RU2444093C1 - Anode for chemical source of current, method to manufacture anode, chemical source of current - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: anode for a chemical source of current with alkaline electrolyte is made of an aluminium-based alloy containing 0.01-0.1% gallium, 0.1-1% indium, 0.2-2% magnesium. Alloying components are introduced into composition of the alloy in the form of aluminium-based alloys containing 0.1-5% gallium, 1-10% indium and 2-20% magnesium. The alkaline electrolyte contains sodium stannate in concentration of 2-10 g/l.

EFFECT: development of the anode and the chemical source of current with the anode capable of long-term operation without passivation.

No cl, 7 dwg, 2 ex

Description

The invention relates to the field of electrical engineering, and more specifically to chemical current sources with an anode of aluminum alloy and an alkaline electrolyte.

A known anode of a chemical current source with an alkaline electrolyte made of aluminum alloy, a method of manufacturing such an anode and a chemical current source containing such an anode [US patent No. 4950560, 08/01/1988, IPC H01M 4/36]. The proposed aluminum-based alloy contains as alloying components two, three or four low-melting elements selected from the group consisting of bismuth, cadmium, thallium, mercury, gallium, indium, lead, tin, zinc, and the ratios of the amounts of alloying elements correspond to the formation of eutectic alloys . Preferred are eutectic mixtures of elements from the group comprising gallium, indium, tin and zinc in amounts of from 0.01 to 3% by weight of the alloy.

A method for manufacturing the anode includes introducing predetermined alloying components into the molten aluminum, mixing the melt, and casting the anode blanks. Additionally, the workpieces can be annealed, quenched, rolled.

The current source includes a housing, an aqueous electrolyte, a gas diffusion air cathode and an anode in the form of a wire made of the proposed alloys, supplied by a special mechanism through a seal in the bottom of the current source housing. The author has shown that only some of the proposed alloys provide both high electrochemical activity and a rather low corrosion rate with hydrogen evolution.

The known method of manufacturing the anode does not provide the necessary uniformity in the distribution of alloying components and the accuracy of achieving a given alloy composition due to the alternate addition of alloying components in the alloy preparation process. The known current source does not have the ability to continuous operation due to passivation of the anode as the accumulation of anode destruction products in the electrolyte.

A current source, a method for manufacturing its anode, and material for manufacturing the active part of the anode are also known [RF patent No. 2168811, 05/05/1999, IPC H01M 12/04, H01M 4/46]. The essential features of the current source are the presence of an additional inoperative chamber, a rotary cover with an electrode block, and the use of anodes of an aluminum alloy of a certain composition. A method of manufacturing the anode includes introducing into the molten aluminum a liquid ligature from fusible components (gallium, tin and lead), mixing the melt and casting an alloy strip onto a rotating mold. The resulting alloy strip can be further subjected to heat treatment and machining to obtain anodes. The aluminum alloy anode material contains 0.25-0.4% tin, 0.005-0.1% gallium and 0.005-0.1% lead.

The disadvantages of the proposed technical solution are the presence in the anode alloy of a toxic element - lead and the high corrosion rate of such an alloy in an alkaline electrolyte.

Closest to the proposed is a technical solution [RF patent No. 2262159, 04/06/2004, IPC H01M 4/46, H01M 6/04], including an anode, a method for manufacturing the anode and a chemical current source with such an anode. The anode is made of an aluminum alloy containing elements selected from the group consisting of magnesium, zinc, gallium, tin, indium, lead, silicon, bismuth, antimony, but preferably indium, tin and silicon or indium, tin and magnesium in a concentration range of 0, 01-2%. A method of manufacturing the anode includes the introduction of alloying components into molten aluminum immediately before casting, intensive mixing of the melt, casting and crystallization of the workpieces, followed by annealing, hot and cold rolling, machining. A chemical current source with an alkaline electrolyte is characterized in that it includes an anode of an alloy of the specified composition, made in accordance with the specified method.

The disadvantages of the proposed technical solution are the passivation of the anode, expressed in a sharp drop in the discharge current, occurring during the discharge during the accumulation of the products of its dissolution in the electrolyte, as well as the heterogeneity and inaccuracy of the composition of the alloy in the accepted method of its preparation.

The objective of the proposed technical solution is to create an anode alloy capable of providing a given cell voltage under load or a given discharge current for a long time, almost until the anode is fully operational, that is, slowing down the process of passivation (blocking) of the anode surface by the products of the anode reaction. At the same time, the alloy must have sufficient resistance to corrosion occurring in an alkaline solution with hydrogen evolution. The task also includes the creation of a method of manufacturing such an anode and a chemical current source capable of continuous operation without passivation of the anode.

