Method for producing a lithium-containing electrode, and electrochemical cell

Abstract

The invention relates to a method for producing a lithium-containing electrode (4) for a lithium-ion-containing accumulator, having the following steps: - producing a porous metal structure (6), - coating a surface (26) of the porous structure (6) with an iron phosphate layer (28), - introducing the porous structure (6) provided with the iron phosphate layer (28) into an electrochemical cell (2) as a first electrode (8) which is used as a cathode (10), - introducing a second lithium-containing electrode (12) into the cell (2), said electrode being used as an anode (14), wherein - lithium compounds (30) are introduced into the second lithium-containing electrode (12), said lithium compounds originating from thermally decomposed electrode material of a lithium-ion accumulator, - introducing a non-aqueous electrolyte (16) into the electrochemical cell (2), - closing the electrochemical cell (2) under inert conditions, - applying an electrical current to the electrodes (8), (12) of the electrochemical cell (2) such that lithium ions (18) migrate from the lithium-containing anode (14) to the cathode (10) in the form of the porous structure (6) through the non-aqueous electrolyte (16), and - the surface (26) of the porous structure (6) provided with the iron phosphate layer (28) is converted into a lithium iron phosphate layer (32).

Description

[0001] Description

[0002] Process for producing a lithium-containing electrode and electrochemical cell

[0003] The invention relates to a method for producing a lithium-containing electrode according to patent claim 1 and to an electrochemical cell according to patent claim 11.

[0004] The recovery of valuable metals such as nickel, cobalt, and lithium from lithium-ion batteries occurs after cell reprocessing—i.e., after an electrical safety discharge, deactivation of remaining lithium metal, and evaporation of the electrolytes through a pyrometallurgical and hydrometallurgical process. In addition to cobalt-nickel-copper alloys, the pyrometallurgical process also produces lithium-containing slag. The lithium contained in this lithium-containing slag is to be recycled.

[0005] According to the state of the art, this lithium is extracted from the slag using hydrometallurgical processes. The quenched slag is crushed using rod mills and then passed over a magnetic disk to remove ferromagnetic alloy components trapped in the slag, such as nickel and cobalt. The slag is then leached with sulfuric acid. The lithium ions go into solution and the remaining solids, which include gypsum and silicates, are separated by filtration. To prevent unwanted precipitation of lithium carbonate during subsequent purification steps, the filtrate is diluted below the solubility limit of lithium carbonate. The diluted filtrate is adjusted to a pH of 7 by adding calcium oxide to remove impurities such as aluminum, magnesium, iron, manganese, silicon and sulfate.At this pH value, aluminum, iron and silicon as well as some heavy metals precipitate as hydroxides. Some of the sulfate combines with the calcium oxide to form sparingly soluble calcium sulfate (gypsum). After a solid / liquid separation, the pH value is raised to 12 by adding more calcium oxide. At this pH value, magnesium and other metals that are present in the solution as hydroxides or sulfate residues are completely precipitated. After a further solid / liquid separation, excess calcium is precipitated as lime by adding sodium carbonate and separated from the solution by filtration. The solution is greatly concentrated by evaporating the water and the lithium is precipitated as lithium carbonate by adding sodium carbonate at 100 °C. The separated lithium carbonate is washed with ethanol because, unlike water, lithium carbonate is insoluble in ethanol. The purity of this crude carbonate is approx.98% and requires repeated refining for reuse in batteries. The total recovery of lithium, i.e. the yield from the slag, using this method according to the state of the art is approximately 65%. This low yield is due to the fact that part of the lithium is bound into the mixed metal oxides with aluminum, magnesium, iron, or manganese during the precipitation of the impurities with calcium oxide. This lithium is so firmly bound chemically that it would have to be separated from the starting solution using a solvent extraction process in order to significantly increase the recovery.

