WO2017169163A1 - Negative electrode for alkali secondary cell and alkali secondary cell including negative electrode - Google Patents

Abstract

A nickel hydrogen secondary cell 2 is provided with a separator 28, and an electrode group 22 comprising a positive electrode 24 and a negative electrode 26. The negative electrode 26 comprises a negative electrode core and a negative electrode mixture held on the negative electrode core. The negative electrode mixture contains a negative electrode additive powder and a hydrogen occluding alloy powder comprising particles of a hydrogen occluding alloy. The negative electrode additive is ytterbium fluoride.

Description

Negative electrode for alkaline secondary battery and alkaline secondary battery including the negative electrode

The present invention relates to a negative electrode for an alkaline secondary battery and an alkaline secondary battery including the negative electrode.

Nickel metal hydride secondary batteries are known as a kind of alkaline secondary batteries. This nickel metal hydride secondary battery is used in various portable devices and various devices such as hybrid electric vehicles because it has a higher capacity and better environmental safety than nickel cadmium secondary batteries. The use is expanding. Thus, since the use is expanding, higher performance is desired for the nickel-hydrogen secondary battery.

One of the performances required for nickel metal hydride secondary batteries to be enhanced is cycle life characteristics. That is, improvement in cycle life characteristics is required so that the number of times that the battery can be repeatedly charged and discharged can be increased as much as possible. Therefore, many studies have been made to improve the cycle life characteristics of nickel metal hydride secondary batteries. Examples of research for improving the cycle life characteristics of nickel metal hydride secondary batteries include the following.

Since a normal nickel metal hydride secondary battery is designed to have a negative electrode capacity larger than the positive electrode capacity, oxygen gas generated from the positive electrode during overcharge is absorbed and consumed by the negative electrode. However, if the gas absorption performance at the negative electrode is low, the internal pressure of the battery is likely to increase, and the safety valve of the battery is activated accordingly, and the electrolyte is discharged to the outside. As a result, the electrolyte in the battery is depleted and the cycle life of the battery is hindered. For this reason, studies have been made to improve the gas absorption performance of the negative electrode as one method for improving the cycle life of the battery. As another study, in a hydrogen storage alloy containing Al, by controlling the weight ratio of Al in the surface layer, the conductivity of the negative electrode is prevented from decreasing, and even when charging and discharging are repeated. Studies have been made to improve the cycle life characteristics of nickel-metal hydride secondary batteries by preventing a decrease in discharge capacity accompanying a decrease in voltage (see, for example, Patent Document 1).

JP 2007-123228 A

By the way, in the various devices as described above, the usage conditions have become more severe as the application has been expanded. For this reason, nickel metal hydride secondary batteries mounted on these devices may be used even in a low temperature environment such as 0 ° C. to −30 ° C., for example. However, the conventional nickel metal hydride secondary battery has a problem that the discharge capacity under the low temperature environment as described above is significantly lower than the discharge capacity under the room temperature environment of about 25 ° C. The main cause of this problem is that the activity of the surface of the hydrogen storage alloy is remarkably lowered under a low temperature environment, and the reactivity of the negative electrode is greatly lowered.

Such a decrease in the activity on the surface of the hydrogen storage alloy in a low-temperature environment occurs in the same way even in a battery with improved cycle life characteristics as described above. It is difficult to achieve both improvement in characteristics and low-temperature discharge characteristics. That is, at present, a battery in which both improvement in cycle life characteristics and improvement in low-temperature discharge characteristics are sufficiently achieved has not yet been developed.

Therefore, since the applications are expanding as described above, it is desired to develop a high-performance nickel metal hydride secondary battery that can be repeatedly used even under more severe use conditions.

The present invention has been made based on the above circumstances, and its object is to provide a negative electrode for an alkaline secondary battery capable of achieving both improvement in cycle life characteristics and improvement in low-temperature discharge characteristics, and the present invention. An object of the present invention is to provide an alkaline secondary battery including a negative electrode.

According to the present invention, a negative electrode core body and a negative electrode mixture held on the negative electrode core body are provided, and the negative electrode mixture is composed of a hydrogen storage alloy powder composed of hydrogen storage alloy particles and a negative electrode additive. There is provided a negative electrode for an alkaline secondary battery, comprising powder, wherein the negative electrode additive is ytterbium fluoride.

