Cylindrical alkaline storage battery

Abstract

This alkaline storage battery comprises: a spiral electrode group (22) in which a positive electrode plate (24), a negative electrode plate (26), and a separator (28) are superimposed; an exterior can (10) in which the spiral electrode group is accommodated together with an alkaline electrolytic liquid; and a positive electrode terminal (20) electrically connected to the positive electrode plate. The negative electrode plate includes an outermost peripheral negative electrode plate part (26e) electrically connected with an inner peripheral wall (10a) of the exterior can, an innermost peripheral negative electrode plate part (26f) facing the positive electrode plate only on the outer-peripheral side, and a body negative electrode plate part (26g) that connects the outermost peripheral negative electrode plate part and the innermost peripheral negative electrode plate part. The negative electrode plate includes a negative electrode core (26a), and a negative electrode mixture layer (26b) supported on the negative electrode core. The negative electrode plate is configured such that the porosity of a first negative electrode mixture layer portion (26h) of the negative electrode mixture layer, said portion being positioned at the innermost peripheral negative electrode plate part, is greater than the porosity of a second negative electrode mixture layer portion (26i) of the negative electrode mixture layer, said portion being positioned at the outermost peripheral negative electrode plate part and the body negative electrode plate part.

Description

[Technical Field]

[0001] The present invention relates to a cylindrical alkaline storage battery. [Background technology]

[0002] An alkaline storage battery includes an electrode group formed by stacking positive and negative electrode plates and a separator. In the electrode group, the separator is disposed between the positive and negative electrode plates. In the alkaline storage battery, the electrode group is, for example, spirally wound and housed in a conductive cylindrical outer can together with an alkaline electrolyte. In the alkaline storage battery, a predetermined electrochemical reaction occurs between the positive and negative electrode plates, which face each other via the separator, thereby causing charging and discharging.

[0003] For example, Patent Document 1 describes a cylindrical battery in which a spiral electrode group, in which a positive electrode plate and a negative electrode plate are spirally wound with a separator interposed therebetween, is housed in a cylindrical battery case. The cylindrical battery described in Patent Document 1 is configured so that the packing density of the negative electrode active material in the outermost periphery is smaller than the packing density of the negative electrode active material in the main body, in order to prevent the substrate from breaking at the end of the winding. This makes it easier to deform the outermost periphery and reduces the stress applied to the substrate, thereby preventing breakage due to deformation of the substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-175370 Summary of the Invention [Problem to be solved by the invention]

[0005] Recently, there has been an increasing demand for higher capacity alkaline storage batteries. To achieve this, the opposing area between the positive and negative electrodes may be increased by, for example, increasing the number of turns of the spiral electrode assembly. However, increasing the number of turns of the spiral electrode assembly results in a larger curvature at the innermost periphery of the electrode assembly, which can lead to cracks occurring in the negative electrode plate at the innermost periphery. If a crack occurs in the negative electrode plate and a portion of the negative electrode plate breaks through the separator, a short circuit may occur, resulting in direct contact between the negative and positive electrodes.

[0006] Furthermore, as alkaline storage batteries become more powerful, the amount of material (such as separators) in the battery increases. Therefore, if the battery is heated by an external factor (for example, if it is thrown into a fire or left on a heater), the separators may melt inside the battery case and clog the battery's exhaust valve. If the exhaust valve becomes clogged, the internal pressure of the battery cannot be released, reducing the safety of the battery.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide an alkaline storage battery that achieves high capacity while simultaneously improving short-circuit quality and safety. [Means for solving the problem]

