JPH1131503A - Manufacture of pole plate and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance adhesion strength between a collector and an active material layer by applying an active material paste formed by kneading electrode active material powder, a rubber binding and solvent of specific ratio the collector, and thereafter, by drying while controlling, so that the solvent evaporated is until a specific ratio is reached with in a specific time. SOLUTION: Sol-like active material paste, having proper fluidity by a solvent amount of 40 to 70 vol.% requeis a time of 0.5 to 2.5 minutes to turn into a non-fluid state of 35 vol.% by drying after application to a collector usually. Therefore, drying is conducted, for instance, by a constant temperature and constant pressure over. By this evaporation speed, the same becomes gel-like as the uniformization of binding agent distribution due to uniformaliziation of a solvent in an active paste layer is maintained, no separation of the active material and the binding agent is allowed which results from gravity difference or the like. When a positive electrode plate and a negative electrode plate by this manufacturing method are wound around into a spiral shape via a separator and are contained in a battery case, space use efficiency is high, since adhesion strength between a collector and an active material layer is strong so that a small radius of curvature is well acceptable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an electrode plate used for a non-aqueous electrolyte secondary battery such as a lithium secondary battery, and a non-aqueous electrolyte secondary battery using the electrode plate produced by the method. It is about.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As such a secondary battery, a cylindrical lithium secondary battery using a lithium-containing double oxide such as LiCoO ₂ for a positive electrode and a carbon material for a negative electrode has been actively researched and developed. In particular, since this type of battery uses a non-aqueous electrolyte, the electrode plate is formed in a sheet shape in order to increase the surface area of the electrode plate from the viewpoint of current characteristics. In order to accommodate this sheet-shaped electrode plate in a cylindrical battery case with a good accommodation ratio, many configurations have been proposed in which the sheet is spirally wound. Such a sheet-like electrode plate is formed by applying an active material paste in which active material powder is dispersed on a metal foil current collector to a thickness of several tens to several hundreds μm, drying the material, and then filling the active material paste. Rolled to increase the rate. This active material paste is obtained by mixing and kneading the active material powder and a binder with water or an organic solvent.

In assembling a cylindrical battery, a sheet-like electrode plate having a thick active material layer coated on a metal current collector is bent with a small radius of curvature. Big stress occurs. Here, the binder in the active material layer plays a role of binding the active materials and bonding the metal current collector and the active material. As the binder, generally, a polytetrafluoroethylene resin dispersion having a stable paste state is used, but in order to further increase the adhesive strength between the metal current collector and the active material, styrene butadiene rubber or the like is used instead. It has been found that it is better to use a rubber binder as a main component.

[0004]

However, in the study of the present inventors, the active material paste containing a rubber-based binder as a main component shows that the active material paste coated on the metal current collector is not used. It has been found that if the drying rate is not appropriate, the adhesive strength between the metal current collector and the active material layer is reduced, and the active material layer may fall off from the metal current collector.

[0005] In view of the above problems, the present invention provides a rubber-based binder having excellent adhesive strength between a current collector and an active material layer.
An object of the present invention is to provide a method for manufacturing an electrode plate capable of stabilizing the excellent adhesive strength and a non-aqueous electrolyte secondary battery using the electrode plate manufactured by the method.

[0006]

In order to achieve the above object, a method for manufacturing an electrode plate according to the present invention comprises an active material paste obtained by kneading an electrode active material powder, a rubber-based binder and 40 to 70 vol% of a solvent. After being applied to the current collector, the solvent evaporation rate of the active material paste applied to the current collector is adjusted so that the time required for reducing the solvent amount to 35 vol% is 0.5 to 2.5 minutes. Characterized by drying.

According to the method for manufacturing an electrode plate of the present invention, the active material paste in a fluid state (sol state) having a solvent amount of 40 to 70 vol% is applied to a current collector, and then the solvent amount is 35 vol. %, The rate of evaporation of the solvent from the surface of the active material paste layer is limited so that the time required to reduce the amount to 0.5% or more is maintained, so that the amount of solvent in the active material paste layer is kept uniform. Uniform distribution of the binder is maintained, and the time during which the active material paste is in a fluidized state is limited so that the above-mentioned time is 2.5 minutes or less. Uniform distribution of the binder is maintained without separation from the binder due to a gravity difference or the like. Then, the solvent amount of the active material paste applied to the current collector is 35 vol.
%, The active material paste becomes in a non-fluid state (gel state), so that no movement of the binder in the active material paste layer occurs regardless of the subsequent evaporation rate of the solvent. Therefore, since the amount and distribution of the binder near the current collector surface of the active material layer become uniform, while using a rubber-based binder having excellent adhesive strength between the current collector and the active material layer, the excellent Adhesive strength can be stabilized.

