JPH0121588B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for increasing the capacity and density of a sealed nickel-cadmium storage battery, in which cadmium oxide is added to a highly porous nickel-plated iron fiber sintered body using ethylene glycol, isopropyl alcohol,
A negative electrode made by filling a fluid paste with only an organic solvent such as glycerin, and a positive electrode made by filling a conventional nickel powder sintered body with a nickel hydroxide active material, especially thick positive electrodes with a thickness of 0.8 m/m or more. It is characterized by a combination of. The purpose is to determine the capacity density (Ah/l) of sealed nickel-cadmium batteries.
The aim is to improve the performance, extend the lifespan, and significantly reduce costs. Attempts to use fiber sintered bodies as positive electrode current collectors for alkaline batteries were published in Japanese Patent Publication No. 50-2249 and Japanese Unexamined Patent Publication No. 1983-1989.
It is described in No. 151834, Japanese Unexamined Patent Publication No. 55-37745, etc. As is well known, the positive electrode reaction is a homogeneous solid-phase reaction involving Ni(OH) ₂ +OH ^- charge --- --- discharge β-NiOOH + H ₂ O + e ^- , and is different from the elution deposition reaction such as that at the negative electrode. Unlike simple metals, Ni(OH) ₂ and NiOOH have extremely poor conductivity. Therefore, a current collector with as large a specific surface area as possible is required, but in the conventional method of producing iron fibers by inexpensive cutting, the specific surface area is about 1/10 that of the current nickel powder sintered body. However, problems remain in the active material utilization rate, high rate discharge characteristics, charging efficiency, etc. The present inventor found that when fiber sintered bodies are used for positive electrode current collectors whose performance is affected by surface area, they are inferior to nickel powder sintered bodies in many aspects, but when used for negative electrodes, the reaction mechanism is different. On the contrary, it was found that the performance was improved compared to the nickel powder sintered body. In the negative electrode reaction, the active material Cd(OH) ₂ is once dissolved by charging, becomes Cd(OH) ₄ ^2- ions, and is further reduced to metal Cd. Discharge is the opposite. Since the active material itself controls conductivity as it is reduced to metal cadmium, the specific surface area of the current collector does not greatly affect performance, rather the electrolyte is smoothly supplied to each reaction point. is necessary. In the case of sintered nickel powder, which has mostly pores of 10 μm or less, the electrolyte is blocked, resulting in poor discharge voltage characteristics or active material utilization. Therefore, in order to improve these, 10μ
It is desirable that most of the above pores be occupied, and in this respect the fiber sintered body can be easily adjusted by selecting the fiber diameter. In addition, by creating a structure in which most of the pores are 10μ or larger, the active material can be filled with a simplified process such as a paste method, which is impossible for nickel powder sintered bodies. In recent years, the capacity density of sealed nickel-cadmium storage batteries has been increased across the board, from small scale units of several hundred mAh to large scale units of several hundred Ah, but it is particularly active in the field of cylindrical sealed storage batteries of approximately 1 to 5 Ah. being developed. This field has special uses as a power source for guide lights and emergency lights, and in this case 5℃~50℃
Under an unprecedentedly wide temperature range, 1/30C
When charged with a moderate current, sufficient performance must be maintained even under harsh usage conditions. Therefore, for example, in a cylindrical sealed storage battery called NR-C type with dimensions of 25 φ x 49 mm, the nominal capacity is limited to about 1.8 Ah when using conventional positive and negative electrodes made of sintered nickel powder. On the other hand, the combination of a conventional nickel powder sintered positive electrode and a conventional paste negative electrode using a nickel-plated perforated steel plate improves somewhat, but the nominal capacity is limited to about 2.0 Ah. The present invention further improves the capacity density. Conventionally, sintered type and paste type negative electrode plates for nickel cadmium storage batteries are generally known. However, the sintering method uses expensive carbonyl/nickel powder as raw materials and requires large-scale equipment and equipment.
In today's world, where inexpensive and high capacity density electrode plates are required due to the disadvantages of requiring a complicated active material impregnation process and low capacity density, the paste type is more advantageous than the sintered type, while the conventional Paste-type negative electrode plates are made by mixing cadmium oxide, nickel powder, short polymer fibers, etc., adding a viscous aqueous solution containing a small amount of an organic thickener, and applying the paste to both sides of a nickel-metallic perforated steel core. Created by painting. The water contained in the paste liquid and
The Cdo powder reacts and is bonded together as Cdo·H ₂ O, or Cd(OH) ₂ (cementation), and is retained without falling off the core metal during coating. When applying this paste liquid to perforated steel plates, etc.,
