Nickel-metal hydride battery and manufacturing method for the nickel-metal hydride battery

Abstract

To realize a nickel-metal hydride battery in which an increase in internal pressure of a battery is suppressed.SOLUTION: In a nickel-metal hydride battery, a battery element in which a positive electrode containing nickel and a negative electrode 22 containing a hydrogen storage alloy are wound with a separator interposed therebetween so that the negative electrode 22 becomes an outermost periphery is housed in a cylindrical outer can. The negative electrode 22 includes: a first layer 210 on a first surface 200a side of a core body 200; and a second layer 220 on a second surface 200b side. In a first portion 230 which is the outermost periphery of the battery element, the first layer 210 faces the outer can, and the second layer 220 faces the positive electrode via the separator. A first average particle diameter of the hydrogen storage alloy contained in the first portion 230 is smaller than a second average particle diameter of the hydrogen storage alloy contained in a second portion 240 other than the first portion by 10 μm or more, and a thickness of the first layer 210 of the first portion 230 is smaller than a thickness of the second layer 220 of the first portion 230 and is in a range of 1 to 3 times the first average particle diameter.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a nickel-metal hydride battery and a method for manufacturing the nickel-metal hydride battery. [Background technology]

[0002] Nickel-metal hydride batteries (also called "nickel-metal hydride secondary batteries") are known as one type of battery, using nickel for the positive electrode and a hydrogen storage alloy for the negative electrode. For example, a battery element in which a positive electrode and a negative electrode are wound with a separator interposed between them so that the negative electrode is at the outermost periphery is housed in a cylindrical outer can, or a battery in which a hydrogen storage alloy with a larger average particle size is used in the outermost periphery of the negative electrode, which faces the positive electrode only on the inner surface, than in the remaining portion of the negative electrode (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-256522 Summary of the Invention [Problem to be solved by the invention]

[0004] In nickel-metal hydride batteries, oxygen gas generated at the positive electrode during overcharge can cause an increase in internal battery pressure. One method for suppressing this increase in internal battery pressure has been proposed. The battery element is made up of a positive electrode and a negative electrode wound around a separator, with the negative electrode positioned at the outermost periphery. The outermost periphery of the negative electrode, which faces the positive electrode where oxygen gas is generated on the inner side, is thickened on the inner side facing the positive electrode, while the outermost periphery is thinned on the outer side not facing the positive electrode. However, with previous technologies, it was sometimes difficult to form such a region partially at the outermost periphery of the negative electrode and sufficiently suppress the increase in internal battery pressure.

[0005] In one aspect, the present invention aims to provide a nickel-metal hydride battery that can suppress an increase in the internal pressure of the battery. [Means for solving the problem]

[0006] In one aspect, there is provided a nickel-metal hydride battery including: a cylindrical outer can; and a battery element housed in the outer can, wherein a positive electrode containing nickel and a negative electrode containing a hydrogen storage alloy are wound with a separator interposed between them so that the negative electrode is at the outermost periphery; the negative electrode includes a core having a first surface and a second surface opposite to the first surface, a first layer provided on the first surface side, and a second layer provided on the second surface side; in the first portion which is the outermost periphery, the first layer faces the outer can, and the second layer faces the positive electrode with the separator interposed between them; a first average particle diameter of the hydrogen storage alloy contained in the first portion of the negative electrode is smaller by 10 μm or more than a second average particle diameter of the hydrogen storage alloy contained in a second portion of the negative electrode other than the first portion; and a thickness of the first layer in the first portion is smaller than a thickness of the second layer in the first portion and is in the range of 1 to 3 times the first average particle diameter.

[0007] In another aspect, there is provided a method for producing the nickel-metal hydride battery described above. [Effects of the Invention]

[0008] In one aspect, it becomes possible to realize a nickel-metal hydride battery in which the increase in internal battery pressure is suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a nickel-metal hydride battery. [Figure 2] FIG. 2 is a diagram illustrating an example of a negative electrode used in a battery element of a nickel-metal hydride battery. [Figure 3] FIG. 1 is a diagram (part 1) illustrating an example of a method and apparatus used to form a negative electrode. [Figure 4] FIG. 2 is a diagram (part 2) illustrating an example of a method and apparatus used to form a negative electrode. DETAILED DESCRIPTION OF THE INVENTION

[0010] Figure 1 is a diagram illustrating an example of a nickel-metal hydride battery. Figure 1(A) shows a schematic cross-sectional view of a main part of an example of a nickel-metal hydride battery. Figure 1(B) shows a schematic cross-sectional view of the nickel-metal hydride battery taken along line II in Figure 1(A).

[0011] The nickel-metal hydride battery 1 shown in FIGS. 1(A) and 1(B) includes an outer can 10, a battery element 20, a positive electrode lead 30, an insulating plate 40, an insulating plate 50, an alkaline electrolyte 60, a sealing plate 70, and a gasket 80.

[0012] The outer can 10 is a cylindrical, conductive container with a bottom and one open end. The outer can 10 is made of a metal material such as stainless steel. The open end of the outer can 10 is subjected to drawing and crimping, and a conductive sealing plate 70 provided with a positive electrode terminal 71 is fixed via a gasket 80. The sealing plate 70 is made of a metal material such as stainless steel. The outer can 10 is sealed by the gasket 80 and the sealing plate 70.

