Method for the direct recycling of cathode and anode materials from scrap from the production of lithium-ion batteries

Abstract

A process for the direct recycling of cathode and anode materials from electrode scrap, generated as production waste from lithium-ion battery manufacturing, is to be provided that enables the recycling of electrode scrap from LIB production through mechanical stress without negatively altering the active materials, so that it can be reintroduced into production. This is achieved by pre-shredding the electrode scrap into bulk material prior to the mechanical stress and by performing the mechanical stress under cryogenic conditions, where the temperature leads to partial embrittlement or embrittlement of the binder.

Description

[0001] The invention relates to a process for the direct recycling of cathode and anode materials from scrap generated during the production of lithium-ion batteries.

[0002] The basic components of a lithium-ion battery are anode, cathode, electrolyte, and a separator.

[0003] During the production of lithium-ion batteries, the so-called current collector foils, i.e., metal foils, are coated with active electrode materials. The cathode consists of an aluminum foil coated with active materials, e.g., a mixture of lithium nickel manganese cobalt mixed oxide (NMC), lithium iron phosphate (LFP), or other active cathode materials, as well as binders, conductive materials, and other additives. The anode consists of a copper foil coated with a mixture of graphite, sometimes silicon, binders, conductive materials, and other additives.

[0004] Following the coating and subsequent calendering of the electrodes, large quantities of scrap from coated electrodes are generated due to edge trimming, sorting out of areas with coating defects, rejects from start-up and shut-down processes, etc.

[0005] Until now, this electrode scrap has been sent to the recycling of used batteries. There, it cannot be treated separately, so the active materials are subsequently found as a mixture, known as black mass. The coating materials cannot be directly reused in the production process; they are processed metallurgically.

[0006] Since the scrap from production is still sorted and generally not contaminated, it is advisable to divert it during the production process, process it and return the processed active materials to production.

[0007] The first methods for mechanical processing in the production process are known.

[0008] EP 2 975 686 B1 already discloses a process for recycling cathode material from the production of lithium-ion batteries. This process yields recycled cathode material from which recycled cathodes for lithium-ion batteries can be produced without further chemical or physical purification steps. It has been determined that the binder does not need to be removed from the recycled cathode material to maintain the conductivity properties of the recycled cathode material at a high level. During the treatment, pre-crushed cathode starting material is treated in an impact mill, followed by filtering for dust removal and screening. The aluminum foil can be recycled in a single step with a yield of 99%. A hammer mill is used as the impact mill.By using a hammer mill, both types of particles are obtained with a sufficiently large difference in particle size due to their properties, so that they can be easily separated by sieving.

[0009] The recycling of electrode scrap is also known from EP 3940872B1. Here, too, recycling occurs within the production process. The waste generated during the stamping of the positive or negative electrode plate is recycled. The process comprises (a) dry grinding of the electrode scrap, including the active material layer, (b) sequentially screening the material from the mill with multiple screens to remove the active material from the fragments, and separating the smallest and larger active material flakes to obtain the reusable product. The mill can be a pin mill, a disc mill, a cutting mill, or a hammer mill. The active material can be returned directly to the production process without further processing.

[0010] KR1020140085768A discloses a process for producing active material for cathodes of lithium batteries from lithium battery scrap.

[0011] First, the cathode scrap of the lithium batteries is pulverized and sorted to separate the active material, which is then adjusted by adding fresh material, mixed in a ball mill, jet mill or SAG mill and crushed to the desired particle size.

[0012] The invention is based on the object of providing an alternative to the state of the art.

[0013] The aim is to provide a process that enables the recycling of electrode scrap from lithium-ion battery production without adversely altering the active materials, so that they can be directly recycled into production. Furthermore, the object of the invention is to provide a process that is optimized for mechanically stressing electrode scrap and separating the electrode foils from the electrode coating materials.

[0014] The goal is to ensure that the electrode coating materials are not contaminated with moisture or metal impurities. Furthermore, a process is to be provided that can be used for the recycling of both anodes and cathodes.

