JP7093985B2 - Carbon coat layer, current collector, battery, carbon coat layer formation method and gravure plate - Google Patents

Description

The present invention relates to a carbon coat layer coated on a collector used for a lithium ion secondary battery, a lithium ion capacitor, and an electric double layer capacitor, a paint, a current collector, a battery, a method for forming a carbon coat layer, and a gravure plate. Regarding.

The recent market for lithium-ion secondary batteries has expanded from consumer products such as laptop computers and mobile phones to electric vehicles, hybrid vehicles, and stationary storage batteries (Energy Storage System, hereinafter simply referred to as "ESS"). Has been done. Such lithium ion secondary batteries are required to have high output and safety for both positive and negative electrode active materials, and active materials such as ternary type, Mn type and Fe type are being studied for positive electrodes. In addition, treatment of current collectors for these batteries and the like has also been studied (see, for example, Patent Document 1).

In the above battery, when the adhesion between the active material (also referred to as the active material) of the positive electrode or the negative electrode and the current collector (also referred to as the current collector foil) is due to a chemical bond, due to deterioration due to a chemical reaction during repeated charging and discharging. The adhesion may be reduced. Further, in a laminated lithium ion secondary battery or the like, if the current collector and the active material are not in close contact with each other, the active material may peel off during sheet cutting, resulting in contamination. be.

Therefore, the present inventors have formed a carbon coat layer on the current collector, and by providing unevenness due to the carbon material on the surface on the side in contact with the active material, the active material and the current collector are in close contact with each other. We have proposed a carbon coat layer that can increase the force (see Patent Document 2).

Japanese Unexamined Patent Publication No. 2001-52710 JP-A-2015-088333

The carbon coat layer having irregularities formed on the metal foil can be used for the active material layer and the current collector foil when a active material having low resistance such as LiCoO ₂ is used as compared with the conventional current collector foil without carbon coating. Since a carbon coat layer with high resistance is inserted between them, reduction of resistance cannot be expected. However, by forming irregularities on the surface of the coating film of the carbon-coated foil, the active materials such as ternary type, Mn type, and Fe type are entangled with the coating film on which the active materials have formed irregularities during coating, resulting in adhesion. Is improved, interfacial resistance can be reduced, high output and improved cycle characteristics are achieved.

Therefore, an object of the present invention is a carbon coat layer to be applied to a current collector such as a lithium ion battery or a lithium ion capacitor, which has better adhesion to positive electrode and negative electrode active material layers than conventional ones and also has internal resistance. It is an object of the present invention to provide a lower carbon coat layer and a paint, a current collector, a battery, a method for forming the carbon coat layer, and a gravure plate used for the carbon coat layer.

The present invention that solves the above problems is as follows.
(1) A carbon coat layer containing a carbon material provided on the current collector.
It has a predetermined uneven pattern on the surface on the side that comes into contact with the active material, and has a predetermined uneven pattern.
A carbon coat layer characterized in that unevenness is provided on a surface having the unevenness pattern by the carbon material.

(2) The carbon coat layer according to (1) above, wherein the recesses constituting the uneven pattern have dimensions larger than the maximum particle size of the active material.

(3) The carbon coat layer according to (1) or (2) above, wherein the dimensions of the recesses constituting the uneven pattern are 0.01 mm or more and 10 mm or less.

(4) The carbon coat layer according to any one of (1) to (3) above, wherein the height difference of the unevenness due to the carbon material is 0.5 μm or more and 4.0 μm or less.

(5) The carbon coat layer according to any one of (1) to (4) above, wherein the carbon material is at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes.

(6) The carbon coat layer according to any one of (1) to (5) above, wherein carbon materials having different particle sizes are combined.

(7) A paint used to form a carbon coat layer on a current collector.
Contains carbon material,
The viscosity is 10 mPa · s or more and 10,000 mPa · s or less.
A coating material, characterized in that unevenness due to the carbon material is formed on the surface on the side in contact with the active material by coating on the current collector.

(8) The coating material according to (7) above, wherein the carbon material is at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes.

(9) The paint according to (7) or (8) above, wherein carbon materials having different particle sizes are combined.

(10) The current collector having the carbon coat layer according to any one of (1) to (6) above.

(11) The battery including the current collector according to (10) above.

