Lithium metal anode and related methods

Abstract

A lithium metal anode includes a lithium metal or lithium metal alloy foil coated with a cured polymer composite material comprising a siloxane-based polymer and a lithium salt. Further described are related methods for applying a coating solution according to this disclosure to the lithium metal or lithium metal alloy foil to form a coated lithium metal anode, related coating solutions, and a secondary battery including said anode.

Description

Related applications

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 544,380, filed October 16, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] This disclosure generally relates to lithium metal anodes, methods for their production, and their use as components in secondary batteries. Background Technology

[0003] This section provides information that may relate to aspects of the compositions or methods described herein and / or claimed hereinafter, or provides contextual information for aspects of the compositions or methods described herein and / or claimed hereinafter. This information is background that helps to better understand the disclosed subject matter. This background may include a discussion of “related” techniques. The relevance of such techniques in no way implies that they are also “prior” techniques. Related techniques may or may not be prior art. The discussion should be understood from this perspective, rather than as an admission of prior art.

[0004] Rechargeable lithium (Li) batteries have proven their importance in a wide range of applications, from portable devices to electric vehicles (EVs). A new generation of lithium batteries with high capacity and high energy density is needed to meet the growing market demand. Lithium metal anodes (LMAs) are considered the "holy grail" among candidate anode materials because they possess the highest theoretical capacity (3860 mA hg⁻¹) and the lowest electrochemical potential (-3.04 V relative to the standard hydrogen electrode). Furthermore, LMAs can enable the development of future high-energy storage applications, such as Li-sulfur batteries and Li-air batteries.

[0005] However, the practical application of LMA has been limited by several key issues. First, there is the problem of reaction between metallic Li and the electrolyte, which is well known to form a solid electrolyte interface (SEI) on the surface of the lithium metal anode. Unlike commercially available graphite anodes, the passivation layer formed on lithium metal is not robust enough to withstand the electrode morphology changes during Li plating / stripping, resulting in continuous consumption of both electrolyte and lithium ions and rapid capacity decay during cycling. Uneven Li plating / stripping leads to uncontrolled lithium dendrite growth, which may potentially penetrate the membrane and cause internal short circuits, raising safety concerns. Third, the significant volume change of LMA during cycling is a challenge. As a “matrix-free” electrode, lithium metal undergoes infinite volume changes in each charge and discharge cycle, leading to the formation of moss-like lithium or isolated lithium islands (so-called “dead” Li). Finally, the high reactivity of lithium metal with O2, N2, CO2 and / or moisture (H2O) in the air makes lithium processing and storage a significant challenge. For example, these reactions limit lithium processing to costly drying chambers or argon-filled glove boxes and also hinder the development of high-energy-density Li-air batteries. Furthermore, if the LMA experiences packaging leakage or mechanical damage, allowing water to penetrate the damaged packaging, serious safety hazards such as combustion or even explosion may occur.

[0006] Therefore, there is an ongoing need to develop product and process advancements that can address one or more of these and related challenges. Summary of the Invention

[0007] This invention describes several embodiments of the currently disclosed subject matter, and in many cases, variations and arrangements of these embodiments. This invention is merely exemplary for the numerous and different embodiments. References to one or more representative features of the given embodiments are also exemplary. Such embodiments may generally have or not have one or more of the mentioned features; similarly, those features can be applied to other embodiments of the currently disclosed subject matter, whether or not they are listed in this invention. To avoid excessive repetition, this invention does not list or propose all possible combinations of such features.

[0008] In summary, this disclosure addresses this need by providing a protective coating for lithium metal anodes and by providing an improved coating form and manufacturing method for lithium metal anodes. The coating employed contains a siloxane-based polymer, a lithium salt, and an organic solvent. The coating can be applied to the surface of lithium metal or lithium metal alloy foil in an organic-based (e.g., ether-based) solution via dip coating, roll coating, or spray coating. In many cases, to obtain a high-quality coating film, additional curing agent components and a drying process are included in the coating solution. The thickness and composition of the coating can also be customized by, for example, changing the ratio between materials, temperature, and / or coating time. Optionally, in many cases, a washing step may also be included to further improve coating quality and optimize the manufacturing process. The designed coating addresses the key challenges of LMAs (Lithium Metal Anodes) that need to be overcome to construct high-performance LMAs that simultaneously exhibit improved air / water resistance to ensure sufficient lithium shelf life and reduce safety concerns.

[0009] Therefore, in one aspect of this disclosure, a lithium metal anode is provided. The anode comprises a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, said polymer composite material being composed of a siloxane-based polymer and a lithium salt.

[0010] In another aspect of this disclosure, the foil is part of a laminate consisting of a foil and a substrate. In one particular aspect, the substrate includes copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, or surface-treated stainless steel.

[0011] In one aspect of this disclosure, the siloxane-based polymer of the lithium metal anode includes polydimethylsiloxane.

[0012] In another aspect, the lithium salt of the lithium metal anode contains boron.

[0013] In another aspect of this disclosure, the lithium salt of the lithium metal anode includes lithium bis(oxalate)borate.

[0014] In another aspect of this disclosure, the siloxane-based polymer in the lithium metal anode includes polydimethylsiloxane, the lithium salt includes lithium bis(oxalate)borate, and the amount of polydimethylsiloxane used to form the cured polymer composite material is in the range of about 0.3% by weight to about 30% by weight based on the total weight of the solution applied for coating the foil, and the amount of lithium bis(oxalate)borate used to form the cured polymer composite material is in the range of about 0.1% by weight to about 10% by weight based on the total weight of the solution applied for coating the foil.

