JP6082616B2 - Alkaline storage battery - Google Patents

Description

  The present invention relates to an alkaline storage battery having a special separator configuration.

  In recent years, the use of secondary batteries (storage batteries) has expanded, and has come to be used in a wide range of applications such as personal computers, portable terminals, electric vehicles, hybrid vehicles, electric bicycles, and electric tools. Among these, alkaline storage batteries represented by nickel-hydrogen storage batteries and nickel-cadmium storage batteries are used in various applications such as dry-cell secondary batteries and large batteries for hybrid vehicles. And as a separator which isolate | separates a positive electrode and a negative electrode used for this kind of alkaline storage battery and hold | maintains alkaline electrolyte, the nonwoven fabric which consists of polyolefin fiber excellent in alkali resistance is generally used.

  Since this type of polyolefin fiber is inferior in hydrophilicity with an alkaline electrolyte, it is necessary to improve the hydrophilicity by applying a hydrophilic treatment. Therefore, in order to improve the hydrophilicity of the separator made of polyolefin fiber with the alkaline electrolyte, the nonwoven fabric made of polyolefin fiber is treated with sulfuric acid treatment (sulfonation treatment), fluorine treatment, corona discharge treatment, graft polymerization treatment or interface. Various hydrophilic treatments such as addition of an activator have been performed, and it has come to be used as a separator having excellent hydrophilicity.

  The sulfonation treatment has not only hydrophilicity but also a self-discharge suppressing effect of the storage battery, and is regarded as a useful treatment. However, it is generally known that when the sulfonation treatment is performed strictly on the separator, damage to the polyolefin fibers increases, and the strength and life characteristics deteriorate.

  In addition, in order to improve the shielding property while reducing the basis weight, a separator having a configuration containing main fibers and ultrafine fibers is used as a nonwoven fabric separator made of polyolefin fibers. About the separator which consists of such a main fiber and an ultrafine fiber, it has been pointed out that the damage to the ultrafine fiber by sulfonation treatment may lead to an increase in the internal resistance of the storage battery and a deterioration of the life.

  In addition, as another method for increasing hydrophilicity, there is a method of imparting a surfactant to the separator. However, since the activator inhibits the electrode reaction and increases the internal resistance, it is difficult to increase the output of the storage battery. Has been pointed out.

  Furthermore, it is also known to use corona discharge treatment as another method for increasing hydrophilicity. Corona discharge treatment causes little damage to the fibers and has a great hydrophilic effect. In particular, it is known that a storage battery with improved self-discharge suppression, output characteristics, and life characteristics can be manufactured by performing a process that combines a corona discharge process and a sulfonation process (Patent Document 1). reference).

  In addition, with the recent increase in capacity of storage batteries, there is an increasing demand for reducing the thickness of the separator. However, when the distance between the electrodes in the electrode group is shortened due to the thin separator design (especially in the case of foam metal type positive electrodes) ) Internal short circuit increases due to burrs and cracks in the electrode plate. As a countermeasure, it is necessary to increase the fiber density of the separator or to increase the thickness of the separator, but the result is contrary to the demand for higher output.

  In such a flow, a technique for providing a long-life alkaline storage battery with excellent battery characteristics and no short circuit by using a combination of two types of separators has been proposed. In the present technology, a first separator imparted with hydrophilicity by sulfuric acid treatment (sulfonation treatment) and a second separator imparted with hydrophilicity without using sulfuric acid treatment are used (see Patent Document 2). .

Japanese Patent Laid-Open No. 7-1341979 JP 2004-031293 A

  According to the method described in Patent Document 1, it is possible to improve storage battery characteristics such as self-discharge suppression. However, since the sulfonation process is used in the manufacturing process of the separator according to the technology of this document, the thickness of the separator is further reduced and the internal short circuit is prevented in response to the demand for higher output of the storage battery. Therefore, it is difficult to certify that sufficient strength is secured.

