JP2001043862A - Epoxy binder, composition for electrode material using same, electrode material using same composition, and electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode material resistant to being swelled with an electrolyte, giving a long time till a rupture valve operates, and giving a long service life to a battery. SOLUTION: An epoxy binder is used containing (A) an epoxy resin with two or more functions, (B) a novolak-type phenolic hardening agent, (C) one kind or more selected from among a group made up of a ureic accelerator, a phosphoric accelerator, and an accelerator made of aminic salt. and (D) a phenoxy resin. The use of this binder can provide an electrode material resistant to being swelled with an electrolyte, giving a long time till a rupture valve operates, and giving a long service life to a battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an epoxy binder, a composition for an electrode material using the binder, an electrode material using the composition, and an electrode from the electrode material.

[0002]

2. Description of the Related Art Lithium batteries use lithium, which is light and has a high tendency to ionize, as an electrode active material, and is widely used as a small, lightweight, high energy density battery.

Conventionally, electrode materials for lithium batteries include:
There is known an active material in which a thermoplastic resin such as polyvinylidene fluoride (PVDF) is blended as a binder, and this is formed into a band or a sheet. The electrode material as described above is used in a lithium battery in a state of being simply wound.

[0004] However, the electrode material using the above-mentioned thermoplastic resin as a binder tends to swell and be deformed by the electrolytic solution, causing problems such as swelling and enlarging the case enclosing it. Is generated. As a safety measure, a gasket (a rupture valve) is used to evacuate gas. However, if the valve is operated, liquid leakage may occur at the same time. In the case of a return-type gasket, liquid leakage is likely to occur due to repeated degassing, and when the liquid leakage occurs, the gasket cannot be used and the life of the battery is extended.

[0005] Therefore, the electrode material is unlikely to swell with the electrolytic solution, and can maintain the shape before being sealed after being sealed in the case together with the electrolytic solution. There is a demand for an electrode material that can be wound easily, as the time required for the valve to operate becomes longer, the life of the battery becomes longer.

[0006] When a so-called nail penetration test, which is one of the safety tests of a conventional lithium battery, is performed, the electrodes are short-circuited, internal heat is generated (100 ° C or more), and the electrolytic solution becomes gas. As a result, there is a problem that the battery swells greatly, and a rupture valve is used as a safety measure to release gas.

[0007]

In view of the above, the present invention has a sheet-like material forming ability similar to that of a conventional binder using a thermoplastic resin, and has a predetermined shape through a predetermined process. After that, by selecting a curable resin that does not easily swell with a solvent for the binder, it can be firmly stuck and provide an electrode material with improved swelling characteristics,
This was made to improve the safety of the battery.

That is, the present invention relates to (A) an epoxy resin having two or more functional groups, (B) a novolak-type phenol-based curing agent, (C) a urea-based accelerator, a phosphorus-based accelerator, and an accelerator comprising amine salts. An epoxy binder containing at least one member selected from the group consisting of (D) and a phenoxy resin (Claim 1), and further comprising (E) a surfactant (Claim 2). ,
Furthermore, the epoxy binder according to claim 1 or 2 containing a solvent (claim 3), a composition for an electrode material in which an active material is blended with the epoxy binder according to claim 3 (claim 4), and the active material is cobalt oxide The composition according to claim 4 comprising lithium and carbon black (claim 5), and a sheet-like electrode material obtained by applying the composition according to claim 4 or 5 to a base material and removing a solvent (hereinafter referred to as “material”). The present invention relates to an electrode (Claim 7) in which the electrode material according to Claim 6 is wound and cured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The epoxy binder (1) of the present invention comprises a bifunctional or higher functional epoxy resin (A) (hereinafter also referred to as epoxy resin (A)), a novolak type phenolic curing agent (B) (hereinafter referred to as "B"). One or more (C) selected from the group consisting of a curing agent (B), a urea-based accelerator, a phosphorus-based accelerator, and an accelerator comprising a salt of an amine (hereinafter also referred to as an accelerator (C)) ) And a phenoxy resin (D).

