CN1123474A - Hydrogen storing alloy, method for surface improvement of same, negetive pole of battery and alkali dischargable battery - Google Patents

Abstract

A hydrogen-absorbing alloy which is excellent in stability in an aqueous solution and in mechanical pulverizability is disclosed. This hydrogen-absorbing alloy contains an alloy represented by the following general formula (I) Mg2M1y (I) wherein M1 is at least one element selected but excluding Mg, elements which are capable of causing an exothermic reaction with hydrogen, Al and B from elements which are incapable of causing an exothermic reaction with hydrogen; and y is defined as more than 1 and no more than 1.5.

Description

Hydrogen storage alloy, method for surface modification of hydrogen storage alloy, negative electrode for battery, and alkaline rechargeable battery

The invention relates to a hydrogen storage alloy, a surface modification method of the hydrogen storage alloy, a negative electrode for a battery and an alkaline storage battery.

The hydrogen storage alloy is an alloy capable of stably absorbing and storing hydrogen (normal temperature and pressure gas) equivalent to several tens of thousands of times of its own volume. Therefore, the hydrogen storage alloy is expected as a material capable of safely and conveniently storing, storing and transporting hydrogen as an energy source. Research into the use of the above-mentioned differences in characteristics between hydrogen absorbing alloys for chemical heat pumps and compressors is also ongoing and has partially reached practical use. In addition, studies have been recently made on using hydrogen stored in the hydrogen storage alloy as an energy source and using the hydrogen as an electrode material for a metal hydride battery (e.g., a nickel hydride secondary battery) by utilizing high catalytic activity of hydrogen absorption and desorption reactions with respect to the hydrogen storage alloy.

As described above, hydrogen storage alloys have various potential application possibilities due to their physical and chemical properties, and are considered to be one of important industrial materials in the future.

As the metal that adsorbs hydrogen, a metal element (for example, platinum group element, lanthanum group element, alkaline earth element, etc.) that can react exothermically with hydrogen, that is, that forms a stable compound with hydrogen may be used as a single element, and an alloy of these metal elements with other metals may be used. The first advantage of alloying is that the metal-hydrogen bonding force is moderately weakened, so that not only hydrogen absorption reaction but also hydrogen desorption reaction can be easily carried out. The second advantage is that the hydrogen absorption and desorption characteristics such as the size of hydrogen pressure (equilibrium pressure; plateau pressure) necessary for the reaction, the width of the equilibrium region (plateau region), and the change (flatness) of the equilibrium pressure during the hydrogen absorption process can be improved. A third advantage is improved chemical and physical stability.

Therefore, when the metal element capable of exothermic reaction with hydrogen is a and the other metal is B, conventional hydrogen storage alloys can be roughly classified into: (1) AB₅(e.g., LaNi)₅、CaNi₅Etc.), (2) AB₂System (e.g. MgZn)₂、ZrNi₂Etc.), (3) AB type (e.g., TiNi, TiFe, etc.), (4) A₂B is (e.g. Mg)₂Ni、Ca₂Fe, etc.), (5) others, such as alloys with G-P regions (Cluster alloy). Wherein LaNi of (1)₅The Laves phase alloy (2) or partial alloy (3) is reactive with hydrogen at around room temperature and has high chemical stability, and therefore has been widely studied as an electrode material for the rechargeable battery.

However, A in the above (4)₂The hydrogen storage alloy of B series has the following problems: the stability with hydrogen is too high, and the hydrogen is difficult to release after absorbing the hydrogen, and the hydrogen absorbing reaction and the hydrogen releasing reaction do not occur or the reaction is very slow to proceed unless the temperature is higher (200-. The chemical stability, especially in aqueous solutions, is relatively low. In additionIn addition, such alloys are hard and difficult to crush. Thus A above₂The B-based hydrogen occluding alloy is not sufficiently used except for storage and transportation purposes, but has a potential hydrogen absorption capacity equal to or higher than that of other alloy systems in terms of unit volume, and twice or several times as high as that of the latter in terms of unit weight. A above₂If the B-series hydrogen storage alloy eliminates the existing problems, the B-series hydrogen storage alloy can be used in the same application field with other alloy systems, and further develops a new application field of the hydrogen storage alloy.

The alloy system of (5) is reported in academic reports, but has not yet reached a practical stage.

On the other hand, Japanese patent laid-open No. 6-76817 discloses that the compositional formula is Mg_2-xNi_1-yA_yB_x(wherein x is 0.1 to 1.5, Y is 0.1 to 0.5, A is an element selected from the group consisting of Sn, Sb and Bi, and B is an element selected from the group consisting of Li, Na, K and Al) such as Mg_1.5Al_0.5Ni_0.7Sn_0.3、Mg_1.8Al_0.2Ni_0.8Sn_0.2And the like. In addition, the patent also disclosesThe use of the above hydrogen storage alloy as a negative electrode material for alkaline batteries is disclosed. However, the hydrogen occluding alloy disclosed in the patent is essentially A₂In the B system, hydrogen absorption and desorption characteristics at normal temperature are poor. As described in the patent, hydrogen can be absorbed and desorbed at a standard temperature and pressure by covering the surface of the above alloy with a Ni metal compound or a P metal compound.

As described above, in various hydrogen occluding alloys, A₂The B alloy is light in weight and large in capacity, and can be generally produced in a composition centered on the alkaline earth metal of the ferroiron group, so that the raw material cost is low. However, the above hydrogen occluding alloy also has the aforementioned problems.

The purpose of the present invention is to provide a hydrogen occluding alloy having improved chemical stability (particularly stability in an aqueous solution) and machinability.

It is another object of the present invention to provide a hydrogen storage alloy having improved hydrogen storage characteristics, particularly at room temperature.

It is still another object of the present invention to provide a method for modifying the surface of a hydrogen-absorbing alloy, which can improve the surface activity of the hydrogen-absorbing alloy and can easily absorb hydrogen sufficiently.

It is another object of the present invention to provide a negative electrode for a battery having good stability against electrode reaction and an alkaline storage battery having improved charge-discharge cycle characteristics.

It is still another object of the present invention to establish a method for evaluating the deterioration rate of a magnesium-containing hydrogen absorbing alloy, and to provide a negative electrode and an alkaline storage battery which exhibit sufficient reversibility and stability to the cell reaction and are practically usable.

According to the present invention, there is provided a hydrogen occluding alloy represented by the general formula (1)

Mg₂M1_y(1) Wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is other than Mg, and y is 1<y.ltoreq.1.5.

The present invention also provides a hydrogen occluding alloy represented by the general formula (2)

Mg_2-xM2_xM1_y(2)Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, 0<x.ltoreq.1.0, 1<y.ltoreq.2.5.

Further, the present invention provides a hydrogen occluding alloy represented by the general formula (3)

M_2-xM2_xM1_y(3) Wherein M is at leastone element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu, Ti, Zr, Hf, Pd, Pt, M2 is at least one element selected from elements capable of reacting exothermically with hydrogen, Al and B, and elements other than M, M1 is at least one element selected from elements not reacting exothermically with hydrogen, except for M and M2, and x and Y are each 0.01<x.ltoreq.1.0, and 0.5<y.ltoreq.1.5.

In addition, the invention also provides a method for modifying the surface of the hydrogen storage alloy by using the R-X compound for treatment, wherein R is alkyl, alkenyl, alkynyl, aryl or a substitute thereof, and X is a halogen element.

Further, the present invention provides a hydrogen occluding alloy having a half width [ Delta]([ 2]theta]) of at least one of peaks of three strong lines among peaks obtained by X-ray diffraction using CuK α as an X-ray source of 0.3 DEG to [ Delta]([ 2]theta]) to 10 deg.

The present invention also provides a peak having a magnesium content of 10% or more and an apparent half width [ delta](2 [ theta]) of 20 DEG or more in an x-ray diffraction peak from CuK α as a radiation source₁) Is delta (2 theta) of not less than 0.3 DEG₁) A peak apparent half width [ Delta]([ 2]theta]) of 10 DEG or less or around 40 DEG₂) Is delta (2 theta) of not less than 0.3 DEG₂) Hydrogen storage alloy with the temperature less than or equal to 10 degrees.

The invention also provides a hydrogen storage alloy surface modification method for mechanically treating the hydrogen storage alloy under vacuum, inert gas or hydrogen atmosphere.

The present invention also provides a method for modifying the surface of a hydrogen absorbing alloy, which comprises a step of mixing at least one element selected from the group consisting of elements of groups IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB and IVB, an alloy comprising the above elements, or an oxide of the above elements, in a hydrogen absorbing alloy at a molar ratio of at most equal to one another to prepare a mixture, and a step of mechanically treating the mixture in a vacuum, an inert gas or a hydrogen atmosphere.

The present invention also provides a negative electrode for a battery containing a hydrogen storage alloy represented by the following general formula (1),

Mg₂M1_y(1) wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is not more than 1<y.ltoreq.1.5.

The present invention also provides a rechargeable alkaline storage battery having a negative electrode containing a hydrogen storage alloy represented by the following general formula (I),

Mg₂M1_y(1) wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is not more than 1<y.ltoreq.1.5.

The present invention also provides a negative electrode for a battery containing the hydrogen storage alloy represented by the general formula (2),

Mg_2-xM2_xM1_y(2) wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, 0<X.ltoreq.1.0, 1<y.ltoreq.2.5.

In addition, the present invention provides an alkaline rechargeable battery equipped with a negative electrode containing a hydrogen storage alloy represented by the general formula (2)

Mg_2-xM2_xM1_y(2) Wherein M2 is at least one element selected from the group consisting of elements reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is an element other than Mg and M2, and is an element not reacting exothermically with hydrogenX is more than 0 and less than or equal to 1.0, and y is more than 1 and less than or equal to 2.5.

The present invention also provides a negative electrode for a battery comprising a hydrogen-absorbing alloy in which, among peaks obtained by X-ray diffraction using CuK α as a radiation source, the half width [ Delta]([ 2]theta]) of at least one of the peaks of three strong lines is 0.3 DEG to [ Delta]([ 2]theta]) to 10 deg.

In addition, the present invention provides an alkaline rechargeable battery equipped with a negative electrode comprising a hydrogen storage alloy in which, among peaks obtained by X-ray diffraction using CuK α as an X-ray source, the half width Delta (2 theta) of at least one of the peaks of the three strong lines is 0.3 DEG to Delta (2 theta) to 10 deg.

The present invention also provides a negative electrode for a battery, which contains a magnesium-containing hydrogen storage alloy, and when immersed in an alkali metal hydroxide of 6 to 8, the negative electrode (a) has a rate of elution of magnesium ions into an aqueous solution of an alkali metal hydroxide at normal temperature of 0.5mg/Kg alloy/hr or less, or has a rate of elution of magnesium ions into an aqueous solution of an alkali metal hydroxide at 60 ℃ of 4mg/Kg alloy/hr or less, and (b) has a rate of elution of alloying element into an aqueous solution of an alkali metal hydroxide at normal temperature of 1.5mg/Kg alloy/hr or less, and has a rate of elution of alloying element into an aqueous solution of an alkali metal hydroxide at 60 ℃ of 20mg/Kg alloy/hr or less.

The invention also provides an alkaline rechargeable battery comprising a negative electrode, a positive electrode and an alkaline electrolyte, wherein the negative electrode is accommodated in a container and contains a hydrogen storage alloy containing magnesium, the positive electrode is accommodated in the container and is spaced from the negative electrode by a separator, the electrolyte is also accommodated in the container, the alkaline electrolyte is injected into the container, the container is sealed, and the concentration of magnesium ions in the alkaline electrolyte is 2.2 mg/liter or less after 30 days.

FIG. 1 is a phase diagram of a Mg-Ni alloy.

FIG. 2 is a phase diagram of a La-Ni alloy.

Fig. 3 is a partially cut-away perspective view showing a cylindrical secondary battery of the present invention.

FIG. 4 shows Mg₂Ni_yAnd (3) a characteristic diagram showing the relationship between y in (2) and the amount of magnesium eluted.

Fig. 5 is a schematic view showing measurement of the maximum stress of the strip alloy sheet.

Fig. 6 is a schematic view of a temperature sweep type hydrogen absorption/desorption characteristic evaluation apparatus used in an example of the present invention.

FIG. 7 is a schematic view showing the change in pressure with an increase in temperature (decrease in pressure with hydrogen absorption of the hydrogen occluding alloy) of the hydrogen occluding alloys of examples 16 and 17 and comparative examples 3 and 11.

FIG. 8 is a schematic view showing the change in pressure with an increase in temperature (decrease in pressure with hydrogen absorption of the hydrogen occluding alloy) of the hydrogen occluding alloy of example 18 and comparative example 3.

FIG. 9 is Mg before and after surface modification₂The pressure change of the Ni hydrogen storage alloy when absorbing hydrogen at 25 ℃ is shown.

Fig. 10 is a schematic diagram showing the relationship between the cycle number and the discharge capacity of the simulated batteries provided with the negative electrodes in example 94 and comparative example 15.

The hydrogen occluding alloy of the present invention includes an alloy represented by the general formula (1),

Mg₂M1_y(1) wherein M1 is Mg, an element capable of reacting with hydrogen exothermically, an element other than Al and B, and is at least one element selected from elements not capable of reacting with hydrogen exothermically, and y is 1<y.ltoreq.1.5.

Examples of the element M1 which does not react exothermically with hydrogen, is capable of reacting exothermically with hydrogen in addition to Mg, and contains Al and B include Fe,Ni, Co, Ag, Cd, Mn, In, Se, Sn, Ge, Pb, etc. One or more of these elements M1 may be used, and elements having a larger electronegativity than Mg, i.e., Fe, Ni, Co, Ag, Cd, Mn, In, Se, Sn, Ge, Pb, are preferably used. Particularly, the hydrogen storage alloy formed by alloying iron group elements such as Fe, Ni, Co and the like is chemically stable and has improved hydrogen absorption and desorption reaction performance. When the above-mentioned iron group element is used as M1, an alloy Mg having an electronegativity larger than that of Mg and containing 10% or less of the iron group element in an atomic ratio in pure magnesium may be used in place of part of the iron group element_1-wM1_wThe cell volume of the phase (0<W.ltoreq.0.1) is smaller than that of pure magnesium, e.g. Mn, Ag,Cd. An alloy of at least one element of In.

The lattice sizes of the alloy of the above-mentioned element magnesium and pure magnesium are shown in table 1, respectively. The numerical values shown in table 1 were calculated on the basis of the lattice constants of the alloys obtained from the diffraction pattern of the powder x-ray diffraction method and assuming that the crystal structures of the alloys are hexagonal as in the case of pure magnesium.

Mg as described above_1-wM1_wIn phase, when W exceeds 0.1, Mg_1-wM1_wA structure other than hexagonal crystal may be formed, which may result in failure to correctly evaluate the change in the crystal lattice size of magnesium due to the addition of the element M1. Therefore, 0<W.ltoreq.0.1 is defined, but when it is clearly understood that hexagonal crystals are maintained even when W exceeds 0.1, the element M1 may be selected in the range of W value greater than 0.1.

