Bipolar electrode for metal hydride battery and metal hydride battery equipped with the bipolar electrode

Abstract

To provide a bipolar electrode for a metal hydride battery that prevents the voltage reduction phenomenon and achieves improved long-term reliability, and to provide a metal hydride battery comprising the bipolar electrode.SOLUTION: A bipolar electrode for a metal hydride battery comprises: a current collector; a negative electrode active material layer provided on a first surface of the current collector; and a positive electrode active material layer provided on a second surface of the current collector. The negative electrode active material layer contains metal hydride. The current collector has a steel plate, and an Ni-Fe alloy layer formed on at least one surface of the steel plate.SELECTED DRAWING: Figure 1(a)

Description

[Technical Field]

[0001] The present invention relates to a bipolar electrode for a metal hydride battery and a metal hydride battery equipped with the bipolar electrode. [Background technology]

[0002] A metal hydride battery is generally a secondary battery that includes a positive electrode having a nickel hydroxide such as nickel hydroxide as a positive electrode active material, a negative electrode having a hydrogen storage alloy as a negative electrode active material, and an electrolyte consisting of an aqueous alkali metal solution.

[0003] A known conventional energy storage module is a bipolar battery equipped with bipolar electrodes in which a positive electrode is formed on one side of an electrode plate and a negative electrode is formed on the other side (see, for example, Patent Document 1 below). The bipolar battery is equipped with a stack in which bipolar electrodes and separators are alternately stacked in the stacking direction. Terminal electrodes equipped with only one of a positive electrode or a negative electrode are located at both ends of the stack in the stacking direction. An electrolyte is contained in the internal space formed between the electrodes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-135764 Summary of the Invention [Problem to be solved by the invention]

[0005] Plated steel sheets are used for the current collectors that make up the bipolar electrodes of metal hydride batteries from the viewpoints of cost, resistance to reactivity with the electrolyte, etc. The present inventors manufactured bipolar electrodes using a current collector made of plated steel sheets and negative and positive electrodes containing hydrogen storage alloys, assembled a hydride battery using the bipolar electrodes, and performed a storage test, whereupon a voltage drop (self-discharge) of unknown cause was observed.

[0006] An object of the present invention is to provide a bipolar electrode for a metal hydride battery capable of reducing self-discharge and a metal hydride battery equipped with a bipolar electrode. [Means for solving the problem]

[0007] As a result of extensive research, the inventors of the present invention came up with the idea of reducing hydrogen permeation by using a layer containing a specific material, based on the idea that the phenomenon of hydrogen migration to the counter electrode via the current collector of the bipolar electrode is involved in self-discharge, and discovered that a current collector having a layer containing a specific material can reduce self-discharge, leading to the completion of the present invention. In order to achieve the above object, the bipolar electrode of the metal hydride battery according to this embodiment comprises a current collector, a negative electrode active material layer provided on a first surface of the current collector, and a positive electrode active material layer provided on a second surface of the current collector, wherein the negative electrode active material layer contains a metal hydride, and the current collector comprises a steel plate and a Ni-Fe alloy layer formed on at least one surface of the steel plate. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a bipolar electrode for a metal hydride battery that reduces the voltage drop phenomenon and improves long-term reliability, and also to provide a metal hydride battery equipped with the bipolar electrode. [Brief explanation of the drawings]

[0009] [Figure 1(a)] 1 is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to an embodiment of the present invention. [Figure 1(b)] 1 is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of the results obtained by SEM-EDX (energy dispersive X-ray spectroscopy) of a Ni—Fe alloy layer. [Figure 3] FIG. 1 is an explanatory diagram of an electrochemical hydrogen permeation method. [Figure 4] FIG. 10 is a diagram showing the evaluation results of the hydrogen permeation suppression effect. [Figure 5(a)] FIG. 10 is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to another embodiment. [Figure 5(b)] FIG. 10 is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to another embodiment. [Figure 5(c)] FIG. 10 is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to another embodiment. [Figure 6] 1 is a schematic cross-sectional view showing an example of an electricity storage device to which the bipolar electrode of the metal hydride battery of the present embodiment is applied. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the internal configuration of the electricity storage module in FIG. [Figure 8] FIG. 1 is a schematic diagram of an evaluation battery to which a bipolar electrode of the metal hydride battery of the present embodiment is applied. DETAILED DESCRIPTION OF THE INVENTION

[0010] The bipolar electrode of a metal hydride battery of the present invention, the metal hydride battery, a method for manufacturing the bipolar electrode of the metal hydride battery, and a method for manufacturing a metal hydride battery using the bipolar electrode of the metal hydride battery will be described in detail below.

[0011] Hereinafter, as necessary, a method capable of producing a bipolar electrode for a metal hydride battery of the present invention may be referred to as the electrode production method of the present invention. Furthermore, a method capable of producing a metal hydride battery of the present invention may be referred to as the battery production method of the present invention. A bipolar electrode for a metal hydride battery of the present invention may be referred to as the electrode of the present invention or the bipolar electrode of the present invention. Unless otherwise specified, the numerical ranges "x to y" described in this specification include the lower limit x and the upper limit y. Furthermore, these upper and lower limit values, as well as the numerical values listed in the examples, can be arbitrarily combined to form a numerical range. Furthermore, numerical values arbitrarily selected from within the numerical range can be used as the upper and lower limit values.

[0012] <Bipolar electrode for metal hydride battery: First embodiment> First, the bipolar electrode of the metal hydride battery of the present invention will be described in detail with reference to the following embodiments and drawings. As shown in Figure 1(a), the bipolar electrode 100 of the metal hydride battery of this embodiment comprises a current collector 10, a negative electrode active material layer 20 provided on a first surface (10A) of the current collector 10, and a positive electrode active material layer 30 provided on a second surface (10B) of the current collector 10 that is different from the first surface (10A). The negative electrode active material layer 20 contains a metal hydride, and the current collector 10 includes a steel plate 13 and a Ni-Fe alloy layer 15 provided on at least one surface of the steel plate 13.

[0013] The bipolar electrode 100 of the metal hydride battery of this embodiment basically functions as a bipolar electrode having a negative electrode active material (metal hydride) on a first surface (10A) of a current collector 10 and a positive electrode active material on a second surface (10B) opposite the first surface (10A), but is not limited to this. That is, the electrode of the present invention may also be a bipolar electrode formed by joining a first current collector containing a metal hydride and a second current collector containing a positive electrode active material.

[0014] The current collector 10 includes a Ni-Fe alloy layer 15 on the surface of a steel sheet 13. Examples of the steel sheet 13 include low-carbon steel with a carbon content of less than 0.25% by weight, ultra-low-carbon steel with a carbon content of less than 0.01% by weight, and non-aging ultra-low-carbon steel obtained by adding Ti, Nb, or the like to ultra-low-carbon steel. Examples of low-carbon steel include low-carbon aluminum-killed steel (carbon content: 0.01 to 0.15% by weight) and cold-rolled steel sheets (e.g., SPCC) specified in JIS G 3141:2005. From the viewpoint of rollability and cost efficiency, low-carbon aluminum-killed steel (carbon content: 0.01 to 0.15% by weight) is preferred. The steel sheet 13 is primarily made of Fe, but may contain metal elements other than Fe. The proportion of metal elements other than Fe in the steel sheet 13 is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 2 wt% or less, and particularly preferably 1 wt% or less. The thickness of the current collector 10 can be, for example, 5 μm to 1000 μm.

[0015] The Ni—Fe alloy layer 15 formed on at least one surface of the steel plate 13 is an alloy layer containing an alloy substantially consisting of nickel (Ni) and iron (Fe). The Ni—Fe alloy layer 15 in this embodiment only needs to contain nickel (Ni) and iron (Fe), and there are no particular limitations on the state in which each component is contained. In this specification, the Ni-Fe alloy layer is defined as follows: When elemental analysis of Ni and Fe is performed from the surface to a depth of 10 μm, the Ni-Fe alloy layer is defined as being present in a portion containing at least 1 / 10 of the maximum amount of Ni and Fe contained therein. That is, in the present embodiment, the Ni-Fe alloy layer 15 can be read as the distance between 1 / 10 of the maximum values of Ni and Fe in the area before and after the intersection of the Ni curve and the Fe curve in the results obtained by SEM-EDX (energy dispersive X-ray spectroscopy) as shown in Fig. 2. Fig. 2 is an example of the above analysis results, with the horizontal axis representing the distance (µm) in the depth direction from the surface layer and the vertical axis representing the X-ray intensity of Ni and Fe.

[0016] In this embodiment, the metal elements contained in the Ni-Fe alloy layer 15 are not limited to Ni and Fe, and other metal elements may be contained as long as the object of the present invention can be achieved. For example, the Ni-Fe alloy layer 15 may contain metal elements such as Co and Mo, as well as unavoidable impurities. The proportion of metal elements other than Ni and Fe in the Ni-Fe alloy layer 15 is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 1 wt% or less, and particularly preferably 0.5 wt% or less.

[0017] In this embodiment, we will explain the effect of reducing hydrogen permeation by the Ni-Fe alloy layer 15. That is, the bipolar electrode of the metal hydride battery of this embodiment has the effect of reducing hydrogen permeation by the Ni-Fe alloy layer 15 contained in the current collector. The discharge reaction of a nickel metal hydride battery can be expressed as follows: Positive electrode: NiOOH + H2O + e- → Ni(OH)2+ OH - Negative electrode: MH + OH - → M + HO + e - Furthermore, the reaction at the negative electrode consists of the following two reactions: M-H = M + H + + e - H + + OH - = H2O During the reaction, electrons e - Hydroxyl ions (OH) move from the negative electrode to the positive electrode through the current collector. - The electrons move from the positive electrode to the negative electrode of the adjacent bipolar electrode through the electrolyte. Outside the battery, electrons move from the negative electrode to the positive electrode through an external circuit (load).

