DE2842500A1 - COMPLEX-FORMING SUBSTANCES FOR ZINC-BROMINE BATTERY CELLS - Google Patents

Description

Dipl.-Ing. W. Weinkauff Dr. D. Thomsen

PATENT AGENCY OFFICE

284250Q

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Patent attorney Dipl.-Ing. W. Weinkauff Fuchshohl 71 6000 Frankfurt / M. 50 REGISTERED LETTERS
German Patent Office
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Frankfurt / M .: Munich:

Dipl.-Ing. W. Weinkauff Dr. rer. nat. D. Thomsen (Fuchshohl 71)

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September 25, 1978

GOULD Inc.

in Cleveland, USA

Complexing substances for zinc - bromine battery cells

This invention relates to battery systems which incorporate a bromine positive electrode such as zinc-bromine, as well as an improved technique for the reversible complex binding of bromine in such systems.

Conceptually, the zinc-bromine battery can be considered the simplest electrochemical one Systems count in which only zinc, bromine and zinc bromide are active participate in the reaction in the cell. In its simplest form, a

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Rechargeable zinc-bromine battery can be built with two inert, electrically conductive electrode substrates and an aqueous solution of zinc bromide. A charge / discharge cycle would therefore consist of the galvanic deposition and subsequent anodic decomposition of zinc on the negative electrode and from the release of bromine into the aqueous solution with the subsequent cathodic reduction on the positive electrode.

This inherent simplicity of the system and the fact that both electrode reactions run with good electrochemical reversibility, was early on recognized. The original idea was to find a simpler alternative to lead acid Develop battery. In the meantime there has been a great deal of corporate interest large batteries arose on this system due to the increasing demand for batteries Power to store energy outside of peak consumption times. The requirements for this use case differ considerably from others for rechargeable batteries. The main criteria which this Batteries must meet are acquisition costs, cycle time, degree of safety and light entertainment. To be competitive for the storage of peak energies To be, batteries must have very strict requirements in terms of price and The number of usable charge / discharge cycles is sufficient.

The earliest investigations into the zinc-bromine battery system identified two main problems clear in this system: this type of system has a relatively high level Self-discharge rate Cd.h. low Coulomb energy) due to the nature of the Zinc to deposit dendrites, and with it the risk of a short circuit in the cell.

Subsequent attempts to exploit the zinc-bromine system have therefore focused on the Focused on solving these two problems. It was probably the largest

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Expenditure made for various attempts to improve the Coulomb energy by reducing the concentration of free bromine in the aqueous Zinc bromide electrolytes. An early step towards this is in U.S. Patent No. 1,006. and relates to the use of porous carbon as a structure for the positive electrode. The usefulness of this technique was however, limited by the significant amount of carbon necessary to absorb the bromine through the UTi and the reluctant release of the bromine through it the material when the cell is discharged.

Another attempt related to building complex-forming substances into the electrode structure. US Pat. No. 2,566,114 describes the use of quaternary ammonium bromides such as tetraethylarmranium bromide. These substances form a number of polybromides up to Br _q , In other words, four molecules of bromine per molecule of organic substance could be used. However, when the level of bromination was changed, both solid and liquid polybromides were formed, which resulted in difficulties in retaining the complexes within the electrode structure and in the excessive polarization of the electrodes.

It was later argued, as described in U.S. Patent No. 3,738,870, that the properties of the bromine e-electrode can be visibly improved, when only a single solid bromine complex is formed in the electrode structure. To do this it was obviously necessary to keep the bromine extreme slowly add to the solution containing a bromine ion and a fine suspension of the kcmplex-forming substance contained. With the rapid addition of the bromine were therefore so-called "mixed polybromide-bromine clumps" were formed.

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• More recently it has been found that in the presence of a proton-free dipole in the electrolyte, such as propylene carbonate, and a selected quaternary Anrnon i umbrom i ds insoluble polybromide oils over a wide range of bromination are formed. This is described in U.S. Patent No. 3,816,177.

