JP2002304997A - Lithium ion polymer secondary battery and synthesizing method of binder used for adhesion layer thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion polymer secondary battery excellent in adhesion and conductivity between a collector and an active material layer, capable of improving a cycle capacity keeping characteristic, having an adhesion layer stable against an organic solvent in an electrolyte and excellent in long-term storability, and capable of restraining corrosion of the collector by a strong acid such as hydrofluoric acid generated in the battery. SOLUTION: This lithium ion polymer secondary battery is provided with: a positive electrode with a positive electrode active material layer formed by including a first binder in the active material formed on the surface of the positive electrode collector; a negative electrode with a negative electrode active material layer formed by including a second binder identical to or different from the first one in an active material formed on the surface of the negative electrode collector; and an electrolyte. The battery has the first adhesion layer between the positive electrode collector and the positive electrode active material layer, and has the second adhesion layer between the negative electrode collector and the negative electrode active material layer. The first and second adhesion layers respectively include both a third binder and a conductive substance. The third binder is a high polymer compound prepared by modifying the first binder or the second binder by a modifying substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion polymer secondary battery having an adhesion layer and a method for synthesizing a binder used for the adhesion layer of the battery.

[0002]

2. Description of the Related Art With the spread of portable devices such as video cameras and notebook personal computers in recent years, demand for thin batteries has increased. As this thin battery, a lithium ion polymer secondary battery formed by laminating a positive electrode and a negative electrode is known. The positive electrode is formed by forming an active material layer on the surface of a sheet-shaped positive electrode current collector, and the negative electrode is formed by forming an active material layer on the surface of a sheet-shaped negative electrode current collector. An electrolyte layer is interposed between the positive electrode active material layer and the negative electrode active material layer. In this battery, a positive electrode terminal and a negative electrode terminal for extracting a potential difference in each active material as a current are provided on the positive electrode current collector and the negative electrode current collector,
The lithium ion polymer secondary battery is formed by hermetically sealing the stacked battery with a package. In this lithium ion polymer secondary battery, desired electricity can be obtained by using the positive electrode terminal and the negative electrode terminal drawn out of the package as terminals of the battery.

[0003] A lithium ion polymer secondary battery having such a structure has attracted much attention because of its high battery voltage and high energy density. In order to further increase the discharge capacity of this lithium ion polymer secondary battery, it is necessary to increase the area of the sheet-like positive electrode or negative electrode. If the area of the positive electrode or the negative electrode is simply enlarged, the handling becomes difficult due to the large area. In order to solve this problem, it is conceivable to fold or wind the enlarged sheet-like positive electrode or negative electrode to a desired size. However, when folding or winding is performed in a state where the sheet-like positive electrode or negative electrode is laminated, the positive electrode or the negative electrode in the fold portion is bent, and the sheet in the portion is peeled off from the electrolyte layer and the effective interface between the electrode and the electrolyte is formed. There is a problem that the surface area is reduced and the discharge capacity is reduced, and resistance is generated inside the battery to deteriorate the cycle characteristics of the discharge capacity. Similarly, there is also a problem that the active material layers forming the positive electrode and the negative electrode are separated from the current collector due to the bending at the fold. Further, in this battery, during the charging and discharging processes, the positive electrode and the negative electrode active material layer expand and contract due to insertion and release of lithium ions into the positive electrode and the negative electrode active material. There was also a problem of peeling from the current collector.

Therefore, as a technique for solving the above-mentioned problems, techniques for preventing the active material layer from peeling off from the current collector and lowering the adhesion have been proposed as described below. Japanese Patent Publication No. 7-70328 proposes a current collector coated with a conductive coating film composed of a binder and a conductive filler. In the present invention, a phenol resin, a melamine resin, a urea resin, a vinyl-based resin, an alkyd-based resin, a synthetic rubber, and the like are cited as materials for the binder. In Japanese Patent Application Laid-Open No. 9-35707, a negative electrode material layer containing a binder made of carbon powder and polyvinylidene fluoride (hereinafter referred to as PVdF) is formed on a negative electrode current collector. It is described that an adhesive layer made of an acrylic copolymer mixed with a conductive agent is formed thereon. In this invention, a high adhesive effect can be obtained by using an acrylic copolymer having high adhesiveness to copper for the negative electrode plate in which the negative electrode current collector is formed of copper foil. In Japanese Patent Application Laid-Open No. 10-149810, an undercoat layer formed by applying a polyurethane resin or an epoxy resin is formed between an active material layer and a current collector. In the present invention, the adhesion between the active material coating layer and the current collector in the electrode is improved by forming an undercoat layer coated with a polyurethane resin or an epoxy resin, and the cycle capacity retention characteristics of the battery are improved. be able to.

In Japanese Patent Application Laid-Open No. Hei 10-144298,
An adhesive layer made of graphite and a binder is provided between the negative electrode current collector and the negative electrode active material layer. In the present invention, the graphite contained in the adhesive layer functions to increase the current collection efficiency of the negative electrode. In JP-A-9-213370, graft-polymerized PVdF is used as an electrolyte part of a battery active material layer and a binder of the electrolyte layer. In this invention, the contact efficiency with the current collector is improved by using the graft-polymerized PVdF as the electrolyte part of the battery active material layer and the binder of the electrolyte layer.

[0006]

The characteristics required for the adhesion layer include adhesion to the current collector material, binding to the binder contained in the active material layer, and stability to the organic solvent in the electrolyte. It has excellent long-term storage properties, is thermally stable and does not peel off when exposed to high temperatures, and is electrochemically stable and can withstand repeated charge and discharge. However, in the technique described above, there is a problem that butyl rubber, phenol resin, and the like used as a binder are peeled off because they are affected by the electrolytic solution. Also in the technique shown in the following, since the acrylic copolymer has a strong binding force with the PVdF or the negative electrode current collector contained in the negative electrode material layer, the conductive material was mixed between the negative electrode current collector and the negative electrode material layer. By forming a binder layer containing an acrylic copolymer as a main component, the binding force between the negative electrode current collector and the negative electrode material layer can be increased, but this acrylic copolymer is attacked by the electrolytic solution. Therefore, there was a problem of peeling. Further, in the technique described below, when the polyurethane resin is used as the undercoat layer, the peel strength and the 80% capacity cycle number are improved as compared with the battery without the undercoat layer. I couldn't say. In addition, when an epoxy resin is used, the epoxy resin is eroded by the electrolytic solution, and may be peeled off.

In the technique described in (1), since the same material as the binder contained in the active material is used for the adhesive layer, the adhesion to the active material is good, but the adhesion to the current collector is low. It was not much different from forming the material layer directly on the current collector, and it was not sufficient. In addition, since the electrolyte penetrates into the binder, there is also a problem that the bonding strength with the current collector is weak. In the technique shown in the above, since a graft-polymerized polymer having high adhesion to the current collector is used as a binder for the active material layer, the active material layer can be formed directly on the current collector without providing an adhesion layer. Since such a polymer is hardly soluble, there is a disadvantage that a solvent to be used is limited. Furthermore, it is difficult to completely remove the solvent from the inside of the battery, and there is a possibility that the performance of the battery will be adversely affected if the solvent remains inside the battery.

