Coating slurry, manufacturing method of coating slurry, and mixer

Abstract

To provide a coating slurry capable of suppressing stringiness at the end of coating in intermittent coating slurry containing active material.SOLUTION: A disclosed coating slurry contains an active material, binder, solvent, and additives. The additives include at least one of the following: castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a coating slurry, a method for producing the coating slurry, and a stirring device. [Background technology]

[0002] An electrode used in a battery such as a lithium ion secondary battery includes a current collector and an active material layer formed on the current collector. The electrode is produced by coating a current collector with a slurry containing an active material. A known method for coating a current collector with a slurry is to intermittently coat the current collector with the slurry to form a coated portion and an uncoated portion.

[0003] However, when the process moves from the stage of supplying the slurry to the current collector to form a coated portion to the stage of stopping the supply of the slurry to the current collector to form an uncoated portion, a stringy trace of the slurry is formed at the end of the coating of the coated portion. If this stringy trace is long, it may lead to a decrease in battery capacity. In addition, since a lead connected to a battery terminal is welded to the uncoated portion, for example, the long stringy trace may make it difficult to weld the lead.

[0004] For example, Patent Document 1 discloses a coating device that forms coated and uncoated areas on a substrate, in which a vibration generator is attached to the lip tip of a coating head that ejects slurry onto the substrate. Patent Document 1 also discloses that the vibration generator vibrates the lip tip of the coating head at a desired vibration frequency, thereby improving the liquid cut-off of the coating fluid ejected from the lip tip and suppressing stringy marks that occur at the coating end of the coated portion formed on the substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-176824 A Summary of the Invention [Problem to be solved by the invention]

[0006] The stringiness at the end of the coating is affected by the coating speed of the slurry and the basis weight of the coated area. However, with conventional technology, depending on the conditions of the coating speed of the slurry and the basis weight of the coated area, it may not be possible to sufficiently suppress stringiness at the end of the coating. [Means for solving the problem]

[0007] A coating slurry according to one embodiment of the present disclosure includes an active material, a binder, a solvent, and an additive, and the additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.

[0008] A method for producing a coating slurry according to one embodiment of the present disclosure includes a step of obtaining a coating slurry by stirring a kneaded slurry containing an active material, a binder, and a solvent with an additive, and the additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid. Moreover, a mixing device according to one embodiment of the present disclosure is a mixing device that mixes a kneaded slurry containing an active material, a binder, and a solvent with an additive to obtain a coating slurry, and is characterized in that the additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid. Effect of the Invention

[0009] According to the present disclosure, it is possible to suppress stringiness at the end of coating in intermittent coating of a slurry containing an active material. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an example of the configuration of a coating device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a state in which a coating slurry is applied onto a current collector. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] Fig. 1 is a schematic diagram showing an example of the configuration of a coating device according to the present embodiment. The coating device 1 shown in Fig. 1 includes a kneader 10 as a kneading means, a stirring device 12 as a stirring means, a liquid delivery device 14, and a coating head 16 and an intermittent mechanism 18 as a coating means. The specific operation of the coating device 1 will be described later, but the coating device 1 produces a coated product in which a coated portion 26 in which a coating slurry is applied onto a current collector 34 and an uncoated portion 28 in which the coating slurry is not applied are formed, as shown in Fig. 1.

[0013] The kneader 10 kneads an active material, a binder, and a solvent to obtain a kneaded slurry. The kneading by the kneader 10 is, for example, a mixing method in which raw materials are broken down and dispersed by strong shearing. The kneader 10 may be a known kneader, for example, a Banbury mixer or a pressure kneader in which two rotor blades rotate in a container, or a batch kneader such as a two-shaft planetary mixer / kneader in which two blades simultaneously perform revolution and rotation. In addition, a continuous screw kneader such as a single-shaft kneading extruder or a two-shaft kneading extruder, a spiral mixer such as a kneader using a rotor with pins, or a film mix that confines the slurry in a high-speed rotating thin film by centrifugal force and kneads it may be used.

[0014] The stirring device 12 includes an additive supplying device 20 as an adding means, a controller 22, and an agitator 24. The additive supplying device 20 is electrically connected to the controller 22, and supplies the additive to the agitator 24 based on the amount of additive to be added transmitted from the controller 22.

[0015] The additive is a stringing inhibitor that suppresses stringing at the end of the coating, which will be described later, and contains at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.

