Nickel-metal hydride battery

Abstract

To provide a novel nickel-metal hydride battery which has improved capacity retention.SOLUTION: A nickel-metal hydride battery of the present disclosure includes a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte. A negative electrode active material contained in the negative electrode active material layer is a hydrogen storage alloy having an AB2 main phase, and the A site includes Ti, Zr, or a combination thereof and the B site includes Mn, Cr, Ni, Fe, or a combination thereof. In a first aspect, among all metal atoms in the hydrogen storage alloy, a proportion of Mn is 15 at% or less, a proportion of Cr is 10 at% to 80 at%, a proportion of Ni is 10 at% to 80 at%, and a proportion of Fe is 50 at% or less. In a second aspect, the hydrogen storage alloy contains Al.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to nickel-metal hydride batteries. [Background technology]

[0002] In recent years, hydrogen storage alloys have attracted attention as anodes for alkaline storage batteries, and their development as electrode materials with large discharge capacities is progressing. The properties and performance of these hydrogen storage alloys for electrodes depend heavily on their composition, crystalline structure, and manufacturing method, so these various aspects are being investigated from multiple angles when developing new alloys.

[0003] Although various ideas and improvements have been proposed, the usual method involves melting the constituent elements of various hydrogen storage alloys at high temperatures, cooling the alloy, crushing the alloy mass, and molding it, or mixing the powder with a conductive agent and a resin binder and binding it to a current collector to use as an active material. However, while many of the hydrogen storage alloys to date have a large discharge capacity as active materials, most have poor cycle life characteristics when used in nickel-metal hydride secondary batteries.

[0004] To overcome these drawbacks, in terms of the alloy composition or crystal structure, it has been proposed that the alloy phase has a Laves phase of an intermetallic compound, and the crystal structure is a cubic C15 type or a C14 type. Specifically, Patent Document 1 discloses a hydrogen storage alloy in which the crystal structure of the intermetallic compound as the alloy phase is a cubic C15 type or a hexagonal C14 type belonging to the Laves phase, and the constituent elements Zr, Ti, Nb, V, Ni, Mn, Cr, Co, Fe, Si, Mo, and B are expressed in the following atomic ratio ranges:

[0005] In Patent Document 2, Zr 1-a Mm a Ni b V c Mn d M eThe publication also discloses a hydrogen storage alloy with excellent friability and a negative electrode for a nickel-metal hydride secondary battery that uses this hydrogen storage alloy as an active material, and the alloy has a composition represented by the formula: where M is one or more elements selected from the group consisting of Cr, Fe, Mo, and Nb, and the following relationships are satisfied: 0.03≦a<0.5, 1.0≦b≦1.50, 0.1≦c≦0.5, 0.2≦d≦0.7, 0.05≦e≦0.30, 1.8≦b+c+d+e≦2.3. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-36930 [Patent Document 2] Japanese Patent Application Publication No. 8-73970 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure provides a novel nickel-metal hydride battery with improved capacity retention. [Means for solving the problem]

[0008] As a result of intensive research, the present inventors have found that the above problems can be solved by the following means, and have completed the nickel-metal hydride battery of the present disclosure. <Aspect 1> A nickel-metal hydride battery, a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte solution; the negative electrode active material contained in the negative electrode active material layer is a hydrogen storage alloy having an AB2 type main phase, The A site has Ti, Zr, or a combination thereof; The B site contains Mn, Cr, Ni, Fe, or a combination thereof; and In the total metal atoms of the hydrogen storage alloy, the ratio of Mn is 15 at% or less, the ratio of Cr is 10 at% to 80 at%, the ratio of Ni is 10 at% to 80 at%, and the ratio of Fe is 50 at% or less. Nickel-metal hydride battery. Aspect 2: The nickel-metal hydride battery according to Aspect 1, wherein the atomic ratio of Mn to Cr in the B site of the negative electrode active material is 0.8 or less. <Aspect 3> A nickel-metal hydride battery, a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte solution; the negative electrode active material contained in the negative electrode active material layer is a hydrogen storage alloy having an AB2 type main phase, The A site has Ti, Zr, or a combination thereof; The B site contains Mn, Cr, Ni, Fe, or a combination thereof; and The hydrogen storage alloy contains Al. Nickel-metal hydride battery. Aspect 4: The nickel-metal hydride battery according to Aspect 3, wherein the hydrogen storage alloy contains Al at a ratio of 10 at % or less relative to all metal atoms in the hydrogen storage alloy. [Effects of the Invention]