(12) A method of forming a carbon coat layer on the current collector on the side where the unevenness due to the carbon material comes into contact with the active material, and the following steps:
This includes preparing a paint containing a carbon material and applying the paint onto the current collector using a gravure coating machine.
The gravure plate of the gravure coating machine has a region in which a plurality of cups are formed and a region in which cups are not formed in a region corresponding to a region in which the carbon coat layer is formed on the current collector. A method characterized by.

(13) The method according to (12) above, wherein the region where the cup is not formed has a dimension larger than the maximum particle size of the active material.

(14) The method according to (12) or (13) above, wherein the dimension of the region where the cup is not formed is 0.01 mm or more and 10 mm or less.

(15) The method according to any one of (12) to (14) above, wherein the paint is the paint according to any one of (7) to (9).

(16) A gravure plate for forming a carbon coat layer containing a carbon material on a current collector.
A gravure plate characterized by having a region in which a plurality of cups are formed and a region in which cups are not formed in a region corresponding to a region in which the carbon coat layer is formed on the current collector.

(17) The gravure plate according to (16), wherein the region where the cup is not formed has a dimension larger than the maximum particle size of the active material provided on the carbon coat layer.

(18) The gravure plate according to (16) or (17) above, wherein the dimension of the region where the cup is not formed is 0.01 mm or more and 10 mm or less.

According to the present invention, a predetermined uneven pattern is formed on the surface of the carbon coat layer, and unevenness due to the carbon material is provided on the surface provided with the uneven pattern of the carbon coat layer, so that the filling amount of the active material can be adjusted. The adhesion between the active material and the current collector can be improved, the internal resistance can be reduced, and the excellent characteristics of the charge / discharge cycle can be obtained without reducing the capacity of the battery without damaging the battery.

It is a figure which shows an example of the conventional gravure version. It is a figure which shows an example of the gravure version by this invention. It is a figure which shows another example of the gravure version by this invention.

(Carbon coat layer and gravure version)
Hereinafter, embodiments of the present invention will be described. First, the carbon coat layer according to the present invention is a carbon coat layer containing a carbon material provided on the current collector. Here, it is characterized in that the surface on the side in contact with the active material has a predetermined uneven pattern, and the unevenness is provided on the surface having the uneven pattern by the carbon material.

As described in Patent Document 2 by the present inventors, a coating film of a carbon coat layer (also referred to as a primer layer) or a carbon coat foil (a current collector having a coated carbon coat layer) is referred to as " The surface of the active material side of the "collecting foil with a carbon coat layer" or "carbon coated foil") has fine irregularities, so that active materials such as ternary, Mn, and Fe can be used. At the time of coating, the active material is entangled with the coating film having irregularities, so that the adhesion is improved, the interfacial resistance can be reduced, the high output and the cycle characteristics can be improved.

The carbon-coated layer, which has irregularities formed on metal foil or the like by a carbon material, has a resistance such as LiCoO ₂ (also simply referred to as “LCO”) as compared with a conventional current collector without carbon coating. When a low-grade active material is used, a carbon-coated layer having high resistance is inserted between the active material layer and the current collector, so reduction of resistance cannot be expected. However, even in the case of LCO, when the carbon coat layer is used, the rate characteristics and the cycle characteristics are improved by improving the adhesion.

When the adhesion between the active material of the positive electrode or the negative electrode and the current collector is due to a chemical bond, the adhesion may decrease due to deterioration due to a chemical reaction during repeated charging and discharging, but the coating film having the above-mentioned unevenness is formed. Since the active material is in physical contact with each other, stable low resistance can be obtained without inferiority in adhesion even after repeated charging and discharging, and cycle characteristics can be improved.

Further, in a laminated lithium ion secondary battery or the like, if the adhesion between the current collector and the active material is weak, contamination may occur due to the active material peeling off during sheet cutting, but unevenness may occur. By using the carbon coat layer with the above, the adhesion with the active material is improved, there is no peeling or falling off, no contamination is eliminated, and a safe secondary battery can be obtained.

The present inventors have made the active material and the current collector in order to form a carbon coat layer capable of further enhancing the adhesion between the active material and the current collector as compared with the carbon coat layer described in Patent Document 2. The interface with and was investigated in detail. As a result, it was found that there was a gap at the interface between the carbon coat layer and the active material, and in this portion, the active material and the carbon coat layer, and by extension, the current collector did not adhere well.

The present inventors investigated the cause of the formation of the void. As a result, among the particles constituting the active material, those having a large particle size are not accommodated in the concave portions of the unevenness due to the carbon material on the surface of the carbon coat layer, and as a result, voids are formed between the active material and the carbon coat layer. It turned out that it was done.

