Method for producing electrode for secondary battery

Abstract

In the present invention, in order to produce an electrode in a small number of steps, powder layers (102c, 104c) are formed by applying a powder of an active substance and a powder of a binder-containing binding agent to the surface of collectors (102a, 104a) and then the binder is melted to form active layers (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] However, if the first ink containing the active material and conductive agent and the second ink containing the binder are sprayed separately as in the above-mentioned conventional technology, two ink preparation processes are required, as well as two ink drying processes, resulting in the problem of a large number of processes.

[0005] The problem to be solved by the present invention is to provide a method for producing an electrode for a secondary battery that can be produced with a small number of steps.

[0006] The present invention solves the above problem by scattering an active material powder and a binder powder containing a binder on the surface of a current collector to form a powder layer, and then melting the binder contained in the powder layer to form an active material layer.

[0007] According to the present invention, an electrode is manufactured by a step of forming a powder layer and a step of melting a binder, so that the electrode can be manufactured with a small number of steps.

[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 LiCoO２ , 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] 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 and a binder-containing binding agent powder are spread (laid) on the surface of the current collector to form a powder layer (first step), and then the powder layer is pressed to melt the binder and form an active material layer (second step).

[0029] That is, instead of applying a paste or slurry of active material to which a binder has been added to the surface of a current collector, a powdered active material without a binder and a powdered binder-containing binder are dispersed on the surface of the current collector to form a powdered powder layer, and then this powdered powder layer is pressed to melt the binder, thereby obtaining an active material layer. More specifically, with regard to the positive electrode layer 102, a powdered positive electrode active material without a binder and a powdered binder-containing binder are dispersed on the surface of the positive electrode-side current collector 102a to form a powdered positive electrode powder layer, and then this powdered positive electrode powder layer is pressed while applying heat 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 and a powdered binding agent containing a binder are scattered on the surface of the negative electrode-side current collector 104a to form a powdered negative electrode powder layer, and then this powdered negative electrode powder layer is pressed while applying heat, thereby obtaining 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 and step 2.

[0031] 4 , when the positive electrode layer 102 is manufactured, a mixed powder of a binder-free powdered positive electrode active material and a binder-containing powdered binder is spread on the surface of the positive electrode-side current collector 102a to form a powdered positive electrode powder layer 102c. Similarly, when the negative electrode layer 104 is manufactured, a mixed powder of a binder-free powdered negative electrode active material and a binder-containing powdered binder is spread on the surface of the negative electrode-side current collector 104a to form a powdered negative electrode powder layer 104c. The manufacturing methods for the positive electrode layer 102 and the negative electrode layer 104 are the same except for the materials used. Therefore, the manufacturing method of this embodiment will be described below using the case of manufacturing 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 Mn１．５ 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. 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. Examples of the binder include, but are not limited to, polyvinylidene fluoride (PVdF), a composite of polyvinylidene fluoride and hexafluoropropylene (HFP), and the like.

[0034] Furthermore, components contained in the binder include, in addition to the binder described above, fibrous carbon materials such as carbon fibers typified by vapor-grown carbon fibers (VGCF), carbon nanotubes (CNTs), carbon nanofibers, etc. These fibrous carbon materials have the effect of increasing the entanglement between the powdered active material and powdered conductive additive and the powdered binder.

[0035] In the first step of the manufacturing method of this embodiment, a powder of a positive electrode active material, a powder of a negative electrode active material, a powder of a conductive additive, and a powder of a binder containing a binder or a fibrous carbon material are prepared, and these powders are spread on the surface of the positive electrode side current collector 102 a using a powder spreader 22 shown in FIG. 4.

[0036] 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. Furthermore, the average particle size (primary particle size) of the binder contained in the binding agent is not particularly limited, but from the viewpoint of producing a low-resistance positive electrode layer, it is more preferably smaller than the average particle size of the conductive additive.

[0037] The device for scattering the powder of the positive electrode active material, the powder of the negative electrode active material, the powder of the conductive additive, and the powder of the binder containing the fibrous carbon material on the surface of the current collector is not particularly limited, and any device that can scatter the powder with a uniform film thickness will suffice. 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 end per unit time.

