JP2796674B2 - 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 batteries have Demand is increasing rapidly due to the longer lifespan. 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, when charged with constant electricity in order to keep the battery sealed, reduces the current to about
There is a problem that it must be kept below 1 CA. This is because when the charging current is increased to 1 CA or more, all the oxygen gas generated from the positive electrode plate in the overcurrent 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. Attempts have been made to make it possible, but the charging efficiency of the negative electrode plate is insufficient.

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 alkaline electrolyte contains lithium hydroxide, and the negative electrode plate is made of triiron tetroxide ( Fe ₃ O
₄ ) 0.25% by weight or more and 20% by weight based on the total amount of cadmium
It is characterized by containing the following.

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 triiron tetroxide in the negative electrode active material.

For example, until 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. Although the charging efficiency is about 93%, the charging efficiency is improved to 98% or more when iron tetroxide is contained at 1% by weight based on the total amount of cadmium. Further, it was found that such an effect of increasing the charging efficiency was not transient, but was maintained in a charge / discharge cycle.

Further, since the negative electrode plate according to the present invention contains lithium hydroxide in the alkaline electrolyte, the iron compound in the negative electrode plate dissolves in the alkaline electrolyte and moves to the positive electrode plate, and the charging efficiency of the positive electrode plate decreases. Can be eliminated.

That is, the negative electrode plate for an alkaline secondary battery according to the present invention has an extremely excellent operation effect that the charging efficiency of the negative electrode is high and the charging efficiency of the positive electrode is not reduced.

And by 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 provide a negative electrode plate for an alkaline secondary battery in which an alkaline electrolyte contains lithium hydroxide, and to obtain a cadmium negative electrode plate having excellent charge efficiency, and to apply it to a battery. That is. 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 mixed with iron trioxide whose mixing 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 273 mg and metal cadmium powder 210
After mixing mg and iron trioxide with the blending amount changed in the range of 0 to 84 mg, a tablet-shaped 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 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. The figure shows that the charging rate is improved when the content of triiron tetroxide with respect to the total cadmium content is in the range of 0.25% by weight to 20% by weight. Especially the content rate is 1
In the range of not less than 20% by weight and not more than 20% by weight, the charging efficiency is extremely high at not less than 98%, indicating that the amount of inactive cadmium hydroxide that cannot be charged is reduced.

Further, a difference in charging efficiency is recognized depending on a difference in the active material material. That is, (a) in which cadmium oxide is the main component of the active material is more than the negative electrode plate (b) in which the content of triiron tetroxide is 10% by weight or more and cadmium hydroxide is the main component of the active material raw material, The charging efficiency is increasing.

It is possible to make the content of triiron tetroxide higher than 20% by weight, but the content of the cadmium active material may be 20% by weight or less because the theoretical capacity density of the cadmium active material is greatly reduced. Deemed desirable.

From the above, the content of triiron tetroxide with respect to the total cadmium is suitably 0.25% by weight or more and 20% by weight or less.
When the content is not less than% by weight, it can be said that the main active material material is preferably cadmium oxide.

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

<Cadmium oxide powder> One having 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 <Metal cadmium powder> Electrochemical substitution method 2μ average particle size
m <iron trioxide> Commercially available 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 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 triiron tetroxide, and 0.1 part by weight of polypropylene short fiber 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. Nickel plating this paste (5μm)
Coated on a perforated steel plate, then dried and pressed, the theoretical capacity of cadmium oxide is 960 mAh and the size is 2.9 × 14 × 52 (mm)
Was produced.

 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 was wrapped in a 0.2-mm-thick polyamide nonwoven fabric, and then sandwiched between two positive electrode plates.
Nominal capacity is 700 mAh using 2.4 ml of aqueous solution of potassium hydroxide containing specific gravity of 1.250 (20 ° C) containing 15 g of lithium hydroxide.
A nickel-cadmium battery (A) using a synthetic resin battery case was manufactured. Dimensions are 67 × 16.5 × 8 (mm) , and with a safety valve operating at 0.1 kg / cm ^2. Also,
Since cadmium oxide in the negative electrode plate of this battery consumes water by the reaction shown in the following formula (2) when the electric liquid is charged, 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, 40 parts by weight of metal cadmium powder, 2 parts by weight of triiron tetroxide, and 1 mm long polypropylene short fiber 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 applied to a copper-plated (5 μm) perforated steel plate, and then dried and pressed to obtain a cadmium hydroxide with a theoretical capacity of 960 mAh and dimensions of 2.9 × 14 × 52 (mm).
Was produced.

Next, a triangular nickel-cadmium battery (B) having a configuration similar to that of Example 3 and a nominal capacity of 700 mAh was manufactured using the negative electrode plate and the same positive electrode plate used in 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 A square nickel-cadmium battery (D) having a nominal capacity of 700 mAh was manufactured in the same manner as in Example 3 except that triiron tetroxide was omitted from the composition of the negative electrode plate in Example 3.

