Bipolar electrodes for metal hydride batteries, and metal hydride batteries equipped with the bipolar electrodes.

Abstract

To provide a bipolar electrode of a metal hydride battery, in which a voltage drop phenomenon is reduced and which therefore has improved long-term reliability, and a metal hydride battery comprising the bipolar electrode.SOLUTION: A bipolar electrode of a metal hydride battery is provided, comprising a collector, a negative-electrode active material layer provided on the first surface of the collector, and a positive-electrode active material layer provided on the second surface of the collector. The negative-electrode active material layer includes metal hydride, the collector has a steel plate, and a phosphorus-containing nickel 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 typical metal hydride battery is a secondary battery comprising, for example, a positive electrode having nickel hydroxide such as nickel hydroxide as the positive electrode active material, a negative electrode having a hydrogen storage alloy as the negative electrode active material, and an electrolyte consisting of an alkali metal aqueous solution.

[0003] A conventional energy storage module is known to be a bipolar battery, which has 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 has a laminate in which bipolar electrodes and separators are stacked alternately along the stacking direction. Terminal electrodes, which have only one of either a positive or negative electrode, are located at both ends of the laminate 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 Publication No. 2005-135764 [Overview of the project] [Problems that the invention aims to solve]

[0005] From the standpoint of cost and reactivity resistance to electrolyte, plated steel sheets are used as current collectors for the bipolar electrodes of metal hydride batteries. The present inventors manufactured a bipolar electrode using a current collector made of plated steel sheets and a negative electrode and a positive electrode containing a hydrogen storage alloy. When they assembled a hydride battery using this bipolar electrode and conducted a storage test, they observed a voltage drop (self-discharge) phenomenon of unknown cause.

[0006] The object of the present invention is to provide a bipolar electrode for a metal hydride battery that can reduce self-discharge, and a metal hydride battery equipped with a bipolar electrode. [Means for solving the problem]

[0007] The inventors of this invention, after diligent research, concluded that the phenomenon of hydrogen moving to the counter electrode via the current collector of a bipolar electrode is involved in self-discharge, and conceived the idea of ​​reducing hydrogen permeation by using a layer containing a specific material. They then found that a current collector equipped with a layer containing a specific material can reduce self-discharge, thus completing the present invention. To achieve the above objective, the bipolar electrode of the metal hydride battery according to this embodiment comprises a current collector, a negative electrode active material layer provided on the first surface of the current collector, and a positive electrode active material layer provided on the 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 phosphorus-containing nickel 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 voltage drop phenomena and improves long-term reliability. Furthermore, it is possible to provide a metal hydride battery equipped with such a bipolar electrode. [Brief explanation of the drawing]

[0009] [Figure 1(a)] This is a schematic diagram showing a cross-section of the bipolar electrode of the metal hydride battery of this embodiment. [Figure 1(b)] This is a schematic diagram showing a cross-section of the bipolar electrode of the metal hydride battery of this embodiment. [Figure 2] This is an explanatory diagram of the electrochemical hydrogen permeation method. [Figure 3(a)] This is a schematic diagram showing a cross-section of a bipolar electrode in a metal-hydride battery of another embodiment. [Figure 3(b)] This is a schematic diagram showing a cross-section of a bipolar electrode in a metal-hydride battery of another embodiment. [Figure 3(c)] It is a schematic diagram showing a cross section of a bipolar electrode of a metal hydride battery according to another embodiment. [Figure 4] It 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 5] It is a schematic cross-sectional view showing the internal structure of the electricity storage module in FIG. 4. [Figure 6] It is a schematic diagram of an evaluation battery to which the bipolar electrode of the metal hydride battery of the present embodiment is applied. [Figure 7] It is a bubble chart showing the effect of the bipolar electrode of the metal hydride battery of the present embodiment.

Mode for Carrying Out the Invention

[0010] Hereinafter, the bipolar electrode of the metal hydride battery of the present invention, the metal hydride battery, the method capable of manufacturing the bipolar electrode of the metal hydride battery, and the method capable of manufacturing the metal hydride battery using the bipolar electrode of the metal hydride battery will be described in detail in order.

[0011] Hereinafter, the method capable of manufacturing the bipolar electrode of the metal hydride battery of the present invention may be referred to as the electrode manufacturing method of the present invention as necessary. Also, the method capable of manufacturing the metal hydride battery of the present invention may be referred to as the battery manufacturing method of the present invention. The bipolar electrode of the 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 range "x to y" described in this specification includes the lower limit x and the upper limit y in the range. And these upper limit values, lower limit values, and the numerical values listed in the examples can be combined arbitrarily to constitute a numerical range. Furthermore, a numerical value arbitrarily selected from within the numerical range can be used as the numerical value of the upper limit and the lower limit.

[0012] <Bipolar Electrode of Metal Hydride Battery: First Embodiment> First, the bipolar electrode of the metal hydride battery of the present invention will be described in detail using the following embodiments and figures. 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), wherein the negative electrode active material layer 20 contains a metal hydride, and the current collector 10 is characterized by comprising a steel plate 13 and a phosphorus-containing nickel layer 15 provided on at least one surface of the steel plate 13.

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

[0014] The current collector 10 has a phosphorus-containing nickel layer 15 on the surface of a steel plate 13. Examples of the steel plate 13 include low-carbon steel with a carbon content of less than 0.25 wt%, ultra-low-carbon steel with a carbon content of less than 0.01 wt%, and non-aged ultra-low-carbon steel obtained by adding Ti, Nb, etc. to ultra-low-carbon steel. Examples of low-carbon steel include low-carbon aluminum-killed steel (carbon content 0.01 to 0.15 wt%) and cold-rolled steel sheets (SPCC, etc.) as specified in JIS G 3141:2005. Low-carbon aluminum-killed steel (carbon content 0.01 to 0.15 wt%) is preferred due to its rollability and economic efficiency. The main material of the steel plate 13 is Fe, but it may also contain other metallic elements. The proportion of metallic elements other than Fe in the steel plate 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 exemplified as 5 μm to 1000 μm.

[0015] The phosphorus-containing nickel layer 15 formed on at least one surface of the steel sheet 13 is substantially an alloy layer (nickel-phosphorus alloy layer) containing an alloy composed of nickel (Ni) and phosphorus (P). The phosphorus-containing nickel layer 15 in the present embodiment only needs to contain nickel (Ni) and phosphorus (P), and the state in which each component is contained is not particularly limited.

[0016] In addition, the metal elements contained in the phosphorus-containing nickel layer 15 in the present embodiment are not limited to nickel and phosphorus, and other metal elements may be contained as long as the problems of the present invention can be solved. For example, the phosphorus-containing nickel layer 15 may contain metal elements such as cobalt (Co) and molybdenum (Mo), as well as unavoidable impurities. The proportion of metal elements other than nickel and phosphorus in the phosphorus-containing nickel layer 15 is preferably 10 wt% or less, more preferably 5 wt% or less, still more preferably 1 wt% or less, and particularly preferably 0.5 wt% or less.

[0017] In the present embodiment, the effect of reducing hydrogen permeation by the phosphorus-containing nickel layer 15 will be described. That is, the bipolar electrode of the metal hydride battery of the present embodiment has an effect of reducing hydrogen permeation due to the phosphorus-containing nickel layer 15 contained in the current collector. The discharge reaction of the nickel metal hydride battery is expressed as follows. Positive electrode: NiOOH + H2O + e - → Ni(OH)2 + OH - Negative electrode: MH + OH - → M + H2O + e - Furthermore, the reaction at the negative electrode consists of the following two reactions. MH = M + H + + e - H + + OH - = H2O During the reaction, in the bipolar electrode, the electron e - moves from the negative electrode to the positive electrode through the current collector. The hydroxide ion OH -Electrons move from the positive electrode to the negative electrode of the adjacent bipolar electrode via the electrolyte. Outside the battery, electrons move from the negative electrode to the positive electrode via an external circuit (load).

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

[0019] A hydrogen concentration gradient is created between the negative electrode active material layer (metal hydride MH) and the positive electrode active material layer, resulting in the generation of hydrogen atoms [H] in the negative electrode active material layer through the above reaction. These hydrogen atoms [H] move from the negative electrode active material layer to the positive electrode active material layer, which is the opposite electrode, via the current collector. Since the hydrogen atoms [H] that have moved to the positive electrode are consumed at the positive electrode as shown in the above reaction equation, a hydrogen concentration gradient is always created 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, leading to a decrease in battery voltage. Although the above reaction differs from the reactions that occur at the positive and negative electrodes during normal discharge, the reaction results in the active materials being the same, and the potentials of the positive and negative electrodes decrease as a result of the reaction. The release of hydrogen by metal hydrides is an endothermic reaction, and the reactivity of the active material increases with higher potential; therefore, the above reaction becomes more pronounced at high potential and high temperature. During the reaction, in bipolar electrodes, electrons e - No movement occurs through the current collector.

[0020] Therefore, the inventor conceived of forming a coating on the steel plate constituting the current collector to reduce hydrogen permeation to the counter electrode. Specifically, the inventor conceived of forming a phosphorus-containing nickel layer on at least one surface of the steel plate.

[0021] It has been conventionally known that the delayed fracture phenomenon of steel (hydrogen embrittlement) is governed by hydrogen diffusion. 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, there is no known technique for reducing hydrogen permeation in a steel sheet, assuming a hydrogen concentration gradient occurring on both sides of the steel sheet, as is the case with the bipolar electrode of the present invention. As a result of diligent research by the inventors, it has been found that by forming a phosphorus-containing nickel layer on at least one side of the steel sheet, it is possible to reduce hydrogen permeation in the steel sheet that serves as the current collector material for the bipolar electrode.