In the more recent US Patents No. 4,038Λ59 and No. 4,038Λ60 a large number of substances are described which can be added to the electrolyte of halogen cells in order to bind the halogen in a complex manner. The ..k59 patent lists various alcohols and nitriles which form oil-like insoluble complexes with halogens. These complexing agents can also contain amounts of tetraalkyl sodium. The ... '+ ÖOer patent describes many ethers that form complexes with halogens and also contain amounts of tetraalkylammonium. They form insoluble, oil-like complexes with the halogens. A serious disadvantage of these alcohols, ethers and nitriles is the rapid chemical and electrochemical decomposition of the substances in the presence of bromine and an active bromine / bromide electrode, which makes these substances completely unsuitable for use in a zinc-bromine system.

A main feature of the present invention is therefore a zinc-bromine battery system, which is characterized by a relatively high Coulomb energy. A related and even more essential feature is that casual method of storing bromine in order to reduce the concentration of bromine in the Maintain electrolytes at acceptable levels.

The present invention also has the following features, among others:

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τ Complexing substances, which with bromine are water-insoluble oils lower Viscosity form within a typical range of bromination.

- A complexing agent for bromine, which is stable in the medium of a zinc-bromine battery is.

- A complexing agent that forms polybromide oils with bromine, which are sufficient have a low viscosity so that there is a sufficiently large exchange rate for bromine between the oil and the electrolyte.

- A zinc-bromine battery, the construction of which requires the use of a wide range of materials, because due to this invention the system less is corrosive.

- A battery system whose toxicity is conceivably lower because of the lower Activity of the bromine used.

Other objects and features of the present invention will become apparent from the following Description visible.

The present invention is described here in the essential details, them however, allows many modifications and alternatives. It goes without saying, however, that the invention is not to be limited to the form described, but on the contrary includes all modifications and alternatives that the The sense and the scope of the invention correspond as required in the appendix.

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Thus, for example, while the present invention will be described in principle in connection with a rechargeable zinc-bromine cell or battery system It must be recognized that the invention can also be used in any other system employing a bromine positive electrode. The present For example, the invention can be used in many redoy systems. In fact, the present invention can also be used as a convenient one Process to form bromine complexes for applications other than electrochemistry, e.g. for the storage of bromine before transport or similar Use of such ammonium compounds has certain advantages, it must be pointed out that also use similar phosphorus or sulfur compounds if they meet the criteria for Αττηοη i disconnections, which are described in the following.

The present invention is generally based on the discovery that certain Tetraalkyl ammonium salts form polybromide oils which are essentially insoluble in aqueous solutions, have a sufficiently low viscosity so that a satisfactory exchange rate for the bromine between electrolyte and oil is selected. that are stable in the medium of a zinc-bromine battery and all others Have properties which make such substances suitable for adjustment and maintaining the desired bromine concentration in the aqueous used Zinc bromide electrolytes. In the course of this discussion it will be described which Salts can be used and in what way the polybromides are made.

The basic structure of the cells used is well known. Such a cell consists of a positive electrode (of the bromine electrode), a negative one Electrode C of the zinc electrode), a separator between the electrodes and a .suitable electrolytes.

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When charging, metallic zinc is deposited on the front of the substrate The negative electrode is deposited galvanically and remains there until the discharge. The positive electrode, on the other hand, is a redox electrode.

The separator used must generally fulfill two functions. He must be in Be able to exchange bromine from the positive to the negative electrode to be kept as low as possible. In addition, the material of the separator must be chemical To be inert under the conditions inside the cell and the transport of ions offer a slight resistance. It can be the most diverse known microporous materials and cation exchange materials are used will. For example, the microporous polyethylene separator "Daramic" is suitable According to W. R. Grace).

In order to keep the formation of zinc dendrites low, it is preferred to use a battery system with a circulating electrolyte. Because the electrolyte typically on the side of the separator facing the negative electrode has a much lower concentration of bromine than on the positive side Electrode, two separate circuits are preferably used. In such a In the system, the electrolyte will generally circulate continuously and flow through the cell many times during a single charge / discharge cycle.

The present invention allows the complex formation of the bromine and the Formation of the polybromide oils can be carried out by any method. However, it is advantageous to store the complexing substances separately and to carry out the complex formation in the contact of two liquids, as in the Application by Putt et al. is described. The bromine is split up here between the electrolyte and the bromine oils formed.

