JP2010010097A - Method of manufacturing nickel metal hydride storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel metal hydride storage battery with good overdischarge proof and cycle life characteristics. <P>SOLUTION: The method of manufacturing the nickel metal hydride storage battery includes a process of making an anode contained in an electrode group occlude hydrogen by supplying hydrogen gas into a battery case before sealing the case accommodating electrode groups and an electrolyte. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a nickel-metal hydride storage battery, and specifically to a method for manufacturing a negative electrode with improved resistance to overdischarge.

  Alkaline storage batteries such as nickel metal hydride storage batteries and nickel cadmium storage batteries are widely used for high power applications such as electric tools, electric assist bicycles, cordless vacuum cleaners, and electric vehicles. In particular, for power supplies for electric tools, fast charging and large current discharging at a rate of 1.0 to 7.5 hours are emphasized.

  The voltage of the nickel-metal hydride storage cell is about 1.2V. Therefore, an assembled battery is used in the electric tool in order to ensure a necessary voltage, and the assembled battery is usually composed of 10 to 20 nickel hydride storage batteries connected in series.

  By the way, from the viewpoint of cost reduction and space saving, a power circuit is often not provided with a protection circuit for preventing overdischarge and reverse charging. Since the protection circuit is not provided, each nickel metal hydride storage battery is discharged until its open circuit voltage drops to 0.1 to 0.2 V even if the remaining capacity decreases. That is, the nickel metal hydride storage battery included in the power tool may be overdischarged until the motor of the power tool is not driven.

  In general, a positive electrode containing nickel hydroxide as a positive electrode active material is added with a cobalt component such as cobalt hydroxide or cobalt monoxide as a conductive additive. A part of this cobalt component is electrochemically oxidized into β-cobalt oxyhydroxide having high conductivity at the first charge. Thereby, a conductive network is formed in the positive electrode.

However, when the battery voltage of the nickel-metal hydride storage battery becomes low as described above due to reverse charging, the potential of the positive electrode is changed to the trivalent / divalent equilibrium potential of β-cobalt oxyhydroxide in about a short time (about 0. The β-cobalt oxyhydroxide is reduced to HCoO ²⁻ soluble in the electrolyte (alkaline aqueous solution) and dissolved in the electrolyte. As a result, the conductive network is locally destroyed. Therefore, each time the overdischarge of the nickel hydride storage battery is repeated, the battery capacity gradually decreases. In addition, it is known that when a charge / discharge cycle is performed at high temperature, the collapse of the conductive network tends to be promoted.

Conventionally, in order to provide an alkaline storage battery with excellent cycle life at high temperatures, after the first charge, it is discharged in an environment of 40 to 80 ° C. so that the closed circuit voltage after discharge is 1.15 V or higher. Has been proposed (see Patent Document 1).
Japanese Patent Laid-Open No. 2001-338677

  However, the technique disclosed in Patent Document 1 is not a technique that assumes an extreme reverse charge of 0.1 to 0.2 V per nickel hydride storage battery single cell. For this reason, the elution to the electrolyte of the cobalt compound which forms a conductive network cannot be suppressed completely. Therefore, it is not possible to solve the problem that the conductivity between the positive electrode active materials is reduced by repeating the use including reverse charging.

Furthermore, the problems as described above tend to be promoted by conditions specific to the assembled battery in that the capacity and temperature environment are different for each individual cell included in the assembled battery.
For example, when a single cell having a lower capacity than the others is included in the assembled battery, the single cell having the lower capacity is in a reverse charge state with a reversal by repeating charge and discharge. As a result, not only the above-described deterioration of the positive electrode but also oxygen may be generated from the negative electrode, and the hydrogen storage alloy as the negative electrode active material may be oxidized and deteriorated.
Furthermore, the vicious cycle that the single cell which received such damage deteriorates further by repetition of a charging / discharging cycle arises.

  Further, water in the electrolyte is involved in the reaction accompanying the reversal. For example, in a battery that has undergone reverse charging, water is decomposed and oxygen gas is generated by the reversal of the negative electrode. When the pressure in the battery rises due to the oxygen gas and the safety valve is activated, the electrolyte and the generated gas in the battery are dissipated out of the battery. That is, when the overdischarge enough to cause inversion occurs repeatedly, it is directly connected to the separator dryout which is one of the typical deterioration modes of the battery.

  An object of the present invention is to provide a nickel-metal hydride storage battery having good overdischarge resistance and cycle life characteristics by suppressing the generation of oxygen gas from the negative electrode even when charge / discharge including overdischarge is repeated. And

  The method for producing a nickel metal hydride storage battery according to the present invention includes a step of supplying hydrogen gas into the battery case and occluding hydrogen in the negative electrode included in the electrode group before sealing the battery case containing the electrode group and the electrolyte. It is characterized by having

In one preferred embodiment, the production method of the present invention comprises:
(A) a step of winding a laminate including a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween to obtain a wound electrode group;
(B) A step of accommodating the wound electrode group in a cylindrical battery case,
(C) adding an electrolyte into the cylindrical battery case;
(D) supplying hydrogen gas into the cylindrical battery case containing the wound battery group and occluding hydrogen in the negative electrode; and (E) sealing the cylindrical battery case to form a cylinder A step of obtaining a nickel-metal hydride storage battery.

