JPH05135797A - Hydride secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To suppress the internal pressure rise of a hydride secondary battery, improve charge/discharge cycle characteristics, simplify the activation treatment, reduce a self-discharge, and improve the discharge characteristic at a large- current discharge and the discharge characteristic at a low-temperature discharge. CONSTITUTION:A soluble hydride such as sodium borohydride is incorporated in an electrolyte, or a negative electrode is dipped in an alkaline aqueous solution dissolved with the soluble hydride such as the sodium borohydride before a battery is assembled, and the negative electrode is treated with a reducing agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydride secondary battery and a method for manufacturing the same.

[0002]

2. Description of the Related Art A hydrogen storage alloy has the ability to store and release a large amount of hydrogen, and a hydride secondary battery using this as a negative electrode electrochemically stores a large amount of hydrogen even in an alkaline aqueous solution. Can occlude and release.

In a hydride secondary battery in which this hydrogen storage alloy is used in the negative electrode and nickel hydroxide is used in the positive electrode, the battery reaction proceeds according to the following reaction formula. In the reaction formula, the charging reaction is indicated by an arrow from left to right, and the discharging reaction is indicated by an arrow from right to left. That is, [Equation 1] and [Equation 3] are charge reactions, and [Equation 2] and [Equation 4] are discharge reactions.

[Positive Electrode] [Formula 1] Ni (OH) ₂ + OH ⁻ → NiOOH +
H ₂ O + e ⁻ [Formula 2] Ni (OH) ₂ + OH ⁻ ← NiOOH +
H ₂ O + e ^-

[Anode] [Formula 3] M + H ₂ O + e ⁻ → M (H) + OH ⁻ [Formula 4] M + H ₂ O + e ⁻ ← M (H) + OH ⁻

M in [Equation 3] and [Equation 4] represents a hydrogen storage alloy. In the charging reaction, the hydrogen storage alloy M of the negative electrode electrolyzes the water in the alkaline aqueous solution to store hydrogen into the state shown by M (H) as shown in [Equation 3], and the hydroxyl group (OH ^- ) Is generated, and the hydroxyl group reacts with Ni (OH) _{2 of the} positive electrode as shown in [Equation 1] to give N.
Becomes iOOH, producing water.

This reverse reaction occurs in the discharge reaction. In other words, charging is the storage of hydrogen in a hydrogen storage alloy,
The discharge results in the release of hydrogen from the hydrogen storage alloy.

This hydride secondary battery is industrially manufactured as a cylindrical sealed battery, and is designed so that the capacity of the negative electrode is larger than that of the positive electrode.

This reduces the polarization during discharge, improves the flatness of the discharge voltage, reduces the oxygen generated from the positive electrode during overcharge on the surface of the negative electrode, and returns it to water so that the internal pressure of the battery is not increased. This is because

At this time, the reaction between the positive electrode and the negative electrode is [Formula 5]-
It becomes like [Formula 7]. [Positive electrode] [Formula 5] 4OH ⁻ → 2H ₂ O + O ₂ + 4e ⁻

[Anode] [Formula 6] 4MH + O ₂ → 4M + 2H ₂ O + Q [Formula 7] 4M + 4H ₂ O + 4e ⁻ → 4MH + 4O
H ^-

[0012]

However, since [Equation 6] is a reaction accompanied by heat generation (shown by Q), the temperature of the negative electrode surface rises, and in the initial charge / discharge cycle, from the relation of the equilibrium hydrogen pressure, Hydrogen dissociates from the negative electrode, increasing the internal pressure of the battery.

By further repeating the charge / discharge cycle, the surface of the negative electrode is gradually oxidized, and the hydrogen storage alloy of the negative electrode is pulverized to increase the polarization and the ability to reduce oxygen as described above to water is reduced. Therefore, the pressure inside the battery increases due to oxygen during overcharge.

