Electrochemical production of hydrogen and lithium hydroxide under defined flow conditions.

Abstract

The problem addressed by the present invention is to produce Li using an electrochemical cell with a LiSICon membrane that can be operated economically on an industrial scale. + The objective of this study is to identify a process for the electrochemical production of LiOH from contained water. In particular, the process must have good energy efficiency and achieve high membrane life, even when the feed used contains impurities harmful to the LiSICon material. This problem is solved by establishing flow conditions in the anode compartment of the electrochemical cell such that the anolyte flows along the membrane at a specific minimum cross-flow velocity.

Description

[Technical Field]

[0001] Lithium (Li) is obviously required for the production of lithium-ion batteries (LIBs). Due to its high reactivity, lithium always exists naturally in a bound form, rather than as a pure substance. The starting material used in the production of LIBs is generally lithium in the form of lithium hydroxide (LiOH) or lithium carbonate (Li2CO3).

[0002] In most natural deposits, Li exists in the form of lithium oxide (LiO) or salts such as lithium sulfate (LiSO) or lithium chloride (LiCl). Lithium oxide is a component of ores such as pegmatites, while lithium sulfate and chloride exist in dissolved form in the leachate of Li salt lakes. During the mining process, the extracted lithium compound is converted to lithium carbonate (LiCO) in certain cases. In a further process step, lithium carbonate can be converted to lithium hydroxide by reaction with quicklime or calcium hydroxide. [Background technology]

[0003] The extraction of Li and its conversion to LiOH is described below: 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 Although abundant lithium deposits are known, the production of LiOH from their lithium compounds is very energy intensive, generates large amounts of wastewater, and is a strategic necessity independent of the deposit owners.

[0004] One solution to this problem could be to reprocess materials from spent LIBs so that the lithium contained within them can be reused as a raw material for new batteries.

[0005] Recycling processes for LIBs have been developed to industrial maturity in the past, but most of them have focused on the metals Fe, Ni, Mn, Co, Mg, and Al present in the batteries. The alkali metal Li has not generally been recovered, as its high reactivity makes it difficult to separate from scrap batteries and it is available in sufficient quantities and at low cost from natural deposits. Extracting Li from used LIBs over long periods of time simply seemed uneconomical.

[0006] However, there is currently growing social and economic pressure to recover lithium from used LIBs. To make this idea a reality, it is necessary to supply LIB producers with recycled lithium at an acceptable quality so that the manufacturing process for LIBs from recycled lithium is no different from that using mined virgin lithium. It goes without saying that there must be no adverse effects on battery quality. Therefore, recycled lithium, especially in the form of LiOH, must meet very strict specifications regarding purity. Furthermore, the process for recovering lithium from old batteries must be as energy-efficient as possible. The process should also use as little water as possible.

[0007] Known processes for recovering lithium from old batteries are collated below: 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. The technology referred to simply as "LISM" in the above review paper is the electrolysis of Li-containing water using what are known as LiSICon membranes.

[0008] 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 of Li comes from the crystalline structure of the material. Li ions, simply put, "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 given 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 for Li ions means that LiSICon materials can be used as membranes to separate Li from Li-containing mixtures. Li must be present in the mixture in ionic form, for example, as a Li salt dissolved in water. The driving force required to force the Li ions through the LiSICon membrane is a voltage. For this purpose, an electrochemical cell is constructed containing two electrodes and a LiSICon membrane that divides the cell into two compartments. Each compartment contains an electrode. The compartments are called anodes or cathodes, depending on the polarity of the electrodes present in each compartment. A voltage is applied to the electrodes, and the anion compartment is filled with Li-containing water as the anolyte. The cathode compartment is filled with water as the catholyte. The membrane allows Li cations to pass to the cathode. Thus, the water in the cathode compartment (catholyte) is enriched with Li, while the water on the anode side (anolyte) is depleted of Li. This process is called membrane electrolysis.

[0009] Membrane electrolysis processes for the extraction of lithium using LiSICon membranes have already been described in the prior art.

[0010] For example, Zhen Li et al. describe a process that uses weakly lithium-containing water from the Red Sea as a raw material: Zhen Li et al.:Continuous electrical pumping membrane process for seawater lithium mining.Energy Environ.Sci.,2021,14,3152 DOI:10.1039 / d1ee00354b The Zhen Li research group uses LLTO as a membrane. The target product to be separated is lithium phosphate (Li3PO4), which is suitable for producing lithium iron phosphate (LFP) batteries. LIBs with different cathode materials, such as nickel manganese cobalt (NMC) or lithium manganese oxide (NMO), cannot be directly produced using it.

[0011] Yang et al. have attempted to directly extract metallic lithium from seawater using solar power, LAGP membranes and copper foils.

[0012] Sixie Yang et al.: Lithium Metal Extraction from Seawater.Joule,volume 2,issue 9,2018,pages 1648-1651,DOI 10.1016 / j.joule.2018.07.006. US Patent Application Publication No. 2016 / 0201163 describes the separation of Li ions from saltwater, such as seawater, using LiSICon membranes. The proposed membrane materials are specifically LiN, Li 10 GeP2S 12 , La x Li y TiO2, and Li 1+x+y Al x (Ti,Ge) 2-x Si y P 3-y O 12 The target product is lithium carbonate (Li2CO3).

[0013] WO 2019055730 also relates to the separation of lithium using LiSICon membranes. LLTO, LAGP, and LATP are specifically mentioned. The LiSICon material can be applied to a support structure. The chemical nature of the support structure is not described in detail. Similarly, there is little information about how the LiSICon should be applied to the support structure. The target product to be separated is Li ions.

[0014] US Pat. No. 9,222,148 also discloses the electrolytic separation of lithium hydroxide on a LiSICon membrane and the resulting precipitation of lithium hydroxide hydrate.

[0015] In addition to the use of ceramic LiSICon membranes, electrolytic processes for the separation of lithium operating with organic ion exchange membranes have also been disclosed.

