG. 2 will be described. 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 II of FIG. The nonaqueous secondary battery 1 includes a laminated electrode body formed by laminating a positive electrode 5 and a negative electrode 6 via a separator 7 in a laminated film outer package 2 constituted by two laminated films, and a nonaqueous electrolytic solution. (Not shown) is accommodated, and the laminate film outer package 2 is sealed by heat-sealing the upper and lower laminate films at the outer peripheral portion thereof. In FIG. 2, each layer constituting the laminate film outer package 2 and each layer of the positive electrode 5 and the negative electrode 6 are not shown separately in order to prevent the drawing from becoming complicated.

The positive electrode 5 is connected to the positive electrode external terminal 3 in the battery 1 through a lead body. Although not shown, the negative electrode 6 is also connected to the negative electrode external terminal 4 in the battery 1 through a lead body. is doing. The positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the laminate film exterior body 2 so that they can be connected to an external device or the like.

Example 2
A positive electrode was produced in the same manner as in Example 1, except that the binder of the positive electrode was changed to 3.0 parts by mass the same as that produced in Example 1 and 0.3 parts by mass of PVDF manufactured by Kureha Corporation. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 3
A positive electrode current collector was prepared in the same manner as in Example 1 except that the positive electrode current collector was changed to an aluminum foil having a plurality of through-holes. A water secondary battery was produced. The aluminum foil used for the positive electrode current collector had 10 holes per 1 cm ² area in plan view of the foil and a hole diameter of 80 μm.

Example 4
A positive electrode was produced in the same manner as in Example 1 except that a coating layer having a thickness of 3 μm per side was formed on both sides of an aluminum foil as a positive electrode current collector before forming a positive electrode mixture layer. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that the positive electrode was used. In addition, the said coating layer on a positive electrode electrical power collector is a coating liquid which mixed the water dispersion containing acetylene black: 59 mass parts, acrylic resin: 40 mass parts as a binder, and PVP: 1 mass part as a dispersing agent. Formed using.

Example 5
Implementation was conducted except that the conductive assistant for the positive electrode was changed to acetylene black: 2.5 parts by mass, graphite: 1.5 parts by mass, and carbon nanotubes (average length 2 μm, average diameter 10 nm): 1 part by mass. A positive electrode was produced in the same manner as in Example 1, and a laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 6
The non-aqueous electrolyte was changed to one prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate, diethyl carbonate and α-methyl-γ-butyrolactone were mixed at a volume ratio of 30:20:50. A laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that.

Example 7
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was changed to natural graphite, and a laminated nonaqueous secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Comparative Example 1
A laminate type nonaqueous secondary battery was produced in the same manner as in Example 1 except that the binder of the positive electrode mixture layer was changed to PVDF at the time of producing the positive electrode.

The charge / discharge characteristics of the non-aqueous secondary batteries of Examples and Comparative Examples were evaluated by the following method.

<Measurement of rated capacity>
About each battery for evaluation of an Example and a comparative example, rated capacity (1C) was measured on condition of the following. First, constant current charging is performed at a constant current of 0.1 mA / cm ² until it reaches 3.85 V, and then constant voltage charging is performed at a constant voltage of 3.85 V until the current value decreases to 0.01 mA / cm ^2. went.

However, for the battery of Example 7, the end voltage of constant current charging and the voltage during constant voltage charging were set to 4.2V.

Each battery after charging was discharged at a constant current of 0.1 mA / cm ² until the battery voltage became 1.5 V, and the discharge capacity (mAh) at that time was defined as the rated capacity (1 C) of each battery.

<Charge / discharge characteristics evaluation>
After charging each battery until the depth of charge (SOC: ratio of the charge capacity to the rated capacity) reaches 100% under the same conditions as the above-mentioned rated capacity measurement, a predetermined current value [2C (20 mA), 5C ( 50 mA), 20 C (200 mA) and 50 C (500 mA)], the voltage drop was measured when discharged for 10 seconds.

The voltage drop at each current value: ΔV and the current value at that time: I were plotted on the vertical and horizontal axes, respectively, to determine the resistance value (DCR) of each battery during discharge.

In addition, each battery was discharged until the charging depth reached 0% under the same conditions as in the rated capacity measurement, and predetermined current values [2C (20 mA), 5C (50 mA), 20C (200 mA), and 40 C (400 mA) were obtained. )] Was measured for a voltage increase when charged for 10 seconds.

The voltage rise at each current value: ΔV and the current value at that time: I were plotted on the vertical and horizontal axes, respectively, to determine the resistance value (DCR) for charging each battery.

The evaluation results are shown in Table 1. In each column of Table 1, the DCR value (Ω) is shown when there is no particular problem and each measurement can be performed, and the problem is described when any problem occurs during measurement. .

