JPH09153356A - Hydrogen storage alloy electrode and manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the battery characteristics such as the cycle characteristic, the high rate discharge characteristic, and the like by suppressing occurrence of the inactive state and the pulverization of hydrogen storage alloy. SOLUTION: Hydrogen storage alloy manufactured by a rapidly solidifying method is pulverized so as to manufacture hydrogen storage alloy powder, and one part of the hydrogen storage alloy powder is contained by an electrode 2. Then, among the hydrogen storage alloy powder having various particle diameters, the large particle diameter hydrogen storage alloy powder whose weight cumulation from a large particle side reaches 60% or less is used.

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 electrode used as a negative electrode of a metal-hydrogen alkaline secondary battery, and more specifically, to improve cycle characteristics and high rate discharge characteristics. , And to improvement of hydrogen storage alloy as electrode material.

[0002]

2. Description of the Related Art In recent years, hydrogen storage alloys capable of reversibly storing and releasing hydrogen have been actively developed.
Metal-hydrogen alkaline secondary batteries using such a hydrogen storage alloy as a negative electrode material are lighter in weight and higher in capacity than lead storage batteries, nickel-cadmium storage batteries and the like which have been generally used conventionally. For this reason, it is regarded as promising as the mainstream of the next-generation alkaline secondary batteries.

By the way, the hydrogen storage alloy for batteries must be capable of reversibly storing and releasing hydrogen near room temperature. The following method has been proposed as a method for producing an electrode using such a hydrogen storage alloy.

First, a metal element is weighed, the metal element is melted in a melting furnace, and then this molten metal is cooled by a rapid solidification method such as a roll method to prepare a hydrogen storage alloy ingot. Next, the hydrogen storage alloy ingot is pulverized by a mechanical pulverization method or a hydrogenation pulverization method to prepare a hydrogen storage alloy powder, and then the hydrogen storage alloy powder and a binder are kneaded to form an active material paste. Create. Then, the active material paste was pressure-bonded to both sides of the current collector and pressed to produce the active material paste.

[0005]

However, in the metal-hydrogen alkaline secondary battery using the above-mentioned conventional hydrogen storage alloy electrode, when the hydrogen atoms are stored and released during charge and discharge, the crystal lattice of the alloy is changed. Expansion and contraction stress is applied. For this reason, when repeatedly charged and discharged, the hydrogen storage alloy is gradually pulverized to form a new surface, the elements of the alloy exposed on the new surface are oxidized, and an inert film is formed on the alloy surface,
The elements of the alloy are dissolved in the electrolytic solution to change the alloy composition.

In particular, the hydrogen storage alloy produced by the rapid solidification method (special method, roll method) has a cooling rate higher than that of the ordinary casting method (the method of pouring the molten hydrogen storage alloy into a water-cooled mold for cooling and solidification). For example, in the case of the roll method, since it is large, the alloy on the roll surface side (the portion in contact with the roll where the molten metal of the hydrogen storage alloy is rapidly cooled) and the opposite side to the roll surface (gas The alloy structure and the alloy on the side in contact with the hydrogen storage alloy in which the cooling of the molten metal of the hydrogen storage alloy is slightly slower) differ in the grain structure of the hydrogen storage alloy powder after crushing the hydrogen storage alloy. Specifically, the alloy in the quenching part has a chilled crystal with a uniform structure, and the particle size of the hydrogen storage alloy powder after crushing is high, while the alloy in the slow cooling part has a slightly nonuniform structure. And, and
The particle size of the hydrogen storage alloy powder after crushing is low because of its low hardness.

When an electrode and a battery are produced by using hydrogen storage alloy powders of all sizes, large and small, and the charge and discharge cycle is repeated, the hydrogen storage alloy powders of small size are selectively charged and discharged to form fine powder. While the elements of the alloy exposed on the nascent surface are oxidized, the large-diameter hydrogen storage alloy powder is not charged and discharged and becomes inactive. For these reasons, there is a problem that cycle characteristics and high rate discharge characteristics are deteriorated.