[0018] On the other hand, if the current collector of the bipolar electrode allows hydrogen permeation, the following reaction occurs at the positive and negative electrodes even when the electrode is not connected to an external circuit. Positive electrode: NiOOH + H + + e - → Ni(OH)2 H → H + + e - Negative electrode: H + + e - → H M-H → M + H + + e -

[0019] Due to the hydrogen concentration gradient that occurs between the negative electrode active material layer (metal hydride MH) and the positive electrode active material layer, hydrogen atoms [H] are generated in the negative electrode active material layer through the above reaction. The hydrogen atoms [H] migrate from the negative electrode active material layer through the current collector to the positive electrode active material layer, which is the counter electrode. The hydrogen atoms [H] that migrate to the positive electrode are consumed at the positive electrode as shown in the above reaction equation, resulting in a constant hydrogen concentration gradient between the negative electrode active material layer and the positive electrode active material layer. As a result, this reaction cycle repeats, causing the positive electrode potential to continuously decrease and the negative electrode potential to continuously increase, resulting in a decrease in battery voltage. Although the above reaction differs from the reactions that occur at the positive and negative electrodes during normal discharge, it is the same as the reaction result of the active materials, and the potentials of the positive and negative electrodes decrease as a result of the reaction. The release of hydrogen from the metal hydride is an endothermic reaction, and the higher the potential, the more reactive the active material is. Therefore, the above reaction becomes more pronounced at high potentials and temperatures. During the reaction, electrons e - No migration occurs through the current collector.

[0020] Therefore, the present inventors conceived of forming a coating on the steel sheet constituting the current collector that reduces hydrogen permeation to the counter electrode. Specifically, they conceived of forming a Ni-Fe alloy layer on at least one surface of the steel sheet.

[0021] It has been known that the delayed fracture phenomenon (hydrogen embrittlement) of steel is controlled by the diffusion of hydrogen. These conventional techniques are used to verify the effect of hydrogen retention in steel on the mechanical properties of the steel itself.

[0022] On the other hand, no technology is known for reducing hydrogen permeation through a steel sheet, assuming a hydrogen concentration gradient occurring on both sides of the steel sheet, as in the bipolar electrode of the present invention. As a result of extensive research, the inventors have found that it is possible to reduce hydrogen permeation through the steel sheet that serves as the current collector material for the bipolar electrode by forming a Ni-Fe alloy layer on at least one side of the steel sheet.

[0023] The hydrogen permeation reduction effect of the Ni-Fe alloy layer on steel sheets was evaluated using the electrochemical hydrogen permeation method as follows. Figure 3 shows a schematic diagram of the hydrogen permeation test apparatus used for this evaluation. The hydrogen permeation test apparatus consists of two electrolytic cells, EC1 and EC2, arranged facing each other across a test specimen W. In Figure 3, electrolytic cell EC1 on the left is the cathode (hydrogen entry side), and electrolytic cell EC2 on the right is the anode (hydrogen detection side). Hydrogen is generated in electrolytic cell EC1, and the anode current is measured as the hydrogen permeates through the test specimen W and reaches electrolytic cell EC2. In the figure, RE1 and RE2 are reference electrodes, CE1 and CE2 are counter electrodes, and WE is the working electrode of the test specimen W. These electrodes are connected to potentiostat PS and potentio-galvanostat PS / GS, respectively. Reference electrodes RE1 and RE2 can be Hg / HgO or calomel electrodes. Counter electrodes CE1 and CE2 can be platinum. The electrolyte Ea may be an alkaline electrolyte containing KOH, NaOH, or LiOH.

[0024] A voltage is applied to the counter electrode CE1 using a potentio-galvanostat PS / GS so that the potential on the hydrogen entry side is -0.6 V, -0.45 V, or -0.3 V (vs. RHE (reversible hydrogen electrode)), and the change in current on the hydrogen detection side is measured. The potential on the hydrogen detection side is maintained at +1.45 V (vs. RHE). The liquid temperature is maintained at 65°C, and the solution is deaerated with N2 gas during the test. By measuring and comparing the hydrogen permeation current of various test pieces W, it is possible to consider the effectiveness of test pieces simulating current collectors in reducing hydrogen permeation.

[0025] Using the above hydrogen permeation test device, the hydrogen permeation current was measured using the following two types of test pieces. The results are shown in Figure 4. (Test piece W1) Surface-treated steel sheet with 5 μm thick Ni plating on both sides (Test piece W2) A surface-treated steel sheet with a 3.5 μm thick Ni-Fe alloy layer formed on both sides and a 1 μm thick Ni plating layer formed on the Ni-Fe alloy layer. The steel sheet used was a cold-rolled foil (thickness: 50 μm) of low-carbon aluminum-killed steel. The Ni-plated layer and Ni—Fe alloy layer were formed by the methods described in Examples below.

[0026] For the reason described above, in this embodiment, it is particularly preferable that the Ni—Fe alloy layer 15 be provided on the surface of the steel plate 13 on the negative electrode active material layer 20 side.

[0027] Due to the presumed mechanism of the hydrogen permeation phenomenon as described above, it is preferable that the Ni—Fe alloy layer 15 is provided at least on the surface of the steel sheet 13 on the side of the negative electrode active material layer 20, as shown in Fig. 1(a). That is, the Ni—Fe alloy layer 15 formed between the negative electrode active material layer 20 and the steel sheet 13 prevents hydrogen released by the negative electrode active material layer 20 (i.e., hydrogen storage alloy: metal hydride) from permeating through the steel sheet 13, thereby further reducing hydrogen permeation.

[0028] Furthermore, as shown in FIG. 1(b), it is more preferable that the Ni-Fe alloy layer 15 is provided on both sides of the steel plate 13. That is, in FIG. 1(b), the Ni-Fe alloy layer 15a is provided on the first side of the steel plate 13, and the Ni-Fe alloy layer 15b is provided on the second side on the opposite side. With this configuration, even if hydrogen released from the negative electrode active material layer 20 (i.e., the hydrogen storage alloy: metal hydride) permeates through the Ni-Fe alloy layer 15a and the steel plate 13, it is believed that the hydrogen is captured by the Ni-Fe alloy layer 15b before reaching the positive electrode active material layer 30, thereby avoiding the above-mentioned voltage drop problem. Note that the first side of the steel plate 13 is the same side as the first side (10A) of the current collector. The "both sides" of the steel plate 13 refer to the first side and the second side opposite to the first side.

[0029] When the thickness of the Ni-Fe alloy layer 15 is 1.0 μm or more, it is believed that a sufficient effect of reducing hydrogen permeation can be obtained by the Ni-Fe alloy layer 15. That is, when the thickness of the Ni-Fe alloy layer 15 in the current collector is 1.0 μm or more, it is believed that voltage drop in the battery can be effectively reduced. When the thickness of the Ni-Fe alloy layer 15 is less than 1.0 μm, the desired effect of reducing hydrogen permeation may not be obtained.

[0030] The thickness of the Ni—Fe alloy layer 15 is more preferably 1.2 μm or more, and even more preferably 1.5 μm or more. Furthermore, the Ni—Fe alloy layer 15 is preferably provided on both the first and second surfaces of the steel plate 13.

[0031] The thickness of the Ni-Fe alloy layer 15 can be calculated, for example, by SEM-EDX (energy dispersive X-ray spectroscopy). As described above, the SEM-EDX (energy dispersive X-ray spectroscopy) analysis involves linear analysis of Ni and Fe elements from the surface to a depth of 10 μm in the thickness direction. Measurement conditions can include an acceleration voltage of 10 kV, an observation magnification of 5000x, and a measurement step of 0.01 μm. As shown in FIG. 2, the horizontal axis represents the depth from the surface (μm), and the vertical axis represents the X-ray intensity of Ni and Fe. The distance between 1 / 10 of the maximum values of Ni and Fe, respectively, before and after the intersection of the Ni curve and the Fe curve, can be read from the graph to determine the thickness of the Ni-Fe alloy layer.

[0032] Preferably, the Ni-Fe alloy layer 15 is also provided on the negative terminal electrode, which will be described later. By forming the Ni-Fe alloy layer on the negative terminal electrode, it is possible to reduce the decrease in discharge reserve in a cell (single battery) that includes the negative terminal electrode, which occurs when hydrogen permeates through the negative terminal electrode and leaks to the outside of the battery.

[0033] Next, the active material layers (negative electrode active material layer 20 and positive electrode active material layer 30) of this embodiment will be described. In this embodiment, the negative electrode active material layer 20 contains a negative electrode active material, and optionally contains a negative electrode additive, a binder, and a conductive aid. The positive electrode active material layer 30 contains a positive electrode active material, and optionally contains a positive electrode additive, a binder, and a conductive aid. Hereinafter, matters relating to both the positive electrode active material layer and the negative electrode active material layer will be collectively described as active material layers.

[0034] In this embodiment, the negative electrode active material contained in the negative electrode active material layer 20 is not limited as long as it is used as a negative electrode active material for a nickel-metal hydride battery, i.e., a hydrogen storage alloy (metal hydride). A hydrogen storage alloy is basically an alloy of metal A, which reacts easily with hydrogen but has poor hydrogen release capacity, and metal B, which does not react easily with hydrogen but has excellent hydrogen release capacity. Examples of A include Group 2 elements such as Mg, Group 3 elements such as Sc and lanthanides, Group 4 elements such as Ti and Zr, Group 5 elements such as V and Ta, misch metals containing multiple rare earth elements (hereinafter sometimes abbreviated as Mm), and Pd. Examples of B include Fe, Co, Ni, Cr, Pt, Cu, Ag, Mn, Zn, and Al.

