JPH06111817A - Metal/hydride secondary battery - Google Patents

Abstract

PURPOSE:To provide a metal/hydride secondary battery excellent in both high initial electric discharging rate characteristic and cycle lifetime characteristic by using for a negative electrode a hydrogen storage alloy obtained by rapid cooling and heating treatment under predetermined conditions. CONSTITUTION:Alloy component metals are mixed together by each predetermined amount, followed by heating and melting in the inactive gas atmosphere, to be rapidly cooled at a cooling speed of 1000 deg.C/sec or higher, thus preparing a hydrogen storage alloy. Subsequently, the resultant hydrogen storage alloy is heated at 400-1000 deg.C for a predetermined time, and then, it is mechanically crushed in the inactive gas atmosphere, thereby obtaining hydrogen storage alloy powder having a given particle diameter. A binding agent and a conducting agent are mixed with the hydrogen storage alloy powder, followed by rolling, to thus obtain alloy paste. A predetermined quantity of the alloy paste is covered with a nickel mesh, followed by pressing, thereby manufacturing a paste electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal / hydride secondary battery, and in particular, has improved high rate discharge characteristics at the beginning of the cycle (hereinafter referred to as "initial high rate discharge characteristics") and cycle life characteristics. The present invention relates to improvement of a hydrogen storage alloy as a negative electrode material for the purpose of

[0002]

2. Description of the Related Art In recent years,
Metal / hydride secondary batteries that use a metal compound such as nickel hydroxide for the positive electrode and a new material, a hydrogen storage alloy, for the negative electrode have a higher energy density per unit weight and unit volume than other types of batteries. However, it is in the limelight because it is high and the capacity can be increased.

Conventionally, the hydrogen storage alloy used for the negative electrode of this metal-hydride secondary battery is generally 10 to 100 ° C./sec in cooling rate (cooling rate is after the alloy component metals are mixed and melted). It is produced by solidifying with a different alloy type and production method.). In recent years,
For the purpose of improving the initial discharge characteristics, a hydrogen storage alloy produced by rapid solidification at a cooling rate of 100 ° C./second or more is also produced. The reason for rapid solidification is to obtain an alloy crystal in which the orientation of crystal grains (crystallites) is close to an irregular state at the time of melting, that is, there are many grain boundaries. An excellent negative electrode can be obtained.

The reason for this is that an alloy crystal having a large number of grain boundaries has a large internal stress and is liable to be distorted. Therefore, cracks are likely to occur. This is because the number of active sites (reaction sites) increases with increasing.

However, the above-mentioned conventional metal / hydride secondary battery in which the hydrogen storage alloy obtained by rapid solidification (hereinafter abbreviated as "quenched alloy") is used as it is for the negative electrode has a cycle life. There was a problem that was short.

The reason why the cycle life is shortened is that a quenching alloy having a large number of grain boundaries, that is, a crystal grain that constitutes the alloy is minute, is easily pulverized and the surface thereof is oxidized when the charge / discharge cycle is repeated. Therefore, the contact resistance and reaction resistance of the electrodes increase, and the charge / discharge efficiency decreases.

As described above, in the conventional metal / hydride secondary battery, when the hydrogen storage alloy electrode obtained by rapid solidification for improving the initial high rate discharge characteristic is used, it becomes fine powder and the cycle life characteristic is improved. On the other hand, when using a hydrogen storage alloy electrode with few cracks obtained by slow cooling to improve cycle life characteristics, there was a trade-off problem that the initial high rate discharge characteristics deteriorate. is there.

The present invention has been made to solve the above problems, and an object thereof is to provide a metal / hydride secondary battery excellent in both initial high rate discharge characteristics and cycle life characteristics. To provide.

[0009]

MEANS FOR SOLVING THE PROBLEMS A metal / hydride secondary battery according to the present invention (hereinafter, referred to as "invention battery") for achieving the above object is obtained by melting a mixture of hydrogen storage alloy components. A hydrogen storage alloy obtained by quenching at a cooling rate of 1000 ° C / sec or more and then heat-treating at 400 to 1000 ° C is used for the negative electrode.

The cooling rate of the melt of the mixture of hydrogen storage alloy components is regulated to 1000 ° C./sec or more.
When cooled at a rate of less than 0 ° C / sec, a battery having a large reaction area and a hydrogen storage alloy with a large number of active points cannot be obtained because cracks are too few, and a high rate discharge characteristic is obtained. Because you can't get.