[0015] In another aspect, the coating solution that forms a cured polymer composite material after curing comprises a siloxane-based polymer, a lithium salt, an organic solvent, and a curing agent. In one particular aspect, the organic solvent includes ethers, heterocyclic acetals, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), chloroform, or mixtures of two or more of the foregoing. In yet another particular aspect, the solvent includes ethers, and the ethers are selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing. In another specific aspect, the curing agent consists of poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0016] In another aspect of this disclosure, a method is provided comprising applying a coating solution to a lithium metal or lithium metal alloy foil, the coating solution being at one or more temperatures in the range of about 20°C to about 80°C to form a coated lithium metal anode, wherein the coating solution comprises a siloxane-based polymer, a lithium salt, and an organic solvent.

[0017] In some aspects of this disclosure, the solvent includes ethers, heterocyclic acetals, esters (e.g., carbonates), nitriles, ketones, lactones, or other lithium salt-soluble organic solvents, as well as mixtures of two or more of the foregoing. In other aspects of this disclosure, the solvent includes ethers. In some aspects, the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane (also known as ethylene glycol dimethyl ether, glycol dimethyl ether, or monoethylene glycol dimethyl ether), diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether). Other examples of suitable solvents may include dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, and dimethyl sulfoxide (DMSO), hexane, toluene, and chloroform.

[0018] In some aspects of this disclosure, the coating also includes a curing agent. In other aspects of this disclosure, the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0019] In some aspects of this disclosure, once the coating is formed, it undergoes a post-formation washing process performed before drying at one or more temperatures ranging from about 20°C to about 50°C. In some aspects of this disclosure, the washing solvent includes ethers, hydrocarbons, aromatics, heterocyclic acetals, esters (e.g., carbonates), nitriles, ketones, lactones, or other lithium salt-soluble organic solvents, as well as mixtures of two or more of the foregoing. In some aspects, the washing process may be carried out using one solvent or a combination of solvents applied sequentially, or a mixture of two or more solvents as described above, through one or more steps.

[0020] In some aspects of this disclosure, the method further includes drying the coated lithium metal anode. In other aspects of this disclosure, drying is performed at one or more temperatures in the range of about 20°C to about 80°C. In yet another aspect of this disclosure, the coated Li metal anode is dried by ultraviolet light at ambient temperature. In this way, it may be possible to avoid applying heat.

[0021] In some aspects of this disclosure, a lithium metal foil is laminated onto a substrate prior to coating.

[0022] In some aspects of this disclosure, the lithium salt comprises boron. In other aspects of this disclosure, the lithium salt is lithium bis(oxalate)borate (LiB(C2O4)2), also referred to herein as LiBOB.

[0023] In some aspects of this disclosure, siloxane-based polymers include poly(dimethylsiloxane) (also referred to herein as PDMS).

[0024] In another aspect of this disclosure, the lithium salt of the coating comprises lithium bis(oxalate)borate, the siloxane-based polymer comprises poly(dimethylsiloxane), the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3 wt% to about 30 wt% based on the total weight of the solution, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1 wt% to about 10 wt% based on the total weight of the solution.

[0025] Another aspect of this disclosure provides a secondary battery comprising a cathode, an electrolyte, and a lithium metal anode, the lithium metal anode being composed of a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, the polymer composite material being composed of a siloxane-based polymer and a lithium salt.

[0026] In one aspect of the battery disclosed herein, the foil prior to coating is part of a laminate consisting of foil and a substrate. In another aspect of the battery disclosed herein, the substrate in the laminate comprises copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, surface-treated stainless steel, or another common anode current collector material.

[0027] In another aspect of the battery disclosed herein, the siloxane-based polymer includes polydimethylsiloxane.

[0028] In another aspect of the battery disclosed herein, the lithium salt comprises boron. In yet another aspect of the battery disclosed herein, the lithium salt comprises lithium bis(oxalate)borate.

[0029] In another aspect of the battery disclosed herein, the siloxane-based polymer includes polydimethylsiloxane, the lithium salt includes lithium bis(oxalate)borate, the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3% by weight to about 30% by weight, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1% by weight to about 10% by weight.

[0030] While several embodiments and aspects of this disclosure have been disclosed, other embodiments will become apparent to those skilled in the art from the following detailed description. It will be apparent that modifications can be made to certain embodiments and aspects disclosed herein in various ways that will be obvious to those skilled in the art, without departing from the spirit and scope of the claims set forth below. Therefore, the drawings and detailed descriptions should be considered illustrative in nature rather than restrictive. Attached Figure Description

[0031] To describe in detail certain embodiments of the disclosed subject matter, reference will now be made to the accompanying drawings, in which: Figure 1(a) is a schematic diagram of a dip coating process according to one embodiment of the present disclosure.

[0032] Figure 1(b) is a schematic diagram of a roller coating process according to another embodiment of the present disclosure.

[0033] Figure 1(c) is a schematic diagram of a spraying process according to another embodiment of the present disclosure.

[0034] Figure 2 This is a cross-sectional scanning electron microscope image of a lithium foil coated with a cured polymer composite material consisting of PDMS and LiBOB, according to one embodiment of the present disclosure.

[0035] Figure 3 This is a cross-sectional scanning electron microscope image of a lithium foil coated with a cured polymer composite material consisting of PDMS and LiBOB, according to a second embodiment of the present disclosure.

[0036] Figure 4 This is a cross-sectional scanning electron microscope image of a lithium foil coated with a cured polymer composite material consisting of PDMS and LiBOB, according to a third embodiment of this disclosure.

[0037] Figure 5(a) is a series of five (5) photographs showing the color changes of different lithium foils, coated or uncoated and aged for 3 hours in an ambient air atmosphere with or without 30% relative humidity, and at ambient temperature and pressure, according to the embodiments below.

