JP2012074299A - Nickel-hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel-hydrogen secondary battery in which decrease in the operation voltage can be minimized during discharge while enhancing the utilization rate of a positive electrode active material.SOLUTION: The nickel-hydrogen secondary battery comprises a positive electrode 24 and a negative electrode 26. The positive electrode 24 has the positive electrode active material powder of nickel hydroxide particles 36, and a positive electrode additional material 38 distributed into the positive electrode active material powder and containing at least one kind selected from a group of Y, Yb, Er and their compounds. The negative electrode 26 has the powder 44 of a hydrogen storage alloy 44, and a negative electrode additional material 46 distributed into the powder 44 of the hydrogen storage alloy, and containing at least one kind selected from a group of Bi, In and their compounds.

Description

  The present invention relates to a nickel metal hydride secondary battery.

  Nickel metal hydride secondary batteries are used in various applications such as various portable devices and hybrid electric vehicles because they have higher capacity and better environmental safety than nickel cadmium secondary batteries. It has become. As described above, the discovery of various uses has increased the demand for higher capacity of the nickel-hydrogen secondary battery.

  The positive electrode capacity and the negative electrode capacity of the nickel metal hydride secondary battery are determined by the amounts of nickel hydroxide particles contained in the positive electrode plate and hydrogen storage alloy particles contained in the negative electrode plate, respectively. In general, in a secondary battery, when the battery is overcharged, oxygen gas generated in the positive electrode plate is reduced by the negative electrode plate to prevent an increase in the internal pressure of the secondary battery. A large setting has been made. For this reason, the battery capacity of the nickel hydrogen secondary battery is defined by the positive electrode capacity. Here, in order to increase the capacity of the nickel metal hydride secondary battery, it is necessary to increase the amount of nickel hydroxide particles (positive electrode active material) of the positive electrode, but since the internal volume of the battery is constant, the amount of the positive electrode active material There is a limit to increasing Therefore, in order to further increase the capacity of the battery, it is conceivable to increase the utilization rate of the positive electrode active material. The utilization factor of the positive electrode active material is usually determined by how much power charged in the secondary battery by the charging reaction can be discharged. That is, if more discharge can be performed even when the same amount of the positive electrode active material is used, the utilization rate of the positive electrode active material becomes higher, and the secondary battery has a higher capacity.

  Here, as a nickel metal hydride secondary battery in which the utilization rate of the positive electrode active material is increased, for example, a nickel metal hydride secondary battery disclosed in Patent Document 1 is known.

JP-A-10-012238

By the way, in the case of a nickel metal hydride secondary battery, nickel hydroxide Ni (OH) ₂ (discharge product) is oxidized at the positive electrode, and nickel oxyhydroxide (NiOOH) (charge product) is generated. Charging is performed. This nickel oxyhydroxide has a β type (β-NiOOH) and a γ type (γ-NiOOH), and the γ type is produced after the β type is produced, and the unit mass of the positive electrode compared to the β type. It is known to increase the hit capacity. Therefore, it is considered that the nickel metal hydride secondary battery in which the utilization rate of the positive electrode active material is increased is charged to the point where γ-NiOOH is generated.

  However, γ-NiOOH is less dischargeable than β-NiOOH, and may cause a problem that the operating voltage is lowered when the secondary battery is discharged. This defect occurs more remarkably when the discharge rate of the secondary battery is increased, or when the atmosphere temperature of the secondary battery is low during discharge.

  The present invention has been made on the basis of the above circumstances, and the object thereof is to increase the capacity while suppressing a decrease in operating voltage especially when discharging a secondary battery in a low temperature atmosphere. An object of the present invention is to provide a nickel metal hydride secondary battery that can be used.

  In order to achieve the above object, the present inventors have intensively studied means for suppressing a decrease in the operating voltage of the battery accompanying an improvement in the utilization rate of the positive electrode active material of the nickel hydrogen secondary battery. In the course of this study, the inventors have found that the operating voltage of the battery is improved by including at least one of Bi, In, and compounds of these elements in the negative electrode, and have arrived at the present invention. .

  That is, according to one aspect of the present invention, an electrode group is housed in a container together with an alkaline electrolyte in a sealed state, and the electrode group includes a separator, a positive electrode, and a negative electrode. A positive electrode active material powder made of nickel oxide, and a positive electrode additive that is distributed in the positive electrode active material powder and includes at least one selected from the group consisting of Y, Yb, Er, and compounds of these elements. The negative electrode includes a hydrogen storage alloy powder, and a negative electrode additive containing at least one selected from the group consisting of Bi, In, and a compound of each of these elements, distributed in the hydrogen storage alloy powder. A nickel-metal hydride secondary battery is provided (claim 1).

