Method and process arrangement for prelithiation of an anode for a lithium-ion battery cell

Abstract

The invention relates to a method for prelithiating an anode or anode precursor (10) for a lithium-ion battery cell, which is formed from a current collector foil (11) and an active material layer (13) coated thereon, wherein the active material layer (13) comprises a lithium reservoir (19) containing metallic lithium for carrying out the prelithiation, and wherein, during the prelithiation, positively charged lithium ions intercalate from the lithium reservoir (19) into the graphite structure of the active material layer (13). According to the invention, prelithiation is carried out by photon irradiation (24) onto the lithium reservoir (19), whereby electrons are released from the lithium reservoir (19), leaving behind positively charged lithium ions that intercalate into the relatively negative graphite structure of the anode material layer (13).

Description

[0001] The invention relates to a method for prelithiating an anode for a lithium-ion battery cell according to the preamble of claim 1 and a process arrangement according to claim 10.

[0002] In a lithium-ion battery cell, the anodes can have graphite as the active material, while the cathodes can have lithium metal oxide as the active material, forming a lithium source for the ion flow between the anodes and cathodes. To complete cell assembly, a formation process is carried out in which the battery cell is subjected to at least one charge / discharge cycle to fully form a solid electrolyte interface (SEL) layer and a cathode electrolyte interface (CEI) layer.

[0003] The following problems arise with such a battery cell: The first problem is that during formation, i.e., the first charge / discharge cycle, there is an irreversible loss of battery capacity. During formation, the lithium in the cathode and anode is used to create the Sel (Solid Electrolyte Interface) layer on the anode. This Sel layer is built up during the first charge and discharge cycle. Due to the loss of lithium atoms, the cell's capacity decreases by 10 to 15%. This capacity loss is irreversible.

[0004] A second problem is copper corrosion due to an overcharged anode. If the anode is overcharged, i.e., the potential reaches approximately 1.5 volts or more relative to a base voltage of Li / Li+, then the copper of the anode substrate corrodes. This leads to pitting in the copper substrate. As a result, the adhesion of the anode is reduced and the electronic conductivity is lowered.

[0005] A third problem concerns access to unused lithium and the handling of lithium-rich anodes: Conventional prelithiation processes utilize excess lithium because the lithium metal is incorporated into the active anode material. This increases process costs and complicates the handling of the lithium-rich anode. Since lithium metal is highly reactive under ambient conditions, a dry environment is crucial. Because current state-of-the-art prelithiation techniques utilize lithium metal, the entire electrode fabrication process, including coating, must take place in a dry environment. This increases energy costs and makes handling the lithium-rich anode very difficult.

[0006] A fourth problem concerns the fact that, in the prior art, lithium-coated graphite anode material is difficult to reuse. As the battery, and especially the anode, ages due to lithium plating, the battery loses its capacity very quickly. Even if the anode active material is still in good condition, the lithium plating makes it difficult to use. Such anodes are usually discarded as material waste because it is difficult to repair such lithium-coated anode active material.

[0007] From US patent 2022 / 0328803 A1, a method and apparatus for manufacturing electrodes used in energy storage devices are known. According to this patent, an electrode surface is activated for a pretreatment process to remove loosely held particles from the electrode surface. Furthermore, the method includes a post-treatment of a pre-lithiation layer to improve the subsequent bonding with passivation layers, as well as a post-treatment of the pre-lithiation layer to improve / accelerate the absorption of lithium into the underlying electrode material.

[0008] The problem is solved by the features of claim 1 or 10. Preferred embodiments of the invention are disclosed in the dependent claims.

[0009] The invention relates to a method for prelithiating an anode for a lithium-ion battery cell, which consists of a current collector foil and an active material layer coated thereon. In preparation for prelithiation, the active material layer has a lithium reservoir containing metallic lithium. During prelithiation, positively charged lithium ions are intercalated from the lithium reservoir into the graphite structure of the active material. According to the characterizing part of claim 1, prelithiation is carried out by photon irradiation. During photon irradiation, electrons are ejected from the metallic lithium of the lithium reservoir, while the positively charged lithium ions remain. These intercalate into the relatively negative graphite structure of the anode material layer.

