JP6608558B1 - Nickel metal hydride secondary battery negative electrode active material and nickel metal hydride secondary battery that do not require surface treatment - Google Patents

Abstract

Disclosed are a nickel-metal hydride secondary battery negative electrode active material and a nickel-metal hydride secondary battery made of a hydrogen storage alloy powder that can easily store and release hydrogen without any surface treatment. A general formula: MmNiaMnbAlcCod (wherein Mm is a misch metal, La and Ce are 90% by mass or more based on the total mass of Mm, and 4.30 ≦ a ≦ 4.70, 0) 20 ≦ b ≦ 0.45, 0.35 ≦ c ≦ 0.45, 0 ≦ d ≦ 0.06, 5.25 ≦ a + b + c + d ≦ 5.50), It has excellent oxidizability, preferably, the hydrogen storage amount (H / M) is 0.80 or more and 1.00 or less, the pulverization difficulty is 0.48 or more and 0.60 or less, and the equilibrium (hydrogen) pressure is 0.04 to A nickel hydride secondary battery negative electrode active material and a nickel hydride secondary battery that are not subjected to a surface treatment made of a hydrogen storage alloy powder of 0.06 MPa and an a-axis length of 503 pm or more. [Selection figure] None

Description

  The present invention relates to a hydrogen storage alloy containing nickel as a main component, and particularly when used as a negative electrode active material for a nickel metal hydride secondary battery, a nickel metal hydride secondary battery capable of improving output characteristics without requiring surface treatment. The present invention relates to a negative electrode active material and a nickel metal hydride secondary battery.

Nickel metal hydride rechargeable batteries, which are safer than lithium ion rechargeable batteries with a possibility of fire and explosion, are widely used mainly in hybrid vehicles. Nickel metal hydride secondary batteries generally use nickel oxyhydroxide, which is nickel oxide as the positive electrode active material, and metal hydride (MH) as the negative electrode active material. The electrolyte is an alkaline aqueous solution mainly composed of potassium hydroxide. Is used. For the battery separator, a polypropylene nonwoven fabric imparted with hydrophilicity is usually used. Metal hydride (MH) is a hydrogen storage alloy that stores hydrogen, and LaNi ₅ H ₆ is a typical example. In practical batteries, Mm is substituted for La in terms of cost and performance. A multi-component alloy in which a part of Ni is substituted with Mn, Al, Co or the like using (Mish metal) is generally used.

When nickel-metal hydride secondary batteries are used in hybrid vehicles, charging is performed by converting the kinetic energy generated by regenerative braking into electric energy during deceleration, and discharging is performed using electric energy stored during acceleration for driving an electric motor. It is necessary to repeat charging and discharging particularly in a short time because it is repeated every time acceleration / deceleration is performed.

The rate-limiting for performing charging and discharging in a nickel hydride battery in a short time is the hydrogen absorption / desorption rate of the metal hydride that is the negative electrode active material, and in particular, by the metallic Ni concentrated layer formed on the surface of the metal hydride particles, It is said that necessary functions as a hydrogen storage alloy electrode such as a catalytic function for electrode reaction, a current collecting function as an electron flow path, and a function of suppressing the progress of corrosion are given.

For this reason, various surface treatments are performed in order to prepare the surface of the hydrogen storage alloy so as to be suitable for a charge / discharge reaction and to improve discharge characteristics and life.

In Patent Document 1, the hydrogen storage alloy powder is agitated in a strong alkali or in an acidic solution such as hydrogen fluoride water or acetic acid for the purpose of enhancing the reactivity of the hydrogen storage alloy. A method for removing a surface layer including a coating has been proposed.

Patent Document 2 discloses that a hydrogen storage alloy powder surface is stirred by stirring an elemental storage alloy powder in an alkaline aqueous solution containing lithium hydroxide for the purpose of manufacturing a secondary battery in which self-discharge is suppressed and excellent in high-temperature storage characteristics. A method for removing segregated Mn, Co and Fe has been proposed.

