METHOD AND DEVICE FOR PRODUCING A POLYMER FILM

Description

State of the art

[0001] Modern electrochemical cells, especially those used in lithium-ion batteries, increasingly employ solid electrolytes instead of liquid electrolytes. Solid electrolyte-containing layers can be produced using extrusion processes. For use in electrochemical cells, the solid electrolyte typically requires the addition of larger quantities of other solids, which later perform specific functions within the cell. Active materials, for example, enable the production of electrode foils in which the spaces between the active material particles are filled with the solid electrolyte.

[0002] US2004 / 0029008 A1 discloses a process for the solvent-free production of a laminate consisting of a cathode-active material layer, a polymer gel electrolyte layer, and an anode-active material layer in a co-extrusion process. The resulting laminate is directly laminated onto a current collector film.

[0003] WO 00 / 51806 describes a process for the production of multilayer composite structures by co-extrusion of at least two plastically deformable material compositions through a slot die.

[0004] DE 10118639 A1 discloses a process for the production of trilaminates for polymer lithium batteries by co-extrusion. The process is carried out at temperatures of 130°C to 200°C.

[0005] US 2017 / 028607 describes a device for automatically regulating the pressure of an extruder unit. The pressure is regulated by means of a valve in the flow channel between the extruder and the connected nozzle. JP2012183691 A also discloses these features.

[0006] US 2016 / 023232 discloses a liquid dispensing device comprising a dispensing unit and a pressurization unit. A valve unit is arranged between the dispensing unit and the pressurization unit, enabling the pressurization unit to be closed and the dispensing unit to be connected to a vacuum section. The device reduces the formation of droplets at the dispensing unit when no dispensing is desired. Disclosure of the invention

[0007] A first object of the invention is a device for producing a film from a polymer composition, comprising: (1) at least one extruder unit comprising at least one extruder inlet, at least one extruder screw located in an extruder flow channel, and at least one extruder outlet; (2) at least one discharge unit comprising at least one discharge unit inlet, at least one discharge unit outlet, and at least one shaping die, preferably a slot die, which is arranged in fluid connection with the at least one discharge unit outlet; and (3) at least one distribution unit comprising: (i) at least one distribution unit inlet, which is arranged in fluid connection with the at least one extruder outlet; (ii) at least one first distribution unit outlet, which is arranged in fluid connection with the at least one discharge unit inlet; (iii) at least one second distribution unit outlet, which is arranged in fluid connection with at least one discharge outlet; (iv) at least one distribution unit flow channel.which connects the at least one distribution unit inlet, the at least first distribution unit outlet and the at least second distribution unit outlet, and (v) at least one distribution valve which makes it possible to distribute an extruder discharge, which enters the distribution unit via the at least one distribution unit inlet, to the at least first distribution unit outlet and the at least second distribution unit outlet.

[0008] The production of films by extruding a polymer melt in a conventional extruder is frequently associated with problems, particularly during the start-up process, such as a temporarily high pressure build-up, which can even lead to the shutdown of the entire device due to excessive die pressure and / or excessive screw torque. The inventors of the present application have found that this problem can be effectively prevented with the device proposed herein.

[0009] The device comprises at least one extruder unit, including at least one extruder inlet, at least one extruder screw located in an extruder flow channel, and at least one extruder outlet. The at least one extruder inlet serves to feed the material to be extruded, i.e., the polymer composition, into the extruder unit. Within the extruder unit, at least one extruder screw is located within an extruder flow channel. Often, at least two extruder screws are used, for example, in the form of a twin-screw extruder. These at least two extruder screws can rotate in the same direction or in opposite directions. To achieve the highest possible homogeneity in the extruded material, a counter-rotating twin-screw extruder is frequently used.

[0010] The extruder unit's function is to convert the polymer composition, or its components, into a homogeneous polymer melt and to generate the pressure required for extrusion. The energy needed for melting can often be sufficiently supplied by the energy input from the extruder screws. It is also possible for the extruder unit to be temperature-controlled, i.e., equipped with a temperature control device.

[0011] This makes it possible to supply heat to the extruder unit if the mechanically introduced energy is insufficient to obtain a homogeneous polymer melt. Alternatively, heat can be extracted from the extruder unit via the temperature control device if the temperature inside the extruder unit rises too high and excessive thermal stress on the polymer composition is to be avoided. Preferably, the temperature of the polymer melt in the extruder flow channel is maintained above the melting temperature of the polymer composition and at a value ≤ 160°C.

