DE2008548C3 - Positive electrode for rechargeable electrical zinc-halogen cells of a storage battery - Google Patents

Description

The invention relates to a positive electrode for rechargeable zinc-halogen electric cells an accumulator, made of a metallic carrier and at least one layer connected to it porous carbon.

A positive electrode of this type is known from FR-PS 9 72 048. In this state of the art, Use of chlorine as an electrolyte Zinc as a suitable one that is resistant to chemical influences Material for the negative electrode named. There will also be direct chemical attack by the chlorine the metal of the positive electrode indicated. However, there is no indication of any special material for the positive electrode, for which metal is generally indicated as the material that can be used. These However, the specification is very broad and includes such metals such as B. iron and aluminum. Although the chemical influences of chlorine on the metal are a disadvantage positive electrode has been described, will not be certain material selected for the positive electrode, which is resistant to chlorine

The only statement about the positive electrode is that it is permeable to gas but not to liquids. It is also stated that the chlorine attacks the surface of the positive electrode and that this off porous carbon, while the negative electrode is made of zinc. It will eventually stated that the chlorine acts on the zinc as a negative electrode, but it is not stated how the positive electrode reacts to the zinc. As a result, there are no precise details about the type and Construction of the positive electrode from the prior art mentioned as known. In particular it is left open which materials should be used for the positive electrode in order to keep a constant to provide a rechargeable tin-halogen electric cell for a storage battery.

The well-known positive electrode for rechargeable electrical zinc-halogen cells of a storage battery does not allow frequent recharging over a long life with a good electrical one Output power.

The invention is therefore based on the object of providing an electrode for rechargeable zinc-halogen electrical cells an accumulator of the type mentioned to create that over a long Lifespan is continuously rechargeable and delivers high electrical power in each case.

To solve this problem, the invention provides that the metallic support is made of an anodizable metal from the group I V (A) and V (A) Oc * periodic system and is designed in the form of a lattice that the porous carbon is in granular form with a plastic powder is bound and that the mixture of carbon and plastic is bound to the metallic support under pressure and surrounds it on all sides. Titanium or titanium alloys, in particular, which are in the form of a sieve or a perforated metal block or similar are proposed for the metallic carrier. Like. Are processed. In particular, acetylene black, which is powder-bound in the plastic, is proposed as the porous carbon in granular form.

The crfindiingsgcäßc, processed in granular form-

The porous carbon material bound in plastic powder forms tiny pores in which and through which the electrolyte with trapped or absorbed halogen, especially chlorine, flows. Included contact surfaces arise between the electrolyte and the halogen gas. The one loaded with halogen gas Electrolyte, which is contained in tiny tiny pores or holes within the porous carbon, in particular Acetylene black, only forms a thin liquid film on the carbon surface because the pores or holes are not large enough to hold a mass or drop of liquid. This enables the halogen, especially chlorine, to get through the liquid and out of the liquid, so that it is then free to B. to act as free chlorine and to work with the metallic carrier, in particular made of titanium, to make electrical contact as a positive electrode. The generated electric current flows through the metallic carrier made of titanium out of the battery, since the titanium acts as a current collector and -leiter works It must be noted that there is a three-phase boundary layer between liquid and gas and solid metal is present.

One with the positive ones designed according to the invention Batteries made with electrodes are operated for several months with constant charge and discharge without any apparent wear and tear on the battery components although a relatively high electrical output current was used. The reason this can be seen in the electrode storage effect for halogen, especially chlorine. This effect is based on the fact that the porous carbon used, i.e. H. Acetylene black, is amorphous and that the granular Components are bound with a synthetic plastic, which is opposite to the halogen, d. H. in particular Chlorine, or the electrolyte is inert.

Further advantageous refinements of the invention emerge from the subclaims.

