JP4292125B2 - Positive electrode plate for alkaline storage battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a positive electrode plate for an alkaline storage battery and a method for producing the same, and more particularly to a positive electrode plate using a porous metal substrate having three-dimensional continuous holes.

  Alkaline storage batteries have been widely used as power sources for portable devices as batteries that can be repeatedly charged and discharged. Recently, nickel-metal hydride storage batteries, which have a high energy density and are relatively clean from the environment, have become the mainstream recently, and demand for nickel-metal hydride storage batteries in fields that require high output, such as power tools and HEVs, has increased. ing.

  For the positive electrode plate for an alkaline storage battery, a porous metal substrate is preferably used as a core material. This is because the porous metal substrate can be easily filled with a mixture paste containing an active material and rolled after the mixture is dried, and the capacity density can be improved. In particular, a foamed nickel substrate obtained by electroplating or electrolessly plating nickel on a urethane sheet and then firing it to remove the carbon component is widely used as a porous metal substrate.

Various proposals have been made regarding the method for producing a positive electrode plate for an alkaline storage battery as follows.
(I) A hoop-like porous metal substrate is continuously supplied to a tank containing a mixture paste containing an active material, and the mixture paste is filled into the substrate, and then the mixture paste is filled with a roll smoother. The substrate surface is smoothed, dried, and then rolled (see Patent Document 1).

(Ii) Spray the mixture paste onto the porous metal substrate at high pressure from the nozzle, fill the substrate with the paste (spray filling), and then pass the substrate filled with the paste through the slit to remove excess paste. After drying, rolling is performed.

(Iii) The mixture paste is filled from one surface of the porous metal substrate, and a portion not filled with the paste is left on the majority of the other surface, and then dried and rolled. Preferably, the mixture paste is filled from one surface of the porous metal substrate, and a portion not filled with the mixture paste is left on the other surface (see Patent Documents 2 and 3).

(Iv) While the hoop-shaped porous metal substrate is running in the length direction, the mixture paste is discharged from a nozzle that is brought close to both surfaces of the substrate to fill the paste with the substrate. At that time, the distance between the nozzle and the substrate is set to 1.0 mm or less (see Patent Document 4).

  In the proposals (i) and (ii) above, the mixture paste is filled in the entire porous metal substrate. However, the positive electrode plate for an alkaline storage battery requires an unfilled portion (exposed portion of the substrate) of the mixture for welding the current collector plate (see Patent Document 5). For that purpose, it is necessary to remove the mixture once filled.

  Therefore, for example, a porous metal substrate filled with a mixture is pressed so that a protruding portion is formed, ultrasonic vibration is applied to the protruding portion to remove the mixture from the protruding portion, Then, although the method of utilizing a protruding item | line part as a non-filling part for welding a collector plate is proposed (refer patent document 6), in such a method, the number of processes increases and the loss of an active material is also carried out. Increase in cost.

  In addition, since the filling amount of the mixture paste depends on the porosity of the substrate, it is difficult to quantitatively fill the mixture paste on the substrate with the proposals (i) and (ii) above. Variation occurs. The paste filling rate is defined by the volume percentage of the filled paste with respect to the void volume of the substrate.

  Furthermore, in the proposals (i) and (ii) above, bubbles are mixed in when filling the paste, so that only a paste filling rate of about 90 to 95% can be achieved, and the porous metal is exposed on the substrate surface. Resulting in. As a result, metal burrs are likely to occur when the electrode plate is cut into a predetermined size, and when the electrode plate group is formed by winding the positive electrode and the negative electrode through a separator, the exposed metal causes Short circuit failure occurs. In order to prevent these, it is necessary to increase the thickness of the separator, which makes it difficult to increase the capacity of the battery.

Next, in the above proposal (iii), it is possible to discharge the paste from the die, and the variation in paste filling rate in the longitudinal direction of the substrate is considerably improved. However, since the paste filling rate is further reduced, the variation in the thickness of the electrode plate after rolling becomes large, which is not practical. In terms of battery performance, when metal is exposed on the entire surface of the electrode plate, a part of the metal enters the separator, the distance between the positive electrode and the negative electrode is shortened, and the self-discharge amount is increased.
Also in the proposal (iv), since it is necessary to remove the mixture once filled in order to provide the non-filled portion (exposed portion of the porous metal), the cost increases.

Therefore, from the viewpoint of improving productivity, it has been proposed to apply a mixture paste in stripes on a substrate to form a non-filled portion in which the mixture is not filled with the mixture. An apparatus for performing such stripe coating has also been proposed, and an apparatus having means for adjusting the slit gap has also been proposed (see Patent Document 7). However, stripe coating is effective when a mixture paste is applied to a substrate made of a metal foil, but when a stripe coating is applied to a porous metal substrate, the mixture paste easily enters the unfilled portion. It is not always effective.
JP-A-1-163965 JP-A-9-106814 JP-A-9-27342 JP-A-9-106815 JP 2000-113881 A JP 2002-75345 A JP 2000-233151 A

  As described above, porous metal substrates such as foamed nickel substrates are widely used for the positive plates for alkaline storage batteries. However, the conventional porous metal substrate has a high manufacturing cost and it is difficult to improve the filling rate of the mixture more than the current level.

  A porous metal substrate having a lower basis weight density than conventional ones can be manufactured at a relatively low cost. However, if the basis weight density of the substrate is lower, the current collecting property of the positive electrode is reduced, and high-rate discharge performance and activity are reduced. Reduces the material utilization rate. Further, when stripe coating is performed on a porous metal substrate having a low basis weight density, penetration of the mixture paste into the unfilled portion is promoted, and the loss of the active material increases.

  Therefore, an object of the present invention is to provide a positive electrode plate that uses a substrate with a low basis density and is excellent in current collecting performance. Another object of the present invention is to provide a method for efficiently producing a positive electrode plate by performing stripe coating of a mixture paste on a porous metal substrate having a low basis weight density.