[0023] The effect of a phosphorus-containing nickel layer on reducing hydrogen permeation in steel sheets can be evaluated using an electrochemical hydrogen permeation method as described below. A schematic diagram of the hydrogen permeation test apparatus used for evaluation is shown in Figure 2. The hydrogen permeation test apparatus consists of two electrolytic cells EC1 and EC2, which are positioned opposite each other with the test piece W in between. In Figure 2, electrolytic cell EC1 on the left is the cathode side (hydrogen intrusion side), and electrolytic cell EC2 on the right is the anode side (hydrogen detection side). Hydrogen is generated in electrolytic cell EC1, and the anode current is detected when the hydrogen that has permeated the test piece W and reached electrolytic cell EC2 is oxidized. In the figure, RE1 and RE2 are reference electrodes, CE1 and CE2 are counter electrodes, and WE is the test piece W as the working electrode, connected to a potentiostat PS and a 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 can be an alkaline electrolyte containing KOH, NaOH, and LiOH.

[0024] Voltages are applied to the counter electrode CE1 using a potentiometer-galvanostat PS / GS so that the potential on the hydrogen entry side is -0.6V, -0.45V, and -0.3V (vsRHE (reversible hydrogen electrode)), and the current change on the hydrogen detection side is measured. The potential on the hydrogen detection side is maintained at +1.45V (vsRHE). The liquid temperature is maintained at 65°C, and degassing is performed 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 effect of hydrogen permeation reduction on test pieces that simulate current collectors.

[0025] For the reasons described above, in this embodiment, it is preferable that the phosphorus-containing nickel layer 15 be provided on the side of the steel sheet 13 that faces the negative electrode active material layer 20.

[0026] For the reasons of the estimated mechanism of hydrogen permeation described above, it is preferable that the phosphorus-containing nickel layer 15 be provided at least on the side of the steel plate 13 facing the negative electrode active material layer 20, as shown in Figure 1(a). That is, the phosphorus-containing nickel layer 15 formed between the negative electrode active material layer 20 and the steel plate 13 prevents hydrogen released by the negative electrode active material layer 20 (i.e., hydrogen storage alloy: metal hydride) from permeating through the steel plate 13, thereby further reducing hydrogen permeation. On the other hand, due to the potential relationship, depending on the operating environment of the metal hydride battery, phosphorus may easily leach from the phosphorus-containing nickel layer 15 into the electrolyte on the negative electrode active material layer 20 side. Therefore, from the viewpoint of suppressing such leaching, it is preferable that the phosphorus-containing nickel layer 15 be provided on the positive electrode active material layer 30 side.

[0027] Furthermore, it is even more preferable that the phosphorus-containing nickel layer 15 be provided on both sides of the steel plate 13, as shown in Figure 1(b). That is, in Figure 1(b), the nickel-phosphorus alloy layer 15a is provided on the first side of the steel plate 13, and the phosphorus-containing nickel layer 15b is provided on the second side on the opposite side. With this configuration, even if hydrogen released by the negative electrode active material layer 20 (i.e., hydrogen storage alloy: metal hydride) permeates through the phosphorus-containing nickel layer 15a and the steel plate 13, it is thought that it will be captured by the phosphorus-containing nickel layer 15b before reaching the positive electrode active material layer 30, thus avoiding the voltage drop problem described above. Note that the first side of the steel plate 13 is the same side as the first side (10A) of the current collector. Both sides of the steel plate 13 refer to the first side and the second side opposite to the first side.

[0028] When the thickness of the phosphorus-containing nickel layer 15 is 0.1 μm or more, it is considered that a sufficient effect of reducing hydrogen permeation by the phosphorus-containing nickel layer 15 can be obtained. In other words, when the thickness of the phosphorus-containing nickel layer 15 in the current collector is 0.1 μm or more, it is considered that the voltage drop in the battery can be effectively reduced. When the thickness of the phosphorus-containing nickel layer 15 is less than 0.1 μm, the desired effect of reducing hydrogen permeation may not be obtained.

[0029] Furthermore, it is more preferable that the thickness of the phosphorus-containing nickel layer 15 be 0.2 μm or more, more preferably 0.3 μm or more, and even more preferably 0.6 μm or more. Moreover, it is preferable that the phosphorus-containing nickel layer 15 be provided on both the first and second surfaces of the steel sheet 13. Regarding the upper limit of the thickness of the phosphorus-containing nickel layer 15, from the viewpoint of productivity, it is preferable that it be 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0030] The thickness of the phosphorus-containing nickel layer 15 can be determined, for example, by using the average value of the thicknesses at any 10 points in a cross-sectional SEM image. In this embodiment, the thickness of the phosphorus-containing nickel layer 15 is defined as the average value of one side (divided by the two sides) assuming that phosphorus-containing nickel layers are provided on both the first and second surfaces of the steel plate 13. Therefore, in this embodiment, whether a 0.2 μm phosphorus-containing nickel layer is formed only on the first surface of the steel plate 13 or a 0.1 μm phosphorus-containing nickel layer is formed on both the first and second surfaces of the steel plate 13, the thickness of the phosphorus-containing nickel layer 15 is defined as 0.1 μm in both cases.

[0031] When the phosphorus content ratio in the phosphorus-containing nickel layer 15 is 9.0 wt% or higher, it is considered that a sufficient effect of reducing hydrogen permeation by the phosphorus-containing nickel layer 15 can be obtained. In other words, when the phosphorus content ratio of the phosphorus-containing nickel layer 15 in the current collector is 9.0 wt% or higher, it is considered that the voltage drop in the battery can be effectively reduced. If the thickness of the phosphorus-containing nickel layer 15 is less than 9.0 wt%, the desired effect of reducing hydrogen permeation may not be obtained. There is no particular upper limit on the phosphorus content ratio in the phosphorus-containing nickel layer 15 from the viewpoint of the effect of reducing hydrogen permeation, but from the viewpoint of the production efficiency of the phosphorus-containing nickel layer, it is preferable that the phosphorus content ratio is 15.0 wt% or lower.

[0032] The phosphorus content ratio of the phosphorus-containing nickel layer 15 can be obtained, for example, by ICP (Inductively Coupled Plasma) mass spectrometry.

[0033] When the phosphorus-containing nickel layer 15 contains nickel phosphide, it is considered that a sufficient effect of reducing hydrogen permeation by the phosphorus-containing nickel layer 15 can be obtained. In other words, when the phosphorus-containing nickel layer 15 in the current collector contains nickel phosphide, it is considered that the voltage drop in the battery can be effectively reduced. It has been reported in the literature that nickel-phosphorus alloys can be heat-treated to produce nickel phosphide such as Ni3P, Ni2P, NiP, and metastable crystalline phases. Of these, from the viewpoint of reducing hydrogen permeation, it is preferable that at least Ni3P or a metastable crystalline phase is formed. (Kiyoshi Ito et al. Relationship between the microstructure and thermal equilibrium phase diagram of electrodeposited Ni-P alloy plating films. Journal of the Japan Institute of Metals. 2001, vol. 65, no. 6, pp. 495-501; Masao Matsuoka et al. Phosphorus content and film properties of electroless nickel plating. Kinki Aluminum Surface Treatment Research Association. 1989, no. 136, pp. 4-9; Kanji Masui et al. Structural changes associated with heating of electrodeposited Ni-P alloys. Journal of the Japan Institute of Metals. 1977, vol. 41, no. 11, pp. 1130-1136, etc.)

[0034] Furthermore, it is preferable that the phosphorus-containing nickel layer 15 is also provided on the negative electrode terminal electrode, which will be described later. By forming a phosphorus-containing nickel layer on the negative electrode terminal electrode, it is possible to reduce the decrease in discharge reserve that occurs when hydrogen permeates the negative electrode terminal electrode and leaks out to the outside of the battery in a cell (single cell) including the negative electrode terminal electrode.

[0035] Next, the active material layers of this embodiment (negative electrode active material layer 20 and positive electrode active material layer 30) will be described. In this embodiment, the negative electrode active material layer 20 contains negative electrode active material and optionally includes negative electrode additives, binders, and conductive additives. The positive electrode active material layer 30 contains positive electrode active material and optionally includes positive electrode additives, binders, and conductive additives. Hereafter, matters relating to both the positive electrode active material layer and the negative electrode active material layer will be described collectively as the active material layer.

[0036] 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 the negative electrode active material of a nickel metal hydride battery, i.e., as 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 ability, and metal B, which does not react easily with hydrogen but has excellent hydrogen release ability. 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, mischmetal 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.

[0037] Specific examples of hydrogen storage alloys include AB5 type exhibiting a hexagonal CaCu5 crystal structure, AB2 type exhibiting a hexagonal MgZn2 type or cubic MgCu2 type crystal structure, AB type exhibiting a cubic CsCl type crystal structure, A2B type exhibiting a hexagonal Mg2Ni type crystal structure, solid solution type exhibiting a body-centered cubic structure, and AB3, A2B7, and A5B types which combine the crystal structures of AB5 and AB2 types. 19 Examples of this type can be given. The hydrogen storage alloy may have one of the above crystal structures, or it may have multiple of the above crystal structures.

[0038] 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 Examples include the following. In each of the above crystal structures, some of the metals may be substituted with one or more other types of metals or elements.

