JP2000133273A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having the excellent adhesiveness of a binder to a carrier and capable of obtaining a good cycle characteristic. SOLUTION: This secondary battery is constituted of a positive electrode made of a positive electrode active material, a carrier and a binder, a negative electrode made of a negative electrode active material, a carrier and a binder, and an organic electrolyte. A hardened composition containing an epoxy resin (A), a hardening agent (B), an acrylic copolymer (C) and a hardening accelerator (D) is used for the binder of the positive electrode and/or the negative electrode, or an adhesive layer which is a hardened composition containing the epoxy resin (A), hardening agent (B), acrylic copolymer (C) and hardening accelerator (D) is provided between the carrier and binder (except for the composition of the adhesive layer) of the positive electrode and/or negative electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a support for a binder by improving a binder for holding an active material of an electrode or by providing an adhesive layer between a support for a positive electrode and a negative electrode and the binder. The present invention relates to a secondary battery having excellent adhesion to a body and obtaining good cycle characteristics.

[0002]

2. Description of the Related Art In recent years, with the spread of devices such as portable personal computers and video cameras, there has been an increasing demand for secondary batteries which can be used repeatedly instead of disposable primary batteries. As a secondary battery, Japanese Patent Publication No. 62-23433
A rechargeable lithium battery using a carbon powder such as graphite powder containing lithium and a negative electrode mainly composed of a fluororesin as a binder has been proposed as described in Japanese Patent Application Laid-Open Publication No. H11-209,837. However, a secondary battery using a fluorocarbon resin as a binder is a binder and a support for the electrode (current collector).
And the binder is peeled off from the support, and the cycle life is shortened.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a secondary battery having excellent adhesion between a binder and a support and having a long cycle life. That is, the present inventors have proposed a secondary battery in which a binder is a cured product of a composition containing an epoxy resin, a curing agent, an acrylic copolymer and a curing accelerator, or a support for a binder and a positive electrode and a negative electrode. The present inventors have found that a secondary battery having an adhesive layer, which is a cured product of the above composition, between the body improves the adhesion between the support and the binder and prolongs the cycle life, leading to the present invention.

[0004]

SUMMARY OF THE INVENTION The present invention provides a positive electrode active material,
In a secondary battery composed of a positive electrode comprising a support (also referred to as a current collector; the same applies hereinafter) and a binder, a negative electrode comprising a negative electrode active material, a support and a binder, and an organic electrolytic solution, And / or a secondary battery in which the binder of the negative electrode is a cured product of a composition containing (A) an epoxy resin, (B) a curing agent, (C) an acrylic copolymer, and (D) a curing accelerator.

[0005] The present invention also relates to a method for preparing a positive electrode and / or a negative electrode between a support and a binder (excluding the composition of an adhesive layer).
The present invention relates to a secondary battery having an adhesive layer which is a cured product of a composition containing (A) an epoxy resin, (B) a curing agent, (C) an acrylic copolymer, and (D) a curing accelerator.

In the present invention, the binder is represented by the following (A)
It is preferable to use a cured product of a composition containing (D) to (D). (A) 100 parts by weight of epoxy resin, (B) curing agent
30 to 70 parts by weight, (C) 2 to 6% by weight of glycidyl (meth) acrylate and a weight average molecular weight of 400,
100 to 300 parts by weight of an acrylic copolymer having an epoxy group of 000 or more, (D) a curing accelerator 0.1
~ 5 parts by weight.

In the present invention, a cured product of the composition containing the following (A) to (D) is provided between the support of the positive electrode and / or the negative electrode and the binder (excluding the composition of the adhesive layer). It is preferable to have an adhesive layer that is (A) 100 parts by weight of epoxy resin, (B) curing agent
30 to 70 parts by weight, (C) 2 to 6% by weight of glycidyl (meth) acrylate and a weight average molecular weight of 400,
100 to 300 parts by weight of an acrylic copolymer having an epoxy group of 000 or more, (D) a curing accelerator 0.1
~ 5 parts by weight.