The Erf.ndung is based on an embodiment of a shown in the drawings Accumulator made of rechargeable electric zinc-halogen cells with positive electrodes is shown. It shows

Fig. I a vertical cross section through a positive electrode pair,

FIG. 2 shows a vertical longitudinal section through a positive electrode along the line 11-11 in FIG. 1,

F i g. 3 is a side view of the positive electrode;

4 shows a horizontal cross section through a negative zinc electrode,

F i g. 5 a plan view of the accumulator,

6 shows a horizontal partial cross-section through the Accumulator according to FIG. 5 along the line H-II 'n F i g. 7, 8 and 8a,

7 shows a cross section through part of the accumulator along the line VII-VII in FIG. 5,

8 shows a cross section through part of the accumulator along the line VIII-VIII in FIG. 7,

F i g. 8a one of the FIGS. 8 corresponding cross-section along the line Vl I la-Villa in Fig. 7 and

F i g. 9 shows the principle of the halogen gas circuit in the accumulator.

The accumulator shown is made up of several rechargeable zinc-halogen electric cells with? positive carbon-plastic electrodes 12 and negative zinc-sheet metal-n 13 are formed. The halogen is preferably chlorine, it can also be iodine or bromine, with corresponding modifications of the mechanical Structure of the accumulator are required.

Each positive electrode 12 (Fig. 1 to 3) has a support 1 made of titanium, which can also be another anodizable metal of groups IW (A) or V (A) aes periodic system, such as tantalum or zirconium or Alloys of these metals. The carrier 1 consists of an open network, in particular made of foamed metal or a wire network of the metals, and has a current collector 2 which extends outside the positive electrode 12 and forms an electrical connection.

With the carrier 1, a carbon-plastic mixture 3 is connected such a porous type that in the Use in the accumulator, as will be explained further below, the chlorine ions in the electrolytic Method can migrate through the carrier i. The carbon lies in the form of soot or Carbon grains, preferably with one another to form the carbon-plastic mixture 3 with a plastic such as Polyvin; ! chloride, one synthetic nitrile rubber or polychloroprene are bound. The actual mixing of the Plastic with the carbon can by means of rollers using z. B. a heated drum or a granulating device. Small discs made of carbon or graphite can be used with soaked in a latex or plastic solution that acts as an impermeable barrier between the cells acts Small carbon disks are placed in a large plate, e.g. B. by means of injection molding with training a flexible carbon electrode 12 bound. The application of an active surface to the carbon surface by means of coating, activated carbon powder such as acetylene black, bound with a Solution of plastic, such as polyethylene in carbon tetrachloride or ethylene trichloride. It Catalysts, such as platinum, can be impregnated on the coria fabric and then fired

ι or applied by means of electrolytic deposition ν earth. Where carbon powder is bound with polyethylene dissolved in carbon tetrachloride, an inert filler such as zinc chloride can be used, which is then leached out to form a more porous electrode. The carbon powder can be ^{activated by heating to approximately 400 °} C. in an inert gas such as argon or carbon dioxide or even in chlorine.

The optimal particle size of the carbon depends

ι for satisfactory electrical operation of the Cells from it. that the largest possible surface is formed, but the particles must either naturally, as with acetylene black, stick together or it must stick together by applying the Plastic. If that in .application Coming plastic powder is polychloroprene, the polychloroprene preferably has a particle size from 50 μΐη and 190 μιη to It can also, quaternary ammonium compounds as a surfactant Means to achieve optimal contact angles of the electrolyte with the carbon particles can be applied in a cell. Silica gel can be added to the carbon in order to do so to improve the chlorine storage and the effect of the carbon and silica gel is regarding the Cell performance synergistically. The incorporation of the gel can be done by means of impregnating the whole So as to cause a drop in the electrode

Avoid conductivity, which is otherwise likely occurs in the electrode if the silica previously combined with the carbon used in the cell is mixed.

The carbon-plastic mixture 3 can be bonded to the carrier 1 by means of hot or cold pressing. In this case, pressures of 3135 N and 7845 N / cm ² are applied at temperatures of 15 to 140 ⁰ C.

Instead of the titanium in the positive electrode 12, alloys of titanium or tantalum or zirconium can be used or these metals are used with one another. Once the titanium has been used to accommodate the Carbon has been prepared. must do the same under suitable conditions, such as. B. under water are held so as to prevent the formation of an oxide.

