DE1908956A1 - Electrode for a secondary element - Google Patents

Description

DiPL-ING. KLAUS NEUSECKER

Patent attorney
C! Gs3eldcri-Eiler Am Strauasenkreu ^ £ 3 Postiaci 12 *

Düsseldorf, February 21, 1069 ■ ΉΈ 39.231-A
6867

• Tfestinghouse Electric Corporation,
Pittsburgh, Pennsylvania, V. St. A.

• Electrode for a secondary element

The present invention relates to secondary elements such as Batteries or the like, in particular on aine with a Paste-provided, plate-like iron electrodes for such elements or batteries.

It is known that an iron electrode works in an alkali electrolyte on the basis of the oxidation of metallic iron to form hydroxides or oxides of iron or both. The exact structure of the substance or substances is not fully known. Although the formation of Fe (OH) ₂ , Fa ₃ C ₃ ^and / ^{o <ier} Fe (OH) _{3 has} been assumed as a prerequisite, it doesn't seem like that ? ^G 2 ^Q 4 *** most likely to be the dominant material. The additions to the substances formed are essential because they determine the theoretical limit of the yield or the hours spent per Graaa electrode material. In the following, the term "iron oxide" is used to denote the iron-iron oxide compounds, including both the hydroxides and the oxides ala mixtures thereof.

If the electrode is only used, a d * ait fully equipped battery has a paseivating rate of rapid formation Tilaea on the Eiaonfllahe a * limited harvest. Door practical

909339/1023

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Otherwise, the iron electrode usually consists of iron oxide powder, which is compressed to the desired density. To promote the discharge effect of the compressed powder and besides, the charging of the electrode, to facilitate & rn, is made for the Electrode requires a reaction-promoting additive. Such an additive is said to keep the iron surface in an active state. On the other hand, this is not intended to accelerate the discharge will. A coalition should only expire when the battery speed is removed.

It has already been proposed to add sulfur or sulfur-containing substances to the so-called "iron electrodes" working in an alkali electrolyte, in particular in US Pat limited to very small amounts, such as a sulfur content of 0.05-0.1 % by weight in iron. ■ ■. · ■

The object of the present invention is to provide an improved Electrode door a secondary element or an accumulator, the one increased efficiency and an increased yield guaranteed.

To solve this problem, an electrode for a secondary element, which mixed a plate of kit with each other and thereby active Electrode discharge with iron oxide particles! Fibers according to the invention characterized in that the active mass, based on the weight of the iron, at least 5% by weight of sulfur, selenium, Contains tellurium or mixtures thereof.

The invention is described below together with other features of an example 3 in connection with the associated Drawing explained. In the drawing show:

1 shows a perspective view of a negative electrode according to the invention for a secondary element;

Fig. 2 is a graph showing the yield of an iron electrode with different additions of potassium sulf id and the voltage as a function of the discharge time for identical electrodes of a nickel / iron battery with the same amounts of divalent iron, but different proportions of sulfur;

FIGS. 3 and 4 show the efficiencies for electrodes made of bivalent and trivalent iron with different ones Proportions of added sulfur;

Fig. 5, 6 graphs showing the dependence of the output ^{and 7} booty in volts on the time for iron electrodes

illustrate different additions of potassium sulfide, sulfur powder or potassium sulfide with Carbon B &ck; and

Fig. 8 is a graph showing the effect of the sulfur content on the iron electrode, based on the weight of the active material (Fe ₂ O _3. HgO, FeS _f S) and based on the volume of the

Electrode, for a constant discharge value

2
accordingly reproduces 25 mA / cm.

Referring to Fig. 1, there is generally a negative electrode designated 10 a so-called. Eisenalkaliakumulators reproduced, the one Electrode support structure 12, an active mass 14 and a termination strip has 16 with a terminal lug 18. The electrode IO is for use in a suitable electrolyte such as a 25 wt% aqueous solution of potassium hydroxide (KOH) certainly.

90 983 9

The electrode support structure 12 has a porous structure and contains a latticework of electrically conductive fibers arranged in either a woven or non-woven texture. The support structure 12 can, for example, consist of a latticework with metal fibers
(Iron or nickel), which are compressed with a porosity of 96%.

At its upper end, the electrode support structure 12 is attached to the termination strip 16, which is made of a conductive material,
is made of sheet metal; it can be placed on the upper end of the superstructure
12 must be clamped on in order to keep it in its correct position and to create good electrical contact. The terminal lug 18 forms an integral part of the end strip 16 and extends therefrom in a conventional manner.

