JP5062724B2 - Method for producing nickel electrode for alkaline battery and nickel electrode for alkaline battery - Google Patents

Description

  The present invention relates to a nickel electrode for an alkaline battery used for an alkaline secondary battery and a method for producing the same. In particular, the present invention relates to a nickel electrode for an alkaline battery used for a nickel-hydrogen battery or a nickel-cadmium battery and a method for producing the same.

  2. Description of the Related Art Conventionally, alkaline secondary batteries have been widely used along with lead-acid batteries and lithium ion batteries as secondary batteries used for portable, mobile, and industrial purposes.

  Alkaline secondary batteries are used in a wide range of fields because they are highly reliable, have a long life, are less expensive than lithium ion batteries, and can be reduced in size and weight. In particular, from the standpoint of promoting energy saving and environmental conservation, the range of practical applications has been expanded by automobile manufacturers to hybrid vehicles, and has attracted widespread attention overseas. Currently, nickel-hydrogen batteries are mainly used as the power source.

  By the way, in most alkaline batteries widely used as power sources for various devices ranging from portable equipment to large industrial equipment, a nickel electrode is used as a positive electrode. As the structure of the nickel electrode, a structure in which a positive electrode active material for causing a battery reaction is supported on a current collector having a current collecting function as in the case of other battery electrodes is employed. In this case, the alkaline secondary battery has been put to practical use by inventing a sintered nickel plate obtained by sintering nickel powder instead of the conventional pocket type as a current collector.

  Later, nickel electrodes were made cheaper and higher in capacity. As a cost-effective technique, it was proposed to use a two-dimensional structure such as punching metal instead of a sintered body having a three-dimensional structure. Specifically, it is a technology for producing a nickel electrode by filling a hole in a punching metal with an active material paste (a paste containing an active material), but such a nickel electrode has various problems. Since it has, it has not reached the stage of practical use.

  On the other hand, it is possible to increase the capacity of the nickel electrode by adopting foamed nickel having a three-dimensional structure instead of the sintered body. Foamed nickel is usually produced by a method in which the foamed sheet of urethane resin is nickel-plated and the urethane resin is incinerated and then annealed in a reducing atmosphere to improve the strength of the nickel skeleton. The foamed nickel is filled with an active material paste and pressed to obtain a nickel electrode. The porosity of foamed nickel is very high at 92-96% compared to about 80% of the sintered body. Therefore, more active material can be filled per unit volume, realizing high capacity. it can.

  Foamed nickel had a problem that it was easily damaged at the beginning of development. For example, when a sheet-like nickel electrode is wound and stored in a cylindrical battery container, there has been a problem that foamed nickel is cracked. However, at present, this problem has been solved. Cylindrical and prismatic nickel-hydrogen batteries using foamed nickel current collectors are required not only for portable devices but also for hybrid vehicles that require high output and high reliability. Has been put to practical use. As described above, some nickel-hydrogen batteries use sintered bodies in some devices, but the mainstream carries active materials on foamed nickel electrode substrates (current collectors). It has been replaced by what I let you.

  At present, foamed nickel has reached a level having characteristics suitable not only for high capacity but also for high output as a current collector for battery electrodes. The remaining problem is to reduce the cost of the nickel electrode by reducing the amount of nickel that accounts for the majority of the price of the nickel electrode.

Foamed nickel is first developed, were adopted 500-600 g / m ² as a weight per unit area by weight of nickel. At present, products that can withstand practical use even with a basis weight of about 350 to 400 g / m ² have been developed. However, if the amount of nickel is further reduced, the strength of the nickel electrode decreases, so even if foamed nickel can be produced, there is a very high possibility of breakage during the subsequent nickel electrode production process and battery production. .

  On the other hand, it has been proposed to produce a nickel electrode using a non-woven fabric as a core material and a porous electrode substrate formed by plating nickel on the surface thereof as a current collector. A nickel electrode using a nonwoven fabric as a core material has an advantage that a predetermined strength can be maintained even if the amount of nickel is reduced, and that manufacture is easier than foamed nickel. As an electrode formed by supporting an active material on such an electrode substrate, for example, an electrode described in Patent Document 1 can be given.

  Patent Document 1 discloses a current collector (porous electrode substrate) formed by plating nickel on the surface of a resin nonwoven fabric. Further, an alkaline battery electrode is disclosed in which the electrode substrate is filled with a paste-like active material mixture and then pressure-molded.

JP-A-61-208756

  However, in recent years, there has been a demand for a battery that is not only low in manufacturing cost, but also smaller in size, larger in capacity, and less likely to deteriorate in battery performance due to repeated charging and discharging, as described in Patent Document 1 above. In some cases, the nickel plated electrode cannot meet these requirements. For example, in the battery manufactured using the electrode of Patent Document 1, the battery capacity is significantly reduced due to charging / discharging. This is because the electrode substrate swells with charge / discharge, returns to the thickness before compression, and the active material easily peels from the electrode substrate.

