JP4842605B2 - Method for producing electrode plate for alkaline storage battery - Google Patents

Description

  The present invention relates to an alkaline storage battery such as a nickel / cadmium storage battery or a nickel / hydrogen storage battery, and more particularly, to an alkaline storage battery electrode plate including a sintered electrode plate in which a porous sintered substrate is filled with an active material at a high density. It relates to a manufacturing method.

  Conventionally, as a nickel electrode plate or a cadmium electrode plate used for an alkaline storage battery, a sintered electrode having features such as high utilization of active material, good electrode plate conductivity, and excellent discharge performance and cycle characteristics. Board is widely used. Such a sintered electrode plate is manufactured by filling a nickel sintered substrate with an active material by a so-called chemical impregnation method. Specifically, first, a slurry obtained by kneading nickel powder and a thickener such as carboxymethyl cellulose with water is applied to the conductive core, and then sintered in a reducing atmosphere to produce a porous nickel sintered substrate. To do. Thereafter, the obtained porous nickel sintered substrate is immersed in a solution mainly composed of nitrate (for example, nickel nitrate or cadmium nitrate) to impregnate the nitrate in the pores of the porous nickel sintered substrate.

  Next, after drying, it is immersed in an alkaline solution to convert the nitrate impregnated into the pores of the porous nickel sintered substrate into a hydroxide, finally washed with water, dried and sintered nickel An electrode plate and a sintered cadmium electrode plate are manufactured. In such a chemical impregnation method, a series of treatment steps of nitrate impregnation step → intermediate drying step → alkaline treatment step for converting into active material → water washing step is one cycle, but the amount of active material required in only one cycle Can not be filled in the porous nickel sintered substrate, and normally, the filling cycle is repeated until the necessary filling amount is obtained, and drying is carried out as the last step for production.

  By the way, whenever the immersion treatment of the porous nickel sintered substrate is repeated in the alkali treatment step described above, nitrate ions are accumulated in the alkaline liquid by the nitrate impregnated in the porous nickel sintered substrate. In this case, when the nitrate ions in the alkaline solution increase, the nitrate ions remain on the sintered substrate immersed in the form of sodium nitrate or the like, and an electrode plate having deteriorated characteristics can be obtained. Therefore, it has been proposed in Patent Document 1 (US Pat. No. 3,647,586) to take measures to prevent nitrate ions from accumulating in the alkaline solution.

Here, in what was disclosed by patent document 1, the alkali liquid used in an alkali treatment process is circulated to the nitrate ion removal apparatus, the nitrate ion in an alkali liquid is removed, and nitrate ion accumulates in an alkali liquid. I'm trying not to be.
US Pat. No. 3,647,586

  However, even when nitrate ions are removed using the nitrate ion removing device proposed in Patent Document 1 described above, a phenomenon occurs in which the charge / discharge characteristics of the obtained electrode plate deteriorate. Thus, as a result of various studies on the cause of the deterioration of the charge / discharge characteristics, the present inventors have obtained the knowledge that chromium ions in the alkaline solution may have an effect. Here, when a predetermined amount or more of chromium ions are present in the alkaline solution, the chromium ions adhere to the electrode plate in the alkali treatment. And when the electrode plate which chromium ion adhered was used, the active material utilization rate fell and the problem that charging / discharging characteristics fell occurred. This is presumably because the presence of chromium ions on the surface of the electrode plate inhibits the reaction of the electrode plate and deteriorates the charge / discharge characteristics.

  Therefore, when the cause of the presence of chromium ions in the alkaline solution was investigated, it was clearly found that the material of the alkaline solution bath used in the alkali treatment process and the core material of the sintered electrode plate were stainless steel. became. That is, the chromium contained in the stainless steel is slightly accumulated in the alkaline solution and gradually accumulated. In this case, if the material of the alkaline solution tank or the core of the sintered electrode plate is changed from a material containing chromium such as stainless steel to a material not containing chromium, the presence of chromium ions in the alkaline solution can be prevented. . However, since it has been widely performed for many years to form the core of the alkaline bath and the sintered electrode plate, changing these materials from stainless steel to many materials is of this kind. This is not possible due to economic reasons that the cost of the plates increases.