In the final charge / discharge cycle, the negative electrode further deteriorates, the capacity is regulated to the negative electrode, a large amount of hydrogen is generated during overcharge, and the pressure in the battery is further increased by a large amount of hydrogen and oxygen. However, this causes leakage of electrolyte and increase in internal resistance.

As a result, the safety of the battery is lowered, and the charge / discharge capacity is lowered, which causes the battery life to be shortened.

Therefore, in order to solve this problem, a method of adding a noble metal catalyst such as platinum to the negative electrode to promote ionization of oxygen gas or a method of providing an oxygen gas absorption layer has been used. However, catalysts such as platinum are expensive and costly, and when the absorption layer is installed inside the battery or in the negative electrode, the filling amount of the active material is reduced and the volume efficiency is reduced.

Further, the hydrogen storage alloy of the negative electrode is used in the production of the negative electrode after melting the alloy material in an arc (high frequency) melting furnace to form an ingot, and then finely pulverizing it by absorbing and releasing hydrogen. There is.

When the negative electrode is produced by a paste method, the above hydrogen storage alloy powder is mixed with a dispersion liquid of polytetrafluoroethylene as a binder, which is applied to a current collector and dried. Thus, the negative electrode is manufactured.

Since this negative electrode is usually produced in air, a thin oxide layer is formed on the surface of the hydrogen storage alloy powder.

Therefore, when the negative electrode having the oxide layer and the positive electrode are combined and discharged in an electrolytic solution, several cycles of charge and discharge are required until the discharge capacity reaches a predetermined value due to the oxide layer. become.

That is, unless the oxide layer is removed by repeating charge and discharge several times, a predetermined discharge capacity cannot be obtained.

Therefore, after the battery is assembled, a high temperature (40 to 70
A so-called activation treatment is carried out such as aging for a long time at (° C.) or treating the hydrogen-absorbing alloy powder with an alkaline aqueous solution before producing the negative electrode (for example, JP-A-63).
No. 146353).

Further, instead of the activation treatment, it is also practiced to carry out all the battery manufacturing steps in an inert gas atmosphere or a hydrogen atmosphere.

However, when aging at a high temperature for a long time, the separator is damaged, and when the hydrogen storage alloy powder is treated with an alkaline aqueous solution, it becomes difficult to handle it in the subsequent production of the negative electrode.

In addition, in order to manufacture a battery in a specific atmosphere, a large amount of equipment is required.

Furthermore, in the hydride secondary battery, self-discharge is promoted by the oxygen generation due to the self-decomposition of the nickel electrode of the positive electrode or the oxygen remaining inside the battery, and the speed thereof is faster than that in the nickel-cadmium battery. For,
The hydride secondary battery also has a problem that the capacity of the battery due to self-discharge is larger than that of the nickel-cadmium battery. Further, in the hydride secondary battery, if the negative electrode is not sufficiently activated, there arises a problem that the discharge voltage is lowered and the discharge capacity is reduced when discharged at a large current or a low temperature.

The present invention solves various problems in the hydride secondary battery as described above, the increase in the internal pressure of the battery is small, the activation treatment can be simplified, the self-discharge is small, and the high-current discharge is small. An object is to provide a hydride secondary battery having excellent characteristics and low-temperature discharge characteristics.

[0028]

The present invention provides a hydride secondary battery having a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, and an electrolytic solution containing an alkaline aqueous solution. Is treated with a reducing agent such as soluble hydride, specifically, the soluble hydride such as sodium borohydride is contained in the electrolytic solution, or the negative electrode is treated with soluble hydrogen such as sodium borohydride. Provided is a technique for suppressing an increase in battery internal pressure, simplifying activation treatment, reducing self-discharge, and improving large-current discharge characteristics and low-temperature discharge characteristics by immersing in an alkaline aqueous solution in which a compound is dissolved. It is a thing.

