JP3094033B2 - Nickel hydride rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a nickel-metal hydride secondary battery, and more particularly to a nickel-metal hydride secondary battery having an improved hydrogen storage alloy negative electrode.

(Prior Art) Recent advances in electronic technology have led to power savings and advances in packaging technology, which have led to cordless and portable electronic devices that were not expected in the past. For this reason, a secondary battery, which is a power supply incorporated in the electronic device, is also required to have a high capacity. As such a secondary battery, an alkaline secondary battery using a negative electrode having a structure in which hydrogen storage alloy particles are fixed to a conductive core serving as a current collector has been proposed, and has begun to attract attention. The negative electrode using the hydrogen storage alloy can increase the energy density per unit weight or unit volume as compared with cadmium, which is a conventional representative negative electrode material for an alkaline secondary battery, and has a high battery capacity. In addition to being capable of reducing the risk of environmental pollution, the battery has excellent battery characteristics.

Conventionally, as a hydrogen storage alloy negative electrode of the nickel-metal hydride secondary battery, a three-dimensional conductive core such as a foamed metal or a sintered fiber is used as a current collector, and a hydrogen storage alloy powder is added to the core together with a binder. Filled non-sintered types are known. However, such a hydrogen storage alloy negative electrode may be broken at the time of pressure molding in the manufacturing process because the conductive core as a current collector has poor mechanical strength. Further, since the conductive core is expensive, there is a problem that the cost of a nickel-metal hydride secondary battery incorporating a negative electrode having the core is high.

For this reason, U.S. Pat.No. 4,849,312 discloses a non-sintering hydrogen storage alloy using a two-dimensionally punched metal as a current collector, which is inexpensive compared to the three-dimensionally conductive core. A negative electrode is disclosed. Such a hydrogen storage alloy negative electrode is prepared by rapidly stirring a hydrogen storage alloy powder and polyacrylic acid salt, polytetrafluoroethylene and carboxymethylcellulose blended as necessary, to prepare a paste, and applying the paste to punched metal. -It is obtained by drying and pressing.

However, the non-sintered hydrogen storage alloy negative electrode cannot have a sufficiently high utilization factor as compared with the negative electrode using the conductive core of the three-dimensional structure as a current collector, and the nickel-hydrogen secondary battery incorporating the negative electrode However, it was difficult to sufficiently cope with the increase in the capacity of the device. Further, there is a fear that the punched metal as the current collector is broken at the time of pressure molding in the manufacturing process of the negative electrode, and the dried paste is separated from the punched metal.

(Problem to be Solved by the Invention) An object of the present invention is to provide a nickel-metal hydride secondary battery in which the capacity of a hydrogen storage alloy negative electrode is improved to achieve high capacity.

Another object of the present invention is that when a non-sintered nickel positive electrode and a hydrogen storage alloy negative electrode are spirally wound with a separator interposed therebetween, the punched metal of the negative electrode projects or a paste containing hydrogen storage alloy powder is used. An object of the present invention is to provide a high-reliability, high-capacity nickel-metal hydride secondary battery in which the battery is prevented from falling off.

Still another object of the present invention is to provide a nickel-metal hydride secondary battery having improved charge / discharge cycle life.

[Structure of the Invention] (Means for Solving the Problems) A nickel-metal hydride secondary battery according to the present invention has a non-sintered structure in which a paste containing nickel hydroxide, cobalt monoxide and a binder is formed on a conductive core. A nickel-hydrogen battery comprising: an electrode group in which a formula nickel positive electrode and a hydrogen storage alloy negative electrode are spirally wound with a separator interposed therebetween; an alkaline electrolyte; and a container accommodating the electrode group and the alkaline electrolyte. In the following battery, the negative electrode is 100 parts by weight of a hydrogen storage alloy powder, 0.005 to 1 part by weight of a polyacrylate, 0.01 to 1 part by weight of carboxymethyl cellulose, 0.5 to 7 parts by weight of a fluororesin, and 0.1 to 0.1 parts by weight of a conductive material powder. The paste containing 4 parts by weight is perforated so that an equilateral triangle is always formed when the centers of three adjacent holes are connected, and the hole diameter is 1 to 5 mm and the opening ratio is 45 to 70%. For punched metal The punched metal with respect to the entire thickness of the negative electrode is 10%.
It occupies a thickness of about 35%, and the winding direction of the electrode group is parallel to one side of the equilateral triangle of the punched metal.

Further, another nickel-metal hydride secondary battery according to the present invention,
An electrode group formed by spirally winding a non-sintered nickel positive electrode and a hydrogen storage alloy negative electrode in which a paste containing nickel hydroxide, cobalt monoxide and a binder is formed on a conductive core with a separator interposed therebetween, An alkaline electrolyte, a nickel-metal hydride secondary battery including a container in which the electrode group and the alkaline electrolyte are stored, wherein the negative electrode includes a hydrogen storage alloy powder, a binder, and a conductive material powder, A paste having a viscosity of 100P to 400P and a rotational viscosity ratio (R) of 1.5 to 4 shown in the following equation (1) is formed so that an equilateral triangle is always formed when the centers of three adjacent holes are connected. The electrode group is formed in a punched metal having a hole diameter of 1 to 5 mm and an opening ratio of 45 to 70%, and the winding direction of the electrode group is one side of the equilateral triangle of the punched metal. And in parallel.

R = V ₁ / V ₂ (1) where V ₁ is the temperature measured by a Brookfield viscometer (single cylindrical viscometer) calibrated with a viscosity standard solution described in ASTM.
25 ° C., a viscosity measured at a rotational speed of 6 rpm, V ₂ is AS
Using a Brookfield viscometer (single cylindrical viscometer) calibrated with the viscosity standard solution described in TM, temperature 25 ° C, rotation speed 60
It shows the viscosity measured under rpm conditions.

