Lithium metal anode and method of manufacturing the same

Abstract

Lithium metal anodes and methods of making the same are disclosed. An anode for an electrochemical cell for a secondary lithium metal battery is made by applying a precursor solution to a major surface of a lithium metal substrate to form a protective interfacial layer thereon. The precursor solution includes a first mixture of organic solvents, a dioxolane, and a fluorinated organosilane. The protective interfacial layer exhibits a composite structure including a polymeric matrix component and a lithium-containing dispersed component embedded in the polymeric matrix component.

Description

Technical Field

[0001] This invention relates to lithium metal battery packs, and more particularly to an interface coating for lithium metal anodes. Background Technology

[0002] Lithium metal is an ideal anode material for rechargeable lithium metal battery packs due to its high specific capacity (3,860 mAh / g) and low reduction potential (-3.04 V relative to the standard hydrogen electrode). In lithium metal battery packs, elemental lithium metal is deposited onto and peeled off the surface of the negative electrode current collector during charging and discharging, resulting in significant volume changes in the negative electrode during battery cycling. Due to the low reduction potential of lithium metal, redox reactions can inherently occur at the interface between the lithium metal anode and the organic liquid electrolyte, such as during the initial charging of the battery pack. This can lead to the in-situ formation of an electrically insulating and ion-conducting layer called the solid electrolyte interface (SEI) on the surface of the lithium metal anode.

[0003] Forming a natural SEI on the surface of the lithium metal anode prevents the organic liquid electrolyte from being directly exposed to the lithium metal surface and can help promote uniform deposition and stripping of lithium ions at the anode during battery cycling, which can help prevent lithium dendrite nucleation and growth. However, the inherent mechanical stability and flexibility of the naturally formed SEI layer may not be sufficient to compensate for the large volume changes experienced by the lithium metal anode during repeated battery cycling. Cracks or damage to the SEI layer during the battery's lifespan may lead to repeated direct exposure of the organic liquid electrolyte to the lithium metal anode, forming additional SEI material, as well as further decomposition of the liquid electrolyte and consumption of active lithium.

[0004] It is desirable to develop a method for forming an electrically insulating and ion-conducting layer on the surface of a lithium metal anode, which exhibits good mechanical stability and flexibility and can suppress undesirable side reactions between the lithium metal of the anode and the liquid electrolyte during the initial charging and lifespan of the battery pack. Summary of the Invention

[0005] In a method for manufacturing the negative electrode of an electrochemical cell used in a secondary lithium metal battery pack, a precursor solution is applied to the main surface of a lithium metal substrate to form a protective interface layer thereon. The precursor solution comprises an organic solvent mixture, dioxanes, and fluorinated organosilanes. The protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersed component embedded within the polymer matrix component.

[0006] The dioxacyclopentanes can be compounds containing a dioxacyclopentane ring.

[0007] The dioxacyclopentanes can be 1,3-dioxacyclopentanes.

[0008] The dioxane may be included in the precursor solution in an amount of 1% to 60% by weight, constituting the precursor solution.

[0009] The fluorinated organosilane can be a compound having the following formula: R'R" n SiX 4–n , where n = 0, 1 or 2, and where R' is a polyfluorinated C1–C8 alkyl group, R" is a methyl group, and X is a methoxy or chlorine atom.

[0010] The fluorinated organosilane may be at least one of (3,3,3-trifluoropropylmethyl)dimethoxysilane, (3,3,3-trifluoropropyl)trimethoxysilane, 1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyldimethylchlorosilane, 1H,1H,2H,2H-perfluorooctylmethyldichlorosilane, (1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane.

[0011] The fluorinated organosilane may be included in the precursor solution in an amount of 1% to 10% by weight, constituting the precursor solution.

[0012] The organic solvent mixture may contain a mixture of acyclic ethers and cyclic ethers.

[0013] The organic solvent mixture may contain a mixture of 1,2-dimethoxyethane and tetrahydrofuran.

[0014] The polymer matrix component can be chemically bonded to the main surface of the lithium metal substrate via multiple silicon-oxygen bonds and / or alkoxide bonds.

[0015] The polymer matrix component may contain multiple siloxane bonds.

[0016] The lithium-containing dispersion may contain lithium fluoride.

[0017] The method may further include removing unreacted dioxane compounds, fluorinated organosilane compounds, and / or migrated reaction byproducts from the protective interface layer.

[0018] Unreacted dioxolane compounds, fluorinated organosilane compounds, and / or mobile reaction byproducts can be removed from the protective interface layer by washing it with a nonpolar organic solvent.

