alpha-ALUMINA, SLURRY, POROUS MEMBRANE, LAMINATED SEPARATOR, AND NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND METHOD FOR PRODUCING SAME

Abstract

An object of the present invention is to provide an alumina used for a slurry for reducing unevenness in a surface of a porous membrane. The present invention is an α-alumina wherein a crystallite size obtained by a Rietveld analysis is not greater than 95 nm, and a lattice strain obtained by the Rietveld analysis is not greater than 0.0020. A BET specific surface area by a nitrogen adsorption method of the α-alumina is preferably not greater than 10 m.sup.2/g. A particle diameter D50 equivalent to 50% cumulative percentage by volume of the α-alumina is also preferably not greater than 2 μm.

Claims

1. An α-alumina wherein a crystallite size obtained by a Rietveld analysis is not greater than 95 nm, and a lattice strain obtained by the Rietveld analysis is not greater than 0.0020.

2. The α-alumina according to claim 1, wherein a BET specific surface area by a nitrogen adsorption method is not greater than 10 m.sup.2/g.

3. The α-alumina according to claim 1, wherein a particle diameter D50 equivalent to 50% cumulative percentage by volume is not greater than 2 μm.

4. The α-alumina according to claim 1, wherein the crystallite size is not less than 50 nm and not greater than 95 nm, and the lattice strain is not less than 0.0001 and not greater than 0.0010.

5. A slurry comprising: the α-alumina according to claim 1; a binder; and a solvent.

6. A porous membrane comprising the α-alumina according to any claim 1.

7. A laminated separator comprising: a separator; and the porous membrane, according to claim 6, laminated on at least one of surfaces of the separator.

8. A nonaqueous electrolyte secondary battery comprising: a positive electrode; a negative electrode; a nonaqueous electrolyte; and a separator, wherein the porous membrane according to claim 6 is formed on at least one of surfaces of the positive electrode, the negative electrode, and the separator.

9. A method for producing a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, the method comprising: applying the slurry according to claim 5 to at least one of surfaces of the positive electrode, the negative electrode, and the separator; and drying the slurry to form a porous membrane on the at least one of the surfaces.

10. The α-alumina according to claim 2, wherein a particle diameter D50 equivalent to 50% cumulative percentage by volume is not greater than 2 μm.

11. The α-alumina according to claim 10, wherein the crystallite size is not less than 50 nm and not greater than 95 nm, and the lattice strain is not less than 0.0001 and not greater than 0.0010.

Description

EXAMPLES

[0100] The present invention will be described below in more detail by means of examples. The present invention is not limited by the following examples, and can also be carried out with appropriate modifications being made within the range of the gist described above and below, and any of these modifications are included in the technical scope of the present invention.

[0101] Alumina powders obtained in an example and comparative examples described below were measured in the following method.

(1) Crystallite Size and Lattice Strain

[0102] X-ray diffraction measurement was performed by the 2θ/θ method for pulverized alumina powder in each of example 1 and comparative example 1, and for unpulverized alumina powder in comparative example 2, to obtain actual-measurement data of the X-ray diffraction profiles. In the X-ray diffraction measurement, D8 ADVANCE manufactured by Bruker was used, CuKα rays were used as an X-ray source, and a voltage was 40 kV and a current was 40 mA at the measurement. Scanning was performed by a continuous measurement method in a range of 2θ from 5 to 80°, at the scanning speed of 5s, with the step width of 0.020°. Based on analyzed results of the XRD diffraction profiles by Rietveld refinement using RIETAN-FP v2.63, a value of 2θ at each of peaks at 2θ values from 40° to 80° and an integral breadth were obtained, and the crystallite size and the lattice strain were assessed by the above-described Halder-Wagner method.

[0103] (2) BET Specific Surface Area by Nitrogen Adsorption Method

[0104] For aluminum hydroxide powder, raw material alumina powder, alumina powder obtained by pulverizing raw material alumina powder, and unpulverized alumina powder, a nitrogen adsorption BET specific surface area was obtained by a one-point method in a nitrogen adsorption method by using “FlowSorb III 2310” manufactured by Shimadzu Corporation as a specific surface area measuring apparatus, in compliance with the method specified in JIS-Z8830 (2013). The measurement conditions were as follows.

[0105] Carrier gas: nitrogen/helium mixed gas

[0106] Filling amount of sample: 0.1 g

[0107] Sample pretreatment condition: treatment at 200° C. for 20 minutes

[0108] Nitrogen adsorption temperature: liquid nitrogen temperature (not higher than −196° C.)

[0109] Nitrogen desorption temperature: room temperature (about 20° C.)