Although it has advantageous characteristics for the above reasons, a fiber substrate with a porous structure loses the fluidity of the liquid due to this cementation, making it impossible to fill the inside of the pores with the paste liquid. Therefore, it is essential to create a paste solution that has fluidity and does not cause cementation. Furthermore, the biggest drawback of this conventional paste-type negative electrode plate is that the negative electrode active material is held to the base material only by organic polymers such as short fibers, which can cause it to fall off and burn out due to repeated charging and discharging. Generally, the lifespan is shorter than that of a condensate. Or, unlike the sintered type, the nickel powder is not sintered, but only physically mixed, so its action as a conductive material is insufficient, and the plate resistance value is lower than that of the sintered type. It is large and cannot be ignored, especially during high rate discharge. Since the performance of paste-type negative electrode plates is often influenced by the structure of the base material, in addition to the above-mentioned perforated steel plates, various other devices have been devised, such as expanded metal, wire mesh, and perforated steel plates with irregularities on both sides. Among these, expanded metal is preferable, but it is still not practical because it is expensive and has a sharp surface that tends to cause a short circuit with the opposite electrode when using a thin separator such as non-woven fabric. It has not been converted. The nickel-plated iron fiber sintered body of the present invention improves the drawbacks of conventional paste-type cadmium negative electrode plates, and provides paste-type negative electrodes with excellent current collection properties, active material retention, mechanical strength, active material utilization rate, etc. The present invention provides a base material for a board. The iron fibers used in the present invention can be obtained by cutting an iron wire by moving it back and forth over dozens of serrated knives, as has been known for a long time. A suitable fiber diameter is about 4 to 100 microns.
The fiber diameter is determined by the pitch width of the serrated knife, but if it is thinner than 4μ, the fiber may break during cutting, or the production speed will be extremely reduced, resulting in a significant increase in cost. If the thickness is larger than 100μ, the holes (pores) in the current collector are very rough, resulting in a decrease in high rate discharge performance and drop-off of active material particles. Since this iron fiber is very cheap, it has been used in the field as disposable bamboo material. Because there was no demand for high capacity density as there is today, and because iron fiber manufacturing equipment was expensive, it was never used as a paste-type negative electrode plate base material. Fiber length ranges from several centimeters to several tens of centimeters
cm, long fibers can be freely created, and when sintered, a sintered body with extremely high strength can be obtained, such as a sintered nickel powder.
A conductive core such as a perforated steel plate for reinforcement is not required. Porosities of about 90% to 98% can be used. The higher the porosity of the current collector, the more active material can be filled, which is desirable, but from the viewpoint of practical strength, it is 98%.
is the limit. On the other hand, the capacity must be higher than 90% and the electrolyte must diffuse into the electrode. 90
If it is smaller than %, the electrolytic solution will not diffuse well into the electrode, resulting in poor high rate discharge performance and a high required amount cannot be obtained. After applying nickel plating to this sintered body, it is used as a paste-type negative electrode base material. Width 5
In order to continuously produce sintered bodies in units of ~30 cm and lengths of 50 to 100 m, it is necessary to produce a felt state in which the cut iron fibers are alternately intertwined with each other and the fibers have a certain directionality. However, since it is a sintered body of oriented fibers, it has excellent electrical conductivity and tensile strength in the fiber direction, as shown in the table (Differences in properties depending on the fiber direction of the present invention), but the length It is somewhat inferior in the direction and perpendicular direction. Due to this directionality, when a spiral-wound battery was fabricated in a direction perpendicular to the fiber direction, the electrode plate was cut at the beginning of winding and at the outermost periphery, resulting in numerous minute short circuits. On the other hand, when the winding direction was made to be in the fiber direction, this problem was solved, and the specific resistance was also lowered and high rate discharge characteristics were improved. With this configuration, it can be assembled in the same manner as a conventional sintered electrode plate. On the other hand, when using nickel plating, this difference decreases as the plating thickness increases, and when the thickness becomes 2μ or more, it can be practically ignored as shown in FIGS. 1 and 2. The appropriate size of the micropores in the sintered body is 10 to 50μ. If the micropores are smaller than 10μ, it is difficult to fill with fluid paste, and if the micropores are larger than 50μ, the paste once filled will be washed away, resulting in uneven electrode plates.
The fluid paste solution is prepared from only the active material powder and an organic solvent, and no binder such as tetrafluoroethylene or rubber is mixed therein. When such a binder is used, the viscosity of the paste increases, making it impossible to fill the pores.