  Accordingly, a main object of the present invention is to provide a method for producing a nickel electrode for an alkaline battery and a nickel electrode for an alkaline battery, which have a desired capacity and can suppress deterioration of battery performance associated with charge / discharge. .

  As a result of various studies on nickel electrodes for alkaline batteries that have a desired capacity and can suppress deterioration of battery performance, the present inventors have obtained the following knowledge

  First, it was examined to regulate the compression ratio of the nickel electrode for foamed nickel. The foamed urethane that becomes the core when producing the foamed nickel has a limit of about 1200 to 1300 μm in terms of handling, and if it is less than that, the urethane will be damaged in the subsequent steps such as plating. Accordingly, the thickness after nickel plating is almost the same, 1200 to 1300 μm, and foam nickel having a thickness less than that is not used as an electrode substrate. For example, when a nickel electrode having a thickness of 500 μm is manufactured after pressurization using the foamed nickel having the above thickness, the nickel skeleton in the electrode substrate made of foamed nickel is compressed to 1 / 2.4 to 1 / 2.6. The In the electrode substrate having such a compression ratio, when the active material swells due to repeated charging and discharging, the electrode substrate has a large force to return to the original thickness, and the force to suppress the swelling of the active material is weak. It turned out to be easy to swell. Thus, it became clear that the ratio which compresses an electrode substrate is very important.

  Next, different from foamed nickel, various studies were made focusing on an electrode substrate using a non-woven fabric whose thickness can be freely produced. As a result, it has been found that the capacity retention rate of the battery can be improved by adjusting the initial thickness of the electrode substrate and defining the compression ratio within an appropriate range.

  Furthermore, as a result of studying to reduce the force that the electrode substrate tries to return to its original thickness along with charge / discharge, heat treatment after compression of the electrode substrate further suppresses battery capacity reduction due to charge / discharge I got the knowledge that I can do it.

This invention is prescribed | regulated based on the said knowledge.
The method for producing a nickel electrode for an alkaline battery according to the present invention is a method for producing a nickel electrode for an alkaline battery by filling an electrode substrate in which the surface of a non-woven fiber is coated with nickel with an active material mixture, and then pressing to form an electrode. is there. The pressure molding uses an electrode substrate having a thickness of 2.3 t or less, where t is the thickness of the electrode after pressure molding, and is from 80 ° C. to 130 ° C. for 5 minutes to 60 minutes after pressure molding. The heat treatment is performed.

  The nickel electrode for alkaline battery of the present invention is a nickel electrode for alkaline battery, in which an active material mixture is filled into an electrode substrate in which the surface of a nonwoven fabric fiber is coated with nickel, and then pressed to form an electrode. When the thickness of the electrode after pressure forming is t, an electrode substrate having a thickness of 2.3 t or less is pressure formed. It is characterized by being obtained by performing a heat treatment at 80 ° C. or higher and 130 ° C. or lower for 5 minutes or longer and 60 minutes or shorter after the pressure molding.

  By defining the ratio of compression (pressure forming) of the electrode substrate after filling the active material mixture, it is possible to fill the electrode substrate with a sufficient amount of the active material mixture and to provide pores in the electrode substrate. It is possible to make it difficult to peel off the active material fixed on the surface.

  As described above, the nickel electrode formed by compressing the electrode substrate tends to return to the thickness before compression as the battery is charged / discharged. This is because the active material undergoes a volume change with charge / discharge, and as a result, the entire electrode swells. For example, when nickel hydroxide is used as the active material, the active material repeatedly changes between nickel hydroxide and nickel oxyhydroxide with the charge / discharge reaction. At this time, if the compressibility of the electrode substrate is high, the electrode substrate easily returns to the thickness before compression due to the swollen active material, and the swollen active material easily peels from the electrode substrate. When the active material peels from the electrode substrate, the degree of contact between the electrode substrate, which is a current collector, and the active material is reduced, and the discharge capacity of the battery is reduced. When the electrode swells, the electrolyte concentrates inside the electrode and the separator is relatively compressed. As a result, the amount of electrolyte in the separator decreases, the internal resistance of the battery increases, and the discharge capacity of the battery decreases. For these reasons, when the thickness of the electrode substrate is more than 2.3 times that of the nickel electrode, the electrode substrate has a large force to return to the original thickness, and the electrode substrate has a weak force to suppress the swelling of the active material. Therefore, the active material is frequently peeled from the electrode substrate, and the battery discharge capacity is significantly reduced. The nickel electrode of the present invention has a thickness of the electrode substrate of 2.3 t or less, so that the return allowance of the electrode substrate is relatively small and the swelling of the active material can be suppressed. Is unlikely to occur. A more preferable thickness of the electrode substrate is 1.8 t or less.