In treating the negative electrode with the reducing agent, it is preferable to use a soluble hydride as the reducing agent, and it is most preferable to treat it with an alkaline aqueous solution thereof. The form of treatment may include a soluble hydride such as sodium borohydride in the electrolytic solution, but by immersing the negative electrode in an alkaline aqueous solution in which a soluble hydride such as sodium borohydride is dissolved. Good. Therefore, first, using sodium borohydride (NaBH ₄ ) as a soluble hydride and including it in the electrolytic solution, for example, sodium borohydride is stable in an alkaline aqueous solution. [Formula 8], [Formula 9]
Hydrogen is released as shown in.

[Formula 8] NaBH ₄ → Na ⁺ + BH ₄ ⁻ [Formula 9] BH ₄ ⁻ + 2H ₂ O → BO ₂ ⁻ + 4H ₂

The reaction represented by the following [Formula 10] occurs at an equilibrium potential of −1.23 V (vs. Hg / HgO). [Formula 10] BH ₄ ⁻ + 8OH ⁻ → BO ₂ ⁻ + 6H
₂ O + 8e ^-

The hydrogen generated in the above [formula 9] is occluded in the negative electrode, and the reaction shown in the [formula 10] occurs on the surface of the negative electrode, so that the charging reaction of the [formula 3] is induced and the negative electrode is charged. Will be in a state of

Since the charging reaction proceeds in this way,
The oxide layer on the surface of the negative electrode is removed, and as a result, the aging process at high temperature for a long time after the battery is assembled is not required, and the activation process is simplified.

For example, after assembling the battery, the temperature at 25-80 ° C.
By storing for 1 to 4 hours, the activation treatment can be performed, and the time required for the activation treatment is shortened compared to the conventional case where the activation treatment required a long time exceeding 12 hours. ..

Then, in the charge / discharge cycle, when hydrogen is generated inside the battery due to deterioration of the negative electrode, the hydrogen is dissolved in the electrolytic solution, reacts with BO ₂ ^−, and returns to BH ₄ ⁻ again.

That is, the reverse reaction of [Equation 9] occurs, and as a result, the increase of the internal pressure of the battery at the time of overcharge is suppressed by the addition of sodium borohydride, and as a result, the increase of the internal voltage of the battery causes the increase of the overvoltage. And the occurrence of liquid leakage are suppressed, and hydrogen from the negative electrode is suppressed from reaching the positive electrode and causing self-discharge. The above-described suppression effect is similarly produced even when the negative electrode is immersed in an alkaline aqueous solution in which a soluble hydride such as sodium borohydride is dissolved.

In the present invention, examples of the soluble hydride include sodium borohydride (NaBH) described above.
₄ ), potassium borohydride (KBH ₄ ), lithium aluminum hydride (LiAlH ₄ ), and various other compounds are used. These soluble hydrides are strong reducing agents and can be added in a small amount in the above [Formula 8] to [Formula 10].
The reaction shown in 1 occurs in a short time.

The electrolytic solution is composed of an alkaline aqueous solution,
As this alkaline aqueous solution, for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide is used.

The amount of the soluble hydride contained in the electrolytic solution is preferably such that the concentration of the soluble hydride in the electrolytic solution is in the range of 0.001 to 5% by weight. Similarly, when preparing an alkaline aqueous solution for dipping the negative electrode separately, the concentration of the soluble hydride is preferably in the range of 0.001 to 5% by weight.

When the concentration of the soluble hydride in the electrolytic solution or the alkaline aqueous solution is less than 0.001% by weight,
Since the reaction represented by the above [Formula 8] to [Formula 10] does not sufficiently occur, the effect is not sufficiently obtained, and when it exceeds 5% by weight, the reaction represented by [Formula 8] to [Formula 10] rapidly proceeds. Therefore, the hydrogen storage alloy of the negative electrode may be peeled off from the substrate. A particularly preferable concentration of the soluble hydride in the electrolytic solution or the alkaline aqueous solution is in the range of 0.2 to 3% by weight.

