JP2015207453A - Method for manufacturing electrode for nonaqueous electrolyte secondary batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electrode for nonaqueous electrolyte secondary batteries, which includes an electrode active material layer having a laminate structure including a pattern layer, has a desired pattern, and enables the stable formation of a pattern layer having satisfying surface flatness and satisfying in-plane uniformity in film thickness.SOLUTION: A method for manufacturing an electrode for nonaqueous electrolyte secondary batteries comprises the steps of: (A) forming a first paste layer 121P for an unpatterned layer, (B) drying at least a part of a front-side surface of the first paste layer 121P into a dried part 121D, and (C) performing a pattern print of a second paste layer 122P for a patterned layer, sequentially. Supposing that the cavity volume fraction of the dried part 121D is P(%), and the liquid component volume fraction of the second paste layer 122P immediately after the application thereof is L(%), the steps (B) and (C) are performed under the condition that the following expression is satisfied: 45%≤P/L×100(%)≤59%.

Description

  The present invention relates to a method for producing an electrode for a nonaqueous electrolyte secondary battery.

Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are used in hybrid vehicles (HV), plug-in hybrid vehicles (PHV), electric vehicles (EV), and the like.
A nonaqueous electrolyte secondary battery includes a positive electrode and a negative electrode that are a pair of electrodes, a separator that insulates between them, and a nonaqueous electrolyte.
As a structure of the electrode (positive electrode or negative electrode) for the nonaqueous electrolyte secondary battery, a structure including a current collector and an electrode active material layer (positive electrode active material layer or negative electrode active material layer) formed thereon is known. It has been.
The positive electrode active material layer is, for example, coated on a current collector such as an aluminum foil with a paste containing a positive electrode active material containing Li or the like and a dispersant such as N-methyl-2-pyrrolidone (NMP) and dried. , Formed by pressing.
The negative electrode active material layer is formed by, for example, applying a paste containing a negative electrode active material containing carbon and a dispersant such as water on a current collector such as copper foil, drying, and pressing. .

Considering the improvement in energy density, the electrode active material layer is preferably a thick film and a high density.
In order to increase the thickness of the electrode active material layer, the electrode active material layer can have a laminated structure.
Conventionally, when the electrode active material layer has a laminated structure, there is a method of repeating the application and drying of the electrode active material layer paste by the number of layers. Patent Document 1 also discloses a method of drying a plurality of paste layers at once after applying the electrode active material layer paste a plurality of times in order to simplify the process (Claim 1).

JP 2011-210478 A

Even if the electrode active material layer is made thicker and densified by the laminated structure, the conductivity of conductive ions such as Li ions decreases due to the increase in the thickness of the electrode active material layer and the decrease in voids. It is difficult to obtain an increase in battery capacity commensurate with the total thickness of the layers.
When the electrode active material layer has a laminated structure, the conductivity of conductive ions such as Li ions can be improved by providing at least one, preferably a plurality of through holes in at least one layer. The paste layer having a through hole can be formed by pattern printing by screen printing or the like.
However, since a paste containing a liquid component such as N-methyl-2-pyrrolidone (NMP) or water is fluid, even if a paste layer having a desired pattern having a through hole is formed, the paste is immediately after coating to drying. There is a risk that the pattern will collapse due to leveling.
If the amount of the liquid component in the paste is reduced, leveling can be suppressed, but the coating property and leveling property are deteriorated, and the surface flatness and the in-plane uniformity of the film thickness may be deteriorated. This may cause in-plane variations in electrode characteristics, which is not preferable.
The “surface flatness of the layer” referred to in the present specification is the overall surface flatness excluding the portion where the through hole is formed. Similarly, “in-plane uniformity of film thickness” is the in-plane uniformity of the overall film thickness excluding the portion where the through hole is formed.

  The present invention has been made in view of the above circumstances, includes an electrode active material layer having a laminated structure including a pattern layer, has a desired pattern, and has excellent surface flatness and in-plane uniformity of film thickness. It aims at providing the manufacturing method of the electrode for nonaqueous electrolyte secondary batteries which can form a pattern layer stably.