[0038] Figure 5(b) is a bar graph showing the remaining electrochemically available lithium after a 3-hour aging test at different lithium metal anodes according to the examples below.

[0039] Figure 6(a) is a graph comparing the number of cycles of electrochemical discharge capacity of Li metal anodes with and without surface coating before aging tests, as described in the embodiments below.

[0040] Figure 6(b) is a graph comparing the number of cycles of electrochemical discharge capacity of Li metal anodes with and without surface coating after aging for 3 hours in an ambient air atmosphere with 30% relative humidity at ambient temperature and pressure, as described in the embodiments below.

[0041] While the claimed subject matter is readily subject to various modifications and alternatives, the accompanying drawings illustrate specific embodiments described in detail herein by way of example. However, it should be understood that the description of specific embodiments herein is not intended to limit the claimed subject matter to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope defined by the appended claims. Detailed Implementation

[0042] Illustrative aspects of the subject matter further claimed below will be disclosed based on the definitions provided below. For clarity, not all features of actual implementations are described in this specification. It should be understood that in the development of any such actual implementation, numerous implementation-specific decisions must be made to achieve the developer's specific objectives, such as compliance with system-related constraints and business-related constraints, which will vary between different implementations. Furthermore, it should be understood that such development efforts, while complex and time-consuming, will remain a routine task for those skilled in the art who will benefit from this disclosure.

[0043] definition To more clearly define the terms used in this disclosure, the following definitions are provided. Unless otherwise stated, the following definitions apply to this disclosure. Terms not appearing below have their general and customary meanings as understood by one of ordinary skill in the art in the context of this disclosure, relating to the technical field of this disclosure. If any definition or usage provided herein by reference in any document incorporated herein by reference conflicts with the definition or usage provided herein, the definition or usage provided herein shall prevail.

[0044] In this disclosure, the features of the subject matter are described such that combinations of different features are conceivable within a particular aspect. For each aspect and feature disclosed herein, all combinations are considered without adversely affecting the design, system, composition, process, or method described herein, with or without a specific description of such combinations. Furthermore, unless otherwise expressly stated, any aspect or feature disclosed herein may be combined to describe an inventive design, system, composition, process, or method consistent with this disclosure.

[0045] In this disclosure, while compositions and / or processes or methods are generally described as “comprising” various components or steps, the compositions and methods may also be “substantially composed of various components or steps” or “composed of various components or steps”, unless otherwise stated. For example, a method consistent with aspects of the disclosed subject matter may include the indicated process steps; alternatively, it may consist substantially of the indicated process steps; or alternatively, it may consist of the indicated process steps.

[0046] Unless otherwise stated, the terms “a / an” and “the” are intended to include a plurality of alternatives, such as at least one, one or more, and one or more.

[0047] Unless otherwise stated, the term "contact" is used herein to describe systems, compositions, processes, and methods in which components are contacted, combined, or incorporated together in any order, in any manner, and for any duration. For example, components can be incorporated by blending or mixing using any suitable technique.

[0048] The terms “room temperature” or “ambient temperature” are used herein to describe any temperature between 15°C and 35°C in which no external heat or cooling source is applied directly to the reaction vessel. Therefore, the terms “room temperature” and “ambient temperature” cover individual temperatures between 15°C and 35°C, as well as any and all ranges, subranges, and combinations thereof, in which no external heating or cooling source is applied directly to the reaction vessel.

[0049] The term “atmospheric pressure” is used in this document to describe the pressure of the Earth’s air where no external means of pressure alteration are used. Generally, unless practiced at extreme altitudes on Earth, “atmospheric pressure” is approximately 1 atmosphere (or, alternatively, approximately 14.7 psi or approximately 101 kPa).

[0050] The term "about" means that a quantity, size, formulation, parameter, or other quantity and characteristic is not and need not be exact, but may be an approximation, including being larger or smaller as needed to reflect tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art. Generally, a quantity, size, formulation, parameter, or other quantity or characteristic is "about" or "approximate," whether or not such an explicit statement is made. The term "about" also covers quantities that differ due to different equilibrium conditions of the composition resulting from a particular initial mixture. Whether or not modified by the term "about," the claims include equivalent values ​​of the stated quantities.

[0051] This document discloses various ranges of numerical values. When this document discloses or claims any type of range of numerical values ​​(e.g., “ranging from…”, “in a range of from…”, “in the range of from…”, “in a range of…”, “in a range of…”), it is intended that each possible number or ratio be disclosed or claimed individually so that such a range can reasonably encompass, including the endpoints of the range and any subranges and combinations thereof covered therein, unless otherwise stated.

[0052] The embodiments disclosed herein may provide material that is listed as suitable for satisfying specific features of an embodiment defined by the term "or". For example, specific features of the disclosed subject matter may be disclosed as follows: feature X can be A, B, or C. It is also considered that for each feature, the statement may also be presented as a list of alternatives, such that the statement "feature X is A, alternatively B, or alternatively C" is also an embodiment of this disclosure, regardless of whether the statement is explicitly stated.

[0053] Although any methods and materials similar to or equivalent to those described herein may be used in the practice or testing of the topics described herein, typical methods and materials are described herein.

[0054] All publications and patents mentioned herein are incorporated herein by reference for the purpose of describing and disclosing, for example, constructs and methodologies described in the publications and that may be used in conjunction with the subject matter described herein.

