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

Abstract

To provide a positive electrode plate for a battery, a battery, and a method for manufacturing a positive electrode plate for a battery, achieving improvement in manufacturing quality while ensuring good battery characteristics.SOLUTION: A positive electrode plate for a battery includes a metal porous body 30 having a skeleton 32 of a three-dimensional network structure and a positive electrode mixture 40 containing a positive electrode active material and filled into pores 31 of the metal porous body 30. When a region located on a side of one surface 30a of the metal porous body 30 is a front face side portion P1, a region located on a side of a rear face 30b is a rear face side portion P3, and a region sandwiched between the front face side portion P1 and the rear face side portion P3 is a central portion P2, the front face side portion P1 and the rear face side portion P3 include the skeleton 32 having, as a main structure, a hollow structure in which a hollow portion 34 where the positive electrode mixture 40 is not filled is formed, and the central portion P2 includes the skeleton 32 having, as a main structure, a compressed structure in which a compressed portion 35 where the hollow portion 34 is collapsed is formed. The metal porous body 30 has skeleton density that is lowest in the front face side portion P1 and highest in the central portion P2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present 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]

[0002] Examples of batteries used as power sources for electronic devices and as driving power sources for vehicles such as electric vehicles (EVs) and hybrid vehicles (HVs) include secondary batteries such as alkaline storage batteries. Electrodes used in secondary batteries such as alkaline storage batteries include a conductive current collector and a composite material (composite material) containing an active material and the like held on the current collector. For example, a positive electrode plate in which an active material is filled into the pores of a porous metal body that functions as a current collector is suitably used as an electrode constituting an alkaline storage battery.

[0003] Patent Document 1 discloses an electrode for a secondary battery, which comprises a three-dimensional metal porous body and a composite containing an active material and a binder, and in which the composite is filled into the three-dimensional metal porous body, and which is characterized in that it comprises a first filled portion, a second filled portion which has a higher binder content than the first filled portion and in which the binder is distributed approximately uniformly in the thickness direction, and an unfilled portion which is not filled with the composite, and in which at least one of the second filled portions is adjacent to the unfilled portion, and in which the unfilled portion constitutes at least one of the edge edges. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-9869 Summary of the Invention [Problem to be solved by the invention]

[0005] The technology described in Patent Document 1 discloses that it is possible to eliminate the risk of short circuits due to the detachment of active materials while maintaining battery characteristics. However, with the technology described in Patent Document 1, the distribution of skeletal density of the metal porous body is approximately uniform in the thickness direction. Therefore, in order to ensure the filling of the composite material throughout the thickness direction, complex control of coating conditions (e.g., viscosity of the paste, coating amount, coating method, etc.) is required in the coating process when filling the three-dimensional porous body with a paste, which is a precursor of the composite material, and precision in matching the conditions is also required, which poses a problem of a risk of reducing manufacturing quality.

[0006] The present invention has been made to solve such problems, and aims to provide a battery positive electrode plate, a battery, and a method for manufacturing a battery positive electrode plate that improves manufacturing quality while ensuring good battery characteristics. [Means for solving the problem]

[0007] A positive electrode plate for a battery according to one embodiment includes a metal porous body having a skeleton with a three-dimensional mesh structure, and a positive electrode composite material containing a positive electrode active material and filled into the pores of the metal porous body. When a region located on one surface side of the metal porous body is defined as a front side portion, a region located on the other surface, i.e., the back side portion, is defined as a back side portion, and a region sandwiched between the front side portion and the back side portion is defined as a central portion, the front side portion and the back side portion include skeletons whose main structure is a hollow structure in which hollow portions that are not filled with the positive electrode composite material are formed, and the central portion includes a skeleton whose main structure is a compressed structure in which compressed portions are formed by crushing the hollow portions, and the skeletal density of the metal porous body is smallest on the front side portion and greatest in the central portion.

[0008] Moreover, a battery according to one embodiment is a battery in which an electrode assembly having a separator interposed between a positive electrode plate and a negative electrode plate is housed in a battery case together with an electrolyte, the positive electrode plate having a metal porous body with a skeleton having a three-dimensional mesh structure, and a positive electrode composite containing a positive electrode active material filled in the metal porous body, and when a region located on one surface side of the metal porous body is defined as a front side portion, a region located on the other surface, i.e., a back side portion, is defined as a back side portion, and a region sandwiched between the front side portion and the back side portion is defined as a central portion, the front side portion and the back side portion include skeletons having a main structure of a hollow structure in which a hollow portion not filled with the positive electrode composite is formed, and the central portion includes a skeleton having a main structure of a compressed structure in which a compressed portion in which the hollow portion is crushed is formed, and the skeletal density of the metal porous body is smallest on the front side portion and greatest in the central portion.