Hereinafter, a nickel hydrogen secondary battery according to the present invention will be described in detail with reference to FIG.

The non-sintered nickel positive electrode 1 is spirally wound between a hydrogen storage alloy negative electrode 2 containing a hydrogen storage alloy powder and a separator 3 made of a nonwoven fabric made of a synthetic resin, and has a bottomed cylindrical container 4. Is housed inside. The alkaline electrolyte is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is arranged at the upper opening of the container 4. The ring-shaped insulating gasket 7 is disposed between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and the sealing plate is formed on the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is hermetically fixed via the gasket 7. One end of the positive electrode lead 8 is connected to the positive electrode 1, and the other end is connected to the lower surface of the sealing plate 6. A positive electrode terminal 9 having a hat shape is mounted on the sealing plate 6 so as to cover the hole 5. The rubber safety valve 10
The hole 5 is disposed in a space surrounded by the sealing plate 6 and the positive terminal 9.

The non-sintered nickel positive electrode 1 has a structure in which a paste containing nickel hydroxide, cobalt monoxide (CoO), and a binder is formed on a conductive core serving as a current collector. The positive electrode 1 is made of the above nickel hydroxide, cobalt monoxide (CoO)
A paste is prepared by mixing a binder with water, and the paste is applied to the core, dried, and then, if necessary, processed by a roller press or the like.

It is desirable that the amount of cobalt monoxide blended in the paste of the positive electrode 1 be in the range of 2 to 20% by weight based on the nickel hydroxide.

Examples of the binder mixed in the paste of the positive electrode 1 include polyacrylates such as sodium polyacrylate and potassium polyacrylate, carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE).
And at least one kind selected from fluorine resins. In particular, use polyacrylate, CM
It is desirable that the paste be composed of C and a fluorine-based resin and have the same component composition as the binder in the paste used for the negative electrode. When constituting a binder from these three components,
Polyacrylic acid 0.0 to 100 parts by weight of the nickel hydroxide
5 to 1 part by weight, CMC 0.05 to 1 part by weight and fluororesin 0.5
It is desirable to add about 5 parts by weight.

Examples of the conductive core of the positive electrode 1 include those having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those having a three-dimensional structure such as foamed metal and reticulated metal fiber.

The hydrogen storage alloy negative electrode 2 is composed of 100 parts by weight of a hydrogen storage alloy powder, 0.005 to 1 part by weight of a polyacrylate, 0.01 to 1 part by weight of carboxymethyl cellulose, and 0.5 to 1 part by weight of a fluororesin.
A paste containing 7 parts by weight and a conductive material powder of 0.1 to 4 parts by weight is formed into a punched metal having a hole diameter of 1 to 5 mm and a porosity of 45 to 70%, and the thickness of the punched metal occupying the entire thickness. It is configured to have a height of 10 to 35%. Such negative electrode 2
The hydrogen storage alloy powder, polyacrylate, carboxymethylcellulose, fluororesin and conductive material powder.
A paste is prepared by mixing 1 to 4 parts by weight in the presence of water, and the paste is applied to punched metal having the hole diameter and the opening ratio described above. It is manufactured by further drying and, if necessary, press-molding with a roller press or the like.

The hydrogen storage alloy blended in the paste of the negative electrode 2 is not particularly limited, and can store hydrogen electrochemically generated in an electrolytic solution and easily release the stored hydrogen during discharge. Anything that can be done is acceptable. For example, the general formula XY _5-a Z _a (where, X is a rare earth element including La,
Y represents Ni, Z represents at least one element selected from Co, Mn, Al, V, Cu, and B, and a represents 0 ≦ a <2.0. Specifically, LaNi ₅ , MmNi ₅ , LmNi
₅ (Lm; lanthanum-enriched misch metal), and some of these Nis are converted to Al, Mn, Fe, Co, Ti, Cu, Zn, Zr, Cr, B
And multi-elements substituted with such elements.

Examples of the polyacrylate mixed in the paste of the negative electrode 2 include sodium polyacrylate and ammonium polyacrylate. The reason for limiting the mixing ratio of the polyacrylate to the hydrogen storage alloy powder is as follows. When the amount of the polyacrylate is less than 0.005 parts by weight, the hydrogen storage alloy powder cannot be sufficiently dispersed and held in the paste,
The paste dried at the time of pressure molding is peeled off from the punched metal, and a predetermined negative electrode cannot be produced. On the other hand, if the amount of the polyacrylic acid salt exceeds 1 part by weight, not only is the improvement in the dispersibility and retention of the hydrogen storage alloy powder in the paste impossible, but also the surface of the applied surface when the paste is applied to the punched metal. Flatness is impaired.

The reason why the ratio of CMC to the hydrogen storage alloy powder mixed in the paste of the negative electrode 2 is limited is as follows. When the amount of the CMC is less than 0.01 part by weight, not only takes much time to prepare the paste, but also sedimentation of the hydrogen storage alloy powder having a large specific gravity occurs, and the stability of the paste is reduced. On the other hand, if the amount of the CMC exceeds 1 part by weight, the surface of the hydrogen-absorbing alloy powder is covered with the CMC, and the oxygen gas absorption reaction of the negative electrode decreases, causing an increase in the internal pressure of the secondary battery incorporating the negative electrode.

The fluorine-based resin blended in the paste of the negative electrode 2 has a function of fiberizing at the time of rolling and binding the hydrogen storage alloy powder. Examples of the fluorine-based resin include polytetrafluoroethylene (PTFE). The reason for limiting the mixing ratio of the fluorine-based resin to the hydrogen storage alloy powder is as follows. When the amount of the fluororesin is less than 0.5 parts by weight,
The binding effect is reduced, and the paste dried at the time of pressure molding peels off the punched metal, so that a negative electrode cannot be manufactured. On the other hand, if the amount of the fluororesin exceeds 7 parts by weight, the oxygen gas absorption reaction of the negative electrode in which the surface of the hydrogen storage alloy powder is covered with the resin decreases, and the internal pressure of the secondary battery incorporating the negative electrode decreases. Invite a rise.

