Battery and method for producing positive electrode

Abstract

A battery 100 comprises a positive electrode 34 and a negative electrode 32, wherein the positive electrode 34 has a positive electrode current collector 341, a conductive layer 342 that is layered on the positive electrode current collector and that has conductivity, and a positive active material layer 343 that is layered on the conductive layer and that includes a positive electrode active material. Thus, provided is a battery that has a structure in which corrosion is less likely to occur in its positive electrode current collector and a method for producing a positive electrode in which corrosion is less likely to occur in its positive electrode current collector, even when water is used as a solvent to disperse a positive electrode active material.

Description

Battery and method for manufacturing positive electrode

[0001] The present invention relates to a battery and a method for manufacturing a positive electrode.

[0002] Conventionally, batteries such as lithium-ion batteries are composed of, for example, a positive electrode, a negative electrode, and an electrolyte, and the positive electrode is configured by applying a positive electrode active material to a positive electrode current collector. Conventionally, a positive electrode is produced by dispersing a positive electrode active material in a solution to prepare a positive electrode slurry, and then applying this positive electrode slurry to a positive electrode current collector. A solvent such as NMP (N-methyl-2-pyrrolidone) is used as the solution used to prepare the positive electrode slurry, but solvents such as NMP have a high environmental impact. On the other hand, a negative electrode is produced by dispersing a negative electrode active material in a solution to prepare a negative electrode slurry, and then applying this negative electrode slurry to a negative electrode current collector. Water can be used as the solution used to prepare the negative electrode slurry.

[0003] Patent Document 1 describes a positive electrode plate for a lithium-ion secondary battery that includes a positive electrode current collector, a positive electrode composite layer, and an insulating protective layer adjacent thereto. The insulating protective layer is thinner than the positive electrode composite layer and has a larger porosity than the positive electrode composite layer. In a coating process, the positive electrode composite paste and the insulating protective paste are simultaneously applied to the surface of the positive electrode current collector using a die nozzle. In a pressing process, at least a portion of a mixed layer of the positive electrode composite paste and the insulating protective paste, which is formed at the boundary where the positive electrode composite layer and the insulating protective layer overlap, is pressed together with the positive electrode composite layer, without compressing the insulating protective layer.

[0004] In Patent Document 2, a porous insulating layer-forming composition is used to form a porous insulating layer on an active material layer disposed on the main surface of a current collector, and the active material layer is Li ＋The porous insulating layer-forming composition is described as including at least an active material capable of electrochemically absorbing and desorbing carbon monoxide and an active material layer binder. The porous insulating layer-forming composition includes at least a solvent containing an organic solvent, insulating inorganic particles, and a binder. The binder is a polymer containing, as structural units relative to the total mass of the binder, 30% by mass to 60% by mass of an aromatic vinyl compound, 20% by mass to 69% by mass of a (meth)acrylic acid ester, 5% by mass to 35% by mass of a (meth)acrylic acid ester containing a hydroxyl group or an ether group, and 1% by mass to 10% by mass of a vinyl compound having an acidic functional group.

[0005] Patent Document 3 describes an energy storage element including an electrode having an electrode substrate, a conductive layer containing a particulate conductive additive superimposed on the electrode substrate, and an active material layer containing a particulate active material superimposed on the conductive layer. The conductive layer is porous due to voids between particles of the conductive additive, and when the conductive layer on the electrode substrate is partitioned into a lattice shape in one direction and another direction perpendicular to the one direction at intervals of a length equal to / 4 of the average particle diameter of the active material, the proportion of squares in which the electrode substrate is covered with the conductive additive is 90 to 99%, and the average number of consecutive squares in one direction and the other direction where the electrode substrate is not covered at all with the conductive additive and is exposed is 2 or less.

[0006] JP 2023-83044 A JP 2020-126722 A JP 2017-183083 A

[0007] In conventional technology, a solvent is used to prepare a positive electrode slurry. Therefore, it is desirable to prepare the positive electrode slurry using water, similar to the negative electrode slurry. However, dispersing a positive electrode active material in water results in a strongly alkaline solution. A positive electrode current collector, for example, made of aluminum (Al), may corrode when in contact with a strongly alkaline liquid. The present invention aims to provide a battery having a structure in which corrosion of the positive electrode current collector is resistant even when water is used as a solvent to disperse the positive electrode active material, and a method for manufacturing a positive electrode in which corrosion of the positive electrode current collector is resistant.