[0039] The surface of the negative electrode active material may be treated by known methods. In particular, it is preferable to use an alkali-treated hydrogen storage alloy as the negative electrode active material. Alkali treatment means treating the hydrogen storage alloy with an alkaline aqueous solution containing an alkali metal hydroxide.

[0040] 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 solutions, will leach from the surface of the hydrogen storage alloy. Here, since Ni has low solubility in alkaline solutions, the Ni concentration on the surface of the hydrogen storage alloy will be higher than that inside the alloy. Hereafter, the part of the hydrogen storage alloy with a higher Ni concentration compared to the interior will be called the Ni-enriched layer. It is believed that the performance of the negative electrode active material is improved due to the presence of the Ni-enriched layer.

[0041] Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide, with sodium hydroxide being preferred. Using an aqueous solution of sodium hydroxide as the alkaline aqueous solution may improve the battery characteristics of the nickel metal hydride battery of the present invention compared to using lithium hydroxide or potassium hydroxide as the alkaline aqueous solution.

[0042] A strongly basic alkaline aqueous solution is preferred. Examples of alkali metal hydroxide concentrations in the alkaline aqueous solution include 10-60% by mass, 20-55% by mass, 30-50% by mass, and 40-50% by mass.

[0043] The alkali treatment is preferably carried out by immersing the hydrogen storage alloy in an alkaline aqueous solution. This treatment is preferably performed under stirring conditions and also under heating conditions. Examples of heating temperatures include 50-150°C, 70-140°C, and 90-130°C. The heating time can be appropriately determined depending on the concentration of the alkaline aqueous solution and the heating temperature, but examples include 0.1-10 hours, 0.2-5 hours, and 0.5-3 hours.

[0044] From the perspective of the alkali treatment described above, hydrogen storage alloys containing rare earth elements and Ni are preferred.

[0045] The negative electrode active material is preferably in powder form, 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.

[0046] The negative electrode active material layer preferably contains 85 to 99% by mass of the negative electrode active material relative to the total mass of the negative electrode active material layer, and more preferably contains 90 to 98% by mass.

[0047] Negative electrode additives are added to the negative electrode of nickel metal hydride batteries to improve their battery characteristics. The negative electrode additive is not limited to those used as negative electrode additives in nickel metal hydride batteries. Specific negative electrode additives include fluorides of rare earth elements 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.

[0048] The negative electrode active material layer preferably contains a negative electrode additive in an amount of 0.1 to 10% by mass, and more preferably in an amount of 0.5 to 5% by mass, relative to the total mass of the negative electrode active material layer.

[0049] Next, the positive electrode active material contained in the positive electrode active material layer 30 of this embodiment may be nickel hydroxide used as the positive electrode active material for nickel metal hydride batteries, and may be partially doped with other metals. Specific examples of positive electrode active materials include nickel hydroxide and metal-doped nickel hydroxide. Examples of metals used to dope 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.

[0050] The surface of the positive electrode active material may be treated by known methods. The positive electrode active material is preferably in powder form, 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 analyzer.

[0051] The positive electrode active material layer preferably contains the positive electrode active material in an amount of 75 to 99% by mass, more preferably 80 to 97% by mass, and even more preferably 85 to 95% by mass, relative to the total mass of the positive electrode active material layer.

[0052] Positive electrode additives are added to the positive electrode of nickel metal hydride batteries to improve their battery characteristics. The positive electrode additive is not limited to those used as positive electrode additives in nickel metal hydride batteries. Specific examples of positive electrode additives include niobium compounds such as Nb2O5, tungsten compounds such as WO2, WO3, Li2WO4, Na2WO4, and K2WO4, ytterbium compounds such as Yb2O3, titanium compounds such as TiO2, yttrium compounds such as Y2O3, zinc compounds such as ZnO, calcium compounds such as CaO, Ca(OH)2, and CaF2, and other rare earth oxides.

[0053] The positive electrode active material layer preferably contains a positive electrode additive in an amount of 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the total mass of the positive electrode active material layer.

[0054] In this embodiment, the binder and conductive additive included in the active material layer as needed will be described below.

[0055] The binder plays the role of securing the active material and other components to the surface of the current collector. The binder is not limited to those used as electrode binders in 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 carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose; 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.

[0056] The active material layer preferably contains a binder in an amount of 0.1 to 15% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 7% by mass, relative to the total mass of the active material layer. This is because too little binder reduces the moldability of the electrode, and too much binder lowers the energy density of the electrode.

[0057] Conductive additives are added to enhance the conductivity of electrodes. Therefore, conductive additives may be added as needed if the conductivity of the electrodes is insufficient, but they may not be added if the conductivity of the electrodes is sufficiently good. Conductive additives may be added to the active material layer in powder form, or they may be used in a state where they coat the surface of the active material particles. Any chemically inert electron conductor can be used as a conductive additive. Specific examples of conductive additives 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.

[0058] The negative electrode active material layer 20 preferably contains a conductive additive in an amount of 0.1 to 5% by mass, more preferably 0.2 to 3% by mass, and even more preferably 0.3 to 1% by mass, relative to the total mass of the negative electrode active material layer. The positive electrode active material layer 30 preferably contains a conductive additive in an amount of 0.1 to 10% by mass, more preferably 0.2 to 7% by mass, and even more preferably 0.3 to 5% by mass, relative to the total mass of the positive electrode active material layer.

[0059] <Bipolar electrodes for metal-hydride batteries: 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. This embodiment differs from the first embodiment described above in that a nickel layer 17 is formed on at least one of the outermost surfaces of the current collector 10. Therefore, these differences will be mainly described, and components having the same function as those in the first embodiment described above will be given the same reference numerals and their descriptions will be omitted as appropriate.

[0060] As shown in Figure 3(a), in the bipolar electrode 200 of the metal hydride battery of this embodiment, a phosphorus-free nickel layer 17 is formed on the outermost surface on the same side as one side (first surface) 10A of the current collector 10. That is, a phosphorus-free nickel layer 17 is further formed between the phosphorus-containing nickel layer 15 and the negative electrode active material layer 20. In this embodiment, as shown in Figure 3(b), a nickel layer 17a may be formed on the outermost surface on the same side as one side (first surface) 10A of the current collector 10, and a nickel layer 17b may be formed on the outermost surface on the same side as the other side (second surface) 10B. In Figure 3(b), a nickel layer 17a is further formed between the phosphorus-containing nickel layer 15a and the negative electrode active material layer 20, and a nickel layer 17b is further formed between the phosphorus-containing nickel layer 15b and the positive electrode active material layer 30.

[0061] The effects obtained by forming an additional nickel layer 17 between the phosphorus-containing nickel layer 15 and the negative electrode active material layer 20 and / or the positive electrode active material layer 30, that is, by forming the nickel layer 17 on the surface of the phosphorus-containing nickel layer 15, or by forming the nickel layer 17 on the outermost surface of the current collector 10, are as follows.

[0062] Although the phosphorus-containing nickel layer 15 has electrolyte resistance, it is conceivable that, depending on the operating environment of the metal hydride battery, a small amount of phosphorus may leach from the phosphorus-containing nickel layer 15 into the electrolyte. By forming a phosphorus-free nickel layer 17 on the surface of the phosphorus-containing nickel layer 15, it is considered that the leaching of phosphorus from the phosphorus-containing nickel layer 15 into the electrolyte can be effectively reduced. In particular, since phosphorus is considered to be more likely to leach from the negative electrode active material layer 20 side due to the potential relationship, it is preferable that the nickel layer 17 be provided on the surface of the phosphorus-containing nickel layer 15 formed on the negative electrode active material layer 20 side of the current collector 10.

[0063] Furthermore, as mentioned above, it is preferable that the phosphorus-containing nickel layer 15 is also provided on the negative electrode terminal electrode. In this case as well, in order to suppress the elution of phosphorus from the phosphorus-containing nickel layer 15 into the electrolyte, it is preferable that the negative electrode terminal electrode has a phosphorus-free nickel layer 17 on its surface.

[0064] Furthermore, from the viewpoint of reducing the leaching of phosphorus from the phosphorus-containing nickel layer 15 and more effectively obtaining the effect of reducing hydrogen permeation, it is preferable to form the phosphorus-containing nickel layer 15 on at least the positive electrode active material layer 30 side of the current collector 10, and it is even more preferable to have a nickel layer 17 on the surface of the phosphorus-containing nickel layer 15 for the reason that leaching can be reduced more effectively. Moreover, it is particularly preferable to have a nickel layer 17 on the outermost surface of both sides of the current collector 10.

[0065] The thickness of the nickel layer 17 is not particularly limited, but is preferably 0.2 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more. In other words, when the thickness of the nickel layer 17 in the current collector is 0.2 μm or more, it is considered that the resistivity of the current collector can be effectively reduced. If the thickness of the nickel layer 17 is less than 0.2 μm, the effect of reducing the resistivity of the current collector may not be obtained. On the other hand, regarding the upper limit of the thickness of the nickel layer 17, from the viewpoint of productivity, it is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0066] The metal elements contained in the nickel layer 17 are not limited to nickel (Ni), but may also include other metal elements. For example, the nickel layer 17 may contain metal elements such as cobalt (Co) and molybdenum (Mo). The proportion of metal elements other than nickel in the nickel 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.

[0067] Regarding the method for forming the nickel layer 17, one method is to form a phosphorus-containing nickel layer 15 and then perform nickel plating. Examples of nickel plating methods include electrolytic plating and electroless plating. Of these, electrolytic plating is particularly preferred from the viewpoint of cost and film thickness control.

