Secondary battery

Abstract

To provide a high-capacity secondary battery.SOLUTION: A secondary battery comprising a positive electrode layer, wherein the positive electrode layer contains, as a positive electrode active material, at least one of a Ni-based hydroxide containing a nickel element and a Co-coated Ni-based hydroxide having a coating layer containing a cobalt element on at least a part of a surface of the Ni-based hydroxide, and the positive electrode layer contains, as an additive, a first additive containing a boron element or a mixed additive of the first additive and a second additive containing a cobalt element.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[0002] Various technologies have been proposed regarding batteries such as those disclosed in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-68108 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-18743 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses an electrode active material containing at least one of vanadium metal and a vanadium compound, and at least nickel hydroxide or a hydrogen storage alloy, with the aim of providing an alkaline secondary battery that has excellent utilization of the active material over a wide temperature range and does not contain cadmium. However, conventional secondary batteries have a small capacity and there is room for improvement. One method for increasing the capacity of a secondary battery is to increase the amount of positive electrode active material, but the internal volume of a battery is fixed, and there is a limit to how much the amount of positive electrode active material can be increased.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a high-capacity secondary battery. [Means for solving the problem]

[0006] The secondary battery of the present disclosure is a secondary battery having a positive electrode layer, wherein the positive electrode layer contains, as a positive electrode active material, at least one of a Ni-based hydroxide containing nickel element and a Co-coated Ni-based hydroxide having a coating layer containing cobalt element on at least a portion of the surface of the Ni-based hydroxide, and the positive electrode layer contains, as an additive, a first additive containing boron element or a mixed additive of the first additive and a second additive containing cobalt element. [Effects of the Invention]

[0007] The present disclosure can provide a high-capacity secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a secondary battery that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field.

[0009] The present disclosure provides a secondary battery including a positive electrode layer, wherein the positive electrode layer includes, as a positive electrode active material, at least one of a Ni-based hydroxide containing nickel element and a Co-coated Ni-based hydroxide having a coating layer containing cobalt element on at least a portion of the surface of the Ni-based hydroxide, and the positive electrode layer includes, as an additive, a first additive containing boron element or a mixed additive of the first additive and a second additive containing cobalt element.

[0010] In the secondary battery of the present disclosure, the battery capacity has been successfully improved by combining at least one of a Ni-based hydroxide and a Co-coated Ni-based hydroxide as a positive electrode active material in the positive electrode layer with either a first additive containing elemental boron or a mixed additive of the first additive and a second additive containing elemental cobalt. This is thought to be because the inclusion of either the first additive or the mixed additive containing elemental boron in the positive electrode layer improves the utilization of the Ni-based hydroxide and the Co-coated Ni hydroxide as positive electrode active materials, thereby increasing the energy density.

[0011] In the present disclosure, the secondary battery may be, for example, an alkaline secondary battery. Here, alkaline secondary battery is a general term for secondary batteries whose electrolyte is an alkaline aqueous solution, and examples thereof include nickel-metal hydride batteries, nickel-cadmium batteries, nickel-zinc batteries, and nickel-iron batteries. The secondary battery of the present disclosure includes a positive electrode layer, and typically includes a positive electrode, an electrolyte layer, and a negative electrode. The structure of the battery is not particularly limited, and may be a wound type, a laminated type, or a bipolar type.

[0012] [Positive electrode] The positive electrode has at least a positive electrode layer, and may have a positive electrode current collector as necessary.

[0013] As described above, the positive electrode layer contains a specific positive electrode active material and a specific additive. The positive electrode layer contains, as a positive electrode active material, at least one of a nickel-based hydroxide containing nickel element and a cobalt-coated nickel-based hydroxide. Examples of Ni-based hydroxides include nickel hydroxide and nickel oxyhydroxide. Nickel hydroxide is in the form of nickel hydroxide (II) [Ni(OH)] when the secondary battery is discharged, and is in the form of nickel oxyhydroxide [NiOOH] when the secondary battery is charged. In other words, a secondary battery using nickel hydroxide as the positive electrode active material contains at least one of nickel hydroxide (II) and nickel oxyhydroxide. The Ni-based hydroxide may contain elements and groups other than Ni and hydroxyl groups, and may contain metals such as magnesium, calcium, aluminum, manganese, and zinc in solid solution.