  Moreover, according to the method described in Patent Document 2, it is possible to provide a separator that can ensure strength and prevent internal short circuit. However, in order to increase the shielding property while reducing the basis weight, it is difficult to ensure sufficient hydrophilicity only by the sulfonation treatment when the first separator is manufactured from a combination of the main fiber and the ultrafine fiber. Achieving power and long life is difficult.

  It is an object of the present invention to provide an alkaline storage battery that achieves high output and long life while ensuring the strength of the separator.

  The alkaline storage battery of the present invention is an alkaline storage battery including an electrode group in which a positive electrode and a negative electrode are wound through a separator, and the separator is a first nonwoven fabric made of polyolefin subjected to sulfuric acid treatment and corona discharge treatment. And a second separator made of a polyolefin non-woven fabric that is not subjected to hydrophilic treatment.

  As one aspect of the present invention, for example, the inner side and the outer side of the winding start portion of the positive electrode are covered with respect to the electrode group around which the second separator is wound.

  As one aspect of the present invention, for example, the outside of the winding end portion of the positive electrode is covered with respect to the electrode group around which the second separator is wound.

  As an aspect of the present invention, for example, the electrode group around which the second separator is wound covers the inside and outside of the positive electrode winding start portion and the outside of the positive electrode winding end portion.

  As one aspect of the present invention, for example, the first separator is composed of a main fiber using a polyolefin-based adhesive fiber and an ultrafine fiber using a high-strength polypropylene.

As one aspect of the present invention, for example, the degree of sulfuric acid treatment of the first separator is in the range of 1.5 × 10 ^{−3 to} 3.5 × 10 ⁻³ with respect to the value represented by the following calculation formula. Alkaline storage battery. Degree of sulfuric acid treatment = (SO ₄ amount in separator (g) / SO ₄ formula amount) / (Separator weight (g) × 3 / (propylene molecular weight))

  As one aspect of the present invention, for example, in the second separator covering the inside and outside of the positive electrode winding start portion, the length of the second separator from the positive electrode winding start portion is set in a range of 5 to 30 mm. Has been.

  According to the present invention, the first and second separators can provide an alkaline storage battery that achieves high output and long life while ensuring the strength of the separator.

The perspective view which shows the internal structure of the alkaline storage battery of one Embodiment of this invention. Sectional drawing of the winding start part of the electrode group in the alkaline storage battery of embodiment Sectional drawing of the winding end part of the electrode group in the alkaline storage battery of embodiment Enlarged photograph of the separator showing the state where the main fibers and ultrafine fibers are intertwined Table showing experimental results on battery characteristics of Examples and Comparative Examples

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

  FIG. 1 is a diagram showing an internal structure of a nickel metal hydride battery that is an alkaline storage battery according to an embodiment of the present invention. Although the present embodiment shows an example of a cylindrical battery, the present invention is not limited to a nickel metal hydride battery, and can be applied to other types.

  The outer shape of the alkaline storage battery 1 is configured by a metal outer can 2, a positive electrode side cap 3, and a negative electrode side cap 4. A positive electrode side cap 3 having a positive electrode terminal 3a and a negative electrode side cap 4 having a negative electrode terminal 4a are attached to both ends of a cylindrical metal outer can 2, and a safety valve 5 and a gasket 8 are formed in an internal space formed by these members. Members such as the positive electrode 10, the negative electrode 20, and the separator 30 are accommodated.

  The safety valve 5 is a member that opens when a pressure exceeding a certain value is applied to the internal space of the alkaline storage battery 1 and plays a role of releasing the pressure, and the gasket 8 is a member that prevents leakage of an internal liquid such as an electrolytic solution. . The kind of these members is not particularly limited.

  The alkaline storage battery 1 of the present embodiment has a cylindrical appearance, and the plate-like positive electrode 10 and the plate-like negative electrode 20 are spirally wound via a nonwoven fabric separator 30, and are placed in the internal space of the alkaline storage battery 1. Has been placed. In the case of a nickel metal hydride battery, the positive electrode 10 is configured by embedding an active material such as nickel hydroxide in a predetermined substrate or the like. In particular, a foam metal type (SME) positive electrode is constituted by filling a porous material with a porous foam metal and filling an active material in a hole, but the type of the positive electrode 10 is not particularly limited. . Although the negative electrode 20 is comprised by apply | coating the fine powder of a well-known hydrogen storage alloy to a metal porous plate, for example, the kind of negative electrode 20 is not specifically limited.

