Direct recycling of lithium ion battery cathodes

Abstract

The present disclosure relates to methods and devices for direct recycling of alkali metal ion battery electrode production scrap.

Description

[0001] Direct Recycling of Lithium Ion Battery Cathodes

[0002] Field of the invention

[0003] The present disclosure relates to methods and devices for direct recycling of alkali metal ion battery electrode production scrap.

[0004] Background

[0005] Two different basic approaches are used in the recycling of alkali metal ion battery materials, in particular, cathode active materials (CAM) present in the batteries. One approach comprises the complete destruction and dissolution of the cathode active materials by metallurgical processes and subsequent synthesis of new cathode active materials from the metal salts obtained. The other approach comprises the separation of the cathode active materials or anode active materials from other battery components and direct re-introduction of the particulate material obtained into electrode production - the so-called "direct recycling".

[0006] Direct recycling is especially of interest for production scrap, as the electrode active material in such materials is almost virgin. One challenge in direct recycling is avoiding contamination of the recovered electrode active material. In the worst case, foreign particles present as impurities might cause fatal battery failures. In particular, contamination by aluminum particles in the case of cathodes, or copper particles in the case of anodes, of lithium ion batteries may occur upon the detachment of the electrode active material from the respective current collector foil.

[0007] EP 3 940 874 A1 discloses a reuse method of electrode scrap and a method of fabricating a recycled electrode using the same. The reuse method of electrode scrap includes (a) dry milling electrode scrap remaining after punching an electrode sheet including an active material layer on a current collector to obtain milled products; and (b) screening active material layer flakes from current collector fragments in the milled products by sieving the milled products, and collecting the screened active material layer flakes to obtain reusable particles.

[0008] In EP 3 940 872 A1 and EP 2 975 686 A1 , respectively, a rotor impact mill has been suggested for the detachment of the cathode active material from the cathode current collector foil. However, own experiments indicate comparatively high contamination of the material obtained with aluminum.

[0009] Christian Hanisch et al.: "In-Production Recycling of Active Materials from Lithium-Ion Battery Scraps", ECS Trans. 64 (2015) 131 -145 describe a process involving mechanical detachment using a cutting mill. The content of aluminum impurities in the product obtained was in the range of from 0.8 to 3%.

[0010] Christian Hanisch et al.: "Recovery of Active Materials from Spent Lithium-Ion Electrodes and Electrode Production Rejects" in J. Hesselbach and C. Herrmann (eds.): "Glocalized Solutions for Sustainability in Manufacturing: Proceedings of the 18th CIRP International Conference on Life Cycle Engineering, Technische Universitat Braunschweig, Braunschweig, Germany, May 2nd - 4th, 2011", Springer-Verlag, Berlin, Heidelberg 2011 , pp.85-89 describe the influence of the peripheral speed of a cutting mill on the detachment. The peripheral speed was varied between 1.2 and 10 m / s, and the content of aluminum impurities in the product obtained was in the range of from 0.7 to 1%.

[0011] CN 104 577 249 A relates to a method for recycling waste lithium cobalt oxide lithium ion batteries. The used lithium ion batteries are soaked with NaCI solution and discharged. The discharged battery is crushed by a punching machine, and the broken battery casing and the battery core material are subjected to vibration sieving. Large piece of iron and magnetic constituents are recovered from the sieved material by magnetic separation. The remaining material comprises a plastic outer casing, and the battery core material includes a plastic diaphragm, a battery positive electrode with aluminum foil as a current collector, and a negative electrode with copper foil as a current collector. The sieved material is an electrode powder mixed material produced during the crushing process, and the main components are LiCoO2powder and graphite powder.

[0012] Summary of the invention

[0013] The present disclosure provides a method of recycling electrode active material from alkali ion battery (comprising lithium ion batteries or sodium ion batteries or potassium ion batteries or magnesium ion batteries) electrodes which comprise electrode active material coated on a metal foil. The method of the present disclosure avoids applying strong mechanical forces to the electrode during comminution. A rotary die cutting machine or a punch press is used to provide smooth cutting conditions and prevent abrasion of metal particles from the electrode current collector foil during comminution. The electrode active material is delaminated from the comminuted electrodes and the pieces of metal foil obtained are separated from the electrode active material, which then is recycled into the production of new alkali ion battery electrodes.

[0014] Brief description of the drawings

[0015] Figs. 1 a, 1 b show an exemplary rotary die cutting machine comminuting an alkali metal ion battery electrode,

[0016] Fig. 2 is a schematic drawing of an exemplary punch press comminuting an alkali metal ion battery electrode.