[0055] Detailed description A. Coating The aspects of the subject matter disclosed herein relate to one or more processes for producing anodes, said processes including applying a coating solution to a lithium metal or lithium metal alloy foil at one or more temperatures in the range of about 20°C to about 80°C. The foil may be primarily or entirely lithium metal or a lithium metal alloy. Examples of suitable lithium alloys include Li-Al, Li-Mg, and Li-Sn alloys, etc. The physical dimensions of the foil may vary, but will typically have an average thickness in the range of about 1 to about 1000 micrometers.

[0056] The coating composition will contain lithium salt, siloxane-based polymer, and organic solvent.

[0057] The lithium salt may vary, but will contain boron in at least one particular aspect. Suitable examples of boron-containing lithium salts include lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate, etc. In another aspect of this disclosure, the lithium salt comprises lithium bis(oxalate)borate. The amount of lithium salt used may vary, but for boron-containing lithium salts, the amount will range from about 0.1% by weight to about 10% by weight, based on the total weight of the coating.

[0058] The siloxane-based polymer may be selected from hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane, dodecylhexasiloxane, poly(dimethylsiloxane), etc., but in at least one aspect of this disclosure, it will include poly(dimethylsiloxane). The amount of siloxane-based polymer used may also vary, but it is generally in the range of 0.3% by weight to about 30% by weight based on the total weight of the coating solution.

[0059] The organic solvent can be any LiBOB-soluble organic solvent. Suitable non-limiting examples of such solvents include ethers, heterocyclic acetals, carbonates, nitriles, ketones, lactones, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), and chloroform. In one aspect of this disclosure, the organic solvent includes ethers, heterocyclic acetals, or mixtures of two or more of the foregoing. In another aspect of this disclosure, the solvent includes ethers. In another and further aspect, the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

[0060] In some cases, a curing agent is required to minimize drying time. When a curing agent is included in a coating formulation, it can be any curing agent that will harden or accelerate the coating on one or more surfaces of the foil to which it is applied without affecting the desired properties of the anode. Suitable, non-limiting examples of curing agents include poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0061] Coating mixtures can be formed simply by combining and mixing their components. Forming a coating mixture does not require special treatment or processes, although it may sometimes require a stirring process ranging from minutes to hours to obtain a homogeneous coating solution with different polymers and lithium salts. Furthermore, the solution can be adjusted according to the solubility of the coating components used. For example, dip coating is a combination of physical and chemical reactions.

[0062] It should also be noted that the mass ratio of polymer to salt in the coating solution can be varied to optimize the thickness of the resulting coating.

[0063] B. Application of the coating The coating solution is applied to a lithium metal or lithium metal alloy foil (either on its own or as part of a laminate of foil and substrate) at one or more temperatures ranging from about 20°C to about 80°C to form a coated lithium metal anode. The composition and dimensional characteristics of the foil may vary, but in at least some aspects of this disclosure, the planar dimensions of the foil will depend on the process used to coat the foil. The average foil thickness is typically in the range of about 1 to about 1000 micrometers.

[0064] Lithium metal or lithium metal alloy foil coating processes typically involve applying a coating to a lithium metal or lithium metal alloy foil (with or without a substrate) anode material, followed by drying (optionally under vacuum) of the resulting coated anode material. Dip-coating processes can be used for batch processes involving discrete segments or sheets of foil, as typically shown in Figure 1(a).

[0065] Lithium metal or lithium metal alloy foil anode material coating can also be performed using a rolling process. In such cases, the foil or foil / substrate laminate can be rolled onto one or more reels having dimensions that can vary depending on the needs and performance of the available equipment. In one embodiment, the foil / laminate material is fed from each reel into a bath or tank of coating solution, where it is processed continuously for the desired period of time, driven by the configuration of the immersion equipment, coating solution tank, and rolling system, as well as the speed of the roller conveyor. Once the fed anode material exits the coating solution bath, it is preferably fed at a sufficient speed into a dryer to allow the material to reach the desired residence time under drying conditions, and can then be fed onto a rolled finished (coated) anode material reel to provide a continuous coating and winding process, as shown in Figure 1(b). In another embodiment shown in Figure 1(c), foil / laminated material is fed from each reel and passed through a spraying zone, wherein a mixed (preferably mixed with an inert carrier gas) coating solution is sprayed onto the foil as it passes through the spraying zone, and then the sprayed foil is fed into a dryer assembly to dry it, and then rolled onto a reel of finished (coated) anode material.

[0066] As previously described, in some aspects of this disclosure, the coating process further includes a washing step prior to drying. Washing solvents include ethers, hydrocarbons, aromatics, heterocyclic acetals, esters (e.g., carbonates), nitriles, ketones, lactones, or other lithium salt-soluble organic solvents, as well as mixtures of two or more of the foregoing. In some aspects, the washing process may be carried out using a single solvent, sequentially applied different solvents, or a mixture of two or more solvents as described above, through one or more steps.

[0067] As previously described, in some aspects of this disclosure, the coating process also includes drying the coated lithium metal anode. While different temperature and pressure conditions are conceivable, drying is preferably carried out at one or more temperatures in the range of about 20°C to about 80°C. The selected drying temperature can be increased from room temperature to, for example, 80°C to shorten the process.

[0068] C. Anode-equipped secondary battery according to this disclosure The secondary battery disclosed herein will include a cathode, an electrolyte, and a lithium metal anode, said lithium metal anode being composed of a lithium metal or lithium metal alloy foil coated in accordance with the teachings described herein.

[0069] The cathode can be any material suitable for lithium secondary batteries, such as, for example, nickel-containing layered oxide cathodes, lithium iron phosphate (LFP) or lithium manganese iron phosphate (LMFP), sulfur, etc.

