Cylindrical alkaline storage battery

Abstract

The present disclosure provides an alkaline storage battery exhibiting excellent battery characteristics over a wide range of temperatures. In the alkaline storage battery (10) according to the present disclosure, a wound electrode group is divided into a first portion (I) including the circumferentially outermost portion of each of a positive electrode (1) and a negative electrode (2), and a second portion (II) on the circumferentially inner side from the first portion (I). The first portion (I) includes the circumferentially outermost portion of the positive electrode (1) and the portion from a position b1 of the negative electrode opposite the circumferentially innermost position a1 of the circumferentially outermost portion of the positive electrode (1) to an outermost end b2 of the negative electrode. (1) The capacities N1 and N2 per unit area of the negative electrode (2) in the first portion (I) and the second portion (II), respectively, satisfy N2 > N1. (2) The capacities Pa of the positive electrode (1) and Na of the negative electrode (2) across the entire first portion as well as the capacities Pb of the positive electrode (1) and Nb of the negative electrode (2) across the entire second portion satisfy 1.04 ≤ Na / Pa ≤ 1.26 and 1.80 ≤ Nb / Pb ≤ 2.22.

Description

Cylindrical alkaline storage battery

[0001] The present disclosure relates to cylindrical alkaline storage batteries.

[0002] An alkaline storage battery includes, for example, an electrode group including a positive electrode, a negative electrode, and a separator disposed therebetween, an alkaline electrolyte, and a metal battery case (outer can) that houses these. Among alkaline storage batteries, nickel-metal hydride storage batteries primarily use nickel oxides, including nickel oxyhydroxide and nickel hydroxide, as the positive electrode active material, and a hydrogen storage alloy as the negative electrode active material. Various improvements have been attempted in the electrode group or its components to improve the performance of alkaline storage batteries.

[0003] Patent Document 1 discloses a battery comprising: an electrode group formed by winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a strip-shaped first separator interposed between the positive electrode and the negative electrode; an electrolyte; a bottomed cylindrical battery case having an opening for accommodating the electrode group and the electrolyte; and a sealing plate for sealing the opening; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on both surfaces of the negative electrode current collector; the negative electrode comprises a thin portion provided in a region of length L3 from the outer end of the negative electrode, a tapered portion adjacent to the thin portion, and a main body portion other than the thin portion; and the thickness t of the negative electrode active material layer on the outer circumferential side of the main body portion １ｏ and the thickness t of the negative electrode active material layer on the outer periphery of the thin-walled portion. ３ｏ is t １ｏ >t ３ｏ The thickness t of the negative electrode active material layer on the outer circumferential side of the tapered portion is satisfied. ２ｏ is tapered from the main body side toward the thin-walled portion side, and the electrode group is arranged so that the outer end of the positive electrode overlaps the tapered portion via the first separator, and further includes a second separator arranged between the outer end of the positive electrode and the tapered portion.

[0004] Patent Document 2 proposes a nickel-metal hydride storage battery for backup power supply, which comprises a positive electrode mainly made of nickel hydroxide, a negative electrode mainly made of hydrogen storage alloy powder, a separator, and an alkaline electrolyte, and which is subjected to maintenance charging by an intermittent charging method, in which the theoretical electric capacity ratio of the positive electrode to the negative electrode is 1:1.5 to 1:2.0, and the amount of the alkaline electrolyte is 1.7 to 3.5 g per 1 Ah of the theoretical electric capacity of the positive electrode.

[0005] International Publication No. 2017 / 09219 JP 11-329481 Publication

[0006] Alkaline storage batteries are sometimes required to have excellent battery characteristics over a wide temperature range.

[0007] One aspect of the present disclosure includes a wound electrode group, an alkaline electrolyte, and a cylindrical case that accommodates them; wherein the electrode group includes a negative electrode including a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen, a positive electrode, and a separator interposed between the positive electrode and the negative electrode, which are wound in a spiral shape; the electrode group is divided into a first portion including an outermost portion of each of the positive electrode and the negative electrode, and a second portion that is more inward than the first portion; and in the electrode group, the outermost portion of the negative electrode is located more outer than the outermost portion of the positive electrode, and the first portion includes: (i) the outermost portion of the positive electrode; and (ii) a portion of the negative electrode from position b1 that faces an innermost position a1 of the outermost portion of the positive electrode via the separator, to an outermost end b2 of the negative electrode. (1) The capacity N1 per unit area of ​​the negative electrode present in the first portion and the capacity N2 per unit area of ​​the negative electrode present in the second portion satisfy N2>N1, and (2) the capacity Pa of the positive electrode in the entire first portion, the capacity Pb ​​of the positive electrode in the entire second portion, the capacity Na of the negative electrode in the entire first portion, and the capacity Nb of the negative electrode in the entire second portion satisfy 1.04≦Na / Pa≦1.26, and 1.80≦Nb / Pb≦2.22.

[0008] The present disclosure makes it possible to provide an alkaline storage battery that exhibits excellent battery characteristics.

[0009] The present invention relates to a cylindrical alkaline storage battery, a cylindrical alkaline storage battery, and a cylindrical alkaline storage battery.

[0010] Alkaline storage batteries are required to have excellent discharge characteristics, such as the ability to discharge smoothly even at low temperatures (e.g., −20°C). Increasing the hydrogen equilibrium pressure is advantageous for ensuring excellent discharge characteristics at low temperatures. However, increasing the hydrogen equilibrium pressure can easily generate hydrogen gas and increase the internal pressure of the battery when the battery is exposed to high temperatures (e.g., when the battery is stored at high temperatures). Increased internal pressure of the battery can lead to electrolyte leakage. Therefore, there is a trade-off between high-temperature storage characteristics and low-temperature discharge characteristics, and it is generally difficult to achieve both. Thus, it is difficult to ensure excellent battery characteristics (such as high-temperature storage characteristics and low-temperature discharge characteristics) in alkaline storage batteries over a wide temperature range, for example, from −30°C to +105°C.