As shown in Table 1, a negative electrode containing soft carbon as a negative electrode active material and having a negative electrode mixture layer having an appropriate density, lithium iron phosphate as a positive electrode active material, and a specific binder The non-aqueous secondary batteries of Examples 1 to 6 having a positive electrode that has a low DCR in both charging and discharging and a large current compared to the battery of Comparative Example 1 using PVDF as the positive electrode binder. Even in the case of discharge, good output characteristics were exhibited.

On the other hand, the battery of Example 7 using natural graphite as the negative electrode active material showed better charge / discharge characteristics than Comparative Example 1, but when charged at a current value of 40 C, lithium ions to the negative electrode Insertion could not catch up, and lithium dendrite was deposited on the negative electrode surface, which penetrated the separator to the positive electrode, causing a short circuit. Therefore, it was found that soft carbon and hard carbon are more suitable than graphite as the negative electrode active material of the non-aqueous secondary battery of the present invention.

Example 8
<Preparation of positive electrode>
The same positive electrode mixture-containing composition as that prepared in Example 1 was applied to both sides of an aluminum foil (current collector) having a thickness of 15 μm, and vacuum-dried at 120 ° C. for 12 hours to obtain both sides of the aluminum foil. A positive electrode mixture layer was formed on the substrate, pressed, and cut into a predetermined size to obtain a strip-like positive electrode.

In addition, when applying the positive electrode mixture-containing paste to the aluminum foil, a part of the aluminum foil was exposed, and the back surface was also applied as the application portion on the surface. The thickness of the positive electrode mixture layer of the obtained positive electrode (thickness per one side of the aluminum foil as the positive electrode current collector) was 41 μm.

In order to make the strip-shaped positive electrode into a tab portion, a part of the exposed portion of the aluminum foil (positive electrode current collector) protrudes, and a portion where the positive electrode mixture layer is formed has a substantially rectangular shape with curved corners. Thus, a positive electrode for a battery having a positive electrode mixture layer on both surfaces of the positive electrode current collector was obtained. FIG. 3 is a plan view schematically showing the battery positive electrode (however, in order to facilitate understanding of the structure of the positive electrode, the size of the positive electrode shown in FIG. 3 does not necessarily match the actual one). Not) The positive electrode 10 has a tab portion 13 punched out so that a part of the exposed portion of the positive electrode current collector 12 protrudes, and the shape of the forming portion of the positive electrode mixture layer 11 is a substantially rectangular shape with four corners curved. In the figure, the lengths a, b and c were 61 mm, 137 mm and 10 mm, respectively.

<Production of negative electrode>
The negative electrode active material: 96 parts by mass of soft carbon, acrylic resin: 2 parts by mass, CMC: 2 parts by mass, and water were mixed to prepare a negative electrode mixture-containing paste. The negative electrode mixture-containing paste is applied to both sides of a copper foil having a thickness of 10 μm and dried to form a negative electrode mixture layer on both sides of the copper foil, and press treatment is performed to set the density of the negative electrode mixture layer to 1. After adjusting to 0 g / cm ³ , it was cut into a predetermined size to obtain a strip-shaped negative electrode. In addition, when apply | coating the negative mix containing paste to copper foil, a part of copper foil was exposed and the back surface also made the application part the part made into the application part on the surface. The thickness of the negative electrode mixture layer of the obtained negative electrode (thickness per one side of the copper foil as the negative electrode current collector) was 61.5 μm.

In order to make the strip-shaped negative electrode into a tab portion, a part of the exposed portion of the copper foil (negative electrode current collector) protrudes, and the negative electrode mixture layer forming portion has a substantially square shape with four corners curved. Then, a negative electrode for a battery having a negative electrode mixture layer on both surfaces of the negative electrode current collector was obtained. FIG. 4 is a plan view schematically showing the battery negative electrode (however, in order to facilitate understanding of the structure of the negative electrode, the size of the negative electrode shown in FIG. 4 does not necessarily match the actual one). Not) The negative electrode 20 has a shape having a tab portion 23 punched out so that a part of the exposed portion of the negative electrode current collector 22 protrudes, and the shape of the forming portion of the negative electrode mixture layer 21 is a substantially rectangular shape with four corners curved. In the drawing, the lengths d, e, and f were 64 mm, 142.5 mm, and 10 mm, respectively.

<Preparation of non-aqueous electrolyte>
LiPF ₆ is dissolved at a concentration of 1.2 mol / L in a solvent in which propylene carbonate (PC) and α-methyl-γ-butyrolactone (MBL) are mixed at a volume ratio of 3: 7, and vinylene carbonate (VC) is further added to 2 A nonaqueous electrolytic solution was prepared by adding in an amount of 5% by mass.

<Battery assembly>
A laminated electrode body was formed using 18 positive electrodes for a battery in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector and 19 negative electrodes for a battery in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector. In the laminated electrode body, the upper and lower ends are the negative electrodes for the battery, and the positive electrode for the battery and the negative electrode for the battery are interposed between them. The tab portions between the positive electrodes and the tab portions between the negative electrodes were welded to each other with a ratio of 50%).

