JPH11219721A - Alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the reaction utilization factor of an active material by adding a specific quantity of lithium hydroxide at its solubility or above to an aqueous solution solved with one or plural materials within a group of cesium hydroxide, rubidium hydroxide, potassium hydroxide and sodium hydroxide at a specific concentration to obtain an alkaline electrolytic solution in the suspended state. SOLUTION: Lithium hydroxide is added at the deposited quantity of 80 g/l or below in an aqueous solution to the aqueous solution solved with an electrolyte selected from cesium hydroxide, rubidium hydroxide, potassium hydroxide and sodium hydroxide at the concentration of 5 mol/1 or above to obtain an alkaline electrolytic solution. The alkaline electrolytic solution is injected into a metal case inserted with an electrode group spirally wound with a nickel positive electrode, a negative electrode and a separator to obtain an alkaline storage battery. A sufficient quantity of alkaline cations, particularly lithium ions, can exist against a positive electrode active material, power acceptability at a high temperature is improved, and a battery capacity is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-capacity alkaline storage battery comprising a nickel positive electrode, a negative electrode, a separator and an alkaline electrolyte, and more particularly to an improvement in the alkaline electrolyte.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices, there has been a demand for an alkaline storage battery to have a higher capacity as a power source. In particular, nickel-hydrogen storage batteries are secondary batteries consisting of a positive electrode made of an active material mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy, and are rapidly becoming high-capacity and highly reliable secondary batteries. It is becoming popular. Hereinafter, the positive electrode of this alkaline storage battery will be described.

The positive electrode for an alkaline storage battery is roughly classified into a sintered type and a non-sintered type. The former impregnates a nickel salt solution such as a nickel nitrate aqueous solution into a porous nickel sintered substrate having a porosity of about 80% obtained by sintering nickel powder,
Then, a nickel hydroxide active material is produced in the porous nickel sintered substrate by immersing it in an alkaline aqueous solution or the like to produce the substrate. Since it is difficult for this electrode to increase the porosity of the substrate any more, the amount of the filled active material cannot be increased, and there is a limit to increasing the capacity.

As the latter non-sintered positive electrode, for example, a sponge-like porous substrate made of nickel metal and having a three-dimensionally continuous porosity of 95% or more disclosed in Japanese Patent Application Laid-Open No. 50-36935 is disclosed. And nickel hydroxide powder as an active material. This is currently widely used as a positive electrode for high capacity secondary batteries. In this non-sintered positive electrode, it has been proposed to fill a porous substrate with spherical nickel hydroxide from the viewpoint of increasing the capacity. This means that the pore size of the sponge-like porous substrate is 200 to 50.
About 0 μm, and the pores have a particle size of several μm to several tens μm.
Is filled with spherical nickel hydroxide. In this configuration, the charge / discharge reaction of nickel hydroxide near the nickel metal skeleton where the conductive network is maintained proceeds smoothly, but the reaction of nickel hydroxide separated from the skeleton does not sufficiently proceed. Therefore, in this non-sintered positive electrode, a conductive agent is used in addition to the active material, nickel hydroxide, in order to improve the utilization of the filled nickel hydroxide. In this way, the spherical nickel hydroxide particles are electrically connected to each other and between the nickel hydroxide particles and the substrate skeleton. As the conductive agent, a cobalt compound such as cobalt hydroxide or cobalt monoxide, metallic cobalt, metallic nickel or the like is used. Thus, the non-sintered positive electrode can be filled with the active material at a high density, and the capacity can be increased as compared with the sintered positive electrode.

As another means for increasing the capacity, there is a method of adding lithium hydroxide to the electrolyte to improve the characteristics of the positive electrode. This is achieved by incorporating lithium ions into nickel hydroxide and improving the charging efficiency by increasing the ionic conductivity due to the increase in lattice defects of nickel hydroxide, or by increasing the oxygen generation overvoltage of the positive electrode with lithium hydroxide having a large charge density. The charging efficiency is improved by increasing the size, and the capacity is increased.

