DE2206828A1 - Activated iron electrode material - Google Patents

Description

DIPL.-ING. KLAUS NEUBECKER

Patent attorney
4 Düsseldorf 1 Schadowplatz 9

Düsseldorf, February 1972

Westinghouse Electric Corporation
'Pittsburgh, Pa., V. St. A.

.Activated pilaster electrode material

The present invention relates to iron negative electrodes for an iron / nickel or iron / air collector.

Regarding the design of collector or battery cells
certain parameters, such as the weight amount of iron oxide, in grams, that can be absorbed per electrode volume unit in cm 3. Hence every possibility comes the actual evaluation
of iron oxide is of considerable practical importance
to. A serious problem with sealed battery cells with alkaline iron electrodes is the violent evolution of hydrogen gas during most of the charging process.

The iron battery electrode plate has a fine-grain iron powder that is deposited in a supporting base plate and compressed to a desired density. When using pure
Isenoxiclpulver as an active electrode material in an alkaline electrolyte results from the rapid formation of a
passivating film on the iron surface is a limitation
the evaluation of the battery.

To facilitate the discharge of the electrode plate, the

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active electrode material an additive promoting the reaction is necessary. Such an additive should have the ability to activate the entire substance, but only proportionally be present in small amounts.

It is known to use iron oxide powder in an iron negative electrode To add iron sulfides or elemental sulfur as additives. This caused sulfide absorption by the iron electrode from a solution of hydrogen sulfide in the electrolyte or a mechanical mixing of the iron sulfide with iron oxide and fusing of the elemental sulfur with iron oxide at increased Temperatures with itself.

The object of the present invention is to provide an electrode material create aas does not have these disadvantages and a better efficiency in the practical use of the electrode plates enables. This object is achieved according to the invention by that an activated iron electrode material is the product of the reaction of particles of iron oxide, iron oxide hydrate or mixtures containing it with a sulfur-substituted organic acid.

The invention is explained below using an exemplary embodiment explained in connection with the accompanying drawing. In the drawing show:

1 shows an electrode plate filled with the active battery material according to the invention;

2 is a graph showing the relative performance of various Illustrates sulfur-containing activators in iron electrodes;

3 is a diagram illustrating the charge acceptance behavior of iron electrodes activated with thioacetic acid; and

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4 is a diagram showing the charge absorption behavior of with Thio malic acid activated iron electrodes illustrated.

Line battery version, in which the active material after the Invention can use, has a plurality of alternating negative (Lisen) and positive (nickel) plates, between which there are separating plates and all of them are ro. with an alkaline bloktrolytes are in contact. The entire plate structure and the electrolyte are in a housing with a cover, a venting device as well as positive and negative connections.

Preferred electrode plates, as shown in Fig. 1 of the drawing are made of fibers, preferably nickel fibers, or rivet-coated fibers such as coil-coated steel or Lisen made. Line such plate 10 has the shape of a flexible, stretchable compressed 3ogens of relatively smooth, iu essentially in contact, mixed together metal fibers, as indicated in a region 11 of the plate 10. The embodiment shown in the aera is the upper edge 12 of the plate 10 is compressed to a great density. The compressed area of the upper edge 12 forms an attachment base uie connecting lugs 13 can be attached, for example, by spot welding can. The plate preferably has a porosity between 75 and 95%, i.e. H. , it has a board density between 5 and 25% the theoretical density. The spaces between the fibers forming the base plate are covered with activated iron electrode material filled to form the actual flexor plate.

The metal fibers are preferably metallurgically in a protective atmosphere at temperatures up to the melting point of fibers used interconnected by diffusion. Such a metallurgical diffusion bond occurs no melting of the fibers. When the fibers melt, protuberances are formed which fill them with active material (Filling volume) inside the base plate. At the pre-

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The additional plate design should only allow interdiffusion of metal atoms occur at the metal interface corresponding to contact points 14 along the fiber length. Through metallurgical diffusion bonding an electrode structure with a large pore volume is obtained, in which the active material in paste form or other shape can be introduced. The metallurgical diffusion bond also increases the resistance of the electrode plate and thus the internal cell resistance of a finished cell is considerably reduced. However, the invention can also be used in the Can be used in connection with other panel structures.