[0014] The Co-coated Ni-based hydroxide may be the above-mentioned Ni-based hydroxide, at least a part of the surface of which is coated with a Co-coating layer containing cobalt element. By using the Co-coated Ni-based hydroxide, the conductivity of the positive electrode layer is improved, and an increase in energy density can be expected. The Co coating layer may be a metallic cobalt layer, a cobalt compound layer such as cobalt hydroxide or cobalt oxyhydroxide, or both a metallic cobalt layer and a cobalt compound layer. The Co coating layer may contain metal elements other than cobalt, such as calcium, magnesium, or zinc.

[0015] Note that cobalt hydroxide is oxidized to cobalt oxyhydroxide by initial charging or the like, and therefore Ni-based hydroxide coated with cobalt hydroxide may exist in the secondary battery as Ni-based hydroxide coated with cobalt oxyhydroxide. The coverage of the Ni-based hydroxide surface with the Co coating layer is not particularly limited, but may be, for example, 1 to 100%.

[0016] As the positive electrode active material, only a Ni-based hydroxide may be used alone, only a Co-coated Ni-based hydroxide may be used alone, or a combination of a Ni-based hydroxide and a Co-coated Ni-based hydroxide may be used. The total content of the Ni-based hydroxide and the Co-coated Ni-based hydroxide in the positive electrode layer may be, for example, 75 to 99 mass % or 85 to 95 mass % when the mass of the entire positive electrode layer is 100 mass %.

[0017] The positive electrode layer contains either a first additive containing elemental boron or a mixed additive of the first additive and a second additive containing elemental cobalt. The shapes of the first additive and the second additive are not particularly limited, and various shapes such as powder and fiber can be adopted.

[0018] The first additive containing elemental boron may be boron alone or a boron compound. Examples of boron compounds include oxides and hydroxides. Examples of boron oxides include diboron trioxide (BO) and boric acid (HBO). The first additive may be a single type or a combination of two or more types. The first additive, whether boron elemental or a compound such as an oxide or hydroxide, converges to a thermodynamically stable state when the positive electrode layer is in contact with an alkaline aqueous solution and simultaneously exposed to the positive electrode potential. Therefore, whether the first additive is boron elemental or a compound such as an oxide or hydroxide, it is believed possible to improve the utilization rate of the positive electrode active material, Ni-based hydroxide or Co-coated Ni-based hydroxide. From the perspective of acquisition cost, boron oxide may be advantageous in some cases. The content of the first additive in the positive electrode layer may be, for example, 0.1 to 10 mass % or 0.5 to 5 mass % when the mass of the entire positive electrode layer is taken as 100 mass %.

[0019] Examples of the second additive containing elemental cobalt include metallic cobalt, as well as cobalt compounds such as cobalt hydroxide and cobalt oxyhydroxide. The ratio of the first additive and the second additive in the mixed additive is not particularly limited, and may be, for example, such that, when the mass of the entire positive electrode layer is 100 mass%, the content of the first additive is 0.1 to 10 mass% and the content of the second additive is 0.1 to 20 mass%, or such that the content of the first additive is 0.5 to 5 mass% and the content of the second additive is 0.5 to 10 mass%. In the mixed additive, each of the first additive and the second additive may be a single type, or two or more types may be combined.

[0020] The positive electrode layer may contain, in addition to the positive electrode active material and the additive, other components such as a conductive material, a binder, an additive different from the additives described above, as necessary. Examples of conductive materials include carbon black, graphite, Ketjenblack (KB), etc. The content of the conductive material in the positive electrode layer can be, for example, 0.1 to 10 mass % when the mass of the entire positive electrode layer is taken as 100 mass %.

[0021] Examples of binders include carboxymethyl cellulose (CMC), polypropylene (PP), diutan gum, polyvinyl alcohol (PVA), hydroxypropyl cellulose (HPC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), acrylonitrile, etc. One type of binder may be used alone, or two or more types may be used in combination. The content of the binder in the positive electrode layer can be, for example, 0.015 to 15 mass % when the mass of the entire positive electrode layer is taken as 100 mass %.

[0022] The positive electrode layer can be produced, for example, as follows. First, a conductive material, a binder, and the like are added to the positive electrode active material and additives, which are essential materials in the present disclosure, as needed, and water is further added and kneaded to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to and filled on a conductive porous positive electrode current collector (e.g., foamed nickel), dried, and then pressed to produce a positive electrode including a positive electrode layer and a positive electrode current collector.