[0016] The controller 22 sets the amount of additives to be added. The controller 22 is, for example, an IC (Integrated Circuit) chip equipped with a computer having a processor such as a CPU (Central Processing Unit) and operating according to a control program, or an IC chip of an ASIC (Application Specific Integrated Circuit). The controller 22 stores, for example, a map that specifies the relationship between the coating speed of the coating slurry and the amount of additives to be added, or a map that specifies the relationship between the basis weight of the coating section 26 and the amount of additives to be added. The controller 22 may store a table, a function formula, or the like that specifies the relationship between the coating speed of the coating slurry or the basis weight of the coating section 26 and the amount of additives to be added. The map is created in advance by experiments, etc. In general, the faster the coating speed is, or the greater the basis weight of the coating section 26 is, the longer the length of the stringy trace at the coating end of the coating section 26 is. Therefore, in order to obtain the stringiness suppression effect, the map indicates that the amount of the additive added increases with an increase in coating speed or an increase in the basis weight of the coated portion 26, for example.

[0017] The agitator 24 mixes the kneaded slurry with additives to obtain a coating slurry. The agitation by the agitator 24 is, for example, a stirring method in which a circulating flow of the raw materials is formed and mixed uniformly by weaker shear than that of the kneader 10. The agitator 24 may be a known agitator, such as a magnetic stirrer, a three-one motor, a homogenizer, a media mill, a colloid mill, a homomixer, a homodisper, a planetary mixer, an in-line mixer, or a pipeline mixer.

[0018] The liquid delivery device 14 delivers the coating slurry to the coating head 16, and is, for example, a pump.

[0019] The coating head 16 generally uses a type called a slot die, which ejects the coating slurry from a slit of a certain width. The slit is generally formed by sandwiching a plate of the required thickness called a shim between the upstream head and the downstream head. Also, a liquid reservoir called a manifold is generally provided on the upstream head side, and the coating is generally performed by ejecting the coating slurry through this.

[0020] The intermittent mechanism 18 is described as an example of a coating liquid suction type, but is not limited to this type. For example, the intermittent mechanism 18 intermittently sucks in the coating slurry supplied to the coating head 16, and instantaneously makes the pressure inside the coating head 16 negative. As a result, the coating slurry is intermittently discharged from the coating head 16, and a coated portion 26 and an uncoated portion 28 are formed.

[0021] An example of the operation of the coating device 1 according to this embodiment will be described.

[0022] An active material, a binder, and a solvent are fed into the kneader 10 and kneaded by the kneader 10 to obtain a kneaded slurry (first step). The obtained kneaded slurry is supplied to the agitator 24 through the flow path 30a. Here, the controller 22 searches a map that defines the relationship between the coating speed of the coating slurry and the amount of additive added or a map that defines the relationship between the basis weight of the coating section 26 and the amount of additive added, using a coating speed of the coating slurry or basis weight of the coating section 26 that is set in advance as a key, and obtains the amount of additive added that corresponds to the coating speed of the coating slurry or the basis weight of the coating section 26 that is set in advance.

[0023] The coating speed of the coating slurry or the basis weight of the coating section 26 that is set in advance is a coating condition that is set by an operator or the like when operating the apparatus. The operator inputs the coating speed of the coating slurry and the basis weight of the coating section 26 from the input device. Then, the input information on the coating speed of the coating slurry and the basis weight of the coating section 26 is transmitted to the controller 22. Alternatively, the operator inputs coating conditions such as the rotation speed of the roll 32 and the discharge amount of the coating head 16 from the input device. In this case, for example, information on the input coating conditions is transmitted to the controller 22, and the controller 22 calculates the coating speed of the coating slurry or the basis weight of the coating section 26 from the coating conditions such as the rotation speed of the roll 32 and the discharge amount of the coating head 16.

[0024] The controller 22 transmits to the additive supplying device 20 an amount of additive to be added that corresponds to a preset coating speed of the coating slurry or a basis weight of the coating section 26, and the additive supplying device 20 supplies the additive to the agitator 24 based on the received amount of additive to be added. Then, the agitator 24 agitates the kneaded slurry and the additive to obtain a coating slurry (second step).

