Nickel-metal hydride secondary batteries

Abstract

A nickel-hydrogen secondary battery (2) comprises an outer can (10) and an electrode group (22) housed in the outer can (10) together with an alkaline electrolyte. The electrode group (22) is formed by overlapping a positive electrode (24) containing a positive electrode mixture and a negative electrode (26) containing a negative electrode mixture via a separator (28). The positive electrode mixture comprises nickel hydroxide solid-dissolved with zinc as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture comprises hydrogen storage alloy particles and a negative electrode additive. The negative electrode additive is a composite of yttrium fluoride loaded on carbon black, and the composite covers a portion of the surface of the hydrogen storage alloy particles.

Description

Technical Field

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

[0002] As a type of alkaline secondary battery, a nickel-hydrogen secondary battery is known. The capacity of the nickel-hydrogen secondary battery is higher than that of the nickel-cadmium secondary battery and the environmental safety is also excellent. Therefore, the nickel-hydrogen secondary battery is gradually used in various portable devices and various machines such as hybrid electric vehicles, and its use is becoming more and more extensive. With the expansion of such uses, it is expected that the nickel-hydrogen secondary battery will have higher performance. One of the performances that should be improved in such nickel-hydrogen secondary batteries is the cycle life characteristics. If the cycle life characteristics are improved and the number of times the battery can be repeatedly charged and discharged is greater, the convenience of the nickel-hydrogen secondary battery will be higher.

[0003] The main reason for the depletion of the cycle life of nickel-metal hydride secondary batteries is that during the repeated charge and discharge process, the alkaline electrolyte becomes unevenly distributed or depleted within the battery, thereby hindering the contact between the alkaline electrolyte and the positive and negative electrodes, and preventing the battery reaction from proceeding. For example, the positive electrode expands due to the battery reaction, compressing the diaphragm, causing the alkaline electrolyte to be removed from the diaphragm. As a result, the alkaline electrolyte is unevenly distributed in the non-diaphragm area of ​​the battery, causing the diaphragm to dry out, a phenomenon known as dry-out. This prevents discharge and exhausts the battery life.

[0004] In order to suppress this undesirable situation and extend the cycle life, a countermeasure is taken to add zinc compounds to the positive electrode (for example, refer to Japanese Patent Publication No. 04-137368). When the zinc compound is added, the positive electrode expansion can be suppressed, the alkaline electrolyte can be taken away from the separator, and the battery cycle life can be improved.

[0005] However, the reality is that simply suppressing positive electrode expansion by adding the zinc compound as described above cannot fully meet the recent demand for improved battery cycle life. Therefore, in order to suppress the uneven distribution of the alkaline electrolyte within the battery as described above, the injection amount of the alkaline electrolyte is increased to seek to improve the cycle life characteristics.

[0006] Incidentally, when a nickel-metal hydride secondary battery reaches an overcharged state, a reaction occurs in which oxygen is generated from the positive electrode, causing the internal pressure of the battery to rise. This increase in internal pressure triggers the activation of the battery's safety valve, releasing oxygen and discharging the alkaline electrolyte to the outside. This causes the alkaline electrolyte to dry up and the battery life to end. However, in nickel-metal hydride secondary batteries, a reaction also occurs in which the negative electrode absorbs the oxygen generated during overcharge. In other words, nickel-metal hydride secondary batteries have a function that can suppress the increase in internal pressure caused by oxygen. Thus, conventional nickel-metal hydride secondary batteries can suppress the increase in internal pressure, thereby preventing the reduction in battery life characteristics caused by the discharge and drying up of the alkaline electrolyte as the safety valve activates.

[0007] Here, the oxygen absorption reaction in the negative electrode occurs at the three-phase interface between the solid phase, gas phase, and liquid phase. To form a good three-phase interface, a certain amount of residual space is required within the battery. However, as mentioned above, when a large amount of alkaline electrolyte is injected into the battery to suppress the degradation of cycle life characteristics caused by uneven distribution of the alkaline electrolyte, insufficient residual space exists, and a good three-phase interface cannot be formed. Therefore, the oxygen absorption reaction cannot proceed smoothly, oxygen cannot be fully absorbed, and the internal pressure of the battery increases. As a result, the battery's safety valve activates, and the alkaline electrolyte is discharged to the outside, causing so-called leakage. If leakage occurs, the alkaline electrolyte dries up within the battery, resulting in the undesirable situation of premature battery life. In other words, even if a large amount of alkaline electrolyte is injected, the cycle life characteristics may be reduced. Leakage is particularly prone to occur in the early stages of the charge and discharge cycle. Specifically, during the initial charge-discharge cycle, alkaline electrolyte may not fully permeate the electrode assembly, especially the separator, and may remain on the upper portion of the electrode assembly. Furthermore, insufficient activation of the battery may prevent the oxygen absorption reaction from proceeding smoothly. Consequently, the battery's internal pressure can easily rise, triggering the safety valve to discharge the alkaline electrolyte remaining on the upper portion of the electrode assembly, causing leakage.