[0019] In another method for manufacturing the negative electrode of an electrochemical cell used in a secondary lithium metal battery pack, a continuous lithium metal layer is formed on the main surface of a metal substrate. A precursor solution is applied to the main opposing surface of the continuous lithium metal layer to directly form a protective interface layer on the main opposing surface of the continuous lithium metal layer. The precursor solution comprises a mixture of organic solvents, dioxanes, and fluorinated organosilanes. The protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersed component embedded in the polymer matrix component. The polymer matrix component is chemically bonded to the main opposing surface of the continuous lithium metal layer via multiple silicon-oxygen bonds and / or alkoxide bonds.

[0020] The polymer matrix component may contain multiple siloxane bonds, and the lithium-containing dispersion component may contain lithium fluoride.

[0021] The precursor solution can be applied to the main opposing surfaces of the continuous lithium metal layer by immersing the metal substrate in the precursor solution.

[0022] An electrochemical cell for a lithium metal battery pack is disclosed. The electrochemical cell includes a positive electrode, a lithium metal negative electrode spaced apart from the positive electrode, and a non-aqueous liquid electrolyte in contact with the positive and negative electrodes. The positive electrode comprises a transition metal oxide capable of reversible lithium-ion intercalation. The lithium metal negative electrode includes a lithium metal layer disposed on a negative electrode current collector. The lithium metal layer has a predominant opposing surface facing the positive electrode. A protective interface layer is formed directly on the predominant opposing surface of the lithium metal layer along the interface between the lithium metal negative electrode and the non-aqueous liquid electrolyte. This protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersed component embedded in the polymer matrix component. The polymer matrix component is chemically bonded to the lithium metal layer via multiple silicon-oxygen bonds and / or alkoxide bonds.

[0023] The lithium metal layer may contain more than 97% lithium by weight.

[0024] The transition metal oxide of the positive electrode can be a high-nickel-content lithium nickel cobalt manganese oxide with the following chemical formula: , where a = 0.1–0.2 and b = 0.1–0.2.

[0025] The non-aqueous liquid electrolyte may contain a non-aqueous aprotic organic solvent and a lithium salt dissolved in the non-aqueous aprotic organic solvent.

[0026] The present invention discloses the following technical solutions:

[0027] Option 1. A method for manufacturing a negative electrode of an electrochemical cell for use in secondary lithium metal battery packs, the method comprising:

[0028] The precursor solution is applied to the main surface of the lithium metal substrate to form a protective interface layer thereon.

[0029] The precursor solution comprises an organic solvent mixture, dioxanes, and fluorinated organosilanes, and

[0030] The protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersion component embedded in the polymer matrix component.

[0031] Option 2. According to the method of Option 1, wherein the dioxacyclopentanes are compounds containing a dioxacyclopentane ring.

[0032] Option 3. The method according to Option 1, wherein the dioxacyclopentane is 1,3-dioxacyclopentane.

[0033] Option 4. According to the method of Option 1, wherein the dioxacyclopentane is included in the precursor solution in an amount of 1% to 60% by weight of the precursor solution.

[0034] Option 5. The method according to Option 1, wherein the fluorinated organosilanes are compounds having the following formula: R'R" n SiX 4–n , where n = 0, 1 or 2, and where R' is a polyfluorinated C1–C8 alkyl group, R" is a methyl group, and X is a methoxy or chlorine atom.

[0035] Option 6. According to the method of Option 5, the fluorinated organosilane is at least one selected from (3,3,3-trifluoropropylmethyl)dimethoxysilane, (3,3,3-trifluoropropyl)trimethoxysilane, 1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyldimethylchlorosilane, 1H,1H,2H,2H-perfluorooctylmethyldichlorosilane, (1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane.

[0036] Option 7. The method according to Option 1, wherein the fluorinated organosilane is contained in the precursor solution in an amount of 1% to 10% by weight of the precursor solution.

[0037] Option 8. The method according to Option 1, wherein the organic solvent mixture comprises a mixture of acyclic ethers and cyclic ethers.

[0038] Option 9. The method according to Option 8, wherein the organic solvent mixture comprises a mixture of 1,2-dimethoxyethane and tetrahydrofuran.

[0039] Option 10. According to the method of Option 1, wherein the polymer matrix component is chemically bonded to the main surface of the lithium metal substrate via a plurality of silicon-oxygen bonds and / or alkoxide bonds.

