Lithium metal protection using reactive gas combinations

Abstract

The disclosure relates to lithium metal protection using reactive gas combinations. A passivation process for a lithium metal anode includes subjecting a lithium metal to a passivation gas having the following composition: two or more gases selected from the group consisting of CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally, a rare gas. The passivation gas reacts with the lithium metal to form a passivation layer on the lithium metal having a depth of less than ten microns.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 696,996, filed September 20, 2024, the contents of which are incorporated herein by reference in their entirety for all purposes. Technical Field

[0003] This disclosure relates to combinations of reactive gases that produce a passivation layer on lithium metal, thereby protecting the lithium metal from further environmental degradation. Background Technology

[0004] In lithium metal batteries, lithium is deposited onto the anode during each use cycle. This fresh lithium deposit is highly pure and readily reacts with most gases. This corrosion reaction is irreversible, reducing the amount of lithium metal available for deposit and shortening battery life. Generally, battery life ends when the lithium metal anode has lost approximately 20% of its surface area.

[0005] Argon is typically used in battery cells to protect lithium metal from reacting with oxygen, nitrogen, moisture, and other gases in the air. Argon is designed to prevent lithium oxidation, hydration, or the formation of nitrides. However, in actual manufacturing, some contamination of the argon gas or surface within the battery cell, however slight, is unavoidable. The lithium metal is exposed to this environment within its container, with the edges of the lithium metal being particularly vulnerable. This exposure leads to a reduction in battery life. Summary of the Invention

[0006] This article discloses specific implementations of a passivation gas for lithium metal in a gaseous environment, such as a lithium metal anode in an electrochemical battery cell. The passivation gas undergoes a limited reaction with lithium metal to produce a dense passivation layer with minimal depth that hinders further reaction with lithium metal. The passivation layer formed by the reaction of the passivation gas with lithium metal limits lithium metal loss and extends cycle life.

[0007] The specific implementation of the passivation gas for lithium metal has the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F and SiH4.

[0008] Another specific embodiment of the passivation gas for lithium metal has the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F and SiH4; and an inert gas.

[0009] The specific implementation of the passivation process for lithium metal was also disclosed.

[0010] In one implementation, a passivation process for lithium metal includes subjecting the lithium metal to a passivation gas having a composition of: two or more gases selected from the group consisting of CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally a noble gas. The passivation gas reacts with the lithium metal to form a passivation layer on the lithium metal having a depth of less than ten microns.

[0011] In another implementation, a passivation process for a lithium metal battery cell includes subjecting the lithium metal to a first passivation gas during cell formation, the first passivation gas having a composition of: two or more gases selected from the group consisting of CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally a noble gas. Then, the lithium metal is subjected to a second passivation gas during packaging for use, the second passivation gas having a composition of: two or more gases selected from the group consisting of CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally a noble gas. The first passivation gas and the second passivation gas can be the same or different. BRIEF DESCRIPTION OF DRAWINGS

[0012] The following detailed description is best understood when read in conjunction with the accompanying drawings, of which: It should be emphasized that various elements of the drawings - including the various features of the figures - are not to scale. Rather, the dimensions of the various features are arbitrarily expanded or reduced for clarity.

[0013] Figure 1 is a schematic of an electrochemical cell as disclosed herein.

[0014] Figure 2 is a flowchart of a passivation process as disclosed herein. DETAILED DESCRIPTION

[0015] Lithium metal batteries have higher energy density than conventional lithium ion batteries. However, there are challenges in integrating lithium metal into electrochemical cells. The lithium metal plated on the anode in each cycle is of high purity and is prone to react with most any gas present in the electrochemical cell container environment. This corrosion reaction is irreversible, reducing the life of the battery. Therefore, maintaining the environment within the cell free of reactive gases and contaminants is important to achieve the desired battery life. However, in real-world manufacturing, it is impractical to obtain a reactive gas and / or contaminant free environment. As an example, an amount of H2O or O2 as low as <0.1 ppm can cause lithium metal corrosion. Trace amounts of H2O can have a large impact on CO2, O2, and N2 reactivity and can be a major cause of lithium corrosion in the cell.

[0016] Attempts have been made to use argon gas to create a non-reactive environment for electrochemical cell units. Results have shown that it is not practical to manufacture anodes or electrochemical cell units with a pure argon environment or a completely clean environment.

[0017] Disclosed herein is a passivation gas for use as an anode of lithium metal in an electrochemical cell unit. The passivation gas reacts with the lithium metal to a limited extent, producing a dense passivation layer with minimal depth that hinders further reactions between the lithium metal and other reactants. The passivation layer produced from the reaction of the passivation gas with the lithium metal limits the loss of lithium metal and extends the cycle life.

[0018] The passivation gas can be applied to any lithium metal in a gaseous environment. Any surface of the lithium metal exposed to the passivation gas will be passivated and converted to a different lithium compound, depending on the passivation gas used. The passivation gas can also be applied during the formation of the electrochemical cell unit, during the packaging of the cell unit for use, and during the manufacture of the lithium metal anode when the lithium metal anode is assembled into the cell unit at different locations of the manufacture of the lithium metal anode. The electrochemical cell unit can be an all-solid-state battery (ASSB) cell unit, such as Figure 1 the illustrated cell unit. Figure 1 The electrochemical cell unit 100 of the illustrated cell unit can be configured as a layered ASSB cell unit with an active layer including a cathode 102 having an active cathode material, an electrolyte 104 that is a solid electrolyte material, an anode current collector 106, and a passivated lithium metal anode 108 as disclosed herein. Further, Figure 1 The electrochemical cell unit 100 of the illustrated cell unit can include a cathode current collector 110 configured such that the active layer is interposed between the anode current collector 106 and the cathode current collector 110. Alternatively, the electrochemical cell unit 100 can use a liquid or gel electrolyte as the electrolyte 104 and can further include a separator in the liquid or gel electrolyte between the lithium metal anode 108 and the cathode 102. A battery is formed from a plurality of electrochemical cell units 100.

