Removal of a molten lithium contamination layer to improve wettability on current collectors

Abstract

A method for removing impurities from a bath comprising molten lithium comprises melting bulk lithium in a bath to form molten lithium comprising an impurity layer; immersing one end of either a metal foam or a metal mesh into the bath; moving either the metal foam or the metal mesh horizontally through the bath to remove the impurity layer; and removing either the metal foam or the metal mesh from the bath.

Description

INTRODUCTION

[0001] The information contained in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.

[0002] The present disclosure relates to methods for removing an impurity layer from molten lithium to improve wettability on current collectors for battery cell electrodes.

[0003] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, comprise one or more electric machines and a battery system with one or more battery cells, battery modules, and / or battery packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving.

[0004] Battery cells comprise one or more cathode electrodes, anode electrodes, and separators arranged in a battery cell housing. The cathode electrodes comprise a cathode active material layer arranged on a cathode current collector. The anode electrodes comprise an anode active material layer arranged on an anode current collector. SUMMARY

[0005] A method for removing impurities from a bath comprising molten lithium comprises melting bulk lithium in a bath to form molten lithium comprising an impurity layer; immersing one end of either a metal foam or a metal mesh into the bath; moving either the metal foam or the metal mesh horizontally through the bath to remove the impurity layer; and removing either the metal foam or the metal mesh from the bath.

[0006] For other features, either the metal foam or the metal mesh is made of a material selected from the group consisting of aluminum, magnesium, and their alloys. Either the metal foam or the metal mesh comprises the metal foam. Either the metal foam or the metal mesh comprises the metal mesh. The metal mesh comprises a plurality of mesh layers that are stacked.

[0007] For other features, the metal foam or metal mesh has a thickness in the range of 3 to 5 mm.

[0008] In other features, the contaminant layer has a thickness, and either the metal foam or the metal mesh is inserted under a surface of the bath that is greater than or equal to the thickness of the contaminant layer.

[0009] In other features, the contamination layer has a thickness in the range of 1 mm to 3 mm below a surface of the bath.

[0010] In other features, the method includes coating an anode current collector in the bath after removing the contaminant layer.

[0011] A system for coating anode current collectors with molten lithium comprises a bath containing molten lithium with a contaminant layer. A conveyor assembly comprises either a continuous metal mesh or a continuous metal foam arranged around rollers. The continuous metal foam or mesh is made of a material selected from the group consisting of aluminum, magnesium, and their alloys. The conveyor assembly is arranged such that either the continuous metal mesh or the continuous metal foam is inserted below a surface of the bath that is greater than or equal to the thickness of the contaminant layer.

[0012] In other features, a sensor is configured to detect the contamination level of the contaminant layer. A positioning device is configured to insert and remove the conveyor assembly from the bath. A controller is configured to remove the conveyor assembly from the bath in response to the contamination level being below a predetermined contamination level.

[0013] In other features, a current collector supply assembly includes a current collector roller configured to supply a current collector, a roller immersed in the bath, and a roller configured to receive an anode electrode. A sensor is configured to detect a contamination level of the contaminant layer.

[0014] In other features, a positioning device is configured to insert and remove the current collector feed assembly from the bath. A controller is configured to remove the conveyor assembly from the bath in response to the contamination level exceeding a predetermined contamination level. The continuous metal foam or continuous metal mesh comprises the continuous metal mesh. The continuous metal mesh comprises a plurality of mesh layers that are stacked.