[0025] The coating slurry obtained by the agitator 24 is supplied to the coating head 16 through the flow path 30b by the liquid delivery device 14. Then, the roll 32 is rotated at a set rotation speed, and while the strip-shaped current collector 34 is transported in the X direction, the coating slurry is discharged from the coating head 16 to the current collector 34 at a set discharge rate. In addition, the intermittent mechanism 18 is periodically operated to stop the discharge of the coating slurry from the coating head 16. In this manner, the coating slurry is intermittently applied to the current collector 34, and the coated portion 26 and the uncoated portion 28 are formed (third step).

[0026] Fig. 2 is a schematic diagram showing a state in which the coating slurry is applied onto a current collector. As shown in Fig. 2, the coating slurry is intermittently applied onto the current collector 34, so that a plurality of coated portions 26 and uncoated portions 28 are alternately formed on the current collector 34. The coated portions 26 refer to the region from the coating start end P1 to the coating end end P2. The uncoated portions 28 are later used for welding leads and cutting off each electrode for one battery.

[0027] Normally, even when the discharge of the coating slurry from the coating head 16 stops, the coating slurry spreads from the coating head 16 due to its surface tension, so that the coating slurry spreads from the coating end portion P2 toward the uncoated portion 28 along the conveying direction X, and stringy marks 36 tend to form. If the length L of the stringy marks 36 is large, this may cause poor lead welding in the uncoated portion 28 or a decrease in the capacity of the battery.

[0028] However, in the present disclosure, the coating slurry contains the above-mentioned specific additive. This makes it possible to suppress stringing at the coating end P2. Incidentally, as described above, stringing at the coating end P2 is affected by the coating speed and the basis weight of the coating part 26. Specifically, the faster the coating speed is, or the greater the basis weight of the coating part 26 is, the longer the length L of the stringing mark 36 becomes. Therefore, in order to provide a coating slurry that has a stringing suppression effect for any coating speed or basis weight, it is possible to include, for example, an excessive amount of the above-mentioned additive in the coating slurry, but in that case, for example, there is a risk that the manufacturing cost of the battery will increase or that the battery performance will deteriorate. However, in the present disclosure, since it is possible to add an optimal amount of additive according to the coating speed of the coating slurry and the basis weight of the coating part 26, it is possible to provide a coating slurry that has a stringing suppression effect for any coating speed or basis weight, and it is also expected to have the effect of suppressing the manufacturing cost of the battery and the deterioration of the battery performance.

[0029] In addition, in battery manufacturing, multiple coating lines with different coating speeds and coating weights of the coating part 26 may be provided according to the capacity, size, etc. of the battery. As disclosed herein, by dividing the process into a first step of obtaining a kneaded slurry and a second step of adding an optimal amount of additive to the kneaded slurry according to the coating speed of the coating slurry and the coating weight of the coating part 26, for example, the kneaded slurry obtained in the first step can be divided into small portions, and the second step can be performed for each of the small portions. This makes it possible to prepare multiple coating slurries suitable for the coating speed and coating weight of the coating part 26 of each of the multiple coating lines and supply them to each coating line.

[0030] The coated product having coated portion 26 and uncoated portion 28 formed on current collector 34 is dried and rolled as necessary, and applied to an electrode of a battery.

[0031] The materials such as the additives, active material, binder, solvent, and current collector 34 will be described in detail below.

[0032] The additives are castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene monomethyl ether acetate, polyamine, and polycarboxylic acid, as mentioned above. Among these, cellulose nanofiber and polyethylene oxide are preferred because they have a high effect of suppressing stringiness at the coating end P2. The additives are mainly added in the second step, but the addition in the first step is not limited. In other words, the additives may be added in the first and second steps. Polyethylene oxide refers to polyethylene with a carboxyl group (-COOH) attached to the end. The castor oil may be hydrogenated castor oil.

[0033] The additive contains cellulose nanofibers, and the cellulose nanofibers preferably contain lignocellulose. By containing lignocellulose, the additive becomes closer to lipophilicity, and for example, the dispersibility of the additive in an organic solvent-based coating slurry is improved.

[0034] When cellulose nanofibers are included as an additive, it is preferable that the cellulose nanofibers contain 50% or more (relative particle amount with the whole being 100%) of cellulose particles having a number average width of 3 to 100 nm in the short width direction, an aspect ratio of 40 or more, and a number average width of 100 μm or more in the long width direction. This makes it possible to more effectively suppress stringiness at the coating end portion P2, for example.

