EP4314391A2

EP4314391A2 - Stabilized electrodes

Info

Publication number: EP4314391A2
Application number: EP22715629.6A
Authority: EP
Inventors: Volker PRESSER; Lei Wang; Srimuk PATTARACHAI
Original assignee: Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Current assignee: Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Priority date: 2021-04-01
Filing date: 2022-03-24
Publication date: 2024-02-07
Also published as: JP2024511802A; WO2022207449A3; KR20230164126A; WO2022207449A2; DE102021108464A1

Abstract

The invention relates to an electrode material for extracting an elemental ion from a liquid medium, comprising at least one electrode material having at least one ion sieve that is capable of retaining or releasing an elemental ion, or a mixture of such ion sieves, wherein the ion sieve or ion sieves is or are coated with carbon.

Description

Stabilized electrodes

description

field of invention

The invention relates to an electrode material for extracting an element ion from a liquid medium.

State of the art

The demand for rechargeable lithium-ion-based energy storage has increased dramatically due to the expected sharp increase in the deployment of mobile electronics and electric vehicles powered by lithium-ion batteries. It is predicted that between 2015 and 2050, five million tons of lithium, more than a third of the total lithium reserves available on land, will be consumed and lithium reserves could be exhausted by 2080. Currently, most lithium is extracted from brine due to its relatively low cost and richer reserves compared to mineral resources. There is a great demand for low-cost, environmentally friendly methods of using lithium can be obtained quickly and in large quantities. There are several methods such as solar evaporation, adsorption and electrolysis to recover lithium from brine. Although the method of solar evaporation is the most widely used, it is time-consuming and space-consuming. Adsorption methods require large amounts of acids for regeneration and electrolysis methods suffer from relatively low lithium recovery efficiency and membrane fouling. Consequently, there is a need to develop advanced, sustainable and effective technologies for lithium recovery.

Electrochemical processes are particularly promising for lithium production because of the simplicity of the process, the energy efficiency, and the high lithium selectivity. In the work by Kanoh et al. from 1993, λ-MnO ₂ (lithium extraction) and Pt (O ₂ production) were introduced as electrodes for lithium extraction. (Kanoh, H.; Ooi, K.; Miyai, Y.; Katoh, S., Electrochemical recovery of lithium ions in the aqueous phase. Separation Science and Technology 1993, 28, (1-

3), 643-651.) In 2012, Pasta et al. introduced a new cell concept in which lithium iron phosphate (LiFePO ₄ ) and silver serve as cathode and anode (Pasta, M.; Battistel, A.; La Mantia, F., Batteries for lithium recovery from brines. Energy & Environmental Science 2012, 5, (11), 9487.). In this

In a cell, a cycle comprises two half-cycle processes of capture and release. During charging, the lithium and chloride ions are trapped by iron phosphate and silver, respectively; during discharging, the ions are released from the electrodes into the solution. In the years that followed, many studies were reported on lithium extraction from brine, and almost all of them are green due to the high selectivity Manufacturing process of LiFePO ₄ performed on the basis of LiFePO ₄ . For example, Trocoli et al. (Trocoli, R.; Battistel, A.; La Mantia, F., Nickel hexacyanoferrate as suitable alternative to Ag for electrochemical lithium recovery. ChemSusChem 2015, 8, (15), 2514-2519.) on the use of a cell with LiFePO ₄ and NiHCFe as electrodes for the extraction of lithium from the Atacama brines; the lithium concentration in the feed water increased from 4% to 11%, with an energy consumption of 8.7 Wh/mol. Kim et al. used polydopamine-coated LiFePO ₄ and Pt immersed in I-/I ₃ - as electrodes; this cell achieved >4000-fold enhancement relative to Li/Na ion selectivity (Kim, J.-S.; Lee, Y.-H.; Choi, S.; Shin, J.; Dinh, HC.; Choi , JW, An electrochemical cell for selective lithium capture from seawater.Environmental Science & Technology 2015, 49, (16), 9415-9422.). In these works, the stability of the electrons is usually not examined. Furthermore, it is not known whether cations in addition to lithium, such as Na ⁺ , Ca ²⁺ , Mg ²⁺ , have an adverse effect on the stability of LiFePO ₄ .

However, for the effective use of the electrodes, particularly for water treatment, a higher cycle stability with a lower loss of capacity is necessary. The stability of known electrode materials is insufficient for this.

task

The object of the invention is an electrode material with improved stability, in particular for use in aqueous Solutions to specify, and the use of such an electrode material, and a method for water treatment.

This object is solved by the inventions with the features of the independent claims. Advantageous developments of the invention are characterized in the dependent claims. The wording of all claims is hereby made part of the content of this description by reference. The inventions also include all reasonable and in particular all mentioned combinations of independent and/or dependent claims.

The invention relates to an electrode material for extracting an element ion from a liquid medium comprising at least one electrode material comprising at least one ion sieve capable of embedding or releasing an element ion, or a mixture of such ion sieves, the ion sieve or ion sieves having Carbon is coated or are.

Surprisingly, the electrode material is suitable for CDI (capacitive deionization) or FDI (Faradaic deionization).

Surprisingly, it was found that such a coating of the ion sieve significantly increases the stability of the ion sieve and thus also of the electrode material, without there being any losses in the extraction. The coating also improves the tolerance of other cations in the liquid medium, such as potassium ions, sodium ions or magnesium ions.

The extraction is preferably a desalination, in particular CDI or FDI. Desalination means that ions from a medium surrounding the electrodes are stored in the electrode.

In a preferred embodiment, this element ion is a lithium ion.

The ion sieve can be in the form of a depleted ion sieve (in the case of lithium, a delithified ion sieve) and a lithium-intercalated ion sieve. In the lithium-intercalated form it is preferably a lithium-containing metal oxide, which can also be a complex oxide, or a lithium-containing metal phosphate. It is preferably a complex oxide comprising lithium and at least one other element selected from Co, Mg, Cr, Mn, Ni, Fe, Al, Mo, V, W or Ti. It can be LiNi0 ₂ , LiCo0 ₂ , _LiMn2O4 _,

LiNio. ₃₄ Mn _0.33 Co _0.33 O ₂ or a lithium iron phosphate or a mixture thereof. A lithium iron phosphate, LiMn ₂ O ₄ , or a mixture thereof is preferably selected. The lithium iron phosphate is preferably selected from LiFePO ₄ , Li _x Me _y FePO ₄ , LiFeMe _y PO ₄ or a mixture thereof, where Me is Mn, Co, Mo, Ti,

Al, Ni, Nb or a mixture thereof and 0<x<1; and 0<y<1.