  2 is a cross-sectional view of a winding start portion of an electrode group according to an embodiment of the invention, and FIG. 3 is a cross-sectional view of a winding end portion of the electrode group of an embodiment of the present invention. The electrode group means a plurality of layers that are wound to form a laminate of electrodes (including the positive electrode 10 and the negative electrode 20). In other words, FIG. 2 corresponds to an enlarged view near the center of the circular cross section of the alkaline storage battery 1, and FIG. 3 is an enlarged view of the outermost layer of the circular cross section of the alkaline storage battery 1 near the ends of the electrode group and the separator 30. It corresponds to. In the present embodiment, the separator 30 includes a first separator 31 and a second separator 32. The number of layers described above, that is, the number of windings of the positive electrode 10 and the negative electrode 20 is not particularly limited.

  In this embodiment, the 1st separator 31 is comprised from the polyolefin nonwoven fabric which performed the sulfuric acid process (sulfonation process) and the corona discharge process. In particular, in the present embodiment, the first separator 31 is composed of a main fiber using a polyolefin-based adhesive fiber and an ultrafine fiber using a high-strength polypropylene. FIG. 4 is an enlarged photograph of the first separator 31 of the embodiment. The magnification is 500 times, and the image is taken using a scanning electron microscope. As can be seen from this enlarged photograph, the main fiber 31a using the polyolefin-based adhesive fiber and the ultrafine fiber 31b using the high-strength polypropylene are intertwined.

  The order of the sulfuric acid treatment and the corona discharge treatment when forming the first separator 31 is not particularly limited, but the effect of the corona discharge treatment decreases with time, so that the corona treatment discharge is performed after the sulfuric acid treatment. It is common. The sulfuric acid treatment is generally a treatment for attaching hydrophilic sulfonic acid groups to the surface of the fiber from fuming sulfuric acid, but its detailed mode is not particularly limited. Further, the corona discharge treatment is a treatment for generating a hydrophilic polar group on the surface of the fiber, and its detailed mode is not particularly limited. By using the sulfuric acid treatment and the corona discharge treatment together, it is possible to effectively increase the hydrophilicity of the first separator 31 and manufacture a storage battery with improved self-discharge suppression, output characteristics, and life characteristics.

When the first separator 31 is treated with sulfuric acid, the value represented by the following formula, that is, the degree of sulfuric acid treatment is preferably in the range of 1.5 × 10 ^{−3 to} 3.5 × 10 ^−3. The sulfuric acid treatment is performed.
Degree of sulfuric acid treatment = (SO ₄ amount in separator (g) / SO ₄ formula amount) / (Separator weight (g) × 3 / (propylene molecular weight))

  The above formula for the degree of sulfuric acid treatment expresses the amount of sulfone groups in the separator. If the value of the sulfuric acid treatment degree is too low, sufficient self-discharge performance may not be obtained. On the other hand, if it is too high, not only will the fiber be damaged, the shielding properties will be lowered and the life characteristics will be lowered, but also the excessive sulfone group will inhibit the battery reaction and the output characteristics may also be lowered.

  The second separator 32 is made of a polyolefin non-woven fabric that is not subjected to hydrophilic treatment such as sulfuric acid treatment, corona discharge treatment, surfactant application, plasma treatment, fluorine gas treatment, acrylic acid graft polymerization treatment and the like. The second separator 32 is intended to ensure strength and life, and unlike the first separator 31, it is necessary that the raw material polyolefin nonwoven fabric is not subjected to any hydrophilic treatment.

  In the present embodiment, a first separator 31 that has been subjected to sulfuric acid treatment and corona discharge treatment and a second separator 32 that has not been subjected to hydrophilic treatment are used as the separator 30. With this configuration, it is possible to achieve strength and cost reduction suitable for practical use while improving the output performance of the alkaline storage battery 1.