  Preferably, the surface of the positive electrode active material powder is coated with at least one selected from the group consisting of cobalt and a cobalt compound.

  More preferably, the content of the negative electrode additive is in the range of 0.3 to 1.5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy.

Further, the hydrogen storage alloy has the general _formula: having a composition represented by _{Ln 1-x Mg x Ni y} -a-b Al a M b, in the above formula, Ln is, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr and Ti represent at least one element selected from the group consisting of Ti, , Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and at least one element selected from the group consisting of B, subscripts a, b, x and y each represent a number satisfying 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 0.05 ≦ x ≦ 0.30, and 2.8 ≦ y ≦ 3.9. (Claim 4).

Furthermore, it is preferable that the hydrogen storage alloy has a Ce ₂ Ni ₇ type crystal structure.

  In the nickel metal hydride secondary battery according to the present invention, a positive electrode additive containing at least one selected from the group consisting of Y, Yb, Er, and a compound of each of these elements in the positive electrode, and Bi, In, and these elements in the negative electrode And a negative electrode additive containing at least one selected from the group consisting of these compounds. The positive electrode additive contributes to improving the utilization factor of the positive electrode active material, and the negative electrode additive material contributes to the improvement of the operating voltage of the battery while maintaining the effect of improving the utilization factor of the positive electrode active material. A hydrogen secondary battery has a high utilization rate of the positive electrode active material and a high operating voltage of the battery, and its industrial value is extremely high.

It is the perspective view which fractured | ruptured and showed the nickel-hydrogen secondary battery which concerns on one Embodiment of this invention. It is the perspective view which fractured | ruptured partially and showed the nickel-hydrogen secondary battery containing the positive mix which coat | covered the surface of positive electrode active material particle | grains with the electrically conductive agent.

Hereinafter, a nickel metal hydride secondary battery (hereinafter simply referred to as a battery) according to the present invention will be described with reference to the drawings.
The battery to which the present invention is applied is not particularly limited. For example, a case where the present invention is applied to an AA size 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 upper end opened. The bottom wall of the outer can 10 has conductivity and functions as a negative electrode terminal. In the opening of the outer can 10, a conductive disc-shaped cover plate 14 and a ring-shaped insulating packing 12 surrounding the cover plate 14 are arranged, and the insulating packing 12 caulks the opening edge of the outer can 10. By doing so, it is fixed to the opening edge of the outer can 10. 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.

  However, the cover plate 14 has a gas vent hole 16 in the center, and a rubber valve element 18 that closes the gas vent hole 16 is disposed on the outer surface of the cover plate 14. Further, a cylindrical positive terminal 20 with a flange is fixed on the outer surface of the cover plate 14 so as to cover the valve body 18, and the positive terminal 20 presses the valve body 18 toward the cover plate 14. Therefore, the gas vent hole 16 is normally hermetically 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 opens the gas vent hole 16. As a result, the gas vent hole 16 and the positive electrode terminal 20 are opened from the outer can 10. Gas is released via That is, the vent hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

  An electrode group 22 is accommodated in the outer can 10. Each of the electrode groups 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28, and these 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 lid plate 14, and both ends of the positive electrode lead 30 are connected to the inner end of the positive electrode 24 and the lid plate 14, respectively. . Accordingly, the positive electrode terminal 20 and the positive electrode 24 of the cover plate 14 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. A circular 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 provided in the insulating member 32. A circular insulating member 34 is also arranged between the electrode group 22 and the bottom of the outer can 10.

  Further, the outer can 10 is filled with a predetermined amount of an alkaline electrolyte (not shown). The alkaline electrolyte is impregnated in the separator 28, and a charge / discharge reaction between the positive electrode 24 and the negative electrode 26 is performed. To advance. The type of the alkaline electrolyte is not particularly limited, and examples thereof include an aqueous sodium hydroxide solution, an aqueous lithium hydroxide solution, an aqueous potassium hydroxide solution, and an aqueous solution obtained by mixing two or more of these, Further, the concentration of the alkaline electrolyte is not particularly limited, and for example, a concentration of 8N (normality) can be used.

  As a material for 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 substrate having a porous structure and a positive electrode mixture held in the pores of the positive electrode substrate.
As such a positive electrode substrate, for example, a net-like, sponge-like or fibrous metal body plated with nickel can be used.

