JP4454260B2 - Separator for alkaline secondary battery - Google Patents

Description

  The present invention relates to an alkaline secondary battery separator and an alkaline secondary battery using the same.

  In recent years, various types of batteries for portable, mobile, and stationary use, especially secondary batteries, have been pursued for higher quality such as higher performance, safety, and long-term storage. Technical requirements for separators, which are the main constituent materials, are also increasing.

  The separator is interposed between the positive electrode and the negative electrode to hold the electrolytic solution and to separate both electrodes, so that the negative electrode material and the positive electrode material do not move to the counter electrode. It is necessary to have a function of completely separating and preventing self-discharge by preventing an internal short circuit of the battery.

  Moreover, it is a characteristic required as a separator that it is excellent in the liquid-retention property of electrolyte solution, has good ionic conductivity, and has low electric resistance. Furthermore, in order to prevent gas leakage from the battery and leakage prevention from overcharging due to gas absorption in the Neumann negative electrode, it is also essential that oxygen generated from the positive electrode can pass through the separator during charging.

  Furthermore, it is a performance that is naturally required to be physically and chemically stable even at high temperatures and not to contain impurities that adversely affect the negative electrode and the positive electrode.

  In addition, depending on the type of battery and the assembly method, the electrolyte absorption rate is fast, it has sufficient mechanical strength, flexibility, heat resistance, good cutting properties, etc., and easy incorporation into the battery. This is also a characteristic required for battery production.

  From these viewpoints, dry nonwoven fabrics and wet nonwoven fabrics of synthetic fibers excellent in alkali resistance are used as separators for alkaline secondary batteries. Conventionally, as such a nonwoven fabric, a polyamide nonwoven fabric has been mainly used, but at present, a polyolefin nonwoven fabric has been put into practical use and has become a representative material for a separator.

  Polyolefins are hydrophobic and are not suitable as separators as they are, so in order to improve the affinity for electrolytes, addition of surfactants and inorganic powders, introduction of ion exchange groups such as sulfone groups, fluorine gas treatment, etc. Various methods for improving water absorption have been proposed. Furthermore, a structure in which a gas permeable portion and an electrolyte solution holding portion are present, and a mixed textile fabric of a parent electrolyte solution fiber and a lyophobic solution fiber have been proposed. There is also a proposal to improve the lyophilic property by partially saponified polyvinyl alcohol and a surfactant. (For example, refer to Patent Documents 1 to 7 below).

  By the way, since the separator does not contribute to the battery capacity, if it occupies many parts in the battery, it leads to a decrease in the battery capacity and the output, so that it is basically desired that the separator be as thin as possible. In particular, recently used batteries for hybrid vehicles and power tools are required to have high output, so the thickness of the positive and negative electrodes is reduced, and the separator needs to be thin. Has been.

  Lithium ion batteries and the like use thin microporous polyolefin separators having a thickness of about 40 to 15 μm. However, in alkaline secondary batteries such as nickel-hydrogen batteries that perform complete charge and discharge, nickel electrode variability is reduced. Such a thin separator is not generally adopted because of prevention of short-circuit due to, necessity of passing oxygen from the positive electrode during overcharge, and the like.

Furthermore, when the polyolefin non-woven fabric is thinned, the strength is reduced and the risk of short-circuiting is increased, and problems such as breakage of the separator during battery construction occur, making it unsuitable for mass production. It is also necessary that the electrolyte retainability is good. From such a viewpoint, a polyolefin nonwoven fabric having a thickness of about 120 to 150 μm is usually used as a material for the separator of the alkaline secondary battery.
Japanese Patent Laid-Open No. 5-109397 JP 7-29559 A JP-A-8-64193 JP 10-125300 A Japanese Patent Application Laid-Open No. 11-120982 JP-A-11-120983 JP-A-5-193092

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is a thin film separator suitable as a separator for a high-power alkaline secondary battery, which is suitable for mass production. A novel alkaline secondary battery that has sufficient mechanical strength, good ionic conductivity, low battery internal resistance, and good gas permeability, and can improve battery characteristics, particularly output characteristics. It is to provide a separator for a secondary battery.

  The present inventor has intensively studied to achieve the above-described object. As a result, a separator that can achieve the above-described object by impregnating polyvinyl alcohol after impregnating with a polyvinyl alcohol non-woven fabric having a smaller film thickness than those commonly used as separators, after being subjected to a treatment for improving the affinity for the electrolytic solution. The present invention has been found and the present invention has been completed.