The object of the present invention is to finely pulverize a hydrogen storage alloy with the progress of charge / discharge cycles, which makes it possible to obtain a metal-hydrogen alkaline secondary battery having excellent cycle characteristics and high rate discharge characteristics. Another object of the present invention is to provide a hydrogen storage alloy electrode that is less likely to be deactivated and a manufacturing method thereof.

[0009]

Means for Solving the Problems A hydrogen storage alloy electrode according to the present invention for achieving the above object is obtained by pulverizing a hydrogen storage alloy produced by a rapid solidification method, and A hydrogen storage alloy electrode containing hydrogen having a large particle size such that the value represented by the following mathematical formula 3 is 60% or less among the hydrogen storage alloy powders having various particle sizes when the hydrogen storage alloy is pulverized. The storage alloy powder is contained.

[0010]

(Equation 3)

The method for producing a hydrogen storage alloy electrode according to the present invention is the first method for producing a hydrogen storage alloy by the rapid solidification method.
A step, a second step of crushing the hydrogen-absorbing alloy to produce a hydrogen-absorbing alloy powder, and a value of 60% of the value of the hydrogen-absorbing alloy powder having various particle diameters at the time of the crushing. And a third step of selecting a hydrogen storage alloy powder having a large particle size as follows.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy electrode of the present invention has a hydrogen storage alloy powder produced by crushing a hydrogen storage alloy produced by a rapid solidification method, and the value represented by the following formula 4 is 60.
The hydrogen-absorbing alloy powder having a large particle size is contained so that the content of the hydrogen-absorbing alloy powder is not more than%.

[0013]

(Equation 4)

Details will be described with reference to FIG. In FIG. 2, the vertical axis represents% by weight, the horizontal axis represents the particle size, the total amount of hydrogen storage alloy powder at the time of crushing is indicated by A + B, and the total amount of hydrogen storage alloy powder from the large particle size side is indicated by A. An unused hydrogen storage alloy powder is indicated by B. Then, only the hydrogen-storing alloy powder on the large particle size side is separated so that the value represented by the above mathematical expression 4 becomes 60% or less, and only the separated hydrogen-storing alloy powder on the large particle size side is used as the hydrogen storage alloy electrode. It is used.

With such a structure, all the hydrogen storage alloys are uniformly charged and discharged without selectively charging and discharging only the hydrogen storage alloy having a small diameter when charging and discharging the battery. Therefore, it is possible to suppress the hydrogen storage alloy from becoming inactive or being pulverized.

Examples of the rapid solidification method include a roll method, an atomizing method, a centrifugal atomizing method, and an underwater casting method (unlike the ordinary casting method, the molten hydrogen storage alloy is cooled in water so that it is rapidly cooled). However, the method is not limited to these methods. When the above-mentioned roll method is used, the roll method has a particularly high cooling rate among the rapid solidification methods, so that the above-mentioned effects such as prevention of pulverization are further exhibited.

As a method of crushing the above-mentioned hydrogen storage alloy ingot, a hydrogenation crushing method or a mechanical crushing method can be used.
In particular, when the hydrogenation and pulverization method is used, the hydrogenation and pulverization method pulverizes the hydrogen storage alloy by taking in and out hydrogen similarly to the charging and discharging of the battery, and therefore, it is strong in pulverization during charging and discharging of the battery. It has a correlation. Therefore, the object of the present invention can be further achieved by using the hydro-grinding method.

As the hydrogen storage alloy, Mm _1.0 Ni
_3.4 Co _0.8 Al _0.2 Mn _0.6 , LaNi ₅ , MmNi
_{Although 5 and the} like are exemplified, it goes without saying that the hydrogen storage alloy is not limited to these.

If the value of the above equation 4 is set too small, the amount of unused hydrogen storage alloy powder increases and the manufacturing cost rises. Therefore, the value of the above equation 4 is 40 to 60%.
It is desirable to be between.

