JPH07105228B2 - Cadmium negative electrode plate and alkaline secondary battery using the negative electrode plate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cadmium negative electrode plate and an alkaline secondary battery using the negative electrode plate.

2. Description of the Related Art Currently, lead batteries and nickel-cadmium batteries are mainly used as secondary batteries, and nickel-cadmium batteries are particularly good at high-rate discharge and lead-free. Demand is rapidly increasing because of its longer life than batteries. On the other hand, with the recent trend toward smaller and lighter electronic devices, there has been a demand for higher capacity and shorter charging time for secondary batteries.

The conventional alkaline secondary battery using the cadmium negative electrode plate has the following problems. It relates to a cadmium negative electrode plate and has a large amount of cadmium hydroxide that does not participate in the charge / discharge reaction. That is, the charging efficiency of cadmium hydroxide until the generation of hydrogen gas is usually about 90%, and the remaining about 10% of cadmium hydroxide occupies an unnecessary volume without any use. Further, taking a nickel-cadmium battery as an example, in order to keep the battery in a hermetically sealed state, a so-called reserved cadmium hydroxide of 20% or more of the capacity of the positive electrode plate was required in the negative electrode plate. This reserve cadmium hydroxide compensates for the activation of metallic nickel, which is a holder for the positive electrode active material, into the active material and the space volume in the battery, and does not contribute to the discharge capacity. Having these cadmium hydroxides is one of the factors that hinder the high capacity of the cadmium negative electrode plate and the battery.

In addition, the conventional nickel-cadmium battery has a current of about 1 C when charged at a constant current to keep the battery sealed.
It has a problem that it must be kept below A. This is because when the charging current is increased to 1 CA or more, all the oxygen gas generated from the positive electrode plate cannot be absorbed by the negative electrode plate in the overcharge region, and eventually the safety valve operates and the electrolyte solution This is because it causes a decrease in capacity and a deterioration in capacity and life characteristics. Therefore, Japanese Patent Application No. Sho 62-83582
As disclosed in Japanese Patent Application No. 63-13345 and Japanese Patent Application No. 63-13345, the potential change in the process of hydrogen generation on the negative electrode plate during charging is detected as a change in charging voltage to facilitate charge control and to achieve rapid charging. Although there is an attempt to make it possible, it is insufficient in terms of charging efficiency of the negative electrode plate.

Means for Solving the Problems The present invention relates to a cadmium negative electrode plate and an alkaline secondary battery provided with the negative electrode plate, wherein the negative electrode plate contains cuprous oxide (Cu ₂ O) with respect to the total amount of cadmium. 0.5% by weight or more 20
It is characterized by containing less than or equal to wt%.

Action As a result of studying the charging efficiency of the cadmium negative electrode plate, it was found that the charging efficiency was increased by containing cuprous oxide in the negative electrode active material.

For example, hydrogen gas is generated when a cadmium negative electrode plate containing cadmium hydroxide or cadmium hydroxide and metal cadmium as the active material is charged with a current of 1 CA based on the theoretical capacity of cadmium oxide or cadmium hydroxide. The charging efficiency up to about 93% is about 93%, but if the content of cuprous oxide is 1% by weight based on the total amount of cadmium, the charging efficiency is improved to 96% or more. Further, it has been found that such an effect of enhancing the charging efficiency is not transient but lasts in the charge / discharge cycle.

And by using such a negative electrode plate with excellent charging efficiency, it is easy to control the charge by detecting the potential change resulting in hydrogen generation during charging of the negative electrode plate as the change in the terminal voltage. If set, the current becomes small in the overcharge region, so that the alkaline secondary battery can be rapidly charged and the electrolyte solution is not reduced.

Examples The present invention will be described in detail below with reference to preferred examples.

An object of the present invention is to obtain a cadmium negative electrode plate having excellent charging efficiency and to apply it to a battery. Therefore, the cadmium negative electrode plate will be described first.

[Example 1] 240 mg of cadmium oxide powder, 210 mg of metal cadmium powder, and cuprous oxide whose compounding amount was changed in the range of 0 to 84 mg were mixed, and then pressure-molded at a pressure of 230 kg / cm ² , Tablets with a theoretical capacity of total cadmium of 200 mAh. Furthermore, this tablet
It was wrapped with a 20 mesh nickel net to give a negative electrode plate. This is referred to as a negative electrode plate group (a).

