Secondary battery

Abstract

The invention discloses a secondary battery. Provided is a high-capacity secondary battery. The secondary battery is provided with a positive electrode layer containing, as a positive electrode active material, at least one of a Ni-based hydroxide containing elemental nickel and a Ni-based hydroxide coated with Co, the Co-coated Ni-based hydroxide has a coating layer containing elemental cobalt on at least a portion of the surface of the Ni-based hydroxide, and the positive electrode layer contains, as an additive material, a first additive material containing elemental boron, or a mixed additive material containing elemental boron. The mixed additive material is a mixed material of the first additive material and a second additive material containing cobalt element.

Description

Technical Field

[0001] This disclosure relates to secondary batteries. Background Technology

[0002] Various technologies have been proposed for batteries as disclosed in Patent Documents 1 and 2.

[0003] [Prior Technology Documents]

[0004] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2001-68108

[0006] [Patent Document 2] Japanese Patent Application Publication No. 2007-18743 Summary of the Invention

[0007] Patent Document 1 discloses an electrode active material containing at least one of vanadium metal and vanadium compounds, with the aim of providing an alkaline secondary battery that has excellent utilization of active material over a wide temperature range and is cadmium-free; and nickel hydroxide or a hydrogen storage alloy. However, conventional secondary batteries have small capacities, leaving room for improvement.

[0008] One method to increase the capacity of a secondary battery is to increase the amount of positive electrode active material. However, the internal volume of the battery is fixed, and there is a limit to how much positive electrode active material can be increased.

[0009] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide a high-capacity secondary battery.

[0010] The secondary battery disclosed herein is a secondary battery having a positive electrode layer, wherein the positive electrode layer comprises at least one of a Ni-based hydroxide and a Co-coated Ni-based hydroxide as the positive electrode active material, wherein the Ni-based hydroxide contains nickel, and the Co-coated Ni-based hydroxide is a material having a coating containing cobalt on at least a portion of the surface of the Ni-based hydroxide. The positive electrode layer comprises a first additive material or a mixed additive material as an additive material, wherein the first additive material contains boron, and the mixed additive material is a mixture of the first additive material and a second additive material containing cobalt.

[0011] This disclosure provides a high-capacity rechargeable battery. Detailed Implementation

[0012] The following describes embodiments of this disclosure. Furthermore, matters necessary for implementing this disclosure, other than those specifically mentioned in this specification (e.g., the general structure and manufacturing process of a secondary battery not characterized by this disclosure), can be grasped by those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0013] This disclosure provides a secondary battery having a positive electrode layer, wherein the positive electrode layer comprises at least one of a Ni-based hydroxide and a Co-coated Ni-based hydroxide as the positive electrode active material, the Ni-based hydroxide containing nickel, and the Co-coated Ni-based hydroxide having a coating containing cobalt on at least a portion of its surface, the positive electrode layer comprising a first additive material or a mixture of additive materials, the first additive material containing boron, and the mixture of additive materials being a mixture of the first additive material and a second additive material containing cobalt.

[0014] In the secondary battery disclosed herein, the battery capacity is successfully improved by combining the following positive electrode active material with the following material in the positive electrode layer: the positive electrode active material is at least one of Ni-based hydroxide and Co-coated Ni-based hydroxide; the material is either a first additive containing boron or a mixed additive; and the mixed additive is a mixture of the first additive and a second additive containing cobalt. This is believed to be because by including any of the boron-containing first additive and the mixed additive in the positive electrode layer, the utilization rate of Ni-based hydroxide and Co-coated Ni-based hydroxide as positive electrode active materials is improved, resulting in higher energy density.

[0015] In this disclosure, alkaline secondary batteries are cited as examples of secondary batteries. Here, alkaline secondary batteries refer to a general term for secondary batteries whose electrolyte is an alkaline aqueous solution, such as nickel-metal hydride batteries, nickel-cadmium batteries, nickel-zinc batteries, and nickel-iron batteries.