[0016] For example, EP 3805428 A1 describes the electrolytic production of lithium hydroxide. Similar to electrolysis, the electrochemical conversion of lithium to lithium hydroxide is also performed. To obtain the necessary reactants, water undergoes simultaneous electrochemical splitting. This is performed using a bipolar, three-compartment cell equipped with ion-exchange membranes. Commercially available Asahi® AVV, Nafion® 902, Fumatech® FAB, Fumatech® FKB, and Neosepta® CMB ion-exchange membranes are used. The chemistry of these ion-exchange membranes is not disclosed in EP 3805428 A1, but they are likely organic membrane materials. The three-compartment cell operates in an acidic medium. The feed uses water containing Li salts, specifically lithium sulfate (LiSO4) or lithium chloride (LiCl). The volumetric flow rate and gap size through the exemplary cell are specified, but the cell width is not. The flow internals within the cell are not addressed.

[0017] A two-stage electrolytic production of lithium hydroxide from aqueous lithium sulfate and / or lithium bisulfate with simultaneous water splitting is disclosed in U.S. Pat. No. 10,036,094. The first stage uses an electrochemical cell with two compartments, and the second stage uses a three-compartment cell. The prevailing pH in the three-compartment cell can be between 8 and 10. The cell is equipped with an ion-exchange membrane. The chemical composition of the ion-exchange membrane is not given. The following commercially available membranes are mentioned: Fumatech® FAB, Astom® ACM, Asahi® MV, Nafion® 324, and Astom® AHA. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] US Patent Application Publication No. 2016 / 0201163 [Patent Document 2] International Publication No. 2019055730 [Patent Document 3] U.S. Patent No. 9222148 [Patent Document 4] U.S. Patent Application Publication No. 20120103826 [Patent Document 5] European Patent Application Publication No. 3805428 [Patent Document 6] U.S. Patent No. 10036094

Non-licensed literature

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[0020] 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 have lower ion selectivity than inorganic LiSICon materials. They are + Not only Na + As well as the purity of the target product, the electrical efficiency of the process is also reduced: if electrolysis is carried out using a non-ion selective 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 ++ and Ca ++ Over time, these cations poison the membrane, thereby limiting the useful life of organic ion exchange membranes.

[0021] Glass-ceramic LiSICon materials promise better ion selectivity. However, the stability of LiSICon membranes against impurities remains a critical issue for industrial implementation here. For example, Li ions generated in the reprocessing of spent LIBs are also present. + The contained water is especially Na + and K. + These cations appear to occupy defects in the crystal structure, thereby allowing Li ions to pass through the membrane. + This virtually stops cation transport. The useful life of the electrochemical cell then expires. The high cost of LiSICon materials means that recycling Li from LIBs is uneconomical if the membrane has a short useful life. Furthermore, brine from Li-salt lakes has a naturally high sodium content, making it impossible to contact known LiSICon membranes. Therefore, lithium from the lakes must be dissolved and then recrystallized via a stepwise process that requires energy-intensive thermal separation and / or large amounts of water. While water can be evaporated here by solar radiation, water to dissolve LiCl is scarce in the South American desert. Therefore, this route is highly problematic there.

[0022] Another practical problem is the high specific electrical resistivity of LiSICon materials. This results in electrochemical cells with high ohmic internal resistance, which means that the process has correspondingly high electrical energy requirements. To reduce this, the membrane could theoretically be made thinner. However, a thinner material would have a shorter lifetime in aggressive environments.

[0023] Based on all the above, the problem addressed by the present invention is to produce LiSiCon films using LiSiCon membranes that can be operated economically even on an industrial scale. + The objective of this study is to identify a process for the electrochemical production of LiOH from water. In particular, the process must have good energy efficiency and achieve high membrane life, even when the feed used contains impurities that are harmful to the LiSICon material.

[0024] The problem is a process for producing hydrogen and lithium hydroxide, comprising: a) providing a feed containing at least water, Li ions, and also impurities, wherein the concentration of Li ions in the feed, C F is at least 200 ppm (by weight) or between 500 ppm (by weight) and 140,000 ppm (by weight), in each case based on the total weight of the feed; b) providing a lean working medium comprising water and lithium hydroxide dissolved therein, wherein the concentration C of lithium hydroxide in the lean working medium is M0 is at least 50 ppm (by weight) based on the total weight of the lean working medium; c) providing at least one electrochemical cell, the electrochemical cell having the following characteristics: i. the electrochemical cell includes a first compartment having an anode disposed therein; ii. the electrochemical cell includes a second compartment having a cathode disposed therein; iii. the electrochemical cell includes a flat sheet membrane separating a first compartment from a second compartment, the flat sheet membrane having an area A; iv. the flat sheet membrane comprises an inorganic material that is conductive to Li ions and electrically insulating; d) providing at least one voltage source connected to the anode via a first electrical lead and connected to the cathode via a second electrical lead; e) continuously filling the first compartment with a feed; f) filling the second compartment with a lean working medium; g) charging the electrochemical cell with a voltage U drawn from a voltage source so that a current I flows between the anode and the cathode, the ratio Q of the current intensity of the current I to the area A of the flat sheet membrane being 100 A / m 2 ~500A / m 2 or 150A / m 2 ~350A / m 2the charging step; h) continuously withdrawing wastewater from the first compartment, the wastewater containing at least water, dissolved Li salts therein, oxygen, and also impurities, wherein the concentration of Li ions in the wastewater, C W is the concentration of Li ions in the feed, C, based on the total weight of the wastewater. F Lower than, pull out step; i) withdrawing from the second compartment a rich working medium comprising water and lithium hydroxide, and also comprising hydrogen, the concentration C of lithium hydroxide in the rich working medium being M1 is the concentration C of lithium hydroxide in the lean working medium, based on the total weight of the rich working medium. M0 Higher than Due to the continuous charging of feed into the first compartment and the continuous withdrawal of wastewater from the first compartment, a first flow is generated that flows through the first compartment along the flat sheet membrane at a cross-flow velocity CFV, and the cross-flow velocity CFV is greater than 220 mm / s, or greater than 350 mm / s, or greater than 470 mm / s. [Brief explanation of the drawings]

[0025] [Figure 1] The functional principle of simultaneous Li+ membrane electrolysis and water electrolysis in an electrochemical cell using a LiSICon membrane is presented. [Figure 2] 1 shows the functional principle of recirculation between the electrochemical cell and the separation device. [Figure 3] 1 shows plots of water splitting voltage and cell internal resistance. [Figure 4] The relationship between LiOH concentration and permeability is shown in graph form. [Figure 5] 1 shows in graphical form the transmittance as a function of voltage for the LATSP. [Figure 6] 1 shows in graphical form the transmittance as a function of voltage for the LAGP. [Figure 7] 1 shows in graphical form the permeance as a function of voltage for the LATSP. [Figure 8]1 shows in graphical form the permeance and transmission as a function of membrane thickness. [Figure 9] The dependence of permeance on volumetric flow rate for the LATSP is shown in graphical form. [Figure 10] 1 shows in graphical form the dependence of permeance on volumetric flow rate for LAGP. [Figure 11] 1 shows a plot of measured permeance versus volumetric flow rate. [Figure 12] Permeance as a function of voltage with (▲) and without (O) spacers is shown. [Figure 13] 1 shows the results of a replicate of Experiment 11 using only an anolyte solution having a concentration of 0.1 mol / L LiOH. DETAILED DESCRIPTION OF THE INVENTION

[0026] An important aspect of the present invention is that flow conditions within the first compartment of the electrochemical cell are established so that the anolyte flows along the membrane at a specified minimum cross-flow velocity.

