CIRCUIT ARRANGEMENTS WITH ELECTROCHEMICAL CELL AND METHOD FOR OPERATING AN ELECTROCHEMICAL CELL

Abstract

Circuit arrangement comprising: an electrochemical cell (100) from a group comprising an electrolytic cell, a thermally regenerable electrochemical cell or a galvanic primary cell, the electrochemical cell (100) comprising: a first electrode (110) which is liquid during operation of the electrochemical cell (100), a second electrode (120), and an electrolyte (150) in contact with the first electrode (110) and in contact with the second electrode (120); and a control circuit (200) electrically connected to the first electrode (110) and the second electrode (120), wherein the control circuit (200) is configured to operate the electrochemical cell (100) in first phases with a first current direction between the first electrode (110) and the second electrode (120) and during second phases with a second current direction opposite to the first current direction.

Description

TECHNICAL FIELDThe present application relates to a circuit arrangement with an electrochemical cell, in particular with a galvanic cell or an electrolysis cell. The application also relates to operating methods for electrochemical cells.BACKGROUNDElectrochemical cells generate electrical energy by chemical reactions (galvanic cell) and / or trigger chemical reactions (electrolytic cell) with supplied electrical energy.In an electrolytic cell, an external voltage acting between two electrodes excites a current flow between the two electrodes, which in turn initiates an otherwise non-spontaneous chemical reaction in the cell. For example, in an electro-metallurgical cell, a pure element is recovered from a melt of salts and / or oxides containing this element by melt flow electrolysis.In a galvanic cell, a chemical reaction and, if appropriate, an additional concentration gradient between two electrodes causes an ion flow between the electrodes. The ion flow through the galvanic cell initiates an electron flow through an external load connected between the two electrodes.In a (galvanic) primary cell, a portion of the chemical energy present in the initial state of the galvanic cell is converted into electrical energy. The electrochemical reaction occurring in this case is generally not reversible. Primary cells are non-rechargeable.In a thermally regeneratable system, an ion flow between two electrodes of a thermally regeneratable cell initiates an external electron flow. The chemical energy lost by the ion transport is compensated in the thermally regeneratable system by supplying thermal energy.A (galvanic) secondary cell temporarily stores electrical energy supplied during a charging cycle in the form of chemical energy and releases the electrical energy again in the course of a discharging cycle. The electrochemical reaction occurring in this case is highly reversible. Secondary cells are rechargeable. Secondary cells can be recharged, for example, by a charge carrier flow (conventional secondary cell) impressed from the outside.US 2019 / 0 379 233 A1 relates to the battery control circuit of a vanadium redox accumulator which uses vanadium compounds in aqueous solutions for both electrolytes. The vanadium redox accumulator is charged during normal operation with a voltage between 40 V and 80 V. During an initialization phase, the vanadium redox accumulator is initialized via a current source converter (current source converter), which increases the voltage across the electrodes of the vanadium redox accumulator from 0V to about 60V.Electrodes made of liquid materials are subject to changes due to aging to a lesser extent than electrodes made of solid materials, so that the service life of electrochemical cells with liquid electrodes is longer than that of electrochemical cells with solid electrodes. Electrochemical cells with liquid electrodes also make comparatively high current densities possible, can be constructed comparatively easily from cost-effective materials and scale in this case comparatively uncomplicated.U.S. Pat. No. 9,076,996 B2 describes a secondary cell with two electrically conductive liquids as electrodes and with a molten salt as electrolyte. By locally introducing temperature, convection cells are created which swirl the transition layers between the electrolyte and the electrodes and thus improve the feeding of fresh reactive material to and / or the removal of reaction products from the transition layers.The embodiments are based on the object of further improving the efficiency of electrochemical cells with at least one liquid electrode. The object is achieved with the circuit arrangements and methods according to the subordinate claims. Advantageous embodiments are evident from the dependent claims.The following figures show embodiments of the circuit arrangements according to the invention or of the operating method according to the invention. The elements and structures shown in the figures are not necessarily shown to scale with respect to one another. Like reference numerals refer to like or corresponding elements and structures.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1A shows a schematic block diagram of a switching arrangement according to an embodiment with an electrochemical cell configured as a galvanic secondary cell. FIGS. 1B-1D show time plots of the operating mode, cell voltage, and diffusion overvoltage of the electrochemical cells of FIG. 1A. FIG. 2A shows a schematic block diagram of a switching arrangement according to an embodiment with an electrochemical cell configured as an electrolytic cell. FIG. 2B shows a schematic block diagram of a switching arrangement with an electrochemical cell configured as an electrolytic cell and with a pole changer according to another embodiment. FIGS. 2C-2E show time plots of the operating mode, cell voltage, and diffusion overvoltage of the electrochemical cells of FIGS. 2A and 2B. FIGS. 3A-3C show schematic cross-sectional representations of electrochemical cells of further switching arrangements according to the embodiment. FIGS. 4A and 4B show schematic cross-sectional representations of an electrochemical cell of a further switching arrangement according to the embodiment in different operating phases. FIGS. 4C-4E show time plots of cell voltage, lithium concentration, and mass transfer efficiency in the electrochemical cell of FIGS. 4A and 4B. FIG. 5 shows a schematic block diagram of an energy store.DETAILED DESCRIPTIONIn the following detailed description, reference is made to the accompanying drawings. The accompanying drawings form a part of the specification and show by way of illustration specific embodiments in which the invention may be practiced. Directional terminology such as "top", "bottom", "front", "rear", "front", "rear", etc. is used with reference to the orientation of the figure(s) described. Since components of embodiments may be positioned in a number of different orientations, the directional terminology is for the purpose of illustration only and is not to be considered limiting in any way. It is to be understood that there are other embodiments and that structural or logical changes may be made to the embodiments illustrated in the figures and / or described below without departing from the claimed subject matter. It is also understood that the features of the various exemplary embodiments described herein may also be combined with one another, unless expressly or inherently stated otherwise.Within the scope of this description, the term "electrically connected" describes an ohmic, in particular a low-ohmic, non-rectifying, electrically conductive connection between two conductive structures. The term "electrically coupled" also includes connections via passive and / or non-linear elements for transmitting signals and / or energy between two electrically coupled, conductive structures.An embodiment includes circuitry having a control circuit and an electrochemical cell.The electrochemical cell includes a first electrode, a second electrode, and an electrolyte. The electrolyte is in contact with the first electrode and in contact with the second electrode. The first electrode is liquid during operation of the electrochemical cell and may function as the positive electrode or as the negative electrode of the electrochemical cell.In particular, the electrochemical cell is operated at a temperature at which the first electrode is liquid, e.g. above the melting temperature of the material of the first electrode. For example, the electrochemical cell is operated at a temperature of at least 100 degrees Celsius, for example at least 600 degrees Celsius.In the