In another preferred embodiment, the production method of the present invention comprises:
(A) stacking a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween to obtain a stacked electrode group;
(B) housing the stacked electrode group in a rectangular battery case, and closing the opening of the rectangular battery case with a sealing body having a liquid injection hole;
(C) a step of injecting an electrolyte into the prismatic battery case from the injection hole,
(D) supplying hydrogen gas into the prismatic battery case containing the stacked battery group, and occluding hydrogen in the negative electrode; and (e) closing the liquid injection hole, thereby A step of sealing the battery case to obtain a prismatic nickel metal hydride storage battery.

  In the above manufacturing method, the step of occluding hydrogen in the negative electrode may include the step of occluding hydrogen in the hydrogen storage alloy contained in the negative electrode so that the atomic ratio of hydrogen to the hydrogen storage alloy is 0.2 or less. preferable. The step of occluding hydrogen in the negative electrode preferably includes a step of depressurizing the inside of the battery case before supplying hydrogen gas to the battery case.

  In the manufacturing method, the step of sealing the battery case is preferably performed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen, argon, and helium, or in air.

  The positive electrode active material includes core particles and a cobalt compound supported on the surface of the core particles. The core particles include nickel hydroxide as a main component. The cobalt compound includes cobalt hydroxide and cobalt oxide. And at least one selected from the group consisting of cobalt oxyhydroxide.

  By the production method of the present invention, the discharge reserve can be provided in advance on the negative electrode. By providing such a discharge reserve, even if a negative electrode reversal occurs due to overdischarge, the discharge reserve is preferentially consumed, so that the generation of oxygen due to the electrolysis of the electrolyte in the negative electrode can be suppressed. . Furthermore, since the generation of oxygen is suppressed, the oxidative deterioration of the hydrogen storage alloy that is the negative electrode active material can also be suppressed. Therefore, the manufacturing method of the present invention can provide a nickel-metal hydride storage battery having improved overdischarge resistance and cycle life characteristics.

The method for producing a nickel metal hydride storage battery according to the present invention is characterized in that hydrogen is stored in the negative electrode before the battery case containing the electrode group and the electrolyte is sealed, preferably just before the battery case is sealed. According to the present invention, a discharge reserve (occluded hydrogen) can be provided in advance in the negative electrode. As described above, by providing the discharge reserve in advance, even if the inversion occurs due to overdischarge, the consumption reaction of the discharge reserve provided in the negative electrode occurs preferentially over the oxygen generation reaction due to the electrolysis of the electrolyte. For this reason, decomposition | disassembly of the electrolyte which arises in a negative electrode is suppressed, and separator dry out is suppressed. Therefore, the overdischarge resistance of the nickel metal hydride storage battery can be improved. Furthermore, since the oxidation of the hydrogen storage alloy that is the negative electrode active material is also suppressed, the performance of the negative electrode can be maintained over a long period of time.
Therefore, the manufacturing method of the present invention can provide a nickel-metal hydride storage battery having improved overdischarge resistance and cycle life characteristics.

  The shape of the nickel metal hydride storage battery produced by the production method of the present invention is not particularly limited, and may be a cylindrical shape or a square shape. As an example, the case where the nickel metal hydride storage battery is a cylindrical type and the case where it is a square type will be described below.

(Embodiment 1)
An example of a cylindrical nickel-metal hydride storage battery is shown in FIG.
In the present embodiment, the production method of the present invention comprises:
(A) a step of winding a laminate including a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween to obtain a wound electrode group;
(B) The process of accommodating a wound electrode group in a cylindrical battery case (C) The process of adding electrolyte in a cylindrical battery case,
(D) supplying hydrogen gas into a cylindrical battery case containing the wound battery group and occluding hydrogen in the negative electrode; and (E) sealing the cylindrical battery case to form a cylindrical nickel-metal hydride battery. The process of obtaining.

  The positive electrode 11 containing a positive electrode active material and the negative electrode 12 containing a negative electrode active material can be produced by methods known in the art.

  The positive electrode 11 can include, for example, a positive electrode mixture containing a positive electrode active material and a porous substrate holding the positive electrode mixture. Such a positive electrode can be produced by filling a porous base material with a positive electrode mixture paste containing a positive electrode active material, drying, and rolling. The positive electrode mixture paste can be produced by dispersing a positive electrode active material and, if necessary, a positive electrode mixture containing a binder and a conductive agent in a dispersion medium.

As the positive electrode active material, materials known in the art can be used.
As a material constituting the porous substrate, materials known in the art can be used. For example, a foamed nickel sheet or the like can be used as the porous substrate.

  The negative electrode 12 includes, for example, a negative electrode current collector and a negative electrode mixture supported thereon. The negative electrode mixture includes a hydrogen storage alloy that is a negative electrode active material, and, if necessary, a binder and a conductive agent. Such a negative electrode can be produced by dispersing a negative electrode mixture in a dispersion medium to obtain a negative electrode mixture paste, applying the obtained negative electrode mixture paste, drying, and rolling.