  Since the electrode substrate is premised on compression molding (pressure molding), the electrode substrate may have a thickness of more than t and 2.3 t or less. However, the closer the thickness of the electrode substrate before compression is to the thickness of the nickel electrode, the smaller the amount of active material that can be filled in the pores. Further, in such an electrode substrate, when the amount of the active material for securing the capacity required for the battery to be manufactured is large, the active material that has not been filled in the pores adheres to the surface of the electrode substrate. When the active material adhering to the surface of the electrode substrate swells as the battery is charged / discharged, the swelling cannot be suppressed due to the network structure of the electrode substrate, so that the active material is easily peeled off from the electrode substrate. Therefore, the capacity of a battery manufactured using this electrode is reduced, and its life is shortened. In consideration of the above, it is preferable that the thickness of the electrode substrate is 1.3 t or more in order to ensure a sufficient battery capacity and to obtain a long-life battery. A more preferable thickness of the electrode substrate is 1.4 t or more.

  In addition, the above-described compression of the electrode substrate takes into consideration the amount of the active material to be filled, and suppresses an extreme elongation (for example, an elongation exceeding 10%) to the extent that the three-dimensional network structure of the electrode substrate is not destroyed. It is preferable. For example, when filling the electrode substrate with a thickness of 900 μm with a small amount of active material, compressing the electrode substrate to 500 μm rather than compressing the electrode substrate to 600 μm will firmly compress the active material filled in the electrode substrate. Thus, the adhesion between the active materials and between the active material and the electrode substrate is increased. By adjusting the compression ratio in accordance with the amount of the active material to be filled in this way, it is possible to effectively suppress peeling of the active material that accompanies charge / discharge.

  For press molding of the electrode substrate filled with the active material, press or rolling can be used. In particular, since the roller press machine can quickly and easily press-mold the electrode substrate, the mass productivity of the nickel electrode can be improved. Further, the roller press has an advantage that a long electrode substrate can be uniformly pressure-formed.

  In addition, the electrode can be made difficult to swell by performing heat treatment at 80 ° C. or higher and 130 ° C. or lower for 5 minutes to 60 minutes after pressure molding. This is because the fibers inside the electrode substrate are once softened by heat treatment and then solidified in a compressed state. When the heat treatment temperature is 80 ° C. or lower, the degree of softening of the fiber is small, and the fiber is hard to solidify in a compressed state. If the temperature is 130 ° C. or higher, some of the fibers are melted, and the molten fibers wrap around the active material and become resistance. If the heat treatment time within the above temperature range is less than 5 minutes, the fiber is not sufficiently softened, and therefore it is difficult to solidify in a compressed state. Moreover, since the fiber is sufficiently softened in about 60 minutes in any of the above temperature ranges, the heat treatment for more than 60 minutes reduces the productivity of the electrode substrate. In addition, what is necessary is just to select suitably the temperature and time of the heat processing mentioned above with the material of the nonwoven fabric which can be utilized suitably for the electrode substrate mentioned below.

  The nonwoven fabric that is the core material of the electrode substrate is made of a material that can maintain the strength of the electrode substrate. Considering alkali resistance, oxidation resistance, price, etc. as the material, polyolefin resins such as polyethylene and polypropylene, polymers and mixtures thereof, or core-sheath structures in which polyethylene is coated on a polypropylene skeleton, etc. It can be suitably used. These polyolefin-based resins improve the strength of the electrode substrate, make it difficult to expand the electrode substrate, and make it difficult to cause poor contact between the electrode substrate, which is a current collector, and the active material paste. Moreover, flexibility is imparted to the electrode substrate so that the electrode substrate is not easily cracked during pressure molding. In addition, when an electrode substrate having a polymer having a functional group containing nitrogen such as polyamide as a core material is used for a nickel-hydrogen battery, self-discharge of the battery becomes large. In addition, polymers such as polyvinyl alcohol having a hydroxyl group and polyvinyl acetate having an acetate group do not have good alkali resistance and oxidation resistance.

The basis weight of the nonwoven fabric used for the electrode is not particularly limited. However, if the nonwoven fabric is made bulky and the void volume is increased, the amount of active material that can be filled can be increased, so that a high-capacity battery similar to conventional foamed nickel can be obtained. Moreover, in order to ensure the strength at the time of pressure molding in the subsequent process, the basis weight of the nonwoven fabric is preferably within the range of ^{20 to} 100 g / m ² . In the nonwoven fabric produced based on the above-mentioned weight per unit area, the ratio of the pores (porosity) in the volume can be set to the same level as the foamed nickel. Preferably, the weight of the nonwoven fabric is adjusted to 85 to 98% by adjusting the basis weight. More preferably, the porosity of the nonwoven fabric is 90 to 96%. Here, even when nickel is plated on the surface of the non-woven fabric, the thickness of the nickel to be plated is very thin, and the porosity is not substantially changed.