[0008] Therefore, there is a demand for the development of a nickel-hydrogen secondary battery that can suppress the occurrence of leakage, particularly the occurrence of leakage in the initial stage of the charge and discharge cycle, even when a large amount of alkaline electrolyte is injected. Summary of the Invention

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a nickel-hydrogen secondary battery having excellent cycle life characteristics.

[0010] According to the present invention, a nickel-metal hydride secondary battery is provided, comprising a container and an electrode group housed in the container together with an alkaline electrolyte, the electrode group being formed by overlapping a positive electrode comprising a positive electrode mixture and a negative electrode comprising a negative electrode mixture via a separator, the positive electrode mixture comprising nickel hydroxide having a zinc solid solution as a positive electrode active material and zinc oxide as a positive electrode additive, the negative electrode mixture comprising hydrogen storage alloy particles and a negative electrode additive, the negative electrode additive being a composite of yttrium fluoride supported on carbon black, the composite covering a portion of the surface of the hydrogen storage alloy particles.

[0011] The nickel-hydrogen secondary battery of the present invention comprises a container and an electrode assembly housed within the container along with an alkaline electrolyte. The electrode assembly is formed by stacking a positive electrode comprising a positive electrode mixture and a negative electrode comprising a negative electrode mixture, with a separator interposed therebetween. The positive electrode mixture comprises nickel hydroxide having a zinc solid solution as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture comprises hydrogen storage alloy particles and a negative electrode additive, wherein the negative electrode additive is a composite of yttrium fluoride supported on carbon black, the composite covering a portion of the surface of the hydrogen storage alloy particles. This configuration allows the nickel-hydrogen secondary battery of the present invention to suppress increases in internal battery pressure and prevent leakage during the initial stages of the charge and discharge cycle, resulting in excellent cycle life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a partially cutaway perspective view of a nickel-hydrogen secondary battery according to one embodiment. DETAILED DESCRIPTION

[0013] Hereinafter, a nickel-hydrogen secondary battery (hereinafter referred to as a battery) 2 according to one embodiment will be described with reference to the drawings.

[0014] The battery 2 is, for example, a cylindrical battery of AA size. Figure 1 As shown, the battery 2 has an outer can 10 as a container, which is in the shape of a bottomed cylinder with an open top. The outer can 10 is conductive, and its bottom wall 35 functions as a negative terminal. A sealing body 11 is fixed to the opening of the outer can 10. The sealing body 11 includes a cover plate 14 and a positive terminal 20, which not only seals the outer can 10 but also provides the positive terminal 20. The cover plate 14 is a circular plate-shaped member with conductivity. The cover plate 14 and an annular insulating gasket 12 surrounding the cover plate 14 are arranged in the opening of the outer can 10. The insulating gasket 12 is fixed to the opening edge 37 of the outer can 10 by riveting the opening edge 37 of the outer can 10. That is, the cover plate 14 and the insulating gasket 12 cooperate with each other to hermetically seal the opening of the outer can 10.

[0015] Here, the cover plate 14 has a central through-hole 16 in the center, and a rubber valve body 18 is disposed on the outer surface of the cover plate 14, blocking the central through-hole 16. Also on the outer surface of the cover plate 14 is a flanged cylindrical metal positive electrode terminal 20, electrically connected to the valve body 18 so as to cover the valve body 18. This positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. Furthermore, a vent hole (not shown) is opened in the positive electrode terminal 20.

[0016] Normally, central through-hole 16 is hermetically sealed by valve body 18. However, when gas is generated within outer can 10 and the internal pressure increases, valve body 18 is compressed by the internal pressure, causing central through-hole 16 to open. Consequently, gas is discharged from outer can 10 through central through-hole 16 and a vent (not shown) in positive electrode terminal 20. In other words, central through-hole 16, valve body 18, and positive electrode terminal 20 form a safety valve for the battery.

[0017] The outer can 10 houses an electrode group 22. The electrode group 22 includes a strip-shaped positive electrode 24, a negative electrode 26, and a separator 28. Specifically, the positive electrode 24 and the negative electrode 26 are wound into a spiral shape with the separator 28 interposed therebetween. That is, the positive electrode 24 and the negative electrode 26 overlap with each other via the separator 28. The outermost periphery of the electrode group 22 is formed by a portion (the outermost peripheral portion) of the negative electrode 26 and contacts 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.

[0018] Inside the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the cover plate 14. Specifically, one end of the positive electrode lead 30 is connected to the positive electrode 24, and the other end is connected to the cover plate 14. Thus, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. Furthermore, a circular upper insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the upper insulating member 32. Furthermore, a circular lower insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

[0019] Furthermore, a predetermined amount of alkaline electrolyte (not shown) is injected into the outer can 10. The alkaline electrolyte impregnates the electrode group 22 and is primarily retained in the separator 28. The electrochemical reaction (charge-discharge reaction) during the charge-discharge reaction between the positive electrode 24 and the negative electrode 26 occurs in the alkaline electrolyte. As the alkaline electrolyte, an aqueous solution containing at least one of KOH, NaOH, and LiOH as a solute is preferably used.

