SI8612094A8 - Process for making metal element for electric current taking off the electrode of metallic oxide, which is touch with alcalic agent - Google Patents

Description

P 2094/86

VARTA Batterie Aktiengesellschaft

A process for producing a metal pantograph from a metal oxide electrode in contact with an alkaline electrolyte

The field of technology

The invention belongs to the field of basic electrical elements, and more specifically to the field of elements for the direct conversion of chemical energy into electricity, or to the field of depositing substances on a metal object and electrolytic processes therefor.

According to the international patent classification, the subject matter of the invention is classified in classes H 01M 4/66, C 23C 14/24, C 23C 04/06, C 25D 03/00.

Technical prob1em

It is an object of the invention to develop a method for making a current collector equipped with an additional foreign metal for a positive metal oxide electrode at a galvanic primary element, in particular an alkaline manganese cell, by which the contact resistance between the client and the electrode is minimized and will also be independent in the long term from storage and voltage stable.

The state of the art

It is known from experience that there is a disadvantage of such primary elements that, after prolonged lying times, they cannot be taken away from such a high discharge current as in the state immediately after manufacture. Particularly in cells with an alkaline Mn0 _o / Zn primary ά i system, during storage, a positive electrode of metal oxide under certain conditions creates a poorly conductive coating that leads to an undesirable increase in the internal resistance of the cell. As manganese dioxide is pressed directly on a steel or nickel plated steel vessel, it is explained by the lack of operational readiness of the stored cells by oxidative change of the nickel coating, thereby increasing the contact resistance in the transition region between the metal oxide and the positive current collector.

The occurrence of poorly conductive boundary surfaces at the contact of a pantograph with an electrochemically active substance is also present in primary cells with a solid electrolyte and has been attempted, as can be seen in U.S. Pat. No. 2,861,116, to prevent this by using as much as possible inert material. Among other things, platinum, palladium, tantalum, molybdenum, silver, nickel, lead, gold, titanium, zirconium and carbon seemed appropriate.

- 3 With patent file DE 1 421 582, these claims are dismissed as being too general. For galvanic primary elements, which can be classified as a generic designation, gold is recommended as the preferred choice, in the form of a gold coating on a positive pole steel vessel.

The not insignificant disadvantage of gold or gold plated pick contact is definitely its price due to the material and process. In the case of the use of mercuric oxide as a positive electrode material, it cannot be avoided that the gold is gradually amalgamated with mercury generated upon discharge of HgO, so that its suitability for the resistance of SS: initially low contact resistance during storage seems at least questionable. This reservation is even more valid for silver as a consumable material, which is also amalgamated with HgO and finally dissolves under the conditions of operation of the cell.

Description of the solution to a technical problem with examples of implementation

Said technical problem is solved by a method for producing a metal pantograph from a metal oxide electrode in contact with an alkaline electrolyte, the method according to the invention characterized in that the client sheet is galvanized in aqueous solution 50 to 50 seconds 100 g of C0SOH.7H2O cobalt sulphate in 50 ml of water at an electric current of 20 to 50 mA / cm ² .

The nickel surface is very suitable for applying cobalt or cobalt compound to the pantograph.

In principle, a carefully cleaned surface of sheet steel is also appropriate.

The steel sheet used to make elemental vessels is generally galvanized and heat treated in addition. Incandescent diffusion results in the deep penetration of nickel atoms into the steel surface. Nickel-plated, sheet steel thus achieves the quality of deep drawing.

In view of the application of the cobalt according to the invention to the pantograph, it is particularly advantageous that it permits the unconventional transformation of the steel sheet, e.g. with deep draw, full scale.

It is not necessary that either the cobalt layer itself or, for example: 'the nickel layer applied to the deep drawn steel sheet, be completely non-porous.

Finally, it is possible to add the cobalt of the invention to the nickel-coated nickel-coated pantographs for alkaline MnO ₂ electrodes.

The invention will be further described on the basis of embodiments and figures.

FIG. 1 shows a drop in voltage U (mV) as a measure of contact resistance at different client surfaces after each three different storage times.

FIG. 2 shows the voltages at the load U (V) of Zn / Mn0 ₂ primary cells of type LR 14, depending on the time t (weeks) of storage, compared to cells that were cobalted or equipped with cobalted or non-cobalted cells. gold plated positive pantograph.

FIG. 3 shows a comparison of the previously named cells in their emptying behavior.

For practical application of cobalt or. cobalt compounds on the client's surface have different routes. The chemical process consists in the elimination of cobalt from the cobalt salt solution by means of a reducing agent in a uniform layer on the client metal. If nickel forms a suitable base for elimination, it has a particularly favorable catalytic action.

