WO2020203149A1

WO2020203149A1 - Secondary battery

Info

Publication number: WO2020203149A1
Application number: PCT/JP2020/010907
Authority: WO
Inventors: 斎藤　緑; 堀内　博志; 伸之岩根; 拓樹橋本; 将之井原
Original assignee: 株式会社村田製作所
Priority date: 2019-03-29
Filing date: 2020-03-12
Publication date: 2020-10-08

Abstract

This secondary battery comprises: a positive electrode that contains a fluorine-containing polymer compound having a melting point of at most 166°C; a negative electrode; and an electrolytic solution containing at least one of a hydroxytoluene compound, a hydroxyanisole compound, and a phosphorous acid compound in an amount of the at least one of a hydroxytoluene compound, a hydroxyanisole compound, and a phosphorous acid compound of 0.0001 mass% to 0.1 mass%.

Description

Rechargeable battery

This technology relates to a secondary battery equipped with an electrolytic solution together with a positive electrode and a negative electrode.

Various electronic devices such as mobile phones are widespread. For this reason, a secondary battery is being developed as a power source that is compact and lightweight and can obtain a high energy density. This secondary battery includes an electrolytic solution together with a positive electrode and a negative electrode, and the positive electrode contains a positive electrode binder and the like together with a positive electrode active material.

Since the configuration of the secondary battery affects the battery characteristics, various studies have been made on the configuration of the secondary battery. Specifically, in order to improve the safety of the secondary battery, a fluorine-based binder having a melting point of 166 ° C. or lower is used as the positive electrode binder (see, for example, Patent Document 1). Further, in order to prevent thermal runaway at the time of abnormality, antioxidants such as phenolic antioxidants and phosphite antioxidants are used as additives for the electrolytic solution (see, for example, Patent Document 2). ).

JP-A-2018-152293 JP-A-10-247517

Electronic devices equipped with secondary batteries are becoming more sophisticated and multifunctional. For this reason, the frequency of use of electronic devices is increasing, and the usage environment of electronic devices is expanding. Therefore, there is still room for improvement in the battery characteristics of the secondary battery.

This technology was made in view of such problems, and its purpose is to provide a secondary battery capable of obtaining excellent battery characteristics.

The secondary battery of one embodiment of the present technology includes a positive electrode containing a fluorine-containing polymer compound having a melting point of 166 ° C. or lower, a negative electrode, a hydroxytoluene compound represented by the following formula (1), and the following formula ( It contains at least one of a hydroxyanisole compound represented by 2) and a phosphorous acid compound represented by the following formula (3), and at least one of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound. It includes an electrolytic solution having a content of one type of 0.0001% by mass or more and 0.1% by mass or less.

(Each of R1 to R4 is one of a hydrogen group and an alkyl group. However, at least two of R1 to R4 are tertiary alkyl groups.)

(Each of R5 to R8 is one of a hydrogen group and an alkyl group. However, at least one of R5 to R8 is a tertiary alkyl group.)

(Each of R9 to R13 is either a hydrogen group or an alkyl group.)

According to the secondary battery of one embodiment of the present technology, the positive electrode binder of the positive electrode contains a fluorine-containing polymer compound having a melting point of 166 ° C. or lower, and the electrolytic solution is a hydroxytoluene compound, a hydroxyanisole compound and phosphorous acid. It contains at least one of the compounds, and the content of at least one of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound in the electrolytic solution is within the above range. Therefore, excellent battery characteristics can be obtained.

Note that the effect of the present technology is not necessarily limited to the effect described here, and may be any effect of a series of effects related to the present technology described later.

It is a perspective view which shows the structure of the secondary battery of one Embodiment of this technique. It is sectional drawing which enlarges and shows the structure of the wound electrode body shown in FIG. It is sectional drawing which shows the structure of the secondary battery (winding electrode body) of the modification 1. FIG.

Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of explanation is as follows.

1. 1. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Modification example 3. Applications for secondary batteries

<1. Rechargeable battery ＞
First, the secondary battery of one embodiment of the present technology will be described.

As will be described later, the secondary battery described here is a lithium ion secondary battery whose battery capacity can be obtained by using the occlusion and release of lithium (lithium ion), and includes an electrolytic solution together with a positive electrode and a negative electrode. In this secondary battery, for example, in order to prevent lithium metal from depositing on the surface of the negative electrode during charging, the electrochemical capacity per unit area of the negative electrode is larger than the electrochemical capacity per unit area of the positive electrode. It has become.

<1-1. Configuration>
FIG. 1 shows the perspective configuration of the secondary battery, and FIG. 2 shows an enlarged cross-sectional configuration of the wound electrode body 10 shown in FIG. However, FIG. 1 shows a state in which the wound electrode body 10 and the exterior member 20 are separated from each other, and FIG. 2 shows only a part of the wound electrode body 10.

In this secondary battery, for example, as shown in FIG. 1, a battery element (wound electrode body 10) is housed inside a film-like exterior member 20 having flexibility (or flexibility). A positive electrode lead 11 and a negative electrode lead 12 are connected to the wound electrode body 10. That is, the secondary battery shown in the figure is a so-called laminated film type secondary battery.

[Exterior member]
As shown in FIG. 1, the exterior member 20 is, for example, a single film that can be folded in the direction of the arrow R, and has a recess 20U for accommodating the wound electrode body 10. The exterior member 20 may be a polymer film, a metal foil, or a laminated film in which a polymer film and a metal foil are laminated on each other. Of these, a laminated film is preferable. This is because sufficient sealing property and sufficient durability can be obtained.

Specifically, the exterior member 20 is, for example, a laminated film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order from the inside, and in the exterior member 20, for example, the outside of the fusion layer. The peripheral edges are fused to each other. The fused layer is, for example, a polypropylene film or the like. The metal layer is, for example, an aluminum foil. The surface protective layer is, for example, a nylon film or the like.

However, the exterior member 20 may be two laminated films. In this case, for example, the outer peripheral edges of the fusion layer are fused to each other. Regardless of whether the number of laminated films is one or two, the outer peripheral edges of the fused layer may be bonded to each other via an adhesive.

For example, the adhesion film 31 is inserted between the exterior member 20 and the positive electrode lead 11, and the adhesion film 32 is inserted between the exterior member 20 and the negative electrode lead 12, for example. Each of the

adhesive films

31 and 32 is, for example, a polypropylene film or the like.

[Wound electrode body]
As shown in FIGS. 1 and 2, for example, the wound electrode body 10 includes an electrolytic solution which is a liquid electrolyte together with a positive electrode 13, a negative electrode 14, and a separator 15. In the wound electrode body 10, for example, the positive electrode 13 and the negative electrode 14 are laminated with each other via the separator 15, and the positive electrode 13, the negative electrode 14 and the separator 15 are wound. The electrolytic solution is impregnated in the positive electrode 13, the negative electrode 14, and the separator 15. The surface of the wound electrode body 10 may be covered with a protective tape (not shown).

(Positive electrode)
As shown in FIG. 2, the positive electrode 13 includes, for example, a positive electrode current collector 13A and positive electrode active material layers 13B provided on both sides of the positive electrode current collector 13A. However, the positive electrode active material layer 13B may be provided on only one side of the positive electrode current collector 13A.

The positive electrode current collector 13A contains a conductive material such as aluminum. The positive electrode active material layer 13B contains a positive electrode active material and a positive electrode binder. However, the positive electrode active material layer 13B may further contain other materials such as a positive electrode conductive agent.

