JP3116681B2 - Non-sintered nickel electrode and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-sintered nickel positive electrode used for an alkaline storage battery. An alkaline storage battery is provided.

[0002]

2. Description of the Related Art A typical positive electrode for an alkaline storage battery is a nickel oxide electrode. These electrodes are roughly classified into sintered electrodes and non-sintered electrodes. In the former, a nickel nitrate aqueous solution or the like is added to a microporous sintered substrate obtained by sintering nickel powder by an immersion method, and after drying, is converted into nickel hydroxide by immersing in a caustic alkali aqueous solution.
This is to obtain an electrode plate. This method is complicated,
There is a disadvantage that the packing density of nickel hydroxide as an active material is smaller than that of a non-sintered electrode described later. However, the electrode is characterized by excellent high-rate discharge characteristics, cycle life, and the like, and is widely used depending on the application. On the other hand, as a non-sintered electrode, there is an electrode manufacturing method called a pocket type in the past, and recently, a method of directly filling nickel hydroxide as an active material powder into a foamed nickel porous material has been put to practical use. According to the latter method, the method of manufacturing the electrode can be simplified, and a porous nickel foam having a high porosity can be obtained. However, the foamed nickel porous body is produced by electroplating, and has a disadvantage that the material cost is high. Therefore, non-sintered electrodes using inexpensive punching metal, expanded metal, or the like instead of the foamed nickel porous body as the electrode support have been developed. These electrode supports are
Since it does not have a three-dimensional structure such as a sintered substrate and a foamed nickel porous body, when used as an electrode, the holding power of the active material is poor, and during electrode fabrication or repeated charging and discharging In such cases, the active material is likely to fall off. Furthermore, since the electron conductivity in the thickness direction of the electrode is poor and the electrode characteristics are greatly reduced, it has not been put to practical use except for some electrodes.

[0003]

The above-mentioned electrode manufacturing method using a punching metal, an expanded metal or the like as an electrode support is based on a method in which an active material powder is formed into a paste with a solution of a polymer binder and a conductive powder. It has an advantage that an electrode can be easily manufactured by coating and drying on an electrode support. However, the adhesion between the porous metal body as an electrode support and the active material layer is weak, and when used as a battery electrode, the porous metal body and the active material layer are easily peeled off. As a result,
When the electrode support also serves as a current collector, the electrical resistance of the electrode increases, causing a reduction in discharge voltage and discharge capacity. If a large amount of binder is added to the active material layer in order to solve this problem, the peeling phenomenon is suppressed, but the reactivity of the active material is reduced, and the discharge characteristics are adversely affected.

In order to strengthen the adhesion between the porous metal body and the active material layer, a thermoplastic polymer resin layer serving as an adhesive is formed on the surface of the porous metal body, and the active material layer is formed on the upper layer. After the formation, the adhesion between the porous metal body and the active material layer can be improved by heating. However, an insulating layer is formed between the porous metal body and the active material layer, so that the current collecting property of the electrode is reduced and the reactivity of the electrode is hindered.

[0005]

According to the present invention, there is provided a non-sintered nickel positive electrode comprising: In the method, a conductive layer composed of a conductive powder having a particle diameter of 20 to 100 μm and a thermoplastic polymer binder was formed between the porous metal body and the electrode active material layer.

After the formation of the electrode active material layer, it is preferable to perform heat treatment by heating to a temperature higher than the melting point of the thermoplastic polymer binder. It is also preferable to form a conductive layer on the surface of the porous metal body, form an alkali-resistant metal plating layer on the conductive layer, and then form an electrode active material layer.

[0007]

With the above construction, a conductive layer is formed between the porous metal body and the electrode active material layer, and the conductive layer tends to be rougher than the surface of the porous metal body. Thus, the adhesion at the interface is improved and the electrode active material layer can be firmly bonded, as compared with the case where the electrode active material layer is formed directly on the surface of the porous metal body. As a result, not only is the processability of the electrode improved, but also when a battery is formed using the electrode and charged and discharged, the phenomenon of separation of the electrode support and the active material layer is suppressed, and the discharge voltage and discharge capacity are reduced. A battery with improved cycle life characteristics with improved reduction is obtained.

