JP4193923B2 - Alkaline storage battery - Google Patents

Description

[0001]
[Industrial application fields]
  The present inventionThe present invention relates to a storage battery, particularly an alkaline storage battery.
[0002]
[Prior art and its problems]
With the reduction in size and weight of electronic devices such as mobile phones, it is required to increase the energy density while reducing the size and weight of alkaline storage batteries that are portable power sources. In order to meet such demands, various improvements and modifications of battery constituent members have been studied, such as increasing the capacity of the positive and negative electrode active materials and reducing the thickness of the battery case material. Here, the separator, which is one element of the battery constituent member, is a battery constituent member that is not directly related to the battery capacity unlike the active material or the like, but is a member that affects the miniaturization of the battery by the volume occupancy in the battery. Therefore, the thinning is a concern.
[0003]
By the way, the separator used for alkaline storage batteries is a fabric usually formed using polyolefin fibers excellent in heat resistance and oxidation resistance, and is manufactured by a dry method or a wet method. Here, the dry method is a method of producing a nonwoven fabric from polyolefin fibers by a technique such as a needle punch method, but the nonwoven fabric obtained by this method is often dense and heterogeneous, and has the required strength and short circuit resistance. In order to achieve the properties, it is necessary to set the thickness to at least about 120 μm, and it is difficult to reduce the thickness of the separator. In addition, since the average fiber diameter of the polyolefin fibers used here is a few tens of μm and is thick, the retention of the electrolyte solution decreases as the film becomes thinner, and it is difficult to hold the amount of electrolyte solution required for the battery. become.
[0004]
On the other hand, the wet method is a method for producing a non-woven fabric by making a polyolefin fiber, and since a polyolefin fiber having a smaller fiber diameter than that of the dry method can be used, the short circuit resistance and the electrolyte solution are reduced. A dense and uniform thin-film nonwoven fabric excellent in retention can be obtained. However, when the nonwoven fabric obtained by this method holds the electrolytic solution, the nonwoven fabric is uniformly held as a whole, so that the air permeability is lowered. For this reason, when such a nonwoven fabric is used as a separator for an alkaline storage battery, particularly for a sealed high energy density alkaline storage battery, it is difficult to smoothly transmit oxygen gas generated in the positive electrode to the negative electrode during overcharge. Thus, the oxygen gas absorption reaction on the negative electrode side is hindered, which may increase the internal pressure of the battery and shorten the battery life. In particular, a phenomenon in which the electrolyte is taken into the positive electrode due to repeated charge and discharge cycles, and the electrolyte in the separator becomes insufficient, increasing the internal resistance of the battery and leading to a life earlier than expected (separator dryout phenomenon) In order to prevent a shortage of the electrolyte on the positive electrode side by using an excessive electrolyte, the air permeability on the negative electrode side is further reduced, leading to an increase in the internal pressure of the battery. easy.
[0005]
In addition, the nonwoven fabric produced by the wet method has insufficient strength, and particularly when subjected to a sulfonation treatment to suppress self-discharge and increase capacity retention, the strength tends to further decrease. There is a high possibility that the battery will be damaged in the manufacturing process of the storage battery, and there is a possibility that the deterioration will progress early and a short circuit will occur in the battery.
[0006]
An object of the present invention is to realize a separator for an alkaline storage battery that achieves both electrolyte retention and air permeability.
Another object of the present invention is to realize an alkaline storage battery that hardly causes a separator dry-out phenomenon and that does not easily increase an internal pressure even during overcharge.
[0011]
[Means for Solving the Problems]
  The alkaline storage battery of the present invention comprises a first layer comprising a breathable nonwoven fabric formed using polyolefin ultrafine fibers having an average fiber diameter of 0.5 to 9 μm, and a polyolefin fiber having an average fiber diameter of at least 10 μm. A second layer made of a fabric having air permeability formed by using the separator is separately prepared, and the first layer and the second layer are laminated and integrated, and disposed on the first layer side of the separator. The separator includes a negative electrode disposed on the second layer side of the separator, and the separator has a thickness ratio (first layer / second layer) of the first layer to the second layer of 0.1-0. Set to 6And has a sulfonic acid group.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The alkaline storage battery separator according to the present invention is configured in a two-layer structure including a first layer and a second layer.
