Method and apparatus for drying electrode coatings

Abstract

The present invention relates to a method for drying a pasty coating of an electrode material on a ribbon-shaped electrode foil in a drying oven with a variable drying rate. It further comprises a drying oven with a transport device for guiding the electrode foil with the pasty coating applied to a front surface through the drying oven along a drying section, and drying nozzles arranged along the drying section in the guiding direction.

Description

[0001] The present invention relates to electrode foils for the manufacture of batteries and to methods for the manufacture of electrode foils. Furthermore, the invention relates to methods for drying a pasty coating of an electrode material on a continuous belt in a drying oven during the manufacture of the electrode foil.

[0002] Electrode foils are used to manufacture batteries, and these are produced in a continuous process. They are manufactured by guiding a carrier film with a pasty coating applied to one side along a drying section of a drying oven, where the pasty coating is dried by a drying stream from drying nozzles.

[0003] In current technology, electrode foils for lithium-ion batteries are typically manufactured by coating a substrate with a paste-like active material. The substrate is an aluminum foil (cathode) or a copper foil (anode). The active material for the cathode is often lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), or lithium nickel manganese cobalt oxide (Li(NiMnCo)O2). Graphite is most commonly used as the anode material, but materials such as silicon or lithium titanate are also employed.

[0004] The active material is produced by mixing a binder, such as polyvinylidene fluoride (PVDF), conductivity additives, such as carbon nanomaterials, and a solvent, such as N-methyl-2-pyrrolidone. This resulting pasty material is applied to a substrate by casting, rolling, spraying, and / or screen printing.

[0005] The coated substrate is dried to remove the solvent and fix the electrode material to the substrate. The electrode foils are then compacted by rolling to improve density and contact performance.

[0006] The drying step has proven to be crucial for the quality of the electrode foil, as a number of problems can occur during this process.

[0007] If drying is uneven, parts of the electrode foil may contain more solvent than others after drying. If residual solvent remains in the electrode, it can impair its chemical stability and lead to undesirable chemical reactions during the battery cycle. This can result in inhomogeneities in the electrode structure, leading to uneven power output, uneven current density distribution, and consequently, a reduced battery lifespan.

[0008] Furthermore, excessively rapid drying can lead to the formation of blisters or cracks in the active material of the coating. Such defects can impair electrical conductivity and reduce the mechanical stability of the electrode foil.

[0009] Excessively high drying temperatures can alter the microstructure of the active material, which can negatively affect the electrochemical properties of the electrode material and lead to reduced capacity and efficiency.

[0010] Various methods for solving these problems are known from the prior art. For example, publication WO 2010 / 026285 A1 proposes drying the coated anode for a specific period of time at a specific temperature.

[0011] Document US 10,381,164 B2 describes a freeze-drying process at reduced pressure. Furthermore, processes are also known in which drying is carried out using a laser or a pulsed IR emitter.

[0012] Document WO 2021 / 072548 A1 describes a process in which the coating is dried at a defined ambient temperature, with a defined supply air temperature, velocity, and humidity, and with the additional use of infrared radiation. The infrared radiation source is positioned at a specific distance from the object being dried.

[0013] However, the current state of the art has disadvantages, as no method has yet been provided that satisfactorily solves the problems that arise during drying.

[0014] Therefore, one object of the present invention is to overcome the disadvantages of the prior art and in particular to provide a method by which electrode foils for battery production can be provided with a coating having low residual moisture and high adhesion of the coating.

[0015] This problem is solved by a method for producing an electrode foil according to claim 1, and by a device for drying electrode coatings according to the dependent claim.

[0016] Further advantageous embodiments of the present invention are specified in the dependent claims.

[0017] According to a first aspect, a method for producing an electrode foil for a battery is provided, wherein a pasty coating of an electrode material is applied to a ribbon-shaped support material and dried in a drying oven, comprising the following steps: - Guiding the carrier material with the pasty coating applied to a front surface through the drying oven along a drying section, wherein the drying section has a starting section, a middle section and a final section successively in the guiding direction; - Application of drying streams of a drying gas to the carrier material along the drying section to achieve a varying drying rate; wherein the drying rate in the middle section is reduced with respect to the drying rate of the initial section and / or the final section.

[0018] Air is the preferred drying gas. In another embodiment, the drying gas can contain or be a protective gas such as argon or nitrogen.

[0019] Furthermore, the drying rate in the middle section can be between 40% and 70% of the drying rate in the initial section or the drying rate in the final section.

[0020] According to another embodiment, the drying rate can be adjusted by the temperature of the drying stream and / or by the impact velocity of the drying stream on the front surface.

[0021] The temperature of the drying stream is preferably adjusted by heating the drying gas outside the drying section. Alternatively, or in addition to heating the drying stream, the drying section itself can also be heated.

[0022] The impact velocity of the drying stream is determined by the fan size, the blade design and the number of blades, and can be variably controlled by the fan speed.