[0008] In order to achieve the above object, the alkaline storage battery according to the present invention comprises a spiral electrode group formed by overlapping a strip-shaped positive electrode plate, a strip-shaped negative electrode plate, and a strip-shaped separator disposed between the positive electrode plate and the negative electrode plate, the spiral electrode group being formed in a spiral shape; a conductive cylindrical outer can in which the spiral electrode group is housed together with an alkaline electrolyte; and a positive electrode terminal electrically connected to the positive electrode plate, the negative electrode plate having an outermost negative electrode plate portion located at the outermost periphery of the spiral electrode group and electrically connected to an inner peripheral wall of the outer can; the negative electrode plate is configured to include an innermost negative electrode plate portion facing the positive electrode plate only at the outermost negative electrode plate portion, and a main negative electrode plate portion connecting the outermost negative electrode plate portion and the innermost negative electrode plate portion, the negative electrode plate being configured to include a metallic negative electrode core and a negative electrode mixture layer having a negative electrode active material supported on the negative electrode core throughout, and the negative electrode plate is configured such that the porosity of a first negative electrode mixture layer portion located in the innermost negative electrode plate portion is greater than the porosity of a second negative electrode mixture layer portion located in the outermost negative electrode plate portion and the main negative electrode plate portion.

[0009] In an alkaline storage battery according to one embodiment of the present invention, the negative electrode plate is configured in an annealed state so that a first negative electrode core portion located in the innermost negative electrode plate portion of the negative electrode core has a bending rigidity smaller than that of a second negative electrode core portion located in the outermost negative electrode plate portion and the main body negative electrode plate portion. [Effects of the Invention]

[0010] In the alkaline storage battery according to the present invention, the negative electrode plate is configured such that the porosity of the first negative electrode mixture layer portion located in the innermost negative electrode plate portion is greater than the porosity of the second negative electrode mixture layer portion located in the outermost negative electrode plate portion and the main negative electrode plate portion. Therefore, even if the number of windings of the spiral electrode group is increased to achieve a high capacity alkaline storage battery and the curvature of the innermost negative electrode plate portion is increased, the flexibility of the first negative electrode mixture layer portion is enhanced, thereby preventing cracks from occurring in the innermost negative electrode plate portion. This prevents short circuits that occur with high battery capacity. Furthermore, even if the battery is heated by an external factor (e.g., if it is thrown into a fire or left on a heater), the molten separator can be reliably permeated into the voids in the first negative electrode mixture layer portion. This prevents the molten separator from clogging the battery's exhaust valve and reduces the internal pressure of the outer can, thereby ensuring the safety of the battery. Therefore, it is possible to provide an alkaline storage battery that achieves high capacity while simultaneously improving short-circuit quality and safety. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a partially cutaway perspective view of an alkaline storage battery according to one embodiment. [Figure 2] 2 is a cross-sectional view showing a state in which the spiral electrode group of the alkaline storage battery of FIG. 1 is inserted into an outer can. [Figure 3] 2 is a side view showing an expanded negative electrode plate in the alkaline storage battery of FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of a nickel-metal hydride secondary battery 2 (hereinafter simply referred to as "battery 2") will be described as an example of an alkaline storage battery according to one embodiment. Note that in this embodiment, an AA-sized cylindrical battery 2 will be described, but the size of the battery 2 is not limited to this and may be other sizes such as AAA. Furthermore, the alkaline storage battery may be any battery that uses an alkaline solution as the electrolyte, and may be, for example, a nickel-cadmium storage battery.

[0013] FIG. 1 is a partially cutaway perspective view of a nickel-metal hydride secondary battery 2 (alkaline storage battery) according to one embodiment. FIG. 2 is a cross-sectional view showing a spiral electrode group 22 of the nickel-metal hydride secondary battery 2 of FIG. 1 inserted into an outer can 10. FIG. 3 is a side view showing an expanded negative electrode plate 26 of the nickel-metal hydride secondary battery 2 of FIG. 1. For ease of explanation, the direction of arrow a is defined as the upper side, and the direction of arrow b is defined as the lower side, with respect to the axis x of the cylindrical outer can 10. Here, the upper side refers to the side of the battery 2 where the positive electrode terminal 20 is provided, and the lower side refers to the side of the battery 2 where the bottom wall 35 is provided, i.e., the side opposite the upper side. Furthermore, in a direction perpendicular to the axis x (hereinafter also referred to as the "radial direction"), the direction away from the axis x is defined as the outer circumferential side (the direction of arrow c), and the direction toward the axis x is defined as the inner circumferential side (the direction of arrow d).

