JP2019087489A - Carbon coated layer, paint, current collector, battery, method of forming carbon coated layer and gravure plate - Google Patents

Abstract

An object of the present invention is to improve the adhesion between a positive electrode and a negative electrode active material layer in a current collector such as a lithium ion battery or a lithium ion capacitor, and to reduce the internal resistance.
A carbon coat layer including a carbon material provided on a current collector, the surface having a predetermined concavo-convex pattern on the surface in contact with an active material, and the concavo-convex pattern is formed by the carbon material It is characterized by being provided on the surface which it has.
[Selected figure] Figure 2

Description

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

  The recent market for lithium ion secondary batteries has been developed from consumer products such as laptop computers and mobile phones to electric vehicles and hybrid vehicles and also storage batteries for stationary use (Energy Storage System (hereinafter sometimes simply referred to as "ESS"). It is done. Such lithium ion secondary batteries are required to have high output and safety for both positive and negative electrode active materials, and for positive electrodes, active materials such as ternary, Mn and Fe based materials are being studied. Further, in these batteries and the like, processing of the current collector is also studied (see, for example, Patent Document 1).

  In the above battery, when the adhesion between the active material of the positive electrode or the negative electrode (also referred to as the active material) and the current collector (also referred to as the current collector foil) is a chemical bond, the charge and discharge are repeated due to chemical reaction and the like. The adhesion may be reduced. Further, in the laminated lithium ion secondary battery and the like, if the adhesion between the current collector and the active material is weak, there is a risk that contamination may occur due to peeling of the active material when performing sheet cutting. is there.

  Therefore, the present inventors are the carbon coat layer formed on the current collector, and the adhesion between the active material and the current collector is provided by providing the unevenness by the carbon material on the surface in contact with the active material. The carbon coat layer which can raise power was proposed (refer to patent documents 2).

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

In the case of using a low-resistance active material such as LiCoO ₂ as compared to a conventional current collector foil not provided with a carbon coat, the carbon coat layer in which the unevenness is formed on the metal foil, the active material layer and the current collector foil Since a carbon coat layer with high resistance is inserted between them, reduction in resistance can not be expected. However, by forming irregularities on the surface of the coating film of the carbon-coated foil, the active material such as a ternary, Mn, or Fe-based material is coated when the active material is entangled with the coating film on which the irregularities are formed. Interface resistance can be reduced, leading to high power and further improvement of cycle characteristics.

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

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

(2) The carbon coat layer according to (1), wherein the concave portion constituting the concavo-convex pattern has a dimension larger than the maximum particle diameter of the active material.

(3) The carbon coat layer according to the above (1) or (2), wherein the dimension of the concave portion constituting the concavo-convex pattern is 0.01 mm or more and 10 mm or less.

(4) The carbon coat layer according to any one of (1) to (3), wherein the height difference of the unevenness by 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), 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 the above (1) to (5), wherein carbon materials of different particle sizes are combined.

(7) A paint used to form a carbon coat layer on a current collector,
Containing carbon material,
Viscosity is 10 mPa · s or more and 10000 mPa · s or less,
The coating material characterized in that the unevenness | corrugation by the said carbon material is formed in the surface of the side which contacts an active material by coating on the said collector.

(8) The paint according to (7), 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 of different particle sizes are combined.

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

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

(12) A method of forming on a current collector a carbon coat layer provided on the side where irregularities due to a carbon material come in contact with an active material, and the following steps:
Providing a paint comprising a carbon material, and applying the paint on 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 no cups are formed in the region corresponding to the formation region of the carbon coat layer on the current collector. How to feature

(13) The method according to (12), wherein the area in which the cup is not formed has a size larger than the maximum particle size of the active material.

(14) The method according to (12) or (13), wherein the dimension of the region in which 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), 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 printing plate having a region in which a plurality of cups are formed and a region in which a cup is not formed in a region corresponding to a region where the carbon coat layer is formed on the current collector.