As the hydrogen storage alloy, any material known in the art can be used without particular limitation as long as it is stable against an alkaline aqueous solution and functions sufficiently in a sealed battery at room temperature.
The material constituting the negative electrode current collector is not particularly limited. For example, an iron punching metal plated with nickel can be used as the negative electrode current collector.

As the binder and the conductive agent added to the positive electrode and the negative electrode, materials known in the art can be used.
As the binder, an organic resin binder can be used, and an organic resin binder excellent in alkali resistance, oxidation resistance and the like is particularly preferable. For example, polytetrafluoroethylene (PTFE), styrene-butylene copolymer rubber (SBR), or the like can be used. These materials may be used alone or in combination of two or more.
As the conductive agent, nickel powder, carbon black powder, graphite powder, or the like can be used. These materials may be used alone or in combination of two or more. The particle shape of the conductive agent is not particularly limited, and may be any of spherical shape, flake shape, fiber shape, needle shape, and the like.

  Next, using the positive electrode and the negative electrode obtained as described above, a wound electrode group is prepared (step (A)). Specifically, a laminate composed of the positive electrode 11, the negative electrode 12, and the separator 13 disposed therebetween is wound in a spiral shape to obtain a wound electrode group 14 that is highly bound. As the separator 13, for example, a nonwoven fabric made of polyolefin such as polypropylene can be used. The separator 13 is preferably subjected to sulfonation treatment or the like in order to increase the affinity with the electrolyte.

  The obtained electrode group 14 is accommodated in the cylindrical battery case 15 (step (B)). A positive electrode 11 protrudes from one end face of the electrode group 14 in the winding axis direction, and a flat positive collector plate 16 is connected to the positive electrode 11. A negative electrode 12 protrudes from the other end face of the electrode group 14, and a flat negative collector plate 17 is connected to the negative electrode 12. The electrode group 14 is accommodated in the battery case 15 such that the negative electrode current collector plate 17 is in contact with the inner bottom surface of the battery case 15. The negative electrode current collector plate 17 is welded to the inner bottom surface of the battery case 15.

  One end of a positive electrode lead plate 18 is welded to the positive electrode current collector plate 16. The other end of the positive electrode lead plate 18 is welded to the bottom of a sealing plate 21 having an external terminal 19 and a safety valve mechanism including a rubber valve 20.

  Next, an electrolyte is injected into the battery case 15 (step (C)). As the electrolyte, an alkaline aqueous solution having a predetermined concentration can be used. For example, an alkaline aqueous solution containing KOH, NaOH, and LiOH at a predetermined ratio, an alkaline aqueous solution containing KOH at a concentration of 4 to 6M, or the like can be used.

  The sealing plate 21 is inserted into the opening of the battery case 15. At this time, the insulating gasket 22 is interposed between the sealing plate 21 and the opening end of the battery case 15.

  In addition, as a constituent material of the battery case 15, the positive electrode current collector plate 16, the negative electrode current collector plate 17, the positive electrode lead plate 18, the sealing plate 21, the gasket 22, and the like, materials known in the art can be used.

  Next, before the battery case 15 is sealed by sealing the opening end of the battery case 15 to the sealing plate 21 via the gasket 22, hydrogen gas is supplied into the battery case 15 and hydrogen is stored in the negative electrode. (Process (D): Negative electrode chemical conversion process).

Occlusion of hydrogen in the negative electrode can be achieved by setting the inside of the battery case 15 to an atmosphere containing hydrogen gas. The atmosphere containing hydrogen gas may be a mixed atmosphere of hydrogen gas and air, or may be an atmosphere consisting only of hydrogen gas (hydrogen gas atmosphere).
For example, the battery case 15 can be filled with an atmosphere containing hydrogen gas by disposing the battery case 15 before sealing in a chamber filled with a mixed atmosphere of air and hydrogen gas.
Or the battery case 15 before sealing is arrange | positioned in the chamber which can be pressure-reduced, and the said chamber is pressure-reduced. Next, by introducing hydrogen gas into the decompressed chamber, the battery case 15 can be filled with a hydrogen gas atmosphere.

  In particular, it is preferable to decompress the inside of the battery case 15 before supplying hydrogen gas into the battery case 15, that is, to fill the inside of the battery case 15 with a hydrogen gas atmosphere. By reducing the pressure in the battery case 15 and then filling the battery case 15 with hydrogen gas, the pressure of the hydrogen gas in the battery case 15 can be accurately controlled. Further, if hydrogen is stored in the negative electrode in the presence of oxygen gas, the battery may generate heat.

  The pressure of the hydrogen gas in the battery case 15, that is, the pressure of the hydrogen gas contained in the atmosphere containing the hydrogen gas in which the electrode group 14 is placed is appropriately set according to the required amount of discharge reserve.

In the step (D), the amount of discharge reserve provided in the negative electrode, that is, the amount of hydrogen stored in the hydrogen storage alloy is such that the ratio H / M of the number of hydrogen atoms H stored to the number M of hydrogen storage alloys is 0. It is preferable that the amount is 2 or less.
The amount of hydrogen stored in the hydrogen storage alloy can be determined by creating a pressure-composition isotherm. FIG. 2 shows an example of the pressure-composition isotherm. In FIG. 2, the vertical axis represents the equilibrium hydrogen pressure, and the horizontal axis represents the ratio M / H (hydrogen storage amount) of the number of hydrogen atoms H stored with respect to the number of atoms M of the hydrogen storage alloy. FIG. 2 is a pressure-composition isotherm at 20 ° C. of MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 (Mm: Misch metal).