[0020]

【Example】

(First Example) (Example I) [Preparation of Hydrogen Storage Alloy] Commercially available Mm (Misch metal), Ni, Co, Al and Mn were used in a molar ratio of 1.0:
A so-called roll method in which the melt is mixed at a ratio of 3.4: 0.8: 0.2: 0.6, melted in a high-frequency melting furnace to prepare a melt, and the melt is ejected onto the peripheral surface of a roll rotating at a high speed. Solidified by. At this time, the cooling rate of the molten metal was 10 × 10
^The roll peripheral speed was adjusted so as to be ³ ° C / sec or more. Through the above steps, the composition formula Mm _1.0 Ni _{3. 4} Co _0.8 Al
A hydrogen storage alloy ingot represented by _0.2 Mn _0.6 was obtained.

[Preparation of Hydrogen Storage Alloy Electrode] The above hydrogen storage alloy ingot was mechanically pulverized by a ball mill in an inert gas to prepare hydrogen storage alloy powder. At this time, the grinding time was 13 minutes and 30 seconds. Next, the hydrogen-absorbing alloy powder was classified according to particle size, and then the hydrogen-absorbing alloy powder was separated by meshing so that the value represented by the equation 4 was 40%. The average particle size of the hydrogen storage alloy powder thus separated is 50 μm.

Next, 5 wt% of polytetrafluoroethylene powder as a binder was added to the above hydrogen absorbing alloy powder on the large particle size side as an active material to prepare an active material paste. Then, this active material paste was pressure-bonded to both sides of a current collector made of punching metal, and further pressed to produce a negative electrode. The electrode thus manufactured is hereinafter referred to as an electrode A1 of the invention.

[Positive Electrode] As a positive electrode, a known sintered nickel positive electrode was prepared.

[Electrolytic Solution] A 30% by weight KOH aqueous solution was prepared.

[Production of Battery] A cylindrical battery of the present invention was produced using the positive and negative electrodes and the alkaline electrolyte described above. A non-woven fabric was used as the separator, which was impregnated with the electrolytic solution.

FIG. 1 is a sectional view schematically showing a battery using the electrode A1 of the present invention. The battery of the present invention shown in FIG.
The negative electrode 2, a separator 3 separating these two electrodes, a positive electrode lead 4, a negative electrode lead 5, a positive electrode external terminal 6, a negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are accommodated in the negative electrode can 7 in a state of being spirally wound via the separator 3 into which the electrolytic solution is injected, and the positive electrode 1 is connected to the positive electrode external terminal via the positive electrode lead 4. 6, and the negative electrode 2 is connected to a negative electrode can 7 via a negative electrode lead 5 so that chemical energy generated inside the battery can be taken out as electric energy to the outside. The theoretical capacity of the battery thus manufactured is 1000 mAh.

(Embodiment II) The value represented by the above equation 4 is 60.
%. An electrode and a battery were produced in the same manner as in Example I above, except that the negative electrode was produced by adjusting the content to be%. However, the average particle size of the hydrogen storage alloy powder was 50 μm as in Example I.
The crushing time of the hydrogen storage alloy in this Example II was set to 13 minutes in order to obtain m. The electrode thus manufactured is hereinafter referred to as an electrode A2 of the invention.

(Example III) An electrode and a battery were produced in the same manner as in Example I except that the negative electrode was produced using a hydrogen storage alloy powder having an average particle size of 40 μm. In addition, as in the above-mentioned Example I, the value shown by the above-mentioned equation 4 should be 60%,
The grinding time of the hydrogen storage alloy in Example III was set to 14 minutes. The electrode thus manufactured is hereinafter referred to as an electrode A3 of the invention.

(Comparative Examples I and II) An electrode and a battery were prepared in the same manner as in Example I except that the negative electrode was prepared by adjusting the values shown in the above equation 4 to be 80% and 100%, respectively. Was produced. However, the grinding time of the hydrogen storage alloy was set to 12 minutes and 10 minutes, respectively, so that the average particle diameter of the hydrogen storage alloy powder was set to 50 μm as in Example I. The electrodes thus manufactured are hereinafter referred to as a comparison electrode X1 and a comparison electrode X2, respectively.

(Comparative Example III) The above Comparative Example except that a negative electrode was prepared using a hydrogen storage alloy powder having an average particle size of 40 μm.
An electrode and a battery were prepared in the same manner as II. As in Comparative Example II, the crushing time of the hydrogen storage alloy in Comparative Example III was set to 1 so that the value expressed by the equation 4 was 100%.
It was 1 minute. The electrode thus manufactured is hereinafter referred to as a reference electrode X3.