[0010] In the present invention, the following measures are taken to provide a pre-lithiated anode: The anode coating (i.e., the active material layer of the anode) is wet- or dry-coated, then dried, and subsequently calendered and subjected to cutting operations, as is the case in conventional processes. According to the invention, a prelitharization process is carried out after calendering. Once the anode coating has been dried roll-to-roll in the drying station and then calendered, it enters the prelitharization zone, where lithium ions (i.e., not lithium metal) penetrate the carbon-based anode and charge the anode to a voltage of about 1 volt or less with respect to a base voltage of Li / Li+.

[0011] In one embodiment, the anode is temporarily bonded to a thin lithium metal foil (approximately 1 mm), with a polymer electrolyte (PEO) serving as the bonding and electrolyte medium. Both the anode and the lithium metal foil move at a constant linear speed within the prelitharization chamber. The prelitharization chamber can be heated to a temperature of up to 130°C to allow solvent evaporation.

[0012] Electromagnets or permanent magnets are positioned at the sides of the moving anode (along with the lithium-metal foil). The anode moves within the magnetic field along with the lithium-metal foil. Since both the lithium-metal foil and the anode are electrically conductive and move within the magnetic field, a Lorentz force acts on the lithium-metal foil and the anode, respectively. This causes electrons on both the lithium-metal foil and the anode to move towards the outer surface of the anode. An excess of electrons builds up on the outer surface of the anode, i.e., on the lithium-metal foil. This leads to the accumulation of a negative charge on the outer surface and thus to the generation of an induced voltage. Because both the lithium-metal foil and the anode are constantly moving within the magnetic field, a Lorentz force is continuously exerted, generating an excess of electrons on the outer surface of the electrode and the lithium-metal foil.The electron excess depends on the size of the magnetic field and the speed of the anode.

[0013] In the next phase, the lithium metal foil is irradiated with UV rays. Because UV rays have a very short wavelength, they possess higher energy than other light rays. When photons strike the lithium metal foil, electrons are emitted from it. The kinetic energy of the photons is sufficient to detach the electrons from the atomic lattice and then propel them away at a sufficient speed so that they cannot return to the lithium metal foil.

[0014] Since electrons are already present in excess on the outer surface of the lithium metal foil due to the Lorentz force, it is easy to remove the excess electrons through photon collisions. This removal of excess electrons leads to an electron deficiency. Due to this electron deficiency, more electrons migrate from the underside of the lithium metal foil to the outer surface (due to the Lorentz force). This results in an increased number of positive lithium ions being formed inside the lithium metal foil.

[0015] Excess lithium ions beneath the lithium-metal foil migrate to the carbon-based anode active material, which carries a stronger negative charge. This means that the lithium ions intercalate within the carbon and / or form a covalent lithium-carbon compound (C6Li). This accelerates prelithiation through a combination of the Lorentz force and electron emission from photon irradiation. The polymer electrolyte facilitates the transfer of lithium ions to the anode. The lithium ions are not forced into the carbon by thermal or mechanical energy; this occurs solely through solid-state diffusion. After prelithiation in the dry zone, the anode is wound. The polymer electrolyte further aids lithium ion diffusion into the carbon.

[0016] At the end of the prelitharization zone, the lithium metal foil is removed from the anode. The removed lithium metal foil returns to its original position and is reapplied to the anode. It is important that a polymer electrolyte is applied between the anode and the lithium metal foil. The prelitharization chamber is maintained at a maximum temperature of 130°C. This temperature ensures solvent removal, high conductivity of the polymer electrolyte (PEO), and easy electron release from the lithium metal foil, as the electrons are already in an unstable state due to their high internal energy. This reduces the energy required for UV radiation.

