WO2003056645A2

WO2003056645A2 - Method and device for regenerating zinc electrodes

Info

Publication number: WO2003056645A2
Application number: PCT/EP2002/014678
Authority: WO
Inventors: Hans Jürgen PAULING; Hans-Ulrich Reichardt; Roman Pauling; Jens Taleikis
Original assignee: Zoxy Energy Systems Ag
Priority date: 2001-12-28
Filing date: 2002-12-20
Publication date: 2003-07-10
Also published as: AU2002358785A8; DE10164300A1; AU2002358785A1; WO2003056645A3; DE10164300B4; ZA200204013B

Abstract

The invention relates to a method for regenerating zinc electrodes, especially for rechargeable zinc-air batteries. According to said method, zinc oxide is introduced into an electrolyte received in a dissolving chamber, in order to produce zinc ions, the zinc ions in the electrolyte being then at least partially converted into zincate ions. The electrolyte containing the zincate ions dissolved therein is then supplied to a reactor vessel and the zincate ions in the reactor vessel are at least partially electrolytically converted into zinc on a carrier cathode, zinc, especially in the form of a zinc sponge, being formed on said carrier cathode. The inventive method is characterised in that a mixture of zinc oxide of any origin, especially zinc oxide from waste products, is used as the starting material for the zinc oxide. The invention also relates to a device for regenerating zinc electrodes, especially for rechargeable zinc-air batteries, said device being especially used to carry out the inventive method.

Description

Method and device for regenerating zinc electrodes

The invention relates to a method for regenerating zinc electrodes, in particular for rechargeable zinc-air batteries, according to the preamble of claim 1 and a device for regenerating zinc electrodes, in particular for rechargeable zinc-air batteries, in particular for carrying out the inventive method.

In a generic method, zinc oxide is provided to provide zinc ions in an electrolyte which is accommodated in a dissolving container, the zinc ions are at least partially converted into zincate ions in the electrolyte, and the electrolyte is dissolved with the zincate ions therein fed to a reactor vessel and the zincate ions are at least partially converted electrolytically to zinc in the reactor vessel on a carrier cathode, zinc, in particular as a zinc sponge, being deposited on the carrier cathode.

Accumulators, fuel cells and batteries play an increasingly important role due to the flexibility and mobility that can be achieved with such a network-independent power supply system.

From an economic point of view, zinc-air batteries are particularly interesting, where only the zinc as a metallic active material for the negative electrode must be stored in the battery. Oxygen is taken out as a reactant during discharge from the surrounding air and released there when it is recharged. As a result, a higher charge and energy density can be achieved for zinc-atmospheric oxygen batteries than with other electrochemical energy stores, which is an important criterion for many areas of application. For example, specific energy densities in the order of 100 to 150 Wh / kg are achieved for zinc-atmospheric oxygen batteries, which corresponds to approximately twice the value for a nickel-cadmium accumulator and approximately four times the specific energy density of a lead accumulator. Zinc-atmospheric-oxygen batteries are still characterized by inexpensive battery components and good environmental compatibility.

The article by Haas, S. Müller and K. Wiesner, Chemie Ingenieur Technik 68, pp. 524-542 (1996) provides an overview of the prior art of rechargeable zinc-atmospheric oxygen batteries.

A problem area with rechargeable zinc electrodes is the morphology changes which occur with increasing number of charge-discharge cycles. These morphology changes are manifested in the formation of dendrites and in changes in the electrode geometry, which are referred to as "shape change". These changes in geometry result from an uneven deposition of the zinc on the electrode with an increasing number of charge-discharge cycles. The zinc tends to densify in a central area of the electrode, which is accompanied by a reduction in the reactive surface and thus a deterioration in the electrical properties. The service life of a zinc electrode is therefore limited by the processes mentioned, so that a used zinc electrode either has to be replaced by a newly manufactured electrode or has to be regenerated.

In this context, it is known from DE 197 08 208 C2 to regenerate zinc electrodes using raw zinc, old, worn zinc electrodes, which have dropped significantly in their electrical performance properties, as counter electrodes for closing the material cycle in relation to the active zinc to be deposited is used.