The current collector 2 is in contact via the carbon-plastic mixture 3 and extends up to to the outside of the positive electrode 12. Another example of applying the carbon to the Titanium consists in enclosing the titanium mesh in a sack filled with carbon grains.

In particular, the carbon and the plastic can be bound together using acetylene black, of the ten-fold weight is wetted in water at 50 ⁰ C with about, wherein the water one or two drops of acetone are added. A 5% nitrile plastic latex compound is diluted with about 10 times the amount of cold water and slowly added to the carbon with stirring. The stirring must be vigorous and thorough, but care must be taken to ensure that the mixture is not beaten. Stirring must stop once the plastic has been absorbed and a crumbly product has formed. The best results have been obtained with the plastic which contains 5 to 25 percent by weight of the bonded mixture. The correct particle size of the latex should be selected, which leads to the optimal conductivity and strength values for the three-dimensional

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Plastic or other suitable material are held together. The positive electrode 12 is in the Cover is included or formed as a part thereof. In the lower part of the two electrodes

12 are on the outside inner and outer spacers 6 and 7 for the below intended purpose. The positive electrodes 12 extend under the spacers 6, 7 forming a channel 8 as a chlorine gas channel in the cell.

The in the K ι g. Negative metal electrode shown in Fig. 4

13 consists of a Mctallnct /. 38 similar to that in the positive electrode 12 of FIG. I to 3 existing net-like support 1. This Mctallnct / 38 is provided with a coating 9 made of zinc. Spacers 10 made of a suitable inert plastic, preferably a microporous plastic such as / ... B. polyvinyl chloride, are provided to ensure that the negative metal electrode 13 is spaced apart from the positive electrode 12 in the assembled cell. Suitable plastics for the spacers 10 are polyethylene or polytrafluoroethylene.

When manufacturing the negative metal electrode 13 zinc powder with ammonium chloride can be sintered under pressure at 250 ° C on the metal zinc 38 made of titanium w ::: den. taking the amount of ammonium chloride below Formation of the desired porosity of about 50 percent by volume is set. The Titan supports a reduction in zinc migration. The negative electrodes 13 with an enlarged surface lead to higher maximum currents. The zinc powder can be mixed with the metal mesh 38 with be connected to a plastic, as in the case of the carbon-plastic mixture 3 in the positive Electrode 12 is applied.

About the brittleness of titanium by the action of hydrogen can be switched off by zinc plating or plating with a noble metal to be protected. The zinc can either be electroplated or sprayed or dipped of the metal mesh 38 in molten zinc, which is with

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Carbon is held. The nitrile plastic hardens during the chlorination, whereby the electrode assembly is networked in situ.

The resulting electrode assembly is preferably 30-50% porous.

In order to improve the adhesion of the carbon to the carrier 1, this can be treated by means of etching in a 4% ammonium bifluoride solution. Hietan in connection is a covering with water or with dilute hydrochloric acid, is pressed onto the carrier 1 to the carbon. Optionally, the carrier 1 can be plated with platinum by any known method or provided with a nitrite layer .

The positive electrode 12 made from the carrier 1 and the carbon-plastic mixture 3 is shown in FIGS. 1 to 3 so shown that a cover made of a plastic frame 4 made of high density polyethylene, polypropylene or polyamide is present. This plastic frame 4 in film form can be deployed in any known manner so that the surfaces of the carbon-plastic mixture 3 remain free.

The in the F i g. 1 to 3 shown positive electrode pair is composed of two positive electrodes 12, as already described above, formed from each other at the upper end by a connecting part 5

I I

is to be plated. The zinc can get on the metal mesh 38 made of titanium can optionally be ironed on under pressure in the usual way. It can also be a Pressing onto the metal mesh 38 can be carried out in any suitable manner.

With reference to FIGS. 5 to 8A, the accumulator has alternating positive carbon-metal electrodes 12 as shown in FIGS. 1 to 3 and negative zinc electrodes 13 as shown in FIG. 3 arranged side-by-side in a housing 11. 4, all of which are immersed in an electrolyte 14. The positive electrodes 12 are connected to a connection terminal 15 and the negative electrodes 13 are connected to a connection terminal 16, as will be explained below.

