JP2001052732A - Cylindrical alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical alkaline secondary battery having high production efficiency. SOLUTION: A group of electrodes formed by winding a positive electrode and a negative electrode carrying an electrode mix respectively on a current collecting base with the intervention of a separator are sealed in a cylindrical battery can together with an alkali electrolyte. Either one of the current collecting bases 20 of the positive electrode and the negative electrode comprises a metallic porous body, an average hole diameter Rb on one surface of the metallic porous body is smaller than an average hole diameter Ra on the other surface, and the electrodes are wound with this one surface directed outward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical alkaline secondary battery, and more particularly, to a cylindrical alkaline secondary battery provided with an electrode having an electrode mixture supported on a current collecting substrate.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium secondary batteries have been widely used as chargeable / dischargeable and portable alkaline secondary batteries. Furthermore, in recent years, the above-mentioned alkaline secondary battery has been used as a power source for various electronic devices and mobile phones, or as a drive power source for electric vehicles and bicycles with electric assist, which are being developed recently. For this reason, there is an increasing demand for higher capacity alkaline secondary batteries. For these reasons, attention has been paid to nickel-hydrogen secondary batteries having a larger discharge capacity and a larger volume energy density than nickel-cadmium secondary batteries.

[0003] By the way, as a positive electrode (Ni electrode) of a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery,
A sintered type and a paste type are known. Of these, the sintered Ni electrode has an N electrode on the surface of the grid serving as the core material.
It is manufactured by impregnating an active material into a current collector substrate obtained by sintering i-powder. However, since the porosity of the substrate is not so high (about 80
%), It is difficult to increase the amount of the active material carried on the substrate to increase the battery capacity.

On the other hand, a paste-type Ni electrode is a paste (electrode mixture) containing an active material on a mesh-like and highly porous (about 95%) current collecting substrate such as a sintered body of Ni fiber or sponge-like Ni. ) Is applied and filled, and the skeleton (N
Since the proportion of i) is small and the proportion of voids is large, the filling rate of the active material can be increased to provide a high capacity battery. In addition,
The sponge-like Ni substrate is formed by applying an electroless Ni plating to a foamed resin sheet and then applying an Ni electroplating to form a mesh Ni.
It is manufactured by forming a skeleton and then burning off the resin inside the Ni plating layer.

[0005] For example, in a cylindrical nickel-hydrogen secondary battery, a paste (positive electrode mixture) containing Ni hydroxide, which is a positive electrode active material, and a binder is applied to the above-mentioned current-collecting substrate made of sponge-like Ni. A positive electrode is prepared by drying and rolling, and a paste (a negative electrode mixture) containing a hydrogen storage alloy powder and a binder is applied to a current collecting substrate made of punched metal to similarly prepare a negative electrode. An electrode group formed by winding a negative electrode and a negative electrode through a separator is sealed in a battery can together with an alkaline electrolyte.

[0006]

However, in the case where a cylindrical battery is formed by winding the above-mentioned paste-type Ni electrode, a part of the current collector substrate is broken and protrudes, and penetrates through the separator to form a negative electrode. May come in contact. When such a battery is used, insulation failure or short circuit is caused. Therefore, the battery is rejected as a defective product at an inspection stage, but the production yield (production efficiency) is reduced accordingly. . In particular, the demand for nickel
In order to supply a hydrogen secondary battery at low cost and with high reliability, it is important to increase the production efficiency of the battery.

[0007] By the way, such breakage of the current collecting substrate is as follows.
It is generated from a portion where the skeleton of the porous body is thin. However, if the skeleton of the substrate is thick, it is not preferable because the porosity decreases and the filling rate of the active material decreases. On the other hand, if the skeleton of the substrate is too thick, rupture will occur due to higher stress during winding, and the degree of rupture will be greater than in the case where the skeleton is thin, so there is a possibility that the rupture portion will protrude and penetrate the separator. Get higher.

[0008] The present invention provides a cylindrical alkaline secondary battery in which the current collector substrate is broken during production of the cylindrical alkaline secondary battery to prevent defective insulation and short-circuit of the battery, thereby improving the production efficiency. With the goal.

[0009]

SUMMARY OF THE INVENTION The present invention focuses on the fact that when a current collecting substrate made of a porous body is wound, a breakage occurs from a thin portion of the skeleton, and the thickness of the skeleton is changed on the front and back sides. The technical idea is to use an electric board. In the present invention, by winding the thin side of the skeleton of the current collecting substrate outward, the breaking of the current collecting substrate at this portion is promoted to release the stress applied to the current collecting substrate. As a result, breakage of the inside of the current collecting substrate is prevented.