[0070] The electrolyte can be any electrolyte suitable for use in a secondary lithium battery. Non-limiting examples of such electrolytes include liquid (carbonate-based, ether-based, etc.) electrolytes and solid (sulfide-based, oxide-based, polymer-salt complex) electrolytes.

[0071] In some aspects of this disclosure, the lithium metal or lithium metal alloy foil of the battery is part of a laminate consisting of a foil and a substrate, and the laminate is a laminate coated according to the process of this disclosure.

[0072] When used, the substrate to which the lithium metal or lithium metal alloy foil is laminated may include copper or surface-treated copper, nickel, stainless steel, etc., and in one particular aspect of this disclosure, copper foil is included. The substrate can be laminated onto the lithium metal or lithium metal alloy foil using any lamination technique, thereby providing an anode suitable for the intended use and application of a secondary battery.

[0073] Example The subject matter has been generally described, and specific embodiments of the subject matter of this disclosure are given below to demonstrate its practice and advantages. It should be understood that the embodiments are given by way of illustration and are not intended to limit the appended claims in any way.

[0074] PDMS / LiBOB coating Poly(dimethylsiloxane) (PDMS) and LiBOB, in a mass ratio (wt%) ranging from 0.1 / 0.3 to 10 / 30, were dissolved in a mixture of 1,3-dioxolane (DOL) and dimethoxyethane (DME) (v / v 1:1). In this case, the weight ratio of PDMS to LiBOB was 1 / 0.3 (for experimental solutions PDMS / LiBOB type 1 or "v1") and 3 / 0.75 (for experimental solutions PDMS / LiBOB type 2 or "v2"), for example, a mixture of PDMS and LiBOB. The prepared solution was stirred for several minutes to several hours to obtain a uniform coating solution. Laminated lithium + copper foil with an average thickness of 75 µm and a width of 80 mm was immersed in the prepared solution for 1 minute to several hours under an argon atmosphere without a pre-washing step. After the coating step, the foil was dried in a vacuum chamber for approximately 30 minutes. For comparison, two coatings (v1 and v2) with different PDMS to LiBOB mass ratios, as well as a coating containing only LiBOB, were prepared for further investigation. Figure 2 A cross-sectional image of a Li foil coated with a cured polymer composite material consisting of PDMS and LiBOB is shown. The image reveals a coating with an average thickness in the range of 100–200 nm, as determined by SEM, indicating that a uniform coating can be achieved using this dip-coating method.

[0075] PDMS / LiBOB containing curing agent A PDMS-LiBOB coating solution was prepared in a DME / DOL solution (1 / 1, volume ratio) using 3 wt% PDMS, 0.75 wt% LiBOB, and 0.3 wt% SYLGARD® 184 from Dow as a curing agent. Laminated lithium + copper foil with an average thickness of 75 µm and a width of 80 mm was immersed in the prepared solution for 15 minutes under an argon atmosphere without pre-washing, under ambient temperature and pressure conditions. The foil was then removed from the solution and dried at approximately 90 °C for 15–20 minutes. Figure 3 The image shows a cross-sectional SEM image of the dried foil and the location of the coating, which has an average thickness of about 1 micrometer as determined by SEM.

[0076] PDMS / LiBOB coating at 45°C and washing with hexane A PDMS-LiBOB coating solution was prepared using 3 wt% PDMS and 3 wt% LiBOB in a DME / DOL solution (1 / 1, volume ratio). Laminated lithium + copper foil with an average thickness of 75 µm and a width of 80 mm was immersed in the prepared solution for 1 minute under an argon atmosphere without pre-washing, at 45 °C and ambient pressure. The foil was then removed from the coating solution and immersed in DME solvent or a washing bath consisting of DME solvent for 1 minute or less at room temperature, followed by immersion in a washing bath of hexane solvent for less than 10 seconds. The washed foil was then removed from the final washing bath and allowed to dry (in less than 1 minute). Figure 4 The image shows a cross-sectional SEM image of the dried foil and a coating with an average thickness of less than or equal to 50 nm, as determined by SEM.

[0077] Performance of the protected Li electrode: Shelf life of the Li anode To investigate the shelf life and stability of lithium anodes in a high-humidity atmosphere, lithium foil was exposed to an ambient air atmosphere and controlled relative humidity (ranging from 1% to 30%) for several minutes to several hours to observe color changes during the aging process. Figure 5(a) shows a series of coated Li foils after being exposed to ambient air atmosphere at 30% relative humidity for 3 hours. For comparison, an image of the color change of the original lithium foil is also added to this figure. After 3 hours of aging, the original lithium foil turned black, indicating severe oxidation of lithium. In contrast, the coated foils showed better protection against humid atmospheric conditions. Among them, the PDMS / LiBOB v2 coated foil retained its metallic color after aging, indicating that this type of coating can significantly improve the oxidation resistance and stability of the coated foil in a humid atmosphere.

[0078] The discoloration indicates that lithium reacts with O2, CO2, N2, or moisture to form impurities such as Li2O, LiOH, Li3N, or Li2CO3 on and inside the lithium foil. Therefore, a significant amount of electrochemically available lithium is consumed and reduced in the lithium foil during this process. To determine the remaining electrochemically available lithium, a simple electrochemical stripping method was used as a quantitative method to quantify the lithium loss after exposure under these non-drying conditions. Calculations show that a 5 µm Li foil has approximately 1 mAh / cm³. 2 The capacity, and therefore the electrochemical stripping capacity of the aged Li foil can be converted into thickness. The percentage of remaining active lithium after aging, compared to the thickness measured physically before aging, can be expressed by the following equation (1): Capacity decay was observed in the original sample after 1 hour of aging. Similar calculations were applied to all types of foil after 3 hours of aging, and the results are plotted in Figure 5(b). As shown in the figure, the original lithium lost 13% of its active lithium after 3 hours of aging, consistent with the visual discoloration. In contrast, the LiBOB-coated sample retained 94% of its usable lithium, and the PDMS / LiBOB v2 coating showed a maximum of 99% of usable lithium. These results provide a quantitative way to determine the aging effects of lithium metal anodes and the loss of electrochemically active lithium in humid atmospheres compared to relying solely on visual indications.