When the soluble hydride is contained in the electrolytic solution or the alkaline aqueous solution, the soluble hydride may be added to the prepared electrolytic solution or the alkaline aqueous solution for the negative electrode immersion treatment, or the electrolytic solution or the alkaline aqueous solution may be added. Soluble hydride may be added at the time of preparation to prepare an electrolytic solution or alkaline aqueous solution containing soluble hydride. Further, after the battery is assembled, the electrolyte may be held by any member in the battery system so that the electrolyte contains a predetermined amount of soluble hydride. Separately from the inclusion of the soluble hydride in the electrolytic solution, the negative electrode is preliminarily charged in advance by incorporating it in an alkaline aqueous solution containing a soluble hydride such as sodium borohydride before incorporating the negative electrode into the battery. Even if it does so, the same effect can be obtained.

In the present invention, the hydrogen storage alloy used for the negative electrode is, for example, Ti ₁₇ Zr as used in the examples.
₁₆ V ₂₃ Ni ₃₇ Cr ₇ etc., La _0.9 Zr _0.1 N
i _{4. 5} Al _0.5, TiNi system, TiNiZr system, (Ti
_2-X Zr _X V _4-X Ni) _1-Z Cr ₂ (x = 0 to 1.5,
Examples include hydrogen storage alloys such as y = 0.6 to 3.5, z ≧ 0.2) and MmNi ₅ series. The hydrogen storage alloy is an alloy capable of reversibly storing and releasing hydrogen, and is usually synthesized in a state of completely desorbing (releasing) hydrogen. And
In the negative electrode using this hydrogen storage alloy, charging is storage of hydrogen and discharging is release of hydrogen.

The negative electrode may be produced by either a sintering type or a paste type. The method of producing a negative electrode by a sintering method is, for example, a porous metal such as a wire mesh, a punching metal or an expanded metal is used as a substrate, and the powder of the above hydrogen storage alloy is pressure-bonded to the substrate and sintered to obtain a sheet form. It is a method of producing a negative electrode by molding into a negative electrode, and the method of producing a negative electrode by a paste method is to make the powder of the hydrogen storage alloy into a paste with a binder and the like, and to make the paste from the porous metal. It is a method for producing a negative electrode by applying it to a base body, drying it, and pressing it with a press or the like.

The nickel oxide or nickel hydroxide used for the positive electrode may be, for example, nickel monoxide (Ni).
O), nickel dioxide (NiO ₂ ), nickel hydroxide [Ni (OH) ₂ ], and the like. However, these are when the positive electrode is in a discharged state, and when the positive electrode is in a charged state, the above nickel oxide and nickel hydroxide exist as other compounds.

The positive electrode is, for example, a sintered type in which a nickel sintered body is used as a base material and nickel oxide or nickel hydroxide is filled therein, or a porous metal such as a wire mesh, punching metal, expanded metal, or metal foam. Is used as a base material, and nickel oxide or nickel hydroxide is attached to the base material to form a sheet-shaped molded body. In the practice of the present invention, for example, a sintering type or a paste type is used. The known nickel electrode prepared in 1. can be used.

[0046]

EXAMPLES Next, the present invention will be described more specifically with reference to examples.

Example 1 Commercially available Ti (titanium), Zr (zirconium), V
(Vanadium), Ni (nickel) and Cr (chromium) are weighed so as to have a composition of Ti ₁₇ Zr ₁₆ V ₂₃ Ni ₃₇ Cr ₇ and heated and melted in a high frequency melting furnace to obtain a multiphase alloy having the above composition. Obtained.

This alloy was placed in a pressure-resistant container, the interior of the container was vacuum-sucked to 10 ^-4 torr, and 3 (Ar) was used.
After purging twice, the hydrogen pressure is 24 kg / cm ²
After holding for a period of time and exhausting hydrogen, the hydrogen storage alloy powder having a particle diameter of 20 to 100 μm was obtained by heating at 400 ° C. to completely desorb hydrogen.