[0016] The secondary battery disclosed herein has a positive electrode layer, and typically has a positive electrode, an electrolyte layer, and a negative electrode.

[0017] There are no particular limitations on the composition of the battery; it can be wound, stacked, or bipolar.

[0018] [positive electrode]

[0019] The positive electrode has at least a positive electrode layer, and may also have a positive electrode current collector as needed.

[0020] The positive electrode layer, as described above, contains specific positive electrode active materials and specific additives.

[0021] The positive electrode layer comprises at least one of a Ni-based hydroxide containing nickel and a Ni-based hydroxide coated with Co as the positive electrode active material.

[0022] Examples of Ni-based hydroxides include nickel hydroxide and nickel hydroxy oxide.

[0023] Furthermore, nickel hydroxide is nickel hydroxide(II)[Ni(OH)2] during discharge of the secondary battery and becomes nickel hydroxyl oxide[NiOOH] during charging of the secondary battery. That is, a secondary battery using nickel hydroxide as the positive electrode active material will contain at least one of nickel hydroxide(II) and nickel hydroxyl oxide.

[0024] Ni-based hydroxides can also contain elements and groups other than Ni and hydroxyl groups, such as magnesium, calcium, aluminum, manganese, zinc, etc., which can be dissolved in solid solution.

[0025] As a Ni-based hydroxide coated with Co, examples include those described above where at least a portion of the surface of the Ni-based hydroxide is coated with a Co coating containing cobalt. By using a Co-coated Ni-based hydroxide, the conductivity of the positive electrode layer is improved, and an increase in energy density can be expected.

[0026] Co coatings can be metallic cobalt layers, or cobalt compound layers such as cobalt hydroxide or cobalt hydroxyoxide. Alternatively, they can be both metallic cobalt layers and cobalt compound layers. Co coatings can also contain metals other than cobalt, such as calcium, magnesium, and zinc.

[0027] Furthermore, since cobalt hydroxide is oxidized to cobalt hydroxyl oxide through initial charging, etc., Ni-based hydroxides coated with cobalt hydroxide sometimes exist in the secondary battery in the form of Ni-based hydroxides coated with cobalt hydroxyl oxide.

[0028] There is no particular limitation on the coverage rate of Co coating on Ni-based hydroxide surfaces, but it can be, for example, 1 to 100%.

[0029] As a positive electrode active material, Ni-based hydroxides can be used alone, or Ni-based hydroxides coated with Co can be used alone, or a combination of Ni-based hydroxides and Ni-based hydroxides coated with Co can be used.

[0030] The total content of Ni-based hydroxides in the positive electrode layer and Ni-based hydroxides coated with Co can be, for example, 75 to 99% by mass when the total mass of the positive electrode layer is set to 100% by mass, or 85 to 95% by mass.

[0031] The positive electrode layer includes either a first additive containing boron or a mixed additive, wherein the mixed additive is a mixture of the first additive and a second additive containing cobalt. The shapes of the first and second additives are not particularly limited and can be various forms such as powder or fibers.

[0032] The first additive containing boron can be elemental boron or a boron compound. Examples of boron compounds include oxides and hydroxides. Examples of boron oxides include boron trioxide (B₂O₃) and boric acid (H₃BO₃). The first additive can be only one type or a combination of two or more types.

[0033] Regardless of whether the first additive is elemental boron or a compound such as an oxide or hydroxide, it thermodynamically converges to a stable state by being exposed to the positive electrode potential while in contact with an alkaline aqueous solution. Therefore, it is believed that regardless of whether the first additive is elemental boron or a compound such as an oxide or hydroxide, the utilization rate of Ni-based hydroxides and Co-coated Ni-based hydroxides as positive electrode active materials can be improved. From a cost perspective, boron oxides sometimes have an advantage.

[0034] The content of the first additive material in the positive electrode layer can be, for example, 0.1 to 10% by mass when the total mass of the positive electrode layer is set to 100% by mass, or 0.5 to 5% by mass.