The present invention comprises a strip-shaped porous metal substrate and a mixture filled in the substrate, and the substrate includes an unfilled portion that is not filled with the mixture along at least one of the two sides in the longitudinal direction. The substrate has a basis weight density of 150 to 350 g / m ² and the mixture contains an active material and a rubber-like polymer. Since the basis weight density of the substrate is as low as 150 to 350 g / m ² , it is possible to obtain a positive electrode with a higher capacity at a lower cost than in the past. In addition, since the mixture contains an active material and a rubbery polymer, a positive electrode plate that is flexible and does not easily cut the current collection network can be obtained even when the basis weight density of the substrate is low. Can provide a good battery. Furthermore, since the mixture includes an active material and a rubbery polymer, a positive electrode plate that is less likely to cause metal burrs and cracks can be obtained even if the basis weight density of the substrate is low.

  The active material is composed of nickel oxide particles such as nickel hydroxide and nickel oxyhydroxide. From the viewpoint of increasing the high rate discharge characteristics and the active material utilization rate, the oxyhydroxide having an oxidation number of 2.9 to 3.4 is used. It is desirable to use nickel oxide particles having cobalt supported on the surface. Further, from the viewpoint of enhancing the effect of preventing short circuit, the surface of the substrate is preferably coated with a layer (hereinafter referred to as a surface mixture layer) made of a mixture having a thickness of 10 to 100 μm. Further, it is desirable to use iron or nickel plated with nickel as the porous metal of the substrate.

  From the viewpoint of obtaining suitable flexibility, the glass transition temperature of the rubbery polymer is desirably -100 to + 20 ° C, and the amount of the rubbery polymer contained in the mixture is 100 parts by weight of the active material. 0.2 to 5 parts by weight is preferred.

The present invention also provides a porous metal substrate by controlling the thickness of a hoop-shaped porous metal having a basis weight density of 150 to 350 g / m ² , and a mixture containing an active material and a rubbery polymer on the substrate. The paste is filled in a stripe shape so that an unfilled portion not filled with one or more strips is formed, the substrate filled with the mixture paste is dried, and the substrate filled with the dried mixture is obtained. Rolling to form an electrode plate, cutting the electrode plate along at least a non-filled portion, and processing to a predetermined size , wherein the mixture paste has a 20 rpm viscosity of 3 to 15 Pa · s, and a viscosity ratio: It is related with the manufacturing method of the positive electrode plate for alkaline storage batteries whose 2 rpm viscosity / 20 rpm viscosity is 2 or more .

  The step of filling the substrate with the mixture paste in stripes is to form the stripes of the mixture paste from a plurality of die nozzles facing each other through gaps of a predetermined width toward the substrate running in the longitudinal direction through the gaps. It is possible to efficiently perform the discharge.

  When performing the step of filling the substrate with the mixture paste in stripes, the filling amount of the mixture paste on the substrate with an X-ray or β-ray weight meter and / or the filling width of the mixture paste on the substrate with an image recognition device It is desirable to control the distance between the die nozzle and the substrate or the flow rate of the mixture paste discharged from the die nozzle.

  In order to efficiently fill the substrate with the mixture paste in stripes, the die nozzle has a slit-like outlet for discharging the mixture paste, and the slit-like outlet is divided into a plurality of sections by one or more partitions. It is desirable to use a die nozzle. From the same point of view, the die nozzle is composed of a combination of a plurality of units each having a slit-like outlet for discharging the mixture paste, and the plurality of units are arranged so that the slit-like outlets are in a straight line. Can also be used.

  From the viewpoint of stabilizing the mixture paste filling rate of the substrate, the plurality of die nozzles facing each other through the gap of a predetermined width discharge the mixture paste at positions shifted from each other by 1 to 5 mm along the running direction of the substrate. It is desirable to have a slit-shaped outlet.

  The thickness of the substrate obtained by controlling the thickness of the hoop-shaped porous metal by a pressing process or the like is preferably 200 to 1500 μm, and the porosity is preferably 88 to 97%. The volume of the mixture paste filled in the substrate is preferably set to 95 to 150% of the void volume of the substrate (paste filling rate is 95 to 150%).

  When a mixture paste is applied in a stripe shape to a porous metal substrate having a low basis weight density, the mixture may easily enter a non-filled portion where the mixture is not filled due to dripping. Therefore, from the viewpoint of preventing dripping, it is desirable that the mixture paste has a 20 rpm viscosity of 3 to 15 Pa · s and a viscosity ratio: 2 rpm viscosity / 20 rpm viscosity of 2 or more. In addition, the viscosity of the mixture paste is measured at room temperature (25 ° C.). Further, the 2 rpm viscosity of the mixture paste is desirably 10 to 70 Pa · s. The mixture paste contains, for example, a conductive agent, a thickener, and water in addition to the active material and the rubbery polymer.

  In the present invention, a substrate having a low basis density is used, and the active material and the rubbery polymer are included in the mixture, so that the capacity is flexible, the current collecting network is not easily cut, and metal burrs and cracks are prevented. A positive electrode plate that is less likely to occur can be obtained at a lower cost than in the past. That is, if the positive electrode plate of the present invention is used, an alkaline storage battery that is excellent in high rate discharge characteristics, has a large discharge capacity even when discharged at a large current, and has an excellent active material utilization rate and charge / discharge cycle characteristics, has been obtained. Can also be obtained at low cost. Further, according to the production method of the present invention, the stripe coating of the mixture paste can be performed with high productivity, and the loss of the active material is greatly reduced.

The positive electrode plate for an alkaline storage battery of the present invention comprises a strip-shaped porous metal substrate and a mixture filled in the substrate, and the substrate is mixed along at least one of the two sides in the longitudinal direction. Has an unfilled portion that is not filled. Here, the positive electrode plate for an alkaline storage battery according to the present invention is mainly characterized in that the basis density of the porous metal substrate is 150 to 350 g / m ² and the mixture contains an active material and a rubbery polymer.

Since a porous metal substrate having a low basis weight density can be manufactured at a low cost, the manufacturing cost of the positive electrode is reduced. However, the porous metal substrate having a low basis weight density is likely to cut the metal skeleton, and the current collecting network is likely to be broken during the manufacturing process of the positive electrode. Therefore, conventionally, a porous metal substrate having a basis weight density larger than 350 g / m ² has been used. On the other hand, in the present invention, since the mixture contains a rubbery polymer, flexibility is imparted to the positive electrode, and such a problem is unlikely to occur. Therefore, a porous metal substrate having a basis weight density of 150 to 350 g / m ² can be effectively used. From the viewpoint of cost reduction, the weight density of the porous metal substrate is more preferably 190 to 250 g / m ² .

