DE1939794B2 - NEGATIVE MAGNESIUM ELECTRODE FOR GALVANIC ELEMENTS - Google Patents

Description

The invention proposes magnesium alloys, which improved electrochemical Have properties when used as negative electrodes in galvanic elements.

The main types of battery systems or galvanic elements in which magnesium alloys are used are the magnesium seawater cells, which usually use silver chloride as the cathode · τ> (positive electrode) as well as the dry magnesium cells of the Leclanche type, in which Manganese dioxide or other materials can be used as a depolarizer. Magnesium alloy electrodes are usually used in seawater batteries> o in the form of sheets or foils with a thickness of 0.16-0.65 mm used. With certain larger batteries, however, stronger electrodes can also be used Form of cast or extruded sheets can be used. In cells of the Magnesium Leclanche « Typically, the electrode is in sheet metal form or in the form of extruded cylindrical cans before.

The magnesium alloy that is currently widely used for magnesium seawater batteries is the AZ61 alloy, which contains around 6% aluminum, 1% zinc and 0.2% manganese. It has been shown that this alloy provides the best compromise of the properties which is necessary for the successful use of a magnesium seawater cell, namely a high electrode potential when working with high discharge speeds and the formation of a very fine, granular reaction product, which can be easily flushed from the cell without clogging or occluding the cell. A solution treatment extending over several hours at 400 "C is essential in order to produce a uniform single-phase structure which gives this alloy the required properties. Typical cell voltages for this alloy in the form of thin, roughened sheets when these are in a magnesium-seawater-silver chloride cell Working under flowing seawater with a salt content of 21 at 20 to 25 "C and an electrode spacing of 0.5 to 0.58 mm at a current density of about 0.31 A / cm ² are in the order of magnitude of 1.0 volts.

By adding other elements to the specified Alloy composition, other alloys have been developed which have higher electrode potentials under discharge without any noticeable deterioration in the shape of the To give reaction product. Such alloys can be 6% aluminum, 1% zinc, 0.2% manganese, up to Contains 10% lead or 1 to 10% lead and 0.5 to 5% mercury. Such alloys are in U.S. Patent 3,288,649.

A typical alloy containing about 7% aluminum, 1% zinc, 0.2% manganese and 0.5% lead was rolled out on a thin sheet and then subjected to a solution treatment to give a uniform single phase structure, followed by the Surface has been roughened with a wire brush. When such an alloy was used in a magnesium-seawater-silver chloride cell with a flowing electrolyte and an electrode spacing of 0.5 to 0.58 mm at a current density of 0.31 A / cm ² , cell voltages of the order of magnitude of Get 1.15 volts.

Pure magnesium is unsuitable per se for these purposes, since during the use of the Cell the reaction product formed is thick, flaky and sticky and leads to the magnesium too polarize and clog the cell. Similarly, lead or mercury can be added to pure magnesium alone the desired combination of a high potential and a fine non-clogging Reaction product can not be achieved.

It has now been found that, by adding thallium, it becomes pure within certain limits Magnesium alloys can be produced which, when discharged, have a very high electrode potential and which do not form a thick reaction product that easily clogs the cell. Magnesium alloys containing thallium can be pressed into thin sheets without difficulty or rolled out.

The invention thus relates to a negative magnesium electrode for galvanic elements made from a magnesium alloy with the following alloy components:

Thallium 1 until 15th Wt% aluminum 0 until 10 Wt% mercury 0 until 5 Wt% lead 0 until 5 Wt% zinc 0 until 3 Wt% manganese 0 until 1 Wt% Calcium 0 until 1 Wt%

cadmium
magnesium

0 to 1% by weight
at least 80% by weight

The following Table I shows typical electrode potential values and details about the result Reaction product, as found from experiments in which the magnesium alloys as Anodes (negative electrodes) in an electrical

Table I.

Electric circuit were used so as to mimic the discharge ratios, which in a high Sea water cell exhibiting energy density occur. The alloys were in the form of round ones cast bars which have been solution treated to give a uniform single phase structure result.

alloy Middle electrodes
potential (volts)
with reference to non-
polarized AgCI Pure Mg 1.57 Mg + 6% Al + 1% Zn + 0.2% Mn 1.55 Mg + 6% Al + 1% Zn + 0.2% Mn + 5% Pb 1.74 Mg + 5% Hg 2.00 Mg + 5% Pb 1.70 Mg + 7 '/ 2% tsp 1.85 Mg + 11% tsp 1.98

Condition of the electrode surface

thick adhering precipitate
pure

almost completely pure
voluminous precipitation
thick adhering precipitate
very fine powdery precipitate medium-fine powdery precipitate

The potential values are given in volts with reference to AgCI, with no drop in resistance within the Cell was present.