[0006]

However, there is a limit in increasing the capacity if only the technique of packing a large amount of the active material into the substrate or the technique of improving the utilization rate of the positive electrode active material as described above is used. There was room for

[0007] In particular, when a large number of electrode constituent materials such as a positive electrode and a negative electrode are packed in a battery case having a fixed volume, there is a problem that a sufficient battery capacity at ordinary temperature and high temperature cannot be obtained. this is,
When a large amount of electrode constituent materials such as positive and negative electrodes are packed, the space in which the alkaline electrolyte can be injected is reduced in the battery, and as a result, the amount of alkali cations is smaller than the amount of positive electrode active materials compared to the conventional one. It turned out that it was largely caused.

[0008] Among them, lithium ion, which has a favorable effect on battery characteristics, has low solubility of lithium hydroxide in an alkaline electrolyte. Therefore, industrially relatively inexpensive potassium hydroxide or sodium hydroxide is used alone or in a mixed aqueous solution. At present, only a small amount was added. Further, from the viewpoint of injecting a predetermined amount of an aqueous solution into a metal case and preparing a battery, when dissolving a large amount of lithium hydroxide having a low solubility in water, a relatively large amount of another alkali hydroxide is dissolved. It was necessary to reduce the amount, and as a result, the electrolyte was diluted, and the reaction utilization of the active material could not be sufficiently increased.

[0009]

SUMMARY OF THE INVENTION In consideration of the above problems, the present invention provides an alkaline storage battery in which a predetermined amount of an alkaline electrolyte is injected into a metal case in which an electrode group including a nickel positive electrode, a negative electrode and a separator is inserted. In, the alkaline electrolyte is cesium hydroxide, rubidium hydroxide, potassium hydroxide and sodium hydroxide alone or a plurality of aqueous solutions in which a lithium hydroxide of the solubility or more is added to an aqueous solution By using the electrolyte solution in the state, the battery capacity at normal temperature and high temperature is improved.

Here, as the mother liquor of the alkaline electrolyte, a single or mixed aqueous solution of cesium hydroxide, rubidium hydroxide, potassium hydroxide or sodium hydroxide having a concentration of preferably 5 mol / l or more is preferably used. By adding more than its solubility, it is possible to improve the utilization rate of the active material not only at normal temperature but also at high temperature, increase the charge acceptability, and obtain a high battery capacity.

Also, preferably, when the amount of lithium hydroxide precipitated in a suspended state in an alkaline aqueous solution is 80 g / l or less, a battery having a high capacity can be produced.

Further, the amount of lithium hydroxide precipitated in the alkaline aqueous solution is such that lithium ions already dissolved in the electrolyte during the initial charge / discharge cycle of the battery or when left at high temperature are converted into hydroxide or hydroxide by the positive electrode active material. In the process of being immobilized as ions by infiltration solid solution and / or chemisorption, it is preferable to dissolve so as to compensate for the decrease in lithium ions in the electrolytic solution, and to finally dissolve all the ions.

On the other hand, there is provided an alkaline storage battery comprising a nickel positive electrode, a negative electrode, a separator, and an alkaline electrolyte, wherein at least lithium is present in the positive electrode active material and the electrolyte, and When all the alkali metal elements present in the battery are regarded as the respective hydroxides, the same effect can be obtained as long as the alkali metal elements are present in a state of being more than the solubility with respect to the amount of water present inside the battery. It is preferable that lithium hydroxide or lithium ion be immobilized in the positive electrode active material and not be precipitated in the electrolyte as lithium hydroxide.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION According to the first aspect of the present invention, cesium hydroxide, rubidium hydroxide and potassium hydroxide are placed in a metal case in which an electrode group in which a nickel positive electrode and a negative electrode are spirally wound with a separator inserted therein. And 5 or more electrolytes selected from the group consisting of
In an aqueous solution dissolved at a concentration of 1 / l or more, lithium hydroxide having a solubility equal to or more than its solubility and the amount of precipitation in the aqueous solution is 80 g / l.
An alkaline storage battery characterized in that a predetermined amount of an alkaline electrolyte added in the following amount is injected. As a result, a sufficient amount of alkali cations, particularly lithium ions, can be present in the positive electrode active material. This improves the charge acceptance at high temperatures and increases the battery capacity.