[Charge / Discharge Cycle Test I] First, for batteries using the electrodes A1 to A3 of the present invention and the reference electrodes X1 to X3, after charging at 100 mA for 16 hours at room temperature (25 ° C.) and resting for 1 hour, , 200 mA, discharge end voltage 1.
The battery was activated by performing 3 cycles of 1 cycle including a step of discharging to 0 V and resting for 1 hour.

Next, each battery was charged at 1500 mA for 48 minutes at room temperature (25 ° C.) and rested for 1 hour.
A charging / discharging cycle test in which one cycle includes a step of discharging at 1500 mA to an end-of-discharge voltage of 1.0 V and resting for 1 hour was performed, and the time when the battery capacity reached 500 mA (half the initial capacity) was defined as the life. The results are shown in Table 1 below.

[0033]

[Table 1]

As shown in Table 1 above, in the battery using the electrodes A1 to A3 of the present invention in which the value represented by the formula 4 is 60% or less, the reference electrode X1 in which the value represented by the formula 4 exceeds 60%. It can be seen that the cycle life is longer than that of the battery using ~ X3. This is the electrode A1 of the present invention.
In the battery using ~ A3, since all the hydrogen storage alloys are uniformly charged and discharged without selectively charging and discharging only the hydrogen storage alloy having a small diameter, it is possible to prevent the hydrogen storage alloy from being pulverized. On the other hand, in the battery using the reference electrodes X1 to X3, only the hydrogen storage alloy having a small diameter is selectively charged and discharged, and therefore, the hydrogen storage alloy is promoted to be pulverized. it is conceivable that.

(Examples IV and V) Electrodes and batteries were produced in the same manner as in Examples I and II above, except that the anode was produced by using the atomization method as the method for casting the hydrogen storage alloy. The atomizing method is a method of spraying the molten hydrogen-absorbing alloy produced in the same manner as in Example I from the pores by the argon gas pressure and quenching it. The average particle size of the hydrogen storage alloy powder after this spraying was 100 μm, and it was then mechanically crushed. The electrodes thus manufactured are hereinafter referred to as electrodes A4 and A5 of the invention, respectively.

(Comparative Examples IV and V) Electrodes were prepared in the same manner as in Comparative Examples I and II except that the anode was prepared by using the atomizing method shown in Examples IV and V as a method for casting the hydrogen storage alloy. And the battery was produced. The electrodes thus manufactured are hereinafter referred to as reference electrodes X4 and X5, respectively.

[Charge / Discharge Cycle Test II] Inventive Electrode A
With respect to the battery using No. 4, A5 and the comparative electrodes X4, X5, activation of the battery and a charge / discharge cycle test were performed under the same conditions and method as in the charge / discharge cycle test I. The results are also shown in Table 1 above.

As shown in Table 1, in the battery using the electrodes A4 and A5 according to the present invention, the value of which is 60% or less, the reference electrode X4 whose value of 60 is more than 60%. It is recognized that the cycle life is longer than that of the battery using X5. It is considered that this is due to the same reason as that shown in the charge / discharge cycle test I.

(Comparative Examples VI to IX) The same procedure as in Example I, Example II, Comparative Example I and Comparative Example II was repeated except that a negative electrode was produced by using a normal casting method as a method for casting a hydrogen storage alloy. To produce electrodes and batteries. The casting method is a method of pouring a molten hydrogen-absorbing alloy produced in the same manner as in Example I into a water-cooled copper mold to cool it. The electrodes thus manufactured are hereinafter referred to as comparative electrodes X6 to X9, respectively.

[Charge / discharge cycle test III] Comparative electrode X6
For the batteries using X9 to X9, the battery activation and the charge / discharge cycle test were performed under the same conditions and method as in the charge / discharge cycle test I. The results are also shown in Table 1 above.

