Undercoat foil for energy storage device electrode

Abstract

This undercoat foil for an energy storage device electrode comprises a collector base plate, and an undercoat layer formed on at least one surface of the collector base plate, the undercoat layer containing carbon nanotubes, and the coating amount per collector base plate surface being 0.1 g/m.sup.2 or less. Since this undercoat foil can be effectively welded by ultrasound, the use thereof allows a low-resistance energy storage device and a simple and effective production method therefor to be provided.

Claims

1. An undercoat foil for an energy storage device electrode, comprising a current-collecting substrate and an undercoat layer formed on at least one side of the current-collecting substrate, wherein the undercoat layer is formed from a composition comprising carbon nanotubes, a carbon nanotube dispersant and a crosslinking agent, and has a coating weight per side of the current-collecting substrate of at least 0.001 g/m.sup.2 and less than 0.05 g/m.sup.2; and the carbon nanotube dispersant is a pendant oxazoline group-containing vinyl polymer.

2. The undercoat foil for an energy storage device electrode of claim 1, wherein the undercoat layer is formed on at least one side of the current-collecting substrate in such a way as to cover the entire surface thereof.

3. The undercoat foil for an energy storage device electrode of claim 1 or 2, wherein the undercoat layer includes a matrix polymer.

4. The undercoat foil for an energy storage device electrode of claim 1, wherein the undercoat layer has a thickness of from 0.01 to 10 μm.

5. The undercoat foil for an energy storage device electrode of claim 1, wherein the current-collecting substrate is aluminum foil or copper foil.

6. An energy storage device electrode comprising the undercoat foil for an energy storage device electrode of claim 1 and an active material layer formed over part or all of a surface of the undercoat layer.

7. The energy storage device electrode of claim 6, wherein the active material layer is formed over part of the undercoat layer surface.

8. The energy storage device electrode of claim 7, wherein the active material layer is formed in such a way as to cover all regions of the undercoat layer other than a peripheral edge thereof.

9. An energy storage device comprising the energy storage device electrode of any one of claims 6 to 8.

10. An energy storage device comprising at least one electrode assembly comprised of one or a plurality of the electrodes of claim 7 or 8 and a metal tab, wherein at least one of the electrodes is ultrasonically welded to the metal tab at a region of the electrode where the undercoat layer is formed and the active material layer is not formed.

11. The energy storage device of claim 10, wherein the metal tab is made of at least one metal selected from the group consisting of aluminum, copper and nickel.

12. A method for manufacturing an energy storage device comprising one or a plurality of the electrodes of claim 7 or 8, which method comprises the step of ultrasonically welding at least one of the electrodes to the metal tab at a region of the electrode where the undercoat layer is formed and the active material layer is not formed.

13. The undercoat foil for an energy storage device electrode of claim 1, wherein the concentration of the carbon nanotube dispersant in the composition is 0.001 to about 30 wt %.

14. The undercoat foil for an energy storage device electrode of claim 1, wherein the amount of crosslinking agent is 0.001 to 80 wt % based on the dispersant.

15. The undercoat foil for an energy storage device electrode of claim 1, wherein the crosslinking agent is crosslinked with the dispersant in the undercoat layer.

Description

EXAMPLES

(1) Working Examples and Comparative Examples are given below to more fully illustrate the invention, although the invention is not limited by these Examples. The instruments used in the Examples were as follows.

(2) (1) Probe-type ultrasonicator (dispersion treatment):

(3) Instrument: UIP1000 (Hielscher Ultrasonics GmbH)
(2) Wire bar coater (thin-film production): Instrument: PM-9050MC (SMT Co., Ltd.)
(3) Ultrasonic welder (ultrasonic welding test) Instrument: 2000Xea (40:0.8/40MA-XaeStand), from Emerson Japan, Ltd.
(4) Charge/discharge measurement system (evaluation of secondary battery): Instrument: HJ1001 SM8A (Hokuto Denko Corporation)
(5) Micrometer (measurement of binder and active material layer thicknesses): Instrument: IR54 (Mitutoyo Corporation)
(6) Homogenizing disperser (mixing of electrode slurry) Instrument: T.K. Robomix (with Homogenizing Disperser model 2.5 (32 mm dia.)), from Primix Corporation
(7) Thin-film spin-type high-speed mixer (mixing of electrode slurry) Instrument: Filmix model 40 (Primix Corporation)
(8) Planetary centrifugal mixer (degassing of electrode slurry) Instrument: Thinky Mixer ARE-310 (Thinky)
(9) Roll press (compressing of electrode): Instrument: HSR-60150H ultra-small desktop hot roll press (Hohsen Corporation)