That is, the present invention provides the following separator for an alkaline secondary battery and an alkaline secondary battery.
1. A separator for an alkaline secondary battery, wherein a polyolefin non-woven fabric having a thickness of 50 to 110 μm subjected to a treatment for improving the affinity for an electrolytic solution is used as a support and is impregnated with polyvinyl alcohol.
2. Item 2. The separator for an alkaline secondary battery according to Item 1, wherein the treatment for improving the affinity for the electrolytic solution is treatment for bringing the polyolefin nonwoven fabric into contact with fuming sulfuric acid or fluorine gas.
3. Item 1 or 2 above, wherein the porosity of the polyolefin nonwoven fabric before impregnation with polyvinyl alcohol is 40 to 60%, and the rate of decrease in porosity after impregnation with polyolefin is 10% or less of the porosity before impregnation. The separator for alkaline secondary batteries described in 1.
4). 4. An alkaline secondary battery comprising the separator according to any one of items 1 to 3 as a constituent element.
5). 5. The alkaline secondary battery according to item 4, which is a nickel-hydrogen battery.
6). Item 6. The alkaline secondary battery according to Item 5, wherein the nickel electrode is the following (i) or (ii):
(I) a nickel electrode obtained by applying a nickel electrode active material to a two-dimensional base material;
(Ii) A nickel electrode including a base material for an electrode and a nickel electrode active material on which concave and convex portions are formed by mechanical processing, wherein the concave portion of the base material is filled with the active material, and the convex portion of the base material Is a nickel electrode in which the surface is exposed or the active material is attached.

  In the present invention, a polyolefin nonwoven fabric having a thickness of about 50 to 110 μm, preferably about 60 to 95 μm, is used as a separator material. Such a polyolefin non-woven fabric has a considerably thin film thickness as compared to the thickness of the polyolefin non-woven fabric for separators of about 120 to 150 μm, but it is sufficient by performing an impregnation treatment with polyvinyl alcohol described later. It has a high mechanical strength.

The type of polyolefin is not particularly limited, and for example, polyethylene, polypropylene, a mixture of polyethylene and polypropylene, and the like can be used.
It is preferable to use a polyolefin nonwoven fabric having a porosity of about 40 to 60%. By using such a polyolefin non-woven fabric and impregnating with polyvinyl alcohol by the method described later, an increase in battery internal resistance can be suppressed, and further, gas permeability can be maintained, and battery characteristics, particularly output characteristics can be maintained. Can be improved.

  The polyolefin non-woven fabric needs to be subjected to treatment, so-called lyophilic treatment, in order to improve the affinity for the electrolyte. By using a non-woven fabric that has been subjected to such treatment, the electrolyte retainability is excellent.

  Specifically, those treated with fuming sulfuric acid, treated with fluorine gas, or the like can be used. About these processing methods, what is necessary is just to follow well-known conditions, for example, the process by fuming sulfuric acid immerses in a 2-10 wt% fuming sulfuric acid bath at about 15-45 degreeC for about 2 minutes-10 minutes, After removing the fuming sulfuric acid, washing with water, neutralization, washing with water and drying may be performed to a degree of sulfonation of about 1 to 2 wt%.

  In addition, the treatment with fluorine gas is, for example, putting a non-woven fabric in a sealed container to be in a vacuum state, and containing a mixed gas composed of about 10% of oxygen or sulfurous acid gas and about 1 to 5% of fluorine gas, and the remainder consisting of nitrogen gas. And after reacting at room temperature for about 1 to 5 minutes, the inside of the sealed container is replaced with nitrogen gas, and then the nonwoven fabric is taken out.

  The separator of the present invention is a polyolefin nonwoven fabric that has been subjected to the above-described lyophilic treatment as a support and is impregnated with polyvinyl alcohol. Polyvinyl alcohol is ion-permeable and excellent in film-forming ability. By impregnating this into a polyolefin nonwoven fabric, the nonwoven fabric can be reinforced to improve mechanical strength, and further, oxidation resistance, It can also be excellent in alkali resistance and the like.

  As a method of impregnating polyvinyl alcohol, for example, a polyolefin nonwoven fabric may be immersed in an aqueous solution containing polyvinyl alcohol and then dried.

  As polyvinyl alcohol, it is preferable to use a thing with a polymerization degree of about 500-2000, for example.

