DE2008548B2 - Positive electrode for rechargeable electrical zinc-halogen cells of a storage battery - Google Patents

Description

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

A positive electrode of this type is known from FR-PS 9 72 048. In this prior art, in Use of chlorine as an electrolyte Zinc as a suitable, resistant to chemical influences

is g ss material named for the negative electrode It is also the direct chemical attack by the chlorine on the metal of the positive electrode is indicated. Something is missing however, any indication of special material for the positive electrode, for which generally metal is specified as a usable material. These However, the specification is very broad and includes such metals such as B. iron and aluminum. Although the disadvantage is the chemical influences of chlorine on the metal of the positive electrode has not been described 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 is the surface the positive electrode attacks and that this off made of porous carbon whereas 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

) 5 the positive electrode reacts to the zinc Construction of the positive electrode from the prior art mentioned as known. In particular it is left open which materia'en for the positive Electrode should be used to make a continuously rechargeable tin-halogen electric cell for to create an accumulator.

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 electrical zinc

V) to create halogen cells of an accumulator of the type mentioned at the beginning, which can be continuously recharged over a long service life and which emits high electrical power in each case. To solve this problem, the invention provides

v that the metallic support is made of an anodizable metal from group W (A) and V (A) of the periodic table and in the form of a lattice, that the porous carbon is bound in granular form with a plastic powder and that the mixture of Carbon and plastic on the metallic carrier is bound under pressure and surrounds it on all sides. Titanium or titanium alloys, in particular, are proposed for the metallic carrier, which are shown in FIG Form of a sieve or a perforated metal sheet or the like. Are processed. As porous carbon in granular form is proposed in particular acetylene black, which is bound in the plastic powder

The invention, 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, in particular chlorine, flows contact surfaces arise between the electrolyte and the halogen gas. The one loaded with halogen gas Electrolyte that is in the tiny little pores or Holes within the porous carbon, especially acetylene black, are only thin Liquid film forms on the carbon surface because the pores or holes are not large enough to accommodate a To absorb bulk or a 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 e.g. B. as free chlorine to act and with the metallic carrier, in particular made of titanium, electrically as a positive electrode to contact. The generated electrical current flows through the metallic support made of titanium from the Battery out as the Titan works as a collector and conductor. It must be noted that here is a There is a three-phase boundary layer between liquid, gas and solid metal

A storage battery produced with the positive electrodes designed according to the invention is a plurality of batteries Months of constant charging and discharging without any apparent evidence Wear to the battery components has been noted although with a relatively high electrical The reason for this is in the electrode storage effect for Halogen, especially chlorine, can be seen. This effect is based on the fact that the porous carbon used, d. H. Acetylene black, is amorphous and that the granular components are bound with a synthetic plastic which is resistant to the halogen, i.e. H. especially chlorine, or the electrolyte is inert

Further advantageous refinements of the invention emerge from the subclaims.

The invention is based on one in the Drawings illustrated embodiment of a battery from rechargeable electrical Zinc-halogen cells with positive electrodes shown. It shows

F i g. 1 shows 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 is a plan view of the outside the accumulator,

F i g. G a horizontal partial cross-section through the accumulator according to FIG. 5 along the line H-II in FIG. 7, 8 and 8a,

7 shows a cross section through part of the Accumulator along the line VII-VII in F i g. 5,

8 shows a cross section through part of the Accumulator along the line VIII-VIH in F i g. 7,

F i g. 8a one of the FIGS. 8 corresponding cross section along the line VIIIa-VHIa in F i g. 7 and

F i g. 9 shows a schematic diagram of the halogen gas circuit in the accumulator.