[0009] In addition, the manufacturing method of the battery positive electrode plate according to one embodiment includes the steps of: eye the porous metal body has a porous metal body forming step of forming a porous metal body having a skeleton with a structure; a coating step of filling the pores of the porous metal body with a positive electrode paste containing a positive electrode active material from one surface in the thickness direction toward the other surface, i.e., the back surface; and a composite forming step of drying the filled positive electrode paste to form a positive electrode composite, wherein if the region located on the front surface side is defined as a front surface side portion, the region located on the back surface side is defined as a back surface side portion, and the region sandwiched between the front surface side portion and the back surface side portion is defined as a central portion, the front surface side portion and the back surface side portion include a skeleton having a main structure of a hollow structure in which a hollow portion that is not filled with the positive electrode composite is formed, and the central portion includes a skeleton having a main structure of a compressed structure in which a compressed portion is formed by crushing the hollow portion, and the skeletal density of the porous metal body is smallest on the front surface side and greatest in the central portion. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a battery positive electrode plate, a battery, and a method for manufacturing a battery positive electrode plate that improves manufacturing quality while ensuring good battery characteristics. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a cross section of a battery according to a first embodiment. [Figure 2]1 is a schematic diagram showing a cross section of a positive electrode plate according to a first embodiment. [Figure 3] 3 is a schematic diagram for explaining the current flowing in the positive electrode plate shown in FIG. 2. FIG. [Figure 4] 3 is a table illustrating the properties of the positive electrode plate shown in FIG. 2. [Figure 5] 3 is a flowchart showing a method for manufacturing a positive electrode plate according to the first embodiment. [Figure 6] FIG. 3 is a cross-sectional view illustrating a metal porous body forming step. [Figure 7] FIG. 2 is a cross-sectional view of a positive electrode plate included in an evaluation battery of a comparative example. [Figure 8] 8 is a table illustrating the properties of the positive electrode plate shown in FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0012] Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. For clarity, the following description and drawings have been simplified as appropriate. In the following description, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0013] As one preferred embodiment of the battery 1 according to this embodiment, an alkaline storage battery will be specifically described. In the following description, when the structures and members on the positive and negative electrode sides of the battery 1 are collectively referred to, they may be referred to as "positive and negative electrodes." For convenience, the cross sections of the skeleton 32 and the like are shown in the drawings, and the size and density are not shown to match those of the actual structures. In the following description, the "cross section" refers to a cross section taken along the thickness direction of the positive electrode plate 15. The thickness direction of the positive electrode plate 15 is substantially the same as the thickness direction of the porous metal body 30.

[0014] First, an overview of a battery 1 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing a cross section of a battery according to embodiment 1. The battery 1 shown in Fig. 1 is a nickel-metal hydride storage battery in which an electrode assembly 20, which includes a positive electrode plate 15 containing a positive electrode active material and a negative electrode plate 16 containing a negative electrode active material, with a separator 17 interposed therebetween, is connected to positive and negative electrode current collector plates 21 and 22, and is housed together with an electrolyte in a battery case 2 such as a battery case.

[0015] A microporous film, a nonwoven fabric, or the like can be used as the separator 17. Examples of materials for the microporous film or the nonwoven fabric include polyolefin resins such as polyethylene (PE) and polypropylene (PP), fluororesins, and polyamide resins.

[0016] An alkaline aqueous solution is used as the electrolyte. The specific gravity of the electrolyte is, for example, 1.03 to 1.55. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and sodium hydroxide. From the viewpoint of increasing charging efficiency, it is preferable that 75 mol % or more of the alkali metal hydroxide is sodium hydroxide.

[0017] The electrode assembly 20 is, for example, a laminate formed by alternately stacking a plurality of positive electrode plates 15 and a plurality of negative electrode plates 16 with separators 17 interposed therebetween. Positive and negative electrode lead portions 15a, 16a are formed at the ends of the positive electrode plates 15 and the negative electrode plates 16, respectively. The positive electrode lead portion 15a of the positive electrode plate 15 is joined perpendicularly to the joining surface of the positive electrode current collector plate 21 by a joining method such as welding. The negative electrode lead portion 16a of the negative electrode plate 16 is also joined perpendicularly to the joining surface of the negative electrode current collector plate 22 by a joining method such as welding.

[0018] The negative electrode plate 16 includes a plate-shaped substrate and a negative electrode composite material containing a negative electrode active material supported on the substrate. The negative electrode composite material contains, for example, a hydrogen storage alloy as the negative electrode active material. The type of hydrogen storage alloy is not particularly limited, but examples include an alloy of misch metal (Mm), which is a mixture of rare earth elements, and nickel (Ni), and alloys in which part of the alloy is replaced with aluminum (Al), cobalt (Co), manganese (Mn), or the like.

[0019] The negative electrode mixture may further contain a conductive material, a binder, a thickener, and other additives as needed. Examples of conductive materials that can be used include graphites such as natural graphite and artificial graphite, and carbon blacks such as acetylene black (AB). Examples of binders that can be used include fluorine-based resins such as polytetrafluoroethylene (PTFE), vinyl alcohol polymers, and the like. Examples of thickeners that can be used include celluloses such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and the like.

[0020] The negative electrode composite is filled into the substrate except for one end in the width direction. The end of the substrate not filled with the negative electrode composite is compressed, and a metal member such as an iron material is welded to form a negative electrode lead portion 16a. The negative electrode lead portion 16a is electrically connected to a negative electrode terminal 4 provided on the battery case 2 via a negative electrode current collector plate 22.

[0021] Next, the configuration of the positive electrode plate 15 will be described with appropriate reference to FIGS. 2 and 3. FIG. 2 is a schematic diagram showing a cross section of the positive electrode plate according to the first embodiment. FIG. 3 is a schematic diagram for explaining the current flowing in the positive electrode plate shown in FIG. 2. Note that FIG. 3 shows the same cross section as FIG. 2. As shown in FIGS. 1 to 3, the positive electrode plate 15 has a plate-shaped porous metal body 30 and a positive electrode composite material 40 filled in pores 31 of the porous metal body 30.

[0022] The positive electrode mixture 40 contains, for example, nickel hydroxide as a positive electrode active material. The positive electrode mixture 40 may further contain a conductive material, a binder, a thickener, and may contain other additives as necessary. Examples of the conductive material that can be used include cobalt hydroxide (Co(OH)2) and cobalt (Co). Examples of the binder that can be used include fluorine-based resins such as polytetrafluoroethylene (PTFE), vinyl alcohol-based polymers, and the like. Examples of the thickener that can be used include carboxymethyl cellulose (CMC), methyl cellulose (MC), and the like.

