Production of hydrogen and lithium oxide in an alkaline environment

Description

[0001] Lithium (Li) is essential for the production of lithium-ion batteries (LIBs). Due to its high reactivity, lithium does not occur naturally as a pure substance, but always in a bound form. The starting material for the production of LIBs is usually lithium hydroxide (LiOH) or lithium carbonate (Li 2 CO 3 ).

[0002] In most natural deposits, Li is present in the form of lithium oxide (Li2O) or salts such as lithium sulfate (Li2SO4) or lithium chloride (LiCl). Lithium oxide is a component of ores such as pegmatite, while lithium sulfate and lithium chloride are dissolved in the brines of Li salt lakes. During mining, the extracted lithium compound is converted into lithium carbonate (Li2CO3). In a further process step, the lithium carbonate can be converted into lithium hydroxide using quicklime or calcium hydroxide. The extraction of Li and its conversion to LiOH is described in: Wietelmann, U. and Steinbild, M. (2014). Lithium and Lithium Compounds. In Ullmann's Encyclopedia of Industrial Chemistry, (Ed.). DOI: 10.1002 / 14356007.a15_393.pub2

[0003] Rich lithium deposits are known, but the production of LiOH from the lithium compounds found there is highly energy- and wastewater-intensive. Furthermore, there is a strategic need to be independent of the deposit owners.

[0004] One solution to this problem could be to recycle used LIBs so that the lithium they contain can be reused as a raw material for new batteries.

[0005] Recycling processes for LIBs have already been developed to technical maturity in the past, but mostly with the goal of recovering the metals they contain, such as Fe, Ni, Mn, Co, Mg, and Al. The alkali metal Li was generally not recovered because its high reactivity makes it difficult to separate from battery scrap, and it was available in sufficient quantities at low cost from natural deposits. For a long time, the extraction of Li from used LIBs simply seemed uneconomical.

[0006] Meanwhile, social and economic pressure to recover lithium from used lithium batteries has increased. The success of this project requires that recycled lithium can be offered in a quality acceptable to lithium battery producers, so that the manufacturing processes for lithium batteries from recycled lithium are no different from those for mined fresh lithium. Battery quality must, of course, not suffer. Consequently, recycled lithium, especially in the form of LiOH, must meet very demanding purity specifications. Furthermore, the process for recovering lithium from used batteries must be as energy-efficient as possible. The process should also consume little water.

[0007] Known processes for recovering lithium from used batteries have been compiled: 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 104121 DOI: 10.1016 / j.mineng. 2017.04.008.

[0008] A technology that is only mentioned in passing as "LISM" in the above review article is the electrolysis of Li-containing waters in the presence of so-called LiSICon membranes.

[0009] LiSICon stands for Lithium Super Ionic Conductor. It is a class of inorganic, (glass) ceramic material that is electrically insulated but also has intrinsic conductivity for lithium ions. The transport mechanism for lithium is based on the material's crystal structure. Simply put, the lithium ions are "passed through" the crystals. Commercially available LiSICon materials include lithium aluminum titanium phosphate (LATP), lithium aluminum titanium silicon phosphate (LATSP), lithium aluminum germanium phosphate (LAGP), and lithium lanthanum titanium oxide (LLTO). These materials were originally developed as solid-state electrolytes for LIBs. An overview of the transport mechanisms of LiSICons, their crystal structure, and production can be found at: 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-lon Conductors for All-Solid-State Li-Ion Batteries. ACS Energy Lett. 2017, 2, 12, 2734-2751 DOI: 10.1021 / acsenergylett.7b00849

[0010] Spezielle LiSICon Stöchiometrien werden beschrieben von: Sofia Saffirio et al.Li1.4Al0.4Ge0.4Ti1.4(PO4)3 promising NASICON-structured glass-ceramic electrolyte for all-solid-state Li-based batteries: Unravelling the effect of diboron trioxide, Journal of the European Ceramic Society, Volume 42, Issue 3, 2022, Pages 1023-1032 DOI 10.1016 / j.jeurceramsoc.2021.11.014. Eongyu Yi et al. Materials that can replace liquid electrolytes in Li batteries: Superionic conductivities in Li1.7Al0.3Ti1.7Si0.4P2.6O12. Processing combustion synthesized nanopowders to free standing thin films. Journal of Power Sources, Volume 269, 2014, Pages 577-588, DOI 10.1016 / j.jpowsour.2014.07.029.

[0011] Due to their selective conductivity for Li ions, LiSICon materials can be used as membranes for separating Li from Li-containing mixtures. The Li must be present in the mixture in ionic form, such as a Li salt dissolved in water. An electrical voltage is required as the driving force to convey the Li ions through the LiSICon membrane. For this purpose, an electrochemical cell is constructed that comprises two electrodes and a LiSICon membrane, which divides the cell into two compartments. Each compartment contains an electrode. Depending on the polarity of the electrode contained in the compartment, the compartments are referred to as anodic or cathodic. An electrical voltage is applied to the electrodes, and the Li-containing water is poured into the anionic compartment. The cathodic compartment is filled with water. The membrane passes the Li cations through to the cathode.The water in the cathodic compartment is therefore enriched with Li, while the water on the anodic side is depleted of Li. Such a process is called membrane electrolysis.

[0012] Membrane electrolytic processes for the extraction of lithium using LiSICon membranes have already been described in the state of the art.

[0013] For example, Zhen Li et al. describe a process that uses the low-lithium-content water of 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

[0014] Zhen Li's research group uses LLTO as a membrane. The separated target product is lithium phosphate (Li 3 PO 4 ), which is a potential candidate for the production of lithium iron phosphate (LFP) batteries. LlB with a different cathode material, such as nickel manganese cobalt (NMC) or lithium manganese oxide (NMO), cannot be produced directly using this method.

[0015] Using solar power, a LAGP membrane, and copper foil, Yang et al. aim to extract metallic lithium directly from seawater: 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.

[0016] US 2016 / 0201163 A1 describes the separation of Li ions from a brine such as seawater using LiSICon membranes. Specifically, Li 3 N, Li 10 GeP 2 S 12 , and La x Li y TiO 2 , Li 1+x+y Al x (Ti, Ge) 2-x Si y P 3-y O 12 are proposed as membrane materials. The target product is lithium carbonate (Li 2 CO 3 ).

[0017] WO 2019055730 A1 also deals with the separation of lithium using LiSICon membranes. Specifically, LLTO, LAGP, or LATP are mentioned. The LiSICon material can be applied to a support structure. The chemical nature of the support structure is not described in detail. Nor is it described how the LiSICon is applied to the support structure. The separated target product is Li ions.

[0018] From US9222148B2 it is known to separate lithium hydroxide by membrane electrolysis on a LiSICon membrane and then to precipitate lithium hydroxide hydrate.

[0019] In addition to the use of ceramic LiSICon membranes, electrolytic processes for the separation of lithium are also known, which work with organic ion exchange membranes.

[0020] EP 3805428 A1 describes the electrolytic production of lithium hydroxide. In addition to electrolysis, an electrochemical conversion of lithium to lithium hydroxide is carried out. To obtain the necessary reactants, water is simultaneously split electrochemically. A bipolar three-chamber cell with an ion exchange membrane is used for this purpose. The commercial ion exchange membranes used are Asahi®< AVV, Nation®< 902, Fumatech®< FAB, Fumatech®< FKB, and Neosepta®< CMB. The chemical nature of these ion exchange membranes is not disclosed in EP 3805428 A1, but it is highly likely that they are organic membrane materials. The three-chamber cell operates in an acidic environment. Water containing lithium salts, such as lithium sulfate (Li 2 SO 4 ) or lithium chloride (LiCl), is used as feed.