[0014] As shown in FIG. 1 , the battery 2 includes a cylindrical outer can 10 with a bottom and an open top (in the direction of arrow a). The outer can 10 is electrically conductive, and a bottom wall 35 on the bottom (in the direction of arrow b) functions as a negative electrode terminal. A sealing body 11 is fixed to the opening of the outer can 10. This sealing body 11 includes a lid plate 14 and a positive electrode terminal 20 and seals the outer can 10. The lid plate 14 is a conductive, disc-shaped member. The lid plate 14 and a ring-shaped insulating gasket 12 surrounding the lid plate 14 are disposed within the opening of the outer can 10, and the insulating gasket 12 is fixed to the opening edge 37 of the outer can 10 by crimping the opening edge 37 of the outer can 10. In other words, the lid plate 14 and the insulating gasket 12 cooperate to hermetically close the opening of the outer can 10.

[0015] The cover plate 14 has a central through-hole 16 in the center, and a rubber valve body 18 that closes the central through-hole 16 is disposed on the outer surface, which is the upper surface, of the cover plate 14. Furthermore, a metallic positive electrode terminal 20 that is cylindrical with a flange is electrically connected to the outer surface of the cover plate 14 so as to cover the valve body 18. This positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. The positive electrode terminal 20 has a gas vent hole (not shown) opened therein.

[0016] Normally, the central through-hole 16 is airtightly closed by the valve body 18. On the other hand, if gas is generated inside the outer can 10 and the pressure of the gas increases, the valve body 18 is compressed by the gas pressure and opens the central through-hole 16, resulting in the gas being released from inside the outer can 10 to the outside through the central through-hole 16 and a gas vent hole (not shown) in the positive terminal 20. In other words, the central through-hole 16, the valve body 18, and the positive terminal 20 form a safety valve for the battery 2.

[0017] As shown in Fig. 1, the exterior can 10 accommodates a spiral electrode group 22. The spiral electrode group 22 is formed by stacking strip-shaped positive electrode plates 24, negative electrode plates 26, and separators 28 one on top of the other. The spiral electrode group 22 is formed in a spiral shape with the separators 28 sandwiched between the positive electrode plates 24 and the negative electrode plates 26. That is, the positive electrode plates 24 and the negative electrode plates 26 are stacked one on top of the other with the separators 28 interposed therebetween.

[0018] A positive electrode lead 30 is disposed within the exterior can 10 between the upper end of the spiral electrode group 22 and the cover plate 14. More specifically, one end of the positive electrode lead 30 is connected to the positive electrode plate 24, and the other end is connected to the cover plate 14. Therefore, the positive electrode terminal 20 and the positive electrode plate 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. A circular upper insulating member 32 is disposed between the cover plate 14 and the spiral electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the upper insulating member 32. A circular lower insulating member 34 is also disposed between the spiral electrode group 22 and the bottom wall 35 of the exterior can 10.

[0019] Furthermore, a predetermined amount of alkaline electrolyte (not shown) is poured into the exterior can 10. This alkaline electrolyte is impregnated into the spiral electrode group 22 and promotes an electrochemical reaction (charge / discharge reaction) during charge / discharge between the positive electrode plate 24 and the negative electrode plate 26. As the alkaline electrolyte, it is preferable to use an aqueous solution containing at least one of KOH, NaOH, and LiOH as a solute.

[0020] The separator 28 may be made of, for example, a polyamide fiber nonwoven fabric to which hydrophilic functional groups have been added, or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene to which hydrophilic functional groups have been added.

[0021] The positive electrode plate 24 includes a conductive positive electrode substrate having a porous structure and a positive electrode mixture held within the pores of the positive electrode substrate. For example, a foamed nickel sheet can be used as the positive electrode substrate. The positive electrode mixture includes positive electrode active material particles and a binder. A positive electrode additive may also be added to the positive electrode mixture as needed.

