JP3342699B2 - Hydride battery and method for charging negative electrode thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydride battery and a method for charging a negative electrode thereof.

[0002]

2. Description of the Related Art A hydrogen storage alloy has the ability to store and release a large amount of hydrogen. In a hydride battery using the same as a negative electrode, the negative electrode can electrochemically store a large amount of hydrogen even in an alkaline aqueous solution. Occlusion and release.

The charge / discharge reaction of the negative electrode at this time proceeds according to the following reaction formulas (1) and (2). In the reaction formula, the charge reaction is indicated by an arrow from left to right, and the discharge reaction is indicated by an arrow from right to left. That is, [Equation 1] is a charging reaction, and [Equation 2] is a discharging reaction.

[Negative electrode] [Formula 1] M + H ₂ O + e ⁻ → M (H) + OH ⁻ [Formula 2] M + H ₂ O + e ⁻ ← M (H) + OH ⁻

[0005] M in [Equation 1] and [Equation 2] indicates a hydrogen storage alloy. In the charging reaction, the hydrogen storage alloy M of the negative electrode electrolyzes water in the alkaline aqueous solution to occlude hydrogen as shown in [Equation 1] and becomes a state indicated by M (H). This reverse reaction occurs. That is, charging is storing of hydrogen in the hydrogen storage alloy, and discharging is releasing of hydrogen in the hydrogen storage alloy.

For example, in a hydride battery-based secondary battery having a negative electrode using the above-mentioned hydrogen storage alloy, a positive electrode using nickel hydroxide, and an electrolyte solution composed of an alkaline aqueous solution as an electrolyte, the charge / discharge of the negative electrode The charge / discharge reaction of the positive electrode corresponding to the reaction proceeds according to the following reaction formulas [Formula 3] and [Formula 4]. [Equation 3] is a charging reaction, and [Equation 4] is a discharging reaction.

[Positive electrode] [Equation 3] Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ [Equation 4] Ni (OH) ₂ + OH ⁻ ← NiOOH + H ₂ O + e ⁻

In the charging reaction shown in [Equation 3], the hydroxyl group (OH ⁻ ) generated at the negative electrode reacts with Ni (OH) _{2 of the} positive electrode to form NiOOH, thereby generating water.

[0009]

The hydrogen storage alloy used for the negative electrode is obtained by melting an alloy material in an arc (high frequency) melting furnace, forming it into an ingot, and then pulverizing the alloy by absorbing and releasing hydrogen. , And a negative electrode.

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

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

Therefore, when the negative electrode and the positive electrode on which the oxide layer is formed are combined and discharged in an electrolytic solution, a problem arises in that a predetermined discharge capacity cannot be obtained. In the secondary battery, it is necessary to repeat charging and discharging several times in order to remove the oxide layer.

In order to solve such a problem relating to the hydrogen storage alloy, after assembling the battery, the battery is heated to a high temperature (40 to 70).
C.) for a long time, or a hydrogen storage alloy powder is treated with an alkaline aqueous solution to produce a negative electrode, and so-called activation treatment is performed (for example, Japanese Unexamined Patent Publication No. Sho 63).
146353).

Further, instead of the activation treatment, all the battery manufacturing steps are performed in an inert gas atmosphere or a hydrogen atmosphere.

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

Further, in order to manufacture a battery in a specific atmosphere, a large amount of equipment is required. But,
If the activation of the negative electrode is not sufficiently performed, there arises a problem that a discharge voltage is reduced and a discharge capacity is reduced when the battery is discharged at a large current or a low temperature.

The present invention solves various problems in a hydride battery using the above-mentioned hydrogen storage alloy for a negative electrode, simplifies activation treatment, and has a large current discharge characteristic.
An object is to provide a hydride battery having excellent low-temperature discharge characteristics.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a hydride battery having a positive electrode, a negative electrode containing a hydrogen storage alloy, and an electrolyte, wherein a soluble hydride such as sodium borohydride is contained in a battery system, It is an object of the present invention to provide a technology for simplifying an activation process and improving a large-current discharge characteristic and a low-temperature discharge characteristic by storing hydrogen released from a compound in a negative electrode by storing the hydrogen in the negative electrode.

