JP3316687B2 - Nickel-metal hydride storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, a negative electrode using an electrochemical oxidation-reduction reaction of hydrogen for an electromotive reaction, and a hydroxide. The present invention relates to a nickel-metal hydride storage battery including a non-sintered positive electrode containing nickel as a main active material.

[0002]

2. Description of the Related Art A nickel-metal hydride storage battery is provided with a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, a negative electrode using an electrochemical oxidation-reduction reaction of the hydrogen for an electromotive reaction, A positive electrode using nickel hydroxide as an active material,
An alkaline electrolyte such as a potassium hydroxide aqueous solution.

The negative electrode is called a hydrogen storage electrode, and the hydrogen storage alloy used for this electrode includes LaNi ₅ , ZrNi ₂ , TiNi
And intermetallic compounds such as Ti ₂ Ni, and those obtained by substituting constituent elements of these intermetallic compounds with other elements. If the composition of these hydrogen storage alloys is different, properties such as the amount of hydrogen storage, the equilibrium hydrogen pressure, and the storage capacity characteristics when charging and discharging are repeated in an alkaline electrolyte will change. Attempts have been made to improve the performance of the storage electrode.

When this hydrogen storage electrode is compared with a cadmium electrode operating in the same alkaline electrolyte, the operating potentials of these electrodes are almost the same, and the discharge capacity per electrode volume is such that the hydrogen storage electrode is a cadmium electrode. 2 to 3 times as large as Therefore, when a hydrogen storage electrode is used as the negative electrode of a conventional alkaline storage battery using a cadmium electrode, the volume of the negative electrode is reduced and the volume of the positive electrode is reduced so that the ratio of the discharge capacity between the positive electrode and the negative electrode becomes constant. Therefore, an alkaline storage battery having the same operating voltage as a storage battery using a cadmium electrode and having a discharge capacity 1.5 times or more can be obtained.

As the nickel hydroxide electrode as the positive electrode of this battery, a sintered or non-sintered type used for nickel-cadmium storage batteries has been used.

[0006] A sintered nickel hydroxide electrode is obtained by impregnating a porous substrate obtained by sintering carbonyl nickel or the like with a solution mainly composed of a nickel salt and neutralizing the solution with an alkali solution, or using the cathode as a cathode. In this method, nickel hydroxide is filled in the pores of the nickel sintered body with nickel hydroxide by pyrolyzing the nickel salt by heating or electrolyzing the substrate.

[0007] Since the sintered nickel hydroxide electrode has a pore diameter of the nickel sintered body significantly smaller than that of the foam used for the substrate of the non-sintered nickel electrode, the active material powder can be directly filled. Have difficulty. In addition, since the concentration of nickel contained in a single volume of the nickel salt solution is significantly lower than the concentration of nickel contained in a unit volume of nickel hydroxide having a desired packing density, a practical active material filling rate is reduced. In order to obtain an electrode, it is necessary to repeat the active material filling step. Therefore, the sintered nickel hydroxide electrode has excellent high-rate discharge characteristics, but has a high manufacturing cost.

[0008] The non-sintered nickel hydroxide electrode is formed by adding an alkali-resistant conductive three-dimensional porous body made of foamed nickel or a sintered nickel fiber to an active material powder mainly composed of nickel hydroxide and a metal. At least one selected from the group consisting of cobalt, cobalt hydroxide, and cobalt oxide
And an additive consisting of two components.

[0009] Unlike the sintered nickel hydroxide electrode, this positive electrode has a sparse nickel network.
The current collecting property in the electrode is not high. Therefore, a method of adding at least one powder selected from the group consisting of cobalt metal, cobalt hydroxide, and cobalt oxide is used. These additives are oxidized when the positive electrode is charged, and have a great effect of facilitating discharge of nickel hydroxide, which is a positive electrode active material, and increasing the active material utilization of the positive electrode. This electrode is excellent in productivity but inferior in high-rate discharge characteristics.

