JPS645421B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to increasing the capacity density of a sealed nickel cadmium storage battery. Conventional technology and its problems In recent years, the capacity density of sealed nickel cadmium storage batteries has been increased in general, from small ones of several hundred mAh to large ones of several hundred Ah, but in particular, cylindrical sealed batteries of about 1 to 5 Ah have been developed. It is being actively developed in the storage battery field. This field has a special purpose as a power source for guidance lights and emergency lights, and in this case, charging with a microcurrent of about 1/30C under an unprecedentedly wide temperature range of 5℃ to 50℃ is extremely difficult. Sufficient high performance must be maintained under the conditions of use. Therefore, for example, the dimensions called NR-C type
For a 25φ x 49mm cylindrical sealed storage battery, the nominal capacity is limited to about 1.8Ah 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. 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 a raw material, requires large-scale equipment, a complicated active material impregnation process, and has a low capacity density. Nowadays, when electrode plates with high capacity density are required, the paste type is more advantageous than the sintered type. On the other hand, 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 creating a highly viscous paste solution. Created by painting on both sides. The water contained in this paste solution reacts with the CdO powder, forming CdO・H ₂ O.
That is, the powders are bonded together as Cd(OH) ₂ (cementation), and are held without falling off the core metal during coating. When applying to perforated steel plates, etc.,
This paste liquid has favorable properties for the reasons mentioned above, but it is not suitable for fiber substrates with porous structures.
Due to this cementation, the fluidity of the liquid is lost and the inside of the pores cannot be filled 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 higher than that of the sintered type. , which 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. or,
In paste-type electrode plates using substrates such as expanded metal, wire mesh, perforated steel plates, etc., binders are used because it is difficult to hold the paste on the substrate. However, this binder covers the surface of the active material and becomes an electrode with high resistance, which is not preferable. Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and provides excellent current collection properties, active material retention properties, mechanical strength, active material utilization rate, etc. using an alkali-resistant metal fiber sintered body. The purpose of the present invention is to provide a sealed nickel-cadmium storage battery that is a battery that combines a paste-type negative electrode plate and a positive electrode plate, and that has improved capacity density, extended life, and reduced cost. Structure of the Invention In order to achieve the above object, the present invention has a wire diameter of 4 to 4.
The 100μ alkali-resistant metal fibers are lined up in a certain direction, and the thickness is nickel-metalized.
Add cadmium oxide to a sintered body with a porosity of 2 μ or more and a porosity of 90% or more using only a water-free organic solvent such as ethylene glycol, isopropyl alcohol, or glycerin to form a paste solution that maintains fluidity. This is a sealed nickel-cadmium storage battery characterized by using a negative electrode plate obtained by filling the battery. There are various ways to create metal fibers, but for example, steel wool is created by cutting iron wire with dozens of knives to create a wire with a diameter of about 4 to 100 μm. It is made into wool. 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 steel wool manufacturing equipment was expensive, it was never used as a paste-type negative electrode plate base material. Fiber length is from several centimeters to several tens of centimeters
Since long fibers can be freely created, when sintered, a sintered body with extremely high strength can be obtained, so perforated steel plates for reinforcement such as nickel powder sintered bodies, etc. No conductive core required. Porosities of about 90 to 98% can be used. Nickel fibers can be used as is, but iron fibers require nickel plating because they have corroded areas. This sintered body is used as a paste-type negative electrode base material. Width 5-30cm, length 50-100
In order to continuously produce a sintered body in meters, it is necessary to intertwine these fibers alternately to produce a felt state in which the fibers have a certain directionality. However, since it is a sintered body of fibers with directionality, as shown in the table (differences in properties depending on the direction of the fiber sintered body of the present invention), (A) it has excellent electrical conductivity and tensile strength in the fiber direction. (B) However, it is somewhat inferior in the longitudinal direction and perpendicular direction. Due to this directionality, when a spiral-wound battery was created using a sintered body 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 micro short circuits. On the other hand, when a sintered body in which the winding direction was the fiber direction was used, this problem was solved, 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 nickel plating is used, 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.