[0011] (Technology 1) In view of the above, the present disclosure provides a cylindrical alkaline storage battery that includes a wound electrode group, an alkaline electrolyte, and a cylindrical case that accommodates them. The electrode group includes a negative electrode containing a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen, a positive electrode, and a separator interposed between the positive electrode and the negative electrode, which are spirally wound. The electrode group is divided into a first portion including the outermost portions of the positive electrode and the negative electrode, and a second portion located more inward than the first portion. In the electrode group, the outermost portion of the negative electrode is located more outward than the outermost portion of the positive electrode. The first portion includes: (i) the outermost portion of the positive electrode; and (ii) a portion of the negative electrode that faces the innermost position a1 of the outermost portion of the positive electrode via the separator, from position b1 to the outermost end b2 of the negative electrode. In addition, in the cylindrical alkaline storage battery, (1) a capacity N1 per unit area of ​​the negative electrode present in the first portion and a capacity N2 per unit area of ​​the negative electrode present in the second portion satisfy N2>N1, and (2) a capacity Pa of the positive electrode in the entire first portion, a capacity Pb ​​of the positive electrode in the entire second portion, a capacity Na of the negative electrode in the entire first portion, and a capacity Nb of the negative electrode in the entire second portion satisfy 1.04≦Na / Pa≦1.26, and 1.80≦Nb / Pb≦2.22.

[0012] In the present disclosure, in a cylindrical alkaline storage battery, as described above, the Na / Pa ratio and the Nb / Pb ratio are set to specific ranges, where N2 > N1, for the first and second portions of the electrode group. This ensures high discharge characteristics at low temperatures (e.g., temperatures below 0°C (e.g., between −30°C and 0°C)) and achieves high-temperature storage characteristics. More specifically, by satisfying 1.04≦Na / Pa and 1.80≦Nb / Pb, the discharge reaction in the negative electrode is facilitated, resulting in high-temperature discharge characteristics. Furthermore, by satisfying 1.04≦Na / Pa≦1.26 and 1.80≦Nb / Pb≦2.22, the generated hydrogen gas can be smoothly absorbed when the battery is stored at high temperatures (e.g., temperatures above 80°C (e.g., between 80°C and 120°C)), and the presence of an appropriate residual space within the battery allows the battery to absorb internal pressure. The relationship between N2 and N1, and the Na / Pa ratio and the Nb / Pb ratio, allow a larger amount of hydrogen gas to be absorbed in the second portion. Therefore, even if a relatively large amount of hydrogen gas is generated during high-temperature storage, an increase in the internal pressure of the battery can be suppressed. Thus, the present disclosure provides excellent battery characteristics (more specifically, low-temperature discharge characteristics and high-temperature storage characteristics) over a wide temperature range.

[0013] (Technology 2) In the above (Technology 1), the hydrogen storage alloy may have a hydrogen equilibrium pressure of 0.73 MPa or more and 1.51 MPa or less at 45°C. By using a hydrogen storage alloy having a hydrogen equilibrium pressure in this range, an increase in the internal pressure of the battery can be suppressed even when the battery is stored at high temperatures for a longer period of time, compared to when the Na / Pa ratio and Nb / Pb ratio are outside the above ranges. In this specification, the hydrogen equilibrium pressure at 45°C refers to the hydrogen equilibrium pressure when the hydrogen storage capacity of the hydrogen storage alloy, H / M, is 0.5.

[0014] (Technology 3) In the above (Technology 1) or (Technology 2), the negative electrode is AB ５ Type hydrogen storage alloy, A ２ B ７ type hydrogen storage alloy, and A ５ B １９ The hydrogen storage alloy may include at least one selected from the group consisting of hydrogen storage alloys of the type.

[0015] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the negative electrode in the first portion may include a portion thinner than the thickness of the negative electrode in the second portion. In this case, it is easy to reduce the diameter of the electrode group while ensuring excellent battery characteristics over a wide temperature range, and it is easy to increase the capacity of the battery.

[0016] (Technology 5) In any one of the above (Technology 1) to (Technology 3), the thickness of the negative electrode in the first portion may be the same as the thickness of the negative electrode in the second portion. Even in this case, excellent battery characteristics can be ensured over a wide temperature range.

[0017] The alkaline storage battery of the present disclosure will be described in more detail below, including the above-mentioned (Technology 1) to (Technology 5). At least one selected from the components described below can be arbitrarily combined with at least one of the above-mentioned (Technology 1) to (Technology 5) for the alkaline storage battery of the present disclosure, as long as such combination is technically possible.

[0018] [Alkaline Storage Battery] The alkaline storage battery of the present disclosure includes a wound electrode group, an alkaline electrolyte, and a cylindrical case that accommodates these.

[0019] (Electrode Group) In the electrode group, a negative electrode containing a hydrogen storage alloy capable of electrochemically absorbing and desorbing hydrogen, a positive electrode, and a separator interposed between the positive electrode and the negative electrode are spirally wound.

[0020] The electrode group is divided into a first portion including the outermost peripheral portions of the positive electrode and the negative electrode, and a second portion located more inward than the first portion. In the electrode group, the outermost peripheral portion of the negative electrode is located more outer than the outermost peripheral portion of the positive electrode.

[0021] Fig. 2 is a schematic diagram illustrating the first and second parts when the electrode group is opened. Fig. 2 is a schematic cross-sectional view of the outermost peripheral part and its neighboring part of the wound electrode group cut along the length direction of each electrode. Fig. 3 is a schematic cross-sectional view illustrating the electrode group (wound electrode group). Fig. 3 is a schematic cross-sectional view of the wound electrode group cut in a direction perpendicular to the winding axis.