[Table] When a paste solution is prepared from cadmium oxide and a water-free organic solvent such as ethylene glycol, isopropyl alcohol, or glycerin, no cementation occurs and the paste solution flows. It turns out that sex is not lost. A predetermined amount of this paste liquid is filled into the fiber sintered body. Thereafter, the negative electrode plate is prepared by drying, roller pressing, chemical conversion, and cutting into predetermined dimensions, just as in the case of making a normal paste electrode plate. The conventional paste-type negative electrode plate is used as a conductive material.
Although ~15 wt% of nickel powder is required, the nickel-plated iron fiber sintered body of the present invention does not require nickel powder because the fiber itself has this function. Furthermore, since a reinforcing core such as a perforated steel plate is not required, when this sintered body is used as a base material, the dead volume is smaller than that of a conventional paste electrode plate. Because it acts so effectively as a base material, plates with higher capacitance densities than conventional ones can be made. This sintered body can also be used as a current collector in the positive electrode plate, but the charging efficiency is inferior to that of the nickel powder sintered body at low charging rates of about 1/30 C at high temperatures of 40° C. or higher. For this reason, nickel powder sintered bodies must be used as positive electrode current collectors in batteries for emergency lights and guide lights, but this does not pose much of a problem when used near normal room temperature. Conventionally, nickel powder sintered bodies are often used with a thickness of around 0.7m/m, but as the thickness becomes thinner, the proportion of conductive cores such as perforated steel plates increases, so it is necessary to use as much as possible to achieve high capacity density. A thick sintered body is preferable. However, if it becomes too thick, it will cause problems with electrolyte diffusion, etc.
m/m is effective. When using the electrolyte at high temperatures of 40°C or higher, the conventional KOH-LiOH system does not have sufficient oxygen overvoltage at the positive electrode, and the NaOH-LiOH system has a higher oxygen overvoltage, so it has better charging efficiency. .
Battery performance is also influenced by the concentration of the NaOH-LiOH electrolyte, and there is an optimum concentration. An embodiment of the present invention will be described below. Iron fibers having a fiber diameter of about 10 to 30 microns are created by cutting iron. The fiber length varies depending on the length of the raw material iron wire to be cut or the quality of the iron, but if it is 1 cm or more, it will not have a major effect on the strength of the sintered body. Here, one of approximately 5 to 10 cm was used. Width 20 while maintaining a certain direction while intertwining the fibers.
After removing the elasticity of the 80cm long felt in a reducing atmosphere, press it.
Sinter at 1000-1100°C in a reducing atmosphere such as hydrogen. Press pressure and sintering time affect porosity, but the iron fiber sintered body obtained here has an average porosity of 95.
It is about %. Thereafter, according to a conventional method, the iron fiber sintered body is plated with electric nickel to a thickness of 2 to 3 μm. Cadmium oxide: ethylene glycol: isopropyl alcohol was added to this sintered body by a calender roll method in a weight ratio of 8:2:0.5.
After applying the active material in paste form and drying it with hot air at approximately 100℃ for 10 minutes, it was charged to 150% of the theoretical capacity with a charging current of 3mA/cm ² in a KOH electrolyte with a specific gravity of 1.20, and the current was 6mA. Organic substances such as ethylene glycol and isopropyl alcohol are completely removed by a conventional chemical conversion treatment that involves discharging to OV with a discharge current of /cm ² and then washing with water. After completion of chemical formation, it is punched out to a predetermined size to form an electrode plate. On the other hand, the positive electrode plate is made by impregnating a nickel plaque with a porosity of approximately 80%, which is made by sintering nickel powder onto a perforated steel plate, with a nickel nitrate solution, and repeating the usual process of electrolytic reduction in sodium hydroxide several times to make the active material. After that, chemical conversion is performed to remove impurities. After punching to a predetermined size, a sealed battery was created using the electrode plates and separator. The dimensions of the positive electrode plate of the created battery are
200 ^l × 39 ^w × 0.85 ^t mm, negative electrode plate dimensions are 240 ^l × 39 ^w ×
A polypropylene nonwoven fabric was used for the separator at 0.65 ^t . The battery size is a 25φ x 49mm sealed cylindrical battery, which is the same size as a commercially available battery with a nominal capacity of 1800mAh. The nominal capacity of the created battery is 2300mAh. The electrolyte composition used was a mixed aqueous solution of 3-5N sodium hydroxide and 0.5-1.5N lithium hydroxide, and a mixed aqueous solution of 5N potassium hydroxide and 1.0N lithium hydroxide. The typical performance of this battery at room temperature is 1/10C at a charging current of 15
Charging for 24 hours and discharging to 1.00V with a current of 1/5C and 1C, and charging for 24 hours with a current of 1/30C using an induction light standard test at 5℃ and 45℃.
Performance achieved by discharging to 1.15V with a 1C current, and charging for 48 hours with a 1/30C current according to the emergency lighting standard test at 45℃, then discharging to 1.15V with a 1C current. As shown in the table, the actual capacity of the battery according to the present invention using a mixed aqueous solution of sodium hydroxide and lithium hydroxide is 2.7 to 2.8 Ah, and the nominal capacity is 2400 to 2500 Ah.
The capacity is equivalent to mAh. On the other hand, in the guidance light and emergency light standard tests, it has higher performance than the current 1800mAh battery that uses sintered positive and negative electrode plates.