[0008] A first object of the present invention is to provide a lithium ion polymer battery which is excellent in adhesion and conductivity between a current collector and an active material layer and which can improve cycle capacity retention characteristics. A second object of the present invention is to provide a lithium ion polymer battery in which the adhesion layer is stable with respect to the organic solvent in the electrolytic solution and has excellent long-term storage properties. A third object of the present invention is to provide a lithium ion polymer battery capable of suppressing corrosion of a current collector by a strong acid such as hydrofluoric acid generated in the battery. A fourth object of the present invention is to provide a method for synthesizing a binder used for an adhesion layer of a lithium ion polymer secondary battery having excellent adhesion between a current collector and an active material layer and excellent conductivity.

[0009]

The invention according to claim 1 is
As shown in FIG. 1, a positive electrode 11 in which a positive electrode active material layer 13 in which a first binder is included in an active material is formed on a surface of a positive electrode current collector 12, and a surface of a negative electrode current collector 16. Improvement of a lithium ion polymer secondary battery including an electrolyte 18 and a negative electrode 14 having a negative electrode active material layer 17 in which a second binder the same as or different from the first binder is contained in the active material. It is.
Its characteristic configuration is that the positive electrode current collector 12 and the positive electrode active material layer 1
3 and a second contact layer 21 between the negative electrode current collector 16 and the negative electrode active material layer 17. The first and second contact layers 19 and 21 are The third binder includes both the first binder and the second binder.
A polymer compound obtained by modifying a binder with a modifying substance. In the invention according to claim 1, the third binder contained in the first and second adhesion layers is the first binder or the second binder contained in the positive electrode active material layer or the negative electrode active material layer, respectively. Since it is a polymer compound modified with a modifying substance, it has high adhesion to a positive electrode active material layer or a negative electrode active material layer. Also, the first
A polymer compound obtained by modifying the binder or the second binder is added to the third compound.
When used as a binder, the adhesion to the positive electrode current collector or the negative electrode current collector is also greatly improved as compared with the use of a conventional binder.

[0010] The invention according to claim 2 is the invention according to claim 1, wherein one or both of the first and second binders is made of polytetrafluoroethylene, polychlorotrifluoroethylene, PVdF, or fluorine. It is a lithium-ion polymer secondary battery which is a fluorine-containing polymer compound selected from vinylidene fluoride-hexafluoropropylene copolymer or polyvinyl fluoride. In the invention according to claim 2, as the binder, polytetrafluoroethylene and PVdF are preferable because of high durability to the electrolytic solution.

The invention according to claim 3 is the invention according to claim 1, wherein the modifying substance is ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile. , A lithium ion polymer secondary battery which is a compound selected from vinylidene chloride, methacrylic acid, methyl methacrylate or isoprene. In the invention according to claim 3, it is preferable to use acrylic acid, methyl acrylate, methacrylic acid, and methyl methacrylate as the modifying substance because good adhesion to the current collector can be obtained.

The invention according to claim 4 is the invention according to claim 1, wherein the thickness of the first and second adhesion layers is 0.5 to 30.
It is a lithium ion polymer secondary battery having a size of μm. In the invention according to claim 4, the thickness of the first and second adhesion layers is 0.5 to 30 μm. If the thickness is less than 0.5 μm, the function of protecting the current collector from corrosion decreases, and the cycle characteristics of the discharge capacity deteriorate. In addition, it becomes difficult to uniformly disperse the conductive powder at the time of forming the first and second adhesion layers, which causes an increase in internal impedance. If it exceeds 30 μm, the volume and the weight of the portion that does not contribute to the battery reaction increase, so that the volume and the weight energy density decrease. The thickness of the adhesion layer is preferably from 1 to 15 μm.

The invention according to claim 5 is the invention according to claim 1 or 4, wherein the first and second adhesion layers further contain a dispersant in an amount of 0.1 to 20% by weight. Battery. In the invention according to claim 5, the conductive substance can be uniformly dispersed in the first and second adhesion layers by including the dispersant in the first and second adhesion layers in an amount of 0.1 to 20% by weight. Examples of the dispersant include acidic polymer-based dispersants, basic polymer-based dispersants, and neutral polymer-based dispersants. When the content is less than 0.1% by weight, the dispersion of the conductive powder is not different from the case where the dispersant is not added, and the effect of the addition is not obtained. If it exceeds 20% by weight, the dispersion state of the conductive powder does not change and does not contribute to the battery reaction, so that it is not necessary to add excessively. The content of the dispersant is 2 to 15% by weight.
Is preferred.

The invention according to claim 6 is the invention according to claim 1, wherein the conductive material is a carbon material having a particle size of 0.5 to 30 μm and a degree of graphitization of 50% or more, and the first and second conductive materials are used. A lithium ion polymer secondary battery in which the weight ratio of the third binder and the conductive substance (third binder / conductive substance) contained in the adhesion layer is 13/87 to 50/50. In the invention according to claim 6, the weight ratio of the third binder to the conductive substance is 13/8.
7 to 50/50. If the weight ratio is less than 13/87, the ratio of the polymer is too small to obtain a sufficient adhesion. When the weight ratio exceeds 50/50, the amount of the conductive substance is small, the electron transfer between the current collector and the active material layer cannot be sufficiently performed, and the internal impedance increases. The weight ratio of the third binder to the conductive substance is preferably from 14/86 to 33/67.

The invention according to claim 7 is the invention according to claims 1 to 6
A method for synthesizing a third binder contained in an adhesion layer of a lithium ion polymer secondary battery according to any one of the above, wherein the third binder is any one of a first binder and a second binder or It is synthesized by denaturing both with a denaturing substance. When the synthesized third binder is 100% by weight, the ratio of the denaturing substance contained in the third binder is 2 to 50% by weight. This is a method for synthesizing a characteristic binder. In the invention according to claim 7, when the synthesized third binder is 100% by weight, the ratio of the modifying substance contained in the third binder is set to the above ratio, so that the adhesion and the conductivity are excellent. A third binder is obtained. If the ratio of the modified substance contained in the binder is less than the lower limit, it is difficult to dissolve in the solvent, and if it exceeds the upper limit, the adhesive strength to the current collector decreases. The ratio of the modifying substance contained in the binder is preferably 70 to 90% by weight.

The invention according to claim 8 is the invention according to claim 7, wherein the modification with the modifying substance is performed after irradiating one or both of the first and second binders with radiation. This is a synthesis method carried out by mixing a modified substance with an irradiated substance and performing graft polymerization. The invention according to claim 9 is the invention according to claim 7, wherein the modification with the modifying substance is performed by mixing the modifying substance with one or both of the first and second binders and applying radiation to the mixture. And a graft polymerization is carried out by irradiating the polymer.

The invention according to claim 10 is the invention according to claim 8 or 9
In the invention according to the above, the radiation irradiation to one or both of the first and second binders, the absorbed dose to one or both of the first and second binders is 1 to 120 kGy This is a synthesis method performed by irradiating γ rays. In the invention according to claim 10, the absorbed dose is 1 to 1
Irradiation of γ rays is performed so as to be 20 kGy. If the absorbed dose is less than the lower limit and exceeds the upper limit, a problem occurs in that the adhesive strength of the obtained binder is reduced.

[0018]

Next, an embodiment of the present invention will be described. In the lithium ion polymer secondary battery of the present invention, the first and second adhesion layers each include both a third binder and a conductive material, and the third binder is the first binder or the second binder. It is a polymer compound obtained by modifying an agent with a modifying substance. "Modification" means that the property changes, and in this specification, by modifying a polymer compound with a modifying substance, not only the property of a conventional polymer compound but also the property of a modifying substance , Which means that both have new properties.