following, for simplification, an entirety of a solid, gaseous and / or liquid material is respectively referred to as an electrode, which is oxidized and / or reduced during operation of the electrochemical cell.The electrochemical cell can have solid and chemically inert connection structures, which each contact one of the electrodes and via which electrons are supplied or discharged. For example, the electrochemical cell can have a connection structure made of an inert foam or a metal which is solid during operation of the electrochemical cell, wherein the liquid electrode can fill pores of the connection structure.The first liquid electrode may comprise at least one metal, a metal alloy, a semimetal or a semimetal alloy. For example, the first electrode can consist completely or at least almost completely of a metal, a metal alloy, a semimetal or a semimetal alloy. In the following, the semimetal is understood to be any of the elements boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), bismuth (Bi), selenium (Se) and tellurium (Te). Metals are all elements which are on the left in the Periodic Table of the Elements of the Periodic Table of the Elements formed by the semimetals mentioned.As a negative electrode, the first liquid electrode may comprise, consist essentially of, or consist entirely of a molten pure metal of the first or second main group of the periodic table or aluminum (Al). For example, the metals magnesium (Mg), calcium (Ca), aluminum (Al), potassium (K), sodium (Na), lithium (Li) and barium (Ba) each have a sufficiently high electrical conductivity in the molten state. The negative electrode may also comprise, consist essentially of or consist entirely of a molten alloy of two or more metals, at least one of the metals belonging to the alloy of the first or second main group.As a positive electrode (cathode), the first liquid electrode may consist, for example, of sulfur (S), selenium (Se), a molten pure metal or a molten pure semimetal, such as, for example, lead (Pb), antimony (Sb), aluminum (Al), bismuth (Bi), magnesium (Mg), mercury (Hg), thallium (Tl), cadmium (Cd), indium (In), tin (Sn), zinc (Zn) or tellurium (Te), or of a molten alloy of two or more metals and / or semimetals, for example Pb-Bi or Pb-Bi-Sn, it also being possible for one or more of the metals to be present in the negative electrode, and wherein, in the case of an electro-metallurgical cell, the positive electrode may additionally contain the metal to be recovered, e.g. cerium (Ce) or neodymium (Nd). In addition to the melt, the positive electrode may contain one or more solid phases, for example solid phases of the constituents of the melt, for example Li-Bi, Li 3 Bi and Li 2 Bi.For example, the first, liquid electrode can comprise as positive electrode exclusively or far predominantly one or more of the elements arsenic (As), antimony (Sb), bismuth (Bi), mercury (Hg), selenium (Se) or tellurium (Te), which in the liquid state each have a sufficiently high electrical conductivity. The second electrode can be solid, liquid or gaseous during operation of the electrochemical cell.As the liquid electrode, the second electrode may have any composition mentioned above for the first electrode. As a solid electrode, the second electrode may be made of a pure metal or a metal alloy having a melting point above the temperature at which the electrochemical cell is operated.The electrolyte can separate the first electrode and the second electrode from one another, wherein on the one hand the ionic conductivity of the electrolyte with respect to the relevant ion is high, and on the other hand the electron conductivity of the electrolyte is relatively low. For example, the relevant ion conductivity of the electrolyte may be more than 0.01 S / cm, for example more than 0.05 S / cm.The electrolyte may contain salt(s) or consist of a salt. For example, the electrolyte contains an alkali salt, an alkaline earth salt or a mixture of several salts. For example, the electrolyte may comprise or consist of a chloride and / or a fluoride of one of the materials of one of the two electrodes.During regular operation of such an electrochemical cell, an ion current flows in the electrochemical cell from the first to the second electrode or from the second to the first electrode. In the case of an electrolytic cell, the ion current is excited by an external voltage acting between the two electrodes and in turn initiates an otherwise non-spontaneous chemical reaction in the electrochemical cell. In the case of a primary galvanic cell, the ion current is driven by a chemical reaction, wherein the ion current in the electrochemical cell keeps an electron flow through an external load connected between the two electrodes. In the case of a secondary galvanic cell, an ion current flows from one electrode to the other in one charging cycle and in the opposite direction during a discharging cycle. In either case, the ion current carries material from one electrode to the other.A material transport to the first liquid electrode brought about by the ion current leads to a gradual accumulation of the transported material in the first liquid electrode. A material transport from the first liquid electrode to the second electrode leads to a gradual depletion of the transported constituent material in the first liquid electrode. Different properties of the transported material and of the material of the first electrode, for example different atomic masses, can lead to a stable lamination with different proportions of the transported or depleted material in a boundary layer in the first electrode facing the electrolyte.In the absence of convection, further material transport through the stably layered boundary layer is then only possible by diffusion. A diffusion overvoltage falls across the boundary layer, by which the effective cell voltage is reduced.According to one embodiment, according to which the electrochemical cell is designed as a galvanic primary cell, as a thermally regeneratable electrochemical cell or as an electrolytic cell, a control circuit which is electrically connected to the first electrode and to the second electrode is configured in such a way that the electrochemical cell is operated in first phases with a first current direction between the first electrode and the second electrode and during second phases with a second current direction which is opposite the first current direction.The first phases correspond to a control operation of the electrochemical cell in which a stably layered boundary layer is formed in the first, liquid electrode adjacent to the electrolyte. During the first phase, the galvanic primary cell and the thermally regeneratable electrochemical cell emit electrical energy. An electrolysis cell recovers a target material from a starting material during the first phase.The change of the current direction in the second phases leads to a brief change of direction of the ion current and thus also of the material transport in the electrochemical cell. Ions which migrate towards the first electrode during the regulating operation are carried away from the first electrode. The ions move away from the first electrode. The layering in the boundary layer is disturbed. The diffusion overvoltage is reduced and the concentration driven convection is re-excited, whereby the constituents in the liquid electrode can better mix. The resulting homogenization of the first, liquid electrode increases the efficiency of the electrochemical cell.The second phases may follow the first phases immediately or at a short distance of less than one minute. Alternatively, the second phase begins after a first recovery time has elapsed after the end of the first phase, wherein the first recovery time may be at least 30 seconds.The first phases may follow the second phases immediately or at a short distance of less than 5 minutes. Alternatively, the first phase begins after a second recovery time has elapsed after the end of the second phase, wherein the second recovery time may be at least 20 seconds.The current intensity in the second phases can substantially correspond to the current intensity in the first phases. Alternatively, the current intensity in the second phases can deviate significantly from the current intensity in the first phases, wherein the current intensity in the second phases can be greater or less in magnitude than the current intensity in the first phases.According to one embodiment, the change between the first phase and the second phase can take place according to a predefined rule. The predefined rule can define, for example, the time for a change from the first