[0017] Once the pre-lithiated anode, which is still supplied as a continuous strip, is complete, it is rewound and stored in a dry room. It is important to note that the lithium in the anode is not present as lithium metal, but rather as a covalent bond with carbon. This means it is less corrosive than in other pre-lithiation processes.

[0018] The inventive method can also be used to reuse an anode coated with lithium by lithium plating as a renewed anode for a new battery cell. In contrast to the first embodiment, a separate lithium metal foil is not required here, since the lithium is already present on the anode as a lithium layer. In the prelitharization process, the lithium metal is converted into lithium ions. The lithium ions then react with the carbon of the anode and form covalent bonds. The lithium ions are also formed by photon collisions accelerated by the Lorentz force.

[0019] As mentioned above, the lithium-metal foil is applied to the active material layer of the anode via an interlayer of polymer electrolyte. The electrolyte (in particular PEO) temporarily creates an adhesive bond and eliminates gaps between the anode surface and the lithium-metal foil. According to the invention, the lithium-metal foil experiences a Lorentz force, which moves the electrons on the outer surface of the lithium-metal foil. This results in an excess of electrons on the outer surface of the lithium-metal foil. UV radiation is directed onto the lithium-metal foil, causing electrons to be released from it. This creates an electron deficiency on the surface of the lithium-metal foil. Consequently, more electrons migrate from the interior of the lithium-metal foil to the surface. Additionally, the Lorentz force continues to act, also moving electrons to the outer surface of the lithium-metal foil.This leads to an excess of positively charged lithium ions within the lithium surface. These lithium ions migrate through the electrolyte (PEO) and are incorporated into the anode, or intercalated. The electrolyte (PEO) exhibits high lithium-ion conductivity at 130°C. The anode's active material can also contain a PEO electrolyte or a lithium-ion-conducting binder, such as CMC-Li or LiPPA. This ensures that the lithium ions are incorporated into the anode's active material.

[0020] At the end of the prelitharization chamber, the lithium metal foil is peeled off the anode surface. The lithium metal foil is then returned to the inlet of the prelitharization chamber so that it can be reapplied to the anode surface.

[0021] In an alternative version, the process can also be carried out without lithium metal foil. If the anode surface has a lithium plating, this plating is used for lithium intercalation into the anode surface.

[0022] In another alternative embodiment, the process can also be carried out when metallic lithium, as a nanopowder with a PEO binder, is mixed with the active material of the anode. Here, lithium metal powder is used for lithium intercalation.

[0023] It is also possible to use other state-of-the-art liquid electrolytes such as ethylene carbonate, diethylene carbonate, dimethylene carbonate, propylene carbonate, and ethylene methyl carbonate instead of PEO. These electrolytes are mixed with the anode material.

[0024] Another possibility is to mix lithium nanopowders together with the lithium-conducting binder CMC-Li and LiPPA and the polymer electrolyte (PEO) with the active anode material by dry mixing and dry coating. This lithium metal within the active anode material is used as a lithium-rich anode material for the pre-lithiation process described above.

[0025] However, in this version, the lithium is present in a metallic form that is unusable. When this anode material, embedded in lithium metal, enters the prelitharization chamber, as explained above, the lithium metal is converted into positively charged lithium ions. These then form covalent bonds with carbon. In this case, no lithium metal foil is required, since the lithium metal is already present in the active anode material before it enters the prelitharization chamber.

[0026] Another option is to use UV-curing resins in conjunction with an electrolyte (such as polymer electrolyte PEO). In this method, after the lithium metal foil is removed, UV radiation is additionally directed onto the binder. This cures the binder. This cured binder protects against anode swelling. Swelling in the anode normally occurs due to lithium deposits.

[0027] The option of incorporating lithium metal into the active anode material during dry mixing and dry coating is less advisable. It is less advantageous because the lithium metal is difficult to handle within the anode material. The entire electrode process must be carried out in a dry environment. Furthermore, the lithium particles, located deep within the active material, are not exposed to UV radiation, resulting in lower electron emission.