The heat treatment temperature is 400 to 1000 °.
The range of C is regulated by heat treatment at a temperature of less than 400 ° C, so that the crystals do not grow sufficiently because the diffusion in the solid phase does not occur sufficiently, so that a battery with a long cycle life can be obtained. On the other hand, if heat treatment is performed at a temperature higher than 1000 ° C, the hydrogen storage alloy partially remelts and a segregation phase appears to reduce the hydrogen storage capacity during charging. Because you cannot get it.

The heat treatment time varies depending on the type of the hydrogen storage alloy, but it is usually sufficient to perform the heat treatment for about 2 hours. If the heat treatment time is less than 2 hours, the cycle life tends to be shortened. Note that cooling of the hydrogen storage alloy after the heat treatment is performed by slow cooling. Therefore, the heat treatment in the present invention is a kind of annealing.

As the hydrogen storage alloy in the present invention, for example, LaNi ₅ , TiNi ₂ and the like, La is Mm.
(Misch metal: mixture of rare earth metals) and the like, those partially substituted with Ni, Co, Mn, Al, etc. may be mentioned, but not limited thereto.

As described above, according to the present invention, in order to obtain a metal / hydride secondary battery excellent in both initial high rate discharge characteristics and cycle life characteristics, after rapid cooling at a predetermined cooling rate,
The greatest feature is that a hydrogen storage alloy obtained by heat treatment (annealing) at a predetermined temperature is used as a negative electrode material. Therefore, the positive electrode in the battery of the present invention, the separator,
For other members constituting the battery such as the electrolytic solution, various materials that have been practically used or proposed for the metal / hydride secondary battery can be used without limitation.

For example, when the present invention is applied to a nickel / hydride secondary battery, the same materials as the positive electrode, the separator and the electrolytic solution used in the nickel / cadmium secondary battery can be used.

That is, a sintered nickel electrode can be suitably used as the positive electrode, a polypropylene non-woven fabric as the separator, and a 30 wt% potassium hydroxide aqueous solution can be suitably used as the alkaline electrolyte, but there is no particular limitation. .

[0017]

Since the hydrogen storage alloy used for the negative electrode of the battery of the present invention is obtained by being rapidly cooled at a predetermined cooling rate, it has a large number of cracks, which results in a large reaction area and a large number of active sites. There are also many.

Further, since the hydrogen storage alloy in the battery of the present invention is obtained by being further heat-treated at a predetermined temperature after the above-mentioned rapid cooling, only grain boundaries of large crystal grains exist and small crystal grains are present. There are almost no grain boundaries. Therefore, even if the number of cycles is increased, it is difficult for the hydrogen-absorbing alloy to be pulverized, and contact resistance and reaction resistance are less likely to increase.

[0019]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

(Production Example 1) A predetermined amount of each alloy component metal of Mm, Ni, Co, Al, and Mn (commercial pure metal having a purity of 99.9% or more) was weighed and mixed, and an inert gas (argon) was used. The composition formula MmNi _3.2 CoAl _0.4 Mn was put into a copper crucible in an arc furnace in an atmosphere, heated and melted, and then rapidly cooled at a cooling rate of 1 × 10 ⁵ ° C / sec by a roll method.
A hydrogen storage alloy represented by _0.4 was produced.

Next, the hydrogen storage alloy is further added with 10
After heat treatment (annealing) at 00 ° C for 8 hours, mechanically pulverize in an inert gas (argon) to obtain an average particle size of 15
0 μm of hydrogen storage alloy powder was obtained.

To 1 g of this hydrogen storage alloy powder, 0.2 g of polytetrafluoroethylene (PTFE) as a binder
And 1.2 g of carbonyl nickel as a conductive agent were mixed and rolled to obtain an alloy paste.

A predetermined amount of this alloy paste was wrapped in nickel mesh and pressed to produce a disk-shaped paste electrode PE1 having a diameter of 20 mm.

(Production Example 2) The cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE2 was produced in the same manner as in Production Example 1 except that the time was changed to 1 × 10 ⁴ ° C / sec.

(Production Example 3) Cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE3 was produced in the same manner as in Production Example 1 except that the time was changed to 1 × 10 ³ ° C / sec.

(Production Example 4) The cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE4 was produced in the same manner as in Production Example 1 except that the time was changed to 1 × 10 ² ° C / sec.

(Production Example 5) The cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE5 was produced in the same manner as in Production Example 1 except that the temperature was changed to 10 ° C / sec instead of sec.

(Production Example 6) The cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE6 was produced in the same manner as in Production Example 1 except that 1 ° C / sec was used instead of sec.

(Initial High Rate Discharge Characteristics) The initial high rate discharge characteristics of the paste electrodes PE1 to PE6 produced in Production Examples 1 to 6 were examined by assembling test cells.

