JP6915510B2 - Alkaline storage battery - Google Patents

Description

The present disclosure relates to alkaline storage batteries.

Japanese Patent Application Laid-Open No. 2002-184405 (Patent Document 1) states that polytetrafluoroethylene (PTFE) is used as a binder for a paste-type positive electrode (also referred to as a “non-sintered positive electrode”) of an alkaline storage battery. It is disclosed.

Japanese Unexamined Patent Publication No. 2002-184405

Conventionally, a nickel foam (Ni) substrate is used for the paste type positive electrode. That is, a paste-type positive electrode is manufactured by filling the foamed Ni substrate with a paste containing a positive electrode active material and a binder.

For example, in high-power applications such as for hybrid vehicles (HVs), it is required to reduce the thickness of the positive electrode and increase the area of the positive electrode. The nickel foam substrate has a three-dimensional structure (sponge-like structure). The electrode base material having a three-dimensional structure is considered to be unsuitable for thin and large-area applications from the viewpoint of material cost and the like. Therefore, an electrode base material having a two-dimensional (planar) structure is being studied.

A metal foil can be considered as an electrode base material having a two-dimensional structure. The paste is applied to the surface of the metal foil and dried to form a positive electrode active material layer. However, when the electrode base material is two-dimensional, a higher binding force is required for the binder contained in the paste as compared with the case where the electrode base material is three-dimensional.

Fluorine binders such as PTFE have low resistance and are suitable for high output applications. That is, the use of a fluorine-based binder for the binder of the paste-type positive electrode is expected to reduce the internal resistance. However, it is considered that the binding force of the fluorine-based binder is insufficient for the electrode base material (metal foil) having a two-dimensional structure.

An object of the present disclosure is to increase the binding force of the positive electrode active material layer and reduce the internal resistance of the alkaline storage battery.

Hereinafter, the technical configuration and the action and effect of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The scope of claims should not be limited by the correctness of the mechanism of action.

The alkaline storage battery of the present disclosure includes at least a positive electrode, a negative electrode and an alkaline aqueous solution. The positive electrode includes at least a metal leaf and a positive electrode active material layer. The positive electrode active material layer is formed on the surface of the metal foil. The positive electrode active material layer contains at least a positive electrode active material, a fluorine-based binder and a rubber-based binder. Fluorine-based binders and rubber-based binders are water-insoluble, respectively. The content of the fluorine-based binder in the positive electrode active material layer is 50% by mass or more and 83% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder.

Rubber binders have high resistance. However, rubber binders have a high binding force. As described above, the fluorine-based binder has low resistance and low binding force. Therefore, when a fluorine-based binder and a rubber-based binder are mixed and used, it is expected that the binding force is improved and the internal resistance is increased as compared with the case where the fluorine-based binder is used alone.

However, according to the new findings of the present disclosure, by mixing the fluorine-based binder and the rubber-based binder at a specific mixing ratio, the binding force is improved and the internal resistance is reduced as compared with the case where the fluorine-based binder is used alone. Can be done.

That is, in the present disclosure, the content of the fluorine-based binder in the positive electrode active material layer is 50% by mass or more and 83% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder. In this range, sufficient binding force is expected for the metal foil. Moreover, it is expected that the internal resistance will be reduced as compared with the single use of the fluorine-based binder.

FIG. 1 is a schematic view showing an example of the configuration of the alkaline storage battery of the present embodiment. FIG. 2 is a cross-sectional conceptual diagram showing a first example of the configuration of the electrode group of the present embodiment. FIG. 3 is a cross-sectional conceptual diagram showing a second example of the configuration of the electrode group of the present embodiment. FIG. 4 is a graph showing the relationship between the content of the fluorine-based binder and the binding force. FIG. 5 is a graph showing the relationship between the content of the fluorine-based binder and the internal resistance.

Hereinafter, embodiments of the present disclosure (referred to as “the present embodiment” in the present specification) will be described. However, the following description does not limit the scope of claims. For example, a nickel-metal hydride battery will be described below as an example of an alkaline storage battery. However, the alkaline storage battery of the present embodiment should not be limited to the nickel-metal hydride battery as long as it can be charged and the electrolytic solution is an alkaline aqueous solution. The alkaline storage battery of the present embodiment may be, for example, a nickel cadmium battery, a nickel zinc battery, or the like. Hereinafter, the alkaline storage battery may be abbreviated as "battery".