If the basis weight density of the porous metal substrate is less than 150 g / m ² , it becomes difficult to handle the substrate, and it becomes difficult to prevent the current collector network from being cut and burrs, and the strength of the substrate is too low. It becomes difficult to continuously fill the mixture paste using the hoop-shaped substrate. On the other hand, when the basis weight density exceeds 350 g / m ² , the manufacturing cost of the positive electrode plate cannot be reduced, and the ratio of the substrate volume in the electrode plate increases, so that the capacity of the electrode plate can be increased. Damaged.
The porous metal substrate is preferably made of nickel-plated iron or nickel, and particularly preferably made of nickel.

  When the basis weight density of the porous metal substrate is low, burrs of the substrate are more likely to occur in the positive electrode manufacturing process than in the past. Therefore, from the viewpoint of enhancing the effect of preventing the short circuit failure of the battery due to burrs, the surface of the substrate is preferably covered with a surface mixture layer having a thickness of 10 to 100 μm. That is, it is desirable that the substrate be loaded with a mixture having a volume equal to or larger than the void volume of the substrate.

  The glass transition temperature of the rubbery polymer is desirably -100 to + 20 ° C. If the glass transition temperature is less than −100 ° C., the effect of binding the active material by the rubbery polymer is reduced, and if it exceeds + 20 ° C., sufficient flexibility may not be imparted to the positive electrode plate. When a rubbery polymer having a glass transition temperature of −100 to + 20 ° C. is included in the mixture, the mixture is given appropriate flexibility, so that the mixture is removed during the electrode plate rolling process and the cutting process. Can be suppressed. Moreover, also when comprising an electrode group, the softness | flexibility of a mixture suppresses generation | occurrence | production of a crack.

  Particularly suitable examples of the rubber-like polymer having the above physical properties include a copolymer of tetrafluoroethylene and propylene and a copolymer of tetrafluoroethylene, propylene and vinylidene fluoride. Among the latter copolymers, those having a vinylidene fluoride unit content of 5 mol% or less are particularly preferred in terms of good alkali resistance. Also, styrene-butadiene rubber (SBR), perfluoroelastomer, and the like can be suitably used.

  The amount of the rubbery polymer contained in the mixture is preferably 0.2 to 5 parts by weight and particularly preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the active material. If the amount of the rubbery polymer is too large, the discharge characteristics and the capacity of the positive electrode will be reduced, and if the amount of the rubbery polymer is too small, the flexibility of the positive electrode will be reduced and the current collecting performance will be reduced. Burrs and cracks are likely to occur.

  From the viewpoint of improving the current collection performance, the mixture preferably contains a conductive agent. As the conductive agent, cobalt oxyhydroxide is preferable, and cobalt oxyhydroxide having an oxidation number of 2.9 to 3.4 is particularly preferable. Moreover, when using nickel oxide particles carrying cobalt oxyhydroxide having an oxidation number of 2.9 to 3.4 on the surface as the active material, the current collecting performance can be improved efficiently with a small amount of conductive agent. . The nickel oxide particles carrying cobalt oxyhydroxide on the surface can be obtained by treating the nickel oxide particles carrying cobalt hydroxide on the surface with hot alkali. The amount of the conductive agent contained in the mixture is generally 2 to 15 parts by weight with respect to 100 parts by weight of the active material. When cobalt oxyhydroxide is supported on the active material surface, it is preferable to use 3 to 10 parts by weight of cobalt oxyhydroxide with respect to 100 parts by weight of the active material.

Next, the alkaline storage battery positive electrode plate of the present invention will be described with reference to an example of a production method.
First, a mixture paste is prepared by dispersing a mixture in a liquid component such as water. The mixture contains an active material and a rubbery polymer as essential components. The mixture may further contain a conductive agent, a thickener and the like. In particular, the thickener is effective for controlling the viscosity of the mixture paste.

  As the thickener, it is preferable to use cellulosic thickeners such as carboxymethylcellulose (CMC) and methylcellulose (MC), thickening polysaccharides such as xanthan gum, guar gum, carrageenan, and diyutan gum. The amount of the thickener contained in the mixture paste is generally 0.05 to 0.3 parts by weight with respect to 100 parts by weight of the active material.

  From the viewpoint of imparting appropriate thixotropy to the mixture paste, it is particularly preferable to use a thickening polysaccharide. Furthermore, thickening polysaccharides are excellent as thickeners in terms of improving the cycle characteristics of alkaline storage batteries because they are less soluble in alkaline aqueous solutions than cellulosic thickeners.

  In order to fill the gap in the substrate with the paste, it is necessary to give the paste some fluidity. However, after the substrate is filled with the paste, the paste needs to be held at the filling position to prevent dripping. For this purpose, it is preferable to use a paste having high thixotropy (a paste having a low viscosity at high shear and a high viscosity at low shear). In particular, in the present invention, since a substrate having a low basis weight is used, it is desired to prevent dripping using a paste having high thixotropy. In the present invention, the thixotropy of the paste is evaluated by viscosity ratio: 2 rpm viscosity / 20 rpm viscosity. The viscosity of the paste is measured at 25 ° C.

  A paste suitable for filling a substrate with a low basis weight has a viscosity of 20 rpm of 3 to 15 Pa · s and a viscosity ratio of 2.0 or more. When the viscosity at 20 rpm is less than 3 Pa · s, dripping may occur. When the viscosity at 20 rpm exceeds 15 Pa · s, it may be difficult to fill the gaps in the substrate with paste. On the other hand, when the viscosity ratio is less than 2, a suitable balance between paste filling property and fluidity cannot be obtained. The viscosity ratio is more preferably 3 or more. There is a limit to increasing the viscosity ratio, and the upper limit is about 7. The 2 rpm viscosity of the paste is desirably 10 to 70 Pa · s.

The porous metal substrate is a hoop-shaped porous metal having a basis weight density of 150 to 350 g / m ² , and is adjusted to a thickness suitable for the substrate of the electrode plate. The thickness of the porous metal substrate is preferably 200 to 1500 μm. When the thickness of the substrate is less than 200 μm, the pore diameter of the voids of the substrate becomes too small, and the mixture paste hardly penetrates into the substrate. On the other hand, when the thickness of the substrate exceeds 1500 μm, the method of discharging the paste from the die coat has insufficient pressure and may not be filled into the substrate.