[0015] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are for illustrative purposes only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a side cross-sectional view of an example of a battery cell including anode electrodes, cathode electrodes, and separators according to the present disclosure; Fig. 2A is a plan view of an example of an anode current collector according to the present disclosure; Fig. 2B is a side cross-sectional view of an example of an anode electrode including a lithium-coated grid current collector according to the present disclosure; Fig. Figure 3 is a side cross-section of an example of bulk lithium (such as lithium foil or rod) with a native oxide layer prior to melting; Fig. Figure 4 is a side cross-section of an example of a bath comprising molten lithium with an upper layer of impurities; Fig. 5A and Fig. 5B are plan and perspective views of examples of metal mesh and foam, respectively, according to the present disclosure; Fig. 6 is a side cross-sectional view of an example of a bath comprising molten lithium, wherein an upper layer comprises impurities removed by the metal mesh or foam according to the present disclosure; Fig. 7 is a flow diagram of an example of a method for removing impurities from a molten lithium bath according to the present disclosure; Fig. 8 is a side cross-sectional view of an example of a molten lithium bath having a top layer comprising impurities being removed by a conveyor comprising continuous metal mesh or continuous metal foam in accordance with the present disclosure; Fig. 9 is a side cross-sectional view of an example of a bath including an anode current collector incorporated into the bath of Fig. 8 is introduced; and Fig. 10 is a side cross-sectional view of an example of a bath comprising molten lithium, wherein an upper layer comprises impurities that are removed by a conveyor comprising continuous metal mesh or continuous metal foam and an anode current collector introduced into the bath in accordance with the present disclosure.

[0017] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0018] While the present disclosure relates to methods for removing a contaminant layer from a bath comprising molten lithium before coating anode current collectors with the molten lithium in the bath, the method may also be used for removing a contaminant layer from a lithium bath prior to coating other types of substrates.

[0019] The present disclosure relates to a method for removing a contaminant layer from the surface of a bath comprising molten lithium prior to wetting the lithium on a current collector for an electrode of a battery cell. Lithium metal is highly reactive with oxygen, moisture, and nitrogen. A native surface oxide layer forms on commercially available lithium metal foils / rods. When lithium is melted, a layer of contaminants forms on the surface layer of the molten lithium. The contaminants are rich in nitrides and oxides / carbonates, which can develop due to inadequate control of nitrogen or oxygen in a glove-box environment.

[0020] The impurities found on the surface of the molten lithium are difficult to remove from the melt pool. If the impurity layer forms, the molten lithium in the pool cannot be used to coat the anode current collectors. Therefore, the impurities must be removed quickly and effectively to ensure both the production speed and the quality of the anode electrode.

[0021] A method for removing contaminants according to the present disclosure includes using a metal mesh / foam to remove or skim contaminants from a molten lithium bath. In some examples, the metal mesh / foam is made of a material (such as aluminum (Al), magnesium (Mg), and their alloys) that is more reactive with the contaminants than lithium. For example, magnesium is more stable with oxides than lithium. Therefore, magnesium is a good material for removing oxide-based contaminants. Both aluminum and magnesium are more stable with nitrides than lithium. Therefore, aluminum, magnesium, and their alloys are good materials for removing nitride-based contaminants.

[0022] In some examples, the metal in the metal foam / mesh reacts with both the lithium melt and impurities on a surface layer of the molten lithium. An interfacial reaction between the lithium / impurity and the metal mesh / foam causes a layer of lithium, along with the impurities or slag, to adhere to the metal mesh / foam.

[0023] The pores of the metal mesh / foam provide additional space and surface area to trap the contaminants. This process provides an effective way to quickly remove contaminants from the lithium bath and expose the liquid lithium for successful wetting onto current collectors in the manufacture of lithium anode electrodes.

[0024] In particular, the method according to the present disclosure uses porous metal (e.g., aluminum, magnesium, and their alloys) to remove contaminants from the surface of a molten lithium bath. The metal reacts spontaneously with the surface lithium layer and undergoes a surface reaction with the components of the contaminant layer, such as the lithium-rich nitrides and / or oxides in the contaminant layer.

[0025] In some examples, the metal used comprises pure aluminum or an aluminum alloy that is soluble in lithium and exhibits higher nitride stability than lithium. Aluminum reacts spontaneously with both lithium and the impurities (e.g., oxide or nitride) in the impurity layer. In some examples, the metal used comprises pure magnesium or a magnesium alloy that is soluble in lithium and exhibits higher oxide and nitride stability than lithium. Magnesium reacts spontaneously with lithium as well as with the impurities (oxide or nitride) in the impurity layer.

[0026] In some examples, the metal is in the form of a metal mesh or a metal foam. The porous structure of the metal mesh / foam helps to capture and remove the impurities. In some examples, the metal mesh / foam is about 3-5 mm thick so that it can be partially immersed in the molten lithium bath. In some examples, the thickness of the impurity layer is in the range of 1 to 3 mm. In some examples, the metal mesh / foam is immersed about 1 to 3 mm below the surface of the bath to skim the surface of the lithium layer along with any surface impurities. In some examples, the metal mesh / foam is immersed slightly below the surface of the bath to skim the surface of the lithium layer along with any surface impurities and to minimize reaction with the molten lithium.