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• According to this invention, therefore, the electrolyte solution becomes excessively bromine freed by the formation of the oils and can be put into a memory or back again be pumped into the cell. Further details of suitable procedures are provided at Putt et al. Just describe it.

In accordance with the present invention are the complexing Substances Salts which, in contact with bromine, form liquid polybromide oils in one continuous and characteristic area of bromination. The salts used must therefore form liquid oils under the conditions of a bromination of at least 3-7, preferably 3-9, and must have a viscosity of no more than 30 centipoise at the operating temperature of the cell (which is up to to 50 ° - 60 ° Celcius for a zinc-bromine cell), preferably less than 20 centipoise and in the best case 10-15 centipoise.

Was given top instruction on an important aspect of the present invention discovered that certain unsymmetrical tetraalkylammonium salts act on complex formation Oils that are liquid with bromine form in the entire desired range of bromination. These salts and the resulting polybromide oils have the necessary Properties for use in a zinc-bromine battery system, especially when a circulating electrolyte is used. The tetraalkyl portion, which in the Bromination range 3-9 at room temperature, i.e. 23 ° C, forms liquid oils, include diethyldimethyl, ethyl trimethyl, ethyldimethylpropyl, diethylmethylpropyl, Ethylmethyldipropyl and diethyldipropyl. A methyltriethylammonium salt can also be used be used as it is in the 3-7 bromination range Polybromide oil forms.

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While the division of the bromine by means of the complex-forming described Substances may be sufficient, in some cases it may be desirable to increase the concentration of bromine in the electrolyte, or what is more typical, lower than when using a single complexing agent can be reached. This can of course be achieved to a certain extent are made by using a mixture of two or more of the substances described above. However, it is a merit of this invention that this Effect can also be achieved in a fine adjustment by mixing one of the previously described complexing substances with the appropriate amount an additional complexing agent. This will give the opportunity to get the ones you want Achieve results even more enhanced by a mixture of any of these Tetraalkylarrmonium proportions can be used regardless of whether the individual parts of the mixture itself would form the necessary polybromide oil or not. The versatility of this procedure is well illustrated by the absolute number of these Tetraacyarrmonium proportions in relation to the seven Species which by themselves form liquid oils in the necessary bromination range.

Furthermore, and as a result of another feature of this invention, the Polybromide oils described are also formed by means of a mixture of salts of two or more Tetraaky arrmonium portions, each of which is not one would form sufficient liquid polybromide oil. The versatility achieved with this is evident.

In each of these representations, a salt (C salts) with a tetraalkylammonium component which alone does not form a liquid polybromide oil must be the correct one Mixing with the other salt (C salts), of course, a liquid polybromide oil produce. The correct amounts can be obtained very quickly from the

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.Complex formation with bromine and the determination of the bromine content, the viscosity and other desirable properties of the mixture.

It must also be emphasized here that in all representations the vet— The tetraalkylammonium components used do not have to be unsubstituted. It are therefore used in this specification under the term "tetraalkyl-" both understood substituted and unsubstituted portions. All substituted Groups must result in a stable material in the intended median, i.e. that chlorine and bromine can be used to substitute the tetraalkyl moieties.

The viscosity of the polybromide oil phase in a zinc-bromine battery system that is designed for high yield is a critical factor in the selection of the substance or substances for complex formation of the bromine. The transport of the bromine between the aqueous electrolyte phase and the polybromide-oil phase is typically limited within the oil phase by its higher viscosity. This is known from the equations representing the mass transport coefficients define for liquid-liquid extractions. Under typical working conditions is the mass transport coefficient for the oil phase only in the The order of magnitude of that for the aqueous phase if the viscosity of the oil phase goes to zero. Given the working conditions, the properties of a zinc-bromine battery to the extent that the viscosity of the oil phase is reduced.

Another important consideration regarding the viscosity of the oil phase is the effort that is necessary to mix the oil and aqueous phases effectively. For example, the required pump output is proportional to the viscosity of the oil, when the oil phase circulates through a contact column by means of a pump.

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In the case of an oil with a higher viscosity, the necessary pump output is higher and thus the total energy yield of the battery is lower.

