Process for producing separator for batteries, the separator for batteries, and alkaline storage batteries using the same

Method for manufacturing battery separator, battery separator and alkaline storage battery using the separator

<p>1. . . Nickel cathode</p><p>2. . . Hydrogen-absorbing alloy anode</p><p>3. . . Divider</p><p>4. . . Positive lead terminal</p><p>5. . . Positive terminal</p><p>6. . . Safety valve</p><p>7. . . Gasket</p><p>8. . . Electric tank</p><p>9. . . Polyolefin resin fiber</p><p>10. . . The space within the partition</p><p>11. . . Low melting point polyethylene</p><p>12. . . Steam treatment tank</p><p>13. . . Sulfonation treatment tank</p><p>14. . . Shield</p><p>15. . . Inside the sulfonation tank</p><p>x. . . Sulfonated polyolefin resin fiber</p><p>y. . . Polypropylene</p><p>z. . . Polyethylene</p>

Fig. 1 is a schematic diagram of a sulfonated polyolefin separator according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a sulfonated polyolefin separator according to an embodiment of the present invention.

Fig. 3 is a schematic view of the BB section in Fig. 1.

Fig. 4 is a schematic diagram of the CC section in Fig. 1.

Fig. 5 is a diagram of an apparatus for sulfonating a non-woven fabric composed of polyolefin resin fibers according to an embodiment of the present invention.

Fig. 6 is a diagram of a cylindrical sealed Ni/MH battery (AA size) according to an embodiment of the present invention.

Fig. 7 shows the relationship between the sulfonation rate and the tensile strength test in the separator of one embodiment of the present invention.

Fig. 8 shows the high-speed discharge characteristics of a cylindrical sealed Ni/MH battery according to an embodiment of the present invention.

[Background of the invention]

The present invention relates to the improvement of the separator for alkaline storage batteries and the higher output of storage batteries using the separator.

In the early 20th century, Sweden invented the Youngner battery, the nickel-cadmium battery (Ni/Cd battery), which became hermetically sealed in the 1940s, and was used as a small secondary power source for home appliances, communications, office equipment, and sundries around 1970. As a secondary battery represented by alkaline storage batteries, it has achieved amazing growth. However, around 1990, there was the development of nickel/hydrogen storage batteries (Ni/MH batteries) using hydrogen-absorbing alloys instead of cadmium electrodes. The subsequent development of lithium secondary batteries was used as a new power source for portable electronic devices. It has surpassed Ni/Cd batteries in terms of production volume and production value.

In the future, in addition to the above-mentioned uses, mass-produced hybrid electric vehicles (HEV) and electric vehicles will be mass-produced in 1997. The substantial expansion of the market for electric motorcycles and electric assisted bicycles is predictable, so it is expected that high-performance secondary batteries such as power sources (hereinafter referred to as mobile power sources) can be developed.

For this purpose, high performance is particularly required for high output (high power), and high reliability and high energy density (small size, light weight) are required at the same time.

Alkaline batteries, which perform better in these characteristics, are attracting attention as a supplement to mobile power supplies. Especially in alkaline storage batteries, based on the image of using environmentally friendly materials and the reasons for their high energy density, the most noticeable is the continuous Ni/MH battery mounted on the mass-produced HEV.

Therefore, for the sake of specific description, the high-power battery series, which is the object of the present invention, will be described by taking Ni/MH, in particular, cylindrical sealed Ni/MH batteries as an example.

Ni/MH batteries and Ni/Cd batteries are also 1.2V alkaline storage batteries, which are characterized by high reliability at high power density. However, it is slightly inferior to Ni/Cd batteries in terms of high power. For example, if thin strip-shaped positive and negative electrodes are used in the battery structure to match the high power, it will bring the support and separator of the electrode active material into the battery. As a result of the increase in the volume ratio, the battery's original feature of high energy density is impaired and other problems. That is, for Ni/MH batteries, there is a strong demand for improvements in high-power characteristics that are insufficient.

In the past, for the high power of alkaline storage batteries, the methods that were mostly used in the past were to focus on the material of the positive and negative electrodes, the material and the concentration of the electrolyte, and further use improvements in the structure of the two electrodes and the structure of the battery to reduce the battery. Internal impedance. However, the improvement of the separator, which is greatly related to the ion passing speed between the positive and negative electrodes, that is, the increase in the output of the battery, may have better effects than the above-mentioned improvement items depending on the situation, and its side effect is to stabilize the self-discharge at a low level. Waiting is of great help to the improvement of reliability, so it has been paid attention to since before. Therefore, in view of the higher power of Ni/MH batteries, it is expected that the separator can be further improved.

In addition, the basic conditions that a separator for a sealed Ni/MH battery should have in common with general sealed alkaline storage batteries are summarized as follows:

(1) It is a material that is chemically stable to electrolytes.

(2) Shield the electrical conduction between the positive electrode and the falling objects of the positive electrode, and the negative electrode and the falling objects of the negative electrode.

(3) Contain an appropriate amount of electrolyte in the internal space.

(4) There is a proper space through which the oxygen generated by the anode can pass.

The high-power applications here are based on the development of low-impedance and high-reliability separators under these basic conditions. As long as a highly reliable separator can be developed, even if the positive and negative electrodes are processed to be thinner and longer in order to increase high power, by thinning the separator, the worrying extreme of energy density can be suppressed reduce.