In this case, the porosity (porosity) of the current collecting substrate is set to keep the amount of the active material carried in the thickness direction of the current collecting substrate constant.
Needs to be constant in the thickness direction. Therefore, in the present invention, when the skeleton of the substrate is made thin, a large number of small holes having an average pore diameter are distributed in that portion. Adjustments have been made so that they are relatively less distributed.

Then, in order to achieve the above-mentioned object,
In the cylindrical alkaline secondary battery according to the present invention, an electrode group formed by winding a positive electrode and a negative electrode each having an electrode mixture supported on a current collecting substrate through a separator is formed by alkaline electrolysis. Enclosed in a battery can together with the liquid, at least one of the current collector substrate of the positive electrode and the negative electrode is made of a porous metal, and the average pore size on one surface of the porous metal material is larger than the average pore size on the other surface. The electrode group is wound with the one surface facing outward.

The average pore diameter of the porous metal body is 300 to 60.
It is preferably 0 μm (claim 2). Furthermore, at least one of the positive electrode and the negative electrode current collecting substrates is formed of a laminate of a first base material and a second base material, each of which is formed of a porous metal, and The average pore size is smaller than the average pore size of the first substrate,
A cylindrical alkaline secondary battery is provided, wherein the electrode group is wound with the second substrate facing outward (claim 3).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a cylindrical alkaline secondary battery according to the present invention will be described by taking a nickel-hydrogen secondary battery as an example. In FIG. 1, a cylindrical nickel-metal hydride secondary battery has an electrode group 5 composed of a positive electrode 2, a negative electrode 4, and a separator 3 interposed between the positive electrode 2 and the negative electrode 4, which is spirally wound. It is manufactured by being housed in a bottomed cylindrical container 1 (AA size) together with an electrolytic solution. Here, the negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1.

A circular sealing plate 7 having a hole 6 in the center is disposed in the upper opening of the container 1, and a ring-shaped insulating gasket is provided between the periphery of the sealing plate 7 and the inner surface of the upper end 1 a of the container 1. The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking processing for reducing the diameter of the upper end 1a inward. The positive electrode lead 9 has one end connected to the positive electrode 2 and the other end connected to the lower surface of the sealing plate 7.

The hat-shaped positive electrode terminal 10 is mounted on a sealing plate 7 so as to cover the hole 6, and a space surrounded by the positive electrode terminal 10 and the sealing plate 7 is filled with a rubber safety valve 11. Usually, the hole 6 is closed. The circular holding plate 12 made of an insulating material having a hole in the center is disposed on the positive terminal 10 so that the projection of the positive terminal 10 protrudes from the hole, and the outer tube 13 is provided on the periphery of the holding plate 12, and The side surface and the bottom peripheral edge of the container 1 are covered.

The positive electrode 2 is manufactured by applying a positive electrode mixture (paste) to a current collecting substrate 20 described later, and the negative electrode 4 is manufactured by applying a negative electrode mixture to a predetermined current collector sheet. As shown in FIG. 2, each of the current collecting substrates 20 has a sponge-like N
i, the average pore diameter Rb of the second base material 20b on the upper surface side of the current collecting substrate 20 is equal to that of the lower surface side of the first base material 20a and the second base material 20b. The first
Is smaller than the average pore diameter Ra of the base material 20a. In this case, it is necessary to make the porosity (porosity) of each base material equal in order to keep the amount of the active material carried on each base material 20a, 20b constant. That is, the areas of the holes per unit area of the base materials 20a and 20b are made equal, and (Ra / 2) ² × π × 4 = (Rb / 2) ² × π × 9 (1).

If the hole intervals (the thickness of the skeleton) of the base materials 20a and 20b are Sa and Sb, respectively, the length of one side of each base material in the figure is equal, so that 3Sa + 2Ra = 4Sb + 3Rb (2) . Therefore, from the equations (1) and (2), the relationship of Sa = 1.5Sb (3) is obtained. That is, the skeleton of the second base material 20b having a small average pore diameter is smaller than that of the first base material 20a.

The current collecting substrate 20 thus obtained is
After the positive electrode mixture is applied to both surfaces, the negative electrode is laminated via the separator as described above to form an electrode group, and as shown in FIG. 3, the second base material 20b faces outward. It is wound. At this time, the amount of deformation is larger on the outside of the current collecting substrate 20 than on the inside, and the thickness of the skeleton of the second base material 20b is smaller than that of the first base material 20a. The fracture proceeds from the side of the second base material 20b.