[0012] The extruder unit is connected to the distribution unit via at least one extruder outlet in fluid communication. The extruder unit is thus connected to the distribution unit. "In fluid communication" within the meaning of this application means that a connection in the form of a cavity, continuously permeable to fluids such as gases, liquids, or melts, exists, which connects the fluid-connected areas.

[0013] The distribution unit comprises at least one distribution unit inlet, at least one distribution unit flow channel, at least one first and at least one second distribution unit outlet, and at least one distribution valve.

[0014] The at least one distribution unit flow channel connects the at least one distribution unit inlet, the at least first distribution unit outlet, and the at least second distribution unit outlet. It is designed to ensure an uninterrupted flow of the extruder discharge. The distribution unit flow channel thus consists of at least one main channel, which connects the at least one distribution unit inlet and the at least first distribution unit outlet via fluid flow, and one secondary channel, which connects the at least one distribution unit inlet and the at least second distribution unit outlet via fluid flow.

[0015] Within the distribution unit flow channel, at least one distribution valve is arranged. A distribution valve within the meaning of this invention is any device that can regulate the distribution of the polymer melt to the main channel and the secondary channel of the distribution unit flow channel, preferably continuously. The distribution valve is designed to allow the extruder discharge, which enters the distribution unit via the at least one distribution unit inlet, to be distributed to the at least first and at least second distribution unit outlets. The distribution valve can, for example, be a three-way valve. In one embodiment of the invention, the distribution valve is able to direct the extruder discharge completely to either the at least first or the at least second distribution unit outlet.In an alternative embodiment, the distribution valve is able to direct part of the extruder discharge to the at least first distribution unit outlet and the remaining part to the at least second distribution unit outlet.

[0016] The distribution valve can be actuated electrically, hydraulically, or mechanically. Such distribution valves are known to those skilled in the art. Preferably, the distribution valve is actuated electrically or hydraulically.

[0017] The distribution unit comprises at least one first distribution unit outlet, which is connected in fluid communication to at least one delivery unit inlet of the delivery unit. The delivery unit is described in more detail below.

[0018] The distribution unit comprises at least one second distribution unit outlet, which is arranged in fluid connection with at least one drain outlet. The drain outlet can in turn be connected to the extruder inlet in order to return the polymer composition leaving the device via the drain outlet to the process.

[0019] The distribution unit preferably also includes a temperature control device which maintains the temperature within the distribution unit above the melting temperature of the polymer composition and at a value ≤ 160°C.

[0020] The dispensing unit of the device according to the invention comprises at least one dispensing unit inlet, at least one dispensing unit outlet, and at least one forming nozzle. The dispensing unit inlet is connected to the first distribution unit outlet via a fluid flow channel and is thus supplied with the homogeneous polymer melt from the extruder unit during the process. The dispensing unit inlet is also connected to the dispensing unit outlet via a fluid flow channel within the dispensing unit. This outlet is in turn connected to at least one forming nozzle, in particular a slot die, preferably a wide-slot die. This makes it possible to pre-form the polymer melt into polymer layers.

[0021] The dispensing unit preferably also includes a temperature control device which maintains the temperature within the dispensing unit above the melting temperature of the polymer composition and at a value ≤ 160°C.

[0022] In a preferred embodiment of the invention, at least one additional roller is arranged downstream of the dispensing unit. This roller enables the pre-formed polymer melt to be further shaped after dispensing from the dispensing device, thus producing a polymer film of the desired thickness. Preferably, the at least one roller, like the extruder unit, is temperature-controlled. In a particularly preferred embodiment, the device comprises a plurality of downstream rollers, for example, in the form of a calender.

