JP6057369B2 - Nickel metal hydride secondary battery - Google Patents

Description

  The present invention relates to a nickel metal hydride secondary battery.

  Nickel metal hydride secondary batteries are used in various applications such as various portable devices and hybrid electric vehicles because they have higher capacity and better environmental safety than nickel cadmium secondary batteries. It is like that.

The hydrogen storage alloy used for the negative electrode of this nickel metal hydride secondary battery is a material capable of occluding and releasing hydrogen, and is one of important constituent materials in the nickel metal hydride secondary battery. As such a hydrogen storage alloy, for example, a LaNi ₅ type hydrogen storage alloy which is a rare earth-Ni type hydrogen storage alloy having a CaCu ₅ type crystal as a main phase is generally used.

  By the way, the nickel hydride secondary battery may be used even in a low temperature environment such as 0 ° C. to −20 ° C. due to the discovery of various uses as described above. However, the conventional nickel metal hydride secondary battery has a problem that the discharge capacity under a low temperature environment as described above is significantly lower than the discharge capacity under a room temperature environment of about 25 ° C. The main cause of this defect is that the reaction resistance of the negative electrode is greatly increased due to a decrease in the surface activity of the hydrogen storage alloy in a low temperature environment. In order to solve this problem, various measures for suppressing an increase in the reaction resistance of the negative electrode have been studied. Among these, as a good countermeasure, the particle size of the hydrogen storage alloy particles is made smaller. According to this measure, since the reaction point in the negative electrode can be increased, the battery reaction can be promoted as the reaction point increases, and the increase in the reaction resistance of the negative electrode can be suppressed even in a low temperature environment. .

However, in this case, as the particle size of the hydrogen storage alloy particles becomes smaller, the surface area of the entire hydrogen storage alloy increases, and the contact area with the alkaline electrolyte increases, so the alkaline electrolyte and the hydrogen storage alloy Degradation of the hydrogen storage alloy due to the reaction of proceeds easily. Further, when the hydrogen storage alloy is repeatedly stored and released with hydrogen due to the charge / discharge reaction of the battery, the alloy is cracked and pulverized. In particular, the LaNi ₅ -based hydrogen storage alloy is easily pulverized. And when the alloy is cracked and pulverized, many new surfaces with high reactivity are generated, so although the reaction point can be expected to increase, the hydrogen electrolyte alloy reacts with the alkaline electrolyte in the battery and this new surface. Will be more oxidized and deteriorated.

  Here, when the alkaline electrolyte and the hydrogen storage alloy react, the electrolyte is consumed and decreased with the reaction. When the alkaline electrolyte decreases, the internal resistance increases due to the dry-out of the separator, making it difficult to discharge. A battery using a hydrogen storage alloy that has a small particle size and is easily pulverized easily consumes an electrolytic solution, and discharge becomes difficult at a stage where the number of charge / discharge cycles is relatively small, resulting in a short cycle life.

  That is, when a hydrogen storage alloy having a small particle size is used, the low-temperature discharge characteristics can be improved, but the cycle life characteristics are deteriorated. In addition, since the hydrogen storage alloys that are generally used conventionally are easily pulverized, the cycle life characteristics are more likely to deteriorate.

  Therefore, recently, in order to achieve both low-temperature discharge characteristics and cycle life characteristics, a rare earth-Mg-Ni hydrogen storage alloy having a composition in which a part of the rare earth element of the rare earth-Ni system hydrogen storage alloy is replaced with Mg is used. It has been tried. This rare-earth-Mg-Ni-based hydrogen storage alloy is less likely to be pulverized than conventional rare-earth-Ni-based hydrogen storage alloys and is suitable for extending the life of the battery. Examples of such rare earth-Mg—Ni-based hydrogen storage alloys include hydrogen storage alloys as disclosed in Patent Document 1.

JP-A-11-323469

  By the way, in the nickel metal hydride secondary battery using the rare earth-Mg—Ni-based hydrogen storage alloy as a negative electrode material, it is possible to suppress a decrease in cycle life characteristics due to the pulverization of the hydrogen storage alloy to some extent. However, even in such a nickel metal hydride secondary battery, if the hydrogen storage alloy particles are reduced in size to improve the low temperature discharge characteristics, the cycle life characteristics are still deteriorated. I can't get it. Therefore, in order to obtain a cycle life characteristic comparable to that of a conventional battery, a measure for not reducing the diameter of the rare earth-Mg—Ni-based hydrogen storage alloy particles can be considered. However, this cannot sufficiently meet the demand for improvement in low-temperature discharge characteristics with respect to nickel-hydrogen secondary electricity. That is, in a conventional nickel metal hydride secondary battery, there is a trade-off relationship between low-temperature discharge characteristics and cycle life characteristics.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a nickel metal hydride secondary battery excellent in low temperature discharge characteristics while maintaining cycle life characteristics.

