JP2015011896A - Method for manufacturing secondary battery electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a secondary battery electrode, capable of suppressing the segregation of a binder in the vicinity of a current collector foil.SOLUTION: A method for manufacturing a secondary battery electrode includes: a powder molding step S20 of supplying granulated particles 21 on a current collector foil 2 to form a powder molding layer 110, the granulated particles containing an electrode active material and a binder 20 and serving as a powdery electrode mixture; a mixture paste coating step S30 of applying an electrode mixture paste 23 containing an electrode active material and the binder 20, on the current collector foil 2 including the powder molding layer 110 formed thereon; and a drying step S40 of drying the current collector foil 2 including the electrode mixture paste 23 applied thereon to form a mixture paste layer 120.

Description

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

  Conventionally, an electrode used for a secondary battery such as a lithium ion battery or a nickel metal hydride battery is a paste-like mixture containing an active material, a conductive material, a binder (binder), and the like applied on a current collector foil. Manufactured by drying.

  Further, as a method for manufacturing a battery electrode, a method for manufacturing a battery electrode having a structure in which a mixture layer containing an active material and a binder is held by a current collector is known (see, for example, Patent Document 1). .

  In Patent Document 1, in order to suppress the segregation of the binder in the electrode for the secondary battery, a binder capturing liquid capable of capturing the binder is applied to the surface of the current collector, and the current collecting is applied with the binder capturing liquid. A method of obtaining an electrode in which a mixture layer (mixture layer) is formed on a current collector (current collector foil) by applying a mixture paste containing an active material and a binder to the surface of the body and then drying the paste Is disclosed.

JP 2011-187343 A

  However, as described in Patent Document 1, when an electrode is formed by applying a mixture paste to a current collector foil, the binder is segregated on the electrode surface side (surface layer side), and the vicinity of the current collector foil There is a problem that the amount of the binder on the side is reduced, and the binder cannot be held near the current collector foil.

  Specifically, for example, in manufacturing a lithium ion secondary battery by applying a mixture paste, when the mixture paste is dried rapidly after application of the mixture paste, binder migration (binder particles in the coating liquid) Therefore, there is a problem that the binder is segregated on the electrode surface side (surface layer side). When the binder is segregated on the electrode surface side (surface layer side) as described above, as a result, the adhesion between the current collector foil and the electrode mixture layer is weakened, and the peel strength of the electrode mixture layer is reduced. May be a factor.

  As shown in FIG. 6, the cause of the segregation of the binder as described above is that after the mixture paste is applied to the current collector foil (FIGS. 6A and 6B), the coating is dried. As the solvent in the agent paste evaporates, the binder in the vicinity of the current collector foil moves to the upper layer (surface layer) of the electrode (FIG. 6 (c)) and is completely dried in that state (FIG. 6 (d)). This is probably because of this. In order to suppress such binder migration, there is a measure of setting mild drying conditions when drying after applying the mixture paste, but drying is increased as a contradiction.

  Then, this invention is made | formed in view of the said subject, Comprising: It aims at providing the manufacturing method of the electrode for secondary batteries which can suppress the segregation of the binder of current collection foil vicinity.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in the manufacturing method of the electrode for secondary batteries of Claim 1,
A powder molding step for forming a powder molding layer by supplying granulated particles as a powder electrode mixture containing an electrode active material and a binder on the current collector foil, and the powder molding layer is formed A mixture paste application step of applying an electrode mixture paste containing an electrode active material and a binder on the collected current foil, and drying the current collector foil coated with the electrode mixture paste to obtain a mixture paste layer And a drying step for forming the film.

  In the manufacturing method of the electrode for secondary batteries of Claim 2, the amount of the binder contained in the said powder molding layer is comprised more than the amount of the binder contained in the said mixture paste layer.

  In the manufacturing method of the electrode for secondary batteries of Claim 3, the binder application | coating process which apply | coats a binder on the said current collection foil is provided before the said powder shaping | molding process.

  According to the present invention, it is possible to suppress the segregation of the binder in the vicinity of the current collector foil during the manufacture of the electrode and to hold the binder in the vicinity of the current collector. As a result, the peel strength between the current collector and the electrode mixture layer is improved.

  Further, as an incidental effect of the present invention, when the electrode mixture layer is formed only with the granulated particles, the basis weight of the electrode mixture layer varies due to the low fluidity of the granulated particles. The basis weight of the electrode mixture layer is improved by forming a layer formed by applying and drying a paste-like electrode mixture on the layer made of particle particles.

The figure which showed typically the manufacturing apparatus which enforces the manufacturing method of the electrode for secondary batteries which concerns on one Embodiment of this invention. The figure which shows the flow of the manufacturing method of the electrode for secondary batteries which concerns on one Embodiment of this invention. The figure which showed the migration suppression image in the case of manufacture of the electrode for secondary batteries of this invention. The graph which compared the electrode peeling strength of the Example and the comparative example 1. FIG. The graph which shows the fabric weight precision of the foil width direction (TD direction) of each electrode (negative electrode) which concerns on an Example and the comparative example 2. FIG. The figure which showed the image of the binder migration generation | occurrence | production situation in the manufacture of the conventional electrode.