According to a second aspect of the present invention, the electrolyte concentration of the alkaline electrolyte mother liquor is 5 mol / l or more and 11 mol / l or less, and cesium hydroxide, rubidium hydroxide, potassium hydroxide or hydroxide having this concentration is used. This is an alkaline storage battery in which an alkaline electrolyte obtained by adding lithium hydroxide having a solubility equal to or higher than its solubility is injected into a single or mixed aqueous solution of sodium. The electrolyte concentration of the alkaline electrolyte mother liquor is 5 m
The reason for setting it to ol / l or more is that a high active material utilization cannot be obtained even if lithium hydroxide having a solubility higher than the solubility is added to an alkaline electrolyte having a lower concentration.

According to a third aspect of the present invention, lithium hydroxide or lithium ions are fixed to the positive electrode active material with the lapse of time inside the battery, and as a result, the precipitated lithium hydroxide elutes into the electrolytic solution. Thus, an alkaline storage battery in which lithium hydroxide is not finally precipitated in the alkaline electrolyte. If the lithium element is precipitated in the electrolyte as an alkali hydroxide for a long period of time, the charge / discharge reaction of the electrode may be inhibited depending on the situation, and the utilization rate of the active material may be reduced. Therefore, it is preferable that all lithium elements are in a dissolved state in water.

According to a fourth aspect of the present invention, there is provided an alkaline storage battery comprising a nickel positive electrode, a negative electrode, a separator, and an alkaline electrolyte, wherein at least lithium element is present in the positive electrode and the electrolyte and is present inside the battery. When each of the alkali metal elements is regarded as a respective hydroxide, the alkali metal element is present in excess of its solubility with respect to the amount of water present inside the battery. With such an alkaline storage battery, the utilization rate of the active material is high similarly to the above, and the battery capacity at normal temperature and high temperature can be improved.

According to a fifth aspect of the present invention, a portion of the lithium hydroxide or lithium ion present in the battery which is higher than the solubility of the electrolyte is immobilized on the positive electrode active material, and the lithium hydroxide is freely precipitated in the electrolyte. It does not stipulate.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. However, the present invention is not limited to only the following examples, and can be implemented with appropriate changes within the scope of the present invention.

(Example) First, an electrolytic solution to be injected into a battery was prepared. 5 m of potassium hydroxide in 1 liter of distilled water
ol, 7 mol, 9 mol, and 11 mol, respectively, and the amount of lithium hydroxide monohydrate precipitated at or above its solubility is 40 g / l at room temperature.
2, X3 and X4 were produced.

Further, 7 mol of potassium hydroxide is present in 1 liter of distilled water, and the amount of lithium hydroxide monohydrate which precipitates in excess of the solubility is 1 g / l, 20 g at room temperature.
/ L, 80 g / l of electrolyte solutions X5, X6 and X7 were prepared.

Separately, a battery group of batteries into which these alkaline electrolytes were injected was prepared.

For the positive electrode, paste was prepared by adding 10 wt% of cobalt hydroxide powder to spherical nickel hydroxide powder and further adding a predetermined amount of pure water. The paste was filled into a sponge-like porous substrate made of nickel metal and continuously three-dimensionally having a porosity of 95% or more, dried, and rolled to form electrodes. This electrode is designated as Y1.

In the same manner as described above, an electrode Y2 was prepared by adding a cobalt compound powder containing lithium in advance to spherical nickel hydroxide powder. Here, the cobalt compound containing lithium in advance was obtained by stirring and heating and oxidizing cobalt hydroxide in a high-temperature alkaline solution containing lithium. It is a compound containing 0.3 mol of Li.

These electrodes Y1 and Y2 and a negative electrode mainly composed of a known hydrogen storage alloy are spirally wound through a hydrophilic polypropylene nonwoven fabric separator and inserted into a battery case. Batteries Z1 and Z2 were produced.

The above-mentioned electrolytic solution X was added to each of seven batteries Z1.
A fixed amount of 1, X2, X3, X4, X5, X6, and X7 was injected and sealed, and batteries A, B, C, D, E, F, and G were produced.

Further, a fixed amount of an aqueous solution mainly composed of potassium hydroxide is injected into the battery Z2, and a sealed battery H is charged with lithium hydroxide monohydrate powder in advance into the battery Z1, and then an aqueous solution mainly composed of potassium hydroxide is charged. , And 10 wt% of cobalt hydroxide powder and lithium hydroxide monohydrate powder were added to nickel hydroxide powder, and after mixing and stirring, the mixture was continuously three-dimensionally made of nickel metal. A battery J was prepared using an electrode that was filled into a sponge-like porous substrate having a porosity of 95% or more, dried, and then rolled. here,
The batteries H, I, and J were adjusted so that the amount of potassium, the amount of lithium, and the amount of water existing inside the batteries were the same as those of the battery F.