[0038] 4, a powder mixture containing a positive electrode active material powder, a conductive additive powder, and a binder powder is placed in a powder spraying device 22, and vibration is applied to the powder mixture to simultaneously spray the positive electrode active material powder, the conductive additive powder, and the binder powder onto the surface of the positive electrode current collector 102a. As a result, a positive electrode powder layer 102c is formed on the surface of the positive electrode current collector 102a. This positive electrode powder layer 102c is a deposit of dry powder or wet powder with a very small amount of liquid component.

[0039] In the second step shown on the right side of Fig. 4, a press device 24 is used to melt (or soften) the binder contained in the binding agent. Examples of the press device 24 include the single-roll press shown in the figure, a double-roll press in which a workpiece is passed between two rollers, and a flat-plate press in which a workpiece is pressed with two flat plates. The press device 24 preferably includes a heating means. This results in the formation of a positive electrode active material layer 102b on the surface of the positive electrode current collector 102a.

[0040] By carrying out the treatments in the first and second steps described above, 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 treatments in the first and second steps are similarly 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.

[0041] 4, in forming the positive electrode powder layer 102c, a mixed powder of a positive electrode active material powder, a conductive additive powder, and a binder 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, the conductive additive powder, and the binder 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.

[0042] In contrast, in the manufacturing method of the embodiment shown in FIG. 5 , in the first step on the left, a mixed powder of a positive electrode active material powder and a conductive additive powder is contained in a powder sprayer 22, and a binder powder is contained in a powder sprayer 23. Similar to the powder sprayer 22 shown in FIG. 4 , the illustrated powder sprayer 22 applies vibrations of a predetermined frequency to the contained powder, causing a constant amount of powder to fall from the end per unit time. In contrast, the illustrated powder sprayer 23 applies a supply pressure to the contained powder to spray the powder under pressure. In other words, the powder sprayer 23 can spray the powder under pressure at a higher pressure than the powder sprayer 22, which sprays the powder by gravity.

[0043] Then, the powder sprayer 22 applies vibrations to the powder, thereby spraying the mixed powder of the positive electrode active material powder and the conductive additive powder onto the surface of the positive electrode-side current collector 102a. Next, the powder sprayer 23 sprays binder powder under pressure onto the surface of the positive electrode-side current collector 102a onto which the mixed powder of the positive electrode active material powder and the conductive additive powder has been sprayed. This allows the binder powder to penetrate deeply into the mixed powder of the positive electrode active material powder and the conductive additive powder sprayed onto the surface of the positive electrode-side current collector 102a, improving the dispersibility of the binder.

[0044] 5, in forming the positive electrode 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.

[0045] In the manufacturing method of the embodiment shown in FIG. 6 , in the first step on the left, a powder of the positive electrode active material is placed in a powder spraying device 22, a powder of the conductive additive is placed in a 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 powder layer 102c formed after the spraying.

[0046] Then, in the first step, a powder spraying device 23 sprays binder powder under pressure onto the surface of the positive electrode side current collector 102a on which the mixed powder of the positive electrode active material powder and the conductive additive powder has been sprayed.

[0047] As described above, the manufacturing method of this embodiment includes a first step of spreading a powder of a positive electrode active material and a powder of a binder containing a binder on the surface of the positive electrode current collector 102a to form the positive electrode powder layer 102c, and a second step of melting the binder contained in the positive electrode powder layer 102c to form the positive electrode active material layer 102b, thereby enabling the manufacturing of a positive electrode with fewer steps. Similarly, the manufacturing method of this embodiment includes a first step of spreading a powder of a negative electrode active material and a powder of a binder containing a binder on the surface of the negative electrode current collector 104a to form the negative electrode powder layer 104c, and a second step of melting the binder contained in the negative electrode powder layer 104c to form the negative electrode active material layer 104b, thereby enabling the manufacturing of a negative electrode with fewer steps.

[0048] Furthermore, according to the manufacturing method of this embodiment, in the first step, the positive electrode powder layer 102c or the negative electrode powder layer 104c is formed by scattering a mixed powder of an active material powder and a binder powder on the surface of the current collector, thereby improving the dispersibility of the binder.