The positive electrode mixture is schematically shown in a circle Q in FIG. 1, and includes positive electrode active material particles 36 and a positive electrode additive 38. Further, the positive electrode mixture can include a conductive agent 40 and a binder 42 as necessary, and the binder 42 binds the positive electrode active material particles 36, the positive electrode additive 38 and the conductive agent 40 to each other. At the same time, it serves to bind the positive electrode mixture to the positive electrode substrate.
The positive electrode active material particles 36 are nickel hydroxide particles or higher order nickel hydroxide particles. These nickel hydroxide particles may be in the form of a solid solution containing cobalt, zinc, cadmium and the like.

  The positive electrode additive 38 contains at least one selected from the group consisting of Y, Yb, Er, and compounds of these elements. The positive electrode additive 38 is in the form of particles and is distributed between the positive electrode active material particles 36. Here, examples of each compound of Y, Yb, and Er include yttrium oxide, ytterbium oxide, erbium oxide, yttrium carbonate, ytterbium carbonate, erbium carbonate, yttrium fluoride, ytterbium fluoride, and erbium fluoride. The positive electrode additive 38 suppresses the decrease in conductivity of the positive electrode active material and contributes to the improvement of the utilization rate of the positive electrode active material.

As the conductive agent 40, for example, one or more selected from cobalt compounds such as cobalt oxide (CoO) and cobalt hydroxide (Co (OH) ₂ ) and cobalt (Co) can be used. . The conductive agent 40 is added to the positive electrode mixture as necessary.Additionally, the conductive agent 40 is added to the positive electrode mixture in the form of a powder covering the surface of the positive electrode active material 38. It may be included.

  As the binder 42 of the positive electrode mixture, for example, carboxymethylcellulose, methylcellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropylcellulose) dispersion, and the like can be used.

The positive electrode 24 can be manufactured, for example, as follows.
First, a paste containing a positive electrode active material powder composed of nickel hydroxide particles 36, a positive electrode additive 38, water, and, if necessary, a conductive agent 40 and a binder 42 is prepared. The paste is filled, for example, in a sponge-like nickel metal body and dried. After drying, the metal body filled with nickel hydroxide particles and the like is roll-rolled and then cut to produce the positive electrode 24.

The negative electrode 26 has a conductive negative electrode substrate (core body) having a strip shape, and a negative electrode mixture is held on the negative electrode substrate.
The negative electrode substrate is made of a sheet-like metal material in which through holes are distributed. For example, a punched metal sheet or a sintered substrate obtained by molding and sintering metal powder can be used. The negative electrode mixture is not only filled in the through holes of the negative electrode substrate, but also held in layers on both surfaces of the negative electrode substrate.

  Although the negative electrode mixture is schematically shown in a circle R in FIG. 1, hydrogen storage alloy particles 44 capable of occluding and releasing hydrogen as a negative electrode active material, and suppressing a decrease in operating voltage of the battery during discharge And negative electrode additive 46. The negative electrode mixture may further include a conductive additive 47 and a binder 48 as necessary, and the binder 48 simultaneously binds the hydrogen storage alloy particles 44, the negative electrode additive 46, and the conductive additive 47 to each other. It serves to bind the negative electrode mixture to the negative electrode substrate. Here, a hydrophilic or hydrophobic polymer or the like can be used as the binder 48, and carbon black or graphite can be used as the conductive auxiliary agent 47.

The composition of the hydrogen storage alloy in the hydrogen storage alloy particles 44 can be freely selected, but the general formula:
Ln _1-x Mg _x Ni _y-a-b Al _a M _b (I)
It is preferable to use what is represented by these.

  However, in the general formula (I), Ln is derived from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr and Ti. Represents at least one element selected from the group consisting of M, V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B. Represents at least one element selected from the group, and the subscripts a, b, x, and y are 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, and 0.05 ≦ x ≦ 0. 30 represents a number satisfying 2.8 ≦ y ≦ 3.9.

The hydrogen storage alloy represented by the general formula (I) has a crystal structure such as CaCu ₅ type, Pr ₅ Co ₁₉ type, PuNi ₃ type, and Ce ₂ Ni ₇ type depending on the composition. _It preferably has a ₂ Ni ₇ type structure. This is because, when the crystal structure is different, the behavior of the pulverization of the alloy is different. Pr ₅ Co ₁₉ type and PuNi ₃ type are less likely to be pulverized than CaCu ₅ type, and Ce ₂ Ni ₇ type Further, pulverization hardly occurs. This is because when the pulverization occurs, a new surface in which the additive does not exist is generated, and thus the effect of the additive is reduced. However, if the pulverization is difficult to occur, the relative ratio of the area where the additive is present increases.

