Positive electrode plate for battery, battery, and method for manufacturing positive electrode plate for battery

Abstract

This invention provides a positive electrode plate for batteries, a battery, and a method for manufacturing a positive electrode plate for batteries that ensures good battery characteristics while improving manufacturing quality. The positive electrode plate for batteries comprises: a porous metal body including a three-dimensional mesh structure framework; and a positive electrode composite material containing a positive electrode active material filling the pores of the porous metal body. Specifically, when a region located on one surface side of the porous metal body is designated as a surface side portion, a region located on the back side is designated as a back side portion, and a region sandwiched between the surface side portion and the back side portion is designated as a central portion, the surface side portion and the back side portion comprise a framework with a hollow structure primarily consisting of hollow portions formed by the unfilled positive electrode composite material, and the central portion comprises a framework primarily consisting of a compressed structure with compressed portions formed by the crushing of the hollow portions. The framework density of the porous metal body is lowest at the surface side portion and highest at the central portion.

Description

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Japanese Patent Application No. 2021-212225, filed on December 27, 2021, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a positive electrode plate for a battery, a battery, and a method for manufacturing a positive electrode plate for a battery. Background Technology

[0004] Batteries used as power sources for electronic devices, electric vehicles (EVs), and hybrid electric vehicles (HVs) include secondary batteries such as alkaline batteries. Electrodes for secondary batteries such as alkaline batteries include a conductive current collector and a composite material containing active materials held in the current collector. For example, as an electrode constituting an alkaline battery, a positive electrode plate is preferably used, in which active materials are filled into the pores of a porous metal body that functions as a current collector.

[0005] Japanese Patent Application Publication No. 2009-9869 discloses an electrode for a secondary battery and a method for manufacturing the same. The electrode for a secondary battery includes a three-dimensional porous metal body and an agent containing an active material and a binder. The three-dimensional porous metal body is filled with the agent. The electrode for a secondary battery is characterized by including a first filling portion, a second filling portion having a higher binder content than the first filling portion and a generally uniform distribution of the binder in the thickness direction, and a non-filled portion not filled with the agent. At least one of the second filling portions is adjacent to the non-filled portion, such that the non-filled portion constitutes at least one end edge. Summary of the Invention

[0006] The technology described in Japanese Patent Application Publication No. 2009-9869 maintains battery characteristics while eliminating the possibility of short circuits caused by the shedding of active material. However, in the technology described in Japanese Patent Application Publication No. 2009-9869, the distribution of the skeleton density of the metal porous body is approximately uniform in the thickness direction. Therefore, in order to ensure the filling properties of the composite material throughout the thickness direction, the coating process of filling the three-dimensional porous body with the paste, which serves as a precursor to the composite material, requires complex control of coating conditions (such as the viscosity of the paste, the coating amount, the coating method, etc.), and also requires high precision in matching these conditions. This may lead to a reduction in manufacturing quality.

[0007] This invention was made to solve such problems, and its purpose is to provide a positive electrode plate for a battery, a battery, and a method for manufacturing a positive electrode plate for a battery that ensures good battery characteristics while improving manufacturing quality.

[0008] One embodiment of the positive electrode plate for a battery includes: a porous metal body with a three-dimensional mesh structure framework, and a positive electrode composite material containing a positive electrode active material filling the pores of the porous metal body. In a configuration where a region on one surface side of the porous metal body is designated as a surface side portion, a region on the back side side (which is another surface) is designated as a back side portion, and a region sandwiched between the surface side portion and the back side portion is designated as a central portion, the surface side portion and the back side portion contain a framework with a hollow structure as its main structure, forming hollow portions unfilled with the positive electrode composite material. The central portion contains a framework with a compression structure as its main structure, forming compressed portions formed by the crushing of the hollow portions. The framework density of the porous metal body is lowest on the surface side portion and highest in the central portion.

[0009] Furthermore, in one embodiment, the battery contains an electrode body with a separator between the positive and negative electrodes, along with an electrolyte, within a battery case. In this battery, the positive electrode plate has: a porous metal body including a three-dimensional mesh structure framework, and a positive electrode composite material containing a positive electrode active material that fills the porous metal body. In this case, when a region located on one surface side of the porous metal body is designated as a surface side portion, a region located on the back side, which is another surface, is designated as a back side portion, and a region sandwiched between the surface side portion and the back side portion is designated as a central portion, the surface side portion and the back side portion contain a framework with a hollow structure as its main structure. The hollow structure forms a hollow portion that is not filled with the positive electrode composite material. The central portion contains a framework with a compression structure as its main structure. The compression structure forms a compressed portion formed by the crushing of the hollow portion. The framework density of the porous metal body is lowest at the surface side portion and highest at the central portion.

[0010] Furthermore, one embodiment of the battery positive electrode plate manufacturing method includes: a metal porous body forming step, a coating step, and a composite material forming step. In the metal porous body forming step, a metal porous body including a three-dimensional mesh structure framework is formed. In the coating step, the pores of the metal porous body are filled with a positive electrode paste containing a positive electrode active material from one surface to the back surface, which is another surface, in the thickness direction. In the composite material forming step, the filled positive electrode paste is dried to form a positive electrode composite material. In the case where the region located on the surface side is designated as the surface side portion, the region located on the back side is designated as the back side portion, and the region sandwiched between the surface side portion and the back side portion is designated as the central portion, the surface side portion and the back side portion include a framework with a hollow structure as the main structure. The hollow structure forms a hollow portion without positive electrode composite material filling. The central portion includes a framework with a compression structure as the main structure. The compression structure forms a compressed portion formed by the crushing of the hollow portion. The framework density of the metal porous body is the lowest in the surface side portion and the highest in the central portion.

[0011] According to the present invention, a positive electrode plate for a battery, a battery, and a method for manufacturing a positive electrode plate for a battery can be provided that ensures good battery characteristics while improving manufacturing quality.

