JP2012033286A - Binder for forming secondary battery positive electrode, electrode mixture for forming secondary battery positive electrode, electrode structure, and secondary battery - Google Patents

Abstract

An object of the present invention is to provide a binder for forming a positive electrode of a secondary battery that has long-term durability and contributes to improvement of battery characteristics.
A binder for forming a positive electrode of a secondary battery according to the present invention includes a fluorine-based polymer electrolyte having a structural unit represented by the following formula (1), and at least one specific site in the fluorine-based polymer electrolyte. Part is an alkali metal atom, an alkaline earth metal atom, or an ammonium group.
_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( CF ₂ ) _f −X ⁴ )] _g − (1)
[Selection figure] None

Description

  The present invention relates to a non-aqueous secondary battery, an aqueous secondary battery, particularly preferably a non-aqueous lithium ion secondary battery, a binder for secondary battery positive electrode formation that can contribute to improvement of battery characteristics, the binder and a powder electrode material. And an electrode structure formed by using the electrode mixture.

  In recent years, development of high-performance batteries has been actively promoted in response to demands for reducing the size and weight of portable electronic devices such as mobile phones and digital cameras. And the demand of the secondary battery which can be repeatedly used by charge is growing greatly. In particular, lithium-ion secondary batteries are being developed for use in electric vehicles in addition to applications such as mobile phones and laptop computers, and the range of their use is greatly expanding.

  A lithium ion secondary battery has a structure in which an electrode produced through a separator between a positive electrode and a negative electrode is housed in a container together with an electrolytic solution (in the case of a lithium ion polymer battery, a gel instead of a liquid). Is.

  The positive electrode of the lithium ion secondary battery is made of an active material for a positive electrode such as a lithium composite oxide containing a transition metal such as lithium cobaltate, and a conductive material mainly made of a carbon material as necessary. A layer is formed on a metal current collector such as a foil. Usually, a positive electrode of such a lithium ion secondary battery is prepared by adding a conductive material and a binder to a positive electrode active material, and kneading and preparing a paste in the presence of a solvent such as N-methyl-2-pyrrolidone (NMP). It is obtained by applying onto a metal current collector with a doctor blade or the like and drying. Here, the binder is used for bonding a positive electrode active material and a conductive material, a mixture of the positive electrode active material and the conductive material, and a metal current collector.

  In addition, a nonaqueous solvent such as ethylene carbonate or diethyl carbonate is used for the electrolytic solution of the lithium ion secondary battery, and usually a supporting electrolytic salt is added.

  Since the lithium ion secondary battery has the above-described configuration, the binder for forming the positive electrode includes (1) adhesiveness between the positive electrode active material and the conductive material, and a mixture of the positive electrode active material and the conductive material. And (2) excellent corrosion resistance to the electrolyte, (3) stable in harsh environments that receive voltage in the battery, and (4) electrodes. Therefore, it is required that the internal resistance is small and high conductivity can be maintained.

  Conventionally, a polyvinylidene fluoride (PVDF) resin or the like is often used as a binder for forming a positive electrode. Patent Document 1 discloses a binder for forming a non-aqueous battery electrode comprising a polyvinylidene fluoride resin in which hydrogen in a vinylidene fluoride polymer unit is substituted with a sulfonic acid group.

Japanese Patent No. 3784494

  However, PVDF resin and the like conventionally used as a positive electrode forming binder do not have ionic conductivity. Here, ionic conductivity refers to a phenomenon in which electric current is carried by the movement of ions, which are charged particles, when a voltage is applied. In order to obtain durability that can withstand practical use, it is necessary to increase the content of the binder, and as a result, the content of the binder that is an ion-insulating substance, ie, a substance having no ionic conductivity, increases. However, there is a limit in improving battery characteristics. Further, the binder for forming a non-aqueous battery electrode disclosed in Patent Document 1 exhibits adhesion to a powder electrode material and a current collector with a small amount of use, and can contribute to improvement of battery characteristics, but cycle characteristics are insufficient. There is a problem.

  The main object of the present invention is to provide a secondary battery positive electrode-forming binder that has long-term durability and contributes to improving battery characteristics. A further object of the present invention is to provide an electrode mixture containing a mixture of the binder and the powder electrode material, an electrode structure formed using the electrode mixture, and an aqueous / non-aqueous secondary battery. .

  According to the study by the present inventors, in order to achieve the above-mentioned object, a fluorine-based polymer electrolyte having a structural unit represented by a specific formula is included, and specific sites in the fluorine-based polymer electrolyte are included. It has been found that it is extremely effective to use a secondary battery positive electrode-forming binder containing a fluorine-based polymer electrolyte, at least a part of which is an alkali metal atom, an alkaline earth metal atom or an ammonium group.

  That is, the present invention is as follows.

[1]
Including a fluorine-based polymer electrolyte having a structural unit represented by the following formula (1):
The binder for secondary battery positive electrode formation whose at least one part of Z in this fluorine-type polymer electrolyte is an alkali metal atom, an alkaline-earth metal atom, or an ammonium group.