It is also known from the above-mentioned article by 0. Haas, S. Müller and K. Wiesener to remove the used zinc electrode or the zinc oxide powder sludge formed and / or the electrolyte solution oversaturated with zincate from the battery and cathodically outside the battery again to reduce active zinc.

These regeneration processes can only be carried out if a corresponding amount of raw zinc or zinc oxide from degraded electrodes is available. When raw zinc from used electrodes is used, the regeneration is also comparatively energy-intensive, since the raw zinc has to be electrolytically deposited on the electrode in a preceding process step, which can be regarded as the last charge of the battery.

The object of the invention is to provide a method for regenerating zinc electrodes which is particularly versatile and with which zinc electrodes of consistently high quality can be produced or regenerated. Furthermore, a device for regenerating zinc electrodes is to be created, with which zinc electrodes can be regenerated in a particularly environmentally friendly manner.

This object is achieved by the method with the features of claim 1 and by the device with the features of claim 12.

Advantageous developments of the method and preferred embodiments of the device according to the invention are specified in the dependent claims.

A method of the type specified above is further developed according to the invention in that a mixture of zinc oxide of any origin, in particular zinc oxide from waste materials, is used as the starting material for the zinc oxide.

As the main idea of the invention, instead of the almost exclusive use of raw zinc, zinc oxide of any origin has been used as the starting material for the regeneration of zinc electrodes.

A first essential advantage of the invention lies in the surprising finding that the electrodes produced or regenerated with the method according to the invention have no quality differences compared to those which were produced or regenerated exclusively using raw zinc.

Surprisingly, the quality of the regenerated zinc electrodes does not depend on the proportion of raw zinc used in the total amount of zinc used, so that raw zinc can in principle be completely dispensed with. Another important advantage of the invention is that zinc oxide from any waste materials can be used and thus these materials can be meaningfully recycled. In this way, the invention makes a contribution to sustainable materials management.

In addition, since the use of raw zinc can largely be dispensed with, the method according to the invention can save considerable costs.

In a particularly preferred embodiment of the process, with the aid of raw zinc anodes, which can be introduced into the reactor in a defined manner, a fine adjustment of a zincate concentration in the reactor vessel is carried out. A possibly fluctuating concentration of the zincate ions introduced by dissolving zinc oxide in the electrolyte can thus be compensated for and zinc anodes with very good electrical performance parameters can be produced.

In a further advantageous variant of the method, a substantial proportion of the zincate ions, in particular a proportion of more than 90%, is provided by zinc oxide of any origin, it being possible in principle to completely dispense with the use of raw zinc. Existing waste materials can then be used very effectively with very little use of raw materials and energy.

The process according to the invention can in particular be carried out batchwise. This can be advantageous if, for reasons of process control, different zincate concentrations in the electrolyte are to be adjustable in different phases of the regeneration, for example in order to achieve certain growth results in the zinc electrodes to be produced or regenerated. The process can be carried out batchwise, for example, by a) dissolving zinc oxide in the electrolyte in the dissolving tank in a first process step until a working concentration of zincate ions is reached, b) subsequently by the electrolyte with the dissolved zincate ions in the Reactor vessel is directed, in particular pumped, c) that subsequently the electrolysis is carried out in the reactor vessel with the deposition of zinc on the carrier cathode until the zincate concentration in the reactor vessel has dropped to an initial concentration, d) that the electrolyte with the initial concentration of zincate Ions are returned to the dissolving container, in particular pumped, and e) that process steps a) to d) are repeated until a defined amount of zinc has been deposited on the carrier cathode.

In order to specifically influence a zincate concentration in the electrolyte in the reactor vessel, a portion of the zincate ions can be provided by raw zinc anodes. In this context, it is particularly preferred to extend a phase in which there is essentially the working concentration of zincate ions by providing an increasing proportion of the zincate ions through raw zinc anodes, which are introduced into the reactor vessel in a defined manner.

