JP2853414B2 - Paste type cadmium negative electrode and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paste type cadmium negative electrode used for a nickel cadmium storage battery or the like.

[0002]

2. Description of the Related Art A paste-type cadmium negative electrode for an alkaline storage battery generally comprises a cadmium oxide powder or a cadmium hydroxide powder, a conductive powder such as carbonyl nickel and graphite, a binder such as polyvinyl alcohol and carboxymethyl cellulose. It is manufactured by adding a solvent such as water or ethylene glycol and kneading to form a paste, applying it to a conductive core such as a nickel-plated apertured steel sheet, drying and then forming it in an alkaline solution. Is common. The purpose of the chemical conversion step is to convert a part or all of a cadmium compound in a discharged state, such as cadmium oxide and cadmium hydroxide used as an active material, into a metal cadmium in a charged state, and to provide a precharged portion in the negative electrode. It is in. If the precharged portion does not exist in the negative electrode, the negative electrode has a lower utilization factor than the positive electrode, so that the discharge is dominated by the negative electrode and the high-rate discharge characteristics of the battery deteriorate.
In addition, since the negative electrode undergoes complete discharge, the charge / discharge cycle characteristics of the battery deteriorate significantly. For these reasons, formation is performed as one of the methods for providing a pre-charged portion.
In this chemical conversion step, 20 to 100% of the capacity of the negative electrode is charged, and the electric power required for charging is large. In addition, it is not easy to uniformly form charged metal cadmium in the electrode in the formation step, and characteristics are likely to vary. In order to solve such a problem, Japanese Patent Publication No. 57-37986 has been proposed.
As disclosed in Japanese Patent Application Publication No. 57-5265, a method has been proposed in which an active metal cadmium powder is added at the time of kneading the active material powder in an amount equivalent to the preliminary charge amount, thereby eliminating the need for a chemical conversion step.

[0003]

However, in the paste-type cadmium negative electrode manufactured by the above method, the physical contact between the metal cadmium powders is weak at the initial stage after the construction of the battery, and a sufficient conductive matrix is formed. Therefore, there was a phenomenon that the charge and discharge characteristics were inferior to those of a cadmium negative electrode having a chemical conversion step. In general, a paste-type cadmium negative electrode has a low strength of an electrode plate and a reinforcing material and a binder are added in order to increase the strength, but these are one of the causes of lowering the capacity density. An object of the present invention is to solve the above problems and to provide a high-performance paste-type cadmium negative electrode that does not require a chemical conversion step.

[0004]

In order to achieve this object, the paste-type cadmium negative electrode of the present invention is obtained by applying an active material mainly composed of metal cadmium powder and cadmium oxide powder on a conductive core and drying it. The paste-type cadmium negative electrode is characterized in that the metal cadmium powders are partially fused together to form a conductive network skeleton of the metal cadmium powder. In addition, the method for producing a paste-type cadmium negative electrode of the present invention is characterized in that, in order to produce the paste-type cadmium negative electrode, an active material mainly composed of metal cadmium powder and cadmium oxide powder is coated on a conductive core and dried. By heating in an inert gas atmosphere, the metal cadmium powder is partially fused to form a conductive network skeleton of the metal cadmium powder.

[0005]

After coating and drying an active material mainly composed of metal cadmium powder and cadmium oxide powder on a conductive core, the melting point of the metal cadmium is 32 in an inert gas atmosphere.
By heating at a temperature of 0 ° C. or less, the metal cadmium powder is easily partially fused with each other, and the sublimation temperature is 700 ° C.
Cadmium oxide powder at 0 ° C. does not change. Therefore,
The metal cadmium powder that has only been in physical contact is bonded in a network to form a uniform conductive network, thereby improving the utilization rate of the cadmium active material. In addition, this network can increase the holding power of the active material and increase the electrode plate strength.

[0006]

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

Cadmium oxide powder having an average particle diameter of 1 μm and metal cadmium powder having an average particle diameter of 10 μm are in a weight ratio of 60: 4.
After mixing at a ratio of 0 and kneading with an ethylene glycol solution of polyvinyl alcohol to form a paste, this was applied to a nickel-plated apertured steel sheet, dried and then heated at 300 ° C. for 10 minutes in an inert gas atmosphere. The electrode plate was about 0.5 mm thick.

Next, the coated plate is put at a specific gravity of 1.20 and a temperature of 2
It was immersed in a KOH aqueous solution at 0 ° C. for 15 minutes to convert a part of cadmium oxide in the electrode plate into cadmium hydroxide, and then washed and dried. This electrode plate is referred to as a.

Next, as a comparative example, after the coating and drying,
An electrode plate was obtained by alkali treatment without heat treatment. This electrode plate is referred to as b.

These cadmium negative electrodes a and b are combined with a sintered nickel positive electrode to produce prototypes of sealed storage batteries A and B equivalent to 600 mAh, and a discharge rate characteristic test for evaluating the discharge characteristics of the negative electrodes, A battery internal pressure test for evaluating the oxygen gas absorption performance and a measurement of the falling rate of the negative electrode active material after winding were performed. The discharge characteristics were evaluated by the ratio of the discharge capacity when discharged at various rates after the battery was charged to the discharge capacity when discharged at a current equivalent to 0.2 C. The internal pressure of the battery at the time of overcharging was evaluated by a peak value at the time of overcharging at 20 ° C with a current equivalent to 1 to 3C. The falling rate of the negative electrode active material was evaluated from the weight of the negative electrode before winding and the weight of the negative electrode after winding.

