JP3369148B2 - Alkaline storage battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an alkaline storage battery, and more specifically to an alkaline storage battery using a hydrogen storage alloy having a segregation phase as a negative electrode active material.

[0002]

2. Description of the Related Art With the miniaturization of portable electronic devices, safer and higher capacity secondary batteries are required, and alkaline storage batteries (nickel-hydrogen storage batteries) using a hydrogen storage alloy as a negative electrode active material are further required. Investigations for higher capacity are continuing. As the hydrogen storage alloy which is the negative electrode active material of this battery, Mm (Misch metal), Ni (nickel), Co (cobalt), Mn (manganese) and Al
A misch metal alloy composed of (aluminum) or the like, and a Laves alloy composed of Zr (zirconium), Ni, V (vanadium), Mn, or the like are well known, but generally a misch metal alloy. Alloys are widely used.

The composition of this misch metal alloy is disclosed in Japanese Examined Patent Publication No. 5-15774, Japanese Examined Patent Publication No. 5-86029, Japanese Unexamined Patent Publication No. 1-162741 and the like. Metal alloys are
In order to prevent pulverization and improve the corrosion resistance to the electrolytic solution, the alloy is characterized by having a substantially stoichiometric composition containing a relatively large amount of Co.

It is also possible to use a hydrogen storage alloy having a non-stoichiometric composition in which the content of the rare earth element is larger than that in the stoichiometric composition, as disclosed in JP-A-2-277737 and JP-A-2-22.
It is proposed in Japanese Patent No. 0356.

[0005]

However, alloys having a large Co content in the above stoichiometric composition have a relatively small discharge capacity, which is an obstacle to increasing the capacity of the battery. Further, since Co is an expensive metal, the appearance of a hydrogen storage alloy having a low Co content is demanded in terms of cost.

On the other hand, an alloy having a non-stoichiometric composition has the advantage that it is possible to increase the capacity by adding a rare earth element in excess of the stoichiometric composition. Since a segregated phase containing a large amount of about several tens of μm is nonuniformly precipitated in the alloy, there is a problem that the corrosion resistance is inferior to that of the alloy having the above stoichiometric composition. Therefore, in JP-A-2-220356, the alloy is made into a single phase by using the rapid solidification method. However, the activation of the alloy is delayed due to the single phase formation, and the hysteresis in the absorption and desorption of hydrogen. Is large, and there is a problem that the discharge characteristics are deteriorated especially at low temperatures.

As another example of the non-stoichiometric composition, Japanese Patent Laid-Open No. 7-286225 discloses a hydrogen storage alloy composed of a plurality of phases in which a Co content is suppressed and a second phase not involved in hydrogen storage is deposited. However, when the proportion of the second phase is increased, the hydrogen storage amount is significantly reduced, and therefore simply increasing the capacity of the second phase cannot achieve high capacity. Further, even in such a hydrogen storage alloy, the second phase in the alloy is as large as several tens of μm, and the second phase precipitates unevenly in the alloy. A powder containing a large particle size or a powder containing a small particle size that does not contain this phase, on the contrary, is formed, and the particle size distribution of the alloy powder is widened and the uniformity is impaired, resulting in poor corrosion resistance compared to an alloy containing a large amount of Co. In particular, there is also a problem that the battery characteristics deteriorate after being kept at a high temperature of 70 ° C. or higher for a long time.

Further, in order to keep the internal pressure of the battery low and to improve the cycle life, an alloy having a relatively low equilibrium pressure in hydrogen storage, that is, an equilibrium pressure at 45 ° C. of 0.1 to 0.1 is used.
Although it is general to use an alloy of about 0.6 atm, according to the study by the present inventors, a hydrogen storage alloy having a non-stoichiometric composition with a reduced Co content as described above has a temperature of −15 ° C. It was found that the discharge at a high rate could not be sufficiently performed at the following low temperatures.

As a method of improving the high rate discharge characteristics at low temperature of an alkaline storage battery using a hydrogen storage alloy, a negative electrode has been conventionally treated with an alkali or acid solution at the time of preparation of the negative electrode, and then the battery is treated in an inert atmosphere. Is proposed (for example, Japanese Patent Laid-Open No. 8-279356), but in these methods as well, an alkaline storage battery using a non-stoichiometric hydrogen storage alloy having a reduced Co content as a negative electrode active material is also used. However, the high rate discharge characteristics at low temperatures could not be sufficiently improved.

Further, it has been proposed to incorporate a zinc compound into the positive electrode for the purpose of preventing cycle deterioration of the positive electrode. However, in a battery using such a positive electrode, the deterioration of discharge characteristics at low temperature is more remarkable. There was a problem of becoming. Therefore, the conventional alkaline storage battery using the hydrogen storage alloy as the negative electrode active material is significantly inferior in discharge characteristics at low temperature as compared with the alkaline storage battery (nickel-cadmium storage battery) using cadmium (Cd) as the negative electrode active material.

In addition, since it is premised that mobile phones and the like, which have been rapidly popularized in the last few years, can be used under a wide range of temperatures, they can reliably operate even at low temperatures after being held at high temperatures for a long time as described above. There is a demand for a battery that can be used, and development of a battery that uses a hydrogen storage alloy that has a low equilibrium pressure and that can discharge at a high rate even at low temperatures as a negative electrode active material has been earnestly desired.

In view of the above circumstances, it is a first object of the present invention to provide an alkaline storage battery having a high capacity and capable of performing a high rate discharge at a low temperature, using a hydrogen storage alloy as a negative electrode active material.
A second object of the present invention is to provide an alkaline storage battery having excellent high temperature storage characteristics, that is, an alkaline storage battery capable of high rate discharge at a low temperature even after being held at a high temperature for a long time.