Next, the laminated electrode body is inserted into the depression of an aluminum laminate film having a thickness of 5.7 mm, a width of 78 mm, and a height of 161 mm in which the depression is formed so that the laminated electrode body is accommodated, and the above-mentioned laminated electrode body is inserted thereon The aluminum laminate film of the same size as the above was placed, and three sides of both aluminum laminate films were heat-welded. And the said non-aqueous electrolyte was inject | poured from the remaining 1 side of both aluminum laminate films. Thereafter, the remaining one side of both aluminum laminate films was vacuum heat sealed to produce a non-aqueous secondary battery having the cross-sectional structure shown in FIG. 6 with the appearance shown in FIG.

Here, FIG. 5 and FIG. 6 will be described. FIG. 5 is a plan view schematically showing a non-aqueous secondary battery, and FIG. 5 is a cross-sectional view taken along the line II-II in FIG. The nonaqueous secondary battery 100 includes a laminated electrode body 102 constituted by laminating a positive electrode and a negative electrode with a separator in an aluminum laminated film outer package 101 constituted by two aluminum laminated films, and a nonaqueous electrolytic solution. (Not shown) is housed, and the aluminum laminate film outer package 101 is sealed by heat-sealing the upper and lower aluminum laminate films at the outer peripheral portion thereof. In FIG. 6, in order to avoid complication of the drawing, each layer constituting the aluminum laminate film outer package 101 and the positive electrode, the negative electrode and the separator constituting the laminated electrode body 102 are shown separately. Absent.

Each positive electrode of the laminated electrode body 102 is integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the positive electrode external terminal 103 in the battery 100, although not shown. The negative electrodes of the laminated electrode body 102 are also integrated by welding the tab portions together, and the integrated product of the welded tab portions is connected to the negative electrode external terminal 104 in the battery 100. The positive electrode external terminal 103 and the negative electrode external terminal 104 are drawn out to the outside of the aluminum laminate film exterior body 101 so that they can be connected to an external device or the like.

Example 9
A non-aqueous secondary battery was prepared in the same manner as in Example 8 except that the solvent of the non-aqueous electrolyte was changed to a mixture of PC, MBL, and ethyl methyl carbonate (EMC) at a volume ratio of 3: 5: 2. Produced.

Example 10
A non-aqueous secondary battery was produced in the same manner as in Example 8 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 11
A non-aqueous secondary battery was produced in the same manner as in Example 9 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 12
A nonaqueous secondary battery was produced in the same manner as in Example 8 except that the solvent of the nonaqueous electrolyte was changed to a mixture of ethylene carbonate (EC) and MBL at a volume ratio of 3: 7.

Example 13
A non-aqueous secondary battery was produced in the same manner as in Example 8, except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the non-aqueous electrolyte.

Example 14
A non-aqueous secondary battery was produced in the same manner as in Example 9 except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the non-aqueous electrolyte.

Example 15
A non-aqueous secondary battery was produced in the same manner as in Example 13 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 16
A non-aqueous secondary battery was produced in the same manner as in Example 14 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 17
A nonaqueous secondary battery was prepared in the same manner as in Example 9 except that a coating layer having a thickness of 1 μm per side was formed on both sides of an aluminum foil as a positive electrode current collector before forming the positive electrode mixture layer. Produced. In addition, the said coating layer on a positive electrode electrical power collector is a coating liquid which mixed the water dispersion containing acetylene black: 59 mass parts, acrylic resin: 40 mass parts as a binder, and PVP: 1 mass part as a dispersing agent. Formed using.

Example 18
A nonaqueous secondary battery was produced in the same manner as in Example 17 except that the thickness of the coat layer on the surface of the positive electrode current collector was changed to 10 μm.

Example 19
The solvent of the non-aqueous electrolyte was changed to a mixture of EC and diethyl carbonate (DEC) at a volume ratio of 3: 7, and VC was added to the non-aqueous electrolyte in an amount of 2.5% by mass. Produced a non-aqueous secondary battery in the same manner as in Example 8.

Comparative Example 2
A nonaqueous secondary battery was produced in the same manner as in Example 8 except that the binder of the positive electrode mixture layer was changed to PVDF at the time of producing the positive electrode.

For each of the nonaqueous secondary batteries of Examples 8 to 19 and Comparative Example 2, the following evaluations were made after measuring the rated capacity under the above conditions.

<High output characteristics evaluation (maximum discharge pulse current measurement)>
For each of the batteries of Examples 8 to 19 and Comparative Example 2, constant current charging was performed at room temperature (25 ° C.) until the current value of 1C reached 3.85 V, and then the current value decreased to 0.1 C. After performing a constant voltage charge at 3.85 V, the battery was discharged at a current value of 5 C for 10 seconds, and a voltage ΔV reduced in 10 seconds from the start of discharge was measured.

