Operation of electrochemical cells in the context of treating lithium-containing water

Abstract

The present invention relates to the operation of an electrochemical cell (0) for the purpose of treating lithium-containing water. It is based on the objective of operating the cell (0) with a better current yield in order to keep its permeance constant and improve the purity of the target product (LiOH). An essential 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). The basic idea of ​​the process according to the invention is to use an inorganic cathode separator (4) with an ion selectivity in favor of lithium. This allows for the production of less cationic impurities (Me m+ ) can be converted into undesired by-products, which increases the current yield and improves the purity of the target product (LiOH). The anode separator (2) is anion-conducting. A further essential aspect of the operation according to the invention is that two electrochemical processes are carried out simultaneously: on the one hand, membrane-supported electrodialysis of ions, and on the other hand, electrolysis of water.

Description

[Technical Field]

[0001] The present invention relates to the operation of an electrochemical cell for the purpose of treating lithium-containing water. [Background technology]

[0002] Lithium-containing water is a mixture containing primarily water and lithium compounds dissolved therein. Other dissolved substances may also be present therein, such as sulfates, hydrogen sulfates, carbonates, bicarbonates, hydroxides, chlorides, or fluorides of the following elements: B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, and Cu. In addition, the lithium-containing water may contain organic compounds.

[0003] Lithium-containing water occurs naturally, for example as Li brine in salt lakes, as seawater, or as groundwater. In addition, lithium-containing water occurs in deep boreholes or as mine water. Finally, lithium-containing water is also produced in the recycling of used lithium-ion batteries (LIBs) and the production of new LIBs. Thus, the origins of lithium-containing waters are diverse, and therefore their compositions are also diverse: not only the Li concentration, but also the amount and type of other dissolved substances can vary considerably.

[0004] Lithium-containing water is used as a starting material to obtain lithium-containing compounds, in particular lithium carbonate (Li2CO3) or lithium hydroxide (LiOH). Both are required for the production of LIBs. Due to the exponential growth in demand for new LIBs and the increasing amount of used LIBs, many processes have been developed to treat lithium-containing water, usually with the aim of obtaining lithium carbonate (Li2CO3) or lithium hydroxide (LiOH) with the highest possible purity. The processes are optimized, on the one hand, with respect to the desired target compound and, on the other hand, with respect to the composition of the lithium-containing water used. An overview is provided below.

[0005] 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. Such processes, which operate primarily thermally or via crystallization effects, are commercially widespread, particularly in the production of primary lithium from salt lakes, and are in many ways very resource intensive.

[0006] For this reason, newer processes for obtaining lithium compounds from lithium-containing water have been developed, which operate using electrical energy. These processes are electrochemical processes, in particular electrolysis or electrodialysis. The fundamental advantage of these electrochemical processes is that they are very resource-friendly when using green electricity. The disadvantage is that the complex equipment technology, especially the electrochemical cells in which the process takes place, is very demanding from a materials science perspective.

[0007] A selection of electrochemical processes for separating lithium from recycled water from used batteries or from seawater is summarized: 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. In Section 2.2, Choubey et al. describe a modern electrodialysis process carried out in electrochemical cells, each containing two different ion-conducting membranes: an anion-conducting membrane and a cation-conducting membrane. The desired ionic conductivity of the membrane is achieved by impregnating it with an ionic liquid.

[0008] Canadian Patent Publication No. 3,077,834 describes a process for preparing high-purity lithium hydroxide from heavily contaminated sources, such as brine from salt lakes. It discloses a complex interconnection of different purification stages, including electrodialysis using a three-chamber cell equipped with bipolar membranes. The bipolar membranes are a combination of anion-exchange and cation-exchange membranes. The chemical nature of these membranes is not disclosed in Canadian Patent Publication No. 3,077,834.

[0009] EP 2 841 623 B1 discloses a process for preparing lithium hydroxide using an electrochemical cell having three compartments and two separators (known as a three-chamber cell). The three-chamber process known from EP 2 841 623 B1 involves feeding an aqueous stream containing lithium sulfate into the center compartment of the three-chamber cell. Lithium hydroxide is introduced into the cathode compartment, and aqueous ammonia is fed into the anode compartment. An aqueous solution containing lithium hydroxide is withdrawn from the cathode compartment of the cell, and ammonium sulfate is formed in the anode compartment. In addition, oxygen is formed on the anode side, and hydrogen is formed on the cathode side. The three-chamber cell is operated under basic conditions.

[0010] The three-chamber cell known from EP 2841623 essentially has two membranes separating the central compartment from the anode and cathode compartments. Materials including perfluorinated polymers and styrene or divinylbenzene membranes are considered membrane materials. In particular, cation exchange membranes or PEEK-reinforced membranes should be used. Examples mentioned are commercially available ion exchange membranes such as Asahi AAV, Fumatech FAB, Astrom Neosepta®, or Lanxess Ionac®. The chemical nature of these ion exchange membranes is not disclosed in EP 2841623, but they are likely to be organic membrane materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Canadian Published Patent No. 3077834 [Patent Document 2] European Patent No. 2841623 [Non-patent literature]

[0012] [Non-Patent Document 1] 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. [Non-patent document 2] 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. Summary of the Invention [Problem to be solved by the invention]

[0013] A fundamental drawback of polymeric membranes is their permeability to water, which leads to dilution of the anolyte with water from the catholyte. Furthermore, organic ion exchange membranes are not suitable for Li + Not only Na + In addition to the purity of the target product, the current yield of the process is also problematic: when electrolysis is carried out using an organic membrane, the unwanted Na+ The transport of Na to the second compartment also consumes valuable electrical energy. + is converted to undesired by-products by unintended electrochemical processes, reducing the energy efficiency of the process based on the yield of the target product, Li. Finally, these films are 2+ and Ca 2+ These cations poison the membrane over time, resulting in a decrease in its conductivity to lithium: this is manifested in the fact that the membrane's permeance, i.e., its area-based Li conductivity based on its thickness, decreases. This means that less lithium can precipitate from lithium-containing water. The reduced current efficiency, increased contamination of the target product by foreign cations, and decreased permeance quickly make the operation of the electrochemical cell uneconomical. [Means for solving the problem]

[0014] With respect to this prior art, the present invention is based on the objective of operating an electrochemical cell with a better current yield in order to keep its permeance constant and improve the purity of the target product.

[0015] This objective is achieved by operating the electrochemical cell as follows: a) At least one electrochemical cell is provided having at least the following characteristics: i) the electrochemical cell includes an anode and a cathode; ii) the electrochemical cell includes a cathode separator and an anode separator; iii) the electrochemical cell includes an anode compartment, a central compartment, and a cathode compartment; iv) a cathode separator separates the central compartment from the cathode compartment; v) an anode separator separates the central compartment from the anode compartment; vi) The cathode separator comprises an inorganic material that is electrically insulating and conductive to anions and cations, the conductivity of the cations being greater than the conductivity of the anions, and the ... conductive to Li cations (Li + ) is the conductivity to cationic impurities (Me m+ ) is greater than the conductivity for vii) The anode separator is an anion (X n- , O.H. - ) and cations, and n- , O.H. - ) is greater than the conductivity to cations; viii) the inorganic and / or organic material is electrically insulating; b) A catholyte is provided in the cathode compartment, the catholyte comprising at least water (HO), Li cations (Li + ), hydroxide ion (OH - ) including; c) A central electrolyte is provided in the central compartment, the central electrolyte comprising at least water (HO), Li cations (Li + ), anion (X n- ) and cationic impurities (Me m+ ) including; d) An anolyte is provided in the anode compartment, the anolyte comprising at least water (HO) and anions (X n- ) including; e) at least one voltage source is provided that can be connected to the anode via a first electrical lead and to the cathode via a second electrical lead; f) A voltage U obtained from a voltage source is applied to the electrochemical cell so that a current I flows between the anode and the cathode.

[0016] The basic idea of ​​the process according to the invention is to use an inorganic cathode separator with an ion selectivity in favor of lithium. This means that the material from which the cathode separator is produced is a material that is selective for Na. + or other cationic impurities Me m+than other cations such as Li + This means that it has high conductivity for cations, which results in fewer cationic impurities entering the cathode compartment where they can be converted to undesired by-products, which increases the current yield and improves the purity of the target product.

[0017] Li over other cations + A preferred inorganic material with high conductivity for Li is known as LiSICon. LiSICon stands for Lithium Superionic Conductor. It is a type of inorganic (glass) ceramic material that is electrically insulating, but at the same time has intrinsic conductivity for Li ions. The transport mechanism for Li comes from the crystalline structure of the material. Li ions simply "pass" through the crystal. 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 electrolytes for LIBs. An overview of the transport mechanism of LiSICons, their crystalline structures, and production is presented 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. A particular LiSICon stoichiometry is described by: Sofia Saffirio et al.Li 1.4 Al 0.4 Ge 0.4 Ti 1.4 (PO4)3promising 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 Li 1.7 Al 0.3 Ti 1.7 Si 0.4 P 2.6 O 12 .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. Their selective conductivity towards Li ions means that LiSICon materials can be used as membranes to separate lithium from Li-containing mixtures, where the lithium must be present in ionic form, for example as a Li salt dissolved in water.