[0027] The anolyte is the material in the first compartment. The inflow is the feed, and the outflow from the first compartment is wastewater. Within the first compartment, the anolyte is converted from feed to wastewater by an electrochemical process within the cell.

[0028] Cross-flow velocity (CFV) is an established operational parameter from membrane technology. It is calculated from the ratio of the volumetric flow rate Q through the first compartment to the flow cross-section of the first compartment, i.e., the product of the membrane width b transverse to the flow direction and the gap height h between the membrane and the anode.

[0029] CFV=Q / (b*h) The insight in this case is that the cross-flow velocity CFV must be greater than 220 mm / s. A cross-flow velocity CFV of greater than 350 mm / s is better, and a cross-flow velocity CFV of greater than 470 mm / s is even better.

[0030] A high cross-flow velocity can have the effect that impurities present in the anolyte coming from the feed are less likely to settle on the membrane and flow out again with the wastewater from the first compartment, meaning that they cannot clog the membrane and thereby reduce its permeance.

[0031] Experimental data confirm that membrane permeance increases as cross-flow velocity increases. Permeance indicates how much mass of lithium is transported through the membrane per unit membrane area and unit time. Permeance is therefore a measure of the efficiency of the process. Therefore, at higher cross-flow velocities, the profitability of the process is expected to increase.

[0032] The cross-flow velocity cannot be increased to an infinitely high level because increasing turbulence would be introduced into the flow, increasing the flow resistance, which would require an increased driving force to pump the anolyte into the first compartment.

[0033] To achieve a good trade-off between the achieved permeance and the applied drive performance, it makes sense to limit the cross-flow velocity. Therefore, the cross-flow velocity (CFV) must be lower than the critical velocity. The achievable critical velocity depends on the setup of the electrochemical cell and its auxiliary units and can be, for example, 600 mm / s, 960 mm / s, 1500 mm / s, 2400 mm / s, 3780 mm / s, or 6000 mm / s.

[0034] Surprisingly, it has been found that flow internals, such as spacers, attached to spirally wound modules can have a negative effect on the permeance of the process. This is surprising, since spacers are routinely used in membrane processes. Therefore, in a preferred development of the invention, flow internals, such as spacers, are omitted.

[0035] According to the present invention, flat sheet membranes are used.Heretofore, it has not been possible to realize electrochemical cells with hollow fiber membranes.

[0036] Flat-sheet membranes are preferably used in flat-sheet modules. Their use in spiral-wound modules is not preferred because electrical wiring there proves to be complicated. Furthermore, flow control in spiral-wound modules proves problematic because in electrolysis, both half-cells must be filled with electrolyte or electrolyte must flow through them; in gas separations, which are typically operated in spiral-wound modules, only the permeate needs to be removed.

[0037] It is advantageous if a flow is established not only through the first compartment but also through the second compartment. Thus, in a further embodiment of the invention, the loading of lean working medium into the second compartment and the withdrawal of rich working medium from the second compartment are carried out continuously, so that a second flow occurs through the second compartment.

[0038] The flow conditions in the second compartment are preferably set up so that the working medium (catholyte) exhibits a laminar flow, so that the second compartment has low flow resistance and, as a result, little energy is required to transport the working medium.

[0039] Due to the flow conditions prevailing in the cell, the feed may contain impurities that are generally harmful to the Li-conducting membrane material. More specifically, the defined flow conditions in the membrane make it possible to work with feeds containing one or more of the following anions: sulfate, carbonate, hydroxide, and chloride.

[0040] In addition to the anions mentioned, the feed may also contain impurities in the form of compounds of the following elements: B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu, C. The listed alkali and alkaline earth metals are elements found with lithium in natural deposits, while the other metals mentioned are used as conductors or cathode materials in LIBs and are therefore present in the feed obtained from the reprocessing of spent LIBs. Carbon originates from organic materials used in LIBs, such as films, separators, adhesives, or sealants.

[0041] According to the present invention, a membrane containing inorganic materials is used. Therefore, the required ion selectivity is achieved differently than in the case of polymeric membranes. The membrane is preferably made entirely of inorganic materials. Composite membranes that contain inorganic materials only as a coating on a support material or in which inorganic materials are dispersed in different types of matrix materials have proven to be an incorrect approach.

[0042] The advantage of inorganic membranes over polymeric membranes is also due to their mechanical rigidity: at higher cross-flow velocities, inorganic membranes vibrate less than polymeric membranes.

[0043] For the process to work, the inorganic material must conduct Li ions and simultaneously act as an electrical insulator.

[0044] The specific conductivity σ of Li-ions is at least 1*10 at a temperature of 23°C. -5 S / m or at least 5*10 -5 S / m or at least 10*10 -5 S / m and 100*10 -5 The Li conductivity of the material is measured by impedance spectroscopy. This measurement is performed as follows: The measurement setup consists of 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.

[0045] 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.

[0046] 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).

[0047] The specific conductivity of electrons (electrical conductivity) is 10 -7 Less than S / cm (10 -9 S / m), or 10 -12 Less than S / m or 10 -16 S / m. Therefore, from the viewpoint of electronic conduction, inorganic materials are classified as non-conductors.

[0048] It is preferred to use LiSICon as the inorganic material. LiSICon material is a glass-ceramic material that conducts lithium ions and simultaneously acts as an electrical insulator. In principle, all known LiSICon materials can be used as inorganic materials for the purposes of the present invention. Known LiSICon materials meet the above-specified requirements for both the electrical conductivity and ionic conductivity of inorganic materials.