[0010]

When the nickel electrode used in a nickel metal hydride storage battery is overcharged with a current larger than, for example, one hour, the nickel hydroxide charge product has a γ phase. A compound called nickel oxyhydroxide is easily formed. Since the compound of the γ phase has a large molar volume, when it is generated, the positive electrode plate expands to absorb the electrolyte solution in the separator or to decrease the strength of the positive electrode plate. In addition, since the water and potassium ions are inserted into the crystal of the γ phase, it is considered that the electrolyte is further absorbed.

When such a phenomenon occurs, the electrolyte in the separator is absorbed by the positive electrode during the repetition of the charge / discharge cycle, and the amount of the electrolyte in the separator is reduced.
The internal resistance of the metal hydride storage battery is increased, making it difficult to charge and discharge the battery, resulting in a disadvantage that the charge and discharge cycle life of the battery is shortened.

Conventionally, the performance of nickel hydroxide electrodes has been studied in detail in nickel-cadmium batteries, and various measures have been taken to suppress the γ phase of nickel hydroxide electrodes. Therefore, in the conventional nickel-metal hydride storage battery, the means performed in the nickel-cadmium storage battery has been adopted in order to suppress the generation of the γ phase of the positive electrode. Specifically, as in the case of a nickel cadmium battery, a method of coprecipitating cadmium with nickel hydroxide or adding an oxide or hydroxide of cadmium as another phase with nickel hydroxide. is there.

However, these means have the following disadvantages.

According to the means for adding cadmium, the formation of the γ phase of nickel hydroxide can be suppressed. When cadmium is added, the means of adding cadmium oxide or cadmium hydroxide without co-precipitation with nickel hydroxide suppresses the formation of γ phase compared to the means of co-precipitating cadmium with nickel hydroxide. The effect is great. However, it is suspected that cadmium is a cause of environmental pollution. And in nickel / metal hydride storage batteries,
Unless cadmium is added to the positive electrode, a battery containing no cadmium can be obtained. Therefore, it is desired not to use cadmium for the positive electrode.

Therefore, a nickel-metal hydride storage battery which does not add cadmium and suppresses an increase in the internal resistance of the battery as the charge / discharge cycle progresses has been desired.

[0016]

In order to solve the above-mentioned problems, the present invention comprises a non-sintered positive electrode mainly composed of nickel hydroxide and a negative electrode mainly composed of a hydrogen storage alloy. In a nickel-metal hydride battery, the nickel hydroxide provides a nickel-metal hydride battery containing magnesium hydroxide on the surface of the nickel hydroxide powder . Further, in order to further enhance the effect, the nickel hydroxide contains, in addition to magnesium hydroxide, nickel hydroxide containing cobalt hydroxide co-precipitated with nickel hydroxide in nickel hydroxide. I will provide a.

[0017]

According to the means of the present invention, a nickel-metal hydride storage battery is charged even when cadmium is not added,
Generation of the γ phase of the positive electrode is effectively suppressed. As a result, absorption of the electrolytic solution in the separator by the positive electrode is effectively suppressed, and the charge / discharge cycle life of the nickel-metal hydride storage battery is extended.

In the meantime, part of the magnesium added to the nickel hydroxide powder by the means of the present invention is dissolved in the alkaline electrolyte. When the nickel hydroxide electrode is combined with a cadmium electrode to form a nickel-cadmium storage battery, the magnesium eluted in the electrolytic solution moves to the cadmium electrode, making it extremely difficult to charge the cadmium electrode. Occurs.

However, in the present invention, since this nickel hydroxide electrode is combined with a hydrogen storage electrode to constitute a nickel metal hydride storage battery, the negative electrode is not a cadmium electrode but a hydrogen storage electrode. No inconvenience occurs.

That is, although the nickel hydroxide electrode constituting the present invention has disadvantages when applied to the positive electrode of a nickel-cadmium storage battery, it is applied to the positive electrode of a nickel-metal hydride storage battery as in the present invention. In such a case, the operation and effect of extending the charge / discharge cycle life as described above can be obtained without causing such inconvenience.

[0021]

EXAMPLES [accumulator (A1)] (Comparative Example) 蓄 cell (A1) was constructed as follows.

