JPS59165371A - Cathode plate for alkaline storage battery - Google Patents

Abstract

PURPOSE:To increase capacity in normal temperature use and suppress capacity drop in high temperature use by adding cobalt to the inside of a cathode active material in addition to the surface of the cathode active material. CONSTITUTION:A layer of cobalt hydroxide alone is formed on the surface of active material of a porous metal substrate holding the active material obtained by uniformly dispersing cobalt hydroxide in nickel hydroxide. 0.5-5wt% cobalt hydroxide to nickel hydroxide is dispersed. For example, a sintered nickel substrate is immersed in nitrate solution containing nickel nitrate and cobalt nitrate and having a specific gravity of 1.7, then nickel and cobalt are converted into hydroxides in alkaline solution, and they are washed and dried. This process is repeated several times to obtain desired filling amount. Then this substrate is immersed in a sp. gr. 1.4 cobalt nitrate solution and treated in alkaline solution, washed, and dried to form a cobalt layer on the surface of an active material. Thereby, a cathode plate having cobalt on its surface and in its inside is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an anode plate for an alkaline storage battery having a layer in which cobalt hydroxide exists alone on the surface of an active material.

←) Conventional & Technique The anode plate of conventional alkaline storage batteries is made by coating the core with a slurry mainly composed of carbonyl nickel powder, and sintering this in a reducing atmosphere to form a porous nickel substrate containing mainly nickel nitrate. It is manufactured by impregnating the substrate with an impregnating liquid as a component and then immersing it in an alkaline solution to convert nickel nitrate in the holes of the substrate into nickel hydroxide, which is an anode active material. However, the anode plates obtained in this way cannot meet recent market demands, and there is a need to develop an anode plate with a large plate capacity and a large volumetric energy density. As a result of experiments, the present inventors found that the utilization rate of the active material and the capacity of the electrode plate were improved by the presence of cobalt hydroxide alone on the surface layer of the active material. It has been found that an anode plate in which cobalt oxide is present alone has a lower capacity than a conventional plate when used at high temperatures.

(c) Purpose of the Invention In view of the above, the object of the present invention is to obtain an alkaline storage battery or battery that improves the condition when used at room temperature and suppresses the decrease in capacity when used at high temperatures. do.

B) Structure of the Invention The present invention provides that the living substance is a mixed crystal in which cobalt hydroxide is uniformly present in nickel hydroxide, and that cobalt hydroxide is formed on the surface of the active material of a porous metal substrate holding this active material. The present invention is an anode plate for an alkaline storage battery, which has a layer in which nickel hydroxide is present alone, and the amount of cobalt hydroxide in the surface layer of the active material is 0.5 to 5% by weight based on the nickel hydroxide.

(e) Examples Before presenting examples of the present invention, the appropriate amount and characteristics of cobalt hydroxide added to the surface layer of the active material and present alone will be explained based on experiments.

Experiment 1 An electrode plate with a utilization rate of 76% that held a nickel anode active material was attached to a sintered nickel substrate by a chemical impregnation method using an impregnating liquid mainly composed of nickel nitrate, and the content of nickel and cobalt was After being immersed for 5 minutes in a nitrate-impregnated solution with a specific gravity of 1.4, an anode plate was prepared by performing a full caustic treatment, washing with water, and drying, and using this plate, the utilization rate was measured. FIG. 1 shows the relationship between the composition of nickel and cobalt in the nitrate impregnation solution and the utilization rate. As is clear from the drawing, the higher the content of cobalt in the surface layer of the active material, the higher the utilization rate.The impregnating liquid composition has a cobalt content of at least 75%, preferably 100%, to achieve a high utilization rate. It can be seen that the following can be obtained.

Experiment 2 The same electrode plate as in Experiment 1 with a utilization rate of 76% was immersed in cobalt nitrate aqueous solutions with different specific gravity for 5 minutes, followed by alkali treatment, water washing, and drying to change the amount of cobalt added to the surface layer of the active material. An anode plate was prepared and the utilization rate was measured using this plate.

FIG. 2 shows the relationship between the cobalt addition rate (the ratio of cobalt hydroxide in the surface layer of the active material to nickel hydroxide in the active material) and the utilization rate. From Figure 2, there is no optimum value for the amount of cobalt added to the surface layer of the active material, and the amount of cobalt hydroxide added is 15 to 5.0% by weight of O to the nickel hydroxide of the active material. You can see the benefits that will increase the usage rate.

Experiment 6 An anode plate in which the amount of cobalt added to the surface layer of the active material was varied was obtained by the same operation as in Experiment 2, and the anode plate and cadmium cathode plate were wound together via a separator and inserted into an outer can, and then used as an electrolyte. A KOH solution was injected and the container was sealed to produce a battery having a nominal capacity of 1200 mAH. This battery was charged at 0.1C for 16 hours at 20"C and 60°C, and then discharged at room temperature at 10C to measure the capacity. Figure 6 shows the cobalt addition rate and the amount of cobalt added to the surface layer of the active material of the anode. , shows the relationship with the capacity calculated by the following formula.

Figure 6 shows that as the amount of cobalt added to the surface layer of the active material increases, the capacity ratio decreases, and as the amount of cobalt added to the surface layer of the active material increases, the capacity deterioration during 6U'C charging becomes more significant. .