A 1st layer consists of a nonwoven fabric which has air permeability formed using extra fine fiber. The ultrafine fibers used here are those obtained by spinning a polyolefin resin, that is, polyolefin ultrafine fibers, having an average fiber diameter of 0.5 to 9 μm, preferably 2 to 7 μm. is there. When this average fiber diameter is less than 0.5 μm, the air permeability of the first layer is lowered, and it becomes difficult to smoothly transmit oxygen gas generated when the alkaline storage battery is overcharged. On the other hand, when it exceeds 9 μm, the retention of the electrolytic solution by the separator is lowered.
[0013]
The first layer made of a nonwoven fabric using such polyolefin-based ultrafine fibers has an air permeability of at least 4 cc / cm.²It is preferably set to 1 / second. Air permeability is 4cc / cm²If it is less than / sec, it may be difficult to smoothly permeate oxygen gas generated when the alkaline storage battery is overcharged. When the separator of the present invention is used for an alkaline storage battery, the internal pressure of the battery is likely to increase. There is a possibility. The upper limit value of the air permeability of the first layer is not particularly limited, but is usually 30 cc / cm from the viewpoint of maintaining good retention of the electrolytic solution.²/ Sec or less, preferably 25 cc / cm²It is more preferable to set it to less than / sec.
[0014]
The thickness of the first layer is usually preferably set to 20 to 60 μm, and more preferably set to 25 to 50 μm. When this thickness is less than 20 micrometers, there exists a possibility that the electrolyte solution retainability of the separator of this invention may fall. On the other hand, when it exceeds 60 μm, the electrolyte retention of the separator of the present invention is further increased, but the thickness of the entire separator is increased, which may be an obstacle to miniaturization of the alkaline storage battery. is there.
[0015]
The nonwoven fabric which comprises the above-mentioned 1st layer can be manufactured by the melt blow method, for example. Specifically, the molten polyolefin resin extruded from the spinning holes (nozzles) is spun into ultrafine fibers using a high-temperature and high-speed air current blown from the periphery of the spinning holes, and this is spun on a collecting conveyor net or rotating drum. The fiber web can be formed by spraying on the fiber.
[0016]
On the other hand, the second layer is made of a fabric having air permeability. This fabric is formed using a polyolefin fiber obtained by spinning a polyolefin resin, and has various forms such as a nonwoven fabric, a woven fabric or a knitted fabric. Here, the polyolefin fiber used has an average fiber diameter of at least 10 μm. When this average fiber diameter is less than 10 μm, the mechanical strength of the separator decreases. As a result, the handling property of the separator during assembly of the alkaline storage battery is reduced, and the separator is easily broken during the repeated charge / discharge cycle, causing a short circuit, and the possibility of shortening the life of the alkaline storage battery is increased. .
[0017]
The upper limit of the average fiber diameter of the polyolefin fibers constituting the above-mentioned fabric is not particularly limited, but it is usually preferably set to 50 μm or less from the viewpoint of obtaining a fabric with good fiber dispersion. More preferably, it is set to 40 μm or less.
[0018]
The second layer made of the above-described fabric has a higher air permeability than the first layer. When the air permeability of the second layer is smaller than that of the first layer, the permeability of oxygen gas generated when the alkaline storage battery is overcharged may be reduced, and the internal pressure of the alkaline storage battery may be easily increased. Incidentally, the air permeability of the second layer is usually 35 to 150 cc / cm.²Is preferably set to 40/100 cc / cm²More preferably, it is set to / sec. Air permeability is 150cc / cm²When exceeding / sec, it may be difficult to impart the required mechanical strength to the separator.
In the present invention, the air permeability of the first layer and the second layer is determined by an air permeability test using a Frazier type tester described in JIS-1096.
