Method for manufacturing secondary battery

Abstract

In order to suppress a decrease in charging density, a method for manufacturing secondary battery according to the present invention comprises: a current collector singulation step for preparing a piece of current collector (11) corresponding to the size of a secondary battery (10) to be manufactured; a powder layer formation step for forming an active material powder layer (12) by spraying powder of an active material on a surface of the current collector; an active material layer formation step for applying an ink containing a binder to the active material powder layer by an inkjet method, and drying the ink to form an active material layer (13); and a stacking step for stacking an electrode (14) having the active material layer formed on the surface of the current collector, and a separator (15).

Description

Secondary battery manufacturing method

[0001] The present invention relates to a method for manufacturing 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 the conductive agent are ejected by an inkjet method as in the above-mentioned conventional technology, the particle size of the active material and the conductive agent needs to be 1 μm or less in relation to the nozzle diameter of the inkjet. However, since a solid electrolyte interphase (SEI) film that causes a decrease in charge density is formed on the outermost surface of the active material, when the particles of the active material and the conductive agent are made small in diameter and the surface area is increased as in the above-mentioned conventional technology, there is a problem that the charge density decreases.

[0005] The problem to be solved by the present invention is to provide a method for manufacturing a secondary battery that can suppress a decrease in charge density.

[0006] The present invention solves the above problem by preparing a current collector in the form of an individual piece corresponding to the size of the secondary battery to be manufactured, scattering active material powder on the surface of the current collector to form an active material powder layer, applying ink containing a binder to the active material powder layer by an inkjet method, and drying the ink to form an active material layer.

[0007] According to the present invention, since it is not necessary to use an active material with a small diameter, it is possible to suppress a decrease in charge density.

[0008] FIG. 1 is a plan view showing an example of a secondary battery to which an embodiment of a manufacturing method 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 portion of the power generating element of FIG. 1; FIG. 4 is a process chart (part 1) showing an embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 5 is a process chart (part 2) showing an embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 6 is a process chart (part 1) showing another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 7 is a process chart (part 2) showing another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 8 is a process chart (part 1) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 9 is a process chart (part 2) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 10 is a process chart (part 1) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 11 is a process chart (part 2) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 12 is a process chart (part 2) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention; FIG. 13 is a process chart (part 1) showing yet another embodiment of a manufacturing method for a secondary battery according to the present invention;

[0009] Hereinafter, with reference to the drawings, an embodiment of the present invention will be described. {Secondary Battery Structure} First, an example of the structure of a secondary battery 10 to which the manufacturing method of a secondary battery 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. FIG. 3 is an enlarged cross-sectional view showing a portion of the power generating element 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. Note that the manufacturing method of the present invention is not limited to secondary batteries having the structures shown in FIGS. 1 to 3, and may be applied to secondary batteries having 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] As shown in FIG. 3 , 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. Examples of the conductive resin include a resin obtained by adding a conductive filler to a non-conductive polymeric 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. ２ and 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] 2, in the secondary battery 10 of this example, three positive electrode side current collectors 102a constituting three positive electrode layers 102 are each 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] 3, the negative electrode layer 104 has a negative electrode 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 current collector 104a. The negative electrode 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, each of the three negative electrode current collectors 104a constituting the three negative electrode layers 104 is joined to one negative electrode tab 106. The negative electrode tab 106 may be made of copper foil, copper alloy foil, copper-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 of this example is not particularly limited, and examples thereof include an electrolytic solution and a gel polymer electrolyte. High lithium ion conductivity can be ensured by using these electrolytes. Alternatively, a solid electrolyte or a semi-solid electrolyte, such as a sulfide solid electrolyte or an oxide solid electrolyte, may be used as the electrolyte in the electrolyte layer 103 of this example.

[0024] As shown in FIG. 2 , the positive electrode layers 102 and the negative electrode layers 104 are alternately stacked with the electrolyte layers 103 interposed therebetween, and further, the electrolyte layers 103 are stacked on the top and bottom layers, respectively, thereby forming the power generating element 101.

[0025] 1 and 2, 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 of polyethylene, polypropylene, or the like, 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] <<Method for Manufacturing Electrode>> Next, an embodiment of the method for manufacturing a secondary battery according to the present invention will be described. Fig. 4A is a process diagram showing an embodiment of the method for manufacturing a secondary battery according to the present invention, and Fig. 4B is a subsequent process diagram.