Further, each battery is sequentially subjected to constant current-constant voltage charging under the above conditions and constant current discharge for 10 seconds at each current value of 10C, 20C, 30C, 40C, and 50C to obtain ΔV at each current value. Was measured in the same manner, and ΔV at each current value was plotted. The plotted points are arranged almost on a straight line, and the current value at the point where the straight line intersects the line of ΔV = 1.3 V is defined as the maximum discharge pulse current. When the maximum discharge pulse current exceeded 50 C, the current value was calculated by extending the straight line of the plot.

<High temperature storage characteristics evaluation>
For each of the batteries of Examples 8 to 19 and Comparative Example 2, constant current charging was performed at room temperature (25 ° C.) until the current value of 1C reached 3.85 V, and then the current value decreased to 0.1 C. After performing constant voltage charging at 3.85 V, constant current discharging was performed at a current value of 1 C until the battery voltage reached 2.0 V, and the discharge capacity (initial capacity) was measured.

Next, each battery subjected to constant current-constant voltage charging under the same conditions as the initial capacity measurement was stored in a constant temperature bath at 100 ° C. for 48 hours. Then, each battery was taken out from the thermostat, and after returning to room temperature, thickness was measured and the increase rate (%) of the thickness after high temperature storage was calculated | required from the comparison with the thickness before storage.

For each battery whose thickness was measured, after performing constant current discharge at 1 C until the battery voltage reached 2.0 V, constant current-constant voltage charging and constant current discharging were performed under the same conditions as at the initial capacity measurement. The discharge capacity (recovery capacity) was measured. A value obtained by dividing the obtained recovery capacity by the initial capacity was expressed as a percentage to obtain a capacity recovery rate.

Table 2 shows the configurations of the nonaqueous electrolyte solutions according to the nonaqueous secondary batteries of Examples 8 to 19 and Comparative Example 2, and Table 3 shows the evaluation results.

As shown in Table 3, the nonaqueous secondary batteries of Examples 8 to 19 using an olivine type compound as a positive electrode active material and using a positive electrode containing a specific binder were comparative examples using PVDF as the positive electrode binder. Compared with the battery No. 2, the maximum discharge pulse current value was large and the output characteristics were excellent.

In addition, the non-aqueous secondary batteries of Examples 8 to 18 using specific lactones as the non-aqueous electrolyte solvent have a general solvent configuration (combination of chain carbonate and cyclic carbonate) in the non-aqueous secondary battery. Thus, the capacity recovery rate after high-temperature storage was higher than that of the non-aqueous secondary battery of Example 19 and the rate of increase in thickness was small, and the battery was excellent in high-temperature storage characteristics.

Example 20
As in Example 8, except that a nonwoven fabric (average pore diameter: 0.8 μm, thickness: 25 μm, porosity: 55%) composed of polyethylene nanofibers (average fiber diameter 500 nm) was used as the separator. Three types of non-aqueous secondary batteries were prepared.

Example 21
A nonaqueous secondary battery was produced in the same manner as in Example 20, except that the positive electrode current collector was changed to the aluminum foil having a plurality of through holes used in Example 3.

Example 22
Non-aqueous secondary as in Example 20, except that a coating layer having a thickness of 0.3 μm per side was formed on both sides of the aluminum foil as the positive electrode current collector before forming the positive electrode mixture layer. A battery was produced. In addition, the said coating layer on a positive electrode electrical power collector is a coating liquid which mixed the water dispersion containing acetylene black: 59 mass parts, acrylic resin binder: 40 mass parts, and polyvinylpyrrolidone: 1 mass part as a dispersing agent. Formed using.

Example 23
The non-aqueous electrolyte was changed to one prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate, diethyl carbonate and α-methyl-γ-butyrolactone were mixed at a volume ratio of 30:20:50. A nonaqueous secondary battery was fabricated in the same manner as in Example 20 except that.

Example 24
In the same manner as in Example 20, three types of non-aqueous secondary batteries having different average pore diameters of the nonwoven fabric were produced. The average pore diameter of the used nonwoven fabric is three types of 0.008 μm, 0.8 μm and 2 μm.

For each of the nonaqueous secondary batteries of Examples 20 to 24 and Example 8, the rated capacity was measured under the above conditions, and the following evaluations were made.

<Charge / discharge characteristics evaluation>
Under the same conditions as the above-mentioned rated capacity measurement, each battery was charged until the SOC reached 100%, and then the voltage drop was measured when discharged at a predetermined current value (2C, 5C, 20C and 50C) for 10 seconds. did.

Moreover, about each battery, it discharged until the charge depth became 0% on the same conditions as the time of the said rated capacity measurement, and the voltage rise when charging for 10 seconds with a predetermined current value (2C, 5C, 20C and 40C) It was measured.

<High temperature storage characteristics evaluation>
For each of the batteries of Examples 20 to 24 and Example 8, each battery was charged until the SOC reached 100% under the same conditions as those for the rated capacity measurement. Next, each battery after charging was stored in a constant temperature bath at 100 ° C. for 48 hours, allowed to cool at room temperature for 2 hours, and then subjected to constant current discharge (discharge end voltage: 1.5 V) at 0.1 mA / cm ^2. The discharge capacity (maintenance capacity) was measured.

