JP3263511B2 - Alkaline secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery, and more particularly to a chemical conversion treatment step which is a post-process by shortening the formation time (ripening time) of a three-dimensional network structure (conductive matrix) made of CoOOH. The present invention relates to an alkaline secondary battery provided with a paste-type nickel positive electrode that can be shifted to an earlier stage.

[0002]

2. Description of the Related Art Generally, a sintered nickel positive electrode is used in an alkaline secondary battery using a nickel electrode as a positive electrode, such as a nickel-cadmium secondary battery and a nickel-hydride secondary battery. Has been
In recent years, a paste-type nickel electrode has been proposed for the purpose of facilitating the battery manufacturing process and increasing the capacity of the battery, and some of them have been put to practical use. This paste-type nickel electrode is prepared by coating a slurry containing granular nickel hydroxide as a positive electrode active material with a conductive substrate (porous current collector) having a two-dimensional porous structure such as a punching metal or a sponge-like or fibrous material. It was produced by filling a conductive substrate having a dimensional structure (these are also included in the porous current collector in this specification).

However, in this paste-type nickel positive electrode, the active material is filled in the pores of the porous current collector having a considerably large pore size, and thus the paste-type nickel positive electrode is separated from the porous current collector. The resistance between the active material and the porous current collector becomes larger than the resistance between the active material located near the porous current collector and the porous current collector. For this reason, the paste type nickel positive electrode has a problem that the active material utilization is lower than that of the sintered nickel positive electrode in which all the active materials are located in contact with the porous current collector.

In order to solve this problem, there has been proposed a method of producing a positive electrode by adding CoO powder soluble in an alkaline electrolyte to a slurry (JP-A-61-138458 and JP-A-62-138458). No. 256366). According to this method, the CoO existing between the particles of nickel hydroxide is used.
Powder was dissolved in the alkaline electrolyte HCoOO ^- next,
Dissolution, which is then precipitated as β-Co (OH) ₂ ,
Through the precipitation reaction, a uniform β-Co (OH) ₂ layer is formed on the surface of each nickel hydroxide particle. And this β-C
The o (OH) ₂ layer is oxidized when the positive electrode potential becomes noble by subsequent charging and changes to CoOOH, and C 2
Since a three-dimensional network structure made of oOOH is formed, the resistance between the active material located away from the porous current collector and the porous current collector is reduced, and the utilization rate of the active material is increased. Can be. Conventionally, as the CoO powder, a powder having an average particle size of about 1 μm has been generally used. This is because when the average particle size of the CoO powder exceeds 1 μm, the solubility in the alkaline electrolyte decreases, and when the average particle size of the CoO powder decreases to less than 1 μm, the particles easily aggregate to form secondary particles. This is because the solubility is reduced.

However, CoO having an average particle size of 1 μm
Even if the powder is used, it is difficult to say that the amount dissolved in the alkaline electrolyte is sufficient. As a result, a three-dimensional network structure composed of CoOOH is formed to such an extent that the utilization rate of the active material can be sufficiently increased. Must be aged for at least one day after battery assembly. For this reason, there was a problem that it was not possible to shift to a subsequent step such as a chemical conversion treatment at an early stage.

The present invention has been made in view of the above circumstances, and an object of the present invention is to form β-Co (OH) ₂ in a positive electrode by aging for a short time. An object of the present invention is to provide an alkaline secondary battery provided with a paste-type nickel positive electrode, which can promptly shift to a post-process such as treatment.

[0007]

In order to achieve the above object, an alkaline secondary battery according to the present invention (hereinafter referred to as "battery of the present invention")
Called. ) Is a slurry obtained by kneading an active material powder mainly composed of nickel hydroxide, a Co compound soluble in an alkaline electrolyte, and a thickener solution obtained by dissolving a thickener in water. Is filled in the pores of a porous current collector, and a paste-type nickel positive electrode obtained by drying and solidifying is stored in a battery can, and the alkaline electrolyte is poured into the battery can to convert the Co compound into β. —Co (OH) ₂ is deposited on the surface of the active material powder, and then the β-Co (O
H) In an alkaline secondary battery provided with a positive electrode formed by oxidizing ₂ to form a three-dimensional network structure of CoOOH in the pores, the Co compound has an average particle diameter of 2 μm.
The following CoF ₂ powder is used in an amount of 3 to 15% by weight based on the total amount of the CoF ₂ powder and the active material powder.