[0027] In some examples, the metal mesh / foam is made of anodized aluminum. Anodizing forms a layer of aluminum oxide (Al2O3). The aluminum oxide layer prevents the aluminum from lithiating, while triggering an interfacial reaction between the oxide and the lithium, causing the surface lithium layer (along with the impurities) to stick to the metal mesh / foam.

[0028] In some examples, a production line for anode electrodes is equipped with a bath cleaning assembly. In some examples, interchangeable lithium plating and contaminant removal assemblies are used. In other examples, the production line includes both lithium plating and contaminant removal assemblies to continuously remove the contaminant layers during production.

[0029] With reference now to Fig. 1, a battery cell 10 comprises C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order within a battery cell core 12, where C, S, and A are integers greater than zero. The C cathode electrodes 20-1, 20-2,..., and 20-C comprise cathode active material layers 24 arranged on one or both sides of a cathode current collector 26.

[0030] The A anode electrodes 40-1, 40-2, ..., and 40-A include anode active material layers 42 disposed on one or both sides of the anode current collectors 46. In some examples, the A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charging / discharging. In some examples, the anode active material layer 42 includes lithium (deposited using molten lithium) on the anode current collector 46 (e.g., a mesh such as copper).

[0031] In some examples, the cathode active material layers 24 and / or the anode active material layers 42 comprise coatings comprising one or more active materials, one or more conductive additives, and / or one or more binder materials applied to the current collectors (e.g., using a wet or dry roll-to-roll process).

[0032] In some examples, the cathode current collector 26 and / or the anode current collector 46 comprise a metal foil, a metal mesh, perforated metal, three-dimensional (3D) metal foam, and / or expanded metal. In some examples, the current collectors are made of one or more materials selected from a group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or their alloys. The outer tabs 28 and 48 are connected to the current collectors of the cathode electrodes and anode electrodes, respectively, and can be arranged on the same or different sides of the battery cell core 12. The outer tabs 28 and 48 are connected to the terminals of the battery cells.

[0033] With reference now to Fig. 2A and Fig. 2B shows an example of an anode current collector 46. In Fig. 2A shows the anode current collector 46. In Fig. 2B, the anode electrode 40 includes the anode current collector 46 coated with a lithium layer 50.

[0034] With reference now to Fig. 3 and Fig. 4, a bath of molten lithium can be used to coat the anode current collector. In Fig. 3, melting bulk lithium 60 (e.g., a foil or rod) produces molten lithium (desired) and impurities (undesired). Bulk lithium 60 is shown prior to melting and includes a lithium metal body 64 with a native oxide layer 66. In Fig. 4 comprises a bath 82 of molten lithium 84. A layer of impurities 86 rises to the surface and comprises impurities that should be removed from the bath 82 before coating the anode current collectors.

[0035] Lithium metal is highly reactive with oxygen, moisture, and nitrogen. Commercially available lithium metal foils / rods exhibit a native surface oxide. When bulk lithium is melted in a crucible, the surface of the molten lithium is covered with a sticky layer of impurities. An impurity layer (rich in nitrides and oxides / carbonates) can form on the molten lithium due to inadequate control of N2 or O2 in a glove box environment. The impurities on the surface of molten lithium are extremely sticky to the underlying lithium and are difficult to remove from the melt pool.

[0036] Analysis of the impurity layer by X-ray photoelectron spectroscopy (XPS) indicates that the impurity layer comprises a mixture of lithium carbonate (LiCO3), lithium oxide (Li2O), and lithium nitrate (Li3N). Impurities must be removed from the surface of the molten lithium bath to enable uniform wetting of the "pure" lithium onto the anode current collector. The impurities prevent direct contact between the anode current collector and the lithium, thereby hindering wetting onto the anode current collector. The impurities adhere to the anode current collector and degrade the quality of the anode electrode. Impurities adhering to the anode electrode create a rough anode surface and uneven lithium deposition, which is unsustainable for practical production applications. The impurity layer is difficult to break up, capture, and / or remove with tools.The contaminants do not stick to tools made of materials such as stainless steel.