  It is desirable to control the porosity of the porous metal substrate to 88 to 97%. When the porosity is less than 88%, the permeability of the paste into the substrate is reduced, and when it exceeds 97%, the substrate strength is reduced, and the mixture paste is continuously filled using a hoop-like substrate. Becomes difficult.

Next, a process of applying the mixture paste to the obtained substrate will be described.
The mixture paste is applied to the substrate in stripes so as to form an unfilled portion in which one or more strips of the mixture are not filled. At that time, the mixture paste having the above-described viscosity or viscosity ratio can be easily filled into the substrate, and the mixture paste hardly enters the unfilled portion. The width of the unfilled portion is preferably 1 to 10 mm, but is not particularly limited.

  If the substrate filled with the mixture paste is dried and the substrate filled with the dried mixture is rolled, an electrode plate of the original fabric can be obtained. When cutting the electrode plate to a predetermined size, by cutting along the non-filled portion, the current collector is located near the cut portion without performing the step of removing the once filled mixture. And an exposed portion of the substrate for welding the lead. Therefore, the manufacturing method of the positive electrode plate can be simplified and the occurrence of loss of the active material can be prevented. In addition, when cutting along the non-filling portion, it is possible to prevent the active material from dropping off.

  When filling the substrate with the mixture paste, it is efficient to use a die coat as shown in FIGS. As shown in FIG. 2, at least a pair of die nozzles 21 are opposed to each other through a gap having a predetermined width. The substrate 22 travels in the longitudinal direction through the gap. The at least one pair of die nozzles 21 facing each other discharges the mixture paste 23 toward the traveling substrate 22. At that time, the substrate paste 22 is filled with the mixture paste 23 in a stripe shape including the non-filling portion 24. Therefore, the die nozzle 21 preferably has a slit-shaped outlet 11 as shown in FIG.

  The die nozzle 21 in FIG. 1 has a slit-shaped outlet 11 for discharging the mixture paste, and the slit-shaped outlet 11 is divided into a plurality of sections by a single partition 12. The number of the partitions 12 is not limited to one, and two or more partitions can be provided in correspondence with the number of necessary non-filled portions. Since the mixture paste is not discharged from the portion shielded by the partition, an unfilled portion is formed on the substrate corresponding to the position of the partition. As a result, the mixture paste is applied in stripes. The die nozzle may be a combination of a plurality of units each having a slit-like outlet for discharging the mixture paste. In that case, the plurality of units are arranged so that their slit-shaped outlets are aligned.

  When using a plurality of die nozzles 21 facing each other through gaps of a predetermined width as shown in FIG. 2, slit-like outlets 31 for discharging the mixture paste are mutually connected along the running direction of the substrate 22 as shown in FIG. It is desirable to arrange with a shift of 1 to 5 mm (width b in FIG. 3). When the position of the opposing die nozzle 21 is shifted by 1 mm or more, as the paste enters the space inside the substrate 22, the air filled in the space sequentially moves to the portion where the paste is not filled. . Therefore, the paste filling rate of the substrate 22 can be brought close to the closest packing. The distance between the substrate surface and the nozzle tip (slit-shaped outlet) (width a in FIG. 3) is preferably 10 to 500 μm.

  On the other hand, when the slit-shaped outlets 31 arranged on both sides of the substrate are completely opposed, when the paste enters the gap inside the substrate 22 from both sides at the same time, air may remain near the center in the substrate thickness direction. is there. When the deviation is 5 mm or more, the substrate meanders in the thickness direction, and the thickness variation of the mixture layer gradually increases.

  When the mixture paste is filled in the porous metal substrate having voids inside, the width (filling width) of the mixture paste actually filled in the substrate varies with respect to the width of the slit-shaped exit of the die nozzle. Such fluctuations are caused by variations in paste viscosity and substrate wettability. If the filling width fluctuates, the width of the non-filled portion that is not filled with the mixture also fluctuates, and the capacity variation and the dimensional variation of the positive electrode plate after cutting increase.

  From the viewpoint of stabilizing the variation in the filling width, the correlation between the filling amount and the filling width and the paste viscosity, the paste discharge amount, the pressure in the vicinity of the slit outlet, the distance between the die nozzle and the substrate, and the like are set in advance. It is desirable to feed back to the coating process. For example, it is desirable to monitor the filling amount and filling width in the substrate and control the distance between the die nozzle and the substrate or the mixture paste flow rate discharged from the die nozzle in accordance with the information obtained by the monitor. The filling amount can be monitored by using an X-ray weighing machine or a β-ray weighing machine, and the filling width can be monitored by using an image recognition device.

  The volume of the mixture paste filled in the substrate is desirably 95 to 150%, more preferably 100 to 130% of the void volume of the substrate. By making this amount (paste filling rate) 95% or more, when the electrode plate 40 is cut by the cut surfaces 41 and 42 as shown in FIG. 4, the cut surface 41 is filled with the mixture. The exposed substrate area can be reduced. As a result of the cutting, for example, a positive electrode plate 50 as shown in FIG. 5 is obtained. An unfilled portion 51 is formed on one side of the two sides in the longitudinal direction of the positive electrode plate 50 corresponding to the cut surface 42. Further, when the paste filling rate exceeds 100%, the surface mixture layer 61 is formed on the electrode plate as shown in FIG. 6A, so that the porous metal 62 can be prevented from being exposed. . In the conventional positive electrode plate, the mixture does not protrude from the substrate surface as shown in FIG. 6B, but according to the present invention, the effect of preventing the mixture from falling off due to the rubbery polymer is obtained. It is possible to obtain an electrode plate having a structure as shown in FIG.

  When the surface mixture layer is formed on the electrode plate, the occurrence of cracks and short circuits can be prevented when the positive electrode plate and the negative electrode plate are wound through the separator. As a result, the separator can be thinned, and the battery capacity can be greatly improved. However, if the filling rate exceeds 150%, the mixture layer thickness becomes non-uniform due to dripping, or the current collecting performance decreases.