[0008] Further, after the electrode is formed, heat treatment is performed at a temperature higher than the softening point of the thermoplastic polymer binder used for forming the conductive layer, thereby promoting the action. Furthermore, by forming the alkali-resistant metal plating layer after forming the conductive layer on the surface of the porous metal body, the plating layer is formed with the surface maintaining the unevenness. When an electrode active material layer is formed on the upper layer, electron conductivity is further improved, and various characteristics of the battery can be improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) As shown in FIG. 1, an opening 1 having a hole diameter of 2 mmφ and a center pitch a of 2.5 mm was formed in an iron plate having a thickness of 0.1 mm. To produce punched metal. Using this punching metal, a conductive paint composed of a mixed solution of graphite powder and styrene-butadiene rubber (SBR) fine powder dispersed in water was applied to the non-opening portion 2 of the punching metal. Similarly, a conductive layer was formed using nickel powder or cobalt powder instead of graphite powder, or a mixture of graphite and nickel, graphite and cobalt, and nickel and cobalt at a weight ratio of 50% each. When forming these conductive layers, conductive powders having different particle diameters were used.

Next, for 100 g of nickel hydroxide powder, 10 g of graphite powder, 50 g of a 3 wt% aqueous solution of carboxymethyl cellulose (CMC), 5 g of a 48% dispersion of styrene-butadiene rubber (SBR), 5 g of cobalt powder ( 10 g of an average particle diameter of 1.5 μm) were mixed to form a paste. This paste was applied to both surfaces of the punched metal on which the conductive layer was formed, passed through a stainless steel slit, adjusted to a constant thickness, dried, and then pressed to form an electrode active material layer. The non-sintered nickel electrode obtained in this manner was put into a width of 38 mm and a length of 220 mm.
mm to obtain a positive electrode for a C2 cylindrical sealed battery. Summarizes the type and particle size range of the conductive powder used to form the conductive layer, the presence or absence of heat treatment, the theoretical electrochemical capacity calculated from the nickel hydroxide contained in the electrode, and the packing density calculated from the electrode volume The results are shown in Table 1.

[0012]

[Table 1]

The nickel electrodes a to p shown in Table 1 were combined with a known cadmium electrode and a non-woven fabric made of a polyamide resin to form C-type batteries A to P having a nominal capacity of 2.2 Ah. The electrolyte used was 6 ml of a 31 wt% aqueous solution of lithium hydroxide in which 30 g / l of lithium hydroxide was dissolved per cell.

The batteries A to P constructed under the above conditions are charged at 0.1 C for 15 hours, and after a 1-hour pause,
The battery was discharged until the battery voltage reached 1.0 V, and three cycles were repeated under these conditions. Then, under the same charging conditions, the discharge characteristics in the fourth cycle were set to 0.5 C and the discharge in the fifth cycle were set to 1 C, and the discharge characteristics were compared.

Table 2 shows the utilization calculated from the discharge at the third cycle (the theoretical capacity of the electrodes a to p shown in Table 1 is 100%).
), The discharge capacity ratio obtained from the discharges in the fourth and fifth cycles (the ratio when the discharge capacity in the third cycle is set to 100%).

After the sixth cycle, the charging / discharging current is set to 0.2 C, the charging time is 7 hours, and the discharging is 1.0 V
The cycle life characteristics were evaluated under the conditions described above. Table 3 shows the results.

[0017]

[Table 2]

[0018]

[Table 3]

From the results shown in Table 2, it can be seen that, by forming the conductive layer, the adhesion between the electrode active material layer and the porous metal body as the electrode support is improved, and the utilization rate of nickel hydroxide is improved. I understand. As shown in Table 1, an electrode capable of extracting a large discharge capacity was obtained despite the small amount of nickel hydroxide filled in the nickel positive electrode. The effect of the conductive layer is also recognized from Table 2 in which the high-rate discharge characteristics are compared. This is due to the fact that the electrical resistance of the electrode has been reduced due to the improved adhesion. Originally, it is considered that forming the electrode active material layer directly on the surface of the porous metal body reduces the electric resistance of the electrode. However, as in the present invention, the specific surface area of the contact surface is increased, and the adhesion is improved. It is considered that the contact resistance was reduced and the high rate discharge characteristics were improved.

On the other hand, from the results shown in Table 3, the battery A of the conventional example has a weak adhesion between the porous metal and the electrode active material layer. The active material layer peels off and gradually becomes unable to charge and discharge,
It is considered that the cycle life characteristics decreased. Also,
Since the cycle life of the battery B in which the conductive layer was formed with relatively fine powder was shortened, it is considered that the effect of improving the adhesion was small when the particle diameter was small. On the other hand, it has been found that the batteries C to F of the present invention can have a longer life than the batteries A and B, though the life characteristics are slightly different.