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

  According to the present invention, since the predetermined concavo-convex pattern is formed on the surface of the carbon coat layer and the concavo-convex with the carbon material is provided on the surface provided with the concavo-convex pattern of the carbon coat layer The adhesion between the active material and the current collector is improved, the internal resistance can be reduced, and excellent characteristics in charge and discharge cycles can be obtained without reducing the capacity of 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. FIG. 7 shows another example of a gravure plate according to the present 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 provided on a current collector and containing a carbon material. Here, it is characterized in that the surface on the side in contact with the active material has a predetermined unevenness pattern, and the unevenness is provided on the surface having the unevenness pattern by a carbon material.

  As described in Patent Document 2 by the present inventors, a coated film of a carbon coating layer (also referred to as a primer layer) or a carbon coated foil (a carbon foil coated with a coated carbon coating layer) The surface on the side of the active material of the current collector foil with a carbon coat layer or "carbon coated foil" has fine irregularities, whereby a ternary, Mn, Fe, etc. active material is obtained. At the time of coating, since the active material is entangled with the coating film having the unevenness formed thereon, the adhesion is improved, the interface resistance can be reduced, and the cycle characteristic can be improved with high output.

A carbon coat layer in which a carbon material has irregularities formed on a metal foil or the like has a resistance such as LiCoO ₂ (also referred to simply as “LCO”) as compared with a conventional current collector not provided with a carbon coat. When a low active material is used, a carbon coat layer having high resistance is inserted between the active material layer and the current collector, and therefore, reduction in resistance can not be expected. However, even in the case of LCO, when the carbon coat layer is used, the adhesion property is improved and the rate characteristics and the cycle characteristics are improved.

  When the adhesion between the active material of the positive electrode or the negative electrode and the current collector is a chemical bond, the adhesion may be deteriorated due to chemical reaction while repeating charge and discharge, but the coating film having the above-mentioned unevenness is formed Since the active material and the active material are in close physical contact with each other, stable low resistance can be obtained without deterioration in adhesion even if charge and discharge are repeated, and cycle characteristics can be improved.

  Further, in the case of a laminated lithium ion secondary battery or the like, if the adhesion between the current collector and the active material is weak, there is a risk that contamination may occur due to the separation of the active material at the time of sheet cutting. By using the carbon coat layer to which is attached, the adhesion to the active material is improved, there is no peeling or falling off, the contamination is also eliminated, and a safe secondary battery can be obtained.

  In order to form a carbon coat layer capable of further enhancing the adhesion between the active material and the current collector than the carbon coat layer described in Patent Document 2, the inventors of the present invention have proposed an active material and a current collector. We investigated in detail the interface with. As a result, it was found that voids were present at the interface between the carbon coat layer and the active material, and in this part, the active material and the carbon coat layer, and hence the current collector, did not adhere well.

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

  Therefore, the inventors of the present invention diligently studied a method of reducing the voids to improve the adhesion between the active material and the carbon coat layer, and hence the current collector. As a result, a carbon coating layer is formed on the current collector using a gravure coating machine, and the gravure plate of the gravure coating machine has a region in which a plurality of cups are formed and a region in which no cups are formed. I thought about establishing it.

That is, in the conventional gravure plate 10 illustrated 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 , And is engraved innumerably throughout the area of the gravure plate 10 to be coated. Then, the cup 11 is filled with a paint, and then transferred to a base material (current collector) such as an aluminum foil, whereby a carbon coat layer having a flat surface is formed on the base material.

On the other hand, in the gravure plate 1 according to the present invention illustrated in FIG. 2, the region 13 in which the cup 11 of a predetermined shape (for example, a square) and a predetermined dimension (for example, 0.1 mm ^□ ) is not engraved is For example, it is provided at a predetermined interval (for example, 0.1 mm). Thereby, on the surface of the gravure plate 1, the area 12 in which the cup 11 is engraved draws a lattice pattern with the clearance C (0.2 mm in FIG. 2).