[0008]

Next, the secondary battery of the present invention will be described in detail. Constituent (A) of the binder in the present invention
The epoxy resin is not particularly limited as long as it has adhesiveness after curing, but is bifunctional or more, and has a molecular weight of 5,000.
It is preferably 0 or less, and more preferably the molecular weight is 3,000 or less. In particular, the use of a bisphenol A type or bisphenol F type liquid resin having a molecular weight of 500 or less is more preferable because the fluidity during lamination is improved. Bisphenol A type or bisphenol F type liquid resins having a molecular weight of 500 or less include Epicoat 807,
E. epicoat 827, epicoat 828 (both Yuka Shell Epoxy), D.I. E. FIG. R. 330, D.I. E. FIG. R. 33
1, D. E. FIG. R. 361 (Dow Chemical Japan), Y
D128, YDF170 (Toto Kasei) and the like are commercially available.

Further, as the epoxy resin (A) in the present invention, a polyfunctional epoxy resin may be added to increase the glass transition point (Tg). Specifically, examples of the polyfunctional epoxy resin include a phenol novolak type epoxy resin and a cresol novolak type epoxy resin. Phenol novolak type epoxy resin is EPPN-20
1 (Nippon Kayaku), cresol novolac type epoxy resin is ESCN-001, ESCN-195 (Sumitomo Chemical Co., Ltd.), EOCN1012, EOCN1025, EO
CN1027 (Nippon Kayaku) and the like are commercially available.

The component (B) curing agent of the binder in the present invention is not particularly limited, as long as it is generally used as a curing agent for epoxy resins, but it is not limited to amines, polyamides, acid anhydrides, polysulfides. , Boron trifluoride and bisphenol A, bisphenol F and bisphenol S having two or more phenolic hydroxyl groups in one molecule. In particular, a phenol novolak resin, a bisphenol novolak resin, and a cresol novolak resin are preferable because they have excellent electric corrosion resistance during moisture absorption. Examples of such a curing agent include phenolite LF2882, phenolite LF2822, phenolite TD-2090,
Phenolite TD-2149, Phenolite VH415
0, phenolite VH4170 (Dainippon Ink and Chemicals) and the like are commercially available.

In the present invention, the compounding amount of the curing agent (B) is
(A) 30 to 100 parts by weight of the total amount of epoxy resin
Preferably it is 70 parts by weight. (B) If the compounding amount of the curing agent is less than 30 parts by weight, unreacted epoxy resin components remain in the electrode and the heat resistance tends to be deteriorated. The curing agent component of the reaction remains, and the heat resistance tends to deteriorate.

As the constituent (C) acrylic copolymer of the binder in the present invention, an acrylic copolymer having an epoxy group containing glycidyl (meth) acrylate is preferable, and HTR-860P-3 (Teikoku Chemical) Industry) are commercially available. Further, the amount of glycidyl (meth) acrylate used as the functional group monomer is preferably 2 to 6% by weight based on the total amount of the acrylic copolymer. The amount of glycidyl (meth) acrylate is 2
If the amount is less than 6% by weight, the adhesive strength tends to decrease. If the amount exceeds 6% by weight, the rubber tends to gel. Further, as the (C) acrylic copolymer,
For example, ethyl (meth) acrylate, butyl (meth)
It can be obtained by polymerizing acrylate or a mixture of both by pearl polymerization, solution polymerization or the like.

The weight average molecular weight of the acrylic copolymer (C) in the present invention is preferably 400,000 or more. If the weight average molecular weight is less than 400,000, the strength and flexibility of the binder layer and the adhesive layer tend to decrease.

In the present invention, the amount of the acrylic copolymer (C) is preferably 100 to 300 parts by weight based on 100 parts by weight of the total amount of the epoxy resin (A) and the curing agent (B). (C) The amount of the acrylic copolymer is 1
If the amount is less than 00 parts by weight, the strength and flexibility of the binder and the adhesive layer tend to decrease, and if it exceeds 300 parts by weight, the operability at high temperatures tends to decrease.

It is preferable to use various imidazoles as the curing accelerator (D) in the present invention. Specific examples include 2-methylimidazole, 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, and the like, and 2E4MZ, 2PZ
-CN, 2PZ-CNS (these are Shikoku Chemicals) are commercially available.