The epoxy resin (A) is a component mainly used for improving problems such as swelling and deformation of the electrode material by the electrolytic solution by three-dimensionally crosslinking when forming the electrode material. It is. When the electrode material is wound and cured, the curing agent (B) can cure the epoxy resin (A) at 80 ° C. or lower, which is an essential condition from the viewpoint of not deteriorating the characteristics of the separator described below. It is a component that can be used and is mainly used to make an epoxy binder into a one-pack type. Further, the accelerator (C) moderately accelerates the reaction between the epoxy resin (A) and the curing agent (B) at 60 to 80 ° C, but does not substantially act as an accelerator at 40 ° C or lower, so-called It is a component used as an accelerator that can be made into a liquid composition. And phenoxy resin (D)
Is a component having good compatibility with the components (A) to (C) and used mainly for imparting a film-forming property to the epoxy binder.

The bifunctional or higher functional epoxy resin (A) is not particularly limited as long as it has a three-dimensional cross-linking ability when converted into an epoxy binder (1), and is not particularly limited. Epoxy resin can be used.

Among the epoxy resins (A), the number average molecular weight is from 220 to 2,000 from the viewpoints of good workability, and obtaining an epoxy binder exhibiting suitable strength.
Furthermore, 220-600, epoxy equivalent is 110-10
00, more preferably 110 to 300.

Specific examples of the epoxy resin (A) include, for example, bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol AD
Bisphenol type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, glycidylamine type epoxy resin, alicyclic epoxy resin, dicyclopentadiene type epoxy resin such as diglycidyl ether and chain oligomer mixture obtained by partial condensation of these , Phenol novolak type epoxy resin, cresol novolak type epoxy resin, glycidyl etherified product of mononuclear phenols (hydroquinone, resorcin, catechol, pyrogallol, etc.), glycidyl esterified product such as phthalic acid and hydrogenated phthalic acid, polyether-modified epoxy Resins and copolymers with other polymers such as silicone-modified epoxy resins. These may be used alone or in combination of two or more. Among them, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, and the like are preferable because they are inexpensive and easily available.

The epoxy binder is 3
Part of the epoxy resin (A), as long as a strong electrode material that has dimensional cross-linking ability and is not easily swollen by the electrolytic solution is obtained.
For example, 30% by weight (hereinafter referred to as%) or less may be used instead of a monofunctional epoxy resin (epoxy compound). Examples of monofunctional epoxy resins include, for example, ter
Monoglycidyl compounds such as t-butylphenyl glycidyl ether, 2-ethylhexyl glycidyl ether, sec-butylphenyl glycidyl ether and phenyl glycidyl ether are exemplified. These may be used alone or in combination of two or more.

The novolak type phenolic curing agent (B) is not particularly limited as long as it can cure the epoxy binder at 80 ° C. or lower.

The molecular weight and hydroxyl equivalent of the curing agent (B) are not particularly limited. However, the number average molecular weight is 200 to 200 in view of good workability and an epoxy binder exhibiting suitable strength. 1000, even 300-50
It is preferably 0.

Examples of the curing agent (B) include various conventionally known phenol novolak resins and cresol novolak resins. These may be used alone,
Two or more kinds may be used in combination. Of these, phenol novolak resins are preferred.

A part of the curing agent (B) (for example, 50
% Or less) may be used in place of polyhydric phenols (the mononuclear phenols, bisphenols such as bisphenol A and bisphenol AD).

The accelerator (C) can moderately accelerate the curing reaction between the epoxy resin (A) and the curing agent (B) at 60 to 80 ° C., but at 40 ° C. or lower, the accelerating effect is substantially reduced. Since it does not appear, even when mixed with a solvent, 40
It is a component which can be converted into a one-pack composition having excellent storage stability at a temperature of not more than 25 ° C, more preferably not more than 25 ° C, especially not more than 10 ° C.

As the accelerator (C), a urea accelerator,
One or more of the phosphorus-based accelerator and the accelerator comprising an amine salt may be at least 60 ° C, and more preferably at least 70 ° C.
Heating at a temperature of 0 ° C. or lower, more preferably 75 ° C. or lower, for 10 to 24 hours is preferable in that the reaction between the epoxy resin (A) and the curing agent (B) can be accelerated and cured.

Examples of the urea-based accelerator include, for example, U
Preferred examples include -CAT 3503N (aliphatic dimethyl urea) (manufactured by San Apro Co., Ltd.) and U-CAT 3502T (aromatic dimethyl urea) (manufactured by San Apro Co., Ltd.).

Examples of the phosphorus-based accelerator include, for example, TPP-S (triphenylphosphine / triphenylboron complex) (manufactured by Hokko Chemical Industry Co., Ltd.) and TPTP (tri-p-phosphine) (Hokko Chemical Industry Co., Ltd.). Co., Ltd.) is a preferred example.