[0013] The battery element 20 is an example of a power generating element housed in the exterior can 10. The battery element 20 includes a sheet-shaped positive electrode 21, a sheet-shaped negative electrode 22, and a sheet-shaped separator 23. The battery element 20 has a configuration in which the positive electrode 21 and the negative electrode 22 are spirally wound with the separator 23 interposed therebetween. In the nickel-metal hydride battery 1, the battery element 20 is wound so that the negative electrode 22 is located at the outermost periphery of the battery element 20.

[0014] Here, the positive electrode 21 contains nickel (Ni), for example, nickel hydroxide (Ni(OH)2). The negative electrode 22 contains a hydrogen storage alloy, for example, a hydrogen storage alloy containing lanthanum (La), samarium (Sm), magnesium (Mg), nickel (Ni), and aluminum (Al), for example, La 0.30 Sm 0.70 Mg 0.10 Ni 3.30 Al 0.20 The hydrogen storage alloy of the negative electrode 22 includes AB5 type, AB 3.5Type, AB 3.8 Various hydrogen storage alloys such as PET may be used. The separator 23 may be made of a microporous film, woven fabric, nonwoven fabric, or the like. For example, the separator 23 may be made of a polypropylene nonwoven fabric.

[0015] The battery element 20, in which the positive electrode 21, the negative electrode 22, and the separator 23 are wound, is housed in the outer can 10 together with an alkaline electrolyte 60. The alkaline electrolyte 60 may contain, for example, at least one of potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH).

[0016] Inside the exterior can 10, for example, an insulating plate 40 and an insulating plate 50 are provided on the bottom and the top of the battery element 20 housed therein, respectively. The positive electrode 21 of the battery element 20 housed in the outer can 10 is electrically connected to a positive electrode terminal 71 of a sealing plate 70 that is insulated from the outer can 10 via a gasket 80 and seals the open end of the outer can 10, via a conductive positive electrode lead 30 that penetrates the insulating plate 50. The negative electrode 22 of the battery element 20 housed in the outer can 10 is either in direct contact with the inner wall of the outer can 10 that is insulated from the sealing plate 70 that has the positive electrode terminal 71 via the gasket 80, or is connected to the inner wall of the outer can 10 using a conductive negative electrode lead or the like (not shown), and is thereby electrically connected to the outer can 10. The outer can 10 (for example, a part of its bottom surface) functions as a negative electrode terminal.

[0017] The nickel-metal hydride battery 1 having the above-described configuration is manufactured, for example, using the following method. A cylindrical can with a bottom is prepared as the outer can 10. For example, a can made of stainless steel or nickel-plated iron is prepared as the outer can 10.

[0018] Also prepared are a sheet-shaped positive electrode 21 containing nickel, a sheet-shaped negative electrode 22 containing a hydrogen storage alloy, and a sheet-shaped separator 23. The positive electrode 21 is prepared, for example, by filling a nickel foam with a positive electrode mixture paste (or positive electrode mixture slurry) containing nickel hydroxide, drying and rolling it, and cutting it to a predetermined size.

[0019] The negative electrode 22 is prepared, for example, by coating (applying) a negative electrode mixture paste (or a negative electrode mixture slurry) containing a hydrogen storage alloy on both sides of a sheet-shaped core, drying and rolling the coated sheet, and cutting it to a predetermined size. As an example, a punched metal sheet is used for the core of the negative electrode 22. The punched metal sheet may be an iron strip with numerous through holes and nickel-plated on its surface. In this case, the negative electrode mixture paste containing a hydrogen storage alloy is formed on both sides of the punched metal sheet and in the through holes.

[0020] The negative electrode mixture paste is applied to both sides of the core body using, for example, a so-called impregnation method, in which the core body is passed through a hopper storing the negative electrode mixture paste. After the negative electrode mixture paste is applied to the core body, it is passed through a slit blade with a specific opening size to adjust the thickness of the negative electrode mixture paste formed on both sides of the core body. Drying, rolling, and cutting are then performed to form a negative electrode 22, in which a negative electrode mixture layer formed from the negative electrode mixture paste is provided on each side of the core body. If the core body has through holes, a portion of the negative electrode mixture layer is also formed in the through holes.

[0021] As the separator 23, for example, a nonwoven fabric made of polypropylene fibers having sulfonic groups is prepared. The prepared sheet-like positive electrode 21, negative electrode 22, and separator 23 are used to fabricate the battery element 20. That is, the positive electrode 21 and the negative electrode 22 are spirally wound with the separator 23 interposed therebetween, with the negative electrode 22 positioned at the outermost periphery, to fabricate the cylindrical battery element 20.

[0022] The fabricated battery element 20 is inserted and housed in the outer can 10. Before the battery element 20 is housed, an insulating plate 40 is provided on the bottom of the outer can 10. After the battery element 20 is housed, an insulating plate 50 is provided on the top of the battery element 20 inside the outer can 10. The open end of the outer can 10 is drawn to form a drawn portion (beading portion).

[0023] A predetermined alkaline electrolyte 60 is then poured into the exterior can 10 housing the battery element 20. Thereafter, a sealing plate 70 connected to the positive electrode 21 of the battery element 20 by a positive electrode lead 30, i.e., a sealing plate 70 equipped with a positive electrode terminal 71, is placed on the drawn portion of the exterior can 10 formed by drawing, with a gasket 80 provided on its outer edge, and the open edge of the exterior can 10 is crimped. As a result, the sealing plate 70 is fixed to the exterior can 10 via the gasket 80, and a sealed structure is achieved by the exterior can 10, the gasket 80, and the sealing plate 70.