[0023] The metal porous body 30 is filled with the positive electrode composite material 40 except for one end in the width direction. The end of the metal porous body 30 that is not filled with the positive electrode composite material 40 is compressed, and a metal member such as an iron material is welded to it to form a positive electrode lead portion 15a. The positive electrode lead portion 15a is provided near the center in the thickness direction of the metal porous body 30, and is electrically connected to the positive electrode terminal 3 provided in the battery case 2 via a positive electrode current collector plate 21.

[0024] The porous metal body 30 functions as a carrier that supports the positive electrode composite 40 and as a current collector. The porous metal body 30 includes a skeleton 32 with a three-dimensional network structure, pores 31 that are filled with the positive electrode composite 40, hollow portions 34 that are not filled with the positive electrode composite 40, and compressed portions 35 where the hollow portions 34 are crushed. The porous metal body 30 preferably has a porosity of 90% or more and an average pore diameter of 100 μm to 200 μm.

[0025] The porous metal body 30 has a skeleton 32 made of a conductive metal or its alloy. The porous metal body 30 is preferably a foamed metal, and for example, foamed nickel made of nickel or a nickel alloy can be suitably used. Foamed nickel has many interconnected pores inside and can be easily compressed.

[0026] The porous metal body 30 has one surface 30a and the other surface, that is, a back surface 30b, which are opposed in the thickness direction of the porous metal body 30. The positive electrode plate 15 including the porous metal body 30 is configured so that the distribution of the skeletal density of the porous metal body 30 is non-uniform in the thickness direction.

[0027] 2 and 3, the positive electrode plate 15 is divided into three equal regions in the thickness direction, and the region of the positive electrode plate 15 located on the front surface 30a side of the porous metal body 30 (positive electrode plate 15) is referred to as a front surface side portion P1, the region of the positive electrode plate 15 located on the back surface 30b side of the porous metal body 30 (positive electrode plate 15) is referred to as a back surface side portion P3, and the region of the positive electrode plate 15 sandwiched between the front surface side portion P1 and the back surface side portion P3 is referred to as a center portion P2. Here, the skeleton 32 of the porous metal body 30 will be described in detail. When the front surface side portion P1, the center portion P2, and the back surface side portion P3 are not particularly distinguished from each other, they may be simply referred to as "regions."

[0028] Skeleton 32 of porous metal body 30 has a substantially polygonal cross section in the thickness direction of metal layers 33a, 33b, and 33c constituting skeleton 32, with each side of the substantially triangle being recessed inward. The structure of skeleton 32 is distinguished by whether or not hollow portions 34 that are not filled with positive electrode composite 40 are formed.

[0029] The skeleton 32 constituting the front side portion P1 and the back side portion P3 has a hollow structure in which a hollow portion 34 is formed. The skeleton 32 constituting the center portion P2 has a compressed structure in which a compressed portion 35 is formed by crushing the hollow portion 34. When the positive electrode plate 15 (metal porous body 30) is viewed in cross section, the hollow portion 34 is a portion surrounded by each of the metal layers 33a and 33c (skeleton 32), and the compressed portion 35 is a portion surrounded by the metal layer 33b (skeleton 32). The compressed structure has a structure in which the compressed portion 35 is formed to be more compressed than the hollow portion 34, so that the degree of inward depression of each side of the approximately triangle is greater than in the hollow structure, and the metal layers 33b constituting each side are in close contact with each other. The compressed portion 35 does not necessarily have to be completely crushed.

[0030] The ratio of the hollow portions 34 to the compressed portions 35 in the positive electrode plate 15 is preferably 7:3 to 3:7, and particularly preferably 1:1. The hollow structure of the skeleton 32 on the outer side (front side portion P1 and back side portion P3) in the thickness direction of the positive electrode plate 15 ensures three-dimensional strength and improves the durability of the positive electrode plate 15. This makes it possible to suppress defects such as bending of the positive electrode plate 15 that may occur due to three-dimensional external forces (e.g., external forces due to bending) applied during the manufacturing process of the battery 1. Furthermore, the formation of the compressed portions 35 in the positive electrode plate 15 reduces the proportion of the hollow portions 34, thereby relatively increasing the porosity of the positive electrode plate 15. On the other hand, increasing the proportion of the compressed portions 35 increases the porosity but decreases the durability. By setting the ratio of the hollow portions 34 to the compressed portions 35 in the positive electrode plate 15 within the above range, it is possible to achieve both high porosity and high durability of the positive electrode plate 15.

[0031] Furthermore, because the skeleton 32 in the center portion P2 has a compressed structure, the hollow volume of the entire porous metal body 30 is reduced, and the porosity of the positive electrode plate 15 is improved compared to when the skeleton 32 has only a hollow structure. Higher porosity of the positive electrode plate 15 improves the retention of electrolyte around the positive electrode active material, allowing smoother ion movement around the positive electrode active material. As a result, the internal resistance of the battery 1 can be reduced.

[0032] The metal porous body 30 included in the positive electrode plate 15 is formed so that the skeletal density is lowest in the front side portion P1 and highest in the center portion P2. When the total of the front side portion P1, center portion P2, and back side portion P3 is taken as 100%, the skeletal density of the metal porous body 30 is preferably 20% to 30% in the front side portion P1, 40% to 50% in the center portion P2, and 25% to 35% in the back side portion P3.

[0033] As shown in FIG. 3 , the high skeletal density of the central portion P2 improves the current collection performance of the central portion P2, resulting in a thicker current path CP in the central portion P2. When the current path CP in the central portion P2 is thicker, the current flowing through the current path CP can be more easily extracted from the positive electrode lead portion 15a, which is located at a position corresponding to the central portion P2 in the thickness direction of the positive electrode plate 15. As a result, the internal resistance of the battery 1 is reduced. Furthermore, within the positive electrode plate 15, a column of current concentration is formed at the central portion P2, allowing current to flow evenly outward from this column in the thickness direction. This improves the utilization efficiency of the entire positive electrode active material present in the positive electrode plate 15 and promotes uniform chemical reactions, thereby suppressing an increase in the internal pressure of the battery due to gas generation during charging.