The problem is solved by the fact that gallium (0.01-0.1%), indium (0.1-1%) and magnesium (0.2-2%) are added to the composition of the anodic alloy based on aluminum, and alkaline electrolyte contains sodium stannate in a concentration of 2-10 g / l. Alloying components are introduced into the aluminum melt in the form of aluminum-based alloys containing 0.1-5% gallium, 1-10% indium or 2-20% magnesium.

The essence of the invention is illustrated by examples.

Example 1

Cooking ligatures.

99.9% purity aluminum (“h” grade reagent) is loaded into a crucible and heated to a temperature of 780 ° C after melting. Before casting, a corresponding alloying additive is introduced into each portion of molten aluminum in quantities that ensure the manufacture of master alloys with a given content of the alloying component. The melt is mixed and poured into molds. The obtained ingots of ligatures with sizes convenient for subsequent dosing are used for the manufacture of anodes of the required composition.

Alloy preparation, anode manufacturing.

In the manufacture of anodes, 99.9% purity aluminum is charged into the crucible and heated to a temperature of 770 ° C. After melting into the crucible, with stirring, load ligature ingot segments in quantities that provide a given content of alloying components in the anode alloy. The resulting melt is poured into molds made according to the size of the anodes.

For the manufacture of anodes from an alloy composition of 0.5% wt. Mg, 0.5% In, 0.05% Ga, the remainder of the aluminum in the crucible load 84 parts by weight aluminum, 5 parts by weight Al-Mg ligatures with a content of 10% Mg, 10 parts by weight Al-In ligatures with a content of 5% In, 1 part by weight Al-Ga ligatures with a content of 5% Ga.

For the manufacture of anodes from an alloy with a composition of 0.6% Mg, 0.1% Sn, 0.05% Ga, the remaining aluminum is loaded into the crucible 91 parts by weight aluminum, 6 parts by weight Al-Mg ligatures with a content of 10% Mg, 2 parts by weight Al-Sn ligatures with a content of 5% Sn, 1 part by weight Al-Ga ligatures with a content of 5% Ga.

The cooled metal in the form of plates of a given size is removed from the molds and used as anodes of the current source.

Example 2

According to the method described in example 1, anodes of the composition - 1: 0.5% Mg, 0.5% In, 0.05% Ga, the rest were aluminum, composition - 2: 0.6% Mg, 0.1% Sn, 0.05% Ga, the rest is aluminum, composition - 3 from aluminum with a purity of 99.9%. The polarization value of the anodes of compositions 1 and 2 at current densities of 0.1 A / cm ² is 120-140 mV lower than for the anode of composition 3 (at temperatures of 40-60 ° C, electrolyte 4 M NaOH + 0.05 M sodium stannate ) At the same time, the corrosion rate of the anode of composition 1 is 1.2 times lower than that of the anode of composition 3 at 50 ° C (electrolyte 4 M NaOH + 0.05 M sodium stannate), and the corrosion rate of the anode of composition 2 is 2.5 times higher than the anode of composition 3 under the same conditions. The corrosion current density of the anode of composition 3 under these conditions was 12 mA / cm ² .

When using anodes in a working cell of an air-aluminum current source with an electrolyte of 4 M NaOH + 0.05 M sodium stannate at a temperature of 55 ° C and an operating current density of 0.11 A / cm ² , the corrosion current density of anodes of composition 3 was 10 mA / cm ² , and for anodes of composition 1 - 7 mA / cm ² .

The corrosion rate of composition anode 3 at 50 ° C in an electrolyte of 4 M NaOH without stannate is 20 times higher than its corrosion rate in an electrolyte of 4 M NaOH + 0.05 M sodium stannate.

Anodes of compositions 1, 2, 3 and an anode of composition 4 (0.5% Zn, 0.05% Ga, the rest are aluminum) were used to fabricate cells of air-aluminum chemical current sources (VA HIT) with an air gas diffusion cathode and alkaline electrolyte. The cells had a prismatic shape with a side wall made of a gas diffusion cathode. The anode was made of an aluminum alloy plate of a given composition. The anode plate was parallel to the air cathode (figure 1).

The initial gap between the anode and cathode was 3 mm. As the electrolyte, an alkaline electrolyte of 4 M NaOH + 0.05 M sodium stannate was used. The discharge of the cells was carried out through a constant load, providing a working current density of the discharge at the level of 0.1 A / cm ² . Cells with anodes of compositions 2, 3, 4 stopped working as effective current sources at the point in time when precipitation of aluminum hydroxide from the solution began. At this time, deep passivation of the anodes occurred and the internal resistance of the cells in a short time increased by 50 times or more. The spent electrolyte in the cells was a clear liquid with a small amount of aluminum hydroxide precipitate.

For the anode alloy of composition 1, the phenomenon of deep passivation of the anodes is not observed. Cells with anodes from this alloy continued to work as an effective current source two or more times longer than cells with anodes of other compositions. At the end of the working cycle, the electrolyte spent in such cells was a thick white paste of aluminum hydroxide.