[0021] From US2012 / 103826 an alternative process for the production of lithium hydroxide is known,

[0022] US 10036094 B2 discloses a two-stage electrodialytic / electrolytic production of lithium hydroxide from aqueous lithium sulfate and / or lithium bisulfate with simultaneous water splitting. A two-compartment electrochemical cell is used in the first stage, and a three-compartment cell is used in the second stage. A pH of 8 to 10 can prevail in the three-compartment cell. The cells are equipped with ion exchange membranes. The chemical composition of the membranes is not disclosed. The following commercial membranes are mentioned: Fumatech®< FAB, Astom®< ACM, Asahi®< MV, Nation®< 324, or Astom®< AHA.

[0023] A fundamental disadvantage of polymer membranes is their water permeability. This dilutes the anolyte with water from the catholyte. Furthermore, organic ion exchange membranes are less ion-selective than inorganic LiSiCon materials: They allow not only Li +< but also Na +< to pass through, so that the purity of the target product is compromised as soon as Na is present in the feed. In addition to the purity of the target product, the electrical efficiency of the process also suffers: During electrolysis with non-ion-selective membranes, the valuable electrical energy is also consumed to transport unwanted Na +< into the second compartment. Once in the second compartment, the Na +< is also converted into unwanted by-products via unintended electrochemical processes. Relative to the yield of the target product Li, the energy efficiency of the process is limited.Finally, these membranes are sensitive to the presence of divalent cations such as Mg 2+< and Ca 2+<. These cations poison the membrane over time, thus limiting the service life of organic ion exchange membranes.

[0024] The (glass)ceramic LiSICon materials promise better ion selectivity. However, a highly relevant problem for industrial practice continues to be the stability of the LiSICon membrane with respect to impurities. For example, the Li+<-containing waters produced during the processing of used LIB contain additional cations, particularly Na+< and K+<, which cause lasting damage to the LiSICon material. These cations apparently permanently occupy the defects in the crystal structure, making transport of the Li+< cations through the membrane virtually impossible. The operating life of the electrochemical cell is then over. Because LiSICon material is very expensive, recycling Li from LiB is uneconomical given the short lifetime of the membrane. The brine from Li salt lakes also naturally contains high levels of sodium and therefore cannot be applied to known LiSICon membranes.Therefore, lithium from salt lakes continues to be thermally separated, an energy-intensive process, and / or gradually dissolved and recrystallized using large amounts of water. Although the water is evaporated by solar radiation, the water needed to dissolve LiCl is scarce in the deserts of South America. This method poses major problems there.

[0025] Another practical problem is the high specific electrical resistance of the LiSICon material. This results in a high internal resistance in the electrochemical cell, resulting in a correspondingly high electrical energy requirement for the process. To reduce this resistance, the membrane could theoretically be thinned. However, due to its thin material, its service life in aggressive environments would then be limited.

[0026] Accordingly, the present invention seeks to provide a process for the electrochemical production of LiOH from Li +< -containing water using a LiSICon membrane, which can also be operated economically on an industrial scale. In particular, the process should be highly energy efficient and achieve a long membrane service life even when the feed used contains impurities that are harmful to LiSICon materials.

[0027] This object is achieved by a method according to claim 1.

[0028] A first object of the invention is therefore a process for the production of hydrogen and lithium hydroxide with the following steps: a) Providing a feed containing at least water, Li cations, anions, and impurities, wherein the concentration of Li cations in the feed CF 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, wherein the pH of the feed measured at 25°C by means of a glass electrode is between 2 and 9; b) Providing a lean working medium containing water and lithium hydroxide dissolved therein, wherein the concentration of lithium hydroxide in the lean working medium CM0, based on the total weight of the lean working medium, is at least 50 ppm by weight; c) providing a basic compound; d) providing at least one electrochemical cell, wherein the electrochemical cell has the following features: i. the electrochemical cell comprises a first compartment in which an anode is arranged; ii. the electrochemical cell comprises a second compartment in which a cathode is arranged; iii. the electrochemical cell comprises a membrane separating the first compartment from the second compartment, wherein the membrane has the area A; iv.the membrane contains an inorganic material which has conductivity for Li ions and which is electrically insulating; e) providing at least one electrical voltage source which is connected to the anode via a first electrical line and to the cathode via a second electrical line; f) dosing the basic compound to the feed so that an intermediate is obtained, wherein the pH of the intermediate, measured by means of a glass electrode at 25°C, is between 9 and 13, g) supplying the first compartment with the intermediate; h) supplying the second compartment with the lean working medium; i) supplying the electrochemical cell with an electrical voltage U obtained from the electrical voltage source, such that an electrical current . I flows between anode and cathode, where the quotient Q is the current intensity of the electric current Iand the area A of the membrane is between 100 A / m 2< and 500 A / m 2< or between 150 A / m 2< and 350 A / m 2<; j) withdrawing wastewater containing at least water, Li salts dissolved therein, oxygen, and impurities from the first compartment, wherein the concentration of Li ions in the wastewater Cw, based on the total weight of the wastewater, is lower than the concentration of Li ions in the feed CF ; k) withdrawing a rich working medium containing water and lithium hydroxide and hydrogen from the second compartment, wherein the concentration of lithium hydroxide in the rich working medium C M1 relative to the total weight of the rich working medium is greater than the concentration of lithium hydroxide in the poor working medium C M0 .

[0029] A special aspect of the process according to the invention is that, simultaneously, lithium is selectively separated by the membrane and water electrolysis takes place in the cell. During water electrolysis, water (H2O) is electrochemically separated into H2 and O2. OH-< and hydrogen are formed at the cathode. However, the OH-< anions cannot cross the LiSiCon membrane and combine with the Li+< cations arriving in the cathodic compartment to form lithium hydroxide (LiOH). Oxygen and H+< are formed at the anode.

[0030] When Li+ membrane separation and water electrolysis are operated simultaneously in the electrochemical cell with a LiSICon membrane, lithium hydroxide (LiOH) and molecular hydrogen (H2) are directly produced. LiOH is dissolved in water, and a small amount of H2 is also dissolved, but most of it is expelled as a gas. The water containing the LiOH, as well as the dissolved and gaseous H2, are removed from the cathodic compartment of the cell. The LiOH is separated from the water. In this way, LiOH can be obtained which—due to the selective migration of lithium ions through the membrane—has a sufficient purity for use in battery production.

[0031] The hydrogen produced at the same time can be captured and used in the hydrogen economy. If the electrochemical cell is powered by green electricity, the process also leaves a low carbon footprint.

[0032] The feed for the combined Li separation and water electrolysis requires water containing Li +< cations. Such water is either generated during the processing of spent LiB or a Li brine from a natural deposit is used.

[0033] A key aspect of the process according to the invention is that the electrochemical process is carried out in a basic environment, more precisely at pH 9 to 13. This enables efficient water electrolysis, which in turn is a prerequisite for the direct production of LiOH. Furthermore, initial long-term tests indicate that LiSICon materials exhibit a particularly long service life in this pH range – even at high current densities.

[0034] A pH value between 9 and 13 is preferentially maintained in both the first and second compartments. The pH value can be the same or different in both cells, as long as the respective value is between 9 and 13. When considering the half-cell reactions of water decomposition, it turns out that the combination of an anolyte cell operated with an acidic feed and a catholyte cell operated with a basic working medium requires a higher voltage for water decomposition than the combination of two half-cells, each with a basic feed. Thus, a basic pH value in both half-cells (compartments) is particularly advantageous, as a lower voltage is required for the same processes.Compared to a process in which the anolytic compartment has an acidic pH and the cathodic compartment has a basic pH, the energy savings due to the reduced voltage in a process in which both compartments are basic are in the range of approximately 5 to 15%, depending on the voltage level selected for the membrane process.