[0023] Another object of the invention is a method for producing a film from a polymer composition, wherein the method comprises the following process steps: (a) Providing a polymer melt from at least one polymer composition; (b) Extruding the polymer melt in at least one extruder unit, which is arranged via at least one extruder outlet in fluid communication with at least one distribution unit, which comprises at least the following elements: (i) at least one distribution unit inlet, which is arranged in fluid communication with the at least one extruder outlet, (ii) at least one first distribution unit outlet, which is arranged in fluid communication with the at least one discharge unit inlet, (iii) at least one second distribution unit outlet, which is arranged in fluid communication with at least one discharge outlet, (iv) at least one distribution unit flow channel, which connects the at least one distribution unit inlet, the at least first distribution unit outlet and the at least second distribution unit outlet to each other,and (v) at least one distribution valve which makes it possible to distribute an extruder discharge, which enters the distribution unit via the at least one distribution unit inlet, to the at least first distribution unit outlet and the at least second distribution unit outlet; (c) introducing the polymer melt via the at least first distribution unit outlet into a dispensing unit comprising at least one dispensing unit inlet, at least one dispensing unit outlet, and at least one forming nozzle which is arranged in fluid communication with the at least one dispensing unit outlet, such that the polymer melt leaves the dispensing unit through the at least one forming nozzle in order to obtain a preformed polymer melt; and (d) optionally further forming of the preformed polymer melt, in particular rolling of the preformed polymer melt, in order to obtain a film of desired thickness, . characterized in that at the beginning of the process the extruder discharge is wholly or partially discharged via the at least one second distribution unit outlet to the at least one discharge outlet until the extruder discharge has achieved sufficiently homogeneous properties, in particular a sufficiently homogeneous composition and a sufficiently homogeneous viscosity.

[0024] Preferably, the device described above is used to carry out the method.

[0025] First, a polymer melt is prepared from a polymer composition. The polymer composition comprises at least one thermoplastic organic polymer. In a preferred embodiment, the polymer composition comprises at least one thermoplastic organic polymer and at least one particulate and / or fibrous material. In this context, particulate and / or fibrous material is understood to be a material that exists as a solid in the polymer melt, i.e., one that itself has a higher melting point. A polymer melt according to the invention thus also comprises molten polymer compositions that include molten polymer components and solid components, particularly in the form of particles. Particulate materials typically have a mean particle diameter of 1 to 1000 µm, particularly 20 to 500 µm.The particle diameter can vary greatly depending on the type of particulate material. Fibrous materials typically have a fiber diameter of 1 to 1000 µm, especially 20 to 500 µm, and a fiber length of 0.1 to 10 mm.

[0026] Polymer melts containing particulate material can lead to increased pressures during the extrusion process. Therefore, the present method is particularly advantageous for polymer compositions containing particulate and / or fibrous materials.

[0027] In one embodiment of the invention, the polymer composition comprises at least one polymeric solid electrolyte and at least one particulate material from the group consisting of at least one electrode active material, at least one conducting additive, at least one inorganic solid electrolyte and mixtures of the aforementioned.

[0028] Suitable polymeric solid electrolytes include, for example, polyethylene oxide, polypentyl malonates, polypentyl oxalates, poly(1,3-nonyldiketones), polybutanoic anhydrides, polypentenoic anhydrides, polycyanoethyl acrylates, and / or polycyanoalkyl acrylates as polymer components. Typically, the polymeric solid electrolyte also includes at least one lithium salt to improve ionic conductivity, for example, lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0029] In addition to lithium salt, various materials can be used as particulate materials, depending on the intended use of the film to be produced.

[0030] The previously described polymer composition consisting of a solid polymer electrolyte including lithium salt can be used, for example, for the production of separator films. In addition, other particulate materials such as sulfide glasses, perovskite compounds of the formula Li 3x La 2 / 3-x TiO 3 (with 2 / 3 ≥ x ≥ 0, LLTO), garnet compounds such as Li 7 La 3 Zr 2 O 12 (LLZO), glass ceramics of the NASICON type, etc., can be added.

[0031] The polymer compositions described above can also be used to produce electrode foils by adding at least one electrode active material to the polymer composition.

[0032] Examples of suitable particulate cathode active materials include: layered oxides such as lithium nickel cobalt aluminum oxides (NCA; e.g., LiNi 0.8 Co 0.15 Al 0.05 O 2 ), lithium nickel cobalt manganese oxides (NCM; e.g., LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC (811)), LiNi 0.33 Mn 0.33 CO 0.33 O 2 (NMC (111)), LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC (532)), LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC (622)), high-energy lithium nickel cobalt manganese oxides (overlithiated lithium nickel cobalt manganese oxides), LiCoO 2. 2 , Olivines such as lithium iron phosphate (LiFePO4, LFP), lithium manganese phosphate (LMP) or lithium cobalt phosphate (LCP), spinels such as LiMn2O4, Li2MnO3, Li1.17Ni0.17Co0.1Mn0.56O2 or LiNiO2, lithium-rich FCCs such as Li2MO2F (with M = V, Cr), conversion materials such as FeF3 and / or sulfur-containing materials such as SPAN.

