SEPARATOR FOR A NON-AQUEOUS ELECTROLYTE BATTERY, NON-AQUEOUS ELECTROLYTE BATTERY, AND METHOD OF MANUFACTURING NON-AQUEOUS ELECTROLYTE BATTERY

Abstract

In an embodiment of the present disclosure, provided is a separator for a non-aqueous electrolyte battery, the separator being composed of a composite membrane comprising: a porous substrate; and an adhesive porous layer provided on one side or both sides of the porous substrate and containing an adhesive resin, wherein the adhesive porous layer further contains an acrylic resin in a state in which the acrylic resin is mixed with the adhesive resin, a peel strength between the porous substrate and the adhesive porous layer is 0.20 N/10 mm or more, and a Gurley value is 200 sec/100 cc or less.

Claims

1. A separator for a non-aqueous electrolyte battery, the separator being composed of a composite membrane comprising: a porous substrate; and an adhesive porous layer provided on one side or both sides of the porous substrate and containing an adhesive resin, wherein: the adhesive porous layer further contains an acrylic resin in a state in which the acrylic resin is mixed with the adhesive resin, a peel strength between the porous substrate and the adhesive porous layer is 0.20 N/10 mm or more, and a Gurley value is 200 sec/100 cc or less.

2. The separator for a non-aqueous electrolyte battery according to claim 1, wherein a content of the acrylic resin in the adhesive porous layer is from 5% by mass to 50% by mass based on a total mass of the adhesive resin and the acrylic resin.

3. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the adhesive resin is a polyvinylidene fluoride resin.

4. The separator for a non-aqueous electrolyte battery according to claim 1, wherein a crystallinity of the adhesive resin in the adhesive porous layer is from 10% to 55%.

5. The separator for a non-aqueous electrolyte battery according to claim 1, wherein: the adhesive porous layer further contains an inorganic filler, and a content of the inorganic filler in the adhesive porous layer is from 5% by mass to 75% by mass based on a total mass of the adhesive resin, the acrylic resin, and the inorganic filler.

6. The separator for a non-aqueous electrolyte battery according to claim 1, wherein the acrylic resin is a copolymer containing a constitutional unit derived from at least one monomer of a carboxylate ester.

7. A non-aqueous electrolyte battery, comprising: a positive electrode; a negative electrode; and the separator for a non-aqueous electrolyte battery according to claim 1 arranged between the positive electrode and the negative electrode, wherein electromotive force is obtained by doping/dedoping lithium.

8. A method of manufacturing the non-aqueous electrolyte battery according to claim 7, the method comprising: arranging the separator for a non-aqueous electrolyte battery between the positive electrode and the negative electrode to prepare a layered body; preparing an outer packaging body by placing the layered body and an electrolytic solution in an outer packaging material; applying heat and pressure to the outer packaging body in a layering direction of the positive electrode, the separator for a non-aqueous electrolyte battery and the negative electrode in the layered body at a temperature of from 80° C. to 100° C.; and sealing the outer packaging body.

9. The separator for a non-aqueous electrolyte battery according to claim 2, wherein the adhesive resin is a polyvinylidene fluoride resin.

Description

EXAMPLES

[0155] Hereinafter, the invention is described in further detail with reference to Examples. Materials, amount of use, proportion, procedure, or the like described below can be appropriately modified without deviating from the spirit of the invention. Therefore, the scope of the invention should not be construed to be limited by the following specific examples.

[0156] <Measurement Method>

[0157] The following measurement methods have been applied to Examples and Comparative Examples below.

[Film Thickness]

[0158] The film thickness (μm) of a separator and a porous substrate was determined by measuring 20 points with a contact thickness gauge (LITEMATIC manufactured by Mitutoyo Corporation), and arithmetically averaging the measured values. A cylindrical measurement terminal having a diameter 5 mm was used, and was adjusted such that a load of 7 g was applied during measurement.

[0159] The thickness of the adhesive porous layer was determined by subtracting the film thickness of the porous substrate from the film thickness of the separator to obtain the total thickness of both sides and making half of the total thickness as one side thickness.

[0160] [Weight per Unit Area]

[0161] The weight per Unit Area (weight per 1 m.sup.2) was determined by cutting a sample into a 10 cm×10 cm piece, measuring the weight of the piece, and dividing the weight by the area.