The hydrogen storage alloy particles 44 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 heat-treated by heating for 5 to 24 hours in an inert gas atmosphere at 900 to 1200 ° C. Thereafter, the ingot is pulverized and classified to a desired particle size by sieving, whereby hydrogen storage alloy particles 44 are obtained.

  The negative electrode additive 46 contains at least one selected from the group consisting of Bi, In, and compounds of these elements. The negative electrode additive 46 is in the form of particles and is distributed between the hydrogen storage alloy particles 44. Here, examples of Bi and In compounds include bismuth oxide, indium oxide, bismuth carbonate, indium carbonate, bismuth fluoride, and indium fluoride.

  As described above, an increase in the amount of charge to the positive electrode causes a negative effect such as a decrease in the operating voltage of the battery. However, such an adverse effect is caused by the negative electrode additive 46 suppressing the decrease in the operating voltage of the battery and increasing the operating voltage. It is solved by making. Here, when the content of the negative electrode additive in the negative electrode mixture is less than 0.3 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy, use at a low temperature (−10 ° C.) when used at room temperature (25 ° C.) Over time, the battery operating voltage is not improved. On the other hand, when the content of the negative electrode additive exceeds 1.5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy, the operating voltage of the battery decreases when used at a low temperature (−10 ° C.). Therefore, in order to exert the effect of improving the operating voltage, it is preferable to set the content of the negative electrode additive in the range of 0.3 to 1.5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy.

The negative electrode 26 can be manufactured, for example, as follows.
First, a paste (for a negative electrode) is prepared by kneading a hydrogen storage alloy powder composed of hydrogen storage alloy particles 44, a negative electrode additive 46, and optionally a conductive additive, a binder 48 and water. The obtained paste is applied to the negative electrode substrate and dried. After drying, the negative electrode substrate to which the hydrogen storage alloy particles 44 and the like are attached is rolled and cut, whereby the negative electrode 26 is produced.

1. Production of Battery Example 1
(1) Preparation of positive electrode While stirring a mixed aqueous solution of nickel sulfate, zinc sulfate and cobalt sulfate so that the amount of zinc is 3% by weight and 1% by weight of cobalt, nickel hydroxide aqueous solution is gradually added to this mixed aqueous solution. During the reaction, the pH was stabilized at 13 to 14 to precipitate nickel hydroxide composite particles.
The obtained composite particles were washed three times with 10 times the amount of pure water, and then dehydrated and dried to produce nickel hydroxide particles as the positive electrode active material 36.

  Next, 100 parts by weight of the prepared nickel hydroxide particles were mixed with 10 parts by weight of cobalt hydroxide (conductive agent 40), 0.5 parts by weight of yttrium oxide (positive electrode additive 38), and 40 parts by weight of HPC (hydroxypropylcellulose ( A positive electrode active material slurry was prepared by mixing the dispersion solution of the binder 42)), and this positive electrode active material slurry was applied to and filled in a foamed nickel sheet as a positive electrode substrate. The foamed nickel sheet to which the nickel hydroxide particles adhered was dried and then rolled and cut to obtain a positive electrode. Here, the positive electrode mixture in the obtained positive electrode has an aspect in which the positive electrode additive 38 and the powdered conductive agent 40 are present between the positive electrode active materials 36 as indicated by a circle Q in FIG. .

(2) Production of hydrogen storage alloy and negative electrode First, a rare earth component containing 60% by weight of lanthanum, 20% by weight of cerium, 5% by weight of praseodymium, and 15% by weight of neodymium was prepared. The obtained rare earth component, nickel, cobalt, manganese and aluminum were weighed to prepare a mixture in which these were in a molar ratio of 1.00: 3.80: 0.70: 0.25: 0.35. The resulting mixture was melted in an induction melting furnace and made into an ingot. Next, this ingot was subjected to a heat treatment for 10 hours in an argon atmosphere at a temperature of 1000 ° C., and the composition was (La _0.60 Ce _0.20 Pr _0.05 Nd _0.15 ) Ni _3.80 Co. An ingot of a hydrogen storage alloy having _0.70 Mn _0.25 Al _0.35 was obtained. Thereafter, the ingot was mechanically pulverized in an inert atmosphere and sieved to select a powder composed of hydrogen storage alloy particles remaining between 400 mesh and 200 mesh. As a result of measuring the particle size distribution of the obtained hydrogen storage alloy powder using a laser diffraction / scattering particle size distribution measuring device, the particles corresponding to 50% by weight of the hydrogen storage alloy powder have an average particle size of 30 μm and a maximum particle size. The diameter was 45 μm.