[0035] Specific hydrogen storage alloys include AB5 type, which exhibits a hexagonal CaCu5 type crystal structure; AB2 type, which exhibits a hexagonal MgZn2 type or cubic MgCu2 type crystal structure; AB type, which exhibits a cubic CsCl type crystal structure; A2B type, which exhibits a hexagonal Mg2Ni type crystal structure; solid solution type, which exhibits a body-centered cubic structure; and AB3 type, A2B7 type, and A5B type, which are combinations of the AB5 type and AB2 type crystal structures. 19 The hydrogen storage alloy may have one of the above crystal structures, or may have a plurality of the above crystal structures.

[0036] Examples of AB5 type hydrogen storage alloys include LaNi5, CaCu5, and MmNi5. Examples of AB2 type hydrogen storage alloys include MgZn2, ZrNi2, and ZrCr2. Examples of AB type hydrogen storage alloys include TiFe and TiCo. Examples of A2B type hydrogen storage alloys include Mg2Ni and Mg2Cu. Examples of solid solution type hydrogen storage alloys include Ti-V, V-Nb, and Ti-Cr. Examples of AB3 type hydrogen storage alloys include CeNi3. Examples of A2B7 type hydrogen storage alloys include Ce2Ni7. A5B 19 As a hydrogen storage alloy, Ce5Co 19 , Pr5Co 19 In each of the above crystal structures, a portion of the metal may be substituted with one or more other metals or elements.

[0037] The surface of the negative electrode active material may be treated by a known method. In particular, it is preferable to use an alkali-treated hydrogen storage alloy as the negative electrode active material. The alkali treatment means treating the hydrogen storage alloy with an alkaline aqueous solution in which an alkali metal hydroxide is dissolved.

[0038] For example, when a hydrogen storage alloy containing rare earth elements and Ni is treated with an alkaline aqueous solution containing an alkali metal hydroxide, the rare earth elements, which are highly soluble in alkaline aqueous solutions, are eluted from the surface of the hydrogen storage alloy. Because Ni has low solubility in alkaline aqueous solutions, the Ni concentration at the surface of the hydrogen storage alloy is higher than that at the interior of the alloy. Hereinafter, the portion of the hydrogen storage alloy where the Ni concentration is higher than that at the interior is referred to as the Ni-enriched layer. The presence of the Ni-enriched layer is believed to improve the performance of the negative electrode active material.

[0039] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, and among these, sodium hydroxide is preferred. By using a sodium hydroxide aqueous solution as the alkaline aqueous solution, the battery characteristics of the nickel metal hydride battery of the present invention may be more favorable than when using lithium hydroxide or potassium hydroxide as the alkaline aqueous solution.

[0040] The alkaline aqueous solution is preferably a strongly basic one. The concentration of the alkali metal hydroxide in the alkaline aqueous solution can be, for example, 10 to 60 mass %, 20 to 55 mass %, 30 to 50 mass %, or 40 to 50 mass %.

[0041] The alkali treatment is preferably carried out by immersing the hydrogen storage alloy in an alkaline aqueous solution. This is preferably carried out under stirring conditions, and is also preferably carried out under heated conditions. Examples of the heating temperature range include 50 to 150°C, 70 to 140°C, and 90 to 130°C. The heating time may be determined appropriately depending on the concentration of the alkaline aqueous solution and the heating temperature, and examples of the heating time include 0.1 to 10 hours, 0.2 to 5 hours, and 0.5 to 3 hours.

[0042] From the viewpoint of the above-mentioned alkali treatment, it is preferable that the hydrogen storage alloy contains a rare earth element and Ni.

[0043] The negative electrode active material is preferably in a powder state, and the average particle size thereof is preferably in the range of 1 to 100 μm, more preferably in the range of 3 to 50 μm, and even more preferably in the range of 5 to 30 μm.

[0044] The negative electrode active material layer preferably contains the negative electrode active material in an amount of 85 to 99 mass %, and more preferably 90 to 98 mass %, based on the mass of the entire negative electrode active material layer.

[0045] The negative electrode additive is added to the negative electrode to improve the battery characteristics of the nickel metal hydride battery. The negative electrode additive is not limited as long as it is used as a negative electrode additive for the nickel metal hydride battery. Specific negative electrode additives include rare earth element fluorides such as CeF3 and YF3, bismuth compounds such as Bi2O3 and BiF3, indium compounds such as In2O3 and InF3, and the compounds exemplified as positive electrode additives.

[0046] The negative electrode active material layer preferably contains the negative electrode additive in an amount of 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, based on the mass of the entire negative electrode active material layer.

[0047] Next, the positive electrode active material contained in the positive electrode active material layer 30 of this embodiment may be any nickel hydroxide that is used as a positive electrode active material in nickel metal hydride batteries, and may be partially doped with other metals. Specific examples of the positive electrode active material include nickel hydroxide and metal-doped nickel hydroxide. Examples of metals that can be doped into nickel hydroxide include Group 2 elements such as magnesium and calcium, Group 9 elements such as cobalt, rhodium, and iridium, and Group 12 elements such as zinc and cadmium.

[0048] The surface of the positive electrode active material may be treated by a known method. The positive electrode active material is preferably in a powder state, and its average particle size is preferably in the range of 1 to 100 μm, more preferably in the range of 3 to 50 μm, and even more preferably in the range of 5 to 30 μm. In this specification, the average particle size refers to the D50 value measured using a general laser diffraction particle size distribution analyzer.

[0049] The positive electrode active material layer preferably contains the positive electrode active material in an amount of 75 to 99 mass %, more preferably 80 to 97 mass %, and even more preferably 85 to 95 mass %, based on the mass of the entire positive electrode active material layer.

[0050] The positive electrode additive is added to the positive electrode of a nickel metal hydride battery to improve its battery characteristics. The positive electrode additive is not limited as long as it is suitable for use as a positive electrode additive in a nickel metal hydride battery. Specific examples of the positive electrode additive include niobium compounds such as NbO, tungsten compounds such as WO, WO, LiWO, NaWO, and KWO, ytterbium compounds such as YbO, titanium compounds such as TiO, yttrium compounds such as YO, zinc compounds such as ZnO, calcium compounds such as CaO, Ca(OH), and CaF, and other rare earth oxides.

[0051] The positive electrode active material layer preferably contains the positive electrode additive in an amount of 0.1 to 10 mass %, more preferably 0.5 to 5 mass %, based on the mass of the entire positive electrode active material layer.

[0052] In this embodiment, the binder and the conductive additive that are optionally contained in the active material layer will be described below.

[0053] The binder serves to bind the active material and the like to the surface of the current collector. The binder is not limited as long as it is used as a binder for electrodes of nickel metal hydride batteries. Specific examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; polyolefin resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose; copolymers such as styrene-butadiene rubber; and (meth)acrylic resins such as polyacrylic acid, polyacrylic acid esters, polymethacrylic acid, and polymethacrylic acid esters, which contain (meth)acrylic acid derivatives as monomer units.

[0054] The active material layer preferably contains 0.1 to 15 mass % of the binder, more preferably 1 to 10 mass %, and even more preferably 2 to 7 mass %, based on the total mass of the active material layer, because too little binder reduces the formability of the electrode, and too much binder reduces the energy density of the electrode.

[0055] The conductive additive is added to increase the conductivity of the electrode. Therefore, the conductive additive may be added optionally when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive additive may be added to the active material layer in a powder form, or may be used in a state in which it coats the surfaces of the active material particles. Any chemically inactive electron conductor may be used as the conductive additive. Specific examples of the conductive additive include metals such as cobalt, nickel, and copper; metal oxides such as cobalt oxide; metal hydroxides such as cobalt hydroxide; and carbon materials such as carbon black, graphite, and carbon fiber.

[0056] The negative electrode active material layer 20 preferably contains 0.1 to 5 mass % of the conductive additive, more preferably 0.2 to 3 mass %, and even more preferably 0.3 to 1 mass %, relative to the mass of the entire negative electrode active material layer. The positive electrode active material layer 30 preferably contains 0.1 to 10 mass % of the conductive additive, more preferably 0.2 to 7 mass %, and even more preferably 0.3 to 5 mass %, relative to the mass of the entire positive electrode active material layer.

[0057] <Bipolar electrode for metal hydride battery: second embodiment> Next, the bipolar electrode of the metal hydride battery of the present invention will be described in more detail using the following second embodiment. Note that this embodiment differs from the first embodiment in that a Ni layer 17 is formed on at least one outermost surface of the current collector 10. Therefore, these differences will be mainly described, and components having the same functions as those in the first embodiment will be assigned the same reference numerals and their description will be omitted as appropriate.

[0058] As shown in FIG. 5(a), in the bipolar electrode 200 of the metal hydride battery of this embodiment, a Ni layer 17 is formed on the outermost surface on the same side as one surface (first surface) 10A of the current collector 10. That is, a Ni layer 17 is further formed between the Ni—Fe alloy layer 15 and the negative electrode active material layer 20. Note that in this embodiment, as shown in FIG. 5(b), a Ni layer 17a may be formed on the outermost surface on the same side as one surface (first surface) 10A of the current collector 10, and a Ni layer 17b may be formed on the outermost surface on the same side as the other surface (second surface) 10B. Note that in FIG. 5(b), a Ni layer 17a is further formed between the Ni—Fe alloy layer 15a and the negative electrode active material layer 20, and a Ni layer 17b is further formed between the Ni—Fe alloy layer 15b and the positive electrode active material layer 30.

