Method for producing lithium-containing electrode and electrochemical cell

Abstract

The invention relates to a method for producing a lithium-containing electrode (4) of a lithium-ion-containing battery, comprising the following steps:-producing a metal foil (6),-applying a graphite layer (28) to a surface (26) of the metal foil (6),-introducing the metal foil (6) provided with the graphite layer (28) as a first electrode (8) into an electrochemical cell (2), which first electrode (8) serves as a cathode (10),-introducing a second lithium-containing electrode (12) into the cell (2), the second lithium-containing electrode (12) acts as an anode (14),-wherein a lithium compound (30) derived from the thermally decomposed electrode material of the lithium-ion battery is introduced into the second lithium-containing electrode (12),-a non-aqueous electrolyte (16) is introduced into the electrochemical cell (2),-the electrochemical cell (2) is closed under inert conditions,-an electric current is applied to the electrodes (8), (12) of the electrochemical cell (2), and-the lithium-containing electrode (12) is applied to the non-aqueous electrolyte (16). The non-aqueous electrolyte (16) is embedded in order to migrate lithium ions (18) from the lithium-containing anode (14) through the non-aqueous electrolyte (16) to the cathode (10) present in the form of a metal foil (6) provided with a graphite layer (28), and the surface (26) of the metal foil (6) provided with the graphite layer (28) is embedded in order to form lithium ions.

Description

[0001] The present invention relates to a method for producing a lithium-containing electrode according to claim 1 and to an electrochemical cell according to claim 13.

[0002] The recovery of valuable metals such as nickel, cobalt and lithium from lithium-ion batteries is carried out by pyrometallurgical and hydrometallurgical processes after the battery treatment, i.e. after the electrically safe discharge, the deactivation of the residual lithium metal and the evaporation of the electrolyte. In addition to the cobalt-nickel-copper alloy, lithium-containing slags are also produced in the pyrometallurgical process. The lithium contained therein is to be recovered from these lithium-containing slags.

[0003] According to the prior art, lithium is obtained from the slag by means of a hydrometallurgical process. The quenched slag is comminuted using a rod mill and then placed on a magnetic disc to remove the ferromagnetic alloy components, such as nickel and cobalt, which are entrained in the slag. The slag is then leached using sulphuric acid. At this point, the lithium ions go into solution and the remaining solids, which contain gypsum and silicates, are separated off by filtration. In order to prevent the unwanted precipitation of lithium carbonate in the subsequent purification steps, the filtrate is diluted to below the solubility limit of lithium carbonate. The pH value of the diluted filtrate is adjusted to 7 by adding calcium oxide in order to remove impurities such as aluminium, magnesium, iron, manganese, silicon and sulphates. At this pH value, aluminium, iron, silicon and some heavy metals precipitate as hydroxides. Some of the sulphates form insoluble calcium sulphate (gypsum) with the calcium oxide. After the solid / liquid separation, the pH value is increased to 12 by adding more calcium oxide. At this pH value, magnesium and other metals present in the solution as hydroxide or sulphate residues precipitate completely. After a further solid / liquid separation, the excess calcium is precipitated as lime by adding sodium carbonate and separated from the solution by filtration. The solution is highly concentrated by evaporation of the water and, at 100°C, lithium is precipitated as lithium carbonate by adding sodium carbonate. The separated lithium carbonate is washed with ethanol, since lithium carbonate is insoluble in ethanol, in contrast to water. The purity of this crude carbonate is about 98% and requires repeated refining for reuse in batteries. Using this prior art method, the overall recovery of lithium, i.e. the yield from the slag, is about 65%. The reason for the low yield is that, in the process of precipitating the impurities with calcium oxide, a part of the lithium is bound to mixed metal oxides with aluminium, magnesium, iron or manganese. This lithium is very tightly bound chemically so that it has to be separated from the starting solution using a solvent extraction process in order to significantly increase the recovery.

[0004] The above-mentioned prior art method exhibits a very high wet-chemical complexity, which is not profitable in terms of economy and ecology. Therefore, it is an object of the present invention to provide a method for the reuse of lithium and an electrochemical cell, whereby a higher yield than in the prior art is achieved and the recovered lithium can be reused in new electrodes.