[0024] Using this method, the nickel-metal hydride battery 1 is manufactured. Here, the battery element 20 of the nickel-metal hydride battery 1 described above will be further explained. It is known that the nickel-metal hydride battery 1 can experience an increase in internal battery pressure due to oxygen gas generated at the positive electrode 21 of the battery element 20 during overcharge. One method for suppressing this increase in internal battery pressure is to thicken the negative electrode mixture layer on the inner surface facing the positive electrode 21 and to thin the negative electrode mixture layer on the outer surface not facing the positive electrode 21 in the outermost peripheral portion of the negative electrode 22 that faces the positive electrode 21 only on the inner surface side of the battery element 20 wound so that the negative electrode 22 is at the outermost periphery. This is for the following reason.

[0025] That is, oxygen gas is generated from the positive electrode 21 more actively on the outer surface side of the positive electrode 21. Therefore, the reduction reaction of oxygen gas in the negative electrode 22 is likely to occur more actively on the inner surface side of the negative electrode 22 that faces the outer surface side of the positive electrode. Therefore, in the portion of the negative electrode 22 that forms the outermost periphery of the battery element 20, it is considered that an increase in the internal pressure of the battery can be suppressed by arranging a thicker negative electrode mixture layer (more hydrogen storage alloy) on the inner surface side (inside relative to the core) that faces the positive electrode 21 rather than on the outer surface side (outside relative to the core) that does not face the positive electrode 21.

[0026] When forming the negative electrode 22 using the impregnation method, the thickness of the negative electrode mixture paste formed on both sides of the core is adjusted by applying a negative electrode mixture paste to the core to form a negative electrode mixture layer and then passing the applied paste through a slit blade with a specific opening size. Therefore, if the negative electrode mixture paste on the inner surface side of the outermost periphery of the negative electrode 22 is made thicker, the negative electrode mixture paste on the outer surface side of the outermost periphery will be relatively thinner. Therefore, when forming the negative electrode 22 using the impregnation method, it is considered preferable to thicken the negative electrode mixture layer on the inner surface (the negative electrode mixture paste for forming it) and relatively thin the negative electrode mixture layer on the outer surface (the negative electrode mixture paste for forming it) in this way in order to suppress an increase in the internal battery pressure of the nickel-metal hydride battery 1.

[0027] However, the thickness of the negative electrode mixture layer of the negative electrode 22 depends on the particle size of the hydrogen-absorbing alloy contained in the negative electrode mixture paste used to form the layer. Therefore, depending on the particle size of the hydrogen-absorbing alloy used, it may be difficult to form a thin negative electrode mixture layer on the outer surface of the outermost periphery of the negative electrode 22. For example, it is difficult to form a negative electrode mixture layer by applying a negative electrode mixture paste with a thickness smaller than the particle size of the hydrogen-absorbing alloy. Furthermore, if the negative electrode mixture paste contains a hydrogen-absorbing alloy with a particle size larger than the opening size of the slit blade through which the negative electrode mixture paste is passed after application to adjust the thickness, streaky scratches may be formed as the paste passes through.

[0028] In view of this, a nickel-metal hydride battery 1 capable of suppressing an increase in the battery internal pressure is realized by using a negative electrode 22 having the following exemplary configuration. Fig. 2 is a diagram illustrating an example of a negative electrode used in a battery element of a nickel-metal hydride battery, showing a schematic cross-sectional view of a main part of an example of the negative electrode.

[0029] The negative electrode 22 used in the battery element 20 of the nickel-metal hydride battery 1 includes, for example, a core 200, a first layer 210, and a second layer 220, as shown in Fig. 2. The core 200 is a punched metal sheet or the like. The first layer 210 is provided on a first surface 200a of the core 200, and the second layer 220 is provided on a second surface 200b of the core 200 opposite to the first surface 200a. The first layer 210 and the second layer 220 are negative electrode mixture layers formed from a negative electrode mixture paste containing a hydrogen storage alloy.

[0030] The negative electrode 22 has a first portion 230 and a second portion 240. The first portion 230 is the outermost portion of the battery element 20 in which the negative electrode 22 is wound together with the positive electrode 21 and the separator 23. The second portion 240 is the portion of the negative electrode 22 other than the first portion 230. The end 22b of the negative electrode 22 on the second portion 240 side is the winding start point when the negative electrode 22 is wound into the battery element 20, and the end 22a of the negative electrode 22 on the first portion 230 side is the winding end point when the negative electrode 22 is wound into the battery element 20.

[0031] When the negative electrode 22 is wound into the battery element 20, it is wound so that the first layer 210 faces the outer surface side (or the outer periphery side of the wound battery element 20) and the second layer 220 faces the inner surface side (or the center side of the wound battery element 20). Therefore, the first layer 210 of the first portion 230 that forms the outermost periphery of the battery element 20 faces the outer can 10 that houses the battery element 20. The second layer 220 of the first portion 230 that forms the outermost periphery of the battery element 20 faces the positive electrode 21 with the separator 23 interposed between them. The first layer 210 and the second layer 220 of the second portion 240 other than the first portion 230 that forms the outermost periphery of the battery element 20 both face the positive electrode 21 with the separator 23 interposed between them.