[0035] Since lithium-containing recyclable material streams from battery recycling or seawater are generally not basic, but rather tend to be acidic (pH 4 to 9), the pH is adjusted by adding a basic compound to the feed. Only the resulting intermediate, with the desired pH of 9 to 13, is fed into the cell. The pH values ​​are given for temperatures of 25°C. The pH measurement is performed using a glass electrode calibrated with a commercially available test fluid.

[0036] According to the invention, the cathodic compartment is supplied with a working medium. This is water with varying concentrations of LiOH. In the inlet to the second compartment, the concentration c M0 of LiOH is at least 50 ppm by weight. In the effluent, the concentration c M1 of LiOH is much higher. Therefore, the inlet is referred to as " poor working medium" during which the process " rich working medium" is called. The attributes poor and rich refer to the LiOH content. The lower limit of LiOH in the poor working medium c M0 > 50 wt. ppm must be maintained so that the process can start with a low electrical resistance in the working medium: It has been shown that the desired production of LiOH and H 2 is much less successful if the second compartment is charged with water that is free of LiOH. There is no specific upper limit of the LiOH concentration in the poor working medium. However, c M0 < c M1 must apply, since otherwise the process does not produce any LiOH. The 50 wt. ppm LiOH correspond to 15 wt. ppm lithium.

[0037] Another key aspect of the process according to the invention is the high current density at which it is operated. Specifically, the current density, i.e., the quotient Q of the current intensity I and the membrane area A, is between 100 A / m 2 and 500 A / m 2 , or preferably between 150 A / m 2 and 350 A / m 2 . These high current densities allow for high current efficiency, but require good stability of the membrane material under harsh conditions. Therefore, an inorganic material is chosen as the membrane material, which is both electrically insulating and capable of conducting Li ions. Examples of suitable membrane materials are (glass) ceramic LiSiCons.

[0038] As a basic compound used to adjust the pH of the intermediate, one of the following substances or mixtures thereof is preferably used: calcium hydroxide (Ca(OH)2), potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), ammonium hydroxide (NH4OH). These substances are preferably used as aqueous solutions, such as potassium hydroxide solution, sodium hydroxide solution, lithium hydroxide solution, or ammonia water. These aqueous solutions are easy to dose. Potassium hydroxide solution and sodium hydroxide solution are comparatively inexpensive. Lithium hydroxide solution is preferably produced in the process itself.

[0039] Ca(OH) 2 is particularly preferred as the basic compound. Calcium hydroxide is particularly used in its hydrated form, namely as slaked lime. Slaked lime is readily available. Compared to potassium hydroxide and sodium hydroxide, slaked lime has the advantage of containing hardly any K and Na. Consequently, the intermediate is not contaminated with the membrane poisons K +< and Na +<.

[0040] Ideally, the basic compound is added to the feed in such a way that the pH of the intermediate, measured at 25°C using a glass electrode, is between 9 and 12. Within this pH range, water splitting works quite well and the membrane is not attacked. The glass electrode for determining the pH value must be calibrated as usual with a defined test liquid.

[0041] The electrochemical cell can also be operated at temperatures other than 25°C. The pH value does not need to be adjusted: the intermediate should have a pH value at cell temperature corresponding to a pH of 9 to 12 at 25°C. The cell temperature can be between 20°C and 70°C.

[0042] The addition of the basic compound also has the advantage of binding unwanted ions present in the feed. This protects the membrane and improves product purity. In particular, the addition of the basic compound makes it possible to process feed containing one or more of the following anions: sulfate, carbonate, hydroxide, chloride, and fluoride.

[0043] This list assumes that in aqueous solutions, the anions are in equilibrium with the corresponding protonated ions. The exact concentrations depend on the exact pH of the respective solution and can be calculated using the corresponding acid and base constants. The calculation is presented in: Ruland (ed.) et al.: Analytics: Data, Formulas, Exercises. Edition 109, 2019, Walter de Gruyter GmbH & Co. KG, pages 257f.

[0044] 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, and C. The listed alkali and alkaline earth metals are accompanying elements of lithium from natural deposits, while the other metals mentioned are used as conductor or cathode materials in LIB and are therefore found in feeds obtained from the reprocessing of spent LIB. The carbon originates from organic compounds that were present in LIB, such as films, separators, sealants, or adhesives.

[0045] According to the invention, a membrane containing an inorganic material is used. Unlike polymer membranes, this allows the required ion selectivity to be achieved. Preferably, the membrane consists entirely of the inorganic material. Composite membranes that contain the inorganic material only as a coating on a support material or in which the inorganic material is dispersed in a different matrix material have proven to be a mistake.

[0046] For the process to work, the inorganic material must conduct Li ions and at the same time be electrically insulated.

[0047] The specific conductivity σ for Li-ions should be at least 1*10 -5< S / m or at least 5*10 -5< S / m or at least 10*10 -5< S / m and a maximum of 100*10 -5< S / m at a temperature of 23°C. The Li conductivity of the material is measured using impedance spectroscopy. This measurement is performed as follows: The measurement setup consists of two cylindrical electrodes, between which the sample is placed. To ensure optimal contact with the electrodes and reproducible contract pressure, a weight is placed on the sample.

[0048] A potentiostat (ZAHNER-elektrik I. Zahner-Schiller GmbH & Co. KG, Kronach-Gundelsdorf, Germany) is connected to the electrodes and controlled by Thales software (ZAHNER). Measurements are performed in a frequency range of 1 Hz to 4 MHz and an amplitude of 5 mV using polished samples onto which a thin, conductive gold layer has been sputtered.

[0049] The measurement results are presented in Nyquist diagrams and evaluated using the Analysis software (ZAHNER). The electrical resistance is read from the maximum of the Nyquist diagram curve. The specific ionic conductivity σ [mS / cm] is then calculated using the formula σ=(h 10 4< ) / (R π / 4 d 2< ), where h is the sample height in mm, R is the measured electrical resistance in Ω, and d is the sample diameter in mm.

[0050] The specific conductivity for electrons γ (electrical conductivity) should be less than 10 -7 < S / cm (10 -9 < S / m) or less than 10 -12 < S / m or less than 10 -16 < S / m at a temperature of 23°C. Therefore, the inorganic material is classified as a non-conductor from an electron-conducting perspective.

[0051] LiSICon is preferably used as the inorganic material. LiSICon materials are (glass) ceramic materials that conduct lithium ions while simultaneously electrically insulating them. In principle, all known LiSICon materials can be used as inorganic materials within the meaning of the invention. Known LiSICon materials meet the above-mentioned requirements for both the electrical conductivity and the ionic conductivity of the inorganic material.

[0052] For example, the LiSICon material lithium aluminum titanium phosphate (LATP) can be used. Accordingly, a variant of the invention provides that the inorganic material is a compound with the following stoichiometry: Li 1+x Al x Ti 2-x (PO 4 ) 3 , where 0.1≤x≤0.3, preferably x=0.3.

[0053] Alternatively, the LiSICon material lithium aluminum germanium phosphate (LAGP) can be used. Accordingly, a variant of the invention provides that the inorganic material is a compound with the following stoichiometry: Li 1+x Al x Ge 2-x (PO 4 ) 3 , where x=0 or x=0.2 or x=0.4.

[0054] Alternatively, the LiSICon material lithium aluminum titanium silicon phosphate (LATSP) can be used. Accordingly, a variant of the invention provides that the inorganic material is a compound with the following stoichiometry: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 , where 0.1≤x≤0.3 and 0.2≤y≤0.4.

[0055] As an alternative to the aforementioned phosphates, the oxide LiSICon material lithium lanthanum titanium oxide (LLTO) can be used. Accordingly, a variant of the invention provides that the inorganic material is a compound with the following stoichiometry: Li 3x La (2 / 3)-x□(1 / 3)-2x TiO 3 , where 0≤x≤0.16.

