Thermo-mechanical separation process for a multilayer film

Abstract

Recycling process for a coated film, wherein the film is a so-called current collector film of a lithium-ion cell film, wherein the coated film has a metallic carrier film on which a coating is applied by means of a thermoplastic binder, comprising the steps: - Heating the coated film to a binder softening temperature, - applying a mechanical separation stress to the coated film in such a way that the coating and the metallic carrier film separate at least partially under the influence of this stress, - Separating the metallic carrier foil and the coating into at least two different material batches, one of these batches comprising at least substantially the metallic carrier foil and the other batch comprising at least substantially the coating.

Description

The invention relates to a thermo-mechanical separation method for a multilayer film. DE 10 2016 015 199 A1 discloses a solvent and a method for dissolving at least two plastics from a solid within a suspension.The recycling, i.e. the recovery or recovery of raw materials from the production process of lithium ion cells or from these cells in the automobile industry, is explained below; this is not to be understood as a limitation of the invention to such an application. Coated foil materials are used for the production of lithium ion cells. For the recycling of such lithium ion cells, in particular of production rejects during their production, the separation of substances of the coated film material plays an important role. Such a film material can be used in various embodiments as an electrode material or also as a so-called current collector film. The so-called active material of the lithium-ion cell, which is used on the so-called cathode of such cells, is of value in the case of lithium-ion cells and relates to a not inconsiderable proportion of the cells, based on the production costs.Efficient recovery of the active cathode material thus not only enables more cost-effective production, but also more durable production of lithium ion cells compared to the production of such cells from raw materials, which are obtained directly from soil estimates.For the production of cathodes for lithium ion cells, it is known from the prior art to disperse active materials, additives and also PVDF binders (polyvinylidene fluoride binder) in solvents and then apply them to a metallic carrier film. After the layer applied to the metallic carrier film has been dried, the binder is cured / dried and ensures the adhesion of the active material to this metallic carrier film. In the production of an electrode for a lithium ion cell, the coated metallic carrier film produced beforehand, in particular its coating, is calendared (in particular setting the desired layer thicknesses, porosity or homogeneity) and finished within the scope of cell assembly for use in electrified motor vehicles.Lithium ion cells produced in this way, which reach the end of their lifetime (end-of-life), can be recycled, in particular in order to recover raw materials therefrom for the production of new lithium ion cells. Furthermore, electrode waste or sections, such as can be obtained during the production of such lithium ion cells, can also be recycled. In both cases, raw materials for lithium ion cell production are then available which were not obtained directly from soil estimates. Processes known from the prior art for this recycling are complex and complicated with regard to energy and costs.In particular with regard to production rejects which originate from the production of the lithium ion cells, the advantage results that these rejects have generally not yet been electrochemically changed.In the recycling of production rejects, in particular thus of foil sections which are produced in the production of lithium ion cells as a result of the system, the separation of active electrode material and the metallic carrier foil on which it is applied plays an important role. It is generally known that recycling of such production rejects is purely mechanical, for example by shredding, grinding and sieving. Additionally or alternatively, solvent-based methods are used. However, the use of solvents is not only expensive to mechanical separation processes, but also requires environmental protection measures.It is also known to use a so-called thermal method for the separation described above, which is aimed at the decomposition of the PVDF binder at high temperatures. In such a thermal method, gaseous hydrogen fluoride (HF) may be formed, which reacts with the lithium from the active electrode material, in particular thus with material from the coating of the metallic carrier film, to form inactive lithium fluoride and thus reduces the capacity of the recovered active material.Against the aforementioned background, it is an object of the invention to specify a method for separating coating and metallic carrier film, in particular with respect to production rejects from the production of lithium ion cells, which method is improved compared to the known prior art. This object is achieved by a method according to claim 1, preferred developments of the invention are the subject matter of the dependent claims.For the purposes of the invention, a recycling method for a coated film is understood to mean a method for separating coated film, as is used in the production of a lithium ion cell, into the main constituents thereof. Furthermore, for the purposes of the invention, such a coated foil is understood to mean a coated current collector foil which is used for producing a lithium ion