DE2229977A1 - METHOD OF APPLYING A NEGATIVE ACTIVE MASS TO AN ELECTRICALLY CONDUCTIVE SUPPORT - Google Patents

Description

Dipl.-Ing. H. Sauenland · Dr.-lng. R. König · Dipl.-Ing. K. Bergen

Patent Attorneys · 4000 Düsseldorf · Cecilienallee 7S · Telephone

Our file: 27,527 June 19, 1972

International Nickel Limited, Thames House, Millbank, London , SW. 1 England

"Method for applying a negative active composition to an electrically conductive carrier"

In nickel-iron accumulators, the active mass usually consists Made from a mixture of <^ - iron and magnetite (Fe ^ O ^) and is usually made by flushing a fine-grained pure iron with hot water, then heating in the presence of air on steam-heated tables manufactured. The mixture consisting of ^ iron and magnetite is then finely ground and tamped into tubes or bags that serve as conductors.

From the point of view of the capacity resulting from the reversible reduction and oxidation of the iron oxide during loading and unloading, normally not more than 20 to 23% of the iron of the mass is used. The invention is therefore based on the object of creating an active mass in which a higher percentage of iron, for example 40%, is used. Furthermore, the object is to create a method, naph which an active iron mass adhering firmly to a foil or another conductor, for example made of nickel, iron, copper or a nickel-iron

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Alloy, can be applied.

In the case of accumulators, the aim is the weight ratio to make the active mass as large as possible for the metal required for holding or holding it, in order to reduce the total weight of the accumulator in this way.

The object on which the invention is based is achieved by initially using an iron (II) ion and electrolytes containing ammonium ions, the active material is galvanically deposited on a carrier will. The galvanic deposition can take place in the presence of a ferrous ammonium salt, in which it preferably iron ammonium sulphate or iron ammonium sulphamate acts. The electrolyte need not necessarily contain a single salt; he can also take Using a mixture of iron (II) sulphate and ammonium sulphate or the corresponding sulphamates will.

The chemical composition of a mass deposited from the aforementioned electrolyte varies between pure iron on the one hand via iron oxide to pure iron (IIl) hydroxide depending on the process conditions, in particular depending on the pH of the electrolyte and the cathode current density. It is of particular importance to coordinate the process conditions so that at least part of the active material consists of iron oxide, hydrated oxide or hydroxide. The presence of substantial amounts of finely divided iron, for example 30 to 40%, in the active composition is without great disadvantage, although the active composition is preferably or at least to the greatest extent _; Part is oxidic.

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ORlQtNAL INSPECTED

However, the pH must be carefully adjusted, i.e. high enough to ensure that the Precipitation is at least partially oxidic, while on the other hand it must not be so high that it is coarse Iron (II) hydroxide precipitates out of solution. At low pH-value only iron and no iron oxide or hydroxide is deposited on the cathodic carrier. With increasing pH, iron (II) hydroxide becomes more and more common deposited on the cathode until essentially all of the iron is removed at a pH of about 5.5 the bath is precipitated as iron (II) hydroxide.

Although a high current density is always preferable, hydrogen can be generated at the cathode. which reduces the adhesion of the active composition to the film or the carrier. The maximum permissible current

density is therefore 140 mA / cm, but preferably 20

up to 100 mA / cm. If the current density is within the aforementioned range, the pH must be at least 2.5, preferably however 3 to 4.4 or 3 to 4. Unless the

If the current density exceeds 100 mA / cm, the pH should be slightly below 2.5, but not below 1.0.

Since it is essential to adjust the pH in the above-mentioned manner, the electrolyte must be buffered. as Buffers are particularly suitable, the dihydrogen phosphates of the alkali metals, especially sodium, which is the Electrolytes can be added pure or in phosphoric acid.

The alkali metal crime rates and lacquer rates are also used as buffers suitable, which can be added themselves or in the form of the alkalis with the corresponding acids. Through trials

2 0 ii 8 8 3 / Γ) S 3 9

it was found that the precipitate contains a small amount of anions of the buffer, which in the individual case of the current density and the concentration of the buffer is dependent.

The pH value of each electrolyte and buffer can be adjusted using caustic potash.