  The nonwoven fabric can be produced by a dry method formed in a gas phase or a wet method in which fibers are dispersed and dispersed in water. The nonwoven fabric obtained by the wet method has less variation in the basis weight and thickness than the nonwoven fabric obtained by the dry method, and a uniform current collector can be ensured. Moreover, you may use a nonwoven fabric, after performing the entanglement process which entangles the fibers of a nonwoven fabric, and the heat processing which fuse | melts the contact point of fibers, and improving a intensity | strength. In addition, you may perform the hydrophilic treatment for improving the adhesiveness of a nonwoven fabric and nickel to a nonwoven fabric.

The amount of nickel coated on the surface of the nonwoven fabric may be an amount that can exhibit sufficient performance as a current collector. Preferably, the amount of nickel to be coated is about 50 to 220 g / m ² . The amount of nickel can be significantly less than the basis weight of 350 to 400 g / m ^{2 of} foamed nickel that has been put into practical use, so that the nickel electrode can be made inexpensive. When the amount of nickel is less than 50 g / m ² , the strength of the nickel electrode becomes a problem.

  As a method for coating the non-woven fabric with nickel, a known preferable method may be selected. For example, the method of coating nickel may be electroless plating, electrolytic plating, or a vapor phase method such as sputtering. Further, the nonwoven fabric may be coated with nickel by combining the above methods. Preferably, electroless plating is performed after imparting conductivity to the surface of the nonwoven fabric by electroless plating or sputtering. The electroplating may be performed using a plating bath, and a watt bath, a chloride bath, a sulfamic acid bath, or the like can be suitably used as the plating bath. A pH buffering agent or a surfactant may be added to these plating baths.

  When the nickel electrode of the present invention is used in a nickel-hydrogen battery, nickel hydroxide can be cited as an active material to be supported on the electrode substrate. In order to carry this active material on the electrode substrate, it is preferable to prepare a paste-like active material mixture containing the active material as a main ingredient and pressurize and fill the electrode substrate. By filling with pressure, the active material can be evenly distributed inside the electrode substrate. In addition, after filling the active material mixture, the active material can be fixed to the electrode substrate by drying the electrode substrate.

  In addition to nickel hydroxide, the nickel-hydrogen battery active material mixture includes a conductive auxiliary agent that supplements the conductivity of nickel hydroxide, and a bond that improves the adhesion between the electrode substrate, which is a current collector, and the active material. It is preferable that an adhesive is included. As the conductive aid, graphite, cobalt, cobalt compounds, and the like can be suitably used. In particular, when spherical nickel hydroxide whose surface is coated with cobalt oxide is used as an active material, a reduction in discharge capacity can be suppressed even when the amount of nickel in the electrode substrate is reduced. On the other hand, carboxymethyl cellulose or the like can be used as the binder.

  What is necessary is just to select suitably the thickness of the electrode when press-molding an electrode substrate into a nickel electrode according to the use of an electrode. For example, the thickness of the nickel electrode to be used is about 350 to 550 μm in a battery for high output used in a hybrid vehicle or an electric tool, and the thickness of the nickel electrode to be used in a battery for high capacity used in a digital camera etc. The length is about 550 to 700 μm. Further, the capacity density required for the battery used in these applications is about 300 to 550 mAh / cc for high output applications, and about 550 to 750 mAh / cc for high capacity applications.

  As described above, when an alkaline battery is manufactured using the nickel electrode of the present invention described above, this electrode may be used as it is, or may be used after being folded. Further, a battery may be manufactured by placing a reinforcing expanded metal or punching metal along the nickel electrode.

  According to the method for producing a nickel electrode for an alkaline battery of the present invention, it is possible to obtain a nickel electrode for an alkaline battery in which the capacity is high even when the electrode is thin, and the capacity maintenance rate is hardly lowered even during repeated charge and discharge.

  In addition, if the nickel electrode for alkaline battery of the present invention is used, the capacity is high even if the electrode thickness is thin, and the capacity maintenance rate is difficult to decrease even during repeated charge and discharge, so a high-performance alkaline battery is manufactured. Can do.

<Example 1>
In this example, a non-woven core material was coated with nickel to form an electrode substrate. Here, while changing the thickness of an electrode substrate, the ratio which compresses an electrode substrate was changed, and the several electrode for batteries was produced. The active material filled in the electrode substrate is a positive electrode active material for nickel-hydrogen batteries, and the manufactured electrode is a nickel electrode for nickel-hydrogen batteries.

In producing a nickel electrode of a nickel-hydrogen battery, first, nonwoven fabrics having thicknesses of 1200, 1000, 900, 800, 700, and 600 μm were prepared. The nonwoven fabric was produced by a wet method so that the ratio of polyethylene fiber and polypropylene fiber was 8: 2. This nonwoven fabric had a porosity of 90%, a pore diameter of 15 to 200 μm, an average fiber diameter of 15 μm, a weight per unit area of 65 g / m ² , and a width of 600 mm.

Next, a conductive layer was formed on the surface of each non-woven fabric by a known sputtering apparatus so that electrolytic plating could be performed. Sputtering involves placing an electrode substrate and a nickel piece in a vacuum vessel, applying a high DC voltage while introducing an inert gas, and causing the ionized inert gas to collide with the nickel, thereby causing the nickel to fall on the nonwoven fabric. It is a method of forming. The amount of nickel coated on the nonwoven fabric by sputtering was 8 g / m ² .

