JP6719101B2 - Nickel-hydrogen battery and manufacturing method thereof - Google Patents

Description

The present invention relates to a nickel-hydrogen battery including a wound electrode group.

The electrode group of the wound-type nickel-hydrogen battery has a strip-shaped positive electrode mainly composed of nickel hydroxide and a strip-shaped negative electrode mainly composed of a hydrogen-absorbing alloy, and a separator interposed between them to form a spiral coil. It is composed by turning. The electrode group is housed in a battery case together with an alkaline aqueous solution which is an electrolytic solution. The negative electrode is formed by filling a negative electrode current collector having a plurality of through holes with a composition containing a hydrogen storage alloy. Usually, the outermost periphery of the electrode group is composed of a negative electrode. Since the negative electrode forming the outermost periphery has a small contribution to the battery reaction, it has been proposed to make the thickness thinner than other portions (Patent Document 1).

In order to uniformly proceed the battery reaction in the electrode group, it is desirable that the electrode group be impregnated with a sufficient amount of alkaline aqueous solution as an electrolytic solution, and that the concentration of the alkaline aqueous solution is also uniform. On the other hand, in the nickel-hydrogen battery, a plurality of reactions proceed as follows.

At the positive electrode, the following charging reaction proceeds. The discharge reaction is a reverse reaction.
Ni(OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1)

However, in the positive electrode at the end of charging or at the time of overcharging, the following water splitting reaction proceeds and oxygen is generated.
_{^{OH - → 1 / 4O 2 +}} 1 / 2H 2 O + e - (2)

At the negative electrode, the following charging reaction proceeds. The discharge reaction is a reverse reaction.
M + H ₂ O + e ⁻ → MH + OH ⁻ (3)

Further, in the negative electrode, the following water splitting reaction proceeds, and hydrogen is generated.
H ₂ O + e ⁻ → 1/2H ₂ + OH ⁻ (4)

The generated hydrogen is absorbed by the hydrogen storage alloy of the negative electrode as described below to generate a metal hydride.
M + 1/2H ₂ → MH (5)

The metal hydride reacts with oxygen generated at the positive electrode as follows.
MH + 1/4O ₂ → M + 1/2H ₂ O (6)

Oxygen and hydrogen generated by the side reactions of the formulas (2) and (4) cause a rise in the internal pressure of the battery, so that the reactions of the formulas (5) and (6) at the negative electrode are rapidly advanced to convert the gas into water. It is desired to bring it back.

JP, 2005-56674, A

The negative electrode forming the outermost periphery of the electrode group has a small contribution to the battery reaction, and therefore consumes less water during charging, but also has a large contribution to absorbing the gas generated in the battery, and thus more water can be collected. To generate. Therefore, the concentration of the alkaline aqueous solution tends to decrease near the outermost negative electrode. Moreover, since the outermost peripheral negative electrode is thinner than the other portions, the amount of the alkaline aqueous solution impregnated is small, and the influence of the concentration decrease is likely to be large.

Further, when the outermost peripheral negative electrode is thinned, it is difficult to uniformly fill the through holes of the negative electrode current collector with the hydrogen storage alloy, and the through holes may not be completely filled with the composition. Therefore, when making the outermost negative electrode thin, it is considered desirable to reduce the opening diameter of the through holes of the negative electrode current collector or to reduce the density of the through holes. Therefore, the fluidity of the electrolyte tends to be low at the outermost periphery of the electrode group.

In the above environment, the concentration of the alkaline aqueous solution tends to be non-uniform depending on the location of the electrode, the charge state of the positive electrode varies, and a partially deeply charged portion occurs. In the deeply charged portion, the reaction of self-decomposition of the positive electrode is likely to occur, so that self-discharging (particularly short-term self-discharging) tends to be promoted as compared with the case where the entire electrode is uniformly charged.

In view of the above, the nickel-hydrogen battery according to one aspect of the present disclosure has a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode such that the negative electrode forms the outermost periphery. It is provided with a wound electrode group, an electrolytic solution, and a battery case accommodating the electrode group and the electrolytic solution. The negative electrode includes a porous negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. The opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is the first opening, and the opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is the opening. When forming the second opening, the amount of the hydrogen storage alloy contained per unit area of the second portion is smaller than the amount of the hydrogen storage alloy contained per unit area of the first portion. Further, the area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap each other satisfy 0.4<S2/S1.

A method of manufacturing a nickel-hydrogen battery according to another aspect of the present disclosure includes (i) a step of preparing a strip-shaped positive electrode, (ii) a step of preparing a strip-shaped negative electrode, and (iii) the positive electrode and the negative electrode. A step of forming an electrode group by interposing a separator between the positive electrode and the negative electrode and winding so that the negative electrode forms the outermost periphery, and (iv) the electrode group together with an electrolytic solution in a battery case. And a step of accommodating. The negative electrode prepared in the step (ii) is a porous negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. And The opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is the first opening, and the opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is the opening. When forming the second opening, the amount of the hydrogen storage alloy contained per unit area of the second portion is smaller than the amount of the hydrogen storage alloy contained per unit area of the first portion. Further, the electrode group is configured such that the area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap each other satisfy 0.4<S2/S1.