The electrolysis is preferably carried out at room temperature to 30 ^{° C.} The electrolyte preferably contains 0.1 to 0.65 M (NH ₂ ) 2 SO ₄ FeSO ₄ .6H ₂ O and 0.1 to 0.5 M NaH _£ PO ₄ .2H ₂ O. The anode is preferably made of Iron and is therefore soluble in the electrolyte.

The thickness of the precipitate increases essentially with the duration of the electrolysis, so that this takes place under the same process conditions is a practical indication of the depth of precipitation. The precipitation thickness is when using of films as a carrier preferably 10 to 100 / ^ m, although greater thicknesses of precipitation can be applied when the active mass is removed from the carrier.

The precipitate is blue-black and colloidal Appearance with a very large surface. The precipitate produced using the process according to the invention The accumulators produced have a good initial capacity; however, the capacity drops with repeated Charge and discharge cycles from undesirably low values.

A particularly important feature of the invention is that small amounts of sulfur, either as elemental sulfur, or as iron sulfide, can be introduced into the precipitate. It was found that the sulfur is the initial capacity

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ziisb increased and. the cycle duration is greatly increased. The sulfur is preferably added to the electrolyte as sodium methabisulfite in an amount of beneficial

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10 Ms 10 M added. Other sulfur carriers, including those which are chemically stable in the electrolyte, can also be used Thiourea and Natriurathiοsulfat can be used. Colloidal sulfur itself can also be obtained from a sulfur-containing one Buffer, for example from a buffer solution of sodium sulfite and sulfurous acid, which during The electrolysis is partially decomposed and releases sulfur, which can be introduced into the precipitate. The amount the sulfur introduced into the active material is preferably 0.1 to 1.0%.

The sulfur can be in the precipitate even during the initial electrolytic charging can be introduced from the conductive support to the negative electrode active mass. The sulfur can also consist of an alkali metal sulfide or polysulfide in the electrolyte originate, the concentration of which is 10 to 10 molar ..

The precipitate advantageously also contains copper. The electrolyte can contain a soluble copper salt, preferably copper sulfate, in such an amount that the precipitate contains 1 to 20% of the iron weight of copper. When copper is introduced in this way, the anode is preferably insoluble.

The invention is explained in more detail below on the basis of exemplary embodiments , in which the active material was applied to a 7 μm thick nickel foil by electrolysis at room temperature. In each case the weight increase measured in mg / cm and in most cases also the iron content of the precipitate was determined.

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In addition, the initial capacity became after a full charge in a solution containing 20% KOH and 1.5 g / L LiOH

Measured in mAh / cm of the electrode surface before the voltage against a mercury / mercury oxide comparison electrode fell to -0.6V; moreover, in most cases, the capacity also increased after several charging and discharging cycles determined in the same solution.

example 1

The electrolyte contained 0.6 M iron (II) ammonium sulfate (FeSO ₄ (NH ^) ₂ SO ₄ .6H ₂ O) and 0.5 M sodium _{biphosphate (NaH 2} PO 2H ₉ O) at a pH value of 3, 1. The electrolysis lasted

12.8 minutes at a cathode current density of 70 mA / cm, The increase in weight was 6.8 mg / cm with a precipitation density of 62 ^ m on both sides of the film.

/ ρ

The initial capacity was 1.6 mAh / cm and the capaci

after 10 charge and discharge cycles at 0.2 mAh / cm.

Example 2

In the case of an electrolyte of the type described in Example 1, the pH was increased to 3.3 by adding 0.2 M NaOH

set. The cathode current density was 50 mA / cm, and after 18 minutes of electrolysis there was a weight increase

would take from 12.24 mg / cm with a precipitation density of 100 ferns, on each side of the film. The initial capacity is

carried 1.56 mAh / cm and the capacity after 10 charging and discharging

charging cycles 0.18 mAh / cm.

Since the precipitate in the case of Examples 1 and 2 no

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Containing sulfur, the capacity was very low in both cases after 10 cycles. For this reason, the Examples described below, each sulfur introduced into the active material.

Example 3

The electrolyte contained 0.4 M iron (II) ammonium sulfate, 0.2 M sodium dihydrogen phosphate, 0.1 M sodium hydroxide and 0.001 M sodium methabisulfite at pH 3.6. After 12 minutes of electrolysis at a current density of 90 mA / cm, the sulfur content of the precipitate was 0.163%.