[0033] Examples of suitable particulate anode active materials include: graphite, amorphous carbon (hard carbon), silicon, lithium titanate and / or metallic lithium.

[0034] To improve electrical conductivity, conductive additives such as carbon black, graphite, graphene, carbon fibers, and / or carbon nanotubes can be added to the polymer compositions used to manufacture electrode foils. These are particulate or fibrous materials within the meaning of this application. Other examples of fibrous materials include fibrous additives such as glass fibers, polymer fibers (especially polymer binder fibers), or carbon fibers.

[0035] The polymer composition preferably comprises at least 30 wt.% of particulate and / or fibrous material, more preferably at least 50 wt.%, and particularly at least 60 wt.%, based on the total weight of the polymer composition. The polymer composition preferably comprises at most 90 wt.% of particulate and / or fibrous material, more preferably at most 85 wt.%, and particularly at most 75 wt.%, based on the total weight of the polymer composition.

[0036] The polymer composition described above is provided as a polymer melt in a first process step. The polymer melt can be produced separately and introduced into the extruder unit as such, or it can be generated from the polymer composition within the extruder unit. Preferably, the polymer melt is produced directly within the extruder unit by melting the polymer composition.

[0037] The polymer composition can be provided separately by mixing the components or directly by adding the components to the extruder unit. Preferably, the polymer composition is provided by adding the components to the extruder unit and then immediately transferred into the polymer melt within the extruder unit.

[0038] After leaving the extruder unit, the polymer melt is fed to the distribution unit described above. This unit includes a distribution valve that regulates the flow of the polymer melt to the dispensing unit or the outlet. At the beginning of the process, i.e., when the described device is restarted after a standstill, the necessary homogeneity of the polymer melt upon exiting the extruder unit, particularly with regard to composition (proportion of particulate and / or fibrous material), temperature, and / or viscosity, is often not guaranteed. If introduced into the forming die of the dispensing unit, such a polymer melt would cause a significant pressure increase within the device, potentially leading to the shutdown of the entire system.According to the invention, at the beginning of the process, the distribution valve is therefore adjusted so that the polymer melt is discharged completely or partially, preferably completely, from the device via the outlet. This so-called reject can be discarded or recycled back into the process by reintroducing the reject as a polymer composition into the extruder unit.

[0039] As soon as a stable, homogeneous polymer melt is detected at the outlet, the distribution valve is adjusted according to the invention so that the polymer melt is fed wholly or partially, preferably wholly, to the delivery unit via the first distribution unit outlet.

[0040] In the dispensing unit, the polymer melt is pre-shaped and exits the unit through the shaping die. Preferably, a slot die, in particular a wide-slot die, is used. This produces continuous polymer sheets that can be rolled or calendered in a further step to obtain films of the desired thickness.

[0041] The temperature of the polymer composition or the polymer melt during extrusion, and preferably throughout the entire process, is in a range above the melting temperature of the polymer composition and ≤ 160°C.

[0042] The polymer films produced according to the inventive method have a film thickness of ≤ 1 mm, in particular ≤ 0.5 mm.

[0043] As previously described, polymer films can be produced using the proposed method, which can be used as active material films and / or solid electrolyte films for electrochemical cells, especially for lithium-containing battery cells. Advantages of the invention

[0044] The inventive method and the inventive device for producing polymer films make it possible to avoid the shutdown of the extruder unit due to increased pressure or torque during the start-up process. Furthermore, avoiding unwanted machine shutdowns results in less material waste. The inventive method is also more energy-efficient during the start-up process and leads to reduced degradation of the polymer composition, as it is subjected to lower pressure, shorter temperature exposure, and lower shear stress during start-up. Brief description of the drawings

[0045] Exemplary embodiments of the invention are explained in more detail with reference to a drawing and the following description: Figure 1 shows a schematic representation of a device according to the invention during the start-up process; and Figure 2 shows a schematic representation of a device according to the invention during the ongoing process. Embodiments of the invention