[0020] Materials for the separator 28 include, for example, polyamide fiber nonwoven fabrics imparted with hydrophilic functional groups, and polyolefin fiber nonwoven fabrics such as polyethylene or polypropylene imparted with hydrophilic functional groups. Specifically, nonwoven fabrics primarily composed of polyolefin fibers that have been sulfonated to impart sulfonic acid groups are preferred. Sulfonic acid groups are imparted to the nonwoven fabric by treating it with a sulfuric acid-containing acid, such as sulfuric acid or fuming sulfuric acid. Batteries using separators containing fibers with sulfonic acid groups exhibit excellent self-discharge performance.

[0021] 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. For example, foamed nickel can be used as the positive electrode core material.

[0022] The positive electrode mixture contains a positive electrode active material, a positive electrode additive, and a binder. The binder not only bonds the positive electrode active material and the positive electrode additive to each other, but also bonds the positive electrode active material and the positive electrode additive to the positive electrode core material. Examples of binders include carboxymethyl cellulose, methyl cellulose, PTFE (polytetrafluoroethylene) dispersion, and HPC (hydroxypropyl cellulose) dispersion.

[0023] Nickel hydroxide is used as the positive electrode active material. The nickel hydroxide is in powdered form. Specifically, nickel hydroxide powder, which is an aggregate of nickel hydroxide particles, is used. The nickel hydroxide particles are preferably high-valent nickel hydroxide particles.

[0024] The nickel hydroxide particles used are those containing a solid solution of Zn. Zn as the solid solution component contributes to suppressing the expansion of the positive electrode.

[0025] 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 relative to 100 parts by mass of nickel hydroxide.

[0026] The nickel hydroxide particles described above preferably use nickel hydroxide particles in which Co is also solid-dissolved. Co as the solid-dissolved component helps to improve the conductivity between the positive electrode active material particles and improve the charge acceptance. Here, when the content of solid-dissolved Co in the nickel hydroxide particles is small, the effect of improving the charge acceptance is small. On the contrary, if the content is too much, the grain growth of the nickel hydroxide particles is hindered. Therefore, the nickel hydroxide particles preferably use nickel hydroxide particles in a form containing 0.5% by mass or more and 5.0% by mass or less of Co as a solid-dissolved component.

[0027] The nickel hydroxide particles are preferably coated with a surface layer containing a cobalt compound. The surface layer is preferably a high-valent cobalt compound layer containing a high-valent cobalt compound having a valence of tri or more.

[0028] The high-valent cobalt compound layer has excellent conductivity and forms a conductive network. As the high-valent cobalt compound layer, a layer containing a cobalt compound such as trivalent or higher-valent cobalt oxyhydroxide (CoOOH) is preferably used.

[0029] The positive electrode active material can be prepared, for example, as follows.

[0030] First, nickel sulfate and zinc sulfate are weighed to achieve a predetermined composition to prepare a mixed aqueous solution. An aqueous sodium hydroxide solution is slowly added to the mixed aqueous solution to cause a reaction, thereby precipitating nickel hydroxide particles composed mainly of nickel hydroxide and containing zinc as a solid solution. In the case where cobalt is also dissolved in the solution, nickel sulfate, zinc sulfate, and cobalt sulfate are weighed to achieve a predetermined composition to prepare a mixed aqueous solution. An aqueous sodium hydroxide solution is slowly added to the mixed aqueous solution while stirring the obtained mixed aqueous solution to cause a reaction, thereby precipitating nickel hydroxide particles composed mainly of nickel hydroxide and containing zinc and cobalt as solid solutions.

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

[0032] First, the nickel hydroxide particles having zinc solid solution obtained as above, or the nickel hydroxide particles having zinc and cobalt solid solution obtained, are put into an ammonia aqueous solution, and an aqueous solution of cobalt sulfate is added to the aqueous solution. Thus, intermediate particles having a cobalt hydroxide layer are formed, which have nickel hydroxide particles as cores and cobalt hydroxide precipitated on the surface of the cores. The obtained intermediate particles are put into a 25% by mass sodium hydroxide aqueous solution. Here, when the mass of the aggregate of the intermediate particles having a cobalt hydroxide layer, i.e., the mass of the intermediate powder, is recorded as P and the mass of the sodium hydroxide aqueous solution is recorded as Q, their mass ratio is P:Q=1:10. In addition, the sodium hydroxide aqueous 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] The heat-treated intermediate powder is then washed with water and dried at 50°C to 80°C to obtain a positive electrode active material powder comprising nickel hydroxide particles whose surfaces are covered with high-valent cobalt oxide. The heat treatment converts the cobalt hydroxide on the surface of the intermediate particles into a highly conductive high-valent cobalt compound (such as cobalt oxyhydroxide) with a valence greater than three.

