JP3214569B2 - Method for producing hydride secondary 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 method for producing a hydride secondary battery having low self-discharge.

[0002]

2. Description of the Related Art A positive electrode of a hydride secondary battery is manufactured through a neutralization step in which a sintered substrate is impregnated with an aqueous solution containing nickel nitrate, and then impregnated with an aqueous alkaline solution to convert nickel nitrate to nickel hydroxide. You.

The neutralization step will be described with reference to an example in which sodium hydroxide (NaOH) is used as an alkali. The neutralization step proceeds according to the following reaction formula. Ni (NO ₃ ) ₂ + 2NaOH → Ni (OH) ₂ +
2NaNO ₃

That is, nickel nitrate [Ni (N
O ₃ ) ₂ ] and sodium hydroxide (NaOH) react to produce nickel hydroxide [Ni (OH) ₂ ] and sodium nitrate (NaNO ₃ ), and nitrate ions (NO
₃ ^-) concentration increases.

[0005]

[SUMMARY OF THE INVENTION Then, after the positive electrode the above neutralization, water washing, chemical conversion but is ready to use as an electrode through the (charging and discharging) step, water washing, in the chemical conversion step NO ₃ ^- (nitrate ion) Is difficult to completely remove.

[0006] Therefore, after the assembly of the battery, NO ₃ from the positive electrode into the electrolyte solution ^- (nitrate ions) are eluted, chain and repeatedly each as shown in the following equation reaction at the negative electrode and the positive electrode, the electric capacity after storage is [E.g. U. Falk: A
Ikaline Storage Batterie
s, 631 (1969)]. Note that M in the reaction formula indicates a hydrogen storage alloy.

Negative electrode 2MH + NO ₃ ⁻ → 2M + NO ₂ ⁻ + H ₂ O 6MH + NO ₂ ⁻ → 6M + NH ₃ + H ₂ O + OH ⁻

Positive electrode 6NiOOH + NH ₃ + OH ⁻ + H ₂ O → 6Ni (O
H) ₂ + NO ₂ ^-

As described above, the hydride secondary battery has a problem that self-discharge easily occurs after the battery is assembled.

[0010] Therefore, NO ₃ by electrolysis ^- to the title compound (nitrate ions) and ammonium ions (NH ₄ ^+), N
O ₃ ^- is possible to remove the adverse effects have been proposed by. However, according to this method, the process is complicated and the sintered substrate may be damaged by electrolysis.

Further, repeated water washing step, further boiled to NO ₃ ^- but has also been possible to remove, in the case of this method has poor workability, over the productivity is inferior, sintering by boiling The substrate and the active material may be damaged.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the conventional hydride secondary battery and to provide a hydride secondary battery with less self-discharge.

[0013]

According to the present invention, the battery is charged in an open system after the battery is assembled and stored at 30 to 60 ° C.
NO ₃ ^- by removing (nitrate ion) is obtained by achieving the above object.

[0014] That is, by charging and storage in an open system, NO ₃ ^- is NH ₃ as follows ^- is reduced to (ammonia), escapes to the outside of the battery system.

2MH + NO ₃ ⁻ → 2M + NO ₂ ⁻ + H ₂ O 6MH + NO ₂ ⁻ → 6M + H ₂ O + OH ⁻ + NH ₃ ↑

[0016] As a result, NO ₃ ^- self-discharge is suppressed by, so fewer hydride secondary battery self-discharge is obtained.

It is appropriate that the charging is performed at 0.05 to 1C. In particular, it is preferable to carry out at 0.1 to 0.5C. The reason why charging and storage are performed in an open system is that it is suitable for dissipating NH ₃ generated by reduction outside the battery system.

The reason why the battery is stored at 30 to 60 ° C. after charging is to promote the above-described reduction reaction of NO ₃ ^- to NH ₃ (ammonia).

The higher the temperature is, the more the above-mentioned reduction reaction is promoted. However, the upper limit of the temperature is specified to be 60 ° C. in order to prevent the separator from being damaged. That is, in this type of battery, a polypropylene non-woven fabric or a polyamide non-woven fabric is frequently used as a separator, but when the polypropylene non-woven fabric or the polyamide non-woven fabric exceeds 60 ° C., it is easily affected by heat. Also, the lower limit of the temperature is specified as 30 ° C.
If the temperature is lower than 30 ° C., the effect of accelerating the above-mentioned reduction reaction is small.