The negative electrode additive powder made of ytterbium fluoride is preferably added in an amount of 0.10 parts by mass or more and 1.00 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy powder.

The hydrogen storage alloy has the general formula: Ln _1-x Mg _x Ni _ya-b Al _a M _b (where Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy Represents at least one element selected from Ho, Er, Tm, Yb, Lu, Sc, Y, Ti and Zr, and M represents V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, It represents at least one element selected from Zn, Sn, In, Cu, Si, P and B, and the subscripts a, b, x and y are 0.05 ≦ a ≦ 0.30 and 0 ≦ b ≦, respectively. 0.50, 0.05 ≦ x ≦ 0.30, and the relationship represented by 2.8 ≦ y ≦ 3.9 is satisfied).

Further, according to the present invention, a container and an electrode group accommodated together with an alkaline electrolyte in the container, the electrode group is composed of a positive electrode and a negative electrode that are overlapped via a separator, and the negative electrode is An alkaline secondary battery, which is a negative electrode for an alkaline secondary battery having any one of the above-described configurations, is provided.

The negative electrode for an alkaline secondary battery of the present invention contains a negative electrode additive powder in a negative electrode mixture, and the negative electrode additive is ytterbium fluoride. With this configuration, the gas absorption performance as a whole of the negative electrode is improved, and the activity of the surface of the hydrogen storage alloy is increased. For this reason, the alkaline secondary battery including the negative electrode of the present invention can achieve both improvement in cycle life characteristics and improvement in low-temperature discharge characteristics.

It is the perspective view which fractured | ruptured and showed the nickel-hydrogen secondary battery which concerns on one Embodiment of this invention.

Hereinafter, a nickel metal hydride secondary battery (hereinafter simply referred to as a battery) 2 according to the present invention will be described with reference to the drawings.

The battery 2 to which the present invention is applied is not particularly limited. For example, a case where the present invention is applied to an AA-sized cylindrical battery 2 shown in FIG. 1 will be described as an example.

As shown in FIG. 1, the battery 2 includes an outer can 10 having a bottomed cylindrical shape with an open top. The outer can 10 has conductivity, and its bottom wall 35 functions as a negative electrode terminal. A sealing body 11 is fixed to the opening of the outer can 10. The sealing body 11 includes a cover plate 14 and a positive electrode terminal 20, and seals the outer can 10 and provides the positive electrode terminal 20. The cover plate 14 is a disk-shaped member having conductivity. A cover plate 14 and a ring-shaped insulating packing 12 surrounding the cover plate 14 are disposed in the opening of the outer can 10, and the insulating packing 12 is formed by caulking the opening edge 37 of the outer can 10. It is fixed to the opening edge 37. That is, the lid plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the outer can 10.

Here, the lid plate 14 has a central through hole 16 in the center, and a rubber valve body 18 for closing the central through hole 16 is disposed on the outer surface of the lid plate 14. Further, a metal positive electrode terminal 20 having a flanged cylindrical shape is electrically connected to the outer surface of the cover plate 14 so as to cover the valve element 18. The positive terminal 20 presses the valve body 18 toward the lid plate 14. The positive electrode terminal 20 has a gas vent hole (not shown).

Normally, the central through hole 16 is airtightly closed by the valve body 18. On the other hand, when gas is generated in the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure, and the central through hole 16 is opened. As a result, the central through hole 16 and the positive electrode terminal 20 are opened from the outer can 10. Gas is released to the outside through a gas vent hole (not shown). That is, the central through hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

The outer can 10 accommodates an electrode group 22. Each of the electrode groups 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28, which are wound in a spiral shape with the separator 28 sandwiched between the positive electrode 24 and the negative electrode 26. That is, the positive electrode 24 and the negative electrode 26 are overlapped with each other via the separator 28. The outermost periphery of the electrode group 22 is formed by a part of the negative electrode 26 (the outermost periphery) and is in contact with the inner peripheral wall of the outer can 10. That is, the negative electrode 26 and the outer can 10 are electrically connected to each other.