[0032] In the negative electrode 22, the first layer 210 and the second layer 220 of the first portion 230 contain a hydrogen storage alloy having a first average particle size. In the negative electrode 22, the first layer 210 and the second layer 220 of the second portion 240 contain a hydrogen storage alloy having a second average particle size different from the first average particle size. The first average particle size of the hydrogen storage alloy contained in the first layer 210 and the second layer 220 of the first portion 230 is smaller than the second average particle size of the hydrogen storage alloy contained in the first layer 210 and the second layer 220 of the second portion 240 by 10 μm or more.

[0033] Furthermore, in the negative electrode 22, the thickness T1 of the first layer 210 in the first portion 230 (or the height T1 from the first surface 200a of the core 200) is smaller than the thickness T2 of the second layer 220 in the first portion 230 (or the height T2 from the second surface 200b of the core 200). The thickness T1 of the first layer 210 in the first portion 230 is set to be in the range of 1 to 3 times the first average particle size of the hydrogen storage alloy contained in the first layer 210. Furthermore, in the negative electrode 22, the thickness T1 of the first layer 210 in the first portion 230 is smaller than the thickness T3 of the first layer 210 in the second portion 240 (or the height T3 from the first surface 200a of the core 200).

[0034] The negative electrode 22 having the above-described configuration is used in the battery element 20 of the nickel-metal hydride battery 1. In the negative electrode 22, a hydrogen storage alloy having a relatively small first average particle diameter is used in the first portion 230, which forms the outermost periphery of the battery element 20. This allows the thickness T1 of the first layer 210 of the first portion 230 of the battery element 20, which does not face the positive electrode 21, to be relatively thin. When the negative electrode 22 is formed by an impregnation method, the thickness T1 of the first layer 210 in the first portion 230 can be made relatively thin, and the thickness T2 of the second layer 220 in the first portion 230 can be made relatively thick. Furthermore, when the negative electrode 22 is formed by an impregnation method, the use of a hydrogen storage alloy having a relatively small first average particle diameter prevents the formation of streaky scratches when the negative electrode 22 is passed through a slit blade with a certain opening dimension to adjust the thickness after application of the negative electrode mixture paste.

[0035] In the negative electrode 22, the second layer 220 of the first portion 230, which forms the outermost periphery of the battery element 20 and faces the positive electrode 21, can be made of a hydrogen storage alloy with a relatively small first average particle diameter, resulting in a relatively large thickness T2. Furthermore, the first layer 210 and the second layer 220 of the second portion 240, which faces the positive electrode 21, can both be made of a hydrogen storage alloy with a relatively large second average particle diameter, resulting in relatively large thicknesses T2 and T3. Therefore, oxygen gas generated at the positive electrode 21 of the battery element 20 during overcharge can be effectively reduced by the second layer 220 of the first portion 230 and the first layer 210 and the second layer 220 of the second portion 240. This effectively suppresses an increase in the internal battery pressure of the nickel-metal hydride battery 1.

[0036] If the first average particle size of the hydrogen storage alloy in the first portion 230 is less than 10 μm, the coating mass may vary, and if it exceeds 55 μm, it may be difficult to form a sufficiently thin first layer 210. Therefore, the first average particle size of the hydrogen storage alloy in the first portion 230 is preferably set to 10 μm or more and 55 μm or less, and more preferably set to 10 μm or more and 35 μm or less in order to form a sufficiently thin first layer 210 in the first portion 230.

[0037] Furthermore, if the second average particle diameter of the hydrogen storage alloy in the second portion 240 is less than 65 μm, the battery life may be shortened, and if it exceeds 100 μm, the particles may penetrate the separator 23 and come into contact with the positive electrode 21, which may easily cause a short circuit. Therefore, the second average particle diameter of the hydrogen storage alloy in the second portion 240 is preferably set to be 65 μm or more and 100 μm or less.

[0038] However, the first average particle size and the second average particle size of the hydrogen storage alloy are not limited to the above-mentioned exemplary ranges, and can be set appropriately based on the shape, specifications, required characteristics, etc. of the battery element 20 and the nickel-metal hydride battery 1 in which the negative electrode 22 is used.

[0039] Next, the formation of the negative electrode 22 as described above will be described. 3 and 4 are diagrams illustrating an example of a method and apparatus used to form a negative electrode. An apparatus 300 as shown in FIG. 3 is used to form the negative electrode 22. The apparatus 300 includes a turn roll 310, a hopper 320, and a slit blade 330. In the apparatus 300, the core 200 used to form the negative electrode 22 is changed in direction by the rotating turn roll 310 and sent to a hopper 320 that stores a negative electrode mixture paste. The core 200 is then passed through the hopper 320, where the negative electrode mixture paste is applied. In the apparatus 300, the core 200 that has been coated with the negative electrode mixture paste is then passed between a first blade portion 331 and a second blade portion 332 of a slit blade 330, whereby the thickness of the negative electrode mixture paste is adjusted.

[0040] 3 shows, as an example, a core 200 such as a punched metal sheet having a region 201 in which a large number of through-holes are formed. In addition, in FIG. 3, the core 200 and a region 202 of the core 200 after coating, surrounded by a dashed line, correspond to the region that will be dried, rolled, and cut after coating to finally become a single sheet-like negative electrode 22.