The positive electrode active material contains any one or more of the positive electrode materials capable of occluding and releasing lithium. The positive electrode material contains, for example, a lithium-containing compound, and the lithium-containing compound is a compound containing one or more kinds of transition metal elements as constituent elements together with lithium. The type of the lithium-containing compound is not particularly limited, and examples thereof include a lithium composite oxide and a lithium phosphoric acid compound. Specifically, the layered rock salt type lithium composite oxides are, for example, LiNiO ₂ , LiCoO ₂ , LiCo _0.98 Al _0.01 Mg _0.01 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , Li _1.2 Mn _0.52 Co _0.175 Ni _0.1 O ₂ and Li _1.15 (Mn _0.65 Ni _0.22 Co _0.13 ) O ₂ . The spinel-type lithium composite oxide is, for example, LiMn ₂ O ₄ . Olivin-type lithium phosphate compounds include, for example, LiFePO ₄ , LimnPO ₄ , Limn _0.5 Fe _0.5 PO ₄ , LiMn _0.7 Fe _0.3 PO _4, and LiMn _0.75 Fe _0.25 PO ₄ .

The positive electrode binder contains a fluorine-containing polymer compound having a melting point of 166 ° C. or lower. This fluorine-containing polymer compound is a polymer compound containing fluorine as a constituent element, and the type of the fluorine-containing polymer compound may be only one type or two or more types. This is because the affinity of the positive electrode binder with the positive electrode active material is improved, and the surface of the positive electrode active material is well coated with the positive electrode binder. As a result, the decomposition reaction of the electrolytic solution due to the reactivity of the positive electrode active material is suppressed. The lower limit of the melting point is not particularly limited, but the melting point is, for example, 150 ° C. or higher.

The melting point of this positive electrode binder (fluorine-containing polymer compound) is measured by, for example, the procedure described below. First, the positive electrode 13 is taken out from the secondary battery, and then the positive electrode active material layer 13B is recovered by peeling the positive electrode current collector 13A from the positive electrode active material layer 13B. The positive electrode active material layer 13B is a positive electrode mixture described later and contains a soluble component together with an insoluble component. The insoluble component is a positive electrode active material, a positive electrode conductive agent, and the like, and the soluble component is a positive electrode binder. Subsequently, the positive electrode mixture is added to the solvent, and then the solvent is sufficiently stirred to obtain a positive electrode mixture solution. The type of solvent is not particularly limited, but is, for example, a non-aqueous solvent (organic solvent) such as N-methyl-2-pyrrolidone. Subsequently, the insoluble component is removed from the positive electrode mixture solution by filtering the positive electrode mixture solution. Subsequently, the precipitate is recovered by evaporating and drying the filtered positive electrode mixture solution. This precipitate is a substance in which the soluble component in the positive electrode mixture solution is solidified, that is, a positive electrode binder. Finally, the melting point (° C.) of the precipitate is measured by analyzing the precipitate (fluorine-containing polymer compound which is a positive electrode binder) using differential scanning calorimetry (DSC).

The type of the fluorine-containing polymer compound is not particularly limited, but is, for example, a polymer using vinylidene fluoride. The polymer using this vinylidene fluoride may be a homopolymer of vinylidene fluoride (polyvinylidene fluoride), or a copolymer of vinylidene fluoride and one or more other polymer compounds. It may be. This copolymer is, for example, a copolymer of vinylidene fluoride and hexafluoropropylene.

Among them, polyvinylidene fluoride is preferable. This is because the homopolymer is less likely to swell and dissolve in the electrolytic solution than the copolymer. As a result, the homopolymer can obtain a higher binding force than the copolymer. However, a part of polyvinylidene fluoride may be modified. Specifically, a part of polyvinylidene fluoride such as a terminal may be modified with a carboxylic acid such as maleic acid.

The content of the positive electrode binder (fluorine-containing polymer compound) in the positive electrode active material layer 13 is not particularly limited, but is preferably 0.7% by mass to 2.8% by mass. This is because the positive electrode active material layer 13B is stably formed while ensuring the binding property and the coating amount.

Specifically, when the content of the fluorine-containing polymer compound is 0.7% by mass or more, the binding property between the positive electrode active materials via the positive electrode binder is improved, and the positive electrode binder is used. Since the binding property of the positive electrode active material layer 13B (positive electrode active material) to the positive electrode current collector 13A is also improved, the positive electrode active material layer 13B is less likely to fall off from the positive electrode current collector 13A. Further, since the amount of the positive electrode binder coated on the surface of the positive electrode active material is sufficiently large, the decomposition reaction of the electrolytic solution is less likely to occur on the surface of the positive electrode active material.

On the other hand, when the content of the fluorine-containing polymer compound is 2.8% by mass or less, the flexibility of the positive electrode active material layer 13B is improved. As a result, when the positive electrode 13 is wound in the step of forming the wound electrode body 10, the positive electrode 13 is less likely to crack.

When determining the content of this fluorine-containing polymer compound, for example, after recovering the above-mentioned positive electrode active material layer 13B (positive electrode mixture), the positive electrode mixture is analyzed using thermal weight measurement (TG). The content (mass%) of the positive electrode binder (fluorine-containing polymer compound) is calculated based on the weight loss.

The positive electrode binder may further contain any one or more of other materials such as synthetic rubber and other polymer compounds. However, the above-mentioned fluorine-containing polymer compound is excluded from the other polymer compounds described here. The synthetic rubber is, for example, styrene-butadiene rubber. Other polymeric compounds are, for example, polyimides and polyamides.

The positive electrode conductive agent contains, for example, any one or more of conductive materials such as carbon materials, and the carbon materials include, for example, graphite, carbon black, acetylene black, and Ketjen black. is there. However, the conductive material may be a metal material, a conductive polymer, or the like.

(Negative electrode)
As shown in FIG. 2, the negative electrode 14 includes, for example, a negative electrode current collector 14A and negative electrode active material layers 14B provided on both sides of the negative electrode current collector 14A. However, the negative electrode active material layer 14B may be provided on only one side of the negative electrode current collector 14A.

The negative electrode current collector 14A contains a conductive material such as copper. The negative electrode active material layer 14B contains any one or more of the negative electrode materials capable of occluding and releasing lithium as the negative electrode active material. However, the negative electrode active material layer 14B may further contain other materials such as a negative electrode binder and a negative electrode conductive agent.

The negative electrode material includes, for example, a carbon material and a metal-based material. Of course, the negative electrode material may contain both a carbon material and a metal-based material.

Specifically, the carbon material is, for example, easily graphitizable carbon, non-graphitizable carbon, graphite, and the like. However, the carbon material may be low crystalline carbon or amorphous carbon. The shape of the carbon material is, for example, fibrous, spherical, granular and scaly. The metal-based material is a material containing any one or more of metal elements and metalloid elements capable of forming an alloy with lithium. The metal-based material may be a simple substance, an alloy, a compound such as an oxide, a mixture of two or more kinds thereof, or a material containing one kind or two or more kinds of phases thereof. Good. Further, the metal-based material may contain one kind or two or more kinds of non-metal elements. Specifically, metal elements and semi-metal elements include, for example, magnesium, boron, aluminum, gallium, indium, silicon, germanium, tin, lead, bismuth, cadmium, silver, zinc, hafnium, zirconium, ittrium, palladium and platinum. And so on.