[0013]

Means for Solving the Problems In order to solve the above problems, the present inventors have conducted various studies on hydrogen storage alloys used as negative electrode active materials for alkaline storage batteries, and as a result, Mm
(Mm represents a mixture of two or more kinds of rare earth elements containing 30% by weight or more of La), and at least Ni, Co, M
A hydrogen storage alloy containing n and Al as constituent elements,
The hydrogen storage alloy has a segregation phase mainly composed of Ni,
And the number of segregated phases exposed in an arbitrary 15 μm square area of the alloy cross section (however, the number of segregated phases in which the diameter of the circle circumscribing the segregated phase with the minimum diameter is 0.05 μm or more) is 1 to 40 Using an alloy as a negative electrode active material and M in the positive electrode
When the n content is 0.6 to 6 mg / Ah with respect to the capacity of the positive electrode, it is possible to obtain an alkaline storage battery having high capacity, capable of high rate discharge at low temperature, and excellent in high temperature storage characteristics. Found. In the present invention, the diameter of the circle circumscribing the segregation phase of the hydrogen storage alloy with the minimum diameter is 0.05 to 1.
A preferable mode is that it is 0 μm and that the positive electrode contains zinc ions or a zinc compound.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage alloy used in the present invention is produced, for example, as follows. First, Mm
(Mm represents a mixture of 30 wt% or more of La and other rare earth elements such as Ce and Nd) and each metal element of Ni, Co, Mn, and Al in a high-frequency melting furnace or the like to melt the alloy. After that, a phase having a CaCu ₅ type crystal structure (hereinafter, referred to as “main phase”) is formed by a method of rapidly solidifying this by using a rotating roll or the like at a cooling rate of about 300 to 1000 ° C./sec. A hydrogen storage alloy having a segregated phase mainly containing Ni and almost no rare earth element is obtained.

In the present invention, Mm (Misch metal) is required to contain La in an amount of 30% by weight or more. However, when La is less than 30% by weight, the equilibrium pressure becomes high and the hydrogen storage capacity is high. This is because the hydrogen storage capacity of the alloy decreases and the capacity decreases. As the content of La in Mm increases,
Although the capacity and the high rate discharge characteristics at low temperature are improved, if the amount of La is too much, the corrosion resistance of the hydrogen storage alloy may be deteriorated and the cycle life of the battery may be shortened.
The content of a is preferably 70% by weight or less. Further, in the production of the hydrogen-absorbing alloy, the composition ratio of the metal elements other than Mm (misch metal), to represent a hydrogen storage alloy by the general formula _{MmNi X Co Y Mn S Al T} , in atomic ratio, Mm (misch 5.03 to 5.4 (ie 5.03 ≦ X + Y + S +) for 1)
T ≦ 5.4) and the composition ratio of Ni, Co, Mn and Al is 3.8 to 4.3 (ie 3.8 ≦).
X ≦ 4.3), Co is 0.2 to 0.7 (that is, 0.
2 ≦ Y ≦ 0.7), Mn is 0.1 to 0.5 (that is,
It is preferable that 0.1 ≦ S ≦ 0.5) and T is 0.1 to 0.4 (that is, 0.1 ≦ T ≦ 0.4).

The ratio of other metal elements to Mm (Misch metal) is related to the precipitation of the segregated phase, and when this value is smaller than 5.03 (that is, 5.03> X +).
In the case of Y + S + T), the alloy (in the present specification, the portion related to the present invention, which is simply referred to as “alloy”, means “hydrogen storage alloy”), is a segregation mainly composed of Ni because it approaches a single phase. Phase formation becomes difficult. On the other hand, when the ratio of the other metal elements to Mm (Misch metal) is larger than 5.4 (that is, X + Y + S + T>
In the case of 5.4), the number of segregated phases becomes too large to obtain a high capacity alloy, and when the battery is constructed, the total amount of metal elements eluted from the segregated phase into the electrolytic solution is large. This is one of the causes of deterioration of discharge characteristics at low temperature. That is, in order to satisfy the condition that the number of segregated phases exposed in an arbitrary 15 μm square area of the alloy cross section is 1 to 40,
The ratio of metal elements other than Mm (Misch metal) to Mm (Misch metal) 1 is preferably 5.03 to 5.4. Further, the respective proportions of Ni, Co, Mn, and Al also change the melting point of the alloy, the solid solution limit of the main phase, and the like, and affect the precipitation morphology of the segregated phase. That is, Ni, Co, M
n and Al to Mm (Misch metal) 1 are 3.8 to 4.3 (that is, 3.8 ≦ X ≦ 4.
3), 0.2 to 0.7 (that is, 0.2 ≦ Y ≦ 0.
7), 0.1-0.5 (that is, 0.1 ≦ S ≦ 0.
5), 0.1-0.4 (that is, 0.1 ≦ T ≦ 0.
When it is 4), it is easy to obtain an alloy satisfying the condition of the segregation phase in the present invention. The hydrogen storage alloy of the present invention may have a composition in which a small amount (usually 10 atomic% or less) of Ni, Co, Mn, Al, etc. is replaced with another metal such as Cu, Cr.

The cooling rate of the molten alloy is preferably in the range of 300 to 1000 ° C./sec as described above. If the cooling rate of the molten metal is slower than the above range, the segregation phase becomes too large and the distribution of the segregation phase becomes non-uniform, which may impair the homogeneity of the alloy and cause a problem in corrosion resistance. In addition, the presence of the coarse segregation phase causes the crushed alloy to have a broad particle size distribution, and the proportion of powder having a coarse particle size increases, which may reduce the yield. On the other hand, if the cooling rate is faster than the above range, the alloy is made into a single phase, and there is a possibility that problems such as slow activation and deterioration of discharge characteristics at low temperature may occur as described later.