[0006] This described prior art process demonstrates the very high wet-chemical complexity, which is both economically and ecologically unprofitable. The object of the invention is therefore to provide a process and an electrochemical cell for recycling lithium, achieving a higher yield than in the prior art and simultaneously enabling the recycled lithium to be recycled in a new electrode.

[0007] The solution to the problem consists in a method for producing a lithium-containing electrode having the features of patent claim 1 and in an electrochemical cell having the features of patent claim 11. The method for producing a lithium-containing electrode for a lithium-ion-containing accumulator according to patent claim 1 comprises the following steps:

[0008] Producing a porous metallic structure, coating a surface of the porous structure with an iron phosphate layer, introducing the porous structure provided with the iron phosphate layer into an electrochemical cell as a first electrode which serves as a cathode, introducing a second lithium-containing electrode into the cell which serves as anode, wherein lithium compounds originating from thermally decomposed electrode material of a lithium-ion accumulator are introduced into the second lithium-containing electrode, introducing a non-aqueous electrolyte into the electrochemical cell, closing the electrochemical cell under inert conditions, applying electric current to the electrodes of the electrochemical cell,so that lithium ions migrate from the lithium-containing anode through the non-aqueous electrolyte to the cathode in the form of the porous structure and the surface of the porous structure provided with the iron phosphate layer is converted into a lithium iron phosphate layer.

[0009] The invention described here differs fundamentally from the prior art in that the slag, which contains lithium compounds and is usually obtained from the thermal decomposition of rechargeable batteries, is not broken down using wet-chemical methods, but is instead re-incorporated into an electrode and an electrochemical cell. The process differs from a conventional electrochemical cell and a conventional lithium-ion battery in that the lithium ions migrate from the aforementioned electrode with the lithium slag via an electrolyte to the cathode and are deposited in a specially designed layer, namely an iron phosphate layer.

[0010] Furthermore, the described method also differs from the prior art in that the cathode in this electrochemical cell or in this process is designed in such a way that, due to its porous structure and the iron phosphate layer provided thereon, a large surface is formed on which, after the transport of the lithium ions, a lithium iron phosphate layer forms. This formed lithium iron phosphate layer, in turn, creates a new electrode. This new electrode, due to its surface structuring and its surface coating, is already designed as an electrode for a new lithium-ion battery, in this case, for example, in the form of a cathode (in an accumulator (battery), the positively charged electrode is referred to as the cathode during the discharge process).

[0011] The described process not only offers a technically inexpensive and economical way of recycling the lithium-containing slag that accrues during the thermal decomposition of old batteries, but the described process also provides a manufacturing process for a completely new, directly reusable electrode for a lithium-containing accumulator, in this case for a lithium iron phosphate battery.

[0012] In principle, the porous metallic structure can be produced using a variety of manufacturing processes. Processes for producing metallic foams by gas injection are, for example, suitable for this purpose. However, additive manufacturing processes are particularly advantageous for producing the metallic structure, in particular powder bed processes such as a laser melting process or an electro-beam melting process, in which the surface structure and porosity can be designed precisely according to the requirements of an electrode. With the additive process described, the optimal structure, which is necessary for the deposition of lithium ions and the production of the lithium iron phosphate layer, can be represented almost perfectly, whereas with foamed metals the surface is more like a random surface.An aluminum alloy and / or a nickel alloy are particularly suitable as base materials for the porous metallic structure for additive manufacturing.

[0013] The non-aqueous electrolyte preferably comprises ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or an ionic liquid. Propylene carbonate is particularly preferred because it is inexpensive to produce and can be operated without problems. Ionic liquids are salts whose melting point is in particular less than 100 °C. Like all salts, they comprise anions and cations. By varying these, the physicochemical properties of an ionic liquid can be varied within wide limits and optimized to meet technical requirements. Typical cations can be imidazolium or pyridinium, ammonium and / or phosphonium. Possible anions are halides and weakly coordinating ions such as tetrafluoroborates or hexafluorophosphates, but also trifluoroacetates, triflates and tosylates.