  As shown in FIG. 2, in the present embodiment, the second separator 32 covers the inner side surface 10 a and the outer side surface 10 b of the winding start portion of the positive electrode 10. The inner side surface 10a is the surface of the positive electrode 10 located on the center side of the circular cross section, and the outer side surface 1b is the surface of the positive electrode 10 located on the outermost layer side of the circular cross section. Further, the second separator 32 also covers the end face 10 c of the winding start portion of the positive electrode 10. In other words, the second separator 32 is in contact with the first separators 31 on both sides of the positive electrode 10 while covering the end of the winding start portion. Therefore, at the end of the winding start portion of the positive electrode 10, two layers of the first separator 31 and the second separator 32 are interposed between the positive electrode 10 and the negative electrode 20.

  Further, as shown in FIG. 3, the second separator 32 covers the outer side 10 b of the end of winding of the positive electrode 10. In other words, the second separator 32 covers the outside of the end of the winding end of the positive electrode 10. Therefore, two layers of the first separator 31 and the second separator 32 are interposed between the outer side of the positive electrode 10 and the negative electrode 20 at the end of the winding end of the positive electrode 10.

  The winding start part of the positive electrode 10 and the negative electrode 20 is a part where burrs and cracks of the electrode plate are likely to occur, and the end part of winding is a part where burrs of the electrode plate are likely to occur, as shown in FIGS. By using two types of separators, it is possible to ensure strength and suppress the occurrence of internal short circuits. Since the second separator 32 is not subjected to hydrophilic treatment such as sulfuric acid treatment, the strength can be easily secured. 2 and 3 are not necessarily employed, and the configuration of FIG. 2 may be employed for the winding start portion, and another configuration different from FIG. 3 may be employed for the winding end portion. Conversely, the configuration of FIG. 3 may be adopted at the winding end portion, and another configuration different from that of FIG. 2 may be adopted as the configuration of the winding start portion. Of course, the second separator 32 is not limited to the winding start portion and the winding end portion, but can be disposed in other portions, or can be disposed in the entire region from the winding start portion to the winding end portion. it can.

  In particular, since the second separator 32 is partially used (only the winding start portion and / or the winding end portion), the disadvantages such as insufficient retention of the electrolytic solution derived from the absence of the hydrophilic treatment are avoided. However, it is possible to ensure output characteristics, strength and life sufficient for practical use. As described above, in the present embodiment, since the second separator 32 is partially used, the thickness of the separator increases as a whole, and the output as a storage battery decreases and the increase in cost is suppressed. can do. In addition, by arranging the second separator 32 at the winding start portion and winding end portion where the burrs and cracks of the electrode plate are likely to occur, high strength, long life, and prevention of internal short circuit are efficiently achieved. . In particular, the combination of the first separator 31 having a high hydrophilicity and the second separator 32 having a low hydrophilicity and an excellent strength makes it possible to obtain a storage battery having an excellent total balance.

  In the present embodiment, as shown in FIG. 2, the length of the winding start portion of the second separator 32 in the winding direction, more precisely, the length L1 on the outer side surface 10b and the length L2 on the inner side surface 10a. Is set in a range of 5 to 30 mm from the winding start portion (end surface 10 c) of the positive electrode 10. In other words, the length of the second separator 32 at the winding start portion is set to 5 mm at the shortest and 30 mm at the longest. By setting to such a range, it is possible to obtain a suitable alkaline storage battery 1 that ensures a balance with respect to factors such as high output, high strength, and cost reduction. Regarding the magnitude relationship between the length L1 and the length L2, L1> L2 in the example of FIG. 2, but L1 = L2 or L1 <L2 may be satisfied. In the embodiment, the first separator 31 and the second separator 32 are present at the winding start portion and the winding end portion in a compressed state. A part of the first separator 31 may be deleted, and the second separator 32 may be embedded in the deleted part, and the method of overlaying the first separator 31 and the second separator 32 is not particularly limited.