[0018] The use of LiSICon to separate lithium from aqueous streams is known in principle from the prior art.

[0019] For example, WO2019055730 broadly describes the selective acquisition of lithium on LiSICon films.

[0020] In WO2022157624 a three-chamber cell LLTO membrane is used for electrodialysis of seawater for the purpose of obtaining lithium.

[0021] U.S. Patent Application Publication No. 2012103826 describes both a two-chamber cell with a LiSICon membrane and a three-chamber cell with compartments separated by organic cation and anion exchange membranes, which are used to obtain lithium products.

[0022] An essential aspect of the process according to the present invention is that it is carried out in a three-chamber cell. While the simplest electrochemical cell contains only two compartments separated from each other by exactly one separator, a three-chamber cell has two separators that divide the cell into three compartments. In this specification, the two separators are referred to as an anode separator and a cathode separator. The anode separator is located on the anode side, and the cathode separator is installed on the cathode side. Therefore, the essential components of a three-chamber cell are an anode, an anode separator, a cathode separator, and a cathode. The first anode compartment is formed between the anode and the anode separator. The second cathode compartment is formed between the cathode separator and the cathode. The third compartment is created in the center between the anode and the cathode separator and is therefore called the central compartment.

[0023] In addition to the basic functional elements mentioned above, the electrochemical cell according to the present invention may additionally contain further components, such as catalysts for facilitating water electrolysis, porous transport layers (PTLs), flow fields (FFs) for transporting the electrolyte, or spacers. Furthermore, individual functional elements may also be combined to form an integrated component, for example, to form a membrane electrode assembly (MEA). It is also possible to connect multiple electrochemical cells to each other to form an aggregate, for example, by series or parallel connection. In the case of a series connection, the anode of one cell can be in direct electrical contact with the cathode of an adjacent cell, and vice versa. Direct-contact electrodes of different polarities can also be combined into bipolar plates.

[0024] In addition to the solid-state functional elements listed above, electrochemical cells also contain a liquid electrolyte necessary for the cell's operation. In this case, the electrolyte contained in the anode compartment is called the anolyte, and the electrolyte present in the cathode compartment is called the catholyte. Thus, the anolyte is in contact with the anode, and the catholyte is in contact with the cathode. The electrolyte present in the central compartment is referred to herein as the central electrolyte. It is separated from the two electrodes by two separators.

[0025] In principle, the electrochemical cell is operated according to the present invention as follows: the central electrolyte serves as the feed for the process; it contains lithium cations, which are part of the target product. The central electrolyte is supplied from the lithium-containing water to be treated. The target product is synthesized at the cathode. As a result, the target product is found in the catholyte. The anolyte acts as a sink for anionic impurities, against which the cathode separator is protected according to the present invention.

[0026] A further essential aspect of the process according to the invention is that two electrochemical processes are carried out simultaneously, namely membrane-supported electrodialysis of ions on the one hand and electrolysis of water on the other hand.

[0027] Electrodialysis, on the one hand, removes the Li cations Li present in the central electrolyte.+ In addition, the anionic impurities X present in the feed are enriched in the catholyte. n- is electrodialytically enriched in the anolyte to prevent the impurities from contacting the cathode separator. In this way, the cathode separator is free of anionic impurities X n- To make this possible, the anode separator is anion-conducting.

[0028] In parallel, in the process according to the invention, water is electrochemically split into hydrogen and oxygen (electrolysis). The hydroxide ions OH formed as intermediates during the water splitting combine with enriched Li cations in the catholyte to form the desired target product, lithium hydroxide (LiOH) or its monohydrate (LiOHOHO).

[0029] A particular advantage of the inventive combination of an anion-exchange membrane as the anode separator and an inorganic ion-selective LiSICon membrane as the cathode separator is that the anion-exchange membrane protects the LiSICon membrane from the harmful effects of anions such as sulfate, carbonate, hydroxide, chloride, and fluoride present in the feed. These anions are transferred to the anode compartment, i.e., through the organic anion-exchange membrane, so that they cannot damage the LiSICon membrane. As a result, the life of the LiSICon material used as the cathode separator is significantly improved, especially when the feed contains large amounts of anionic impurities. The latter is particularly true when lithium-containing water resulting from the recycling or production of lithium-ion batteries is used as the feed.

[0030] The process according to the invention is preferably carried out continuously. This means that at least the flowable components, i.e., the electrolyte and the current supply, are provided permanently. The provision of non-flowable components, such as the cell and the voltage source, is always permanent in any case, even if these components only need to be provided once. The individual process steps of the operation are carried out simultaneously in a continuous process.

[0031] Preferably, the process is partially carried out in a basic medium. More precisely, basic conditions should be present in the central electrolyte and in the catholyte. This means that more hydroxide ions (OH-) are present in the central electrolyte. The pH of the central electrolyte, measured using a glass electrode at a temperature of 25°C, should be between 9 and 12. If it is not within this range, the lithium-containing water used as the central electrolyte must be adjusted to a pH value before processing. The basicity of the central electrolyte is important because the LiSICon membrane material used has maximum stability under these conditions. Acidic conditions damage the material over relatively long operating times and therefore must be avoided.

[0032] The anolyte is preferably strongly acidic or at least one of the anodic reactions, the formation of protons, causes the pH of the anolyte to decrease continuously, often reaching a pH of less than 4 as measured using a glass electrode at a temperature of 25°C.

[0033] The anions present in the central electrolyte are specifically sulfate, hydrogen sulfate, carbonate, hydrogen carbonate, hydroxide, chloride, or fluoride. These anions are also regularly found in lithium-containing water and therefore in the central electrolyte. The central electrolyte has a higher concentration of the aforementioned anions than hydroxide ions.

[0034] Cationic impurities, also present 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 water. Alkali and alkaline earth metals occur particularly in naturally occurring lithium-containing brines, while metal cations are particularly found in lithium-containing water derived from the processing of spent LIBs or from waste products from LIB production. Such streams also often contain carbon compounds derived from adhesives, binders, LIB anode materials, carbon black, or plastic packaging for LIBs. These, in turn, may contain carbon-containing acids or their cations, but may also contain uncharged organic decomposition products from upstream steps in LIB recycling.

[0035] According to the present invention, the cathode separator is lithium selective; this means that it conducts Li cations better than other cations. The specific Li of the inorganic material used as the cathode separator + The conductivity σ is at least 1*10 -5 S / cm, or better at least 5*10 -5 S / cm, or even better at least 10*10 -5 S / cm, and up to 100*10 -5 S / cm. The specific ionic conductivity σ is measured by impedance spectroscopy. The temperature dependent value should be measured at 23°C. Impedance spectroscopy is performed as follows:

[0036] The measurement setup comprises two cylindrical electrodes between which the sample is placed. A weight is placed on the sample to ensure optimal contact with the electrodes and a reproducible contact pressure.

[0037] A potentiostat (Zahner-Elektrik I. Zahner-Schiller GmbH & Co. KG, Kronach-Gundelsdorf, Germany) is connected to the electrodes and controlled via Thales software (Zahner). Measurements are performed in the frequency range of 1 Hz to 4 MHz and at an amplitude of 5 mV using samples polished and sputtered onto a thin conductive gold layer.

[0038] The measurement results are presented in the form of a Nyquist plot and evaluated using analytical software (Zahner). The electrical resistance is read at the maximum value of the Nyquist plot curve. The specific ionic conductivity σ [mS / cm] is then calculated using the formula σ = (h 10 4 ) / (R π / 4 d 2 ) where h is the height of the sample (mm), R is the measured electrical resistance (Ω), and d is the diameter of the sample (mm).

[0039] Such Li selectivity and conductivity are achieved by most LiSICon materials, and therefore the cathode separator is preferably produced using, contains, or even consists entirely of LiSICon materials.

[0040] Specifically, the following LiSICon is useful:

[0041] LATP with the following stoichiometry: 1+x Al x Ti 2-x (PO4)3 In the formula, 0.1≦x≦0.3, and preferably x=0.3.

[0042] LATSP with the following stoichiometry:Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 wherein 0.1≦x≦0.3 and 0.2≦y≦0.4.

[0043] LAGTSP:Li with the following stoichiometry: 1+x+y Al x Ti 2-x Si y P 3-y O 12 *nGeO2 In the formula, 0≦x≦1, 0≦y≦1, and 0≦n≦1.