The method for producing an electrode for a non-aqueous electrolyte secondary battery of the present invention is as follows:
Using a paste containing an electrode active material and a dispersant, a non-aqueous solution for forming an electrode active material layer having a multilayer structure including a non-pattern layer and a pattern layer formed on the non-pattern layer on a current collector A method for producing an electrode for an electrolyte secondary battery, comprising:
Forming a first paste layer for the non-pattern layer (A);
A step (B) of drying at least a part of the first paste layer on the surface side to form a drying unit;
(C) sequentially printing the second paste layer for the pattern layer,
When the void volume ratio of the dry part is P (%) and the liquid component volume ratio immediately after the application of the second paste layer is L (%), the conditions satisfy the following formula (1-1): Step (B) and step (C) are performed.
45% ≦ P / L × 100 (%) ≦ 59% (1-1)

In the present invention, “the void volume ratio of the drying section” is determined by the volume of the entire drying section, the density of the drying section, and the material specific gravity of the drying section.
The “liquid component volume ratio immediately after application of the second paste layer” is the liquid component volume ratio of the paste used.

If 45% ≦ P / L × 100 (%) ≦ 59%, after the second paste layer is applied, the liquid component in this layer is dried formed in the first paste layer as a base It is possible to penetrate into the voids of the part in an appropriate amount. As a result, the second paste layer has a good pattern between immediately after coating and drying, because the amount of liquid component is moderately decreased and the fluidity is moderately decreased and its leveling is moderately suppressed. Retained.
If 45% ≦ P / L × 100 (%) ≦ 59%, this layer even after the liquid component in the second paste layer has permeated into the dry part formed in the first paste layer as the base The liquid component remains moderately inside. As a result, even if the surface flatness and the in-plane uniformity of the film thickness of the second paste layer are not good immediately after coating, the second paste layer is properly leveled immediately after coating until drying. Surface flatness and in-plane uniformity of film thickness are improved.
Due to the above-described effects, according to the method for manufacturing an electrode for a nonaqueous electrolyte secondary battery of the present invention, a pattern layer having a desired pattern and having excellent surface flatness and in-plane uniformity of film thickness can be stably formed. Can be formed.

In the step (C), it is preferable to screen-print the second paste layer using a roll screen having a pattern corresponding to the pattern of the pattern layer.
The roll-shaped screen has a small contact area with the second paste layer and can be easily separated from the second paste layer. Therefore, it is possible to prevent the paste once applied from being peeled off together with the screen and to partially remove the pattern, and a pattern layer having a desired pattern can be stably formed.

In the step (B), only a part on the surface side of the first paste layer is dried to form the drying section,
When the median diameter of the electrode active material is D50, the thickness of the first paste layer after the step (B) is T, and the thickness of the dry part is H, the following formula (2-1) is obtained. It is preferable to implement a process (B) on the conditions to satisfy.
D50 ≦ H ≦ T × 0.7 (2-1)

  In the present specification, the “median diameter D50” is a particle diameter in which the mass of particles larger than the median diameter D50 is 50% of the mass of all particles in the particle size distribution.

  In the step (B), only a part on the surface side is dried, and the amount of liquid component is relatively large as compared with the drying part, and an undried part having relatively high fluidity can be left. . When the above formula (2-1) is satisfied, even if the second paste layer is applied with a low surface flatness due to, for example, an inclination in the width direction of a squeegee used for screen printing, it has a relatively high fluidity. Due to the presence of the drying section, the second paste layer can be naturally restored to a flat state. Thereby, even if the second paste layer is formed with low surface flatness, a pattern layer with good surface flatness and in-plane uniformity of film thickness can be stably formed.

  According to the present invention, a pattern layer having a laminated structure including a pattern layer, having a desired pattern, and having excellent surface flatness and in-plane uniformity of film thickness is stably formed. The manufacturing method of the electrode for nonaqueous electrolyte secondary batteries which can be provided can be provided.

1 is a schematic overall view illustrating a configuration example of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. It is a schematic cross section of the electrode laminated body in the nonaqueous electrolyte secondary battery of FIG. It is a schematic cross section of the electrode of one embodiment concerning the present invention. FIG. 4 is a manufacturing process diagram of the electrode shown in FIG. 3. FIG. 4 is a manufacturing process diagram of the electrode shown in FIG. 3. FIG. 4 is a manufacturing process diagram of the electrode shown in FIG. 3. FIG. 4 is a manufacturing process diagram of the electrode shown in FIG. 3. FIG. 4 is a manufacturing process diagram of the electrode shown in FIG. 3. It is a graph which shows the evaluation result of Example 1-1 and Comparative Examples 1-1 and 1-2. It is a SEM perspective photograph of the negative electrode manufactured in Example 1-1. It is a graph which shows the evaluation result of Test Examples 2-1 and 2-2.