[0017] Detailed description

[0018] The method of the present disclosure comprises a. comminuting alkali ion battery electrodes comprising electrode active material coated on a metal foil by die cutting using a rotary die cutting machine or a punch press, completely cutting the foil into pieces without leaving a residual web of punched foil, b. removing any particles having a length in at least two dimensions of less than 100 pm from the comminuted electrodes in a first separation step, e.g., by dry sieving (e.g., in a vibratory screen or circular vibratory screen), air classification, cyclonic separation (dry or wet), wet sieving, or combinations thereof, c. subsequently treating the comminuted electrodes with a solvent able to dissolve a binder polymer present in the coating of the metal foil to delaminate the electrode active material from the metal foil, and to produce a slurry comprising dispersed electrode active material and pieces of metal foil, d. separating the pieces of metal foil from the slurry comprising dispersed electrode active material in a second separation step, e.g., by wet sieving or wet separation (hydrocyclone), e. optionally, providing a current collector metal foil and coating it with the slurry comprising dispersed electrode active material obtained in step d.

[0019] In the method of the present disclosure, off-spec electrodes from alkali ion battery production are comminuted into smaller pieces by die cutting using a rotary die cutting machine or a punch press. It is desired to keep as much as possible of the coating attached to the current collector foils in the comminution step, avoiding any detachment of the coating under the processing conditions. The die cutting, also known as clicking, is preferably performed as wedge cutting on a rotary or flatbed press.

[0020] In one embodiment of the method, the die cutting or punching is performed under dry conditions. In another embodiment of the method, the off-spec electrodes are wetted with a suitable solvent, preferably the solvent that will be employed in the coating, that is able to be absorbed by the binder polymer present in the coating prior to the cutting. Wetting renders the coating more ductile and helps to avoid detachment of coating particles. The wetting may be performed at elevated temperatures, depending on the type of solvent. Water may be best used in a temperature range of 20 to 90°C; in the case of N- methylpyrrolidone (NMP), a temperature range of 20 to 150°C may be applied. After the comminution, the wetted comminuted material may be dried. Alkali ion battery electrodes comprise an electrode active material coated on a current collector metal foil. In some embodiments, the metal foil is comprised of aluminum. In other embodiments, the metal foil is comprised of copper. The coating comprises fine particles of electrode active material and a polymeric binder. In some embodiments, the binder polymer comprises polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose, or styrene-butadiene rubber (SBR).

[0021] In some embodiments, the electrode is a cathode comprising a cathode active material (CAM) coated on an aluminum foil. Examples of cathode active materials include LiNixMnyCo;-x-yO2, LiMn2O4, LiFePO4, Na2 / 3Fei / 2Mni / 2O2, and Nai.88Fe[Fe(CN)6]-0.18 H2O. In some embodiments, the electrode is an anode comprising an anode active material coated on a copper foil. Examples of anode active materials include graphite, hard carbon, and molybdenum disulfide.

[0022] The alkali ion battery electrodes are comminuted using a rotary die cutting machine or a punch press, completely cutting the metal foil of the battery electrodes into pieces without leaving a residual web of punched foil.

[0023] In an embodiment, the rotary die cutting machine features a roller having an array of blades or wedges arranged on its surface which cut the battery electrodes into pieces by pressing the blades towards the foil against a counter roller cylinder (rotary die cutter) or a flat plate (punch press). In some embodiments, the blades or wedges are arranged on the roller surface in radial and longitudinal direction, forming a grid. In some embodiments, the blades or wedges form a rectangular grid. In some embodiments, the distance between two adjacent blades or wedges is in the range of from 5 mm to 50 mm. In other embodiments, the blades or wedges form a diamond-shaped grid, in another embodiment, the blades or wedges form a hexagonal grid, or a trigonal grid. The grids of blades or wedges are designed in such a way that the foils are completely cut into pieces without leaving a residual web of punched foil. In an embodiment, the punch press features a die having an array of blades or wedges arranged on its surface which cut the battery electrodes into pieces. In some embodiments, the blades or wedges of the die form a grid. In some embodiments, the blades or wedges form a rectangular grid. In some embodiments, the distance between two adjacent blades or wedges is in the range of from 5 mm to 50 mm. In other embodiments, the blades or wedges form a diamond-shaped grid, a hexagonal grid, or a trigonal grid.

[0024] In one embodiment, the electrode foil to be punched is laid upon a soft carrier foil. This allows for avoiding contact between the blades and the surface of the counter roller or flat plate when punching through the electrode foil completely.