In order to achieve the above object, the present inventor has intensively studied the activation of the surface of the hydrogen storage alloy in a low temperature environment. The present inventor has, in this review process, in the case of adopting the TeO ₂ as an additive to the alkaline electrolyte, the TeO ₂ is obtained a finding of activating the surface of hydrogen-absorbing alloy even in a low temperature environment, such a finding Based on the above, it has been found that adding TeO ₂ as an additive to the alkaline electrolyte is effective in improving the low-temperature discharge characteristics. In general, it is known that adding an additive to an alkaline electrolyte lowers the conductivity of the alkaline electrolyte and lowers the discharge characteristics of the battery in a low-temperature environment. That is usually avoided. However, the present inventor has arrived at the present invention to achieve both low-temperature discharge characteristics and cycle life characteristics of a battery by adding an additive to the alkaline electrolyte based on the above knowledge.

That is, according to the present invention, a container and an electrode group housed in an airtight state together with an alkaline electrolyte in the container, the electrode group is composed of a positive electrode and a negative electrode superimposed via a separator, The negative electrode includes a rare earth-Mg—Ni-based hydrogen storage alloy having a crystal structure in which an AB ₂ type subunit and an AB ₅ type subunit are stacked, and the alkaline electrolyte includes TeO _2. A nickel metal hydride secondary battery is provided.

Further, the TeO ₂ is preferably included so that the amount added per capacity (Ah) of the battery is 0.28 × 10 ⁻⁴ g / Ah or more.

Furthermore, the hydrogen storage alloy has the general _{formula: Ln 1-x Mg x Ni} ya Al a ( In the formula, Ln is Zr, Ti and at least one element selected from rare earth elements, the subscript x, y, a Each have a composition represented by 0.05 ≦ x ≦ 0.30, 2.8 ≦ y ≦ 3.8, and 0.05 ≦ a ≦ 0.30) Is preferred.

The nickel metal hydride secondary battery of the present invention has the following effects. That is, since TeO ₂ is contained in the alkaline electrolyte, the surface of the hydrogen storage alloy can be activated even under a low temperature environment of 0 ° C. to −20 ° C., and the battery reaction can be promoted. Low temperature discharge characteristics can be improved. That is, since the cell reaction is promoted by the TeO _2, it is not necessary to reduce the particle size of the hydrogen storage alloy particles in order to increase the reaction point. Therefore, it is possible to employ hydrogen storage alloy particles having a particle size comparable to that of the hydrogen storage alloy particles having a particle size capable of obtaining cycle life characteristics equivalent to those of conventional batteries. Moreover, the hydrogen storage alloy included in the negative electrode is a rare earth-Mg—Ni based hydrogen storage alloy having a crystal structure having a so-called superlattice structure in which AB ₂ type subunits and AB ₅ type subunits are laminated. Compared to conventional rare earth-Ni alloys, it is difficult to pulverize. From these facts, the nickel metal hydride secondary battery of the present invention has a sufficient cycle life and improved low-temperature discharge characteristics.

It is the perspective view which fractured | ruptured and showed the nickel-hydrogen secondary battery which concerns on one Embodiment of this invention.

  Hereinafter, a nickel-hydrogen secondary battery (hereinafter simply referred to as a battery) 2 according to the present invention will be described with reference to the drawings.

  The battery 2 to which the present invention is applied is not particularly limited. For example, a case where the present invention is applied to an AA size cylindrical battery 2 shown in FIG. 1 will be described as an example.

  As shown in FIG. 1, the battery 2 includes an outer can 10 having a bottomed cylindrical shape with an open upper end. The outer can 10 has conductivity, and its bottom wall 35 functions as a negative electrode terminal. In the opening of the outer can 10, a disc-shaped cover plate 14 having conductivity and a ring-shaped insulating packing 12 surrounding the cover plate 14 are arranged. The insulating packing 12 caulks the opening edge 37 of the outer can 10. It is fixed to the opening edge 37 of the outer can 10 by processing. That is, the lid plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the outer can 10.