[0012] The above and other objects, features and advantages of this disclosure will be more fully understood from the detailed description given below and the accompanying drawings, which are given by way of example only, and should therefore not be construed as limiting the scope of this disclosure. Attached Figure Description

[0013] Figure 1 This is a schematic diagram showing a cross-section of the battery involved in Embodiment 1.

[0014] Figure 2 This is a schematic diagram showing the cross-section of the positive electrode plate involved in Embodiment 1.

[0015] Figure 3 It is used for in Figure 2 The diagram illustrates the current flowing within the positive electrode plate.

[0016] Figure 4 This is an explanation Figure 2 The table shows the properties of the positive electrode plate.

[0017] Figure 5 This is a flowchart illustrating the manufacturing method of the positive electrode plate according to Embodiment 1.

[0018] Figure 6 It is a cross-sectional view illustrating the process of forming porous metal bodies.

[0019] Figure 7 This is a cross-sectional view of the positive electrode plate contained in the comparative example evaluation battery.

[0020] Figure 8 This is an explanation Figure 7 The table shows the properties of the positive electrode plate. Detailed Implementation

[0021] Implementation Method 1

[0022] Embodiments of the present invention will now be described with reference to the accompanying drawings. Furthermore, to make the description clearer, the following description and drawings have been appropriately simplified. In the following description, the same or equivalent elements are labeled with the same reference numerals, and repeated descriptions are omitted.

[0023] As a preferred embodiment of the battery 1 according to this embodiment, an alkaline storage battery will be specifically described. Furthermore, in the following description, when the structures and components of the positive and negative electrode sides of the battery 1 are shown in general terms, they will sometimes be uniformly referred to as "positive and negative electrodes." Also, in the figures, for convenience, the cross-sections of the frame 32, etc., are schematically shown, and their size and density are not illustrated according to actual conditions. Furthermore, in the following description, "cross-section" refers to a cross-section along the thickness direction of the positive electrode plate 15. The thickness direction of the positive electrode plate 15 is approximately aligned with the thickness direction of the porous metal body 30.

[0024] First, see Figure 1 The general outline of the battery 1 involved in this embodiment will be described. Figure 1 This is a schematic diagram showing a cross-section of the battery involved in Embodiment 1. Figure 1 The battery 1 shown is a nickel-metal hydride battery in which an electrode body 20, with a separator 17 between a positive electrode plate 15 containing positive electrode active material and a negative electrode plate 16 containing negative electrode active material, is connected to current collector plates 21 and 22 of the positive and negative electrodes, and is contained together with electrolyte in a battery case 2 such as a battery casing.

[0025] As the separator 17, microporous membranes, non-woven fabrics, etc. can be used. Examples of materials for microporous membranes or non-woven fabrics include polyolefin resins such as polyethylene (PE) and polypropylene (PP), fluoropolymers, and polyamide resins.

[0026] An alkaline aqueous solution can be used as the electrolyte. The specific gravity of the electrolyte is, for example, 1.03 to 1.55. Examples of alkali metal hydroxides include lithium hydroxide, potassium hydroxide, and sodium hydroxide. From the viewpoint of improving charging efficiency, sodium hydroxide with an alkali metal hydroxide content of 75 mol% or higher is preferred.

[0027] The electrode body 20 is, for example, a laminate formed by alternating layers of multiple positive electrode plates 15 and multiple negative electrode plates 16 with every other spacer 17. Positive and negative electrode leads 15a and 16a are formed at the ends of the positive electrode plates 15 and 16, respectively. The positive electrode lead 15a of the positive electrode plate 15 is joined perpendicularly to the joint surface of the positive current collector plate 21 by a joining method such as welding. Similarly, the negative electrode lead 16a of the negative electrode plate 16 is joined perpendicularly to the joint surface of the negative current collector plate 22 by a joining method such as welding.

[0028] The negative electrode plate 16 includes a plate-shaped substrate and a negative electrode composite material containing a negative electrode active material loaded on the substrate. The negative electrode composite material may contain, for example, a hydrogen storage alloy as the negative electrode active material. The type of hydrogen storage alloy is not particularly limited; examples include alloys of mixed rare earth elements (Mm) and nickel (Ni), or alloys obtained by replacing a portion of the alloy with aluminum (Al), cobalt (Co), manganese (Mn), etc.

[0029] The negative electrode composite material may further contain conductive materials, binders, thickeners, and other additives as needed. Conductive materials may include, for example, graphite-based materials such as natural graphite and artificial graphite, and carbon black-based materials such as acetylene black (AB). Binders may include, for example, fluorinated resins such as polytetrafluoroethylene (PTFE) and vinyl alcohol polymers. Thickeners may include, for example, cellulose-based materials such as carboxymethyl cellulose (CMC) and methyl cellulose (MC).

[0030] Except for one end in the width direction, a negative electrode composite material is filled into the substrate. A metal component such as iron is welded to the end of the substrate that is not filled with negative electrode composite material to form a negative electrode lead portion 16a. The negative electrode lead portion 16a is electrically connected to the negative terminal 4 provided in the battery compartment 2 via the negative electrode current collector 22.

[0031] Next, see appropriate references. Figure 2 and Figure 3 The structure of the positive electrode plate 15 is explained. Figure 2 This is a schematic diagram showing the cross-section of the positive electrode plate involved in Embodiment 1. Figure 3 It is used for in Figure 2 A schematic diagram illustrating the current flowing within the positive electrode plate is shown. Additionally, Figure 3 It shows the relationship with Figure 2 Same cross-section. For example... Figures 1-3 As shown, the positive electrode plate 15 has a plate-shaped metal porous body 30 and a positive electrode composite material 40 filled with pores 31 in the metal porous body 30.

[0032] The positive electrode composite material 40 contains, for example, nickel hydroxide as the positive electrode active material. The positive electrode composite material 40 may further contain conductive materials, binders, thickeners, and other additives as needed. Conductive materials may include, for example, cobalt hydroxide (Co(OH)2) or cobalt (Co). Binders may include, for example, fluorinated resins such as polytetrafluoroethylene (PTFE) or vinyl alcohol polymers. Thickeners may include, for example, carboxymethyl cellulose (CMC) or methyl cellulose (MC).