TABLE 1

Alloy composition	Unit cell volume (nm)3)
		Mg (pure magnesium)	0.0462
Mg0.99Ag0.01	0.0459
		Mg0.9Cd0.1	0.0452
Mg0.95In0.05	0.0460

Based on the relationship between a) and the amount of hydrogen absorbed and b) chemical stability and machinabilityThe relationship indicates the reason why y in M1 is defined to be 1 to 1.5 in the above formula (1).

a) Relation with amount of hydrogen absorbed

When the ratio of Mg having hydrogen absorption ability to M1 (which hardly forms hydride) is 2: y, it is necessary that y is 1 (i.e., Mg) according to stoichiometry₂M1). However, as described below, when y is 1 or less in practice, there are problems of chemical stability and machinability, which are to be solved by the present invention. Further, when y is too large, there are problems in that the utility is not satisfactory, for example, when y>2, Mg is present microscopically₂The crystal in which M1 is a matrix cannot exist alone but forms MgM1₂I.e. Laves phase. This MgM1₂Type alloys also have hydrogen absorption capability, but MgM1 per unit weight₂The hydrogen absorption amount of the type alloy is only equivalent to Mg₂In the case of the M1 type alloy, 40 to 70%, too large a value of y is disadvantageous in view of the volume density.

b) Composition ratio of Mg to M1, chemical stability and machinability

Mg₂M1 type hydrogen occluding alloy is generally formed only at a point of Mg: M1 of 2: 1, and is not allowed to maintain Mg substantially although₂The composition of M1 structure but lack or excess of local Mg or M1 fluctuates. This can be illustrated in terms of a phase diagram. In FIG. 1, as Mg₂Representative example of M1 Mg₂Phase diagram of Ni (Mg-Ni system), AB is shown in FIG. 2₅LaNi of type₅Phase diagram of (La-Ni). See "Binary Alloy Phase Diagrams", (ASM International (USA), 1990). From figure 1 to figure2 it can be seen that Mg is present in the Mg-Ni phase diagram₂Ni is shown by a single line, while LaNi is on the La-Ni phase diagram₅Is expressed in terms of a certain range. One reason for this is that certain shifts in the solution composition occur during alloy manufacture resulting in LaNi₅Actually form what can be considered as LaNi₅Alloys of the same type and Mg₂Ni is Mg when the composition of the molten metal is deviated₂Ni precipitates in a two-phase eutectoid state together with the excess component. That is, y is an arbitrary positive number, and when Mg: Ni is 2: y, if y<1, then Mg₂Ni and excessive Mg are eutectically precipitated, and if y is more than 1, Mg is formed₂Ni and MgNi₂Eutectic or Mg of₂Ni、MgNi₂And eutectic crystals of Ni.

Mg has a lower chemical stability such as corrosion resistance and oxidation resistance, and is less viscous and ductile than NiThe extensibility is large. In addition, Mg₂Ni and MgNi₂In contrast, Mg, especially in the hydrogen-absorbed state₂Ni is a highly polarized structure and is therefore easily attacked by moisture and oxygen. Thus, the alloy with y<1 lacks chemical stability and Mg with high viscosity exists at grain boundaries, so that it can resist mechanical stress but has low workability. On the other hand, when y>1, not only no Mg is present but also Mg is formed₂Ni surface is coated with MgNi₂Or a structure surrounded by Ni, and thus chemical stability is improved. When y>1, the Ni-rich grain boundary phase having high rigidity and low viscosity causes brittle fracture, and thus the mechanical processing is easy.

As described above, when the ratio of Mg to M1 is 2: y, the machinability is improved under the condition that y>1, while the capacity isnot dependent on MgM1₂In view of maintaining sufficient capacity, the upper limit value of y must be 1.5. Also, when only the chemical stability is considered, it is preferable that y is 1<y.ltoreq.1.5.

In the case where the ratio of Mg to M1 is 2: y, the lower limit of y is basically slightly larger than 1, but actually, the alloy has a composition shift or segregation, and therefore, the condition that y is higher than 1 in all parts of the alloy depends on the uniformity of the alloy. Specifically, (a) when an alloy is produced by casting a molten component element produced in an induction furnace or an arc furnace into a mold using a normal metal ingot, y is preferably 1.05 or less; (b) when the solution of the component elements is brought into contact with a low-temperature and high-heat capacity substance such as a rotating roll or a liquid, or the melt is sprayed into a gas or a liquid to be rapidly cooled to produce an alloy, y is preferably 1.02 or more; (c) when several pure metals or master alloys are mixed according to alloy components and then the alloy is produced by hot rolling, hot pressing or mechanical mixing without a melting step, y is preferably 1.02 or more.

The method (a) is widely used because segregation is easily formed during slow cooling and it is difficult to improve uniformity as compared with other methods, but the process is simple. In the method (c), the uniformity of the alloy is easily affected by the production conditions, and the lower limit value of y may be further increased depending on the conditions. The method (b) has high uniformity. In addition, when the uniformity of the composition and the structure is improved by optimizing the production conditions or annealing after the production, y is 1.01 or more, and the object of the present invention can be achieved. For the uniformity determination, various electron microscope surface analysis methods (EDX, EPMA, etc.) and x-ray diffraction measurement methods can be used. For example, in the surface analysis method, the composition distribution of the alloy cross section is determined to be uniform when 90% or more of the area of the cross section is in phase. In the x-ray determination method, uniformity was determined by using a standard that the ratio of the diffraction peak intensity of a master alloy belonging to Mg or M1 or a single element contained in the master alloy to the diffraction peak intensity in the case where each element exists alone is expressed in percentage and the total of them is 5% or less, and it is expected that the lower limit value of alloy y produced by other methods is also approximately in the range of 1.01 to 1.10 from these structures.

The hydrogen absorbing alloy of the present invention allows the addition of 20 atomic% or less of group VB or group VIB elements to the alloy represented by the above general formula (1).

The hydrogen occluding alloy of the present invention described above comprises a hydrogen occluding alloy represented by the general formula (1): mg (magnesium)₂M1_y(wherein M1 represents Mg, an element capable of reacting with hydrogen exothermically, an element other than Al and B, at least one element selected from elements not capable of reacting with hydrogen exothermically, and 1<y.ltoreq.1.5). That is, the hydrogen occluding alloy of the general formula (1) has a high chemical stability and machinability because y of M1 (e.g., Ni) is larger than 1 and smaller than 1.5, and has A₂B type alloys (e.g. Mg)₂Ni) original high hydrogen absorption performance.

Therefore, the hydrogen occluding alloy of the present invention can maintain a good hydrogen occluding property even when it is reacted with hydrogen gas containing a small amount of oxidizing gas such as oxygen or water vapor. In addition, even if the alloy is contacted with anaqueous solution, the hydrogen storage performance is not easy to be reduced, thereby expanding the use randomness of the alloy.

Further, the hydrogen occluding alloy of the present invention having good workability is advantageous in the case where the alloy must be processed in advance into a size or shape suitable for use.

Further, the hydrogen storage alloy gradually becomes finer due to expansion and contraction of crystal lattice caused by hydrogen absorption and desorption, and thus physical properties (for example, bulk density, contact resistance, electrical conductivity, and the like) are changed. In the case where such a change causes a problem, the alloy may be preliminarily pulverized and thenAnd then is used. The hydrogen occluding alloy of the present invention is more preferable than the conventional Mg₂A of Ni or the like₂The B-type alloy has good processability and is easy to crush, and the problems can be well solved.

As described above, the hydrogen occluding alloy of the present invention comprising the alloy represented by the general formula (1) can be efficiently used as an electrode material for rechargeable batteries because of its simple and easy preprocessing before use and management of conditions in use.

Additional hydrogen storage alloys of the present invention include alloys represented by the general formula (2),

Mg_2-xM2_xM1_y(2) wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, A1 and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2, and elements not capable of reacting exothermically with hydrogen, 0<x.ltoreq.1.0, 1<y.ltoreq.2.5.

The same elements as those described for the alloy of the general formula (1) can be used for M1.

The element other than Mg in M2 capable of reacting with hydrogen to generate heat, that is, the element capable of spontaneously forming a hydride, includes, for example, alkaline earth elements such as Be, Ca, Sr and Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and TbRare earth elements including yttrium, such as Lu, IV such as Ti, Zr, Hf, etc_AGroup elements, Pd, Pt, etc. VIII_AA group element. One or more kinds of M2 may be used in combination.

M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, and preferably selected from the group consisting of B, Be, Y, Pd, Ti, Zr, Hf, Th, V, Nb, Ta, Pa, and Al, which are elements having a larger electronegativity than Mg. By selecting an element having a larger electronegativity than Mg as M2, the difference in electronegativity with hydrogen is reduced, hydrogen in the crystal lattice is destabilized, and hydrogen storage characteristics are improved. Especially when the alkaline earth metal Be is alloyed with Mg, a chemically stable alloy can Be formed. In addition, IV_AThe group elements, Ti, Zr, Hf, react readily with hydrogen to form hydrides.

Further, M2 is an element selected from the group consisting of elements capable of reacting with hydrogen exothermically, Al and B, except MgThe other elements, preferably Mg of an alloy in which 10% or less of the elements are mixed into pure magnesium_1-wM1_wThe lattice volume of the phase (W is more than 0 and less than or equal to 0.1) is smaller than that of pure magnesium, namely at least one element selected from Li and Al.

The value of x defined by the above general formula (2) is based on the following reasons. When x ishigher than 1.0, Mg₂M1_yThe loss of hydrogen storage characteristics (hydrogen absorption amount, flatness of step region, reversibility of hydrogen absorption and dehydrogenation) is large, and the crystal structure itself cannot be maintained. A particularly preferred range for x is 0.05. ltoreq. x.ltoreq.0.5.

The y value defined by the above general formula (2) is based on the following reasons. The benefits of y being higher than 1 are for the same reasons as explained for the alloy in formula (1) above. When y exceeds 2.5, not only the amount of hydrogen that the alloy can absorb is reduced, but also it is difficult to maintain the original structure of the alloy. The preferable range of y is 1.01. ltoreq. y.ltoreq.1.5, more preferably 1.02. ltoreq. y.ltoreq.1.5, still more preferably 1.05. ltoreq. y.ltoreq.1.5.

The hydrogen absorbing alloy of the present invention allows addition of 20 atomic% or less of group VB or group VIB elements to the alloy represented by the above general formula (2).

The above-described additional hydrogen occluding alloy of the present invention comprises a hydrogen occluding alloy represented by the general formula (2): mg (magnesium)_2-xM2_xM1_y(wherein M2 is an element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and at least one element other than Mg, M1 is an element other than Mg and M2, is at least one element selected from the group consisting of elements not capable of reacting exothermically with hydrogen, 0<x.ltoreq.1.0, 1<y.ltoreq.2.5). That is, since a part of Mg in the hydrogen absorbing alloy including the alloy of the general formula (2) is replaced with M2 such as Al, the alloy is similar to the conventional alloy A₂The B-type hydrogen storage alloy has significantly improved hydrogen storage characteristics, particularly significantly reduced hydrogen absorption temperature, and has A₂The B-type hydrogen storage alloy has original high hydrogen storage performance. Compared with the prior rare earth hydrogen storage alloy, the alloy has the advantages of large hydrogen absorption amount, low cost and light weight. Meanwhile, hydrogen occluding alloys including the alloy of the general formula (2) have a characteristic that y of M1 (e.g., Ni) is more than 1 and less than 2.5, and thus have good chemical stability and mechanical additionAnd (4) workability. Therefore, the hydrogen storage alloy can maintain good hydrogen storage performance even when it is reacted with hydrogen gas containing a few oxidizing gases such as oxygen and water vapor. In addition, even if the alloy is contacted with an aqueous solution, the hydrogen storage performance is not easy to be reduced, thereby expanding the use randomness of the alloy.

As described above, the hydrogen occluding alloy of the present invention comprising the alloy represented by the general formula (2) has a significantly reduced hydrogen absorption temperature and has A₂The B-type hydrogen storage alloy has original high hydrogen storage performance, and meanwhile, preprocessing treatment before use and condition management in use are simple and easy to operate, so that the B-type hydrogen storage alloy can be effectively used as an electrode material of a rechargeable battery.

Other hydrogen occluding alloys of the present invention include an alloy represented by the following general formula (3),

M_2-xM2_xM1_y(3) wherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu, Ti, Zr, Hf, Pd, Pt, M2 is at least one element selected from elements capable of reacting exothermically with hydrogen, Al and B, and elements other than M, M1 is at least one element selected from elements not reacting exothermically with hydrogen, except for M and M2, and x and Y are each 0.01<x.ltoreq.1.0, and 0.5<y.ltoreq.1.5.

M1 is the same element as described for the hydrogen occluding alloy including the alloy represented by the general formula (1).

M2 is the same element as described for the hydrogen occluding alloy including the alloy represented by the general formula (2).

In the combination of M, M1 and M2, a ternary alloy in which M is Zr, M1 is Fe, and M2 is Cr, and a quaternary alloy in which M is Zr, M1 is Ni and Co, and M2 is V are preferable.

The reason why the y value of M1 and the x value of M2 defined in the above formula (3) are as follows.

When the y value is less than 0.5, M, M1 and M2 are precipitated as single phases, respectively, and thus the hydrogen-absorbing alloy does not exhibit the characteristics and is chemically unstable. A value higher than 1.0 (e.g., 1.01) is set as the lower limit of y. On the other hand, when y is higher than 2.0, the amount of hydrogen stored in the alloy decreases, and it is difficult to maintain the original structure of the alloy. The upper limit value of y is 1.5.

When the value of x is less than 0.01, a hydrogen occluding alloy having good hydrogen occluding characteristics at low temperature cannot be obtained, and when the value of x is more than 1.0, the crystal structure is changed while A is lost₂The original characteristics of B-series alloy. The preferred value of x is 0.05 to 0.5.

Other hydrogen occluding alloys of the present invention described above include alloys represented by the general formula (3):

M_2-xM2_xM1_y(3) (wherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu, Ti, Zr, Hf, Pd, Pt, M2 is at least one element selected from elements capable of reacting exothermically with hydrogen, Al and B, and elements other than M, M1 is at least one element selected from elements not capable of reacting exothermically with hydrogen, except for M and M2, and x and Y are each 0.01<x.ltoreq.1.0, 0.5<y.ltoreq.1.5). That is, the hydrogen absorbing alloy including the alloy of the above general formula (3) is similar to the conventional alloy A in that M (for example, Zr) is partially replaced with M2 (for example, Al)₂The B-type hydrogen storage alloy has significantly improved hydrogen storage characteristics, particularly significantly reduced hydrogen absorption temperature, and has A₂The B-type hydrogen storage alloy has original high hydrogen storage performance. In addition, hydrogen is stored in the presence of a conventional rare earth elementCompared with gold, the hydrogen absorption amount per unit weight is large, the cost is low, and the weight is light.

The hydrogen occluding alloy of the present invention including the alloy represented by the general formula (3) has a significantly reduced hydrogen absorption temperature and has A₂The B-type hydrogen storage alloy has originally high hydrogen storage performance and thus can be effectively used as an electrode material for rechargeable batteries.

The surface modification method of the hydrogen storage alloy of the present invention is to treat the hydrogen storage alloy with an R-X compound (wherein R is an alkyl group, an alkenyl group, an alkynyl group, an aryl group or a substituent thereof, and X is a halogen element).

The hydrogen occluding alloy may be, for example, (1) AB as described above₅Is (e.g. LaNi)₅System, CaNi₅Series, etc.), (2) AB₂System (e.g. MgZn)₂System, ZrNi₂Etc., (3) AB series (e.g., TiNi series, TiFe series, etc.), (4) A₂B is (e.g. Mg)₂Ni based, Ca₂Fe system), and the like.

Further, the hydrogen occluding alloy is composed of an alloy containing an alloy represented by the following general formula (4),

Mg_2-XM2_xM1_y(4) wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of Mg and M2, and elements not capable of reacting exothermically with hydrogen, and x and y are 0. ltoreq. x.ltoreq.1.0, and 0.5. ltoreq. y.ltoreq.2.5, respectively.

The same elements as those described for the alloy of the general formula (1) are used for M1. The same elements as those described for the alloy of the general formula (2) are used for M2.

In particular, the above AB₅System, A₂The B-based hydrogen occluding alloy or the hydrogen occluding alloy including the alloy represented by the above general formula (4) is particularly suitable.