Depending on the use, it may be necessary to convert the ion sieve from the lithium-intercalated form to the depleted form.

The lithium-intercalated ion sieve is coated with a layer of carbon. This layer is preferably obtained by carbonization, in particular by carbonization of Alkyl esters, especially of crosslinked polyalkyl esters. Preferred electrode materials are LiFePO ₄ /C, Li _x Me _y FePO ₄ /C, LiFe _x Me _y PO ₄ /C, in particular LiFePO ₄ /C. A thin and at the same time permeable layer is obtained as a result of the carbonization. The layer preferably comprises graphitic carbon. The carbon can also be entirely graphitic.

A layer thickness of at least 2 nm (measured with TEM) is preferred.

The coated ion sieve is preferably obtained by carbonizing an ion sieve with a specific surface area of at least 10 m ² /g. The carbonization is preferably carried out with the lithium-intercalated form.

In a preferred embodiment, the ion sieve is in the form of particles. Preferably with a maximum extension of 2 gm, preferably 1 gm (measured with TEM), particularly preferably 700 μm. Regardless of this, the minimum dimension of the particles is preferably at least 10 nm, in particular at least 20 nm.

The ion sieve is preferably in crystalline form.

In a preferred embodiment, the particles are coated with the carbon layer.

The invention also relates to an electrode for extracting an element ion from a liquid medium, comprising at least one ion sieve as the electrode material, which is capable of storing or releasing an element ion, or a Mixture of such ion sieves, where the ion sieve or ion sieves is or are coated with carbon.

The electrode can also include other elements, such as carrier materials or matrix materials.

The liquid medium is preferably water. The at least one ion sieve is preferably the ion sieve as described for the electrode.

The invention also relates to a method for extracting an element ion using at least one electrode material according to the invention. The element ion is preferably a lithium ion.

Individual process steps are described in more detail below. The steps do not necessarily have to be carried out in the specified order, and the method to be described can also have further steps that are not mentioned.

In the method, the storage or release of the element ion can be controlled by applying a specific voltage. As a result, the element ion can be selectively extracted from the surrounding medium, in particular water, and also released back into it. If this happens in different media, it is possible to deplete the elemention in one medium while it is released in another medium. This makes it possible, for example, to selectively deplete this element ion from, in particular, aqueous media. Storage and delivery correspond to a cycle that is repeated over and over again. The carbon coating means that the storage capacity of the electrode decreases significantly less than without this coating. This makes it at all possible to use the ion sieves according to the invention economically in such processes.

The lithium-intercalated ion sieve is coated with a layer of carbon. This layer is preferably obtained by carbonization, in particular by carbonization of alkyl esters, in particular of crosslinked polyalkyl esters. Carbonization can preferably be achieved by coating the ion sieve in an ester and then carbonizing at temperatures in excess of 600°C. The ion sieve is preferably dispersed in a mixture of a hydroxyl compound and a carboxylic acid and, preferably after formation of the ester, heated to above 100° C., preferably 101 to 300° C., in particular 150° C. to 250° C., preferably 200° C to remove any water that may be present. After 1 to 5 hours, the mixture is heated to above 500° C., preferably 501° C. to 900° C., in particular 550° C. to 800° C., very particularly 600° C. to 800° C., very particularly 700° C, heated. This is preferably done for over 4 hours, preferably 4 to 7 hours. The carbonization, preferably both temperature treatments, are carried out under low-oxygen, preferably oxygen-free conditions, preferably under protective gas such as nitrogen or argon. The mass ratio between the ion sieve and the mixture of hydroxyl compound and carboxylic acid is preferably between 3:1 and 1:3, preferably 2:1 to 1:2, very preferably 1.2:1 and 1:1.2, in particular 1.1 :1 and 1:1.1. The hydroxyl compound and the carboxylic acid are preferably compounds having a molecular weight mass below 400 g/mol. The hydroxyl compound can be used in excess to the carboxylic acid, based on the hydroxyl groups in relation to the carboxylic acid groups. Preferred hydroxyl compounds are alcohols such as methanol, ethanol, propanol, butanol, diols such as ethylene glycol, 1,3-propanediol, polyethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,8-octanediol, triols such as Glycerol, preference is given to alcohols having more than one hydroxyl group, in particular diols.

Examples of carboxylic acids, which preferably contain 1 to 24 carbon atoms, are monocarboxylic acids (e.g. formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, capric acid, stearic acid, phenylacetic acid, benzoic acid, polycarboxylic acids with 2 or more carboxyl groups (e.g. oxalic acid, Malonic acid, adipic acid, succinic acid, glutaric acid, phthalic acid, trimesic acid, trimellitic acid), unsaturated carboxylic acids (e.g. acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and oleic acid) and hydroxycarboxylic acids (e.g. glycolic acid, lactic acid, malic acid and Citric acid).

One or more carboxylic acids with more than one carboxylic acid group are preferred, in particular together with a hydroxyl compound with more than one hydroxyl group. As a result, a crosslinked polyester compound is obtained as an intermediate, which is then carbonized, particularly preferably a tricarboxylic acid such as citric acid, in particular with a diol such as ethylene glycol. The carboxylic acids are preferably used in anhydrous form.

For the formation of the ester, it may be necessary for the composition to be heated to up to 100° C., preferably up to 90° C., in particular to 30° C. up to 100° C., in particular 50ºC to 90ºC. This treatment is preferably carried out for at least 1 hour, in particular at least 2 hours, preferably 1 to 10 hours, preferably 2 to 8 hours, in particular 3 to 5 hours. With this treatment an ion sieve coated with the ester is obtained.

Catalysts such as metal compounds such as ferrocene can also be used. However, this is not preferred.

This carbonization produces a particularly homogeneous, thin and sufficiently porous carbon layer on the ion sieve.

In one embodiment, the invention relates to a method for the selective extraction of lithium from an aqueous solution and recovery and enrichment of lithium in brine, comprising the following steps: a) providing a device comprising a cell for receiving the brine; filling the cell with brine; b) placing a conductive substrate coated with an ion sieve in the cell and placing another conductive substrate in the cell, at least one of the two conductive substrates, and during performance of the method, the ion sieve being suitable therefor , Li ⁺ to store or deliver. Depending on how the process is carried out and the type of conductive substrates used, the process can be carried out in terms of replacing the brine, dividing the cell into sub-cells which, if necessary separated by a membrane vary. This applies in particular if the further conductive substrate is not an ion filter but a chemically neutral electrode such as activated carbon. This can simplify the structure of the cell.