<Alkaline storage battery>
FIG. 1 is a schematic view showing an example of the configuration of the alkaline storage battery of the present embodiment.
The battery 100 is a nickel metal hydride battery. The battery 100 includes an exterior material 90. The exterior material 90 can be formed of, for example, a metal material, a polymer material, or the like. The exterior material 90 is square. However, the exterior material 90 may be cylindrical. The exterior material 90 includes a positive electrode terminal 91 and a negative electrode terminal 92. The exterior material 90 houses the first electrode group 51 and the alkaline aqueous solution.

FIG. 2 is a cross-sectional conceptual diagram showing a first example of the configuration of the electrode group of the present embodiment.
The first electrode group 51 is a stacked type. The first electrode group 51 is formed by alternately stacking one or more layers of a positive electrode 10 and a negative electrode 20. A separator 30 is arranged between each of the positive electrode 10 and the negative electrode 20. The separator 30 is impregnated with an alkaline aqueous solution. That is, the battery 100 includes at least a positive electrode 10, a negative electrode 20, and an alkaline aqueous solution.

The first electrode group 51 may be of a winding type. That is, the first electrode group 51 may be formed by laminating the positive electrode 10, the separator 30, and the negative electrode 20 in this order, and further winding them in a spiral shape.

《Positive electrode》
The positive electrode 10 has a sheet shape. The positive electrode 10 includes at least a metal foil 11 and a positive electrode active material layer 12. The metal foil 11 is an electrode base material having a two-dimensional structure. The metal foil 11 functions as a positive electrode current collector. The metal foil 11 is electrically connected to the positive electrode terminal 91.

The metal foil 11 may be, for example, a Ni foil, a Ni-plated metal foil, or the like. The Ni-plated metal foil may be, for example, a Ni-plated steel foil or the like. The metal foil 11 may have a thickness of, for example, 5 μm or more and 35 μm or less. For example, a through hole or the like may be formed in the metal foil 11. The metal leaf 11 may have irregularities on its surface, for example.

The positive electrode active material layer 12 is formed on the surface of the metal foil 11. The positive electrode active material layer 12 is formed by applying a paste containing a positive electrode active material or the like to the surface of the metal foil 11 and drying it. That is, the positive electrode active material layer 12 is a coating layer. The positive electrode active material layer 12 may have a 0.02 g / cm ² or more 0.035 g / cm ² or less in basis weight for example on one surface. The basis weight indicates the coating mass per unit area (when dried). The positive electrode active material layer 12 may be formed on both the front and back surfaces of the metal foil 11.

The positive electrode active material layer 12 contains at least a positive electrode active material, a fluorine-based binder, and a rubber-based binder. The positive electrode active material in the discharged state is nickel hydroxide (II) [Ni (OH) ₂ ]. The positive electrode active material in the charged state is nickel oxyhydroxide (NiOOH). That is, the positive electrode active material _{contains at least one of Ni (OH) 2} and NiO (OH). The positive electrode active material may contain a trace amount of a metal element (additional element) other than Ni. The additive element may be, for example, magnesium (Mg), aluminum (Al), manganese (Mn), zinc (Zn) or the like.

In the positive electrode active material layer 12, the total content of the fluorine-based binder and the rubber-based binder may be, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. The total content of the fluorine-based binder and the rubber-based binder may be, for example, 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

In this embodiment, a fluorine-based binder and a rubber-based binder are used at a specific mixing ratio. That is, the content of the fluorine-based binder in the positive electrode active material layer 12 is 50% by mass or more and 83% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder. In this range, sufficient binding force is expected for the metal foil 11. Moreover, it is expected that the internal resistance will be reduced as compared with the single use of the fluorine-based binder.

The content of the fluorine-based binder may be 50% by mass or more and 63% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder. Improvement of binding force is expected in this range. The content of the fluorine-based binder may be 63% by mass or more and 83% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder. Reduction of internal resistance is expected in this range.