  The present invention has been made to solve the above problems, and charging / discharging of an electrode plate that has been subjected to alkali treatment even if stainless steel containing chromium or the like is used for the core of an alkaline solution bath or a sintered electrode plate. An object of the present invention is to provide a production method in which the characteristics are not deteriorated.

  In order to solve the above problems, the alkaline storage battery manufacturing method of the present invention includes a dipping step of immersing a porous sintered substrate in an aqueous solution mainly containing nitrate, and a porous material immersed in an aqueous solution mainly containing this nitrate. An intermediate drying step of heating and drying the sintered substrate, an alkali immersion step of immersing the intermediate dried porous sintered substrate in an alkaline solution, and a filling cycle consisting of a water washing step of removing the alkali content, The chromium ion concentration in the alkali solution in the alkali dipping process is regulated to 50 ppm or less.

Thus, when the chromium ion concentration in the alkali solution in the alkali dipping step is regulated to 50 ppm or less, even if chromium ions adhere to the electrode plate in the alkali treatment, the amount of non-adherence is extremely small, and the active material utilization rate is low. Decrease can be prevented and charge / discharge characteristics can be improved.
In this case, in order to regulate the chromium ion concentration in the alkaline solution to 50 ppm or less, when the chromium ion concentration in the alkaline solution exceeds 50 ppm, a part of the alkaline solution is discarded and a new alkaline solution is added. If added, the chromium ion concentration in the alkaline solution can be easily regulated to 50 ppm or less, which is desirable.

  Next, a preferred embodiment of the method for producing an alkaline storage battery of the present invention will be described below. However, the present invention is not limited to the following embodiment, and may be changed as appropriate without departing from the scope of the present invention. Can be implemented. FIG. 1 is a cross-sectional view schematically showing a nickel-cadmium storage battery according to an embodiment of the present invention.

1. Nickel Sintered Substrate A slurry was prepared by kneading a methyl cellulose solution, a completely foamed organic hollow sphere mainly composed of a methyl methacrylate-acrylonitrile copolymer as a pore-forming agent, and nickel powder while vacuuming. The obtained slurry was applied to both surfaces of a conductive core 11a (12a) formed by un-plating stainless steel and dried, and then sintered at 1000 ° C. for 10 minutes in a reducing atmosphere. A nickel sintered substrate 11b (12b) having a degree of 84% and a thickness of 0.60 mm was produced.

2. Nickel positive electrode plate The nickel sintered substrate 11b produced as described above is immersed in a nitrate solution (having a specific gravity of 1.30 at 25 ° C.) having a composition ratio of Ni: Co = 1: 1 in terms of metal mass ( (First immersion step). Then, it was made to dry at 50 degreeC for 30 minutes (intermediate drying process). Next, nitrate was deposited in the pores of the nickel sintered substrate 11b by immersing in an aqueous solution of sodium hydroxide having a concentration of 8.0 mol / l and a temperature of 80 ° C. for 30 minutes for alkali treatment (alkali treatment step). Was replaced with hydroxide. Thereafter, an alkali heat treatment was performed for 60 minutes by adjusting the atmospheric temperature to 100 to 150 ° C.

  Subsequently, it was immersed (second immersion step) in a nitrate solution (with a specific gravity of 1.70 at 80 ° C.) having a composition ratio of Ni: Co: Cd = 97: 1: 2 in terms of metal mass. Then, it was made to dry at 50 degreeC for 30 minutes (intermediate drying process). Next, after alkali treatment (alkali treatment step) by immersing in an aqueous solution of sodium hydroxide having a concentration of 8.0 mol / l and a temperature of 80 ° C. for 30 minutes, the alkali content is removed by rinsing in ion-exchanged water ( Washing step). Then, it was dried at 50 ° C. for 30 minutes (drying process) to remove moisture. Then, it returned to said 2nd immersion process again, and the predetermined amount of active materials was filled by repeating the immersion process similar to the above, an intermediate drying process, an alkali treatment process, a water washing process, and a drying process 7 times. A nickel positive electrode plate 11 was produced.