The electrode can preferably be used in a cell for capacitive deionization (CDI), in particular a flow cell.

In one embodiment, the invention relates to a method for selectively extracting lithium from an aqueous solution and recovering and concentrating lithium in brine, comprising the following steps: a) providing a device for electrodialysis, comprising an electrodialysis cell, dividing the electrodialysis - cell into a lithium salt compartment and a caustic compartment by means of an anion exchange membrane; filling the liquor chamber with brine; and filling the lithium salt compartment with a support electrolyte solution, such as a solution of NaCl, KC ₁ , NH ₄ Cl, Na ₂ SO ₄ , K ₂ SO ₄ , NaNO ₃ or KNO ₃ ; b) placing a conductive substrate coated with a depleted ion sieve in the liquor compartment to act as a cathode, placing a conductive substrate coated with a lithium intercalated ion sieve in the lithium salt compartment to act as an anode act, wherein at least one of the two conductive substrates, preferably both, comprises the ion sieve according to the invention as electrode material, and during the implementation of the electrodialysis, the ion sieve is suitable for storing Li ⁺ in the liquor chamber in order to convert it into a to transform another lithium-intercalated ion sieve under an external electric potential, wherein the lithium-intercalated ion sieve is suitable to deliver Li ⁺ into a conductive solution in order to transform into another ion sieve under the external electric potential, whereby after the storage or release of Li ⁺ through the depleted ion sieve and the lithium-intercalated ion sieve, enriched in the lithium salt chamber to yield a lithium-enriched solution.

After step 2), Li ⁺ is stored in the lye chamber in the ion sieve, which thereby transforms into the lithium-intercalated ion sieve, while the lithium-intercalated ion sieve in the lithium salt chamber releases Li + into the conductive solution and transforms it into the ion sieve. Therefore, the two electrodes can be reused by swapping the positions.

Thus, after step 2), the following step can be carried out:

removing a liquid from the liquor chamber after lithium storage; refilling of the caustic chamber with the brine; swapping the positions of the cathode and the anode; and continuing the electrodialysis.

Optionally, after step 2), to avoid swapping the positions of the cathode and the anode, the following step can be performed to separate Li ⁺ from other cations and enrich Li ⁺ : maintaining the positions of the cathode and the anode; removing a liquid from the liquor chamber after lithium storage; transferring a lithium solution from the lithium salt compartment to the caustic compartment; and refilling the lithium salt compartment with the brine; that is, changing the functions of the liquor compartment and the lithium salt compartment and continuing the electrodialysis. Therefore, as soon as the above process is repeated, the functions of the caustic chamber and the lithium salt chamber are switched.

Insofar as they are to function as ion filters, only electrode material according to the invention is preferably used in the electrodes, so that high stability of the electrodes is achieved over many cycles. As a result, better extraction of the lithium can be achieved. The presence of other cations such as Mg ²⁺ , Ca ²⁺ or Na ⁺ is also better tolerated.

The brine is selected from a solution comprising lithium ions, a primary brine, an evaporated brine, an evaporated brine after potassium extraction, or a mixture thereof. It can be liquid from geothermal extraction or similar process liquids.

The conductive substrate is a ruthenium-coated titanium mesh, graphite plate, platinum group metal or alloy foil thereof, carbon cloth or graphite foil.

Parameters of the process are as follows: solution temperature: 0-80°C; pH value: 2-12; and voltage between the two electrodes: 0.5-2 V. In one embodiment of the invention, the concentration of the oxygen dissolved in the medium is lowered, preferably during the incorporation of the element ion. This is preferably achieved by flushing the medium with a non-oxidizing gas, preferably nitrogen. This expels the oxygen from the medium. By lowering the oxygen content, the service life of the electrode is further increased. This process can also be used to increase the cycle stability of ion sieves without carbonization.

The invention therefore also relates to a method for extracting an element ion from a liquid medium comprising an electrode material as described according to the invention, wherein the material can also have no carbon layer in which the oxygen content of the medium has been reduced by flushing with a non-oxidizing gas. This gas is preferably nitrogen. The method is preferably carried out using an electrode material according to the invention.

The invention also relates to a device for carrying out the method according to the invention. Such an electrodialysis device comprises at least one electrodialysis cell divided into a lithium salt compartment and a lye compartment by means of an anion exchange membrane; and at least one cathode and at least one anode, the cathode and the anode each being arranged in the two chambers and the cathode and anode comprising the ion sieve according to the invention in the respective form as the electrode material. A further aspect of the invention comprises the use of the ion sieve according to the invention in a method for extracting the element ion from a liquid medium, preferably an aqueous medium, in particular water.

A further aspect of the invention includes the use of an electrode according to the invention in a method for extracting the element ion from a medium, preferably an aqueous medium.

Industrial waste water or process liquids such as battery recycling solution or rinsing liquids, or waste water from mining such as mine water are particularly suitable as a medium for the extraction of element ions, in particular lithium. It can also be liquids which are obtained from boreholes, for example from hydrothermal sources or for geothermal heat extraction or heat pumps.

Further details and features emerge from the following description of preferred exemplary embodiments in conjunction with the dependent claims. The respective features can be implemented individually or in combination with one another. The options for solving the task are not limited to the exemplary embodiments.

For example, range information always includes all - not mentioned - intermediate values and all conceivable sub-intervals.