[0037] With reference now to Fig. 5A to 6, a metal net 110 ( Fig. 5A) or a metal foam 114 ( Fig. 5B) can be used to remove impurities from a bath 150. In Fig. 6, the bath 150 comprises molten lithium 154, and a layer 158 comprises impurities. A metal mesh or foam 162 is introduced into the bath and moved horizontally through the bath 150 to remove the impurities in layer 158.

[0038] The metal (e.g., aluminum, magnesium, and / or alloys) reacts with both the lithium melt and the nitride components in the impurity layer. The interfacial reaction between the lithium / impurity and the metal causes the surface of the lithium layer, along with the slag, to adhere to the metal mesh / foam. The pores of the metal mesh / foam provide additional space and surface area to capture the impurities. The impurities in the bath can be quickly removed by spontaneous reaction with the metal mesh / foam. In some examples, impurities in the bath can be removed in less than 5 seconds.

[0039] In some examples, the metal foam / mesh comprises aluminum foam or mesh. However, other metals may also be used. In some examples, the metal used for the foam / mesh forms more stable oxide and / or nitride bonds than lithium. The metal of the foam / mesh reacts spontaneously with the slag and lithium (e.g., metal-lithium phase diagrams indicate the solubility of lithium in the metal), and the metal does not dissolve into the lithium (e.g., metal-lithium phase diagrams indicate intermetallic formation with lithium, which prevents the dissolution of the metal into the lithium).

[0040] With reference now to Fig. 7 shows a method for removing contaminants. At 210, a metal foam or mesh made of aluminum, magnesium, or their alloys is provided. In some examples, multiple layers of metal mesh are stacked together to increase strength / rigidity. At 214, a portion of the metal mesh or foam is immersed in the bath. At 218, the metal mesh or foam is moved horizontally through the bath to remove the slag. At 222, the metal mesh or foam is removed from the bath. After removing the contaminants, the bath is used to coat anode current collectors.

[0041] With reference now to Fig. 8 and Fig. 9, a conveyor 319 (for removing impurities) and a current collector feed assembly 358 (for feeding the anode current collector) are alternately immersed in a bath 310. In Fig. 8, the bath 310 comprises molten lithium 314 having an upper layer 318 comprising impurities. A conveyor 319 comprises a continuous metal mesh or foam belt 326 suspended from rollers 322 connected to a frame 323. The continuous metal mesh or foam belt 326 is passed around the rollers 322 and through at least one upper contaminant layer of the bath to remove the contaminants in the upper layer 318. In some examples, a brush 338 is used to remove contaminants from the continuous metal mesh or foam belt 326. In some examples, one or more sensors 340 are used to detect the impurity content. In some examples, in response to the sensor 340, a positioning device 337 is actuated to remove the conveyor 319 when the contamination level falls below a predetermined value.A controller 339 may be used to monitor the sensor 340 and to control the conveyor 319.

[0042] In Fig. 9, after the contaminants in the upper layer 318 have been removed, the conveyor 319 is removed from the bath 310 by the positioning device 337. A current collector feed assembly 358 with a frame 361 is used to introduce the anode current collector into the bath 310. A roller 360 attached to the frame 361 feeds an anode current collector 362 around rollers 363 and through the molten lithium 314 to coat the anode current collector 362 and form an anode electrode 366. The anode electrode 366 is collected on a roller 368. One or more sensors 340 can be used to monitor the level of contamination in the bath 310 or on the anode current collector or electrode. A controller 373 monitors one or more of the sensors 340 to determine a contamination level in the bath.When the contamination level in the bath rises above a predetermined level, a positioning device 371 removes the current collector feed assembly 358. In some examples, the positioning devices 337 and 371 are separate devices. In some examples, the positioning devices 337 and 371 are combined into a single device.