Ni/Cd batteries that have been mass-produced in the past, mainly cylindrical sealed Ni/Cd batteries, used non-woven fabrics composed of polyamide-based resin fibers as separator materials. This type of separator is now the mainstream.

Regarding the cylindrical sealed Ni/MH battery, when a conventional polyamide-based separator is used, the self-discharge is extremely large, which causes practical problems. But in response to this problem, such as the 171st. ECS (USA) Fall Mtg, EXt. AbSt., VOl. 88-2, 127 (l988), J. Electrochemm. Soc., VOl. 143, NO. 6, 1904 (1996) According to other reports, by adopting polyolefin-based separators that are chemically more stable to alkaline electrolytes, practically fatal shortcomings will disappear. This reason is due to the fact that ammonia, nitrite ions, or nitrate ions, which are the minute decomposition products of polyamide resins, are different from Ni/Cd batteries in Ni/MH batteries, which often have hydrogen. The positive electrode active material is more Quickly decompose.

However, in general, polyolefin-based separators have poor affinity for aqueous solutions (hydrophobicity), so the polyolefin-based resin fibers must be treated with hydrophilicity. Therefore, the hydrophilic treatments that have been used in the industry are as follows: 1) Surfactant treatment, 2) The method of grafting polymerization of groups with hydrophilic groups such as acrylic acid, 3) Hydrophilic sulfo groups or their equivalent groups The method of chemical reaction on the fiber surface.

However, it must be used for high power, in other words, for high-speed charging and discharging in a high-temperature environment, the above 3) method has a stable hydrophilic group, so it has the best performance in the important long-term maintenance of hydrophilicity and self-discharge characteristics. Excellent.

At present, the general method is to entangle the polyolefin resin fiber (especially, the core-sheath type polyolefin resin fiber whose fiber core is made of polypropylene resin and the surface layer is made of polyethylene resin). The produced non-woven fabric is immersed in high-temperature concentrated sulfuric acid for sulfonation. This has been proposed in Japanese Patent Laid-Open No. 01-132044 and U.S. Patent (USP) No. 5,100,723.

These proposals have been adopted for consumer batteries and the like, but for high-power batteries, as described above, the higher the liquid retention property corresponding to the hydrophilicity of the separator, the lower the internal impedance of the battery, so the degree of sulfonation must be increased.

However, the degree of sulfonation, that is, the ratio of the amount of sulfur (S) in the polyolefin resin to the number of carbon (C), a non-woven fabric composed of polyolefin resin fibers with a fiber diameter of about 10 μm, which is commonly used, is immersed in high-temperature concentrated sulfuric acid or smoked. In the method of sulfuric acid, at most 3×10 ^-3 ~5×10 ^-3 . This is based on the fact that the degree of sulfonation of this method exceeds 3×10 ^-3 After left and right, part of the resin will even be sulfonated inside, and even carbonized depending on the situation, so that the physical strength of the fiber itself becomes extremely low, and as a result, the strength required to form the battery plate group will not be obtained. Therefore, it is difficult for the conventional method to further improve the liquid retention.

This tendency is more pronounced as the fiber diameter is smaller, and it becomes more difficult to introduce non-woven fabrics composed of ultra-fine fibers (due to the high reliability when used in separators, so it is expected to be thinner). Therefore, the electrodes are made thinner and longer in order to increase the power, and the conventionally thick separators must also be elongated, which will reduce the energy density of the battery. However, it has been found that with SO ₃ The gas reaction sulfonation method, compared with the previous method, can inhibit the carbonization inside the fiber and make the physical strength of the fiber less easy to decrease. In addition, in the previously mentioned patents, in addition to the use of high-temperature concentrated sulfuric acid and fuming sulfuric acid, although there is no particular detailed description, it also mentions the combination with SO ₃ The method of gas reaction.

However, if only the non-woven fabric composed of polyolefin fibers and SO ₃ The gas reaction will cause the sulfonation of the fiber surface to be extremely non-uniform. On the contrary, the hydrophilicity of the entire non-woven fabric will decrease and the battery impedance will increase. The following results can be obtained. The internal impedance of the AA battery structure using the general-purpose sulfonated separator is 8~10mΩ, but only the general-purpose sulfonated separator is made of the aforementioned non-woven fabric and SO ₃ Instead of the separator formed by the gas reaction, the internal impedance of the battery structure with the same other components increases to 10~13mΩ.

The non-woven fabric composed of sulfonated polyolefin resin fibers is an extremely important material for Ni/MH battery separators for high-power applications, that is, high-speed charge and discharge applications at high temperatures, but it is required for high-power applications In terms of imparting higher hydrophilicity, that is, increasing the degree of sulfonation, conventional methods have reached their limit. That is, the conventional industrial treatment with concentrated sulfuric acid or fuming sulfuric acid will cause the strength of the fiber itself to decrease, and there will be problems such as breakage of the separator when forming the electrode group.

Therefore, it is possible to suppress the reduction of strength with SO ₃ Although the method of gas sulfonation has attracted attention, it is only combined with SO ₃ The gas reaction and sulfonation only take place locally on the surface of the fiber, and it is difficult to sulfonate the whole uniformly, but there is a problem that the internal impedance of the battery becomes high.