The exemplary embodiments are shown schematically in the figures. The same reference numerals in the individual figures denote the same or functionally the same or in terms of their Functions corresponding elements. Show in detail:

1A-F transmission electron micrographs of LiFePO ₄ (A and B) and LiFePO ₄ /C (C and D); (E) X-ray diffraction patterns (F) and Raman spectra of LiFePO ₄ and LiFePO ₄ /C;

Fig. 2A,B (A) Change in conductance of the two channels, (B) and the lithium chloride removal capacity (left axis, squares) and energy consumption of the whole cell in 24 cycles in aqueous 10 mM LiCl (right axis, circles);

Fig. 3A-F Cyclic voltammograms (1 mV/s) of LiFePO ₄ in aqueous electrolytes with a concentration of LiCl, NaCl, MgCl ₂ and CaCl ₂ at (A) 1 M, (B) 100 mM and (C)

10mM; (D and E) Specific capacity of LiFePO ₄ for selected LiCl mixtures recorded at 0.1 A/g (D: absolute value; E: relative value). (F) Nyquist

Representation and equivalent circuit for the system of the mixed electrolyte system;

4A,B (A) The post-mortem X-ray diffraction patterns and (B) Raman spectra of delithified LiFePO ₄ after 100 cycles in different electrolytes;

Fig. 5A-F (A) The comparison of the stability of LiFePO ₄ in 5 mM

LiCl + 50 mM NaCl with N ₂ purge, O ₂ purge, or no pretreatment operated in a three-electrode configuration at 0.1 A/g. (B to D); Effluent concentration of lithium and sodium using LiFePO ₄ electrodes in 5 mM LiCl + 50 mM NaCl (B) without treatment, (C) with O ₂ purge, or (D) with N ₂ purge. (E) Comparison of lithium extraction capacity and the corresponding capacity retention of LiFePO ₄ in 5 mM LiCl + 50 mM NaCl with no treatment, with Ch sparge, or N ₂ sparge. (F) Energy consumption of LiFePO ₄ in 5 mM LiCl + 50 mM NaCl without treatment with O ₂ purge and N ₂ purge;

Fig. 6A-F Comparison of the stability of LiFePO ₄ and LiFePO ₄ /C in (A) 1M LiCl and (B) 5mM LiCl + 50mM NaCl solution in a three-electrode system at 0.1 A/g . (C) The post-mortem X-ray diffraction pattern of LiFePO ₄ and LiFePO ₄ /C after 100 cycles in 1 M LiCl and 5 mM LiCl + 50 mM NaCl solution (1: LiFePO ₄ after 100 cycles in 5 mM LiCl + 50 mM NaCl; 2: LiFePO ₄ /C after 100 cycles in 5 mM LiCl + 50 mM NaCl; 3: LiFePO ₄ after 100 cycles in 1 M LiCl; 4: LiFePO ₄ C after 100 cycles in 1 M LiCl; 5: LiFePO ₄ electrode; 6: LiFePO ₄ /C powder 8: C PDF 89-8487 7: LiFePO ₄ PDF 81-1173 9: NaCl PDF 05-0628);

(D) The effluent concentration of lithium and sodium using LiFePO ₄ /C electrodes in 5mM LiCl + 50mM NaCl with N ₂ purge. (E) The lithium separability and retention in 5mM LiCl + 50mM NaCl of LiFePO ₄ /C or LiFePO ₄ in 5mM LiCl + 50mM NaCl with N ₂ purge. (F) Energy consumption in 5mM LiCl + 50mM NaCl from LiFePO ₄ /C or LiFePO ₄ ;

7A,B calibration curves (relationship of the ion concentration and characteristic peak intensity) of lithium (A) and sodium (B);

8 Raman spectra of delithified LiFePO ₄ at different points of a sample;

Fig. 9 Post-mortem X-ray diffractograms of LiFePO ₄ after 100 cycles in 5 mM LiCl + 50 mM NaCl with N ₂ flushing, O ₂ purge, and no pretreatment; (7: C PDF 89-8487; 8: LiFePO ₄ PDF 81-1173; 9: NaCl PDF 05-0628).

Materials and Methods

Synthesis of LiFePO ₄ , LiFePO ₄ /C and electrode preparation

Commercially available LiFePO ₄ (SÜD-CHEMIE) with a specific surface area of 16 m ² /g was used. LiFePO ₄ /C was synthesized in a two-step process, analogous to Ma, Z.; Fan, Y.; Shao, G.; Wang, G.; Song, J.; Liu, T., In situ catalytic synthesis of high-graphitized carbon-coated LiFePO ₄ nanoplates for superior Li-ion battery cathodes. ACS Applied Materials & Interfaces 2015, 7, (4), 2937-2943.. First, the LiFePO ₄ as received (0.4 g) and 0.21 g ethylene glycol were dissolved in 10 mL citric acid solution (0.18 g anhydrous citric acid in 10 mL distilled water) while stirring. LiFePO ₄ was added last. The suspension was heated to +80 °C for 3 hours to obtain the LiFePO ₄ coated with the alkyl ester compound. The encapsulating alkyl ester was then carbonized in two heating steps in argon. First, the sample was heated to +200 °C for 2 h to remove the water in the materials, and then the sample was heated to +700 °C and held for 6 h to obtain the hybrid of LiFePO ₄ and carbon .

The electrodes were fabricated by mixing and grinding the active material (LiFePO ₄ or LiFePO ₄ /C), acetylene black, and polyvinylidene fluoride (Sigma-Aldrich) in a mass ratio of 8:1:1 in l-methyl-2-pyrrolidinone ( Sigma-Aldrich) to form a slurry. The slurry was drawn down with a doctor blade (200 gm thick) on graphite paper (300 gm thick, SGL) applied and then left overnight at room temperature in the hood. The electrode was then dried at +80 °C in a vacuum oven for 24 h.

Electrochemical Measurements

The electrochemical behavior of LiFePO ₄ and LiFePO ₄ /C was investigated in a specially designed cell in a three-electrode system. Electrodes with a diameter of 12 mm made of LiFePO ₄ , LiFePO ₄ /C or activated carbon electrode (YP-80F,

Kuraray) were used as working electrode (LiFePO ₄ , LiFePO ₄ /C) or counter electrode (activated carbon). The electrodes were arranged in a sandwich and separated by a glass fiber mat (diameter 13 mm, GF/A, Whatman) in the cell body. An Ag/AgCl reference electrode (3 M KCl, BASi) was mounted laterally in the cell body. Before testing, the assembled cells were filled with various electrolytes. For single salt electrolytes, 1 M LiCl, 1 M MgCl ₂ , 1 M CaCl ₂ and 1 M NaCl were used. 5 mM LiCl and 50 mM MeCl _x (Me = Na, Ca, Mg, X according to the charge of Me) were used for the mixed salt electrolyte.

The cell was connected to the potentiostat/galvanostat VSP300 (Bio-Logic) and the cyclic voltammogram with the scan rate of 0.1 mV/s and a cutoff potential of -0.4 V to +0.8 V vs. Ag /AgCl applied. In order to test the performance stability of LiFePO ₄ and LiFePO ₄ /C, galvanostatic charge/discharge measurements with potential limitation were carried out. Before the electrochemical operation, the electrolyte was continuously purged with nitrogen gas for 1 h to remove the dissolved oxygen in the electrolyte (only when studying the effect of oxygen). The concentration of dissolved oxygen after gas flushing is given in Table 2.