As described above, polyolefin fibers are selected as the fibers constituting the first separator 31 and the second separator 32. Examples of the polyolefin used include, but are not limited to, polyethylene and polypropylene. The thicknesses of the first separator 31 and the second separator 32 are preferably set in the range of 0.10 to 0.20 mm, but the thickness can be appropriately set. Further, the basis weight (weight per unit area) of the first separator 31 and the second separator 32 is preferably set in the range of 45 to 75 g / m ² , but is not particularly limited.

  The diameter (diameter) of the main fiber in the first separator 31 is preferably 5 μm or more, and the diameter of the ultrafine fiber is preferably 2 μm or less. Although the 2nd separator 32 can also be formed with the same fiber as the 1st separator 31, the ultrafine fiber 31b is not necessarily required and arbitrary polyolefin fibers can be selected.

  Hereinafter, examples and comparative examples will be described.

[Example 1]
(Preparation of separator)
A separator using a polyolefin adhesive fiber and high-strength polypropylene fiber as a material and blending an appropriate amount of ultrafine fibers with a basis weight of 65 g / m ² was prepared by a known method. This separator was used as the second separator.

Further, this separator was treated with sulfuric acid by a known method so that a value represented by the following calculation formula was 2.5 × 10 ⁻³ .
Degree of sulfuric acid treatment = (SO ₄ amount in separator (g) / SO ₄ formula amount) / (Separator weight (g) × 3 / (propylene molecular weight))

  Furthermore, the separator produced as described above was produced using a known method, and a separator subjected to surface modification by corona discharge treatment was produced. This separator was used as the first separator.

(Preparation of positive electrode)
A nickel hydroxide powder was used as an active material, a cobalt compound and a rare earth oxide were added as additives, and kneaded with a thickener, a binder, and pure water to prepare a positive electrode mixture paste. This positive electrode mixture paste is filled in a foam metal type (SME; Sponge Metal) porous body as a core, dried and pressed to a predetermined thickness, then cut to a predetermined dimension and having a theoretical capacity of 6000 mAh. A positive electrode was prepared.

(Preparation of negative electrode)
A hydrogen storage alloy powder was used as an active material, acetylene black and rare earth oxide were added as additives, and kneaded with a thickener, binder, and pure water to prepare a negative electrode mixture paste. This negative electrode mixture paste was applied to a punching metal as a core, dried and pressed to a predetermined thickness, and then cut into predetermined dimensions to produce a negative electrode having a theoretical capacity of 9000 mAh.

(Production of electrode group)
The first separator, the second separator, the positive electrode, and the negative electrode prepared as described above were prepared, and the lengths L1 and L2 in the winding direction of the winding start portion of the second separator as shown in FIG. As shown in FIG. 3, the second separator was wound in a spiral shape so as to cover the outside of the winding end portion of the positive electrode, so that the electrode group was produced.

(Production of nickel metal hydride battery)
A positive electrode current collector and a negative electrode current collector were each welded to the planar portion of the electrode group produced as described above. Further, after being inserted into an outer can serving also as a negative electrode terminal, an alkaline electrolyte composed of potassium hydroxide, sodium hydroxide and lithium hydroxide having a specific gravity of 1.26 is injected at a rate of 2.4 ml / Ah with respect to the positive electrode capacity. Then, a nickel metal hydride battery was produced. This battery is referred to as Example 1.

[Example 2]
A nickel-metal hydride battery produced in the same manner as in Example 1 except that the sulfuric acid treatment degree of the first separator was set to 1.0 × 10 ⁻³ with ^respect to Example 1 is referred to as Example 2.

[Example 3]
A nickel-metal hydride battery produced in the same manner as in Example 1 except that the sulfuric acid treatment degree of the first separator was set to 1.5 × 10 ⁻³ with ^respect to Example 1 is referred to as Example 3.

[Example 4]
A nickel-metal hydride battery manufactured in the same manner as in Example 1 except that the sulfuric acid treatment degree of the first separator was set to 3.5 × 10 ⁻³ with ^respect to Example 1 is referred to as Example 4.