Therefore, the present inventors have diligently studied a method of reducing the above-mentioned voids to improve the adhesion between the active material and the carbon coat layer, and by extension, the current collector. As a result, a carbon coat layer was formed on the current collector using the gravure coating machine, and the gravure plate of the gravure coating machine provided a region where a plurality of cups were formed and a region where the cups were not formed. I came up with the idea of setting it up.

That is, in the conventional gravure plate 10 exemplified in FIG. 1, the cup 11 having a predetermined shape (for example, a pyramid shape) and a predetermined size (for example, 50 μm ^□ , depth 20 μm) partitioned by the bank B is provided. , The gravure plate 10 is engraved innumerably over the entire area of the size to be painted. Then, after the cup 11 is filled with the paint, it is transferred to a base material (current collector) such as aluminum foil to form a carbon coat layer having a flat surface on the base material.

On the other hand, in the gravure plate 1 according to the present invention exemplified in FIG. 2, the region 13 in which the cup 11 having a predetermined shape (for example, a square) and a predetermined size (for example, 0.1 mm ^□ ) is not carved is provided. , For example, they are provided at predetermined intervals (for example, 0.1 mm). As a result, on the surface of the gravure plate 1, the region 12 in which the cup 11 is carved draws a grid pattern with a clearance C (0.2 mm in FIG. 2).

By forming the carbon coat layer using such a gravure plate 1, the uneven pattern reflecting the pattern on the surface of the gravure plate 1 (lattice pattern in FIG. 2) is reflected on the surface of the carbon coat layer in contact with the active material. Is transcribed. That is, in the formed carbon coat layer, a convex portion is formed in the portion corresponding to the region 12 in which the cup 11 is carved, and a concave portion is formed in the portion corresponding to the region 13 in which the cup 11 is not carved. A grid-like uneven pattern is formed on the surface of the surface. When the active material is applied onto the carbon coat layer, the active material having a large particle size is accommodated in the recesses forming the uneven pattern on the surface of the carbon coat layer. As a result, as compared with the case of using the conventional gravure plate 10 shown in FIG. 1, the voids between the active material and the carbon coat layer can be reduced, and the active material and the carbon coat layer, and eventually the current collector. It is possible to improve the adhesion of the carbon fiber.

The shape of the uneven pattern on the surface of the carbon coat layer (that is, the region 12 in which the cup 11 is carved in the gravure plate 1) is not particularly limited, and is linear (striped), lattice-shaped, or hexagonal when viewed in a plan view. , Polygonal shape, circular shape, elliptical shape, etc. Above all, a grid pattern is preferable because the adhesion between the active material and the current collector can be further improved.

Further, the shape of the concave portion (that is, the region 13 in the gravure plate 1) constituting the uneven pattern is not particularly limited, and when viewed in a plan view, it is linear (striped), square, hexagonal, polygonal, or circular. , Oval shape, etc. Above all, the shape of the recess (region 13) is preferably square because the adhesion between the active material and the current collector can be further improved.

Further, the size of the concave portion of the uneven pattern (that is, the region 13 in the gravure plate 1) is preferably larger than the maximum particle size of the active material, whereby the gap between the active material and the carbon coat layer is formed. It is possible to further improve the adhesion between the active material and the current collector. Specifically, the size of the recess (region 13) is preferably 0.01 mm or more and 10 mm or less, and more preferably 0.1 mm or more and 1 mm or less.

Further, the depth of the concave portion of the uneven pattern on the surface of the carbon coat layer is preferably 0.1 μm or more and 5.0 μm or less. As a result, the voids between the active material and the carbon coat layer can be further reduced, and the adhesion between the active material and the current collector can be further improved. The depth is more preferably 0.2 μm or more and 3.0 μm or less.

In order to realize the depth of the concave portion of the uneven pattern, the depth of the cup 11 carved in the gravure plate 1 is preferably 0.01 mm or more and 0.20 mm or less. As a result, the voids between the active material and the carbon coat layer can be further reduced, and the adhesion between the active material and the current collector can be further improved. The depth is more preferably 0.01 mm or more and 0.10 mm or less.