In addition, the electrodes were delithed before the electrochemical test to avoid an increase in the lithium concentration in the electrolyte due to the charging process of LiFePO ₄ and LiFePO ₄ /C. In order to delith the electrode, the electrodes were charged with a current of 0.1 A/g with a cut-off voltage of +0.4 V versus Ag/AgCl in a three-electrode system in 1 M LiCl electrolyte. Electrochemical impedance spectroscopy (EIS) was measured at the formal potential in the frequency range from 1 MHz to 10 MHz and with an excitation voltage of 5 mV vs. Ag/AgCl.

The conductivities of LiCl, MgCl ₂ , CaCl ₂ and NaCl with different concentrations were tested using an electrochemical microcell HC cell with Pt electrodes (RHD Instruments) and an electrochemical Modulab workstation (Solartron Analytical). The Pt electrode crucible was sealed after 0.9 mL of each electrolyte was added to the measuring cup with a syringe. A thermal compound (Eurotherm 2000) was used in the center of the closed cell and base unit to improve heat transfer between them. The potentiostatic impedance at each temperature was measured after the temperature had stabilized for 10 minutes. The impedance was measured from 1 Hz to 3 MHz at open circuit potential (OCV) at different temperatures from +10 °C to +60 °C in steps of Δ10 °C and at +25 °C. The conductivity and activation energy values were calculated according to Equations 1 and 2.

Equation 1 where s is the conductivity (S/cm), R is the resistivity (W), A is the area (cm ² ) and 1 is the length (cm). The value of 1/A was obtained from 0.1M KCl aqueous standard (VWR) with a conductivity of 12.880 mS/cm at +25°C. Equation 2 where s is the conductivity, T is the temperature (K), A obtained from experiment, k is the Boltzmann constant (1.38064910 ^-23 J/K) and E _a is the activation energy (kJ/mol).

Lithium selectivity experiments

Lithium extraction experiments were performed in a multi-channel cell. Two water channels were provided through the gasket filled with glass fiber mat (GF/A, Whatman) (area = 6.76 cm ² , thickness = 500 μm) and through an anion exchange membrane (FAS-PET-130, Fumatech) Cut. The LiFePO ₄ or LiFePO ₄ /C electrodes were located at the end of the channel and contacted with the graphite current collector. Before the experiment, an electrode was delithified by the above-mentioned method. The channel with a pre-treated electrode is called "Channel 1" and the other one is called "Channel 2".

A 10 liter tank with LiCl (10 mM) with a flow rate of 3 mL/min was used as feed water, while a constant current (40 mA/g) with a cell voltage between -0.4 V and +0.4 V was applied with a VSP300 potentiostat/galvanostat system. During the entire experiment, the electrolyte was continuously purged with N ₂ gas to remove the dissolved oxygen. The mass of the electrode was 8 mg and the change in conductivity and pH of two channels was recorded online by conductivity sensors (Metrohm, PT1000) and pH- Sensors (WTW SensoLyt 900P) recorded. Lithium is extracted throughout the cycle; therefore, the lithium removal capacity and the power consumption of the cell in one cycle were calculated according to Equations 3 and 4.

Lithium chloride extraction capacity (mg _LiCL /g _electrode ) ⁼ Equation 3 where v is the flow rate (mL/min), M _LiCi is the molecular weight of LiCl (42.4 g/mol), m _total is the mass of the electrodes (g), t is the time (min) and Δc _channel 1 and Δc _channel 2 the Change in concentration of LiCl (mmol/L) in channel 1 and channel 2 respectively. Equation 4 where DE is the cell voltage (V), q the charge (As), v the flow rate (mL/min), t the time (min) and Δc _channel 1 and Δc _channel 2 the change in concentration of LiCl (mmol/L ) are in channel 1 or channel 2.

To study the selectivity and stability of LiFePO ₄ and LiFePO ₄ /C, we used an electrolyte containing 5 mM LiCl and 50 mM NaCl with a volume of 10 L. The output of channel 2 was connected to an inductively coupled optical plasma Emission spectrometer (ICP-OES, ARCOS FHX22, SPECTRO Analytical Instruments) connected to quantify the change in concentration of the cations. The mass of the electrodes was about 18 mg; a low specific current of 30 mA/g and a flow rate of 1.2 mL/min were used to amplify the ICP signal. The calibration curve was constructed according to the correlation between the intensity of each wavelength and the concentration of the solution (Figures 7A and 7B). The intensities measured from the extracted sample were converted into concentration profiles. The loading and unloading processes ran in opposite directions and the potential for energy recovery was negligible; therefore, the lithium extraction amount and the energy consumption in a half cycle according to Equations 5 and 6 were calculated to evaluate the performance of LiFePO ₄ and LiFePO ₄ /C.

Equation 5 where v is the flow rate (mL/min), M _Li is the molecular weight of Li (6.99 g/mol), m _total is the mass of the electrode (g), t is the time over the lithium extraction step (min) and Δc _channel 2 is the concentration change of Li ⁺ (mM) in channel 2. Equation 6 where DE is the cell voltage (V), q is the charge (As), v is the flow rate (mL/min), t is the time over the lithium extraction step (min) and c _channel 2 is the concentration of Li (mM) in channel 2 is

Material Characterization

The surface morphology of LiFePO ₄ and LiFePO ₄ /C was studied by scanning electron microscopy (JEOL JSM 7500F) at 1 kV. The X-ray diffractometry was carried out in a D8 Advance diffractometer (Bruker AXS) with a copper X-ray source (Cu-Kα, 40 kV, 40 mA) and a Goebel mirror in the point focus (0.5 mm). Raman spectra were recorded on a Renishaw via system using a Nd:YAG laser with an excitation wavelength of 532 nm. The spectral resolution was 1.2 cm ^-1 and the diameter of the laser spot on the sample was about 2 μm with a total power consumption of 0.2 mW. Characterization of LiFePO ₄ and LiFePO ₄ /C

FIG. 1A shows the transmission electron micrographs of LiFePO ₄ . LiFePO ₄ particles are typically about 300 nm long and about 150 nm long. At higher resolution (Figure 1B) grating fringes with the typical spacing of 0.34-0.35 nm can be seen in alignment with the (111) and (021) planes of LiFePO ₄ . LiFePO ₄ /C shows the ubiquitous presence of carbon encapsulating the LiFePO ₄ particles (Figures IC and ID).