In order to cause the negative electrode to store hydrogen in the battery and bring it into a charged state, it is preferable to use a soluble hydride as the hydrogen source, and it is particularly preferable to use the soluble hydride contained in an aqueous alkaline solution. is there. As a form in which the soluble hydride is contained in the battery, a soluble hydride such as sodium borohydride may be contained in the electrolytic solution. For example, sodium borohydride (NaBH ₄ ) may be used as the soluble hydride. For example, when it is contained in an electrolytic solution, sodium borohydride is stable in an alkaline aqueous solution and releases hydrogen as shown in [Formula 5] and [Formula 6].

[0020] [Formula 5] ^{_{NaBH 4 → Na + + BH 4}} - [Formula 6] ^{_{BH 4 - + 2H 2 O →}} BO 2 - + 4H 2

A reaction represented by the following [Formula 7] occurs at an equilibrium potential of −1.23 V (vs. Hg / HgO). [Formula 7] BH ₄ ⁻ + 8OH ⁻ → BO ₂ ⁻ + 6H ₂ O + 8e ⁻

The hydrogen generated in the above [Equation 6] is occluded by the negative electrode, and the negative electrode is charged, and the reaction shown in [Equation 7] occurs on the surface of the negative electrode. Is induced.

Since the charging reaction proceeds in this manner,
The oxide layer on the surface of the negative electrode is removed, and as a result, the aging treatment at a high temperature for a long time after the battery is assembled becomes unnecessary, and the activation treatment is simplified.

For example, after assembling the battery, the temperature is adjusted to 0.2 at 25 to 80 ° C.
By storing for 1 to 4 hours, the activation process can be performed, and the time required for the activation process is reduced as compared with the conventional case where the activation process requires a long time exceeding 12 hours. .

In the present invention, examples of the soluble hydride include the above-mentioned sodium borohydride (NaBH).
₄ ), various compounds such as potassium borohydride (KBH ₄ ) and lithium aluminum hydride (LiAlH ₄ ) are used. These soluble hydrides are strong reducing agents, and the reaction shown in the above [Equation 5] to [Equation 7] occurs in a short time with a small amount of addition.

When an electrolytic solution composed of an alkaline aqueous solution is used as the electrolyte, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide or lithium hydroxide is used as the alkaline aqueous solution.

The amount of the soluble hydride when contained in the electrolyte is preferably such that the concentration of the soluble hydride in the electrolyte is in the range of 0.001 to 5% by mass.

When the concentration of the soluble hydride in the electrolyte is 0.0
When the amount is less than 01% by mass, the above [Equation 5] to [Equation 7]
When the amount exceeds 5% by mass, the reactions represented by [Formula 5] to [Formula 7] occur rapidly. There is a risk of peeling off from Particularly preferred concentrations of the soluble hydride in the electrolyte range from 0.2 to 3% by weight.

When the soluble hydride is contained in the electrolytic solution, the soluble hydride may be added to the prepared electrolytic solution, or the soluble hydride may be added at the time of preparing the electrolytic solution to remove the soluble hydride. It may be prepared as an electrolyte solution in a contained state. Furthermore, after assembly of the battery, any of the members in the battery system may be held so that the electrolyte solution contains a predetermined amount of soluble hydride.