[0025] An important aspect is the feeding of the electrodes to the rotary die cutting machine or punch press. In an embodiment of the method, battery electrode coils are uncoiled and fed to the rotary die cutting machine or punch press. Electrode coils can either be uncoiled and directly fed to the rotary die cutting machine, or flattened by rollers prior to feeding them to the rotary die cutting machine. In the case of a punch press, the foils generally are first cut into larger pieces that can be cut by the punching tool.

[0026] In another embodiment of the method, cuttings of alkali ion battery electrodes are conveyed to the rotary die cutting machine or punch press on a perforated conveyor belt where the cuttings are held by application of underpressure. Any cuttings that are not held by the underpressure are swept back into the feeder. In another embodiment, single cuttings are transferred by a vacuum nozzle which holds the cuttings by underpressure and releases them by interrupting the vacuum, e.g., to a conveyor belt. Such a system is preferably designed to be operated by robots.

[0027] The electrode pieces obtained by die cutting with a rotary cutting die or punching with a punch press are first sent to a first separation step, wherein any fine particles are separated from the cuttings. In case of dry operation, sieves or air classifiers or combinations of these are employed. In case of wet separation, wet sieves, inclined classifiers, wet cyclones (hydrocyclones), or combinations of these are used, and the liquid preferably is the same that is used in all other wet process steps including the coating step e), if applicable. These fine particles may contain fine metal particles from the current collector foils which should not get into the electrodes produced from the recycled electrode active material and contaminate them. Therefore, the fine fraction obtained in the first separation step is sent to a different recycling process, e.g., a pyro- or hydrometallurgical process as known in the art. It is thus desirable to minimize the generation of fines in the comminution step.

[0028] After comminuting the battery electrodes and removing any particles having a length in at least two dimensions of less than 100 pm from the comminuted electrodes, the comminuted electrodes are treated with a solvent able to dissolve a binder polymer present in the coating of the metal foil in order to delaminate the electrode active material from the metal foil and to produce a slurry comprising dispersed electrode active material and pieces of metal foil.

[0029] In an embodiment of the method, the coarse material obtained after the first separation step is transferred to a reactor, and the electrode pieces are treated with a solvent able to dissolve the binder polymer in the coating of the electrode pieces. In an embodiment of the method, the solvent comprises N-methyl-2- pyrrolidone (NMP). In another embodiment, the solvent comprises DMSO and / or water. Preferably, the solvent is the same solvent that is used in the electrode coating during the fabrication of the electrodes. In the case of dry- coated electrodes, a solvent is used that is able to dissolve the binder, and the solvent will be removed finally by solid-liquid separation and drying to obtain a dried electrode active material. In an embodiment of the method, the same solvent is used in all steps. The solvent is equivalent to the solvent that is used in the coating process of the electrode production.

[0030] The rotary die cutting machine or punch press produces flat sheets of foil that are difficult to handle with respect to sieving and conveying. The handling of such foil pieces can be improved by corrugating or crumpling the foil pieces. For instance, profiled rollers that gear into each other may be used to emboss the profile of the rollers onto the foil pieces, thereby facilitating sieving and conveying of the foil pieces. Another alternative is to use profiled rollers that emboss their profile pattern on the foil pieces. This can be done in a punch by exchanging the blades by a profiled pattern.

[0031] In an embodiment of the method, the comminuted electrodes are corrugated before treating the comminuted electrodes with a solvent in step c), preferably before the separation step b). In an embodiment of the method, the coarse material is first treated by profiled rollers that gear into each other before it enters the reactor, preferably before the separation step b). The profiled rollers emboss a profile on the electrode carrier foil sheets, which facilitates handling of the electrode pieces and prevents the adhesion of the sheets to each other or to walls of the reactor.

[0032] In another embodiment of the method, the pieces of metal foil obtained in step c) are corrugated before separating the pieces of metal foil from the slurry comprising dispersed electrode active material by wet sieving in step d). In a further embodiment, profiled rollers that gear into each other are used to corrugate the pieces of metal foil. The metal foil pieces suspended in the solvent are treated by profiled rollers before the suspension is transferred to the sieve.

[0033] After the solvent treatment, the mixture of detached coating and electrode carrier foil pieces suspended in the solvent are transferred to a sieve or wet cyclone (hydrocyclone), or a combination of both, to separate the electrode carrier foil pieces from the detached coating. The pieces of metal foil are separated from the slurry comprising dispersed electrode active material by wet sieving or classification by wet cyclones (hydrocyclones).