[0014] In an advantageous embodiment of the invention, the lithium of the lithium compound in the second electrode comprises lithium calcium silicates and / or lithium magnesium silicates and / or lithium manganese oxides and / or lithium cobalt oxides and / or lithium nickel oxides. These are typically compounds that are present in the slag or ash produced during the thermal decomposition of lithium-ion batteries.

[0015] The lithium iron phosphate applied to the surface of the metallic structure is preferably designed in such a way that the structure maintains an open porosity. This allows the lithium ions that pass through the non-aqueous electrolyte to the cathode to accumulate on the largest possible surface and react to form lithium iron phosphate.

[0016] When coating the surface of the porous structure with iron phosphate, the structure is preferably immersed in a dispersion of phosphoric acid and magnetite at a temperature between 80 ° C and 110 ° C. Preferably, an oxidizing agent, in particular hydrogen peroxide, is also added.

[0017] The process and the electrochemical cell operate under inert conditions. Argon is a particularly suitable inert gas. Nitrogen would react with the lithium ions in the non-aqueous electrolyte. A vacuum atmosphere is also inefficient due to the high vapor pressure of the materials used.

[0018] Another component of the invention is an electrochemical cell for producing an electrode for a lithium accumulator. This cell comprises an anode with a lithium compound derived from the thermal decomposition of used lithium accumulators and a cathode comprising a porous metallic structure coated with an iron phosphate layer on its surface, the anode and the cathode being separated from each other by a non-aqueous electrolyte.

[0019] The advantages of this electrochemical cell over the prior art have already been explained with regard to the process according to the invention. These include, on the one hand, the technically inexpensive, direct recycling of lithium-containing compounds from the thermal decomposition of old batteries with simultaneous production of a new cathode for a lithium iron phosphate battery. This electrochemical cell is particularly advantageous when there are several pairs of anodes and cathodes connected in parallel. In this way, upscaling for the production of anodes can take place and lithium slag from the recyclate of old batteries can be recycled on an industrial scale.

[0020] To produce the second electrode, the anode of the electrochemical cell, it is advantageous to mix the lithium compound, i.e., the slag from the thermal decomposition of old accumulators, with a conductive material, particularly carbon particles, and then compress it. Porous carbon particles are particularly preferred. Such a compressed electrode made of lithium compounds and carbon particles is particularly well suited for use in the electrochemical cell described.

[0021] Further embodiments and features are explained in more detail with reference to the following figures. Features with the same designation but in different embodiments are provided with the same reference symbol. The illustrations in the following figures are purely schematic representations and do not represent a limitation of the scope of protection.

[0022] Showing:

[0023] Figure 1 shows an electrochemical cell for producing a lithium-containing electrode and a corresponding method therefor,

[0024] Figure 2 shows an upscaling version of the electrochemical cell according to Figure 1 ,

[0025] Figure 3 is a schematic representation of the electrodes to explain the microstructure, Figure 4 is a schematic representation of a laser melting process for producing a porous structure,

[0026] Figure 5 is a schematic enlarged view of an electrode produced by the described method in the described electrochemical cell.

[0027] Figure 1 schematically describes an electrochemical cell 2 and a method for operating this cell 2. The electrochemical cell 2 comprises a first electrode 8, which is designed as a cathode 10. The cell 2 also comprises a second, lithium-containing electrode 12, which is designed as an anode 14. Both electrodes 8, 12 are immersed in a non-aqueous, liquid electrolyte 16, wherein when an electric current is applied via contacts 46, lithium ions 18, which are characterized by the Li+, migrate from the anode 14 to the cathode 10 in the cell 2. Furthermore, the electrochemical cell 2 is operated under inert gas 44, in this case argon, wherein the inert gas 44 is discharged from the cell 2 and in an inert gas circuit 44, where it is processed in a gas cleaning system 36 and then fed back to the cell 2.Furthermore, the electrolyte 16 is also treated, for which purpose an electrolyte circulation system 38 is used, which contains a pump 40 and a filter 42. In this case, propylene carbonate is used as the electrolyte 16.