It has been shown that one therefore preferably has a viscosity of

10-15 centipoise observes for the oil phase at the operating temperature of the cell or battery used. The yield will be considerably lower if the viscosity increases to 30 centipoise. A further increase in viscosity results in an increasing deterioration in the performance data. The Point can be reached where the cell or battery is essentially no longer working.

The importance of the low viscosity oils according to the present specification finding can be assessed accordingly when considering the course of a charge / discharge cycle. In the charging phase, the Coulomb energy Lowered by higher viscosity of the oil, because the bromine exchange in the Oil phase runs too slowly and self-discharge occurs. on the other hand causes too little exchange of the bromine from the oil in during the discharge phase the electrolyte that no constant voltage is maintained.

With regard to the salt used, any anion can be taken from the idea which is not oxidized at a potential lower than that of bromine and that also does not form an insoluble compound in the electrochemical environment of the cell. Although there are advantages to using a bromide, in chloroids can be used in the same way. In addition, the salt can be in the form of perchlorates as long as the medium in the cell does not contain calcium ions contains.

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The polybromide oils according to the present invention can be applied to any can be produced in any way. For example, this can be the one you want Bromide or another salt dissolved in water and then liquid bromine in at least equimolar proportions are added to the desired oil obtain. The oil forms immediately and can be removed from the bottom of the reaction vessel can be removed using a pipette or other equipment. alternative to In this process, the bromine, if desired, the salt or an aqueous Solution of the salt are added. The maximum yield is typically achieved when the oil is formed in water.

By using organic complexing agents for the bromine, its concentration can be reduced independently controlled in the aqueous phase. The relative amount of oil or salt that should be used can be determined by being starting from the polybromide oil with the highest bromination level works backwards. From the number of moles of bromine that are produced in a certain size cell and from the bromination stage of the oil or salt that is needed to start As the reaction desires, one can determine the amount of oil or salt that is added must become. That is, if you think of one distribution of the bromine and another Would like to assume characteristics that an oil with a bromination level of 7 provides and if theoretically 10 moles of bromine are produced then one should have 5 moles Use oil from a bromination level 3.

When considering the individual concentration ranges, it should be noted that the Bromine concentration is kept as low as possible to reduce the degree of decomposition of the material caused by the bromine and natural Goes hand in hand with an increase in Coulombs energy. On the other hand, there is one lower limit, which is determined by the necessary transport of dissolved bromine

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Positive electrode substrate during discharge. If this If mass transport is delayed, an undesired polarization arises.

Similarly, the bromine concentration should be on the side of the Separators are extremely low compared to the negative electrode, i.e. about 0.005 molar, and zinc-bromine reactions that do not see the Faraday Follow laws, keep them small. In theory, the separator should have this concentration keep it low, but no separator can actually be a complete one Prevent the transport of bromine, each particular type having a concentration gradient-dependent limit before it allows excess bromine to pass through. For this There is a defined upper reason depending on the performance of the separator Limit for the bromine concentration on the positive electrode side.

When an aqueous zinc bromide electrolyte in a 1 molar concentration is used with a porous flow-through electrode, the bromine concentration is maintained preferably in the range of 5-15 g / l electrolyte or even better 5-10 g / l. This type of electrode is generally advantageous because of the optimal Coulomb energy. However, if flow electrodes are not used, then it is necessary the proportion of bromine in the electrolyte that is maintained can be increased because of the resulting different characteristics for mass transportation.

It has generally been found desirable to adjust the pH of the To keep electrolytes within certain limits so that the reaction at the negative electrode proceeds satisfactorily. As is well known, zinc is that is galvanically deposited during the charging phase, at a pH value of approx. 4 or greater it is somewhat mossy and does not adhere very well. This allows a

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Restriction of the flow of the electrolyte arise, and due to the bad Adhesion of the zinc to the electrode has a low Coulomb energy. on the other hand a problem arises at very low pH values below 1 due to the Sure corrosion on the deposited zinc and thus again a low Coulomb energy. For these reasons, an average pH value is in the range of 1 - 3 advantageous, whereby firmly adhering zinc layers are obtained. This can be can be achieved easily in a zinc-bromine battery, as no reactions are precorming, which cause any rapid pH changes, and because the zinc bromide dissolved in the water has a pH value of approx. 4. The pH itself can can then be increased by adding HC1 or HBr.