[0044] LAGTP:Li with the following stoichiometry 1.4 Al 0.4 (Ge 1-x Ti x ) 1.6 (PO4)3 where 0≦x≦1.

[0045] LAGP with the following stoichiometry:Li 1+x Al x Ge 2-x (PO4)3 where x=0 or x=0.2 or x=0.4.

[0046] LLTO:Li with the following stoichiometry: 3x La (2 / 3)-x□(1 / 3)-2x TiO3 where 0≦x≦0.16.

[0047] Doped LLZO:Li with the following stoichiometry: 6.4 La3Zr 1.4 M 0.6 O 12 wherein M is selected from the group consisting of the following elements: Ta, Sb, Nb.

[0048] Undoped LLZO with the following stoichiometry: Li7La3Zr2O 12 .

[0049] LiSICon is commercially available, for example, as LAGP Ampcera™ from MSE Supplies®, Tucson, USA.

[0050] The material from which the anode separator is produced or which it contains is an anion-conducting organic material. Such materials are often also called ionomers. This is preferably a polymer having a backbone to which at least one cationic functional group is attached. The latter is preferably a quaternized trialkylammonium salt. The backbone used is preferably polystyrene, polysulfone, poly(ether sulfone), or poly(phenylene oxide), polyvinylidene fluoride, or polytetrafluoroethylene. Very particularly preferably, the quaternized trialkylammonium salt is attached to a backbone consisting of polystyrene, polysulfone, poly(ether sulfone), or poly(phenylene oxide) via benzyl (methyl) groups. The anion-conducting polymer thus obtained is used to produce the anode separator, and the anode separator is present in the anode separator or the anode separator is entirely composed of this polymer.

[0051] Such polymers are commercially available: examples that may be mentioned are Fumasep FAPQ from Fumatech, Neosepta membranes from ASTOM, Selemion membranes from AGC, and AHA membranes from Eurodia Industrie SAS.

[0052] In a preferred embodiment of the invention, an electrochemical cell is used that has an auxiliary cathode in contact with the central electrolyte and connected to a voltage source via a third electrical lead.

[0053] Thus, an electrochemical cell equipped with an auxiliary cathode has the following characteristics:

[0054] ix) the electrochemical cell includes an auxiliary cathode; x) the auxiliary cathode is in contact with the central electrolyte; xi) The auxiliary cathode may be connected to a voltage source via a third electrical lead.

[0055] The auxiliary cathode opens up the possibility of operating the cell in particularly preferred operating modes characterized by different operating conditions.

[0056] In a first variant, the operation is divided into at least two operating states, namely: p) a production state, in which the anode and the cathode are connected to a voltage source via first and second electrical leads, respectively, and a voltage U is applied to the anode and the cathode such that a current I flows between the anode and the cathode; r) having a regeneration state in which the anode and auxiliary cathode are connected to a voltage source via the first and third electrical leads, respectively, and a voltage U is applied to the anode and auxiliary cathode such that a current I flows between the anode and auxiliary cathode.

[0057] During production, Li is separated from the central electrolyte to form LiOH; during regeneration, the cathode separator is regenerated. This involves flushing out the metal ions from the cathode separator, which cannot pass through the separator and become concentrated on its surface because the no longer-existing voltage prevents their removal. The membrane surface is thus cleansed of impurities, resulting in a significant recovery of the original permeance and permeability.

[0058] According to a preferred embodiment of the first operating variant, there is an alternation between two operating states (production / regeneration), where the regeneration phase is significantly shorter than the production phase. In particular, the duration of the production state t P is the duration of the playback state t R should continue for more than 10 or even 100 times the time. t P >f*t R and f is greater than 1, or f is greater than 10, or f is greater than 100.

[0059] It is possible not only to turn on the auxiliary cathode temporarily, but also to leave it permanently on, so that a combined production / regeneration state is implemented. In this second variant of the operating mode, the auxiliary cathode is dimensioned to be smaller in area than the actual cathode. In particular, the auxiliary cathode area A AKis A K >f * A AK and f should be chosen to be greater than 1, or greater than 10, or greater than 100. The area A K is the area of ​​the cathode. The area factor f here corresponds to the time factor f of the alternating operating mode.

[0060] In the combined production and regeneration state, the anode is connected to a voltage source via a first electrical lead, the cathode and auxiliary cathode are connected to a voltage source via a second electrical lead, and a voltage U is applied to the anode, cathode, and auxiliary cathode such that a current I flows between the anode, cathode, and auxiliary cathode.

[0061] The advantage of the combined production and regeneration state is that the means for switching the production state (switching relay) can be omitted. The disadvantage is that the ratio f cannot be changed as easily.

[0062] Also advantageous is a third operating mode having two operating states, namely a combined production and regeneration state and a pure production state. This involves alternation between a production state (p) and a combined production and regeneration state (k), with each production state (p) being t P Each combined production and regeneration state (k) is executed for a duration of t K runs for a duration of t P >g * t K and g is greater than 50, or g is greater than 500, or g is greater than 5000.

[0063] Here, the coefficient g is significantly higher than in the other two operating modes (coefficient f). This results in particularly long production runs. In the long term, this therefore increases the productivity of the electrochemical cell.

[0064] The auxiliary cathode is preferably located outside the central compartment, so that it does not occupy space within the cell and does not interfere with ion exchange. It is sufficient for the auxiliary cathode to be in contact with the central electrolyte. Surprisingly, it is sufficient to place the auxiliary cathode in the storage vessel of the central electrolyte or in the supply line of the central electrolyte.

[0065] The auxiliary electrode is preferably made of a woven material. These include linear structures such as sewing thread, weaving yarn, wire, or fiber, as well as woven fabrics such as woven fabric, weft knit, warp knit, laid scrim, felt, or nonwoven fabric. The woven material must be electrically conductive and cathodically active. This is achieved, for example, with a nickel-containing material. In the simplest case, nickel-containing stainless steel is used as the auxiliary cathode material. Pure nickel can also be used. In the simplest case, the material is used as a wire or wire mesh. Of course, it is also possible to use pure titanium or relatively high-quality electrode materials such as Ti, Pt, or Nb.

[0066] When an electrochemical cell is operated according to the present invention, electrolysis of water and electrodialysis of anions occur, according to the concept of electrochemical modeling. This is manifested through the formation of oxygen at the anode and hydrogen at the cathode, as well as the depletion of anions in the central electrolyte and the enrichment of anions in the anolyte. Furthermore, operation according to the present invention results in 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 precipitated separately within it. This all occurs simultaneously.

[0067] The operation of the electrochemical cell described herein preferably involves the electrolysis of water (HO) and anions (X n- ) Particularly preferably, the procedure also includes the synthesis of lithium hydroxide and / or lithium hydroxide monohydrate (LiOH〇HO).

[0068] The process according to the invention will now be explained in more detail on the basis of an exemplary embodiment. [Brief explanation of the drawings]

[0069] [Figure 1] The basic structure of the three-chamber cell is shown. [Figure 2] 1 shows the apparatus with a three-chamber cell in continuous operation. [Figure 3] 1 shows membrane dialysis in operation. [Figure 4] Shows water electrolysis in operation. [Figure 5p] 1 shows a three-chamber cell with a full-area auxiliary cathode in production operation. [Figure 5r] 1 shows a three-chamber cell with a full-area auxiliary cathode during regeneration operation. [Figure 6] 1 shows a three-chamber cell with a reduced auxiliary cathode in combined operation. [Figure 7] 1 shows a three-chamber cell with a perforated auxiliary cathode in combined operation. [Figure 8] 1 shows a three-chamber cell with an upstream auxiliary cathode in combined operation. [Figure 9] 1 shows the conductivity as a function of concentration of LiOH solutions (25° C.). [Figure 10] The progression of measurement points from Experiments 1a and 1b is shown. DETAILED DESCRIPTION OF THE INVENTION

[0070] FIG. 1 shows the basic structure of an electrochemical three-chamber cell operated in the process according to the invention.

[0071] The electrochemical cell 0 includes two electrodes, anode 1 and cathode 2. Two separators, anode separator 3 and cathode separator 4, are located between the anode 1 and cathode 2. The anode separator 3 is closer to the anode 1 than the cathode separator 4, which is closer to the cathode 2 than the anode separator 3. Between the electrodes 1 and 2 and the separators 3 and 4, there are three compartments 5, 6, and 7 within the electrochemical cell 0, which is also referred to as a three-chamber cell. The first compartment 5 extends between the anode 1 and anode separator 3 and is therefore referred to as the anode compartment 5. The second compartment 6 similarly extends between the cathode separator 4 and cathode 2 and is therefore referred to as the cathode compartment 6. The third compartment 7 is located in the middle of the electrochemical cell 0 and is therefore referred to as the central compartment 7. The central section 7 is bounded on one side by the anode separator 3 and on the other side by the cathode separator 4 .