Since the modified polymer compound is based on the first binder or the second binder in the active material layer, it has high adhesion to the active material layer. On the other hand, the modification with the modified substance having high adhesion to the current collector significantly improves the adhesion to the current collector as compared with the case where the same binder as the active material layer is used. For this reason, peeling of the active material layer from the current collector is suppressed, and cycle characteristics are improved. In addition, the modified polymer compound becomes chemically stable by being modified compared to the binder used for the active material layer, and the active material layer is not separated from the current collector without being dissolved in the electrolytic solution. Is suppressed. Also, for the same reason, the conductive material dispersed in the adhesion layer is maintained without collapsing, so that good electron conduction is maintained,
Excellent long-term storage and cycle characteristics. In addition, since the current collector is coated on the chemically stable layer, even when hydrofluoric acid or the like is generated inside the battery, the adhesion layer serves as a protective layer and the corrosion of the current collector can be suppressed. Furthermore, the modified polymer compound is thermally stable due to modification compared to the binder used for the active material layer, and does not dissolve in the solvent in the battery even when the battery is exposed to high temperatures. Can be suppressed. The modified polymer compound is electrochemically stable by being modified compared to the binder used for the active material layer, and does not deteriorate even if the positive electrode is placed under a high potential when fully charged, and has stable adhesion Keep power and conductivity. Further, since it is difficult for the electrolyte to penetrate into the modified polymer compound, the electrolyte is hardly attached to the current collector, and elution of the positive electrode current collector at the time of full charge can be suppressed.

Next, the procedure for manufacturing the lithium ion polymer secondary battery of the present invention will be described. First, the binder contained in each of the positive electrode active material layer and the negative electrode active material layer is modified with a modifying substance, and this modified polymer compound is used as a third binder for the first and second adhesion layers. The first and second adhesion layers are chemical,
Because it is required to be electrochemically and thermally stable,
The polymer compound serving as the base of the first or second binder and the modified polymer compound used for the active material is preferably a polymer compound containing fluorine in the molecule. Examples of the fluorine-containing polymer compound include polytetrafluoroethylene, polychlorotrifluoroethylene, PVdF, vinylidene fluoride-hexafluoropropylene copolymer, and polyvinyl fluoride.

Techniques for modifying the fluorine-containing polymer compound include graft polymerization and crosslinking. Compounds such as ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride, methacrylic acid, methyl methacrylate, etc. No.
Particularly when acrylic acid, methyl acrylate, methacrylic acid, or methyl methacrylate is used, good adhesion to the current collector can be obtained. Examples of the modifying substance used for crosslinking include compounds having two or more unsaturated bonds, such as butadiene and isoprene. Crosslinking may be performed by vulcanization.

In this embodiment, graft polymerization will be described. Examples of the method of graft polymerization include a catalyst method, a chain transfer method, a radiation method, a photopolymerization method, and a mechanical cleavage method. For example, in the radiation method, a polymer compound and a compound to be a grafting material can be polymerized together by radiating radiation continuously or intermittently. It is preferable to pre-emit the polymer compound that is the group. Specifically, after irradiating the polymer compound with radiation, the object to be irradiated is mixed with a modifying substance to be a grafting material, so that the polymer compound is a main chain and the modifying substance is a side chain. A molecular compound can be obtained. Radiation used for the graft polymerization includes an electron beam, X-ray or γ-ray. Irradiation with γ-rays is performed so that the absorbed dose to the polymer compound becomes 1 to 120 kGy. By irradiating the high molecular compound which is the main group with a radiation, a radical is formed at one end, and the grafted material is easily polymerized. The following chemical formulas (1) and (2) show the graft polymerization of PVdF and acrylic acid by a radiation method.

[0023]

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[0024]

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As shown in the chemical formula (1), a radical is formed at one end of PVdF by irradiating PVdF with γ-rays as radiation. As shown in chemical formula (2), acrylic acid is brought into contact with the PVdF having a radical at one end, and the double bond of acrylic acid is graft-polymerized to the radical of PVdF.

As another example, chemical formulas (3) and (4) show the graft polymerization of PVdF and methacrylic acid.

[0027]

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[0028]

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As shown in the chemical formula (3), PVdF forms a radical at one end of the PVdF by irradiating γ-rays as radiation, and methacrylic acid is contacted with PVdF having a radical at one end in the chemical formula (4). Let me, PVd
The double bond of methacrylic acid is graft-polymerized to the radical of F.

Graft polymerization includes the length of time that the activated main group is in contact with the grafting material, the degree of preactivation of the main group by radiation, the degree to which the grafted material can penetrate the main group, Polymerization differs depending on the temperature at which the grafted material is in contact with the grafting material. When the grafting material is an acid, the degree of grafting can be observed by sampling a solution containing the compound that is the grafting material, titrating with an alkali, and measuring the concentration of the remaining acid compound. . The proportion of grafting in the obtained composition is desirably 10 to 30% of the final weight.

The thus obtained graft polymerized modified polymer compound is used as a third binder for the adhesion layer, and the third binder is dissolved in a solvent to prepare a polymer solution. The first and second adhesive layer slurries are prepared by dispersing a conductive substance in the first and second adhesive layers. Particle size 0.5 to 3 for conductive materials
A carbon material having 0 μm and a degree of graphitization of 50% or more is used. The slurry of the adhesion layer is prepared by mixing the third binder and the conductive substance so that the weight ratio (third binder / conductive substance) becomes 13/87 to 50/50. Dimethylacetamide (hereinafter referred to as DMA), acetone, dimethylformamide, and N-methylpyrrolidone are used as the solvent.

Next, sheet-shaped positive and negative electrode current collectors were prepared, respectively, and the first and second adhesive layer slurries prepared on the positive and negative electrode current collectors were respectively coated and dried by a doctor blade method, and dried. After adhesion layer thickness is 0.5
A positive or negative electrode current collector having first and second adhesion layers of about 30 μm is formed. The thickness of the adhesive layer between the positive electrode and the negative electrode after drying is preferably 1 to 15 μm. The sheet-like positive electrode current collector includes an Al foil, and the negative electrode current collector includes a Cu foil. Here, the doctor blade method is one of the methods of forming ceramics into a sheet, and the thickness of the slip carried on a carrier such as a carrier film or an endless belt is determined by a knife edge called a doctor blade and a carrier. This is a method of precisely controlling the thickness of the sheet by adjusting the distance between the sheets.

Next, the components required for the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer are mixed, respectively, to form a slurry for coating the positive electrode active material layer, a slurry for coating the negative electrode active material layer, and a slurry for coating the electrolyte layer. Prepare each slurry. The obtained slurry for coating a positive electrode active material layer is applied to a positive electrode current collector having a first adhesion layer by a doctor blade method, dried, and rolled to form a positive electrode. Similarly, for the negative electrode,
The obtained slurry for coating a negative electrode active material layer is coated on a negative electrode current collector having a second adhesion layer by a doctor blade method, dried, and rolled to form a negative electrode. The positive electrode or negative electrode active material layer is formed so that the thickness after drying is 20 to 250 μm. The electrolyte layer is obtained by drying the obtained electrolyte layer coating slurry on a release paper so that the electrolyte layer has a dry thickness of 10 to 15%.
It is coated and dried by a doctor blade method so as to have a thickness of 0 μm, and is formed by peeling off from release paper. Alternatively, the electrolyte layer coating slurry may be applied to the surface of the positive electrode or the surface of the negative electrode and dried to form an electrolyte layer. The formed positive electrode, electrolyte layer, and negative electrode are sequentially laminated, and the laminate is thermocompression-bonded to form a sheet-like electrode body as shown in FIG.

