Method for manufacturing pre-lithiated negative electrode for solid-state battery

Abstract

Embodiments of the present invention provide a method of making a pre-lithiated negative electrode comprising preparing a negative electrode assembly comprising a negative electrode current collector and an intermediate layer disposed on a surface of the negative electrode current collector wherein the intermediate layer comprises silver particles and a carbon material; applying an electrolyte to the intermediate layer; manufacturing a pressurized structure by stacking a lithium supply layer on the intermediate layer coated with the electrolyte; and performing pre-lithiation by applying pressure to the pressurized structures in a stacking direction of the pressurized structures to convert the intermediate layer into a coating layer, thereby forming a pre-lithiated negative electrode, in which the coating layer includes a [gamma] 3-phase Li-Ag alloy formed by reacting the silver particles with lithium when the pre-lithiation is performed.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a pre-lithiated anode for a solid-state battery. Background Art

[0002] Recently, the automotive industry, which is involved in transportation, has shown significant interest in electric vehicles using secondary batteries to address environmental concerns caused by carbon dioxide (CO2) emissions and avoid the use of fossil fuels. While currently available lithium-ion batteries offer a range of approximately 40 kilometers on a single charge, they still present issues such as instability at high temperatures and fire hazards. To address these issues, numerous companies are racing to develop next-generation secondary batteries.

[0003] All-solid-state batteries have attracted attention as the next generation of secondary batteries. Compared to lithium-ion batteries that use flammable organic solvents as electrolytes, all-solid-state batteries have the advantages of lower fire and explosion risks and higher mechanical strength because all components of all-solid-state batteries are formed from solids. All-solid-state batteries generally include a positive electrode (cathode), a negative electrode (anode), and a solid electrolyte layer. The positive electrode includes a positive electrode active material layer bonded to a positive electrode current collector, and the negative electrode includes a negative electrode active material layer bonded to a negative electrode current collector. The solid electrolyte layer is located between the positive and negative electrode active material layers.

[0004] The negative electrode active material layer is usually formed by mixing a negative electrode active material such as graphite and silicon with a solid electrolyte to ensure lithium-ion conduction. Compared with lithium-ion batteries, the energy density of conventional all-solid-state batteries is lower because the specific gravity of the solid electrolyte is lower than that of the liquid electrolyte.

[0005] In order to solve such problems, a storage-type negative electrode-free all-solid-state battery is proposed, in which the negative electrode active material layer is removed or only a small amount of negative electrode active material is used, and lithium ions (Li + ) is directly deposited on the negative electrode current collector as lithium metal or lithium alloy.

[0006] In a storage-type anode-free all-solid-state battery, when charging, lithium ions (Li + ) are released from the positive electrode active material layer. Lithium ions pass through the solid electrolyte layer and receive electrons on the surface of the negative electrode current collector, undergoing a reduction reaction to produce lithium metal. The reverse electrochemical reaction occurs during discharge. This means that anode-free all-solid-state batteries can be charged and discharged without the presence of negative electrode active material.

[0007] In this regard, it is known that the electrochemical characteristics of anode-free all-solid-state batteries can be improved by inserting a separate layer including silver (Ag) and carbon material alloyed with lithium between the solid electrolyte layer and the anode current collector, but there is a problem of reduced initial cycle efficiency due to irreversible reactions occurring during the initial charging and discharging process.

[0008] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art. Summary of the Invention

[0009] The present invention relates to a method for manufacturing a pre-lithiated anode for a solid-state battery. A specific embodiment relates to a method for manufacturing a pre-lithiated anode, wherein a lithium alloy having a specific phase is formed by pre-lithiating a layer including silver (Ag) particles and a carbon material, thereby improving the initial cycle efficiency and coulombic efficiency of an all-solid-state battery including the manufactured pre-lithiated anode.

[0010] The embodiments of the present invention can solve the problems associated with the prior art. The embodiments of the present invention provide a method for manufacturing a pre-lithiation negative electrode, which can improve the initial charge / discharge cycle efficiency and coulombic efficiency of the negative electrode-free all-solid-state battery while maintaining excellent electrochemical properties of the negative electrode-free all-solid-state battery.

[0011] The embodiments of the present invention are not limited to the above-mentioned embodiments. The embodiments of the present invention will become more clear through the following description, and the embodiments of the present invention can be implemented by the methods described in the claims and their combinations.

[0012] One embodiment of the present invention may provide a method for manufacturing a pre-lithiated negative electrode, the method comprising preparing a negative electrode assembly comprising a negative electrode current collector and an intermediate layer disposed on at least one surface of the negative electrode current collector; applying an electrolyte solution to the intermediate layer; manufacturing a pressurization structure by stacking a lithium supply layer on the intermediate layer coated with the electrolyte, and performing pre-lithiation by applying pressure to the pressurization structure along a stacking direction of the pressurization structure to convert the intermediate layer into a coating layer, wherein the intermediate layer may include silver (Ag) particles and a carbon material, and the coating layer may include a γ3-phase Li-Ag alloy formed by reacting the silver particles with lithium when performing pre-lithiation.

[0013] In a preferred embodiment, the electrolyte may include a lithium salt and an organic solvent.

[0014] In another preferred embodiment, the lithium salt may include a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) and combinations thereof.

[0015] In another preferred embodiment, the organic solvent may include a solvent selected from the group consisting of ester-based solvents, ether-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, carbonate-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, dioxolane-based solvents and sulfolane-based solvents and combinations thereof.

[0016] In another preferred embodiment, the area of the lithium supply layer may be larger than the area of the negative electrode assembly.

[0017] In another preferred embodiment, the pressure applied to the pressurizing structure may be 0.01 MPa to 0.1 MPa.