The positive electrode was manufactured as follows. That is, an aqueous solution of sodium hydroxide is added to a mixed aqueous solution of nickel sulfate and magnesium sulfate, and the activity of nickel hydroxide in which 5 mol% of magnesium hydroxide is coprecipitated with respect to the total of nickel hydroxide and magnesium hydroxide is added. Material powder (a) was produced. 95 parts by weight of this active material powder and 5 parts by weight of cobalt hydroxide powder were mixed, and purified water was added thereto and kneaded to prepare a paste-like mixture. Next, the porosity is about
This paste-like mixture is filled into a foamed nickel porous body having a thickness of about 0.7 mm at 98 %%, dried, pressed and cut, and the active material filled portion has a thickness of 0.55 mm and a width of 14 mm. , Length 57
mm non-sintered nickel hydroxide electrode was obtained.

The negative electrode was manufactured as follows. That is, the composition of the alloy is LmNi _3.8 Co _0.7 Al _0.5 (where Lm is about 9
A lanthanum-rich misch metal which is a rare earth metal mixture containing 0% by weight of La. ), Each component element was melted in a high-frequency induction heating furnace in a vacuum, and the obtained ingot was pulverized to obtain a hydrogen storage alloy powder having an average particle size of about 30 μm. Next, 100 parts by weight of this alloy powder and 3 parts by weight of carbon black were mixed, and 40 parts by weight of a 3% by weight aqueous solution of polyvinyl alcohol was added thereto to prepare a paste-like mixture. Then, a perforated steel plate with a thickness of about 0.08 mm (plated area of about 50
%), Apply the paste-like mixture (a), adjust the thickness with a doctor blade, dry, pressurize, and cut. The active material carrier has a thickness of 0.30 mm and a width of 0.30 mm. Was obtained and a hydrogen storage electrode having a length of 58 mm was obtained.

One battery has four positive plates and a negative plate.
5 sheets and a thickness of 0.10 mm given hydrophilicity by a surfactant
And laminated using one polypropylene separator. This laminated body was housed in a nickel-plated iron prismatic battery case with a thickness of about 0.4 mm, and an electrolyte solution in which 10 g / l lithium hydroxide was dissolved in a 7 M aqueous potassium hydroxide solution was injected. The periphery of the metal lid provided with the safety valve also serving as the terminal was welded to the periphery of the battery case to seal the battery. Thus, a sealed nickel-metal hydride storage battery (A1) of a comparative example was manufactured.

The positive electrode of one battery is filled with about 3.0 g of nickel hydroxide and about 0.167 g of cobalt hydroxide. Assuming that nickel hydroxide follows a one-electron reaction, the theoretical capacity of nickel hydroxide contained in one positive electrode of this battery is about 870 mAh (= 289 × 3.0).

On the other hand, the negative electrode of one battery contains about 4.6 g of a hydrogen storage alloy. When charging and discharging this hydrogen storage alloy, the amount of electricity charged without releasing hydrogen gas is about 270 m / g of this hydrogen storage alloy.
Ah, and this charged amount of electricity is discharged almost as it is. Therefore, the hydrogen storage alloy of the negative electrode of one battery is charged without generating hydrogen gas until the charged amount of electricity becomes about 1240 mAh (= 270 × 4.6). [Storage battery (A2)] (Example of the present invention) Instead of the positive electrode active material (A) of the storage battery (A1), nickel hydroxide powder not coprecipitating with magnesium hydroxide was immersed in an aqueous solution of magnesium sulfate, and then water was added. By reacting with an aqueous solution of sodium oxide, magnesium hydroxide of 5 mol% with respect to the total of nickel hydroxide and magnesium hydroxide is deposited on the surface of the nickel hydroxide powder, and the positive electrode active material powder (a) is produced. Made. Then, instead of the positive electrode active material (A) in the storage battery (A1), a positive electrode active material (A) is used, and other configurations are the same as those of the storage battery (A1).
Sealed nickel-metal hydride storage battery of the present invention (A2)
Was made. [Storage Battery (A3)] ( Comparative Example) Instead of the positive electrode additive (A) of the storage battery (A1), an aqueous sodium hydroxide solution was added to a mixed aqueous solution of nickel sulfate, magnesium sulfate, and cobalt sulfate, and magnesium hydroxide and A positive electrode active material powder (C) comprising nickel hydroxide to which cobalt hydroxide was added by coprecipitation was produced.
The positive electrode active material (c) includes nickel hydroxide, magnesium hydroxide, and cobalt hydroxide,
Magnesium hydroxide and cobalt hydroxide are each contained in an amount of 2.5 mol%. Then, a sealed nickel-metal hydride storage battery (A3) of a comparative example was manufactured in the same manner as the storage battery (A1) except that the positive electrode active material (A) was used instead of the positive electrode active material (A). did. Instead of the storage battery (A4)] (invention examples) cathode active material of the battery (A1) (a), by adding an aqueous solution of sodium hydroxide in a mixed aqueous solution of nickel sulfate and cobalt sulfate, coprecipitated cobalt hydroxide To prepare a powder mainly composed of the added nickel hydroxide. Then, the powder mainly composed of nickel hydroxide is immersed in an aqueous solution of magnesium sulfate, and then reacted with an aqueous solution of sodium hydroxide to precipitate magnesium hydroxide on the surface of the powder mainly composed of nickel hydroxide. A positive electrode active material powder (d) was produced. This positive electrode active material (d) contains 2.5% by mole of each of magnesium hydroxide and cobalt hydroxide based on the total of nickel hydroxide, magnesium hydroxide, and cobalt hydroxide.
Then, the sealed nickel-metal hydride storage battery (A4) of the present invention is manufactured in the same manner as the storage battery (A1) except that the positive electrode active material (A) is used instead of the positive electrode active material (A). did.