  By forming a carbon coat layer using such a gravure plate 1, a concavo-convex pattern reflecting the pattern on the surface of the gravure plate 1 (lattice form in FIG. 2) on the surface of the carbon coat layer in contact with the active material. Is transferred. That is, in the formed carbon coat layer, a convex portion is formed in a portion corresponding to the area 12 in which the cup 11 is engraved, and a concave portion is formed in a portion corresponding to the area 13 in which the cup 11 is not engraved. A lattice-like uneven pattern is formed on the surface of. 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 portion that constitutes the concavo-convex pattern on the surface of the carbon coat layer. As a result, compared with the case where the conventional gravure plate 10 shown in FIG. 1 is used, the gap between the active material and the carbon coat layer can be reduced, and the active material and the carbon coat layer, and hence the current collector Adhesion can be improved.

  The shape of the concavo-convex pattern on the surface of the carbon coat layer (that is, the area 12 where the cup 11 is engraved in the gravure plate 1) is not particularly limited, and linear (stripe), lattice, hexagonal when planarly viewed It can be polygonal, circular, elliptical or the like. Among them, a lattice shape is preferable because the adhesion between the active material and the current collector can be further improved.

  In addition, the shape of the concave portion (that is, the region 13 in the gravure plate 1) constituting the above-mentioned concavo-convex pattern is not particularly limited, and when planarly viewed, linear (stripe), square, hexagon, polygon, circular , Oval, etc. Among them, the shape of the recess (region 13) is preferably a square, because the adhesion between the active material and the current collector can be further improved.

  In addition, it is preferable that the size of the concave portion of the concavo-convex pattern (that is, the area 13 in the gravure plate 1) has a size larger than the maximum particle diameter of the active material, thereby the gap between the active material and the carbon coat layer The adhesion between the active material and the current collector can be further improved. 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.

  Furthermore, as for the depth of the recessed part of the uneven | corrugated pattern of the carbon-coat layer surface, 0.1 micrometer or more and 5.0 micrometers or less are preferable. Thereby, the space 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 concavo-convex 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. Thereby, the space 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 (region 13 in the gravure plate 1) of the concave and convex pattern of the carbon coat layer” specifically refers to the shape of the concave portion (region 13 in the gravure plate 1) of the concave and convex pattern. In the case of a line (stripe), the distance between adjacent lines (stripes), the square, the hexagon, in the case of a polygon, the length of the longest side of the lattice or polygon, in the case of a circle The diameter of the circle means the major axis of the ellipse in the case of the ellipse.

  Moreover, "the depth of the recess of the concavo-convex pattern of the carbon coat layer" means the difference between the height of the periphery of the recess and the height of the deepest portion of the recess.

  Furthermore, “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 portion of the cup 11.

  Further, the size and depth of the concave portion of the uneven pattern of the carbon coat layer may be determined by fixing the carbon coat layer with a binder, cutting the cross section, and measuring with a scanning electron microscope (simply referred to as "SEM") or It can measure with a micrometer. In the measurement with a scanning electron microscope (SEM) or a micrometer, the film thickness is measured at five or more portions of each of the convex portion and the concave portion, and is represented by an average film thickness obtained by averaging those measured values. In addition, the height difference of unevenness | corrugation may arise to a 0.1 micrometer unit or less, it is more preferable to the measurement of a fabric weight, or the observation by SEM to be a measurement by a micrometer.

  In the present invention, the carbon coating layer is provided on the current collector using a gravure coating machine. The carbon coat layer has a surface on which a concavo-convex pattern reflecting the pattern (in the form of lattice in FIG. 2) of the gravure plate surface of the gravure coating machine is transferred and carbon is formed on the surface on which the concavo-convex pattern of the carbon coat layer is formed. Fine irregularities are also formed by the material.

  The current collector may be made of an ordinary material or form such as aluminum foil, copper foil, stainless steel foil, and the like.