The fluorine-based binder of this embodiment is water-insoluble. A fluorine-based binder is a polymer material containing a fluorine atom. Fluorine-based binders also tend to have excellent oxidation resistance. Fluorine-based binders include, for example, PTFE, polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVdF), polyvinylidene fluoride (PVF), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and tetrafluoroethylene-perfluoro. It may be an alkyl vinyl ether copolymer (PFA), a tetrafluoroethylene-hexafluoropropene copolymer (FEP), a vinylidene fluoride-hexafluoropropene copolymer (PVdF-HFP), or the like. One kind of fluorine-based binder may be used alone. Two or more kinds of fluorine-based binders may be used in combination.

The rubber-based binder of this embodiment is water-insoluble. The rubber-based binder is a rubber-like polymer material containing a carbon-carbon double bond in the main chain. The rubber-based binder may be, for example, styrene-butadiene rubber (SBR), butadiene rubber (BR), acrylate-butadiene rubber (ABR), acrylonitrile-butadiene rubber (NBR), isoprene rubber (IR), chloroprene rubber (CR), or the like. .. One kind of rubber binder may be used alone. Two or more types of rubber binders may be used in combination.

The positive electrode active material layer 12 may further contain a thickener. The thickener is a polymer material that imparts viscosity to the paste. The thickener may be water soluble. The content of the thickener in the positive electrode active material layer 12 may be, for example, 0.1 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. The thickener should not be particularly limited. The thickener may be, for example, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA) or the like. One type of thickener may be used alone. Two or more kinds of thickeners may be used in combination.

The positive electrode active material layer 12 may further contain a conductive material. The content of the conductive material in the positive electrode active material layer 12 may be, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. The conductive material should not be particularly limited. The conductive material may be, for example, cobalt oxyhydroxide (CoOOH), cobalt hydroxide (II) [Co (OH) ₂ ], cobalt oxide (II) [CoO], or the like. One kind of conductive material may be used alone. Two or more kinds of conductive materials may be used in combination. The conductive material may cover the surface of the positive electrode active material (particles).

《Negative electrode》
The negative electrode 20 is in the form of a sheet. The negative electrode 20 includes at least a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode current collector 21 is electrically connected to the negative electrode terminal 92. The negative electrode current collector 21 should not be particularly limited. The negative electrode current collector 21 may be, for example, a perforated steel plate or the like. The perforated steel plate may be Ni-plated.

The negative electrode active material layer 22 is formed on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be formed on both the front and back surfaces of the negative electrode current collector 21. The negative electrode active material layer 22 contains at least the negative electrode active material. The negative electrode active material is a hydrogen storage alloy.

Hydrogen storage alloys reversibly store and release protium (atomic hydrogen). The hydrogen storage alloy should not be particularly limited. The hydrogen storage alloy may be, for example, an AB ₅ type alloy or the like. Examples of the AB ₅ type alloy include LaNi ₅ and MmNi ₅ (“Mm” indicates mischmetal) and the like. One kind of hydrogen storage alloy may be used alone. Two or more kinds of hydrogen storage alloys may be used in combination. The negative electrode active material layer 22 may further contain a binder. The binder may be, for example, SBR or the like.

《Separator》
The separator 30 is arranged between the positive electrode 10 and the negative electrode 20. The separator 30 is electrically insulating. The separator 30 is a porous sheet. The separator 30 may have a thickness of, for example, 50 μm or more and 120 μm or less. The separator 30 may be, for example, a non-woven fabric made of polyolefin, a non-woven fabric made of polyamide, or the like.

《Alkaline aqueous solution》
The alkaline aqueous solution is impregnated in the separator 30. The alkaline aqueous solution contains water and alkali metal hydroxides. The alkaline aqueous solution may contain, for example, an alkali metal hydroxide of 1 mL / l or more and 20 mL / l or less. The alkali metal hydroxide may be, for example, potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH) or the like. One kind of alkali metal hydroxide may be used alone. Two or more kinds of alkali metal hydroxides may be used in combination.

《Bipolar structure》
FIG. 3 is a cross-sectional conceptual diagram showing a second example of the configuration of the electrode group of the present embodiment.
The alkaline storage battery of the present embodiment may have a bipolar structure. Since the positive electrode of the present embodiment has low resistance and can be formed thin, it is also suitable for a bipolar battery.