  As an aqueous solution containing polyvinyl alcohol, for example, a concentration of about 5% by weight or less, preferably about 3 to 5% by weight is preferably used. By using an aqueous solution having such a concentration, it becomes easy to improve the mechanical strength of the nonwoven fabric while maintaining the permeability and ion conductivity of oxygen ions. At this time, if the concentration of the polyvinyl alcohol solution is too high, the impregnation amount of the polyvinyl alcohol is increased and the porosity of the nonwoven fabric is decreased. As a result, the permeation of oxygen gas during charging is suppressed, and the battery internal pressure during charging is reduced. It is easy to cause an adverse effect such as an increase or a decrease in the ionic conductivity of the separator and a decrease in voltage during a high discharge such as 10C or more.

  Regarding the impregnation amount of polyvinyl alcohol, the decrease rate of the porosity of the polyolefin nonwoven fabric by impregnating the polyvinyl alcohol is about 10% or less, particularly about 5 to 10% of the porosity of the nonwoven fabric before impregnation. It is preferable. By setting the impregnation amount to this level, the reinforcing effect by the polyvinyl alcohol can be sufficiently exerted, and an appropriate porosity can be maintained, and good ion conductivity and gas permeability can be obtained.

  The polyolefin nonwoven fabric obtained by the above-described method is useful as a separator for alkaline secondary batteries, and in particular, can exhibit excellent performance as a separator for nickel-hydrogen batteries.

  When a nickel-hydrogen battery is manufactured using the separator of the present invention, other components may be the same as those of a known nickel-hydrogen battery.

  However, for nickel electrodes, if a base material used for general-purpose sintered nickel electrodes or foamed nickel electrodes is used, the separator may be damaged by burrs, so a two-dimensional structure such as punching metal or screen It is preferable to use a base material prepared by coating a nickel electrode active material. Since the separator of the present invention has a thin film thickness, it is preferable to prevent occurrence of a short circuit due to burrs by using such a nickel electrode.

  Furthermore, as a nickel electrode base material, a base material that is mechanically processed to provide unevenness can also be used. As an example of the nickel electrode using such a base material, there can be mentioned one obtained by forming a concavo-convex portion on a punching metal and applying the nickel electrode active material paste as an electrode base material. In the case of using such a nickel electrode, as in the case of using a two-dimensional base material, there is almost no damage to the separator due to burrs, and the output characteristics are good and the nickel-hydrogen battery has a long life. it can. The nickel electrode will be described below.

  What is necessary is just to use what the uneven | corrugated | grooved part was formed by mechanical processing, such as embossing, as a base material for electrodes of a nickel electrode, for example, using a punching metal with a porosity of 20% or less, preferably about 5-15% be able to.

  The method for producing such an electrode substrate is not particularly limited, for example, using a thin metal material, using a mold for punching metal processing and a mold for forming an embossed structure, It is preferable to manufacture by mechanical processing.

  The material of the electrode substrate is not particularly limited, and for example, a metal plate such as a nickel plate or a nickel-plated iron plate can be used.

  The thickness of the punching metal for forming the electrode substrate is not particularly limited as long as it can be easily machined, for example, about 15 to 60 μm, preferably 20 What is necessary is just to be 50 micrometers.

  Although there is no limitation in particular about the hole diameter of a punching metal, Usually, it may be about 0.1-1 mm, and it is preferable to set it as about 0.3-0.8 mm.

  There is no particular limitation on the size of the concavo-convex portions formed by embossing, and it is only necessary that the concavo-convex portions that can be filled with the active material are alternately formed. For example, the distance between the recesses, that is, the width of the recesses may be about 0.5 to 1.5 mm.

The apparent thickness of the base material after embossing the punched metal base material is not particularly limited, but may be, for example, about 0.2 to 0.5 mm. In addition, the weight per unit area of the substrate is usually about 200 to 500 g / m ² .

  The base material should just be planar as a whole, and can be made into planar shape or curved surface shape according to the usage form of an electrode.

  As a method of filling the electrode active material into the recesses of the electrode base material having the above-described structure, a paste containing a nickel electrode active material is used, and this is sufficiently applied to the whole of the electrode base material including the recesses. Just do it. As the paste itself containing the active material, the same paste as that conventionally used for electrodes formed by applying paste, so-called paste type electrodes, can be used.

  The method for applying the paste containing the nickel electrode active material to the electrode substrate is not particularly limited, and may be the same as the usual paste application method. The simplest method includes a method of passing a substrate through the paste. In addition, a method such as a method of spraying the paste from both sides may be applied as appropriate to apply the paste to the entire substrate including the recesses.