The hydrogen storage alloy obtained as described above can be subjected to a heat treatment to reduce the strain in the crystal, thereby improving the storage and release characteristics of hydrogen. be able to. The heat treatment temperature is preferably in the range of approximately 800 to 1000 ° C. If the heat treatment temperature is lower than the above range, the effect of reducing strain is reduced, and if it is higher than the above range, the segregation phase may disappear or the segregation phase may become coarse.

Here, a preferable precipitation form of the segregation phase in the present invention will be described. When the alloy cross section was polished and examined by a scanning electron microscope (SEM), it was observed that the cut surface of the segregation phase 21 was scattered in the alloy cross section in the form of islands or strings as shown in FIG. To be done. This individual segregation phase is preferably distributed uniformly in the alloy cross section,
When the area of 15 μm square is arbitrarily set, it is necessary to have 1 to 40 segregated phases in any area. However, the segregated phase counted from 1 to 40 is intended to have a diameter of a circle circumscribing the segregated phase with a minimum diameter of 0.05 μm or more. As described above, the present invention requires that 1 to 40 segregated phases are present in an arbitrary 15 μm square area of the alloy cross section when the segregated phases are not in the area at all. The reason is that the activation of the hydrogen storage alloy becomes slow and the discharge at low temperature becomes difficult, and when there are more than 40 segregated phases in the above region, the corrosion resistance of the hydrogen storage alloy decreases, and The reason is that the proportion of the main phase is reduced and the capacity is reduced.

Further, in the hydrogen storage alloy of the present invention, when a circle 22 circumscribing each segregated phase with the minimum diameter is drawn as shown in FIG. 1, the diameter is 0.05.
10 to 10 μm is preferable, and 0.2 to 7 μm is particularly preferable.
Is more preferable. According to the study by the present inventors, it has been found that the segregated phase having the diameter smaller than 0.05 μm or larger than 10 μm hardly contributes to the improvement of the characteristics at low temperature.

Further, it is preferable that the segregation phase has a composition mainly composed of Ni in order to improve discharge characteristics at a low temperature. That is, N of the segregation phase is measured by an energy dispersive X-ray spectrometer (EDS) of a transmission electron microscope (TEM).
The i content is preferably 50% by weight or more, and particularly preferably 55% by weight or more, and in other constituent elements, Mn is 28% by weight.
It is particularly preferable that the content is 20% by weight or less.

The reason why an alkaline storage battery having a large capacity and excellent discharge characteristics at low temperatures can be obtained by using the hydrogen storage alloy having a segregated phase according to the present invention is not always clear at present. However, it is considered as follows. That is, firstly, in the hydrogen storage alloy of the present invention, since the segregation phase is uniformly distributed in any small area of 15 μm square, the hydrogen storage alloy is uniformly pulverized, and further, the hydrogen storage alloy is It is possible to obtain a hydrogen storage alloy powder having a uniform particle size when pulverized. Secondly, since a part of the metal elements constituting the segregation phase exposed on the surface of the hydrogen storage alloy is easily eluted into the electrolytic solution, the activation of the hydrogen storage alloy is facilitated. Thirdly, Ni, which is a constituent element of the segregation phase, remains on the surface of the hydrogen storage alloy and functions as a catalyst, and a large number of interfaces between the segregation phase and the main phase are formed inside the hydrogen storage alloy. It is believed that this improves the discharge characteristics at low temperatures. Therefore, when the number and size of the segregated phases exposed on the surface of the hydrogen storage alloy are smaller than the above range, the activation is delayed because the elution of the metal element forming the segregated phase in the electrolytic solution does not occur sufficiently. On the other hand, if it is larger than the above range, the formation ratio of the interface with the main phase becomes small, and in any case, the discharge characteristics at low temperature cannot be improved.

By using the above hydrogen storage alloy as the negative electrode active material, it is possible to obtain an alkaline storage battery having high capacity and excellent high rate discharge characteristics at low temperature. However, it was also clarified that, depending on the alloy composition, the above hydrogen storage alloy also has a discharge characteristic after being held at high temperature for a long time, particularly when discharged at low temperature, the discharge capacity is lower than that before holding. .

The inventors of the present invention also examined the above problem and found that the amount of Mn in the positive electrode was 0.6 with respect to the capacity of the positive electrode.
It was found that the problem can be solved by adjusting the amount to 6 mg / Ah. That is, in the alkaline storage battery like the present invention,
In general, an activation treatment and a chemical conversion treatment are performed after the battery is assembled, and the former activation treatment is stored under heating at about 50 to 80 ° C. Therefore, by such heating, hydrogen having a segregation phase of the present invention is obtained. It is considered that in the storage alloy, the metal element eluted from the segregation phase or the main phase into the electrolyte moves to the positive electrode, and the type and amount of the metal element affect the characteristics of the battery. Further, the above phenomenon can similarly occur when the battery is held (stored) at a high temperature during use after the chemical conversion treatment. Of the metal elements eluted during the high temperature storage, Mn, in particular, tends to precipitate as an oxide on the surface of the active material when the battery is charged in the positive electrode, and depending on the amount of the precipitation, it interferes with the charge / discharge reaction, and at low temperature. It is considered that this causes the deterioration of the discharge characteristics of. Particularly when the battery is stored at a high temperature, the above-described migration of Mn to the positive electrode becomes remarkable, and the characteristics are likely to be deteriorated. Therefore, the present inventors set the amount of Mn contained in the positive electrode after charging / discharging at least several times to 0.6 to 6 mg / Ah, preferably 0.6 to 5 mg / Ah with respect to the capacity of the positive electrode. It was found that the problem that the capacity decreases at low temperature discharge after high temperature storage can be solved. The Mn content referred to in the present invention is a value measured by atomic absorption spectrometry, and the capacity of the above-mentioned positive electrode means that the battery has a capacity of 0.25 C at 20 ° C. (170 m in the example).
It is a discharge capacity value (actual measurement value) when the battery is charged in A) for 6 hours, rested for 1 hour, and then discharged up to 1.0 V at 0.2 C (140 mA in the example).