[0028] The manufacturing method of a secondary battery electrode of this embodiment (hereinafter also simply referred to as the manufacturing method) includes a current collector singulation step of preparing individual pieces of current collector 11 according to the size of secondary battery 10 to be manufactured; a powder layer formation step of spraying active material powder on the surface of individual pieces of current collector 11 to form active material powder layer 12; an active material layer formation step of applying ink containing a binder to active material powder layer 12 by an inkjet method and drying the ink to form active material layer 13; a pressurizing step of pressurizing active material layer 13 in the layer formation direction; and a lamination step of laminating electrode 14 having active material layer 13 formed on the surface of current collector 11 and separator sheet 15. The current collector 11 here includes the above-mentioned positive electrode side current collector 102 a and negative electrode side current collector 104 a, the active material powder layer 12 and the active material layer 13 include the above-mentioned positive electrode active material layer 102 b and negative electrode active material layer 104 b, and the separator sheet 15 includes the above-mentioned electrolyte layer 103 (separator 103 a).

[0029] In the current collector singulation process of this embodiment, as shown in FIG. 4A , a current collector sheet 11A wound into a roll is cut into individual pieces of current collector 11 using a cutting device 27 to a size corresponding to the size of the secondary battery 10 to be manufactured. In the manufacturing method of this embodiment, the current collector sheet 11A wound into a roll is singulated before forming the active material layer 13, rather than forming an active material layer or the like on its surface and then cutting the continuous current collector sheet 11A. This is because if the active material layer 13 and separator sheet 15 were formed on the surface of the current collector 11 and then singulated, the cut portions of the brittle active material layer 13 would crumble. Furthermore, handling the current collector sheet 11A wound into a roll requires a considerable amount of process space, and the use of a moisture-sensitive material for the positive electrode active material requires a large dry room space.

[0030] The size of the current collector 11 to be singulated in the current collector singulation step of this embodiment is not particularly limited, and may be any size that does not ultimately require cutting of the active material layer 13. For example, the current collector 11 may be cut to the size of the current collector 11 included in the finished secondary battery 10. Alternatively, the current collector 11 may be singulated to a larger size, leaving margins around the periphery to form the active material powder layer 12, the active material layer 13, and the separator sheet 15, and then some or all of the margins around the periphery may be cut off. This prevents the fragile active material layer 13 from collapsing, and also reduces the space required in the dry room because the current collector 11 is cut into individual pieces and is handled.

[0031] In the manufacturing method of this embodiment, to form the active material layer 13 on the surface of the individual current collector 11, an active material powder is dispersed on the surface of the current collector to form the active material powder layer 12 (powder layer forming step), and then an ink containing a binder is applied to the active material powder layer 12 by inkjet printing, and the ink is then dried to form the active material layer 13 (active material layer forming step). The powder layer forming step and the active material layer forming step include a step of forming the positive electrode active material layer 102b on the surface of the positive electrode current collector 102a and a step of forming the negative electrode active material layer 104b on the surface of the negative electrode current collector 104a, as shown in FIGS. 4A and 4B , the positive electrode active material layer is represented by 13P, the negative electrode active material layer is represented by 13N, the positive electrode current collector is represented by 11P, and the negative electrode current collector is represented by 11N.

[0032] That is, in the manufacturing method of this embodiment, instead of applying a paste or slurry active material containing a binder to the surface of current collector 11, a powdered active material without adding a binder is scattered on the surface of current collector 11 to form powdered active material powder layer 12, and then a liquid ink containing a binder is applied to the surface of this powdered active material powder layer 12 by an inkjet method, and finally the liquid ink is dried to obtain active material layer 13.

[0033] More specifically, with respect to the positive electrode layer 102 shown in the upper part of Fig. 4A , a powdered positive electrode active material without binder is sprayed onto the surface of an individual piece of a positive electrode-side current collector 11P to form a powdered positive electrode active material powder layer, and then a liquid ink containing a binder is applied to the surface of this powdered 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 13P. Similarly, more specifically, with respect to the negative electrode layer 104 shown in the lower part of Fig. 4A , a powdered negative electrode active material without binder is sprayed onto the surface of an individual piece of a negative electrode-side current collector 11N 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 13N.

[0034] 8 is a process diagram showing one embodiment of the powder layer forming step and the active material layer forming step. In the manufacturing process of this embodiment, a conveyor device 21 is provided that transports the positive electrode side current collector 11P or the negative electrode side current collector 11N at a constant speed in the direction of the arrow. The individual positive electrode side current collector 11P or the individual negative electrode side current collector 11N is transported at a constant speed from left to right in FIG. 8, and the processes are performed in the order of the powder layer forming step → the active material layer forming step.