[0049] Furthermore, according to the manufacturing method of this embodiment, in the first step, the positive electrode powder layer 102c or the negative electrode powder layer 104c is formed by scattering an active material powder on the surface of the current collector and then scattering a binder powder on the surface of the current collector, or by scattering a binder 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 binder can be omitted.

[0050] Furthermore, according to the manufacturing method of this embodiment, the binder powder is dispersed under pressure in the first step, which can improve the agitation properties with the previously dispersed active material powder.

[0051] Furthermore, according to the manufacturing method of this embodiment, in the first step, the active material powder is sprayed under pressure onto the surface of the current collector at a first pressure, and then the binder powder is sprayed under pressure onto the surface of the current collector at a second pressure that is greater than the first pressure, thereby improving the agitation property with the previously sprayed active material powder.

[0052] Furthermore, according to the manufacturing method of the present embodiment, in the first step, the powder of the active material is mixed with the powder of the conductive additive, thereby forming an electron conduction path and reducing the electron transfer resistance of the positive electrode active material layer 102 b and the negative electrode active material layer 104 b, thereby improving the high-rate output characteristics of the battery.

[0053] Furthermore, according to the manufacturing method of this embodiment, the average particle size of the binder powder is smaller than the average particle size of the conductive additive powder, so that a positive electrode with lower resistance (higher performance) can be obtained.

[0054] Furthermore, according to the manufacturing method of this embodiment, the binder contains binder powder and fibrous carbon material, which can enhance the entanglement of the powdered active material and powdered conductive additive with the powdered binder.

[0055] Furthermore, according to the manufacturing method of this embodiment, the powder layer is hot-pressed in the second step, so that shape characteristics such as the thickness of the active material layer can be set at the same time as the binder is melted.

[0056] 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.

[0057] 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 powder layer 103... Electrolyte layer 103a... Separator 104... Negative electrode layer 104a... Negative electrode side current collector 104b... Negative electrode active material layer 104c... Negative electrode powder layer 105... Positive electrode tab 106... Negative electrode tab 107... Upper exterior member 108... Lower exterior member 109... Sealing film 21... Conveyor device 22, 23, 25... Powder spraying device 24... Press device

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising: a first step of spreading an active material powder and a binder powder containing a binder on the surface of a current collector to form a powder layer; and a second step of melting the binder contained in the powder layer to form an active material layer.

2. A method for manufacturing an electrode for a secondary battery as described in claim 1, wherein in the first step, the powder layer is formed by scattering a mixed powder of the active material powder and the binder powder onto the surface of the current collector.

3. A method for manufacturing an electrode for a secondary battery as described in claim 1, wherein in the first step, the powder layer is formed by spraying the powder of the active material on the surface of the current collector, and then spraying the powder of the binder on the surface of the current collector, or by spraying the powder of the binder on the surface of the current collector, and then spraying the powder of the active material on the surface of the current collector.

4. The method for producing an electrode for a secondary battery according to claim 3, wherein in the first step, the powder of the binder is sprayed under pressure.

5. A method for manufacturing an electrode for a secondary battery as described in claim 4, wherein in the first step, the powder of the active material is sprayed under pressure onto the surface of the current collector at a first pressure, and then the powder of the binder is sprayed under pressure onto the surface of the current collector at a second pressure greater than the first pressure.

6. The method for producing an electrode for a secondary battery according to any one of claims 1 to 5, wherein in the first step, a powder of a conductive assistant is mixed with the powder of the active material.

7. The method for manufacturing an electrode for a secondary battery according to claim 6, wherein the average particle size of the binder powder is smaller than the average particle size of the conductive additive powder.

8. A method for manufacturing an electrode for a secondary battery according to any one of claims 1 to 7, wherein the binder contains powder of the binder and a fibrous carbon material.

9. The method for producing an electrode for a secondary battery according to any one of claims 1 to 8, wherein in the second step, the powder layer is hot-pressed.

10. A method for manufacturing a secondary battery, comprising stacking one electrode manufactured by the method according to any one of claims 1 to 9 and the other electrode manufactured by the method according to any one of claims 1 to 9 with a separator interposed therebetween.

11. A method for producing a secondary battery, comprising the method according to any one of claims 1 to 9.

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