Density and viscosity of the 6 complexing substances obtained Polybromide oils are listed in Tables 1 + 2 throughout preferred Bromination area.

Table 1

Density in g / cm ³ at 25 ° Celsius

Tetraalkyl part of the substance

Ethyl tr! Methyl

Diethy! Dimethyl

Et hy1d imethy1propy1 Diethylmethylpropyl dimethyldipropyl

Ethylmethyldipropyl

Bromination level

3 5 7th 9 2,084 2.158 2,240 2,318 1,980 2,070 2,170 2,260 1,850 1.965 2,088 2,181 1,782 1,948 2,083 2.134 1,738 1,877 2,032 2.118 1,662 1,809 1,973 2,073

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Table 2

Viscosity in centipoise at 23 ° Celcius room temperature

Tetraalkyl part of the substance

Ethyl trimethyl
Diethy! Dimethyl
Ethy1d imethy1propy1 DiethyImethy1propy1 D imethy1d i propy1
EthyImethy1d i propy1

Bromine generation stage

3 5 7th 9 11.1 10.5 8.7 7.9 12.6 11.3 9.9 9.0 19.3 16.5 14.8 12.8 28.1 19.2 14.8 15.6 32.5 20.0 13.7 13Λ 75.3 37.1 24.9 20.9

It can be seen that the liquid oils formed are sufficiently low Viscosity have to make the necessary exchange of the bromine between the oils and to allow the electrolyte.

Table 3 shows the concentration of dissolved bromine in a 1.0 molar Zinc bromide electrolytes in equilibrium with the oils according to the present Invention.

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3 5 25th 7th 9 11.4 15.8 20th .3 39.8 5.7 10.8 17th .5 35.1 3.0 7.6 18th .4 32.9 3.3 6.6 18th .5 31.8 1.7 6.4 16 .9 34.2 1Λ 4.9 .3 30.9

Table 3

Dissolved bromine in g / l in the electrolyte at 25 ° C. Tetraalkyl proportion of the substance bromination stage

Ethyl trimethyl diethy dimethyl Ethyld imethy1propy1 Diethy! Methylpropy1 DimethyIdipropy1 EthyImethyldipropyl

Under equilibrium conditions, the various oils produce one sufficient low bromine concentration in the electrolyte, as can be seen from the table.

Since, as is well known, active zinc-bromine batteries, especially those of the size necessary for storing peak energies, work exothermically and inevitably require higher working temperatures, temperatures up to 60 ° C are found. Tables 4 - 6 show the characteristics of the ethyltrimethyl complex binder shown in the temperature range of 25 ° - 60 ° C.

Table 4 Dissolved bromine in g / l in the electrolyte

Temperature in ⁰ C bromination stage

3 5 7 9

25 "11.6 17.4 27.2 41.1

45 13.2 19.9 23.2 28.7

60 21.2 19.3 20.5 43.8

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284250Q

^:: Footnote to Table 4 CS.-16-)

The bromine proportions at this temperature correspond to the values in Table 3 for this substance, but measured at a different time. The noted Differences in the concentrations are an indication of those in the experiment contained fluctuation ranges.

Temperature in C

25 45 60

Table 5

Density in

Bromination stage 3 5 7 9 2,084 2,158 2,240 2,318 2,080 2,134 2,206 2,275 2,077 2,114 2,191 2,149

Temperature in ⁰ C

25 45 60

Table 6

Viscosity in centipoise

Bromination stage

3 5 7 9

11.1 10.5 8.7 7.9

6.0 5.6 5.8 4.8

4.4 4.1 3.9 3.9

It can be seen that the properties of this complexing agent are at the higher Temperatures are satisfactory. The visible one is particularly important Reduction in viscosity at higher temperatures in terms of this caused higher exchange rate for the bromine.

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Tables 7-9 show the characteristics of the diethyldimethyl complex binder in the temperature range of 25 ° - 60 ° C.

Table 7 Dissolved bromine in g / l in the electrolyte

Temperature in ⁰ C 'bromination stage

3 5 7 9

25 "6.7 10.4 22.2 34.2

45 6.5 13.1 26.6 42.5

60 8.3 23.6 26.6 41.7

"This also applies to these values in comparison with those in Table 3 What was said in the footnote to Table 4.