[0072] The material properties of the separators 3, 4 are important: the anode separator 3 must be conductive for anions. If the anode separator 3 also has cation conductivity, the cation conductivity must be lower than the anion conductivity. This is the case for most anion-conducting materials. Suitable anion-conducting materials are organic. Examples are polymers with a backbone to which at least one cationic functional group is attached. The cationic functional group is capable of conducting anions, in particular hydroxide ions (OH - ) through the anode separator 3, but protons (H +Cations such as cations (e.g., cations of cations like cations (e.g., cations of cations like cations of cations like cations of cations of cations of cations of cations of anions) can hardly pass through the anode separator 3. The cathode separator 4 is constructed 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 of Li cations (Li+) must be greater than that of other cations such as Ca+ or Na+. This results in Li cations passing preferentially through the cathode separator 4, while other cations are transported at least more slowly or even not at all. The cathode separator 4 is substantially impermeable to anions. A suitable material with these properties is inorganic LiSICon, i.e., a specific type of (glass) ceramic that has an inherent conductivity for Li ions. At least one of the two separators 3, 4 must be electrically insulating. This is the case for inorganic LiSICon. When inorganic LiSICon is used as the cathode separator, the electrical conductivity of the organic anode separator 1 is less important. However, it is preferable to use an organic anode separator with similarly low electrical conductivity.

[0073] Specifically, the specific electron conductivity γ (electrical conductivity) of the electrically insulating separator at a temperature of 23°C is 10 -7 Less than S / cm (10 -9 S / m), or 10 -12 Less than S / m or 10 -16 The specific conductivity γ must be less than 1 / 2 S / m. Such values ​​are typical for inorganic materials. From the viewpoint of electronic conductivity, they may qualify as non-conductors. The LiSICon described has a specific conductivity of this magnitude and can therefore be considered an electrical insulator. Ionomers used as anode separators do not necessarily achieve these specific conductivities. Therefore, it is preferable to use a cathode separator as an electrical insulator. The specific electronic conductivity γ is measured by impedance spectroscopy, as described above for ionic conductivity.

[0074] The electrical conductivity of at least one of the two separators 3, 4 is important because the two electrodes 1, 2 must be electrically insulated from each other. This prevents an electrical short circuit from occurring within the electrochemical cell 0 when a voltage U is applied to the electrodes 1, 2. To apply such a voltage U, a voltage source 8 is provided that can be conductively connected to the anode 1 and the cathode 2 via a first electrical lead 9 and a second electrical lead 10, respectively. The interconnections are selected so that the positive terminal (+) of the voltage source 8 is connected to the anode 1 and the negative terminal (-) is connected to the cathode 2. Thus, 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 level of the voltage U are explained in more detail below.

[0075] In addition to the aforementioned solid components of electrochemical cell 0, the cell also includes flowable elements in the form of three electrolytes 11, 12, and 13. The first electrolyte 11 resides in the first anode compartment 5 and is therefore referred to as anolyte 11. The second electrolyte 12 resides in the second cathode compartment 6 and is similarly referred to as catholyte 12. A central electrolyte 13 is disposed in the central compartment 7. All electrolytes 11, 12, and 13 are flowable but not necessarily entirely liquid. They may be multiphase mixtures having liquid, solid, and gas phases. However, all three electrolytes contain at least liquid water. The exact compositions of the individual electrolytes 11, 12, and 13 are described below. It is important to understand that the compositions of the anolyte, catholyte, and central electrolyte are constantly changing during the ongoing operation of electrochemical cell 0.

[0076] Furthermore, the three electrolytes 11, 12, 13 may preferably be exchanged continuously so that, despite the changing composition, a steady flow process occurs through the three compartments 5, 6, 7 of the electrochemical cell 0. This is shown in Figure 2 based on a schematic setup of the device 14.

[0077] Within the device 14, the electrochemical cell 0 is divided into two circuits 15, 16: an anode circuit 15 and a cathode circuit 16. In the anode circuit 15, the anolyte 11 circulates through the anode compartment 5, and the catholyte 12 circulates through the cathode compartment 6. The central electrolyte 13 does not circulate, but rather flows once through the central compartment 7 in a straight path 17.

[0078] Alternatively, as shown in Figure 2, it is also possible to circulate the central electrolyte 13 through the central compartment 7. A large buffer vessel for the central electrolyte is required for this purpose, from which it is fed to the central compartment 7. The central electrolyte withdrawn from the central compartment 7 is recycled to the buffer vessel. During operation, the Li concentration in this central circuit continues to decrease until it reaches a "limiting concentration". The entire contents of this buffer vessel are then replaced, and the next batch is processed, with lithium separated.

[0079] With respect to the circulation of the anolyte 11 and catholyte 12 shown in FIG. 2, it should be noted that these two electrolytes 11, 12 are provided continuously, i.e., in respective circuits 15, 16. The central electrolyte 13 is also provided continuously in the device 14 shown in FIG. 2, but in a straight path 17. Alternatively, it is conceivable to not flow all three electrolytes 11, 12, 13, and thus provide them only once to each of the compartments 5, 6, 7. This is a batch process and is not preferred. A mixed continuous / batch operation is also conceivable, for example, in which the anolyte 11 and catholyte 12 are circulated continuously and the central electrolyte is introduced only once as a batch into the central compartment 7. Similarly, it is conceivable to provide only the catholyte 12 as a batch, while continuously replacing the anolyte 11 and the central electrolyte 13.

[0080] Thus, when reference is made herein to providing electrolyte, this encompasses both one-off provision (batch) and continuous provision in circuits 15, 16 or linear passages 17. Operation of the electrochemical cell according to the invention also includes mixed forms of one-off and continuous supply of electrolyte 11, 12, 13 (continuous / batch operation).

[0081] The operation of the electrochemical cell 0 according to the invention serves for the treatment of lithium-containing water. The device 14 shown in FIG. 2 is therefore a device for treating lithium-containing water. The lithium-containing water is fed to the central compartment 7 as fresh water 18. From a process-related point of view, the fresh water 18 can be considered as a feed. When the voltage U is switched on, various electrochemical processes take place in the electrochemical cell 0, which will be explained in more detail below. These processes involve the conversion of lithium present in the fresh water 18, or more precisely the lithium cations Li dissolved therein, into + This results in lithium being depleted from the fresh water 18 and enriched in the catholyte 12. During the depletion of lithium from the fresh water 18, the fresh water becomes wastewater 19, which is withdrawn from the central compartment 7. The Li concentration in the wastewater 19 is therefore lower than that in the fresh water 18. Thus, the wastewater 19 is significantly depleted 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 to the wastewater 19 due to lithium depletion can be understood in terms of the previously discussed change in the composition of the electrolyte during cell operation. The compositions of the anolyte 11 and catholyte 12 also change as a result of the electrochemical process.

[0082] Li is enriched in the catholyte 12, so that the catholyte 12 withdrawn from the cathode compartment 6 + The lithium concentration in the cathode compartment 6 is determined by the catholyte 12 - The lithium concentration in the extracted catholyte 12 + is lithium-rich, but the supplied catholyte 12 - To allow for the circulation of catholyte 12, a primary separation device 20 is incorporated into the cathode circuit 16 to separate the desired lithium compound, i.e., lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH₂O) from the lithium-rich catholyte 12. + The resulting low-lithium catholyte 12 -is left behind and recycled to the cathode compartment 6. From a process-related point of view, the separated lithium hydroxide (monohydrate) represents the target product of the process.

[0083] Similarly, the secondary separator 21 separates unwanted anions X present in the fresh water 18. n- The unwanted anions X are incorporated into the anolytic circuit 15, which serves to extract the unwanted anions X from the process. n- are, for example, sulfate or chloride or other monovalent or polyvalent negatively charged ions. These ions originate from salts dissolved in the fresh water 18. To ensure that the charge balance remains the same and to prevent the development of a concentration of anions in the central electrolyte or even undesirable anodic reactions such as forming chlorine gas (Cl), these anions are depleted from the central electrolyte 13 and enriched in the anolyte 11. Thus, these anions X n- The concentration of increases in the anolyte 11, resulting in the anolyte 11 withdrawn from the anode compartment + Anion X in n- The concentration of the anolyte 11 - Therefore, the extracted anolyte 11 + is enriched in these anions, but the supplied anolyte 11 - The exact process of how anions are enriched in the anolyte is explained below. However, the anions X in the anolyte 11 n- It is important to mention that anions may combine to form other substances, especially acids, salts or molecular gases, depending on the composition of the anolyte. Therefore, anions may also be separated as part of such compounds by the secondary separation device 21. If these compounds are harmless, the withdrawn anolyte 11 + can also be disposed of as a second wastewater, in which case the anolytic circuit 15 is omitted; the secondary separation device 21 is not required.