[1] Production of Undercoat Foil

Comparative Example 1-1

(4) First, 0.50 g of PTPA-PBA-SO.sub.3H having the formula shown below and synthesized by the same method as in Synthesis Example 2 of WO 2014/042080 was dissolved as the dispersant in 43 g of 2-propanol and 6.0 g of water as the dispersion media, and 0.50 g of MWCNTs (NC7000, from Nanocyl; diameter, 10 nm) was added to the resulting solution. This mixture was ultrasonically treated for 30 minutes at room temperature (about 25° C.) using a probe-type ultrasonicator, thereby giving a black MWCNT-containing dispersion in which MWCNTs were uniformly dispersed and which was free of precipitate.

(5) Next, 3.88 g of the polyacrylic acid (PAA)-containing aqueous solution Aron A-10H (solids concentration, 25.8 wt %; from Toagosei Co., Ltd.) and 46.12 g of 2-propanol were added to 50 g of the resulting MWCNT-containing dispersion and stirring was carried out, giving Undercoat Slurry A1.

(6) The resulting Undercoat Slurry A1 was uniformly spread with a wire bar coater (OSP 13, wet film thickness, 13 μm) onto aluminum foil (thickness, 20 μm) as the current-collecting substrate and subsequently dried for 20 minutes at 120° C. to form an undercoat layer, thereby producing Undercoat Foil B1. Twenty pieces of the undercoat foil cut to dimensions of 5×10 cm were prepared and their weights were measured, following which the weight of the metal foil after rubbing off the undercoat layer using paper permeated with a 1:1 (weight ratio) mixture of 2-propanol and water was measured. The coating weight of the undercoat layer, as calculated from the weight difference in the undercoat foil before and after rubbing off the undercoat layer, was 0.167 g/m.sup.2.

(7) In addition, Undercoat Slurry A1 was similarly coated as well onto the opposite side of Undercoat Foil B1 and dried, thereby producing Undercoat Foil C1 having undercoat layers formed on both sides of aluminum foil.

(8) ##STR00006##

Working Example 1-1

(9) Undercoat Slurry A1 prepared in Comparative Example 1-1 was diluted 2-fold with 2-propanol, giving Undercoat Slurry A2.

(10) Aside from using the resulting Undercoat Slurry A2, Undercoat Foils B2 and C2 were produced in the same way as in Comparative Example 1-1. The coating weight of the undercoat layer on Undercoat Foil B2 was calculated and found to be 0.088 g/m.sup.2.

Working Example 1-2

(11) Undercoat Slurry A1 prepared in Comparative Example 1-1 was diluted 4-fold with 2-propanol, giving Undercoat Slurry A3.

(12) Aside from using the resulting Undercoat Slurry A3, Undercoat Foils B3 and C3 were produced in the same way as in Comparative Example 1-1. The coating weight of the undercoat layer on Undercoat Foil B3 was calculated and found to be 0.042 g/m.sup.2.

Working Example 1-3

(13) Undercoat Slurry A1 prepared in Comparative Example 1-1 was diluted 6-fold with 2-propanol, giving Undercoat Slurry A4.

(14) Aside from using the resulting Undercoat Slurry A4, Undercoat Foils B4 and C4 were produced in the same way as in Comparative Example 1-1. The coating weight of the undercoat layer on Undercoat Foil B4 was calculated and found to be 0.032 g/m.sup.2.