[0005] The object is achieved in that the method for producing a lithium-ion containing electrode of a lithium-ion battery has the features of claim 1 and the electrochemical cell has the features of claim 13.

[0006] The method for producing a lithium-ion containing electrode of a lithium-ion battery according to claim 1 comprises the following steps: - producing a metal foil, - applying a graphite layer on the surface of the metal foil, - introducing the metal foil provided with the graphite layer as a first electrode into an electrochemical cell, which first electrode serves as a cathode, - introducing a second lithium-ion containing electrode into the cell, which second lithium-ion containing electrode serves as an anode, - wherein lithium compounds originating from the decomposition, in particular thermal decomposition, of the electrode material of the lithium-ion battery are introduced into the second lithium-ion containing electrode, - introducing a non-aqueous electrolyte into the electrochemical cell, - closing the electrochemical cell under inert conditions, - applying an electric current to the electrodes of the electrochemical cell to cause lithium ions to migrate from the lithium-ion containing anode through the non-aqueous electrolyte to the cathode present in the form of the metal foil provided with the graphite layer, and - the graphite layer of the metal foil is intercalated with lithium ions.

[0007] The above invention differs fundamentally from the prior art in that the lithium compound containing slag, which is usually obtained from the thermal decomposition of the battery, is not decomposed using wet-chemical methods, but is introduced again into the electrode and the electrochemical cell. The method differs from conventional electrochemical cells and conventional lithium-ion batteries in that lithium ions migrate from the electrode of the above-mentioned lithium containing slag through the electrolyte to the cathode and are intercalated into a layer specially provided for this purpose, namely the graphite layer.

[0008] Intercalation means that molecules or ions, optionally also atoms, are intercalated into chemical compounds, wherein their structure does not change significantly during the intercalation of these substances. In this particular case, lithium ions will be positioned between the individual graphene layers of the graphite, since intercalation (intercalation) between the graphene layers only requires the overcoming of weak van der Waals forces.

[0009] In addition, the method differs from the prior art in that the cathode of the electrochemical cell or the method carried out therein is designed as a new electrode by means of the electrically conductive metal foil provided with the graphite containing layer, in which lithium ions are intercalated, which is formed again during the method. This new electrode has been designed as an electrode for a new lithium-ion battery, for example in the form of an anode, by structuring its surface and its surface coating.

[0010] The method not only provides a technically less complex and economical method for reusing the lithium-containing dross produced during the decomposition, in particular thermal decomposition, of old accumulators, but at the same time it provides a production method for completely new, directly reusable electrodes for lithium-containing accumulators.

[0011] In an advantageous embodiment of the application, the metal foil is a copper foil. Copper has an extremely high electrical conductivity and is therefore very suitable as an electrode material. Furthermore, copper is relatively inexpensive and easy to handle technically. In principle, other highly conductive metals, such as silver, gold or aluminium, are also suitable as a material for the metal foil.

[0012] In particular, the copper foil is produced using electrolytically purified copper, which has a purity of at least 99.9%, particularly preferably 99.99%. The electrical conductivity of copper increases with increasing purity.

[0013] For the graphite used, it is also advisable to use a material that is as pure as possible and as free of defects in the crystal structure as possible. Therefore, it is preferable to use synthetically produced graphite.

[0014] Furthermore, in order to achieve good coating properties, the graphite is provided with a binder and applied to the metal foil 6 in the form of this mixture, preferably by means of wet-chemical methods. It is preferable to use polyacrylic acid (PAA), acrylic-based copolymers (ACM), styrene-butadiene rubber (SPR) and / or carboxymethyl cellulose as a binder. Furthermore, the mixture of graphite and binder is preferably provided with an electrically conductive additive, in particular carbon black, in order to produce the graphite layer.