According to the present disclosure, the fluidity of the electrolyte at the outermost periphery of the electrode group is improved, so that the concentration of the electrolytic solution is made uniform in the electrode group, and the self-discharge of the nickel hydrogen battery is suppressed.

It is a figure which shows an example of the relationship of the 1st opening in the 1st part of the negative electrode which adjoins the innermost periphery of a positive electrode, and the 2nd opening in the 2nd part of the negative electrode which adjoins the outermost periphery of a positive electrode. It is a figure which shows the variation of the arrangement pattern of the through-hole of a negative electrode electrical power collector as an example. 1 is a cross-sectional view schematically showing a nickel hydrogen battery according to an embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing the nickel hydrogen battery of FIG. 3. FIG. 3 is an enlarged view of a part surrounded by a circle indicated by III in FIG. 4.

The nickel-hydrogen battery according to the embodiment of the present invention includes a wound electrode group. The wound electrode group is formed by winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode so that the negative electrode forms the outermost periphery. The electrode group is housed in the battery case together with the electrolytic solution.

The negative electrode includes a negative electrode current collector having a plurality of through holes and a negative electrode active material layer formed on both surfaces of the negative electrode current collector. The negative electrode active material layer contains a hydrogen storage alloy. However, the amount of hydrogen storage alloy (Wo) contained per unit area of the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is the unit area of the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode. Is less than the amount of hydrogen storage alloy (Wi) contained in. Wo is the total amount of the hydrogen storage alloy contained in the second portion of the negative electrode divided by the projected area when the second portion is flattened and the negative electrode is viewed from the thickness direction, and Wi is the negative electrode. The total amount of the hydrogen storage alloy contained in the first part is divided by the projected area when the first part is developed flat and the negative electrode is viewed in the thickness direction.

Typically, the negative electrode includes a thin portion provided in a region having a length L3 from the outer end of the negative electrode, a tapered portion having a length L2 adjacent to the thin portion, and a main body having a length L1 other than the thin portion. Prepare The thickness t1 of the main body and the thickness t3 of the thin portion satisfy t1>t3. The thickness t1 of the main body is preferably 0.1 to 0.6 mm, for example.

The thickness t3 of the thin portion may satisfy t1>t3. The length L3 of the thin portion is, for example, 50 to 115%, preferably 70 to 110% or 80 to 105% of the length of the outermost periphery of the negative electrode.

The thickness t2 of the tapered portion is gradually reduced from the main body portion toward the thin portion. The length L2 of the tapered portion is preferably longer than ⅙ of the outermost circumference of the negative electrode, and may be ⅕ or more or ¼ or more. The length L2 of the tapered portion is preferably 1/2 or less of the length of the outermost circumference of the negative electrode.

When the opening of the through hole in the first portion of the negative electrode adjacent to the inner side of the outermost periphery of the positive electrode is the first opening and the opening of the through hole in the second portion of the negative electrode adjacent to the outermost periphery of the positive electrode is the second opening. The area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap satisfy 0.4<S2/S1. By increasing the overlapping portion of the first opening and the second opening in this way, the fluidity of the electrolyte at the outermost periphery of the electrode group is improved. The positive electrode of the nickel-hydrogen battery, including the core material, is porous, and the electrolyte can flow in the thickness direction of the positive electrode. Therefore, in the overlapping portion of the first opening and the second opening, a passage communicating with the first portion and the second portion of the negative electrode is formed. As a result, the water generated near the outermost circumference can be quickly diffused to the inner circumference side, and the ions on the inner circumference side can be quickly diffused to the outermost circumference side. Therefore, unevenness in the concentration of the alkaline aqueous solution is reduced in the entire electrode group, variation in charging reaction is suppressed, and self-discharge is suppressed.

The first opening is a general term for the openings of the plurality of through holes in the first portion of the negative electrode, and the area of the openings of the individual through holes is not referred to as S1. The second opening is a general term for the openings of the plurality of through holes in the second portion of the negative electrode, and the area of the openings of the individual through holes is not called S2. Regarding the opening divided into the boundary between the first portion and the second portion, only a part that enters the first portion becomes the first opening, and the remaining portion becomes the second opening. Similarly, the opening divided into the boundary between the first portion and the main body portion on the inner peripheral side is the first opening only in a part that enters the first portion. Similarly, the opening divided into the boundary between the second portion and the thin-walled portion on the outer peripheral side is the second opening only in a part that enters the second portion.

The through hole of the negative electrode current collector is designed to be considerably small from the viewpoint of maintaining the strength of the negative electrode and suppressing the falling of the negative electrode active material layer. Further, the first portion adjacent to the inner peripheral side and the second portion adjacent to the outer peripheral side of the positive electrode have different curvatures and peripheral lengths. Therefore, even if the first opening and the second opening that 100% overlap accidentally exist, the overlapping portion becomes small between the first opening and the second opening adjacent to them, and the S2/S1 ratio is usually 0.4. Less than

To make the S2/S1 ratio larger than 0.4, the sizes of the first opening and the second opening, the vertical direction of the through hole (width direction of the negative electrode current collector) and the horizontal direction (length of the negative electrode current collector) are set. It is necessary to strictly design the pitch in the direction), the thickness of the electrodes and the separator, and to align the first opening and the second opening when forming the electrode group. According to such work, it is possible to increase the S2/S1 ratio to 0.5 or more or 0.6 or more.