[0035] 8 , 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 11P to form a powdered positive electrode active material powder layer 12P. 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 11N 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 process will be described below using the case of producing the positive electrode layer 102 as an example.

[0036] 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.

[0037] 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 powder layer formation 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 11P using a powder spraying device 22 shown in FIG. 8.

[0038] 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.

[0039] 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.

[0040] 8 , 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 a piece of positive electrode-side current collector 11P. As a result, a positive electrode active material powder layer 12P is formed on the surface of positive electrode-side current collector 11P. This positive electrode active material powder layer 12P is a deposit of dry powder or wet powder with a very small amount of liquid component.

[0041] In the active material layer forming step shown in FIG. 8 , 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 powdery positive electrode active material powder layer 12P or the powdery negative electrode active material layer by an inkjet method. That is, as shown in FIG. 8 , 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 12P. The inkjet applicator 23 is fixed to the top of a conveyor device 21 in the active material layer forming step, and ejects a constant amount of ink 30 onto the positive electrode active material powder layer 12P formed on the surface of an individual positive electrode current collector 11P, which is being transported at a constant speed. This allows the ink 30 to penetrate into the powdery positive electrode active material powder layer 12P, forming a wet deposit.

[0042] The inkjet method is a printing method in which liquid ink is ejected from a nozzle and adhered to a target object. Inkjet methods are classified into piezoelectric, thermal inkjet, and bubble jet (registered trademark) methods depending on the method of ejecting the ink. The piezoelectric method ejects ink from a nozzle by deforming a piezoelectric element that is placed at the bottom of an ink chamber that stores ink. The thermal inkjet method heats the ink using a heater and ejects the ink using the energy of a steam explosion that occurs when the ink vaporizes. Like the thermal inkjet method, the bubble jet (registered trademark) method also ejects ink using the energy of a steam explosion that occurs when the ink vaporizes. Although the thermal inkjet method and the bubble jet (registered trademark) method differ in the heating location, they share the same basic principle. The manufacturing method of this embodiment may be any of the piezoelectric, thermal inkjet, and bubble jet (registered trademark) methods.

[0043] 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. In addition, water-based binders such as styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) can also be used, in which case the solvent is water.

[0044] 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.

[0045] 8 , the ink 30 is dried by evaporating the solvent contained in the ink 30 using a drying device 24. As a result, a positive electrode active material layer 13P is formed on the surface of the positive electrode-side current collector 11P. In this drying step, since it is only necessary to evaporate the solvent contained in the ink 30 applied in the previous step, 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 and an air blowing means.

[0046] In the manufacturing method of the embodiment shown in Fig. 8, when forming the positive electrode active material powder layer 12P, a mixed powder of the positive electrode active material powder and the conductive additive powder is simultaneously sprayed onto the surface of the positive electrode side current collector 11P 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. 9 is a process diagram showing another embodiment of the powder layer forming process and the active material layer forming process.

[0047] In the manufacturing method of the embodiment shown in FIG. 9 , in the powder layer formation step on the left side, the positive electrode active material powder is placed in powder spraying device 22, the conductive additive powder is placed in powder spraying device 25, and vibration is applied to each powder, thereby separately spraying the positive electrode active material powder and the conductive additive powder onto the surface of positive electrode-side current collector 11P. In this case, the positive electrode active material powder may be sprayed onto the surface of positive electrode-side current collector 11P, and then the conductive additive powder may be sprayed onto the surface of positive electrode-side current collector 11P. Alternatively, the conductive additive powder may be sprayed onto the surface of positive electrode-side current collector 11P, and then the positive electrode active material powder may be sprayed onto the surface of positive electrode-side current collector 11P. 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 12P formed after the spraying.

[0048] 4A , by carrying out the above-described powder layer forming step and active material layer forming step, a positive electrode active material layer 13P is formed on one surface of the positive electrode side current collector 11P shown in the upper part of Fig. 4A , and in the subsequent inversion step, the positive electrode side current collector 11P is turned over, and the same powder layer forming step and active material layer forming step are carried out on the other surface of the positive electrode side current collector 11P. The same treatment is also carried out on the negative electrode layer 14N (104) shown in the lower part of Fig. 4A .

[0049] In the pressurizing step of this embodiment, the positive electrode active material layer 13P and the negative electrode active material layer 13N are each pressed in the layer formation direction using a pressurizing device 26 equipped with a pressure roller. This densifies the positive electrode active material layer 13P and the negative electrode active material layer 13N, increasing the charge density. Note that the pressurizing step using the pressurizing device 26 may be performed after the lamination step shown in FIG. 4B in addition to or instead of after the active material layer formation step.