[0034] In one embodiment, a single sieve having a mesh width of 100 pm is used to separate the metal foils, allowing the separation of fine and coarse particles in one step. Since usually the size difference between the metal foils and the fine particles is very large, a separation by sieving in several consecutive steps may be advantageous. Thus, in another embodiment, the metal foils are separated with a coarse mesh, e.g., 1 mm, in a first sieving stage, then the slurry obtained is sieved using a 100 pm mesh to separate fine particles. In such a sequence of sieving stages, at least one stage may be performed by a wet cyclone (hydrocyclone) instead of a sieve.

[0035] In an embodiment of the method, wet sieving in step d) involves an inclined classifier. In a further embodiment of the method, a sieve screen used for wet sieving in step d) is sprayed with solvent to wash off particles of electrode active materials adhering to the pieces of metal foil. In a further embodiment of the method, the solvent is obtained from the slurry obtained in step d) by solid / liquid separation.

[0036] In an embodiment of the method, fine particles are removed from the slurry obtained after step d) by sieving on a sieve screen with a fine mesh (100 pm) or by classification in wet cyclones (hydrocyclones). After the separation of the carrier foil pieces, the slurry of detached coating obtained may be sieved on another sieve screen with even finer mesh (<100 pm, or < 50 pm, or even <20 pm) to remove fine particles.

[0037] The slurry comprising electrode active material obtained can be used for coating current collector foils, i.e., for the production of alkali ion battery cathodes or anodes. In one embodiment of the method, pristine electrode active material and / or binder polymer and / or conductivity-enhancing additives are added to the slurry obtained in step d) to adjust the composition of the slurry to match the specifications of a slurry usable for battery electrode coating. In an embodiment, the conductivity enhancing additives comprise carbon black.

[0038] In an embodiment, the method consists of steps a) to d) performed in sequence. In another embodiment, the method consists of steps a) to e) performed in sequence. Description of the drawings

[0039] Fig. 1 a shows an exemplary rotary die cutting machine comminuting an exemplary alkali metal ion battery electrode.

[0040] The rotary die cutting machine comprises a roller 11 a equipped with a plurality of blades (wedges) 12 and a counter roller 11 b. The blades 12 are arranged on the surface of the roller 11 a in radial and longitudinal direction, respectively, forming a rectangular grid (cutting die).

[0041] The coated electrode 20 which comprises a layer 22 of active electrode material coated on a metal foil 21 is fed to the space between the rollers 11 a and 11 b from the side or from above, and the blades 12 on the roller 11 a cut the electrode 20 into rectangular pieces. Die cutting as shown here as wedge cutting is a way of comminution where the blades penetrate into the material and divide it into pieces.

[0042] Fig. 1 b shows the same exemplary scheme of a rotary die cutting machine, except that a carrier foil 23 is introduced between the coated electrode 20 and the counter roller 11 b.

[0043] Fig. 2 schematically shows a punch press. A hydraulic prop 31 is moved up and down, pressing the tool 32 comprising the blades 12 into the coated electrode 20 which is positioned on a bench 33.

[0044] Examples

[0045] Example 1a (comparative)

[0046] 5040 g of a 15 pm aluminum foil were fed into a rotary cutting die equipped with a 13x13 mm punch pattern on the roller. The material was sieved using a sieve with 100 pm mesh width. No particles <100 pm were found. Example 1b (comparative)

[0047] 3950 g of the coarse material >100 pm from example 1 a were introduced into a rotor impact mill of the type Alpine LU100 equipped with a 100 mm plate beater and a 2 mm round hole sieve. The mill was operated at 10.000 rpm at a throughput of 0.75 kg / h. The material obtained contained 0.25 wt% of Alparticles <100 pm, 11.7% between 100 and 500 pm and 88% >500 pm measured by sieve analysis.

[0048] These examples demonstrate the advantage of a rotary cutting die vs. a rotor impact mill for the comminution of aluminum foils avoiding the formation of small Al particles <100 pm.

[0049] Example 2

[0050] An aluminum foil (thickness 16 pm) coated with LFP typically employed in commercial lithium-ion batteries was comminuted into squares of 13x13 mm by a rotary cutting die (Spilker GmbH, D-33818 Leopoldshohe) equipped with punching knifes. This material was sieved using a 100 pm mesh and contained no fine particles <100 pm. 7 g of the coarse material >100 pm were suspended in 28 g NMP and heated at 120°C. The hot slurry was stirred with a glass blade stirrer at 300 rpm. After cooling down to ambient temperature, the slurry was wet sieved using a 100 pm sieve and the material <100 pm was filtered, washed first with NMP and subsequently with deionized water, and then dried. No aluminum could be detected by XRF In the filter residue. The delamination efficiency was 96%.

