JP2591988B2 - Cadmium negative electrode plate and alkaline secondary battery using the negative electrode plate - Google Patents

Description

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 At present, lead batteries and nickel-cadmium batteries are mainly used as secondary batteries. In particular, nickel-cadmium batteries have good characteristics in high-rate discharge and lead-free batteries. Demand is increasing rapidly due to its longer life than batteries. On the other hand, with the recent reduction in size and weight of electronic devices, there is a demand for secondary batteries to have higher capacity and shorter charging time.

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

In addition, a conventional nickel-cadmium battery reduces the current when charged at a constant current in order to keep the battery sealed.
There is a problem that it must be kept below 1 CA. This is because if the charging current is increased to 1 CA or more, all the oxygen gas generated from the positive electrode plate in the overcharge region cannot be absorbed by the negative electrode plate, and eventually the safety valve operates and the electrolyte solution is discharged. This is due to the decrease in the capacity and the deterioration of the life characteristics. Therefore, Japanese Patent Application No. 62-83582
As proposed in Japanese Patent Application No. 63-13345 and Japanese Patent Application No. 63-13345, a potential change in the process of generating hydrogen on the negative electrode plate during charging is detected as a change in charging voltage to facilitate charging control, and rapid charging is performed. There is an attempt to make it possible, but it is insufficient in terms of the 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 potassium titanate in an amount of 0.25% by weight or more based on the total cadmium amount.
% By weight or less.

Action As a result of examining the charging efficiency of the cadmium negative electrode plate,
It was found that the charging efficiency was increased by including potassium titanate in the negative electrode active material.

For example, hydrogen gas is generated when a cadmium negative electrode plate mainly containing cadmium hydroxide or cadmium oxide and metal cadmium as an active material is charged with a current of 1 CA based on the theoretical capacity of cadmium oxide or cadmium hydroxide. The charging efficiency is about 93%, but when potassium titanate is contained at 1% by weight based on the total amount of cadmium, the charging efficiency is improved to 98% or more.

Also, using such a negative electrode plate with excellent charging efficiency,
If the potential change leading to hydrogen generation during the charging of the negative electrode plate is detected as a change in terminal voltage, charging control is easy, and if a constant voltage is set at that point, the current decreases in the overcharge region, so An alkaline secondary battery that can be charged and has no loss of electrolyte is obtained.

Examples Hereinafter, the present invention will be described in detail using 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 and 210 mg of metal cadmium powder
And potassium titanate whose blending amount was changed in the range of 0 to 84 mg, and then pressed under a pressure of 230 kg / cm ² to obtain tablets having a total cadmium theoretical capacity of 200 mAh. Further, this tablet was wrapped with a nickel mesh of 20 mesh to obtain a negative electrode plate.
This is referred to as a negative electrode plate group (a).

[Example 2] Cadmium hydroxide powder 237 mg and metal cadmium powder 210
mg and potassium titanate whose blending amount was changed in the range of 0 to 84 mg, and the theoretical capacity was 200 m in the same manner as in Example 1.
An Ah tablet-shaped negative electrode plate was used. This is referred to as a negative electrode plate group (b).

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

These negative electrodes are placed in an aqueous potassium hydroxide solution having a specific gravity of 1.250 (20 ° C.), and two nickel plates are used as counter electrodes, and 1 CA (100 mA) based on the theoretical capacity of the cadmium oxide powder or cadmium hydroxide powder at the time of compounding is used. The charge / discharge was repeated with the current of, and the charging efficiency was determined from the following equation (1).

The result is shown in FIG. From the figure, there is no difference due to the use of cadmium oxide or cadmium hydroxide as the active material raw material, and the charging efficiency is improved when the content of potassium titanate with respect to the total cadmium content is 0.25% by weight or more. In particular, the content is 0.5% by weight or more and 15% by weight.
In the following range, the charging efficiency is extremely high at 97% or more, indicating that inactive cadmium hydroxide that cannot be charged is reduced.