In the present invention, the compounding amount of the (D) curing accelerator is 100% of the total amount of the (A) epoxy resin and (B) the curing agent.
It is preferably 0.1 to 5 parts by weight based on parts by weight. (D) If the compounding amount of the curing accelerator is less than 0.1 part by weight, outgas tends to be easily generated at the time of curing the epoxy resin, and if it exceeds 5 parts by weight, the storage stability of the epoxy resin solution is reduced. Tends to be worse.

In the present invention, the above (A) to (D)
Is cured at 150 to 240 ° C. for 30 minutes to 2 hours to form a binder.

In the present invention, a coupling agent is preferably added to improve the adhesion between different kinds of materials, and among them, a silane coupling agent is more preferable. Examples of the silane coupling agent include γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N
-Β-aminoethyl-γ-aminopropyltrimethoxysilane and the like. Specifically, NCUA-187
(Γ-glycidoxypropyltrimethoxysilane), N
CU A-189 (γ-mercaptopropyltrimethoxysilane), NCU A-1100 (γ-aminopropyltriethoxysilane), NCU A-1160 (γ-
Ureidopropyltriethoxysilane), NCU A-
1120 (N-β-aminoethyl-γ-aminopropyltrimethoxysilane, manufactured by Nippon Unicar) and the like are commercially available.

The amount of the coupling agent used in the present invention is determined according to the effect of addition, heat resistance and cost.
The amount is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the total amount of the epoxy resin, the (B) curing agent, the (C) acrylic copolymer, and the (D) curing accelerator.

As the positive electrode active material of the secondary battery according to the present invention, a material usually used in a secondary battery can be used. Specifically, lithium cobalt oxide, lithium cobalt nickel oxide, manganese dioxide, vanadium oxide, iron sulfide and the like can be mentioned.

As the negative electrode active material of the secondary battery according to the present invention, a material usually used in a secondary battery can be used. Specifically, carbon, coke, a fired body of an organic polymer material, polyacetylene, polypyrrole, and the like can be given.

The support of the positive electrode and the negative electrode of the secondary battery according to the present invention is not particularly limited, but aluminum is preferable as the positive electrode support and copper is preferable as the negative electrode support.

The organic electrolyte for the secondary battery according to the present invention is not particularly limited. For example, ethylene carbonate, dimethyl carbonate, butylene carbonate, propylene carbonate and the like can be used in the form of LiClO ₄ , LiPF ₆ ,
A solution in which an electrolyte such as LiBF ₄ or LiCl is dissolved can be used.

In the present invention, the binder for the positive electrode and / or the negative electrode, or the adhesive layer between the support (current collector) of the positive electrode and the negative electrode and the binder are (A) epoxy resin, (B) It preferably contains a curing agent, (C) an acrylic copolymer and (D) a curing accelerator, and has an elastic modulus at 25 ° C of 20 to 2,000 MPa. If the elastic modulus is less than 20 MPa, the film electrode tends to be sticky and difficult to handle, and if it exceeds 2,000 MPa, the binder layer containing the active material is supported when the film electrode is spirally formed. It tends to peel off from the body. Where 2
The elastic modulus at 5 ° C. was determined by measuring the tensile elastic modulus with a DVE rheometer (V4 manufactured by Rheology).

In the present invention, when the above composition is used as an adhesive layer between the support of the positive electrode and the negative electrode and the binder, the binder may be a cured product of the above composition such as polyvinylidene fluoride or the like. It is preferable to apply the above composition to a support using a conventionally known substance. The application method is not particularly limited, and examples thereof include a roll coat, a reverse roll coat, a gravure coat, a bar coat, and a spin coat.

The thickness of the adhesive layer in the present invention is preferably 0.05 to 10 μm, more preferably 0.1 to 5 μm. If the thickness of the adhesive layer is less than 0.05 μm, there is a tendency that sufficient adhesive strength cannot be obtained.
If it exceeds μm, the conductivity tends to deteriorate.

In the above-mentioned adhesive layer in the present invention, a conductive material such as silver or copper filler or the above-mentioned active material can be added to the above-mentioned resin in order to improve electric characteristics.