[0022] The binder functions to bind the positive electrode active material particles to each other and to bind the positive electrode active material particles to the positive electrode substrate. Examples of binders that can be used include carboxymethyl cellulose, methyl cellulose, PTFE (polytetrafluoroethylene) dispersion, and HPC (hydroxypropyl cellulose) dispersion. Examples of positive electrode additives include zinc oxide and cobalt hydroxide.

[0023] The positive electrode active material particles are nickel hydroxide particles commonly used for nickel-hydrogen secondary batteries. The nickel hydroxide particles are preferably highly ordered nickel hydroxide particles. The positive electrode active material particles are manufactured by a manufacturing method commonly used for nickel-hydrogen secondary batteries.

[0024] Next, the positive electrode plate 24 can be manufactured, for example, as follows. First, a positive electrode mixture slurry containing positive electrode active material particles, water, and a binder is prepared. The prepared positive electrode mixture slurry is filled into, for example, a foamed nickel sheet and dried. After drying, the foamed nickel sheet filled with nickel hydroxide particles and the like is rolled and cut to manufacture the positive electrode plate 24.

[0025] Next, the negative electrode plate 26 will be described. As shown in Figures 2 and 3, the negative electrode plate 26 has a band-like shape as a whole and includes a metal negative electrode core 26a and a negative electrode mixture layer 26b containing a negative electrode active material supported on the negative electrode core 26a. The negative electrode core 26a is electrically conductive. The negative electrode mixture layer 26b is formed on both sides (front surface 26c and back surface 26d) of the negative electrode core 26a.

[0026] The negative electrode mixture layer 26b is formed of a negative electrode mixture containing a negative electrode active material. The negative electrode mixture is not only filled into the through-holes of the negative electrode core 26a, but is also supported in layers on the front surface 26c and back surface 26d of the negative electrode core 26a to form the negative electrode mixture layer 26b. The negative electrode mixture contains hydrogen storage alloy particles capable of absorbing and releasing hydrogen as the negative electrode active material, a conductive agent, a binder, and a negative electrode auxiliary.

[0027] The binder described above functions to bind the hydrogen storage alloy particles, conductive agent, etc. to each other and also to the negative electrode substrate 26a. The binder is not particularly limited, and binders commonly used in nickel-hydrogen secondary batteries, such as hydrophilic or hydrophobic polymers and carboxymethyl cellulose, can be used. Furthermore, styrene-butadiene rubber, sodium polyacrylate, etc. can be used as the negative electrode auxiliary. The hydrogen storage alloy in the hydrogen storage alloy particles is not particularly limited, and it is preferable to use one commonly used in nickel-hydrogen secondary batteries. The conductive agent is one commonly used in the negative electrodes of nickel-hydrogen secondary batteries, such as carbon black.

[0028] 1 and 2, the negative electrode plate 26 includes an outermost negative electrode plate portion 26e, an innermost negative electrode plate portion 26f, and a main negative electrode plate portion 26g. As shown in Fig. 2, the outermost negative electrode plate portion 26e is located at the outermost periphery of the spiral electrode group 22 and is electrically connected to the inner circumferential wall 10a of the outer can 10. Specifically, as shown in Fig. 3, the outermost negative electrode plate portion 26e is the portion that becomes the winding end side (the side of arrow e) when forming the spiral electrode group 22 from the negative electrode plate 26.

[0029] The innermost circumferential negative electrode plate portion 26f is located at the opposite end of the outermost circumferential negative electrode plate portion 26e and faces the positive electrode plate 24 only on the outer circumferential side (the range from A to B in FIGS. 2 and 3). Specifically, as shown in FIG. 3, the innermost circumferential negative electrode plate portion 26f is the portion that becomes the winding start side (the side of arrow f) when forming the spiral electrode group 22 from the negative electrode plate 26, and is located opposite the outermost circumferential negative electrode plate portion 26e when the negative electrode plate 26 is unfolded. Furthermore, the main negative electrode plate portion 26g is a portion that connects the outermost circumferential negative electrode plate portion 26e and the innermost circumferential negative electrode plate portion 26f.