[0015] The non-aqueous electrolyte preferably comprises ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or an ionic liquid. Propylene carbonate is particularly preferred, as it is inexpensive to produce and can be handled without problems. Ionic liquids are salts whose melting point is particularly below 100°C. Like all salts, they comprise anions and cations. By varying these, the physicochemical properties of ionic liquids can be varied within very wide limits and optimised to meet technical requirements. Typical cations can be, for example, imidazolium or pyridinium, ammonium and / or phosphonium. Possible anions include halide ions and weakly coordinating ions, such as tetrafluoroborate or hexafluorophosphate, as well as trifluoroacetate, triflate and tosylate.

[0016] In an advantageous embodiment of the application, the lithium of the lithium compound in the second electrode comprises lithium calcium silicate and / or lithium magnesium silicate and / or lithium manganese oxide and / or lithium cobalt oxide and / or lithium nickel oxide. They are usually compounds contained in the dross or ash produced at this time during the thermal decomposition of lithium-ion accumulators.

[0017] The operation of the method and the operation of the electrochemical cell are effected under inert conditions. Argon is particularly suitable as inert gas. Nitrogen would react with lithium ions in the non-aqueous electrolyte. The efficiency of a vacuum atmosphere is also low due to the high vapour pressure of the materials used under vacuum conditions.

[0018] A further component of the application is an electrochemical cell for producing an electrode of a lithium accumulator. It comprises an anode and a cathode, the anode containing a lithium compound derived from the thermal decomposition of a used lithium accumulator, the cathode comprising a metal foil provided on its surface with a graphite layer, and wherein the anode and the cathode are separated from one another by a non-aqueous electrolyte.

[0019] The advantages of the electrochemical cell relative to the prior art have been explained in connection with the method of the application. These advantages include, on the one hand, the direct re-use of the lithium-containing compounds from the thermal decomposition of old accumulators in a technically uncomplicated manner, while at the same time a new cathode of a lithium accumulator is produced.

[0020] It is particularly advantageous if the electrochemical cell is designed so that there are a plurality of pairs of anodes and cathodes connected in parallel. Thereby the production scale of the anodes can be enlarged and the lithium dross from the old accumulator recyclate can be re-used on an industrial scale.

[0021] For the production of the second electrode, i.e. the anode of the electrochemical cell, it is suitable to mix the lithium compound, i.e. the dross from the thermal decomposition of the old accumulator, with an electrically conductive material, in particular carbon particles, and then to press. The use of porous carbon particles is particularly preferred. This electrode pressed from lithium compound and carbon particles is particularly well suited for the electrochemical cell described.

[0022] Further embodiments and further features are explained in more detail with reference to the following figures. Features having the same name in different embodiments are denoted by the same reference signs. The illustrations in the following figures are purely schematic and do not constitute a restriction of the scope of protection.

[0023] Shown is: Figure 1 Electrochemical cell for producing a lithium-containing electrode and corresponding method, Figure 2 Figure 1 Enlarged scale version of the electrochemical cell, Figure 3 Figure 1 Schematic illustration of the electrode for explaining the microstructure. Figure 4 Figure 3 Enlarged partial IV for explaining the microstructure.

[0024] Figure 1An electrochemical cell 2 and a method for operating the cell 2 are schematically depicted. The electrochemical cell 2 comprises a first electrode 8, which is designed as a cathode 10. The cell 2 further 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 lithium ions 18 (denoted as Li + ) migrate from the anode 14 to the cathode 10 in the cell 2 when an electric current is applied via contacts 46. Furthermore, the electrochemical cell 2 is operated under an inert gas 44 (in this case argon), wherein the inert gas 44 is removed from the cell 2 and enters an inert gas loop 44, where it is treated in a gas purification system 36 and returned back to the cell 2. Furthermore, the electrolyte 16 is also treated for which an electrolyte circulation system 38 is used, which comprises a pump 40 and a filter 42. In this case, propylene carbonate is used as electrolyte 16.