[0034] Other properties of the positive electrode plate 15 resulting from the skeletal density of the porous metal body 30 will be described with reference to Fig. 4. Fig. 4 is a table illustrating the properties of the positive electrode plate shown in Fig. 2. The table shown in Fig. 4 shows 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 porous metal body 30.

[0035] Here, we will explain the permeability of the electrolyte in each region of the positive electrode plate 15. As the skeleton density varies in the thickness direction of the positive electrode plate 15, the higher the skeleton density, the longer the distance the electrolyte must travel because the electrolyte must flow around the surface of the skeleton 32. This is thought to result in a deterioration in the permeability of the electrolyte. As a result, the electrolyte permeates easily through the front side portion P1 and less easily through the center portion P2, and the back side portion P3 is less permeable than the front side portion P1 and more permeable than the center portion P2.

[0036] In this way, by varying the skeletal density in the thickness direction of the positive electrode plate 15 and making the skeletal density at the surface side portion P1 the smallest, it is possible to improve 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 is increased, which improves the retention of the electrolyte around the positive electrode active material and facilitates the movement of ions around the positive electrode active material. As a result, the internal resistance of the battery 1 can be reduced.

[0037] The structure (hollow structure and compressed structure) of the skeleton 32 of the porous metal body 30 can be understood, for example, by observing a cross section of the positive electrode plate 15 with a scanning electron microscope (SEM). In performing the SEM observation, for example, the positive electrode plate 15 solidified with an appropriate resin may be cut in the thickness direction, the cut surface obtained may be polished, and the cross section of the positive electrode plate 15 may then be used for SEM observation.

[0038] In addition, the skeletal density of the metal porous body 30 can be determined, for example, by obtaining a three-dimensional model of the metal porous body 30 contained in the positive electrode plate 15 using X-ray CT (X-ray computed tomography) and performing image analysis on this three-dimensional model.

[0039] When X-ray CT is used, the three-dimensional model of the porous metal body 30 is divided into three equal parts in the thickness direction, and three-dimensional models of the front-side metal portion M1, the central metal portion M2, and the back-side metal portion M3 are obtained. Ra body The products are measured and Body The product can be used to calculate the respective skeletal densities.

[0040] Here, the front surface side metal portion M1 is a region located on the front surface 30a side of the metal porous body 30, and is a portion that constitutes the front surface side portion P1. The back surface side metal portion M3 is a region located on the back surface side of the metal porous body 30, and is a portion that constitutes the back surface side portion P3. The central metal portion M2 is a region of the metal porous body 30 that is sandwiched between the front surface side metal portion M1 and the back surface side metal portion M3, and is a portion that constitutes the central portion P2. When no particular distinction is made between the front surface side metal portion M1, the central metal portion M2, and the back surface side metal portion M3, they may each be simply referred to as a "region."

[0041] Next, a method for manufacturing the positive electrode plate 15 having the above configuration will be described with reference to Fig. 5. The figure is a flowchart showing a method for manufacturing the positive electrode plate according to the first embodiment. As shown in Fig. 5, the method for manufacturing the positive electrode plate 15 includes the following steps S1 to S3.

[0042] Step S1 is a three-dimensional network eye Step S2 is a porous metal body forming step in which a porous metal body 30 having a skeleton 32 with a positive electrode active material is filled into the porous metal body 30 from one surface 30a in the thickness direction toward the other surface, the back surface 30b. Step S3 is a composite forming step in which the filled positive electrode paste is dried to form a positive electrode composite 40. Each of the above steps will be described in more detail.

[0043] First, the metal porous body forming step will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view showing the metal porous body forming step. In the metal porous body forming step, the metal that constitutes the metal porous body 30 is attached to the surface of the resin skeleton of the resin porous body, and then the internal resin skeleton is decomposed or dissolved and removed by heat treatment or the like to obtain a pre-compressed metal porous body 120, and the metal porous body 30 is formed by compressing this pre-compressed metal porous body 120.

[0044] Examples of materials for the resin porous body include foamed resins such as polyurethane, melamine, polypropylene, and polyethylene, with foamed polyurethane being preferred due to its high porosity. 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, electrolytic plating is preferred as a method for attaching metal to the surface of the resin skeleton, as it allows for easy adjustment of the thickness of the metal layers 123a, 123b, and 123c.

[0045] When the metal porous body 30 is made of foamed nickel, a strip-shaped urethane foam 110 (porous resin body) having a urethane skeleton 112 (resin skeleton) on the surface of which electroless nickel plating has been applied is transported at a predetermined speed, as shown in S1-1 of Fig. 6. The transported urethane foam 110 is immersed in an electrolytic nickel plating solution for a predetermined time, and a plating process is performed in which an electric current is passed through a front-side electrode 101 provided on a front surface 110a of the urethane foam 110 and a back-side electrode 102 provided on a back surface 110b of the urethane foam 110.

[0046] By plating, metal layers 123a, 123b, and 123c, which are nickel-plated layers that function as current collectors, can be formed on the surface of urethane skeleton 112. After plating, urethane foam 110 is burned off to obtain pre-compressed metal porous body 120 having three-dimensional mesh-like skeleton 122 and pores 121 corresponding to the shape of urethane foam 110 with interconnected pores 111.