[0028] Figure 2 shows an analogous embodiment of the electrochemical cell 2 from Figure 1, however, a plurality of pairs of first electrons 8 and second electrons 12, i.e. pairs of cathodes 10 and anodes 14, are connected in parallel in this cell 2. The contact 46 as well as the inert gas circuit 34 and the electrolyte circulation system 38 are designed analogously to cell 2 in Figure 1. This embodiment according to Figure 2 serves in particular to achieve upscaling for the processing of lithium-containing compounds and the production of an electrode 4 (cf. Figure 5). In the following, the electrochemical process and the preparatory

[0029] Processes for manufacturing the anode 14 and the cathode 10 for the electrochemical cell 2 are described in more detail.

[0030] Since lithium has the lowest standard potential of -3.04 V in the periodic table and is therefore the least noble of all elements, electrolytes containing H30 + -ions dissociate, so mainly aqueous electrolytes are not used for cells containing lithium. During electrochemical deposition, hydrogen would otherwise be deposited rather than lithium. The electrochemical window of water is 1.2 V. In this electrochemical potential of the electrode, the electrolyte is neither oxidized nor reduced. This range results from the difference between oxidation potential (anodic limit) and reduction potential (cathodic limit). Outside of this range, the electrolyte reacts at the electrode surface. Water is electrolyzed in the process.

[0031] Instead of water, aprotic, polar solvents such as ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or ionic liquids are used for the deposition of lithium. The organic carbonates and ionic liquids have a larger electrochemical window. For propylene carbonate, the electrochemical window is 4 V, and ionic liquids show a value of 3 V to 6 V. Since the electrochemical window is reduced from 4 V to 2 V by small amounts of water (approx. 3 wt. %), it is necessary to work in anhydrous form. In addition, lithium reacts with nitrogen to form lithium nitride and with oxygen to form lithium oxide even at room temperature. For this reason, the electrochemical cell 2 is purged with inert gas 44, in particular argon or sulfur dioxide.The gas purging of cell 2 takes place in the inert gas circuit 34, with the inert gas 44 constantly circulated between cell 2 and the gas purification system 36 and continuously processed. The gas purification system 36 removes oxygen and moisture from the inert gas 44 using a copper catalyst and a molecular sieve. This achieves purity levels of up to < 1 ppm O2 and < 1 ppm H2O.

[0032] In addition, the electrochemical cell 2 must be sealed off from the environment to prevent atmospheric moisture, oxygen, or nitrogen from entering the cell 2. For treatment, the electrolyte 16 is also continuously pumped through filter systems 42 by means of a pump 40 and returned to the sealed electrochemical cell 2.

[0033] To produce the second electrode 12, i.e. the cathode 14, a lithium slag is used which is produced during the thermal decomposition of old, used lithium-ion batteries. This second electrode 12 therefore comprises lithium compounds 30, as is shown, for example, in Figure 3. These lithium compounds 30, which can also be referred to as lithium slag because they originate from the thermally decomposed residues of lithium batteries, contain lithium calcium silicates, lithium magnesium silicates, lithium fluoride and / or lithium aluminite. During the decomposition of certain NMC batteries which contain manganese, lithium manganese oxide (Li2Mn2O3 or the associated spinel type LiMn2O4) is also present in the slag, depending on the manganese content. This lithium slag must first be processed mechanically by breaking up the slag and grinding it into particles in a vibrating disc mill or a ball mill.The powder obtained from the slag is then thoroughly mixed with electrically conductive carbon particles 31 (e.g. electrically conductive soot, porous conductive carbon powder or graphite) in a plowshare mixer for battery masses. The mixing drum has a ceramic lining. Mixing elements, mixer shaft and measuring heads are preferably provided with a thin, extremely strong ceramic coating (e.g. aluminum oxide or tungsten carbide) so that foreign ions can be avoided. Homogeneous mixing is achieved in the plowshare mixer in a short time. Porous conductive carbon powder in the form of carbon particles 31, available for example under the trade name Porocarb, is particularly well suited as an additive for electrode formulation because local areas of high porosity are present after electrode compaction.