[0084] If a useful acid such as sulfuric acid H2SO4 or hydrochloric acid HCl is formed in the anodic reaction, the withdrawn anolyte 11 + The acid-containing anolyte 11 can also be used to treat black mass, which is a mixture formed during the decay of spent LIBs. In addition to lithium, it also contains the electrode materials Ni, Mn, Co, Al, Fe, and graphite that may be typically found in LIBs, as well as copper as a conductor material. The metals contained in black mass can be dissolved using the acids mentioned above. Therefore, the acid-containing anolyte 11 can be used to treat black mass in upstream process steps of LIB processing. + It would be possible to use

[0085] As already mentioned, in the operation according to the invention of the electrochemical cell 0, various electrochemical processes take place simultaneously. Exactly which processes take place depends on the exact composition of the electrolytes 11, 12, 13. However, in each case, membrane-supported electrodialysis of the ions present and electrolysis of water take place simultaneously. For a better understanding, we will now describe both processes separately: electrodialysis according to FIG. 3 and electrolysis according to FIG. 4.

[0086] The electrodialysis shown in FIG. 3 is carried out on the one hand by removing the Li cations Li present in the central electrolyte 13. + in the catholyte 12. Furthermore, the unwanted anions X present in the central electrolyte 13 and originating from the fresh water 18 n- 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 free of anions X n- and is protected from contamination by the products of the anodic reaction. In addition, the anions X from the central electrolyte 13 n- The depletion of α- and β-anions reduces the formation of undesired compounds of these anions with free Li cations, thereby increasing the yield of the target compound, lithium hydroxide, LiOH.

[0087] Electrodialysis, as shown in FIG. 3 and described herein, is made possible by the specific ionic conductivity of the separator material used and is driven by an applied voltage U. The polarity of voltage source 8 is selected so that cathode 2 is negatively charged and anode 1 is positively charged. According to a commonly recognized model of electrochemistry, negatively charged anions migrate toward anode 1, while positively charged cations are attracted in the opposite direction to cathode 2. To balance the charges, a current I flows from anode 1 to cathode 2 along electrical leads 9, 10.

[0088] The anode separator 3 located in the middle has inherent anion conductivity, so the anions X n- and OH - can enter the anolyte 11 from the central electrolyte 13, which typically contains more hydroxide ions OH than other anions. - Since the concentration of Li is low, it is mainly non-hydroxide ions that migrate through the anode separator 3. Vice versa, Li cations Li + enters the catholyte 12 from the central compartment 7 due to the inherent lithium ion conductivity of the cathode separator 4. Since the cathode separator 4 is made of a material that has a higher conductivity for Li cations than for other cations, other monovalent or polyvalent metal cations Me present in the freshwater 18 as impurities are not present. m+ Although the cationic impurity Me is also heading towards the cathode 2 due to its positive charge, it is barely able to exit the central electrolyte 13 in the direction of the catholyte 12. m+ Only a small portion of the cationic impurity Me passes through the cathode separator 4 and forms undesirable by-products in the catholyte 12 (not shown). m+ The majority of the cationic impurity Me remains in the central electrolyte 13 and is discharged from the process with the wastewater 19. Due to the specific cation selectivity of the cathode separator 4 in favor of lithium, the cationic impurity Me m+ Since little electrical energy is wasted to transport LiOH / LiOHOH2O from the central compartment 7 to the cathode compartment 6, the purity of the target product LiOH / LiOHOH2O is increased and the current yield of the process is improved.

[0089] The electrochemical splitting (electrolysis) of water HO into hydrogen H and oxygen O, as shown in Figure 4, is carried out in the process according to the invention in parallel with the electrodialysis shown in Figure 3. More precisely, two water splitting operations are carried out in parallel here: basic water splitting according to equation (1) in the catholyte and acidic water splitting according to equation (2) in the anolyte.

[0090] 2H2O+2e - →H2+2OH - (1) Reduction / Cathode Reaction H2O → 1 / 2 O2 + 2H + +2e - (2) Oxidation / anodic reaction In this process, the electrochemical cell 0 is filled with a basic aqueous electrolyte and a voltage is applied between the anode 1 and the cathode 2. The basic electrolytes in this case are the central electrolyte 13 and the catholyte 12. It must therefore be ensured that the central electrolyte 13 and the catholyte 12 are provided in the alkaline range. Since the starting materials used as electrolytes can be acidic depending on their origin, these electrolytes must also be basified. Correspondingly, alkaline lithium-containing water is supplied to 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, which come from LiOH, are then released. - causes alkalinity in the catholyte 12. The minimum amount of LiOH is ensured by operating the primary separation device 20 so that LiOH is not completely removed from the cathode circuit 17. To start the process, an initial dose of LiOH is added to the catholyte 12.

[0091] In the cathode side of the three-chamber cell, i.e., the central electrolyte 13 and catholyte 12, water HO is converted into hydrogen H and hydroxide ions OH - The anode separator 3 is mainly decomposed into anions X n-to the anode compartment 5, where they can be oxidized to form the corresponding compound, such as chlorine in the case of chloride ions. In addition, at the anode 1, water HO is oxidized, producing protons H + and oxygen O2 is formed (Equation 2). This results in the formation of oxygen O2 on the anode side and hydrogen H2 on the cathode side. At the anode, the corresponding acid of the anion, e.g., hydrochloric acid or sulfuric acid in their respective dissociated forms, is also formed from the protons.

[0092] Furthermore, hydroxide ions OH in the catholyte 12 - The presence of Li cations Li present in the catholyte + This results in the formation of lithium hydroxide, LiOH (Equation 3).

[0093] Li + +OH - →LiOH (3) Synthesis of LiOH LiOH is initially in dissolved form, i.e., Li + Cation and hydroxide ion OH - As soon as the concentrations of these ions reach their saturation limit, solid lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH≈H₂O) precipitates and becomes the target product of the process.

[0094] The target products are obtained from the catholyte 12 by a primary separator 20. Hydrogen, H2, and oxygen, O2, are by-products. Because they are in gaseous form, the two by-products can be easily vented from the catholyte 12 and anolyte 11 and thus collected and used. Separators for the by-products, hydrogen, H2, or oxygen, O2, are not absolutely necessary, but are contemplated.

[0095] To understand the entire process, let us consider the Li cations Li that form LiOH in the catholyte 12. + It is important to realize that the Li cations Li migrated in the catholyte 12 only via membrane-supported electrodialysis (Fig. 3). + The hydroxide ion OH- is instead formed in the catholyte 12, i.e., by a cathodic reaction in which water splits according to equation 1 (FIG. 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.

[0096] In a particular embodiment of operation according to the invention, the electrochemical cell is operated with an auxiliary cathode. Figures 5p, 5r, 6, 7, and 8 each show a three-chamber cell configuration with an auxiliary cathode. In Figures 5p and 5r, the cathode is a full-area auxiliary cathode 221, and in each of Figures 6, 7, and 8, it is a reduced-area auxiliary cathode 222. In all cases, the auxiliary cathode 221 / 222 is in contact with the central electrolyte 13.

[0097] The auxiliary cathode 221 shown in Figures 5p and 5r has the same area as the two other electrodes 1, 2. The auxiliary cathode 221 can be connected to the negative pole of the voltage source 8 via a third electrical lead 23 (Figure 5r). The connection between the negative pole of the voltage source 8 and the cathode 2 via the second electrical lead 10 is then interrupted, and a current I flows between the anode and the auxiliary cathode 221. In this operating state shown in Figure 5r, the electrochemical cell 0 is in a regeneration operation. In the regeneration operation, hydroxide ions OH - These ions are transported to the proton H via the formation of water molecules HO. + The pH in the central electrolyte 13 is thus increased in order to operate in the desired basic range of pH 9 to 10.5. A regeneration operation is performed whenever the pH drops to an undesirably acidic value below 8. The pH is adjusted very quickly by the auxiliary electrode 221: the regeneration operation only needs to take about 1 / 100 of the time of the production operation. Therefore, there is no need to add basic compounds to the central electrolyte 13.

[0098] After regeneration is complete (FIG. 5r), there is a switch back to production operation (FIG. 5p). In this case, the negative pole of voltage source 8 is connected to cathode 2 via second electrical lead 10. Current I flows between anode 1 and cathode 2. Auxiliary cathode 221 is de-energized.

[0099] Instead of alternating between production and regeneration, it is also possible to continuously increase the pH using a reduced auxiliary electrode 222, also in contact with the central electrolyte 13 (FIG. 6). The area of ​​the auxiliary electrode 222 is smaller than that of the other two electrodes 1 and 2, for example, about 1 / 100th of that of the other two electrodes 1 and 2. The auxiliary electrode 222 is permanently connected to the negative pole of the voltage source 8 via a second electrical lead 10; the second electrical lead 10 is correspondingly branched. Thus, a current I permanently flows between the anode 2 and the auxiliary cathode 222 and the cathode 2. Due to the smaller area of ​​the auxiliary cathode 222, a small amount of hydroxide ions OH, sufficient to keep the pH constant within the desired basic range of 9 to 10.5, are released. - is formed in the central electrolyte 13. In that case, no basic substance needs to be added. Permanent operation with a reduced auxiliary cathode 222 can be considered a combined regeneration / production state.