[0040] Option 11. The method according to Option 1, wherein the polymer matrix component comprises a plurality of siloxane bonds.

[0041] Option 12. The method according to Option 1, wherein the lithium-containing dispersion component comprises lithium fluoride.

[0042] Option 13. The method according to Option 1 further includes:

[0043] Unreacted dioxolane compounds, fluorinated organosilane compounds, and / or mobile reaction byproducts are removed from the protective interface layer.

[0044] Option 14. The method according to Option 13, wherein unreacted dioxane compounds, fluorinated organosilane compounds and / or migrated reaction byproducts are removed from the protective interface layer by washing the protective interface layer with a nonpolar organic solvent.

[0045] Option 15. A method for manufacturing a negative electrode of an electrochemical cell for use in secondary lithium metal battery packs, the method comprising:

[0046] A continuous lithium metal layer is formed on the main surface of a metal substrate; and

[0047] The precursor solution is applied to the main opposing surfaces of the continuous lithium metal layer to form a protective interface layer directly on the main opposing surfaces of the continuous lithium metal layer.

[0048] The precursor solution comprises a mixture of organic solvents, dioxanes, and fluorinated organosilanes.

[0049] The protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersion component embedded in the polymer matrix component, and

[0050] The polymer matrix component is chemically bonded to the main opposing surfaces of the continuous lithium metal layer via multiple silicon-oxygen bonds and / or alkoxide bonds.

[0051] Option 16. The method according to Option 15, wherein the polymer matrix component comprises a plurality of siloxane bonds, and wherein the lithium-containing dispersion component comprises lithium fluoride.

[0052] Option 17. An electrochemical cell for a lithium metal battery pack, the electrochemical cell comprising:

[0053] The positive electrode contains a transition metal oxide that can undergo reversible lithium-ion intercalation.

[0054] A lithium metal anode spaced apart from the positive electrode, the lithium metal anode comprising a lithium metal layer disposed on a negative electrode current collector, the lithium metal layer having a predominant opposing surface facing the positive electrode; and

[0055] A non-aqueous liquid electrolyte that comes into contact with the positive electrode and lithium metal negative electrode ions.

[0056] A protective interface layer is formed directly on the main opposing surfaces of the lithium metal layer along the interface between the lithium metal anode and the non-aqueous liquid electrolyte.

[0057] The protective interface layer exhibits a composite structure comprising a polymer matrix component and a lithium-containing dispersion component embedded in the polymer matrix component, and

[0058] The polymer matrix component is chemically bonded to the lithium metal layer via multiple silicon-oxygen bonds and / or alkoxide bonds.

[0059] Option 18. The electrochemical battery according to Option 17, wherein the lithium metal layer contains more than 97% lithium by weight.

[0060] Option 19. The electrochemical cell according to Option 17, wherein the transition metal oxide of the positive electrode is a high-nickel-content lithium nickel cobalt manganese oxide having the following chemical formula: , where a = 0.1–0.2 and b = 0.1–0.2.

[0061] Option 20. The electrochemical cell according to Option 17, wherein the non-aqueous liquid electrolyte comprises a non-aqueous aprotic organic solvent and a lithium salt dissolved in the non-aqueous aprotic organic solvent.

[0062] The foregoing summary is not intended to represent every possible embodiment or aspect of this disclosure. Rather, the foregoing summary is intended to illustrate some novel aspects and features disclosed herein. The foregoing features and advantages, as well as other features and advantages, of this disclosure will become apparent when taken in conjunction with the accompanying drawings and appended claims, through the following detailed description of representative embodiments and models for carrying out this disclosure. Attached Figure Description

[0063] The illustrative embodiments will now be described with reference to the accompanying drawings, wherein the same reference numerals denote the same elements, and wherein:

[0064] Figure 1 It is a schematic side cross-sectional view of an electrochemical cell including a negative electrode, a positive electrode, and a liquid electrolyte in contact with the negative and positive electrode ions, wherein the negative electrode includes a lithium metal layer disposed on the main surface of the negative electrode current collector and a protective interface layer formed directly on the main opposite surface of the lithium metal layer.

[0065] Figure 2 This is a schematic side cross-sectional view of a double-sided negative electrode, which includes a negative electrode current collector having first and second lithium metal layers disposed on its opposing first and second sides, and first and second protective interface layers formed on the main opposing surfaces of the first and second lithium metal layers.

[0066] Figure 3 It is used for manufacturing Figure 2 A schematic side cross-sectional view of a device with a double negative electrode.