The second electrode group 52 includes a bipolar electrode 40 and a separator 30. The second electrode group 52 is formed by alternately stacking the bipolar electrodes 40 and the separator 30. Current collecting leads 41 are connected to the bipolar electrodes 40 arranged at both ends in the stacking direction (y-axis direction in FIG. 3). The current collector lead 41 is electrically connected to an external terminal.

The bipolar electrode 40 includes a metal foil 11, a positive electrode active material layer 12, and a negative electrode active material layer 22. The metal foil 11 has a first main surface 1 and a second main surface 2. The second main surface 2 is the opposite surface of the first main surface 1. The positive electrode active material layer 12 is arranged on the first main surface 1. The negative electrode active material layer 22 is arranged on the second main surface 2. The details of the metal foil 11, the positive electrode active material layer 12, and the negative electrode active material layer 22 are as described above.

In the bipolar electrode 40, the metal foil 11 serves as both a positive electrode current collector and a negative electrode current collector. That is, in the bipolar electrode 40, the metal foil 11 and the positive electrode active material layer 12 correspond to the positive electrode. In the bipolar electrode 40, the metal foil 11 and the negative electrode active material layer 22 correspond to the negative electrode. The separator 30 is impregnated with an alkaline aqueous solution. That is, the bipolar battery also contains at least a positive electrode, a negative electrode, and an alkaline aqueous solution.

Hereinafter, examples of the present disclosure will be described. However, the following description does not limit the scope of claims.

<Manufacturing of alkaline storage batteries>
<< Example 1 >>
1. 1. Production of positive electrode The following materials were prepared.
Positive electrode active material: Nickel hydroxide powder Fluorine binder: PTFE
Rubber binder: SBR
Metal leaf 11: Ni foil

A paste was prepared by mixing a positive electrode active material, a fluorine-based binder, a rubber-based binder, and water. The paste was applied to the surface of the metal foil 11 and dried to form the positive electrode active material layer 12. From the above, the positive electrode 10 was manufactured.

In the positive electrode active material layer 12, the total content of the fluorine-based binder and the rubber-based binder is 1 part by mass with respect to 100 parts by mass of the positive electrode active material. The mixing ratio of the fluorine-based binder and the rubber-based binder is "fluorine-based binder: rubber-based binder = 5: 5 (mass ratio)". That is, the content of the fluorine-based binder in the positive electrode active material layer 12 is 50% by mass with respect to the total of the fluorine-based binder and the rubber-based binder.

2. Manufacture of Battery An exterior material 90, a negative electrode 20, a separator 30, and an alkaline aqueous solution for a nickel-metal hydride battery were prepared. The negative electrode 20 contains a hydrogen storage alloy. The first electrode group 51 was formed. The first electrode group 51 includes a positive electrode 10, a negative electrode 20, and a separator 30. The first electrode group 51 was housed in the exterior material 90. An alkaline aqueous solution was injected into the exterior material 90. The exterior material 90 was sealed. From the above, the battery 100 was manufactured.

<< Example 2 >>
The battery 100 was manufactured in the same manner as in Example 1 except that the mixing ratio of the fluorine-based binder and the rubber-based binder was changed to "fluorine-based binder: rubber-based binder = 5: 3 (mass ratio)". .. The content of the fluorine-based binder in the positive electrode active material layer 12 is 63% by mass with respect to the total of the fluorine-based binder and the rubber-based binder.

<< Example 3 >>
The battery 100 was manufactured in the same manner as in Example 1 except that the mixing ratio of the fluorine-based binder and the rubber-based binder was changed to "fluorine-based binder: rubber-based binder = 5: 1 (mass ratio)". .. The content of the fluorine-based binder in the positive electrode active material layer 12 is 83% by mass with respect to the total of the fluorine-based binder and the rubber-based binder.

<< Comparative Example 1 >>
The battery 100 was manufactured in the same manner as in Example 1 except that the mixing ratio of the fluorine-based binder and the rubber-based binder was changed to "fluorine-based binder: rubber-based binder = 10: 0 (mass ratio)". .. The content of the fluorine-based binder in the positive electrode active material layer 12 is 100% by mass with respect to the total of the fluorine-based binder and the rubber-based binder.

