JPH11224671A - Nonaqueous electrolyte secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve adhesion between electrode active material carriers and between the electrode active material carrier and a current collector and to improve the cycle characteristic of a battery by using a resin composition obtained by reacting a coupling agent with a resin having the reactive functional group as a binder. SOLUTION: A resin composition obtained by reacting a resin having the reactive functional group with a coupling agent having the functional group reacting with the functional group of the resin is used as the binder component of a binder for forming an electrode layer. A polyamide imide resin is preferably used for the resin having the reactive functional group. The polyamide imide resin is excellent in electrolyte resistance and heat resistance. The content of the coupling agent against the resin having the reactive functional group is set to the range of 0.1-50 wt.%. The weight ratio between the binder component and the electrode active material carrier in an electrode mix layer is preferably set to 3:97-20:80. The deterioration of the electrode layer and the peeling of the electrode active material carrier from a current collector in repeated charges/discharges can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics. More specifically, the present invention relates to a non-aqueous electrolyte secondary battery having an electrode layer formed by molding an electrode active material carrier using a binder component, and more particularly to a feature of the binder component.

[0002]

2. Description of the Related Art In recent years, demands for high energy density secondary batteries have increased with the advance of high performance, miniaturization, and weight reduction of portable electronic devices, and with the progress of research and development for practical use of electric vehicles. ing. Nickel-cadmium batteries and lead batteries have been widely used in the past, but these batteries have a low discharge capacity per volume or weight and a low discharge voltage. It was not able to fully meet the demand for batteries.

In recent years, as a battery system satisfying these requirements, a non-aqueous electrolyte secondary battery using a material capable of inserting and extracting lithium metal or lithium ion as a negative electrode has been receiving attention.
Research is being actively conducted. However, in the case of a nonaqueous electrolyte secondary battery using metallic lithium as the negative electrode, dissolution of metallic lithium, generation of dendrites during deposition, and miniaturization of deposited lithium cause internal short-circuits and reduced electrode activity. However, there is a problem that sufficient cycle characteristics cannot be obtained.

A lithium ion nonaqueous electrolyte secondary battery using a negative electrode made of a material capable of inserting and extracting lithium ions as an electrode active material carrier, for example, a carbonaceous material, can obtain a high discharge voltage close to the case of using a metal lithium anode. In addition, even when the charge and discharge cycle proceeds, there is no generation of dendrites and finely divided lithium as in the case of a metal lithium anode, and an internal short circuit does not easily occur, and excellent battery performance with little deterioration in cycle characteristics is exhibited.

The negative electrode of such a non-aqueous electrolyte secondary battery is
The powder is prepared by uniformly dispersing the powder of the electrode active material carrier and the binder resin in a solvent to form a paste, applying the paste on a metal foil, drying and pressing.

However, in the above-mentioned non-aqueous electrolyte secondary battery, the adhesion between the electrode active material carrier and the metal foil is small, and peeling occurs during repeated charging and discharging, and the cycle characteristics are not sufficient. There is a need for further improvements.

[0007]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a non-aqueous electrolyte comprising an electrode layer in which an electrode active material carrier is formed using a binder component. The purpose is to improve the cycle characteristics of the secondary battery.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies and as a result, have found that a resin having a reactive functional group in a binder component and a functional group that reacts with the functional group of the resin have been developed. The present inventors have found that it is useful to use a resin composition obtained by reacting with a coupling agent having the same, and have reached the present invention.

That is, the present invention relates to a nonaqueous electrolyte secondary battery provided with an electrode layer formed by molding an electrode active material carrier using a binder component, wherein the binder component has a resin having a reactive functional group and A non-aqueous electrolyte secondary battery comprising a resin composition obtained by reacting a functional group with a coupling agent having a functional group that reacts.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the non-aqueous electrolyte secondary battery of the present invention, by using a resin composition obtained by reacting a coupling agent with a resin having a reactive functional group as a binder resin, electrode active material carriers or electrode active material carriers are used. To improve the adhesion between the metal foil and the current collector. Thereby, the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.

In the present invention, the electrode active material carrier is a substance capable of inserting and extracting lithium ions.
Further, the binder component refers to a binder for forming an electrode layer.