In the present specification, the "dimension of the concave portion of the concave-convex pattern of the carbon coat layer (region 13 in the gravure plate 1)" specifically means the shape of the concave portion of the concave-convex pattern (region 13 in the gravure plate 1). In the case of a line (striped), the distance between adjacent lines (stripes), in the case of a square, hexagon, or polygon, the length of the longest side of a grid or polygon, and in the case of a circle, the length of the longest side. In the case of an ellipse, it means the diameter of a circle, and in the case of an ellipse, it means the major axis of an ellipse.

Further, the "depth of the concave portion of the uneven pattern of the carbon coat layer" means the difference between the height of the peripheral edge of the concave portion and the height of the deepest portion of the concave portion.

Further, the "depth of the cup 11 carved in the gravure plate 1" means the difference between the height of the peripheral edge of the cup 11 and the height of the deepest part of the cup 11.

The dimensions and depth of the concave portions of the uneven pattern of the carbon coat layer are measured by hardening the carbon coat layer with a binder, cutting a cross section, and measuring with a scanning electron microscope (also simply referred to as "SEM"). It can be measured with a microscope. In the measurement with a scanning electron microscope (SEM) or a micrometer, the film thickness is measured at 5 or more points in each of the convex and concave portions, and the measured values are expressed as the average film thickness. It should be noted that the height difference of the unevenness may occur up to 0.1 μm unit or less, and the measurement of the basis weight or the observation by SEM is preferable to the measurement by the micrometer.

In the present invention, a carbon coat layer is provided on the current collector using a gravure coating machine. The carbon coat layer has an uneven pattern that reflects the pattern on the surface of the gravure plate of the gravure coating machine (lattice pattern in FIG. 2) transferred to the surface thereof, and carbon is transferred to the surface on which the uneven pattern of the carbon coat layer is formed. Fine irregularities due to the material are also formed.

As the current collector, a current collector made of ordinary materials and forms such as aluminum foil, copper foil, and stainless steel foil can be used.

The carbon material may be at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes (also simply referred to as “CNT”). The carbon material acts as a conductive material and improves the adhesion between the current collector and the active material through the unevenness.

The carbon coat layer is not particularly limited in shape, film thickness, etc. as long as the adhesion between the current collector and the active material is improved without impairing the filling amount of the active material.

The carbon coat layer can be preferably formed as a coating film having a film thickness of 5 μm or less, preferably 4 μm or less, more preferably 3 μm or less, and most preferably 2 μm or less. This is because when the film thickness is 5 μm or less, it is advantageous in terms of low resistance. Comparing the resistance of the carbon coat layer and the current collector foil, the current collector foil is usually lower, so if the film thickness exceeds 5 μm, the resistance tends to be too high, and a film thickness of 5 μm or less is good.

The film thickness can be measured by solidifying the carbon coat layer with a binder, cutting the cross section, and measuring with a scanning electron microscope (also simply called "SEM"), measuring with a micrometer, or measuring 50 mm x 50 mm. After measuring the weight of the cut coated product (carbon coat layer + current collector foil), weigh the collector foil after removing the carbon coat layer cleanly with a solvent, and measure the weight of the collector foil due to the difference. Obtained from the specific weight. In the measurement with a scanning electron microscope (SEM) or a micrometer, the film thickness is measured at 5 or more points in each of the convex and concave portions, and the measured values are expressed as the average film thickness. It should be noted that the height difference of the unevenness may occur up to 0.1 μm unit or less, and the measurement of the basis weight or the observation by SEM is preferable to the measurement by the micrometer.

The height difference of the unevenness due to the carbon material of the carbon coat layer is not particularly limited as long as the adhesion between the current collector and the active material is improved without impairing the filling amount of the active material.

The height difference (also referred to as unevenness difference) due to the carbon material is preferably 0.2 to 4.0 μm, more preferably 0.2 to 3.0 μm, still more preferably 0.2 to 2.0 μm, and most preferably 0.5 in the coating film. It is ~ 2.0 μm. When the height difference of the unevenness is within these ranges, the larger the height difference is, the better the bite with the active material is, so that the maximum height difference of the film thickness of the coating film is good. In most cases, the height difference of the unevenness is preferably about 80% of the thickness of the convex portion of the coating film at the maximum. If the height difference exceeds 80% of the thickness at the convex portion, the thickness of the coating film is almost eliminated and the current collector may not be different from the exposed state, which is not preferable.