In the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the cover plate 14. Specifically, the positive electrode lead 30 has one end connected to the positive electrode 24 and the other end connected to the lid plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. A circular upper insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the upper insulating member 32. A circular lower insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

Furthermore, a predetermined amount of alkaline electrolyte (not shown) is injected into the outer can 10. The alkaline electrolyte is impregnated in the electrode group 22 to advance an electrochemical reaction (charge / discharge reaction) during charge / discharge between the positive electrode 24 and the negative electrode 26. As the alkaline electrolyte, an alkaline electrolyte containing at least one of KOH, NaOH, and LiOH as a solute is preferably used.

As the material of the separator 28, for example, a polyamide fiber nonwoven fabric, or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene provided with a hydrophilic functional group can be used.

The positive electrode 24 is composed of a conductive positive electrode base material having a porous structure and a positive electrode mixture held in the pores of the positive electrode base material.

As such a positive electrode base material, for example, a sheet of nickel foam (nickel foam) can be used.

The positive electrode mixture includes positive electrode active material particles and a binder. Moreover, a positive electrode additive is added to the positive electrode mixture as necessary.

The above-described binder serves to bind the positive electrode active material particles to each other and to bind the positive electrode active material particles to the positive electrode base material. Here, as the binder, for example, carboxymethylcellulose, methylcellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropylcellulose) dispersion, and the like can be used.

Moreover, examples of the positive electrode additive include zinc oxide and cobalt hydroxide.

As the positive electrode active material particles, nickel hydroxide particles generally used for nickel metal hydride secondary batteries are used. As the nickel hydroxide particles, it is preferable to employ nickel hydroxide particles having higher order.

Further, it is preferable to use the nickel hydroxide particles in which Co is dissolved. Co as this solid solution component contributes to the improvement of conductivity between the positive electrode active material particles, and improves the charge acceptance. Here, if the content of Co dissolved in the nickel hydroxide particles is small, the effect of improving the charge acceptability is small, and conversely if too large, the grain growth of the nickel hydroxide particles is inhibited. . For this reason, it is preferable to use the thing of the aspect which contains 0.5 mass% or more and 5.0 mass% or less of Co as a solid solution component as nickel hydroxide particle.

In addition, it is preferable to further dissolve Zn in the above-described nickel hydroxide particles. Here, Zn suppresses the expansion of the positive electrode accompanying the progress of the charge / discharge cycle, and contributes to the improvement of the cycle life characteristics of the battery.

The content of Zn dissolved in the nickel hydroxide particles is preferably 2.0% by mass or more and 5.0% by mass or less with respect to nickel hydroxide.

Moreover, it is preferable that the nickel hydroxide particles described above are covered with a surface layer made of a cobalt compound. As the surface layer, it is preferable to employ a higher-order cobalt compound layer made of a cobalt compound higher-ordered to be trivalent or higher.

The above-described higher cobalt compound layer is excellent in conductivity and forms a conductive network. As this higher-order cobalt compound layer, it is preferable to employ a layer made of a cobalt compound such as cobalt oxyhydroxide (CoOOH) higher-ordered to three or more valences.

The positive electrode active material particles as described above are manufactured by a manufacturing method generally used for nickel metal hydride secondary batteries.

Next, the positive electrode 24 can be manufactured, for example, as follows.
First, a positive electrode mixture slurry containing positive electrode active material particles, water, and a binder is prepared. The prepared positive electrode mixture slurry is filled in, for example, a foamed nickel sheet and dried. After drying, the foamed nickel sheet filled with nickel hydroxide particles and the like is rolled and then cut to produce the positive electrode 24.

Next, the negative electrode 26 will be described.
The negative electrode 26 has a conductive negative electrode core having a strip shape, and a negative electrode mixture is held in the negative electrode core.

The negative electrode core is made of a sheet-like metal material in which through holes are distributed. For example, a punching metal sheet can be used. The negative electrode mixture is not only filled in the through hole of the negative electrode core, but also held in layers on both surfaces of the negative electrode core.

The negative electrode mixture includes hydrogen storage alloy particles capable of occluding and releasing hydrogen as a negative electrode active material, a conductive agent, a binder, and a negative electrode additive. Moreover, you may add a negative electrode auxiliary additive to a negative electrode mixture as needed.