In the above R-X compound, R is alkyl, alkenyl, alkynyl, aryl or a substitute thereof, X is a halogen element, and the reactivity is, in order from high to low, iodide>bromide>chloride. Examples of such R-X compounds include methyl iodide, ethyl bromide, 1, 2-dibromoethane, 1, 2-diiodoethane, and the like.

The R-X compound (halide) is preferably reacted with the hydrogen occluding alloy in the presence of a solvent to modify the surface.

The solvent may be, for example, diethyl ether, Tetrahydrofuran (THF), di-n-propyl ether, di-n-butyl ether, di-isopropyl ether, diglyme, dioxane, Dimethoxyethane (DME), etc. These solvents may be used alone or in combination, and diethyl ether and THF are preferred. When the above-mentioned R-X compounds are alkyl halides, alkenyl halides and aryl halides, the solvents used are preferably etheric solvents. When the R-X compound is an alkenyl compound or an aryl compound, THF having a higher coordinating ability is preferably used as the solvent. In the above-mentioned R-X compounds, bromide and iodide are easily reacted in ether. Among the above R-X compounds, a chlorine compound having low reactivity and a substituted bromide compound may be reacted in THF.

The concentration of the solution obtained by dissolving the above-mentioned R-X compound in a solvent must be selected in consideration of the following 1) to 3).

1) The reactivity of the halide (if the reactivity is low, it is added at a high concentration).

2) The ease with which side reactions occur (allyl chloride and benzyl chloride are readily set aside due to the coupling reaction, low concentrations are used).

3) Stability of solubility of the product (low concentration is used when solubility is low). If the concentration is not less than the saturation concentration, a solid may precipitate after cooling, which may cause non-uniformity).

The addition of a catalyst to a solvent in which the above-mentioned R-X compound is dissolved is effective for accelerating the reaction. Examples of the catalyst include condensed polycyclic hydrocarbons such as dicyclopentadiene, indene, naphthalene, azulene, heptalene, biphenylene, benzodiindene, acenaphthylene, fluorene, フエナレン, phenanthrene, anthracene, ァルオランセン, ァセァエナンスリレン, ァンスリレン, terphenylene, pyrene, perylene, tetracene, heptadiene, picene, perylene, pentaphene, pentacene, tetraphenylene, hexylene, hexacene, rubinthema, coronene, ditriphenylene, heptophene, heptaphene, and ovalene, and anthracene is preferably used. When a magnesium-containing hydrogen storage alloy is treated with a THF solution of an R-X compound to which anthracene is added, the mixture of anthracene and magnesium forms a magnesium-anthracene equilibrium. Therefore, in the reaction system of the following formula (III), the reaction can be promoted to proceed rightward by simply adding anthracene as a catalyst, and a good surface modification can be achieved.

In the surface modification method of the present invention, addition of R-MX (M is a component of a hydrogen occluding alloy) synthesized in advance at the initial stage of the reaction is an effective industrial method for performing dehydration and activation in the system.

By the above-mentioned method for modifying a hydrogen absorbing alloy of the present invention, the hydrogen absorption characteristics, particularly the activity, can be improved as compared with an unmodified hydrogen absorbing alloy.

That is, as one of the methods for improving the hydrogen storage performance of the hydrogen storage alloy, surface modification of the hydrogen storage alloy can be mentioned. The activity of the hydrogen absorbing alloy in absorbing hydrogen is caused by a mechanism called surface segregation, and is related to the ease of formation of the surface catalyst layer and the catalyst performance. When the hydrogen-storing alloy is treated with the R-X compound, the component element M of the hydrogen-storing alloy undergoes the following reaction

M + R-X → R-Mx (I) or

M＋αR－X→αR＋MX_α(II)

When the surface treatment is carried out in the above reaction, the surface of the hydrogen absorbing alloy or the vicinity thereof is smoothly segregated, and active species forming a catalyst are generated on thesurface of the hydrogen absorbing alloy.

For example, treatment of Mg with bromoethane₂In the case of Ni-based hydrogen occluding alloy, magnesium of the hydrogen occluding alloy undergoes the following reaction

(III)

By the above reaction (surface modification), covering Mg is removed₂An oxide film on the surface of Ni, and nickel which functions as a dissociation catalyst for hydrogen during hydrogen storage are present on the surface, thereby improving the hydrogen storage characteristics.

Examples of the element reacting with the R-X compound include, in addition to magnesium, rare earth element Ln (Ln: lanthanum, cerium, praseodymium, neodymium, promiscuous, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc.). The reaction of Ln with 1, 2-diiodoethane dissolved in THF in an argon or nitrogen atmosphere at room temperature givesTo LnI₂

(IV)

Among rare earth elements, La, Nd, Sm and Lu are easy to react with 1, 2-diiodoethane, and the reactivity is La more than Nd more than Sm more than Lu in sequence.

For example, LaNi₅When the hydrogen storage alloy is reacted with 1, 2-diiodoethane, La in the hydrogen storage alloy undergoes the following reaction

(V)

By the above reaction (surface modification), the LaNi coating was removed₅An oxide film on the surface, and nickel which functions as a dissociation catalyst for hydrogen during hydrogen storage appear on the surface, thereby improving the hydrogen storage characteristics.

After the treatment with the solvent in which the above-mentioned R-X compound is dissolved, only a small amount of halogen (for example, 1% by weight or less) remains on the surface of the hydrogen absorbing alloy, and therefore the original characteristics of the hydrogen absorbing alloy are not lost.

Another hydrogen occluding alloy of the present invention is characterized in that at least one peak of three strong lines has a half width [ Delta]([ 2]theta]) of 0.3 DEG to [ Delta]([ 2]theta]) to 10 DEG in an X-ray diffraction peak using CuK α as an X-ray source.

The composition system of the hydrogen occluding alloy includes, for example, (1) AB as described above₅Is (e.g. LaNi)₅、CaNi₅Etc.), (2) AB₂System (e.g. MgZn)₂、ZrNi₂Etc.), (3) AB type (e.g., TiNi, TiFe, etc.), (4) A₂B is (e.g. Mg)₂Ni、Ca₂Fe, etc.).

Further, the hydrogen occluding alloy preferably includes an alloy represented by the following general formula (4).

Mg_2-xM2_xM1_y(4) Wherein M2 is an element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, at least one element other than Mg, M1 is an element other than Mg and M2, at least one element selected from the group consisting of elements not capable of reacting exothermically with hydrogen, and x and y are 0. ltoreq. x.ltoreq.1.0, and 0.5. ltoreq. y.ltoreq.2.5, respectively.

The same elements as those described for the alloy of the general formula (1) are used for M1.

The same elements as those described for the alloy of the general formula (2) are used for M2.

In particular, comprisingMg₂The hydrogen storage alloy of Ni series or the alloy represented by the above general formula (4) contains 10% or more of magnesium, and the apparent half width Delta (2 theta) of the peak in the vicinity of 20 DEG in the X-ray diffraction peak using CuK α as the X-ray source is preferable₁) Is delta (2 theta) of not less than 0.3 DEG₁)≤Apparent half width Δ (2 θ) of peak at 10 ° or around 40 °₂) Is delta (2 theta) of not less than 0.3 DEG₂)≤10°。

The reason why Δ (2 θ) is defined is as follows. When Δ (2 θ) is less than 0.3 °, the hydrogen absorption rate is significantly reduced, whereas when Δ (2 θ) is more than 10 °, the hydrogen absorption amount of the hydrogen absorbing alloy is reduced, so that the range of Δ (2 θ) is 0.3 ° ≦ Δ (2 θ)₂) Preferably less than or equal to 10 degrees.

In the above hydrogen occluding alloy, the crystallite size is D, and preferably, D is 0.8nm or more and 50nm or less. Such hydrogen storage alloys having a predetermined crystallite size have improved hydrogen absorption and desorption characteristics because the diffusion path of hydrogen is increased and the distance is shortened. The reason why the crystallite size is defined is that when D is less than 0.8nm, the hydrogen absorption amount may decrease, whereas when D is greater than 50nm, the hydrogen diffusion path is blocked.

The above hydrogen occluding alloy preferably contains hydrogen atoms selected from the group consisting of group IVA: at least one element of group VA, group VIA, group VIIA, group VIIIA, group IB, group IIB, group IIIB, group IVB, an alloy or a metal oxide comprising the above elements.

Another method for modifying the surface of a hydrogen absorbing alloy of the present invention is characterized by mixing at least one element selected from the groupconsisting of group IVA, group VA, group VIA, group VIIA, group VIIIA, group IB, group IIB, group IIIB and group IVB, an alloy of the above elements or a mixture of metal oxides, either alone or in a hydrogen absorbing alloy, in an equimolar ratio, and subjecting the mixture to mechanical treatment in a vacuum, an inert gas or a hydrogen atmosphere.

The above-mentioned element, alloy or metal oxide can function as a catalyst for hydrogenation by being forcibly added to the above-mentioned hydrogen storage alloy. Such catalysts are preferably selected from elements, alloys or metal oxides having a high catalytic activity for the reaction with hydrogen. That is, if considering the application of the reaction heat with hydrogen to a positive (endothermic) type or to a battery, it is preferable to use a material having a large exchange current density i0 in the negative electrode (hydrogen electrode) reaction. Such elements are group IV, VA, VIA, VIIA, VIIIA and IB elements, for example V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, lr, Pd, Ni, Pt, Cu, Ag, Au, etc.

Further, in the alloy composed of at least one element selected from the group consisting of group IVA, group VA, group VIA, group VIIA, group VIIIA, group IB, group IIB, group IIIB and group IVB, the resulting alloy has higher catalytic activity than the hydrogen electrode reaction of a single element due to the mutual stacking action between the elements, and is therefore more preferable. Examples thereof include Ni-Ti based alloys, Ni-Zr based alloys, Co-Mo based alloys, Ru-V based alloys, Pt-W based alloys, Pd-W based alloys, Pt-Pd based alloys, V-Co based alloys, V-Ni based alloys, V-Fe based alloys, Mo-Co based alloys, Mo-Ni based alloys, W-Ni based alloys, and W-Co based alloys. Of these alloys, MoCo is especially preferred₃、WCo₃、MoNi₃、WNi₃And the like, so that the hydrogen storage property of the hydrogen storage alloy is improved.

In the metal oxide composed of the above elements, the exchange current density i is preferably selected₀Large, e.g. FeO, RuO₂、CoO、Co₂O₃、Co₃O₄、RhO₂、lrO₂NiO, etc.

The mechanical treatment may be carried out by placing the hydrogen-absorbing alloy alone or a mixture of the hydrogen-absorbing alloy and the above-mentioned elements, or an alloy or metal oxide composed of these elements in a container containing balls such as a planetary ball mill, a spiral ball mill, a rotary ball mill, or an attritor, and by impacting the hydrogen-absorbing alloy or mixture by collision between the container and the balls or between the balls.

When the container is sealed, the sealing may be performed in a device such as a dry box filled with an inert atmosphere such as argon, or the container may be provided with an exhaust valve to exhaust the gas in the container. In some cases, hydrogen gas may be introduced for the treatment. In such a device, although the container is sealed, the joint portion of the container is impacted by an internal impact to lower the sealing property, and it is preferable to add a double lid to the container or fill the device itself with an inert gas atmosphere in order to secure the sealing property. Or put it into a vacuum chamber. When an inert atmosphere is used, the purity of the inert gas is preferably controlled, and for example, the inert gas is preferably controlled so that the oxygen concentration is 100ppm or less and the water concentration is 50ppm or less. The hydrogen absorbing alloy powder or metal powder used as the raw material is preferably also operated in an inert gas to avoid oxidation.

When mechanical treatment is carried out by a planetary ball mill or the like, it is preferable that the treatment time is 1 to 1000hours, and if the treatment time is less than 1 hour, the hydrogen storage characteristics of the hydrogen storage alloy are not significantly changed, whereas if it exceeds 1000 hours, slow oxidation occurs and the production cost is increased.

The modified hydrogen absorbing alloy powder obtained by the above mechanical treatment preferably has a particle size of 0.1 to 50 μm. Annealing treatment may be carried out as required, and the treatment temperature depends on the composition of the hydrogen occluding alloy, and is generally 100-500 ℃. Further, the elements mixed by the treatment may form an aggregate with the alloy, and the hydrogen storage characteristics may be improved by the aggregation. The coagulation ratio is preferably 10% by weight or more.

By adopting the hydrogen storage alloy surface modification method, the initial activity and the hydrogen storage characteristic of the hydrogen storage alloy can be obviously improved by mixing at least one element selected from IVA group, VA group, VIA group, VIIA group, VIIIA group, IB group, IIB group, IIIB group and IVB group, alloy formed by the elements or mixture of metal oxides in the hydrogen storage alloy according to the highest molar ratio and carrying out mechanical treatment in vacuum, inert gas or hydrogen atmosphere.

The method of improving the hydrogen storage characteristics of the hydrogen storage alloy may include: 1) by coating, 2) local chemical modification, 3) mechanochemical modification, 4) modification by encapsulation, 5) irradiation with radiation, and the like. The method for modifying a hydrogen absorbing alloy of the present invention focuses on 3) in the above method, and mechanical treatment of the hydrogen absorbing alloy significantly improves the initial activity and hydrogen absorbing characteristics of the hydrogen absorbing alloy.

The mechanical modification of the invention not onlychanges the structure of the particles, but also changes the physical properties of the particles through the change of the surface structure, namely, the internal energy of the hydrogen storage alloy can be changed. Further, the generation of fine particles may be accompanied by generation of a fresh surface and increase in surface energy.

The mechanical modification of the present invention changes the surface and structure of the hydrogen storage alloy, and the resulting stress causes structural failure, plus the shift and regularity of atomic and molecular positions are reduced, resulting in an increase in potential energy. By this action, the catalytic activity can be increased and the selectivity of the catalytic reaction can be improved.

On the other hand, one of the phenomena caused by the modification is lattice defects in the hydrogen storage alloy. The lattice defects include plastic deformation generated in the particles due to the increased mechanical energy of modification, and residual stress caused by a temperature difference or phase change within the particles due to locally generated heat, in addition to lattice defects allowed by thermodynamics in an ideal crystal. By these influences, the hydrogen storage characteristics of the hydrogen storage alloy can also be improved.

After the mechanical modification of the hydrogen occluding alloy, when the X-ray diffraction peak of the sample was measured using CuK α as the X-ray source, the profile was found to be broadened.

In the above (a), the crystallite size D can be expressed by the Scherrer's formula

D＝(0.9λ)/(Δ(2θ)coSθ) (VI)

D: crystallite size Δ (2 θ): apparent half width

λ: x-ray wavelength for measurement θ: bragg angle of diffraction lines

Also, using the formula of Stokes&Wilson, the crystallite size ε can be expressed as follows

ε＝λ/(β_icosθ) (VII)

Epsilon crystallite size β_i: integral amplitude

λ: x-ray wavelength for measurement θ: bragg angle of diffraction lines

From the above two formulae, it is considered that the broadening of the X-ray diffraction peak in the mechanically treated hydrogen occluding alloy is caused by the reduction of the crystallites after the mechanical treatment.