The storage period varies depending on the storage temperature, but is preferably 16 hours to 5 days, particularly preferably 2 to 4 days.

After storage, stirring or bubbling with an inert gas such as argon allows efficient escape of ammonia to the outside of the battery system. Therefore, it is preferable to stir or bubble with an inert gas after storage.

The above stirring and bubbling are preferably performed for one hour or more. Moreover, you may use stirring and bubbling together.

In the present invention, a nickel electrode, which is a so-called sintered nickel electrode, is used as the positive electrode. The production of this positive electrode is carried out by means conventionally used when producing the sintered nickel electrode. Can be.

For example, a nickel sintered body is used for the sintered base, and a nickel sintered body manufactured by a conventional method can be used. For example, a nickel slurry containing nickel powder as a main component is applied to a punching metal made of nickel, and heated in a reducing atmosphere to sinter nickel to produce a nickel sintered body.

The impregnation of the sintered substrate with the aqueous solution containing nickel nitrate is performed in the same manner as in the conventional method. As the aqueous solution containing nickel nitrate, an aqueous solution containing nickel nitrate alone or an aqueous solution containing a mixture of nickel nitrate and cobalt nitrate is usually used. In the above, the reason why cobalt nitrate is contained is that cobalt hydroxide (cobalt nitrate is changed to cobalt hydroxide by neutralization) improves the conductivity of nickel hydroxide as an active material and increases the utilization rate of the positive electrode. Because.

The washing with water after neutralization with an aqueous alkali solution can be carried out by a conventionally employed method.

For the negative electrode, for example, a sintering method in which a hydrogen storage alloy powder is pressed and sintered on a current collector made of a porous metal such as a wire mesh, a punching metal, and an expanded metal;
The hydrogen storage alloy powder is formed into a paste together with a binder and the like, and the paste is attached to the current collector made of the porous metal, dried, and then formed into a sheet-like molded body by a paste method of pressing with a press or the like. , By heat treatment.

As the hydrogen storage alloy used for the negative electrode, for example, (Ti _0.5 Zr _1.5
V _1.0 Ni _3.0 ) _0.8 Cr _0.2 , Ti ₁₇ Z
r ₁₆ V ₂₃ Ni ₃₇ Cr ₇ , TiNi-based, TiNiZr-based,
(Ti _2-x Zr _x V _4-y Ni) _1-z Cr _z (x = 0 to
1.5, y = 0.6-3.5, z ≧ 0.2) system, LaN
i ₅ systems include hydrogen absorbing alloy such as MmNi ₃ system. 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). In the negative electrode using this hydrogen storage alloy, charging is storing hydrogen and discharging is releasing hydrogen.

In the positive electrode, nickel is in a hydroxide state, ie, nickel hydroxide, in a discharged state, and nickel is in an oxyhydroxide state, ie, NiOOH, in a charged state.
The positive electrode is usually manufactured in a state where the positive electrode is in a discharged state.

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

[0031]

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

Example 1 Ti (titanium), Zr (zirconium), V (vanadium), Ni (nickel), and Cr (chromium) were weighed at a predetermined composition ratio, and were heated and melted by an arc melting furnace.
A multi-phase alloy having a composition of i _0.5 Zr _1.5 V _1.0 Ni _3.0 ) _0.8 Cr _0.2 was obtained.

This alloy was placed in a pressure vessel, and the pressure in the vessel was evacuated to 10 ^-4 torr by vacuum and argon was introduced. After repeating this operation three times, 14 kg / cm ² of hydrogen was introduced, and after holding for 24 hours, hydrogen was exhausted.
By heating to ° C. to completely desorb hydrogen, a hydrogen storage alloy was obtained in the form of fine powder having a particle size of 20 to 100 μm.

The obtained hydrogen-absorbing alloy powder was dispersed on a nickel support (a nickel mesh having a wire diameter of 0.178 mm and a mesh of 14 mesh) and pressure-bonded at 5 tons, in an atmosphere having an Ar / H ₂ gas ratio of 96: 4. Sintering was performed at 1050 ° C. for 5 minutes to produce a negative electrode.

The production of a nickel sintered body used as a sintered base of the positive electrode was performed as follows.