[Example 5]
A nickel-metal hydride battery produced in the same manner as in Example 1 except that the sulfuric acid treatment degree of the first separator was set to 4.0 × 10 ⁻³ with ^respect to Example 1 is referred to as Example 5.

[Example 6]
A nickel-metal hydride battery manufactured in the same manner as in Example 1 except that the second separator at the winding start portion is not disposed with respect to Example 1 is referred to as Example 6.

[Example 7]
A nickel-metal hydride battery manufactured in the same manner as in Example 1 except that the second separator at the end of winding is not disposed with respect to Example 1 is referred to as Example 7.

[Example 8]
In contrast to Example 1, the lengths L1 and L2 in the winding direction of the winding start portion of the second separator were prepared in the same manner as in Example 1 except that the length L1 and L2 were 5 mm from the start of winding of the positive electrode. A nickel metal hydride battery is referred to as Example 8.

[Example 9]
In contrast to Example 1, the lengths L1 and L2 in the winding direction of the winding start portion of the second separator were prepared in the same manner as in Example 1 except that the length L1 and L2 were 20 mm from the start of winding of the positive electrode. A nickel metal hydride battery is referred to as Example 9.

[Example 10]
In contrast to Example 1, the lengths L1 and L2 in the winding direction of the winding start portion of the second separator were prepared in the same manner as in Example 1 except that the length L1 and L2 were 30 mm from the start of winding of the positive electrode. A nickel metal hydride battery is referred to as Example 10.

[Example 11]
A nickel-metal hydride battery manufactured in the same manner as in Example 1 except that a polyolefin-based adhesive fiber is used as a material and a first separator not containing ultrafine fibers is used as Example 11 is referred to as Example 11.

[Comparative Example 1]
A nickel hydride battery manufactured in the same manner as in Example 1 except that only the sulfuric acid treatment is applied to the first separator and the second separator at the winding start portion and the winding end portion is not disposed. Set to 1.

[Comparative Example 2]
Compared to Example 1, a nickel-metal hydride battery produced in the same manner as in Example 1 except that the first separator is subjected only to corona discharge treatment and the second separator at the winding start portion and winding end portion is not disposed. Example 2.

[Comparative Example 3]
A nickel-metal hydride battery manufactured in the same manner as in Example 1 except that the second separator at the winding start portion and the winding end portion is not disposed with respect to Example 1 is referred to as Comparative Example 3.

[Comparative Example 4]
Compared to Example 1, a nickel-metal hydride battery produced in the same manner as in Example 1 except that the second separator also had a sulfuric acid treatment degree of 2.5 × 10 ⁻³ as in the case of the first separator was a comparative example. 4.

  After leaving each of the above batteries for 24 hours, the following initial charge / discharge and activation charge / discharge were performed in an atmosphere at 25 ° C., and then various evaluations were performed. The results are shown in FIG.

Initial charge / discharge conditions:
Charging: 15 hours at 600 mA (1 hour after charging)
Discharge ... Until reaching 1.0V at 1200mA

Activation / discharge conditions:
Charging: discharging at 6500 mA for 1 hour: repeating this 10 times until reaching 1.0 V at 6000 mA.

(Internal resistance test)
The following four types of discharge were performed after charging.
Charge: 1 hour at 3000 mA Discharge: 20 seconds at 6000 mA, 5 minutes of rest, charge: 20 seconds at 6000 mA, 5 minutes of rest: 20 seconds at 18000 mA, 5 minutes of rest, Charging: 20 seconds at 18000 mA, 5 minutes of resting discharge: 20 seconds at 36000 mA, resting 5 minutes, charging: 20 seconds at 36000 mA, resting 5 minutes discharging: 20 seconds at 60000 mA, Pause 5 minutes, Charging ... 20 seconds at 60000 mA, Pause 5 minutes

By reading the voltage drop _VA after 10 seconds in these four types of discharges, and dividing this _VA by each current value, DCIR (internal resistance value) is calculated, and the DCIR of the battery of Example 1 is calculated. The ratio when set to 1 is shown in FIG. 5 as an index of output characteristics.