[0009] According to the present disclosure, a novel nickel-metal hydride battery having an improved capacity retention rate can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a nickel-metal hydride battery of the present disclosure. [Figure 2] FIG. 2 is a graph showing the changes in discharge capacity and capacity retention rate over time in Comparative Example 1 and Examples 1 to 4. [Figure 3] FIG. 3 is a graph showing the changes in discharge capacity and capacity retention rate over time in Comparative Example 1 and Examples 5 to 8. [Figure 4] FIG. 4 is a graph showing the changes in discharge capacity and capacity retention rate over time in Comparative Example 1 and Examples 9 to 12. [Figure 5] FIG. 5 is a graph showing the changes in discharge capacity and capacity retention rate over time in Comparative Example 1 and Examples 13 and 14. [Figure 6] FIG. 6 is a graph showing the changes in discharge capacity and capacity retention rate in Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0011] Nickel-metal hydride battery The nickel-metal hydride battery of the present disclosure comprises: a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte solution; the negative electrode active material contained in the negative electrode active material layer is a hydrogen storage alloy having an AB2 type main phase, The A site has Ti, Zr, or a combination thereof; The B site contains Mn, Cr, Ni, Fe, or a combination thereof.

[0012] In the first embodiment, of all metal atoms in the hydrogen storage alloy, the proportion of Mn is 15 at% or less, the proportion of Cr is 10 at% to 80 at%, the proportion of Ni is 10 at% to 80 at%, and the proportion of Fe is 50 at% or less.

[0013] In a second embodiment, the hydrogen storage alloy contains Al, which may be present in the B site or in the grain boundary phase.

[0014] The present inventors have discovered that Mn, an element with a relatively low oxidation potential among the metal elements constituting the negative electrode active material of a nickel-metal hydride battery, dissolves from the negative electrode active material during charge-discharge cycles due to its low resistance to leaching in electrolytes that are generally strongly alkaline, resulting in a decrease in capacity due to charge-discharge cycles.

[0015] In response to this, the present inventors have found that the above two aspects can suppress the elution of Mn, and as a result, can suppress the decrease in capacity due to charge-discharge cycles.

[0016] More specifically, in the first embodiment, by reducing the amount of Mn, the amount of eluted Mn is reduced, and thus the reduction in battery capacity can be suppressed.

[0017] In the second embodiment, the addition of Al increases the alkali resistance of the hydrogen storage alloy, thereby making it possible to suppress the elution of Mn.

[0018] FIG. 1 schematically illustrates the configuration of a nickel-metal hydride battery 100 according to a first embodiment of the present disclosure. As illustrated in FIG. 1, the nickel-metal hydride battery 100 may include a positive electrode 10, a separator 20, and a negative electrode 30. The positive electrode 10 may include a positive electrode active material layer 11 and a positive electrode current collector 12, and the negative electrode 30 may include a negative electrode active material layer 31 and a negative electrode current collector 32. In this case, the negative electrode active material layer 31 may contain the above-described negative electrode active material. Although not illustrated, the above-described aqueous electrolyte may be contained in the positive electrode active material layer 11 and the negative electrode active material layer 31.

[0019] Each component of the present disclosure will be described below.

[0020] <Negative electrode current collector layer> The negative electrode current collector layer may be composed of a known metal usable as a negative electrode current collector for nickel-metal hydride batteries. Examples of such metals include metal materials containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. In particular, considering stability in an aqueous electrolyte, the negative electrode current collector may contain at least one element selected from the group consisting of Al, Ti, Pb, Zn, Sn, Mg, Zr, and In, or may contain at least one element selected from the group consisting of Ti, Pb, Zn, Sn, Mg, Zr, and In, or may contain Ti. Al, Ti, Pb, Zn, Sn, Mg, Zr, and In all have low work functions, and are therefore unlikely to cause electrolysis of the aqueous electrolyte even when in contact with the aqueous electrolyte.

[0021] <Negative electrode active material layer> The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may contain a conductive additive and a binder in addition to the negative electrode active material. The thickness of the negative electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0022] (Negative electrode active material) The negative electrode active material contains a hydrogen storage alloy having an AB2 type main phase.

[0023] The content of the negative electrode active material is not particularly limited, and may be, for example, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 45% by mass or more, relative to the mass of the negative electrode active material layer, or may be 99% by mass or less, 97% by mass or less, 95% by mass or less, 29% by mass or less, 90% by mass or less, 88% by mass or less, 85% by mass or less, 83% by mass or less, 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less.