"Nonaqueous electrolyte secondary battery"
With reference to the drawings, a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described.
FIG. 1 is a schematic overall view of the nonaqueous electrolyte secondary battery of the present embodiment.
FIG. 2 is a schematic cross-sectional view of an electrode laminate.
FIG. 3 is a schematic cross-sectional view of an electrode according to an embodiment of the present invention. The electrode shown in this figure is a positive electrode or a negative electrode in a nonaqueous electrolyte secondary battery.

As shown in FIG. 1, the nonaqueous electrolyte secondary battery 1 of the present embodiment is one in which an electrode laminate 20 and a nonaqueous electrolyte (reference number omitted) are accommodated in an exterior body (battery container) 11. . Two external terminals (plus terminal and minus terminal) 12 for external connection are provided on the outer surface of the exterior body 11.
As shown in FIG. 2, the electrode laminate 20 is formed by laminating a pair of electrodes 21 via a separator 22 that insulates them. The pair of electrodes 21 are a positive electrode 21A and a negative electrode 21B.

As shown in FIG. 3, the electrode 21 (positive electrode 21A or negative electrode 21B) has an electrode active material layer 120 having a laminated structure of a non-pattern layer (lower layer) 121 and a pattern layer (upper layer) 122 on a current collector 110. It is formed.
The non-pattern layer is a layer having no pattern, and is a so-called solid film.
The pattern layer is a layer having a pattern, and is a layer in which a portion coated with a material and a portion not coated are present.
In the present embodiment, the pattern layer 122 has at least one, preferably a plurality of through holes 122A.
In the illustrated example, the pattern layer 122 has a plurality of through holes 122A.
In the figure, reference numeral S denotes the surface of the electrode active material layer 120 (the surface of the electrode 21).
In the illustrated example, the electrode active material layer 120 has a two-layer structure, but the number of layers can be appropriately designed as long as the layer structure includes a non-pattern layer and a pattern layer formed on the non-pattern layer. . Specifically, the electrode active material layer 120 may have a plurality of non-pattern layers under the uppermost pattern layer.
In the pattern layer 122, the shape and size of each through-hole 122A are designed as appropriate. Moreover, when the pattern layer 122 has a plurality of through holes 122A, the planar arrangement pattern of the plurality of through holes 122A is appropriately designed.

In the present embodiment, since the electrode active material layer 120 has a laminated structure, the electrode active material layer 120 can be made thicker, thereby improving the energy density.
In this embodiment, since the electrode active material layer 120 includes the pattern layer 122 having at least one, preferably a plurality of through-holes 122A, even if the electrode active material layer 120 is thickened, Li The conductivity of conductive ions such as ions can be improved.

Examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery.
Hereinafter, main components will be described by taking a lithium ion secondary battery as an example.

(Positive electrode)
There is not any specific restriction on the positive electrode active material, for _{example, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNiO 2, LiNi x Co (1-x) O 2, and _{LiNi x Co y Mn (1-} x-y) O _And lithium-containing composite oxides such as ₂ (where 0 <x <1, 0 <y <1).

(Negative electrode)
The negative electrode active material is not particularly limited, and a material having a lithium storage capacity of 2.0 V or less on the basis of Li / Li + is preferably used. As the negative electrode active material, carbon such as graphite, metallic lithium, lithium alloy, transition metal oxide / transition metal nitride / transition metal sulfide capable of doping / dedoping lithium ions, and these A combination etc. are mentioned.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, known ones can be used, and liquid, gel-like or solid non-aqueous electrolytes can be used.
For example, a lithium-containing electrolyte is dissolved in a mixed solvent of a high dielectric constant carbonate solvent such as propylene carbonate or ethylene carbonate and a low viscosity carbonate solvent such as diethyl carbonate, methyl ethyl carbonate, or dimethyl carbonate. A water electrolysis solution is preferably used.
As the mixed solvent, for example, a mixed solvent of ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) is preferably used.
Examples of the lithium-containing electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiPF _n {C _k F _{(2k + 1) )} (6-n) (} n = 1~5 integer, k = 1 to 8 integer) lithium salts such as, and combinations thereof.