  With respect to 100 parts by weight of the obtained hydrogen storage alloy powder, 0.4 part by weight of sodium polyacrylate, 0.1 part by weight of carboxymethyl cellulose, 0.3 part by weight of bismuth oxide, and styrene butadiene rubber (SBR) disversion (solid content 50% by weight) 1.0 parts by weight (in terms of solid content), 1.0 part by weight of carbon black, and 30 parts by weight of water were added and kneaded to prepare a slurry.

This slurry was applied to both surfaces of an iron perforated plate as a negative substrate so that the thickness was uniform and constant. This perforated plate has a thickness of 60 μm, and its surface is plated with nickel.
After the slurry was dried, the perforated plate to which the hydrogen storage alloy powder adhered was further rolled and cut to prepare an AA size negative electrode in which the amount of hydrogen storage alloy per negative electrode was 9.0 g.

(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, and its thickness was 0.1 mm (weight per unit area 40 g / m ² ).
The electrode group 22 was housed in a bottomed cylindrical outer can 10 and an alkaline electrolyte composed of a 30 wt% aqueous sodium hydroxide solution containing lithium and potassium was injected. Thereafter, the opening of the outer can 10 was closed with a cover plate 14 or the like, and an AA size sealed nickel-metal hydride secondary battery 2 having a nominal capacity of 2000 mAh was assembled. This nickel metal hydride secondary battery is referred to as battery A.

Example 2
A nickel-hydrogen secondary battery (battery B) similar to battery A of Example 1 was assembled except that the amount of bismuth oxide added to the negative electrode was 0.5 parts by weight.

Example 3
A nickel-hydrogen secondary battery (battery C) similar to battery A of Example 1 was assembled except that the amount of bismuth oxide added to the negative electrode was 1.0 part by weight.

Example 4
A nickel-hydrogen secondary battery (battery D) similar to battery A of Example 1 was assembled except that the amount of bismuth oxide added to the negative electrode was 2.0 parts by weight.

Example 5
A nickel-hydrogen secondary battery (battery G) similar to battery A of Example 1 was assembled except that ytterbium oxide was added to the positive electrode instead of yttrium oxide.

Example 6
A nickel-hydrogen secondary battery (battery H) similar to battery A of Example 1 was assembled except that erbium oxide was added to the positive electrode instead of yttrium oxide.

Example 7
A nickel-hydrogen secondary battery (battery I) similar to battery A of Example 1 was assembled except that indium oxide was added to the negative electrode instead of bismuth oxide.

Example 8
Nickel similar to battery A of Example 1 except that the composition of the hydrogen storage alloy was (La _0.3 Nd _0.3 Sm _0.4 ) _0.85 Mg _0.15 Ni _3.55 Al _0.25 A hydrogen secondary battery (battery K) was assembled.

Example 9
Nickel similar to battery A of Example 1 except that the composition of the hydrogen storage alloy was (La _0.3 Nd _0.3 Sm _0.4 ) _0.85 Mg _0.15 Ni _2.92 Al _0.10 A hydrogen secondary battery (battery L) was assembled.

Example 10
Nickel similar to battery A of Example 1 except that the composition of the hydrogen storage alloy was (La _0.3 Nd _0.3 Sm _0.4 ) _0.85 Mg _0.15 Ni _3.35 Al _0.20 A hydrogen secondary battery (battery M) was assembled.

Example 11
As shown in a circle S in FIG. 2, a nickel-hydrogen secondary battery (battery) similar to the battery A of Example 1 except that the surface of the positive electrode active material 36 in the positive electrode mixture is coated with the conductive agent 50 N) was assembled.