[0059] The thickness of the Ni layer 17 is not particularly limited, but is preferably, for example, 0.1 μm to 10.0 μm.

[0060] The metal element contained in the Ni layer 17 is not limited to Ni, and other metal elements may be contained. For example, the Ni layer 17 may contain metal elements such as Co and Mo. The proportion of metal elements other than Ni in the Ni layer 17 is preferably 10 wt% or less, more preferably 5 wt% or less, even more preferably 1 wt% or less, and particularly preferably 0.5 wt% or less.

[0061] The Ni layer 17 can be formed by leaving a Ni layer in which Fe is not diffused during heat treatment to form the Ni-Fe alloy layer 15, or by forming the Ni-Fe alloy layer 15 and then performing Ni plating again. From the viewpoint of corrosion resistance to the electrolytic solution, the above-mentioned method of providing the Ni layer 17 by Ni plating again is preferred, and examples of plating methods include electrolytic plating and electroless plating. Of these, electrolytic plating is particularly preferred from the viewpoints of cost, film thickness control, etc.

[0062] In this embodiment, the Ni layer 17 may be a roughened Ni layer 17c. The roughened Ni layer 17c refers to a Ni layer having a surface roughness greater than that of the Ni-Fe alloy layer 15 or the steel plate 13 on the surface in contact with the negative electrode active material layer 20 or the positive electrode active material layer 30. By forming the Ni layer 17 as the roughened Ni layer 17c, the bonding strength between the current collector 10 and the bonding member can be improved. For example, at the bonding interface between the current collector 10 and the sealing portion (described later), molten resin penetrates between the multiple protrusions, thereby exerting an anchoring effect. This improves the bonding strength between the bipolar electrode of this embodiment and the sealing member. Furthermore, the provision of the roughened Ni layer 17c increases the surface area, thereby improving the heat dissipation properties of the electrode.

[0063] The surface roughness of the roughened Ni layer 17c can be expressed numerically using known parameters. For example, the parameter can be defined by the ten-point average roughness Rzjis, and Rzjis is preferably 2.0 μm to 16.0 μm. The ten-point average roughness Rzjis is measured in accordance with JIS B0601:2013, and is preferably measured using a laser microscope.

[0064] 5(c), when the roughened Ni layer 17c is formed, an underlying Ni layer 17d may be formed between the Ni-Fe alloy layer 15 and the roughened Ni layer 17c as appropriate. By providing the underlying Ni layer 17d with a thickness of about 0.1 μm to 10 μm, it is possible to obtain effects such as improving the adhesion of the roughened Ni layer 17c and suppressing the occurrence of pinholes.

[0065] <Bipolar electrode manufacturing method> Next, a method for manufacturing a bipolar electrode for a metal hydride battery according to the present invention will be described with reference to the following embodiment. The method for manufacturing a bipolar electrode for a metal hydride battery according to this embodiment includes a current collector forming step (step 1) and an active material layer forming step (step 2). The current collector forming step (step 1) includes a step of providing a Ni layer on at least one surface of a steel sheet (step 1a), and a step of heat-treating the steel sheet with the Ni layer to diffuse Ni in the Ni layer and Fe in the steel sheet, thereby forming a Ni-Fe alloy layer (step 1b). The current collector forming step (step 1) may further include a roughened Ni layer forming step (step 1c). The active material layer forming step (step 2) includes a step of forming a negative electrode active material layer on a first surface of the current collector (step 2a), and a step of providing a positive electrode active material layer on a second surface of the current collector (step 2b).

[0066] Step 1a will be described in detail below. For example, a Ni layer is formed on the surface of the steel sheet by electroplating using a Ni plating bath. The Ni plating bath may be a plating bath commonly used in Ni plating, such as a Watts bath, a citric acid bath, a sulfamic acid bath, a boron fluoride bath, or a chloride bath. For example, the Ni layer may be formed using a Watts bath with a bath composition of 200-350 g / L of nickel sulfate hexahydrate, 20-60 g / L of nickel chloride hexahydrate, and 10-50 g / L of boric acid, at a pH of 1.5-5.0, a bath temperature of 40-80°C, and a current density of 1-40 A / dm 2 The Ni layer can be formed under the following conditions: The thickness of the Ni layer is preferably 0.05 to 5.0 μm, and more preferably 0.1 to 3.0 μm.

[0067] Regarding step 1b, the heat treatment may be performed by either a continuous annealing method or a box annealing method (batch annealing). The heat treatment conditions may be appropriately selected depending on the required thickness of the Ni-Fe alloy layer and the Ni plating layer. For example, when continuous annealing is used, the heat treatment temperature is preferably set to 700 to 800°C, and the heat treatment time is preferably set to 10 to 300 seconds. When box annealing is used, the heat treatment temperature is preferably set to 450 to 600°C, the heat treatment time is preferably set to 1 to 10 hours, and the heat treatment atmosphere is preferably a non-oxidizing atmosphere or a reducing protective gas atmosphere. When the heat treatment atmosphere is a reducing protective gas atmosphere, the protective gas is preferably a 75% hydrogen-25% nitrogen protective gas produced by the ammonia crack method known as hydrogen-enriched annealing, which has good heat transfer. Then, by thermal diffusion during the heat treatment, a Ni-Fe alloy layer can be formed in which the Ni in the Ni layer and the Fe in the steel sheet are diffused. In this case, the structure may be such that Fe diffuses up to the surface of the Ni layer, or a part of the Ni layer may remain in which Fe has not diffused.

[0068] Regarding step 1c, a roughened Ni layer can be formed on the Ni-Fe alloy layer formed in step 1b by depositing nickel particles in an aggregated state using a method such as electroplating. That is, the roughened Ni layer is present between the Ni-Fe alloy layer and the negative electrode active material layer or the positive electrode active material layer. The roughened Ni layer formed in step 1c has a surface roughness greater than that of the Ni-Fe alloy layer or the steel sheet on the surface that contacts the negative electrode active material layer 20 or the positive electrode active material layer 30 formed in the active material layer formation step (step 2) described below. Note that, in addition to electroplating, methods such as sputtering and a roll press with a roughened surface can also be used to form the roughened Ni layer in step 1c. Furthermore, step 1c may include a step of forming a base Ni layer before forming the roughened Ni layer.

[0069] Regarding step 2, to form an active material layer on the surface of the current collector, the active material may be applied to the surface of the current collector using a conventionally known method such as roll coating, die coating, dip coating, doctor blade coating, spray coating, or curtain coating. Specifically, the active material, solvent, and optionally a binder, conductive additive, and additive are mixed to form a slurry, which is then applied to the surface of the current collector and dried. Examples of solvents include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried electrode may be compressed to increase electrode density. The order in which the active material layers are formed on the surfaces of the current collector may be such that the negative electrode active material layer is formed first and then the positive electrode active material layer, or the reverse order may be used. The negative electrode active material layer and the positive electrode active material layer may be formed simultaneously. That is, the order in which the active material layer formation step (step 2) is performed is not limited as long as it includes the step of forming the negative electrode active material layer on the first surface of the current collector (step 2a) and the step of forming the positive electrode active material layer on the second surface of the current collector (step 2b).

[0070] <Metal hydride battery and its manufacturing method> The metal hydride battery of the present invention is characterized by being composed of a stack of bipolar electrodes of the present invention. Other configurations may be those disclosed in documents such as JP 2020-140773 A. That is, the metal hydride battery of the present invention comprises a bipolar electrode having a negative electrode active material layer on a first surface of a current collector and a positive electrode active material layer on a second surface. As described above, the current collector comprises a steel plate and a Ni-Fe alloy layer provided on at least one surface of the steel plate. The number of bipolar electrodes in the metal hydride battery of the present invention may be one or more, and can be increased or decreased depending on the desired capacity. The metal hydride battery of the present invention can be manufactured by placing a separator between the bipolar electrodes and airtightly sealing them after injecting an electrolyte. The metal hydride battery of the present invention is, for example, a nickel-metal hydride battery.

[0071] The metal hydride battery of the present invention will be described below using a nickel metal hydride battery as an example of an embodiment, but the present invention is not limited to this.

[0072] 6 is a schematic cross-sectional view showing one embodiment of a power storage device. The power storage device 1 includes a module stack 2 including a plurality of stacked power storage modules 4, and a restraining member 3 that applies a restraining load to the module stack 2 in the stacking direction D of the module stack 2.

[0073] The module stack 2 includes a plurality of power storage modules 4 and a plurality of cooling plates 5. In this embodiment, three power storage modules 4 and four cooling plates 5 are alternately stacked so that the cooling plates 5 are located on both sides of the power storage modules 4. Hereinafter, the direction in which the power storage modules 4 are stacked is referred to as the "stacking direction D." Furthermore, the direction intersecting or perpendicular to the stacking direction D is referred to as the horizontal direction.

[0074] The energy storage module 4 is a bipolar metal hydride battery and has a rectangular shape when viewed from the stacking direction D. In the following description, a nickel metal hydride battery is used as the energy storage module 4. Adjacent energy storage modules 4 in the stacking direction D are electrically connected via a cooling plate 5. In the module stack 2, a negative electrode terminal 6 is connected to the cooling plate 5 located at one end in the stacking direction D. A positive electrode terminal 7 is connected to the cooling plate 5 located at the other end in the stacking direction D. The negative electrode terminal 6 and the positive electrode terminal 7 are drawn out, for example, from the edge of the cooling plate 5 in a direction intersecting the stacking direction D. The negative electrode terminal 6 and the positive electrode terminal 7 are connected to an external circuit, such as a vehicle (not shown), and the energy storage device 1 is charged and discharged by the external circuit. The cooling plate 5 is made of aluminum.