Although it is possible to increase the content of potassium titanate to more than 20% by weight, the content of the cadmium active material is reduced to 20% by weight because the theoretical capacity density of the cadmium active material is greatly reduced.
It is considered desirable that:

From the above, it can be said that the content of potassium titanate with respect to all cadmium is suitably from 0.25% by weight to 20% by weight.

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

<Cadmium oxide powder> One with an average particle diameter of 1 μm manufactured by the atomization method <Cadmium hydroxide powder> The above cadmium oxide powder immersed in purified water and hydrated <Cadmium metal powder> Electrochemical substitution method 2μ average particle size
<potassium titanate> Commercially available reagent Next, the 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 that can have a higher capacity and a shorter charging time. The effect is more clear when used in batteries that do not. that is,
This is because the cadmium negative electrode plate of the present invention has excellent charging efficiency. Accordingly, in the following examples, a battery having no cadmium hydroxide reserve will be described as an example.

The positive electrode active materials that can be used in the alkaline battery of the present invention are nickel hydroxide, manganese dioxide, and silver oxide. Among these, the active material that is generally used is nickel hydroxide, and therefore, the description will be focused on nickel-cadmium batteries.

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

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

Example 3 60 parts by weight of cadmium oxide powder and metal cadmium powder 40
Parts by weight, 2 parts by weight of potassium titanate, and 0.1 part by weight of short fiber made of polypropylene 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 is plated with nickel (5
μm), applied to a perforated steel plate, and then dried and pressed to obtain a cadmium oxide with a theoretical capacity of 960 mAh and dimensions of 2.9 × 14 × 52.
(Mm) negative electrode plate was manufactured.

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

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

Next, one negative electrode plate is wrapped in a non-woven fabric of polyamide having a thickness of 0.2 mm, and then sandwiched between two positive electrode plates.
Using 2.4 ml of 1.250 (20 ° C.) aqueous potassium hydroxide solution,
A nickel-cadmium battery (A) using a synthetic resin battery case with a nominal capacity of 700 mAh was manufactured. External dimensions are 67 x 1
6.5 × a 8 (mm), and with a safety valve operating at 0.1 kg / cm ^2. In addition, since cadmium oxide in the negative electrode plate of this battery consumes water by the reaction represented by the following formula (2) when the electrolytic solution is added, extra water corresponding to the consumed amount was injected.

CdO + H ₂ O → Cd (OH) ₂ (4) [Example 4] 68.5 parts by weight of cadmium hydroxide powder, 40 parts by weight of metal cadmium powder, 2 parts by weight of potassium titanate, and a short fiber made of polypropylene having a length of 1 mm 0.1 parts by weight are mixed with 30 ml of ethylene glycol containing 1.5% by weight of polyvinyl alcohol to form a paste. This paste is plated with copper (5μ
m) Coated on perforated steel sheet, then dried and pressurized, the theoretical capacity of cadmium hydroxide is 960mAh and the size is 2.9 × 14 × 52
(Mm) negative electrode plate was manufactured.

Next, a square nickel-cadmium battery (B) having a nominal capacity of 700 mAh and a configuration similar to that of Example 3 was manufactured using the above-described negative electrode plate and the same positive electrode plate as that of Example 3.

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

Comparative Example 1 The same procedure as in Example 3 was carried out except that potassium titanate was omitted from the composition of the negative electrode plate in Example 3, and the nominal capacity was 70%.
A 0 mAh square nickel-cadmium battery (D) was fabricated.

The batteries (A), (B),
(C) and (D) were subjected to a constant voltage charge of 1.90 V for 30 minutes at a maximum current of 3 CA at 20 ° C., followed by a current of 0.2 CA.
A charge / discharge cycle of discharging to 0.5 V was performed 250 times. FIG. 2 shows the capacity retention ratio in each cycle when the discharge capacity in the first cycle is 100. From the figure, it can be seen that the batteries (A), (B) and (C) of the present invention have a clearly higher capacity retention than the comparative battery (D).
The reason for this is that the charging efficiency of the negative electrode active material of the battery of the present invention is extremely high, and even with a large current such as 3 CA, the amount of charge electricity until the negative electrode potential rises at the end of charging is large. This is because there is almost no decrease in the cycle.