(Separator)
The separator may be a film that electrically insulates the positive electrode and the negative electrode and is permeable to lithium ions, and a porous polymer film is preferably used.
As the separator, for example, a porous film made of polyolefin such as a porous film made of PP (polypropylene), a porous film made of PE (polyethylene), or a laminated porous film of PP (polypropylene) -PE (polyethylene) is preferably used. It is done.

(Exterior body (battery container))
A well-known thing can be used as an exterior body.
As a type of the secondary battery, there are a cylindrical type, a coin type, a square type, a film type (laminate type), and the like, and an exterior body can be selected according to a desired type.

"Method for manufacturing electrode for non-aqueous electrolyte secondary battery"
With reference to drawings, the manufacturing method of said electrode 21 (positive electrode 21A or negative electrode 21B) for nonaqueous electrolyte secondary batteries is demonstrated.
4A to 4E are process diagrams, and each figure is a schematic cross-sectional view corresponding to FIG.

  As shown in FIG. 3, the electrode 21 (positive electrode 21A or negative electrode 21B) of the non-aqueous electrolyte secondary battery 1 of the above embodiment is formed on the current collector 110 from the non-pattern layer (lower layer) from the current collector 110 side. An electrode active material layer 120 having a laminated structure of 121 and a pattern layer (upper layer) 122 is formed.

  In this embodiment, the electrode active material layer 120 having the above-described stacked structure is formed on the current collector 110 using a paste containing an electrode active material and a dispersant.

In the positive electrode 21 </ b> A, a metal foil such as an aluminum foil is preferably used as the current collector 110.
There is not any specific restriction on the positive electrode active material, the lithium ion secondary battery, for _{example, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNiO 2, LiNi x Co (1-x) O 2, and LiNi _x Co _y Mn Examples include _(1-xy) lithium-containing composite oxides such as O ₂ (where 0 <x <1, 0 <y <1).
The paste for forming the positive electrode active material layer includes one or more positive electrode active materials described above and a dispersant such as N-methyl-2-pyrrolidone (NMP).
The paste for forming the positive electrode active material layer is preferably one or more of the positive electrode active materials described above, a conductive aid such as carbon powder, a binder such as polyvinylidene fluoride (PVDF), N- And a dispersing agent such as methyl-2-pyrrolidone (NMP).
The paste for forming the positive electrode active material layer includes a liquid component such as a dispersant such as NMP.
The amount of the liquid component in the positive electrode active material layer forming paste is not particularly limited, and may be within a range in which coating can be satisfactorily performed as in the known technique.

In the negative electrode 21 </ b> B, a metal foil such as a copper foil is preferably used as the current collector 110.
The negative electrode active material is not particularly limited, and a lithium ion secondary battery having a lithium storage capacity of 2.0 V or less on the basis of Li / Li + is preferably used. As the negative electrode active material, carbon such as graphite, metallic lithium, lithium alloy, transition metal oxide / transition metal nitride / transition metal sulfide capable of doping / dedoping lithium ions, and these A combination etc. are mentioned.
The paste for forming the negative electrode active material layer includes one or more negative electrode active materials described above and a dispersant such as water.
The negative electrode active material layer forming paste is preferably one or more negative electrode active materials described above, a binder such as styrene-butadiene rubber-based polymer (SBR), carboxymethylcellulose Na salt (CMC), and the like. A thickener and a dispersant such as water.
Usually, a binder such as a styrene-butadiene rubber-based polymer (SBR) is used for paste production in the form of a latex containing a dispersant.
The paste for forming the negative electrode active material layer includes a liquid component such as a dispersant such as water and a dispersant in the SBR latex.
The amount of the liquid component in the paste for forming the negative electrode active material layer is not particularly limited, and may be within a range where the coating can be satisfactorily performed as in the known technique.

  The composition or liquid component amount of the paste for the non-pattern layer 121 and the paste for the pattern layer 122 may be the same or non-identical, and is appropriately adjusted to satisfy the following formula (1-1).

(Process (A))
First, as shown in FIG. 4A, a paste for forming an electrode active material layer is applied onto the current collector 110 by a known method using a coating die or the like, and a first pattern for the non-pattern layer 121 is formed. A paste layer 121P is formed.