Next, embodiments of the invention will be described.
The manufacturing method of the electrode for secondary batteries which concerns on this embodiment is applicable when manufacturing the electrode (electrode sheet) which a nonaqueous electrolyte secondary battery (for example, lithium ion secondary battery) has.

  First, a lithium ion secondary battery will be described as an example of a non-aqueous electrolyte secondary battery including an electrode manufactured using the method for manufacturing a secondary battery electrode according to the present embodiment.

[Nonaqueous electrolyte secondary battery (lithium ion secondary battery)]
A lithium ion secondary battery (not shown) is formed, for example, by accommodating an electrode body including a sheet-like positive electrode (positive electrode sheet) and a negative electrode (negative electrode sheet) in a superimposed or wound state in the battery container. It is configured as a cylindrical battery, a square battery, a laminated battery, or the like. Specifically, a lithium ion secondary battery forms an electrode body by laminating a positive electrode and a negative electrode formed in a sheet shape by overlapping or spirally winding them through a separator. It is manufactured by filling the electrolytic solution in a state where the body is accommodated in the battery housing, and sealing the battery housing. The lithium ion secondary battery manufactured in this manner includes an electrode body including a positive electrode, a negative electrode, a separator, and the like, and a battery container that holds the electrode body, and the electrolyte solution is non-aqueous. An electrolyte is used.

  The positive electrode (positive electrode sheet) forms on the current collector foil an electrode mixture layer containing an electrode material such as a positive electrode active material capable of inserting and extracting lithium ions, a conductive material, a binder (binder), and a thickener. It is a thing. As the positive electrode (positive electrode sheet), a positive electrode manufactured by the method for manufacturing an electrode for a secondary battery according to the present embodiment can be used.

As the positive electrode active material, a positive electrode active material such as a lithium transition metal composite oxide can be used. As the positive electrode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and a lithium transition metal composite oxide in which a part thereof is substituted with another element can be used.

  The conductive material is for ensuring the electrical conductivity of the positive electrode. As the conductive material, carbon material powders such as natural graphite, artificial graphite, acetylene black (AB), and carbon black can be used.

  The negative electrode (negative electrode sheet) has an electrode mixture layer including a negative electrode active material, a binder (binder), and an electrode material such as a thickener that can occlude lithium ions during charging and can be released during discharging. Is formed. As the negative electrode (negative electrode sheet), a negative electrode produced by the method for producing an electrode for a secondary battery according to the present embodiment can be used.

  The negative electrode is not particularly limited as long as it can use a negative electrode active material having the characteristics of occluding lithium ions during charging and releasing lithium ions during discharging. Examples of the material having such characteristics include lithium metal, carbon materials such as graphite and amorphous carbon, and the like. Among them, it is preferable to use a carbon material having a relatively large voltage change with charging / discharging of lithium ions, and it is more preferable to use a carbon material made of natural graphite or artificial graphite having high crystallinity.

  The binder (binder) plays a role of binding and bonding the positive electrode active material, the conductive material particles, the negative electrode active material particles, and the like. In addition, the binder plays a role of binding and holding these particles and the current collector foil. As such a binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), a fluorine-containing resin such as fluorine rubber, or a thermoplastic resin such as polypropylene is used. it can.

The thickener is for imparting viscosity to the electrode mixture paste (positive electrode mixture paste or negative electrode mixture paste). As the thickener, for example, polyethylene oxide (PEO), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and the like are used.
In addition, a thickener is used when it is desired to give viscosity to the electrode mixture paste, and may be appropriately used as necessary.

  The separator is for electrically insulating the positive electrode and the negative electrode and holding the non-aqueous electrolyte. Examples of the material constituting the separator include a porous synthetic resin film, particularly a porous film such as a polyolefin-based polymer (polyethylene, polypropylene).

Examples of the electrolytic solution include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). A solution in which a lithium salt such as LiPF ₆ , LiClO ₄ , LiBF ₄ or the like is dissolved as a supporting electrolyte in a mixed organic solvent such as a chain carbonate such as can be used.

  The positive electrode (positive electrode sheet) and the negative electrode (negative electrode sheet) described above are overlapped or wound via a separator to form an electrode body, and the positive electrode and the negative electrode terminal communicated to the outside from the positive electrode and the negative electrode. Are electrically connected to each other, and this electrode body is housed in an appropriate battery housing (a metal or resin casing, a bag body made of a metal laminate film such as aluminum), these positive electrodes, and A lithium ion secondary battery is configured by filling a nonaqueous electrolyte between the negative electrodes and sealing the battery housing.

  Next, the manufacturing apparatus 1 for manufacturing the electrode for secondary batteries which concerns on this embodiment is demonstrated using FIG.