<< Comparative Example 2 >>
The battery 100 was manufactured in the same manner as in Example 1 except that the mixing ratio of the fluorine-based binder and the rubber-based binder was changed to "fluorine-based binder: rubber-based binder = 0:10 (mass ratio)". .. The content of the fluorine-based binder in the positive electrode active material layer 12 is 0% by mass with respect to the total of the fluorine-based binder and the rubber-based binder.

<Evaluation>
1. 1. Measurement of binding force An adhesive tape was attached to the positive electrode active material layer 12. The positive electrode active material layer 12 was peeled off from the metal foil 11 by pulling the adhesive tape in parallel with the coating direction of the positive electrode active material layer 12. The binding force at this time was measured. The results are shown in FIG.

2. Measurement of internal resistance The initial charge / discharge of the battery 100 was carried out under the following conditions. Here, "C" represents the magnitude of the current rate. At a current rate of 1C, the rated capacity of the battery 100 is discharged in 1 hour.

Charging: Current rate = 0.1C, Charging time = 15 hours Discharging: Current rate = 0.2C, Final voltage = 1V

After the initial charge / discharge, the battery 100 was activated by charging / discharging the battery 100 under the following conditions.

Charging: Current rate = 0.5C, Charging time = 2 hours Discharging: Current rate = 0.5C, Termination voltage = 1V

After activation, the SOC (state of charge) of the battery 100 was adjusted to 50%. Direct current internal resistance (DC-IR) was measured at 50% SOC. The results are shown in FIG.

<Result>
FIG. 4 is a graph showing the relationship between the content of the fluorine-based binder and the binding force.
In the range where the content of the fluorine-based binder is 50% by mass or more and 83% by mass or less (Examples 1 to 3), the binding force tends to be improved as compared with the single use of the fluorine-based binder (Comparative Example 1). ..

FIG. 5 is a graph showing the relationship between the content of the fluorine-based binder and the internal resistance.
In the range where the content of the fluorine-based binder is 50% by mass or more and 83% by mass or less (Examples 1 to 3), the internal resistance tends to be reduced as compared with the single use of the fluorine-based binder (Comparative Example 1). ..

From the above, the content of the fluorine-based binder in the positive electrode active material layer 12 is 50% by mass or more and 83% by mass or less with respect to the total of the fluorine-based binder and the rubber-based binder, so that the binding force of the positive electrode active material layer 12 is enhanced. Moreover, it is considered that the internal resistance of the battery 100 can be reduced.

The embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The technical scope defined by the description of the claims includes all changes within the meaning and scope equivalent to the claims.

1 1st main surface, 2 2nd main surface, 10 positive electrode, 11 metal foil, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode current collector, 22 negative electrode active material layer, 30 separator, 40 bipolar electrode, 41 current collector Lead, 51 1st electrode group, 52 2nd electrode group, 90 exterior material, 91 positive electrode terminal, 92 negative electrode terminal, 100 battery.

Claims (3)

Contains at least a positive electrode, a negative electrode and an aqueous alkaline solution,
The positive electrode contains at least a metal leaf and a positive electrode active material layer.
The positive electrode active material layer is formed on the surface of the metal foil.
The positive electrode active material layer contains at least a positive electrode active material, a fluorine-based binder, and a rubber-based binder.
The fluorine-based binder and the rubber-based binder are water-insoluble, respectively.
The rubber-based binder does not contain a fluorine atom and does not contain a fluorine atom.
The content of the fluorine-based binder in the positive electrode active material layer is not more than 50 wt% or more 6 3% by weight, based on the sum of the fluorine-based binder and the rubber-based binder,
Alkaline storage battery. The fluorobinder includes polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, ethylene-chlorotrifluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropene. One or more selected from the group consisting of a copolymer and a vinylidene fluoride-hexafluoropropene copolymer, and
The rubber-based binder is one or more selected from the group consisting of styrene-butadiene rubber, butadiene rubber, acrylate-butadiene rubber, isoprene rubber, and chloroprene rubber.
The alkaline storage battery according to claim 1. The fluorine-based binder is polytetrafluoroethylene and
The rubber-based binder is styrene-butadiene rubber.
The alkaline storage battery according to claim 2.

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