[0027]

[0028]

[0029]

[0030]

[0031] [battery (C1)] (Comparative Example) without co-precipitation of calcium hydroxide in the positive electrode active material of the battery (A1), other configurations are the same as the storage battery (A1), sealed in Comparative Example A nickel-metal hydride storage battery (C1) was manufactured. [Storage battery (C2)] (Comparative example) The sealed nickel-metal of the comparative example is the same as the storage battery (A3) without co-precipitating magnesium hydroxide on the positive electrode active material of the storage battery (A3). A hydride storage battery (C2) was manufactured. [Storage Battery (E1)] (Comparative Example) The following cadmium negative electrode (H) was used without using a hydrogen storage electrode as a negative electrode of the storage battery (A1). In this battery, the thickness of the battery was increased by an amount corresponding to the increase in the thickness of the negative electrode plate, as compared with the storage battery (A1). The other configuration was the same as that of the storage battery (A1), and a sealed nickel-cadmium storage battery (E1) of a comparative example was manufactured.

The negative electrode (h) of this battery was manufactured as follows. That is, 100 parts by weight of cadmium oxide powder,
And 30 parts by weight of metal cadmium powder, and
A paste-like mixture was prepared by adding 40 parts by weight of an aqueous solution of polyvinyl alcohol having a weight percentage of 40%. Then, a perforated steel plate with a thickness of about 0.08 mm made of nickel plated iron plate (opening ratio is about
50%), apply this paste-like mixture, adjust the thickness with a doctor blade, dry, press and cut, the active material carrying part has a thickness of 0.6 mm and a width of 15 mm , Length 0.5
An cadmium electrode of 8 mm was obtained. In the cadmium electrode, of the metal cadmium, which is a charge product, the amount of difficulty in discharging is significantly larger than that of the hydrogen storage electrode, so that it acts as a charge product so as to limit the discharge of the battery at the positive electrode. Metal cadmium powder is provided in advance.

[0033] The battery one negative electrode, about 3.1g of cadmium oxide and approximately 0.93g of: metal cadmium (theoretical capacity of about 440 mAh) is contained. [Storage Battery (E2)] (Comparative Example) In addition to using a cadmium negative electrode (H) instead of the hydrogen storage electrode of the negative electrode of the storage battery (A2), the thickness of the battery was increased by the increase in the thickness of the negative electrode. A sealed nickel-cadmium storage battery (E2) of a comparative example was manufactured in the same manner as the storage battery (A2). [Storage Battery (E3)] (Comparative Example) In addition to using a cadmium negative electrode (h) instead of the hydrogen storage electrode of the negative electrode of the storage battery (A3), the thickness of the battery was increased by the increase in the thickness of the negative electrode. The sealed nickel-cadmium storage battery (E3) of the comparative example was manufactured in the same manner as the storage battery (A3). [Storage Battery (E4)] (Comparative Example) In addition to using a cadmium negative electrode (h) instead of the hydrogen storage electrode of the negative electrode of the storage battery (A4), the thickness of the battery was increased by the increased thickness of the negative electrode. The sealed nickel-cadmium storage battery (E4) of the comparative example was manufactured in the same manner as the storage battery (A4). [Experiment] For the formation of the ten types of storage batteries described above, two charge / discharge cycles were performed under the following conditions before the charge / discharge cycle.