Examples of the conductive material powder mixed into the paste of the negative electrode 2 include carbon black, graphite powder, and metal powder. The reason for limiting the mixing ratio of the conductive material powder to the hydrogen storage alloy powder is as follows. When the amount of the conductive material powder is less than 0.1 part by weight, the conductivity of the negative electrode is reduced, and the discharge voltage is reduced. On the other hand, if the amount of the conductive material powder exceeds 4 parts by weight, the density of the hydrogen-absorbing alloy powder in the dried paste decreases, and the amount of the hydrogen-absorbing alloy per unit volume of the negative electrode decreases. A hydrogen secondary battery cannot be obtained.

The reason why the hole diameter of the punched metal constituting the negative electrode 2 is limited is as follows. If the hole diameter of the punched metal is less than 1 mm, the paste formed on the front and back of the punched metal cannot be interconnected through the holes, so that the adhesive strength of the paste decreases. On the other hand, if the hole diameter of the punched metal exceeds 5 mm, the distortion generated in the punched metal at the time of press molding increases, and the conductivity is reduced.

The reason for limiting the porosity of the punched metal constituting the negative electrode 2 is as follows. When the porosity of the punched metal is less than 45%, the porosity of the negative electrode decreases, and the ratio of the hydrogen storage alloy powder decreases, so that the utilization rate of the negative electrode decreases. In addition, the paste dried at the time of pressure molding in the step of manufacturing the negative electrode is separated from the punched metal. On the other hand, the opening rate of the punched metal is
If it exceeds 70%, the strength of the punched metal is reduced, and the punched metal is broken at the time of pressure molding in the negative electrode manufacturing process.

The thickness of the punched metal constituting the negative electrode 2 is 0.05
It is desirable to set it to mm or more. The reason for this is that if the thickness of the punched metal is less than 0.05 mm, the strength of the punched metal is reduced, and the punched metal may be broken during the pressure forming in the negative electrode fabrication process. When the punched metal is too thick, the amount of the hydrogen storage alloy powder occupying in the negative electrode decreases, and the utilization rate decreases. Therefore, it is desirable that the upper limit thickness of the punched metal is 0.15 mm.

The reason why the thickness ratio of the punched metal to the entire thickness of the negative electrode 2 is limited is as follows. When the thickness ratio of the punched metal is less than 10%, the volume ratio of the punched metal, which is the current collector, in the negative electrode is reduced, so that not only a sufficient current collecting effect cannot be obtained but also the strength is reduced. Breaking and meandering occur during press forming. On the other hand, the thickness ratio of the punched metal is 35%
Beyond the above, when the same volume of paste is included regardless of the thickness of the punched metal, the porosity of the paste of the negative electrode decreases, the amount of hydrogen storage alloy powder decreases, and the utilization rate of the negative electrode decreases.

When the negative electrode 2 is spirally wound together with the positive electrode 1 with the separator 3 interposed therebetween and stored in the container 4,
It is preferable that the punched metal forming the negative electrode 2 has a shape in which a line connecting the centers of adjacent holes forms a triangle so as to form an equilateral triangle. In this case, the positive electrode 1 and the negative electrode 2 with the separator 3 interposed therebetween are wound in a direction parallel to one side of the equilateral triangle of the punched metal.

As another form of the negative electrode 2, a hydrogen storage alloy powder,
A paste containing a binder and a conductive material powder, having a viscosity of 100 P to 400 P and a rotational viscosity ratio of 1.5 to 4, is prepared with a pore size of 1 to 5 mm and a porosity of 45 to 70.
% Punched metal. Such a negative electrode 2 prepares a paste having the viscosity and the rotational viscosity ratio by stirring the hydrogen storage alloy powder, the binder and the conductive material powder in the presence of water, and setting the paste to the pore diameter and the porosity. After being applied to the punched metal, it is manufactured by scraping off excess paste with a slit as necessary, drying it further, and pressing it with a roller press or the like as necessary. In the production process of such a negative electrode, it is possible to prepare a paste having the viscosity and the rotational viscosity ratio by controlling the stirring speed and the stirring time in addition to the binder amount and the water content.

As the binder, polyacrylate, CMC and PTF
It is desirable to use a fluororesin such as E. When the binder is composed of these three components, the polyacrylic acid salt is used in an amount of 0.005 to 100 parts by weight of the hydrogen storage alloy powder.
It is preferable to mix 1 part by weight, 0.01 to 1 part by weight of carboxymethyl cellulose, and 0.5 to 7 parts by weight of a fluororesin.

As the conductive material powder, for example, carbon black,
Examples thereof include graphite powder and metal powder. The mixing ratio of the conductive material powder to the hydrogen storage alloy powder is preferably 0.1 to 4 parts by weight per 100 parts by weight of the hydrogen storage alloy powder.

The viscosity of the paste is a value measured using a Brookfield viscometer (single cylindrical viscometer) calibrated with a viscosity standard solution described in ASTM at a rotation speed of 6 rpm and a temperature of 25 ° C. The reason for limiting the viscosity of the paste is as follows. If the viscosity of the paste is less than 100P, the paste cannot be applied to the punched metal with a sufficient thickness, and a practically usable negative electrode cannot be obtained. On the other hand, if the viscosity of the paste exceeds 400P, most of the applied paste is peeled off from the punched metal when excess paste is scraped off through the slit after the application step.

The rotational viscosity ratio (R) of the paste is defined by the following equation.

Temperature by R = V ₁ / V ₂ where, V ₁ is Brookfield viscometer calibrated with viscosity standard solution according to ASTM (single cylindrical viscometer)
It shows the viscosity measured under the conditions of 25 ° C. and 6 rpm. V ₂ is AS
Using a Brookfield viscometer (single cylindrical viscometer) calibrated with the viscosity standard solution described in TM, temperature 25 ° C, rotation speed 60
It shows the viscosity measured under rpm conditions.