For the height difference of the unevenness due to the carbon material, the paint according to the present invention described later is applied to the aluminum foil, the carbon coat layer is hardened with a binder, the cross section is cut, and the thickness of the coating film of the concave portion and the convex portion is scanned electron microscope. It can be obtained by observing by (SEM). Here, the height difference of the unevenness is measured up to 0.1 μm unit, the number of measurements is 5 or more for each of the convex portion and the concave portion, and it is calculated from the average value of the measured values of the convex portion and the concave portion (convex portion). Average thickness of recesses-average thickness of recesses).

For the formation of unevenness by the carbon material, carbon materials having different shapes and different particle sizes can be combined. For example, by combining a paint used for forming a carbon coat layer with a particle size of a large particle size and a particle size of a small particle size of carbon black, it is possible to make the coating film uneven and improve the adhesion. ..

The particle size can be measured by a laser method or a dynamic light scattering method. Here, the particle size is expressed as an average particle size. The details of the dynamic light scattering method conform to the description of JIS Z 8826.

The carbon material has an average particle size of 100 to 2000 nm, preferably an average particle size of 200 to 1600 nm, more preferably an average particle size of 200 to 1000 nm, most preferably an average particle size of 300 to 700 nm, and an average grain size. Two or more kinds of particles having a diameter of 1000 to 4000 nm, preferably an average particle diameter of 1200 to 3000 nm, more preferably an average particle diameter of 1000 to 2000 nm, and most preferably an average particle diameter of 800 to 1500 nm can be used. This is because it is advantageous to make the difference in particle size in this way in that unevenness is easily formed. Further, in order to facilitate entanglement with the active material, it is a combination of particle sizes required to form irregularities that make maximum use of the thickness of the coating film.

The carbon material should be blended so as to prevent close packing on the surface of the carbon coat layer. For example, when carbon black having an average particle size of 300 to 700 nm is A and carbon black having an average particle size of 800 to 1500 nm is B, a weight ratio of A: B = 100: 1 to 900 is preferable. The combination can be preferably 100: 10 to 700, more preferably 100: 10 to 500, and most preferably 100: 10 to 300. When the ratio is set in this way, it is difficult for the carbon coat layer to be packed densely and it is easy to make irregularities. On the other hand, inside the carbon coat layer, carbon black A having a small particle size contributes to the close packing and the resistance is lowered. Because it is advantageous.

As for graphite, graphite having an average particle size of 0.5 μm to 5.0 μm is desirable. This is because in the particle size range of an average particle size of 0.5 μm to 5.0 μm, graphite becomes a nucleus, which is advantageous in that unevenness is easily formed. Further, by using graphite having a particle size roughly the same as the target coating film thickness, it is easy to become a nucleus.

As the carbon material, a carbon material such as carbon black that is secondarily agglomerated may be used by adjusting the particle size with a crusher or a disperser such as a ball mill, a bead mill, or a homomixer.

As the carbon material, graphite may be used as large particles in order to make irregularities. Further, a carbon material such as carbon nanotubes may be used for the purpose of forming irregularities.

The active material is not particularly limited, and various substances can be used. For example, ternary system, Mn system, Fe system, LCO, etc. may be used.

The particle size of the particles constituting the active material varies depending on the material, but is, for example, 0.2 to 10.0 μm in the case of Fe-based material and 0.5 to 20.0 μm in the case of Mn-based material.

(paint)
The paint according to the present invention is a paint used for forming the carbon coat layer according to the present invention on a current collector. Here, the paint contains a carbon material and has a viscosity of 10 mPa · s or more and 10,000 mPa · s or less, and unevenness due to the carbon material is formed on the surface on the side in contact with the active material by coating on the current collector. It is characterized by that.

As described above, when the carbon coat layer is formed on the current collector using the gravure coater, the surface of the carbon coat layer is provided by providing the plate of the gravure coater with an uneven pattern having a predetermined shape. A concavo-convex pattern that reflects the concavo-convex pattern is formed on the surface. When the active material is applied to the surface of the carbon coat layer, the active material having a large particle size is accommodated in the concave portions of the uneven pattern on the surface of the carbon coat layer, and the voids between the active material and the carbon coat layer are reduced. It is possible to improve the adhesion between the active material and the carbon coat layer, and by extension, the current collector.