Charging: current is supplied at a current of 80 mA for 16 hours.
Leave for a time.

Discharge: terminal voltage 1.0 V at a current of 160 mA
And let stand for 1 hour.

The charge / discharge cycle life test of these batteries was performed under the following conditions. The charge and discharge of the battery were performed at 20 ° C.

Charging: electricity is supplied at a current of 800 mA for 1.2 hours and left for 30 minutes.

Discharge: terminal voltage 1.0 V at a current of 800 mA
And let stand for 30 minutes.

The internal resistance of the battery during this test was 1 KH
z was measured by the AC method, and the number of charge / discharge cycles until the value reached 5 times the value of the internal resistance after charge / discharge in the initial formation was determined as the charge / discharge cycle life of the battery. Further, the leakage of the electrolyte solution during charging was observed by observing the safety valve of the battery.

Table 1 shows the charge / discharge cycle life of the battery and the presence or absence of leakage of the electrolyte in this test.

[0041]

[Table 1]

That is, the nickel-cadmium storage batteries (E1), (E2), (E3) and (E4) of the comparative examples
In this case, the electrolyte leaks, the internal resistance of the battery increases, and the charge / discharge cycle life is significantly shortened. This is because magnesium added to the positive electrode moves to the negative electrode and the cadmium charging reaction is hindered, and a large amount of hydrogen gas is generated from the negative electrode during charging of the battery, resulting in a significant increase in the internal pressure of the battery. , The safety valve opens and the electrolyte overflows,
This is because the internal resistance of the battery has increased.

A sealed nickel-metal hydride storage battery (C1) of a comparative example having no positive electrode provided with magnesium and
In the case of (C2) and (C2), although the internal short circuit and leakage of the electrolyte do not occur as in the sealed nickel-cadmium storage battery, the internal resistance is increased, and the charge / discharge cycle life is about 600 cycles.

On the other hand, each of the sealed nickel-metal hydride storage batteries (A2) and (A4) of the present invention has a capacity of 800 volts without causing an internal short circuit of the battery or leakage of the electrolyte.
Even if the charge and discharge are performed for more than one cycle, the internal resistance does not increase. This is because the co-precipitation of magnesium in the positive electrode active material and the formation of magnesium on the surface of the positive electrode active material effectively suppressed the generation of the γ phase in the positive electrode.

In addition, the nickel of Examples of the present invention and Comparative Examples
A comparison of metal hydride storage batteries shows that:

That is, the charge / discharge cycle life is (A
2) is longer than (A1), (A4) is longer than (A3)
Long . Therefore, in both cases where and without coprecipitation of cobalt hydroxide with nickel hydroxide, magnesium hydroxide is more likely to precipitate on the surface of nickel hydroxide than co-precipitate with nickel hydroxide. It can be said that the charge / discharge cycle life of the hydride storage battery is prolonged.

The charge / discharge cycle life of (A3) is longer than (A1), (A4) is longer than (A2),
(B3) is longer than (B1) and (B4) is longer than (B2). Therefore, in both the case where magnesium hydroxide is co-precipitated on nickel hydroxide and the case where magnesium hydroxide is precipitated on the surface of nickel hydroxide, it is more preferable to co-precipitate cobalt hydroxide on nickel hydroxide than in nickel-metal hydride storage batteries. It can be said that there is an effect of prolonging the charge / discharge cycle life.