In addition, the reason why the X-ray diffraction peak becomes broad must be considered the crystallite strain of the above (b). The lattice distortion occurring here may be considered as a change or variation in the plane pitch. According to Stokes&Wilson's formula, differential strain η of crystallites and diffraction products based thereonFraming β'_iHave the following relationship

β′_i＝2ηtanθ (VIII)

The profile broadening caused by both the non-uniform strain of the crystallite size can be expressed by the following formula of Hall

β＝β_i＋β′_i(IX)

Therefore, the broadening of the profile in the mechanically treated hydrogen storage alloy is due to both crystallite size and non-uniform strain. Due to these two factors, the characteristics of the hydrogen occluding alloy can be improved. That is, the mechanical treatment makes the crystallites of the hydrogen absorbing alloy smaller, increases the path for hydrogen diffusion, and shortens the distance, thereby improving the hydrogen absorption and dehydrogenation characteristics of the hydrogen absorbing alloy. As previously mentioned, such crystallite sizes D are 0.8nm ≦ D ≦ 50 nm. Further, when the hydrogen absorbing alloy is mechanically treated, the surface-to-surface distance of the hydrogen absorbing alloy particles is changed by the impact energy, and lattice distortion is formed in the hydrogen absorbing alloy, so that energy in the lattice is changed by the lattice distortion formed in the hydrogen absorbing alloy, and hydrogen absorption and hydrogen desorption are facilitated.

Further, the hydrogen absorbing alloy subjected to the mechanical treatment has a profile width represented by an apparent half width [ Delta]([ 2]theta)]of the formula (VI) of 0.3 DEG to [ Delta]([ 2]theta]to 10 deg.

It is considered that the activity of the hydrogen storage alloy upon hydrogen absorption is related to the ease of formation of the catalyst layer on the surface and the performance of the catalyst. From this point of view, the hydrogen storage characteristics of the hydrogen storage alloy can be improved by the above-described action. In order to further improve the hydrogen storage characteristics, a catalyst is provided which is obtained by mixing at least one element selected from the group consisting of elements of groups IVA, VA, VIA, VIIA, VIIIA, IB, IIB, IIIB and IVB, an alloy comprising the above elements, or a metal oxide, in a hydrogen storage alloy in an amount of up to equimolar amount, and subjecting the mixture to mechanical treatment in a vacuum, an inert gas or a hydrogen atmosphere to hydrogenate the mixture. Since the initial activity can be improved by forcibly adding a catalyst, which is a hydrogenation catalyst during occlusion, to the surface of the alloy by mechanical treatment, the initial activity and hydrogen storage characteristics of the hydrogen storage alloy can be remarkably improved by such a surface modification method.

For example, in Mg₂Ni is mixed with a certain proportion in the Ni-based hydrogen storage alloy, and whenthe Ni is mechanically treated in inert gas such as argon, nickel which plays a role of a hydrogen dissociation catalyst when absorbing hydrogen is added to the surface layer, thereby improving the characteristics of the hydrogen storage alloy. In addition, the crystal grains of the alloy are reduced, the grain boundary ratio is increased, and at the same time, nonuniform strain is generated in the crystal, so that hydrogen can be easily absorbed.

An example of a cylindrical nickel-hydrogen rechargeable battery among alkaline rechargeable batteries according to the present invention will be described with reference to fig. 3.

As shown in fig. 3, a bottomed cylindrical container 1 contains an electrode group 5 formed by spirally winding a laminate of a positive electrode 2, a separator 3, and a negative electrode 4. The negative electrode 4 is disposed on the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The container 1 contains an alkaline electrolyte. A circular first sealing plate 7 having a hole 6 at the center is provided at the upper opening of the container 1, an annular insulating grid 8 is disposed between the periphery of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is airtightly fixed to the container 1 by the grid 8 by caulking to reduce the diameter of the opening inward. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. A cap-shaped positive electrode terminal 10 is attached to the seal 7 so as to cover the hole 6. A safety valve 11 made of rubber is disposed in a space surrounded by the sealing plate 7 and the positive electrode terminal 10 to plug the hole 6. A circular pressing plate 12 made of an insulating material and having a hole at the center is disposed on the positive electrode terminal 10, and a protrusion of the positive electrode terminal 10 protrudes from the hole of the pressing plate 12. The outer tube 13 encases the periphery of the platen 12, the sides of the container 1 and the bottom periphery of the container 1.

The positive electrode 2, the separator 3, the negative electrode 4, and the electrolytic solution are explained below.

1) Positive electrode 2

The positive electrode 2 can be produced, for example, by adding a conductive material to nickel hydroxide powder as an active material, mixing the resultant with a polymer binder and water to form a paste, filling the paste in a conductive substrate, drying the paste, and molding the dried paste.

Examples of the conductive material include cobalt oxide, cobalt hydroxide, metallic cobalt, metallic nickel, and carbon.

Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene, and the like.

Examples of the conductive substrate include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

2-1) negative electrode 4

The negative electrode 4 is produced by adding a conductive material to hydrogen storage alloy powder, mixing the mixture with a polymer binder and water to form a paste, filling the paste in a conductive substrate, drying the paste, and molding the dried paste.

As the above hydrogen occluding alloy, hydrogen occluding alloys including alloys represented by the above general formula (1) or general formula (2) can be used.

Further, among the X-ray diffraction peaks using CuK α as an X-ray source, an alloy in which the half width Delta (2 theta) of at leastone peak in the three-strong line is 0.3 DEG to Delta (2 theta) to 10 DEG can be used as the hydrogen-absorbing alloy, and it is preferable that the hydrogen-absorbing alloy satisfies the relationship of D being 0.8nm to 50nm, where D is the crystallite size.

The polymer binder may be the same as that used for the positive electrode 2.

Examples of the conductive substrate include a planar substrate such as a perforated metal, expanded metal, perforated steel plate, or nickel mesh, and a three-dimensional substrate such as a felt-like porous metal or sponge-like metal substrate.

The negative electrode containing a hydrogen storage alloy comprising the alloys represented by the above general formulae (1) and (2) as a negative electrode material has improved reactivity by optimizing the magnesium content in the alloy, and also has improved resistance to deterioration, i.e., stability of the hydrogen storage alloy during hydrogen absorption and desorption, i.e., charge and discharge cycles. Further, the provision of such a negative electrode makes it possible to provide an alkaline storage battery having good large-capacity charge/discharge characteristics.

2-2) negative electrode 4

The negative electrode is a negative electrode containing a magnesium-containing hydrogen storage alloy, and when immersed in an alkali metal hydroxide of 6 to 8 degrees C, (a) the elution rate of magnesium ions into an alkali metal hydroxide aqueous solution at normal temperature is 0.5mg/kg alloy/hr or less, or the elution rate of magnesium ions into an alkali metal hydroxide aqueous solution at 60 degrees C is 4mg/kg alloy/hr or less, and (b) the elution rate of an alloy component element into an alkali metal hydroxide aqueous solution at normal temperature is 1.5mg/kg alloy/hr or less, or the elution rate of an alloy component element into an alkali metal hydroxide aqueous solution at 60 degrees C is 20mg/hg alloy/hr or less.

The present inventors established a method for evaluating the deterioration rate of a magnesium-containing hydrogen storage alloy, and according to this method, found a negative electrode comprising the above hydrogen storage alloy exhibiting sufficient reversibility and stability against electrode reaction.

The ion elution rate, i.e., the corrosion rate of the hydrogen absorbing alloy in an aqueous alkali metal hydroxide solution is a parameter for characterizing the static stability of the alloy, and generally, the dynamic cycle stability cannot be inferred from this characteristic alone. This is considered to be because the cycle stability of the hydrogen absorbing alloy is greatly influenced by the dynamic characteristics such as the influence of strain applied to crystal lattices by hydrogen among crystal lattices of the alloy during hydrogen absorption and hydrogen desorption, in addition to the static characteristics of the alloy itself defined by chemical and physical modifications caused by addition of a different element, contact with a different substance, or surface treatment.

As a result of evaluating the characteristics of a negative electrode (hydrogen electrode) made of a hydrogen storage alloy containing magnesium, which has been subjected to various treatments and various compositions, it was found that at least the hydrogen storage alloy having high reversibility exhibited sufficient stability to satisfy the following conditions.

Namely, the conditions as the negative electrode are as follows: when magnesium alone is considered, the rate of elution of magnesium ions into an aqueous alkali metal hydroxide solution at room temperature is 0.5mg/kg alloy/hr or the rate of elution of magnesium ions into an aqueous alkali metal hydroxide solution at 60 ℃ is 4mg/kg alloy/hr in the case of immersion in an aqueous alkali metal hydroxide solution of 6 to 8, and when all elements contained in the alloy are considered, (b) the rate of elution of alloy component elements into an aqueous alkali metal hydroxide solution at room temperature is 1.5mg/kg alloy/hr or the rate of elution of alloy component elements into an aqueous alkali metal hydroxide solution at 60 ℃ is 20mg/kg alloy/hr.

The reason for adopting the dissolution rate of 60 ℃ is that the ion elution rate of a practical alloy at room temperature is as small as 0.5mg/kg alloy/hr, and 60 ℃ is specified for increasing the elution reaction rate and improving the measurement time and accuracy.

Therefore, it is also possible to set a predetermined value indicating a substantially equivalent dissolution rate at other temperatures and evaluate the value. However, since a side reaction may occur by changing the temperature of the atmosphere and a separate change may occur depending on the composition and treatment of the alloy, it is not preferable to measure the temperature at a high temperature of 60 ℃ or higher.

As the easiest method for the negative electrode, a method using an alloy of: when the hydrogen-absorbing alloy is immersed in an aqueous solution of an alkali metal hydroxide of a prescribed degree of 6 to 10, the elution rate of magnesium ions into the electrolyte is 0.5mg/kg alloy/hr or less, and 4mg/kg alloy/hr or less at 60 ℃, and the sum of the elution rates of the alloying element elements is 1.5mg/kg alloy/hr or less at room temperature and 20mg/kg alloy/hr or less at 60 ℃.

3) Partition board 3

The separator 3 may be made of, for example, a polypropylene nonwoven fabric, a nylon nonwoven fabric, or a polymer nonwoven fabric obtained by blending polypropylene fibers and nylon fibers. The polypropylene nonwoven fabric subjected to surface hydrophilization treatment is particularly suitable as a separator.

4) Alkaline electrolyte

The alkaline electrolyte may be, for example, an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), a mixed solution of NaOH and LiOH, a mixed solution of KOH, LiOH and NaOH, or the like.

Another alkaline storage battery of the present invention is an alkaline storage battery comprising a negative electrode, a positive electrode and an alkaline electrolyte solution accommodated in a container, wherein the negative electrode comprises a hydrogen storage alloy containing magnesium, and the positive electrode is disposed so as to be spaced apart from the negative electrode by a separator, wherein the alkaline electrolyte solution is injected into the container, the container is closed, and the concentration of magnesium ions in the alkaline electrolyte solution is 2.2 mg/liter or less after 30 days.

The reason for the predetermined electrolyte concentration will be described below only in the case of an alkaline storage battery.

In general, the amount of electrolyte in an alkaline battery is limited to the minimum, and a small amount of ion elution easily causes an increase in the ion concentration of the electrolyte, and the ion elution rate decreases with an increase in the ion concentration eluted from the electrolyte, and the ion concentration increase rate in the electrolyte should be negligibly decreased in a short time. Therefore, the ion concentration of the electrolyte in the battery can be regarded as a parameter in addition to the ion elution rate.

As described above, another alkaline storage battery according to the present invention has been established which is provided with a negative electrode comprising a hydrogen storage alloy having sufficient reversibility and stability against electrode reaction, and thus can provide a method for evaluating the deterioration rate of a magnesium-containing hydrogen storage alloy, which can replace conventional alkaline storage batteries (nickel-cadmium batteries or those using LaNi)₅Nickel-metal hydride storage batteries and the like based on hydrogen storage alloys).

The amount of magnesium ions eluted from the electrolyte of an alkaline storage battery is limited, and short-circuiting due to the formation of dendrites can be effectively prevented.

Preferred embodiments are described in detail below.

Examples 1 to 5 and comparative examples 1 to 6

Melting Mg and Ni in atmosphere of atmospheric pressure and argon gas by high-frequency induction furnace to obtain Mg-Ni alloy₂Ni_y11 hydrogen occluding alloys represented by y having the values shown in Table 2.

The particle diameters of the 11 hydrogen-absorbing alloys obtained were made uniform to 45 to 75 μm, and a certain amount of the alloy was immersed in an 8N aqueous solution of potassium hydroxide at 60 ℃ for 5 hours, and then the concentration of magnesium ions eluted into the solution was measured, and the relative value of the concentration of magnesium eluted and the concentration of magnesium eluted per mole of Mg in the alloy were determined from the measured values. The relative value of the eluted magnesium concentration was calculated from the eluted concentration of pure magnesium as 100. These results are shown in table 2 below. Fig. 4 shows normalized data obtained by dividing the ratio of magnesium contained in the alloy by the amount of elution.

The hydrogen occluding alloys were crushed to a particle size of 75 μm or less, and each of them was placed in a pressure-resistant container, hydrogen gas was introduced at 300 ℃ under 10 atmospheric pressure, and the amount of hydrogen absorbed in the alloy was calculated from the pressure decrease after 24 hours, and the amount of the hydrogen absorbed was shown in Table 2.

TABLE 2

	Mg2NiyComposition of		Concentration of dissolved Mg		Amount of hydrogen absorbed With Mg2NiyHz Z when it represents
						Mg∶Ni Molar ratio of	y	Relative value	In the alloy each Molar Mg
	Comparative example 1	100∶0	0	100						1.00	0
Comparative example 2					75∶25	0.667	19	0.25	1.4
	Comparative example 3	2∶1	1.000	18						0.27	3.2
Example 1					40∶21	1.050	8	0.12	3.4
	Example 2	64∶36	1.125	7						0.11	3.5
Example 3					5∶3	1.200	7	0.11	3.3
	Example 4	8∶5	1.250	8						0.13	3.0
Example 5					4∶3	1.500	10	0.18	2.3
	Comparative example 4	8∶7	1.750	105						1.97	0.7
Comparative example 5					50∶50	2.000	145	2.90	0.4
	Comparative example 6	1∶2	4.000	240						7.20	0.5

As can be seen from Table 2, the alloy is represented by Mg₂Ni_yThe hydrogen occluding alloy shown in the above shows that when the amount y of Ni is small, the amount of eluted Mg ions is lower than that of pure Mg, but when the value of y exceeds 1.5, the amount of eluted Mg ions increases sharply, and particularly in the hydrogen occluding alloy in which y is less than 1.5 and more than 1, the amount of eluted Mg ions is low. In addition, made of Mg₂Ni_yThe hydrogen absorbing properties of the hydrogen occluding alloy shown in the above were not greatly changed when the y value of the Ni content was about 1, but when the y value exceeded 1.5, the hydrogen absorbing properties were drastically reduced, and it was found that Mg₂Ni_yThe hydrogen storage alloy has good chemical stability and hydrogen storage property, and the y value of the hydrogen storage alloy is more than 1 and less than or equal to 1.5.

Example 6 and comparative example 7

Melting Mg and Ni in atmosphere of atmospheric pressure and argon gas byhigh-frequency induction furnace to obtain Mg-Ni alloy₂Ni_1.15(example 6) and Mg₂Ni_0.84(comparative example 7) two kinds of hydrogen occluding alloy ingots. The above hydrogen-absorbing alloy ingots were cut with a diamond cutter, respectively, to prepare 5 strip-shaped alloy pieces having the dimensions shown in Table 3 below. Since the alloy sheet was easily broken due to scratches and unevenness on the surface, the alloy sheet surface was polished with 0.3 μm diamond polishing paste to prevent breakage, and then subjected to the next stress measurement. The maximum stress of each strip-shaped alloy piece was measured, and as shown in fig. 5, the strip-shaped alloy piece 21 was placed on two sets of support rods 22 arranged in parallel at an interval of 20mm, and the force required for bending the strip-shaped alloy piece 21 was obtained at the center portion of the strip-shaped alloy piece 21 between the support rods 22 by using an indenter 23, thereby calculating the maximum stress.