However, as a result of the study by the present inventors, it was found that when the viscosity of the paint containing the carbon material is not in the appropriate range, the uneven pattern of the plate of the gravure coating machine is not transferred well to the surface of the carbon coat layer. did. Therefore, as a result of diligent studies on the viscosity range of the paint that satisfactorily transfers the uneven pattern of the plate of the gravure coating machine to the carbon coat layer, it is important that the viscosity is 10 mPa · s or more and 10,000 mPa · s or less. I found that. More preferably, the viscosity is 100 mPa · s or more and 600 mPa · s or less.

The coating material according to the present invention can be prepared by blending a binder and the above-mentioned carbon material in a solvent. Further, the viscosity of the paint can be adjusted by the blending ratio of the solvent, the binder and the carbon material.

As described above, the carbon material may be at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes. The carbon material acts as a conductive material and improves the adhesion between the current collector and the active material through the unevenness.

For example, the paint can be blended with carbon black having different grain sizes in order to make the surface of the carbon coat layer uneven due to the carbon material, with an average grain size of 300 to 700 nm and an average grain size of 800 to 1500 nm. By using carbon black with two types of grain size, carbon black A with a small grain size contributes to the densest filling inside the carbon coat layer, while it is difficult to fill the surface of the carbon coat layer with unevenness easily. , Resistance can be lowered. Then, a coating film having an unevenness difference of 0.5 to 2.0 μm can be formed as a carbon coat layer.

In addition, in order to make unevenness with the carbon material, dilute with the solvent used for the paint, remove the solid content, and then apply the coating. Can also be used.

The binder is not particularly limited, and an aqueous solution of various chemicals such as polyolefin can be used.

The solvent is not particularly limited, and either water or an organic solvent may be used. When a water-soluble binder is used, water, preferably ion-exchanged water or pure water, can be used, and when a binder soluble in an organic solvent is used, an organic solvent can be used.

A dispersion as a paint can be prepared by blending a binder and a carbon material such as carbon black, graphite, graphene, or CNT that forms the above-mentioned unevenness of the carbon coat layer and forms conductivity in the solvent. ..

Further, a dispersant can be used as a paint, if necessary, and the dispersant is not particularly limited, and various ordinary chemicals such as carboxymethyl cellulose (also simply referred to as “CMC”) can be used.

The disperser is not particularly limited, such as a homomixer, a kneader, a ball mill, a bead mill, etc., and it is preferable to use a normal device capable of sufficiently and evenly dispersing to produce a uniformly dispersed paint.

(Method of forming carbon coat layer)
The method for forming the carbon coat layer according to the present invention is a method for forming the carbon coat layer on the current collector on the side where the unevenness due to the carbon material comes into contact with the active material, and is the following step, that is, the carbon material. The present invention includes preparing a paint containing the above-mentioned paint and applying the paint onto the current collector using a gravure coating machine. Here, in the gravure version of the gravure coating machine, as shown in FIG. 2, a region 12 in which a plurality of cups 11 are formed in a region corresponding to a region corresponding to the formation region of the carbon coat layer on the current collector. It is characterized by having a region 13 in which the cup 11 is not formed.

The shape of the region 12 in which the cup 11 of the gravure plate 1 is formed is not particularly limited, and when viewed in a plan view, it may be linear (striped), grid-like, hexagonal, polygonal, circular, elliptical, or the like. As described above, it is preferable to have a grid pattern because the adhesiveness between the active material and the current collector can be further improved. When the shape of the region 12 is linear (striped), the direction of the linear wire may be parallel to, perpendicular to, or intersecting the flow direction of the current collector.

Further, the shape of the region 13 in the gravure plate 1 is not particularly limited, and can be a square, a hexagon, a polygon, a circle, an ellipse, or the like when viewed in a plan view. Above all, as described above, a square shape is preferable because the adhesion between the active material and the current collector can be further improved.

Further, it is preferable that the region 13 has a size larger than the maximum particle size of the active material, the size of the region 13 is preferably 0.01 mm or more and 10 mm or less, and the depth of the cup 11 is 0.01 mm. As described above, it is preferable that the thickness is 0.20 mm or less.

Further, as the above-mentioned paint, the above-mentioned paint according to the present invention can be used.

According to the present invention, in the gravure plate 1 of the gravure coating machine, a region 12 in which a plurality of cups 11 are formed and a cup 11 are formed in a region corresponding to a region in which a carbon coat layer is formed on a current collector. Since no region 13 is provided, the surface of the formed carbon coat layer has irregularities reflecting the shape of the region where the cup 11 is formed (lattice-like in FIG. 2) on the surface of the gravure plate of the gravure coating machine. The pattern is transferred. Then, when the active material is applied onto the carbon coat layer, the active material having a large particle size is accommodated in the concave portions of the uneven pattern on the surface of the carbon coat layer, and the voids between the active material and the carbon coat layer are reduced. , The adhesion between the carbon coat layer and the current collector can be improved.