In the present invention, as the hydrogen storage alloy used for the negative electrode, for example, Ti ₁₇ Zr
La _0.9 Zr _0.1 N, including ₁₆ V ₂₃ Ni ₃₇ Cr ₇
i _{4. 5} Al _0.5, TiNi system, TiNiZr system, (Ti
_{2-X Zr X V 4-} X Ni) 1-Z Cr 2 (x = 0~1.5,
y = 0.6 to 3.5, z ≧ 0.2) and MmNi ₅ based hydrogen storage alloys. The hydrogen storage alloy refers to an alloy capable of reversibly storing and releasing hydrogen, and is usually synthesized in a state where hydrogen is completely desorbed (released). And
In the negative electrode using the hydrogen storage alloy, charging is storing hydrogen and discharging is releasing hydrogen.

The negative electrode may be manufactured by either a sintering method or a paste method. The method of producing a negative electrode by a sintering method refers to, for example, a method in which a porous metal such as a wire mesh, a punching metal, or an expanded metal is used as a base material, and the above-described hydrogen storage alloy powder is press-bonded thereto, sintered, and formed into a sheet. This is a method of producing a negative electrode by molding into a paste, and the method of producing a negative electrode by the paste method is to paste the hydrogen storage alloy powder together with a binder and the like, and then paste the paste from the porous metal. This is a method in which a negative electrode is produced by attaching to a substrate to be formed, followed by drying and pressure bonding with a press or the like.

As the material used for the positive electrode, for example, nickel monoxide (NiO), nickel dioxide (Ni
O ₂ ), nickel hydroxide such as nickel hydroxide [Ni (OH) ₂ ], and nickel hydroxide. However,
These are when the positive electrode is in a discharged state, and when the positive electrode is in a charged state, the nickel oxide or nickel hydroxide exists as another compound.

The positive electrode is, for example, a sintered type in which a nickel sintered body is used as a base and filled with nickel oxide or nickel hydroxide, or a porous metal such as a wire mesh, a punched metal, an expanded metal, or a metal foam. Is formed into a sheet-like molded body by a paste method or the like in which a nickel oxide or a nickel hydroxide is attached to the substrate, and in the practice of the present invention, for example, a sintered method or a paste method The known nickel electrode prepared in the above can be used.

[0034]

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

Example 1 Commercially available Ti (titanium), Zr (zirconium), V
(Vanadium), weighed Ni a (nickel) and Cr (chromium) so that the composition of _{Ti 17 Zr 16 V 23 Ni 37} Cr 7, dissolved by heating by high frequency melting furnace, a multi-phase alloy having the above composition Obtained.

This alloy was placed in a pressure vessel, the inside of the vessel was evacuated to 1.33 × 10 ⁻² Pa (10 ⁻⁴ torr), and purged three times with Ar (argon). The mixture was held at 1.37 MPa (14 kg / cm ² ) for 24 hours, and after evacuation of hydrogen, the mixture was heated at 400 ° C. and completely devolved with hydrogen to obtain a hydrogen storage alloy powder having a particle size of 20 to 100 μm.

A dispersion of polytetrafluoroethylene was added to 16 g of the hydrogen-absorbing alloy powder and the solid content of the dispersion was 4% of the total weight.
It was added and kneaded so as to give a mass%.

The kneaded material was rolled by a roller to 280 mm
× 38mm × 0.4mm sheet, crimped on nickel current collector (wire diameter 0.178mm, 14 mesh nickel net, nickel end attached to one end) Thus, a negative electrode was produced.

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

The negative electrode and the positive electrode are spirally wound through a separator to form a spiral electrode body as shown in FIG. 1, and the spiral electrode body has the same volume as a single-size battery case. And sealed, thereby producing a battery capable of measuring the internal pressure as shown in FIG.

The spiral electrode body shown in FIG. 1 will be described.
Then, 1 is a positive electrode, and this positive electrode 1 was produced by a sintering method.
It consists of a nickel electrode. 2 is a negative electrode, and this negative electrode 2
Ti ₁₇Zr₁₆V_{twenty three}Ni₃₇Cr₇Occlusion with the composition of
It consists of a molded body containing gold. However, these positive electrodes 1 and negative
A base is used for the pole 2 also as a current collector.
However, if they are shown in FIG.
1 do not show them.