FIG. IE shows the X-ray diffractogram of LiFePO ₄ and LiFePO ₄ /C. The diffraction patterns of LiFePO ₄ /C are the same as that of LiFePO ₄ identified as an orthorhombic phase (PDF 81-1173), indicating that the carbon coating process does not destroy the inherent structure of LiFePO ₄ . FIG. 1F shows the Raman spectra of LiFePO ₄ and LiFePO ₄ /C. The band at 952 cm ^-1 can be attributed to the symmetric stretching of the PO bonds of LiFePO ₄ . And the peaks at 1338 cm ^-1 and 1598 cm ^-1 correspond to the D-band and G-band of carbon, respectively. The D band (disordered peak) is due to the A _1g vibrational mode and the G band (graphitic peak) to the E _2g vibrational mode of CC bond stretching. Therefore, both commercial LiFePO ₄ and LiFePO ₄ /C exhibit the presence of incompletely graphitic carbon; in the case of the former, carbon is a minority phase.

Lithium extraction of LiFePO ₄ in aqueous 10 mM LiCl The Li removal capacity of LiFePO ₄ in aqueous 10 mM LiCl was quantified. When a specific current of 30 mA/g is applied during charging, the conductivity in channel 1 decreases while the conductivity in channel 2 increases (Figure 2A). This corresponds to the reduction of the cathode with the uptake of lithium and the oxidation of the anode with the release of the lithium into the feedwater stream (equation 7). The reverse process is observed during the discharge process. The lithium extraction capacity of the cell does not decrease during 24 cycles with an average capacity of 79±6 mg _LiCi /electrode corresponding to 13±1 mg _Li /electrode (Figure 2B), indicating that LiFePO ₄ in vented , aqueous 10 mM LiCl is stable. The average energy consumption of the cell is 3 Wh/mol _Licl corresponding to 3 Wh/mol _Li

Li _1-x FePO ₄ + xLi ⁺ + xe = LiFePO ₄ Equation 7

The effect of other cations compared to lithium

Cyclic voltammetry was performed to investigate the selectivity behavior of LiFePO ₄ towards Li ⁺ compared to other cations. For this purpose, the electrochemical performance in different single cation electrolytes was compared. As shown in Figures 3A, 3B and 3C, a pair of redox peaks appear in all types of electrolytes. The lowest peak current was measured using an aqueous 1 M CaCl ₂ electrolyte. At 1 M LiCl, the peak redox currents are highest and the peak potentials are shifted to a more positive range compared to the other electrolytes, reflecting the contribution of lithium in could be due to the solution leaching from the electrode.

To further quantify the potential shift, the formal potential (E _1/2 ) was examined. According to Table 3, the formal potential in LiCl solution decreases with decreasing concentration. During the charging process (the first electrochemical process during cyclic voltammetry), the Li ⁺ in the LiFePO ₄ is released into the electrolyte. Therefore, when tested in electrolytes with other cations, such as NaCl, MgCl ₂ or CaCl ₂ , the cyclic voltammograms and the formal potential are almost identical.

In order to reduce the loss of additional lithium ions from the electrode to the electrolyte and to compare the electrolytes of different concentrations, the LiFePO ₄ electrodes were delithified before the galvanostatic charge/discharge test. A significant decrease in the initial capacity of LiFePO ₄ was observed in all electrolytes (Figures 3D and 3E). The capacity decreases slowest in the mixed solution of Li ⁺ and Na ⁺ and fastest in the Ca ²⁺ -containing electrolyte, with a retention of 60% and 46% after 100 cycles, respectively. First the capacity increases and then decreases in 5 mM LiCl + 50 mM MgCl ₂ solution; the increase may be due to the incorporation of trace amounts of Mg ²⁺ . Compared to other cations, Mg ²⁺ intercalates more easily into the structure of LiFePO ₄ . However, the intercalation of both Mg ²⁺ and Li ⁺ is not fully reversible, so the capacity continues to decrease. To investigate why the capacity of LiFePO ₄ electrodes decreases during cycling, the post-mortem X-ray diffraction pattern of delithified LiFePO ₄ charging and discharging 100 cycles in different electrolytes was measured. Besides the influence on the stability, cations other than Li ⁺ also have an influence on the kinetics, which is obtained from electrochemical impedance measurements. The Nyquist representations consist of two semicircles and a line (Figure 3F).

The semicircle at high frequency represents the capacitance response of the electrolyte; accordingly, it only occurs in significant amplitude when the low-concentration electrolytes are examined. The semicircle at medium frequency represents the charge transfer resistance (R _ct ).

The slanting line at low frequency represents the Warburg impedance (W ₁ ), which corresponds to lithium-ion diffusion. The value of R _ct and W ₁ is calculated according to the simulated circuit as shown in Table 1. Ca ²⁺ and Mg ²⁺ are detrimental to the charge transfer process, with R _ct ^_ values of 38.7 Ω·cm ² and 37.3 Ω·cm ² , respectively, which are almost twice the R _ct value in pure 5 mM LiCl (20.1 W cm ² ). The ^Rct values in _5mM LiCl and 50mM NaCl are similar to those in pure LiCl electrolyte. The effect of other cations on the Warburg impedance follows the pattern observed for the R _ct value, and the Warburg impedances in Mg ²⁺ - and Ca ²⁺ -containing electrolyte are higher than those in Na ⁺ - containing and pure LiCl. This result indicates that lithium ions are more difficult to diffuse into the liquid side in the former electrolytes than in the latter. The different effects have their origin in the different conductivities of the cations.

As can be seen in FIG. 4A, the delithified LiFePO ₄ is composed of the heterosite FePO ₄ and LiFePO ₄ since the LiFePO ₄ is not completely delithified. This result agrees with the Raman data (Figure 8). When Raman measurements are taken at two randomly selected points, it indicates Point 1 has only one peak (952 cm ^-1 ) consistent with the Raman spectra of LiFePO ₄ (Figure 1F). Elsewhere the observed peaks correspond with FePO ₄ . After 100 cycles in 5 mM LiCl, some diffraction peaks such as 37.4° 2θ ((211) plane of heterosite FePO ₄ ) disappear, indicating the structure breakage of FePO ₄ . The situation is different after 100 cycles in Ca ²⁺ -containing electrodes, where the diffraction peaks at 18.13° 2Θ, corresponding to the (020) plane of the heterosite FePO ₄ , disappear, which indicates the considerable capacity loss. FIG. 4B shows the Raman spectra of the electrodes after 100 cycles in different electrolytes. After charging/discharging in NaCl, LiCl and CaCl ₂ electrolyte the peaks are at 488 cm ^-1 (Li cage/asymmetric bending PO ₄ ^3- ), 596 cm ^-1 (asymmetric bending PO ₄ ^3- , v ₄ ), 652 cm ^-1 (symmetric bending PO ₄ ^3- ,v ₂ ) and 691 cm ^-1 not evident, indicating PO bond breakage; this is another reason for the degradation of LiFePO ₄ performance, namely the loss of oxygen species.