Nickel was plated on the non-woven fabric provided with conductivity. Nickel plating was performed in a Watt bath containing nickel sulfate 330 g / L, nickel chloride 50 g / L, and boric acid 40 g / L as main components. Specifically, the above-mentioned non-woven fabric imparted with electrical conductivity wound around a carrier was fed into a watt bath, and nickel was plated so that the average amount of nickel to be coated was 200 g / m ² . As a counter electrode of the nonwoven fabric provided with conductivity, a titanium basket containing a nickel piece was used. Since the thickness of the nickel plated on the nonwoven fabric is very thin, about 3 μm, the thickness of the electrode substrate is almost the same as the thickness before coating the nickel.

  Each electrode substrate was filled with an active material paste by a press-fitting method. However, the electrode substrates having thicknesses of 1200 μm and 1000 μm were adjusted to a thickness of 900 μm with a roller press in order to uniformly fill the pores of the electrode substrate with the active material paste in the next step. The thickness adjustment was performed in order to improve the surface smoothness of the substrate and to suppress in-plane variation in the filling amount of the active material paste. The active material paste to be filled in the electrode substrate was a paste prepared by mixing 70 parts by weight of cobalt-coated nickel hydroxide powder and 5 parts by weight of oxycobalt oxide and adding a 0.5% carboxymethylcellulose aqueous solution. Cobalt oxyhydroxide equivalent to 5.5% of the total weight of the nickel hydroxide powder is coated on the surface of the cobalt-coated nickel hydroxide powder by a known method. The filling of the active material paste was somewhat difficult only on the 600 μm electrode substrate, and the active material paste remained attached to the electrode substrate surface.

  Immediately after filling the paste, the surface of the electrode substrate was smoothed and dried at 90 ° C. After drying, the electrode substrate holding the active material was compressed (press-molded) to a thickness of 450 μm by a roller press having an embossed 30 cm diameter roller.

  In this example, the pressure-formed electrode substrates were each heat-treated at 110 ° C. for 20 minutes to obtain nickel electrodes a to f. Table 1 shows the thickness of nickel electrodes a to f before pressure molding (electrode substrate thickness), the thickness after pressure molding (thickness of nickel electrode), and the compression ratio (thickness before pressure molding). / Thickness after pressure molding).

  The nickel electrodes in Table 1 were cut into strips having a width of 32 mm and a length of 280 mm to form positive electrodes, and batteries A to F were produced using these positive electrodes a to f. The battery was manufactured by stacking a positive electrode, a separator, and a negative electrode, wound like a roll, and housed in a SubC size battery case (cylindrical container: φ23 mm × 43 mm) to fill the electrolyte. When winding the positive electrode and the negative electrode, the positive electrode and the negative electrode are shifted in the longitudinal direction of the battery case. A so-called tabless method was adopted in which the long-side end of the strip-shaped negative electrode was welded to a disk-shaped current collector disposed at the bottom of the tank.

  A known hydrogen storage alloy was used for the negative electrodes of the batteries A to F. The negative electrode was manufactured by applying a paste-like hydrogen storage alloy to a punching metal manufactured by plating nickel on an iron plate, smoothing the surface, and then pressure forming with a roller press. The paste-like hydrogen storage alloy is a 1% carboxymethylcellulose aqueous solution of MmNi-based ternary hydrogen storage alloy containing Al, Mn, and Co (Mm is a rare earth mixture mainly composed of Ce, La, Pr, and Nd). It was obtained by adding to The negative electrode has a width of 32 mm, a length of 280 mm, and a thickness of 380 μm. Moreover, N / P which is the capacity | capacitance of the negative electrode with respect to the capacity | capacitance of a positive electrode is 1.5. In addition, the capacity | capacitance of a negative electrode is larger than the capacity | capacitance of a positive electrode because the negative electrode absorbs the gaseous oxygen generated in a battery at the time of overcharge.

  For the separators of the batteries A to F, a polypropylene nonwoven fabric that has been subjected to a hydrophilic treatment and has an affinity for the electrolytic solution is used. The separator had a thickness of 130 μm, a width of 32 mm, and a length of 280 mm. Moreover, the electrolytic solution was obtained by dissolving lithium hydroxide in a 30% caustic potash solution so as to be 20 g / L.

  As a result of calculation based on the discharge capacity of 289 mA / g per unit weight of nickel hydroxide, the nominal capacity of each produced battery was in the range of 2.35 to 2.38 mAh, and there was almost no difference.