The details regarding the negative electrode binder are the same as the details regarding the positive electrode binder, for example. However, the negative electrode binder may contain a fluorine-containing polymer compound, or may contain other materials such as synthetic rubber and other polymer compounds. The details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent, for example.

(Separator)
The separator 15 is interposed between the positive electrode 13 and the negative electrode 14. The separator 15 includes, for example, a porous film containing any one or more of synthetic resin and ceramic, and may be a laminated film in which two or more types of porous films are laminated to each other. The synthetic resin is, for example, polyethylene.

(Electrolytic solution)
The electrolytic solution contains an additive compound, and the additive compound contains any one or more of a hydroxytoluene compound, a hydroxyanisole compound, and a phosphorous acid compound. The type of the hydroxytoluene compound may be only one type or two or more types. The fact that the number of types may be one or more is the same for the hydroxyanisole compound and the phosphite compound.

(Additional compound: hydroxytoluene compound)
The hydroxytoluene compound is a compound represented by the following formula (1). As is clear from the formula (1), this hydroxytoluene compound is p-hydroxytoluene (p-cresol) having four substituents (R1 to R4).

As described above, each of R1 to R4 is not particularly limited as long as it is either a hydrogen group or an alkyl group. The type (number of carbon atoms) of the alkyl group is not particularly limited, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group and a decyl group.

The alkyl group may be linear or branched with one or more side chains. That is, when the alkyl group has 4 or more carbon atoms, the alkyl group may be branched as well as linear. Specifically, taking a butyl group having 4 carbon atoms as an example, the butyl group is a linear n-butyl group which is a primary alkyl group (-CH ₂ CH ₂ CH ₂ CH ₃ ). It may be a branched sec-butyl group (-CH (CH ₃ ) CH ₂ CH ₃ ) which is a secondary alkyl group, or a branched iso-butyl group (-CH (CH ₃ ) CH ₂ CH ₃ ) which is a secondary alkyl group. CH ₂ CH (CH ₃ ) ₂ ) may be used, or a branched tert-butyl group (-C (CH ₃ ) ₃ ), which is a tertiary alkyl group, may be used.

However, as described above, two or more of R1 to R4 are tertiary alkyl groups. Therefore, the hydroxytoluene compound has 2 to 4 tertiary alkyl groups. The type of the tertiary alkyl group is not particularly limited, but among them, a tertiary butyl group (tert-butyl group) is preferable. This is because steric hindrance caused by the tertiary alkyl group is less likely to occur, so that the solubility and compatibility of the hydroxytoluene compound are ensured.

The number and position of the tertiary alkyl group are not particularly limited, but among them, one of R1 and R2 is a tertiary alkyl group, and one of R3 and D4 is a third. It is preferably a primary alkyl group. This is because when the number of tertiary alkyl groups is two, steric hindrance caused by the two tertiary alkyl groups is less likely to occur.

(Additional compound: hydroxyanisole compound)
The hydroxyanisole compound is a compound represented by the following formula (2). As is clear from the formula (2), this hydroxyanisole compound is a p-hydroxyanisole having four substituents (R5 to R8).

As described above, each of R5 to R8 is not particularly limited as long as it is either a hydrogen group or an alkyl group. Details regarding the alkyl group are as described above.

However, as described above, one or more of R5 to R8 are tertiary alkyl groups. Therefore, the hydroxyanisole compound has 1 to 4 tertiary alkyl groups. Details regarding the tertiary alkyl group are as described above. That is, the tertiary alkyl group is preferably a tertiary butyl group (tert-butyl group) because the solubility and compatibility of the hydroxyanisole compound are guaranteed.

The number and position of the tertiary alkyl group are not particularly limited, but it is preferable that any one of R5 to R8 is a tertiary alkyl group. This is because the steric hindrance caused by the tertiary alkyl group is minimized.

(Additional compound: Phosphorous acid compound)
The phosphorous acid compound is a compound represented by the following formula (3). As is clear from the formula (3), this phosphorous acid compound is a phosphorous acid ester having a benzene ring into which five substituents (R9 to R13) have been introduced.

(Each of R9 to R13 is either a hydrogen group or an alkyl group.)

As described above, each of R9 to R13 is not particularly limited as long as it is either a hydrogen group or an alkyl group. Details regarding the alkyl group are as described above.

Since the type of the alkyl group is not particularly limited, the alkyl group may be a primary alkyl group, a secondary alkyl group, or a tertiary alkyl group. Details regarding the tertiary alkyl group are as described above. That is, since the solubility and compatibility of the phosphorous acid compound are guaranteed, the tertiary alkyl group is preferably a tertiary butyl group (tert-butyl group).

The number and position of the tertiary alkyl group is not particularly limited. Above all, each of R9 to R13 is preferably a hydrogen group. This is because steric hindrance caused by the tertiary alkyl group does not occur. Alternatively, any two of R9 to R13 are preferably tertiary alkyl groups. This is because when the number of tertiary alkyl groups is two, steric hindrance caused by the two tertiary alkyl groups is less likely to occur.

In particular, when any two of R9 to R13 are tertiary alkyl groups, it is preferable that the two tertiary alkyl groups are not adjacent to each other. That is, for example, when R9 is a tertiary alkyl group, R10 located next to R9 is not a tertiary alkyl group, and among R11 to R13 not located next to R9. Is preferably a tertiary alkyl group. This is because steric hindrance caused by the two tertiary alkyl groups is less likely to occur.

(Specific examples of added compounds)
Specifically, the hydroxytoluene compound is, for example, a compound represented by each of the following formulas (1-1) and (1-2). The compounds represented in each of the formulas (1-1) and (1-2) have, for example, two tertiary alkyl groups (tert-butyl groups).

The hydroxyanisole compound is, for example, a compound represented by each of the following formulas (2-1) and (2-2). The compounds represented by the formulas (2-1) and (2-2) respectively have, for example, one tertiary alkyl group (tert-butyl group).

The phosphorous acid compound is, for example, a compound represented by each of the following formulas (3-1) and (3-2). The compound represented by the formula (3-1) does not have a tertiary alkyl group. The compound represented by the formula (3-2) has two tertiary alkyl groups for each benzene ring.

(Content of added compound)
However, the content of the added compound in the electrolytic solution is 0.0001% by mass to 0.1% by mass. When the electrolytic solution contains any two or more of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound as the additive compound, the content of the additive compound described here is any two types. This is the sum of the above contents.

The electrolyte solution further contains, for example, a solvent and an electrolyte salt. However, the type of the solvent may be only one type or two or more types. The fact that the number of types may be one or two or more is the same for the electrolyte salt.

(solvent)
The solvent includes, for example, a non-aqueous solvent (organic solvent). The electrolytic solution containing a non-aqueous solvent is a so-called non-aqueous electrolytic solution, and the above-mentioned additive compounds (hydroxytoluene compound, hydroxyanisole compound and phosphite compound) are excluded from the solvent (non-aqueous solvent) described here. To.

The type of non-aqueous solvent is not particularly limited, and is, for example, cyclic carbonate ester, chain carbonate ester, lactone, chain carboxylic acid ester, mononitrile compound, dioxane compound and the like. Cyclic carbonates are, for example, ethylene carbonate and propylene carbonate. Chain carbonates include, for example, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. Lactones include, for example, γ-butyrolactone and γ-valerolactone. Chain carboxylic acid esters include, for example, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate and propyl propionate. Mononitrile compounds include, for example, acetonitrile, methoxyacetonitrile and 3-methoxypropionitrile. The dioxane compound is, for example, 1,3-dioxane and 1,4-dioxane.