The battery shown is made up of several rechargeable zinc-halogen electric cells positive carbon-plastic electrodes 12 and negative zinc electrodes, 1 13 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 (FIGS. 1 to 3) has a support 1 made of titanium, which can also be another anodizable metal from groups W (A) or V (A) of the periodic table, such as tantalum or Zirconium or alloys made from these metals. The carrier 1 consists of an open network, in particular made of foamed metal or a wire mesh of the

ίο 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 can migrate through the carrier t during the electrolytic process. The carbon is in the form of soot or carbon grains, preferably with one another forming the carbon-polymer mixture 3 with a plastic such as polyvinyl chloride, a synthetic nitrile rubber or polychloroprene are bound. The actual mixing of the plastic with the carbon can be done by means of rollers

J5 using e.g. 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 can be done with active

! 5 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 applied to the carbon by means of impregnation and subsequent firing or applied by means of electrolytic deposition. There where carbon powder with polyethylene dissolved in carbon tetrachloride, an inert filler such as zinc chloride can be used. which then forms a more porous

Electrode is leached out. The carbon powder

can by means of heating to about 400 ⁰ C in an inert

Gas, like argon or carbon dioxide, or even chlorine

to be activated.

The optimal particle size of the carbon depends

w for satisfactory electrical operation of the Cells depend on the greatest possible surface area being formed, but the particles must either naturally, as with acetylene black, stick together or it must stick together by applying the

; Plastic can be effected. If that in use Coming plastic powder is polychloroprene, the polychloroprene preferably has a particle size of 50 μπι and 190μπι on. It can also quaternary ammonium compounds as a surface

M> chenactive means for the purpose of achieving optimal contact angles of the electrolyte with the carbon particles in a cell can be used. It can Silica gel can be added to the carbon in order to improve the chlorine storage and the effect

f> 5 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 that is otherwise likely to occur in the electrode if the silica was previously used mixed with the carbon used in the cell.

The carbon-plastic mixture 3 can be bonded to the carrier I 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 o, alloys of titanium or tantalum or zirconium or these metals can be used with one another. Once the titanium has been prepared to take up the carbon, it must be kept under suitable conditions, such as, for example, under water, in order to prevent the formation of an oxide.

The current collector 2 is connected via the carbon Plastic service mixture J in contact and further vi example extends up to the outside of the positive electrode 12. A applying the carbon to the titanium is that the titanium mesh is enclosed in a container filled with carbon grains bag .

In particular, the carbon and the plastic can be bonded to one another using acetylene black, which is wetted with about 10 times the weight of water at 50 ° C., one or two drops of acetone being added to the water. The mixture is diluted with a 5% Nitrilkunststofflatexmasse ν about the ten-fold amount of cold water ι and added slowly with stirring to the carbon. The stirring must be vigorous and thorough. ! ecioch must be worked carefully to this end. ν ..; the mixture is not beaten. Stirring must stop as soon as the plastic has been absorbed i => is ¹ and a crumbly product has formed. Best results have been obtained with the plastic containing 5-25% 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 network of plastic in which the carbon is held. The nitrile plastic hardens during the chlorination, as a result of which the electrode arrangement is crosslinked in situ. Yy

The resulting electrode arrangement is preferred 30-50% porous.

In order to improve the adhesion of the carbon to the carrier 1, it can be treated by etching in a 4% ammonium bifluoride solution. This is followed by covering with water or with dilute hydrochloric acid until the carbon is pressed onto the carrier 1. 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 inclined positive electrode pair is formed from two positive electrodes 12, as already described above, which are held together at the upper end by means of a connecting part 5 made of plastic or other suitable material. The positive electrode 12 is included in the coating or is formed as a part thereof. In the lower area 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 F i g. Negative metal electrode shown in Fig. 4

13 consists of a metal net 38 similar to the net-like carrier I present in the positive electrode 12 according to FIGS. 1 to 3. This metal net 38 is provided with a coating 9 made of zinc. There are spacers IC made of a suitable inert plastic, preferably a microporous plastic, such as. B. polyvinyl chloride, provided so as to ensure that the negative metal electrode IJ is in the spacing ratio from the positive electrode 12 in the assembled cell. Suitable plastics for the spacers 10 are polyethylene or polytetrafluoroethylene.

In preparing the negative metal electrode 13 of zinc powder can at 250 ⁰ C aul the metal net 38 gesinteri of titanium under pressure with ammonium chloride, wherein the amount of ammonium chloride to form the desired porosity is set from about 50 volume "-Prozent. The titanium helps reduce zinc migration. The negative electrodes 13 with an enlarged surface lead to higher maximum currents. The zinc powder can be connected to the metal mesh 38 by means of mixing with a plastic, as is used in the case of the carbon-plastic mixture 3 in the positive electrode 12.