Nickel powder is added to a gel obtained by mixing 30 g of methylcellulose and 1 liter of water to form a nickel slurry, and this nickel slurry is applied to both surfaces of a punching metal (thickness: 70 μm, opening ratio: 25%) made of nickel. Then, by heating at 900 ° C. for 20 minutes in a reducing atmosphere to sinter nickel, a nickel sintered body was produced.

The filling of the active material into the pores of the nickel sintered body was performed as follows.

[0038] Co (NO ₃₎ in water 0.8 l _2.6
H ₂ O and 100 g, Ni a _{(NO 3) 2 · 6H 2} O 10
00g and 5g of HNO ₃ were dissolved to prepare an impregnation solution, and the nickel sintered body was immersed in this solution for 10 minutes.
After removing from the solution and drying at 100 ° C for 30 minutes,
30% NaOH (sodium hydroxide) heated to 80 ° C
Immersed in an aqueous solution for 10 minutes to obtain cobalt nitrate [Co (NO
₃ ) ₂ ) is neutralized and cobalt hydroxide [Co (OH) ₂ ]
And nickel nitrate [Ni (NO ₃ ) ₂ ] was neutralized and converted to nickel hydroxide [Ni (OH) ₂ ].

This impregnation step was repeated to produce a so-called sintered nickel electrode. Adjust the order of washing during washing after electrode fabrication, NO ₃ in the positive electrode ^- (nitrate ions) 5
The content was set to 00 ppm and 1000 ppm.

Using this positive electrode and the negative electrode, a battery (open-type model cell) shown in FIG. 1 was produced. In FIG. 1, 1 is the above positive electrode, and 2 is a negative electrode. Reference numeral 3 denotes a separator, and a polypropylene nonwoven fabric having a thickness of about 300 μm is used for the separator 3.

A reference electrode 4 is a mercury / mercury oxide electrode. Reference numeral 5 denotes an electrolytic solution, and an aqueous solution of potassium hydroxide having a concentration of 30% (to which 17 g / l of lithium hydroxide is added) is used as the electrolytic solution 5. Reference numerals 6 and 7 denote nickel current collectors, 8 denotes platinum for the lead of the reference electrode 4, 9
Is a battery container made of polypropylene.

The negative electrode capacity of the battery is 20
At 0 mAh, the positive electrode capacity is 130 mAh.

The above battery was charged at 30 mA for 10 hours, and then immediately charged and discharged at 30 mA to a battery voltage of 0.9 V as one cycle.
Charge at 0 mA for 10 hours (0.1 C), and after charging, 45 ° C
For 3 days. After storage, the electrolytic solution was bubbled with argon gas for 1 hour.

The NO in the electrolyte ₃ ^- ion species concentration containing nitrogen before and after storage for batteries with 500ppm and 1000ppm concentrations were determined by ion chromatography. NH ₃ (ammonia) becomes ammonia gas in the alkaline aqueous solution and escapes outside the battery system.
The mixture was trapped with 0.1 N hydrochloric acid. Table 1 shows the concentration change of the ionic species before and after storage.

[0045]

[Table 1]

As shown in Table 1, after storage at 45 ° C. for 3 days, most of NO ₃ ⁻ (nitrate ion) is reduced by the hydrogen of the negative electrode to become NH ₃ (ammonia) (partly becomes N ₂ ). It was thought that the gas had escaped from the battery system due to bubbling.

[0047] That is, charges in an open system, by storing, before storing NO ₃ was 500ppm for ^- is reduced to 30ppm after storage, NO was 1000ppm before saving ₃ ^- is after storage to 85ppm Diminished.

The battery after the storage was further subjected to 10 mA at 30 mA.
After charging for a period of time, store in a sealed state at 45 ° C. for 5 days. After storage, discharge at 30 mA to a battery voltage of 0.9 V.
The obtained discharge capacity was defined as the discharge capacity after storage, and the capacity retention with respect to the discharge capacity before storage was determined by the following equation.

Capacity retention (%) = A / B × 100 A: Discharge capacity after storage at 45 ° C. for 5 days B: Discharge capacity without storage

The capacity retention ratio and NO ₃ ^- the relationship between (nitrate ion) concentration in conjunction with the case of the later of Comparative Example 1 shown in FIG.