Each of the produced batteries A to F was formed by the steps shown below.
1． Charge at 130% of nominal capacity at a constant current of 0.2C (C is the charge / discharge coefficient), discharge once at a final voltage of 0.95V at 0.2C
2． Charge at 120% of nominal capacity with a constant current of 0.3C, discharge once with a final voltage of 0.95V at 0.3C
3． Charging 120% of nominal capacity at a constant current of 0.5C, discharging once at a final voltage of 0.90V at 0.5C

  The performance of the batteries A to F produced as described above at room temperature was examined. The performance of the battery was evaluated by the capacity maintenance rate accompanying the charge / discharge cycle. Specifically, batteries A to F are each placed in an atmosphere of 25 ° C., charged at a constant current of 1 C using the CC-ΔV method (ΔV = −5 mV), and then discharged to a termination voltage of 0.9 V at a constant current of 1 C. This cycle was repeated with 1 cycle. The CC-ΔV method is a charging method in which charging is performed with a constant current value, and charging is terminated when the voltage drops ΔV from the peak position. And the capacity maintenance rate of each battery in 250, 500, 750, 1000, and 1250 cycles was investigated. The capacity retention ratio is the ratio (%) of the discharge capacity in each cycle when the discharge capacity in the first cycle after the formation is 100. The results are shown in Table 2.

  As is clear from the results in Table 2, it was found that all batteries maintained a discharge capacity of 84% or more even after charging and discharging for 1250 cycles, and had a long life. Comparing the performance of each battery in more detail, there was no significant difference in the discharge capacities of the batteries A to F with respect to 750 cycles of charge / discharge, and all the batteries maintained a discharge capacity of 95% or more. On the other hand, in 1000 cycles, it became clear that the batteries B to E (compression ratio 1.56 to 2.22) had less capacity reduction than the battery A (compression ratio 2.67). Furthermore, in 1250 cycles, it is clear that batteries C to D (compression ratio 1.56 to 2.00) are long-life batteries with less capacity reduction than other batteries (compression ratios 1.33, 2.22, and 2.67). It was. That is, it has been clarified that the life of the battery can be significantly improved by adjusting the compressibility of a nickel electrode in which an active material is filled in a non-woven electrode substrate and pressed.

  By the way, it is known that, at high temperatures, the nickel electrode is more susceptible to excessive oxidation due to charging and swelling due to charging / discharging than normal temperature. Therefore, the battery performance of the batteries A to F under a high temperature environment was evaluated as a condition that is more severe than the above-described conditions. The test was conducted under the same charge / discharge conditions as the test at 25 ° C. described above except that the temperature around the battery was changed from 25 ° C. to 45 ° C. Note that, under a high temperature environment, the charging efficiency of the nickel electrode slightly decreased, and thus the discharge capacity at the first cycle of each battery was 98% of the nominal capacity. Therefore, the capacity maintenance rate of each battery was evaluated with this capacity as 100. The results are shown in Table 3.

  As is clear from Table 3, in 300 cycles, batteries B to E maintained a discharge capacity of 91% or more, whereas batteries A and F had a capacity of 88% or less. Furthermore, as charging / discharging was repeated, the difference between the capacity maintenance rates of the batteries B to E and the capacity maintenance rates of the batteries A and F became significant. From the above, unlike the condition at 25 ° C., under the condition at 45 ° C., all batteries have a large degree of decrease in discharge capacity with the progress of the charge / discharge cycle. However, among these batteries, the batteries B to E were found to have a long life because the decrease in discharge capacity was suppressed more than other batteries.

Although not shown in Table 3, for comparison, a battery using general-purpose foamed nickel as a positive electrode was produced, and charge / discharge characteristics were tested under the above-described conditions. The positive electrode has a nickel weight of 420 g / m ² , a thickness of 1250 μm, a nickel current collector with a porosity of 93%, adjusted to 900 μm, filled with an active material paste, and pressure-molded to a thickness of 450 μm. This is a nickel electrode. The battery using the foamed nickel electrode showed almost the same life characteristics as the battery A, and was found to be inferior to the batteries B to E using the nickel electrode of the present application.

As described above, as is clear from Example 1, it was found that the battery using the electrode substrate having a nonwoven fabric of about 1.5 to 2.3 times the thickness of the desired nickel electrode has a long life. . On the other hand, it was revealed that the battery life was inferior when a non-woven fabric of about 2.7 times or more and 1.3 times or less was used as the skeleton. Further, the elongation of the electrode a of the battery A was more than 10%, and the elongation of the electrodes b to f was 10% or less. The elongation of the electrode was determined by the following equation by measuring the length after compression and the length before compression.
Elongation = {(Length after compression−Length before compression) / Length before compression} × 100

<Example 2>
In this example, a battery having a higher output than that of the battery of Example 1 was produced. Generally, a battery for high output is manufactured by reducing the thickness of an electrode to be used and reducing the amount of active material per unit area. Therefore, in Example 2, nickel electrodes i to vi having nickel electrodes (positive electrodes) with an average thickness of 380 μm were produced.

