JPS6180771A - Enclosed type metallic oxide/hydrogen storage battery - Google Patents

Abstract

PURPOSE:To obtain a storage battery having an hydrogen occluded alloy negative electrode with a positive and a negative electrode capacity condition of objective one without making hydrogen atmosphere at all the processes by adding alcohol and lithium hydroxide into an electrolyte. CONSTITUTION:Alcohol, which is selected from lithium hydroxide or methanol or propanol, is added to an electrolytic liquid which is consisting of potassium hydroxide or sodium hydroxide as sub-component of it. Alcohol corresponding to negative electrode capacity to be charged excessively is added into the electrolytic liquid, and when the charging is performed, a positive electrode is not being charged, on the contrary, since the negative electrode is being charged ordinary, the proper charging condition of the positive and negative electrode is realized. And, by adding designated amount of lithium hydroxide into the electrolyte, the produced CO3<2-> ion is precipitated as Li2CO3, and the reducing of the CO3<2-> ion concentration can be obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a sealed metal oxide with a hydrogen storage alloy as a negative electrode.
Concerning improvements to hydrogen storage batteries.

[Technical background of the invention and its problems]

Sealed metal oxide/hydrogen storage batteries that use a metal oxide electrode for the positive electrode and a hydrogen storage alloy for the negative electrode have recently been attracting attention as high energy density batteries. This storage battery is a type of alkaline storage battery, and when assembling it, its basic structure, configuration, etc. must be the same as, for example, a nickel-cadmium storage battery. One of the important characteristics of such a storage battery is the capacity balance between the positive and negative electrodes.

Sealed alkaline batteries are usually assembled in such a way that the electrode capacity is greater at the negative electrode than at the positive electrode. and,
When all processes are completed and the storage battery is completed, part of the excess negative electrode capacity must be in a charged state, and the remaining part must be in an uncharged state. . The reason for this is that only when the capacity state of the positive and negative electrodes achieves the state described above, the internal pressure of the battery will not rise during overcharging, the maximum number of customers will be obtained during discharging, and the battery life will not deteriorate easily. It is.

By the way, in order to assemble an alkaline storage battery having the capacity states of the positive and negative electrodes described above, it is necessary to charge the negative electrode in advance by the required amount. Therefore, in 2.Kel cadmium storage batteries, a method is usually adopted in which the cadmium negative electrode is charged in advance during the chemical formation process. The cadmium negative electrode charged to the required amount during the chemical formation process is washed with water.

After drying, it is assembled into a sealed container together with the positive electrode.

However, if we try to apply the same process to the cadmium negative electrode to the hydrogen storage alloy negative electrode of a sealed metal oxide/hydrogen storage battery, since the charged and active material is hydrogen, hydrogen will be easily extracted in the process after the chemical formation process. I'll let it out.

That is, in air, hydrogen burns on the surface of the hydrogen storage alloy negative electrode, and in inert gas, although no combustion occurs, it is immediately released.

In order to prevent such loss of hydrogen, it is necessary to carry out all processes after the chemical conversion step in an atmosphere having a hydrogen partial pressure that is at least higher than the equilibrium plateau pressure of the hydrogen storage alloy used in the negative electrode. However, in such a case, the following problems arise. In other words, when materials used for battery assembly are transferred between a process adjusted to a hydrogen atmosphere and a process using a normal air atmosphere, the hydrogen may ignite, resulting in dangerous work. Become. If we try to prevent this, we will need beautiful equipment and complicated operations.

As described above, it is extremely difficult to bring a portion of the hydrogen storage alloy negative electrode into a charged state in advance through a chemical conversion process.

[Purpose of the invention]

The present invention aims to provide a sealed metal oxide/hydrogen storage battery having a hydrogen storage alloy negative electrode with the desired positive and negative electrode capacity without creating a hydrogen gas atmosphere during the entire battery assembly process. be.

[Summary of the invention]

A feature of the present invention is that in a closed-type metal oxide/hydrogen storage battery having a hydrogen storage alloy negative electrode, by adding alcohol to the electrolyte, only the negative electrode is charged to achieve an appropriate charging state, and at the same time hydroxide By adding lithium, harmful CO3- produced by decomposition of alcohol is removed L l 2
It is to remove it in the form of CO3. The outline will be explained below.

Alcohols such as CH30H, C2H50H, and C3H7OH easily undergo anodic oxidation in an alkaline aqueous solution, and moreover, this proceeds at a lower potential than the charging of the Kel electrode, that is, the oxidation reaction, shown in the following formula [1].

N1(OH)z+OH-+N100H+HzO+e
(1) The above reaction is expressed by the seven-dimensional formula [2].