[0025] Figure 2 A design similar to the electrochemical cell 2 in Figure 1 is shown, but in this cell 2 a plurality of pairs of first electrodes 8 and second electrodes 12, i.e. a plurality of pairs of cathodes 10 and anodes 14, are connected in parallel. The design of the contacts 46 as well as the inert gas loop 34 and the electrolyte circulation system 38 is similar to the cell 2 in Figure 1 . This design according to Figure 2 is especially used to scale up the treatment of lithium-containing compounds and the production of electrodes 4 (see Figure 3 and 4 ). The electrochemical process as well as the preparation flow for producing the anodes 14 and cathodes 10 of the electrochemical cell 2 will be discussed in more detail below.

[0026] Since lithium has the lowest standard potential of -3.04 V in the periodic table of elements and thus is the least noble of all elements, an electrolyte that dissociates H3O + ions, i.e. mainly aqueous electrolytes, cannot be used for lithium-containing cells. Otherwise, during the electrochemical deposition, it is more likely that hydrogen is deposited instead of lithium. The electrochemical window of water is 1.2 V. At this electrode potential, the electrolyte is neither oxidized nor reduced. This range is determined by the difference between the oxidation potential (anodic limit) and the reduction potential (cathodic limit). Outside this range, the electrolyte reacts at the electrode surface. In this process, water is electrolyzed.

[0027] For the deposition of lithium, instead of water, an aprotic polar solvent is used, such as ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or an ionic liquid. Organic carbonates and ionic liquids have a larger electrochemical window. The electrochemical window of propylene carbonate is 4 V, the values for ionic liquids are 3 V to 6 V. Since the electrochemical window drops from 4 V to 2 V due to a small water input of about 3 wt.%, it is necessary to operate in a water-free state. Furthermore, lithium reacts with nitrogen to form lithium nitride and with oxygen to form lithium oxide, even at room temperature. Therefore, the electrochemical cell 2 is purged with an inert gas 44, in particular argon or sulfur dioxide. The gas purge of the cell 2 takes place in an inert gas circuit 34, in which the inert gas 44 is continuously circulated and continuously treated between the cell 2 and a gas purification system 36. The gas purification system 36 removes oxygen and moisture from the inert gas 44 using a copper catalyst and a molecular sieve. A purity of up to <1 ppm O2 and <1 ppm H2O is thereby achieved.

[0028] Furthermore, the electrochemical cell 2 must be closed with respect to the environment, whereby no moisture from the air and no oxygen or nitrogen enters the cell 2. For the treatment, the electrolyte 16 is also continuously pumped through a filter device 42 by a pump 40 and back into the closed electrochemical cell 2.

[0029] For the production of the second electrode 12, i.e. the anode 14, lithium dross produced in the thermal decomposition process of used old lithium-ion batteries is used. Thus, this second electrode 12 contains lithium compounds 30, as shown for example in Figure 3 These lithium compounds 30, which can also be referred to as lithium dross, since they also originate from the thermal decomposition residue of lithium batteries, contain lithium calcium silicate, lithium magnesium silicate, lithium fluoride and / or lithium aluminate. Lithium manganese oxide (Li2Mn2O3 or related spinel type LiMn2O4) is also present in the dross during the decomposition of certain manganese-containing NMC battery packs, depending on the manganese content. The lithium dross must first be subjected to a mechanical treatment, in which the dross is broken up and ground to particles in a vibrating pan mill or a ball mill. The resulting powder from the dross is then intimately mixed with electrically conductive carbon particles 31, such as electrically conductive carbon black, porous electrically conductive carbon powder or graphite, in a plowshare mixer for battery materials. The mixing drum has a ceramic lining. The stirring elements, stirring shaft and measuring head are preferably provided with a thin solid ceramic layer, such as aluminum oxide or tungsten carbide, so that extraneous ions can be avoided. In the plowshare mixer, homogeneous and complete mixing is achieved in a short time. Porous electrically conductive carbon powder in the form of carbon particles 31, such as available under the trade name Porocarb, is particularly well suited for use as an additive for the electrode formulation, since local areas of high porosity occur after the electrode is compacted.

[0030] The macroporous carbon particles 31 serve to increase the ionic conductivity in the electrode 12. With the ongoing degradation of the anode, the capacity loss is reduced by the proportion of macropores. 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 press mold and compacted during the pressing process. This can be uniaxial pressing using an upper punch or isostatic pressing by means of an air jet in an oil bath at a pressure of about 300 bar. The electrode, which is preferably cylindrical, is thus formed. The second electrode 12 thus produced is introduced into the battery 2 as anode 14.

