JPH09180753A - Nickel-metal hydride battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a cycle life characteristic by satisfying the requirements for both self-discharging restraint and productivity. SOLUTION: A separator made of polyolefine nonwoven or woven fabric subjected to hydrophilic treatment by means other than sulfonation is used as a separator, and a sulfonated polyolefine resin is laid in a battery jar, in addition to the separator. In this case, a nonwoven or woven fabric form of the resin is used as the sulfonated polyolefine resin.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to suppression of self-discharge of a nickel metal hydride battery.

[0002]

2. Description of the Related Art A positive electrode having nickel hydroxide as a main active material, a negative electrode mainly having a hydrogen storage alloy, and a positive electrode and a negative electrode interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode and the negative electrode from each other. Equipped with a separator and a battery container
Metal hydride batteries have a higher energy density than nickel-cadmium batteries and do not contain cadmium in the negative electrode active material, which is environmentally preferable and has been recently used as a power source for portable devices and electric vehicles. There is.

For the positive electrode, the separator, the electrolytic solution and the battery container of this battery, those similar to the nickel-cadmium battery were used.

[0004]

However, such a nickel-metal hydride battery has a problem that the self-discharge is larger than that of the nickel-cadmium battery.

The main cause of self-discharge in nickel-cadmium batteries is "nitrate-" due to nitrate radicals remaining as impurities in the positive electrode active material and negative electrode active material due to the raw material salt and decomposition products of the polyamide separator. nitrite shuttl
It is known that there is an e "mechanism, and it is considered that the same mechanism is operating in a nickel-metal hydride battery. In a nickel-metal hydride battery, the hydrogen storage alloy of the negative electrode A mechanism is conceivable in which the positive electrode active material is reduced by the released hydrogen gas.

In the nickel-metal hydride battery, when a sintered nickel hydroxide electrode manufactured by using an aqueous solution containing nickel nitrate is used as a positive electrode, it is charged in an open system after battery assembly and stored at 30 to 60 ° C. There has been proposed a manufacturing method for removing nitrate ions. (Japanese Patent Laid-Open No. 4-3202071
issue). However, in this method, while the battery is charged in an open system and left to stand, the alkaline electrolyte absorbs carbonate in the air and contaminates the electrolyte, or the water in the alkaline electrolyte evaporates. Therefore, there was a problem that the concentration and amount of the electrolytic solution changed. In addition, in order to suppress self-discharge, a method of suppressing the generation of nitrate radicals has been proposed by using a polyolefin nonwoven fabric hydrophilized by sulfonation as an alternative to the polyamide separator. When this type of separator is used, self-discharge is suppressed, but there is a problem in that it takes time to inject the electrolyte solution when assembling the battery, which lowers productivity. In addition, in order to suppress nitrate radicals, a means of using a polyolefin separator subjected to a hydrophilic treatment with fluorine gas,
There is a means of using a separator in which a portion of ethyl vinyl alcohol is introduced into the structure of the polyolefin fiber to impart hydrophilicity. Some of these separators have an electrolytic solution absorption rate higher than that of the sulfonated polyolefin, and have desirable properties for improving battery productivity. Further, the amount of nitrogen contained in these separators is as small as that of the sulfonated polyolefin separator. Further, the polyolefin separator has higher durability in an alkaline electrolyte than the polyamide separator and is also excellent in charge / discharge cycle life characteristics. However, even if a polyolefin separator subjected to a hydrophilic treatment by means other than sulfonation is used, self-discharge cannot be suppressed as much as when a sulfonated polyolefin separator is used.

[0007]

According to the present invention, in order to solve the above-mentioned problems, a positive electrode containing nickel hydroxide as a main active material, a negative electrode mainly containing a hydrogen storage alloy, the positive electrode and the negative electrode. A separator made of a non-woven fabric or a woven fabric made of polyolefin hydrophilized by means other than sulfonation for electrically insulating the positive electrode and the negative electrode by interposing between them, an alkaline electrolyte, and a battery container A nickel-metal hydride battery comprising: a nickel-metal hydride battery in which a sulfonated polyolefin resin is provided in a battery container separately from a separator. Further, the sulfonated polyolefin resin provides a nickel metal hydride battery in a fibrous state. Further, there is provided a nickel metal hydride battery in which the sulfonated polyolefin resin fiber is a non-woven fabric or a woven fabric. Further, there is provided a nickel-metal hydride battery in which the sulfonated polyolefin nonwoven fabric is in contact with the electrode plate group on the side surface or the bottom surface of the electrode plate group including a positive electrode, a separator and a negative electrode.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A nickel metal hydride battery according to the present invention is installed in a battery separately from a polyolefin separator in which a sulfonated polyolefin resin is hydrophilized by a method other than sulfonation. This way,
It has a function of suppressing self-discharge, and its effect is much larger than that when a polyolefin separator hydrophilized by a method other than sulfonation is used. According to the present invention, by using a separator that absorbs the electrolytic solution faster than a separator made of sulfonated polyolefin, the time required for the liquid injection step is significantly shortened as compared with the conventional technique using a separator made of sulfonated polyolefin. be able to.