[0100] A particular advantage of the reduced auxiliary cathode 222 is that it can also be arranged outside the electrochemical cell 0, for example in the supply line of the central electrolyte 13, thereby saving space in the central compartment 7. A corresponding embodiment is shown in FIG.

[0101] Additionally, it is also possible to alternate the reduced auxiliary cathode 222 between a pure production state and a combined regeneration / production state. This is a mixture of the operating states shown in Figures 5p, 5r, and 6. This allows for more flexibility in determining the area and cycle time of the reduced auxiliary cathode 222. This mixed operation is not depicted.

[0102] 7 shows a further embodiment of an electrochemical cell 100 having a reduced auxiliary cathode 222. The reduction in the auxiliary cathode 222 is achieved by using a porous fabric, such as a mesh cloth, as the auxiliary cathode. The porosity reduces the surface area A of the auxiliary cathode 222. AK is the surface area A of cathode 2 K This is not immediately apparent in Figure 7 because the fabric-assisted cathode 222 extends through the entire central section 7. The advantage of using a fabric-assisted cathode is that it has better ion permeability than a full-area auxiliary cathode, and therefore less interference with ion exchange.

[0103] 8 also shows a further embodiment of the electrochemical cell 0 with a reduced auxiliary cathode 222. Here, the auxiliary cathode 222 is arranged outside the central compartment 7, more precisely in the supply line 24 for the central electrolyte 13. The central electrolyte 13 flows in a straight passage 17 through the supply line 24 to the central compartment 7 and exits it again (not shown). The advantage of arranging the auxiliary cathode 222 in the supply line 24 is that ions can move in the central compartment 7 without being hindered by the auxiliary cathode 222. Contact between the auxiliary cathode 222 and the central electrolyte 13 in the supply line 24 is sufficient. [Example]

[0104] The advantages achieved by the process regime according to the present invention will now be demonstrated using experimental data.

[0105] Experimental setup The electrochemical cell 0 used to conduct the experiments is shown in Figure 8. It contains three compartments 5, 6, and 7. Compartments 7 and 6 are separated by an ion exchange membrane known as the cathode separator 4. Compartments 5 and 7 are separated from each other by a membrane known as the anode separator 3. The anode 1 is located in the first compartment 5. The central compartment 7 contains an auxiliary cathode 222 in the supply line for the central electrolyte 13. The cathode 2 is located in the third compartment 6. The first compartment 5 can also be referred to as the anode compartment, and the third compartment 6 can also be referred to as the cathode compartment. The middle compartment 7 can also be referred to as the central compartment 7.

[0106] A first electrical lead 9 connects anode 1 to voltage source 8. A second electrical lead 10 connects cathode 2 to voltage source 8. A branch of second electrical lead 10 connects voltage source 8 to auxiliary cathode 222. The polarity of voltage source 8 is selected so that the positive terminal of voltage source 8 is connected to anode 1 and the negative terminal of voltage source 8 is connected to cathode 2 and auxiliary cathode 222.

[0107] A current I flows through electrical leads 9 and 10 via a voltage source 8. Because the ion exchange membrane 4 is electrically insulating, there is no electrical short circuit between the two electrodes 1 and 2 through the ion exchange membrane 4.

[0108] The ion exchange membrane 4 is a flat sheet membrane made entirely from LiSICon material. The other membrane 3 is also a flat sheet membrane; it is made from an anion conducting polymer such as AHA membrane, Eurodia Industrie SAS, or Neosepta membrane from ASTOM.

[0109] The auxiliary cathode 222 is a wire made of titanium, platinum, or stainless steel. The cathode 2 is also a flat metal plate made of titanium or nickel. In the simplest case, a stainless steel plate is used as the cathode. The anode 1, cathode 2, and the two membranes 3, 4 have the same shape. They can be rectangular or circular. The auxiliary cathode 222 is a wire whose area protruding into the supply line 24 for the central electrolyte 13 occupies 2% of the active area A of the cathode 2. This is not shown to scale in the side view of Figure 8. Instead of a metal plate, it is also possible to use expanded metal, grids, or meshes of a certain material as electrodes.

[0110] The electrochemical cell 0 has an active area A corresponding to the surface area of ​​the two membranes 3, 4, the anode 1 and the cathode 2. As mentioned above, the auxiliary cathode 222 is smaller; its active surface area is only 2 / 100*A.

[0111] During operation, compartments 5 and 7 are filled with feed 13. Compartments 5 and 7 can have the same feed 13, or a different solution 11 than 13 is present in one of the chambers. Feed 13 is an aqueous solution containing Li+ cations. From an electrochemical point of view, feed 13 can be considered an anolyte.

[0112] Feed 13 may be Li leachate from natural deposits or a material stream resulting from the processing of spent LIBs. 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 low Li concentration and must first be concentrated before use in the process. Feed 13 also contains anions such as sulfate or chloride. Feed 13 also contains impurities. The anions and impurities are not shown in FIG. 1. The main component of feed 13 is water.

[0113] The cathode compartment 6 contains a poor working medium 12 - It is filled with poor working medium 12 -is water with a low concentration of Li+ cations. - From an electrochemical point of view, the lean working medium 12 can be considered a catholyte.

[0114] In addition, a voltage U obtained from a voltage source 8 is supplied to the electrochemical cell 0. This has the following effect:

[0115] First, water electrolysis is carried out, 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 pass through the LiSICon membrane 4 and are absorbed by the Li-SiCon membrane 4 present in the cathode compartment 6. + At anode 1, oxygen and H + In the central compartment 7 (containing the auxiliary cathode 222), OH − anions are formed which keep the pH in compartment 7 stable.

[0116] The formation of LiOH in the cathode compartment 6 is sustained by the migration of Li+ cations from the feed 13 in the direction of the cathode 2, driven by the voltage U. They cross the LiSICon membrane 4 due to the membrane's conductivity for Li ions and accumulate in the working medium 12 (membrane electrolysis). This causes the rich working medium 12 withdrawn from the cathode compartment 6 to accumulate. + is formed. Wealth working medium 12 + The Li+ ion concentration in the poor working medium 12 - Higher than average.

[0117] Therefore, in electrochemical cell 0, water electrolysis, Li + The membrane electrolysis and synthesis of LiOH proceed simultaneously.

[0118] Thus, the simultaneous operation of Li+ membrane electrolysis and water electrolysis in an electrochemical cell leads to the direct formation of lithium hydroxide LiOH and molecular hydrogen H2. The hydrogen is at least partially dissolved; it may also be present in the form of gas bubbles. Depending on the temperature and the presence of crystallization species, LiOH can be already present in the cathode compartment 6 or in the rich working medium 12. + It settles immediately after being withdrawn.

[0119] Feed 13 is depleted in Li+ as a result of membrane electrolysis, producing wastewater 19.

[0120] Experimental procedure To perform electrolysis, electrolyte is first filled into the two anolyte and catholyte containers and the supply hoses are disconnected. The electrolyte container that supplies the part of the cell directly facing the membrane is hereafter referred to as the center compartment. The electrolysis cell is then assembled in the next step. During assembly, the membrane should be prevented from drying out by performing the procedure quickly. Once the electrolysis cell is assembled, it is connected to the anolyte and catholyte containers and the intermediate chamber. Here, care is taken to ensure that the inlet and outlet flows are connected on the same side in each case. The supply lines to the cell can then be carefully opened; the supply hoses for the catholyte and intermediate chambers should now be opened simultaneously.

[0121] The anodes and cathodes used were in each case circular disks with a diameter of 19.5 mm and a thickness of 1 mm. The material was in each case IrTi mixed oxide (12 g Ir / m) from Metakem GmbH, 61250 Usingen, Germany. 2 The titanium expanded metal plate was coated on both sides with titanium carbide (1 AF D 1.5 mm).

[0122] The auxiliary cathode used was a 2 mm thick wire protruding approximately 3 mm into the feed line of the central compartment: titanium wire coated with 12 g Ir / m2 of IrTi mixed oxide from Metakem GmbH (61250 Usingen, Germany).

[0123] The anode and cathode are connected to a voltage source, a Keithley 2400 potentiostat manufactured by Tektronix UK Ltd. (Berkshire, UK). An auxiliary cathode is connected to the cathode.

[0124] The sampled membranes were also circular disks with a diameter of about 25 mm. The membrane thickness was about 1 mm. The sampled LiSICon membrane material was Ampcera™ LISICON LAGP manufactured by MSE Supplies®, Tucson, USA. The sampled organic anion exchange membrane material was AHA membrane, Eurodia Industrie SAS.

