Method for processing a material web with a lithium surface, processing device, lithium metal anode, and secondary battery

Abstract

A lithium surface, in particular for an anode of a secondary battery, is processed in that a material web (3) with a surface made of lithium is unwound from a first roll (4), exposed to laser radiation under the effect of a protective gas, and wound onto another roll (5).

Description

[0001] Method for processing a material web with a lithium surface, processing device, lithium metal anode and secondary battery

[0002] The invention relates to a method for laser processing a material web with a lithium surface. Furthermore, the invention relates to a processing device for treating a lithium surface with laser radiation. Furthermore, the invention relates to a lithium metal anode and a battery, in particular a secondary battery, comprising a number of such anodes.

[0003] DE 10 2019 216 070 A1 discloses a method for processing a lithium foil or a lithium-coated metal foil using a laser beam. The use of laser radiation with a wavelength between 200 nm and 1 pm is recommended. The laser-processed foil is said to be particularly suitable for use in a solid-state battery. The foil can be a pure lithium foil or a lithium-coated metal foil, in particular copper or aluminum foil. According to DE 10 2019 216 070 A1, the wavelength of the laser radiation is, for example, in the range between 500 nm and 550 nm, i.e., in the green range. Advantages over laser radiation in the NIR range, for example, with a wavelength of 1030 nm, are said to result from the comparatively high absorption coefficient. For this reason, laser radiation in the blue, violet, or UV range is also suitable for processing the lithium surface.The process described in DE 10 2019 216 070 A1 is designed to cut, weld, drill, remove or structure surfaces of the lithium-containing foil.

[0004] Various devices and methods for machining workpieces intended for use in lithium-ion batteries are disclosed in documents CN 113843189 B, CN 115709344 A, and CN218014605 U. CN 116130787 A deals with the machining of both cathodes and anodes of electrochemical systems, namely lithium-ion batteries. In the case of the cathode, laser material removal is proposed. This is intended, in particular, to prevent lithium deposition.

[0005] DE 10 2018 127 787 A1 deals with a structured metal electrode and its combination with a non-liquid electrolyte. Lithium is mentioned as a possible material for metal batteries, alongside iron, sodium, calcium, magnesium, and aluminum. The advantage of lithium is emphasized as its higher theoretical energy density compared to lithium-ion batteries. According to DE 10 2018 127 787 A1, recesses in a metal electrode can be created, for example, by means of embossing processes using stamps or by means of rollers, in particular calender rollers. The use of a laser is also mentioned, but not further discussed. In any case, the creation of blind-hole-like recesses is envisaged. According to DE 10 2018 127 787 A1, the structuring of the material can be carried out using a roll-to-roll process.

[0006] Further processing methods are known from CN 202 695 602 U, CN 201 394 697 Y, US 2022 / 0 376 226 A1 , DE 10 2019 110 375 A1 , De 10 2020 112 500 A1 and DE 10 2010 044 080 A1.

[0007] Regarding the processing of metallic lithium, reference is also made to the following publication:

[0008] D. Park et al.: Design and Manufacturing of Low Relative Humidity Chamber for Laser Processing of Lithium Metal, https: / / doi.org / 10.21203 / rs.3,rs-1029786 / v1, November 2, 2021

[0009] This publication describes in detail possible steps for laser processing of lithium, whereby the laser radiation acts on the lithium surface through a glass plate. The invention is based on the object of expanding the laser processing of lithium surfaces compared to the cited prior art, with particular emphasis on suitability for the series production of electrochemical cells.

[0010] This object is achieved according to the invention by a method for processing a lithium surface having the features of claim 1. The object is also achieved by a processing device according to claim 6. The device according to claim 6 and the method according to claim 1 are suitable for producing lithium metal anodes according to claim 9 and batteries, i.e., primary or secondary batteries, according to claim 10.

[0011] According to claim 1, a strip material is processed by unwinding a material web whose surface contains lithium from a first roll, exposing it to laser radiation under a protective gas, and winding it onto another roll. Preferably, the lithium-containing surface consists of lithium; in this context, a surface formed by lithium is also referred to if the surface is at least partially passivated.

[0012] The electrochemical battery, in particular a secondary battery, according to the application is, in particular, a solid-state battery. For example, the battery is designed as a lithium / sulfur battery or a lithium / air battery. Compared to lithium-ion batteries, solid-state batteries are characterized in particular by a higher energy density. The lithium metal anode according to claim 9 is also suitable for secondary batteries with liquid electrolyte.

[0013] The processing method according to claim 1 can be used in the context of battery production on an industrial scale. Laser irradiation achieves a high surface quality, which in particular effectively prevents the formation of dendrites during subsequent operation of the electrochemical cell. A significant influence on this is the homogeneous initial current density distribution, which is achieved due to the high surface quality during battery operation.