Further, as an accelerator comprising a salt of the above amines, for example, U-CAT SA 102 (DBU
-Octylate) (manufactured by San Apro Co., Ltd.), U-CAT
SA 603 (DBU-formate) (San Apro Co., Ltd.)
And U-CAT SA 841 (partial DBU salt of phenol novolak resin) (manufactured by San-Apro Co., Ltd.).

The phenoxy resin (D) has, for example, the general formula (I) in the molecule:

[0025]

Embedded image

Is a thermoplastic resin having a degree of polymerization of about 18 to 70 and a sheet forming ability. Since the epoxy binder (1) contains a phenoxy resin, it can be formed into a sheet. Further, a sheet-like material can be obtained only by mixing with a solvent, blending the active material, and then removing the solvent. Furthermore, the phenoxy resin is soluble in a solvent described below and has excellent compatibility with the epoxy resin, but hardly dissolves in an electrolyte such as ethylene carbonate or diethylene carbonate,
It is suitable as a component of an epoxy binder used for an electrode material.

The phenoxy resin (D) may be a thermoplastic resin having only the unit represented by the general formula (I), or may be a copolymer with other components. In the latter case, the proportion of the portion composed of the unit represented by the general formula (I) accounts for 80 to 99% of the whole molecule, and more preferably 90 to 9%.
It is preferably 9% from the viewpoint of solubility in a solvent, compatibility with an epoxy resin, and the like.

Examples of the unit other than the unit represented by the general formula (I) include units such as bisphenol F and bisphenol AD other than bisphenol A.

The number average molecular weight of the phenoxy resin is preferably from 5,000 to 20,000, more preferably from 10,000 to 16,000, from the viewpoint of sheet forming ability.

The mixing ratio of the epoxy resin (A) and the curing agent (B) in the epoxy binder (1) of the present invention is such that 0.8 to 1.2 equivalents of phenolic hydroxyl group per equivalent of epoxy group, and Is preferably 0.9 to 1.1 equivalents. If the amount of the phenolic hydroxyl group relative to the epoxy group is too large, tack tends to remain in the cured electrode material, and the swelling prevention effect tends to be small.If the amount is too small, the electrode material tends to be easily damaged. Occurs.

The amount of the accelerator (C) used is 5 parts by weight (hereinafter referred to as “parts”) per 100 parts by weight of the epoxy resin (A).
It is preferably from 10 to 10 parts, more preferably from 7 to 8 parts. 10
If the amount exceeds the above range, the storage stability of the epoxy binder (I) tends to deteriorate, and if the amount is less than 5 parts, an appropriate curing acceleration effect tends to be hardly obtained.

Further, the amount of the phenoxy resin (D) used is 40 to 8 with respect to 100 parts of the epoxy resin (A).
0 parts, and more preferably 50 to 70 parts. The usage amount is 4
If the amount is less than 0 parts, the sheet-like material is difficult to obtain, the sheet tends to be loosened, and the tack tends to be easily removed. If the amount exceeds 80 parts, the sheet-like material is cracked when the sheet-like material is wound. Tend to enter.

For the same reason, the ratio of the phenoxy resin to the total amount of the epoxy resin (A), the curing agent (B), the accelerator (C) and the phenoxy resin (D) is as follows:
It is preferably from 15 to 35%, more preferably from 20 to 30%.

The epoxy binder (1) of the present invention comprises:
In order to adjust the wettability with the active material particles, a surfactant (E) is added as necessary, and an epoxy binder (2)
You may use as. As will be described later, an electrode obtained by forming a sheet, winding and curing is in a state where active material particles are tightly packed, and the particles are in contact with each other somewhere. Therefore, the binder needs to have sufficient wettability so as to sufficiently bind the respective particles and not to cover the surface of the particles excessively. If the wettability with the particles is poor, the electrode material cannot function sufficiently as a binder, and the strength of the electrode material tends to be weak.If the wettability is too good, the particle surface is covered with the binder too much and the electrolyte solution -The contact area between particles becomes small, and the performance as an electrode material tends to decrease. If the wettability is too good, the amount of the epoxy binder (1) used may be reduced.

The surfactant (E) can be used without particular limitation as long as it has an effect of lowering the surface tension of the epoxy binder (1).

Surfactants (E) include anionic, nonionic, cationic and amphoteric surfactants when classified according to ionicity.
There are a fluorine type, a silicon type, an aliphatic polyester type, and the like. For example, from the types of atoms contained, a fluorine type is preferable because it can impart appropriate wettability.