[0068] In this embodiment, the nickel layer 17 may also be a roughened nickel layer 17c. A roughened nickel layer 17c means a nickel layer having a surface roughness greater than that of the phosphorus-containing nickel layer 15 or the steel plate 13 on the surface that contacts the negative electrode active material layer 20 or the positive electrode active material layer 30. By making the nickel layer 17 a roughened nickel layer 17c, the bonding strength between the current collector 10 and the member to which it is joined can be improved. For example, at the bonding interface between the current collector 10 and the seal portion described later, molten resin enters between multiple protrusions, and an anchoring effect is exerted. This improves the bonding strength between the bipolar electrode and the seal in this embodiment.

[0069] The surface roughness of the roughened nickel layer 17c can be expressed using known parameters. For example, the parameter can be defined by the ten-point average roughness Rzjis, and it is preferable that Rzjis is between 2.0 μm and 16.0 μm. The ten-point average roughness Rzjis is measured in accordance with JIS B0601:2013, and it is preferable to measure it using a laser microscope.

[0070] When forming the roughened nickel layer 17c, as shown in Figure 3(c), an underlay nickel layer 17d may be formed between the phosphorus-containing nickel layer 15 and the roughened nickel layer 17c as appropriate. By providing an underlay nickel layer 17d of about 0.1 μm to 10 μm, effects such as improving the adhesion of the roughened nickel layer 17c and suppressing the occurrence of pinholes can be obtained.

[0071] <Method for manufacturing bipolar electrodes> Next, a method for manufacturing a bipolar electrode for a metal hydride battery according to the present invention will be described by the following embodiments. The method for manufacturing a bipolar electrode for a metal hydride battery according to this embodiment includes a current collector formation step (step 1) and an active material layer formation step (step 2). The current collector forming step (step 1) includes the step of providing a phosphorus-containing nickel layer on at least one surface of the steel plate (step 1a). The current collector forming step (step 1) may include a step (step 1b) of forming nickel phosphide in the phosphorus-containing nickel layer by heat-treating the steel sheet on which the phosphorus-containing nickel layer is provided. The current collector forming step (step 1) may include a nickel layer forming step (step 1c) in which a nickel layer is formed between the phosphorus-containing nickel layer and the negative electrode active material layer or the positive electrode active material layer. The current collector formation step (step 1) may further include a roughened nickel layer formation step (step 1d). The active material layer formation step (step 2) includes the steps of forming a negative electrode active material layer on the first surface of the current collector (step 2a) and providing a positive electrode active material layer on the second surface of the current collector (step 2b).

[0072] Step 1a is described as follows: For example, a nickel-phosphorus alloy plating layer is formed on the surface of the steel sheet using a nickel-phosphorus alloy plating bath by electroplating. A known plating bath can be used as the nickel-phosphorus alloy plating bath. For example, the nickel-phosphorus alloy plating layer can be formed under the following plating conditions. [Example of nickel-phosphorus alloy plating bath and electrolytic plating conditions] bath composition Nickel sulfate hexahydrate: 150~250g / L Nickel chloride hexahydrate: 5-50 g / L Boric acid: 20-50 g / L Trisodium citrate (anhydrous): 1-100 g / L Phosphorous acid: 5-100 g / L Disodium hydrogen phosphite: 5-200 g / L ·Temperature: 25~80℃ pH: 1.0~6.0 • Stirring: Air stirring or jet stirring ·Current density: 1~40A / dm 2 The thickness of the phosphorus-containing nickel layer (nickel-phosphorus alloy plating layer) is preferably 0.1 μm or more. On the other hand, from the viewpoint of productivity, the upper limit of the thickness of the phosphorus-containing nickel layer (nickel-phosphorus alloy plating layer) is preferably 3.0 μm or less, more preferably 2.0 μm or less, and even more preferably 1.0 μm or less.

[0073] Step 1b can be described as follows: The heat treatment may be carried out by either continuous annealing or box annealing (batch annealing). The heat treatment conditions should be appropriately selected to allow nickel phosphide to form in the phosphorus-containing nickel layer. Examples of heat treatment temperature and time include the formation of nickel phosphide as Ni3P in the phosphorus-containing nickel layer by heat treatment at 400°C for 1 hour, and the formation of a metastable crystalline phase when heated at a heating rate of 20°C / min and reaching 360°C.

[0074] Step 1c can be described as follows: A nickel layer can be formed on the phosphorus-containing nickel layer formed in Step 1b by nickel plating using a method such as electroplating. In other words, the nickel layer will be located between the phosphorus-containing nickel layer and the negative electrode active material layer or the positive electrode active material layer. Note that in Step 1c, methods other than electroplating, such as electroless plating, can be applied to form the nickel layer.

[0075] Furthermore, when a drying process is included after plating, and when another plating layer is formed on top of the dried plating layer, it is preferable to ensure good plating adhesion between the upper and lower layers by applying, for example, the strike nickel plating shown below. <Strike Nickel Plating Conditions> ·Bath composition: Nickel sulfate hexahydrate: 100~300g / L Sulfuric acid: 10~150g / L ·Bath temperature: 60℃ ·Current density: 5~40A / dm 2 Plating time: 1-60 seconds

[0076] Step 1d can be described as follows: A roughened nickel layer can be formed by depositing nickel granules in an aggregated state on the phosphorus-containing nickel layer formed in Step 1b, or on the nickel layer formed in Step 1c, using a method such as electroplating. In other words, the roughened nickel layer will be located between the phosphorus-containing nickel layer and the negative electrode active material layer or the positive electrode active material layer. The roughened nickel layer formed in Step 1d will have a surface roughness greater than that of the phosphorus-containing nickel 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 later. In addition to electroplating, other methods such as sputtering or a roll press with a roughened surface can be applied as methods for forming the roughened nickel layer in Step 1d. Furthermore, Step 1d may include a step of forming an underlayment nickel layer before forming the roughened nickel layer.

[0077] Step 2 involves applying an active material layer to the surface of the current collector using conventionally known methods such as roll coating, die coating, dip coating, doctor blade coating, spray coating, or curtain coating. Specifically, the active material, solvent, and optionally binders, conductive additives, and other additives 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 material may be compressed to increase electrode density. Furthermore, the order in which the active material layers are formed on the surface of the current collector may be such that the negative electrode active material layer is provided first, followed by the positive electrode active material layer, or in the reverse order. Alternatively, the negative electrode active material layer and the positive electrode active material layer may be provided simultaneously. In other words, the active material layer formation step (step 2) is not limited in order 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 providing the positive electrode active material layer on the second surface of the current collector (step 2b).

[0078] <Metal Hydride Battery and Method for Manufacturing the Same> The metal hydride battery of the present invention is characterized by having stacked bipolar electrodes of the present invention. For other configurations, configurations disclosed in literature such as Japanese Patent Application Publication No. 2020-140773 can be applied. That is, the metal hydride battery of the present invention includes a bipolar electrode having a negative electrode active material layer on the first surface of a current collector and a positive electrode active material layer on the second surface. As described above, the current collector comprises a steel plate and a phosphorus-containing nickel layer provided on at least one surface of the steel plate. In the metal hydride battery of the present invention, the number of bipolar electrodes can be one or more, and the number of bipolar electrodes can be increased or decreased according to the desired capacity. The metal hydride battery of the present invention can be manufactured by interposing a separator between the bipolar electrodes and sealing it hermetically after injecting the electrolyte. The metal hydride battery of the present invention is, for example, a nickel metal hydride battery.

[0079] The present invention will be described below using a nickel metal hydride battery as an example embodiment, but the present invention is not limited thereto.

[0080] Figure 4 is a schematic cross-sectional view showing one embodiment of an energy storage device. The energy storage device 1 comprises a module stack 2 including a plurality of stacked energy 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.

[0081] The module stack 2 includes a plurality of energy storage modules 4 and a plurality of cooling plates 5. In this embodiment, three energy storage modules 4 and four cooling plates 5 are stacked alternately such that the cooling plates 5 are located on both sides of the energy storage modules 4. Hereinafter, the direction in which the energy storage modules 4 are stacked will be referred to as the "stacking direction D". The direction that intersects or is perpendicular to the stacking direction D will be referred to as the horizontal direction.

[0082] The energy storage module 4 is a bipolar metal hydride battery and is rectangular in shape when viewed from the stacking direction D. In the following description, a nickel metal hydride battery is used as an example of the energy storage module 4. Energy storage modules 4 adjacent to each other in the stacking direction D are electrically connected via cooling plates 5. In the module stack 2, the negative electrode terminal 6 is connected to the cooling plate 5 located at one end in the stacking direction D. The 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, for example, drawn out 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 charging and discharging of the energy storage device 1 is performed by the external circuit. The cooling plate 5 is made of aluminum.

[0083] In this embodiment, the outermost layer of the module stack 2 (the outermost layer of the stack) is the cooling plate 5, but the outermost layer of the module stack 2 may be the energy storage module 4. In this case, the negative terminal 6 or the positive terminal 7 is connected to the energy storage module 4 that constitutes the outermost layer of the stack.