CxHyOz + (7+ 6x -2z)OH-→
xcO32-+ (y+3x-z)H2O+ (y+
4x-2z)s I:2) Therefore, when trying to secure the negative electrode capacity that should be overcharged, if the above alcohol is added to the electrolytic solution according to the amount and charging is performed, the positive electrode will have [ The reaction of formula [2] proceeds instead of formula 1, and in the end, the positive electrode is not charged at all.

On the other hand, since the negative electrode is charged normally, an appropriate charging state of the positive and negative electrodes is achieved here.

In the discharge reaction, the reverse reaction of formula [2] does not proceed, so that the appropriate state of charge of the positive and negative electrodes is maintained in principle after this. However, in reality, the CO generated in equation [2]
The presence of 32- ions deteriorates the electrode properties of the nickel positive electrode and the hydrogen storage alloy negative electrode. That is, the capacity of the positive electrode gradually decreases due to CO32- ions, and the flatness of the discharge level of the negative electrode becomes poor, so that the battery voltage during high rate discharge also decreases. Therefore, although adding alcohol to the electrolyte is effective in achieving an appropriate state of charge,
This will have negative effects in the long run. Therefore, in order to realize a battery with good characteristics, it is necessary to reduce the amount of CO32- ions produced and to reduce the concentration of CO32- ions in the electrolyte. This includes CH30H, C2H4OH, C3H60H as seen from the formula [2].
It is preferable to use an alcohol with a small amount of carbon such as CD. However, even if such a lower alcohol is used, CO32- ions are generated.

Therefore, in the present invention, K Li0I is further added to the electrolytic solution consisting of KOH and NaOH aqueous solutions.The solubility of L12CO3 is 1.33g/100g@H20 (20°C), whereas the solubility of Na'2Co5 is 21.6g/100
g-12 (20℃), 2CO3 is 105.5 g/
100 g-H2O (20°C). Therefore, by adding a predetermined amount of LiOH to the electrolyte, CO
The 32- ion precipitates as Lt2co3, and the concentration of the CO32- ion in the electrolytic solution does not exceed the above-mentioned solubility.

The solubility of LIOH (molecular weight 23.95) is 12.7 g
/100g-) i20 (0℃), heavier L12
The solubility is higher than that of C03 (molecular weight 73.89), and the intended purpose can be fully achieved.

Now, when considering an AA-sized sealed battery, the required amount of electrolytic solution is approximately 2.0- as 8 M-KOH.

Battery rated capacity i 500 mA (theoretical charging capacity is 600 mA)
mAh), the required theoretical capacity of the negative electrode is 11
00mA, and considering that the amount that should be in an excessively charged state is a maximum of 250mAh, from the above formula [2], 0.05
g (1,6×10=mol) of methanol are required. At this time, all methanol has reacted, and all Lt2c
Assuming that it becomes o3, 0.12g (1,6X10
This means that L12CO3 of -5-8/) was produced in the alkaline solution of 24 (2.6gO solution with specific gravity of 163*>).

The situation is slightly different between water and alkaline solution, but as a first approximation, if the solubility of L12CO3 in both is equal,
The actual amount of Lt2co3 dissolved in 2.6g of alkaline aqueous solution is 1.33X (2,6/100) = 0.035g (
4.7 x 10-4 mol), and if at least LiOH is sufficient in the electrolyte, 0.12-0.035=110
．． 095g Lt2co3 (1,3X 10-S mol)
will precipitate as a solid in the electrolyte. That is, LI
Compared to the electrolytic solution without OH addition, the amount of CO32- is extremely small in the electrolytic solution to which LiOH is sufficiently added (1.6×10=mol: 4.7×10−4 mol).

Therefore, a battery using an electrolyte containing LiOH can have a longer lifespan than a battery without the addition of LiOH.

Using the AA battery mentioned above as an example, and considering methanol as the alcohol, the amount of alcohol added is o, oi.
It is desirable to keep it in the range of ~0.09g! Delicious.

The reason for this is that the excess capacity of the negative electrode relative to the positive electrode is 5
00 mAh, but some of this must remain uncharged, so it is considered appropriate to leave about 50 mAh to 450 mAh in a charged state. Therefore, these differ depending on the theoretical capacity of the positive and negative electrodes filled when assembling the battery, the life of the electrodes, etc. Further, the amount of LiOH to be added may be appropriately selected depending on the type of alcohol (carne amount) and the amount to be added.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 In this example, nickel oxide was used as the positive electrode, and LaNi4,7
Ato, 3 (Equilibrium Norad pressure is about 0.5 atm at 30°C
) with the negative electrode as an example of a AA-sized sealed Nl/i (2 battery).The capacity of the positive and negative electrodes was set as follows so that the rated capacity of this battery was 500mAh. The theoretical capacity is 600 mAh, and the theoretical capacity of H2 pole is 1
It was set to 100mAh. Therefore, the excess capacity of H2 pole 5
It is necessary to set a part of 00 mAh to a charging state and the rest to a charging state, and here, 250 mA is set as a charging state.
h and were set at 250 mAh in an uncharged state.