The above-described binder serves to bind the hydrogen storage alloy particles, the conductive agent, etc. to each other and at the same time bind the hydrogen storage alloy particles, the conductive agent, etc. to the negative electrode core. Here, the binder is not particularly limited, and for example, a binder generally used for nickel hydride secondary batteries such as a hydrophilic or hydrophobic polymer, carboxymethyl cellulose, or the like is used. be able to.

Also, as the negative electrode auxiliary additive, styrene butadiene rubber, sodium polyacrylate, or the like can be used.

The hydrogen storage alloy in the hydrogen storage alloy particles is not particularly limited, and a hydrogen storage alloy generally used for nickel hydrogen secondary batteries can be employed. Here, as a preferable hydrogen storage alloy, a rare earth-Mg—Ni-based hydrogen storage alloy containing rare earth elements, Mg and Ni is used. As this rare earth-Mg—Ni-based hydrogen storage alloy, it is preferable to use an alloy having a composition represented by the following general formula (I).
Ln _1-x Mg _x Ni _yyab Al _a M _b (I)

However, in the general formula (I), Ln is selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ti, and Zr. Represents at least one element selected, and M is at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B The subscripts a, b, x, and y are 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 0.05 ≦ x ≦ 0.30, and 2.8 ≦ y, respectively. The relationship shown by ≦ 3.9 is satisfied.

Here, in the hydrogen storage alloy according to the present invention, when Ln and Mg in the general formula (I) are A components and Ni and Al are B components, AB ₂ type subunits and AB ₅ type subunits are laminated. A so-called superlattice structure having an A ₂ B ₇ type structure or an A ₅ B ₁₉ type structure is formed. Hydrogen hydrogen storage alloy of a rare earth -Mg-Ni system which forms such a superlattice structure, and advantages of occluding and releasing hydrogen, which is a feature of the AB ₅ type alloy is stable, which is characteristic of AB ₂ type alloy It has the advantage of having a large amount of occlusion. For this reason, since the hydrogen storage alloy which concerns on general formula (I) is excellent in hydrogen storage capacity, it contributes to the capacity increase of the battery 2 obtained. In addition, the hydrogen storage alloy having a so-called superlattice structure as represented by the general formula (I) is not easily broken and pulverized even if the battery is charged and discharged, that is, the hydrogen is stored and released repeatedly. Contributes to improved life characteristics.

The particles of the hydrogen storage alloy are obtained, for example, as follows.
First, metal raw materials are weighed and mixed so as to have a predetermined composition, and this mixture is melted in, for example, an induction melting furnace to form an ingot. The obtained ingot is subjected to heat treatment by heating in an inert gas atmosphere at 900 to 1200 ° C. for 5 to 24 hours. Thereafter, the ingot is pulverized and sieved to obtain hydrogen storage alloy particles having a desired particle diameter.

Here, the particle size of the hydrogen storage alloy particles is not particularly limited, but those having an average particle size of 55.0 to 70.0 μm are preferably used. In the present specification, the average particle diameter means an average particle diameter corresponding to 50% of integration based on a mass standard obtained by a laser diffraction / scattering method using a particle size distribution measuring apparatus.

As the conductive agent, a conductive agent generally used for a negative electrode of a nickel metal hydride secondary battery is used. For example, carbon black or the like is used.

Next, ytterbium fluoride is used as the negative electrode additive. Rare earth element fluorides are believed to protect the surface of the hydrogen storage alloy and inhibit corrosion. For this reason, it is considered that the cycle life characteristics of the battery are improved by adding ytterbium fluoride which is a rare earth element fluoride. Here, ytterbium fluoride increases the activity of the hydrogen storage alloy compared to lanthanum fluoride and cerium fluoride, and thus contributes to the improvement of the low-temperature discharge characteristics of the battery. In addition, ytterbium fluoride has better gas absorption performance than lanthanum fluoride and cerium fluoride, contributes to improvement of the gas absorption performance of the negative electrode, and further contributes to improvement of the cycle life characteristics of the battery.