  In Patent Document 3, for the purpose of producing a nickel-metal hydride storage battery with excellent high cycle life performance, the element storage alloy powder is brought into contact with an alkaline aqueous solution of 9 mol / l or more and 110 ° C. or more, or 10 mol / l or more and 80 ° C. or more. In the surface layer of the hydrogen storage alloy powder, the nickel concentration at a portion 10 nm away from the interface with the particle surface is substantially the same as the nickel concentration of the particle, and between the particles and the surface layer generated during storage and release of hydrogen. A method for suppressing distortion has been proposed.

  In Patent Document 4, for the purpose of producing a nickel-metal hydride storage battery having excellent high cycle life characteristics, a durable nickel coating film is formed on the surface of the hydrogen storage alloy powder particles by an electroless nickel plating method. A method for suppressing elution of constituent components has been proposed.

JP-A-2018-14244 JP 2010-262663 A JP 2010-50011 A JP 2006-286345 A

As described above, the LaNi _5- based hydrogen storage alloy powder as the metal hydride raw material needs to be treated on the surface of the powder in order to exhibit its potential in the negative electrode active material of the nickel hydride secondary battery. In fact, hydrogen storage alloy powders that have been developed but do not require surface treatment have not yet been developed.

  In view of the above circumstances, an object of the present invention is to provide a nickel-hydrogen secondary battery negative electrode active material and a nickel-hydrogen secondary battery that can obtain high output characteristics without requiring a special surface treatment step.

The inventors of the present invention have intensively studied to solve the above-mentioned problems. The general formula MmNiaMnbAlcCod (where Mm represents Misch metal in the left formula, 4.30 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.45). , 0.35 ≦ c ≦ 0.45, 0 ≦ d ≦ 0.06, 5.25 ≦ a + b + c + d ≦ 5.50), it is easy to occlude and release hydrogen without surface treatment. In particular, when used as a negative electrode for a nickel metal hydride secondary battery, it was found that high output characteristics can be obtained without providing a surface treatment step, and the present invention has been completed.

  That is, the gist of the present invention is as follows.

(1) A nickel-metal hydride battery negative electrode active material made of LaNi ₅ series hydrogen storage alloy powder, wherein the hydrogen storage alloy powder has a general formula MmNiaMnbAlcCod (in the left formula, Mm represents Misch metal and 90% of the total Mm La and Ce occupy mass% or more, 4.30 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.45, 0.35 ≦ c ≦ 0.45, 0 ≦ d ≦ 0.06. 25 ≦ a + b + c + d ≦ 5.50) and has an excellent oxygen resistance when oxygen is increased by a heat treatment at 250 ° C. for 50 minutes in air for 0.8 mass% or less. A negative electrode active material for a nickel-metal hydride secondary battery, which is a hydrogen storage alloy powder and is not subjected to surface treatment.

  (2) The hydrogen storage alloy powder has a hydrogen storage amount (H / M) in a range of 0.80 or more and 1.00 or less, and a pulverization difficulty in a range of 0.48 or more and 0.60 or less. The nickel-hydrogen secondary battery negative electrode active material according to (1), wherein the negative electrode active material is within the range (preferably 0.50 to 0.58).

  (3) The negative electrode active material for a nickel-metal hydride secondary battery according to (1) or (2), wherein the hydrogen storage alloy powder has an a-axis length of 503 pm or more obtained from the powder X diffraction measurement result .

  (4) The nickel-hydrogen secondary battery negative electrode according to any one of (1) to (3), wherein the hydrogen storage alloy powder has an equilibrium (hydrogen) pressure of 0.04 to 0.06 MPa. Active material.

  (5) The nickel hydride secondary battery negative electrode active material according to any one of (1) to (4), a conductive additive, and a binder are kneaded and then applied to a current collector. The manufacturing method of the negative electrode for nickel hydride secondary batteries.

  (6) A nickel metal hydride secondary battery using the nickel metal hydride secondary battery negative electrode active material according to any one of (1) to (4).

  (7) A hybrid vehicle characterized in that the motor is driven by the nickel metal hydride secondary battery according to (6).