[0024] (Negative electrode active material: hydrogen storage alloy) The hydrogen storage alloy has an AB2 type main phase, where the atom with the larger atomic radius is referred to as "A" and the atom with the smaller atomic radius is referred to as "B" among two types of atoms with different sizes.

[0025] The A site contains Ti, Zr, or a combination thereof.

[0026] The B site contains Mn, Cr, Ni, Fe, or a combination thereof.

[0027] The hydrogen storage alloy of the present disclosure can be obtained by mixing and melting the constituent metals, for example, by arc melting.

[0028] (Hydrogen Storage Alloy: First Aspect) In a first aspect of the hydrogen storage alloy of the present disclosure, the Mn content may be 15 at% or less, 14 at% or less, 13 at% or less, 12 at% or less, 11 at% or less, 10 at% or less, 9 at% or less, 8 at% or less, 7 at% or less, 6 at% or less, 5 at% or less, 4 at% or less, 3 at% or less, 2 at% or less, 1 at% or less, or 0 at% relative to the total metal atoms of the hydrogen storage alloy.

[0029] In a first aspect of the hydrogen storage alloy of the present disclosure, the Cr content may be 10 at% or more, 12 at% or more, 15 at% or more, or 18 at% or more, and may be 80 at% or less, 75 at% or less, 70 at% or less, 65 at% or less, 60 at% or less, 55 at% or less, 50 at% or less, 45 at% or less, 40 at% or less, or 38 at% or less, relative to the total metal atoms of the hydrogen storage alloy.

[0030] In a first aspect of the hydrogen storage alloy of the present disclosure, the Ni content may be 10 at% or more, 12 at% or more, 15 at% or more, or 18 at% or more, relative to the total metal atoms of the hydrogen storage alloy, and may be 80 at% or less, 75 at% or less, 70 at% or less, 65 at% or less, 60 at% or less, 55 at% or less, 50 at% or less, 45 at% or less, 40 at% or less, 38 at% or less, 35 at% or less, or 32 at% or less.

[0031] In a first aspect of the hydrogen storage alloy of the present disclosure, the Fe content may be 50 at% or less, 45 at% or less, 40 at% or less, 35 at% or less, 30 at% or less, 25 at% or less, 20 at% or less, 15 at% or less, 10 at% or less, 5 at% or less, 3 at% or less, 2 at% or less, 1 at% or less, or 0 at% or less, relative to the total metal atoms of the hydrogen storage alloy.

[0032] In a first aspect of the hydrogen storage alloy of the present disclosure, the content of metal atoms belonging to the A site may be 20 at% or more, 25 at% or more, 28 at% or more, 30 at% or more, 33 at% or more, 35 at% or more, or 38 at% or more, relative to the total metal atoms in the hydrogen storage alloy, and may be 60 at% or less, 55 at% or less, 53 at% or less, 50 at% or less, 48 ​​at% or less, or 45 at% or less.

[0033] In a first aspect of the hydrogen storage alloy of the present disclosure, the content of metal atoms belonging to the B site may be 40 at% or more, 45 at% or more, 47 at% or more, 50 at% or more, 52 at% or more, or 55 at% or more, and may be 80 at% or less, 75 at% or less, 72 at% or less, 70 at% or less, 67 at% or less, 65 at% or less, or 62 at% or less, relative to the total metal atoms in the hydrogen storage alloy.

[0034] In the first embodiment of the hydrogen storage alloy of the present disclosure, the atomic ratio of Ni to Cr is preferably 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less from the viewpoint of capacity retention. This atomic ratio may be 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more.

[0035] In the first aspect of the hydrogen storage alloy of the present disclosure, from the viewpoint of capacity retention, it is preferable that the atomic ratio of Mn to Cr is 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, or 0. When all or part of the Mn in a conventional hydrogen storage alloy is replaced with Cr, which has a similar atomic radius and relatively high corrosion resistance, elution of components of the hydrogen storage alloy during charge-discharge cycles can be suppressed.

[0036] (Hydrogen Storage Alloy: Second Aspect) In a second embodiment, the hydrogen storage alloy of the present disclosure contains Al.