Example 2 Cadmium hydroxide powder 273 mg and metal cadmium powder 210 mg
After mixing with cuprous oxide whose compounding amount was changed in the range of 0 to 84 mg, a tablet type negative electrode plate having a theoretical capacity of 200 mAh was prepared in the same manner as in Example 1. This is referred to as a negative electrode plate group (b).

The total amount of cadmium is included in the cadmium negative electrode plate.
It is the total amount of Cd atoms.

These negative plates were placed in an aqueous cadmium hydroxide solution with a specific gravity of 1.250 (20 ° C), using two nickel flat plates as counter electrodes, and 1CA (100mA) based on the theoretical capacity of the cadmium oxide powder or cadmium hydroxide powder at the time of compounding. The charging / discharging was repeated with the current of, and the charging efficiency was calculated from the following formula (1).

The results are shown in FIG. From the figure, it can be seen that the charging efficiency is improved when the content of cuprous oxide is 0.5 wt% or more and 20 wt% or less with respect to the total amount of cadmium. Especially the content rate is 2.
In the range of 5% by weight or more and 10% by weight or less, the charging efficiency is extremely high at 97% or more, which shows that the amount of inactive cadmium hydroxide that cannot be charged is reduced.

Although it is possible to increase the content of cuprous oxide to more than 20% by weight, the content of cuprous oxide should be 20% by weight or less because the decrease in the theoretical capacity density of the cadmium active material becomes large. Considered desirable.

From the above, it can be said that the content of cuprous oxide with respect to all cadmium is preferably 0.5% by weight or more and 20% by weight or less.

The properties of each raw material used in the examples are shown below.

<Cadmium oxide powder> Atomized particles with an average particle size of 1 μm <Cadmium hydroxide powder> The above cadmium oxide powder is immersed in purified water for hydration <Cadmium metal powder> Electrochemical substitution method Average particle size 2μm
<Cuprous oxide> Commercial reagent Next, a battery using the cadmium negative electrode plate of the present invention having extremely high charging efficiency described in the above examples was evaluated.

The cadmium negative electrode plate of the present invention can be used for a conventional nickel-cadmium battery that requires a reserve cadmium hydroxide, and also has a reserve cadmium hydroxide capable of higher capacity and shorter charging time. The effect is more clear when used in batteries that do not. This is due to the excellent charging efficiency of the cadmium negative electrode plate of the present invention. Therefore, in the following embodiments, a battery having no reserve cadmium hydroxide will be described as an example.

Positive electrode active materials that can be used in the alkaline battery of the present invention are nickel hydroxide, manganese dioxide and silver oxide. Of these, nickel hydroxide is the most commonly used active material, so a nickel-cadmium battery will be mainly described.

The cadmium negative electrode plate used in the present invention can be manufactured basically using the following current collector. That is, it is a net of nickel, copper or cadmium, an expanded metal, a perforated plate or a metal foam having a three-dimensional structure which also serves as a collector and an active material holder, or a mat of metal fibers.

Further, iron plated with nickel, iron plated with nickel or copper with copper, and iron plated with nickel, copper, or cadmium can also be used.

[Example 3] 60 parts by weight of cadmium oxide powder, 40 parts by weight of metal cadmium powder, 3 parts by weight of cuprous oxide, and 0.1 parts by weight of polypropylene short fibers having a length of 1 mm were used, and ethylene containing 1.5% by weight of polyvinyl alcohol was used. Mix with 30 ml of glycol to make a paste. This paste was applied to a nickel-plated (5 μm) perforated steel plate, and then dried and pressed to produce a negative electrode plate having a theoretical capacity of cadmium oxide of 960 mAh and dimensions of 2.9 × 14 × 52 (mm).

On the other hand, the positive electrode plate was manufactured by the following method.

Sintering method with porosity of about 80%, nickel content on the nickel substrate, cobalt content of 8 mol% to the total of nickel and cobalt
Aqueous solution of cobalt nitrate and nickel nitrate [PH =
2, specific gravity 1.50 (20 ℃)], and then specific gravity 1.200 (20
C.) aqueous sodium hydroxide solution, washed with hot water and dried. Repeating this operation, the total theoretical capacity of nickel hydroxide and cobalt hydroxide is 400mAh and the size is 1.4 × 14 × 52m.
A m positive plate was manufactured.