As the negative electrode current collector having a plurality of through holes, it is preferable to use a metal foil in which through holes, which are generally called punching metal, are arranged in a plane in a predetermined pattern. The through hole is a hole that penetrates from one surface of the sheet-shaped current collector to the other surface. The shape of the cross section of the through hole perpendicular to the thickness direction of the current collector may be, for example, a circle, an ellipse, a polygon having an R-shaped corner, or the like. These shapes may be distorted.

The arrangement pattern of the through holes on the surface of the negative electrode current collector is such that the through holes are adjacent to six arbitrary holes of the negative electrode current collector (except for the through holes near the end of the negative electrode current collector). Patterns are preferred. Above all, a pattern in which the centers of the seven through holes are arranged at the center of the regular hexagon and the six vertices thereof is preferable. Such an arrangement is also called a staggered arrangement.

In order to facilitate the production of a negative electrode having a thin outermost periphery and increase the number of overlapping portions of the through holes, the maximum diameter of the through holes (the diameter or the opening diameter when the opening is circular) is set to the first portion and the second portion of the negative electrode. In each part, 0.5 to 2.0 mm is preferable, and 0.8 to 1.5 mm is more preferable.

The porosity (opening ratio) of the negative electrode current collector excluding the uncoated portion is preferably 25 to 50%, more preferably 30 to 45%. When the through holes having the maximum diameter are arranged in a predetermined pattern so as to have the porosity, the interval between adjacent through holes (that is, the pitch between the centers of gravity of the openings) is optimized, and the overlapping portion of the through holes is reduced. It is advantageous to increase the number.

The pitch in the vertical direction (the width direction of the negative electrode current collector) between the centers of gravity of the openings is preferably 1.1 to 1.8 mm, more preferably 1.2 to 1.75 mm. Further, the pitch in the lateral direction (the lengthwise direction of the negative electrode current collector) between the centers of gravity of the openings is preferably 0.55 to 1.0 mm, more preferably 0.66 to 0.90 mm.

The larger the pitch and the smaller the openings of the through holes, the smaller the overlapping ratio of the first openings and the second openings. Therefore, it is not easy to satisfy 0.4<S2/S1 without using the negative electrode collector satisfying the above conditions. Here, FIG. 1 shows a state in which the length of one circumference is viewed in a plan view in the positive electrode before being wound or when the wound positive electrode is unfolded. An example of the relationship between the first opening 11b of the first portion of the negative electrode adjacent to the inner side and the second opening 11a of the second portion of the negative electrode adjacent to the outermost outermost periphery of the positive electrode is shown. For example, when the opening diameter and the pitch of the through holes are both 1.4 mm, the arrangement of the first openings 11b is as shown in FIG. 1(b). When the perimeter of the second portion of the negative electrode is 41 mm and the perimeter of the first portion is 38 mm, the arrangement of the second openings 11a of the through holes when the perimeter of the second portion is converted (reduced) to 38 mm is , As shown in FIG. Therefore, in the wound electrode group, the overlapping relationship between the first opening 11b and the second opening 11a is as shown in FIG. 1(c). As described above, since the overlapping portion of the first opening 11b and the second opening 11a tends to be small, in order to satisfy 0.4<S2/S1, a design for that is necessary.

For example, even if the porosity (opening ratio) and the opening diameter of the negative electrode current collector are the same, it is possible to increase/decrease S2/S1 by changing the pitch in the vertical direction or the horizontal direction. FIG. 2A shows an arrangement pattern of through holes in which the horizontal pitch is smaller than the vertical pitch. FIG. 2B shows the case where the horizontal pitch and the vertical pitch are the same, and FIG. 2C shows the case where the horizontal pitch is larger than the vertical pitch. Among these, when the pattern of FIG. 2A is used, S2/S1 can be maximized. When the pitch P1 in the horizontal direction is made smaller than the pitch P2 in the vertical direction, the ratio of the pitch P2 in the vertical direction to the pitch P1 in the horizontal direction: P2/P1 may be larger than 1, and may be 1.05 or more, for example. ..

From the viewpoint of making it easier for the negative electrode to satisfy 0.4<S2/S1, the arrangement patterns may be different in the first portion and the second portion of the negative electrode. For example, the maximum diameter of the through holes, the porosity, and the opening may be different. At least one of the pitches between the centers of gravity may be different from each other.

The thickness of the portion (skeleton) other than the through holes of the negative electrode current collector is, for example, preferably 20 to 100 μm, more preferably 30 to 70 μm.

Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy and the like.

When at least a part of the separator is made of polypropylene, it is preferable that at least a part of the polypropylene is sulfonated. Since sulfonated polypropylene (SPP) has a high affinity with an alkaline aqueous solution, the use of SPP makes it easier to further improve the fluidity of the electrolyte in the electrode group.

The hydrogen storage alloy amount (Wo) contained per unit area of the second portion of the negative electrode is preferably 40 to 80 mass% of the hydrogen storage alloy amount (Wi) contained per unit area of the first portion of the negative electrode, and 50 ˜70% by mass is more preferred. Most or all of the second portion of the negative electrode is usually a thin portion. By limiting the amount of alloy in the thin portion within the above range, the amount of alloy used for gas absorption and promoting the generation of water can be appropriately maintained. Further, since the volume of the separator in the outermost peripheral region is relatively large, it is easy to secure a sufficient amount of the electrolytic solution in the outermost peripheral region, and the charging reaction is easily made uniform.