Finally, a positive electrode lead and a negative electrode lead made of Ni were welded to the positive electrode current collector and the negative electrode current collector, respectively, and housed in a bag-shaped laminated package material having an opening. The opening is sealed by thermocompression bonding under the conditions, whereby a sheet-shaped lithium ion polymer secondary battery can be manufactured.

[0035]

Next, examples of the present invention will be described together with comparative examples. <Example 1> First, PVdF was used as the first and second binders.
50 g of powder and 260 g of a 15% by weight aqueous solution of acrylic acid were prepared as modifying substances. Next, the PVdF powder was put in a polyethylene pack and vacuum-packed,
Cobalt 6 so that the absorbed dose to dF is 50 kGy
Γ-rays were irradiated using 0 as a γ-ray source. Next, the gamma-irradiated PVdF powder is taken out of the polyethylene pack, transferred to a nitrogen atmosphere, supplied with PVdF in 260 g of a 15% by weight aqueous solution of acrylic acid, kept at 80 ° C., reacted with the aqueous solution of acrylic acid, and reacted with the above-mentioned chemical formula. Acrylic acid-grafted PVdF (Acrylic) produced by the graft polymerization shown in (2)
Acid grafting PolyVinylidene Fluoride, AA-
It is called g-PVdF. ) Was synthesized. A sample of the reaction solution was collected, and the amount of acrylic acid that had undergone graft polymerization reaction with PVdF was measured successively by titration, and AA-g-PVdF was measured.
When the content ratio of the grafted acrylic acid group in the inside became 17% by weight, the reaction was stopped, and the obtained solid product was washed with pure water and dried to obtain a third binder. .

Example 2 A third binder was obtained in the same manner as in Example 1, except that the modifying substance was 260 g of a 15% by weight aqueous solution of methacrylic acid. <Example 3> A third binder was obtained in the same manner as in Example 1, except that the modifying substance was 260 g of a 15% by weight aqueous solution of methyl acrylate. <Example 4> A third material was prepared in the same manner as in Example 1 except that the modified substance was 260 g of a 15% by weight aqueous solution of methyl methacrylate.
A binder was obtained.

Comparative Example 1 A commercially available acrylate-methacrylate copolymer was prepared as a third binder. <Comparative Example 2> PVdF commercially available as the third binder
Was prepared. <Comparative Example 3> PVdF commercially available as a third binder
Was prepared. <Comparative Example 4> A third binder was obtained in the same manner as in Example 1 except that the modifying substance was changed to 2600 g of an aqueous solution containing 1% by weight of crotonic acid.

<Comparative Evaluation 1> Examples 1-4 and Comparative Example 1
The following evaluation tests were performed using the third binder obtained in Nos. 4 to 4. Solubility test for dimethylacetamide 4 g of the third binder obtained in each of Examples 1 to 4 and Comparative Examples 1 to 4 was collected, and 56 g of DMA was added to this sample.
Was added and stirred while heating to 60 ° C. to obtain a polymer solution. This solution was stored in a glass bottle, and the state of precipitation in the solution after standing for one day was confirmed.

Adhesion Test for Copper Foil and Aluminum Foil First, using the third binder obtained in Examples 1 to 4 and Comparative Examples 1 to 4, a polymer solution similar to the polymer solution in the evaluation test described above was prepared. Each was prepared. Then, these solutions were each 30 mm wide, 200 mm long and 14 mm thick.
A μm surface was uniformly coated on a degreased Cu foil, and an Al foil having a width of 10 mm, a length of 100 mm, and a thickness of 20 μm was degreased on the surface to form a peel sample for an adhesion test. The prepared sample was dried at 80
Drying was performed at 5 ° C. for 5 days. Next, the dried sample was evaluated for a binder for Cu foil and Al foil using a peel tester. In the peeling test method, the Cu foil side of the sample was fixed to a test table when measuring, and the Al foil bonded to the Cu foil was pulled vertically upward at a rate of 100 mm / min, so that the Al foil was removed from the Cu foil. The force applied to peel was measured.

Test of Cycle Capacity Maintenance Characteristics of Battery When Used for Adhesion Layer of Battery First, 2 g of each of the third binders obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was collected, and this sample was prepared. DMA
200 g was added and stirred while heating to 60 ° C. to obtain a polymer solution. The solution has a specific surface area of 150 m ² / g.
Of the graphite powder and 1.2 g of a dispersant for dispersing the graphite powder were prepared to prepare an adhesive layer slurry. Next, as a positive electrode current collector, a thickness of 20 μm and a width of 25
Prepare a 0 μm Al foil, apply and dry the adhesive layer slurry prepared on this Al foil by a doctor blade method,
The thickness of the adhesive layer after drying was controlled within the range of 10 ± 1 μm. The thickness of the negative electrode current collector is 14 μm and the width is 250 μm.
Was prepared, and the slurry for the adhesive layer prepared on the surface of the Cu foil was applied and dried by a doctor blade method, and the thickness of the adhesive layer after drying was controlled within the range of 10 ± 1 μm.
Next, the respective components shown in Table 1 below were mixed for 2 hours by a ball mill to prepare a slurry for coating a positive electrode active material layer, a slurry for coating a negative electrode active material layer, and a slurry for coating an electrolyte layer, respectively.

[0041]

[Table 1]

The obtained slurry for coating the positive electrode active material was coated on the surface of the Al foil having the adhesion layer with a dry thickness of 80 μm for the positive electrode active material layer.
The coating was dried by a doctor blade method so as to have a thickness of μm, dried, and then rolled to form a positive electrode. Similarly, the negative electrode active material coating slurry is coated and dried by a doctor blade method so that the dry thickness of the negative electrode active material layer becomes 80 μm on the surface of the Cu foil having the adhesion layer, and then rolled to form a negative electrode. did. Further, the slurry for coating the electrolyte layer is applied to each of the positive electrode and the negative electrode by a doctor blade method so that the dry thickness becomes 50 μm, and the positive electrode and the negative electrode having these electrolyte layers are laminated and thermocompression-bonded to form a sheet. An electrode body having a shape of was prepared. A positive electrode lead and a negative electrode lead made of Ni are respectively formed on the prepared electrode body as a positive electrode current collector,
It was welded to the negative electrode current collector, housed in a laminated package material processed into a bag shape having an opening, and sealed by thermocompression bonding of the opening under reduced pressure conditions to produce a sheet-shaped battery. Next, the obtained sheet-shaped battery was charged with a maximum charging voltage of 4 V and a charging current of 0.
A charging step of performing charging for 2.5 hours under the condition of 5A;
1. The discharge voltage becomes the minimum discharge voltage at a constant current discharge of 5A.
The charge / discharge cycle was repeated with the discharge step of discharging until reaching 75 V as one cycle, and the charge / discharge capacity of each cycle was measured to determine the number of cycles that decreased to 80% of the initial discharge capacity.