[0022] Fig. 2 is a diagram for explaining the first part. Figs. 2 and 3 are not intended to be the only specific embodiments. The descriptions and components of Figs. 2 and 3 may be combined with any of the components described herein. The description following Figs. 2 and 3 is for explaining the cylindrical alkaline storage battery of the present disclosure, and is not limited to the embodiment of Figs. 2 and 3.

[0023] As shown in Fig. 3, in a wound electrode group, a negative electrode 1 and a positive electrode 2 are spirally wound with a separator 3 interposed therebetween. In the electrode group, the outermost peripheral portion of the negative electrode 1 is located outside the outermost peripheral portion of the positive electrode 2, with a separator 3 interposed therebetween. A further separator 3 may be disposed outside the outermost peripheral portion of the negative electrode 1. In this case, the state in which the portion including the outermost peripheral portion of each electrode group is opened corresponds to Fig. 2.

[0024] 2 , the first portion I includes (i) the outermost peripheral portion 2a of the positive electrode 2, and (ii) a portion of the negative electrode 1 that faces the innermost position a1 of the outermost peripheral portion 2a of the positive electrode 2 via the separator 3, from position b1 to the outermost end b2 of the negative electrode 1. The first portion may further include (iii) a portion of the separator 3 that faces the negative electrode 1 between positions b1 and b2. This portion of the separator 3 that faces the negative electrode 1 may be a portion interposed between the positive electrode 2 and the negative electrode 1, or may be a portion located further outward from this portion and the outermost peripheral portion of the negative electrode 1. The inner peripheral portion of the electrode group other than the first portion I is the second portion II.

[0025] The cylindrical alkaline storage battery of the present disclosure satisfies (1) N2>N1 and (2) 1.04≦Na / Pa≦1.26 and 1.80≦Nb / Pb≦2.22. These ensure high discharge performance at low temperatures and achieve excellent high-temperature storage characteristics. In other words, excellent battery characteristics can be achieved over a wide temperature range.

[0026] N1, N2, Na, Nb, Pa, and Pb relating to the capacities of the negative electrode and positive electrode can be determined from the negative electrode and positive electrode taken out of the battery by the following procedure.

[0027] First, the mass ratio between the first portion and the second portion is determined for each of the positive electrode and the negative electrode.

[0028] The positive electrode mixture is removed from the positive electrode plate, and the amount of nickel hydroxide contained therein is determined. For example, the positive electrode mixture is dissolved in hydrochloric acid, and the Ni concentration in the solution is determined by inductively coupled plasma (ICP) emission spectroscopy. The mass of nickel hydroxide contained in the positive electrode is determined from this Ni concentration. The mass ratio of this nickel hydroxide and the mass ratio of the first and second portions of the positive electrode are used to determine the mass ratio of nickel hydroxide contained in each portion. The positive electrode capacities Pa and Pb of each portion are determined from the mass ratio of nickel hydroxide contained in the first and second portions and the theoretical capacity of nickel hydroxide, 289 mAh / g.

[0029] The negative electrode mixture is removed from the negative electrode plate, and the electrode capacity of the negative electrode is determined. For example, the removed negative electrode mixture and nickel powder are mixed in a mass ratio of 1:1. 1 g of the resulting mixture is pressed under a pressure of 10 tf / cm using a tablet molding machine (inner diameter 10 mm). ２ A pellet is produced by pressing the pellet to a pressure of approximately 980 MPa for 5 minutes. The pellet is sandwiched between nickel mesh, the periphery spot-welded, and a nickel lead wire is spot-welded to produce an electrode containing a negative electrode mixture. The resulting electrode, along with a sintered nickel electrode serving as a counter electrode, is immersed in a 7 mol / L potassium hydroxide aqueous solution to produce a battery with a limited negative electrode capacity. This battery is charged in a thermostatic chamber at 25°C for 16 hours, for example, at a current of 30 mA per gram of negative electrode mixture (30 mA / g), followed by a 10-minute pause and then discharged at a current of 60 mA per gram of negative electrode mixture until the voltage drops to -0.5 V relative to the mercury oxide electrode. The electrode capacity per gram of negative electrode mixture is calculated from the discharge capacity at this time. The capacities N1 and N2 per unit area of ​​each portion are then calculated based on this capacity and the mass ratio of the first and second portions.

[0030] Multiplying N1 by the area of ​​the first portion gives Na, and multiplying N2 by the area of ​​the second portion gives Nb.

[0031] (Negative Electrode) The negative electrode includes, for example, a negative electrode mixture layer. The negative electrode may include a core material and the negative electrode mixture layer attached to the core material.

[0032] Examples of the negative electrode core material include known core materials. Examples of the negative electrode core material include a conductive substrate. The substrate may be in the form of a sheet. The substrate may be a porous substrate having a plurality of through holes, or may be a substrate without through holes. Examples of the porous substrate include punched metal, sintered metal powder, expanded metal, and metal net (such as nickel net).

[0033] Examples of materials constituting the core include iron or iron alloys (such as stainless steel), nickel or its alloys, etc. The core may be plated as needed.

[0034] The negative electrode mixture layer is formed, for example, on at least the surface of the core material. The negative electrode mixture layer may be formed on one surface of the sheet-shaped core material, or may be formed on both surfaces. When the core material is porous, the negative electrode mixture layer may be formed by filling the pores of the core material with the negative electrode mixture. The negative electrode mixture layer can be formed by molding the negative electrode mixture or by attaching it to the core material.