The rotational viscosity ratio of the paste was limited for the following reasons. The rotational viscosity ratio of the paste is
If it is less than 1.5, the dripping of the paste after application becomes large, and it becomes impossible to stably form a paste having a desired thickness on punched metal. On the other hand, if the rotational viscosity ratio of the paste exceeds 4, it becomes impossible to remove excess paste through the slits satisfactorily. In addition, when the paste is flowed in the coating tank during the coating step, the viscosity in the flowing part is too low, and the components in the paste are easily separated, so that the paste component of the negative electrode becomes unstable.

Examples of the synthetic resin non-woven fabric forming the separator 3 include a polypropylene non-woven fabric, a nylon non-woven fabric, and a non-woven fabric in which a polypropylene fiber and a Ninlo fiber are mixed.

Examples of the alkaline electrolyte include a mixture of sodium hydroxide (NaOH) and lithium hydroxide (LiOH), a mixture of potassium hydroxide (KOH) and LiOH, or a mixture of NaOH, KOH and LiOH.
An OH mixture or the like can be used. In particular, KOH and LiOH
Is preferably used as an alkaline electrolyte.

In FIG. 1 described above, the separator 3 was interposed between the non-sintered nickel positive electrode 1 and the hydrogen storage alloy negative electrode 2 and spirally wound and housed in the bottomed cylindrical container 4. A separator may be interposed between the non-sintered nickel positive electrode and the plurality of hydrogen storage alloy negative electrodes to form a laminate, and the laminate may be housed in a bottomed cylindrical container.

(Action) According to the present invention, a paste having a composition in which a predetermined amount of a polyacrylic acid salt, carboxymethylcellulose, and a fluororesin are mixed with a hydrogen storage alloy powder and a predetermined amount of a conductive material powder is mixed is used as a current collector. A structure in which a paste containing a hydrogen-absorbing alloy powder having a high mechanical strength with respect to the punched metal and a surface property having good reactivity with hydrogen gas or the like is firmly formed by being formed into a punched metal. A hydrogen storage alloy negative electrode of the above can be obtained.
Further, the punched metal has a hole diameter of 1 to 5 mm and an opening ratio of 45.
By defining the content to be about 70%, the active material containing the hydrogen storage alloy powder at a high density and having a good porosity related to the penetration of the alkaline electrolyte can be formed in the punched metal. A high hydrogen storage alloy negative electrode can be obtained. Moreover, since the punched metal has sufficient strength and can improve the adhesion of the paste, the punched metal may be broken at the time of pressure molding in the negative electrode manufacturing process, or the dried paste may be removed from the punched metal. Peeling can be prevented. Furthermore, by setting the thickness of the punched metal to 10 to 35% of the total thickness,
Since an active material having sufficient mechanical strength, high porosity and a large contact area with an alkaline electrolyte can be formed on the punched metal, a hydrogen storage alloy negative electrode having a high utilization factor can be obtained. Such a mechanical strength is high, the hydrogen storage alloy negative electrode and the non-sintered nickel positive electrode having a high utilization rate are accommodated in a container with a separator interposed therebetween, and an alkaline electrolyte is accommodated in the container, thereby achieving a high efficiency. A reliable and high-capacity nickel-metal hydride secondary battery can be obtained.

In addition, if the positive electrode and the negative electrode are formed using a paste containing a binder having the same composition as polyacrylate, CMC, and a fluororesin, the liquid absorbing property of the alkaline electrolyte to the positive electrode and the negative electrode can be improved. And the current distribution of the positive electrode and the negative electrode during charge and discharge can be made uniform. As a result, the charge / discharge reaction at both electrodes can be smoothed, and an increase in the internal pressure and a decrease in the discharge capacity accompanying the progress of the charge / discharge cycle can be suppressed. Therefore, a nickel-hydrogen secondary battery having a long charge-discharge cycle life can be obtained.

Further, as the punched metal constituting the hydrogen storage alloy negative electrode, a punched metal having a shape perforated such that a line connecting the centers of adjacent holes forms an equilateral triangle is used, and the negative electrode and the non-sintered type are used. If the nickel positive electrode is wound in a direction parallel to one side of the equilateral triangle of the punched metal with the separator interposed therebetween, it is possible to prevent the punched metal from protruding or the paste from falling in the negative electrode, and the utilization rate of the negative electrode is high. Thus, a high capacity nickel-metal hydride secondary battery can be obtained.

That is, when the hydrogen-absorbing alloy negative electrode having the paste fixed to the punched metal is spirally wound together with the positive electrode with the separator interposed therebetween, the punched metal as the current collector is perpendicular to the winding direction and has a hole. Break at the line including the center. There are two types of winding directions of such a negative electrode, namely, a case where it is parallel to one side of an equilateral triangle which is the above-described punched metal hole array and a case where it is perpendicular to one side of the equilateral triangle of the above-described punched metal. When wound in the direction parallel to one side of the former equilateral triangle, the interval between the fold lines is the same as the length of one side of the equilateral triangle.
1/2. On the other hand, in the case of winding in the direction perpendicular to one side of the latter equilateral triangle, the interval between the fold lines is the length of one side of the equilateral triangle. Becomes Therefore, by winding the negative electrode and the positive electrode so as to be parallel to one side of the equilateral triangle of the punched metal with the separator interposed therebetween, the interval between the fold lines can be shortened. The formed punched metal is spirally wound while being bent at a small angle. As a result, especially in the initial stage of winding where the bending angle tends to be large, it is possible to prevent the punched metal from protruding to the outside of the negative electrode and to prevent the paste from falling off in the negative electrode. You can get a battery.