Comparative Example 1 In the same manner as in Example 1, the NO ₃ ^- concentration was 500 ppm and 1 ppm.
Using the positive electrode adjusted to 000 ppm, the same battery as in Example 1 was assembled, and the same charging and discharging as in Example 1 was repeated for three cycles, then charged at 30 mA for 10 hours, and then sealed at 45 ° C. for 5 hours. Stored for days.

The battery after storage was charged at 30 mA with a battery voltage of 0.9.
The battery was discharged to V, and the obtained discharge capacity was defined as the discharge capacity after storage, and the capacity retention with respect to the discharge capacity before storage was determined in the same manner as in Example 1. FIG. 2 shows the relationship between the capacity retention rate and the NO ₃ ⁻ (nitrate ion) concentration.

[0053] In FIG. 2, NO ₃ ^- after neutralization with positive (aqueous alkaline solution prepared in free conditions,
The same washing and charging / discharging treatment was carried out at 45 ° C. for 5 days, except that the water washing step was repeated and boiling was carried out for 7 hours to remove NO ₃ ⁻ ). Discharge to battery voltage 0.9V at 30mA,
The obtained discharge capacity is defined as the discharge capacity after storage, and the capacity retention ratio with respect to the discharge capacity before storage is obtained. The result is shown at the point where the NO ₃ ^- concentration is 0 ppm.

As shown in FIG. 2, the battery of Example 1 had a high capacity retention rate, and when NO ₃ ⁻ was 0 (that is, the battery was assembled after almost completely removing NO ₃ ⁻ in the positive electrode). Battery).

On the other hand, the battery of Comparative Example 1 had NO ₃
^- depending on the concentration of ions, the capacity retention rate decreased.

As described above, the excellent capacity retention of the battery of Example 1 is due to the N contained in the positive electrode during battery assembly.
O ₃ ^- (which included 500ppm and 1000ppm)
Was removed by charging and storage after battery assembly.

[0057] and the negative electrode prepared in Example 1, after repeated washing step after neutralization with an aqueous alkali solution, NO ₃ was boiled for a further 7 hours ^- using the positive electrode was hardly contains, Figure 1 The battery having the open system structure shown in FIG.

And the (nitrite) was added to a 500ppm and 1000 ppm ^- [0058] NO ₂ in the electrolyte during the battery after assembling.

This battery was charged at 30 mA in the same manner as in Example 1.
The battery was charged for 0 hours, immediately charged and discharged at 30 mA to a battery voltage of 0.9 V as one cycle. This cycle was repeated three times, and then charged at 30 mA for 10 hours.
Stored at 5 ° C. for 3 days. After storage, the electrolytic solution was bubbled with argon gas for 1 hour.

The concentrations of ionic species containing nitrogen before and after storage were measured in the same manner as in Example 1. Table 2 shows the results.

[0061]

[Table 2]

As shown in Table 2, the battery was charged and then charged for 45 minutes.
Storage for 3 days at 500 ° C before storage
There was NO ₂ ^- is reduced to 220ppm after storage, NO ₂ that was 1000ppm before saving ^- it is after storage 31
It decreased to 0 ppm.

[0063] According from the results, the present invention, NO ₃ ^-
It can be seen that NO ₂ ⁻ (nitrite ion) generated in the step of reducing (nitrate ion) to NH ₃ (ammonia) is also removed.

The battery after storage was further subjected to 10 mA at 30 mA.
After charging for a period of time, store in a sealed state at 45 ° C. for 5 days. After storage, discharge at 30 mA to a battery voltage of 0.9 V.
The obtained discharge capacity was defined as the discharge capacity after storage, and the capacity retention ratio with respect to the discharge capacity before storage was determined in the same manner as in Example 1.

[0065] Capacity retention ratio and NO ₂ ^- the relationship between the (nitrite ion) concentration in conjunction with the case of the later of Comparative Example 2 shown in FIG.

After so contains little, NO ₂ ^{- -} [0066] NO ₃ in the same manner as in Comparative Example 2 Example 2 using (nitrite) cathode was 500ppm and 1000ppm added, the same cell as in Example 2 After assembling and repeating the same charge and discharge as in Example 2 three times, the battery was charged at 30 mA for 10 hours, and then stored in a sealed state at 45 ° C. for 5 days.

The battery after storage was 30 mA, and the battery voltage was 0.1 mA.
The battery was discharged to 9 V, and the obtained discharge capacity was defined as the discharge capacity after storage.
As well as sought. FIG. 3 shows the relationship between the capacity retention and the NO ₂ ⁻ (nitrite ion) concentration.