[0046] In Figure 1Figure 1 shows an embodiment of the device 1 according to the invention during the start-up process of polymer film production. The device 1 comprises an extruder unit 10, a distribution unit 20, and a discharge unit 30. The extruder unit 10 is fed with the polymer composition 40 via the extruder inlet 11. The extruder screw 12, rotating in the extruder flow channel 13, conveys the polymer composition 40 in the conveying direction 50 to the extruder outlet 14. During this process, the polymer composition 40 is melted, the polymer melt 41 is formed, and the pressure in the extruder unit 10 is increased. The polymer melt 41 passes through the extruder outlet 14 and the immediately connected distribution unit inlet 21 into the distribution unit 20.The polymer melt 41 flows through the distribution unit flow channel 22 to the distribution valve 25, which, depending on the selected setting, directs the polymer melt 41 to the first distribution unit outlet 23 or to the second distribution unit outlet 24. The in . Figure 1 The setting of the distribution valve 25 shown is selected such that the polymer melt 41 is directed to the second distribution unit outlet 24 and thus to the drain outlet 26. The in Figure 1 The illustrated setting of the distribution valve 25 thus enables the device to be started up according to the invention without the risk of shutdown due to increased pressures or torques.

[0047] In Figure 2 is the device made of Figure 1The device is shown, with the difference that the setting of the distribution valve 25 is selected such that the polymer melt 41 is fed into the dispensing unit 30 via the first distribution unit outlet 23. The dispensing unit has a dispensing unit inlet 31, a dispensing unit outlet 32, and a dispensing unit flow channel 33, which connects the dispensing unit inlet 31 and the dispensing unit outlet 32. A forming nozzle 34, in this case a slot nozzle, is arranged at the dispensing unit outlet 32, which preforms the polymer melt 41 into a polymer layer. The rollers, in particular calenders, which are optionally arranged downstream, are not shown here. All parts of the device can be tempered to a temperature above the melting temperature of the polymer composition and to a value ≤ 160°C by means of temperature control devices.

[0048] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

1. Process for producing a film from a polymer composition (40), wherein the process comprises the following process steps: (e) providing a polymer melt (41) composed of at least one polymer composition (40); (f) extruding the polymer melt (41) in at least one extruder unit (10) that is arranged via at least one extruder outlet (14) in fluid connection with at least one distribution unit (20) comprising at least the following elements: (vi) at least one distribution unit inlet (21) that is arranged in fluid connection with the at least one extruder outlet (14), (vii)at least one first distribution unit outlet (23) that is arranged in fluid connection with the at least one delivery unit inlet (31), (viii) at least one second distribution unit outlet (24) that is arranged in fluid connection with at least one outflow outlet (26), (ix) at least one distribution unit flow channel (22) that connects the at least one distribution unit inlet (21), the at least first distribution unit outlet (23) and the at least second distribution unit outlet (24) to one another, and (x) at least one distribution valve (25) that permits an extruder discharge reaching the distribution unit (20) via the at least one distribution unit inlet (21) to be distributed to the at least first distribution unit outlet (23) and to the at least second distribution unit outlet (24); (g) introducing the polymer melt (41) via the at least first distribution unit outlet (23) into a delivery unit (30) comprising at least one delivery unit inlet (31), at least one delivery unit outlet (32), and at least one shaping nozzle (34) that is arranged in fluid connection with the at least one delivery unit outlet (32), such that the polymer melt (41) exits the delivery unit (30) through the at least one shaping nozzle (34) so as to obtain a preformed polymer melt (41); and (h) optionally further shaping the preformed polymer melt (41), in particular passing the preformed polymer melt (41) through rollers so as to obtain a film of desired thickness, characterized in that, at the beginning of the process, the extruder discharge is delivered in full or in part via the at least one second distribution unit outlet (24) to the at least one outflow outlet (26) until the extruder discharge has attained sufficiently homogeneous properties.

2. Process according to Claim 1, wherein the polymer melt (41) comprises at least one thermoplastic organic polymer and at least one particulate and / or fibrous material.

3. Process according to Claim 1 or 2, wherein the temperature of the polymer melt (41) during extrusion is ≤ 160°C.

4. Process according to any of Claims 1 to 3, wherein the polymer composition (40) comprises at least one polymeric solid electrolyte and at least one particulate and / or fibrous material from the group consisting of at least one electrode active material, at least one conductive additive, at least one inorganic solid electrolyte and mixtures of the above.

5. Process according to any of Claims 1 to 4, wherein the polymer film produced according to this process has a film thickness of ≤ 1 mm.

6. Process according to any of Claims 1 to 5, wherein the produced polymer film is an active material film and / or a solid electrolyte film for an electrochemical cell, especially a lithium-containing battery cell.

7. Use of the process according to any of Claims 1 to 6 for producing an active material film and / or a solid electrolyte film for an electrochemical cell, especially a lithium-containing battery cell.