Further, by forming a paste containing a binder and a conductive material powder in a hydrogen storage alloy powder and having a predetermined viscosity and a rotational viscosity ratio into a punched metal having a predetermined pore diameter and a predetermined porosity, the punched metal is formed. In contrast, it is possible to obtain a hydrogen storage alloy negative electrode having a structure in which a paste having a desired thickness is stably formed. Therefore, the active material having sufficient mechanical strength, high porosity, and a large contact area with an alkaline electrolyte is formed by the interaction between the characteristics of the paste, the pore diameter of the punched metal, and the definition of the porosity. A negative electrode and a non-sintered nickel positive electrode are accommodated in a container with a separator interposed therebetween, and an alkaline electrolyte is accommodated in the container since a hydrogen-absorbing alloy negative electrode having a high utilization rate formed on a metal can be obtained. By doing so, a secondary battery can be obtained with high reliability and high capacity nickel-metal hydride.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

Example 1 _{First, LmNi 4.2 Co 0.2 Mn 0.3 Al} 0.3 (Lm denotes a La-rich misch metal) was prepared hydrogen absorbing alloy powder of 200 mesh pass in composition. Subsequently, the hydrogen storage alloy powder 10
0 parts by weight of sodium polyacrylate, CMC, a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt%), carbon black and water are mixed and stirred at the ratios shown in Table 1 below to obtain 17 types. A paste was prepared. Subsequently, these pastes were applied to a punched metal having a pore diameter of 2.0 mm, a porosity of 50%, and a thickness of 0.1 mm, dried and then rolled by a roller press, and cut to prepare a hydrogen storage alloy negative electrode. . In this negative electrode, the thickness ratio of the punched metal to the entire thickness was set to 20%.

The applicability of the paste and the strength of the negative electrode in the process of producing each of the hydrogen storage alloy negative electrodes were examined. The results are shown in Table 2 below.

As is clear from Tables 1 and 2, 0.005 to 1 part of sodium polyacrylate was added to 100 parts by weight of the hydrogen storage alloy powder.
Parts by weight, CMC of 0.01 to 1 part by weight, PTFE of 0.5 to 7 parts by weight, and conductive powder in the range of 0.1 to 4 parts by weight. It can be seen that the negative electrodes (No. 1 to No. 12) according to the present invention obtained by coating, drying, and roll pressing both have good coatability and strength. On the other hand, sodium polyacrylate, CMC, PTFE and conductive material powder are applied to a punched metal with a paste having a composition outside the above range,
Negative electrode obtained by drying and roll pressing (No13 to No17)
Indicates that the coating properties are poor or the strength is deteriorated.

Example 2 First, 90 parts by weight of nickel hydroxide and 10 parts by weight of cobalt monoxide were dry-mixed together with CMC and PTFE, and then pure water was added and kneaded to prepare a paste. Subsequently, this paste was filled in a nickel sintered fiber core, dried, pressed, and cut to produce a non-sintered nickel positive electrode.

Next, between the non-sintered nickel positive electrode, the first
No.2, No6, No9, and No12 hydrogen storage alloy negative electrodes shown in the table are arranged with a separator made of polypropylene non-woven fabric interposed to form an electrode group, and the capacity regulated by the negative electrode capacity using this electrode group is 900 mAh. Four test cells shown in FIG. 2 were assembled. In FIG. 2, an electrode group 15 composed of a non-sintered nickel positive electrode 12 and a hydrogen storage alloy negative electrode 13 interposed between separators 14 made of polypropylene nonwoven fabric is housed in a bottomed rectangular cylindrical container 11. Have been. The electrode group
Reference numeral 15 is sandwiched by two holding plates 16 made of an insulating material and arranged on both sides of each positive electrode 12. The container 11 contains an alkaline electrolyte 17 composed of an 8N-KOH solution. Note that a reference electrode 17 is accommodated in the container 11.

For each of the test cells obtained, 0.1 g / g of hydrogen storage alloy.
After charging at a current density of 17 Ah, charging and discharging were repeated until the voltage reached 0.8 V, and the ratio of the amount of discharged electricity to the amount of charged electricity (utilization rate) was measured. As a result, it was confirmed that the utilization rate of each test cell was 100%.

Example 3 First, 0.5 parts by weight of sodium polyacrylate, 0.125 parts by weight of CMC, a dispersion of polytetrafluoroethylene (in terms of solid content; 1.5 parts by weight) were added to 100 parts by weight of the same hydrogen storage alloy powder as in Example 1, and A paste was prepared by stirring and mixing 1.0 part by weight of carbon black with water. Subsequently, the thickness is 0.1 mm, the hole diameter is 2.0 mm, and the opening ratio is
35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75
% Of punched metal was prepared, the paste was applied to the punched metal, dried, and then rolled by a roller press to produce nine types of hydrogen storage alloy negative electrodes. Note that all of these negative electrodes had the same thickness and the same hydrogen storage alloy density, and the thickness ratio of the punched metal to the entire thickness was 20%.

The presence / absence of paste peeling and the presence / absence of breakage of the punched metal during rolling in the production process of each hydrogen storage alloy negative electrode were examined. The results are shown in Table 3 below.

As is clear from Table 3, in the hydrogen storage alloy negative electrode (No. 1) in which the porosity of the punched metal is 40%, the dried paste is peeled off from the punched metal during rolling. Further, it can be seen that in the negative electrode (No. 8) in which the porosity of the punched metal is 75%, the punched metal breaks during rolling. On the other hand, the hole opening ratio of punched metal is 45
It can be seen that the negative electrode (No. 2 to No. 7) according to the present invention, which is about 70%, has good characteristics without peeling of the dried paste or breakage of the punched metal.

Example 4 No. 3 shown in Table 3 was placed between the positive electrodes as in Example 2 above.
The negative electrode of 1 to No7 constitutes an electrode group via a separator made of polypropylene nonwoven fabric, and the capacity regulated by the negative electrode capacity using an alkaline electrolyte solution of 8N-KOH is 900 mAh
7 kinds of test cells having the same structure as that of FIG. 2 were assembled.