The maximum stress is calculated as follows. The width of the strip-shaped alloy sheet is W (mm), the thickness is T (mm), the distance between the support rods is 20mm, the force required for bending is f/N, and the maximum stress sigma is

The maximum stress of the strip-shaped alloy sheet sample determined in this manner is shown in table 3 below.

TABLE 3

		Size of sample		Breaking load N	Moment of force 103Nm	Section modulus 10-9m	Maximum stress 106Nm-2
								Thickness of mm	Width of mm
		Fruit of Chinese wolfberry Applying (a) to Example (b) 6	Sample No. 1							0.49	10.1	2.05	10.2	0.41	25.2
2	0.50			9.9	2.83	14.2	0.41	34.5
			3						0.65	9.6	3.14	15.7	0.67	23.3
4	1.03			10.3	11.3	56.3	1.82	30.9
			5						1.05	10.1	11.7	58.4	1.85	31.6
Ratio of Compared with Example (b) 7	Sample No. 1			0.37	9.7	2.45	12.3	0.22							55.3
		2	0.60						10.6	6.20	31.0	0.64	48.7
	3			0.60	10.9	5.39	26.9	0.65						41.3
		4	1.22						10.5	26.9	134	2.60	51.8
	5			1.30	10.3	27.7	138	2.92						47.3

As can be seen from Table 3, Mg in comparative example 7₂Ni_0.84Strip-shaped alloy sheet of Hydrogen absorbing alloy made of the Mg of example 6₂Ni_1.15The strip-shaped alloy sheet made of the hydrogen storage alloy has lower stress and good crushing and processing properties.

As seen from the SEM (scanning Electron microscope) photograph of the cross-section of the hydrogen occluding alloy of example 6, most of Mg₂Ni phase, the remainder being phases consisting only of Ni, and Mg₂A small amount of a phase having a high Mg content is present at the grain boundary of the Ni phase. Such a tissue was also confirmed by an EPMA (X-ray microanalyzer). In the hydrogen occluding alloy of example 6, the phase having a high Mg content accounts for 8 to 9% of the total, and Mg₂The Ni phase and the phase composed of only Ni account for 90% or more. In the same SEM photograph as that of the hydrogen occluding alloy of comparative example 7, most of Mg was observed₂Ni phase, the remainder being phases consisting only of Ni, and Mg₂A considerable amount of a phase containing a high amount of Mg exists at the grain boundary of the Ni phase. In the hydrogen occluding alloy of comparative example 7, the phase having a high Mg content accounts for 20% or more of the total.

As is clear from example 6 and comparative example 7, the composition distribution of the structure cross section in the alloy showed 90% or more of uniformity (Mg) as compared with the cross-sectional area₂Ni phase) has good chemical stability and machinability.

Examples 7 to 14 and comparative examples 8 to 10

In the presence of Mg_2-xM2_xM1_yIn the composition range of (1), Mg is prepared_2-xM2_xAnd M1, and the values of x and y are shown in Table 4 below for 11 hydrogen occluding alloys.

Strip-shaped alloy pieces having the same dimensions as those of sample 2 of example 6 were prepared from these hydrogen occluding alloys, and the maximum stress was determined by the above equation using the experimental apparatus shown in the same manner as in FIG. 5, and the results are shown in Table 4.

TABLE 4

	Hydrogen-storage alloy Mg2-xM2xM1y	y value	Maximum stress 106Nm-2
				Example 7	Mg2Ni0.95Fe0.1	1.05	28.1
Example 8	Mg2Ni0.95Co0.1	1.05	28.6
				Example 9	Mg2Ni0.9Cu0.2	1.10	31.2
Example 10	Mg1.9Ca0.1Ni1.1	1.10	28.2
				Example 11	Mg1.9La0.1Ni1.1	1.10	29.3
Example 12	Mg2Ni0.9Sn0.25	1.15	30.2
				Example 13	Mg2Ni1Se0.1	1.10	34.9
Example 14	Mg1.9Ca0.1Ni0.9Sn0.15	1.05	30.8
				Comparative example 8	Mg2Ni0.95Fe0.05	1.00	44.8
Comparative example 9	Mg1.9Al0.1Ni0.9	0.90	54.3
				Comparative example 10	Mg2Ni0.45Sn0.45	0.90	53.3

As can be seen from Table 4, in Mg_2-xM2_xM1_yIn the composition range of (1), the maximum stress is 30X 10 for the hydrogen occluding alloys of examples 7 to 14 in which the value of y is larger than 1⁶Nm^-2In contrast, the hydrogen occluding alloys of comparative examples 8 to 10, in which the y value is less than 1, in the above composition should be 50X 10 at maximum⁶Nm^-2Several tens of percent larger than the hydrogen occluding alloys of examples 7 to 14.

Example 15

Mg for producing molten metal containing predetermined amounts of Mg and Ni by slow cooling₂Ni_yThe hydrogen occluding alloy shown in (1) was sealed in a quartz tube in an argon atmosphere and annealed slowly at 500 ℃ for 1 month to obtain Mg having y equal to 1.01₂Ni_1.01The hydrogen occluding alloy of (1).

The obtained hydrogen storage alloy is soaked in an alkaline aqueous solution, and the amount of dissolved magnesium ions is measured. As a result, the relative amount of eluted magnesium ions was 9, and the value obtained by dividing the amount by 66.4% of the magnesium content in the alloy was 0.14, which showed good chemical stability.

FIG. 6 is a schematic view of a hydrogen absorption/desorption characteristic evaluation apparatus for evaluating the temperature sweep of the hydrogen absorbing alloy of example 16 and thereafter. The hydrogen cylinder 31 is connected to a sample container 33 via a pipe 32. The pipe 32 branches off halfway, the end of the branch pipe 34 is connected to a vacuum pump 35, and a pressure gauge 36 is attached to a pipe portion further branched off from the branch pipe 34. First and second valves 371 and 372 are attached to the pipe 32 between the hydrogen cylinder 31 and the sample container 33 from the side of the hydrogen cylinder 31. The pressure accumulation container 38 is connected to the portion of the pipe 32 between the first and second valves 371 and 372. A third valve 373 is installed on a portion of the branch pipe 34 between the vacuum pump 35 and the pressure gauge 36. The sample container 33 is provided with a heater 39. A thermocouple 40 is inserted into the sample container 33. A temperature controller 42 controlled by a computer 41 is connected to the thermocouple 40 and the heater 39. The temperature of the heater 39 is adjusted based on the detectedtemperature output from the thermocouple 40. A recorder 43 controlled by a computer 41 is connected to the pressure gauge 36 and the temperature controller 42.

Examples 16 and 17 and comparative example 11

Prepared at Mg_2-xM2_xM1_yMg with M1 ═ Ni, M2 ═ Al, x ═ 0.1, and y ═ 1.05_1.9Al_0.1Ni_1.05Example 16. Mg of formula M1 ═ Ni, M2 ═ Al, x ═ 0.1, and y ═ 1_1.9Al_0.1Ni (comparative example 11), M1 ═ Ni, M2 ═ Mn, x ═ 0.11, and y ═ 1.05 Mg_1.9Mn_0.1Ni_1.05Example 17 and Mg₂Hydrogen occluding alloy of Ni (comparative example 3).

The hydrogen storage alloy is charged into the sample container 33 shown in FIG. 6, the first valve 371 is closed, the second and third valves 372 and 373 are opened, the vacuum pump 35 is started, and the air in the pipe 32, the branch pipe 34, the pressure accumulation container 38, and the sample container 33 is removed. After the second and third valves 372 and 373 are closed, the first valve 371 is opened, hydrogen is supplied from the hydrogen cylinder 31, and the inside of the pipe 32, the branch pipe 34, the pressure accumulation container 38, and the sample container 33 is replaced with hydrogen. Subsequently, the first valve 371 is closed, and the amount of hydrogen introduced is calculated from the system internal pressure indicated by the pressure gauge 36 at that time. The second valve 372 is opened to supply hydrogen into the sample container 33, the temperature is monitored by the thermocouple 40, and then the temperature in the sample container 33 is raised at a constant rate by the control of the computer 41 and the temperature controller 42, and the temperature is scanned by the heater 39 receiving the control signal. The pressure change in the container 33 at this time is detected by the pressure gauge36 and recorded by the recorder 43, and fig. 7 shows the pressure change (pressure decrease accompanying hydrogen absorption by the hydrogen absorbing alloy) caused by the temperature rise in the sample container 33.

As can be seen in FIG. 7, with Mg_1.9Al_0.1Ni Hydrogen storage alloy (comparative example 11) in comparison with Mg_1.9Al_0.1Ni_1.05The hydrogen occluding alloy (example 16) can absorb hydrogen at a lower temperature, and further, Mg_1.9Mn_0.1Ni_1.05Hydrogen storage alloys (example 17), optionally in a specific Mg ratio₂The hydrogen storage alloy of Ni (comparative example 3) absorbed hydrogen at a lower temperature. In particular, the hydrogen storage alloy of example 16 in which M2 is Al has a lower hydrogen storage temperature than the alloy of example 17 in which M2 is Mn. Further, the hydrogen occluding alloys of examples 16 and 17 have Mg₂The hydrogen storage alloy of Ni (comparative example 3) has the same hydrogen storage amount. From this, it was found that the replacement of Mg with M2(Al or Mn) makes it possible to achieve a low hydrogen storage temperature while maintaining a high hydrogen storage amount.

In addition, for Mg_1.9Al_0.1Ni_1.05、Mg_1.9Mn_0.1Ni_1.05Hydrogen storage alloy (A)Examples 16, 17) and Mg_1.9Al_0.1Ni、Mg₂Ni hydrogen storage alloys (comparative examples 11 and 3) were analyzed for the relationship between hydrogen storage concentration and temperature, and examined for the temperature required for hydrogen absorption to a H/M of 0.1 (the ratio of the number of hydrogen atoms absorbed to the number of hydrogen atoms in the hydrogen storage alloy was 0.1). Further, the relative values of the concentration of magnesium eluted from the hydrogen occluding alloys of examples 16 and 17 and comparative examples 11 and 3 and the concentration of magnesium ions eluted per mole of Mg in the alloys were measured in the same manner as in example 1. The results of calculating the relative value of the concentration of eluted magnesium from the elution concentration of pure magnesium as 100 are shown in Table 5 below.

TABLE 5

	Hydrogen-storage alloy Mg2-xM2xM1y	y value	Concentration of dissolved Mg		Temperature of (℃)
						Relative value	In the alloy each Molar Mg
			Example 16	Mg1.9Al0.1Ni1.05				1.05	7	0.11	70
Comparative example 11	Mg1.9Al0.1Ni	1.00			17	0.27	75
			Example 17	Mg1.9Ni1.06Mn0.1				1.16	7	0.12	110
Comparative example 3	Mg2Ni	1.00			18	0.27	140

As can be seen from Table 5, the hydrogen occluding alloy in which Mg is replaced with M2(Al or Mn) and the y value of M1 is larger than 1 can realize a low temperature of hydrogen occluding temperature and an improvement in chemical stability.

Example 18

For in Mg_2-xM2_xM1_yMg with M1 ═ Ni, Co, M2 ═ Al, x ═ 0.1, and y ═ 1.10_1.9Al_0.1Ni_0.55Co_0.55Using the temperature scanning hydrogen absorption/desorption characteristic evaluation apparatus shown in FIG.6, the pressure change (pressure decrease due to hydrogen absorption of the hydrogen absorbing alloy) caused by the temperature increase of the sample vessel was measured in the same manner as in EXAMPLE 16, and as a result, a characteristic chart shown in FIG. 8 was obtained, in which FIG. 8 also shows Mg mentioned above₂Results of the Ni Hydrogen storage alloy (comparative example 3).

As can be seen from fig. 8, the hydrogen storage alloy of Ni and Co in which M1 is present realizes a low temperature hydrogen storage temperature while maintaining a high hydrogen storage amount.

Further, the hydrogen occluding alloy of example 18 was measured for the relative value of the concentration of magnesium eluted and the concentration of magnesium ions eluted per mole of Mg in the alloy in the same manner as in example 1. The relative value of the concentration of magnesium eluted was calculated with the concentration of pure magnesium as 100. As a result, the concentration of eluted magnesium ions per mole of Mg of the alloy having a relative value of the concentration of eluted magnesium of 8 was 0.13.

Examples 19 and 20 and comparative example 12

For in M_2-xM2_xM1_yZr with M-Zr, M1-Fe, M2-V, x-0.1 and y-1.05_1.9V_0.1Fe_1.05Example 19, Zr in the above formula where M ═ Zr, M1 ═ Fe, M2 ═ Cr, x ═ 0.1, and y ═ 1.05_1.9Cr_0.1Fe_1.05Example 20 and Zr₂A hydrogen absorbing alloy of Fe (comparative example 12) was measured for a change in pressure due to an increase in temperature of the sample container (a decrease in pressure accompanying hydrogen absorption by the hydrogen absorbing alloy) by the same method as in example 16 using the temperature sweep hydrogen absorption/desorption characteristic evaluation apparatus shown in fig. 6, and a temperature required for hydrogen absorption until H/M becomes 0.1 (the ratio of the number of absorbed hydrogen atoms to the number of hydrogen atoms in the hydrogen absorbing alloy is 0.1) was obtained.

TABLE 6

	Hydrogen-storage alloy M2-xM2xM1y	y value	Temperature of (℃)
				Example 19	Zr2Fe1.05V0.11	1.16	340
Example 20	Zr2Fe1.05Cr0.11	1.16	295
				Comparative example 12	Zr2Fe	1.00	380

As can be seen from Table 6, the hydrogen occluding alloys in which M is Zr, M2(V, Cr) is substituted for Zr, and the y value of M1 is larger than 1 (examples 19 and 20) can realize a low temperature of the hydrogen occluding temperature.

Examples 21 to 26 and comparative examples 13 and 14

Melting Mg, Ni, Ag, Cd, Ca, Pd, Al, In, Co and Ti In a high-frequency induction furnace under atmospheric pressure and argon atmosphere to obtain a product_2-xM2_xM1_yThe 9 hydrogen occluding alloys shown in the following Table 7.

Each of the above-mentioned hydrogen occluding alloys was loaded in the sample container 33 of FIG. 6, and the first valve 37 was closed₁Opening the second and third valves 37₂、37₃The vacuum pump 35 is started to remove air from the pipe 32, the branch pipe 34, the pressure accumulation container 38, and the sample container 33. Closing the second and third valves 37₂、37₃Thereafter, the first valve 37 is opened₁Hydrogen is supplied from the hydrogen cylinder 31, and the inside of the pipe 32, the branch pipe 34, and the pressure storage container 38 is replaced with hydrogen. Then, the first valve 37 is closed₁Opening the second valve 37₂Hydrogen is supplied into the sample container 33 to confirm the pressure and temperature recorded by the recorder 39And (4) degree.

In examples 21 to 26, the pressure of the hydrogen cylinder 1 for replacing the difference in the pressure accumulation vessels was set so that the pressure (initial pressure) was about 10 atmospheres, and the measurement start temperature was room temperature (about 25 ℃).

Then, the temperature in the sample container 33 is raised at a rate of 0.5 ℃/min under the control of the computer 41 and the temperature controller 42, and the temperature is scanned by the heater 39 receiving the control signal. The temperature change and the pressure change in the sample container 33 at this time are detected by the thermocouple 40 and the pressure gauge 36, and recorded by the recorder 43.