Further, the non-aqueous solvent may be, for example, an unsaturated cyclic carbonate, a halogenated carbonate, a sulfonic acid ester, an acid anhydride, a dinitrile compound, a diisocyanate compound, a phosphoric acid ester or the like. Unsaturated cyclic carbonates are, for example, vinylene carbonate, vinyl carbonate ethylene, methylene carbonate and the like. Halogenated carbonic acid esters include, for example, 4-fluoro-1,3-dioxolane-2-one, 4,5-difluoro-1,3-dioxolane-2-one and fluoromethylmethyl carbonate. The sulfonic acid ester is, for example, 1,3-propane sultone and 1,3-propene sultone. Acid anhydrides include, for example, succinic anhydride, glutaric anhydride, maleic anhydride, ethanedisulfonic anhydride, propandisulfonic anhydride, sulfobenzoic anhydride, sulfopropionic anhydride and sulfobutyric anhydride. Dinitrile compounds include, for example, succinonitrile, glutaronitrile, adiponitrile, phthalonitrile and the like. The diisocyanate compound is, for example, hexamethylene diisocyanate. Phosphate esters include, for example, trimethyl phosphate and triethyl phosphate.

Above all, the solvent preferably contains a chain carboxylic acid ester. This is because lithium is easily occluded and released in the positive electrode active material while the decomposition reaction of the electrolytic solution is suppressed. The content of the chain carboxylic acid ester in the solvent is not particularly limited, but is preferably 10% by mass to 40% by mass. This is because lithium is sufficiently easily occluded and released in the positive electrode active material.

Further, the solvent preferably contains a halogenated carbonic acid ester such as 4-fluoro-1,3-dioxolane-2-one described above. This is because the decomposition reaction of the electrolytic solution is suppressed. The content of the halogenated carbonic acid ester in the electrolytic solution is not particularly limited, but is preferably 1% by mass to 10% by mass.

Further, the solvent preferably contains a dioxane compound such as 1,3-dioxane described above. This is because the decomposition reaction of the electrolytic solution is suppressed. The content of the dioxane compound in the electrolytic solution is not particularly limited, but is preferably 0.1% by mass to 1.5% by mass.

(Electrolyte salt)
The electrolyte salt contains, for example, a light metal salt such as a lithium salt. Specifically, the lithium salt is, for example, lithium hexafluorophosphate, lithium borate tetrafluoride, lithium hexafluorophosphate, lithium perchlorate, lithium trifluoromethanesulfonate, bis (fluorosulfonyl) imide lithium. , Bis (trifluoromethanesulfonyl) imide lithium, bis (pentafluoroethanesulfonyl) imide lithium, tris (trifluoromethanesulfonyl) methyl lithium, lithium chloride, lithium bromide, lithium fluorophosphate, lithium difluorophosphate and bis (oxalat) For example, lithium borate. The content of the electrolyte salt is not particularly limited, but is, for example, 0.3 mol / kg to 3.0 mol / kg with respect to the solvent.

[Positive lead and negative electrode lead]
The positive electrode lead 11 is connected to the positive electrode 13 (positive electrode current collector 13A) and is led out from the inside of the exterior member 20 to the outside. The positive electrode lead 11 contains a conductive material such as aluminum, and has a shape such as a thin plate or a mesh.

The negative electrode lead 12 is connected to the negative electrode 14 (negative electrode current collector 14A) and is led out from the inside of the exterior member 20 to the outside. The lead-out direction of the negative electrode lead 12 is the same as the lead-out direction of the positive electrode lead 11, for example. The negative electrode lead 12 contains a conductive material such as nickel and has a shape similar to that of the positive electrode lead 11.

<1-2. Operation>
In this secondary battery, for example, during charging, lithium ions are released from the positive electrode 13 and the lithium ions are occluded in the negative electrode 14 via an electrolytic solution. Further, in the secondary battery, for example, at the time of discharging, lithium ions are released from the negative electrode 14 and the lithium ions are occluded in the positive electrode 13 via the electrolytic solution.

<1-3. Manufacturing method>
In the case of manufacturing this secondary battery, for example, as described below, a positive electrode 13 and a negative electrode 14 are prepared and an electrolytic solution is prepared, and then the positive electrode 13, the negative electrode 14 and the electrolytic solution are used to prepare a secondary battery. Assemble the batteries.

[Preparation of positive electrode]
First, a positive electrode active material, a positive electrode binder containing a fluorine-containing polymer compound, and a positive electrode conductive agent, if necessary, are mixed with each other to obtain a positive electrode mixture. Subsequently, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to an organic solvent or the like. Finally, the positive electrode active material layer 13B is formed by applying the positive electrode mixture slurry on both sides of the positive electrode current collector 13A. After that, the positive electrode active material layer 13B may be compression-molded using a roll press or the like. In this case, the positive electrode active material layer 13B may be heated, or compression molding may be repeated a plurality of times. As a result, the positive electrode active material layers 13B are formed on both sides of the positive electrode current collector 13A, so that the positive electrode 13 is produced.

[Preparation of negative electrode]
Negative electrode active material layers 14B are formed on both sides of the negative electrode current collector 14A by the same procedure as the procedure for producing the positive electrode 13 described above. Specifically, the negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are mixed to form a negative electrode mixture, and then the negative electrode mixture is added to an organic solvent or the like to form a paste-like negative electrode mixture slurry. To prepare. Subsequently, the negative electrode active material layer 14B is formed by applying the negative electrode mixture slurry on both sides of the negative electrode current collector 14A. After that, the negative electrode active material layer 14B may be compression-molded. As a result, the negative electrode active material layers 14B are formed on both sides of the negative electrode current collector 14A, so that the negative electrode 14 is produced.

[Preparation of electrolyte]
After adding the electrolyte salt to the solvent, the added compound is added to the solvent. As the additive compound, any one or more of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound is used. As a result, the electrolyte salt is dissolved in the solvent and the added compound is dispersed or dissolved, so that the electrolytic solution is prepared. However, when preparing an electrolytic solution, the added compound is added so that the content of the added compound in the electrolytic solution is within a predetermined range (= 0.0001% by mass to 0.1% by mass). Adjust the amount.

[Assembly of secondary battery]
First, the positive electrode lead 11 is connected to the positive electrode 13 (positive electrode current collector 13A) by a welding method or the like, and the negative electrode lead 12 is connected to the negative electrode 14 (negative electrode current collector 14A) by a welding method or the like. Subsequently, the positive electrode 13 and the negative electrode 14 are laminated with each other via the separator 15, and then the positive electrode 13, the negative electrode 14 and the separator 15 are wound to form a wound body.

Subsequently, the exterior member 20 is folded so as to sandwich the wound body, and then the outer peripheral edges of the two sides of the exterior member 20 are fused to each other by using a heat fusion method or the like to form a bag. The winding body is housed inside the exterior member 20. Finally, after injecting an electrolytic solution into the bag-shaped exterior member 20, the outer peripheral edges of the remaining one side of the exterior member 20 are fused to each other by using a heat fusion method or the like. The exterior member 20 is sealed. In this case, the adhesion film 31 is inserted between the exterior member 20 and the positive electrode lead 11, and the adhesion film 32 is inserted between the exterior member 20 and the negative electrode lead 12. As a result, the wound body is impregnated with the electrolytic solution, so that the wound electrode body 10 is formed. Therefore, since the wound electrode body 10 is housed inside the exterior member 20, the secondary battery is completed.

