Negative electrode for alkaline storage battery and alkaline storage battery using said negative electrode

Abstract

To provide a negative electrode for an alkaline storage battery that improves both cycle life and low-temperature discharge characteristics and the alkaline storage battery using the same.SOLUTION: A negative electrode (26) for an alkaline battery includes a metallic negative electrode core and a negative electrode alloy layer including at least a hydrogen storage alloy and yttrium fluoride, the negative electrode alloy layer being supported by the negative electrode core. Yttrium fluoride particles are formed so that the average particle diameter is 1 μm or more and 7 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for an alkaline storage battery and an alkaline storage battery using the negative electrode. [Background technology]

[0002] An alkaline storage battery includes an electrode group in which a positive electrode, a negative electrode, and a separator are stacked. In the electrode group, the separator is disposed between the positive electrode and the negative electrode. In such an alkaline storage battery, for example, the electrode group is spirally wound and housed in a conductive cylindrical outer can together with an alkaline electrolyte. In such an alkaline storage battery, a predetermined electrochemical reaction occurs between the positive electrode and the negative electrode facing each other via the separator, thereby causing charging and discharging. For example, Patent Document 1 describes a nickel-metal hydride secondary battery as an example of an alkaline storage battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-149299 Summary of the Invention [Problem to be solved by the invention]

[0004] Nickel-metal hydride secondary batteries, being high-capacity and environmentally safe, are being used in a wide variety of applications, including as interchangeable alkaline batteries, backup power sources, and in-vehicle applications. As their applications expand, various methods are being investigated to extend the life (improve the cycle life) of nickel-metal hydride secondary batteries, such as adding Co to the hydrogen storage alloy to suppress pulverization and treating the alloy surface with alkali to suppress corrosion.

[0005] However, in conventional nickel-metal hydride secondary batteries, although the addition of Co to the alloy or alkali treatment of the alloy surface improves the cycle life, it is known that this generally reduces the reactivity of the alloy, and the discharge characteristics, particularly at low temperatures, deteriorate. Thus, it has been difficult to achieve both improved cycle life and improved low-temperature discharge characteristics in nickel-metal hydride secondary batteries.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a negative electrode for an alkaline storage battery that achieves both an improvement in cycle life and an improvement in low-temperature discharge characteristics, and an alkaline storage battery using the negative electrode. [Means for solving the problem]

[0007] In order to achieve the above object, the negative electrode for an alkaline storage battery according to the present invention comprises a metal negative electrode core and a negative electrode mixture layer that contains at least a hydrogen storage alloy and yttrium fluoride and is supported on the negative electrode core, and is characterized in that the yttrium fluoride particles are formed so as to have an average particle diameter of 1 μm or more and 7 μm or less. [Effects of the Invention]

[0008] In the negative electrode for an alkaline storage battery according to the present invention, the yttrium fluoride particles contained in the negative electrode mixture layer are formed to have an average particle diameter of 1 μm or more and 7 μm or less. Therefore, when the negative electrode is used in an alkaline storage battery, the properties of yttrium fluoride enhance the reactivity of the hydrogen storage alloy during low-temperature discharge and suppress corrosion of the hydrogen storage alloy by an alkaline electrolyte. Specifically, the properties of yttrium enhance the reactivity of the hydrogen storage alloy during low-temperature discharge, and the properties of fluorine suppress corrosion of the hydrogen storage alloy by an alkaline electrolyte. Furthermore, because the average particle diameter of the yttrium fluoride particles is 1 μm or more and 7 μm or less, the yttrium fluoride particles can be sufficiently dispersed among the hydrogen storage alloy, further enhancing the reactivity of the hydrogen storage alloy during low-temperature discharge and more reliably suppressing corrosion of the hydrogen storage alloy by an alkaline electrolyte. In this way, a negative electrode for an alkaline storage battery that achieves both improved cycle life and improved low-temperature discharge characteristics can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a partially cutaway perspective view of an alkaline storage battery according to one embodiment. [Figure 2] 1 shows the results of a cycle test and a low-temperature discharge test of the alkaline storage batteries according to the examples, together with those of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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, as one embodiment, an AA-sized cylindrical battery 2 will be described. However, the battery 2 is not limited to this, and may be of other sizes such as AAA, or may be, for example, a prismatic battery.

[0011] 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 shows the results of a cycle test and a low-temperature discharge test of the battery 2 according to the example, along with a comparative example. 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. In addition, 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).

[0012] 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.