[Table] A paste solution is prepared from only cadmium oxide and water-free organic solvents such as ethylene glycol, isopropyl alcohol, and glycerin to these metal fiber sintered bodies, and the negative electrode active material is made into a fluid paste. Fill the specified amount. 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. Conventional paste-type negative electrode plates require 10 to 15 wt% nickel powder as a conductive material, but the metal fiber sintered body of the present invention does not require nickel powder because the fibers themselves have 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. Plates with higher capacitance densities than conventional ones can be made to act very effectively as substrates. 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 0.7 mm, but as the thickness decreases, the proportion of conductive cores such as perforated steel plates increases. Consolidation is preferable. However, if it becomes too thick, it will cause problems such as diffusion of the electrolyte, so a thickness of about 0.8 to 1.0 mm is effective. When using the electrolyte at high temperatures of 40℃ 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. On the other hand, regarding the discharge voltage characteristics, the _lower the concentration electrolyte, ^the higher the voltage, and _the better. When the alkali concentration becomes low, the resistance increases and the active material utilization rate decreases. For this reason, if a sodium hydroxide concentration of 5N or less is used, the negative electrode may be limited and cannot be used. However, in the case of fiber sintered bodies, they do not have micropores of 10μ or less like nickel powder sintered bodies, so
Since the OH ^- ions required for the reaction can be smoothly supplied from the bulk, there is almost no resistance even when a sodium hydroxide concentration of about 4N is used, and good discharge pressure characteristics are exhibited. Embodiment An embodiment of the present invention will be explained below. For example, in the case of iron fiber, which is widely known as being cheap, firstly, by cutting the iron, it becomes 10 to 30 μm.
Create iron fibers with a fiber diameter of approximately 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. After entwining the fibers with each other and maintaining a certain direction, the felt was made into a felt state with a width of 20 cm and a length of 80 m. After removing the elasticity in a reducing atmosphere, it was pressed and heated at 1000-1100°C with hydrogen, etc. Sinter in a reducing atmosphere. Press pressure and sintering time affect porosity, but the iron fiber sintered body obtained here has an average porosity of about 95%. Thereafter, the iron fiber sintered body is plated with electric nickel to a thickness of 2 to 3 μm according to a conventional method. This sintered body was processed by a calender roll method so that the weight ratio of cadmium oxide, ethylene glycol, and isopropyl alcohol was 8:8.
After applying a paste active material with a ratio of 2:0.5 and drying it with hot air at about 100℃ for 10 minutes,
Ethylene glycol is converted into ethylene glycol by a conventional chemical conversion treatment in which 150% of the theoretical capacity is charged with a charging current of 3 mA/cm ² in a KOH electrolyte, discharged to 0 V with a current of 6 mA/cm ² , and then washed with water. , completely removes organic substances such as isopropyl alcohol. 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 on a perforated steel plate, with a nickel nitrate solution.
A conventional operation of electrolytic reduction in sodium hydroxide is repeated several times to fill the active material, and then chemical conversion is performed to remove impurities. After punching to a predetermined size, a sealed battery was created using the electrode plates and the separator. The positive electrode plate dimensions of the created battery were 200 x 39 W x 0.85 tmm, the negative electrode plate dimensions were 240 x 39 W x 0.65 tmm, and a polypropylene nonwoven fabric was used for the separator. Battery dimensions are 25φ×
Commercially available nominal capacity 1800m with 49mm cylindrical sealed battery
It is the same size as an Ah battery. The nominal capacity of the created battery is 2300mAh. The electrolyte compositions used were 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. This battery was charged for 15 hours at a normal performance of 1/10C charging current at room temperature, 1/5C, 1C.
Method of discharging to 1.00V with a current of discharge and 5
℃, a method of charging for 24 hours with a 1/30C constant charge current according to the induction light standard test at 45℃, and discharging to 1.15V with a 1C constant discharge current, and a method of charging at 1/30C according to the emergency light standard test at 45℃. Charge it for 45 hours with a stream of water.
When the performance was investigated by 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 was 2.7 to 2.8Ah. It has a high capacity equivalent to a nominal capacity of 2400 to 2500mAh. On the other hand, in the guidance light and emergency light standard tests, the nominal capacity was 1800 m using the current sinter type positive and negative electrode plates.
Higher performance than Ah batteries.

[Table] (Note) In the table, (A) is a battery configured according to the present invention and has a nominal capacity of 2300 mAh, and (B) is a battery using a conventional sintered electrode plate and has a nominal capacity of 1800 mAh.
is 15 at 25℃ and 1/10C to check the actual capacity.
This is the capacity when charged for an hour and discharged to a final voltage of 1.00V at 1/5C. indicates the performance according to the induction light standard test at 45℃, indicates the performance according to the induction light standard test at 5℃, and This shows the performance according to the 45℃ emergency lighting standard test. The discharge pressure characteristics are also the third
It is excellent as shown in the figure. The reason for this is that, as shown in Figure 4, the utilization rate of the negative electrode active material of the present invention is improved by about 7 to 10% compared to the conventional sinter method and about 15% compared to the conventional paste method. It is thought that this is because the resistivity was minimized as much as possible in consideration of the characteristics of the battery, and since there is no negative polarization, when it is made into a battery, it can exhibit perfect positive discharge characteristics. Furthermore, while the conventional paste-type electrode plate has a planar substrate and electrodes cannot be formed unless the active material is held on the substrate by a binder, the paste-type electrode plate used in the present invention The active material is held by a porous substrate entangled with fibers without using an adhesive. 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. Effects of the Invention As described above, the present invention comprehensively improves fiber properties, active material filling method, electrolyte composition, etc.
This technology has realized a battery with a high capacity density that exceeds that of conventional sintered batteries, has a long life span, and can reduce costs, so 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.

Claims (1)

[Scope of Claims] 1 A sintered body made of alkali-resistant metal fibers with a wire diameter of 4 to 100μ arranged in a fixed direction and with a nickel plating thickness of 2μ or more and a porosity of 90% or more, in which cadmium oxide is added to ethylene glycol. , a negative electrode plate obtained by filling the sintered body with a paste liquid that maintains fluidity using only a water-free organic solvent such as isopropyl alcohol or glycerin. type 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. The sealed nickel cadmium storage battery described. 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 sodium hydroxide and 0.5-1.0N lithium hydroxide.