Furthermore, for each battery, after performing constant current-constant voltage charging (charge end current: 0.01 mA / cm ² ) under the above conditions, constant current discharge (discharge end voltage: 1.5 V) at 0.2 mA / cm ² was performed. ) And the discharge capacity (recovery capacity) was measured.

The ratio between the maintenance capacity (mAh) and the rated capacity was defined as a capacity maintenance ratio, and the ratio between the recovery capacity (mAh) and the rated capacity was determined as a capacity recovery ratio, and the high-temperature storage characteristics of each battery were evaluated.

<Charge / discharge cycle characteristics evaluation>
For each of the batteries of Examples 20 to 24 and Example 8, constant current-constant voltage charging with a constant current of 1 mA / cm ² and a constant voltage of 3.85 V under an environment of 50 ° C. (end-of-charge current: 0.01 mA) / Cm ² ) and a 1 mA / cm ² constant current discharge (end-of-discharge voltage: 1.5 V) is repeated 1000 cycles, and the discharge capacity at the 1000th cycle relative to the discharge capacity at the 1st cycle. The ratio was defined as the capacity maintenance rate.

The evaluation results for the batteries of Examples 20 to 23 are shown in Tables 4 and 5, and the evaluation results for the battery of Example 24 are shown in Tables 6 and 7.

As shown in Tables 4 and 5, the non-aqueous secondary batteries of Examples 20 to 23 using nonwoven fabrics having appropriate average pore diameters as separators are the batteries of Example 8 using general-purpose polyethylene microporous films. As a result, the battery resistance can be lowered, and a battery having excellent output characteristics that can cope with both discharging with a large current and charging with a large current can be constructed. In addition, in the batteries of Examples 20 to 23, a short circuit due to lithium dendrite precipitation during charging did not occur, and excellent results in high temperature storage characteristics and charge / discharge cycle characteristics were obtained.

As is clear from the results of Example 24 shown in Tables 6 and 7, when a nonwoven fabric is used as the separator of the nonaqueous secondary battery of the present invention, if the average pore diameter is too large, lithium dendrite precipitation is caused. Since the output characteristics are liable to deteriorate if the average pore diameter is too small, the nonwoven fabric preferably has an average pore diameter of 0.1 to 1 μm.

Example 25
<Binder composition>
Butadiene: 6 parts by mass, styrene, 11.5 parts by mass, methyl methacrylate: 3.5 parts by mass, acrylic acid: 0.5 parts by mass and itaconic acid: 2.5 parts by mass, sodium dodecylbenzenesulfonate: 0 Together with 1 part by weight, potassium persulfate: 1 part by weight, sodium bisulfite: 0.5 part by weight, α-methylstyrene dimer: 0.2 part by weight, dodecyl mercaptan: 0.1 part by weight and water: 200 parts by weight The mixture was put into an autoclave and reacted at 70 ° C. for 2 hours. Furthermore, butadiene: 31.5 parts by mass, styrene, 31.5 parts by mass, methyl methacrylate: 8 parts by mass, acrylonitrile: 4 parts by mass, acrylic acid: 0.5 parts by mass and itaconic acid: 0.5 parts by mass , Slowly added over 6 hours to react. Three hours after the start of the addition of the above components, 0.5 part by mass of α-methylstyrene dimer and 0.1 part by mass of dodecyl mercaptan were added, and after the addition of all the components was completed, the reaction temperature was raised to 80 ° C. The mixture was further reacted for 2 hours. Next, the pH of the composition after completion of the reaction is adjusted to 7.5, and the remaining monomer component is treated by steam distillation, whereby a polymer having a unit represented by the general formula (1) in the molecule (A ) Containing the binder B2 for the positive electrode mixture layer was synthesized.

<Preparation of positive electrode>
A belt-like positive electrode was produced in the same manner as in Example 8 except that the binder B2 was used for the preparation of the positive electrode mixture-containing composition and the binder of the positive electrode mixture layer was changed to B2.

<Battery assembly>
A nonaqueous secondary battery was produced in the same manner as in Example 8 except that the positive electrode was used.

Example 26
A nonaqueous secondary battery was produced in the same manner as in Example 25 except that the positive electrode current collector was changed to the aluminum foil having a plurality of through holes used in Example 3.

Example 27
Nonaqueous secondary as in Example 25, except that a coating layer having a thickness of 0.3 μm per side was formed on both sides of the aluminum foil as the positive electrode current collector before forming the positive electrode mixture layer. A battery was produced. In addition, the said coating layer on a positive electrode electrical power collector is a coating liquid which mixed the water dispersion containing acetylene black: 59 mass parts, acrylic resin binder: 40 mass parts, and polyvinylpyrrolidone: 1 mass part as a dispersing agent. Formed using.