Examples of the fluorine-based surfactant include:
Examples include Florard FC-430 (manufactured by Sumitomo 3M Limited) and Florard FC-171 (manufactured by Sumitomo 3M Limited).

The amount of the surfactant (E) to be used is preferably 1 to 5 parts, more preferably 2 to 3 parts, per 100 parts of the epoxy resin (A). If the amount is less than 1 part, the effect of improving the wettability between the active material and the binder and facilitating the formation of a sheet cannot be sufficiently obtained, and if the amount is more than 5 parts, the binder component becomes particles when a necessary amount of the binder is used. There is a tendency that the covering area increases and the contact area between the electrolyte solution and the particles decreases, resulting in an increase in electric resistance.

The above-mentioned epoxy binder of the present invention (1)
Alternatively, a solvent may be further added to (2).

The solvent must be one that can be removed by drying at a temperature lower than the heat-resistant temperature of the separator in a drying step described later. In addition, the time required for the drying step is 5 to 20 minutes in terms of productivity and the like.
Further, since it is preferably about 10 minutes or less, a separator having a boiling point of about 20 ° C. or a high vapor pressure at a temperature of 80 ° C. or less, for example, a vapor pressure at 80 ° C. Is 200mm
Hg or more is preferable.

Specific examples of the solvent include, for example, methyl ethyl ketone (bp 79.6 ° C.), benzene (bp 80.1 ° C.), and toluene (bp 110.
Vapor pressure at 6 ° C and 80 ° C of 300 mmHg, methyl isobutyl ketone (bp 115.9 ° C, vapor pressure at 80 ° C of 240 mmHg), ethyl acetate (bp 77.1)
° C), carbon tetrachloride (bp 76.8 ° C), dioxane (bp 101.3 ° C, vapor pressure 400 mm at 80 ° C)
Hg), THF (bp 66 ° C.) and the like.

The amount of the solvent used is 200 to 600 parts per 100 parts of the total amount of the epoxy resin (A), the curing agent (B), the accelerator (C) and the phenoxy resin (D).
Parts, more preferably 300 to 400 parts, since the viscosity of the electrode material composition containing an appropriate amount of the active material is optimal for coating.

The epoxy binder (1) of the present invention,
The composition for an electrode material of the present invention can be manufactured by adding a solvent to (2) as described above and further blending an active material.

The active material depends on the electrode to be manufactured. For example, lithium cobalt oxide (LiCo
O ₂ ), lithium manganate (LiMn ₂ O ₄ ), LiN
Examples include a mixture of a lithium compound such as iO ₂ and a carbon-based material such as carbon black and acetylene black. The particle size and the like may be the same as those generally used. Among these, a mixture of LiCoO ₂ and carbon black is preferred because of its excellent charge / discharge performance, voltage flatness and the like.

The usage ratio of the epoxy binders (1) and (2) and the active material is, for example, epoxy binders (1) and (2) / active material in a weight ratio of 2/98 to 8/9.
2, and more preferably 4/96 to 6/94, from the viewpoint that the electric resistance of the battery can be minimized. The viscosity of the composition is, for example, 10,000 to
The slurry is preferably 50,000 cP (25 ° C.). If the amount of the binder in the composition is too small, a sheet-like material cannot be formed.If the amount is too large, the surface of the active material particles is too covered with the binder, and the contact area between the electrolyte solution and the particles becomes small. There is a tendency for performance to decrease.

The combination of the active material and the solvent is not particularly limited. For example, when a mixture of lithium cobalt oxide and carbon black is used as the active material, the heat resistance temperature of the separator is about 80 ° C. For example, methyl ethyl ketone having a good boiling point of 79.6 ° C. and compatibility with the phenoxy resin is preferable.

The composition for an electrode material is applied to a predetermined thickness on a flexible base material such as an aluminum foil or a steel foil, and then the solvent is removed in a drying furnace. The sheet-like electrode material obtained by removing the solvent has flexibility and can be wound together with the base material. In addition, the normal winding is performed after the sheet-like electrode material, the counter electrode, and the separator are stacked in several layers so that the counter electrodes do not contact each other using the separator. The electrode of the present invention can be obtained by heating and curing the wound material at a temperature of 80 ° C. or less, which is the heat-resistant temperature of the separator, for about 8 to 16 hours.