[0023] [Electrolyte layer] The electrolyte layer includes at least an electrolyte, which may be an electrolytic solution. The electrolyte may be, for example, an alkaline aqueous solution containing a hydroxide such as potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. The hydroxide concentration in the electrolyte may be, for example, 1 to 10 mol / L. The electrolyte is usually impregnated in a separator before being incorporated into the battery. The separator is made of an insulating material to ensure insulation between the positive and negative electrodes. Examples of separators include nonwoven fabrics and woven fabrics made from one or more insulating materials, such as synthetic resins (e.g., polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid, polyester, and polyacrylonitrile), polysaccharides (e.g., cellulose and amylose), natural polymers (e.g., fibroin, keratin, and lignin), and ceramics.

[0024] [Negative electrode] The negative electrode can have a known structure, and usually has a negative electrode layer containing at least a negative electrode active material, and may have a negative electrode current collector as needed. Examples of negative electrode active materials include hydrogen storage alloys. Examples of hydrogen storage alloys include AB-type alloys such as TiFe and TiCo, AB-type alloys such as MgZn2, ZrMn2, ZrV2, ZrCr2, and ZrNi2, A2B-type alloys such as Mg2Ni and Mg2Cu, and AB5-type alloys such as CaNi5, LaNi5, and MmNi5 (Mm stands for a rare earth element mixture called misch metal). Among these, the hydrogen storage alloy may contain at least one selected from the group consisting of rare earth elements, Mg, and Ni. The negative electrode layer may contain 85 to 100% by mass of the negative electrode active material, assuming that the mass of the entire negative electrode layer is 100%.

[0025] The negative electrode layer may be a substrate carrying a hydrogen storage alloy or a molded body of the hydrogen storage alloy. Examples of the substrate that can be used include porous metals such as foamed nickel substrates and perforated metal plates such as punched metals. The negative electrode layer may contain, as necessary, a conductive material, a binder, an additive, etc. Examples of conductive materials include carbon black, graphite, and ketjen black. Examples of binders include those exemplified as binders contained in the positive electrode. Examples of additives include Y2O3.

[0026] The negative electrode layer can be produced, for example, as follows. First, a conductive material, a binder, and the like are added to a hydrogen storage alloy, which is the negative electrode active material, as needed, and water is further added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to and filled on a negative electrode current collector, which is a conductive porous material (for example, a foamed nickel substrate), and then dried and pressed to produce a negative electrode comprising a negative electrode layer and a negative electrode current collector.

[0027] The secondary battery of the present disclosure may have other configurations than those described above, for example, known configurations such as terminals and a battery case. Examples of applications of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered automobiles, diesel-powered automobiles, etc. The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices. [Example]

[0028] Example 1 The materials shown in Table 1 were mixed together, and water was added to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry was applied to a positive electrode current collector and dried to prepare a positive electrode comprising a positive electrode layer and a positive electrode current collector.

[0029] [Table 1]

[0030] Furthermore, the materials shown in Table 2 were mixed together, and water was added to prepare a negative electrode mixture slurry. The obtained negative electrode mixture slurry was applied to a negative electrode current collector and dried to prepare a negative electrode comprising a negative electrode layer and a negative electrode current collector.

[0031] [Table 2]

[0032] A small cell battery was assembled using the prepared positive and negative electrodes, a separator, and an electrolyte (aqueous potassium hydroxide solution), and the full charge capacity at 25°C was measured.

[0033] (Comparative Examples 1 to 6) Small cell batteries were fabricated in the same manner as in Example 1, except that the positive electrode composite slurries were prepared using 1.5 mass% MoO3 (Comparative Example 1), 1.5 mass% VO5 (Comparative Example 2), 1.5 mass% WO3 (Comparative Example 3), 1.5 mass% YO3 (Comparative Example 4), 1.5 mass% Sb2O3 (Comparative Example 5), and 1.5 mass% ZrO2 (Comparative Example 6) instead of 1.5 mass% B2O3, and the full charge capacity at 25°C was measured.

[0034] The relative initial full charge capacity was calculated for Example 1 and Comparative Examples 2 to 6, with the initial full charge capacity of Comparative Example 1 taken as 100%. The results are shown in Table 3.

[0035] [Table 3]

[0036] As shown in Table 3, it was confirmed that the battery of Example 1, which used B2O3 containing boron element and metallic Co as additives, had a larger capacity than any of the batteries of Comparative Examples 1 to 6, which did not use an additive containing boron element.

Claims

[Claim 1] A secondary battery including a positive electrode layer, the positive electrode layer includes, as a positive electrode active material, at least one of a Ni-based hydroxide containing nickel element and a Co-coated Ni-based hydroxide having a coating layer containing cobalt element on at least a part of a surface of the Ni-based hydroxide, The positive electrode layer contains, as an additive, a first additive containing elemental boron, or a mixed additive of the first additive and a second additive containing elemental cobalt.

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