Comparative Example 1-2

(15) First, 2.0 g of the oxazoline polymer-containing aqueous solution Epocros WS-700 (Nippon Shokubai Co., Ltd.; solids concentration, 25 wt %; weight-average molecular weight, 4×10.sup.4; oxazoline group content, 4.5 mmol/g) as the dispersant was mixed together with 17.5 g of distilled water, and 0.5 g of MWCNTs was mixed therein. The resulting mixture was ultrasonically treated for 30 minutes at room temperature using a probe-type ultrasonicator, thereby giving a black MWCNT-containing dispersion in which MWCNTs were uniformly dispersed and which was free of precipitate.

(16) Next, 0.7 g of the ammonium polyacrylate (PAA-NH.sub.4)-containing aqueous solution Aron A-30 (solids concentration, 31.6 wt %; from Toagosei Co., Ltd.), 0.2 g of sodium alginate (Na alginate, from Kanto Chemical Co., Ltd.; extra pure reagent) and 49.1 g of distilled water were added to 50 g of the resulting MWCNT-containing dispersion and stirring was carried out, giving Undercoat Slurry A5.

(17) The resulting Undercoat Slurry A5 was uniformly spread with a wire bar coater (OSP 13, wet film thickness, 13 μm) onto aluminum foil (thickness, 20 μm) as the current-collecting substrate and subsequently dried for 20 minutes at 120° C. to form an undercoat layer, thereby producing Undercoat Foil B5. Twenty pieces of the undercoat foil cut to dimensions of 5×10 cm were prepared and their weights were measured, following which the weight of the metal foil after rubbing off the undercoat layer using paper permeated with water was measured. The coating weight of the undercoat layer, as calculated from the weight difference in the undercoat foil before and after rubbing off the undercoat layer, was 0.113 g/m.sup.2.

(18) In addition, Undercoat Slurry A5 was similarly coated as well onto the opposite side of Undercoat Foil B5 and dried, thereby producing Undercoat Foil C5 having undercoat layers formed on both sides of aluminum foil.

Working Example 1-4

(19) Aside from using a different wire bar coater (OSP 4, wet film thickness, 4 μm), Undercoat Foils B6 and C6 were produced in the same way as in Comparative Example 1-2. The coating weight of the undercoat layer on Undercoat Foil B6 was calculated and found to be 0.035 g/m.sup.2.

Working Example 1-5

(20) Aside from using a different wire bar coater (OSP 3, wet film thickness, 3 μm), Undercoat Foils B7 and C7 were produced in the same way as in Comparative Example 1-2. The coating weight of the undercoat layer on Undercoat Foil B7 was calculated and found to be 0.027 g/m.sup.2.

Working Example 1-6

(21) Aside from using a different wire bar coater (OSP 2, wet film thickness, 2 μm), Undercoat Foils B8 and C8 were produced in the same way as in Comparative Example 1-2. The coating weight of the undercoat layer on Undercoat Foil B8 was calculated and found to be 0.016 g/m.sup.2.

Comparative Example 1-3

(22) Aside from using acetylene black (AB, from Denka Co. Ltd.) instead of MWCNTs, Undercoat Slurry A9 and Undercoat Foils B9 and C9 were produced in the same way as in Comparative Example 1-1. The coating weight of the undercoat layer on Undercoat Foil B9 was calculated and found to be 0.166 g/m.sup.2.

Comparative Example 1-4

(23) Aside from using AB instead of MWCNTs, Undercoat Slurry A10 and Undercoat Foils B10 and C10 were produced in the same way as in Working Example 1-1. The coating weight of the undercoat layer on Undercoat Foil B10 was calculated and found to be 0.081 g/m.sup.2.

Comparative Example 1-5

(24) Aside from using AB instead of MWCNTs, Undercoat Slurry A11 and Undercoat Foils B11 and C11 were produced in the same way as in Working Example 1-2. The coating weight of the undercoat layer on Undercoat Foil B11 was calculated and found to be 0.036 g/m.sup.2.

Comparative Example 1-6

(25) Aside from using AB instead of MWCNTs, Undercoat Slurry A12 and Undercoat Foils B12 and C12 were produced in the same way as in Working Example 1-3. The coating weight of the undercoat layer on Undercoat Foil B12 was calculated and found to be 0.026 g/m.sup.2.