  The secondary battery electrode manufacturing apparatus 1 (hereinafter referred to as the manufacturing apparatus 1) according to the present embodiment applies a binder 20 to the current collector foil 2 (binder coating) while conveying the current collector foil 2. Three layers (binder layers) are formed on the current collector foil 2 by continuously performing the four steps of supplying and molding the powder composed of the granulated particles 21, applying the electrode mixture paste 23, and drying the electrode mixture paste 23. 100, an electrode mixture layer 200 (see FIG. 3) comprising a powder molding layer 110 and a mixture paste layer 120). As shown in FIG. 1, the manufacturing apparatus 1 is mainly composed of a conveying means 3, a binder applying means 4, a powder molding apparatus 5, a mixture paste applying means 6, and a drying furnace 15 as a drying means. ing.

  The current collector foil 2 is a thin long sheet-like electrode base material used when manufacturing a secondary battery electrode. The current collector foil 2 is a metal foil (for example, an aluminum foil for the positive electrode and a copper foil for the negative electrode) on which the predetermined electrode mixture layer 200 is formed by the manufacturing apparatus 1 on one side surface or both side surfaces (in this embodiment, one side surface). ).

  The conveying means 3 engages the current collecting foil 2 supplied from a supply roller (not shown) provided on the upstream side of the conveying means 3 with a plurality of rollers, and a predetermined conveying speed ( In this embodiment, it is an apparatus for conveying in order to the binder application | coating means 4, the powder shaping | molding apparatus 5, the mixture paste application | coating means 6, and the drying furnace 15 in order of 2 m / min). The conveyance means 3 includes a plurality of guide rollers 3a, 3b, 3c, a backup roller 6a included in the mixture paste application means 6, a supply roller (not shown) as a current collector foil supply unit, and a current collector foil winding It is mainly comprised from the winding roller (not shown) which is a part. The winding roller is provided on the downstream side of the drying furnace 15. As shown in FIG. 1, by setting the current collector foil 2 on the transport means 3, a transport path for the current collector foil 2 is formed. Further, the current collector foil 2 is wound around the supply roller for a predetermined length in advance, and the current collector foil 2 drawn out from the supply roller passes through the plurality of guide rollers 3a, 3b, 3c and the outer peripheral surface of the backup roller 6a. And the current collector foil 2 extended from the backup roller 6 a is wound around the winding roller via the drying furnace 15. Thus, when the take-up roller is driven to rotate at a predetermined speed by a drive means (not shown), the current collector foil 2 wound around the supply roller is drawn out, first conveyed to the binder application means 4, and then guided to the guide roller. It is conveyed to the powder molding device 5 via 3a and 3b, and then conveyed to the mixture paste applying means 6 via the guide roller 3c. The current collector foil 2 is transported while being supported by the outer peripheral surface of the backup roller 6a on the back side, and is transported so as to face the die coater 6b. Then, the current collector foil 2 that has passed through the mixture paste applying means 6 passes through the drying furnace 15 and is taken up by a take-up roller. That is, the conveying means 3 rotates the winding roller by a driving means (not shown), whereby the current collector foil 2 is fed along the conveying path at a predetermined conveying speed at the binder applying means 4, the powder molding apparatus 5, and the mixture. It is possible to convey the paste to the paste applying means 6 and the drying furnace 15 in order.

[Binder application method (gravure coater)]
The binder application unit 4 is provided on the upstream side of the conveying path of the current collector foil 2 in the manufacturing apparatus 1, and the slurry-like binder 20 is applied to one side surface (surface) of the current collector foil 2 with a predetermined basis weight. A gravure coater capable of applying (coating) the binder 20. The binder application unit 4 includes a rotatable pressure roller 7, a gravure roller 8 that is pressure-bonded to the pressure roller 7 via the current collector foil 2, a storage tray 9 that stores the binder 20, and a blade 10. The binder application unit 4 can apply the slurry binder 20 to one side surface (surface) of the current collector foil 2 fed from a supply roller (not shown) by the pressure roller 7 and the gravure roller 8.

  Specifically, a part (lower part) of the gravure roller 8 arranged on the lower side of the current collector foil 2 conveyed along the conveyance path is immersed in the binder 20 in the storage tray 9 and is collected along the conveyance path. It arrange | positions so that a part (lower part) of the press roller 7 arrange | positioned above the electric foil 2 may press the other side surface (back surface) of the current collection foil 2 conveyed along a conveyance path | route. The gravure roller 8 has a so-called predetermined-type gravure pattern on its outer peripheral surface, and the gravure pattern is formed by a predetermined-type engraving. The gravure roller 8 is rotated in a direction opposite to the conveying direction of the current collector foil 2 by a driving unit (not shown). When the gravure roller 8 rotates, the binder 20 in the storage tray 9 adheres to the outer peripheral surface of the gravure roller 8, and the binder 20 attached to the gravure roller 8 is scraped by the blade 10 so that the adhesion amount of the binder 20 becomes a predetermined amount. Be dropped. Then, the gravure roller 8 having a predetermined amount of the binder 20 attached to the outer peripheral surface presses one side surface (the front surface) of the current collector foil 2, whereby the binder 20 is formed on the current collector foil 2 with a predetermined basis weight and predetermined patterning. One side (surface) is applied (coated). Thus, the binder coating means 4 forms a binder layer (binder coat) 100 on one side surface (surface) of the current collector foil 2. Although details will be described later, in the method for manufacturing an electrode for a secondary battery according to the present embodiment, the binder layer 100 is disposed on one side (surface) of the current collector foil 2 by the binder coating unit 4 and is the lowest layer in the electrode mixture layer 200. As the first formed.