[0033] Except for one end in the width direction, the metal porous body 30 is filled with positive electrode composite material 40. The positive electrode lead portion 15a is formed by welding a metal component such as iron while the end of the metal porous body 30 without positive electrode composite material 40 is compressed. The positive electrode lead portion 15a is located near the center in the thickness direction of the metal porous body 30 and is electrically connected to the positive terminal 3 provided in the battery compartment 2 via the positive electrode current collector 21.

[0034] The porous metal body 30 functions as a carrier for the positive electrode composite material 40 and as a current collector. The porous metal body 30 includes a three-dimensional mesh structure framework 32, pores 31 filled with the positive electrode composite material 40, hollow portions 34 unfilled with the positive electrode composite material 40, and compressed portions 35 formed by crushing the hollow portions 34. The porosity of the porous metal body 30 is preferably 90% or higher, and the average pore size is preferably 100 μm to 200 μm.

[0035] The porous metal 30 has a framework 32 made of a conductive metal or its alloy. The porous metal 30 is preferably a foamed metal, for example, nickel foam made of nickel or a nickel alloy is preferred. The nickel foam has multiple interconnected pores internally and can be easily compressed.

[0036] The porous metal body 30 has one surface 30a opposite to each other in its thickness direction and a back surface 30b as the other surface. Furthermore, the positive electrode plate 15 containing the porous metal body 30 is configured such that the skeleton density distribution of the porous metal body 30 in the thickness direction of the positive electrode plate is non-uniform.

[0037] In this embodiment, as Figure 2 and Figure 3As shown by the double-dotted lines, for each region in which the positive electrode plate 15 is divided into three equal parts in its thickness direction, the region of the positive electrode plate 15 located on the surface 30a side of the metal porous body 30 (positive electrode plate 15) is designated as the surface side P1, the region of the positive electrode plate 15 located on the back side 30b side of the metal porous body 30 (positive electrode plate 15) is designated as the back side P3, and the region of the positive electrode plate 15 sandwiched between the surface side P1 and the back side P3 is designated as the central part P2. This provides a detailed explanation of the framework 32 of the metal porous body 30. Furthermore, unless otherwise specified, the surface side P1, the central part P2, and the back side P3 are sometimes simply referred to as "regions".

[0038] The framework 32 of the porous metal body 30 has a roughly polygonal cross-sectional shape in the thickness direction of the metal layers 33a, 33b, and 33c constituting the framework 32, and is mainly a roughly triangular shape with each side concave inward. Furthermore, the structure of the framework 32 is distinguished by whether or not a hollow portion 34 of the unfilled positive electrode composite material 40 is formed.

[0039] The framework 32 constituting the surface side P1 and the back side P3 has a hollow structure with a hollow portion 34. The framework 32 constituting the central portion P2 has a compression structure with a compression portion 35 formed by compressing the hollow portion 34. When the positive electrode plate 15 (metal porous body 30) is viewed in cross-section, the hollow portion 34 is the part surrounded by metal layers 33a and 33c (framework 32), and the compression portion 35 is the part surrounded by metal layer 33b (framework 32). Since the compression structure has a structure with a compression portion 35 that is significantly compressed compared to the hollow portion 34, the degree of indentation towards the inner side of each side of the approximately triangular shape is greater than that of the hollow structure, and the metal layers 33b constituting each side are in close contact with each other. The compression portion 35 does not necessarily have to be completely compressed.

[0040] The ratio of hollow portion 34 to compressed portion 35 in the positive electrode plate 15 is preferably 7:3 to 3:7, and particularly preferably 1:1. By making the framework 32 on the outer side (surface side P1 and back side P3) of the positive electrode plate 15 in the thickness direction hollow, three-dimensional strength and durability of the positive electrode plate 15 can be ensured. This suppresses defects such as bending of the positive electrode plate 15 that may occur due to three-dimensional external forces (e.g., forces from bending processes) during the manufacturing process of the battery 1. Furthermore, by forming the compressed portion 35 within the positive electrode plate 15, the proportion of hollow portion 34 is reduced, and the porosity of the positive electrode plate 15 can be relatively increased. On the other hand, a higher proportion of compressed portion 35 results in higher porosity but lower durability. By keeping the ratio of hollow portion 34 to compressed portion 35 in the positive electrode plate 15 within the above-mentioned range, both high porosity and high durability of the positive electrode plate 15 can be achieved.

[0041] Furthermore, the framework 32 of the central P2 has a compressed structure, thereby reducing the overall hollow volume of the metal porous body 30. Compared to the case where the framework 32 is only a hollow structure, the porosity of the positive electrode plate 15 is increased. If the porosity of the positive electrode plate 15 is higher, the electrolyte retention around the positive electrode active material is improved, and the movement of ions around the positive electrode active material becomes smoother. As a result, the internal resistance of the battery 1 can be reduced.

[0042] Furthermore, the framework density of the metal porous body 30 contained in the positive electrode plate 15 is such that the framework density is lowest in the surface side portion P1 and highest in the central portion P2. Regarding the ratio of the framework density of the metal porous body 30, when the total of the surface side portion P1, the central portion P2, and the back side portion P3 is set to 100%, it is preferable that the surface side portion P1 is 20% to 30%, the central portion P2 is 40% to 50%, and the back side portion P3 is 25% to 35%.

[0043] like Figure 3 As shown, due to the high skeleton density of the central portion P2, the current collection capacity of the central portion P2 is improved, thus the current path CP of the central portion P2 becomes thicker. If the current path CP at the central portion P2 becomes thicker, it is easier to extract the current flowing through the current path CP from the positive electrode lead portion 15a, which is located in the thickness direction of the positive electrode plate 15 corresponding to the central portion P2. As a result, the internal resistance of the battery 1 decreases. Furthermore, within the positive electrode plate 15, a current-concentrated column is formed at the central portion P2, from which the current flows uniformly outward in the thickness direction. Therefore, the overall utilization efficiency of the positive electrode active material present in the positive electrode plate 15 is improved, promoting a uniform chemical reaction, thus suppressing the generation of gas during charging and preventing an increase in the battery's internal pressure.