The absence of deep passivation for anodes of composition 1, in contrast to anodes of other compositions, was observed for cells of different sizes. With an excess of anode material, the work of cells of different geometric sizes with anodes of compositions 2, 3, 4 always stopped simultaneously with the beginning of precipitation of aluminum hydroxide from the solution, and cells with anodes of composition 1 continued to work until the electrolyte in them was thickened with precipitated hydroxide aluminum to a state of viscous paste.

Figure 2 shows the discharge characteristics of VA HIT cells with a cathode area of 4 cm ² and an electrolyte volume of 5 ml when operating at a load of 3 ohms. Numbers 1-4 indicate the discharge curves corresponding to the compositions of 1-4 anode alloys.

Figure 3 shows the discharge characteristics of VA HIT cells with a cathode area of 30 cm ² and an electrolyte volume of 60 ml operating at a load of 0.5 Ohm when using anodes of compositions 1 and 3 (curves 1 and 3, respectively). In all cases, the capacity of cells with anodes of composition 1 is more than 2 times higher than the specific capacities of the same cells with anodes of a different composition.

The anodes of composition 1 are produced almost completely, evenly over the entire surface. The anode of composition 1 - after 10 minutes (figure 4) and after 10 hours (figure 5) work at a current density of 0.1 A / cm ² .

Example 3

According to the method described in example 1, anodes of the composition 0.5% Mg, 0.25% In, 0.04% Ga, the rest aluminum (non-blocking anode alloy) and the composition 0.5% Mg, the rest aluminum (blocking) were made anode alloy). The fabricated anodes were used to charge the flow cell of an air-aluminum current source. The cell had a prismatic shape and an air cathode area of 300 cm ² . The electrolyte (4 M NaOH + 0.05 M sodium stannate) was pumped through the cell at a constant rate, after which it entered the crystallizer refrigerator, where aluminum hydroxide precipitated. At the outlet of the refrigerator, the electrolyte was filtered and fed back into the cell. The cell was discharged through a constant load of 0.04 Ohms, which provided a discharge current density of 0.1 A / cm ² . When fresh electrolyte is poured into the system, the difference in the operation of cells with anodes of different compositions is due to the difference in the polarization characteristics of the alloys. Alloy composition 1 has the best polarization characteristics and, accordingly, a greater operating voltage at the load. Figure 6 shows the discharge characteristics of the VA HIT cell when using a "fresh" electrolyte. The solid curves are a non-blocking anode alloy, the dashed curves are a blocking anode alloy.

After the onset of precipitation of aluminum hydroxide in the crystallizer (corresponds to a time T = 200 min), cells with anodes of different compositions continue to work without changing the discharge characteristics. At time T = 450 min, when a large amount of precipitate of aluminum hydroxide was accumulated in the crystallizer, the cells were stopped, and the electrolyte was drained from them into the crystallizer. 8 hours after the cells were turned off, the spent electrolyte from the crystallizer, saturated with aluminum hydroxide solution, again began to be pumped through the cells.

7 shows the exit to the operating mode for cells with a locking and non-locking electrodes when you restart the cells using an electrolyte saturated with aluminum hydroxide.

a) Non-blocking anode alloy. Turn on the circulation of cold electrolyte through the cell with the connected load, exit to the operating mode.

b) Blocking anode alloy: 1 - pumping through a cell with a connected load of cold electrolyte; 2 - load shedding while maintaining electrolyte circulation; 3 - load inclusion; 4 - pumping through the cell with the included load of the electrolyte, heated to 55 ° C; 5 - load shedding while maintaining the circulation of hot electrolyte; 6 - turning on the load, turning off the heating of the electrolyte, exit to working mode. When using an anode of composition 1, the cell with the connected load enters the operating mode shortly after the start of pumping of the electrolyte (Fig. 7). In order to bring to operation the cell with a blocked anode of composition 2, it is necessary to disconnect the load and pump through the cell for several minutes the electrolyte, previously heated to a temperature of 50-55 ° C (Fig.7).

The above examples show that the proposed anode, its manufacturing method and a chemical current source with such an anode can be implemented to achieve the claimed technical result.

Claims (3)

1. The anode for a chemical current source with an alkaline electrolyte, made of an aluminum-based alloy with alloying elements selected from the group consisting of indium, tin, zinc, magnesium, gallium, with an alloying element content of from 0.05 to 5 wt.%, characterized in that the alloy contains 0.01-0.1% gallium, 0.1-1% indium, 0.2-2% magnesium. 2. A method of manufacturing the anode, characterized in that the alloying components are introduced into the alloy in the form of aluminum alloys containing 0.1-5% gallium, 1-10% indium and 2-20% magnesium. 3. A chemical current source containing an anode, a gas diffusion cathode and an alkaline electrolyte, characterized in that the anode is made according to claims 1 and 2, and the electrolyte contains sodium stannate at a concentration of 2-10 g / l.

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