[0056] However, LiSICon, which is derived from lithium aluminum germanium phosphate but also contains titanium, is particularly preferred. It is referred to as LAGTP.

[0057] Accordingly, a preferred variant of the invention provides that the inorganic material is a compound of the following stoichiometry: Li 1.4 A 0.4 (Ge 1-x Ti x ) 1.6 (PO 4 ) 3 where: 0≤x≤1.

[0058] A particularly preferred embodiment of the invention provides for the use of a LATSP that additionally contains germanium. It is referred to here as LAGTSP.

[0059] Accordingly, a particularly preferred variant of the invention provides that the inorganic material is a compound of the following stoichiometry: Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 * nGeO 2 where: 0≤x≤1 and 0≤y≤1 and 0≤n≤1

[0060] A LAGTSP is available, for example, from OHARA GmbH, Hofheim, Germany under the product name LICGC ®< AG01

[0061] The lithium hydroxide is contained in the rich working medium and is withdrawn from the second compartment with it. To make it usable, it must be separated from the rich working medium. A separation apparatus is provided for this purpose. A preferred development of the invention therefore provides the following additional process steps: m) providing a separation apparatus; n) separating lithium hydroxide from the rich working medium using the separation apparatus.

[0062] After separating the lithium hydroxide from the rich working medium, the working medium can either be disposed of as wastewater or, preferably, recycled as a lean working medium. For this, the separation apparatus must be operated in such a way that the LiOH is not completely separated, but rather that the minimum concentration c m0 of 50 wt. ppm LiOH is not undercut. The working medium can then be recycled to the second compartment as a lean working medium. This creates a working medium cycle between the second compartment and the separation apparatus.

[0063] A preferred development of the invention therefore provides the following additional process steps: n) separating lithium hydroxide from the rich working medium with the aid of the separation apparatus, so that the poor working medium is obtained, wherein the step b) providing a poor working medium containing water and lithium hydroxide dissolved therein, wherein the concentration of lithium hydroxide in the poor working medium C M0 based on the total weight of the lean working medium is at least 50 ppm by weight; is carried out using the separation apparatus.

[0064] To enable the circulation of the working fluid between the separation device and the second compartment, it makes sense to locate both devices at the same location. This same location is considered to be a coherent production facility. Consequently, the electrochemical cell and separation device are part of a coherent facility.

[0065] It is also conceivable to install the separation device at a different location away from the electrochemical cell. However, this would require transporting the working fluid between the cell and the separation device. However, this makes little sense from an energy perspective.

[0066] Preferably, at least the electrochemical cell is operated continuously. This means that both compartments are continuously flowing. The first compartment is flowed by intermediate, producing wastewater, while the second compartment is flowed by working medium, which flows in as a lean working medium and flows out as a rich working medium. This allows for a higher throughput, while also continuously removing membrane-damaging components of the intermediate and working medium. Therefore, better membrane durability can be expected in continuous operation than in batch operation.

[0067] A key aspect of the process is that hydrogen and lithium hydroxide are produced simultaneously. This is made possible by the combined membrane electrolysis of Li+ and electrochemical water splitting in a basic environment.

[0068] The electrical voltage applied to the electrochemical cell is, at best, constant over time (DC voltage). However, it has proven advantageous to periodically vary the voltage over time. This improves the membrane's service life. One explanation for this could be that membrane-damaging ions are flushed away from the membrane during periods of cell shutdown.

[0069] A preferred development of the method therefore provides that the electrical voltage drawn from the electrical voltage source changes periodically over time.

[0070] Preferably, the voltage changes in a wave-like manner. The waveform can be a sine, a square, a triangle, or a sawtooth.

[0071] In the simplest case, the waveform is achieved by periodically changing the polarity of the voltage (alternating voltage).

[0072] However, it is particularly preferred that the voltage be changed by periodically switching it on and off. A constant value is maintained in the switched-on state. This creates a square wave. In this context, the voltage is also referred to as pulsed voltage. It has proven advantageous to make the times during which the voltage is switched on longer than the times during which it is switched off. The switch-on times are preferably 3 to 7 times as long as the switch-off times, preferably about 5 times as long.

[0073] A preferred development of the method accordingly provides that the waveform is rectangular and is formed by a first wave section in which the voltage is switched on with a constant value and a second wave section following the first wave section in which the voltage is switched off, wherein the length of the first wave section is λ 1, wherein the length of the second wave section is λ 2 and wherein λ 1 = ϕ * λ 2 mit 3 < ϕ < 7 .

[0074] Regarding the periodic change of the voltage, it should be noted that the voltage does not necessarily have to change polarity like an alternating voltage. It is conceivable to change the voltage with an amplitude of U=0; however, it is preferable to leave the polarity (i.e., the sign) of the voltage constant and only change the magnitude of the voltage. A preferred development of the method therefore provides for the polarity of the electrical voltage to be maintained.

[0075] The invention will now be explained in more detail using process flow diagrams. These are shown in: Figure 1: Principle of simultaneous membrane electrolysis of Li +< and water electrolysis in an electrochemical cell with LiSICon membrane; Figure 2: Principle of the circuit between the electrochemical cell and the separation device.

[0076] The electrochemical cell 0 required for carrying out the process is in Figure 1It comprises a first compartment 1 and a second compartment 2. Both compartments 1, 2 are separated from each other by a membrane 3. An anode 4 is arranged in the first compartment 1. A cathode 5 is arranged in the second compartment 2. The first compartment 1 can therefore also be referred to as the anodic compartment, while the second compartment 2 is referred to as the cathodic compartment.

[0077] A first electrical line 6 connects the anode 4 to a voltage source 7. A second electrical line 8 connects the cathode 5 to the voltage source 7. The polarity of the voltage source 7 is selected such that the positive pole of the voltage source 7 is connected to the anode 4, while the negative pole of the voltage source 7 is connected to the cathode 5. This polarity is always maintained, even if the magnitude of the electrical voltage U drawn from the voltage source 7 changes over time. In the simplest case, however, U is constant over time.

[0078] An electric current flows through the two electrical lines 6, 8 and via the electrical voltage source 7 I . Since the membrane 3 is electrically insulated, there is no electrical short circuit between the two electrodes 4, 5 via the membrane 3.

[0079] Membrane 3 is a flat membrane made entirely of LiSiCon material. Anode 4 is a flat metallic sheet containing titanium, niobium, or tantalum. Cathode 5 is also a flat metallic sheet containing titanium or nickel. In the simplest case, stainless steel sheet is used as the cathode. Anode 4, cathode 5, and membrane 3 have the same shape; they can be rectangular or circular. This is clearly visible in the side view of the Figure 1 not visible. Instead of sheet metal, expanded metal, grids, or meshes made of the specified materials can also be used as electrodes.

[0080] The electrochemical cell 0 has an active area A which corresponds to the area of ​​the membrane 3, the anode 4 and the cathode 5.

[0081] During operation, the first compartment 1 is charged with an intermediate 9. Intermediate 9 is an aqueous solution containing Li+ cations. From an electrochemical perspective, intermediate 9 can be considered an anolyte.

[0082] The intermediate 9 is obtained by mixing a feed 10 with a basic compound 11. The feed 10 can be a Li liquor from a natural deposit or a material stream resulting from the processing of spent LIB. The concentration of Li+ cations in the feed 10 (formula letter er) should be at least 200 wt. ppm, based on the total mass of the feed. Seawater has a lower Li concentration and would therefore need to be concentrated before being used in the process. The feed 10 also contains anions such as sulfate or chloride. The feed 10 also contains impurities. Anions and impurities are present in Figure 1Not shown. The main component of feed 10 is water H 2 O. The pH of the feed is between 2 and 9.