  More specifically, in the preparation of the positive electrode, after nickel hydroxide was precipitated in the mixed aqueous solution, sulfuric acid was added to the mixed aqueous solution in which the nickel hydroxide was precipitated while maintaining the pH during the reaction at 9-10. An aqueous cobalt solution was added. As a result, composite particles having spherical hydroxide particles whose main component is nickel hydroxide as nuclei and cobalt hydroxide precipitated on the surface of the nuclei were obtained. The cobalt hydroxide was precipitated at a ratio of 10% by weight with respect to the spherical hydroxide particles. Next, the composite particles are washed three times with 10 times the amount of pure water, and then dehydrated and dried to obtain a coated nickel hydroxide active material (positive electrode active material 36) having a cobalt coating layer (conductive agent 50). Produced. And here, without adding a powdery conductive agent, 100 parts by weight of the coated nickel hydroxide active material, 0.5 parts by weight of yttrium oxide (positive electrode additive 38) and 40 parts by weight of HPC (binder 42). A nickel metal hydride secondary battery similar to the battery A of Example 1 was produced except that the dispersion liquid was mixed to produce a positive electrode active material slurry.

Example 12
Nickel similar to battery N of Example 11 except that the composition of the hydrogen storage alloy was (La _0.3 Nd _0.3 Sm _0.4 ) _0.85 Mg _0.15 Ni _3.35 Al _0.20 A hydrogen secondary battery (battery P) was assembled.

Comparative Example 1
A nickel-hydrogen secondary battery (battery E) similar to battery A of Example 1 was assembled except that bismuth oxide was not added to the negative electrode.

Comparative Example 2
A nickel-hydrogen secondary battery (battery F) similar to battery A of Example 1 was assembled except that yttrium oxide was not added to the positive electrode.

Comparative Example 3
The composition of the hydrogen storage alloy was (La _0.3 Nd _0.3 Sm _0.4 ) _0.85 Mg _0.15 Ni _3.55 Al _0.25 , and no bismuth oxide was added to the negative electrode. Assembled a nickel-hydrogen secondary battery (battery J) similar to battery A of Example 1.

Comparative Example 4
A nickel-hydrogen secondary battery (battery O) similar to battery N of Example 11 was assembled except that bismuth oxide was not added to the negative electrode.

2. Evaluation method of nickel metal hydride secondary battery and hydrogen storage alloy (1) Initial activation treatment After charging battery A to battery P at a temperature of 25 ° C for 16 hours with a charging current of 0.1C The initial activation treatment for discharging until the battery voltage reached 0.5 V at a discharge current of 0.2 C was repeated twice.

(2) Utilization rate of positive electrode active material The batteries A to P after the initial activation treatment were charged at a current of 1.0 C in an atmosphere at 25 ° C. for 1 hour, and then 0.2% in the same atmosphere. The discharge capacity of the battery was measured when the battery was discharged at a current of C until the battery voltage reached 0.8V. The discharge capacity at this time is taken as the measured discharge capacity. On the other hand, the discharge capacity obtained from the amount of all active materials contained in the positive electrode is defined as the theoretical capacity. And the utilization factor of the positive electrode active material shown by (II) type | formula was calculated | required.

Utilization rate of positive electrode active material = (actually measured capacity / theoretical capacity) × 100 (II)
The utilization ratio of the positive electrode active material of each battery is shown in Table 1 as an index when the utilization ratio of the battery of Comparative Example 1 is 100.

(3) Operating voltage The batteries A to P that have been initially activated are charged for 1 hour at a current of 1.0 C in an atmosphere at 25 ° C., and then at a current of 4.0 C in the same atmosphere. While measuring the discharge capacity of the battery when discharged until the battery voltage reached 0.8V, the voltage of the battery at the middle of the total discharge time was determined as the operating voltage during 4C discharge. These results are shown in Table 1 with a difference (unit: mV) in which the operating voltage at the time of 4C discharge in Comparative Example 1 is a subtraction term.

  Furthermore, for each battery, it was charged at a current of 1.0 C in an atmosphere of 25 ° C. for 1 hour, and then discharged until the battery voltage was 0.8 V at a current of 1.0 C in an atmosphere of −10 ° C., While measuring the battery discharge capacity at low temperature, the voltage of the battery at the middle of the total discharge time was determined as the operating voltage at -10 ° C discharge. These results are shown in Table 1 with a difference (unit: mV) in which the operating voltage at −10 ° C. discharge in Comparative Example 1 was used as a subtraction term.

(4) Crystal structure of hydrogen storage alloy A part of the powder of the hydrogen storage alloy immediately after pulverization described above was used, and X-ray diffraction measurement (XRD measurement) was performed on the selected alloy powder. For the measurement, a device manufactured by Rigaku Corporation (parallel beam X-ray diffractometer) is used. The measurement specifications here are: X-ray source: CuKα, tube voltage: 50kV, tube current: 300mA, scan speed: 1 ° / min Sample rotation speed: 60 rpm. Based on the profile of the measurement results, the crystal structure of the hydrogen storage alloy was identified. The specific results are also shown in Table 1.