  Similarly to Example 1, the nickel electrodes i to vi were prepared by filling an electrode substrate having a different thickness with an active material paste and compressing the active material paste to a thickness of 380 μm. The electrodes i and ii were adjusted to have a thickness comparable to the thickness of the electrode iii before press molding before filling the paste for the purpose of making the filling of the active material paste uniform. Table 4 shows the thickness of the nickel electrodes i to vi before pressure molding, the thickness after pressure molding, and the compression ratio.

  The nickel electrode shown in Table 4 was cut to a width of 32 mm and a length of 315 mm to obtain a positive electrode. With respect to this positive electrode, a negative electrode was prepared using the same MmNi-based ternary hydrogen storage alloy as in Example 1. The dimensions of the negative electrode in this example are a width of 32 mm, a length of 315 mm, a thickness of 380 μm, and a capacity ratio N / P of 1.4. In addition, the same separator and electrolyte as in Example 1 were used. These positive electrodes (i to vi), separators, and negative electrodes were wound in a stacked state and housed in a SubC size container to produce tabless batteries I to VI. The nominal capacity of each battery ranged from 2.20 to 2.22 mAh, with little difference between each battery.

Each of the produced batteries I to VI was formed by the steps shown below.
1． Charge at 130% of nominal capacity at a constant current of 0.2C, discharge once at a final voltage of 0.95V at 0.2C
2． Charging 120% of nominal capacity at a constant current of 0.5C, discharging once at a final voltage of 0.90V at 0.5C

  The performance of the batteries at 45 ° C. of the batteries I to VI produced as described above was examined. The performance of the battery was evaluated by the capacity maintenance rate accompanying the charge / discharge cycle. The evaluation method is the same as in Example 1. Note that, under a high temperature environment, the charging efficiency of the nickel electrode slightly decreased, and thus the discharge capacity at the first cycle of each battery was 98% of the nominal capacity. Therefore, the capacity maintenance rate of each battery was evaluated with this capacity as 100. The results are shown in Table 5.

  As is clear from Table 5, batteries II to V (compression ratio 1.58 to 2.37) maintained a discharge capacity of 92% or more at 250 cycles, whereas batteries I (compression ratio 2.63) and VI (Compression rate 1.32) decreased the discharge capacity to 89% or less. Further, as the number of cycles increased, the difference between the capacity of the batteries II to V and the capacity of the batteries I and VI became significant. Furthermore, at 800 cycles, the capacity of batteries III to V (compression ratio 1.58 to 2.11) is maintained at 85% or higher, whereas the capacity of batteries I, II (compression ratio 2.37) and VI is less than 80%. Met. From the above, it is clear that a battery having very excellent life characteristics can be produced by using a nickel electrode having a compression ratio in a predetermined range in a battery for high output use with a thin electrode. became. Furthermore, the elongation of the electrodes i and ii of the batteries I and II was over 10%, and the elongation of the other electrodes was 10% or less.

  Although not shown in Table 5, the performance of the battery using foamed nickel as the positive electrode was also examined in this example. The thickness of the foamed nickel before press molding was 1250 μm, and the compression ratio was 3.29. The battery using this had a much lower capacity than battery I.

<Example 3>
In this example, a battery having a higher capacity than the battery of Example 1 was produced. A high-capacity battery is manufactured by increasing the thickness of the electrode used and increasing the filling amount of the active material. Therefore, in Example 3, nickel electrodes g to l having a nickel electrode (positive electrode) thickness of 530 μm on average were produced.

  Similarly to Example 1, the nickel electrodes g to l were prepared by filling an electrode substrate with different thicknesses with an active material paste and compressing to a thickness of 530 μm. The electrode g and the electrode h were adjusted to have the same thickness as that of the electrode l before filling the paste in order to make the filling property of the active material paste uniform. Table 6 shows the thickness of the nickel electrodes g to l before pressing, the thickness after pressing, and the compression ratio.

  The nickel electrode (positive electrode) shown in Table 6 was cut to have a width of 32 mm and a length of 230 mm. For this positive electrode, a negative electrode was produced using the same ternary hydrogen storage alloy as in Example 1. The negative electrode has a width of 32 mm, a length of 230 mm, and a thickness of 380 μm. N / P in this example is 1.4. In addition, the same separator and electrolyte as in Example 1 were used. These positive electrodes (g to l), separators, and negative electrodes were wound in a stacked state and housed in a SubC size container to produce tabless batteries G to L. The nominal capacity of each battery ranged from 2.82 to 2.84 mAh, and there was little difference between each battery.

Each of the produced batteries G to L was formed by the steps shown below.
1． Charge at 130% of nominal capacity with a constant current of 0.1C, discharge once with a final voltage of 0.95V at 0.2C
2． Charge at 130% of nominal capacity at a constant current of 0.2C, discharge once at a final voltage of 0.95V at 0.2C
3． Charging 120% of nominal capacity at a constant current of 0.5C, discharging once at a final voltage of 0.90V at 0.5C

  The performance of the batteries G to L produced as described above at 45 ° C. was examined. The performance of the battery was evaluated by the capacity maintenance rate accompanying the charge / discharge cycle. The evaluation method is the same as in Example 1. Note that because of the high temperature environment, the discharge capacity of the first cycle of each battery was 97% of the nominal capacity. Therefore, the capacity maintenance rate of each battery was evaluated with this capacity as 100. The results are shown in Table 7.