Comparative Example 1-7

(26) Aside from using AB instead of MWCNTs, Undercoat Foils B13 and C13 were produced in the same way as in Comparative Example 1-2. The coating weight of the undercoat layer on Undercoat Foil B13 was calculated and found to be 0.146 g/m.sup.2.

Comparative Example 1-8

(27) Aside from using AB instead of MWCNTs, Undercoat Foils B14 and C14 were produced in the same way as in Working Example 1-4. The coating weight of the undercoat layer on Undercoat Foil B14 was calculated and found to be 0.052 g/m.sup.2.

Comparative Example 1-9

(28) Aside from using AB instead of MWCNTs, Undercoat Foils B15 and C15 were produced in the same way as in Working Example 1-5. The coating weight of the undercoat layer on Undercoat Foil B15 was calculated and found to be 0.044 g/m.sup.2.

Comparative Example 1-10

(29) Aside from using AB instead of MWCNTs, Undercoat Foils B16 and C16 were produced in the same way as in Working Example 1-6. The coating weight of the undercoat layer on Undercoat Foil B16 was calculated and found to be 0.029 g/m.sup.2.

(30) [Ultrasonic Welding Test]

(31) Ultrasonic welding tests were carried out by the following method on each of the undercoat foils produced in Working Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-10.

(32) Using an ultrasonic welder from Emerson Japan, Ltd. (2000Xea, 40:0.8/40MA-XaeStand), five pieces of undercoat foil having undercoat layers formed on both sides were stacked on top of an aluminum tab (Hohsen Corporation; thickness, 0.1 mm; width, 5 mm) on an anvil, a horn was brought down onto the foil from above, and welding was carried out by applying ultrasonic vibrations. The welding surface area was set to 3×12 mm. Cases in which, after welding, the undercoat foil in contact with the horn does not tear, but the foil does tear when one tries to separate the tab and the undercoat foil were rated as “Pass”; cases in which, after welding, the tab and the foil separate were rated as “Fail”. The results are shown in Table 1.

(33) TABLE-US-00001 TABLE 1 Under- Coating Weld- coat Carbon Dispersant, weight ability foil material etc. (g/m.sup.2) (pass/fail) Comparative Example 1-1 C1 MWCNT PTPA-S, PAA 0.167 Fail Working Example 1-1 C2 MWCNT PTPA-S, PAA 0.088 Pass Working Example 1-2 C3 MWCNT PTPA-S, PAA 0.042 Pass Working Example 1-3 C4 MWCNT PTPA-S, PAA 0.032 Pass Comparative Example 1-2 C5 MWCNT WS-700, PAANH.sub.4, Na alginate 0.113 Fail Working Example 1-4 C6 MWCNT WS-700, PAANH.sub.4, Na alginate 0.035 Pass Working Example 1-5 C7 MWCNT WS-700, PAANH.sub.4, Na alginate 0.027 Pass Working Example 1-6 C8 MWCNT WS-700, PAANH.sub.4, Na alginate 0.016 Pass Comparative Example 1-3 C9 AB PTPA-S, PAA 0.166 Fail Comparative Example 1-4 C10 AB PTPA-S, PAA 0.081 Pass Comparative Example 1-5 C11 AB PTPA-S, PAA 0.036 Pass Comparative Example 1-6 C12 AB PTPA-S, PAA 0.026 Pass Comparative Example 1-7 C13 AB WS-700, PAANH.sub.4, Na alginate 0.146 Fail Comparative Example 1-8 C14 AB WS-700, PAANH.sub.4, Na alginate 0.052 Pass Comparative Example 1-9 C15 AB WS-700, PAANH.sub.4, Na alginate 0.044 Pass Comparative Example 1-10 C16 AB WS-700, PAANH.sub.4, Na alginate 0.029 Pass

(34) As shown in Table 1, in cases where the coating weight exceeded 0.1 g/m.sup.2, the welding strength between the tab and the undercoat foil was inadequate and separation between the tab and the undercoat foil arose. In cases where the coating weight was 0.1 g/m.sup.2 or less, the welding strength between the tab and the undercoat foil was adequate; when an attempt was made to separate the tab and the undercoat foil, the undercoat foil tore. It is apparent from these results that, in order to weld the undercoat foil and the metal tab to a sufficient strength, the coating weight of the undercoat layer must be set to not more than 0.1 g/m.sup.2.