【table】

[Table] (Note) A in the table is based on the battery configuration of the present invention and has a nominal capacity of 2300 mAh, and B in the table is a battery using a conventional sintered electrode plate and has a nominal capacity of 1800 mAh. is at 25℃1/10C to check the actual capacity.
This is the capacity when charged for 15 hours and discharged to a final voltage of 1.00V at 1/5C. indicates the performance according to the 45℃ induction light standard test, indicates the performance according to the 5℃ induction light standard test, and is 45 This shows the performance according to the °C emergency lighting standard test. The discharge voltage characteristics are also excellent as shown in FIG. The reason for this is that the utilization rate of the negative electrode active material of the present invention is about 7 to 10% higher than the conventional sinter method, and about 15% higher than the conventional paste method. It is thought that this is because, by reducing as much as possible, there is no negative polarization and perfect positive discharge characteristics can be exhibited. (Figure 4) Figure 5 shows the pore size distribution of the fiber sintered body (A) according to the present invention and the conventional nickel powder sintered body (B). It can be seen that it accounts for the majority. An electrolytic solution that is well-balanced at a low temperature of 5°C to a high temperature of 45°C is considered to be a mixed solution containing around 4N of sodium hydroxide and around 1N of lithium hydroxide. As described above, the present invention comprehensively improves fiber properties, active material filling method, electrolyte composition, etc.
This work succeeded in creating a battery with a higher capacity density than conventional sintered batteries, and its industrial value is enormous.

[Brief explanation of drawings]

Figures 1 and 2 show changes in characteristics depending on the thickness of the nickel plating of the fiber sintered body of the present invention.
is the fiber direction, and B is the direction perpendicular to the fibers. In FIG. 3, A shows the discharge voltage characteristics of the battery of the present invention and B shows the discharge pressure characteristics of the conventional battery using sintered electrode plates in the 45°C guide light standard test. FIG. 4A shows the change in the active material utilization rate of the negative electrode plate of the present invention, B shows the conventional sintered electrode plate, and C shows the conventional paste-type electrode plate. FIG. 5 shows the pore size distribution of the sintered body measured by a mercury porosimeter, where B indicates the nickel powder sintered body and A indicates the nickel-plated iron fiber sintered body.

Claims (1)

[Scope of Claims] 1 Cutting iron fibers with a wire diameter of 4 to 100μ are arranged in a certain direction, and a sintered body with a porosity of 90% or more with a nickel plating thickness of 2μ or more is coated with cadmium oxide and ethylene glycol. A negative electrode plate obtained by forming a paste solution that maintains fluidity using only a water-free organic solvent such as isopropyl alcohol or glycerin and filling the sintered body with micropores of 10 to 50μ. A sealed nickel cadmium storage battery characterized by the use of a sealed nickel cadmium storage battery. 2. Claim 1, characterized in that when a negative electrode plate using a directional fiber sintered body is used in a spiral-wound sealed nickel cadmium battery, the winding direction and the fiber direction are made to match. sealed nickel cadmium storage battery. 3. The sealed nickel-cadmium storage battery according to claim 1, wherein the electrolytic solution used is a mixed aqueous solution containing 3.5-4.5N lithium hydroxide and 0.5-1.0N lithium hydroxide.