[0084] The cooling plate 5 is provided with multiple flow channels 5a through which a coolant such as air circulates, releasing the heat generated in the energy storage module 4 to the outside of the energy storage device 1. The flow channels 5a extend in directions that intersect (are perpendicular to) the stacking direction D and the exit directions of the negative electrode terminal 6 and positive electrode terminal 7, respectively. The cooling plate 5 is conductive and functions as a connecting member that electrically connects the energy storage modules 4 together. In addition, the cooling plate 5 also functions as a heat dissipation plate that dissipates the heat generated in the energy storage module 4 by circulating the coolant through these flow channels 5a. In this embodiment, in a plan view from the stacking direction D, the area of ​​the cooling plate 5 is smaller than the area of ​​the energy storage module 4. However, from the viewpoint of improving heat dissipation, in a plan view from the stacking direction D, the area of ​​the cooling plate 5 may be the same as the area of ​​the energy storage module 4, or it may be larger than the area of ​​the energy storage module 4. Furthermore, the energy storage module 4 may be heated by circulating a high-temperature coolant through the flow channels 5a.

[0085] 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 module 4 and the cooling plate 5 when viewed from the stacking direction D in a plan view. An insulating film F is placed between the end plates 8 and the module stack 2. The film F insulates the end plates 8 from the module stack 2.

[0086] An insertion hole 8a is provided on the edge of the end plate 8 at a position that is outside the module stack 2 when viewed from the stacking direction D. The fastening bolt 81 is passed from the insertion hole 8a of one end plate 8 to the insertion hole 8a of the other end plate 8. A nut 82 is screwed onto the tip of the fastening bolt 81 that protrudes from the insertion hole 8a of the other end plate 8. In this way, the energy storage module 4 and the cooling plate 5 are sandwiched between the two end plates 8 and unitized as the module stack 2. In addition, a restraining load is applied to the module stack 2 in the stacking direction D.

[0087] Next, the configuration of the energy storage module 4 will be described in detail. Figure 5 is a schematic cross-sectional view showing the internal configuration of the energy storage module shown in Figure 4. As shown in Figure 5, the energy storage module 4 comprises 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 sealing portion 12 that integrates the electrode stack 11 and the conductive plates 40.

[0088] The electrode stack 11 is composed of multiple electrodes stacked along the stacking direction D of the energy storage module 4 via separators SP. 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 in shape when viewed from the stacking direction D.

[0089] The bipolar electrode 100 (200) includes a current collector 10 which includes one side (first side) 10A and the other side (second side) 10B opposite to the first side 10A, a negative electrode active material layer 20 provided on the first side 10A, and a positive electrode active material layer 30 provided on the other side 10B. The positive electrode active material layer 30 is formed by coating the current collector 10 with positive electrode active material. The negative electrode active material layer 20 is formed by coating the current collector 10 with 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 in one direction in the stacking direction D, separated by a separator SP. 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 bipolar electrode 100 (200) adjacent to it in the other direction of stacking direction D, separated by a separator SP.

[0090] The negative electrode terminal electrode 18 comprises a current collector 10 and a negative electrode active material layer 20 provided on one side 10A of the current collector 10. The negative electrode terminal electrode 18 is positioned at one end of the electrode stack 11 in the stacking direction D such that one side 10A faces the center of the stacking direction D in the electrode stack 11. The other side 10B of the current collector 10 of the negative electrode terminal electrode 18 constitutes the outer surface of the electrode stack 11 in the stacking direction D and is electrically connected to one of the cooling plates 5 (see Figure 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.

[0091] The positive terminal electrode 19 comprises a current collector 10 and a positive electrode active material layer 30 provided on the other side 10B of the current collector 10. The positive terminal electrode 19 is positioned at the other end of the electrode stack 11 in the stacking direction D such that the other side 10B faces the center of the stacking direction D in the electrode stack 11. 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 side 10A of the current collector 10 of the positive terminal electrode 19 constitutes the outer surface of the electrode stack 11 in the stacking direction D and is electrically connected to the other cooling plate 5 (see Figure 6) adjacent to the energy storage module 4 via a conductive plate 40.

[0092] The current collector 10 is a plated steel plate. The edge portion 10C of the current collector 10 is an uncoated area where the positive electrode active material and negative electrode active material are not coated, and is rectangular in shape. The positive electrode active material constituting the positive electrode active material layer 30 can be the one described above. The negative electrode active material constituting the negative electrode active material layer 20 can be the one described above. In this embodiment, the area where the negative electrode active material layer 20 is formed on one side 10A of the current collector 10 is slightly larger than the area where the positive electrode active material layer 30 is formed on the other side 10B of the current collector 10.

[0093] The conductive plate 40 is a conductive plate-shaped member provided to suppress the deterioration of the electrode laminate 11. The conductive plate 40 is an uncoated foil in which no active material layer is formed on both sides. The conductive plate 40 is made of, for example, nickel. The conductive plate 40 has a central portion 41 that is in contact with the cooling plate 5 and a rectangular frame-shaped edge portion 42 that surrounds the central portion 41. The edge portion 42 is the part 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 constitutes the outer wall of the energy storage module 4 at both ends in the lamination direction D. If the conductive plate 40 is not provided, the negative electrode termination electrode 18 and the positive electrode termination electrode 19 constitute the outer wall.

[0094] The sealing portion 12 is formed in a rectangular frame shape as a whole, for example, from an insulating resin. The sealing portion 12 is provided along the side surface 11a of the electrode laminate 11 so as to surround the edge 10C of the current collector 10 and the edge 42 of the conductive plate 40. The sealing portion 12 holds the edge 10C of the current collector 10 and the edge 42 of the conductive plate 40. The sealing portion 12 has a plurality of first sealing portions 21 coupled to the edge 10C of the current collector 10 and the edge 42 of the conductive plate 40, and second sealing portions 22 that surround the first sealing portions 21 from the outside along the side surface 11a and are coupled to each of the first sealing portions 21. The constituent material of the first sealing portions 21 and the second sealing portions 22 is, for example, polypropylene.

[0095] The first sealing portion 21 is continuously provided around the entire circumference of the edge 42 of the conductive plate 40, or around the entire circumference of the edge 10C on the other side 10B of the current collector 10, and forms a rectangular frame shape when viewed from the stacking direction D. For the negative terminal electrode 18 and the positive terminal electrode 19, the first sealing portion 21 is provided on the edges 10C of both the one side 10A and the other side 10B of the current collector 10.

[0096] The first seal portion 21 is hermetically joined by welding to the edge 42 of the conductive plate 40 or the other surface 10B of the current collector 10, for example, by ultrasonic or thermocompression bonding. The first seal portion 21 is, for example, a film having a predetermined thickness in the lamination direction D. The first seal portion 21 may be formed by punching out a resin sheet, by arranging a plurality of 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 out a resin sheet. The thickness of the first seal portion 21 is, for example, 50 μm or more and 250 μm or less. The inside of the first seal portion 21 is located between the edges 10C of adjacent current collectors 10 in the lamination direction D. The outside of the first seal portion 21 protrudes outward from the edge of the current collector 10, and its tip is 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 from each other or in contact with each other. Furthermore, the outer edges of the first seal portions 21 may be joined to each other, for example, by hot plate welding.

[0097] 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 resin injection molding and extends along the entire length of the electrode stack 11 in the stacking direction D. The second seal portion 22 is a rectangular frame shape that extends in the axial direction of the stacking direction D. The second seal portion 22 is welded to the outer surface of the first seal portion 21, for example, by the heat during injection molding.

[0098] 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 spaces between adjacent bipolar electrodes 100 (200) along the stacking direction D, between adjacent negative terminal electrodes 18 and bipolar electrodes 100 (200) along the stacking direction D, and between adjacent positive terminal electrodes 19 and bipolar electrodes 100 (200) along the stacking direction D. As a result, an airtightly partitioned internal space V is formed between adjacent bipolar electrodes 100 (200), between negative terminal electrodes 18 and bipolar electrodes 100 (200), and between positive terminal electrodes 19 and bipolar electrodes 100 (200). An electrolyte (not shown) is contained in this internal space V. The electrolyte is impregnated into the separator SP, the positive electrode active material layer 30, and the negative electrode active material layer 20.

[0099] The bipolar electrodes 100 (200) and seal portion 12 adjacent to each other in the stacking direction D, the bipolar electrodes 100 (200) and seal portion 12 adjacent to the negative terminal electrode 18, and the bipolar electrodes 100 (200) and seal portion 12 adjacent to the positive terminal electrode 19 each constitute a cell (single cell).

[0100] Next, an example of a method for manufacturing the energy storage module according to this embodiment will be described. First, the 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 prepared. Subsequently, the first seal portion 21 is welded to the other side 10B of the current collector 10 and to one side 40a of the conductive plate 40. As a result, the first seal portion 21 is bonded 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 side 10A of the current collector 10 of the positive terminal electrode 19.

[0101] Next, the electrode stack 11 is formed (second step). In the second step, first, a stack S is formed by alternately stacking bipolar electrodes 100 (200) to which the first seal portion 21 is attached, and separators SP along the stacking direction D. Subsequently, a negative electrode terminal electrode 18 is placed at one end of the stack S in the stacking direction D, and a positive electrode terminal electrode 19 is placed at the other end of the stack S in the stacking direction D. This forms an electrode stack 11 having bipolar electrodes 100 (200), separators SP, a negative electrode terminal electrode 18, and a positive electrode terminal electrode 19. At this time, the stacked first seal portion 21 forms an internal space V between the electrodes included in the electrode stack 11 and seals the internal space V.

[0102] Next, the conductive plate 40 to which the first seal portion 21 is attached is stacked on the electrode laminate 11 (third step). In the third step, the first seal portion 21 attached to the conductive plate 40 is positioned next to the negative terminal electrode 18 and the positive terminal electrode 19 in the stacking direction D.

