JPH11307116A - Cadmium negative electrode for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxygen gas absorbing performance improving effect by virtue of carbon coating while restraining harmful influence of the carbon coating. SOLUTION: A carbon aqueous solution in which 1.00 pts.wt. of polytetrafluoroethylene(PTFE) as a binder and 3.00 pts.wt. of acetylene black as carbon powder are dissolved is applied to the surface of an outermost peripheral part 11 to become the outermost periphery when a base negative electrode 10 and a positive electrode is spirally wound with a separator in between. If carbon in an amount of 0.005-0.6 mg/cm<2> is stuck on both surfaces of the outermost peripheral part 11 by the coating of the carbon aqueous solution, an oxygen gas absorbing performance improving effect can be provided while restraining harmful influence of the carbon coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a cadmium negative electrode used for a nickel-cadmium storage battery has a sintering method in which a porous sintered substrate formed by sintering nickel powder is filled with a negative electrode active material made of cadmium oxide or cadmium hydroxide. A negative electrode,
There is a non-sintered negative electrode in which a negative electrode active material made of cadmium oxide or cadmium hydroxide is kneaded with a synthetic fiber, a paste, or the like, and applied as a paste to a conductive core (substrate) such as a punched metal.

In recent years, demands for higher capacity, higher current charge / discharge characteristics, and longer life of alkaline storage batteries have been increased, and various improvements have been made to meet these demands. For example, for higher capacity, increasing the packing density of the active material,
Alternatively, the purpose has been achieved by reducing the thickness of the separator for separating the positive and negative electrodes.

However, when the active material is filled at a high density to increase the capacity, a space (remaining space) for holding the electrolytic solution in the electrode is occupied by the active material and must be held in the electrode. The amount of electrolyte will be reduced. For this reason, the amount of active material in contact with the electrolyte decreases, making it difficult for the charge-discharge reaction at the negative electrode to proceed smoothly.As the charge-discharge cycle progresses, metal cadmium that cannot be discharged is accumulated. Become.

[0005] As a result, problems such as deterioration of oxygen gas absorption performance or deterioration of charge / discharge characteristics due to reduction of the active material utilization rate occur. Therefore, both requirements for high capacity and large current charge / discharge characteristics are required. Is very difficult to satisfy.

Therefore, as a method for improving the oxygen gas absorption performance of a cadmium negative electrode, Japanese Patent Publication No. 2-50585 proposes to provide a conductive layer of carbon by coating carbon on the entire surface of the cadmium negative electrode. In the method proposed in Japanese Patent Publication No. 50585/1990, the conductivity of the cadmium negative electrode surface is improved, so that the electric gas absorption reaction can be promoted, and the gas pressure inside the battery is reduced. , And the life of the battery can be prolonged.

[0007]

However, in the method proposed in Japanese Patent Publication No. 50585/1990, since carbon is applied to the entire surface of the cadmium negative electrode, it is charged at a high rate (high rate). -When the discharge is performed, the carbon film inhibits a chemical reaction on the surface of the cadmium negative electrode and generates an overvoltage. For this reason, the charging voltage increases,
There is a risk that the discharge voltage will drop.

When a large amount of carbon is applied, the carbon reacts with oxygen generated at the time of charging to form a carbonate group,
There is also a problem that the concentration of the electrolytic solution is reduced by dissolving in the alkaline electrolytic solution, and eventually the battery capacity is reduced. Conversely, if a small amount of carbon is applied to the entire surface of the cadmium negative electrode in order to avoid such adverse effects, the carbon concentration on the cadmium negative electrode surface will be low, so that the effect of improving the conductivity will be weakened and oxygen gas This causes a problem that the absorption reaction is not promoted.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to suppress oxygen gas absorption by carbon coating while suppressing the adverse effects of carbon coating. It is an object of the present invention to obtain a performance improving effect. For this reason, the cadmium negative electrode for an alkaline storage battery of the present invention is arranged such that the cadmium negative electrode is located at the outermost peripheral portion of the spirally wound spiral electrode body, and a portion located at the outermost peripheral portion of the cadmium negative electrode. Has carbon coated.

