JP2980371B2 - Hydrogen storage alloy for secondary batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a hydrogen storage alloy for a secondary battery used as a negative electrode material for an alkaline secondary battery.

(Prior Art) It is known that an alkaline secondary battery using a LaNi _5- based hydrogen storage alloy as a negative electrode has a higher capacity and a higher energy density than a nickel-cadmium secondary battery having the same volume. Such an alkaline secondary battery is subject to corrosion due to the reaction of the hydrogen storage alloy with an electrolytic solution, and hydrogen storage and storage due to charge and discharge.
Since the pulverization due to the repeated release lowers the charge / discharge cycle life, the characteristics of the hydrogen storage alloy determine the final battery characteristics.

For this reason, many reports have been made to improve the characteristics by diversifying the hydrogen storage alloy. As a typical example, the Ni portion of the LaNi ₅ hydrogen storage alloy is represented by Co, Al, M
It is known that substitution with n, Fe, Cr, or the like reduces the hydrogen equilibrium pressure at the time of absorbing and releasing hydrogen, and improves the corrosion resistance of the alloy. In addition, L of the LaNi _5- based hydrogen storage alloy
It is also known that substituting part a with another rare earth element can improve the cycle life of the secondary battery.

By the way, when producing a negative electrode from a hydrogen storage alloy, by using an alloy powder activated by hydrogenation in advance, or by using a mechanically pulverized alloy and charging it after battery production and before shipping. An electrochemically hydrogen activated alloy powder is used. Since hydrogen activation (hydrogen storage) is performed in any of the alloy powders, the hydrogen storage alloy undergoes volume expansion. However, the order LaNi ₅ type hydrogen absorbing alloy and the hydrogen storage alloy of Ni and La and other elements substitutions have high homogeneity in high purity, it said volume is no portion where the strain is concentrated upon inflation, a rather slight in manufacturing Cracks are caused due to uneven concentration of alloy components caused by the difference in conditions, and a large difference occurs in the manner of the cracks. as a result,
The particle size distribution of the hydrogen-absorbing alloy particles cracked by the hydrogenation may be remarkably widened, or the average particle size may significantly change depending on the production lot. Therefore, the alkaline secondary battery incorporating the negative electrode produced from the hydrogen-activated hydrogen storage alloy has a problem that the characteristics such as the life are varied.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and the progress of cracks due to volume expansion at the time of hydrogen absorption is almost constant, and the particle size distribution is narrow and average. An object of the present invention is to provide a hydrogen storage alloy for a secondary battery capable of achieving a uniform particle size.

[Constitution of the Invention] (Means for Solving the Problems) The hydrogen storage alloy for a secondary battery according to the present invention is LnNi _x A _y
(Ln is at least one rare earth element containing Y, A is Co,
Al, Fe, Si, Cr, Cu, at least one of Mn, x and y each represent 4.5 <x + y <5.5, x> 2.5), in the hydrogen storage alloy represented by Pb or Pb compound at the grain boundary It is characterized by being precipitated.

The composition of Ln in the general formula representing the hydrogen storage alloy is La
40-50% by weight, Ce 0-10% by weight, Pr 5-15% by weight, Nd30-
45% by weight, other rare earth elements and impurities 0-5% by weight
It is desirable that A in the general formula is Co, M
More preferably, it is composed of three elements of n and Al.

The reason why x and y in the general formula representing the hydrogen storage alloy are limited is that if they depart from the above range, it becomes impossible to maintain the hydrogen storage capacity and improve the corrosion resistance.

As the Pb compound precipitated at the grain boundary, for example, PbLn
(Ln is at least one rare earth element containing Y).

The amount of Pb contained in the alloy is preferably in the range of 10 to 1500 ppm, more preferably 20 to 1000 ppm. The reason for this is that if the Pb content is less than 10 ppm, it is not only difficult to sufficiently induce cracks originating from Pb or a Pb compound due to volume expansion during hydrogen absorption, but also due to the non-uniform concentration of alloy components and the like. Since cracks are generated based on the difference in strength, the number of cracks may increase. On the other hand, the Pb amount is 1500
If the concentration exceeds ppm, cracks due to volume expansion during hydrogen storage become remarkable, and when a negative electrode made of the hydrogen storage alloy is incorporated in a secondary battery, the contact area with the electrolyte increases more than necessary and hydrogen There is a risk of accelerating the progress of corrosion of the storage alloy.