[0067] This disclosure is readily modified and substituted, with representative embodiments illustrated by way of example in the accompanying drawings and described in detail below. The inventive aspects of this disclosure are not limited to the specific forms disclosed. Rather, this disclosure is intended to cover modifications, equivalents, combinations, and alternatives that fall within the scope of this disclosure as defined by the appended claims. Detailed Implementation

[0068] The method disclosed herein can be used to form a protective interface layer that provides ion conduction and electrical insulation on the main opposing surfaces of a lithium metal anode before incorporating it into an electrochemical cell within a lithium metal battery pack. The resulting protective interface layer exhibits excellent flexibility and mechanical stability, and effectively accommodates the volume changes experienced by the lithium metal anode during cycling within the lithium metal battery pack. The formation of the protective interface layer of this disclosure is non-in-situ and does not lead to the decomposition of the liquid electrolyte or the consumption of active lithium metal.

[0069] Figure 1 A schematic side cross-sectional view of an electrochemical cell 10 is depicted, which can be combined with one or more additional electrochemical cells to form a secondary lithium battery pack, such as a lithium metal battery pack (not shown). The electrochemical cell 10 includes a negative electrode 12, a positive electrode 14 spaced apart from the negative electrode 12, a non-aqueous liquid electrolyte 16 providing a medium for conducting lithium ions between the negative electrode 12 and the positive electrode 14, and a porous separator 18 electrically separating the negative electrode 12 and the positive electrode 14 while allowing lithium ions to pass through. The negative electrode 12 is disposed on the main surface 20 of the negative electrode current collector 22, and the positive electrode 14 is disposed on the main surface of the positive electrode current collector 24. In practice, the negative electrode current collector 22 and the positive electrode current collector 24 can be electrically coupled to a power source or load 26 via an external circuit 28.

[0070] The negative electrode 12 includes an electrochemically active material layer in the form of a lithium metal layer 30 disposed on the main surface 20 of the negative electrode current collector 22 and a protective interface layer 32 formed on the main opposing surface 34 of the lithium metal layer 30.

[0071] The lithium metal layer 30 can be directly or indirectly disposed on the main surface 20 of the negative electrode current collector 22. The lithium metal layer 30 may comprise a lithium metal alloy or may be substantially composed of lithium (Li) metal. For example, the lithium metal layer 30 may contain more than 97% lithium by weight, or more preferably more than 99% lithium. The lithium metal layer 30 preferably does not contain any other elements or compounds that undergo reversible redox reactions with lithium during the operation of the electrochemical cell 10. For example, the lithium metal layer 30 preferably does not contain an intercalation host material formulated to undergo reversible insertion or intercalation of lithium ions, or an alloy material that can be alloyed with lithium electrochemistry to form a compound phase. Furthermore, the lithium metal layer 30 preferably does not contain conversion materials or alloy materials that can be alloyed with lithium electrochemistry to form a compound phase. Examples of materials preferably excluded from the lithium metal layer 30 include carbon-based materials (e.g., graphite, activated carbon, carbon black, and graphene), silicon and silicon-based materials, tin oxide, aluminum, indium, zinc, cadmium, lead, germanium, tin, antimony, titanium oxide, lithium titanium oxide, lithium titanate, lithium oxide, metal oxides (e.g., iron oxide, cobalt oxide, manganese oxide, copper oxide, nickel oxide, chromium oxide, ruthenium oxide, and / or molybdenum oxide), metal phosphides, metal sulfides, and metal nitrides (e.g., phosphides, sulfides, and / or nitrides of iron, manganese, nickel, copper, and / or cobalt). The lithium metal layer 30 does not contain a polymer binder. Examples of polymer binders preferably excluded from the lithium metal layer 30 include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid. Depending on the state of charge of the electrochemical cell 10, the lithium metal layer 30 may have a thickness greater than 0 micrometers and less than or equal to 100 micrometers.

[0072] The lithium metal layer 30 can have a thickness of 0.1 micrometers to 100 micrometers.

[0073] The protective interface layer 32 creates an electrically insulating and ion-conducting interface between the lithium metal layer 30 and the non-aqueous liquid electrolyte 16 within the electrochemical cell 10. This interface is configured, for example, to promote Li + Uniform deposition and stripping of ions on the negative electrode current collector 22 and suppression of undesirable parasitic side reactions between the lithium metal layer 30 and the non-aqueous liquid electrolyte 16 improve coulombic efficiency and cycle stability. The protective interface layer 32 is formed directly on the main opposing surface 34 of the lithium metal layer 30 and is configured to prevent direct contact between the lithium metal layer 30 and the non-aqueous liquid electrolyte 16 during storage and operation of the electrochemical cell 10.