The non-aqueous electrolyte secondary battery of the present invention comprises a resin composition obtained by reacting a resin whose binder component has a reactive functional group with a coupling agent having a functional group that reacts with the functional group of the resin. It is characterized by becoming. Here, the reactive functional group of the resin and the coupling agent is not particularly limited as long as a combination capable of forming a bond with each other is selected,
For example, vinyl group, amino group, epoxy group, methacryl group, mercapto group, chloro group, hydroxyl group, carboxyl group, alkylene oxide group, isocyanate group,
Examples thereof include an alkylene nitride group, an oxazoline group, an N-methylol group, and an N-alkoxymethyl group. Among them, an amino group, an epoxy group, and an isocyanate group are particularly preferable in terms of reactivity and adhesion.

The resin having such a reactive functional group can form a bond by reacting with a coupling agent having a reactive functional group which reacts with the functional group of the resin. By using the resin composition reacted with the coupling agent as a binder resin in this manner, the adhesion between the electrode active material carriers or between the electrode active material carriers and the metal foil as the current collector is improved, and the Even during charge and discharge, deterioration of the electrode layer and peeling of the electrode active material carrier from the current collector are suppressed. Thereby, the cycle characteristics of the non-aqueous electrolyte secondary battery can be improved.

When a resin having no reactive functional group or a resin having a low reactive functional group, for example, polyethylene, polypropylene, styrene butadiene rubber, nitrile butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride or the like is used. The interaction between the resin and the coupling agent is small, and the effect of improving the cycle characteristics is not sufficient.

As the resin having a reactive functional group, a polyamideimide resin is particularly preferred. Polyamide imide resin has excellent electrolyte solution resistance and heat resistance, and has excellent properties as a binder resin for an electrode material for a non-aqueous electrolyte secondary battery. The polyamideimide resin is synthesized from tricarboxylic acid as an acid component and diamine or diisocyanate as an amine component.

Examples of the tricarboxylic acid as an acid component used in the synthesis of the polyamideimide resin include trimellitic acid, butane-1,2,4-tricarboxylic acid, and naphthalene-1,2,4-tricarboxylic acid. And are usually used as these anhydrides, acid chlorides and the like. Preferred is trimellitic anhydride.

Some of the above tricarboxylic acids can be replaced by the following dicarboxylic acids, polycarboxylic acids, and their anhydrides and acid chlorides.

Examples of the dicarboxylic acids include aliphatic dicarboxylic acids and aromatic dicarboxylic acids.

As the aliphatic dicarboxylic acid, oxalic acid,
Examples include malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, tridecandioic acid, cyclohexanedicarboxylic acid, and acid chlorides thereof. Among them, adipic acid, sebacic acid and azelaic acid are preferred.

As the aromatic dicarboxylic acid, for example, isophthalic acid, 5-tert-butyl-1,3-benzenedicarboxylic acid, terephthalic acid, diphenylmethane-4,4 '
-Dicarboxylic acid, diphenylmethane-2,4-dicarboxylic acid, diphenylmethane-3,4-dicarboxylic acid, diphenylmethane-3,3'-dicarboxylic acid, 1,2-diphenylethane-4,4'-dicarboxylic acid, diphenylethane- 2,4-dicarboxylic acid, diphenylethane-3,
4-dicarboxylic acid, diphenylethane-3,3'-dicarboxylic acid, 2,2-bis (4-carboxyphenyl) propane, 2- (2-carboxyphenyl) -2- (4-
(Carboxyphenyl) propane, 2- (3-carboxyphenyl) -2- (4-carboxyphenyl) propane, diphenylether-4,4′-dicarboxylic acid, diphenylether-2,4-dicarboxylic acid, diphenylether-3,4-dicarboxylic Acid, diphenylether-3,3'-dicarboxylic acid, diphenylsulfone-4,
4'-dicarboxylic acid, diphenylsulfone-2,4-dicarboxylic acid, diphenylsulfone-3,4-dicarboxylic acid, diphenylsulfone-3,3'-dicarboxylic acid, benzophenone-4,4'-dicarboxylic acid, benzophenone-3 , 3'-Dicarboxylic acid, cyclohexane-1,4
-Dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, naphthalenedicarboxylic acid, bis [(4-carboxy) phthalimide]-
4,4′-diphenyl ether, bis [(4-carboxy) phthalimide] -α, α′-meta-xylene, and acid chlorides thereof. Preferred are isophthalic acid and terephthalic acid.