Example 28
Implementation was conducted except that the conductive assistant for the positive electrode was changed to acetylene black: 2.5 parts by mass, graphite: 1.5 parts by mass, and carbon nanotubes (average length 2 μm, average diameter 10 nm): 1 part by mass. A nonaqueous secondary battery was produced in the same manner as in Example 25.

Example 29
The non-aqueous electrolyte was changed to one prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which ethylene carbonate, diethyl carbonate and α-methyl-γ-butyrolactone were mixed at a volume ratio of 30:20:50. A nonaqueous secondary battery was fabricated in the same manner as in Example 25 except that.

<Evaluation of storage stability of positive electrode mixture-containing composition>
For the positive electrode mixture-containing composition used for forming the positive electrode mixture layer of the positive electrode according to the nonaqueous secondary battery of Example 1, Example 25 and Comparative Example 1, the presence or absence of thickening after 12 hours from the preparation was observed. did. As a result of observation, the positive electrode mixture-containing composition according to Example 25 using a binder that does not contain a vinylidene fluoride unit in the molecule does not increase in viscosity even after 12 hours from preparation, and fluidity is maintained. And had good storage stability.

On the other hand, the positive electrode mixture-containing composition according to Example 1 using the binder synthesized in the coexistence of PVDF and the positive electrode mixture-containing composition according to Comparative Example 1 using PVDF as the binder were 12 hours after preparation. Later, it thickened and lost its fluidity.

From the above results, the formation of the positive electrode mixture layer of the positive electrode according to the nonaqueous secondary battery of the present invention does not contain a fluorine-containing ethylenic unit such as vinylidene fluoride or the proportion thereof from the viewpoint of productivity. It is desirable to use a binder with a small amount.

For each of the nonaqueous secondary batteries of Examples 25 to 29, the rated capacity was measured under the above conditions, and then the following evaluation was performed.

The evaluation results are shown in Table 8 together with the evaluation results of the battery of Example 8 described above.

As shown in Table 8, the lithium iron phosphate which is an olivine type compound is used as a positive electrode active material, and the positive electrode mixture layer contains a polymer (A) having a unit represented by the general formula (1) in the molecule. In addition, the non-aqueous secondary batteries of Examples 25 to 29 using the binder B2 that does not contain the fluorine-containing ethylenic unit, when charged with a large current compared to the battery of Example 8 using the binder B1, In any of the discharges, the DCR value could be further reduced, and even more excellent output characteristics were exhibited.

Example 30
<Preparation of non-aqueous electrolyte>
LiPF ₆ is dissolved at a concentration of 1.2 mol / L in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7, and further vinylene carbonate (2.5% by mass) VC) and 1.0% by mass of phosphoric acid (tris) trimethylsilyl were added to prepare a non-aqueous electrolyte.

<Battery assembly>
A nonaqueous secondary battery was produced in the same manner as in Example 8 except that the nonaqueous electrolyte was used.

Example 31
The non-aqueous electrolyte solution was changed to a mixture of propylene carbonate (PC) and α-methyl-γ-butyrolactone (MBL) at a volume ratio of 3: 7 in the same manner as in Example 30. A secondary battery was produced.

Example 32
A non-aqueous secondary battery was prepared in the same manner as in Example 30 except that the solvent of the non-aqueous electrolyte was changed to a mixture of PC, MBL, and ethyl methyl carbonate (EMC) at a volume ratio of 3: 5: 2. Produced.

Example 33
A nonaqueous secondary battery was fabricated in the same manner as in Example 30, except that LiBF ₄ was used in an amount that would give a concentration of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the nonaqueous electrolyte.

Example 34
A non-aqueous secondary battery was produced in the same manner as in Example 31 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 35
A non-aqueous secondary battery was produced in the same manner as in Example 32 except that LiBF ₄ was used in an amount of 1.0 mol / L instead of LiPF ₆ as the lithium salt of the non-aqueous electrolyte.

Example 36
A non-aqueous secondary battery was produced in the same manner as in Example 30 except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the non-aqueous electrolyte.

Example 37
A non-aqueous secondary battery was produced in the same manner as in Example 31 except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the non-aqueous electrolyte.

Example 38
A nonaqueous secondary battery was fabricated in the same manner as in Example 32, except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the nonaqueous electrolyte.

Example 39
A nonaqueous secondary battery was produced in the same manner as in Example 33 except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the nonaqueous electrolyte.

Example 40
A nonaqueous secondary battery was produced in the same manner as in Example 34, except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the nonaqueous electrolytic solution.

Example 41
A nonaqueous secondary battery was produced in the same manner as in Example 35, except that LiBOB was further added in an amount of 0.03 mol / L as the lithium salt of the nonaqueous electrolyte.

Example 42
A nonaqueous secondary battery was produced in the same manner as in Example 30, except that the amount of phosphoric acid (tris) trimethylsilyl added in the nonaqueous electrolytic solution was changed to 0.1% by mass.

