JP2018142451A - Battery electrode binder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery electrode binder capable of obtaining an electrochemical device whose electrode has excellent flexibility in the course of improving a large capacity of a second battery.SOLUTION: Battery electrode binder (D) is used containing a polymer (C) in which a monomer (A) having two to six ethylenic polymerizable groups (a) and a monomer (B) having an ion dissociative functional group (b) are made to react as essential components.SELECTED DRAWING: None

Description

  The present invention relates to a battery electrode binder, an electrode containing the battery electrode binder, and an electrochemical device having the electrode.

Non-aqueous electrolyte secondary batteries such as lithium-ion batteries are characterized by high voltage and high energy density, so they are widely used in the field of portable information devices and are used for mobile terminals such as mobile phones and notebook computers. The position as a standard battery has been established.
While its uses are expanding, application to hybrid vehicles and electric vehicles in addition to conventional uses is also being studied, and some have already been put into practical use. In order to further spread these, there is a demand for higher capacity and higher output of secondary batteries, and various techniques have been applied.

In order to improve the capacity, it is necessary to increase the amount of the active material in the secondary battery. As a technique for this purpose, there are an improvement in the electrode density, an increase in the thickness of the electrode, and the like. However, taking these methods reduces the flexibility of the electrode, and when the electrode is wound, there is a problem that a crack occurs on the bent surface, resulting in a decrease in yield in the manufacturing process.

  In order to solve such a problem, in Patent Document 1, the electrode adhesion to the current collector is devised by devising the combination of the electrode binder and the thickener used in the electrode slurry preparation step and the composition of the electrode binder. Improvements have been made through improvements. Patent Document 2 discloses a technique for improving the flexibility of an electrode by modifying it to inhibit crystallization of the electrode binder.

International Publication WO2009-063907 JP 2011-171181 A

  An object of the present invention is to provide a battery electrode binder capable of obtaining an electrochemical device excellent in flexibility of an electrode among improvements for increasing the capacity of a secondary battery.

The inventors of the present invention have reached the present invention as a result of studies to achieve the above object.
That is, the present invention relates to a monomer (A) having 2 to 6 ethylenically polymerizable groups (a), at least one ion-dissociative functional group (b) and one ethylenically polymerizable group ( a binder for a battery electrode containing a polymer (C) obtained by reacting the monomer (B) having a) as an essential component; an active material (E) and a current collector (D) with this electrode binder (D) An electrode formed by binding F); an electrochemical device using the electrode binder for the electrode.

  The binder for battery electrodes of the present invention has an effect that the flexibility of the electrode can be improved while maintaining a high capacity.

  Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited to only the embodiments described below, and includes various modifications that are implemented without departing from the scope of the present invention.

The binder (D) for battery electrodes of the present invention comprises a monomer (A) having 2 to 6 ethylenically polymerizable groups (a), at least one ion dissociative functional group (b) and one It contains a polymer (C) obtained by reacting the monomer (B) having an ethylenically polymerizable group (a) as an essential component. The battery electrode binder (D) may contain only the polymer (C), or may contain one or more other components.

The monomer (A) essential for the battery electrode binder of the present invention has a structure having 2 to 6 ethylenically unsaturated bond groups (a) which are carbon-carbon double bonds. In addition, (A) may have an ion dissociable functional group (b) described later.
Examples of the ethylenically unsaturated bond group (a) include (meth) acryloyl group, vinyl group and allyl group.
Of these, a (meth) acryloyl group is preferred.

Specific examples of the monomer having 2 to 6 ethylenically polymerizable groups (a) include 1,4-butanediol diacrylate, ethylene glycol diacrylate, 1,4-pentaerythritol diacrylate, and dipentaerythritol. Examples include hexaacrylate, 1,4-cyclohexanedimethanol divinyl ether, diethylene glycol diallyl ether, trimethylolpropane diallyl ether, and pentaerythritol triallyl ether.

A single ethylenically unsaturated bond group (a) does not have elasticity because the polymer does not have a branched structure, and the flexibility is insufficient. On the other hand, when the number is 7 or more, the crystallinity is high and the flexibility is insufficient.

  The monomer (B) essential for the battery electrode binder of the present invention has an ion dissociable functional group (b) and only one ethylenically polymerizable group (a).

  Here, the ion dissociable functional group is a functional group that dissociates into an anion and a cation in a solution.

  The ion dissociable functional group (b) is not particularly limited as long as it is a functional group capable of dissociating into an anion and a cation in a solution, and examples thereof include those represented by the following general formula (1).

