JP6876663B2 - Composition for battery electrode and binder composition for battery electrode - Google Patents

Description

The present invention relates to a composition for a battery electrode and a binder composition for a battery electrode.

In recent years, electronic devices have become more and more miniaturized. Lithium-ion secondary batteries or nickel-metal hydride batteries that use lithium ions or substances that reversibly store and release hydrogen as electrodes are lightweight and have high energy density, and are used for portable electronic devices such as mobile phones and laptop computers. It is becoming more important as a central power source for. Each of these secondary battery electrodes has a structure in which an active material is coated on a metal base material (hereinafter referred to as a current collector), and is usually a polymer binder as a binder for binding the active material to the current collector. Is being used. This polymer binder is required to have bondability with an active material, resistance to an electrolytic solution, stability in an electrochemical environment, and the like. In particular, in the case of a lithium ion secondary battery, a fluorine-based polymer such as polyvinylidene fluoride has been conventionally dissolved in a solvent such as N-methyl-2-pyrrolidone and used as a binder. Is likely to segregate on the electrode surface, and there is a problem that the binding force is insufficient, and improvement is desired. For example, Japanese Patent Application Laid-Open No. 04-51459 (Patent Document 1) uses a binder for an electrode made of a non-fluorinated aqueous dispersion and a coating composition for an electrode to suppress segregation of the binder and improve the binding force. It is possible to provide various electrodes. However, there is a concern that the long-term stability of the paint such as viscosity may be insufficient due to the water-based coating composition. Further, according to WO2004 / 107481 (Patent Document 2), it is possible to improve the stability of the binder composition and the coating composition by combining the binder and the dispersant in a specific polymerization method. Proposed.

Japanese Unexamined Patent Publication No. 04-51459

International Publication WO2004 / 107481

However, it cannot be said that the stability of the composition for a battery electrode containing the binder or the binder itself such as pH and viscosity is sufficient.
An object of the present invention is to provide a composition for a battery electrode, which has little change with time such as viscosity over a long period of time. As a result, it is an object of the present invention to provide an electrode having excellent binding force and a battery having good battery characteristics.

In order to solve the above-mentioned problems, the composition for a battery electrode of the present invention comprises 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-. It is characterized by containing at least one selected from the group consisting of benzoisothiazolin-3-one.

The composition for a battery electrode of the present invention has stable physical properties such as viscosity for a long period of time, and it is possible to obtain an electrode having extremely stable quality such as binding force. As a result, a battery having good battery characteristics can be obtained. can get.

The composition for a battery electrode of the present invention comprises 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and 1,2-benzoisothiazolin-3-one. Contains one or more selected from the group.

In addition, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzoisothiazolin-3-one, 2,2-dibromo-3-nitrillo From the viewpoint of non-formaldehyde emission, it is preferable to contain at least one selected from the group consisting of propionamide and 2-n-octyl4-isothiazolin-3-one.

Furthermore, 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 1,2-benzoisothiazolin-3-one, 2,2-dibromo-3-one One selected from the group consisting of nitrilopropionamide, 2-n-octyl4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, and 2,2-dibromo-2-nitroethanol. It is more preferable to contain the above from the viewpoint of the effect of maintaining the long-term stability of the composition for a battery electrode.

The amount of the above compound added is not particularly limited, but is 0.00001 to 1 part by weight based on the solid content of the composition for the battery electrode, or 0.001 to 10 parts by weight based on the solid content of the binder for the battery electrode. preferable. If it is less than 0.00001 parts by weight with respect to the composition for battery electrodes or less than 0.001 parts by weight with respect to the solid content of the binder for battery electrodes, it tends to be difficult to exhibit the effect of stabilizing the composition over time with time. If it exceeds 1 part by weight with respect to the composition for the battery electrode or 10 parts by weight with respect to the solid content of the binder for the battery electrode, the binding force tends to decrease, which is not preferable. It is more preferably 0.0001 to 0.1 parts by weight based on the solid content of the composition for the battery electrode, or 0.01 to 1 part by weight based on the solid content of the binder for the battery electrode.