  Here, the cover plate 14 has a central through hole 16 in the center, and a rubber valve body 18 that closes the central through hole 16 is disposed on the outer surface of the cover plate 14. Further, a flanged cylindrical positive terminal 20 is fixed on the outer surface of the cover plate 14 so as to cover the valve body 18, and the positive terminal 20 presses the valve body 18 toward the cover plate 14. The positive electrode terminal 20 has a gas vent hole (not shown).

  Normally, the central through hole 16 is hermetically closed by the valve body 18. On the other hand, if gas is generated in the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the central through hole 16. As a result, the central through hole 16 and the positive electrode terminal 20 are opened from the outer can 10. Gas is released to the outside through the vent holes. That is, the central through hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

  An electrode group 22 is accommodated in the outer can 10. Each of the electrode groups 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28, which are wound in a spiral shape with the separator 28 sandwiched between the positive electrode 24 and the negative electrode 26. That is, the positive electrode 24 and the negative electrode 26 are overlapped via the separator 28. The outermost periphery of the electrode group 22 is formed by a part of the negative electrode 26 (the outermost periphery) and is in contact with the inner peripheral wall of the outer can 10. That is, the negative electrode 26 and the outer can 10 are electrically connected to each other.

  In the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the lid plate 14. Specifically, the positive electrode lead 30 has one end connected to the inner end of the positive electrode 24 and the other end connected to the lid plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. A circular insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the insulating member 32. A circular insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

Further, a predetermined amount of alkaline electrolyte (not shown) is injected into the outer can 10. The alkaline electrolyte is impregnated in the electrode group 22 to advance a charge / discharge reaction between the positive electrode 24 and the negative electrode 26. TeO ₂ is added to the alkaline electrolyte. Specifically, an alkaline electrolyte containing NaOH as a main solute is prepared, and TeO ₂ is added to the alkaline electrolyte. At this time, TeO ₂ is preferably added so as to be 0.28 × 10 ⁻⁴ g / Ah or more per battery capacity (Ah). Thereby, the low-temperature discharge characteristics of the battery can be improved. Moreover, the low temperature discharge characteristics of the battery are improved by adding more TeO ₂ . However, when the amount of TeO ₂ added exceeds 2.8 × 10 ⁻⁴ g / Ah, the conductivity of the alkaline electrolyte may start to be inhibited. Therefore, the amount of TeO ₂ added is preferably 2.8 × 10 ⁻⁴ g / Ah or less.

Here, as the alkaline electrolyte of the present invention, an alkaline electrolyte containing NaOH as a main solute is used, and specifically, an aqueous sodium hydroxide solution is used. Then, TeO ₂ is added to this aqueous sodium hydroxide solution. In addition, the solute of the alkaline electrolyte may include at least one of KOH and LiOH. Here, when KOH and LiOH are also included as the solute of the alkaline electrolyte, the amount of NaOH is larger than the amount of these KOH and LiOH. A battery using such an alkaline electrolyte mainly composed of NaOH exhibits excellent self-discharge characteristics.

  As a material of the separator 28, for example, a polyamide fiber nonwoven fabric or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene provided with a hydrophilic functional group can be used. Specifically, it is preferable to use a non-woven fabric mainly composed of polyolefin fibers that have been subjected to sulfonation treatment and are provided with sulfone groups. Here, the sulfone group is imparted by treating the nonwoven fabric with an acid containing a sulfuric acid group such as sulfuric acid or fuming sulfuric acid. A battery using a separator including such a fiber having a sulfone group exhibits excellent self-discharge characteristics.

  The positive electrode 24 is composed of a conductive positive electrode current collector having a porous structure and a positive electrode mixture retained in the pores of the positive electrode current collector.

  As such a positive electrode current collector, for example, a nickel-plated net-like, sponge-like or fibrous metal body, or foamed nickel (nickel foam) can be used.

  The positive electrode mixture includes positive electrode active material particles, a conductive material, a positive electrode additive, and a binder. This binder serves to bind the positive electrode active material particles, the conductive material, and the positive electrode additive, and at the same time, bind the positive electrode mixture to the positive electrode current collector. Here, as the binder, for example, carboxymethylcellulose, methylcellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropylcellulose) dispersion, and the like can be used.