[0035] The number-average width can be measured by the following method. First, an aqueous dispersion of cellulose nanofibers with a solid content of 0.05 to 0.1% by mass is prepared, and the dispersion is cast on a carbon film-coated grid that has been hydrophilized to prepare a sample for observation with a transmission electron microscope (TEM). Then, observation is performed with an electron microscope image at a magnification of 5,000 times, 10,000 times, or 50,000 times depending on the size of the fibers that constitute the fiber. At that time, an axis of an arbitrary image width is assumed in the obtained image in the vertical and horizontal directions, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers cross the axis. Then, after obtaining an observation image that satisfies this condition, two random axes are drawn vertically and horizontally on the image, and the width of the fibers crossing the axis is visually read. In this way, at least three images of the surface portion that do not overlap are taken with an electron microscope, and the value of the width of the fibers crossing each of the two axes is read (thus, at least 20 × 2 × 3 = 120 pieces of width information is obtained). From the data on the number average width of the fibers thus obtained, the number average widths of the shorter and longer widths are calculated.

[0036] The aspect ratio of the cellulose nanofibers is calculated according to the following formula (1) using the number average width of the shorter width and the number average width of the longer width calculated as described above.

[0037] Aspect ratio = average width of longer side / average width of shorter side (1) The additive contains cellulose nanofibers, and the cellulose nanofibers are preferably contained in an amount of 0.01% by mass to 0.2% by mass relative to 100% by mass of the solid content of the coating slurry, which, for example, suppresses an increase in the viscosity of the coating slurry and facilitates intermittent coating.

[0038] The active material is appropriately selected depending on the type of battery or electrode to which the coating product is applied. For example, in the case of a positive electrode of a lithium ion secondary battery, lithium transition metal composite oxides and the like can be mentioned. Specifically, lithium cobalt oxide, lithium manganate, lithium nickel oxide, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide and the like can be mentioned. In addition, for example, Al, Ti, Zr, Nb, B, W, Mg, Mo and the like may be added to these lithium transition metal composite oxides. In addition, for example, in the case of a negative electrode of a lithium ion secondary battery, carbon materials and non-carbon materials capable of absorbing and releasing lithium ions can be mentioned. Examples of carbon materials include graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke and the like. Examples of non-carbon materials include silicon, tin, and alloys and oxides mainly composed of these.

[0039] The binder is not particularly limited as long as it is a substance that ensures the binding between the coating portion 26 and the current collector 34, and examples thereof include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., and may also be a partially neutralized salt), polyvinyl alcohol (PVA), and the like.

[0040] The solvent is not particularly limited as long as it can disperse the active material and the binder, and examples of the solvent include water, alcohol, and N-methyl-2-pyrrolidone (NMP).

[0041] The current collector 34 is appropriately selected depending on the type of battery or electrode to which the coated product is applied, and for example, in the case of a positive electrode of a lithium ion secondary battery, examples include a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, a film with the metal disposed on the surface, etc. Also, for example, in the case of a negative electrode of a lithium ion secondary battery, examples include a foil of a metal such as copper that is stable in the potential range of the negative electrode, a film with the metal disposed on the surface, etc.

[0042] The kneaded slurry or the coating slurry may contain a filler that imparts additional functions to the coated portion 26. For example, a conductive agent that increases the conductivity of the coated portion 26 may be included. Examples of the conductive agent include carbon black, acetylene black, and ketjen black.

[0043] <Experimental Example 1> A lithium transition metal composite oxide as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in a mass ratio of 98:1:1, and an appropriate amount of N-methyl-2-pyrrolidone as a solvent was added thereto. The mixture was kneaded using a kneader (Hivis Dispermix 3D-2, manufactured by Primix Corporation) to obtain a kneaded slurry.

[0044] To 500 L of the kneaded slurry, 0.1 mass % of cellulose nanofibers (L100, manufactured by Mori Machinery Co., Ltd.) was added, and the mixture was stirred with a stirrer (Homodisper 2.5 type, manufactured by Primix Corporation) to obtain a coating slurry.

[0045] As shown in Fig. 1, while rotating the roll and transporting the aluminum foil as a current collector in the transport direction X, the coating slurry was intermittently discharged from the coating head to form coated and uncoated areas on the aluminum foil. The coating conditions were a coating speed of the coating slurry of 40 m / min and a coating weight of 200 g / m 2 Coating was performed so that the length of the coated portion in the transport direction X was 200 mm, and the length of the uncoated portion in the transport direction X was 10 mm.