[0014] The processing of the lithium surface using a roll-to-roll process, with the entire production plant being enclosed in a gas-tight enclosure, enables high processing speeds without any loss of quality compared to processes in which individual flat workpieces are positioned one after the other in a processing area.

[0015] The processing method according to the application is highly automatable and scalable. The laser beam can be guided over the workpiece, which has the lithium surface, by a laser deflection unit. Alternatively, a fixed optics system can be used, which is guided mechanically, for example, via linear axes.

[0016] Argon is particularly suitable as a shielding gas. The water and oxygen content in the atmosphere in which the lithium surface is processed is below 1 ppm in industrially viable processes.

[0017] In all cases, the processing device according to the application comprises a processing chamber designed to laser process a material web having a lithium surface, which is unwound from a first roll and wound onto a second roll. Both rolls, i.e., coils, can be located within the processing chamber. Alternatively, both rolls can be located outside the processing chamber. It is also possible to arrange one of the two rolls inside the processing chamber and the other roll outside the processing chamber.

[0018] A surface treatment according to claim 1 is also possible for very thin and correspondingly mechanically sensitive lithium layers. A lithium-coated metal foil, for example, with copper or nickel, can be used as the main component of a substrate. Preferably, the substrate is made of a material whose melting temperature is significantly higher than the melting temperature of the material at the surface. For example, that melting temperature is at least 500°C higher. In principle, a substrate can be coated on one or both sides. Instead of a metal foil, another cell layer of an electrochemical cell or an electrically conductive polymer film can be used as the substrate.

[0019] In all cases, the foil containing metallic lithium is particularly suitable for the production of lithium metal anodes. A secondary battery can contain a large number of such anodes, for example, several tens or even over a hundred. For example, there are 20 to 30 layers coated with lithium on both sides.

[0020] Regarding the application of the lithium coating to the substrate, which is in the form of a foil or sheet, suitable coating methods known from the prior art can be used. For example, lithium is vapor-deposited onto the metallic substrate, in particular a copper substrate. Roll-plating is also a possible method for applying a lithium layer. The thickness of the lithium layer is, for example, in the range of 1 μm to 500 μm. The metallic substrate can provide a current collector within an electrochemical cell.

[0021] There are various process variants for irradiating the lithium surface: Continuously operated laser beam sources are just as suitable as pulsed laser beam sources. In the latter case, femtosecond to millisecond pulses can be used. By adjusting process parameters such as the pulse peak fluence, the pulse repetition rate, the laser wavelength, the beam feed rate, and the process strategy, including the beam trajectory, the processing result can be influenced within wide limits. Optionally, the laser irradiation process includes multiple repetitions, whereby the processing result is influenced by repeatedly guiding the laser beam over the same surface section of the workpiece. In particular, it is possible to specifically modify the surface morphology of the workpiece as well as the chemical state of the lithium metal anode surface.In general, laser radiation is suitable for either melting, evaporating or ablating material on the surface of the lithium-coated foil or the free-standing lithium foil.

[0022] For example, an uneven surface morphology present on the lithium surface to be processed can be smoothed by creating a continuous melt pool with a laser, exploiting surface tension. Furthermore, laser-induced evaporation of material layers in the nanometer or micrometer range can remove passivating surface layers from the lithium foil or the lithium-coated foil. The re-formation of a passivation layer can be prevented by using a protective gas or dry air. In alternative process variants, laser processing is carried out in an atmosphere that specifically leads to the formation of a passivation layer.

[0023] Compared to processes that mechanically treat a lithium surface, for example by scraping or polishing, the processing method according to the application is characterized in all variants by a gentle treatment of the surface.

[0024] An embodiment of the invention is explained in more detail below with reference to a drawing. In the drawings:

[0025] Fig. 1 shows a system for processing a lithium surface in a schematic representation,

[0026] Fig. 2 shows a workpiece to be machined with the system according to Fig. 1, namely a lithium-coated foil. A processing device, designated overall by reference numeral 1, comprises a processing chamber 2 containing an atmosphere of defined composition. The processing device 1 is designed to process a foil 3 having a lithium surface using a laser 6.

[0027] The unprocessed film 3 is initially located on a coil 4, i.e., on a roll, and after laser processing, is wound onto another roll 5. This realizes the concept of roll-to-roll processing. The film 3 can, in principle, be separated into individual sections at any point, with laser beam separation being particularly possible.

[0028] In this case, the foil 3 to be processed is a lithium-coated copper foil. The copper substrate, designated 11, is provided with a lithium coating 12 having a thickness d. The total thickness of the foil 3 is designated D. The total thickness D is a multiple of the thickness d of the lithium coating 12. Instead of a copper substrate, the use of a nickel substrate 11 is also possible. In the case outlined, the lithium coating 12 is vapor-deposited onto the substrate 11. Alternatively, the use of a foil 3 onto which the lithium coating 12 is plated is also possible. Furthermore, the production of the lithium coating 12 by melt deposition is also possible.