[0031] The associated cathode 10 of the electrochemical cell has been pre-structured so that it is converted into an electrode 4 of a lithium accumulator during the process in the electrochemical cell 2. This means that the cathode 10 in the battery is changed during the operation of the battery so that it becomes a new, independent lithium-containing electrode 4 at the end of the process (see Figure 4 ). The positive electrode, i.e. the electrode 4 of the lithium accumulator, consists of a current collector, a metal foil 6 and an energy storage layer. This layer is a graphite layer 28, which contains lithium ions embedded therein.

[0032] For the production of the first electrode 8, synthetic graphite is preferably used. Synthetic graphite differs from natural graphite in that it is more highly pure, of better quality and has a reproducibility of the matching properties. This results in a higher cycle stability between the charging process and the discharging process and better overall charging properties. The synthetic graphite is applied to a copper foil (metal foil 6) with a binder (e.g. polyacrylic acid (PAA), acrylic copolymer-based (ACM), styrene-butadiene rubber (SPR), carboxymethyl cellulose, which is dissolved in water) and a conductive additive (e.g. carbon black). After the wet-chemical application of the electrode paste, drying is carried out immediately in an impingement jet dryer in order to remove the solvent used (e.g. ethanol or water). In the impingement jet dryer, the paste film with the copper foil is kept in a suspended state and is dried during the run by means of a high-speed impact of the to-be-dried strip by a nozzle and an air jet, which achieves a high heat transfer here. Subsequent drying is then also carried out in a vacuum oven in order to reduce the residual moisture to a few ppm.

[0033] The copper foil is electrolytically purified copper, which is drawn into a foil. The purity of the copper purified in this way is very high, > 99.99%.

[0034] Figure 3 The microstructure of the respective electrode 12, 8 in the battery 2 is shown very schematically. Shown on the left is the anode 14 as second electrode 12. As described above, it contains the lithium-containing compound 30, i.e. the treated lithium dross with the above-mentioned lithium compound. Furthermore, the structure is also provided with electrically conductive carbon particles 31 and is compacted to form the electrode 12. Figure 3The right-hand side shows the cathode 10. This is a metal foil 6, in this case a copper foil, which is provided with a graphite layer 28 into which lithium ions 18 are intercalated during operation of the battery 2.

[0035] Figure 4 A schematic microstructure of the resulting electrode 4 is shown, which shows Figure 3 an enlarged view of the local IV. The electrode 4 is thus provided with a graphite layer 28, into which lithium ions 18 are intercalated between the individual graphene layers 29 of the graphite layer 28. In principle, the electrode 4 according to Figure 4 the electrode 4 can be used in new lithium accumulators, for example as an anode.

[0036] In the method for producing the electrode 4, the recycled lithium-containing material is thus used to directly produce a new ready-to-use electrode 4 for a new accumulator.

[0037] List of reference signs 2 electrochemical cell 4 lithium-containing electrode 6 metal foil 8 first electrode 10 cathode 12 second electrode 14 anode 16 nonaqueous electrolyte 18 lithium ions 26 surface metal foil 28 graphite layer 29 graphene layer 30 lithium compound 31 carbon particles 34 inert gas circuit 36 gas purification system 38 electrolyte circulation system 40 pump 42 filter 44 inert gas 46 contact point.

