Nickel-metal hydride secondary battery

Abstract

To provide a nickel metal hydride secondary battery excellent in cycle life characteristics.SOLUTION: A nickel metal hydride secondary battery 2 comprises an outer can 10 and an electrode assembly 22 housed in the outer can 10 together with an alkaline electrolytic solution. The electrode assembly 22 is such that a positive electrode 24 including a positive electrode mixture and a negative electrode 26 including a negative electrode mixture are superimposed with a separator 28 interposed therebetween. The positive electrode mixture includes nickel hydroxide forming a solid solution with zinc as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture includes hydrogen absorbing alloy particles and a negative electrode additive. The negative electrode additive is a composite in which yttrium fluoride is supported on carbon black, and a surface of the hydrogen absorbing alloy particles is partially coated with the composite.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a nickel-hydrogen secondary battery.

Background Art

[0002] A nickel-hydrogen secondary battery is known as a type of alkaline secondary battery. This nickel-hydrogen secondary battery has a higher capacity than a nickel-cadmium secondary battery and is also excellent in environmental safety. Therefore, it has come to be used in various devices such as various portable devices and hybrid electric vehicles, and its applications are expanding more and more. With such an expansion of applications, higher performance is desired in nickel-hydrogen secondary batteries. One of the performances to be improved in such nickel-hydrogen secondary batteries is cycle life characteristics. If the cycle life characteristics are improved and the number of times the battery can be repeatedly charged and discharged increases, the convenience of the nickel-hydrogen secondary battery will be improved.

[0003] The main cause of the cycle life of a nickel-hydrogen secondary battery running out is that during repeated charging and discharging of the battery, the alkaline electrolyte becomes unevenly distributed or depleted in the battery, so that the contact between the alkaline electrolyte and the positive and negative electrodes is inhibited, and the battery reaction does not proceed. For example, when the positive electrode swells due to the battery reaction and the separator is compressed, the alkaline electrolyte is taken away from the separator. As a result, the alkaline electrolyte is unevenly distributed in parts of the battery other than the separator, and the separator dries out, so-called dry-out occurs. Then, discharging becomes impossible and the battery life ends.

[0004] In order to suppress such problems and extend the cycle life, a measure has been taken to add a zinc compound to the positive electrode (see, for example, Patent Document 1). When such a zinc compound is added, the swelling of the positive electrode and the deprivation of the alkaline electrolyte from the separator are suppressed, and an improvement in the cycle life of the battery is achieved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 04-137368 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, at present, simply suppressing the swelling of the positive electrode by adding a zinc compound as described above does not sufficiently meet the recent demand for improving the cycle life characteristics of batteries. Therefore, in order to suppress the uneven distribution of the alkaline electrolyte in the battery as described above, the injection amount of the alkaline electrolyte is increased to improve the cycle life characteristics.

[0007] By the way, in a nickel-metal hydride secondary battery, when it is in an overcharged state, a reaction occurs in which oxygen gas is generated from the positive electrode, and the internal pressure of the battery increases. If the internal pressure of the battery continues to rise, the safety valve of the battery will operate, releasing oxygen gas and also discharging the alkaline electrolyte to the outside, resulting in the depletion of the alkaline electrolyte and the end of the battery life. However, in a nickel-metal hydride secondary battery, at the negative electrode, a reaction that absorbs the oxygen gas generated during overcharging also occurs in parallel. That is, a nickel-metal hydride secondary battery has a function of suppressing the increase in the internal pressure of the battery due to oxygen gas. Thus, since a normal nickel-metal hydride secondary battery can suppress the increase in the internal pressure of the battery, it is possible to suppress the deterioration of the battery life characteristics due to the release and depletion of the alkaline electrolyte when the safety valve operates.

[0008] Here, the oxygen gas absorption reaction at the negative electrode proceeds at the three-phase interface where the solid phase, gas phase, and liquid phase coexist. To form a good three-phase interface, a certain amount of surplus space is required inside the battery. However, when a large amount of alkaline electrolyte is injected into the battery to suppress the degradation of the cycle life characteristics due to the uneven distribution of the alkaline electrolyte as described above, the surplus space becomes insufficient, and a good three-phase interface cannot be formed. Then, the oxygen gas absorption reaction does not proceed smoothly, the oxygen gas is not sufficiently absorbed, and the internal pressure of the battery increases. As a result, the safety valve of the battery operates and the alkaline electrolyte is released to the outside, causing so-called leakage. When leakage occurs, the alkaline electrolyte in the battery is depleted, resulting in a problem that the life of the battery ends prematurely. That is, even if more alkaline electrolyte is injected, the cycle life characteristics may be degraded. In particular, leakage is likely to occur in the initial stage of the charge-discharge cycle. Specifically, in the initial stage of the charge-discharge cycle, the alkaline electrolyte that has not fully penetrated into the electrode group, especially the separator, may remain in the upper part of the electrode group, and the activation treatment of the battery may not be sufficient, and the oxygen gas absorption reaction may not proceed smoothly. For this reason, the internal pressure of the battery is likely to increase, the safety valve operates, and the alkaline electrolyte remaining in the upper part of the electrode group is discharged, causing leakage.