[0019]
Further, the thickness of the second layer is usually preferably set to 50 to 150 μm, and more preferably set to 60 to 120 μm. When this thickness is less than 50 μm, the mechanical strength of the separator of the present invention may be insufficient. On the other hand, if it exceeds 150 μm, the mechanical strength of the separator of the present invention will increase, but the thickness of the separator as a whole will increase, which may be an obstacle to miniaturization of the alkaline storage battery.
[0020]
The polyolefin-based resin constituting the polyolefin-based ultrafine fiber and the polyolefin-based fiber used in the first layer and the second layer, respectively, is not particularly limited, and is usually a known one such as a polyethylene resin or a polypropylene resin. Various things, or a mixture thereof. Incidentally, when the ultrafine high molecular weight polyethylene fiber is blended with the polyolefin ultrafine fiber and the polyolefin fiber made of such a polyolefin resin, a separator having higher strength and short circuit resistance can be realized.
[0021]
The separator of the present invention has a two-layer structure in which the first layer and the second layer are laminated as described above, but the overall thickness is preferably normally set to 90 to 190 μm, 95 More preferably, it is set to ˜180 μm. When this thickness is less than 90 μm, the separator may have insufficient strength. On the contrary, when it exceeds 190 μm, the volume occupancy rate of the separator in the alkaline storage battery is increased, which may make it difficult to reduce the size of the alkaline storage battery.
[0022]
In the separator of the present invention, the thickness is set as described above, and the thickness ratio between the first layer and the second layer (first layer / second layer) is set to 0.1 to 0.6. It is preferable that it is set to 0.2 to 0.5. When this ratio exceeds 0.6, the strength of the separator is reduced, and the permeability of oxygen gas generated when the alkaline storage battery is overcharged may be reduced. On the other hand, when it is less than 0.1, there is a possibility that the retention of the electrolytic solution by the separator is lowered.
[0023]
The separator of the present invention has a two-layer structure in which the first layer and the second layer are laminated as described above, but preferably has ion exchange capacity. The ion exchange capacity here is a cation exchange capacity, for example, due to an acidic group such as a sulfonic acid group, a carboxyl group, or an acidic hydroxyl group. Here, it is particularly preferable that the separator of the present invention has a sulfonic acid group and exhibits ion exchange ability by the sulfonic acid group. In this case, the separator of the present invention can effectively suppress self-discharge of an alkaline storage battery, particularly a nickel metal hydride battery, and can increase the capacity retention of the battery.
[0024]
The ion exchange capacity of the separator of the present invention is preferably 0.03 to 0.5 meq / g as the exchange amount of potassium ions. When this exchange amount is less than 0.03 milliequivalent / g, the hydrophilicity of the separator and the electrolyte solution retainability are lowered, which may make it difficult to increase the energy density of the alkaline storage battery. Moreover, it becomes difficult to effectively suppress the self-discharge of the alkaline storage battery, and as a result, it may be difficult to increase the capacity retention of the alkaline storage battery. Conversely, if it exceeds 0.5 meq / g, the strength of these fibers will be reduced when such ion exchange capacity is imparted to the above-mentioned fibers constituting the first layer and the second layer. As a result, the mechanical strength of the separator is lowered.
[0025]
In addition, the ion exchange capacity in this invention is measured with the following method. When the end of the ion exchange group is a proton, 1/10 mol / dm^ThreeThe KOH (potassium hydroxide) aqueous solution is immersed in a separator, and the amount of KOH consumed by the neutralization reaction is determined by titration with a hydrochloric acid normal solution, and the calculation is performed based on the result. On the other hand, when a salt is bonded to the end of the ion exchange group, 1 mol / dm^ThreeAfter immersing the separator in a hydrogen chloride aqueous solution in advance to replace the end of the ion exchange group with a proton, the same measurement method as in the case where the end of the ion exchange group is a proton is followed.