From the above results, the following can be considered. FIG. 2 is a schematic view of a cross section of the non-sintered nickel electrode obtained by the present invention. In the figure, 3 indicates a conductive layer, 4 indicates a punching metal, and 5 indicates an electrode active material layer. FIG. 2 (a)
FIG. 2B shows a case where a powder having a small particle diameter is used, and FIG. FIG. 2 (a), FIG.
2B, the conductive layer of FIG. 2A has a relatively smooth surface, and FIG. 2B has a rough surface. As a result, it is considered that the electrode active material layer was firmly bound, the peeling phenomenon was hard to occur, and a long-life battery was obtained. Therefore, in order to obtain a structure as shown in FIG.
It is effective to use a conductive powder of 0 to 100 μm. Further, in the battery G having a larger particle diameter, the bonding force between the porous metal body and the conductive layer was reduced, separation from the interface was recognized, and it was considered that the life was reduced, and the particle diameter of the conductive layer was 20 to 100 μm. It can be said that the effect of the present invention is remarkably exhibited by using the powder.

In the comparison of the batteries C and D, and the batteries E and F after the preparation of the electrodes with and without the heat treatment, in each case, the cycle life was improved by the heat treatment. From this result, it is considered that the adhesion between the conductive layer and the electrode active material layer was further improved, and it can be expected that the effect of the present invention can be promoted by performing the heat treatment.

The effects are also observed in batteries HM using nickel or cobalt in addition to carbon as the conductive powder, and the effects of the present invention can be obtained if the conductive powder is alkali-resistant. Conceivable.

Further, in the batteries N, O and P in which a conductive layer was formed by mixing carbon and nickel, carbon and cobalt, and nickel and cobalt by 50% by weight, the results shown in Tables 2 and 3 were obtained. Thus, the effect of the present invention is recognized,
It has been found that even when two kinds of conductive powders are mixed, it is effective. From this, it can be expected that a similar effect is observed when three types are mixed.

In the examples, punched metal was used as the metal porous body. However, the same applies to the case where an electrode is manufactured using expanded metal, a foamed nickel porous body having an average hole diameter of 1 to 2 mm, and the like. The effect of the present invention was recognized, and it was found that the effect of the present invention can be exerted even with a porous metal body other than the punching metal.

Example 2 Using a punching metal similar to the porous metal shown in Example 1 and an iron punching metal not subjected to nickel plating, graphite powder of 20 to 50 μm and styrene-butadiene rubber (SBR) were used. A) a conductive paint composed of a mixture of fine powders dispersed in water was applied to the non-opening portions of the punching metal. Similarly, conductive layers of nickel and cobalt were formed as conductive powder. Next, nickel electroplating was performed on the surface of the porous metal body on which these conductive layers were formed to form an electrode active material layer mainly composed of the nickel hydroxide powder shown in Example 1. The thus obtained non-sintered nickel electrode q ~
Table 4 shows the conditions for preparing v, the theoretical capacity, and the like.

[0027]

[Table 4]

Using nickel electrodes q to v shown in Table 4, single-type cylindrical sealed batteries Q to V were produced in the same manner as in Example 1, and the battery characteristics were examined. Table 5 shows the results of the comparison of the discharge characteristics, and Table 6 shows the results of the cycle life test.

[0029]

[Table 5]

[0030]

[Table 6]