[0009] Therefore, there is a demand for the development of a nickel-hydrogen secondary battery that can suppress the occurrence of leakage, particularly leakage in the initial stage of the charge-discharge cycle, even when a large amount of alkaline electrolyte is injected.

[0010] The present invention has been made based on the above circumstances, and an object thereof is to provide a nickel-hydrogen secondary battery having excellent cycle life characteristics.

Means for Solving the Problems

[0011] According to the present invention, there is provided a nickel-hydrogen secondary battery including a container and an electrode group accommodated in the container together with an alkaline electrolyte. The electrode group is formed by laminating a positive electrode including a positive electrode mixture and a negative electrode including a negative electrode mixture with a separator interposed therebetween. The positive electrode mixture includes nickel hydroxide in which zinc is solid-solved as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture includes hydrogen storage alloy particles and a negative electrode additive. The negative electrode additive is a composite in which ytterbium fluoride is supported on carbon black, and the composite covers a part of the surface of the hydrogen storage alloy particles.

Advantages of the Invention

[0012] The nickel-hydrogen secondary battery of the present invention includes a container and an electrode group accommodated in the container together with an alkaline electrolyte. The electrode group is formed by laminating a positive electrode including a positive electrode mixture and a negative electrode including a negative electrode mixture with a separator interposed therebetween. The positive electrode mixture includes nickel hydroxide in which zinc is solid-solved as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture includes hydrogen storage alloy particles and a negative electrode additive. The negative electrode additive is a composite in which ytterbium fluoride is supported on carbon black, and the composite covers a part of the surface of the hydrogen storage alloy particles. With this configuration, the nickel-hydrogen secondary battery of the present invention can suppress an increase in the internal pressure of the battery and prevent leakage of the electrolyte at the initial stage of the charge-discharge cycle, and thus has excellent cycle life characteristics.

Brief Description of the Drawings

[0013]

Figure 1

Embodiments for Carrying Out the Invention

[0014] Hereinafter, a nickel-hydrogen secondary battery (hereinafter referred to as a battery) 2 according to an embodiment will be described with reference to the drawings.

[0015] The battery 2 is, for example, an AA-sized cylindrical battery. Specifically, as shown in FIG. 1, the battery 2 includes an outer can 10 that forms a bottomed cylindrical shape with an open upper end. 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. This sealing body 11 includes a cover plate 14 and a positive electrode terminal 20, seals the outer can 10, and provides the positive electrode terminal 20. The cover plate 14 is a disk-shaped member having conductivity. Inside the opening of the outer can 10, a cover plate 14 and an annular insulating packing 12 surrounding the cover plate 14 are arranged, and the insulating packing 12 is fixed to the opening edge 37 of the outer can 10 by caulking the opening edge 37 of the outer can 10. That is, the cover plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the outer can 10.

[0016] Here, the cover plate 14 has a central through hole 16 at the center, and a rubber valve body 18 that closes the central through hole 16 is arranged on the outer surface of the cover plate 14. Further, on the outer surface of the cover plate 14, a metal positive electrode terminal 20 having a cylindrical shape with a flange is electrically connected so as to cover the valve body 18. This positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. Note that a gas vent hole (not shown) is opened in the positive electrode terminal 20.

[0017] Normally, the central through hole 16 is airtightly closed by the valve body 18. On the other hand, when gas is generated inside the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure, opening the central through hole 16. As a result, gas is released from the inside of the outer can 10 to the outside through the central through hole 16 and the gas vent hole (not shown) of the positive electrode terminal 20. That is, the central through hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

[0018] The exterior can 10 houses an electrode group 22. This electrode group 22 includes a strip-shaped positive electrode 24, a negative electrode 26, and a separator 28 respectively. Specifically, these positive electrode 24 and negative electrode 26 are wound in a spiral state with the separator 28 sandwiched therebetween. 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 (the outermost peripheral part) of the negative electrode 26 and is in contact with the inner peripheral wall of the exterior can 10. That is, the negative electrode 26 and the exterior can 10 are electrically connected to each other.

[0019] Inside the exterior can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the lid plate 14. Specifically, one end of the positive electrode lead 30 is connected to the positive electrode 24, and the other end thereof is 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 lid plate 14. A circular upper insulating member 32 is disposed between the lid 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. Also, a circular lower insulating member 34 is disposed between the electrode group 22 and the bottom of the exterior can 10.

[0020] Furthermore, a predetermined amount of an alkaline electrolytic solution (not shown) is injected into the exterior can 10. The alkaline electrolytic solution is impregnated in the electrode group 22 and is mainly held by the separator 28. This alkaline electrolytic solution causes an electrochemical reaction (charge and discharge reaction) during charge and discharge between the positive electrode 24 and the negative electrode 26 to proceed. As this alkaline electrolytic solution, it is preferable to use an aqueous solution containing at least one of KOH, NaOH, and LiOH as a solute.