[0013] 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.

[0014] 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.

[0015] As shown in FIG. 1 , a spiral electrode group 22 (electrode group) is housed in an outer can 10. This spiral electrode group 22 is formed by stacking strip-shaped positive electrodes 24, negative electrodes 26, and separators 28 one on top of the other. The spiral electrode group 22 is formed in a spiral shape with the separator 28 sandwiched between the positive electrodes 24 and the negative electrodes 26. That is, the positive electrodes 24 and the negative electrodes 26 are stacked radially with the separator 28 interposed between them. The outermost periphery of the spiral electrode group 22 is formed by a part of the negative electrode 26 and is in contact with the wall of the outer can 10 facing the inner periphery. That is, the negative electrodes 26 and the outer can 10 are electrically connected to each other.

[0016] 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 24, and the other end is connected to the cover plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 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.

[0017] 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 24 and the negative electrode 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.

[0018] 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. Specifically, it is preferable to use a nonwoven fabric made of polyolefin fibers to which sulfonation has been applied to add sulfonic groups. The sulfonic groups are added by treating the nonwoven fabric with an acid containing sulfonic groups, such as sulfuric acid or fuming sulfuric acid. Sulfonation of the separator in this way not only imparts hydrophilic properties but also contributes to suppressing self-discharge of the battery.

[0019] The positive electrode 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. Examples of such a positive electrode substrate include a nickel-plated mesh-like, sponge-like, or fibrous metal body, or nickel foam. The positive electrode mixture includes positive electrode active material particles, a conductive agent, a positive electrode additive, and a binder.

[0020] The binder of the positive electrode mixture binds the positive electrode active material particles, the conductive agent, and the positive electrode additive, and also binds the positive electrode mixture 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. Furthermore, a positive electrode additive is added as needed to improve the characteristics of the positive electrode. Examples of major positive electrode additives include yttrium oxide, zinc oxide, and cobalt hydroxide.

[0021] The positive electrode active material particles are nickel hydroxide particles commonly used for nickel-hydrogen secondary batteries. It is preferable to use highly-ordered nickel hydroxide particles. It is preferable to dissolve at least one of zinc, magnesium, and cobalt in these nickel hydroxide particles. The positive electrode active material particles described above are manufactured by a manufacturing method commonly used for nickel-hydrogen secondary batteries. The conductive agent may be one or more selected from cobalt compounds such as cobalt oxide (CoO) and cobalt hydroxide (Co(OH)2), and cobalt (Co). The conductive agent is added to the positive electrode mixture as needed, and may be added in the form of a powder or a coating covering the surface of the positive electrode active material.

[0022] Next, the positive electrode 24 can be manufactured, for example, as follows. First, a positive electrode mixture slurry is prepared containing a positive electrode active material powder consisting of positive electrode active material particles, a conductive agent, a positive electrode additive, water, and a binder. The obtained positive electrode mixture slurry is filled into, for example, a nickel foam and dried. After drying, the nickel foam filled with nickel hydroxide particles and the like is rolled and then cut into a predetermined shape. This produces a positive electrode 24 holding the positive electrode mixture.

[0023] Next, the negative electrode 26 will be described. The negative electrode 26 includes a metal negative electrode core and a negative electrode mixture layer supported on the negative electrode core, and is strip-shaped as a whole. The negative electrode core is electrically conductive. The negative electrode core is a strip-shaped metal material with through holes (not shown) distributed therein, and may be, for example, a punched metal sheet. The negative electrode mixture layer is formed by a negative electrode mixture applied in layers to both sides (front and back) of the negative electrode core. The negative electrode mixture is not only filled in the through holes of the negative electrode core, but is also supported in layers on the front and back surfaces of the negative electrode core to form the negative electrode mixture layer. The negative electrode mixture includes hydrogen storage alloy particles capable of absorbing and releasing hydrogen as a negative electrode active material, yttrium fluoride (hereinafter also referred to as YF3), a conductive agent, a binder, and a negative electrode auxiliary.

[0024] Here, the hydrogen storage alloy is an alloy capable of absorbing and releasing hydrogen, which is a negative electrode active material. The hydrogen storage alloy in the hydrogen storage alloy particles is not particularly limited, and it is preferable to use one that is used in general nickel-metal hydride secondary batteries. For example, the hydrogen storage alloy may be a rare earth-Mg-Ni hydrogen storage alloy containing rare earth elements, Mg, and Ni. The hydrogen storage alloy particles are preferably formed so that their volume mean particle diameter (MV) is 15 μm or more and 90 μm or less. In this specification, the volume mean particle diameter (MV) of the hydrogen storage alloy particles refers to the mean particle diameter at which the particle size distribution is measured using a laser diffraction / scattering particle size distribution analyzer (device name: SRA-150, MT-3300, manufactured by Microtrac) and the volume-based cumulative average particle diameter is 50%.