[0035] The negative electrode mixture contains a powder of a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen as a negative electrode active material, and may further contain a dispersion medium. Furthermore, the negative electrode mixture may contain known components used in negative electrode mixtures, such as a binder, a conductive agent, a thickener, etc., as needed. Specifically, the negative electrode mixture layer can be formed, for example, by applying the negative electrode mixture to a core material, removing the dispersion medium by drying, and then applying pressure in the thickness direction.

[0036] The hydrogen storage alloy may be, for example, a material that can absorb hydrogen electrochemically generated in an alkaline electrolyte during charging and easily release the absorbed hydrogen during discharging. Hydrogen storage alloys known in the field of nickel-metal hydride batteries may also be used.

[0037] Among these, hydrogen storage alloys containing Ni and Mg are preferred, and in addition to these elements, the alloy may further contain at least one element selected from the group consisting of elements of periods 4 and 6 of groups 2 to 6 of the periodic table (including lanthanoid elements), elements of periods 4 of groups 7 to 9 and 11 to 12 of the periodic table, and elements of periods 3 to 5 of groups 13 and 14 of the periodic table.

[0038] The hydrogen storage alloy preferably contains the elements Ln, Ni, and Al. In addition to these elements, it may further contain Mg, or may further contain the element M (at least one selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B). The element Ln is at least one selected from the group consisting of Group 3 and Group 4 elements of the periodic table. The element Ln is preferably at least one selected from the group consisting of Y, lanthanoid elements, Zr, and Ti (particularly, at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, and Zr). The element Ln may contain La and an element other than La (such as Ce), or may contain Nd.

[0039] In a hydrogen storage alloy containing elements Ln, Ni, Al, and optionally Mg, the molar ratio x of Mg to the total of elements Ln and Mg may be 0≦x≦0.20 or 0≦x≦0.15. When the hydrogen storage alloy contains Mg, the lower limit of the above range of x may be 0<x. The molar ratio y of Ni to the total of elements Ln and Mg may be 2.5≦y≦5.0 or 3.0≦y≦4.5. The molar ratio α of Al to the total of elements Ln and Mg may be 0.01≦α≦0.45 or 0.10≦α<0.40.

[0040] When the hydrogen storage alloy contains the element M, the molar ratio z of the element M to the total of the elements Ln and Mg is 0.01≦z≦0.8, preferably 0.1≦z≦0.75.

[0041] The element M preferably contains at least Co and may further contain Mn. The molar ratio z1 of Co to the total of the elements Ln and Mg may be, for example, 0.10≦z1≦0.70 or 0.10≦z1≦0.60. The molar ratio z2 of Mn to the total of the elements Ln and Mg may be, for example, 0.10≦z2≦0.50 or 0.20≦z2≦0.40.

[0042] The hydrogen storage alloy is, for example, AB ２ Type, AB ３ type (i.e., CeNi ３ type), AB ５ Mold (LaNi ５ , MmNi ５ (Mm indicates mischmetal) etc.), A ２ B ７ type (i.e., Ce ２ Ni ７ type), A ５ B １９ The negative electrode may have a crystal structure such as an AB type. The negative electrode may contain at least one selected from these crystal structures. ５ Type hydrogen storage alloy, A ２ B ７ type hydrogen storage alloy, and A ５ B １９ The hydrogen storage alloy may include at least one selected from the group consisting of hydrogen storage alloys of the type.

[0043] The hydrogen equilibrium pressure of the hydrogen storage alloy at 45°C may be 0.45 MPa or more, or may be 0.73 MPa or more. From the viewpoint of easily ensuring higher low-temperature discharge characteristics, the hydrogen equilibrium pressure of the hydrogen storage alloy at 45°C is preferably 0.73 MPa or more. In this case, excellent discharge performance can be ensured even at extremely low temperatures such as -30°C. The hydrogen equilibrium pressure of the hydrogen storage alloy at 45°C may be 1.82 MPa or less, or may be 1.51 MPa or less. From the viewpoint of obtaining higher high-temperature storage characteristics, the hydrogen equilibrium pressure of the hydrogen storage alloy at 45°C is preferably 1.51 MPa or less.

[0044] The hydrogen equilibrium pressure of the hydrogen storage alloy at 45° C. may be 0.45 MPa or more (or 0.73 MPa or more) and 1.82 MPa or less, or 0.45 MPa or more (or 0.73 MPa or more) and 1.51 MPa or less.

[0045] As the dispersion medium, known media such as water, organic media, and mixtures thereof can be used. Examples of organic media include alkanols such as ethanol and isopropanol; aliphatic ketones such as acetone; aliphatic nitriles such as acetonitrile; ethers such as diethyl ether and tetrahydrofuran; and N-methyl-2-pyrrolidone. Although it depends on the types of other components contained in the negative electrode mixture, such as the binder, it is preferable that the dispersion medium contains at least water.

[0046] Examples of binders include resin materials (thermoplastic resins, thermosetting resins, etc.), for example, rubber-like materials such as styrene-butadiene copolymer rubber (SBR); polyolefin resins such as polyethylene and polypropylene; fluororesins such as PTFE, tetrafluoroethylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene copolymer (for example, copolymers with olefins such as ethylene), polyvinylidene fluoride, and vinylidene fluoride copolymer; acrylic resins such as ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and ethylene-methyl acrylate copolymer, and Na ion crosslinkers thereof. These binders can be used alone or in combination of two or more.

[0047] The amount of the binder may be 0.01 parts by mass or more and 5 parts by mass or less, or 0.05 parts by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the hydrogen storage alloy powder.

