Method for producing secondary battery electrode

Abstract

In order to suppress the occurrence of cracking, the present invention disperses an active material powder onto the surface of a current collector (102a, 104a) to form an active material powder layer (102c, 104c), applies an ink (30) containing a binder onto the active material powder layer (102c, 104c) with an ink-jet method, and dries the ink (30) to form an active material layer (102b, 104b).

Description

Method for manufacturing electrodes for secondary batteries

[0001] The present invention relates to a method for producing an electrode for a secondary battery.

[0002] A known method for producing an electrode catalyst layer for a secondary battery involves ejecting a first ink containing an active material and a conductive agent but not a binder using an inkjet method, and then ejecting a second ink containing a binder but not an active material or a conductive agent using an inkjet method (Patent Document 1).

[0003] Patent No. 4720176

[0004] When the active material and conductive agent are ejected by an inkjet method as in the above-described conventional technology, the particle size of the active material and conductive agent must be 1 μm or less in relation to the nozzle diameter of the inkjet. However, in the inkjet method, the ink containing the active material and conductive agent is made low-viscosity by the solvent. When the solvent of the ejected ink evaporates, the small-diameter particles of the active material and conductive agent move to the evaporation point of the solvent, causing cracks in the electrode. This results in the problem that it is not possible to fabricate a thick-film electrode.

[0005] The problem to be solved by the present invention is to provide a method for manufacturing a secondary battery electrode that can suppress the occurrence of cracks.

[0006] The present invention solves the above problem by scattering active material powder on the surface of a current collector to form an active material powder layer, then applying an ink containing a binder to the active material powder layer using an inkjet method, and drying the ink to form an active material layer.

[0007] According to the present invention, it is not necessary to use an active material with a small diameter, and therefore cracking of the electrode can be suppressed.

[0008] Fig. 1 is a plan view showing an example of a secondary battery to which an embodiment of a method for manufacturing an electrode for a secondary battery according to the present invention can be applied. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is an enlarged cross-sectional view showing a part of the power generating element in Fig. 1. Fig. 4 is a process diagram showing an embodiment of a method for manufacturing an electrode for a secondary battery according to the present invention. Fig. 5 is a process diagram showing another embodiment of a method for manufacturing an electrode for a secondary battery according to the present invention. Fig. 6 is a process diagram showing yet another embodiment of a method for manufacturing an electrode for a secondary battery according to the present invention.

[0009] Hereinafter, with reference to the drawings, an embodiment for carrying out the present invention will be described. <Secondary Battery Structure> First, an example of the structure of a secondary battery 10 to which an embodiment of the electrode manufacturing method according to the present invention can be applied will be described. Fig. 1 is a plan view showing the secondary battery 10 of this example, and Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Note that the structure of the secondary battery 10 shown in Fig. 1 is not limited to the structure shown in Figs. 1 and 2, and may be applied to secondary batteries of other structures.

[0010] As shown in FIGS. 1 and 2 , the secondary battery 10 of this example is composed of a power generating element 101 having three positive electrode layers 102, seven electrolyte layers 103, and three negative electrode layers 104, positive electrode tabs 105 connected to the three positive electrode layers 102, respectively, negative electrode tabs 106 connected to the three negative electrode layers 104, and an upper exterior member 107 and a lower exterior member 108 that accommodate and seal the power generating element 101, positive electrode tabs 105, and negative electrode tabs 106.

[0011] The numbers of the positive electrode layers 102, the electrolyte layers 103, and the negative electrode layers 104 are not particularly limited, and the power generating element 101 may be configured with one positive electrode layer 102, three electrolyte layers 103, and one negative electrode layer 104, or the numbers of the positive electrode layers 102, the electrolyte layers 103, and the negative electrode layers 104 may be appropriately selected as needed.