[0044] See Figure 4 Other properties of the positive electrode plate 15 resulting from the skeletal density of the metal porous body 30 will be explained. Figure 4 This is an explanation Figure 2 The table shows the properties of the positive electrode plate. Figure 4 The table shown illustrates the permeability of the electrolyte, the permeability of the positive electrode paste, and the shedding of the positive electrode paste for each region of the positive electrode plate 15 or the metal porous body 30.

[0045] Here, the permeability of the electrolyte in each region of the positive electrode plate 15 is explained. With varying skeleton density along the thickness direction of the positive electrode plate 15, a higher skeleton density requires the electrolyte to flow around the surface of the skeleton 32, thus increasing the electrolyte's travel distance. As a result, the permeability of the electrolyte is considered to deteriorate. Consequently, the electrolyte permeates easily at the surface side P1, is difficult to permeate at the central part P2, and is more difficult to permeate at the back side P3 than at the surface side P1 but easier than at the central part P2.

[0046] In this way, by setting different skeleton densities in the thickness direction of the positive electrode plate 15, the skeleton density of the surface side P1 is minimized, which improves the permeability of the electrolyte into the positive electrode plate 15. Furthermore, by reducing the proportion of the hollow portion 34, the porosity of the positive electrode plate 15 increases, thus improving electrolyte retention around the positive electrode active material and facilitating the movement of ions around the positive electrode active material. As a result, the internal resistance of the battery 1 can be reduced.

[0047] For example, the structure (hollow structure and compressed structure) of the framework 32 of the aforementioned porous metal 30 can be understood by observing the cross-section of the positive electrode plate 15 using a scanning electron microscope (SEM). During SEM observation, for example, the cut surface obtained by cutting the positive electrode plate 15, which is fixed with a suitable resin, in the thickness direction can be ground, and then the cut surface can be used to perform SEM observation of the cross-section of the positive electrode plate 15.

[0048] In addition, for example, an X-ray CT (X-ray computed tomography) can be used to obtain a three-dimensional model of the metal porous body 30 contained in the positive electrode plate 15, and the image analysis of the three-dimensional model can be performed to determine the skeleton density of the metal porous body 30.

[0049] When using X-ray CT, the surface area and volume of the surface metal part M1, the central metal part M2, and the back metal part M3 can be measured respectively by dividing the three-dimensional model of the metal porous body 30 into three equal parts in the thickness direction, and the skeletal density of each part can be calculated using the measured surface area and volume.

[0050] Here, the surface-side metal portion M1 is the region located on the surface 30a side of the porous metal body 30, and constitutes the surface-side portion P1. The back-side metal portion M3 is the region located on the back side of the porous metal body 30, and constitutes the back-side portion P3. The central metal portion M2 is the region sandwiched between the surface-side metal portion M1 and the back-side metal portion M3 in the porous metal body 30, and constitutes the central portion P2. Furthermore, unless otherwise specified, the surface-side metal portion M1, the central metal portion M2, and the back-side metal portion M3 are sometimes simply referred to as "region".

[0051] Next, see Figure 5 A description of the manufacturing method of the positive electrode plate 15 having the above structure. Figure 5 This is a flowchart illustrating a method for manufacturing the positive electrode plate according to Embodiment 1. Figure 5 As shown, the manufacturing method of the positive electrode plate 15 includes the following steps S1 to S3.

[0052] Step S1 is a metal porous body forming process that forms a metal porous body 30 with a three-dimensional mesh structure framework 32. Step S2 is a coating process that fills the metal porous body 30 with a positive electrode paste containing a positive electrode active material from one surface 30a to the back surface 30b, which serves as another surface, in the thickness direction. Step S3 is a composite material forming process that dries the filled positive electrode paste to form a positive electrode composite material 40. The above processes will be described in more detail.

[0053] First, see Figure 6 The process for forming porous metal bodies is explained. Figure 6 This is a cross-sectional view showing the metal porous body forming process. In the metal porous body forming process, after the metal constituting the metal porous body 30 is attached to the surface of the resin skeleton of the resin porous body, the internal resin skeleton is decomposed or melted and removed by heat treatment or the like to obtain the pre-compression metal porous body 120, and the pre-compression metal porous body 120 is compressed to form the metal porous body 30.

[0054] Examples of resin porous materials include polyurethane, melamine, polypropylene, and polyethylene foam resins. Due to their high porosity, polyurethane foam is preferred. The porosity of the resin porous body is preferably 80% to 98%, and the average pore size is preferably 50 μm to 500 μm. Furthermore, as a method for attaching metal to the surface of the resin skeleton, electroplating is preferred because the thickness of the metal layers 123a, 123b, and 123c is easily adjustable.

[0055] When the porous metal body 30 is nickel foam, such as Figure 6 As shown in S1-1, a strip of polyurethane foam 110 (resin porous body) obtained by electroless nickel plating on the surface of a polyurethane skeleton 112 (resin skeleton) is conveyed at a predetermined speed. The conveyed polyurethane foam 110 is immersed in an electrolytic nickel plating solution for a predetermined time, and an electroplating process is performed simultaneously. In this electroplating process, current flows through a surface-side electrode 101 provided on the surface 110a side of the polyurethane foam 110 and a back-side electrode 102 provided on the back side 110b side of the polyurethane foam 110.

[0056] Electroplating can be used to form nickel plating layers, namely metal layers 123a, 123b, and 123c, on the surface of the polyurethane skeleton 112, which function as current collectors. After electroplating, by burning off the polyurethane foam 110, a pre-compression metal porous body 120 can be obtained, which includes a three-dimensional mesh-like skeleton 122 and pores 121 corresponding to the shape of the polyurethane foam 110 having communicating pores 111.