The pressure in the sample container 33, which changes with the temperature rise, is monitored as described above, and the temperature at which the M/H becomes 0.1 (that is, the number of hydrogen storage atoms per mole of metal atom of the alloy becomes 0.1) is obtained from the pressure drop, and is used as the minimum temperature standard at which the hydrogen storage reaction of the hydrogen storage alloy can be performed. Further, the relative values of the concentration of magnesium eluted from the hydrogen occluding alloys of examples 21 to 26 and comparative examples 3, 13 and 14 and the concentration of magnesium ions eluted per mole of Mg in the alloys were measured in the same manner as in example 1. The results of calculating the relative value of the concentration of magnesium eluted from pure magnesium with the concentration of pure magnesium as 100 are shown in Table 7 below.

TABLE 7

	Hydrogen-storage alloy Mg2-xM2xM1y	y value	Concentration of dissolved Mg		Temperature of (℃)
						Relative value	In the alloy Per mole of Mg
			Example 21	Mg2Ag0.22Ni1.11				1.11	7	0.11	120
Comparative example 13	Mg1.9Al0.1Ni	1.00			17	0.27	75
			Example 22	Mg2Co1.24In0.35				1.59	8	0.14	110
Example 23	Mg2Co1.11In0.11	1.22			9	0.15	150
			Example 24	Mg1.5Ca0.5Ni1.5Ag0.5				2.00	7	0.19	115
Example 25	Mg1.76Ca0.5Ni1.5Ag0.38	1.88			7	0.15	110
			Example 26	Mg2Ni1.25In0.25W0.25				1.75	6	0.11	125
Comparative example 3	Mg2Ni	1.00			18	0.27	140
			Example 14	Mg2Co				1.00	58	0.87	170

As is apparent from Table 7, the hydrogen storage alloys of examples 21 to 26 were reduced in hydrogen storage temperature and improved in chemical stability as compared with the hydrogen storage alloys of comparative examples 3, 13 and 14.

Example 27

A round-bottomed flask equipped with a rotor was equipped with an argon inlet tube, a dropping funnel and an Arin condenser, and a round-bottomed flask was charged with Mg₂The Ni hydrogen storage alloy is decompressed by a vacuum pump, heated and dried by an air heating gun, and then argon gas is replaced. Then, THF was added to the round-bottom flask while introducing argon gas thereinto, followed by stirring, and 1-bromo-3-ethane was slowly dropped from the dropping funnel to start the reaction between the hydrogen occluding alloy and 1-bromo-3-ethane. Stopping stirring after the dripping quenching is finished, precipitating and filtering to obtain the surface modified hydrogen storage alloy.

The hydrogen storage characteristics of the obtained surface-modified hydrogen storage alloy and the hydrogen storage alloy before surface modification were evaluated by the hydrogen absorption and desorption characteristic evaluation apparatus shown in FIG. 6. The measurement is carried out bymonitoring the pressure change in the reaction vessel when a certain amount of hydrogen is introduced into the reaction vessel.

The above hydrogen occluding alloys were charged into the sample container 33 of FIG. 6, and the first valve 37 was closed₁Opening the second and third valves 37₂、37₃The vacuum pump 35 is started to remove air from the pipe 32, the branch pipe 34, the pressure accumulation container 38, and the sample container 33. Closing the second and third valves 372 and 37₃Thereafter, the first valve 37 is opened₁Hydrogen is supplied from the hydrogen cylinder 31, and the inside of the pipe 32, the branch pipe 34, and the pressure storage container 38 is replaced with hydrogen. Then, the first valve 37 is closed₁The amount of hydrogen is calculated from the system internal pressure indicated by the pressure gauge 36 at this time. Then the second valve 37 is opened₂Hydrogen is supplied into the sample container 33, and the temperature is monitored by the thermocouple 40. The temperature in the sample container 33 is made constant by controlling the heater 39 with the computer 41 and the temperature controller 42. By pressureThe gauge 36 detects the change in pressure in the container 33 at this time, and records it with the recorder 43.

Mg before and after surface modification is shown in FIG. 9₂Pressure change caused by hydrogen absorption of the Ni hydrogen storage alloy at 25 ℃ (accompanied by a decrease in pressure of hydrogen absorption of the hydrogen storage alloy).

As can be seen from FIG. 9, when a certain hydrogen pressure is applied, Mg before surface modification₂The Ni hydrogen storage alloy does not generate pressure change at all and keeps a certain pressure. Conversely, surface modified Mg₂The pressure in the system of the Ni hydrogen storagealloy is changed sharply, and a large amount of hydrogen is absorbed. This is about 200 ℃ or more lower than the temperature required for hydrogen absorption in the past, i.e., unmodified Mg if there is no higher temperature condition (200 ℃ C.) -, 300 ℃ C.)₂The Ni hydrogen storage alloy does not undergo hydrogen absorption and hydrogen desorption reactions or the reaction is extremely slow. On the contrary, the hydrogen occluding alloy subjected to the surface modification treatment of example 27 can absorb hydrogen at around room temperature.

Examples 28 to 59

The hydrogen storage alloys having the compositions shown in tables 8 to 10 below were surface-modified in the same manner as in example 27, and the hydrogen storage characteristics at 25 ℃ of each hydrogen storage alloy before and after the surface modification were evaluated by the hydrogen absorption and desorption characteristic evaluation apparatus shown in FIG. 6, and the results are shown in tables 8 to 10 below. X in tables 8 to 10 represents the amount MH of hydrogen absorbed in the hydrogen occluding alloy_x。

TABLE 8

	Alloy (I)	X (before treatment)	X (after treatment)
				Example 28	Mg2Ni	0	3.0
Example 29	Mg2Cu	0	2.0
				Example 30	Mg2Co	0	3.5
Example 31	Mg2Fe	0	4.0
				Example 32	LaNi5	0.1	6.0
Example 33	MmNi 5	0	3.0
				Example 34	CaNi 5	0	4.0
Example 35	TiFe	0.1	0.5
				Example 36	TiCo	0	0.5
Example 37	ZrMn2	0.1	3.0
				Example 38	ZrNi2	0.1	3.0

TABLE 9

	Alloy (I)	X (before treatment)	X (after treatment)
				Practice ofExample 39	Mg2Ni0.8Co0.2	0	2.3
Example 40	Mg2Ni0.9Co0.2	0	2.9
				EXAMPLE 41	Mg2.1Ni1.8Fe0.1	0	3.0
Example 42	Mg2Ni0.7Mo0.2Rh0.2	0	3.1
				Example 43	Mg1.8Zr0.2Ni	0	2.5
Example 44	Mg1.3Y0.5Ni	0	2.0
				Example 45	Mg2Ir0.1Ni	0	2.4
Example 46	Mg1.9Al0.1Ni0.9Mn0.2	0	3.5
				Example 47	Mg2Cu0.5Cd0.5	0	1.6
Example 48	Mg2Cu0.8Pd0.4	0	2.0

Watch 10

	Alloy (I)	X (before treatment)	X (after treatment)
				Example 49	Mg2Ti0.1Ni	0	2.3
Example 50	Mg2Nb0.1Ni1.2	0	3.1
				Example 51	Mg2Ta0.1Ni1.8	0	2.8
Example 52	LaAl0.3Ni3.8Mn0.4Co0.5	0.5	5.0
				Example 53	MmAl0.6Ni3.7Mn0.3Zr0.4	1.0	5.0
Example 54	CaNi4.0Mn0.5Al0.4Si0.1	0.7	4.5
				Example 55	TiFe0.4Mn0.5	0.2	2.1
Example 56	TiMn1.6Co0.1	0	2.6
				Example 57	ZrCo1.1Mn1.3	0.2	3.0
Example 58	Zr0.6Ti0.4V0.6Ni1.1Mn0.2	0.1	3.5
				Example 59	ZrMn0.6V0.2Ni1.5Co0.1	0.2	3.1

As can be seen from tables 8 to 10, the hydrogen storage characteristics are improved by the surface activation of the hydrogen storage alloy after the surface modification.

Example 60

Mixing Mg₂The Ni hydrogen storage alloy was placed in a stainless steel vessel with a double-layer lid together with a stainless steel ball, and an argon atmosphere having an oxygen concentration of 1ppm or less and a water concentration of 0.5ppm or less was charged, and the vessel was sealed with an O-ring, and then the ball mill was operated at 200 rpm for 100 hours (mechanical treatment).

The hydrogen storage characteristics of the hydrogen absorbing alloy subjected to the mechanical treatment and the hydrogen absorbing alloy before the treatment were evaluated by the hydrogen absorption and desorption characteristic evaluation apparatus shown in FIG. 6. The measurement is carried out by monitoring the pressure change in the reaction vessel when a certain amount of hydrogen is introduced into the reaction vessel.

The hydrogen occluding alloys were charged into the sample container 33 shown in FIG. 6, and the first valve 37 was closed₁Opening the second and third valves 37₂、37₃The vacuum pump 35 is started to remove air from the pipe 32, the branch pipe 34, the pressure accumulation container 38, and the sample container 33. Closing the second and third valves 37₂、37₃Thereafter, the first valve 37 is opened₁Hydrogen is supplied from the hydrogen cylinder 31, and the inside of the pipe 32, the branch pipe 34, and the pressure storage container 38 is replaced with hydrogen. Then, the first valve 37 is closed₁The amount of hydrogen introduced is calculated from the system pressure indicated by the pressure gauge 36 at this time. Then the second valve 37 is opened₂Hydrogen is supplied into the sample container 33, and the temperature is monitored by the thermocouple 40. The temperature in the sample container 33 is made constant by controlling the heater 39 with the computer 41 and the temperature controller 42. The pressure change in the container 33 at this time is detected by the pressure gauge 36 and recorded by the recorder 43.

The results of evaluation of hydrogen storage characteristics at 25 ℃ of the hydrogen storage alloy powder before and after the above mechanical treatment are shown in Table 11.

Example 61

0.5 mol of Mg₂Mixing Ni hydrogen storage alloy with 0.5 mol of Ni powder as catalyst, and mixing the mixtureThe mixture was put into a stainless steel vessel with a double-layer lid together with stainless steel balls, and an argon atmosphere with an oxygen concentration of 1ppm or less and a water concentration of 0.5ppm or less was charged, the vessel was sealed with an O-ring, and the ball mill was operated at 200 rpm for 100 hours (mechanical treatment).

Using the hydrogen absorption and desorption characteristics evaluation apparatus shown in FIG. 6, the hydrogen occluding alloy subjected to the above-described mechanical treatment and Mg before the treatment were evaluated in the same manner as in example 60₂Hydrogen storage characteristics of the Ni hydrogen storage alloy. The evaluation results of hydrogen storage characteristics at 25 ℃ are shown in Table 11 below.

Examples 62 to 92

Hydrogen-absorbing alloys having the compositions shown in the following tables 11 to 13 were subjected to mechanical treatment in the same manner as in example 60, and the hydrogen-absorbing characteristics at 25 ℃ of the hydrogen-absorbing alloys before and after the mechanical treatment were evaluated by the hydrogen absorption and desorption characteristic evaluation apparatus shown in FIG. 6, and the results are shown in the following tables 11 to 13. X in tables 11 to 13 represents the amount MH of hydrogen absorbed in the hydrogen occluding alloy_x。

TABLE 11

	Alloy (I)	X (before treatment)	X (after treatment)
				Example 60	Mg2Ni	0	3.0
Example 61	Mg2Ni (Ni mixed)	0	3.5
				Example 62	Mg2Cu	0	2.5
Example 63	Mg2Co	0	3.8
				Example 64	Mg2Fe	0	4.4
Example 65	LaNi5	0.1	6.0
				Example 66	MmNi 5	0	3.5
Example 67	CaNi 5	0	4.5
				Example 68	TiFe	0.1	1.6
Example 69	TiCo	0	1.8
				Example 70	ZrMn2	0.1	3.2
Example 71	ZrNi2	0.1	3.6

TABLE 12

	Alloy (I)	X (before treatment)	X (after treatment)
				Example 72	Mg2Ni0.7Cu0.3	0	2.9
Example 73	Mg2Ni0.9Co0.2	0	3.4
				Example 74	Mg2Ni0.8Fe0.1	0	3.5
Example 75	Mg2Ni0.7Rh0.2Ru0.2	0	3.7
				Example 76	Mg1.9Zr0.1Ni	0	3.0
Example 77	Mg1.8Cr0.1Ni	0	2.6
				Example 78	Mg2Mo0.1Ni	0	2.4
Example 79	Mg1.9V0.1Ni0.9Mn0.2	0	3.4
				Example 80	Mg2Cu0.5W0.5	0	1.6
Example 81	Mg2Cu0.7Cd0.4	0	2.0

Watch 13

	Alloy (I)	X (before treatment)	X (after treatment)
				Example 82	Mg2Y0.1Ni1.1	0	2.3
Example 83	Mg2Ir0.1Ni1.5	0	3.1
				Example 84	Mg2Pt0.1Ni1.9	0	2.8
Example 85	LaAl0.3Ni3.5Mn0.4Co0.7	0.5	6.0
				Example 86	MmAl0.3Ni4.1Mn0.3Co0.3	1.0	6.0
Example 87	CaAl0.3Ni4.3Mn0.4	0.6	5.5
				Example 88	TiFe0.6Mn0.3	0.3	2.1
Example 89	TiMn0.6Co0.4	0	2.5
				Example 90	ZrCo0.9Mn1.1	0.1	3.5
Example 91	Zr0.5Ti0.5Ni1.3V0.7	0.2	3.9
				Example 92	ZrMn0.5Ni1.5V0.3	0.1	3.4

As can be seen from tables 11 to 13, the surface activation of the hydrogen absorbing alloy and the hydrogen absorbing property are improved by the mechanical treatment.

Example 93

The hydrogen absorbing alloy powder obtained in example 61 and electrolytic copper powder were mixed in a weight ratio of 1: 1, and 1g of the mixture was pressed with a tablet forming machine (inner diameter. phi.10 mm) at a pressure of 20 tons for 3 minutes to prepare a tablet. The sheets were sandwiched by a nickel metal mesh, and the peripheral portions thereof were spot-welded and crimped, and then a nickel lead wire was spot-welded to prepare a hydrogen storage alloy electrode (negative electrode).

Comparative example 15

Except using Mg without mechanical treatment₂A hydrogen absorbing alloy electrode (negative electrode) was produced in the same manner as in example 93 except for using the Ni hydrogen absorbing alloy powder.

The negative electrodes of example 93 and comparative example 15 were immersed in 8 predetermined potassium hydroxide aqueous solutions together with sintered nickel electrodes as counter electrodes, respectively, and charge and discharge cycle tests were carried out at 25 ℃ under such conditions that charging was carried out at a current of 100mA per 1g of hydrogen absorbing alloy for 10 hours, then the charging was stopped for 10 minutes, and discharging was carried out at a current of 20mA per 1g of hydrogen absorbing alloy to-0.5V per 1g of mercury oxide electrode, and such cycles were repeated, and the results are shown in FIG. 10. In FIG. 10, A is a composition containing Mg without mechanical treatment₂The charge and discharge characteristics curve of comparative example 15 of the Ni hydrogen storage alloy negative electrode, and B is the charge and discharge characteristics curve of example 93 using the hydrogen storage alloy negative electrode containing a mechanical treatment.

As can be seen from fig. 10, comparative example 15 (characteristic curve a) was not chargeable and dischargeable at normal temperature, and the discharge capacity was hardly shown. On the other hand, the embodiment 93 (characteristic curve B) showed a discharge capacity of 750mAh/g from the first cycle, and the discharge capacity was significantly increased by the mechanical treatment. Therefore, mechanical treatment is an effective method for significantly improving the discharge characteristics of a secondary battery having a negative electrode containing a hydrogen storage alloy.