For each of the test cells obtained, 0.1 g / g of hydrogen storage alloy.
After charging at a current density of 17 Ah, charging and discharging were repeated until the voltage reached 0.8 V, and the ratio (utilization rate) to the amount of discharged electricity relative to the amount of charged electricity was measured. FIG. 3 shows the results.
FIG. 3 is a characteristic diagram showing the relationship between the porosity of punched metal and the utilization rate of the negative electrode in the hydrogen storage alloy negative electrode incorporated in each secondary battery.

As is clear from FIG. 3, in the secondary battery incorporating a negative electrode having a punched metal having a porosity of 45 to 70%, the utilization rate of the negative electrode is almost 100%. In contrast,
In a secondary battery incorporating a negative electrode having punched metal with a porosity of 40%, the utilization rate of the negative electrode is about 90%. This is considered to be due to the fact that when the porosity of the punched metal is less than 45%, the voids in the negative electrode are reduced, and the proportion of the hydrogen storage alloy in contact with the alkaline electrolyte is reduced.

Example 5 First, cobalt monoxide was added to 100 parts by weight of nickel hydroxide.
Parts by weight, 0.25 parts by weight of sodium polyacrylate, CMC 0.2
5 parts by weight, PTFE dispersion (in terms of solid content; 1.5 parts by weight) and water were added and mixed to prepare a paste. Subsequently, the paste was filled in a nickel sintered fiber core, dried, subjected to roller pressing, and cut to produce a non-sintered nickel positive electrode.

Further, 0.5 part by weight of sodium polyacrylate, 0.125 part by weight of CMC, 1 part by weight of PTFE dispersion (solid content; 1.5 parts by weight) and 1 part by weight of carbon black were added to 100 parts by weight of the same hydrogen storage alloy powder as in Example 1. To prepare a paste. Subsequently, the paste was applied to a punched metal having a pore diameter of 2.0 mm, a porosity of 50%, and a thickness of 0.1 mm, dried, rolled by a roller press, and cut to produce a hydrogen storage alloy negative electrode. did. In addition,
In this negative electrode, the thickness ratio of the punched metal to the entire thickness was set to 20%.

Then, the separator is made of polypropylene non-woven fabric sandwiched between the positive electrode and the negative electrode and spirally wound, and the resultant is stored in a mild steel bottomed cylindrical container, and further in the container.
A nickel-hydrogen secondary battery having a nominal capacity of 900 mAh and having the structure shown in FIG. 1 described above was accommodated in an alkaline electrolyte comprising a mixture of 7N-KOH and 1N-LiOH.

Comparative Example 1 A sintering nickel positive electrode and a negative electrode similar to that of Example 5 were spirally wound with a separator made of polypropylene non-woven fabric interposed therebetween and stored in a mild steel bottomed cylindrical container. A nickel-hydrogen secondary battery having a nominal capacity of 900 mAh and a structure shown in FIG. 1 described above was assembled in which an alkaline electrolyte composed of a mixture of 7N-KOH and 1N-LiOH was accommodated.

Regarding the obtained secondary batteries of Example 5 and Comparative Example 1,
The battery is charged at a current of 300 mA for 4.5 hours, and the charge and discharge cycle of discharging at a current of 900 mA until the battery voltage becomes 1 V is repeated, and the ratio of the discharge capacity in each cycle to the initial discharge capacity is measured as the efficiency of the secondary battery. A discharge cycle test was performed. The result is shown in FIG.

As is clear from FIG. 4, the secondary battery of Example 5 has a longer cycle life than the secondary battery of Comparative Example 1. This is because the secondary battery of Example 5 uses sodium polyacrylate, CMC, and PTFE as a binder for both the positive electrode and the negative electrode, and is a non-sintered electrode. This is due to the fact that the liquid absorption rate became almost the same, the liquid retention balance became good, and a uniform reaction was performed without causing a partial reaction on both electrode surfaces.

Example 6 First, 0.5 parts by weight of sodium polyacrylate, 0.125 parts by weight of CMC, PTFE dispersion (in terms of solid content; 1.5 parts by weight) and 1 part by weight of carbon black were added to 100 parts by weight of the hydrogen storage alloy powder as in Example 1. A paste was prepared by stirring and mixing the parts with water. Subsequently, in the coating tank containing the paste, the pore diameter was 2.0 mm, and the porosity was 50%.
%, A punched metal having a thickness of 0.1 mm is carried in, the punched metal is vertically lifted from the coating tank, and excess paste is removed through a slit to form a fixed thickness on the front and back surfaces of the punched metal. Was applied. Then, after drying at 80 ° C., it is rolled by a roller press, and the thickness ratio of the punched metal to the total thickness is 5%, 10%.
%, 20%, 30%, 40%, and 50%, and further cut to produce six types of hydrogen storage alloy negative electrodes.

Next, an electrode group was formed between each of the negative electrodes between the positive electrodes as in Example 2 with a separator made of a polypropylene nonwoven fabric interposed therebetween, and the capacity regulated by the negative electrode capacity using an alkaline electrolyte solution of 8N-KOH was 900 mAh. 6 test cells having the same structure as that of FIG. 2 were assembled.

For each of the test cells obtained, 0.1 g / g of hydrogen storage alloy.
After charging at a current density of 17 Ah, charging and discharging were repeated until the voltage reached 0.8 V, and the ratio of the amount of discharged electricity to the amount of charged electricity (utilization rate) was measured. The results are shown in FIG.
FIG. 5 shows the relationship between the thickness ratio of punched metal to the total thickness of the negative electrode and the utilization rate of the negative electrode.