The state in which Pb or a precipitate containing Pb exists in the hydrogen storage alloy can be verified by the following method.

. Particles having a size of 75 μm or less are prepared by a pulverizing step including at least one hydrogen storage / release for the hydrogen storage alloy. Subsequently, the particles are immersed in an aqueous solution of 0.2% by weight of nitric acid, 0.2% by weight of lactic acid and 0.6% by weight of acetic acid. The content of Pb or Pb compound in the eluted material when 5 to 15% by weight of the hydrogen storage alloy is dissolved by such immersion is W ₁ , the content of Pb in the entire alloy is W ₂ , Ratio (W ₁ /
It is verified that the following formula (1) is satisfied when W ₂ ) is R ₁ and the ratio of the total weight of the eluate to the alloy weight is R ₂ .

R ₂ <R ₁ (1). The alloy particles obtained by subjecting the hydrogen storage alloy to hydrogenation and pulverization once at 0 ° C. under a hydrogen pressure of 10 atm are sieved through a sieve having a mesh interval of 25 μm. It is verified that the passing rate when passing through such a sieve is 40% by weight or less.

Further, another hydrogen storage alloy for a secondary battery according to the present invention is LnNi _x A _y (where Ln is at least one of rare earth elements containing Y).
Species, A is at least one of Co, Al, Fe, Si, Cr, Cu, and Mn
1μm species, x, y respectively 4.5 <x + y <5.5, the hydrogen storage alloy represented by x> 2.5), during the polishing surface 1 mm ²
It has a long axis as described above, and is characterized in that there are an average of 300 or less grains containing 1% by weight or more of Pb or a Pb compound.

The major axis of the grains existing in the polished surface 1 mm ² was limited for the following reason. 1μ
If it is less than m, it is unlikely to be a starting point of cracks when storing hydrogen,
Another factor, for example, a small difference in hardness due to uneven distribution of alloy constituent elements often causes cracking, so that alloy pulverization becomes remarkable, and when a negative electrode manufactured from the hydrogen storage alloy is incorporated in a secondary battery In addition, the contact area with the electrolyte is increased more than necessary, and the progress of corrosion of the hydrogen storage alloy is accelerated. A more preferred long axis of the grains is in the range of 1 to 20 μm.

The reason for limiting the number of grains present in the polishing surface 1 mm ^2, the number is cracking is significantly associated with exceeding the volume expansion during the hydrogen occluding 300, two negative electrode produced from the hydrogen storage alloy This is because when the battery is incorporated in a secondary battery, the contact area with the electrolytic solution increases more than necessary, thereby accelerating the progress of corrosion of the hydrogen storage alloy. A more preferred number of grains is in the range of 20 to 200.

(Function) According to the hydrogen storage alloy according to the present invention, since it is represented by LnNi _x A _y and has a structure in which Pb or a Pb compound is precipitated at the grain boundary, the volume at the time of hydrogen storage in the hydrogen activation step is obtained. Upon expansion, the precipitation site of Pb or the Pb compound acts as strain, and cracks are concentrated at the site. That is, the crack caused by the volume expansion of the hydrogen storage alloy during hydrogen storage
Alternatively, it can be controlled by the location where the Pb compound is deposited.
As a result, the progress of cracks due to volume expansion during hydrogen storage can be substantially constant, and a narrow particle size distribution and a uniform average particle size can be achieved. Therefore, by using the negative electrode made from such a hydrogen storage alloy, the surface area of the negative electrode, that is, the rate of increase of the contact area with the alkaline electrolyte can be kept constant, and the corrosion deterioration rate of the hydrogen storage alloy due to the reaction with the electrolyte can be reduced. Since it can be kept constant, an alkaline secondary battery having a long cycle life and stable characteristics can be obtained.

According to another hydrogen storage alloy according to the present invention, LnNi
is represented by _x A _y, have more long axis 1μm in the polishing surface 1 mm ^2, the grains mean 300 containing 1% by weight or more of Pb or Pb compounds
Since the number of particles is less than or equal to the number, the particles of the predetermined component act as strains during volume expansion at the time of hydrogen storage in the hydrogen activation step, and cracks are concentrated at the positions. That is, the cracks associated with the volume expansion of the hydrogen storage alloy during hydrogen storage can be controlled by the locations where the grains are deposited. As a result, the progress of cracks due to volume expansion during hydrogen storage can be substantially constant, and a narrow particle size distribution and a uniform average particle size can be achieved. Therefore, by using the negative electrode manufactured from such a hydrogen storage alloy, the surface area of the negative electrode, that is, the rate of increase of the contact area with the alkaline electrolyte can be constant,
Since the corrosion deterioration rate of the hydrogen storage alloy due to the reaction with the electrolyte can be kept constant, an alkaline secondary battery having a long cycle life and stable characteristics can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail.