[0049] For example, the LiSICon material lithium aluminum titanium phosphate (LATP) can be used. Thus, in one variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0050] [ka]

[0051] [wherein 0.1≦x≦0.3, preferably x=0.3].

[0052] Alternatively, the LiSICon material lithium aluminum germanium phosphate (LAGP) can be used. Thus, in one variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0053] [ka]

[0054] [wherein x=0 or x=0.2 or x=0.4].

[0055] Alternatively, the LiSICon material lithium aluminum titanium silicon phosphate (LATSP) can be used. Thus, in one variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0056] [ka]

[0057] [wherein 0.1≦x≦0.3 and 0.2≦y≦0.4].

[0058] However, it is particularly preferred to use LiSICon, which is derived from lithium aluminum germanium phosphate but also contains titanium, and is called LAGTP.

[0059] Thus, in a preferred variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0060] [ka]

[0061] [wherein 0≦x≦1].

[0062] In a particularly preferred development of the invention, LATSPs are used which additionally contain germanium, and are referred to as LAGTSPs.

[0063] Thus, in a particularly preferred variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0064] [ka]

[0065] [Where 0≦x≦1 and 0≦y≦1 and 0≦n≦1].

[0066] LAGTSP is available, for example, from Ohara GmbH, Hofheim, Germany under the product name LICGC® AG01.

[0067] As an alternative to the phosphates mentioned, the oxide LiSICon material lithium lanthanum titanium oxide (LLTO) can be used. Thus, in one variant of the invention, the inorganic material is a compound of the following stoichiometry:

[0068] [ka]

[0069] [wherein 0≦x≦0.16].

[0070] The lithium hydroxide is present in the rich working medium and is withdrawn from the second compartment together with it. To be able to utilize it, it must be separated from the rich working medium. For this purpose, a separation device is provided. Therefore, a preferred development of the invention comprises the following additional process steps: k) providing a separation device; l) Separating the lithium hydroxide from the rich working medium using a separator.

[0071] After the lithium hydroxide is separated from the rich working medium, the working medium can be disposed of as wastewater or, preferably, reused as lean working medium. For this, the LiOH is not completely separated, but instead a specific minimum concentration of 50 ppm LiOH is used. m0 The separation apparatus must be operated so that the working medium is maintained above 0.05%. This allows the working medium to be recycled to the second compartment as lean working medium. This allows the working medium to be recirculated between the second compartment and the separation apparatus.

[0072] A preferred development of the invention therefore comprises the following additional process steps: l) separating the lithium hydroxide from the rich working medium using a separator to obtain lean working medium; Steps below: b) providing a lean working medium comprising water and lithium hydroxide dissolved therein, wherein the concentration C of lithium hydroxide in the lean working medium is M0 is at least 50 ppm (by weight) based on the total weight of the lean working medium; This is done using a separation device.

[0073] To allow for the recirculation of the working medium between the separator and the second compartment, it makes sense to install both devices in the same location. This should be understood to mean an integrated production facility. The electrochemical cell and the separator are therefore part of an integrated facility.

[0074] It is also conceivable that the separation device could be located at a different location from the electrochemical cell, but in that case the working medium would have to be transported between the cell and the separation device, which makes little sense from an energy point of view.

[0075] Preferably, at least the electrochemical cell is operated continuously on both the anolyte side and the catholyte side. This means that the second compartment is continuously charged with lean working medium and continuously withdrawn with rich working medium, resulting in a second flow through the second compartment. As a result, there is a constant breakthrough flow in both compartments. The first compartment has a continuous breakthrough flow of feed, resulting in the production of wastewater, while the second compartment has a breakthrough flow of working medium, which enters as lean working medium and exits as rich working medium. This allows for both higher throughput and continuous withdrawal of membrane-damaging components of the feed and working medium. Therefore, continuous operation is expected to achieve better membrane stability than batch operation on the catholyte side.

[0076] Even in continuous operation, care must be taken to ensure that the anolyte flow conditions according to the present invention are maintained, i.e., that the first flow passes along the membrane at a sufficiently high cross-flow velocity through the first compartment. However, with respect to the catholyte flow conditions in the second compartment, the goal should be to achieve laminar flow, since this reduces the flow resistance in the second compartment and means that less energy is required to move the working medium. Thus, in certain embodiments, the second flow is laminar.

[0077] Drawing Description: The present invention will now be described in detail with reference to a process flow diagram, in which the diagram shows:

[0078] Figure 1 shows the simultaneous Li+ / Li ... + The functional principles of membrane electrolysis and water electrolysis are shown.

[0079] FIG. 2 shows the functional principle of the recirculation between the electrochemical cell and the separation device.

[0080] The electrochemical cell 0 required to carry out the process is shown in Figure 1. It comprises a first compartment 1 and a second compartment 2. The two compartments 1 and 2 are separated from each other by a membrane 3. An anode 4 is located in the first compartment 1. A cathode 5 is located in the second compartment 2. Thus, the first compartment 1 can be referred to as the anode compartment, and the second compartment 2 can be referred to as the cathode compartment.

[0081] A first electrical lead 6 connects the anode 4 to a voltage source 7. A second electrical lead 8 connects the cathode 5 to the voltage source 7. The selected polarity of the voltage source 7 is such that the positive terminal of the voltage source 7 is connected to the anode 4 and the negative terminal of the voltage source 7 is connected to the cathode 5.

[0082] An electric current I flows through two electrical leads 6 and 8 via a voltage source 7. There is no electrical short circuit between the two electrodes 4 and 5 through the membrane 3, as the membrane 3 acts as an electrical insulator.

[0083] The membrane 3 is a flat sheet membrane made entirely of LiSICon material. The anode 4 is a flat metal plate made of titanium, niobium, or tantalum. The cathode 5 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 4, cathode 5, and membrane 3 have the same shape and can be rectangular or circular. This is not clear from the side view in Figure 1. Instead of metal plates, it is also possible to use expanded metal, grids, or meshes of certain materials as electrodes.

[0084] The electrochemical cell 0 has an active area A, which essentially corresponds to the surface area of ​​the membrane 3, anode 4, and cathode 5. By installing sealing elements, the active area can be reduced relative to the actual area of ​​the electrodes and membrane. The active area is the fraction of the area available for the electrochemical process in the cell 0.