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

  The film thickness can be measured by setting the carbon coat layer with a binder, cutting the cross section, and measuring with a scanning electron microscope (also simply referred to as “SEM”), or measuring with a micrometer, or 50 mm × 50 mm. The weight of the cut coated article (carbon coat layer + current collector foil) was measured, and then the weight of the current collector foil after the carbon coat layer was finely peeled off using a solvent was measured, and the weight per unit area and the difference Calculated from specific gravity. In the measurement with a scanning electron microscope (SEM) or a micrometer, the film thickness is measured at five or more portions of each of the convex portion and the concave portion, and is represented by an average film thickness obtained by averaging those measured values. In addition, the height difference of unevenness | corrugation may arise to a 0.1 micrometer unit or less, it is more preferable to measure by a fabric weight or to observe by SEM, rather than the measurement by a micrometer.

  There is no particular limitation on the height difference of the unevenness due to the carbon material of the carbon coat layer, 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) of the unevenness 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, the better the scoop with the active material, so the maximum height difference of the film thickness of the coating film is better. In most cases, it is preferable that the height difference of the unevenness be at most about 80% of the thickness at the convex portion of the coating film. When the height difference exceeds 80% of the thickness at the convex portion, the thickness of the coating film is almost lost, and it is not preferable because the current collector may not change from the exposed state.

  The height difference of unevenness by carbon material applies the paint according to the present invention to be described later on aluminum foil, hardens the carbon coat layer with a binder, cuts the cross section, and measures the thickness of the coating of concave and convex portions with a scanning electron microscope It can obtain | require by observing by (SEM). Here, the height difference of the unevenness is measured to the nearest 0.1 μm, and the number of measurements is 5 or more each for each of the projections and recesses, and calculated from the average value of the respective measured values of the projections and recesses (protrusion Of the thickness of the-average of the thickness of the recess).

  Carbon materials of different shapes and different particle sizes can be combined in the formation of the unevenness by the carbon material. For example, by combining the particle size (structure) of the carbon black with the particle size of the large particle size and the particle size of the small particle size in the paint used to form the carbon coat layer, the coating film can be made uneven to improve 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 Z8826.

  The carbon material has an average particle size of 100 to 2000 nm, preferably 200 to 1600 nm, more preferably 200 to 1000 nm, and most preferably 300 to 700 nm, and an average particle size A particle 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 the difference in particle size is advantageous in that it is easy to form asperities. In addition, in order to facilitate entanglement with the active material, it is a combination of particle sizes necessary to form asperities utilizing the thickness of the coating film to the maximum.

  The carbon material may be blended so as not to be close-packed on the surface of the carbon coat layer. For example, when carbon black having a particle size of 300 to 700 nm in average particle size is A, and carbon black having a particle size of 800 to 1,500 nm in average particle size is B, a weight ratio of A: B = 100: 1 to 900 is suitably obtained. Preferably, 100: 10 to 700, more preferably 100: 10 to 500, and most preferably 100: 10 to 300 can be combined. When the ratio is made this way, close packing does not easily occur on the surface of the carbon coat layer and irregularities are easily formed, while carbon black A having a small particle size contributes to close packing within the carbon coat layer and resistance decreases. It is because it is advantageous.

  As for graphite, graphite having a particle size of 0.5 μm to 5.0 μm in average particle size is desirable. This is because, in the particle size range of the average particle diameter of 0.5 μm to 5.0 μm, it is advantageous in that the graphite becomes a core and the unevenness becomes easy to be formed. Moreover, it becomes easy to become a nucleus by using the graphite of the same particle size as the thickness of the coating film made into the objective.

  The carbon material may be used after adjusting the particle size of a carbon material such as carbon black which has been secondarily aggregated by a grinder or a disperser such as a ball mill, bead mill, homomixer or the like.

  The carbon material may use graphite as large particles in order to make it uneven. Moreover, you may use carbon materials, such as a carbon nanotube, in order to form an unevenness | corrugation.