[0048] As the conductive agent, various electron conductive materials can be used. Examples of the conductive agent include graphite (natural graphite (e.g., flake graphite), artificial graphite, expanded graphite, etc.), carbon black (e.g., acetylene black, ketjen black, etc.), conductive fiber (e.g., carbon fiber, metal fiber, etc.), metal powder (e.g., copper powder), and organic conductive material (e.g., polyphenylene derivative). The conductive agent may be used alone or in combination of two or more.

[0049] The amount of the conductive agent may be 0.01 parts by mass or more and 5 parts by mass or less, or 0.05 parts by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the hydrogen storage alloy powder.

[0050] The conductive agent may be added to the negative electrode mixture and mixed with other components. Alternatively, the surface of the hydrogen storage alloy powder may be coated with the conductive agent in advance. The conductive agent can be coated by a known method, such as sprinkling the conductive agent on the surface of the hydrogen storage alloy powder, applying a dispersion containing the conductive agent and drying it, or mechanically coating the surface by a mechanochemical method. These coating methods may also be combined.

[0051] The thickener imparts viscosity to the negative electrode mixture (slurry or paste-like negative electrode mixture). The thickener can be appropriately selected depending on the type of dispersion medium. Examples of thickeners include cellulose derivatives such as carboxymethyl cellulose (CMC) and its modified forms (including salts such as Na salts), methyl cellulose, etc.; acrylic resins having acrylic acid units or methacrylic acid units, such as polyacrylic acid and polymethacrylic acid, or salts thereof; saponified polymers having vinyl acetate units, such as polyvinyl alcohol; and polyalkylene oxides, such as polyethylene oxide. These thickeners can be used alone or in combination of two or more.

[0052] When the dispersion medium contains water, it is preferable to use, among the above-mentioned thickeners, a component having a hydrophilic group such as a carboxyl group (or a salt thereof), a hydroxyl group, or a polyoxyethylene unit.

[0053] The amount of the thickener may be 0.01 parts by mass or more and 5 parts by mass or less, or may be 0.05 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the hydrogen storage alloy powder.

[0054] In the present disclosure, the Na / Pa ratio and the Nb / Pb ratio are set to specific ranges. These ratios may be adjusted, for example, by adjusting the amount of electrode mixture filled in the electrode or the thickness of the electrode between the first and second portions. For example, the thickness of the negative electrode in the first portion may be smaller than the thickness of the negative electrode in the second portion. The thickness of the negative electrode in the first portion may be the same as the thickness of the negative electrode in the second portion. In this case, the Na / Pa ratio and the Nb / Pb ratio may be adjusted by adjusting the amount of negative electrode mixture filled in the first and second portions.

[0055] (Positive Electrode) As the positive electrode, for example, a known positive electrode for an alkaline storage battery (such as a known positive electrode for a nickel-metal hydride storage battery) is used.

[0056] The positive electrode may include a core material and an active material or an active material layer attached to the core material. The positive electrode may be a positive electrode formed by sintering an active material powder, or a non-sintered positive electrode.

[0057] The positive electrode can be formed, for example, by applying a positive electrode mixture (slurry or paste-like positive electrode mixture) containing at least a positive electrode active material to a core material. More specifically, the positive electrode can be formed by applying the positive electrode mixture to the core material, drying to remove the dispersion medium, and rolling.

[0058] The positive electrode core material can be a known core material. Examples of the positive electrode core material include a porous substrate (nickel foam, sintered nickel plate, etc.) formed of nickel or a nickel alloy. When a porous substrate is used as the positive electrode core material, the positive electrode mixture is filled into the pores of the positive electrode core material.

[0059] The positive electrode active material may be, for example, a nickel compound (specifically, nickel oxide) such as nickel hydroxide or nickel oxyhydroxide. The positive electrode active material may be used alone or in combination of two or more.

[0060] The positive electrode mixture in a slurry or paste form usually contains a dispersion medium, which may be selected from the dispersion mediums exemplified for the negative electrode mixture.

[0061] If necessary, known components used in positive electrodes (conductive agents, binders, etc.) may be added to the positive electrode mixture.

[0062] Examples of the binder include hydrophilic or hydrophobic polymers, and may be selected from the binders and thickeners exemplified for the negative electrode mixture. The binder may be used alone or in combination with two or more. The amount of the binder may be 0.1 parts by mass or more and 10 parts by mass or less, or 0.5 parts by mass or more and 7 parts by mass or less, relative to 100 parts by mass of the positive electrode active material.

[0063] The conductive agent may be selected from the conductive agents exemplified for the negative electrode mixture, or a conductive cobalt oxide such as cobalt hydroxide or γ-type cobalt oxyhydroxide may be used. The conductive agent may be used alone or in combination of two or more. The amount of the conductive agent may be 0.1 parts by mass or more and 10 parts by mass or less, or 0.5 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the positive electrode active material.

[0064] The positive electrode mixture may contain known additives, for example, metal compounds (oxides, hydroxides, etc.) such as zinc oxide and zinc hydroxide.

[0065] (Separator) The separator is not particularly limited, and known separators used in alkaline storage batteries (e.g., nickel-metal hydride storage batteries) may be used. Examples of separator forms include microporous membranes, nonwoven fabrics, and woven fabrics. The separator can be made of an insulating material. Examples of separator materials include polyolefin resins (polyethylene, polypropylene, etc.) and polyamide resins.

[0066] (Alkaline Electrolyte) As the alkaline electrolyte, for example, an aqueous solution containing an alkaline solute is used. Examples of the solute include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and sodium hydroxide. The solute may be used alone or in combination of two or more.

[0067] The concentration of the alkaline solute in the alkaline electrolyte may be 3 mol / L or more and 10 mol / L or less, or 5 mol / L or more and 9 mol / L or less.The specific gravity of the alkaline electrolyte may be 1.03 or more and 1.55 or less, or 1.11 or more and 1.32 or less.