As is clear from FIG. 5, the test cell incorporating each hydrogen storage alloy negative electrode in which the thickness ratio of the punched metal to the entire thickness is in the range of 10 to 35% has almost 100% utilization. I understand. On the other hand, the utilization rate of the secondary batteries incorporating the hydrogen storage alloy negative electrodes in which the thickness ratio of the punched metal to the total thickness is 5%, 40%, and 50% is reduced.
90% or less. This is because in a test cell incorporating a negative electrode in which the thickness ratio of punched metal to the total thickness is 5%, a sufficient current collecting effect cannot be obtained because the punched metal as a current collector is thin. Things. In addition, the thickness ratio of punched metal to the total thickness is 40%, 50%
In the test cell incorporating each of the negative electrodes, the porosity of the negative electrode was reduced, and the number of hydrogen storage alloys that could contact the alkaline electrolyte was reduced.

Example 7 First, 0.5 parts by weight of sodium polyacrylate, 0.125 parts by weight of CMC, PTFE dispersion (solid content; 1.5 parts by weight) and 1 part by weight of carbon black were added to 100 parts by weight of the hydrogen storage alloy powder as in Example 1. A paste was prepared by stirring and mixing the parts with water. Subsequently, as shown in FIG. 6, a line 2 connecting the centers of two adjacent holes 21 having a diameter of 2.0 mm.
A punched metal 23 having a staggered angle of 60%, a hole opening ratio of 50%, and a thickness of 0.1 mm was prepared by punching holes 2a, 22b, and 22c so as to form an equilateral triangle. The paste is applied to this punched metal 23,
After drying, the resultant was rolled by a roller press and further cut to produce a hydrogen storage alloy negative electrode.

Next, a separator made of a polypropylene non-woven fabric was sandwiched between the positive electrode and the negative electrode as in Example 2, and as shown in FIG.
Spirally wound in a direction (direction of arrow A) parallel to the above, stored in a mild steel bottomed cylindrical container, and further in the container.
A nickel-hydrogen secondary battery having a nominal capacity of 900 mAh and having the structure shown in FIG. 1 described above was accommodated in an alkaline electrolyte comprising a mixture of 7N-KOH and 1N-LiOH.

Comparative Example 2 As shown in FIG. 7, adjacent lines 31a, 32b, and 32c connecting the centers of the holes 31 having a hole diameter of 2.0 mm form a regular triangle. A punched metal 33 having a thickness of 0.1 mm was prepared. Subsequently, the same paste as in Example 7 was applied to the punched metal 33 and dried,
The resultant was rolled by a roller press and further cut to prepare a hydrogen storage alloy negative electrode.

Next, a separator made of a polypropylene non-woven fabric was sandwiched between the positive electrode and the negative electrode as in Example 2, and as shown in FIG.
Spirally wound in a direction (direction of arrow B) perpendicular to the above, stored in a mild steel bottomed cylindrical container, and further in the container.
A nickel-hydrogen secondary battery having a nominal capacity of 900 mAh and having the structure shown in FIG. 1 described above was accommodated in an alkaline electrolyte comprising a mixture of 7N-KOH and 1N-LiOH.

Each of the obtained secondary batteries of Example 7 and Comparative Example 2 was
100 batteries were prepared, and for each battery, the number of insulation failures was determined by measuring the insulation resistance by applying a direct current of 300 V between the positive electrode and the negative electrode. As a result, in Example 7, the number of insulation failures was 3 out of 100. On the other hand, in Comparative Example 12, the number of insulation failures was 17 out of 100.

From the results described above, it was confirmed that the secondary battery of Example 7 had a significantly lower incidence of insulation failure than the secondary battery of Comparative Example 2. This is because, in the secondary battery of Example 7, when the negative electrode and the positive electrode are wound with a separator interposed therebetween, as shown in FIG.
While l ₁ is half the length of one side of the equilateral triangle, in the secondary battery of Comparative Example 2, as shown in FIG. 7, the interval l ₂ between the fold lines of the punched metal 33 of the negative electrode is The length of one side of the equilateral triangle It becomes big. Therefore, since the negative electrode incorporated in the secondary battery of Example 7 is wound while being bent at a smaller angle than the negative electrode incorporated in the secondary battery of Comparative Example 2, the projection of the punched metal and the electrode It is considered that the falling off of the active material was prevented.

Example 8 First, a paste was prepared by stirring and mixing the same hydrogen storage alloy powder, sodium polyacrylate, CMC, PTFE, and carbon black as in Example 1 with water.
At this time, while adjusting the amounts of the respective components as shown in Table 4 below, by adjusting the stirring time and stirring speed, six kinds of pastes having the viscosity and the rotational viscosity ratio shown in Table 5 below were prepared. . The viscosity was determined by a measuring method (temperature: 25 ° C.) using a Brookfield viscometer calibrated with a viscosity standard solution described in ASTM. Subsequently, in the coating tank containing each of the pastes, a hole diameter of 2.0 mm,
A punched metal having a porosity of 50% and a thickness of 0.1 mm is carried in, the punched metal is vertically lifted from the coating tank, and excess paste is removed through a slit to remove the surface of the punched metal. A paste having a predetermined thickness was applied to the back surface. Next, after drying at 80 ° C., it was rolled by a roller press and further cut to produce six types of hydrogen storage alloy negative electrodes. In each of the negative electrodes, the thickness ratio of the punched metal to the entire thickness was 20%.

In producing the above-described negative electrode, the applicability of the paste to punched metal and the slittability (scraping property) were evaluated. The results are shown in Table 5 below.