3. Evaluation results Table 1 clearly shows the following.
(1) When comparing Examples 1 to 4 (Batteries A to D) in which bismuth oxide was added to the negative electrode and Comparative Example 1 (Battery E) in which no bismuth oxide was added to the negative electrode, Examples 1 to 4 and Comparative Examples Although there is no difference in the utilization rate of the positive electrode active material between 1 and 4, when looking at the operating voltage at the time of 4C discharge and −10 ° C. discharge, Examples 1-4 are compared with Comparative Example 1 in both operations. Both voltages are high. This means that a decrease in both operating voltages is suppressed when the battery is discharged.

(2) Moreover, when Examples 1-4 (battery AD) are compared with each other, it turns out that the effect which suppresses the fall of the above-mentioned operating voltage changes with the addition amount of the bismuth oxide to a negative electrode. Specifically, when the addition amount exceeds 0.3 parts by weight, the effect of suppressing a decrease in the operation voltage appears for both the operation voltage at the time of 4C discharge and −10 ° C. discharge, but the addition amount is 2% by weight. When it becomes a part, it turns out that the effect which suppresses the fall of the operating voltage at the time of -10 degreeC discharge does not appear, conversely, the fall of the operating voltage is accelerated | stimulated further. From this, the addition amount of bismuth oxide is preferably set in the range of 0.3 to 1.5 parts by weight, more preferably in the range of 0.3 to 1.0 parts by weight, with respect to 100 parts by weight of the positive electrode active material.

(3) Further, comparing Example 1 (Battery A) in which yttrium oxide was added to the positive electrode and Comparative Example 2 (Battery F) in which yttrium oxide was not added to the positive electrode, Comparative Example 2 (Battery F) It can be seen that, compared with Example 1 (battery A), the utilization rate of the positive electrode active material, that is, the increase in the capacity of the battery is greatly reduced, and at the same time, the effect of suppressing the reduction in both operating voltages is not achieved.
Although the mechanism by which the additive to the positive electrode and the negative electrode exerts the above synergistic effect has not been clarified, when the reduction of both operating voltages is to be suppressed by adding bismuth oxide to the negative electrode, the positive electrode also has yttrium oxide. It can be seen that further suppression of both operating voltage drops can be achieved by adding.

(4) If Example 1 (Battery A), Example 5 (Battery G) and Example 6 (Battery H) are compared with each other, ytterbium oxide or erbium oxide is added as a positive electrode additive instead of yttrium oxide. It can also be seen that, as in the case of yttrium oxide, the reduction in both operating voltages can be suppressed simultaneously with the improvement of the utilization rate of the positive electrode active material.

(5) From the comparison between Example 1 (Battery A) and Example 7 (Battery I), both bismuth oxide and indium oxide as the negative electrode additive have the effect of suppressing both operating voltage drops. It can be seen that the indium oxide addition does not reach the bismuth oxide addition.

(6) Example 1 (battery A) in which the hydrogen storage alloy of the negative electrode has a composition of CaCu ₅ type crystal structure and Example 8 (battery K) in which the hydrogen storage alloy has a composition of Pr ₅ Co ₁₉ type crystal structure )), It can be seen that Example 8 (Battery K) is superior to Example 1 (Battery A) in suppressing the decrease in operating voltage when discharged at −10 ° C. Here, in Comparative Example 3 (Battery J), the hydrogen storage alloy has the same composition and the same crystal structure as in Example 8 (Battery K), but the negative electrode additive was not added. The suppression of both operating voltage drops has not been achieved. Therefore, both of the above-mentioned effects of suppressing the decrease in operating voltage are not obtained by changing the composition or crystal structure of the hydrogen storage alloy, but the oxidation of the hydrogen storage alloy having a specific crystal structure and the negative electrode additive material. It can be seen that this is achieved even more in combination with the addition of bismuth.

(7) If attention is paid to the crystal structures of the hydrogen storage alloys of Example 8 (Battery K), Example 9 (Battery L), and Example 10 (Battery M), the crystal structure of the hydrogen storage alloy is PuNi ₃ type. Example 9 is somewhat inferior to both Pr ₅ Co ₁₉ type examples 8 in reducing the operating voltage drop, while Ce ₂ Ni ₇ type example 10 is both in comparison with example 8. It turns out that it is further excellent in suppression of the operating voltage fall. From this, it can be seen that the crystal structure of the hydrogen storage alloy greatly affects the suppression of both operating voltage drops, and it can be seen that the Ce ₂ Ni ₇ type contributes most to the suppression of both operating voltage drops.