In order to keep the amount of Mn in the positive electrode within the above range, there is also a method of appropriately changing the composition of the hydrogen storage alloy and the manufacturing conditions to lower the amount of Mn in the segregation phase. M in the positive electrode by containing a zinc compound
The amount of n can be reduced. Therefore, the segregation phase M
It is preferable to use a method of incorporating zinc ions or a zinc compound in the positive electrode together with an alloy having a reduced n amount.

The reason why the presence of the above zinc ion or zinc compound in the positive electrode can improve the characteristics in low temperature discharge after high temperature storage is not always clear at present, but it is considered as follows. That is, when a zinc compound is added to the inside of the battery, a part or all of it becomes zinc ions, and these ions move in the battery in the same manner as Mn by a charge / discharge reaction, and Mn dissolved in the electrolytic solution from the hydrogen storage alloy. It suppresses the migration of ions to the positive electrode, and
The amount of n is 0.6 to 6 mg (that is, 0.
6 to 6 mg / Ah), and also prevents Mn oxides from being formed on the surface of the positive electrode or the positive electrode active material, and they work synergistically to improve low temperature discharge characteristics after high temperature storage. It is considered possible.

In the present invention, examples of the zinc compound include zinc oxide, zinc hydroxide, zinc chloride, zinc complex, and the like. Any method can be adopted as long as it can be dissolved as zinc ions in the liquid. Further, as described above, zinc ions can move in the battery due to the charge / discharge reaction, and therefore, they may be contained in at least one of the positive electrode, the negative electrode, the electrolytic solution, and the separator. That is, when a zinc compound is contained in at least one of them, the zinc compound contained therein becomes zinc ions, and the zinc ions are moved by charge / discharge reaction, and are present as zinc ions or zinc compounds in the positive electrode. As
It is considered that it suppresses the movement of Mn and also suppresses the precipitation of Mn on the surface of the positive electrode. However, in consideration of efficiency, it is preferable that the zinc compound is contained in the positive electrode or the electrolytic solution, and at least in the electrolytic solution.

When the zinc compound is contained in the positive electrode, the content of the zinc compound is preferably 0.5 to 10 parts by weight, more preferably 1 to 5 parts by weight, based on 100 parts by weight of nickel hydroxide in terms of zinc oxide. preferable. When the negative electrode contains a zinc compound, the content of the zinc compound is 0.01 in terms of zinc oxide based on 100 parts by weight of the hydrogen storage alloy.
Is preferably 2 to 2 parts by weight, more preferably 0.05 to 0.7 parts by weight. When the electrolytic solution contains a zinc compound, the concentration of the zinc compound in the electrolytic solution is preferably 30 to 65 g / l in terms of zinc oxide, and more preferably 40 to 55 g / l. When containing a zinc compound in the separator,
The content of the zinc compound is 0.00 in terms of weight per 1 m ² of separator (that is, g / m ² ) in terms of zinc oxide.
15-0.3 g / m ² is preferable, 0.03-0.15
g / m ² is more preferable. By setting the content of the zinc compound in the above range, it is possible to sufficiently suppress the movement of Mn to the positive electrode, and it is possible to reduce the influence of the precipitation of Mn oxide on the positive electrode surface. The electrochemical reaction of nickel hydroxide can be well maintained, and thereby the low temperature discharge characteristics after high temperature storage can be improved.

In the present invention, for the negative electrode, for example, the hydrogen storage alloy obtained as described above is crushed, and if necessary,
It is prepared by adding a binder, a conductive auxiliary agent, etc. as appropriate, forming a paste in the presence of water or a solvent, coating and filling the paste on a support, drying and then compression-molding. However, the method for producing the negative electrode is not limited to the above-mentioned case. The positive electrode is manufactured by a sintering method or a paste method by using nickel hydroxide as an active material, and if necessary, a binder, a conductive auxiliary agent, etc. are appropriately added. Then, the positive electrode and the negative electrode are wound via a separator into an electrode body or the like having a winding structure, and the electrode body or the like having the winding structure is inserted into a battery can, and after injecting an electrolytic solution, the battery can An alkaline storage battery can be obtained by sealing the opening.

Examples of the binder include polytetrafluoroethylene, sodium polyacrylate, polyvinyl alcohol, and a copolymer of styrene and an acrylic compound. Among them, a copolymer of styrene and a monomer mixture containing 2-ethylhexyl acrylate as a main component has a high affinity with the hydrogen storage alloy of the present invention, and good dispersibility can be obtained even in a small amount. Particularly preferably used. The amount of the binder used is 0.5 to 5 with respect to 100 parts by weight of the hydrogen storage alloy powder.
It is preferable to use parts by weight.

The negative electrode of the present invention may further contain a thickener such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyoxyethylene and the like. Among the above-mentioned thickeners, polyoxyethylene is particularly preferably used because it does not increase the viscosity when formed into a paste. The content of the thickener is preferably 1 to 5 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder.

In the alkaline storage battery of the present invention, the active material-containing layer may be formed on only one surface of the support at substantially the innermost and outermost peripheral portions of the negative electrode of the wound electrode body. preferable. The reason for this is, as will be described in detail in Examples, that the electrode body having such a winding structure reduces the active material-containing layer in the surplus portions of the substantially innermost peripheral portion and the substantially outermost peripheral portion of the negative electrode. This is because the positive electrode active material can be increased, a battery having a large electric capacity can be obtained, and the cost can be reduced.

[0033]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only those examples. In the following examples and the like,% indicating the concentration of a solution or dispersion is% by weight.