Examples of the polycarboxylic acid include, for example,
Butane-1,2,3,4-tetracarboxylic acid, pyromellitic acid, benzophenone-3,3 ′, 4,4′-tetracarboxylic acid, diphenylether-3,3 ′, 4,4 ′
-Tetracarboxylic acid, biphenyl-3,3 ', 4,4'
-Tetracarboxylic acid, naphthalene-2,3,6,7-tetracarboxylic acid, naphthalene-1,2,4,5-tetracarboxylic acid, naphthalene-1,2,5,8-tetracarboxylic acid and the like. You. In addition, these anhydrides, chlorides and the like are also included. Of these, pyromellitic acid is preferred.

These acid components can be used alone or as a mixture of two or more types together with the carboxylic acid as long as the properties as the binder resin in the present invention are not impaired.

On the other hand, examples of the amine component include diamine and diisocyanate, but are not particularly limited.

Examples of the diamine include m-phenylenediamine, p-phenylenediamine, m-xylylenediamine, p-xylylenediamine, 1,4-naphthalenediamine, 1,5-naphthalenediamine, and 2,6-naphthalenediamine. , 2,7-naphthalenediamine, 2,2
-Bis (4-aminophenyl) hexafluoropropane, 4,4'-diaminodiphenylmethane, 4,4'-
Diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4-
Diaminodiphenyl ether, 3,4-diaminobiphenyl, 4,4′-diaminobenzophenone, 3,3′-
Diaminobenzophenone, isopropylidene dianiline, o-tolidine, 2,4-tolylenediamine, 1,3
-Bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 2,2-bis [4
-(4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone,
Bis [4- (3-aminophenoxy) phenyl] sulfone, 4,4′-bis (4-aminophenoxy) biphenyl, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, Fats such as aromatic diamines such as 4'-diaminodiphenyl sulfide and 3,3'-diaminodiphenyl sulfide, methylene diamine, ethylene diamine, propylene diamine, tetramethylene diamine, hexamethylene diamine, hexafluoro methylene diamine, hexafluoro isopropylidene diamine Aromatic diamine; isophorone diamine, 4,4 '
And alicyclic diamines such as dicyclohexylmethanediamine.

Examples of the diisocyanate include those obtained by replacing the amino group of the above diamine with a -N = C = O group. Among these, 4,4'-diaminodiphenylmethane, isophoronediamine, 4,4'-dicyclohexylmethanediamine, or diisocyanates thereof are preferable in terms of reactivity, solubility, cost, and the like.

The above-mentioned acid component and amine component are usually used in the synthesis of a polyamideimide resin by mixing them in equimolar amounts. However, if necessary, one of the components may be slightly increased or decreased.

The polyamide-imide resin of the present invention comprises:
It is synthesized from the acid component and the amine component, and the synthesis method is not particularly limited, and examples thereof include a melt polymerization method and a solution polymerization method.

Various additional components may be added to the polyamideimide resin of the present invention as needed. Examples of the additive component include a synthetic resin surfactant such as polyester, polyamide, polyimide, acrylic, NBR, SBR, and PVDF, and a plasticizer. The additive component is
The above acid component and / or
Alternatively, a part of the amine component may be replaced and subjected to copolymerization, or may be added by mixing with the synthesized polyamideimide resin.

As the coupling agent, for example, vinyltrichlorosilane, vinyltris (β-methoxyethoxy)
Silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β ( Aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ
Silane coupling agents such as aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, isopropyl Triisostearoyl titanate, tetraoctyloxytitanium di (dilauryl phosphite), tetra (2,2-diallyloxymethyl-1-butenoxytitanium di (di-tridecyl) phosphite, tetraisopropyldi (dioctyl phosphite) Titanate, isopropyl tri (dioctyl pyrophosphate) titanate, titanium di (dioctyl pyrophosphate) oxyacetate, di (dioctyl pyrophosphate) ethylene titanate, isopropyl Examples include titanium coupling agents such as tri (N-ethylaminoethylamino) titanate and isopropyl tridodecylbenzenesulfonyl titanate, and aluminum coupling agents such as acetoalkoxy aluminum diisopropylate and aluminum monoacetyl acetonate. There is no particular limitation as long as it can form a bond with a functional functional group.

The content of the coupling agent with respect to the resin having a reactive functional group is preferably 0.1 to 50.
% By weight. More preferably, it is in the range of 0.5 to 25% by weight. When the content of the coupling agent is 0.1
If the amount is less than 10% by weight, the effect of improving the cycle characteristics due to the effect of the addition of the coupling agent is undesirably reduced. Further, when the content of the coupling agent is more than 50% by weight,
The adhesive strength of the electrode layer by the binder resin becomes small, which is not preferable.

