Electrode mixture layer composition for nonaqueous electrolyte secondary battery, manufacturing method thereof and use therefor

Abstract

An electrode mixture layer composition for a nonaqueous electrolyte secondary battery contains an active material, water and a binder. The binder contains a crosslinked polymer of a monomer component including an ethylenically unsaturated carboxylic acid monomer, and a salt thereof. The crosslinked polymer is a polymer that is crosslinked with allyl methacrylate, and an amount of the allyl methacrylate used is 0.1 to 2.0 parts by weight relative to total 100 parts by weight of non-crosslinking monomers, and a content of the crosslinked polymer and salt thereof is 0.5% to 5.0% by weight of the active material.

Claims

1. An electrode mixture layer composition for a nonaqueous electrolyte secondary battery, containing an active material, water and a binder, wherein the binder contains a crosslinked polymer of a monomer component including an ethylenically unsaturated carboxylic acid monomer, or a salt of the crosslinked polymer, the crosslinked polymer is a polymer that is crosslinked with allyl methacrylate, and an amount of the allyl methacrylate used is 0.1 to 2.0 parts by weight relative to total 100 parts by weight of non-crosslinking monomers, a content of the crosslinked polymer or the salt thereof is 0.5% to 5.0% by weight of the active material, and a ratio of the ethylenically unsaturated carboxylic acid monomer of a total amount of the non-crosslinking monomers is in a range of 50% to 100% by weight.

2. The electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 1, wherein the crosslinked polymer is a polymer that is crosslinked with allyl methacrylate and a polyfunctional allyl compound, and an amount of the allyl methacrylate and polyfunctional allyl compound is 0.1 to 3.0 parts by weight relative to total 100 parts by weight of the non-crosslinking monomers.

3. The electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 1, wherein a degree of neutralization of the crosslinked polymer is 20 to 100 mol %.

4. A method of manufacturing an electrode mixture layer composition for a nonaqueous electrolyte secondary battery, the method comprising: precipitation-polymerizing a monomer component including an ethylenically unsaturated carboxylic acid monomer and allyl methacrylate in an aqueous medium to obtain a crosslinked polymer; and mixing an active material, the crosslinked polymer or a salt of the crosslinked polymer in an amount of 0.5% to 5.0% by weight relative to the active material and water to thereby manufacture an electrode mixture layer composition for a nonaqueous electrolyte secondary battery, wherein the monomer component contains the ethylenically unsaturated carboxylic acid monomer in a range of 50% to 100% by weight of non-crosslinking monomers which are included in the monomer component and the allyl methacrylate in an amount of 0.1 to 2.0 parts by weight relative to total 100 parts by weight of the non-crosslinking monomers.

5. A nonaqueous electrolyte secondary battery electrode comprising a mixture layer constituted of the electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 1 on a surface of a collector.

6. A nonaqueous electrolyte secondary battery comprising: the nonaqueous electrolyte secondary battery electrode according to claim 5; a separator; and a nonaqueous electrolyte solution.

7. The electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 2, wherein a degree of neutralization of the crosslinked polymer is 20 to 100 mol %.

8. A nonaqueous electrolyte secondary battery electrode comprising a mixture layer constituted of the electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 2 on a surface of a collector.

9. A nonaqueous electrolyte secondary battery electrode comprising a mixture layer constituted of the electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 3 on a surface of a collector.

10. A nonaqueous electrolyte secondary battery electrode comprising a mixture layer constituted of the electrode mixture layer composition for a nonaqueous electrolyte secondary battery according to claim 7 on a surface of a collector.

11. A nonaqueous electrolyte secondary battery comprising: the nonaqueous electrolyte secondary battery electrode according to claim 8; a separator; and a nonaqueous electrolyte solution.

12. A nonaqueous electrolyte secondary battery comprising: the nonaqueous electrolyte secondary battery electrode according to claim 9; a separator; and a nonaqueous electrolyte solution.

13. A nonaqueous electrolyte secondary battery comprising: the nonaqueous electrolyte secondary battery electrode according to claim 10; a separator; and a nonaqueous electrolyte solution.

14. A binder for a nonaqueous electrolyte secondary battery comprising: a crosslinked polymer of a monomer component including an ethylenically unsaturated carboxylic acid monomer or a salt of the crosslinked polymer, the crosslinked polymer being a polymer that is crosslinked with allyl methacrylate in an amount of 0.1 to 2.0 parts by weight relative to total 100 parts by weight of non-crosslinking monomers which are included in the monomer component, and a ratio of the ethylenically unsaturated carboxylic acid monomer to the total amount of non-crosslinking monomers being in a range of 50% to 100% by weight.