-A ^- M ⁺ (1)
Examples of A ⁻ in the formula (1) include monovalent anions such as carboxylate ions, sulfonate ions, and phosphate ions.
In the formula (1), M ⁺ is a monovalent metal ion or hydrogen ion, preferably a monovalent metal ion. Examples of the metal ion include lithium, sodium, potassium and the like.

  Among these, specific examples of the ion dissociable functional group (b) include carboxylic acid, sulfonic acid, phosphoric acid, lithium carboxylate, sodium carboxylate, potassium carboxylate, sodium sulfonate, lithium sulfonate, and potassium sulfonate. , Lithium phosphate and sodium phosphate.

  Specific examples of the monomer (B) having an ion dissociable functional group (b) include acrylic acid, methacrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, sodium acrylate , Lithium acrylate, potassium acrylate, sodium methacrylate, lithium methacrylate, sodium 2-acrylamide-2-methylpropanesulfonate, lithium 2-acrylamide-2-methylpropanesulfonate, sodium styrenesulfonate, lithium styrenesulfonate , Sodium vinyl sulfonate, lithium vinyl sulfonate, and potassium vinyl sulfonate.

The polymer (C) of the present invention may be a copolymer obtained by reacting the monomer (A) and the monomer (B), or other monomers other than (A) and (B). And a copolymer of (A) and (B).
The copolymerization ratio of monomers other than (A) and (B) in the polymer (C) is preferably 0 to 90% by weight, more preferably 0 to 90% by weight based on the weight of (C). 70% by weight.

  In the present invention, the battery includes an electrochemical device such as a lithium ion battery or a lithium ion capacitor.

The electrode of the present invention is formed by binding the active material (E) and the current collector (F) to the battery electrode binder (D) of the present invention.
The electrode of the invention may contain a conductive additive (G) as necessary. As the electrode binder, the electrode binder (D) of the present invention can be used alone or in combination with other electrode binders.

  Examples of other electrode binders that can be used in combination with the electrode binder (D) of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, styrene-butadiene rubber, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. The high molecular compound of these is mentioned.

As the active material (E), a negative electrode for a lithium ion battery is obtained by using the negative electrode active material (E1), and a negative electrode for a lithium ion capacitor is obtained by doping lithium into (E1).
Moreover, as an active material (E) for positive electrodes, the positive electrode active material (E2) for lithium ion batteries and the positive electrode active material (E3) for lithium ion capacitors are mentioned.

As the negative electrode active material (E1), graphite, amorphous carbon, a polymer compound fired body (for example, a product obtained by firing and carbonizing a phenol resin, a furan resin, etc.), cokes (for example, pitch coke, needle coke, and petroleum coke), And carbon fibers, conductive polymers (for example, polyacetylene and polypyrrole), tin, silicon, and metal alloys (for example, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy). .

Examples of the positive electrode active material (E2) for lithium ion batteries include composite oxides of lithium and transition metals (for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and LiMn ₂ O ₄ ), transition metal oxides (for example, MnO ₂ and V ₂ O). ₅ ), transition metal sulfides (eg, MoS ₂ and TiS ₂ ), and conductive polymers (eg, polyaniline, polyvinylidene fluoride, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polycarbazole).
Examples of the positive electrode active material (E3) for lithium ion capacitors include activated carbon, carbon fiber, and conductive polymer (for example, polyacetylene and polypyrrole).

The current collector (F) holds the active material (E) and supplies current to the active material. Examples of the current collector (F) include metal foils such as aluminum foil and copper foil.

The electrode of this invention may contain the conductive support agent (G) as needed.
As the conductive auxiliary agent (G), carbon blacks (for example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black) and metal powder (for example, aluminum powder and nickel powder), conductive metal Examples thereof include oxides (for example, zinc oxide and titanium oxide).

  Examples of the solvent used in preparing the electrode of the present invention include water, N-methylpyrrolidone, acetone and toluene.

The preferred contents of (D), (E), and (G) based on the total weight of the electrode binder (D), active material (E), and conductive additive (G) in the electrode of the present invention are as follows. It is.
The content of the active material (E) is preferably 70 to 98% by weight, more preferably 90 to 98% by weight from the viewpoint of battery capacity.
The content of the electrode binder (D) is preferably 0.5 to 29% by weight, more preferably 1 to 10% by weight from the viewpoint of battery capacity.
The content of the conductive auxiliary agent (F) is preferably 0 to 29% by weight, more preferably 0 to 10% by weight, from the viewpoint of output characteristics.

Examples of the electrochemical device of the present invention include a primary battery, a secondary battery, a capacitor, and a capacitor.
Although the form is not limited in the present invention, it is particularly suitable for lithium ion batteries and lithium ion capacitors.