The content of cadmium hydroxide in the negative plates of the batteries (A), (B), (C) and (D) was about 0.95 times the weight ratio of nickel hydroxide in the positive electrode [2.73 (g / Ah). /2.89 (g / A
h)]. The properties of the raw materials such as cadmium oxide used in the production of the negative electrode plate are the same as those used in the above-mentioned embodiment of the tablet-type negative electrode plate.

As described above, the battery of the present invention can be super-rapidly charged by a simple charging method called constant voltage control.

The charging method used was a method of charging at a constant voltage by regulating the maximum current.However, after charging at a constant current used in a conventional nickel-cadmium battery, the charging voltage decreased due to gas absorption. It is not a complicated charging system such as a method of detecting charging and terminating charging or a method of detecting heat generation due to gas absorption and terminating charging. One of the features of the present invention is that a constant voltage charging system, which has been conventionally difficult to apply to a nickel-cadmium battery, can be easily performed. That is, in the conventional nickel-cadmium battery, the difference between the voltage in the charging process and the voltage at the end of charging is 150 to 2 at most.
The constant voltage charging method could not be applied because it was as small as 00 mV, but in the case of the battery according to the present invention, the difference reached 400 mV or more at a current of 0.2 CA or more, so that it was easy to detect a change in the charging voltage. It is. In this case, the battery may be charged at a constant current and the current may be reduced after detecting an increase in the charging voltage, or the battery may be charged at a constant voltage. The safety valve was activated when a 1.9V constant voltage charge of a conventional nickel-cadmium battery (AA size) with a nominal capacity of 700mAh using a conventional sintered electrode plate and a maximum current of 3CA was performed for 30 minutes. And a liquid leak occurred. This means that the charging voltage of a conventional battery is 1.9V
, Because the battery is 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 a copper or cadmium having a large overvoltage of hydrogen generation, for example, Copper or cadmium net, expanded metal, perforated plate or three-dimensional metal foam or metal fiber mat that also serves as current collector and active material holder, and copper or cadmium plating on iron or nickel Those that do are suitable. However, even with a nickel current collector with a small overvoltage for hydrogen generation,
The active material can be used as a current collector by reducing a material having a small hydrogen overvoltage such as nickel powder to 5% by weight or less, for example.

In the above embodiments of the present invention, nickel hydroxide was used as the positive electrode active material. However, even when manganese dioxide was used as the active material, the same effect as that of a nickel-cadmium battery was obtained. Hereinafter, a case where the present invention is applied to a manganese dioxide-cadmium battery will be described using preferred examples.

Example 6 100 parts by weight of metal cadmium powder, 2 parts by weight of potassium titanate, and 0.1 part by weight of polypropylene short fiber having a length of 1 mm were mixed with 30 ml of ethylene glycol containing 1.5% by weight of polyvinyl alcohol and paste. Shape. This paste is applied to copper expanded metal, and then dried and pressed to obtain a metal cadmium capacity of 800 mAh and dimensions.
A 2.9 × 14 × 52 (mm) negative electrode plate 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
After kneading 10 parts by weight with 30 ml of an aqueous dispersion of 60% by weight of polytetrafluoroethylene, the mixture is formed into a sheet by a roller, and further pressed on a 20 mesh nickel mesh from both sides to have a theoretical capacity of 200 mAh and a size of 1.4 × A 14 × 52 (mm) positive electrode plate was manufactured.

Next, after wrapping the above-mentioned one negative electrode plate with a non-woven fabric made of polyvinyl alcohol having a thickness of 0.2 mm, sandwiched between the two positive electrode plates,
A rectangular manganese dioxide-cadmium battery (E) using a synthetic resin battery container with a nominal capacity of 240 mAh using a potassium hydroxide aqueous solution having a specific gravity of 1.350 (20 ° C.) as an electrolyte was manufactured. This battery has an outer diameter of 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 a comparative example was manufactured in the same manner as in Example 6 except that potassium titanate was omitted from the formulation of the negative electrode plate of Example 6.