When an alloy consisting of manganese with 7 '/ 2% thallium was rolled into a thin sheet and then heat treated to obtain a uniform structure, and these sheets in a magnesium-seawater-silver chloride cell with flowing electrolyte and an electrode gap of 0, 5 to 0.58 mm under a current density of about 0.31 A / cm ² , cell voltages of 1.4 volts were observed.

Because of the high solubility of thallium in magnesium, the possibility that the thallium forms a desired secondary phase in the metal during processing is very substantially reduced. The solution treatment of the binary alloy is therefore only required for the reason to to achieve an even distribution of the thallium in the material.

The electrode potential of alloys containing thallium can be increased by increasing the thallium content by up to 15%, but no further advantage is obtained beyond this value. This can be seen from the figure of the drawings, which shows the change in the maximum and mean potential for a discharge lasting 5 minutes and also the evolution of hydrogen as a function of the thallium content. These values were obtained in an experiment in which the cross-section of a cast rod was used as the anode in a cell containing seawater, the other electrode being a platinum mesh. Current was passed through the cell in order to simulate a battery discharge of 0.31 A / cm ² , and the electrode potentials on the magnesium surface were measured against a silver / silver chloride capillary electrode. During this experiment, the hydrogen evolving on the anode was collected.

For use in seawater batteries are the

jo optimal alloys those which during show the least amount of sludge formation during discharge, which also corresponds to the least amount of water generated. So these are those alloys that are between 4 and 12% and especially thallium

υ those between 5 and 10%, for example between Contains 6 and 9% thallium.

For magnesium dry cells and for batteries in which there is only a small flow of seawater, the shape of the reaction product is not so

■ to critical, as for pure seawater batteries, and as a result lower concentrations of thallium can be used for such purposes, which a result in larger electrode potential and with which during use thicker and more strongly adhesive Reaction products are formed.

If aluminum is added to magnesium alloys containing thallium, then during use a fluffier but less adhesive reaction product, which with increasing aluminum

> O salary is getting finer and finer. Aluminum in a lot from 4 to 7% in the alloy results in a fine flaky precipitate which falls off the surface the plate can be easily washed off, but it builds up with smaller amounts of aluminum thick, flaky precipitate on the surface of the material, which leads to a drop in potential Has.

For example, when an ^{alloy containing 7]} /:% thallium and 5% aluminum is included among the in

W) the conditions laid down in Table I are checked, this results in an electrode potential of 1.78VoIt with an almost completely clean surface, and an alloy containing 11% thallium and 5% aluminum gives an electrode potential of 1.83 volts

hj with just a loose powdery precipitate on the surface. Additions of up to 10% aluminum can be used in the alloys.
In Table II the Snunniinepn iirwl i \ io

Sludge formation properties for different alloys compiled, which were obtained in a single-cell test setup with flowing artificial sea water with a salt content of 21 at a temperature of 25 ° C. In this experiment, cells measuring 152 × 50 mm were assembled by juxtaposing a magnesium alloy sheet and a silver chloride foil between silver conductors. The electrolyte distance between the magnesium and the silver chloride was maintained by glass spheres which were embedded in the silver chloride. It was measured with an electrode gap of 0.6 mm and a linear electrolyte flow rate of 6 cm / sec. worked between the plates. The cells were constantly discharged to r, for 10 minutes at 0.31 A / cm ^2.

Table II

Stress and sludge formation in various alloys due to the addition of mercury or lead to the Magnesium battery alloys increase the electrode potential of the alloy. It is found been that by adding lead and / or mercury to the thallium-containing alloys a further increase in the electrode potential can be achieved, although a somewhat greater one Sludge formation takes place. Additions of up to 5%, for example 0.5 to 5%, of each of these elements can be used be made. By adding mercury to thallium alloys containing aluminum will be barely profitable improvement in tension and little improvement in Sludge properties achieved. Examples of such alloys are shown in Table II.

alloy

% TI% ΛΙ

% Hg% Pb

Typical voltage values according to time in minutes '/ 2 1 I' / 2 2 4

Mud condition

9 2 1 7th 2 1 7 '/ 2 2 2 8th 2 9 5 5 5 7th 5 7 '/ 2 5 8th 5 9 7 '/ j 5 7 '/: 5 7 Ί: 5 ΊΊ: ΛΖ6Ι Al'65