phase to the second phase and / or the time for a change from the second phase to the first phase.For example, the starting time and the duration of the second phases can be dependent on an internal state of the electrochemical cell, in the case of a galvanic cell for example on the state of charge. Alternatively, the time and duration of the second phase may be controlled independently of the internal state of the electrochemical cell. A ratio between the duration of a second phase and the duration of an immediately preceding first phase can be, for example, in a range from 1:5 up to 1:100.According to another embodiment, the electrochemical cell can be designed as a galvanic secondary cell which is charged in a charging cycle and discharged in a discharging cycle.The first electrode can function as the positive electrode (cathode) or as the negative electrode (anode) of the electrochemical cell, wherein the designation of cathode and anode conventionally results from the function of the electrochemical cell during discharge.For such an electrochemical cell, a control circuit electrically connected to the first electrode and to the second electrode is configured such that the electrochemical cell is operated with a first current direction between the first electrode and the second electrode during first phases of a charging cycle and with a second current direction opposite to the first current direction during second phases of the charging cycle and / or the electrochemical cell is operated with the second current direction during first phases of a discharging cycle and with the first current direction during second phases of the discharging cycle, wherein a change between the first phase and the second phase takes place in each case according to a predefined rule. The predefined rule can define, for example, the time for a change from the first phase to the second phase and / or the time for a change from the second phase to the first phase.The predefined rule contains exclusively or at least predominantly conditions and parameters which result from the properties of the electrochemical cell itself. In particular, the predefined rule is completely independent or at least largely independent of rules according to which the electrochemical cell is switched from the charging cycle to the discharging cycle and / or from the discharging cycle to the charging cycle as a function of external conditions. External conditions include, for example, the economic availability of externally provided electrical power for operation of the electrochemical cell in the charging cycle, the external need for electrical energy provided by the electrochemical cell, and an intervention via an operator interface.The predefined rule can specify the starting time and / or the duration of a second phase, for example, as a function of a state of charge of the secondary cell. Alternatively, the predefined rule can specify the time and duration of a second phase independently of the state of charge of the secondary cell. The ratio between the duration of a second phase and the duration of an immediately preceding first phase can be, for example, in a range from 1:5 up to 1:100.For example, positively charged ions are transported from the first electrode to the second electrode or negatively charged ions are transported from the second electrode to the first electrode in the charging cycle in the electrochemical cell. In the discharge cycle, positively charged ions, for example, are transported from the second electrode to the first electrode or negatively charged ions are transported from the first electrode to the second electrode in the electrochemical cell.The change of the current direction in the second phases leads to a brief change of direction of the material transport in the electrochemical cell. Ions that travel towards the first electrode during the control operation are repelled by the first electrode. The ions move away from the first electrode. The layering in the boundary layer is disturbed. The diffusion overvoltage is reduced and the concentration driven convection is re-excited, whereby the constituents in the liquid electrode can better mix. The homogenization of the liquid electrode associated therewith increases the efficiency of the electrochemical cell.The current intensity in the second phases can substantially correspond to the current intensity in the first phases. Alternatively, the current intensity in the second phases can deviate significantly from the current intensity in the first phases, wherein the current intensity in the second phases can be greater or less in magnitude than the current intensity in the first phases.According to an embodiment of a switching arrangement with a galvanic secondary cell, the control circuit may comprise a charging / discharging circuit which is configured to switch the electrochemical cell to a current / voltage source during the first phases of the charging cycle and to an electrical load during the second phases of the charging cycle. Alternatively or additionally, the charging / discharging circuit can be configured to switch the electrochemical cell to an electrical load during the first phases of the discharging cycle and to a current / voltage source during the second phases of the second cycle.The charging / discharging circuit may be configured to perform the switching between the first phase and the second phase according to a predetermined rule.The electrical load for the second phase of the charging cycle can be an electrical load (sink) provided only for this purpose or can be identical to the electrical load for the discharging cycle.The current / voltage source for the second phase of the discharge cycle may be a current / voltage source provided only for this purpose or may be identical to the current / voltage source for the charge cycle.The second phases may follow the first phases immediately or at a short distance of less than 1 minute. Alternatively, the second phase begins after a first recovery time has elapsed after the end of the first phase, wherein the first recovery time may be at least 30 seconds.The first phases may follow the second phases immediately or at a short distance of less than 5 minutes. Alternatively, the first phase begins after a second recovery time has elapsed after the end of the second phase, wherein the second recovery time may be at least 20 seconds.According to a further embodiment of a switching arrangement with a galvanic secondary cell, the switching arrangement can have a battery of similar electrochemical cells (secondary cells), wherein the charging / discharging circuit can then be configured to switch at least a second of the electrochemical cells as the current / voltage source to the first electrochemical cell during the second phases of a discharging cycle of a first of the electrochemical cells.For example, the circuit arrangement is designed such that each of the electrochemical cells of the circuit arrangement can be switched to at least one of the other electrochemical cells for a short time during the respective discharge cycle, wherein the states of charge of the electrochemical cells concerned differ to such an extent that the one electrochemical cell causes a current reversal in the other electrochemical cell.With such a circuit arrangement, the efficiency of a battery with electrochemical cells of the same type can be significantly increased with comparatively little additional outlay.According to a further embodiment of a switching arrangement with a galvanic secondary cell, the switching arrangement can have a battery of similar secondary cells, wherein the charging / discharging circuit is configured to switch at least a second of the electrochemical cells as the electrical load to the first electrochemical cell during the second phases of a charging cycle of a first of the electrochemical cells.For example, the circuit arrangement is designed such that each of the electrochemical cells of the circuit arrangement can be switched to at least one of the other electrochemical cells for a short time during the respective charging cycle, wherein the states of charge of the electrochemical cells concerned differ to such an extent that the one electrochemical cell causes a current reversal in the other electrochemical cell.With such a circuit arrangement, too, the charging efficiency of a battery with electrochemical cells of the same type can be significantly increased with comparatively little additional outlay.According to a further embodiment of a switching arrangement with a galvanic secondary cell, the control circuit can have an alternating