As is clear from Table 5, the viscosity at a rotation speed of 6 rpm is
It can be seen that with a paste (No. 1) less than 100P, the applicability to the punched metal deteriorates, and a negative electrode having the desired thickness cannot be produced. In the case of a paste (No. 4) having a viscosity of more than 400 P at a rotation speed of 6 rpm, the applicability to the punched metal and the cutting property are both deteriorated, and the applied paste is almost peeled off from the punched metal. It turns out that a negative electrode cannot be produced. Furthermore, the viscosity at a rotation speed of 6 rpm is 100-400
Even in the range of P, the paste having a rotational viscosity ratio of less than 1.5 (No. 5) does not have a stable paste thickness, and the rotational viscosity ratio is 4%.
In the case of a paste exceeding No. 6 (No. 6), most of the applied paste not only peels off the punched metal, but also the components become unstable. In contrast, the viscosity at a rotation speed of 6 rpm is 100-400
A paste having a p and a rotational viscosity ratio of 1.5 to 4 (No. 2 and No. 3) was excellent in applicability to a punched metal and cutting performance, and a good negative electrode was produced.

Example 9 No. 2 and N shown in Table 5 were placed between the positive electrodes as in Example 2.
The negative electrode of o3 constitutes an electrode group via a separator made of a polypropylene non-woven fabric, and the capacity regulated by the negative electrode capacity using the electrode group and an alkaline electrolyte composed of 8N-KOH is the same as in FIG. 2 in which the capacity is 900 mAh. Six test cells of the structure were assembled.

For each of the test cells obtained, 0.1 g / g of hydrogen storage alloy.
After charging at a current density of 17 Ah, charging and discharging were repeated until the voltage reached 0.8 V, and the ratio of the amount of discharged electricity to the amount of charged electricity (utilization rate) was measured. As a result, it was confirmed that the utilization rate of each test cell was 100%.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a nickel-metal hydride secondary battery that achieves high capacity by improving the utilization rate of a hydrogen storage alloy negative electrode and has an improved charge / discharge cycle life. .

[Brief description of the drawings]

FIG. 1 is a partially exploded perspective view showing a nickel-metal hydride secondary battery according to the present invention, FIG. 2 is a cross-sectional view showing a test cell used in an embodiment, and FIG. FIG. 4 is a characteristic diagram showing the relationship between the porosity of punched metal of the negative electrode and the utilization rate of the negative electrode. FIG. 4 shows Example 5 and Comparative Example 1.
FIG. 5 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and efficiency in the nickel-metal hydride secondary battery of FIG. 5, and FIG. 5 is a graph showing the relationship between the thickness ratio of punched metal to the total thickness of the negative electrode and the negative electrode in the nickel-metal hydride secondary battery of Example 6. FIG. 6 is a characteristic diagram showing the relationship between the negative electrode of Example 7 and the negative electrode of Comparative Example 2; FIG. 6 is a plan view for explaining the hole arrangement and winding direction of the punched metal used for the negative electrode of Example 7; FIG. 4 is a plan view for explaining a hole arrangement and a winding direction of a punched metal used for the embodiment. 1,12 ... positive electrode, 2,13 ... hydrogen storage alloy negative electrode, 3,14
... separator, 4, 11 ... container, 6 ... sealing plate, 17 ...
... Electrolyte, 23 ... Punched metal.

Continued on the front page (72) Inventor Yuji Sato 1 Toshiba Research Institute, Komukai, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Hiroyuki Takahashi 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Inside Battery Co., Ltd. (72) Inventor Hirotaka Hayashida 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Research Institute Co., Ltd. (72) Inventor Ichiro Saruwatari 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (56) References JP-A-64-649 (JP, A) JP-A-1 -279563 (JP, A) JP-A-63-266768 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/62 H01M 10/30 H01M 4/64-4/74 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A non-sintered nickel positive electrode in which a paste containing nickel hydroxide, cobalt monoxide and a binder is formed on a conductive core, and a hydrogen storage alloy negative electrode are spirally wound with a separator interposed therebetween. A nickel-hydrogen secondary battery, comprising: a group of electrodes, an alkaline electrolyte, and a container in which the group of electrodes and the alkaline electrolyte are stored, wherein the negative electrode is 100 parts by weight of a hydrogen storage alloy powder, polyacryl. 0.005 to 1 part by weight of carboxymethyl cellulose
A paste containing 0.01 to 1 part by weight, 0.5 to 7 parts by weight of a fluororesin, and 0.1 to 4 parts by weight of a conductive material powder is perforated so as to always form an equilateral triangle when connecting the centers of three adjacent holes. With a hole diameter of 1 to 5 mm and an aperture ratio of 4
5 to 70% of the punched metal is formed, wherein the punched metal is 10 to 10% of the total thickness of the negative electrode.
The nickel-metal hydride secondary battery occupies a thickness of 35%, and a winding direction of the electrode group is parallel to one side of the equilateral triangle of the punched metal. 2. A non-sintered nickel positive electrode in which a paste containing nickel hydroxide, cobalt monoxide and a binder is formed on a conductive core, and a hydrogen storage alloy negative electrode are spirally wound with a separator interposed therebetween. A nickel-hydrogen secondary battery, comprising: an electrode group, an alkaline electrolyte, and a container in which the electrode group and the alkaline electrolyte are stored, wherein the negative electrode comprises a hydrogen storage alloy powder, a binder, and a conductive material. When a paste containing material powder and having a viscosity of 100P to 400P and a rotational viscosity ratio (R) of 1.5 to 4 shown in the following formula (1) is connected to the centers of three adjacent holes, an equilateral triangle is always formed. The electrode group is formed in a punched metal having a hole diameter of 1 to 5 mm and an opening ratio of 45 to 70%. The winding direction of the electrode group is the same as that of the punched metal. Characterized by being parallel to one side of the equilateral triangle Nickel-hydrogen secondary battery. R = V ₁ / V ₂ (1) where V ₁ is a temperature of 25 using a Brookfield viscometer (single cylindrical viscometer) calibrated with a viscosity standard solution described in ASTM.
° C., a viscosity measured at a rotational speed of 6 rpm, V ₂ is ASTM
Using a Brookfield viscometer (single cylindrical viscometer) calibrated with the viscosity standard solution described in the above, the temperature is 25 ° C and the rotation speed is 60 rp.
The viscosity measured under the condition of m is shown.