[0085] During operation, the first compartment 1 is filled with a feed 10. The feed 10 is an aqueous solution containing Li+ ions. From an electrochemical point of view, the feed 10 can be considered an anolyte.

[0086] Feed 10 may be a Li leachate from natural deposits or a material stream resulting from the processing of spent LIBs. The concentration of Li+ cations in feed 10 (with formula symbol c F ) 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 10 also contains anions such as sulfate or chloride. Feed 10 also contains impurities. The anions and impurities are not shown in Figure 1. The main component of feed 10 is water, HO.

[0087] The second compartment is filled with lean working media 12. The lean working media 12 is Li + Cation concentration C M0 The concentration of water is low. M0 is at least 50 ppm (by weight) based on the total mass of the lean working medium 12. From an electrochemical point of view, the lean working medium 12 can be considered a catholyte.

[0088] The electrochemical cell 0 is also charged with a voltage U drawn from a voltage source 7. This has the following effects:

[0089] First, water electrolysis occurs, where water (H2O) is electrochemically split into hydrogen (H2) and oxygen (O2). At the cathode 5, OH - However, OH - The anions cannot pass through the membrane 3 and are transported to the cathode compartment 2 via the Li + At the anode 4, oxygen and H + is formed.

[0090] The formation of LiOH in the cathode compartment 2 is sustained by the migration of Li+ cations from the feed 10 to the cathode 5, driven by the voltage U. They cross the membrane 3 due to the membrane's Li-ion conductivity and accumulate in the working medium (membrane electrolysis). This forms a rich working medium 13 that is withdrawn from the second compartment 2. The Li+ ion concentration in the rich working medium 13 is higher than in the lean working medium 12, so c M1 >c M0 is.

[0091] Therefore, in electrochemical cell 0, water electrolysis, Li + The membrane electrolysis and synthesis of LiOH proceed simultaneously.

[0092] Thus, simultaneous operation of Li+ membrane electrolysis and water electrolysis in an electrochemical cell results in the direct formation of lithium hydroxide (LiOH) and molecular hydrogen (H2). LiOH dissolves in water. Some of the hydrogen is dissolved and some is present in gaseous form. The reaction product LiOH and water containing dissolved H2 are withdrawn from the cathode compartment of the cell as the rich working medium 13. Similarly, gaseous hydrogen (H2) is withdrawn from the second compartment 2.

[0093] As a result of membrane electrolysis, the feed 10 becomes depleted in Li+, producing wastewater 14. W <c F Here, the formula symbol c W represents the Li ion concentration in the wastewater 14 based on the total mass of the wastewater 14. F represents the concentration of Li ions in the feed 10 based on the total mass of the feed 10.

[0094] Figure 1 also shows how the crossflow velocity, CFV, is determined. This involves measuring the distance, or gap height, h, between the membrane 3 and the anode 4. Furthermore, the width, b, of the membrane 3 is measured transversely to the flow direction. Width, b, extends perpendicular to the plane of the drawing in Figure 1. The volumetric flow rate, Q, of the anolyte through the first compartment is then determined.

[0095] The cross flow velocity, CFV, can then be determined as follows:

[0096] CFV=Q / (b*h). If the flat sheet membrane used is not rectangular, the average width must be used. When circular cells / membranes are used, the width b is taken to be 1 / 2√2 (approximately 70%) of the maximum width of the channel cross section. The maximum width of the channel cross section is the diameter of the active area A. Thus, for a circular flat sheet membrane with diameter D, the width b is equal to the length of the sides of a square, the perimeter of which has diameter D of the circular active area A of the cell. Therefore, b=1 / 2√2*D.

[0097] FIG. 2 shows how LiOH is extracted as the target product 15 from the rich working medium 13.

[0098] For this purpose, a separation device 16 is provided to which the rich working medium 13 is conveyed. The separation device 16 separates the target product 15, which has a particularly high concentration of LiOH, from the rich working medium 13. The target product also contains water and impurities, depending on the desired specifications of the target product.

[0099] Separator 16 can be a distillation column or a crystallizer.

[0100] The LiOH-depleted effluent stream from the separator 16 is recycled to the second compartment 2 of the electrochemical cell 0 as lean working medium 12 .

[0101] As mentioned above, the poor working medium 12 is required to have a specific LiOH concentration C so that the process in the electrochemical cell 0 can be initiated in the desired manner due to the low initial resistance. M0 It is necessary to have a concentration c M0 The desired concentration C must be at least 50 ppm (by weight) based on the total mass of the lean working medium 12. M0 To ensure this, the separator 16 operates such that not all of the LiOH is separated from the rich working medium 13.

[0102] In addition to lithium hydroxide LiOH, the process also produces H2, which is partially dissolved in the rich working medium 13 and is withdrawn together with LiOH from the second compartment 2. Furthermore, gaseous hydrogen H2 accumulates in the cell.

[0103] Since hydrogen H2 is easily degassed from water, it does not require much effort to remove it from the working medium. Only when hydrogen H2 is utilized as the second target product, a corresponding second separation device is provided (not shown) from which hydrogen can be obtained separately with suitable quality / purity.

[0104] The water HO present in the rich working medium 13 is recycled as completely as possible as the lean working medium 12. Only the water (of crystallization) present in the target product 15 is lost from the process; this must be replenished to the lean working medium 12 as needed (not shown). The water in the feed 10 is not finally recycled between the second compartment 2 and the separation device 16 because the membrane 3 is impermeable to water. [Example]

[0105] The invention will now be described in detail with reference to experimental descriptions.

[0106] General experimental setup and procedures To carry out electrolysis, the electrolysis cell is first assembled and the anolyte and catholyte containers are connected, with care being taken to ensure that the inlet and outlet flows are connected on the same side in each case.

[0107] In one experimental design, the anode and cathode are both described as planar electrodes. These comprise titanium plates with a diameter of 19.5 mm and a thickness of 1.5 mm, coated on both sides with IrTi mixed oxide (12 g Ir / m²) from Metakem GmbH, 61250 Usingen, Germany.

[0108] The sampled membranes were also circular disks with a diameter of approximately 25 mm. The membrane thickness ranged from 0.3 mm to 2 mm. The membrane materials tested are specified in the individual examples.