[Summary of the invention]

The present invention provides a method for manufacturing a separator and the separator, which in the treatment of non-woven fabrics is provided with a pre-treatment step through a nearly saturated water vapor stream, and a pre-treatment step immediately after the pre-treatment step, which mainly contains SO ₃ The steps in the gas flow can solve the above-mentioned local reaction problem, and can introduce uniform sulfonation and other hydrophilic groups on the surface of the non-woven fabric, which can make the whole non-woven fabric have a much higher sulfonation degree than before, and produce highly hydrophilic polyolefins. It is a separator of resin fiber, and its strength can withstand the tension required to form the electrode plate group of the battery.

Yet another object relates to the application of the aforementioned separator, which is not only used in batteries for conventional purposes, but also can provide batteries with high power characteristics, which are extremely important for mobile power supply applications. At the same time, according to this improvement, the sulfonation of a non-woven fabric composed of ultra-fine polyolefin resin fibers with a fiber diameter of 5 μm or less (highly reliable and thinner is possible when used in separators in the past) is also possible for the same reason. At this time, due to the use of very fine fibers, its surface area will be larger and the sulfonation rate will be higher. That is, by using the thin separator, it is possible to provide a Ni/MH battery with high reliability and high energy density in addition to the improvement of high power characteristics, which is also the object of the present invention.

In the present invention, in order to improve the high power characteristics of alkaline storage batteries, especially Ni/MH batteries, the sulfonation rate of the non-woven fabric of polyolefin resin fibers used as a separator is increased to improve the hydrophilicity, that is, the liquid retention property. Upgrade to a higher level than before.

The conventional method of using concentrated sulfuric acid has difficulty in increasing the sulfonation rate. The manufacturing method of the separator of the present invention, in order to uniformly apply the sulfonation to the fiber surface of the non-woven fabric without greatly reducing the fiber strength, is carried out (1 ) After passing the non-woven fabric through a stream of water vapor close to the saturated humidity, (2) immediately expose it to SO ₃ Sulfonate in the gas stream, (3) If necessary, wash the residual sulfur compounds in the non-woven fabric and dry it.

As a result, the non-woven fabric made of polyolefin resin fibers of the present invention is sulfonated to form a separator that will not cause the strength of the fiber itself to decrease, but can increase the sulfonation rate, and the increase in the sulfonation rate can be achieved by changing the exposure SO ₃ Time in the gas stream. In addition, the so-called sulfonation rate is represented by the ratio of the amount of sulfur to the amount of carbon in the base fabric constituting the separator (S/C), which may be the ratio of the number of sulfur atoms to the number of carbon atoms, or It is the ratio of the molar number of sulfur atoms to the molar number of carbon atoms.

In addition, a non-woven fabric composed of ultra-fine polyolefin resin fibers has a much larger fiber surface area than before. Even if the same operation is performed, the degree of sulfonation can be greatly increased while ensuring the strength of the fiber itself.

The cylindrical sealed (and square sealed) Ni/MH battery composed of the above-mentioned general-purpose sulfonated separator to increase the degree of sulfonation is characterized by high power characteristics, that is, it can suppress high-speed discharge. The voltage drops. In addition, when the non-woven fabric composed of the above-mentioned ultra-fine fibers is used to further increase the degree of sulfonation, it will be more suitable for high-power applications, and because the pores in the non-woven fabric composed of the ultra-fine fibers are small and uniform, even thinner than before will not occur. As a result of the reliability problem, the energy density is not reduced, and cylindrical sealed and square sealed Ni/MH batteries suitable for high-power applications can be obtained. In addition, ultrafine fibers refer to those having an average fiber diameter of 5 μm or less.

Schematic description

Fig. 1 is a schematic diagram of a sulfonated polyolefin separator according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a sulfonated polyolefin separator according to an embodiment of the present invention.

Fig. 3 is a schematic view of the BB section in Fig. 1.

Fig. 4 is a schematic diagram of the CC section in Fig. 1.

Fig. 5 is a diagram of an apparatus for sulfonating a non-woven fabric composed of polyolefin resin fibers according to an embodiment of the present invention.

Fig. 6 is a diagram of a cylindrical sealed Ni/MH battery (AA size) according to an embodiment of the present invention.

Fig. 7 shows the relationship between the sulfonation rate and the tensile strength test in the separator of one embodiment of the present invention.

Fig. 8 shows the high-speed discharge characteristics of a cylindrical sealed Ni/MH battery according to an embodiment of the present invention.

Symbol description of main components

1. . . Nickel cathode

2. . . Hydrogen-absorbing alloy anode

3. . . Divider

4. . . Positive lead terminal

5. . . Positive terminal

6. . . Safety valve

7. . . Gasket

8. . . Electric tank

9. . . Polyolefin resin fiber

10. . . The space within the partition

11. . . Low melting point polyethylene

12. . . Steam treatment tank

13. . . Sulfonation treatment tank

14. . . Shield

15. . . Inside the sulfonation tank

x. . . Sulfonated polyolefin resin fiber

y. . . Polypropylene

z. . . Polyethylene

[Implementation of invention]

Hereinafter, the embodiment will be described with reference to the drawings. Here, as described above, a cylindrical sealed Ni/MH storage battery is taken as an example of an alkaline storage battery, and a specific description will be given below.