(Life test)
The following charging, resting, and discharging were performed.
Charging: 1.6 hours at 3000 mA in an atmosphere of 25 ° C.
Rest: 2 weeks under 65 ° C atmosphere.
Discharge: Until reaching 1.0 V at 2000 mA in a 25 ° C. atmosphere.

  The period until the capacity at the time of discharging reaches 60% of the initial stage was defined as the battery life period. The ratio when the lifetime in Example 1 is 1 is shown in FIG. 5 and used as an index of lifetime characteristics.

(Self-discharge test)
Charging: 1.6 hours at 3000 mA in an atmosphere of 25 ° C.
Rest: 10 days in a 45 ° C atmosphere.
Discharge: Until reaching 1.0 V at 2000 mA in a 25 ° C. atmosphere.

  The discharge capacity at this time was used as an index of self-discharge characteristics, and the ratio when the remaining capacity of Example 1 was 1 is shown in FIG.

(Evaluation of occurrence of micro short circuit)
The following charging was performed.
Charging: 1.6 hours at 3000 mA in an atmosphere of 25 ° C.

  Then, it was immersed in liquid nitrogen for 10 minutes, a voltage of 500 V was applied between the positive electrode and the negative electrode, and it was judged that a micro short circuit occurred when conductivity was confirmed, and was used as an index of the degree of micro short circuit occurrence. FIG. 5 shows an index when the degree of occurrence of a short-circuit in Example 1 is 1.

(Comparison of Example and Comparative Example)
FIG. 5 is a table showing experimental results regarding the battery characteristics of the above-described Examples and Comparative Examples. As described above, the battery characteristics of the storage battery were compared from the following four viewpoints: 1) output characteristics, 2) life characteristics, 3) self-discharge characteristics, and 4) the degree of occurrence of a short circuit.

  From the results shown in FIG. 5, a well-balanced characteristic was obtained with respect to all aspects of the nickel-metal hydride battery according to the example. However, the nickel-metal hydride battery according to the comparative example has more minute shorts than the example. It is understood.

  By increasing the thickness and basis weight of the first separator, it is possible to suppress the occurrence of a micro short circuit without the second separator, but in this case, the dimensions of the electrode plate are shortened and the DCIR is increased. Compatibility with output characteristics becomes difficult.

Regarding the degree of sulfuric acid treatment, when it is reduced to 1.0 × 10 ^{−3 in} Example 2, although not extreme, a decrease in self-discharge characteristics is observed. Moreover, when it ^raises to 4.0 * 10 <^{-3> of} Example 5, the damage to the fiber of a separator will become large and the fall of a lifetime characteristic will be seen although it is not extreme. Moreover, since an excessive sulfone group exists, an electrode reaction is inhibited and DCIR is increased.

Therefore, it can be considered that the sulfuric acid treatment degree is in the range of 1.5 × 10 ^{−3 to} 3.5 × 10 ⁻³ .

  From the results of Examples 6 and 7, the second separator can achieve the effect of the occurrence of micro short-circuiting only at the end of winding or only at the beginning of winding, but the degree of occurrence of micro-short-circuiting is further suppressed when both are provided.

  When the length of the second separator from the positive electrode winding start portion is 5 mm or less, the portion where cracks are likely to occur is not sufficiently protected, and the effect of suppressing the occurrence of a short-circuit is reduced, though not extremely. Furthermore, in order to increase the electrode reaction resistance as the second separator becomes longer, it is conceivable that the length of the winding start portion of the positive electrode of the second separator is set in the range of 5 to 30 mm.

  From the results of Example 11, when the ultrafine fiber is not blended in the first separator, the shielding property becomes insufficient but not extreme, and even when the sulfuric acid treatment and the corona treatment are performed, the life characteristics are lowered. The degree of micro short-circuit occurrence is also slightly increased. Needless to say, when the sulfuric acid treatment or the corona treatment is not performed, the life characteristics are further deteriorated.