  Here, a nickel positive electrode plate a1 was prepared by performing an alkali treatment using an alkaline solution having a chromium ion concentration of 0 ppm in the alkaline solution. Further, a nickel positive electrode plate a2 was prepared by performing an alkali treatment using an alkali solution having a chromium ion concentration of 9 ppm in the alkali solution, and the alkali treatment was performed using an alkali solution having a chromium ion concentration of 25 ppm in the alkali solution. What was produced was used as the nickel positive electrode plate a3. Further, a nickel positive electrode plate a4 was prepared by performing an alkali treatment using an alkali solution having a chromium ion concentration of 50 ppm in the alkali solution, and the alkali treatment was performed using an alkali solution having a chromium ion concentration of 60 ppm in the alkali solution. The nickel positive electrode plate a5 was produced by performing this process.

3. Cadmium Negative Electrode Plate On the other hand, the nickel sintered substrate 12b produced as described above was immersed (immersion process) in a cadmium nitrate solution (with a specific gravity of 1.70 at 80 ° C.). Then, it was made to dry at 50 degreeC for 30 minutes (intermediate drying process). Next, it is immersed for 30 minutes in a sodium hydroxide aqueous solution (chromium ion concentration is 0 ppm) at a concentration of 8.0 mol / l and a temperature of 80 ° C. for alkali treatment (alkali treatment step). Cadmium nitrate deposited in the pores was replaced with cadmium hydroxide. Subsequently, it was washed with ion-exchanged water to remove the alkali (water washing step). Then, it was dried at 50 ° C. for 30 minutes (drying process) to remove moisture. Then, the cadmium negative electrode filled with a predetermined amount of active material is obtained by returning to the above immersion process again and repeating the same immersion process, intermediate drying process, alkali treatment process, water washing process and drying process five times. A plate 12 was produced.

4). Nickel-cadmium storage battery Next, a separator 13 made of a nonwoven fabric made of polypropylene was prepared. Thereafter, using the nickel positive electrode plate 11 (a1, a2, a3, a4, a5) and the cadmium negative electrode plate 12 produced as described above, a separator 13 is interposed therebetween, and these are spirally formed. A spiral electrode group was produced by winding the electrode assembly in a spiral shape. Thereafter, the negative electrode current collector 12c was resistance-welded to the lower part of the obtained spiral electrode group, and the positive electrode current collector 11c was resistance-welded to the upper part of the spiral electrode group to produce spiral electrode bodies. Next, after inserting the spiral electrode body into a bottomed cylindrical metal outer can 14 in which nickel was plated on iron, the negative electrode current collector 12c and the bottom of the metal outer can 14 were spot welded.

  On the other hand, a sealing body 15 comprising a positive electrode cap 15a and a lid body 15b is prepared, and the lead portion 11d provided on the positive electrode current collector 11c is brought into contact with the bottom portion of the lid body 15b so that the bottom portion and the lead portion of the lid body 15b 11d was welded. In the sealing body 15 including the positive electrode cap 15a and the lid body 15b, a gas vent hole 15c is formed at the center of the lid body 15b, and a disc-shaped valve body 15d is formed so as to close the gas vent hole 15c. Is arranged. And the coil spring 15f is arrange | positioned between the spring seat 15e arrange | positioned on the disk shaped valve body 15d, and the positive electrode cap 15a.

  Thereafter, the upper outer peripheral surface of the metal outer can 14 was grooved to form an annular groove 14 a on the upper portion of the outer can 14. Thereafter, an electrolyte solution (7N potassium hydroxide (KOH) aqueous solution containing lithium hydroxide (LiOH) and sodium hydroxide (NaOH) and having a lithium concentration of 0.05 mol / l) was poured into the outer can 14. The sealing gasket 16 attached to the sealing body 15 is placed in the annular groove portion 14a of the outer can 14, and the front end portion 14b of the outer can 14 is caulked and sealed to the sealing body 15 side to seal the nickel-cadmium storage battery. 10 (A1, A2, A3, A4 and A5) were assembled.

  Here, a battery using the nickel positive electrode plate a1 is referred to as a battery A1, a battery using the nickel positive electrode plate a2 is referred to as a battery A2, a battery using the nickel positive electrode plate a3 is referred to as a battery A3, and a battery using the nickel positive electrode plate a4. Was made into a battery A4, and a battery using a nickel positive electrode plate a5 was taken as a battery A5. In this case, the batteries A1, A2, A3, A4 and A5 were SC-sized batteries with a nominal capacity of 1900 mAh.