The manufacturing method of the separator of the present invention is to implement sulfonation on the fiber surface uniformly and without reducing the fiber strength. As shown in Figure 5, the non-woven fabric is exposed to a stream of water vapor close to the saturated humidity and immediately exposed to the main Contains SO ₃ Oxygen SO ₃ Gas flow is its characteristic. In the present invention, the non-woven fabric is exposed to SO ₃ Before the gas step, a step of exposing the non-woven fabric to a stream of water vapor close to the saturated humidity is carried out, so that the surface of the fiber can be uniformly sulfonated.

In the method for manufacturing the partition of the present invention, the water vapor stream close to the saturated humidity preferably has a humidity of about 80% or more. If the humidity is above 80%, the step of exposing to the water vapor stream close to the saturated humidity and exposing the non-woven fabric to SO ₃ There will be more sufficient time between the gas flow steps, so it is more advantageous in the manufacturing process. In order not to reduce the fiber strength of the non-woven fabric, the temperature of the water vapor stream close to the saturated humidity is preferably below the melting point of the polyolefin resin that constitutes the lowest melting point of the non-woven fabric. Since it does not impair the physical strength of the non-woven fabric, The manufacturing process is more favorable. Expose the non-woven fabric to SO ₃ After the gas step, the free sulfur compound remaining in the non-woven fabric is washed and dried to prevent the remaining impurities from being mixed into the battery. If necessary, it is better to make the thickness uniform after drying. In order to suppress the fluffing of the fiber, apply a roll pressure at 60~90°C with a calender roll or the like to smooth the surface of the separator and then adjust it to the desired thickness.

Although the porosity of the separator of the present invention can be set to be larger, when the porosity exceeds about 70vol%, the tensile strength of the nonwoven fabric of general polyolefin fibers will be greatly reduced from before sulfonation, so it is preferably 70vol %the following. On the contrary, if it is below about 50vol%, although the capacity as a separator will be improved, the oxygen generated in the positive electrode of the battery will not easily move to the negative electrode during charging, and it will become unable to withstand the pressure rise caused by rapid charging. The porosity is preferably about 50 vol% or more.

The aforementioned SO ₃ SO in the airflow ₃ The gas preferably has a concentration in the range of 5-10%, and the residual SO after the reaction ₃ The gas is recirculated in sequence while adjusting to this concentration range. When the aforementioned concentration is less than 0.5%, the sulfonation time is too long, and the sulfonation speed is too high if it is higher than 10%, and it becomes difficult to control the uniform sulfonation rate of the entire non-woven fabric, so it is not good.

In addition, the alkaline storage battery of the present invention, as shown in Fig. 3, is a nickel positive electrode plate made of nickel hydroxide powder as the main material for general use, and AB is the main material for general use. ₅ The alloy negative electrode plate made of hydrogen-absorbing alloy powder is wound through a separator (made by sulfonating polyolefin resin fibers to form a non-woven fabric) to obtain an electrode group. Insert a cylindrical metal box into one end of the electrode group, and then inject alkaline After the electrolyte, the cover is sealed to form a cylindrical sealed nickel. Hydrogen storage battery.

The usual method for high-power applications is to make the positive and negative electrodes thinner than conventional batteries and widen the opposing area of the two electrodes. As an example of the positive electrode, the conventional electrode having a thickness of 0.6 to 0.8 mm is thinned to 0.5 to 0.6 mm, and corresponding to this, the length of the electrode and the length of the separator are achieved. However, when a separator of the same thickness is used, the volume occupied by the separator in the battery becomes larger along with the elongated shape, resulting in an extreme decrease in battery capacity. However, in the present invention, even if the thickness of the positive electrode is set to 0.3-0.5 mm, the same high-reliability battery as in the past can still be obtained, and the intended high-power characteristics can be further improved. This is based on the previous sulfonation method using concentrated sulfuric acid or only SO ₃ The uniformity and high sulfonation rate of the thin, ultra-fine polyolefin resin fiber, which is extremely difficult under the gas treatment method, can be achieved without greatly reducing the physical strength in the present invention. Of course, the present invention can also apply the conventional polyolefin resin fiber to a uniform and high sulfonation rate, and if the present invention is applied to the separator of a general-purpose battery, the general-purpose battery can be increased in power.

The following is a description of the separator manufacturing method of the present invention and the battery using the separator.

Figure 1 is a series of diagrams showing the non-woven fabric entangled by ultra-fine fiber bundles as a sulfonate

An example of a nonwoven fabric composed of polyolefin resin fibers after sulfonation. FIG. 2 is a diagram showing a nonwoven fabric composed of core-sheath fibers as an example of a nonwoven fabric composed of polyolefin resin fibers after sulfonation. The sulfonation system is concentrated near the surface of each fiber and is uniformly formed, which is approximately 3×10 compared to the sulfonation rate of the universal separator ^-3 , Its sulfonation rate is as high as (5~30)×10 ^-3 . Since sulfonation is concentrated near the surface of each fiber, the resin inside the fiber remains intact without being sulfonated, that is, inside, since it is not subjected to sulfonation or further carbonization, the initial physical strength can be maintained roughly. The separator shown in Figs. 1 and 2 has a high sulfonation rate, so it can uniformly and a large amount of electrolyte, and can reduce the internal impedance of the battery. In addition, in the general-purpose AA-size battery structure, if the separator shown in Figure 1 and Fig. 2 is used, the internal impedance of the battery is 8-10mΩ compared to the AA-size battery structure using the general-purpose separator. The internal impedance of the battery of the battery structure drops to 3~6mΩ.

