JP6100536B2 - Electrode manufacturing method - Google Patents

Description

  The present invention relates to an electrode manufacturing method, and more particularly to manufacturing an electrode used in a lithium ion battery or the like.

Conventionally, a battery such as a lithium ion battery is formed by laminating a sheet-like positive electrode and a negative electrode via a separator and winding the laminate into a cylindrical shape or the like.
A sheet-like electrode used as a positive electrode and a negative electrode is obtained by forming an active material layer as a positive electrode or a negative electrode on the surface of a foil (base) obtained by rolling aluminum or copper.

The active material layer is made by dispersing a powder material such as an active material or a conductive aid in a solution in which a binder (binder) or a thickener is dissolved in an organic solvent, and making this into a slurry. It was formed by applying to (wet coating method).
In such a wet coating method, the process of evaporating the solvent is indispensable, so local exhaust is required, and not only the equipment becomes large, but also because of the wet process, the viscosity adjustment at the time of blending of the powder material such as the active material Since the coating film was not sufficiently stable due to the influence of humidity and the like, a dry coating method in which an active material, a conductive additive and a binder are powder-coated on a base has been developed (Patent Document 1). reference).

In Patent Document 1, the average particle diameter of the active material is 1 to 50 μm (preferably 20 to 30 μm), the average particle diameter of the conductive assistant (conductive material powder) is 0.01 to 5 μm (preferably 0.03 to 2 μm), The average particle size of the binder is 0.1 to 50 μm (preferably 1 to 10 μm).
These active materials, conductive additives and binder powders are vibrated with a vibrator during electrostatic coating, and are charged positively and negatively with respect to the base by the electrode for electrolysis, and are then brought to the base by electrostatic force. Adsorbed. And by heating in a drying furnace, a binder is fuse | melted and an active material and a conductive support agent are fixed on a base.
Patent Document 1 also describes that a binder is melt-adhered to an active material in advance to form a composite powder, and this is powder-coated on a base.

JP 2001-351616 A

However, in the dry coating method of Patent Document 1, the adhesion strength of the active material layer to the base is insufficient, and electrode formation defects may occur.
On the other hand, in the powder coating with the composite powder described in Patent Document 1, in order to perform powder coating with the composite powder, as a pre-process for producing the composite powder by a spray drying method or the like, PVDF dissolved in a solvent ( Polyvinylidene fluoride) must be sprayed on the active material and then dried to evaporate the solvent, which is difficult to adopt due to the same problems as existing wet coating methods.
For these reasons, the dry coating method described in Patent Document 1 is difficult to put into practical use, and the current situation is that it depends on the above-described conventional wet coating method.

  The objective of this invention is providing the manufacturing method of the electrode which can ensure the adhesive strength of the active material layer with respect to a base with a simple manufacturing process.

In the present invention, the problem of the adhesion strength of the active material layer to the base or the problem of poor electrode formation in Patent Document 1 described above depends on the behavior of the powder of the active material, the conductive additive, and the binder, This is based on the original knowledge of the inventors of the present invention based on the particle size ratio and the active material, and the mutual binding of the conductive additive and the binder before electrostatic coating.
That is, as shown in FIG. 7, when the active material layer 72 is formed by performing electrostatic coating on the base 71, the average particle size of the binder 74 with respect to the average particle size of the active material 73 that is the main component thereof. Is large (average particle size ratio is large, for example, greater than 0.7), the particles of the binder 74 melt and flow into the particles of the active material 73 in the heating step after electrostatic coating, and the predetermined adhesion In order to obtain the strength, it is necessary to blend so that the binder 74 of the mixed powder described later becomes 15% by weight or more.

  In addition, since the active material 73 has a low volume resistivity, the electric charge applied by the power supply device in the coating booth tends to escape and it is difficult to attach the active material 73 alone. On the other hand, since a thermoplastic resin such as PVDF used for the binder 74 has a volume specific resistance value suitable for electrostatic coating, the charged electric charge does not escape and easily adheres to the base 71. Therefore, when the active material 73 and the binder 74 are simultaneously electrostatically coated, the binder 74 first adheres to the base, and the active material 73 adheres only a small amount later. The active material 73 and the binder 74 are not uniformly distributed in the thickness direction in the material layer 72. For this reason, the bias of components occurs in the active material layer 72, so that the active material layer 72 having adhesion strength cannot be generated in heating in the subsequent process, and the performance as an electrode cannot be exhibited.