The second process is the electrochemical reduction of cobalt ions, which removes any oxide coating by cathodic polarization of the parent metal.

Further processes are of a physically metallurgical nature to which cobalt is applied e.g. by evaporation or by hot cladding.

An implementation example

The electrochemical method is particularly well-practiced, especially since it can be cleverly coupled to the electroplating of a base metal, e.g. deep drawn steel sheets.

As has been shown during this time, not all aqueous solutions of cobalt ions are equally suitable. Thus, e.g. Co (N0g) ₂ is completely unsuitable due to the formation of ammonia leading to unwanted parallel reactions.

With very good success, an aqueous solution of cobalt sulphate, preferably obtained from 50 to 100 g of CoSOjj, may be used. 7 H ₂ O in 50 ml of HgO.

For. cathode nickel surface treatment is appropriate

2 current density in the range of 5 to 100 raA / cm, preferably 20 to 50 mA / cm.

Under this condition, a processing time of only 10 to 50 seconds is sufficient to achieve a reduction in the contact resistance of the invention. The resulting layer has a thickness in / tm region. The processing temperature may lie in the room temperature range.

This treatment will hereinafter be referred to as cobaltation. After treatment, the cobalt surface is washed with distilled and desalinated water and dried in the usual way, e.g. with hot air.

The surprising effect of client cobaltation was experimentally verified, using different contact surfaces for comparative test in the resistance measurement apparatus.

The test apparatus specially designed for this purpose has been adopted in each case during non-oxidizing, e.g. a gold-plated, contact surface, and between a contact surface that has been pre-machined and to be examined, a tablet Mn0 ₂ electrode, with the adjustable pressure on the layer stack compensated with appropriate support. The Mn0 ₂ tablet was soaked in about 40% KOH and the surrounding casing prevented it from drying out as well as reacting KOH with CO ^ from the air. The contact surfaces surrounding both sides of the Mn0 ₂ electrode were connected via an external circuit containing a device for adjusting the constant current i, an ammeter to control it, and a voltmeter to determine the voltage drop U at a given current i. The voltage drop is determined after a certain current i has been set by the device for setting the constant current, from the union U = i (R ^ + R ₂ + Rg), in which they mean the contact resistance between the non-oxidizing contact surface and the Mn0 ₂ tablet, R ₂ resistance Mn0 ₂ tablets and R3 contact resistance between Mn0 ₂ tablet and the contact surface to be investigated.

With a brown manganese tablet of selected dimensions 10 mm x 5 mm (diameter x height) and a composition of 88% Mn0 ₂ , 10% graphite and 2% polyethylene as a binder, it was possible to prove at a pressure of p = 75 bar and at a given temperature that changes in resistance arising from storage solely caused by changes in contact resistance R ^, that is, resistance between the brown manganese tablet and between the disposable layer of the client, if it is e.g. nickel plated steel, as is commonly used in Zn / Mn0 ₂ alkaline systems · In other words, resistances R ^ (between gilded client and Mn0 ₂ tablet) and R ₂ (resistance Mn0 ₂ tablets) are not only stable with respect to storage , but also in ~ Selected installation relatively small with respect to the resistance R ^.

According to this measurement method, differently selected and prepared pantographs were used, which give rise to the resistance R ^, with the drop in voltage U defined above.

a) immediately after mounting in the measuring device,

b) after 24 hours of lying,

c) after 96 h of lying under 90 ° C ambient temperature and constant measuring current i = 500 mA.

The relatively short lying time combined with the relatively high ambient temperature is sufficient to judge the quality of the client, which is characterized by type and pre-treatment. Lying for one month at 70 ° C corresponds to a storage time of 1 to 1.5 years at room temperature.

The findings of electrical research are explained in more detail with the help of pictures.

- 8 In Figs. 1, for differently selected and machined pantographs 1 to 7, are plotted in the form of bar diagrams of the U = iR values obtained by this so-called measuring method, with three measuring values of U for the above lying times a for each client. , b) and c). The u-values of U are read on the ordinates. \ large values of U mean high resistances R ^ and vice versa

Column 1 shows the result obtained on the untreated, nickel-plated steel surface.

As can be seen, the contact resistance in the given conditions increases in 96 h by five times.

Column 2 shows the behavior of gilded nickel contact compared to diagram 1. It can be seen that even after 96 h, the resistance does not exceed the initial resistance according to Diagram 1.

Column 3 shows the behavior of a nickel surface treated with fine sanding paper. Grinding was performed in order to remove any stronger nickel oxide layers before conducting the contact experiment. It is evident that the initial value obtained is comparable to the value of gold (diagram 2). But after only 24 hours, the relatively small initial resistance had almost increased. After 96 h, the initial resistance increased to more than 14 times.