[0050] In the lamination process of this embodiment, as shown in FIG. 4B , individual separator sheets 15 corresponding to the size of the secondary battery are prepared, and these individual separator sheets 15 are laminated with electrodes 14 each having an active material layer 13 formed on the surface of an individual current collector 11. The size of the separator sheets 15 to be singulated in the lamination process of this embodiment is not particularly limited. For example, the separator sheets 15 may be cut to the size of the separator sheets 15 included in the finished secondary battery 10. Alternatively, the separator sheets 15 may be singulated to a larger size and laminated with the electrodes 14, after which some or all of the surrounding margins may be cut off. Examples of the separator sheets 15 in this example include porous sheet separators made of polymers or fibers that absorb and retain electrolyte, and nonwoven fabric separators.

[0051] 4B , the positive electrode 14 (positive electrode layer 102 shown in FIG. 3 ) is indicated as a positive electrode layer 14 P, and the negative electrode 14 (negative electrode layer 104 shown in FIG. 3 ) is indicated as a negative electrode layer 14 N. Specifically, as shown in FIG. 4B , from top to bottom, the following layers are stacked: a positive electrode layer 14 P having an active material layer formed on only one side of a current collector 11, a separator sheet 15, a negative electrode layer 14 N having active material layers formed on both sides, a separator sheet 15, a positive electrode layer 14 P having active material layers formed on both sides, a separator sheet 15, a negative electrode layer 14 N having active material layers formed on both sides, a separator sheet 15, a positive electrode layer 14 P having active material layers formed on both sides, and a negative electrode layer 14 N having an active material layer formed on only one side of a current collector 11.

[0052] The power generating element 101 shown in FIG. 2 is manufactured by the above steps. This is then housed in the upper exterior member 107 and the lower exterior member 108 shown in the same figure, an electrolyte is poured into them, they are sealed, and predetermined processes such as an aging process and an initial charging process are carried out to complete the secondary battery 10.

[0053] 4A and 4B , in the lamination step shown in Fig. 4B , after preparing individual separator sheets 15 corresponding to the size of the secondary battery, electrodes 14 and separator sheets 15 are laminated. Alternatively, a separator powder layer may be formed by scattering a powder of a separator constituent material on the surface of an active material layer, and then an ink containing a binder may be applied to the separator powder layer by an inkjet method, and the ink may be dried to form the separator layer. Fig. 5A is a process diagram showing another embodiment of a method for manufacturing a secondary battery according to the present invention, and Fig. 5B is a subsequent process diagram.

[0054] The method for manufacturing a secondary battery electrode of this embodiment includes a current collector singulation step of preparing individual pieces of current collector 11 corresponding to the size of secondary battery 10 to be manufactured; a powder layer formation step of spraying active material powder on the surface of individual pieces of current collector 11 to form active material powder layer 12; an active material layer formation step of applying a binder-containing ink to active material powder layer 12 by inkjet printing and drying the ink to form active material layer 13; a separator layer formation step of spraying a separator constituent material powder on the surface of the active material layer to form a separator powder layer, and then applying a binder-containing ink to the separator powder layer by inkjet printing and drying the ink to form separator layer 15L; and a pressurization step of pressurizing active material layer 13 and separator layer 15L in the stacking direction.

[0055] The current collector singulation step, powder layer formation step, and active material layer formation step shown in Figure 5A are the same as those in the embodiment shown in Figure 4A, and therefore the descriptions therein are incorporated herein by reference and will not be repeated. In the separator layer formation step of this embodiment, a separator powder layer is formed by scattering a powder of a separator constituent material on the surface of the active material layer (separator powder layer formation step), and then an ink containing a binder is applied to the separator powder layer by an inkjet method, and the ink is dried to form the separator layer 15L (separator layer formation step). Figure 10 is a process diagram showing the separator powder layer formation step and separator layer formation step according to this embodiment. This step corresponds to the "lamination step of laminating a separator and an electrode having an active material layer formed on the surface of a current collector" in the present invention.

[0056] 10 uses an electrode in which a positive electrode active material layer 13P is formed on one side of a positive electrode-side current collector 11P, and a separator layer 15L is formed on the surface of the positive electrode active material layer 13P. Note that the target for forming the separator layer 15L is not limited to the electrode in which a positive electrode active material layer 13P is formed on one side of a positive electrode-side current collector 11P shown in FIG. 5A , but may also be an electrode in which a positive electrode active material layer 13P is formed on both sides of a positive electrode-side current collector 11P, or an electrode in which a negative electrode active material layer 13N is formed on one or both of a negative electrode-side current collectors 11N.

