JP2017228398A - Manufacturing method of negative electrode for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of the negative electrode for secondary battery in which generation of sheer is suppressed, and adjustment width of roller cavity is wide.SOLUTION: A wet powder 101 containing a negative electrode active material is prepared. A powder layer 102 is formed by supplying the wet powder 101 to a first roller cavity 21. A negative electrode material layer 103 is formed on the surface of a current collector foil 104, by supplying the powder layer 102 and current collector foil 104 to a second roller cavity 22. Average grain size D50(μm), maximum particle size Dmax(μm), and tap density ρ (g/cm) of the negative electrode material, and the basis weight Cw(mg/cm) of the negative electrode material layer satisfy expression (I):D50×ρ÷Cw≤2.9, and expression (II):Dmax×ρ÷Cw<9.3.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a method for manufacturing a negative electrode for a secondary battery.

  JP 2014-165156 A (Patent Document 1) discloses a method of forming a negative electrode mixture layer on the surface of a current collector foil by supplying a negative electrode mixture paint and a current collector foil to a roll gap. Yes.

JP 2014-165156 A

  Conventionally, a negative electrode for a secondary battery (hereinafter sometimes simply referred to as “negative electrode”) is manufactured by applying a negative electrode mixture coating material on the surface of a current collector foil. In general, the coating is performed by a slot die method. With the slot die method, high viscosity paint cannot be applied. Therefore, a large amount of solvent is consumed to adjust the viscosity of the paint. In order to dry the paint after coating, a large-scale drying facility is also required.

  As the solvent amount of the paint is decreased, the paint eventually becomes wet powder (hereinafter referred to as “wet powder”). If this wet powder can be applied to the surface of the current collector foil, the solvent cost and the drying cost can be reduced as compared with the slot die method described above.

  As a wet powder coating method, a method of forming and transferring a film by supplying wet powder and a current collector foil to the gap between the rolls is conceivable. However, this method has room for improvement in the following points. That is, when the roll gap is narrowed, particles are likely to clog the roll gap. When particles are clogged in the roll gap, a portion where the negative electrode mixture is missing (a defect called “through”) occurs. Since the negative electrode including the sheer causes a voltage defect or the like, it cannot be used for the secondary battery. By increasing the roll gap, the occurrence of see-through tends to be suppressed. However, if the roll gap is widened, the wet powder is difficult to adhere to the surface of the current collector foil, making it difficult to manufacture the negative electrode itself.

  The basis weight of the negative electrode mixture layer (the mass of the negative electrode mixture layer per unit area) is changed according to the required characteristics of the secondary battery. However, when wet powder is used, the range of the basis weight is narrowly limited. In particular, it is very difficult to produce a negative electrode with a small basis weight. This is because, as described above, the adjustment width of the roll gap in which the negative electrode can be manufactured without causing the see-through is narrow.

  Then, this indication aims at providing the manufacturing method of the negative electrode for secondary batteries by which generation | occurrence | production of a see-through is suppressed and the adjustment width | variety of a roll gap | interval is wide.

In the manufacturing method of the negative electrode for secondary batteries of this indication, the negative electrode for secondary batteries is manufactured with the following coating devices.
The coating apparatus includes a first rotating roll, a second rotating roll, and a third rotating roll. The first rotating roll, the second rotating roll, and the third rotating roll have rotation axes parallel to each other. A first roll gap is formed between the first rotating roll and the second rotating roll. A second roll gap is formed between the second rotating roll and the third rotating roll.
The manufacturing method of the negative electrode for secondary batteries of this indication contains the following (a)-(c).
(A) preparing a wet powder containing a negative electrode active material;
(B) Forming a powder layer by supplying wet powder to the first roll gap.
(C) A negative electrode mixture layer is formed on the surface of the current collector foil by supplying the powder layer and the current collector foil to the second roll gap.
In the method for producing a negative electrode for a secondary battery of the present disclosure, the average particle diameter D50 [μm] of the negative electrode active material, the maximum particle diameter Dmax [μm] of the negative electrode active material, and the tap density ρ [g / cm ³ ] of the negative electrode active material. The negative electrode for a secondary battery is manufactured so that the basis weight Cw [mg / cm ² ] of the negative electrode composite material layer satisfies the following formulas (I) and (II).
D50 × ρ ÷ Cw ≦ 2.9 (I)
Dmax × ρ ÷ Cw <9.3 (II)

  In the manufacturing method of the present disclosure, a negative electrode active material having a moderately low tap density ρ is used. The first roll gap is set wider within the range in which the powder layer can be formed. Thus, a thick powder layer having a low density is formed in the first roll gap. The powder layer is transferred to the surface of the current collector foil by the second roll gap. Thereby, a negative electrode composite material layer is formed.