  The positive electrode active material particles are nickel hydroxide particles or higher order nickel hydroxide particles. In addition, it is preferable to dissolve at least one of zinc, magnesium, and cobalt in these nickel hydroxide particles.

As the conductive material, for example, one or more selected from cobalt compounds such as cobalt oxide (CoO) and cobalt hydroxide (Co (OH) ₂ ) and cobalt (Co) can be used. This conductive material is added to the positive electrode mixture as necessary, and is added to the positive electrode mixture in the form of a powder and a coating covering the surface of the positive electrode active material. It may be.

  The positive electrode additive is added to improve the characteristics of the positive electrode. For example, yttrium oxide, zinc oxide, or the like can be used.

The positive electrode active material particles can be produced, for example, as follows.
First, an aqueous solution of nickel sulfate is prepared. Nickel hydroxide particles are precipitated by gradually adding a sodium hydroxide aqueous solution to the nickel sulfate aqueous solution for reaction. Here, when zinc, magnesium and cobalt are dissolved in nickel hydroxide particles, nickel sulfate, zinc sulfate, magnesium sulfate and cobalt sulfate are weighed so as to have a predetermined composition, and a mixed aqueous solution thereof is prepared. While stirring the resulting mixed aqueous solution, a sodium hydroxide aqueous solution is gradually added to the mixed aqueous solution to cause the reaction, thereby precipitating positive electrode active material particles mainly composed of nickel hydroxide and containing zinc, magnesium and cobalt as solid solutions. Let

The positive electrode 24 can be manufactured as follows, for example.
First, a positive electrode mixture paste including a positive electrode active material powder made of the positive electrode active material particles obtained as described above, a conductive material, a positive electrode additive, water, and a binder is prepared. The obtained positive electrode mixture paste is filled in, for example, foamed nickel (nickel foam) and dried. After drying, foamed nickel (nickel foam) filled with nickel hydroxide particles or the like is roll-rolled and then cut. Thereby, the positive electrode 24 carrying the positive electrode mixture is produced.

Next, the negative electrode 26 will be described.
The negative electrode 26 has a conductive negative electrode substrate (core body) having a strip shape, and a negative electrode mixture is held on the negative electrode substrate.
The negative electrode substrate is made of a sheet-like metal material in which through holes are distributed. For example, a punched metal sheet or a sintered substrate obtained by molding and sintering metal powder can be used. The negative electrode mixture is not only filled in the through holes of the negative electrode substrate, but also held in layers on both surfaces of the negative electrode substrate.

  The negative electrode mixture includes hydrogen storage alloy particles capable of occluding and releasing hydrogen as a negative electrode active material, a conductive material, and a binder. This binder serves to bind the hydrogen storage alloy particles and the conductive material to each other and at the same time bind the negative electrode mixture to the negative electrode substrate. Here, a hydrophilic or hydrophobic polymer or the like can be used as the binder, and carbon black or graphite can be used as the conductive material.

As the hydrogen storage alloy in the hydrogen storage alloy particles, a rare earth-Mg—Ni-based hydrogen storage alloy containing rare earth elements, Mg and Ni is used. Specifically, the rare earth-Mg—Ni-based hydrogen storage alloy mainly has an AB ₃ phase, an A ₂ B ₇ phase, or an A ₅ B ₁₉ phase in which an AB ₂ type subunit and an AB ₅ type subunit are laminated. It has a crystal structure, that is, a superlattice structure. Rare-earth-Mg-Ni-based hydrogen storage alloys having a so-called superlattice structure in which AB ₂ type subunits and AB ₅ type subunits are laminated are compared with conventional rare earth-Ni-based alloys in storing and releasing hydrogen. Since it has the property of suppressing cracking of the alloy, pulverization is suppressed. For this reason, in such a hydrogen storage alloy, a highly reactive new surface is hardly generated, and the corrosion reaction of the hydrogen storage alloy by the electrolyte can be suppressed. As a result, consumption of the electrolytic solution accompanying the corrosion reaction can be reduced, the occurrence of the dry-out phenomenon can be suppressed, and the cycle life characteristics of the battery 2 obtained can be improved.

Further, the rare earth-Mg—Ni-based hydrogen storage alloy having the superlattice structure as described above has the advantage of stable hydrogen storage and release, which is a feature of the AB ₅ type alloy, and a feature of the AB ₂ type alloy. It also has the advantage of a large hydrogen storage capacity. For this reason, since the hydrogen storage alloy which concerns on this invention is excellent in hydrogen storage capability, it contributes also to the high capacity | capacitance of the battery 2 obtained.