Comparative Example 1-11

(35) Aside from using copper foil (thickness, 15 μm) instead of aluminum foil, Undercoat Foil C16 was produced in the same way as in Comparative Example 1-1.

Working Example 1-7

(36) Aside from using copper foil (thickness, 15 μm) instead of aluminum foil, Undercoat Foil C17 was produced in the same way as in Working Example 1-1.

Working Example 1-8

(37) Aside from using copper foil (thickness, 15 μm) instead of aluminum foil, Undercoat Foil C18 was produced in the same way as in Working Example 1-2.

Working Example 1-9

(38) Aside from using copper foil (thickness, 15 μm) instead of aluminum foil, Undercoat Foil C19 was produced in the same way as in Working Example 1-3.

(39) [Ultrasonic Welding Test]

(40) Apart from using nickel-plated copper tabs (Hohsen Corporation; thickness, 0.1 mm; width, 5 mm), ultrasonic welding tests were carried out by the same method as described above on the undercoat foils produced in Working Example 1-7 to 1-9 and Comparative Example 1-11. Cases in which, after welding, the undercoat foil in contact with the horn does not tear, but the foil does tear when one tries to separate the tab and the undercoat foil were rated as “Pass”; cases in which, after welding, the tab and the foil separate were rated as “Fail”. The results are shown in Table 2.

(41) TABLE-US-00002 TABLE 2 Weld- Under- Coating ability coat Carbon Dispersant, weight (pass/ foil material etc. (g/m.sup.2) fail) Comparative C16 MWCNT PTPA-S, PAA 0.167 Fail Example 1-11 Working C17 MWCNT PTPA-S, PAA 0.088 Pass Example 1-7 Working C18 MWCNT PTPA-S, PAA 0.042 Pass Example 1-8 Working C19 MWCNT PTPA-S, PAA 0.032 Pass Example 1-9

(42) As shown in Table 2, in cases where copper foil was used as the current-collecting substrate, in order to weld the undercoat foil and the metal tab to a sufficient strength, it was necessary for the coating weight of the undercoat layer to be set to not more than 0.1 g/m.sup.2.

[2] Production of Lithium-Ion Secondary Battery Using Lithium Manganate as Positive Electrode

Comparative Example 2-1

(43) The following were mixed together in a homogenizing disperser at 3,500 rpm for 1 minute: 26.1 g of lithium manganate (LMO, from Toyoshima Manufacturing Co., Ltd.) as the active material, 19.3 g of an NMP solution of polyvinylidene fluoride (PVdF) (12 wt %; KF Polymer L#1120, from Kureha Corporation) as the binder, 0.58 g of AB as a conductive additive and 3.99 g of N-methylpyrrolidone (NMP). Next, using a thin-film spin-type high-speed mixer, mixing treatment was carried out for 60 seconds at a peripheral speed of 20 m/s, in addition to which deaeration was carried out for 2 minutes at 1,000 rpm in a planetary centrifugal mixer, thereby producing an electrode slurry (solids concentration, 58 wt %; LMO:PVdF:AB=90:8:2 (weight ratio).

(44) The resulting electrode slurry was spread uniformly (wet film thickness, 100 μm) over the entire surface of the undercoat layer on Undercoat Foil B1 that had an undercoat layer coated on one side and was produced in Comparative Example 1-1, following which the slurry was dried at 80° C. for 30 minutes and then at 120° C. for 30 minutes, thereby forming an active material layer on the undercoat layer. This layer was then pressed with a roll press, producing Electrode D1 having an active material layer thickness of 30 m.

(45) The resulting Electrode D1 was die-cut in the shape of a 10 mm diameter disk and the weight was measured, following which the electrode disk was vacuum dried at 100° C. for 15 hours and then transferred to a glovebox filled with argon.