Hydrogen storage alloys generally include an A element having a high hydrogen affinity and a B element having a low hydrogen affinity. The element B, which has a low hydrogen affinity, plays a role of preventing significant crystal defects from being generated when the alloy expands and contracts due to the absorption and desorption of hydrogen. On the other hand, when the ratio of the B element having a low hydrogen affinity to the A element having a high hydrogen affinity (B/A ratio) becomes large, the hydrogen storage capacity becomes low and it becomes difficult to increase the discharge capacity.

Examples of hydrogen storage alloys include A ₂ B ₇ type (Ce ₂ Ni ₇ type, Gd ₂ Co ₇ type, etc.), A ₅ B ₁₉ type (Pr ₅ Co ₁₉ type, Ce ₅ Co ₁₉ type, etc.), AB ₅ type Those having a crystal structure such as (CaCu ₅ type or MmNi ₅ type), AB ₃ type (CeNi ₃ type), AB ₂ type (MgCu ₂ type, etc.), or a mixture thereof can be used. In addition, Mm shows misch metal. Among them, A ₂ B ₇ type and A ₅ B ₁₉ type alloys are preferable because they are suitable for high capacity.

In the alloy or mixture of alloys used, the A element is at least one selected from the group consisting of Mg, Zr and rare earth elements, and the B element is an element other than the A element, such as Ni and Al. , Mn, Co and the like. The ratio of the number of moles of element B to the number of moles of element A: B/A is preferably 3.3 to 3.8 in order to efficiently increase the capacity of the negative electrode. If the capacity of the alloy can be increased, it is easy to increase the volume of the separator or the electrolytic solution in the electrode group, which is advantageous for uniformizing the charging reaction.

Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary.

[Cylindrical Ni-MH battery]
FIG. 3 schematically shows an example of the configuration of a cylindrical nickel-hydrogen battery (hereinafter referred to as a cylindrical battery). The cylindrical battery includes a bottomed cylindrical battery case 4 also serving as a negative electrode terminal, an electrode group housed in the battery case 4, and an electrolyte solution (not shown). In the electrode group, the strip-shaped negative electrode 1, the strip-shaped positive electrode 2, and the strip-shaped separator 3 interposed therebetween are spirally wound. A sealing plate 7 having a safety valve 6 is arranged in the opening of the battery case 4 via an insulating gasket 8, and the opening end of the battery case 4 is caulked inward to seal the cylindrical battery. .. The sealing plate 7 also functions as a positive electrode terminal, and is electrically connected to the positive electrode 2 via the positive electrode current collector plate 9.

FIG. 4 is a cross-sectional view schematically showing the cylindrical battery of FIG. FIG. 5 shows an enlarged view of the vicinity of the outer ends of the negative electrode 1 and the positive electrode 2 (that is, the portion surrounded by the circle indicated by III in FIG. 4). The negative electrode 1 constitutes the outermost circumference of the electrode group. In a nickel-hydrogen battery, hydrogen gas and oxygen gas are generated during overcharge, but by providing a negative electrode active material layer that does not face the positive electrode on the outer peripheral side of the thin portion, the gas generated during overcharge can be efficiently absorbed. With it can be converted to water. In addition, it is preferable that the outermost periphery of the negative electrode 1 is electrically connected by contacting with the battery case 4.

The number of windings of the negative electrode can be selected according to the size of the cylindrical battery. For example, when the outer diameter of the cylindrical battery is 6 to 24 mm, it can be set to 2 to 10 and may be set to 3 to 6.

In FIG. 4, the electrode group is arranged such that the outer end of the positive electrode 2 overlaps the tapered portion 1 b with the separator 3 interposed therebetween. It is preferable to dispose the positive electrode and the negative electrode so that the position of the end face of the outer end of the positive electrode is near the center in the length direction of the tapered portion. For example, the positive electrode of the positive electrode may be positioned such that the end face of the outer end of the positive electrode is located in a region of ±0.2×L2 (preferably a region of ±0.1×L2) with the center of the taper portion in the longitudinal direction sandwiched therebetween. It is preferable to overlap the outer end with the tapered portion.

A porous sheet 3a is arranged between the outer end of the positive electrode 2 and the tapered portion 1b. It is preferable that the porous sheet 3a is disposed so as to overlap the outer end of the positive electrode 2 so as to protect the outer end of the positive electrode 2. With such a configuration, the electrode group can be easily inserted into the battery case, and the occurrence of an internal short circuit can be suppressed. The length of the porous sheet 3a is, for example, 50 to 200% of L2, and may be 80 to 100%. The porous sheet 3a may be arranged between the tapered portion of the negative electrode and the separator as in the illustrated example, or may be arranged between the outer end of the positive electrode and the separator.

The constituent elements of the cylindrical battery will be described more specifically below.