Therefore, in the present invention, the average particle diameter ratio of the binder with respect to the active material is limited to a range of 0.7 or less, and in order to prevent the bias in the active material layer, the active material is coated before electrostatic coating. It is assumed that processing is performed so that the substance and the binder are bonded to each other.
For this purpose, the present invention has the following configuration.

In order to produce an electrode having an active material layer containing an active material and a binder on the surface of the base, the powder of the active material and the binder are mixed to produce a mixed powder. The mixed powder is electrostatically coated on the surface of the base, and the coated powder is heated and fused to produce an electrode,
The average particle size ratio of the binder powder to the active material powder is 0.7 or less,
Before the mixed powder is applied to the surface of the base, the binder powder is bonded to the active material powder.

In the present invention, before the mixed powder is applied to the surface of the base, the powder of the active material and the powder of the binder are introduced into a stirrer having a rotating blade, and the mixed powder is generated by stirring. In addition, it is possible to employ a process in which the powder of the active material and the powder of the binder in the mixed powder are bonded by frictional charging.
When such a stirrer is used, adjustment is made to increase the rotational speed of the rotary blades to such an extent that sufficient frictional charging is generated in each powder. Specifically, the result of stirring is observed, and adjustment is performed so as to obtain a state in which the powder of the binder is bonded to the powder of the active material.

In the present invention, the active material powder and the binder powder are bonded to each other before the mixed powder is applied to the base surface, and the binder particles having a small average particle size ratio are the active material particles. It is in a state of being attached around the particle. By coating the surface of the base in such an adhesion state, the active material layer formed on the surface of the base is not biased between the active material and the binder, and is firmly bonded by heat fusion. Active material layer.
Thereby, the manufacturing method of an electrode which can ensure the adhesion strength of the active material layer with respect to a base with a simple manufacturing process is realizable.

As the electrostatic coating, for example, an electrostatic fluid dipping method or an electrostatic powder spray method can be used.
An existing crusher and classifier are used as means for bringing the binder powder into an average particle size ratio of 0.7 or less with respect to the active material powder.
As a means for heating and fusing the mixed powder, in addition to a method of passing through a heating furnace, a roll press with heating can be used. If the pressing is performed, it is also suitable for increasing the strength by reducing the interval between the particles in the active material layer.

In the present invention, the mixed powder preferably contains 85 to 95% by weight of the active material and 15 to 5% by weight of the binder.
In the present invention, an active material layer suitable for an electrode used for a lithium ion battery or the like can be formed.
Note that the active material layer may contain a conductive additive in addition to the active material and the binder, and a suitable component ratio of such a conductive additive is approximately 5% by weight.

  According to the present invention as described above, it is possible to realize an electrode manufacturing method in which the manufacturing process is simple and the adhesion strength of the active material layer to the base can be ensured.

The schematic diagram which shows the manufacturing apparatus of one Embodiment of this invention. The schematic diagram which shows the electrostatic coating in the said embodiment. The schematic diagram which shows the coating result by the said embodiment. The graph which shows the relationship between the binder weight% in the said embodiment, and an average particle diameter ratio. The graph which shows the relationship between the discharge capacity and binder weight% in the said embodiment. The graph which shows the relationship between the contact | adhesion intensity | strength and stirrer rotation speed in the said embodiment. The schematic diagram which shows the conventional active material layer. The schematic diagram which shows the electrostatic coating using a small diameter binder. The schematic diagram which shows the coating result by the electrostatic coating of the said FIG.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows an electrode manufacturing apparatus 1 for manufacturing an electrode according to the present invention.
The electrode manufacturing apparatus 1 manufactures an electrode 70 (see FIG. 3) having an active material layer 72 including an active material 73 and a binder 74 on the surface of a base 71. A landing part 4 and a winding part 5 are provided.