Test of Adhesion of Adhesion Layer to Current Collector When Used as Adhesion Layer of Battery First, the above-described evaluation was performed using the third binder obtained in Examples 1 to 4 and Comparative Examples 1 to 4. Sheet-shaped batteries similar to the sheet-shaped batteries of the test were produced. Next, the battery was subjected to 100 charge / discharge cycles under the same conditions as in the above-described evaluation test in a 70 ° C. environment. Then 100
When the storage package of the sheet-shaped battery after the charge and discharge of the cycle is removed, the positive electrode and the negative electrode of the battery are peeled off and separated from each other, and the separated positive electrode adhesion layer and negative electrode adhesion layer are pinched and pulled with tweezers Next, it was confirmed whether or not the adhesion layer was separated from the current collector.

Table 2 shows the evaluation results in the above evaluation tests. The symbols in the evaluation test column in Table 2 have the following meanings. A: Uniform precipitation-free solution.

The symbols in the evaluation test column in Table 2 have the following meanings. A: The adhesion layer has extremely good adhesion to the current collector, and does not peel off. ：: The adhesion layer is partially peeled off from the current collector. Δ: The adhesion layer is separated from the current collector over a wide area. X: The adhesion layer is completely peeled off from the current collector.

[0046]

[Table 2]

As is apparent from Table 2, the evaluation test D
Examples 1 to 4 and Comparative Examples 1 to 4 dissolve characteristics in MA.
Each of the third binders obtained in the above can be completely dissolved in DMA, and furthermore, even if this solution is allowed to stand for one day, no precipitation occurs, indicating that it is suitable as a slurry for coating. In the adhesion test for the Cu foil and the Al foil in the evaluation test, the test using the third binder obtained in Comparative Examples 2 to 4 resulted in 2 N / cm or less, and the adhesion effect was insufficient as the adhesion layer material. It turns out there is. In contrast, Example 1
A bonded to a Cu foil using the third binder obtained in
All of the 1 foils had a peel strength from the Cu foil of 10 N / cm or more, and exhibited sufficient strength to bond the active material of the battery and the current collector.

In the cycle capacity retention characteristic test of the evaluation test, the third binder of Examples 1 to 4 was used in comparison with the 80% capacity cycle number of the battery using the third binder of Comparative Examples 1 to 4. The 80% capacity cycle numbers of the batteries that were used indicate high cycle numbers. This is because the third binders of Examples 1 to 4 have excellent adhesive properties and high durability to the electrolytic solution.
It is considered that the cycle capacity maintenance characteristics were improved. In the adhesion test of the adhesion layer to the current collector in the evaluation test, the adhesion layers using the third binder of Examples 1 to 4 were compared with Comparative Examples 1 to 4.
It was harder to peel off from the current collector than the adhesion layer using the third binder, indicating that the adhesion to the current collector was excellent. Comparative Example 1, in which a copolymer containing no fluorine was used as the third binder, had high adhesion properties to Cu foils and Al foils, but had insufficient electrolyte resistance properties, and showed adhesion after repeated charge / discharge cycles. A phenomenon occurred in which the layer was separated from the current collector of the battery.

From the above evaluation tests, the modified substances, in particular, acrylic acid, methyl acrylate, methacrylic acid, and the modified polymer compound obtained by grafting methyl methacrylate onto PVdF were used as the third binder in the first and second adhesion layers. It turned out to be suitable for.

<Examples 5 to 11 and Comparative Examples 5 and 6> First, 50 g of PVdF powder was used as the first and second binders.
260 g of a 15% by weight aqueous solution of acrylic acid was prepared as a modifying substance. Next, the PVdF powder was put in a polyethylene pack, vacuum-packed, and irradiated with γ-rays using cobalt 60 as a γ-ray source so that the absorbed dose to PVdF became 50 kGy. Next, the PVdF powder irradiated with γ-rays is taken out from the polyethylene pack and transferred to a nitrogen atmosphere.
AA-g-PVdF was synthesized by supplying PVdF to 260 g of a 15% by weight aqueous solution of acrylic acid and maintaining the temperature at 80 ° C. to react with the aqueous solution of acrylic acid. A sample of the reaction solution was collected, and the amount of acrylic acid that had undergone graft polymerization reaction with PVdF was measured successively by titration. The content of the grafted acrylic acid group in AA-g-PVdF was 2% by weight (Example 1). 5), 7% by weight (Example 6), 10% by weight (Example 7), 13% by weight (Example 8), 17% by weight (Example 9), 25% by weight (Example 10), 40% by weight % (Example 11), 1% by weight (Comparative Example 5) and 55% by weight (Comparative Example 6), the reaction was stopped, and the resulting solid product was washed with pure water and dried. Example 5
11 and the third binders of Comparative Examples 5 and 6.

<Comparative Evaluation 2> Using the third binders obtained in Examples 5 to 11 and Comparative Examples 5 and 6, the same tests as Evaluation Test 1 to Evaluation Test 1 in Comparative Evaluation 1 were performed. Of AA-g-PVdF, the influence of the content of acrylic acid groups on the adhesive properties and the electrical properties of the battery was investigated. Table 3 shows the results of the evaluation test and the evaluation test, FIG. 2 shows the results of the evaluation test, and FIG. 3 shows the results of the evaluation test. The symbols in the evaluation test column in Table 3 are as follows:
It has the following meaning. A: Uniform precipitation-free solution. ：: Dissolved in DMA, but a small amount of precipitate was generated in the solution. ×: Insoluble in DMA.

The symbols in the evaluation test column in Table 3 have the following meanings. A: The adhesion layer has extremely good adhesion to the current collector, and does not peel off. ：: The adhesion layer is partially peeled off from the current collector. X: The adhesion layer is completely peeled off from the current collector.

[0053]

[Table 3]

As is clear from Table 3, the evaluation test D
In the dissolution property to MA, the third binders of Examples 5 to 9 in which the content ratio of the acrylate group is 25% by weight or less
It was completely dissolved in MA, and no precipitation occurred even when left to stand. Example 10 in which the content of acrylic acid groups was 25% by weight
It became difficult to dissolve the third binder in DMA, and a small amount of precipitate appeared when the dissolved solution was allowed to stand for one day. This small amount of precipitation is such that the solution is redissolved by stirring the solution for a long time with a homogenizer for a long time, which is a level that does not cause any problem in bonding to copper foil or aluminum foil. In contrast, Comparative Example 6, in which the content of acrylic acid groups was 55% by weight, was hardly soluble in DMA, indicating that it was not suitable for bonding to copper foil or aluminum foil. In addition, the content ratio of the acrylic acid group is 1
% By weight of Comparative Example 5 dissolved in DMA without problems. FIG. 2 shows the adhesion test for the Cu foil and the Al foil in the evaluation test.
As shown in the above, the adhesive strength of the Cu foil and the Al foil bonded with AA-g-PVdF correlates with the content ratio of the acrylic acid group contained in AA-g-PVdF. The results of Comparative Example 6 show that when the content ratio is 55% by weight or more, the adhesive effect is reduced. This is probably because AA-g-PVdF was insufficiently dissolved in DMA, as is clear from the results of the evaluation test. Also in Comparative Example 5 in which the content ratio of the acrylic acid group was 1% by weight, the adhesive strength was reduced. In order to obtain sufficient adhesive properties from the results of Examples 5 to 11,
The content ratio of acrylic acid group in AA-g-PVdF is 2 to 5
It is understood that 0% by weight is necessary, and 10 to 30% by weight is preferable.