  The lithium ion battery of the present invention uses the electrode of the present invention as the positive electrode or the negative electrode when the electrolytic solution is injected into the battery can containing the positive electrode, the negative electrode, and the separator to seal the battery can. It can be obtained by using the electrolytic solution of the invention or a combination thereof.

  As a separator in a lithium ion battery, a microporous film made of polyethylene or polypropylene film, a multilayer film of porous polyethylene film and polypropylene, a nonwoven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and silica, alumina on the surface thereof And those having ceramic fine particles such as titania attached thereto.

  As the battery can in the lithium ion battery, metal materials such as stainless steel, iron, aluminum and nickel-plated steel can be used, but plastic materials can also be used depending on the battery application. Further, the battery can can be formed into a cylindrical shape, a coin shape, a square shape, or any other shape depending on the application.

  The lithium ion capacitor of the present invention can be obtained by replacing the positive electrode with a positive electrode for a lithium ion capacitor and replacing the battery can with a capacitor can in the basic configuration of the lithium ion battery of the present invention. Examples of the material and shape of the capacitor can include the same as those exemplified for the battery can.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

Production Example 1
In a flask equipped with a stirrer and a thermometer, 1 part of ethylene glycol diacrylate (A-1), 40 parts of acrylic acid, 59 parts of octyl acrylate, 400 parts of N-methylpyrrolidone, and initiator V-65 (NOF Corporation) 1 part) was charged and heated at 60 ° C. for 6 hours to obtain a polymer (C-1). The polymer was neutralized with an aqueous lithium hydroxide solution, and water was distilled off by heating under reduced pressure to obtain a battery electrode binder (D-1) of the present invention.

Production Example 2
In Example 1, ethylene glycol diacrylate (A-1) is 1 part of pentaerythritol ethoxytetraacrylate (A-2), acrylic acid (B-1) is 40 parts of vinyl sulfonic acid (B-2), A battery electrode binder (D-2) of the present invention was obtained in the same manner as in Example 1 except that the octyl acrylate was changed to 59 parts of vinyl ether and the aqueous lithium hydroxide solution was changed to a sodium hydroxide solution.

Production Example 3
In Example 1, the same operation as Example 1 was carried out except that ethylene glycol diacrylate (A-1) was changed to 1 part of dipentaerythritol hexaacrylate (A-3) and octyl acrylate was changed to 59 parts of acrylamide. The battery electrode binder (D-3) of the present invention was obtained.

Production Example 4
In Example 1, ethylene glycol diacrylate (A-1) was added to 1 part of 1,4-cyclohesanedimethanol divinyl ether (A-4), and acrylic acid (B-1) was added to vinyl sulfonic acid (B-2). The battery electrode binder (D-4) of the present invention was the same as in Example 1 except that 40 parts, octyl acrylate was changed to 59 parts of acrylamide, and the lithium hydroxide aqueous solution was changed to a sodium hydroxide aqueous solution. Got.

Production Example 5
In Example 1, ethylene glycol diacrylate (A-1) is added to 1 part of trimethylolpropane diallyl ether (A-5), acrylic acid (B-1) is added to 40 parts of styrene sulfonic acid (B-3), and octyl is added. A battery electrode binder (D-5) of the present invention was obtained in the same manner as in Example 1 except that the acrylate was changed to 59 parts of diethylaminoethyl acrylate and the aqueous lithium hydroxide solution was changed to an aqueous sodium hydroxide solution.

Production Example 6
In Example 1, except that acrylic acid (B-1) was changed to 40 parts of styrene sulfonic acid (B-3), octyl acrylate was changed to 59 parts of benzyl methacrylate, and the lithium hydroxide aqueous solution was changed to an aqueous sodium hydroxide solution, The same operation as in Example 1 was performed to obtain a battery electrode binder (D-6) of the present invention.

Production Example 7
In Example 1, except having changed octyl acrylate with 59 parts of N-vinyl pyrrolidone, operation similar to Example 1 was performed and the battery electrode binder (D-7) of this invention was obtained.

Production Example 8
Example 1 is the same as Example 1 except that acrylic acid (B-1) is changed to 40 parts of 2-acrylamido-2-methylpropanesulfonic acid (B-4) and octyl acrylate is changed to 59 parts of vinyl ether. The battery electrode binder (D-8) of the present invention was obtained.

Production Example 9
In Example 1, except that ethylene glycol diacrylate (A-1) was changed to 10 parts of 1,4-cyclohesanedimethanol divinyl ether (A-4) and octyl acrylate was changed to 50 parts of acrylamide. The same operation as 1 was performed to obtain the battery electrode binder (D-9) of the present invention.