As described above, the creating unit 2 mixes the powder of the active material 73 and the powder of the binder 74 to create the mixed powder 75.
The preparation unit 2 includes an active material tank 22 and a binder tank 23 at the upper part of the gantry 21, and includes a stirrer 24 and a metering feeder 25 below each of them, and pneumatic transportation from the lower part of the gantry 21 to the coating unit 3. A machine 26 is provided.

  The active material tank 22 stores powder of the active material 73 and supplies the active material 73 to the stirrer 24. As the active material 73, a carbon material such as natural graphite or artificial graphite is used for a cathode, and lithium manganate is used for a positive electrode. Carbon black or the like may be added to the active material 73 as a conductive aid.

The binder tank 23 stores the powder of the binder 74 and supplies the binder 74 to the agitator 24. PVDF (polyvinylidene fluoride) is used as the binder 74.
Although details will be described later, the particle size of the binder 74 is smaller than the particle size of the active material 73.

The stirrer 24 is provided with a rotating blade (not shown) inside a stirring tank having a closed structure, and strongly strengthens the active material 73 and the binder 74 supplied from the active material tank 22 and the binder tank 23. Mix to produce a mixed powder 75.
The stirrer 24 can adjust the rotation speed of the rotary blade, and the rotary blade can obtain the desired triboelectric charge on each particle of the mixed powder 75 (particles of the active material 73 and particles of the binder 74). So that the rotation speed is adjusted.

The fixed amount feeder 25 feeds the mixed powder 75 generated by the stirrer 24 by a predetermined amount per time.
The pneumatic transporter 26 conveys the mixed powder 75 sent out from the fixed amount feeder 25 by an air flow supplied from the outside, and supplies it to the coating unit 3.

  The preparation unit 2 creates a mixed powder 75 in which the active material 73 and the binder 74 are mixed, and the created mixed powder 75 has positive and negative particles in the active material 73 and the binder 74. It is charged and sent out in a state where the particles of the binder 74 having a small particle diameter are electrostatically adsorbed on the particle surface of the active material 73 having a large particle diameter (see FIG. 2).

The coating unit 3 performs dry coating of the mixed powder 75 on the surface of the base 71.
The coating unit 3 includes an unwinder 32 at the upper part of the gantry 31, and includes a roller group 33 that conveys the base 71 fed from the unwinder 32 from the upper part to the lower part of the gantry 31. A painting booth 34 that surrounds a vertically extending base 71 is installed inside the gantry 31, and a dust collector 36 and an electrode 35 for electrostatic painting are installed in the painting booth 34.

The unwinder 32 is provided with a base 71 wound in a coil shape, and the base 71 is continuously drawn out from the coil. As the base 71, a copper foil is used for the negative electrode, and an aluminum foil is used for the positive electrode. These foils are supplied as a belt-like sheet having a thickness of several tens of μm and a width of several hundreds of mm.
The roller group 33 is configured to guide the base 71 drawn out from the unwinder 32, send it in the vertical direction in the gantry 31, and send it out to the fusion part 4 as a subsequent process.

The painting booth 34 has a closed structure that surrounds the base 71 stretched in the vertical direction in the gantry 31 and shields it from the outside air.
Air containing the mixed powder 75 is supplied to the lower part of the coating booth 34 by the air transporter 26 of the preparation unit 2.

The electrodes 35 are arranged on the inner wall surface of the painting booth 34 and face the painting surface side of the base 71 at a predetermined interval. A high voltage is applied between the electrode 35 and the base 71 from an external power supply device (not shown).
When the air containing the mixed powder 75 supplied to the lower part of the coating booth 34 passes between the electrode 35 and the base 71, the mixed powder 75 is charged, and the charged mixed powder 75 is electrostatically adsorbed on the surface of the base 71. Thus, the active material layer 72 is formed.

As shown in FIG. 2, in the mixed powder 75 electrostatically adsorbed on the base 71, the binder 74 having a small particle size is attached to the surface of the particle of the active material 73 having a large particle size by static electricity. These are electrostatically attracted to the base 71 as integral particles. For this reason, the bias | inclination of the component in the active material layer 72 like the past does not arise, and the active material 73 can be reliably bound by the minimum binding material 74.
The dust collector 36 is installed in the upper part of the painting booth 34, sucks the air for conveyance in the painting booth 34, collects the dust, and discharges it outside.