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 charge 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 rise of the negative electrode potential in the charge cycle is large. This is because there is almost no decrease in the cycle.

The amount of cadmium hydroxide in the negative plates of the batteries (A), (B), (C) and (D) was about 0.95 times the weight 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 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 perform ultra-rapid charging by a simple charging method called constant voltage control, and is excellent in capacity retention.

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, it is easy to detect a change in the charging voltage so that the difference reaches 400 mV or more at a current of 0.2 CA or more. 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 is because the battery was overcharged because the charging voltage of the conventional battery did not reach 1.9V.

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 which also serves as current collector and active carrier, 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 triiron tetroxide, and 0.1 part by weight of short fiber made of polypropylene having a length of 1 mm were mixed with 1.
Mix with 30 ml of ethylene glycol containing 5% by weight polyvinyl alcohol to form a paste. This paste is applied to a copper expanded metal, and then dried and pressed to obtain a metal cadmium with a capacity of 800 mAh and a size of 2.9 x 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
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,
Specific gravity containing 15 g of lithium hydroxide per electrolyte
A rectangular manganese dioxide-cadmium battery (E) having a nominal capacity of 240 mAh and a synthetic resin battery case was manufactured using 2.7 ml of 1.350 (20 ° C.) aqueous potassium hydroxide solution. This battery has an outer diameter of 67 × 16.5 × 8 (mm) and 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 triiron tetroxide 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.

It can be seen from the figure that the battery (E) of the present invention, which has a negative electrode plate having excellent charge efficiency and almost no decrease in the cycle of charge efficiency, has a significantly smaller capacity decrease than the comparative battery (F) and has passed 1000 cycles However, it can be seen that 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, 2 parts by weight of triiron tetroxide, and 0.1 part by weight of a short fiber made of polypropylene having a length of 1 mm were added to 1. parts by weight.
Mix with 30 ml of ethylene glycol containing 5% by weight polyvinyl alcohol to form a paste. This paste was applied to a cadmium-plated (15 μm) copper expanded metal, and then dried and pressed to produce a negative electrode plate having a theoretical capacity of metal cadmium of 1000 mAh and dimensions of 3 × 14 × 52 (mm). .

 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, and then subjected to electric field oxidation 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 was wound four times with a cellophane having a thickness of 0.02 mm, and then sandwiched between two positive electrode plates.
A rectangular silver oxide-cadmium battery (G) having a nominal capacity of 500 mAh was manufactured using 3 ml of an aqueous potassium hydroxide solution having a specific gravity of 1.250 (20 ° C.) containing 15 g of lithium hydroxide. 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 produced in the same manner as in Example 7 except that triiron tetroxide was omitted from the formulation 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 charge voltage characteristics when the operation of discharging at the same current after discharging at 300 mAh at a current of 0.2 CA at 20 ° C. was repeated.

As shown in 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 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 material may be a material having a nickel, copper or cadmium layer on the surface of iron in addition to nickel, copper or cadmium, a material having a layer of copper or cadmium on the surface of nickel, and a material having a layer of cadmium on the copper surface. It has a layer.

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

The reason why the electrolyte containing lithium hydroxide was used in the embodiment of the battery is as follows. That is, the iron compound in the negative electrode plate is dissolved in the alkaline electrolyte and moves to the positive electrode plate,
In particular, when the positive electrode active material is nickel hydroxide, an overvoltage caused by the generation of oxygen gas at the time of charging is reduced, resulting in a disadvantage that charging efficiency of the positive electrode active material is reduced. However, since such a disadvantage can be solved by using an alkaline electrolyte containing lithium hydroxide, the electrolyte of a battery provided with a negative electrode plate containing an iron compound desirably contains lithium hydroxide. The amount is preferably 10 g or more and 30 g or less per electrolyte.

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. Then, the disadvantage that the iron compound in the negative electrode plate dissolves in the alkaline electrolyte and moves to the positive electrode plate and the charging efficiency of the positive electrode plate is reduced can be solved by the lithium electrolyte contained in the alkaline electrolyte.

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 triiron tetroxide and charging efficiency in a cadmium negative electrode plate of the present invention. FIG. 2 is a diagram showing a capacity retention ratio in a charge / discharge cycle of a nickel-cadmium battery of the present invention and a battery for comparison. 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 negative electrode plate for an alkaline secondary battery in which an alkaline electrolyte contains lithium hydroxide, wherein the negative electrode plate contains 0.25 to 20% by weight of iron tetroxide with respect to the total amount of cadmium. A cadmium negative electrode plate characterized by the above-mentioned. 2. An alkaline secondary battery comprising: a positive electrode plate mainly composed of any one of nickel hydroxide, manganese dioxide and silver oxide as an active material; and the cadmium negative electrode plate according to claim 1.