Next, one negative electrode plate was wrapped in 0.2 mm thick polyamide non-woven fabric and then sandwiched between two positive electrode plates to give a specific gravity of 1.
Using 2.4 ml of 250 (20 ° C) potassium hydroxide aqueous solution, nickel with a nominal capacity of 700 mAh in a synthetic resin battery case
A cadmium battery (A) was manufactured. External dimensions are 67 x 16.5
It is × 8 (mm) and has a safety valve that operates at 0.1 kg / cm ² . In addition, since cadmium oxide in the negative electrode plate of this battery consumes water by the reaction shown in the following formula (2) when an electrolytic solution is added, extra water corresponding to the consumed amount was injected.

CdO + H ₂ O → Cd (OH) ₂ (2) [Example 4] 68.5 parts by weight of cadmium hydroxide powder and metal cadmium powder
40 parts by weight, 3 parts by weight of cuprous oxide and 0.1 part by weight of polypropylene short fibers having a length of 1 mm are mixed with 30 ml of ethylene glycol containing 1.5% by weight of polyvinyl alcohol to form a paste. This paste was applied to a copper-plated (5 μm) perforated steel plate, which was then dried and pressed to produce a negative electrode plate having a theoretical capacity of 960 mAh for cadmium hydroxide and a size of 2.9 × 14 × 52 (mm).

Next, a prismatic nickel-cadmium battery (B) having a nominal capacity of 700 mAh and having the same configuration as in Example 3 was manufactured by using the above-mentioned negative electrode plate and the same positive electrode plate as that used in Example 3.

Example 5 Instead of the current collector of the negative electrode plate in Example 3, that is, the perforated steel plate plated with nickel, cadmium plating (5 μm)
A rectangular nickel-cadmium battery (C) having a nominal capacity of 700 mAh in the same manner as in Example 3 except that the perforated steel sheet was used.
Was produced.

Comparative Example 1 A prismatic nickel-cadmium battery (D) having a nominal capacity of 700 mAh was manufactured in the same manner as in Example 3, except that cuprous oxide was omitted from the formulation of the negative electrode plate in Example 3.

Batteries (A), (B), (C) manufactured as described above
And (D) at 20 ° C, maximum current of 3CA, 1.90V
After carrying out the constant voltage charging for 30 minutes, the battery was discharged 250 times at a current of 0.2 CA to a charge / discharge cycle of 250 times. FIG. 2 shows the capacity retention rate in each cycle when the discharge capacity in the first cycle is 100. It can be seen from the figure that the batteries (A), (B), and (C) of the present invention have a clearly higher capacity retention rate than the comparative battery (D). This is because the charging efficiency of the negative electrode active material of the battery of the present invention is extremely high,
This is because, even with such a large current, the amount of charge electricity until the rise of the negative electrode potential at the end of charge is large, and there is almost no decrease in the cycle of charging efficiency.

The content of cadmium hydroxide in the negative electrode plates of the batteries (A), (B), (C) and (D) was approximately 0.95 times the weight ratio of nickel hydroxide in the positive electrode [2.73 (g / Ah) /2.88 (g / A
h)]. The properties of the raw materials such as cadmium oxide used for manufacturing the negative electrode plate are the same as those used in the above-mentioned tablet-shaped negative electrode plate.

As described above, the battery of the present invention is capable of ultra-rapid charging by a simple charging method called constant voltage control, and has an excellent capacity retention rate.

As the charging method, a method of controlling the maximum current to perform constant voltage charging was applied, but this method shows that after charging with the constant current used in the conventional nickel-cadmium battery, the charging voltage decreases due to gas absorption. It is not a complicated charging system such as a method of detecting the occurrence of charging and stopping the charging or a method of detecting heat generation due to gas absorption and stopping the charging. Further, one of the features of the present invention is that the constant voltage charging method, which has been difficult to apply in the conventional nickel-cadmium battery, can be easily performed. That is, in the conventional nickel-cadmium battery, the difference between the voltage during the charging process and the voltage at the end of charging is 150 to 200 at most.
The constant voltage charging method could not be applied because it was as low as mV, but in the case of the battery according to the present invention, the difference reaches 400 mV or more at a current of 0.2 CA or more, so it is easy to detect a change in charging voltage. Is. In this case, charging may be performed with a constant current and then the current may be reduced after detecting an increase in the charging voltage, or charging may be performed with a constant voltage. In addition, when a cylindrical nickel-cadmium battery (AA size) with a nominal capacity of 700 mAh using a conventional sintered electrode plate was charged with a constant voltage of 1.9 V at a maximum battery current of 3 CA for 30 minutes, the safety valve was activated. Then, liquid leakage occurred. This is because the charging voltage of the conventional battery did not reach 1.9V and the battery was overcharged.