If the time during which the active material layer is in a fluid state is shorter than 0.5 minutes, migration occurs in which the binder in the active material layer moves to the atmosphere side, and the binder on the current collector side runs short. As a result, the adhesive strength between the current collector and the active material layer is lowered, which is not preferable. If the time is longer than 2.5 minutes, the active material and the binder are gradually separated in the active material layer due to a gravity difference or the like. As a result, the distribution of the binder becomes non-uniform. As a result, the adhesive strength between the current collector and the active material layer in the portion where the binder is insufficient is undesirably reduced. Note that the initial solvent amount of the active material paste was 40 vol.
%, The fluidity of the active material paste is too small to apply, which is not preferable.
If it exceeds 1%, the fluidity is too large and it is difficult to apply a uniform thickness, which is not preferable.

A nonaqueous electrolyte secondary battery of the present invention uses a positive electrode plate or a negative electrode plate manufactured by the above-described method of manufacturing an electrode plate of the present invention, and the positive electrode plate and the negative electrode plate are spirally interposed via a separator. The battery is wound and incorporated in a cylindrical battery case.

According to the non-aqueous electrolyte secondary battery of the present invention, the positive electrode plate or the negative electrode plate produced by the method for producing an electrode plate of the present invention has a strong and stable adhesive strength between the current collector and the active material layer. Therefore, even if the active material layer is bent with a small radius of curvature, the active material layer does not peel off. Therefore, the positive electrode plate and the negative electrode plate can be spirally wound with the separator interposed therebetween, and can be efficiently incorporated into the cylindrical battery case. Further, the electrodes can be arranged in the space near the central axis of the cylindrical battery case, which is particularly useful for a cylindrical non-aqueous electrolyte secondary battery having a small diameter.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

One embodiment of the method for manufacturing an electrode plate according to the present invention includes a first step of obtaining an active material paste, a second step of applying the active material paste to a current collector, and an active material applied to the current collector. A third step of drying the material paste until the amount of the solvent is 35 vol% or less, a fourth step of drying the active material paste almost completely, and rolling and cutting the dried product to obtain an electrode. And a fifth step of obtaining a plate. The above second to fourth steps are performed by the manufacturing apparatus shown in FIG.

First, as shown in FIG. 1, the manufacturing apparatus comprises a feeding machine 14 for feeding a tape-shaped current collector 12 (13);
Four rollers 15 for supporting the running current collector 12 (13) so as not to loosen, and the running current collector 12 (1
3) Active material coater 16 for applying active material paste
A constant temperature / humidity chamber 17 arranged downstream of the active material coater 16 in the traveling direction to control the temperature and humidity of the atmosphere in the chamber; and a current collector 12 (1) arranged downstream of the constant temperature / humidity chamber 17 in the traveling direction.
The drying furnace 18 for drying the active material paste applied to 3) almost completely and the current collector 12 (1 for almost completely dried)
And 3) a winder 19 that winds at a variable traveling speed.

The constant temperature / humidity chamber 17 is used in the third step, and has a length in the traveling direction of the current collector 12 (13) of 50%.
By controlling the temperature and humidity of the atmosphere in the tank of 0 mm, the active material paste applied to the current collector 12 (13) is dried while controlling the evaporation rate of the solvent. The drying furnace 18 is used in the fourth step, and includes a heater and a fan.

The first step is a step of obtaining each of a positive electrode active material paste and a negative electrode active material paste.

The positive electrode active material paste contains 55% by weight of LiCoO ₂ powder as a positive electrode active material, 1.5% by weight of carbon black as a conductive material, 3.0% by weight of styrene butadiene rubber as a binder, and carboxyl as a thickener. 0.5 wt% of methylcellulose and 40 wt% of water as a paste solvent were blended and kneaded. The water content of the obtained positive electrode active material paste was 64 vol% in volume ratio. The positive electrode active material is, for example, LiN in addition to LiCoO _2.
iO ₂ or LiMn ₂ O ₄ may be used.

The negative electrode active material paste contains 53% by weight of graphite powder as a negative electrode active material, 6.0% by weight of styrene butadiene rubber as a binder, 1.0% by weight of carboxymethyl cellulose as a thickener, and 40% by weight of water as a paste solvent. %, Blended and kneaded. The water content of the obtained negative electrode active material paste was 53 vol% in volume ratio. The negative electrode active material has a lattice spacing of 002 planes of 3.35 to 3.80.
炭素 carbon material powder is preferable, in addition to the graphite powder, for example, petroleum coke, cresol resin fired carbon powder, furan resin fired carbon powder, polyacrylonitrile resin fired carbon powder, vapor grown carbon powder, mesophase pitch fired carbon powder Good.