[0008] In order to solve the above problems, the battery of the present invention includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode current collector, a conductive layer that is laminated on the positive electrode current collector and has conductivity, and a positive electrode active material layer that is laminated on the conductive layer and contains a positive electrode active material.

[0009] In order to solve the above-mentioned problems, the method for manufacturing a positive electrode of the present invention includes a coating solution preparation step of preparing coating solutions for forming a conductive layer that is laminated on a positive electrode current collector and has conductivity, and a positive electrode active material layer that is laminated on the conductive layer and contains a positive electrode active material; a coating step of applying the coating solutions to both main surfaces of the positive electrode current collector so that the positive electrode current collector, the conductive layer, and the positive electrode active material layer are laminated in this order; and a drying step of drying the applied coating solutions.

[0010] According to the present invention, it is possible to provide a battery having a structure in which corrosion of the positive electrode current collector is resistant even when water is used as a solvent for dispersing the positive electrode active material, and a method for manufacturing a positive electrode in which corrosion of the positive electrode current collector is resistant.

[0011] 1 is an external perspective view of a flat wound secondary battery; 2 is an exploded perspective view of a prismatic secondary battery; 3 is an exploded perspective view showing a state in which a portion of a wound electrode group is developed; 4 (a) is a diagram showing the structure of a positive electrode according to a first embodiment; 5 (b) is a diagram showing the structure of a conventional positive electrode; 6 is a diagram showing the structure of a positive electrode according to a second embodiment; 7 is an enlarged view of the interfaces of a conductive layer 342, a positive electrode active material layer 343, and a positive electrode insulating layer 344; and 8 is a flowchart illustrating a method for manufacturing a positive electrode.

[0012] FIG. 1 is a perspective view of the exterior of a flat wound secondary battery. The flat wound secondary battery 100 is an example of a battery, and the present invention will be described here as being applied to a lithium-ion secondary battery. The flat wound secondary battery 100 includes a battery can 1 and a lid (battery lid) 6. The battery can 1 has a side surface having a pair of opposing wide side surfaces 1b with a relatively large area and a pair of opposing narrow side surfaces 1c with a relatively small area, a bottom surface 1d, and an opening 1a above the battery can 1. In this embodiment, the battery can 1 and battery lid 6 are an example of a battery container.

[0013] The wound pack 3 is housed in the battery can 1, and an upper opening 1a of the battery can 1 is sealed by a battery lid 6. The battery lid 6 is a substantially rectangular flat plate and is welded to close the opening 1a of the battery can 1, sealing the battery can 1. A positive electrode external terminal 14 and a negative electrode external terminal 12 are provided on the battery lid 6. The wound pack 3 is charged and power is supplied to an external load via the positive electrode external terminal 14 and the negative electrode external terminal 12. A gas release valve 10 is integrally provided on the battery lid 6, and when the pressure inside the battery container rises, the gas release valve 10 opens to release gas from the inside and reduce the pressure inside the battery container. This ensures the safety of the flat wound secondary battery 100.

[0014] 2 is an exploded perspective view of a prismatic secondary battery. The battery can 1 of the flat wound secondary battery 100 has a rectangular bottom surface 1d, rectangular cylindrical side surfaces 1b and 1c rising from the bottom surface 1d, and an opening 1a that opens upward at the upper ends of the side surfaces 1b and 1c. A wound group 3 is housed in the battery can 1 via an insulating protective film 2.

[0015] The wound group 3 is wound in a flat shape, and therefore has a pair of curved portions that face each other and have a semicircular cross section, and a flat portion that is formed continuously between the pair of curved portions. The wound group 3 is inserted into the battery can 1 from one curved portion side so that the winding axis direction is along the width direction of the battery can 1, and the other curved portion side is arranged on the upper opening side.