In the present invention, as a method of incorporating the above-mentioned compounds in the composition for battery electrodes, these may be directly added to the composition for battery electrodes, or a battery in which these substances are previously contained in a binder. Any method may be used in which the binder composition for electrodes is added to the composition for battery electrodes.

The binder used in the composition for the battery electrode of the present invention is not particularly limited, but is limited to styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), methyl methacrylate butadiene rubber (MBR), and butadiene rubber (BR). ), And water-based emulsions such as acrylic rubber latex containing (meth) acrylic acid ester as the main monomer, and one or more of them can be used. Further, it is more preferable that these copolymers are modified with a functional group-containing monomer such as an unsaturated carboxylic acid monomer from the viewpoint of viscosity stability of the composition for a battery electrode.

The composition for a battery electrode of the present invention contains an active material and a binder for each of the positive electrode and the negative electrode. The type of active material is not particularly limited, but for example, in the case of a non-aqueous electrolyte secondary battery, graphite, carbon fiber, resin calcined carbon, linear graphite hybrid, coke, thermally decomposed air layer growth carbon, furfuryl alcohol resin. Calcined carbon, polyacene-based organic semiconductors, mesocarbon microbeads, mesophase pitch-based carbon, graphite whisker, pseudo-isotropic carbon, calcined products of natural materials, and carbonaceous materials such as crushed products of these, transitions of MnO2, V2O5, etc. Examples thereof include metal oxides and composite oxides containing lithium such as LiCoO2, LiMnO2, and LiNiO2, and one type or a mixture of two or more types can be used.

The composition for a battery electrode of the present invention has a binder content of 0.1 to 10 parts by weight (solid content), more preferably 1 to 7 parts by weight (solid content), based on 100 parts by weight (solid content) of the active material. It is preferable to use in. If the blending amount of the binder is less than 0.1 parts by weight, good binding force to the current collector or the like tends not to be obtained, and if it exceeds 10 parts by weight, the overvoltage increases remarkably when assembled as a battery, and the battery characteristics. It tends to have an adverse effect on the battery, which is not preferable.

Various additives such as a water-soluble thickener may be added to the composition for battery electrodes of the present invention, if necessary. For example, water-soluble thickeners such as carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized surfactant, phosphorylated starch, casein, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, etc. Examples thereof include dispersants such as sodium polyacrylate, nonionic and anionic surfactants as stabilizers for latex.

The composition for a battery electrode of the present invention is applied to a current collector, dried, and used as a battery electrode. Further, any coater head such as a reverse roll method, a comma bar method, a gravure method, or an air knife method can be used as a method for applying the composition for a battery electrode to a current collector, and as a drying method, it is left-dried or blown-dried. Machines, hot air dryers, infrared heaters, far infrared heaters, etc. can be used.

As for the current collector, separator, non-aqueous electrolyte solution, terminal, insulator, battery container, etc. used when manufacturing a battery using the composition for a battery electrode of the present invention, existing ones can be used without particular limitation. Is.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is changed. In the examples, the part indicating the ratio and% are based on the weight. The evaluation of various physical properties in the examples was based on the following method.