1.17 1.17 1.16 1.14 1.10 1.06 1.05 black down
hit metal 1.20 1.20 1.20 1.19 1.15 1.12 1.15 low black
Precipitation on metal 1.23 1.23 1.23 1.23 1.25 1.24 1.14 the same 1.26 1.28 1.32 1.41 1.36 1.11 0.84 adhere moderately
the black film 1.35 1.35 1.37 1.39 1.30 1.05 0.71 strong black
Movie 1.25 1.28 1.29 1.31 1.34 1.19 1.00 the same 1.25 1.30 1.33 1.33 1.24 1.06 1.00 looser flaky
Precipitation 1.32 1.32 1.31 1.30 1.18 1.10 1.03 the same 1.35 1.33 1.30 1.27 1.17 0.99 1.02 stronger flaky
Precipitation 1.36 1.33 1.30 1.28 1.17 1.00 1.06 the same 1.10 1.10 1.10 1.08 1.08 0.96 0.94 pure surface 1.27 1.28 1.27 1.26 1.21 1.15 1.13 pretty pure
surface 1.28 1.29 1.28 1.27 1.22 1.17 1.15 the same 1.30 1.30 1.28 1.26 1.21 1.15 1.12 less powdery
Precipitation 1.31 1.32 1.30 1.27 1.22 1.15 1.10 medium powdery
Precipitation 1.39 1.37 1.32 1.29 1.14 0.86 0.72 very strong
Precipitation 1.25 1.27 1.27 1.26 1.21 1.17 1.16 pure surface 1.21 1.22 1.22 1.21 1.18 1.12 1.12 pure surface 1.20 1.25 1.26 1.26 1.21 1.17 1.12 medium strength
Precipitation 1.04 1.04 1.04 1.03 0.97 0.92 0.91 pure surface 1.15 1.18 1.18 1.17 Ι, Π 1.05 1.03 low black
powdery nicdcr-
clever

The alloys according to the invention can thus contain the following elements:

Preferred

optimum

Thallium 1 to 15% by weight 4-10% 6-8%

Aluminum 0 to 10% by weight 0-7% 4-6%

(e.g. 1-7%) mercury 0 to 5% by weight

Lead 0 to 5% by weight
Zinc 0 to 3% by weight
Manganese 0 to 1% by weight
Calcium 0 to 1% by weight
Cadmium 0 to 1% by weight

The water-activated battery can contain a cathode part using a silver chloride

10

15th

or cuprous chloride plate in conjunction with a silver foil or other conductive material and an anode made of the magnesium alloy in the form of a thin-rolled sheet of 0.13 to 0.64 mm (e.g. 0.25 to 0.5 mm) spaced 0.5 to 2.5 mm from the chloride.

The heat treatment of the alloy may be carried out at temperatures of 350 to 450 ⁰ C for 4 to 60 hours, and it is carried out for example at 380 to 420 ° C 8 to 24 hours at alloys containing up to 12% thallium.

The alloys according to the invention contain at least 80% magnesium.

The subject matter of the invention can also be used in conjunction with an "air battery", like them is described, for example, in British Patent 1140 635, in that the anode consists of a of the alloys described here. The anode can be 1.27 to 3.8 mm thick be rolled out or pressed out.

1 sheet of drawings

Claims (5)

Patent claims: 1. Negative magnesium electrode for galvanic elements made of a magnesium alloy with the following Alloy components: Thallium 1 to 15 wt% aluminum Obis 10% by weight mercury Obis 5% by weight lead 0 to 5% by weight zinc Obis 3 wt% manganese Obis 1% by weight Calcium Obis 1% by weight Cadium Obis 1% by weight magnesium at least 80 C 2. Electrode according to claim 1, characterized in that the alloy is 4 to 10% thallium and contains 1 to 7% aluminum. 3. Electrode according to claim 1 or 2, characterized in that the alloy is 6 to 8% thallium and contains 4 to 6% aluminum. 4. Electrode according to claim 3, characterized in that the alloy 6 to 8% thallium, Contains 4 to 6% aluminum and 0.5 to 5% lead and / or mercury. 5. A method for pretreating the electrode according to claims 1 to 4, characterized in that that the electrode is subjected to a heat treatment at 350 to 450 "C for 4 to 60 hours will.