  As is clear from Table 7, at 200 cycles, batteries H to K (compression ratio 1.42 to 2.17) maintain a capacity of 90% or more, whereas battery G (compression ratio 2.36) and battery L (compression) The rate 1.23) had a capacity of 87% or less. Furthermore, with the increase in the charge / discharge cycle, the difference between the capacities of the batteries H to K and the capacities of the batteries G and L became significant. From the above, it is clear that a battery having very excellent life characteristics can be produced by using a nickel electrode having a compression ratio in a predetermined range in a battery for high capacity use with a thick battery. became. Furthermore, the elongation of the electrode g of the battery G was more than 10%, and the elongation of the other electrodes was 10% or less.

  Although not shown in Table 7, the performance of the battery using foamed nickel as the positive electrode was also examined in this example. The thickness of the foamed nickel before press molding was 1250 μm, and the compression rate was the same as that of the battery G. The battery using this had almost the same capacity maintenance rate as the battery G.

In addition, this invention is not limited to the above-mentioned Example at all. That is, the configuration of the nickel electrode described in the above-described embodiments can be appropriately changed without departing from the gist of the present invention. For example, even when a battery is manufactured using a nickel electrode in which the amount of nickel coated on the nonwoven fabric is about 50 to 150 g / m ^2, higher life characteristics can be expected than a battery using a conventional nickel electrode.

  The nickel electrode for alkaline batteries of the present invention and the method for producing the same can be suitably used for the production of batteries in which battery performance is unlikely to deteriorate with repeated charging and discharging.

Claims (12)

A method for producing a nickel electrode for an alkaline battery comprising filling an electrode substrate in which the surface of a non-woven fiber is coated with nickel into an active material mixture, followed by pressure forming into an electrode,
The nonwoven fabric is a polyolefin resin,
The pressure molding is performed such that t is 350 μm to 700 μm using an electrode substrate having a thickness of 1.4 t to 1.8 t, where t is the thickness of the electrode after pressure molding.
A method for producing a nickel electrode for an alkaline battery, comprising performing heat treatment at 80 ° C. to 130 ° C. for 5 minutes to 60 minutes after the pressure forming. ^{2. The} nickel for alkaline batteries according to claim 1, wherein electroplating is performed so that the amount of nickel coated on the electrode substrate is 50 to 220 g / m ² after imparting conductivity to the surface of the nonwoven fabric. Electrode manufacturing method. The method for producing a nickel electrode for an alkaline battery according to claim 2 , wherein the imparting of conductivity to the surface of the nonwoven fabric is performed by either a sputtering method or electroless plating. The said pressure molding is performed with a roller press, The manufacturing method of the nickel electrode for alkaline batteries as described in any one of Claims 1-3 characterized by the above-mentioned. The active material mixture contains nickel hydroxide as the active material,
Furthermore, cobalt or a cobalt compound is contained, The manufacturing method of the nickel electrode for alkaline batteries as described in any one of Claims 1-4 characterized by the above-mentioned. The production of a nickel electrode for an alkaline battery according to any one of claims 1 to 4, wherein the active material mixture contains spherical nickel hydroxide whose surface is coated with cobalt oxide as an active material. Method. A nickel electrode for an alkaline battery obtained by filling an electrode substrate in which the surface of the non-woven fiber is coated with nickel with an active material mixture, followed by pressure molding,
The nonwoven fabric is a polyolefin resin,
When the thickness of the pressure molding after the electrode was t, the electrode substrate having a thickness of 1.4t~1.8t, t is pressure-molded so that 350μm~700μm, 80 ℃ after this pressing A nickel electrode for an alkaline battery obtained by performing a heat treatment at 130 ° C. or lower for 5 minutes to 60 minutes. Alkaline battery nickel electrode according to claim 7, the amount of nickel to be coated on the surface of the nonwoven fabric is characterized in that it is a 50~220g / m ^2. The nickel electrode for an alkaline battery according to claim 7 or 8 , wherein the active material mixture contains nickel hydroxide as an active material, and further contains cobalt or a cobalt compound. The nickel electrode for an alkaline battery according to claim 7 or 8 , wherein the active material mixture contains spherical nickel hydroxide whose surface is coated with cobalt oxide.   The thickness t is 350 μm to 550 μm,
  11. The nickel electrode for an alkaline battery according to claim 7, wherein the nickel electrode for an alkaline battery has a capacity density of 300 mAh / cc to 550 mAh / cc for high output use.   The thickness t is 550 μm to 700 μm,
  The nickel electrode for an alkaline battery according to any one of claims 7 to 10, wherein the nickel electrode for an alkaline battery for high capacity use has a capacity density of 550 mAh / cc to 750 mAh / cc.