[0074] The protective interface layer 32 can exhibit an organic-inorganic composite structure, which includes a polymer matrix component and an inorganic lithium-containing dispersion component embedded in the polymer matrix component.

[0075] The polymer matrix component may be substantially amorphous and may contain a variety of organic compounds chemically bonded to the main opposing surface 34 of the lithium metal layer 30 via silicon-oxygen (–Si–O–Li) bonds or alkoxide bonds (R–O–Li), wherein R may be C1–C6 alkyl. In several aspects, at least some of the organic compounds bonded to the main opposing surface 34 of the lithium metal layer 30 via silicon-oxygen bonds may be represented by the following chemical formula: R–Si–O–Li, wherein R may be polyfluorinated or perfluorinated C3–C8 alkyl. For example, in several aspects, at least some of the organic compounds bonded to the main opposing surface 34 of the lithium metal layer 30 may be represented by the following chemical formula: R–Si–O–Li, wherein R is one or more of –CH2CH2CF3; –CH2CH2(CF2)3CF3; or –CH2CH2(CF2)5CF3. Not intended to be theoretically constrained, it is believed that the perfluoroalkyl moiety (–CF2–) and trifluoromethyl end group (–CF3) in the polymer matrix component of the protective interface layer 32 may help improve Li + Ions are transported through the protective interface layer 32 during the cycling of the electrochemical cell 10.

[0076] The polymer matrix component may contain multiple interconnected siloxane bonds (–Si–O–Si–), which can provide a protective interface layer 32 with improved mechanical stability and flexibility compared to the natural SEI layer that is inherently formed in situ on the lithium metal layer 30 due to the parasitic reaction between the lithium metal layer 30 and the non-aqueous liquid electrolyte 16.

[0077] The inorganic lithium-containing dispersion may contain one or more lithium-containing inorganic ionic compounds embedded in and encapsulated within the polymer matrix component. These lithium-containing inorganic ionic compounds may include compounds of lithium fluoride (LiF).

[0078] The protective interface layer 32 can exhibit a thickness of 10 nanometers to 5 micrometers.

[0079] The protective interface layer 32 can exhibit a porosity of up to 60%.

[0080] The cathode 14 is porous and may contain one or more electrochemically active materials capable of undergoing reversible redox reactions with lithium, such as materials capable of undergoing lithium intercalation and deintercalation, alloying and dealloying, or plating and peeling. In one form, the cathode 14 may contain an intercalation host material capable of undergoing reversible insertion or intercalation of lithium ions. In such cases, the intercalation host material of the cathode 14 may include layered oxides represented by the formula LiMeO2, olivine-type oxides represented by the formula LiMePO4, spinel-type oxides represented by the formula LiMe2O4, lithium hydroxyphosphide represented by one or two of the following formulas LiMeSO4F or LiMePO4F, or combinations thereof, wherein Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or combinations thereof). In another form, the cathode 14 may contain a conversion material comprising a component capable of undergoing a reversible electrochemical reaction with lithium, wherein the component undergoes a phase transition or crystal structure change accompanied by a change in oxidation state. In such cases, the conversion material of the cathode 14 may comprise sulfur, selenium, tellurium, iodine, halides (e.g., fluorides or chlorides), sulfides, selenides, tellurides, iodides, phosphides, nitrides, oxides, oxysulfides, oxyfluorides, sulfur fluoride, sulfur oxyfluoride, or lithium and / or its metal compounds. Examples of suitable metals included in the conversion material of the cathode 14 include iron, manganese, nickel, copper, and cobalt.

[0081] In several respects, the cathode 14 may comprise an electrochemically active material in the form of layered high-nickel-content lithium nickel cobalt manganese oxide (LiNiCoMnO2 or NCM). In such cases, nickel (Ni), cobalt (Co), and manganese (Mn) may be present in the electrochemically active material in a ratio of 3–9.5:0–3:0.5–3 or 6–8:1–2:1–2.

[0082] The electrochemically active material of the positive electrode 14 may be mixed with a polymer binder to provide structural integrity to the positive electrode 14. Examples of polymer binders include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer (EPDM) rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid, and mixtures thereof. The positive electrode 14 may optionally contain particles of conductive material, which may include, for example, very fine particles of high surface area carbon black.

