Mixer for producing an electrode mixture comprising a pressure-based conveying device, and use of said mixer

Abstract

The present invention relates to a mixer (1) for producing an electrode mixture, comprising a mixing container (2) which can be rotated about a mixing container axis and which has a rotationally symmetrical and preferably circular container bottom and a container wall; a stripping device (11) which can be moved relative to the mixing container and touches the container bottom or is arranged at a distance of less than (2) mm from the container bottom; and a pressure-based conveying device for removing the electrode mixture from the mixing container, wherein the pressure-based conveying device has a conveying channel which is arranged on or in the stripping device, having an inlet which is arranged in the vicinity of the container base, and an outlet.

Description

[0001] Maschinenfabrik Gustav Eirich GmbH & Co. KG

[0002] Our reference number: 240842WO

[0003] Mixer for producing an electrode mixture with pressure-based conveying device

[0004] The present invention relates to a mixer for producing an electrode mixture, comprising a mixing vessel rotatable about a mixing vessel axis and having a rotationally symmetrical and preferably circular vessel bottom and wall. Such mixers are generally known.

[0005] However, their use for producing electrode mixtures is limited. This is partly because the production of electrode mixtures, and especially dry electrode mixtures, often requires rapid heating and cooling of the mixture. This is only easily achievable if the container wall and the entire bottom of the mixing container have a double jacket to accommodate a cooling and / or heating fluid, thus eliminating the need for a drain plug in the bottom. Removing the finished mixture from the mixing container then becomes difficult, as the mixture often has a sticky, clay-like consistency.

[0006] Electrode mixtures are used, for example, in the production of batteries.

[0007] In recent years, battery technology, and in particular lithium-ion technology, has moved into the spotlight, as it is essential for the functionality of, for example, fully electric vehicles, but also for stationary energy storage systems. A typical lithium-ion cell has a copper foil acting as the anode and an aluminum foil acting as the cathode. The foils are usually coated on both sides with active material and, at least for the production of a cathode, with additives. Furthermore, the particles of the active material must be bonded both to each other and to the metal foil, for which a binder material is used. To produce the layers, the starting materials, i.e., the active material, the binder, and, if applicable, the additives, must be mixed together and dispersed into a slurry. A liquid solvent, such as...Water is added to the electrode mixture, which then has to be removed again in complex drying processes after the mixture has been applied to the foil. Since this is very time-consuming and energy-intensive, there is a need for the production of dry electrode mixtures that possess sufficient quality for manufacturing dry electrodes. Due to the complex properties of the active material used—often PTFE—the electrode mixture must be heated during the mixing process, usually to more than 45 °C. To process PTFE, shear forces often have to be applied to fibrillate it, i.e., to break it down into a multitude of fine fibers or fibrils. However, when heated, it is not easy to remove the electrode mixture from the mixing container because it has a highly adhesive, clay-like consistency.The ease of removing the electrode mixture can possibly be improved by cooling the electrode mixture, but this is also time-consuming, especially since the mixing container must be reheated immediately after removing the electrode mixture for processing the next batch.

[0008] The object of the present invention is therefore to provide a mixer for producing an electrode mixture which enables early removal of the electrode mixture even under difficult conditions.

[0009] According to the invention, this problem is solved by providing a scraper device which is movable relative to the mixing container and touches the bottom of the container or is less than 2 mm away from the bottom of the container, as well as a pressure-based conveying device for removing the electrode mixture from the mixing container.

[0010] A pressure-based conveying device is a device for transporting fluid or solid materials through a conveying channel, such as a pipe or hose, by generating a controlled pressure differential between an inlet and an outlet. This pressure differential causes a continuous material transport, in which, depending on the device's design, a gas, a liquid, or the material being conveyed itself is used as the conveying medium. The pressure differential can be achieved either by generating an overpressure (pressure conveying) or a vacuum (vacuum conveying).

[0011] Pressure-based conveying systems include, in particular:

[0012] • Pneumatic conveying systems that use gases – typically air – as the conveying medium and are particularly suitable for transporting solid particles such as powders or granules. The flow of the conveying gas draws the material into the conveying element or transports it by pressure. • Hydraulic conveying systems that use liquids as the conveying medium and are frequently used for transporting liquids or liquid mixtures such as emulsions or suspensions. The flow of the liquid moves the material within the conveying element.

[0013] These conveying systems enable the transport of various material forms, such as liquids, suspensions, powders, or granular solids. They are designed so that the flow generated by the pressure difference transports the material safely and efficiently.