[0034] Next, zinc oxide is used as a positive electrode additive. This zinc oxide is in powdered form. In other words, a collection of zinc oxide particles, i.e., zinc oxide powder, is used. The amount of zinc oxide powder added is preferably 0.5 parts by mass or more and 1.0 parts by mass or less per 100 parts by mass of the positive electrode active material powder.

[0035] Furthermore, among the positive electrode additives, yttrium oxide or niobium oxide is preferably added as needed.

[0036] Next, the positive electrode 24 can be produced, for example, as follows.

[0037] First, a positive electrode additive, water, and a binder are added to the aggregate of positive electrode active material particles obtained above, i.e., the positive electrode active material powder, and kneaded to form a positive electrode mixture slurry. The resulting positive electrode mixture slurry is then filled into, for example, a nickel foam and dried. After drying, the nickel foam filled with nickel hydroxide particles is rolled and then cut. This produces a positive electrode 24 containing the positive electrode mixture.

[0038] Next, the negative electrode 26 will be described.

[0039] The negative electrode 26 includes a conductive negative electrode core formed in a strip shape, and a negative electrode mixture is held in the negative electrode core.

[0040] The negative electrode core is a sheet of metal material with distributed through holes, such as a perforated metal sheet. The negative electrode mixture is not only filled in the through holes of the negative electrode core, but also forms a layer and is retained on both sides of the negative electrode core.

[0041] The negative electrode mixture includes hydrogen storage alloy particles capable of storing and releasing hydrogen as a negative electrode active material, a negative electrode additive, a binder, and a negative electrode auxiliary agent.

[0042] The binder serves to bond the hydrogen storage alloy particles, the negative electrode additive, etc. to each other and to the negative electrode core. The binder is not particularly limited, and examples of binders commonly used in nickel-hydrogen secondary batteries include hydrophilic or hydrophobic polymers and carboxymethyl cellulose.

[0043] In addition, as the negative electrode auxiliary agent, styrene butadiene rubber, sodium polyacrylate, etc. can be used.

[0044] The type of hydrogen storage alloy in the hydrogen storage alloy particles is not particularly limited, but a rare earth-Mg-Ni hydrogen storage alloy containing a rare earth element, Mg, and Ni is preferably used. More preferably, a hydrogen storage alloy having a composition represented by the following general formula (I) is used.

[0045] Ln 1-x Mg x Ni y-z Al z …(I)

[0046] 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 respectively satisfy the relationship represented by 0.05≤x≤0.30, 2.8≤y≤3.8 and 0.05≤z≤0.30.

[0047] The hydrogen storage alloy particles can be obtained, for example, as follows.

[0048] First, metallic raw materials are weighed and mixed to achieve a desired composition. The mixture is then melted in, for example, a high-frequency induction melting furnace to form an ingot. The resulting ingot is then heat treated at 900-1200°C in an inert atmosphere for 5-24 hours. The ingot is then mechanically pulverized in an inert atmosphere and sieved and classified to obtain hydrogen storage alloy particles of the desired size.

[0049] The particle size of the hydrogen storage alloy particles is not particularly limited, but preferably has an average particle size of 55.0 to 70.0 μm. In this specification, the average particle size refers to the average particle size at 50% cumulative mass, and is determined using a particle size distribution analyzer and laser diffraction / scattering.

[0050] The negative electrode additive is a composite of yttrium fluoride and carbon black as a conductive material. Specifically, it is a composite of yttrium fluoride supported on carbon black.

[0051] Yttrium fluoride can be used in powdered form. In other words, an aggregate of yttrium fluoride particles, i.e., yttrium fluoride powder, can be used. Yttrium fluoride particles preferably have an average particle size of 1 μm to 7 μm.

[0052] As the form of carbon black, powdered carbon black composed of aggregates of primary particles can be 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 to 100 μm.

[0053] Furthermore, hollow carbon black having a primary particle having a hollow shell structure is preferably used as carbon black. This hollow carbon black has better electrical conductivity than ordinary carbon black.

[0054] The composite of yttrium fluoride and carbon black as a negative electrode additive can be prepared, for example, as follows.

[0055] Yttrium fluoride powder, carbon black powder, sodium polyacrylate, carboxymethyl cellulose and water are kneaded to form a paste. In the resulting paste, a composite of yttrium fluoride supported on carbon black is formed.

[0056] Next, the negative electrode 26 can be produced, for example, as follows.