[0057] In addition, such as Figure 6As shown in S1-3, a metal porous body 30 is formed by compressing the pre-compression metal porous body 120 in the thickness direction. The compression of the pre-compression metal porous body 120 can be performed using a stamping device such as a roll press. This results in a metal porous body 30 with a predetermined thickness, having the lowest skeleton density in the surface-side metal portion M1 and the highest skeleton density in the central metal portion M2.

[0058] Furthermore, polyurethane foam 110 is produced by generating bubbles using a foaming agent, but polyurethane remains in the gaps between the bubbles during foaming, specifically in the gaps formed by three bubbles, resulting in a three-dimensional porous body with a roughly triangular framework. Since this polyurethane foam 110 is used as a substrate, nickel foam with a roughly triangular framework can be obtained. Because a portion of the roughly triangular framework combines with multiple other frameworks to form a roughly polygonal shape, the actual cross-section of the nickel foam is observed in a form where they are mixed together.

[0059] Here, the average thickness of the metal layer 123a forming the skeleton 32 (which constitutes the surface-side metal portion M10) is set as T1, the average thickness of the metal layer 123b forming the skeleton 32 (which constitutes the central metal portion M20) is set as T2, and the average thickness of the metal layer 123c forming the skeleton 32 (which constitutes the back-side metal portion M30) is set as T3. The surface-side metal portion M10 is the region located on the surface 120a side of the porous metal body 120 before compression, and is the portion that becomes the surface-side metal portion M1 through compression. The back-side metal portion M30 is the region located on the back side 120b side of the porous metal body 120 before compression, and is the portion that becomes the back-side metal portion M3 through compression. The central metal portion M20 is the region sandwiched between the surface-side metal portion M10 and the back-side metal portion M30 in the porous metal body 120 before compression, and is the portion that becomes the central metal portion M2 through compression. In addition, without specifically distinguishing between the surface-side metal part M10, the central metal part M20, and the rear-side metal part M30, they are sometimes simply referred to as "areas".

[0060] In the metal porous body formation process, the metal porous body 120 before compression is formed such that the average thickness T1 of metal layer 123a is the largest and the average thickness T2 of metal layer 123b is the smallest. That is, the average thicknesses of metal layers 123a, 123b, and 123c are formed to satisfy the relationship T1 > T3 > T2.

[0061] By varying the average thicknesses T1, T2, and T3, the crushability (compression resistance) of the skeleton 32 relative to the compression caused by a fixed stamping pressure can be determined for each region. Larger average thicknesses T1, T2, and T3 result in higher compression resistance, making it less prone to crushing, and thus lower skeleton density after compression. Conversely, smaller average thicknesses T1, T2, and T3 result in lower compression resistance, making it more prone to crushing, and thus higher skeleton density after compression.

[0062] The average thicknesses T1, T2, and T3 of the metal layers 123a, 123b, and 123c can be adjusted by electroplating conditions such as the current values ​​of the surface-side electrode 101 and the back-side electrode 102, and the immersion time in the electrolytic nickel plating solution. For example, when the current value of the surface-side electrode 101 is set to be greater than the current value of the back-side electrode 102, the average thickness T1 can be made greater than the average thickness T3.

[0063] The methods for measuring the average thicknesses T1, T2, and T3 will be explained using the measurement sequence of average thickness T1 as an example. When measuring the average thickness T1, firstly, the cross-section of the porous metal body 120 before compression is observed using SEM. A cross-section of metal layer 123a, where the metal layer 123a is cut along its thickness direction and has a roughly triangular cross-section, is selected from the surface-side metal portion M10. Then, the thickness at the center of each of the three sides constituting the selected metal layer 123a is measured, and the average value of these thicknesses is taken as the average thickness T1 of the metal layer 123a. Similarly, the average thickness T2 of metal layer 123b is measured for the central metal portion M20, and the average thickness T3 of metal layer 123c is measured for the back-side metal portion M30.

[0064] return Figure 5 In the coating process, a positive electrode paste is prepared to fill the pores 31 of the metal porous body 30 obtained in the metal porous body formation process. The positive electrode paste can be prepared by mixing positive electrode active material, conductive material, binder, thickener, and other additives as needed, and then adding solvent for kneading. The positive electrode paste is a precursor to the positive electrode composite material 40.

[0065] Then, the prepared positive electrode paste is filled into the pores 31 of the metal porous body 30. The positive electrode paste is filled except at the two ends in the width direction of the metal porous body 30. The metal porous body 30 has a surface 30a and a back surface 30b opposite each other in its thickness direction. The positive electrode paste is coated from the surface 30a side of the metal porous body 30. When the positive electrode paste is coated on the surface 30a of the metal porous body 30, due to gravity, the positive electrode paste penetrates from the surface 30a to the back surface 30b and is exposed on the back surface 30b.

[0066] The coating of the positive electrode paste is preferably performed in a manner that allows the positive electrode paste to penetrate from the surface 30a to the back surface 30b of the metal porous body 30. Since high-precision coating is possible, a die coater is preferably used. When using a die coater, the outlet of the die head of the die coater is aligned with the surface 30a of the metal porous body 30, and the positive electrode paste is discharged from the outlet onto the surface 30a of the metal porous body 30, which is being conveyed at a predetermined speed. This allows the positive electrode paste to fill the pores 31 of the metal porous body 30.

[0067] See here. Figure 4 The permeability and shedding properties of the positive electrode paste in each region of the metal porous body 30 are explained. Due to the different skeleton density in the thickness direction of the metal porous body 30, the positive electrode paste is easy to penetrate in the surface metal part M1, difficult to penetrate in the central metal part M2, and difficult to penetrate in the back metal part M3 than in the surface metal part M1, but easier to penetrate than in the central metal part M2.