[0014] The present invention has been developed for the production of dry electrode mixtures. This is also the preferred use of the mixer according to the invention. However, it can also be used for wet electrode mixtures. The invention is explained below with reference to the production of dry electrode mixtures. It is understood, however, that all the described features could also be used for wet electrode mixtures.

[0015] According to the invention, the pressure-based conveying device has a conveying channel arranged on or in the scraper device, with an inlet located near the bottom of the container and an outlet. Typically, the scraper device is stationary and, for example, held from above into the open-topped mixing container while the mixing container rotates around its axis. The scraper device has two main functions: firstly, to support the mixing process by collecting the mixing components adhering to the bottom and, if applicable, the container wall, and returning them to the actual mixing process; and secondly, according to the invention, a conveying channel is arranged on or preferably in the scraper device, which can, for example, be connected to a vacuum source to extract the dry electrode mixture via the inlet of the conveying channel. The pressure differential required for conveying can be applied only when needed, i.e.,They are usually produced at the end of the mixing process.

[0016] The cross-section of the conveying channel is preferably selected such that a material discharge of at least 10 l / min, preferably at least 50 l / min and particularly preferably at least 100 l / min is possible at differential pressures of max. 1 bar and at liter densities of the mixture of 0.3 to 2.6 kg / l.

[0017] To improve the mixing process, a preferred embodiment provides a mixing tool within the mixing container, which is rotatable about a mixing tool axis. The mixing container axis and the mixing tool axis are spaced a distance a > 0 from each other and are arranged parallel to one another. If a = 0, the mixing tool axis would lie exactly on the container axis. While this is generally possible, a preferred embodiment provides for a > 0. In the case a = 0, the mixing container would preferably be stationary and not rotatable.

[0018] In a preferred embodiment, the scraper device further comprises a first end that touches the container wall or is less than 2 mm from the container wall, and a second end that is further away from the container wall than the first end. The inlet of the conveying channel is then arranged closer to the second end than to the first end, with the distance of the inlet from the first end preferably being at least twice, and particularly preferably at least four times, as the distance of the inlet from the second end. By thus positioning the inlet further towards the center of the mixing container base, it is ensured that the dry electrode mixture is always initially drawn from a particularly well-mixed area of ​​the mixing container.

[0019] The conveying channel can then extend vertically upwards from the first end of the scraper device out of the mixing container. In a preferred embodiment, however, the scraper device additionally has a wall section extending from the bottom of the container along the container wall, which touches the container wall or has a distance from the container wall of less than 2 mm. The conveying channel can then also be routed through or arranged on this wall section.

[0020] This also removes any material adhering to the walls of the mixing vessel and returns it to the mixing process. The scraper thus serves as both a bottom and wall scraper. Furthermore, the conveying channel can be routed close to the bottom of the mixing vessel, protected from damage by the material. Additionally, any separate channel not integrated with the wall and bottom scraper, which is immersed in the material, impedes its uniform movement and thus impairs the mixing result.

[0021] Because the conveying channel is integrated into the wall and bottom scraper, the mixture experiences virtually no additional disturbance during material circulation, resulting in reliable and complete removal of the mixture. Since the scraper and the mixing container move relative to each other, the scraper has an upstream side to which the dry electrode mixture flows during operation due to the direction of rotation of the mixing container. In a preferred embodiment, the inlet of the conveying channel is located on the upstream side and preferably also on the side of the scraper facing the bottom of the container. This ensures highly efficient removal of the dry electrode mixture through the conveying channel of the pressure-based removal device.

[0022] In a further preferred embodiment, the scraper device has a guide lip on its side facing the bottom of the container, which is preferably made of a plastic. The guide lip is arranged and designed such that, during operation of the mixer, it directs the dry electrode mixture at the bottom of the container towards the inlet of the conveying channel. For example, the guide lip can surround the inlet of the conveying channel on the side facing the bottom of the container, at least on the side facing away from the inflow. During the rotation of the mixing container, the guide lip can therefore hold the dry electrode mixture directly in front of the inlet of the conveying channel and thus direct the flow into the conveying channel.In a preferred embodiment, the guide lip has a curved section in the part that touches the bottom of the container or is less than 2 mm from the bottom of the container.

[0023] The conveying channel preferably has a circular cross-section. The scraper is advantageously designed on its side facing away from the bottom of the container either convexly curved, saddle-shaped, or shed-shaped. It is essential that even at low fill levels, no material components can remain on the top of the scraper, but rather that they are returned to the mixing process as completely as possible.