As shown in FIG. 3, the battery of Example 2 has a higher capacity retention than the battery of Comparative Example 2. This is because in the battery of Example 2, NO ₂ ⁻ (nitrite ion) contained in the positive electrode was used.
Is removed by charging and storage after battery assembly.

Example 3 A battery similar to the one assembled in Example 1 was charged at 30 mA for 10 hours in the same manner as in Example 1, and immediately discharged at 30 mA to a battery voltage of 0.9 V as one cycle.
After repeating this three cycles, the battery was charged at 30 mA for 10 hours, and after charging, stored at 60 ° C. for 3 days. After storage, the electrolytic solution was bubbled with argon gas for 1 hour.

The battery after storage was further charged at 30 mA for 10 hours, stored in a sealed state at 45 ° C. for 5 days, and discharged after storage at 30 mA until the battery voltage became 0.9 V. The capacity was defined as the discharge capacity after storage, and the capacity retention with respect to the discharge capacity before storage was determined in the same manner as in Example 1. FIG. 4 shows the results.

[0071] As shown in FIG. 4, the battery of Example 3, NO ₃ in the positive electrode at the time of battery assembly ^- or contained 500ppm and even when moistened 1000 ppm, higher capacity retention, NO ₃ ^- is It was almost the same as the capacity retention in the case of 0.

Example 4 A battery similar to the one assembled in Example 1 was charged at 30 mA for 10 hours in the same manner as in Example 1, and immediately discharged at 30 mA to a battery voltage of 0.9 V as one cycle.
After repeating this three cycles, the battery was charged at 30 mA for 10 hours, and after charging, stored at 30 ° C. for 5 days. After storage, the electrolyte was bubbled with argon gas for 1 hour.

The battery after storage was further charged at 30 mA for 10 hours, stored in a sealed state at 45 ° C. for 5 days, and discharged after storage at 30 mA until the battery voltage became 0.9 V. The capacity was defined as the discharge capacity after storage, and the capacity retention with respect to the discharge capacity before storage was determined in the same manner as in Example 1. The result is shown in FIG.

[0074] As shown in FIG. 5, the battery of Example 4, NO ₃ in the positive electrode at the time of battery assembly ^- or contained 500ppm and even when moistened 1000 ppm, higher capacity retention, NO ₃ ^- is It was almost the same as the capacity retention in the case of 0.

[0075]

As described above, according to the present invention, a hydride secondary battery with low self-discharge can be provided by charging the battery in an open system after battery assembly and storing the battery at 30 to 60 ° C. .

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a hydride secondary battery according to the present invention.

FIG. 2 shows NO ₃ of the battery of Example 1 and the battery of Comparative Example 1.
^- is a diagram showing the relationship between (nitrate ion) concentration and capacity retention.

FIG. 3 shows NO ₂ of the battery of Example 2 and the battery of Comparative Example ₂
^- is a diagram showing the relationship between (nitrite ion) concentration and capacity retention.

FIG. 4 is a diagram showing the relationship between the NO ₃ ⁻ (nitrate ion) concentration and the capacity retention of the battery of Example 3.

FIG. 5 is a diagram showing the relationship between the NO ₃ ⁻ (nitrate ion) concentration and the capacity retention of the battery of Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 5 Electrolyte

Continuation of the front page (72) Inventor Toshikatsu Mabe 1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Ltd. (56) References JP-A-55-25953 (JP, A) JP-A-63-160160 ( JP, A) JP-A-1-267966 (JP, A) JP-A-2-301971 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/28 H01M 10/34

Claims (2)

(57) [Claims] 1. A positive electrode produced through a neutralization step of impregnating a sintered substrate with an aqueous solution containing nickel nitrate and then impregnating an aqueous alkaline solution to convert nickel nitrate to nickel hydroxide, and a hydrogen storage alloy. In the manufacture of a hydride secondary battery having a negative electrode and an electrolytic solution composed of an alkaline aqueous solution, a hydride which is charged in an open system after battery assembly, stored at 30 to 60 ° C., and removes nitrate ions A method for manufacturing a secondary battery. 2. The method for producing a hydride secondary battery according to claim 1, wherein the storage is followed by stirring or bubbling with an inert gas.