[0037] In a second aspect of the hydrogen storage alloy of the present disclosure, the Al content may be 1 at% or more, 3 at% or more, 5 at% or more, or 7 at% or more, and may be 10 at% or less, or 9 at% or less, relative to the total metal atoms of the hydrogen storage alloy.

[0038] In a second aspect of the hydrogen storage alloy of the present disclosure, the Mn content may be 20 at% or less, 19 at% or less, 18 at% or less, 17 at% or less, 16 at% or less, 15 at% or less, 14 at% or less, 13 at% or less, 12 at% or less, 11 at% or less, 10 at% or less, 9 at% or less, 8 at% or less, 7 at% or less, 6 at% or less, 5 at% or less, 4 at% or less, 3 at% or less, 2 at% or less, 1 at% or less, or 0 at% relative to the total metal atoms of the hydrogen storage alloy.

[0039] In the second embodiment of the hydrogen storage alloy of the present disclosure, the contents of metal atoms other than Al and Mn can be referred to the description of the first embodiment.

[0040] (Conductive additive) The conductive additive optionally contained in the positive electrode active material layer may be any of those known as conductive additives used in nickel-metal hydride batteries, such as metal powder, metal oxide, and carbon material. Examples of the metal powder include Ni powder, specifically, Ketjen Black (KB), vapor-grown carbon fiber (VGCF), acetylene black (AB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon black, coke, and graphite. Alternatively, the conductive additive may be a metal material that can withstand the environment in which the battery is used. Only one type of conductive additive may be used alone, or two or more types may be used in combination. The conductive additive may be in various forms, such as powder or fiber.

[0041] The amount of the conductive additive contained in the negative electrode active material layer is not particularly limited, and may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 7% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, or 45% by mass or more, relative to the mass of the negative electrode active material, or 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less.

[0042] (binder) The binder optionally contained in the negative electrode active material layer can be any binder known to be used in potassium ion secondary batteries. Examples include styrene butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC)-based binders, acrylonitrile butadiene rubber (ABR)-based binders, butadiene rubber (BR)-based binders, polyvinylidene fluoride (PVDF)-based binders, and polytetrafluoroethylene (PTFE)-based binders. One type of binder may be used alone, or two or more types may be used in combination.

[0043] The amount of binder contained in the negative electrode active material layer is not particularly limited, and may be, for example, 1% by mass or more, or 2% by mass or more, relative to the mass of the negative electrode active material, and may be 20% by mass or less, 18% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, 7% by mass or less, 5% by mass or less, 4% by mass or less, or 3% by mass or less.

[0044] <Positive electrode current collector layer> The positive electrode current collector layer may be made of a known metal that can be used as a positive electrode current collector for nickel-metal hydride batteries. Examples of such metals include metal materials containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. The shape of the positive electrode current collector is not particularly limited. It may take various forms, such as a foil, a mesh, or a porous form. The above metal may be deposited or plated on the surface of a substrate.

[0045] <Cathode active material layer> The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may further contain an optional conductive additive, a binder, etc. The thickness of the positive electrode active material layer is not particularly limited, but may be, for example, 0.1 μm or more or 1 μm or more, or 1 mm or less or 100 μm or less.

[0046] The types of conductive additives and binders optionally contained in the positive electrode active material layer are not particularly limited, and can be appropriately selected from, for example, those exemplified as conductive additives and binders optionally contained in the negative electrode active material layer. The amounts of conductive additives and binders contained in the positive electrode active material layer are not particularly limited, and the amounts mentioned for the negative electrode active material layer can be referenced.

[0047] (Cathode active material) As the positive electrode active material, any nickel compound, particularly nickel hydroxide, that can be used to form a nickel-metal hydride battery in combination with an aqueous electrolyte and the negative electrode of the present disclosure can be used, such as nickel hydroxide (Ni(OH)2), nickel oxyhydroxide (NiO(OH)), etc.

[0048] The content of the positive electrode active material is not particularly limited, and may be, for example, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more, or may be 99% by mass or less, 97% by mass or less, 95% by mass or less, 29% by mass or less, 90% by mass or less, 88% by mass or less, 85% by mass or less, 83% by mass or less, or 80% by mass or less, relative to the mass of the positive electrode active material layer.

[0049] <Aqueous electrolyte> The aqueous electrolyte used in the nickel-metal hydride battery of the present disclosure contains an aqueous solvent and an alkali metal hydroxide dissolved in the aqueous solvent.