(Negative electrode)
The negative electrode has a main body portion, a taper portion, and a thin portion that forms the outermost periphery of the electrode group. Providing a thin portion on the outermost circumference is advantageous because it is possible to reduce the amount of the negative electrode active material that is not used in the electrode reaction and also reduce the volume required for it. Further, hydrogen gas or oxygen gas generated during overcharge can be absorbed. The main body is a region located on the center side (or inner peripheral side) of the electrode group, both surfaces facing the positive electrode, and mainly responsible for the electrode reaction. However, the thickness of the negative electrode active material layer may be partially reduced in the region of the main body portion that does not face the positive electrode at the innermost periphery of the negative electrode, if necessary.

As shown in FIG. 4, most of the first portion of the negative electrode 1 adjacent to the inner side of the outermost periphery of the positive electrode 2 is composed of the main body portion 1 a, and the second portion of the negative electrode 1 adjacent to the outermost side of the outermost periphery of the positive electrode 2. Most of the thin-walled portion 1c consists of the thin portion 1c. Since the position of the end surface of the outer end of the positive electrode 2 is located near the center in the length direction of the tapered portion 1b, the tapered portion 1b is divided into the first portion and the second portion.

The negative electrode active material layer only needs to contain at least the negative electrode active material, and may be a negative electrode mixture layer containing a binder, a conductive agent, a thickener, and the like.

As the binder, a resin material, for example, a rubber-like material such as styrene-butadiene copolymer rubber (SBR), a polyolefin resin, a fluororesin such as polyvinylidene fluoride, an acrylic resin (including its Na ion crosslinked body), etc. It can be illustrated. Examples of the thickener include carboxymethyl cellulose (CMC) and salts thereof, polyvinyl alcohol, polyethylene oxide and the like. Examples of the conductive agent include carbon black, conductive fibers, and organic conductive materials.

The negative electrode is formed, for example, by applying a slurry containing the components of the negative electrode active material layer to a negative electrode current collector, compressing it in the thickness direction, and, if necessary, drying it at an appropriate stage.

(Positive electrode)
As the positive electrode, either a sintered positive electrode or a paste positive electrode may be used. The sintered positive electrode is manufactured by impregnating a nickel sintered substrate (positive electrode current collector) with a nickel compound. The paste-type positive electrode is manufactured by filling a positive electrode mixture paste containing a nickel compound into a foamed nickel substrate (positive electrode current collector). The positive electrode mixture may contain a conductive agent, a binder, a thickener and the like in addition to the positive electrode active material. The positive electrode can be obtained by a known method.

As the nickel compound, nickel hydroxide, nickel oxyhydroxide or the like is used. A conductive cobalt oxide such as cobalt hydroxide or cobalt oxyhydroxide may be used as the conductive agent.

(Separator)
As the separator, a microporous film, a non-woven fabric or the like can be used. The material of the microporous membrane or the non-woven fabric may be appropriately selected, and examples thereof include polyolefin resins such as polyethylene and polypropylene, fluororesins, and polyamide resins. The separator may be subjected to hydrophilic treatment such as corona discharge treatment, plasma treatment and sulfonation treatment. A sulfonic acid group is introduced into the separator by the sulfonation treatment. Especially, when forming at least one part of a separator with polypropylene, it is preferable to sulfonate at least one part of polypropylene. By using sulfonated polypropylene (SPP), the fluidity of the electrolytic solution in the electrode group can be further improved. The thickness of the separator is, for example, 10 to 300 μm, and may be 15 to 200 μm. The porous sheet is not particularly limited, but is preferably formed of the same material as the separator.

The sulfonation degree of the separator may be, for example, 1×10 ⁻³ or more, preferably 1.5×10 ⁻³ or more, more preferably 1.9×10 ⁻³ or more. The degree of sulfonation of the separator is, for example, 4.3×10 ⁻³ or less, preferably 4.1×10 ⁻³ or less, and more preferably 4×10 ⁻³ or less. The degree of sulfonation of the separator is represented by the ratio of sulfur atom to carbon atom contained in the separator.

(Electrolyte)
An alkaline aqueous solution is used as the electrolytic solution. The specific gravity of the electrolytic solution is, for example, 1.03 to 1.55. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide. From the viewpoint of improving charging efficiency, it is preferable that 75 mol% or more of the alkali metal hydroxide is sodium hydroxide. As a result, self-discharge becomes easier to be suppressed.

The hydroxide ion concentration of the electrolytic solution is preferably 5.0 to 8.5 mol/L. The electrolyte containing sodium hydroxide has a high conductivity in the above concentration range, and within the above concentration range, the conductivity gradually decreases as the hydroxide concentration increases. However, such a decrease in conductivity is very gradual, and a sufficiently high value can be maintained. On the other hand, when water is generated in the outermost peripheral region and the hydroxide concentration is lowered, the conductivity in the outermost peripheral region is gradually increased, so that the influence due to the decrease in the hydroxide concentration is easily mitigated.

Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1
According to the following procedure, an AA cylindrical nickel-metal hydride storage battery having a capacity of 2400 mAh was produced.

(1) Preparation of Negative Electrode An iron punching metal having a surface plated with nickel was prepared as a negative electrode current collector. The shape of the cross section of the through hole perpendicular to the thickness direction of the current collector was circular. The arrangement pattern of the through holes was a zigzag arrangement in which the centers of the seven through holes were arranged at the center of the regular hexagon and the six vertices thereof. The maximum diameter of the through hole (diameter of the opening) was 1 mm. The porosity (opening ratio) of the negative electrode current collector was 35%. The pitch between the centers of gravity (centers) of the openings was 1.42 mm in the vertical direction and 0.79 mm in the horizontal direction. The thickness of the skeleton of the negative electrode current collector was 35 μm.