_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( CF ₂ ) _f −X ⁴ )] _g − (1)
(In the formula (1),
X ¹ , X ² and X ³ are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms,
a and g are 0 ≦ a <1, 0 <g ≦ 1, a + g = 1,
b is an integer of 0 to 8,
c is 0 or 1,
d, e and f are each independently an integer of 0 or more and 6 or less, and 0 <d + e + f,
R ¹ and R ² are each independently a halogen atom, a perfluoroalkyl group or a fluorochloroalkyl group having 1 to 10 carbon atoms,
X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ (where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom or an ammonium group). )
[2]
The binder for forming a secondary battery positive electrode according to [1], wherein at least a part of Z in the fluorine-based polymer electrolyte is an alkali metal atom.

[3]
The binder for forming a secondary battery positive electrode according to [1], wherein at least a part of Z in the fluorine-based polymer electrolyte is lithium.

[4]
Furthermore, a non-ion conductive binder is included,
The binder for secondary battery positive electrode formation in any one of [1]-[3] whose content of this nonionic conductive binder is 90 mass% or less.

[5]
An electrode mixture for a secondary battery positive electrode, comprising the binder for secondary battery positive electrode formation according to any one of [1] to [4] and a powder electrode material.

[6]
The electrode mixture for secondary battery positive electrode according to [5], wherein the content of the binder for forming a secondary battery positive electrode is 0.5 to 15% by mass.

[7]
A current collector and an electrode mixture for a secondary battery positive electrode according to [5] or [6],
An electrode structure in which a layer of the electrode mixture for a secondary battery positive electrode is formed on at least one surface of the current collector.

[8]
An aqueous secondary battery comprising a positive electrode, a negative electrode, a separator and an aqueous electrolyte,
An aqueous secondary battery, wherein the positive electrode is the electrode structure according to [7].

[9]
A non-aqueous secondary battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution,
A nonaqueous secondary battery, wherein the positive electrode is the electrode structure according to [7].

[10]
A non-aqueous lithium ion secondary battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution,
The non-aqueous lithium ion secondary battery whose said positive electrode is an electrode structure of [7].

  The binder for forming a positive electrode of a secondary battery of the present invention has long-term durability. When the binder is used, an electrode contributing to improvement of battery characteristics can be formed through an ion conduction effect, and the performance of the secondary battery can be improved. Can be improved.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following description, and various modifications can be made within the scope of the gist thereof.

[Binder for secondary battery positive electrode formation]
The binder for forming a secondary battery positive electrode according to the present embodiment includes a fluorine-based polymer electrolyte having a structural unit represented by the following formula (1), and at least a part of Z in the fluorine-based polymer electrolyte is , An alkali metal atom, an alkaline earth metal atom, or an ammonium group, preferably an alkali metal atom, and more preferably lithium. In the present embodiment, “at least a part of Z in the fluorine-based polymer electrolyte” means 10% or more of Z in the fluorine-based polymer electrolyte, and is 50% or more. Preferably, it is 90% or more.

-[CF ₂ CX ¹ X ² ] _a- [CF ₂ -CF (-O- (CF ₂ -CF (CF ₂ X ³ )) _b -O _c- (CFR ¹ ) _d- (CFR ² ) _e- ( CF ₂ ) _f -X ⁴ )] _g- (1)
In formula (1), X ¹ , X ² and X ³ are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms, preferably a halogen atom.

a and g are 0 ≦ a <1, 0 <g ≦ 1, a + g = 1,
b is an integer of 0 to 8,
c is 0 or 1;
d, e, and f are each independently an integer of 0 or more and 6 or less, provided that 0 <d + e + f.

R ¹ and R ² are each independently a halogen atom, a perfluoroalkyl group having 1 to 10 carbon atoms or a fluorochloroalkyl group, preferably a perfluoroalkyl group having 1 to 10 carbon atoms.

X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ, where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom or an ammonium group, preferably an alkali metal. . The ammonium group is NH ₄ , NH ₃ R ₁ , NH ₂ R ₁ R ₂ , NHR ₁ R ₂ R ₃ or NR ₁ R ₂ R ₃ R ₄ (R ₁ , R ₂ , R ₃ , R ₄ are alkyl Group or arene group).

  Further, by using a high ion exchange group-containing resin or the like, it is possible to freely control at least a part of the fluorine-based polymer electrolyte as a cross-linked structure, such as a dissolved component or a swollen component.

  In the secondary battery positive electrode forming binder according to the present embodiment, the content of the fluorine-based polymer electrolyte is preferably 10 to 100% by mass, more preferably 30 to 100% by mass, and still more preferably 50. ˜100 mass%. Since the fluorine-based polymer electrolyte has ion conductivity, by setting the content of the fluorine-based polymer electrolyte in the above range, ion conductivity in the obtained electrode structure is improved, and battery characteristics are improved. Connected.

  The fluorine-based polymer electrolyte used in the present embodiment can be produced, for example, by subjecting a precursor polymer represented by the following formula (2) to alkali hydrolysis, acid treatment or the like.