[0057] First, the aggregate of hydrogen storage alloy particles obtained as described above, i.e., hydrogen storage alloy powder, is added to a paste containing a composite of yttrium fluoride supported on carbon black and kneaded. Thereby, the above-mentioned composite is partially covered on the surface of the hydrogen storage alloy particles. Then, by further adding styrene-butadiene rubber powder and water to the above-mentioned paste and kneading them, a negative electrode mixture paste is prepared. The obtained negative electrode mixture paste is applied to the negative electrode core and dried. After drying, the negative electrode core retaining the hydrogen storage alloy powder, negative electrode additives, etc. is rolled as a whole to increase the filling density of the hydrogen storage alloy, thereby obtaining an intermediate product of the negative electrode. Next, the intermediate product of the negative electrode is cut into a specified shape. In this way, the negative electrode 26 is manufactured.

[0058] The positive electrode 24 and the negative electrode 26 produced as described above are wound in a spiral shape with the separator 28 interposed therebetween, thereby forming the electrode group 22 .

[0059] The electrode group 22 thus obtained is housed in an outer can 10. A predetermined amount of alkaline electrolyte is then injected into the outer can 10. The outer can 10 containing the electrode group 22 and alkaline electrolyte is then sealed with a sealer 11 equipped with a positive electrode terminal 20, thereby obtaining the battery 2 of the present invention. The resulting battery 2 is subjected to an initial activation treatment to prepare it for use.

[0060] [Example]

[0061] 1. Battery Manufacturing

[0062] (Example 1)

[0063] (1) Manufacturing of positive electrode

[0064] Nickel sulfate, zinc sulfate, and cobalt sulfate were weighed to obtain 4.0 parts by mass of zinc and 1.0 parts by mass of cobalt per 100 parts by mass of nickel hydroxide. This was then added to a 1 mol / L aqueous sodium hydroxide solution containing ammonium ions to prepare a mixed aqueous solution. While stirring the resulting mixed aqueous solution, a 1 mol / L aqueous sodium hydroxide solution was slowly added to the mixed aqueous solution to allow the reaction to proceed. During this reaction, the pH was stabilized at 11, thereby producing matrix particles composed primarily of nickel hydroxide with zinc and cobalt solid-dissolved therein.

[0065] The resulting matrix particles were washed three times with 10-fold amounts of pure water, then dehydrated and dried. Furthermore, the particle size of the resulting matrix particles was measured using a laser diffraction / scattering particle size distribution analyzer. The results showed that the average particle size of the matrix particles at 50% cumulative mass was 8 μm.

[0066] Next, the resulting matrix particles were placed in an aqueous solution of cobalt sulfate. While stirring the aqueous solution, a 1 mol / L aqueous sodium hydroxide solution was slowly added dropwise to allow the reaction to proceed. A precipitate was generated while maintaining the pH at 11 during the reaction. The generated precipitate was then filtered, separated, washed with pure water, and vacuum-dried. This yielded intermediate product particles having a 5% by mass cobalt hydroxide layer on the surface of the matrix particles. The thickness of the cobalt hydroxide layer was approximately 0.1 μm.

[0067] Next, the intermediate product particles were placed in a 25% by mass sodium hydroxide aqueous solution. Here, the mass of the aggregate of the intermediate product particles, i.e., the powder, is denoted by P, and the mass of the sodium hydroxide aqueous solution is denoted by Q. The mass ratio was set to P:Q = 1:10. The sodium hydroxide aqueous solution to which the intermediate product powder was added was then heated at a constant temperature of 85°C for 8 hours while being stirred.

[0068] The intermediate product powder subjected to the above heat treatment was washed with pure water and dried with warm air at 65°C. This yielded a positive electrode active material powder, which was an aggregate of positive electrode active material particles having a surface layer containing a high-valent cobalt oxide on the surface of matrix particles containing a solid solution of Zn and Co.

[0069] Next, 0.5 parts by mass of yttrium oxide powder, 0.3 parts by mass of niobium oxide powder, 0.5 parts 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 to 100 parts by mass of the positive electrode active material powder obtained above, and the mixture was kneaded to prepare a slurry of the positive electrode mixture.

[0070] Then, the positive electrode mixture slurry was filled into the sheet-like nickel foam as the positive electrode core material. Here, the nickel foam used had a surface density (basis weight) of about 350 g / m 2 , nickel foam with a porosity of 95% and a thickness of 1.3mm.

[0071] After the nickel foam filled with the positive electrode mixture slurry is dried, the nickel foam filled with the positive electrode mixture is heated to a density of 3.0 g / cm3 of the positive electrode active material calculated by the following formula (II): 3 After adjusting and rolling in a manner, it is cut into a specified size to obtain a positive electrode 24 for AA size.

[0072] Filling density of positive electrode active material [g / cm 3 = Mass of positive electrode mixture [g] ÷ (Electrode height [cm] × Electrode length [cm] × Electrode thickness [cm] - Mass of nickel foam [g] ÷ Density of nickel [g / cm 3 ])…(II)

[0073] (2) Manufacturing of negative electrode

[0074] After mixing the metal materials of La, Sm, Mg, Ni, and Al at a predetermined molar ratio, the mixture is placed in a high-frequency induction melting furnace to be melted, and the mixture is cooled to produce an ingot.