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

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

(paint)
The paint according to the present invention is a paint used to form the carbon coat layer according to the present invention on the current collector. Here, the paint contains a carbon material and has a viscosity of 10 mPa · s or more and 10000 mPa · s or less, and as a result of coating on the current collector, the unevenness due to the carbon material is formed on the surface in contact with the active material It is characterized by

  As described above, when a carbon coating layer is formed on a current collector using a gravure coating machine, the surface of the carbon coating layer is provided by providing a concavo-convex pattern of a predetermined shape on a plate of the gravure coating machine. The uneven | corrugated pattern which reflected the said uneven | corrugated pattern is formed. Then, when the active material is applied to the surface of the carbon coat layer, the active material having a large particle diameter is accommodated in the concave portion of the concavo-convex pattern on the surface of the carbon coat layer, and the space between the active material and the carbon coat layer is reduced. The adhesion between the active material and the carbon coat layer and hence the current collector can be improved.

  However, as a result of examinations by the present inventors, it is found that the concavo-convex pattern of the plate of the gravure coating machine is not well transferred onto the surface of the carbon coat layer when the viscosity of the coating containing the carbon material is not within the appropriate range. did. Therefore, as a result of intensive investigations on the viscosity range of the coating material for satisfactorily transferring the concavo-convex pattern of the plate of the gravure coating machine to the carbon coating layer, the present inventors must set the viscosity to 10 mPa · s or more and 10000 mPa · s or less. I found out that More preferably, the viscosity is 100 mPa · s or more and 600 mPa · s or less.

  The paint according to the present invention can be prepared by blending a binder and the above-mentioned carbon material in a solvent. In addition, 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 works as a conductive material, and improves the adhesion between the current collector and the active material through the unevenness.

  For example, in order to make the surface of a carbon coat layer uneven with a carbon material, carbon black different in particle size can be blended in a paint, and the particle size of 300 to 700 nm of average particle size and the particle size of 800 to 1500 nm of average particle size By using carbon black of two different particle sizes, close packing is hard to occur on the surface of the carbon coat layer and unevenness is easily made, while inside the carbon coat layer, carbon black A having a small grain size contributes to close packing. , Resistance can be lowered. And a coating film with an unevenness difference of 0.5 to 2.0 μm can be formed as a carbon coat layer.

  Moreover, in order to add the unevenness | corrugation by a carbon material, it dilutes with the solvent used for a coating material, drops after solid content and coats, the mark which the solvent volatilized turns into a void and forms unevenness in a carbon coat layer. Can also be used.

  The binder is not particularly limited, and aqueous solutions of various agents such as polyolefin can be used.

  The solvent is not particularly limited, and either water or an organic solvent may be used. In the case of using a water-soluble binder, water, preferably ion exchange water or pure water can be used, and in the case of using a binder that dissolves in an organic solvent, an organic solvent can be used.

  It is possible to form a dispersion as a paint by blending a binder and a carbon material such as carbon black, graphite, graphene, CNT, etc., which causes the conductivity to be formed by forming a binder and the irregularities of the carbon coat layer described above. .

  In the paint, if necessary, a dispersant can be used, and the dispersant is not particularly limited, and various usual agents such as carboxymethylcellulose (also simply referred to as "CMC") can be used.

  The dispersing machine is not particularly limited, such as a homomixer, a kneader, a ball mill, a bead mill, etc. It is good to prepare a uniformly dispersed paint using a usual sufficiently uniform dispersing device.

(Formation method of carbon coat layer)
The method for forming a carbon coat layer according to the present invention is a method for forming on a current collector a carbon coat layer provided on the side where irregularities due to a carbon material are in contact with an active material. And applying the paint onto the current collector using a gravure coater. Here, as illustrated in FIG. 2, the gravure plate of the gravure coating machine has a region 12 in which a plurality of cups 11 are formed in the region corresponding to the formation region of the carbon coat layer on the current collector, And a region 13 where 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 plan, it may be linear (stripe), lattice, hexagon, polygon, circle, oval, etc. As described above, it is preferable to be in the form of a lattice because the adhesion 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 line may be parallel to, perpendicular to, or intersected with the flow direction of the current collector.