-[CF ₂ CX ¹ X ² ] _a- [CF ₂ -CF (-O- (CF ₂ -CF (CF ₂ X ³ )) _b -O _c- (CFR ¹ ) _d- (CFR ² ) _e- ( CF ₂ ) _f -X ⁵ )] _g- (2)
(In formula (2), X ¹ , X ² and X ³ are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms. A and g are 0 ≦ a <1, 0 < g ≦ 1, a + g = 1, b is an integer of 0 or more and 8 or less, c is 0 or 1. d, e and f are each independently an integer of 0 or more and 6 or less (provided that 0 < R ¹ and R ² are each independently a halogen atom, a perfluoroalkyl group or a fluorochloroalkyl group having 1 to 10 carbon atoms, and X ⁵ is COOR ³ , COR ⁴ or SO. ₂ R ⁴ , where R ³ is a hydrocarbon alkyl group having 1 to ³ carbon atoms, and R ⁴ is a halogen atom.
The precursor polymer can be produced, for example, by copolymerizing a fluorinated olefin compound and a vinyl fluoride compound.

Here, examples of the fluorinated olefin compound include CF ₂ = CF ₂ , CF ₂ = CFCl, CF ₂ = CCl _{2 and the} like.

As the fluorinated vinyl compound, _{e.g., CF 2 = CFO (CF 2} ) m -SO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) m -SO 2 F, CF 2 = CF _{(CF 2) m -SO 2 F} , CF 2 = CF (OCF 2 CF (CF 3)) m - (CF 2) m-1 -SO 2 F, CF 2 = CFO (CF 2) m -CO 2 R _{, CF2 = CFOCF 2 CF (CF} 3) O (CF 2) m -CO 2 R, CF 2 = CF (CF 2) m -CO 2 R, CF 2 = CF (OCF 2 CF (CF 3)) m - (CF _{2) 2} -CO ₂ R and the like. In the above formula, m represents an integer of 1 to 8, and R represents a hydrocarbon alkyl group having 1 to 3 carbon atoms.

  The precursor polymer as described above can be synthesized by a known means. Such a synthesis method is not particularly limited, and examples thereof include the following methods.

  (I) A method in which a polymerization solvent such as a fluorinated hydrocarbon is used, and polymerization is performed by reacting the polymerization solvent in a state in which a vinyl fluoride compound and a gas of a fluorinated olefin compound are charged and dissolved (solution polymerization). Examples of the fluorine-containing hydrocarbon include a group of compounds collectively referred to as “fluorocarbon” such as trichlorotrifluoroethane, 1, 1, 1, 2, 3, 4, 4, 5, 5, 5-decafluoropentane, and the like. It can be preferably used.

  (Ii) A method of polymerizing a fluorinated olefin compound and a vinyl fluoride compound using a vinyl fluoride compound itself as a polymerization solvent without using a solvent such as a fluorine-containing hydrocarbon (bulk polymerization).

  (Iii) A method (emulsion polymerization) in which an aqueous solution of a surfactant is used as a polymerization solvent, and the polymerization is carried out by reacting a vinyl fluoride compound and a gas of a fluorinated olefin compound in this polymerization solvent in a state of being charged and dissolved.

  (Iv) A method in which an aqueous solution of a surfactant and a co-emulsifier such as alcohol is used, and the aqueous solution is charged and emulsified with a vinyl fluoride compound and a gas of a fluorinated olefin compound to perform polymerization (miniemulsion polymerization, Microemulsion polymerization).

  (V) A method in which an aqueous solution of a suspension stabilizer is used, and polymerization is performed by reacting the aqueous solution in a state of filling and suspending a vinyl fluoride compound and a gas of a fluorinated olefin compound (suspension polymerization).

  In the present embodiment, a melt mass flow rate (measurement was performed at 270 ° C. under a load of 2160 g in accordance with JIS K 7210) as an index of the polymerization degree of the precursor polymer. Can be used. In the present embodiment, the MFR of the precursor polymer is preferably 0.01 g / 10 min or more, more preferably 0.1 g / 10 min or more, and further preferably 0.3 g / 10 min or more. The upper limit of MFR is not limited, but is preferably 100 g / 10 min or less, more preferably 10 g / 10 min or less, and further preferably 5 g / 10 min or less.

  Hereinafter, a method in which at least a part of Z (hereinafter also referred to as “functional group” or “terminal functional group”) in the fluorine-based polymer electrolyte is an alkali metal atom, an alkaline earth metal atom, or an ammonium group will be described. To do.

  The precursor polymer produced as described above can be hydrolyzed in a basic solution to obtain a fluorine-based polymer electrolyte substituted with a functional group. For example, by subjecting the precursor polymer to a hydrolysis treatment in an aqueous lithium hydroxide solution, a lithium-chlorinated fluorine-based polymer electrolyte can be obtained.

  In addition, after the precursor polymer is hydrolyzed with a basic liquid, washed with water, and acid-treated to protonate the terminal functional group of the precursor polymer, the terminal functional group is then immersed and stirred again in a basic solution. Can be obtained. For example, the precursor polymer is hydrolyzed with a basic solution containing an aqueous potassium hydroxide solution and methyl alcohol, washed with water, and acid-treated with hydrochloric acid, whereby the terminal functional group is protonated and a fluorine-based polymer. By obtaining an electrolyte and immersing and stirring the protonated fluorine-based polymer electrolyte in an aqueous lithium hydroxide solution, a fluorine-based polymer electrolyte having a terminal functional group lithium-chlorinated can be obtained.