In order to prevent the titanium from becoming brittle due to the action of hydrogen, the same can be achieved with a Zinc plating or plating with a noble metal to be protected. The zinc can be either medium; Electroplating or by spraying or dipping of the metal mesh 38 in molten zinc covered with a layer of molten zinc chloride is to be plated. The zinc can be applied to the metal mesh 38 made of titanium under pressure if necessary in the usual way Way to be mangled. It can also be pressed onto the metal mesh 38 in any suitable manner Way to be done.

With reference to FIGS. 5 to 8A, the accumulator has alternating positive carbon-metal electrodes 12 according to FIGS. 1 to 3 and negative zinc electrodes 13 according to FIG. 3 arranged side-by-side in a housing 11. 4 on, all in one ?! Electrolytes 14 are immersed. The positive electrodes 12 are connected to a connection terminal 15 and the negative electrodes 13 are connected to a connection terminal It, 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 tall and thin and arranged side-by-side under the formation of the accumulator, with the The housing 11 is designed as a single wall sections 17 which are liquid-tight to one another by means of tie rods 18 are brought into contact. The Zeüwand sections 17 stand on a base part 19 and are by means of a; Cover 20 covered, whereby all connections are liquid-tight. The cells are covered by plates 21

an electrically conductive inert material, such as. B. titanium or titanium alloy separately. Along the sides of the cell casing lie at right angles to the electrodes 12, 13 similar plates 22, one of which in F i g. 6 and 8 is shown.

Each cell consists alternately of positive and negative electrodes 12 and 13, each of which is electrically connected to the plates 21 and 22 by means of the current collector 2. The positive electrodes 12 are held together at their lower ends by the inner and outer spacers 6 and 7, respectively, which are snapped into place over the entire length of the cells, forming a dense arrangement of the carbon-metal electrodes 12. The upper connecting parts 5 of the positive electrodes 12 are kept in contact by means of the tie rod 18. The negative electrodes 13 are arranged so that the same up in the cell between the positive

Eiciuiuiicii 12 ei MicC'ncii, vuii wu diene miiieiS lid

Spacers 10 are kept separate. The plates 21, 22 are sealed by means of sealing rings 22a in recesses 22ί> in the cell wall sections 17 (FIG. 6).

The connection terminals 15, 16 are preferably square plates with surface dimensions of approximately 7.5 cm, 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 Halogenfcaseinlaß 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 in the 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 is in communication with the hollow interiors of all positive electrodes 12 for the purpose described below. The 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 above the electrolyte 14 for the purpose of expanding the same

The cover 20 of the housing 11 has a pressure relief valve 26 which is connected through a pipe 27 and drainage openings 28 with the space 25 above the electrolyte 14 and below the cover 20 so that when the gas pressure inside the accumulator is exceeded above a predetermined Value of the pressure through the pressure relief valve 26 and through the halogen absorption chamber 29 to the outside air. This ensures that no toxic or harmful halogen, ζ. B. chlorine gas, can escape to the outside air. In the event of the gases escaping through the valve 26, they are replaced in the cell from the halogen cylinder 30 described below

Referring to FIG. 9 is in the cell or Accumulator chlorine circuit of the chlorine cylinder 30 via a Druckrecelventil 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.

ίο This is fed through line 35 to the accumulator, ie the electrolyte, together with condensed water vapor and liquid.

Although the accumulator can be operated with any halogen, chlorine is preferred as the easiest to handle. The description of the cell or the accumulator with reference to the drawing is based solely on chlorine. Appropriate adjustments are borrowed for working with bromine (ΐικί / υΰΐΜ * juii er iuruei.

The electrolyte 14 present in the accumulator is Zinc chloride in aqueous solution. There may be some mercury, indium or gallium in 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 be used, such polyelectrolytes in small amounts of less than 0.5 wt.% of the Electrolytes are used. Thiourea in an amount of about 1% by volume in the electrolyte also supports the suppression of dendrite formation.