<1-4. Actions and effects>
According to this secondary battery, the positive electrode 13 contains a fluorine-containing polymer compound having a melting point of 166 ° C. or lower. Further, the additive compound of the electrolytic solution contains any one or more of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound, and the content of the added compound in the electrolytic solution is 0.0001. It is from% by mass to 0.1% by mass. Therefore, excellent battery characteristics can be obtained for the reasons described below.

The fluorine-containing polymer compound having a melting point of 166 ° C. or lower coats the surface of the positive electrode active material thinly in a wide range as compared with the positive electrode binder having a melting point higher than 166 ° C. Therefore, the decomposition reaction of the electrolytic solution due to the reactivity of the surface of the positive electrode active material is suppressed.

On the other hand, when the potential of the positive electrode 13 becomes high, a part of the fluorine-containing polymer compound is decomposed due to the activation of the oxidation reaction on the surface of the positive electrode active material, so that the decomposition product containing fluorine is produced. appear. Since this decomposition product induces deterioration of the positive electrode active material and a redox reaction, it becomes a factor of deteriorating battery characteristics such as cycle characteristics. In particular, decomposition products are likely to be remarkably generated when the secondary battery is stored at a high temperature.

Therefore, when the electrolytic solution contains the above-mentioned predetermined amount of the added compound, the start of the oxidation reaction is suppressed on the surface of the positive electrode active material, so that the generation of decomposition products is also suppressed. Therefore, even if the secondary battery is used (charged / discharged) and stored in a high temperature environment, the oxidation reaction of the fluorine-containing polymer compound is specifically suppressed, so that the function of the fluorine-containing polymer compound is maintained. Therefore, since the decomposition reaction of the electrolytic solution is continuously suppressed, excellent battery characteristics can be obtained.

In particular, when the content of the fluorine-containing polymer compound in the positive electrode active material layer 13B is 0.7% by mass to 2.8% by mass, the binding property and the coating amount of the fluorine-containing polymer compound are guaranteed. Since the positive electrode active material layer 13B is stably formed, a higher effect can be obtained.

Further, if the fluorine-containing polymer compound contains polyvinylidene fluoride, a high binding force can be obtained, so that a higher effect can be obtained.

Further, in the formula (1) relating to the hydroxytoluene compound, if any one of R1 and R2 is a tertiary alkyl group and one of R3 and R4 is a tertiary alkyl group, 2 Since steric hindrance caused by one tertiary alkyl group is less likely to occur, a higher effect can be obtained.

Further, in the formula (2) relating to the hydroxyanisole compound, if any one of R5 to R8 is a tertiary alkyl group, the steric hindrance caused by the tertiary alkyl group is minimized, which is higher. The effect can be obtained.

Further, in the formula (3) relating to the phosphorous acid compound, if each of R9 to R13 is a hydrogen group, steric hindrance caused by the tertiary alkyl group does not occur, so that a higher effect can be obtained. Alternatively, if any two of R9 to R13 are tertiary alkyl groups, steric hindrance caused by the two tertiary alkyl groups is less likely to occur, so that a higher effect can be obtained.

Further, if the tertiary alkyl group is a tertiary butyl group, steric hindrance caused by the tertiary alkyl group is less likely to occur. Therefore, since solubility and compatibility are ensured, a higher effect can be obtained.

Further, when the solvent of the electrolytic solution contains a chain carboxylic acid ester and the content of the chain carboxylic acid ester in the solvent is 10% by mass to 40% by mass, the decomposition reaction of the electrolytic solution is suppressed. Since lithium is easily occluded and released in the positive electrode active material, a higher effect can be obtained.

Further, if the electrolytic solution contains a halogenated carbonic acid ester and the content of the halogenated carbonic acid ester in the electrolytic solution is 1% by mass to 10% by mass, the decomposition reaction of the electrolytic solution is suppressed. A higher effect can be obtained.

Further, if the electrolytic solution contains a dioxane compound and the content of the dioxane compound in the electrolytic solution is 0.1% by mass to 1.5% by mass, the decomposition reaction of the electrolytic solution is suppressed. A higher effect can be obtained.

<2. Modification example>
The configuration of the secondary battery described above can be appropriately changed as described below. However, any two or more of the series of modifications described below may be combined with each other.

[Modification 1]
FIG. 3 shows the cross-sectional configuration of the secondary battery (wound electrode body 10) of the modified example 1, and corresponds to FIG. In FIG. 2, an electrolytic solution which is a liquid electrolyte is used. For example, as shown in FIG. 3, an electrolyte layer 16 which is a gel-like electrolyte may be used instead of the electrolytic solution.

In the wound electrode body 10 using the electrolyte layer 16, for example, the positive electrode 13 and the negative electrode 14 are laminated with each other via the separator 15 and the electrolyte layer 16, and the positive electrode 13, the negative electrode 14, the separator 15 and the electrolyte layer 16 are laminated with each other. Is wound around. The electrolyte layer 16 is interposed between the positive electrode 13 and the separator 15, and is interposed between the negative electrode 14 and the separator 15, for example.

Specifically, the electrolyte layer 16 contains a polymer compound together with the electrolytic solution, and the electrolytic solution is held by the polymer compound in the electrolyte layer 16. The structure of the electrolytic solution is as described above. The polymer compound may be a homopolymer such as polyvinylidene fluoride, a copolymer such as a copolymer of vinylidene fluoride and hexafluoropyrene, or both. When forming the electrolyte layer 16, for example, a precursor solution containing an electrolytic solution, a polymer compound, an organic solvent, or the like is prepared, and then the precursor solution is applied to each of the positive electrode 13 and the negative electrode 14.

Even in this case, the same effect can be obtained because the lithium ions can move between the positive electrode 13 and the negative electrode 14 via the electrolyte layer 16.

[Modification 2]
The separator 15 may include, for example, a base material layer and polymer compound layers provided on both sides of the base material layer. However, the polymer compound layer may be provided on only one side of the base material layer.

The base material layer is, for example, the above-mentioned porous membrane. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because it has excellent physical strength and is electrochemically stable. The polymer compound layer may contain a plurality of inorganic particles. This is because when the secondary battery generates heat, heat is dissipated by a plurality of inorganic particles, so that the safety of the secondary battery is improved. The type of the inorganic particles is not particularly limited, but is, for example, insulating particles such as aluminum oxide and aluminum nitride. When forming the separator 15, for example, a precursor solution containing a polymer compound, an organic solvent, or the like is prepared, and then the precursor solution is applied to both surfaces of the base material layer.

Even in this case, since the positive electrode 13 and the negative electrode 14 are separated from each other via the separator 15, the same effect can be obtained.

<3. Applications for secondary batteries>
Secondary batteries are used in machines, devices, appliances, devices and systems (aggregates of multiple devices, etc.) that can use the secondary batteries as a power source for driving and a power storage source for storing power. If there is, there is no particular limitation. The secondary battery used as a power source may be a main power source or an auxiliary power source. The main power source is a power source that is preferentially used regardless of the presence or absence of another power source. The auxiliary power supply may be a power supply used in place of the main power supply, or may be a power supply that can be switched from the main power supply as needed. When a secondary battery is used as an auxiliary power source, the type of main power source is not limited to the secondary battery.