A dispersion of polytetrafluoroethylene was added to 16 g of the hydrogen-absorbing alloy powder to obtain a solid content of 4 g of the total weight.
It was added and kneaded so that it would be in a weight percentage.

This kneaded material is rolled by a roller to 280 mm.
Sheets of × 38 mm × 0.4 mm are crimped onto a nickel current collector (having a wire diameter of 0.178 mm and made of a 14-mesh nickel net with a nickel lead body attached to one end). Then, a negative electrode was produced.

A known nickel electrode (240 mm × 38 mm) produced by a sintering method was used for the positive electrode. In order to set the nominal capacity of the battery to 3500 mAh, the negative electrode has a theoretical capacity of 52
The theoretical capacity of the positive electrode is 40 mA.
What was produced so that it might be set to 00 mAh was used.

The negative electrode and the positive electrode are spirally wound via a separator to form a spiral electrode body as shown in FIG. 1, and the spiral electrode body has the same volume as that of a size C battery case. Then, the battery was put into the pressure resistant container and sealed, and a battery capable of measuring the internal pressure as shown in FIG. 2 was produced.

The spiral electrode body shown in FIG. 1 will be described. 1 is a positive electrode, and the positive electrode 1 is a nickel electrode produced by a sintering method. Reference numeral 2 is a negative electrode, and this negative electrode 2 is composed of a molded body containing a hydrogen storage alloy having a composition of Ti ₁₇ Zr ₁₆ V ₂₃ Ni ₃₇ Cr ₇ . However, although the base body is used for the positive electrode 1 and the negative electrode 2 so as to also function as a current collector, it is not shown in FIG. 1 because they are complicated when shown in FIG. ..

3 is a separator, and this separator 3
Is made of polyamide non-woven fabric, and the positive electrode 1 and the negative electrode 2 are spirally wound via the separator 3 to form a spiral electrode body as shown in the drawing.

Explaining the battery shown in FIG. 2, the spiral electrode body 4 is housed in a pressure vessel 5, the negative electrode lead body 6 is spot-welded to the inner wall of the pressure vessel 5, and the positive electrode lead body 7 is an electrode body. 4 Taken out from the acrylic plate portion 8 on the upper side. The electrolytic solution is injected into the pressure-resistant container 5 through the injection port 9, and the injection port 9 is sealed after the injection of the electrolytic solution, which is shown in FIG. The internal pressure of the battery can be read by a gauge (Bourdon gauge) 10.

The electrolytic solution used is 0.2% by weight of sodium borohydride in 30% by weight potassium hydroxide aqueous solution.
It was contained, and the injection amount was 6.5 ml. After injecting the electrolytic solution, the battery was stored at 60 ° C. for 2 hours.

After storage, the battery was charged at 350 mA for 15 hours and discharged at 700 mA to 0.9V. This one
The cycle was taken as a cycle, and the discharge capacity for each cycle when charging / discharging up to 6 cycles was examined.

Example 2 500 ml of a solution prepared by dissolving 0.2% by weight of sodium borohydride in a 30% by weight aqueous solution of sodium hydroxide was prepared, and this solution was kept at 25 ° C., in which the negative electrode in Example 1 was placed. Was immersed for 2 hours. Then, the negative electrode was taken out in an inert atmosphere, washed and dried, and a battery was manufactured in the same manner as in Example 1. However, the electrolyte used was a 30 wt% potassium hydroxide aqueous solution, and the injection amount was 6.5.
However, the electrolytic solution does not contain sodium borohydride as in Example 1. Also for this battery, after injecting the electrolytic solution, it was stored at 60 ° C. for 2 hours and then charged and discharged in the same manner as in Example 1 to examine the discharge capacity for each cycle.

Comparative Example 1 A battery was prepared in the same manner as in Example 1 except that a 30 wt% potassium hydroxide aqueous solution containing no sodium borohydride was used as the electrolytic solution. Also for this battery, after the electrolyte was injected, it was stored at 60 ° C. for 2 hours, then charged and discharged in the same manner as in Examples 1 and 2, and the discharge capacity for each cycle was examined.