Examples of the present invention will be described below.
Example 1
(I) Active Material Nickel hydroxide solid solution particles, which are active materials, were prepared using the following known methods. That is, a sodium hydroxide aqueous solution is gradually added dropwise to an aqueous solution containing nickel sulfate as a main solute and containing a predetermined amount of cobalt sulfate and zinc sulfate while adjusting the pH with aqueous ammonia to obtain spherical nickel hydroxide solid solution particles. Was precipitated.
Next, the obtained nickel hydroxide solid solution particles were washed with water and dried to obtain mother particles. The average particle diameter of this powder by a laser diffraction particle size meter was 10 μm, and the specific surface area measured by the BET method was 12 m ² / g.

Cobalt hydroxide fine particles were supported on nickel hydroxide solid solution particles (mother particles) by the following known method. That is, nickel hydroxide solid solution particles and a 1 mol / L cobalt sulfate aqueous solution were gradually added to a sodium hydroxide aqueous solution, and the mixture was stirred while adjusting the pH of the aqueous solution to be 12 at 35 ° C. Cobalt hydroxide fine particles (β type) were deposited on the surface of the solid solution particles. The average particle diameter observed from the SEM image of the obtained particles was 10 μm, and the specific surface area measured by the BET method was 12 m ² / g.

  Next, nickel hydroxide solid solution particles having cobalt hydroxide fine particles supported on the surface are accommodated in a treatment tank, and an alkaline aqueous solution having a concentration of 45% by weight is mixed therein at a rate of 0.07 L / Kg. Hot air at 0 ° C. was fed at a rate of 4 L / min / Kg and dried to convert the surface cobalt hydroxide into highly conductive cobalt oxyhydroxide (cobalt average valence of 3.1).

(Ii) Mixture paste Nickel hydroxide solid solution particles carrying cobalt oxyhydroxide on the surface were used as the active material.
For the binder, an aqueous dispersion of a rubbery polymer having a glass transition temperature of −3 ° C. (“Afras (trade name)” manufactured by Asahi Glass Co., Ltd.) (content of rubbery polymer: 35% by weight) Was used. The rubbery polymer is a copolymer containing a tetrafluoroethylene unit and a propylene unit at a molar ratio of 55:45, and has a density of 1.55 g / cm ³ .
As the thickener, 1% by weight aqueous solution of carboxymethylcellulose (CMC) and xanthan gum were used.

A mixture paste was prepared in the following manner using the above raw materials.
First, 100 parts by weight of the active material and 0.2 parts by weight of xanthan gum were put into a kneader and sufficiently mixed with a stirring blade. Subsequently, 5 parts by weight of the CMC aqueous solution was gradually dropped into the mixer while mixing was continued, and 3 parts by weight of a binder was further added as a rubbery high molecular weight. In this way, a mixture paste containing an active material and aphras at a weight ratio of 100: 3 and having a water content of 17% by weight was prepared.

  The obtained mixture paste had a 2 rpm viscosity of 25 Pa · s, a 20 rpm viscosity of 5 Pa · s, and a viscosity ratio (2 rpm viscosity / 20 rpm viscosity) of 5. Since the viscosity of such a paste decreases when the shear rate γ increases, the discharge from the discharge portion of the die coat proceeds very smoothly. Further, when the substrate after paste filling is dried, no shear stress is applied to the paste, but the viscosity of the paste increases when the shear rate γ decreases, so that no dripping of the paste occurs. That is, the paste has viscoelasticity (rheology) that is very suitable for filling by die coating.

(Iii) Positive electrode plate The mixture paste was filled in a stripe shape so that an unfilled portion not filled with a single mixture was formed at the center of a 160 mm wide hoop-shaped porous metal substrate made of nickel. The porous metal substrate used here was nickel-plated on a foamed urethane sheet, then baked at 600 ° C. to remove the urethane, and the remaining porous metal was pressed to adjust the thickness to 700 μm. The weight per unit area was 200 g / m ² and the porosity was 97%.

  The step of filling the substrate with the mixture paste is to discharge the mixture paste in stripes from a pair of die nozzles facing each other through a gap of a predetermined width toward the substrate traveling in the longitudinal direction through the gap. I went there. In the pair of die nozzles, slit-like outlets for discharging the mixture paste were arranged with a 0.5 mm deviation along the running direction of the substrate. The volume of the mixture paste filled in the substrate was set to be 130% of the void volume of the substrate.

  The slit-shaped outlet of the die nozzle that discharges the mixture paste has a width of 148 mm, and a portion of 68 to 80 mm from one end of the slit-shaped outlet was closed with a partition having a width of 12 mm. Since the paste was not discharged from the portion blocked by the partition, an unfilled portion having a width of 12 mm was formed in the center of the substrate.

  When filling the substrate with the mixture paste, the filling width was managed while monitoring with a camera, and fluctuations in the filling width were corrected by automatically adjusting the distance between the opposing die nozzles. The distance between the die nozzle and the substrate was adjusted at any time within a range of 10 to 500 μm on both sides of the substrate.

  Thereafter, the substrate filled with the mixture paste was dried with hot air at 110 ° C. for 5 minutes. The substrate filled with the mixture after drying was rolled to a thickness of 500 μm using a roll press to obtain an electrode plate. The obtained electrode plate was cut at least along the unfilled portion as shown in FIG. As a result, as shown in FIG. 5, a positive electrode plate A having an unfilled portion in which one side of the two sides in the longitudinal direction is not filled with the mixture was obtained. The main part of the positive electrode plate A had a cross section as shown in FIG. Since the unfilled portion of the mixture is a portion where the current collector plate is welded, the material was folded twice so as to maintain the strength.

<< Comparative Example 1 >>
(I) Active material Nickel hydroxide solid solution particles carrying cobalt hydroxide fine particles on their surfaces are accommodated in a treatment tank, and an alkaline aqueous solution having a concentration of 45% by weight is mixed therewith at a rate of 0.05 L / Kg, and then the temperature Is the same as in Example 1 except that 60 ° C. hot air is fed at a rate of 1 L / min / Kg and dried to convert the surface cobalt hydroxide into cobalt oxyhydroxide (cobalt average valence 2.8). The active material was obtained.