Particularly good results are achieved if a zinc oxide amount of 20 to 38 g / 1, in particular 25 to 35 g / 1, preferably 28 to 32 g / 1, is added to the electrolyte in the dissolving container to produce the working concentration of zincate ions becomes. KOH, in particular a 6-molar KOH solution, is preferably used as the electrolyte.

An increase in the quality of the regenerated electrodes can also be achieved by continuously controlling the mass flows of zinc oxide, raw zinc and / or zinc deposited on the carrier cathode.

In terms of the device, the object specified above is achieved by a device having the features of patent claim 12.

In such a device, which is particularly suitable for carrying out the method according to the invention, the following components are provided according to the invention:

a dissolving container for receiving an electrolyte and for receiving zinc oxide of any origin, in particular zinc oxide from waste materials,

a reactor vessel for receiving the electrolyte with zincate ions dissolved therein and for carrying out an electrolytic regeneration of the zinc electrodes,

- A, in particular controllable, fluid connection between the dissolving tank and the reactor tank and

- With a control device for the targeted setting of a concentration of the zincate ions in the electrolyte in the dissolving tank and / or in the reactor tank.

A core idea of the device according to the invention can be seen that the dissolving container is designed to receive zinc oxide of any origin, in particular to receive zinc oxide from waste materials. In this way, any zinc oxide waste materials can be used and the regeneration can be carried out with an extremely low use of raw materials and energy. In a particularly preferred embodiment of the device according to the invention, a first fluid connection for supplying electrolyte solution with a high concentration of zincate ions into the reactor container and a second fluid connection for discharging electrolyte solution with a reduced concentration of zincate ions from the reactor container is between the dissolving container and the reactor container intended. This enables continuous process control, which can be advantageous, for example, if a constant concentration of zincate ions is to be set in the reactor vessel practically over the entire regeneration process.

In order to retain solid particles, in particular zinc particles, which can adhere to the waste materials used, a filter device can also be provided between the dissolving tank and the reactor tank, in particular in the first fluid connection and / or in the second fluid connection.

A stirring device can be provided to accelerate the dissolution process of the zinc oxide in the electrolyte in the dissolving container.

A further preferred embodiment of the device is characterized in that a feed device for the defined introduction of raw zinc anodes into the electrolyte solution accommodated in the reactor vessel is provided, which is in operative connection with the control device. This enables precise adjustment of the zincate ion concentration in the reactor vessel.

Further advantages and properties of the method and the device according to the invention are described below with reference to the attached schematic figures. There shows:

1 shows a schematic illustration of the method according to the invention in the case of a continuous method;

2 shows a schematic representation of the method according to the invention in the case of a discontinuous method; and

3 shows the quantities of zinc oxide used in the method according to the invention and the essential chemical reactions taking place at the electrodes.

A continuous variant of the method according to the invention and the components of a device according to the invention are explained below with reference to FIGS. 1 and 3.

In a dissolving container 12, in which a 6 molar KOH solution is received as the electrolyte, zinc oxide from waste materials is continuously filled in such a way that a

Working concentration of C = 30 g / 1 is maintained. In order to facilitate or accelerate the dissolving process, a stirring device 26 is provided, which in particular can be a magnetic stirrer.

In the electrolyte, the zinc oxide ZnO together with

Water H O and hydroxide ions OH to zincate

2 2-ion Zn (OH) implemented as this in equation

II. 1) is shown in Fig. 3. Via a pipeline 20 as a fluid connection, the KOH

Electrolyte with the working concentration of zincate ions

Zn (OH) pumped into a reservoir container 17,

4 being solid particles, in particular zinc particles, which may be mixed with the waste materials used in the

Electrolytes 14 have reached the release container 12, from a

Filter device 24 are retained.

2- In the reactor vessel the zincate ions Zn (OH)

4 on a carrier electrode 30 with release of hydroxide ions

OH and electrons according to the equation 1.2) shown in Fig. 3 electrolytically converted to zinc, which is deposited on the carrier cathode 30. The electrical parameters of the electrolysis are preferably set such that the sponge-like structure preferred for zinc electrodes, which is also referred to as zinc "sponge", can form on the carrier cathode 30. Electrolyte solution 14 depleted in zincate ions is pumped via a pipeline 22 as a fluid connection from the reactor vessel 17 back into the dissolving vessel 12.