  The relationship between the equilibrium hydrogen pressure and the ratio H / M can be seen from the pressure-composition isotherm. Therefore, the amount of hydrogen stored in the hydrogen storage alloy can be controlled by adjusting the pressure of the hydrogen gas contained in the atmosphere in which the electrode group is placed. Specifically, when a mixed atmosphere of hydrogen gas and air is used, the partial pressure of hydrogen gas may be adjusted. When a hydrogen gas atmosphere is used, the hydrogen gas pressure may be adjusted.

  The pressure-composition isotherm can be measured according to JIS H7201-11991. As a pressure-composition isotherm measuring device, for example, a Siebert device can be used.

  In addition, the temperature when hydrogen is stored in the hydrogen storage alloy is not particularly limited, but may be 20 to 35 ° C.

  In the step (D), by setting the atomic ratio H / M of hydrogen to the hydrogen storage alloy to 0.2 or less, the amount of discharge reserve provided in the negative electrode can be further optimized. For this reason, even if the negative electrode inversion occurs due to reverse charging, the consumption reaction of the discharge reserve provided in the negative electrode occurs preferentially. For this reason, the oxygen generation reaction which arises by the electrolysis of electrolyte in a negative electrode can fully be suppressed. Furthermore, since generation of oxygen in the negative electrode is suppressed, deterioration due to oxidation of the hydrogen storage alloy can be suppressed even if inversion occurs. Therefore, the overdischarge resistance and cycle life characteristics can be further improved.

  According to the study by the present inventors, in a hydrogen storage alloy generally used for nickel metal hydride storage batteries, if the ratio H / M is 0.2 or less, the hydrogen storage amount is almost equal to the pressure-composition. It was found that it entered the α phase formation region of the isotherm.

When the ratio H / M is larger than 0.2, the discharge reserve provided in the negative electrode becomes excessive, and the amount of charge reserve is reduced correspondingly. For this reason, the charge reserve cannot sufficiently absorb the gas generated at the time of overcharge, the battery internal pressure rapidly increases, and the safety valve operates. For this reason, electrolyte and generated gas may leak out of the battery, thereby increasing internal resistance and reducing cycle life characteristics.
When the ratio H / M is greater than 0.2, the hydrogen storage amount enters the plateau region of the pressure-composition isotherm. In the plateau region of the pressure-composition isotherm, the amount of hydrogen occlusion changes greatly with a slight change in the equilibrium hydrogen pressure. For this reason, in order to store hydrogen in the hydrogen storage alloy so as to obtain a predetermined hydrogen storage amount (ratio H / M) that gives a plateau region, it is necessary to precisely control the equilibrium hydrogen pressure, the environmental temperature, and the like. . Therefore, it is not economical in terms of capital investment, productivity, etc., to make the amount of hydrogen stored in the hydrogen storage alloy the hydrogen storage amount that gives the plateau region.

  Finally, the open end of the battery case 15 is caulked to the sealing plate 21 via the gasket 22 to seal the battery case 15. Thus, a cylindrical nickel-metal hydride storage battery can be obtained (step (E)).

The battery case 15 may be sealed in the air. Alternatively, it may be performed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen, argon and helium.
In particular, the battery case 15 is preferably sealed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen gas, argon gas, and helium gas. When an unsealed battery is left in the air for a long time (for example, when the production line has been shut down for a long time due to a process trouble, etc.), the negative electrode that has occluded hydrogen reacts gradually with oxygen in the air. There is a possibility of fever. When heat is generated in the battery, loss due to evaporation of the electrolyte may occur. Therefore, the battery case 15 is preferably sealed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen gas, argon gas, and helium gas.
The battery case 15 may be sealed under normal pressure.

  In the present invention, the positive electrode active material includes core particles containing nickel hydroxide as a main component and a cobalt compound supported on the surface of the core particles. The cobalt compound includes cobalt hydroxide, cobalt oxide, and It is preferable to include at least one selected from the group consisting of cobalt oxyhydroxide.

As the core particles containing nickel hydroxide as a main component, for example, spherical nickel hydroxide particles can be used. The core particles preferably have a β-type crystal structure (CdI ₂ structure). Further, the core particle may be a nickel hydroxide solid solution containing a small amount of elements such as cobalt, zinc, magnesium, etc., produced by a known reaction crystallization method. The amount of metal elements other than Ni in the solid solution is preferably 2 to 10 mol% of the total metal elements.

  The cobalt compound supported on the surface of the core particle includes at least one selected from the group consisting of cobalt hydroxide, cobalt oxide, and cobalt oxyhydroxide. The cobalt oxide preferably has a cobalt valence of 2 or more. Among these, cobalt oxyhydroxide having a cobalt valence exceeding 3.0, such as γ-cobalt oxyhydroxide, is most preferable.