  Since the powder layer is once leveled by the first roll gap, clogging of particles is unlikely to occur in the second roll gap. That is, even if the second roll gap is narrowed, the see-through hardly occurs. As described above, the powder layer has a low density (mass per unit volume). Therefore, when the powder layer is appropriately compressed, a negative electrode mixture layer with a small basis weight (mass per unit area) can be formed.

  Since the powder layer is thick, the second roll gap can be widened. That is, even if the second roll gap is wide, a force is applied to the powder layer and the current collector foil, so that the powder layer can be transferred to the surface of the current collector foil. Thus, according to the manufacturing method of the negative electrode for secondary batteries of this indication, the adjustment width | variety of a roll gap | interval expands.

  However, the above formulas (I) and (II) need to be satisfied. The left sides of the above formulas (I) and (II) are factors that affect the occurrence of see-through (average particle size D50 and maximum particle size Dmax), and factors that affect the difficulty of transferring the powder layer (tap density ρ and Weight per unit area Cw). When the left side of the formula (I) is 2.9 or less and the left side of the formula (II) is less than 9.3, the occurrence of see-through is suppressed and the adjustment range of the roll gap is expanded.

It is a flowchart which shows the outline of the manufacturing method of the negative electrode for secondary batteries which concerns on embodiment of this indication. It is a schematic sectional view showing an example of composition of a coating device concerning an embodiment of this indication.

  Hereinafter, an embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit the invention of the present disclosure.

<Method for producing negative electrode for secondary battery>
FIG. 1 is a flowchart showing an outline of a method for manufacturing a secondary battery negative electrode according to the present embodiment. The manufacturing method of the present embodiment includes wet powder preparation 201, powder layer formation 202 and negative electrode mixture layer formation 203. In the manufacturing method of the present embodiment, typically, a negative electrode for a lithium ion secondary battery is manufactured. However, the negative electrode for a secondary battery produced in the present embodiment is not necessarily limited to a lithium ion secondary battery.
Hereinafter, the manufacturing method of this embodiment will be described in order.

<< Preparation of Wet Powder 201 >>
The manufacturing method of this embodiment includes preparing a wet powder containing a negative electrode active material.
The wet powder is prepared by mixing a negative electrode active material, a binder, and a solvent. For mixing, a general powder mixing apparatus can be used. For example, a planetary mixer, a high speed mixer (product name, manufactured by Earth Technica) or the like can be used. The mixing conditions (rotation speed of the stirring blade, mixing time, etc.) are appropriately adjusted according to the amount of processing.

  The wet powder is prepared, for example, to have a solid content ratio of 63% by mass or more. The “solid content ratio” is a mass ratio of components other than the solvent. The solid content ratio may be 65% by mass to 85% by mass, 67% by mass to 80% by mass, or 70% by mass to 80% by mass. The solvent type is appropriately selected according to the binder type. The solvent may be, for example, ion exchange water.

  The negative electrode active material typically includes graphite. The graphite may be natural graphite or artificial graphite. The negative electrode active material may include, for example, non-graphitizable carbon, graphitizable carbon, and the like.

  In order to suppress the occurrence of see-through, the negative electrode active material desirably has a small average particle diameter D50. The average particle size D50 indicates a particle size of 50% cumulative from the fine particle side in the volume-based cumulative particle size distribution. The average particle diameter D50 is preferably 10 μm or more and 20 μm or less.

  In order to suppress the occurrence of see-through, the negative electrode active material desirably has a small maximum particle diameter Dmax. The maximum particle size Dmax indicates a 99% cumulative particle size (D99) from the fine particle side in the volume-based cumulative particle size distribution. The maximum particle size Dmax is preferably 40 μm or more and 80 μm or less. The average particle diameter D50 and the maximum particle diameter Dmax are measured by a laser diffraction / scattering method.

In order to form a thick powder layer having a low density, the negative electrode active material desirably has a low tap density ρ. The tap density [rho, preferably not more than 1.00 g / cm ³ or more 1.15 g / cm ^3, more preferably not more than 1.00 g / cm ³ or more 1.12 g / cm ^3, even more preferably 1. It is 00 g / cm ³ or more and 1.07 g / cm ³ .