[0028]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto. Example 1 (Preparation of positive electrode) As an epoxy resin, 30 parts by weight of a bisphenol A type epoxy resin (epoxy equivalent: 200, manufactured by Yuka Shell Epoxy Co., Epicoat 828), a cresol novolak type epoxy resin (epoxy equivalent: 220, manufactured by Sumitomo Chemical Co., Ltd.) ESCN001) 10 parts by weight, a phenol novolak resin (Plyofen LF2882, manufactured by Dainippon Ink and Chemicals, Inc.) as a curing agent for the epoxy resin, 25 parts by weight, and an epoxy group-containing acrylic rubber (molecular weight 1, 1) 00000
0, 100 parts by weight, HTR-860P-3, manufactured by Teikoku Chemical Industry, curing accelerator (2PZ-CN, manufactured by Shikoku Chemicals)
An epoxy resin solution in which 0.5 part by weight was dissolved in 495 ml of cyclohexanone was prepared. The epoxy resin solution was cured at 200 ° C. for 1 hour to form a film, and the elastic modulus at 25 ° C. was measured.
Then, LiCo ₂ was added to 20 parts by weight of the above epoxy resin solution.
90 parts by weight and 5 parts by weight of a graphite powder as a conductive agent are dissolved and kneaded in 300 ml of N-methyl-2-pyrrolidone to prepare a varnish for a positive electrode, and a 20 μm-thick aluminum foil of a support (current collector) is prepared. On both sides, and vacuum dried at 200 ° C. for 1 hour to produce a positive electrode. (Preparation of negative electrode) To 20 parts by weight of the above epoxy resin solution,
95 parts by weight of graphite powder having an average particle diameter of 10 μm are dissolved and kneaded in 300 ml of N-methyl-2-pyrrolidone to prepare a varnish for a negative electrode, and both surfaces are coated on a 10 μm-thick aluminum foil of a support (current collector). This was applied and vacuum-dried at 200 ° C. for 1 hour to produce a negative electrode. (Preparation of Secondary Battery) The prepared film-shaped positive electrode and the film-shaped negative electrode were laminated via a 25-μm polypropylene separator and spirally wound many times to produce a spirally wound electrode body. The spiral electrode body was placed in a nickel-plated iron battery can, the positive electrode was connected to the battery lid by a positive electrode lead, and the negative electrode was connected to the battery can by a negative electrode lead. An organic electrolyte obtained by dissolving LiPF ₆ at a ratio of 1 mol / liter in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 was injected into the battery can to produce a secondary battery. .

Example 2 (Preparation of Positive Electrode) 90 parts by weight of LiCo ₂ as a positive electrode active material and 6 parts by weight of graphite powder as a conductive agent were mixed with N-methyl-2.
-Dissolved in 300 ml of pyrrolidone, and polyvinylidene fluoride (KF # 1100 manufactured by Kureha Chemical Industry) 4 as a binder
The weight part was kneaded to obtain a varnish for a positive electrode. The epoxy resin solution prepared in Example 1 was applied to both sides of an aluminum foil of a support (current collector) having a thickness of 20 μm, and dried at 150 ° C. for 3 minutes to prepare a current collector. The above-described varnish for a positive electrode was applied to both surfaces of a current collector, and vacuum-dried at 200 ° C. for 1 hour to prepare a positive electrode. (Preparation of negative electrode) 95 parts by weight of graphite powder having an average particle diameter of 10 μm, polyvinylidene fluoride (KF # 1 manufactured by Kureha Chemical Industry Co., Ltd.)
100) 5 parts by weight of N-methyl-2-pyrrolidone 30
The resultant was dissolved and kneaded in 0 ml to prepare a negative electrode varnish. The epoxy resin solution prepared in Example 1 was applied to both sides of a copper foil of a support (current collector) having a thickness of 10 μm, and this was applied at 150 ° C. for 3 hours.
After drying for minutes, a current collector was prepared. The above-mentioned varnish for a negative electrode was applied on both sides of a current collector, and vacuum-dried at 200 ° C. for 1 hour to produce a negative electrode. (Preparation of Secondary Battery) A secondary battery was prepared in the same manner as in Example 1 except that the above positive electrode and negative electrode were used.

Example 3 In preparing a positive electrode, an epoxy resin solution 2 was used as a binder.
A secondary battery was fabricated in the same manner as in Example 1, except that 0 parts by weight was changed to 5 parts by weight of polyvinylidene fluoride.