switching device with a bridge and with a first, a second and with a third switching contact device. The alternating switching device is configured such that the bridge connects the first switching contact device alternately to the second or the third switching contact device. The first switching contact device is electrically connected to the first or to the second electrode. The second switching contact device is electrically connected to the electrical load. The third switching contact device is connected to the current / voltage source.The control circuit can comprise a control unit which controls the changeover switching device according to the predefined rule.According to one embodiment, according to a first predefined rule, for the change from the first phase to the second phase and / or the change from the second phase to the first phase, a maximum duration for each first phase can be shorter than a duration after which a diffusion overvoltage of more than 1% of a nominal cell voltage is established.For a galvanic secondary cell, the nominal cell voltage results from the redox potentials and / or chemical activities of the electrode materials and corresponds approximately to the maximum cell voltage in the fully charged state. The nominal cell voltage is in the range from 0.2 V to 3 V, for example in the range from 0.3 V to 1 V, for electrochemical cells with liquid electrodes.For example, the maximum duration for each first phase can be shorter than a time duration after which a diffusion overvoltage of more than 0.5% or more than 0.1% of the cell voltage is established, whereby a mixing of the liquid electrode can be achieved which is sufficient for a perceptible improvement in the efficiency.According to one embodiment, according to a second predefined rule, a minimum duration for each second phase can be at least 0.5 s, at least 1 s or at least 5 s for the change from the first phase to the second phase and / or the change from the second phase to the first phase. A current reversal of a minimum duration of at least 0.5 s, 1 s or 5 s may be sufficient to swirl the layered boundary layer in such a way that sufficient material transport by concentration-driven convection is subsequently ensured again for a relatively long period of time. A maximum duration of the second phases may be, for example, 10 minutes, 5 minutes, 60 s or 10 s. A further extension of the second phases often contributes only to a small extent to improving the charging / discharging efficiency in some types of electrochemical cells.According to one embodiment, according to a third predefined rule, for the change from the first phase to the second phase and / or the change from the second phase to the first phase, a ratio of an average duration of the first phases to an average duration of the second phases can be greater than 5:1, for example greater than 8:1 or greater than 10:1. The average duration takes into account at least 50 directly successive changes from the first phase to the second phase and from the second phase to the first phase.According to one embodiment, the electrolyte may be liquid during operation of the electrochemical cell. The density of the electrolyte may be less than or greater than the density of the first liquid electrode. A boundary layer between the liquid electrolyte and the first liquid electrode may have a horizontal portion. At least along the horizontal section, an ion current from the second electrode to the first, liquid electrode can lead to an accumulation of material from the second electrode in a boundary layer of the first electrode facing the second electrode.If the electrolyte has a lower density than the first electrode and if the density of the transported material is lower than the density of the first electrode, then a stable density lamination with a vertical gradient can be established in a boundary layer of the first electrode towards the electrolyte. Within the stable density layering, the concentration of the transported material decreases with increasing distance from the electrolyte.Similarly, during operation of the electrochemical cell, an ion current away from the liquid electrode may result in depletion of one of the alloying elements in the liquid electrode material. Different densities between the starting material and the material depleted of the flowed-off alloying element can also lead in this case to a stable density lamination in a boundary layer of the first liquid electrode towards the electrolyte.If, for example, the first liquid electrode is disposed on the electrolyte (i.e. if the first liquid electrode is disposed above the electrolyte), then the concentration of the substance carrying the ion current continuously decreases with increasing approach to the electrolyte within the boundary layer. A diffusion overvoltage can drop across the layer depleted of this substance, by which the effective cell voltage is reduced.In electrochemical cells having a horizontal interface between liquid electrolyte and liquid first electrode, the stable dense lamination in a boundary layer of the first electrode to the electrolyte can be fluidized particularly effectively by a brief reversal of the ion transport.According to one embodiment, a density of the first electrode can be at least twice or at least three times a density of a substance which is transported from the second electrode to the first electrode or from the first electrode to the second electrode during operation of the electrochemical cell. The substance transported to the first electrode builds up an interface layer with stable density lamination in the first electrode. The stable density layering has the result that a further distribution of the transported substance in the first electrode and a further mixing with the material of the first electrode are only possible by diffusion.FIGS. 1A to 1D relate to a switching arrangement 10 having an electrochemical cell 100 configured as a galvanic secondary cell, having a first, liquid electrode 110, a second, solid or liquid electrode 120 and a solid or liquid electrolyte 150 between the first and the second electrode 110, 120.According to FIG. 1A, the switching arrangement 10 comprises a control circuit 200 in addition to the electrochemical cell 100. The control circuit comprises a control unit 220 and an alternating switching device 210 having three switching contact devices 211, 212, 213. The first switching contact device 211 is electrically connected to the second electrode 120 of the electrochemical cell 100. The second switching contact device 212 is electrically connected to a first terminal of an electrical load 900. The third switching contact device 213 is connected to a first terminal of a current / voltage source 800. A bridge 215 of the change-over switching device 210 connects the first switching contact device 211 to the second switching contact device 212 in a first switching position I or, in a second switching position II, connects the first switching contact device 211 to the third switching contact device 213. The first electrode 110 of the electrochemical cell 100, the second terminal of the electrical load 900 and the second terminal of the current / voltage source 800 are electrically connected to one another.In switching position I, the electrochemical cell 100 is at the electrical load and is discharged. In the switching position I, the electrochemical cell 100 passes through regular first phases of a discharge cycle. In switching position II, electrochemical cell 100 is connected to current / voltage source 800, for which it is assumed below that its operating voltage UBis at all times higher than cell voltage UCof electrochemical cell 100, so that current / voltage source 800 in switching position II of electrochemical cell 100 introduces an ion current whose direction is opposite to the ion current during discharge. In the switching position II, the electrochemical cell 100 passes through second phases of the discharge cycle.The control unit 220 connected to the change-over switching device 210 in terms of information causes changes between the switching positions I and II according to predefined rules.FIGS. 1B to 1D show temporal changes in the switching position, the cell voltage, and the diffusion overvoltage of the electrochemical cell 100 of FIG. 1A in the case where the direction of the ion current is reversed in the electrochemical cell 100 at regular intervals during a discharge cycle for periods of the same duration.According to FIG. 1B, during a discharge cycle of the electrochemical cell 100, the control unit 220 of FIG. 1A initiates a change from the shift position I