Here, the rare earth-Mg-Ni according to the present invention having a crystal structure mainly composed of AB ₃ phase, A ₂ B ₇ phase or A ₅ B ₁₉ phase in which AB ₂ type subunit and AB ₅ type subunit are laminated. The system hydrogen storage alloy can be formed by having the composition represented by the following general formula (I).
Ln _1-x Mg _x Ni _ya Al _a (I)
However, in the general formula (I), Ln represents at least one element selected from Zr, Ti, and rare earth elements, and the subscripts x, y, and a are 0.05 ≦ x ≦ 0.30, 2. It is necessary to satisfy the conditions of 8 ≦ y ≦ 3.8 and 0.05 ≦ a ≦ 0.30. In addition, the above-mentioned rare earth elements specifically indicate Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

Next, the hydrogen storage alloy particles described above are obtained, for example, as follows.
First, metal raw materials are weighed and mixed so as to have a predetermined composition, and this mixture is melted in an induction melting furnace, for example, and then cooled to an ingot. The obtained ingot is subjected to heat treatment by heating for 5 to 24 hours in an inert gas atmosphere at 900 to 1200 ° C. Thereafter, the ingot cooled to room temperature is pulverized and classified to a desired particle size by sieving to obtain hydrogen storage alloy particles.

Moreover, the negative electrode 26 can be manufactured as follows, for example.
First, a negative electrode mixture paste is prepared by kneading a hydrogen storage alloy powder composed of hydrogen storage alloy particles, a conductive material, a binder and water. The obtained negative electrode mixture paste is applied to the negative electrode substrate and dried. After drying, the negative electrode substrate to which the hydrogen storage alloy particles and the like are attached is subjected to roll rolling and cutting, whereby the negative electrode 26 is produced.

  The positive electrode 24 and the negative electrode 26 manufactured as described above are spirally wound with the separator 28 interposed therebetween, and are formed in the electrode group 22.

The electrode group 22 thus obtained is accommodated in the outer can 10. Subsequently, a predetermined amount of an alkaline electrolyte containing TeO ₂ is injected into the outer can 10. Thereafter, the outer can 10 containing the electrode group 22 and the alkaline electrolyte is sealed by the cover plate 14 provided with the positive electrode terminal 20, and the battery 2 according to the present invention is obtained.

The battery 2 of the present invention is a battery that maintains cycle life characteristics and is superior in low-temperature discharge characteristics than the conventional ones due to the synergistic effect of the combination of the above-described components. Specifically, the battery 2 of the present invention employs a rare earth-Mg—Ni-based hydrogen storage alloy for the negative electrode and adds TeO ₂ to the alkaline electrolyte, thereby maintaining low cycle discharge characteristics while maintaining the cycle life characteristics of the battery. It is possible to improve. More specifically, first, TeO ₂ can bring the surface of the hydrogen storage alloy into an active state even in a low temperature environment, so that the effect of improving the low temperature discharge characteristics of the battery is exhibited. The rare earth-Mg-Ni alloy has a higher initial activity and is less likely to be pulverized as compared with the conventional AB ₅ hydrogen storage alloy, and therefore the effect of improving the low-temperature discharge characteristics of TeO ₂ is further increased. This makes it possible to suppress an increase in the reaction resistance of the negative electrode without increasing the surface area of the hydrogen storage alloy, maintaining cycle life characteristics and improving low-temperature discharge characteristics for the resulting nickel-hydrogen secondary battery. can do.

1. Production of battery (Example 1)

(1) Production of hydrogen storage alloy and negative electrode First, a first mixture containing 20% by mass of lanthanum, 39.5% by mass of praseodymium, 39.5% by mass of neodymium, and 0.01% by mass of zirconium was prepared. The obtained first mixture, magnesium, nickel, and aluminum were weighed to prepare a second mixture having a molar ratio of 0.83: 0.17: 3.10: 0.20. The obtained second mixture was melted in an induction melting furnace and made into an ingot. Next, the ingot was subjected to a heat treatment for 10 hours in an argon gas atmosphere at a temperature of 1000 ° C., and a hydrogen storage alloy whose composition was (La _0.20 Pr _0.395 Nd _0.395 Zr _0.01 ) _0.83 Mg _0.17 Ni _3.10 Al _0.20 Got the ingot. Thereafter, the ingot was mechanically pulverized in an argon gas atmosphere and sieved to select a powder composed of hydrogen storage alloy particles remaining between 400 mesh and 200 mesh. As a result of measuring the particle diameter of the obtained hydrogen storage alloy particles, the average particle diameter of the hydrogen storage alloy particles was 65 μm.