To 100 parts by mass of hydrogen storage alloy powder (La _0.40 Ce _0.60 Ni _3.63 Co _0.76 Mn _0.42 Al _0.29 , average particle size=about 45 μm), 0.7 parts by mass of SBR as a binder and CMC0. 15 parts by mass, 0.3 part by mass of Ketjen Black as a conductive agent, and 0.7 part by mass of yttrium oxide as an oxidation inhibitor were added, and an appropriate amount of water was added and mixed to prepare a negative electrode mixture slurry. Prepared. The SBR was used in the form of an aqueous dispersion.

The obtained negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector. At this time, the coating amount of the negative electrode mixture slurry was changed in the lengthwise direction of the negative electrode current collector so that the thicknesses of the negative electrode active material layers on both surfaces of the main body portion, the tapered portion, and the thin portion were different. The coating film of the negative electrode mixture slurry was dried at 95° C. for 10 minutes, and then the coating film was pressed by a roller together with the negative electrode current collector to form a negative electrode.

The ratio (Wo/Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is set to 60% by mass. did.

(2) Production of Positive Electrode A paste type positive electrode was produced by the following procedure.

First, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt as coprecipitated components was added to the aqueous cobalt sulfate solution. While stirring the obtained mixture, an aqueous sodium hydroxide solution (sodium hydroxide concentration: 1 mol/L) was gradually added dropwise to adjust the pH to 11, and then the stirring was continued for a predetermined time. The precipitate was filtered off from the obtained mixture. The precipitate separated by filtration was washed with water and vacuum dried to obtain a powder in which the surface of the nickel hydroxide particles was coated with 5% by mass of cobalt hydroxide.

To 1 part by mass of the powder obtained above, 10 parts by mass of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 48% by mass) was added. The obtained mixture was heated at 85° C. for 8 hours under stirring, then washed with water and dried at 65° C. By this heat treatment, in the layer containing cobalt hydroxide on the surface of the nickel hydroxide particles, a part of the cobalt hydroxide is converted to a higher order and converted into cobalt oxyhydroxide, and sodium is introduced. Composite particles were obtained in which a coating layer containing cobalt oxyhydroxide and 1% by mass of sodium was formed on the surface of the nickel hydroxide particles.

To 100 parts by mass of the mixed powder of the obtained composite particles and zinc oxide, 25 parts by mass of an aqueous solution containing CMC as a binder (CMC concentration: 1% by mass) was added and mixed to obtain a positive electrode mixture. An agent slurry was prepared. The mass ratio of the composite particles and zinc oxide in the mixed powder was 100:2.

The obtained positive electrode mixture slurry was filled into the pores of a nickel foam (area density (area weight) about 325 g/m ² , thickness about 1.2 mm) as a positive electrode current collector, and dried. The dried product was rolled to a thickness of 0.66 mm to obtain a positive electrode (length 118 mm, width 44.7 mm, thickness 0.66 μm). An exposed portion of the core material that does not hold the active material was provided at one end of the positive electrode current collector in the lengthwise direction, and the positive electrode lead was connected to this exposed portion.

(3) Production of nickel-hydrogen storage battery A separator (length 325 mm, width 46.7 mm, thickness 82 μm) was placed between the negative electrode obtained in (1) above and the positive electrode obtained in (2) above. Then, an electrode group was prepared by winding these into a spiral shape. At this time, the negative electrode was wound such that the main body was on the inner peripheral side, the thin portion was on the outer peripheral side, and the outer end of the positive electrode overlapped with the tapered portion of the negative electrode. Further, a porous sheet (length 10 mm, width 46.7 mm, thickness 82 μm) cut out from the same material as the separator was arranged between the outer end of the positive electrode and the tapered portion and between the tapered portion and the separator. .. The porous sheet was arranged so that the end face on the outer peripheral side of the positive electrode was located near the center in the length direction. The number of windings of the negative electrode in the electrode group was 6.

As the separator and the porous sheet, a non-woven fabric made of sulfonated polypropylene (hereinafter, SPP, degree of sulfonation of 1.90×10 ⁻³ , thickness of 82 μm, mass per unit area of 50 g/m ² ) was used.

When the opening of the through hole in the first portion of the negative electrode is the first opening and the opening of the through hole in the second portion of the negative electrode is the second opening, the area S1 of the first opening and the first opening and the second opening are The area S2 of the overlapping portion was designed so as to satisfy S2/S1=0.50.

The obtained electrode group was inserted into an AA-shaped bottomed cylindrical metal battery case (outer diameter 14.60 mm) having a ring-shaped groove on the opening side, and the outermost negative electrode (thin portion) was inserted. The inner surface of the battery case was contacted. Further, the positive electrode lead connected to the positive electrode was welded to the inner bottom surface of the lid cover plate. The sealing body is provided with a lid plate having a circular gas vent hole in the center, an insulating packing attached to the peripheral edge of the lid plate, and a central portion of the top surface of the lid plate so as to close the gas vent hole. And a cap-shaped positive electrode terminal having a protruding portion that covers the valve body.