15. The binder according to claim 14, wherein the range is 70% to 100% by weight.

Description

EXAMPLES

(1) The present teachings will be described in detail below based on examples. However, the present teachings are not limited by these examples. In the following, parts and % mean parts by weight and % by weight unless otherwise specified.

Manufacturing Example 1: Manufacture of Crosslinked Polymer R-1

(2) A reaction vessel equipped with a stirring blade, a thermometer, a reflux condenser and a nitrogen introduction pipe was used for polymerization.

(3) 295 parts of methanol, 100 parts of acrylic acid (hereunder called AA) and 0.42 parts of allyl methacrylate (Mitsubishi Gas Chemical Company, Inc., hereunder called AMA) were loaded into the reaction vessel. Next, 18 parts of caustic soda flakes and 10 parts of ion-exchange water were added slowly under stirring so that internal temperature was maintained at 40 C. or less.

(4) The reaction vessel was thoroughly purged with nitrogen, and heated to raise the internal temperature to 68 C. Once the internal temperature was confirmed to have stabilized at 68 C., 0.014 parts of 4,4-azobiscyanovaleric acid (Otsuka Chemical Co., Ltd., product name ACVA) were added as a polymerization initiator, and since white turbidity of the reaction solution was observed at this point, this was taken as the polymerization starting point. The polymerization reaction was continued with the external temperature (water bath temperature) adjusted so that the solvent was gently refluxed, an additional 0.07 parts of ACVA were added once 4 hours had elapsed since the polymerization starting point, and solvent reflux was then continued. Cooling of the reaction solution was initiated 8 hours after the polymerization starting point, and once the internal temperature had fallen to 30 C., 32 parts of caustic soda flakes were gradually added in such a way that the internal temperature did not exceed 50 C. Once addition of the caustic soda flakes was complete and the internal temperature had fallen to 30 C. or less, the polymerization reaction solution (polymer slurry) was filtered by suction filtration. The filtered polymer was washed with methanol in twice the amount of the polymerization reaction solution, and a filtrate cake was collected and vacuum dried for 6 hours at 100 C. to obtain a crosslinked polymer R-1 in powder form. The crosslinked polymer R-1 had a degree of neutralization of 90 mol %. Because the crosslinked polymer R-1 was hygroscopic, it was stored and sealed in a container having water vapor barrier properties.

Manufacturing Examples 2 to 9: Manufacture of Crosslinked Polymers R-2 to R-9

(5) The crosslinked polymers R-2 to R-9 were obtained in powder form by the same procedures as in Manufacturing Example 1 except that the amounts of the starting materials were as shown in Table 1.

(6) TABLE-US-00001 TABLE 1 Manufacturing Example (ME) No. ME 1 ME 2 ME 3 ME 4 ME 5 ME 6 ME 7 ME 8 ME 9 Crosslinked polymer R-1 R-2 R-3 R-4 R-5 R-6 R-7 R-8 R-9 (Parts) Monomer AA 100 100 100 100 100 70 100 100 100 loaded AAM 30 Crosslinking agent AMA 0.42 0.30 0.47 0.30 1.12 0.30 220 P-30 0.70 1.50 0.70 0.70 T-20 1.40 1.10 Initial NaOH flakes 18.0 18.0 18.0 18.0 18.0 18.0 18.0 18.0 18.0 Ion-exchange water 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 Methanol 295.0 295.0 295.0 295.0 295.0 295.0 295.0 295.0 295.0 Polymerization initiator Initial 0.014 0.014 0.014 0.014 0.014 0.014 0.014 0.014 0.014 ACVA Additional 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.070 0.070 Additional NaOH flakes 32.0 32.0 32.0 32.0 32.0 17.0 32.0 32.0 32.0 Initial monomer concentration (% by weight) 23.6% 23.6% 23.5% 23.5% 23.6% 23.6% 23.6% 23.6% 23.5% Crosslinking agent (mol %) to monomers 0.240% 0.368% 0.690% 0.642% 0.640% 0.367% 0.197% 0.370% 1.257% Degree of neutralization (%) 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0%

(7) The compounds used in Table 1 are explained below in detail.