  Dispersion of sodium acrylate 0.4 parts by mass, carboxymethyl cellulose 0.1 parts by mass, styrene butadiene rubber (SBR) (solid content 50% by weight) with respect to 100 parts by mass of the obtained hydrogen storage alloy powder. 0 parts by mass (in terms of solid content), 1.0 part by mass of carbon black, and 30 parts by mass of water were added and kneaded to prepare a paste of a negative electrode mixture.

  The paste of the negative electrode mixture was applied to both sides of an iron perforated plate as a negative electrode substrate so that the thickness was uniform and constant. This perforated plate has a thickness of 60 μm, and its surface is plated with nickel.

  After drying the paste, the perforated plate to which the hydrogen storage alloy powder is adhered is further rolled to increase the amount of alloy per volume, and then cut and cut for AA size containing rare earth-Mg-Ni based hydrogen storage alloy. A negative electrode 26 was prepared.

(2) Preparation of positive electrode Nickel sulfate, zinc sulfate, magnesium sulfate and cobalt sulfate were weighed so as to be 3% by mass of zinc, 0.4% by mass of magnesium and 1% by mass of cobalt with respect to nickel. In addition to a 1N (normality) aqueous sodium hydroxide solution containing ions, a mixed aqueous solution was prepared. While stirring the obtained mixed aqueous solution, a 10N (normality) aqueous sodium hydroxide solution was gradually added to the mixed aqueous solution to cause a reaction. During the reaction, the pH was stabilized at 13 to 14 and water was added. Nickel hydroxide particles mainly composed of nickel oxide and solid-dissolved in zinc, magnesium and cobalt were produced.

  The obtained nickel hydroxide particles were washed three times with 10 times the amount of pure water, then dehydrated and dried. The obtained nickel hydroxide particles have a spherical shape with an average particle diameter of 10 μm.

  Next, 10 parts by mass of cobalt hydroxide powder was mixed with 100 parts by mass of the positive electrode active material powder made of nickel hydroxide particles produced as described above, and further 0.5 parts by mass of yttrium oxide, 0.3 parts by mass. A positive electrode mixture paste is prepared by mixing 40 parts by mass of zinc oxide and 40 parts by mass of HPC dispersion liquid, and this positive electrode mixture paste is applied to sheet-like foamed nickel (nickel foam) as a positive electrode current collector. -Filled. The foamed nickel to which the positive electrode mixture was adhered was dried and then rolled. The foamed nickel to which the positive electrode mixture that had been rolled was adhered was cut into a predetermined shape and formed on the positive electrode 24 for AA size. The positive electrode 24 carries a positive electrode mixture so that the positive electrode capacity is 2000 mAh.

(3) Assembly of Nickel Metal Hydride Battery The obtained positive electrode 24 and negative electrode 26 were spirally wound with a separator 28 sandwiched between them, and an electrode group 22 was produced. The separator 28 used for the production of the electrode group 22 here was made of a nonwoven fabric made of polypropylene fiber subjected to sulfonation treatment, and its thickness was 0.1 mm (weight per unit area 53 g / m ² ).

On the other hand, an alkaline electrolyte composed of an aqueous solution containing NaOH, LiOH and KOH was prepared. Here, the concentration of NaOH was 7.0 N (normality), the concentration of LiOH was 0.8 N (normality), and the concentration of KOH was 0.02 N (normality). Then, to this alkaline electrolyte solution 1 liter was added TeO ₂ so that 0.3 g (TeO ₂ addition concentration: 0.3g / l).

Next, the electrode group 22 was housed in the bottomed cylindrical outer can 10 and a predetermined amount of an alkaline electrolyte to which TeO ₂ was added was injected. Thereafter, the opening of the outer can 10 was closed with the cover plate 14 or the like, and the AA size nickel-hydrogen secondary battery 2 having a nominal capacity of 2000 mAh was assembled. This nickel metal hydride secondary battery is referred to as battery a.