[Powder molding equipment]
The powder molding apparatus 5 is provided on the downstream side of the binder application unit 4 in the transport path of the current collecting foil 2 guided by the guide roller 3b and the guide roller 3c, and the current collector transported along the transport path. By continuously supplying granulated particles 21 that are powdered electrode mixture to the foil 2 and press-molding (compression molding) the current collector foil 2 to which the granulated particles 21 are supplied. This is an apparatus for forming a powder molding layer 110 composed of granulated particles 21. As shown in FIG. 1, the powder molding apparatus 5 mainly includes a powder supply apparatus 11, a flattening means (squeegee 12), and a molding means 13.
The granulated particles 21 that are the powdery electrode mixture are granulated by a spray drying apparatus (not shown) described later.
Moreover, although the powder molding apparatus 5 of this embodiment is a structure provided with the planarization means (squeegee 4), it is not specifically limited to the structure of this embodiment. That is, the flattening means (squeegee 12) in the powder molding apparatus 5 is not an essential component.

  The powder supply device 11 supplies the granulated particles 21 which are powdery electrode mixture onto the current collector foil 2 and forms the supplied granulated particles 21 as a deposited layer on the current collector foil 2. Device (powder feeder). The powder supply device 11 can continuously supply a certain amount of the granulated particles 21 onto the current collector foil 2 and deposit the granulated particles 21 on the current collector foil 2.

  The conveyance means 3 is a means for conveying the current collector foil 2 in order to the powder supply device 11, the squeegee 12, and the molding means 13 in the powder molding apparatus 5. The conveying means 3 can convey the granulated particles 21 supplied from the powder supply device 11 onto the current collector foil 2 to the downstream side by driving a driving means (not shown).

  The squeegee 12 is a blade member that is provided on the downstream side of the powder supply device 11 and has a sharp tip at the tip. The squeegee 12 faces the tip downward and has a predetermined gap between the tip and the surface of the current collector foil 2. The arrangement is fixed so as to have a gap (Gap). The squeegee 12 planarizes the granulated particles 21 supplied onto the current collector foil 2 by the powder supply device 11 and deposits the powdered granulated particles 21 having the same thickness as the predetermined interval. It is a planarization means for forming.

The molding means 13 is a roll-type pressure molding means provided on the downstream side of the squeegee 12, and has a plurality of rotatable press rollers (upper and lower pressure rollers in this embodiment) 13a and 13a. The molding means 13 is a hot press capable of heating and pressing in the thickness direction of the current collector foil by inserting the current collector foil 2 on which the deposited layer of the granulated particles 21 is formed between the upper and lower press rollers 13a and 13a. It is a means and what is called a roll press process is possible. Specifically, the molding means 13 holds each of the press rollers 13a and 13a while holding the current collector foil 2 on which the powdery deposited layer made of the granulated particles 21 is formed between the press rollers 13a and 13a. A thickness or density (electrode) is applied to the current collector foil 2 discharged from the downstream side of the molding means 13 by performing a roll press process under predetermined hot press conditions (heating temperature / pressing pressure) while rotating in opposite directions. It is possible to form the powder molding layer 110 having an appropriately adjusted density. Although details will be described later, in the method for manufacturing an electrode for a secondary battery according to the present embodiment, the powder molding layer 110 is an electrode mixture layer on the current collector foil 2 on which the binder layer 100 is formed by the powder molding device 5. 200 is formed as a lower layer. In this powder molding device 5, powder-like granulated particles 21 are supplied on a binder layer 100 composed of a slurry-like binder 20 applied to the current collector foil 2 by the binder application unit 4, and are rolled. By processing, the powder molding layer 110 is formed on the binder layer 100.
In addition, in the powder molding apparatus 5 of this embodiment, although it is the structure provided with the shaping | molding means 13 (heat press means), it does not specifically limit to the structure of this embodiment. That is, the molding means 13 (heat press means) in the powder molding apparatus 5 is not an essential configuration.

[Mixture paste application means]
The mixture paste applying means 6 is composed of an electrode active material, a binder and a solvent on a powder molding layer 110 (lower layer in the electrode mixture layer 200) composed of powdered granulated particles 21 containing an electrode active material and a binder. It is a means for apply | coating the electrode mixture paste 23 which is a paste-like electrode mixture containing these. As shown in FIG. 1, the mixture paste application unit 6 is mainly composed of a backup roll 6a, a die coater 6b, a pump 6c, and a tank 6d.
In addition, although the mixture paste application | coating means 6 of this embodiment is a structure provided with the die coater 6b, it is not limited to the structure of this embodiment in particular. That is, the die coater 6b in the mixture paste application unit 6 is not an essential component.