[0079] Performance of the protected Li electrode: Electrochemical performance To further confirm the effect of the protective coating on the Li metal foil, the electrochemical cycling performance of the lithium metal anode before and after aging was investigated in button cells, with the counter electrode being a 14 mm diameter NMC 622 cathode. 40 μL of electrolyte (EC / DEC: 3 / 7 wt / wt + 5 wt% FEC in 1.2 M LiPF6) was used for each button cell. Li foil discs with a diameter of 16 mm were stamped. A polypropylene separator was used to separate the lithium foil and the NMC cathode in the button cells. Three formation cycles were performed in button cells with a charge / discharge rate of C / 10 based on the NMC cathode capacity, within a voltage range of 2.5–4.3 V. After charging to 4.3 V, a constant voltage hold was applied until the current dropped to C / 30. After the formation cycle, the button cells were cycled at a higher rate, charged at C / 7 and held at a constant voltage of 4.3 V until the current dropped to C / 20, and discharged at C / 2 with the same cutoff voltage as the formation cycle, at 2.5 V. The discharge capacity of the button cell was calculated based on the mass of NMC in the cathode. As shown in Figure 6a, the pristine Li, LiBOB, and PDMS / LiBOB v2 lithium batteries exhibited very similar discharge capacities within 150 cycles, which can be attributed to the abundant additional lithium from the anode side. Therefore, even the pristine lithium metal battery retained over 80% of its capacity after 400 cycles. Similar behavior between coated and uncoated batteries also demonstrates that the applied coating does not affect lithium diffusion during cycling. However, after aging for 3 hours in ambient air at 30% relative humidity, the pristine lithium battery showed rapid capacity decay after only about 15 cycles (see Figure 6(b)). Considering that 87% of the active lithium was retained after aging, this does not seem entirely attributable to the loss of active lithium due to lithium reaction. A possible cause of such rapid capacity decay is the poor ionic conductivity or surface roughness of the passivation layer formed during aging. It appears to play a crucial role in the electrochemical performance of the anode electrode. Using the PDMS / LiBOB v1 / v2 coating, the capacity decay was small after 140 cycles and the cycling performance was similar to that of the original sample before aging, indicating that the coating is very effective in maintaining the shelf life of lithium electrodes and / or minimizing degradation in humid atmospheres.

[0080] Other aspects of this disclosure The subject matter has been described above with reference to numerous aspects and specific embodiments. Based on the above detailed description, many variations will occur to those skilled in the art. All such apparent variations are within the full scope of the appended claims. Other aspects of the subject matter disclosed herein may include, but are not limited to, the following (aspects are described as “comprising”, but alternatively, may be “substantially composed of” or “consisting of”): Aspect 1. A lithium metal anode comprising a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, said polymer composite material comprising a siloxane-based polymer and a lithium salt.

[0081] Aspect 2. The lithium metal anode as described in aspect 1, wherein the foil is part of a laminate consisting of the foil and a substrate.

[0082] Aspect 3. The lithium metal anode as described in aspect 2, wherein the substrate comprises copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, or surface-treated stainless steel.

[0083] Aspect 4. The lithium metal anode of any one of Aspects 1-3, wherein the siloxane-based polymer comprises polydimethylsiloxane.

[0084] Aspect 5. The lithium metal anode as described in any one of Aspects 1-4, wherein the lithium salt comprises boron.

[0085] Aspect 6. The lithium metal anode as described in aspect 5, wherein the lithium salt comprises lithium bis(oxalate)borate.

[0086] Aspect 7. The lithium metal anode of any one of Aspects 1-3, wherein the siloxane-based polymer comprises polydimethylsiloxane, the lithium salt comprises lithium bis(oxalate)borate, and the amount of polydimethylsiloxane used to form the cured polymer composite material is in the range of about 0.3% by weight to about 30% by weight based on the total weight of the solution applied for coating the foil, and the amount of lithium bis(oxalate)borate used to form the cured polymer composite material is in the range of about 0.1% by weight to about 10% by weight based on the total weight of the solution applied for coating the foil.

[0087] Aspect 8. The lithium metal anode of any one of Aspects 1-3, wherein the coating solution forming the cured polymer composite material after curing comprises the siloxane-based polymer, the lithium salt, an organic solvent, and a curing agent.

[0088] Aspect 9. The lithium metal anode as described in Aspect 8, wherein the organic solvent comprises ether, heterocyclic acetal, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), chloroform, or a mixture of two or more of the foregoing.

[0089] Aspect 10. The lithium metal anode of aspect 9, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

[0090] Aspect 11. The lithium metal anode of any one of Aspects 8-10, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0091] Aspect 12. A lithium metal or lithium metal alloy anode coating solution, comprising the following: Siloxane-based polymers; Lithium salts; and Organic solvents.

[0092] Aspect 13. The coating solution as described in aspect 12, wherein the lithium salt comprises boron.

[0093] Aspect 14. The coating solution of any one of Aspects 12-13, wherein the solvent comprises an ether, a heterocyclic acetal, or a mixture of two or more of the foregoing.

