JP2000160265A - Hydrogen storage alloy and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a service life characteristic of a hydrogen storage alloy without deteriorating electrode capacity and discharge rate characteristic when used as a nickel - hydrogen secondary battery cathode active material by heating and melting a raw material for Mm-Ni-Mn-Al-Co hydrogen storage alloy, rapidly solidifying the resultant molten alloy by a single drum method or a twin drum method at specific rapid solidification rate, and omitting subsequent heat treatment. SOLUTION: A Mm-Ni-Mn-Al-Co alloy is an AB5-type hydrogen storage alloy having CaCu5-type crystal structure and represented by a formula (where Mm is misch metal; X is vanadium or titanium; the symbols (a) to (e) are molar numbers based on one mole of Mm and satisfy 4.00<=a<=4.30, 0.30<=b<=0.50, 0.20<=c<=0.45, 0.20<=d<=0.60, 0<=e<=0.05, and 5.00<=a+b+c+d+e<=5.35, respectively; and (f) is 19-21 wt.%). Mm is a misch metal of rare earths such as La, Ce, Pr, Nd, and Sm, and lanthanum content in the hydrogen storage alloy is 19-21 wt.%. Rapid solidification rate is >=10 k3/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy and a method for producing the same. The present invention relates to a hydrogen storage alloy having improved cycle characteristics) and a method of manufacturing the same at low cost and with excellent productivity.

[0002]

2. Description of the Related Art In recent years,
As a high-capacity alkaline secondary battery replacing the nickel-cadmium secondary battery, a nickel-hydrogen secondary battery using a hydrogen storage alloy for a negative electrode has been receiving attention. At present, as the hydrogen storage alloy, a five-element hydrogen storage alloy of Mm (mish metal), which is a rare earth-based mixture, and Ni, Al, Mn, and Co is widely used.

[0003] This Mm-Ni-Mn-Al-Co alloy can form a negative electrode with a relatively inexpensive material as compared with a La-based alloy, has a long cycle life, and has a small internal pressure rise due to gas generated during overcharge. Since a nickel-metal hydride secondary battery can be obtained, it is widely used as an electrode material.

[0004] Currently used Mm-Ni-Mn-A
As a method for producing the l-Co alloy, a predetermined ratio of a hydrogen storage alloy material is heated and melted, and then cast, and then heat-treated in an inert gas atmosphere, or a predetermined ratio of a hydrogen storage alloy material is heated and melted. A method of ultra-quick solidification at a rapid cooling rate, followed by heat treatment in an inert gas atmosphere.

[0005] However, these methods involve the steps of casting or ultra-quick solidification and heat treatment, so that they have a problem of high cost and poor productivity. Further, when these hydrogen storage alloys are used as a negative electrode active material of a nickel-hydrogen secondary battery, further improvement in battery characteristics has been desired.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hydrogen storage device which, when used as a negative electrode active material of a nickel-hydrogen secondary battery, has improved life characteristics (cycle characteristics) without lowering electrode capacity and discharge rate characteristics. An object of the present invention is to provide an alloy and a method of manufacturing the alloy at low cost and excellent in productivity.

[0007]

As a result of various studies, the present inventors have found that a hydrogen storage alloy having a specific composition can be homogenized without heat treatment after ultra-rapid solidification, and nickel-containing alloy can be obtained. It has been found that good battery characteristics can be obtained when used as a negative electrode active material of a hydrogen secondary battery.

The present invention has been made on the basis of the above findings, and heat-melts a hydrogen-absorbing alloy raw material and ultra-quench solidifies at a super-quenching speed of 10 K ³ / sec or more using a single roll method or a twin roll method, characterized in that subsequently not performed heat treatment, there is provided a method of manufacturing the AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following formula. Formula _{Mm (La f) Ni a Mn} b Al c Co d X e ( wherein, Mm is the mischmetal, X is vanadium or titanium, 4.00 ≦ a ≦ 4.30,0.30 ≦ b ≦ 0. 5
0, 0.20 ≦ c ≦ 0.45, 0.20 ≦ d ≦ 0.6
0, 0 ≦ e ≦ 0.05, 5.00 ≦ a + b + c + d + e
≦ 5.35, wherein a to e are moles per mole of Mm, and f is 19 to 21% by weight.