[0015] In a method of the type described above, the object is achieved according to the invention by the characterising part of the main claim.

[0016] In the process according to the invention, the electrode coating material is mechanically separated from the current collector foils and metal foils and then returned to the lithium-ion battery production process in a pure state. The mechanical stressing of the electrode scrap fragments is achieved by cryogenic impact stressing, for example, in an impact mill, which utilizes the effect of binder embrittlement.

[0017] The binders contained in the coating material mixtures not only ensure the cohesion of the active material particles, but also promote the adhesion of the cathode and anode coatings to the respective metal foils. When processing the coated metal foils, it is important to break this adhesion as much as possible and thus separate the coatings from the metal foils. In a further step, the coating materials can then be separated from the stripped metal foils.

[0018] To ensure this, it is proposed that the coated electrode foils, which are wound up as coils or as more or less deformed fragments, are first fed to a pre-shredding process, preferably a cutting mill, but alternatively also to a shredder, in order to convert them into a bulk material, whereby the coils are first unwound if they are too large for the described pre-shredding process.

[0019] If coating material has already detached during the pre-shredding process, it can then be separated, e.g., by screening or stream classification (sifting). If the amount of detached coating material is too small, this step can be omitted.

[0020] The crushed, still largely coated, electrode foil fragments are then subjected to further mechanical stress, e.g., in an impact mill or other mill, a mixer, etc. This mechanical stress deforms the ductile electrode foil fragments and removes the brittle coatings from the metal foils.

[0021] To improve the separation of the coating materials, it is recommended to ensure very low temperatures during mechanical stress to embrittle the binders. This significantly reduces the adhesion between the coatings and the metal foils, allowing significantly more coating material to be separated. The yield of separated coating material can be increased.

[0022] The processing temperature should be below the glass transition temperature of the binder. For a PVDF binder, the glass transition temperature is between -38 and -40°C, depending on the type.

[0023] On the other hand, the low temperatures can reduce the stress energy required for separation, which leads to less contamination with metal particles, as these are subjected to less stress. This can be achieved, for example, with a cryogenically operated impact mill, in which the pre-crushed, still largely coated electrode foil fragments are cooled to very low temperatures in a suitable cooler, e.g., a vortex screw cooler, using a suitable coolant, e.g., liquid nitrogen, before being fed to the impact mill, e.g., a universal mill of the UPZ type from Hosokawa Alpine AG equipped with a plate beater and a grinding track or discharge screen. The mechanical stress takes place at a temperature below minus 40°C, preferably below minus 60°C, and particularly preferably below minus 80°C.

[0024] The speed of the mill can be adjusted according to requirements in order to achieve the best possible separation of the coating materials from the metal foils while simultaneously minimizing contamination with metal particles.

[0025] The metal foils are then separated from the coating material again using a sieve or stream classification. The separated coating material can then be further processed, e.g., ground and further classified, to ensure the properties required for reuse. Contaminants containing metal particles can be removed using suitable separation processes.

[0026] Ideally, the parameters of cryogenic grinding and subsequent classification can be adjusted so that the separated active material corresponds to the grain size and the mixing ratio of active material, binder and additives of the primary materials of the production process in order to replace partial quantities.

[0027] Furthermore, operation with liquid nitrogen also ensures an inert atmosphere and minimal moisture in the product. This serves to protect against explosions and product contamination by, among other things, atmospheric oxygen, carbon dioxide, and humidity.

[0028] If the stress in the impact mill is not cryogenic, significantly less coating material is separated or significantly higher stress energies are required for separation.

[0029] The present invention has recognized that the mechanical stress on the electrode scrap fragments can be optimized to prevent unnecessary shredding of the foils and to improve separation of the coating and reduce the stress energy.

[0030] In one embodiment of the invention, the pre-crushing in the cutting mill can already be carried out with coolant in order to optimize the crushing.