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

  Furthermore, it is preferable that the area 13 have a size larger than the maximum particle size of the active material, and the size of the area 13 is preferably 0.01 mm or more and 10 mm or less, and the depth of the cup 11 is 0.01 mm It is as above-mentioned that it is preferable that it is 0.20 mm or less.

  Furthermore, the paint according to the present invention described above can be used as the paint.

  According to the present invention, in the gravure plate 1 of the gravure coating machine, the region 12 in which the plurality of cups 11 are formed, and the cup 11 are formed in the region corresponding to the formation region of the carbon coat layer on the current collector. Since the non-region 13 is provided, the surface of the formed carbon coat layer has irregularities that reflect the shape of the region where the cup 11 is formed (lattice shape in FIG. 2) of the gravure plate surface of the above-mentioned gravure coating machine The pattern is transferred. Then, when the active material is applied on the carbon coat layer, the active material having a large particle diameter is accommodated in the concave portion of the concavo-convex pattern on the surface of the carbon coat layer to reduce the space between the active material and the carbon coat layer. The adhesion between the carbon coat layer and the current collector can be improved.

  Further, according to the present invention, adhesion to the active material can be improved even if the surface of the substrate is made uneven by utilizing the void of the mark from which the solvent has volatilized.

  Furthermore, according to the present invention, in the case of using a carbon material of a single particle size and in the case of blending a plurality of carbon materials such as carbon black having different particle sizes, in the case of a coating film having a flat dry coating film. Instead, it is possible to form a difference of unevenness with 0.2 to 4.0 μm, etc. When the active material is coated, the active material is entangled in the uneven portion, and high physical strength of adhesion can be obtained.

  The improvement of 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 a cellotape (registered trademark) (NITTO TAPE No, 31B) is attached to the coated surface of a test piece cut to a width of 10 mm, a force is applied in the vertical direction, and the coating starts to peel off (N (Newton)) Read As a measuring instrument, DIGITAL FORCE GAUGE manufactured by Imada Seisakusho Co., Ltd. can be used. More detailed conditions are described in JIS C5016.

  The improvement in peel strength is well correlated with the cell surface resistance, reduction in internal resistance, and improvement in cycle characteristics. The fact that the peel strength is strong means that the adhesion with the active material is good, so that the interface resistance and the internal resistance can be reduced, and the cycle characteristics also become good.

  As shown in the examples described later, the carbon coat layer can have a film thickness of 2 μm or less, and the internal resistance can be increased by increasing the adhesion between the active material and the current collector without impairing the filling amount of the active material. Thus, excellent characteristics in charge and discharge cycles can be obtained without reducing the battery capacity.

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

  The invention will now be described by way of example. Hereinafter, 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 pulverized to an average particle size of 450 nm using a bead mill, and a sufficiently uniformly dispersed paint was prepared using a stirrer. The prepared coating is applied to an aluminum foil by a gravure coating machine using the gravure plate 1 (clearance 0.2 mm pitch, one side of area 12 is 0.1 mm, one side of area 13 is 0.1 mm) shown in FIG. And a dry film thickness of 1.5 μm was formed. The depth of the recess was 1.5 μm. After applying and drying a paste of active material (10 μm · LCO: 100 parts, PVDF: 2 parts) on the coating film, the adhesion of the active material was evaluated by peel strength. The obtained results are shown in Table 1.

The film thickness measures the weight of the coated product (carbon coat layer + current collector foil) cut into 50 mm x 50 mm as described above, and the current collector foil after the carbon coat layer is finely peeled off using a solvent Weight was measured and measured from the weight difference.
The unevenness difference is measured by SEM observation of the cross section as described above. The measurement was performed at each of five places of the convex and the concave, and the average was calculated.
Particle size was measured by dynamic light scattering.
Peel strength was measured as described above.