[0016] The exposed positive electrode foil portion 34c of the wound pack 3 is electrically connected to the positive electrode external terminal 14 provided on the battery lid 6 via a positive electrode current collector (current collector terminal) 44. In addition, the exposed negative electrode foil portion 32c of the wound pack 3 is electrically connected to the negative electrode external terminal 12 provided on the battery lid 6 via a negative electrode current collector (current collector terminal) 24. As a result, power is supplied from the wound pack 3 to an external load via the positive electrode current collector 44 and the negative electrode current collector 24, and externally generated power is supplied to the wound pack 3 via the positive electrode current collector 44 and the negative electrode current collector 24 for charging.

[0017] A gasket 5 and an insulating plate 7 are provided on the battery lid 6 to electrically insulate the positive electrode current collector plate 44, the negative electrode current collector plate 24, and the positive electrode external terminal 14 and the negative electrode external terminal 12 from the battery lid 6. After the electrolyte is poured into the battery can 1 through the pouring hole 9, a pouring plug 11 is joined to the battery lid 6 by laser welding to seal the pouring hole 9 and hermetically seal the flat wound secondary battery 100.

[0018] Here, examples of materials for the positive electrode external terminal 14 and the positive electrode current collector plate 44 include aluminum alloys, and examples of materials for the negative electrode external terminal 12 and the negative electrode current collector plate 24 include copper alloys. Examples of materials for the insulating plate 7 and the gasket 5 include insulating resin materials such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy fluororesin.

[0019] The battery lid 6 is provided with a liquid filling port 9 for injecting an electrolyte into the battery container, and after the electrolyte is injected into the battery container, the liquid filling port 9 is sealed with a liquid filling plug 11. The electrolyte to be injected into the battery container may be, for example, a non-aqueous electrolyte in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in a carbonate ester organic solvent such as ethylene carbonate.

[0020] The positive electrode external terminal 14 and the negative electrode external terminal 12 have welded joints that are welded to bus bars, etc. The welded joints have a rectangular parallelepiped block shape that protrudes upward from the battery lid 6, with the lower surface facing the surface of the battery lid 6 and the upper surface parallel to the battery lid 6 at a predetermined height.

[0021] The positive electrode connection portion 14 a and the negative electrode connection portion 12 a respectively protrude from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12, and have a cylindrical shape whose tips can be inserted into the positive electrode side through-hole 46 and the negative electrode side through-hole 26 of the battery lid 6. The positive electrode connection portion 14 a and the negative electrode connection portion 12 a penetrate the battery lid 6 and protrude further into the battery can 1 than the positive electrode current collector base 41 and the negative electrode current collector base 21 of the positive electrode current collector 44 and the negative electrode current collector 24, and their tips are crimped to integrally fix the positive electrode external terminal 14, the negative electrode external terminal 12, the positive electrode current collector 44, and the negative electrode current collector 24 to the battery lid 6. A gasket 5 is interposed between the positive electrode external terminal 14, the negative electrode external terminal 12, and the battery lid 6, and an insulating plate 7 is interposed between the positive electrode current collector 44, the negative electrode current collector 24, and the battery lid 6.

[0022] The positive current collector plate 44 and the negative current collector plate 24 have rectangular plate-shaped positive current collector base 41 and negative current collector base 21 arranged opposite the underside of the battery lid 6, and positive electrode side connection end 42 and negative electrode side connection end 22 that are bent at the side edges of the positive current collector base 41 and negative current collector base 21, extend along the wide surface of the battery can 1 toward the bottom side, and are connected in an overlapping state facing the positive electrode foil exposed portion 34c and negative electrode foil exposed portion 32c of the wound group 3. The positive electrode current collector base 41 and the negative electrode current collector base 21 are respectively formed with a positive electrode side opening hole 43 and a negative electrode side opening hole 23 through which the positive electrode connection portion 14a and negative electrode connection portion 12a are inserted.

[0023] An insulating protective film 2 is wound around the wound group 3 with a central axis extending in a direction along the flat surface of the wound group 3 and perpendicular to the winding axis direction of the wound group 3. The insulating protective film 2 is made of a single sheet or multiple film members made of a synthetic resin such as PP (polypropylene), and has a length that allows it to be wound around a winding center extending in a direction parallel to the flat surface of the wound group 3 and perpendicular to the winding axis direction.