Comparative production example 1
A flask equipped with a stirrer and a thermometer was charged with 40 parts of acrylic acid (B-1), 60 parts of octyl acrylate, 400 parts of N-methylpyrrolidone and 1 part of V-65 (manufactured by NOF Corporation) at 60 ° C. for 6 hours. The polymer (C′-1) was obtained by heating. This polymer was neutralized with an aqueous lithium hydroxide solution, and water was distilled off by heating under reduced pressure to obtain a battery electrode binder (D′-1) for a comparative example.

Comparative production example 2
To a flask equipped with a stirrer and a thermometer, KRM8904 (manufactured by Daicel Ornex, aliphatic urethane acrylate having 9 acryloyl groups) (A′-1) 1 part, acrylic acid (B-1) 40 parts, octylacrylate 59 parts, 400 parts of N-methylpyrrolidone and 1 part of V-65 (manufactured by NOF Corporation) were charged and heated at 60 ° C. for 6 hours to obtain a polymer (C′-2). The polymer was neutralized with an aqueous lithium hydroxide solution, and the water was distilled off by heating under reduced pressure to obtain a battery electrode binder (D′-2) for a comparative example.

Comparative production example 3
A flask equipped with a stirrer and a thermometer was charged with 5 parts of ethylene glycol diacrylate (A-1), 95 parts of acrylamide, 400 parts of N-methylpyrrolidone and 1 part of V-65 (manufactured by NOF Corporation). The battery electrode binder (D'-3) for a comparative example was obtained by heating for a time.

The formulations of Production Examples 1-9 and Comparative Production Examples 1-3 are summarized in Table 1.

The flexibility was evaluated by a bending strength test of the positive electrode and the negative electrode by the following method.

[Production of positive electrode for lithium ion battery]
LiCoO ₂ powder 97.0 parts, carbon black 1.49 parts, polyvinylidene fluoride 1.49 parts and battery electrode binders (D-1) to (D-9) and (D'-1) to (D'- 3) After 0.2 parts were sufficiently mixed in a mortar, 70.0 parts of N-methylpyrrolidone was added and further mixed well in a mortar to obtain a slurry.
The obtained slurry was applied on one surface of an aluminum electrolytic foil having a thickness of 20 μm using a wire bar in an open atmosphere, dried at 80 ° C. for 1 hour, and further under reduced pressure (1.3 kPa), 80 A positive electrode was prepared by drying at 2 ° C. for 2 hours. In addition, the blank 1 which does not put the binder for battery electrodes, and the blank 2 which lowered the electrode density without putting the binder for battery electrodes were also produced.

[Production of negative electrode for lithium ion battery]
95 parts of natural graphite, 2.49 parts of carboxymethylcellulose, 2.49 parts of styrene-butadiene rubber, binders for battery electrodes (D-1) to (D-9) and (D'-1) to (D'-3) 0.2 parts and 100 parts of water were charged and mixed well in a mortar to obtain a slurry. The obtained slurry was applied to one side of a 20 μm-thick copper foil using a wire bar, dried at 50 ° C. for 1 hour, and further dried under reduced pressure (1.3 kPa) at 105 ° C. for 2 hours. A negative electrode was created. In addition, the blank 3 which does not put the binder for battery electrodes, and the blank 4 which lowered the electrode density without putting the binder for battery electrodes were also produced.

[Preparation of single electrode cell for positive electrode and negative electrode evaluation]
A positive electrode or a negative electrode prepared so that the metallic lithium at the other end and the composite material coating surface and the coating surface face each other at one end in the 2032 type coin cell, and a separator (polypropylene nonwoven fabric) is inserted between the electrodes, A cell for a secondary battery was prepared by using LiPF ₆ dissolved in an ethylene carbonate / dimethyl carbonate mixed solution (1: 1) so as to be 1 mol / 1 L as an electrolyte.

[Battery capacity (single electrode cell for positive electrode evaluation)]
(1) Under an environment of 20 ° C., the battery was charged to a voltage of 4.4 V with a current of 1 C using a charge / discharge measuring device “HJ1001SD8” [manufactured by Hokuto Denko Corporation].
(2) After 10 minutes of rest, the discharge capacity obtained by discharging the voltage to 3.0 V with a current of 1 C was defined as the battery capacity.
(3) Table 2 shows the relative value (%) obtained by dividing the discharge capacity measured in each Example and Comparative Example using a single electrode cell for positive electrode evaluation by the discharge capacity of the blank 1 as the battery capacity.
Battery capacity (%) of single electrode cell for positive electrode evaluation = (discharge capacity measured in each example and comparative example / discharge capacity of blank 1)