  The tap density ρ is measured as follows. A 100 ml graduated cylinder is prepared. The mass of the graduated cylinder is measured. The negative electrode active material is sufficiently dried. 100 ml of the negative electrode active material is put into the measuring cylinder. The mass M of 100 ml of the negative electrode active material is measured. The opening of the measuring cylinder is closed with a rubber plug. The measuring cylinder is tapped 250 times on the rubber plate. The tapping is performed so that the measuring cylinder naturally falls from a height of about 5 cm. The volume V of the compressed negative electrode active material is read. By dividing the mass M by the volume V, the tap density ρ is calculated.

  The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyacrylic acid (PAA), and the like. The amount of the binder may be, for example, about 0.5 to 3 parts by mass with respect to 100 parts by mass of the negative electrode active material.

<< Formation of Powder Layer 202 and Formation of Negative Electrode Mixing Layer 203 >>
The formation 202 of the powder layer and the formation 203 of the negative electrode mixture layer are performed by a coating apparatus. Here, first, the coating apparatus will be described.

FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the coating apparatus according to the present embodiment.
The coating apparatus 10 includes a first rotating roll 11, a second rotating roll 12, and a third rotating roll 13. The first rotating roll 11, the second rotating roll 12, and the third rotating roll 13 have rotation axes that are parallel to each other. The 1st rotation roll 11, the 2nd rotation roll 12, and the 3rd rotation roll 13 are rotationally driven in the direction of the arrow drawn on each roll. The length of each arrow indicates the peripheral speed of each roll. The longer the arrow, the faster the peripheral speed. The wet powder 101 (and the powder layer 102) moves from a rotating roll having a relatively low peripheral speed to a rotating roll having a relatively high peripheral speed.

  In FIG. 1, the roll diameter increases in the order of the first rotary roll 11, the second rotary roll 12, and the third rotary roll 13. However, each roll diameter may not satisfy such a relationship. For example, the first rotating roll 11, the second rotating roll 12, and the third rotating roll 13 may all be the same diameter roll.

  The coating apparatus 10 includes a hopper 14. The hopper 14 is filled with wet powder 101. A first roll gap 21 is formed between the first rotary roll 11 and the second rotary roll 12. The hopper 14 supplies the wet powder 101 to the first roll gap 21. The wet powder 101 is formed into the powder layer 102 by the first roll gap 21.

  That is, the method for manufacturing a negative electrode for a secondary battery according to the present embodiment includes forming the powder layer 102 by supplying the wet powder 101 to the first roll gap 21. For example, the first roll gap 21 is adjusted within a range of 40 μm to 150 μm.

  A second roll gap 22 is formed between the second rotary roll 12 and the third rotary roll 13. The second rotating roll 12 supplies the powder layer 102 to the second roll gap 22. The third rotating roll 13 supplies the current collector foil 104 to the second roll gap 22. The current collector foil 104 may be a copper (Cu) foil, for example. The current collector foil 104 has a thickness of, for example, 5 μm or more and 20 μm or less. In the second roll gap 22, the powder layer 102 is transferred to the surface of the current collector foil 104. Thereby, the negative electrode mixture layer 103 is formed.

  That is, in the method for manufacturing a negative electrode for a secondary battery of the present embodiment, the negative electrode mixture layer 103 is formed on the surface of the current collector foil 104 by supplying the powder layer 102 and the current collector foil 104 to the second roll gap 22. Forming. The second roll gap 22 is adjusted, for example, within a range of 50 μm to 100 μm.

Thereafter, the negative electrode mixture layer 103 may be dried, or the negative electrode mixture layer 103 may be rolled. In this embodiment, since the solid content ratio of the wet powder 101 is high, drying and rolling may be substantially unnecessary. After the negative electrode mixture layer 103 is formed on one surface of the current collector foil 104, the negative electrode mixture layer 103 may be further formed on the other surface of the current collector foil 104. That is, the negative electrode mixture layer 103 may be formed on both surfaces of the current collector foil 104.
From the above, the negative electrode 100 is manufactured.

The basis weight of the negative electrode mixture layer 103 is measured in a state where substantially all of the solvent is evaporated. In the present embodiment, the negative electrode mixture layer 103 with a small basis weight can be formed. The negative electrode mixture layer 103 may be formed, for example, to have a basis weight of 8 mg / cm ² or less, may be formed to have a basis weight of 7 mg / cm ² or less, or 6 mg / cm 2. ^It may be formed to have a basis weight of ² or less. Negative electrode composite material layer 103 may be formed to have a basis weight of, for example, 5 mg / cm ² or more.