[0034] The macroporous carbon particles 31 are used to improve the ionic conductivity in the electrode 12. As the anode degradation progresses, the proportion of macropores reduces capacity loss. Furthermore, the porosity of the particles 31 increases the mechanical stability of the electrode 12 after compaction. The mixed powder (mixture of lithium compound 30 and carbon particles 31) is filled into a mold and compacted in a pressing process. This can be uniaxial pressing using an upper punch or by isostatic pressing at approximately 300 bar in an oil bath. In this way, a preferably cylindrical electrode is formed. This second electrode 12 produced in this way is introduced into the cell 2 as the anode 14.

[0035] The associated cathode 10 of the electrochemical cell is constructed in advance in such a way that it is converted into an electrode 4 of a lithium iron phosphate accumulator (LFP battery) during the process in the electrochemical cell 2. This means that the cathode 10 in the cell is modified during cell operation in such a way that at the end of the process it appears as a new, independent, lithium-containing electrode 4 (cf. Figure 5). This positive electrode of an LFP battery, i.e. the electrode 4, consists of a current collector and an energy storage layer. This layer is the electrochemically active material lithium iron phosphate. The current collector, on the other hand, can be in the form of a metal foil or, preferably, a porous metal structure. In this case, it is in the form of a porous metal structure made, for example, from aluminum or nickel or an alloy of these elements.This porous metal structure 6 can preferably be produced by an additive manufacturing process, for example using a selective laser melting process or a selective electron beam melting process. This is described as an example in Figure 4. In this process, aluminum or nickel in powder form is applied to a base plate as a powder bed 54. The applied metal powder is then completely remelted locally using a laser beam 50 from a laser 48 and, after solidification, forms a solid metal layer. The base plate is lowered by the amount of the layer thickness and more powder is applied from a powder supply 56, for example using a doctor blade 58. This cycle is repeated until all layers have been remelted and the finished porous structure 6 has been created.

[0036] In this way, it is possible to form complex structures that have precisely the surface properties that are optimal for the operation of the electrode 4. For this purpose, a digital twin of the structure 6 and a process control system can be precisely digitally mapped using a CAD process. In contrast to possible foaming processes for metallic foams, a predetermined structure 6 can be created in this way. The digital twin of the structure 6 and the process control system can be stored in a database and retrieved by a database user as needed.

[0037] The finished porous structure 6 is cleaned of excess powder and further processed. When representing the structure 6, layer thicknesses of 15 pm to 500 pm are possible, i.e., the structure 6 is already finished as a current collector after approximately two to three cycles. Since the data for guiding the laser 48 (or alternatively an electron beam, which is not shown here) is generated from a 3D CAD body using software, there is a great deal of geometric freedom for the electrode shape. With the aforementioned additive manufacturing processes, selective laser melting or selective electron beam melting, periodically open-cell (open-pored) metal structures with a defined pore size and cell geometry can be produced. The periodically cellular metal structures are based on a tetradecahedral geometry with a cylindrical cell web morphology. A tetradecahedron is a polyhedron with 14 faces.Open-cell metal structures have the advantage of an enlarged surface area for the increased absorption of energy-storing material and thus for an increase in energy density.

[0038] The open-pore, porous metal structure 6 made of aluminum or nickel, or alloys thereof, is then coated with a layer of iron phosphate to absorb lithium ions. For this purpose, the metal surfaces are electroplated with iron in an iron electrolyte. The electrolyte contains water-soluble iron(II) salts such as iron(II) sulfate or iron(II) fluoroborate, and ammonium chloride as the conductive salt.