[0024] 3 is an exploded perspective view showing a part of the wound electrode pack in an expanded state. The wound electrode pack 3 is formed by winding a negative electrode 32 and a positive electrode 34 in a flat shape with separators 33 and 35 interposed therebetween. The wound electrode pack 3 has the negative electrode 32 as the outermost electrode, and the separators 33 and 35 wound further outside the negative electrode 32. The separators 33 and 35 serve to insulate the positive electrode 34 from the negative electrode 32.

[0025] The portion of the negative electrode 32 coated with the negative electrode mixture layer 32b is wider in the width direction than the portion of the positive electrode 34 coated with the positive electrode mixture layer 34b, so that the portion coated with the positive electrode mixture layer 34b is always sandwiched between the portions coated with the negative electrode mixture layer 32b. The positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c are bundled together at their flat portions and connected by welding or the like. Note that although the separators 33 and 35 are wider in the width direction than the portion coated with the negative electrode mixture layer 32b, they are wound in positions where the metal foil surfaces of the ends are exposed at the positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c, so this does not hinder the bundling and welding.

[0026] The negative electrode 32 has a negative electrode active material mixture on both sides of a negative electrode foil, which is a negative electrode current collector, and a negative electrode foil exposed portion 32c, where the negative electrode active material mixture is not applied, is provided at the other end of the positive electrode foil in the width direction. The positive electrode foil exposed portion 34c and the negative electrode foil exposed portion 32c are regions where the metal surface of the electrode foil is exposed, and are wound so as to be located on one side and the other side in the winding axis direction.

[0027] The negative electrode 32 has a structure in which negative electrode active material layers containing a negative electrode active material are laminated on both main surfaces of a negative electrode foil, which is a negative electrode current collector. One end of the negative electrode foil in the width direction is provided with a negative electrode foil exposed portion 32c, which is not coated with the negative electrode active material mixture.

[0028] The negative electrode 32 can be produced as follows: Pitch-coated natural graphite particles and artificial graphite particles are prepared as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the dispersant, and then mixed together. Ion-exchanged water is added to the resulting mixture to adjust the viscosity, thereby obtaining a negative electrode slurry, which is a coating solution for coating the negative electrode active material.

[0029] For example, a copper foil having a thickness of 10 μm was prepared as the negative electrode current collector. The negative electrode slurry was simultaneously applied to both sides of the copper foil using a die coater to form two layers (front and back) of the negative electrode slurry. The negative electrode slurry layer was then dried and pressed to form a negative electrode active material layer, thereby obtaining a negative electrode 32. In this case, the negative electrode 32 includes a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector and containing a negative electrode active material. The negative electrode 32 may further include an insulating negative electrode insulating layer laminated on the negative electrode active material layer.

[0030] Next, a detailed description will be given of the structure of the positive electrode 34. Hereinafter, the structure of the positive electrode 34 will be described with reference to a first embodiment and a second embodiment.

[0031] [First Embodiment] FIG. 4( a) is a diagram showing the structure of a positive electrode 34 according to a first embodiment. The illustrated positive electrode 34 includes a positive electrode collector 341, a conductive layer 342, and a positive electrode active material layer 343. FIG. 4( b) is a diagram showing the structure of a conventional positive electrode 34. Comparing FIG. 4( b) with FIG. 4( a), it differs in that the conductive layer 342 is absent, but the other aspects are the same. The positive electrode collector 341 has a function of supplying current to the positive electrode active material of the positive electrode active material layer 343. The positive electrode collector 341 is foil-shaped and is also referred to as a positive electrode foil. The positive electrode collector 341 is made of, for example, aluminum (Al). That is, the positive electrode collector 341 is, for example, aluminum foil. Note that the material is not limited to this and may be, for example, an Al-Mn alloy.