[0047] 6, the pre-compression porous metal body 120 is compressed in the thickness direction to form the porous metal body 30. A pressing means such as a roll press can be used to compress the pre-compression porous metal body 120. This makes it possible to obtain a porous metal body 30 having a predetermined thickness, with the surface-side metal portion M1 having the smallest skeletal density and the central metal portion M2 having the largest skeletal density.

[0048] The urethane foam 110 is made by generating bubbles using a foaming agent, and urethane 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 skeleton. Using this urethane foam 110 as the base material, nickel foam with a roughly triangular skeleton is obtained. Some of the roughly triangular skeleton bonds with other skeletons to form a roughly polygonal shape, so the cross section of the actual nickel foam is observed to have a mixture of these shapes.

[0049] Here, T1 denotes the average thickness of the metal layer 123a constituting the skeleton 32 constituting the front-side metal portion M10, T2 denotes the average thickness of the metal layer 123b constituting the skeleton 32 constituting the central metal portion M20, and T3 denotes the average thickness of the metal layer 123c constituting the skeleton 32 constituting the back-side metal portion M30. The front-side metal portion M10 is a region located on the front surface 120a side of the pre-compression metal porous body 120, and is a portion that becomes the front-side metal portion M1 when compressed. The back-side metal portion M30 is a region located on the back surface 120b side of the pre-compression metal porous body 120, and is a portion that becomes the back-side metal portion M3 when compressed. The central metal portion M20 is a region of the pre-compression metal porous body 120 sandwiched between the front-side metal portion M10 and the back-side metal portion M30, and is a portion that becomes the central metal portion M2 when compressed. When the front side metal portion M10, the central metal portion M20, and the back side metal portion M30 are not particularly distinguished from each other, they may be simply referred to as "regions."

[0050] In the metal porous body forming step, the pre-compressed metal porous body 120 is formed so that the average thickness T1 of the metal layer 123a is the largest and the average thickness T2 of the metal layer 123b is the smallest. In other words, the metal layers 123a, 123b, and 123c are formed so that the average thicknesses thereof satisfy the relationship T1>T3>T2.

[0051] Such differences in the average thicknesses T1, T2, and T3 allow the skeleton 32 to have different crush resistance (resistance) against compression at a constant press pressure for each region. The larger the average thicknesses T1, T2, and T3, the higher the resistance and the more difficult it is to crush, resulting in a lower skeleton density after compression. The smaller the average thicknesses T1, T2, and T3, the lower the resistance and the more easily it is to crush, resulting in a higher skeleton density after compression.

[0052] The average thicknesses T1, T2, and T3 of the metal layers 123a, 123b, and 123c can be adjusted by the current values ​​of the front-side electrode 101 and the back-side electrode 102, the plating conditions such as the immersion time in the electrolytic nickel plating solution, etc. For example, by setting the current value of the front-side electrode 101 to be larger than the current value of the back-side electrode 102, the average thickness T1 can be made larger than the average thickness T3.

[0053] The methods for measuring the average thicknesses T1, T2, and T3 will be described using the procedure for measuring the average thickness T1 as an example. To measure the average thickness T1, first, a cross section of the pre-compressed porous metal body 120 is observed using an SEM, and a cross section of the metal layer 123a is selected from the front-side metal portion M10, where the metal layer 123a is cut in the thickness direction and has a substantially triangular cross section. The thicknesses of the three central sides of the selected metal layer 123a are then measured, and the average value is taken as the average thickness T1 of the metal layer 123a. Similarly, the average thickness T2 of the metal layer 123b is measured for the central metal portion M20, and the average thickness T3 of the metal layer 123c is measured for the back-side metal portion M30.

[0054] Returning to FIG. 5, in the coating step, a positive electrode paste is prepared to fill the pores 31 of the porous metal body 30 obtained in the porous metal body forming step. The positive electrode paste can be prepared by mixing a positive electrode active material, a conductive material, a binder, a thickener, and other additives as needed, adding a solvent to the mixture, and kneading the mixture. The positive electrode paste is a precursor of the positive electrode mixture 40.

[0055] The prepared positive electrode paste is then filled into the pores 31 of the porous metal body 30. The positive electrode paste is filled in all areas of the porous metal body 30 except for both ends in the width direction. The porous metal body 30 has a front surface 30a and a back surface 30b that face each other in the thickness direction. The positive electrode paste is applied from the front surface 30a side of the porous metal body 30. When the positive electrode paste is applied to the front surface 30a of the porous metal body 30, gravity causes the positive electrode paste to permeate from the front surface 30a toward the back surface 30b and become exposed at the back surface 30b.

[0056] The positive electrode paste is preferably applied by a coating method that allows the positive electrode paste to permeate from the front surface 30a to the back surface 30b of the porous metal body 30. A die coater is preferably used because it allows for accurate coating. When using a die coater, the discharge outlet of the die head of the die coater is positioned opposite the front surface 30a of the porous metal body 30, and the positive electrode paste is discharged from the discharge outlet onto the front surface 30a of the porous metal body 30, which is being transported at a predetermined speed, thereby filling the pores 31 of the porous metal body 30 with the positive electrode paste.

[0057] 4, the penetration and shedding of the positive electrode paste in each region of the porous metal body 30 will be described. Due to differences in skeletal density in the thickness direction of the porous metal body 30, the positive electrode paste penetrates easily into the front-side metal portion M1 but less easily into the central metal portion M2, and penetrates less easily into the back-side metal portion M3 than into the front-side metal portion M1 but more easily than into the central metal portion M2.

[0058] When the positive electrode paste is applied from the surface 30a side of the metal porous body 30, the positive electrode paste smoothly penetrates into the area of ​​the surface side metal portion M1, is received in the area of ​​the central metal portion M2, and then the positive electrode paste that leaves the area of ​​the central metal portion M2 gradually penetrates into the area of ​​the back side metal portion M3, so that the positive electrode paste remains stably within the metal porous body 30.