[0024] The outlet of the conveying channel can be connected to a vacuum source, i.e., for example, to a suitable pump, so that the dry electrode mixture, when it is to be removed from the mixing container, can be drawn in via the inlet of the conveying channel and removed from the channel via the outlet.

[0025] In a further preferred embodiment, the distance *a* between the container axis and the axis of the mixing tool is greater than zero, and the mixing tool has at least one agitation element that is in contact with the container bottom or has a distance from the container bottom of less than 2 mm. This agitation element, similar to the scraper device, is designed to loosen any mixture adhering to the container bottom and return it to the mixing process. Since the mixing tool rotates about its axis, which is spaced apart from the container axis, the agitation element describes a cycloid on the container bottom. The agitation element never touches the container wall, so the circular container bottom has an outer ring into which the agitation element does not penetrate.To ensure optimal mixing, the second end of the scraper device should extend at least to the inner edge of this outer circular ring. It is particularly preferred that the inlet of the conveying channel also extends at least to the inner edge of this circular ring. In a preferred embodiment, the agitation element is arranged such that the axis of rotation of the mixing container lies on the circle traversed by the agitation element during the rotation of the mixing tool. In a further advantageous embodiment, the agitation element is shaped so that, during the rotation of the mixing tool, it conveys the mixture outwards towards the container wall, where it can be captured by the guide lip of the scraper device and directed to the inlet of the conveying channel. This allows for almost complete emptying of the mixer, even in the center of the mixing container.The vortex element is geometrically designed so that, upon impact with the mixture, it deflects a large portion of it radially outwards in the direction of rotation. Viewed from above, it can, for example, have a triangular, rhomboid, or trapezoidal cross-section, or consist of an obliquely arranged cuboid.

[0026] Furthermore, it has been shown that it is advantageous if the scraper device is not arranged exactly radially to the container wall. It is advantageous if an imaginary line passing through both the first and second ends forms an angle α less than 90° with a tangent to the circular container base at the point where the imaginary line intersects the circular circumference of the container base. The angle α is preferably between 30° and 60° and best between 40° and 50°.

[0027] Since the mixture, as explained above, has the property of being highly adhesive, it has proven advantageous to supply additional air or gas, such as dry nitrogen, via an air supply duct with an air supply outlet. It is beneficial if the air supply outlet is positioned such that the incoming air is directed either towards the inlet of the conveying duct or towards an area located upstream of the inlet. This mixes the dry electrode mixture with the air, so-called false air, further fluidizing it and thus improving its transportability. The risk of larger clumps of electrode mixture being drawn into the conveying duct and clogging it can therefore be significantly reduced.

[0028] Further advantages, features, and applications of the present invention will become clear with reference to the following description of preferred embodiments and the accompanying figures. These show:

[0029] Figure 1 shows a schematic sectional view through a first embodiment of the invention,

[0030] Figure 2 shows a detailed view of the scraper device of the embodiment shown in Figure 1, Figure 3 shows a detailed enlargement of the scraper device shown in Figure 2.

[0031] Figure 4 shows a detailed view of an alternative embodiment of a scraper device and

[0032] Figure 5 shows a schematic view from above into the mixing container of the mixer according to the invention.

[0033] Figure 1 shows a schematic sectional view through a first embodiment of a mixer 1 according to the invention. The mixer 1 has a mixing container 2 with a circular base and a hollow cylinder adjoining it, forming the container wall. The container 2 is mounted on a base 3 via rotary bearings 4 and is rotatable about a mixing container axis 5. A mixing tool 17 is arranged inside the mixing container 2, which has a series of arms 9 and downward-pointing agitation elements 10 on the lowest arm, which, in the embodiment shown, rest directly on the base of the mixing container 2. The mixing tool 17 is rotatable about a mixing tool axis 6 by means of a motor 7, which drives a belt 8. The mixing tool axis 6 and the mixing container axis 5 are spaced apart from each other by a distance a. When the mixing container 2 and the mixing tool 17 are rotated, the mixture, i.e., the material to be mixed, can be stirred up within the mixing container.The dry electrode mixture is mixed very homogeneously. Dispensing is achieved using a pressure-based conveying device. This device is arranged within a scraper 11, which extends horizontally from a first end, which rests against the container wall, to a second end located radially further inwards. Furthermore, the scraper extends upwards from the container bottom along the container wall in the direction of the container axis. The scraper has a guide lip 12, which is made of plastic and rests against the container bottom or wall, or has a distance of only a few hundredths of a millimeter, max. a few tenths of a millimeter, from the mixing container.Since the guide lip 12 is subjected to high mechanical stress due to direct contact with the metal container bottom and / or material adhering to the container wall and bottom in conjunction with the container's rotational movement, it is preferably designed as a rigid molded part to prevent bending and tearing of elastic guide lips. To prevent material adhesion in the gap below the deflector and the mixing container, the guide lip 12 is preferably arranged on the upstream side of the scraper device.