Preparation of Copolymer Latex A In a pressure-resistant polymerization reactor, under a nitrogen atmosphere, 1,3-butadiene 2 parts, styrene 4 parts, acrylonitrile 1.5 parts, methyl methacrylate 1 part, hydroxyethyl acrylate 2 parts, Acrylic acid (0.6 parts), fumaric acid (1.9 parts), t-dodecyl mercaptan (0.05 parts), cyclohexene (5 parts), sodium dodecylbenzene sulfonate (0.6 parts), and pure water (100 parts) were added to raise the temperature to 50 ° C. Later, 1 part of potassium persulfate was added to initiate polymerization. 3 hours after the start of polymerization, 20 parts of 1,3-butadiene, 42 parts of styrene, 15 parts of acrylonitrile, 10 parts of methyl methacrylate, 0.45 parts of t-dodecyl mercaptan, 0.2 parts of sodium dodecylbenzene sulfonate, 20 parts of pure water. The part was added, the temperature of the polymerization reaction tank was raised to 60 degrees, and the polymerization was continued. After 12 hours from the start of the polymerization, the polymerization was stopped and the pH was adjusted to 7.5 with an aqueous sodium hydroxide solution. Then, steam distillation was carried out at 90 ° C. for 15 hours to remove unreacted monomers and other low boiling point compounds to obtain a copolymer latex A having a number average particle size of 160 nm and a gel content of 85%. ..

<Examples 1 to 15>
Preparation of composition for negative electrode Using natural graphite with an average particle size of 20 μm as the negative electrode active material, 1 part by weight of carboxymethyl cellulose aqueous solution as a thickener and common weight as a binder with respect to 100 parts by weight of natural graphite. The combined latex A is kneaded with 2 parts by weight of solid content, the amounts of the compounds shown in Tables 1 and 2 are added, and an appropriate amount of water is added so that the total solid content is 40%, and the composition for the negative electrode is prepared. Prepared.
Here, in Example 13, first, 0.2 parts by weight of 2-methyl-4-isothiazolin-3-one was added to 100 parts by weight of the solid content of the copolymer latex A, and the mixture was sufficiently stirred. Polymer latex A'was prepared. A composition for a negative electrode was prepared in the same manner as in Example 1 except that the copolymer latex A'was added in place of the copolymer latex A.

Preparation of Negative Electrode Sheet Each negative electrode composition is applied to a copper foil having a thickness of 20 μm as a current collector, dried at 120 ° C. for 5 minutes, and pressed at room temperature to obtain a negative electrode having a coating layer thickness of 80 μm. Obtained.

Preparation of Copolymer Latex B In a pressure-resistant polymerization reactor, 7 parts of butyl acrylate, 1 part of methyl methacrylate, 1 part of hydroxyethyl acrylate, 2 parts of itaconic acid, 2 parts of acrylic acid, ethylene glycol di After adding 0.5 part of methacrylate, 0.3 part of cyclohexene, 0.2 part of sodium dodecylbenzenesulfonate and 100 parts of pure water to raise the temperature to 65 ° C., 0.8 part of potassium persulfate was added to start the polymerization. did. 1 hour after the start of polymerization, 50 parts of butyl acrylate, 13 parts of methyl methacrylate, 11 parts of styrene, 3 parts of acrylamide, 2 parts of hydroxyethyl acrylate, 5 parts of methacrylic acid, 2.5 parts of ethylene glycol dimethacrylate, 0 parts of t-dodecyl mercaptan. .02 parts, 0.5 parts of sodium dodecylbenzenesulfonate and 20 parts of pure water were added, the temperature of the polymerization reaction tank was raised to 70 ° C., and the polymerization was continued. The polymerization was stopped 6 hours after the start of the polymerization, and the pH was adjusted to 7.5 with an aqueous sodium hydroxide solution. Then, steam distillation was carried out at 90 ° C. for 15 hours to remove unreacted monomers and other low boiling point compounds to obtain a copolymer latex B having a number average particle diameter of 230 nm and a gel content of 85%. ..

<Examples 16 to 30>
Preparation of positive electrode composition 100 parts by weight of LiCoO2 as positive electrode active material, 5 parts by weight of acetylene black as a conductive agent, 1 part by weight of carboxymethyl cellulose aqueous solution as a thickener, and copolymer latex B as a binder. 2 parts by weight of the solid content and the amounts of the compounds shown in Tables 3 and 4 were added, and an appropriate amount of water was added and kneaded so that the total solid content was 40% to prepare a positive electrode composition.
Here, in Example 28, first, 0.2 parts by weight of 2-methyl-4-isothiazolin-3-one was added to 100 parts by weight of the solid content of the copolymer latex B, and the mixture was sufficiently stirred. Polymer latex B'was prepared. A composition for a negative electrode was prepared in the same manner as in Example 16 except that the copolymer latex B'was added in place of the copolymer latex B.