Experiment 4 An anode plate obtained by immersing an electrode plate with a utilization rate of 76% similar to Experiment 1 in an aqueous cobalt nitrate solution with a specific gravity of 1.4 at room temperature for 5 minutes, followed by alkali treatment, washing with water, and drying. Using the electrode plates with a utilization rate of 76%, the same operations as in Experiment 6 were performed to create a battery with a nominal capacity of 1200 mAh. A battery in which cobalt was added to the surface layer of the anode active material prepared by the above process was designated as A, and a battery in which cobalt was not added to the surface layer of the anode active material was designated as B. Using these batteries A and B, the charging temperature was changed to 0. .Charged at 1C for 16 hours, then charged at room temperature for 10 hours.
The capacity was measured by discharging the battery. Figure 4 shows the relationship between charging temperature and capacity for City 1 Ponds A and B.

From Figure 4, battery A has a considerably higher capacity than battery B when the charging temperature is around 20°C, but when the charging temperature is around 40°C, battery A has a considerably higher capacity than battery B.
It can be seen that when the temperature exceeds °C, battery A has a lower capacity than battery B.

The present inventors added cobalt to the surface layer of the active material in order to suppress the deterioration of the high-temperature characteristics of the anode plate. Since we have found that this method is effective, we will explain it below using an example of a dormitory.

A sintered nickel substrate was immersed in a nitrate aqueous solution with a specific gravity of 1.7 in which the mixing ratio of nickel nitrate and cobalt nitrate was varied, and then nickel and cobalt were converted to hydroxide in an alkaline aqueous solution, and washed with water. After repeating the drying filling operation several times to obtain the desired filling amount, the specific gravity is further increased to 1.
．． The electrode plates were immersed in the aqueous cobalt nitrate solution of No. 4 for 5 minutes, then treated with alkali, washed with water, and dried to produce anode plates having a cobalt layer on the surface of the active material and different amounts of cobalt added inside the active material. The anode plate obtained in this way has cobalt hydroxide uniformly dispersed in nickel hydroxide inside the active material, and approximately 6% by weight of pure water on the surface of the active material, which is aligned with the nickel hydroxide of the active material. A cobalt oxide layer is formed. Using this anode plate, we measured the relationship between the addition rate of cobalt hydroxide to nickel hydroxide inside the active material of an anode plate having a cobalt layer on the surface of the active material and the utilization rate of the active material, and the results are shown in Figure 5. Shown below. Cobalt only inside the active material,
It is known that when added uniformly, the utilization rate of the active material improves as the amount of cobalt added increases, and the utilization rate reaches its maximum value when the amount added is about 10% by weight. However, as shown in FIG. 5, when cobalt is added alone to the surface of the active material, the effect of adding cobalt inside the active material is not seen at all; rather, as the amount of cobalt added inside the active material increases, The utilization rate of the active material decreases, especially when the amount of cobalt added inside the active material is 10% by weight or more.

Next, using the above-mentioned anode plate having a cobalt layer on the surface of the active material and cobalt added inside the active material, the same operation as in Experiment 4 was performed to obtain a nominal volume: It1200mA)i(7
) Create a N pond, o at 20℃ and 6o'c, 1 at 1C.
The battery was charged for 6 hours and then discharged at room temperature for 10 minutes to measure 1 stroke. FIG. 6 shows the relationship between the capacity and the addition ratio of cobalt hydroxide to nickel hydroxide inside the active material of an anode plate in which cobalt is added to the surface layer of the active material. @6 From Figure 6, when exposed to light at 20°C, the capacity is reduced compared to when no cobalt hydroxide is added inside the active material, but this is true for battery B, which did not have cobalt added to the surface of the active material shown in Experiment 4. Compared to,
Since the capacity of battery B when charged at 20°C is 1270 mAM, it is shown in Figure 6. The Li-pond shows a higher capacity than Battery B when the cobalt addition rate inside the active material is within 10% by weight. In addition, when charging at 60°C, the capacity starts from the capacity when no cobalt hydroxide is added inside the active material, and increases as the amount of cobalt hydroxide added inside the active material increases.
The capacity is maximized when the cobalt addition rate inside the active material is 6% to 9%. Compared to battery B shown in Experiment 4,
Since the capacity of Battery B at 5 hours after charging at 60°C is 8QQmAli, the battery shown in Figure 6 has a cobalt addition rate of 6% to 9% by weight inside the active material, and the capacity is almost the same as Battery B. There is.

(f) Effects of the Invention By adding cobalt to the surface of the positive electrode active material and also to the inside of the positive electrode active material, the present invention achieves a high capacity when used at room temperature compared to conventional batteries. This has the effect of providing an alkaline storage battery with the same capacity when used at high temperatures.

[Brief explanation of drawings]

Figure 1 shows the composition of nickel and cobalt in the surface layer of the active material,
Figure 2 shows the relationship between the cobalt addition rate in the surface layer of the active material and the utilization rate, and Figure 6 shows the relationship between the cobalt addition rate in the surface layer of the active material and the battery capacity rate. diagram showing,
Figure 4 shows the relationship between charging temperature and battery capacity, Figure 5 shows the relationship between the cobalt addition rate inside the active material and the utilization rate, and Figure 6 shows the relationship between the cobalt addition rate inside the active material and the battery capacity. FIG. 3 is a diagram showing the relationship with capacity. Figure 1 Figure 2 Cobalt fka O#ry, + Circle! ;11! ('vinegar

Claims (1)

[Claims] (11) The main active material is a mixed crystal in which cobalt hydroxide is uniformly present in nickel hydroxide, and the surface of the active material of the porous metal substrate holding this active material is coated with water. 1. An anode plate for an alkaline storage battery, comprising a layer in which cobalt oxide exists alone, and the amount of cobalt hydroxide in the surface layer of the active material is 0.5 to 5 times the weight of the nickel hydroxide. (2) The anode plate for an alkaline storage battery according to claim 1, wherein the amount of cobalt hydroxide in the nickel hydroxide is within 9% by weight based on the nickel hydroxide.