The weight gain was 6.05 mg / cm and the iron content in the active mass at 77%. The capacity behaved as follows when charging and discharging.

1st cycle 1.28 mAh / cm ²

.20. Cycle 2.36 "

40th cycle 2.34 »

100th cycle 1.83 ".

Example 4

The electrolyte contained 0.6 M ferrous ammonium sulfate, 0.6 M Sodium dihydrogen phosphate and 0.00006 M sodium methabisulfite. The electrolysis lasted 12.8 minutes at a pH of 3 to 4 and a current density of 70 mA / cm. It resulted a sulfur content in the precipitate of 0.10%, a weight

increased by 7.8 mg / cm and an iron content of the precipitate of 67%. During loading and unloading, the capacity behaved as follows:

1st cycle 0.89 mAh / cm ²
20th cycle 0.63 "

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40th cycle 0.34 mAh / cm ² 100th cycle 0.06 ".

Example 5

The experiment of Example 4 was repeated, except that the content of the electrolyte was sodium methabisulfite 0.0006M was increased. The sulfur content of the precipitation

was found to be 0.4%, the weight increase to 7.5 mg / cm and the iron content is 62%. Held during loading and unloading the capacity is as follows:

1. cycle 0.86 mAh / cm ² 20th cycle 1.66 » 40. cycle 1.37 " 100. cycle 0.56 ». Example 6

A different buffer was used in this attempt. The electrolyte contained 0.5 M ferrous ammonium sulfate, 0.1 M Lactic acid, 0.033 M sodium hydroxide, and 0.001 M sodium methabisulfite. After 9 minutes of electrolysis at a current density of 70 mA / cm and a pH of 3.7, this resulted

a weight gain of 4.1 mg / cm. The initial capacity

was 0.52 mAh / cm, while the capacity after the 9th cycle was 0.50 mAh / ole ² .

Example 7

In this experiment, a different buffer was used again for comparison with Example 6. The electrolyte contained 0.5 M iron (II) ammonium sulfate, 0.1 M tartaric acid, 0.066 M sodium hydroxide and 0.001 M sodium bisulfite for a

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a pH of 2.7. After 9 minutes of electrolysis gave at a current density of 70 mA / cm a weight increase

wax of 6.05 mg / cm. The initial capacity of 1.31 fell

up to the 9th cycle to 0.46 mAh / cm.

Example 8

In this experiment, a different sulfur compound was added to the electrolyte; it contained 0.6 M iron (II) ammonium sulfate, 0.1 M sodium dihydrogen phosphate and 0.002 M thiourea. The electrolysis lasted 12.8 minutes

a pH of 3 to 4 and a current density of 70 mA / cm. This resulted in a sulfur content of the precipitate of

0.17% and a weight gain of 11.2 mg / cm as well as a Iron content of the precipitate of 63%. The capacity developed as follows:

1. cycle 0.92 mAh / cm ² 20th cycle 0.61 » 40. cycle 0.87 " 100. cycle 1.36 ». Example 9

The experiment of Example 8 was repeated, but with instead of the thiourea, the electrolyte 0.002 M sodium thiosulfate were added. Revealed in the attempt

a weight increase of 10.8 mg / cm and an iron content of the precipitate of 75.7%. The capacities changed during loading and unloading as follows:

1. cycle 1, 09 p
mAh / cm 20th cycle O, 67 Il 40. cycle 2, 27 Il
•

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Example 10

Another experiment was carried out to show that the sulfur carrier can also be used as a buffer. The electrolyte contained 0.5 M iron (II) ammonium sulfate, 0.03 M sodium sulfite and was flushed through with sulfur dioxide if it contained 0.1 M sulfuric acid. To 10-minute electrolysis at a pH of 3.8 and

a current density of 60 mA / cm resulted in a weight

2 2

increased by 4.3 mg / cm. The initial capacity of 0.93 mAh / cm

increased to 1.02 mAh / cm on the 20th cycle.

Examples 3 and 8 show in particular that the presence of a certain amount of sulfur in the precipitate after leads to an increase in capacity during several cycles Examples 4 and 5 show the importance of the precipitate containing sufficient sulfur.