Next, an alkaline aqueous solution was injected into the battery case as an electrolytic solution, the opening of the battery case was covered with a sealing body, and caulking was performed with an insulating packing to seal the battery case. The diameter was reduced by pressing the peripheral surface of the battery case from the outside. Then, by pressing the battery case in the height direction, the groove formed on the opening side of the battery case was pressure-bonded so that the total battery height was 50.25 mm.

As the alkaline aqueous solution, a 5.0 mol/L sodium hydroxide aqueous solution was used.

A donut-shaped insulating member was placed on the top of the sealing body in a state where the protruding portion of the positive electrode terminal was projected from the central hole of the insulating member. Then, by attaching an outer label so as to cover the peripheral portion of the sealing body (the peripheral portion of the insulating member arranged on the sealing body), the peripheral surface of the battery case, and the peripheral portion of the bottom surface of the battery case. A nickel hydrogen storage battery (A1) was obtained. A total of 50 batteries A1 were produced by the same procedure.

(4) Evaluation (self-discharge index)
At 20° C., it was charged at 240 mA for 16 hours, discharged at 2400 mA for 30 minutes, charged at 240 mA for 11 hours, discharged at 2400 mA for 30 minutes, and then stored at 45° C. for 72 hours to activate the negative electrode. After cooling to 20° C., discharge was performed at 2400 mA to 1.0 V. Next, after charging for 16 hours at 240 mA, a cycle of discharging at 2400 mA to 1.0 V was repeated three times, and the discharge capacity at the third cycle was taken as the capacity before storage. Next, the battery was charged at 240 mA for 16 hours, left at 45° C. for 7 days, and then discharged at 2400 mA to 1.0 V to determine the capacity after storage.

The difference between the capacity before storage and the capacity after storage was determined as the self-discharge amount for 50 cells, and the average value of 50 cells was determined and indexed. Specifically, the average value of the self-discharge rate obtained from (capacity before storage−capacity after storage)/(capacity before storage)×100 was used as the reference value 100 for the self-discharge rate of the battery of Example A2. It was standardized so as to be a self-discharge index. The results are shown in Table 1.

Example 2
The opening diameter and the opening ratio are the same as in Example 1, and the pitch between the centers of the openings in the height direction (longitudinal direction) of the battery and the pitch between the centers of the openings in the horizontal direction are changed to determine the area of the first opening. Nickel-metal hydride storage battery (A2) in the same manner as in Example 1 except that S1 and the area S2 of the portion where the first opening and the second opening overlap satisfy S2/S1=0.40. 50 were prepared and evaluated.

Example 3
The opening diameter and the opening ratio are the same as in Example 1, and the pitch between the centers of the openings in the height direction of the battery and the pitch between the centers of the openings in the lateral direction are changed to change the area S1 of the first opening to Fifty nickel-metal hydride storage batteries (A3) were produced in the same manner as in Example 1 except that the area S2 of the portion where the first opening and the second opening overlap each other was set to satisfy S2/S1=0.60. And evaluated.

Example 4
The opening diameter and the opening ratio are the same as in Example 1, the pitch between the centers of the openings in the height direction of the battery in the first opening and the pitch between the centers of the openings in the lateral direction, and the height of the battery in the second opening. The pitch between the centers of the openings in the direction and the pitch between the centers of the openings in the lateral direction were changed to different values. Thus, the same as Example 1 except that the area S1 of the first opening and the area S2 of the portion where the first opening and the second opening overlap satisfy S2/S1=0.80. Then, 50 nickel-hydrogen storage batteries (A4) were produced and evaluated.

Comparative Example 1
The opening diameter and the opening ratio are the same as in Example 1, and the pitch between the centers of the openings in the height direction of the battery and the pitch between the centers of the openings in the lateral direction are changed to change the area S1 of the first opening to Fifty nickel-metal hydride storage batteries (B1) were produced in the same manner as in Example 1 except that the area S2 of the portion where the first opening and the second opening overlap satisfied S2/S1=0.35. And evaluated.

Comparative example 2
In the same manner as in Comparative Example 1 except that the material of the separator was changed to a polypropylene non-woven fabric hydrophilized by corona discharge (hereinafter, PP, thickness 82 μm, mass per unit area 50 g/m ² ), Fifty nickel hydride storage batteries (B2) were produced and evaluated.

Example 5
The ratio (Wo/Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is set to 80% by mass. 50 nickel-metal hydride storage batteries (A5) were produced and evaluated in the same manner as in Example 1 except for the above.

Example 6
The ratio (Wo/Wi) of the hydrogen storage alloy amount Wo contained per unit area of the second portion of the negative electrode to the hydrogen storage alloy amount Wi contained per unit area of the first portion is set to 40% by mass. 50 nickel-metal hydride storage batteries (A6) were prepared and evaluated in the same manner as in Example 1 except for the above.

Example 7
Example 1 except that the hydrogen storage alloy was changed to an alloy Zr _0.01 La _0.44 Nd _0.45 Mg _0.10 Ni _3.15 Al _0.15 Co _0.20 having an A ₂ B ₇ type main phase and the separator thickness was changed to 92 μm. Similarly, 50 nickel-hydrogen storage batteries (A7) were produced and evaluated.