[0059] For example, if the skeletal density of the back-side metal portion M3 is set to the lowest, the positive electrode paste will be more likely to escape from the back surface 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 area of ​​the back-side metal portion M3. In this way, by using the metal porous body 30, the filling of the positive electrode paste is stable without complex control of the coating conditions, and a high-quality positive electrode plate 15 can be obtained.

[0060] In the subsequent composite formation process, the positive electrode paste filled into the porous metal body 30 in the coating process is dried using an appropriate drying method to remove the solvent contained in the positive electrode paste. The dried product is then compressed using a press such as a roll press to adjust the density and thickness of the positive electrode plate 15. In this manner, a positive electrode plate 15 can be formed in which the positive electrode composite 40 is filled into the pores 31. By adjusting the coating weight of the electrolytic nickel plating solution during the plating process and the thickness of the positive electrode plate 15, the necessary number of pores 31 can be ensured relative to the amount of positive electrode paste filled. The manufacturing method for the positive electrode plate 15 according to this embodiment allows the manufacture of a positive electrode plate 15 having a skeletal density ratio within the above range.

[0061] Next, evaluation batteries (Example and Comparative Example) were prepared in which the density distributions of the skeletons 32, 132 of the metal porous bodies 30, 130 were different from each other, and the DC internal resistance and internal pressure characteristics were evaluated. First, the evaluation batteries were fabricated as follows.

[0062] (Example) [Preparation of positive electrode plate] The positive electrode plate 15 was fabricated according to the flowchart illustrated in FIG. 5. First, in the metal porous body formation process, a urethane foam 110 with a porosity of 90%, an average pore diameter of 500 μm, and a thickness of 1 mm to 2 mm was prepared, and its surface was subjected to electroless nickel plating to provide electrical conductivity. Next, the electrically conductive urethane foam 110 was plated under plating conditions set so that the current value of the front-side electrode 101 was greater than that of the back-side electrode 102. This plating process formed 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 on the surface of the urethane skeleton 112. The internal urethane foam 110 was then burned off to obtain a pre-compressed metal porous body 120. The pre-compressed metal porous body 120 was then compressed in the thickness direction using a roll press. In this way, a porous metal body 30 having a porosity of 90%, an average pore diameter of 300 μm, and a thickness of 1 mm was obtained.

[0063] A positive electrode paste was prepared by adding water to Ni(OH)2 as a positive electrode active material, Co(OH)2 as a conductive material, and CMC as a thickener, and kneading them. 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 porous metal body 30 using a die coater, filling the pores 31 of the porous metal body 30 with the positive electrode paste, and then drying. The positive electrode paste had a basis weight of 100 mg / cm. 2 The coating amount was adjusted so that the thickness was 0.5 mm, and then the resultant was cut to a predetermined size and a positive electrode lead portion 15a was joined to obtain a positive electrode plate 15.

[0064] The ratio of hollow portions 34 to compressed portions 35 in the positive electrode plate 15 obtained in this manner was 1:1. The proportions of skeletal density of the porous metal body 30 included in the positive electrode plate 15 were 25% in the front side portion P1, 45% in the central portion P2, and 30% in the back side portion P3. Furthermore, in the coating process, the yield of filling the porous metal body 30 with the positive electrode paste increased by 5% compared to when the porous metal body 130 having a substantially uniform skeletal density distribution in the thickness direction was filled with the positive electrode paste.

[0065] [Preparation of negative electrode plate] The negative electrode plate 16 was fabricated as follows. A negative electrode paste containing a MmNi5-based hydrogen storage alloy as a main component was prepared as the negative electrode active material. The prepared negative electrode paste was filled into a punched metal substrate, which was then dried, rolled, and cut to a predetermined size. The negative electrode plate 16 was then obtained by joining the negative electrode lead portion 16a.

[0066] [Construction of evaluation battery] The positive electrode plate 15 and the negative electrode plate 16, each prepared as described above, were placed opposite each other, and a separator 17 made of a hydrophilically treated nonwoven polypropylene (PP) fabric was placed between them to form an electrode assembly 20. The electrode assembly 20 was then housed in a metal battery case, and an aqueous potassium hydroxide solution, which was an electrolyte, was added and sealed to construct an evaluation battery for the example. The positive electrode plate 15 was positioned so that its surface (the surface on the side of surface 30a) faced the surface of the negative electrode plate 16.

[0067] (Comparative Example) A positive electrode plate 150 was produced in the same manner as in the Example except that the plating conditions in the metal porous body forming step were changed, and an evaluation battery for the Comparative Example was constructed using this positive electrode plate 150 in the same manner as in the Example. The configuration of the evaluation battery for the Comparative Example will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view of a positive electrode plate included in the evaluation battery for the Comparative Example.

[0068] The plating conditions for forming the porous metal body 130 were set so that the current value of the front-side electrode 101 and the current value of the back-side electrode 102 for the conductive urethane foam 110 were approximately equal. This plating process formed a metal layer 133 with an average thickness T4 of 8 μm on the surface of the urethane skeleton 112. The urethane inside was then burned off, and the resulting material was compressed in the thickness direction using a roll press. In this way, a porous metal body 130 with a porosity of 90%, an average pore diameter of 300 μm, and a thickness of 1 mm was obtained.

[0069] 7, the positive electrode plate 150 included in the evaluation battery of the comparative example includes a skeleton 132 having a main structure of a hollow structure in which a hollow portion 34 is formed that is not filled with the positive electrode composite material 40. In the positive electrode plate 150, the hollow portion 34 exists, but the compressed portion 35 does not exist.