(8) AA: Acrylic acid

(9) AAM: Acrylamide

(10) AMA: Allyl methacrylate

(11) P-30: Pentaerythritol triallyl ether (Daiso Chemical Co., Ltd., product name Neoallyl P-30)

(12) T-20: Trimethylol propane diallyl ether (Daiso Chemical Co., Ltd., product name Neoallyl T-20)

(13) ACVA: 4,4-azobiscyanovaleric acid (Otsuka Chemical Co., Ltd.)

Preparation and Evaluation of Nonaqueous Electrolyte Secondary Battery Electrode Example 1-1

(14) The coating properties of a mixture layer composition using graphite as the negative electrode active material and the crosslinked polymer R-1 as the binder were measured, as was the peeling strength between the formed mixture layer and a collector (that is, the binding properties of the binder).

(15) 100 parts of artificial graphite (Nippon Graphite Industries, Co., Ltd., product name CGB-10) and 3 parts of the crosslinked polymer R-1 in powder form were thoroughly mixed in advance, after which 126 parts of ion-exchange water were added, and the mixture was pre-dispersed with a disperser and then dispersed for 15 seconds at a peripheral speed of 20 m/second with a thin film swirling mixer (Primix Corporation, FM-56-30) to obtain a negative electrode mixture layer composition in slurry form.

(16) Using a variable applicator, this mixture layer composition was coated onto a 20 m-thick copper foil (Nippon Foil Mfg. Co., Ltd.) so that the dried and pressed film thickness was 50 m, and then immediately dried for 10 minutes at 100 C. in a ventilating dryer to form a mixture layer. The external appearance of the resulting mixture layer was observed with the naked eye, and the coating properties were evaluated according to the following standard and judged as good A.

(17) (Coating Property Evaluation Standard)

(18) A: No streaks, spots or other appearance defects observed on surface

(19) B: Slight streaks, spots or other appearance defects observed on surface

(20) C: Obvious streaks, spots or other appearance defects observed on surface

(21) (90 Peel Strength (Binding Ability))

(22) The mixture layer density was adjusted with a roll press to 1.70.05 g/cm.sup.3 to prepare an electrode, which was then cut into a 25 mm-wide strip to prepare a sample for peel testing. The mixture layer side of this sample was affixed to a horizontally fixed double-sided tape and peeled at 90 at a rate of 50 mm/minute, and the peel strength between the mixture layer and the copper foil was measured. The peel strength was as high as 6.0 N/m, exhibiting a favorable strength.

(23) In general, when an electrode is cut, worked and assembled into a battery cell, the peel strength of at least 1.0 N/m is necessary to prevent the problem of detachment of the mixture layer from the collector (copper foil). The high peel strength in this case means that the binder provides excellent binding between the active materials and between the active material and the electrode, and suggests that it is possible to obtain a battery with excellent durability and little loss of capacity during charge-discharge cycle testing.

Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-4

(24) Mixture layer compositions were prepared by the same procedures as in Example 1-1 except that the crosslinked polymers used as binders were as shown in Tables 2 and 3, and the coating properties and 90 peeling strengths were evaluated. The results are shown in Tables 2 and 3.

(25) TABLE-US-00002 TABLE 2 Example Example Example Example Example Example Example Example Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 Mixture layer Active material CGB-10 100 100 100 100 100 100 100 100 100 composition Crosslinked R-1 3.0 (parts) polymer R-2 3.0 R-3 3.0 R-4 3.0 1.0 4.0 R-5 3.0 1.0 R-6 3.0 R-7 R-8 R-9 Ion-exchange Water 126 126 126 126 126 126 109 109 156 Total 229 229 229 229 229 229 210 210 260 Solids (%) 45.0% 45.0% 45.0% 45.0% 45.0% 45.0% 48.0% 48.0% 40.0% concentration Degree of neutralization of polymer (%) 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% powder Coating properties of slurry A A B A B A B A A 90 peeling strength (N/m) 6.0 8.2 12.4 9.8 5.8 7.1 1.2 2.4 16.3

(26) TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Example 1-1 Example 1-2 Example 1-3 Example 1-4 Mixture Active material CGB-10 100 100 100 100 layer Crosslinked R-1 composition polymer R-2 (parts) R-3 R-4 0.3 R-5 R-6 R-7 3.0 R-8 3.0 R-9 3.0 Ion-exchange water 126 126 126 100 Total 229 229 229 201 Solids concentration (%) 45.0% 45.0% 45.0% 50.0% Degree of neutralization of polymer powder (%) 90.0% 90.0% 90.0% 90.0% Coating properties of slurry C C C C 90 peeling strength (N/m) 0.7 1.0 4.2