(8) When comparing Example 1 (Battery A), Example 11 (Battery N), and Comparative Example 4 (Battery O), focusing on the form of addition of the conductive agent, a cobalt compound as a conductive agent in the positive electrode mixture In Example 11 and Comparative Example 4 in which the surface of the nickel hydroxide particles was coated with a cobalt compound as a conductive agent, compared with Example 1 in which was added in the form of powder. Improvement of utilization rate is recognized.

  From this, it can be seen that it is effective to coat the surface of nickel hydroxide particles as the positive electrode active material with a cobalt compound as a conductive agent in order to improve the utilization rate of the positive electrode active material. Here, in the case of the comparative example 4, although the utilization factor of the positive electrode active material is improved, both operating voltage drops are further advanced. This is considered to be due to the fact that the discharge property of the positive electrode was lowered due to the accelerated generation of γ-NiOOH on the positive electrode during charging as described above.

  On the other hand, Example 11, which differs from Comparative Example 4 only in that bismuth oxide was added to the negative electrode, intended to suppress both operating voltage drops, regardless of the decrease in dischargeability due to the generation of γ-NiOOH. It can be seen that both the improvement in the utilization rate of the positive electrode active material and the suppression of the decrease in both operating voltages are achieved.

(9) Since Example 12 (Battery P) can achieve both the improvement in the utilization rate of the positive electrode active material and the suppression of both operating voltage drops during 4C discharge and −10 ° C. discharge, It can be seen that the configuration is optimal for achieving both the improvement of the utilization factor and the suppression of the operating voltage drop. Specifically, in the case of Example 12 (battery P), the positive electrode includes nickel hydroxide particles coated with a cobalt compound and yttrium oxide as a positive electrode additive, and the negative electrode has a Ce ₂ Ni ₇ type crystal structure. And a bismuth oxide as a negative electrode additive.
The present invention is not limited to the above-described embodiment and examples, and various modifications are possible. For example, the nickel-metal hydride secondary battery may be a prismatic battery, and the mechanical structure is There is no particular limitation. Further, in each of the above-described embodiments, the crystal structure of the hydrogen storage alloy is not limited to CaCu ₅ type, PuNi ₃ type, Pr ₅ Co ₁₉ type, Ce ₂ Ni ₇ type, but CeNi ₃ type, Gd ₂ Co ₇ type, Ce ₅ Co ₁₉ type or the like may be used.

2 Nickel-hydrogen secondary battery 24 Positive electrode 26 Negative electrode 36 Nickel hydroxide particles 38 Positive electrode additive 40 Conductive agent 42 Binder 44 Hydrogen storage alloy particles 46 Negative electrode additive 48 Binder 50 Conductive agent

Claims (5)

In the nickel hydride secondary battery in which the electrode group is housed in a sealed state together with the alkaline electrolyte in the container, and the electrode group is composed of a separator, a positive electrode, and a negative electrode,
The positive electrode is
A positive electrode active material powder made of nickel hydroxide;
A positive electrode additive that is distributed in the positive electrode active material powder and includes at least one selected from the group consisting of Y, Yb, Er, and a compound of each of these elements;
The negative electrode is
Hydrogen storage alloy powder,
A nickel-metal hydride secondary battery comprising: a negative electrode additive containing at least one selected from the group consisting of Bi, In, and a compound of each of these elements, distributed in the hydrogen storage alloy powder.   2. The nickel-hydrogen secondary battery according to claim 1, wherein a surface of the positive electrode active material powder is coated with at least one selected from the group consisting of cobalt and a cobalt compound.   The nickel-hydrogen secondary battery according to claim 1 or 2, wherein the content of the negative electrode additive is in the range of 0.3 to 1.5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy. . The hydrogen storage alloy is
General formula:
Ln _1-x Mg _x Ni _y-a-b Al _a M _b
Having a composition represented by
In the above formula,
Ln is at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Zr, and Ti. Represents the elements of
M represents at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B;
The subscripts a, b, x, and y satisfy 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 0.05 ≦ x ≦ 0.30, and 2.8 ≦ y ≦ 3.9, respectively. The nickel hydride secondary battery according to claim 1, wherein the nickel hydride secondary battery represents a number. The hydrogen storage alloy is
The nickel-hydrogen secondary battery according to claim 1, wherein the nickel-hydrogen secondary battery has a Ce ₂ Ni ₇ type crystal structure.

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