In the second step, a cathode active material paste is applied to a 20 μm thick current collector 12 made of Al foil, and a 16 μm thick C
The negative electrode active material paste was continuously and uniformly applied to a thickness of about 150 μm on the current collector 13 made of u foil. Current collector 12 (1
The traveling speed of 3) is 200 to 1000 by the winder 19.
It was set in the range of mm / min. The active material coater 16 is configured to control the discharge speed of the active material in accordance with the traveling speed set as described above, so as to secure a constant coating thickness of about 150 μm.

In the third step, the active material paste applied to the current collector 12 (13) is controlled by controlling the temperature and humidity of the atmosphere in the constant temperature and humidity chamber 17 so that the amount of water (the amount of solvent) Is 3
The time required to reduce to 5 vol% is 0.5-2.
Drying was performed while variably controlling the evaporation rate of water so as to obtain 5 minutes. Specifically, Example 1 of the negative electrode current collector 13,
Corresponding to the traveling speeds of 1000 and 500 and 200 mm / min for 2 and 3 respectively, the water content immediately after passing through the constant temperature and humidity chamber 17 having a length of 500 mm is 35 ± 1 vol%.
The temperature and humidity of the atmosphere in the tank were variably controlled so that As shown in Table 1, in Examples 1, 2 and 3, the times were set to 0.5, 1.0 and 2.5 minutes, respectively. In addition, the said time in the positive electrode current collector 12 was made into fixed 1.0 minute.

In the fourth step, the temperature inside the drying furnace 18 is set to about 150 ° C., and the water content of the active material paste applied to the current collector 12 (13) and dried to about 35 vol% in the third step is obtained. Is almost completely removed, and is naturally cooled to take up the winder 1
9 rolled up.

In the fifth step, the product obtained by drying is rolled in order to increase the packing density of the active material, and finally cut into dimensions to be used for one battery, and each of the positive electrode plate and the negative electrode plate is cut. was gotten.

[0022]

[Table 1]

Example 1 of the negative electrode plate thus obtained
The adhesive strength of the active material layers of Nos. 1 to 3 was evaluated by a scratch strength using a continuous load type scratch strength tester (JIS K6718). This test is to determine the presence or absence of peeling by scratching at a scratching speed of 600 mm / min while vertically pressing a scratching blade having a width of 5 mm against the upper surface of the active material layer. The applied load is increased, and the minimum load when the active material layer peels off is the scratch strength of the sample. Table 1 summarizes the evaluation results together with Comparative Examples 1 and 2.

As shown in Table 1, the negative electrode plate was formed by a current collector 13
The water content of the active material paste applied to the
%, The adhesive strength of the active material layer to the current collector 13 is strong and stable in the range of 0.5 to 2.5 minutes.

The adhesive strength of Comparative Example 1 in which the time was 0.3 minutes and Comparative Example 2 in which the time was 4.0 minutes were both reduced.

One embodiment of the nonaqueous electrolyte secondary battery of the present invention uses the positive electrode plate and the negative electrode plate according to the above embodiment, and has a cylindrical lithium 17 mm diameter and 50 mm length as shown in FIG. A secondary battery, an electrode group, an electrolytic solution,
And a battery case for accommodating them.

The electrode group includes a sheet-like positive electrode plate 1, a sheet-like negative electrode plate 3, a sheet-like separator 5 insulating between the positive electrode plate 1 and the negative electrode plate 3, a positive electrode lead 2, and a negative electrode lead 4.
And an upper insulating plate 6 and a lower insulating plate 7. The positive electrode plate 1 and the negative electrode plate 3 are stacked with a separator 5 made of a porous polypropylene film interposed therebetween, spirally wound, and housed tightly in a cylindrical battery case. In particular, the negative electrode plate 3 is that of the second embodiment.

The electrolytic solution was prepared by mixing LiPF in an organic solvent mixture of equal volume of ethylene carbonate, diethyl carbonate and methyl propionate.
₆ is a non-aqueous electrolyte in which 1.5 mol / liter is dissolved. This non-aqueous electrolyte is accommodated in a battery case and filled in continuous voids in the positive electrode active material layer and the negative electrode active material layer. In the battery reaction, the positive electrode passes through the fine pores of the porous separator 5. L between plate 1 and negative plate 3
Responsible for i-ion transfer.