[0041] The hopper 320 has a first compartment 321 and a second compartment 322 separated by a hopper partition 320a. A first paste 321a, which is a negative electrode mixture paste containing a hydrogen storage alloy with a first average particle size, is stored in the first compartment 321. A second paste 322a, which is a negative electrode mixture paste containing a hydrogen storage alloy with a second average particle size larger than the first average particle size, is stored in the second compartment 322. In this manner, the hopper 320 is prepared in advance, with the first paste 321a and the second paste 322a stored in the first compartment 321 and the second compartment 322, respectively, and the core 200 is passed through the hopper 320.

[0042] When the core body 200 passes through the hopper 320, the core body 200 is passed so that the first portion 230 (FIGS. 2 and 3) that forms the outermost periphery of the battery element 20 passes through the first compartment 321, and the second portion 240 (FIGS. 2 and 3) other than the first portion 230 passes through the second compartment 322. This allows the first paste 321a to be applied to the first portion 230 and the second paste 322a to be applied to the second portion 240 simultaneously.

[0043] The core body 200, which has passed through the first section 321 and the second section 322 of the hopper 320 and has been coated with the first paste 321a and the second paste 322a, is passed between the first blade portion 331 and the second blade portion 332 of the slit blade 330, and the thickness of the coated first paste 321a and the second paste 322a is adjusted.

[0044] FIG. 4 is a schematic plan view of a slit blade 330 through which the core 200 of the negative electrode 22 passes after coating, as viewed from the direction in which the core 200 passes. The slit blade 330 has, for example, a first blade portion 331 and a second blade portion 332 as shown in FIG. 4. The first blade portion 331 has an edge 331a that faces the core 200 passing through in a plan view, and a recess 331b that is recessed more than the end portions is provided in the center of the edge 331a. The width of the recess 331b is adjusted to the width of a second compartment 322 provided in the hopper 320 of the device 300 (FIG. 3) in which the second paste 322a is stored. The second blade portion 332 has a linear edge 332a that faces the core 200 passing through in a plan view.

[0045] In the device 300 (FIG. 3), the first blade portion 331 and the second blade portion 332 are arranged so that the edge 331a, where the recess 331b of the first blade portion 331 is provided, and the linear edge 332a of the second blade portion 332 are opposed to each other at a distance to provide a constant opening dimension, thereby forming a slit blade 330. The distance between the portion of the edge 331a of the first blade portion 331 outside the recess 331b and the opposing portion of the edge 332a of the second blade portion 332 is smaller than the distance between the recess 331b of the edge 331a of the first blade portion 331 and the opposing portion of the edge 332a of the second blade portion 332.

[0046] The core body 200, to which the first paste 321a and the second paste 322a have been simultaneously applied in the hopper 320 (FIG. 3), passes between the first blade portion 331 and the second blade portion 332 of the slit blade 330. When passing through, the position of the core body 200 relative to the edge 331a of the first blade portion 331 and the edge 332a of the second blade portion 332 is adjusted.

[0047] The portion of the core 200 (first portion 230) that passes through the first section 321 of the hopper 320, in which the first paste 321a is stored, passes between the portion outside the recess 331b of the edge 331a of the first blade portion 331 and the opposing portion of the edge 332a of the second blade portion 332, i.e., a portion where the distance between them is relatively small. The portion of the core 200 (second portion 240) that passes through the second section 322 of the hopper 320, in which the second paste 322a is stored, passes between the recess 331b of the edge 331a of the first blade portion 331 and the opposing portion of the edge 332a of the second blade portion 332, i.e., a portion where the distance between them is relatively large.

[0048] This adjusts the thickness T1a of the first paste 321a applied to the first surface 200a of the first portion 230 of the core body 200, which forms the outermost periphery of the battery element 20, and the thickness T2a of the first paste 321a applied to the second surface 200b of the first portion 230. At the same time, it adjusts the thickness T3a of the second paste 322a applied to the first surface 200a of the second portion 240 other than the first portion 230 of the core body 200, and the thickness T2a of the second paste 322a applied to the second surface 200b of the second portion 240. The thickness T3a of the second paste 322a applied to the first surface 200a of the second portion 240 is adjusted not only by the position of the core body 200, but also by the depth from the edge 331a of the recess 331b in the first blade portion 331.

[0049] As the core 200 passes over the first blade portion 331 and the second blade portion 332 of the slit blade 330, a first paste 321a containing a hydrogen storage alloy with a relatively small first average particle size is formed relatively thinly on the first surface 200a side and relatively thickly on the second surface 200b side in the first portion 230. Furthermore, since the recess 331b is provided in the edge 331a of the first blade portion 331, a configuration is obtained in which the first paste 321a formed on the first surface 200a side of the first portion 230 of the core 200 is thinner than the second paste 322a formed on the first surface 200a side of the second portion 240 containing a hydrogen storage alloy with a relatively large second average particle size.

[0050] 3 and 4, the core 200, in which the first portion 230 and the second portion 240 are coated with the first paste 321a and the second paste 322a, respectively, is dried, rolled, and cut to form the sheet-like negative electrode 22 (portion 202 formed in region 201) as shown in FIG. 2. That is, the first layer 210 (negative electrode mixture layer) of the negative electrode 22 shown in FIG. 2 is formed from the first paste 321a and the second paste 322a (negative electrode mixture paste) coated on the first surface 200a side of the core 200. The second layer 220 (negative electrode mixture layer) of the negative electrode 22 shown in FIG. 2 is formed from the first paste 321a and the second paste 322a (negative electrode mixture paste) coated on the second surface 200b side of the core 200. Furthermore, the relationship in thickness between the first paste 321a and the second paste 322a (negative electrode mixture paste) applied to the first surface 200a side and the second surface 200b side of the core body 200 is also maintained in the relationship in thickness between the first layer 210 and the second layer 220 (negative electrode mixture layer) formed by drying and rolling after application.