Furthermore, rather than a polyamide separator,
By using a polyolefin separator having excellent durability in an alkaline electrolyte, a battery having not only self-discharge performance but also excellent cycle life performance can be obtained.

The reason why the self-discharge is reduced when the hydrophilization treatment by sulfonation is performed is not well understood at present, but the sulfo group on the surface probably has some ion exchange ability, It may have the function of reducing nitrogen roots in the battery that are involved in self-discharge. Alternatively, if a sulfonated polyolefin is installed, the distribution of the electrolytic solution may change, and it may be difficult for hydrogen gas released from the hydrogen storage alloy to reach the positive electrode. Alternatively, when the sulfonated polyolefin is dipped in an alkaline electrolyte, some substance that suppresses self-discharge may be released.

In any case, by disposing the sulfonated polyolefin in the battery separately from the separator,
This effectively suppresses self-discharge, and at the same time eliminates the disadvantages of using a sulfonated polyolefin separator or a polyamide separator.

[0012]

The present invention will be described in detail with reference to preferred embodiments. [Battery A] (Product of the Present Invention) A positive electrode was prepared as follows.

That is, an active material powder obtained by coprecipitating a small amount of cobalt hydroxide and zinc hydroxide in nickel hydroxide is mainly mixed with cobalt hydroxide powder, and water is added to this and kneaded to form a paste. Was prepared. The cobalt hydroxide powder is an additive for improving the utilization rate of the active material of the positive electrode active material and obtaining the discharge reserve of the negative electrode. A similar effect can be obtained by using cobalt metal or cobalt oxide. Next, this paste was filled in a foamed nickel porous body having an average pore diameter of about 300 μm, dried, pressurized, and cut into a predetermined size to obtain a positive electrode plate.

The negative electrode was manufactured by the following method.

That is, misch metal (hereinafter referred to as Mm. The main components are La: about 45% by weight, Ce: about 5).
%, Pr: about 10% by weight, Nd: about 40% by weight),
The metallic materials of Ni, Co, Mn and Al are replaced by MmNi
_It was melted in a high frequency induction furnace so as to have a composition of _3.5 Co _0.8 Al _0.4 Mn _0.3 , cast into a mold and solidified. Then, the ingot was pulverized and sieved to obtain a hydrogen storage alloy powder having an average particle size of several tens of μm. Next, 100 parts by weight of this hydrogen-absorbing alloy powder and a small amount of carbon black as a conductive auxiliary agent were kneaded with an aqueous solution of polyvinyl alcohol or the like having a function of a thickener and a binder to prepare a paste-like material. . Next, this paste-like material is made to have a thickness of about 80.
A negative electrode was obtained by coating a perforated steel plate made of iron plated with nickel and having an aperture ratio of about 50% at μm, dried, pressed, and cut into a predetermined size.

Then, these three positive electrodes and four negative electrodes are laminated with one separator each consisting of a polyolefin nonwoven fabric hydrophilized with fluorine gas, with a height of 57 mm, a width of 15 mm, and a vertical length. A 4.8 mm plate group was constructed. And on the bottom of this electrode group, horizontal 1
A sulfonated polyolefin non-woven fabric having a size of 5 mm, a length of 4.8 mm, and a thickness of 200 μm was placed and stored in a nickel-plated iron battery container. And 7 mol KOH
An alkaline electrolyte prepared by dissolving 10 g / l of LiOH in an aqueous solution is injected, and the battery is sealed with a lid having a positive electrode terminal that also serves as a safety valve, forming a prismatic sealed nickel metal hydride battery with a nominal capacity of 1000 mAh. did.