to the shift position II at the points in time t 01, t 11, t 21 and a change from the shift position II to the shift position I at the points in time t 02, t 12, t 22.FIG. 1C shows the curve of the cell voltage UC of the electrochemical cell 100. The cell voltage UC gradually decreases in the first phases between the times t 02 and t 11 and between t 12 and t 21 by discharging the electrochemical cell 100 via the electric load 900. In the second phases between the times t 11 and t 12 and between the times t 21 and t 22, the voltage across the electrochemical cell 100 is obtained from the operating voltage UBof the current / voltage source 800.FIG. 1D shows the profile of the diffusion overvoltage UODin the electrochemical cell 100. The diffusion overvoltage UOD gradually builds up during the discharge phases between the times t 02 and t 11 and between t 12 and t 21 by material transport to the liquid electrode. Between the times t 11 and t 12 and between the times t 21 and t 22, the change in the direction of the ion current takes place a convection in the electrochemical cell 100, as a result of which the diffusion overvoltage is again virtually completely reduced. The maximum effective diffusion overvoltage UOD 1 can be set to, for example, not more than 0.1% of the nominal cell voltage by suitable selection of the length of the discharge phases.FIGS. 2A to 2E relate to switching arrangements 10, 11 each having an electrochemical cell 100 configured as an electrolytic cell, having a first, liquid electrode 110, a second, solid or liquid electrode 120 and a solid or liquid electrolyte 150 between the first and second electrodes 110, 120.According to FIG. 2A, the switching arrangement 10 comprises a control circuit 200 in addition to the electrochemical cell 100. The control circuit comprises a control unit 220 and an alternating switching device 210 with three switching contact devices 211, 211', 212, 212'213, 213', each provided twice. Each of the first switching contact devices 211, 211' is electrically connected to one of the two electrodes 110, 120 of the electrochemical cell 100, respectively. Each of the second switching contact devices 212, 212' is electrically connected to one of the electrodes of a first current / voltage source 810. Each of the third switching contact devices 213, 213' is electrically connected to one of the electrodes of a second current / voltage source 820, respectively. A first and a second bridge 215, 215' of the change-over switching device 210 connect in each case one of the first switching contact devices 211, 211' to one of the second switching contact devices 212, 212' in a first switching position I or in each case one of the first switching contact devices 211, 211' to one of the third switching contact devices 213, 213' in a second switching position II.The second and third switching contact devices 212, 212', 213, 213' are assigned to the two current / voltage sources 810, 820 in each case such that, in the first switching position I, the first current / voltage source 810 is connected to the first and second electrodes 110, 120 of the electrochemical cell 100, and that, in the second switching position II, the second current / voltage source 820 is connected to the first and second electrodes 110, 120 of the electrochemical cell 100. The first and the second current / voltage sources 810, 820 are configured such that, when the switching positions are changed, the current direction through the electrochemical cell 100 is reversed.For example, the current operating voltage of one of the two current / voltage sources 810, 820 is higher than the current cell voltage of the electrochemical cell 100 and the current operating voltage of the other of the two current / voltage sources 810, 820 is lower than the current cell voltage of the electrochemical cell 100. According to another example, the polarity of the voltage applied to the electrochemical cell 100 in the second switching position II is opposite to the polarity of the voltage applied to the electrochemical cell 100 in the first switching position I.In the switching position I, the electrochemical cell 100 passes through regular first phases in which a target material is obtained from a starting material by electrolysis. In switching position II, an ion current is applied to electrochemical cell 100, the direction of which is opposite to the ion current during electrolysis. In the switching position II, the electrochemical cell 100 passes through second phases.The control unit 220 connected to the change-over switching device 210 in terms of information controls changes between the switching positions I and II according to predetermined rules.In the switching arrangement 11 of FIG. 2B, a pole inverter 215 (cross switch) provided between the electrochemical cell 100 and a current / voltage source 830 forces a change in the polarity of the voltage applied to the electrochemical cell 100.According to another embodiment, the electrochemical cell 100 remains permanently connected to the first current / voltage source 810, wherein the first current / voltage source 810 is configured such that it can also be operated as a sink (two-quadrant power supply). The second current / voltage source 820 is omitted. The switching between the first current / voltage source 810 and the second current / voltage source 820 for adjusting the current direction through the electrochemical cell 100 shown in FIG. 2A is omitted. Instead, the current direction through the electrochemical cell 100 is adjusted by correspondingly raising the effective source voltage of the first current / voltage source 810 above the current voltage of the electrochemical cell 100 or by lowering the source voltage of the first current / voltage source 810 below the current voltage of the electrochemical cell 100.FIGS. 2C to 2E show temporal changes in the switching position, the cell voltage, and the diffusion overvoltage of the electrochemical cells 100 of FIGS. 2A and 2B in the case where the direction of the ion current is reversed at regular intervals for periods of the same duration in the electrochemical cell 100, for example, during electrolysis.According to FIG. 2C, the control unit 220 of FIG. 2A or 2B interrupts the electrolysis at the times t 01, t 11, t 21 during the change from the shift position I to the shift position II and resumes the electrolysis at the times t 02, t 12, t 22 with the change from the shift position II to the shift position I. The distances between the times t 01 and t 11 and between the times t 21 may be of equal length.FIG. 2D shows the curve of the cell voltage UC acting on the electrochemical cell. The polarity of the cell voltage changes between the first phases and the second phases. The magnitude of the negative voltage UB 2 may be equal to, greater than, or less than the magnitude of the positive voltage UB 1.FIG. 2E shows the profile of the diffusion overvoltage UODin the electrochemical cell 100. The diffusion overvoltage UOD gradually builds up during electrolysis by material transport to the liquid electrode. Between the times t 11 and t 12 and between the times t 21 and t 22, the change in the direction of the ion current takes place a convection in the electrochemical cell, by means of which the diffusion overvoltage is again virtually completely reduced.For example, the electrochemical cell 100 is configured as an electrolytic cell for removing fission products accumulated in salt melts. The salt melt comprises, for example, one or more chlorides, for example LiCl and / or KCl. The cleavage products comprise cations, e.g. Sr 2+ ions and / or Ba 2+ ions.The salt melt comprising the cleavage products forms the electrolyte. An electron conductor such as a metal constitutes the anode. A negatively polarized amount of liquid metal forms the first electrode and acts as a cathode. The liquid metal comprises, for example, bismuth. The fission products are deposited into the liquid metal, where liquid metal and fission products alloy, e.g., to Sr(Bi) and / or Ba(Bi).The electrolytic cell 100 is operated at at least 780 degrees Celsius. Due to gravity and density, a stable layer of alloyed liquid metal of lower density is deposited over a bath of significantly higher density. The stable density layering dampens the impulse exchange by convection and thus impedes the further mass transfer.A short intermediate reversal of the current direction leads at the surface of the alloyed liquid metal to the transition of material of lower density (e.g. Sr and / or Ba) into the electrolyte and thus locally to an increase of the density in a boundary layer of the liquid metal to