Further, the present invention is represented by the following general formula _{Mm (La f) Ni a Mn} b Al c Co d X e ( wherein, Mm is the mischmetal, X is vanadium or titanium, 4.00 ≦ a ≦ 4. 30, 0.30 ≦ b ≦ 0.5
0, 0.20 ≦ c ≦ 0.45, 0.20 ≦ d ≦ 0.6
0, 0 ≦ e ≦ 0.05, 5.00 ≦ a + b + c + d + e
≦ 5.35, wherein a to e are moles per mole of Mm, and f is 19 to 21% by weight.
_{When a} standard sample is obtained by heat treating LaNi ₅ at 1060 ° C. for 3 hours and having a _5- type crystal structure, the X-ray diffraction diffracts the standard sample in the range of 20 ° ≦ 2θ ≦ 70 °. the value of the line half width is intended to provide a AB ₅ -type hydrogen absorbing alloy, characterized in that it comprises at least two more than a relative ratio 1.10.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The production method of the present invention will be described below in detail. In the production method of the present invention, the molten metal obtained by weighing and mixing the hydrogen-absorbing alloy raw materials so as to have the following alloy composition is subjected to a single-roll method or a twin-roll method to obtain 10 ³ K / Sec or more, preferably 10 ³ to 10
Ultra-quick solidification at a rapid cooling rate of about ⁵ K / sec.

[0011] The hydrogen storage alloy thus obtained is
Since it has already been homogenized, it is used as a negative electrode active material of a nickel-hydrogen secondary battery without heat treatment in an inert gas atmosphere, for example, in an argon gas. By not performing the heat treatment on the hydrogen storage alloy in this way, the cost is greatly reduced and the productivity is improved.

[0012] hydrogen-absorbing alloy in the manufacturing method of the present invention have the general formula _{Mm (La f) Ni a Mn} b Al c Co d X e ( wherein, Mm is the mischmetal, X is vanadium or titanium, 4.00 ≦ a ≦ 4.30, 0.30 ≦ b ≦ 0.5
0, 0.20 ≦ c ≦ 0.45, 0.20 ≦ d ≦ 0.6
0, 0 ≦ e ≦ 0.05, 5.00 ≦ a + b + c + d + e
≦ 5.35, wherein a to e are moles per mole of Mm, and f is 19 to 21% by weight.
AB ₅ type hydrogen storage alloy having a ₅ type crystal structure.

Here, Mm is La, Ce, Pr, Nd,
It is a misch metal that is a rare earth-based mixture such as Sm. The content of lanthanum contained in the misch metal is 19 to 21% by weight in the hydrogen storage alloy. Also,
X is vanadium or titanium. Then, the hydrogen storage alloy in AB ₅ type hydrogen storage alloy having a crystal structure type ₅ CaCu, a non-stoichiometric composition of B-site rich AB _5.00 ~ _5.35.

In this hydrogen storage alloy, Ni _a Mn _b
Al _c Co _d X (number of moles Mm1 mol) composition ratio of _e is one having the following relationship. That is, N
The ratio of i is 4.00 ≦ a ≦ 4.30, the ratio of Mn is 0.30 ≦ b ≦ 0.50, and the ratio of Al is 0.2
0 ≦ c ≦ 0.45, and the proportion of Co is 0.20 ≦ d ≦
0.60, and the ratio of X (V or Ti) is 0 ≦ e ≦
0.05, and a + b + c + d + e is 5.00 to
It is in the range of 5.35.

In such a hydrogen-absorbing alloy composition, as described above, using the single-roll method or the twin-roll method, ultra-rapid solidification is performed, and then, without heat treatment, the negative electrode active material of the nickel-hydrogen secondary battery is directly used. Good battery characteristics such as cycle characteristics can be obtained. Next, the composition ratio of each element will be described.

As described above, the ratio a of Ni is 4.00 to 4.0.
4.30, preferably 4.0 to 4.2, and a is 4.
If it is less than 00, the hydrogen storage capacity is impaired, and if it exceeds 4.30, pulverization and deterioration of life characteristics are recognized, and the plateau pressure increases.

The ratio b of Mn is 0.30 to 0.50, preferably 0.35 to 0.4. If b is less than 0.30, the plateau pressure increases and the hydrogen storage capacity is impaired.
When it exceeds 0.50, corrosion of the alloy becomes severe, and early deterioration of the alloy is recognized.