In this case, the second base material 20b breaks with a relatively small stress, and forms a large number of cracks C and protrusions F.
Since the stress applied to the current collecting substrate 20 is released in the process, the first base material 20a having a thick skeleton and high strength is used.
(The inside of the current collecting substrate 20) is not broken, and the entire current collecting substrate 20 is prevented from being broken. Furthermore, since the second base material 20b breaks with a small stress, the crack C or the protrusion F has a fine crack shape, and the amount of protrusion of the break is large, so that it is unlikely that the breaker penetrates the separator.

The front and back surfaces of the current collecting substrate 20 (each base material 20)
a, 20b) have an average pore diameter of 300 to 600 μm.
m is preferably in the range. Average pore size is 300μm
If it is less than the above, there is a possibility that the skeleton at that portion becomes thin and the strength of the entire current collecting substrate is reduced. on the other hand,
When the thickness exceeds 600 μm, the current collecting substrate breaks with higher stress, so that the degree of breakage increases as compared with the case where the skeleton is thin, and the possibility that the broken portion protrudes and penetrates the separator increases. is there.

As a method of manufacturing the current collecting substrate 20, for example, foamed resin sheets having different sizes and distributions of foamed resin are attached to each other, a conductive agent is applied to the resin,
By plating, the first base material and the second base material can be integrally formed. Further, after laminating a first base material and a second base material each formed of a sintered sheet of Ni fibers having different fiber diameters, the whole may be sintered.

The current collecting substrate 20 only needs to have different average hole diameters on the front and back sides. The current collecting substrate 20 is not limited to the above-described substrate having a two-layer structure. For example, as shown in FIG.
A current collecting substrate may be manufactured by laminating more than two layers of the base material. In FIG. 4, the current collecting substrate 30 is formed by laminating a first base material 30a, a second base material 30b, and a third base material 30c each formed of a sintered sheet of Ni fiber from the lower surface side. . The fiber diameter of the first base material 30a is the thickest, and
The base 30b and the third base 30c have smaller fiber diameters in this order. Therefore, the average pore diameter of the first base material 30a is the largest, and hereinafter, the second base material 30b and the third base material 30c
In order. Then, the current collecting substrate 30
Is designed to break from the upper surface side during winding.

In addition to the above, a current collecting substrate having an average pore diameter continuously changed from one surface to the other surface may be used. Such a current collecting board can be manufactured by, for example, continuously changing the diameter of the Ni fiber in the thickness direction and laminating, and then sintering the whole. The positive electrode 2 and the negative electrode 4 may be manufactured as follows.

First, the positive electrode 2 is prepared by kneading nickel hydroxide, which is a positive electrode active material, with a conductive agent, a binder, and water to form a paste. Then, it can be formed by molding. As the conductive agent, for example, metal cobalt, cobalt oxide, cobalt hydroxide and the like can be used. These conductive agents may be coated on the surface of the nickel hydroxide, or may be added to the nickel hydroxide. Further, the conductive agent may be coated on the surface of the nickel hydroxide, and the conductive agent may be further added to the nickel hydroxide.

Examples of the binder include carboxymethylcellulose (CMC), methylcellulose, hydroxypropylmethylcellulose, PVA, SBR, sodium polyacrylate, polytetrafluoroethylene (P
TFE) can be used. Note that it is preferable to use, as the above-described nickel hydroxide, a solid solution of at least one selected from Zn, Co, Cd, and a rare earth element, since charging efficiency and cycle characteristics are improved. When nickel hydroxide was measured by X-ray powder diffraction (Cu-Kα ray), the peak half width r of the (001) plane was 0.5 to 0.9 ° / 2.
When θ and the peak intensity are p, p / r is 1
More preferably, it is 2,000 to 2,000. Here, if the half width r is less than 0.5 ° / 2θ, a sufficient discharge capacity cannot be obtained, and if it exceeds 0.9 ° / 2θ, the crystallinity is lost and the charging efficiency at a high rate is obtained. Is likely to decrease.