The electrode layer of the present invention is prepared by applying a paste-like mixture obtained by mixing and dispersing the above binder component (in an unreacted or / and reacted state) and a particulate electrode active material carrier in a solvent onto a metal foil, followed by drying. Formed.

The solvent used in the above mixture is N-methyl-
It is preferable to include at least one of 2-pyrrolidone, γ-butyrolactone, cyclohexanone, and xylene. Particularly preferably, from the viewpoint of solubility, N-methyl-
2-pyrrolidone.

The electrode layer and the method for producing the same according to the present invention can be applied to either or both of the negative electrode and the positive electrode of a non-aqueous electrolyte secondary battery. As the electrode active material carrier, various materials known as a negative electrode material and a positive electrode material can be used, and the type thereof is not particularly limited, for example, a carbonaceous material, lithium, a lithium-aluminum alloy, a tin oxide, titanium dioxide, Examples include transition metal lithium composite oxides such as vanadium pentoxide, lithium cobaltate, lithium nickelate, and lithium permanganate, conductive polymers, and disulfide compounds. The negative electrode material is preferably a carbonaceous material. The positive electrode material is preferably a transition metal lithium composite oxide.

When a carbonaceous material is used as the negative electrode material, the carbonaceous material may be a low-crystalline carbon material obtained by firing at a relatively low temperature of 2000 ° C. or less, or a raw material that is easily crystallized at 3000 ° C. Highly crystalline carbon materials that have been treated at a nearby high temperature can preferably be used. For example,
Pyrolytic carbons, cokes, mesophase pitch-based carbons, artificial graphites, natural graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and the like can be used.

In particular, the spacing between the (002) planes is 3.7.
0 Å or more, true specific gravity of less than 1.70 g / cc, and a low crystalline carbon material having no peak at 700 ° C. or more in differential thermal analysis in an air stream, or a true specific gravity with a high negative electrode mixture filling property of 2. A highly crystalline carbon material of 10 g / cc or more can be preferably used. The average particle size of the carbonaceous material may be a known value, preferably 5 to 100.
It is about μm, more preferably in the range of 10 to 50 μm.

In the present invention, the weight ratio of the binder component to the electrode active material carrier in the electrode mixture layer is preferably 3: 9.
7 to 20:80, more preferably 5:95 to 10:90
It is. When the content of the electrode active material carrier is larger than the above range, cracks are generated in the electrode mixture layer, and the electrode mixture layer tends to be easily separated from the current collector such as a metal foil. If the content of the carbonaceous material is less than the above range, the charge / discharge cycle characteristics of the battery tend to be reduced.

As the non-aqueous solvent of the non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, non-aqueous solvents conventionally used in various non-aqueous electrolyte secondary batteries can be preferably used. . For example, in the case of a lithium ion nonaqueous electrolyte secondary battery, a high dielectric constant solvent such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, and a low viscosity solvent such as 1,2-dimethoxyethane and 2- Methyl tetrahydrofuran, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like can be used.

As described above, the electrolyte used for preparing a non-aqueous electrolyte by dissolving it in a non-aqueous solvent generally differs depending on the type of conductive ion. LiClO ₄ , LiAsF ₆ ,
LiPF ₆ , LiBF ₄ , LiCl, LiBr, CH ₃
It is preferable to use SO ₃ Li, CF ₃ SO ₃ Li, or the like. These can be used alone or in combination of two or more.

Other structures such as the separator, battery can, and PTC element of the non-aqueous electrolyte secondary battery of the present invention can be the same as those of the conventional lithium ion non-aqueous electrolyte secondary battery.

The shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a button shape can be used as needed. .

[0041]

EXAMPLES Hereinafter, the nonaqueous electrolyte secondary battery of the present invention will be described in detail with reference to examples. The present invention is not limited by these examples.

Example 1 (1) Synthesis of Binder Resin 96 g of trimellitic anhydride and 10 of sebacic acid were placed in a reaction vessel.
1 g, 265 g of 4,4′-dicyclohexylmethane diisocyanate and 1 g of potassium fluoride were added to N-methyl-2-
Charge with 900 g of pyrrolidone and raise the temperature to 200 ° C.
After reacting for an hour, N-methyl-2 was further added while cooling.
950 g of pyrrolidone was added to obtain a polyamideimide resin solution having a solid content of 20% by weight. With respect to 98.75 parts by weight of the solid content of this resin solution, 1.25 parts by weight of γ-
Glycidoxypropyltrimethoxysilane was added as a coupling agent, the temperature was raised to 80 ° C., and the mixture was reacted for 1 hour to obtain a binder resin solution.