The ratio c of Al is 0.20 to 0.45. If c is less than 0.20, the plateau pressure, which is the pressure at which the hydrogen storage alloy is released, increases, and the energy efficiency of charging and discharging deteriorates. If it exceeds, the amount of hydrogen storage decreases.

The ratio d of Co is 0.20 to 0.60, preferably 0.4 to 0.60. If d is less than 0.20, the cycle life becomes poor. And the cost cannot be reduced.

The proportion e of V or Ti is 0 to 0.05, and when e exceeds 0.05, the pulverization characteristics are impaired.

A + b + c + d + e (hereinafter sometimes collectively referred to as x) is 5.00 to 5.35, and x is 5.
If it is less than 00, the battery life and pulverization characteristics are impaired, and 5.3
If it exceeds 5, the hydrogen storage properties will be impaired.

Next, the hydrogen storage alloy of the present invention will be described. The hydrogen storage alloy of the present invention has a CaCu ₅ type crystal structure represented by the above chemical formula, and has a LaNi ₅ of 1060
When the sample heat-treated at 3 ° C. for 3 hours was used as a standard sample, in the X-ray diffraction, 20 ° ≦ 2θ ≦ 7
0 The value of the diffraction line half width in the range of ° is AB ₅ type hydrogen storage alloy having at least two more than a relative ratio 1.10.

As described above, at least two samples having the above alloy composition and having a half value width of diffraction line of 1.10 or more in the range of 20 ° ≦ 2θ ≦ 70 ° with respect to the above-mentioned standard sample, AB ₅ type hydrogen storage alloy having at least one
When used as a negative electrode active material of a hydrogen secondary battery, the life characteristics (cycle characteristics) can be improved without lowering the electrode capacity and discharge rate characteristics.

This hydrogen storage alloy is subjected to coarse pulverization and fine pulverization.
Used as a negative electrode active material of a nickel-hydrogen secondary battery,
It has good battery characteristics as described above.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like. The percentages in Table 1 are based on weight.

Comparative Example 1 Mm, Ni, Mn, Al, C
o and Cu in alloy composition of Mm (La 19% by weight) Ni
_3.95 Mn _0.45 Al _0.30 Co _0.40 Cu _0.10 (x = 5.2
0), each hydrogen-absorbing alloy raw material is weighed and mixed, the mixture is put in a crucible, fixed in a high-frequency melting furnace, evacuated to 10 ^-2 to 10 ^-4 Torr, and then an argon gas atmosphere. After being heated and melted in the flask, it was poured into a water-cooled copper mold and cast at 1430 ° C. to obtain an alloy. Further, this alloy was heated at 1060 ° C. in an argon gas atmosphere.
Heat treatment for 3 hours to obtain hydrogen storage alloy, nickel-
It was used as a negative electrode active material of a hydrogen secondary battery.

Comparative Example 2 Mm, Ni, Mn, Al, C
o and Cu in alloy composition of Mm (La 19% by weight) Ni
_3.95 Mn _0.45 Al _0.30 Co _0.40 Cu _0.10 (x = 5.2
0), each hydrogen storage alloy raw material is weighed and mixed, the mixture is put in a crucible, fixed in a high-frequency melting furnace, evacuated to 10 ^-3 Torr, and then heated and melted in an argon gas atmosphere. And then 10 ³ to 10 ⁵ K / se
Ultra-rapid solidification was performed by a single roll method at a cooling rate of about c to obtain a hydrogen storage alloy. This alloy was used as a negative electrode active material of a nickel-hydrogen secondary battery without heat treatment.

Comparative Example 3 Mm, Ni, Mn, Al, C
o and V are alloyed with MmNi_4.12Mn_0.35Al _0.32C
o_0.40V_0.01(X = 5.20)
Weigh and mix the storage alloy materials and place the mixture in a crucible.
And fix it in a high-frequency melting furnace.^-2-10^-FourUp to Torr
After vacuuming, heat and dissolve in an argon gas atmosphere.
After that, it is poured into a water-cooled copper mold and cast at 1430 ° C.
Thus, a hydrogen storage alloy was obtained. Without heat treating this alloy,
It was used as a negative electrode active material for a nickel-hydrogen secondary battery.

Examples 1 to 9 Hydrogen storage alloys were obtained in the same manner as in Comparative Example 2 except that each hydrogen storage alloy raw material was used so that the alloy composition was as shown in Table 1. This alloy was used without heat treatment as a negative electrode active material of a nickel-hydrogen secondary battery.