[0162] [Coating Amount of Adhesive Porous Layer]

[0163] A separator was cut into 10 cm×10 cm, the mass was measured, and the mass was divided by the area to obtain the weight per Unit Area of the separator. A porous substrate used for preparing the separator was cut into 10 cm×10 cm, the mass was measured, and the weight was divided by the area to obtain the weight per Unit Area of the porous substrate. Then, the weight per Unit Area of the porous substrate was subtracted from the weight per Unit Area of the separator, whereby the coating amount of the adhesive porous layer was determined. When the adhesive porous layer was formed on both sides, the coating amount per one side was obtained by dividing the coating amount obtained as described above by 2.

[0164] [Porosity]

[0165] The porosity of a separator was calculated by the following Formula.

ε={1−Ws/(ds.Math.t)}×100

[0166] Here, ε is the porosity (%), Ws is the weight per Unit Area (g/m.sup.2), ds is the true density (g/cm.sup.3), and t is the film thickness (μm).

[0167] The porosity ε (%) of a separator formed by layering a polyethylene porous substrate and a porous layer composed only of a polyvinylidene fluoride resin was calculated by the following Formula.

ε={1−(Wa/0.95+Wb/1.78)/t}×100

[0168] Here, Wa is the weight per Unit Area (g/m.sup.2) of the polyethylene porous substrate, Wb is the weight (g/m.sup.2) of the polyvinylidene fluoride resin, and t is the film thickness (μm) of the separator.

[0169] The porosity ε (%) was calculated using the following Formula for a separator in which a porous layer obtained by mixing a polyvinylidene fluoride resin and an acrylic resin was layered.

ε={1−[Wa/0.95+Wb/(1.78×(B/100)+1.19×(C/100))]/t}×100

[0170] Here, B is the content concentration (% by mass) of the polyvinylidene fluoride resin, and C is the content concentration (% by mass) of the acrylic resin.

[0171] [Gurley Value]

[0172] The Gurley value (sec/100 cc) was measured by using Gurley Type Densometer (G-B2C, manufactured by Toyo Seiki Seisaku-Sho, Ltd.) in accordance with JIS P8117.

[0173] [Peel Strength of Porous Substrate and Adhesive Porous Layer]

[0174] A coated sample specimen was cut out in a size of 7 cm in length in the longitudinal direction and 1.2 cm in length in the width direction, and a transparent double-sided tape (manufactured by 3M Japan Limited) was attached to the sample surface. Next, the peeling strength at which an adhesive porous layer and a porous substrate were separated using a tensile strength measuring device (Tensilon RTC-1210A, manufactured by ORIENTEC CORPORATION) was measured and then converted into a value (unit: N/10 mm) per length of 10 mm in width.

[0175] [Adhesive Strength with Electrode (with Electrolytic Solution)]

[0176] A positive electrode and a negative electrode prepared by the following method were joined via a separator, an electrolytic solution was injected, and this battery element was sealed in an aluminum laminate pack with a vacuum sealer to prepare a test cell. After pressing the test cell with a heat press machine, the cell was disassembled and the strength when peeling off the electrode and the separator at 180° was measured to evaluate the adhesive strength with the electrode in the electrolytic solution. The hot press was performed under the condition that a pressure of 1.0 MPa was applied to the joined electrode and the separator, the temperature was 100° C., and the time was 10 seconds.

[0177] [Adhesive Strength with Electrode (without Electrolytic Solution)]

[0178] A positive electrode and a negative electrode prepared by the following method were joined via a separator, and in a state in which an electrolytic solution was not injected, this battery element was sealed in an aluminum laminate pack with a vacuum sealer to prepare a test cell. After pressing the test cell with a heat press machine, the cell was disassembled and the strength when peeling off the electrode and the separator at 180° was measured to evaluate the adhesive strength. The heat pressing was performed under the condition that a pressure of 1.0 MPa was applied to the joined electrode and the separator, the temperature was 100° C., and the time was 10 seconds.

[0179] [Charge Amount]

[0180] The voltage value (kV) of the static electricity charged on the surface of a separator was measured using Lightmatic VL-50 manufactured by Mitutoyo Corporation, and three measured values were averaged to obtain the charge amount.