(46) A stack of six pieces of lithium foil (Honjo Chemical Corporation; thickness, 0.17 mm) that had been die-cut to a diameter of 14 mm was set on a 2032 coin cell (Hohsen Corporation) cap to which a washer and a spacer had been welded, and one piece of separator (Celgard 2400) die-cut to a diameter of 16 mm that had been permeated for at least 24 hours with an electrolyte solution (Kishida Chemical Co., Ltd.; ethylene carbonate:diethyl carbonate=1:1 (volume ratio) solution containing 1 mol/L of lithium hexafluorophosphate as the electrolyte) was laid on the foil. The Electrode D1 was then placed on top thereof with the active material-coated side facing down. Next, one drop of electrolyte solution was deposited thereon, after which the coin cell case and gasket were placed on top and sealing was carried out with a coin cell crimper. The cell was then left at rest for 24 hours, giving a secondary battery for testing.

Working Example 2-1

(47) Aside from using Undercoat Foil B2 produced in Working Example 1-1, Electrode D2 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Working Example 2-2

(48) Aside from using Undercoat Foil B3 produced in Working Example 1-2, Electrode D3 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Working Example 2-3

(49) Aside from using Undercoat Foil B4 produced in Working Example 1-3, Electrode D4 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-2

(50) Aside from using Undercoat Foil B5 produced in Comparative Example 1-2, Electrode D5 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Working Example 2-4

(51) Aside from using Undercoat Foil B6 produced in Working Example 1-4, Electrode D6 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Working Example 2-5

(52) Aside from using Undercoat Foil B7 produced in Working Example 1-5, Electrode D7 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Working Example 2-6

(53) Aside from using Undercoat Foil B8 produced in Working Example 1-6, Electrode D8 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-3

(54) Aside from using Undercoat Foil B9 produced in Comparative Example 1-3, Electrode D9 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-4

(55) Aside from using Undercoat Foil B10 produced in Comparative Example 1-4, Electrode D10 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-5

(56) Aside from using Undercoat Foil B11 produced in Comparative Example 1-5, Electrode D11 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-6

(57) Aside from using Undercoat Foil B12 produced in Comparative Example 1-6, Electrode D12 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-7

(58) Aside from using Undercoat Foil B13 produced in Comparative Example 1-7, Electrode D13 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-8

(59) Aside from using Undercoat Foil B14 produced in Comparative Example 1-8, Electrode D14 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-9

(60) Aside from using Undercoat Foil B15 produced in Comparative Example 1-9, Electrode D15 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-10

(61) Aside from using Undercoat Foil B16 produced in Comparative Example 1-10, Electrode D16 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

Comparative Example 2-11

(62) Aside from using pure aluminum foil, Electrode D17 and a secondary battery for testing were produced in the same way as in Comparative Example 2-1.

(63) The physical properties of the electrodes as positive electrodes were evaluated under the following conditions for the lithium-ion secondary batteries produced in above Working Examples 2-1 to 2-6 and Comparative Examples 2-1 to 2-11. Table 2 shows the average voltage during 3 C discharge. Current: Constant-current charging at 0.5 C, and constant-current discharging at 0.5 C, 3 C, 5 C and 10 C (the capacity of LMO was set to 148 mAh/g and the discharge rate was raised every 5 cycles, after which the discharge rate at the end was returned to 0.5 C) Cut-off voltage: 4.50 V-3.00 V Temperature: room temperature

(64) TABLE-US-00003 TABLE 3 Average Coating voltage Undercoat Carbon weight (V) during foil material Dispersant, etc. (g/m.sup.2) 3 C discharge Comparative Example 2-1 B1 MWCNT PTPA-S, PAA 0.167 3.88 Working Example 2-1 B2 MWCNT PTPA-S, PAA 0.088 3.88 Working Example 2-2 B3 MWCNT PTPA-S, PAA 0.042 3.89 Working Example 2-3 B4 MWCNT PTPA-S, PAA 0.032 3.88 Comparative Example 2-2 B5 MWCNT WS-700, PAANH.sub.4, Na alginate 0.113 3.89 Working Example 2-4 B6 MWCNT WS-700, PAANH.sub.4, Na alginate 0.035 3.88 Working Example 2-5 B7 MWCNT WS-700, PAANH.sub.4, Na alginate 0.027 3.88 Working Example 2-6 B8 MWCNT WS-700, PAANH.sub.4, Na alginate 0.016 3.87 Comparative Example 2-3 B9 AB PTPA-S, PAA 0.166 3.70 Comparative Example 2-4 B10 AB PTPA-S, PAA 0.081 3.77 Comparative Example 2-5 B11 AB PTPA-S, PAA 0.036 3.48 Comparative Example 2-6 B12 AB PTPA-S, PAA 0.026 3.38 Comparative Example 2-7 B13 AB WS-700, PAANH.sub.4, Na alginate 0.146 3.85 Comparative Example 2-8 B14 AB WS-700, PAANH.sub.4, Na alginate 0.052 3.43 Comparative Example 2-9 B15 AB WS-700, PAANH.sub.4, Na alginate 0.044 3.27 Comparative Example 2-10 B16 AB WS-700, PAANH.sub.4, Na alginate 0.029 3.38 Comparative Example 2-11 — — — — 3.44