(Process (B))
Next, as shown in FIG. 4B, at least a part of the first paste layer 121P on the surface side is dried to form a drying unit 121D.
In this step, all of the first paste layer 121P may be used as the drying unit 121D, but it is preferable to dry only a part of the surface side of the first paste layer 121P to form the drying unit 121D.
In the illustrated example, the half of the surface side of the first paste layer 121P is used as the drying unit 121D.
In the figure, reference numeral 121W denotes an undried portion.

The drying method is the same as the known method, and examples thereof include a method of heating and drying using hot air or a heater.
In this step, drying of the first paste layer 121P proceeds from the side opposite to the current collector 110, that is, the exposed surface side of the first paste layer 121P. Therefore, the thickness of the drying part 121D can be adjusted as appropriate by adjusting the drying time.

(Process (C))
Next, as shown in FIGS. 4C and 4D, the second paste layer 122P for the pattern layer 122 is pattern-printed.

The pattern printing method is not particularly limited, and screen printing or the like is preferable.
In screen printing, a screen 210 having an opening pattern (not shown) corresponding to the pattern of the pattern layer 122 is used.
As the screen, a metal mesh having a linear pattern such as a lattice pattern, or a screen in which a pattern layer having an arbitrary opening pattern is formed using an emulsion containing a photosensitive agent on the metal mesh is used.
Screen printing can be performed as follows.
The screen 210 is brought into contact with the printing surface, a paste (not shown) is supplied thereon, and the paste is pressed against the screen 210 using the squeegee 220. The paste passes through the opening of the screen 210 and is applied onto the surface to be printed.

  For example, when a metal mesh having a grid-like linear pattern is used as the screen 210, the intersecting portion of the grid-like linear pattern and the vicinity thereof become the through-hole 122A of the second paste layer 122P.

The shape of the screen 210 is not particularly limited, and may be a flat plate shape or a roll shape.
As shown in the figure, it is preferable to screen-print the second paste layer 122P using a roll-shaped screen.
In this case, printing is performed by rotating the roll screen relative to the printing surface. It is preferable to fix the center position of the roll-shaped screen in a rotatable state and to translate the printing surface side while changing the contact position with respect to the roll-shaped screen.
The roll-shaped screen has a small contact area with the printing surface and can be easily separated from the printing surface. For this reason, it is possible to suppress the paste that has been applied once from being peeled off together with the screen 210 and to partially remove the pattern, and it is possible to stably form the second paste layer 122P having a desired pattern.

In this embodiment, the void volume ratio of the drying part 121D formed in the first paste layer 121P is P (%), and the liquid component volume ratio immediately after the application of the second paste layer 122P is L (%). Then, the step (B) and the step (C) are performed under the condition that satisfies the following formula (1-1).
45% ≦ P / L × 100 (%) ≦ 59% (1-1)

If 45% ≦ P / L × 100 (%) ≦ 59%, after applying the second paste layer 122P, the liquid component in this layer is formed in the first paste layer 121P as the base. It is possible to penetrate into the gap of the drying unit 121D in an appropriate amount.
Usually, the liquid component in the second paste layer 122P can permeate into the gaps in the drying section 121D immediately after coating, specifically in about several seconds.
As a result, the second paste layer 122P has a moderately reduced liquid component amount, moderately reduced fluidity, and moderately suppressed leveling. Holds well.

Usually, the surface of the second paste layer 122P immediately after coating has a surface roughness on the order of μm. For example, when the roll-shaped screen 210 is used, minute surface irregularities are generated between a portion where the roll is strongly hit and a portion where the roll is not.
If 45% ≦ P / L × 100 (%) ≦ 59%, the liquid component in the second paste layer 122P penetrates into the drying part 121D formed in the first paste layer 121P as the base. However, a moderate amount of liquid component remains in this layer. As a result, even if the surface flatness and in-plane uniformity of the film thickness of the second paste layer 122P are not good immediately after coating, the second paste layer can be obtained by appropriate leveling immediately after coating until drying. The surface flatness of 122P and the in-plane uniformity of film thickness are improved.