As shown in Table 1, a battery using the reference electrodes X6 and X7 having a value shown by the formula 4 of 60% or less, and a reference electrode X having a value shown by the formula 4 of more than 60%.
No difference in cycle life is observed between the batteries using No. 8 and X9. It is considered that this is because in the casting method in which the molten hydrogen-absorbing alloy is not rapidly cooled, the pulverization is performed uniformly, so that the difference in the structure due to the grain size is small. Therefore, the present invention is useful when the rapid solidification method for quenching the molten hydrogen storage alloy is used.

[Assembly of Test Cell] The electrodes A1 to A1 of the present invention
A5 and the same hydrogen storage alloy powder as the hydrogen storage alloy powder used for the reference electrodes X1 to X9 are added to 1 g each, carbonyl nickel powder as a conductive agent 1.2 g, and polytetrafluoroethylene (PTFE) powder as a binder 0 .2g
Were mixed and rolled to obtain 14 kinds of alloy pastes. Then, a predetermined amount of each alloy paste was wrapped in nickel mesh and pressed to produce the electrodes a1 to a5 of the present invention and the reference electrodes x1 to x9. Next, a sintered nickel positive electrode having a sufficiently larger capacity than this electrode was placed in a closed container, and an excessive amount of KOH as an electrolytic solution was further added to prepare a test cell.

[High Rate Discharge Characteristic Test] First, the electrode a of the present invention
The test cells using 1 to a5 and the comparative electrodes x1 to x9 were charged at 50 mA per gram of alloy for 8 hours and rested for 1 hour, and then discharged at 200 mA per gram of alloy to a discharge end voltage of 1.0V. The discharge capacity at this time is C _H. Next, after resting for 1 hour (which restores the voltage), the discharge end voltage is 1.0 at 50 mA / g of alloy.
Discharged to V. The discharge capacity at this time is C _L. Then, the high rate discharge characteristic (%) was calculated by the following expression 5.

[0044]

(Equation 5)

The results are also shown in Table 1 above. As shown in Table 1, in the test cell using the electrodes a1 to a5 of the present invention, the value of which is represented by the formula 4 is 60% or less, the reference electrodes x1 to x5 whose value represented by the formula 4 exceeds 60%. It is recognized that the high-rate discharge characteristics are excellent as compared with the test cell using. This is because in the test cell using the electrodes a1 to a5 of the present invention, all the hydrogen storage alloys are uniformly charged and discharged, so that the activation of the entire electrode is achieved, whereas the comparison electrodes x1 to x5 are used. It is considered that this is because in the test cell, since the large-diameter hydrogen storage alloy is not charged / discharged, activation of the entire electrode cannot be achieved.

Incidentally, a test cell using the reference electrodes x6 and x7 whose value shown by the formula 4 is 60% or less and a test cell using the reference electrodes x8 and x9 whose value shown by the formula 4 exceeds 60%. There is no difference in high rate discharge characteristics between the cell and the cell.
This is because the casting method that does not quench the molten hydrogen storage alloy,
It is considered that this is because the difference in the structure due to the particle size is small because the pulverization is performed uniformly. Therefore, the present invention is useful when the rapid solidification method for quenching the molten hydrogen storage alloy is used.

(Second Embodiment) (Examples I to V) As a pulverization method of a hydrogen storage alloy, a hydrogenation pulverization method in which hydrogen is occluded and released in a hydrogen storage alloy and pulverized is used, except that the first embodiment is used. Electrodes and batteries were produced in the same manner as in Examples I to V. The electrodes produced in this manner are hereinafter referred to as present invention electrodes B1 to B5, respectively.

(Comparative Examples I to IX) Comparative Example I of the first embodiment except that a hydrogenation crushing method in which hydrogen is occluded and released by a hydrogen occluding alloy is used as a pulverizing method of a hydrogen occluding alloy
-An electrode and a battery were produced in the same manner as in Comparative Example IX. The electrodes prepared in this manner are referred to below as comparative electrodes Y, respectively.
1 to Y9.

[Charge / Discharge Cycle Test] Inventive Electrodes B1 to
With respect to the battery using B5 and the comparative electrodes Y1 to X9, activation and charging / discharging cycle test of the battery were performed under the same conditions and method as in the charging / discharging cycle test I of the first embodiment.
The results are shown in Table 2 below.