[0050] The pH of the aqueous electrolyte may be 10.0 or higher, 11.0 or higher, 11.5 or higher, 12.0 or higher, 12.5 or higher, 13.0 or higher, or 13.5 or higher.

[0051] (aqueous solvent) The aqueous solvent is a solvent containing water. The aqueous solvent may contain water as a main component. That is, based on the total amount (100 mol%) of the aqueous solvent constituting the electrolytic solution, water may account for 50 mol% or more, 70 mol% or more, 90 mol% or more, or 95 mol% or more. The upper limit of the proportion of water in the aqueous solvent is not particularly limited, and the aqueous solvent may be 100 mol%, i.e., the entire amount may be water.

[0052] The aqueous solvent may consist of only water, or may further contain one or more organic solvents selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. The solvent other than water may account for 50 mol % or less, 30 mol % or less, 10 mol % or less, or 5 mol % or less of the total amount of the aqueous solvent constituting the electrolyte (100 mol %).

[0053] (alkali metal hydroxides) Examples of alkali metal hydroxides that can be used include potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH).

[0054] The concentration of the alkali metal hydroxide may be 1 mol / L or more, 2 mol / L or more, 3 mol / L or more, 4 mol / L or more, or 5 mol / L or more, and may be 20 mol / L or less, 18 mol / L or less, 15 mol / L or less, 12 mol / L or less, 10 mol / L or less, 9 mol / L or less, 8 mol / L or less, or 7 mol / L or less.

[0055] <Other configurations> In addition to the above configuration, the nickel-metal hydride battery may also have other obvious battery components such as terminals and a battery case.

[0056] A nickel-metal hydride battery having the above configuration can be manufactured, for example, by forming a positive electrode active material layer on the surface of a positive electrode current collector by a dry or wet method to obtain a positive electrode, forming a negative electrode active material layer on the surface of a negative electrode current collector by a dry or wet method to obtain a negative electrode, and disposing a separator between the positive electrode and the negative electrode and impregnating them with an aqueous electrolyte solution. [Example]

[0057] The present disclosure will be specifically explained with reference to examples and comparative examples, but the present disclosure is not limited to these.

[0058] Using the reagents for each metal element in the atomic ratios shown in Table 1, 15g ingots were prepared by arc melting. The alloys were prepared by homogenizing the materials by performing the melting three times. The purity of Zr in the reagents used was 98%, and the purity of the other metal elements was 99.9%.

[0059] The obtained alloy was pulverized in a manual stamp mill (Tokyo Glass Instruments, DA-30) and classified into particles of 38 to 100 μm using a 38 μm sieve and a 100 μm sieve.

[0060] The obtained alloy was quantitatively analyzed by ICP.

[0061] For the first embodiment, the amounts of reagents added are shown in Table 1, and the measured ICP values ​​are shown in Table 2.

[0062] For the second embodiment, the amounts of reagents added are shown in Table 3, and the measured ICP values ​​are shown in Table 4.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] [Table 4]

[0067] <<Preparation of evaluation cell>> An evaluation cell was prepared as follows.

[0068] First, a negative electrode was prepared. More specifically, a paste-like composition was prepared by kneading 49 parts by mass of the above-described alloy as the negative electrode active material, 49 parts by mass of Ni powder as a conductive additive, and 2 parts by mass of carboxymethyl cellulose (CMC) as a binder. This paste-like composition was filled into a negative electrode current collector, subsequently dried in a vacuum at 80°C, and then roll-pressed (clearance 300 μm) at approximately 8 kN to obtain a negative electrode. The negative electrode current collector used was porous Ni (Celmet #7, manufactured by Sumitomo Electrochemical Co., Ltd., thickness 1.6 mm) with a Ni tab welded thereto. The capacity was adjusted to approximately 240 mAh.

[0069] Next, a positive electrode was prepared. More specifically, a paste-like composition was prepared by kneading 88 parts by mass of nickel hydroxide (Ni(OH)2) as a positive electrode active material, 10 parts by mass of cobalt oxide (CoO) as a conductive additive, and 1 part by mass each of two types of binders (carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA)). This paste-like composition was filled into the porous nickel, followed by vacuum drying at 80°C and then roll pressing at approximately 8 kN to obtain a positive electrode. The capacity ratio of the negative electrode to the positive electrode was adjusted to negative electrode:positive electrode = 1:4.5.