[0046] <Experimental Example 2> Intermittent coating was carried out in the same manner as in Experimental Example 1, except that polyethylene oxide (ET4010, manufactured by Kusumoto Chemicals Co., Ltd.) was added instead of the cellulose nanofibers.

[0047] <Experimental Example 3> Intermittent coating was carried out in the same manner as in Experimental Example 1, except that Amide (ET2020, manufactured by Kusumoto Chemicals Co., Ltd.) was added instead of cellulose nanofiber.

[0048] <Experimental Example 4> Intermittent coating was carried out in the same manner as in Experimental Example 1, except that castor oil (RM1920, manufactured by BASF) was added instead of cellulose nanofiber.

[0049] <Experimental Example 5> Intermittent coating was carried out in the same manner as in Experimental Example 1, except that cellulose nanofibers were not added.

[0050] The length of the stringy marks at the coating end was determined for Experimental Examples 1 to 5. Specifically, three coated parts were randomly selected from the multiple coated parts formed intermittently, the lengths of the stringy marks at the coating end in the three selected coated parts were measured, and the average value was determined, which was defined as the stringy mark length L. The length of the stringy marks at the coating end in the three coated parts is the average value of the lengths of the multiple stringy marks formed at each coating end.

[0051] The length L of the stringing trace in Experimental Example 5 was 100, and the length L of the stringing trace in Experimental Example 1 was 45 when expressed as a relative value. In other words, the length of the stringing trace at the end of the coating was shortened by adding cellulose nanofibers. Similarly, it was 50 for polyethylene oxide in Experimental Example 2, 67 for amide in Experimental Example 3, and 77 for castor oil in Experimental Example 4. In addition, coating slurries were prepared to which modified silicone, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid were added, and intermittent coating was performed in the same manner as in Experimental Example 1. As a result, in all of the above cases, the length L of the stringing trace was shorter than that of Experimental Example 5. [Explanation of symbols]

[0052] 1 coating device, 10 kneader, 12 agitator, 14 liquid delivery device, 16 coating head, 18 intermittent mechanism, 20 additive supply device, 22 controller, 24 agitator, 26 coating section, 28 uncoated section, 30a, 30b flow paths, 32 roll, 34 current collector, 36 string marks, P1 coating start end, P2 coating end end, X conveying direction.

Claims

1. A coating slurry comprising an active material, a binder, a solvent, and an additive, The coating slurry, wherein the additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.

2. 2. The coating slurry of claim 1, wherein the additive comprises the cellulose nanofibers, the cellulose nanofibers comprising lignocellulose.

3. The coating slurry according to claim 1, wherein the additive comprises the cellulose nanofibers, the cellulose nanofibers having a number average width in the short width direction of 3 to 100 nm, an aspect ratio of 40 or more, and 50% or more of the particles having a number average width in the long width direction of 100 μm or more (relative particle amount with the whole being 100%).

4. The coating slurry according to claim 1, wherein the additive comprises the cellulose nanofiber, and the cellulose nanofiber is contained in an amount of 0.01% by mass to 0.2% by mass relative to 100% by mass of a solid content of the coating slurry.

5. The method includes a step of stirring a kneaded slurry containing an active material, a binder, and a solvent with an additive to obtain a coating slurry, The method for producing a coating slurry, wherein the additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.

6. 6. The method for producing a coating slurry according to claim 5, wherein in the step, when the coating slurry is intermittently applied to a current collector to form a coated portion and an uncoated portion, an amount of the additive to be added to the kneaded slurry is set according to a coating speed of the coating slurry or a basis weight of the coated portion that is set in advance, and the additive is added to the kneaded slurry based on the set amount.

7. A mixing device for mixing a kneaded slurry containing an active material, a binder, and a solvent with an additive to obtain a coating slurry, comprising: The additive includes at least one of castor oil, cellulose nanofiber, modified silicone, amide, polyethylene oxide, propylene glycol monomethyl ether acetate, polyamine, and polycarboxylic acid.

8. An adding means for adding the additive to the kneaded slurry; and a controller that sets an amount of the additive added by the adding means in accordance with a preset coating speed of the coating slurry or a basis weight of the coated portion when the coating slurry is intermittently applied to a current collector to form a coated portion and an uncoated portion.

Images