[0103] Next, a second seal portion 22 is formed to connect each first seal portion 21 (fourth step). In the fourth step, resin is injection molded onto the outer surface of each first seal portion 21 using, for example, a mold. The second seal portion 22 is then formed by curing the resin by cooling or the like. This forms a seal portion 12 having the first seal portion 21 and the second seal portion 22. At this time, the conductive plate 40 may be welded to each first seal portion 21 that connects to the negative terminal electrode 18 and the positive terminal electrode 19. Although not shown in the figures, after the fourth step, an electrolyte is injected into each internal space V. Through these steps, the energy storage module 4 is manufactured.

[0104] The nickel metal hydride battery of this embodiment preferably includes various components arranged in a known nickel metal hydride battery. 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 comprise a single battery module or a plurality of battery modules arranged in series.

[0105] As the separator, any known material may be used, and examples include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as synthetic resins like polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (aromatic polyamide), polyester, and polyacrylonitrile; polysaccharides like cellulose and amylose; natural polymers like fibroin, keratin, lignin, and suberin; and ceramics. The separator may also have a multilayer structure. It is preferable that the surface of the separator is treated to make it hydrophilic. Examples of hydrophilic treatments include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment.

[0106] The electrolyte can 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 consist of only one type of strong basic aqueous solution, or a mixture of multiple types. Furthermore, the electrolyte may contain known additives used in electrolytes for nickel metal hydride batteries.

[0107] The nickel metal hydride battery of the present invention is provided with sealing portions between its electrodes to prevent electrolyte leakage, suppress mixing of electrolytes between electrodes, and prevent contact between the electrolyte, positive electrode active material layer and negative electrode active material layer and the outside air. The sealing portions are arranged in close contact with two adjacent current collectors and surround the entire area where the electrolyte, positive electrode active material layer and negative electrode active material layer are located. The sealing portions may be arranged in double or triple layers around the area where the electrolyte, positive electrode active material layer and negative electrode active material layer are located.

[0108] Examples of materials for the sealing portion include alkali-resistant insulating resins such as polypropylene, polyphenylene sulfide, and modified polyphenylene ether. Alternatively, materials commonly referred to as gaskets or packings may be used as the sealing portion. The sealing portion may be formed by pressing the sealing portion material against the current collector, by heat-pressing it against the current collector, or by bonding it to the current collector using an adhesive.

[0109] Preferably, an insulating outer frame that does not conduct electricity is placed around the periphery of the electrodes. The outer frame serves to maintain the shape of the electrodes and prevent short circuits between them. The aforementioned sealing portion is placed inside the outer frame. The outer frame may also serve as the sealing portion. Examples of materials for the outer frame include synthetic resin, or synthetic resin containing insulating oxides or insulating ceramics.

[0110] The nickel metal hydride battery of the present invention preferably includes a cooling plate to dissipate heat generated during charging and discharging. The cooling plate is preferably positioned on the outside of the battery module, along the surface of the electrodes. If there are multiple battery modules, it may be positioned between each battery module.

[0111] The cooling plate is preferably made of a metal with excellent thermal conductivity, such as aluminum. The cooling plate is preferably a plate-like body that can be stacked on the surface of the battery module, and more preferably one with through-holes for air cooling.

[0112] In the nickel metal hydride battery of the present invention, the battery module is preferably restrained by a restraining device in the thickness direction, i.e., the direction in which the electrodes are stacked. By restraining the battery module in the stacking direction, the electrolyte can be evenly penetrated into the positive electrode active material layer and the negative electrode active material layer, uneven expansion of the electrodes due to charging and discharging can be suppressed, and fluctuations in the battery's resistance can be suppressed. Furthermore, the sealing effect of the seal portion can be suitably maintained.

[0113] The restraining member may restrain one battery module or multiple battery modules. Preferably, the restraining member consists of two restraining plates and a fastening member that fastens the two restraining plates together. Examples of fastening members include bolts and nuts. The material of the restraining member is preferably one that is highly resistant to strong alkalis. Specific examples of restraining member materials include synthetic resins and insulating ceramics. Alternatively, a battery container housing the battery modules may be used as the restraining member.

[0114] The battery container is a container that houses the battery module. Any battery container used for a known nickel-metal hydride battery may be used. The shape of the battery container is not particularly limited; various shapes such as rectangular, cylindrical, coin-shaped, and laminated can be used. The material of the battery container should preferably be highly resistant to strong alkalis. Specific examples of battery containers include nickel containers, resin containers, metal containers with nickel plating on the inner surface, and metal containers with a resin coating layer on the inner surface.

[0115] The restraining member and battery container may be equipped with exhaust valves, and may also be equipped with an electrolyte refill port.

[0116] The nickel metal hydride battery of the present invention may be installed in vehicles and industrial vehicles. 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 installing a nickel metal hydride battery in a vehicle, it is preferable to connect multiple nickel metal hydride batteries in series to form a battery pack. In addition to vehicles, devices that may be equipped with nickel metal hydride batteries include personal computers, portable communication devices, various home appliances powered by batteries, office equipment, and industrial equipment. Furthermore, the nickel metal hydride battery of the present invention may be used in energy storage devices and power smoothing devices for wind power generation, solar power generation, hydroelectric power generation and other power systems, power supply sources for the power and / or auxiliary equipment of ships, power supply sources for the power and / or auxiliary equipment of aircraft, spacecraft, etc., auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile household robots, system backup power supply, power supply for uninterruptible power supply, and energy storage devices that temporarily store the power necessary for charging in electric vehicle charging stations.

[0117] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. The present invention can be implemented in various forms with modifications, improvements, etc., that can be made by those skilled in the art, without departing from the spirit of the invention.

[0118] The energy storage module according to the present invention is not limited to the above embodiment, and various other modifications are possible. The above embodiment and the contents of each modification may be appropriately selected and combined.

[0119] In the above embodiment, the phosphorus-containing nickel layer 15 is formed on both sides of the current collector 10 that constitutes the bipolar electrode 100 (200), the negative terminal electrode 18, and the positive terminal electrode 19. However, it may also be formed on only one side of the current collector 10. When the phosphorus-containing nickel layer 15 is provided on one side of the current collector 10, it is preferable to provide it on the first side (first surface) 10A. Furthermore, the phosphorus-containing nickel layer 15 does not need to be provided on the current collector 10 that constitutes the positive terminal electrode 19.

[0120] In the above embodiment, the other surface 10B of the current collector 10 included in the bipolar electrode is roughened, but this is not limited to this. For example, only the portion of the other surface 10B included in the coupling region with the first seal portion 21 may be roughened. Alternatively, only the portion of one surface 40a of the conductive plate 40 included in the coupling region with the first seal portion 21 may be roughened.

[0121] In the above embodiment, the current collector and the conductive plate are rectangular in shape when viewed from above, but are not limited to this. The current collector and the conductive plate may be polygonal, circular, or elliptical in shape when viewed from above. Similarly, the end plate, the separator, and the sealing portion (specifically, the first sealing portion and the second sealing portion) may not each be rectangular in shape when viewed from above. [Examples]

[0122] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

[0123] (Example 1) <Manufacturing of current collectors> First, a cold-rolled foil (50 μm thick) 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%, remainder: Fe and unavoidable impurities

[0124] Next, the prepared steel plates were subjected to electrolytic degreasing and pickling by sulfuric acid immersion. Then, nickel-phosphorus alloy plating was performed under the following conditions to form a nickel-phosphorus alloy layer with a phosphorus content of 13.0 wt% and a thickness of 0.75 μm (phosphorus-containing nickel layer formation process). The conditions for nickel-phosphorus alloy plating were as follows.

[0125] <Nickel-phosphorus alloy plating conditions> Bath composition: Nickel sulfate hexahydrate: 190 g / L Nickel chloride hexahydrate: 20 g / L Boric acid: 30g / L Trisodium citrate (anhydrous): 10g / L Phosphorous acid: 65g / L Disodium hydrogen phosphite: 50 g / L ·Temperature: 60℃ pH: 1.5~3.0 • Stirring: Air stirring or jet stirring ·Current density: 1~40A / dm 2 The current density in Example 1 is 5A / dm². 2 In other examples and comparative examples, the phosphorus content ratio was controlled by varying the current density within the above range.

[0126] The phosphorus content ratio was obtained using an ICP (Inductively Coupled Plasma) mass spectrometer. The thickness of the nickel-phosphorus alloy layer was obtained by taking the average of the thicknesses at 10 arbitrary points in the cross-sectional SEM image. In this example and the following examples, in the example where the nickel-phosphorus alloy layer was formed on only one side of the current collector, the thickness of the nickel-phosphorus alloy layer was taken as the average value obtained by dividing the thickness by the two surfaces, assuming that it was formed on both sides. On the other hand, in the example where the nickel-phosphorus alloy layer was formed on both sides of the current collector, the thickness of the nickel-phosphorus alloy layer was taken as the average of the thicknesses at 10 arbitrary points on each surface.