[0110] (3) Ratio of BET Specific Surface Area by Water Adsorption Method to BET Specific Surface Area by Nitrogen Adsorption Method

[0111] A water adsorption BET specific surface area was measured by using “BELSORP-18” manufactured by MicrotracBEL Corp. in a multipoint method. The measurement conditions were as follows. In the water adsorption cross-sectional area of 0.125 nm.sup.2 and under the relative pressure P/P0=0.1 to 0.3 as a range of analysis of the water adsorption BET specific surface area, the water adsorption BET specific surface area was calculated, and the water adsorption BET specific surface area was divided by the nitrogen adsorption BET specific surface area calculated in the above-described (2) to obtain the ratio.

[0112] The measurement conditions were as follows.

[0113] Filling amount of sample: 1 g

[0114] Sample pretreatment condition: treatment under vacuum at 150° C. for five hours

[0115] Temperature of thermostatic chamber: 50° C.

[0116] Adsorption temperature: 25° C.

[0117] Saturated vapor pressure: 3.169 kPa

[0118] Adsorption equilibrium time: 500 seconds

[0119] (4) Measurement of Powder Particle Size Distribution

[0120] A particle size distribution of each of aluminum hydroxide powder, raw material alumina powder, and alumina powder obtained by pulverizing unpulverized alumina powder was measured in a laser diffraction method by using “Microtrac MT3300 EXII” manufactured by MicrotracBEL Corp. as a laser particle size distribution measurement apparatus, to obtain a particle diameter D50 equivalent to 50% cumulative percentage by volume. Furthermore, for the alumina powder obtained by pulverizing the raw material alumina powder in each of example 1 and comparative example 1, and the unpulverized alumina powder in comparative example 2, a particle diameter D90 equivalent to 90% cumulative percentage by volume was also obtained. Powder dispersion liquid obtained by adding powder to be measured, to 0.2 mass % of aqueous sodium hexametaphosphate solution, so as to obtain a proper laser scattering intensity, and dispersing the powder at 40W by an ultrasonic wave built in the device for five minutes, was used as the measurement sample. The refractive index of the aluminum hydroxide was 1.57 and the refractive index of the alumina was 1.76.

[0121] (5) Measurement of Particle Size Distribution of Alumina Powder in Slurry

[0122] A solution was obtained by dissolving PVDF-HFP (poly(vinylidene fluoride-hexafluoropropylene), Solef21510 manufactured by Solvay) in N-methyl-2-pyrrolidone (NMP) solvent so as to contain 2 mass % of the PVDF-HFP. The alumina powder was added to the solution, stirred, and mixed such that 10 parts by mass of the PVDF-HFP was contained with respect to 100 parts by mass of alumina to obtain a slurry. The slurry was measured by using a laser particle size distribution measurement apparatus [“Microtrac MT3300 EXII” manufactured by MicrotracBEL Corp.] in a laser diffraction method, and a particle size distribution of the alumina in the slurry was measured, to obtain a particle diameter D50 equivalent to 50% cumulative percentage by volume, a particle diameter D90 equivalent to 90% cumulative percentage by volume, and a particle diameter D100 equivalent to 100% cumulative percentage by volume. The slurry subjected to dispersion treatment at 40W by an ultrasonic wave built in the device for five minutes, was used as a measurement sample. The refractive index of the alumina was 1.76.

Example 1

[0123] Aluminum hydroxide powder in which the particle diameter D50 equivalent to 50% cumulative percentage by volume was 4 μm, the BET specific surface area was 1.7 m.sup.2/g, and an amount of Na was 0.03 mass %, was obtained by the Bayer process. The aluminum hydroxide powder was calcined by a tunnel kiln at 1280° C. for two hours, thereby obtaining raw material alumina powder, in which the BET specific surface area was 3.8 m.sup.2/g, and the particle diameter D50 equivalent to 50% cumulative percentage by volume was 5 μm.

[0124] Next, 0.2 mass % of propylene glycol (indicated as “PG” in Table 1) as an adhesion inhibitor in a pulverizer was added to the raw material alumina powder, and the raw material alumina powder was pulverized by a jet mill under the following conditions, to obtain α-alumina powder having physical properties indicated below in Table 1.

[0125] (Jet Mill Conditions)

[0126] Device: PJM-280SP manufactured by Nippon Pneumatic Mfg. Co., Ltd.