In the cycle capacity retention characteristic test of the evaluation test, as shown in FIG. 3, the same tendency as the test result of the adhesive strength of the evaluation test was shown. In the adhesion test of the adhesion layer to the current collector in the evaluation test, as is clear from Table 3, as a result of analyzing the battery adhesion layer after the charge / discharge cycle, the adhesion characteristics of the adhesion layer were evaluated and evaluated. Similarly to the above, when the content ratio of the acrylate group in AA-g-PVdF is 2 to 50% by weight, it is suitable as a binder for a battery, and it is understood that 10 to 30% by weight is preferable.

<Examples 12 to 16 and Comparative Examples 7 and 8> First, 50 g of PVdF powder was used as the first and second binders.
260 g of a 15% by weight aqueous solution of acrylic acid was prepared as a modifying substance. Next, the PVdF powder was placed in a polyethylene pack and vacuum-packed, and the absorbed dose to PVdF was 90 kGy (Example 12) and 70 kGy, respectively.
(Example 13), 50 kGy (Example 14), 20 kG
y (Example 15), 10 kGy (Example 16), 130
Irradiation with γ-rays was performed using cobalt 60 as a γ-ray source so as to obtain kGy (Comparative Example 7) and 0.5 kGy (Comparative Example 8).
Next, the gamma-irradiated PVdF powder is taken out from the polyethylene pack, transferred to a nitrogen atmosphere, supplied with PVdF in 260 g of a 15% by weight aqueous solution of acrylic acid, kept at 80 ° C., reacted with the aqueous solution of acrylic acid, and reacted with AA- g-PVdF was synthesized. A sample of the reaction solution was collected, and the amount of acrylic acid that had been graft-polymerized to PVdF was measured sequentially by titration. When the content of acrylic acid groups in AA-g-PVdF reached 17% by weight, the reaction was stopped. The solid products thus obtained were washed with pure water and dried, and these were used as third binders of Examples 12 to 16 and Comparative Examples 7 and 8, respectively.

<Comparative Evaluation 3> Using the third binders obtained in Examples 12 to 16 and Comparative Examples 7 and 8, the same tests as Evaluation Test 1 to Comparative Test 1 were performed.
Table 4 shows the results of the evaluation test and the evaluation test, FIG. 4 shows the results of the evaluation test, and FIG. 5 shows the results of the evaluation test. The symbols in the evaluation test and the evaluation test column in Table 4 have the same meanings as the symbols used in Comparative Evaluation 2.

[0058]

[Table 4]

As is clear from Table 4, D in the evaluation test was
With respect to the solubility characteristics for MA, in Examples 13 to 16 in which the absorbed dose was less than 70 kGy, the synthesized AA-g-PVdF could be dissolved in DMA even at room temperature. Absorbed dose is 90
In Example 12 of kGy, the synthesized AA-g-PVdF was dissolved in DMA maintained at a high temperature (85 ° C.). In contrast, in Comparative Example 7 in which the absorbed dose was 130 kGy, it was found that dissolution in DMA was almost impossible even with stirring. In the adhesion test for the Cu foil and the Al foil in the evaluation test, as shown in FIG. 4, the adhesive strength of the Cu foil and the Al foil bonded with AA-g-PVdF was AA-g-PVdF.
It correlates with the content of acrylic acid groups contained therein. In the results of Comparative Examples 7 and 8, the absorbed dose was 1 kGy or less,
When it is more than kGy, it can be seen that the adhesive strength of AA-g-PVdF is low and is not suitable as a binder. The reason for this is that when the absorbed dose is 1 kGy or less, the number of acrylic acid groups to be grafted is small.
This is probably due to the poor dissolution of -g-PVdF.

In the cycle capacity maintenance characteristic test of the evaluation test, as shown in FIG. 5, the same tendency as the test result of the adhesive strength of the evaluation test was shown. From this result, 400
It has been found that the absorption dose is preferably in the range of 1 kGy to 120 kGy in order to produce a battery capable of maintaining 80% capacity over cycles. In the adhesion test of the adhesion layer to the current collector in the evaluation test, as is clear from Table 4, as a result of analyzing the adhesion layer of the battery after performing the charge / discharge cycle, the absorbed dose was 1 kGy to 120 kGy.
It can be seen that AA-g-PVdF synthesized using the above is suitable as a binder for an adhesion layer of a battery. In order to obtain stable adhesion characteristics, PVd having a γ-ray absorbed dose of 20 to 100 kGy
It is preferable to use F as a raw material.

Example 17 First, 1st was used as the third binder.
A obtained by graft-polymerizing 7% by weight of acrylic acid to PVdF
2 g of Ag-PVdF was prepared. This AA-g-PVdF
To 2 g, 98 g of DMA was added as a solvent, and dissolved with a homogenizer to obtain a polymer solution. 8 g of graphite powder having a specific surface area of 150 m ² / g was prepared as a conductive substance, and this graphite powder was dispersed in 80 g of DMA to prepare a dispersion. This dispersion was added to the above polymer solution to prepare an adhesive layer slurry. 20 μm thick and 2 width as positive electrode current collector
A 50 mm Al foil is prepared, and the adhesive layer slurry prepared on the Al foil is applied and dried by a doctor blade method, and the Al layer having an adhesive layer thickness of 5 μm after drying has an adhesive layer.
A foil was obtained. On the other hand, the negative electrode current collector has a thickness of 10 μm and a width of 2 μm.
A Cu foil of 50 mm is prepared, and the Cu foil is coated and dried by a doctor blade method.
A Cu foil having a μm adhesion layer was obtained. Next, the components shown in Table 1 were mixed for 2 hours by a ball mill to prepare a slurry for coating the positive electrode active material layer, a slurry for coating the negative electrode active material layer, and a slurry for coating the electrolyte layer.

The obtained slurry for coating the positive electrode active material layer was coated on an Al foil having an adhesion layer so that the dry thickness of the positive electrode active material layer was 80%.
The coating was dried by a doctor blade method so as to have a thickness of μm, dried, and rolled to form a positive electrode. The obtained negative electrode active material layer coating slurry is coated and dried by a doctor blade method on a Cu foil having an adhesion layer so that the dry thickness of the negative electrode active material layer becomes 80 μm, and the negative electrode is rolled. Formed. The obtained slurry for coating an electrolyte layer is coated and dried by a doctor blade method on a release paper having a thickness of 25 μm and a width of 250 mm so that the dry thickness of the electrolyte layer becomes 50 μm, and the electrolyte layer sheet is peeled off from the release paper. Was formed. The formed positive electrode, electrolyte sheet and negative electrode were sequentially laminated, and the laminate was thermocompression-bonded to produce a sheet-like electrode body. Next, a positive electrode lead and a negative electrode lead made of Ni were welded to the positive electrode current collector and the negative electrode current collector, respectively, and housed in a bag-shaped laminated package material having an opening, and this electrode body was placed under reduced pressure conditions. The opening was sealed by thermocompression bonding to produce a sheet-shaped battery.

Example 18 A modified polymer represented by the above formula (2) was prepared by graft-polymerizing 17% by weight of methacrylic acid to polyvinylidene fluoride, using the modified polymer used for the adhesion layer (Methacrylic Acid grafting PolyVinylidene Fluorid).
e, MA-g-PVdF), and a battery was fabricated in the same manner as in Example 17. <Example 19> In preparing the adhesive layer slurry, when the conductive material was dispersed in a solvent, 1.2 g of a dispersant was added to adjust the content of the acidic polymer-based dispersant to 10.7% by weight of the solid.
A battery was fabricated in the same manner as in Example 17, except that the content was changed to% by weight. <Example 20> In the preparation of the adhesive layer slurry, when the conductive substance was dispersed in a solvent, 1.2 g of a dispersant was added to adjust the content of the acidic polymer-based dispersant to 10.7% by weight of the solid substance.
A battery was fabricated in the same manner as in Example 18, except that the content was changed to% by weight.