[0083] The basic compound 11 is ideally calcium hydroxide Ca(OH)2 (slaked lime). Dosing the basic compound 11 into the feed 10 produces the intermediate 9. The purpose of adding the basic compound 11 to the feed 10 is to increase the pH to the alkaline range, more precisely to a pH between 9 and 13. According to the invention, the electrochemical processes in the cell are carried out in a basic environment. The dose of the basic compound 11 is therefore selected such that the pH of the intermediate assumes a value between 9 and 13. The intermediate 9 is fed into the first compartment 1.

[0084] The second compartment is loaded with a lean working medium 12. The lean working medium 12 is water H 2 O with a low concentration CM0 Li +< cations. The concentration c 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 is to be regarded as a catholyte.

[0085] The electrochemical cell 0 is also subjected to an electrical voltage U drawn from the voltage source 7. This has the following effect: Firstly, water electrolysis occurs, in which water (H 2 O) is electrochemically separated into hydrogen (H 2 ) and oxygen (O 2 ). At the cathode 5, OH -< and hydrogen are formed. However, the OH -< anions cannot cross the membrane 3 and combine with the Li +< cations present in the cathodic compartment 2 to form lithium hydroxide (LiOH). At the anode 4, oxygen and H +< are formed.

[0086] The formation of LiOH in the cathodic compartment 2 is maintained by the migration of Li+ cations from the intermediate 9 towards the cathode 5, driven by the voltage U. They overcome the membrane 3 due to its Li conductivity and accumulate in the working medium (membrane electrolysis). This creates a rich working medium 13, which is withdrawn from the second compartment 2. The concentration of Li+ ions in the rich working medium 13 is higher than in the poor working medium 12; c M1 > c M0 .

[0087] In the electrochemical cell 0, water electrolysis, membrane electrolysis of Li +< and synthesis of LiOH occur simultaneously.

[0088] When Li+ membrane electrolysis and water electrolysis are operated simultaneously in the electrochemical cell, lithium hydroxide (LiOH) and molecular hydrogen (H2) are directly produced. The LiOH is dissolved in the water, while the hydrogen is partially dissolved in the water and also exists in gaseous form. The water, along with the LiOH and dissolved hydrogen, is withdrawn from the cathodic compartment of the cell as a rich working medium (13). Gaseous hydrogen is also withdrawn from the second compartment (2).

[0089] The intermediate 9 is depleted of Li + by membrane electrolysis, resulting in wastewater 14. c W < c F . The formula letter c W stands for the concentration of Li ions in the wastewater 14, relative to the total mass of the wastewater 14. The formula letter c F stands for the concentration of Li ions in the feed 10, based on the total weight of the feed 10.

[0090] In Figure 2 It is shown how LiOH is obtained as target product 15 from the rich working medium 13.

[0091] For this purpose, a separation apparatus 16 is provided, into which the rich working medium 13 is introduced. The separation apparatus 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 specification of the target product.

[0092] The separation apparatus 16 may be a distillation column or a crystallizer.

[0093] The LiOH-depleted output stream of the separation apparatus 16 is recycled as lean working medium 12 into the second compartment 2 of the electrochemical cell 0.

[0094] As already mentioned, the poor working medium 12 must have a certain concentration CM0 of LiOH so that the process in the electrochemical cell 0 starts as desired thanks to a low starting resistance. C M0 should be at least 50 ppm by weight based on the total mass of the lean working medium 12. In order to achieve the required concentration C M0 is ensured, the separation apparatus 16 is operated in such a way that it does not completely separate the LiOH from the rich working medium 13.

[0095] In addition to lithium hydroxide LiOH, the process also produces hydrogen H 2 . The hydrogen H 2 is at least partially dissolved in the rich working medium 13 and is withdrawn from the second compartment 2 together with the LiOH. Part of the hydrogen escapes from the second compartment 2 in the gaseous state.

[0096] Since hydrogen H2 easily evaporates from water, no great effort is required to remove it from the rich working medium. Only if the hydrogen H2 is to be used as a second target product is a second separation device required to extract the hydrogen separately in a suitable quality / purity (not shown).

[0097] The water H2O contained in the rich working medium 13 is almost completely recycled as the lean working medium 12. Only the water contained in the target product 15 is lost from the process. It must be added accordingly to the lean working medium 12 (not shown). The water contained in the intermediate 9, originating from the feed, does not enter the circuit between the second compartment 2 and the separation apparatus 16 because the membrane 3 is impermeable to water. Examples Experimental setup and implementation

[0098] The following describes the influence of impurities in the form of foreign ions on ceramic, lithium-conductive membranes during electrolysis. Furthermore, the effects of pH and voltage cycling are described.

[0099] To perform the electrolysis, the electrolysis cell is first assembled and connected to the anolyte and catholyte tanks. Care is taken to ensure that the inlet and return lines are connected to the same side.

[0100] A round disc with a diameter of 19.5 mm and a thickness of 1 mm was used as the anode and cathode. The material in each case was a titanium expanded metal sheet coated on both sides with IrTi mixed oxide, 12 g Ir / m2, 1 AF D1.5 mm, from Metakem GmbH, 61250 Usingen, Germany.

[0101] The sampled membranes were also circular discs with a diameter of approximately 25 mm. The thickness of the membranes was approximately 1 mm. The material of the sampled membranes is specified in the individual examples.

[0102] The electrolysis unit and the corresponding storage tanks are blanketed with nitrogen throughout the entire process to prevent the formation of lithium carbonate. Each cell has a separate anolyte and catholyte tank. Each tank is filled with approximately 1 kg of liquid; the exact mass is determined by backweighing. In all experiments, the catholyte was always a 5 mmol / L LiOH solution (equivalent to 120 wt. ppm LiOH). The anolyte is a lithium salt solution in various concentrations and with various lithium salts.

[0103] The experiment is started by switching on the pumps and the desired voltage. The maximum flow rate is 900 mL / minute. Sampling occurs every half hour or at longer intervals as agreed. 3 mL of pre-flow is drawn and discarded. With each sample, the current is recorded, and the pH and conductivity of the sample are determined. The samples are then returned to the appropriate containers to maintain a nearly constant volume.

[0104] After the experiment, the containers are emptied, and all lines and the membrane are rinsed with deionized water. The cell is disassembled, the membrane is photographed, and SEM images of the catholyte and anolyte sides are taken to document any damage or changes to the membranes.

[0105] Several experiments were conducted with pH adjustment of the anolyte to confirm the hypothesis that a low pH negatively impacts membrane performance. Experiments without pH adjustment led to very poor results. In experiments with pH adjustment, the pH of the anolyte solution is adjusted to the desired range before the experiment begins using the appropriate dose of a basic compound. If the pH drops during the experiment, additional additions are made to maintain the pH. In comparison, experiments in which the pH decreases according to the natural behavior of the solutions during electrolysis.

[0106] In experiments with pulsed voltage, the voltage supply is interrupted at a defined time interval, so that no voltage is applied to the electrochemical cell during that time. Over time, the voltage is applied in a rectangular wave without a change in polarity. This is intended to flush the membrane of potentially interfering ions (H') during the voltage-free period, reducing membrane damage and improving membrane performance.

[0107] Membrane performance is measured by the parameters of 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 membrane area and time. Permeability also takes membrane thickness into account and thus allows for comparison between different membrane types with varying thicknesses. Both parameters are necessary for a comprehensive description of performance, as extremely thin membranes would enable extremely high permeance. However, if concentration polarization effects occur in the membrane cell, the permeabilities would be incorrectly represented. Taking membrane thickness into account is then no longer useful, as transport is not limited by the membrane.

[0108] All measured values ​​shown in the examples are subject to a measurement error of approximately + / - 10%, which can be attributed to inaccuracies in the positioning of the electrodes relative to each other, the determination of the thickness of the membrane samples and the concentration determination via conductivity measurements.