As described above, when the LaNi _5- based hydrogen storage alloy powder of the present invention is used particularly as a negative electrode for a nickel-metal hydride secondary battery, high output characteristics comparable to those obtained when surface treatment is performed without providing a surface treatment step. Therefore, it is possible to provide a nickel-hydrogen secondary battery that is inexpensive and has high performance, particularly suitable for a hybrid vehicle.

If the LaNi _5- based hydrogen storage alloy powder that does not require the surface treatment step of the present invention is used as a negative electrode active material for a nickel metal hydride secondary battery, the nickel metal hydride secondary having excellent output characteristics similar to those when the surface treatment is performed. A battery can be provided.

The hydrogen-absorbing alloy containing nickel as a main component of the present invention is characterized in that the oxygen concentration increase is 0.8% by mass or less when heat resistance is performed in air at 250 ° C. for 50 minutes and the antioxidant property is examined. General formula MmNiaMnbAlcCod (where Mm represents Misch metal in the left formula, 4.30 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.45, 0.35 ≦ c ≦ 0.45, 0 ≦ d) ≦ 0.06, 5.25 ≦ a + b + c + d ≦ 5.50), and La and Ce occupy 90% by mass or more of the entire Mm.
Although it is not completely elucidated why the nickel hydride secondary battery having excellent output characteristics can be manufactured without performing the surface treatment with such a composition, the intermetallic compound Ni ₃ that undergoes consistent precipitation by increasing the nickel content Mn, which has low diffusibility in Al, is substituted and dissolved in the Al site to increase the electrical conductivity of the particles. Also, due to the high antioxidant property of the nickel compound, the oxidation of the particles does not proceed during the alloy pulverization and pulverization processes. For the reason.
In addition, when the LaNi _5- based hydrogen storage alloy powder having the above composition is used as a nickel-hydrogen secondary battery negative electrode, a battery having excellent output characteristics can be obtained.
In the surface treatment, in order to artificially create a nickel enriched layer, it is unavoidable to dissolve La and other transition metal passivation films in the treatment liquid. In the nickel concentrated layer, the original hydrogen storage alloy skeleton is destroyed, and hydrogen ions are not easily released into the electrolyte. On the other hand, in the hydrogen storage alloy powder that does not require the surface treatment process of the present invention, the hydrogen storage alloy skeleton is maintained up to the particle surface that is in direct contact with the electrolyte, and the movement of hydrogen ions is higher than that of the surface treatment. Therefore, when used as a negative electrode active material for a nickel metal hydride secondary battery, a battery having excellent output characteristics can be produced.

In the case of a hydrogen storage alloy represented by the general formula MmNiaMnbAlcCod, when a is less than 4.30, the antioxidant property is lowered and a surface treatment step is required. On the other hand, when a exceeds 4.70, so-called phase separation in which Ni precipitates alone in the alloy occurs, and the battery performance deteriorates.
Similarly, when b is less than 0.20, the equilibrium (hydrogen) pressure increases and exceeds 0.06 MPa, and when b exceeds 0.45, the equilibrium pressure decreases and becomes less than 0.04 MPa.
Similarly, when c exceeds 0.45, the hydrogen storage amount decreases due to lattice distortion, the hydrogen storage amount (H / M) becomes less than 0.80, and when c becomes less than 0.35, the degree of difficulty in pulverization is 0. Over 60.
By setting d to 0 or more, the Vickers hardness of the alloy is small, that is, there is an effect of increasing the difficulty of pulverization by making the alloy tenacious, but since it is an expensive metal, it does not exceed 0.06 for adjusting the pulverization degree. Add as follows.

The hydrogen storage alloy represented by the general formula MmNiaMnbAlcCod of the present invention has an antioxidant performance within a range where the oxygen concentration increase is 0.8 mass% or less when heat treatment is performed in air at 250 ° C. for 50 minutes. , B, c and d can be freely taken, but a trace component for improving the performance of the nickel-hydrogen secondary battery can be added. For example, alkaline earth elements such as Mg, Sr, and Ca, and transition elements such as V, Cr, Fe, and Cu can be added.
When the oxygen concentration increase exceeds 0.8% by mass, the antioxidant property is lowered, and a surface treatment is required when producing a nickel-hydrogen secondary battery negative electrode.