The proportion of active material can be produced by reacting iron oxide particles with sulfur-containing organic acids. The iron particles are in the form of a fine grain powder for which the average particle size range is between about 0.2 and 74 microns. The active particles have at least one iron oxide or an iron oxide hydrate and the additive. The iron particle component can, for example, iron (II) oxide (FeO), iron (III) oxide (Fe ₂ O3), iron (II, III) oxide (FeO-Fe ₂ O ₃ or Fe3O4), iron (III) - Oxide hydrate (Fe ₂ O3 * H ₂ O) and mixtures thereof.

Suitable commercial iron oxide compounds are Mapico Black (from Columbian Carbon Company) with about 99% Fe3O4 (22% FeO + 77 'i Fe ₂ O3) and Meramec 25 (from St. Joseph Lead Company) with about 94% Fe3O ₄ and 5 % Fe ₂ O ₃ and SiO ₂ , Ca ₂ O, Al ₂ O ₃ , and also MgO impurities.

The Eisenpartikelkoraponente can through contact with sulfur-substituted organic acids with a thio structure such as thioacetic acid, thioiscpropionic acid, thioformic acid and thiobenzoic acid, also with a dithio structure such as dithiodiglycolic acid and DitLiodibenzoic acid be formed. Examples of the contact of an acid with a thio structure are the reactions:

0 ρ

FeO + 2H-SC-CII ₃ > Fe (SC-CH ₃ ) ₂ + H ₂ O;

Iron (II) oxide thioacetic acid iron thiosalt \

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JO -CH ₃ »2 [Fe (SC-CH ₃ J ₃ ] + 3H ₂ O

Ferric oxide thioacetic acid iron thio salt

^6-12 ° _> 2 [Fe (SC-CH ₃ ) ₃ ] + 6H ₂ S

2Fe ₂ O ₃

4FeS + 23 + 6Ii ₂ O

Iron sulfide

The reaction product of ferrous oxide and thioacetic acid appears being a dark green jüisen (II) thioacetate, one at room temperature stable connection. Rapid disintegration occurs when the solid is heated or when it is boiled with water a wide variety of products including iron sulfide and hydrogen sulfide results. The corresponding reaction with iron (III) oxide is quite complex, as shown above, and yields iron QEQ thioacetate. Iron (III) thioacetate is not stable at room temperature and undergoes slow hydrolysis, which then leads to Iron acetate, iron sulfide and sulfur yields. With regard to the sulfur-containing thioacids, it can be assumed that the electrode activating substance has a mixture of iron thiosalt and iron sulfide.

The sulfur-substituted organic acids with a thio structure, such as 'They are intended to be used in conjunction with the invention ciie structure;

lib-e-R

wherein R a '/ asserstoffradikal, a linear alkyl radical having from 1 to' j Koiilenstoffatomen, the monovalent branched carbon chain radical

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- Cri

(X = alkyl radical with 1 to 4 carbon atoms) a monovalent organic homocyclic radical from the group containing -CgK5 and -CsH ^ j radicals, a monovalent organic heterocyclic radical from the group containing -CsH ^ and -C ^ HsO radicals and a monovalent organic alicyclic radical like etv / a the ~ ^C 6 ^H 11 ^{radical is}

The sulfur-substituted to be used in connection with the invention Organic acids with a dithio structure have the structural formula:

O O

Il U

HSC-Y-CSH,

where ¥ is a radical from the group consisting of -CH ₂ OCH ₂ - and -C2H4OC2H4-radicals as well as divalent organic homocyclic radicals such as -Cgii4 ~.

The iron particle component can also be activated by contact with sulfur-substituted organic acids with a mercapto-carboxylic acid structure such as thio malic acid (HOOCCH (SH) CH ₂ COOH), thioglycolic acid (mercapto-lacetic acid), mercapto-propionic acid and mercapto-butyric acid. An example of the KontakiP / fine mercapto-car donic acid includes the reaction:

O
Il
HOC 36 2 ., O
Il
OC. Fe ₂ O3 + 2 HS. CKo
\ l
Vn
CL
HOC / 08 ^Fe \ T / ^ci1
Il L O O Lisen (III)
Oxia S-Fe chelate 06 Thio apple
acid > 098

The reaction product of ferric oxide and thio malic acid is a chelate with 1: 1 stoichiometry. This chelate is opposite Hydrolysis stable, and with regard to the electrode it can be said that it did not initially ate any iron sulfide or elemental Contains sulfur. It can be assumed that in this case organic sulfur-iron chelate acts as the electrode activator is sam.