[0181] [Crystallinity of Polyvinylidene Fluoride Resin]

[0182] An adhesive porous layer peeled off from a separator was used as a specimen and sealed in an aluminum pan for measurement, and the crystallinity of a polyvinylidene fluoride resin was determined by DSC (differential scanning calorimeter). For the measurement, DSCQ-20 (manufactured by TA Instruments Japan Inc.) was used, the heat of fusion of the polyvinylidene fluoride resin present in the adhesive porous layer was determined from the area of the endothermic peak appearing when the temperature was raised from 30° C. to 200° C. at a rate of 10° C./min, and the crystallinity Xc (%) was calculated by the following Formula (1).

Xc={ΔH/ΔHm.sup.*}×100  (1)

[0183] Heat of fusion of complete crystal of polyvinylidene fluoride resin: ΔHm.sup.*=104.7 J/g

[0184] [Handling Properties]

[0185] A separator was conveyed under conditions (conveying speed: 40 m/min., unwinding tension: 0.3 N/cm, winding tension: 0.1 N/cm), and after conveying, a peel of an adhesive porous layer was visually observed. Evaluation in accordance with the following evaluation criteria was then performed. As a foreign matter generated by peeling fell off from the separator, a matter fell off from the separator during conveying, a matter trapped by the end face of a winding roll, and a matter observed on the surface of the roll were counted.

<Evaluation Criteria>

[0186] A: No peeling
B: Foreign matters generated by peeling: from one to five per 1000 m.sup.2
C: Foreign matters generated by peeling: from more than five to 20 per 1000 m.sup.2
D: Foreign matters generated by peeling: more than 20 per 1000 m.sup.2

[0187] [Cycle Characteristics]

[0188] Charge/discharge was repeated for a battery manufactured as described below under the environment of 30° C. with a charging conditions (1C, 4.2 V, constant-current and constant-voltage charging) and discharging conditions (1C, 2.75 V, cutoff constant-current discharging). The value obtained by dividing the discharging capacity at the 300-th cycle by the initial capacity was defined as a capacity retention rate (%), and used as an index of cycle characteristics.

[0189] [Load Characteristics]

[0190] For a battery manufactured as described below, the discharge capacity at the time of discharging at 0.2 C under the environment of 25° C., the discharge capacity at the time of discharging at 2 C were measured, and the value (%) obtained by dividing the latter by the former was taken as load characteristics. Here, the charging conditions were constant current constant voltage charging of 0.2 C and 4.2 V for 8 hours, and the discharging condition was constant current discharge of 2.75 V cutoff.

Example 1

(Manufacturing of Separator)

[0191] Vinylidene fluoride-hexafluoropropylene copolymer (KF 9300 manufactured by Kureha Chemical Industry Co., Ltd.) was used as the polyvinylidene fluoride resin and a copolymer of methyl methacrylate and methacrylic acid (PMMA; manufactured by Mitsubishi Rayon Co., Ltd.—ACRYPET MD001) was used as the acrylic resin. The polyvinylidene fluoride resin and the acrylic resin were mixed at a mass ratio of 75/25 and dissolved in a mixed solvent containing dimethylacetamide and tripropylene glycol (dimethylacetamide/tripropylene glycol=80/20 mass ratio) so that the components of the polyvinylidene fluoride resin and the acrylic resin were 3.8% by mass to prepare a coating slurry.

[0192] This was applied to both sides of a microporous polyethylene membrane (porous substrate; TN 0901: manufactured by SK Corporation) having a thickness of 9 μm, a Gurley value of 150 sec/100 cc, and a porosity of 43% on an equal basis and solidified by dipping in a coagulation liquid (35° C.; water/dimethylacetamide/tripropylene glycol =62.5/30/7.5 mass ratio) including water, dimethylacetamide, and tripropylene glycol.

[0193] This was washed with water and dried to obtain a separator for a non-aqueous electrolyte battery (composite membrane) according to one embodiment of the invention in which an adhesive porous layer containing a mixture of a polyvinylidene fluoride resin and an acrylic resin in a compatible state is formed on both surfaces of a microporous polyethylene membrane.

[0194] (Preparation of Negative Electrode)

[0195] 300 g of artificial graphite as a negative electrode active material, 7.5 g of a water-soluble dispersion including a modified form of a styrene-butadiene copolymer in an amount of 40% by mass as a binder, 3 g of carboxymethyl cellulose as a thickener, and a proper quantity of water were stirred using a double-arm mixer, thereby preparing a slurry for a negative electrode. This slurry for a negative electrode was coated on a copper foil having a thickness of 10 μm as a negative electrode current collector, and the resulting coated membrane was dried, followed by pressing, to prepare a negative electrode having a negative electrode active material layer.