[0023] In a particularly preferred embodiment, the drying rate is varied by the impact velocity of the drying stream and the temperature of the drying stream is kept constant.

[0024] According to another aspect of the invention, the temperature of the drying stream is controlled and regulated as a function of a modeled or measured temperature of the pasty coating with electrode material applied to a front surface.

[0025] For the evaporation or removal of solvent from the coating, its temperature within the electrode material is of particular importance. Therefore, it is advantageous to control or regulate the temperature of the drying flow based on the surface temperature of the coated electrode. In particular, it can be provided that the temperature of the drying flow is controlled or regulated so that the surface temperature of the coated electrode corresponds to a predetermined target temperature.

[0026] In one embodiment, the target temperatures are specified as follows: at the end of the initial section, a surface temperature of 58 °C for the pasty coating applied to a front surface; in the middle of the intermediate section, a surface temperature of 57.8 °C; at the end of the intermediate section, a surface temperature of 58.1 °C; and at the end of the final section, a surface temperature of 70 °C. An adhesion strength of at least 95.83 N / cm² for the electrode coating can be achieved. 2 and a residual moisture content of the electrode coating of less than CM-0.6% is achieved.

[0027] According to a further embodiment, fans with drying nozzles, in particular impact jet nozzles, are arranged along the drying section to expel the drying streams, wherein the impact velocity of each of the drying streams on the front surface is adjusted by adjusting a fan speed of the respective fan to generate the respective drying stream.

[0028] Impact jet nozzles are special nozzles designed to create a drying jet that impacts a solid surface and then spreads out in different directions.

[0029] In one embodiment, they have a variable gap so that the width or cross-section of the drying stream jet can be adjusted.

[0030] According to a further embodiment, the drying streams are selected such that they have a linearly or monotonically decreasing impact velocity in the initial section along the drying path and / or that they have a linearly or monotonically increasing impact velocity in the final section along the drying path.

[0031] According to the invention, the drying rate can change directly during the transition between the individual sections or, more preferably, comprise a transition zone in which the drying rate is adjusted, particularly linearly, from a first value to a second value. This is particularly advantageous when the drying rates in the individual sections of the drying process are constant.

[0032] According to another embodiment, support currents from Venturi nozzles are directed onto a rear surface of the carrier material / electrode foil along the guiding direction, wherein the support currents have the same or different flow velocities.

[0033] Venturi nozzles are special nozzles that utilize the Venturi effect to reduce the pressure of a flowing liquid or gas and increase its velocity. The resulting pressure drop is used to create a vacuum, drawing the rear surface of the carrier material towards it. This secures the carrier material in place, ensuring that the front surface maintains a constant distance from the impact jet nozzles.

[0034] In a particularly preferred embodiment, the Venturi nozzles are adjusted so that the generated negative pressure corresponds to the impact velocity of the drying streams.

[0035] According to a further embodiment of the invention, a drying oven is provided for drying a ribbon-shaped electrode foil with an applied pasty coating of an electrode material, comprising: - a transport device designed to guide a carrier material, in particular a carrier film, with the pasty coating applied to a front surface through the drying oven along a drying section, wherein the drying section has a starting section, a middle section and a final section; - drying devices arranged along the drying section in the guiding direction, each designed to apply a drying stream of a drying gas to the substrate material, so that a drying rate varying along the drying section is achieved; wherein the varying drying rate in the middle section is reduced with respect to the drying rate of the initial and final sections.

[0036] According to another aspect of the invention, fixing nozzles, in particular Venturi nozzles, are included along the drying path opposite the drying nozzles.

[0037] The drying nozzles are arranged in such a way that they can direct the drying flow onto the pasty coating applied to the front surface of the carrier material, and the support nozzles fix the rear surface of the carrier material.

[0038] According to another aspect of the invention, the drying nozzles preferably correspond to impact jet nozzles with a variable gap for adjusting the drying flow.

[0039] In another embodiment, the internal pressure of the drying oven is adjustable.

[0040] Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of a device for drying an electrode coating; Fig. 2 a diagram of the drying rate, temperature and impact velocity of the drying stream in the initial section, the middle section and the final section.

[0041] Fig. Figure 1 shows a drying oven 200 for drying a ribbon-shaped carrier film 210 as a carrier material with an applied pasty coating 211 of an electrode material. The ribbon-shaped carrier material is provided on a spool, with the pasty coating being applied before being fed into the drying oven 200.

[0042] The substrate material is conductive and usually consists of a metallic material, such as aluminum or copper, with a thickness between 10-200 µm.

[0043] The electrode material can, for example, contain lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4) or lithium nickel manganese cobalt oxide (Li(NiMnCo)O2) and be produced by mixing with a binder, such as polyvinylidene fluoride or PVDF, conductivity additives, such as carbon nanomaterials, and solvents such as N-methyl-2-pyrrolidone.