The battery case includes a case body 8 obtained by deep drawing an stainless steel sheet having resistance to organic electrolyte and a safety valve 1.
And a sealing plate 1 serving as a positive electrode external terminal
0 and an insulating gasket 9 for insulating and gas-sealing between the case body 8 and the negative electrode external terminal.

According to this cylindrical lithium secondary battery, even when the positive electrode plate and the negative electrode plate are bent with a small radius of curvature, the active material layer does not peel off, and the positive electrode plate and the negative electrode plate are spirally interposed via the separator. And efficiently incorporated into the cylindrical battery case.

In the above embodiment, styrene butadiene rubber was used as the binder, but the present invention is not limited to this, and other rubber binders such as isoprene rubber, chloroprene rubber, acrylic rubber, urethane rubber, Silicone rubber or fluorine rubber may be used.

In the above embodiment, water was used as the paste solvent. However, the present invention is not limited to this, and general organic solvents having an appropriate vapor pressure, for example, N-methylpyrrolidone, xylene, toluene, acetone , Methyl ethyl ketone, methyl isobutyl ketone, cyclohexane, ethanol, methanol, methyl acetate, ethyl acetate, butyl acetate, methylene chloride, ethylene chloride.

In the above-described embodiment of the cylindrical lithium secondary battery, the method of manufacturing the electrode plate of the present invention is applied to both the positive electrode plate and the negative electrode plate. Even if the method for manufacturing an electrode plate of the present invention is applied only to the electrode plate having a weaker adhesive strength, a great effect can be obtained.

In the above embodiment, the method of manufacturing an electrode plate in which the positive electrode active material and the negative electrode active material occlude and release Li reversibly and a lithium secondary battery using the electrode plate according to the method have been described. Alternatively, the present invention can be applied to a method of manufacturing an electrode plate that reversibly stores and releases H, Na, or K, and a non-aqueous solution secondary battery using the electrode plate.

[0035]

According to the method for manufacturing an electrode plate of the present invention, the active material paste in a fluid state (sol state) having a solvent amount of 40 to 70 vol% is applied to a current collector and then the solvent amount is reduced. Takes 0.5% to decrease to 35% by volume.
The evaporation rate of the solvent from the surface of the active material paste layer is limited so as to be more than one minute, so that the amount of the solvent in the active material paste layer is kept uniform and the distribution of the binder is kept uniform. Since the time during which the active material paste is in a fluidized state is limited so that the above-mentioned time is 2.5 minutes or less,
The uniform distribution of the binder is maintained without the active material and the binder being separated in the active material layer due to a gravity difference or the like. And
Solvent amount of active material paste applied to current collector is 35 vo
When the active material paste is reduced to 1%, the active material paste becomes in a non-fluid state (gel state), so that the binder does not move in the active material paste layer regardless of the subsequent evaporation rate of the solvent. Therefore, since the amount and distribution of the binder near the current collector surface of the active material layer become uniform, while using a rubber-based binder having excellent adhesive strength between the current collector and the active material layer, the excellent Adhesive strength can be stabilized.

According to the non-aqueous electrolyte secondary battery of the present invention, the positive electrode plate or the negative electrode plate produced by the method for producing an electrode plate of the present invention has a strong and stable adhesive strength between the current collector and the active material layer. Therefore, even if the active material layer is bent with a small radius of curvature, the active material layer does not peel off. Therefore, the positive electrode plate and the negative electrode plate can be spirally wound with the separator interposed therebetween, and can be efficiently incorporated into the cylindrical battery case.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a method for manufacturing an electrode plate of the present invention.

FIG. 2 is a schematic sectional view showing one embodiment of a non-aqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

 1 positive electrode plate 3 negative electrode plate

Claims (2)

[Claims] 1. An electrode active material powder, a rubber binder and a solvent
After the active material paste kneaded with 0 to 70 vol% is applied to the current collector, the time required for the active material paste applied to the current collector to reduce the solvent amount to 35 vol% is 0.5 to 0.5 vol%. A method for producing an electrode plate, characterized in that drying is performed while controlling the evaporation rate of the solvent so as to be 2.5 minutes. 2. A cylindrical battery case using a positive electrode plate or a negative electrode plate manufactured by the method for manufacturing an electrode plate according to claim 1, wherein the positive electrode plate and the negative electrode plate are spirally wound via a separator. Non-aqueous electrolyte secondary battery characterized by being incorporated in a battery.