In this sulfonation, as long as it contains SO ₃ SO of gas (as sulfur component) ₃ Gas flow treatment can be carried out, in the air or inert gas, by containing at least SO ₃ SO gas ₃ The treatment of the gas stream can also add sulfonic groups near the surface of the fiber. A functional group in which the oxygen atom of the element constituting the sulfo group is substituted by a fluorine atom, or a functional group formed by adding carbonate ions to the sulfo group, replaces the sulfo group and introduces it into the vicinity of the fiber surface. The separator is rendered hydrophilic Base, and because the introduction of sulfonic groups near the fiber surface shows the same characteristics, so in SO ₃ A trace amount of fluorine gas or carbonic acid gas may be added to the gas for processing. That is, the aforementioned SO ₃ The gas stream contains at least SO ₃ For gas, HF gas with a concentration of 1% or less and/or CO with a concentration of 1% or less can be mixed as required ₂ gas. When the HF gas concentration is more than 1%, the fiber itself will undergo excessive fluorination, which will reduce the hydrophilicity, and CO ₂ When the gas concentration is more than 1%, it will start to hinder the sulfonation reaction.

Particularly, the partition of FIG. 1 will be described in detail below. The partition is made of at least two different polyolefin-based resin ultra-fine fiber bundles tied together by the entanglement part, compared with the partition in Figure 2, its space is more uniform and dense and has a surface area of 3 to 4 times . Therefore, the separator of FIG. 1 has excellent ability as a separator, and its sulfonation rate is also much higher than that of the separator of FIG. 2, which is suitable for batteries that require higher power.

At the same time (a) Because of its excellent ability as a separator and high enough reliability, there is no problem even if it is about 80 μm thinner than the conventional separator with a thickness of about 150 μm. As a result, the gap between the positive electrode and the negative electrode can be further narrowed. Reduce the internal impedance of the battery. Of course, the thinning of the separator will reduce the volume occupied by the separator in the battery, which in turn leads to an increase in the capacity of the separator. When applied to the general-purpose AA size Ni/MH battery, the capacity is increased by about 5% in calculation.

As mentioned above, even if the thickness of the positive electrode is reduced to 0.3~0.5mm, and the thickness of the negative electrode is reduced to 0.15~0.3mm, the use of this thin and highly reliable separator will not cause a significant reduction in capacity, and can suppress high-power batteries. The capacity is reduced.

In addition, it is better to increase the battery capacity than to suppress the decrease in the battery capacity, so it is more preferable to combine it with an electric tank whose side wall is thinner than before. That is, the conventional AA standard electric tank tank generally used a side wall thickness of about 0.25mm, and by thinning it to 0.15mm, a capacity increase of about 4% can be expected. In addition, even if the side wall becomes thinner, its resistance to battery internal pressure is still practical.

In addition, if the electrode is made thinner, it can replace the expensive three-dimensional network electrode support that is indispensable for thick electrodes, that is, the electrode base, and use a cheap electrode base obtained by simply mechanically processing the metal foil. Or, by electrolytic method, a simple and inexpensive electrode substrate obtained by electrolysis into the same shape can be obtained, which has the side effect of reducing the cost of the battery.

As a result, by using the separator of the present invention, the internal impedance of the battery due to the separator can be greatly reduced, and the high-speed discharge characteristics (high-power characteristics) can be significantly improved. At the same time, by using the thin separator with high sulfonation rate composed of the ultra-fine polyolefin resin fiber of the present invention, even if the thin electrode for high power use is used, the capacity of the battery will not be reduced. On the contrary, the combined sidewall is thicker The thin metal cylindrical cell will increase the battery capacity, and with the thinning of the electrode, it will be possible to use a low-cost electrode substrate, so it is possible to achieve a lower cost of the battery.

Fig. 1 of the present invention shows an example of dividing the ultra-fine fiber bundle into eight, and it may also be an ultra-fine fiber bundle that can be divided into more. In addition, FIG. 1 shows an example of two types of polyolefin-based resins having a substantially triangular cross-section, and there may be more types of polyolefin-based resins or those with different degrees of polymerization. In this case, it is preferable that a material having excellent mechanical strength exists.

The description so far is a specific description of a cylindrical sealed Ni/MH battery. Based on the same principle, the present invention is also applicable to a square sealed Ni/MH battery. Based on the same principle, the present invention can also be easily applied to cylindrical sealed and rectangular sealed Ni/Cd batteries, large rectangular nickel-cadmium storage batteries, and the like.

Next, specific examples of the present invention will be explained using examples, but the present invention is not limited to these specific examples. In addition, complexation is performed by a well-known method. The tensile strength, the molar number of sulfur atoms or carbon atoms, the battery voltage, and the discharge rate are also measured according to known methods.