[0035] In addition to metallic cobalt, other cobalt compounds such as cobalt hydroxide and cobalt hydroxyoxide can also be listed as secondary additives containing cobalt.

[0036] The ratio of the first additive and the second additive in the mixed additives is not particularly limited. For example, when the total mass of the cathode layer is set to 100% by mass, the ratio could be 0.1% to 10% by mass of the first additive and 0.1% to 20% by mass of the second additive. Alternatively, the ratio could be 0.5% to 5% by mass of the first additive and 0.5% to 10% by mass of the second additive. In the mixed additives, the first additive and the second additive can each be only one type, or a combination of two or more types can be used.

[0037] In addition to the above-mentioned positive electrode active material and the above-mentioned additives, the positive electrode layer may also contain other components such as conductive materials, binders, and additives different from the above-mentioned additives, as needed.

[0038] Examples of conductive materials include carbon black, graphite, and Ketjen black (KB). The content of the conductive material in the positive electrode layer can be, for example, 0.1% to 10% by mass, assuming the total mass of the positive electrode layer is 100% by mass.

[0039] Examples of adhesives include carboxymethyl cellulose (CMC), polypropylene (PP), diutan gum, polyvinyl alcohol (PVA), hydroxypropyl cellulose (HPC), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and acrylonitrile. An adhesive can be a single type or a combination of two or more.

[0040] The content of the binder in the positive electrode layer, for example, can be set to 0.015 to 15% by mass when the total mass of the positive electrode layer is set to 100% by mass.

[0041] The positive electrode layer can be fabricated as follows: First, conductive materials, binders, etc., are added as needed to the positive electrode active material and additives, which are essential materials in this disclosure, and then water is added to mix them to prepare a positive electrode slurry. Next, the positive electrode slurry is coated and filled into a positive electrode current collector (e.g., nickel foam), which is a conductive porous body, and then dried and pressed, thereby fabricating a positive electrode having a positive electrode layer and a positive electrode current collector.

[0042] [Electrolyte layer]

[0043] The electrolyte layer contains at least an electrolyte. The electrolyte can be an electrolyte solution.

[0044] Examples of electrolytes include alkaline aqueous solutions containing hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide. The concentration of hydroxides in the electrolyte can be set to, for example, 1 to 10 mol / L.

[0045] The electrolyte is typically filled into the battery while still encapsulated in a separator. To ensure insulation between the positive and negative electrodes, the separator is made of an insulating material. Examples of separators include nonwoven fabrics and woven fabrics that use one or more insulating materials, such as synthetic resins like polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid, polyester, and polyacrylonitrile; polysaccharides like cellulose and amylose; natural polymers like silk fibroin, keratin, and lignin; and insulating materials like ceramics.

[0046] [negative electrode]

[0047] The negative electrode can adopt a known structure, usually having a negative electrode layer containing at least a negative electrode active material, and may also have a negative electrode current collector as needed.

[0048] Examples of hydrogen storage alloys that can be used as negative electrode active materials include, for example, hydrogen storage alloys. Examples of hydrogen storage alloys include AB-type alloys such as TiFe and TiCo, AB2-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 (where Mm refers to a mixture of rare earth elements known as misch metal). These alloys can contain at least one element selected from rare earth elements, Mg, and Ni.

[0049] When the total mass of the negative electrode layer is set to 100%, the negative electrode layer can contain 85 to 100% by mass of negative electrode active material.

[0050] The negative electrode layer can be a layer on which a hydrogen storage alloy is supported, or it can be a molded body of the hydrogen storage alloy. As a substrate, porous metals such as nickel foam substrates and perforated metal plates such as perforated metals can be used.

[0051] The negative electrode layer may also include conductive materials, binders, additives, etc., as needed. Examples of conductive materials include carbon black, graphite, and Ketjen black. Examples of binders used in the positive electrode include binders. Examples of additives include Y₂O₃.