When P / L is less than 45, the amount of voids in the drying unit 121D that is the base is excessive with respect to the amount of liquid component in the second paste layer 122P, and thus the liquid component in the second paste layer 122P is the base. It cannot penetrate well into the gaps of the drying part 121D. As a result, the fluidity in the second paste layer 122P does not deteriorate satisfactorily, and the pattern may be destroyed after applying the paste by leveling, and the through-holes may be blocked or reduced.
When P / L exceeds 59, the amount of voids in the drying unit 121D that is the base is excessive with respect to the amount of liquid component in the second paste layer 122P, so the liquid component in the second paste layer 122P is the base. It will permeate | penetrate too much into the space | gap of drying part 121D. As a result, in the case where the surface flatness and film thickness uniformity of the second paste layer 122P are not good immediately after coating, the surface flatness and film thickness in-plane by leveling immediately after coating until drying. There is no improvement in uniformity.

Since the pattern layer 122 having a desired pattern and excellent surface flatness and in-plane uniformity of the film thickness can be more stably formed, the step (B) is performed under the condition satisfying the following formula (1-2). And it is preferable to implement a process (C), and it is more preferable to implement a process (B) and a process (C) on the conditions which satisfy | fill the following formula (1-3).
47% ≦ P / L × 100 (%) ≦ 57% (1-2)
50% ≦ P / L × 100 (%) ≦ 55% (1-3)

  In the present embodiment, the liquid component in the second paste layer 122P penetrates into the drying unit 121D as the base, and the amount of the liquid component in the second paste layer 122P is reduced. Therefore, in the subsequent step (D) Also, the effect of improving the drying efficiency of the second paste layer 122P can be obtained.

In the step (B), it is preferable to dry only a part on the surface side of the first paste layer 121P to form a drying unit 121D.
Further, when the median diameter of the electrode active material in the paste is D50, the thickness of the first paste layer 121P after the step (B) is T, and the thickness of the drying part 121D is H, the following formula (2 It is preferable to implement a process (B) on the conditions which satisfy -1).
D50 ≦ H ≦ T × 0.7 (2-1)

  Refer to FIG. 4B for the film thickness T of the first paste layer 121P and the thickness H of the drying unit 121D after the step (B).

  As described above, in the step (B), only a part of the surface side is dried, and the amount of the liquid component is relatively large as compared with the drying unit 121D, and undried with relatively high fluidity. The part 121W can be left. When the above formula (2-1) is satisfied, even if the second paste layer 122P is applied with low surface flatness due to, for example, inclination in the width direction of the squeegee used for screen printing, the fluidity is relatively high. Due to the presence of the undried portion 121W, the second paste layer 122P can be naturally restored to a flat state. Thereby, even if the second paste layer 122P is formed with low surface flatness, the pattern layer 122 having good surface flatness and in-plane uniformity of film thickness can be stably formed.

When H <D50, the thickness H of the drying part 121D becomes too small, and there is a possibility that the liquid component in the second paste layer 122P in the step (C) may not sufficiently penetrate into the drying part 121D.
When H> T × 0.7, the thickness of the undried portion 121W becomes too small, and the second paste layer 122P is applied with low surface flatness due to the inclination in the width direction of the squeegee used for screen printing. In some cases, the paste layer 122P may not be sufficiently restored to a flat state.

Since the effect of stably forming the pattern layer 122 having good surface flatness and in-plane uniformity of film thickness can be obtained more stably, the process (B) is performed under the condition satisfying the following formula (2-2). Is preferably carried out, and it is more preferred that the step (B) is carried out under conditions that satisfy the following formula (2-3).
D50 ≦ H ≦ T × 0.6 (2-2)
D50 ≦ H ≦ T × 0.5 (2-3)

(Process (D), (E))
After performing the step (C), the undried portion 121W and the second paste layer 122P of the first paste layer 121P are dried by a known method (step (D)).
Finally, press working is performed by a known method (step (E)).
Through the above steps, the electrode active material layer 120 composed of the non-pattern layer 121 and the pattern layer 122 is formed.

  As described above, according to the present embodiment, the electrode active material layer 120 having a laminated structure including the pattern layer 122 is provided, has a desired pattern, and has excellent surface flatness and in-plane uniformity of film thickness. The manufacturing method of the electrode 21 for nonaqueous electrolyte secondary batteries which can form the pattern layer 122 stably can be provided.

  Examples and comparative examples according to the present invention will be described.

(Example 1-1 and Comparative Examples 1-1 and 1-2)
In Example 1-1 and Comparative Examples 1-1 and 1-2, a negative electrode in which an electrode active material layer having a laminated structure of a non-pattern layer (lower layer) and a pattern layer (upper layer) was formed on a current collector Manufactured.