(65) From these results, it is apparent that, in secondary batteries having an undercoat foil which is ultrasonically weldable and has a coating weight of 0.1 g/m.sup.2 or less, when AB was used as the carbon material, the average voltage decreased rapidly, the voltage sometimes being lower than in secondary batteries where pure aluminum foil was used. By contrast, when MWCNTs were used as the carbon material, the average voltage was high and a sufficiently low resistance was achieved.

[3] Production of Laminate Cell Using Lithium Manganate as Positive Electrode

Working Example 3-1

(66) The following were mixed together in a homogenizing disperser at 3,500 rpm for 1 minute: 26.1 g of lithium manganate (LMO, from Toyoshima Manufacturing Co., Ltd.) as the active material, 19.3 g of an NMP solution of polyvinylidene fluoride (PVdF) (12 wt %; KF Polymer L#1120, from Kureha Corporation) as the binder, 0.58 g of AB as a conductive additive, and 3.99 g of N-methylpyrrolidone (NMP). Next, using a thin-film spin-type high-speed mixer, mixing treatment was carried out for 60 seconds at a peripheral speed of 20 m/s, in addition to which deaeration was carried out for 2 minutes at 1,000 rpm in a planetary centrifugal mixer, thereby producing an electrode slurry (solids concentration, 58 wt %; LMO:PVdF:AB=90:8:2 (weight ratio).

(67) The Undercoat Foil B3 coated on one side with an undercoat layer that was produced in Working Example 1-2 was cut out into a rectangular shape measuring 8 cm on the short sides and 20 cm on the long sides. The electrode slurry obtained as described above was spread uniformly thereon in a 20 cm band having a width of 5 cm at the center, leaving 1.5 cm free of slurry at both edges on the short sides, following which the slurry was dried at 80° C. for 30 minutes and then at 120° C. for 30 minutes, thereby forming an active material layer on the undercoat layer. This layer was then rolled with a roll press, producing an electrode sheet having an active material layer thickness of 30 μm. The coating weight of the active material, which was determined by die-cutting the electrode sheet in the form of a disk having a diameter of 10 mm and measuring the weight, was 7.58 mg/cm.sup.2.

(68) The resulting electrode sheet was die-cut to dimensions of 4 cm×5 cm for a region coated with the active material layer and dimensions of 1.5 cm×1 cm for a region not coated with the active material layer on the long side, thereby giving positive electrode E1. An aluminum tab (4 mm wide×6.5 cm; thickness 0.1 mm; Hohsen Corporation) was welded with an ultrasonic welder to the region where the undercoat layer was formed and the active material layer was not formed.

(69) The following were mixed together in a homogenizing disperser at 3,500 rpm for 1 minute: 11.3 g of graphite (abbreviated below as “Gr”; CGB-15 from Nippon Graphite Industries, Ltd.) as the active material, 3.22 g of an aqueous dispersion of a polyacrylonitrile binder (14.9 wt %; LA-132, from Chengdu Indigo Power Sources Co., Ltd.) as the binder, 0.24 g of AB as a conductive additive, and 15.3 g of water. Next, using a thin-film spin-type high-speed mixer, mixing treatment was carried out for 60 seconds at a peripheral speed of 20 m/s, in addition to which deaeration was carried out for 2 minutes at 1,000 rpm in a planetary centrifugal mixer, thereby producing an electrode slurry (solids concentration, 40 wt %; Gr:LA-132:AB=94:4:2 (weight ratio).