[0083] The non-aqueous liquid electrolyte 16 is ion-conducting and provides an ion conduction pathway for transporting lithium ions between the negative electrode 12 and the positive electrode 14. During assembly, the electrochemical cell 10 can be permeated with the non-aqueous liquid electrolyte 16 to allow the lithium metal layer 30 to physically contact the positive electrode 14, for example, by wetting it with the non-aqueous liquid electrolyte 16. The non-aqueous liquid electrolyte 16 can be in the form of a non-aqueous liquid electrolyte solution, a gel electrolyte, or a solid electrolyte. When the non-aqueous liquid electrolyte 16 is in the form of a non-aqueous liquid electrolyte solution, it can contain a lithium salt dissolved or ionized in a non-aqueous aprotic organic solvent or a mixture of non-aqueous aprotic organic solvents. Examples of lithium salts include LiClO4, LiAlCl4, LiI, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, Li2CO3, LiPF6, and combinations thereof. Examples of non-aqueous aprotic organic solvents include cyclic carbonates (i.e., ethylene carbonate, propylene carbonate), acyclic carbonates (i.e., dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate), aliphatic carboxylic acid esters (i.e., methyl formate, methyl acetate, methyl propionate), γ-lactones (i.e., γ-butyrolactone, γ-valerolactone), acyclic ethers (i.e., 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), and / or cyclic ethers (i.e., tetrahydrofuran, 2-methyltetrahydrofuran). When the non-aqueous liquid electrolyte 16 is in the form of a gel or plasticized polymer electrolyte, the non-aqueous liquid electrolyte 16 may comprise a polymeric host material impregnated with a non-aqueous liquid electrolyte solution. Examples of polymer host materials include poly(vinylidene fluoride) (PVdF), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(ethylene oxide) (PEO), polyacrylate, and poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP).

[0084] The porous separator 18 is configured to physically separate the negative electrode 12 and the positive electrode 14 from each other while allowing lithium ions to pass through. The porous separator 18 exhibits an open microporous structure and may contain organic and / or inorganic materials. The porous separator 18 may contain nonwoven materials, such as sheets, webs, or felts made of oriented or randomly oriented fibers. The porous separator 18 may contain microporous polymeric materials, such as microporous polyolefin-based membranes or films. For example, the porous separator 18 may contain a single polyolefin or a combination of polyolefins, such as polyethylene (PE), polypropylene (PP), polyamide (PA), poly(tetrafluoroethylene) (PTFE), polyvinylidene fluoride (PVdF), and / or poly(vinyl chloride) (PVC). In one form, the porous separator 18 may contain a laminate of one or more polymeric materials, such as a laminate of PE and PP. The porous separator 18 may contain a ceramic coating (not shown). The ceramic coating can be applied to one or both sides of the porous separator 18 and can have a thickness of 1 micrometer to 20 micrometers. The material constituting the ceramic coating can be selected from: alumina (Al2O3), silicon dioxide (SiO2), and combinations thereof.

[0085] The negative and positive current collectors 22 and 24 can be in the form of thin and flexible porous or non-porous conductive metal substrates. The term "metal" as used herein refers to materials made of a single-element metal or mixtures of two or more elements, at least one of which is a metal. One or more other elements can be nonmetals or different metals. In several respects, the negative current collector 22 may comprise copper (Cu), nickel (Ni), iron (Fe) alloys (e.g., stainless steel), or titanium (Ti). Other conductive metals may, of course, be used if desired.

[0086] Now refer to Figure 2 and 3 The double-sided negative electrode 112 can be manufactured using a continuous roll-to-roll process. Figure 2 The bifacial negative electrode 112 described in the text is similar in many ways to the one described above relative to... Figure 1 The description of the negative electrode 12, and the description of the common theme, will not be repeated here.

[0087] The double-sided negative electrode 112 includes a negative electrode current collector 122 having a first main surface 120 and an opposing second main surface 121. A first lithium metal layer 130 is disposed on the first main surface 120 of the negative electrode current collector 122, and a second lithium metal layer 131 is disposed on the second main surface 121 of the negative electrode current collector 122. A first protective interface layer 132 is formed on the main opposing surface 134 of the first lithium metal layer 130, and a second protective interface layer 133 is formed on the main opposing surface 135 of the second lithium metal layer 131.