When the cadmium negative electrode is disposed at the outermost periphery of the spirally wound spiral electrode body, only one surface of the cadmium negative electrode at the outermost periphery is opposed to the positive electrode. Therefore, during charging, the amount of active material (reaction amount) at which the cadmium negative electrode at the outermost periphery reacts with the positive electrode opposite to the cadmium negative electrode at the outermost periphery is reduced to about half as compared with the cadmium negative electrode at the inner peripheral portion. Metal cadmium content is also reduced. Therefore, in the present invention, carbon is applied only to the cadmium negative electrode disposed at the outermost periphery of the spiral electrode body.

As described above, if carbon is applied only to the portion disposed on the outermost peripheral portion of the cadmium negative electrode, the conductivity of this portion is improved, the charging reaction is promoted, and the amount of generated metal cadmium is reduced. Increase. Therefore, contact between the metal cadmium and oxygen gas in this portion is facilitated, and the oxygen gas absorption performance is improved. In other words, instead of applying carbon to the entire cadmium negative electrode, the carbon is applied only to the portion located at the outermost peripheral portion when it is spirally wound, so that the carbon film is applied to the cadmium negative electrode at the inner peripheral portion. Therefore, when charging / discharging is performed at a high rate (high rate), the carbon film does not hinder the reaction, and overvoltage does not occur. Even if carbon is not applied to the cadmium negative electrode on the inner periphery, this part is opposed to the positive electrode on both sides, so sufficient metal cadmium necessary for gas absorption is generated, and the gas absorption function is secured. it can.

[0012] Even when carbon is applied only to the outermost portion of the cadmium negative electrode,
If the amount of carbon applied is too large, this carbon reacts with the oxygen generated during charging to form a carbonate group, which dissolves in the alkaline electrolyte to cause a decrease in the concentration of the electrolyte, and eventually lowers the battery capacity. However, the amount of carbon applied is 0.005 to 0.6 mg per unit area (cm ² ).
By doing so, it is possible to prevent a decrease in battery capacity. Even with such a small amount of carbon, by applying only to the portion arranged at the outermost peripheral portion of the spirally wound spiral electrode body of the cadmium negative electrode, a reduction in carbon concentration is suppressed, The conductivity can be maintained and the oxygen gas absorption reaction can be promoted.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in the following order.

1. Preparation of Cadmium Negative Electrode First, after forming a nickel sintered porous body (porosity 80%) on the surface of an electrode core made of punched metal, a predetermined amount of a cadmium active material was introduced into the nickel sintered porous body by a chemical impregnation method. Fill. That is, by repeating the process of impregnating the nickel sintered porous body with cadmium nitrate and then performing alkali treatment to generate cadmium hydroxide several times, a predetermined amount of cadmium active material (mainly cadmium hydroxide) The negative electrode active material) is filled in the nickel sintered porous body. Next, the electrode filled with the active material is placed in an alkaline aqueous solution (for example, potassium hydroxide aqueous solution (KOH)).
After being placed inside and being formed by performing charge and discharge, it is washed with water and dried to form the base negative electrode 10.

Embodiment 1 When the base negative electrode 10 is spirally wound through a positive electrode (not shown) and a separator, the surface of the outermost peripheral portion 11 which is the outermost periphery of the spiral electrode body is exposed to 100 parts by weight of water. Polytetrafluoroethylene (PTFE) as binder
An aqueous carbon solution in which 1.00 parts by weight and 3.00 parts by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as carbon powder are applied is applied. By applying the carbon aqueous solution, 0.03 mg / cm ² of carbon per unit area adheres to both surfaces of the outermost peripheral portion 11. Thereafter, drying is performed to produce the negative electrode a of Example 1.