Examples 1-6 Commercially available Mm (30-70% by weight La, 10-50% by weight Ce, 0-30% by weight Nd and 0-6% by weight Pr).
And their proportions differ in each embodiment, but they are within the above range and there is no great difference in characteristics), the raw materials of Ni, Co, Mn and Al are changed in composition ratio and the high frequency melting furnace is used. After being melted in an argon gas atmosphere, the alloy is rapidly cooled at a cooling rate of about 800 ° C./sec.
Six types of hydrogen storage alloys (hydrogen storage alloys A to F) having the compositions shown in Table 1 below were manufactured by heat treatment at 00 ° C. for 3 to 10 hours. These hydrogen storage alloys A to F are used as the negative electrode active materials of the model cells and sealed alkaline storage batteries of Examples 1 to 6, respectively, as described later in detail.

Of the hydrogen storage alloys A to F, the hydrogen storage alloy A is shown in FIG. 1 (magnification: about 2).
000 times). In FIG. 1, the segregation phase 21
The cross section of is shown in black, and the other parts show the main phase. Five areas of arbitrary 15 μm square of the cross section of this hydrogen storage alloy A were set, and the number of segregated phases existing in the area was measured. The number was 15 to 25 in any area. there were. Further, the diameter of the circle circumscribing these segregated phases with the minimum diameter is 0.3 to 4 μm, and the energy dispersive X of a transmission electron microscope (TEM) is used.
Electron beam accelerating voltage: 200k using line spectrometer (EDS)
When the compositional analysis of the segregated phase was performed under the conditions of eV, beam diameter: 1 nm, and sample current of 200 pA, the segregated phase contained 57 wt% Ni and 26 wt% Mn, as well as Al and Co. When the other hydrogen storage alloys B to F are also examined in the same manner, the number of segregation phases is in the range of 1 to 40, and the diameter of the circle circumscribing the segregation phase with the minimum diameter is in the range of 0.2 to 7 μm. The Ni content of the segregated phase was 50% by weight or more, and the Mn content was 28% by weight or less.

The composition of these hydrogen storage alloys A to F, the number of segregated phases (the number of segregated phases existing in each of 15 arbitrary square areas of 15 μm in the cross section, indicated by the range from the minimum value to the maximum value) And the diameter of the circle circumscribing the segregation phase with the minimum diameter (the diameter of each circle circumscribing the segregation phase with the minimum diameter present in each of the above 5 arbitrary areas of 15 μm square, from the minimum value to the maximum value). The values are shown in Table 1). Further, using these hydrogen storage alloys A to F as negative electrode active materials, model cells and sealed alkaline storage batteries of Examples 1 to 6 were produced, respectively, and the capacity (mAh / g) of the alloy (hydrogen storage alloy) was used in the model cells. ) Was measured, and the discharge capacity of the sealed alkaline storage battery at low temperature and high rate discharge and the discharge capacity at low temperature and high rate discharge after high temperature storage were measured. However, the details will be described together with the case of Comparative Example 1 described later, and the results are shown in Table 2 described later.

Comparative Example 1 A hydrogen storage alloy G having the composition shown in Table 1 was produced in the same manner as in Example 1 except that the composition ratios of Mm, Ni, Co, Mn and Al were changed. This hydrogen storage alloy G is a hydrogen storage alloy in which the number of segregation phases exceeds 40. In addition, in Table 1, a hydrogen storage alloy is simplified and shown as "alloy" because of space considerations.

Further, a model cell and a sealed alkaline storage battery of Comparative Example 1 were produced using the hydrogen storage alloy G, and in the same manner as in Example 1, the capacity (mAh / g) of the alloy (hydrogen storage alloy) was determined in the model cell. For the sealed alkaline storage batteries, the discharge capacity at low temperature and high rate discharge and the discharge characteristics at low temperature and high rate discharge after high temperature storage were measured. They will be described in detail later.

[0039]

[Table 1]

Each hydrogen storage alloy A to the composition shown in Table 1 above
G was pulverized to have an average particle size of about 30 μm, and the hydrogen storage alloy powder was used as a negative electrode active material to prepare a model cell and a sealed alkaline storage battery.

The model cell was manufactured as follows.
0.25 g of each of the above hydrogen storage alloys A to G was sampled, the hydrogen storage alloy powder was mixed with 0.75 g of Cu powder, and then pressure-molded into pellets having a diameter of 15 mm,
This was used as a negative electrode with a Ni net having a lead wire. This negative electrode was immersed in a 30% aqueous potassium hydroxide solution at 80 ° C. for 1 hour, and a known sintered nickel positive electrode having a capacity sufficiently larger than that of the negative electrode was placed on both sides of the negative electrode via a separator made of a polypropylene nonwoven fabric. After arranging and fixing the whole, it was immersed in an electrolytic solution composed of a sufficient amount of a 30% potassium hydroxide aqueous solution to prepare a model cell of negative electrode capacity regulation.

In order to measure the capacity of each hydrogen storage alloy of this model cell, 25 mA × for those model cells was measured.
Charging for 5 hours, resting for 0.5 hours, discharging of 25 mA (final voltage: −0.65 V with respect to Hg / HgO reference electrode) was repeated 10 cycles, and the discharge capacity at the discharge of the 10th cycle was measured, It was defined as the capacity of the hydrogen storage alloy. The results are shown in Table 2 below.

The sealed alkaline storage battery was manufactured as follows. First, the negative electrode was manufactured as follows. To 100 parts by weight of the above hydrogen storage alloy powder, 2 parts by weight of nickel powder, 20 parts by weight of 6% polyethylene oxide aqueous solution and 1.7 parts by weight of 40% styrene-2-ethylhexyl acrylate copolymer dispersion were added and mixed. Then, a paste for the negative electrode was prepared. This paste is applied on both sides of a support made of punching metal, dried to form an active material-containing layer, and then a part of the active material-containing layer on one surface of the support is removed to obtain one surface of the support. A portion having no active material-containing layer is provided on the substrate, and then the sheet is pressed and cut to have a length of 69 mm and a width of 36 mm as shown in FIG.
× A sheet-like negative electrode having a thickness of 0.33 mm (a part of the thickness is 0.20 mm) was finished. The weight of the hydrogen storage alloy in the negative electrode was about 3.4 g.