The battery C of Table 2 shown in Example 1 was obtained by forming a conductive layer and then directly forming an electrode active material layer on the conductive layer. The battery Q of Table 5 was formed of a conductive layer and an electrode active material layer. The interface has a nickel plating layer. Comparing the high-rate discharge characteristics of both batteries, the discharge capacity at 1C of battery Q was increased. Similarly, in comparison between Battery I and Battery R, and between Battery L and Battery S, it was found that the high-rate discharge characteristics of Nickel-Plated Battery R and Battery S were improved. Furthermore, in the comparison of Tables 3 and 6 showing the results of examining the cycle life, no significant change was observed, and good results were shown. From these results, it can be said that the nickel plating has an effect on the high-rate discharge characteristics, and thus does not cause a decrease in the cycle life characteristics. On the other hand, the electrodes t to v in Table 4 are obtained by directly forming a conductive layer on a porous metal body made of iron in which nickel plating is not applied to a punching metal. Usually, if iron is exposed on the surface, it oxidizes during storage or electrochemically oxidizes when used as a nickel positive electrode. To prevent this, nickel plating is performed. However, as in the present invention, it is considered that there is an effect of rust prevention by coating with a conductive layer and further performing nickel plating thereon, and the batteries T to T using the electrodes t to v are used.
V was produced and its effect was examined. As shown in the test results in Tables 4 and 5, it was found that the batteries exhibited high-rate discharge characteristics and cycle life characteristics comparable to those of batteries Q to S obtained from electrodes using ordinary punching metal. . Therefore, if the electrodes t to v are used, nickel plating is performed after the formation of the conductive layer, and the nickel plating at the time of forming the punched metal can be omitted, which should not lead to an increase in cost.

In the second embodiment, carbon particles having a particle diameter of 20 to 50 μm and nickel and cobalt having a particle diameter of 20 to 100 μm are shown as the conductive powder.
As a result, a result similar to that in Example 1 was obtained as a result of comparison in the case of less than 20 μm and in the case of exceeding 100 μm.
The range of μm is considered optimal. Further, in Example 2, the result of performing nickel plating on the upper layer portion on which the conductive layer was formed was shown. However, when plating with cobalt, the same effect can be obtained even when performing alloy plating of cobalt and nickel. It has been found that any alkali-resistant metal plating layer may be used. Further, similar effects were also observed in expanded metal instead of punched metal, and it was found that the same can be applied to the present invention.

[0033]

As described above, according to the present invention,
Without using a relatively expensive sintered sintered nickel electrode substrate and foamed nickel porous nickel foam,
An inexpensive metal porous body can be used as an electrode support, and the phenomenon of peeling of the electrode support and the electrode active material layer that occurs in this case can be suppressed, and a long-life battery can be formed, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a punching metal which is a kind of a porous metal used in the present invention.

FIG. 2 is a schematic view of an electrode cross section of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Opening 2 No opening 3 Conductive layer 4 Punching metal 5 Electrode active material layer

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Yanagihara 1006 Kazuma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-58-25081 (JP, A) JP-A-63- 19762 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/24-4/32

Claims (10)

(57) [Claims] 2. The method according to claim 1, wherein the particle diameter is 20 to 10 on the surface of the porous metal body.
A non-sintered nickel electrode comprising a conductive layer made of a conductive powder of 0 μm and a thermoplastic polymer binder formed thereon, and an electrode active material layer formed thereon. 2. The non-sintered nickel electrode according to claim 1, wherein the conductive powder is one kind or a mixture of two or more kinds selected from carbon, nickel and cobalt. 3. The non-sintered nickel electrode according to claim 1, wherein the metal porous body is one selected from punched metal, expanded metal, and foamed metal porous body. 4. The non-sintered nickel electrode according to claim 1, wherein an alkali-resistant metal plating layer is provided between the conductive layer and the electrode active material layer. 5. A particle size of 20 to 10 on the surface of a porous metal body.
After forming a conductive layer made of a 0 μm conductive powder and a thermoplastic polymer binder, an electrode active material layer is formed thereon, and heat treatment is performed at a temperature equal to or higher than the softening point of the thermoplastic polymer binder. A method for producing a non-sintered nickel electrode. 6. A particle size of 20 to 10 on the surface of a porous metal body.
After forming a conductive layer composed of a conductive powder of 0 μm and a thermoplastic polymer binder, an alkali-resistant metal plating layer is formed on the conductive layer, and then an electrode active material layer is formed. Manufacturing method of sintered nickel electrode. 7. The method for producing a non-sintered nickel electrode according to claim 5, wherein the conductive powder is one kind or a mixture of two or more kinds selected from carbon, nickel and cobalt. . 8. The method for producing a non-sintered nickel electrode according to claim 5, wherein the metal porous body is one selected from a punching metal, an expanded metal, and a foamed metal porous body. 9. The method for producing a non-sintered nickel electrode according to claim 6, wherein the material of the porous metal body is a punching metal or an expanded metal made of iron. 10. The method for producing a non-sintered nickel electrode according to claim 6, wherein the alkali-resistant metal plating layer is a nickel plating layer.