[0075] In this embodiment, the outermost layer (outermost layer of the stack) of the module stack 2 is the cooling plate 5, but the outermost layer of the module stack 2 may be the power storage module 4. In this case, the negative electrode terminal 6 or the positive electrode terminal 7 is connected to the power storage module 4 that constitutes the outermost layer of the stack.

[0076] The cooling plate 5 has a plurality of flow paths 5a formed therein for circulating a refrigerant such as air, and dissipates heat generated in the electricity storage modules 4 to the outside of the electricity storage device 1. The flow paths 5a extend, for example, along a direction intersecting (orthogonal to) the stacking direction D and the direction in which the negative electrode terminals 6 and the positive electrode terminals 7 are drawn out. The cooling plate 5 is electrically conductive and functions as a connecting member that electrically connects the electricity storage modules 4 to each other. The cooling plate 5 also functions as a heat dissipation plate that dissipates heat generated in the electricity storage modules 4 by circulating a refrigerant through these flow paths 5a. In this embodiment, the area of the cooling plate 5 is smaller than the area of the electricity storage modules 4 in a plan view seen from the stacking direction D. However, from the viewpoint of improving heat dissipation, the area of the cooling plate 5 may be the same as or larger than the area of the electricity storage modules 4 in a plan view seen from the stacking direction D. Furthermore, the electricity storage modules 4 may be heated by circulating a high-temperature refrigerant through the flow paths 5a.

[0077] The restraining member 3 has a pair of end plates 8 that sandwich the module stack 2 in the stacking direction D, and fastening bolts 81 and nuts 82 that fasten the end plates 8 together. The end plates 8 are rectangular metal plates that are slightly larger than the energy storage modules 4 and cooling plates 5 in a plan view seen from the stacking direction D. An insulating film F is disposed between the end plates 8 and the module stack 2. The film F provides insulation between the end plates 8 and the module stack 2.

[0078] Insertion holes 8a are provided at the edges of the end plates 8 at positions that are outer than the module stack 2 when viewed from the stacking direction D. Fastening bolts 81 are passed through the insertion holes 8a of one end plate 8 toward the insertion holes 8a of the other end plate 8. Nuts 82 are threaded onto the tips of the fastening bolts 81 that protrude from the insertion holes 8a of the other end plate 8. In this way, the energy storage modules 4 and the cooling plates 5 are sandwiched between the two end plates 8 and unitized as the module stack 2. A restraint load is applied to the module stack 2 in the stacking direction D.

[0079] Next, the configuration of the energy storage module 4 will be described in detail. Fig. 7 is a schematic cross-sectional view showing the internal configuration of the energy storage module shown in Fig. 6. As shown in Fig. 7, the energy storage module 4 includes an electrode stack (cell stack) 11, conductive plates 40 located on both outer sides of the electrode stack 11 in the stacking direction D, and a resin seal portion 12 that integrates the electrode stack 11 and the conductive plates 40.

[0080] The electrode stack 11 is composed of multiple electrodes stacked along the stacking direction D of the energy storage module 4 with separators SP interposed between them. These electrodes include a stack of multiple bipolar electrodes 100 (200), a negative terminal electrode 18, and a positive terminal electrode 19. The bipolar electrodes 100 (200) and separators SP are rectangular when viewed from the stacking direction D.

[0081] The bipolar electrode 100 (200) has a current collector 10 including one surface (first surface) 10A and another surface (second surface) 10B opposite to the one surface 10A, a negative electrode active material layer 20 provided on the one surface 10A, and a positive electrode active material layer 30 provided on the other surface 10B. The positive electrode active material layer 30 is formed by coating the current collector 10 with a positive electrode active material. The negative electrode active material layer 20 is formed by coating the current collector 10 with a negative electrode active material. In the electrode stack 11, the positive electrode active material layer 30 of one bipolar electrode 100 (200) faces the negative electrode active material layer 20 of another bipolar electrode 100 (200) adjacent to it on one side of the stacking direction D, with a separator SP sandwiched therebetween. In the electrode stack 11, the negative electrode active material layer 20 of one bipolar electrode 100 (200) faces the positive electrode active material layer 30 of another adjacent bipolar electrode 100 (200) on the other side in the stacking direction D, with the separator SP sandwiched therebetween.

[0082] The negative electrode terminal electrode 18 has a current collector 10 and a negative electrode active material layer 20 provided on one surface 10A of the current collector 10. The negative electrode terminal electrode 18 is disposed at one end of the electrode laminate 11 in the stacking direction D so that the one surface 10A faces the center of the electrode laminate 11 in the stacking direction D. The other surface 10B of the current collector 10 of the negative electrode terminal electrode 18 constitutes the outer surface of the electrode laminate 11 in the stacking direction D and is electrically connected to one of the cooling plates 5 (see FIG. 6 ) adjacent to the energy storage module 4 via a conductive plate 40. The negative electrode active material layer 20 of the negative electrode terminal electrode 18 faces the positive electrode active material layer 30 of the bipolar electrode 100 (200) via a separator SP.

[0083] The positive terminal electrode 19 has a current collector 10 and a positive electrode active material layer 30 provided on the other surface 10B of the current collector 10. The positive terminal electrode 19 is arranged at the other end of the electrode laminate 11 in the stacking direction D so that the other surface 10B faces the center of the electrode laminate 11 in the stacking direction D. The positive electrode active material layer 30 of the positive terminal electrode 19 faces the negative electrode active material layer 20 of the bipolar electrode 100 (200) via a separator SP. One surface 10A of the current collector 10 of the positive terminal electrode 19 forms the outer surface of the electrode laminate 11 in the stacking direction D and is electrically connected to the other cooling plate 5 (see FIG. 6 ) adjacent to the energy storage module 4 via a conductive plate 40.

[0084] The current collector 10 is a plated steel sheet. An edge portion 10C of the current collector 10 is an uncoated region where the positive electrode active material and the negative electrode active material are not coated, and has a rectangular frame shape. The positive electrode active material constituting the positive electrode active material layer 30 may be any of the above-described positive electrode active materials. The negative electrode active material constituting the negative electrode active material layer 20 may be any of the above-described negative electrode active materials. In this embodiment, the formation region of the negative electrode active material layer 20 on one surface 10A of the current collector 10 is slightly larger than the formation region of the positive electrode active material layer 30 on the other surface 10B of the current collector 10.

[0085] The conductive plate 40 is a conductive plate-like member provided to suppress deterioration of the electrode stack 11. The conductive plate 40 is an uncoated foil on both sides of which no active material layer is formed. The conductive plate 40 is made of, for example, nickel. The conductive plate 40 has a central portion 41 that contacts the cooling plate 5 and a rectangular frame-shaped edge portion 42 that surrounds the central portion 41. The edge portion 42 is a portion that is held by the sealing body (seal portion) 12. The thickness of the conductive plate 40 is, for example, 0.1 μm or more and 1000 μm or less. The conductive plate 40 forms the outer wall of the energy storage module 4 at both ends in the stacking direction D. If the conductive plate 40 is not provided, the negative electrode terminal electrode 18 and the positive electrode terminal electrode 19 form the outer wall.

[0086] The seal portion 12 is formed, for example, from an insulating resin, into a rectangular frame shape as a whole. The seal portion 12 is provided along the side surface 11a of the electrode stack 11 so as to surround the edge portion 10C of the current collector 10 and the edge portion 42 of the conductive plate 40. The seal portion 12 holds the edge portion 10C of the current collector 10 and the edge portion 42 of the conductive plate 40. The seal portion 12 has a plurality of first seal portions 21 joined to the edge portion 10C of the current collector 10 and the edge portion 42 of the conductive plate 40, and second seal portions 22 that surround the first seal portions 21 from the outside along the side surface 11a and are joined to each of the first seal portions 21. The first seal portions 21 and the second seal portions 22 are made of, for example, polypropylene.

[0087] The first seal portion 21 is provided continuously around the entire periphery of the edge portion 42 of the conductive plate 40, or around the entire periphery of the edge portion 10C on the other surface 10B of the current collector 10, and forms a rectangular frame when viewed from the stacking direction D. In the negative electrode terminal electrode 18 and the positive electrode terminal electrode 19, the first seal portion 21 is provided on the edge portions 10C of both the one surface 10A and the other surface 10B of the current collector 10.

[0088] The first seal portion 21 is hermetically welded to the edge portion 42 of the conductive plate 40 or the other surface 10B of the current collector 10, for example, by ultrasonic or thermocompression bonding, and is airtightly joined. The first seal portion 21 is, for example, a film having a predetermined thickness in the stacking direction D. The first seal portion 21 may be formed by punching a resin sheet, by arranging multiple resin sheets in a frame shape, or by injection molding using a mold. In this embodiment, the first seal portion 21 is formed by punching a resin sheet. The thickness of the first seal portion 21 is, for example, 50 μm or more and 250 μm or less. The inner sides of the first seal portion 21 are located between the edge portions 10C of the current collectors 10 adjacent to each other in the stacking direction D. The outer sides of the first seal portion 21 protrude outward beyond the edges of the current collector 10, and their leading ends are held by the second seal portion 22. The first seal portions 21 adjacent to each other along the stacking direction D may be spaced apart or may be in contact with each other. Furthermore, the outer edge portions of the first seal portions 21 may be joined to each other by, for example, hot plate welding.