[0025] The yttrium fluoride particles are formed to have an average particle size of 1 μm or more and 7 μm or less, preferably 1 μm or more and 3 μm or less. In this specification, the average particle size of the yttrium fluoride particles means the particle size at which the cumulative frequency of all particles is 50% (D50) when the particle size distribution is measured using a laser diffraction / scattering particle size distribution analyzer (device name: HRA manufactured by Microtrac). , i.e., the median diameter .

[0026] The hydrogen storage alloy particles and yttrium fluoride particles can be obtained, for example, as follows: First, metal raw materials are weighed and mixed to obtain a predetermined composition, and an ingot is prepared from this mixture by a predetermined manufacturing method. The obtained ingot is crushed and sieved using a classifier to obtain hydrogen storage alloy particles and yttrium fluoride particles of the desired particle size.

[0027] The binder in the negative electrode mixture functions to bind the hydrogen storage alloy particles, the conductive agent, etc. to each other and also to bind the hydrogen storage alloy particles, the conductive agent, etc. to the negative electrode core. 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. The negative electrode auxiliary can be styrene-butadiene rubber, sodium polyacrylate, etc. The conductive agent can be a conductive agent commonly used in nickel-hydrogen secondary batteries, such as carbon black.

[0028] The negative electrode 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, yttrium fluoride, a conductive agent, a binder, and water are prepared. For the hydrogen storage alloy powder and yttrium fluoride, metal raw materials are weighed and mixed to achieve a predetermined composition. An ingot is prepared from this mixture using a predetermined manufacturing method. The resulting ingot is crushed and sieved using a classifier to obtain hydrogen storage alloy particles and yttrium fluoride particles of the desired particle size. These are then kneaded to prepare a paste of the negative electrode mixture. The resulting paste is applied to a negative electrode core and dried. The entire mixture is then rolled to increase the packing density of the hydrogen storage alloy and yttrium fluoride, and then cut into a predetermined shape to manufacture the negative electrode 26.

[0029] The positive electrode 24 and negative electrode 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 treatment to be ready for use.

[0030] Next, the functions and effects of the negative electrode 26 and battery 2 according to one embodiment will be described. As described above, according to the negative electrode 26 according to one embodiment, the yttrium fluoride particles contained in the negative electrode mixture layer are formed to have an average particle diameter of 1 μm or more and 7 μm or less, preferably 1 μm or more and 3 μm or less. Therefore, when the negative electrode 26 is used in the battery 2, the properties of yttrium fluoride enhance the reactivity of the hydrogen storage alloy during low-temperature discharge and suppress corrosion of the hydrogen storage alloy by alkaline electrolyte. Specifically, the properties of yttrium improve the reactivity of the hydrogen storage alloy during low-temperature discharge, and the properties of fluorine suppress contact between the hydrogen storage alloy and alkaline electrolyte, thereby suppressing corrosion of the hydrogen storage alloy by alkaline electrolyte. Furthermore, because the average particle diameter of the yttrium fluoride particles is 1 μm or more and 7 μm or less, preferably 1 μm or more and 3 μm or less, the yttrium fluoride particles can be sufficiently dispersed (scattered) among the hydrogen storage alloy. This further enhances the reactivity of the hydrogen storage alloy during low-temperature discharge. Furthermore, corrosion of the hydrogen storage alloy by the alkaline electrolyte is more reliably suppressed, reducing the consumption of alkaline electrolyte due to corrosion of the hydrogen storage alloy, thereby improving the cycle life. In this way, it is possible to provide a negative electrode 26 for a nickel-metal hydride secondary battery 2 and a battery 2 that achieve both improved cycle life and improved low-temperature discharge characteristics.

[0031] Here, if the average particle size of the yttrium fluoride particles is larger than the desired range, the yttrium fluoride cannot be sufficiently dispersed in the hydrogen storage alloy. That is, the distribution of the yttrium fluoride becomes localized. Furthermore, if the average particle size of the yttrium fluoride is smaller than the desired range, the yttrium fluoride particles aggregate, which makes it impossible to sufficiently disperse the yttrium fluoride in the hydrogen storage alloy. Thus, if the average particle size of the yttrium fluoride is outside the desired range, the reactivity of the hydrogen storage alloy during low-temperature discharge cannot be sufficiently increased, and corrosion of the hydrogen storage alloy by the alkaline electrolyte cannot be sufficiently suppressed.