  In Comparative Examples 1 to 3, since the second separator is not installed, the occurrence of a minute short circuit is remarkably increased.

  Further, in the case of Comparative Example 1 in which only the sulfuric acid treatment is applied to the first separator, the electrolyte solution does not sufficiently penetrate into the separator, so that not only the output characteristics but also the life characteristics are deteriorated.

  In the case of Comparative Example 2 in which only the corona treatment is applied to the first separator, since the sulfone group does not exist, the self-discharge characteristic is remarkably lowered, and the life characteristic is also lowered accordingly.

  Even in the case of Comparative Example 3 in which the first separator is subjected to sulfuric acid treatment and corona treatment, the life characteristics are deteriorated due to the effect of not protecting the portion that is likely to cause a micro short circuit.

  Therefore, in order to obtain an alkaline storage battery that combines the suppression of minute short circuits, high output characteristics, and excellent life characteristics, the first separator is subjected to sulfuric acid treatment and corona treatment, and the second separator that is not subjected to hydrophilic treatment is disposed. It becomes essential.

  In addition, when the second separator is treated with sulfuric acid as in Comparative Example 4, the effect of suppressing the occurrence of micro short-circuiting is obtained compared to other comparative examples that do not have the second separator. Since the strength decreases, the effect is suppressed. Although the result by sulfuric acid treatment was shown this time, the same tendency is obtained also about other hydrophilic treatment. Therefore, the second separator is required not to perform a hydrophilic treatment.

  The present invention is intended to be variously modified and applied by those skilled in the art based on the description in the specification and well-known techniques without departing from the spirit and scope of the present invention. Included in the scope for protection. Moreover, you may combine each component in the said embodiment arbitrarily in the range which does not deviate from the meaning of invention.

  ADVANTAGE OF THE INVENTION According to this invention, the alkaline storage battery which can achieve high output is maintained, maintaining the intensity | strength of a separator, and the possibility of further implementation and the improvement of the convenience are anticipated in various fields.

DESCRIPTION OF SYMBOLS 1 Alkaline storage battery 2 Metal outer can 3 Positive electrode side cap 4 Negative electrode side cap 5 Safety valve 8 Gasket 10 Positive electrode 20 Negative electrode 30 Separator 31 First separator 32 Second separator

Claims (6)

An alkaline storage battery comprising an electrode group in which a positive electrode and a negative electrode are wound through a separator,
The separator includes a first separator made of a polyolefin nonwoven fabric subjected to sulfuric acid treatment and corona discharge treatment, and a second separator made of a polyolefin nonwoven fabric not subjected to hydrophilic treatment ,
The said 2nd separator is an alkaline storage battery which covers the inner side and the outer side of the winding start part of a positive electrode with respect to the wound electrode group . The alkaline storage battery according to claim 1,
The second separator is an alkaline storage battery that covers the outside of the winding end portion of the positive electrode with respect to the wound electrode group. The alkaline storage battery according to claim 1,
The second separator is an alkaline storage battery that covers the inner side and the outer side of the winding start portion of the positive electrode and the outer side of the winding end portion of the positive electrode with respect to the wound electrode group. The alkaline storage battery according to any one of claims 1 to 3 ,
The first separator is an alkaline storage battery comprising a main fiber using a polyolefin-based adhesive fiber and an ultrafine fiber using high-strength polypropylene. The alkaline storage battery according to any one of claims 1 to 4 ,
The degree of the sulfuric acid treatment of the first separator is an alkaline storage battery in a range of 1.5 × 10 ^{−3 to} 3.5 × 10 ⁻³ with respect to a value represented by the following calculation formula.
Degree of sulfuric acid treatment = (SO ₄ amount in separator (g) / SO ₄ formula amount) / (Separator weight (g) × 3 / (propylene molecular weight)) The alkaline storage battery according to claim 1 or 3 ,
The alkaline storage battery in which the length from the winding start part of the positive electrode of the second separator is set in the range of 5 to 30 mm in the second separator that covers the inside and the outside of the winding start part of the positive electrode.