  If there is already a fluorinated polymer electrolyte with protonated terminal functional groups instead of the precursor polymer, similarly, for example, immerse the protonated fluorinated polymer electrolyte in an aqueous lithium hydroxide solution. By stirring, a fluorine-based polymer electrolyte having a terminal functional group lithium-chlorinated can be obtained.

When the fluorine-based polymer electrolyte is liquid, the terminal functional group can be substituted by a method using an ion exchange resin. For example, after filling an ion exchange resin of SO ₃ H type into a resin tower, a saturated LiCl aqueous solution is passed through the resin tower to make it SO ₃ Li type, and then a fluorine-based polymer electrolyte solution with terminal functional groups protonated is obtained. By flowing it through the resin tower, a fluorine-based polymer electrolyte whose terminal functional group is lithium chloride can be obtained.

  Some examples have been given as examples of the terminal functional group substitution method, but the present invention is not limited thereto.

  The terminal functional group is preferably substituted with an alkali metal atom from the viewpoint of being mainly applied to a lithium ion battery, and particularly preferably substituted with lithium.

  The binder for forming a secondary battery positive electrode according to the present embodiment may further contain a non-ion conductive binder. In particular, when excessive swelling or solubility increase in the electrolytic solution is observed, it is preferable to contain a nonionic conductive binder, and at least part of the fluorine-based polymer electrolyte may be crosslinked. Good.

  As the nonionic conductive binder, at least one kind is freely selected from polyvinylidene fluoride (PVDF), styrene-butadiene random copolymer, and other known ones.

  In the binder for secondary battery positive electrode formation according to the present embodiment, the mixing ratio of the fluorine-based polymer electrolyte and the nonionic conductive binder is such that the content of the fluorine-based polymer electrolyte is 10 to 100% by mass. Preferably, it is 30 to 100% by mass, more preferably 50 to 100% by mass, and the content of the nonionic conductive binder is preferably 90 to 0% by mass, more preferably 70 to 0% by mass. More preferably, it is 50-0 mass%. In the secondary battery positive electrode forming binder according to the present embodiment, by increasing the fluorine polymer electrolyte ratio, that is, the ion conductive binder ratio, the ion conductivity in the resulting electrode structure is improved, and the battery characteristics are improved. It leads to improvement.

  The binder for secondary battery positive electrode formation concerning this Embodiment can be melt | dissolved, and a binder solution can be obtained. When an organic solvent is used to obtain the binder solution, it is preferably a polar solvent, such as N-methyl-2-pyrrolidone, dimethylformamide, N, N-dimethylacetamide, N, N-dimethylsulfoxide, hexamethylphospho Examples include amide, 1,4-dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, and the like. These organic solvents are used alone or in combination of two or more.

  In consideration of environmental sanitation and the like, an aqueous solvent such as water or a mixed solvent of water and alcohols is preferable instead of an organic solvent. As the solvent for dissolving the binder for forming a secondary battery positive electrode according to the present embodiment, either an organic solvent or an aqueous solvent can be used.

  The excellent binder effect of the binder for forming a secondary battery positive electrode according to the present embodiment has been confirmed in Examples described later. In addition, when the secondary battery positive electrode forming binder according to the present embodiment is used, the battery characteristics are improved because the binder has long-term oxidation resistance in an oxidizing atmosphere and is similar to a conventional binder. Unlike the almost perfect ion insulator, it is understood that it is a binder that contributes to carrier ion conduction.

[Electrode mixture for secondary battery positive electrode]
The electrode mixture for a secondary battery positive electrode according to the present embodiment includes the above-described binder for forming a positive electrode of the secondary battery and a powder electrode material.

  The powder electrode material is an electrode active material and a conductive additive added as necessary. Examples of the electrode active material include metal oxide active materials described later. Examples of the conductive aid include graphite, acetylene black, carbon black, ketjen black, and carbon fiber.

  In the electrode mixture for the secondary battery positive electrode according to the present embodiment, the content of the binder for forming the secondary battery positive electrode is preferably 0.5 to 15% by mass, more preferably 0.7 to 10% by mass, Preferably it is 1.0-8.0 mass%. The content of the binder for forming the secondary battery positive electrode is preferably 15% by mass or less from the viewpoint of contact resistance between the active material and the conductive material or with the current collector, and the active material, the conductive material and the current collector From an adhesive viewpoint, 0.5 mass% or more is preferable.

[Electrode structure]
The electrode structure according to the present embodiment includes a current collector and the electrode mixture for secondary battery positive electrode described above, and a layer of the electrode mixture for secondary battery positive electrode is formed on at least one surface of the current collector. Is formed.

  As the current collector, a metal foil such as aluminum, titanium, and stainless steel can be used, and an aluminum foil is preferably used.

  The electrode structure according to the present embodiment can be used as a positive electrode of a secondary battery.

A metal oxide active material can be used as the active material contained in the positive electrode. Examples of the metal oxide based active material include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , LiFePO _{4 and the} like. The metal oxide active material may be used alone, or a plurality of metal oxide active materials may be mixed and used.