Further, according to the present invention, it is possible to improve the adhesion to the active material even if unevenness is formed by utilizing the voids of the trace of the volatilization of the solvent.

Further, according to the present invention, in both the case where a carbon material having a single particle size is used and the case where a plurality of carbon materials such as carbon black having different particle sizes are blended, a coating film having a flat dry coating film can be used. It is possible to form a difference in unevenness such as 0.2 to 4.0 μm from the ruggedness, and when the active material is applied, the active material is entangled with the uneven portion, and high physical strength and high adhesion can be obtained.

The improvement in the adhesion between the carbon coat layer and the active material layer can be evaluated by the peel strength. Peel strength is the value when cellophane tape (registered trademark) (NITTO TAPE No, 31B) is attached to the coated surface of the test piece cut to a width of 10 mm, and force is applied in the vertical direction to peel it off [N (Newton)]. To read. DIGITAL FORCE GAUGE manufactured by Imada Seisakusho Co., Ltd. can be used as the measuring instrument. More detailed conditions are described in JIS C 5016.

The improvement in peel strength has a sufficient correlation with the reduction of the interfacial resistance and the internal resistance of the battery and the improvement of the cycle characteristics. Having a strong peel strength means that the adhesion with the active material is good, so that the interfacial resistance and the internal resistance can be reduced, and the cycle characteristics are also good.

As shown in Examples described later, the film thickness of the carbon coat layer can be 2 μm or less, and the internal resistance is increased by increasing the adhesion between the active material and the current collector without impairing the filling amount of the active material. Can be reduced, and excellent characteristics for the charge / discharge cycle can be obtained without reducing the capacity of the battery.

(Current collector and battery)
The current collector provided with the carbon coat layer described above, or a battery, a capacitor, or the like including the current collector is also within the scope of the present invention. When incorporating the carbon coat layer according to the present invention, the configuration of the current collector, the battery, the capacitor and the like is not particularly limited as long as it is a normal one, and it can be provided in the current collector such as a lithium ion battery and a lithium ion capacitor. ..

Next, the present invention will be described by way of examples. In the following, parts by weight are simply referred to as "parts".

(Example 1)
A slurry of 20 parts of carbon black as a carbon material, 2 parts of CMC as a dispersant, and 78 parts of pure water was prepared.
With respect to the prepared slurry, 15 parts of an aqueous polyolefin solution was added as a binder to a carbon black solution crushed to an average particle size of 450 nm using a bead mill, and a sufficiently uniformly dispersed paint was prepared using a stirrer. The created paint was applied to the aluminum foil by a gravure coating machine using the gravure plate 1 (clearance 0.2 mm pitch, one side of the area 12 is 0.1 mm, one side of the area 13 is 0.1 mm) shown in FIG. , A coating film having a dry film thickness of 1.5 μm was formed. The depth of the recess was 1.5 μm. After applying and drying the active material paste (10 μm, LCO: 100 parts, PVDF: 2 parts) on the coating film, the adhesion of the active material was evaluated by the peel strength. The results obtained are shown in Table 1.

As for the film thickness, after measuring the weight of the coated product (carbon coat layer + current collector foil) cut to 50 mm × 50 mm as described above, the current collector foil after removing the carbon coat layer cleanly with a solvent. Was measured and measured from the weight difference.
The unevenness difference is measured by observing the cross section by SEM as described above. The measurement was performed at 5 points each of the convex part and the concave part, and they were averaged and calculated.
The particle size was measured by a dynamic light scattering method.
Peel strength was measured as described above.

(Example 2)
A 5 μm graphite powder was added to the carbon black solution of Example 1 to prepare a dispersion liquid using a bead mill, and then 15 parts of a polyolefin aqueous solution was also added to prepare a paint. Similarly, the aluminum foil is coated using a gravure coating machine using the gravure plate 1 (clearance 0.2 mm pitch, one side of the region 13 is 0.1 mm) shown in FIG. 2, and a coating film having a dry film thickness of 1.5 μm is applied. After the same active material paste was formed and applied and dried, the adhesion of the active material was evaluated by the peel strength. The results obtained are shown in Table 1.