The active mass 14 is arranged on the support structure 12 and in the interstices of the support structure 12 and consists of a mixture of powders which are applied to the fiber network in the form of a paste
or a slurry was applied, which is then dried
and pressed in a mold to the desired thickness. The active mass is made by first making a slurry of particles
with a size corresponding to a range of 80-130 mesh size (ie 80-130 openings per linear cm). The particles
contain at least one iron oxide and the additive. The iron oxides include iron (III) oxide, iron (II) oxide, iron (II, 11I) oxide (known as magnetite) and iron hydroxide, preferably in the
Form of precipitation.

The additives include sulfur / selenium, tellurium and mixtures thereof. The additives can be added either as an element or as a salt thereof. For example, sulfur can be added in the form of sulfur flowers, as colloidal sulfur or as a salt such as potassium iron sulfide (KFeS ₂ ).

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For example, for every 100 g of the iron contained in the oxide, 5 to 66, preferably 12 to 19 g of sulfur can be added to the oxide and then mechanically mixed thereby, or the sulfur can be dissolved in a solvent, mixed with the iron oxide and then mixed the solvent will be evaporated. The optimal sulfur content is around 15 g. The iron oxide and the sulfur or Sulfur-containing salts form an intimate mixture, which then by adding enough water to a porridge or a Paste is converted to the mixture on the fibrous support structure 12 to be able to apply, where it is then pressed to the desired thickness, also dried to all free moisture eliminate.

The purpose of the additive is to prevent passivation of the iron during discharge and to create favorable conditions for effective charge absorption. A small amount of additive contained in the iron oxides Fe ₂ ⁰ 3 ^{or Fe} 3 ° 4 ^and / ° ^the iron hydroxide (Fe (OH) ₃ ) apparently leads to a greater degree of irregularity in the crystal structure, so that diffusion and the The electrical conductivity of the material can be increased, but the hydrogen overvoltage during charging and the absorption of hydrogen by the iron are also likely to be influenced. By such a combined effect, the additives affect the rate and degree of completeness of the conversion of the iron oxides during the charging process. When an electrode is made, it is in a discharged state. It then has to be charged by passing a current through it for the conversion of the iron oxides into ferrous metal. The presence of an additive increases the charge absorption and prevents passivation of the iron after the subsequent discharge of the electrode.

Embodiment

On a support structure or a grid made of nickel wool with a degree of coarseness of (000) or (00) sin pulp was feinpülvrigeri

Iron oxide applied. The network formed from the wool became cut into strips of 20 χ 10 cm, into which a pulp of iron oxide particles brought and then partially dried. Thereafter the network (support structure) coated with the iron oxide was placed in a container in which it was placed under moderate pressure between Filter paper layers were pressed into a flat plate and freed from excess moisture by drying. The pressed one Plate was then provided with pressed nickel leads as electrical connections and with a large section Filter paper wrapped in to prevent abrasion of the plate when it is assembled to prevent menbau. It then became either side of the iron electrode k in each case a conventional nickel electrode arranged and the thereby The resulting assembly is placed in a vented cell.

Salts of divalent and trivalent iron can be used in making effective electrodes. When using divalent iron, the pulp was obtained by dissolving Sg iron (II) ammonium sulfate, which contains 1.4 g of iron and is capable of a theoretical yield of 1.09 Ah in 100 ml of water when two electron conversion processes occur and the resulting solution was then filtered. 45 ml of molar KOH solution were added to this solution. This produced a precipitate which was applied to the electrode. To * zttzufügen sulfur, a part of the KOH was replaced by a molar KoS solution, the 45 ml per ml of the KGA Lösüng used Q ₈ Ü32 g of sulfur contained * The K "S solution was prepared by dissolving of solid K ₂ S made in water.

For the investigations with trivalent iron, iron (in) ammonium sulfate was used as the starting salt, 8 g of which contained 0.928 g of iron, which when oxidized to the double state gave a theoretical yield of oil ^ fnV \ Eg 100-ml WaSser.-dissolved ^^ Bll ^ -Lösün ^ rWiMt §e * f £ liiNFBSi £ ^: -düreh-ZugÄbe- of 50

delt. The actual amounts of KgS molar solution used were 0.1, 1.5, 10 and 15 ml, which were brought to 50 ml with molar KOH solution.

The battery cells were filled with 8 mol of aqueous KOH solution and within 10 hours to at least 150% of their theoretical Capacity charged. The discharge took place over a 10 ohm resistor within about 3 hours. The voltage drop across the Resistance was recorded continuously, which was simultaneously the The current draw was approximately 100 mA. The capacity of the electrode was determined by integrating the current / time curves.

The property first examined was the influence of sulfur on the efficiency of the electrode. Since the same for all examinations Amount of iron salt was used, the values obtained indicate a definite tendency. Although the fabric formed does not has been analyzed for sulfur, it is assumed that the Total sulfur contained in the precipitate in the same proportion is how it was added to the KOH solution. In the case of the The total sulfur was obtained from divalent iron in the FeS-LowercIilag built in, while for the trivalent iron half of the sulfur was present as elemental sulfur.