[0012] The positive electrode layer 102 includes a positive electrode current collector 102a extending to the positive electrode tab 105 and a positive electrode active material layer 102b formed on each of the two main surfaces of the positive electrode current collector 102a. The positive electrode current collector 102a can be made of an electrochemically stable metal foil, such as aluminum foil, aluminum alloy foil, copper-titanium foil, or stainless steel foil. Metals that can be used to form the positive electrode current collector 102a include nickel, iron, copper, and the like, as well as clad materials of nickel and aluminum and clad materials of copper and aluminum. The positive electrode current collector 102a is not limited to a metal material; a conductive resin can also be used, such as a resin obtained by adding a conductive filler to a non-conductive polymer material as needed.

[0013] The positive electrode active material constituting the positive electrode active material layer 102b is not particularly limited, but may be LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ A composite oxide containing lithium and nickel is preferably used, and Li(Ni—Mn—Co)O is more preferably used. ２and those in which a portion of these transition metals is substituted with other elements (hereinafter also simply referred to as "NMC composite oxides"). NMC composite oxides also include composite oxides in which a portion of the transition metal elements is substituted with other metal elements. In this case, examples of the other elements include Ti, Zr, Nb, W, and P. Note that positive electrode active materials other than those mentioned above may also be used.

[0014] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, or the like. The content of the positive electrode active material in the positive electrode active material layer 102b is not particularly limited. The positive electrode active material layer 102b may further contain a conductive additive as needed. The conductive additive forms an electron conduction path and reduces the electron transfer resistance of the positive electrode active material layer 102b and the negative electrode active material layer 104b, thereby contributing to improving the high-rate output characteristics of the battery.

[0015] Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel, silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF)), carbon nanotubes (CNT), carbon nanofibers, and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). Furthermore, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives. Among these conductive additives, from the viewpoint of electrical stability, it is preferable to include at least one selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon, more preferably at least one selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon, and even more preferably at least one selected from the group consisting of carbon. These conductive additives may be used alone or in combination of two or more.

[0016] The conductive additive is preferably in the form of particles or fibers. When the conductive additive is in the form of particles, the shape of the particles is not particularly limited, and may be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, or spindle shape.

[0017] In the secondary battery 10 of this example, each of the three positive electrode collectors 102a constituting the three positive electrode layers 102 is joined to one positive electrode tab 105. The positive electrode tab 105 may be made of aluminum foil, aluminum alloy foil, copper foil, nickel foil, or the like.

[0018] The negative electrode layer 104 has a negative electrode side current collector 104a extending to the negative electrode tab 106 and a negative electrode active material layer 104b formed on each of the two main surfaces of the negative electrode side current collector 104a. The negative electrode side current collector 104a can be made of an electrochemically stable metal foil such as nickel foil, copper foil, stainless steel foil, or iron foil.

[0019] The negative electrode active material constituting the negative electrode active material layer 104b is not particularly limited, but examples thereof include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb ２ O ５ , Li ４ Ti ５ O １２ Examples of the metal active material include simple metals such as In, Al, Si, and Sn, TiSi, La, ３ Ni ２ Sn ７ and other alloys.

[0020] The negative electrode active material may be a metal containing Li. Such a negative electrode active material is not particularly limited as long as it is an active material containing Li, and may be Li metal or a lithium alloy containing Li. Examples of lithium alloys include alloys of lithium and at least one metal selected from gold (Au), magnesium (Mg), aluminum (Al), calcium (Ca), zinc (Zn), tin (Sn), and bismuth (Bi). Examples of lithium alloys include alloys of lithium and two or more of the above-mentioned metals. Specific examples of lithium alloys include lithium-gold alloys (Li-Au), lithium-magnesium alloys (Li-Mg), lithium-aluminum alloys (Li-Al), lithium-calcium alloys (Li-Ca), lithium-zinc alloys (Li-Zn), lithium-tin alloys (Li-Sn), and lithium-bismuth alloys (Li-Bi).