[0094] Aspect 15. The coating solution of aspect 14, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

[0095] Aspect 16. The coating solution of any one of Aspects 12-13, wherein the solvent comprises dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), or chloroform.

[0096] Aspect 17. The coating solution as described in any one of Aspects 12-16, further comprising a curing agent.

[0097] Aspect 18. The coating solution as described in aspect 17, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0098] Aspect 19. The coating solution of any one of Aspects 12-18, wherein the siloxane-based polymer comprises polydimethylsiloxane.

[0099] Aspect 20. The coating solution as described in any one of Aspects 12-19, wherein the lithium salt comprises lithium bis(oxalate)borate.

[0100] Aspect 21. The coating solution of aspect 19, wherein the lithium salt comprises lithium bis(oxalate)borate, the polydimethylsiloxane in the coating solution is in the range of about 0.3% by weight to about 30% by weight of the total weight of the solution, and the amount of lithium bis(oxalate)borate in the coating solution is in the range of about 0.1% by weight to about 10% by weight of the total weight of the solution.

[0101] Aspect 22. A method comprising applying a coating solution to a lithium metal or lithium metal alloy foil to form a coated lithium metal anode, wherein the coating solution comprises a siloxane-based polymer, a lithium salt, and an organic solvent.

[0102] Aspect 23. The method according to aspect 22, wherein the solvent comprises an ether, a heterocyclic acetal, or a mixture of two or more of the foregoing.

[0103] Aspect 24. The method according to aspect 23, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

[0104] Aspect 25. The method according to aspect 23, wherein the solvent comprises dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), or chloroform.

[0105] Aspect 26. The method according to any one of Aspects 22-25, wherein the coating further comprises a curing agent.

[0106] Aspect 27. The method according to aspect 26, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

[0107] Aspect 28. The method according to any one of aspects 22-27, further comprising drying the coated lithium metal anode.

[0108] Aspect 29. The method according to aspect 28, wherein the drying is carried out at one or more temperatures in the range of about 20°C to about 80°C.

[0109] Aspect 30. The method according to any one of Aspects 22-29, wherein the lithium metal foil is laminated onto the substrate prior to coating.

[0110] Aspect 31. The method according to any one of Aspects 22-30, wherein the lithium salt comprises boron.

[0111] Aspect 32. The method according to any one of aspects 22-31, wherein the coating step is performed. Aspect 32. The method according to aspect 31, wherein the lithium salt comprises lithium bis(oxalate)borate.

[0112] Aspect 33. The method according to any one of Aspects 22-32, wherein the siloxane-based polymer comprises poly(dimethylsiloxane).

[0113] Aspect 34. The method according to aspect 22, wherein the lithium salt comprises lithium bis(oxalate)borate, the siloxane-based polymer comprises poly(dimethylsiloxane), the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3 wt% to about 30 wt% based on the total weight of the solution, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1 wt% to about 10 wt% based on the total weight of the solution.

[0114] Aspect 35. The method according to any one of aspects 22-34, further comprising washing the coated lithium metal anode with one or more washing solvents to form a washed coated lithium metal anode.

[0115] Aspect 36. The method according to aspect 35, wherein the washing is performed prior to drying and at one or more temperatures in the range of about 20°C to about 50°C.

[0116] Aspect 37. The method according to aspect 36 further includes drying the washed coated lithium metal anode.

[0117] Aspect 38. A secondary battery comprising: cathode, Electrolytes, and A lithium metal anode, the lithium metal anode comprising a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, the polymer composite material comprising a siloxane-based polymer and a lithium salt.

[0118] Aspect 39. The secondary battery as described in aspect 38, wherein the foil prior to being coated is part of a laminate consisting of the foil and a substrate.

[0119] Aspect 40. The secondary battery as described in aspect 39, wherein the substrate comprises copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, or surface-treated stainless steel.

[0120] Aspect 41. The secondary battery of any one of Aspects 38-40, wherein the siloxane-based polymer comprises polydimethylsiloxane.

[0121] Aspect 42. The secondary battery of any one of Aspects 38-41, wherein the lithium salt comprises boron.

[0122] Aspect 43. The secondary battery as described in aspect 42, wherein the lithium salt comprises lithium bis(oxalate)borate.

[0123] Aspect 44. The secondary battery of any one of Aspects 38-40, wherein the siloxane-based polymer comprises polydimethylsiloxane, the lithium salt comprises lithium bis(oxalate)borate, the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3% by weight to about 30% by weight, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1% by weight to about 10% by weight.

[0124] While the invention has been described according to one or more preferred embodiments, it should be understood that other modifications may be made without departing from the scope of the invention, which is set forth in the claims below.

Claims

1. A lithium metal anode comprising a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, said polymer composite material being composed of a siloxane-based polymer and a lithium salt.

2. The lithium metal anode of claim 1, wherein the foil is part of a laminate consisting of the foil and a substrate.

3. The lithium metal anode of claim 2, wherein the substrate comprises copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, or surface-treated stainless steel.

4. The lithium metal anode of any one of claims 1-3, wherein the siloxane-based polymer comprises polydimethylsiloxane.

5. The lithium metal anode according to any one of claims 1-4, wherein the lithium salt comprises boron.

6. The lithium metal anode of claim 5, wherein the lithium salt comprises lithium bis(oxalate)borate.

7. The lithium metal anode of any one of claims 1-3, wherein the siloxane-based polymer comprises polydimethylsiloxane, the lithium salt comprises lithium bis(oxalate)borate, the amount of polydimethylsiloxane used to form the cured polymer composite material is in the range of about 0.3% by weight to about 30% by weight based on the total weight of the solution applied for coating the foil, and the amount of lithium bis(oxalate)borate used to form the cured polymer composite material is in the range of about 0.1% by weight to about 10% by weight based on the total weight of the solution applied for coating the foil.