Example 1 First, a rare earth element Ln (La; 45% by weight, Ce;
10% by weight, Pr; 10% by weight, Nd; 40% by weight), Ni, Co, Mn,
Al as a component, LnNi _4.2 Co _0.2 Mn by high frequency melting
An alloy having a composition of _0.3 Al _0.3 was prepared and quantitatively analyzed.
It was confirmed that the Pb content was 10 ppm or less. Also, Pb
As a rare earth element Ln (La; 4; 99.9% pure)
5% by weight, Ce; 10% by weight, Pr; 10% by weight, Nd; 40% by weight),
Ni, and Co, Mn, Al, and constituents Pb, to prepare an alloy having a composition of LnNi _4.2 Co _0.2 Mn _0.3 Al _0.3 by high frequency melting, it was confirmed that the Pb content of about 2000ppm by quantitative analysis.

Next, the two alloys alone or the Pb content was adjusted by mixing and arc melting in an inert atmosphere,
Pb content is less than 10ppm, 50ppm, 200ppm, 500pp respectively
Two alloy samples each having m, 1000 ppm, and 2000 ppm were prepared, and annealed at 1000 ° C. for 10 hours in an inert atmosphere. Some of these 12 samples were mechanically crushed,
After sieving, particles of 25 to 75 μm were taken out, 96% by weight of these alloy particles and 4 parts by weight of polytetrafluoroethylene were mixed, kneaded and pressed on a nickel mesh to prepare a hydrogen storage alloy negative electrode. Subsequently, these hydrogen storage alloy negative electrodes were wound through a separator together with a nickel electrode for a nickel-cadmium battery to form an electrode group, and these electrode groups were loaded into a container equipped with a sensor for measuring internal pressure, and 8 mol / mol. KOH
The electrolyte was injected, and a secondary battery having a positive electrode capacity of 1000 mAh and a negative electrode capacity of 1500 mAh was assembled.

On the other hand, about 0.5 g of each of the alloy particles was weighed, and these alloy particles were immersed in 100 ml of an aqueous solution of 0.2% by weight of nitric acid, 0.2% by weight of lactic acid and 0.6% by weight of acetic acid for 10 minutes. While measuring W ₁ ), the ratio (R ₂ ) of the total weight of the eluate to the weight of the alloy was measured. In addition, analysis was performed using the rest of the 12 samples, and the Pb content (W ₂ ) in the entire alloy was measured. These results are shown in Table 1 below, and the ratio (W ₁ / W ₂ ) of the content of Pb in the eluate to the content of Pb in the entire alloy is shown as R ₁ .

About the obtained secondary battery, charging; 1000 mA, 90 minutes,
Discharge; charge and discharge were repeated under the conditions of 1000 mA and a cutoff voltage of 1 V, and the number of cycles required for the battery internal pressure to exceed 15 kg / cm ² at the end of charging was measured. The results are shown in Table 1 below together with the various measurement results of the alloy particles described above.

As is clear from Table 1 below, the content of Pb in the eluted material is W ₁ , the content of Pb in the entire alloy is W ₂ ,
When the ratio of the Pb content (W ₁ / W ₂ ) is R ₁ and the ratio of the total weight of the eluted material to the alloy weight is R ₂ , the following formula is satisfied: R ₂ <R _1, and the Pb content of the alloy is 10%. Appropriate amount of Pb which is ~ 15000ppm
The secondary batteries (Nos. 3 to 10 in Table 1) incorporating the hydrogen-absorbing alloy negative electrode produced from the alloy particles having precipitated thereon are secondary batteries (Nos. 1 and 2 in Table 1) that do not satisfy the above formula. It can be seen that it has an excellent cycle life as compared with 2, 11, 12).