(Comparative Example) An electrolytic solution X8 in which 3 mol of potassium hydroxide is present in 1 liter of distilled water and the amount of lithium hydroxide monohydrate that precipitates at or above its solubility is 40 g / l at room temperature, 7 mol of potassium hydroxide is present in 1 liter of distilled water, and lithium hydroxide monohydrate is present in excess of its solubility.
The electrolytic solution X9, which is 1 L, the electrolytic solution X10 in which 40 g of lithium hydroxide monohydrate is completely dissolved in 1 liter of 7N (N) potassium hydroxide, and the electrolytic solution X11 containing only 7N potassium hydroxide The batteries were fabricated and injected into the battery Z1, respectively, to fabricate batteries K, L, M, and N of the comparative example.

(Evaluation of Batteries) The batteries A to J of these examples and the batteries K to N of the comparative examples were charged and discharged after being left for 24 hours after injection of the electrolyte. The content of the charge and discharge was 289 mAh / assuming that the reaction of nickel hydroxide was a one-electron reaction.
The battery was charged at a current value of 0.1 CmA at 20 ° C. for 15 hours and left at 20 ° C. for 1 hour with respect to the theoretical capacity of the positive electrode calculated from the amount of electricity in g. The operation of discharging until reaching 1 V was repeated twice. Then, aging was performed for 1 week in an atmosphere of 45 ° C. to obtain a battery for evaluation.

The active material utilization of the battery at normal temperature was determined as follows. Assuming that the reaction of nickel hydroxide is a one-electron reaction, the positive electrode theoretical capacity calculated from the amount of electricity of 289 mAh / g was charged at 20 ° C. with a current value of 0.1 CmA for 15 hours, and left at 20 ° C. for 1 hour. After that, the battery was discharged at 20 ° C. with a current value of 0.2 CmA until the battery voltage became 1 V. At this time, the percentage of the value obtained by dividing the actually discharged capacity by the theoretical capacity of the positive electrode was defined as the active material utilization rate.

The active material utilization during charging in a high-temperature atmosphere was determined by the following evaluation. After charging at 45 ° C. with a current value of 0.1 CmA for 15 hours, leaving at 20 ° C. for 3 hours,
The battery was discharged with a current value of 0.2 CmA at 0 ° C. until the battery voltage became 1 V. At this time, the percentage of the value obtained by dividing the actually discharged capacity by the theoretical capacity of the positive electrode was defined as the active material utilization rate at the time of charging in a high-temperature atmosphere.

The results obtained in the above evaluation are shown in Table 1 below.
The results are shown in (Table 2) and (Table 3).

[0033]

[Table 1]

As shown in Table 1, the batteries A to D of the examples of the present invention have higher active material utilization rates at room temperature than the batteries K, M, and N of the comparative examples. It can be seen that it is effective to add an alkaline electrolyte obtained by adding lithium hydroxide having a solubility equal to or higher than the aqueous solution of potassium hydroxide.

[0035]

[Table 2]

As shown in Table 2, even when a 7 mol / l aqueous solution of potassium hydroxide was used, the batteries E, F, and G of Examples were at room temperature more than the batteries L, M, and N of Comparative Examples. And a high utilization rate of the active material during charging in a high-temperature atmosphere. When the amount of lithium hydroxide monohydrate existing in excess of the solubility and precipitated in the electrolytic solution exceeds 80 g / l, it can be seen that the active material utilization rate is reduced. This is because in a region exceeding 80 g / l, the volume occupied by the precipitate is large, the amount of electrolyte (aqueous solution) required for the battery is insufficient, the internal resistance of the battery is increased, and the battery capacity is reduced. is there.