In particular, inside the housing 11 are a A plurality of cells are arranged, some of which are shown in cross-section in FIGS. 7, 8 and 8A are shown. the Cells extend across the accumulator and are large and thin and side-by-side below Formation of the accumulator arranged, wherein the housing 11 is designed as cell wall sections 17, which are brought into contact with one another in a liquid-tight manner by means of tie rods 18. The cell wall sections 17 stand on a base part 19 and are covered by a cover 20, whereby all connections are liquid-tight. The cells are through plates 21

an electrically conductive inert material, such as. I). Titanium or titanium alloy separately. Along the sides of the cell casing are at right angles to the Electrodes 12, 13 like plates 22, one of which in F i g. 6 and 8 is shown.

Each cell alternates between positive and negative electrodes 12 and 13, each of which is electrically Mittelr the current collector 2 is connected to the plates 21 and 22, respectively. The positive electrodes 12 are on theirs lower ends held together by the inner: md outer spacers 6 and 7, which are below Formation of a dense arrangement of the carbon metal electrodes 12 over the entire length of the cells are locked into place. The upper connecting parts 5 of the positive electrodes 12 are brought into contact held by means of the pull rod 18. The negative electrodes 13 are arranged so that the same extend upward in the cell between the positive electrodes 12, from where these by means of the Spacers 10 are kept separate. The plates 21, 22 are in recesses by means of sealing rings 22.) 226 served in the cell wall sections 17 (Fig.b).

The terminals 15, 16 are preferably square plates with surface dimensions of approximately 7.5 cm, with the current collectors 15a and 16a covering a large area with a U or X shape.

In the interior of the housing there is the electrolyte 14, described below, in which all electrodes 12, 13 are immersed. A halogen gas inlet 23 is provided at one end of each cell, which by means of a channel (not shown) preferably through the hollow space in one of the positive electrodes 12 with a gas channel 24 formed by the channels 8 of the positive electrode 12 at the bottom of the housing 11 under the electrode 12, 13 extending electrolyte 14 is in communication. The gas channel 24 is closed at the cell ends by the plastic frame 4 of the terminal positive electrodes 12 and, with the hollow interior space of all positive electrodes 12, represents the ", VCilCr ϋΓιΐΟΓι L / CjCitfiCOCi'lcll A-WCV-Λ III Vci LMMUUng. UCV electrolyte 14 extends into the gas channel 24 with the formation of a gas seal, but the gas can bubble out into the electrolyte 14 as soon as the gas pressure inside the positive electrodes 12 rises sufficiently.

The level of the electrolyte 14 is adjusted under the cover 20 of the housing 11 so that a space 25 remains over the electrolyte 14 for the purpose of expanding the same.

The cover 20 of the housing 11 has a pressure relief valve 26 on, through a tube 27 and drain holes 28 with the space 25 above the electrolyte 14 and below the cover 20 is connected so that when the gas pressure inside the accumulator is exceeded over a predetermined value the pressure through the pressure relief valve 26 and through the Halogen absorption chamber 29 passes through to the outside air. This ensures that no toxic or harmful halogen, e.g. B. chlorine gas, can escape to the outside air. In the event of an exit of the gases through valve 26 will be the same in the cell based on that described below Halogen cylinder 30 replaced.

Referring to FIG. 9 is in the cell or Accumulator chlorine circuit of the chlorine cylinder 30 via a pressure control valve 31 with the gas inlets 28 of the Accumulator connected. The gas outlets 23 at the upper end of the accumulator are connected to a pipe 32 connected back to the chlorine cylinder 30 by a UV lamp 33, as described below, and a halogen condenser 34 leads. The UV lamp 33 lies closely adjacent to the line 32 in a known manner and serves to remove hydrogen which may possibly occur in the halogen gas, wherein it is converted to hydrochloric acid.

This is through the line 35 to the accumulator, i. H. supplied to the electrolyte, together with condensed water vapor and liquid.