[Characteristic evaluation] Examples 1 to 9 and Comparative Examples 1 to
With respect to the hydrogen storage alloy obtained in 3, the PCT capacity, the pulverized residual rate, the aluminum elution rate, and the 1C electrode capacity at 0 ° C. were measured by the following methods. Table 2 shows the results.
Shown in

<PCT capacity> The hydrogen storage alloy is pulverized, classified to a particle size of 22 to 53 microns, and a predetermined amount is collected.
Filled into T holder. PCT holder 10 ^-3 Torr
After vacuum suction at r or lower, 30 atm of hydrogen gas was introduced therein, heated to 250 ° C. and maintained for 10 minutes. afterwards,
After cooling, hydrogen gas was absorbed in the hydrogen-absorbing alloy powder. This was performed twice, and an activation process was performed. After performing the activation treatment, vacuum suction is performed, and the hydrogen gas pressure is set to 30 by an automatic PCT device.
The PCT capacity up to atm was measured.

<Remaining ratio of pulverization> 30 ba
r hydrogen gas is introduced into the hydrogen-absorbing alloy powder classified to a particle size of 22 to 53 microns, and then evacuated and exhausted.
The value after the repetition was indicated by an index with the value of Comparative Example 1 being 100.

<Aluminum dissolution rate> An aluminum dissolution test was performed.
C.) for 48 hours, the amount of aluminum was quantified by ICP analysis, and indicated by an index with the value of Comparative Example 1 being 100.

<0 ° C., 1 C electrode capacity> (Preparation of electrode cell) Hydrogen storage alloy powder, nickel powder and polyethylene powder classified to a particle size of 22 to 53 μm in a ratio of 1: 3: 0.12 (weight ratio). After mixing, a predetermined amount of the obtained mixed powder was sampled, and a pellet having a diameter of 18 mm was prepared by a press to prepare a negative electrode.

A separator was sandwiched between the positive electrode (sintered nickel hydroxide) and the negative electrode, and closely attached with clips. This was put in a cup-shaped container, and a 31% by weight aqueous solution of an electrolytic solution (KOH) was injected until it was immersed in all of the positive electrode and the negative electrode, thereby producing an electrode cell. This electrode cell was connected to a charging / discharging device.

(Setting of charging / discharging device conditions) Setting of charging / discharging device conditions using this electrode cell is as follows. 1) Initial activation ・ Charge: 0.2C, 130% ・ Discharge: 0.2C, 0.7V cut ・ Cycle: 15 cycles ・ Temperature: 20 ° C

2) Measurement of electrode capacity at 0 ° C. and 1C After the completion of the initial activation, the electrode capacity was measured at 0 ° C. and 1C under the following conditions.・ Charge: 0.2 C, 130% ・ Discharge: 1 C, 0.7 V cut ・ Cycle: 1 cycle ・ Temperature: 0 ° C. The electrode capacity value (mAh / g) at 0 ° C. and 1 C gives low-temperature high-rate characteristics. evaluated.

[0038]

[Table 1]

[0039]

[Table 2]

As shown in Table 2, Examples 1 to 9
Compared with Comparative Example 1, the PCT capacity and the pulverized residual rate are equivalent, and the aluminum elution rate and the electrode capacity (low-temperature high-rate characteristics) are excellent. Examples 1 to 9 are superior to Comparative Example 2 in PCT capacity and electrode capacity (low-temperature high-rate characteristics). In Comparative Example 1, since the casting and the heat treatment were performed as described above, the production cost was high.

In Comparative Example 3, since the heat treatment was not performed, the cost was low. However, since the manufacturing method was casting, a large number of deviated phases were observed, and the output characteristics were good. The fine powder exhibiting life characteristics is extremely poor in residual ratio and Al elution ratio, and cannot be used as a negative electrode active material for nickel-hydrogen secondary batteries.

[Evaluation of X-ray Diffraction] The hydrogen storage alloys obtained in Examples 1 to 9 and Comparative Examples 1 to 3 were subjected to X-ray diffraction to obtain La.
Ni ₅ to 1060 ° C., when a standard sample which was heat treated 3 hours, against the standard sample, 20 ° ≦ 2θ ≦ 7
The relative ratio of the values of the half width of the diffraction line in the range of 0 ° was obtained. Table 3 shows the results. FIG. 1 shows an X-ray diffraction pattern of the standard sample (LaNi ₅ ), and FIGS.