(Production Example 1 of Positive Electrode)

A paste containing commercially available spherical nickel hydroxide powder and fluororesin powder with an average particle size of about 15μm was coated on a nickel foil with a thickness of 30μm with numerous irregularities by a known method, dried by a known method, and then pressurized. A positive electrode with a thickness of 400μm is obtained. Cut into a size of 40mm wide and 170mm long to produce a thin and long positive electrode with a theoretical capacity of about 1700mAh.

(Production Example 2 of Positive Electrode)

A positive electrode was produced according to the same method as in positive electrode manufacturing example 1, except that a general-purpose foamed metal positive electrode with a thickness of 0.7 mm was used and it was cut into a size of 40 mm in width and 85 mm in length.

(Negative electrode manufacturing example 1)

Will contain commercially available AB with an average particle size of about 10μm ₅ An aqueous solution paste of a hydrogen-absorbing alloy is coated on a nickel foil with numerous irregularities and a thickness of 30 μm by a known method, dried by a known method and then pressurized to obtain an electrode for a negative electrode with a thickness of 240 μm. Cut into a long electrode with a width of 40mm and a length of 230mm to produce a negative electrode with a theoretical capacity of about 2400mAh.

(Negative electrode manufacturing example 2)

The negative electrode was fabricated according to the same method as the negative electrode manufacturing example 1, except that a general-purpose coating hydrogen-absorbing alloy negative electrode with a thickness of 0.35 mm was used and it was cut into a size of 40 mm in width and 140 mm in length.

(Example 1)

As shown in Figure 3, the ultra-fine fiber polyolefin fiber and polyethylene fiber are integrated into a bundled fiber that can be divided into 8 divisions. In the circumferential direction of the cross section of the bundled fiber, the ultra-fine fiber polyolefin fiber and polyethylene fiber are arranged in a staggered manner. The cross part of the fiber (diameter 10μm) is complexed with low melting point polyethylene, and the average thickness is 100μm, the porosity is 60%, and the tensile strength is 6.2kg/cm. ² The non-woven fabric. Arrange the aforementioned non-woven fabric under high-speed water flow, divide the unentangled part of the bundled fibers constituting the non-woven fabric into individual ultra-fine fibers, and adjust the thickness of the non-woven fabric to 70~80μm by passing through a heated roller room at about 80°C to obtain the final product. The shape is a loop-shaped non-woven fabric as shown in Fig. 1. Next, the non-woven fabric was exposed to an ambient atmosphere with a humidity of about 95% and a temperature of about 70°C for about 10 seconds in the steam tank shown in Fig. 5-13, and then immediately moved to the sulfonation treatment tank shown in Fig. 13 Exposure to 50°C, about 3wt% SO ₃ The sulfonation treatment is carried out in a gas flow for 20 seconds, and the final thickness is 70~80μm and the sulfonation rate is about 20×10 after washing and drying. ^-3 The divider. After drying the water generated by the water washing, the thickness of the separator is uniformized in the range of 70 to 80 μm by passing through a heated roll at about 80° C., and the operation of flattening the surface is performed.

(Examples 2~4)

In addition to 50°C, about 3wt% of SO ₃ Except for the adjustment of the exposure time in the gas flow, the sulfonation rate is 5×10 by the same method as in Example 1. ^-3 、10×10 ^-3 、30×10 ^-3 The divider.

(Examples 5~7)

Except for non-woven fabrics made of universal core-sheath polyolefin fibers with a fiber diameter of about 9mm, and 50°C, about 3wt% of SO ₃ Except for the adjustment of the exposure time in the gas stream, the sulfonation rate is 15×10 by the same method as in Example 1. ^-3 、10×10 ^-3 、5×10 ^-3 The divider.

(Examples 8~10)

Except that the thickness of the non-woven fabric is thickened while maintaining the porosity at about 60 vol%, the sulfonation rate is about 20×10 by the same method as in Example 1. ^-3 , The final thickness is 100~120μm, 140~160μm, 200~220μm.

(Examples 11~14)

Except that the thickness of the non-woven fabric is 100~120μm, 140~160μm, 200~220μm, and 50°C, about 3wt% SO ₃ Except for the adjustment of the exposure time in the gas flow, the sulfonation rate was 3×10 by the same method as in Example 1. ^-3 , Separator with thickness of 100~120μm, 140~160μm, 200~220μm.

(Example 15)

Except for the non-woven fabric with a porosity of about 60% and a thickness of 120μm composed of a universal core-sheath type polyolefin fiber with a fiber diameter of about 9mm, and a 50°C, about 3wt% SO ₃ The exposure time in the gas flow is adjusted to 12 seconds, and the sulfonation rate is about 10×10 by the same method as in Example 1. ^-3 , A separator with a thickness of 100~120μm.

(Examples 16~18)

Except that the thickness of the non-woven fabric is thickened while maintaining the porosity at about 60 vol%, the sulfonation rate is about 20×10 by the same method as in Example 1. ^-3 , The final thickness is 80~100μm, 140~160μm, 200~220μm.