(Example 3)
Using the paint to which the graphite powder of Example 2 was added, the aluminum foil was coated with a gravure coating machine using the gravure plate 2 (clearance 0.3 mm pitch, one side of the region 13 was 0.2 mm) shown in FIG. A coating film having a dry film thickness of 1.5 μm was formed, and the same active material paste was applied. After drying, the adhesion of the active material was evaluated by peel strength. The results obtained are shown in Table 1.

(Comparative example)
Using the paint of Example 1, coat the aluminum foil with a gravure coating machine using a flat plate without unevenness to form a coating film with a dry film thickness of 1.5 μm, and apply the same active material paste. After drying, the adhesion of the active material was evaluated by the peel strength. The results obtained are shown in Table 1.

The values in Table 1 show relative values when the value when the peel strength of the coating film coated only with the active material paste without applying the primer layer was evaluated as "100".

From the results of the comparative example, it can be seen that the peel strength is about twice as strong just by preparing the primer foil containing the carbon material, rather than directly applying the active material to the plain foil. Then, from the results of Examples 1 to 3, by applying using a gravure plate with a grid pattern with a clearance of 0.2 or 0.3 mm, the peel strength is 2.5 times or more that of the primer foil and 5 times or more that of the plain foil. It can be seen that is getting stronger. From the above, according to the present invention, the interfacial resistance can be reduced and the cycle characteristics can be improved.

According to the present invention, a gravure coating machine is used to form an uneven pattern having a predetermined shape on the surface of a carbon coat layer, and the surface of the carbon coat layer on which the uneven pattern is formed is provided with unevenness due to a carbon material. Thereby, in a current collector such as a lithium ion battery and a lithium ion capacitor, the adhesion to the active material layer of the positive electrode and the negative electrode can be improved, and the internal resistance can be lowered.

1,2,10 Gravure version 11 cups 12 cups carved area 13 cups not carved area B bank C clearance

Claims (14)

A carbon coat layer containing a carbon material provided on a current collector by a gravure coating machine.
The surface on the side in contact with the active material has an uneven pattern that reflects the pattern on the surface of the gravure plate of the gravure coating machine, and the unevenness due to the carbon material is provided on the surface having the uneven pattern. A carbon coat layer characterized by that. The carbon coat layer according to claim 1, wherein the recesses constituting the uneven pattern have dimensions larger than the maximum particle size of the active material. The carbon coat layer according to claim 1 or 2, wherein the size of the recesses constituting the uneven pattern is 0.01 mm or more and 10 mm or less. The carbon coat layer according to any one of claims 1 to 3, wherein the height difference of the unevenness due to the carbon material is 0.5 μm or more and 4.0 μm or less. The carbon coat layer according to any one of claims 1 to 4, wherein the carbon material is at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes. The carbon coat layer according to any one of claims 1 to 5, wherein carbon materials having different particle sizes are combined. A current collector having the carbon coat layer according to any one of claims 1 to 6. A battery including the current collector according to claim 7. It is a method of forming a carbon coat layer provided on the side where the unevenness due to the carbon material comes into contact with the active material on the current collector, and the following steps:
This includes preparing a paint containing a carbon material and applying the paint onto the current collector using a gravure coating machine.
The gravure plate of the gravure coating machine has a region in which a plurality of cups are formed and a region in which cups are not formed in a region corresponding to a region in which the carbon coat layer is formed on the current collector. ,
The surface on the side in contact with the active material has an uneven pattern reflecting the pattern on the surface of the gravure plate of the gravure coating machine, and the unevenness due to the carbon material is provided on the surface having the uneven pattern. A method characterized by forming a carbon coat layer. The method according to claim 9, wherein the region where the cup is not formed has a dimension larger than the maximum particle size of the active material. The method according to claim 9 or 10, wherein the dimension of the region where the cup is not formed is 0.01 mm or more and 10 mm or less. A gravure plate for forming a carbon coat layer containing a carbon material on a current collector.
A gravure plate characterized by having a region in which a plurality of cups are formed and a region in which cups are not formed in a region corresponding to a region in which the carbon coat layer is formed on the current collector. The gravure plate according to claim 12, wherein the region where the cup is not formed has a dimension larger than the maximum particle size of the active material provided on the carbon coat layer. The gravure plate according to claim 12 or 13, wherein the dimension of the region where the cup is not formed is 0.01 mm or more and 10 mm or less.

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