[0051] Example 3 (comparative)

[0052] An aluminum foil (thickness 16 pm) coated with LFP typically employed in commercial lithium-ion-batteries was treated in a Pallmann PS 3 1 / 2 granulator equipped with a square hole bottom sieve mesh 15 mm at a peripheral speed of 12 m / s. Linder these conditions, 3 wt% of a sieve fraction <100 pm were obtained. 7 g of the coarse material >100 pm were suspended in 28 g NMP heated at 120°C. The hot slurry was stirred with a glass blade stirrer at 300 rpm. After cooling down to ambient temperature, the slurry was wet-sieved with a 100 pm sieve and the material <100 pm was filtered, washed first with NMP and then with deionized water, and dried. The filter residue contained 0.25 wt% Al, measured by XRF. The delamination efficiency was 91%.

[0053] These examples show that punching / die cutting has two advantages: 1 ) no or very low losses of coating during the dry comminution, and 2) no formation of fine aluminum particles upon delamination in the solvent.

[0054] List of reference signs

[0055] 11 a roller

[0056] 11 b counter roller

[0057] 12 blades

[0058] 20 coated electrode

[0059] 21 metal foil

[0060] 22 layer of active electrode material

[0061] 23 carrier foil

[0062] 31 hydraulic prop

[0063] 32 punching tool

[0064] 33 bench

Claims

Claims1. A method of recycling electrode active material from alkali metal ion battery electrodes which comprise an electrode active material coated on a metal foil, the method comprising a. comminuting the electrodes by die cutting using a rotary die cutting machine or a punch press, completely cutting the metal foil into pieces without leaving a residual web of punched foil, b. removing any particles having a length in at least two dimensions of less than 100 pm from the comminuted electrodes in a first separation step, c. subsequently treating the comminuted electrodes with a solvent able to dissolve a binder polymer present in the coating of the metal foil to delaminate the electrode active material from the metal foil, and to produce a slurry comprising dispersed electrode active material and pieces of metal foil, d. separating the pieces of metal foil from the slurry comprising dispersed electrode active material in a second separation step, e. optionally, providing a current collector metal foil and coating it with the slurry comprising dispersed electrode active material obtained from step d.

2. The method of claim 1 , wherein the first separation step involves dry sieving, air classification, dry or wet cyclonic separation, wet sieving, or combinations thereof.

3. The method of claim 1 or 2, wherein the second separation step involves wet sieving or wet cyclonic separation, or combinations thereof.

4. The method of any one of claims 1 to 3, wherein the comminuted electrodes are corrugated before treating the comminuted electrodes with a solvent in step c.

5. The method of any one of claims 1 to 3, wherein the pieces of metal foil obtained in step c are corrugated before separating the pieces of metal foil from the slurry comprising dispersed electrode active material in step d.

6. The method of claim 4 or 5, wherein profiled rollers that gear into each other are used to corrugate the comminuted electrodes or the pieces of metal foil, respectively.

7. The method of any one of claims 1 to 6, wherein alkali ion battery electrode coils are uncoiled and fed to a rotary die cutting machine or a punch press.

8. The method of claim 7, wherein alkali ion battery electrodes are flattened by rollers prior to feeding them to the rotary die cutting machine or punch press.

9. The method of any one of claims 1 to 8, wherein cuttings of alkali ion battery electrodes are conveyed to a rotary die cutter or punch press on a perforated conveyor belt where the cuttings are held by application of underpressure.

10. The method of any one of claims 1 to 9, wherein particles having a length in at least two dimensions of less than 100 pm are removed from the slurry obtained after step d) by sieving on a sieve screen with a fine mesh.11 . The method of any one of claims 1 to 9, wherein particles having a length in at least two dimensions of less than 100 pm are removed from the slurry obtained after step d) by employing wet cyclones (hydrocyclones).

12. The method of any one of claims 1 to 11 , wherein pristine electrode active material and / or binder polymer and / or conductivity enhancing additives areadded to the slurry obtained in step d) to adjust the composition of the slurry to match the specifications of a slurry for an alkali ion battery electrode coating.

13. The method of any one of claims 1 to 12, wherein the solvent comprisesN-methyl-2-pyrrolidone (NMP).

14. The method of any one of claims 1 to 12, wherein the solvent comprises DMSO and / or water15. The method of any one of claims 1 to 14, wherein the binder polymer comprises polyvinylidene fluoride (PVDF).

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