[0075] The ingot was then subjected to a heat treatment at 1000°C in an argon atmosphere for 10 hours for homogenization, followed by mechanical pulverization in an argon atmosphere to obtain a rare earth-Mg-Ni hydrogen storage alloy powder. The particle size distribution of the resulting rare earth-Mg-Ni hydrogen storage alloy powder was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac SRA-150). The results showed an average particle size of 65 μm at 50% cumulative mass.

[0076] The composition of the hydrogen storage alloy powder was analyzed by high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES). The results showed that the composition was La 0.27 Sm 0.63 Mg 0.10 Ni 3.33 Al 0.17 Furthermore, X-ray diffraction measurement (XRD measurement) of the hydrogen storage alloy powder revealed that the crystal structure was a so-called superlattice structure of the A2B7 type (Ce2Ni7 type).

[0077] Next, a negative electrode mixture was manufactured. First, as a first-stage process, 0.1 parts by mass of an aggregate of yttrium fluoride particles having an average particle size of 1 μm, i.e., yttrium fluoride powder, and 0.50 parts by mass of hollow carbon black having a hollow shell structure (specifically, Ketjen Black (registered trademark) manufactured by Lion Specialty Chemicals Co., Ltd. was used). As a physical property value of the hollow carbon black, the specific surface area measured by the BET method was 1270 m 2 A powder (having a porosity of 80%, an average primary particle size of 34.0 nm, and an aggregate length of 10 μm) was mixed with 0.30 parts by mass of sodium polyacrylate powder, 0.05 parts by mass of carboxymethyl cellulose powder, and 20 parts by mass of water at 25°C. This prepared a first paste. A composite of the negative electrode additive, yttrium fluoride supported on carbon black, was formed in the resulting first paste.

[0078] Next, as a second step, 100 parts by mass of the hydrogen storage alloy powder obtained above was added to the first paste and kneaded, thereby partially covering the surface of the hydrogen storage alloy particles with the composite of yttrium fluoride supported on carbon black.

[0079] Furthermore, 0.5 parts by mass of styrene-butadiene rubber powder and 15 parts by mass of water were added to the first paste, and the mixture was kneaded at 25° C. to prepare a negative electrode mixture paste.

[0080] The negative electrode mixture paste was evenly applied to both sides of a punched metal sheet, serving as the negative electrode core, at a constant thickness. The through-holes were also filled with the negative electrode mixture paste. The punched metal sheet was a 50μm-thick iron strip with numerous through-holes distributed throughout its thickness. Its surface was nickel-plated.

[0081] After the negative electrode mixture paste is dried, the packing density of the hydrogen storage alloy in the punched metal sheet holding the hydrogen storage alloy is calculated by the following formula (III) to be 6.4 g / cm 3 The conditions were adjusted and rolled to obtain an intermediate product of the negative electrode.

[0082] The 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 punched metal sheet [g] ÷ density of iron [g / cm 3 ])…(III)

[0083] The intermediate negative electrode product was then cut into a predetermined size to obtain an AA-size negative electrode 26. Furthermore, a separate sample was taken from the intermediate negative electrode product and observed using a scanning electron microscope. The results confirmed that the surfaces of the hydrogen storage alloy particles were partially covered with a composite of yttrium fluoride supported on carbon black.

[0084] (3) Assembly of nickel-hydrogen secondary batteries

[0085] The positive electrode 24 and the negative electrode 26 obtained above were wound into a spiral shape with the separator 28 interposed therebetween to produce the electrode group 22. The separator 28 used in the production of the electrode group 22 was a sulfonated polypropylene fiber nonwoven fabric with a thickness of 0.1 mm (basic weight 40 g / m2). 2 ).

[0086] On the other hand, an aqueous solution containing KOH, NaOH, and LiOH as solutes, namely an alkaline electrolyte, was prepared. The mass mixing ratio of KOH, NaOH, and LiOH in this alkaline electrolyte was KOH:NaOH:LiOH=4:5:1, and the specific gravity was 1.31.

[0087] Next, the electrode assembly 22 was placed in a bottomed cylindrical outer can 10, and 2.0 g of the prepared alkaline electrolyte was injected. The opening of the outer can 10 was then sealed with a sealer 11, thereby assembling an AA-size battery 2 with a nominal capacity of 2000 mAh.

[0088] (4) Initial activation treatment

[0089] The resulting battery 2 was charged at a temperature of 25°C for 16 hours at a charging current of 1.0 It, then discharged at a discharge current of 1.0 It until the battery voltage reached 1.0 V. This charge-discharge cycle was repeated three times. This initial activation treatment was performed, bringing the battery 2 to a usable state.