The negative electrode additive powder made of ytterbium fluoride is added in an amount of 0.10 parts by mass or more and 1.00 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy powder made of the hydrogen storage alloy particles described above. preferable. When the amount of the negative electrode additive powder composed of ytterbium fluoride is less than 0.10 parts by mass, the effect of improving the cycle life characteristics and low-temperature discharge characteristics of the battery as described above decreases. On the other hand, when the amount of the negative electrode additive powder composed of ytterbium fluoride exceeds 1.00 parts by mass, the surface of the hydrogen storage alloy is excessively covered, and the discharge characteristics deteriorate. Therefore, the amount of the negative electrode additive powder made of ytterbium fluoride is 0.10 parts by mass or more and 1.00 parts by mass with respect to 100 parts by mass of the hydrogen storage alloy powder made of hydrogen storage alloy particles as described above. The following is preferable.

The negative electrode 26 can be manufactured as follows, for example.
First, a hydrogen storage alloy powder composed of the above hydrogen storage alloy particles, a negative electrode additive powder composed of ytterbium fluoride, a conductive agent, a binder, and water were prepared, and these were kneaded. A negative electrode mixture paste is prepared. The obtained negative electrode mixture paste is applied to the negative electrode core and dried. After drying, the negative electrode core to which the hydrogen storage alloy particles and the like are attached is rolled to increase the filling density of the hydrogen storage alloy, and then cut into a predetermined shape, whereby the negative electrode 26 is manufactured.

The positive electrode 24 and the negative electrode 26 manufactured as described above are spirally wound with the separator 28 interposed therebetween, whereby the electrode group 22 is formed.

The electrode group 22 thus obtained is accommodated in the outer can 10. Subsequently, a predetermined amount of alkaline electrolyte is injected into the outer can 10. Thereafter, the outer can 10 containing the electrode group 22 and the alkaline electrolyte is sealed by the sealing body 11 provided with the positive electrode terminal 20, and the battery 2 according to the present invention is obtained. The obtained battery 2 is subjected to an initial activation process and is in a usable state.

[Example]
1. Production of battery (Example 1)

(1) Preparation of positive electrode Nickel sulfate, zinc sulfate, and cobalt sulfate were weighed so that Zn might be 2.5% by mass and Co might be 1.0% by mass with respect to Ni. In addition to the aqueous sodium hydroxide solution, a mixed aqueous solution was prepared. While stirring the resulting mixed aqueous solution, a 10N sodium hydroxide aqueous solution was gradually added to the mixed aqueous solution to cause a reaction. The pH during the reaction was stabilized at 13 to 14, and nickel hydroxide was mainly used. Then, base particles composed of nickel hydroxide particles in which Zn and Co were dissolved were produced.

The obtained base particles were washed three times with 10 times the amount of pure water, and then dehydrated and dried. In addition, as a result of measuring the particle size of the obtained base particles using a laser diffraction / scattering type particle size distribution analyzer, the average particle size corresponding to 50% of the integration of the base particles based on the mass standard was 8 μm. .

Next, the obtained base particles are put into a cobalt sulfate aqueous solution, and while stirring this cobalt sulfate aqueous solution, a 1 mol / l sodium hydroxide aqueous solution is gradually dropped and reacted, and the pH during the reaction here A precipitate was formed while maintaining Next, the produced precipitate was separated by filtration, washed with pure water, and then vacuum-dried. As a result, intermediate product particles having a base particle 38 as a nucleus and a 5 mass% cobalt hydroxide layer on the surface of the nucleus were obtained. The thickness of the cobalt hydroxide layer was about 0.1 μm.

Then, the intermediate product particles were put into a 25% by mass sodium hydroxide aqueous solution. Here, when the mass of the powder composed of the intermediate product particles is P and the mass of the aqueous sodium hydroxide solution is Q, the mass ratio is set to P: Q = 1: 10. And the heat processing which hold | maintains the temperature for 8 hours with a constant temperature at 85 degreeC is stirred, stirring the sodium hydroxide aqueous solution to which this intermediate product particle powder was added.

The powder consisting of the intermediate product particles subjected to the above heat treatment was washed with pure water and dried by applying hot air of 65 ° C. As a result, a positive electrode active material powder made of positive electrode active material particles having a surface layer made of cobalt oxide on the surface of base particles made of nickel hydroxide particles in which Zn and Co were dissolved was obtained.