Cobalt oxyhydroxide whose cobalt valence exceeds 3.0 is difficult to be reduced by overdischarge. On the other hand, cobalt oxyhydroxide having a cobalt valence of more than 3.0 is less likely to form a discharge reserve in the initial charge after battery assembly than a cobalt oxide having a cobalt valence of about 2. .
In the present invention, as described above, before the battery case is sealed, hydrogen gas is supplied into the battery case and hydrogen is occluded in the negative electrode. That is, a discharge reserve is provided. Therefore, in the present invention, by using a positive electrode active material containing cobalt oxyhydroxide whose cobalt valence exceeds 3.0, it is possible to provide an alkaline storage battery having even better overdischarge resistance and cycle life characteristics. it can.

A positive electrode active material containing nickel hydroxide particles and a cobalt compound having a cobalt valence of more than 3.0 supported thereon can be produced, for example, as follows.
First, a surface layer made of cobalt hydroxide is formed on the surface of nickel hydroxide particles. Next, the nickel hydroxide particles provided with the surface layer are wetted with an alkaline aqueous solution. The particles are dried with hot air while heating. For the heating, microwave heating is mainly used.
In this way, a positive electrode active material containing nickel hydroxide particles and a cobalt compound having a valence of cobalt supported thereon of more than 3.0 can be obtained.
The surface layer obtained through the treatment under the violent oxidation conditions as described above contains an oxide containing cobalt having a high valence. For this reason, the positive electrode active material having such a surface layer is not easily damaged by overdischarge, and thus the conductive network between the positive electrode active materials is maintained for a long time.
Note that the manufacturing method as described above is disclosed in JP-A-11-97008.

  The amount of the cobalt compound contained in the surface layer is preferably 2 to 15 parts by weight per 100 parts by weight of the core particles.

(Embodiment 2)
FIG. 3 shows a prismatic nickel metal hydride storage battery according to another embodiment of the present invention. The square battery 30 in FIG. 3 is basically the same as the cylindrical battery in FIG. 1 except that a stacked electrode group and a square battery case are used.

First, the positive electrode 31 and the negative electrode 32 are laminated | stacked through the separator 33, and a lamination type electrode group is obtained (process (a)). As the positive electrode 31, the negative electrode 32, and the separator 33, the same ones as in the first embodiment can be used. In the battery 30 of FIG. 3, the positive electrode 31 is accommodated in a bag-shaped separator 33.
The stacked electrode group may be wound and used as a wound electrode group.

Next, the obtained stacked electrode group is accommodated in a rectangular battery case 34, and the opening of the rectangular battery case 34 is closed with a sealing body 35 having a liquid injection hole (step (b)). Specifically, one end of the positive electrode lead plate 36 is welded to the positive electrode constituting the stacked electrode group, and one end of the negative electrode lead (not shown) is welded to the negative electrode. Further, an insulating plate 37 is mounted on the upper part of the stacked electrode group. The stacked electrode group is accommodated in the rectangular battery case 34. The other end of the positive electrode lead is connected to the lower surface of the sealing plate, and the other end of the negative electrode lead is connected to the lower portion of the negative electrode terminal 39 inserted through the insulating material 38 into the terminal hole at the center of the sealing plate. The negative electrode terminal 39 has a liquid injection hole for injecting an electrolyte.
Next, the opening end of the rectangular battery case 34 and the peripheral edge of the sealing plate 35 are welded, and the opening of the rectangular battery case 34 is closed with the sealing plate. An insulator 40 is provided below the sealing body 35.

  Next, an electrolyte is injected into the battery case from the injection hole (step (c)). The same electrolyte as in Embodiment 1 can also be used.

  After injecting the electrolyte, hydrogen gas is supplied into the prismatic battery case, and hydrogen is occluded in the negative electrode (step (d)). This process (d) can be performed similarly to the process (D) of Embodiment 1.

  Finally, a plug provided with a safety valve 41 is welded to the liquid injection hole, the liquid injection hole is closed, and the rectangular battery case is sealed. Thus, a prismatic nickel metal hydride storage battery can be obtained (step (e)). This step (e) may be performed in the air as in the step (E) of the first embodiment, or an atmosphere containing at least one inert gas selected from the group consisting of nitrogen, argon and helium. It may be done in. Similarly to the above, the battery case is preferably sealed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen gas, argon gas, and helium gas.

  Also in this embodiment, materials known in the art can be used as constituent materials such as a battery case, a positive electrode lead, a negative electrode lead, an insulating plate, and an insulating material.

  Hereinafter, the present invention will be specifically described with reference to examples.

Example 1
In this example, a cylindrical nickel metal hydride storage battery as shown in FIG. 1 was produced.

(Preparation of positive electrode)
As the positive electrode active material, nickel hydroxide having a surface layer made of a cobalt oxide having a cobalt valence of more than 3.0 was used. The amount of the cobalt oxide was 7 weights per 100 parts by weight of nickel hydroxide.
A positive electrode active material was prepared as follows.
First, cobalt hydroxide was supported on the surface of nickel hydroxide based on a known method (see JP-A-10-12237).
Next, the obtained nickel hydroxide particles supporting cobalt hydroxide were sufficiently moistened with an aqueous solution containing 48% by weight of sodium hydroxide. Thereafter, the nickel hydroxide particles were maintained at 110 ° C., and heated air of 110 ° C. was blown onto the nickel hydroxide particles and dried for about 1 hour. By this step, the surface layer becomes a cobalt oxide containing γ-cobalt oxyhydroxide as a main component.
The obtained particles were washed with water and dried to obtain nickel hydroxide having cobalt oxide having a cobalt valence exceeding 3.0 on the surface.