In the examples, the highest active material utilization was exhibited when the amount of lithium hydroxide monohydrate precipitated above the solubility was 20 g / l. As a result of disassembling this battery,
Below this, no free-separated lithium hydroxide was observed. This indicates that during the initial charge / discharge cycle of the battery or when left at high temperatures, some lithium hydroxide or lithium ions dissolved in the alkaline electrolyte penetrate into the positive electrode active material and / or are fixed by chemisorption. It is considered to be Therefore, some lithium hydroxide or lithium ions penetrate into the positive electrode active material and are fixed by chemisorption by the initial charge / discharge cycle or by leaving at high temperature, and they are separated and precipitated in the electrolyte in the supersaturated state until then. It is preferable to dissolve all the lithium hydroxide in the alkaline electrolyte so as to compensate for the decrease in lithium ions in the electrolyte.

[0038]

[Table 3]

As shown in (Table 3), the batteries H,
I and J have the same effects as the battery F of the example, and have a higher active material utilization rate at the time of charging at room temperature than the battery M of the comparative example. Therefore, at least lithium is present in the positive electrode active material and the electrolytic solution, and all the alkali metal elements present inside the battery are not changed to the same state as the comparative example batteries K and L in the battery state. When it is considered as a hydroxide, it can be understood that it is sufficient that the hydroxide is present in excess of its solubility with respect to the amount of water existing inside the battery.

The above evaluation was performed using an aqueous solution of potassium hydroxide alone as an alkaline electrolyte and an aqueous alkaline solution to which lithium hydroxide was added. However, it is also possible to use an aqueous solution of cesium hydroxide, rubidium hydroxide and sodium hydroxide alone or an aqueous alkali solution obtained by adding lithium hydroxide to a mixed aqueous solution of potassium hydroxide and sodium hydroxide instead of the aqueous solution of potassium hydroxide alone. If the electrolyte concentration is within the above range, substantially the same effects as above can be obtained even if the amount of lithium hydroxide changes.

[0041]

As described above, in the alkaline storage battery according to the present invention, cesium hydroxide, cesium hydroxide, and a metal case in which an electrode group including a nickel positive electrode, a negative electrode, and a separator are inserted.
In an aqueous solution in which a single or a plurality of electrolytes selected from the group consisting of rubidium hydroxide, potassium hydroxide and sodium hydroxide are dissolved at a concentration of 5 mol / l or more, lithium hydroxide has a solubility of not less than its solubility and the amount of precipitation in the aqueous solution is 8
By injecting a predetermined amount of the alkaline electrolyte added in an amount of 0 g / l or less, it is possible to dramatically improve the battery capacity under normal temperature and high temperature atmosphere.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hajime Konishi 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (5)

[Claims] 1. A metal case in which an electrode group in which a nickel positive electrode, a negative electrode and a separator are spirally wound is inserted therein.
Lithium hydroxide is dissolved in an aqueous solution in which a single or a plurality of electrolytes selected from the group consisting of cesium hydroxide, rubidium hydroxide, potassium hydroxide and sodium hydroxide are dissolved at a concentration of 5 mol / l or more, and the solubility is equal to or higher than that of lithium hydroxide. An alkaline storage battery, characterized in that a predetermined amount of an alkaline electrolyte added at a deposition amount of 80 g / l or less is injected. 2. The cesium hydroxide, rubidium hydroxide,
The alkaline storage battery according to claim 1, wherein the concentration of a single or a plurality of electrolytes selected from the group consisting of potassium hydroxide and sodium hydroxide in an aqueous solution is 5 mol / l or more and 11 mol / l or less. 3. The amount of lithium hydroxide added is such that lithium ions dissolved in the electrolyte are fixed or inserted as hydroxides or ions into the positive electrode active material during the initial charge / discharge cycle of the battery or at high temperature. In the process of being done,
Dissolve to compensate for the decrease in lithium ions in the electrolyte,
2. The alkaline storage battery according to claim 1, wherein the total amount of the alkaline storage battery is completely soluble. 4. A nickel positive electrode, a negative electrode, a separator,
An alkaline storage battery comprising an alkaline electrolyte, wherein at least a lithium element is present in the nickel positive electrode and the alkaline electrolyte, and all the alkali metal elements present inside the battery are regarded as respective hydroxides. An alkaline storage battery, wherein the total amount of the alkali hydroxide is equal to or higher than its solubility with respect to the amount of water present inside the battery. 5. A portion of the lithium hydroxide or lithium ion present in the battery which is higher than the solubility of the electrolyte is fixed to the positive electrode active material, and lithium hydroxide is not freely precipitated in the electrolyte. The alkaline storage battery according to claim 4, wherein