Specifically, the uses of the secondary battery are as follows, for example. Electronic devices (including portable electronic devices) such as video cameras, digital still cameras, mobile phones, laptop computers, cordless phones, headphone stereos, portable radios, portable TVs and portable information terminals. It is a portable household appliance such as an electric shaver. A storage device such as a backup power supply and a memory card. Power tools such as electric drills and saws. It is a battery pack that is installed in notebook computers as a removable power source. Medical electronic devices such as pacemakers and hearing aids. It is an electric vehicle such as an electric vehicle (including a hybrid vehicle). It is a power storage system such as a household battery system that stores power in case of an emergency. Of course, the use of the secondary battery may be other than the above-mentioned use.

An embodiment of this technology will be described.

(Experimental Examples 1-1 to 1-13)
As will be described below, after producing the laminated film type secondary batteries shown in FIGS. 1 and 2, the battery characteristics of the secondary batteries were evaluated.

[Making secondary batteries]
When producing the positive electrode 13, first, the positive electrode active material (lithium cobalt oxide (LiCoO ₂ )), the positive electrode binder (polyfluoride vinylidene (PVDF) which is a fluorine-containing polymer compound), and the positive electrode conductive agent are used. By mixing with (graphite), a positive electrode mixture was obtained. In this case, the mixing ratio (mass ratio) of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent was set to positive electrode active material: positive electrode binder: positive electrode conductive agent = 95: x: 5-x. The specific mixing ratio (mass%) of the positive electrode binder, that is, the content (mass%) of the positive electrode binder in the positive electrode active material layer 13B described later is as shown in Table 1. The melting point of the positive electrode binder (PVDF) is 155 ° C., as shown in Table 1. Subsequently, a positive electrode mixture was added to an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, a positive electrode mixture slurry is applied to both sides of the positive electrode current collector 13A (strip-shaped aluminum foil, thickness = 12 μm) using a coating device, and then the positive electrode mixture slurry is dried to obtain a positive electrode active material. Layer 13B was formed. Finally, the positive electrode active material layer 13B was compression-molded using a roll press machine.

When producing the negative electrode 14, first, 97 parts by mass of the negative electrode active material (graphite), 2 parts by mass of the negative electrode binder (styrene butadiene rubber), and 1 part by mass of the thickener (carboxymethyl cellulose) are mixed. By doing so, it became a negative electrode mixture. Subsequently, a negative electrode mixture was added to an aqueous solvent (pure water), and then the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, a negative electrode mixture slurry is applied to both sides of the negative electrode current collector 14A (band-shaped copper foil, thickness = 15 μm) using a coating device, and then the negative electrode mixture slurry is dried to obtain a negative electrode active material. Layer 14B was formed. Finally, the negative electrode active material layer 14B was compression-molded using a roll press machine.

When preparing the electrolytic solution, first, a solvent (ethylene carbonate as a cyclic carbonate and diethyl carbonate as a chain carbonate) was prepared. In this case, the mixing ratio (mass ratio) of the solvent was set to ethylene carbonate: diethyl carbonate = 30:70. Subsequently, an electrolyte salt (lithium hexafluorophosphate (LiPF ₆ )) was added to the solvent, and the solvent was stirred. In this case, the content of the electrolyte salt was set to 1 mol / kg with respect to the solvent. Finally, an additive compound (hydroxytoluene compound) was added to a solvent containing an electrolyte salt, and then the solvent was stirred. The types of the hydroxytoluene compounds and the content (% by mass) of the hydroxytoluene compounds in the electrolytic solution are as shown in Table 1.

In this case, for comparison, the electrolytic solution was prepared by the same procedure except that the added compound (hydroxytoluene compound) was not used. Further, for comparison, an electrolytic solution was prepared by the same procedure except that another compound was used instead of the hydroxytoluene compound. The other compound is a compound (phenol) represented by the following formula (4-1).

When assembling the secondary battery, first, the positive electrode lead 11 made of aluminum was welded to the positive electrode current collector 13A, and the negative electrode lead 12 made of copper was welded to the negative electrode current collector 14A. Subsequently, the positive electrode 13 and the negative electrode 14 were laminated with each other via the separator 15 (microporous polyethylene film, thickness = 15 μm) to obtain a laminated body. Subsequently, after winding the laminate, a protective tape was attached to the surface of the laminate to obtain a wound.

Subsequently, after folding the exterior member 20 so as to sandwich the wound body, the outer peripheral edges of the two sides of the exterior member 20 were heat-sealed to each other. As the exterior member 20, a fusion layer (polypropylene film, thickness = 30 μm), a metal layer (aluminum foil, thickness = 40 μm), and a surface protective layer (nylon film, thickness = 25 μm) are formed from the inside. An aluminum laminate film laminated in order was used. In this case, the adhesion film 31 (polypropylene film, thickness = 5 μm) is inserted between the exterior member 20 and the positive electrode lead 11, and the adhesion film 32 (polypropylene film) is inserted between the exterior member 20 and the negative electrode lead 12. , Thickness = 5 μm) was inserted.

Finally, after injecting the electrolytic solution into the exterior member 20, the outer peripheral edges of the remaining one side of the exterior member 20 were heat-sealed in a reduced pressure environment. As a result, the wound body was impregnated with the electrolytic solution, so that the wound electrode body 10 was formed and the wound electrode body 10 was sealed inside the exterior member 20. Therefore, the laminated film type secondary battery was completed.

[Evaluation of battery characteristics]
When the battery characteristics (initial charge / discharge characteristics, normal temperature cycle characteristics and high temperature cycle characteristics) of the secondary battery were evaluated, the results shown in Table 1 were obtained.

When examining the initial charge / discharge characteristics, the secondary battery was charged / discharged for one cycle in a room temperature environment (temperature = 23 ° C.) in order to stabilize the state of the secondary battery. After that, the discharge capacity (initial capacity) was measured by charging and discharging the secondary battery for one cycle in the same environment. The value of the initial capacity shown in Table 1 shows a value standardized with the value of the initial capacity in Experimental Example 1-1 as 1.00.

At the time of charging, a constant current was charged with a current of 0.1 C until the voltage reached 4.35 V, and then a constant voltage was charged with the voltage of 4.35 V until the current reached 0.05 C. At the time of discharge, a constant current was discharged with a current of 0.1 C until the voltage reached 2.5 V. 0.1C is a current value that can completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.05C is a current value that can completely discharge the battery capacity in 20 hours.

When investigating the normal temperature cycle characteristics, after stabilizing the state of the secondary battery by the above procedure, first, the secondary battery is charged and discharged for one cycle in a normal temperature environment (temperature = 23 ° C.). , The discharge capacity (discharge capacity in the second cycle) was measured. Subsequently, the discharge capacity (discharge capacity at the 302nd cycle) was measured by charging / discharging the secondary battery for 300 cycles in the same environment. Finally, the normal temperature maintenance rate (%) = (discharge capacity in the 302nd cycle / discharge capacity in the 2nd cycle) × 100 was calculated. The charge / discharge conditions were the same as the charge / discharge conditions when the initial charge / discharge characteristics were examined.

When investigating the high-temperature cycle characteristics, the same procedure is used after the second cycle, except that the secondary battery is charged and discharged in a high-temperature environment (temperature = 45 ° C.), instead of the room temperature maintenance rate (%). The high temperature maintenance rate (%) was calculated.

[Discussion]
As shown in Table 1, when a fluorine-containing polymer compound (PVDF having a melting point of 155 ° C.) is used as the positive electrode binder, the initial volume, the normal temperature maintenance rate, and the high temperature maintenance rate are each of the positive electrode 13. It varied depending on the composition and the composition of the electrolytic solution.