  The backup roll 6a is a roller that is disposed to face the die coater 6b and supports the other surface side (back surface) of the current collector foil 2. The die coater 6 b has a discharge port for discharging the electrode mixture paste 23 to the current collector foil 2. The pump 6c is a pump that supplies the electrode mixture paste 23 from the tank 6d to the die coater 6b. The tank 6 d is a container that stores the electrode mixture paste 23.

  When the mixture paste applying means 6 is operated, the electrode mixture paste 23 stored in the tank 6d is first sucked up by the pump 6c. Then, the electrode mixture paste 23 is supplied from the pump 6c to the die coater 6b, and is supplied to one side surface (surface) of the current collector foil 2 supported by the backup roll 6a through the discharge port of the die coater 6b. In the mixture paste application means 6, the electrode mixture paste 23 is supplied over the powder molding layer 110 formed on the current collector foil 2 by the powder molding device 5. In the die coater 6b, the electrode mixture paste 23 can be continuously applied to the current collector foil 2 moving along the outer peripheral surface of the backup roll 6a.

  The current collector foil 2 to which the electrode mixture paste 23 is applied by the mixture paste application unit 6 is conveyed in the downstream direction of the mixture paste application unit 6 indicated by an arrow in FIG. 1 and is introduced into the drying furnace 15. The current collector foil 2 coated with the electrode mixture paste 23 enters the inside of the drying furnace 15 from the inlet of the drying furnace 15. The drying furnace 15 can dry the electrode mixture paste 23 by evaporating the solvent in the electrode mixture paste 23 by blowing hot air against the current collector foil 2 coated with the electrode mixture paste 23. .

[Spray dryer]
A spray drying apparatus (not shown) is a granulated particle by spray drying an electrode mixture paste prepared using an electrode mixture component containing an electrode active material, a conductive material, a binder, and the like and a solvent for dispersing the component. It is a device for obtaining. Examples of such a spray drying apparatus include a spray dryer that performs spray drying by a spray drying method. If a spray dryer is used, the electrode mixture paste is sprayed in the form of fine particle droplets, which are brought into contact with hot air to instantaneously dry to obtain granulated particles 21.

  Next, the manufacturing method of the electrode for secondary batteries which concerns on one Embodiment of this invention using the manufacturing apparatus 1 mentioned above is demonstrated.

[Method for producing secondary battery electrode]
In the method for manufacturing an electrode for a secondary battery according to the present embodiment, a powder molding comprising a binder layer 100 made of a binder 20 on the current collector foil 2 and granulated particles 21 formed on the binder layer 100 is performed. This is a manufacturing method for manufacturing a sheet-like electrode having a layer 110 and a mixture paste layer 120 formed by applying and drying a paste-like electrode mixture containing an electrode active material and a binder on the powder molding layer 110. . As shown in FIG. 2, this method for manufacturing a secondary battery electrode mainly includes a binder coating step S10, a powder molding step S20, a mixture paste coating step S30, and a drying step S40, which are performed in this order. . The manufacturing method of the secondary battery electrode according to the present embodiment is performed using the manufacturing apparatus 1. When the secondary battery electrode is manufactured using the manufacturing apparatus 1, the manufacturing apparatus 1 includes the manufacturing apparatus 1. It is necessary to prepare the granulated particles 21 and the electrode mixture paste 23 to be supplied in advance. Therefore, first, a granulated particle preparation step and an electrode mixture paste preparation step will be described as preparation steps in the method for manufacturing a secondary battery electrode according to the present embodiment. Below, each said process is demonstrated concretely.

  The granulated particle preparation step includes a paste preparation step and a granulation step.

  The paste production process produces an electrode mixture paste at a predetermined composition ratio and solid content ratio using an electrode mixture component containing an electrode active material, a conductive material, a binder (binder), and the like and a solvent for dispersing the component. It is a process to do.

  As the solvent for dispersion, organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA) and water (purified water, etc.) can be used.

The granulation step is a step of granulating the granulated particles 21 using the electrode mixture paste obtained in the paste preparation step. Specifically, the granulation step uses a spray dryer or the like that is sprayed and heat-dried by a spray-drying method to spray and heat-dry the electrode mixture paste to obtain granulated particles. This is a step of crushing and classifying to produce a granule having properties such as a predetermined particle size and bulk density as the granulated particle 21.
In addition, the paste preparation process and granulation process mentioned above become a preparatory process for starting powder molding in powder molding process S20.
Moreover, the process of preparing the electrode mixture paste 23 used by the mixture paste application means 6 is the same process as the paste preparation process, and the description thereof is omitted.

The binder application step S <b> 10 is a step of applying (coating) the slurry-like binder 20 to one side surface (surface) of the current collector foil 2 with a predetermined basis weight by the binder application unit 4. In the binder application step S10, as shown in FIG. 3, a binder layer (binder coat) 100 is formed on one side surface (surface) of the current collector foil 2. In the binder application step S <b> 10, the current collector foil 2 on which the slurry binder 20 is applied and the binder layer 100 is formed is then conveyed to the powder molding apparatus 5.
In the present embodiment, the binder constituting the binder layer 100 and the binder contained in the granulated particles 21 used in the powder molding layer 110 are the same, but are not particularly limited, and different types of binders are used. Can also be used.