Graphite (median diameter D50: 20 μm or less) as a negative electrode active material, carboxymethyl cellulose Na salt (CMC) as a thickener, latex of styrene-butadiene rubber-based polymer (SBR) as a binder, and a dispersant A negative electrode paste made of water was prepared.
In Example 1-1 and Comparative Examples 1-1 and 1-2, the mass ratio of solid content (negative electrode active material / CMC / binder) is the same for both the lower layer and the upper layer, and the amount of the dispersant is appropriately set. changed.
A metal mesh (thickness 8 μm, wire diameter 50 μm, numerical aperture 165, opening diameter 88 μm × 88 μm) having a grid-like linear pattern was prepared as a roll-shaped screen.

A negative electrode paste was applied on a copper foil as a current collector to form a first paste layer for a non-pattern layer (step (A)). The coating thickness of the first paste layer was in the range of 30 to 80 μm.
Next, using hot air, at least a part of the first paste layer was dried to form a drying section (step (B)). The drying temperature was about 100 ° C. and the drying time was 1 minute or longer. The drying time was changed as appropriate.

Next, the negative paste is screen-printed on the first paste layer after the step (B) using the roll-shaped screen to form a second paste layer for the pattern layer (step (step ( C)). The coating thickness of the second paste layer was in the range of 30 to 80 μm.
When the roll-shaped screen is used, the crossing portion of the lattice-like linear pattern and the vicinity thereof become the through holes of the second paste layer.
After the application of the second paste layer, the undried portion of the first paste layer and the second paste layer were dried using hot air (step (D)). The drying temperature was about 100 ° C., and the drying time was 1 minute or longer.
The thickness after drying of a non-pattern layer and a pattern layer was in the range of 10-60 micrometers.
Finally, press working was performed by a known method to produce a negative electrode.

In Example 1-1 and Comparative Examples 1-1 and 1-2, the void volume ratio P (%) of the dried portion after step (B), the thickness of the dried portion relative to the thickness T of the first paste layer after drying The ratio of H (H / T × 100 (%)), the liquid component volume fraction L (%) of the second paste layer, and P / L × 100 (%) were as shown in Table 1.
In Example 1-1 and Comparative Examples 1-1 and 1-2, H / T × 100 (%) was set to 100%. In these examples, D50 ≦ H.
In these examples, the void volume ratio P of the drying part after the step (B) and the liquid component volume ratio L of the second paste layer were changed.

(Pattern observation)
In each example, the surface of the obtained negative electrode was observed with a scanning electron microscope (SEM), and whether or not a desired pattern was formed was evaluated according to the following criteria. The evaluation results are shown in Table 1.
<Criteria>
○ (Good): There was no pattern collapse, and a plurality of through holes were clearly formed in a desired pattern.
X (defect): The pattern collapsed, and the through-hole was blocked or reduced.

(Measurement of surface roughness)
In each example, the surface roughness of the obtained negative electrode was measured. The measurement result of the surface roughness is shown in FIG. In this figure, the horizontal axis is the position (distance) from one end of the pattern layer in the width direction, and the vertical axis is the thickness of the pattern at a certain position in the width direction.
Further, the surface flatness was evaluated according to the following criteria. The evaluation results are shown in Table 1.
Here, the overall surface flatness excluding the through-hole formation portion was evaluated.
<Criteria>
○ (Good): In the graph showing the measurement result of the surface roughness, the difference between the maximum thickness and the minimum thickness in the portion excluding the formation portion of the through hole is within 5 μm.
X (defect): In the graph showing the measurement result of the surface roughness, the difference between the maximum thickness and the minimum thickness in the portion excluding the formation portion of the through hole is more than 5 μm.

In Example 1-1 that satisfies 45% ≦ P / L × 100 (%) ≦ 59%, after applying the second paste layer, the first paste layer whose liquid component in this layer is the base It was able to permeate in an appropriate amount into the voids of the dry part formed inside. As a result, there was no pattern collapse due to excessive leveling, a plurality of through-holes were neatly formed in a desired pattern, and a pattern layer with good surface flatness could be formed by appropriate leveling.
An SEM perspective photograph of the negative electrode produced in Example 1-1 is shown in FIG. This photograph shows a state in which a plurality of through holes are patterned in a matrix.