[0034] The entire rotatable container 2 is arranged here in an enclosure 20, which is stationary and connected to the base 3. The mixing container preferably has a radius in the lower corner where the wall and floor meet, in order to prevent material deposits in the corner.

[0035] Figure 2 shows a detailed view of the scraper device 11. The plastic guide lip 12, extending along the container wall and base, is also visible. If, as in this embodiment, the mixing container has a radius in the lower corner, the guide lip 12 is designed with a corresponding radius in the corner. The guide lip 12 can preferably be made in one piece, but can also be made in multiple parts. It preferably consists of a rigid, solid plastic, for example, sheet-shaped PA, UHMW, or PTFE.

[0036] Within the scraper device, a conveying channel 21 of the pressure-based conveying device is arranged. The conveying channel 21 has an inlet 13, which is located on the underside, i.e., on the side facing the container bottom, of the scraper device 11, and an outlet 22, which is located on the side facing away from the container bottom. The inlet 13 is furthermore spaced from the container wall and is located at the radially innermost section of the scraper device. The outlet 22 is preferably located at the radially outer section of the scraper device. As can be seen particularly in the detailed enlargement in Figure 3, the guide lip 12 is guided from the upstream side to the rear at the radially inner end of the scraper device 11 and surrounds the inlet 13 on its downstream side and at its radially innermost section. The surrounding, loop-like section of the guide lip 12 is provided with the reference time 12a.Furthermore, an air supply duct 14 with an outlet 16 is visible, which supplies air or gas to the area immediately in front of the inlet of the conveying duct as needed. The front section 12a of the guide lip 12 also has three openings 15 in the example shown. These could, for example, be through-openings through which the material being mixed, held in the loop-like section 12a of the guide lip 12 during the mixing process, can pass to be returned to the mixing process, as long as no material is to be removed via the inlet 13 of the conveying duct 21. Alternatively, the openings 15 could also be further outlet channels of the air supply duct 14, to mix air into the material being mixed in order to fluidize it, so that it can be more easily extracted via the inlet 13 of the conveying duct 21.

[0037] However, for some electrode mixtures, the embodiment shown in Figure 3 is less suitable, since the mixture does not get caught in the front section 12 of the guide lip 12 and then remains there until extraction, so that this part is not homogeneously mixed.

[0038] Figure 4 therefore shows an alternative embodiment. Here, the guide lip 12' with its front section 12a' also surrounds the inlet 13' of the conveying channel, but has openings facing downwards, i.e., on the side facing the bottom of the container, as well as on the upstream side. It is also conceivable, in both the embodiment shown in Figure 3 and the embodiment shown in Figure 4, to omit or shorten the front section 12a or 12a' of the guide lip 12 or 12'.

[0039] Figure 5 shows a schematic top view of the mixing container and its base. The mixing tool 17 and the downward-pointing agitation elements 10 are visible. The mixing tool 17 rotates about its axis, which is spaced apart from the container's axis of rotation. This causes the agitation elements 10 to trace cycloidal curves on the base of the mixing container, indicated by dashed lines 18. In the illustrated embodiment, as the mixing tool 17 rotates about its axis 6, the agitation element 10 passes exactly through the axis of rotation 5 of the mixing container 2.

[0040] It can be seen that an outer circular ring 19 remains at the bottom of the container, which is not swept over by the agitation elements 10 of the mixing tool 17. This area is covered by the scraper device 11, which has a first end that rests against the container wall with the guide lip 12, and a second end in which the inlet 13 of the conveying channel is located. It can be seen that the scraper device 11 does not extend directly radially inwards from the container wall, but is arranged at an angle. Figure 5 shows the angle α, which is defined by an imaginary line extending from the first end to the second end of the scraper device 11 and forming a tangent at the point where the imaginary line intersects the container wall. In the embodiment shown, this angle is approximately 45°.In principle, the use of the pressure-based conveying device according to the invention is not limited to the extraction of dry electrode mixtures, but can be used for all powdered mixtures. It can also be used for extracting agglomerated or granulated bulk materials of all kinds, provided they possess sufficiently good flow properties. Furthermore, the conveying device can also be used for extracting liquids and suspensions from the mixing vessel, such as electrode suspensions for batteries. In this case, the addition of supply air is unnecessary. The suspension is then extracted from the mixer by means of a pump, or preferably a vacuum pump, connected to a collection tank.