[0044] The drying oven 200 includes a transport device 220, which is designed to guide the carrier material 210 with the pasty coating 211 applied to a front surface along a drying section 140.

[0045] The drying section 140 has, in the direction of travel, a starting section 110, a middle section 120, and a final section 130. Drying nozzles 240 are arranged along the drying section 140 in the direction of travel 230. The drying nozzles 240 are each designed to apply a drying stream 250 of a drying gas to the carrier material 210, so that a drying rate that varies along the drying section 140 is achieved.

[0046] The drying nozzles are designed as impact jet nozzles. The impact velocity of the drying stream can be adjusted by the blower power, e.g., controlled by the blower speed, and the opening cross-section of the drying nozzles.

[0047] Furthermore, along the drying section 140, fixing nozzles 260, in particular Venturi nozzles, can be located opposite the drying nozzles 240. The fixing nozzles stabilize the carrier material as it passes through the drying oven and ensure a flat surface on the upper side of the carrier material.

[0048] Fig.Figure 2 shows a diagram 100 with a drying section 140 for the ribbon-shaped carrier material 210 with a pasty coating applied to a front surface along the various sections (110, 120, 130) of a drying section 140, where the temperature 160 of the drying stream is constant and the impact velocity 170 of the drying stream is variable. The impact velocity 170 of the drying stream is monotonically decreasing in the initial section 110, monotonically increasing in the final section 130, and constant in the middle section 120. Furthermore, the drying rate 150 is reduced in the middle section 120 compared to the initial section 110 and the final section 130. Reference symbol list 100 Diagram 110 Initial section 120 Middle section 130 Final section 140 drying section 150 drying rate 160 temperature 170 impact velocity 200 drying oven 210 carrier material 211 Coating 220 Transport device 230 Direction of travel 240 drying nozzles 250 drying current 260 support nozzles QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2010 / 026285 A1

[0010] US 10,381,164 B2

[0011] WO 2021 / 072548 A1

[0012]

Claims

[1] Method (100) for producing an electrode foil for a battery, wherein a pasty coating (211) of an electrode material is applied to a ribbon-shaped support material (210) and dried in a drying oven (200), comprising the following steps: - Guiding the carrier material (210) with the pasty coating (211) applied to a front surface through the drying oven (200) along a drying section (140), wherein the drying section (140) has a starting section (110), a middle section (120) and a final section (130) successively in the guiding direction (230); - Application of drying streams (250) of a drying gas to the carrier material (210) along the drying section (140) to achieve a varying drying rate (150); wherein the drying rate (150) in the middle section (120) is reduced with respect to the drying rate (150) of the initial section (110) and the final section (130). [2] Method according to claim 1, characterized by , that the drying rate (150) is set by the temperature (160) of the drying stream (250) and / or by the impact velocity (170) of the drying stream (250) on the front surface. [3] Method according to any one of the preceding claims, characterized by , that the temperature (160) of the drying stream (250) is controlled or regulated depending on the surface temperature of the pasty coating (211) applied to a front surface. [4] Method according to any one of the preceding claims, characterized by, that fans with drying nozzles (240), in particular impact nozzles, are arranged along the drying section (140) for ejecting the drying streams (250), wherein the impact velocity (170) of each of the drying streams (250) on the front surface is adjusted by adjusting the fan speed of the respective fan for generating the respective drying stream (250) or by adjusting the opening cross-section of the nozzle openings. [5] Method according to any one of the preceding claims, characterized by , that the drying streams (250) are chosen such that they have a linearly or monotonically decreasing impact velocity (170) in the initial section (110) along the drying section (140) and / or that they have a linearly or monotonically increasing impact velocity (170) in the final section (130) along the drying section (140). [6] Method according to any one of the preceding claims, characterized by, that support flows from support nozzles, in particular Venturi nozzles, are directed towards a rear surface of the carrier material (210) along the guide direction (230), wherein the support flows have the same or different flow velocities. [7] Drying oven (200) for drying a ribbon-shaped support material (210) with an applied pasty coating (211) of an electrode material, comprising: - a transport device (220) configured to guide the electrode foil with the pasty coating (211) applied to a front surface through the drying oven (200) along a drying section (140), wherein the drying section (140) has a starting section (110), a middle section (120) and a final section (130); - drying nozzles (240) arranged along the drying section (140) in the guide direction (230), each designed to apply a drying stream (250) of a drying gas to the carrier material (210) so that a drying rate (150) varying along the drying section (140) is achieved; where the varying drying rate (150) in the middle section (120) is reduced with respect to the drying rate (140) of the initial section (110) and the final section (130). [8] Drying oven (200) according to claim 7, wherein support nozzles (260), in particular Venturi nozzles, are included along the drying section (140) opposite the drying nozzles (240). [9] Drying oven according to claim 7 or 8, wherein the drying nozzles (240) are impact jet nozzles with a variable gap for adjusting the drying flow (250).

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