Specifically, when the electrolytic solution contains an additive compound (hydroxytoluene compound) and the content of the additive compound is 0.0001% by mass to 0.1% by mass, which is satisfied. (Experimental Examples 1-3 to 1-6), the initial volume and the room temperature maintenance rate, respectively, as compared with the case where the two conditions are not satisfied (Experimental Examples 1-1, 1-2, 1-7). A high high temperature maintenance rate was obtained while ensuring the above.

In particular, when the above two conditions are satisfied, when the content of the positive electrode binder (fluorine-containing polymer compound) is 0.7% by mass to 2.8% by mass, the initial volume and room temperature A sufficient high temperature maintenance rate was obtained while the maintenance rate was guaranteed (Experimental Examples 1-8 to 1-12).

When the electrolytic solution contains another compound (compound represented by the formula (4-1)) (Experimental Example 1-13), it is compared with the case where the above two conditions are not satisfied. Although a high initial capacity was obtained, the normal temperature maintenance rate and the high temperature maintenance rate were rather low.

(Experimental Examples 2-1 to 2-9)
As shown in Table 2, a secondary battery was prepared and the battery characteristics were evaluated by the same procedure except that the hydroxyanisole compound was used as the additive compound. The types of hydroxyanisole compounds and the content (mass%) of the hydroxyanisole compounds in the electrolytic solution are as shown in Table 2.

Here, for comparison, other compounds were used instead of the hydroxyanisole compound. The other compound is a compound (hydroquinone) represented by the above formula (4-2).

As shown in Table 2, the same results as when the hydroxytoluene compound was used (Table 1) were obtained even when the hydroxyanisole compound was used as the additive compound. That is, when the electrolytic solution contains an additive compound (hydroxyanisole compound) and the content of the additive compound is 0.0001% by mass to 0.1% by mass, the initial volume is satisfied. A high high temperature maintenance rate was obtained while ensuring each of the normal temperature maintenance rate.

When the electrolytic solution contains another compound (compound represented by the formula (4-2)) (Experimental Example 2-9), it is compared with the case where the above two conditions are not satisfied. Although a high initial capacity was obtained, the normal temperature maintenance rate and the high temperature maintenance rate were rather low.

(Experimental Examples 3-1 to 3-10, 4-1 to 4-8)
As shown in Tables 3 and 4, a secondary battery was prepared and the battery characteristics were evaluated by the same procedure except that the phosphorous acid compound was used as the additive compound. The types of phosphorous acid compounds and the content (% by mass) of the phosphorous acid compounds in the electrolytic solution are as shown in Tables 3 and 4.

Here, for comparison, other compounds were used instead of the phosphorous acid compound. As the other compounds, the compound represented by the above formula (4-3) (trimethyl phosphate) and the compound represented by the above formula (4-4) (tridecylphosphite) were used.

As shown in Tables 3 and 4, the same results as when the hydroxytoluene compound was used (Table 1) were obtained even when the phosphorous acid compound was used as the additive compound. That is, when the electrolytic solution contains an additive compound (phosphorous acid compound) and the content of the additive compound is 0.0001% by mass to 0.1% by mass, the first time. A high high temperature maintenance rate was obtained while ensuring each of the capacity and the normal temperature maintenance rate.

When the electrolytic solution contains other compounds (compounds represented by the formulas (4-3) and (4-4), respectively) (Experimental Examples 3-9 and 3-10), the above description is given. Compared with the case where the two conditions were not satisfied, when other compounds were used, a high initial volume and a high room temperature maintenance rate were obtained, but the high temperature maintenance rate was rather low.

(Experimental Examples 5-1 to 5-13, 6-1 to 6-9, 7-1 to 7-10, 8-1 to 8-8)
As shown in Tables 5 to 8, a secondary battery was prepared by the same procedure except that another fluorine-containing polymer compound (PVDF having a melting point of 166 ° C.) was used as the positive electrode binder. And evaluated the battery characteristics.

As shown in Tables 5 to 8, even when the fluorine-containing polymer compound having a melting point of 166 ° C. is used, when the fluorine-containing polymer compound having a melting point of 155 ° C. is used (Tables 1 to 4). ), And the same result was obtained. That is, when the electrolytic solution contains the added compound and the two conditions that the content of the added compound is 0.0001% by mass to 0.1% by mass is satisfied, the initial volume and the room temperature maintenance rate A high high temperature maintenance rate was obtained while each was secured.

(Experimental Examples 9-1 to 9-13, 10-1 to 10-9, 11-1 to 11-10, 12-1 to 12-8)
As shown in Tables 9 to 12, a secondary battery was prepared by the same procedure except that another fluorine-containing polymer compound (PVDF having a melting point of 172 ° C.) was used as the positive electrode binder. At the same time, the battery characteristics were evaluated.

As shown in Tables 9 to 12, when a fluorine-containing polymer compound having a melting point of 172 ° C. is used, a fluorine-containing polymer compound having a melting point of 166 ° C. or less is used (Tables 1 to Table 1). Results different from 8) were obtained. That is, even if the electrolytic solution contains an additive compound, the initial capacity is guaranteed regardless of the content of the fluorine-containing polymer compound and the content of the additive compound, but a high normal temperature maintenance rate and a high high temperature maintenance rate are maintained. I couldn't get it.

From these facts, the initial volume and the initial volume and the condition that the electrolytic solution contains the additive compound and the content of the additive compound is 0.0001% by mass to 0.1% by mass are satisfied. The advantageous tendency of obtaining a high high temperature maintenance rate while ensuring the normal temperature maintenance rate is a special tendency specifically obtained when the melting point of the fluorine-containing polymer compound is 166 ° C. or lower. Therefore, the above-mentioned advantageous tendency cannot be obtained when the melting point of the fluorine-containing polymer compound is higher than 166 ° C.

(Experimental Examples 13-1 to 13-11)
As shown in Table 13, a secondary battery was produced and the battery characteristics were evaluated by the same procedure except that the composition of the electrolytic solution (solvent) was changed. In this case, a part of the chain carbonate ester was replaced with the chain carboxylic acid ester. The types of chain carboxylic acid esters and the content (% by mass) of chain carboxylic acid esters in the solvent are as shown in Table 13. Here, as the chain carboxylic acid ester, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP) and propyl propionate (PP) were used.

Here, the load characteristics were further evaluated as the battery characteristics. When investigating the load characteristics, the state of the secondary battery is stabilized by the above procedure, and then the secondary battery is first charged and discharged for one cycle in the same environment (temperature = 23 ° C.). The discharge capacity (discharge capacity in the second cycle) was measured. Subsequently, the discharge capacity (discharge capacity in the third cycle) was measured by charging and discharging the secondary battery in the same environment. Finally, the load retention rate (%) = (discharge capacity in the third cycle / discharge capacity in the second cycle) × 100 was calculated. The charge / discharge conditions for the second cycle were the same as the charge / discharge conditions when the initial charge / discharge characteristics were examined. The charge / discharge conditions for the third cycle were the same as the charge / discharge conditions for the initial charge / discharge characteristics, except that the charging current and the discharging current were changed to 3C. 3C is a current value that can completely discharge the battery capacity in 1/3 hour.