COMPARATIVE EXAMPLE 1 Water 10 was applied to all surfaces 11 and 12 of base anode 10 described above.
An aqueous solution in which 1.00 part by weight of polytetrafluoroethylene (PTFE) as a binder is dispersed with respect to 0 part by weight is applied. The negative electrode without carbon was dried to prepare a negative electrode b of Comparative Example 1.

Comparative Example 2 Water 10 was applied to all surfaces 11 and 12 of base anode 10 described above.
Carbon in which 1.00 part by weight of polytetrafluoroethylene (PTFE) as a binder and 3.00 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Kogyo) are dissolved in 0 parts by weight. Apply the aqueous solution. By applying the carbon aqueous solution, 0.03 mg / c per unit area is applied to both surfaces of the base negative electrode 10.
carbon m ² is attached. After that, it was dried to obtain Comparative Example 2.
To produce the negative electrode c.

Comparative Example 3 An inner peripheral portion 12 serving as an inner periphery when the above-described base negative electrode 10 is spirally wound through a positive electrode (not shown) and a separator.
1.00 parts by weight of polytetrafluoroethylene (PTFE) as a binder and 3.00 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Kogyo Co.) as a carbon powder with respect to 100 parts by weight of water. Is applied with a carbon aqueous solution in which is dissolved. Due to the application of the carbon aqueous solution, 0.03 per unit area
mg / cm ² of carbon adheres. Thereafter, drying is performed to produce a negative electrode d of Comparative Example 3.

4. Production of Sealed Nickel-Cadmium Storage Battery A predetermined amount of preliminary charge (precharge) was given to the four kinds of cadmium negative electrodes a, b, c, and d produced as described above by partial charge, and thus precharge was given. A cadmium negative electrode and a sintered nickel positive electrode plate are wound so as to face each other with a nylon nonwoven fabric separator interposed therebetween to form four kinds of spiral electrode bodies, and these four kinds of spiral electrode bodies are respectively placed in an outer can. After the insertion, a 30% by weight aqueous solution of potassium hydroxide (KOH) was injected and sealed.
Four types of nickel-cadmium storage batteries (with a nominal capacity of 1700 mAh) of (Example 1), Battery B (Comparative Example 1), Battery C (Comparative Example 2), and Battery D (Comparative Example 3) were produced.

[5] Internal Pressure Rise Test Next, using the four types of nickel-cadmium storage batteries A, B, C, and D prepared as described above, charging was performed at room temperature (25 ° C.) at a current of 9 A, and the peak voltage was exceeded. Thereafter, when the voltage was reduced by 10 mV, the voltage was cut (-delta V method), and the internal pressure of the battery at the peak voltage was measured. The result was as shown in Table 1 below.

[0021]

[Table 1]

As is clear from Table 1, in the battery using the cadmium negative electrode not coated with carbon, such as the battery B (Comparative Example 1), the internal pressure of the battery is very high.
In a battery using a cadmium negative electrode coated with carbon, such as Battery A (Example 1), Battery C (Comparative Example 2), and Battery D (Comparative Example 3), the internal pressure of the battery decreases. However,
In the battery D (Comparative Example 3), since only the inner peripheral portion 12 where sufficient metal cadmium necessary for gas absorption is generated is coated with carbon, the effect of reducing the increase in internal pressure is small.

On the other hand, in the battery using a cadmium negative electrode in which carbon is applied only to the outermost peripheral portion 11 which is the outermost periphery when the spiral electrode body is used as in the battery A (Example 1), the positive electrode In order to improve the conductivity of the outermost peripheral portion 11 where only one side is opposed to the other, a sufficient amount of metal cadmium necessary for gas absorption is generated, and a battery C in which carbon is coated on the entire cadmium negative electrode (Comparative Example 2) It can be seen that the effect of reducing the increase in the internal pressure, which is almost the same as that of (1) is obtained.