The results obtained with the divalent iron are similar to FIG. 2 reproduced and summarized in the graph of FIG. The addition of a relatively large amount of sulfur built into the oxide had a beneficial effect on the utilization of the iron electrode. The efficiency without sulfur was below 10%, rose with the addition of 0.032 g of sulfur per g of iron 20%, increased to about 60% by five times that amount, and decreased then to 50% and 40% for 10 and 15 times that amount of sulfur from each g of iron. The discharge curve had two plateaus about 0.12 V apart. In the area of the first plateau the potential gradually decreased from about 1.4V to about 1.2V, where there was a marked decline. The discharge level remains

90 & 8läi1023

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then reasonably constant at a value of about 1.1 V until a rapid drop in potential indicates that the electrode is discharged.

Similar results were obtained for studies with trivalent Get iron. The iron (III) oxide could only be used without an additive marginally utilize it, and the disk had only a small capacity. The addition of a small amount of sulfur, about 3 riig / g Iron resulted in almost no change in the course of the discharge curve (FIG. 5, dashed line 1). With increasing amounts of sulfur the efficiency increased to a peak value of about 0.15 g Sulfur / g iron, and then when larger amounts of sulfur are added to take off again. The efficiency values achieved are compiled in FIG. The behavior was for divalent and trivalent iron similar.

Fig. 4 also shows the relationships for traversing several Cycles of a plate as obtained with 5 ml of molar KgS solution became. The utilization factor was 63.8% for the first cycle, 56% for the second cycle and 59% V for the third cycle

Investigations have been carried out in which sulfur flowers immediately mixed with the precipitates during their formation. Both to. trivalent and divalent iron solutions were used 0.1 g of sulfur was added and then stirred and the hydroxide precipitated. Otherwise the plates were treated as before. Fig. 6 shows that elemental sulfur increases the efficiency of iron hydroxide increased as battery substance. The effect on the divalent iron was more pronounced than on the trivalent iron, and it resulted utilization factors of 54% and 25% respectively. The curve 2 of the " Fig. 6 shows a certain peculiarity, as the discharge curve after the second plateau to about OJY V äbfiVl and a considerable one Time stayed at this value. This Potentiälplätäu "*" represents another unexplained discharge phenomenon of iSphwefel; wttrde observed that ^ aer efficiency with the Number of charge cycles increased (Fig. 5, curves 1 and 2) while a decrease was observed for KgS.

+) (utilization values)

In general, the addition of conductive substances to the otherwise non-conductive oxide has a beneficial effect on utilization. 1/2, 1 and 2 g of carbon black were added to the ferric solution before the precipitation. A small amount of wetting agent can be used to increase the wetting of the carbon black. As shown in FIG. 7, efficiency values of 70%, 96% and 112% were achieved. The incorporation of more carbon black had no further beneficial effect. The type of installation was changed by partially filtering the precipitate to a thick paste and then stirring in the carbon black, but this apparently did not lead to any additional increase in the effect. The increased utilization persisted into the third and fourth cycle, with values of 70, 96 and 80%. Since efficiency values of 112% were observed, this could be an indication that the discharge _{goes to Fe 3} O ₄ if the active mass has sufficient conductivity, but the possible participation of the wool latticework in the reaction could also explain this be.

Some studies have been carried out by using electrode active material with mixtures of Iron and sulfur in a range of about 5% S and 95% Fe bis

3 used about 66% S and 34% Fe and the capacities in both Ah / cm as well as in Ah / g of active material was measured .. The related Results obtained with these various tests are shown with the two Eurven of FIG. How from it As can be seen, there is a good working range for the same order quantity for the Fe: S wt% ratio between 95: 5 and about 65:35. A preferred range for the efficiency is between 7% and 36% sulfur, with the range of 12% - 19% sulfur Optimal forms.

Claim ·:

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Claims (4)

Pat en t an s'.p'r ü c he λ electrode for a secondary element, which has a plate of mixed together and thereby active electrode mass with iron oxide particles absorbing fibers, characterized in that the active mass (14), based on the weight of the iron, at least 5% by weight of sulfur, selenium, tellurium or Contains mixtures thereof. _% 2. Electrode according to claim 1, characterized in that the active mass (14) 5 - 66 wt%, preferably 12-19 wt%, des
Contains iron weight in sulfur, selenium, tellurium or mixtures thereof. 3. Electrode according to claim 1 or 2, characterized in that
the active mass (14) 10-50% by weight, preferably 35% by weight, of the
Contains iron weight in carbon. 4. Electrode according to claim 1, 2 or 3, characterized in that the fibers are made of nickel, KN / gb 3 909839/1023 Lee on the back