  In the powder molding step S20, the powder molding apparatus 5 continuously supplies the granulated particles 21 serving as a powdered electrode mixture to the current collector foil 2 transported along the transport path. This is a step of forming the powder molding layer 110 which is the lower layer in the electrode mixture layer 200 by press molding (compression molding) the current collector foil 2 supplied with the granulated particles 21. Specifically, in the powder molding step S20, as shown in FIG. 3B, the electrode active material and the binder 20 (binder layer 100) applied to the current collector foil 2 in the binder application step S10 are overlapped. By supplying granulated particles 21, which are a powdered electrode mixture containing a binder, and press-molding them, a powder molding layer 110 made of the granulated particles 21 is formed. The powder molding step S20 is a step performed using the powder molding apparatus 5 and includes a supply step, a flattening step, and a molding step.

  In the supplying step, the powdered granulated particles 21 obtained in the granulating step are supplied onto the current collector foil 2 by the powder supplying device 11 included in the powder molding device 5, and the granulated particles 21 are supplied. Is formed on the current collector foil 2 as a deposited layer.

  In the flattening step, the powdered granulated particles 21 supplied onto the current collector foil 2 by the powder supply device 11 using the squeegee 12 are flattened so that the surface is uniform, and a predetermined gap (Gap) is obtained. ) And the surface of the current collector foil 2 and a deposited layer of the granulated particles 21 having the same thickness dimension.

  In the molding step, the current collector foil 2 on which the powdery deposition layer composed of the granulated particles 21 is deposited is hot-pressed by the molding means 13 under predetermined hot press conditions (heating temperature / pressing pressure). This is a step of forming the powder molding layer 110 thinner than the deposited layer of the granulated particles 21. After completion of the molding step, the current collector foil 2 on which the powder molding layer 110 is formed as the lower layer in the electrode mixture layer 200 is then conveyed to the mixture paste application means 6.

  In the mixture paste application step S30, the electrode mixture paste is superposed on the powder molding layer 110 formed on the current collector foil 2 via the binder layer 100 in the powder molding step S20 by the mixture paste application means 6. 23 is a step of applying 23. In the mixture paste application step S <b> 30, the current collector foil 2 coated with the paste-like electrode mixture paste 23 is then conveyed to the drying furnace 15.

The drying step S40 is a step of drying the current collector foil 2 coated with the electrode mixture paste 23 in the mixture paste coating step S30 by the drying furnace 15. In this drying step, the solvent contained in the electrode mixture paste 23 is volatilized and the electrode mixture paste 23 is dried, whereby the mixture paste layer 120 is formed.
Thus, by the method for manufacturing an electrode for a secondary battery according to the present embodiment, the binder layer 100 that is the lowermost layer, the powder molding layer 110 that is the lower layer, and the upper layer in the electrode mixture layer 200 on the current collector foil 2. An electrode (electrode sheet) in which the mixture paste layer 120 is sequentially laminated is produced.

  The binder layer 100 is a layer provided between the current collector foil 2 and the powder molding layer 110 corresponding to the lower layer of the electrode mixture layer 200, and is a layer made of the binder 20. The binder layer 100 is a layer produced by coating the binder 20 with a predetermined pattern (patterning coating) by a gravure coater which is the binder coating unit 4 in the binder coating step S10.

The powder molding layer 110 is a layer that is provided on the current collector foil 2 via the binder layer 100 and is composed of powdered granulated particles 21 including the electrode active material and the binder 20, and the mixture paste layer 120. This is a layer produced by powder molding using granulated particles 21 which are more binder-rich. That is, the amount of the binder 20 in the powder molding layer 110 is larger than the amount of the binder 20 in the mixture paste layer 120 as an upper layer. The amount of the binder contained in the powder molding layer 110 is preferably about 1.0 to 5.0 wt%.
In addition, by setting the binder amount of the powder molding layer 110 to be larger than the binder amount of the mixture paste layer 120 as the upper layer as described above, the binder 20 is disposed near the current collector foil 2 as the electrode configuration. Since it can hold | maintain more reliably, the peeling strength between the current collection foil 2 and the electrode mixture layer 200 improves.

  The mixture paste layer 120 is a layer formed by applying and drying an electrode mixture paste 23, which is a paste-like electrode mixture containing the electrode active material and the binder 20, on the powder molding layer 110 made of the granulated particles 21. In this layer, the amount of the binder 20 is suppressed as compared with the powder molding layer 110 and the electrode mixture paste 23 is applied. Further, the amount of the binder 20 in the mixture paste layer 120 is configured to be smaller than the amount of the binder 20 in the powder molding layer 110 which is the lower layer. The amount of the binder contained in the mixture paste layer 120 is preferably about 0.5 to 4.0 wt%.