[0021] In the secondary battery 10 of this example, the three negative electrode layers 104 are configured such that each negative electrode side current collector 104a constituting the negative electrode layer 104 is joined to a single negative electrode tab 106. In the secondary battery 10 of this example, each of the three negative electrode side current collectors 104a constituting the three negative electrode layers 104 is joined to one negative electrode tab 106. The negative electrode tab 106 can be made of copper foil, copper alloy foil, copper and nickel clad foil, or the like.

[0022] The electrolyte layer 103 is a layer in which an electrolyte is retained in a separator 103a, and is located between the positive electrode active material layer 102b and the negative electrode active material layer 104b to prevent direct contact between them. The separator 103a in this example has the function of retaining the electrolyte to ensure lithium ion conductivity between the positive electrode layer 102 and the negative electrode layer 104, and the function of acting as a partition wall between the positive electrode layer 102 and the negative electrode layer 104. Examples of the separator 103a in this example include a porous sheet separator made of a polymer or fiber that absorbs and retains the electrolyte, a nonwoven fabric separator, and the like.

[0023] The electrolyte used in the electrolyte layer 103 in this example is not particularly limited, and examples thereof include an electrolytic solution, a gel polymer electrolyte, etc. By using these electrolytes, high lithium ion conductivity can be ensured.

[0024] The positive electrode layers 102 and the negative electrode layers 104 are alternately stacked with the electrolyte layers 103 interposed therebetween, and the electrolyte layers 103 are further stacked on the top and bottom layers, respectively, to form the power generating element 101.

[0025] The power generating element 101 configured as described above is housed and sealed in an upper exterior member 107 and a lower exterior member 108. The upper exterior member 107 and the lower exterior member 108 for sealing the power generating element 101 are formed of a flexible material, such as a resin film such as polyethylene or polypropylene, or a resin-metal thin film laminate material in which both sides of a metal foil such as aluminum are laminated with a resin such as polyethylene or polypropylene, and by heat-sealing the upper exterior member 107 and the lower exterior member 108, the power generating element 101 is sealed with the positive electrode tab 105 and the negative electrode tab 106 protruding to the outside.

[0026] Note that, on the positive electrode tab 105 and the negative electrode tab 106, sealing films 109 are provided at the portions that come into contact with the upper exterior member 107 and the lower exterior member 108, in order to ensure adhesion with the upper exterior member 107 and the lower exterior member 108. The sealing film 109 is not particularly limited, but can be made of, for example, a synthetic resin material that has excellent electrolyte resistance and heat-sealing properties, such as polyethylene, modified polyethylene, polypropylene, modified polypropylene, or ionomer.

[0027] <<Electrode Manufacturing Method>> Next, an embodiment of a method for manufacturing a secondary battery electrode according to the present invention will be described. Fig. 3 is an enlarged cross-sectional view showing a portion of the power generating element 101 of Fig. 1, showing a basic unit structure in which one positive electrode layer 102 and one negative electrode layer 104 are stacked with one electrolyte layer 103 interposed therebetween. As described above, the positive electrode layer 102 has positive electrode active material layers 102b formed on both sides of a positive electrode current collector 102a, and the negative electrode layer 104 has negative electrode active material layers 104b formed on both sides of a negative electrode current collector 104a. The electrolyte layer 103 is made of a separator 103a that holds an electrolyte.

[0028] In the method for manufacturing a secondary battery electrode of this embodiment (hereinafter also simply referred to as the manufacturing method), when forming the positive electrode active material layer 102b on the surface of the positive electrode-side current collector 102a and / or when forming the negative electrode active material layer 104b on the surface of the negative electrode-side current collector 104a, an active material powder is scattered on the surface of the current collector to form an active material powder layer (first step), then an ink containing a binder is applied to the active material powder layer by an inkjet method (second step), and then the ink is dried to form an active material layer (third step).