[0089] The second seal portion 22 is provided on the outside of the electrode stack 11 and the first seal portion 21, and constitutes the outer wall (housing) of the energy storage module 4. The second seal portion 22 is formed, for example, by injection molding of resin, and extends over the entire length of the electrode stack 11 along the stacking direction D. The second seal portion 22 has a rectangular frame shape that extends with the stacking direction D as its axial direction. The second seal portion 22 is welded to the outer surface of the first seal portion 21 by heat, for example, during injection molding.

[0090] The first seal portion 21 and the second seal portion 22 form an internal space V between adjacent electrodes and seal the internal space V. More specifically, the second seal portion 22, together with the first seal portion 21, seals the space between adjacent bipolar electrodes 100 (200) along the stacking direction D, the space between the negative terminal electrode 18 and the bipolar electrode 100 (200) along the stacking direction D, and the space between the positive terminal electrode 19 and the bipolar electrode 100 (200) along the stacking direction D. As a result, airtightly partitioned internal spaces V are formed between adjacent bipolar electrodes 100 (200), between the negative terminal electrode 18 and the bipolar electrode 100 (200), and between the positive terminal electrode 19 and the bipolar electrode 100 (200). This internal space V contains an electrolyte (not shown). The separator SP, the positive electrode active material layer 30, and the negative electrode active material layer 20 are impregnated with the electrolyte.

[0091] The bipolar electrode 100 (200) and the seal portion 12 adjacent to each other in the stacking direction D, the bipolar electrode 100 (200) and the seal portion 12 adjacent to the negative terminal electrode 18, and the bipolar electrode 100 (200) and the seal portion 12 adjacent to the positive terminal electrode 19 each constitute a cell (single battery).

[0092] Next, an example of a manufacturing method of the energy storage module according to this embodiment will be described. First, a first seal portion 21 is bonded to the bipolar electrode 100 (200), the negative terminal electrode 18, the positive terminal electrode 19, and the conductive plate 40 (first step). In the first step, the bipolar electrode 100 (200), the negative terminal electrode 18, the positive terminal electrode 19, and the conductive plate 40 are first prepared. Next, the first seal portion 21 is welded to the other surface 10B of the current collector 10 and one surface 40a of the conductive plate 40. This bonds the first seal portion 21 to each of the bipolar electrode 100 (200), the negative terminal electrode 18, the positive terminal electrode 19, and the conductive plate 40. Furthermore, the first seal portion 21 is also welded to one surface 10A of the current collector 10 of the positive terminal electrode 19.

[0093] Next, the electrode stack 11 is formed (second step). In the second step, first, the bipolar electrodes 100 (200) to which the first seal portions 21 are bonded and the separators SP are alternately stacked along the stacking direction D to form the stack S. Next, the negative electrode terminal electrode 18 is disposed at one end of the stack S in the stacking direction D, and the positive electrode terminal electrode 19 is disposed at the other end of the stack S in the stacking direction D. This forms the electrode stack 11 having the bipolar electrodes 100 (200), the separators SP, the negative electrode terminal electrode 18, and the positive electrode terminal electrode 19. At this time, the stacked first seal portions 21 form an internal space V between the electrodes included in the electrode stack 11 and seal the internal space V.

[0094] Next, the conductive plate 40 to which the first seal portion 21 is bonded is placed on the electrode stack 11 (third step). In the third step, the first seal portion 21 bonded to the conductive plate 40 is disposed adjacent to the negative terminal electrode 18 and the positive terminal electrode 19 in the stacking direction D.

[0095] Next, second seal portions 22 that connect the first seal portions 21 are formed (fourth step). In the fourth step, resin is injection-molded onto the outer peripheral surfaces of the first seal portions 21, for example, using a mold. The resin is then hardened by cooling or the like to form the second seal portions 22. This forms the seal portion 12, which has the first seal portion 21 and the second seal portion 22. At this time, a conductive plate 40 may be welded to each of the first seal portions 21 that connect to the negative terminal electrode 18 and the positive terminal electrode 19. Although not shown, after the fourth step, an electrolyte is injected into each internal space V. Through the above steps, the energy storage module 4 is manufactured.

[0096] The nickel metal hydride battery of this embodiment preferably includes various components that are arranged in known nickel metal hydride batteries. Hereinafter, a battery unit consisting of a positive terminal electrode, a bipolar electrode, a negative terminal electrode, and a separator will be referred to as a battery module. The nickel metal hydride battery of the present invention may include a single battery module or multiple battery modules connected in series.

[0097] Known separators may be used, including porous bodies, nonwoven fabrics, woven fabrics, and the like, made of one or more electrically insulating materials such as synthetic resins (e.g., polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (aromatic polyamide), polyester, and polyacrylonitrile), polysaccharides (e.g., cellulose and amylose), natural polymers (e.g., fibroin, keratin, lignin, and suberin), and ceramics. The separator may also have a multilayer structure. The separator preferably has a hydrophilic surface. Examples of hydrophilic treatments include sulfonation, corona treatment, fluorine gas treatment, and plasma treatment.

[0098] The electrolyte may be a strong basic aqueous solution commonly used as an electrolyte for nickel metal hydride batteries. Specific examples of strong basic aqueous solutions include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, and lithium hydroxide aqueous solution. The electrolyte may be a single strong basic aqueous solution or a mixture of multiple strong basic aqueous solutions. Furthermore, the electrolyte may contain known additives commonly used in electrolytes for nickel metal hydride batteries.

[0099] The nickel metal hydride battery of the present invention has a sealing portion provided between the electrodes to prevent leakage of the electrolyte, suppress intermixing of the electrolyte between the electrodes, and suppress contact of the electrolyte, the positive electrode active material layer, and the negative electrode active material layer with the outside air. The sealing portion is disposed in close contact with two adjacent current collectors and is disposed so as to entirely surround the area where the electrolyte, the positive electrode active material layer, and the negative electrode active material layer are present. The sealing portion may be disposed in two or three layers around the area where the electrolyte, the positive electrode active material layer, and the negative electrode active material layer are present.

[0100] Examples of materials for the sealing portion include insulating resins having alkali resistance, such as polypropylene, polyphenylene sulfide, and modified polyphenylene ether. Also, what is generally called a gasket or packing may be used as the sealing portion. The sealing portion may be formed by pressing the sealing portion material onto the current collector, by thermocompression bonding to the current collector, or by adhering to the current collector using an adhesive.

[0101] It is preferable that an insulating outer frame that does not conduct electricity is disposed around the periphery of the electrode. The outer frame serves to maintain the shape of the electrode and to prevent short circuits between the electrodes. The above-mentioned sealing portion is disposed inside the outer frame. The outer frame may also serve as the sealing portion. Examples of materials for the outer frame include synthetic resins, or synthetic resins containing insulating oxides or insulating ceramics.

[0102] The nickel metal hydride battery of the present invention preferably includes a cooling plate for dissipating heat generated during charging and discharging. The cooling plate is preferably disposed on the outside of the battery module along the electrode surface. When multiple battery modules are present, the cooling plate may be disposed between the battery modules.

[0103] The cooling plate is preferably made of a metal with excellent thermal conductivity, such as aluminum. The cooling plate is preferably in the form of a plate that can be stacked on the surface of the battery module, and more preferably has through holes in the plate that allow air cooling.

[0104] The battery module of the nickel metal hydride battery of the present invention is preferably restrained by a restraining device in the thickness direction, i.e., the stacking direction of the electrodes. By restraining the battery module in the stacking direction, the electrolyte can be evenly permeated into the positive electrode active material layers and the negative electrode active material layers, uneven expansion of the electrodes due to charging and discharging can be suppressed, and fluctuations in battery resistance can be suppressed. In addition, the sealing effect of the seal portion can be favorably maintained.

[0105] The restraining member may restrain one battery module or multiple battery modules. The restraining member preferably comprises two restraining plates and a fastening member that fastens the two restraining plates. Examples of the fastening member include bolts and nuts. The material of the restraining member is preferably one that is highly resistant to strong alkali. Specific examples of the material of the restraining member include synthetic resin and insulating ceramics. Furthermore, the battery container that houses the battery module may also be used as the restraining member.

[0106] The battery container is a container that houses the battery module. Any battery container that is used as a battery container for a known nickel metal hydride battery may be used. The shape of the battery container is not particularly limited, and various shapes such as a rectangular, cylindrical, coin, or laminated shape may be used. The material of the battery container is preferably one that is highly resistant to strong alkalis. Specific examples of the battery container include a nickel container, a resin container, a metal container whose inner surface is nickel-plated, and a metal container having a resin coating layer on its inner surface.

[0107] The restraining member or the battery container may be provided with a gas exhaust valve, and may also be provided with a liquid filling port for refilling the electrolyte.

[0108] The nickel metal hydride battery of the present invention may be installed in a vehicle or industrial vehicle. The vehicle may be any vehicle that uses electrical energy from a nickel metal hydride battery as all or part of its power source, such as an electric vehicle or a hybrid vehicle. When a nickel metal hydride battery is installed in a vehicle, a plurality of nickel metal hydride batteries may be connected in series to form a battery pack. Devices that may be equipped with nickel metal hydride batteries include, in addition to vehicles, various battery-powered home appliances, office equipment, and industrial equipment, such as personal computers and portable communication devices. Furthermore, the nickel metal hydride battery of the present invention may be used in power storage devices and power smoothing devices for wind power generation, solar power generation, hydroelectric power generation, and other power systems; power supplies for power and / or auxiliary equipment of ships and the like; power supplies for power and / or auxiliary equipment of aircraft, spacecraft, and the like; auxiliary power supplies for vehicles that do not use electricity as a power source; power supplies for mobile household robots; system backup power supplies; power supplies for uninterruptible power supplies; and power storage devices that temporarily store the power required for charging at charging stations for electric vehicles.