  Next, the batteries A1, A2, A3, A4 and A5 were charged with a charging current of 190 mA (0.1 It) for 16 hours and then stopped for a predetermined time. Next, the battery was discharged at a discharge current of 380 mA (0.2 It) until the battery voltage reached 0.8 V, and the discharge capacity was determined from the discharge time. Subsequently, the batteries A1, A2, A3, A4 and A5 were disassembled, and the nickel positive plates a1, a2, a3, a4 and a5 were taken out. Then, when the active material mass of each nickel positive electrode plate was measured and the positive electrode active material utilization factor was calculated based on the following formula (1), the results shown in Table 1 below were obtained.

Positive electrode active material utilization rate (%)
= [Battery discharge capacity (mAh) / <Active material mass of positive electrode plate (g) /289.1 (mAh / g)>] × 100 (1)
In the above formula (1), 289.1 means a capacity (mAh) that can be calculated from 1 g of nickel hydroxide.

  As is clear from the results in Table 1 above, the active material utilization is about 90% up to 50 ppm of chromium ions in the alkali treatment solution (sodium hydroxide solution), whereas the concentration of chromium ions is low. It can be seen that when it exceeds 50 ppm, the active material utilization rate decreases. Therefore, if the concentration of chromium ions in the alkali treatment liquid (sodium hydroxide solution) can be maintained so as not to exceed 50 ppm, even if chromium ions adhere to the electrode plate in the alkali treatment, the amount of non-adherence Becomes extremely small, and it is possible to prevent the utilization rate of the active material from being lowered and to improve the charge / discharge characteristics.

  In this case, in order to regulate the chromium ion concentration in the alkaline solution to 50 ppm or less, when the chromium ion concentration in the alkaline solution exceeds 50 ppm, a part of the alkaline solution is discarded and a new alkaline solution is added. If added, the chromium ion concentration in the alkaline solution can be easily regulated to 50 ppm or less, which is desirable. The chromium ion concentration in the alkaline solution can be measured by atomic absorption analysis.

  In the above-described embodiment, the example in which the filling cycle for filling the nickel sintered substrate with nickel hydroxide is repeated seven times has been described. However, the filling cycle is not limited to seven times, and the porosity of the sintered substrate to be used. May be selected as appropriate depending on the nitrate solution used. Similarly, in the above-described embodiment, an example in which a filling cycle for filling a nickel sintered substrate with cadmium hydroxide is repeated five times has been described. However, the filling cycle is not limited to five times, and the porosity of the sintered substrate to be used is not limited. What is necessary is just to select suitably according to the cadmium nitrate solution etc. to be used.

It is sectional drawing which shows typically the nickel-cadmium storage battery which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Cadmium storage battery, 11 ... Nickel positive electrode plate, 11a ... Conductive core, 11b ... Nickel sintered substrate, 11c ... Positive electrode collector, 11d ... Lead part, 12 ... Cadmium negative electrode plate, 12b ... Nickel sintered substrate, 12c ... negative electrode current collector, 13 ... separator, 14 ... outer can, 14a ... annular groove, 14b ... tip, 15 ... sealing body, 15a ... positive electrode cap, 15b ... lid, 15c ... gas vent, 15d ... valve Body, 15e ... Spring seat, 15f ... Coil spring, 16 ... Sealing gasket

Claims (2)

A step of immersing the porous sintered substrate in an aqueous solution mainly containing nitrate; an intermediate drying step of heating and drying the porous sintered substrate immersed in the aqueous solution mainly containing nitrate; and the intermediate drying. A method for producing an alkaline storage battery electrode plate comprising a filling cycle comprising an alkaline immersion step of immersing the porous sintered substrate in an alkaline solution, and a water washing step of removing alkali content,
A method for producing an electrode plate for an alkaline storage battery, characterized in that a chromium ion concentration in the alkaline solution in the alkaline immersion step is regulated to 50 ppm or less. When the chromium ion concentration in the alkali solution exceeds 50 ppm, a part of the alkali solution is discarded, and a new alkali solution is added to lower the chromium ion concentration to 50 ppm or less. The manufacturing method of the electrode plate for alkaline storage batteries of Claim 1.

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