Column 4 shows the result of the test to incorporate Li ion into a nickel oxide surface by cathodic polarization in LiOH solution. As can be seen, at least under the selected conditions, the experiment is negative. 0 problems with MnC ^ / Li / Ni contact system contacts have also recently been reported from other sites (N.A. Fleischer and R.J. Ekern, J. Elektrochem.Soc., Vol. 132, Jan 1985)

The strong deterioration of the contact contact is evident from the bar diagram 5. In this case, the nicked contact contact was experimentally cathodically polarized in the MnSO4 solution, with the manganese fitted with certainty into the nickel layer near the surface. It can be seen that the initial resistance is more than 8 times greater than 96 h of gold resistance (diagram 2).

These results already show that the incorporation of foreign metals or foreign metal ions into the nickel surface layer, as well as the type of pre-treatment of the nickel client, is of great importance for the properties of the contact layer. An important hint that cobalt was responsible for the relatively favorable contact resistance behavior in the design of the boundary layer structure in the desired sense (low resistance, time stability, compatibility with MnC ^ in alkaline electrolyte) was expressed by the previously mentioned Vacon 10 alloy. in the bar chart 6.

To test the effect of cobalt, a nickel-plated steel pantograph, which was used in virtually all measurements, was cathodically polarized in aqueous cobalt ion solution. This has shown a surprisingly positive and unexpected effect to this extent. The result is shown in bar diagram 7. It is evident that the result is comparable to that in gold (diagram 2).

In addition, the result obtained with Vacon 10 shows that not only is electrochemical Co excretion but also its fusion.

A further interesting finding is that the Μηθ £ tablet, which was mounted and investigated as described, binds irresistibly to the cobalt nickel surface as opposed to pure Mn02 / Ni contact. The £ηθ £ tablet acts as if it were welded to the surface of the pantograph according to the invention. It can be assumed that the well-conductive Mn, Co and Ni-oxide / hydroxide structures characteristic of the Mn02 / Co boundary contact can occur here.

Further experimental results, which speak for the advantages of cobalt-equipped current collectors according to the invention, can be seen in FIG. 2 and 3. Load stress behavior depending on storage time and discharge behavior of the three alkaline Zn / Mn02 primary elements of the LR 14 type round faces (according to IEC), each corresponding to curve 1 of a raw nickel plated steel vessel (standard cell) , curve 2 nickel plated and then gilded steel vessels and curve 3 nickel plated and then cobalt steel vessels (according to the invention).

In FIG. 2 is a diagram of U (V) / t (weeks) presents a voltage drop under load with 2 β for a duration of 0.2 sec. depending on storage time at 70 ° C. It can be seen that, after one month, the untreated steel vessel (curve 1) is approximately 300 mV below the voltage of the cobalted vessel (curve 3) after a load U, which (measured at room temperature). Meanwhile, the load voltage of the cobalted vessel (curve 3) lies only about 25 mV lower than the gilded vessel voltage (curve 2). The result is in agreement with the results of FIG. 1, Diagrams 1, 2, 7, and testify to the excellent effect of cobaltation.

FIG. 3 shows the result of a very hard permanent discharge with 2 ^. As can be seen, the cell with the raw steel tank gives a voltage of 0.9 V at the end of the discharge, only a charge of 1.58 amperes, hours (curve 1), and the cell with the cobalt steel tank gives 2.3 amps, hours ( curve 3).

The gilded steel tank cell (curve 2) lies only about 0.2 ampere hours above the cobalted tank result. In this case, cobaltation improved the discharge result by about 50% over the non-cobalted steel vessel.

It should be noted that the results of this species also depend on the quality of the brown manganese used each time. However, it always turns out that the cobalt steel vessels or. cobalt-containing steel vessels too strong relative to non-cobalt-containing steel vessels. From the material presented, it is therefore quite unambiguous that cobalt or. cobaltation yields a contact resistance between the alkaline Mn0 ₂ electrode and the nickel-current pantograph, properties that are almost identical to those of the gold-plated pantograph.

Claims (1)

A process for producing a metal pantograph from a metal oxide electrode in contact with an alkaline electrolyte, wherein the pantograph is a nickel, steel or nickel-plated sheet metal and this sheet contains cobalt at 0.1% atomic concentration on its surface by galvanizing the client sheet in an aqueous solution of 50 to 100 g of CoS0 ^ .7H ₂ 0 cobalt sulphate in 50 ml of water at an electric current of 20 to 50 mA / cm ^{2 for} 10 to 50 seconds.