[0021] As the material of the separator 28, for example, a non-woven fabric made of polyamide fibers to which a hydrophilic functional group is imparted, a non-woven fabric made of polyolefin fibers such as polyethylene and polypropylene to which a hydrophilic functional group is imparted, or the like can be used. Specifically, it is preferable to use a non-woven fabric mainly composed of polyolefin fibers that have been sulfonated and to which sulfonic groups are imparted. Here, the sulfonic groups are imparted by treating the non-woven fabric with an acid containing a sulfuric acid group such as sulfuric acid or fuming sulfuric acid. A battery using a separator containing such fibers having sulfonic groups exhibits excellent self-discharge characteristics.

[0022] The positive electrode 24 includes a conductive positive electrode core material having a porous structure and a positive electrode mixture held in the pores of the positive electrode core material. As the positive electrode core material as described above, for example, foamed nickel can be used.

[0023] The positive electrode mixture includes a positive electrode active material, a positive electrode additive, and a binder. This binder functions to bind the positive electrode active material and the positive electrode additive to each other and to bind the positive electrode active material and the positive electrode additive to the positive electrode core material. Here, as the binder, for example, carboxymethyl cellulose, methyl cellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropyl cellulose) dispersion, or the like can be used.

[0024] Nickel hydroxide is used as the positive electrode active material. As the form of this nickel hydroxide, a powdery one is used. That is, nickel hydroxide powder, which is an aggregate of nickel hydroxide particles, is used. It is preferable to employ nickel hydroxide particles that are highly ordered.

[0025] The above-described nickel hydroxide particles containing Zn in solid solution are used. Zn as this solid solution component contributes to the suppression of the swelling of the positive electrode.

[0026] The content of Zn dissolved in the nickel hydroxide particles is preferably 3.5 parts by mass or more and 4.5 parts by mass or less with respect to 100 parts by mass of nickel hydroxide.

[0027] It is preferable to use nickel hydroxide particles in which Co is further dissolved. Co as this solid solution component contributes to the improvement of the conductivity between the positive electrode active material particles and improves the charge acceptance property. Here, if the content of Co dissolved in the nickel hydroxide particles is too small, the effect of improving the charge acceptance property is small, and conversely, if it is too large, the grain growth of the nickel hydroxide particles is inhibited. For this reason, it is preferable to use nickel hydroxide particles containing 0.5 mass% or more and 5.0 mass% or less of Co as the solid solution component.

[0028] Also, the nickel hydroxide particles described above are preferably in a form in which the surface is covered with a surface layer containing a cobalt compound. As this surface layer, it is preferable to employ a higher-order cobalt compound layer containing a cobalt compound in which the cobalt is oxidized to trivalent or higher.

[0029] The above-mentioned higher-order 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 containing a cobalt compound such as cobalt oxyhydroxide (CoOOH) in which the cobalt is oxidized to trivalent or higher.

[0030] The positive electrode active material can be manufactured, for example, as follows. First, nickel sulfate and zinc sulfate are weighed so as to have a predetermined composition, and a mixed aqueous solution thereof is prepared. A nickel hydroxide-based nickel hydroxide particle in which zinc is dissolved is precipitated by gradually adding an aqueous sodium hydroxide solution to this mixed aqueous solution and reacting them. Here, when further dissolving cobalt, nickel sulfate, zinc sulfate, and cobalt sulfate are weighed so as to have a predetermined composition, and a mixed aqueous solution thereof is prepared. While stirring the obtained mixed aqueous solution, an aqueous sodium hydroxide solution is gradually added to this mixed aqueous solution and reacted to precipitate nickel hydroxide-based nickel hydroxide particles in which zinc and cobalt are dissolved.

[0031] When forming a conductive layer on the surface of the nickel hydroxide particles obtained as described above, for example, the conductive layer is formed by the following procedure.

[0032] First, the nickel hydroxide particles in which zinc is dissolved or the nickel hydroxide particles in which zinc and cobalt are dissolved, obtained as described above, are put into an aqueous ammonia solution, and an aqueous cobalt sulfate solution is added to this aqueous solution. As a result, cobalt hydroxide precipitates on the surface of this nucleus with the nickel hydroxide particles as the nucleus, and intermediate particles having a layer of cobalt hydroxide are formed. The obtained intermediate particles are put into a 25% by mass aqueous sodium hydroxide solution. Here, when the mass of the intermediate powder, which is an aggregate of the intermediate particles having a layer of cobalt hydroxide, is P and the mass of the aqueous sodium hydroxide solution is Q, the mass ratio thereof is set to P:Q = 1:10. Then, the aqueous sodium hydroxide solution to which the intermediate powder is added is heat-treated while stirring for 5 to 10 hours while maintaining the temperature at 80°C to 100°C.

[0033] Thereafter, the intermediate powder that has undergone the above heat treatment is washed with water and dried at 50°C to 80°C, whereby a positive electrode active material powder that is an aggregate of nickel positive electrode active material particles whose surface of the nickel hydroxide particles is coated with a higher-order cobalt oxide is obtained. By the above heat treatment, the cobalt hydroxide on the surface of the intermediate particles becomes a highly conductive higher-order cobalt compound (such as cobalt oxyhydroxide) whose valence exceeds trivalent.