Next, 95 parts by mass of the positive electrode active material powder made of nickel hydroxide particles produced as described above, 3.0 parts by mass of zinc oxide powder, 2.0 parts by mass of cobalt hydroxide powder, and binder A positive electrode mixture slurry was prepared by adding and kneading 50.0 parts by mass of water containing 0.2% by mass of hydroxypropylcellulose powder.

Subsequently, this positive electrode mixture slurry was filled into a sheet-like nickel foam (nickel foam) as a positive electrode base material. Here, a nickel foam having a surface density (weight per unit area) of about 600 g / m ² , a porosity of 95% and a thickness of about 2 mm was used.

After drying the nickel foam filled with the slurry of the positive electrode mixture, the nickel foam filled with the positive electrode mixture has a filling density of the positive electrode active material calculated by the following formula (II) of 3.2 g / cm. After adjusting and rolling to ³ and cutting to a predetermined dimension, an AA size positive electrode 24 made of a non-sintered nickel electrode was obtained.

Packing density [g / cm ³ ] of positive electrode active material = positive electrode mixture mass [g] ÷ (electrode height [cm] × electrode length [cm] × electrode thickness [cm] −nickel foam mass [g] ÷ Specific gravity of nickel [g / cm ³ ]) (II)

(2) Preparation of negative electrode After mixing each metal material of La, Sm, Mg, Ni, and Al so as to have a predetermined molar ratio, the mixture is introduced into an induction melting furnace and melted, and this is cooled to produce an ingot. did.

Next, the ingot was subjected to heat treatment for 10 hours in an argon gas atmosphere at a temperature of 1000 ° C., homogenized, and then mechanically pulverized in an argon gas atmosphere to obtain a rare earth-Mg—Ni-based hydrogen occlusion. An alloy powder was obtained. The obtained rare earth-Mg—Ni-based hydrogen storage alloy powder was measured for particle size distribution using a laser diffraction / scattering type particle size distribution measuring device (device name: SRA-150 manufactured by Microtrac). As a result, the average particle diameter corresponding to 50% integration on a mass basis was 65 μm.

When the composition of this hydrogen storage alloy powder was analyzed by high frequency plasma spectroscopy (ICP), the composition was La _0.30 Sm _0.70 Mg _0.10 Ni _3.33 Al _0.17 . Further, when X-ray diffraction measurement (XRD measurement) was performed on the hydrogen storage alloy powder, the crystal structure was a so-called super lattice structure Ce ₂ Ni ₇ type (A ₂ B ₇ type).

100 parts by mass of ytterbium fluoride powder, 0.50 parts by mass of Ketjen Black (registered trademark) powder, 1.0 part by mass of styrene butadiene rubber powder with respect to 100 parts by mass of the obtained hydrogen storage alloy powder Then, 0.25 part by mass of sodium polyacrylate powder, 0.05 part by mass of carboxymethylcellulose powder and 20 parts by mass of water were added and kneaded in an environment at 25 ° C. to prepare a negative electrode mixture paste.

The negative electrode mixture paste was applied to both sides of a punching metal sheet as a negative electrode substrate so that the thickness was uniform and constant. The negative electrode mixture paste is also filled in the through holes. The punching metal sheet is an iron strip having a large number of through holes, has a thickness of 60 μm, and has a nickel plating on the surface.

After the drying of the negative electrode mixture paste, the punching metal sheet holding the negative electrode mixture has a hydrogen storage alloy filling density (hereinafter referred to as hydrogen storage alloy filling density) calculated by the following formula (III) of 6.2 g / After adjusting and rolling so that it might become cm < ³ >, it cut | disconnected to the predetermined dimension and obtained the negative electrode 26 for AA size.

Hydrogen storage alloy filling density [g / cm ³ ] = hydrogen storage alloy mass [g] ÷ (electrode height [cm] × electrode length [cm] × electrode thickness [cm] −punching metal sheet mass [g] / Iron specific gravity [g / cm ³ ]) ... (III)

(3) Assembly of Nickel Metal Hydride Battery The obtained positive electrode 24 and negative electrode 26 were spirally wound with a separator 28 sandwiched between them, and an electrode group 22 was produced. The separator 28 used for the production of the electrode group 22 here was made of a nonwoven fabric made of polypropylene fiber subjected to sulfonation treatment, and its thickness was 0.1 mm (weight per unit area 40 g / m ² ).