The relationship between the number of charge / discharge cycles and the discharge capacity until reaching the rated capacity (3.5 Ah in the case of these batteries) of the batteries of Examples 1 and 2 and Comparative Example 1 is shown in FIG. 3 shows.

As shown in FIG. 3, in the battery of Comparative Example 1,
Although it was necessary to repeat charging and discharging 5 times to reach the rated capacity of 3.5 Ah, the batteries of Examples 1 and 2 reached the rated capacity only by performing charging and discharging twice. Note that FIG.
In the figure, the □ mark representing the measurement point of the curve showing the relationship between the number of charge / discharge cycles and the discharge capacity of the battery of Example 2 is shown by shifting a part to the left from the predetermined position.

This result is obtained by adding 0.2% by weight of sodium borohydride to the electrolytic solution or immersing the negative electrode in an alkaline aqueous solution containing 0.2% by weight of sodium borohydride. This shows that the number of times of charge / discharge until reaching the capacity can be reduced and the activation process can be simplified.

FIG. 4 shows the relationship between the charging time and the battery voltage when the batteries of Examples 1 and 2 and the battery of Comparative Example 1 were charged at 350 mA. 5 shows the relationship between the charging time and the battery internal pressure of the batteries of Examples 1 and 2 and the battery of Comparative Example 1 at the time of charging.

In FIG. 4, the curves of the first and second embodiments and the first comparative example are attached to the curves which are substantially overlapped with each other, which are the batteries of the first and second embodiments and the first comparative example.
This is because both batteries exhibited similar behavior with respect to battery voltage.

That is, as shown in FIG. 4, the battery voltage gradually increases in the same manner for both the batteries of Examples 1 and 2 and the battery of Comparative Example 1 until the charging time reaches 10 hours. If the time exceeds 10 hours, it does not rise any more.

This indicates that these batteries reach 100% charge when they are charged for 10 hours and are overcharged when they are charged further.

However, the internal pressure of the battery is as shown in FIG.
The battery of Comparative Example 1 behaves differently from the time when the charging time exceeds 9 hours, and the battery internal pressure increases from the time when the charging time exceeds 9 hours. The difference between

On the other hand, in the batteries of Examples 1 and 2, the battery internal pressure rises after the charging time exceeds 10 hours, but the increase is small, and the battery internal pressure rises as compared with the battery of Comparative Example 1. Less is. Particularly, in the battery of Example 2 in which the negative electrode was treated, the battery internal pressure was reduced.

The results show that in the batteries of Examples 1 and 2, sodium borohydride existing in the electrolytic solution or in the negative electrode subjected to the immersion treatment acts on the hydrogen storage alloy to contain hydrogen in the alloy. That is, the negative electrode is consequently precharged to promote the activation of the alloy and suppress the non-equilibrium hydrogen generation that occurs during charging. Therefore, in the battery of Example 2 in which the negative electrode was immersed in an alkaline aqueous solution in which sodium borohydride was previously dissolved so that the sodium borohydride directly acts on the hydrogen storage alloy constituting the negative electrode, the internal pressure of the battery could be further suppressed. it can.

Next, the battery of Example 1 and the battery of Comparative Example 1 were charged at 350 mA for 15 hours to obtain 70
FIG. 6 shows the relationship between the number of charge / discharge cycles and the discharge capacity when charging / discharging was repeated at 0 mA to 0.9 V.

As shown in FIG. 6, the battery of Comparative Example 1 has 40
The discharge capacity dropped sharply around 0 cycle and was so-called lost, and the battery could not be used. However, the battery of Example 1 showed almost no decrease in discharge capacity even after 700 cycles of charging / discharging. Held more than%.

Table 1 shows the results of measuring the battery internal pressures of the battery of Example 1 and the battery of Comparative Example 1 at the 50th cycle, the 200th cycle and the 450th cycle during the charging and discharging.