[0090] (Example 2)

[0091] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that 0.2 parts by mass of yttrium fluoride powder was added to produce a composite of the negative electrode additive. Furthermore, in the negative electrode of Example 2, it was confirmed that the surfaces of the hydrogen storage alloy particles were partially covered with the composite of yttrium fluoride supported on carbon black.

[0092] (Example 3)

[0093] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the solid solution amount of zinc was changed to 3.5 parts by mass to produce the positive electrode active material powder. Furthermore, in the negative electrode of Example 3, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0094] (Example 4)

[0095] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the solid solution amount of zinc was changed to 4.5 parts by mass to produce the positive electrode active material powder. Furthermore, in the negative electrode of Example 4, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0096] (Example 5)

[0097] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the amount of zinc oxide added was changed to 0.75 parts by mass. In the negative electrode of Example 5, it was also confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0098] (Example 6)

[0099] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the amount of zinc oxide added was changed to 1.0 part by mass to produce the positive electrode active material powder. In the negative electrode of Example 6, it was also confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0100] (Example 7)

[0101] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that 0.3 parts by mass of yttrium fluoride powder was added to produce a composite of the negative electrode additive. In the negative electrode of Example 7, it was also confirmed that the surfaces of the hydrogen storage alloy particles were partially covered with the composite of yttrium fluoride supported on carbon black.

[0102] (Example 8)

[0103] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that 0.05 parts by mass of yttrium fluoride powder was added to produce a composite of the negative electrode additive. In the negative electrode of Example 8, it was also confirmed that the surfaces of the hydrogen storage alloy particles were partially covered with the composite of yttrium fluoride supported on carbon black.

[0104] (Example 9)

[0105] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the solid solution amount of zinc was changed to 3.0 parts by mass to produce the positive electrode active material powder. Furthermore, in the negative electrode of Example 9, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0106] (Example 10)

[0107] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the solid solution amount of zinc was changed to 5.0 parts by mass to produce the positive electrode active material powder. In the negative electrode of Example 10, it was also confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0108] (Example 11)

[0109] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the amount of zinc oxide added was changed to 0.25 parts by mass. In the negative electrode of Example 11, it was also confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0110] (Example 12)

[0111] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that the solid solution amount of zinc was changed to 3.0 parts by mass to produce the positive electrode active material powder, and the added amount of zinc oxide was changed to 1.25 parts by mass to produce the positive electrode mixture. Furthermore, in the negative electrode of Example 12, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0112] (Comparative Example 1)

[0113] A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that yttrium fluoride powder was not added to the composite formula for the negative electrode additive, zinc was not dissolved in the positive electrode active material powder, and zinc oxide was not added to the positive electrode mixture. Furthermore, in the negative electrode of Comparative Example 1, it was confirmed that the surfaces of the hydrogen storage alloy particles were not covered by the composite of yttrium fluoride supported on carbon black.

[0114] (Comparative Example 2)

[0115] A nickel-hydrogen secondary battery was produced in the same manner as in Example 1, except that yttrium fluoride powder was not added when producing the negative electrode additive composite. In the negative electrode of Comparative Example 2, it was confirmed that the surfaces of the hydrogen storage alloy particles were not covered with the composite of yttrium fluoride supported on carbon black.

[0116] (Comparative Example 3)

[0117] A nickel-metal hydride secondary battery was produced in the same manner as in Example 1, except that zinc was not dissolved in the positive electrode active material powder and zinc oxide was not added in the positive electrode mixture. Furthermore, in the negative electrode of Comparative Example 3, it was confirmed that the surface of the hydrogen storage alloy particles was partially covered with the composite of yttrium fluoride supported on carbon black.

[0118] (Comparative Example 4)

[0119] A nickel-metal hydride secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode mixture was prepared by mixing all the constituent materials of the negative electrode mixture rather than performing the first and second steps separately. In other words, in Comparative Example 4, no composite of the negative electrode additive, comprising yttrium fluoride supported on carbon black, was formed. Furthermore, in the negative electrode of Comparative Example 4, it was confirmed that the surfaces of the hydrogen storage alloy particles were not covered with the composite of yttrium fluoride supported on carbon black.

[0120] 2. Evaluation of nickel-hydrogen secondary batteries

[0121] (1) Leakage inspection at the initial stage of cycle test

[0122] Batteries from Examples 1 to 12 and Comparative Examples 1 to 4 that had undergone initial activation were charged at 25°C at a charge current of 1.0 It until the battery voltage reached its maximum value and then dropped by 10 mV, a process known as -ΔV controlled charging. After charging, each battery was allowed to stand at 25°C for 30 minutes. Next, the batteries, which had been allowed to stand for 30 minutes, were discharged at 25°C at a discharge current of 1.0 It until the battery voltage reached 1.0 V, and then allowed to stand for 30 minutes. This charge-discharge cycle was considered one cycle, and a cycle test was conducted in which this cycle was repeated 20 times. After the cycle test, each battery was inspected for leakage, and the number of batteries experiencing leakage was counted. The results are shown in Table 1 as the number of batteries experiencing leakage during the initial stage of the cycle test. Furthermore, 100 batteries from each of Examples 1 to 12 and Comparative Examples 1 to 4 were prepared, and the number of batteries experiencing leakage was counted. The smaller the number of leaking blocks, the better the leakage suppression effect is, and thus the better the cycle life characteristics are.