[0043]

[Table 3]

As shown in Table 3 and FIGS. 1 to 4, Examples 1 to 9 were 20 ° with respect to the standard sample (LaNi ₅ ).
In the range of ≦ 2θ ≦ 70 °, the value of the half width of the diffraction line is relative ratio 1.
It has two or more of 10 or more. On the contrary,
In Comparative Example 1, the half-width of the diffraction line was narrow because of the heat treatment. Further, Comparative Example 2 has two or more diffraction line half-width values with respect to the standard sample having a relative ratio of 1.10 or more, but the alloy composition is out of the range specified in the present invention. Therefore, as shown in Table 2 above, the PCT capacity and the electrode capacity are inferior. Furthermore, Comparative Example 3 has two or more diffraction line half-width values with respect to the standard sample whose relative ratio is 1.10 or more. As shown, the pulverized residual ratio showing cycle life characteristics, Al
Very poor dissolution rate.

[0045]

As described above, according to the production method of the present invention, a hydrogen storage alloy having a specific alloy composition can be obtained at low cost and with good productivity. Then, when the hydrogen storage alloy having this specific alloy composition is used as a negative electrode active material of a nickel-hydrogen secondary battery, the electrode capacity,
The life characteristics (cycle characteristics) can be improved without lowering the discharge rate characteristics.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a standard sample (LaNi ₅ ).

FIG. 2 is an X-ray diffraction diagram of a hydrogen storage alloy of Comparative Example 1.

FIG. 3 is an X-ray diffraction diagram of a hydrogen storage alloy of Comparative Example 2.

FIG. 4 is an X-ray diffraction diagram of the hydrogen storage alloy of Example 1.

Continued on the front page (72) Shingo Kikukawa, Inventor 1-5-1, Shiomachi, Takehara-shi, Hiroshima Prefecture Battery Materials Research Laboratory, Mitsui Kinzoku Mining Co., Ltd. (72) Kiyotaka Yasuda 1-5-1, Shiomachi, Takehara-shi, Hiroshima Prefecture Mitsui Kinzoku Mining Co., Ltd. Battery Materials Research Laboratory F-term (reference) 4E004 DB01 DB02 DB03 TA06 5H003 AA04 BB02 BC06 BD00 BD01 BD03 BD04 BD05

Claims (4)

[Claims] 1. A method of heating and dissolving a hydrogen storage alloy raw material, and using a single roll method or a twin roll method, performing ultra-quench solidification at an ultra-rapid cooling rate of 10 K ³ / sec or more, and thereafter performing no heat treatment. manufacturing method of AB ₅ type hydrogen storage alloy having a CaCu ₅ type crystal structure represented by the following formula. Formula _{Mm (La f) Ni a Mn} b Al c Co d X e ( wherein, Mm is the mischmetal, X is vanadium or titanium, 4.00 ≦ a ≦ 4.30,0.30 ≦ b ≦ 0. 5
0, 0.20 ≦ c ≦ 0.45, 0.20 ≦ d ≦ 0.6
0, 0 ≦ e ≦ 0.05, 5.00 ≦ a + b + c + d + e
≦ 5.35, wherein a to e are moles per mole of Mm, and f is 19 to 21% by weight. Wherein the following formula _{Mm (La f) Ni a Mn} b Al c Co d X e ( wherein, Mm is the mischmetal, X is vanadium or titanium, 4.00 ≦ a ≦ 4.30,0. 30 ≦ b ≦ 0.5
0, 0.20 ≦ c ≦ 0.45, 0.20 ≦ d ≦ 0.6
0, 0 ≦ e ≦ 0.05, 5.00 ≦ a + b + c + d + e
≦ 5.35, wherein a to e are moles per mole of Mm, and f is 19 to 21% by weight.
_{When a} standard sample is obtained by heat treating LaNi ₅ at 1060 ° C. for 3 hours and having a _5- type crystal structure, the X-ray diffraction diffracts the standard sample in the range of 20 ° ≦ 2θ ≦ 70 °. AB ₅ type hydrogen storage alloy, characterized in that it has at least two of the line half-width values having a relative ratio of 1.10 or more. 3. A nickel-hydrogen secondary battery using the hydrogen storage alloy obtained by the production method according to claim 1 as a negative electrode active material. 4. A nickel-hydrogen secondary battery using the hydrogen storage alloy according to claim 2 as a negative electrode active material.