FIG. 1 is a schematic perspective view of the assembled test cell. The illustrated test cell 1 includes a disk-shaped paste electrode (test alloy electrode) 2, a cylindrical sintered nickel electrode 3, and an insulation. It is composed of a hermetically sealed container 4 and the like.

The sintered nickel electrode 3 is held by a positive electrode lead 5 connected to the upper surface 6 of the hermetically sealed container 4, and the paste electrode 2 is positioned perpendicular to the substantially center of the sintered nickel electrode 3 in the cylinder. Thus, it is held by the negative electrode lead 7 connected to the upper surface 6 of the closed container 4.

Each end of the positive electrode lead 5 and the negative electrode lead 7 penetrates the upper surface 6 of the closed container 4 and is exposed to the outside, and is connected to the positive electrode terminal 5a and the negative electrode terminal 7a, respectively.

The paste electrode 2 and the sintered nickel electrode 3 are immersed in an alkaline electrolyte (30% by weight potassium hydroxide aqueous solution; not shown) contained in a closed container 4,
The upper space of the alkaline electrolyte is filled with nitrogen gas so that a predetermined pressure is applied to the paste electrode 2.

Further, in the central portion of the upper surface 6 of the closed container 4,
In order to prevent the internal pressure of the closed container 4 from rising above a predetermined pressure, a relief tube 10 including a Bourdon tube (pressure gauge) 8 and a relief valve (relief valve) 9 is attached.

Paste electrodes PE1 to PE1 according to the above test cell
The test results of the initial high rate discharge characteristics of PE6 are plotted on the graph shown in FIG. 2 with the capacity ratio P (%) on the left ordinate and the cooling rate (° C / sec) on the abscissa and plotted with a circle symbol. And show it.
The capacity ratio P (%) is a value calculated by the following equation (1), and is a value serving as a scale for evaluating the quality of the high rate discharge characteristic.

P = (C1 / C2) × 100 (1) where C1 is charged at a current density of 50 mA / g for 8 hours and then discharged at a current density of 200 mA / g to 1.0 V (discharge end voltage). Is a high rate discharge capacity at the beginning of the cycle, and C2 is a discharge capacity at the beginning of the cycle when the battery is charged at a current density of 50 mA / g for 8 hours and then discharged to 1.0 V (discharge end voltage) at a current density of 50 mA / g. Is.

(Cycle Life Characteristics) The cycle life characteristics of each paste electrode produced in Production Examples 1 to 6 were examined using the test cell shown in FIG. The results are shown in the graph shown in FIG. 2 above, where the capacity retention rate M (%) is plotted on the left ordinate and the cooling rate (° C / sec) is plotted on the abscissa, and is plotted by the Δ symbol. The capacity retention rate M (%) is a value calculated by the following equation (2), and is a value that serves as a scale for evaluating cycle life characteristics.

M = (C3 / C2) × 100 (2) Here, C2 has the same meaning as C2 described above, and C3 has a current density of 50 mA after being charged at a current density of 50 mA / g for 8 hours.
It is the discharge capacity at the 500th cycle in the cycle test in which the step of discharging to 1.0 V (discharge end voltage) at mA / g is one cycle.

From FIG. 2, the test cell using the paste electrodes PE1 to PE3 having a cooling rate of 1000 ° C. or higher as the negative electrode was tested using the paste electrodes PE4 to PE6 having a cooling rate of 100 ° C. or lower as the negative electrode. It can be seen that the capacity ratio P is large and the high rate discharge characteristics are excellent as compared with the cell. It can also be seen that the cooling rate has almost no effect on the capacity retention rate M.

(Production Example 7) The cooling rate was 1 × 10 ⁵ ° C /
A paste electrode PE7 was produced in the same manner as in Production Example 1 except that the time was changed to 1 × 10 ⁴ ° C / sec.

(Production Example 8) The heat treatment temperature is 1000 ° C.
A paste electrode PE8 was produced in the same manner as in Production Example 7 except that the temperature was changed to 800 ° C.

(Production Example 9) The heat treatment temperature is 1000 ° C.
A paste electrode PE9 was produced in the same manner as in Production Example 7 except that the temperature was changed to 600 ° C.

(Production Example 10) The heat treatment temperature was 1000 °.
A paste electrode PE10 was produced in the same manner as in Production Example 7 except that 400 ° C. was used instead of C.

(Production Example 11) The heat treatment temperature was 1000 °.
A paste electrode PE11 was produced in the same manner as in Production Example 7 except that C was changed to 200 ° C.