The effect of the oxygen content in the electrolyte

A mixed electrode containing 5 mM LiCl and 50 mM NaCl as feed water was used to study the influence of oxygen content on the stability of LiFePO ₄ . This choice was motivated by the observation that sodium ions have the least impact on the stability of LiFePO ₄ . First, the stability of LiFePO ₄ was tested at 100 mA/g, with a potential range of -0.4 V to +0.5 V versus Ag/AgCl, in 5 mM LiCl + 50 mM NaCl solution, which was pre-electrochemically mixing process was continuously purged of O ₂ and N ₂ . After 100 cycles, LiFePO ₄ retains 69% of the initial capacity in the N ₂ - purged electrolyte, while the capacity retention values in the O ₂ -purged electrolyte and in the untreated electrolyte are 43% and 52%, respectively (FIG. 5A). This indicates that dissolved O ₂ in the electrolyte significantly accelerates the degradation of LiFePO ₄ .

The effluent solution was continuously analyzed by online monitoring with inductively coupled plasma optical emission spectroscopy (ICP-OES). As shown in Figures 5B, 5C and 5D, LiFePO ₄ always maintains good selectivity to lithium regardless of the oxygen content. Similar to the specific capacity trend (Figure 5A), the LiFePO ₄ tested in feedwater with continuous N ₂ purge is the most stable with 70% capacity retention after 10 cycles (Figure 5E).

The lithium extraction capacity is only about half of the initial value in the feedwater without any treatment, which is slightly higher than in the feedwater with continuous O ₂ purge. With higher oxygen content, the capacity decreases with a greater amplitude. In contrast to the Li ⁺ extraction/recovery capacity, the power consumption is stable over the 10 cycles as shown in Figure 5F. This result indicates that the oxygen content has a small impact on the energy consumption of the system but a large impact on the structural and chemical stability of LiFePO ₄ itself.

X-ray diffraction was used to study how dissolved oxygen in the electrolyte affects the stability of LiFePO ₄ . Structural changes in the electrode material were examined after 100 cycles in the electrolyte, which consists of 5 mM LiCl and 50 mM NaCl (FIG. 9). In contrast to measuring only the powder, the cast electrodes show strong reflections from the graphite paper (26.5° 2Θ and 54.6° 2Θ) to recognize; therefore the diffraction pattern was normalized to the peaks not associated with the graphite foil. Compared to the LiFePO ₄ and LiFePO ₄ electrodes, there are two additional peaks at 31.7° 2θ and 45.5° 2θ for all electrodes after 100 cycles, corresponding to the (200) plane and the (220) plane, respectively ; these peaks relate to the presence of a highly symmetrical phase (residual salt). The electrode cycled in the electrolyte with less dissolved oxygen (N ₂ flushing) shows less peak broadening compared to the sample with O ₂ flushing. Apparently, the higher amount of dissolved oxygen leads to more degradation of the LiFePO ₄ material.

Improved stability through carbon coating of LiFePO ₄

In order to increase the stability of LiFePCt, LiFePO ₄ was bonded with layers of carbon to prevent oxygen attack. Figure 6A shows the difference between LiFePO ₄ and LiFePO ₄ /C in aqueous 1 M LiCl. As can be seen, the capacity of LiFePO ₄ /C decreases slightly from 115 mAh/g to 95 mAh/g, with a retention of 83% of the initial capacity after 100 cycles. For comparison, LiFePO ₄ without carbon coating retains only 30% of the initial capacity, with a drop from 92 mAh/g to 27 mAh/g after 100 cycles. Performance at low concentration (5mM LiCl + 50mM NaCl) is similar (Figure 6B). LiFePO ₄ /C still has 85% of the capacity in the first cycle (41 mAh/g and 48 mAh/g, respectively), while LiFePO ₄ only retains 52% of the initial value.

FIG. 6C shows the X-ray diffractograms of LiFePO ₄ /C and LiFePO ₄ electrodes after testing in 1 M LiCl and 5 mM LiCl +

50mM NaCl. To further investigate whether the carbon coating can improve the stability of LiFePO ₄ in lithium extraction, the performance of LiFePO ₄ /C in 10mM LiCl and 5mM LiCl + 50mM NaCl solution (continuous N ₂ purge) under Ver - Tested turning the rocking chair cell. Like LiFePO ₄ , LiFePO ₄ /C also has good selectivity over lithium (FIG. 6D). However, LiFePO ₄ /C has a higher lithium extraction capacity (21.0 mg _Li /Gelectrode compared to 17.8 mg _Li /Gelectrode in the first cycle) and better stability with a retention of 82% after carbon coating as shown in Figure 6E. The higher capacity of LiFePO ₄ /C could be due to the fact that the carbon coating reduces the electronic conductivity of LiFePO ₄ (Li, J.; Qu, Q.; Zhang, L.; Zhang, L.; Zheng, H., A monodispersed nano-hexahedral LiFePO ₄ with improved power capability by carbon-coatings. Journal of alloys and compounds 2013, 579, 377-383.) improved, ie the active materials can be fully utilized at high current. In addition, the carbon layer can block the attack of oxygen and OH- and increase the stability of LiFePO ₄ (He, P.; Liu, J.-L.; Cui, W.-J.; Luo, J.-Y .; Xia, Y-Y Investigation on capacity fading of LiFePO ₄ in aqueous electrolyte Electrochimica Acta 2011, 56,

(5), 2351-2357.). In addition, the additional carbon present in nanohybridized form in LiFePO ₄ /C could effectively lower the resistivity of LiFePO ₄ , which lowers the power consumption (Figure 6F). The average energy consumption of LiFePO ₄ /C in 10 cycles is 3.0±0.5 Wh/mol _Li

The influence of cations and dissolved oxygen on the stability of LiFePO ₄ in a symmetric cell (ie LiFePO ₄ paired with LiFePO ₄ ) was investigated. other cations as Li ⁺ in sols such as Na ⁺ , Mg ²⁺ and Ca ²⁺ affect the stability and electrochemical properties of LiFePO ₄ . Among them, Ca ²⁺ has the most adverse effect, and Na ⁺ shows no obvious influence in the potential range of -0.4V to +0.8V. The stability and electrochemical properties of LiFePO ₄ are affected by Ca2 ₊ . Dissolved oxygen also exacerbates LiFePO ₄ fading. Reducing the dissolved oxygen concentration (N ₂ purge) dramatically increases capacity retention from 47% to 70% in 10 cycles in 5mM LiCl + 50mM NaCl. After carbon coating, the retention further increases to 82%, and the energy consumption decreases to 3.0±0.5 Wh/mol _Li . These two methods improve the performance stability of LiFePO ₄ as a material for lithium extraction. While reducing dissolved oxygen may not be practical in full-scale applications, carbon coating of LiFePO ₄ represents a simple and very promising approach also for larger scales.