  After applying the paste containing the active material to the base material having the concavo-convex structure in this manner, the base is interposed between the slits that are substantially the same as the apparent thickness of the base material when passing through the base material. Allow the material to pass through. Thereby, most of the paste containing the active material can be filled in the recesses of the base material. At this time, the adhesion amount of the active material on the convex portions of the substrate is preferably about 10% by weight or less of the total filling amount of the active material, and more preferably about 5% by weight or less.

  As a method for this, for example, a slit forming member elastically biased in the direction of narrowing the slit interval is used, and the slit interval is set to be the same as the base material thickness or slightly narrower than the base material thickness. And what is necessary is just to let a base material pass between these slits. The elastically formed slit forming member includes a material having elasticity such as rubber, a member that can be pressed in the direction of narrowing the slit interval using a spring, etc., and a circle having both ends fixed by an elastic body. A columnar member or the like can be used. In such a slit forming member, by appropriately setting the strength of elasticity, when the base material passes between the slits, the interval between the slits can be made substantially the same as the thickness of the base material.

  By filling the concave portion of the base material with the active material by the above method, a nickel electrode can be formed according to a conventional method. For example, the base material filled with the active material may be dried and subjected to pressure processing by a flat plate pressure, a roller press or the like so as to have a predetermined thickness. The thickness of the nickel electrode after pressurization is not particularly limited, but is preferably about 0.4 mm or less in consideration of high output characteristics and active material utilization, and about 0.2 to 0.35 mm. It is more preferable that

  According to the above method, the concave portion of the base material is uniformly filled with the active material, so that the partial variation can be greatly reduced, and the electrode has stable performance. When such a nickel electrode is used, the separator can be prevented from being damaged by burrs, and a short circuit can be prevented. Furthermore, a nickel-hydrogen battery having good output characteristics and a long life can be obtained.

  The separator of the present invention is a thin separator suitable for use as a separator for a high output alkaline secondary battery, and has sufficient mechanical strength suitable for mass production. By using such a separator, it is possible to prevent the separator from being damaged during the construction of the battery, and it is possible to prevent a short circuit even if the distance between the electrodes is reduced.

  In addition, the separator of the present invention has good oxidation resistance, alkali resistance and the like, and is excellent in ion conductivity and gas permeability by having an appropriate porosity.

  Furthermore, since the lyophilic treatment is performed, the electrolyte retainability is also good.

  Therefore, by using the separator of the present invention, an alkaline secondary battery having excellent battery characteristics, particularly output characteristics, and a long life can be obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples.

A commercially available polypropylene nonwoven fabric having an average thickness of 95 μm, a weight per unit area of 37 g / m ² , and a porosity of about 50% was immersed in 3% fuming sulfuric acid for 2 minutes to obtain an electrophilic polypropylene nonwoven fabric.

  This polypropylene nonwoven fabric was immersed in a 3% by weight aqueous solution of polyvinyl alcohol having a degree of polymerization of about 2,000 and then dried at 80 ° C. for 2 hours to impregnate polyvinyl alcohol.

The polypropylene nonwoven fabric after the treatment had a porosity of 45%, and the tensile strength was about the same as that of a separator having a thickness of 130 μm and a basis weight of 42 g / m ² .

  Using this as a separator, a nickel-hydrogen battery was produced by the following method.

  As the nickel electrode base material, a substrate having an apparent thickness of 420 μm obtained by forming a concavo-convex structure by mechanically pressing and processing a 35 μm thin plate obtained by plating nickel on iron was used.

  As an active material paste for nickel electrode, 4 parts of cobalt hydroxide is added to 92 parts of nickel hydroxide powder coated with 3% cobalt oxyhydroxide, and after mixing, paste it with 1% carboxymethylcellulose aqueous solution as a binder. A paste containing 3.5% polypropylene emulsion was used, and this paste was applied to both sides of the substrate.

  After that, using two cylindrical slit forming members fixed at both ends with an elastic body, the two columnar structures are expanded, and the substrate coated with the paste by the above method is passed through. The surface was smoothed. Next, after drying, a nickel electrode was obtained by pressing with a roller press to obtain an average thickness of 280 μm.

On the other hand, 1% carboxymethylcellulose aqueous solution was added to MmNi _3.6 Co _0.6 Al _0.4 Mn _0.4 , which is a known hydrogen storage alloy, to form a paste, which was applied to a punching metal having a thickness of 50 μm and a porosity of 50%. . Thereafter, the punching metal coated with the paste was passed through slits with an interval of 220 μm, dried, and then pressed with a roller press to a thickness of 180 μm to obtain a hydrogen storage alloy negative electrode. The negative electrode capacity was set to 170% with respect to the positive electrode capacity.