(Initial high rate discharge characteristics and cycle life characteristics) Paste electrodes PE7 to PE manufactured in Production Examples 7 to 11
The initial high rate discharge characteristics and cycle life characteristics of E11 were investigated by the same method using the above test cell. The results are shown in Fig. 3.

In FIG. 3, the left vertical axis represents the capacity ratio P (%), the right vertical axis represents the capacity maintenance ratio M (%), and the horizontal axis represents the heat treatment temperature (° C). 2 is a graph in which the relationship between the heat treatment temperature and the capacity retention rate M is plotted by the Δ symbol.

From FIG. 3, the heat treatment temperature is 400 to 100.
The test cell using the paste electrodes PE7 to PE10 at 0 ° C for the negative electrode has a heat treatment temperature of 200 ° C as compared to the test cell using the paste electrode PE11 for the negative electrode.
It can be seen that the capacity retention rate M is large and the cycle life characteristics are excellent. It can also be seen that the heat treatment temperature has almost no effect on the capacity ratio P.

(Manufacturing Example 12) The paste electrode P was manufactured in the same manner as in Manufacturing Example 1 except that the heat treatment was not performed after the rapid cooling.
E12 was produced.

(Manufacturing Example 13) A paste electrode P was manufactured in the same manner as in Manufacturing Example 2 except that no heat treatment was performed after the rapid cooling.
E13 was produced.

(Manufacturing Example 14) The paste electrode P was manufactured in the same manner as in Manufacturing Example 3 except that the heat treatment was not performed after the rapid cooling.
E14 was produced.

(Manufacturing Example 15) The paste electrode P was manufactured in the same manner as in Manufacturing Example 4 except that no heat treatment was performed after the rapid cooling.
E15 was produced.

(Manufacturing Example 16) The paste electrode P was manufactured in the same manner as in Manufacturing Example 5 except that the heat treatment was not performed after the rapid cooling.
E16 was produced.

(Manufacturing Example 17) A paste electrode P was manufactured in the same manner as in Manufacturing Example 6 except that no heat treatment was performed after the rapid cooling.
E17 was produced.

(Initial high rate discharge characteristics and cycle life characteristics) Paste electrode PE12 produced in Production Examples 12 to 17
~ PE17 initial high rate discharge characteristics and cycle life characteristics were investigated by the same method using the above test cell. The results are shown in FIG. 4, which shows a graph in the same coordinate system as in FIG.

From FIG. 4, paste electrodes PE12 to PE1 using a hydrogen storage alloy that has not been heat-treated after being rapidly cooled.
It can be seen that the test cells using 4, PE16 and PE17 as the negative electrode have extremely small capacity ratio P or capacity maintenance ratio M and are inferior to either high rate discharge characteristics or cycle life characteristics.

The test cell using the paste electrode PE15 as the negative electrode has the same high rate discharge characteristics and cycle life characteristics, but the cooling rate and the heat treatment temperature are both set within the regulation range of the present invention. Produced paste electrode PE
1, PE2, PE3, PE7, PE8, PE9, PE1
It can be seen that the high-rate discharge characteristics and the cycle life characteristics are generally inferior to the test cell in which 0 was used as the negative electrode.

[0057]

In the battery of the present invention, the hydrogen storage alloy obtained by quenching and heat treatment under predetermined conditions is used for the negative electrode, so that it has excellent initial high rate discharge characteristics and cycle life characteristics. The present invention has excellent unique effects.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a test cell assembled in an example.

FIG. 2 is a graph showing the relationship between the cooling rate and the capacity ratio and the relationship between the cooling rate and the capacity retention rate for the test cells assembled in Production Examples 1 to 6.

FIG. 3 is a graph showing the relationship between the heat treatment temperature and the capacity ratio and the relationship between the heat treatment temperature and the capacity retention rate for the test cells assembled in Production Examples 7 to 11.

FIG. 4 is a graph showing the relationship between the cooling rate and the capacity ratio and the relationship between the cooling rate and the capacity retention rate for the test cells assembled in Production Examples 12 to 17.

[Explanation of symbols]

 1 Test cell (metal / hydride secondary battery) 2 Paste electrode (hydrogen storage alloy electrode; hydride negative electrode) 3 Sintered nickel electrode (metal positive electrode)

Claims (1)

[Claims] 1. A method of melting a mixture of hydrogen storage alloy components,
After quenching at a cooling rate of 000 ° C / sec or more, 400 ~
A metal / hydride secondary battery in which a hydrogen storage alloy obtained by heat treatment at 1000 ° C. is used for a negative electrode.