The battery thus constructed was subjected to chemical conversion by charging and discharging several times at 20 ° C. After formation, 200mA (about 5
(Hour rate) for 6 hours, and discharged at a current of 200 mA, the discharge capacity was about 1000 mAh. In addition, charging and discharging of this battery were both limited by the capacity of the positive electrode. [Battery B] (Product of the Present Invention) The electrode plate group was manufactured in the same manner as the battery A. Then, a sulfonated polyolefin nonwoven fabric having a width of 15 mm, a length of 60 mm, and a thickness of 200 μm was placed on the side surface of this electrode plate group. Similar to the battery A, liquid injection, sealing, and charging / discharging at 25 ° C. were performed several times to perform chemical conversion. [Battery C] (Comparative Example) The positive electrode and the negative electrode were manufactured in the same manner as the battery A. Three positive electrodes and four negative electrodes were laminated with one separator each made of a sulfonated polyolefin non-woven fabric interposed therebetween to form an electrode plate group. Like Battery A, inject and seal, 25 ℃
At that time, formation was performed by charging and discharging several times. [Battery D] (Comparative Example) The positive electrode and the negative electrode were manufactured in the same manner as the battery A. Three positive electrodes and four negative electrodes were laminated with one separator each subjected to a hydrophilizing treatment with fluorine gas, to form an electrode plate group. Similar to the battery A, liquid injection, sealing, and charging / discharging at 25 ° C. were performed several times to perform chemical conversion. [Battery E] (Comparative Example) The positive electrode and the negative electrode were manufactured in the same manner as the battery A. Three positive electrodes and four negative electrodes were laminated with one polyamide separator interposed therebetween to form an electrode plate group. Similar to the battery A, liquid injection, sealing, and charging / discharging at 25 ° C. were performed several times to perform chemical conversion. [Battery F] (Comparative Example) The positive electrode and the negative electrode were manufactured in the same manner as the battery A. Three positive electrodes and four negative electrodes were laminated with one polyamide separator interposed therebetween to form an electrode plate group. Then, on the side surface of this electrode plate group, a width of 15 mm, a length of 60 mm, and a thickness of 20
A 0 μm sulfonated polyolefin nonwoven fabric was installed. Similar to the battery A, liquid injection, sealing, and charging / discharging at 25 ° C. were performed several times to perform chemical conversion.

The test batteries A, B, C obtained in this way
The liquid absorption characteristics when producing D, E and F were compared by the following tests. That is, about 1 ml of the electrolytic solution was dropped onto the electrode plate group of each battery, and the time required to absorb the electrolytic solution was measured. The results are shown in Table 1.

[0019]

[Table 1] Compared with the batteries A, B and D using the separator hydrophilized with fluorine, the battery C of the comparative example using the sulfonated polyolefin separator requires a significantly longer time to absorb the electrolytic solution. I understand. In the batteries A and B of the present invention in which the sulfonated polyolefin nonwoven fabric was installed, the liquid absorption time was able to be the same as that of the battery D of the comparative example. The liquid absorption times of the batteries E and F using the polyamide separator were also the same as those of the battery D.

Next, the self-discharge characteristics were compared under the following conditions. That is, batteries A, B, C, D, E and F
Is first charged at 25 ° C. at 1000 mA (about 1 hour rate) for 66 minutes, then discharged at 200 mA (about 5 hour rate) until the terminal voltage becomes 1.0 V, and the capacity before self-discharge Find out. After that, charge at 1000 mA at 25 ° C for 66 minutes, then store in a constant temperature bath at 40 ° C for 7 days,
After that, residual discharge was carried out at 25 ° C. and 200 mA until the terminal voltage became 1.0 V. The capacity retention rate was calculated from the ratio of the remaining discharge capacity and the discharge capacity before self-discharge. Table 2 shows the results.

[0021]

[Table 2] The capacity retention of the battery C of the comparative example using the sulfonated polyolefin separator was 82%, but 65% of the battery D of the comparative example using the separator hydrophilized with fluorine. On the other hand, in the battery A of the present invention in which the sulfonated polyolefin nonwoven fabric was installed on the bottom surface of the electrode plate group, the capacity retention rate was 73%. Further, in the battery C in which the sulfonated polyolefin nonwoven fabric was installed on the side surface of the electrode plate group, the capacity retention rate was 82%. In the battery E of the comparative example using the polyamide nonwoven fabric, the capacity retention rate decreased to 55%, and also in the battery F of the comparative example in which the sulfonated polyolefin nonwoven fabric was installed on the side surface of the electrode plate group, the capacity retention ratio was 71%. It improved only to about%.