[0029] That is, instead of applying a paste or slurry of active material containing a binder to the surface of the current collector, a powder of active material without a binder is dispersed on the surface of the current collector to form a powder active material powder layer, and then a liquid ink containing a binder is applied to the surface of this powder active material powder layer by an inkjet method, and finally the liquid ink is dried to obtain the active material layer. More specifically, with respect to the positive electrode layer 102, a powder of positive electrode active material without a binder is dispersed on the surface of the positive electrode-side current collector 102a to form a powder positive electrode active material powder layer, and then a liquid ink containing a binder is applied to the surface of this powder positive electrode active material powder layer by an inkjet method, and finally the liquid ink is dried to obtain the positive electrode active material layer 102b. Similarly, more specifically, with regard to the negative electrode layer 104, a powdered negative electrode active material to which no binder is added is scattered on the surface of the negative electrode-side current collector 104a to form a powdered negative electrode active material powder layer, and then a liquid ink containing a binder is applied to the surface of this powdered negative electrode active material powder layer by an inkjet method, and finally the liquid ink is dried to obtain the negative electrode active material layer 104b.

[0030] 4 is a process diagram showing one embodiment of a method for manufacturing a secondary battery electrode according to the present invention. In this embodiment, a conveyor device 21 is provided for conveying a positive electrode current collector 102a or a negative electrode current collector 104a at a constant speed in the direction of the arrow. The sheet-like positive electrode current collector 102a or negative electrode current collector 104a is conveyed at a constant speed from left to right in FIG. 4, and is processed in the order of step 1, step 2, and step 3.

[0031] 4 , when the positive electrode layer 102 is produced, a powdered positive electrode active material without a binder is dispersed on the surface of the positive electrode-side current collector 102a to form a powdered positive electrode active material powder layer. Similarly, when the negative electrode layer 104 is produced, a powdered negative electrode active material without a binder is dispersed on the surface of the negative electrode-side current collector 104a to form a powdered negative electrode active material powder layer. Since the manufacturing methods for the positive electrode layer 102 and the negative electrode layer 104 are the same except for the materials used, the manufacturing method of this embodiment will be described below using the case of producing the positive electrode layer 102 as an example.

[0032] In this specification, the term "powder" refers to an aggregate of particles (including granulated particles) in which the components present in the system exhibit substantially solid properties. The aggregate is defined as including at least one of particle units and aggregates formed by agglomeration of multiple particles. For example, a system in a solution, slurry, or paste state due to the presence of a relatively large amount of liquid components is not considered a "powder." As long as this definition is met, the powder may contain a liquid component such as an electrolyte solution. From the perspective of separating the aggregated particles and uniformly dispersing them on the surface of the current collector, the powder is preferably a dry powder that does not contain a liquid component. From the perspective of easily adjusting the particle size, the powder composed of solid particles may also be a wet powder containing a liquid component such as an electrolyte solution (preferably an electrolyte solution). The content of the liquid component in this case is not particularly limited as long as the "powder" state is maintained, but is preferably 0 to 10% by mass, more preferably 0.01 to 8% by mass, even more preferably 0.1 to 5% by mass, and particularly preferably 0.1 to 3% by mass relative to 100% by mass of the powder composed of solid particles.

[0033] As described above, the positive electrode active material is LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O ２ Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Si-containing active materials such as Li ４ Ti ５ O １２ Examples of the negative electrode active material include, as described above, carbon materials, metal oxides, and metal active materials. Furthermore, a conductive additive is added to the positive electrode active material or the negative electrode active material as needed, and examples of the conductive additive include, as described above, metals, metal oxides, and carbon. Therefore, in the first step of the manufacturing method of this embodiment, a powder of the positive electrode active material, a powder of the negative electrode active material, and a powder of the conductive additive are prepared, and these powders are sprayed onto the surface of the positive electrode side current collector 102a using the powder spraying device 22 shown in FIG. 4.