6. Cycle Test Next, using the four types of nickel-cadmium storage batteries A, B, C, and D prepared as described above, charging was performed at room temperature (25 ° C.) at a current of 9 A, and after exceeding the peak voltage. When the voltage drops by 10 mV, the voltage is cut (-Delta V method), and after charging is suspended for one hour, 1
Discharge is performed at a current of 5 A until the battery voltage becomes 0.8 V. Thereafter, after performing a cycle test in which the discharge was suspended for 1 hour and then charging was performed again under the same conditions as above, FIG.
The result was as shown in the figure. FIG. 2 shows the battery capacity with respect to the number of charge / discharge cycles.

As is clear from FIG. 2, the battery capacity of the battery B (Comparative Example 1), the battery C (Comparative Example 2), and the battery D (Comparative Example 3) are deteriorated. This is because the battery B (Comparative Example 1) uses a cadmium negative electrode to which carbon was not applied, and the internal pressure of the battery increased due to poor gas absorption performance, and the safety valve was activated. It is considered that the electrolytic solution inside the battery was discharged outside the battery and the battery capacity was reduced.

A battery C (Comparative Example 2) in which high-concentration carbon was coated on the entire cadmium negative electrode and a battery D (Comparative Example) in which high-concentration carbon was coated on the inner peripheral portion 12 of the spiral electrode body of the cadmium negative electrode In Example 3), oxygen gas generated at the time of charging reacts with carbon to form a carbonate, and this carbonate dissolves in the alkaline electrolyte to cause a decrease in the concentration of the electrolyte, resulting in deterioration of the battery capacity. Conceivable.

On the other hand, it can be seen that the battery A (Example 1) has no deterioration in battery capacity due to the charge / discharge cycle. this is,
When a cadmium negative electrode in which carbon is applied to the outermost peripheral portion 11 which is the outermost periphery when a spiral electrode body is used as in the battery A (Example 1), the amount of carbon applied as the entire cadmium negative electrode decreases. Therefore, it is considered that the reaction between oxygen gas and carbon generated at the time of charging is reduced, and the amount of carbonate groups generated is small, so that the capacity is not deteriorated.

7. Example 2 Examination of carbon coating amount Example 2 When water is spirally wound through a positive electrode (not shown) of the above-described base negative electrode 10 and a separator, water 100 is applied to the surface of outermost peripheral portion 11 which is the outermost periphery of the spiral electrode body. Polytetrafluoroethylene (PTF) as a binder for parts by weight
E) An aqueous carbon solution in which 1.00 part by weight and 0.3 part by weight of acetylene black as carbon powder (manufactured by Denki Kagaku Kogyo Co., Ltd .: Denka Black) is dissolved is applied. Due to the application of the carbon aqueous solution, 0.003 mg / cm ² of carbon per unit area adheres to both surfaces of the outermost peripheral portion 11. Thereafter, drying is performed to produce the negative electrode e of Example 2.

Example 3 When the above-described base negative electrode 10 is spirally wound with a positive electrode (not shown) and a separator, both surfaces of the outermost peripheral portion 11 which is the outermost periphery of the spiral electrode body are provided with 100 parts by weight of water. Against polytetrafluoroethylene (PTF) as a binder
E) An aqueous carbon solution in which 1.00 part by weight and 0.5 part by weight of acetylene black as a carbon powder (manufactured by Denki Kagaku Kogyo Co., Ltd .: Denka Black) is dissolved is applied. Due to the application of the aqueous carbon solution, 0.005 mg / cm ² of carbon per unit area adheres to both surfaces of the outermost peripheral portion 11. Thereafter, drying is performed to produce the negative electrode f of Example 3.