[0070] [Evaluation of DC internal resistance (DCIR)] The DC internal resistance of each evaluation battery was measured. To measure the DC internal resistance, each evaluation battery was charged until the state of charge (SOC) of the battery reached 50% of its capacity. After that, the battery was rested for 10 minutes. Then, the battery was discharged at 10 A for 10 seconds. After a further rest of 1 minute, the battery was discharged at 50 A for 10 seconds. The DC internal resistance was calculated from the slope of a plot of each current value and the voltage value after each 10-second discharge.

[0071] The DC internal resistance of each test battery was measured, and it was found that the DC internal resistance of the test battery of the Example was reduced by 1% compared to the DC internal resistance of the test battery of the Comparative Example.

[0072] [Battery internal pressure evaluation] A sensor for measuring the internal pressure of the battery was attached to each evaluation battery, and the internal pressure of the battery was monitored over the entire period when the battery was charged for 0.5 hours at a current value of 4 C in an environment of 35° C. As a result of measuring the internal pressure of each evaluation battery, the internal pressure of the evaluation battery of the Example was reduced by 10% compared to the internal pressure of the evaluation battery of the Comparative Example.

[0073] The reasons for these results will be explained by citing the problems with the evaluation battery of the comparative example. Fig. 8 is a table explaining the properties of the positive electrode plate shown in Fig. 7. As with Fig. 4, the table shown in Fig. 8 shows 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 150 or the porous metal body 130.

[0074] 8, the skeletal density of the porous metal body 130 included in the positive electrode plate 150 is formed so as to be approximately equal among a front side portion P10, which is a region located on the front surface 130a side of the porous metal body 130, a back side portion P30, which is a region located on the back surface 130b side, and a central portion P20, which is a region sandwiched between the front side portion P10 and the back side portion P30. In this case, the effect of reducing internal resistance and the effect of improving internal pressure characteristics due to current concentration in the central portion P20 are difficult to obtain.

[0075] Furthermore, since the skeletal density is substantially uniform in the thickness direction of the positive electrode plate 150, differences in electrolyte permeability between regions are suppressed. For example, the higher the skeletal density of the front side portion P10, the more inhibited the permeation of electrolyte into the positive electrode plate 150. Therefore, in the comparative example evaluation battery, which has a higher skeletal density of the front side portion P10 than the evaluation battery of the example, the permeability of electrolyte into the positive electrode plate 150 is reduced. Furthermore, because the metal porous body 130 included in the positive electrode plate 150 has a hollow structure overall, the porosity of the positive electrode plate 150 decreases relatively as the proportion of the hollow portion 34 increases. As a result, improvement in electrolyte retention around the positive electrode active material cannot be expected, and the internal resistance of the battery tends to increase.

[0076] Furthermore, because the skeletal density is substantially uniform in the thickness direction of the positive electrode plate 150, differences in the coating properties and shedding properties of the positive electrode paste between regions are suppressed. Therefore, in order to stably retain the positive electrode paste within the porous metal body 130, complex control of coating conditions, such as the viscosity of the positive electrode paste, the coating amount, and the method of applying the positive electrode paste from the front and back surfaces, is required, and precision in matching the conditions is also required, which poses a problem of a risk of reducing manufacturing quality.

[0077] In contrast, the positive electrode plate 15 according to this embodiment includes a metal porous body 30 having a skeleton 32 with a three-dimensional mesh structure, and a positive electrode composite 40 containing a positive electrode active material and filled into pores 31 of the metal porous body 30. Furthermore, if a region located on one surface 30a of the metal porous body 30 is defined as a front side portion P1, a region located on the other surface, i.e., a back side portion P3, and a region sandwiched between the front side portion P1 and the back side portion P3 is defined as a central portion P2, the front side portion P1 and the back side portion P3 include skeletons 32 having a main structure of a hollow structure in which hollow portions 34 that are not filled with the positive electrode composite 40 are formed, and the central portion P2 includes skeletons 32 having a main structure of a compressed structure in which compressed portions 35 are formed by crushing the hollow portions 34, and the skeleton density of the metal porous body 30 is smallest in the front side portion P1 and greatest in the central portion P2.

[0078] Furthermore, the battery 1 according to this embodiment is a battery 1 in which an electrode body 20, in which a separator 17 is interposed between a positive electrode plate 15 and a negative electrode plate 16, is housed in a battery case 2 together with an electrolyte, and the positive electrode plate 15 has a metal porous body 30 having a skeleton 32 with a three-dimensional mesh structure, and a positive electrode composite 40 containing a positive electrode active material and filled in the metal porous body 30. Furthermore, if the region located on one surface 30a of the metal porous body 30 is defined as a surface side portion P1, the region located on the other surface, i.e., the back surface 30b, is defined as a back surface side portion P3, and the region sandwiched between the surface side portion P1 and the back surface side portion P3 is defined as a central portion P2, the surface side portion P1 and the back surface side portion P3 include a skeleton 32 whose main structure is a hollow structure in which hollow portions 34 that are not filled with the positive electrode composite 40 are formed, and the central portion P2 includes a skeleton 32 whose main structure is a compressed structure in which compressed portions 35 are formed by crushing the hollow portions 34, and the density of the skeleton 32 of the metal porous body 30 is smallest in the surface side portion P1 and greatest in the central portion P2.

[0079] The above-described configuration improves the current collection performance of the central portion P2, thereby reducing internal resistance and improving internal pressure characteristics. Furthermore, reducing the skeletal density of the surface side portion P1 improves the permeability of the electrolyte into the positive electrode plate 15, thereby reducing internal resistance. Furthermore, varying the skeletal density in the thickness direction of the positive electrode plate 15 stabilizes the filling of the positive electrode paste, thereby improving product quality. Thus, this embodiment can improve manufacturing quality while maintaining good battery characteristics.