Example 21 A battery was manufactured in the same manner as in Example 17, except that the dry thickness of each of the adhesion layers provided on the positive electrode current collector and the negative electrode current collector was 0.5 μm. <Example 22> Example 1 except that the dry thicknesses of the adhesion layers provided on the positive electrode current collector and the negative electrode current collector were each set to 1 µm.
A battery was prepared in the same manner as in No. 7. Example 23 A battery was fabricated in the same manner as in Example 17, except that the dry thickness of each of the adhesion layers provided on the positive electrode current collector and the negative electrode current collector was 10 μm. Example 24 A battery was produced in the same manner as in Example 17, except that the dry thickness of each of the adhesion layers provided on the positive electrode current collector and the negative electrode current collector was 15 μm.

Example 25 A battery was prepared in the same manner as in Example 17 except that 2 g of graphite powder, which was a conductive material of the slurry for coating the adhesion layer, was used, and the weight ratio between the binder and the conductive material was 50/50. Produced. <Example 26> A battery was fabricated in the same manner as in Example 17, except that 4 g of graphite powder, which was the conductive material of the slurry for coating the adhesion layer, was used, and the weight ratio of the binder to the conductive material was 33/67. <Example 27> A battery was fabricated in the same manner as in Example 17, except that the weight ratio between the binder and the conductive substance was 14/86, with 12 g of graphite powder as the conductive substance in the slurry for coating the adhesion layer. <Example 28> A battery was fabricated in the same manner as in Example 17, except that the weight ratio of the binder to the conductive substance was 13/87 with the use of 14 g of graphite powder as the conductive substance of the slurry for coating the adhesion layer.

Comparative Example 9 A battery was manufactured in the same manner as in Example 17 except that the adhesion layer was not provided on the positive electrode current collector and the negative electrode current collector. <Comparative Example 10> The binder of the adhesive layer coating slurry was AA.
A battery was prepared in the same manner as in Example 17, except that -g-PVdF was changed to butyl rubber, and the solvent was changed from DMA to toluene. <Comparative Example 11> The binder of the adhesive layer coating slurry was AA.
A battery was produced in the same manner as in Example 17, except that -g-PVdF was changed to an acrylate-methacrylate copolymer and the solvent was changed to water from DMA. <Comparative Example 12> The binder of the slurry for coating the adhesion layer was AA.
A battery was prepared in the same manner as in Example 17, except that -g-PVdF was used as the polyurethane resin, and the solvent was used as the mixed solvent containing 108 g of methyl ethyl ketone and 72 g of methyl isobutyl ketone from DMA. <Comparative Example 13> The binder of the slurry for coating the adhesion layer was AA.
-g-PVdF to epoxy resin, and solvent from DMA to 108 g of methyl ethyl ketone and methyl isobutyl ketone 7
A battery was fabricated in the same manner as in Example 17, except that 2 g of the mixed solvent was used.

<Comparative Example 14> In the preparation of the adhesive layer slurry, the procedure of Example 17 was repeated except that when dispersing the conductive substance in the solvent, 3.5 g of the dispersant was added to make the dispersant content 26% by weight. A battery was similarly manufactured. <Comparative Example 15> A battery was fabricated in the same manner as in Example 17, except that the dry thickness of each of the adhesion layers provided on the positive electrode current collector and the negative electrode current collector was 40 µm. <Comparative Example 16> A battery was fabricated in the same manner as in Example 17, except that 20 g of graphite powder, which was a conductive substance of the slurry for coating the adhesion layer, was used, and the weight ratio of the binder to the conductive substance was 9/91.

<Comparative Evaluation> The batteries obtained in Examples 17 to 28 and Comparative Examples 9 to 16 were subjected to the following evaluation tests. Resistance Test of Adhesion Layer to Electrolyte Solution A negative electrode current collector having an adhesion layer obtained in Examples 17 to 28 and Comparative Examples 9 to 16 was prepared from 20 parts by weight of propylene carbonate, 40 parts by weight of ethylene carbonate, and 40 parts by weight of diethyl carbonate. The negative electrode current collector having the adhesion layer was immersed in the same electrolyte solution for one week, and the amount of weight increase of the negative electrode current collector having the adhesion layer was measured to determine whether the modified polymer as the third binder of the adhesion layer swelled with the electrolyte solution. In addition, the negative electrode current collector Cu foil was rubbed with a finger to check whether or not the adhesion layer was peeled off. Current collector protection performance test of adhesive layer against hydrogen fluoride (HF) A 5 ppm aqueous solution of hydrofluoric acid on the surface of the negative electrode current collector having the adhesive layer obtained in Examples 17 to 28 and Comparative Examples 9 to 16 2 ml was dropped, and the state of the current collector after standing for 24 hours was confirmed.

Adhesion Test of Adhesion Layer to Active Material Layer Adhesive tapes were adhered to the surfaces of the positive electrode current collector and the negative electrode current collector obtained in Examples 17 to 28 and Comparative Examples 9 to 16, and pressed with a rubber roller. . Each of the positive electrode current collector and the negative electrode current collector to which the pressure-sensitive adhesive tape is attached is 10 mm.
A 10 mm wide current collector was pulled vertically upward and the force applied to peel off the active material layer was measured.
Further, the manner of peeling was visually confirmed. Cycle capacity maintenance characteristic test The sheet-shaped batteries obtained in Examples 17 to 28 and Comparative Examples 9 to 16 were subjected to a charge / discharge cycle test, and were subjected to a maximum charge voltage of 4.2 V and a charge of 0.5 A for 2.5 hours. The charge and discharge cycles of discharging and discharging at a constant current of 0.5 A until the discharge voltage becomes 2.75 V (minimum discharge voltage) are repeated, and the discharge capacity of each cycle is measured to obtain an initial discharge capacity of 8
The number of cycles down to 0% was measured.

Table 5 shows the results of the above evaluation tests. The symbols in the evaluation test column in Table 5 have the following meanings. A: Very good, no peeling. ：: good, no peeling Δ: Partially peeled, ×: Completely peeled.

The symbols in the evaluation test column in Table 5 have the following meanings. ：: Very good, no corrosion. ：: good, no corrosion. Δ: Partially corroded. ×: Corroded.

[0072]

[Table 5]

Resistance Test for Electrolytic Solution of Adhesion Layer In Comparative Examples 10 to 13, the amount of increase in the amount of the negative electrode current collector having the adhesion layer is large, and it can be seen that the electrolyte solution swells due to the binder forming the adhesion layer. . On the other hand, Embodiment 1
In Nos. 7 to 28, the amount of increase in the negative electrode current collector having the adhesion layer was slight even after immersion in the electrolytic solution for one week, indicating resistance to the electrolytic solution. Current collector protection performance test against hydrogen fluoride (HF) of adhesion layer Comparative examples 9 and 1
One current collector was corroded by HF. In Comparative Examples 10, 12, and 13, a part was corroded. On the other hand, it can be seen that the current collectors of Examples 17 to 28 were not corroded by HF, and the protection function by the adhesion layer was working.