[0068] When the positive electrode paste is applied from the surface 30a side of the metal porous body 30, the positive electrode paste that is successfully impregnated in the area of ​​the surface side metal part M1 is received by the area of ​​the central metal part M2, and the positive electrode paste that passes through the area of ​​the central metal part M2 gradually impregnates in the area of ​​the back side metal part M3, so that the positive electrode paste remains stably in the metal porous body 30.

[0069] For example, if the skeleton density of the back side metal portion M3 is minimized, the positive electrode paste can easily pass through the back side 30b, increasing the likelihood of the positive electrode paste falling off. In contrast, in this embodiment, the positive electrode paste is less likely to fall off in the region of the back side metal portion M3. Thus, if the metal porous body 30 is used, the filling properties of the positive electrode paste are stable even without complex control of coating conditions, thereby obtaining a high-quality positive electrode plate 15.

[0070] Next, in the composite material forming process, the positive electrode paste filled into the metal porous body 30 in the coating process is dried using an appropriate drying method to remove the solvent contained in the positive electrode paste. Then, the dried positive electrode paste is compressed using a pressing device such as a roller press to adjust the density and thickness of the positive electrode plate 15. In this way, a positive electrode plate 15 in which the positive electrode composite material 40 is filled in the pores 31 can be formed. Furthermore, by adjusting the amount of electrolytic nickel plating solution per unit area and the thickness of the positive electrode plate 15 during the electroplating process, the required number of pores 31 relative to the filling amount of the positive electrode paste can be ensured. According to the manufacturing method of the positive electrode plate 15 according to this embodiment, a positive electrode plate 15 with a skeleton density ratio within the above-mentioned range can be manufactured.

[0071] Next, evaluation batteries (examples and comparative examples) with different density distributions of the frameworks 32 and 132 of the metal porous bodies 30 and 130 were prepared, and their DC internal resistance and internal pressure characteristics were evaluated respectively. First, the evaluation batteries were prepared according to the following procedures.

[0072] (Example)

[0073] [Preparation of the positive electrode plate]

[0074] according to Figure 5 The flowchart described above illustrates the preparation of the positive electrode plate 15. First, in the metal porous body formation process, a polyurethane foam 110 with a porosity of 90%, an average pore size of 500 μm, and a thickness of 1 mm to 2 mm is prepared, and electroless nickel plating and conductive treatment are performed on its surface. Next, the conductive polyurethane foam 110 is electroplated under electroplating conditions where the current value of the surface-side electrode 101 is greater than the current value of the back-side electrode 102. Through this electroplating process, a metal layer 123a with an average thickness T1 of 10 μm, a metal layer 123b with an average thickness T2 of 6 μm, and a metal layer 123c with an average thickness T3 of 8 μm are formed on the surface of the polyurethane skeleton 112. Then, by burning away the internal polyurethane foam 110, a pre-compression metal porous body 120 is obtained. Furthermore, the pre-compression metal porous body 120 is compressed along the thickness direction using a roller press. Thus, a porous metal body 30 with a porosity of 90%, an average pore size of 300 μm, and a thickness of 1 mm was obtained.

[0075] A positive electrode paste was prepared by adding water and mixing Ni(OH)₂ (as the positive electrode active material), Co(OH)₂ (as the conductive material), and CMC (as the thickener). The mass ratio of Ni(OH)₂, Co(OH)₂, and CMC was 90:7:3. Next, the positive electrode paste was applied to the surface 30a of the metal porous body 30 using a die-coating machine, thereby filling the pores 31 of the metal porous body 30 with the positive electrode paste, and then dried. The coating amount of the positive electrode paste was adjusted to achieve a unit area of ​​100 mg / cm². 2 Furthermore, after being rolled to a thickness of 0.5 mm, it is cut to a predetermined size and joined with the positive electrode lead portion 15a to obtain the positive electrode plate 15.

[0076] The hollow portion 34 to the compressed portion 35 in the resulting positive electrode plate 15 has a 1:1 ratio. Furthermore, the skeleton density ratio of the metal porous body 30 contained in the positive electrode plate 15 is 25% for the surface side P1, 45% for the central portion P2, and 30% for the back side P3. Moreover, in the coating process, the yield is 5% higher than when the positive electrode paste is filled into the metal porous body 30, where the skeleton density is approximately uniform in the thickness direction.

[0077] [Making the negative electrode plate]

[0078] The negative electrode plate 16 is manufactured as follows. A negative electrode paste is prepared with MmNi5-based hydrogen storage alloy as the main component, which is used as the negative electrode active material. After filling the prepared negative electrode paste into a perforated metal as a substrate, the negative electrode plate 16 is obtained by drying, rolling, cutting to a predetermined size, and bonding with the negative electrode lead portion 16a.

[0079] [Evaluate the construction of the battery]

[0080] An electrode body 20 is housed within a metal battery casing. Within this electrode body 20, a positive electrode plate 15 and a negative electrode plate 16, fabricated according to the aforementioned principles, are arranged opposite each other. A separator 17, made of non-woven polypropylene (PP) and obtained through a hydrophilic treatment, is placed between the positive electrode plate 15 and the negative electrode plate 16. An aqueous solution of potassium hydroxide, serving as the electrolyte, is added and the casing is sealed, thereby constructing an evaluation battery for this embodiment. The positive electrode plate 15 is configured such that its surface (the surface on the surface 30a side) faces the surface of the negative electrode plate 16.

[0081] (Comparative Example)

[0082] Except for changing the electroplating conditions in the metal porous body formation process, the positive electrode plate 150 was prepared in the same manner as in the embodiment, and the comparative example evaluation battery was constructed using the positive electrode plate 150 in the same manner as in the embodiment. See also Figure 7 The structure of the battery is used to explain the evaluation of the comparative examples. Figure 7 This is a cross-sectional view of the positive electrode plate contained in the comparative example evaluation battery.

[0083] In the electroplating process for forming the porous metal body 130, the current value of the surface-side electrode 101 and the current value of the back-side electrode 102 are set to be approximately the same, and the conductive polyurethane foam 110 is electroplated. Through this electroplating process, a metal layer 133 with an average thickness T4 of 8 μm is formed on the surface of the polyurethane skeleton 112. Then, the material with the internal polyurethane burned off is compressed along the thickness direction using a roller press. Thus, a porous metal body 130 with a porosity of 90%, an average pore size of 300 μm, and a thickness of 1 mm is obtained.