8. The lithium metal anode of any one of claims 1-3, wherein the coating solution forming the cured polymer composite material after curing comprises the siloxane-based polymer, the lithium salt, an organic solvent, and a curing agent.

9. The lithium metal anode of claim 8, wherein the organic solvent comprises ether, heterocyclic acetal, dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), chloroform, or a mixture of two or more of the foregoing.

10. The lithium metal anode of claim 9, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

11. The lithium metal anode of any one of claims 8-10, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

12. A lithium metal or lithium metal alloy anode coating solution, comprising the following: Siloxane-based polymers; Lithium salts; and Organic solvents.

13. The coating solution of claim 12, wherein the lithium salt comprises boron.

14. The coating solution according to any one of claims 12-13, wherein the solvent comprises an ether, a heterocyclic acetal, or a mixture of two or more of the foregoing.

15. The coating solution of claim 14, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

16. The coating solution according to any one of claims 12-13, wherein the solvent comprises dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), or chloroform.

17. The coating solution according to any one of claims 12-16, further comprising a curing agent.

18. The coating solution of claim 17, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

19. The coating solution of any one of claims 12-18, wherein the siloxane-based polymer comprises polydimethylsiloxane.

20. The coating solution according to any one of claims 12-19, wherein the lithium salt comprises lithium bis(oxalate)borate.

21. The coating solution of claim 19, wherein the lithium salt comprises lithium bis(oxalate)borate, the polydimethylsiloxane in the coating solution is in the range of about 0.3% by weight to about 30% by weight of the total weight of the solution, and the amount of lithium bis(oxalate)borate in the coating solution is in the range of about 0.1% by weight to about 10% by weight of the total weight of the solution.

22. A method comprising applying a coating solution to a lithium metal or lithium metal alloy foil to form a coated lithium metal anode, wherein the coating solution comprises a siloxane-based polymer, a lithium salt, and an organic solvent.

23. The method of claim 22, wherein the solvent comprises an ether, a heterocyclic acetal, or a mixture of two or more of the foregoing.

24. The method of claim 23, wherein the solvent comprises an ether, and the ether is selected from the group consisting of: dimethoxyethane, dimethoxymethane, diethyl ether, tetrahydrofuran (THF), methyltetrahydrofuran (2-MeTHF), tert-butyl methyl ether (TBME), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), and triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), and mixtures of any two or more of the foregoing.

25. The method of claim 23, wherein the solvent comprises dimethyl carbonate (DMC), ethylene carbonate (EC), propylene carbonate (PC), acetonitrile, dimethyl-3-pentanone, dimethyl-2-butanone, n-methyl-2-pyrrolidone (NMP), butyrolactone, dimethyl sulfoxide (DMSO), or chloroform.

26. The method according to any one of claims 22-25, wherein the coating further comprises a curing agent.

27. The method of claim 26, wherein the curing agent comprises poly(dimethyl-methylhydrosiloxane), tetramethyltetravinylcyclotetrasiloxane, trimethylated silica, or any combination of two or more of the foregoing.

28. The method according to any one of claims 22-27, further comprising drying the coated lithium metal anode.

29. The method of claim 28, wherein the drying is performed at one or more temperatures in the range of about 20°C to about 80°C.

30. The method according to any one of claims 22-29, wherein the lithium metal foil is laminated onto the substrate prior to coating.

31. The method according to any one of claims 22-30, wherein the lithium salt comprises boron.

32. The method of claim 31, wherein the lithium salt comprises lithium bis(oxalate)borate.

33. The method according to any one of claims 22-32, wherein the siloxane-based polymer comprises poly(dimethylsiloxane).

34. The method of claim 22, wherein the lithium salt comprises lithium bis(oxalate)borate, the siloxane-based polymer comprises poly(dimethylsiloxane), the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3 wt% to about 30 wt% based on the total weight of the solution, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1 wt% to about 10 wt% based on the total weight of the solution.

35. The method according to any one of claims 22-34, further comprising washing the coated lithium metal anode with one or more washing solvents to form a washed coated lithium metal anode.

36. The method of claim 35, wherein the washing is performed prior to drying and at one or more temperatures in the range of about 20°C to about 50°C.

37. The method of claim 36, further comprising drying the washed coated lithium metal anode.

38. A secondary battery, comprising: cathode, Electrolytes, and A lithium metal anode, the lithium metal anode comprising a lithium metal or lithium metal alloy foil coated with a cured polymer composite material, the polymer composite material comprising a siloxane-based polymer and a lithium salt.

39. The secondary battery of claim 35, wherein the foil prior to being coated is part of a laminate consisting of the foil and a substrate.

40. The secondary battery of claim 36, wherein the substrate comprises copper, nickel, stainless steel, surface-treated copper, surface-treated nickel, or surface-treated stainless steel.

41. The secondary battery according to any one of claims 35-37, wherein the siloxane-based polymer comprises polydimethylsiloxane.

42. The secondary battery according to any one of claims 35-38, wherein the lithium salt comprises boron.

43. The secondary battery of claim 39, wherein the lithium salt comprises lithium bis(oxalate)borate.

44. The secondary battery of any one of claims 35-37, wherein the siloxane-based polymer comprises polydimethylsiloxane, the lithium salt comprises lithium bis(oxalate)borate, the amount of polydimethylsiloxane initially in the coating solution is in the range of about 0.3% by weight to about 30% by weight, and the amount of lithium bis(oxalate)borate initially in the coating solution is in the range of about 0.1% by weight to about 10% by weight.

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