[0109] The membrane width (b) across the flow direction was 14 mm in each case. The specified width (b) was equal to the length of the sides of a square, the perimeter of which had the same diameter as the circular active area (A). The gap height (h) between the anode and the membrane was 2.5 mm in each case. When a spacer was used, the gap height was reduced to 1.8 mm or 1.5 mm.

[0110] The electrolysis is blanketed with nitrogen throughout the process to prevent the formation of lithium carbonate. Each cell has a separate anolyte container and a separate catholyte container. Each vessel is filled with approximately 1 kg of liquid. The exact mass is determined by reweighing. The catholyte is always a 5 mmol / L LiOH solution. The anolyte is in each case a lithium salt solution of various lithium salts at various concentrations.

[0111] The experiment begins when the pump is switched on and the desired voltage is applied. The maximum flow rate is between 750 mL / min and 1000 mL / min, depending on the respective experimental setup. Samples are collected every 30 minutes, or at longer intervals if agreed. The first 3 ml of sample collected is discarded. For each sample collected, the output is recorded in each case and the conductivity of the sample is determined. The sample is then returned to a suitable container, keeping the volume substantially constant.

[0112] At the end of the experiment, the vessel is emptied and all leads and membranes are rinsed with demineralized water. The cell is dismantled, the membrane is photographed, and SEM images of the catholyte and anolyte sides are recorded.

[0113] 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.

[0114] 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 concentration by conductivity measurements.

[0115] All ceramics used originated from the manufacturers listed in Table 0 and can be ordered from these sources under the corresponding product designations.

[0116] [Table 0]

[0117] The lithium hydroxide used was analytical grade from Aldrich. All other materials were technical grade.

[0118] Unless otherwise stated, LATSP membranes (LICGC®, Ohara) with a thickness of approximately 1 mm were used. The membrane disks were 100x10 5 Pa~200*10 5 They were produced by the SPS sintering process at a pressure of 100 Pa and a temperature of 950 °C or alternatively were obtained directly from various manufacturers (Ohara, Ampcera, Toshima) in sizes suitable for the measurement cell.

[0119] Sintering process description: Sintering by FAST / SPS The LATSP powder used was sintered using FAST / SPS (Field-Assisted Sintering Technology / Spark Plasma Sintering). Sintering was performed with simultaneous pressure and temperature ramps to achieve high compaction and effective sintering in a very short sintering time. The sintering die assembly consisted of a graphite die with an outer diameter of 80 mm, an inner diameter of 36 mm, and a height of 55 mm, two graphite half-shells with 10 mm wall thicknesses and the same height, and two graphite punches with a diameter of 25 mm and a height of 30 mm. The half-shells were placed in the die, and one punch was introduced into the half-shells from below. Before weighing 2.5 g of powder onto the lower punch and inserting it into the die, a graphite foil was placed on the punch for better contact. After weighing the powder, a second graphite foil was placed on the powder, and the upper punch was introduced into the half-shells. The die assembly was placed in the furnace chamber of a FAST / SPS furnace between two plates, each made of carbon fiber-reinforced graphite. The assembly is contacted via the electrode path and the desired pressure is built up. The die is then heated by an alternating current, allowing it to reach high temperatures in a short time. The temperature is gradually increased to 250°C over 5 minutes, and then continued at a rate of 130°C / min until a maximum temperature of 900°C is reached and held for another 5 minutes. During the temperature increase, the pressure is also increased to 43 MPa over 5 minutes and held for another 5 minutes. At the end of the hold time, the upper electrode is released from contact with the die, allowing it to cool. The sintered film can then be removed from the mold.

[0120] Example 1 (LATSP) First, we investigated the voltage dependence of the ceramic membrane during electrolysis. Electrolysis was performed using 0.1 mol / L LiOH and 1 mol / L LiOH at voltages of 3 V to 6 V and a volumetric flow rate of 600 mL / min through the electrolysis cell. The measurement results are shown in Table 1.

[0121] A graphical plot of the values ​​reveals a linear relationship. The intersection of the line with the x-axis at approximately 2 V is derived from the water decomposition voltage and the internal resistance of the cell. This intersection is virtually identical for both concentrations. The plot is shown in Figure 3.

[0122] [Table 1]

[0123] Example 2 (LATSP) It was also established that membrane performance was independent of anolyte concentration. For this purpose, electrolysis was carried out at voltages of 3 and 6 V, with an initial charge of 0.1, 1.0, 2.0, or 4.0 mol / L LiOH in the anolyte reservoir in each case, and with an anolyte volumetric flow rate through the electrolysis cell of 600 mL / min.

[0124] The mole ratio of LiOH corresponds to the weight ratio of Li as follows: 0.1mol / L=700ppm Li=2400ppm LiOH 1.0mol / L=7000ppm Li=24000ppm LiOH 2.0mol / L=14000ppm Li=48000ppm LiOH 4.0mol / L=28000ppm Li=96000ppm LiOH The results are shown in Table 2. At concentrations between 1 mol / L and 4 mol / L, there is no significant measured increase in membrane performance. At a LiOH concentration of 0.1 mol / L, there is a slight decrease in performance. Figure 4 shows the results in graphical form.

[0125] [Table 2]

[0126] Example 3 (LATSP) The results of the experiments in Examples 1 and 2 show that the lithium permeability through the ceramic ion-conducting membrane is concentration dependent, even though the driving force for the process is the applied voltage difference. To better explain this behavior, additional experiments were performed. These were also performed in a higher voltage range between 3 V and 15 V. The volumetric flow rate through the anolyte compartment of the cell was 600 mL / min, and anolyte concentrations of 0.1 mol / L LiOH, 1.0 mol / L LiOH, and 4.0 mol / L LiOH were used.

[0127] The results of the study are summarized in Table 3.

[0128] [Table 3]

[0129] Figure 5 shows the results in graphical form.

[0130] From a certain voltage above 9 volts, the permeability through the LATSP membrane used does not increase any further, but instead drops significantly. Since this limit appears to be reached at a relatively low voltage and relatively low permeability for a 0.1 mol / L LiOH solution as the anolyte, it was concluded that beyond this limit there is a limit to lithium transport caused by insufficiently rapid transport of lithium at the membrane surface facing the anolyte.