In the present invention, the amount of CoF ₂ powder added is
The reason why the amount is limited to ₃ to 15% by weight based on the total amount of the CoF ₂ powder and the active material powder is that if the addition amount is less than 3% by weight, the three-dimensional network structure composed of CoOOH is sufficiently formed by the chemical conversion treatment. Because it is not formed, the utilization rate of the active material decreases,
On the other hand, when the addition amount exceeds 15% by weight, the amount of CoF ₂ powder becomes too large and the amount of active material relatively decreases, so that the utilization rate of the active material decreases. This is because a battery with a high utilization rate cannot be obtained.

In particular, in order to obtain a battery with a small decrease in battery capacity and a long cycle life, the amount of CoF ₂ powder to be added should be C
It is preferable to regulate the amount to 8 to 12% by weight based on the total amount of the oF ₂ powder and the active material powder. If the amount of CoF ₂ powder is less than 8% by weight, a well-developed three-dimensional network structure is difficult to be formed, and if the amount exceeds 12% by weight, the decrease in the amount of active material To bring down
In any case, the battery capacity at the beginning of the charge / discharge cycle is slightly reduced.

The reason why the average particle size of CoF ₂ powder is restricted to 2 μm or less is that the average particle size of CoF ₂ powder is 2 μm or less.
Exceeds, CoF ₂ since solubility CoF ₂ powder alkaline electrolyte is reduced, also the time of paste preparation
Powder and nickel hydroxide powder are not uniformly mixed
This is because the F ₂ powder is unevenly distributed, so that a sufficiently developed three-dimensional network structure is not formed even when a chemical conversion treatment is performed after aging, and a high active material utilization rate cannot be realized in any case.

[0011]

Since the solubility of CoF ₂ in an alkaline electrolyte is higher than that of CoO, CoF ₂ becomes HCoOO ⁻ and then precipitates as β-Co (OH) _{2 on the} surface of nickel hydroxide particles. That is, aging is completed in a short time. As a result, it is possible to early shift to a subsequent process such as a subsequent chemical conversion treatment.

[0012]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention may be practiced by appropriately changing the gist of the invention. Is possible.

Example 1 AA type (AA size) alkaline secondary batteries (batteries of the present invention) were prepared.

[Positive Electrode] An active material powder composed of nickel hydroxide containing 3% by weight of cadmium hydroxide as a swelling inhibitor and an oxygen overvoltage increasing agent, and chemically converted into CoOOH in a subsequent step (a chemical conversion step described later). Of CoF ₂ powder having an average particle size of 1 μm, which functions as a conductive agent, and is mixed at a weight ratio of 9: 1, and the mixture is mixed with carboxy as a thickener (having a function as a binder after the preparation of the positive electrode). A slurry was prepared by dispersing in a 0.5% by weight aqueous solution of methylcellulose. Next, this slurry was filled into a nickel-plated metal porous body having a porosity of 95% and an average pore diameter of 200 μm, and then dried and molded to produce a positive electrode. Note that CoF ₂
The average particle size of the powder was measured by a laser diffraction type particle size distribution meter.

[Negative electrode] A slurry is prepared by dispersing 100 parts by weight of cadmium oxide as a negative electrode active material and 1 part by weight of nylon fiber as a reinforcing agent in an aqueous solution of 5 parts by weight of hydroxypropyl cellulose as a binder. did. Next, the slurry was applied to a conductive core and dried to prepare a negative electrode.

[Alkaline electrolyte] KOH, NaOH and L
iOH was mixed at a weight ratio of 8: 1: 1 and dissolved in water to prepare an alkaline electrolyte having a specific gravity of 1.30.