(2) Preparation of Carbonaceous Material A carbonaceous material was obtained by sintering mesophase pitch small spheres at 1200 ° C. in an inert gas to obtain a particle size of 1 to 30 μm.

(3) Preparation of electrode 93 parts by weight of the carbonaceous material prepared in (2) and 35 parts by weight (7 parts by weight of solid content) of the binder resin synthesized in (1) were mixed, and N-methyl-2 was added. -The mixture was diluted with pyrrolidone so that the solid content concentration became 50% by weight, dispersed and kneaded to prepare a paste mixture. The obtained paste-like mixture was coated on one surface of a copper foil having a thickness of 10 μm with a dry film thickness of 250 μm.
After coating and drying to a thickness of μm, the electrode was pressed by a hot roll press at 200 ° C. to form an electrode having a thickness of 125 μm including a copper foil.

Example 2 An electrode was prepared in the same manner as in Example 1 except that isocyanatopropyltrimethoxysilane was used as a coupling agent.

Comparative Example 1 An electrode was prepared in the same manner as in Example 1, except that the coupling agent was not reacted.

<Preparation of Battery> The electrodes of Examples 1-2 and Comparative Example 1 prepared as described above were cut into an area of 0.8 cm ² and faced with a lithium foil via a 25 μm-thick porous polypropylene film. Then, a non-aqueous electrolyte obtained by dissolving LiClO ₄ at a ratio of 1 mol / liter in an equal volume mixture of ethylene carbonate and dimethyl carbonate is poured into a nickel-plated iron battery can container, sealed, and sealed. A water electrolyte secondary battery was prepared.

The adhesion of the electrodes prepared in Examples 1 and 2 and Comparative Example 1 and the battery performance of the non-aqueous electrolyte secondary battery prepared using these electrodes were evaluated as follows. .

<Adhesion> The peel strength of the electrode layer and the copper foil in the 180 ° direction was measured using Tensilon manufactured by Toyo Baldwin.

<Evaluation of Battery Performance> With respect to the non-aqueous electrolyte secondary batteries prepared using the electrodes of Examples 1 and 2 and Comparative Example 1, a return voltage of 0 V and a constant current of 0.5 mA / cm ² were obtained. A charge / discharge cycle test was performed between 2V.
The value obtained by dividing the discharge capacity at five cycles by the discharge capacity at two cycles in the charge / discharge cycle test was defined as a capacity retention ratio (%). Table 1 shows the results.

[0051]

[Table 1]

From the results shown in Table 1, the electrodes of Examples 1 and 2
This shows that the adhesion is improved as compared with the electrode of Comparative Example 1. In addition, the non-aqueous electrolyte secondary battery prepared using the electrodes of Examples 1 and 2 has a higher capacity retention ratio than the non-aqueous electrolyte secondary battery prepared using the electrode of Comparative Example 1. Is shown.

[0053]

As described above, the non-aqueous electrolyte secondary battery provided with the electrode layer containing the electrode active material carrier and the binder resin according to the present invention can provide the adhesion between the electrode active material carriers and the current collection with the electrode active material carrier. Adhesion with metal foil which is the body is improved,
Thereby, the charge / discharge cycle characteristics are improved. Therefore, the present invention is suitable as a power supply for various small devices, and particularly for a power storage or an electric vehicle that requires cycle stability.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Tomoharu Kurita 2-1-1 Katata, Otsu City, Shiga Prefecture Toyobo Co., Ltd. Research Laboratory

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising an electrode layer formed by molding an electrode active material carrier using a binder component, wherein the binder component reacts with a resin having a reactive functional group and a functional group of the resin. A non-aqueous electrolyte secondary battery comprising a resin composition obtained by reacting with a coupling agent having a functional group. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin having a reactive functional group is a polyamideimide resin. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the coupling agent with respect to the resin having a reactive functional group is 0.1 to 50% by weight. 4. An electrode active material carrier and a binder component are obtained by being mixed and dispersed in a solvent containing at least one selected from the group consisting of N-methyl-2-pyrrolidone, γ-butyrolactone, cyclohexanone, and xylene. The method for producing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the paste is applied to a metal foil and dried to form an electrode layer.