Embodiment 4 When the above-mentioned base negative electrode 10 is spirally wound with a positive electrode (not shown) and a separator, both surfaces of an outermost peripheral portion 11 which is the outermost periphery of the spiral electrode body are provided with 100 parts by weight of water. Against polytetrafluoroethylene (PTF) as a binder
E) A carbon aqueous solution in which 1.00 parts by weight and 60 parts by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Kogyo Co., Ltd.) as a carbon powder is applied is applied. Due to the application of the aqueous carbon solution, 0.6 mg / cm ² of carbon per unit area adheres to both surfaces of the outermost peripheral portion 11.
Thereafter, drying is performed to produce the negative electrode g of Example 4.

Embodiment 5 When the above-described base negative electrode 10 is spirally wound with a positive electrode (not shown) and a separator, both surfaces of the outermost peripheral portion 11 which is the outermost periphery of the spiral electrode body are provided with 100 parts by weight of water. Against polytetrafluoroethylene (PTF) as a binder
E) An aqueous carbon solution in which 1.00 part by weight and 100 parts by weight of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) as carbon powder are applied is applied. By applying the aqueous carbon solution, 1 mg / cm ² of carbon per unit area adheres to both surfaces of the outermost peripheral portion 11. Thereafter, drying is performed to produce the negative electrode h of Example 5.

Then, e,
A predetermined amount of precharge (precharge) is performed by partially charging the four types of cadmium negative electrodes f, g, and h, and the thus precharged cadmium negative electrode and the sintered nickel positive plate are separated by a nylon nonwoven fabric separator. After being wound so as to face each other with the electrodes interposed therebetween, four types of electrode bodies were inserted into the outer can.
Aqueous potassium hydroxide solution (KOH) was injected and sealed, and batteries E (Example 2), F (Example 3), and G
(Example 4) Four types of nickel-cadmium storage batteries (having a nominal capacity of 1700 mAh) of a battery H (Example 5) were produced.

Next, E,
Using four types of nickel-cadmium storage batteries of F, G, and H, charging was performed at room temperature (25 ° C.) with a current of 9 A, and after the peak voltage was exceeded, the voltage was cut when the voltage dropped by 10 mV ( Then, when the internal pressure of the battery at the peak voltage was measured, the results shown in Table 2 below were obtained. In Table 2, the above-mentioned battery A
(Example 1) is also shown.

[0034]

[Table 2]

As is clear from Table 2, the internal pressure of the battery A (Example 1), the battery F (Example 3), the battery G (Example 4) and the battery H (Example 5) decrease. But
It can be seen that the internal pressure of the battery E (Example 2) has increased. This is because battery A (Example 1: carbon deposition amount of 0.03 mg / cm ² ), battery F (Example 3: carbon deposition amount of 0.005 mg / cm ² ), battery G ( Example 4: Carbon attachment amount of 0.6 mg / cm
² ) and the battery H (Example 5: the amount of deposited carbon is 1 mg / cm ² ), and when a spiral electrode body is used, if the amount of carbon applied to the outermost peripheral portion 11 is large, carbon Since the concentration is high, it is considered that sufficient metal cadmium necessary for gas absorption is generated.

On the other hand, in the case of a spiral electrode body such as a battery E (Embodiment 2: a carbon deposition amount of 0.003 mg / cm ² ), the amount of carbon applied to the outermost peripheral portion 11 is small. It is considered that, because the carbon concentration is low, sufficient cadmium metal required for gas absorption is not generated.

Next, E,
Using four types of nickel-cadmium storage batteries of F, G, and H, charging was performed at room temperature (25 ° C.) with a current of 9 A, and after the peak voltage was exceeded, the voltage was cut when the voltage dropped by 10 mV ( -Delta V method), and after suspending charging for 1 hour, discharging is performed at a current of 15 A until the battery voltage becomes 0.8 V. Thereafter, after performing a cycle test in which the discharge was suspended for 1 hour and then charging was performed again under the same conditions as above, the results shown in FIG. 3 were obtained. FIG. 3 shows the battery capacity with respect to the number of charge / discharge cycles, and also shows the battery A (Example 1) described above.