(27) In Examples 1-1 to 1-9, electrodes were prepared using electrode mixture layer compositions for nonaqueous electrolyte secondary batteries according to the present teachings. Each composition (slurry) had good coating properties, and the peeling strength between the resulting mixture layer and a collector (copper foil) was at least 1.0 N/m in all cases, indicating excellent binding properties. As for comparison between the examples, although the degree of crosslinking of the crosslinked polymer was roughly the same in Example 1-4 as in Example 1-5 and was also roughly the same in Example 1-7 as in Example 1-8, the coating properties and binding properties were greater in Examples 1-4 and 1-8, both of which used the crosslinked polymer R-4, which combines a polyfunctional allyl compound and allyl methacrylate as crosslinking monomers. When these are combined, a crosslinked polymer is obtained with a suitable degree of crosslinking, and it is expected that the microgel will exhibit good swelling and strength, and an excellent dispersion stabilization effect will be obtained.

(28) By contrast, the coating properties and binding properties were insufficient in Comparative Examples 1-1 and 1-2 using crosslinked polymers that do not employ allyl methacrylate as a crosslinking monomer. It is hypothesized that in these cases, no dispersion stabilization effect was obtained because the microgel was insufficiently strong due to the insufficient degree of crosslinking. The coating properties were poor in Comparative Example 1-3, in which more allyl methacrylate was used. It is hypothesized that no dispersion stabilization effect was obtained in this case because the water-swelling properties of the microgel were inadequate due to excessive crosslinking. Moreover, in Comparative Example 1-4 in which the compounded amount of the crosslinked polymer was smaller relative to the active material, the mixture layer exhibited almost no binding properties, and peeling strength could not be measured because the mixture layer peeled off when the electrode was cut to prepare a sample for the peel test.

Example 2-1

(29) A lithium-ion secondary battery was prepared using a mixture layer composition containing hard carbon as a negative electrode material, acetylene black as a conductive aid and the crosslinked polymer R-1 as a binder, and the battery characteristics were evaluated.

(30) 100 parts of hard carbon (Sumitomo Bakelite Co., Ltd., product name LBV-1001), 2 parts of acetylene black (Denki Kagaku Kogyo K.K., product name HS-100) and 3 parts of the crosslinked polymer R-1 in powder form were thoroughly mixed in advance, after which 132 parts of ion-exchange water were added, and the mixture was pre-dispersed with a disperser and then dispersed for 15 seconds at a peripheral speed of 20 m/second with a thin film swirling mixer (Primix Corporation, FM-56-30) to obtain a negative electrode mixture layer composition in slurry form.

(31) Using a direct coating-type coating device with a drying furnace, this mixture layer composition was coated on both sides of a 20 m-thick copper foil (Nippon Foil Mfg. Co., Ltd.) as collector with a coating width of 120 mm, dried, and roll pressed to prepare a negative electrode comprising mixture layers on both sides of the collector. The adhering amount of the mixture layer was 4.96 mg/cm.sup.2 (per side), and the density was 1.0 g/cm.sup.3.

(32) A 15 m-thick aluminum foil collector (Nippon Foil Mfg. Co., Ltd.) having mixture layers constituted of a mixture layer composition containing NCM (Nippon Chemical Industrial Co., Ltd.) as an active material, HS-100 as a conductive aid and polyvinylidene fluoride (Kureha Corporation, product name KF #1000) in proportions of 85.5/4.5/10 (by weight) on both sides of the foil was used as the positive electrode. The adhering amount of the positive electrode mixture layer was 6.80 mg/cm.sup.2 (per side), and the density was 2.78 g/cm.sup.3.

(33) Both the positive and negative electrodes were vacuum dried for 12 hours at 120 C., and slit to 9684 mm in a case of the positive electrode and 10088 mm in a case of the negative electrode. The slit electrodes (7 positive electrodes, 8 negative electrodes) were layered with polyethylene separators between the layers, to assemble a laminate cell. The laminate cell was sealed on three sides, vacuum dried for 5 hours at 60 C., injected with electrolyte solution (1 M, LiPF6 in EC/EMC=3/7 (v/v)), and vacuum sealed. All laminate cell preparation was performed in a dry room.