Table 8

Density in g / cm ^

Temperature in ⁰ C bromination stage

3 5 7 9

25 1,980 2,070 2,170 2,260

45 1,966 2,032 2,119 2,199

60 - 2,027 2,103 2,182

Temperature in ⁰ C

25 45 60

Tabel 9 9 9 9 Viscosity in Cent i po i se 4th 5 .0 7th 4th .6 .6 Bromination stage 9098 3 5 7 12.6 11.3 9. 1 ^ Z ₃ O 8 5 0, _{0 5} 4.9 4.

With this complexing agent you can see that it is a little more effective and that The bromine concentration in the aqueous phase is low but still sufficient low viscosity.

The following examples are intended to illustrate the practice of the present invention to illustrate but not to constitute a limitation.

example 1

It shows the use of an ethyltrimethylammonium bromide complexing agent in a rechargeable 32 Wh zinc-bromine battery system with a porous Flow-through electrode and a circulating electrolyte.

The negative electrode substrate is a flat, non-porous plate made of titanium. The substrate of the positive electrode is a flat plate made of porous titanium with a coating that contains ruthenium. The four applied macroporous "Daramic" separation (according to W. R. Grace) consists of one flat tissue with vertical ribs at regular intervals on either side that serve as channels for the flow of electrolyte.

The composition of the electrolyte in the completely discharged state is as follows: zinc bromide concentration 1.5 molar potassium chloride concentration hO molar

-L

Lead chloride concentration 8vO χ 10 molar

pH 1.0-3.0

The bromine oil when completely discharged is composed of 57 Granm of ethyltrimethylammonium bromide oil and 51 grains of bromine (bromination stage 3).

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During the charging process, the proportion of the complex-bound increases Bromine in the oil and the entire volume of the oil.

The cell works satisfactorily when the following charge / discharge cycle is maintained: Ca) charge with 3 A Cconstant) for 2 hours. The charging voltage is initially approx. 1.90 V at 27 ° C and increases in the course of the charge by approx. 50 mV. Cb) Waiting time of 15 minutes with an open circuit. Cc) discharge with 3 A Cconstant) until the cell voltage drops sharply and Cd) 30 minutes short circuit.

Example 2

It shows the formation of a liquid polybromide oil upon use a mixture of 2 salts, each of which forms a solid complex with Bromine b i1 den.

About 0.02 M of a mixture containing equimolar proportions of tetraethyl arrmonium bromide and Dic \ t hy ldi propy larrmoni bromide was placed together with 100 ml of a 1 M solution of ZnBr ₂ in a 200 ml beaker. Bromine was added four times in equal proportions of approx. 0.02 M each. The solution was stirred to equilibrate between the bromine additions. The results in Table 10 show the properties of the mixture in comparison with those of the individual salts.

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Bromination stage

ο » ο co

Table 10

Equinriolar mixture of tetraethyl- tetraethyl arrmon iumbromid arrmon iumb rom id and diethyl dipropyl alone arrmon iumbromid

More physical
State

Liquid, "
slight light scattering

Liquid, "
slightly dispersive

Liquid,
highly viscous

Solid,
flaky and
crystal1 in

g Br ₂ /! electrolyte

1.5

8.5

11.2

More physical State

Solid, flaky and crystalline 1 in

Solid, crystal in

Solid, crystal in

Solid, crystal1 in D i äthy1d i propy1ammon i umbromi d alone

g Br _2/1
electrolyte More physical
State 0.6 Solid,
finely distributed 3.3 oil,
highly viscous 6.6 Solid lump,
tarry ig 18.9 Solid lump,
tarry ig

g Br ₂ /! electrolyte

1.0

3.8

31.1

As the oil was stirred, it was in the form of small liquid droplets.

CO

cn ο

CD

Table 10 shows that the mixture of the two salts is a useful one Complexing agent is, although the individual salts themselves are not suitable.

Example 3

This example shows the use of an additional complexing agent, the alone normally forms a solid polybromide on its own, together with a complexing agent that forms a liquid polybromide oil to work in this Combination to adjust the bromine content more precisely.