By such a coating part 3, the active material layer 72 can be formed by electrostatically coating the mixed powder 75 on the surface of the base 71 that is continuously fed.
The base 71 having the active material layer 72 formed on the surface is continuously sent to the fusion part 4.

The fused part 4 is used to heat and press the coated active material layer 72 to be fused to the surface of the base 71.
The fusion unit 4 includes a heating device 41 that heats the base 71 continuously sent from the coating unit 3, and a roll press 42 that presses and fixes the heated active material layer 72 to the base 71.

In such a fused portion 4, the heating device 41 can fuse the binding material 74 in the active material layer 72 to securely bind the active material 73. Furthermore, the inter-particle gap of the active material 73 can be compressed by pressing the softened binder 74 by the roll press 42, and the volume density of the active material 73 can be increased.
After such fusion, the base 71 having the active material layer 72 fused on the surface is used as the electrode 70 (see FIG. 3).
The winding unit 5 includes a winding machine 51 and can wind up the electrode 70 formed by the fusion unit 4 in a coil shape.

In the present embodiment, specific conditions based on the present invention are applied to the active material 73 and the binder 74.
In this embodiment, the active material 73 and the binder 74 mixed as the mixed powder 75 are 85 to 95% by weight of the active material 73 and 15 to 5% by weight of the binder 74. This is a range where suitable electrical characteristics can be obtained when the electrode 70 is used, and adhesion strength is suitable.

The average particle size of the particles of the binder 74 is set smaller than the average particle size of the particles of the active material 73, and the average particle size ratio = the average particle size of the binder 74 / the average particle size of the active material 73 is 0. 2 to 0.7 (0.2 to 0.7) (see FIG. 4).
The average particle size of graphite used for the active material 73 is generally about 5 to 30 μm. On the other hand, the average particle size of PVDF used for the binder 74 is generally 150 to 200 μm. For this reason, when using as the binder 74, it grind | pulverizes from several micrometers to about several tens of micrometers previously with a grinder, and it adjusts so that it may become the average particle diameter ratio mentioned above.

In addition, although the binder 74 in the mixed powder 75 is 15 to 5% by weight, the lower limit of the preferable binder 74 is not necessarily 5% by weight in the graph of FIG.
When the average particle size ratio of the binder 74 is 0.2 with respect to the active material 73, the lower limit of the binder 74 may be 5% by weight. However, as the average particle size ratio increases, it becomes difficult to enter between the active materials 73, so that more binders 74 are required for the same active material 73. For this reason, the lower limit of the preferable binder 74 increases as the average particle size ratio increases, and it is desirable to ensure 10% by weight of the binder 74 when the average particle size ratio is 0.7 (FIG. 4). Bottom curve).
More preferably, the binder 74 is 8% by weight or more when the average particle size ratio is 0.2, and the binder 74 is 15% by weight or more when the average particle size ratio is 0.7 (FIG. 4). Upper curve).

Here, in setting the component ratio of the binder 74, it is desirable to consider the relationship with the discharge capacity produced using the electrode 70.
As shown in FIG. 5, when the ratio (horizontal axis) of the binder 74 in the mixed powder 75 increases, the ratio of the active material 73 relatively decreases, so that the discharge capacity (vertical axis) tends to decrease. .

When stirring the mixed powder 75 in the stirrer 24, the rotational speed of the rotating blades of the stirrer 24 is set so that the desired frictional charge is generated in the particles of the active material 73 and the binder 74 in the mixed powder 75. Adjust.
Actually, it is difficult to measure the state of frictional charging in the particles of the active material 73 and the particles of the binder 74 in the mixed powder 75. Therefore, it is desirable to actually manufacture the electrode 70 under some condition settings and evaluate the adhesion strength of the active material layer 72.

In FIG. 6, as a result of manufacturing the electrode 70 by changing the rotation speed with the electrode manufacturing apparatus 1 of this embodiment, the rotation speed of the blades (300 mm diameter) of the stirrer 24 increases as the rotation speed increases from 700 rpm (rotation speed per minute). It was found that the adhesion strength of the material layer 72 gradually increased, and the improvement of the adhesion strength was sharp from around 1300 rpm, and that the strength of 2 to 3 times the adhesion strength near 1300 rpm was obtained at 1500 rpm or higher.
In addition, since a crack may arise in an active material when rotation speed exceeds 1700 rpm, it is desirable to use below this rotation speed.