[0032] The conductive layer 342 is a conductive layer laminated on both main surfaces of the positive electrode current collector 341. The conductive layer 342 includes conductive particles and a water-based binder. The conductive particles are, for example, acetylene black, a type of carbon black. However, the conductive particles are not limited to this. They may also be carbon black other than acetylene black, graphite, nanotubes, metal particles such as silver, copper, or nickel, or metal oxide particles such as silver oxide or indium oxide. The shape of the particles may be powder, spherical, fibrous, or flake-like, and is not particularly limited. The binder is not limited to being water-soluble. For example, even a water-insoluble binder can be mixed with water by emulsifying it with a surfactant. Therefore, not only water-soluble binders but also water-insoluble binders emulsified with a surfactant or the like can be used. Furthermore, for example, the conductive layer 342 is substantially free of a positive electrode active material. This reduces the impact of the positive electrode active material on the positive electrode current collector 341. Alternatively, the positive electrode active material is contained in a proportion (e.g., wt %) lower than the proportion of the positive electrode active material in the positive electrode active material layer 343. For example, the proportion (e.g., wt %) of the positive electrode active material in the adjacent positive electrode active material layer is set to about half or less of the proportion (e.g., wt %) of the positive electrode active material in the adjacent positive electrode active material layer. This is preferable from the viewpoint of reducing the influence of the positive electrode active material.

[0033] The positive electrode active material layer 343 is laminated on both sides of the main surface of the conductive layer 342 and contains a positive electrode active material. The positive electrode active material contained in the positive electrode active material layer 343 is a material that accepts electrons in a battery reaction. When the battery is a lithium ion battery, the positive electrode active material is usually a metal oxide containing lithium ions. Specifically, the positive electrode active material is, for example, NCM (LiNi １／３ Co １／３ Mn １／３ O ２ , lithium nickel cobalt manganese composite oxide). In addition, lithium cobalt oxide (LiCoO ２ ), NCA (LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , lithium nickel cobalt aluminum oxide), LMO (LiMn ２ O ４, lithium manganate), LNMO (LiNi ０．５ Mn １．５ O ４ , lithium nickel manganese oxide), etc. The positive electrode active material layer 343 further contains a water-based binder in addition to the positive electrode active material.

[0034] The aqueous binder contained in the conductive layer 342 and the positive electrode active material layer 343 can be either an emulsion type or a water-soluble type. Examples of emulsion-type binders include polyacrylic acid (PAA). Examples of water-soluble binders include polyacrylamide (PAM). Other binders that can be used include polyvinyl alcohol (PVA), carboxymethyl starch (CMS), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC). The aqueous binder contained in the conductive layer 342 and the positive electrode active material layer 343 is at least one selected from these.

[0035] As described above, in the positive electrode 34 of the first embodiment, the conductive layer 342 and the positive electrode active material layer 343 are laminated in this order on the positive electrode current collector 341. The conductive layer 342 and the positive electrode active material layer 343 correspond to the above-described positive electrode mixture layer 34b. The positive electrode mixture layer 34b is not applied to the entire main surface of the positive electrode current collector 341, but has a positive electrode foil exposed portion 34c. Here, the "main surface" refers to a surface that is much larger in area than the other surfaces. In this case, the positive electrode current collector 341 is foil-shaped as described above, and the side surfaces occupy only a small area. Therefore, in this case, the main surfaces are the two surfaces, the front surface and the back surface, excluding the side surfaces.

[0036] According to the first embodiment, even when water is used as a solvent for dispersing the positive electrode active material, corrosion of the positive electrode current collector 341 is reduced. In other words, because the conductive layer 342 is present between the positive electrode current collector 341 and the positive electrode active material layer 343, even when the positive electrode active material becomes strongly alkaline due to dispersion of the positive electrode active material in water, the positive electrode active material can be prevented from coming into contact with the positive electrode current collector 341. Furthermore, since the conductive layer 342 does not contain a positive electrode active material, it does not become strongly alkaline. As a result, corrosion is reduced even when aluminum or the like is used for the positive electrode current collector 341. Furthermore, because the conductive layer 342 is conductive, it does not impede the function of the positive electrode current collector 341 to supply current to the positive electrode active material. This enables the positive electrode 34 to be manufactured using an aqueous binder. Furthermore, a battery can be manufactured using a method that reduces environmental impact without using a solvent such as NMP.