[0043] In some examples, the contaminant or slag layer is removed from the bath using the metal mesh / foam of conveyor 319. Then, conveyor 319 is removed from the bath, and current collector feed assembly 358 is at least partially submerged. The anode current collector is passed through the molten lithium and becomes coated with lithium. One or more sensors are used to monitor the contaminant uptake in the anode electrode. If the contamination level is greater than a predetermined threshold, current collector feed assembly 358 is removed, and conveyor 319 is used to remove the contaminant layer.

[0044] In some examples, the sensor 340 is selected from a group consisting of a vision system (e.g., for detecting changes in color, texture, or other visible parameters), a surface reflectance sensor (for detecting changes in reflectivity), an eddy current array (for detecting changes in electrical conductivity), an inline X-ray fluorescence sensor, and a hyperspectral imaging system.

[0045] Sensors 340 can be used to provide inline feedback-controlled non-destructive evaluation (NDE) to monitor the quality of the molten lithium pool and the dip-coated anode and detect contaminants. In some examples, one or more sensors 340 provide continuous, wide-area detection of the reflectivity of the surface of the molten lithium pool during and / or after the contaminant removal process and / or during the dip-coating process.

[0046] With reference now to Fig.10, the conveyor 319 and the current collector feed assembly 358 can be used in the same bath to provide continuous production. A hopper 410 is used to feed bulk lithium into the bath 310. Contaminants rise to the surface and are removed by the metal mesh or foam belt 326 of the conveyor 319, which is disposed adjacent to the hopper 410. The current collector feed assembly 358 is disposed adjacent to the conveyor 319 to guide the anode current collector through the bath 310.

[0047] The above description is merely illustrative and is not intended to limit the disclosure, its application, or uses in any way. The broad teachings of the disclosure may be embodied in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, since other changes will become apparent after studying the drawings, the patent specification, and the following claims. It is understood that one or more steps within a method may be performed in different orders (or simultaneously) without altering the principles of the present disclosure.Furthermore, although the embodiments are each described above as having specific features, any one or more of these features described with respect to one embodiment of the disclosure may be implemented and / or combined with features of any of the other embodiments, even if this combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and interchange of one or more embodiments remains within the scope of this disclosure.

[0048] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "beside," "on top of," "over," "below," and "disposed." If a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements between the first and second elements, or an indirect relationship, with one or more intervening elements (either spatial or functional) between the first and second elements.As used herein, the term “A, B and / or C” should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR and should not be understood as “at least one of A, at least one of B and at least one of C”. legend

[0049] In the drawings, Ctrl stands for Strg, or control.

Claims

[1] A method for removing impurities from a bath comprising molten lithium, comprising: Melting bulk lithium in a bath to form molten lithium comprising an impurity layer; Immersing one end of either a metal foam or a metal mesh into the bath; moving either the metal foam or the metal mesh horizontally through the bath to remove the contaminant layer; and Removing either the metal foam or the metal mesh from the bath. [2] The method of claim 1, wherein either the metal foam or the metal mesh is made of a material selected from a group consisting of aluminum, magnesium and their alloys. [3] The method of claim 2, wherein either the metal foam or the metal mesh comprises the metal foam. [4] The method of claim 2, wherein either the metal foam or the metal mesh comprises the metal mesh. [5] The method of claim 4, wherein the metal mesh comprises a plurality of mesh layers stacked. [6] A method according to claim 1, wherein either the metal foam or the metal mesh has a thickness in the range of 3 to 5 mm. [7] The method of claim 1, wherein: the impurity layer has a thickness, and either the metal foam or the metal mesh is inserted under a surface of the bath that is greater than or equal to the thickness of the contaminant layer. [8] The method of claim 1, wherein the contaminant layer has a thickness in the range of 1 mm to 3 mm below the surface of the bath. [9] The method of claim 1, further comprising coating an anode current collector in the bath after removing the contaminant layer. [10] System for coating anode current collectors with molten lithium, comprising: a bath comprising molten lithium comprising an impurity layer; and a conveyor arrangement comprising either a continuous metal mesh or a continuous metal foam arranged around rollers, wherein either the continuous metal foam or the continuous metal mesh is made of a material selected from the group consisting of aluminum, magnesium and their alloys, and wherein the conveying arrangement is arranged such that either the continuous metal mesh or the continuous metal foam is inserted below a surface of the bath which is greater than or equal to the thickness of the contaminant layer.

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