[0034] The volume average particle diameter D50 of the positive electrode active material powder and the negative electrode active material powder is not particularly limited, but if the particle diameter of the powder is too large, the gaps between the particles will become large, which is thought to cause an increase in resistance. Therefore, it is preferably 310 μm or less, more preferably 300 μm or less, more preferably 280 μm or less, even more preferably 240 μm or less, even more preferably 200 μm or less, and particularly preferably 180 μm or less. The lower limit of the volume average particle diameter D50 of the powder particles is not particularly limited, but if the particle diameter is too small, the flowability will be poor and it will be difficult to form the electrode during electrode production. Therefore, it is preferably 43 μm or more, more preferably 45 μm or more, even more preferably 50 μm or more, and particularly preferably 100 μm or more. The average particle diameter (primary particle diameter) of the conductive additive is not particularly limited, but from the viewpoint of the electrical characteristics of the battery, it is preferably 0.01 to 10 μm.

[0035] The device for scattering the positive electrode active material powder, the negative electrode active material powder, and the conductive additive powder on the surface of the current collector is not particularly limited, and any device capable of scattering the powder with a uniform film thickness may be used. The illustrated powder scattering device 22 applies vibrations of a predetermined frequency to the stored powder, causing a constant amount of powder to fall from the edge per unit time.

[0036] 4, a mixed powder of a positive electrode active material powder and a conductive additive powder is placed in a powder spraying device 22, and vibration is applied to the mixed powder to simultaneously spray the positive electrode active material powder and the conductive additive powder onto the surface of the positive electrode current collector 102a. As a result, a positive electrode active material powder layer 102c is formed on the surface of the positive electrode current collector 102a. This positive electrode active material powder layer 102c is a deposit of dry powder or wet powder with a very small amount of liquid component.

[0037] In the second step shown in the center of FIG. 4 , whether the positive electrode layer 102 or the negative electrode layer 104 is being manufactured, a liquid ink 30 containing a binder is applied to the surface of the powdered positive electrode active material powder layer 102c by an inkjet method. That is, as shown in FIG. 4 , an inkjet applicator 23 is used to apply the liquid ink 30 containing the binder to the surface of the positive electrode active material powder layer 102c. The inkjet applicator 23 is fixed to the top of the conveyor device 21 in the second step and ejects a constant amount of ink 30 onto the positive electrode active material powder layer 102c formed on the surface of the positive electrode-side current collector 102a, which is being transported at a constant speed. This allows the ink 30 to penetrate into the powdered positive electrode active material powder layer 102c, forming a wet deposit.

[0038] Inkjet printing is a printing method in which liquid ink is ejected from a nozzle and deposited on a target. Inkjet printing is classified into piezoelectric, thermal inkjet, bubble jet, continuous, and valve types depending on the method of ejecting the ink. Piezoelectric printing uses a piezoelectric element located at the bottom of an ink chamber that stores ink. The piezoelectric element deforms when an electric current flows through it, ejecting the ink from the nozzle. Thermal inkjet printing uses a heater to heat the ink, ejecting it using the energy of a steam explosion that occurs when the ink vaporizes. Like thermal inkjet printing, bubble jet printing also ejects ink using the energy of a steam explosion that occurs when the ink vaporizes. While thermal inkjet printing and bubble jet printing use different heating elements, they share the same basic principle. The continuous method is a method in which ink delivered by a pump and continuously ejected in a linear fashion from a nozzle is vibrated at a specific frequency in the head, creating a constriction in the linear ink, which then breaks into droplets at the constriction. These droplets can be electrically charged to land at a targeted location. The valve method is a method in which a shaft called a valve needle is provided within the head, and ink is pushed out of the nozzle by driving this shaft up and down toward the nozzle inside the head where the ink is stored. The manufacturing method of this embodiment may be any of the following: piezo method, thermal inkjet method, bubble jet (registered trademark) method, continuous method, and valve method.

[0039] The components contained in the ink are a binder and a solvent. The type of binder is not particularly limited, but examples include polyvinylidene fluoride (PVdF) and a composite of polyvinylidene fluoride and hexafluoropropylene (HFP). The solvent is not particularly limited, but examples include N-methylpyrrolidone (NMP) and acetonitrile.