(Ii) Mixture paste Nickel hydroxide solid solution particles carrying cobalt oxyhydroxide on the surface were used as the active material.
As a binder, an aqueous dispersion of polytetrafluoroethylene (PTFE) (PTFE content: 60% by weight) was used.
A 1 wt% aqueous solution of carboxymethylcellulose (CMC) was used as the thickener.

A mixture paste was prepared in the following manner using the above raw materials.
First, 100 parts by weight of the active material was put into a kneader and sufficiently mixed with a stirring blade. Subsequently, 2.5 parts by weight of water and 20 parts by weight of CMC aqueous solution were gradually dropped into the mixer while mixing was continued, and 2 parts by weight of a binder was further added in the amount of PTFE. In this way, a mixture paste containing the active material and PTFE in a weight ratio of 100: 2 and having a moisture content of 19% by weight was prepared.

  The obtained mixture paste had a 2 rpm viscosity of 5 Pa · s, a 20 rpm viscosity of 2 Pa · s, and a viscosity ratio (2 rpm viscosity / 20 rpm viscosity) of 2.5.

(Iii) Positive electrode plate The mixture paste was filled in a hoop-shaped porous metal substrate made of nickel and having a width of 180 mm. The porous metal substrate used here is obtained by performing nickel plating on foamed urethane and then baking at 600 ° C. to remove the urethane. The thickness is 1000 μm, the weight per unit area is 400 g / m ² , and the porosity is 95%. Met.

  The step of filling the substrate with the mixture paste was performed by continuously supplying a hoop-shaped porous metal substrate to a tank containing the mixture paste. In such a method, when the hoop-like porous metal substrate is immersed in a tank filled with the mixture paste, the paste viscosity of 2 rpm viscosity and 20 rpm viscosity are set to the above-mentioned values because of the necessity to penetrate the substrate. So we have to make it low together.

  After filling the substrate with the mixture paste, the surface of the substrate filled with the mixture paste was smoothed with a roll smoother. Next, in the same manner as the electrode plate of Example 1, the active material was removed by applying ultrasonic waves to a predetermined portion of the electrode plate in order to form a non-filled portion of the mixture for welding the current collector plate. .

  The substrate filled with the mixture paste was dried with hot air at 110 ° C. for 15 minutes. The electrode plate after drying was rolled to a thickness of 500 μm using a roll press. The obtained electrode plate was cut and a positive electrode plate B as shown in FIG. 5 was obtained. The main part of the positive electrode plate B had a cross section as shown in FIG. 6B, and the paste filling rate was 90%. Since the unfilled portion of the mixture is a portion where the current collector plate is welded, the material was folded twice so as to maintain the strength.

[Evaluation of electrode plate]
(State of positive electrode plate)
The positive electrode plates A and B were evaluated as follows. Table 1 shows the results.
Evaluation 1: The maximum height of metal burrs and the number of burrs generated during cutting were confirmed by SEM images.
Evaluation 2: A positive electrode plate and a known hydrogen storage alloy electrode were wound through a polypropylene separator having a thickness of 100 μm to produce 1000 electrode plates each, and the mixture that had fallen off during winding with respect to the weight of the positive electrode plate The average value of weight percentage (%) was determined as the mixture dropout rate.
Evaluation 3: A positive electrode plate and a known hydrogen storage alloy electrode were wound through a polypropylene separator having a thickness of 100 μm to produce 1000 electrode plates each, and the short-circuit failure rate was confirmed.
Evaluation 4: The percentage by weight of the mixture that was wasted relative to the weight of the mixture used in the production of the positive electrode plate (for example, the mixture that was removed by ultrasonic waves in the production of the positive electrode plate B) was determined as the mixture loss rate.

  As described above, the positive electrode plate A uses a binder having a low glass transition temperature, which increases the paste filling amount to 130% with respect to the void volume in the substrate, and has excellent binding properties and flexibility. The cutting burrs were greatly reduced with respect to the positive electrode plate B, and the mixture was not dropped off during winding. As a result, no short circuit failure occurred even when a thin separator having a thickness of 100 μm was used.

(Preparation of alkaline storage battery)
Using the positive electrode plate A and the positive electrode plate B, nickel-metal hydride storage batteries having an FSC size and a nominal capacity of 3300 mAh were produced. That is, the positive electrode plate and the negative electrode plate were wound through a polypropylene separator subjected to a hydrophilic treatment with a thickness of 100 μm to constitute an electrode plate group. The electrode plate group was accommodated in the battery case after the current collector plate was welded to the porous metal (unfilled portion) exposed at the end face. A known hydrogen storage alloy electrode was used for the negative electrode. After pouring a specified amount of a 7N to 8N alkaline electrolyte in which potassium hydroxide was dissolved as a main solute in the battery case, the battery case was sealed and initial charge / discharge was performed. Hereinafter, a battery using the positive electrode plate A is referred to as a battery A, and a battery using the positive electrode plate B is referred to as a battery B.

(Active material utilization rate)
Each battery was first charged and discharged at a charge rate of 0.1 C (1C = 3300 mA) for 15 hours, and a charge / discharge cycle of discharging for 6 hours at a discharge rate of 0.2 C was repeated twice. Thereafter, after aging (activation of the negative electrode alloy) at 45 ° C. for 3 days, the active material utilization rate of the positive electrode plate was measured by changing the charge / discharge conditions. The results are shown in Table 2.

  Here, the active material utilization in Table 2 was calculated as a percentage value of the discharge capacity with respect to the positive electrode theoretical capacity of each battery. The theoretical capacity of the positive electrode was a value obtained by multiplying the mass of nickel hydroxide in the positive electrode active material by an electric capacity of 289 mAh / g when it was supposed to have a one-electron reaction.

  The discharge capacity was measured by overcharging at a charge rate shown in Table 2, and then discharging at a discharge rate of 0.2C, 1C, and 2C until the battery voltage reached 0.8V. From Table 2, it can be seen that the active material utilization rate of the battery A produced using the positive electrode plate A of the present invention is higher than that of the battery B using the positive electrode plate B of the comparative example.