[0109] All ceramics used come from the manufacturers listed in Table 0 and can be ordered there under the corresponding product names. Table 0: Ceramics used and their manufacturers Manufacturer Product name Description Stoichiometry OHARA GmbH LICGC ®< PW01 Ohara LiCGC ®< Powder PW01 Li 1.75 Al 0.6 Ti 1.4 Si 0.15 P 2.85 O 12 OHARA GmbH AG01 Ohara LiCGC ®< Ceramic AG01 Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 -GeO 2 OHARA GmbH SP01 Ohara LiCGC ®< Ceramic SP01 Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 Ampcera ™< (sold by MSE Supplies) LISICON LAGP Solid State Electrolyte Membrane for Advanced Lithium Batteries, diameter d=25.4 mm Ampcera LAGP Ceramic Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 , Toshima Manufacturing Co., Ltd. Materials System Division Li0.33La0.55TiO3 d25×0.8mm Toshima LLTO ceramic Li 0.33 La 0.55 TiO 3

[0110] Lithium hydroxide was used by Aldrich in PA grade. All other materials were used in technical grades.

[0111] Unless otherwise stated, approximately 1 mm thick LATSP membranes (LICGC ® , Ohara) were used. The membrane discs were manufactured using an SPS sintering process at a pressure of 100*10 5< Pa to 200*10 5< Pa and a temperature of 950°C, or alternatively, they were purchased directly from various manufacturers (Ohara, Ampcera, Toshima) in the size appropriate for the measuring cells. Description of the sintering process Sintering using FAST / SPS

[0112] The LATSP powder used is sintered using FAST / SPS (field assisted sintering technology / spark plasma sintering). Sintering is carried out with a simultaneous increase in pressure and temperature to achieve high densification and effective sintering in a very short sintering time. The sintering mold consists of a graphite matrix with an outer diameter of 80 mm, an inner diameter of 36 mm and a height of 55 mm, two graphite half-shells with a wall thickness of 10 mm and a similar height, and two graphite punches with a diameter of 25 mm and a height of 30 mm. The half-shells are positioned in the matrix, and a punch is inserted into the half-shells from the bottom. Before 2.5 g of powder is weighed into the matrix onto the lower punch, graphite foil is placed on the punch to improve contact.Once the powder has been weighed, a second graphite foil is placed on the powder and the upper punch is inserted into the half-shells. The die assembly is positioned in the furnace chamber of the FAST / SPS furnace between two plates made of carbon fiber reinforced graphite. The assembly is contacted via the travel path of the electrodes and the desired pressure is built up. The die is also heated using an alternating current, which allows high temperatures to be reached in a short time. After a slow temperature increase to 250 °C over five minutes, the maximum temperature of 900 °C is reached at a heating rate of 130 °C / min, which is then held for a further five minutes. During the temperature increase, the pressure is also increased to 43 MPa within five minutes, where it is also held for five minutes. At the end of the holding time, the upper electrode is released from contact with the die and the die cools down.The sintered membrane can then be removed from the mold. Example 1 (LATSP)

[0113] First, the voltage dependence of the ceramic membranes during electrolysis was investigated. Electrolysis was carried out with 0.1 mol / L LiOH and 1 mol / L LiOH at voltages ranging from 3 V to 6 V. The measured results are presented in Table 1.

[0114] When plotting the values ​​graphically, the linear relationship becomes clear. The intersection point of the x-axis lines at approximately 2 V results from the decomposition voltage of the water and the internal resistance of the cell. This intersection point is almost identical for both concentrations. The graph is in Figure 3 shown. Table 1: Voltage dependence of electrolysis with ceramic membranes permeability Tension (gLi*mm / m 2< *h) [V] 0.1 mol / L 1 mol / L 3 4 6 4 9 13 5 12 15.5 6 17 26 Example 2 (LATSP)

[0115] Furthermore, it was found that the membrane performance is independent of the anolyte concentration. Electrolyses were performed with 0.1, 1.0, 2.0 mol / L LiOH, and 4.0 mol / L LiOH, respectively, which was placed in the anolyte container, at voltages of 3 V and 6 V.

[0116] The molar fractions of LiOH correspond to the following weight fractions of Li: 0.1 mol / L = 700 ppm Li = 2400 ppm LiOH 1.0 mol / L = 7000 ppm Li = 24000 ppm LiOH 2.0 mol / L = 14000 ppm Li = 48000 ppm LiOH 4.0 mol / L = 28000 ppm Li = 96000 ppm LiOH

[0117] The measurement results are shown in Table 2. At concentrations from 1 mol / L to 4 mol / L, no significant increase in membrane performance was measured. A LiOH concentration of 0.1 mol / L achieved a slightly lower performance. A graphical representation shows Figure 4 . Table 2: No dependence on the anolyte concentration Anolyte concentration permeability [minor] (gLi*mm / m 2< *h) 3 V 6 V 0.1 4 17 1 6 30 2 8 32 4 8.5 30.5 Example 3 (LATSP)

[0118] The electrolysis was carried out with 0.1 mol / L of the corresponding lithium salt in the anolyte circuit at 3 V, 4 V, and 6 V. The permeabilities are of a comparable order of magnitude at the beginning of the experiment after a short runtime (indicated in parentheses). As expected, the permeability of lithium hydroxide and lithium carbonate can be increased by increasing the voltage. However, for lithium chloride and lithium sulfate, the permeability decreases with longer runtimes and at higher voltages.

[0119] A pH determination at the end of each experiment showed that the pH values ​​of the lithium chloride and lithium sulfate solutions had dropped to pH 3 to 4.

[0120] Measured values ​​are shown in Table 3. A graphical representation provides Figure 5 . Table 3: Influence of anions on permeability Anion permeability (gLi*mm / m 2< *h) 3V (30 min) 4V (120 min) 6V (360 min) OH-< 3.1 9.4 27 Cl -< 3.2 0.3 0.9 SO4 2-< 3.8 1.2 1.4 CO3 2-< 4.5 6.0 17 Example 4 (LATSP)

[0121] To examine the influence of the pH of the anolyte circuit on membrane performance during electrolysis in more detail, a comparison was carried out with lithium chloride at a concentration of 0.1 mol / L and 1.0 mol / L, at a pH of 4 and 11, and at an electrolysis voltage of 3 V. The pH was adjusted using a few drops of a 1.0 mol / L lithium hydroxide solution. At both concentrations, the increased pH resulted in an increase in permeability. In electrolysis with LiCl solutions without pH adjustment with lithium hydroxide, the pH of the anolyte continuously decreases; therefore, the permeability in these measurements is subject to error when correlated with the pH, as the pH could not be maintained constant over long periods.

[0122] Results are reported in Table 4. A graphical representation is provided Figure 6 . Table 4: Influence of pH on permeability / / Adjustment with LiOH concentration permeability [minor] (gLi*mm / m 2< *h) pH 11 pH 4 0.1 4.5 2 1 5 3 Example 5

[0123] In a 24-hour experiment, the influence of the pH value of the anolyte circuit when increasing the voltage was tested with a 1.0 mol / L LiCI solution.

[0124] A low pH value and an increased voltage (3 to 8 V) do not lead to stable, consistent permeabilities. The pH value varies depending on the test duration until it settles at approximately pH 4 during the test run, meaning the permeability does not maintain a constant value over the test period.