[0088] like Figure 3As shown, in the method of manufacturing the double-sided negative electrode 112, a metal substrate 222 having a first main surface and an opposing second main surface can be provided. The metal substrate 222 includes a first lithium metal layer (not shown) disposed on its first main surface and a second lithium metal layer (not shown) disposed on its second main surface. The metal substrate 222 can be in the form of a thin, continuous metal foil and can be wound onto a first spool 236 during storage. During the manufacturing process, the metal substrate 222 can be unwound from the first spool 236 and transported via a plurality of rollers 238.

[0089] On the metal substrate 222, by applying the precursor solution 240 to the principal opposing surfaces of the first and second lithium metal layers, a first protective interface layer (not shown) can be formed on the principal opposing surface of the first lithium metal layer, and a second protective interface layer (not shown) can be formed on the principal opposing surface of the second lithium metal layer. For example, as Figure 3 As shown, the precursor solution 240 can be applied to the principal opposing surfaces of the first and second lithium metal layers by immersing the metal substrate 222 in a predetermined volume of precursor solution 240. After forming the first and second protective interface layers, the metal substrate 222 can be removed from the precursor solution and rewound onto the second spool 242, for example, for its storage and / or transport. In several aspects, after forming the first and second protective interface layers, the metal substrate 222 can be washed to remove residual reactants and / or migrated reaction byproducts from the first and second protective interface layers. The metal substrate 222 (including the first and second lithium metal layers and the overlying first and second protective interface layers) can be cut into segments of desired lengths and used as bifacial negative electrodes in secondary lithium metal battery packs.

[0090] The precursor solution used to form the first and second protective interface layers may contain dioxanes and fluorinated organosilanes dissolved or dispersed in a nonpolar organic solvent. The dioxanes and fluorinated organosilanes in the precursor solution are formulated to react with the hydroxyl (-OH) groups of lithium metal attached to the main opposing surface of the lithium metal layer, thereby forming a chemical and physical bond with them.

[0091] The dioxacyclopentanes are formulated to react with a lithium metal layer to form various organic compounds chemically bonded to the lithium metal layer via alkoxide bonds (R–O–Li), where R can be C1–C6 alkyl or alkoxy groups. Dioxacyclopentanes are compounds containing a dioxacyclopentane ring, i.e., 5-membered heterocyclic compounds with the chemical formula (CR2)2O2CR2, where R can be the same or different and can contain hydrogen (H), oxygen (=O), or an organic functional group. Examples of organic functional groups include alkyl and alkoxy groups. For example, the dioxacyclopentanes may contain 1,3-dioxacyclopentane; 4,5-diethyl-dioxacyclopentane; 4,5-dimethyl-dioxacyclopentane; 4-methyl-1,3-dioxacyclopentane; and / or 4-ethyl-1,3-dioxacyclopentane. In several aspects, the dioxacyclopentanes may consist essentially of 1,3-dioxacyclopentane.

[0092] The dioxane may be included in the precursor solution in an amount of 1% to 60% by weight, or 10% to 50% by weight of the precursor solution.

[0093] The fluorinated organosilane is formulated to react with a lithium metal layer to form various organic functional compounds bonded to the lithium metal layer via silicon-oxygen (–Si–O–Li) bonds. The fluorinated organosilane can be a fluorinated methoxysilane or a fluorinated chlorosilane. The fluorinated organosilane may have the following chemical formula: R'R". n SiX 4–n Where n = 0, 1, or 2, and where R' is a polyfluorinated or perfluorinated C1–C8 alkyl group, R" is a methyl group (–CH3), and X is a hydrolyzable group. In several aspects, R' can be –CH2CH2CF3; –CH2CH2(CF2)3CF3; or –CH2CH2(CF2)5CF3, and X can be an alkoxy group (e.g., a methoxy group (–OCH3) or a chlorine atom (Cl)). For example, the fluorinated organosilane may include (3,3,3-trifluoropropylmethyl)dimethoxysilane (CAS No. 358-67-8); (3,3,3-trifluoropropyl)trimethoxysilane (CAS No. 429-60-7); 1 H ,1 H ,2 H ,2 H -Perfluorooctylmethyldimethoxysilane, 1 H ,1 H ,2 H ,2 H - Perfluorooctyltrimethoxysilane (CAS No. 85857-17-6); 1 H ,1 H ,2 H ,2 H- Perfluorooctyldimethylchlorosilane (CAS No. 102488-47-1); 1 H ,1 H ,2 H ,2 H - Perfluorooctylmethyldichlorosilane (CAS No. 73609-36-6); (1) H ,1 H ,2 H ,2 H -Perfluoro-n-hexyl)methyldichlorosilane (CAS No. 38436-16-7); and / or 1 H ,1 H ,2 H ,2 H - Perfluorooctyl-trichlorosilane (CAS No. 78560-45-9).