(Examples 19-22)

Except that the thickness of the non-woven fabric is 100~120μm, 140~160μm, 200~220μm, and 50°C, about 3wt% SO ₃ Except for the adjustment of the exposure time in the gas stream, the sulfonation rate was 3×10 by the same method as in Example 15. ^-3 , Separator with thickness of 100~120μm, 140~160μm, 200~220μm.

(Comparative example 1)

The non-woven fabrics used in the examples were immersed in 96wt% concentrated sulfuric acid heated to about 100°C using the conventional high-temperature concentrated sulfuric acid method. In order to avoid the rapid heat generated by the heat of hydration, the sulfuric acid The concentration moves to low concentration in order to remove residual SO ₄^2- The method to implement sulfonation treatment, after washing and drying, the sulfonation rate is 3×10 ^-3 The divider.

(Comparative example 2)

In addition to adjusting the time of non-woven immersion in concentrated sulfuric acid to obtain a sulfonation rate of 3×10 ^-3 Except for the separator, the sulfonation rate of 4×10 is obtained according to the same method as in Comparative Example 1. ^-3 , A separator with a thickness of 70~80μm.

(Comparative Examples 3~5)

A non-woven fabric with a thickness of 70~80μm composed of a universal core-sheath type polyolefin fiber with a fiber diameter of about 9mm, using the conventional high-temperature concentrated sulfuric acid method, that is, immersed in 96wt% concentrated sulfuric acid heated to about 100°C. To avoid the rapid heat generated by the heat of hydration, the residual S0 is removed by sequentially shifting the concentration of sulfuric acid to a lower concentration. ₄^2- The method to implement sulfonation treatment, after washing and drying, the sulfonation rate is 3×10 ^-3 、4×10 ^-3 、7×10 ^-3 The divider.

(Comparative Examples 6~8)

Except that the thickness of the non-woven fabric is 100~120μm, 140~160μm, 200~220μm, the sulfonation rate is 3×10 by the same method as in Comparative Example 3. ^-3 , Separator with thickness of 100~120μm, 140~160μm, 200~220μm.

(Comparative Examples 9-12)

Except that the thickness of the non-woven fabric is 100~120μm, 140~160μm, 200~220μm, and in order to make the sulfonation rate 5×10 ^-3 Besides adjusting the time of immersion in 96wt% concentrated sulfuric acid at about 100°C, the sulfonation rate is 5×10 by the same method as in Comparative Example 3. ^-3 , Separator with thickness of 100~120μm, 140~160μm, 200~220μm.

(Example 23)

The positive electrode and negative electrode made in the above-mentioned positive electrode manufacturing example 1 and negative electrode manufacturing example 1 are wound into a spiral through the separator to form an electrode group, and the electrode group is inserted into the electric tank (the side wall thickness is 0.16 mm, the bottom thickness is 0.25 mm). Nickel steel plate is processed into a cylindrical container with an open end), 1.8cc of approximately 30wt% KOH aqueous solution is injected into the electric tank, and then sealed with a lid with a safety valve to make the AA specification shown in Figure 6 Cylindrical sealed Ni/MH battery.

Both the positive and negative electrodes of this embodiment use thin and long electrodes. In the case where high power is not particularly required, the conventional thickness of the electrode can be used for both electrodes. In this case, the separator of this embodiment is used to make the separator The volume occupied by the battery is reduced, so a higher capacity than before can be obtained. In addition, after obtaining the separator of the present invention as described in this example of life, it may be adjusted to the desired thickness by applying roll pressure at about 70°C again as necessary, which may be better in terms of battery structure.

(Examples 24~30)

Using the separators of Examples 8-14, the AA-size cylindrical sealed Ni/MH storage batteries of Examples 24 to 30 were produced by the same battery construction method as that of Example 23.

(Examples 31~38)

Except for the use of the separators of Examples 15 to 22 and the use of a thick electrode close to the general use of the positive electrode of Example 2 of the positive electrode and the negative electrode of Example 2 of the negative electrode, the same battery construction method as that of Example 23 was used. Examples 31 to 38 are AA-size cylindrical sealed Ni/MH batteries.

(Comparative Examples 13-20)

Using the separators of Comparative Example 3 and Comparative Examples 6-12, respectively, according to the same battery construction method as Example 23, the AA-size cylindrical sealed Ni/MH storage batteries of Comparative Examples 13-19 were made.

(Comparative Example 21)

Similar to Example 1, the final thickness is 70~80μm, and the sulfonation rate is about 20×10 ^-3 The divider. After drying the water generated by the water washing, the thickness of the separator is uniformized in the range of 70 to 80 μm by passing through a heated roll at about 100° C., and the operation is performed to flatten the surface. In the same manner as in Example 23, a cylindrical sealed Ni/MH storage battery of AA specification was produced.