[0028] Overall, the invention offers the following advantages: During pre-lithiation, the anode is charged to less than 1 volt relative to a base voltage of Li / Li+. This prevents copper corrosion during electrolyte exposure. Pre-lithiation reduces the irreversible losses of the first formation cycle, thereby increasing the Coulombic efficiency. Pre-lithiation is performed after calendering and is therefore easy to handle. Subsequent post-calendering processes are carried out in a dry environment, significantly simplifying the handling of the pre-lithiated anode. Pre-lithiation is based on the principle of lithium-ion intercalation, resulting in stronger covalent bonds than in prior art pre-lithiation processes, where the lithium is present in a metallic phase. In this invention, the lithium is not in the metallic phase.The lithium coating can be removed from the anode material using this method, allowing the lithium-coated anode to be converted back into a reusable anode. This means that this method can be used for anode reuse. There is no need for excess lithium. The lithium is only reduced by the foil that is deposited in the anode material. This means that no excess lithium is required. The lithium deposition process is carried out electrochemically and can be easily controlled by the intensity of the UV radiation and the density of the magnetic field. The process is carried out in a dry room in the pre-lithition chamber. Here, the temperature is maintained at a maximum of 130°C, which also helps to remove any residual solvent (water) from the anode.Therefore, the prelithiation process can replace the drying process that is normally performed after calendering. Since intercalation is a solid-state diffusion process, lithium is also intercalated into hard carbon, which typically requires a low current (C-rate) to intercalate lithium. This means that the available capacity of the anode increases. Not only graphite but also hard carbon contributes to the capacity. The electrolyte is embedded in the anode material. This helps to fill the pores of the anode with conductive lithium-ion electrolyte. This reduces tortuosity. The proposed conductive lithium-ion binder also contributes to the conductivity of the lithium ions.

[0029] The following are key aspects of the invention highlighted in detail: The removal of the electrodes from the lithium reservoir can be facilitated by the following measures. According to a first aspect, the anode is moved through a magnetic field at a process velocity during pre-lithiation, thereby generating a Lorentz force acting on the anode. This force displaces the electrons to the outer surface of the anode exposed to photon irradiation. To prevent recombination of the electrons released during photon irradiation and the positively charged lithium ions, it is preferred that the anode be positioned within the electric field of a capacitor. In this way, the released electrodes are accelerated towards the positive capacitor electrode.The process temperature during pre-lithiation is significantly higher compared to a normal room temperature, and can, for example, be in the range of 130°C, which further supports the release of electrons from the lithium reservoir.

[0030] An embodiment of the invention is described below with reference to the accompanying figures: They show: Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 to Fig. 8 different views, each illustrating the process steps for pre-lithiation of the anode.

[0031] In the Fig. Figure 1 is a block diagram of a process arrangement for manufacturing an anode for a lithium-ion battery cell, indicated to the extent necessary for understanding the invention. Accordingly, the process arrangement comprises, in a process sequence, a coating station 1, a drying station 3, a calendering station 5, a prelitharization station 7, and a cutting / punching station 9. In a method for manufacturing the anode, an uncoated conductive foil 11 ( Fig. 2 or Fig. 3) provided as a continuous web, which is guided through stations 1, 3, 5, 7, 9 at a continuous process speed in one process direction FR. In coating station 1, the current collector foil 11 is coated on both sides with an active material layer 13 made of graphite, forming a composite web 10 as an anode precursor. Subsequently, the current collector foil 11, or the composite web 10, passes through drying station 3 to dry the two active material layers 13. In the downstream calendering station 5, the porosity of the dried active material layers 13 is adjusted.

[0032] Following the calender station 5, the composite track 10 passes through a prelitharization chamber 15 ( Fig. 2, Fig. 3 to Fig. 4) the prelitharization station 7, the structure and operation of which are described below. In the further course of the process, the composite web 10 is transferred to the cutting / punching station 9, in which the anode is separated by punching and / or cutting operations.