[0050]

[Table 2]

As shown in Table 2 above, in the battery using the electrodes B1 to B5 of the present invention whose value shown by the above-mentioned equation 4 is 60% or less, the reference electrode Y1 whose value shown by the above-mentioned equation 4 exceeds 60%. It can be seen that the cycle life is longer than that of the batteries using ~ Y5. It is considered that this is due to the same reason as that shown in the charge / discharge cycle test I of the first embodiment.

However, a battery using the reference electrodes Y6 and Y7 whose value shown by the formula 4 is 60% or less and a battery using the reference electrodes Y8 and Y9 whose value shown by the formula 4 exceeds 60%. In, there is no difference in cycle life. It is considered that this is due to the same reason as that shown in the charge / discharge cycle test III of the first embodiment.

[Assembly of Test Cell] The electrodes B1 to B1 of the present invention
Using the same hydrogen storage alloy powder as that used for B5 and the comparison electrodes Y1 to Y9, a test cell was produced by the same method as the method for assembling the test cell of the first embodiment. The electrodes used in these test cells are hereinafter referred to as the electrodes b1 to b5 of the present invention and the comparison electrodes y1 to y9, respectively.

[High Rate Discharge Characteristic Test] First, the electrode b of the present invention
The test cells using 1 to b5 and the comparison electrodes y1 to y9 were tested under the same conditions as the high rate discharge characteristic test of the first embodiment, and the high rate discharge characteristic (%) was calculated by the equation 5. . The results are also shown in Table 2 above.

As shown in Table 2, in the test cell using the electrodes b1 to b5 of the present invention, the value of which is 60% or less, the reference electrode whose value of the above 4 exceeds 60%. It is recognized that the high rate discharge characteristics are superior to the test cells using y1 to y5. It is considered that this is due to the same reason as that shown in the high rate discharge characteristic test of the first embodiment.

A test cell using the reference electrodes y6 and y7 whose value shown by the above formula 4 is 60% or less and a test cell using the reference electrodes y8 and y9 whose value shown by the above formula 4 exceeds 60% are used. There is no difference in high rate discharge characteristics between the cell and the cell.
It is considered that this is due to the same reason as that shown in the high rate discharge characteristic test of the first embodiment.

[0057]

As described above, according to the present invention, it is possible to prevent the hydrogen storage alloy from becoming inactive or pulverized, so that the battery having cycle characteristics and high rate discharge characteristics can be obtained. It has an excellent effect that the characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a battery using an electrode of the present invention.

FIG. 2 is a graph showing the relationship between the particle size and the weight% after crushing a hydrogen storage alloy.

[Explanation of symbols]

 1: Positive electrode 2: Negative electrode 3: Separator

Claims (6)

[Claims] 1. A hydrogen storage alloy electrode containing a part of a hydrogen storage alloy powder produced by pulverizing a hydrogen storage alloy produced by a rapid solidification method, wherein various particles are produced when the hydrogen storage alloy is pulverized. Among the hydrogen storage alloy powders having a diameter, the value represented by the following mathematical formula 1 is 60
% Hydrogen storage alloy powder containing a large particle size hydrogen storage alloy powder. (Equation 1) 2. The hydrogen storage alloy electrode according to claim 1, wherein the rapid solidification method is a roll method. 3. The hydrogen storage alloy electrode according to claim 1, wherein the crushing method of the hydrogen storage alloy ingot is a mechanical crushing method and / or a hydrogenating crushing method. 4. A first step of producing a hydrogen storage alloy by a rapid solidification method, a second step of pulverizing the hydrogen storage alloy to produce a hydrogen storage alloy powder, and various particle sizes during the pulverization. Of the hydrogen storage alloy powders that it has, a third step of selecting a hydrogen storage alloy powder having a large particle size such that the value shown by the following formula 2 is 60% or less, and A method of manufacturing a hydrogen storage alloy electrode, comprising: 5. The method for producing a hydrogen storage alloy electrode according to claim 4, wherein the rapid solidification method is a roll method. 6. The method for producing a hydrogen storage alloy electrode according to claim 4, wherein the method for pulverizing the hydrogen storage alloy ingot is a mechanical pulverization method and / or a hydrogenation pulverization method.