Example 8
Fifty nickel hydride storage batteries (A8) were prepared and evaluated in the same manner as in Example 1 except that an aqueous solution containing a hydroxide ion concentration of the alkaline aqueous solution of 7.0 mol/L was used. ..

Example 9
Fifty nickel hydride storage batteries (A9) were prepared and evaluated in the same manner as in Example 1 except that an aqueous solution containing a hydroxide ion concentration of the alkaline aqueous solution of 8.5 mol/L was used. ..

The results of Examples and Comparative Examples are shown in Table 1. As shown in Table 1, it can be understood that the battery of Comparative Example 1 has a high self-discharge index, whereas the larger the S2/S1 ratio, the lower the self-discharge index. In addition, the self-discharge index can be reduced to 93 by further improving other configurations. Note that the lower the self-discharge index, the more difficult the self-discharge progresses.

Next, each of the evaluated batteries was unsealed, and deviated marking was made on the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode and the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode. did. After that, the electrode group was disassembled, and the arrangement of the first openings in the first portion, the arrangement of the second openings in the second portion, and the area S1 of the first opening were measured. Next, the perimeter of the second portion is converted into the perimeter of the first portion, and the arrangement of the first openings when the lateral length is reduced is calculated, and the first opening and the second opening at that time overlap. The area S2 of the portion was obtained and S2/S1 was confirmed. As a result, in any of the examples, the S2/S1 value of 45 or more batteries out of 50 batteries has an error of ±3% from the designed S2/S1 value, and is considered to be practically the same as the design value. I was able to do it. From the above, when 90% or more of the 50 or more batteries have an S2/S1 value of 0.4<S2/S1, those batteries are considered to have been manufactured by the manufacturing method according to the present invention. You can

The S2/S1 value may be calculated directly from the correspondence pattern between the arrangement pattern of the through holes of the negative electrode current collector and the first opening and the second opening measured from the cross-sectional image (for example, CT image) of the battery. Good.

Since the nickel-hydrogen battery according to the present invention suppresses self-discharge, it is useful as, for example, a backup power source for memory or a vehicle power source.

1: Negative electrode 1a: Body part 1b: Tapered part 1c: Thin part 2: Positive electrode 3: Separator 3a: Porous sheet 4: Battery case 6: Safety valve 7: Sealing plate 8: Insulation gasket 9: Positive electrode current collector plate 11: Negative electrode Current collector 11b: First opening 11a: Second opening

Claims (6)

A strip-shaped positive electrode, a strip-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode, an electrode group wound such that the negative electrode constitutes the outermost periphery, an electrolytic solution, and the electrode group And a battery case accommodating the electrolytic solution,
The negative electrode includes a negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector,
The opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is the first opening, and the opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is When making the second opening,
The amount of the hydrogen storage alloy contained per unit area of the second portion is smaller than the amount of the hydrogen storage alloy contained per unit area of the first portion, and the area S1 of the first opening and the first opening A nickel-hydrogen battery in which an area S2 of a portion where the and the second opening overlap satisfies 0.4<S2/S1. The nickel according to claim 1, wherein the amount of the hydrogen storage alloy contained per unit area of the second portion is 40 to 80 mass% of the amount of the hydrogen storage alloy contained per unit area of the first portion. Hydrogen battery. The hydrogen storage alloy contains an element A and an element B,
The A element is at least one selected from the group consisting of Mg, Zr and rare earth elements,
B element is an element other than A element,
The nickel-hydrogen battery according to claim 1 or 2, wherein the ratio of the number of moles of element B to the number of moles of element A: B/A is 3.3 to 3.8. At least a part of the separator is formed of polypropylene,
The nickel hydrogen battery according to any one of claims 1 to 3, wherein at least a part of the polypropylene is sulfonated. The electrolytic solution contains an alkali metal hydroxide,
75 mol% or more of the alkali metal hydroxide is sodium hydroxide,
The nickel-hydrogen battery according to any one of claims 1 to 4, wherein the electrolyte solution has a hydroxide ion concentration of 5.0 to 8.5 mol/L. (I) a step of preparing a strip-shaped positive electrode,
(Ii) a step of preparing a strip-shaped negative electrode,
(Iii) a step of forming an electrode group by winding the positive electrode and the negative electrode with a separator interposed between the positive electrode and the negative electrode, and winding the negative electrode so as to form the outermost periphery.
(Iv) housing the electrode group in a battery case together with an electrolytic solution,
The negative electrode prepared in the step (ii) includes a negative electrode current collector having a plurality of through holes, and a negative electrode active material layer containing a hydrogen storage alloy formed on both surfaces of the negative electrode current collector. Prepare,
The opening of the through hole in the first portion of the negative electrode adjacent to the inside of the outermost periphery of the positive electrode is the first opening, and the opening of the through hole in the second portion of the negative electrode adjacent to the outside of the outermost periphery of the positive electrode is When making the second opening,
The amount of the hydrogen storage alloy contained per unit area of the second portion is smaller than the amount of the hydrogen storage alloy contained per unit area of the first portion, and the area S1 of the first opening and the first opening The method for manufacturing a nickel-hydrogen battery, wherein the electrode group is configured such that an area S2 of a portion where the first opening and the second opening overlap satisfy 0.4<S2/S1.