(Method for producing hydrogen storage alloy powder)
The hydrogen storage alloy powder of the present invention is manufactured through a weighing process, a mixing process, a casting process, a heat treatment process, a cooling process, and a pulverizing process. In the weighing step, each raw material of the hydrogen storage alloy is weighed so as to have a desired alloy composition. In the mixing step, a plurality of kinds of weighed raw materials are mixed.
In the casting process, the mixed raw material is put into a high-frequency heating melting furnace, the mixed raw material is melted to form a molten metal, and this molten metal is poured into a mold, for example, at a temperature in the range of 1150 ° C to 1550 ° C (casting temperature = at the start of casting) Cast at the temperature of the molten metal in the crucible). Here, the casting temperature is preferably in the range of 1200 ° C to 1450 ° C, more preferably 1300 ° C to 1400 ° C, and further preferably in the range of 1340 ° C to 1360 ° C.
In addition, in the cooling by the mold, the molten metal is directionally solidified so that columnar crystals are likely to grow, so that the composition inside the alloy becomes uniform and the lattice distortion is minimized, so that the nickel-hydrogen secondary battery Cycle life is improved. It is desirable to carry out so as to suppress the generation of segregation phase. The condition for directional solidification is that the temperature gradient in the liquid and solid is positive. In this case, the latent heat generated in the solidification is dissipated through the solid, so that directional solidification occurs, and the solidified structure becomes columnar crystals. Conversely, if a supercooled liquid surrounds the crystal, a negative temperature gradient is generated in the liquid at the solid-liquid surface. In this case, the latent heat of solidification is dissipated through the liquid and the solidified structure becomes equiaxed crystals. In order to cause directional solidification, it is preferable to use a mold having a thermal conductivity of 43 W / (m · ° C.) or higher at 20 ° C. More preferably, a mold having a thermal conductivity of 52 W / (m · ° C.) or higher at 20 ° C. is used.
The alloy after casting is heat-treated at a temperature of 950 ° C. to 1200 ° C. in a non-oxidizing atmosphere in a heat treatment step. In the hydrogen storage alloy according to the present embodiment, the heat treatment temperature is preferably 1000 ° C. to 1150 ° C. The heat treatment time depends on the size of the ingot (hydrogen storage alloy piece) after casting, but is preferably several hours to several tens of hours, and may be set so that the temperature reaches a predetermined temperature up to the center of the ingot. .
In the cooling step, the heat-treated casting is cooled. The cooling method may be air cooling or air cooling. The cooling rate is not particularly limited. The hydrogen storage alloy directionally solidified in the casting process maintains columnar crystals even after heat treatment. A columnar crystal has a feature that it has fewer crystal interfaces and is uniform in the crystal than an equiaxed crystal. The crystal grain boundary is in a state where the atomic arrangement is disordered, and is said to be the starting point of oxidation and destruction.
In the pulverization step, the ingot thus obtained is made into a hydrogen storage alloy powder having a required particle size by coarse pulverization and fine pulverization. For example, the hydrogen storage alloy powder can be obtained by grinding an ingot to a size that passes through a 20 μm sieve.

A nickel metal hydride battery can be manufactured by using the hydrogen storage alloy powder thus obtained as a negative electrode active material, and the manufactured battery can be used in a hybrid vehicle.

The oxygen concentration increase referred to in the present invention is measured as follows.
For example, the hydrogen storage alloy is pulverized by a commonly used method and is reduced to 20 μm or less by sieving. For example, a jaw crusher can be used for roughing, a hammer mill or cutting mill can be used for middle cutting, and a vibration mill can be used for final grinding. At this time, after the middle split, pulverization is performed in an inert atmosphere with nitrogen gas, argon gas or the like in order to prevent unnecessary oxidation of the hydrogen storage alloy. About 1 g of this pulverized hydrogen storage alloy was weighed, put into a ceramic crucible, heated in a furnace heated by a heating wire heater, heated to 250 ° C. in 1.25 hours, held for 50 minutes, and 50 in 1 hour. After the temperature is lowered to ° C., the increase in weight of the alloy powder when naturally cooled is converted into the oxygen concentration to calculate the increase in oxygen concentration.