[0039] The pH of the electrolyte is 3 to 4. Iron deposition is carried out at a temperature of 40°C to 70°C. The current density is 3 A / dm 2 up to 4 A / dm 2To prevent the formation of oxygen at the anode, diethylhydroxylamine is used as an anodic depolarizer. The metal surface to be coated is connected as the cathode. The anodes are made of ultrapure iron (99.99%). The dissolved Fe 2+ -ions migrate to the cathode, where they are reduced to elemental iron, forming a thin iron layer on the metal surface. To produce an iron phosphate layer, phosphoric acid and magnetite (FeaCL) are homogenized in water at 10,000 rpm for approximately ten minutes using a dispersing rod. The iron-prepared surfaces of the porous structure 6 are immersed in this dispersion. Between the Fe 3+ A redox reaction takes place between the oxide magnetite and the elemental iron from the steeled surfaces, whereby in a comproproportionation Fe 2+is formed. The color of the dispersion changes from black to green-brown and the starting materials dissolve into the solution. During this redox reaction, the electrolyte heats up by 2°C to 20°C to temperatures of 20°C to 40°C. As soon as no further temperature increase is observed, the reaction mixture with the metal surfaces is heated to 80°C to 100°C with the addition of hydrogen peroxide (35 wt%). The Fe 2+ -ions become Fe 3+ -ions are oxidized. Oxygen is produced as a decomposition product of hydrogen peroxide. Using rapid tests for Fe 2+The oxidation reaction is checked for completeness by adding ions. The pink-colored electrolyte containing the metal surfaces is kept at 80°C, and the iron (III) phosphate precipitates on the metal surface. After precipitation, the coated metal foils or porous metal structures are dried in a drying oven at 80°C for approximately three hours.

[0040] Figure 3 once again shows a very schematic microstructure of the respective electrodes 12, 8 in the cell 2. On the left side, the anode 14 is shown in the form of the second electrode 12. This comprises, as already described, the lithium-containing compound 30, i.e., the lithium slag with the aforementioned lithium compounds. Furthermore, the structure is provided with conductive carbon particles 31 and compacted into an electrode 12. On the right side of Figure 3, the cathode 10 is shown, in which the porous structure 6 is depicted. The circular sections 3b and 3c, enlarged twice, from the first electrode 8, i.e., the cathode 10, show the porous structure 6, first the surface 26 of this porous structure, and in the next enlarged view, the surface 26 with an iron phosphate layer 28 applied thereto, which was applied using the previously described deposition process.In the enlarged view according to Figure 3c, a dashed line is drawn vertically in this circle. The left side shows the surface 26 with the iron phosphate layer 28 and the right side shows the lithium ions 18 which have already reacted with the iron phosphate layer 28 to form lithium iron phosphate 32. Figure 5 shows the resulting electrode 4 again, which essentially corresponds to the right-hand electrode 8, i.e. the cathode 10 of the cell 2 in the process step according to Figure 3c on the right-hand side. This electrode 4 is thus provided with the lithium iron phosphate layer 32, which is applied to the porous metallic structure 6. In principle, this electrode 4 according to Figure 5 can be used to be inserted into a new lithium iron phosphate accumulator.

[0041] In the described method for producing this electrode 4 , recycled lithium - containing material is used to directly produce a new , ready - to - use electrode 4 for a new accumulator .