[0030] Furthermore, the negative electrode plate 26 is configured so that the porosity of the first negative electrode mixture layer portion 26h located in the innermost peripheral negative electrode plate portion 26f of the negative electrode mixture layer 26b is greater than the porosity of the second negative electrode mixture layer portion 26i located in the outermost peripheral negative electrode plate portion 26e and the main negative electrode plate portion 26g. Here, the porosity of the negative electrode mixture layer 26b can be adjusted in a rolling process (described later) that is performed when manufacturing the negative electrode plate 26. That is, when the negative electrode plate 26 in which the negative electrode mixture layer 26b is formed on the negative electrode core 26a is rolled, the strength of the rolling is changed to adjust the porosity of the negative electrode mixture layer 26b. Specifically, when rolling the negative electrode plate 26, the rolling strength of the first negative electrode mixture layer portion 26h is set lower than the rolling strength of the second negative electrode mixture layer portion 26i, so that the porosity of the first negative electrode mixture layer portion 26h is formed to be greater than the porosity of the second negative electrode mixture layer portion 26i. The porosity of the negative electrode mixture layer 26b is measured by, for example, mercury porosimetry or gas adsorption method. Since the measurement method itself is known, detailed description thereof will be omitted.

[0031] The negative electrode core 26a is a strip-shaped metal material with distributed through-holes (not shown), and may be, for example, a punched metal sheet. The negative electrode plate 26 is configured by annealing the first negative electrode core portion 26j located at the innermost negative electrode plate portion 26f of the negative electrode core 26a so that it has a lower bending rigidity than the second negative electrode core portion 26k located at the outermost negative electrode plate portion 26e and the main negative electrode plate portion 26g. The annealing process is a heat treatment that removes internal strain due to work hardening, softens the structure, and improves ductility. Because the annealing process itself is well known, a detailed description thereof is omitted. The bending rigidity is defined as the product of the bending modulus of elasticity of the negative electrode core 26a and the second moment of area of ​​the negative electrode core 26a. Because the method for calculating bending rigidity is well known, a detailed description thereof is omitted. In this embodiment, in the step of heat treating the negative electrode core 26a, annealing is performed so that the flexural modulus of the first negative electrode core portion 26j becomes smaller than the flexural modulus of the second negative electrode core portion 26k. Specifically, the heating time for the first negative electrode core portion 26j is longer than the heating time for the second negative electrode core portion 26k.

[0032] In order to make the bending rigidity of the first negative electrode core portion 26j lower than that of the second negative electrode core portion 26k, for example, the plate thickness of the first negative electrode core portion 26j may be made thinner than the plate thickness of the second negative electrode core portion 26k.

[0033] The negative electrode plate 26 can be manufactured, for example, as follows. First, hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles as described above, a conductive agent, a binder, and water are prepared and kneaded to prepare a paste of a negative electrode mixture. The entire negative electrode substrate 26a is then annealed at a predetermined temperature for a predetermined time, and the first negative electrode substrate portion 26j is annealed for an additional time. The resulting paste is applied to the negative electrode substrate 26a and dried. The negative electrode plate 26 is then rolled overall in a rolling process to adjust the porosity of the negative electrode mixture layer 26b to a predetermined value. In this manner, the negative electrode plate 26 is manufactured.

[0034] The positive electrode plates 24 and negative electrode plates 26 manufactured as described above are spirally wound with a separator 28 interposed therebetween to form a spiral electrode group 22. The spiral electrode group 22 thus obtained is housed in an outer can 10. Subsequently, a predetermined amount of alkaline electrolyte is poured into the outer can 10. Thereafter, the outer can 10 housing the spiral electrode group 22 and alkaline electrolyte is sealed with a sealing member 11 equipped with a positive electrode terminal 20, thereby obtaining a battery 2 according to one embodiment. The battery 2 is subjected to an initial activation process to be ready for use.