[0026]
In the separator of the present invention, the electrolytic solution is mainly held by the first layer described above, and the required mechanical strength is imparted and the required air permeability is ensured mainly by the second layer. As a result, in the alkaline storage battery using this separator, the electrolytic solution is mainly held on the first layer side, and the distribution of the electrolytic solution is dense on the first layer side and sparse on the second layer side. become. For this reason, since the air permeability of the second layer can be ensured so as not to be hindered by the electrolytic solution, oxygen gas generated when the alkaline storage battery is overcharged can be smoothly permeated. In addition, since the required mechanical strength is imparted by the second layer, this separator can be used when assembling an alkaline storage battery even when it is set to a thin film similar to a conventional thin one manufactured by a wet method. Is easy to handle, and is not easily damaged even during repeated charge / discharge cycles, causing short circuits.
[0027]
  Next, the manufacturing method of the separator for alkaline storage batteries of this invention is demonstrated. Here, an example of manufacturing a separator having ion exchange ability by a sulfonic acid group is taken as an example.I will give you. In this method, a non-woven fabric made of the above-mentioned polyolefin-based ultrafine fibers constituting the first layer and a fabric made of the above-mentioned polyolefin-based fibers constituting the second layer are separately prepared. And the nonwoven fabric for 1st layers and the fabric for 2nd layers are laminated | stacked, and both are integrated. As a method for integrating the two, a method of bonding the two using an adhesive, a method of thermally fusing both, and a method of embossing or pinsonic processing the laminated nonwoven fabric and the fabric Etc. can be adopted.
[0029]
Next, the laminate of the first layer and the second layer formed as described above is subjected to sulfonation treatment to give sulfonic acid groups. Thereby, the target separator is obtained. In this step, the laminate is treated with a sulfonating agent such as fuming sulfuric acid, sulfurous acid gas and concentrated sulfuric acid. As a treatment method, a method of immersing the laminate in fuming sulfuric acid or concentrated sulfuric acid, a method of arranging the laminate in a sulfurous acid gas stream, and the like can be employed. In the present invention, in order to maintain the strength of the first layer and the second layer, it is preferable that the laminate is immersed in concentrated sulfuric acid set at a temperature of 100 ° C. or less to be sulfonated.
[0033]
In the above-described production method, the case of producing a separator having a sulfonic acid group as an ion exchange group has been described. However, in the case of producing a separator having a carboxyl group or an acidic hydroxyl group as an ion exchange group, a technique such as a graft polymerization method is used. Thus, it is preferable to introduce these ion exchange groups in advance into the polyolefin-based resin for forming the fibers for the first layer and the second layer.
[0034]
The separator of the present invention can be used as a separator for alkaline storage batteries such as nickel cadmium storage batteries and nickel hydride storage batteries. With reference to FIG. 1, an example of a nickel metal hydride storage battery using the separator of the present invention will be described. In the figure, a nickel metal hydride storage battery 1 mainly includes a cylindrical liquid-tight battery case 2 having a safety valve (not shown), an electrode group 3 disposed in the battery case 2, and an electrolyte 4 injected into the battery case 2. In preparation.
[0035]
As shown in FIG. 2, the electrode group 3 is made of a sheet-like member in which the positive electrode 6 and the negative electrode 7 are arranged with the separator 5 interposed therebetween, and is arranged in the battery case 2 in a state of being rolled up. ing. Here, the separator 5 is the thing of this invention which consists of a laminated body of the above-mentioned 1st layer 5a and 2nd layer 5b. The positive electrode 6 is a nickel electrode in which a nickel foam substrate is filled with an active material mainly composed of nickel hydroxide, and is disposed on the first layer 5 a side of the separator 5. On the other hand, the negative electrode 7 is a hydrogen electrode obtained by coating a perforated steel sheet with a hydrogen storage alloy together with a binder, and is disposed on the second layer 5 b side of the separator 5.
[0036]
The electrolytic solution 4 is, for example, a potassium hydroxide aqueous solution, and is injected into the battery case 2 in a state where the electrode group 3 is disposed in the battery case 2, and is impregnated in the separator 5.