[0032] Furthermore, in the negative electrode 26 according to one embodiment, the hydrogen storage alloy particles are formed to have an average particle diameter of 15 μm or more and 90 μm or less. Therefore, even if yttrium fluoride particles aggregate, it is believed that the hydrogen storage alloy particles can break down the agglomerations of the yttrium fluoride particles. Breaking down the agglomerations of the yttrium fluoride particles allows the yttrium fluoride to be sufficiently dispersed (scattered) among the hydrogen storage alloy. This enhances the reactivity of the hydrogen storage alloy during low-temperature discharge and suppresses corrosion of the hydrogen storage alloy by alkaline electrolyte. In this way, a negative electrode 26 for a nickel-metal hydride secondary battery 2 and a battery 2 can be provided that achieve both improved cycle life and improved low-temperature discharge characteristics.

[0033] Here, if the hydrogen storage alloy particles have an average particle size larger than the desired range (15 μm to 90 μm), the distance between the hydrogen storage alloy particles will be large, and it is thought that the agglomeration of the yttrium fluoride particles will not be broken down.Also, if the hydrogen storage alloy particles have an average particle size smaller than the desired range (15 μm to 90 μm), the alloy particles will agglomerate and behave as pseudo-large particles, and it is thought that the agglomeration of the yttrium fluoride particles will not be broken down.

[0034] 1. Battery manufacturing [Example 1] (1) Preparation of the positive electrode A sodium hydroxide solution was gradually added to a mixed aqueous solution of nickel sulfate, zinc sulfate, magnesium sulfate, and cobalt sulfate while stirring, so that the nickel metal content was 3% by weight of zinc, 0.4% by weight of magnesium, and 1% by weight of cobalt. The pH during the reaction was stabilized at 13-14, and nickel hydroxide was eluted. This was washed three times with 10 times the amount of pure water, then dehydrated and dried to produce a nickel hydroxide active material. Next, 10% by weight of cobalt hydroxide, 0.5% by weight of yttrium oxide, 40% by weight of HPC dispersion, and 0.3% by weight of zinc oxide were mixed with this active material to produce an active material slurry. This active material slurry was filled into foamed nickel, dried, rolled, and cut to the specified size to produce a positive electrode.

[0035] (2) Preparation of the negative electrode To 100 parts by weight of hydrogen storage alloy powder with an average particle size MV = 65 μm, 0.4 parts by weight of sodium polyacrylate, 0.1 parts by weight of carboxymethyl cellulose (CMC), 2.0 parts by weight of a 50% solids dispersion of styrene butadiene rubber (SBR), 0.5 parts by weight of Ketjen Black, 0.1 parts by weight of YF3 powder with an average particle size = 1 μm, and 30 parts by weight of water were added and kneaded to prepare a paste of a negative electrode mixture. For the hydrogen storage alloy and YF3, ingots produced by a predetermined manufacturing method were crushed and sieved using a classifier to obtain hydrogen storage alloy particles (average particle size MV = 65 μm) and YF3 particles (average particle size = 1 μm) with the desired particle size. This paste was then evenly applied to both sides of a nickel-plated iron perforated plate as a negative electrode core. After the paste was dried, the perforated plate with the hydrogen storage alloy powder attached, that is, the negative electrode substrate, was further rolled to increase the amount of alloy per volume, and then cut to a predetermined size to prepare a negative electrode.

[0036] (3) Assembly and initial activation of nickel-metal hydride secondary batteries The negative electrode and positive electrode prepared in the above process were combined and wound together with a separator 28, and a predetermined amount of electrolyte composed of NaOH, KOH, and LiOH solutions was poured into the combined battery to prepare a nickel-metal hydride secondary battery with a nominal capacity of 2000 mAh. The battery was then charged at 0.2 A for 16 hours and then discharged at 0.4 A until the battery voltage reached 1.0 V, five times for activation.

[0037] [Example 2] A nickel-metal hydride secondary battery was fabricated in the same manner as the battery of Example 1, except that yttrium fluoride (YF3) with an average particle size of 3 μm was used.