[0037] Second Embodiment FIG. 5 is a diagram showing the structure of a positive electrode 34 according to a second embodiment. The illustrated positive electrode 34 differs from the positive electrode 34 shown in FIG. 4 in that it further includes insulating positive electrode insulating layers 344 laminated on both sides of the main surface of a positive electrode active material layer 343, but is otherwise similar. The positive electrode insulating layers 344 contain insulating particles and an aqueous binder. The insulating particles contained in the positive electrode insulating layer 344 are, for example, boehmite. Boehmite is alumina monohydrate with a composition of AlOOH. However, the present invention is not limited to this, and magnesium carbonate (MgCO ３ ), magnesium hydroxide (Mg(OH) ２ ), silicon oxide (SiO ２ ), aluminum oxide (Al ２ O ３ ), boron nitride (BN), silicon nitride (Si ３ N ４ The inorganic particles may be inorganic particles such as those made of resin.

[0038] As described above, in the positive electrode 34 of the second embodiment, the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344 are laminated on the positive electrode current collector 341. The conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344 correspond to the above-described positive electrode mixture layer 34b. Furthermore, the positive electrode mixture layer 34b is not applied to the entire main surface of the positive electrode current collector 341, and has a positive electrode foil exposed portion 34c.

[0039] According to the second embodiment, in addition to the effects of the first embodiment, it is possible to improve the insulating properties and to manufacture a battery with excellent safety with high efficiency.

[0040] The size of the unevenness at the interface between the conductive layer 342 and the positive electrode active material layer 343 is preferably smaller than the size of the unevenness at the interface between the positive electrode active material layer 343 and the positive electrode insulating layer 344. This can improve adhesion.

[0041] FIG. 6 is an enlarged view of the interfaces of the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344. The conductive layer 342 includes conductive particles 342a and an aqueous binder 342b. The positive electrode insulating layer 344 includes a positive electrode active material 343a and an aqueous binder 343b. The interface between the conductive layer 342 and the positive electrode active material layer 343 and the interface between the positive electrode active material layer 343 and the positive electrode insulating layer 344 are uneven, with the former having a smaller surface roughness than the latter. This surface roughness can be evaluated, for example, by surface roughness, which can be expressed, for example, by the arithmetic mean roughness Ra. The positive electrode insulating layer 344 and the negative electrode insulating layer of the negative electrode 32 may also be in contact with each other. This eliminates the need for a separator, thereby reducing costs.

[0042] Next, a method for manufacturing the positive electrode 34 will be described. FIG. 7 is a flowchart illustrating the method for manufacturing the positive electrode 34. First, coating solutions for forming each layer to be laminated on the positive electrode current collector 341 are prepared (S101: coating solution preparation step). When preparing the positive electrode 34 of the first embodiment, these coating solutions are two coating solutions for forming the conductive layer 342 and the positive electrode active material layer 343. When preparing the positive electrode 34 of the second embodiment, these coating solutions are three coating solutions for forming the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344. That is, in the second embodiment, compared to the first embodiment, an additional coating solution for forming the positive electrode insulating layer 344 is prepared.

[0043] In the coating solution preparation step, conductive particles, an aqueous binder, and water in which the conductive particles and the aqueous binder are dispersed are mixed to prepare a coating solution for forming the conductive layer 342. Furthermore, a positive electrode active material, an aqueous binder, and water in which the positive electrode active material and the aqueous binder are dispersed are mixed to prepare a coating solution for forming the positive electrode active material layer 343. Furthermore, insulating particles, an aqueous binder, and water in which the insulating particles and the aqueous binder are dispersed are mixed to prepare a coating solution for forming the positive electrode insulating layer 344. These coating solutions become slurries in which the respective components are dispersed in water. In addition to the above-mentioned components, a dispersant or the like may also be added.