Reference numeral 3 denotes a separator.
Is made of a polyamide non-woven fabric. The positive electrode 1 and the negative electrode 2 are spirally wound through the separator 3 to form a spiral electrode body as shown in the figure.

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

The electrolyte used was prepared by adding 0.2% by mass of sodium borohydride to a 30% by mass aqueous solution of potassium hydroxide.
The injection volume is 6.5 ml. After injecting the electrolyte containing sodium borohydride, 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 0.9 V. This one
The discharge capacity was determined for each cycle when charging and discharging were performed up to six cycles.

Comparative Example 1 A battery was fabricated in the same manner as in Example 1, except that a 30% by mass aqueous solution of potassium hydroxide containing no sodium borohydride was used as an electrolytic solution. This battery was also stored at 60 ° C. for 2 hours after injecting the electrolytic solution, charged and discharged in the same manner as in Example 1, and the discharge capacity of each cycle was examined.

Comparative Example 2 500 ml of a solution prepared by dissolving 0.2% by mass of sodium borohydride in a 30% by mass aqueous sodium hydroxide solution was prepared, and this solution was kept at 25 ° C. Was immersed for 2 hours. Thereafter, the negative electrode was taken out in an inert atmosphere, washed and dried, and a battery was fabricated in the same manner as in Example 1. However, the electrolytic solution used was a 30% by mass aqueous solution of potassium hydroxide, and the injection amount was 6.5.
ml, but this electrolyte solution does not contain sodium borohydride as in Example 1. This battery was also stored at 60 ° C. for 2 hours after injecting the electrolytic solution, charged and discharged in the same manner as in Example 1, and the discharge capacity of each cycle was examined.

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

As shown in FIG. 3, in the battery of Comparative Example 1,
Although it was necessary to repeat charging and discharging five times to reach the rated capacity of 3.5 Ah, the battery of Example 1 reached the rated capacity only by performing charging and discharging twice. In addition, the battery of Example 1 in which the soluble hydride was contained in the electrolytic solution was activated more quickly than the battery of Comparative Example 2 which was configured using the negative electrode immersed in the aqueous alkali solution containing the soluble hydride. Was. In FIG. 3, the measurement points of the curve showing the relationship between the number of charge / discharge cycles and the discharge capacity of the battery of Comparative Example 2 are shown by squares.
The mark is partially shifted leftward from the predetermined position.

This result shows that the content of sodium borohydride in the electrolyte is only 0.2% by mass, so that the number of times of charging and discharging until reaching the rated capacity can be reduced and the activation process can be simplified. Is shown. In addition, it is easier to activate the battery by placing sodium borohydride in the battery and charging the negative electrode in the battery than by assembling the battery using the negative electrode previously charged with sodium borohydride. Is shown.

Example 2 The concentration of sodium borohydride in the electrolyte was 0.1% by mass, 0.2% by mass, 0.5% by mass, 1% by mass, 2% by mass, 3% by mass, and 4% by mass. The battery was assembled in the same manner as in Example 1 except for the above, and stored at 25 ° C., 45 ° C., 60 ° C., and 80 ° C. for 2 hours after the battery assembly.

The battery was charged and discharged in the same manner as in Example 1, and the number of charge and discharge cycles required to reach the rated capacity (3.5 Ah) was examined.

FIG. 4 shows the relationship between the number of charge / discharge cycles required to reach the rated capacity and the concentration of sodium borohydride in the electrolyte at each temperature.

As shown in FIG. 4, by including sodium borohydride in the electrolytic solution, even if its concentration is as low as 0.2% by mass, it does not take until the rated capacity is reached, depending on the temperature. The number of charge / discharge cycles can be reduced.

When the concentration of sodium borohydride is 2% by mass or more, the rated capacity can be reached by two charge / discharge operations even at a normal temperature of 25 ° C.