[0034] Next, zinc oxide is used as the positive electrode additive. As the form of this zinc oxide, a powdery one is used. That is, zinc oxide powder that is an aggregate of zinc oxide particles is used. The addition amount of this zinc oxide powder is preferably 0.5 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the positive electrode active material powder.

[0035] In addition, it is preferable to add yttrium oxide or niobium oxide to the positive electrode additive as necessary.

[0036] Next, the positive electrode 24 can be manufactured, for example, as follows. First, a positive electrode additive, water, and a binder are added to and kneaded with the positive electrode active material powder, which is an aggregate of the positive electrode active material particles obtained as described above, to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry is filled, for example, into foamed nickel and subjected to a drying treatment. After the drying treatment, the foamed nickel filled with nickel hydroxide particles or the like is roll-pressed and then cut. Thereby, the positive electrode 24 containing the positive electrode mixture is obtained.

[0037] Next, the negative electrode 26 will be described. The negative electrode 26 has a strip-shaped conductive negative electrode core, and a negative electrode mixture is held on this negative electrode core.

[0038] The negative electrode core is a sheet-shaped metal material with through holes distributed therein. For example, a punching metal sheet can be used. The negative electrode mixture is not only filled in the through holes of the negative electrode core but also held in layers on both surfaces of the negative electrode core.

[0039] The negative electrode mixture includes hydrogen storage alloy particles capable of occluding and releasing hydrogen as a negative electrode active material, a negative electrode additive, a binder, and a negative electrode auxiliary agent.

[0040] The above-mentioned binder functions to bind the hydrogen storage alloy particles, the negative electrode additive, etc. to each other and at the same time bind the hydrogen storage alloy particles, the negative electrode additive, etc. to the negative electrode core. Here, the binder is not particularly limited, and for example, hydrophilic or hydrophobic polymers, binders generally used for nickel-hydrogen secondary batteries such as carboxymethyl cellulose can be used.

[0041] Also, as the negative electrode auxiliary agent, styrene-butadiene rubber, sodium polyacrylate, etc. can be used.

[0042] The type of the hydrogen storage alloy in the hydrogen storage alloy particles is not particularly limited, but it is preferable to use a rare earth-Mg-Ni-based hydrogen storage alloy containing rare earth elements, Mg, and Ni. More preferably, a hydrogen storage alloy having a composition represented by the following general formula (I) is used.

[0043] Ln 1-x Mg x Ni y-z Al z ···(I) However, in the general formula (I), Ln represents at least one element selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ti, and Zr, and the subscripts x, y, and z satisfy the relationships represented by 0.05 ≦ x ≦ 0.30, 2.8 ≦ y ≦ 3.8, and 0.05 ≦ z ≦ 0.30, respectively.

[0044] The particles of the hydrogen storage alloy can be 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, a high-frequency induction melting furnace to form an ingot. The obtained ingot is subjected to a heat treatment of heating at 900 to 1200 °C in an inert gas atmosphere for 5 to 24 hours. Thereafter, the ingot is mechanically pulverized in an inert gas atmosphere and sieved to obtain particles of the hydrogen storage alloy having a desired particle size.

[0045] Here, the particle size of the hydrogen storage alloy particles is not particularly limited, but preferably, those having an average particle size of 55.0 to 70.0 μm are used. In this specification, the average particle size means the average particle size at which the integration based on the mass standard is 50%, and is obtained by the laser diffraction / scattering method using a particle size distribution measuring device.

[0046] The negative electrode additive is a composite of ytterbium fluoride and carbon black as a conductive material. Specifically, it is a composite in which ytterbium fluoride is supported on carbon black.

[0047] As the form of yttrium fluoride, a powdery one is used. That is, yttrium fluoride powder, which is an aggregate of yttrium fluoride particles, is used. As the yttrium fluoride particles, those with an average particle size of 1 μm to 7 μm are preferably used.

[0048] As the form of carbon black, a powdery one in which aggregates of primary particles are aggregated is used. Here, the average particle size of the primary particles of carbon black is 20 to 50 nm, and the length of the aggregates is 10 μm to 100 μm.

[0049] Also, as the carbon black, it is preferable to use hollow carbon black in which the primary particles have a hollow shell structure. This hollow carbon black is superior in conductivity compared to ordinary carbon black.

[0050] The composite of yttrium fluoride and carbon black as a negative electrode additive can be produced, for example, as follows.

[0051] Yttrium fluoride powder, carbon black powder, sodium polyacrylate, carboxymethyl cellulose, and water are kneaded to prepare a paste. In the obtained paste, a composite in which yttrium fluoride is supported on carbon black is formed.