Preparation of positive electrode sheet Each positive electrode composition is applied to an arnimium foil having a thickness of 20 μm as a current collector, dried at 120 ° C. for 5 minutes, and pressed at room temperature to obtain a positive electrode having a coating layer thickness of 80 μm. Obtained.

Changes in viscosity of composition for battery electrodes over time (stability over time)
The viscosity immediately after the production of the composition for the battery electrode obtained above and the B-type viscosity one week after being left at room temperature were measured with TVB-10M manufactured by Toki Sangyo Co., Ltd. (60 rpm, No. 4 rotor) and described below. The change value R of the viscosity of the composition for the battery electrode with time was obtained from the formula, and the results are shown in Tables 1 to 4. The composition for the battery electrode after being left at room temperature for one week was measured with a spatula at a speed such that bubbles did not enter, after sufficiently stirring until the apparent viscosity became constant.
R = | Viscosity after 1 week at room temperature-Viscosity immediately after production | / Viscosity immediately after production

Measurement of binding force (180 ° peeling strength) The electrode sheet obtained by the above method is cut into strips of 7 cm x 2 cm, a steel plate with a thickness of 1 mm is adhered to the current collector side with double-sided tape, and cellophane on the coating layer side. The adhesive tape was attached, and the stress at the time of peeling in the 180 ° direction at a speed of 100 mm / min was measured with a tensile tester. The results are shown in Tables 1 to 4.

As shown in Tables 1 to 4, the composition for a battery electrode of the present invention has a small change value of viscosity with time and is excellent in viscosity stability. Further, the electrode binding force obtained by applying the composition for a battery electrode of the present invention is also excellent.
In the comparative examples, it is clear that none of them contains the compound specified in the present application, the viscosity stability is significantly inferior, and the binding force is also inferior.

Although the above invention has been provided as an exemplary embodiment of the present invention, this is merely an example and should not be construed in a limited manner. Modifications of the present invention that will be apparent to those skilled in the art are included in the claims described below.

As described above, the composition for a battery electrode of the present invention has a stable viscosity for a long period of time, and it is possible to obtain an electrode having a stable binding force and excellent properties. As a result, a battery having good battery characteristics is obtained, which is extremely useful.

Claims (4)

A composition for a lithium ion secondary battery electrode containing a binder and 2-methyl-4-isothiazolin-3-one.
The binder, except for those having an acrylic rubber latex (alpha, beta-unsaturated nitrile monomer units, Except those having a repeating unit derived from a fluorine-containing ethylenic monomer, further, aliphatic conjugated dienes those having a system monomeric units are divided rather)
Composition for lithium ion secondary battery electrode. 2,2-Dibromo-3-nitrilopropionamide, 2-n-octyl4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-nitroethanol The composition for a lithium ion secondary battery electrode according to claim 1, which comprises one or more selected from the group consisting of. A binder composition for a lithium ion secondary battery electrode containing a binder and 2-methyl-4-isothiazolin-3-one.
The binder, except for those having an acrylic rubber latex (alpha, beta-unsaturated nitrile monomer units, Except those having a repeating unit derived from a fluorine-containing ethylenic monomer, further, aliphatic conjugated dienes those having a system monomeric units are divided rather)
Binder composition for lithium ion secondary battery electrodes. 2,2-Dibromo-3-nitrilopropionamide, 2-n-octyl4-isothiazolin-3-one, 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-2-nitroethanol The binder composition for a lithium ion secondary battery electrode according to claim 3, which comprises one or more selected from the group consisting of.