Comparative Example 3
LiNi _0.5 Co _0.2 Mn _0.3 O _{2 as} positive electrode active material: 93.7 parts by mass, acetylene black as conductive aid: 4.0 parts by mass, and PVDF as a binder at 2.0 A positive electrode was prepared in the same manner as in Example 8 except that a positive electrode mixture-containing composition was prepared by mixing 0.3 part by mass of polyvinyl pyrrolidone (PVP) as a dispersant with 0.3 part by mass and NMP. .

A nonaqueous secondary battery was produced in the same manner as in Example 30 except that this positive electrode was used.

For the nonaqueous secondary batteries of Example 19, Examples 30 to 42, and Comparative Example 3, the following evaluations were performed after measuring the rated capacity under the above conditions.

In addition, about the positive electrode used for the assembly of the non-aqueous secondary battery of each said Example and the comparative example 3, the moisture content of the positive mix layer calculated | required by the said method is each Example: 1480 ppm and comparative example 3: 370 ppm. The water content of each non-aqueous secondary battery as a whole was 1960 ppm for each example and 850 ppm for Comparative Example 3.

<High temperature storage characteristics evaluation>
Each battery after the rated capacity measurement is charged at a constant current at room temperature (25 ° C.) until the current value reaches 1.85 V at a current value of 1 C, and then constant at 3.85 V until the current value decreases to 0.1 C. After voltage charging, constant current discharge was performed at a current value of 1 C until the battery voltage reached 2.0 V, and the discharge capacity (initial capacity) was measured.

Next, each battery subjected to constant current-constant voltage charging under the same conditions as the initial capacity measurement was stored in a constant temperature bath at 100 ° C. for 48 hours. Then, each battery was taken out from the thermostat and returned to room temperature, and then a constant current discharge was performed at 1 C until the battery voltage reached 2.0V. Further, constant current-constant voltage charging and constant current discharging were performed under the same conditions as those for initial capacity measurement, and the discharge capacity (recovery capacity) was measured. A value obtained by dividing the obtained recovery capacity by the initial capacity was expressed as a percentage to obtain a capacity recovery rate.

<Charge / discharge characteristics evaluation>
The non-aqueous secondary batteries of Example 30, Example 33 to 36, Example 40 to 41 and Example 19 after the rated capacity measurement were subjected to constant current-constant voltage charging under the same conditions as at the initial capacity measurement. Thereafter, constant current discharge was performed at a current value of 0.1 C until the battery voltage reached 2.0 V, and the discharge capacity (0.1 C discharge capacity) was measured. Next, after performing constant current-constant voltage charging under the same conditions as described above, constant current discharge was performed at a current value of 10 C until the battery voltage reached 2.0 V, and the discharge capacity (10 C discharge capacity) was measured.

Further, the battery after the measurement was subjected to constant current discharge at a current value of 0.1 C until the battery voltage reached 2.0 V, and then the battery voltage was adjusted to 3.85 V at a current value of 0.1 C. Current charging was performed, and the charging capacity (0.1 C charging capacity) was measured. Subsequently, constant current discharge was performed at a current value of 0.1 C until the voltage reached 2.0 V, and then constant current charging was performed until the battery voltage reached 3.85 V at a current value of 10 C. The charge capacity (10 C charge capacity) ) Was measured.

Then, the value obtained by dividing the 10C discharge capacity by the 0.1C discharge capacity (capacity ratio) and the value obtained by dividing the 10C charge capacity by the 0.1C charge capacity (capacity ratio) are expressed as percentages, respectively. evaluated.

Tables 9 and 10 show the configurations of the nonaqueous secondary batteries of Examples 30 to 42, Example 19 and Comparative Example 3, and Tables 11 and 12 show the evaluation results.

As shown in Tables 9 to 12, using a positive electrode with an appropriate amount of water (500 to 3000 ppm) in the positive electrode mixture layer, containing a phosphate compound having a group represented by the general formula (2) in the molecule The non-aqueous secondary batteries of Examples 30 to 42 using the non-aqueous electrolyte had high capacity recovery at room temperature after high-temperature storage and had excellent high-temperature storage characteristics.

In addition, the non-aqueous secondary batteries of Example 30, Examples 33 to 36, and Examples 40 to 41 using the non-aqueous electrolyte containing the phosphoric acid compound are non-aqueous electrolytes that do not contain the compound. It has an excellent charge / discharge characteristic equivalent to that of the battery of Example 19 using the above, and it can be seen that the addition of the compound can improve the high-temperature storage characteristic without causing deterioration of the charge / discharge performance. It was.

On the other hand, even when the nonaqueous electrolyte containing the phosphoric acid compound is used, the battery of Comparative Example 3 in which the positive electrode mixture layer contains too little water does not sufficiently exhibit the action of the phosphoric acid compound. The characteristics could not be improved sufficiently.

The present invention can be implemented in other forms as long as it does not depart from the spirit of the present invention. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. included.