The separator is generally made of porous polyethylene. If the temperature exceeds 80 ° C., the polyethylene is melted, the pores are closed, and ion conduction is hindered.

The above-mentioned electrode is usually used together with a counter electrode and a separator wound together, and for example, a 1 mol / l solution of lithium hexafluorophosphate (LiPF ₆ ) (solvent: ethylene carbonate, diethylene carbonate or a mixture thereof). And the like are sealed in a predetermined case together with an electrolytic solution and used for a lithium battery.

[0050]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

The raw materials and evaluation methods used in the examples and comparative examples are summarized below.

Epoxy resin EPICLON 835: bisphenol F type epoxy resin, epoxy equivalent: 175 g / eq, phenolic curing agent VH4150 manufactured by Dainippon Ink and Chemicals, Inc .: phenolite VH4150 (trade name),
Phenol novolak resin, phenolic hydroxyl equivalent 1
17 g / eq, Urea-based accelerator UCAT-3503N manufactured by Dainippon Ink and Chemicals, Inc .: Phenoxy resin manufactured by San Apro Co., Ltd. PKHH-PA: Peyfen PKHH-PA (trade name), number average molecular weight 10,000 to 16,000, phenoxy associates (Phenoxy Associate
s) Surfactant FC-430: Florado FC-430 (trade name), Sumitomo 3M Co., Ltd. active material LiCoO ₂ : Honjo FMC Energy Systems Co., Ltd., carbon black: CB2600 (trade name), Solvent MEK manufactured by Mitsubishi Chemical Corporation: Methyl ethyl ketone

(Woundability) The prepared composition for an electrode material was applied on an aluminum foil so as to have a thickness of 180 μm.
Dry at 10 ° C. for 10 minutes to obtain a 1 cm × 10 cm sheet (electrode material). Next, the sheet was wound tightly by hand, and when the sheet was unfolded, the sheet was free from cracks. X.

(Electrolyte Swelling Resistance) A roll of the same sheet-like material used in the rollability test is heated and cured at 80 ° C. for 16 hours to obtain an electrode. The electrode was immersed in propylene carbonate, left at 40 ° C. for 1 week, and then taken out of the solution.
The electrodes are evaluated by finger touch. If the electrode does not change,
The electrode is swollen by the electrolyte and is soft when the electrode is evaluated as x.

Example 1 The components shown in Table 1 were uniformly mixed in the proportions shown in Table 1 to prepare a slurry-like composition for an electrode material, which was evaluated. Table 1 shows the results.

[0056]

[Table 1]

When a lithium battery was actually manufactured using the above-mentioned electrodes and evaluated, a battery having a long time until the rupture valve was operated could be obtained. On the other hand, in the case of a lithium battery having the same structure as described above using PVDF as a binder and an electrode manufactured by a conventional method, only a battery having a short time until the rupture valve was operated was obtained.

[0058]

By using the epoxy binder of the present invention, it is possible to obtain an electrode material which hardly swells, has a long time until the rupture valve is operated, and has a long battery life.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) C08K 3/24 C08K 3/24 5/07 5/07 C08L 61/06 C08L 61/06 63/00 63 / 00 AC 71/10 71/10 H01M 4/02 H01M 4/02 CF term (reference) 4J002 CC03X CD02W CD03W CD04W CD05W CD06W CD13W CH08Y DA038 DE098 EE037 EN006 ET016 EW016 FD14X FD156 FD319 GJ01 4J036 AA01 AB08 A08 AK01 DC25 DD07 FB07 FB12 JA06 5H003 AA06 AA10 BB05 BB11 BB15 5H014 AA02 BB03 BB06 BB08 EE01

Claims (7)

[Claims] (A) a bifunctional or higher functional epoxy resin,
It contains (B) one or more kinds selected from the group consisting of a novolak-type phenol-based curing agent, (C) a urea-based accelerator, a phosphorus-based accelerator and an accelerator composed of a salt of an amine, and (D) a phenoxy resin. Epoxy binder. 2. The epoxy binder according to claim 1, further comprising (E) a surfactant. 3. The epoxy binder according to claim 1, further comprising a solvent. 4. An electrode material composition comprising the epoxy binder according to claim 3 and an active material. 5. The composition according to claim 4, wherein the active material comprises lithium cobaltate and carbon black. 6. A sheet-like electrode material obtained by applying the composition according to claim 4 to a substrate and removing a solvent. 7. An electrode obtained by winding and curing the electrode material according to claim 6.