Adhesion Test of Adhesion Layer to Active Material Layer In Examples 17 to 28, the force applied to peel the active material layer was larger than that in Comparative Examples 9 to 13. Moreover, the peeling method was such that Comparative Examples 9 to 13 had in-plane unevenness, and a peeled portion and a non-peeled portion were formed. In contrast, in Examples 17 to 28, the surface was uniform and the entire surface was peeled off. Cycle capacity retention characteristic test Comparative Examples 9 to 13-8
In each of Examples 17 to 28, the number of cycles was higher than that of the 0% capacity cycle, indicating that the cycle maintenance characteristics by charge / discharge were excellent.

[0075]

As described above, according to the present invention, the first adhesive layer is provided between the positive electrode current collector and the positive electrode active material layer, and the first adhesive layer is formed between the negative electrode current collector and the negative electrode active material layer. A second adhesive layer between the first and second adhesive layers, the first and second adhesive layers each containing both a third binder and a conductive material, wherein the third binder is the first binder or the second binder; Since the agent is a polymer compound modified with a modifying substance, the modified polymer based on the first binder or the second binder has a high adhesion to the positive electrode active material layer or the negative electrode active material layer, Due to the modification, the adhesion to the current collector is greatly improved as compared with the case where a conventional binder is used. As a result, peeling of the active material layer from the current collector can be suppressed, and the conductivity between the current collector and the active material layer is significantly improved, so that the cycle capacity retention characteristics can be improved. In addition, since the electrolyte is not easily immersed in the modified polymer compound, the adhesion layer is stable with respect to the organic solvent in the electrolyte and has excellent long-term storage properties. Even when a strong acid such as hydrofluoric acid is generated in the battery, the modified polymer compound serves as a protective layer, so that corrosion of the current collector can be suppressed.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional configuration diagram showing an electrode body of a lithium ion polymer secondary battery of the present invention.

FIG. 2 is a diagram showing the results of evaluation tests of third binders obtained in Examples 5 to 11 and Comparative Examples 5 and 6.

FIG. 3 is a view showing the results of evaluation tests of third binders obtained in Examples 5 to 11 and Comparative Examples 5 and 6.

FIG. 4 is a view showing the results of evaluation tests of third binders obtained in Examples 12 to 16 and Comparative Examples 7 and 8.

FIG. 5 is a view showing the results of evaluation tests of third binders obtained in Examples 12 to 16 and Comparative Examples 7 and 8.

[Explanation of symbols]

 Reference Signs List 11 positive electrode 12 positive electrode current collector 13 positive electrode active material layer 14 negative electrode 16 negative electrode current collector 17 negative electrode active material layer 18 polymer electrolyte layer 19 first adhesion layer 21 second adhesion layer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09J 127/20 C09J 127/20 127/22 127/22 151/00 151/00 201/00 201/00 H01M 4/02 H01M 4/02 CD 4/66 4/66 A 10/40 10/40 B (72) Inventor Akio Mizuguchi 1002, Mukaiyama, Naka-machi, Naka-gun, Ibaraki Pref. 72) Inventor Akihiro Higami 1002-14 Mukoyama, Naka-machi, Naka-gun, Ibaraki Pref.Mitsubishi Materials Research Laboratory Naka Research Center In the Research Institute Naka Research Center (72) Inventor Tadashi Kobayashi 1-297 Kitabukurocho, Saitama City, Saitama Prefecture Mitsubishi Materials Research Institute Investigation Center Omiya Research Center (72) Inventor Sawako Takeuchi Kitabukurocho, Saitama City, Saitama Prefecture 1-chome 297 Mitsubishi Materials Corporation Research Laboratory Omiya Lab F-term inside the research center (reference) 4J026 AA26 BA02 BA05 BA10 BA20 BA25 BA27 BA31 BA32 BA46 BA47 BB01 BB02 DB03 DB32 DB36 GA08 4J040 DC091 DC101 DL151 GA01 GA03 GA07 GA19 GA22 JB10 KA03 KA32 KA42 LA06 LA09 NA19 5H017 BB02 BB02 DD06 EE06 EE07 EE09 HH01 HH03 HH05 5H029 AJ05 AJ13 AK03 AL07 AM03 AM05 AM07 BJ12 CJ00 DJ07 DJ17 EJ04 EJ11 EJ12 HJ00 HJ01 HJ04 HJ05 HJ12 5H050 AA07 AA18 BA17 CA07 CB08 DA10 HA11 GA00

Claims (10)

[Claims] 1. A positive electrode (11) in which a positive electrode active material layer (13) in which a first binder is contained in an active material is formed on a surface of a positive electrode current collector (12); On the surface of (16), a negative electrode active material layer (1) in which a second binder the same as or different from the first binder is contained in the active material.
In a lithium ion polymer secondary battery including a negative electrode (14) on which a (7) is formed, and an electrolyte (18), a lithium ion secondary battery is provided between the positive electrode current collector (12) and the positive electrode active material layer (13). A first adhesion layer (19), a second adhesion layer (21) between the negative electrode current collector (16) and the negative electrode active material layer (17), and the first and second adhesion layers (19, 21) each include both a third binder and a conductive substance, and the third binder is a high-density substance obtained by modifying the first binder or the second binder with a modifying substance. A lithium ion polymer secondary battery, which is a molecular compound. 2. One or both of the first and second binders are made of polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer or polyvinyl fluoride. The lithium ion polymer secondary battery according to claim 1, which is a selected fluorine-containing polymer compound. 3. The modifying substance is selected from ethylene, styrene, butadiene, vinyl chloride, vinyl acetate, acrylic acid, methyl acrylate, methyl vinyl ketone, acrylamide, acrylonitrile, vinylidene chloride, methacrylic acid, methyl methacrylate or isoprene. The lithium ion polymer secondary battery according to claim 1, which is a compound. 4. The lithium ion polymer secondary battery according to claim 1, wherein each of the first and second adhesion layers has a thickness of 0.5 to 30 μm. 5. The lithium ion polymer secondary battery according to claim 1, wherein the first and second adhesion layers further contain a dispersant in an amount of 0.1 to 20% by weight. 6. A conductive material comprising a carbon material having a particle diameter of 0.5 to 30 μm and a degree of graphitization of 50% or more, wherein a third binder contained in the first and second adhesion layers and the conductive material are used. 2. The lithium ion polymer secondary battery according to claim 1, wherein the weight ratio (third binder / conductive substance) is 13/87 to 50/50. 7. The method for synthesizing a third binder contained in an adhesion layer of a lithium ion polymer secondary battery according to claim 1, wherein the third binder is a first binder. Or, it is synthesized by modifying one or both of the second binder with a modifying substance, and when the synthesized third binder is 100% by weight,
A method for synthesizing a binder, wherein the ratio of the modifying substance contained in the third binder is 2 to 50% by weight. 8. The modification by a modifying substance may be performed after irradiating one or both of the first and second binders with radiation.
The synthesis method according to claim 7, wherein the synthesis is performed by mixing a modified substance with the irradiation target and performing graft polymerization. 9. Modification with a modifying substance is carried out by mixing a modifying substance with one or both of the first and second binders and irradiating the mixture with radiation for graft polymerization. Item 7. The synthesis method according to Item 7. 10. Irradiation to one or both of the first and second binders results in an absorbed dose of 1 to 120 kGy to one or both of the first and second binders. 9. The method according to claim 8, wherein the irradiation is performed by irradiating γ rays.
Or the synthesis method according to 9.