Since the non-aqueous secondary battery of the present invention is excellent in charge / discharge characteristics at a large current, it can be suitably used for in-vehicle or industrial storage batteries by taking advantage of the above characteristics, and is conventionally known. It can also be used for the same applications as non-aqueous secondary batteries such as lithium ion secondary batteries.

DESCRIPTION OF SYMBOLS 1 Non-aqueous secondary battery 2 Laminate film exterior 3 Positive electrode external terminal 4 Negative electrode external terminal 5 Positive electrode 6 Negative electrode 7 Separator 10 Positive electrode 11 Positive electrode mixture layer 12 Positive electrode collector 13 Tab part 20 Negative electrode 21 Negative electrode mixture layer 22 Negative electrode collection Electrical body 23 Tab portion 100 Non-aqueous secondary battery 101 Metal laminate film exterior body 102 Laminated electrode body 103 Positive electrode external terminal 104 Negative electrode external terminal

Claims

A positive electrode having a positive electrode mixture layer containing a positive electrode active material, a binder and a conductive additive on one or both sides of the current collector;
A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder on one or both sides of a current collector;
A non-aqueous secondary battery comprising a separator and a non-aqueous electrolyte containing a lithium salt and an organic solvent,
The positive electrode mixture layer contains an olivine-type compound as the positive electrode active material and a polymer (A) having a unit represented by the following general formula (1) in the molecule as the binder. Non-aqueous secondary battery characterized by.

[In the general formula (1), R 1 represents H or a methyl group, and R 2 represents an alkyl group having 1 to 18 carbon atoms. ]
The non-aqueous secondary battery according to claim 1, wherein the olivine type compound has a surface coated with a carbon material.
The non-aqueous secondary battery according to claim 1 or 2, wherein the content of the polymer (A) in the positive electrode mixture layer is 1 mass% or more and 7 mass% or less.
The nonaqueous secondary battery according to any one of claims 1 to 3, wherein the olivine type compound has a BET specific surface area of 5 m 2 / g or more.
The non-aqueous secondary battery according to any one of claims 1 to 4, wherein the olivine type compound has a BET specific surface area of 25 m 2 / g or less.
The non-aqueous secondary according to any one of claims 1 to 5, wherein the current collector is a metal foil having a plurality of through-holes, or a metal foil having a coating layer containing a carbon material on a surface thereof. battery.
The positive electrode mixture layer contains, as the conductive auxiliary agent, at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphite, and at least one of acetylene black and carbon black. Item 7. The nonaqueous secondary battery according to any one of Items 1 to 6.
The nonaqueous secondary battery according to any one of claims 1 to 7, wherein the negative electrode mixture layer contains at least one of graphitizable carbon and non-graphitizable carbon as the negative electrode active material.
The non-aqueous secondary battery according to any one of claims 1 to 8, wherein the separator has a nonwoven fabric having an average pore diameter of 0.1 to 1 µm.
The non-aqueous secondary battery according to claim 9, wherein the nonwoven fabric is formed of nanofibers having an average fiber diameter of 1 μm or less.
The nonaqueous secondary battery according to any one of claims 1 to 10, wherein the nonaqueous electrolytic solution contains a phosphoric acid compound having a group represented by the following general formula (2) in the molecule.

[In the general formula (2), X represents Si, Ge or Sn, and R 3 , R 4 and R 5 each independently represents an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms. Alternatively, it represents an aryl group having 6 to 10 carbon atoms, and part or all of the hydrogen atoms may be substituted with fluorine. ]
The non-aqueous secondary battery according to claim 11, wherein the content of the phosphoric acid compound having a group represented by the general formula (2) in the molecule in the non-aqueous electrolyte is 7% by mass or less.
The non-aqueous secondary battery according to claim 1, wherein the non-aqueous electrolyte contains a lactone having a substituent at the α-position.
The nonaqueous secondary battery according to any one of claims 1 to 13, wherein the nonaqueous electrolyte contains LiBF 4 or LiBOB.
A positive electrode having a positive electrode mixture layer containing a positive electrode active material, a binder and a conductive additive on one or both sides of the current collector;
A negative electrode having a negative electrode mixture layer containing a negative electrode active material and a binder on one or both sides of a current collector;
A method for producing a non-aqueous secondary battery comprising a separator and a non-aqueous electrolyte containing a lithium salt and an organic solvent,
A positive electrode having a moisture content of 500 to 3000 ppm in the positive electrode mixture layer and a nonaqueous electrolytic solution containing a phosphoric acid compound having a group represented by the following general formula (2) in the molecule are provided inside the outer package. A method for producing a non-aqueous secondary battery, characterized by enclosing.

[In the general formula (2), X represents Si, Ge or Sn, and R 3 , R 4 and R 5 each independently represents an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms. Alternatively, it represents an aryl group having 6 to 10 carbon atoms, and part or all of the hydrogen atoms may be substituted with fluorine. ]
The method for producing a non-aqueous secondary battery according to claim 15, wherein the positive electrode mixture layer contains an olivine type compound as the positive electrode active material.