(34) The battery characteristics of the laminate cell prepared above were evaluated as follows.

(35) (Initial Charge/Discharge Evaluation)

(36) The initial charge-discharge capacity was measured under the following conditions using an SD8 charge/discharge system (Hokuto Denko Corporation).

(37) During measurement, one charge/discharge cycle was performed first to stabilize the battery conditions, after which a second charge/discharge cycle was performed, and it was confirmed that the charge/discharge capacity had stabilized within the design capacity (700 to 800 mAh).

(38) Measurement temperature: 25 C.

(39) Charge: 0.1 C-CC/Cut-off 4.2 V.Math.CV/terminal rate 0.01 C

(40) Discharge: 0.1 C-CC/Cut-off 3.0 V

(41) 2 cycles

(42) In the first cycle the charge capacity was 1142 mAh and the discharge capacity was 769 mAh, while in the second cycle the charge capacity was 778 mAh and the discharge capacity was 755 mAh.

(43) (Low-Temperature Rate Test and AC Impedance Measurement)

(44) A cell that had undergone initial charge/discharge testing was subjected to low-temperature rate testing and AC impedance measurement under the following conditions and order. An SD8 charge/discharge system (Hokuto Denko Corporation) and a VSP impedance measurement system (Bio-Logic Science Instruments) were used for measurement. Measurement temperature: 15 C.

(45) (1) 0.1 C charge/discharge (low-temperature initial charge/discharge) Charge: 0.1 C-CC/Cut-off 4.2 V (pause time 10 minutes) Discharge: 0.1 C-CC/Cut-off 3.0 V

(46) (2) AC impedance measurement Charge: 0.1 C, 2 hours Applied voltage: 10 mV Frequency: 1,000 kHz to 10 mHz (residual discharge treatment 0.1 C to 3V)

(47) (3) 0.5 C charge/discharge Charge: 0.5 C-CC/Cut-off 4.2 V (pause time 10 minutes) Discharge: 0.5 C-CC/Cut off 3.0 V (residual discharge treatment 0.1 C to 3 V)

(48) (4) 1 C charge/discharge Charge: 1 C-CC/Cut-off 4.2 V (pause time 10 minutes) Discharge: 1 C-CC/Cut-off 3.0 V (residual discharge treatment 0.1 C to 3 V)

(49) (5) 2 C charge/discharge Charge: 2 C-CC/Cut-off 4.2 V (pause time 10 minutes) Discharge: 2 C-CC/Cut-off 3.0 V (residual discharge treatment 0.1 C to 3 V)

(50) (6) 3 C charge/discharge Charge: 3 C-CC/Cut-off 4.2 V (pause time 10 minutes) Discharge: 3 C-CC/Cut-off 3.0 V (residual discharge treatment 0.1 C to 3 V)

(51) (7) 4 C charge/discharge

(52) Charge: 4 C-CC/Cut-off 4.2 V

(53) (pause time 10 minutes)

(54) Discharge: 4 C-CC/Cut-off 3.0 V

(55) (residual discharge treatment 0.1 C to 3 V)

(56) The measurement results of (1) above were low-temperature initial charge/discharge capacity 605 mAh, discharge capacity 598 mAh.

(57) When a Nyquist plot was prepared from the measurement results of (2) above, the interface resistance value as estimated from the size of the arc was 0.38.

(58) The discharge capacities obtained from (3) to (7) above, were divided by the discharge capacity obtained in (1) above to calculate the discharge capacity retention rate at each C-rate, which was 0.5 C: 67%, 1 C: 44%, 2 C: 15%, 3 C: 3%, 4 C: 0%. 0% here means that the Cut-off voltage (3.0 V) has reached immediately after the start of discharge due to a voltage drop caused by overvoltage.

(59) (Cycle Test)

(60) A cell that had undergone initial charge/discharge testing was subjected to cycle testing under the following conditions.

(61) Measurement temperature: 25 C.

(62) Charge: 1 C-CC/Cut-off 4.2 V

(63) Discharge: 1 C-CC/Cut-off 3.0 V

(64) 200 cycles

(65) The discharge capacity of the 200th cycle was divided by the discharge capacity of the first cycle to calculate the 200-cycle discharge capacity retention rate, which was 93%.