[0057] In the separator powder layer formation step shown on the left side of Figure 10, a powdered separator constituent material without binder is sprayed onto the surface of the positive electrode active material layer 13P to form a powdered separator powder layer 15P. The separator constituent material is not particularly limited, but examples thereof include aluminum oxide. In the separator powder layer formation step shown in Figure 10, the separator constituent material powder is placed in a powder spraying device 22, and vibration is applied to the powder to spray the separator constituent material powder onto the surface of the positive electrode active material layer 13P. This forms a separator powder layer 15P on the surface of the positive electrode active material layer 13P. This separator powder layer 15P is a deposit of dry powder or wet powder with a very small amount of liquid component.

[0058] In the separator layer forming process shown on the right side of FIG. 10 , a liquid ink 30 containing a binder is applied to the surface of the separator powder layer 15P by an inkjet method. That is, as shown in FIG. 10 , an inkjet applicator 23 is used to apply the liquid ink 30 containing the binder to the surface of the separator powder layer 15P. The inkjet applicator 23 is fixed to the top of the conveyor device 21 used in the separator layer forming process and ejects a constant amount of ink 30 onto the separator powder layer 15P formed on the surface of the positive electrode active material layer 13P, which is being transported at a constant speed. This allows the ink 30 to penetrate the powder separator powder layer 15P and form a wet deposit. Note that the manufacturing method of this embodiment may be any of a piezo method, a thermal inkjet method, and a bubble jet (registered trademark) method.

[0059] 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.

[0060] 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.

[0061] 10 , 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 15L is formed on the surface of the positive electrode active material layer 13P. In this step, since it is only necessary to evaporate the solvent contained in the ink 30 applied in the previous step, 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 and an air blowing means.

[0062] 5A , by carrying out the processes in the separator powder layer forming step and the separator layer forming step described above, a positive electrode active material layer 13P and a separator layer 15L are formed on one surface of a positive electrode-side current collector 11P shown in the upper part of Fig. 5A , and in the subsequent inversion step, the positive electrode-side current collector 11P is turned over, and similar processes are carried out on the other surface of the positive electrode-side current collector 11P to form a positive electrode active material layer 13P and a separator layer 15L. Note that the negative electrode layer 14N (104) shown in the lower part of Fig. 5A is the same as that in the embodiment shown in the lower part of Fig. 4A , and therefore the description therefor is incorporated herein by reference and will not be repeated.

[0063] In the subsequent pressurizing step of this embodiment, the positive electrode active material layer 13P, the separator layer 15L, and the negative electrode active material layer 13N are each pressed in the layer formation direction using a pressurizing device 26 equipped with a pressure roller. This densifies the positive electrode active material layer 13P, the separator layer 15L, and the negative electrode active material layer 13N, increasing the charge density. Note that the pressurizing step using the pressurizing device 26 may be performed after the lamination step shown in FIG. 5B in addition to or instead of after the active material layer formation step or the separator layer formation step.

[0064] In the lamination step of this embodiment, as shown in FIG. 5B , from top to bottom, the following are laminated: a positive electrode layer 14P having an active material layer and a separator layer 15L formed only on one side of a positive electrode current collector; a negative electrode layer 14N having active material layers formed on both sides; a positive electrode layer 14P having an active material layer and a separator layer 15L formed on both sides; a negative electrode layer 14N having active material layers formed on both sides; a positive electrode layer 14P having an active material layer and a separator layer 15L formed on both sides; and a negative electrode layer 14N having an active material layer formed on only one side of a negative electrode current collector.

[0065] The power generating element 101 shown in Figure 2 is manufactured by the above steps, and is then housed in the upper exterior member 107 and the lower exterior member 108 shown in the same figure, an electrolyte is poured into them, and they are sealed. Then, predetermined processes such as an aging process and an initial charging process are performed to complete the secondary battery 10. [Third Embodiment]

[0066] 4A and 4B and 5A and 5B show examples of unipolar electrodes in which active material layers of the same polarity are formed on both sides of a current collector, but the manufacturing method of the present invention can also manufacture bipolar electrodes in which active material layers of opposite polarities are formed on both sides of a current collector. Fig. 6A is a process diagram showing yet another embodiment of the method for manufacturing a secondary battery according to the present invention, and Fig. 6B is a process diagram continuing therefrom.