Examples 94 to 97 and comparative example 15

Mixing Mg₂Ni hydrogen storage alloy and stainless steel ball are put into a stainless steel container with a two-layer cover, argon atmosphere with oxygen concentration below 1ppm and water concentration below 0.5ppm is filled, the container is sealed by an O-shaped sealing ring, and then the ball mill is operated (mechanically treated) at the speed of 200 rpm for 2 hours, 50 hours, 200 hours and 800 hours, so as to respectively obtain 4 kinds of surface modified hydrogen storage alloy powder.

Using the obtained surface-modified hydrogen-absorbing alloysPowder and Mg without mechanical treatment₂The Ni hydrogen storage alloy powder (comparative example 15) was used to produce a hydrogen storage alloy electrode (negative electrode) in the same manner as in example 93. These negative electrodes were immersed in 8 parts of a potassium hydroxide aqueous solution together with a sintered nickel electrode as a counter electrode, respectively, and subjected to charge and discharge cycle tests at 25 ℃ under the same conditions as in example 93, to measure the maximum discharge capacity, and theresults are shown in table 14 below. The average particle diameter of the hydrogen absorbing alloy powder used is also shown in Table 14.

TABLE 14

	Treatment time (h)	Average particle diameter (μm)	Discharge capacity (mAh/g)
				Comparative example 15	0	80	0
Example 94	2	20	115
				Example 95	50	6	523
Example 96	200	2	617
				Example 97	800	1	658

As can be seen from Table 14, as the mechanical treatment time was prolonged, the average particle diameter of the hydrogen absorbing alloy powder was decreased and the discharge capacity was increased.

Examples 98 to 101 and comparative example 15

Mixing Mg₂Ni hydrogen storage alloy and stainless steel ball are put into a stainless steel container with a two-layer cover, argon atmosphere with oxygen concentration below 1ppm and water concentration below 0.5ppm is filled, the container is sealed by an O-shaped sealing ring, and then the ball mill is operated (mechanically treated) at 200 rpm for 3 hours, 40 hours, 300 hours and 650 hours, respectively to obtain 4 kinds of surface modified hydrogen storage alloy powder.

Using each of the obtained surface-modified hydrogen occluding alloy powders and Mg without mechanical treatment₂The Ni hydrogen storage alloy powder (comparative example 15) was used to produce a hydrogen storage alloy electrode (negative electrode) in the same manner as in example 93. These negative electrodes were immersed in 8 parts of a potassium hydroxide aqueous solution together with a sintered nickel electrode as a counter electrode, respectively, and subjected to charge and discharge cycle tests at 25 ℃ under the same conditions as in example 93, to measure the maximum discharge capacity, and the results are shown in table 15 below. Table 15 also shows the hydrogen occluding alloy powder Delta (2 theta) used₂) [ at least one of X-ray diffraction peaks and three-intensity peaks of CuK α as a radiation sourceHalf width of]。

Watch 15

	Treatment time (h)	Δ(2θ2)(°)	Discharge capacity (mAh/g)
				Comparative example 15	0	0.1	0
Example 98	3	0.5	142
				Example 99	40	1.2	503
Example 100	300	3.4	631
				Example 101	650	5.1	649

As can be seen from Table 15, as the mechanical treatment time was prolonged, the crystallites of the hydrogen occluding alloy powder were decreased while generating non-uniform strain in the hydrogen occluding alloy, and thus, Δ (2 θ)₂) The value increases so that the discharge capacity increases.

Example 102-106 and comparative example 15

Mixing Mg₂Ni hydrogen storage alloy and stainless steel ball are put into a stainless steel container with a two-layer cover, argon atmosphere with oxygen concentration below 1ppm and water concentration below 0.5ppm is filled, the container is sealed by an O-shaped sealing ring, and then the ball mill is operated (mechanically processed) at the speed of 200 rpm for 0.5 hour, 2.5 hours, 15 hours, 250 hours and 700 hours, so as to respectively obtain 5 kinds of surface modified hydrogen storage alloy powder.

Using each of the obtained surface-modified hydrogen occluding alloy powders and Mg without mechanical treatment₂The Ni hydrogen storage alloy powder (comparative example 15) was used to produce a hydrogen storage alloy electrode (negative electrode) in the same manner as in example 93. These negative electrodes were immersed in 8 parts of a potassium hydroxide aqueous solution together with a sintered nickel electrode as a counter electrode, respectively, and subjected to charge and discharge cycle tests at 25 ℃ under the same conditions as in example 93, to measure the maximum discharge capacity, and the results are shown in table 16 below. Thecrystallite size of the hydrogen occluding alloy powder used is also shown in Table 16.

TABLE 16

	Treatment time (h)	Size of crystallite (nm)	Discharge capacity (mAh/g)
				Comparative example 15	0	111.5	0
Example 102	0.5	56.2	13
				Example 103	2.5	37.5	124
Example 104	15	23.2	323
				Example 105	250	5.1	626
Example 106	700	2.2	651

As can be seen from Table 16, as the mechanical treatment time was prolonged, the crystallites of the hydrogen occluding alloy powder were decreased while the discharge capacity was increased.

Example 107-

Mixing Mg₂Ni hydrogen storage alloy and stainless steel balls are put into a stainless steel container with a two-layer cover, vacuum, inert gas (argon, nitrogen, helium), hydrogen, oxygen or air are filled into the stainless steel container, the container is sealed by O-shaped sealing rings under various atmospheres respectively, and then the ball mill is operated (mechanically treated) at the speed of 200 rpm for 100 hours to obtain 7 kinds of surface modified hydrogen storage alloy powder.

Using each of the obtained surface-modified hydrogen storage alloy powders, a hydrogen storage alloy electrode (negative electrode) was produced in the same manner as in example 93. These negative electrodes were immersed in an aqueous potassium hydroxide solution defined at 8 degrees centigrade together with a sintered nickel electrode as a counter electrode, respectively, and charge and discharge cycle tests were carried out at 25 degrees centigrade under the same conditions as in example 93 to measure the maximum discharge capacity, and the results are shown in table 17 below.

TABLE 17

	Treatment atmosphere	Discharge capacity (mAh/g)
			Example 107	Argon (99.999%)	605
Example 108	Vacuum	402
			Example 109	Nitrogen (99.999%)	513
Example 110	Helium (99.999%)	526
			Example 111	Hydrogen (99.99999%)	650
Example 112	Oxygen (99.999%)	0
			Example 113	Air (a)	0

As can be seen from table 17, it is preferable that the mechanical treatment is carried out under vacuum, inert gas or hydrogen atmosphere, and the discharge capacity can be significantly increased by carrying out the mechanical treatment under such atmosphere.

Example 114-

As shown in tables 18 to 20 below, negative electrodes containing the hydrogen absorbing alloys obtained by subjecting the hydrogen absorbing alloys to surface modification by mechanical treatment under various conditions in the same manner as in example 93 were prepared, and these negative electrodes were immersed in an aqueous potassium hydroxide solution defined in 8 with a sintered nickel electrode as a counter electrode, respectively, and subjected to charge and discharge cycle tests at 25 ℃ under the same conditions as in example 93 to measure the maximum discharge capacities, and the results are shown in tables 18 to 20 below.

Watch 18

	Alloy (I)	Catalyst species	Treatment time (h)	Discharge capacity (mAh/g)
					Comparative example 15	Mg2Ni	-	-	0
Example 114	Mg2Ni	Ni	100	751
					Example 115	Mg2Ni	-	1	78
Example 116	Mg2Ni	-	25	452
					Example 117	Mg2Ni	-	100	605
Example 118	Mg2Ni	Ni	500	825
					Example 119	Mg2Ni	Co	100	752
Example 120	Mg2Ni	Fe	100	703
					Example 121	Mg2Ni	WCo3	100	642
Example 122	Mg2Ni	IrO2	100	750
					Example 123	Mg2Cu	Cu	100	502
Example 124	Mg2Co	Co	100	712
					Example 125	Mg2Fe	Fe	100	745
Example 126	LaNi5	-	-	274
					Example 127	LaNi5	Pt	100	321
Example 128	LaNi5	MoCo3	100	325
					Example 129	LaNi5	CoO	100	290
Example 130	MmNi5	Rh	100	123
					Example 131	CaNi5	MoNi3	100	150
Example 132	TiFe	Pd		100						154
					Example 133	TiCo	FeO		100		111
Example 134	ZrMn2	WNi3	100	148
					Example 135	ZrNi2	Au	100	85

Watch 19

	Alloy (I)	Catalyst species	Time of treatment (h)	Discharge capacity (mAh/g)
					Example 136	Mg2Ni0.8Co0.2	Ag	100	650
Example 137	Mg2Ni0.6Co0.5	Ir	100	730
					Example 138	Mg2Ni0.7Fe0.2	V	50	360
Example 139	Mg2Al0.7Ni0.8Mn0.2	CoO	100	850
					Example 140	Mg1.9B0.1Ni	NiO	100	605
Example 141	Mg1.8C0.1Ni	Pd	500	625
					Example 142	Mg2Au0.1Ni	Cr	200	652
Example 143	Mg1.8Al0.2Ni0.8Cr0.2	Ni	100	800
					Example 144	Mg2Cu0.8Co0.2	Mn	100	503
Example 145	Mg2Cu0.7Sn0.5	Co3O4	100	524
					Example 146	Mg2Au0.1Ni1.3	Ru	100	605
Example 147	Mg2Ni1.6Ag0.1	Mo	100	553
					Example 148	Mg2Al0.1Ni1.9	RhO2	100	502

Watch 20

	Alloy (I)	Catalyst species	Time of treatment (h)	Discharge capacity (mAh/g)
					Example 149	Mg2Fe0.5Ni0.6Zn0.1	W	100	645
Example 150	LaAl0.3Ni3.7Mn0.5Co0.5	VCo3	100	285
					Example 151	LaZr0.2Al0.4Ni4.4	Ru	100	231
Example 152	LaAl0.3Ni3.7Mn0.5Co0.5	VNi3	100	265
					Example 153	MmAl1.0Ni3.5Si0.5	Nb	100	284
Example 154	MmTi0.3Ni3.6Mn0.4Co0.7	WPt3	100	205
					Example 155	MmAl0.2Ni3.8Mn0.5Cu0.5	Ta	100	250
Example 156	TiFe0.8Mn0.1	Co2O3	100	211
					Example 157	TiCo0.6Mn0.5	V	100	260
Example 158	Zr0.6Ti0.4Ni1.3V0.6	Au	100	390
					Example 159	ZrCo1.0Mn1.3	RuO2	100	350
Example 160	ZrNi1.4Mn0.6V0.3	Ta	100	380

As can be seen from tables 18 to 20, the discharge capacity was increased by the mechanical treatment, and the charge-discharge characteristics were remarkably improved.

Example 161-166 and comparative examples 16 to 18

In the composition of Mg_1.9Al_0.1Ni_1.05The hydrogen storage alloy of (1) was mixed with carbon powder and polytetrafluoroethylene in various amounts, rolled into a sheet, and pressure-bonded onto a nickel metal mesh to prepare 9 kinds of hydrogen electrodes (negative electrodes). These hydrogen electrodes have different hydrophobicity depending on the composition ratio such as the amount of polytetrafluoroethylene added and the pressure change during processing into a pressure-bonded sheet, and the ion elution rate of the hydrogen storage alloy also changes.

Each of the obtained hydrogen electrodes was immersed in an aqueous potassium hydroxide solution of 8 mm, and charged and discharged at room temperature under such a condition that the electrode was charged at a current of 100mA/g for 10 hours and then discharged at a current of 20mA/g to a voltage of-0.5V with respect to the mercury oxide electrode. The relationship between the capacity ratio and the ion elution rate in the 20 th cycle and the 3 rd cycle when charge and discharge were repeated in this manner is shown in table 21 below. The ion elution rate was determined by immersing the hydrogen electrode in an aqueous alkali metal hydroxide solution for 5 hours and determining the amount of eluted components by an icp (inductively coupled plasma) Spectrometry. The amount of aqueous alkali metal hydroxide solution is about 100ml per 1g of alloy in the hydrogen electrode.

TABLE 21

	Ion(s)	Liquid temperature of alkali metal hydroxide Composition of aqueous solution	Dissolution rate mg/kg alloy/hour	The 20 th cycle capacity- Ratio of 3 rd circulation volume%
					Example 161	Mg	8N KOH 25	0.3	70
Example 162	Mg	6N KOH 25	0.5	65
					Example 163	Mg	7N KOH 25 1N LiOH	0.4	77
Example 164	Mg	9N KOH	60	1.2						75
					Example 165	Mg＋Al	8N KOH 25	1.0	72
Example 166	Mg＋Al	8N KOH	60	3.4						68
					Comparative example 16	Mg	8N KOH 25	0.7	32
Comparative example 17	Mg	9N KOH	60	2.3						43
					Comparative example 18	Mg＋Al	8N KOH 25	4.8	30

Example 167-

Carbon powder and polytetrafluoroethylene were mixed in various amounts in hydrogen storage alloys having the compositions shown in the following table 22, and the mixture was rolled into a sheet form and pressure-bonded to a nickel metal mesh to prepare 8 kinds of hydrogen electrodes (negative electrodes).

The relationship between the capacity ratio between the 20 th cycle and the 3 rd cycle when the hydrogen electrodes obtained were immersed in 8 parts of a predetermined potassium hydroxide aqueous solution, subjected to charge and discharge under the same conditions as in example 161 at room temperature, and subjected to repeated charge and discharge, and the ion elution rate obtained by the same method as in example 161 is shown in table 22 below.

TABLE 22

	Hydrogen-storage alloy	Ion species	Composition of aqueous solution	Liquid temperature ℃	Dissolution rate mg/g/b	Cycle No. 20 Cycle No. 3 Ratio%
							Example 167	Mg2Ni1.125	Mg	8N KOH	25	0.2	65
Example 168	Mg2Co1.1In0.11	All elements	8N KOH	25	2.1	72
							Example 169	MgNi1.41Ag0.22	Mg	8N KOH	25	0.2	76
Example 170	Mg1.8Al0.3Ni0.9Pd0.3	Mg	8N KOH	25	0.2	78
							Example 171	Mg1.8Al0.3Ni0.9Pd0.3	All elements	8N KOH		60	4.2	77
Example 172	Mg1.6Al0.3NiMn0.2	Mg	7N KOH 1N LiOH	60	0.5	70
							Example 173	Mg1.6Al0.3Ni0.7Mn0.2Co0.2	All elements	9N KOH		60	3.4	80
Example 174	Mg1.8Al0.3Ni0.9Pd0.3 (use of a powder dipped in 0.01N hydrochloric acid for 30 seconds)	Mg	8N KOH	25	0.2	76

As can be seen from tables 21 and 22, the simulated cells having the hydrogen electrodes (examples 161-174) comprising hydrogen storage alloys satisfying the following conditions had higher capacities than the simulated cells having the hydrogen electrodes (comparative examples 16-18) comprising hydrogen storage alloys other than the following conditions, namely, (a) the elution rate of magnesium ions into an alkali metal hydroxide aqueous solution at room temperature is 0.5mg/kg alloy/hr or less, or the dissolution rate of magnesium ions into the alkali metal hydroxide aqueous solution at 60 ℃ is 4mg/kg alloy/hr or less, and (b) the elution rate of the alloying element into the alkali metal hydroxide aqueous solution at room temperature is 1.5mg/kg alloy/hr or less, or the dissolution rate of the alloy component elements into the alkali metal hydroxide aqueous solution at 60 ℃ is 20mg/kg alloy/hr.

Example 175-

The hydrogen electrodes (negative electrodes) used in examples 161, 167, 168, 169, 172, 173, and 174 and comparative example 18 were stacked on a paste-like nickel electrode (positive electrode) with a nylon nonwoven fabric, and then rolled into a cylindrical shape to prepare 8 kinds of electrode groups. These electrode groups were inserted into an AA-type battery container, and 8 kinds of potassium hydroxide were injected, and then the container was sealed with a sealing plate having a safety valve, thereby assembling 5 kinds of AA-type nickel-metal hydride secondary batteries shown in fig. 3.