[0125] The electrolysis and corresponding storage vessels are blanketed with nitrogen throughout the run to prevent the formation of lithium carbonate. Each cell has separate anolyte and catholyte containers and a separate intermediate chamber. Each vessel is filled with approximately 1 kg of liquid. The exact mass is determined by reweighing. In all experiments, the catholyte at the start of the run was always a 5 mmol / L LiOH solution (equivalent to 120 ppm LiOH by weight). The electrolytes in the anolyte and intermediate chambers are lithium salt solutions containing different lithium salts at different concentrations. The anolyte container and intermediate chamber may contain different solutions from each other. The starting and exact concentrations also change over the course of the experiment, and are therefore also indicated in the experimental diagrams.

[0126] The experiment begins by switching on the pump and applying the desired voltage. During the experiment, the voltage is applied cyclically. This is controlled by a correspondingly programmed Siemens LOGO!230 RC control unit (Siemens).

[0127] The maximum flow rate is 900 ml / min, determined by a Sonotec SONOFLOW CO.55 / 060 V2.0 ultrasonic flow sensor. Samples are collected every 30 minutes, or at longer intervals if agreed. The first 3 ml of sample collected is discarded. After each sample, the respective current is recorded, and the pH and conductivity are determined from the sample. The sample is then returned to a suitable container, keeping the volume substantially constant.

[0128] At the end of the experiment, the vessel is emptied and all leads and membranes are rinsed with demineralized water. The cell is disassembled, the membrane is photographed, and SEM images of the catholyte and anolyte sides are recorded to document any damage or changes to the membrane. The ion-exchange membrane is checked under a microscope for any changes. The side facing the intermediate chamber and the anolyte side are also checked.

[0129] Membrane performance is expressed as permeability (g Li*mm / m 2 *h) and permeance (g Li / m 2 *h). Permeance indicates how much mass of lithium is transported through the membrane per unit membrane area and unit time. Permeance also takes membrane thickness into account, and therefore allows different membrane types with different thicknesses to be compared with each other. Very thin membranes can tolerate very high permeance, but if concentration polarization effects are present in the membrane cell, permeance will give an inaccurate picture, so both are necessary for a comprehensive description of performance. When membrane thickness is taken into account, transport is no longer limited by the membrane and therefore no longer serves a useful purpose.

[0130] All measurements shown in the examples are subject to a measurement error of approximately ±10% due to imprecision in positioning the electrodes relative to each other, in determining the thickness of the film sample, and in determining the concentration by conductivity measurements.

[0131] The concentration was determined in-line by measuring the conductivity. In the experimental results, the conductivity was converted to concentration via the calibration curve shown in Figure 9.

[0132] FIG. 9 shows the conductivity as a function of concentration of LiOH solution (25° C.).

[0133] However, this means that at concentrations above approximately 10% LiOH, it is nearly impossible to accurately monitor the actual concentration by conductivity measurements.

[0134] The intra-experimental variability can be seen in Table 1.

[0135] Table 1: Experimental overview Apart from these, the following experimental conditions were constant: Cycle time: 50 seconds current on - 10 seconds current off Catholyte concentration: 5 mmol / l LiOH-LiOH*H2O, 98%, Thermo Fisher Scientific Voltage: 6V (between the anode and cathode, and between the auxiliary cathode and anode) Membrane: Ampcera® LISCON LAGP

[0136] [Table 1] Test 1a: The experiment was set up as previously described (experimental procedure and details are listed in Table 1).

[0137] An auxiliary cathode in the form of a stainless steel wire mesh (grade 1.4401) with a mesh width of 200 μm was placed in the central compartment, with wires allowing electrical contact from the outside (see Figure 7).

[0138] While starting the pumps for the three circuits, a cyclically applied DC voltage of 6 V was simultaneously applied between the anode and cathode. Over the course of the experiment, the decrease in pH in the middle chamber could be monitored by taking periodic samples. After approximately 24 hours, the pH had decreased from 9 to a value of 7.3. After 24 hours, the pH of the anolyte was 2.5, and the current was approximately 30 mA.

[0139] After these 24 hours, the auxiliary cathode was operated exclusively at a voltage of 6 V for a total of 5 minutes, resulting in a current of up to 200 mA during this period. The pH of the middle chamber rose above 10.

[0140] Test 1b: When the cell is further operated under the same settings as in Experiment 1a (Experiment 1b), again without applying a voltage to the auxiliary cathode, the current through the cell increases to over 70 mA, which is also associated with a correspondingly larger permeance.

[0141] The progression of measurement points from experiments 1a and 1b is shown in the diagram of FIG.

[0142] Figure 10: Diagram of Experiments 1a and 1b.

[0143] For a simplified overview, all results / values ​​are summarized in Table 2.

[0144] Table 2: Measurements from the experiment Test 1c: Next, we use the same measurement setup with the only difference that the auxiliary cathode was designed not as a wire mesh but as a wire in the feed line to the intermediate chamber with a surface area of ​​2% of the electrode and membrane area (Figure 8). The results are also summarized in Table 2.

[0145] Experiments 2-6: These experiments were carried out with 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 the anode was also 6 V. Point measurements of the current at the auxiliary cathode gave values ​​between 1% and 20% of the current flowing between the anode and cathode. All results, after 50 hours of cell operation in each case, are listed in Table 2.

[0146] [Table 2] Comparative experiment: For comparison, a cell without an anion exchange membrane was constructed, as outlined in Table 3.

[0147] Table 3: Summary of the comparative experiment

[0148] [Table 3] The measurements of the comparative experiments are recorded in Table 4.

[0149] Table 4: Measurements of the comparative experiment

[0150] [Table 4] Test 7: As a comparative experiment, the setup used in experiments 1-6 was modified so that the anion exchange membrane between the central compartment and the anode compartment was omitted, resulting in a cell with only two separate compartments: exactly one anode compartment and exactly one cathode compartment. No auxiliary cathode was used.

[0151] As the pH in the anode compartment decreases over the course of the experiment due to proton formation at the anode, there is continuous damage to the ceramic LiSICon membrane from a pH below 7. This means that the results specified in Table 4 are not a constant achieved value, but rather continue to decrease further over the duration of the experiment, particularly after 5-50 hours. As an example, data after approximately 24 hours is shown.

[0152] Test 8: Again, this was similar to experiment 7, except that lithium sulfate solution was used in the experiment.

[0153] Conclusion: The experiments demonstrate that, after the same operating time, higher permeance and permeability are maintained by the operation of a three-chamber cell (Experiments 1a-7) with an anion exchange membrane as the anode separator compared to a two-chamber cell (Experiments 8 and 9). This means that in treating lithium-containing water, the same cathode separator will experience greater wear when installed in a two-chamber cell than in a three-chamber cell. As a result, higher efficiency can be expected from the operation of a three-chamber cell in accordance with the present invention over long periods of use.

[0154] In all experiments, the content of foreign cations in the catholyte was below the detection limit. The purity of the target product was not adversely affected by cathodic impurities present in the central electrolyte, such as sodium.

[0155] Furthermore, the cells operated according to the invention (Experiments 1a-7) pass higher currents than those operated without the invention (Experiments 8 and 9). Therefore, the productivity per unit area is better. As a result, devices operated in this way can be dimensioned to be smaller for the same production output.

[0156] A comparison of operation with an auxiliary cathode configured as a wire mesh (Experiment 1) and one where the auxiliary cathode is implemented in the supply line (Experiment 2ff) shows that the implementation of the auxiliary cathode in the supply line leads to very good permeance during ongoing operation, without the need to periodically switch between various operating states. This simplification of cell design and performance indicates that the placement of the auxiliary cathode in the supply line is a particularly preferred embodiment. [Explanation of symbols]

[0157] 0 Electrochemical cell (3-chamber cell) 1 anode 2 cathodes 3 Anode separator 4. Cathode separator 5 Anode Compartment 6 Cathode Compartment 7 Central Section 8 Voltage Source 9 First Electrical Lead 10 Second Electrical Lead 11 Anolyte 11 - Anolyte supplied (poor anions) 11 + Withdrawn anolyte (anion-rich) 12 Catholyte 12 - Supplied catholyte (low in lithium) 12 + Withdrawn catholyte (rich in lithium) 13 Central Electrolytes 14 Equipment 15 Anode Circuit 16 Cathode Circuit 17 straight passage 18 Freshwater (contains lithium) 19 Wastewater (low in lithium) 20 Primary separation device 21 Secondary separation device 221 Full-area auxiliary cathode 222 Reduced auxiliary cathode 23 Third Electrical Lead 24 Central electrolyte supply line X n- anions Me m+ Cationic Impurities OH - Hydroxide ion H + proton Li + Lithium-cation LiOH Lithium hydroxide H2 Hydrogen O2 oxygen H2O Water