Even if the accumulator can be operated with any halogen, chlorine is the easiest preferred to handle. The description of the cell or the accumulator with reference to the Drawing is only based on chlorine. Corresponding adjustments are necessary for working with Rmm and / or iodine required.

The electrolyte 14 present in the accumulator is zinc chloride in aqueous solution. It can do something Mercury. Indium or gallium to the electrolyte 14 be added in order to avoid the formation of dendrites. When the amount of mercury is on more than 2 wt .-% of the zinc and the temperature of the Electrolyte 14 during the charging of the accumulator, as described below, to over 43 ° C increases, there will always be a certain amount of liquid phase.

This will avoid the formation of dendrites. However, the temperature can also be lower by adding Amounts of tin, indium or gallium can be reduced. These additions also lead to a Increase in hydrogen overvoltages.

Polyelectrolytes, such as polyvinyl alcohol, can be used to prevent the formation of dendrites can be used, with such polyelectrolytes in small amounts of less than 0.5 wt .- '! ■' (> of the electrolyte can be used. Thiourea in

an amount of about 1% by volume in the electrolyter, also supports the suppression of the dendrites education.

The purity of the electrolyte 14 is important to avoid dendrite formation. The ElektrolM 14 can by dissolving zinc chloride in deionized water while stirring in zinc leaves and Allowing to stand for several hours should be cleaned for the purpose of precipitating the impurities. The presence a small amount of zinc oxide aids in the removal of iron, which is known to be a leads to increased dendrite formation. The electrolyte 14 can also mean pre-electrolyze at a set voltage of 2.1 volts can be cleaned, until the current drops to a constant value.

This reduces the self-discharge of the cell, increases the hydrogen overvoltage, and less Causes zinc oxidation when standing. This also means that work must be carried out at a higher pH value can.

It was found that a perfectly optimal

Value for high performance in the electrolyte is present when the pH is between 2.5 and 4.0 and the

Density range from 1.1 to 1.25.

The use of a low density also keeps foaming during charging and discharging Onset of dendrite formation at the back. If dendrites form under these conditions, be wise these take a different shape and resist

long-term short-circuiting of the cell.

Potassium chloride can be introduced into the electrolyte 14 up to saturation in order to increase the conductivity and improve power efficiency. At the same time, the zinc precipitate becomes more moss-like. This can be done by adding a salt of a weak acid such as an acetate to stabilize the pH value adjacent to zinc can be improved.

The addition of an acid-forming depolarizer, like HCIO, it is favorable for the purpose of interrupting the dendrite formation and is made by means of dissolution of chlorine. When using this depolarizer, it may be useful to use a small device, like a pump, to be used in the accumulator, by means of which the electrolyte is made to circulate in the cells will. A speed of about 15-60 cm / sec. is a suitable rotational speed and can be achieved by using or using a pump

LlIl W lvi \ IUIIg UVI ^ -ΙΙΐΟΓυΐα30Π, WÖuÜTCll 31111 UIL UiUSUtIg

automatically pumped around, are effected. The chlorine tends to peel off all the dendrites that grow as it grows get too close to the carbon surface of the positive electrodes 12. The chlorine can be dissolved in the Electrolyte 14, introduced into the cell, is then opposed to solid carbon electrodes is fed to the applied hollow electrodes, the chlorine-depleted electrolyte 14 via the Zinc electrodes are passed before being saturated again with chlorine.

. Referring to Figure 9, the chlorine is maintained in liquid form under high pressure in the chlorine cylinder 30 and to charge the already ^m: t electrolyte 14 filled accumulator, the valve 31 is opened so that the chlorine to the inlet 28 in the cover 20 of the housing 11 can flow. The chlorine then flows down through the terminal positive electrode 12 to the gas duct 24 and from here to the underside of all positive electrodes 12, thereby displacing any electrolyte 14 in the space between the positive carbon-metal electrodes 12. Any excess chlorine that may be present at this point in time is discharged, the accumulator rliirrh leaves the outlet 23 and flows through the tube 32 past the UV lamp 33, d'e works in the usual manner, removing hydrogen and other impurities from the chlorine. The chlorine then passes to the condenser 34 and from there back through the pipe 36 to the chlorine cylinder 30 under a pressure, the valve 31 being closed, which enables the chlorine to enter the chlorine cylinder 30 against the pressure prevailing therein. The hydrogen is removed by converting it into

ίο causes hydrochloric acid, which, as already described, then by means of the line 35 again the accumulator at a suitable entry point in the The middle of the lid 20 is fed, from where a dilution of the electrolyte 14 takes place.