[Evaluation] (Tensile strength)

Regarding the separators of Examples 1 to 7 and Comparative Examples 1 to 5, the tensile strength was measured using a known tensile strength measuring machine. The results are shown in Figure 7. Regarding the separators of Examples 1 to 4, even if the sulfonation rate is increased to 30×10 ^-3 Can still maintain 3kg/cm ² With the above tensile strength, the strength required for the formation of the electrode group can be obtained. In contrast, in Comparative Examples 1 and 2, even if the same non-woven fabrics as in Examples 1 to 7 are used, as the sulfonation rate increases, the tensile strength is greatly reduced when the sulfonation rate is low. In sulfonation rate 3×10 ^-3 Time is no longer practical. In addition, in Examples 5 to 7, the non-woven fabric composed of core-sheath polyolefin fibers with a fiber diameter of about 9 μm was applied to the separator obtained by the sulfonation treatment of the manufacturing method of the present invention, as shown in FIG. 7c. The reduction in tensile strength improved by sulfonation can be reduced. However, the non-woven fabric composed of core-sheath polyolefin fibers used in Examples 5 to 7 has a limited surface area, so the sulfonation rate is limited, and only reaches 15×10 ^-3 about. In addition, as in Comparative Examples 3 to 5, if the non-woven fabric composed of the core-sheath polyolefin fiber is sulfonated according to the conventional method, it will be less than 5×10 ^-3 Above the sulfonation rate, it cannot withstand the strength required for the formation of the plate group. In other words, even if the sulfonation rate is increased, the separator of the present invention does not significantly reduce the tensile strength.

(Small short circuit in cycle life test)

The AA-size cylindrical sealed Ni/MH batteries of Examples 23 to 38 and Comparative Examples 13 to 20 were made into 30 cells respectively, and each 30 cells were subjected to 1C discharge and 1C charge at 20°C (discharge capacity of 110 % Charge) 100 cycles to conduct a cycle life test to investigate the small short circuit of each unit. The results are shown in Tables l~3. The number of short-circuits of the battery is represented by (number of cells with small short-circuits observed)/(number of cells subjected to cycle life test).

<tables><img file="TW511309B_D0001.tif" /></tables>

<tables><img file="TW511309B_D0002.tif" /></tables>

<tables><img file="TW511309B_D0003.tif" /></tables>

Regarding the batteries using the thin electrodes of Examples 23 to 26, as shown in the separator type column of Table 1, even if the thickness is reduced to 70 to 80 μm, the micro short circuit is only limited to 1 cell, and the cell thickness is very close 70μm. Therefore, it is obvious that the separator of the present embodiment has high reliability without generating a small short circuit up to about 80 μm. In addition, the batteries using the thin electrodes of Examples 27 to 30, that is, the sulfonation rate is the same as that of the general-purpose separator, as shown in the separator type column in Table 1, no small short circuit is generated regardless of the thickness . In contrast, the batteries with thin electrodes of Comparative Examples 13-20 have a sulfonation rate of i which is the same as e. When the thickness is as thin as about 120μm, small short circuits will begin to occur, and the sulfonation rate will increase to 5×10. ^-3 In j, a small short circuit begins to occur from the thickness of 160μm. Especially the sulfonation rate is 5×10 ^-3 In the case of a cell made of a separator with a thickness of about 120 μm, 1/3 of the cell has a small short circuit and it is judged to be defective.

In addition, the batteries of Examples 31 to 38 using thick electrodes close to general use, as shown by g and h in the separator type column, did not generate micro short circuits up to 140 μm, and had high reliability.

(High power characteristics)

Regarding the batteries of Examples 24, 27, 31, and 36, and Comparative Examples 15, and 20, 3 cells were selected arbitrarily from a large number of batteries made in advance, and after 3 cycles of charging and discharging were performed to achieve stable characteristics, they were charged by Investigate high-power characteristics up to 50% of the practical amount. The relationship between the discharge rate and battery voltage of the survey results is shown in Figure 8. In the figure, f-100 shows the result of Example 24, e-80 shows the result of Example 27, g-120 shows the result of Example 36, h -120 shows the result of Example 31, i-150 shows the result of Comparative Example 15, and j-200 shows the result of Comparative Example 20.

The f-100 battery, even under the high-speed discharge of 10C, its voltage drop is still very small, not exceeding 60mV, and it shows extremely excellent high-power characteristics. On the other hand, any battery of e-80, g-120, and h-120 has an extreme battery voltage drop during a high-speed discharge of about 8C, but it can maintain 1V or more up to 6C and perform well. In addition, in the batteries of g-120 and h-120, the battery voltage at 10C discharge can maintain more than half of the initial battery voltage compared to g-120, and it is known that increasing the sulfonation rate can significantly Improve high power characteristics. In contrast, with respect to both i-150 and j-200, an extreme battery voltage drop occurred during high-speed discharge at about 8C, and 1V or more could not be secured at 6C, which was judged to be defective.

In addition, regarding the AA-size cylindrical sealed Ni/MH storage battery of Comparative Example 21, by passing the separator between the heated rollers at about 100°C, thermal fusion of the local fibers and hydrophilicity due to the denaturation of the sulfonic group will occur. Decrease, because charging and discharging become difficult, and the cycle life test cannot be performed.

As described above, the manufacturing method of the separator of the present invention can achieve high hydrophilization while ensuring the strength, and the Ni/MH battery using the sulfonated polyolefin separator with a high sulfonation rate of the present invention has excellent high power characteristics. In particular, when thin and extremely fine polyolefin resin fibers are sulfonated into a high sulfonation rate to obtain a separator, a Ni/MH battery with extremely excellent high power characteristics and improved important characteristics such as high capacity can be obtained.

In addition, the specification of the present application includes all the contents described in Japanese Patent Application 2001-109082, which is the basis of the priority claim in this case.