[0084] like Figure 7 As shown, the positive electrode plate 150 contained in the comparative example evaluation battery includes a framework 132 with a hollow structure as its main structure. This hollow structure forms a hollow portion 34 of unfilled positive electrode composite material 40. In the positive electrode plate 150, there is a hollow portion 34, but there is no compressed portion 35.

[0085] Evaluation of DC internal resistance (DCIR)

[0086] The DC internal resistance of each evaluation battery was measured. For each evaluation battery, charging was performed until the state of charge (SOC) reached 50% of the battery capacity. This was followed by a 10-minute pause. Next, a 10-second discharge at 10A was performed. Then, after a 1-minute pause, a 10-second discharge at 50A was performed. The DC internal resistance was calculated based on the slopes of the current and voltage values ​​plotted after 10 seconds of self-discharge.

[0087] As a result of measuring the DC internal resistance of each evaluation battery, the DC internal resistance of the evaluation battery in the embodiment was reduced by 1% compared with that of the evaluation battery in the comparative example.

[0088] [Evaluation of battery internal pressure]

[0089] An internal pressure sensor was installed on each evaluation battery, and the internal pressure of the battery was monitored throughout the entire charging period of 0.5 hours at a current of 4C under an environment of 35°C. As a result of measuring the internal pressure of each evaluation battery, the internal pressure of the evaluation batteries in the embodiment was reduced by 10% compared with the internal pressure of the evaluation batteries in the comparative example.

[0090] To explain why this result was obtained, comparative examples are given to illustrate the problems with the battery. Figure 8 This is an explanation Figure 7 The table shows the properties of the positive electrode plate. Figure 8 In the table shown, with Figure 4Similarly, the permeability of the electrolyte, the permeability of the positive electrode paste, and the shedding of the positive electrode paste are shown for each region of the positive electrode plate 150 or the metal porous body 130.

[0091] like Figure 8 As shown, the framework density of the metal porous body 130 contained in the positive electrode plate 150 is formed such that it has a roughly equal proportion in the region located on the surface 130a side of the metal porous body 130, i.e., the surface side P10, the region located on the back side 130b side, i.e., the back side P30, and the region sandwiched between the surface side P10 and the back side P30, i.e., the central part P20. In this case, it is difficult to obtain the effect of reducing internal resistance and improving internal pressure characteristics due to the current concentration in the central part P20.

[0092] Furthermore, since the skeleton density in the thickness direction of the positive electrode plate 150 is approximately uniform, the difference in electrolyte permeability between each region is suppressed. For example, since the higher the skeleton density of the surface side P10, the more difficult it is for the electrolyte to permeate into the positive electrode plate 150, the electrolyte permeability into the positive electrode plate 150 is reduced in the comparative example's evaluation battery, which has a higher skeleton density in the surface side P10 compared to the evaluation battery of the embodiment. Furthermore, since the metal porous body 130 contained in the positive electrode plate 150 is generally hollow, the porosity of the positive electrode plate 150 relatively decreases as the proportion of hollow portions 34 increases. Therefore, since improved electrolyte retention around the positive electrode active material cannot be expected, the internal resistance of the battery tends to increase.

[0093] Furthermore, since the skeleton density is approximately uniform along the thickness direction of the positive electrode plate 150, the differences in the coatability and shedding properties of the positive electrode paste between each region are suppressed. Therefore, in order to stably retain the positive electrode paste within the metal porous body 130, it is necessary to complexly control coating conditions such as the viscosity of the positive electrode paste, the coating amount, and the method of coating the positive electrode paste from both the surface and the back side. Moreover, the precision of condition matching is required, which may lead to problems that reduce manufacturing quality.

[0094] In contrast, the positive electrode plate 15 of this embodiment includes a porous metal body 30 with a three-dimensional mesh structure skeleton 32 and a positive electrode composite material 40. The positive electrode composite material contains a positive electrode active material, which fills the pores 31 of the porous metal body 30. Furthermore, when the region located on one surface 30a side of the porous metal body 30 is designated as the surface side P1, the region located on the back side 30b side, which is the other surface, is designated as the back side P3, and the region sandwiched between the surface side P1 and the back side P3 is designated as the central part P2, the surface side P1 and the back side P3 include a skeleton 32 with a hollow structure as its main structure. This hollow structure forms a hollow portion 34 that is not filled with the positive electrode composite material 40. The central part P2 includes a skeleton 32 with a compression structure as its main structure. This compression structure forms a compression portion 35 formed by the crushing of the hollow portion 34. The skeleton density of the porous metal body 30 is the lowest in the surface side P1 and the highest in the central part P2.

[0095] Furthermore, in this embodiment, the battery 1 contains an electrode body 20 with a separator 17 between the positive electrode plate 15 and the negative electrode plate 16, along with an electrolyte, in a battery case 2. In the battery 1, the positive electrode plate 15 includes a metal porous body 30 with a three-dimensional mesh structure skeleton 32 and a positive electrode composite material 40. The positive electrode composite material contains a positive electrode active material, and the positive electrode active material fills the metal porous body 30. Furthermore, when the region located on one surface 30a side of the metal porous body 30 is designated as surface side P1, the region located on the back side 30b side which is another surface is designated as back side P3, and the region sandwiched between surface side P1 and back side P3 is designated as central part P2, surface side P1 and back side P3 include a skeleton 32 with a hollow structure as the main structure, which forms a hollow part 34 of the unfilled positive electrode composite material 40. Central part P2 includes a skeleton 32 with a compression structure as the main structure, which forms a compression part 35 formed by the crushing of the hollow part 34. The density of the skeleton 32 of the metal porous body 30 is the smallest in surface side P1 and the largest in central part P2.