[0051] Examples and comparative examples will be described below. Example 1 (Preparation of positive electrode) Nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt was added to an aqueous cobalt sulfate solution. Next, a 1 mol / L aqueous sodium hydroxide solution was slowly added dropwise to the cobalt sulfate solution while stirring to cause a reaction, and a precipitate was formed while maintaining the pH at 11 during the reaction. Next, the formed precipitate was filtered out, washed with water, and then vacuum dried to obtain a nickel hydroxide powder in which the surfaces of the nickel hydroxide particles were coated with 5% by mass of cobalt hydroxide.

[0052] The obtained nickel hydroxide powder coated with cobalt hydroxide was then added to a 25% by mass aqueous solution of sodium hydroxide, with the mass of the nickel hydroxide powder coated with cobalt hydroxide being P and the mass of the aqueous sodium hydroxide solution being Q, such that the mass ratio of P:Q was 1:10. The aqueous sodium hydroxide solution to which the nickel hydroxide powder had been added was then heated at a temperature of 85°C while being stirred for 8 hours.

[0053] Thereafter, the nickel hydroxide powder that had undergone the heat treatment was washed with water and dried at 65° C. to obtain a nickel positive electrode active material powder in which the surfaces of the nickel hydroxide particles were coated with a high-order cobalt oxide. To 100 parts by mass of the obtained nickel positive electrode active material powder, 0.5 parts by mass of yttrium oxide powder, 0.3 parts by mass of niobium oxide powder, 1.0 part by mass of zinc oxide powder, and 50 parts by mass of an aqueous solution containing 0.2% by mass of hydroxypropyl cellulose powder as a binder were added and kneaded to prepare a positive electrode mixture paste.

[0054] Next, the positive electrode mixture paste is applied to a surface density (weight) of approximately 420 g / m 2 The mixture was filled into a nickel foam with a porosity of 95% and a thickness of approximately 1.35 mm, dried, and the mass of the positive electrode mixture [g] ÷ (electrode height [cm] × electrode length [cm] × electrode thickness [cm] - mass of the nickel foam [g] ÷ specific gravity of nickel [g / cm 3 ]) the packing density of the positive electrode active material is 3.2 g / cm 3After adjusting and rolling the mixture so that the thickness was as above, the mixture was cut to a predetermined size to obtain a positive electrode made of a non-sintered nickel electrode.

[0055] (Preparation of negative electrode) The metal materials La, Sm, Mg, Ni, and Al were mixed to a predetermined molar ratio, and then the mixture was charged into an induction melting furnace and melted, followed by cooling to produce an ingot.

[0056] The resulting ingot was then heat-treated at 1000°C for 10 hours in an argon (Ar) gas atmosphere to homogenize it, and then mechanically pulverized in an argon gas atmosphere to obtain rare earth-Mg-Ni based hydrogen storage alloy powder. The particle size distribution of the obtained rare earth-Mg-Ni based hydrogen storage alloy powder was measured using a laser diffraction / scattering particle size distribution analyzer. In Example 1, two types of hydrogen storage alloy powder were obtained, with average particle sizes of 65 μm and 35 μm, which correspond to 50% of the mass-based cumulative particle size. The composition of this hydrogen storage alloy powder was analyzed by high-frequency plasma spectroscopy, and it was found that the composition consisted of La 0.30 Sm 0.70 Mg 0.10 Ni 3.30 Al 0.20 Furthermore, when the hydrogen storage alloy powder was subjected to X-ray diffraction measurement, the crystal structure was found to be of Ce2Ni7 type.

[0057] 10 parts by mass of water, 0.5 parts by mass of Ketjen Black powder, 0.3 parts by mass of sodium polyacrylate powder, and 0.05 parts by mass of carboxymethyl cellulose powder were mixed to form a paste, and yttrium fluoride was supported on the Ketjen Black. Next, 100 parts by mass of hydrogen storage alloy powder with an average particle size of 65 μm was added to this paste to coat the surface of the hydrogen storage alloy. Furthermore, 0.5 parts by mass of styrene butadiene rubber powder and 15 parts by mass of water were added and kneaded in an environment of 25 ° C. to prepare "negative electrode mixture paste A". Similarly, "negative electrode mixture paste B" was prepared using hydrogen storage alloy powder with an average particle size of 35 μm.

[0058] The prepared negative electrode mixture paste A was evenly applied to both sides of a punched metal sheet made of iron serving as a core (core 200), excluding the outermost periphery of the battery element (first portion 230) (second portion 240), and the outermost periphery (first portion 230) was coated with negative electrode mixture paste B so that the outermost surface side not facing the positive electrode was coated thinner. Note that the negative electrode mixture pastes A and B were also filled into the through-holes of the punched metal sheet.