[Preparation of Battery] AA type battery BA1 of the present invention was prepared using the above positive and negative electrodes and an alkaline electrolyte. In addition, a polyamide nonwoven fabric was used as a separator, and this was impregnated with the alkaline electrolyte.

FIG. 1 is a cross-sectional view schematically showing a battery BA1 of the present invention produced. The battery BA1 of the present invention includes a positive electrode 1, a negative electrode 2, a separator 3 for separating these two electrodes, a positive electrode lead 4, and a negative electrode. Lead 5, positive external terminal 6, negative can 7
Etc. The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 in a state of being spirally wound through a separator 3 into which an alkaline electrolyte is injected, and the positive electrode 1 is connected to a positive electrode external terminal via a positive electrode lead 4. 6, and the negative electrode 2 is connected to a negative electrode can 7 via a negative electrode lead 5, so that chemical energy generated inside the battery can be extracted to the outside as electric energy.

Comparative Example 1 A positive electrode was manufactured in the same manner as in Example 1 except that CoO powder having an average particle size of 1 μm was used instead of CoF ₂ powder. Next, an AA type comparative battery BC1 was produced in the same manner as in Example 1 except that this positive electrode was used.

[Relationship between aging period and utilization rate of active material] The battery BA1 of the present invention and the comparative battery BC1 were charged at a current of 0.1 C for 16 hours before aging or after aging for a predetermined period at 25 ° C., and then charged at 1 C for 1 hour. The charging / discharging step of discharging to a discharge end voltage of 0.8 V with the above current was repeated 10 times. This is because a three-dimensional network structure made of CoOOH is formed in the positive electrode by performing a chemical conversion treatment, and the discharge capacity is stabilized. Then, after measuring the discharge capacity of each battery at the tenth discharge when the discharge capacity is stabilized, the utilization rate of the active material is calculated based on the following formula, and the relationship between the aging time and the utilization rate of the active material is examined. Was. The results are shown in FIG.

Active material utilization (%) = 10th discharge capacity
(mAh) × 100 / weight of active material (g) × theoretical capacity per unit weight [285 (mAh / g)]

FIG. 2 is a graph showing the discharge characteristics of each battery, the ordinate representing the utilization rate (%) of the active material of each battery, and the abscissa representing the aging time (h). As shown in the figure, in the battery BA1 of the present invention, the utilization rate of the active material increased to 96% after aging for 6 hours, whereas the comparative battery BC1
In this case, the utilization rate of the active material does not increase to 96% without aging for 24 hours. This indicates that the use of CoF ₂ powder allows β-Co (OH) ₂ to be formed in the positive electrode in a short time.

[0023] <Relationship between CoF ₂ powder having an average particle diameter and the utilization of the active material of> 0.5 [mu] average particle diameter of the CoF ₂ powder
m, 2 μm, 2.5 μm, 3 μm, 4 μm or 5 μm, in the same manner as in Example 1, to produce a battery of the present invention and a comparative battery. Next, after aging for 6 hours, 10 times of charging and discharging were performed under the same conditions as above, and the utilization rate of the active material of each battery at the 10th time was obtained from the above formula, and the average particle size of CoF ₂ powder, the utilization rate of the active material, The relationship was investigated. The results are shown in FIG. FIG. 3 shows the battery BA of the present invention shown in FIG.
The utilization ratio of the active material of No. 1 (average particle size of CoF ₂ powder: 1 μm) is also shown for convenience of comparison.

FIG. 3 is a graph showing the discharge characteristics of each battery, the ordinate indicating the utilization rate (%) of the active material, and the abscissa indicating the average particle size (μm) of the CoF ₂ powder. As shown in the figure, when the average particle size of the CoF ₂ powder is 2 μm or less, the utilization rate of the active material can be increased, and an alkaline secondary battery having excellent discharge characteristics can be obtained.
Therefore, it is necessary to regulate the average particle size of the CoF ₂ powder to 2 μm or less.