Further, the hydrogen storage amount (H / M) and the equilibrium (hydrogen) pressure were measured using commercially available PCT (hydrogen pressure-composition-isothermal line) according to JISH7201 “Method for Measuring Pressure-Isotherm (PCT Line) of Hydrogen Storage Alloy”. Fig.) It can be measured by using a characteristic evaluation device.

Further, the degree of difficulty in pulverization is measured as follows.
Using a PCT (Hydrogen Pressure-Composition-Isotherm) Characteristic Evaluation Device, “Particle size of hydrogen storage alloy powder after 10 cycles of hydrogen storage / release under a holding temperature of 45 ° C. and a hydrogen pressure adjustment of 1.82 MPa” Was divided by “initial particle size of hydrogen storage alloy powder” and indexed as the degree of difficulty in pulverization. That is, as the degree of difficulty in pulverization is closer to 1, it indicates that the hydrogen storage alloy powder is less likely to be pulverized, and as it is closer to 0, the hydrogen storage alloy powder is more likely to be pulverized.
In determining the degree of difficulty in pulverization, the “initial particle size of the hydrogen storage alloy powder” is an average particle size D50 measured using a particle size distribution measuring device 7997 SRA manufactured by Leeds and Northrup. “The particle size of the hydrogen storage alloy powder after 10 storage and release cycles of hydrogen in an environment where the holding temperature is 45 ° C. and the hydrogen pressure is adjusted to 1.82 MPa” is a fully automatic PCT measuring device (1/2 Inch straight tube sample cell, sample amount 3g), hydrogen storage / release cycle was performed 10 times in an environment of holding temperature 45 ° C and hydrogen pressure adjustment 1.82MPa, then particle size distribution measurement made by Leeds and Northrup It is the average particle diameter D50 measured using the apparatus 7997 SRA.
In addition, the activation process of the hydrogen storage alloy powder in the fully automatic PCT measurement apparatus is performed in an environment with an activation temperature of 80 ° C. and a hydrogen pressure of 1.82 MPa, and the hydrogen storage alloy release cycle of the hydrogen storage alloy powder in the apparatus is maintained. The test was carried out in an environment of a temperature of 45 ° C., a hydrogen storage pressure of 1.82 MPa, and a hydrogen release pressure of 0 MPa.

The a-axis length can be measured by performing X-ray diffraction measurement using an X-ray diffraction apparatus. Specifically, a hydrogen storage alloy pulverized to 20 μm or less is used with a powder X-ray diffraction apparatus (manufactured by Rigaku Corporation, SmartLab) at a gonio radius of 300 mm, an X-ray source CuKα ray, a tube voltage of 45 kV, and a tube current of 200 mA. It was measured.
The diffraction angle is in the range of 2θ = 15.0 to 85.0 °, and the scan speed is 4.000 ° / min. The scan step was 0.020 °.
Based on the obtained X-ray diffraction results, the crystal structure was analyzed by the Rietveld method (analysis software SmartLaStudioII, PowderXRD plug-in).

Each of the above measured values is an index representing the following battery characteristics when the hydrogen storage alloy of the present invention is used as the negative electrode of a nickel metal hydride secondary battery.
The hydrogen storage amount (H / M) is related to the battery capacity, and the capacity increases as it increases.
Moreover, the life becomes longer by increasing the difficulty of pulverization with characteristics related to the life during repeated charge and discharge.
The a-axis length is an index related to battery cycle characteristics when the alloy is used as a nickel-metal hydride battery negative electrode, and shows a practical life when it is 503 pm or more.
Equilibrium (hydrogen) pressure is a characteristic related to the ease of taking in and out of hydrogen as a charge carrier, and if it is high, the charge voltage becomes high when used as a nickel metal hydride battery negative electrode.