Thus, in the battery of the present invention, it is advantageous to increase the potential change of the negative electrode plate at the end of charging, and the surface of the current collector is
Basically copper or cadmium with a large overvoltage for hydrogen generation, for example, copper or cadmium net, expanded metal, perforated plate or metal foam or metal with a three-dimensional structure that doubles as a collector and active material holder Fiber mat etc,
Further, as the material, iron or nickel plated with copper or cadmium is suitable. However, even if the current collector of nickel has a small overvoltage for hydrogen generation, it can be used as a current collector if the amount of the material having a low hydrogen overvoltage such as nickel powder is reduced as the active material, for example, 5% by weight or less. You can

In the above-mentioned embodiments of the present invention, nickel hydroxide was used as the positive electrode active material, but manganese dioxide is also used as the active material, and the same effect as the nickel-cadmium battery appears. Hereinafter, the case where the present invention is applied to a manganese dioxide-cadmium battery will be described with reference to preferred examples.

Example 6 100 parts by weight of metallic cadmium powder, 3 parts by weight of cuprous oxide, and 0.1 part by weight of polypropylene short fibers having a length of 1 mm were 1.
Mix with 30 ml of ethylene glycol containing 5% by weight of polyvinyl alcohol to form a paste. This paste is applied to copper expanded metal, then dried and pressed, the capacity of metal cadmium is 800mAh and the size is 2.9 × 14.
A negative electrode plate of × 52 (mm) was manufactured.

On the other hand, the positive electrode plate was manufactured by the following method.

80 parts by weight of manganese dioxide (γ-MnO ₂ ) and graphite 10
After mixing with 30 ml of an aqueous dispersion of polytetrafluoroethylene of 60 wt% and parts by weight, a roller is used to form a sheet, and a nickel mesh of 20 mesh is further pressed from both sides to have a theoretical capacity of 200 mAh and dimensions of 1.4 × 14. A positive electrode plate of × 52 (mm) was manufactured.

Next, after wrapping one of the above negative plates with a non-woven fabric made of polyvinyl alcohol with a thickness of 0.2 mm, sandwich it between two positive plates, and use 2.7 ml of potassium hydroxide aqueous solution with a specific gravity of 1.350 (20 ° C) as the electrolyte. A prismatic manganese dioxide-cadmium battery (E) having a nominal capacity of 240 mAh and using a synthetic resin battery case was produced. The external dimensions of this battery are 67 x 16.5 x 8 (mm),
It has a safety valve that operates at 0.1 kg / cm ² .

Comparative Example 2 A prismatic manganese dioxide-cadmium battery (F) of Comparative Example was produced in the same manner as in Example 6 except that cuprous oxide was omitted from the formulation of the negative electrode plate of Example 6.

The batteries (E) and (F) manufactured as described above were
Fig. 3 shows the results of the capacity transition when the battery was charged and discharged under the condition that the battery was discharged at a current of 2C for 100mAh and then charged at the same current to 1.6V.

It can be seen from the figure that the battery (E) of the present invention having a negative electrode plate with excellent charging efficiency and almost no decrease in cycle of charging efficiency has a clearly smaller capacity decrease than the comparative battery (F), and 1000 cycles have passed. However, it can be seen that the capacity has hardly decreased.

It should be noted that the reserve cadmium hydroxide of these batteries is hardly contained. That is, the content of cadmium hydroxide contained in the negative electrode plate is always about 0.84 times that of manganese dioxide as the positive electrode active material [2.73 (g / Ah) by weight ratio].
/2.34 (g / Ah)].

Although the nickel-cadmium battery and the manganese dioxide-cadmium battery have been described above as examples, a silver oxide-cadmium battery with easy charge control can be obtained even when silver oxide is used as the positive electrode active material.