  As a method for producing the positive electrode, for example, the above-mentioned binder for forming a positive electrode for a secondary battery and a powder electrode material are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent to prepare a positive electrode mixture-containing paste. A method of preparing and applying this positive electrode mixture paste to a positive electrode current collector made of aluminum foil or the like, drying to form a positive electrode mixture layer, and adjusting the thickness by pressurizing as necessary is mentioned. It is done.

  On the other hand, a carbonaceous material is preferably used as the active material contained in the negative electrode. More specifically, for example, graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, graphite, carbon colloid, etc. are preferably used. It is done. The carbonaceous material may be used alone, or a plurality of carbonaceous materials may be mixed and used.

  As a method for producing the negative electrode, for example, a negative electrode active material made of the carbonaceous material is mixed with a binder and a powder electrode material to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent. To prepare a negative electrode mixture-containing paste, apply this negative electrode mixture-containing paste to the negative electrode current collector, dry it to form a negative electrode mixture layer, and pressurize as necessary to adjust the thickness. A method is mentioned.

  Examples of the conductive assistant used in the production of the positive electrode and the negative electrode include graphite, acetylene black, carbon black, ketjen black, and carbon fiber.

[Secondary battery]
The aqueous secondary battery according to the present embodiment is an aqueous secondary battery including a positive electrode, a negative electrode, a separator, and an aqueous electrolyte solution, and the positive electrode is the electrode structure described above.

  The non-aqueous secondary battery according to the present embodiment is a non-aqueous secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode is the above-described electrode structure.

  Furthermore, the non-aqueous lithium ion secondary battery according to the present embodiment is a non-aqueous lithium ion secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution, and the positive electrode is the electrode structure described above. .

  The secondary battery is manufactured by, for example, winding a separator between the positive electrode and the negative electrode to form a laminated structure of a wound structure, or forming a laminated body by bending or laminating a plurality of layers. can do.

  In addition, an electrolytic solution is mainly used as an ion conductive medium between the positive electrode and the negative electrode. Examples of the electrolytic solution include an aqueous electrolytic solution and a non-aqueous electrolytic solution. Examples of the aqueous electrolyte include alkaline aqueous solutions such as potassium hydroxide aqueous solutions that can be used in air batteries. As the non-aqueous electrolyte, for example, an electrolyte such as a lithium salt dissolved in a non-aqueous solvent (organic solvent) can be used.

Here, as the electrolyte, LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ OSO ₂ ) ₂ , LiCl, LiBr, LiC (CF ₃ OSO ₂ ) ₃ , Examples thereof include LiN (CF ₃ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ . Nonaqueous solvents (organic solvents) for dissolving the electrolyte include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, propionic acid. Methyl, ethyl propionate, and mixed solvents thereof are used, but are not necessarily limited thereto.

  The battery form of the non-aqueous lithium ion secondary battery of this embodiment is not limited to a specific one, and a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape, a coin shape, a flat shape, a laminate shape, and the like are preferable. Used.

  Moreover, although the secondary battery to which the above-described electrode structure is applied has been mainly described with a non-aqueous secondary battery, the present invention is not limited to this and can be applied to an aqueous secondary battery. Moreover, it is applicable also to an air metal battery, an all-solid-state battery, etc.

  Hereinafter, the present embodiment will be described more specifically with reference to examples. However, the present embodiment is not limited to these examples.

[Example 1]
(Preparation of fluorinated polymer electrolyte solution)
In a 1 liter stainless steel autoclave, 580 g of CF ₂ ClCFCl ₂ (hereinafter also referred to as “CFC113”) and CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ —SO ₂ F (hereinafter “S monomer”) 280g was charged. Thereafter, the inside of the autoclave was purged with nitrogen and subsequently purged with tetrafluoroethylene (CF ₂ = CF ₂ , hereinafter also referred to as “TFE”). Next, 0.55 g of a CFC113 solution containing 5% by weight of (n-C ₃ F ₇ COO—) ₂ was added into the autoclave, and polymerization was carried out for about 3 and a half hours. The polymerization conditions were a temperature of 35 ° C. and a TFE pressure of 0.160 MPaG. During the polymerization, TFE was fed from outside the system so that the TFE pressure in the autoclave was constant.

  After completion of the polymerization, the inside of the autoclave was purged with TFE, and CFC113 was distilled off at 90 ° C. and normal pressure from the resulting polymerization solution. Subsequently, the remaining S monomer was distilled off at 90 ° C. under reduced pressure. . Furthermore, the liquid after the distillation was dried under reduced pressure at 150 ° C. for 2 days to obtain 10.8 g of a perfluorosulfonic acid resin precursor.

  The obtained perfluorosulfonic acid resin precursor was subjected to hydrolysis treatment by bringing it into contact with an aqueous solution in which potassium hydroxide (15% by mass) and methyl alcohol (50% by mass) were dissolved at 80 ° C. for 20 hours. . The hydrolyzed resin was immersed in 60 ° C. water for 5 hours. Furthermore, the treatment of immersing in a 2N aqueous hydrochloric acid solution at 60 ° C. for 1 hour was repeated 5 times, replacing the aqueous hydrochloric acid solution with a new one each time. The resin after immersion treatment with an aqueous hydrochloric acid solution was washed with ion-exchanged water and dried to obtain a fluorine-based polymer electrolyte in which the counter ion of the ion-exchange group was in a proton state.