[0052] Next, the negative electrode 26 can be produced, for example, as follows. First, the hydrogen storage alloy powder, which is an aggregate of hydrogen storage alloy particles obtained as described above, is added to a paste containing a composite in which ytterbium fluoride is supported on carbon black, and they are kneaded. As a result, the surface of the hydrogen storage alloy particles is partially coated with the above-described composite. Then, styrene-butadiene rubber powder and water are further added to such a paste, and they are kneaded to prepare a negative electrode active material paste. The obtained negative electrode active material paste is applied to a negative electrode core body and subjected to a drying treatment. After drying, the negative electrode core body holding the hydrogen storage alloy powder, negative electrode additive, etc. is rolled as a whole to increase the packing density of the hydrogen storage alloy, whereby an intermediate product of the negative electrode is obtained. Then, this intermediate product of the negative electrode is cut into a predetermined shape. Thereby, the negative electrode 26 is manufactured.

[0053] The positive electrode 24 and the negative electrode 26 manufactured as described above are wound in a spiral shape with the separator 28 interposed therebetween, whereby the electrode group 22 is formed.

[0054] The electrode group 22 obtained in this way is housed in the exterior can 10. Subsequently, a predetermined amount of alkaline electrolyte is injected into the exterior can 10. Then, the exterior can 10 housing the electrode group 22 and the alkaline electrolyte is sealed with a sealing body 11 provided with a 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 treatment and made into a usable state.

[0055] [Examples] 1. Manufacture of battery (Example 1) (1) Manufacture of positive electrode Nickel sulfate, zinc sulfate, and cobalt sulfate were weighed so that the amount of zinc was 4.0 parts by mass and the amount of cobalt was 1.0 part by mass with respect to 100 parts by mass of nickel hydroxide, and these were added to a 1 mol / L aqueous sodium hydroxide solution containing ammonium ions to prepare a mixed aqueous solution. While stirring the obtained mixed aqueous solution, a 1 mol / L aqueous sodium hydroxide solution was gradually added to this mixed aqueous solution to cause a reaction, and the pH during the reaction here was stabilized at 11 to generate base particles mainly composed of nickel hydroxide and in which Zn and Co were solid-dissolved.

[0056] The obtained base particles were washed three times with 10 times the amount of pure water and then subjected to dehydration and drying treatments. For the obtained base particles, as a result of measuring the particle size using a laser diffraction / scattering particle size distribution measuring device, the average particle size corresponding to 50% of the integration based on the mass of such base particles was 8 μm.

[0057] Next, the obtained base particles were put into an aqueous cobalt sulfate solution, and while stirring this aqueous cobalt sulfate solution, a 1 mol / L aqueous sodium hydroxide solution was gradually dropped and reacted, and a precipitate was formed while maintaining the pH during the reaction here at 11. Then, the formed precipitate was filtered off, washed with pure water, and then vacuum dried. Thereby, intermediate product particles having a layer of cobalt hydroxide of 5% by mass on the surface of the base particles were obtained. The thickness of the cobalt hydroxide layer was about 0.1 μm.

[0058] Next, these intermediate product particles were put into a 25% by mass aqueous sodium hydroxide solution. Here, when the mass of the powder which is an aggregate of the intermediate product particles is P and the mass of the aqueous sodium hydroxide solution is Q, the mass ratio thereof was set so as to be P:Q = 1:10. Then, a heat treatment was performed in which the aqueous sodium hydroxide solution added with the powder of this intermediate product was stirred and held at a constant temperature of 85°C for 8 hours.

[0059] The powder of the intermediate product that had undergone the above heat treatment was washed with pure water and dried by blowing warm air at 65°C. Thereby, a positive electrode active material powder which is an aggregate of positive electrode active material particles having a surface layer containing cobalt oxide of a higher order on the surface of the base particles in which Zn and Co are solid-solved was obtained.

[0060] Next, to 100 parts by mass of the positive electrode active material powder obtained as described above, 0.5 part by mass of yttrium oxide powder, 0.3 part by mass of niobium oxide powder, 0.5 part by mass of zinc oxide powder, and 50.0 parts by mass of water containing 0.2% by mass of hydroxypropyl cellulose powder as a binder were added and kneaded to prepare a slurry of a positive electrode mixture.

[0061] Subsequently, the slurry of the positive electrode active material was filled into a sheet-like nickel foam as the positive electrode core material. Here, as the nickel foam, one having a basis weight (areal density) of about 350 g / m 2 , a porosity of 95%, and a thickness of 1.3 mm was used.

[0062] After drying the nickel foam filled with the slurry of the positive electrode active material, the nickel foam filled with the positive electrode active material was adjusted so that the filling density of the positive electrode active material calculated by the following formula (II) was 3.0 g / cm 3 , rolled, and then cut into a predetermined size to obtain a positive electrode 24 for AA size.

[0063] Filling density of positive electrode active material [g / cm 3 = Mass of positive electrode active material [g] ÷ (Electrode height [cm] × Electrode length [cm] × Electrode thickness [cm] - Mass of nickel foam [g] ÷ Density of nickel [g / cm 3 ) ··· (II)

[0064] (2) Manufacture of negative electrode After mixing each metal material of La, Sm, Mg, Ni, and Al so as to have a predetermined molar ratio, it was put into a high-frequency induction melting furnace and melted, and this was cooled to produce an ingot.