[0067] The method for manufacturing a secondary battery electrode of this embodiment includes a current collector singulation step of preparing a current collector 11 in the form of an individual piece corresponding to the size of the secondary battery 10 to be manufactured, a powder layer formation step of scattering powder of an active material for one electrode on the surface of the individual current collector 11 to form an active material powder layer 12, an active material layer formation step of applying ink containing a binder to the active material powder layer 12 by an inkjet method and drying the ink to form an active material layer 13 for one electrode on one surface of the current collector 11, and a powder layer formation step of scattering powder of an active material for the other electrode on the surface of the individual current collector 11 to form an active material layer 13 for one electrode on one surface of the current collector 11. the active material powder layer 13 of the other polarity on the other surface of the current collector 11; a pressurizing step of pressing the active material layer 13 in the layer forming direction; and a lamination step of laminating electrodes 14, each having active material layers 13 of different polarities formed thereon, on both surfaces of the current collector 11.

[0068] The current collector singulation step, powder layer formation step, active material layer formation step, and inversion step shown in the upper and lower panels of FIG. 5A are the same as those in the embodiment shown in FIG. 4A , and therefore their descriptions are incorporated herein by reference and will not be repeated. In the powder layer formation step and active material layer formation step shown in the upper panel of FIG. 5A following these steps, a negative electrode active material layer 13N is formed, which is the opposite electrode to the positive electrode active material layer 13P formed on the opposite surface of the current collector 11. This negative electrode active material layer 13N is formed by the manufacturing method shown in FIG. 8 or FIG. 9 . Similarly, in the powder layer formation step and active material layer formation step shown in the lower panel of FIG. 5A , a positive electrode active material layer 13P is formed, which is the opposite electrode to the negative electrode active material layer 12N formed on the opposite surface of the current collector 11. This positive electrode active material layer 13P is formed by the manufacturing method shown in FIG. 8 or FIG. 9 . This results in a bipolar electrode 14B in which active material layers of opposite polarity are formed on both surfaces of the current collector 11.

[0069] In the subsequent pressurizing step of the present embodiment, the positive electrode active material layer 13P and the negative electrode active material layer 13N of the bipolar electrode 14B are pressed in the layer formation direction using a pressurizing device 26 equipped with a pressure roller, thereby densifying the positive electrode active material layer 13P and the negative electrode active material layer 13N, respectively, and increasing the charge density.

[0070] In the lamination process of this embodiment, as shown in FIG. 6B , from top to bottom, the following are laminated: positive electrode layer 14P in which an active material layer is formed only on one side of current collector 11; separator sheet 15; bipolar electrode 14B in which active material layers of opposite polarities are formed on both sides; separator sheet 15; bipolar electrode 14B in which active material layers of opposite polarities are formed on both sides; separator sheet 15; bipolar electrode 14B in which active material layers of opposite polarities are formed on both sides; separator sheet 15; bipolar electrode 14B in which active material layers of opposite polarities are formed on both sides; and negative electrode layer 14N in which active material layers are formed only on one side of current collector 11.

[0071] The bipolar power generating element 101 is manufactured by the above steps, and is then housed in the upper exterior member 107 and the lower exterior member 108 shown in Figure 2, an electrolyte is poured into them, they are sealed, and predetermined processes such as aging and initial charging are performed to complete the secondary battery 10. [Fourth embodiment]

[0072] 4A to 6B show examples of electrodes in which active material layers 13P, 13N are formed on both sides of current collector 11, but in the manufacturing method of the present invention, a secondary battery can also be manufactured using electrodes (positive electrode layer 14P, negative electrode layer 14N) in which active material layers 13P, 13N are formed on only one side of current collector 11. Fig. 7A is a process diagram showing yet another embodiment of the method for manufacturing a secondary battery according to the present invention, and Fig. 7B is a subsequent process diagram.

[0073] The method for manufacturing a secondary battery electrode of this embodiment, when manufacturing one electrode (positive electrode layer 14P in FIG. 7A ), includes, as shown in the upper part of FIG. 7A , a current collector singulation step of preparing individual pieces of current collector 11 corresponding to the size of secondary battery 10 to be manufactured; a powder layer formation step of spraying active material powder on the surface of individual pieces of current collector 11 to form active material powder layer 12; an active material layer formation step of applying a binder-containing ink to active material powder layer 12 by an inkjet method and drying the ink to form active material layer 13; a separator layer formation step of spraying a separator constituent material powder on the surface of the active material layer to form a separator powder layer, and then applying a binder-containing ink to the separator powder layer by an inkjet method and drying the ink to form separator layer 15L; and a pressurization step of pressurizing active material layer 13 and separator layer 15L in the stacking direction.