Claims

1. The following non-time-series steps: a) providing at least said electrochemical cell having at least the following characteristics: i) the electrochemical cell includes an anode and a cathode; ii) the electrochemical cell includes a cathode separator and an anode separator; iii) the electrochemical cell comprises an anode compartment, a central compartment, and a cathode compartment; iv) the cathode separator separates the central compartment from the cathode compartment; v) the anode separator separates the central compartment from the anode compartment; vi) the cathode separator comprises an inorganic material having conductivity for anions and conductivity for cations, the conductivity for cations being greater than the conductivity for anions, and Li cations (Li ＋ ) is the conductivity to cationic impurities (Me ｍ＋ ) greater than said conductivity to vii) The anode separator is a catalyst containing an anion (X ｎ－ , O.H. － ) and cations, and ｎ－ , O.H. － ) is greater than the conductivity to cations; viii) the inorganic material and / or the organic material are electrically insulating; b) providing a catholyte in the cathode compartment, the catholyte comprising at least water (H ２ O), Li cation (Li ＋ ), hydroxide ions (OH － ) the steps of: c) providing a central electrolyte in the central compartment, the central electrolyte comprising at least water (H ２ O), Li cation (Li ＋ ), anion (X ｎ－ ) and cationic impurities (Me ｍ＋ ) the steps of: d) providing an anolyte in the anode compartment, the anolyte comprising at least water (H ２ O) and an anion (X ｎ－ ) the steps of: e) providing at least one voltage source connectable to said anode via a first electrical lead and to said cathode via a second electrical lead; f) applying a voltage U obtained from the voltage source to the electrochemical cell so that a current I flows between the anode and the cathode; 1. A process for operating an electrochemical cell, comprising:

2. 10. The process of claim 1, wherein at least some of the steps are performed simultaneously and sequentially.

3. The central electrolyte is hydroxide ions (OH － 3. The process of claim 1 or 2, further comprising: a) a central electrolyte having a pH of between 9 and 12 as measured using a glass electrode at a temperature of 25°C.

4. The anion (X ｎ－ 4. The process according to claim 1, wherein the cations of the cations of the formula (I) are selected from the group consisting of sulfates, hydrogen sulfates, carbonates, hydrogen carbonates, hydroxides, chlorides and fluorides.

5. The central electrolyte is a hydroxide ion (OH － ) at a concentration greater than that of the anion (X ｎ－ 5. The process of claim 4, wherein

6. The cationic impurities (Me ｍ＋ 6. The process according to claim 1, wherein Zn is a cation of an element selected from the group consisting of B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu and C.

7. The inorganic material present in the cathode separator has a dielectric constant of at least 1*10 at a temperature of 23° C. as measured by the “impedance spectroscopy” method described herein. －５ S / cm or at least 5*10 －５ S / cm or at least 10*10 －５ S / cm and up to 100*10 －５ 7. The process of any one of claims 1 to 6, having a specific conductivity σ of the Li cations of 0.5 S / cm.

8. The inorganic material is a compound (LATP) with the following stoichiometry: Li １＋ｘ Al ｘ Today ２－ｘ (PO ４ ) ３ [Wherein, 0.1≦x≦0.3, preferably x=0.3] 8. The process according to claim 7, wherein

9. The inorganic material is a compound of the following stoichiometry (LATSP): Li １＋ｘ＋ｙ Al ｘ Ti ２－ｘ Si ｙ P ３－ｙ O １２ [Wherein, 0.1≦x≦0.3 and 0.2≦y≦0.4] 8. The process according to claim 7, wherein

10. The inorganic material is a compound of the following stoichiometry (LAGTSP): Li １＋ｘ＋ｙ Al ｘ Ti ２－ｘ ｳi ｙ P ３－ｙ 9 １２ n1eｯ ２ [Wherein, 0≦x≦1, 0≦y≦1, and 0≦n≦1] 8. The process according to claim 7, wherein

11. The inorganic material is a compound (LAGTP) of the following stoichiometry: Li １．４ Al ０．４ (Ge) １－ｘ Ti ｘ ) １．６ (PO) ４ ) ３ [Wherein, 0≦x≦1] 8. The process according to claim 7, wherein

12. The inorganic material is a compound of the following stoichiometry (LAGP): Li １＋ｘ Al ｘ Ge ２－ｘ (PO) ４ ) ３ [Wherein, x=0 or x=0.2 or x=0.4] 8. The process according to claim 7, wherein

13. The inorganic material is a compound of the following stoichiometry (LLTO): Li ３ｘ The （２／３）－ｘ□（１／３）－２ｘ TO ３ [Wherein, 0≦x≦0.16] 8. The process according to claim 7, wherein

14. The inorganic material is a compound (doped LLZO) of the following stoichiometry: Li ６．４ La ３ Z １．４ M ０．６ O １２ wherein M is selected from the group consisting of the following elements: Ta, Sb, Nb.

8. The process according to claim 7, wherein

15. The inorganic material is a compound (LLZO) of the following stoichiometry: Li ７ The ３ Zhr ２ O １２ 8. The process according to claim 7, wherein

16. 16. The process according to any one of claims 1 to 15, characterized in that the organic material present in the anode separator is a polymer having a backbone with at least one cationic functional group attached thereto.

17. 17. The process of claim 16, wherein the cationic functional group is a quaternized trialkylammonium salt.

18. 18. The process of claim 16 or 17, characterized in that the backbone is selected from the group consisting of polystyrene, polysulfone, poly(ether sulfone) or poly(phenylene oxide), polyvinylidene fluoride, or polytetrafluoroethylene.

19. 17. The process of claim 16, wherein the cationic functional group is a quaternized trialkylammonium salt, the backbone is selected from the group consisting of polystyrene, polysulfone, poly(ether sulfone) or poly(phenylene oxide), and the quaternized trialkylammonium salt is attached to the backbone through a benzyl(methyl) group.

20. Features include: ix) the electrochemical cell includes an auxiliary cathode; x) the auxiliary cathode is in contact with the central electrolyte; xi) the auxiliary cathode may be connected to the voltage source via a third electrical lead; 20. The process according to any one of claims 1 to 19, characterized in that an electrochemical cell is provided, further comprising:

21. The process has two operational states: p) a production state, in which the anode and the cathode are connected to the voltage source via the first and second electrical leads, respectively, and the voltage U is applied to the anode and the cathode such that the current I flows between the anode and the cathode; r) a regenerative state in which the anode and the auxiliary cathode are connected to the voltage source via the first and third electrical leads, respectively, and the voltage U is applied to the anode and the auxiliary cathode such that the current I flows between the anode and the auxiliary cathode; 21. The process of claim 20, comprising:

22. Each production state is t Ｐ The playback state is executed for a duration of t Ｒ characterized by alternation between a production state (p) and a regeneration state (r), carried out for a duration of t Ｐ >f ＊ t Ｒ and f is greater than 1, or f is greater than 10, or f is greater than 100; 22. The process of claim 21.

23. Features include: xii) The cathode is a cathode region A Ｋ having xiii) The auxiliary cathode is an auxiliary cathode region A ＡＫ having and wherein the process is carried out in one operating state, namely: k) a combined production and regeneration state, in which the anode is connected to the voltage source via the first electrical lead, the cathode and the auxiliary cathode are connected to the voltage source via the second electrical lead, and the voltage U is applied to the anode, the cathode and the auxiliary cathode such that the current I flows between the anode, the cathode and the auxiliary cathode; The cathode region A Ｋ and the auxiliary cathode region A ＡＫ teeth, A Ｋ >f ＊ A ＡＫ is selected to be f is greater than 1, or f is greater than 10, or f is greater than 100; 21. The process of claim 20.

24. The process has two operational states: k) said combined production and regeneration state; p) a production state in which the anode and the cathode are connected to the voltage source via the first and second electrical leads, respectively, and the voltage U is applied to the anode and the cathode such that the current I flows between the anode and the cathode; There is an alternation between the production state (p) and the combined production and regeneration state (k), and each production state (p) is t Ｐ , and each combined production and regeneration state (k) is executed for a period of t Ｋ It runs for a period of t Ｐ >g ＊ t Ｋ and g is greater than 50, or g is greater than 500, or g is greater than 5000; 24. The process of claim 23.

25. The process according to any one of claims 20 to 24, characterized in that the auxiliary electrode is arranged outside the central section and / or that the auxiliary electrode consists of a woven material.

26. The operation is carried out by adding water (H ２ O) and anion (X ｎ－ 26. The process according to claim 1, comprising the electrodialysis of

27. The operation may be carried out by using lithium hydroxide and / or lithium hydroxide monohydrate (LiOH). ２ 27. The process of claim 26, comprising the synthesis of

Images