Example 11

Another experiment was carried out to show how copper can also be introduced into the precipitate during electrolysis and sulfur can be introduced into the precipitate during initial charging. The electrolyte contained 0.4 M iron (II) ammonium sulfate, | FeSO ₄ (NH ₄ ) ₂ SO ₄ .6H ₂ o3, 0.1 M lactic acid, 0.05 M sodium hydroxide and 0.04 M copper (II) - Sulfate. The electrolysis lasted 14 minutes at a pH of 2.15 and a current density

p ρ

te of 50 mA / cm; it resulted in a weight increase of 14.5 mg / cm. The copper content in the precipitate was 15.7% of the iron weight. The finished electrode was charged in a solution with 20% KOH, 1.5 g / l LiOH and 7 10 " ³ M sodium sulfide (Na ₂ S.9H ₂ O) and then in a solution with 20% KOH and 1.5 g / l LiOH charged and discharged cyclically.

? η? ■ a a -3 / η ρ 3 r

capacity as follows:

Initial capacity 5.9 mAh / cm 20 cycles 5.1 ti 40 cycles 5.1 ti 60 cycles 4.9 Il
•

According to the method according to the invention, the active mass can be applied to a wide variety of sheet metal supports, however, in order to achieve an optimal capacity / weight ratio, a film that is so thin should be used is how it can be reconciled with the current of the accumulator. Such a film is advantageous perforated and can then be stacked to form accumulator plates according to German patent application P 20 18 974.6.

Because of its excellent properties, the after According to the method according to the invention deposited active material can also be used in tubes or bags. In this case it can the active mass can be continuously removed from the carrier during the galvanic deposition. So can the active mass, for example, deposited on a rotating drum cathode and peeled off from this.

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Claims (18)

International Nickel Limited, Thames House, Millbank, London , SW 1 England Claims; I. Method for applying a negative active mass to an electrically conductive carrier, characterized in that that the active mass electrolytically consists of an iron (II) ions, ammonium ions and a Buffer-containing electrolytes is deposited at least partially oxidically. 2. The method according to claim 1, characterized in that that the active mass is deposited on a foil. 3. The method according to claim 1 or 2, characterized in that the active · mass in a pH of 3 to 4.4 and a current density of 20 to 100 mA / cm is precipitated. 4. The method according to one or more of claims 1 to 3, characterized in that the Electrolyte contains iron (II) ammonium sulphate. 5. The method according to one or more of claims 1 to 4, characterized in that the Electrolyte contains a dihydrogen phosphate of an alkali metal. 6. The method according to one or more of claims 1 to 5, 209883 / Π639 characterized in that the bath temperature is between room temperature and 3O ⁰ C and the bath 0.1 to 0.65 M (NH ^) ₂ SO ₄ FeSO ₄ .6H ₂ O and 0.1 to 0.5 M NaH ₂ PO ₄ Contains .2H ₂ O. 7. The method according to one or more of claims 1 to 5, characterized in that the Electrolyte contains lactic acid. 8. The method according to one or more of claims 1 to 7, characterized in that the Electrolyte contains a sulfur carrier. 9. The method according to claim 8, characterized in that the electrolyte is sodium methabisulfite contains. · 10. The method according to claim 8, characterized in that that the electrolyte contains a decomposing and sulfur-containing buffer. 11. The method according to claim 8, characterized in that the active mass is electrolytic and the sulfur from the electrolyte is introduced into the precipitate upon initial charging. 12. The method according to claim 11, characterized in that that the initial charging is in a solution with potassium hydroxide, lithium hydroxide and an alkali metal sulfide or polysulphide, 13. The method according to one or more of claims 1 to 12, characterized in that the 209B83 / 0839 Electrolyte contains a soluble copper salt in an amount that has a copper content of 1 to 20% of that of iron results in precipitation. 14. The method according to claim 13, characterized in that that the electrolyte contains copper sulfate. 15. The method according to claim 1, characterized in that that the electrolyte contains iron (II) ammonium sulfate and sodium dihydrogen phosphate and the pH Value 3 to 4 and the cathode current density 20 to 100 mA / cm amounts to. 16. The method according to claim 1, characterized in that the active mass is continuous removed from a carrier. 17. Electrode produced by the method of claims 1 to 16, characterized in that the active mass 0.1 to 1.0% sulfur and / or 1 to 20% Copper, based on the iron, contains. 18. Electrode produced by the method of claims 1 to 16, characterized in that the carrier consists of a film. 209883/0639