FIG. 1 shows the relationship between the discharge rate and the discharge capacity ratio. Curves A and B in the figure show the characteristics of the battery using the negative electrodes a and b, respectively. The negative electrode a in which a uniform conductive network is formed in the electrode plate has good discharge characteristics, The negative electrode b has an insufficient conductive network, and has a deteriorated discharge characteristic.

FIG. 2 shows the relationship between the charging rate and the peak value of the battery internal pressure. Curves A and B in the figure show the characteristics of the battery using the negative electrodes a and b, respectively, and the battery using the negative electrode b has a higher internal pressure than the battery using the negative electrode a. This is presumably because the conductive network between the electrode plate surface and the core material is not sufficiently formed, and the gas absorption reaction on the electrode plate surface is not sufficiently performed.

Next, in order to obtain appropriate conditions for the temperature and time in the heat treatment of the electrode plate, a trial production was conducted by changing the heat treatment conditions in the same manner as in the preparation of the electrode plate a. The characteristics of the electrode plate were evaluated based on the falling rate of the negative electrode active material and the discharge characteristics of the battery.

FIG. 3 shows the relationship between the heating temperature and the falling rate of the negative electrode active material when the heating time is fixed at 10 minutes. Similarly, FIG. 4 shows the relationship between the heating temperature and the discharge characteristics of the battery. Heating temperature is 280 ℃
If it is less than 5, the metal cadmium is not sufficiently partially fused, so that the formation of the conductive matrix is insufficient. Therefore, the electrode plate strength is low and the discharge characteristics are deteriorated.
On the other hand, when the temperature exceeds 320 ° C., the metal cadmium powder is partially fused, and then the entire metal cadmium powder is melted and agglomerated. Therefore, both the electrode strength and the discharge characteristics are deteriorated.

FIG. 5 shows the relationship between the heating time and the falling rate of the negative electrode active material when the heating temperature is fixed at 300 ° C. Similarly, FIG. 6 shows the relationship between the heating time and the discharge characteristics of the battery. If the heating time is less than 10 minutes, the formation of the conductive matrix by partial fusion of the metal cadmium powders is insufficient. to degrade.

Next, in order to determine an appropriate mixing ratio of the metal cadmium powder, a trial production was performed by changing the mixing ratio of the cadmium oxide powder and the metal cadmium powder. The characteristics of the electrode plate are
The evaluation was performed based on the falling rate of the negative electrode active material.

FIG. 7 shows the weight ratio of metal cadmium in the active material and the falling rate of the negative electrode active material. If the weight ratio is less than 30%, partial fusion of metal cadmium is less likely to occur, and no improvement in electrode strength is observed. In general, a cadmium negative electrode generates hydrogen gas when fully charged. Since this hydrogen gas cannot be consumed in the battery, the negative electrode capacity is set to be larger than the positive electrode capacity so that the negative electrode is not fully charged. For this reason, when the weight ratio exceeds 50%, it is disadvantageous in battery design. Therefore, it is considered that an appropriate weight ratio of metal cadmium in the active material is 30 to 50%.

[0018]

As described above, according to the present invention, an active material mainly composed of a cadmium metal powder and a cadmium oxide powder is coated on a conductive core and dried, and then the cadmium metal is removed in an inert gas atmosphere. By heating at a temperature of 320 ° C. or less, which is the melting point, a uniform conductive network is formed because of easy partial fusion, and an excellent paste-type cadmium negative electrode can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a discharge rate and a discharge capacity ratio.

FIG. 2 is a diagram showing a relationship between a charging rate and a battery internal pressure.

FIG. 3 is a diagram showing a relationship between a heating temperature and an active material falling rate.

FIG. 4 is a diagram showing a relationship between a heating temperature and a discharge capacity ratio.

FIG. 5 is a diagram showing a relationship between a heating time and an active material falling rate.

FIG. 6 is a diagram showing a relationship between a heating time and a discharge capacity ratio.

FIG. 7 is a diagram showing the relationship between the weight ratio of metal cadmium in the active material and the falling rate of the negative electrode active material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-47067 (JP, A) JP-A-58-16467 (JP, A) JP-A-54-50843 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01M 4/24 H01M 4/26

Claims (4)

(57) [Claims] 1. A paste-type cadmium negative electrode obtained by applying and drying an active material mainly composed of cadmium metal powder and cadmium oxide powder on a conductive core, wherein the metal cadmium powder is partially fused to each other to form a metal cadmium powder. A paste-type cadmium negative electrode, wherein the conductive network skeleton is formed. 2. An active material mainly composed of a metal cadmium powder and a cadmium oxide powder is coated on a conductive core and dried, and then heated in an inert gas atmosphere to partially fuse the metal cadmium powder. And forming a conductive network skeleton of the metal cadmium powder. 3. The method according to claim 2, wherein the ratio of the metal cadmium powder in the active material is 30 to 50% by weight. 4. The heating method according to claim 2, wherein a heating temperature in the step of partially fusing the metal cadmium powder is in a range of 280 to 320 ° C., and a heating time is in a range of 10 to 15 minutes. Manufacturing method.