[0065] Subsequently, this ingot was heat-treated by heating at 1000 °C in an argon gas atmosphere for 10 hours to be homogenized, and then mechanically pulverized in an argon gas atmosphere to obtain rare earth-Mg-Ni-based hydrogen storage alloy powder. About the obtained rare earth-Mg-Ni-based hydrogen storage alloy powder, the particle size distribution was measured by a laser diffraction / scattering type particle size distribution measuring device (device name: SRA-150 manufactured by Microtrac). As a result, the average particle size corresponding to 50% of the integration based on mass was 65 μm.

[0066] When the composition of this hydrogen storage alloy powder was analyzed by high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES), the composition was La 0.27 Sm 0.63 Mg 0.10 Ni3.33 Al 0.17 was the case. Also, when X-ray diffraction measurement (XRD measurement) was performed on this hydrogen storage alloy powder, the crystal structure was the so-called superlattice structure of A 2 B 7 type (Ce 2 Ni 7 type).

[0067] Next, a negative electrode binder was produced. First, as the first step, 0.1 part by mass of yttrium fluoride powder, which is an aggregate of yttrium fluoride particles with an average particle size of 1 μm, 0.50 part by mass of hollow carbon black having a hollow shell-like structure (specifically, Ketjenblack (registered trademark) manufactured by Lion Specialty Chemicals was used. As the physical property values of this hollow carbon black, the specific surface area by the BET method is 1270 m 2 / g, the porosity is 80%, the average particle size of the primary particles is 34.0 nm, and the length of the aggregates is 10 μm.), 0.30 part by mass of sodium polyacrylate powder, 0.05 part by mass of carboxymethyl cellulose powder, and 20 parts by mass of water were prepared, and these were kneaded in an environment at 25°C. In this way, the first paste was prepared. In the obtained first paste, a composite of a negative electrode additive in which yttrium fluoride is supported on carbon black was formed.

[0068] Next, as the second step, 100 parts by mass of the hydrogen storage alloy powder obtained as described above was added to the first paste and kneaded. By this operation, a part of the surface of the hydrogen storage alloy particles was covered with a composite in which yttrium fluoride was supported on carbon black.

[0069] Furthermore, 0.5 part by mass of styrene-butadiene rubber powder and 15 parts by mass of water were added to this first paste, and kneaded in an environment at 25°C to prepare a negative electrode binder paste.

[0070] This negative electrode binder paste was applied evenly to both sides of the punching metal sheet serving as the negative electrode core body so that the thickness was constant. Also, the negative electrode binder paste was filled in the through holes. Note that this punching metal sheet is an iron strip in which a large number of through holes drilled in the thickness direction are distributed, the thickness is 50 μm, and nickel plating is applied to its surface.

[0071] After drying the negative electrode binder paste, the punching metal sheet holding a hydrogen storage alloy or the like was adjusted and rolled so that the filling density of the hydrogen storage alloy calculated by the following formula (III) was 6.4 g / cm 3 to obtain an intermediate product of the negative electrode.

[0072] Filling density of hydrogen storage alloy [g / cm 3 = Mass of hydrogen storage alloy [g] ÷ (Electrode height [cm] × Electrode length [cm] × Electrode thickness [cm] - Mass of punching metal sheet [g] ÷ Density of iron [g / cm 3 ) ··· (III)

[0073] Thereafter, the intermediate product of the negative electrode was cut into a predetermined size to obtain a negative electrode 26 for AA size. Also, a sample was separately collected from the intermediate product of the negative electrode, and the obtained sample was observed by a scanning electron microscope. As a result, it was confirmed that the surface of the particles of the hydrogen storage alloy was partially covered by a composite in which yttrium fluoride was supported on carbon black.

[0074] (3) Assembly of nickel-hydrogen secondary battery The positive electrode 24 and the negative electrode 26 obtained as described above were wound in a spiral shape with a separator 28 sandwiched therebetween to manufacture an electrode group 22. The separator 28 used for manufacturing the electrode group 22 here is a nonwoven fabric made of sulfonated polypropylene fibers, and its thickness is 0.1 mm (basis weight 40 g / m 2 ).

[0075] On the one hand, an alkaline electrolyte solution containing KOH, NaOH, and LiOH as solutes was prepared. This alkaline electrolyte solution has a mass mixing ratio of KOH:NaOH:LiOH = 4:5:1 and a specific gravity of 1.31.

[0076] Next, the above-described electrode group 22 was accommodated in a bottomed cylindrical outer can 10, and 2.0 g of the prepared alkaline electrolyte solution was injected. Thereafter, the opening of the outer can 10 was closed with a sealing body 11, and an AA-sized battery 2 with a nominal capacity of 2000 mAh was assembled.

[0077] (4) Initial activation treatment With respect to the obtained battery 2, in an environment at a temperature of 25°C, after charging for 16 hours with a charging current of 1.0 It, a charge-discharge cycle in which discharging is performed with a discharging current of 1.0 It until the battery voltage reaches 1.0 V is defined as one cycle, and this charge-discharge cycle was repeated 3 times. In this way, the initial activation treatment was performed to make the battery 2 usable.