[0068] 1 is a partially exploded perspective view schematically illustrating the structure of an alkaline storage battery 10. The alkaline storage battery 10 includes a battery case 4, and a wound electrode group and alkaline electrolyte (not shown) housed within the battery case 4. The battery case 4 is a cylindrical case with a bottom. The electrode group is formed by spirally winding the negative electrode 1, the positive electrode 2, and the separator 3 such that the separator 3 is disposed between the negative electrode 1 and the positive electrode 2. The negative electrode 1 includes a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen.

[0069] The opening of the battery case 4 is sealed by a sealing body 7 and an insulating gasket 8. The sealing body 7 includes a positive electrode terminal 5 and a safety valve 6. The positive electrode 2 and the sealing body 7 are electrically connected via a positive electrode current collector plate 9.

[0070] In the wound electrode group, the outermost periphery is the negative electrode 1, and the surface of this negative electrode 1 may be exposed from the separator 3. The battery case 4 may be electrically connected to the negative electrode 1. In this case, the battery case 4 functions as a negative electrode terminal. These configurations can improve current collection properties.

[0071] The cylindrical alkaline storage battery of the present disclosure satisfies N2 > N1, 1.04 ≦ Na / Pa ≦ 1.26, and 1.80 ≦ Nb / Pb ≦ 2.22. This ensures excellent battery characteristics over a wide temperature range. More specifically, it is possible to obtain excellent high-temperature storage characteristics while maintaining the high low-temperature discharge characteristics of the alkaline storage battery.

[0072] [Examples] Hereinafter, the cylindrical alkaline storage battery of the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0073] Example 1 and Comparative Example 1 An AA-type cylindrical nickel-metal hydride storage battery with a rated capacity of 1200 mAh was fabricated according to the following procedure.

[0074] (1) Preparation of Positive Electrode A non-sintered nickel positive electrode was prepared according to the following procedure.

[0075] First, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt as coprecipitated components was added to an aqueous cobalt sulfate solution. While stirring the resulting mixture, a sodium hydroxide aqueous solution (sodium hydroxide concentration: 1 mol / L) was gradually added dropwise to adjust the pH to 11, and stirring was then continued for a predetermined period of time. The precipitate was filtered out from the resulting mixture. The filtered precipitate was washed with water and vacuum dried to obtain a powder in which the surfaces of nickel hydroxide particles were coated with 5% by mass of cobalt hydroxide.

[0076] To 1 part by mass of the powder obtained above, 10 parts by mass of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 48% by mass) was added. The resulting mixture was heated at 85°C for 8 hours while stirring, and then washed with water and dried at 65°C. This heat treatment caused a portion of the cobalt hydroxide in the cobalt hydroxide-containing layer on the surface of the nickel hydroxide particles to be highly ordered and converted to cobalt oxyhydroxide, and sodium was also introduced. Composite particles were obtained in which a coating layer containing cobalt oxyhydroxide and 1% by mass of sodium was formed on the surface of the nickel hydroxide particles.

[0077] A positive electrode slurry was prepared by adding 25 parts by mass of an aqueous solution containing CMC (CMC concentration: 0.2% by mass) as a binder to 100 parts by mass of a mixed powder of 100% by mass of the obtained composite particles and 2% by mass of zinc oxide and mixing them.

[0078] The obtained positive electrode slurry was mixed with nickel foam (areal density (weight per unit area) about 360 g / m) as a positive electrode core material. 2 The mixture was filled into holes (approximately 1.2 mm thick) and dried. The dried product was rolled to a thickness of 0.5 mm and then cut to a predetermined size to obtain a strip-shaped positive electrode with a capacity of 1200 mAh.

[0079] (2) Preparation of negative electrode A mixture was obtained by mixing 100 parts by mass of hydrogen storage alloy powder, 0.2 parts by mass of carboxymethyl cellulose (thickener), 0.2 parts by mass of Ketjen black (conductive material), and 0.5 parts by mass of styrene butadiene rubber (binder). The hydrogen storage alloy had a main phase of AB. ５ La having a crystal structure of type ０．６７９ Ce ０．２９７ Zr ０．０２４ Ni ４．４２５ Co ０．１４６ Mn ０．２１９ Al ０．３９８ A hydrogen storage alloy of the following formula was used: Alloy F, hydrogen equilibrium pressure of 1.12 MPa when hydrogen storage capacity H / M=0.5 at 45° C. Water was added to the resulting mixture and further mixed to prepare a negative electrode paste.

[0080] Next, the negative electrode paste was applied to both sides of a negative electrode current collector to form a coating film. The negative electrode current collector was a nickel-plated punched iron metal. The resulting coating film was dried and then pressed together with the negative electrode current collector to form a negative electrode mixture layer. In Comparative Example 1, the negative electrode mixture layer was formed so that the filling amount was substantially the same across the entire negative electrode. In Example 1, the filling amount of the negative electrode paste was changed between the first and second portions so that the Na / Pa ratio and the Nb / Pb ratio were the values ​​shown in Table 1. In this manner, a strip-shaped negative electrode was obtained. Furthermore, the (Na + Nb) / (Pa + Pb) ratio was set to be equal in Example 1 and Comparative Example 1.

[0081] (3) Fabrication of nickel-metal hydride storage battery The fabricated positive and negative electrodes and a separator were wound together to fabricate a wound body (electrode group). At this time, the positive and negative electrodes were stacked so that N2 > N1 and the Na / Pa and Nb / Pb values ​​were as shown in Table 1. A sulfonated polypropylene nonwoven fabric was used as the separator.