(Example 2)
After adding 5 μm of graphite powder to the carbon black solution of Example 1 and using the same bead mill to prepare a dispersion, a coating solution was prepared by adding 15 parts of an aqueous polyolefin solution as well. Similarly, a gravure coating machine using the gravure plate 1 (clearance 0.2 mm pitch, one side of area 13 is 0.1 mm) shown in FIG. 2 is applied to aluminum foil using a gravure coating machine, and a coating film having a dry film thickness of 1.5 μm is obtained. After forming and coating and drying the active material paste, the adhesion of the active material was evaluated by peel strength. The obtained results are shown in Table 1.

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

(Comparative example)
Using the coating composition of Example 1, the aluminum plate is coated with a gravure coating machine using a flat plate having no unevenness to form a coating having a dry film thickness of 1.5 μm, and the same active material paste is applied The adhesion of the active material after drying was evaluated by the peel strength. The obtained results are shown in Table 1.

  The values in Table 1 indicate relative values when the peel strength of a coating film coated only with the active material paste is evaluated without applying the primer layer and the numerical value is "100".

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

  According to the present invention, a concavo-convex pattern of a predetermined shape is formed on the surface of the carbon coat layer using a gravure coating machine, and the concavo-convex with a carbon material is provided on the surface of the carbon coat layer on which the concavo-convex pattern is formed. Thus, in a current collector such as a lithium ion battery or a lithium ion capacitor, adhesion to the active material layer of the positive electrode or the negative electrode can be improved, and internal resistance can be lowered.

1, 2, 10 Gravure version 11 cup 12 cup engraved area 13 cup uncarved area B bank C clearance

Claims (18)

A carbon coat layer comprising a carbon material provided on a current collector,
The surface on the side in contact with the active material has a predetermined uneven pattern,
A carbon coat layer, wherein unevenness is provided on the surface having the unevenness pattern by the carbon material.   2. The carbon coat layer according to claim 1, wherein the concave portion constituting the concavo-convex pattern has a dimension larger than the maximum particle diameter of the active material.   The carbon coat layer according to claim 1 or 2 whose size of a crevice which constitutes said concavo-convex 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 by 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 of different particle sizes are combined. A paint used to form a carbon coat layer on a current collector,
Containing carbon material,
Viscosity is 10 mPa · s or more and 10000 mPa · s or less,
The coating material characterized in that the unevenness | corrugation by the said carbon material is formed in the surface of the side which contacts an active material by coating on the said collector.   The paint according to claim 7, wherein the carbon material is at least one selected from the group consisting of carbon black, graphite, graphene and carbon nanotubes.   The paint according to claim 7 or 8, wherein carbon materials of different particle sizes are combined.   The current collector which has a carbon coat layer according to any one of claims 1 to 6.   A battery comprising the current collector according to claim 10. It is a method of forming on a current collector a carbon coat layer provided on the side where irregularities due to a carbon material come in contact with an active material, and the following steps:
Providing a paint comprising a carbon material, and applying the paint on 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 no cups are formed in the region corresponding to the formation region of the carbon coat layer on the current collector. How to feature   The method according to claim 12, wherein the area in which the cup is not formed has a dimension larger than the maximum particle size of the active material.   The method according to claim 12 or 13, wherein the dimension of the region in which the cup is not formed is 0.01 mm or more and 10 mm or less.   The method according to any one of claims 12 to 14, wherein the paint is the paint according to any one of claims 7-9. A gravure plate for forming a carbon coat layer containing a carbon material on a current collector,
A gravure printing plate having a region in which a plurality of cups are formed and a region in which a cup is not formed in a region corresponding to a region where the carbon coat layer is formed on the current collector.   The gravure plate according to claim 16, wherein the area in which 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 16 or 17, wherein the dimension of the area in which the cup is not formed is 0.01 mm or more and 10 mm or less.

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