[0041] Reference symbol list

[0042] 1 mixer

[0043] 2 containers

[0044] 3 Stand

[0045] 4 swivel bearings

[0046] 5 Mixing container axis

[0047] 6 Mixing tool axis

[0048] 7 engine

[0049] 8 belts

[0050] 9 arms

[0051] 10 vortex elements

[0052] 11. Scraper device

[0053] 12, 12' Guide lip

[0054] 12a, 12a' front section of the guide lip

[0055] 13 Inlet Conveyor Channel

[0056] 14 Supply air duct

[0057] 15 openings

[0058] 16 Outlet supply air duct

[0059] 17 Mixing tool

[0060] 18 cycloidal curves

[0061] 19 outer ring

[0062] 20 Enclosure

[0063] 21 Conveyor channel

[0064] 22 Outlet Conveyor Channel

Claims

Patent claims 1. Mixer for producing an electrode mixture comprising a mixing vessel rotatable about a mixing vessel axis and having a rotationally symmetrical and preferably circular vessel bottom and vessel wall, a scraper device movable relative to the mixing vessel and touching the vessel bottom or having a distance of less than 2 mm from the vessel bottom, and a pressure-based conveying device for removing the electrode mixture from the mixing vessel, wherein the pressure-based conveying device has a conveying channel arranged on or in the scraper device with an inlet located near the vessel bottom and an outlet.

2. Mixer according to one of the preceding claims, characterized in that a mixing tool is provided in the mixing container, which is rotatable about a mixing tool axis, wherein the mixing container axis and the mixing tool axis are spaced apart from each other by a distance a > 0 and are arranged parallel to each other.

3. Mixer according to one of the preceding claims, characterized in that the scraper device has a first end which touches the container wall or is less than 2 mm away from the container wall, and a second end which is further away from the container wall than the first end, wherein the inlet of the conveying channel is arranged closer to the second end than to the first end, wherein preferably the distance of the inlet from the first end is at least twice and particularly preferably at least four times as large as the distance of the inlet from the second end.

4. Mixer according to one of the preceding claims, characterized in that the scraping device has a wall section extending from the bottom of the container along the container wall, which touches the container wall or has a distance from the container wall of less than 2 mm.

5. Mixer according to one of the preceding claims, characterized in that the scraper device has an upstream side to which the electrode mixture flows during operation due to the direction of rotation of the mixing vessel, wherein the inlet is arranged on the upstream side and preferably also on the side facing the bottom of the vessel.

6. Mixer according to one of the preceding claims, characterized in that the scraper device has a guide lip on its side facing the bottom of the container, which is preferably made of a plastic, wherein the guide lip is arranged and designed in such a way that, during operation of the mixer, it directs the electrode mixture on the bottom of the container towards the inlet.

7. Mixer according to claim 6, characterized in that the guide lip surrounds the inlet on the side facing the bottom of the container at least on the side facing away from the upstream side.

8. Mixer according to one of the preceding claims, characterized in that the conveying channel has a circular cross-section.

9. Mixer according to one of the preceding claims, characterized in that the scraper device is convexly curved or saddle-roof-shaped or pent-roof-shaped on its side facing away from the bottom of the container.

10. Mixer according to one of the preceding claims, characterized in that the outlet is connected to a vacuum source.

11. Mixer according to claim 2 or a dependent claim, characterized in that the distance between the container axis and the axis of the mixing tool is a>0 and the mixing tool has at least one swirling element which is in contact with the container bottom or has a distance to the container bottom which is less than 2 mm, wherein the swirling element never penetrates an outer circular ring of the container bottom during the rotation of the mixing container and the rotation of the mixing tool and the second end extends at least to the inner edge of the circular ring, wherein preferably the inlet extends at least to the inner edge of the circular ring.

12. Mixer according to one of the preceding claims, characterized in that an imaginary line passing through both the first and the second end forms an angle α with a tangent to the circular base of the container at the point where the imaginary line intersects the circular circumference of the base of the container, which is less than 90°, preferably between 30° and 60° and best between 40° and 50°.

13. Mixer according to one of the preceding claims, characterized in that a supply air duct with a supply air outlet is provided.

14. Mixer according to claim 13, characterized in that the supply air outlet is arranged such that the supply air flowing out through the supply air outlet is directed either onto the is directed at the inlet of the conveying channel or at an area located upstream of the inlet of the conveying channel.

15. Use of a mixer according to any of the preceding claims for the production of a dry electrode mixture.

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