The negative electrode shown in FIG. 2 will be described in detail. FIG. 2A is one side view of the negative electrode, FIG. 2B is another side view of the negative electrode, and FIG. c) is a longitudinal sectional view (sectional view taken along the line D-D) of (a). In FIGS. 2A and 2B, in order to make it easy to understand the portions where the active material containing layers 2b and 2c are provided, 2b and 2c are hatched in a cross shape. Here, as is clear from the above description, the active material-containing layer is a layer containing not only the hydrogen storage alloy that is the negative electrode active material but also the binder and the like.

The thickness of the support 2a for the negative electrode 2 is 70 μm.
Punching metal is used, and active material-containing layers 2b and 2c each having a thickness of 130 are formed on both surfaces of the support 2a.
It is formed in μm. However, a part of the negative electrode 2 has a part in which the active material-containing layer is formed only on one surface of the support 2a, and specifically, the total length of the negative electrode 2 is 69 mm.
However, the active material-containing layer is not formed on one surface of the support 2a from the one end E to the other end F of the support 2a, and thereafter the end portion is not formed. The active material containing layer 2b is continuously formed up to F, and the active material containing layer 2c is formed on the other surface of the support 2a from the one end E to the other end F up to 60 mm. ,
The active material-containing layer is not formed for the remaining 9 mm. When the active material containing layer is not formed on the end portion F side, it becomes the innermost peripheral portion of the negative electrode when the electrode body having the wound structure is formed. The portion where the active material-containing layer is not formed up to this point becomes almost the outermost peripheral portion of the negative electrode when the electrode body having the wound structure is formed. It is preferable that the innermost peripheral portion and the substantially outermost peripheral portion are genuinely the innermost peripheral portion and the outermost peripheral portion in the above.
It may not be possible to set the innermost peripheral portion or the outermost peripheral portion as set, because even if such a slight deviation occurs, the characteristics are not significantly affected. In addition, FIG. 2 is a schematic diagram, and for example, the thickness of the support 2a and the thicknesses of the active material-containing layers 2b and 2c are illustrated in a large manner with respect to the length of the negative electrode 2, or the activity of the negative electrode 2 is illustrated. The position of the portion where the substance-containing layer is not formed, the width thereof, and the like are not necessarily shown according to the dimensions.

The structure of the negative electrode 2 is as described above, because both ends of the negative electrode face the positive electrode only on one side when the electrode body having the wound structure is manufactured, and therefore the negative electrode active material in that part is formed. This is because the amount of the positive electrode active material can be increased and the capacity of the battery can be increased by reducing.
However, in the negative electrode having such a structure, the ratio of the amount of the negative electrode active material to the amount of the positive electrode active material is smaller than that of a normal negative electrode having an active material-containing layer uniformly over the entire surface, so that the hydrogen storage material that is the negative electrode active material is absorbed. The alloy is required to have a higher capacity, and the hydrogen storage alloy must have a capacity of at least 300 mAh / g or more in order to obtain a battery having a long cycle life.

The positive electrode was prepared as follows.
Nickel powder 5 against 100 parts by weight of nickel hydroxide
Parts by weight, 6 parts by weight of cobalt oxide (CoO), 10 parts by weight of 10% carboxymethyl cellulose aqueous solution, 5 parts by weight of 60% polytetrafluoroethylene (PTFE) dispersion and 40 parts by weight of deionized water, and mixed to obtain a positive electrode. A paste was prepared. This paste is applied to a support made of nickel foam, filled, dried, pressed and cut to obtain a sheet-like positive electrode having a length of 48 mm, a width of 36 mm and a thickness of 0.59 mm [capacity (theoretical value): 680 mAh]. Then, this positive electrode was used with a nickel lead body attached to the end portion.

A hydrophilic polypropylene non-woven fabric was used as a separator, and the negative electrode and the positive electrode were spirally wound with the separator interposed therebetween to produce an electrode body having a winding structure shown in FIG. The innermost and outermost negative electrodes of this electrode assembly are
It is wound so that only one side has a portion having an active material-containing layer.

Here, the electrode body having the spiral winding structure shown in FIG. 3 will be described. In the production of the electrode body having the spiral structure, the separator 3 is folded back at its central portion,
It is arranged so as to cover both surfaces of the negative electrode 2, and the end portion F (see FIG. 2)
The positive electrode 1 and the negative electrode 2 while making the side closer to the center of the spiral.
And were spirally wound via the separator 3. And
Although not shown in FIG. 3, in the spirally wound electrode body, the negative electrode 2 has at least the active material-containing layer 2b.
Alternatively, 2c faces the positive electrode 1 via the separator 3. In addition, in FIG. 3, the thickness of the innermost peripheral portion and the outermost peripheral portion of the negative electrode 2 is shown to be smaller than that of the other portions, as described above. Is removed to provide a portion having no active material-containing layer on one surface of the support. This is also the case with FIG. 2 described above, but this FIG. 3 is also schematically shown, for example,
The positive electrode 1, the negative electrode 2, the separator 3 and the like are not shown thicker than their lengths, and the respective members are not necessarily shown according to the dimensions. Further, regarding the electrode body having the winding structure shown in FIG. 3, a part not shown in FIG. 3 will be described.
In the innermost peripheral portion of the negative electrode 2, only the active material-containing layer 2b (see FIG. 2) faces the positive electrode 1 via the separator 3, and in the outermost peripheral portion of the negative electrode 2, only the active material-containing layer 2c (see FIG. 2) is formed. The active material-containing layers 2b and 2c are opposed to the positive electrode 1 with the separator 3 interposed therebetween, and the active material-containing layers 2b and 2c are provided in the separator 3 at portions other than the innermost peripheral portion and the outermost peripheral portion.
It faces the positive electrode 1 via. Similarly, although not shown in FIG. 3, a support is exposed on the outer surface side of the outermost peripheral portion of the negative electrode 2, and the support is in contact with the inner wall of the battery can 5.