In order to enable a fine adjustment of the zincate concentration in the electrolyte 14 accommodated in the reactor vessel 18, two anodes 27 made of raw zinc are provided, from which, according to equation I. 1) zinc Zn, electrons are released as zinc ion Zn goes into solution and is then reacted with hydroxide ions OH to zincate Zn (OH). On the anodes

4 are also hydroxide ions OH giving off

Electrons to water H 0 and escaping oxygen

2 gas 0 implemented.

In order to ensure the zincate concentration in the reactor vessel required for the formation of zinc "sponge", one with a measuring sensor 34 for continuous provided concentration determination provided control device 32 which is operatively connected to a device, not shown, for the defined introduction of the raw zinc anodes 27 into the reactor vessel 17. In order to influence the electrolytic growth of zinc on the carrier cathode 30 in a targeted manner, metal ions can also be added to the electrolyte 14 as a metal salt solution, in particular as a lead metal, or a third metal electrode can be provided as a circuit.

A discontinuous variant of the method according to the invention is explained below with reference to FIG. 2. The device used here essentially corresponds to the device 10 shown in FIG. 1.

The individual process steps are indicated schematically in the upper area of FIG. 1, whereas in the lower area the time course of the zincate concentration in the dissolving tank or in the reactor is plotted in a diagram.

The electrolyte 14, which is preferably a 6-molar KOH solution in the dissolving tank 12, is in the start phase of the process designated I. The reactor tank 17 is empty at this time.

In the following process step, designated II in FIG. 2, zinc oxide ZnO is added to the electrolyte until a concentration of C = 30 g / 1 is reached. tech Subsequently, the electrolyte 14, which now has the required working concentration of zincate ions, is pumped via the pipeline 20 into the reservoir container 17. This process step is designated III in FIG. 2. In the reactor vessel 17, the electrolytic regeneration or the reconstruction of the zinc electrodes then takes place in accordance with the chemical equations shown in FIG. 3. Again, the electrical parameters of the electrolysis are adjusted so that the zinc "sponge" preferred for zinc electrodes can form. In the course of this process step, the zincate concentration in the electrolyte 14 in the reactor vessel 17 drops continuously from the working concentration C1 to a lower concentration C2, the electrolysis being carried out until the concentration C2 has reached the initial concentration CO, ie C2 = CO. This process step is designated IV in FIG. 2.

In the last process step, which is denoted by V in FIG. 2, the electrolyte solution 14, which is depleted in zincate ions, is pumped back into the dissolving tank 14 from the reactor tank 17 via one of the pipelines 20 or 22.

The process steps explained are then repeated until a desired amount of zinc is deposited on the carrier cathode or until the zinc "sponge" has reached a desired size.

The diagram shown in FIG. 3 shows the concentrations of zinc oxide in a 6-molar KOH solution which are relevant for the process according to the invention. With

C is the maximum saturation concentration, which is about 40 g / 1 for a 6-molar KOH solution. In practice, however, this saturation concentration C is not used for reasons of energy and time and therefore for reasons of cost. A compromise with regard to the mentioned parameters energy and time is the concentration C, which is about 30 g / 1 tech and the working concentration Cl in Fig.

2 corresponds.

C in FIG. 3 denotes the minimum or starting concentration corresponding to CO or C2, which can theoretically go to 0 g / 1, but in practice, for energy, time and cost reasons, finite minimum concentrations are used.

Claims

1. Process for the regeneration of zinc electrodes, in particular for rechargeable zinc-air batteries, in which

Zinc oxide is added to an electrolyte for the provision of zinc ions, which is accommodated in a dissolving container,

the zinc ions in the electrolyte are at least partially converted to zincate ions,

- The electrolyte with the zincate ions dissolved therein is fed to a reactor vessel and

the zincate ions in the reactor vessel are at least partially converted electrolytically to zinc on a carrier cathode, zinc, in particular as a zinc sponge, being deposited on the carrier cathode, characterized in that a mixture of zinc oxide of any origin is used as the starting material for the zinc oxide, especially zinc oxide from waste materials is used.