[0094] The fluorinated organosilane may be included in the precursor solution in an amount of 1% to 10% by weight, or 2% to 5% by weight of the precursor solution.

[0095] The nonpolar organic solvent may comprise a mixture of one or more nonpolar organic solvents. For example, the nonpolar organic solvent may comprise a mixture of acyclic ethers and cyclic ethers. The acyclic ether may include 1,2-dimethoxyethane (DME); 1,2-diethoxyethane; tetraethylene glycol dimethyl ether; and / or polyethylene glycol dimethyl ether. The cyclic ether may include tetrahydrofuran (THF) and / or 2-methyltetrahydrofuran. In several aspects, the nonpolar organic solvent may comprise a mixture of 1,2-dimethoxyethane and tetrahydrofuran. 1,2-dimethoxyethane and tetrahydrofuran may be contained in the nonpolar organic solvent in a 1:1 volume ratio.

[0096] After forming the first and second protective interface layers on the metal substrate 222 and removing the metal substrate 222 from the precursor solution, the first and second protective interface layers can be washed with an inert liquid to remove residual amounts of dioxanes and fluorinated organosilanes, and / or to remove reaction byproducts not chemically bonded to or embedded in the first and second protective interface layers. The inert liquid may contain a nonpolar organic solvent, such as 1,2-dimethoxyethane and / or tetrahydrofuran. Residual amounts of nonpolar organic solvents and / or inert liquid can be removed from the first and second protective interface layers, for example, by heating the first and second protective interface layers in an inert gas environment (e.g., argon, nitrogen, and / or helium).

[0097] In view of the foregoing disclosure, those skilled in the art will readily understand these and other benefits.

[0098] While some best practices and other embodiments have been described in detail, various alternative designs and embodiments exist to practice the teachings as defined in the appended claims. Those skilled in the art will recognize that modifications can be made to the disclosed embodiments without departing from the scope of this disclosure. Furthermore, this concept explicitly includes combinations and sub-combinations of the described elements and features. The detailed description and accompanying drawings are supporting and illustrating the teachings, the scope of which is defined only by the claims.

Claims

1. A method of manufacturing a negative electrode for an electrochemical cell of a secondary lithium metal battery, the method comprising: applying a precursor solution to a major surface of a lithium metal substrate so as to form a protective interfacial layer thereon, wherein the precursor solution comprises an organic solvent mixture, 10-50 wt.% dioxolanes, and 2-5 wt.% fluorinated organosilane, and wherein the protective interfacial layer exhibits a composite structure comprising a polymeric matrix component and a lithium-containing dispersed component embedded in the polymeric matrix component, wherein the polymeric matrix component is chemically bonded to the major surface of the lithium metal substrate via a plurality of silicon-oxygen bonds and / or alkoxide bonds, wherein the fluorinated organosilane is at least one of (3,3,3-trifluoropropylmethyl)dimethoxysilane, (3,3,3-trifluoropropyl)trimethoxysilane, 1H,1H,2H,2H-perfluorooctylmethyldimethoxysilane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyldimethylchlorosilane, 1H,1H,2H,2H-perfluorooctylmethyldichlorosilane, (1H,1H,2H,2H-perfluoro-n-hexyl)methyldichlorosilane, or 1H,1H,2H,2H-perfluorooctyltrichlorosilane.

2. The method of claim 1, wherein the dioxolanes are compounds containing a dioxolane ring.

3. The method of claim 1, wherein the dioxolanes are 1,3-dioxolane.

4. The method of claim 1, wherein the organic solvent mixture comprises a mixture of acyclic and cyclic ethers.

5. The method of claim 4, wherein the organic solvent mixture comprises a mixture of 1,2-dimethoxyethane and tetrahydrofuran.

6. The method of claim 1, wherein the polymeric matrix component comprises a plurality of siloxane bonds.

7. The method of claim 1, wherein the lithium-containing dispersed component comprises fluorinated lithium.

8. The method of claim 1, further comprising: removing unreacted dioxolane compounds, fluorinated organosilane compounds, and / or mobile reaction byproducts from the protective interfacial layer.

9. The method of claim 8, wherein unreacted dioxolane compounds, fluorinated organosilane compounds, and / or mobile reaction byproducts are removed from the protective interfacial layer by washing the protective interfacial layer with a non-polar organic solvent.

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