[0080] In addition, in the positive electrode plate 15, the skeletal density of the porous metal body 30 is 20% to 30% for the surface side portion P1, 40% to 50% for the center portion P2, and 25% to 35% for the back side portion P3, assuming the total of the surface side portion P1, the center portion P2, and the back side portion P3 to be 100%. By setting the skeletal density of the porous metal body 30 within these ranges, the above-mentioned effects can be obtained more reliably.

[0081] Furthermore, in the positive electrode plate 15, the ratio of the hollow portions 34 to the compressed portions 35 is 7:3 to 3:7, so that the positive electrode plate 15 can have both high porosity and high durability.

[0082] In addition, the manufacturing method of the positive electrode plate 15 according to this embodiment is a three-dimensional mesh eyeThe method includes a metal porous body forming step of forming a metal porous body 30 having a skeleton 32 with a structure, a coating step of filling pores 31 of the metal porous body 30 with a positive electrode paste containing a positive electrode active material from one surface 30a toward the other surface, i.e., the back surface 30b, in the thickness direction, and a composite forming step of drying the filled positive electrode paste to form a positive electrode composite 40. Furthermore, if a region located on the front surface 30a side is defined as a front surface side P1, a region located on the back surface 30b side is defined as a back surface side P3, and a region sandwiched between the front surface side P1 and the back surface side P3 is defined as a central portion P2, the front surface side P1 and the back surface side P3 include skeletons 32 mainly having a hollow structure with hollow portions 34 that are not filled with the positive electrode composite 40, and the central portion P2 includes skeletons 32 mainly having a compressed structure with compressed portions 35 formed by crushing the hollow portions 34, and the density of the skeleton 32 of the metal porous body 30 is smallest in the front surface side P1 and greatest in the central portion P2.

[0083] According to the manufacturing method of the positive electrode plate 15 of this embodiment, it is possible to manufacture the positive electrode plate 15 that exhibits the above-mentioned effects. [Explanation of symbols]

[0084] 1 battery 2 battery case 3 Positive terminal 4 Negative terminal 15, 150 positive plate 15a Positive electrode lead part 16 negative electrode plate 16a Negative electrode lead part 17 Separator 20 Electrode body 21 Positive current collector plate 22 Negative electrode current collector plate 30, 130 Porous metal 30a, 110a, 120a, 130a surface 30b, 110b, 120b, 130b back side 31, 111, 121 vacancies 32, 122, 132 Skeleton 33a, 33b, 33c, 123a, 123b, 123c, 133 metal layer 34 Hollow part 35 Compression section 40 Positive electrode mixture 101 Surface side electrode 102 Back electrode 110 Urethane foam 112 Urethane skeleton 120 Pre-compressed porous metal CP current path M1, M10 Surface side metal part M2, M20 central metal part M3, M30 Back side metal part P1, P10 Front side P2, P20 center P3, P30 back side

Claims

1. a porous metal body having a skeleton with a three-dimensional network structure; a positive electrode mixture containing a positive electrode active material and filling the pores of the metal porous body; and When a region located on one surface side of the metal porous body is defined as a surface side portion, a region located on the other surface, i.e., the back surface side portion, and a region sandwiched between the surface side portion and the back surface side portion is defined as a central portion, the front surface side portion and the back surface side portion include the skeleton having a main structure of a hollow structure in which a hollow portion that is not filled with the positive electrode composite is formed, the central portion includes the skeleton having a compressed structure as a main structure in which a compressed portion is formed by crushing the hollow portion, The skeletal density of the porous metal body is lowest at the side surface portions and highest at the center portion.

2. The positive electrode plate for a battery according to claim 1, wherein the ratio of the skeletal density of the metal porous body is 20 to 30:40 to 50:25 to 35 in the front side portion, the central portion, and the back side portion.

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

7.

4. The battery positive electrode plate according to any one of claims 1 to 3, wherein the metal porous body is a foam metal made of nickel or a nickel alloy.

5. A battery in which an electrode assembly having a separator interposed between a positive electrode plate and a negative electrode plate is housed in a battery case together with an electrolyte, The positive electrode plate is a porous metal body having a skeleton with a three-dimensional network structure; a positive electrode mixture containing a positive electrode active material and filled in the metal porous body; and When a region located on one surface side of the metal porous body is defined as a surface side portion, a region located on the other surface, i.e., the back surface side portion, and a region sandwiched between the surface side portion and the back surface side portion is defined as a central portion, the front surface side portion and the back surface side portion include the skeleton having a main structure of a hollow structure in which a hollow portion that is not filled with the positive electrode composite is formed, the central portion includes the skeleton having a compressed structure as a main structure in which a compressed portion is formed by crushing the hollow portion, A battery in which the skeletal density of the metal porous body is lowest at the side surface portions and highest at the center portion.

6. a metal porous body forming step of forming a metal porous body having a skeleton with a three-dimensional network structure; a coating step of filling pores of the metal porous body with a positive electrode paste containing a positive electrode active material from one surface to the other surface, i.e., a back surface, in a thickness direction; a composite forming step of drying the filled positive electrode paste to form a positive electrode composite; and When the region located on the front surface side is defined as a front surface side portion, the region located on the back surface side is defined as a back surface side portion, and the region sandwiched between the front surface side portion and the back surface side portion is defined as a center portion, the front surface side portion and the back surface side portion include the skeleton having a main structure of a hollow structure in which a hollow portion that is not filled with the positive electrode composite is formed, the central portion includes the skeleton having a compressed structure as a main structure in which a compressed portion is formed by crushing the hollow portion, The method for manufacturing a positive electrode plate for a battery, wherein the skeletal density of the metal porous body is smallest on the side surface portions and largest in the central portion.

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