[0052] The negative electrode layer can be fabricated as follows: First, conductive materials, binders, etc., are added to the hydrogen storage alloy, which serves as the negative electrode active material, as needed, and then water is added to prepare a negative electrode slurry. Next, the negative electrode slurry is coated and filled onto a negative electrode current collector (e.g., a nickel foam substrate), which is a conductive porous body, and then dried and pressed, thereby fabricating a negative electrode having both a negative electrode layer and a negative electrode current collector.

[0053] The secondary battery disclosed herein may also have other configurations than those described above, such as terminals, battery casing, and other known configurations.

[0054] Batteries are used in various applications, including powering hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They can also be used as power sources for other mobile entities (such as trains, ships, and airplanes) and for electrical products such as information processing devices.

[0055] [Example]

[0056] (Example 1)

[0057] The materials shown in Table 1 were mixed, and then water was added to prepare the positive electrode mixture slurry.

[0058] The obtained positive electrode slurry was coated onto the positive electrode current collector and dried to produce a positive electrode with a positive electrode layer and a positive electrode current collector.

[0059] Table 1

[0060]

[0061] In addition, the materials shown in Table 2 were mixed and then water was added to prepare a negative electrode slurry.

[0062] The obtained negative electrode slurry was coated onto the negative electrode current collector and dried to produce a negative electrode with a negative electrode layer and a negative electrode current collector.

[0063] Table 2

[0064]

[0065] Using the fabricated positive and negative electrodes, separator, and electrolyte (potassium hydroxide aqueous solution), a small cell was assembled, and the full-charge capacity at 25°C was measured.

[0066] (Comparative Examples 1-6)

[0067] Based on Example 1, instead of 1.5% by mass of B2O3, 1.5% by mass of MoO3 (Comparative Example 1), 1.5% by mass of V2O5 (Comparative Example 2), 1.5% by mass of WO3 (Comparative Example 3), 1.5% by mass of Y2O3 (Comparative Example 4), 1.5% by mass of Sb2O3 (Comparative Example 5), and 1.5% by mass of ZrO2 (Comparative Example 6) were used to prepare positive electrode slurries. In addition, small cell batteries were fabricated in the same manner, and the full charge capacity at 25°C was measured.

[0068] For Example 1 and Comparative Examples 2-6, the relative initial full charge capacity when the initial full charge capacity of Comparative Example 1 is set to 100% is calculated. The results are shown in Table 3.

[0069] Table 3

[0070] Add materials relative capacity Example 1 <![CDATA[B2O3 + metallic Co]]> 105.8 Comparative Example 1 <![CDATA[MoO3 + metallic Co]]> 100 Comparative Example 2 <![CDATA[V2O5 + metallic Co]]> 99.3 Comparative Example 3 <![CDATA[WO3 + metallic Co]]> 99.1 Comparative Example 4 <![CDATA[Y2O3 + metallic Co]]> 98.7 Comparative Example 5 <![CDATA[Sb2O3 + metallic Co]]> 99.1 Comparative Example 6 <![CDATA[ZrO2 + metallic Co]]> 95.2

[0071] As shown in Table 3, it can be confirmed that the battery of Example 1, which uses B2O3 containing boron and Co as additives, has a larger capacity than any of the batteries in Comparative Examples 1 to 6 that do not use additives containing boron.

Claims

1. A secondary battery having a positive electrode layer, The positive electrode layer comprises at least one of a Ni-based hydroxide and a Co-coated Ni-based hydroxide as the positive electrode active material, wherein the Ni-based hydroxide contains nickel, and the Co-coated Ni-based hydroxide is a material having a coating containing cobalt on at least a portion of the surface of the Ni-based hydroxide. The positive electrode layer includes a first additive material or a mixed additive material as an additive material, wherein the first additive material contains boron, and the mixed additive material is a mixture of the first additive material and a second additive material containing cobalt.

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