[0040] The blending ratio of the binder and solvent components contained in the ink is not particularly limited, as long as the viscosity of the ink is low enough to be applicable to the inkjet method. However, from the viewpoint of improving the efficiency of the ink drying process in the subsequent step, a higher concentration of the binder component is preferable. One method for maintaining a low viscosity is to increase the temperature of the ink. The compounds contained in the ink may also be modified to lower the viscosity. The viscosity of the ink is not particularly limited, but is preferably about 10 to 100 cP.

[0041] 4, the solvent contained in the ink 30 is evaporated using a drying device 24, thereby drying the ink 30. As a result, a positive electrode active material layer 102b is formed on the surface of the positive electrode-side current collector 102a. In the third step, since the solvent contained in the ink 30 applied in the second step only needs to be evaporated, the ink 30 may be left at room temperature. However, from the viewpoint of shortening the drying time, it is preferable to perform forced drying using a drying device 24 having a heating or warming means.

[0042] By carrying out the above-described processes from step 1 to step 3, the positive electrode active material layer 102b is formed on one surface of the positive electrode side current collector 102a, and then the positive electrode side current collector 102a is turned over, and the same processes from step 1 to step 3 are carried out on the other surface of the positive electrode side current collector 102a, thereby producing the positive electrode layer 102 shown in Fig. 3. The same applies to the negative electrode layer 104.

[0043] 4, in forming the positive electrode active material powder layer 102c, a mixed powder of a positive electrode active material powder and a conductive additive powder is simultaneously sprayed onto the surface of the positive electrode-side current collector 102a using a powder sprayer 22. However, the manufacturing method of the present invention is not limited to this process, and the positive electrode active material powder and the conductive additive powder may be sprayed separately without being mixed. FIG. 5 is a process diagram showing another embodiment of the manufacturing method of a secondary battery electrode according to the present invention.

[0044] In the manufacturing method of the embodiment shown in FIG. 5 , in the first step on the left, a powder of the positive electrode active material is placed in powder spraying device 22, a powder of the conductive additive is placed in powder spraying device 25, and vibration is applied to each powder, thereby separately spraying the powder of the positive electrode active material and the powder of the conductive additive onto the surface of the positive electrode-side current collector 102a. In this case, the powder of the positive electrode active material may be sprayed onto the surface of the positive electrode-side current collector 102a, and then the powder of the conductive additive may be sprayed onto the surface of the positive electrode-side current collector 102a. Alternatively, the powder of the conductive additive may be sprayed onto the surface of the positive electrode-side current collector 102a, and then the powder of the positive electrode active material may be sprayed onto the surface of the positive electrode-side current collector 102a. However, spraying the powder with a larger particle size first and then the powder with a smaller particle size will result in better dispersibility of the positive electrode active material and the conductive additive in the positive electrode active material powder layer 102c formed after the spraying.

[0045] 4 and 5, an electrode is produced by forming an active material layer on the surface of a current collector, and a secondary battery can be produced using this electrode and a separately formed porous sheet separator made of polymer or fiber or a nonwoven fabric separator. However, a separator layer may also be formed on the surface of the active material layer using the production method of the present invention. That is, after the third step shown in Fig. 4 or 5, a separator powder layer 103b is formed by scattering a powder of a separator constituent material on the surface of the active material layer (fourth step), then an ink containing a binder is applied to the separator powder layer 103b by an inkjet method (fifth step), and then the ink is dried to form a separator layer 103c (sixth step).

[0046] 6 is a process diagram showing yet another embodiment of the method for manufacturing a secondary battery electrode according to the present invention. In the manufacturing method of the embodiment shown in FIG. 6, an electrode in which a positive electrode active material layer 102b is formed on one side of a positive electrode current collector 102a is used, and a separator layer 103c is formed on the surface of the positive electrode active material layer 102b. Note that the target for forming the separator layer 103c is not limited to an electrode in which a positive electrode active material layer 102b is formed on one side of a positive electrode current collector 102a as shown in the figure, but may also be an electrode in which a positive electrode active material layer 102b is formed on both sides of a positive electrode current collector 102a, or an electrode in which a negative electrode active material layer 104b is formed on one or both of a negative electrode current collectors 104a.