the electrolyte. The local increase in density initiates a natural convection which degrades the concentration gradients in the alloy to improve mass transfer within the electrolytic cell and thus reduce diffusion overvoltages and increase the overall efficiency of deposition.FIGS. 3A-3C show possible embodiments of the electrochemical cell 100 in FIGS. 1A, 2A, and 2B.FIG. 3A shows an electrochemical cell 100 having a first electrode 110 that is liquid in operation, a second electrode 120 that is liquid in operation, and an electrolyte 150 that is liquid in operation between the first electrode 110 and the second electrode 120.A sufficiently temperature-resistant housing 190 accommodates the first electrode 110, the electrolyte 150 and the second electrode 120 and encloses them completely or largely in a form-fitting manner. The housing 190 may be at least partially electrically insulated or comprise an electrically insulating material such that the electrodes 110, 120 are not electrically short-circuited to one another. Furthermore, at least one wall or a part of the housing 190 may be configured to be movable, such that a change in volume of the materials of the electrodes 110, 120 or of the material of the electrolyte 150 may be compensated for. Alternatively or additionally to a movable housing part, a gas cushion can be provided in the housing, wherein a change in volume of the materials of the electrodes 110, 120 and / or of the material of the electrolyte 150 can be compensated by a change in pressure of the gas cushion.The electrodes 110, 120 and the electrolyte 150 may each have a horizontal cross-sectional area in a range from several square centimeters to several square meters, e.g., in a range from about 10 cm 2 or 100 cm 2 to about 25 m 2. The housing 190 may have an internal volume in a range from about 10 cm 3 to several 100 m 3, for example an internal volume of about 5 m 3 to several 100 m 3.The electrochemical cell 100 is, for example, a galvanic secondary cell in which the first electrode 110 can be effective as an anode when charging the electrochemical cell 100 and as a cathode when discharging the electrochemical cell 100, and in which the second electrode 120 can be effective as a cathode when charging the electrochemical cell 100 and as an anode when discharging the electrochemical cell 100. Further, the first electrode 110 may function as the positive electrode and the second electrode 120 may function as the negative electrode.The housing 190 has a first electrical contact structure 191, which directly adjoins the first electrode 110 and which electrically contacts the first electrode 110, and has a second electrical contact structure 192, which directly adjoins the second electrode 110 and which electrically contacts the second electrode 120. The first electrical contact structure 191 and the second electrical contact structure 192 are electrically insulated from one another in such a way that no current flow occurs between the first electrical contact structure 191 and the second electrical contact structure 192 within the housing 190. The first electrical contact structure 191 and the second electrical contact structure 192 can be electrically connected to one another outside the housing 190 in such a way that a desired external current flow is established between the first electrode 110 and the second electrode 120.Via the first contact structure 191 and the second contact structure 192, the electrochemical cell 100 can be charged or discharged. The electrical contact structures 191, 192 may extend partially from the housing wall into the interior of the housing 190 and may, for example, partially dip into the respective electrode 110, 120 that is liquid during operation.The first electrode 110 comprises at least one material from the following group of materials: aluminum, tin, zinc, gallium, selenium, tellurium, bismuth, mercury, indium, cadmium, antimony and thallium. Furthermore, the first electrode 110 can comprise a compound or alloy, wherein the compound or alloy can comprise at least one of the materials mentioned. Furthermore, the first electrode 110 may comprise an alkali metal and / or an alkaline earth metal depending on the state of charge of the electrochemical cell 100.The second electrode 120 may include at least one material selected from the group consisting of aluminum, lithium, sodium, potassium, calcium, cesium, rubidium, barium, and magnesium.The electrolyte 150 may include, for example, a salt, e.g., an alkali salt, an alkaline earth salt, or a mixture of multiple salts. The electrolyte 150 may include, for example, a salt (e.g., a chloride and / or a fluoride) of the respective material of the second electrode 120.The density of the electrolyte 150 is higher than the density of the second electrode 120. The density of the first electrode 110 is higher than the density of the electrolyte 150.For example, the first electrode 110 may comprise antimony with or without magnesium / calcium, the second electrode 120 may comprise magnesium / calcium, and the electrolyte 150 may comprise a mixture of the salts magnesium / calcium chloride, potassium chloride, and sodium chloride. Here, the second electrode 120 has a melting temperature of about 650° C. and a density of about 1584 kg / m 3 the first electrode 110 has a melting temperature of about 630° C. and a density of about 6530 kg / m 3, and the electrolyte 150 (MgCl 2 / / CaC1 2 / / KCl / / NaCl) has a melting temperature of about 400° C. and a density of about 1670 kg / m 3. The electric cell 100 is operable from a temperature of approximately 650° C. and has the layered structure illustrated in FIG. 3A due to the material densities.For example, when discharging the electrochemical cell 100, the magnesium / calcium may give off two electrons, and Mg 2+ / / Ca 2+ cations pass through the electrolyte 150 to the first electrode 110 in which the magnesium / calcium cations are incorporated. In this case, the first electrode 110 can form an alloy of the original material of the first electrode 110 and of the material transported from the second electrode 120 to the first electrode. The electrons released at the second electrode 120 are then available in their sum as usable electric current.According to another example, the (positive) first electrode 110 may comprise bismuth with or without calcium and the second electrode 120 may comprise an alloy of magnesium and calcium. The electrolyte 150 for this example may comprise exactly one of the salts magnesium chloride, calcium chloride, potassium chloride and sodium chloride, or may comprise a mixture of at least two of these salts, such a mixture comprising at least magnesium chloride or calcium chloride.When the electrochemical cell 100 is discharged, the calcium may be depleted from the interface with the electrolyte 150 in the second electrode 120. In a lower portion of the second electrode 120 toward the electrolyte 150, a heavy, low calcium barrier layer having stable density layering develops. In an upper portion of the first electrode 110 toward the electrolyte, a light, calcium-rich interface develops. Both barrier layers reduce the effective cell voltage. If the ion flow in the electrochemical cell 100 is briefly reversed, a light calcium-rich layer develops in the lower section of the upper, second electrode 120, which tends upward against the force of gravity and mixes the second electrode 120 again in the process. A heavy, low-calcium layer develops in the upper portion of the first electrode 110, which tends downward with the force of gravity and thereby mixes the first electrode 110.Alternatively to the described example of a Ca-Mg / / Bi type electrochemical cell (upper electrode contains calcium and magnesium, lower electrode contains bismuth), the electrochemical cell 100 can be, for example, of the Ca-Mg / / Sb, Ca-Mg / / Bi-Sb or Mg-Sb / / Pb type.FIG. 3B shows an electrochemical cell 100 in which the liquid first electrode 110 is captured by a first trough 193 and the liquid second electrode 120 is captured by a second trough 194, wherein the troughs 193, 194 are arranged next to one another in the interior of a housing 190. Each of the wells 193, 194 forms or comprises an electrical contact structure 191, 192. The electrolyte 150 overlies the accessible surfaces of both the first electrode 110 and the second electrode 120.The (positive) first electrode 110 may include bismuth with or without calcium, the (negative) second electrode 120 may include an alloy or mixture of calcium and antimony.When the electrochemical cell 100 is charged, the calcium accumulates in the second electrode 120 