Table 1: Fitted values for delithified LiFePO ₄ in different electrolytes according to the equivalent circuit diagram.

Table 2 Dissolved oxygen concentration after O ₂ purge and N ₂ purge

concentration of O ₂

Condition

(ppm)

Initial 8.8 O ₂ flush for 24 h 12.5 N ₂ flush for 24 h 4.0 Table 3: The formal potential of LiFePCt in LiCl, NaCl, MgCl ₂ and CaCl ₂ at a concentration of 1 M, 100 mM, and 10 mM .

cited literature

Kanoh, H.; Ooi, K.; Miyai, Y.; Katoh, S., Electrochemical recovery of lithium ions in the aqueous phase. Separation Science and Technology 1993, 28, (1-3), 643-651.

Pasta, M.; Battistel, A.; La Mantia, F. Batteries for lithium recovery from brines. Energy & Environmental Science 2012, 5, (11), 9487.

Trocoli, R.; Battistel, A.; La Mantia, F., Nickel hexacyanoferrate as suitable alternative to Ag for electrochemical lithium recovery. ChemSusChem 2015, 8, (15), 2514-2519.

Kim, J.-S.; Lee, Y.-H.; Choi, S.; Shin, J.; Dinh, H.-C.; choi,

J.W., An electrochemical cell for selective lithium capture from seawater. Environmental Science & Technology 2015, 49,

(16), 9415-9422.

Ma, Z.; Fan, Y.; Shao, G.; Wang, G.; Song, J.; Liu, T., In situ catalytic synthesis of high-graphitized carbon-coated LiFePO ₄ nanoplates for superior li-ion battery cathodes. ACS Applied Materials & Interfaces 2015, 7, (4), 2937-2943.

Li, J.; Qu, Q.; Zhang, L.; Zhang, L.; Zheng, H., A monodispersed nano-hexahedral LiFePO ₄ with improved power capability by carbon-coatings. Journal of alloys and compounds 2013, 579, 377-383. Hey, P.; Liu, J.-L.; Cui, W.-J.; Luo, J.-Y.; Xia, Y.-Y., Investigation on capacity fading of LiFePO ₄ in aqueous electrolyte. Electrochimica Acta 2011, 56, (5), 2351-2357.

Claims

patent claims

1. Electrode material for the extraction of an element ion from a liquid medium comprising at least one electrode material comprising at least one ion sieve capable of storing or releasing an element ion, or a mixture of such ion sieves, wherein the ion sieve or ion sieves is or are coated with carbon.

2. Electrode material according to the preceding claim, characterized in that the element ion is a lithium ion.

3. Electrode material according to any one of the preceding claims, characterized in that the ion sieve is a lithium-containing metal oxide or lithium-containing metal phosphate after receiving the element ion.

4. Electrode material according to claim 3, characterized in that the ion sieve comprises a complex oxide lithium and at least one other element selected from Co, Mg, Cr, Mn, Ni, Fe, Al, Mo, V, W or Ti or a is lithium iron phosphate.

5. Electrode material according to claim 4, characterized in that the lithium iron phosphate is selected from LiFePO ₄ , Li _x Me _y FePO ₄ , LiFeMe _y PO ₄ or a mixture, where Me is Mn, Co, Mo, Ti, Al , Ni, Nb or a mixture thereof and 0<x<

1; and 0<y<1.

6. Electrode material according to any one of claims 1 to 5, characterized in that the carbon layer is obtained by carbonization.

7. Electrode material according to any one of claims 1 to 6, characterized in that the ion sieve is present as particles.

8. An electrode for extracting an element ion from a liquid medium, comprising an electrode material according to any one of claims 1 to 7.

9. A method for extracting an element ion from a liquid medium using at least one electrode material according to any one of claims 1 to 7, wherein the application of a voltage controls the incorporation or release of the element ion.

10. The method according to claim 9, comprising the following steps: a) providing a device for electrodialysis, comprising an electrodialysis cell, dividing the electrodialysis cell into a lithium salt chamber and a lye chamber by means of an anion exchange membrane; filling the liquor chamber with brine; and filling the lithium salt compartment with a support electrolyte solution; b) placing a conductive substrate coated with a depleted ion sieve in the caustic compartment to act as a cathode, placing a conductive substrate coated with a lithium intercalated ion sieve in the lithium salt compartment to act as an anode, wherein at least one of the two conductive substrates, preferably both, as Electrode material comprise at least one ion sieve according to one of claims 1 to 7, and during the performance of the electrodialysis, the ion sieve is suitable to intercalate Li+ in the liquor chamber in order to ion sieve into another lithium-intercalated under an external electrical potential transform, wherein the lithium-intercalated ion sieve is capable of releasing Li ⁺ into a conductive solution in order to transform into another ion sieve under the external electrical potential, wherein after the incorporation or release of Li ⁺ through the depleted ion sieve and the lithium intercalated ion sieve, is enriched in the lithium salt chamber to yield a lithium enriched solution.

11. The method according to any one of claims 9 or 10, characterized in that the concentration of the oxygen dissolved in the medium is lowered during the incorporation of the element ion, preferably by flushing the medium with nitrogen.

12. Device for carrying out the method according to any one of claims 9 to 11.

13. Use of the electrode material according to any one of claims 1 to 7 in a method for extracting an element from a liquid medium.

14. A method for extracting an element ion from a liquid medium using at least one ion sieve, wherein the application of a voltage controls the storage or release of the element ion, the concentration of the in the dissolved oxygen medium is lowered by purging the medium with a non-oxidizing gas.