[Battery capacity (single electrode cell for negative electrode evaluation)]
(1) Under an environment of 20 ° C., the battery was charged to a voltage of 0 V with a current of 1 C using a charge / discharge measuring device “HJ1001SD8” [manufactured by Hokuto Denko Corporation].
(2) After 10 minutes of rest, the discharge capacity obtained by discharging the voltage to 1.0 V with a current of 1 C was defined as the battery capacity.
(3) Table 3 shows the relative value (%) obtained by dividing the discharge capacity measured in each Example and Comparative Example using a single electrode cell for negative electrode evaluation by the discharge capacity of the blank 2 as the battery capacity.
Battery capacity (%) of single electrode cell for negative electrode evaluation = (discharge capacity measured in each example and comparative example / discharge capacity of blank 3)

[Bending test]
The bending test was performed according to the type 1 method of JISK 5600-5-1. Do not use a loupe.
A mandrel (2, 3, 4, 5, 6, 8) in which an electrode prepared with the mixture coating surface facing outside is attached to a cylindrical mandrel tester (Allgood Co., Ltd.) and cracks and peeling of the mixture are observed. 10 mm) was determined. The test results were judged according to the following criteria.
The result with an electrode (blank) without an electrode binder was 8 mm. Therefore, the following criteria were used for the determination.
○: 6 mm or less Δ: 8 mm
X: 10 mm or more Both the positive electrode and the negative electrode were measured under the same conditions. The results of the positive electrode are shown in Table 2, and the results of the negative electrode are shown in Table 3.

By using the binder for an electrode of the present invention, it was possible to produce a highly flexible electrode (positive electrode examples 1 to 9 and negative electrode 10 to 18) while maintaining a high capacity.
On the other hand, although the positive electrode of the blank 1 and the negative electrode of the blank 3 which do not contain the binder for electrodes of the present invention show a high capacity, the flexibility is remarkably low. Further, it is generally known that the flexibility is improved when the electrode density is lowered, and the flexibility of the positive electrode of the blank 2 and the negative electrode of the blank 4 which are reduced in the electrode density is improved. On the other hand, when the electrode density is lowered, the amount of active material contained in the electrode is reduced and the capacity is reduced. Therefore, the positive electrode of blank 2 and the negative electrode of blank 4 are compared with the positive electrode of blank 1 and the negative electrode of blank 3 And the capacity decreased.
The flexibility of the electrodes of Comparative Example 1 and Comparative Example 6 using (D′-1) which does not contain (A) and contains only another octyl acrylate having only one (a) with other monomers is low. Further, the electrodes of Comparative Example 2 and Comparative Example 7 using (D′-2) obtained by copolymerizing a monomer having nine ethylenic polymerizable groups (a) have low flexibility. Moreover, since the adhesiveness with an electrical power collector falls when the monomer which has an ionic dissociation group (D'-3) falls, the electrode of the comparative example 3 and the comparative example 8 using this binder for electrodes is also Flexibility is low.

Since the electrode produced by using the electrode binder of the present invention is excellent in flexibility while maintaining a high capacity, it can be suitably used as an electrode binder for high capacity lithium ion batteries and miniaturized lithium batteries. . In addition to those disclosed in the present invention, the present invention can also be applied to lithium ion capacitors.

Claims (8)

  Monomer having 2 to 6 ethylenically polymerizable groups (a) (A), at least one ionically dissociable functional group (b) and one ethylenically polymerizable group (a) Battery electrode binder (D) containing polymer (C) obtained by reacting body (B) as an essential monomer.   The battery electrode binder according to claim 1, wherein the ethylenically polymerizable group (a) is one or more groups selected from the group consisting of a (meth) acryloyl group, a vinyl group and an allyl group. The binder for battery electrodes according to claim 1 or 2, wherein the ion dissociative functional group (b) is a functional group represented by the following general formula (1).
-A ^- M ⁺ (1)
[In the formula (1), M ⁺ represents a monovalent metal ion or hydrogen ion, and A ⁻ represents SO ₃ ^— or CO ₂ ^— . ]   The battery electrode binder according to any one of claims 1 to 3, wherein the content of the monomer (A) contained in the constituent monomer of the polymer (C) is 0.01 wt% to 10 wt%. An electrode formed by binding the active material (E) and the current collector (F) with the battery electrode binder (D) according to any one of claims 1 to 4. The electrochemical device which uses the electrode binder in any one of Claims 1-5 for an electrode.   The electrochemical device according to claim 6, wherein the electrochemical device is a lithium ion battery. The electrochemical device according to claim 6, wherein the electrochemical device is a lithium ion capacitor.