[0125] When the pH is adjusted by adding a small amount of LiOH solution, the permeabilities stabilize at a high level. The results, which are obtained after approximately 3 to 5 hours, are summarized in Table 5. A graphical representation is provided. Figure 7 . Table 5: Dependence of permeability on pH and voltage Tension permeability [V] (gLi*mm / m 2< *h) pH 11 pH 4 3 5 3 4 7 0.5 6 8.5 1.4 8 14.7 1.5 Example 6 (LATSP)

[0126] Since pH adjustment with lithium hydroxide would not be practical, the pH of the anolyte circuit was adjusted with calcium hydroxide (Ca(OH)2) in this experiment. Since calcium hydroxide is poorly soluble, replenishment when the pH drops is difficult: The intermediate contained solids and was slightly turbid. The experiment was conducted with a 0.1 mol / L lithium chloride solution, the pH of which was adjusted to 12 with Ca(OH)2.

[0127] Adjusting the pH with Ca(OH) 2 leads to a significant increase in membrane permeability by more than 50%. The results are summarized in Table 6. A graphical representation is provided. Figure 8 . Table 6: Influence of pH on permeability / / Adjustment via Ca(OH) 2 Tension permeability [V] (gLi*mm / m 2< *h) pH 4 pH 12 4 0.5 5 6 1.4 4.2 8 1.5 4.2 Example 7 (LATSP)

[0128] Even with lithium sulfate Li 2 SO 4 as a salt in the anolyte circuit, the pH drops during electrolysis and the membrane is damaged. Adjusting the pH with Ca(OH) 2 does not improve membrane performance in this case, as sparingly soluble CaSO 4 forms and deposits on the membrane. Adjusting the pH with 1.0 mol / L LiOH solution does not lead to the formation of deposits on the membrane and to a sharp decrease in permeability, but rather improves it. The results are reported in Table 7. A graphical representation is provided. Figure 9 . Table 7: Influence of Li 2 SO 4 on permeability Anolyte ingredients Tension PH value permeability [V] (gLi*mm / m 2< *h) Li2SO4 6 2.7 2.6 Li2SO4 + Ca(OH)2 6 12 0.2 Li2SO4 + LiOH 6 12 21 Example 8 (LATSP)

[0129] Lithium carbonate as a salt in the anolyte exhibits different behavior than lithium chloride and sulfate. At 4 V, the membrane's performance is somewhat lower, but at 6 V it is. Between 8 V and 10 V, the permeability stabilizes at a stable level, so increasing the voltage does not lead to an increase in permeability.

[0130] This is due to the limited solubility of lithium carbonate, which only allows a maximum concentration of approximately 0.15 mol / L. As already explained in Example 2, the permeability is lower at lower lithium concentrations. Furthermore, the pH increase by adding Ca(OH) 2 is only possible to a limited extent due to the buffering effect of Li 2 CO 3 . This, taken together, is responsible for the different behavior of Li 2 CO 3 in the electrolysis experiment compared to LiCl and Li 2 SO 4 . The results are shown in Table 8. Table 8: Influence of Ca(OH) 2 addition on the permeability when using LiCl, Li 2 SO 4 and Li 2 CO 3 Tension permeability [V] [ gLi*mm / m 2< *h ] LiCl Li2CO3 Li2SO4 4 6.1 2.1 6 4.5 11 0.2 8 4.5 11.2 10 10.8 0.4 Example 9 (LATSP)

[0131] To minimize permeability impairment caused by the added Ca(OH)2 solution, tests were conducted with additional voltage cycling. Two different cycling intervals were tested. In cycling interval 1, the voltage is switched on for 10 seconds and then switched off for 2 seconds. This results in a 25% increase in permeability.

[0132] At timing interval 2, the voltage is switched on for 50 seconds and off for 10 seconds, and a permeability improvement of 61% is achieved.

[0133] Table 9 compares one experiment with lithium chloride in various combinations with timing intervals 1 and 2, pH adjustment with LiOH and Ca(OH) 2. The reference value is the comparison value for lithium hydroxide. Lithium chloride with Ca(OH) 2 and timing interval 2 performed best. All experiments were conducted with 0.1 mol / L LiCl, 6 V, and 900 ml / min overflow rate. The results are shown in Table 9, and a graphical representation can be found in Figure 10 . Table 9: Influence of voltage timing, interaction with addition of Ca(OH) 2 Influencing factor Permeability [g mm / m 2< h ] LiOH 27.0 LiCl 1.0 LiCl + Ca(OH)2 6.4 LiCl + Ca(OH)2 + T1 3.6 LiCl + LiOH + T1 4.0 LiCl + Ca(OH)2 + T2 16.6 LiCl + LiOH + T2 13.3 Example 10 (Testing various LiSICon materials)

[0134] The description of the various LiSICon materials in the electrochemical process of lithium hydroxide and hydrogen production is based on the determination of the permeability at different voltages for a basic 1.0 mol / L lithium hydroxide solution as anolyte. The results are presented in Figure 11 shown.

[0135] From this, the properties of the materials can be derived very well; however, it should also be noted that a material with lower permeability can be used well in the described process if the materials are processed into thin membranes.

[0136] The materials tested are listed in Table 0. In the legend of the Figures 11 and 12 LATSP stands for LICGC ®< PW01, LATSP-AG-01 for LiCGC ®< AG01, and LATSP-SP01 for LiCGC ®< SP-01 from Ohara. LAGP stands for the Ampcera material, and LLTO for the Toshima material.

[0137] Alternatively, the behavior of the different ceramics can also be described by the respective permeance ( Fig. 12 This representation is more suitable when mass transport in the electrolysis cell is limited. The reason why the LATSP SP01 differs from the other LiSICons investigated in this representation may be that this material is very thin at 0.15 mm and therefore not as stable as the other materials investigated.

[0138] The Figures 11 and 12 underlying measured values ​​are shown in Table 13: Table 13: Measured values ​​for Example 10 Membrane material Voltage [V] Permeability [g mm / m2 h] Permeance [g / m2 h] LATSP 3.0 4.8 6.7 LATSP 4.0 9.6 LATSP 5.0 17.0 LATSP 6.0 26.8 47.0 LAGP-Ampcera 3.0 5.8 LAGP-Ampcera 6.0 20.5 LAGP-Ampcera 9.0 34.0 LAGP-Ampcera 3.0 2.0 6.8 LAGP-Ampcera 5.0 5.2 17.4 LAGP-Ampcera 7.0 15.6 51.9 LAGP-Ampcera 9.0 21.2 70.5 LATSP-AG-01 3.0 0.8 5.6 LATSP-AG-01 6.0 4.7 31.2 LATSP-AG-01 8.0 9.1 60.5 LATSP-AG-01 9.0 10.9 72.8 LATSP-AG-01 10.0 14.4 95.7 LATSP-AG-01 12.0 18.3 122.0 LLTO-Toshima 4.0 8.0 10.0 LLTO-Toshima 6.0 16.5 20.6 LATSP-SP01 3.0 9.2 61.0 LATSP-SP01 5.0 11.4 76.0 Example 11 (LAGP)

[0139] A basic anolyte solution was contaminated with approximately 1000 ppm (g / g) of each of the following cations: sodium; potassium; magnesium; calcium. Using an LAGP membrane from Ampcera, the lithium can be separated from the solution with the Figure 13 The permeabilities compiled were transferred to the catholyte. All catholytes (purified LiOH) contained less than 10 ppm of the corresponding impurities according to ion chromatographic analysis. A voltage pulse of 5 V was applied in each case, as in Example 9, Pulse 2. Example 12 (LATSP)

[0140] A basic anolyte solution contaminated with approximately 1000 ppm sodium ions. Using a LATSP membrane (LICGC PW01, Ohara, sintered as described above), the lithium can be extracted from the solution with the Figure 14The permeability shown in the catholyte is enriched. For comparison, the permeability in the absence of Na is given. The cell voltage was 5 V, cycled at T2, as described in Example 9. The purified LiOH contained less than 10 ppm sodium ions according to ion chromatographic analysis. ion chromatographic analysis

[0141] In Examples 11 and 12, the contents of Li and Na ions in anolyte and catholyte were determined by ion-exchange chromatography (IEC) as follows: The samples were filtered before measurement using a syringe filter (type Chromafil ®< Xtra MV-20 / 25, pore size 0.20 µm, for aqueous and polar media).