(70) Pure aluminum foil (thickness, 18 μm) was cut out into a rectangular shape measuring 8 cm on the short sides and 20 cm on the long sides. The electrode slurry obtained as described above was spread uniformly thereon in a 20 cm band having a width of 5 cm at the center, leaving 1.5 cm free of slurry at both edges on the short sides, following which the slurry was dried at 80° C. for 30 minutes and then at 120° C. for 30 minutes, thereby forming an active material layer on the undercoat layer. This layer was then pressed with a roll press, producing an electrode sheet having an active material layer thickness of 20 μm. The coating weight of the active material, which was determined by die-cutting the electrode sheet in the form of a disk having a diameter of 10 mm and measuring the weight, was 3.54 mg/cm.sup.2.

(71) The resulting electrode sheet was die-cut to dimensions of 4.4 cm×5.4 cm for a region coated with the active material layer and dimensions of 1.5 cm×1 cm for a region not coated with the active material layer on the long side, thereby giving negative electrode F1. A nickel-coated copper tab (4 mm wide×6.5 cm; thickness 0.1 mm; Hohsen Corporation) was welded with an ultrasonic welder to the region where the active material layer was not formed.

(72) The positive electrode E1 was enclosed by a separator (Celgard 2400) in such a way as to cover the coated side of the electrode, following which the positive electrode E1 and the negative electrode F1 were stacked with the electrode coated sides facing one another, and the tabs were attached to a laminate film (Dai Nippon Printing Co., Ltd.) by heat and pressure bonding. After 9 hours of drying at 100° C. in vacuo, the electrode assembly was transferred to a glovebox filled with argon. Next, 0.5 mL of an electrolyte solution (Kishida Chemical Co., Ltd.; ethylene carbonate:diethyl carbonate=1:1 (volume ratio) solution containing 1 mol/L of lithium hexafluorophosphate as the electrolyte) was injected and allowed to penetrate under reduced pressure of 0.5 atmosphere for 20 minutes, following which free areas of the laminate film were sealed by heat and pressure bonding in a vacuum, thereby producing a laminate cell for testing.

Comparative Example 3-1

(73) Aside from using pure aluminum foil, a positive electrode E2, a negative electrode F2 and a laminate cell for testing were produced in the same way as in Working Example 3-1. The coating weights of the positive electrode and the negative electrode were respectively 7.35 mg/cm.sup.2 and 3.49 mg/cm.sup.2.

(74) The laminate cells produced in Working Example 3-1 and Comparative Example 3-1 were evaluated under the following conditions. Table 4 shows the average voltages and discharge capacities during 1 C discharge. Current: Constant-current charging and discharging at 0.1 C for 2 cycles, followed by constant-current charging at 0.5 C and constant-current discharging at 0.5 C, 3 C, 5 C and 10 C (the capacity of LMO was set to 148 mAh/g and the discharge rate was raised every 3 cycles) Cut-off voltage: 4.50 V-3.00 V Temperature: room temperature

(75) TABLE-US-00004 TABLE 4 Average voltage Capacity Capacity Coating during during during Undercoat Carbon Dispersant, weight 1 C discharge 1 C discharge 3 C discharge foil material etc. (g/m.sup.2) (V) (mAh/g) (mAh/g) Working B3 MWCNT PTPA-S, PAA 0.042 3.80 78.3 67.9 Example 3-1 Comparative — — — — 3.00 0.9 could not Example 3-1 discharge

(76) As demonstrated in Working Example 3-1, a laminate cell can be produced by welding an aluminum tab to, on an undercoat foil that has a coating weight of 0.1 g/m.sup.2 or less and is ultrasonically weldable, a region of the foil where the undercoat layer has been formed and the active material layer has not been formed, without the need for such steps as peeling away the undercoat layer or forming a region that is not coated with the undercoat layer. Moreover, as is apparent from Table 3, in 1 C discharge, when a pure aluminum foil is used, the voltage is low and discharge is substantially impossible, whereas when an undercoat foil is used, discharge is possible because the battery has a low resistance.