In the above embodiment, the total amount of magnesium hydroxide and cobalt hydroxide added to the positive electrode is
Although the case where the amount is fixed to 5 mol% with respect to the total of nickel hydroxide, magnesium hydroxide and cobalt hydroxide has been described, the operation and effect of the present invention are limited to the case of such a specific addition rate. If it is 0.5 mol% or more, a substantial effect can be obtained. However, if the addition ratio is too high, the content of the active material is reduced, so that the discharge capacity per volume of the positive electrode is reduced. Therefore,
The upper limit of the rate of addition of these additives varies for design reasons by those skilled in the art. Substantially, it is desirable to add in a range of 20 mol% or less based on the total of nickel hydroxide, magnesium hydroxide and cobalt hydroxide.

Further, in the above embodiment, the case where magnesium hydroxide and cobalt hydroxide are added together and used at a specific ratio has been described. The mixing ratio according to the design requirement can be appropriately changed and used.

Further, in the above embodiment, the case where the non-sintered nickel hydroxide electrode is used as the positive electrode and the foamed nickel porous material is used as the alkali-resistant conductive support has been described. , Sintered nickel fiber, punched metal, expanded metal,
When a metal net or the like is used, the same operation and effect can be obtained.

In the above embodiment, the case where a rare earth alloy having a specific composition is used as the hydrogen storage alloy of the negative electrode has been described. Alloys with different types of metal elements and compounding ratios, alloys with rare earth elements added with a small amount of Zr, Ti, Hf, etc., and stoichiometric ratios close to ZrNi ₂ that partially replace Zr and Ni with other metals The same operation and effect can be obtained when an alloy substituted with, a TiNi alloy or an alloy partially substituted with a dissimilar metal is used.

In the above embodiment, the case where a plastic bonding electrode is used as the hydrogen storage electrode of the negative electrode has been described. In addition, the hydrogen storage alloy may be converted into an alkali-resistant conductive porous body such as a foamed nickel porous body. Similar effects can be obtained when a filled electrode or an electrode made of a sintered body of a hydrogen storage alloy is used.

Further, in the above embodiment, the case where a nickel-metal hydride storage battery having a rectangular outer shape formed by laminating rectangular electrodes has been described. Similar effects can be obtained even when the shape is different, such as a cylindrical shape or a cylindrical shape in which disk-shaped electrodes are stacked.

In the above embodiment, the sealed type battery was described. However, in the case of an open type battery having a large amount of liquid, the thickness of the positive electrode due to the progress of the charge / discharge cycle can be increased according to the structure of the present invention. Since the increase in the battery thickness is suppressed, an effect of suppressing the increase in the thickness of the battery is achieved.

In the above embodiment, the case where a non-sintered nickel hydroxide electrode is used for the positive electrode and cobalt hydroxide is added in addition to the nickel hydroxide powder has been described. Similar effects can be obtained when cobalt oxide or cobalt metal is added alone, or when two or more selected from the group consisting of cobalt hydroxide, cobalt oxide, and cobalt metal are used. However, when metal cobalt is used, the amount of electricity required to oxidize cobalt to trivalent increases, so that cobalt hydroxide or cobalt oxide is used to prevent the generation of hydrogen from the negative electrode at the end of charging. As compared with the case, an extra hydrogen storage alloy needs to be used for the negative electrode.

[0056]

As described above, by adopting the means of the present invention, it is possible to suppress the increase in the internal resistance of the battery accompanying the progress of the charge / discharge cycle without using cadmium for the positive electrode and to reduce the charge / discharge cycle. A long-life nickel-metal hydride storage battery is obtained.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-78965 (JP, A) JP-A-2-109261 (JP, A) JP-A 64-3958 (JP, A) JP-A-5-95 21064 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/24-4/34 H01M 4/52

Claims (2)

(57) [Claims] The method according to claim 1 nickel hydroxide positive electrode of non-sintered to main active material, nickel and a negative electrode made mainly of a hydrogen storage alloy - in metal hydride storage battery, on the surface of the water nickel oxide powder, A nickel-metal hydride storage battery comprising magnesium hydroxide. 2. The nickel hydroxide according to claim 1, wherein the nickel hydroxide contains, in addition to magnesium hydroxide, cobalt hydroxide co-precipitated with nickel hydroxide in the nickel hydroxide. -Metal hydride storage batteries.