[0031] Liquefied low-boiling gases, preferably liquid nitrogen, can be used as coolant.

[0032] To further develop the invention, the separated coating material can be separated from the electrode scrap shredded in the pre-shredding by classification and the remaining material flow of partially decoated shredded electrode foils can be subjected to cryogenic stress.

[0033] The inert atmosphere is set from the pre-shredding through the cryogenic stress and the separation into stripped electrode foils and separated coating material.

[0034] In a further embodiment, a screening or a flow classification in the form of an air classifier can be used for classification.

[0035] Alternatively, the coating material can also be separated from the gas stream using a cyclone.

[0036] The invention is not limited to the number of treatment steps described. It also does not require linear flow of the product streams; recirculation and other similar features can also be provided.

[0037] Further details, features, and advantages of the method according to the invention emerge from the dependent claims and from the following description of the accompanying figures, in which a preferred embodiment of the invention is shown by way of example. The figure shows: Fig. 1 a diagram of the method according to the invention with its steps

[0038] In Fig. 1 shows the process with its mandatory and optional steps in a flow chart.

[0039] The electrode scrap on coils is first unwound so that it, together with other electrode scrap, is fed into a pre-shredding plant as fragments. The pre-shredding plant is designed as a cutting mill. The pre-shredded electrode scrap is subjected to cryogenic treatment. A vortex screw cooler pressurized with liquid nitrogen is used for cooling upstream of the impact mill (not shown here). The pre-cooled material is fed to an impact mill, in this case a universal mill of the UPZ type from Hosokawa Alpine AG, where it is subjected to stress. The UPZ is equipped with a plate beater and optionally a grinding track or discharge screen. In the subsequent process step, the material is separated into de-coated, shredded electrode foils and separated coating material by classification. A screen with a suitable mesh size or an air classifier is used here.The coating material separated as fines is then fed back into further processing or directly into the electrode production process.

[0040] Optionally, the pre-shredding can be carried out as cryogenic shredding by exposure to liquid nitrogen

[0041] If the coating material detaches easily from the electrode foils, the separated coating material can optionally be separated by classifying after the pre-shredding process. The remaining partially decoated electrode foils are then subjected to cryogenic treatment in the impact mill.

Claims

[1] Process for the direct recycling of cathode and anode materials from electrode scrap, arising as production waste from the production of lithium-ion batteries, comprising the steps: - Providing electrode scrap comprising electrode foil, electrode coating material and binder, - mechanical stress on the electrode scrap, - Separation of the stressed material from the mechanical stress by classification into: - shredded stripped electrode foils and - separated electrode coating material, characterized by , that - the mechanical stressing is preceded by a pre-crushing of the electrode scrap into bulk material and that - the mechanical stress is applied under cryogenic conditions, - where the temperature leads to partial embrittlement or embrittlement of the binder. [2] Method according to claim 1, characterized bythat the mechanical stress occurs at a temperature below minus 40°C, preferably below minus 60°C and particularly preferably below minus 80°C, [3] Method according to claim 1, characterized by that the pre-shredding takes place in a cutting mill. [4] Method according to claims 1 to 3, characterized by that the pre-shredded material is cooled in a cooling device and mechanically stressed under cryogenic conditions in a mill or mixer. [5] Method according to claim 4, characterized by that the mill is an impact mill. [6] Method according to one of the preceding claims, characterized by that the pre-crushing takes place under cryogenic conditions. [7] Method according to one of the preceding claims, characterized by that after pre-crushing, the electrode coating material is separated by classification. [8] Method according to one of the preceding claims, characterized bythat the classification is a screening or a stream classification. [9] Method according to one of the preceding claims, characterized by that liquefied low-boiling gases, preferably liquid nitrogen, are used as coolants. [10] Method according to one of the preceding claims, characterized by that the electrode scrap comes from cathode or anode production. [11] Method according to one of the preceding claims, characterized by that the process is carried out in an inert atmosphere which serves to protect against explosions and the product.

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