Next, the cycle life performances were compared. The charge and discharge cycle is as follows: charging at 1000 mA (about 1 hour rate) for 54 minutes, and charging at 1000 mA (about 1 hour rate) for 4 minutes.
The test was performed under the condition of discharging for 8 minutes. The temperature of the atmosphere was 25 ° C., and a pause of 10 minutes was performed between charging and discharging. 1 kHz every tens of cycles
The internal resistance was measured by the AC method. The discharge capacity was 66 at 1000 mA when measuring the internal resistance.
The measurement was performed under the condition that the battery was charged for 1 minute and discharged to 1.0 V at 200 mA. The change in discharge capacity in the cycle life test is shown in FIG. 1, and the change in internal resistance of the battery is shown in FIG.

In the batteries E and F of the comparative example using the polyamide nonwoven fabric, the internal resistance increased greatly with the progress of the cycle, and the discharge capacity decreased remarkably. Further, compared to the battery C of the comparative example using the separator made of the sulfonated polyolefin nonwoven fabric, the batteries A and B of the present invention and the battery D of the comparative example using the polyolefin separator hydrophilized with fluorine were used. In this case, the increase in internal resistance was small and the decrease in discharge capacity was small. Therefore, it is found that the cycle life performance is most excellent when the polyolefin separator subjected to the hydrophilic treatment with fluorine is used.

In the above examples, the sulfonated polyolefin nonwoven fabric is shown as an example, but the sulfonated polyolefin resin may be used in the form of granules, fibers or films. Further, in the above example, the case where the sulfonated polyolefin nonwoven fabric is installed on the bottom surface and the side surface of the element has been described as an example.
The place of installation may be any place in the battery, such as the upper part of the element, as long as it is different from the separator.

In the above-mentioned examples, the separator made of the polyolefin non-woven fabric which has been subjected to the hydrophilic treatment with fluorine gas has been described as an example, but the hydrophilic treatment is carried out by the method of adding a surfactant or the structure of the polyolefin fiber. It may be applied by a method of introducing a portion of ethyl vinyl alcohol,
Woven cloth may be used instead of non-woven cloth.

Further, in the above-mentioned examples, the composition and blending method of the positive electrode mixture, the composition of the positive electrode, the composition of the hydrogen storage alloy of the negative electrode,
The alloy powder manufacturing method, the positive electrode and the negative electrode manufacturing method, the composition of the electrolytic solution, the configuration of the nickel-metal hydride battery, the conditions of charging and discharging and leaving, etc. were described in detail using a specific specific configuration. However, those having ordinary technical knowledge in the art can make modifications and changes within the scope of the present invention, and such modifications and changes are included in the scope of the present invention.

[0027]

As described in detail above, according to the present invention, in a nickel metal hydride battery, a polyolefin separator hydrophilized by a method other than sulfonation is used, and separately from the separator. By adopting a structure in which a sulfonated polyolefin resin is installed in the battery, the self-discharge rate is reduced without significantly slowing the absorption rate of the electrolytic solution, and the nickel metal hydride battery also has excellent cycle life performance. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram comparing changes in discharge capacity.

FIG. 2 is a diagram comparing changes in internal resistance.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01M 2/16 H01M 2/16 P

Claims (4)

[Claims] 1. A positive electrode having nickel hydroxide as a main active material, a negative electrode mainly having a hydrogen storage alloy, and a positive electrode and a negative electrode interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode and the negative electrode. A nickel-metal hydride battery provided with a separator made of a non-woven fabric or a woven fabric made of polyolefin that has been hydrophilized by a means other than sulfonation, an alkaline electrolyte, and a battery container, which is separate from the separator. A nickel metal hydride battery characterized in that a sulfonated polyolefin resin is disposed in a battery container. 2. The sulfonated polyolefin resin,
The nickel-metal hydride battery according to claim 1, which is fibrous. 3. The nickel-metal hydride battery according to claim 1, wherein the sulfonated polyolefin resin fiber is a non-woven fabric or a woven fabric. 4. The nickel according to claim 1, wherein the sulfonated polyolefin nonwoven fabric is in contact with the electrode plate group at a side surface or a bottom surface of the electrode plate group including a positive electrode, a separator and a negative electrode. Metal hydride battery.