Since this nickel-metal hydride battery 1 uses the thin film of the present invention as the separator 5, the volume occupancy of the separator 5 in the battery case 2 can be reduced, and as a result, it is suitable for a mobile phone or the like. It can be effectively used as a small portable power source.
[0037]
Further, in the nickel metal hydride storage battery 1, the electrolyte solution 4 impregnated in the separator 5 is mainly retained on the first layer 5 a side where the liquid retainability is good, and relatively small on the second layer 5 b side. Will be. That is, the distribution of the electrolyte solution 4 in the separator 5 is densely set on the first layer 5a, that is, the positive electrode 6 side that mainly requires the electrolyte solution, and on the second layer 5b side, that is, the negative electrode 7 side that requires air permeability. It will be set to sparse. For this reason, this nickel metal hydride storage battery 1 ensures the air permeability on the negative electrode 7 side in the separator 5 even when an excessive electrolyte 4 is injected into the battery case 2 in order to prevent the separator dry-out phenomenon. Therefore, oxygen gas generated on the positive electrode 6 side during overcharge can be smoothly transmitted to the negative electrode 7 side and absorbed. Therefore, the nickel-metal hydride storage battery 1 is unlikely to increase in internal pressure due to oxygen gas even during overcharge, and it is difficult to shorten the battery life due to the operation of a safety valve or leakage of liquid.
[0038]
Furthermore, since the nickel hydride storage battery 1 is imparted with the hydrophilicity showing the ion exchange ability as described above to the separator 5, it is difficult to self-discharge and the capacity retention is good.
[0039]
【Example】
Example 1 (Manufacture of separator for alkaline storage battery)
A polypropylene resin having a melt index of 130 g / 10 min is extruded at a temperature of 295 ° C. at a rate of a single hole discharge rate of 0.5 g / min, and this is 0.8 kg / cm.²It is made of polypropylene resin ultrafine fibers having an average fiber diameter of 3 to 4 μm by a melt-blowing method in which the airflow is set at 300 ° C. and the basis weight is 20 g / m.²To produce a nonwoven fabric (first layer nonwoven fabric) having a thickness of 40 μm. The air permeability of this first layer nonwoven fabric was measured using a Frazier type air permeability tester and found to be 10 cc / m.²/ Sec.
[0040]
Also, a polypropylene resin long fiber having an average fiber diameter of 18 μm is made, and the basis weight is 22 g / m.²A non-woven fabric (second layer non-woven fabric) having a thickness of 95 μm was produced. This second layer non-woven fabric had high air permeability and the air resistance was substantially negligible.
[0041]
Next, the 1st layer nonwoven fabric and the 2nd layer nonwoven fabric were laminated | stacked, and both were integrated by the pin sonic process, and the laminated body was obtained. The laminate was pressure adjusted with a calender roll, the thickness was 95 μm, and the basis weight was 42 g / m.²A thin base fabric for a separator was obtained. The obtained thin base fabric for a separator was immersed in 98% concentrated sulfuric acid at 80 ° C. for 1 hour for sulfonation treatment. Thereafter, the thin base fabric for separator was taken out from the concentrated sulfuric acid to remove the attached concentrated sulfuric acid, and further washed with an aqueous potassium hydroxide solution and then washed with water. Thereby, the thin separator by which the sulfonic acid group as an ion exchange group was introduce | transduced into the 1st layer nonwoven fabric and the 2nd layer nonwoven fabric was obtained. The obtained thin separator had an ion exchange capacity of 0.06 meq / g as a potassium ion exchange capacity.
[0042]
Comparative Example 1 (Manufacture of separator for alkaline storage battery)
  Polyoxyethylene alkyl, which is a nonionic surfactant, for the thin separator fabric obtained in the production process of Example 1PhenylHydrophilicity was imparted by treatment with ether. Thereby, a thin separator was obtained.