  In the electrode mixture layer 200, the weight ratio (weight ratio) in the electrode mixture layer 200 in the two layers of the powder molding layer 110 as the lower layer and the mixture paste layer 120 as the upper layer is 10:90 to 90. : 10 is preferable.

  In addition, in the manufacturing method of the electrode for secondary batteries which concerns on this embodiment, it is set as the structure which forms the binder layer 100 which hits the lowest layer as a layer structure of the electrode mixture layer 200, However It does not specifically limit. The binder layer 100 is preferably provided when more binder 20 is held in the vicinity of the current collector foil 2 to ensure peel strength. Therefore, the binder layer 100 can be manufactured by omitting the layer structure of the electrode mixture layer 200.

Next, while following the manufacturing method of the said secondary battery electrode, the negative electrode (negative electrode sheet) is manufactured as an Example of the manufacturing method of the secondary battery electrode using the manufacturing apparatus 1 and spray drying apparatus which were mentioned above, Peel strength and basis weight accuracy were evaluated using the negative electrode. Hereinafter, the present invention will be described with reference to examples and comparative examples.
Hereinafter, an example in which a negative electrode (negative electrode sheet) is manufactured by the method for manufacturing a secondary battery electrode according to the present embodiment will be described, but the present invention is not particularly limited, and the secondary battery electrode according to the present embodiment is not limited. It is also possible to produce the positive electrode (positive electrode sheet) by applying the manufacturing method to the positive electrode (positive electrode sheet).

[Example]
(Paste preparation process)
First, three types of electrode mixture components of graphite as a negative electrode active material, a binder (binder) made of styrene-butadiene copolymer (SBR), and carboxymethyl cellulose (CMC) as a thickener are predetermined. Composition ratio (the binder amount in this example is 5 wt% SBR in all electrode mixture components) and is dispersed in water as a dispersion solvent so that the solid content is 50 wt%. The mixture was kneaded using a mixer to prepare an electrode mixture paste for the granulation process.
In addition, about the electrode mixture paste 23 used by the mixture paste application | coating means 6, although the electrode mixture component and dispersion | distribution solvent of the same kind as the mixture paste produced at the said paste preparation process are used, The amount of SBR used as a binder is 1 wt%.

(Granulation process)
Next, the electrode mixture paste obtained in the paste preparation step was dried by hot air while spraying into the furnace under a predetermined furnace temperature condition by a spray drying method using a spray dryer to obtain granulated particles. . And the granulated particle 21 which has the desired average particle diameter and particle size distribution was obtained by performing the process of crushing and classifying the said granulated particle by a predetermined | prescribed appropriate means.
In addition, as a method of crushing the granulated particles, a known method such as a ball mill can be applied.

(Binder application process S10)
Next, the binder application means 4 causes the slurry-like binder 20 (in this embodiment, styrene-butadiene copolymer (SBR)) to be applied to one side surface (surface) of the current collector foil 2 with a predetermined basis weight. By applying (coating), the lowermost binder layer 100 in the electrode mixture layer 200 was formed (see FIG. 3).

  Next, the granulated particles 21 serving as a powdered electrode mixture are continuously supplied to the current collector foil 2 conveyed along the conveyance path by the powder molding device 5, and the granulation is performed. The current collector foil 2 supplied with the particles 21 was press-molded (compression-molded) to form a powder molded layer 110 as a lower layer in the electrode mixture layer 200 (see FIG. 3B).

(Mixture paste application process S30)
Next, the electrode mixture paste 23 was applied by the mixture paste applying means 6 so as to overlap the powder molding layer 110 formed on the current collector foil 2 via the binder layer 100.

(Drying step S40)
Next, the current collector foil 2 coated with the electrode mixture paste 23 was passed through the drying furnace 15 and dried, thereby forming a mixture paste layer 120 as an upper layer in the electrode mixture layer 200 (FIG. 3 ( c) (d)).
Thus, by the method for manufacturing an electrode for a secondary battery according to this embodiment, the lowermost binder layer 100, the lower powder molding layer 110, and the upper layer in the electrode mixture layer 200 on the current collector foil 2. A negative electrode for evaluation (negative electrode sheet) according to an example in which the mixture paste layer 120 and the laminate were sequentially laminated was prepared. Moreover, the powder molding layer 110 and the mixture paste layer 120 were produced so that the weight ratio (weight ratio) was 50:50.

[Comparative Example 1 (electrode having an electrode mixture layer consisting only of coating paste)]
The same electrode mixture component as in Example 1 is mixed at a predetermined composition ratio and dispersed in water as a dispersion solvent so that the solid content is 50 wt%, and these are mixed using a kneading apparatus (planetary mixer). And kneaded to prepare an electrode mixture paste. This electrode mixture paste was applied onto the current collector foil 2 and dried to prepare an evaluation negative electrode (negative electrode sheet) according to Comparative Example 1. The negative electrode for evaluation according to Comparative Example 1 is a single layer in which the electrode mixture layer on the current collector foil 2 is formed by applying and drying an electrode mixture paste. Moreover, the negative electrode for evaluation according to Comparative Example 1 includes the same kind and the same amount as the negative electrode for evaluation according to Example 1 as a binder.