As is clear from FIG. 3, battery A (Example 1: the amount of carbon adhered was 0.03 mg / cm ² ), battery F (Example 3: the amount of carbon adhered was 0.00)
5 mg / cm ² ) and Battery G (Example 4: one having an attached carbon amount of 0.6 mg / cm ² ) show no deterioration in capacity in the charge / discharge cycle. This is thought to be because the amount of carbon applied as the entire cadmium negative electrode was reduced, and the capacity was not degraded.

On the other hand, the battery E (Example 2: one having an adhesion amount of carbon of 0.005 mg / cm ² ) and the battery H (Example 5: one having an adhesion amount of carbon of 1 mg / cm ² ) , The deterioration of the capacity is observed. This is because in the case of the battery E, the carbon deposition amount was 0.005.
mg / cm ² , the internal pressure of the battery rises due to the decrease in gas absorption performance, and when the safety valve is activated, the electrolyte inside the battery is discharged out of the battery and the battery capacity is reduced. It is probable that the decline occurred. In the battery H, since the amount of deposited carbon is as large as 1 mg / cm ² , oxygen gas generated at the time of charging reacts with carbon to form carbonate, and this carbonate dissolves in the alkaline electrolyte. It is considered that the electrolyte capacity was lowered and the battery capacity was lowered.

From this, it was found that the amount of carbon deposited was 0.0
It is understood that when the content is in the range of 0.05 to 0.6 mg / cm ² , it is possible to improve the oxygen gas absorption performance at the time of large-current charge and discharge while suppressing the adverse effects of carbon coating.

As described above, in the cadmium negative electrode for an alkaline storage battery according to the present invention, carbon is applied only to the cadmium negative electrode arranged at the outermost peripheral portion of the spiral electrode body. As described above, since carbon is applied only to the portion arranged at the outermost peripheral portion of the cadmium negative electrode, the conductivity of this portion is improved, the charging reaction is promoted, and the amount of metal cadmium generated is increased. I do.

For this reason, the contact between the metal cadmium and oxygen gas in this portion is facilitated, and the oxygen gas absorption performance is improved. In other words, carbon is not coated on the entire cadmium negative electrode, but only on the outermost portion when it is wound in a spiral shape. Since there is no film, the carbon film does not hinder the reaction when charging / discharging is performed at a high rate (high rate), and no overvoltage occurs. As a result, the oxygen gas absorption performance is improved, and the capacity deterioration due to the charge / discharge cycle can be prevented.

In the above-described embodiment, an example in which acetylene black is used as carbon has been described. However, it has been confirmed that similar results can be obtained by using other types of carbon such as Ketjen black. .

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cadmium negative electrode of the present invention.

FIG. 2 is a diagram showing the relationship between the number of cycles and the battery capacity when a nickel-cadmium storage battery is configured.

FIG. 3 is a diagram showing the relationship between the number of cycles and the battery capacity when a nickel-cadmium storage battery similar to FIG. 2 is configured.

Claims (3)

[Claims] 1. A cadmium negative electrode for an alkaline storage battery comprising a spiral electrode body formed by spirally winding a negative electrode mainly composed of a cadmium active material and a positive electrode via a separator, wherein the cadmium negative electrode is The cadmium negative electrode is arranged so as to be located at the outermost peripheral portion of the spirally wound spiral electrode body, and a portion of the cadmium negative electrode located at the outermost peripheral portion is coated with carbon. Cadmium negative electrode for alkaline storage batteries. 2. The cadmium negative electrode according to claim 1, wherein the carbon is selected from acetylene black and Ketjen black. 3. The carbon coated on a portion of the cadmium negative electrode located at the outermost peripheral portion has a unit area (cm ² ).
The cadmium negative electrode for an alkaline storage battery according to claim 1 or 2, wherein the cadmium amount is 0.005 to 0.6 mg per unit.