[0131] Example 4 (LAGP) Repeating Example 3 using a different ceramic ion-conducting material (LAGP) with a material thickness of 0.3 mm, an anolyte concentration of 0.1 mol / L LiOH, and an anolyte volumetric flow rate through the electrolysis cell of 600 mL / min shows a similar picture: again, achieving a further increase in permeability by increasing the voltage is not possible beyond a certain limit.

[0132] The results are summarized in Table 4.

[0133] [Table 4]

[0134] Figure 6 shows the results in graphical form.

[0135] Example 5 (LATSP) A series of experiments using 1.0 mol / L LiOH in the anolyte, a volumetric flow rate of 600 mL / min, and membranes of various thicknesses show that the cause is limited transport of lithium ions to the surface of the membrane on the anolyte side, as measured by permeance. The region where lift is no longer possible is between 60 and 75 g / m 2 All experimental series within the range of h.

[0136] Therefore, in a given experimental setup, increasing lithium transport by increasing the voltage difference exceeds this limit.

[0137] The results are summarized in Table 5.

[0138] [Table 5]

[0139] Figure 7 shows the results in graphical form.

[0140] Example 6 (LATSP) A series of experiments at 6 V using 1.0 mol / L LiOH in the anolyte, a volumetric flow rate of 600 mL / min, and membranes of various thicknesses show that permeance and permeability show the expected relationship to each other through membrane thickness up to a membrane thickness of 0.75 mm. For thinner membranes, both deviate toward lower values ​​(unfilled symbols) from the expected behavior shown in Figure 8 as extrapolated values. The values ​​are shown in Table 6.

[0141] [Table 6]

[0142] Figure 8 shows the results in graphical form.

[0143] The various Examples 1-6 show that the technologically desirable high lithium permeance cannot be achieved by thin films or high voltages alone, nor by selecting a ceramic with the highest possible Li conductivity, but that additional measures are required to achieve this.

[0144] Example 7 (LATSP) In electrolysis experiments using 0.1 mol / L and 1.0 mol / L LiOH solutions as anolytes at a voltage of 3 V and various volumetric flow rates, it has previously been observed that lithium transport through the membrane, even at low permeances, depends on the volumetric flow rate and therefore also on the cross-flow rate.

[0145] The results are collated in Table 7.

[0146] [Table 7]

[0147] Figure 9 shows the results in graphical form.

[0148] Example 9 (LAGP) These results suggest, surprisingly, that lithium passage from the stream to the membrane surface has a significant impact on the overall performance of the process, even at very low voltages and permeances. Passage to the surface is governed by the cross-flow velocity at the membrane surface and, therefore, the volumetric flow rate through the anolyte cell.

[0149] A further increase in the volumetric flow rate at a voltage of 6 V and an anolyte concentration of 1.0 mol / L LiOH indicates that this increases the lithium transport (permeance) beyond the previously observed limit of 110 g Li / m 2 It was shown that it is possible to increase the saturation voltage to over 1000 kJ / s.

[0150] The results are collated in Table 8.

[0151] [Table 8]

[0152] Figure 10 shows the results in graphical form.

[0153] Example 10 (LAGP) Further increases in volumetric flow rate at a voltage of 6 V and an anolyte concentration of 1.0 mol / L LiOH were not feasible with the device setup, so the use of alternative electrode geometries and spacer materials was explored as a further measure.

[0154] Spacers are available from the following companies: Fine spacer (72% open) SWM;601 Industrial Drive,Middletown,DE 19709,USA Type Naltex N02016_90PP Coarse spacer (55% open) Intermas Nets SA Ronda Collsabadell,11,08450 Llinars del Valles(Barcelona),Spain The installation of fine spacers reduces the gap height from 2.5 mm to 1.8 mm, while the installation of coarse spacers reduces the gap height to 1.5 mm. The membrane width of 14 mm remains unchanged by the installation of the spacers.

[0155] Table 9 shows the results of investigations using a volumetric flow rate of 70 to 750 mL / min, 6V, and 1 mol / L LiOH solution.

[0156] In all configurations, increasing the volumetric flow rate resulted in increased lithium transport through the membrane. The results show that at a voltage of 6 V, transport depends on the electrode area and the open, accessible area of ​​the membrane (the area not covered by the spacer bars). No increase in permeance is discernible due to the introduction of spacers, which are intended to ensure greater mixing of the feed volumetric flow rates.

[0157] The permeance trends suggest that they converge for all process types above a volumetric flow rate in the anolyte compartment of approximately 1000 mL / min, and therefore it can be assumed that above this volumetric flow rate, the rate is determined solely by transport through the ceramic lithium-ion conducting membrane.

[0158] [Table 9]

[0159] FIG. 11 shows a plot of the measured permeance versus the volumetric flow rate.

[0160] Example 11 (LAGP) The voltage was increased stepwise at a volumetric flow rate of 1000 mL / min. In this experiment, the coarse spacer geometry used (55% open) was able to produce 300 g at 15 V with increasing voltage. Li / m 2 It has been found that voltages of 0.1 V to 0.5 V ensure thorough mixing of a feed containing 1.0 mol / L LiOH up to the point where a permeance of greater than 1.0 mol / L is achieved, beyond which even higher voltages result in a known decrease in permeance.

[0161] Runs attempting to achieve this at the same volumetric flow rate using planar electrodes without spacers gave similar results at the higher voltages investigated.

[0162] Figure 12 shows the permeance as a function of voltage with (▲) and without (O) spacers. The values ​​are shown in Table 10.

[0163] [Table 10]

[0164] This paper demonstrates that by establishing the highest possible cross-flow velocity / volumetric flow rate, it is possible to significantly increase the permeance of LiSICon membranes used in membrane electrolysis to an extent that allows for economical use. Surprisingly, because ceramic membranes are dimensionally stable during use and therefore keep defined flow channels open, the spacers typically used in membrane electrolysis between the polymeric ion-exchange membrane end electrodes are not necessary. Therefore, the use of spacers in combination with ceramic membranes is less preferred, as the polymeric spacer bars block part of the exchange area.

[0165] Example 12 (LAGP) A repeat of Experiment 11 using only an anolyte solution having a concentration of 0.1 mol / L LiOH produced the results shown in Table 11 and in Figure 13, indicated by the "□" data points, when using a planar electrode.