sulfur-substituted sulfur-substituted ones used in connection with the invention organic acids with a mercapto-carboxylic acid structure a structural formula from the group with the structural formula:

R ¹ COOIi,

Sh

contain, wherein R 'from the group of divalent aliphatic hydrocarbon radicals having 1 to 5 carbon atoms - where the (Sh) group bond with each R carbon atom can -, of divalent organic homocyclic radicals like

- and the divalent organic alicyclic radicals such as - and

UOOC R "COOH

Sh

can
be selected /> wcrin R "in turn from the group of trivalent aliphatic hydrocarbon radicals with 1 to 4 carbon atoms - where the (Sh) group can form a bond with any R" carbon atoms - can be selected. Mixtures of these acids can also be used.

other sulfur-substituted organic acids that can be used Allowing alcohol to be used as a solvent instead of water are dithio acids with the structural formula:

HS-C-Z,

wherein Z from the group of alkyl radicals having 1 to 4 carbon atoms, a hydrogen radical and monovalent organic horno-

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cyclic radicals selected from the group of -CgHs and is. The dithio acids are not as valuable as the other acids described above because they are not soluble in water and are relatively unstable at room temperature.

Super-activated ones made as described above Iron electrode materials should have a total sulfur concentration in the range of 0.01 to 1.0 wt% sulfur in the (iron) - (sulfur-substituted organic acid) reaction product for batteries with acceptable electrochemical behavior in all respects to have.

The invention is explained below using the following exemplary embodiments:

Example I.

Six 6.25 cm ² metallurgically bonded, stretchable LS-nickel fiber electrode plates with a porosity of about 85% were filled with an aqueous slurry of iron powder, the iron powder having a particle size of about 44 microns (325 mesh) and a composition of about 94 , 0% Fe3Ü4, 5.0% Fe2O3, 0.3% SiO ₂ , 0.35% Ca20, 0.25% ΛΙ2Ο3 and 0.20% MgO (sold under the trade name Meramec 25 by the St. Joseph Lead Company) would have. The plates filled with iron oxide were then dried, weighed and placed in 200 ml of an aqueous solution of 0.1 molar for about half an hour:

(a) thioacetic acid,

(b) thio malic acid,

(c) thioglycolic acid,

(d) thiobenzoic acid,

(e) dithiodiglycolic acid and

(f) 2-mercaptoethanol (KSCH ₂ Ct ^ OH)

soaked.

The activated panels (a-e) and panel (f) were then dried and weighed. Electrochemical test values were determined for the individual plates using a single nickel / iron

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battery-plate system in 25% by weight KOH electrolyte at a load of 17.6 mA / cm ² for 30 cycles (charge and discharge). The electrochemical behavior of the individual plates is shown with FIG. 2 of the drawing.

Electrodes activated with thioacetic acid, thioglycolic acid, and thio malic acid gave excellent outputs as these materials a high acidity on iron and with the iron oxide surface react quickly. Electrodes activated with thiobenzoic acid or dithiodiglycolic acid showed a moderate capacity. Of the Thiobenzoic acid activator has very limited solubility in Water and had too weak an acidity to react quickly with the iron oxide. The electrode immersed in 2-mercaptoethanol showed a weak electrochemical capacity in relation to the other electrodes and decreased very quickly in level, as 2-mercaptoethanol does not contain an acid group and does not cause any appreciable reaction with the iron oxide. With thioacetic acid and Thio malic acid super-activated electrodes achieved an output power of about 0.53 to 0.62 Ah / g active ^ after 25 cycles Electrode material.

Charge absorption curves for “iron electrodes activated with thioacetic and thio malic acid, measured on the basis of the volume of hydrogen released from the electrode during the charging process, at a charge density of 53.3 mA / cm ² , are shown in FIGS. 3 and 4. A reproducible plateau between 1.15 and 1.22 V compared to an IIg / HgO reference electrode was observed for the super-activated electrode, in which the electrode takes up charge at high speed with negligible generation of gas, as can be seen from FIGS. 3 and 4, Gas formation only becomes important after about 55% of the theoretical charge has been absorbed by the electrode. Such a process enables a shorter charging time and is particularly advantageous for tightly sealed battery cells or cells in which violent evolution of hydrogen gas is harmful.