(Charge / discharge cycle characteristics)
Further, the charge / discharge cycle characteristics of the above two types of batteries were examined.
The charge / discharge cycle was performed under the condition that the battery voltage was discharged to 0.8V at the discharge rate of 1C after being charged by the -ΔV (ΔV = 0.01V) control method at the charge rate of 1C. Then, after charging with a -ΔV (ΔV = 0.01V) control method at a charge rate of 1C for every fixed cycle, the discharge capacity when the battery voltage is discharged to 0.4V with a discharge current of 10A. It was measured. A graph (referred to as graph 1) showing the relationship between the discharge capacity and the number of cycles at this time is shown in FIG. As graph 1 shows, the battery A has a higher capacity than the battery B, and the capacity reduction after the long-term cycle life test is suppressed.

  Further, for the above two types of batteries, a pack in which 10 single cells were connected in series was prepared, and the charge / discharge cycle characteristics of the pack were examined. The charge / discharge cycle is charged at a charge rate of 10 A with a ΔT (ΔT = 3.0 ° C./min) control method, and then at a charge rate of 5 A, a ΔT (ΔT = 3.0 ° C./min) control method. Then, the auxiliary charge was performed, and then the battery was discharged at a discharge current of 20 A until the pack voltage reached 4V. A graph showing the relationship between the discharge capacity and the number of cycles at this time (referred to as graph 2) is shown in FIG.

  As shown in the graph 2, the battery A has a higher capacity than the battery B, and the capacity reduction after the long-term cycle life test is suppressed. In addition, this tendency is more conspicuous than the cycle charge / discharge test in a single cell. This is because, when a charge / discharge cycle is performed in the pack, there is a capacity variation for each single cell, so that some of the batteries in the pack are overdischarged during discharge.

  When the battery is over-discharged, the capacity is reduced due to dropping of the active material due to gas generation from the positive electrode, melting of the separator due to heat generation, reduction of the electrolyte due to operation of the safety valve and increase of internal resistance.

  On the other hand, according to the present invention, when the electrode plate group is wound, the active material hardly falls off, and the burrs and cracks of the electrode plate are much less than in the prior art. It is thought that the capacity | capacitance fall by the short circuit between negative electrodes and dropout of an active material can be suppressed effectively.

Example 2
A positive electrode plate was produced under the same conditions as in Example 1 except that the filling rate of the mixture paste into the porous metal substrate was changed as shown in Table 3.

[Evaluation]
The following measurements were performed on the positive electrode plate. The results are shown in Table 3.
<I> The maximum height of metal burrs generated during cutting was determined.
<Ii> The positive electrode plate and a known hydrogen storage alloy electrode were wound through a polypropylene separator having a thickness of 100 μm to produce 1000 electrode plates each, and the mixture that had fallen off during winding with respect to the weight of the positive electrode plate The average value of weight percentage (%) was determined as the mixture dropout rate.
<Iii> The thickness of the electrode plate before cutting was measured at three arbitrary points, and the difference between the minimum thickness and the maximum thickness was determined.
<Iv> The thickness range of a layer (surface mixture layer) made of a mixture covering the substrate surface was measured.

  From Table 1, it can be seen that when the paste filling rate is 95% or more, the metal burrs are reduced, and the loss of the active material and the variation in thickness are reduced. Moreover, there is a tendency that the higher the paste filling rate, the less the falling off of the active material, which is considered to be due to the effect of the rubbery polymer. However, it can be understood that when the paste filling rate exceeds 150%, the amount of the mixture dropped out and the thickness variation of the electrode plate also increased.

Example 3
A positive electrode plate was produced in the same manner as in Example 2, except that the amount of CMC was changed, or a predetermined amount of xanthan gum was added to change the paste viscosity and the viscosity ratio as shown in Table 4. A nickel metal hydride storage battery was produced in the same manner as in Example 1 except that this positive electrode plate was used.

[Evaluation]
The following measurements were performed on the positive electrode plate and the nickel metal hydride storage battery. The results are shown in Table 4.
<I> Variation in paste filling rate was obtained. Here, when the paste was filled, the paste filling amount was monitored with an X-ray weight meter, the maximum amount and the minimum amount were obtained, and the difference between them was calculated. The percentage value relative to the standard value of the calculated value (theoretical value of the paste filling rate obtained from the porosity of the substrate) was regarded as variation.
<Ii> The active material utilization rate of the positive electrode plate was determined in the same manner as in the battery A of Example 1.

  From Table 4, it can be seen that when the 20 rpm viscosity of the mixture paste is 3 to 15 Pa · s and the viscosity ratio is 2 or more, the variation in the mixture filling rate is small and the active material utilization rate is also good. It can also be seen that the 2 rpm viscosity is preferably 10 to 70 Pa · s. When outside of these ranges, the variation in paste filling rate increases, and the active material utilization rate decreases, because the mixture paste does not sufficiently permeate the substrate, or once it has permeated the viscosity. This is thought to be due to dripping of the liquid due to the low level.

Example 4
A positive electrode plate was produced in the same manner as in Example 1 except that the amount of the binder contained in the mixture was changed as shown in Table 5 per 100 parts by weight of the active material. A nickel metal hydride storage battery was produced in the same manner as in Example 1 except that this positive electrode plate was used.

[Evaluation]
The following measurements were performed on the positive electrode plate and the nickel metal hydride storage battery. The results are shown in Table 5.
<I> The positive electrode plate and a known hydrogen storage alloy electrode were wound through a polypropylene separator having a thickness of 100 μm, and 1000 electrode plates were produced each. The average value of weight percentage (%) was determined as the mixture dropout rate.
<Ii> The positive electrode plate and the known hydrogen storage alloy electrode were wound through a polypropylene separator having a thickness of 100 μm, and 1000 electrode plates were prepared for each to confirm the short-circuit failure rate.
<Iii> The active material utilization rate of the positive electrode plate was determined in the same manner as in the battery A of Example 1.

  From Table 5, when the amount of the binder is 0.2 to 5 parts by weight, preferably 1 to 5 parts by weight per 100 parts by weight of the active material, a battery with a low short-circuit failure rate and a good active material utilization rate is obtained. It turns out that it is obtained. When the amount of the binder increases, the short-circuit defect rate tends to decrease. This is considered to be because the flexibility of the positive electrode plate is increased and the generation of cracks and burrs is suppressed. Further, it can be seen that when the amount of the binder increases, the active material is less likely to fall off. However, when the amount of the binder exceeds 5 parts by weight per 100 parts by weight of the active material, the active material utilization rate decreases, so that the amount is preferably 5 parts by weight or less.