[0074] Furthermore, when producing the other electrode (negative electrode layer 14N in FIG. 7A ), the method for producing a secondary battery electrode of this embodiment includes, as shown in the lower part of FIG. 7A , a current collector singulation step of preparing individual current collectors 11 in the shape of a corresponding size to secondary battery 10 to be produced; a powder layer formation step of spraying active material powder on the surface of individual current collector 11 to form active material powder layer 12; an active material layer formation step of applying ink containing a binder to active material powder layer 12 by an inkjet method and drying the ink to form active material layer 13; and a pressurization step of pressurizing active material layer 13 in the stacking direction.

[0075] Note that, instead of forming the separator layer 15L on the surface of the positive electrode active material layer 13P, the separator layer 15L may be formed on the surface of the negative electrode active material layer 13N. Furthermore, instead of forming the separator layer 15L, a separator sheet 15 may be used.

[0076] In the lamination step of this embodiment, as shown in FIG. 7B , a positive electrode layer 14P in which a positive electrode active material layer and a separator layer 15L are formed on one surface of a current collector 11 is laminated back to back so that the current collectors 11 are in contact with each other, and similarly, a negative electrode layer 14N in which a negative electrode active material layer is formed on one surface of a current collector 11 is laminated back to back so that the current collectors 11 are in contact with each other. As shown in the figure, from top to bottom, the following are stacked: a positive electrode layer 14P in which an active material layer and a separator layer 15L are formed on only one side of the current collector 11; a pair of negative electrode layers 14N in which negative electrode layers 14N in which a negative electrode active material layer is formed on one side of the current collector 11 are stacked back to back; a pair of positive electrode layers 14P in which positive electrode layers 14P in which a positive electrode active material layer and a separator layer 15L are formed on one side of the current collector 11 are stacked back to back; a pair of negative electrode layers 14N in which negative electrode layers 14N in which a negative electrode active material layer is formed on one side of the current collector 11 are stacked back to back; a pair of positive electrode layers 14P in which positive electrode layers 14P in which a positive electrode active material layer and a separator layer 15L are formed on one side of the current collector 11 are stacked back to back; and a negative electrode layer 14N in which a negative electrode active material layer is formed on only one side of the current collector 11 are stacked back to back.

[0077] The power generating element 101 shown in FIG. 2 is manufactured by the above steps. This is then housed in the upper exterior member 107 and the lower exterior member 108 shown in FIG. 2, an electrolyte is poured into them, they are sealed, and predetermined processes such as an aging process and an initial charging process are performed to complete the secondary battery 10.

[0078] [Operations and Effects of the Embodiment] As described above, the manufacturing method of the present embodiment includes a current collector singulation step of preparing individual current collectors 11 in accordance with the size of secondary battery 10 to be manufactured, a powder layer formation step of spraying active material powder on the surface of current collector 11 to form active material powder layer 12, an active material layer formation step of applying a binder-containing ink to active material powder layer 12 by an inkjet method and drying the ink to form active material layer 13, and a lamination step of laminating electrode 14, on which active material layer 13 has been formed, and separator 15, on the surface of current collector 11. Therefore, it is not necessary to use a small-diameter positive electrode active material. Therefore, although an SEI coating that causes a decrease in charge density is formed on the outermost surface of the active material, the decrease in charge density can be suppressed because there is no need to reduce the diameter of the active material particles.

[0079] Furthermore, according to the manufacturing method of this embodiment, the current collector singulation process is performed to prepare individual current collectors 11 corresponding to the size of the secondary battery 10 to be manufactured, eliminating the need to cut the fragile active material layer. As a result, problems such as the collapse of the active material layer can be prevented. Furthermore, since there is no need to handle the current collector sheet 11A wound into a roll, the manufacturing process can be space-saving. Furthermore, since a moisture-sensitive material is used for the positive electrode active material, a dry room process is required, but the space required for the dry room can be reduced. Furthermore, since the binder for the positive electrode layer 14P can be an organic solvent-based binder and the binder for the negative electrode layer 14N can be an aqueous binder, the burden on wastewater treatment is reduced and the process is environmentally friendly.

[0080] Furthermore, according to the manufacturing method of this embodiment, the stacking process includes a process of preparing individual separator sheets 15 according to the size of the secondary battery 10 and a process of stacking the electrodes 14 and the separator sheets 15, so that the capacity of the secondary battery 10 can be reduced by using a thin separator sheet 15.