cell or the like. This coated film has as main components a metallic carrier film and a coating applied to this metallic carrier film. In the context of the invention, the coating is understood to mean, in particular, a chemical substance which is required for energy storage in the lithium-ion cell; furthermore, this coating can be referred to and understood as the active material of the lithium-ion cell.The current collector foil in a lithium ion cell serves for carrying the coating, i.e. the active material, and for supplying or discharging electrical current to this coating by means of the metallic carrier foil. The coating is applied to this metallic carrier film by means of a thermoplastic binder, preferably by means of a so-called PVDF binder (polyvinylidene fluoride binder). The coating can preferably be applied to the metallic carrier film over the entire surface or only in sections. More preferably, the recycling method relates to production waste which arises during the production of a lithium-ion cell.The proposed recycling method can be understood as a combination of at least one thermal and at least one mechanical method step and thus represents a combined recycling method. The proposed recycling method aims to separate the coated film into its main components, one of these main components being the metallic carrier film and the other main component being the coating applied thereon, subsequent to this separation, these main components can be recycled to the production of a coated film for a lithium ion cell or another production method. To achieve the separation of the main constituents, the proposed recycling method has at least the method steps:heating the coated film to a binder softening temperature,applying a mechanical separating stress to the coated film, the coating and the metallic carrier film separating at least partially or preferably completely under the action of this stress, andseparating the metallic carrier film and the coating into at least two different material batches, one of these batches at least substantially comprising the metallic carrier film and the other batch at least substantially comprising the coating.Preferably, individual ones of the proposed method steps can run at least overlapping in time or completely parallel and thus simultaneously.Furthermore, heating of the coated film is understood to mean that heat is supplied to this coated film, so that the latter is heated to a predetermined temperature, this predetermined temperature depending on the thermoplastic binder, by means of which the coating is bonded to the metallic carrier film or is applied to it.For the purposes of the invention, the binder softening temperature is understood to mean a material-specific temperature of the PVDF binder used. The binder softening temperature is preferably to be understood as, at least substantially, the so-called Vicat softening temperature of the material used as PVDF binder, wherein this Vicat softening temperature is to be understood as a heat distortion temperature method according to Vicat and enables quantitative characterization of the heat distortion temperature of a plastic and thus represents a material property of the thermoplastic binder used.Preferably, the binder softening temperature is at most 10° C. less than the Vicat softening temperature of the thermoplastic binder used and more preferably at most 30° C. more than this. More preferably, the binder softening temperature is selected from a temperature range which is at least 125° C. or greater, preferably 140° C. or greater or 150° C. or greater, and more preferably this temperature range is less than 200° C., preferably less than 180° C. and more preferably less than 160° C. More preferably, the binder softening temperature is less than the decomposition temperature of the thermoplastic binder used and more preferably less than the melting temperature of the thermoplastic binder used. In particular, by selecting the binder softening temperature from the proposed temperature range, it is possible on the one hand to achieve a reliable separation of the metallic carrier film from its coating with low energy consumption and, further preferably, this separation is made possible substantially without release of pollutants during the separation of the metallic carrier film and its coating.In a preferred embodiment of the proposed recycling method, heating the coated film to the binder softening temperature takes place before applying the mechanical separating stress. Preferably, heating of the coated film is done completely prior to applying the mechanical release stress. In particular, by applying the heat to the coated film separately in time and applying the mechanical separating stress to the latter, precise temperature control for the recycling process is made possible. More preferably, heating of the coated film begins prior to application of the mechanical release stress thereto and is continued during such application. In particular, by means of such a configuration of the method, good efficiency can be achieved on account of the at least partial parallelization of heating and mechanical separating stress.In a preferred embodiment of the suggested recycling method, the coated film is transported into a softening furnace for applying the binder softening temperature and heated there. Further preferably, the coated film, after reaching the binder softening temperature, is introduced into a separating device for applying the mechanical separating stress. Further preferably, the separating device is designed as an impact mill or as a shredder or the like and