[0109] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be embodied in various forms incorporating modifications and improvements that can be made by those skilled in the art without departing from the spirit of the present invention.

[0110] The energy storage module according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. The contents of the above-described embodiment and modifications may be appropriately extracted and combined.

[0111] In the above embodiment, the Ni-Fe alloy layer 15 is formed on both sides of the current collector 10 constituting the bipolar electrode 100 (200), the negative terminal electrode 18, and the positive terminal electrode 19, but it may be formed on only one side of the current collector 10. When the Ni-Fe alloy layer 15 is provided on one side of the current collector 10, it is preferable to provide it on one side (first side) 10A. Furthermore, the Ni-Fe alloy layer 15 does not necessarily have to be provided on the current collector 10 constituting the positive terminal electrode 19.

[0112] In the above embodiment, the other surface 10B of the current collector 10 included in the bipolar electrode is roughened, but this is not limiting. For example, only a portion of the other surface 10B included in the bonding region with the first seal portion 21 may be roughened. Also, only a portion of one surface 40a of the conductive plate 40 included in the bonding region with the first seal portion 21 may be roughened.

[0113] In the above embodiment, the current collector and the conductive plate are each rectangular in plan view, but this is not limited thereto. The current collector and the conductive plate may each be polygonal, circular, or elliptical in plan view. Similarly, the end plates, separators, and seal portions (specifically, the first seal portion and the second seal portion) do not have to be rectangular in plan view. [Example]

[0114] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0115] Example 1 <Manufacturing of current collectors> First, a cold-rolled foil (thickness: 50 μm) of low-carbon aluminum-killed steel having the chemical composition shown below was prepared as a steel sheet. C: 0.04 wt%, Mn: 0.32 wt%, Si: 0.01 wt%, P: 0.012 wt%, S: 0.014 wt%, balance: Fe and unavoidable impurities

[0116] Next, the prepared steel sheet was subjected to electrolytic degreasing and pickling by immersion in sulfuric acid. Then, Ni plating was performed on both sides of the steel sheet using a Watts bath under the following conditions to a target thickness of 0.35 μm per side, resulting in a Ni coating weight of 3.12 g / m. 2 The Ni plating layer was formed (first Ni plating step). The Ni plating conditions were as follows:

[0117] (First Ni plating conditions) Bath composition: Nickel sulfate hexahydrate: 250g / L Nickel chloride hexahydrate: 45g / L Boric acid: 30g / L Bath temperature: 60℃ pH: 4.0 to 5.0 Agitation: Air agitation or jet agitation Current density: 10A / dm 2

[0118] Next, the steel sheet having the Ni-plated layer formed above was subjected to heat treatment (diffusion step) by box annealing under conditions of a heat treatment temperature of 560°C, a soaking time of 6 hours, and a reducing atmosphere. This heat treatment yielded a surface-treated steel sheet having Ni-Fe alloy layers with a thickness of 1.2 μm per side formed on both sides of the steel sheet.

[0119] The thickness of the Ni-Fe alloy layer was measured using SEM-EDX (energy dispersive X-ray spectroscopy). Specifically, the thickness of the Ni-Fe alloy layer was calculated by linear analysis of Ni and Fe elements from the surface to a depth of 10 μm in the thickness direction using SEM-EDX (energy dispersive X-ray spectroscopy). The measurement conditions were an acceleration voltage of 10 kV, observation magnification of 5000x, and measurement step of 0.01 μm. As shown in Figure 2, the horizontal axis represents the depth from the surface (μm), and the vertical axis represents the X-ray intensity of Ni and Fe. The thickness of the Ni-Fe alloy layer was determined by the distance between 1 / 10 of the maximum values of Ni and Fe, respectively, before and after the intersection of the Ni curve and the Fe curve.

[0120] Next, a 1.0 μm thick Ni underlayer was formed on both surfaces under the following plating conditions (second Ni plating step). <Conditions for Ni undercoat plating> Bath composition: Nickel sulfate hexahydrate 250g / L, nickel chloride hexahydrate 45g / L, boric acid 30g / L pH 4.0-5.0 Bath temperature 60℃ Current density 10A / dm 2

[0121] A roughened Ni layer was formed on the other side (second side) of the surface-treated steel sheet on which the base Ni layer had been formed (third Ni plating step) under the following plating conditions to obtain a current collector. The roughened Ni layer was formed by carrying out a plating step under the following roughened Ni layer plating conditions, followed by a nickel coating treatment under the following nickel coating plating conditions to improve adhesion between the steel sheet and the roughened Ni layer. The nickel deposition weight of the roughened Ni layer was 18.1 g / m 2 It was. <Roughened Ni layer plating conditions> Nickel sulfate hexahydrate concentration in plating bath: 10g / L Nickel chloride hexahydrate concentration in plating bath: 10g / L Chloride ion concentration in plating bath: 3g / L Ratio of nickel ions to ammonium ions in the plating bath: nickel ions / ammonium ions (weight ratio) = 0.17 pH:6 Bath temperature: 50℃ Current density: 12A / dm 2 Plating time: 80 seconds <Nickel plating conditions> Bath composition: Nickel sulfate hexahydrate 250g / L, Nickel chloride hexahydrate 45g / L, Boric acid 30g / L pH: 4.2 Bath temperature: 60℃ Current density: 5A / dm 2 Plating time: 36 seconds

[0122] That is, the current collector in Example 1 manufactured as described above comprises, in order from the surface side of the steel plate 13, a Ni—Fe alloy layer, an underlying Ni layer, and a roughened Ni layer. The steel plate is the base material of the current collector. The Ni—Fe alloy layer and underlying Ni layer are formed on both surfaces (first surface and second surface) of the current collector. The roughened Ni layer is formed only on the other surface (second surface) of the current collector.

[0123] [Bipolar electrode manufacturing] A positive electrode slurry was produced by mixing 94.3 parts by mass of nickel hydroxide powder as the positive electrode active material, 1 part by mass of cobalt powder as a conductive additive, 3.5 parts by mass (solid content) of an acrylic resin emulsion as a binder, 0.7 parts by mass of carboxymethyl cellulose as a binder, 0.5 parts by mass of YO as a positive electrode additive, and an appropriate amount of ion-exchanged water.

[0124] A negative electrode slurry was produced by mixing 97.8 parts by mass of an A2B7 type hydrogen storage alloy as a negative electrode active material, 1.5 parts by mass (solid content) of an acrylic resin emulsion as a binder, 0.7 parts by mass of carboxymethyl cellulose as a binder, and an appropriate amount of ion-exchanged water.

[0125] The negative electrode slurry was applied in the form of a film to a first surface of a current collector. The positive electrode slurry was applied in the form of a film to a second surface of a current collector. The current collector with the applied slurry was dried to remove water and pressed to produce a bipolar electrode in which a positive electrode active material layer and a negative electrode active material layer were formed on the current collector.

[0126] A positive terminal electrode having a positive electrode active material layer formed on a second surface thereof was manufactured in the same manner as the bipolar electrode, except that the negative electrode slurry was not applied to the first surface of the current collector. A negative terminal electrode having a negative electrode active material layer formed on a first surface thereof was manufactured in the same manner as the bipolar electrode, except that the positive electrode slurry was not applied to the second surface of the current collector.

[0127] [Production of evaluation batteries] As the electrolyte, an aqueous solution containing potassium hydroxide at a concentration of 5.4 mol / L, sodium hydroxide at a concentration of 0.8 mol / L, lithium hydroxide at a concentration of 0.5 mol / L, and lithium chloride at a concentration of 0.05 mol / L was prepared. A sulfonated polyolefin fiber nonwoven fabric having a thickness of 104 μm was prepared as the separator SP. The bipolar electrode 100 was sandwiched between a positive terminal electrode 19 and a negative terminal electrode 18 to form an electrode assembly. A separator SP was interposed between the electrodes.

[0128] Resin casings (sealing portions) 12 were placed between the bipolar electrode 100 and the positive terminal electrode 19, and between the bipolar electrode 100 and the negative terminal electrode 18, and the casings were joined by thermocompression bonding. The above-described electrolyte solution was injected between the bipolar electrode 100 and the positive terminal electrode 19, and between the bipolar electrode 100 and the negative terminal electrode 18, and then the casings were hermetically sealed to produce the evaluation battery of Example 1. In this example, the bipolar electrode 100 and the positive terminal electrode 19, and the bipolar electrode 100 and the negative terminal electrode 18 each constitute one cell (single cell), for a total of two cells. A schematic diagram of the configuration of this evaluation battery is shown in FIG. 8.

[0129] Example 2 In the current collector manufacturing process, the target thickness in the first Ni plating step was set to 0.5 μm. Heat treatment was then performed in the subsequent diffusion step. This heat treatment resulted in a surface-treated steel sheet with a Ni-Fe alloy layer having a thickness of 1.5 μm formed on both sides of the steel sheet. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 1.

[0130] Example 3 In the current collector manufacturing process, the target thickness in the first Ni plating step was 1.5 μm. Heat treatment was then performed in the subsequent diffusion step. This heat treatment resulted in a surface-treated steel sheet with a Ni-Fe alloy layer having a thickness of 2.5 μm formed on both sides of the steel sheet. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 1.

[0131] Example 4 In the current collector manufacturing process, the target thickness in the first Ni plating step was 3.0 μm. Furthermore, in the subsequent diffusion step, heat treatment was performed at a heat treatment temperature of 640°C for a soaking time of 2 hours. This heat treatment resulted in a surface-treated steel sheet in which a Ni-Fe alloy layer with a thickness of 3.87 μm was formed on both sides of the steel sheet. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 1.