[0127] Next, a 0.5 μm nickel layer was formed under the following plating conditions (nickel layer formation process). <Nickel Plating Conditions> ·Bath composition: Nickel sulfate hexahydrate: 250g / L Nickel chloride hexahydrate: 45 g / L Boric acid: 30g / L pH: 4.0~5.0 ·Bath temperature: 60℃ ·Current density: 10A / dm 2

[0128] Furthermore, a roughened nickel layer was formed using the following plating conditions (roughened nickel layer formation process) to obtain a current collector. The roughened nickel layer was formed by a plating process using the following roughened nickel plating conditions, followed by a coating nickel plating treatment using the following coating nickel plating conditions to improve the adhesion between the steel sheet and the roughened nickel layer. <Conditions for roughened nickel plating> ·Bath composition: Nickel sulfate hexahydrate concentration in the plating bath: 10 g / L Nickel chloride hexahydrate concentration in the plating bath: 10 g / L Chloride ion concentration in the plating bath: 3 g / L Ratio of nickel ions to ammonium ions in the plating bath: Nickel ion / ammonium ion (weight ratio) = 0.17 • pH: 6 ·Bath temperature: 50℃ ·Current density: 12A / dm 2 Plating time: 80 seconds <Conditions for nickel plating> ·Bath composition: Nickel sulfate hexahydrate: 250g / L Nickel chloride hexahydrate: 45 g / L Boric acid: 30g / L pH: 4.2 ·Bath temperature: 60℃ ·Current density: 5A / dm 2 Plating time: 36 seconds

[0129] In other words, the current collector in Example 1, manufactured as described above, comprises a nickel-phosphorus alloy layer, a nickel layer, and a roughened nickel layer. The steel plate is the base material for the current collector. The nickel layer is formed only on one side (first surface) of the current collector. The nickel-phosphorus alloy layer and the roughened nickel layer are formed only on the other side (second surface) of the current collector.

[0130] [Manufacturing of bipolar electrodes] A positive electrode slurry was prepared 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 of acrylic resin emulsion as a binder (solid content), 0.7 parts by mass of carboxymethylcellulose as a binder, 0.5 parts by mass of Y2O3 as a positive electrode additive, and an appropriate amount of deionized water.

[0131] A negative electrode slurry was prepared by mixing 97.8 parts by mass of A2B7 type hydrogen storage alloy as the negative electrode active material, 1.5 parts by mass of acrylic resin emulsion as a binder (as solid content), 0.7 parts by mass of carboxymethylcellulose as a binder, and an appropriate amount of deionized water.

[0132] The negative electrode slurry was applied in a film-like manner to the first surface of the current collector. The positive electrode slurry was applied in a film-like manner to the second surface of the current collector. The current collector coated with the slurry was dried to remove water, and then 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.

[0133] A positive electrode terminal electrode was manufactured in the same manner as the bipolar electrode, except that a negative electrode slurry was not applied to the first surface of the current collector, with a positive electrode active material layer formed on the second surface. A negative electrode terminal electrode was manufactured in the same manner as the bipolar electrode, except that a positive electrode slurry was not applied to the second surface of the current collector, with a negative electrode active material layer formed on the first surface.

[0134] [Manufacturing of evaluation batteries] As electrolytes, aqueous solutions were prepared with 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. A 104 μm thick polyolefin fiber nonwoven fabric, treated with sulfonation, was prepared as the separator SP. A bipolar electrode 100 was sandwiched between a positive terminal electrode 19 and a negative terminal electrode 18 to form an electrode plate group. The separator SP was placed between the electrodes.

[0135] A resin housing (seal portion) 12 was 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 joined by thermocompression bonding. The evaluation battery of Example 1 was manufactured by injecting the electrolyte 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 sealing them hermetically. In this example, one cell (single cell) is formed by the bipolar electrode 100 and the positive terminal electrode 19, and by the bipolar electrode 100 and the negative terminal electrode 18, for a total of two cells. A schematic diagram of the configuration of this evaluation battery is shown in Figure 6.

[0136] (Example 2) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 1.5 μm in the phosphorus-containing nickel layer formation process. Also, the thickness of the nickel layer was set to 1.0 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 1. The current collector in Example 2, manufactured as described above, comprises a nickel-phosphorus alloy layer, a nickel layer, and a roughened nickel layer. The nickel-phosphorus alloy layer and the nickel layer are formed on both sides of the current collector. The roughened nickel layer is formed only on the other side (second side) of the current collector.

[0137] (Example 3) In the current collector manufacturing process, the thickness of the nickel-phosphorus alloy layer was set to 0.1 μm in the phosphorus-containing nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 1. The current collector in Example 3, manufactured as described above, comprises a nickel-phosphorus alloy layer, a nickel layer, and a roughened nickel layer. The nickel-phosphorus alloy layer is formed on only one side (first surface) of the current collector. The nickel layer is formed on both sides of the current collector. The roughened nickel layer is formed on only the other side (second surface) of the current collector.

[0138] (Example 4) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.25 μm.

[0139] (Example 5) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.5 μm.

[0140] (Example 6) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.75 μm.

[0141] (Example 7) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.75 μm and the phosphorus content ratio was set to 10.0 wt%.

[0142] (Example 8) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.25 μm and the phosphorus content ratio to 15.0 wt%.

[0143] (Example 9) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 3, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.6 μm and the phosphorus content ratio to 15.0 wt%.

[0144] (Example 10) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 2, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.6 μm and the phosphorus content ratio to 12.0 wt%.

[0145] (Example 11) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 2, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 1.0 μm and the phosphorus content ratio to 12.0 wt%.

[0146] (Example 12) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 2, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.2 μm and the phosphorus content ratio to 14.0 wt%.

[0147] (Example 13) In the current collector manufacturing process, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 2, except that the thickness of the nickel-phosphorus alloy layer in the phosphorus-containing nickel layer formation process was set to 0.6 μm and the phosphorus content ratio to 14.0 wt%.

[0148] (Comparative Example 1) Using the steel plate from Example 1, a current collector with a base nickel layer and a roughened nickel layer was manufactured by performing the base nickel plating process and the roughened nickel plating process in the same manner as in Example 1. The thickness of the base nickel layer was 1 μm. Nickel-phosphorus alloy plating to provide a nickel-phosphorus alloy layer was not performed. Except for the change in the current collector, a bipolar electrode and an evaluation battery were manufactured in the same manner as in Example 1.

[0149] (Comparative Example 2) Using the steel plate from Example 1, a current collector with a base nickel layer and a roughened nickel layer was manufactured by performing the base nickel plating process and the roughened nickel plating process in the same manner as in Example 1. The thickness of the base nickel layer was 5 μm. Nickel-phosphorus alloy plating to provide the nickel-phosphorus alloy layer was not performed. Except for the change in the current collector, a bipolar electrode and an evaluation battery were manufactured in the same manner as in Example 1.

[0150] [Test of changes in leakage current due to changes in the presence, thickness, and phosphorus content of the nickel-phosphorus alloy layer] Using the evaluation batteries manufactured as described above, we tested and evaluated the changes in leakage current due to the presence or absence and thickness of the nickel-phosphorus alloy layer in the current collector. Specifically, each of the evaluation batteries in Examples 1 to 13 and Comparative Examples 1 to 2 was subjected to activation treatment by repeatedly charging and discharging. After activation, each evaluation battery was adjusted to a State of Charge (SOC) of 85% and then discharged to 0% SOC. The discharge capacity before storage was measured. Each evaluation battery was again adjusted to a State of Charge (SOC) of 85% and stored in a 65°C constant temperature bath for 65 hours. After storage, each evaluation battery was discharged to 0% SOC, and the discharge capacity after storage was measured. For the comparative example, the storage period was 350 hours, but the discharge capacity after storage was measured in the same manner as the example. The leakage current was calculated using the following formula. (Discharge capacity before storage - Discharge capacity after storage) / Storage time = Leakage current Table 1 shows the leakage current values ​​per unit area for each type.

[0151] A comparison of the comparative example and Example 1 showed that the leakage current was reduced by the nickel-phosphorus alloy layer. Furthermore, Examples 1 to 5 showed that increasing the thickness of the nickel-phosphorus alloy layer was effective in reducing the leakage current. Examples 6 and 7 showed that increasing the phosphorus content ratio in the nickel-phosphorus alloy layer was effective in reducing the leakage current. Figure 7 shows a bubble chart illustrating the relationship between the thickness of the nickel-phosphorus alloy layer, the phosphorus content ratio, and the leakage current value. The size of the bubble represents the magnitude of the leakage current value.

[0152] [Table 1]

[0153] (Example 14) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 0.1 μm and the phosphorus content to 11.0 wt% in the phosphorus-containing nickel layer formation process. In addition, the thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. After the phosphorus-containing nickel layer formation process and before the nickel layer formation process, the nickel-phosphorus alloy layer was heat-treated at 400°C for 4 hours. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 2.

[0154] (Example 15) In the current collector manufacturing process, the thickness of the nickel-phosphorus alloy layer was set to 0.3 μm and the phosphorus content to 11.0 wt% in the phosphorus-containing nickel layer formation process. The thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0155] (Example 16) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 0.5 μm and the phosphorus content ratio to 11.0 wt% in the phosphorus-containing nickel layer formation process. In addition, the thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0156] (Example 17) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 0.1 μm and the phosphorus content ratio to 13.0 wt% in the phosphorus-containing nickel layer formation process. In addition, the thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0157] (Example 18) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 0.3 μm and the phosphorus content ratio to 13.0 wt% in the phosphorus-containing nickel layer formation process. In addition, the thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0158] [Test of changes in leakage current in nickel-phosphorus alloy layers due to the presence or absence of nickel phosphide (Ni3P)] Using the evaluation battery manufactured as described above, the change in leakage current due to the presence or absence of nickel phosphide (Ni3P) in the nickel-phosphorus alloy layer of the current collector was tested and evaluated. Specifically, each of the evaluation batteries in Examples 14 to 18 was subjected to repeated charging and discharging to activate them. After activation, each evaluation battery was adjusted to a State of Charge (SOC) of 85% and then discharged to 0% SOC. The discharge capacity before storage was measured. Each evaluation battery was again adjusted to a State of Charge (SOC) of 85% and stored in a 65°C constant temperature bath for 65 hours. After storage, each evaluation battery was discharged to 0% SOC, and the discharge capacity after storage was measured. 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 values ​​per unit area for each. For example, comparing Example 14 and Example 3, it was shown that even with a low phosphorus content, the presence of nickel phosphide (Ni3P) is effective in reducing leakage current when the thickness of the nickel-phosphorus alloy layer is the same. Furthermore, comparing Example 17 and Example 4, it was shown that even with a thin nickel-phosphorus alloy layer, the presence of nickel phosphide (Ni3P) is effective in reducing leakage current when the phosphorus content of the nickel-phosphorus alloy layer is the same.