[0081] Furthermore, according to the manufacturing method of this embodiment, the lamination step includes a step of scattering a powder of a separator constituent material on the surface of the active material layer 13 to form the separator powder layer 15P, and a step of applying ink containing the binder to the separator powder layer 15P by an inkjet method and drying the ink to form the separator layer 15L. Therefore, by smoothing the surface, gaps between the laminated layers are reduced, improving conductivity and increasing energy density.

[0082] Furthermore, according to the manufacturing method of this embodiment, the separator layer is a separator layer made of a solid electrolyte, so that the adhesion between the electrode 14 and the separator layer 15L is good, and the conductivity can be increased.

[0083] Furthermore, according to the manufacturing method of this embodiment, the step of forming the active material layer on both sides of the current collector is included. Therefore, the binder does not get between the current collector 11 and the active material layer 13, and the conductivity of the electrodes 14 formed on both sides can be increased.

[0084] Furthermore, the manufacturing method of this embodiment includes the steps of forming the active material layer on one side of the current collector and stacking electrodes, each having the active material layer formed on one side of the current collector, back to back so that the current collectors are in contact with each other. Therefore, it is sufficient to only have the step of forming active material layer 13 on one side of current collector 11, thereby simplifying the manufacturing process.

[0085] Furthermore, according to the manufacturing method of the present embodiment, at least one of a pressurizing step of pressing the active material layer in the layer formation direction after the active material layer forming step and a pressurizing step of pressing the stacked electrodes and separator in the stacking direction after the stacking step is included. This makes the active material layer 13, the electrode 14, and the separator dense, thereby enabling an increase in energy density.

[0086] Furthermore, according to the manufacturing method of this embodiment, after the lamination step, there is a step of laminating one electrode manufactured by the current collector singulation step, the powder layer formation step, the active material layer formation step, and the lamination step, via the separator, with the other electrode manufactured by the current collector singulation step, the powder layer formation step, and the active material layer formation step. This makes it possible to obtain a secondary battery 10 that can suppress a decrease in charge density.

[0087] 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 103... Electrolyte layer 103a... Separator 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... Seal film 11... Current collector 11A... Current collector sheet wound into a roll 12... Active material powder layer 12P... Positive electrode active material powder layer 13... Active material layer 13P... Positive electrode active material layer 13N... Negative electrode active material layer 14... Electrode 14P... Positive electrode layer 14N... Negative electrode layer 14B... Bipolar electrode 15... Separator sheet 15P... Separator powder layer 15L... Separator layer 21... Conveyor device 22, 25... Powder scattering device 23... Inkjet coating device 24... Drying device 26... Pressurizing device 27... Cutting device 30... Ink

Claims

1. A method for manufacturing a secondary battery, comprising: a current collector singulation step of preparing a current collector in the form of individual pieces corresponding to the size of the secondary battery to be manufactured; a powder layer formation step of scattering active material powder on the surface of the current collector to form an active material powder layer; an active material layer formation step of applying ink containing a binder to the active material powder layer using an inkjet method and drying the ink to form an active material layer; and a lamination step of laminating an electrode on the surface of the current collector, on which the active material layer has been formed, and a separator.

2. A method for manufacturing a secondary battery as described in claim 1, wherein the stacking process includes the steps of: preparing individual separator sheets according to the size of the secondary battery; and stacking the electrodes and the separator sheets.

3. A method for manufacturing a secondary battery according to claim 1, wherein the lamination step includes the steps of: scattering a powder of a separator constituent material on the surface of the active material layer to form a separator powder layer; and applying ink containing the binder to the separator powder layer by an inkjet method and drying the ink to form a separator layer.

4. The method for producing a secondary battery according to claim 3, wherein the separator layer is made of a solid electrolyte.

5. The method for producing a secondary battery according to any one of claims 1 to 4, further comprising the step of forming the active material layers on both sides of the current collector.

6. A method for manufacturing a secondary battery according to any one of claims 1 to 4, comprising the steps of: forming the active material layer on one side of the current collector; and stacking electrodes, each having the active material layer formed on one side of the current collector, back to back so that the current collectors are in contact with each other.

7. A method for manufacturing a secondary battery according to any one of claims 1 to 6, comprising at least one of a pressurizing step, after the active material layer forming step, of pressing the active material layer in a layer forming direction, and a pressurizing step, after the laminating step, of pressing the laminated electrodes and separator in the laminating direction.

8. A method for manufacturing a secondary battery according to any one of claims 1 to 7, comprising, after the laminating step, a step of laminating one electrode manufactured by the current collector singulating step, the powder layer forming step, the active material layer forming step, and the laminating step, via the separator, the other electrode manufactured by the current collector singulating step, the powder layer forming step, and the active material layer forming step.

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