The negative electrode 4 is prepared by kneading a hydrogen storage alloy powder with a conductive agent, a binder, and water to form a paste, applying it to a current collector sheet described later, drying it, and then molding it into an arbitrary shape. It can be manufactured by processing. The hydrogen storage alloy is not particularly limited as long as it can store and release hydrogen in the electrolytic solution. For example, AB ₅ -based, TiNi-based, TiFe-based, and M
A g ₂ Ni-based alloy can be used. Where A
Is La, Mm (Misch metal), or Lm (La-enriched misch metal). And B is Ni, or Ni and Al, Mn, Co, Ti, Cu, Zn, Z
An alloy with an element selected from the group consisting of r, Cr and B.

[0027] In particular, the general _{formula: LmNi v Co w Mn x Al} y
It is preferable to use a compound represented by Zr _z . Here, 5.1 ≦ v + w + x + y + z (atomic ratio) ≦ 5.4. When the atomic ratio is less than 5.1, the cycle life is reduced, and when the atomic ratio is more than 5.4, the hydrogen storage amount in the negative electrode may be reduced. The rare earth element used for Lm is, for example, Ce, Pr, Nd, in addition to La.
Can be mentioned. Further, it is preferable that the average particle size of these alloy powders is 20 to 70 μm in D50 value. Here, the average particle size defined by the D50 value refers to the particle size when the cumulative number of particles is 50% of the total number of particles when the particle distribution is taken. When the average particle size is less than 20 μm, the cycle life is reduced, and when the average particle size is more than 70 μm, the battery reaction at a low temperature is suppressed and the battery capacity may be reduced.

As the conductive agent, for example, carbon black, graphite and the like can be used. The binder may be the same as that used in the production of the positive electrode, for example. The current collector sheet used for producing the negative electrode includes, for example, nickel, stainless steel and nickel-plated steel sheet, punched metal,
Substrates having a two-dimensional structure, such as expanded metal, plated perforated steel sheet, nickel net, and the like, and substrates having a three-dimensional structure, such as a felt-like metal porous body and a sponge-like metal base, can be used. Further, the above-described current collecting board 20 of the present invention may be used.

As the separator, for example, a nonwoven fabric of polyamide fiber or a nonwoven fabric of olefin fiber such as polyethylene or polypropylene which has been subjected to a hydrophilic treatment can be used. Examples of the alkaline electrolyte used for the nickel-hydrogen secondary battery include NaOH and LiO
H, a mixed solution of KOH and LiOH,
A mixed solution consisting of H, LiOH, and NaOH can be used.

Although the nickel-hydrogen secondary battery has been described in the above embodiment, the present invention can be applied to other cylindrical alkaline secondary batteries such as a nickel cadmium secondary battery. . Further, in the above embodiment, the case where the current collecting substrate of the present invention is applied to the positive electrode has been described. However, the current collecting substrate of the present invention may be applied to the negative electrode, or may be applied to both the positive electrode and the negative electrode. May be.

[0031]

EXAMPLES Examples 1 to 3 and Comparative Examples 1 to 5 Production of Positive Electrode A current collecting substrate made of sponge-like Ni and having a thickness of 1.5 mm and a basis weight of 400 g / m ² shown in FIG. 2 was prepared. This current collecting substrate is obtained by laminating a first foamed resin sheet having an average pore diameter on the inner surface side shown in Table 1 and a second foamed resin sheet having an average pore diameter on the outer surface side corresponding to the inner surface. It is manufactured by sequentially applying electrolytic plating and Ni electroplating, and then burning off the resin inside the Ni plating layer.

The positive electrode mixture was prepared as follows.
First, in X-ray powder diffraction (Cu-Kα ray), the peak half width r of the (001) plane was 0.65 ° / 2θ, and the peak intensity was 17
A nickel hydroxide powder of 00 (AU) was prepared. For 90 parts by weight of this nickel hydroxide, 10 parts by weight of a conductive agent (cobalt oxide) and 5 parts by weight of a binder (PTFE:
MC: 3 parts by weight) and 45 parts by weight of pure water were added and kneaded to obtain a positive electrode mixture.

Then, this positive electrode mixture is applied to a current collecting substrate.
After filling and drying, it was rolled to obtain a positive electrode 2. 2. Production of negative electrode Lm (mainly composed of La, Ce, Nd and Pr), N
i, Co, Mn, Al, and Zr are mixed and dissolved in an Ar atmosphere, and then subjected to a heat treatment at 1000 ° C. for 10 hours in an Ar atmosphere, and mechanically pulverized and passed through a mesh to obtain an average particle size. (D50 value) A hydrogen storage alloy powder of 50 μm was obtained. For 100 parts by weight of the hydrogen storage alloy powder, 1 part by weight of a conductive agent (carbon black) and a binder (PTFE: 1.5
Parts by weight, sodium polyacrylate: 0.5 parts by weight, CM
C: 0.12 parts by weight) and 45 parts by weight of pure water were added and kneaded to obtain a negative electrode mixture.