In FIG. 3, reference numeral 20 denotes a current collecting portion (tab) of the positive electrode 1, which is provided on the outermost peripheral portion of the positive electrode 1. The current collector 20 is formed by crushing a part of the pores of the support of the positive electrode 1 so that the paste containing nickel hydroxide does not enter the pores, leaving only a metal body, and nickel serving as a positive electrode lead body is formed therein. It is constructed by welding one end of the ribbon. As described above, FIG. 3 is also schematically shown, and the battery can 5 is shown only by the thin line on the inner peripheral surface. Further, in FIG. 3, a large gap is shown between the electrode body 4 and the battery can 5, but this is actually shown by showing a thin member with a certain thickness. In reality, a large void as shown in the figure cannot be made.

This electrode body was inserted into a battery can, and a 30% aqueous solution of potassium hydroxide containing 17 g / l of lithium hydroxide containing various concentrations of zinc oxide was injected as an electrolytic solution. AA can be closed by closing the can
A sealed alkaline storage battery having a size shown in FIG. 4 was obtained. That is, the electrolytes used in the batteries of Examples 1 and 6 had a zinc oxide concentration of 65 mg / l, and the electrolytes used in the batteries of Examples 2 and 3 and Comparative Example 1 had a zinc oxide concentration of 30 mg / l. Then, the electrolytic solution used in Examples 4 and 5 had a zinc oxide concentration of 45 mg / l to prepare sealed alkaline storage batteries.

Now, the battery shown in FIG. 4 will be described. The positive electrode 1 is a pasty nickel electrode produced by using nickel hydroxide as an active material as described above, and the negative electrode 2 is used.
Is composed of a paste-type hydrogen storage alloy electrode prepared by using a hydrogen storage alloy as an active material as described above. However, the details of the positive electrode 1 and the negative electrode 2 are not shown in FIG. , Shown as a single structure.
The separator 3 is made of polypropylene non-woven fabric, and the positive electrode 1 and the negative electrode 2 are superposed on each other with the separator 3 interposed therebetween and are spirally wound and inserted into the battery can 5 as an electrode body 4 having a spiral structure. The insulator 14 is disposed on the top of the insulator 14. An insulator 13 is provided on the bottom of the battery can 5 prior to the insertion of the electrode body 4.

The annular gasket 6 is made of nylon 66, and the battery lid 7 is composed of the positive electrode terminal plate 8, the sealing body 9 and the metal spring 10 and the valve body 11 arranged in the internal space formed by them. The opening of the can 5 is sealed with the battery lid 7 or the like. That is, after inserting the wound electrode body 4 and the insulators 13 and 14 into the battery can 5, the bottom of the battery can 5 is formed into an annular groove 5a in the vicinity of the open end. , The annular gasket 6 at the inner peripheral projection of the groove 5a.
The annular gasket 6 and the battery lid 7 are placed in the opening of the battery can 5 by supporting the lower part of the battery can 5, and the portion of the battery can 5 from the groove 5a is tightened inward to seal the opening of the battery can 5. ing. The positive electrode terminal plate 8 is provided with a gas discharge hole 8a,
The sealing plate 9 is provided with a gas detection hole 9a, and the positive electrode terminal plate 8
The metal spring 10 and the valve body 11 are arranged between the sealing plate 9 and the sealing plate 9. Then, the outer peripheral portion of the sealing plate 9 is bent to sandwich the outer peripheral portion of the positive electrode terminal plate 8 to fix the positive electrode terminal plate 8 and the sealing plate 9.

This battery has a metal spring 1 under normal circumstances.
Since the valve body 11 closes the gas detection hole 9a by the pressing force of 0, the inside of the battery is kept in a sealed state, but when gas is generated inside the battery and the pressure inside the battery rises abnormally. , The metal spring 10 contracts to form a gap between the valve body 11 and the gas detection hole 9a, and the gas inside the battery passes through the gas detection hole 9a and the gas discharge hole 8a and is discharged to the outside of the battery. As a result, when the battery internal pressure decreases and the battery internal pressure returns to normal, the metal spring 10 restores to the original state,
The pressing force causes the valve element 11 to close the gas detection hole 9a again and keep the inside of the battery in a sealed structure. As described above, the metal spring 10 and the valve body 11 are the main materials of the safety valve. However, the safety valve is not limited to the metal spring 10 and the valve body 11, and the positive electrode terminal plate 8 and the sealing plate 9 are included. And a member having another function.

The positive electrode lead body 12 is made of a nickel ribbon, and one end thereof is spot-welded to the metal plate-like portion of the support at the outermost peripheral portion of the positive electrode 2 and is assembled as shown by 20 in FIG. The other end part of the positive electrode terminal plate 8 is spot welded to the lower end of the sealing plate 9 so that the positive electrode terminal plate 8 can function as a positive electrode terminal by contact with the sealing plate 9. Then, as described above, the support is exposed on the outer surface side of the outermost peripheral portion of the negative electrode 2, and the support contacts the inner wall of the battery can 5, whereby the battery can 5 functions as a negative electrode terminal. . This FIG. 4 is also schematically shown, and the details of the positive electrode 1, the negative electrode 2, the separator 3, etc. are not shown, and the positions thereof are slightly different from those of FIG. It is shown as if they are arranged, and the cross section of the negative electrode 2 is also shown in a mode different from that in FIG.