  The present invention is widely applicable to a positive electrode plate for an alkaline storage battery using a porous metal substrate having three-dimensional continuous pores, and according to the present invention, it has excellent high-rate discharge characteristics, even when discharged with a large current. An alkaline storage battery having a large discharge capacity and an excellent active material utilization rate and charge / discharge cycle characteristics can be obtained at a lower cost than before. Alkaline storage batteries to which the present invention can be applied include nickel cadmium storage batteries as well as nickel metal hydride storage batteries used as power sources for portable devices, power tools, HEVs, and the like.

It is a front view of an example of the die nozzle used by the present invention. It is a perspective view of an example of the die coat used by the present invention. It is a figure which shows the arrangement | positioning relationship between a die nozzle and a board | substrate. It is a figure which shows an example of the cutting process of the positive electrode plate obtained by stripe application | coating of the mixture paste. It is a front view of an example of the positive electrode plate after cutting into a predetermined size. It is sectional drawing A of the principal part of an example of the positive electrode plate of this invention, and sectional drawing B of the principal part of the conventional positive electrode plate. It is the graph 1 which shows the relationship between the discharge capacity of batteries A and B, and the number of cycles. 3 is a graph 2 showing the relationship between the discharge capacity of the packs of batteries A and B and the number of cycles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Slit-shaped exit 12 Partition 21 Die nozzle 22 Substrate 23 Mixture paste 24 Unfilled part 31 Slit-shaped exit 40 Electrode plate 41 Cut surface 42 Cut surface 50 Positive electrode plate 51 Unfilled part 61 Surface mixture layer 62 Porous metal

Claims (17)

It consists of a strip-shaped porous metal substrate and a mixture filled in the substrate,
The substrate has a non-filling portion that is not filled with the mixture along at least one of the two sides in the longitudinal direction;
The basis weight density of the substrate is 150 to 350 g / m ² ;
A positive electrode plate for an alkaline storage battery, wherein the mixture comprises an active material and a rubbery polymer.   The positive electrode plate for an alkaline storage battery according to claim 1, wherein the active material is nickel oxide particles having cobalt oxyhydroxide having an oxidation number of 2.9 to 3.4 supported on the surface thereof.   The positive electrode plate for alkaline storage batteries according to claim 1, wherein the surface of the substrate is coated with a layer made of the mixture having a thickness of 10 to 100 μm.   The positive electrode plate for an alkaline storage battery according to claim 1, wherein the porous metal of the substrate is made of iron or nickel plated with nickel.   The rubbery polymer has a glass transition temperature of −100 to + 20 ° C., and the amount of the rubbery polymer contained in the mixture is 0.2 to 5 parts by weight with respect to 100 parts by weight of the active material. The positive electrode plate for alkaline storage batteries according to claim 1. By controlling the thickness of a hoop-shaped porous metal having a basis weight density of 150 to 350 g / m ² , a porous metal substrate is obtained,
Filling the substrate with a mixture paste containing an active material and a rubber-like polymer in stripes so as to form a non-filled portion not filled with one or more strips of the mixture,
Drying the substrate filled with the mixture paste;
Rolling the substrate filled with the mixture after drying to form an electrode plate,
Cutting the electrode plate along at least the unfilled portion and processing the electrode plate into a predetermined size ;
The manufacturing method of the positive electrode plate for alkaline storage batteries whose 20 rpm viscosity of the said mixture paste is 3-15 Pa.s, and viscosity ratio: 2rpm viscosity / 20rpm viscosity is 2 or more .   The step of filling the substrate with the mixture paste in the form of stripes is performed from the plurality of die nozzles facing each other through a gap having a predetermined width toward the substrate traveling in the longitudinal direction through the gap. The manufacturing method of the positive electrode plate for alkaline storage batteries of Claim 6 which consists of a process which discharges an agent paste in stripe form.   In the step of filling the substrate with the mixture paste in the form of stripes, the amount of the mixture paste filled into the substrate by an X-ray or β-ray weight meter and / or the filling width of the mixture paste on the substrate by an image recognition device And controlling the distance between the die nozzle and the substrate or the flow rate of the mixture paste discharged from the die nozzle.   The method for producing a positive electrode plate for an alkaline storage battery according to claim 7, wherein the die nozzle has a slit-shaped outlet for discharging the mixture paste, and the slit-shaped outlet is divided into a plurality of sections by one or more partitions.   The die nozzle is composed of a combination of a plurality of units each having a slit-like outlet for discharging the mixture paste, and the plurality of units are arranged so that the slit-like outlets are aligned. The manufacturing method of the positive electrode plate for alkaline storage batteries of description.   The plurality of die nozzles facing each other through the gap of the predetermined width have slit-like outlets for discharging the mixture paste at positions shifted from each other by 1 to 5 mm along the traveling direction of the substrate. Manufacturing method of positive electrode plate for alkaline storage battery.   The method for producing a positive electrode plate for an alkaline storage battery according to claim 6, wherein the substrate has a thickness of 200 to 1500 µm and a porosity of 88 to 97%.   The method for producing a positive electrode plate for an alkaline storage battery according to claim 6, wherein a volume of the mixture paste filled in the substrate is 95 to 150% of a void volume of the substrate. The manufacturing method of the positive electrode plate for alkaline storage batteries of Claim 6 in which the said mixture paste contains at least 1 sort (s) selected from the group which consists of a xanthan gum, a guar gum, a carrageenan, and a diutane gum as a thickener. The method for producing a positive electrode plate for an alkaline storage battery according to claim 6 , wherein the mixture paste has a 2 rpm viscosity of 10 to 70 Pa · s.   The positive electrode for an alkaline storage battery according to claim 6, wherein the mixture paste contains a conductive agent, a thickener and water in addition to the active material and the rubbery polymer, and the active material is made of nickel oxide particles. Board manufacturing method.   The rubbery polymer has a glass transition temperature of −100 to + 20 ° C., and the amount of the rubbery polymer contained in the mixture is 0.2 to 5 parts by weight with respect to 100 parts by weight of the active material. The method for producing a positive electrode plate for an alkaline livestock battery according to claim 6.

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