[0132] Example 5 First, a 200 μm thick low-carbon aluminum-killed steel sheet was prepared and Ni-plated to a target thickness of 2.0 μm using a Watts bath (first Ni-plating step). Next, a softening heat treatment for rolling was performed, followed by rolling to 50 μm. Thereafter, a heat treatment (diffusion step) was performed in a reducing atmosphere at a heat treatment temperature of 480°C for a soaking time of 4 hours, yielding a surface-treated steel sheet having Ni-Fe alloy layers with a thickness of 0.55 μm on both sides. Otherwise, a current collector, a bipolar electrode, and a test battery were manufactured in the same manner as in Example 1.

[0133] (Comparative Example 1) Using the steel sheet of Example 1, a current collector provided with a base Ni layer and a roughened Ni layer was manufactured by performing a second Ni plating step and a third Ni plating step in the same manner as in Example 1. The thickness of the base Ni layer was 1 μm. The first Ni plating step and heat treatment for providing a Ni-Fe alloy layer were not performed. A bipolar electrode and a battery for evaluation were manufactured in the same manner as in Example 1, except for changing the current collector.

[0134] (Comparative Example 2) Using the steel sheet of Example 1, a current collector provided with a base Ni layer and a roughened Ni layer was manufactured by performing a second Ni plating step and a third Ni plating step in the same manner as in Example 1. The thickness of the base Ni layer was 5 μm. The first Ni plating step and heat treatment for providing a Ni-Fe alloy layer were not performed. A bipolar electrode and a battery for evaluation were manufactured in the same manner as in Example 1, except for changing the current collector.

[0135] [Testing the change in leakage current with or without a Ni-Fe alloy layer and with varying thickness] Using the evaluation battery manufactured as described above, a test was conducted to evaluate the change in leakage current depending on the presence or absence of the Ni-Fe alloy layer on the current collector and the change in thickness. That is, the test batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were repeatedly charged and discharged to carry out activation treatment. After activation, each test battery was adjusted to an SOC (State of Charge) of 85% and then discharged to 0% SOC, and the discharge capacity before storage was measured. After activation, each test battery was adjusted to an SOC of 85% and stored in a constant temperature chamber at 65°C for 350 hours. After storage, each test battery was discharged to 0% SOC, and the discharge capacity after storage was measured. The leakage current was calculated using the following formula. (Discharge capacity before storage - Discharge capacity after storage) / Storage time = Leakage current The leakage current values per unit area are shown in Table 1. A comparison between the comparative example and Example 5 showed that the leakage current was reduced by the Ni-Fe alloy layer. Furthermore, Examples 1 to 5 showed that increasing the thickness of the Ni-Fe alloy layer was effective in reducing the leakage current. On the other hand, since there was no change in the leakage current value even when the thickness of the Ni-Fe alloy layer was changed from 1.2 μm to 1.5 μm in Examples 1 and 2, it is believed that a thickness of 1.0 μm for the Ni-Fe alloy layer is sufficient for reducing the leakage current.

[0136] Furthermore, for each of the activated evaluation batteries of Examples 2 to 4 and Comparative Example 1, a charge-discharge cycle was repeated 1500 times at 60°C, where the cells were charged at 1C from 20% SOC to 80% SOC and then discharged at 1C from 80% SOC to 20% SOC. After charging to 80% SOC, each cell was individually discharged at 1C from 80% SOC to 0% SOC, and the discharge capacity after each cycle was measured. The leakage current was calculated using the following formula. The test time was the time required for 1500 charge-discharge cycles. The cell consisting of the bipolar electrode and the positive terminal electrode was designated the hydrogen generation side cell, and the cell consisting of the bipolar electrode and the negative terminal electrode was designated the hydrogen entry side cell. (Discharge capacity of hydrogen generation cell - Discharge capacity of hydrogen entry cell) / Test time = Leakage current The leakage current values per unit area are shown in Table 1.

[0137] [Table 1]

[0138] The evaluation batteries of Example 2 were also evaluated at a low temperature of -40°C as follows. After activation, the evaluation batteries were adjusted to an SOC (State of Charge) of 85% and then discharged to an SOC of 0%, and the discharge capacity before storage was measured. After activation, each evaluation battery was adjusted to an SOC of 85% and stored in a constant temperature chamber at -40°C for 350 hours. After storage, each evaluation battery was discharged to an SOC of 0%, and the discharge capacity after storage was measured. The leakage current was calculated using the following formula. (Discharge capacity before storage - Discharge capacity after storage) / Storage time = Leakage current The leakage current value per unit area is 0.0 μm / m 2 It was.

[0139] [Leakage current test for energy storage modules] Example 6 Current collectors and bipolar electrodes were manufactured in the same manner as in Example 2. Then, a power storage module as shown in FIG. 6 was fabricated using the same separators, active materials, etc. as in the above-mentioned evaluation battery. This power storage module included positive and negative terminal electrodes in addition to 23 stacked bipolar electrodes. The obtained electricity storage module was repeatedly charged and discharged to carry out an activation treatment. The activated energy storage module was adjusted to an SOC (State of Charge) of 85%, then discharged to an SOC of 0%, and the discharge capacity before storage was measured. The activated energy storage module was again adjusted to an SOC of 85% and stored in a constant temperature chamber at 65°C for 170 hours. The stored energy storage module was discharged to an SOC of 0%, and the discharge capacity after storage was measured. The leakage current was calculated using the following formula. (Discharge capacity before storage - Discharge capacity after storage) / Storage time = Leakage current Table 2 shows the leakage current per unit area.

[0140] (Comparative Example 3) An electricity storage module was fabricated and the leakage current was calculated in the same manner as in Example 6, except that the Ni plating (first Ni plating step) and heat treatment (diffusion step) for providing a Ni-Fe alloy layer were not performed in the current collector formation step. The obtained leakage current per unit area is shown in Table 2.

[0141] [Table 2]

[0142] The following describes the effects achieved by the bipolar electrode and energy storage module according to the present embodiment described above. Specifically, the bipolar electrode and energy storage module according to the present embodiment can reduce the amount of hydrogen that permeates the current collector of the bipolar electrode, thereby reducing the voltage drop of the energy storage module. Therefore, according to the present invention, the long-term reliability of the energy storage module and metal hydride battery can be improved. [Explanation of symbols]

[0143] 100: Bipolar electrodes for metal hydride batteries 200: Bipolar electrodes for metal hydride batteries 10: Current collector 10A: First surface of current collector 10B: Second surface of current collector 13: Steel plate 15: Ni-Fe alloy layer 20: Negative electrode active material layer 30: Positive electrode active material layer

Claims

1. A current collector; a negative electrode active material layer provided on a first surface of the current collector; a positive electrode active material layer provided on a second surface of the current collector; Equipped with the negative electrode active material layer contains a metal hydride, The current collector has a steel plate and a Ni—Fe alloy layer formed on at least one surface of the steel plate. A bipolar electrode for a metal hydride battery, comprising:

2. 2. The bipolar electrode for a metal hydride battery according to claim 1, wherein the Ni--Fe alloy layer has a thickness of 1.0 μm or more.

3. 3. The bipolar electrode for a metal hydride battery according to claim 1, wherein the Ni--Fe alloy layer is formed on the same side as the first surface of the current collector.

4. 4. The bipolar electrode for a metal hydride battery according to claim 1, wherein the Ni—Fe alloy layer is formed on both the same side as the first surface and the same side as the second surface of the current collector.

5. 5. The bipolar electrode of a metal hydride battery according to claim 1, wherein the current collector further has a Ni layer between the Ni—Fe alloy layer and the negative electrode active material layer or the positive electrode active material layer.

6. 6. The bipolar electrode of a metal hydride battery according to claim 5, wherein the surface of the Ni layer in contact with the negative electrode active material layer or the positive electrode active material layer has a surface roughness greater than that of the Ni—Fe alloy layer or the steel plate.

7. 7. The bipolar electrode for a metal hydride battery according to claim 6, wherein the surface roughness of the Ni layer is Rzjis=2.0 μm to 16.0 μm in ten-point height average roughness Rzjis.

8. A metal hydride battery comprising a stack of bipolar electrodes of the metal hydride battery according to any one of claims 1 to 7.

9. 9. The nickel metal hydride battery of claim 8, wherein the positive electrode active material layer comprises nickel hydroxide.

10. A method for manufacturing a bipolar electrode of a metal hydride battery, comprising: a current collector forming step; and an active material layer forming step, the current collector forming step includes a step of providing a Ni layer on at least one surface of a steel sheet, and a step of heat-treating the steel sheet provided with the Ni layer to diffuse Ni in the Ni layer and Fe in the steel sheet, thereby forming a Ni—Fe alloy layer, the active material layer forming step includes a step of forming a negative electrode active material layer on a first surface of a current collector, and a step of providing a positive electrode active material layer on a second surface of the current collector; A method for manufacturing a bipolar electrode for a metal hydride battery, comprising:

11. The current collector forming step further includes a roughened Ni layer forming step, 11. The method for manufacturing a bipolar electrode for a metal hydride battery according to claim 10, wherein the roughened Ni layer formed in the roughened Ni layer formation step has a surface roughness between the Ni—Fe alloy layer and the negative electrode active material layer or the positive electrode active material layer that is greater than a surface roughness of the Ni—Fe alloy layer or the steel plate.

12. A step of manufacturing a bipolar electrode by the manufacturing method according to claim 10 or 11; manufacturing a metal hydride battery using the bipolar electrode; A method for manufacturing a metal hydride battery having the above structure.

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