The sealed alkaline storage battery prepared as described above was charged at a current of 15 mA at a temperature of 25 ° C. for 4 hours, then stored at 70 ° C. for 6 hours to be activated, and then at 25 ° C. for 300 hours at 300 mA. Charging and discharging of 300 mA (final voltage 1.0 V) were repeated for 5 cycles to perform chemical conversion treatment,
The capacity of the positive electrode was measured as described later, and the discharge capacity at low temperature high rate discharge and the discharge capacity at low temperature high rate discharge after high temperature storage were examined. The results are shown in Table 2.

The discharge capacity at low temperature and high rate discharge was −20 after charging at a current value of 175 mA for 6 hours at a temperature of 25 ° C.
Hold for 5 hours at a temperature of ℃, then discharge at a current value of 700mA, measure the discharge capacity until the battery voltage becomes 1.0V, and measure the discharge capacity at low temperature and high rate discharge (high temperature storage The discharge capacity in the previous low temperature high rate discharge). However, in the display in Table 2, this discharge capacity at low temperature and high rate discharge was simply referred to as “discharge capacity at low temperature”. Furthermore, after being stored at 70 ° C. for 14 days in a discharged state and then cooled to 25 ° C., after cooling, the discharge capacity at −20 ° C. was measured again in the same manner as above, and the discharge capacity at low temperature and high rate discharge after high temperature storage was measured. And Also, regarding the discharge capacity at low temperature high rate discharge after this high temperature storage, in the display in Table 2, the low temperature high rate discharge was simply referred to as "low temperature discharge capacity".

Next, each battery was disassembled, the positive electrode was taken out, all the positive electrode mixture was dissolved in aqua regia, and ICP analysis (Japan Jarrell Ashe ICP727, single mode)
The Mn content in the positive electrode was measured by. The capacity of the positive electrode used for displaying the Mn content was determined by charging each battery for 6 hours at a current value of 170 mA, then resting for 1 hour, and discharging at a current value of 140 mAh until the battery voltage became 1.0 V. Is the discharge capacity when performing.

Table 2 shows the measurement results of the capacity of the hydrogen storage alloy in the model cell as model cell characteristics. In addition, Table 2 collectively shows the measurement results obtained by measuring the sealed alkaline storage battery manufactured as described above.

[0060]

[Table 2]

As is clear from the results shown in the section of model cell characteristics in Table 2, the hydrogen storage alloys of Examples 1 to 6 have large capacities, and as is clear from the results shown in the section of battery characteristics, The batteries of Examples 1 to 6 have large discharge capacities in low-temperature high-rate discharge before high-temperature storage, and also large discharge capacities in low-temperature high-rate discharge after high-temperature storage, and have excellent low-temperature discharge characteristics after high-temperature storage. It was This is because the hydrogen storage alloys A to F used as the negative electrode active material have appropriate forms such as the number and size of segregation phases, and the Mn content in the positive electrode is 0.6 to 6 mg /
It is thought that this is due to the fact that it was kept within the range of Ah.
In addition, when the positive electrodes of these batteries were examined in the same manner as in the case of measuring the Mn content, zinc compounds were confirmed in the positive electrodes. The battery of the present invention is considered to have excellent corrosion resistance because it has excellent high temperature storage characteristics as described above.
On the other hand, in the hydrogen storage alloy G used as the negative electrode active material of the battery of Comparative Example 1, the elution amount of Mn during storage at high temperature was large because the number of segregated phases was not appropriate,
It is considered that the characteristics were greatly deteriorated.

[0062]

As described above, according to the present invention, there is provided an alkaline storage battery having a high capacity, excellent discharge characteristics at low temperature and high rate discharge, and excellent discharge characteristics at low temperature and high rate discharge after high temperature storage. Could be provided.

[Brief description of drawings]

FIG. 1 is a drawing schematically showing an electron microscope photograph of a cross section of a hydrogen storage alloy A used as a negative electrode active material in the battery of Example 1 of the present invention.

FIG. 2 schematically shows an example of a negative electrode used in the alkaline storage battery of the present invention, in which (a) is one side view of the negative electrode and (b) is another side view of the negative electrode. c) is a sectional view taken along the line D-D in (a) above.

FIG. 3 is a cross-sectional view schematically showing an example of an electrode body having a wound structure used in the alkaline storage battery of the present invention.

FIG. 4 is a vertical cross-sectional view schematically showing an example of the alkaline storage battery of the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 2a support 2b Active material-containing layer 2c Active material containing layer 3 separator 4 Winding structure electrode body 5 battery cans 21 segregated phase 22 Circle circumscribing the segregated phase with the minimum diameter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01M 4/62 H01M 4/62 C (72) Inventor Ryu Nagai 1-88, Tora-Tora, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd. (56) References JP-A-8-96805 (JP, A) JP-A-9-115543 (JP, A) JP-A-8-241713 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) H01M 10/30 H01M 4/24 H01M 4/32 H01M 4/38 H01M 4/62

Claims (3)

(57) [Claims] 1. In an alkaline storage battery having a positive electrode, a negative electrode, a separator and an electrolytic solution, the negative electrode active material in the negative electrode contains Mm (Mm is 30 wt% or more of La.
And a hydrogen storage alloy containing at least Ni, Co, Mn and Al as constituent elements, and having a segregation phase mainly composed of Ni in the hydrogen storage alloy, and A hydrogen storage alloy in which the number of segregated phases exposed in an arbitrary 15 μm square area of the alloy cross section (however, the number of segregated phases in which the diameter of the circle circumscribing the segregated phase with the minimum diameter is 0.05 μm or more) is 1 to 40 And Mn in the positive electrode
Content is 0.6-6 mg / Ah with respect to the capacity of a positive electrode, The alkaline storage battery characterized by the above-mentioned. 2. The alkaline storage battery according to claim 1, wherein a diameter of a circle circumscribing the segregation phase with a minimum diameter is 0.05 to 10 μm. 3. The alkaline storage battery according to claim 1, wherein the positive electrode contains zinc ions or a zinc compound.