2. The method according to claim 1, characterized in that with the aid of raw zinc anodes, which can be introduced into the reactor in a defined manner, a fine adjustment of a zincate concentration in the reactor vessel is carried out.

3. The method according to claim 1 or 2, characterized in that a substantial proportion of the zincate ions, in particular a proportion of more than 90%, is provided by zinc oxide of any origin.

4. The method according to any one of claims 1 to 3, characterized in that the method is carried out batchwise.

5. The method according to any one of claims 1 to 4, characterized in that a) that zinc oxide is dissolved in the electrolyte in the dissolving tank in a first process step until a working concentration of zincate ions is reached, b) that subsequently the electrolyte with the dissolved zincate Ions are passed into the reactor vessel, in particular pumped, c) that subsequently the electrolysis is carried out in the reactor vessel with the deposition of zinc on the carrier cathode until the zincate concentration in the reactor vessel has dropped to an initial concentration, d) that the electrolyte coexists the initial concentration of zincate ions is returned to the dissolving container, in particular pumped, and e) that process steps a) to d) are repeated until a defined amount of zinc has been deposited on the carrier cathode.

6. The method according to any one of claims 1 to 5, characterized in that in order to extend a phase with the working concentration of zincate ions in the reactor vessel, an increasing proportion of the zincate ions by raw zinc anodes, which are introduced into the reactor vessel in a defined manner, provided.

7. The method according to any one of claims 1 to 3, characterized in that the method is carried out continuously.

8. The method according to claim 7, characterized in that g e k e n n z e i c h n e t,

zinc oxide is continuously fed to the dissolving container in such a way that a desired working concentration of zincate ions is maintained,

- The electrolyte with the working concentration of dissolved zincate ions is continuously fed into the reactor vessel, in particular pumped

that the electrolytic deposition of zinc on the carrier cathode is carried out continuously in the reactor vessel,

- That from the reactor tank continuously depleted in zincate ion electrolyte solution is returned to the dissolving tank, in particular pumped.

9. The method according to any one of claims 1 to 8, characterized in that to provide the working concentration of zincate ions, a zinc oxide amount of 20 to 38 g / 1, in particular from 25 to 35 g / 1, in the electrolyte in the dissolving tank becomes.

10. The method according to any one of claims 1 to 9, characterized in that the mass flows of zinc oxide, raw zinc and / or zinc deposited on the carrier cathode are continuously regulated.

11. The method according to any one of claims 1 to 10, characterized in that the electrolyte used is KOH, in particular a 6-molar KOH solution.

12. Device for the regeneration of zinc electrodes, in particular for rechargeable zinc-air batteries, in particular for carrying out the method according to one of claims 1 to 11, with

a dissolving container (12) for receiving an electrolyte (14) and for receiving zinc oxide of any origin, in particular zinc oxide from waste materials,

with a reactor vessel (17) for receiving the electrolyte (14) with zincate ions dissolved therein and for carrying out an electrolytic regeneration of the zinc electrodes,

- With at least one, in particular controllable, fluid connection between the dissolving container (12) and the reactor container (17) and

- With a control device (32) for the targeted setting of a concentration of zincate ions in the electrolyte (14) in the dissolving tank (12) and / or in the reactor tank (17).

13. The apparatus according to claim 12, characterized in that between the dissolving container (12) and the reactor container (17) a first fluid connection (20) for supplying electrolyte solution (14) with a high concentration of zinc ions in the reactor container (17) and one second fluid connection (22) is provided for removing electrolyte solution (14) with a reduced concentration of zincate ions from the reactor vessel (17).

14. Device according to one of claims 12 or 13, characterized in that between the dissolving tank (12) and the reactor tank (17), in particular in the first fluid connection (20) and / or in the second fluid connection (22), a filter device (24) to retain solid particles, in particular zinc particles.

15. Device according to one of claims 12 to 14, characterized in that a feed device for the defined introduction of raw zinc anodes (27) into the reactor vessel (17) accommodated electrolyte solution (14) is provided, which with the control device (32) in Active connection is established.