Ethyl tr imethylamrionium bromide was mixed in different amounts accordingly with ethyltri-n-propylanmonium bromide, which is usually a solid Polybromide produced, but excellent properties with regard to the bromine content Has. Liquid oils were formed in the area of the bromination stage 3-9.

In a 1 molar zinc bromide electrolyte, the addition of ethyltri-npropylanonium bromide gave an increase in the amount of bromine dissolved. In contrast, the addition to a 2 molar zinc bromide electrolyte resulted in lower levels Concentrations of the dissolved bromine.

As can be seen, the present invention provides complexing agents which are described in the chemical and electrochemical environment are stable, and which improve the electrochemical yield of the system satisfactorily by using reduce the concentration of bromine and keep it at the desired level. The ability of the polybromide oils formed, in a useful range of bromination stages to be present as liquids with low viscosity allows many degrees of freedom during operation without the risk of malfunctions,

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as they would occur if a complexing agent depending on the Bromination stage passes from the liquid to the solid phase. The relatively low viscosities of the oils according to this invention are essential for the sufficiently rapid transport of bromine between the oil and the aqueous phase.

909815/0850

Claims (1)

patent claims: ii A cell _- containing a bromine electrode and a bromine complexing substance. Said complexing substance contains at least one quaternary ammonium salt and forms a liquid oil in the range of the bromination stage of at least 3-7. Said liquid oil has a viscosity of less than about 30 centipoise in the operating temperature range of said cell. 2. The cell according to claim 1 is a zinc-bromine cell. 3. A zinc-bromine cell according to claim 2, wherein said complexing Substance is a liquid at a bromination level of 3-9. 4. A zinc-bromine cell according to claim 2, wherein the wuartarian portion of the quaternary arrmonium salt is a compound from the group of ethyltrimethyl-, Dimethyl diethyl, ethyl propyl dimethyl, dimethyl dipropyl, methyl triethyl, MethylpropyIdiäthyl- and Methyläthyldipropyl-. 5. A zinc-bromine cell according to claim 4 - wherein the quaternary portion Is ethyl trimethyl. 6. A zinc-bromine cell according to claim 3, wherein the quaternary portion Is diethyldimethyl. 7. A zinc-bromine cell according to claim 2, wherein the viscosity of said oil is lower than about 20 centipoise. ßflQßifi / ßßh'fl •8th. A zinc-bromine cell according to claim 2, wherein the viscosity of said Oil is lower than about 15 centipoise. 9. A zinc-bromine cell according to claim 4, further comprising a quaternary ammonium salt contains, which normally forms a solid complex with bromine forms. 10. A zinc-bromine cell according to claim 2, which is a mixture of at least contains two quaternary ammonium salts, each of which is normally used for forms a solid complex with bromine. 11. A cell according to claim 1 and substantially as described herein. 12. A cell according to claim 1 and substantially as described herein with Reference to each of the examples. 13. A cell according to any one of claims 1-10. 1 ^. A method of forming bromine complexes in a cell that has a bromine electrode and has an aqueous electrolyte. The procedure includes that a sufficient amount of at least one quaternary Ammonίumsa1ζ in Contact is made with the electrolyte, with bromine im a liquid To form polybromide oil in the range of bromination stages of at least 3-7, said oil having a viscosity of less than about 30 centipoise over the operating temperature range of the cell. flöd8iS / ö650 284250Ü 15. A method according to claim 14 for forming bromine complexes in one Cell that has a bromine electrode and an aqueous electrolyte, and essentially as described here. 16. A process for the formation of bromine complexes in a cell that has a Has bromine electrode and an aqueous electrolyte, and essentially as described herein with respect to each of the examples. 17. A polybromide for use as a complexing agent for bromine in the electrolyte a cell that has a bromine electrode. The polybromide contains at least a quaternary arrmonium salt as a complex with an amount of bromine sufficient to form a liquid polybromide oil in the range of the bromination stages from at least 3-7, said oil having a viscosity less than about 30 centipoise at the operating temperature of the cell. 18. A polybromide according to claim 17 for use as a complexing agent for Bromine in the electrolyte of a cell having a bromine electrode, the polybromide being essentially as described here. 19. A polybromide for use as a complexing agent for bromine in the electrolyte a cell having a bromine electrode, the polybromide being essentially as described herein with reference to each of the examples.