  This fluoropolymer electrolyte was placed in a 5 L autoclave together with an aqueous ethanol solution (water: ethanol = 50.0: 50.0 (mass ratio)), sealed, heated to 160 ° C. while stirring with a blade, and 5 Held for hours. Thereafter, the autoclave was naturally cooled to prepare a uniform fluorine-based polymer electrolyte solution having a solid content concentration of 5% by mass.

(Preparation of fluoropolymer electrolyte membrane)
The fluorine-based polymer electrolyte solution obtained above was concentrated under reduced pressure at 80 ° C. to obtain a cast solution having a solid content concentration of 20% by mass. This cast solution was cast on a tetrafluoroethylene film using a doctor blade. Next, the tetrafluoroethylene film was put in an oven and pre-dried at 60 ° C. for 30 minutes. After preliminary drying, the solvent was removed by further drying at 80 ° C. for 30 minutes, and further heat treatment was performed at 160 ° C. for 1 hour to obtain a fluorine-based polymer electrolyte membrane having a thickness of about 50 μm.

(Lithium chloride of the terminal functional group of fluoropolymer electrolyte)
Fluorine polymer electrolyte membrane 20 cm ² having a film thickness of about 50 μm obtained above is immersed in 30 ml of saturated lithium chloride aqueous solution at 25 ° C. and left for 30 minutes with stirring, and a fluorine-based fluorine functionalized lithium terminal functional group. A polymer electrolyte membrane was obtained.

(Equivalent weight EW measurement)
The equivalent weight EW of the fluorine-based polymer electrolyte membrane obtained above was measured as follows.

  The protons in the saturated lithium chloride aqueous solution containing the lithium-fluorinated fluorine-based polymer electrolyte membrane were neutralized and titrated with 0.01N lithium hydroxide aqueous solution using phenolphthalein as an indicator.

  The fluorine-based polymer electrolyte membrane obtained after neutralization, in which the counter ion of the ion exchange group is in the state of lithium ions, was rinsed with pure water, further vacuum-dried, and weighed. The amount of lithium hydroxide required for neutralization is M (mmol), the weight of the fluorine-based polymer electrolyte membrane in which the counterion of the ion exchange group is lithium ion is W (mg), and the atomic weight of lithium The equivalent weight EW (g / eq) was calculated from the following formula in consideration of the difference between the atomic weight of hydrogen and the atomic weight of hydrogen.

EW = (W / M) -6
Further, the reciprocal of the obtained equivalent weight EW value was taken and multiplied by 1000 to calculate the ion exchange capacity (milli equivalent / g). The equivalent weight EW of the lithium chloride fluorinated polymer electrolyte membrane determined by this method was 970 g / eq (ion exchange capacity: 1.03 meq / g). In general, the lower the value of the equivalent weight EW, the better the ionic conductivity of the obtained fluoropolymer electrolyte membrane.

(PFG-NMR measurement)
The lithium chloride fluoropolymer electrolyte membrane (hereinafter also referred to as “EW970 membrane”) obtained above was placed in a 1M LiTFSI (lithium bistrifluoromethanesulfonylimide) / PC (propylene carbonate) electrolyte solution at room temperature for 15 hours. Soaked above. Thereafter, the EW970 membrane was finely cut to fill the NMR symmetric micro sample tube so that the sample height was about 5 mm (sample area was about 13 cm ² ).

  The PFG-NMR measurement of the EW970 film was performed under the conditions shown in Table 1 using ECA400 manufactured by JEOL.

In the PFG-NMR measurement, the diffusion coefficient (D) was calculated by the following formula (i).

ln (E / E ₀ ) = − Dγ ² δ ² g ² (Δ−δ / 3) (i)
E: observed NMR peak intensity,
E ₀ : NMR peak intensity when no PFG is applied,
γ: Gyromagnetic ratio of nuclear spin,
δ: PFG pulse width,
Δ: Spreading waiting time,
g: Magnetic field gradient strength.

In actual PFG-NMR measurement, in order to eliminate the influence of the change in NMR peak intensity due to NMR relaxation, Δ and δ were fixed values, and g was changed to perform multipoint measurement. The NMR peak intensity obtained by changing the value of g was calculated, and the slope of the diffusion plot plotted with the vertical axis being ln (E / E ₀ ) and the horizontal axis being γ ² δ ² g ² (Δ−δ / 3) The diffusion coefficient was calculated from The results are shown in Table 2.

[Example 2]
With respect to the polymerization conditions for obtaining the perfluorosulfonic acid resin precursor, a fluoropolymer electrolyte membrane was prepared in the same manner as in Example 1 except that the temperature was 30 ° C. and the TFE pressure was 0.170 MPaG. , EW measurement and PFG-NMR measurement were performed. As a result, the EW of the lithium chloride fluorinated polymer electrolyte membrane was 1050 g / eq (ion exchange capacity: 0.95 meq / g) and the diffusion coefficient was 1.26 × 10 ⁻¹³ m ² / s. It was. The lithium chloride fluorine-based polymer electrolyte membrane obtained in Example 2 is hereinafter also referred to as “EW1050 membrane”.