[0159] [Table 2]

[0160] [Leakage current testing in energy storage modules] (Example 19) Using the same current collector manufacturing process as in Example 1, a current collector and bipolar electrode were manufactured comprising a nickel-phosphorus alloy layer, a nickel layer, and a roughened nickel layer having the thickness and phosphorus content ratio shown in Table 3. In the current collector, the nickel-phosphorus alloy layer was formed on both sides, the nickel layer was formed only on one side (first side) of the current collector, and the roughened nickel layer was formed only on the other side (second side) of the current collector. Subsequently, a power storage module as shown in Figure 6 was fabricated using the same separator, active material, etc. as the evaluation battery described above. This power storage module included positive and negative terminal electrodes in addition to 23 stacked bipolar electrodes. The obtained power storage module was repeatedly charged and discharged to perform an activation treatment. After activation, the power storage module was adjusted to a State of Charge (SOC) of 85%, then discharged to SOC 0%, and the discharge capacity before storage was measured. The power storage module was again adjusted to an SOC of 85%, and stored in a constant temperature bath at 65°C for 1680 hours. The energy storage module was discharged to 0% SOC after storage, and its 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 3 shows the leakage current per unit area.

[0161] (Example 20) Except for the thickness and phosphorus content ratio of the nickel-phosphorus alloy layer in the current collector being as shown in Table 3, a power storage module was fabricated in the same manner as in Example 19, and the leakage current was calculated.

[0162] (Example 21) Except for the thickness and phosphorus content ratio of the nickel-phosphorus alloy layer in the current collector being as shown in Table 3, a power storage module was fabricated in the same manner as in Example 19, and the leakage current was calculated.

[0163] (Comparative Example 4) Except for not performing nickel-phosphorus alloy plating (phosphorus-containing nickel layer formation process) to provide a nickel-phosphorus alloy layer in the current collector formation process, and setting the storage time of the energy storage module in a constant temperature bath to 170 hours, an energy storage module was manufactured in the same manner as in Example 19, and the leakage current was calculated. The obtained leakage current per unit area is shown in Table 3.

[0164] [Table 3]

[0165] (Example 22) In the current collector manufacturing process, the thickness of the nickel-phosphorus alloy layer was set to 0.5 μm and the phosphorus content to 13.0 wt% in the phosphorus-containing nickel layer formation process. The thickness of the nickel layer was set to 0.2 μm in the nickel layer formation process. A roughened nickel layer was not formed. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0166] (Example 23) In the manufacturing process of the current collector, the thickness of the nickel-phosphorus alloy layer was set to 0.5 μm and the phosphorus content ratio to 13.0 wt% in the phosphorus-containing nickel layer formation process. In addition, the thickness of the nickel layer was set to 1.5 μm in the nickel layer formation process. Otherwise, the current collector, bipolar electrode, and evaluation battery were manufactured in the same manner as in Example 14.

[0167] [Test of changes in internal resistance (DC resistance) due to changes in nickel layer thickness] Using the evaluation batteries manufactured as described above, the change in internal resistance (DC resistance) due to changes in the thickness of the nickel layer was tested and evaluated in a current collector having a nickel-phosphorus alloy layer. Specifically, for each evaluation battery in Examples 22 to 23, the internal resistance (DC resistance) was measured using the IV test method, and a value (relative value) was obtained that was compared with the internal resistance (DC resistance) of an evaluation battery using a current collector without a nickel-phosphorus alloy layer. In the IV test, under a state of charge (SOC) of 60%, the resistance was calculated from the measurement results of the current and voltage when charging and discharging for 5 seconds each at current values ​​of 1C (Condition 1), 2C (Condition 2), 5C (Condition 3), and 10C (Condition 4), and the internal resistance (DC resistance) of the evaluation battery using a current collector without a nickel-phosphorus alloy layer was evaluated as a relative value with the internal resistance (DC resistance) set to 100. Table 4 shows the relative values ​​of the internal resistance (DC resistance) of each component.

[0168] [Table 4]

[0169] Comparing Examples 22 and 23, it was shown that increasing the thickness of the nickel layer is effective in reducing the internal resistance (DC resistance) of the current collector.

[0170] The effects and benefits of the bipolar electrode and energy storage module according to this embodiment, as described above, will now be explained. Specifically, the bipolar electrode and energy storage module in this embodiment can reduce the voltage drop of the energy storage module by reducing the amount of hydrogen that permeates the current collector of the bipolar electrode. Therefore, according to the present invention, the long-term reliability of the energy storage module and the metal hydride battery can be improved. [Explanation of Symbols]

[0171] 100: Bipolar electrodes in metal hydride batteries 200: Bipolar electrodes for metal hydride batteries 10: Current collector 10A: First surface of the current collector 10B: Second side of the current collector 13: Steel plate 15: Phosphorus-containing nickel layer 20: Negative electrode active material layer 30: Positive electrode active material layer

Claims

1. Current collector and, A negative electrode active material layer is provided on the first surface of the current collector, A positive electrode active material layer is provided on the second surface of the current collector, Equipped with, The negative electrode active material layer contains a metal hydride. The current collector comprises a steel plate and a phosphorus-containing nickel layer formed on at least one surface of the steel plate. The current collector is characterized by having a further nickel layer between the phosphorus-containing nickel layer and the negative electrode active material layer or the positive electrode active material layer, thereby providing a bipolar electrode for a metal hydride battery.

2. The bipolar electrode of a metal hydride battery according to claim 1, wherein the phosphorus-containing nickel layer comprises a nickel-phosphorus alloy.

3. The bipolar electrode for a metal hydride battery according to claim 1 or claim 2, wherein the thickness of the phosphorus-containing nickel layer is 0.1 μm or more.

4. A bipolar electrode for a metal hydride battery according to any one of claims 1 to 3, wherein the phosphorus content ratio in the phosphorus-containing nickel layer is 9.0 wt% to 15.0 wt%.

5. A bipolar electrode for a metal hydride battery according to any one of claims 1 to 4, wherein the phosphorus-containing nickel layer contains nickel phosphide.

6. The bipolar electrode of a metal hydride battery according to any one of claims 1 to 5, wherein the phosphorus-containing nickel layer is formed on the same side as the first surface of the current collector.

7. The bipolar electrode of a metal hydride battery according to any one of claims 1 to 5, wherein the phosphorus-containing nickel layer is formed on the same side as the second surface of the current collector.

8. The bipolar electrode of a metal hydride battery according to any one of claims 1 to 7, wherein the phosphorus-containing nickel layer is formed on both the side identical to the first surface and the side identical to the second surface of the current collector.

9. The bipolar electrode of a metal hydride battery according to claim 8, wherein the surface of the nickel 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 phosphorus-containing nickel layer or the steel plate.

10. The bipolar electrode of a metal hydride battery according to claim 9, wherein the surface roughness of the nickel layer is Rzjis = 2.0 μm to 16.0 μm in terms of a ten-point average roughness Rzjis.

11. A metal hydride battery characterized in that the bipolar electrodes of the metal hydride battery described in any one of claims 1 to 10 are stacked.

12. A nickel metal hydride battery according to claim 11, wherein the positive electrode active material layer contains nickel hydroxide.

13. A method for manufacturing a bipolar electrode of a metal hydride battery, comprising a current collector formation step and an active material layer formation step, The current collector forming step includes the step of providing a phosphorus-containing nickel layer on at least one surface of a steel plate, The active material layer formation step includes the step of forming a negative electrode active material layer on the first surface of the current collector and the step of providing a positive electrode active material layer on the second surface of the current collector. A method for manufacturing a bipolar electrode for a metal hydride battery, characterized in that the current collector forming step further includes a nickel layer forming step of forming a nickel layer between the phosphorus-containing nickel layer and the negative electrode active material layer or the positive electrode active material layer.

14. The method for manufacturing a bipolar electrode for a metal hydride battery according to claim 13, further comprising the step of forming nickel phosphide in the phosphorus-containing nickel layer by heat-treating the steel sheet on which the phosphorus-containing nickel layer is provided.

15. The current collector forming step further includes a roughened nickel layer forming step in which a roughened nickel layer is formed on the nickel layer, A method for manufacturing a bipolar electrode for a metal hydride battery according to claim 13 or claim 14, wherein the roughened nickel layer formed by the roughened nickel layer formation step has a surface roughness greater than that of the phosphorus-containing nickel layer or the steel sheet.

16. A step of manufacturing a bipolar electrode by the manufacturing method described in any one of claims 13 to 15, A process for manufacturing a metal hydride battery using the aforementioned bipolar electrodes, A method for manufacturing a metal hydride battery having [a specific characteristic].

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