[0196] (Preparation of Positive Electrode)

[0197] 89.5 g of lithium cobalt oxide powder as a positive electrode active material, 4.5 g of acetylene black as an electrically conductive additive, and 6 g of polyvinylidene fluoride as a binder were dissolved in N-methyl-pyrrolidone (NMP) such that the content of the polyvinylidene fluoride was 6% by mass, and the obtained solution was stirred using a double-arm mixer, thereby preparing a slurry for a positive electrode. This slurry for a positive electrode was coated on an aluminum foil having a thickness of 20 μm as a positive electrode current collector, and the resulting coated membrane was dried, followed by pressing, to produce a positive electrode having a positive electrode active material layer.

[0198] (Preparation of Battery)

[0199] A lead tab was welded to the positive electrode and the negative electrode, and the positive electrode, the separator, and the negative electrode were layered in this order to prepare a layered body. The layered body was inserted into a pack made of an aluminum laminate film and an electrolytic solution was further injected so that the layered body was impregnated with the electrolytic solution. As the electrolytic solution, 1 M LiPF.sub.6-ethylene carbonate/ethyl methyl carbonate (mass ratio 3/7) was used.

[0200] Thereafter, the inside of the pack was evacuated using a vacuum sealer and temporarily sealed, a heat pressing was performed in the layering direction of the layered body together with the pack using a heat press machine, whereby adhesion between the electrode and the separator and sealing of the pack were performed. The conditions of heat pressing were a load of 20 kg per 1 cm.sup.2 of the electrode, a temperature of 90° C., and a pressing time of 2 minutes.

Examples 2 to 6

[0201] A separator for a non-aqueous electrolyte battery was obtained in the same manner as in Example 1 except that the content ratio (mass ratio) of the polyvinylidene fluoride resin and the acrylic resin in Example 1 was changed as listed in Table 1.

Example 7

[0202] A separator for a non-aqueous electrolyte battery was prepared in the same manner as in Example 1 except that the acrylic resin in Example 1 was changed to polyethyl methacrylate (PEMA; PEMA manufactured by Aldrich Corporation).

Example 8

[0203] A separator for a non-aqueous electrolyte battery was prepared in the same manner as in Example 1 except that the acrylic resin in Example 1 was changed to polybutyl methacrylate (PBMA; PBMA manufactured by Aldrich Corporation).

Example 9

[0204] A separator for a non-aqueous electrolyte battery was prepared in the same manner as in Example 1 except that The content ratio (mass ratio) of the polyvinylidene fluoride resin and the acrylic resin was changed as listed in Table 1, and magnesium hydroxide having an average particle size of 0.8 μm and a BET specific surface area of 6.8 m.sup.2/g (Kisuma 5 P manufactured by Kyowa Chemical Industry Co., Ltd.) was added so that the mass ratio of magnesium hydroxide to a polyvinylidene fluoride resin and an acrylic resin was 40:60 in Example 1.

Comparative Example 1

[0205] A separator for a non-aqueous electrolyte battery was prepared in the same manner as in Example 1 except that a vinylidene fluoride-hexafluoropropylene copolymer (KF 9300 manufactured by Kureha Chemical Co., Ltd.) which is a polyvinylidene fluoride resin is used, and an acrylic resin is not contained.

Comparative Examples 2, 3

[0206] A separator for a non-aqueous electrolyte battery was obtained in the same manner as in Example 1 except that the content ratio (mass ratio) of the polyvinylidene fluoride resin and the acrylic resin in Example 1 was changed as listed in Table 1 It was.

Comparative Example 4

[0207] A separator for a non-aqueous electrolyte battery was prepared in the same manner as in Example 9 except that a vinylidene fluoride-hexafluoropropylene copolymer (KF 9300 manufactured by Kureha Chemical Co., Ltd.) which is a polyvinylidene fluoride resin is used, and an acrylic resin is not contained.