[0142] Before the investigation, the IEC instrument (Metrohm IC 930 Compact, C Supp C6 250 / 4.0, standard (1.7 mM HNO3, 1.7 mM dipicolinic acid), conductivity sensor) was referenced and externally calibrated for Li and Na. The calibration lines used are shown in the Figures 15(for Na) and 16 (for Li). Conclusion

[0143] The experiments show that the permeability of the membranes tested deteriorates due to the presence of lithium sulfate, lithium chloride, and lithium carbonate. However, this damaging effect can be reduced by adding hydroxides such as Ca(OH)2, but also LiOH, especially when the electrical voltage is pulsed. High permeability is a prerequisite for high process efficiency. Therefore, the measures identified help to operate the process more efficiently. List of reference symbols

[0144] 0 electrochemical cell 1 first compartment 2 second compartment 3 membrane 4 anode 5 cathode 6 first electrical line 7 voltage source 8 second electrical line 9 intermediate 10 feed 11 basic compound 12 lean working medium 13 rich working medium 14 wastewater 15 target product 16 separation apparatus H 2 OWater H 2 Hydrogen O 2 Oxygen LiOHLithium hydroxide OH -< OH anions Li +< Lithium cations Uelectrical voltage Ielectrical current Aactive area C F Concentration LiOH in feed CwConcentration LiOH in wastewater C M0 concentration of LiOH in the poor working medium C M1 Concentration LiOH in the rich working medium

Claims

1. Process for producing hydrogen and lithium hydroxide, comprising the following steps: a) providing a feed comprising at least water, Li cations, anions, and also impurities, the concentration of Li cations in the feed CF being 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, the pH of the feed measured at 25°C using a glass electrode being between 2 and 9; b) providing a poor working medium comprising water and lithium hydroxide dissolved therein, the concentration of lithium hydroxide in the poor working medium CM0, based on the total weight of the poor working medium, being at least 50 ppm by weight; c) providing a basic compound; d) providing at least one electrochemical cell, wherein the electrochemical cell has the following properties: i. the electrochemical cell includes a first compartment in which an anode is arranged; ii. the electrochemical cell includes a second compartment in which a cathode is arranged; iii. the electrochemical cell includes a membrane that separates the first compartment from the second compartment, the membrane having the area A; iv. the membrane comprises an inorganic material that possesses conductivity for Li ions and that is electrically insulating; e) providing at least one electrical voltage source that is connected to the anode via a first electrical lead and to the cathode via a second electrical lead; f) metering the basic compound into the feed such that an intermediate is obtained, the pH of the intermediate measured at 25°C using a glass electrode being between 9 and 13; g) charging of the first compartment with the intermediate; h) charging of the second compartment with the poor working medium; i) charging of the electrochemical cell with an electrical voltage U drawn from the electrical voltage source such that an electrical current I flows between the anode and cathode, the ratio Q of the current strength of the electrical current I and the area A of the membrane being between 100 A / m2 and 500 A / m2 or between 150 A / m2 and 350 A / m2; j) withdrawing from the first compartment of wastewater comprising at least water, Li salts dissolved therein, oxygen and also impurities, the concentration of Li ions in the wastewater Cw, based on the total weight of the wastewater, being lower than the concentration of Li ions in the feed CF; k) withdrawing from the second compartment of a rich working medium comprising water and lithium hydroxide and also hydrogen, the concentration of lithium hydroxide in the rich working medium CM1, based on the total weight of the rich working medium, being greater than the concentration of lithium hydroxide in the poor working medium CM0.

2. Process according to Claim 1, characterized in that the basic compound is selected from the group consisting of Ca(OH)2, KOH, NaOH, LiOH and NH4OH.

3. Process according to Claim 2, characterized in that the basic compound is Ca(OH)2.

4. Process according to Claim 1, 2 or 3, characterized in that the pH of the intermediate, measured using a glass electrode at 25°C, is between 9 and 12.

5. Process according to any of Claims 1 to 4, characterized in that the anions present in the feed are selected from the group consisting of sulfate, carbonate, hydroxide, chloride and fluoride.

6. Process according to any of Claims 1 to 5, 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.

7. Process according to any of the preceding claims, wherein the inorganic material present in the membrane possesses a specific conductivity for Li ions σ, measured by the "impedance spectroscopy" method described herein, that at a temperature of 23°C is at least 1*10-5 S / m or at least 5*10-5 S / m or at least 10*10-5 S / m and not more than 100*10-5 S / m.

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

9. Process according to Claim 7, characterized in that the inorganic material is a compound of the following stoichiometry (LATSP):         Li1+x+yAlxTi2-xSiyP3-yO12 in which: 0.1 ≤ x ≤ 0.3 and 0.2 ≤ y ≤ 0.4.

10. Process according to Claim 7, characterized in that the inorganic material is a compound of the following stoichiometry (LAGTSP):         Li1+x+yAlxTi2-xSiyP3-yO12 * nGeO2 in which: 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1 and 0 ≤ n ≤ 1.

11. Process according to Claim 7, characterized in that the inorganic material is a compound of the following stoichiometry (LAGTP):         Li1.4Al0.4(Ge1-xTix)1.6(PO4)3 in which: 0 ≤ x ≤ 1.

12. Process according to Claim 7, characterized in that the inorganic material is a compound of the following stoichiometry (LAGP):         Li1+xAlxGe2-x(PO4)3 in which: x = 0 or x = 0.2 or x = 0.4.

13. Process according to Claim 7, characterized in that the inorganic material is a compound of the following stoichiometry (LLTO):         Li3xLa(2 / 3) -x□(1 / 3) -2xTiO3 in which: 0 ≤ x ≤ 0.16.

14. Process according to any of the preceding claims, comprising the additional steps of: m) providing a separation apparatus; n) separating lithium hydroxide from the rich working medium with the aid of the separation apparatus.

15. Process according to Claim 14, characterized in that the step of n) separating lithium hydroxide from the rich working medium with the aid of the separation apparatus; affords the poor working medium, such that the step of b) providing a poor working medium comprising water and lithium hydroxide dissolved therein, the concentration of lithium hydroxide in the poor working medium CM0, based on the total weight of the poor working medium, being at least 50 ppm by weight; takes place with the aid of the separation apparatus.

16. Process according to Claim 14 or 15, characterized in that the electrochemical cell and the separation apparatus are provided in the same location.

17. Process according to any of Claims 1 to 16, characterized in that at least the electrochemical cell is operated continuously.

18. Process according to any of Claims 1 to 17, characterized in that the production of hydrogen and lithium hydroxide take place simultaneously.

19. Process according to any of the preceding Claims 1 to 18, characterized in that the electrical voltage drawn from the electrical voltage source changes periodically over time.

20. Process according to Claim 19, characterized in that the electrical voltage drawn from the electrical voltage source changes over time in a waveform-like manner, the waveform being selected from the group consisting of the following waveforms: sine, rectangle, triangle or sawtooth.

21. Process according to Claim 20, wherein the waveform is rectangular, that is to say formed from a first wave section in which the voltage is switched on at a constant value and, following on from the first wave section, a second wave section in which the voltage is switched off, where the length of the first wave section is λ1, where the length of the second wave section is λ2 and where the following relationship applies: λ1 = φ* λ2 where 3 < φ < 7.

22. Process according to Claim 19, 20 or 21, characterized in that the polarity of the electrical voltage is maintained.

23. Process according to any of Claims 1 to 22, characterized in that the prevailing pH in both the first compartment and the second compartment, measured at 25°C with a glass electrode, is from 9 to 13.