The negative electrode mixture was applied to a punched metal made of Ni, filled and dried, and then rolled to obtain a negative electrode 4. 3. Assembly of Battery The positive electrode 2 and the negative electrode 4 described above are overlapped with each other via a separator 3 made of non-woven polyolefin non-woven fabric, and wound so that the negative electrode 4 is on the outside to form an electrode group 5. The solution was injected and sealed, and a cylindrical nickel-hydrogen secondary battery shown in FIG. 1 was assembled. 4. Evaluation of Insulation Property A DC voltage of 500 V was applied between the positive electrode and the negative electrode of the above-described battery, and the insulation resistance between the positive electrode and the negative electrode at that time was measured. The insulation resistance of each of the 1000 batteries was measured, and those having a resistance value equal to or lower than a predetermined value were regarded as having insulation failure, the number thereof was counted, and the insulation failure rate was evaluated. Table 1 shows the above results.
Shown in

[0035]

[Table 1]

(1) As is clear from Table 1, the nickel-hydrogen secondary batteries of the present invention all have an insulation failure rate of less than 1%. (2) In the case of Comparative Example 1 in which the outer surface and the inner surface of the current collecting substrate of the positive electrode have the same average pore diameter, the insulation failure rate is higher than that of the example. (3) In Comparative Examples 2 to 4 in which the average pore diameter on the outer surface of the current collecting substrate of the positive electrode is larger than the average pore diameter on the inner surface, the insulation failure rate is higher than in the examples. In particular, in Comparative Example 4 in which the difference between the average pore diameters of the outer surface and the inner surface is the largest, the insulation failure rate is the highest. This clearly shows the superiority of the present invention in which the average pore size on the outer surface of the current collecting substrate is smaller than the average pore size on the inner surface. (4) In the case of Comparative Example 5 in which the average hole diameter on the outside of the current collecting substrate is 250 μm, the substrate strength itself is low, and the insulating failure rate is high because the substrate is broken down to the inside.

[0037]

As is apparent from the above description, in the cylindrical alkaline secondary battery according to the present invention, at least one of the positive and negative electrode current collecting substrates has a different average pore diameter between the front surface and the back surface. It is made of porous material. Since the electrode group is wound with the surface having the smaller average pore diameter of the porous metal body facing outward, the skeleton is thin on the outside of the current collecting substrate, and the fracture easily proceeds with a small stress. However, the inside of the current collecting substrate having a large skeleton is not broken, and the entire current collecting substrate is prevented from being broken. In addition, since the outside of the current collecting substrate is broken into small cracks with a small stress, the degree of breakage increases, and the broken portion rarely penetrates through the separator.

As a result, the insulation failure rate during the production of the battery is significantly reduced, and the production efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view showing the structure of a nickel-hydrogen secondary battery according to the present invention.

FIG. 2 is an exploded perspective view showing a current collecting substrate.

FIG. 3 is a schematic diagram showing a state when a current collecting substrate is wound.

FIG. 4 is a sectional view showing a current collecting substrate having a three-layer structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery can 2 Positive electrode 3 Separator 4 Negative electrode 5 Electrode group 20, 30 Current collecting board Ra, Rb Average pore diameter (of current collecting board)

Claims (3)

[Claims] An electrode group formed by winding a positive electrode and a negative electrode, each having an electrode mixture supported on a current collecting substrate, through a separator, is enclosed in a battery can together with an alkaline electrolyte. In the alkaline secondary battery, at least one of the current collecting substrates of the positive electrode and the negative electrode is made of a porous metal, and the average pore size on one surface of the porous metal material is smaller than the average pore size on the other surface. Wherein the electrode group is wound with the one surface facing outward. 2. The metal porous body has an average pore diameter of 300 to 6.
The cylindrical alkaline secondary battery according to claim 1, wherein the thickness of the cylindrical alkaline secondary battery is 00 µm. 3. At least one of the positive electrode and the negative electrode current collecting substrates comprises a laminate of a first base material and a second base material each made of a porous metal, and
The average pore size of the base material is smaller than the average pore size of the first base material, and the electrode group is wound with the second base material facing outward. Item 3. A cylindrical alkaline secondary battery according to Item 1 or 2.