  In this embodiment, the negative electrode 100 is manufactured so that the above formulas (I) and (II) are satisfied. Therefore, the occurrence of see-through is suppressed, and the adjustment width of the roll gap is wide. The left side “D50 × ρ ÷ Cw” of the above formula (I) is preferably 1.2 or more and 2.5 or less. The left side “Dmax × ρ ÷ Cw” of the formula (II) is preferably 5.4 or more and 9.2 or less.

<Manufacture of negative electrode for secondary battery>
Examples will be described below. However, the following examples do not limit the invention of the present disclosure.

Example 1
The following materials were prepared:
Negative electrode active material: Natural graphite Binder: CMC
Solvent: Ion exchange water Current collector foil: Cu foil

  The average particle diameter D50, maximum particle diameter Dmax, and tap density ρ of natural graphite were measured by the method described above. The results are shown in Table 1 below.

1. Preparation of wet powder 201
The wet powder 101 was prepared by mixing the negative electrode active material, the binder, and the solvent. The solid content ratio of the wet powder 101 was 70% by mass. The solid content was “negative electrode active material: binder = 99: 1” by mass ratio.

2. Formation of powder layer 202 and formation of negative electrode mixture layer 203
A coating apparatus 10 shown in FIG. 2 was prepared. The hopper 14 was filled with the wet powder 101. The wet powder 101 was supplied to the first roll gap 21. Thereby, the powder layer 102 was formed. The powder layer 102 and the current collector foil 104 were supplied to the second roll gap 22. Thereby, the negative electrode mixture layer 103 was formed on the surface of the current collector foil 104. In Example 1, the second roll gap 22 was set to 90 μm. From the above, the negative electrode 100 according to Example 1 was manufactured.

  In the negative electrode 100, the presence or absence of see-through was confirmed by visual observation. In the negative electrode 100 of Example 1, no see-through was confirmed. The basis weight of the negative electrode mixture layer 103 was measured. The results are shown in Table 1 below.

<< Examples 2 to 13 and Comparative Examples 1 to 6 >>
Natural graphite having an average particle diameter D50, a maximum particle diameter Dmax and a tap density ρ shown in Table 1 below was prepared. As shown in Table 1 below, the second roll gap 22 was changed. Except these, the negative electrode 100 which concerns on Examples 2-13 and Comparative Examples 1-6 was manufactured by the same procedure as Example 1. FIG. Each negative electrode 100 was confirmed to be transparent. The results are shown in Table 1 below.

  As shown in Table 1, in the example in which the left side of the formula (I) is 2.9 or less and the left side of the formula (II) is less than 9.3, the occurrence of see-through is suppressed. It was. In contrast, in the comparative example in which the left side of the above formula (I) exceeds 2.9 or the left side of the above formula (II) is 9.3 or more, show-through has occurred. Further, in the example, the adjustment width of the second roll gap 22 was wider than that in the comparative example.

  The embodiments and examples disclosed herein are illustrative in all aspects and should not be construed as being restrictive. The scope of the invention of the present disclosure is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  DESCRIPTION OF SYMBOLS 10 Coating apparatus, 11 1st rotating roll, 12 2nd rotating roll, 13 3rd rotating roll, 14 hopper, 21 1st roll gap | interval, 22 2nd roll gap | interval, 100 negative electrode, 101 wet powder, 102 powder layer , 103 negative electrode composite material layer, 104 current collector foil, 201 preparation of wet powder, 202 formation of powder layer, 203 formation of negative electrode composite material layer.

Claims (1)

A first rotating roll, a second rotating roll, and a third rotating roll;
The first rotating roll, the second rotating roll, and the third rotating roll have rotation axes parallel to each other,
A first roll gap is formed between the first rotating roll and the second rotating roll;
A secondary battery negative electrode manufacturing method for manufacturing a secondary battery negative electrode by a coating apparatus, wherein a second roll gap is formed between the second rotary roll and the third rotary roll.
Preparing a wet powder containing a negative electrode active material;
Supplying the wet powder to the first roll gap to form a powder layer; and supplying the powder layer and the current collector foil to the second roll gap to supply the current collector. Forming a negative electrode mixture layer on the surface of the foil;
Including
Average particle size D50 [μm] of the negative electrode active material, maximum particle size Dmax [μm] of the negative electrode active material, tap density ρ [g / cm ³ ] of the negative electrode active material, and basis weight of the negative electrode mixture layer The negative electrode for a secondary battery is produced so that Cw [mg / cm ² ] satisfies the following formulas (I) and (II):
A method for producing a negative electrode for a secondary battery.
D50 × ρ ÷ Cw ≦ 2.9 (I)
Dmax × ρ ÷ Cw <9.3 (II)

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