[0043]
Comparative Example 2 (Manufacture of separator for alkaline storage battery)
Polypropylene resin fibers having an average fiber diameter of 15 μm are used, and the thickness is 95 μm and the basis weight is 42 g / m by the needle punch method.²A thin base fabric for a separator made of a non-woven fabric was obtained. The thin base separator fabric was subjected to sulfonation treatment and washing treatment in the same manner as in Example 1 to obtain a thin separator.
[0044]
Example 2 (Manufacture of nickel metal hydride storage battery)
A flexible cathode plate was manufactured by filling a nickel foam substrate having a porosity of 95% with an active material containing nickel hydroxide as a main component. In addition, rare earth AB having a ternary composition of MmNiAlCoMn with respect to a perforated steel sheet_FiveType hydrogen storage alloy was applied together with a binder to produce a flexible negative electrode plate.
[0045]
A positive electrode plate was laminated on the first layer nonwoven fabric side of the thin separator obtained in Example 1, and a negative electrode plate was laminated on the second nonwoven fabric side, and this laminate was wound in a spiral shape to produce an electrode group. At this time, the thin separator was not damaged, and a short circuit between the positive electrode plate and the negative electrode plate did not occur. Next, this electrode group was inserted into a cylindrical battery case having a safety valve, and an alkaline electrolyte composed of an aqueous potassium hydroxide solution was injected into the battery case, and then the battery case was sealed and sealed. As a result, an AA size nickel metal hydride storage battery (A) having an energy density of 1,500 mAh was produced.
[0046]
Comparative Example 3 (Manufacture of nickel metal hydride storage battery)
Using the thin separator obtained in Comparative Example 1, the same nickel metal hydride storage battery (B) as in Example 2 was produced.
[0047]
Comparative Example 4 (Manufacture of nickel metal hydride storage battery)
A nickel-metal hydride storage battery (C) similar to that of Example 2 was produced using the thin separator obtained in Comparative Example 2. At this time, when the laminate composed of the positive electrode plate, the thin separator and the negative electrode plate was wound, a crack was generated in the thin separator, and a short circuit was observed.
[0048]
Comparative Example 5 (Manufacture of nickel metal hydride storage battery)
A nickel-metal hydride storage battery (D) similar to that of Example 2 except that a negative electrode plate is laminated on the first layer nonwoven fabric side of the thin separator obtained in Example 1 and a positive electrode plate is laminated on the second layer nonwoven fabric side. Manufactured.
[0049]
Evaluation
About the nickel hydride storage battery (A)-(D) obtained in Example 2 and Comparative Examples 3-5, the overcharge test was implemented by the following method. Moreover, about the nickel metal hydride battery (A)-(C), the self-discharge test and the cycle durability test were further implemented with the following method.
[0050]
Overcharge test
Each nickel metal hydride storage battery was activated by charging and discharging several cycles, and then continuously charged at 20 ° C. with a current value of 0.1 CmA for 48 hours. In the battery (A) of Example 2, no abnormality due to an increase in the internal pressure of the battery such as operation of a safety valve or leakage was observed. On the other hand, in the batteries (B) to (D) of the respective comparative examples, the safety valve was activated and liquid leakage was recognized.
[0051]
Batteries (B) and (C) have reached the above results because of the low electrolyte retention of the thin separator, so that there is free electrolyte on the electrode surface, which occurs on the positive electrode side during overcharge. This is probably because permeation of the oxygen gas to the negative electrode side was hindered and the absorption reaction by the negative electrode did not proceed smoothly. Further, the result of the battery (D) is that the electrolyte solution is densely distributed on the negative electrode side of the separator, so that the permeation of oxygen gas is similarly prevented, and the absorption reaction of oxygen gas by the negative electrode is inhibited. It seems to be.
[0052]
Incidentally, with respect to the thin separator according to Example 1 used in the battery (A) and the thin separator according to Comparative Example 2 used in the battery (C), the electrolyte retention rate during pressurization (1 kgf / cm).²) Was found to be 170% and 90%, respectively, and it was found that the thin-film separator according to Example 1 has excellent electrolyte retention.