[0096] With the above structure, the internal resistance is reduced and the internal pressure characteristics are improved due to the increased current-collecting capacity of the central portion P2. Furthermore, by reducing the skeleton density of the surface portion P1, the permeability of the electrolyte into the positive electrode plate 15 is increased, thus reducing the internal resistance. Moreover, by setting different skeleton densities in the thickness direction of the positive electrode plate 15, the filling properties of the positive electrode paste are stabilized, thereby improving product quality. Thus, according to this embodiment, manufacturing quality can be improved while ensuring good battery characteristics.

[0097] Furthermore, in the positive electrode plate 15, regarding the ratio of the skeleton density of the metal porous body 30, when the total of the surface side P1, the central part P2, and the back side P3 is set to 100%, the surface side P1 is 20% to 30%, the central part P2 is 40% to 50%, and the back side P3 is 25% to 35%. By setting the skeleton density of the metal porous body 30 within this range, the above-mentioned effects can be obtained more reliably.

[0098] Furthermore, in the positive electrode plate 15, the ratio of the hollow portion 34 to the compressed portion 35 is 7:3 to 3:7, thereby achieving both high porosity and high durability of the positive electrode plate 15.

[0099] Furthermore, the manufacturing method of the positive electrode plate 15 according to this embodiment includes: a metal porous body forming process, a coating process, and a composite material forming process. In the metal porous body forming process, a metal porous body 30 including a three-dimensional mesh structure skeleton 32 is formed. In the coating process, the pores 31 of the metal porous body 30 are filled with a positive electrode paste containing a positive electrode active material from one surface 30a to the back surface 30b, which is another surface, in the thickness direction. In the composite material forming process, the filled positive electrode paste is dried to form a positive electrode composite material 40. Furthermore, when the area located on the surface 30a side is designated as surface side P1, the area located on the back side 30b side is designated as back side P3, and the area sandwiched between surface side P1 and back side P3 is designated as central part P2, surface side P1 and back side P3 include a skeleton 32 with a hollow structure as the main structure. The hollow structure forms a hollow part 34 of the unfilled positive electrode composite material 40. Central part P2 includes a skeleton 32 with a compression structure as the main structure. The compression structure forms a compression part 35 formed by the crushing of the hollow part 34. The density of the skeleton 32 of the metal porous body 30 is the smallest in surface side P1 and the largest in central part P2.

[0100] According to the manufacturing method of the positive electrode plate 15 in this embodiment, a positive electrode plate 15 that achieves the above-mentioned effects can be manufactured.

[0101] Based on the above description of the disclosure, it will be apparent that embodiments of this disclosure can be modified in various ways. Such modifications should not be considered a departure from the spirit and scope of this disclosure, and it will be apparent to those skilled in the art that all such modifications are intended to be included within the scope of the appended claims.

Claims

1. A positive electrode plate for a battery, said positive electrode plate having: A porous metal body, the porous metal body comprising a three-dimensional mesh structure framework; and A positive electrode composite material, wherein the positive electrode composite material contains a positive electrode active material and the positive electrode active material fills the pores of the metal porous body. in, When the region located on one surface side of the porous metal body is designated as the surface side portion, the region located on the back side, which is another surface, is designated as the back side portion, and the region sandwiched between the surface side portion and the back side portion is designated as the central portion, The surface side and the back side include a skeleton with a hollow structure as its main structure, the hollow structure forming hollow portions that are not filled with the positive electrode composite material. The central portion includes the skeleton with a compression structure as its main structure, the compression structure being formed by the compression of the hollow portion. The skeletal density of the porous metal is lowest on the side surface and highest in the center.

2. The positive electrode plate for a battery according to claim 1, wherein, Regarding the skeleton density ratio of the metal porous body, when the total of the surface side, the central part, and the back side is set to 100%, the surface side is 20%~30%, the central part is 40%~50%, and the back side is 25%~35%.

3. The positive electrode plate for a battery according to claim 1 or 2, wherein, The ratio of the hollow portion to the compressed portion is 7:3 to 3:

7.

4. The positive electrode plate for a battery according to claim 1, wherein, The porous metal is a foam metal made of nickel or a nickel alloy.

5. A battery, wherein an electrode body with a separator between a positive electrode plate and a negative electrode plate is housed together with an electrolyte in a battery case, wherein in the battery, The positive electrode plate has the following characteristics: A porous metal body, the porous metal body comprising a three-dimensional mesh structure framework; and A positive electrode composite material, wherein the positive electrode composite material contains a positive electrode active material and the positive electrode active material fills the pores of the metal porous body. in, When the region located on one surface side of the porous metal body is designated as the surface side portion, the region located on the back side, which is another surface, is designated as the back side portion, and the region sandwiched between the surface side portion and the back side portion is designated as the central portion, The surface side and the back side include a skeleton with a hollow structure as its main structure, the hollow structure forming hollow portions that are not filled with the positive electrode composite material. The central portion includes the skeleton with a compression structure as its main structure, the compression structure being formed by the compression of the hollow portion. The skeletal density of the porous metal is lowest on the side surface and highest in the center.

6. A method for manufacturing a positive electrode plate for a battery, the method comprising: A metal porous body forming process, wherein a metal porous body comprising a three-dimensional mesh structure is formed; In the coating process, the pores of the metal porous body are filled with a positive electrode paste containing a positive electrode active material from one surface to the back surface, which is another surface, in the thickness direction; and In the composite material forming process, the filled positive electrode paste is dried to form a positive electrode composite material. in, When the region located on the surface side is designated as the surface side portion, the region located on the back side is designated as the back side portion, and the region sandwiched between the surface side portion and the back side portion is designated as the central portion, The surface side and the back side include a skeleton with a hollow structure as its main structure, the hollow structure forming hollow portions that are not filled with the positive electrode composite material. The central portion includes the skeleton with a compression structure as its main structure, the compression structure being formed by the compression of the hollow portion. The skeletal density of the porous metal is lowest on the side surface and highest in the center.

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