The battery can be charged for the first time either electrically or by blowing in chlorine gas the gas circuit can be accomplished. After the battery is discharged, it is again using

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I IMlUUl ClIlVItUIl VIMV3 tltl \ tll3L (according to ll vJMVIMV.3 UUIVtI UVII

Μ Accumulator accomplished by means of connection to the terminals 15,16, with z. B. the usual and in the usual way transformed and rectified current of the power grid is used.
If the dendrites grow to such an extent that the cell or the accumulator is short-circuited, this can be remedied by pouring out the electrolyte 14 and filling it with hydrochloric acid to dissolve the zinc and then washing it out and recharging it with the zinc chloride electrolyte 14 . However, this is not often necessary.

Albeit the carbon-titanium positive electrodes 12 here with respect to those shown in FIGS Shape have been described, it is to be understood that the same are any pleated shape such as circular or oval. Similarly, the zinc-titanium negative electrodes 13 can also be circular or oval.

The accumulator described above is z. B. for use in electrically powered vehicles suitable and continues to find useful application z. B. at Her Solpnelekirolyse. wastewater treatment and other synthetic areas of application.

For this purpose 3 sheets of drawings

Claims (12)

Patent claims: 1. Positive electrode for rechargeable electrical zinc halogen cells of an accumulator, made of a metallic carrier and at least one layer of porous carbon connected to it, characterized in that the metallic carrier (1) consists of an anodizable metal from the group W (A) and V ( A) of the periodic system and is designed in the form of a grid that the porous carbon is bound in granular form with a plastic powder and that the mixture of carbon and plastic is bound to the metallic carrier (1) under pressure and surrounds it on all sides. 2. Positive electrode according to claim I, characterized in that a metallic carrier (1) is used Lattice made of titanium and acetylene black bound in nitrile plastic as porous carbon are. 3. Positive electrode according to claim 2, characterized in that the grid has openings from 0.075 to 0.500 mm in diameter. 4. Positive electrode according to one of claims 1 to 3, characterized in that the grid made of titanium is coated with a nitride film, a mixed oxide film or a boride film. 5. Positive electrode according to one of claims 1 to 3, characterized in that the titanium grid with a higher valence oxide forming element such. B. tantalum, alloyed or is doped. 6. Positive electrode according to claim 5, characterized in that the titanium alloy is up to 5% Contains tantalum. 7. Positive electrode according to claim I _1, characterized in that the plastic powder is polychloroprene. 8. Positive electrode according to claim 7, characterized in that the polychloroprene has a particle size of 50 to 190 μτη . 9. Positive electrode according to claims 1 or 7, characterized in that the plastic powder Represents 5 to 25 weight percent of the bound mixture. 10. Positive electrode according to one of claims 1 to 9, characterized in that the on carbon-plastic mixture adhering to both sides of the grid-like metallic carrier (1) under pressure (3) is provided with a plastic frame (4) which is inert towards halogen and which leaves the surface of the carbon mixture layer exposed is gastight around the edges henimge. 11. Positive electrode according to claim 10, characterized characterized in that the plastic frame (4) made of polyethylene, preferably high density polyethylene, Polypropylene, polytetrafluoroethylene or polyamide. 12. Positive electrode according to claim 10, characterized characterized in that an electrode pair of two spaced apart electrodes (1.2) at least one edge is connected to one another and at one edge for the entry of Halogeii |; as in the enclosed space / wipe the electrodes (12) is open, the open end with a open channel (8) is in communication, which is used to supply the halogen gas in the space between the Electrodes (12) is provided.