Next, the battery of Example 1 and Comparative Examples 1 to
Large current at 25 ° C for battery 2 (3C equivalent)
The discharge characteristics in the discharge were examined. The result is shown in FIG. As shown in FIG. 5, it can be seen that the battery of Example 1 in which sodium borohydride was added to the electrolytic solution was improved in both the discharge voltage and the discharge capacity in the large current discharge as compared with the battery of Comparative Example 1. Furthermore, the battery of Example 1 exhibited excellent discharge voltage and discharge capacity as compared with the battery of Comparative Example 2 in which the negative electrode was immersed in an aqueous alkaline solution in which sodium borohydride was dissolved.

FIG. 6 shows the discharge characteristics of the batteries of Example 1 and Comparative Examples 1 and 2 when discharged at 0 ° C. with a discharge current equivalent to 0.5 C. As shown in FIG. 6, it can be seen that the battery of Example 1 in which sodium borohydride was added to the electrolytic solution had improved discharge voltage and discharge capacity at low-temperature discharge as compared with the battery of Comparative Example 1. Furthermore, the battery of Example 1 exhibited excellent discharge voltage and discharge capacity as compared with the battery of Comparative Example 2 in which the negative electrode was immersed in an aqueous alkaline solution in which sodium borohydride was dissolved.

Example 3 An electrolyte was prepared by adding lithium hydroxide at a ratio of 17 g / l to a 30% by mass aqueous solution of potassium hydroxide and containing 0.2% by mass of lithium aluminum hydride. A battery was assembled in the same manner as in Example 1. After the battery was assembled, the battery was stored at 60 ° C. for 2 hours as in Example 1.

When the number of charge / discharge cycles required to reach the rated capacity of this battery was examined, the same results as in Example 1 were shown.

[0060]

As described above, according to the present invention, the activation treatment is performed by causing the soluble hydride to be contained in the battery and storing the hydrogen released from the soluble hydride in the negative electrode to make the battery charged. The simplification was able to improve the discharge characteristics in a large current discharge and the discharge characteristics in a low temperature discharge.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a spiral electrode body in a hydride 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 batteries of Example 1 and the batteries of Comparative Examples 1 and 2 reach the rated capacity.

FIG. 4 is a diagram showing the relationship between the concentration of sodium borohydride in the electrolyte and the number of charge / discharge cycles until the rated capacity is reached in Example 2.

FIG. 5 is a diagram showing the discharge characteristics of the battery of Example 1 and the batteries of Comparative Examples 1 and 2 at large current discharge.

FIG. 6 is a diagram showing discharge characteristics of the battery of Example 1 and the batteries of Comparative Examples 1 and 2 at low temperature discharge.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akira Kawakami 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Ltd. (56) References JP-A-4-206469 (JP, A) JP-A-4 -322068 (JP, A) JP-A-5-225976 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/24-10/30 H01M 4/00-4/62

Claims (5)

(57) [Claims] 1. A hydride battery having a positive electrode, a negative electrode containing a hydrogen storage alloy, and an electrolyte, wherein a soluble hydride is contained in a battery system. 2. The hydride battery according to claim 1, wherein the negative electrode is in a charged state by storing hydrogen released from the soluble hydride. 3. The method according to claim 1, wherein an electrolyte comprising an aqueous alkaline solution containing a soluble hydride is used as the electrolyte, and the concentration of the soluble hydride in the electrolyte is 0.001 to 5% by mass. 3. The hydride battery according to 2. 4. A hydride battery having a positive electrode, a negative electrode containing a hydrogen storage alloy, and an electrolyte containing a soluble hydride, and storing hydrogen released from the soluble hydride in the hydrogen storage alloy of the negative electrode. A method for charging a negative electrode of a hydride battery, the method comprising: 5. The method for charging a negative electrode of a hydride battery according to claim 4, wherein an alkaline aqueous solution containing a soluble hydride is injected into the battery system.