[0082] Next, the wound body and an alkaline electrolyte solution were placed in a battery case. The alkaline electrolyte solution used was an aqueous solution containing potassium hydroxide at a concentration of 6.6 mol / L and sodium hydroxide at a concentration of 0.5 mol / L.

[0083] Next, the opening of the battery case was sealed with a gasket and a sealing member. At this time, the porous nickel foam (positive electrode current collector) and the sealing member (positive electrode terminal) were electrically connected via a positive electrode lead. Furthermore, the outermost surface of the negative electrode exposed from the separator was electrically connected to the battery case (negative electrode terminal) by contacting it. In this way, a cylindrical nickel-metal hydride storage battery was fabricated.

[0084] (4) Activation of nickel-metal hydride storage battery The fabricated nickel-metal hydride storage battery was charged at room temperature (25° C.) with a charging current of 0.1 It (120 mA) for 16 hours, then rested for 1 hour, and then discharged at a discharging current of 0.2 It (240 mA) until the final voltage reached 1.0 V, after which the battery was rested for 1 hour. This charge-discharge cycle was repeated 5 times at room temperature (25° C.) to activate the nickel-metal hydride storage battery.

[0085] (5) Evaluation (a) High-Temperature Storage Characteristics The activated nickel-metal hydride storage batteries were subjected to a high-temperature storage test, and the presence or absence of leakage was confirmed at predetermined intervals.

[0086] This high-temperature storage test involves alternately repeating charging and storage (intermittent charging and storage) of the nickel-metal hydride battery. Specifically, the nickel-metal hydride battery is charged at 0.1 It in a 20°C atmosphere to 120% of the rated capacity, and then stored in a 105°C atmosphere for 30 hours. This alternating charging and storage is repeated throughout the test.

[0087] The results are shown in Table 1. In Table 1, E1 is Example 1 and C1 is Comparative Example 1.

[0088]

[0089] As shown in Table 1, in Example 1, no leakage was observed even when the battery was stored at a high temperature of 105°C for 330 hours. In contrast, in Comparative Example 1, which had the same Na / Pa ratio and Nb / Pb ratio, leakage was observed after a storage time of 210 hours. Thus, in the Example where N2 > N1 and Na / Pa and Nb / Pb were within specific ranges, the storage time during which leakage was suppressed was much longer than in the Comparative Example.

[0090] Example 2 and Comparative Example 2 The hydrogen storage alloy has a main phase of AB ５ La type crystal structure ０．６９９ Ce ０．３０１ Ni ４．４０４ Co ０．１４７ Mn ０．３５６ Al ０．２８６ A hydrogen storage alloy (Alloy D, hydrogen equilibrium pressure 0.88 MPa when hydrogen storage capacity H / M = 0.5 at 45°C) having the alloy composition shown in Table 1 was used. The Na / Pa ratio and Nb / Pb ratio were adjusted as shown in Tables 2 and 3, respectively, by adjusting the amount of negative electrode paste filled in the first and second portions and by adjusting the overlapping position of the positive electrode and negative electrode when preparing the electrode group. A negative electrode was prepared in the same manner as in Example 1 except for these points, and a cylindrical nickel-metal hydride storage battery was prepared using the prepared negative electrode. The nickel-metal hydride storage battery was activated in the same manner as in Example 1.

[0091] The activated nickel-metal hydride storage batteries were then subjected to the high-temperature storage test (a) above and evaluated for low-temperature discharge characteristics (b) below. The high-temperature storage test was evaluated as follows: A indicates no leakage after 210 hours of storage; B indicates leakage.

[0092] (b) Low-Temperature Discharge Characteristics The activated nickel-metal hydride storage battery was charged at 25°C for 15 hours at 0.1 It (120 mA). After charging, the battery was left at -20°C for 3 hours and discharged at 2 It (2400 mA). The discharge time was measured and the low-temperature discharge characteristics were evaluated according to the following criteria. The evaluation of low-temperature discharge characteristics was carried out for five batteries for each example, and the average value was calculated.

[0093] A: Discharge is possible for 10 minutes or more. B: Discharge time is less than 10 minutes.

[0094] The evaluation results of the high-temperature storage characteristics are shown in Table 2, and the evaluation results of the low-temperature discharge characteristics are shown in Table 3. In each table, the ranges that satisfy both 1.04≦Na / Pa≦1.26 and 1.83≦Nb / Pb≦2.22 are examples, and cases where at least one of the ratios is outside the above ranges are comparative examples.

[0095]

[0096] As shown in Table 2, excellent high-temperature storage properties are obtained within the ranges of 1.04≦Na / Pa≦1.26 and 1.83≦Nb / Pb≦2.22 (Examples). When at least one of the Na / Pa ratio and the Nb / Pb ratio is outside the above ranges, leakage occurs at an earlier stage than in the Examples, and the high-temperature storage properties are inferior.

[0097]

[0098] As shown in Table 3, high low-temperature discharge characteristics are obtained when 1.04≦Na / Pa≦1.26 and 1.83≦Nb / Pb. In other words, in the examples in Table 2 where excellent high-temperature storage characteristics are obtained, high low-temperature discharge characteristics can be ensured.

[0099] Examples 3 to 11 and Comparative Examples 3 to 11 The hydrogen storage alloys used were those that exhibited the hydrogen equilibrium pressure shown in Table 4 when the hydrogen storage capacity H / M was 0.5 at 45°C. A negative electrode was otherwise fabricated in the same manner as in Example 1 or Comparative Example 1, and a cylindrical nickel-metal hydride storage battery was fabricated using the fabricated negative electrode. The nickel-metal hydride storage battery was activated in the same manner as in Example 1. The activated nickel-metal hydride storage battery was subjected to a high-temperature storage test in the same manner as in (a) above, and the storage time at which suppression of leakage was confirmed was determined. The high-temperature storage test was performed for up to 330 hours.