[Comparative Example 2 (electrode having an electrode mixture layer consisting only of powder molding of granulated particles)]
The same electrode mixture component as in Example 1 is mixed at a predetermined composition ratio and dispersed in water as a dispersion solvent so that the solid content is 50 wt%, and these are mixed using a kneading apparatus (planetary mixer). And kneaded to prepare an electrode mixture paste. Using this, granulated particles were produced by spray drying. The granulated particles were supplied onto the current collector foil 2 and an electrode mixture layer was formed on the current collector foil 2 by powder molding to produce a negative electrode (negative electrode sheet) according to Comparative Example 2. The negative electrode for evaluation according to Comparative Example 2 is a single layer in which the electrode mixture layer on the current collector foil 2 is formed by powder molding of granulated particles.
As described above, the peel strength and the basis weight accuracy of the electrode mixture layer are evaluated by using the evaluation electrode (negative electrode) according to the manufactured example and comparative examples 1 and 2. Moreover, the negative electrode for evaluation according to Comparative Example 1 includes the same kind and the same amount as the negative electrode for evaluation according to Example 1 as a binder.

<Peel strength test>
Using a commercially available tensile tester, the peel strength of the electrode mixture layer in each negative electrode (negative electrode sheet) according to Example and Comparative Example 1 was evaluated. The evaluation results are shown in FIG. As is clear from FIG. 4, it was confirmed that the peel strength of the evaluation electrode of the example was remarkably improved as compared with Comparative Example 1 produced by only applying the mixture paste. This is because, in the electrode for evaluation of the example, the lower layer portion (portion in the vicinity of the current collector foil 2) of the electrode mixture layer 200 is first formed on the current collector foil 2 and the binder rich structure is formed thereon. The powder molding layer 110 is formed by powder molding using the particles, and the lower layer portion of the electrode mixture layer 200 in the upper layer portion of the electrode mixture layer 200 (the portion near the surface of the electrode mixture layer 200) In addition, the negative electrode having sufficient peel strength can be obtained by reducing the binder amount and forming the mixture paste layer 120 by paste application, which is a conventionally used application method. That is, in this embodiment, since the binder 20 is held in the vicinity of the current collector foil 2, the adhesion between the current collector foil 2 and the electrode mixture layer 200 is increased, and the current collector foil 2 and the electrode mixture layer are increased. A sufficient peel strength could be ensured between 200.

<Evaluation of basis weight accuracy>
In each evaluation electrode (negative electrode sheet) according to the example and the comparative example 2, the basis weight was measured at five positions between one end and the other end in the foil width direction (TD direction) (see FIG. 5). As can be seen from FIG. 5, the evaluation electrode according to Comparative Example 2 has three points outside the standard range and variation was recognized, but the evaluation electrode according to the example had all five points within the standard range. It was confirmed that there was almost no variation and good basis weight accuracy was obtained. This is because, when the electrode mixture layer is formed only by powder molding as in Comparative Example 2, it is difficult to form the electrode mixture layer with a uniform surface by supplying granulated particles quantitatively and with high accuracy. Therefore, it is considered that variation in the basis weight accuracy of the electrode mixture layer occurred. On the other hand, in this example, since the surface of the powder molding layer 110 was covered with the mixture paste layer 120, it was possible to obtain an electrode in which the basis weight of the electrode mixture layer was uniform.

  As described above, according to the present invention, it is possible to suppress the segregation of the binder in the vicinity of the current collector foil at the time of manufacturing the electrode and hold the binder in the vicinity of the current collector. As a result, the peel strength between the current collector and the electrode mixture layer is improved. Further, as an incidental effect of the present invention, when the electrode mixture layer is formed only with the granulated particles, the basis weight of the electrode mixture layer varies due to the low fluidity of the granulated particles. The basis weight of the electrode mixture layer is improved by forming a layer formed by applying and drying a paste-like electrode mixture on the layer made of particle particles.

2 Current collector foil 20 Binder 21 Granulated particles 100 Binder layer (lowermost layer)
110 Powder molding layer (lower layer)
120 Mixture paste layer (upper layer)

Claims (3)

A powder molding step of forming a powder molding layer by supplying granulated particles to be a powdered electrode mixture containing an electrode active material and a binder on the current collector foil,
A mixture paste application step of applying an electrode mixture paste containing an electrode active material and a binder on the current collector foil on which the powder molding layer is formed,
Drying the current collector foil coated with the electrode mixture paste to form a mixture paste layer; and
A method for producing an electrode for a secondary battery. Configuring the amount of binder contained in the powder molding layer to be greater than the amount of binder contained in the mixture paste layer;
The manufacturing method of the electrode for secondary batteries of Claim 1. Before the powder molding process,
A binder coating step of coating a binder on the current collector foil;
The manufacturing method of the electrode for secondary batteries of Claim 2 or Claim 3.

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