[0038] [Example 3] A nickel-metal hydride secondary battery was fabricated in the same manner as the battery of Example 1, except that yttrium fluoride (YF3) with an average particle size of 7 μm was used.

[0039] [Comparative Example 1] Yttrium fluoride (YF3) is not added to the negative electrode mixture A nickel-metal hydride secondary battery was fabricated in the same manner as in Example 1, except for the above.

[0040] Comparative Example 2 Yttrium fluoride (YF3) with an average particle size of 0.8 μm was used. A nickel-metal hydride secondary battery was fabricated in the same manner as in Example 1, except for the above.

[0041] 2. Evaluation of nickel-metal hydride secondary batteries [Battery characteristic evaluation (cycle test)] The batteries fabricated using the above process were subjected to a cycle life evaluation under the following conditions: charge: 2A (ΔV = -10mV), rest: 20min, discharge: 2A (End V = 1.0V), rest: 10min. ΔV = -10mV refers to charging under -ΔV control (hereinafter simply referred to as -ΔV charging), in which charging is terminated when the battery voltage drops 10mV from its maximum value after reaching its maximum value. Charge and discharge were repeated under these conditions, and the cycle life was determined as the point at which discharge was no longer possible or the discharge capacity fell below 60% of the discharge capacity at the first cycle.

[0042] As shown in FIG. 2, the cycle life is improved in Comparative Example 2 and Examples 1 to 3 compared to Comparative Example 1. However, it can be seen that the cycle life is reduced in Comparative Example 2, in which the average particle diameter of YF3 is 0.8 μm, and Example 3, in which the average particle diameter is 7 μm, compared to Example 1, in which the average particle diameter is 1 μm, and Example 2, in which the average particle diameter is 3 μm. This is thought to be because the distribution of YF3 is localized in the negative electrode, and YF3 is not sufficiently dispersed. Thus, it can be seen that in order to improve the cycle life, it is optimal to set the average particle diameter of YF3 to be 1 μm or more and 3 μm or less.

[0043] [Battery characteristic evaluation (low-temperature discharge test)] The initial capacity of the battery fabricated using the above process was measured by three cycles of "charge: 2A (-ΔV charge), rest: 1 hour, discharge: 2A (End V=1.0V), rest: 1 hour" at 25°C. The discharge capacity was then measured using the following cycles: "charge: 2A (-ΔV charge; 25°C), rest: 3 hours (-10°C), discharge: 2A (End V=1.0V; -10°C), rest: 1 hour (25°C), discharge: 2A (25°C), charge: 2A (-ΔV charge; 25°C), rest: 3 hours (25°C), discharge: 2A (End V=1.0V; 25°C)." The ratio of the 25°C discharge capacity to the -10°C discharge capacity was defined as the low-temperature discharge ratio.

[0044] 2, compared to Comparative Example 1, in which no YF3 was added, Comparative Example 2, in which the average particle size of YF3 was 0.8 μm, showed a decreased low-temperature discharge ratio, whereas Example 1, in which the average particle size of YF3 was 1.0 μm, Example 2, in which the average particle size of YF3 was 3.0 μm, and Example 3, in which the average particle size of YF3 was 7.0 μm showed improved low-temperature discharge ratios. Thus, it is clear that the optimum mean particle size of YF3 is 1 μm or more and 7 μm or less in order to improve low-temperature discharge characteristics.

[0045] 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]

[0046] 2 Nickel-metal hydride batteries (alkaline batteries) 22 Spiral electrode group (electrode group) 24 Positive electrode 26 negative electrode 28 Separator

Claims

1. A negative electrode for an alkaline storage battery, comprising: a metal negative electrode core body; a negative electrode mixture layer that contains at least a hydrogen storage alloy and yttrium fluoride and is supported on the negative electrode core; The yttrium fluoride particles are formed so as to have a median diameter (D50) of 1 μm or more and 7 μm or less, 1. A negative electrode for an alkaline storage battery, wherein the particles of the hydrogen storage alloy are formed so that the mean particle size by volume (MV) is 15 μm or more and 90 μm or less.

2. 2. The negative electrode for an alkaline storage battery in accordance with claim 1, wherein the yttrium fluoride particles are formed so as to have a median diameter (D50) of 1 μm or more and 3 μm or less.

3. an electrode group formed of the negative electrode according to claim 1 or 2, a positive electrode, and a separator disposed between the positive electrode and the negative electrode; an outer can having electrical conductivity and containing the electrode group together with an alkaline electrolyte;

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