[0078] (Example 2) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that 0.2 part by mass of ytterbium fluoride powder was added to produce a composite of the negative electrode additive. In addition, it was confirmed that in the negative electrode according to Example 2, the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0079] (Example 3) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material powder was manufactured such that the solid solution amount of zinc was 3.5 parts by mass. In addition, it was confirmed that in the negative electrode according to Example 3, the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0080] (Example 4) A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material powder was manufactured such that the amount of zinc solid solution was 4.5 parts by mass. In addition, also in the negative electrode according to Example 4, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0081] (Example 5) A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode mixture was manufactured with an addition amount of zinc oxide of 0.75 parts by mass. In addition, also in the negative electrode according to Example 5, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0082] (Example 6) A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material powder was manufactured with an addition amount of zinc oxide of 1.0 parts by mass. In addition, also in the negative electrode according to Example 6, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0083] (Example 7) A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that 0.3 parts by mass of ytterbium fluoride powder was added to manufacture a composite of the negative electrode additive. In addition, also in the negative electrode according to Example 7, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0084] (Example 8) A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that 0.05 parts by mass of ytterbium fluoride powder was added to manufacture a composite of the negative electrode additive. In addition, also in the negative electrode according to Example 8, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with a composite in which ytterbium fluoride was supported on carbon black.

[0085] (Example 9) A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that the positive electrode active material powder was produced such that the amount of zinc dissolved was 3.0 parts by mass. In addition, it was confirmed that in the negative electrode according to Example 9, the surface of the hydrogen storage alloy particles was partially covered with a composite in which yttrium fluoride was supported on carbon black.

[0086] (Example 10) A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that the positive electrode active material powder was produced such that the amount of zinc dissolved was 5.0 parts by mass. In addition, it was confirmed that in the negative electrode according to Example 10, the surface of the hydrogen storage alloy particles was partially covered with a composite in which yttrium fluoride was supported on carbon black.

[0087] (Example 11) A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that the positive electrode mixture was produced with 0.25 parts by mass of zinc oxide added. In addition, it was confirmed that in the negative electrode according to Example 11, the surface of the hydrogen storage alloy particles was partially covered with a composite in which yttrium fluoride was supported on carbon black.

[0088] (Example 12) A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that the positive electrode active material powder was produced such that the amount of zinc dissolved was 3.0 parts by mass and the positive electrode mixture was produced with 1.25 parts by mass of zinc oxide added. In addition, it was confirmed that in the negative electrode according to Example 12, the surface of the hydrogen storage alloy particles was partially covered with a composite in which yttrium fluoride was supported on carbon black.

[0089] (Comparative Example 1) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that yttrium fluoride powder was not added during the production of the composite of the negative electrode additive, zinc was not dissolved during the production of the positive electrode active material powder, and zinc oxide was not added during the production of the positive electrode binder. In addition, in the negative electrode according to Comparative Example 1, it was confirmed that the surface of the hydrogen storage alloy particles was not coated with a composite in which yttrium fluoride was supported on carbon black.

[0090] (Comparative Example 2) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that yttrium fluoride powder was not added during the production of the composite of the negative electrode additive. In addition, in the negative electrode according to Comparative Example 2, it was confirmed that the surface of the hydrogen storage alloy particles was not coated with a composite in which yttrium fluoride was supported on carbon black.

[0091] (Comparative Example 3) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that zinc was not dissolved during the production of the positive electrode active material powder and zinc oxide was not added during the production of the positive electrode binder. In addition, in the negative electrode according to Comparative Example 3, it was confirmed that the surface of the hydrogen storage alloy particles was partially coated with a composite in which yttrium fluoride was supported on carbon black.

[0092] (Comparative Example 4) A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that when manufacturing the negative electrode binder, the first-stage process and the second-stage process were not separated and all the constituent materials of the negative electrode binder were mixed to prepare a negative electrode binder paste. That is, in Comparative Example 4, a composite of a negative electrode additive in which yttrium fluoride was supported on carbon black was not formed. In addition, in the negative electrode according to Comparative Example 4, it was confirmed that the surface of the hydrogen storage alloy particles was not coated with a composite in which yttrium fluoride was supported on carbon black.

[0093] 2. Evaluation of nickel-metal hydride secondary battery (1) Leakage inspection at the initial stage of the cycle test For the batteries of Examples 1 to 12 and Comparative Examples 1 to 4 that had been subjected to the initial activation treatment, in an environment at 25°C, after the battery voltage reached the maximum value with a charging current of 1.0 It, charging was performed until the voltage decreased by 10 mV. This is so-called "ΔV control charging". After charging was completed, each battery was left standing in an environment at 25°C for 30 minutes. Next, for the batteries after being left standing for 30 minutes, in an environment at 25°C, they were discharged with a discharge current of 1.0 It until the battery voltage reached 1.0 V, and then left standing for 30 minutes. One cycle of this charge-discharge was defined as one cycle, and a cycle test was performed by repeating this cycle 20 times. After this cycle test, the presence or absence of leakage was confirmed for each battery, and the number of batteries with leakage was counted. The results were shown in Table 1 as the number of batteries with initial leakage in the cycle test. Note that 100 batteries each of Examples 1 to 12 and Comparative Examples 1 to 4 were prepared, and the number of batteries with leakage among the 100 was counted. The smaller the number of leaking batteries, the better the leakage suppression effect, and thus the better the cycle life characteristics.