A positive electrode mixture paste was prepared by mixing 107 parts by weight of the positive electrode active material, 1 part by weight of zinc oxide, 0.2 part by weight of polytetrafluoroethylene as a binder, and a predetermined dispersion medium. Zinc oxide was added to suppress expansion of the positive electrode.
The obtained mixture paste was filled in a highly porous nickel foam nickel sheet. The sheet was dried, pressure molded, and cut into a predetermined size. Thus, a positive electrode having a theoretical capacity (same as the theoretical capacity of the positive electrode) of 1.3 Ah was obtained.

(Preparation of negative electrode)
As a negative electrode active material, a hydrogen storage alloy represented by MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 (Mm: Misch metal) was used. The hydrogen storage alloy was previously pulverized so as to have a predetermined average particle size (30 μm).

  100 parts by weight of the negative electrode active material, 0.7 parts by weight of styrene-butadiene copolymer rubber as a binder, 0.3 parts by weight of acetylene black as a conductive agent, and a predetermined amount of dispersion medium are mixed. A negative electrode mixture paste was obtained. The obtained negative electrode mixture paste was applied to both sides of a nickel-plated iron punching metal, dried, pressure-molded, and cut into a predetermined size. Thus, a negative electrode having a capacity 1.5 times the theoretical capacity of the positive electrode was obtained.

(Battery assembly)
The positive electrode and the negative electrode obtained as described above were laminated through a separator to obtain a laminate. As the separator, a sulfonated polypropylene nonwoven fabric was used.
The obtained laminate was wound in a spiral shape to obtain a wound electrode group. On one end face in the winding axis direction of the electrode group, an iron positive electrode current collector plate plated with Ni was connected to the positive electrode. On the other end face of the electrode group, an iron negative electrode current collector plate plated with Ni was connected to the negative electrode.

  The electrode group was housed in an iron battery case plated with Ni. At this time, the electrode group was accommodated so that the negative electrode current collector plate was in contact with the inner bottom surface of the battery case. The negative electrode current collector plate was welded to the inner bottom surface of the battery case. One end of a nickel positive electrode lead plate was welded to the positive electrode current collector plate, and the other end of the positive electrode lead plate was connected to the bottom of an iron sealing plate plated with Ni having an external terminal and a safety valve mechanism.

Next, a predetermined amount of electrolyte was injected into the battery case. The electrolyte was prepared by dissolving lithium hydroxide in a potassium hydroxide aqueous solution having a specific gravity of 1.3 so as to have a concentration of 40 g / L.
Thereafter, the sealing plate was inserted into the opening of the battery case. At this time, a nylon gasket was interposed between the sealing plate and the open end of the battery case.

Next, before sealing the battery case, hydrogen gas was supplied into the battery case, and hydrogen was occluded in the negative electrode (negative electrode formation step).
Specifically, first, the battery case before sealing was placed in a vacuum chamber, and the inside of the battery case was evacuated. Next, hydrogen gas was introduced into the vacuum chamber at 20 ° C., and the pressure of the hydrogen gas in the vacuum chamber (that is, the pressure of the hydrogen gas in the battery case) was set to 0.01 MPa. Thus, hydrogen was occluded in the hydrogen storage alloy of the negative electrode so that the ratio H / M was 0.2, and a discharge reserve was provided in the negative electrode.
The ratio H / M when the equilibrium hydrogen pressure was 0.01 MPa was determined from the pressure-composition isotherm (FIG. 2) at 20 ° C. of MmNi _3.55 Mn _0.4 Al _0.3 Co _0.75 (Mm: Misch metal).

  Next, the open end of the battery case was caulked to the sealing plate via a gasket in a normal pressure air atmosphere to seal the battery case. Thus, a nickel metal hydride storage battery was obtained. The obtained nickel metal hydride storage battery was used as the battery of Example 1.

(Example 2)
A battery of Example 2 was obtained in the same manner as Example 1 except that the battery case was sealed in a nitrogen atmosphere at normal pressure.

(Example 3)
A battery of Example 2 was obtained in the same manner as in Example 1 except that in the negative electrode formation step, the pressure of hydrogen gas was 0.016 MPa. In the battery of Example 2, the ratio H / M was 0.5.

Example 4
A battery of Example 4 was obtained in the same manner as Example 3 except that the battery case was sealed in a nitrogen atmosphere at normal pressure.

(Comparative Example 1)
A battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that the negative electrode formation step was not performed.

The batteries of Examples 1 to 4 and the battery of Comparative Example 1 were subjected to the following evaluation.
Each battery was charged at a current of 1 hour rate by a method (-ΔV method) in which charging was stopped when the battery voltage dropped 10 mV from the maximum value. After this charge, it rested for 1 hour. The battery after the rest was subjected to the following step-type overdischarge. First, the battery after resting is discharged at a current of 0.3 hour until the battery voltage becomes 0 V, then discharged at a current of 1 hour until the battery voltage becomes 0 V, and finally It was discharged for 20 seconds at a current of 0.2 hour rate. In the three types of discharges, the battery voltage is discharged and finally discharged until the battery voltage becomes 0V.