As shown in Table 13, when the electrolytic solution contains a chain carboxylic acid ester together with the additive compound (Experimental Examples 13-1 to 13-8), the electrolytic solution contains only the additive compound (Experimental Examples 13-1 to 13-8). Compared with Experimental Example 3-4), a high load maintenance rate was obtained while ensuring the initial capacity, normal temperature maintenance rate, and high temperature maintenance rate.

In particular, when the electrolytic solution contains a chain carboxylic acid ester, a sufficient load retention rate was obtained when the content of the chain carboxylic acid ester was 10% by mass to 40% by mass.

When the electrolytic solution contains only the chain carboxylic acid ester (Experimental Examples 13-9 to 13-11), the electrolytic solution does not contain the additive compound or the chain carboxylic acid ester (Experimental Example 1). Compared with -1), a high load maintenance rate was obtained while ensuring the initial capacity and the normal temperature maintenance rate, but the high temperature maintenance rate was significantly lower.

From these facts, the advantageous tendency that a high load retention rate can be obtained while ensuring the initial capacity, the room temperature maintenance rate, and the high temperature maintenance rate by containing the chain carboxylic acid ester in the electrolytic solution is the advantage of electrolysis. This is a special tendency that is specifically obtained when the liquid contains an additive compound. Therefore, the above-mentioned advantageous tendency cannot be obtained when the electrolytic solution does not contain the additive compound.

(Experimental Examples 14-1 to 14-8)
As shown in Table 14, a secondary battery was produced and the battery characteristics were evaluated by the same procedure except that the composition of the electrolytic solution (solvent) was changed. In this case, another material (additive) was added to the electrolytic solution. The types of additives and the content (% by mass) of the additives in the electrolytic solution are as shown in Table 14. Here, as an additive, 4-fluoro-1,3-dioxolane-2-one (FEC), which is a halogenated carbonic acid ester, was used, and 1,3-dioxane (DOX), which is a dioxane compound, was used.

As shown in Table 14, when the electrolytic solution contains a halogenated carbonic acid ester (Experimental Examples 14-1 to 14-3), the electrolytic solution does not contain a halogenated carbonate (Experimental Example 3). Compared with -4), a higher room temperature maintenance rate and a higher high temperature maintenance rate were obtained while the initial capacity was guaranteed. In particular, when the electrolytic solution contains a halogenated carbonic acid ester, when the content of the halogenated carbonic acid ester is 1% by mass to 10% by mass, a sufficient normal temperature maintenance rate and a sufficient high temperature maintenance rate can be obtained. Was done.

Further, when the electrolytic solution contains a dioxane compound (Experimental Examples 14-4 to 14-6), the initial volume is compared with the case where the electrolytic solution does not contain a dioxane compound (Experimental Example 3-4). A higher room temperature maintenance rate and a higher high temperature maintenance rate were obtained while ensuring the above. In particular, when the electrolytic solution contains a dioxane compound, when the content of the dioxane compound is 0.1% by mass to 1.5% by mass, a sufficient normal temperature maintenance rate and a sufficient high temperature maintenance rate can be obtained. Was done.

When the electrolytic solution contains only a halogenated carbonic acid ester or a dioxane compound (Experimental Examples 14-7, 14-8), the electrolytic solution does not contain an additive compound, a halogenated carbonic acid ester, or a dioxane compound. Compared with (Experimental Example 1-1), although the initial capacity was secured, the normal temperature maintenance rate was lower and the high temperature maintenance rate was the same.

From these facts, since the electrolytic solution contains a halogenated carbonic acid ester or a dioxane compound, the advantageous tendency that a higher high temperature maintenance rate can be obtained while ensuring the initial capacity and the normal temperature maintenance rate is that the electrolytic solution is added. This is a special tendency that is specifically obtained when a compound is contained. Therefore, the above-mentioned advantageous tendency cannot be obtained when the electrolytic solution does not contain the additive compound.

[Summary]
From the results shown in Tables 1 to 14, the positive electrode 13 contains a fluorine-containing polymer compound, the electrolytic solution contains an additive compound, and the content of the additive compound in the electrolytic solution is 0.0001% by mass. When it was about 0.1% by mass, the initial charge / discharge characteristics, the normal temperature cycle characteristics, and the high temperature cycle characteristics were all improved. Therefore, excellent battery characteristics were obtained in the secondary battery.

Although the present technology has been described above with reference to one embodiment and examples, the embodiment of the present technology is not limited to the embodiments described in one embodiment and examples, and thus can be variously modified.

Specifically, the case where the secondary battery of the present technology is a laminated film type secondary battery has been described, but the type of the secondary battery of the present technology is not particularly limited. Specifically, the type of the secondary battery may be another type such as a cylindrical type, a square type and a coin type. Further, although the case where the battery element used in the secondary battery of the present technology has a wound structure has been described, the structure of the battery element is not particularly limited. Specifically, the structure of the battery element may be another structure such as a laminated structure.

Since the effects described in the present specification are merely examples, the effects of the present technology are not limited to the effects described in the present specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

A positive electrode containing a fluorine-containing polymer compound having a melting point of 166 ° C. or lower, and
With the negative electrode
It contains at least one of a hydroxytoluene compound represented by the following formula (1), a hydroxyanisole compound represented by the following formula (2), and a phosphorous acid compound represented by the following formula (3). A secondary solution comprising an electrolytic solution, wherein the content of at least one of the hydroxytoluene compound, the hydroxyanisole compound and the phosphorous acid compound is 0.0001% by mass or more and 0.1% by mass or less. battery.

(Each of R1 to R4 is one of a hydrogen group and an alkyl group. However, at least two of R1 to R4 are tertiary alkyl groups.)

(Each of R5 to R8 is one of a hydrogen group and an alkyl group. However, at least one of R5 to R8 is a tertiary alkyl group.)

(Each of R9 to R13 is either a hydrogen group or an alkyl group.)
The positive electrode includes a positive electrode active material layer containing the fluorine-containing polymer compound.
The content of the fluorine-containing polymer compound in the positive electrode active material layer is 0.7% by mass or more and 2.8% by mass or less.
The secondary battery according to claim 1.
The fluorine-containing polymer compound contains polyvinylidene fluoride.
The secondary battery according to claim 1 or 2.
In the formula (1), one of the R1 and the R2 is the tertiary alkyl group, and one of the R3 and the R4 is the tertiary alkyl group.
The secondary battery according to any one of claims 1 to 3.
In the formula (2), any one of the R5 to R8 is the tertiary alkyl group.
The secondary battery according to any one of claims 1 to 4.
In the above formula (3)
Each of the R9 to R13 is the hydrogen group.
Alternatively, any two of the R9 to R13 are the tertiary alkyl groups.
The secondary battery according to any one of claims 1 to 5.
The tertiary alkyl group is a tertiary butyl group.
The secondary battery according to any one of claims 1 to 6.
The electrolytic solution further contains a solvent and contains a solvent.
The solvent contains a chain carboxylic acid ester and contains
The content of the chain carboxylic acid ester in the solvent is 10% by mass or more and 40% by mass or less.
The secondary battery according to any one of claims 1 to 7.
The electrolytic solution further contains a halogenated carbonic acid ester.
The content of the halogenated carbonic acid ester in the electrolytic solution is 1% by mass or more and 10% by mass or less.
The secondary battery according to any one of claims 1 to 8.
The electrolytic solution further contains a dioxane compound and contains.
The content of the dioxane compound in the electrolytic solution is 0.1% by mass or more and 1.5% by mass or less.
The secondary battery according to any one of claims 1 to 9.