(4) Initial activation treatment After charging the battery a for 16 hours with a charging current of 200 mA (0.1 It) in an environment of a temperature of 25 ° C., a discharging current of 400 mA (0.2 It) The initial activation process for discharging until the battery voltage reached 0.5 V was repeated twice. In this way, the battery a was made usable.

(Example 2)
Secondary nickel hydride as in battery a of Example 1, except that TeO ₂ was added to 3.0 g per 1 liter of alkaline electrolyte (TeO ₂ addition concentration: 3.0 g / l). A battery (battery b) was produced. Then, as in Example 1, the initial activation process was performed to make the battery b usable.

(Comparative Example 1)
A nickel metal hydride secondary battery (battery c) was produced in the same manner as the battery a of Example 1 except that an alkaline electrolyte without addition of TeO ₂ was used. Then, in the same manner as in Example 1, the initial activation process was performed to make the battery c usable.

2. Evaluation of nickel-hydrogen secondary battery (1) TeO ₂ content per unit capacity Charging current of 200 mA (0.1 It) in an environment at a temperature of 25 ° C. with respect to batteries a to c after initial activation treatment After charging for 16 hours, the discharge capacity of the battery was measured when it was discharged at a discharge current of 400 mA (0.2 It) until the battery voltage reached 1.0 V. The TeO ₂ content per 1 Ah was calculated from this discharge capacity, and the results are shown in Table 1.

(2) Discharge characteristics (i) 25 ° C. discharge capacity The battery voltage reaches the maximum value with a charging current of 2000 mA (1.0 It) in an environment of 25 ° C. with respect to the batteries a to c which have been initially activated. After reaching, the battery was charged by so-called -ΔV control (hereinafter, simply referred to as -ΔV charge), which was charged until the voltage decreased by 10 mV, and then left for 3 hours in an environment of 25 ° C. Thereafter, the discharge capacity of the battery was measured when discharged at a discharge current of 2000 mA (1.0 It) at 25 ° C. until the final discharge voltage reached 1.0 V. The discharge capacity at this time is defined as a 25 ° C. discharge capacity. The operating voltage at this time was also measured.

(Ii) −10 ° C. Discharge Capacity The batteries a to c subjected to the initial activation treatment were subjected to −ΔV charging at a charging current of 2000 mA (1.0 It) in an environment of 25 ° C. Thereafter, the battery is left to stand for 3 hours in an environment of −10 ° C., and then discharged in an environment of −10 ° C. with a discharge current of 2000 mA (1.0 It) until the final discharge voltage reaches 1.0V. The discharge capacity of was measured. The discharge capacity at this time is set to −10 ° C. discharge capacity. The operating voltage at this time was also measured.

(Iii) −20 ° C. discharge capacity The batteries a to c subjected to the initial activation treatment were subjected to −ΔV charging at a charging current of 2000 mA (1.0 It) in an environment of 25 ° C. Thereafter, the battery is left for 3 hours in an environment at -20 ° C, and then discharged at a discharge current of 2000 mA (1.0 It) in an environment at -20 ° C until the final discharge voltage becomes 1.0V. The discharge capacity of was measured. The discharge capacity at this time is set to −20 ° C. discharge capacity. The operating voltage at this time was also measured.

  For each value of the 25 ° C. discharge capacity, −10 ° C. discharge capacity, and −20 ° C. discharge capacity determined as described above, the ratio was determined using the value of the 25 ° C. discharge capacity as a reference value. Table 2 shows the discharge capacity ratio with the ratio at each temperature expressed as a percentage. Table 2 also shows the operating voltage under each temperature environment.

  Here, as the value of the discharge capacity ratio at −10 ° C. and −20 ° C. is closer to 100%, the degree of decrease in the discharge capacity under a low temperature environment is less and the low temperature discharge characteristics are better.

(2) Cycle life characteristics (i) Initial capacity measurement The batteries a to c that have been subjected to initial activation treatment are charged at a current of 2000 mA (1.0 It) with a charging current of −ΔV in an environment of 25 ° C. It was. Thereafter, the battery is left to stand for 3 hours in an environment of −10 ° C., and then discharged in an environment of −10 ° C. with a discharge current of 2000 mA (1.0 It) until the final discharge voltage reaches 1.0V. The discharge capacity of was measured. The discharge capacity at this time is defined as the initial capacity.