Charging / discharging as described above was repeated until the discharge capacity decreased to 60% of the positive electrode theoretical capacity. Table 1 shows the number of cycles in which the charge / discharge cycle was repeated (number of cycles up to 60% capacity). The number of cycles can be regarded as a measure of overdischarge resistance and cycle life characteristics.
In this evaluation, the “discharge capacity” was calculated from the time from the start of discharge until the battery voltage reached 0.8 V in the first step of discharge (0.3 hour rate discharge). The results are shown in Table 1. FIG. 4 shows the relationship between the capacity retention ratio and the number of cycles of the batteries of Examples 1 and 3 and the battery of Comparative Example 1. The capacity retention ratio is a value representing the ratio of the discharge capacity to the positive electrode theoretical capacity as a percentage value.

  After the battery was sealed, it was examined whether or not the temperature inside the battery increased (battery heat generation). The results are shown in Table 1.

  Table 1 also shows the pressure of hydrogen gas, the ratio H / M, the hydrogen storage state of the hydrogen storage alloy, and the environment in which the battery is sealed (crimping environment) in the negative electrode formation step.

  As shown in Table 1, in the battery of Comparative Example 1 that was not subjected to the negative electrode formation step, the number of cycles up to 60% capacity was significantly reduced. This is considered as follows. When the battery of Comparative Example 1 is overdischarged and the positive electrode is inverted, the conductive network between the positive electrode active materials is locally collapsed as described above, and the positive electrode is deteriorated. Further, when the negative electrode is inverted, water in the electrolyte is electrolyzed at the negative electrode, and oxygen gas is generated. As a result, separator dry-out, which is one of typical battery deterioration modes, occurs, and the battery internal resistance increases significantly. For this reason, it is considered that the number of cycles in which the discharge capacity is reduced to 60% of the positive electrode theoretical capacity is shortened.

  Further, after the evaluation, the deterioration of the negative electrode capacity of the battery of Comparative Example 1 was investigated. As a result, the magnetic susceptibility of the hydrogen storage alloy contained in the battery of Comparative Example 1 increased and the PCT capacity decreased as compared with the initial charge / discharge cycle. From these results, it was suggested that the remarkable decrease in overdischarge resistance was due to the oxidative deterioration of the hydrogen storage alloy.

  On the other hand, the batteries of Examples 1 to 4 subjected to the negative electrode formation step showed favorable values for the number of cycles up to 60% capacity as compared with the battery of Comparative Example 1. In these batteries, even if negative electrode reversal occurs due to overdischarge, since the consumption reaction of the discharge reserve formed on the negative electrode occurs preferentially over the oxygen generation reaction, decomposition of the electrolyte generated in the negative electrode is suppressed. . Furthermore, since the generation of oxygen is suppressed, the oxidative deterioration of the hydrogen storage alloy is also suppressed. As a result, it is considered that the batteries of Examples 1 to 4 were able to suppress a decrease in discharge capacity even after repeated many charging / discharging including overdischarge. That is, it is considered that both overdischarge resistance and cycle life characteristics have been improved.

The number of cycles up to 60% capacity of the batteries of Examples 3 and 4 in which hydrogen was occluded in the hydrogen storage alloy up to the plateau region ((α + β) phase region) of the pressure-composition isotherm in the negative electrode formation step was It was somewhat lower than that of the 1 and 2 batteries. This result is estimated to be caused by the following causes.
Generally, the sealed nickel-metal hydride storage battery is designed such that the negative electrode capacity is somewhat larger than the positive electrode capacity (positive electrode capacity regulation). Specifically, the negative electrode capacity is designed to be about 1.2 to 2.0 times the positive electrode capacity so as to satisfy the required specifications required of the battery.
When the charged capacity is equal to or greater than the positive electrode capacity, that is, when the battery is charged to the overcharge region, oxygen gas is generated from the positive electrode. At this time, the pressure inside the battery increases as the overcharge depth increases. When the pressure inside the battery exceeds a predetermined value, a safety valve provided in the battery is activated, and oxygen gas and electrolyte leak out of the battery. As a result, the internal resistance increases, and the battery life may be reached. In order to suppress such a decrease in battery life, it is extremely important to provide an appropriate amount of charge reserve in the sealed nickel-metal hydride storage battery.

  In the hydrogen storage alloy included in the batteries of Examples 3 and 4, hydrogen was stored up to the (α + β) phase region of the pressure-composition isotherm in the negative electrode formation step. That is, the negative electrodes of the batteries of Examples 3 to 4 have a discharge reserve somewhat excessively. In the present embodiment, as described above, since the charging is performed by the -ΔV method, the charging amount is equal to or higher than the theoretical capacity. In this case, the amount of charge reserve required during overcharging is relatively reduced. When the amount of charge reserve is insufficient, the generated oxygen gas is not sufficiently absorbed by the charge reserve during overcharge, the battery internal pressure rises significantly, and the safety valve provided in the battery operates. As a result, oxygen gas and electrolyte leak out of the battery, increasing the internal resistance. For this reason, in the batteries of Examples 3 to 4, it is considered that the number of cycles up to 60% capacity is somewhat reduced.