Comparative Example 1 A secondary battery was fabricated in the same manner as in Example 1 except that the epoxy resin solution (20 parts by weight) and the polyvinylidene fluoride (5 parts by weight) were used as binders when producing a positive electrode and a negative electrode. .

Comparative Example 2 In preparing a positive electrode and a negative electrode, 20 parts by weight of an epoxy resin solution was used as a binder in 20 m of N-methyl-2-pyrrolidone.
Polyamide resin dissolved in l (NYLON6 manufactured by Ube Industries) 5
A secondary battery was manufactured in the same manner as in Example 1 except that the weight was changed to parts by weight. The elastic modulus of the above polyamide resin at 25 ° C. was 20,000 MPa.

(Adhesion between support of each battery and binder) Adhesion between the support (current collector) of the positive electrode and the negative electrode prepared in Examples 1 to 3 and Comparative Examples 1 and 2 and the binder. Table 1 shows the results of measuring the strength.

(Cycle Characteristics of Each Battery) The batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were charged at room temperature at a charge current of 1400 mA to a charge end voltage of 4.2 V, and then discharged at a discharge current of 1400 mA. Table 1 shows the results of performing a series of cycle tests of discharging to a discharge end voltage of 2.5 V and measuring the number of cycles (80% capacity cycle number) at which the discharge capacity decreases to 80% of the initial capacity.

[0035]

[Table 1]

In the electrodes of Examples 1 to 3, the adhesion between the support and the binder was strong, and the support and the binder did not peel off during the cycle test, indicating good cycle characteristics. On the other hand, in the electrodes of Comparative Examples 1 and 2, the adhesion between the support and the binder was weak, and some peeling occurred at the interface between the support and the binder during the cycle test, and the 80% capacity cycle number was low. And sufficient cycle characteristics could not be obtained.

[0037]

According to the secondary battery of the present invention, an epoxy resin, a curing agent, and an acrylic resin are applied to the binder of the positive electrode and / or the negative electrode, or the adhesive layer between the support of the positive electrode and the negative electrode and the binder. By using a cured product of the composition containing the polymer and the curing accelerator, the adhesiveness of the binder to the support is excellent, and good cycle characteristics can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Doji 14 Goi South Coast, Ichihara-shi, Chiba F-term (reference) 5H029 AK02 AK03 AL06 AL16 AM03 AM07 DJ08 EJ11 HJ01

Claims (4)

[Claims] A positive electrode comprising a positive electrode active material, a support and a binder, a negative electrode comprising a negative electrode active material, a support and a binder,
And a secondary battery comprising an organic electrolyte, wherein the binder for the positive electrode and / or the negative electrode is (A) an epoxy resin,
A secondary battery which is a cured product of a composition containing (B) a curing agent, (C) an acrylic copolymer, and (D) a curing accelerator. 2. Between the support of the positive electrode and / or the negative electrode and the binder (excluding the composition of the adhesive layer), (A) an epoxy resin, (B) a curing agent, and (C) an acrylic copolymer. A secondary battery having an adhesive layer which is a cured product of a composition containing the coalesced and (D) a curing accelerator. 3. The secondary battery according to claim 1, wherein the binder is a cured product of a composition containing the following (A) to (D). (A) 100 parts by weight of epoxy resin, (B) curing agent
30 to 70 parts by weight, (C) 2 to 6% by weight of glycidyl (meth) acrylate and a weight average molecular weight of 400,
100 to 300 parts by weight of an acrylic copolymer having an epoxy group of not less than 000, (D) a curing accelerator 0.1 to
5 parts by weight. 4. Between the support of the positive electrode and / or the negative electrode and the binder (excluding the composition of the adhesive layer), the following (A) to
The secondary battery according to claim 2, further comprising an adhesive layer that is a cured product of the composition containing (D). (A) 100 parts by weight of epoxy resin, (B) curing agent
30 to 70 parts by weight, (C) 2 to 6% by weight of glycidyl (meth) acrylate and a weight average molecular weight of 400,
100 to 300 parts by weight of an acrylic copolymer having an epoxy group of not less than 000, (D) a curing accelerator 0.1 to
5 parts by weight.