[0073]

[Table 1]

As shown in Table 1, the battery of Comparative Example 1 has 45
After 0 cycles, the battery internal pressure increased to 21 kg / cm ² , but in the battery of Example 1, the battery internal pressure increased to only 5 kg / cm ² even after 450 cycles.

The battery of Example 1 and Comparative Example 1
The battery was stored at 20 ° C. for 30 days, the discharge capacity was measured on each storage day, and the capacity retention ratio with respect to the initial discharge capacity was determined by the following formula.

Capacity retention rate (%) = (A / B) × 100 A: Discharge capacity after storage (mAh) B: Discharge capacity before storage (mAh)

The relationship between the number of days of storage and the capacity retention rate is shown in FIG. As shown in FIG. 7, at the beginning of storage, both the battery of Example 1 and the battery of Comparative Example 1 had almost the same capacity retention rate.
As the storage period increases, a difference occurs between the two, and Example 1
The capacity retention of the battery of No. 1 was larger than that of the battery of Comparative Example 1.

The results show that the self-discharge during storage was suppressed by containing sodium borohydride in the electrolytic solution.

Example 3 The concentrations of sodium borohydride in the electrolytic solution were 0.1% by weight, 0.2% by weight, 0.5% by weight, 1% by weight, 2% by weight, 3% by weight and 4% by weight. And 5% by weight, except that the battery was assembled in the same manner as in Example 1, and after the battery was assembled, it was stored at 25 ° C., 45 ° C., 60 ° C. and 80 ° C. for 2 hours, respectively.

Then, the battery was charged and discharged in the same manner as in Example 1, and the number of charge and discharge cycles until reaching the rated capacity (3.5 Ah) was examined.

FIG. 8 shows the relationship between the number of charge / discharge cycles until reaching the rated capacity and the concentration of sodium borohydride in the electrolytic solution at each temperature.

As shown in FIG. 8, by including sodium borohydride in the electrolytic solution, although depending on the temperature, even when the concentration thereof is as low as 0.2% by weight, it is necessary to reach the rated capacity. The number of charge / discharge cycles can be reduced.

When the concentration of sodium borohydride is 2% by weight or more, the rated capacity can be reached by charging and discharging twice even if the treatment temperature is 25 ° C. and room temperature.

Next, for the batteries of Examples 1 and 2 and the battery of Comparative Example 1, a large current (corresponding to 3 C) at 25 ° C.
The discharge characteristics in discharge were investigated. The result is shown in FIG. As shown in FIG. 9, the battery of Example 1 in which sodium borohydride was added to the electrolytic solution and the battery of Example 2 in which the negative electrode was immersed in an alkaline aqueous solution in which sodium borohydride was dissolved were both Comparative Example 1 It can be seen that both the discharge voltage and the discharge capacity in large current discharge are improved as compared with the battery of No. Among them, the battery of Example 1 in which sodium borohydride was added to the electrolytic solution exhibited particularly excellent discharge voltage and discharge capacity.

Further, FIG. 10 shows the discharge characteristics of the batteries of Examples 1 and 2 and Comparative Example 1 when discharged at 0 ° C. with a discharge current equivalent to 0.5 C. As shown in FIG.
The battery of Example 1 in which sodium borohydride was added to the electrolytic solution and the battery of Example 2 in which the negative electrode was immersed in an alkaline aqueous solution in which sodium borohydride was dissolved were both discharged at a lower temperature than the battery of Comparative Example 1. It can be seen that both the discharge voltage and the discharge capacity are improved. Above all,
The battery of Example 1 in which sodium borohydride was added to the electrolytic solution exhibits particularly excellent discharge voltage and discharge capacity.

Example 4 As the electrolytic solution, except that lithium hydroxide was added to a 30 wt% potassium hydroxide aqueous solution at a rate of 17 g / l and lithium aluminum hydride was contained at 0.2 wt% was used. A battery was assembled in the same manner as in Example 1, and after the battery was assembled, it was stored at 60 ° C. for 2 hours as in Example 1.