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The ratio of total sulfur content for the active material The reaction product within the electrode plates (a-e) and the plate (f) is shown in Table 1 below:

Table 1

Plate (a) (b) (c) (d) (e) (f)

Fill 0.232 0.242 0.233 0.283 0.283 0.306 (g oxide / cm ² )

Total sweat 0.42 0.31 0.19 0.05 0.05 0.05 f el fraction (wt%)

Example II

There were activated electrode plates (g) and (h) v / ie in example I prepared, with the difference that they were for 12 hours in 200 ml 0.1 molareaa aqueous solutions of

(g) thioacetic acid and
(h) thio malic acid

have been softened.

The electrochemical test values were as in connection with Example I determined. The electrodes (g) and (h) super-activated for a longer period of time with thioacetic and thicapic acids reached after 25 cycles an output power of about 0.7 Ah / g active electrode material. The longer treatment of iron oxide with the acid resulted in electrodes with higher efficiency.

The procedures for activating the iron oxide powder are the same the above examples are significantly cheaper and simpler than comparable processes according to the prior art.

These electrodes, which are activated too quickly, show an increase in speed in terms of charge absorption without significant gas evolution, their behavior being favorable in a comparison compared to electrodes, which are caused by the

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molten sulfur processes are activated which normally results in output powers in the range of 0.50 to 0.55 Ah / g active material.

Patent claims:

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Claims (14)

Patent claims: flj Activated iron electrode material, characterized in that that it is the product of the reaction of particles of iron oxide, hydrate of iron oxide or mixtures thereof with a sulfur-substituted one has organic acid. 2. Material according to claim 1, characterized in that the sulfur-substituted organic acid has the structural form. Has: Il IIS-C-R, wherein R is a hydrogen atom, a linear alkyl radical with 1 to 5 carbon atoms, a radical with the structure: I.
- CIi, (where X corresponds to an alkyl radical with 1 to 4 carbon atoms), or a -CH ₅ , -C ₅ II ₄₇ -C ₅ H ₄ INi, -C ₄ II ₃ O or "CgH ₁₁ radical. 3. Material according to claim 1, characterized in that the sulfur-substituted organic acid thioacetic or thiobenzoic acid is. 4. The method according to claim], characterized in that the Schv / efelsubstituierte organic acid is at least one of the compounds with the structural formula: _R | cooH and EOOC-R "-COOII SH SH, wherein R ¹ corresponds to a divalent aliphatic hydrocarbon radical having 1 to 5 carbon atoms, -C ^ H.- or -C ₁ -H ₁ _- and wherein R "corresponds to a trivalent aliphatic hydrocarbon radical having 1 to 4 carbon atoms. 209836/0806 5. Material according to claim 1, characterized in that the sulfur-substituted organic acid is thio malic or thioglycolic acid. 6. Material according to claim 1, characterized in that the sulfur-substituted organic acid has the structural formula: O O Il Il HS-C-Y-C-SIl, wherein Y corresponds to a -CK2OCH2-, -C2H4OC2H4- or -Cß ^ radical. 7. Material according to claim 1, characterized in that the sulfur-substituted organic acid is dithiodiglycolic acid is. 8. Material according to claim 1, characterized in that the sulfur-substituted organic acid has the structural formula; ES-C-Z, wherein Z is an alkyl radical having 1 to 4 carbon atoms, a hydrogen atom or a -C6H5 or -Csl ^ radical is equivalent to. 9. Material according to one or more of claims 1-8, characterized characterized in that the reaction product contains between 0.01 and 1 Gewä sulfur. 10. Electrode plate with a base plate covered with iron electrode material is filled, characterized in that the material is the reaction product of particles of bison oxide, Contains hydrate of iron oxide or mixtures thereof with a sulfur-substituted organic acid. 11. Plate according to claim 10, characterized in that it has a porosity between 75 and 95 "and metallurgically mit- 209836 / Ü80b - Contains 14 interconnected metal fibers. 12. Plate according to claim 10 or 11, characterized in that the particles of FeO, Fe2O3, Fe3O4, Fe2O3-H2O and Geraischen consist of it. 13. Plate according to claim 10, 11 or 12, characterized in that the reaction product between about 0.01 and 1 Gev /% sulfur contains. 14. Plate according to one or more of claims 10-13, characterized characterized in that the sulfur-substituted organic acid has a structure as claimed in any one of claims 2-8. KN / hs 3 209836/0806