[0019] A specific implementation of the passivation gas for the lithium metal anode has the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4. The passivation gas can consist of two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4. Both the concentration and the ratio of the two or more gases are optimized to produce a limited reaction with the lithium metal to form a passivation layer on the lithium metal with a thickness of ten micrometers or less. The passivation layer blocks further gas ingress and blocks lithium diffusion from the interior.

[0020] Another specific embodiment of the passivation gas for lithium metal anodes has the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and an inert gas. The passivation gas may consist of two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and one or more inert gases. The concentrations and ratios of the two or more gases are optimized to produce a limited reaction with the lithium metal, thereby forming a passivation layer with a thickness of ten micrometers or less on the lithium metal. This passivation layer prevents further gas ingress and blocks lithium diffusion from the interior.

[0021] When an inert gas is used as a carrier gas for two or more reactant gases, the two or more reactant gases may be less than or equal to 5.0% by weight of the total passivating gas.

[0022] The combination of two or more gases is important. It has been found that a certain amount of a single reactant gas will produce dendrites. For example, 20% by weight of O2 in argon produces dendritic coatings. As another example, as little as 1.0% by weight of pure CO2 in argon also produces dendritic coatings.

[0023] The specific implementation of the passivation process for lithium metal was also disclosed.

[0024] In one specific implementation, the passivation process for the lithium metal anode includes subjecting the lithium metal to a passivation gas having the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally a rare gas. The passivation gas undergoes a limited reaction with the lithium metal to form a passivation layer on the lithium metal with a depth of less than ten micrometers.

[0025] exist Figure 2 In another specific embodiment shown, the passivation process for a lithium metal battery cell includes step S1: subjecting lithium metal to a first passivation gas during cell formation, the first passivation gas having the following composition: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optional rare gases. The exposed surfaces of the lithium metal will be passivated, including surfaces perpendicular to the anode current collector (i.e., vertical sidewalls perpendicular to the plane of the battery cell) and any lithium metal surfaces not covered by any other device (such as the anode current collector), allowing the lithium metal to be exposed to the environment. The first passivation gas for cell formation is formulated with a ratio and concentration that provides optimal results during the initial few cycles (cell formation).

[0026] Subsequently, in step S2, the lithium metal is subjected to a second passivation gas during encapsulation for use, the second passivation gas having a composition of: two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and optionally a noble gas. The exposed surface of the lithium metal will be passivated, including the surface perpendicular to the anode current collector (i.e. the vertical sidewalls perpendicular to the plane of the cell) and any lithium metal surface not covered by any other means such as the anode current collector, which allows the lithium metal to be exposed to the environment. This second passivation in step S2 can result in a layered structure with a second layer on top of the first passivation layer, or can result in a case where the first layer composition and / or properties are changed by the second passivation. The second passivation gas has a ratio and concentration optimized for the point of application. The first and second passivation gases can be the same or different.

[0027] The passivation gas results in a passivation layer having a Pilling-Bedworth ratio (PBR) of between 1 and 2, inclusive. The PBR represents the degree of volume change that lithium undergoes when it reacts with a gas or gas mixture.

[0028] While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but instead includes various modifications and equivalent arrangements as would be would be apparent to those skilled in the art. Accordingly, it is to be understood that the scope of the disclosure is to be interpreted only in accordance with the appended claims.

Claims

1. A passivating gas for lithium metal, said passivating gas comprising: Two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F and SiH4.

2. A passivating gas for lithium metal, said passivating gas comprising: Two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and Rare gases.

3. The passivating gas according to claim 2, wherein the rare gas is argon.

4. A passivation method for lithium metal, the passivation method comprising: Lithium metal is subjected to a first passivation gas having the following composition: Two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and Optional rare gases, The first passivation gas reacts with the exposed surface of the lithium metal to form a passivation layer with a depth of less than ten micrometers on the exposed surface.

5. The passivation method according to claim 4, wherein the passivation layer has a Pilling-Beedworth ratio between and including 1 and 2.

6. The passivation method according to claim 4, wherein the lithium metal is the anode in an electrochemical battery cell.

7. The passivation method according to claim 6, wherein the electrochemical cell is an all-solid-state cell.

8. The passivation method according to claim 6, wherein the electrochemical cell is a lithium metal cell, wherein subjecting the lithium metal to oxidation occurs during cell formation, the passivation method further comprising: Subsequently, during encapsulation for use, the exposed surface of the lithium metal is subjected to a second passivation gas having the following composition: Two or more gases selected from CO2, O2, H2O, N2, HC, CO, H, He, F, and SiH4; and Optional rare gases.

9. The passivation method according to claim 8, wherein the first passivating gas and the second passivating gas have equivalent compositions.

10. The passivation method according to claim 8, wherein the first passivation gas and the second passivation gas have different compositions.

11. The passivation method of claim 8, wherein the exposed surface of the lithium metal is subjected to the second passivation gas to produce a second passivation layer with a thickness of less than ten micrometers.

12. The passivation method of claim 8, wherein the exposed surface of the lithium metal is subjected to the second passivation gas to alter the composition of the first passivation layer.

13. The passivation method of claim 8, wherein the exposed surface of the lithium metal is subjected to the second passivation gas to alter one or more properties of the first passivation layer.

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