at the interface with the electrolyte 150. In an upper portion of the second electrode 120 toward the electrolyte 150, a light calcium-rich interface having stable density layering develops. In the case of discharging, a light calcium-rich interface having stable density layering develops in an upper portion of the first electrode 110 toward the electrolyte 150. Both barrier layers reduce the effective cell voltage and the efficiency of the electrochemical cell 100. If the ion flow in the electrochemical cell 100 is briefly reversed, a heavy, antimony-rich layer develops in the upper section of the second electrode 120, which tends downward with the force of gravity and mixes the second electrode 120 again in the process. In the upper portion of the first electrode 120, a heavy, low-calcium layer develops, which tends downward with the force of gravity and thereby mixes the second electrode 110.Alternatively to the described example of an electrochemical cell 100 of the type Ca-Sb / / Bi (right electrode contains calcium and antimony, left electrode contains bismuth), the electrochemical cell 100 can be of the type Ca-Mg / / Sb, Ca-Mg / / Bi-Sb or Mg-Sb / / Pb, for example.In FIG. 3C, the electrochemical cell 100 may be configured as a secondary cell with solid electrolyte.The lower (positive) first electrode 110 may comprise bismuth and sodium, the upper (negative) second electrode 120 may comprise sodium.The electrolyte 150 is made of a solid material such as an aluminum ceramic. For example, the electrolyte 150 is a BASE (beta"-alumina solid electrolyte).In operation as a conventional secondary cell, upon discharge of the electrochemical cell 100, in an upper portion of the first electrode 110, the sodium accumulates at the interface with the electrolyte. In a portion of the first electrode 110 facing the electrolyte 150, a light sodium-rich barrier layer with stable density layering develops. The barrier layer reduces the efficiency of the electrochemical cell 100. If the ion flow in the electrochemical cell 100 is reversed briefly, a heavy, low-sodium layer develops in the upper portion of the first electrode 110, which tends downward with the force of gravity and thereby mixes the first electrode 110, thereby improving the efficiency of the electrochemical cell 100 and reducing the likelihood of forming solid intermetallic phases.When operating as a conventional secondary cell, an external electron flow impressed between the first electrode 110 and the second electrode 120 ensures sodium (back) transport from the first electrode 110 to the second electrode 120 in the charging cycle.If the electrochemical cell 100 is operated as a thermally regeneratable electrochemical cell 100 of a thermally regeneratable electrochemical system, then the sodium is separated from the alloy in a distillation apparatus in a spatially separated manner at a higher temperature level. In the distillation apparatus, the sodium is driven out of the alloy by introduction of heat. The condensed sodium and the low-sodium bismuth are supplied again to the respective electrodes of the electrochemical cell 100 after temperature adjustment.Alternatively to the described example of an electrochemical cell 100 of the type Na / / Bi, the electrochemical cell 100 can be of the type Na / / Bi-Pb, Na / / Pb, Na / / Zn or Na / / Pb-Sb, for example.FIGS. 4A and 4B relate to an electrochemical cell 100 in which the first, liquid (positive) electrode 110 comprises bismuth with or without lithium, in which the (negative) second electrode 120 comprises lithium or consists of lithium, and a solid or liquid electrolyte separates the second electrode 120 from the first electrode 110.During the discharging process of the electrochemical cell 100 schematically illustrated in FIG. 4A, lithium is transported from the second electrode 120 to the underlying first electrode 110 and alloyed with the bismuth of the first electrode 110. However, the relatively light lithium does not penetrate deeply into the heavy bismuth. Instead, a light, lithium-rich interface with stable density layering is formed in an upper portion of the first electrode 110 along the interface to the electrolyte 150.The stable density lamination directly reduces the efficiency of the electrochemical cell 100 and may result in the formation of solid intermetallic phases that may also negatively impact the efficiency of the electrochemical cell 100.If the lithium flow in the electrochemical cell 100 is reversed briefly, as is illustrated in FIG. 4B, then the lithium fraction becomes lower precisely at the interface with the electrolyte 150. The portion of the boundary layer directly adjacent to the boundary surface becomes heavier, sinks and thereby mixes the lower part of the boundary layer and the first electrode 110.FIG. 4C shows the time profile of the cell voltage for an illustrative sequence of a charging cycle between t 1 and t 2 and a subsequent discharging cycle between t 3 and t 4. The charging cycle increases the cell voltage UC from a low output value U1 to a higher final value U2, for example to the open circuit voltage in the case of full charge. During the discharge cycle, the cell voltage decreases continuously, with the diffusion overvoltage dropping across the boundary layer further lowering the cell voltage and the electrochemical cell 100 already reaching a lower threshold voltage at an earlier point in time than would be the case without diffusion overvoltage.In FIG. 4D, the dotted line shows the lithium concentration at the interface between the first electrode 110 and the electrolyte. The solid line shows the average lithium concentration in the first electrode 110.A discharge cycle beginning at t=t 0 has, in addition to first phases between t=t 0 and t=t 1 and from t=t 2, a second phase between t=t 1 and t=t 2, in which the current direction in the electrochemical cell 100 is reversed with respect to the first phases. The current flowing during the second phase is selected to be twice as high as the current flowing during the phases. Even a relatively short second phase causes a distinct concentration decrease from 28 m % to 26 m % at the interface in relation to the concentration decrease in the volume of the first electrode 110 and is therefore comparatively effective. The difference between the two lines is a measure of the efficiency of the lithium transport in the first electrode 110.In FIG. 4E, the solid line shows the lithium transport inefficiency for the case shown in FIG. 4D. The dotted line indicates the lithium transport inefficiency for a continuous discharge cycle during which lithium transport within the first electrode is diffusion driven only. The short phase with the reverse current direction clearly lowers the lithium transport inefficiency or clearly increases the efficiency of the lithium transport in the first electrode 110.Alternatively to the described example of an electrochemical cell 100 of the type Li / / Bi, the electrochemical cell 100 can be of the type K / / Hg, K / / Tl, K / / Pb, Li / / Bi, Li / / Cd, Li / / Ga, Li / / In, Li / / Pb, Li / / Pb-Sb, Li / / Sb, Li / / Se, Li / / Se-Te, Li / / Sn, Li / / Te, Li / / Tl, Li / / Zn, Mg / / Sb, Na / / Bi, Na / / Cd, Na / / Hg, Na / / Pb, Na / / Pb-Bi, for example, Na / / Pb-Sb, Na / / Sb, Na / / Sn or Na / / Zn.FIG. 5 shows an electrochemical energy store 20 for an electrical grid 50. the electrochemical energy store 20 comprises a switching arrangement 10 with a battery 40 of electrochemical cells 100 of the same type as described with reference to the preceding figures.The switching arrangement 10 is configured to charge the battery 40 with electrical energy from the electrical grid 50 in the event of a sufficient supply of electrical energy in the electrical grid 50, and to draw electrical energy from the battery 40 and feed it into the electrical grid 50 in the event of a sufficient state of charge and corresponding need in the electrical grid 50.Additionally and largely independently of the exchange of electrical energy with the electrical grid 50, the switching arrangement 10 can be configured to insert short phases in charging cycles of individual ones of the electrical cells 100, during which the ion current direction of the relevant electrochemical cell 100 is reversed with respect to the ion current direction for charging. Alternatively or additionally, the switching arrangement 10 can be configured to insert short phases in discharge cycles of individual ones of the electrochemical cells 100, during which the ion current direction of the respective cell is reversed with respect to the ion current direction for discharge.