First, 7 g of LaN14.7ALQ, 5 powder with a particle size of 20 μm or less and 0.4 g of zinc powder with a particle size of about 10 μm
and 4-tetrafluoroethylene (PT).
A dispersion of FE) was added so that the solid content was 4 g, and then mixed and kneaded. Subsequently, this kneaded material was formed into a sheet-like material of 70-αOmX 0.6+mt using a roll, and then a nickel mesh body with lead pieces attached was pressure-bonded to produce a negative electrode body. Continuing, 50 m
A Ni electrode (theoretical capacity 600 mAh) in a discharge state of ×40 length ×0.6 m × t was prepared as a positive electrode body,
This and the negative electrode body were spirally wound through a 7Δ rotor to produce a unit cell.

Next, the unit cell is stored in an AA battery case,
After connecting the negative electrode lead to the battery case and the positive electrode lead to the positive terminal of the sealing plate, the electrolyte was injected. As this electrolytic solution, an aqueous solution containing Li0H (1 mol) and KOH (7 mol) per liter was taken, and 0.05 g of CH30H was added thereto. In other words, the electrolyte contains 2X10-'' moles of LiOH, and the capacity of CH30H is 25
0 mAh. Subsequently, after containing the electrolyte, the container was immediately sealed to assemble a sealed Nl/H2 battery.

Comparative Example 1 0.05% of CH30H (without LIOI) as electrolyte
A sealed Ni/i (2 battery) was assembled in the same manner as in the example except that an aqueous I3M-KOH solution containing 100 g of I3M was used.

Comparative Example 2 LaN14,7At (1,3 negative electrode was converted into 200%
After charging by mAh, this negative electrode was washed with water, dried, and treated with Nl.
The winding with the positive electrode, storage in the battery case, injection, and sealing were performed in an Ar atmosphere with a hydrogen partial pressure of 0.5 attn (daughter k l at
A sealed type Nl/)I2 battery was assembled using the following method.

Therefore, regarding the batteries of this example and comparative examples 1 and 2,
Charge at 150mAX 5h, 1, Ov at 200mA
A cycle test was conducted in which the battery was discharged to the point where it was discharged.As a result, a characteristic diagram shown as the average value of six batteries was obtained. Note that AC in the figure is the characteristic line for the batteries of this example and comparative examples 1 and 2, respectively.

As is clear from this figure, Comparative Example 2 (characteristic line C) is 10
Comparative example 2 (characteristic line B) reached the end of its life after 150 cycles, while this example (characteristic line entered)
It showed a lifespan of 00 cycles or more. In Comparative Example 2,
The reason why the battery life is short despite using a hydrogen atmosphere during the battery assembly process is thought to be because hydrogen stored in the negative electrode during chemical formation leaks during transfer between processes. It can be seen that the cycle characteristics of these nine batteries vary greatly, and the degree of leakage is considerably dependent on the operating method. Furthermore, Comparative Example 1 shows that the influence of CO32- gradually appears during the cycle, resulting in a shortened lifespan.

〔Effect of the invention〕

As detailed above, according to the present invention, a long-life sealed metal oxide having a hydrogen storage alloy negative electrode with an appropriate positive and negative electrode capacity can be produced without creating a hydrogen gas atmosphere during the entire battery assembly process.・Can provide hydrogen storage batteries.

[Brief explanation of drawings]

The figure is a characteristic diagram showing the relationship between the number of cycles and capacity in the batteries of this example and comparative examples 1 and 2. Applicant's agent Patent attorney Suzue Takehiko Mayful (■
)

Claims (1)

[Claims] A positive electrode whose active material is a metal oxide, a negative electrode whose main component is a hydrogen storage alloy and whose active material is hydrogen, a separator that separates the positive and negative electrodes, an aqueous alkaline electrolyte, these positive and negative electrodes, and the separator. and a sealed container for storing an electrolytic solution, wherein the electrolytic solution contains KOH or NaOH as a main component and LiOH as a subcomponent and an alcohol selected from methanol, ethanol, and propalel. A sealed metal oxide/hydrogen storage battery that is characterized by: