Operation of an electrochemical cell in the context of treating lithium-containing water

Abstract

The invention relates to the operation of an electrochemical cell (0) for the purification of lithium-containing water. The objective is to operate the cell (0) with improved current efficiency, maintain constant permeance, and increase the purity of the desired product (LiOH). A key aspect of the process according to the invention is that it is carried out in a three-chamber cell with an anode separator (3) and a cathode separator (4). A fundamental concept of the process according to the invention is the use of an inorganic cathode separator (4) that exhibits ionic selectivity in favor of lithium. This results in a lower amount of cationic impurities (Me) becoming unwanted byproducts, thereby increasing current efficiency and improving the purity of the desired product (LiOH). The anode separator (2) is anion-conducting.Another essential aspect of the operation according to the invention is that two electrochemical processes are carried out simultaneously, namely, on the one hand, an electrodialysis of ions with membrane support and, on the other hand, an electrolysis of water.

Description

[0001] The invention relates to the operation of an electrochemical cell for the processing of lithium-containing waters.

[0002] Lithium-containing waters are mixtures consisting predominantly of water and dissolved lithium compounds. They may also contain other dissolved substances, such as sulfates, hydrogen sulfates, carbonates, hydrogen carbonates, hydroxides, chlorides, or fluorides of the following elements: B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu. Lithium-containing waters may also contain organic compounds.

[0003] Lithium-containing waters occur naturally, for example as lithium brine in salt lakes, as seawater, or as groundwater. They also originate from deep drilling operations or mine drainage. Finally, lithium-containing waters are produced during the recycling of used lithium-ion batteries (LIBs) and in the production of new LIBs. Just as diverse as the origins of these lithium-containing waters is their composition: not only can the lithium concentration vary considerably, but also the quantity and type of other dissolved substances.

[0004] Lithium-containing water serves as a starting material for the production of lithium compounds, particularly lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH). Both are required for the production of lithium ingots (LIBs). Due to the rapidly increasing demand for new LIBs and the growing volume of spent LIBs, numerous processes for the reprocessing of lithium-containing waters have been developed, most of which aim to obtain lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH) with the highest possible purity. These processes have been optimized both for the desired target compound and for the composition of the lithium-containing water used. An overview is provided in: Wietelmann, U. and Steinbild, M. (2014). Lithium and Lithium Compounds. In Ullmann's Encyclopedia of Industrial Chemistry, (Ed.). DOI: 10.1002 / 14356007.a15_393.pub2.

[0005] Commercially, processing methods that rely primarily on thermal processes or crystallization effects are predominant, particularly in the extraction of primary lithium from salt lakes. This is very resource-intensive in many respects.

[0006] Therefore, newer methods for extracting lithium compounds from lithium-containing waters have been developed, which utilize electrical energy. These are electrochemical processes, particularly electrolysis or electromembrane dialysis. The fundamental advantage of these electrochemical processes is their resource efficiency when using green electricity. A disadvantage is the complex equipment required; in particular, the electrochemical cells in which the processing takes place are very demanding from a materials science perspective.

[0007] A selection of electrochemical processes for separating lithium from water obtained from the recycling of used batteries or seawater has been compiled by: Pankaj K. Choubey et al.: Advance review on the exploitation of the prominent energy storage element Lithium. Part II: From sea water and spent lithium ion batteries (LIBs), Minerals Engineering, Volume 110, 2017, Pages 104-121, DOI: 10.1016 / j.mineng.2017.04.008.

[0008] In section 2.2, Choubey et al. describe modern electrodialytic processes carried out in an electrochemical cell equipped with two different ion-conducting membranes: an anion-conducting membrane and a cation-conducting membrane. The desired ionic conductivity of the membranes is achieved by impregnation with an ionic liquid.

[0009] From EP 2 841 623 B1, a process for the production of lithium hydroxide using an electrochemical cell having three compartments and two separators (a so-called three-chamber cell) is known. In the three-chamber process known from EP 2 841 623 B1, the central compartment of the three-chamber cell is supplied with an aqueous stream containing lithium sulfate. Lithium hydroxide is placed in the cathodic compartment, while ammonia-water is fed into the anodic compartment. An aqueous solution containing lithium hydroxide is withdrawn from the cathodic compartment of the cell, and ammonium sulfate is formed in the anodic compartment. Oxygen is also produced on the anodic side and hydrogen at the cathode. The three-chamber cell is operated under basic conditions.

[0010] The three-chamber cell known from EP 2 841 623 B1 inherently features two membranes that separate the central compartment from the anodic and cathodic compartments, respectively. Possible membrane materials include perfluorinated polymers, styrene, or divinylbenzene membranes. Cation exchange membranes or PEEK-reinforced membranes are particularly likely to be used. Examples cited include the commercial ion exchange membranes Asahi AAV, Fumatech FAB, Astrom Neosepta®, and Lanxess Ionac®. The chemical nature of these ion exchange membranes is not disclosed in EP 2 841 623 B1, but it is highly probable that they are organic membrane materials.

[0011] A fundamental disadvantage of polymer membranes is their water permeability. This dilutes the anolyte with water from the catholyte. Furthermore, organic ion exchange membranes allow not only Li⁺ but also Na⁺ to pass through, thus compromising the purity of the target product as soon as Na⁺ is present in the starting material. Besides the purity of the target product, the energy efficiency of the process also suffers: During electrolysis with organic membranes, valuable electrical energy is also consumed to transport unwanted Na⁺ into the second compartment. Once in the second compartment, the Na⁺ is further converted into unwanted byproducts via unintended electrochemical processes. In terms of the yield of the target product Li⁺, the energy efficiency of the process is limited. Finally, these membranes are sensitive to the presence of divalent cations such as Mg²⁺ and Ca²⁺.Over time, these cations poison the membrane, reducing its conductivity for lithium. This manifests as a decrease in the membrane's permeance, i.e., its surface-specific lithium conductivity relative to its thickness. This means that less lithium can be extracted from the lithium-containing water. Due to reduced power efficiency, increasing contamination of the target product with foreign cations, and decreasing permeance, the operation of the electrochemical cell quickly becomes uneconomical.

[0012] WO2022 / 157624 A1 describes a method for operating an electrochemical cell with three compartments in which the pH value of the central electrolyte is below 7.

[0013] In view of this prior art, the present invention is based on the objective of operating the electrochemical cell with better current efficiency, keeping the permeance constant over time and improving the purity of the target product.

[0014] This problem is solved by operating the electrochemical cell as follows: a) At least one electrochemical cell is provided which has at least the following features: i) the electrochemical cell comprises an anode and a cathode; ii) the electrochemical cell comprises a cathode separator and an anode separator; iii) the electrochemical cell comprises an anodic compartment, a central compartment and a cathodic compartment; iv) the cathode separator separates the central compartment from the cathodic compartment; v) the anode separator separates the central compartment from the anodic compartment; vi) the cathode separator contains an inorganic material which is electrically insulating and which has an anion conductivity as well as a cation conductivity, wherein the cation conductivity is greater than the anion conductivity and wherein the conductivity for Li cations (Li+< ) is greater than the conductivity for cationic impurities (Mem+< );vii) The anode separator contains an organic material which has an anion conductivity (Xn < , OHn < ) and a cation conductivity, wherein the anion conductivity (Xn < , OHn < ) is greater than the cation conductivity; viii) The inorganic material and / or the organic material is electrically insulating; b) A catholyte is provided in the cathodic compartment, wherein the catholyte contains at least: water (H2O), Li cations (Li+ < ), hydroxide ions (OH- < ); c) A central electrolyte is provided in the central compartment, wherein the central electrolyte contains at least: water (H2O), Li cations (Li+ < ), anions (Xn < ) and cationic impurities (Mem+ < ); d) An anolyte is provided in the anodic compartment, the anolyte containing at least: water (H 2 O) and anions (X n-< );e) At least one electrical voltage source is provided, which can be connected to the anode via a first electrical conductor and to the cathode via a second electrical conductor; f) The electrochemical cell is supplied with an electrical voltage supplied by the electrical voltage source; U applied in such a way that an electric current I between the anode and cathode characterized by , that the central electrolyte also contains hydroxide ions (OH-), and that the pH of the central electrolyte is between 9 and 12, measured with a glass electrode at a temperature of 25°C, and that an electrochemical cell is provided which additionally has the following features: ix) the electrochemical cell includes an auxiliary cathode; x) the auxiliary cathode is in contact with the central electrolyte; xi) the auxiliary cathode is connectable to the electrical voltage source via the second electrical conductor; xii) the cathode has a cathode area AK; xiii) the auxiliary cathode has an auxiliary cathode area A AK;and that the process has an operating state, namely: k) a combined production and regeneration state in which the anode is connected to the electrical voltage source via the first electrical line and the cathode and the auxiliary cathode are connected to the electrical voltage source via the second electrical line, and in which the anode, cathode, and auxiliary cathode are subjected to the electrical voltage U, such that the electric current I flows between the anode, cathode, and auxiliary cathode; wherein the cathode area AK and the auxiliary cathode area A AK are chosen such that the following holds: A K > f . A A with f greater than 1 or with f greater than 10 or with f greater than 100.

[0015] A fundamental idea of ​​the process according to the invention is to use an inorganic cathode separator that exhibits ion selectivity favoring lithium. This means that the material from which the cathode separator is manufactured has a higher conductivity for Li+ cations than for other cations such as Na+ or other cationic impurities. This results in fewer cationic impurities entering the cathodic compartment and being converted there into undesirable byproducts, which increases the current yield and improves the purity of the target product.

[0016] As an inorganic material that exhibits a higher conductivity for Li+ ions than for other cations, so-called LiSICons are preferably used. LiSICon stands for Lithium Super Ionic Conductor. It is a class of inorganic, (glass)ceramic materials that are electrically insulating but also exhibit intrinsic conductivity for Li ions. The transport mechanism for Li is based on the crystal structure of the material. In simplified terms, the Li ions are "passed through" the crystals. Commercially available LiSICon materials include lithium aluminum titanium phosphate (LATP), lithium aluminum titanium silicon phosphate (LATSP), lithium aluminum germanium phosphate (LAGP), and lithium lanthanum titanium oxide (LLTO). These materials were originally developed as solid-state electrolytes for lithium-ion batteries (LIBs). An overview of the transport mechanisms of LiSICons, their crystal structure, and their production is provided below. Palakkathodi Kammampata et al.: Cruising in ceramics-discovering new structures for all-solid-state batteries-fundamentals, materials, and performances. Ionics 24, 639-660 (2018) DOI: 10.1007 / s11581-017-2372-7. Yedukondalu Meesala et al.: Recent Advancements in Li-Ion Conductors for All-Solid-State Li-Ion Batteries. ACS Energy Lett. 2017, 2, 12, 2734-2751 DOI: 10.1021 / acsenergylett.7b00849.

[0017] Spezielle LiSICon Stöchiometrien werden beschrieben von: Sofia Saffirio et al.Li1.4Al0.4Ge0.4Ti1.4(PO4)3 promising NASICON-structured glass-ceramic electrolyte for all-solid-state Li-based batteries: Unravelling the effect of diboron trioxide, Journal of the European Ceramic Society, Volume 42, Issue 3, 2022, Pages 1023-1032 DOI 10.1016 / j.jeurceramsoc.2021.11.014. Eongyu Yi et al. Materials that can replace liquid electrolytes in Li batteries: Superionic conductivities in Li1.7Al0.3Ti1.7Si0.4P2.6O12. Processing combustion synthesized nanopowders to free standing thin films. Journal of Power Sources, Volume 269, 2014, Pages 577-588, DOI 10.1016 / j.jpowsour.2014.07.029.

[0018] Due to their selective conductivity for lithium ions, LiSICon materials can be used as membranes for separating lithium from lithium-containing mixtures. The lithium must be present in the mixture in ionic form, for example as a lithium salt dissolved in water.

[0019] It is known in the prior art to use LiSICon for the separation of lithium from aqueous streams (e.g. from WO 2019055730 A1) - but not in combination with an organic ion exchange membrane in a three-chamber cell.

[0020] A key aspect of the method according to the invention is that it is carried out in a three-chamber cell. While a simple electrochemical cell comprises only two compartments separated by exactly one separator, a three-chamber cell has two separators that divide the cell into three compartments. To distinguish between the two separators, we refer to an anode separator and a cathode separator. The anode separator is located on the anode side, while the cathode separator is installed on the cathode side. The essential components of a three-chamber cell are therefore an anode, an anode separator, a cathode separator, and a cathode. The first, anodic compartment is formed between the anode and the anodic separator. The second, cathodic compartment is formed between the cathodic separator and the cathode.The third compartment is formed centrally between the anodic separator and the cathodic separator and is therefore called the central compartment.

[0021] The electrochemical cell according to the invention can, in addition to the aforementioned basic functional elements, also contain further components, such as catalysts for accelerating water electrolysis, porous transport layers (PTLs), flow fields (FFs) for transporting the electrolytes, or spacers. Furthermore, the individual functional elements can also be combined into integrated components, such as membrane electrode assemblies (MEAs). It is also possible for several electrochemical cells to be connected together to form an assembly, for example, by series or parallel connection. In the case of series connection, the anode of one cell can be in direct electrical contact with the cathode of the neighboring cell, and vice versa. Directly contacted electrodes of different polarities can also be combined in a bipolar plate.

[0022] In addition to the listed solid functional elements, the electrochemical cell also includes liquid electrolyte, which is necessary for the cell's operation. In this case, the electrolyte in the anodic compartment is called the anolyte, while the electrolyte in the cathodic compartment is called the catholyte. The anolyte is therefore in contact with the anode, while the catholyte is in contact with the cathode. The electrolyte in the central compartment is called the central electrolyte. It is separated from the two electrodes by the two separators.

[0023] According to the invention, the electrochemical cell operates as follows: The central electrolyte serves as the feed for the process; it contains the lithium cations that are part of the target product. The central electrolyte is supplied with the lithium-containing water to be processed. The synthesis of the target product takes place at the cathode. Consequently, the target product is found in the catholyte. The anolyte serves as a sink for anionic impurities, from which the cathode separator is protected according to the invention.

[0024] Another essential aspect of the method according to the invention is that two electrochemical processes are carried out simultaneously, namely, on the one hand, a membrane-supported electrodialysis of ions and, on the other hand, an electrolysis of water.

[0025] Electrodialysis serves two purposes: firstly, to concentrate the lithium cations (Li⁺) contained in the central electrolyte into the catholyte; and secondly, to electrodialytically concentrate the anionic impurities (Xⁿ⁻) present in the feed into the anolyte. This prevents the anionic impurities from coming into contact with the cathode separator, thus protecting it from being poisoned by these impurities. To achieve this, the anode separator is anionically conductive.

[0026] In parallel, the process according to the invention involves the electrochemical splitting (electrolysis) of water into hydrogen and oxygen. The hydroxide ions (OH-) formed as an intermediate during water splitting combine in the catholyte with the Li+ cations enriched there to form lithium hydroxide (LiOH) or its monohydrate (LiOH∘H₂O), the desired end product.

[0027] The particular advantage of the combination according to the invention of an anion exchange membrane as an anode separator with an inorganic ion-selective LiSICon membrane as a cathode separator lies in the fact that the anion exchange membrane protects the LiSICon membrane from the harmful effects of anions contained in the feed, such as sulfate, carbonate, hydroxide, chloride, and fluoride. These anions are transferred into the anodic compartment via the organic anion exchange membrane, thus preventing them from damaging the LiSICon membrane. The service life of the LiSICon material used as a cathode separator is thereby significantly improved, especially when the feed contains many anionic impurities. This is precisely the case when lithium-containing water, derived from recycling or the production of lithium-ion batteries, is used as the feed.

[0028] The process according to the invention is preferably carried out continuously. This means that at least the supply of the fluid components, namely the electrolytes and the electric current, is continuous. The supply of the non-fluid components, such as the cell and voltage source, is always continuous anyway, even if these components only need to be supplied once. The individual process steps of the operation are carried out simultaneously in the continuous process.

[0029] The process according to the invention is partially operated in an alkaline environment. More precisely, alkaline conditions should prevail in both the central electrolyte and the catholyte. This means that the central electrolyte also contains hydroxide ions (OH-). The pH value of the central electrolyte should be between 9 and 12, measured with a glass electrode at a temperature of 25°C. Lithium-containing waters used as the central electrolyte must be adjusted to their pH value before treatment if they are not already lithium-containing. The alkalinity of the central electrolyte is important because the LiSICon membrane materials used exhibit the greatest stability under these conditions. Acidic conditions lead to material damage over extended operating times and must therefore be avoided.

[0030] The anolyte is preferably strongly acidic, or the pH value of the anolyte is continuously reduced by at least one of the anode reactions, the formation of protons, and often reaches a pH value less than 4, measured with a glass electrode at a temperature of 25°C.

[0031] The anions contained in the central electrolyte are specifically sulfate, hydrogen sulfate, carbonate, hydrogen carbonate, hydroxide, chloride, and fluoride. These anions are regularly found in lithium-containing waters and therefore also in the central electrolyte. There, these anions are more concentrated than the hydroxide ions.

[0032] The cationic impurities also contained in the central electrolyte are specifically cations of the following elements: B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu, and C. These are also frequently found in lithium-containing waters. The alkali and alkaline earth metals occur particularly in lithium-containing brines of natural origin, while the metal cations are found especially in lithium-containing waters derived from the reprocessing of spent lithium incinerators (LIBs) or from production waste during LIB manufacturing. Such streams also often contain carbon compounds originating from adhesives, binders, the anode materials of the LIBs, carbon black, or the plastic packaging of the LIBs. These can then contain carbon-containing acids or their cations, as well as uncharged organic decomposition products from upstream steps of LIB recycling.

[0033] According to the invention, the cathode separator is lithium-selective, meaning it conducts Li cations better than other cations. The specific Li+ conductivity s of the inorganic material used as the cathode separator should be at least 1 x 10-5 S / cm, or preferably at least 5 x 10-5 S / cm, or even better at least 10 x 10-5 S / cm and a maximum of 100 x 10-5 S / cm. The specific ionic conductivity s is measured by impedance spectroscopy. The temperature-dependent value is measured at 23°C. The impedance spectroscopy is performed as follows: The measuring setup comprises two cylindrical electrodes between which the sample is placed. To ensure optimal contact with the electrodes and reproducible contraction pressure, a weight is placed on the sample.

[0034] A potentiostat (ZAHNER-elektrik I. Zahner-Schiller GmbH & Co. KG, Kronach-Gundelsdorf, Germany) is connected to the electrodes and controlled via the Thales software (ZAHNER). The measurements are performed in a frequency range of 1 Hz to 4 MHz and an amplitude of 5 mV using samples that have been polished and sputtered with a thin, conductive gold layer.

[0035] The measurement results are displayed in Nyquist diagrams and evaluated using the software Analysis (ZAHNER). The electrical resistance is read from the maximum of the Nyquist diagram curve. The specific ionic conductivity σ [mS / cm] is then calculated using the formula σ = (h·10⁴< ) / (R·π / 4·d²< ), where h is the height of the sample in mm, R is the measured electrical resistance in Ω, and d is the diameter of the sample in mm.

[0036] The aforementioned lithium selectivity and conductivity are achieved by most LiSICon materials. Therefore, the cathode separator is preferably manufactured using LiSICon material, contains LiSICon, or even consists entirely of LiSICon.

[0037] Specifically, the following LiSICons are being considered: LATP with the following stoichiometry: Li 1+x Al x Ti 2-x (PO 4 ) 3 where: 0.1≤x≤0.3, preferably x=0.3. LATSP with the following stoichiometry: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 where: 0.1≤x≤0.3 and 0.2≤y≤0.4. LAGTSP with the following stoichiometry: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 * nGeO 2 where: 0≤x≤1 and 0≤y≤1 and 0≤n≤1. LAGTP with the following stoichiometry: Li 1.4 Al 0.4 (Ge 1-x Ti x ) 1.6 (PO 4 ) 3 where: 0≤x≤1. LAGP with the following stoichiometry: Li 1+x Al x Ge 2-x (PO 4 ) 3 where: x=0 or x=0.2 or x=0.4. LLTO with the following stoichiometry: Li 3x La (2 / 3)-x□(1 / 3)-2x TiO 3 where: 0≤x≤0.16. Doped LLZO with the following stoichiometry: Li 6.4 La 3 Zr 1.4 M 0.6 O 12 where M is selected from the group consisting of the following elements: Ta, Sb, Nb. Undoped LLZO with the following stoichiometry: Li 7 La 3 Zr 2 O 12

[0038] LiSICons are commercially available, for example the LAGP Ampcera ™< from MSE Suplies ®< , Tucson, USA.

[0039] The material from which the anode separator is made, or which it contains, is an anion-conducting organic material. Such materials are also often referred to as ionomers. This is preferably a polymer having a backbone to which at least one cationic functional group is bonded. The latter is preferably a quaternized trialkylammonium salt. Polystyrene, polysulfone, polyethersulfone, polyphenylene oxide, polyvinylidene fluoride, or polytetrafluoroethylene is preferably used as the backbone. Most preferably, the quaternized trialkylammonium salt is bonded to a backbone of polystyrene, polysulfone, polyethersulfone, or polyphenylene oxide via a benzyl methyl group. The resulting anion-conducting polymer is used in the manufacture of the anode separator, is contained within the anode separator, or the anode separator consists entirely of this polymer.

[0040] Such polymers are commercially available. Examples include: Fumasep FAPQ from Fumatech, Neosepta membranes from ASTOM, Selemion membranes from AGC, and AHA membrane from Eurodia Industrie SAS.

[0041] A preferred embodiment of the invention provides that an electrochemical cell with an auxiliary cathode is used. The auxiliary cathode is contacted with the central electrolyte and connected to the electrical voltage source via a third electrical conductor. The operation according to the invention then has at least two operating states, namely: p) a production state in which the anode and the cathode are connected to the electrical voltage source via the first and second electrical lines respectively, and in which the anode and cathode are connected to the electrical voltage U be subjected to such pressure that the electric current Ibetween the anode and the cathode; r) a regeneration state in which the anode and the auxiliary cathode are connected to the electrical voltage source via the first and third electrical lines respectively, and in which the anode and auxiliary cathode are connected to the electrical voltage U be subjected to such pressure that the electric current I flows between the anode and the auxiliary cathode.

[0042] During production, lithium is separated from the central electrolyte and lithium hydroxide (LiOH) is formed. During regeneration, the cathode separator is regenerated. This process cleanses the cathode separator of surface-concentrated metal ions that cannot pass through it, as the absence of an electrical voltage no longer impedes their removal. This process removes impurities from the membrane surface, largely restoring its original permeance and permeability.

[0043] According to one embodiment, the system alternates between the two operating states (production / regeneration). The regeneration phase is significantly shorter than the production phase. Specifically, the duration of the production state should be... t P lasts more than 10 or even more than 100 times as long as the duration of the regeneration state. t R . Therefore, the following applies: t P > f* t R with f greater than 1 or with f greater than 10 or with f greater than 100.

[0044] Instead of only switching on the auxiliary cathode intermittently, it is also possible to leave the auxiliary cathode permanently switched on, thus operating in a combined production / regeneration state. The auxiliary cathode is therefore dimensioned to be smaller in area than the actual cathode. Specifically, the auxiliary cathode area should be A AK are chosen in such a way that the following applies A K >f* AAK with f greater than 1, or with f greater than 10, or with f greater than 100. The area A K is the area of ​​the cathode. The area factor f corresponds here to the time factor f of the alternating operating mode.

[0045] In the combined production and regeneration state, the anode is connected to the electrical voltage source via the first electrical conductor, and the cathode and auxiliary cathode are connected to the electrical voltage source via the second electrical conductor. The anode, cathode, and auxiliary cathode are subjected to the electrical voltage U, so that the electric current I flows between the anode, cathode, and auxiliary cathode.

[0046] The advantage of the combined production and regeneration state is that the means for switching between the production states (switching relays) can be eliminated. The disadvantage is that the ratio f cannot be changed as easily.

[0047] An operating mode with two operating states is also advantageous: a combined production and regeneration state and a pure production state. In this mode, the system alternates between the production state (p) and the combined production and regeneration state (k), with each production state (p) remaining active for a period of time. t P is carried out and wherein a single combined production and regeneration state (k) is maintained for a duration of t K is carried out, whereby the following applies t P > g ∗ t K with g greater than 50 or with g greater than 500 or with g greater than 5000.

[0048] The factor g is significantly higher here than in the other two operating modes (factor f). This results in a particularly long production cycle. The productivity of the electrochemical cell is thus increased in the long term.

[0049] The auxiliary cathode is preferably positioned outside the central compartment. This way, it takes up no space within the cell and does not impede ion exchange. It is sufficient for the auxiliary cathode to be in contact with the central electrolyte. Surprisingly, it is even sufficient to place the auxiliary cathode in the reservoir of the central electrolyte or in the supply line to the central electrolyte.

[0050] The auxiliary electrode preferably consists of a textile material. This includes linear textile structures such as threads, yarns, wires, or fibers, as well as planar textile structures such as woven fabrics, knitted fabrics, warp-knitted fabrics, nonwovens, felts, or fleeces. The textile material must be electrically conductive and cathodically active. This is achieved, for example, with nickel-containing materials. In the simplest case, nickel-containing stainless steel is used as the material for the auxiliary cathode. Pure nickel can also be used. The material is typically used as a wire or wire mesh. Of course, pure titanium or higher-grade electrode materials, such as Ti, Pt, Nb, etc., can also be used.

[0051] When the electrochemical cell is operated according to the invention, electrolysis of water and electrodialysis of anions occur, as described in the electrochemical model. This manifests itself through the formation of oxygen at the anode and hydrogen at the cathode, as well as through the depletion of anions in the central electrolyte and their accumulation in the anolyte. Furthermore, operation according to the invention leads to the electrochemical synthesis of lithium hydroxide and / or lithium hydroxide monohydrate at the cathode. These target products can be separated from the catholyte or even precipitate spontaneously within it. All of this occurs simultaneously.

[0052] The method according to the invention will now be explained in more detail using exemplary embodiments. For this purpose, the following are shown: Fig. 1: Basic structure of a three-chamber cell; Fig. 2: System with three-chamber cell in continuous operation; Fig. 3: Membrane dialysis in operation; Fig. 4: Water electrolysis in operation; Fig. 5p: Three-chamber cell with full-surface auxiliary cathode in production operation; Fig. 5r: Three-chamber cell with full-surface auxiliary cathode in regeneration operation; Fig. 6: Three-chamber cell with reduced-size auxiliary cathode in combined operation; Fig. 7: Three-chamber cell with perforated auxiliary cathode in combined operation; Fig. 8: Three-chamber cell with upstream auxiliary cathode in combined operation.

[0053] Figure 1 shows the basic structure of an electrochemical three-chamber cell as operated in the inventive method.

[0054] The electrochemical cell 0 comprises two electrodes, namely an anode 1 and a cathode 2. Between anode 1 and cathode 2 are two separators: an anode separator 3 and a cathode separator 4. Anode separator 3 is located closer to anode 1 than cathode separator 4, while cathode separator 4 is located closer to cathode 2 than anode separator 3. Between electrodes 1 and 2 and separators 3 and 4 are three compartments 5, 6, and 7 within the electrochemical cell 0, which is why it is also referred to as a three-chamber cell. The first compartment, 5, extends between anode 1 and anode separator 3 and is therefore called the anodic compartment 5. The second compartment 6 extends analogously between cathode separator 4 and cathode 2 and is therefore called cathodic compartment 6.The third compartment 7, accordingly referred to as the central compartment 7, is located in the center of the electrochemical cell 0. The central compartment 7 is bounded on one side by the anode separator 3 and on the other side by the cathode separator 4.

[0055] The materiality of separators 3 and 4 is important: The anode separator 3 must be conductive for anions. If the anode separator 3 also conducts cations, its conductivity for cations should be lower than that for anions. This is the case for most anion-conducting materials. Suitable anion-conducting materials are organic in nature. Examples include polymers with a backbone to which at least one cationic functional group is attached. The cationic functional group enables intrinsic transport of anions, especially hydroxide ions (OH⁻), through the anode separator 3, while cations such as protons (H⁺) can hardly cross it. The cathode separator 4 is configured in the opposite way: It has a higher conductivity for cations than for anions.Furthermore, the cation conductivity of the cathode separator 4 is selective: the conductivity for Li cations (Li+) must be greater than for other cations such as Ca+ or Na+. This results in the cathode separator 4 preferentially allowing Li cations to pass through, while other cations are transported at least more slowly or not at all. The cathode separator 4 is practically impermeable to anions. Suitable materials exhibiting these properties are inorganic LiSICons, a special type of (glass) ceramic with intrinsic conductivity for Li ions. At least one of the two separators 3, 4 must be electrically insulating. This is the case with inorganic LiSICons. If an inorganic LiSICon is used as the cathode separator, the electrical conductivity of the organic anode separator 1 is of secondary importance.However, an organic anode separator is preferably used, which also has low electrical conductivity.

[0056] Specifically, the specific conductivity for electrons (γ) of the electrically insulating separator at a temperature of 23°C should be less than 10⁻⁷ < S / cm (10⁻⁹ < S / m), less than 10⁻¹² < S / m, or less than 10⁻¹⁶ < S / m. Such values ​​are typical for inorganic materials, which, from an electron-conducting perspective, are classified as non-conductors. The described LiSICons exhibit specific conductivities in this range and are therefore considered electrical insulators. Ionomers used as anode separators do not always achieve these specific conductivities. Therefore, the cathode separator is preferably used as the electrical insulator. The specific conductivity for electrons is measured by impedance spectroscopy, as described above for ionic conductivity.

[0057] The electrical conductivity of at least one of the two separators 3, 4 is significant, because the two electrodes 1, 2 must be electrically insulated from each other. This prevents an electrical short circuit within the electrochemical cell 0 when an electrical voltage U is applied to electrodes 1, 2. An electrical voltage source 8 is provided for applying such a voltage U. This source can be electrically connected to the anode 1 and cathode 2, respectively, via a first electrical conductor 9 and a second electrical conductor 10. The connection is chosen such that the positive terminal (+) of the electrical voltage source 8 is connected to the anode 1, while the negative terminal (-) is connected to the cathode 2. Consequently, when the voltage source 8 is switched on, the cathode 2 is negatively charged, while the anode 1 is positively charged. The switching of the voltage source 8 and the voltage level UThis will be explained in more detail later.

[0058] In addition to the previously described solid components of the electrochemical cell 0, it also includes fluid elements in the form of three electrolytes 11, 12, and 13. The first electrolyte 11 is located in the first, anodic compartment 5 and is accordingly referred to as anolyte 11. The second electrolyte 12 is located in the second, cathodic compartment 6 and is analogously referred to as catholyte 12. The central electrolyte 13 is located in the central compartment 7. All electrolytes 11, 12, and 13 are fluid but not necessarily completely liquid. They can be multiphase mixtures with a liquid, a solid, and a gaseous phase. However, all three electrolytes contain at least liquid water. The exact composition of the individual electrolytes 11, 12, and 13 will be explained later. It is important to understand that the composition of the anolyte, catholyte, and central electrolyte is constantly changing during the operation of the electrochemical cell O.

[0059] Furthermore, the three electrolytes 11, 12, 13 can preferably be replaced continuously, so that despite the changing composition, a steady flow process is established through the three compartments 5, 6, 7 of the electrochemical cell 0. This is in Figure 2 illustrated using a schematic setup of plant 14.

[0060] Within the system 14, the electrochemical cell 0 is integrated into two circuits 15, 16, namely an anodic circuit 15 and a cathodic circuit 16. In the anodic circuit 15, the anolyte 11 circulates through the anodic compartment 5, while the catholyte 12 circulates through the cathodic compartment 6. The central electrolyte 13 does not circulate but flows through the central compartment 7 only once in a straight pass 17.

[0061] Unlike in Figure 2It is also possible, as shown, to circulate the central electrolyte 13 through the central compartment 7. This requires a large buffer tank for the central electrolyte, from which the central compartment 7 is supplied with central electrolyte. The central electrolyte drawn from the central compartment 7 is recycled into the buffer tank. During operation, the lithium concentration in this central circuit would continuously decrease until a "limit concentration" is reached. At that point, the entire contents of this buffer tank would be replaced, and the next batch would be processed and the lithium separated.

[0062] With regard to the in Figure 2 The depicted circulation of anolyte 11 and catholyte 12 should be noted in that these two electrolytes 11, 12 are continuously supplied, namely in their respective circuits 15, 16. The central electrolyte 13 is also supplied in the Figure 2The electrolytes 11, 12, and 13 are continuously supplied in the depicted system 14, but only in straight-through section 17. Alternatively, it would be conceivable to refrain from circulating any of the three electrolytes 11, 12, and 13 and accordingly supply them only once in their respective compartments 5, 6, and 7. This would be a batch process, which is not preferred. A mixed continuous / batch operation is also conceivable, in which, for example, anolyte 11 and catholyte 12 circulate continuously, while the central electrolyte is supplied only once as a batch in the central compartment 7. It is also conceivable to supply only the catholyte 12 as a batch and to replace anolyte 11 and the central electrolyte 13 continuously.

[0063] When we refer to the provision of electrolytes here, this includes both batch provision and continuous provision in a circuit 15, 16 or in a straight line 17. The operation of the electrochemical cell according to the invention also includes mixed forms of batch and continuous provision of the electrolytes 11, 12, 13.

[0064] The operation of the electrochemical cell 0 according to the invention serves the processing of lithium-containing waters. Consequently, the operation in Figure 2The depicted system 14 is a plant for processing lithium-containing water. The lithium-containing water is fed into the central compartment 7 as fresh water 18. From a process engineering perspective, the fresh water 18 is considered the feed. Within the electrochemical cell 0, various electrochemical processes take place when voltage U is applied; these will be explained in detail later. These processes lead to the removal of the lithium contained in the fresh water 18, more precisely, the dissolved lithium cations Li⁺, from the fresh water 18 and its enrichment in the catholyte 12. During the removal of lithium from the fresh water 18, it becomes wastewater 19, which is drawn off from the central compartment 7. The Li concentration in the wastewater 19 is therefore lower than the Li concentration in the fresh water 18. The wastewater 19 is thus relatively low in lithium.From an electrochemical perspective, both the fresh water 18 and the wastewater 19 can be considered the central electrolyte 13. The transition of the fresh water 18 into the wastewater 19 due to lithium depletion is to be understood as the previously discussed change in the electrolyte composition during cell operation. The anolyte 11 and the catholyte 12 also change their composition as a result of the electrochemical processes: Li is enriched in the catholyte 12, so that the lithium concentration in the catholyte 12+<, which is drawn from the cathodic compartment 7, is higher than in the catholyte 12-<, which is fed into the cathodic compartment 7. The drawn-off catholyte 12+< is rich in lithium, while the fed-in catholyte 12-< is low in lithium.To enable the catholyte 12 to be recirculated, a primary separation unit 20 is integrated into the cathodic circuit 16. This unit separates the desired lithium compound, namely lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH∘H₂O), from the lithium-rich catholyte 12+<, leaving behind the lithium-poor catholyte 12-<, which is then recycled into the cathodic compartment 7. From a process engineering perspective, the separated lithium hydroxide (monohydrate) represents the target product of the process.

[0065] Similarly, a secondary separation apparatus 21 is integrated into the anolytic cycle 15, which serves to remove unwanted anions X n-< contained in the fresh water 18 from the process. These unwanted anions X n-< are, for example, sulfates or chlorides, or other mono- or polyvalent negatively charged ions. These ions originate from salts dissolved in the fresh water 18. To ensure that the charge balance remains constant and to prevent an accumulation of anions in the central electrolyte or even unwanted anode reactions such as the formation of chlorine gas (Cl₂), these anions are removed from the central electrolyte 13 and concentrated in the anolyte 11. The concentration of these anions X n-< therefore increases in the anolyte 11, so that the concentration of anions X n-< in the anolyte 11 +< withdrawn from the first compartment is greater than in the supplied anolyte 11 -< .The withdrawn anolyte 11+< is therefore rich in these anions, while the supplied anolyte 11-< is anion-poor. The precise process by which the anions are enriched in the anolyte will be explained later. It is important to note, however, that the anions Xn-< in the anolyte 11 can combine to form other substances, especially acids, salts, or molecular gases, depending on the anolyte's composition. The anions can therefore also be separated by the secondary separation unit 21 as part of such a compound. Provided these compounds are harmless, the withdrawn anolyte 11+< can also be disposed of as a secondary wastewater. In this case, the anolytic cycle 15 is omitted, and the secondary separation unit 21 would be unnecessary.

[0066] If usable acids such as sulfuric acid (H₂SO₄) or hydrochloric acid (HCl) are formed in an anode reaction, the withdrawn anolyte can also be used to treat black mass. Black mass is a mixture that forms during the disintegration of spent lithium-ion batteries (LIBs). Besides lithium, it contains the electrode materials typically found in LIBs: nickel (Ni), manganese (Mn), cobalt (Co), aluminum (Al), iron (Fe), and graphite, as well as copper as a conductor material. The aforementioned acids can be used to dissolve metals contained in the black mass. An acidic, withdrawn anolyte could therefore be used in upstream process stages of LIB reprocessing.

[0067] As already mentioned, various electrochemical processes take place simultaneously in the operation of the electrochemical cell 0 according to the invention. Which processes occur exactly depends on the precise composition of the electrolytes 11, 12, 13. In any case, however, membrane-based electrodialysis of the ions present and electrolysis of water take place simultaneously. For better understanding, both processes will now be explained separately: electrodialysis using Figure 3 and electrolysis based on Figure 4 .

[0068] The in Figure 3The electrodialysis described serves, on the one hand, to enrich the Li cations (Li⁺) contained in the central electrolyte 13 in the catholyte 12. Furthermore, the unwanted anions (Xⁿ⁻) contained in the central electrolyte 13 and originating from the fresh water 18 are electrodialytically enriched in the anolyte 11 to prevent these anions from coming into contact with the cathode separator 4. In this way, the cathode separator 4 is protected from being poisoned by the anions (Xⁿ⁻) and by products of the anode reaction. Moreover, the removal of the anions (Xⁿ⁻) from the central electrolyte 13 reduces the formation of unwanted compounds between these anions and the free Li cations. This increases the yield of the target compound, lithium hydroxide (LiOH).

[0069] The in Figure 3The electrodialysis shown and described here is made possible by the special ionic conductivity of the separator materials used and by the applied electrical voltage. U The polarity of the electrical voltage source 8 is chosen such that the cathode 2 is negatively charged, while the anode 1 is positively charged. Following the generally accepted models of electrochemistry, the negatively charged anions migrate towards the anode 1, whereas the positively charged cations are attracted in the opposite direction towards the cathode 2. An electric current flows to balance the charge. I along the electrical lines 9, 10 from the anode 1 to the cathode 2.

[0070] The anions X n-< and OH -< can pass from the central electrolyte 13 into the anolyte 11 because the anode separator 3 lying in the way has an intrinsic anion conductivity. Since hydroxide ions (OH⁻) are generally less concentrated than other anions in the central electrolyte 13, predominantly non-hydroxide ions migrate through the anode separator 3. Conversely, due to the intrinsic lithium ion conductivity of the cathode separator 4, Li⁺ cations migrate from the central compartment 7 into the catholyte 12. Because the cathode separator 4 is made of a material with a higher conductivity for Li⁺ cations than for other cations, other monovalent or polyvalent metal cations (Me⁻) present as impurities in the fresh water 18 can hardly leave the central electrolyte 13 towards the catholyte 12, even though their positive charge also tends to migrate towards the cathode 2.Only a small fraction of the cationic impurities Me<m+> manage to cross the cathode separator 4 and form undesirable byproducts in the catholyte 12 (not shown). The majority of the cationic impurities Me<m+> remain in the central electrolyte 13 and are removed from the process with the wastewater 19. Thanks to the specific cation selectivity of the cathode separator 4 in favor of lithium, the purity of the target product LiOH / LiOH∘H₂O is increased, and the process's power efficiency is improved, as very little electrical energy is wasted transferring the cationic impurities Me<m+> from the central compartment 7 to the cathodic compartment 6.

[0071] Parallel to the in Figure 3 In the electrodialysis process shown, the process according to the invention involves the following: Figure 4The electrochemical splitting (electrolysis) of water (H₂O) into hydrogen (H₂) and oxygen (O₂) is shown. More precisely, two water splitting reactions are carried out in parallel: a basic water splitting reaction according to equation (1) in the catholyte and an acidic water splitting reaction according to equation (2) in the anolyte. 2 H₂O + 2 e⁻ → H₂ + 2 OH⁻ (1) Reduction / Cathode reaction H₂O → ½ O₂ + 2 H⁺ + 2 e⁻ (2) Oxidation / Anode reaction

[0072] In the present process, the electrochemical cell 0 is filled with a basic, water-based electrolyte, and a voltage is applied between anode 1 and cathode 2. In this case, the basic electrolytes are the central electrolyte 13 and the catholyte 12. Consequently, it must be ensured that the central electrolyte 13 and catholyte 12 are provided in an alkaline state. Since the starting materials used as electrolytes can be acidic depending on their origin, these electrolytes must first be made basic. The corresponding alkaline, lithium-containing water is introduced into the central compartment 7 as fresh water 18. The alkalinity of the catholyte 12 is preferably ensured by a minimum amount of lithium hydroxide dissolved in the catholyte 12. The hydroxide ions OH⁻ originating from the LiOH are responsible for the alkalinity of the catholyte 12.The minimum amount of LiOH is ensured by operating the primary separation apparatus 20 in such a way that the LiOH is not completely removed from the cathodic circuit 17. To start the process, a starting dose of LiOH is added to the catholyte 12.

[0073] On the cathode side of the three-chamber cell, i.e., in the central compartment 13 and the cationic compartment 12, water (H₂O) is decomposed into hydrogen (H₂) and hydroxide ions (OH⁻) (Equation 1). The anode separator 3 primarily transports anions (Xⁿ⁻) into the anionic compartment 5, where they can be oxidized to corresponding compounds such as chlorine in the case of chloride ions. Additionally, water (H₂O) is oxidized at the anode 1, producing protons (H⁺) and oxygen (O₂) (Equation 2). In this way, oxygen (O₂) is formed on the anode side, while hydrogen (H₂) is produced on the cathode side. At the anode, the corresponding acids of the anions, such as hydrochloric acid or sulfuric acid, are also formed from the protons, each in dissociated form.

[0074] Furthermore, the presence of hydroxide ions OH⁻ in the catholyte 12 leads to their combination with the Li cations Li⁺ present there, forming lithium hydroxide LiOH (Equation 3). Li⁺ + OH⁻ → LiOH (3) Synthesis of LiOH

[0075] The LiOH initially exists in solution, i.e., as Li+ cations and hydroxide ions OH-. As soon as the concentration of these ions reaches the saturation limit, solid lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH∘H2O) precipitates, the target product of the process.

[0076] The target product is obtained from the catholyte 12 via the primary separation apparatus 20. Hydrogen (H₂) and oxygen (O₂) are byproducts. Due to their gaseous state, these two byproducts readily escape from the catholyte 12 and the anolyte 11, respectively, and can be collected and utilized accordingly. A separate separation apparatus for the byproducts hydrogen (H₂) or oxygen (O₂) is not strictly necessary, but is conceivable.

[0077] To understand the overall process, it is important to recognize that the Li cations Li+<, which form LiOH in the catholyte 12, are only produced via membrane-based electrodialysis ( Figure 3 ) have entered the catholyte 12. The hydroxide ions OH⁻, which combine with the immigrated Li⁺ cations in catholyte 12 according to equation 3, are formed in catholyte 12, namely by the cathode reaction of water splitting according to equation 1 ( Figure 4 ). The operation of the electrochemical cell 0 according to the invention is therefore based on the simultaneous performance of water electrolysis and membrane-supported electrodialysis.

[0078] A particular embodiment of the operation according to the invention provides that the electrochemical cell is operated with an auxiliary cathode. Figures 5p , 5r , 6 , 7 and 8 Each shows a configuration of a three-chamber cell with an auxiliary cathode. In Figure 5pand 5r This is a full-surface auxiliary cathode 221, in which Figure 6 , 7 and 8 each by a reduced auxiliary cathode 222. In all cases, the auxiliary cathode 221 / 222 is in contact with the central electrolyte 13.

[0079] The in the Figures 5p , 5r The auxiliary cathode 221 shown has the same area as the other two electrodes 1, 2. The auxiliary cathode 221 can be connected to the negative terminal of the voltage source 8 via a third electrical conductor 23 ( Figure 5r The connection between the negative terminal of the voltage source 8 and the cathode 2 via the second electrical conductor 10 is then interrupted, so that the current I flows between the anode and the auxiliary cathode 221. In this, in Figure 5rIn the depicted operating state, electrochemical cell 0 is in regeneration mode. During regeneration, hydroxide ions (OH⁻) are formed at the auxiliary cathode 221 according to equation (1). These hydroxide ions capture protons (H⁺) by forming a water molecule (H₂O). In this way, the pH value in the central electrolyte 13 is increased to operate within the desired alkaline range of pH 9 to 10.5. Regeneration is always activated when the pH value drops to an undesirable, acidic value below 8. Adjusting the pH value via the auxiliary electrode 221 is very rapid: Regeneration only needs to take about 1 / 100th of the operating time of the production cycle. Therefore, adding alkaline compounds to the central electrolyte 13 is not necessary.

[0080] After completion of regeneration ( Figure 5r ) is switched back to production operation ( Figure 5pIn this circuit, the electrical voltage source 8 is connected with its negative terminal to the cathode 2 via the second electrical conductor 10. The current I flows between anode 1 and cathode 2. The auxiliary cathode 221 is de-energized.

[0081] Instead of alternating between production and regeneration, it is also possible to continuously raise the pH value using a miniaturized auxiliary electrode 222, which is also contacted with the central electrolyte 13 ( Figure 6The surface area of ​​the auxiliary electrode 222 is smaller than that of the other two electrodes 1 and 2, for example, by only about 1 / 100th. The auxiliary electrode 222 is permanently connected to the negative terminal of the electrical voltage source 8 via the second electrical conductor 10; the second electrical conductor 10 is branched accordingly. Thus, the current I flows continuously between anode 2 and the auxiliary cathode 222 and cathode 2. Due to the smaller surface area of ​​the auxiliary cathode 222, only a small number of hydroxide ions (OH⁻) are formed in the central electrolyte 13, enough to keep the pH value constant in the desired alkaline range of 9 to 10.5. Therefore, the addition of alkaline substances is not necessary. Continuous operation with the reduced-size auxiliary cathode 22 can be considered a combined regeneration / production state.

[0082] A particular advantage of the miniaturized auxiliary cathode 222 is that it can also be placed outside the electrochemical cell 0, for example in the supply line of the central electrolyte 13. This saves space in the third compartment 7. A corresponding embodiment is shown in Figure 8 depicted.

[0083] It is also possible to alternate the miniaturized auxiliary cathode 222 between a pure production state and a combined regeneration / production state. This is a mixture of the ones described in the Figures 5p , 5r , 6 The operating states shown are depicted. This allows for greater flexibility in dimensioning the area of ​​the reduced auxiliary cathode 222 and in the timing. This mixed operation is not shown.

[0084] Figure 7Figure 1 shows another embodiment of an electrochemical cell 0 with a miniaturized auxiliary cathode 222. The miniaturization of the auxiliary cathode 222 is achieved by using a porous textile, such as a mesh fabric, as the auxiliary cathode. Due to its porosity, the auxiliary cathode 222 has a surface A AK, which is smaller than the surface A K of the cathode 2. In Figure 7 This is not immediately apparent because the textile auxiliary cathode 222 extends through the entire central compartment 7. The advantage of using a textile auxiliary cathode is that it has better permeability for ions than a full-surface auxiliary cathode and therefore impedes ion exchange less.

[0085] Figure 8Figure 1 shows another embodiment of an electrochemical cell 0 with a reduced-size auxiliary cathode 222. Here, the auxiliary cathode 222 is arranged outside the central compartment 7, more precisely, in a supply line 24 for the central electrolyte 13. The central electrolyte 13 flows in a straight line 17 through the supply line 24 into the central compartment 7 and then exits it again (not shown). The advantage of arranging the auxiliary cathode 222 in the supply line 24 is that the ions can move freely within the central compartment 7, unimpeded by the auxiliary cathode 222. Contact between the auxiliary cathode 222 and the central electrolyte 13 within the supply line 24 is sufficient. Examples:

[0086] The advantages achieved through the process according to the invention will now be demonstrated using experimental data: Experimental setup

[0087] The electrochemical cell 0 used for conducting the experiments is in Figure 8 The apparatus is depicted. It comprises three compartments 5, 6, and 7. Compartments 7 and 6 are separated by an ion-exchange membrane, the so-called cathode separator 4. Compartments 5 and 7 are separated from each other by a membrane, the so-called anode separator 3. An anode 1 is located in the first compartment 5. In the central compartment 7, an auxiliary cathode 222 is located in the inlet line for the central electrolyte 13. A cathode 2 is located in the third compartment 6. Compartment 5 can also be referred to as the anodic compartment, while the third compartment 6 is referred to as the cathodic compartment. The central compartment 7 can also be referred to as the central compartment 7.

[0088] A first electrical conductor 9 connects the anode 1 to a voltage source 8. A second electrical conductor 10 connects the cathode 2 to the voltage source 8. A branch of the second electrical conductor 10 connects the cathode 8 to the auxiliary cathode 222. The polarity of the voltage source 8 is chosen such that the positive terminal of the voltage source 8 is connected to the anode 1, while the negative terminal of the voltage source 8 is connected to the cathode 2 and the auxiliary cathode 222.

[0089] An electric current I flows through the electrical conductors 9 and 10 and through the electrical voltage source 8. Since the ion exchange membrane 4 is electrically insulating, there is no electrical short circuit between the two electrodes 1 and 2 via the ion exchange membrane 4.

[0090] The ion exchange membrane 4 is a flat membrane made entirely of LISiCon material. The other membrane 3 is also a flat membrane, but it is made of an anion-conductive polymer, such as an AHA membrane from Eurodia Industrie SAS or a Neosepta membrane from ASTOM.

[0091] The auxiliary cathode 222 is a wire containing titanium, platinum, or stainless steel. The cathode 2 is also a flat metal sheet containing titanium or nickel. In the simplest case, stainless steel sheet is used as the cathode. Anode 1, cathode 2, and the two membranes 3 and 4 have the same shape; they can be rectangular or circular. The auxiliary cathode 222 is a wire whose area projecting into the supply line 24 for the central electrolyte 13 constitutes 2% of the active area A of the cathode 2. This is shown in the side view of the Figure 8Not shown to scale. Expanded metal, grids, or meshes made of the specified materials can also be used as electrodes instead of sheet metal.

[0092] The electrochemical cell 0 has an active area A, which corresponds to the surface area of ​​the two membranes 3, 4, the anode 1 and the cathode 2. As mentioned, the auxiliary cathode 222 is smaller, its active surface area being only 2 / 100*A.

[0093] During operation, compartments 5 and 7 are supplied with a feed 13. The same feed 13 can be found in both compartments 5 and 7, or one of the compartments may contain a different solution 11. The feed 13 is an aqueous solution containing Li+ cations. From an electrochemical perspective, the feed 13 can be considered an anolyte.

[0094] Feed 13 can be a lithium brine from a natural deposit or a feed stream generated during the reprocessing of spent lithium ingots. The concentration of Li+ cations in Feed 13 should be at least 200 ppm by weight, based on the total mass of the feed. Seawater has a lower Li concentration and would therefore need to be concentrated before being used in the process. Feed 13 also contains anions such as sulfate or chloride. Feed 13 also contains impurities. Anions and impurities are in Figure 1 Not shown. The main component of feed 13 is water.

[0095] The third compartment 6 is supplied with a low-energy working medium 12-<. The low-energy working medium 12-< is water with a low concentration of Li+ cations. The concentration is at least 50 ppm by weight based on the total mass of the low-energy working medium 12-<. From an electrochemical perspective, the low-energy working medium 12 can be considered a catholyte.

[0096] The electrochemical cell 0 is also supplied with an electrical voltage U from the voltage source 8. This causes the following: Firstly, water electrolysis occurs, in which water is electrochemically split into hydrogen and oxygen. OH- and hydrogen are formed at the cathode 2 and the auxiliary cathode 222. However, the OH- anions cannot cross the LiSiCon membrane 4 and combine with the Li+ cations present in the cathodic compartment 6 to form lithium hydroxide. Oxygen and H+ are formed at the anode 1. In the central compartment 7 (the one with the auxiliary cathode 222), OH- anions are formed, which keep the pH value stable in compartment 7.

[0097] The formation of LiOH in the cathodic compartment 6 is maintained by the migration of Li+ cations from feed 13 towards cathode 2, driven by the voltage U. They overcome the LiSiCon membrane 4 due to its conductivity for Li ions and accumulate in the working medium 12 (membrane electrolysis). This creates a rich working medium 12+<, which is drawn off from the third compartment 3. The concentration of Li+ ions in the rich working medium 12+< is higher than in the poor working medium 12-<.

[0098] In electrochemical cell 0, water electrolysis, membrane electrolysis of Li+ and synthesis of LiOH take place simultaneously.

[0099] During the simultaneous operation of Li+ membrane electrolysis and water electrolysis in the electrochemical cell, lithium hydroxide (LiOH) and molecular hydrogen (H2) are directly produced. The hydrogen is at least partially dissolved; it can also be present in gas bubbles. Depending on the temperature and the presence of crystallization nuclei, the LiOH precipitates either in the cathodic compartment 6 or immediately after the removal of the rich working medium 12+<.

[0100] The feed 13 is depleted of Li+ by membrane electrolysis, resulting in a wastewater 19. Experimental procedure

[0101] To carry out electrolysis, the electrolytes are first filled into the two anolyte containers and the catholyte container, with the inlet hoses clamped off. The electrolyte container that supplies the cell section directly adjacent to the membrane is referred to as the central compartment. The electrolysis cell is then assembled. During assembly, the membranes should not be allowed to dry out by performing the process quickly. Once the electrolysis cell is assembled, it is connected to the anolyte and catholyte containers as well as the central chamber. Care is taken to ensure that the inlet and outlet are connected to the same side. The inlet lines to the cell can now be carefully opened, with the inlet hoses for the catholyte and the central chamber being opened simultaneously.

[0102] A round disc with a diameter of 19.5 mm and a thickness of 1 mm was used as both the anode and cathode. The material was titanium expanded metal sheet, coated on both sides with IrTi mixed oxide, 12 g Ir / m², 1 AF D1.5 mm, from Metakem GmbH, 61250 Usingen, Germany.

[0103] A 2 mm diameter wire, extending approximately 3 mm into the inlet pipe of the central compartment, served as the auxiliary cathode. The material was a titanium wire coated with IrTi mixed oxide, 12 g Ir / m², from Metakem GmbH, 61250 Usingen, Germany.

[0104] The anode and cathode are connected to the voltage source, the Keithley 2400 potentiostat from Tektronix UK Ltd., Berkshire, UK. The auxiliary cathode is connected to the cathode.

[0105] The sampled membranes were also circular discs with a diameter of approximately 25 mm. The membranes were approximately 1 mm thick. The material of the sampled LiSiCon membranes was Ampcera™ LISICON LAGP, from MSE Supplies®, Tucson, USA. The material of the sampled organic anion exchange membranes was an AHA membrane from Eurodia Industrie SAS.

[0106] The electrolysis process and the corresponding reservoirs are kept under a nitrogen blanket throughout the entire procedure to prevent the formation of lithium carbonate. Each cell has a separate anolyte and catholyte reservoir, as well as a separate intermediate chamber. Each reservoir is filled with approximately 1 kg of liquid; the exact mass is determined by backweighing. In all experiments, the catholyte at the start of the experiments was always a 5 mmol / L LiOH solution (corresponding to 120 wt ppm LiOH). The anolyte and the electrolyte in the intermediate chamber are lithium salt solutions of varying concentrations and with different lithium salts. The anolyte reservoir and the intermediate chamber can contain different solutions. The starting concentrations, as well as the exact concentrations, vary during the course of the experiment and are therefore also shown in the diagram for each experiment.

[0107] The experiment is started by switching on the pumps and the desired voltage. During the experiment, the voltage is pulsed, controlled by the appropriately programmed Siemens LOGO! 230 RC control unit from Siemens.

[0108] The maximum flow rate is 900 mL / minute and is determined using a Sonotec SONOFLOW CO.55 / 060 V2.0 ultrasonic flow sensor. Sampling is performed every half hour or at longer intervals by arrangement. A 3 mL sample is drawn and discarded. The flow rate is recorded for each sample, and the pH and conductivity are determined. The samples are then returned to their respective containers to maintain a nearly constant volume.

[0109] After the experiment, the containers are emptied and all lines, including the membrane, are rinsed with deionized water. The cell is disassembled, the membrane is photographed, and SEM images of the catholyte and anolyte sides are taken to document any damage or changes to the membranes. The ion exchange membrane is then microscopically examined for any alterations. Both the side facing the middle chamber and the anolyte side are inspected.

[0110] Membrane performance is measured using the parameters of permeability (gLi*mm / m²*h) and permeance (gLi / m²*h). Permeance indicates how much mass of lithium is transported across the membrane per unit area and time. Permeability also takes membrane thickness into account, thus allowing for the comparison of different membrane types with varying thicknesses. Both values ​​are necessary for a comprehensive description of performance, as extremely thin membranes would allow for an enormously high permeance, but if concentration polarization effects occur within the membrane cell, the permeabilities would be inaccurately represented. Considering membrane thickness is then no longer meaningful, since transport is not limited by the membrane.

[0111] All measured values ​​shown in the examples are subject to a measurement error of approximately + / - 10%, which can be attributed to inaccuracies in the positioning of the electrodes relative to each other, the determination of the thickness of the membrane samples, and the determination of the concentration via conductivity measurements.

[0112] The concentration was determined inline via conductivity measurement. (The text abruptly shifts to a different topic:) Figure 9 The calibration curve shown translates the conductivity into a concentration in the test results. Figure 9: Conductivity as a function of the concentration of a LiOH solution (25°C)

[0113] Consequently, at concentrations above approximately 10% LiOH, accurate monitoring of the actual concentration via conductivity measurements is hardly possible.

[0114] The variations within the trials are shown in Table 1. Table 1: Experiment overview Apart from that, the following constant experimental conditions prevailed: Timing: Power on for 50 seconds - power off for 10 seconds Catholyte concentration: 5 mmol / I LiOH - LiOH*H2O, 98%, Thermo Fisher Scientific Tension: 6 V (between anode and cathode, and between auxiliary cathode) and anode) Membrane: Ampcera ®< LISCON LAGP Table 1 Test No.: Qualification attempt Anion exchange membrane Central electrolyte Anolyte 1a inventive AHA membrane Eurodia Industrie SAS, St Martin, FR 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 1b inventive AHA membrane Eurodia Industrie SAS, St Martin, FR 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 1c inventive AHA membrane Eurodia Industrie SAS, St Martin, FR 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 2 inventive AHA membrane 1.43 M LiCl + 0.0045 M NaCl, ≥99%, Carl Roth GmbH + Co. KG 1.43 M LiCl + 0.0045 M NaCl, ≥99%, Carl Roth GmbH + Co. KG 3 inventive AHA membrane 1.43 M LiCl +0.0045 M NaF, PanReac Applichem GmbH +0.015 M CaCl 2 ≥99%, Carl Roth GmbH + Co. KG 1.43 M LiCl +0.0045 M NaF, PanReac Applichem GmbH +0.015 M CaCl 2 ≥99% Carl Roth GmbH + Co. KG 4 inventive AHA membrane 0.72 M Li 2 SO 4 , ≥99% Carl Roth GmbH + Co. KG +0.004 M Na 2 SO 4 Carl Roth GmbH + Co. KG 0.72 M Li 2 SO 4 , ≥99% Carl Roth GmbH + Co. KG +0.004 M Na 2 SO 4 Carl Roth GmbH + Co. KG 5 inventive AHA membrane 9.4 M LiCl ≥99%, Carl Roth GmbH + Co. KG 9.4 M LiCl ≥99%, Carl Roth GmbH + Co. KG 6 inventive AHA membrane 9.4 M LiCl + 0.043 M NaCl + 0.026 M KCl, ≥99.5%, Carl Roth GmbH + Co. KG 9.4 M LiCl + 0.043 M NaCl + 0.026 M KCl, ≥99.5% Carl Roth GmbH + Co. KG Attempt 1a:

[0115] The experimental setup was carried out as described above (experimentation and detailed execution as described in Table 1).

[0116] In the central compartment, an auxiliary cathode in the form of a stainless steel wire mesh (grade 1.4401) with a 200µm mesh size was inserted and provided with a wire which allows electrical contact from the outside (see Figure 7 ).

[0117] With the commissioning of the pumps for the three circuits, a pulsed DC voltage of 6V was simultaneously applied between the anode and cathode. During the experiment, the decrease in the pH value of the middle chamber can be monitored via regular sampling. After approximately 24 hours, it drops from pH 9 to a value of 7.3. The pH value of the anolyte after 24 hours was 2.5, and the current was approximately 30 mA.

[0118] After these 24 hours, only the auxiliary cathode was operated for a total of 5 minutes at a voltage of 6V. This resulted in a current of up to 200mA during this period. The pH value of the middle chamber rose to more than 10. Attempt 1b:

[0119] If the cell is operated again under the same settings as in attempt 1a ( Attempt 1b ), now without applied voltage to the auxiliary cathode, the current through the cell rises to more than 70mA, which is also associated with a correspondingly larger permeance.

[0120] The course of the measurement points from experiment 1a and 1b is shown in the diagram of the Figure 10 depicted. Figure 10: Diagram for experiments 1a and 1b

[0121] For easier overview, all results / values ​​are summarized in Table 2. Table 2: Measured values ​​from the experiments Attempt 1c:

[0122] Using the same measurement setup with the sole difference that the auxiliary cathode was now designed not as a wire mesh, but as a wire in the inlet line to the middle chamber with a surface area of ​​2% of the electrode and membrane area ( Figure 8 The results are also summarized in Table 2. Attempts 2 to 6:

[0123] These experiments were conducted using the same setup as in experiment 1c. The voltage between the anode and cathode was 6 V, and the voltage between the auxiliary cathode and anode was also 6 V. Spot measurements of the current at the auxiliary cathode yielded values ​​between 1 and 20% of the current flowing between the anode and cathode. All results after 50 hours of cell operation are listed in Table 2. Table 2: Test No.: U [V] I [mA] Permeance [g Li / m 2< h] Permeability [g Li mm / m 2< h] pH anolyte pH Central electrolyte pH catholyte 1a 6 30 27 8.5 2.5 7.3 12 1b 6 >70 >35 >12 2.0 11 12 1c 6 78 43 12.8 2.1 9.5 12 2 6 80 42 12.6 2.6 10.2 12 3 6 75 39 11.7 2.6 10.1 12 4 6 60 30 8.9 2.0 9.5 12 5 6 60 33 11 1.0 7.3 12 6 6 64 45 13.6 0.2 7.6 12 Comparative trials:

[0124] For comparison, cells without an anion exchange membrane were constructed. An overview is provided in Table 3. Table 3: Overview of comparative trials

[0125] Table 3: Test No.: Qualification attempt anion exchange membrane Central electrolyte = anolyte 7 not inventive no 1 M LiCl ≥99%, Carl Roth GmbH + Co. KG 8 not inventive no 0.5 M Li 2 SO 4 , ≥99% Carl Roth GmbH + Co. KG

[0126] The measured values ​​from the comparative tests are listed in Table 4. Table 4: Measured values ​​from comparative tests

[0127] Table 4: Test No.: U [V] I [mA] Permeance [g Li / m 2 < h] permeability [g Li mm / m 2< h] pH anolyte pH Central electrolyte pH catholyte 7 6 19 18 6 2.0 2.0 12 8 6 17 15 5 1.7 1.7 12 Attempt 7:

[0128] For comparison, the setup used in experiments 1 to 6 was modified by omitting the anion exchange membrane between the central compartment and the anodic compartment, so that the cell has only two separate compartments: exactly one anodic and exactly one cathodic compartment. No auxiliary cathode was used.

[0129] Since the pH value in the anodic compartment decreases during the experiment due to proton formation at the anode, damage to the ceramic LiSiCon membrane occurs continuously below a pH value of 7. This means that the results listed in Table 4 are not constant values, but rather decrease steadily over the course of the experiment, particularly between 5 and 50 hours. The data after approximately 24 hours are shown as an example. Attempt 8:

[0130] The same applies here as in experiment 7, except that a lithium sulfate solution was used for the experiments. Conclusion:

[0131] The experiments demonstrate that, compared to a two-chamber cell (experiments 8 and 9), the operation of a three-chamber cell with an anion exchange membrane as an anode separator according to the invention (experiments 1a to 7) results in higher permeance and permeability after the same operating time. This means that the same cathode separator experiences greater wear during the treatment of lithium-containing water when installed in a two-chamber cell than in a three-chamber cell. Consequently, higher efficiency can be expected over a long service life when operating the three-chamber cell according to the invention.

[0132] In all experiments, the levels of foreign cations in the catholyte were below the detection limit. The purity of the target product was not affected by cathodic impurities such as sodium contained in the central electrolyte.

[0133] Furthermore, a higher current flows during the operation of the cell according to the invention (experiments 1a to 7) than during operation without the invention (experiments 8 and 9). Consequently, the productivity per unit area is better. This means that a system operated in this way can be smaller while maintaining the same production output.

[0134] A comparison of operation with an auxiliary cathode implemented as a wire mesh (Experiment 1) and with operation where the auxiliary cathode is located in the inlet (Experiments 2 ff.) shows that placing the auxiliary cathode in the inlet leads to very good permeance during continuous operation, without the need for regular switching between different operating states. This simplification in the cell design, as well as in its implementation, demonstrates that placing the auxiliary cathode in the inlet is the particularly preferred embodiment. Reference symbol list

[0135] 0 Electrochemical cell (three-chamber cell) 1 Anode 2 Cathode 3 Anode separator 4 Cathode separator 5 Anodic compartment 6 Cathodic compartment 7 Central compartment 8 Electrical voltage source 9 First electrical line 10 Second electrical line 11 Anolyte 11 -< Anolyte being fed in (low in anions) 11 +< Anolyte being drawn off (rich in anions) 12 Catholyte 12 -< Catholyte being fed in (low in lithium) 12 +< Catholyte being drawn off (rich in lithium) 13 Central electrolyte 14 System 15 Anodic circuit 16 Cathodic circuit 17 Straight passage 18 Fresh water (lithium-containing) 19 Wastewater (low in lithium) 20 Primary separation apparatus 21 Secondary separation apparatus 221 Full-surface auxiliary cathode 222 Reduced-size auxiliary cathode 23 Third electrical conductor 24 Central electrolyte supply line X n-< Anions Me m+< Cationic impurities OH -< Hydroxide ions H +< Protons Li +< Lithium cations LiOH Lithium hydroxide H 2 Hydrogen O 2 Oxygen H 2 O Water

Claims

1. Process for operating an electrochemical cell (0), comprising the following, non-chronological steps: a) providing at least the electrochemical cell (0) having at least the following features: i) the electrochemical cell (0) comprises an anode (1) and a cathode (2); ii) the electrochemical cell (0) comprises a cathode separator (4) and an anode separator (3); iii) the electrochemical cell (0) comprises an anodic compartment (5), a central compartment (7) and a cathodic compartment (6); iv) the cathode separator (4) separates the central compartment (7) from the cathodic compartment (6); v) the anode separator (3) separates the central compartment (7) from the anodic compartment (5); vi) the cathode separator (4) comprises an inorganic material having a conductivity for anions (Xn-) and a conductivity for cations (Li+, Mem+), the conductivity for cations (Li+, Mem+) being greater than the conductivity for anions (Xn-) and the conductivity for Li cations (Li+) being greater than the conductivity for cationic impurities (Mem+); vii) the anode separator (3) comprises an organic material having a conductivity for anions (Xn-, OH-) and a conductivity for cations (Li+, Mem+), the conductivity for anions (Xn-, OH-) being greater than the conductivity for cations (Li+, Mem+); viii) the inorganic material and / or the organic material is electrically insulating; b) providing a catholyte (12) in the cathodic compartment (6), the catholyte (12) comprising at least: water (H2O), Li cations (Li+), hydroxide ions (OH-); c) providing a central electrolyte (13) in the central compartment (7), the central electrolyte (13) comprising at least: water (H2O), Li cations (Li+), anions (Xn-) and cationic impurities (Mem+); d) providing an anolyte (11) in the anodic compartment (5), the anolyte (11) comprising at least: water (H2O) and anions (Xn-); e) providing at least one electrical voltage source (8) which can be connected to the anode (1) via a first electrical lead (9) and to the cathode (2) via a second electrical lead (10); f) applying an electrical voltage U obtained from the electrical voltage source (8) to the electrochemical cell (0) such that an electrical current I flows between the anode (1) and cathode (2); characterized in that the central electrolyte (13) additionally also comprises hydroxide ions (OH-), and in that the pH of the central electrolyte (13) is between 9 and 12, measured using a glass electrode at a temperature of 25°C, and in that an electrochemical cell (0) additionally having the following features is provided: ix) the electrochemical cell (0) comprises an auxiliary cathode (222); x) the auxiliary cathode (222) is in contact with the central electrolyte (13); xi) the auxiliary cathode (222) can be connected to the electrical voltage source (8) via the second electrical lead (10); xii) the cathode (2) has a cathode area AK; xiii) the auxiliary cathode (222) has an auxiliary cathode area AAK; and in that the process has one operating state, namely: k) a combined production and regeneration state in which the anode (1) is connected to the electrical voltage source (8) via the first electrical lead (9) and the cathode (2) and the auxiliary cathode (222) are connected to the electrical voltage source (8) via the second electrical lead (10) and in which the electrical voltage U is applied to the anode (1) and cathode (2) and auxiliary cathode (222) so that the electrical current I flows between the anode (1) and cathode (2) and auxiliary cathode (222); where the cathode area AK and the auxiliary cathode area AAK are selected such that A K > f ∗ A AK where f is greater than 1 or where f is greater than 10 or where f is greater than 100.

2. Process according to Claim 1, characterized in that at least some of the steps are performed simultaneously and continuously.

3. Process according to either of Claims 1 and 2, characterized in that the anions (Xn-) are selected from the group consisting of sulfate, hydrogensulfate, carbonate, hydrogencarbonate, hydroxide, chloride and fluoride.

4. Process according to Claim 3, characterized in that the central electrolyte (13) has a higher concentration of the anions (Xn-) selected from said group than hydroxide ions (OH-).

5. Process according to any of Claims 1 to 4, characterized in that the cationic impurities (Mem+) are cations of elements selected from the group consisting of B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu and C.

6. Process according to any of the preceding claims, where the inorganic material present in the cathode separator (4) has a specific conductivity for Li ions s, measured by the "impedance spectroscopy" method described herein, that at a temperature of 23°C is at least 1*10-5 S / cm or at least 5*10-5 S / cm or at least 10*10-5 S / cm and at most 100*10-5 S / cm.

7. Process according to Claim 6, characterized in that the inorganic material is a compound of the following stoichiometry (LATP):         Li1+xAlxTi2-x(PO4)3 in which: 0.1 ≤ x ≤ 0.3, where preferably x = 0.3.

8. Process according to Claim 6, characterized in that the inorganic material is a compound of the following stoichiometry (LATSP):         Li1+x+yAlxTi2-xSiyP3-yO12 in which: 0.1 ≤ x ≤ 0.3 and 0.2 ≤ y ≤ 0.4.

9. Process according to Claim 6, characterized in that the inorganic material is a compound of the following stoichiometry (LAGTSP):         Li1+x+yAlxTi2-xSiyP3-yO12 * nGeO2 in which: 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1 and 0 ≤ n ≤ 1.

10. Process according to Claim 6, characterized in that the inorganic material is a compound of the following stoichiometry (LAGTP):         Li1.4Al0.4(Ge1-xTix)1.6(PO4)3 in which: 0 ≤ x ≤ 1.

11. Process according to Claim 6, characterized in that the inorganic material is a compound of the following stoichiometry (LAGP):         Li1+xAlxGe2-x (PO4)3 in which: x = 0 or x = 0.2 or x = 0.4.

12. Process according to any of Claims 1 to 11, characterized in that the organic material present in the anode separator (3) is a polymer having a backbone to which at least one cationic functional group is bonded.

13. Process according to Claim 12, characterized in that the cationic functional group is a quaternized trialkylammonium salt.

14. Process according to Claim 12 or 13, characterized in that the backbone is selected from the group consisting of polystyrene, polysulfone, poly(ethersulfone) or poly(phenylene oxide), polyvinylidene fluoride, or polytetrafluoroethylene.

15. Process according to Claim 12, characterized in that the cationic functional group is a quaternized trialkylammonium salt, in that the backbone is selected from the group consisting of polystyrene, polysulfone, poly(ethersulfone) or poly(phenylene oxide), and in that the quaternized trialkylammonium salt is attached to the backbone via a benzyl(methyl) group.

16. Process according to Claim 1, characterized in that the process has two operating states, namely: k) the combined production and regeneration state (k), p) a production state (p) in which the anode (1) and the cathode (2) are connected to the electrical voltage source (8) via the first and the second electrical lead (9 and 10), respectively, and in which the electrical voltage U is applied to the anode (1) and cathode (2) so that the electrical current I flows between the anode (1) and cathode (2); there being an alternating change between the production state (p) and the combined production and regeneration state (k), where an individual production state (p) is carried out over a duration of tP and where an individual combined production and regeneration state (k) is carried out over a duration of tK, where t P > g ∗ t K where g is greater than 50 or where g is greater than 500 or where g is greater than 5000.

17. Process according to either of Claims 1 and 16, characterized in that the auxiliary electrode (222) is arranged outside the central compartment (7) and / or in that the auxiliary electrode (222) consists of a textile material.

18. Process according to any of the preceding Claims 1 to 17, characterized in that the operation involves an electrolysis of water (H2O) and an electrodialysis of anions (Xn-).

19. Process according to Claim 18, characterized in that the operation involves the synthesis of lithium hydroxide and / or lithium hydroxide monohydrate (LiOH∘H2O).

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