[0044] Next, a coating solution is applied to both main surfaces of the positive electrode collector 341 (S102: coating step). At this time, when forming the positive electrode 34 of the first embodiment, the coating solution is applied so that the positive electrode collector 341, the conductive layer 342, and the positive electrode active material layer 343 are layered in this order. On the other hand, when forming the positive electrode 34 of the second embodiment, the coating solution is applied so that the positive electrode collector 341, the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344 are layered in this order. The coating solution can be applied using, for example, a die coater. At this time, the coating solutions for forming the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344 may be applied simultaneously or separately.

[0045] Furthermore, the applied coating solution is dried (S103: drying step). The coating solution can be dried, for example, by heating it in a dryer. After drying, it is preferable to smooth the coating film by pressing it.

[0046] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples as long as the gist of the invention is not exceeded.

[0047] [Preparation of Positive Electrode 34] Example 1 In Example 1, a positive electrode 34 having the configuration shown in Fig. 4(a) was prepared. That is, a positive electrode 34 including a positive current collector 341, a conductive layer 342, and a positive active material layer 343 was prepared.

[0048] <Coating Solution Preparation Process> 72 g of water, 50 g of acetylene black powder as conductive particles, and 24 g of 38 wt % polyacrylic acid as an emulsion-type aqueous binder were added to 156 g of a 2 wt % CMC (carboxymethyl cellulose) aqueous solution and stirred for 10 minutes. 4 g of water was added to 10 g of the resulting slurry to dilute it, creating a coating solution for the conductive layer 342. Furthermore, 300 g of NCM as a positive electrode active material, 18 g of acetylene black powder as a conductive additive, and 19 g of 38 wt % polyacrylic acid as an aqueous binder were added to 125 g of a 1.2 wt % CMC aqueous solution and stirred for 60 minutes, creating a coating solution for the positive electrode active material layer 343.

[0049] <Coating Step> The coating solutions for forming the conductive layer 342 and the positive electrode active material layer 343 were each set in a die coater, and coated onto one main surface of a positive electrode current collector 341 made of Al foil with a thickness of 0.133 mm. Next, the other main surface of the positive electrode current collector 341 was coated in the same manner. As a result, two coating layers, namely, the conductive layer 342 and the positive electrode active material layer 343, were formed on both surfaces of the positive electrode current collector 341.

[0050] <Drying Step> The coating film was then dried by heating it in a dryer at 120°C for 1 minute. The dried coating film was then pressed in a press to produce a positive electrode 34 in which a conductive layer 342 and a positive electrode active material layer 343 were laminated in this order on both sides of a positive electrode current collector 341. At this time, the conductive layer 342 and the positive electrode active material layer 343 had thicknesses of 45 µm and 60 µm, respectively.

[0051] Example 2 In Example 2, a positive electrode 34 having the configuration shown in Fig. 5 was produced. That is, a positive electrode 34 including a positive electrode current collector 341, a conductive layer 342, a positive electrode active material layer 343, and a positive electrode insulating layer 344 was produced.

[0052] <Coating solution preparation process> The coating solution for the conductive layer 342 and the coating solution for the positive electrode active material layer 343 were prepared in the same manner as in Example 1. In addition, a coating solution for the positive electrode insulating layer 344 was prepared by adding 2000 g of boehmite as insulating particles, 105 g of 38 wt % polyacrylic acid as an emulsion-type aqueous binder, 52 g of a dispersant, and 1211 g of a 1.2 wt % CMC aqueous solution to 1248 g of water and stirring for 90 minutes.

[0053] <Coating Step> The coating solutions for forming the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344 were each set in a die coater, and coated onto one main surface of a positive electrode current collector 341 made of Al foil with a thickness of 0.133 mm. Next, the other main surface of the positive electrode current collector 341 was coated in the same manner. As a result, three coating layers, i.e., the conductive layer 342, the positive electrode active material layer 343, and the positive electrode insulating layer 344, were formed on both surfaces of the positive electrode current collector 341.

[0054] <Drying step> Thereafter, drying and pressing were performed in the same manner as in Example 1, whereby a positive electrode 34 was produced in which a conductive layer 342, a positive electrode active material layer 343, and a positive electrode insulating layer 344 were laminated in this order on both sides of a positive electrode current collector 341.

[0055] Comparative Example 1 A positive electrode 34 was produced in the same manner as in Example 1, except that the conductive layer 342 was not formed. In this case, a positive electrode 34 in which a positive electrode active material layer 343 was formed on both surfaces of a positive electrode current collector 341 could be produced.

[0056] [Evaluation Method and Evaluation Results] For Examples 1 and 2 and Comparative Example 1, cross sections were observed using an optical microscope to check for the presence or absence of corrosion of the positive electrode current collector 341. As a result, for Examples 1 and 2, no corrosion of the positive electrode current collector 341 occurred. On the other hand, for Comparative Example 1, corrosion of the positive electrode current collector 341 was observed. In other words, it was confirmed that the provision of the conductive layer 342 protects the positive electrode current collector 341 and prevents corrosion.

[0057] 1... battery can, 6... battery lid, 32... negative electrode, 33, 35... separator, 34... positive electrode, 341... positive electrode current collector, 342... conductive layer, 343... positive electrode active material layer, 344... positive electrode insulating layer, 100... secondary battery

Claims

1. A battery comprising a positive electrode and a negative electrode, wherein the positive electrode comprises: a positive electrode current collector; a conductive layer laminated on the positive electrode current collector and having conductivity; and a positive electrode active material layer laminated on the conductive layer and containing a positive electrode active material.

2. The battery according to claim 1, wherein the conductive layer comprises conductive particles and a water-based binder.

3. The battery according to claim 1, wherein the positive electrode active material layer further contains a water-based binder.

4. The battery according to claim 2 or 3, wherein the aqueous binder is at least one selected from the group consisting of polyacrylamide (PAM), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethyl starch (CMS), polyethylene oxide (PEO), polypropylene oxide (PPO), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), and carboxymethyl cellulose (CMC).

5. The battery according to claim 1, further comprising an insulating positive electrode insulating layer laminated on the positive electrode active material layer.

6. The battery according to claim 5, wherein the positive electrode insulating layer contains insulating particles and a water-based binder.

7. The battery according to claim 5, wherein the negative electrode comprises a negative electrode current collector, a negative electrode active material layer laminated on the negative electrode current collector and containing a negative electrode active material, and an insulating negative electrode insulating layer laminated on the negative electrode active material layer, and the positive electrode insulating layer and the negative electrode insulating layer are in contact with each other.

8. The battery according to claim 5, wherein the degree of unevenness at the interface between said conductive layer and said positive electrode active material layer is smaller than the degree of unevenness at the interface between said positive electrode active material layer and said positive electrode insulating layer.

9. A method for manufacturing a positive electrode, comprising: a coating solution preparation step of preparing coating solutions for forming a conductive layer to be laminated on a positive electrode current collector and having conductivity, and a positive electrode active material layer to be laminated on the conductive layer and containing a positive electrode active material; a coating step of applying the coating solutions to both main surfaces of the positive electrode current collector so as to laminate the positive electrode current collector, the conductive layer, and the positive electrode active material layer in this order; and a drying step of drying the applied coating solutions.

10. A method for manufacturing a positive electrode according to claim 9, wherein the coating solution preparation step prepares a coating solution for forming the conductive layer by mixing conductive particles, a water-based binder, and water in which the conductive particles and the water-based binder are dispersed.

11. The method for manufacturing a positive electrode according to claim 9, wherein in the coating solution preparation step, the coating solution for forming the positive electrode active material layer is prepared by mixing the positive electrode active material, an aqueous binder, and water in which the positive electrode active material and the aqueous binder are dispersed.

12. A method for manufacturing a positive electrode according to claim 9, wherein the coating solution preparation step further prepares a coating solution for forming an insulating positive electrode insulating layer to be laminated on the positive electrode active material layer, and the coating step applies the coating solution to both main surfaces of the positive electrode current collector so as to laminate the positive electrode current collector, the conductive layer, the positive electrode active material layer, and the positive electrode insulating layer in this order.

13. A method for manufacturing a positive electrode according to claim 12, wherein the coating solution preparation step involves mixing insulating particles, a water-based binder, and water for dispersing the insulating particles and the water-based binder to prepare a coating solution for forming the positive electrode insulating layer.

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