The purity of the electrolyte 14 is important to avoid dendrite formation. The electrolyte 14 can be cleaned by dissolving zinc chloride in deionized water while stirring in zinc dust and allowing it to stand for several hours in order to precipitate the impurities. The presence of a small amount of zinc oxide assists in the removal of iron from which it is known that it leads to an increased dendrite The electrolyte 14 can be cleaned at a set voltage of 2.1 volts also medium Vorelektrolysieren until the current at a constant value drops This reduces the self-discharge of the cell, increases the hydrogen overvoltage and causes less zinc oxidation when standing. This also means that it is possible to work at a higher pH value.

It was found that a perfectly optimal Value for high performance in the electrolyte

is present when the pH rises to $ 2 to 4.0 and the

Density range from 1.1 to 1.25. The application of a low density also lasts

foaming during charging and the onset of dendritic formation at the back. If form dendrites under these conditions, they have a different shape and resist

long-term short-circuiting of the cell.

The electrolyte 14 can reach saturation Potassium chloride are introduced so as to improve conductivity and current efficiency. At the same time, the zinc precipitate becomes more moss-like. This can be done by adding a weak salt Acid, such as an acetate, can be enhanced to stabilize the pH adjacent to the zinc.

The addition of an acid forming depolarizer, such as HCIO, is necessary to disrupt the Dendrite formation is favorable and is formed by dissolving the chlorine. When applying this depolarizer it may be convenient to use a small device, such as a pump, in the accumulator which the electrolyte is made to circulate in the cells. A speed of about 15-60 cm / sec. is a suitable rotational speed and can be achieved by using or using a pump Development of chlorine bubbles, which causes the solution 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 FIG. 9, the chlorine is held in liquid form under high pressure in the chlorine cylinder 30 and the valve 31 is opened for the purpose of charging the accumulator already filled with electrolyte 14, so that the chlorine can flow to the inlet 28 in the cover 20 of the housing 11. 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, displacing any electrolyte 14 in the space between the positive carbon-metal electrodes 12 and any excess chlorine that may be released at this point in time is, leaves the accumulator through the outlet 23 and flows through the tube 32 past the UV lamp 33, d '\ ^{m works} in the usual way, 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

To causes hydrochloric acid, which, as already described, then by means of line 35 again the Accumulator is fed to a suitable entry point in the middle of the lid 20, from where a Diluting electrolyte 14 occurs.

The battery can be charged for the first time either electrically or by blowing chlorine gas through the gas circuit. After discharging the battery, the same is done again by passing an electric current through the battery 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 plate-like 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. in brine electrolysis, 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 a battery, 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 group IVfA _- J 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 1, characterized in that a metallic carrier (1) is used Lattice made of titanium and used as porous carbon in nitrile caoutchouc-bonded acetylene black are. 3. Positive electrode according to claim 2, characterized in that the grid has openings of 0.075 to 0.500 mm in diameter. 4. Positive electrode according to one of claims I to 3, characterized in that the grid made of titanium has an overlay of nitride film, mixed oxide film or boride film 5. Positive electrode according to one of claims 1 to 3, characterized in that the titanium grid with an oxide of higher valence constituent element, such as B. tantalum, alloyed or doped 6. Positive electrode according to claim 5, characterized characterized in that the titanium alloy contains up to 5% tantalum 7. Positive electrode according to claim 1, characterized in that the plastic powder is polychloroprene. 8. Positive electrode according to claim 7, characterized in that the polychloroprene is a Has particle size of 50 to 190 μm 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 (3) adhering under pressure to both sides of the grid-like metallic carrier (1) is provided with a plastic frame (4) which is inert towards halogen and which is placed around the edges in a gas-tight manner, leaving the surface of the carbon mixture layer free 11. Positive electrode according to claim 10, characterized characterized in that the plastic frame (4) consists of polyethylene, preferably high-density polyethylene, polypropylene, polytetrafluoroethylene or polyamide 12. Positive electrode according to claim 10, characterized characterized in that an electrode pair consisting of two electrodes (12) arranged at a distance is applied at least one edge is connected to one another and at one edge for the entry of halogen gas into the enclosed space between the electrodes (12) is open, the open end with a open channel (8) is in communication, the for Supply of the halogen gas into the space between the Electrodes (12) is provided