[0100] In Table 4, C3 to C11 are Comparative Examples 3 to 11, and E3 to E11 are Examples 3 to 11. Table 4 also shows the alloy composition of the main phase of each hydrogen storage alloy.

[0101]

[0102] As shown in Table 4, even when alloys with the same hydrogen equilibrium pressure are used, the storage time during which leakage is suppressed is longer in Examples in which the Na / Pa ratio and Nb / Pb ratio are within a specific range than in Comparative Examples in which either the Na / Pa ratio or the Nb / Pb ratio is outside that range. From the viewpoint of easily ensuring higher high-temperature storage properties, the hydrogen equilibrium pressure of the hydrogen storage alloy at 45°C is preferably 1.51 MPa or less.

[0103] Furthermore, for Examples 3 to 11 and Comparative Examples 3 to 11, the low-temperature discharge characteristics were evaluated in accordance with the above-mentioned case (b). However, after charging, the batteries were left at −30°C for 3 hours and then discharged at 2 It (2400 mA) to determine the discharge time. As a result, it was found that a hydrogen equilibrium pressure of 0.73 MPa or higher at 45°C is preferable from the viewpoint of easily ensuring better low-temperature discharge characteristics.

[0104] Example 12 and Comparative Example 12 A negative electrode was fabricated in which the thickness of the first portion was smaller than the thickness of the second portion. The Na / Pa ratio and Nb / Pb ratio were adjusted as shown in Table 5. A negative electrode was fabricated in the same manner as in Example 1, except for the above. A cylindrical nickel-metal hydride storage battery was fabricated using the fabricated negative electrode. The nickel-metal hydride storage battery was activated in the same manner as in Example 1.

[0105] The activated nickel-metal hydride storage batteries were then evaluated for high-temperature storage characteristics (a) above, and the results are shown in Table 5. In Table 5, E12 is an example, and C12 is a comparative example.

[0106]

[0107] Even when the thickness of the negative electrode in the first portion is made smaller than the thickness of the negative electrode in the second portion, by keeping the Na / Pa ratio and Nb / Pb ratio within a specific range, high high-temperature storage characteristics can be obtained (E12) as shown in Table 5. By reducing the thickness of the negative electrode in the first portion, the diameter of the electrode group can be reduced, thereby increasing the capacity of the alkaline storage battery.

[0108] In the alkaline storage battery of the present disclosure, when comparing the performance of Examples and Comparative Examples, the ratio Nt / Pt of the total capacity Nt of the negative electrode to the total capacity Pt of the positive electrode in the electrode group is made uniform between the Examples and Comparative Examples, thereby making it possible to particularly clearly demonstrate the superiority of the battery performance of the Examples. For example, the ratio Nt / Pt is 1.701 in both the Examples and Comparative Examples. In the alkaline storage battery of the present disclosure, the ratio Nt / Pt is not limited to 1.701.

[0109] The alkaline storage battery of the present disclosure exhibits excellent battery characteristics over a wide temperature range. Therefore, the alkaline storage battery has high reliability and is suitable for use as a power source for various devices, in addition to being a replacement for dry batteries. However, the uses of the alkaline storage battery are not limited to these.

[0110] 1: Negative electrode 2: Positive electrode 3: Separator 4: Battery case 7: Sealing body 8: Insulating gasket 9: Positive electrode current collector plate 10: Alkaline storage battery I: First part II: Second part 2a: Outermost part of the positive electrode in the electrode group

Claims

1. A wound type electrode group and an alkaline electrolyte, and a cylindrical case that accommodates them, wherein the electrode group comprises a negative electrode containing a hydrogen storage alloy capable of electrochemically absorbing and releasing hydrogen, a positive electrode, and a separator interposed between the positive electrode and the negative electrode, which are wound in a spiral shape, the electrode group being divided into a first portion including the outermost peripheral portions of the positive electrode and the negative electrode, and a second portion located more inward than the first portion, wherein the outermost peripheral portion of the negative electrode in the electrode group is located more outer than the outermost peripheral portion of the positive electrode, and the first portion comprises: (i) the outermost peripheral portion of the positive electrode; and (ii) a portion of the negative electrode from position b1 that faces the innermost position a1 of the outermost peripheral portion of the positive electrode via the separator, to the outermost end b2 of the negative electrode, (1) A cylindrical alkaline storage battery in which a capacity N1 per unit area of ​​the negative electrode present in the first portion and a capacity N2 per unit area of ​​the negative electrode present in the second portion satisfy N2>N1, and (2) a capacity Pa of the positive electrode in the entire first portion, a capacity Pb ​​of the positive electrode in the entire second portion, a capacity Na of the negative electrode in the entire first portion, and a capacity Nb of the negative electrode in the entire second portion satisfy 1.04≦Na / Pa≦1.26, and 1.80≦Nb / Pb≦2.

22.

2. The cylindrical alkaline storage battery according to claim 1, wherein the hydrogen storage alloy has a hydrogen equilibrium pressure at 45°C of 0.73 MPa or more and 1.51 MPa or less.

3. The negative electrode is AB ５ Type hydrogen storage alloy, A ２ B ７ type hydrogen storage alloy, and A ５ B １９ 3. The cylindrical alkaline storage battery according to claim 1, comprising at least one selected from the group consisting of hydrogen storage alloys of the type A and B.

4. The cylindrical alkaline storage battery according to claim 1 or 2, wherein the thickness of the negative electrode in the first portion includes a portion thinner than the thickness of the negative electrode in the second portion.

5. A cylindrical alkaline storage battery according to claim 1 or 2, wherein the thickness of the negative electrode in the first portion is the same as the thickness of the negative electrode in the second portion.

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