[0029] The laser intended for processing the lithium surface defined by the coating 12 is designated 6. In the arrangement shown, laser radiation is generated outside the processing chamber 2, guided into the processing chamber 2 by means of a light guide 13, and there directed onto the surface of the workpiece, i.e., the film 3, by means of a beam deflection unit 14. Likewise, the entire laser 6 could be arranged within the processing chamber 2.

[0030] Alternatively, the laser 6 could be arranged entirely outside the processing chamber 2, in which case a window permeable to laser radiation would have to be provided in the processing chamber 2. Regardless of the location of the processing device 1 where individual components of the laser 6 are located, linear or rotary drives can be provided for adjusting or moving such components.

[0031] In a manner not shown, at least one of the rollers 4, 5 could be located outside the processing chamber 2. In this case, the laser 6 is operated in a pulsed mode. Alternatively, continuous laser irradiation of the flat workpiece, i.e., the coated film 3, is possible. In both cases, the laser radiation can be infrared radiation, radiation in the visible light range, or UV radiation.

[0032] To create an atmosphere suitable for laser processing in the processing chamber 2, there is, in the present case, a compressed gas tank 8, which is connected to the processing chamber 2 via a pipeline 7 and a valve 9. Gas sensors (not shown) are located in the processing chamber 2, which monitor the atmosphere, in particular for compliance with maximum values ​​for the oxygen and water vapor content.

[0033] Optionally, a plurality of gas tanks 8 are provided in the processing chamber 2 to generate a gas mixture. Gas purification can be provided to reduce gas consumption. Devices for monitoring the processing process can be built into the processing chamber 2 and / or arranged outside the processing chamber 2 in a manner not shown. In any case, the laser 6 is suitable for removing passivation layers from the film 3, whereby, in principle, targeted processing of partial areas of the film 3, i.e., the material web to be processed, is also possible. Regardless of the size of the processed area, the laser 6 influences the microstructure, i.e., topography, as well as the chemical composition of the workpiece surface in order to adjust the desired electrochemical functionality of the film 3. A pump for conveying gaseous medium, which is also connected to the processing chamber 2, is designated 10.The protective gas atmosphere within the processing chamber 2 prevents oxidation of the workpiece processed by laser 6, i.e., the foil 3. An exhaust system that generates a laminar gas flow ensures that removed lithium does not redeposit on the foil 3.

[0034] The finished foil 3 wound on the roll 5 and having a metallic lithium surface can be formed into a lithium metal anode and installed in a secondary battery immediately after treatment by the processing device 1 as part of a series production process, wherein the installation of the metallic anode in the secondary battery can also take place under a protective gas atmosphere.

[0035] List of reference symbols

[0036] Processing device

[0037] processing chamber

[0038] film, material web

[0039] Coil, roll of film to be processed

[0040] Coil, roll of processed film

[0041] Laser

[0042] pipeline

[0043] compressed gas tank

[0044] fitting

[0045] pump

[0046] Substrat

[0047] coating, lithium layer

[0048] light guide

[0049] Beam deflection unit

[0050] Layer thickness

[0051] Total thickness

Claims

Patent claims 1 . Method for processing a material web (3) which has a substrate (11) made of a lithium-free carrier material and a lithium-containing surface, wherein the material web (3) is unwound from a first roll (4), exposed to laser radiation under protective gas and wound onto a further roll (5).

2. Method according to claim 1, characterized in that the material web (3) the surface of the material web (3) is formed by a lithium layer (12).

3. Method according to claim 1 or 2, characterized in that the substrate (11) is formed from nickel or copper.

4. Method according to one of claims 1 to 3, characterized in that the surface is continuously irradiated by laser (6).

5. Method according to one of claims 1 to 3, characterized in that the surface is exposed to pulsed laser radiation.

6. Processing device (1) for treating a material web (3) with a substrate (11) and a lithium-containing surface with laser radiation, comprising a processing chamber (2) which is designed to process the lithium surface by laser (6) from a first roll (4) and wound onto a second roll (5).

7. Processing device (1) according to claim 6, characterized in that the two rollers (4, 5) on which the unprocessed or the processed material web (3) is located, are arranged within the processing chamber (2).

8. Processing device (1) according to claim 6, characterized in that the two rollers (4, 5) on which the unprocessed and the processed material web (3) are located, respectively, are arranged outside the processing chamber (2).

9. A lithium metal anode for an electrochemical cell, comprising a metallic lithium surface machined with the machining device (1) according to claim 6 by the method according to claim 1.

10. A battery comprising a number of lithium metal anodes constructed according to claim 9.

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