<Relationship between Solubility of CoF ₂ Powder and CoO Powder in Alkaline Aqueous Solution and Stirring Time> Under an atmosphere of 25 ° C., the average particle diameter is 1 μm, 2 μm or 5 μm, respectively.
μF CoF ₂ powder and CoO powder having an average particle size of 1 μm were added to a KOH solution and stirred for a predetermined time to dissolve the CoF ₂ powder and CoO powder in an alkaline aqueous solution (the amount of Co ²⁺ per liter of alkaline aqueous solution ⁾ . Amount)
The relationship between the solubility of CoF ₂ powder and CoO powder in an aqueous alkaline solution and the stirring time was examined. FIG. 4 shows the results.

FIG. 4 shows the amounts of CoF ₂ powder and CoO powder having the above average particle sizes dissolved in an aqueous alkaline solution, the ordinate represents the amounts of CoF ₂ powder and CoO powder dissolved in an aqueous alkaline solution (mg / liter), and The horizontal axis is a graph showing stirring time (h). As shown in the figure, CoF ₂ powder having an average particle diameter of 2 μm or less is CoO powder having an average particle diameter of 1 μm regardless of the length of stirring time. Although the amount of dissolution in an alkaline aqueous solution is larger, the amount of CoF ₂ powder having an average particle size of 5 μm is smaller than that of a CoO powder having an average particle size of 1 μm regardless of the length of stirring time. You can see that there is.

As described above, the average particle size of the CoF ₂ powder is 2 μm.
When the average particle diameter of CoF ₂ powder exceeds 2 μm, the utilization rate of the active material decreases as shown in FIG.

<Relationship between the amount of CoF ₂ powder added and the utilization rate of the active material> The amount of CoF ₂ powder added was determined to be 0% by weight, 1% by weight, 2% by weight, 3% by weight, and 5% by weight. %, 7% by weight, 10% by weight, 13% by weight, 15% by weight, 16% by weight or 18% by weight (% by weight is the total amount of the active material powder containing 3% by weight of cadmium hydroxide and the CoF ₂ powder.
It is the ratio assuming weight%, and the weight% appearing below
Is also synonymous. ), And a battery of the present invention and a comparative battery were prepared in the same manner as in Example 1. The battery of the present invention was prepared in the same manner as in Example 1 except that the addition amount was changed in the same manner as described above, and that the average particle size of the CoF ₂ powder was 2 μm, 0.75 μm, or 0.5 μm, respectively. A comparative battery was manufactured. Next, after aging each battery for 6 hours, 10 cycles of charging and discharging were repeated under the same conditions as above.
The utilization rate of the active material of each battery at the cycle was determined from the above formula, and the relationship between the amount of CoF ₂ powder added and the utilization rate of the active material was examined. FIG. 5 shows the results.

FIG. 5 is a graph showing the discharge characteristics of each battery, the ordinate indicating the utilization rate (%) of the active material, and the abscissa indicating the amount of CoF ₂ powder added (% by weight). As shown in the figure, the addition amount is 3 to 1 regardless of the particle size of the CoF ₂ powder.
It can be seen that when the content is 5% by weight, the utilization rate of the active material can be increased, and an alkaline secondary battery having excellent discharge characteristics can be obtained. Therefore, the amount of CoF ₂ powder, to the total amount of CoF ₂ powder and active material powder 3-1
It is necessary to regulate to the range of 5% by weight.

<Relationship between the amount of CoF ₂ powder added and the remaining capacity of the battery at the 100th cycle> The following test was conducted in order to find a suitable range of addition of CoF ₂ powder.

The amount of CoF ₂ added was 3% by weight, 4% by weight, 6% by weight, 8% by weight, 10% by weight, 12% by weight,
A battery of the present invention was produced in the same manner as in Example 1 except that the content was 4% by weight or 16% by weight. A battery of the present invention was produced in the same manner as in Example 1 except that the amount of addition was changed in the same manner as described above, and that the average particle size of CoF ₂ was 2 μm, 0.75 μm, or 0.5 μm, respectively. did. After aging each of these batteries for 6 hours, a charge / discharge cycle test was performed under the same conditions as above to determine the remaining capacity of the battery at the 100th cycle, and the relationship between the amount of CoF ₂ powder added and the remaining capacity of the battery was determined. Investigated the relationship. FIG. 6 shows the results. In addition, 1
The remaining battery capacity at the 00th cycle is the ratio of the battery capacity at the 100th cycle to the battery capacity at the 1st cycle.