Meanwhile, an alkaline electrolyte composed of an aqueous solution containing KOH, NaOH and LiOH as solutes was prepared. This alkaline electrolyte has a mass mixing ratio of KOH, NaOH and LiOH of KOH: NaOH: LiOH = 15: 2: 1 and a specific gravity of 1.30.

Next, the above-described electrode group 22 was accommodated in the bottomed cylindrical outer can 10 and 2.4 g of the prepared alkaline electrolyte was injected. Thereafter, the opening of the outer can 10 was closed with the sealing body 11, and the AA size nickel-hydrogen secondary battery 2 having a nominal capacity of 1500 mAh was assembled.

(4) Initial activation treatment The obtained battery 2 was charged at 1.0 It for 16 hours in an environment at a temperature of 25 ° C., and then the battery voltage became 1.0 V at 1.0 It. The charging / discharging cycle which makes the charging / discharging operation | work to discharge 1 cycle was repeated 3 times. Thus, the initial activation process was performed, and the battery 2 was made usable.

(Example 2)
A nickel-hydrogen secondary battery was fabricated in the same manner as in Example 1 except that the amount of ytterbium fluoride powder added was 0.50 parts by mass.

(Example 3)
A nickel-hydrogen secondary battery was fabricated in the same manner as in Example 1 except that the amount of ytterbium fluoride powder added was 1.00 parts by mass.

(Comparative Example 1)
A nickel-hydrogen secondary battery was fabricated in the same manner as in Example 1 except that the ytterbium fluoride powder was not added.

(Comparative Example 2)
Instead of adding ytterbium fluoride powder, lanthanum fluoride powder was added instead, and the addition amount of this lanthanum fluoride powder was 0.50 parts by mass. A nickel-hydrogen secondary battery was produced.

(Comparative Example 3)
Instead of adding ytterbium fluoride powder, instead of adding cerium fluoride powder, the addition amount of this cerium fluoride powder was 0.50 parts by mass. A nickel-hydrogen secondary battery was produced.

2. Evaluation of nickel metal hydride secondary battery (1) Cycle life characteristics test The batteries of Examples 1 to 3 and Comparative Examples 1 to 3 that had been subjected to initial activation treatment were tested at 1.0 It in a 25 ° C environment at 1.0 It. After the voltage reached the maximum value, it was charged until it decreased by 10 mV, and then left for 30 minutes. Next, the battery after being left for 30 minutes was discharged at 1.0 It under the same environment until the voltage of the battery became 1.0 V, and then left for 30 minutes.

Charging / discharging was repeated with the above-described charging / discharging cycle as one cycle, and the discharge capacity in each cycle was measured. Here, the discharge capacity at the charge and discharge in the first cycle was set as the initial capacity, and the capacity maintenance rate in each cycle was calculated from the following formula (IV).
Capacity maintenance rate (%) = (discharge capacity / initial capacity in each cycle) × 100 (IV)

Then, the number of cycles until the capacity maintenance ratio reached 60% for each battery was counted. The number of times was defined as the cycle life. Further, the battery of Comparative Example 1 to which no negative electrode additive was added was used as a reference product, and the ratio of the cycle number of each battery was determined when the cycle number of this reference product was 100. This ratio is shown in Table 1 as the cycle life characteristic ratio. In addition, it has shown that it is excellent in the cycle life characteristic, so that the value of this cycle life characteristic ratio is large.

(2) Low-temperature discharge characteristic test The battery voltage reached the maximum value at 1.0 It in an environment of 25 ° C. for the batteries of Examples 1 to 3 and Comparative Examples 1 to 3 that had been subjected to the initial activation treatment. Thereafter, the battery was charged until it decreased by 10 mV, and then allowed to stand in an environment of −10 ° C. for 3 hours.

Next, the battery after being left for 3 hours was discharged at −10 ° C. in an environment of −10 ° C. until the battery voltage reached 1.0 V, and the discharge capacity at this time was determined.