[0094]

Table 1

[0095] (2) Discussion (i) In the positive electrode, zinc is dissolved in the positive electrode active material, zinc oxide is included as a positive electrode additive, and in the negative electrode, a negative electrode additive composed of a composite in which ytterbium fluoride is supported on carbon black partially covers the surface of the hydrogen storage alloy particles. In nickel-metal hydride secondary batteries of Examples 1 to 12 in this mode, compared with nickel-metal hydride secondary batteries of Comparative Examples 1 to 4 in a mode where zinc is not dissolved in the positive electrode active material, zinc oxide as a positive electrode additive is not included, or the surface of the hydrogen storage alloy particles is not covered by the above-described composite in the negative electrode, the number of leaked batteries is small. From this, it can be said that in the positive electrode, zinc is dissolved in the positive electrode active material, zinc oxide is included as a positive electrode additive, and in the negative electrode, a negative electrode additive composed of a composite in which ytterbium fluoride is supported on carbon black partially covers the surface of the hydrogen storage alloy particles, thereby suppressing an increase in the internal pressure of the battery and preventing leakage at the initial stage of the charge-discharge cycle.

[0096] (ii) Comparing Example 1 and Comparative Example 4, it can be seen that the number of leaked batteries in Example 1 is smaller than that in Comparative Example 4, and Example 1 is excellent in the leakage suppression effect. In Example 1 and Comparative Example 4, the composition of the positive electrode active material, the composition of the constituent materials of the positive electrode additive, and the composition of the constituent materials of the negative electrode additive are the same. However, in Example 1, the negative electrode additive takes the form of a composite of ytterbium fluoride and carbon black and partially covers the surface of the hydrogen storage alloy particles, while in Comparative Example 4, the negative electrode additive does not take the form of a composite of ytterbium fluoride and carbon black, and the surface of the hydrogen storage alloy particles is not covered by the composite. From this, it can be said that the negative electrode additive taking the form of a composite of ytterbium fluoride and carbon black and this composite partially covering the surface of the hydrogen storage alloy particles is particularly effective in suppressing an increase in the internal pressure of the battery and suppressing leakage of the battery.

[0097] (iii) From the results of Examples 1, 2, 7, and 8 in which the addition amount of yttrium fluoride was changed, it can be seen that the liquid leakage suppression effects of Examples 1 and 2 are more excellent. Therefore, it can be said that the addition amount of yttrium fluoride is preferably 0.1 part by mass or more and 0.2 part by mass or less with respect to 100 parts by mass of the hydrogen storage alloy.

[0098] (iv) From the results of Examples 1, 3, 4, 9, and 10 in which the zinc solid solution amount was changed, it can be seen that the liquid leakage suppression effects of Examples 1, 3, and 4 are more excellent. Therefore, it can be said that the zinc solid solution amount is preferably 3.5 parts by mass or more and 4.5 parts by mass or less with respect to 100 parts by mass of nickel hydroxide.

[0099] (v) From the results of Examples 1, 5, 6, 11, and 12 in which the addition amount of zinc oxide was changed, it can be seen that the liquid leakage suppression effects of Examples 1, 5, and 6 are more excellent. Therefore, it can be said that the addition amount of zinc oxide is preferably 0.5 part by mass or more and 1.0 part by mass or less with respect to 100 parts by mass of the positive electrode active material.

Explanation of symbols

[0100] 2 Nickel-metal hydride secondary battery 22 Electrode group 24 Positive electrode 26 Negative electrode 28 Separator

Claims

1. A container and an electrode group accommodated in the container together with an alkaline electrolyte solution, The electrode group is formed by laminating a positive electrode containing a positive electrode active material mixture and a negative electrode containing a negative electrode active material mixture via a separator, The positive electrode active material mixture contains nickel hydroxide in which zinc is dissolved as a positive electrode active material and zinc oxide as a positive electrode additive, The negative electrode active material mixture contains hydrogen storage alloy particles and a negative electrode additive, The negative electrode additive is a composite in which yttrium fluoride is supported on carbon black, The composite covers a part of the surface of the hydrogen storage alloy particles, a nickel-metal hydride secondary battery.

2. The zinc is dissolved in an amount of 3.5 parts by mass or more and 4.5 parts by mass or less with respect to 100 parts by mass of the nickel hydroxide, The zinc oxide is added in an amount of 0.5 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, The yttrium fluoride is 0.1 parts by mass or more and 0.2 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy, the nickel-metal hydride secondary battery according to Claim 1.

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