further preferably the coated film is transported into this separating device in the heated state, preferably in the state heated to binder softening temperature.In a further preferred embodiment, during the application of the mechanical separating stress, heat is further supplied to the coated film, in particular in order to keep it at the binder softening temperature or to heat it to the latter. Further preferably, a combined device for heating the coated film and for applying the mechanical separating stress is proposed; in simplified terms, such a combined device can be understood as a heated separating device, preferably as a heated impact mill or a heated shredder or the like. Further preferably, in this combined device, the heating of the coated film takes place simultaneously or preferably at least in a temporally overlapping manner with the application of the mechanical separating stress. In particular by means of a combined device, an efficient, in particular a time-efficient, recycling method is accordingly made possible.Individual features of the invention are explained in more detail below with reference to the at least partially schematic figures, in which: FIG. 1 : schematically, the recycling of coated film using the proposed method, FIG. 2 : Flow chart for the proposed method.FIG. 1 shows a schematic recycling method for a coated film 1. This coated foil 1 is designed as a so-called current collector foil of a lithium ion cell foil and has a metallic carrier foil 2 and a coating 3 with active material of a lithium ion cell. The coating 3 is applied to this metallic carrier film 2 by means of a thermoplastic binder. By means of the thermoplastic binder, the coating 3 and the metallic carrier film 2 are bonded to one another in a materially integral manner.In order to heat the coated film 1 to a binder softening temperature, the latter is transported by a raw material conveying device 4 into a rotary kiln which is designed as a softening kiln 4. By applying heat in this rotary kiln, the coated film 1 is heated to the binder softening temperature. With a further conveying device 6, the coated film heated to binder softening temperature is transported into the separating device 7 designed as a cutter mill. In the separating device 7, a mechanical separating stress is applied to the coated foil in such a way that the coating and the metallic carrier foil are separated from one another under the action of this stress.In the sorting device 8, the metallic carrier film freed of the coating and the coating detached therefrom are separated into two different material batches. The metallic carrier film freed of the coating is transported away from the sorting device 8 by the carrier film conveying device 9 and fed to the material batch 11 which comprises the metallic carrier film. Furthermore, the coating detached from the metallic carrier foil is transported away from the sorting device 8 by the coating conveying device 10 and fed to the material batch 12 which comprises the coating.FIG. 2 shows a schematic process sequence for the proposed recycling method. In the proposed method, the following is used:heating the coated film to a binder softening temperature in a first step 101,a second step 102 involves applying a mechanical separating stress to the heated coated film in such a way that the coating and the metallic carrier film at least partially separate under the action of this stress, andin a third step 103, metallic carrier film which is at least substantially freed of the coating thereof and the coating which is detached from the carrier film is separated into at least two different, preferably single-grade, material batches, wherein one of these batches at least substantially comprises the metallic carrier film and the other batch at least substantially comprises the coating detached from the carrier film.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2016 015 199 A1

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Claims

Recycling method for a coated film, wherein the film is a so-called current collector film of a lithium ion cell film, wherein the coated film (1) has a metallic carrier film (2) on which a coating (3) is applied by means of a thermoplastic binder, having the steps: - (101) heating the coated film to a binder softening temperature, - (102) applying a mechanical separating stress to the coated film (1), wherein the coating (2) and the metallic carrier film (3) at least partially separate under the action of this stress, - separating the metallic carrier film (2) and the coating (3) into at least two different material batches, wherein one of these batches (11) at least substantially comprises the metallic carrier film and the other batch (12) at least substantially comprises the coating.Recycling method according to claim 1, characterized in that the binder softening temperature is greater than 125°C and less than 200°C.Recycling method according to one of the preceding claims, characterized in that the heating of the coated film (1) to the binder softening temperature takes place before the application of the mechanical separating stress.Recycling method according to Claim 3, characterized in that the coated film (1) is transported into a softening furnace (5) for application of the binder softening temperature and is heated there.Recycling method according to one of Claims 1 to 2, characterized in that the heating of the coated film (1) takes place simultaneously or at least in a temporally overlapping manner with the application of the mechanical separating stress.

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