[0166] [Table 11]

[0167] Again, the permeance can be increased by increasing the voltage. However, as previously described in Example 11, beyond a certain limit, further increases in permeability are not achievable, and increasing the voltage further decreases the permeance. The permeance limit is lower than when using the 1.0 mol / L solution (reference "O" data point) as shown in Example 11, but is more than twice as high as in a comparable experiment with a lower cross-flow velocity.

[0168] It has been confirmed herein that by establishing the highest possible cross-flow velocity / volume flow rate, it is possible to significantly increase the permeance of LiSICon membranes used in membrane electrolysis to an extent that makes their economical use possible. [Explanation of symbols]

[0169] 0 Electrochemical Cell 1. First Section 2 Second Section 3 membrane 4 anodes 5 cathode 6 First Electrical Lead 7. Voltage Source 8 Second Electrical Lead 9 Unassigned 10 Supplies 11 Unassigned 12 Poor working medium 13 Wealth Working Media 14 Wastewater 15 Target product 16 Separation device H2O Water H2 Hydrogen O2 oxygen LiOH Lithium hydroxide OH - OH anion Li + Lithium-cation U Voltage I current A active area C F LiOH concentration in the feed C W LiOH concentration in wastewater C M0 LiOH concentration in the poor working medium C M1 LiOH concentration in the working medium b Width of the membrane transverse to the flow direction h is the height of the gap between the membrane and the anode Q is the volumetric flow rate through the first compartment CFV Crossflow Velocity

Claims

1. 1. A process for producing hydrogen and lithium hydroxide, comprising: a) providing a feed containing at least water, Li ions, and also impurities, wherein the concentration of Li ions in the feed is C Ｆ is at least 200 ppm (by weight) or between 500 ppm (by weight) and 140,000 ppm (by weight), in each case based on the total weight of the feed; b) providing a lean working medium comprising water and lithium hydroxide dissolved therein, wherein the concentration C of lithium hydroxide in said lean working medium is Ｍ０ is at least 50 ppm (by weight) based on the total weight of the lean working medium; c) providing at least one electrochemical cell having the following characteristics: v. the electrochemical cell includes a first compartment having an anode disposed therein; vi) the electrochemical cell includes a second compartment having a cathode disposed therein; vii. the electrochemical cell includes a flat sheet membrane separating a first compartment from a second compartment, the flat sheet membrane having an area A; viii. the flat sheet membrane comprises an inorganic material that is conductive to Li ions and electrically insulating; d) providing at least one voltage source connected to said anode via a first electrical lead and connected to said cathode via a second electrical lead; e) continuously filling said first compartment with said feed; f) filling the second compartment with the lean working medium; g) charging the electrochemical cell with a voltage U drawn from the voltage source so that a current I flows between the anode and the cathode, wherein the ratio Q of the current intensity of the current I to the area A of the flat sheet membrane is 100 A / m ２ ~500 A / m ２ or 150 A / m ２ ~350 A / m ２ a charging step; h) continuously withdrawing wastewater from the first compartment, the wastewater also containing at least water, dissolved Li salts therein, oxygen, and impurities, wherein the concentration of Li ions in the wastewater, C Ｗ is the concentration C of Li ions in the feed, based on the total weight of the wastewater. Ｆ Lower than, pull out step; i) withdrawing from said second compartment a rich working medium comprising water and lithium hydroxide, and also comprising hydrogen, wherein the concentration C of lithium hydroxide in said rich working medium is Ｍ１ is the concentration C of lithium hydroxide in the lean working medium based on the total weight of the rich working medium Ｍ０ Higher than the continuous charging of the feed to the first compartment and the continuous withdrawal of wastewater from the first compartment causes a first stream to flow through the first compartment along the flat sheet membrane at a cross-flow velocity CFV, the cross-flow velocity CFV being greater than 220 mm / s, or greater than 350 mm / s, or greater than 470 mm / s.

2. 2. The process of claim 1, wherein the cross-flow velocity CFV is less than a critical velocity, the critical velocity being selected from the group consisting of the following critical velocities: 600 mm / s, 960 mm / s, 1500 mm / s, 2400 mm / s, 3780 mm / s and 6000 mm / s.

3. 3. The process according to claim 1 or 2, characterized in that the first compartment does not include a flow interior.

4. The process of claim 3, wherein the first compartment does not contain a spacer.

5. The process according to any one of claims 1 to 4, characterized in that the flat sheet membrane is attached to a flat sheet module.

6. 6. The process of any one of claims 1 to 5, wherein the feed contains anions selected from the group consisting of sulfate, carbonate, hydroxide and chloride.

7. 7. The process according to any one of claims 1 to 6, characterized in that the feed contains impurities in the form of compounds of elements selected from the group consisting of B, Na, Mg, Al, Si, K, Ca, Mn, Fe, Co, Ni, Cu and C.

8. The inorganic material present in the flat sheet film has an impedance of at least 1*10 at a temperature of 23° C. as measured by the “impedance spectroscopy” method described herein. －５ S / m or at least 5*10 －５ S / m or at least 10*10 －５ S / m and 100*10 －５ 8. The process of any one of claims 1 to 7, having a Li-ion conductivity of 0.5 S / m or less.

9. The inorganic material is a compound (LATP) with the following stoichiometry: 【Chemical 1】 [Wherein, 0.1≦x≦0.3, preferably x=0.3] 9. The process according to claim 8, wherein

10. The inorganic material is a compound of the following stoichiometry (LATSP): 【Chemistry 3】 [Wherein, 0.1≦x≦0.3 and 0.2≦y≦0.4] 9. The process according to claim 8, wherein

11. The inorganic material is a compound of the following stoichiometry (LAGTSP): 【Chemistry 5】 [Wherein, 0≦x≦1, 0≦y≦1, and 0≦n≦1] 9. The process according to claim 8, wherein

12. The inorganic material is a compound (LAGTP) of the following stoichiometry: 【Chemistry 4】 [Wherein, 0≦x≦1] 9. The process according to claim 8, wherein

13. The inorganic material is a compound of the following stoichiometry (LAGP): 【Chemistry 2】 [Wherein, x=0 or x=0.2 or x=0.4] 9. The process according to claim 8, wherein

14. The inorganic material is a compound of the following stoichiometry (LLTO): 【Chemistry 6】 [Wherein, 0≦x≦0.16] 9. The process according to claim 8, wherein

15. A process according to any one of claims 9 to 14, characterized in that said flat sheet membrane consists entirely of said inorganic material.

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