  The separator was placed between the two electrodes, the electrode group was wound, and inserted into a so-called SubC battery case. As an electrolytic solution, an electrolytic solution in which 25 g / liter of lithium hydroxide was dissolved in 30% potassium hydroxide was added. Then, a nickel terminal was attached to the electrode group by welding in a tabless manner, and the lid and the positive electrode were welded with a nickel plate and then sealed. The nickel-hydrogen battery thus obtained is referred to as battery A.

  As a comparison, a polypropylene non-woven fabric having an average thickness of 95 μm and having the same average thickness as that described above was used as a separator without impregnation with polyvinyl alcohol. -A hydrogen battery was made. This is referred to as battery B.

  Regarding the battery A and battery B described above, when the damage state of the separator when the electrode group was wound was examined, in battery B, 4 cells out of 100 cells were partially damaged, and 2 cells out of the remaining 96 cells were short-circuited. In contrast, battery A was neither damaged nor short-circuited.

  From this result, it was confirmed that by impregnating the polypropylene non-woven fabric with polyvinyl alcohol, the mechanical strength was improved and the separator could be prevented from being damaged during the construction of the battery.

  On the other hand, a polypropylene nonwoven fabric in which a polypropylene nonwoven fabric having a thickness of 130 μm was immersed in 3% fuming sulfuric acid for 2 minutes and subjected to an electrolysis treatment was used as it was as a separator without impregnation with polyvinyl alcohol. A nickel-hydrogen battery was produced in the same manner. This is referred to as a battery C.

  Using the battery A and the battery C thus obtained, a charge / discharge test was performed by the following method. About these batteries, the capacity | capacitance in 0.2 C discharge in a full charge was 3.1 Ah for battery A, and 2.6 Ah for battery C.

  First, the known discharge capacity after chemical conversion was examined for both batteries. Charging was performed at 120% of the discharge capacity, and the ambient temperature was 35 ° C. This measurement was performed in 50 to 54 cycles. The results are shown in Table 1 below.

  As is clear from Table 1, the battery A using the separator having a thin film thickness showed a higher discharge capacity.

  Next, the relationship between the discharge current and discharge average voltage of both batteries was determined. Charging was performed at 120% of the discharge capacity, and the ambient temperature was 35 ° C. This measurement was performed in 60 to 64 cycles. The results are shown in Table 2 below.

  As is clear from the above results, the battery A had higher output. In battery A, the separator is thin and the distance between the electrodes is small, which is considered to be the cause of high output.

  Next, charging and discharging were repeated under the conditions of 110% charge of discharge capacity at 25 ° C. and 0.5 C, and terminal voltage of 0.9 V at 5 C, and the battery life was confirmed. Table 3 shows the relationship between the number of cycles and the capacity retention rate when the capacity in 20 cycles is 100.

  As is clear from the above results, the battery A using a polypropylene nonwoven fabric impregnated with polyvinyl alcohol as a separator had a longer life than the battery C using a thicker nonwoven fabric as a separator. From this result, it can be seen that impregnation with polyvinyl alcohol improves the electrolytic solution holding performance of the separator.

Claims (4)

A polyolefin non-woven fabric having a thickness of 50 to 110 μm, which has been subjected to a treatment for improving the affinity for the electrolyte , is used as a support, and this is impregnated with polyvinyl alcohol (excluding those treated with sulfuric acid). A separator for an alkaline secondary battery. The separator for an alkaline secondary battery according to claim 1, wherein the treatment for improving the affinity for the electrolytic solution is a treatment for bringing the polyolefin nonwoven fabric into contact with fuming sulfuric acid or fluorine gas. A porosity of 40 to 60% of the previous polyolefin nonwoven impregnating polyvinyl alcohol, the reduction rate of porosity after impregnation with polyolefin is 10% or less of porosity before impregnation claim 1 or 2 The separator for alkaline secondary batteries described in 1. The alkaline secondary battery which contains the separator for alkaline secondary batteries in any one of Claims 1-3 as a component, and also has a nickel electrode of following (ii):
(Ii) A nickel electrode including a base material for an electrode and a nickel electrode active material on which concave and convex portions are formed by mechanical processing, wherein the concave portion of the base material is filled with the active material, and the convex portion of the base material Is a nickel electrode in which the surface is exposed or the active material is attached.