[0047] In the fourth step shown on the left side of FIG. 6 , a powdered separator constituent material without binder is spread on the surface of the positive electrode active material layer 102b to form a powdered separator powder layer 103b. The separator constituent material is not particularly limited, but examples thereof include aluminum oxide. In the fourth step shown in FIG. 6 , the separator constituent material powder is placed in a powder spreader 22, and vibration is applied to the powder to spread the separator constituent material powder on the surface of the positive electrode active material layer 102b. This forms a separator powder layer 103b on the surface of the positive electrode active material layer 102b. This separator powder layer 103b is a deposit of dry powder or wet powder with a very small amount of liquid component.

[0048] In the fifth step shown in the center of FIG. 6 , a liquid ink 30 containing a binder is applied to the surface of the separator powder layer 103b by an inkjet method. That is, as shown in FIG. 6 , an inkjet application device 23 is used to apply the liquid ink 30 containing the binder to the surface of the separator powder layer 103b. The inkjet application device 23 is fixed to the top of the conveyor device 21 in the fifth step and ejects a constant amount of ink 30 onto the separator powder layer 103b formed on the surface of the positive electrode active material layer 102b, which is being transported at a constant speed. As a result, the ink 30 penetrates the separator powder layer 103b and forms a wet deposit. Note that the manufacturing method of this embodiment may be any of a piezo method, a thermal inkjet method, a bubble jet (registered trademark) method, a continuous method, and a valve method.

[0049] The components contained in the ink are a binder and a solvent. The type of binder is not particularly limited, but examples include polyvinylidene fluoride (PVdF) and a composite of polyvinylidene fluoride and hexafluoropropylene (HFP). The solvent is not particularly limited, but examples include N-methylpyrrolidone (NMP) and acetonitrile.

[0050] The blending ratio of the binder and solvent components contained in the ink is not particularly limited, as long as the viscosity of the ink is low enough to be applicable to the inkjet method. However, from the viewpoint of improving the efficiency of the ink drying process in the subsequent step, a higher concentration of the binder component is preferable. One method for maintaining a low viscosity is to increase the temperature of the ink. The compounds contained in the ink may also be modified to lower the viscosity. The viscosity of the ink is not particularly limited, but is preferably about 10 to 100 cP.

[0051] 6, the solvent contained in the ink 30 is evaporated using a drying device 24, thereby drying the ink 30. As a result, a separator layer 103c is formed on the surface of the positive electrode active material layer 102b. In the sixth step, all that is required is to evaporate the solvent contained in the ink 30 applied in the fifth step, so the ink 30 may be left at room temperature. However, from the viewpoint of shortening the drying time, it is preferable to perform forced drying using a drying device 24 having a heating or warming means.

[0052] As described above, the manufacturing method of this embodiment includes a first step of spraying a positive electrode active material powder onto the surface of the positive electrode current collector 102a to form the positive electrode active material powder layer 102c, a second step of applying a binder-containing ink 30 to the positive electrode active material powder layer 102c using an inkjet method, and a third step of drying the ink 30 to form the positive electrode active material layer 102b. This eliminates the need for a small-diameter positive electrode active material. This can prevent electrode cracks from occurring when the ink 30 dries. Similarly, the manufacturing method of this embodiment includes a first step of spraying a negative electrode active material powder onto the surface of the negative electrode current collector 104a to form the negative electrode active material powder layer 104c, a second step of applying a binder-containing ink 30 to the negative electrode active material powder layer 104c using an inkjet method, and a third step of drying the ink 30 to form the negative electrode active material layer 104b. This eliminates the need for a small-diameter negative electrode active material. Therefore, cracks in the electrodes that occur when the ink 30 dries can be suppressed.