Examples 2-2 to 2-4 and Comparative Examples 2-1 to 2-3

(66) Laminate cells were assembled by the same operations as in Example 2-1 except that the crosslinked polymers used as binders were as shown in Table 4, and the battery characteristics were evaluated. The results are shown in Table 4.

(67) In Comparative Example 2-3, the styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) shown below were used as binders.

(68) SBR: JSR Corporation, product name TRD2001, 1.5 parts as solids

(69) CMC: Daicel FineChem Ltd., product name CMC2200, 1.5 parts as solids

(70) TABLE-US-00004 TABLE 4 Example Example Example Example Comparative Comparative Comparative 2-1 2-2 2-3 2-4 Example 2-1 Example 2-2 Example 2-3 Negative electrode LBV-1001 (parts) 100 100 100 100 100 100 100 mixture layer composition HS-100 (parts) 2 2 2 2 2 2 2 Crosslinked polymer type R-1 R-4 R-4 R-4 R-4 R-9 SBR/CMC (parts) 3.0 1.0 3.0 4.0 6.0 3.0 3.0 Ion-exchange water (parts) 128 126 128 140 162 128 128 Total 233 229 233 246 270 233 233 Solids concentration (%) 45.1% 45.0% 45.1% 43.1% 40.0% 45.1% 45.1% Degree of neutralization 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% of crosslinked polymer (%) First cycle charge capacity (mAh) 1,142 1,174 1,149 1,136 1,114 1,143 1,165 First cycle discharge capacity (mAh) 769 789 772 762 749 768 769 Second cycle charge capacity (mAh) 778 796 781 773 758 773 784 Second cycle discharge capacity (mAh) 755 774 758 751 737 752 758 Interface resistance value () 0.38 0.24 0.33 0.38 0.64 0.40 0.61 Low-temperature initial charge capacity (mAh) (0.1 C.) 605 630 615 607 595 602 609 Low-temperature initial discharge capacity (mAh) (0.1 C.) 598 621 606 599 588 596 599 Low-temperature rate test 0.5 C. 67% 75% 71% 68% 63% 61% 64% Discharge capacity retention rate 1.0 C. 44% 58% 50% 44% 33% 38% 39% (% of 0.1 C.) 2.0 C. 15% 31% 24% 14% 4% 5% 8% 3.0 C. 3% 19% 10% 2% 0% 0% 0% 4.0 C. 0% 5% 1% 0% 0% 0% 0% Cycle test (1C., 200 cycles) discharge capacity retention rate (%) 93% 93% 95% 94% 94% 79% 92%

(71) The compounds used in Table 4 are specified here.

(72) LBV-1001: Hard carbon (Sumitomo Bakelite Co., Ltd.)

(73) HS-100: Acetylene black (Denki Kagaku Kogyo K.K.)

(74) In Examples 2-1 to 2-4 pertaining to the nonaqueous electrolyte secondary battery of the teachings, the discharge capacity retention rate after cycle testing was 93% to 95%, indicating excellent cycle characteristics. All these examples also exhibited good high-rate characteristics. It is thought that this is because, due to the characteristics of the crosslinked polymers used, the interface resistance values are reduced and electronic resistance is reduced due to favorable homogeneous dispersion of active materials and conductive aids, thereby reducing the internal resistance of the battery. In particular, comparing Examples 2-1 and 2-3, in which the amount of the crosslinked polymer is the same, the discharge capacity retention rate was higher at high current densities and the high-rate characteristics were better in Example 2-3, which used the crosslinked polymer R-4 having a particularly good dispersion stabilizing effect.

(75) By contrast, the cycle characteristics were low79%in Comparative Example 2-2, which used the crosslinked polymer R-9 with no allyl methacrylate as a crosslinking monomer. In Comparative Example 2-3 using SBR and CMC as binders, the high-rate characteristics are poorer than in the examples. In Comparative Example 2-3, it is believed that the interface resistance increased because the binder did not have sufficient carboxyl groups, and the high rate characteristics declined as a result. The high-rate characteristics were also unsatisfactory in Comparative Example 2-1, in which the content of the crosslinked polymer was high.

INDUSTRIAL APPLICABILITY

(76) An electrode obtained from the electrode mixture layer composition for a nonaqueous electrolyte secondary battery of the teachings has an excellent binding force and exhibits the effect of reduced battery resistance as well. As a consequence, a nonaqueous electrolyte secondary battery equipped with this electrode exhibits superior high-rate characteristics and durability (cycle characteristics), and can be applied to vehicular secondary batteries.