[0059] The negative electrode mixture pastes A and B were applied using the above-mentioned device 300 (Figures 3 and 4), with the second paste 322a in the second section 322 being negative electrode mixture paste A and the first paste 321a in the first section 321 being negative electrode mixture paste B, and a core was passed through these pastes, and the core was then passed through a slit blade 330.

[0060] In Example 1, the coating thickness of the outermost periphery of the battery element was 0.252 mm on the inner surface side facing the positive electrode (referred to as the "thick-coated side") and 0.063 mm on the outer surface side not facing the positive electrode (referred to as the "thin-coated side"), and the thickness ratio of the front and back (referred to as the "front and back thickness ratio") calculated by dividing the thickness [mm] of the thin-coated side by the thickness [mm] of the thick-coated side was 25%.

[0061] After drying the coated negative electrode mixture pastes A and B, they were rolled and cut to the specified dimensions to obtain negative electrodes. The mass of the hydrogen storage alloy [g] ÷ (electrode height [cm] × electrode length [cm] × electrode thickness [cm] - mass of the punched metal sheet [g] ÷ specific gravity of iron [g / cm 3 The packing density of the hydrogen storage alloy calculated by the formula (1) is 6.0 g / cm at the open pores. 3 It was.

[0062] (Manufacture of nickel-metal hydride batteries) The positive electrode and negative electrode obtained as described above were spirally wound with a separator sandwiched between them to prepare a battery element. The battery element was wound so that the negative electrode was positioned at the outermost periphery of the battery element. The separator was a nonwoven fabric made of polypropylene fibers having sulfonic groups, with a thickness of 0.1 mm (basis weight 40 g / m 2 ) was used.

[0063] The fabricated battery element was placed in a cylindrical outer can with a bottom, and 2.2 g of alkaline electrolyte was poured in. The mass ratio of potassium hydroxide:sodium hydroxide:lithium hydroxide was 6:0.5:1, and the specific gravity was 1.28. The outer can was then sealed with the required electrical connections and a sealing plate, resulting in the fabrication of an AA-size sealed nickel-metal hydride battery with a rated capacity of 2000 mAh.

[0064] <Example 2> The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 25 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Example 2, the coating thickness of the outermost periphery of the battery element was 0.274 mm on the thick-coated side and 0.041 mm on the thin-coated side, with a front-to-back thickness ratio of 15%.

[0065] Example 3 The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 15 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Example 3, the coating thickness of the outermost periphery of the battery element was 0.290 mm on the thick-coated side and 0.025 mm on the thin-coated side, with a front-to-back thickness ratio of 9%.

[0066] Example 4 The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 55 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Example 4, the coating thickness of the outermost periphery of the battery element was 0.216 mm on the thick-coated side and 0.099 mm on the thin-coated side, with a front-to-back thickness ratio of 46%.

[0067] <Example 5> The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 45 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Example 5, the coating thickness of the outermost periphery of the battery element was 0.235 mm on the thick-coated side and 0.080 mm on the thin-coated side, with a front-to-back thickness ratio of 34%.

[0068] <Comparative Example 1> The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 65 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Comparative Example 1, the coating thickness of the outermost periphery of the battery element was 0.197 mm on the thick-coated side and 0.118 mm on the thin-coated side, with a front-to-back thickness ratio of 60%.

[0069] <Comparative Example 2> The average particle size of the hydrogen storage alloy in negative electrode mixture paste B was set to 35 μm, and a nickel-metal hydride battery was fabricated in the same manner as in Example 1. In Comparative Example 2, the coating thickness of the outermost periphery of the battery element was 0.175 mm on the thick-coated side and 0.140 mm on the thin-coated side, with a front-to-back thickness ratio of 80%.

[0070] <Evaluation> (Initial activation process) For each of the nickel-metal hydride batteries of Examples 1-5 and Comparative Examples 1-2, an initial activation treatment was performed by repeating five charge-discharge cycles, each cycle consisting of charging for 16 hours at a charging current of 0.4 A (0.1 C) and discharging until the battery voltage reached 1.0 V at a discharging current of 0.8 A (0.2 C).

[0071] (battery internal pressure measurement) For each of the nickel-metal hydride batteries of Examples 1-5 and Comparative Examples 1-2, a pressure sensor was attached to the bottom of the outer can, and the batteries were charged at an ambient temperature of 25° C. with a charging current of 1.5 A for 90 minutes, and the internal pressure of each battery was measured.

[0072] The average particle size of the hydrogen storage alloy used in the outermost part of the battery element for each of Examples 1-5 and Comparative Examples 1-2, the coating thickness and front / back thickness ratio of the thick-coated and thin-coated sides of that part, and the measured internal battery pressure are shown in Table 1 below.

[0073] [Table 1]

[0074] In the nickel-metal hydride batteries of Examples 1-5 and Comparative Examples 1-2, the sum of the thicknesses of the thick-coated and thin-coated sides of the outermost periphery of the battery element was constant (0.315 mm), and the thin-coated side was thinner, making the thick-coated side relatively thicker. The smaller the average particle size of the hydrogen storage alloy used in the outermost periphery, the thinner the thin-coated side could be made.

[0075] As in Examples 1-5, when the average particle size (15 μm-55 μm) of the hydrogen storage alloy used in the outermost portion of the battery element is 10 μm or more smaller than the average particle size of 65 μm of the hydrogen storage alloy used in other portions or the average particle size of 65 μm of the hydrogen storage alloy in Comparative Example 1, the increase in internal battery pressure of the nickel-metal hydride battery is suppressed. The increase in internal battery pressure is suppressed more as the average particle size of the hydrogen storage alloy becomes smaller and the thinner coated side becomes thinner, or as the thick coated side becomes relatively thicker and the front / back thickness ratio becomes lower.