  In Comparative Example 1-1 where P / L × 100 (%) <45%, the amount of voids in the dry portion in the first paste layer as the base is too small relative to the amount of liquid component in the second paste layer. For this reason, the liquid component in the second paste layer could not penetrate well into the voids in the dry part in the first paste layer as the base. As a result, pattern collapse due to excessive leveling occurred, and through holes were blocked or reduced.

  In Comparative Example 1-2 where P / L × 100 (%)> 59%, the amount of voids in the dry portion in the first paste layer as the base is excessive with respect to the amount of liquid component in the second paste layer. For this reason, the liquid component in the second paste layer excessively penetrated into the voids of the dry part in the first paste layer as the base. As a result, the nonuniformity of the film thickness immediately after coating was maintained due to insufficient leveling, and the surface flatness was not improved.

(Test Examples 2-1 and 2-2)
In Test Examples 2-1 and 2-2, the drying time of the first paste layer was changed, and in step (C), the squeegee was intentionally inclined in the width direction, and the second paste layer was applied. A negative electrode was produced in the same manner as Example 1-1 except that.

In Test Examples 2-1 and 2-2, the void volume ratio P (%) of the dried part after step (B), the ratio of the thickness H of the dried part to the thickness T of the first paste layer after drying (H / T × 100 (%)), the liquid component volume ratio L (%) of the second paste layer, and P / L × 100 (%) were as shown in Table 2.
In all examples, D50 ≦ H.

The obtained negative electrode was evaluated in the same manner as in Example 1-1.
The measurement result of the surface roughness is shown in FIG.
Table 2 shows the results of pattern observation and surface flatness evaluation.

In Test Examples 2-1 and 2-2, 45% ≦ P / L × 100 (%) ≦ 59% is satisfied, and surface flatness is good under normal coating conditions as in Example 1-1. A simple pattern layer can be formed.
In these test examples, the squeegee was intentionally inclined in the width direction, and the second paste layer was applied under conditions worse than the actual application conditions.
In Test Example 2-1 where D50 ≦ H ≦ T × 0.7 is satisfied, an undried portion having relatively high fluidity remains sufficiently after the first paste layer is dried. Therefore, even if there is an inclination in the width direction immediately after application of the second paste layer, the second paste layer can be naturally restored to a flat state due to the presence of an undried portion having relatively high fluidity. And a pattern layer having good surface flatness could be formed.
In Test Example 2-2 where H> T × 0.7, the thickness of the undried portion having a relatively high fluidity remaining after drying of the first paste layer is insufficient, and the fluidity is relatively high. Due to the presence of the undried portion, the inclination in the width direction seen immediately after the application of the second paste layer could not be restored to a flat state.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 11 Exterior body 20 Electrode laminated body 21 Electrode 21A Positive electrode 21B Negative electrode 22 Separator 110 Current collector 120 Electrode active material layer 121 Non-pattern layer 121P 1st paste layer 121D Drying part 121W Undrying part 122 Pattern Layer 122A Through-hole 122P Second paste layer 210 Screen 220 Squeegee

Claims (3)

Using a paste containing an electrode active material and a dispersant, a non-aqueous solution for forming an electrode active material layer having a multilayer structure including a non-pattern layer and a pattern layer formed on the non-pattern layer on a current collector A method for producing an electrode for an electrolyte secondary battery, comprising:
Forming a first paste layer for the non-pattern layer (A);
A step (B) of drying at least a part of the first paste layer on the surface side to form a drying unit;
(C) sequentially printing the second paste layer for the pattern layer,
When the void volume ratio of the dry part is P (%) and the liquid component volume ratio immediately after the application of the second paste layer is L (%), the conditions satisfy the following formula (1-1): Performing step (B) and step (C);
Manufacturing method of electrode for nonaqueous electrolyte secondary battery.
45% ≦ P / L × 100 (%) ≦ 59% (1-1) In the step (C), the second paste layer is screen-printed using a roll-shaped screen having a pattern corresponding to the pattern of the pattern layer.
The manufacturing method of the electrode of Claim 1. In the step (B), only a part on the surface side of the first paste layer is dried to form the drying section,
When the median diameter of the electrode active material is D50, the thickness of the first paste layer after the step (B) is T, and the thickness of the dry part is H, the following formula (2-1) is obtained. The step (B) is performed under the satisfying conditions.
The manufacturing method of the electrode of Claim 1 or 2.
D50 ≦ H ≦ T × 0.7 (2-1)