[Comparative Example 1]
A 12% by mass polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution (Kureha KF Binder # 1120) was poured into a petri dish, and finally dried at 160 ° C. to a thickness of 50 μm. A cast film of polyvinylidene fluoride (PVDF) (hereinafter also referred to as “PVDF film”) was produced. As a result of the PFG-NMR measurement of the PVDF film, a lithium diffusion plot inside the PVDF film was not obtained. From this, it was confirmed that there was no lithium ion conductivity in the PVDF membrane.

From the results of Examples 1 and 2 and Comparative Example 1, the binder containing the fluorine-based polymer electrolyte of the present embodiment acts not only as an ionic insulating binder but also as a binder contributing to ionic conduction. It was also found that the binder contributes to the improvement of battery performance.

  Next, battery evaluation was performed by the following method.

[Example 3]
(Ion exchange and solvent replacement)
The fluorine polymer electrolyte solution obtained in Example 1 was placed in an eggplant flask and subjected to distillation operation. Thereafter, distilled water was added to the eggplant flask to obtain a fluorine-based polymer electrolyte aqueous solution containing only water as a solvent.

Next, after filling an ion exchange resin (SO ₃ H type, Diaion made by Mitsubishi Chemical) into a resin tower and flowing a saturated lithium chloride aqueous solution into the resin tower to make an SO ₃ Li type, the above-mentioned fluorine-based polymer electrolyte aqueous solution is used. Was passed through a resin tower to obtain a solution containing a fluorinated polymer electrolyte in which the polymer terminal was lithiated. This solution was placed in an eggplant flask and subjected to a distillation operation. Then, N-methyl-2-pyrrolidone was put into the eggplant flask, and the solvent was replaced (EW970 product).

(Preparation of positive electrode)
Lithium cobalt acid (LiCoO ₂ ) having an average particle diameter of 5 μm as a positive electrode active material, carbon powder having an average particle diameter of 3 μm as a conductive additive, and the above-mentioned fluorine-based polymer electrolyte as a binder, In this manner, the mixture was mixed in N-methyl-2-pyrrolidone to prepare a slurry solution so that the solid content was 60% by mass. The slurry solution was applied to one side of a 20 μm thick aluminum and dried to remove the solvent. Thereafter, the aluminum was rolled with a roll press and punched into a disk shape having a diameter of 16 mm, which was used as a positive electrode.

  In electrode preparation, it may be preferable from the viewpoints of solubility and dispersibility to prepare an electrode before lithium-chlorinating the fluorine-based polymer electrolyte and then lithium-chlorinate after electrode preparation.

(Preparation of negative electrode)
Mesocarbon microbeads having an average particle size of 5 μm as the negative electrode active material, and a diene-based binder as the binder (glass transition temperature: −5 ° C., particle size when dried: 120 nm, dispersion medium: water, solid content concentration 40%) A slurry solution was prepared so that the solid content concentration of the negative electrode active material was 60% by mass. This slurry solution was applied to a 10 μm thick copper surface and dried to remove the solvent. Thereafter, the copper was rolled with a roll press and punched into a disk shape having a diameter of 16 mm, which was used as a negative electrode.

(Production of battery)
The positive electrode and the negative electrode produced by the above-described method are overlapped via a separator made of polyethylene (film thickness 25 μm, porosity 50%, pore diameter 0.1 μm to 1 μm), and then inserted into a SUS disk type battery. Then, 1 ml of the electrolyte was injected and sealed to prepare a battery. As the electrolytic solution, ethylene carbonate and methyl ethyl carbonate were adjusted so as to have a mass ratio of 1: 2, and then a solution in which LiPF ₆ was adjusted to 1 mol / L as an electrolyte was used.

(Measurement of initial charge efficiency and charge / discharge cycle test)
The measurement of the initial charging efficiency and the charge / discharge cycle test of the produced battery were performed using a charge / discharge device HJ-201B manufactured by Hokuto Denko Corporation.

  In order to calculate the initial charging efficiency of the battery, the battery was charged at a constant current of 0.67 mA, reached 4.2 V, and then charged at a constant voltage of 4.2 V for a total of 8 hours. Thereafter, the battery was discharged at a constant current of 0.67 mA until the voltage reached 3.0V. The initial charge efficiency of the battery was a value obtained by dividing the capacity at the first discharge by the capacity at the first charge. The ambient temperature of the battery was 20 ° C.

  As a battery charge / discharge cycle test, first, the battery was charged at a constant current of 2 mA, reached 4.2 V, and then charged at a constant voltage of 4.2 V for a total of 3 hours. Thereafter, the battery was discharged at a constant current of 2 mA, and when it reached 3.0 V, charging was repeated again. One cycle means that charging and discharging are performed once. The ambient temperature of the battery was 20 ° C.

  The capacity retention rate at the 300th cycle was calculated as follows to evaluate the cycle characteristics of the battery. The results are shown in Table 3.

  Capacity maintenance rate at 300th cycle = (discharge capacity at 300th cycle) / (discharge capacity at the second cycle) × 100 (%).