[0123] [Table 1]

[0124]

[0125] (2) Investigation

[0126] (i) The nickel-metal hydride secondary batteries of Examples 1 to 12, in which the positive electrode active material contained zinc dissolved in a solid solution and zinc oxide as a positive electrode additive, and the negative electrode additive, consisting of a composite of yttrium fluoride supported on carbon black, partially covered the surface of the hydrogen storage alloy particles in the negative electrode, showed fewer leaking batteries than the nickel-metal hydride secondary batteries of Comparative Examples 1 to 4, in which the positive electrode active material did not contain zinc dissolved in a solid solution, did not contain zinc oxide as a positive electrode additive, or the surface of the hydrogen storage alloy particles in the negative electrode were not covered with the composite. This suggests that by dissolving zinc dissolved in a solid solution and containing zinc oxide as a positive electrode additive in the positive electrode active material, and partially covering the surface of the hydrogen storage alloy particles in the negative electrode with a composite of yttrium fluoride supported on carbon black, the increase in battery internal pressure can be suppressed, preventing leakage in the initial stages of the charge and discharge cycle.

[0127] (ii) Comparing Example 1 with Comparative Example 4, it can be seen that the number of leaking blocks in Example 1 is less than that in Comparative Example 4, indicating that Example 1 has a superior leakage suppression effect. While the compositions of the positive electrode active material, the positive electrode additive, and the negative electrode additive are identical in Example 1 and Comparative Example 4, the negative electrode additive in Example 1 is in the form of a composite of yttrium fluoride and carbon black, partially covering the surface of the hydrogen storage alloy particles. In contrast, in Comparative Example 4, the negative electrode additive is not in the form of a composite of yttrium fluoride and carbon black, and the surface of the hydrogen storage alloy particles is not covered by the composite. This suggests that the use of a composite of yttrium fluoride and carbon black as a negative electrode additive, with the composite partially covering the surface of the hydrogen storage alloy particles, is particularly effective in suppressing increases in battery internal pressure and suppressing battery leakage.

[0128] (iii) From the results of Examples 1, 2, 7, and 8 in which the amount of yttrium fluoride added was changed, it can be seen that Examples 1 and 2 have a better leakage suppression effect. Therefore, it can be said that the amount of yttrium fluoride added is preferably not less than 0.1 parts by mass and not more than 0.2 parts by mass relative to 100 parts by mass of the hydrogen storage alloy.

[0129] (iv) From the results of Examples 1, 3, 4, 9, and 10 in which the amount of zinc solid solution was changed, it can be seen that Examples 1, 3, and 4 have a more excellent leakage suppression effect. Therefore, it can be said that the amount of zinc solid solution is preferably 3.5 parts by mass or more and 4.5 parts by mass or less relative to 100 parts by mass of nickel hydroxide.

[0130] (v) From the results of Examples 1, 5, 6, 11, and 12 in which the amount of zinc oxide added was changed, it can be seen that Examples 1, 5, and 6 have a more excellent leakage suppression effect. Therefore, it can be said that the amount of zinc oxide added is preferably not less than 0.5 parts by mass and not more than 1.0 parts by mass relative to 100 parts by mass of the positive electrode active material.

Claims

1. A nickel-hydrogen secondary battery comprising a container (10), and an electrode group (22) housed in the container (10) together with an alkaline electrolyte, characterized in that: The electrode group (22) is formed by stacking a positive electrode (24) containing a positive electrode mixture and a negative electrode (26) containing a negative electrode mixture via a separator (28). The positive electrode mixture includes nickel hydroxide solid-dissolved with zinc as a positive electrode active material and zinc oxide as a positive electrode additive. The negative electrode mixture comprises hydrogen storage alloy particles and negative electrode additives, The negative electrode additive is a composite of yttrium fluoride loaded on carbon black. The composite covers a portion of the surface of the hydrogen storage alloy particle, The zinc is solid-solved in an amount of 3.5 parts by mass or more and 4.5 parts by mass or less relative 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 relative to 100 parts by mass of the positive active material. The yttrium fluoride is contained in an amount of 0.1 parts by mass or more and 0.2 parts by mass or less relative to 100 parts by mass of the hydrogen storage alloy. The hydrogen storage alloy has a composition shown in the following general formula (I): Ln 1-x Mg x Ni y-z Al z ...(I) 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 respectively satisfy the relationship represented by 0.05≤x≤0.30, 2.8≤y≤3.8 and 0.05≤z≤0.30.

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