[0053] Furthermore, according to the manufacturing method of this embodiment, in the first step, the positive electrode active material powder layer 102c or the negative electrode active material powder layer 104c is formed by scattering a mixed powder of an active material powder and a conductive additive powder on the surface of the current collector, thereby improving the dispersibility of the conductive additive.

[0054] Furthermore, according to the manufacturing method of this embodiment, in the first step, the positive electrode active material powder layer 102c or the negative electrode active material powder layer 104c is formed by scattering an active material powder on the surface of the current collector and then scattering a conductive additive powder on the surface of the current collector, or by scattering a conductive additive powder on the surface of the current collector and then scattering an active material powder on the surface of the current collector, so that the step of mixing the active material and the conductive additive can be omitted.

[0055] Furthermore, according to the manufacturing method of this embodiment, in the second step, the ink containing the binder does not contain an active material or a conductive additive, so there is no need to use a small-diameter active material, which further reduces cracking of the electrode that occurs when the ink 30 is dried.

[0056] Furthermore, according to the manufacturing method of this embodiment, after the third step, the manufacturing method includes a fourth step of scattering a powder of a separator constituent material onto the surface of the positive electrode active material layer 102b or the negative electrode active material layer 104b to form the separator powder layer 103b, a fifth step of applying an ink 30 containing a binder onto the separator powder layer 103b by an inkjet method, and a sixth step of drying the ink 30 to form the separator layer 103c, so that the separator 103a can also be manufactured simultaneously as the separator layer 103c.

[0057] Furthermore, according to the manufacturing method of this embodiment, one of the positive electrode or negative electrode manufactured as described above and the other of the positive electrode or negative electrode manufactured as described above are stacked together with the separator 103 a interposed therebetween, thereby making it possible to provide a secondary battery in which cracking of the electrodes is suppressed.

[0058] DESCRIPTION OF SYMBOLS 10... Secondary battery 101... Power generating element 102... Positive electrode layer 102a... Positive electrode side current collector 102b... Positive electrode active material layer 102c... Positive electrode active material powder layer 103... Electrolyte layer 103a... Separator 103b... Separator powder layer 103c... Separator layer 104... Negative electrode layer 104a... Negative electrode side current collector 104b... Negative electrode active material layer 105... Positive electrode tab 106... Negative electrode tab 107... Upper exterior member 108... Lower exterior member 109... Sealing film 21... Conveyor device 22, 25... Powder spraying device 23... Inkjet coating device 24... Drying device 30... Ink

Claims

1. a first step of scattering an active material powder on a surface of a current collector to form an active material powder layer; a second step of applying an ink containing a binder onto the active material powder layer by an inkjet method; and a third step of drying the ink to form an active material layer.

2. 2. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein in the first step, the active material powder layer is formed by scattering a mixed powder of the active material powder and a conductive additive powder on the surface of the current collector.

3. In the first step, the active material powder layer is The active material powder is dispersed on the surface of the current collector, and then the conductive additive powder is dispersed on the surface of the current collector, or 2. The method for manufacturing an electrode for a secondary battery according to claim 1, wherein the electrode is formed by scattering a powder of a conductive additive on the surface of the current collector, and then scattering a powder of the active material on the surface of the current collector.

4. 4. The method for manufacturing an electrode for a secondary battery according to claim 2, wherein in the second step, the ink containing the binder does not contain the active material or the conductive additive.

5. a fourth step of forming a separator powder layer by scattering a powder of a separator constituent material on the surface of the active material layer after the third step; a fifth step of applying the ink containing the binder onto the separator powder layer by an inkjet method; 4. The method for manufacturing an electrode for a secondary battery according to claim 1, further comprising a sixth step of drying the ink to form a separator layer.

6. One electrode manufactured by the method according to any one of claims 1 to 3; A method for manufacturing a secondary battery, comprising stacking the other electrode manufactured by the method according to any one of claims 1 to 3 with a separator interposed therebetween.

7. A method for producing a secondary battery, comprising the method according to any one of claims 1 to 3.