[Example 4]
In (ion exchange and solvent substitution), the initial charge efficiency was measured and the charge / discharge cycle was tested in the same manner as in Example 3 except that the fluorine-based polymer electrolyte solution obtained in Example 2 was used. The results are shown in Table 3.

[Example 5]
In (Preparation of positive electrode), the same procedure as in Example 3 was conducted except that a mixed binder having a mass ratio of 2.5 for the fluorine-based polymer electrolyte and 2.5 for the polyvinylidene fluoride (PVDF) was used. The charge efficiency was measured and the charge / discharge cycle was tested. The results are shown in Table 3.

  The polyvinylidene fluoride (PVDF) constituting the mixed binder is a 12% by mass polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution (Kureha KF Binder # 1120). Prepared.

[Example 6]
In (ion exchange and solvent substitution), the initial charge efficiency was measured and the charge / discharge cycle was tested in the same manner as in Example 5 except that the fluorine-based polymer electrolyte solution obtained in Example 2 was used. The results are shown in Table 3.

[Example 7]
In (Preparation of positive electrode), the same procedure as in Example 3 was performed except that a mixed binder having a mass ratio of fluorinated polymer electrolyte of 0.5 and polyvinylidene fluoride (PVDF) of 4.5 was used as a binder. The charge efficiency was measured and the charge / discharge cycle was tested. The results are shown in Table 3.

  The polyvinylidene fluoride (PVDF) constituting the mixed binder is a 12% by mass polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution (Kureha KF Binder # 1120). Prepared.

[Example 8]
In (ion exchange and solvent substitution), the initial charge efficiency was measured and the charge / discharge cycle was tested in the same manner as in Example 7 except that the fluorine-based polymer electrolyte solution obtained in Example 2 was used. The results are shown in Table 3.

[Comparative Example 2]
In (Preparation of positive electrode), the measurement of the initial charge efficiency and the charge / discharge cycle test were performed in the same manner as in Example 3 except that polyvinylidene fluoride (PVDF) was used as the binder. The results are shown in Table 3.

  The polyvinylidene fluoride (PVDF) constituting the binder is a 12% by mass polyvinylidene fluoride (PVDF) / N-methyl-2-pyrrolidone (NMP) solution (Kureha KF Binder # 1120). Prepared.

From the results in Table 3, it was found that the non-aqueous lithium ion secondary battery of the present embodiment is suppressed in capacity reduction even after 300 cycles and has good cycle characteristics.

  It is clearly shown that the binder containing the fluorine-based polymer electrolyte of the present embodiment contributes to the improvement of battery performance by acting as a binder that contributes to ion conduction rather than acting as a simple ion insulating binder. It was done.

Claims (10)

Including a fluorine-based polymer electrolyte having a structural unit represented by the following formula (1):
The binder for secondary battery positive electrode formation whose at least one part of Z in this fluorine-type polymer electrolyte is an alkali metal atom, an alkaline-earth metal atom, or an ammonium group.
_{^{- [CF 2 CX 1 X 2}} ] a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - ( CF ₂ ) _f −X ⁴ )] _g − (1)
(In the formula (1),
X ¹ , X ² and X ³ are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms,
a and g are 0 ≦ a <1, 0 <g ≦ 1, a + g = 1,
b is an integer of 0 to 8,
c is 0 or 1,
d, e and f are each independently an integer of 0 or more and 6 or less, and 0 <d + e + f,
R ¹ and R ² are each independently a halogen atom, a perfluoroalkyl group or a fluorochloroalkyl group having 1 to 10 carbon atoms,
X ⁴ is COOZ, SO ₃ Z, PO ₃ Z ₂ or PO ₃ HZ (where Z is a hydrogen atom, an alkali metal atom, an alkaline earth metal atom or an ammonium group). )   The binder for secondary battery positive electrode formation of Claim 1 whose at least one part of Z in the said fluorine-type polymer electrolyte is an alkali metal atom.   The binder for secondary battery positive electrode formation of Claim 1 whose at least one part of Z in the said fluorine-type polymer electrolyte is lithium. Furthermore, a non-ion conductive binder is included,
The binder for secondary battery positive electrode formation as described in any one of Claims 1-3 whose content of this nonionic conductive binder is 90 mass% or less.   The electrode mixture for secondary battery positive electrodes containing the binder for secondary battery positive electrode formation as described in any one of Claims 1-4, and powder electrode material.   The electrode mixture for a secondary battery positive electrode according to claim 5, wherein the content of the binder for forming a secondary battery positive electrode is 0.5 to 15% by mass. A current collector and the electrode mixture for a secondary battery positive electrode according to claim 5 or 6,
An electrode structure in which a layer of the electrode mixture for a secondary battery positive electrode is formed on at least one surface of the current collector. An aqueous secondary battery comprising a positive electrode, a negative electrode, a separator and an aqueous electrolyte,
An aqueous secondary battery, wherein the positive electrode is the electrode structure according to claim 7. A non-aqueous secondary battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution,
A nonaqueous secondary battery, wherein the positive electrode is the electrode structure according to claim 7. A non-aqueous lithium ion secondary battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte solution,
A non-aqueous lithium ion secondary battery, wherein the positive electrode is the electrode structure according to claim 7.