As described above, according to the present embodiment, the powder of the active material 73 and the powder of the binder 74 are frictionally charged by stirring before the mixed powder 75 is applied to the surface of the base 71, and the average particle The particles of the binder 74 having a small diameter ratio are attached around the particles of the active material 73. By coating the surface of the base 71 in such an attached state, the active material layer 72 formed on the surface of the base 71 is not biased between the active material 73 and the binder 74, and heat fusion is performed. Thus, the electrode 70 having the strong active material layer 72 can be obtained.
Thereby, the electrode 70 in which the manufacturing process is simple and the adhesion strength of the active material layer 72 to the base 71 is ensured can be manufactured.

Note that the present invention is not limited to the above-described embodiment, and modifications and the like within a scope in which the object of the present invention can be achieved are included in the present invention.
For example, as the active material 73, other metal oxides such as lithium nickelate or lithium cobaltate may be used in addition to lithium manganate for the positive electrode. Moreover, although a conductive support agent may be added to the active material 73, the conductive support agent is not limited to graphite but may be other conductive materials.

The binder 74 is not limited to PVDF, and PTEF (tetrafluoroethylene) may be used, or other thermoplastic resin suitable for heat fusion may be used.
In the electrode manufacturing apparatus 1, each component of the creation unit 2, the coating unit 3, the fusion unit 4, and the winding unit 5 may be appropriately changed or may include other additional elements.
In the above-described embodiment, when the stirrer 24 is installed in the preparation unit 2 of the electrode manufacturing apparatus 1 and the mixed powder 75 is generated, the friction material electrification by stirring is used to apply the binder 74 to the powder of the active material 73. The powder was bound.
On the other hand, you may perform the process which combines the powder of the binder 74 with the powder of the active material 73 mechanochemically.

As a reference form not included in the present invention , in the preparation unit 2 of the electrode manufacturing apparatus 1 of FIG. 1 described above, a mechanofusion apparatus (for example, “Hybridization System NHS” manufactured by Nara Seisakusho Co., Ltd.) is used instead of the stirrer 24. Alternatively, a “circulating mechanofusion system AMS” apparatus manufactured by Hosokawa Micron Corporation can be installed.
According to this reference embodiment, the mechanofusion device, a powder of powder and binder 74 of active material 73 mechanochemically bound, Ru can be generated as a mixed powder 75.

  The present invention is a method for manufacturing an electrode, and can be used for manufacturing an electrode used in a lithium ion battery or the like.

DESCRIPTION OF SYMBOLS 1 ... Electrode manufacturing apparatus 2 ... Creation part 21 ... Base 22 ... Active material tank 23 ... Binder tank 24 ... Stirrer 25 ... Fixed quantity supply machine 26 ... Air transporter 3 ... Coating part 31 ... Base 32 ... Unwinder 33 ... Roller group 34 ... Painting booth 35 ... Electrode 36 ... Dust collector 4 ... Fusion part 41 ... Heating device 42 ... Roll press 5 ... Winding part 51 ... Winding machine 70 ... Electrode 71 ... Base 72 ... Active material layer 73 ... Active Substance 74 ... Binder 75 ... Mixed powder

Claims (2)

In order to manufacture an electrode having an active material layer including an active material and a binder on the surface of the base, a powder mixture is prepared by mixing the powder of the active material and the powder of the binder, and the mixed powder Electrostatic coating on the surface of the base, and a method of manufacturing an electrode for heating and fusing the coated mixed powder,
The average particle size ratio of the binder powder to the active material powder is 0.7 or less,
Before applying the mixed powder to the base surface and a powder of the powder and the binder of the active material, introduced into a stirrer having rotating blades, it generates the mixed powder by stirring, the mixture A method for producing an electrode, comprising performing a process of bonding the powder of the active material in the powder and the powder of the binder by frictional charging. In the manufacturing method of the electrode of Claim 1,
The mixed powder comprises 85 to 95% by weight of the active material and 15 to 5% by weight of the binder.

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