(Ii) Cycle test The batteries a to c subjected to the initial activation treatment were charged with -ΔV at a charging current of 2000 mA (1.0 It) in an environment of 25 ° C, and then left for 20 minutes.
The battery was discharged at a discharge current of 2000 mA (1.0 It) at 25 ° C. until the battery voltage reached 1.0 V, and then left for 10 minutes.

  When the charge / discharge cycle was 1 cycle and the initial capacity of each battery was 100%, the number of cycles until the capacity maintenance rate with respect to the initial capacity was below 60% was counted, and the number of cycles was defined as the cycle life. Here, assuming that the number of cycles when the battery c of Comparative Example 1 reached the cycle life was 100, the ratio to the cycle life of each battery was determined, and the results are shown in Table 1 as the cycle life characteristic ratio.

(3) Discussion (i) TeO ₂ Examples 1 and 2 using the alkaline electrolyte containing battery in a low-temperature environment than the battery of Comparative Example 1 using the alkaline electrolyte containing no TeO ₂ High discharge capacity and excellent low-temperature discharge characteristics. Specifically, the discharge capacity ratio in the environment of −10 ° C. in the battery of Example 1 is improved by 0.9% compared to the battery of Comparative Example 1. And the discharge capacity ratio in the -10 degreeC environment in the battery of Example 2 is improved 1.1% compared with the battery of the comparative example 1. FIG. On the other hand, the discharge capacity ratio at −20 ° C. in the battery of Example 1 is improved by 2.2% compared to the battery of Comparative Example 1. And the discharge capacity ratio in the -20 degreeC environment in the battery of Example 2 is improved 2.2% compared with the battery of the comparative example 1. FIG.

  In addition, the batteries of Examples 1 and 2 have a higher operating voltage in a low temperature environment than the battery of Comparative Example 1. Specifically, in the environment of −10 ° C., the batteries of Example 1 and Example 2 have their operating voltages increased by 2 mV compared to the battery of Comparative Example 1, respectively. On the other hand, the battery of Example 1 under the environment of −20 ° C. has an operating voltage increased by 2 mV compared to the battery of Comparative Example 1, and the battery of Example 2 under the environment of −20 ° C. is the battery of Comparative Example 1. In comparison, the operating voltage is increased by 3 mV.

(Ii) The cycle life characteristic ratio of the batteries of Examples 1 and 2 shows the same value as the cycle life characteristic ratio of the battery of Comparative Example 1. That is, it can be said that even when TeO ₂ is added to the electrolytic solution, a battery having a cycle life equivalent to that of a battery without addition of TeO ₂ can be obtained.

(Iii) From the above results, in a nickel metal hydride secondary battery using a rare earth-Mg—Ni-based hydrogen storage alloy for the negative electrode, by adding TeO ₂ to the alkaline electrolyte, while maintaining cycle life characteristics, It can be said that the low-temperature discharge characteristics can be improved. In particular, in order to improve the low-temperature discharge characteristics, it can be said that the amount of TeO ₂ in the battery is preferably 0.28 × 10 ⁻⁴ g / Ah or more.

  The present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the nickel metal hydride secondary battery may be a prismatic battery and has a mechanical structure. Is not exceptionally limited.

2 Nickel metal hydride secondary battery 22 Electrode group 24 Positive electrode 26 Negative electrode 28 Separator

Claims (2)

A container, and an electrode group housed in an airtight state together with an alkaline electrolyte in the container,
The electrode group is composed of a positive electrode and a negative electrode superimposed via a separator,
The negative electrode includes a rare earth-Mg-Ni-based hydrogen storage alloy having a crystal structure in which AB ₂ type subunits and AB ₅ type subunits are stacked,
The alkaline electrolyte, only including the TeO _2,
The amount of TeO ₂ added per battery capacity (Ah) is 0.28 × 10 ⁻⁴ g / Ah or more and 2.8 × 10 ⁻⁴ g / Ah or less.
Nickel metal hydride secondary battery characterized by the above. The hydrogen storage alloy is
General _{formula: Ln 1-x Mg x Ni} y-a Al a ( In the formula, Ln is, Zr, at least one element selected from Ti and rare earth elements, the subscript x, y, a, respectively, 0. 05 ≦ x ≦ 0.30,2.8 ≦ y ≦ 3.8,0.05 ≦ a ≦ 0.30 , wherein it has a composition represented in claim 1, wherein in the illustrated) NiMH secondary battery.

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