[0042] Reference symbol list

[0043] 2 electrochemical cell

[0044] 4 lithium-containing electrode

[0045] 6 porous metallic structure

[0046] 8 first electrode

[0047] 10 Cathode

[0048] 12 second electrode

[0049] 14 Anode

[0050] 16 non-aqueous electrolyte

[0051] 18 lithium ions

[0052] 20 additive manufacturing processes

[0053] 22 Powder bed process

[0054] 24 laser melting processes

[0055] 26 Surface porous structure

[0056] 28 Iron phosphate layer

[0057] 30 lithium compounds

[0058] 31 carbon particles

[0059] 32 Lithium iron phosphate layer

[0060] 34 Inert gas circuit

[0061] 36 Gas cleaning system

[0062] 38 Electrolyte circulation system

[0063] 40 Pump

[0064] 42 filters

[0065] 44 Inert gas

[0066] 46 Contacting

[0067] 48 lasers

[0068] 50 laser beam

[0069] 52 Laser optics

[0070] 54 Powder bed

[0071] 56 powder supply

[0072] 58 squeegees

Claims

Patent claims 1. A method for producing a lithium-containing electrode (4) for a lithium-ion battery, comprising the following steps: - producing a porous metallic structure (6) , - coating a surface (26) of the porous structure (6) with an iron phosphate layer (28), - introducing the porous structure (6) provided with the iron phosphate layer (28) into an electrochemical cell (2) as the first electrode (8) which serves as the cathode (10), - introducing a second, lithium-containing electrode (12) into the cell (2) which serves as an anode (14), - wherein lithium compounds (30) originating from thermally decomposed electrode material of a lithium-ion accumulator are introduced into the second lithium-containing electrode (12), - introducing a non-aqueous electrolyte (16) into the electrochemical cell (2), - closing the electrochemical cell (2) under inert conditions, - applying electric current to the electrodes (8), (12) of the electrochemical cell (2) so that lithium ions (18) migrate from the lithium-containing anode (14) through the non-aqueous electrolyte (16) to the cathode (10) in the form of the porous structure (6) and - the surface (26) of the porous structure (6) provided with the iron phosphate layer (28) is converted into a lithium iron phosphate layer (32).

2. Method according to claim 1, characterized in that the porous structure (6) is produced by means of an additive process (20).

3. Method according to claim 2, characterized in that the porous structure (6) is produced by means of a powder bed process (22).

4. The method according to claim 3, characterized in that the powder bed method (22) is a laser melting method (24) or an electron beam melting method.

5. Method according to one of the preceding claims, characterized in that a base material of the porous metallic structure (6) is an aluminum and / or nickel alloy.

6. Method according to one of the preceding claims, characterized in that the non-aqueous electrolyte (16) comprises ethylene, propylene or dimethyl carbonate, acetonitrile or an ionic liquid.

7. Method according to one of claims 2 to 6, characterized in that the lithium compound (30) comprises lithium calcium silicates and / or lithium magnesium silicates and / or lithium manganese oxides and / or lithium cobalt oxides and / or lithium nickel oxides.

8. Method according to one of the preceding claims, characterized in that the lithium iron phosphate is applied to a surface (26) of the structure (6) in such a way that an open porosity of the structure (6) is maintained.

9. Method according to one of the preceding claims, characterized in that for coating the surface of the porous structure (6) with iron phosphate, the porous structure (6) is immersed in a dispersion of phosphoric acid and magnetite and is heated to a temperature between 80°C and 110°C, while an oxidizing agent, in particular hydrogen peroxide, is added.

10. Method according to one of the preceding claims, characterized in that the inert conditions are provided by argon as a protective gas.

11. Electrochemical cell for producing an electrode of a lithium accumulator comprising an anode (14) with lithium compounds (30) which originate from a thermal decomposition of used lithium accumulators and a cathode (10) which comprises a porous metallic structure (6) which is provided on its surface (26) with an iron phosphate layer (28) and wherein the anode (14) and the cathode (10) are separated from one another by a non-aqueous electrolyte (16).

12. Electrochemical cell according to claim 11, characterized in that in the electrochemical cell (2) there are several pairs of anodes (14) and cathodes (10) connected in parallel.

13. Electrochemical cell according to claim 11 or 12, characterized in that the lithium compounds (30) are mixed with carbon particles (32), preferably with porous carbon particles (32).

14. Electrochemical cell according to one of claims 11 to 14, characterized in that the porous metallic structure (6) is produced by an additive manufacturing process (20).

15. Computer program comprising a digital twin for digitally mapping the structure (6) from a method according to one of claims 1 to 10 or from an electrochemical cell according to one of claims 11 to 14.

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