Claims

1. Method for producing a lithium-containing electrode (4) of a lithium-ion battery, comprising the following steps: - producing a metal foil (6), - applying a graphite layer (28) on a surface (26) of the metal foil (6), - introducing the metal foil (6) provided with the graphite layer (28) as a first electrode (8) into an electrochemical cell (2), which first electrode (8) serves as a cathode (10), - introducing a second lithium-containing electrode (12) into the cell (2), which second lithium-containing electrode (12) serves as an anode (14), - wherein lithium compounds (30) derived from a decomposed electrode material of a lithium-ion battery 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 an electric current to the electrodes (8), (12) of the electrochemical cell (2) in order to cause lithium ions (18) to migrate from the lithium-containing anode (14) through the non-aqueous electrolyte (16) to the cathode (10) present in the form of the metal foil (6) provided with the graphite layer (28), and - the surface (26) of the metal foil (6) provided with the graphite layer (28) is embedded to form lithium ions. The metal foil (6) is a copper foil. The copper foil is produced using electrolytic purification of copper. The purity of the copper is at least 99.9%, preferably 99.99%. The graphite is synthetically produced graphite. The graphite is provided with a binder and is applied to the metal foil (6). The binder comprises polyacrylic acid (PAA), acrylic-based copolymer (ACM), styrene-butadiene rubber (SPR) and / or carboxymethyl cellulose. The mixture of graphite and binder used to produce the graphite layer (28) is provided with an electrically conductive additive, in particular carbon black. The lithium compounds (30) are derived from a thermally decomposed electrode material of a lithium-ion battery. The non-aqueous electrolyte (16) comprises ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or an ionic liquid.

2. The method of claim 1, wherein, The lithium compounds (30) comprise lithium calcium silicate and / or lithium magnesium silicate and / or lithium manganese oxide and / or lithium cobalt oxide and / or lithium nickel oxide.

3. The method of claim 2, wherein, The inert conditions are provided by argon as a protective gas.

4. The method of claim 3, wherein, 13. Electrochemical cell for producing an electrode of a lithium battery, comprising an anode (14) containing lithium compounds (30) derived from a decomposition of a used lithium battery and a cathode (10) comprising a metal foil (6) provided with a graphite layer (28) on a surface (26) thereof, and wherein the anode (14) and the cathode (10) are separated from each other by a non-aqueous electrolyte (16).

5. The method according to any of the preceding claims, characterized in that, There are multiple pairs of anodes (14) and cathodes (10) connected in parallel in the electrochemical cell (2).

6. The method according to any of the preceding claims, characterized in that, The lithium compounds (30) are mixed with carbon particles (32), preferably with porous carbon particles (32).

7. The method of claim 6, wherein, The metal foil (6) is a copper foil.

8. The method according to any one of claims 6 or 7, characterized in that, The copper foil is produced using electrolytic purification of copper.

9. The method according to any of the preceding claims, characterized in that, The purity of the copper is at least 99.9%, preferably 99.99%.

10. The method according to any of the preceding claims, characterized in that, The graphite is synthetically produced graphite.

11. The method according to any of the preceding claims, characterized in that, The graphite is provided with a binder and is applied to the metal foil (6).

12. The method according to any of the preceding claims, characterized in that, The binder comprises polyacrylic acid (PAA), acrylic-based copolymer (ACM), styrene-butadiene rubber (SPR) and / or carboxymethyl cellulose. The mixture of graphite and binder used to produce the graphite layer (28) is provided with an electrically conductive additive, in particular carbon black.

14. The electrochemical cell of claim 13, wherein, The lithium compounds (30) are derived from a thermally decomposed electrode material of a lithium-ion battery.

15. The electrochemical cell of claim 13 or 14, wherein, The non-aqueous electrolyte (16) comprises ethylene carbonate, propylene carbonate or dimethyl carbonate, acetonitrile or an ionic liquid. The lithium compounds (30) comprise lithium calcium silicate and / or lithium magnesium silicate and / or lithium manganese oxide and / or lithium cobalt oxide and / or lithium nickel oxide. The inert conditions are provided by argon as a protective gas.

13. Electrochemical cell for producing an electrode of a lithium battery, comprising an anode (14) containing lithium compounds (30) derived from a decomposition of a used lithium battery and a cathode (10) comprising a metal foil (6) provided with a graphite layer (28) on a surface (26) thereof, and wherein the anode (14) and the cathode (10) are separated from each other by a non-aqueous electrolyte (16). There are multiple pairs of anodes (14) and cathodes (10) connected in parallel in the electrochemical cell (2). The lithium compounds (30) are mixed with carbon particles (32), preferably with porous carbon particles (32).

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