[0035] Next, the operation and effects of the nickel-metal hydride secondary battery 2 according to one embodiment will be described. As described above, in the nickel-metal hydride secondary battery 2 according to one embodiment, the negative electrode plate 26 is configured such that the porosity of the first negative electrode mixture layer portion 26h located in the innermost negative electrode plate portion 26f of the negative electrode mixture layer 26b is greater than the porosity of the second negative electrode mixture layer portion 26i located in the outermost negative electrode plate portion 26e and the main negative electrode plate portion 26g. Therefore, even if the number of turns of the spiral electrode group 22 is increased to achieve a higher capacity of the battery 2 and the curvature of the innermost negative electrode plate portion 26f is increased, the increased flexibility of the first negative electrode mixture layer portion 26h can prevent cracks from occurring in the innermost negative electrode plate portion 26f. Furthermore, because cracks from occurring in the innermost negative electrode plate portion 26f are prevented, cracks from occurring in the positive electrode plate 24 corresponding to the innermost negative electrode plate portion 26f are also prevented. In this way, the occurrence of short circuits due to the increased capacity of the battery 2 can be prevented.

[0036] Furthermore, even if the battery 2 is heated by an external factor (e.g., if it is thrown into a fire or left on a heater), the melted separator 28 can be reliably permeated into the voids in the first negative electrode mixture layer portion 26h. In particular, because the separator 28 is often surplus on the inner circumferential side of the spiral electrode group 22 ( FIG. 2 ), a larger amount of the separator 28 may melt on the inner circumferential side of the spiral electrode group 22. According to the battery 2 of this embodiment, the porosity of the first negative electrode mixture layer portion 26h is configured to be greater than the porosity of the second negative electrode mixture layer portion 26i, so that the melted separator 28 on the inner circumferential side of the spiral electrode group 22 can be reliably captured. In this way, for example, it is possible to prevent the melted separator 28 from clogging the safety valve for the battery 2 formed by the central through-hole 16, the valve body 18, and the positive electrode terminal 20, thereby ensuring the safety of the battery 2. Therefore, it is possible to provide a battery 2 that achieves high capacity while simultaneously improving short-circuit quality and safety.

[0037] Furthermore, in the battery 2 according to one embodiment, the negative electrode plate 26 is configured in a state in which the first negative electrode core portion 26j located in the innermost peripheral negative electrode plate portion 26f of the negative electrode core 26a is annealed to have a lower bending rigidity than the second negative electrode core portion 26k located in the outermost peripheral negative electrode plate portion 26e and the main negative electrode plate portion 26g. Thus, in the battery 2, the portion of the negative electrode core 26a corresponding to the first negative electrode mixture layer portion 26h formed with a high porosity (i.e., the first negative electrode core portion 26j) is formed with a lower bending rigidity. This improves the adhesion of the first negative electrode mixture layer portion 26h to the first negative electrode core portion 26j, thereby preventing the first negative electrode mixture layer portion 26h from peeling off from the first negative electrode core portion 26j. This prevents the negative electrode mixture of the negative electrode mixture layer 26b from clogging the safety valve, ensuring the safety of the battery 2.

[0038] Furthermore, because the negative electrode substrate 26a has a smaller bending rigidity at the first negative electrode substrate portion 26j, even when the number of turns of the spiral electrode group 22 is increased to increase the curvature of the innermost circumferential negative electrode plate portion 26f in order to achieve a higher capacity of the battery 2, the occurrence of cracks in the first negative electrode substrate portion 26j can be suppressed. Therefore, the occurrence of cracks in the innermost circumferential negative electrode plate portion 26f corresponding to the first negative electrode substrate portion 26j can be suppressed. In this way, the occurrence of short circuits due to the increase in capacity of the battery 2 can be suppressed.