Example 7 100 parts by weight of metallic cadmium powder, 3 parts by weight of cuprous oxide, and 0.1 part by weight of polypropylene short fibers having a length of 1 mm were used as 1.5 parts by weight.
Mix with 30 ml of ethylene glycol containing wt% polyvinyl alcohol to form a paste. This paste was applied to cadmium-plated (5 μm) expanded copper metal, then dried and pressed to produce a negative electrode plate with a theoretical capacity of 1000 mAh for metal cadmium and dimensions of 3 × 14 × 52 (mm). .

On the other hand, the positive electrode plate was manufactured by the following method.

A theoretical capacity of 500 mAh was obtained by subjecting silver oxide powder, which is an active material, and expanded metal of silver, which is a current collector, to pressure sintering in a conventional method, to electric field oxidation in a potassium hydroxide aqueous solution, followed by washing with water and drying. A positive electrode plate with dimensions of 1.3 × 14 × 52 (mm) was manufactured.

Next, the above negative electrode plate was wound four times with 0.02 mm thick cellophane and then sandwiched between two positive electrode plates to give a specific gravity as an electrolyte.
A prismatic silver oxide-cadmium battery (G) having a nominal capacity of 500 mAh was produced using 3 ml of 1.250 (20 ° C.) potassium hydroxide aqueous solution. The outer diameter was 67 × 16.5 × 8 (mm), and the battery case was made of synthetic resin. It also has a safety valve that operates at a pressure of 0.5 kg / cm ² .

Comparative Example 3 A prismatic silver oxide-cadmium battery (H) was manufactured in the same manner as in Example 7, except that cuprous oxide was omitted from the formulation of the negative electrode plate of Example 7.

The reserve cadmium hydroxide for these batteries is
It is almost absent, and the content of cadmium hydroxide contained in the negative electrode plate is always about 1.4% by weight of silver of the positive electrode active material.
It is double [2.73 (g / Ah) /2.01 (g / Ah)].

The batteries (G) and (H) manufactured as described above are used for 20
Charging voltage characteristics when repeating the operation of discharging 300mAh at a current of 0.2CA at 300 ℃ and then charging at the same current.
As shown in the figure.

From the figure, the voltage rise at the end of charging of the silver oxide-cadmium battery (G) of the present invention occurs later than that of the comparative battery (H), and the charging efficiency thereof is close to 100%. The difference in the timing of voltage increase between the two batteries is based on the charging efficiency of the negative electrode plate, and it is clear that the battery of the present invention has an excellent capacity retention rate.

The characteristics of the cadmium negative electrode plate and the battery of the present invention have been described in the above examples.

As the current collector of the cadmium negative electrode plate of the present invention, the surface thereof may be nickel, copper or cadmium, as described in each example. That is, as the material, in addition to nickel, copper and cadmium, a material having a nickel, copper or cadmium layer on the surface of iron, a material having a layer of copper or cadmium on the surface of nickel, and a material of cadmium on the surface of copper. It has a layer.

Expanded metal, mesh, perforated plate, foam or fiber mat can be used as the shape.

EFFECTS OF THE INVENTION As described above, the cadmium negative electrode plate of the present invention has extremely high charging efficiency, and therefore has almost no inactive cadmium hydroxide. Therefore, the substantial capacity density becomes higher than that of the conventional cadmium negative electrode plate.

In addition, in an alkaline secondary battery using this, charge control is easy by adjusting the amount ratio of the positive and negative electrode active materials, and super rapid charging with a large current of 1 CA or more is possible. In addition, since this battery requires almost no reserve cadmium hydroxide, it is possible to increase the capacity.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the content rate of cuprous oxide and the charging efficiency in the cadmium negative electrode plate of the present invention. FIG. 2 is a diagram showing a capacity retention rate in a charge / discharge cycle of a battery for comparison with the nickel-cadmium battery of the present invention. FIG. 3 is a diagram showing the capacity retention rate in the charge / discharge cycle of the manganese dioxide-cadmium battery of the present invention and a battery for comparison. FIG. 4 is a diagram showing the charging characteristics of a battery for comparison with the silver oxide-cadmium battery of the present invention.

Claims (2)

[Claims] 1. A cadmium negative electrode plate containing 0.5% by weight or more and 20% by weight or less of cuprous oxide with respect to the total amount of cadmium. 2. An alkaline secondary battery comprising a positive electrode plate containing nickel hydroxide, manganese dioxide or silver oxide as an active material, and a cadmium negative electrode plate according to claim 1.