[0033] The Fig. 2, Fig. 3 to Fig. 4 each show an entrance area ( Fig. 2), a central area ( Fig. 3) and an exit area ( Fig. 4) the prelitharization chamber 15, through which the composite web 10 is moved in the manufacturing direction FR at the process speed. The composite web 10 consists of the conductive foil 11 and the active material layers 13 coated on both sides of the conductive foil 11. In the entrance area ( Fig. 2) In the prelitharization chamber 15, the composite web 10 unwound from a winding roller 14 is coated on both sides with lithium metal foils 19 and an intermediate polymer electrolyte 20 onto the respective active material layer 13 by means of pressure rollers 17. The polymer electrolyte 20 is applied according to the Fig. 2. Lithium is injected by means of nozzles 16 into the wedge-shaped gap between the lithium metal foils 19 that converge with the composite web 10. The two lithium metal foils 19 form a lithium reservoir for the pre-lithiation that takes place in the further course of the process.

[0034] For the purpose of carrying out prelithiation, the prelithiation chamber 15 has a magnet arrangement 21 ( Fig. 3), a UV lamp 23 ( Fig. 5) and a capacitor 25 ( Fig. 5) in the prelithiation process. In the prelithiation, positively charged lithium ions are generated in the lithium metal foils 19, which intercalate from the respective lithium metal foil 19 into the graphite structure of the active material layer 13. For this purpose, the composite sheet 10 is moved through a magnetic field of the magnet arrangement 21, thereby exerting a magnetic field strength B on the composite sheet 10. The magnetic field strength B is in the Fig. 3 oriented transversely to the manufacturing direction FR, wherein the two magnetic poles 27, 29 are positioned in transverse alignment in the view shown from above on both sides of the conductor foil 11; that is, each magnetic pole 27, 29 is arranged with a transverse offset to the respective longitudinal edge of the composite track 11.

[0035] In this way, the composite track 10 running through the magnet arrangement 21 is built up according to the one described in the Fig. The left-hand rule illustrated a Lorentz force F. Lon, by means of which the electrons in the composite path 10 are moved to the anode outer side facing the UV emitter 23, i.e. the lithium metal foil 19, as described in the Fig. 5 is indicated. According to the Fig. 5 or Fig. Electrons move from the active material layer 13 and the lithium metal foil 19 towards the side of the composite track 10 facing the UV lamp 23, creating an electron surplus there. Thus, there is an electron surplus on the outer surface of the composite track 10 facing the UV lamp 23. Therefore, electrons can be released from the lithium metal foil 19 by means of photon irradiation 24 by the UV lamp 23, while positively charged lithium ions remain in the lithium metal foil 19. These intercalate into the relatively negative graphite structure of the anode material layer 13, according to the Fig. 7 forming C6Li, in which six carbon atoms absorb a positively charged lithium ion and an electron.

[0036] To prevent recombination of the electrodes extracted from the lithium metal foils 19 with the positively charged lithium ions, the magnetic field ( Fig. 3) an electric field of the capacitor 25 ( Fig. 5) superimposed. Accordingly, the electrons released by means of the photon radiation 24 are accelerated in the direction of the positive capacitor electrode 31 of the capacitor 25.

[0037] Through the interaction of the UV emitter 23 with the capacitor 25 and the magnet arrangement 21, electrons are constantly released from the surface of the lithium metal foil 19, leading to an increased formation of lithium ions within the lithium metal foil 19. These lithium ions migrate through the polymer electrolyte 20 towards the anode active material.