Evaluation

[0208] For the separators of Examples and Comparative Examples, the film thickness, the porosity, the Gurley value, the peel strength of the substrate and the adhesive porous layer, the adhesive strength to the electrode, the charge amount, the crystallinity of the polyvinylidene fluoride resin, and the handling properties were evaluated. For batteries using each separator, cycle characteristics and load characteristics were evaluated. The results are listed in Table 1. The coating amount and coating thickness of the adhesive porous layer listed in Table 1 are the coated amount per side and the coated thickness per finished surface.

TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Example 1 2 3 4 5 6 7 Adhesive Content of adhesive resin mass % 75 95 90 85 65 50 75 porous layer Content of acrylic PMMA mass % 25 5 10 15 35 50 — resin PEMA mass % — — — — — — 25 PBMA mass % — — — — — — — Content of inorganic filler mass % — — — — — — — Coated amount (one side) g/m.sup.2 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Coated thickness (one side) μm 1.5 1.5 1.5 1.5 1.5 1.5 1.5 properties of Film thickness μm 12 12 12 12 12 12 12 separator Gurley value sec/100 cc 181 199 191 186 171 162 182 Porosity % 55 65 59 57 51 46 56 Peel strength N/10 mm 0.81 0.21 0.31 0.41 0.51 0.41 0.76 Adhesive Strength with N/15 mm 0.100 0.050 0.080 0.080 0.125 0.150 0.100 Electrode (with Electrolytic Solution) Adhesive Strength with N/15 mm 0.140 0.050 0.060 0.070 0.170 0.200 0.150 Electrode (without Electrolytic Solution) Charge amount kV 1.70 1.96 1.89 1.81 1.62 1.39 1.75 Crystallinity of adhesive % 31 55 46 41 26 11 31 resin Handling properties — A B B A A A A Evaluation Cycle characteristics % 97 95 95 96 98 97 98 of battery Load characteristics % 94 91 92 93 94 95 94 Com- Com- Com- Com- Example Example parative parative parative parative 8 9 Example 1 Example 2 Example 3 Example 4 Adhesive Content of adhesive resin mass % 75 30 100 97.5 40 40 porous layer Content of acrylic PMMA mass % — 10 — 2.5 60 — resin PEMA mass % — — — — — — PBMA mass % 25 — — — — — Content of inorganic filler mass % — 60 — — — 60 Coated amount (one side) g/m.sup.2 1.0 1.0 1.0 1.0 1.0 1.0 Coated thickness (one side) μm 1.5 1.5 1.5 1.5 1.5 1.5 properties of Film thickness μm 12 12 12 12 12 12 separator Gurley value sec/100 cc 183 160 205 220 160 180 Porosity % 57 65 62 61 40 60 Peel strength N/10 mm 0.77 0.30 0.15 0.15 0.10 0.05 Adhesive Strength with N/15 mm 0.100 0.050 0.020 0.030 0.150 0.020 Electrode (with Electrolytic Solution) Adhesive Strength with N/15 mm 0.140 0.070 0.005 0.005 0.200 0.002 Electrode (without Electrolytic Solution) Charge amount kV 1.65 0.85 2.00 2.00 1.32 1.10 Crystallinity of adhesive % 33 32 58 54 5 60 resin Handling properties — A B C C C D Evaluation Cycle characteristics % 97 98 94 94 96 95 of battery Load characteristics % 93 93 90 91 94 92

[0209] As listed in Table 1, in Examples the adhesive resin and the acrylic resin were contained in a mixed state, the peel strength and the Gurley value between the porous substrate and the adhesive porous layer satisfied a predetermined range. As a result, peeling was suppressed, the handling property was excellent, and the manufacturing yield was improved.

[0210] Regardless of the presence or absence of the electrolytic solution, the adhesion between the electrode and the electrode was favorable, and the ion permeability of the adhesive porous layer was also excellent. Therefore, the cycle characteristics and load characteristics were excellent.

[0211] In contrast, in Comparative Examples in which the peeling strength and the Gurley value do not satisfy predetermined ranges, the peeling strength between the porous substrate and the adhesive porous layer was low, and the handling properties were remarkably inferior. The adhesion between the electrode and the electrode was also insufficient.

[0212] In Comparative Examples 3 to 4, although the ion permeability was favorable, the peeling strength between the porous substrate and the adhesive porous layer remarkably decreased and the manufacturing yield was low.

[0213] The disclosure of Japanese Patent Application No. 2014-253109 is incorporated by reference herein in its entirety.

[0214] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if such individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.