[0070] Next, an electrolyte solution was prepared. Pure water was added to KOH to adjust the KOH concentration to 6 mol / L, obtaining 90 ml of electrolyte solution. The electrolyte solution and a separator (PE / PP nonwoven fabric, 150 μm thick) were then placed in a container, followed by a negative electrode (working electrode), a positive electrode (counter electrode), and a Hg / HgO electrode (reference electrode), to obtain an evaluation cell.

[0071] <Charge / discharge test (25°C)> The obtained evaluation cell was subjected to charge-discharge acclimatization until the negative electrode capacity was saturated. More specifically, the following charge-discharge cycles (1) to (4) were performed. (1) The battery was charged at 0.1 C for 14 hours and then discharged at 0.1 C until the negative electrode potential reached −0.6 V. (2) The battery was charged at 0.5 C for 2.2 hours and then discharged at 0.5 C until the negative electrode potential reached −0.6 V. (3) The battery was then charged at 0.1 C for 14 hours and then discharged at 0.1 C until the negative electrode potential reached −0.6 V. (4) The above charge / discharge cycles (1) to (3) were repeated until the 0.1 C discharge capacity was saturated, and the obtained electrode capacity was taken as the initial capacity.

[0072] The intersections with the vertical axes of the graphs shown in FIGS. 2 to 6 correspond to this initial capacity.

[0073] After the charge-discharge test, the evaluation cell was charged for 5 hours at 0.1 C. Next, while observing the amount of electricity, the cell was repeatedly charged and discharged at 0.5 C, with 20 cycles between a potential corresponding to an SOC of 25% and a potential corresponding to an SOC of 75%, to perform charge-discharge equivalent to an SOC of 1000%.

[0074] After this cycle, the battery was charged at 0.1 C for 14 hours, and then discharged at 0.1 C until the negative electrode potential reached −0.6 V, to check the capacity.

[0075] The above charge / discharge cycle and capacity check were repeated every 1000% SOC to record the change in capacity for each 1000% SOC. This procedure was repeated until charging / discharging equivalent to 10,000% SOC was performed.

[0076] The evaluation results of the examples and comparative examples are shown in FIGS.

[0077] 2 to 5 and Tables 1 and 2, it can be seen that in Examples 1 to 12, in which the Mn content was set to 15 at % or less by reducing the amount of Mn or substituting all or part of the Mn with Cr or Fe compared to Comparative Example 1 (base composition), the capacity retention rate was improved.

[0078] Furthermore, it can be seen from FIG. 6 and Tables 3 and 4 that Examples 13 and 14, in which Al was added, had a good capacity retention rate. [Explanation of symbols]

[0079] 10 positive electrode 11 Cathode active material layer 12 Positive electrode current collector 20 Separator 30 negative electrode 31 Negative electrode active material layer 32 Negative electrode current collector 100 Nickel-metal hydride batteries

Claims

1. A nickel-metal hydride battery, a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte solution; The negative electrode active material contained in the negative electrode active material layer is AB ２ A hydrogen storage alloy having a main phase of the type: The A site is composed of a combination of Ti and Zr, The B site consists of a combination of Cr and Ni, or a combination thereof with Mn and / or Fe, and In the total metal atoms of the hydrogen storage alloy, the ratio of Mn is 15 at% or less, the ratio of Cr is 10 at% to 38 at%, the ratio of Ni is 10 at% to 32 at%, and the ratio of Fe is 50 at% or less. Nickel-metal hydride battery.

2. 2. The nickel-metal hydride battery according to claim 1, wherein the atomic ratio of Mn to Cr in the B site of the negative electrode active material is 0.8 or less.

3. A nickel-metal hydride battery, a positive electrode active material layer, a negative electrode active material layer, and an aqueous electrolyte solution; The negative electrode active material contained in the negative electrode active material layer is AB ２ A hydrogen storage alloy having a main phase of the type: The A site is composed of a combination of Ti and Zr, the B site is composed of a combination of Cr and Ni, or a combination thereof with Mn and / or Fe and / or Al; The hydrogen storage alloy contains Al, and In the total metal atoms of the hydrogen storage alloy, the ratio of Mn is 15 at% or less, the ratio of Cr is 10 at% to 80 at%, the ratio of Ni is 10 at% to 80 at%, and the ratio of Fe is 50 at% or less. Nickel-metal hydride battery.

4. 4. The nickel-metal hydride battery according to claim 3, wherein said hydrogen storage alloy contains Al at a ratio of 10 at % or less to the total metal atoms of said hydrogen storage alloy.

Images