The batteries (E) and (F) produced as described above
FIG. 3 shows the results of the change in capacity when the battery was charged and discharged under the condition that the battery was discharged at a current of 0.2 C for 100 mAh and then charged at the same current up to 1.6 V.

From FIG. 3, it is apparent that the battery (E) of the present invention having a negative electrode plate having excellent charge efficiency and almost no decrease in the cycle of the charge efficiency has a significantly smaller capacity decrease than the comparative battery (F), and has a capacity of 1000 cycles. Even after the passage, the capacity hardly decreased.

In addition, these batteries are in a state where cadmium hydroxide for reserve is hardly contained. In other words, the content of cadmium hydroxide contained in the negative electrode plate is always about 0.84 times the weight ratio of manganese dioxide of the positive electrode active material [2.73 (g / A
h) /2.34 (g / Ah)].

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

Example 7 100 parts by weight of metal cadmium powder and potassium titanate 2
Parts by weight 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 is applied to a cadmium-plated (5 μm) copper expanded metal, and then dried and pressed to obtain a metal cadmium having a theoretical capacity of 1000 mAh and a size of 3 × 14 × 52 (mm).
Was produced.

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

A silver oxide powder as an active material and a silver expanded metal as a current collector are sintered under pressure by a conventional method, electrolytically oxidized in an aqueous solution of potassium hydroxide, washed with water and dried to obtain a theoretical capacity of 500 mAh. A positive electrode plate having dimensions of 1.3 × 14 × 52 (mm) was manufactured.

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

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

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

The batteries (G) and (H) produced as described above
FIG. 4 shows the charging voltage characteristics at the time of repeating the operation of discharging at 300 mAh at 20 ° C. with a current of 0.2 CA and then charging at the same current.

From FIG. 4, the voltage rise at the end of charging of the silver oxide-cadmium battery (G) of the present invention occurs later than in the comparative battery (H), and its charging efficiency is almost 100%. The difference in the timing of the voltage rise 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.

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

As described in each embodiment, the current collector of the cadmium negative electrode plate of the present invention may have a surface of nickel, copper or cadmium. In other words, the materials include nickel, copper, and cadmium, as well as those having a layer of nickel, copper, or cadmium on the surface of iron, those having a layer of copper or cadmium on the surface of nickel, and those of cadmium on the surface of copper. It has a layer.

The shape is expanded metal, net,
Perforated plates, foams or fiber mats can be used.

Effect of the Invention As described above, the cadmium negative electrode plate of the present invention has very high charging efficiency, and therefore has almost no inactive cadmium hydroxide. Therefore, the substantial capacity density is 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 ultra-rapid charging with a large current of 1 CA or more is possible.
In addition, since this battery hardly needs cadmium hydroxide for reserve, high capacity can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the content of potassium titanate and charging efficiency in the cadmium negative electrode plate of the present invention, and FIG. 2 is a graph showing the relationship between the nickel-cadmium battery of the present invention and a battery for comparison. The figure which showed the capacity retention in the charge / discharge cycle. FIG. 3 is a diagram showing a capacity retention ratio in a charge / discharge cycle of a manganese dioxide-cadmium battery of the present invention and a battery for comparison. FIG. 4 is a view showing charging characteristics of a silver oxide-cadmium battery of the present invention and a battery for comparison.

Claims (2)

(57) [Claims] 1. A cadmium negative electrode plate comprising 0.25% by weight or more and 20% by weight or less of potassium titanate based on the total amount of cadmium. 2. An alkaline secondary battery comprising: a positive electrode plate mainly composed of nickel hydroxide, manganese dioxide or silver oxide as an active material; and the cadmium negative electrode plate according to claim 1.