As described above, there are various indexes indicating the characteristics of the negative electrode of the nickel-metal hydride secondary battery, but the general formula MmNiaMnbAlcCod (in the left formula, Mm represents Misch metal, 4.30 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.45, 0.35 ≦ c ≦ 0.45, 0 ≦ d ≦ 0.06, 5.25 ≦ a + b + c + d ≦ 5.50). A hydrogen storage alloy for a nickel hydrogen secondary battery can be manufactured.

  Hereinafter, the present invention will be specifically described with reference to examples (invention examples) and comparative examples, but the present invention is not limited thereto.

Example 1
Each metal raw material of La and Ce as Ni, Mn, Al, Co, and Mm was weighed so as to have the alloy composition shown in Table 1. These raw materials were put in a crucible in a melting furnace and evacuated, and then an argon gas atmosphere was set. Next, it is melted by heating with a high-frequency heating device, casted by pouring the molten metal into a mold having a thermal conductivity of 52 W / (m · ° C.) at 20 ° C., and subjected to heat treatment in an inert atmosphere at 1100 ° C. × 12 hours for alloy ingot Got.
The obtained alloy ingot was coarsely pulverized by a crusher under an inert atmosphere, followed by pulverization using a cutting mill manufactured by Frucsch under an inert atmosphere, followed by a particle size (500 μm or less) passing through a sieve mesh of 500 μm. ).
Further, the powder was finely pulverized using a cyclomill manufactured by Yoshida Seisakusho to obtain a hydrogen storage alloy powder having a particle size passing through a sieve mesh of 20 μm.

(Measurement of oxygen concentration)
About the obtained hydrogen storage alloy powder, the oxygen concentration increase was calculated by converting the weight increase after being held in air at 250 ° C. for 50 minutes in terms of oxygen concentration.
The results are shown in Table 2.

(Measurement of PCT characteristics)
About the obtained hydrogen storage alloy powder, the hydrogen storage amount (H / M) and the equilibrium pressure were measured by a PCT characteristic evaluation apparatus.
The results are shown in Table 2.

(Measurement of pulverization difficulty)
The degree of difficulty in pulverization was measured using a particle size distribution measuring device and a PCT characteristic evaluation device.
The results are shown in Table 2.

(Measurement of a-axis length)
The a-axis length was measured using a powder X-ray diffractometer.
The results are shown in Table 2.

(Measurement of output characteristics)
A model battery for measuring output characteristics when the hydrogen storage alloy powder of the present invention produced as described above was used as a nickel metal hydride battery negative electrode was prepared by the following procedure, and the discharge capacity was measured as the output characteristics.
First, 0.5 g of a hydrogen storage alloy powder having a particle size of 20 μm or less prepared as described above without any surface treatment, and polytetrafluoroethylene (average molecular weight 5000-20000) 0 manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. 0.1 g, 0.05 g of acetylene carbon black (50% compressed) manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. and 0.6 g of distilled water were kneaded to obtain an active material paste.
The active material paste is uniformly filled into foamed nickel (Celmet # 7, porosity = 96%) manufactured by Sumitomo Electric, which is a current collector (30 mm × 40 mm, t = 1.6 mm), and dried at 80 ° C. After holding in a thermostat for 30 minutes, it was pressure-molded at 100 MPa to form a negative electrode (capacity = about 180 mAh).
A ternary (nickel, cobalt, zinc) nickel hydroxide electrode (capacity = about 600 mAh) is used for the positive electrode.
A negative electrode was sandwiched between two positive electrodes through a separator, and further pressed from both sides with an acrylic plate to obtain a negative electrode capacity-regulated model battery.
A mercury oxide electrode (Hg / HgO) was used as the reference electrode for measuring the negative electrode potential, and a 5M potassium hydroxide solution was used as the electrolyte.