Each of the batteries thus obtained was repeatedly charged and discharged under the conditions that the battery was charged for 10 hours under a current of 50mA/g alloy and the battery was discharged under the conditions that the battery was charged to a battery voltage of 0.9V under a current of 20mA/g alloy, and the discharge capacities at the 3 rd cycle and the 20 th cycle were compared. The battery was disassembled on day 30 after the completion of the battery, and the amount of Mg ions in the electrolyte was analyzed by IPC Spectrometry, and the results are shown in Table 23 below.

TABLE 23

	Using hydrogen electrodes Example number of	Ion species	Concentration of mg/l	20 th/3 rd cycle Ratio%
					Example 175	Example 161	Mg	1.2	68
Example 176	Example 167	Mg	1.1	63
					Example 177	Example 168	Mg	1.7	57
Example 178	Example 169	Mg	1.2	62
					Example 179	Example 172	Mg	1.3	59
Example 180	Example 173	Mg	1.2	66
					Example 181	Example 174	Mg	1.4	78
Comparative example 19	Comparative example 18	Mg	2.8	34

As is apparent from Table 23, the storage battery of example 175-181 in which the magnesium ion concentration in the alkaline electrolyte was 2.2 mg/liter or less after the injection of the alkaline electrolyte and the closing of the container for 30 days or more had a higher capacity than the storage battery of comparative example 19 except the above conditions.

As described above, the hydrogen storage alloy of the present invention has excellent low-temperature hydrogen storage characteristics and chemical stability in addition to its original characteristics of light weight, large capacity, low cost, etc., and thus further expands various application fields (storage, transportation, storage, transportation of heat, conversion of thermal-mechanical energy, separation and purification of hydrogen, separation of hydrogen isotopes, batteries using hydrogen as an active substance, catalysts in synthetic chemistry, temperature sensors, etc.) in which other alloy systems have been used so far, expanding new application fields of hydrogen storage alloys, and achieving very significant effects.

The hydrogen storage alloy and the surface modification method thereof are easy to activate and can improve the hydrogen storage property. The use of such a hydrogen-absorbing alloy as a negative electrode and an alkaline storage battery equipped with the negative electrode can realize a large capacity.

The negative electrode for a battery and the alkaline storage battery of the present invention can be applied to the charge and discharge reaction of a magnesium-containing hydrogen storage alloy which has been difficult in the past, and therefore, can stably perform the charge and discharge reaction for a long period of time and has a high capacity and a very significant effect.

Claims (58)

1. Hydrogen storage alloy comprising alloy represented by the following general formula (1)

Mg₂M1_y(1) Wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is not more than 1<y.ltoreq.1.5.

2. A hydrogen occluding alloy as recited in claim 1, wherein M1 in the general formula (1) is an element other than Mg, an element capable of reacting exothermically with hydrogen, Al and B, and an element which does not react exothermically with hydrogen and has a larger electronegativity than Mg.

3. A hydrogen occluding alloy as recited In claim 2, wherein M1 is at least one element selected from the group consisting of Ag, Cd, Mn, In, Fe, Ni and Co.

4. A hydrogen occluding alloy as recited in claim 1, wherein y in the general formula (1) is in the range of 1.01. ltoreq. y.ltoreq.1.5.

5. A hydrogen occluding alloy as recited in claim 1, wherein y in the general formula (1) is in the range of 1.02. ltoreq. y.ltoreq.1.5.

6. A hydrogen occluding alloy as recited in claim 1, wherein y in the general formula (1) is in the range of 1.05. ltoreq. y.ltoreq.1.5.

7. Hydrogen storage alloy comprising alloy represented by the following general formula (2)

Mg_2-xM_2xM1_y(2) Wherein M2 is an element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, at least one element other than Mg, M1 is an element other than Mg and M2, at least one element selected from the group consisting of elements not reacting exothermically with hydrogen, 0<x.ltoreq.1.0,1＜y≤2.5。

8. a hydrogen occluding alloy as recited in claim 7, wherein M1 in the general formula (2) is other than Mg andelements other than M2 are those which do not react exothermically with hydrogen, have a larger electronegativity than Mg, and are mixed in an alloy of pure magnesium at an atomic ratio of 10% or less_1-wM1_wThe phase (W0<W0.1) has a cell volume smaller than that of pure magnesium.

9. A hydrogen occluding alloy as recited In claim 8, wherein M1 is at least one element selected from the group consisting of Ag, Cd, Mn, In, Fe, Ni and Co.

10. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (2) is an element selected from the group consisting of an element capable of reacting exothermically with hydrogen, Al and B, an element other than Mg, and is an element having a larger electronegativity than Mg.

11. A hydrogen occluding alloy as recited in claim 10, wherein M2 is at least one element selected from the group consisting of B, Be, Y, Pd, Ti, Zr, Hf, Th, V, Nb, Ta, Pa and Al.

12. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (2) is an element selected from the group consisting of elements reacting exothermically with hydrogen, Al and B, elements other than Mg, and Mg in an alloy in which Mg is mixed in pure magnesium at an atomic ratio of 10% or less_1-wM1_wThe phase (W0<W0.1) has a cell volume smaller than that of pure magnesium.

13. A hydrogen occluding alloy as recited in claim 12, wherein M2 is at least one element selected from the group consisting of Li and A1.

14. A hydrogen occluding alloy as recited in claim 7, wherein M2 in the general formula (2) is an element selected from the group consisting of elements reacting exothermically with hydrogen, Al and B, elements other than Mg, and Mg in an alloy having an electronegativity larger than that of Mg and mixed in pure magnesium at an atomic ratio of 10% or less_1-wM1_wThe phase (W0<W0.1) has a cell volume smaller than that of pure magnesium.

15. A hydrogen occluding alloy as recited in claim 7, wherein x in the general formula (2) is 0.01. ltoreq. x.ltoreq.1.0.

16. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (2) is 1.01. ltoreq. y.ltoreq.2.5.

17. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (2) is 1.02. ltoreq. y.ltoreq.2.5.

18. A hydrogen occluding alloy as recited in claim 7, wherein y in the general formula (2) is 1.05. ltoreq. y.ltoreq.2.5.

19. Hydrogen storage alloy comprising alloy represented by the following general formula (3)

M_2-xM2_xM1_y(3) Wherein M is at least one element selected from Be, Ca, Sr, Ba, Y, Ra, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu, Ti, Zr, Hf, Pd, Pt, M2 is at least one element selected from elements capable of reacting exothermically with hydrogen, Al and B, and elements other than M, M1 is at least one element selected from elements not capable of reacting exothermically with hydrogen, except for M and M2, x and Y are each 0.01<x.ltoreq.1.0, 0.5<y.ltoreq.1.5.

20. A hydrogen occluding alloy as recited in claim 19, wherein M2 is any one of Al, Mn, Cr and V.

21. A hydrogen occluding alloy as recited in claim 19, wherein M is Zr, M1 is Fe, and M2 is Cr.

22. A hydrogen occluding alloy as recited in claim 19, wherein M is Zr, M1 is Fe, and M2 is V.

23. A hydrogen occluding alloy as recited in claim 19, wherein x in the general formula (3) is 0.05. ltoreq. x.ltoreq.0.5.

24. A hydrogen occluding alloy as recited in claim 19, wherein y in the general formula (3) is 1<y.ltoreq.1.5.

25. A surface modification method of hydrogen storage alloy is characterized in that R-X compound is adopted to treat the hydrogen storage alloy, wherein in the formula, R is alkyl, alkenyl, alkynyl, aryl or a substitute thereof, and X is halogen element.

26. The surface modification method of claim 25, wherein the hydrogen storage alloy comprises an alloy represented by the following general formula (4)

Mg_2-xM2_xM1_y(4) Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, and x and y are 0. ltoreq. x.ltoreq.1.0, and 0.5. ltoreq. y.ltoreq.2.5, respectively.

27. The surface modification method of claim 25, wherein the hydrogen storage alloy is a₂And B alloy, wherein A represents an element capable of exothermically reacting with hydrogen, and B represents an element incapable of exothermically reacting with hydrogen.

28. The surface modification method of claim 25, wherein the hydrogen storage alloy is AB₅An alloy wherein A represents an element capable of reacting exothermically with hydrogen and B represents an element incapable of reacting exothermically with hydrogen.

29. The surface modification method of claim 25, wherein the R-X compound is reacted with the hydrogen storage alloy in the presence of an organic solvent.

30. The surface modification method of claim 29, wherein the organic solvent is tetrahydrofuran.

31. The surface modification method of claim 29, wherein the organic solvent is diethyl ether.

32. The surface modification method of claim 29, wherein a catalyst is further added to the solution of the R-X compound dissolved with the organic solvent.

33. The surface modification method of claim 32 wherein the catalyst is a condensed polycyclic hydrocarbon.

34. A hydrogen occluding alloy, characterized in that at least one of peaks obtained by X-ray diffraction using CuK α as a radiation source has a half width of 0.3 DEG to 10 DEG (2 theta).

35. A hydrogen occluding alloy characterized in that, in an X-ray diffraction peak using CuK α as a radiation source, the apparent half width delta (2 theta) of the peak is around 20 DEG₁) Is delta (2 theta) of not less than 0.3 DEG₁)10 DEG or less, or an apparent half width Delta (2 theta) of a peak in the vicinity of 40 DEG₂)，0.3°≤Δ(2θ₂)≤10°。

36. A hydrogen occluding alloy as recited in claim 35, wherein said alloy is A₂B alloy, wherein A represents an element capable of exothermically reacting with hydrogen, and B represents an element incapable of exothermically reacting with hydrogen.

37. A hydrogen occluding alloy as recited in claim 35, wherein said alloy comprises an alloy represented by the following general formula (4)

Mg_2-xM2_xM1_y(4) Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, and x and y are 0. ltoreq. x.ltoreq.1.0, and 0.5. ltoreq. y.ltoreq.2.5, respectively.

38. A surface modification method of a hydrogen storage alloy is characterized in that the hydrogen storage alloy is subjected to mechanical treatment in vacuum, inert gas or hydrogen atmosphere.

39. The surface modification method of claim 38, wherein the hydrogen storage alloy is a₂And B alloy, wherein A represents an element capable of exothermically reacting with hydrogen, and B represents an element incapable of exothermically reacting with hydrogen.

40. The surface modification method of claim 38, wherein the hydrogen storage alloy comprises an alloy represented by the following general formula (4)

Mg_2-xM2_xM1_y(4) Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, and x and y are 0. ltoreq. x.ltoreq.1.0, and 0.5. ltoreq. y.ltoreq.2.5, respectively.

41. A method for modifying the surface of a hydrogen-absorbing alloy, characterized by comprising a step of mixing at least one element selected from the group consisting of group IVA, group VA, group VIA, group VII, group VIIIA, group IB, group IIB, group IIIB and group IVB, an alloy of these elements or an oxide of these elements in a hydrogen-absorbing alloy at a molar ratio of at most equal to one another to prepare a mixture, and a step of subjecting the mixture to mechanical treatment in a vacuum, an inert gas or a hydrogen atmosphere.

42. The surface modification method of claim 41, wherein the hydrogen storage alloy is A₂And B alloy, wherein A represents an element capable of exothermically reacting with hydrogen, and B represents an element incapable of exothermically reacting with hydrogen.

43. The surface modification method according to claim 41, wherein the hydrogen storage alloy comprises an alloy represented by the following general formula (4)

Mg_2-xM2_xM1_y(4) Wherein M2 is at least one element selected from the group consisting of elements reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is an element other than Mg and M2, and is selected from the group consisting of elements not reacting exothermically with hydrogenX and y are 0-1.0, and y is more than 0.5-2.5.

44. The surface modification method according to claim 41, wherein the element is at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ru, Co, Rh, Ir, Pd, Ni, Pt, Cu, Ag, and Au.

45. The surface modification method of claim 41 wherein the alloy of the element is MoCo₃、WCo₃、MoNi₃Or WNi₃。

46. The surface modification method of claim 41, wherein the oxide of the element is FeO, RuO₂、CoO、Co₂O₃、Co₃O₄、RhO₂、IrO₂、NiO。

47. Negative electrode for battery comprising hydrogen storage alloy represented by the following general formula (1)

Mg₂M1_y(1) Wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is not more than 1<y.ltoreq.1.5.

48. The anode of claim 47, wherein M1 is Ni.

49. Alkaline rechargeable battery having negative electrode comprising hydrogen storage alloy represented by the following general formula (1)

Mg₂M1_y(1) Wherein M1 is at least one element selected from the group consisting of Mg, an element capable of reacting exothermically with hydrogen, Al and B, and is not more than 1<y.ltoreq.1.5.

50. Negative electrode for battery comprising hydrogen storage alloy represented by the following general formula (2)

Mg_2-xM2_xM1_y(2) Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, 0<x.ltoreq.1.0, 1<y.ltoreq.2.5.

51. The negative electrode as claimed in claim 50, wherein M1 in the general formula (2) is Ni and Pt.

52. The negative electrode as claimed in claim 50, wherein M2 in the general formula (2) is Pd.

53. The negative electrode as claimed in claim 50, wherein the value of y in the general formula (2) is 1.01. ltoreq. y.ltoreq.1.5.

54. Alkaline rechargeable battery having negative electrode comprising hydrogen storage alloy represented by the following general formula (2)

Mg_2-xM2_xMl_y(2) Wherein M2 is at least one element selected from the group consisting of elements capable of reacting exothermically with hydrogen, Al and B, and elements other than Mg, M1 is at least one element selected from the group consisting of elements other than Mg and M2 and elements not capable of reacting exothermically with hydrogen, 0<x.ltoreq.1.0, 1<y.ltoreq.2.5.

55. A negative electrode for a battery comprising a hydrogen storage alloy, characterized in that, among peaks obtained by X-ray diffraction using CuK α as a radiation source, at least one peak among peaks of three strong lines has a half width [ Delta]([ 2]theta]) of 0.3 DEG to [ Delta]([ 2]theta]) to 10 deg.

56. An alkaline rechargeable battery having a negative electrode comprising a hydrogen storage alloy, characterized in that, among peaks obtained by X-ray diffraction using CuK α as a radiation source, at least one peak among peaks of three strong lines has a half width [ Delta]([ 2]theta]) of 0.3 DEG to [ Delta]([ 2]theta]) to 10 deg.

57. A negative electrode for a battery comprising a hydrogen storage alloy containing magnesium, characterized in that, when immersed in an aqueous alkali metal hydroxide solution of 6 to 8, the elution rate of (a) magnesium ions into the aqueous alkali metal hydroxide solution at normal temperature is 0.5mg/kg alloy/hr or less, or the elution rate of magnesium ions into the aqueous alkali metal hydroxide solution at 60 ℃ is 4mg/kg alloy/hr or less, and the elution rate of (b) alloying element into the aqueous alkali metal hydroxide solution at normal temperature is 1.5mg/kg alloy/hr or less, or the elution rate of alloying element into the aqueous alkali metal hydroxide solution at 60 ℃ is 20mg/kg alloy/hr or less.

58. An alkaline rechargeable battery comprising a negative electrode, a positive electrode and an alkaline electrolyte, the negative electrode, the positive electrode and the alkaline electrolyte being accommodated in a container, the negative electrode comprising a hydrogen storage alloy containing magnesium, and the negative electrode and the positive electrode sandwiching a separator therebetween, characterized in that the alkaline electrolyte is injected into the container and the container is sealed, and the concentration of magnesium ions in the alkaline electrolyte is 2.2mg/l or less after 30 days.

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