Example 2 LnNi _4.2 Co _0.2 Mn _0.3 A produced in the same manner as in Example 1.
l Two kinds of alloys with different compositions of Pb with a composition of _0.3 were used, mixed at different proportions of these alloys, arc melted in an inert atmosphere, and then annealed at 1000 ° C for 10 hours in an inert atmosphere. By doing so, 12 kinds of samples having different Pb contents were prepared. When the Pb content was measured by analyzing a part of these 12 kinds of samples, the results shown in Table 2 below were obtained, and it was confirmed that there was almost no fluctuation in the concentration of the main constituents. Subsequently, the remaining part was degassed at 80 to 90 ° C. in a vacuum, then cooled to absorb and release hydrogen under a hydrogen pressure of 9 to 10 atm, and further sieved to collect particles of 25 to 75 μm. . Through these steps, 12 kinds of alloy particles having a passing amount of a 25-mesh sieve shown in Table 2 below were obtained.

Next, 96% by weight of each of the alloy particles and 4% by weight of polytetrafluoroethylene were mixed and kneaded and pressed on a nickel net to prepare a hydrogen storage alloy negative electrode. Subsequently, these hydrogen storage alloy negative electrodes were wound through a separator together with a nickel electrode for a nickel-cadmium battery to form an electrode group, and these electrode groups were loaded into a container equipped with a sensor for measuring internal pressure, and 8 mol / mol. Inject KOH electrolytic solution, positive electrode capacity 1000mA
h, a secondary battery having a negative electrode capacity of 1500 mAh was assembled.

About the obtained secondary battery, charging; 1000 mA, 90 minutes,
Discharge; charge and discharge were repeated under the conditions of 1000 mA and a cutoff voltage of 1 V, and the number of cycles required for the battery internal pressure to exceed 15 kg / cm ² at the end of charging was measured. The result 2
Also shown in the table.

As is clear from Table 2 below, a hydrogen storage alloy negative electrode produced from alloy particles having a passage amount of 40% by weight or less through a mesh sieve having a spacing of 25 μm, that is, alloy particles in which a predetermined amount of Pb is precipitated at grain boundaries, is used. Installed secondary batteries (No. 3 in Table 2,
Nos. 4, 8) are secondary batteries (No. 1, 2, 5, 7, 9, 10, 10 in Table 2) using alloy particles having a passing amount of more than 40% by weight.
It can be seen that it has a superior cycle life as compared to 11 and 12).

Example 3 LnNi containing about 2000 ppm of Pb by the same method as in Example 1.
_3.9 Co _0.5 Mn _0.3 Al _0.3 alloy and LnNi _3.9 containing 10 ppm or less of Pb
After preparing Co _0.5 Mn _0.3 Al _0.3 alloys, changing the proportions of these alloys and mixing them, arc melting was performed in an inert atmosphere, and annealing was performed at 1000 ° C. for 10 hours under an inert atmosphere to reduce the Pb content. Twelve different samples were made. When the Pb content was measured by analyzing a part of these 12 kinds of samples, the results shown in Table 3 below were obtained, and it was confirmed that there was almost no fluctuation in the concentration of the main constituents. Subsequently, the remaining part is degassed in a vacuum at 80 to 90 ° C., cooled, absorbed and released of hydrogen under a hydrogen pressure of 9 to 10 atm, and further sieved.
7575 μm particles were collected. Through these steps, 12 kinds of alloy particles having a passing amount of a 25-mesh sieve shown in Table 3 below were obtained.

Next, 96% by weight of each of the alloy particles and 4 parts by weight of polytetrafluoroethylene were mixed and kneaded and pressed on a nickel mesh to prepare a hydrogen storage alloy negative electrode. Subsequently, these hydrogen storage alloy negative electrodes were wound through a separator together with a nickel electrode for a nickel-cadmium battery to form an electrode group, and these electrode groups were loaded into a container equipped with a sensor for measuring internal pressure, and 8 mol / mol. Inject KOH electrolytic solution, positive electrode capacity 1000mA
h, a secondary battery having a negative electrode capacity of 1500 mAh was assembled.

About the obtained secondary battery, charging; 1000 mA, 90 minutes,
Discharge; charge and discharge were repeated under the conditions of 1000 mA and a cutoff voltage of 1 V, and the number of cycles required for the battery internal pressure to exceed 15 kg / cm ² at the end of charging was measured. 3
Also shown in the table.