[0076] On the other hand, even when the average particle size (35 μm) of the hydrogen storage alloy used in the outermost part of the battery element is relatively small, as in Comparative Example 2, if the thin-coated side becomes thicker to a thickness of about four times the average particle size and the front / back thickness ratio becomes high, it becomes difficult to suppress the increase in the internal pressure of the battery.

[0077] For these reasons, in a nickel-metal hydride battery, it is preferable that the outermost periphery of the battery element use a hydrogen storage alloy whose average particle size is at least 10 μm smaller than that of the remaining portions. Furthermore, it is preferable that the thickness of the thin-coated side of the outermost periphery of the battery element, which is thinner than the thick-coated side, be in the range of 1 to 3 times the average particle size of the hydrogen storage alloy used in the outermost periphery.

[0078] During overcharge, oxygen gas is generated from the positive electrode of the battery element more actively on the outer surface of the positive electrode. Therefore, the reduction reaction of oxygen gas at the negative electrode tends to occur more actively on the inner surface of the negative electrode facing the outer surface of the positive electrode. Therefore, by designating the outer surface of the negative electrode, which does not face the positive electrode, as the thin-coated side and the inner surface facing the positive electrode as the thick-coated side, i.e., by placing more negative electrode mixture on the inner surface, it is believed that the increase in internal battery pressure can be effectively suppressed. [Explanation of symbols]

[0079] 1 Nickel-metal hydride battery 10 outer can 20 Battery elements 21 Positive electrode 22 Negative electrode 22a, 22b ends 23 Separator 30 Positive lead 40, 50 Insulating plate 60 Alkaline electrolyte 70 Sealing plate 71 Positive terminal 80 gaskets 200 Core 200a 1st page 200b 2nd page 201 areas 202 parts 210 1st layer 220 2nd layer 230 Part 1 240 Part 2 300 equipment 310 Turn Roll 320 Hopper 321 Section 1 321a First Paste 322 Section 2 322a Second Paste 330 Slitting blade 331 1st blade part 331a, 332a Edge 331b Recess 332 2nd blade part T1, T1a, T2, T2a, T3, T3a thickness

Claims

1. A cylindrical outer can; a battery element housed in the outer can, the battery element being formed by winding a positive electrode containing nickel and a negative electrode containing a hydrogen storage alloy with a separator interposed therebetween so that the negative electrode is positioned at the outermost periphery; Including, the negative electrode includes a core having a first surface and a second surface opposite to the first surface, a first layer provided on the first surface side, and a second layer provided on the second surface side, wherein, in the first portion that forms the outermost periphery, the first layer faces the outer can, and the second layer faces the positive electrode via the separator, a first average particle diameter of the hydrogen storage alloy contained in the first portion of the negative electrode is smaller by 10 μm or more than a second average particle diameter of the hydrogen storage alloy contained in a second portion other than the first portion of the negative electrode; A nickel-metal hydride battery, wherein the thickness of the first layer in the first portion is smaller than the thickness of the second layer in the first portion and is in the range of 1 to 3 times the first average particle size.

2. 2. The nickel-metal hydride battery according to claim 1, wherein the thickness of the first layer in the first portion is smaller than the thickness of the first layer in the second portion.

3. providing a positive electrode comprising nickel; providing a negative electrode including a hydrogen storage alloy; providing a separator; forming a battery element in which the positive electrode and the negative electrode are wound with the separator interposed therebetween so that the negative electrode is at the outermost periphery; a step of housing the battery element in a cylindrical outer can; Including, The step of preparing the negative electrode includes: providing a core body; preparing a hopper having a first compartment in which a first paste containing the hydrogen storage alloy having a first average particle size is stored, and a second compartment in which a second paste containing the hydrogen storage alloy having a second average particle size larger than the first average particle size is stored; passing the core body through the hopper so that a first portion of the core body, which is the outermost periphery of the core body, passes through the first compartment and a second portion of the core body other than the first portion passes through the second compartment, thereby simultaneously coating the first paste onto the first portion and the second paste onto the second portion; A method for manufacturing a nickel-metal hydride battery, comprising:

4. the core body has a first surface and a second surface opposite to the first surface, the negative electrode includes a first layer provided on the first surface side and a second layer provided on the second surface side, and in the first portion which becomes the outermost periphery, the first layer faces the outer can and the second layer faces the positive electrode via the separator, The step of preparing the negative electrode includes: a step of simultaneously applying the first paste and the second paste, the first average particle size of which is smaller than the second average particle size by 10 μm or more; a step of passing the core body after the first paste and the second paste are applied through a slit blade to make the thickness of the first layer in the first portion smaller than the thickness of the second layer in the first portion and within a range of 1 to 3 times the first average particle diameter; The method for producing the nickel-metal hydride battery according to claim 3 , comprising:

5. The step of preparing the negative electrode includes:

5. The method for manufacturing a nickel-metal hydride battery according to claim 4, further comprising a step of passing the core body after the first paste and the second paste are applied through the slit blade, thereby making the thickness of the first layer in the first portion smaller than the thickness of the first layer in the second portion.

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