[0039] [Example] As shown in the table below, in this example, a battery 2 was prepared in which the porosity of the first negative electrode mixture layer portion 26h was set to 1.47 times the porosity of the second negative electrode mixture layer portion 26i, and the annealing treatment time of the first negative electrode mixture layer portion 26j was set to twice the annealing treatment time of the second negative electrode mixture layer portion 26k. In contrast, as Comparative Example 1, a battery was prepared in which the porosity of the first negative electrode mixture layer portion 26h and the porosity of the second negative electrode mixture layer portion 26i were set to the same as the porosity of the second negative electrode mixture layer portion 26i of the battery 2 in the example, and the annealing treatment time of the first negative electrode mixture layer portion 26j and the annealing treatment time of the second negative electrode mixture layer portion 26k were set to the same as the annealing treatment time of the second negative electrode mixture layer portion 26k of the battery 2 in the example. Furthermore, as Comparative Example 2, a battery was prepared in which the porosity of the first negative electrode mixture layer portion 26h was set to 1.47 times the porosity of the second negative electrode mixture layer portion 26i, and the annealing treatment time of the first negative electrode core portion 26j and the annealing treatment time of the second negative electrode core portion 26k were set to the same as the annealing treatment time of the second negative electrode core portion 26k of Battery 2 in the Example. One hundred such batteries 2 were manufactured for short-circuit defect confirmation, and 20 were manufactured for burner testing. Note that the burner testing is a test specified in the UL standard (UL2054:2004 Clause 22), and therefore a detailed description of the test method will be omitted. As a result, Battery 2 in the Example had zero short-circuit occurrences and zero failures in the burner test. In contrast, in the battery in Comparative Example 1, short circuits occurred in 10 of 100 cells, and three of 20 cells failed the burner test. In addition, in the battery according to Comparative Example 2, although the number of short circuits was zero, 5 out of 20 cells failed the burner test. Thus, it was confirmed that when the porosity was set as in Battery 2 according to this example and an annealing treatment was performed, no short circuits occurred in Battery 2 and the battery passed the burner test. [Table 1]

[0040] While the preferred embodiments of the present invention have been described above, the present invention is not limited to the nickel-metal hydride secondary battery 2 according to the above-described embodiments, but includes all aspects encompassed by the concept and scope of the present invention, and each configuration may be combined selectively as appropriate. Furthermore, the shape, material, arrangement, size, etc. of each component in the above-described embodiments may be modified as appropriate depending on the specific embodiment of the present invention. [Explanation of symbols]

[0041] 2 Nickel-metal hydride secondary battery (alkaline storage battery) 10 Outer can 10a Inner wall 20 Positive terminal 22 Spiral electrode group 24 positive electrode plate 26 Negative electrode plate 26a Negative electrode core 26b Negative electrode mixture layer 26e Outermost negative electrode plate part 26f Innermost negative electrode plate part 26g Main body negative electrode part 26h First negative electrode mixture layer 26i Second negative electrode mixture layer 26j 1st negative electrode core part 26k 2nd negative electrode core part 28 Separator

Claims

[Claim 1] a spiral electrode group formed in a spiral shape by overlapping a strip-shaped positive electrode plate, a strip-shaped negative electrode plate, and a strip-shaped separator disposed between the positive electrode plate and the negative electrode plate; a conductive cylindrical outer can in which the spiral electrode group is housed together with an alkaline electrolyte; a positive electrode terminal electrically connected to the positive electrode plate, the negative electrode plate includes an outermost negative electrode plate portion located at the outermost periphery of the spiral electrode group and electrically connected to the inner circumferential wall of the outer can, an innermost negative electrode plate portion located at an opposite end of the outermost negative electrode plate portion and facing the positive electrode plate only on the outer periphery, and a main body negative electrode plate portion connecting the outermost negative electrode plate portion and the innermost negative electrode plate portion, the negative electrode plate includes a metal negative electrode core and a negative electrode mixture layer having a negative electrode active material supported on the negative electrode core, the negative electrode plate is configured such that the porosity of a first negative electrode mixture layer portion located in the innermost circumferential negative electrode plate portion is greater than the porosity of a second negative electrode mixture layer portion located in the outermost circumferential negative electrode plate portion and the main body negative electrode plate portion, the negative electrode plate is configured in a state that has been annealed so that a first negative electrode core portion of the negative electrode core, which is located in the innermost negative electrode plate portion, has a bending rigidity that is smaller than that of a second negative electrode core portion, which is located in the outermost negative electrode plate portion and the main body negative electrode plate portion.

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