As is clear from Table 3 below, a hydrogen storage alloy negative electrode prepared from alloy particles having a passing amount of 40% by weight or less through a mesh sieve having a spacing of 25 μm, that is, alloy particles in which a predetermined amount of Pb is precipitated at grain boundaries, is used. Installed secondary battery (No. 2 in Table 3,
Nos. 3, 6, 8, and 9) are secondary batteries (Nos. 1, 4, 5, and 5 in Table 3) using alloy particles whose passing amount exceeds 40% by weight.
7, 10 to 12).

Using Example 4 in the same manner as in Example 1 _{LnNi 4.2 Co 0.2 Mn 0.3 Al 0.3} 2 kinds of alloys having different Pb content in the composition of the prepared in, and mixed by changing a more proportion of these alloys alone or mixed After that, arc melting in an inert atmosphere,
Pb content is less than 10ppm, 50ppm, 200ppm, 500pp respectively
Five alloy samples each having m, 1000 ppm, and 2000 ppm were prepared, and annealed at 1000 ° C. for 10 hours in an inert atmosphere. Some of these 30 samples were mechanically crushed,
After sieving, particles of 25 to 75 μm were taken out, 96% by weight of these alloy particles and 4 parts by weight of polytetrafluoroethylene were mixed, kneaded and pressed on a nickel mesh to prepare a hydrogen storage alloy negative electrode. Subsequently, these hydrogen storage alloy negative electrodes were wound together with a nickel electrode for a nickel-cadmium battery through a separator to form an electrode group, and these electrode groups were loaded into a container equipped with a sensor for measuring internal pressure, and 8 mol / mol. K
Inject OH electrolyte, positive electrode capacity 1000mAh, negative electrode capacity 1500mAh
Was assembled.

On the other hand, the content of Pb in each of the alloy particles was measured. After the surfaces of the alloy particles were polished, the particles were observed with a scanning electron microscope to determine the major axis length and the number of precipitated particles containing Pb per 1 mm ² of the polished surface of the alloy. The results are shown in Table 4 below.

About the obtained secondary battery, charging; 1000 mA, 90 minutes,
Discharge; charge and discharge were repeated under the conditions of 1000 mA and a cutoff voltage of 1 V, and the number of cycles required for the battery internal pressure to exceed 15 kg / cm ² at the end of charging was measured. The result 4
The table is also shown together with the various measurement results of the alloy particles described above.

As is clear from Table 4 below, hydrogen prepared from alloy particles having a major axis of 1 μm or more in a polished surface of 1 mm ² and having an average of 300 or less precipitated particles containing 1% by weight or more of Pb exist. It can be seen that the secondary battery incorporating the storage alloy negative electrode has excellent cycle life.

[Effects of the Invention] As described in detail above, according to the hydrogen storage alloy according to the present invention, the progress of cracks due to volume expansion during hydrogen storage is almost constant, and a narrow particle size distribution and a uniform average particle size can be achieved. Further, by using the negative electrode made of such a hydrogen storage alloy, a remarkable effect such as a secondary battery having an excellent sunkle life can be obtained.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideki Matsunaga 1st place, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture (72) Inventor Momoko Takemura 1 Komukai-Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Address Toshiba Research Institute, Inc. (72) Inventor Kazuta Takeno 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (72) Inventor Hiroshi Endo Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Toshiba Research Consulting Co., Ltd. (56) References JP-A-2-277737 (JP, A) JP-A-1-162741 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) C22C 19/00 F H01M 4/38

Claims (3)

(57) [Claims] 1. LnNi _x A _y (Ln is at least one kind of rare earth element containing Y, A is at least one kind of Co, Al, Fe, Si, Cr, Cu and Mn, and x and y are each 4.5 <x + y <5.5, x> 2.
In the hydrogen storage alloy represented by (Fig. 5), Pb
Alternatively, a hydrogen storage alloy for a secondary battery, wherein a Pb compound is precipitated. 2. The hydrogen storage alloy according to claim 1, wherein the amount of Pb contained in the alloy is 10 to 1500 ppm. 3. LnNi _x A _y (Ln is at least one kind of rare earth element containing Y, A is at least one kind of Co, Al, Fe, Si, Cr, Cu and Mn, and x and y are each 4.5 <x + y. <5.5, x> 2.
5) The hydrogen storage alloy represented by 5), characterized in that the polished surface has a major axis of 1 μm or more in 1 mm ² , and that there is an average of 300 or less grains containing 1% by weight or more of Pb or a Pb compound. Hydrogen storage alloy for secondary batteries.