Claims

A circuit arrangement comprising: an electrochemical cell (100) from a group comprising an electrolytic cell, a thermally regeneratable electrochemical cell or a galvanic primary cell, wherein the electrochemical cell (100) comprises: a first electrode (110) which is liquid during operation of the electrochemical cell (100), a second electrode (120), and an electrolyte (150) in contact with the first electrode (110) and in contact with the second electrode (120); and a control circuit (200) electrically connected to the first electrode (110) and the second electrode (120), wherein the control circuit (200) is configured to operate the electrochemical cell (100) in first phases with a first current direction between the first electrode (110) and the second electrode (120) and during second phases with a second current direction opposite to the first current direction.A circuit arrangement comprising: an electrochemical cell (100) comprising: a first electrode (110) that is liquid during operation of the electrochemical cell (100), a second electrode (120), and an electrolyte (150) in contact with the first electrode (110) and in contact with the second electrode (120); and a control circuit (200) electrically connected to the first electrode (110) and the second electrode (120), wherein the control circuit (200) is configured to operate the electrochemical cell (100) with a first current direction between the first electrode (110) and the second electrode (120) during first phases of a charging cycle and with a second current direction opposite the first current direction during second phases of the charging cycle and / or to operate the electrochemical cell (100) with the second current direction during first phases of a discharging cycle and with the first current direction during second phases of the discharging cycle, wherein a change between the first phase and the second phase takes place in each case according to a predefined rule.Circuit arrangement according to the preceding claim, wherein the control circuit (200) comprises a charging and discharging circuit which is configured to switch the electrochemical cell (100) to a current or voltage source (800) during the first phases of the charging cycle and to an electrical load (900) during the second phases of the charging cycle and / or to switch the electrochemical cell (100) to an electrical load (900) during the first phases of the discharging cycle and to a current or voltage source (800) during the second phases of the discharging cycle.Circuit arrangement according to the preceding claim, comprising a plurality of the electrochemical cells (100), wherein the charging and discharging circuit is configured to switch a second of the electrochemical cells (100) as the current or voltage source (800) to the first electrochemical cell (100) during the second phases of a discharge cycle of a first of the electrochemical cells (100).Circuit arrangement according to one of the two preceding claims, comprising a plurality of the electrochemical cells (100), wherein the charging and discharging circuit is configured to switch a second of the electrochemical cells (100) as the electrical load (900) to the first electrochemical cell (100) during the second phases of the charging cycle of a first of the electrochemical cells (100).Circuit arrangement according to one of the three preceding claims, wherein the control circuit (200) has an alternating switching device (210), the alternating switching device (210) has a bridge (215), a first, a second and a third switching contact device (211, 212, 213), and wherein the bridge (215) is configured to alternately connect the first switching contact device (211) to the second or the third switching contact device (212, 213), and wherein the first switching contact device (211) is connected to the first or to the second electrode (110, 120), the second switching contact device (212) to the electrical load (900) and the third switching contact device (213) to the current or voltage source (900).Circuit arrangement according to one of the preceding claims, wherein the electrolyte (150) is liquid during operation of the electrochemical cell (100).Circuit arrangement according to one of the preceding claims, wherein a density of the first electrode (110) is at least twice a density of a substance transported from the second electrode (120) to the first electrode (110) or from the first electrode (110) to the second electrode (120) during operation of the electrochemical cell (100).Method for operating an electrochemical cell (100) from a group comprising an electrolytic cell, a thermally regeneratable electrochemical cell and a galvanic primary cell, wherein the electrochemical cell (100) has a liquid first electrode (110), a second electrode (120) and an electrolyte (150) in an operating state, and wherein the electrochemical cell (100) is operated during first phases with a first current direction between the first electrode (110) and the second electrode (120) and during second phases with a second current direction opposite the first current direction.Method according to the preceding claim, wherein a change between the first phase and the second phase takes place according to a predetermined rule.Method for operating an electrochemical cell, wherein the electrochemical cell (100) has a liquid first electrode (110), a second electrode (120) and an electrolyte (150) in an operating state, and wherein the electrochemical cell (100) is operated with a first current direction between the first electrode (110) and the second electrode (120) during first phases of a charging cycle and with a second current direction opposite the first current direction during second phases of the charging cycle, and / or the electrochemical cell (100) is operated with the second current direction during first phases of a discharging cycle and with the first current direction during second phases of the discharging cycle, wherein a change between the first phase and the second phase takes place in each case according to a predefined rule.Method according to the preceding claim, wherein, according to a first predefined rule, for the change from the first phase to the second phase and / or the change from the second phase to the first phase, a maximum duration for each first phase is dimensioned shorter than a time duration after which a diffusion overvoltage of more than 0.1% of a nominal cell voltage is established.Method according to one of the two preceding claims, wherein according to a second predefined rule for the change from the first phase to the second phase and / or the change from the second phase to the first phase, a minimum duration for each second phase is 1s.Method according to one of the three preceding claims, wherein according to a third predefined rule for the change from the first phase to the second phase and / or the change from the second phase to the first phase, a ratio of a total duration of the first phases to a total duration of the second phases is greater than 5:1.

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