For reference, a negative electrode was produced using a negative electrode active material paste obtained by subjecting a hydrogen storage alloy to surface treatment, and a battery was produced in the same manner as described above.
In this case, before preparing the active material paste, the hydrogen storage alloy powder is put into a 31 wt% potassium hydroxide solution, stirred at 50 ° C. for 2 hours (50 rpm), and then subjected to a surface treatment that is washed with water. It was.

In the measurement of output characteristics, the charge / discharge test is performed at 0.2C (1C: current value for charging or discharging the entire capacity of the battery in 1 hour) for 6 hours, after 30 minutes of rest, between positive electrode and negative electrode at 0.2C It was discharged until the voltage of 0.8V became 0.8 V to obtain a discharge capacity, and this was measured.
The results are shown in Table 2.

(Examples 2-3 and Comparative Examples 1-3)
In Examples 2 to 3 and Comparative Examples 1 to 3, as in Example 1, the alloys were adjusted so that the respective component ratios shown in Table 1 were obtained, and 1100 ° C. × 12 hours in an inert atmosphere. Heat treatment and pulverization were performed to measure each characteristic. The measurement results are shown in Table 2.
In Table 2, “Yes / with surface treatment” means that in preparing the active material paste, the hydrogen storage alloy powder was put into a 31 wt% potassium hydroxide solution and stirred at 90 ° C. for 2 hours (50 rpm). m) After that, the surface treatment of washing with water was performed.

As is clear from Table 2, the nickel-metal hydride secondary batteries using the hydrogen storage alloys obtained in Examples 1 to 3 are almost equivalent in the “No” case (corresponding to the present invention) and the “Yes” case. As a result, the output characteristics were excellent even without surface treatment.

  As described above, it was confirmed that excellent output characteristics can be obtained when the hydrogen storage alloy of the present invention is used as a negative electrode material for a nickel metal hydride secondary battery for hybrid vehicles.

By using the hydrogen storage alloy for a negative electrode of a nickel metal hydride secondary battery that does not require surface treatment of the present invention as a negative electrode material for a nickel metal hydride secondary battery for a hybrid vehicle, a secondary battery having excellent output characteristics can be manufactured at low cost. The cost and performance of hybrid vehicles can be reduced.

Claims (7)

A nickel-metal hydride battery negative electrode active material comprising a LaNi _5- based hydrogen storage alloy powder, wherein the hydrogen storage alloy powder has a general formula MmNiaMnbAlcCod (where Mm represents a misch metal and 90% by mass or more of the entire Mm) La and Ce occupy 4.30 ≦ a ≦ 4.70, 0.20 ≦ b ≦ 0.45, 0.35 ≦ c ≦ 0.45, 0 ≦ d ≦ 0.06, 5.25 ≦ a + b + c + d ≦ 5.50), and a hydrogen storage alloy powder excellent in antioxidation property with an oxygen concentration increase of 0.8% by mass or less when heat-treated in air at 250 ° C. for 50 minutes. A negative electrode active material for a nickel metal hydride secondary battery that is not subjected to a surface treatment.   The hydrogen storage alloy powder has a hydrogen storage amount (H / M) in the range of 0.80 or more and 1.00 or less, and the pulverization difficulty is in the range of 0.48 or more and 0.60 or less. The negative electrode active material of a nickel metal hydride secondary battery according to claim 1.   The nickel-hydrogen secondary battery negative electrode active material according to claim 1 or 2, wherein the hydrogen storage alloy powder has an a-axis length of 503 pm or more obtained from a powder X diffraction measurement result.   The nickel-hydrogen secondary battery negative electrode active material according to any one of claims 1 to 3, wherein the hydrogen storage alloy powder has an equilibrium (hydrogen) pressure of 0.04 to 0.06 MPa.   The nickel-metal hydride secondary battery negative electrode active material according to any one of claims 1 to 4, a conductive additive, and a binder are kneaded and then applied to a current collector. Manufacturing method of negative electrode.   A nickel metal hydride secondary battery using the nickel metal hydride secondary battery negative electrode active material according to any one of claims 1 to 4. A hybrid vehicle, wherein the motor is driven by the nickel metal hydride secondary battery according to claim 6.