  Therefore, in the negative electrode formation step, hydrogen can be stored in the hydrogen storage alloy so that the ratio H / M is 0.2 or less so as to enter the α-phase formation region of the pressure-composition isotherm. preferable.

The batteries of Examples 1 and 3 in which the battery case was sealed in the air generated some heat. This heat generation is considered to be caused by a reaction between a hydrogen storage alloy (metal hydride) storing hydrogen and oxygen in the air.
Conventionally, in order to improve the chemical reactivity of the negative electrode, the surface of the hydrogen storage alloy is often treated with a high-temperature acid or alkali before producing the negative electrode. When the hydrogen storage alloy is subjected to the above-described treatment, if the battery case is sealed in a normal pressure air environment, the hydrogen storage alloy and oxygen gas may react to generate heat. For these reasons, in order to prevent heat generation of the battery when a process trouble occurs after being subjected to the hydrogen storage process, the time during which the battery is retained, the economics of the atmospheric gas used, and the predetermined characteristics are obtained. Therefore, it is preferable to select an environment in which the step of sealing the battery case is performed by sufficiently considering the reactivity of the negative electrode active material after the treatment to be performed. For example, the step of sealing the battery case is preferably performed in an atmosphere made of an inert gas.

  According to the production method of the present invention, a nickel metal hydride storage battery having improved overdischarge resistance can be provided. Such a nickel metal hydride storage battery can be suitably used as a power source for an electric tool, an assist bicycle, a cordless vacuum cleaner, or the like.

1 is a longitudinal sectional view schematically showing a nickel metal hydride storage battery according to an embodiment of the present invention. The pressure-composition isotherm at 20 degreeC of a predetermined hydrogen storage alloy is shown. It is the perspective view which notched some nickel hydride storage batteries which concern on another embodiment of this invention. 4 is a graph showing the overdischarge resistance of nickel-metal hydride batteries produced in Examples 1 and 3 and Comparative Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cylindrical battery 11, 31 Positive electrode 12, 32 Negative electrode 13, 33 Separator 14 Electrode group 15, 34 Battery case 16 Positive electrode current collecting plate 17 Negative electrode current collecting plate 18, 36 Positive electrode lead plate 19 External terminal 20 Rubber valve body 21, 35 Sealing body 22 Gasket 30 Square battery 37 Insulating plate 38 Insulating material 39 Negative electrode terminal 40 Insulator 41 Safety valve

Claims (7)

A method for producing a nickel metal hydride storage battery,
Before sealing a battery case containing an electrode group including a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween, and an electrolyte, The manufacturing method of the nickel hydride storage battery including the process of occluding hydrogen. (A) a step of winding a laminate including a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween to obtain a wound electrode group;
(B) A step of accommodating the wound electrode group in a cylindrical battery case,
(C) adding an electrolyte into the cylindrical battery case;
(D) supplying hydrogen gas into the cylindrical battery case containing the wound battery group and occluding hydrogen in the negative electrode; and (E) sealing the cylindrical battery case to form a cylinder The manufacturing method of the nickel hydride storage battery of Claim 1 including the process of obtaining a type nickel hydride storage battery. (A) stacking a positive electrode including a positive electrode active material, a negative electrode including a hydrogen storage alloy as a negative electrode active material, and a separator disposed therebetween to obtain a stacked electrode group;
(B) housing the stacked electrode group in a rectangular battery case, and closing the opening of the rectangular battery case with a sealing body having a liquid injection hole;
(C) a step of injecting an electrolyte into the prismatic battery case from the injection hole,
(D) supplying hydrogen gas into the prismatic battery case containing the stacked battery group, and occluding hydrogen in the negative electrode; and (e) closing the liquid injection hole, thereby The manufacturing method of the nickel hydride storage battery of Claim 1 including the process of sealing a battery case and obtaining a square-shaped nickel hydride storage battery.   The step of occluding hydrogen in the negative electrode includes the step of occluding hydrogen in the hydrogen storage alloy included in the negative electrode so that an atomic ratio of hydrogen to the hydrogen storage alloy is 0.2 or less. The manufacturing method of the nickel hydride storage battery in any one of -3.   The method for producing a nickel-metal hydride storage battery according to claim 1, wherein the step of occluding hydrogen in the negative electrode includes a step of decompressing the inside of the battery case before supplying hydrogen gas to the battery case. .   The step of sealing the battery case is performed in an atmosphere containing at least one inert gas selected from the group consisting of nitrogen, argon, and helium, or in air. Method for producing a nickel-metal hydride storage battery. The positive electrode active material includes core particles and a cobalt compound supported on the surface of the core particles,
The core particles include nickel hydroxide as a main component,
The said cobalt compound is a manufacturing method of the nickel hydride storage battery in any one of Claims 1-6 containing at least 1 sort (s) selected from the group which consists of cobalt hydroxide, a cobalt oxide, and a cobalt oxyhydroxide.

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