With respect to this battery, the number of charge / discharge cycles required to reach the rated capacity, the relationship between the charging time and the battery internal pressure, the change in the battery internal pressure due to the charge / discharge cycle, and the like were examined. The results are shown.

[0088]

As described above, according to the present invention, the negative electrode is treated with a reducing agent by containing the soluble hydride in the electrolytic solution or immersing the negative electrode in an alkaline aqueous solution in which the soluble hydride is dissolved. By processing, suppress the rise in battery internal pressure, improve the charge-discharge cycle characteristics,
It was possible to simplify the activation process, reduce self-discharge, and improve the discharge characteristics in large current discharge and discharge characteristics in low temperature discharge.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a spiral electrode body in a hydride secondary battery of the present invention.

FIG. 2 is a schematic perspective view of a battery capable of measuring a battery internal pressure.

FIG. 3 is a diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity until the rated capacities of the batteries of Examples 1 and 2 and the battery of Comparative Example 1 are reached.

FIG. 4 is a diagram showing the relationship between the charging time and the battery voltage of the batteries of Examples 1 and 2 and the battery of Comparative Example 1.

5 is a diagram showing the relationship between the charging time and the battery internal pressure of the batteries of Examples 1 and 2 and the battery of Comparative Example 1. FIG.

FIG. 6 is a diagram showing a change in discharge capacity with an increase in the number of charge / discharge cycles of the battery of Example 1 and the battery of Comparative Example 1.

FIG. 7 is a diagram showing changes in the capacity retention rate of the battery of Example 1 and the battery of Comparative Example 1 as the number of days of storage increased.

8 is a diagram showing the relationship between the concentration of sodium borohydride in the electrolytic solution and the number of charge / discharge cycles until reaching the rated capacity in Example 3. FIG.

FIG. 9 is a diagram showing discharge characteristics of the batteries of Examples 1 and 2 and the battery of Comparative Example 1 at large current discharge.

FIG. 10 is a diagram showing discharge characteristics at low temperature discharge of the batteries of Examples 1 and 2 and the battery of Comparative Example 1.

[Explanation of symbols]

 1 positive electrode 2 negative electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Kawakami 1-88, Tora, Ibaraki, Osaka Prefecture Hitachi Maxell Co., Ltd.

Claims (9)

[Claims] 1. In a hydride secondary battery having a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, and an electrolytic solution containing an alkaline aqueous solution, the negative electrode is treated with a reducing agent. A hydride secondary battery characterized by the above. 2. The hydride secondary battery according to claim 1, wherein the reducing agent is a soluble hydride. 3. The hydride secondary battery according to claim 1, wherein the reducing agent is an alkaline aqueous solution of a soluble hydride. 4. A hydride secondary battery having a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, and an electrolytic solution comprising an alkaline aqueous solution, wherein the electrolytic solution is sodium borohydride or the like. A hydride secondary battery containing a soluble hydride. 5. The hydride secondary battery according to claim 4, wherein the soluble hydride is sodium borohydride and its concentration in the electrolytic solution is 0.001 to 5% by weight. 6. After assembly of the battery, 0.1 to 4 at 25 to 80 ° C.
The method for manufacturing a hydride secondary battery according to claim 4, wherein the method is storage for a time. 7. In manufacturing a hydride secondary battery having a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, and an electrolytic solution containing an alkaline aqueous solution, the negative electrode is sodium borohydride or the like. A method for producing a hydride secondary battery, which comprises immersing the soluble hydride in 1. in an aqueous alkaline solution. 8. The hydride according to claim 7, wherein the soluble hydride is sodium borohydride and the concentration of sodium borohydride in the alkaline aqueous solution is 0.001 to 5% by weight. Next battery manufacturing method. 9. The method for producing a hydride secondary battery according to claim 7, wherein the temperature of the alkaline aqueous solution in which the soluble hydride is dissolved is 25 to 80 ° C.