[0127] Feeding rate of alumina raw material powder: 10 kg/h

[0128] Gauge pressure at air supply port during pulverization: 0.7 MPa

Comparative Example 1

[0129] Aluminum hydroxide powder in which the particle diameter D50 equivalent to 50% cumulative percentage by volume was 50 μm, the BET specific surface area was 0.2 m.sup.2/g, and an amount of Na was 0.13 mass %, was obtained by the Bayer process. The aluminum hydroxide powder was calcined by a rotary kiln, thereby obtaining raw material alumina powder in which the BET specific surface area was 3.7 m.sup.2/g, and the particle diameter D50 equivalent to 50% cumulative percentage by volume was 54 μm.

[0130] The raw material alumina powder was pulverized by a vibration mill under the following conditions to obtain α-alumina powder having physical properties indicated below in Table 1.

[0131] (Vibration mill conditions)

[0132] Device: YAMP-4JNT manufactured by URAS TECHNO CO., LTD

[0133] Pot volume: 2 liters

[0134] Pot material: alumina

[0135] Pulverization medium: φ15 mm alumina ball

[0136] Filling amount of pulverization medium: 3 kg

[0137] Charged amount of raw material alumina: 50 g

[0138] Pulverization amplitude: 3 mm

[0139] Pulverization time: 3 hours

Comparative Example 2

[0140] Aluminum hydroxide powder in which the particle diameter D50 equivalent to 50% cumulative percentage by volume was 50 μm, the BET specific surface area was 0.2 m.sup.2/g, and an amount of Na was 0.13 mass %, was obtained by the Bayer process for which the same conditions as in comparative example 1 were adopted. The aluminum hydroxide powder was calcined by a rotary kiln, thereby obtaining raw material alumina powder in which the BET specific surface area was 3.7 m.sup.2/g, and the particle diameter D50 equivalent to 50% cumulative percentage by volume was 54 μm.

[0141] Results of measurement of the pulverized alumina powder obtained in each of example 1 and comparative example 1 and the raw material alumina powder obtained in comparative example 2 according to the above-described (1) to (5) are indicated in

TABLE-US-00001 TABLE 1 Conditions of producing alumina Raw material Aluminum hydroxide alumina BET BET specific specific surface surface area by Amount area by D50 nitrogen of Na nitrogen D50 Pulverizing adhesion (μm) (m.sup.2/g) (mass %) Kiln (m.sup.2/g) (μm) method inhibitor Example 1 4 1.7 0.03 Tunnel 3.8 5 Jet mill PG kiln 0.2% Comparative 50 0.2 0.13 Rotary 3.7 54 Vibration mill Absence Example 1 kiln Comparative 50 0.2 0.13 Rotary 3.7 54 Absence Absence Example 2 kiln Physical properties of alumina powder BET specific Water surface Particle size dispersed crystallite lattice BET/ area by in NMP/PVDF size strain Nitrogen nitrogen D50 D90 D50 D90 D100 (nm) (—) BET (m.sup.2/g) (μm) (μm) (μm) (μm) (μm) Example 1 87 0.0003 0.68 4.5 1.1 2.0 1.5 2.3 4.6 Comparative 81 0.0022 1.36 7.1 0.5 3.4 1.1 21 125 Example 1 Comparative 97 0.0004 0.90 3.7 54 85 60 93 209 Example 2

[0142] According to Table 1, in example 1, it is found that the α-alumina powder having the crystallite size of not greater than 95 nm and the lattice strain of not greater than 0.0020 could be obtained and D90 and D100 had small values in the slurry containing the α-alumina powder, the binder, and the solvent, that is, generation of coarse particles was inhibited. In example 1, the aluminum hydroxide powder in which the values of the particle diameter D50 equivalent to 50% cumulative percentage by volume, the BET specific surface area, and the amount of Na were appropriately adjusted was calcined to prepare the raw material alumina powder, and the raw material alumina powder was pulverized by the jet mill to obtain the α-alumina powder. Meanwhile, the α-alumina powder of comparative example 1 had the lattice strain of greater than 0.0020, and D90 and D100 were each large in the slurry containing the α-alumina powder, the binder, and the solvent, that is, coarse particles were generated. In comparative example 1, the aluminum hydroxide powder in which the value of the particle diameter D50 equivalent to 50% cumulative percentage by volume was large, the BET specific surface area was small, and the amount of Na was large, was calcined to prepare the raw material alumina powder, and the raw material alumina powder was pulverized by the vibration mill to obtain the α-alumina powder. Furthermore, the raw material alumina powder obtained merely by calcining the same aluminum hydroxide powder as in comparative example 1, that is, the unpulverized alumina powder, had the crystallite size of greater than 95 nm, and D90 and D100 were each large in the slurry containing the unpulverized alumina powder, the binder, and the solvent, that is, coarse particles were generated.