Here, assuming the discharge capacity value of Comparative Example 1 as 100, the ratio to the discharge capacity value of each battery was determined, and the results are shown in Table 1 as the low-temperature discharge characteristic ratio.

In addition, it has shown that it is excellent in the low temperature discharge characteristic, so that the value of this low temperature discharge characteristic ratio is large.

(3) Discussion (i) In the batteries of Examples 1 to 3 using ytterbium fluoride as the negative electrode additive, the battery of Comparative Example 2 in which lanthanum fluoride was added as the negative electrode additive and cerium fluoride as the negative electrode additive. It can be seen that the low-temperature discharge characteristics are improved as compared with the added battery of Comparative Example 3. Rare earth element fluoride is thought to protect the surface of the hydrogen storage alloy and suppress corrosion. However, when ytterbium fluoride is used as the negative electrode additive, the hydrogen storage alloy has a lower capacity than lanthanum fluoride or cerium fluoride. Since the activity of the surface is increased, the battery using ytterbium fluoride is considered to exhibit excellent low-temperature discharge characteristics.

(Ii) In the batteries of Examples 1 to 3 using ytterbium fluoride as the negative electrode additive, the battery of Comparative Example 2 in which lanthanum fluoride was added as the negative electrode additive and the comparative example in which cerium fluoride was added as the negative electrode additive It can be seen that the cycle life characteristics are improved as compared with the battery No. 3. It is considered that ytterbium fluoride has an effect of improving the gas absorption performance of the negative electrode, and the mass reduction of the electrolyte solution in the battery in the cycle life characteristic test is considered to be suppressed by this ytterbium fluoride.

(Iii) From the above, it can be said that when ytterbium fluoride is added as a negative electrode additive to the negative electrode of a nickel metal hydride secondary battery, it is possible to improve both the cycle life characteristics of the battery and the low temperature discharge characteristics of the battery. . Here, when the amount of ytterbium fluoride added is 0.10 parts by mass or more and 1.00 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy powder, both cycle life characteristics and low-temperature discharge characteristics are improved. Therefore, it can be said that the amount of ytterbium fluoride added is preferably within this range.

Note that the present invention is not limited to the above-described embodiments and examples, and various modifications are possible. The battery to which the present invention is applied may be an alkaline secondary battery, and includes, for example, a nickel zinc secondary battery in addition to the nickel hydrogen secondary battery. Further, the structure of the battery is not particularly limited, and may be a square battery as well as a circular battery.

2 Nickel metal hydride secondary battery 22 Electrode group 24 Positive electrode 26 Negative electrode 28 Separator

Claims (4)

A negative electrode core;
A negative electrode mixture held on the negative electrode core body,
The negative electrode mixture includes a hydrogen storage alloy powder composed of hydrogen storage alloy particles and a negative electrode additive powder,
The negative electrode additive is ytterbium fluoride,
Negative electrode for alkaline secondary battery. 2. The alkali according to claim 1, wherein the negative electrode additive powder made of ytterbium fluoride is added in an amount of 0.10 parts by mass to 1.00 parts by mass with respect to 100 parts by mass of the hydrogen storage alloy powder. Negative electrode for secondary battery. The hydrogen storage alloy has the general formula: Ln _1-x Mg _x Ni _ya-b Al _a M _b (where Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy Represents at least one element selected from Ho, Er, Tm, Yb, Lu, Sc, Y, Ti and Zr, and M represents V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, It represents at least one element selected from Zn, Sn, In, Cu, Si, P and B, and the subscripts a, b, x and y are 0.05 ≦ a ≦ 0.30 and 0 ≦ b ≦, respectively. 0.50, 0.05 ≦ x ≦ 0.30, and the relationship represented by 2.8 ≦ y ≦ 3.9 is satisfied). The negative electrode for alkaline secondary batteries as described. A container, and an electrode group housed together with an alkaline electrolyte in the container,
The electrode group is composed of a positive electrode and a negative electrode superimposed via a separator,
The alkaline secondary battery, wherein the negative electrode is a negative electrode for an alkaline secondary battery according to any one of claims 1 to 3.

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