[0053]
Self-discharge test
Each nickel-metal hydride storage battery is fully charged to 150% of capacity at a current value of 0.1 CmA in an environment at an ambient temperature of 20 ° C., and then discharged until the battery voltage reaches 1 V at a current value of 0.2 CmA. The battery capacity of was determined. Next, each battery was fully charged again under the same conditions and left in a 45 ° C. thermostat. In addition, the leaving period was set to two types of 7 days and 35 days.
[0054]
After leaving, the battery was discharged under the same conditions as described above to determine the battery capacity. Then, the ratio of the battery capacity after being left to the initial battery capacity was determined, and this was used as the capacity retention rate. The results are shown in FIG. From FIG. 3, it can be seen that the battery (A) exhibits an excellent capacity retention rate over the batteries (B) and (C) and is difficult to self-discharge.
[0055]
Cycle durability test
Each nickel metal hydride battery was charged to 120% of the capacity at a current value of 0.3 CmA in an environment at an ambient temperature of 20 ° C., and discharged until the battery voltage reached 1 V at a current value of 0.5 CmA. Each battery was repeatedly charged / discharged with this charging / discharging operation as one cycle, and the discharge capacity and the change in internal resistance for each cycle were measured. The results are shown in FIG.
[0056]
As shown in FIG. 4, the battery (A) shows a stable cycle characteristic for a long time, but the battery (B) has an early increase in internal resistance and the capacity is reduced, and the battery (C) is lower than the battery (B). Although the cycle characteristics are relatively stable, it can be seen that the internal resistance gradually increases and the capacity decreases. The reason why the internal resistance of the battery (B) increased early was thought to be that the surfactant applied to the separator was released or decomposed early, and thereby the hydrophilicity of the separator itself was reduced early. On the other hand, the reason why the internal resistance gradually increased in the battery (C) seems to be that the positive electrode gradually swelled as the charge / discharge cycle was repeated, thereby causing a separator dry-out phenomenon.
[0057]
Incidentally, when the battery (A) was disassembled, although the positive electrode was swollen, it was confirmed that the electrolyte was held in the separator, particularly on the first layer nonwoven fabric side, which suppressed the separator dry-out phenomenon. It was confirmed that
[0059]
【The invention's effect】
  Of the present inventionAlkaline storage batteryA first layer composed of a non-woven fabric having breathability formed using polyolefin ultrafine fibers having an average fiber diameter of 0.5 to 9 μm, and a breathability formed using polyolefin fibers having an average fiber diameter of at least 10 μm. And separately preparing a second layer made of a fabric having a first layer and a second layer laminated together.Since the positive electrode is disposed on the first layer side of the separator and the negative electrode is disposed on the second layer side, the separator dry-out phenomenon is unlikely to occur, and the internal pressure is unlikely to increase even during overcharge.
[Brief description of the drawings]
FIG. 1 is a partially cutaway perspective view of a nickel metal hydride storage battery according to an embodiment of the present invention.
FIG. 2 is a partial sectional view of an electrode group used in the nickel metal hydride storage battery.
FIG. 3 is a diagram showing a result of a self-discharge test of a battery carried out in an example.
FIG. 4 is a diagram showing a cycle durability test result of a battery implemented in an example.
[Explanation of symbols]
1 Nickel metal hydride storage battery
5 Separator
5a 1st layer
5b Second layer
6 Positive electrode
7 Negative electrode

Claims (1)

A first layer made of a non-woven fabric having air permeability formed using polyolefin ultrafine fibers having an average fiber diameter of 0.5 to 9 μm, and an air permeability formed using polyolefin fibers having an average fiber diameter of at least 10 μm. A second layer made of a fabric having a separator, and a separator in which the first layer and the second layer are laminated and integrated;
A positive electrode disposed on the first layer side of the separator;
A negative electrode disposed on the second layer side of the separator,
In the separator, the thickness ratio (first layer / second layer) between the first layer and the second layer is set to 0.1 to 0.6, and the separator has a sulfonic acid group. ,
Alkaline storage battery.

Images