[0038] After prelithiation, the two lithium metal foils 19 are removed in the exit area of ​​the prelithiation chamber 15 by means of a scraper 18 ( Fig. 4) is again detached from the active material layers 13 of the composite web 10. Subsequently, the composite web 10 is wound onto a winding reel 26 and transferred to the cutting / punching station 9. Reference symbol list 1 coating station 3 drying stations 5 Calendering station 7 Prelithi station 9 Cutting / Punching Station 10 Combined railway 11 Conductor foil 13 Active material layer 14 Unwinding roller 15 Prelithary chamber 16 nozzle 17 printing rollers 18 wipers 19 Lithium metal foil 20 Polymer electrolyte 21 Magnet arrangement 23 UV lamps 24 photon irradiation 25 Capacitor 26 winding roller 27, 29 magnetic poles 31 Capacitor electrode FR Manufacturing direction F L Lorentz force B magnetic field strength 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] US 2022 / 0328803 A1

[0007]

Claims

[1] Method for prelithiating an anode or anode pre-product (10) for a lithium-ion battery cell, which is formed from a current collector foil (11) and an active material layer (13) coated thereon, wherein the active material layer (13) has a lithium reservoir (19) containing metallic lithium for carrying out the prelithiation, and wherein, during the prelithiation, positively charged lithium ions intercalate from the lithium reservoir (19) into the graphite structure of the active material layer (13), characterized by , that to carry out prelithiation, photon irradiation (24) is applied to the lithium reservoir (19), whereby electrons are released from the lithium reservoir (19) and positively charged lithium ions remain, which intercalate into the relatively negative graphite structure of the anode material layer (13). [2] Method according to claim 1, characterized by, that during prelithiation the anode or the anode pre-product (10) is moved through a magnetic field (B) at a process velocity, thereby building up a Lorentz force (F) acting on the anode L ), by means of which electrons in the anode or the anode precursor (10) are displaced to an anode outer surface exposed to photon irradiation (24), thereby supporting the removal of the electrodes from the lithium reservoir (19). [3] Method according to claim 1 or 2, characterized by, that to avoid recombination of the electrons released from the lithium reservoir (19) and the positively charged lithium ions, the anode or the anode pre-product (10) is arranged in the electric field of a capacitor (25) in which the released electrons are accelerated towards the positive capacitor electrode (31), and / or that the process temperature during pre-lithiation is greatly increased compared to room temperature, in particular to a range of 130°C, thereby aiding the release of electrons from the lithium reservoir (19). [4] Method according to any one of the preceding claims, characterized by , that the photon irradiation (24) is carried out by high-energy UV radiation with a very short wavelength to assist in the release of electrons from the lithium reservoir (19). [5] Method according to any one of the preceding claims, characterized by, that the prelithiation is integrated into a process sequence for the manufacture of the anode, in which the current collector foil (11) passes through the process sequence as an endless web, which has the following process steps: - Coating, in which the current collector foil (11) is coated with the active material, forming a composite track (10) as an anode pre-product, - Drying, in which the active material layer (13) of the composite web (10) is dried, - Calendering, in which the porosity of the dried active material layer (13) of the composite web (10) is adjusted, - Cutting / punching, in which the composite web (10) is separated to the anode, and in particular that pre-lithiation takes place after calendering. [6] Method according to any one of the preceding claims, characterized by, that the lithium reservoir (19) is a lithium layer coated on the active material layer (13), and that in particular the lithium layer (19) is a lithium metal foil which is applied to the active material layer (13) of the anode or the anode pre-product (10) in preparation for pre-lithiation, in particular with an intermediate polymer electrolyte (20), such as PEO, and that in particular the lithium metal foil (19) is removed from the active material layer (13) after pre-lithiation has been carried out. [7] Method according to claim 6, characterized by , that the lithium layer is a deposition of metallic lithium on the active material layer (13) resulting in particular from lithium plating, which is created during the charging / discharging process in battery cell operation. [8] Method according to claim 6, characterized bythat the lithium layer is a composite layer in which metallic lithium in powder form, especially as nanopowder, is embedded in a binder material, especially PEO. [9] Method according to any one of claims 1 to 4, characterized by that the lithium reservoir is mixed directly into the active material of the anode as metallic lithium powder, especially nanopowder. [10] Process arrangement for carrying out a method according to one of the preceding claims, in particular with a prelithiation station (7) having a prelithiation chamber (15) in which the prelithiation can be carried out.

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