FIG. 6 is a graph showing the cycle characteristics of each battery, the ordinate represents the battery capacity remaining rate (%) at the 100th cycle, and the abscissa represents the amount of CoF ₂ powder added (% by weight). , and the when the added amount of CoF ₂ powder regardless average particle size of CoF ₂ powder as shown in the drawing and 8-12 wt%, it is possible to increase the battery residual capacity ratio of the 100th cycle It can be seen that an alkaline secondary battery having excellent cycle characteristics can be obtained. Therefore, the amount of CoF ₂ powder added is preferably in the range of 8 to 12% by weight based on the total amount of CoF ₂ powder and active material powder.

In the above embodiment, the case where the present invention is applied to an AA type battery is described as an example. However, the shape of the battery of the present invention is not particularly limited, and other shapes such as a flat type, a square type, etc. The present invention can be applied to alkaline rechargeable batteries of various shapes.

[0034]

As the CoF ₂ powder has a high solubility in an alkaline electrolyte, the aging time can be shortened. For this reason, it is possible to early shift to a post-process such as a chemical conversion treatment.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an AA battery of the present invention.

FIG. 2 is a graph showing the relationship between each aging time (h) of the battery of the present invention and a comparative battery and the utilization rate (%) of an active material.

FIG. 3 is a graph showing a relationship between an average particle size (μm) of CoF ₂ powder and a utilization rate (%) of an active material.

FIG. 4 is a graph showing the relationship between the stirring time (h) and the amounts of CoO powder and CoF ₂ powder dissolved in an aqueous alkali solution (mg / liter).

FIG. 5 is a graph showing the relationship between the amount of CoF ₂ powder added (% by weight) and the utilization rate (%) of an active material.

FIG. 6 is a graph showing the relationship between the amount of CoF ₂ powder added (% by weight) and the remaining battery capacity (%).

[Explanation of symbols]

 BA1 Battery of the present invention 1 Positive electrode 2 Negative electrode 3 Separator

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toshihiko Saito 2-5-5-Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-53-51449 (JP, A) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H01M 4/52 H01M 4/32 H01M 4/62

Claims (2)

(57) [Claims] An active material powder comprising nickel hydroxide as a main component, a Co compound soluble in an alkaline electrolyte, and a thickener solution obtained by dissolving a thickener in water. The obtained slurry is filled in the pores of a porous current collector, and a paste-type nickel positive electrode obtained by drying and solidifying is stored in a battery can, and the alkaline electrolyte is poured into the battery can to form the Co compound. Is precipitated on the surface of the active material powder as β-Co (OH) ₂ , and then converted to β-Co (OH) ₂ by a chemical conversion treatment.
In alkaline secondary battery comprising a positive electrode comprising a three-dimensional network structure consisting of CoOOH is oxidized to form the porous inside of, as the Co compound, the average particle size 2μm or less of CoF ₂ powder, the CoF ₂ powder And 3 to 15% by weight based on the total amount of the active material powder and the alkaline material. 2. A method comprising kneading an active material powder containing nickel hydroxide as a main component, a Co compound soluble in an alkaline electrolyte, and a thickener solution obtained by dissolving a thickener in water. The obtained slurry is filled in the pores of a porous current collector, and a paste-type nickel positive electrode obtained by drying and solidifying is stored in a battery can, and the alkaline electrolyte is poured into the battery can to form the Co compound. Is precipitated on the surface of the active material powder as β-Co (OH) ₂ , and then converted to β-Co (OH) ₂ by a chemical conversion treatment.
In alkaline secondary battery comprising a positive electrode comprising a three-dimensional network structure consisting of CoOOH is oxidized to form the porous inside of, as the Co compound, the average particle size 2μm or less of CoF ₂ powder, the CoF ₂ powder And 8 to 12% by weight based on the total amount of the active material powder and the alkaline material.