[0018] In another preferred embodiment, the pre-lithiation can be carried out for more than 5 hours but less than 10 hours. In addition, the pre-lithiation can be carried out for 5 hours to 7 hours.

[0019] In another preferred embodiment, the prelithiation can be performed at room temperature.

[0020] In another preferred embodiment, the γ3 phase Li—Ag alloy may be represented by Formula 1 below.

[0021] Formula 1:

[0022] Li x Ag (x is 1.98 to 2.25)

[0023] In another preferred embodiment, the γ3 phase Li—Ag alloy can be irreversibly formed.

[0024] In yet another preferred embodiment, the coating may not include γ2 phase Li—Ag alloy and γ1 phase Li—Ag alloy.

[0025] In another preferred embodiment, the carbon material may include at least one carbon material selected from the group consisting of a particulate carbon material, a fibrous carbon material, and a combination thereof.

[0026] In another preferred embodiment, the manufacturing method may further include collecting the pre-lithiated negative electrode including the negative electrode current collector and the coating after pre-lithiation, removing remaining impurities from the pre-lithiated negative electrode with a washing solvent, and drying the pre-lithiated negative electrode from which the impurities have been removed.

[0027] Other aspects and preferred embodiments of the invention are discussed below.

[0028] The above features and other features of embodiments of the present invention are discussed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other features of embodiments of the present invention will now be described in detail with reference to certain exemplary embodiments shown in the accompanying drawings, which are given hereinafter by way of illustration only and therefore do not limit the present invention, in which:

[0030] Figure 1 A method for manufacturing a pre-lithiated negative electrode according to an embodiment of the present invention is shown;

[0031] Figure 2 1. A process for forming a Li-Ag alloy in a pre-lithiation process according to an embodiment of the present invention is shown;

[0032] Figure 3 An all-solid-state battery including a negative electrode manufactured according to an embodiment of the present invention is shown;

[0033] Figure 4 shows the phase diagram of Li-Ag alloy;

[0034] Figure 5 1. In the manufacturing process of the negative electrode according to the comparative preparation example, the in-situ XRD result measured by applying voltage or current is shown;

[0035] Figure 6 1. In the manufacturing process of the negative electrode according to the preparation example, the in-situ XRD result measured by applying voltage or current is shown;

[0036] Figure 7 Shows the XRD results of the negative electrode manufactured by adjusting the pre-lithiation time;

[0037] Figure 8 shows the initial charge / discharge results of a coin cell manufactured according to a comparative example;

[0038] Figure 9 shows the initial charge / discharge results of the coin cell manufactured according to the embodiment;

[0039] Figure 10 The coulombic efficiency of the coin cells manufactured according to the embodiment is shown.

[0040] It should be understood that the accompanying drawings are not necessarily drawn to scale, but rather present various preferred features in a somewhat simplified manner to illustrate the basic principles of the embodiments of the present invention. The specific design features of the embodiments of the present invention as disclosed herein (including, for example, specific dimensions, orientations, locations, and shapes) will be determined in part by the specific intended application and use environment.

[0041] In the drawings, like reference numerals refer to like or equivalent parts of the present invention throughout the several views. DETAILED DESCRIPTION

[0042] The above-mentioned objects, other objects, advantages and features of the embodiments of the present invention will become apparent from the following description of the embodiments with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed herein, and the present invention can be implemented in various different forms. The embodiments are provided to provide a detailed description of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0043] In the accompanying drawings, even if the same or similar elements are described in different figures, they are represented by the same reference numerals. In the accompanying drawings, for clarity of description, the size of the structure is amplified compared to its actual size. In the following description of the embodiment, terms such as "first", "second" etc. can be used to describe various elements, but these elements are not limited. These terms are only used to distinguish one element from other elements. For example, without departing from the scope and spirit of the present invention, the first element can be referred to as the second element, and similarly, the second element can be referred to as the first element. Singular expressions can include plural expressions unless they have significantly different meanings in the context.

[0044] In the following description of the embodiments, terms such as "including", "comprising", "having", etc. should be interpreted as indicating the presence of the features, numbers, steps, operations, elements or parts or their combinations stated in the specification, but do not exclude the presence of one or more other features, numbers, steps, operations, elements, parts or their combinations or the possibility of adding them. In addition, it should be understood that when a part such as a layer, film, region or plate is referred to as being "on" another part, the part can be "directly above" the other part or other parts can be placed between the two parts. In the same way, it should also be understood that when a part such as a layer, film, region or plate is referred to as being "under" another part, the part can be "directly under" the other part or other parts can be placed between the two parts.

[0045] Unless the context clearly indicates otherwise, all numbers, values and / or expressions representing the amounts of components, reaction conditions, polymer compositions and mixtures used in this specification are approximate values, which reflect the various measurement uncertainties generated when these values are obtained from substantially different things. Therefore, it should be understood that they are modified by the term "about". In addition, it should be understood that when a numerical range is disclosed in the specification, unless otherwise defined, such range includes all continuous values from the minimum value to the maximum value within the range. In addition, if such a range involves an integer, unless otherwise defined, the range includes all integers from the minimum integer to the maximum integer.

[0046] It is known that the electrochemical characteristics of a storage-type negative electrode-free all-solid-state battery are improved by inserting a separate layer including silver (Ag) and a carbon material that forms an alloy with lithium between the solid electrolyte layer and the negative electrode current collector. In this negative electrode-free all-solid-state battery, the negative electrode active material layer is removed or only a small amount of negative electrode active material is used, and lithium ions (Li + ) is directly deposited on the negative electrode current collector as lithium metal or lithium alloy. However, this technology has the problem of reduced initial cycle efficiency due to irreversible reactions during the initial charge and discharge process.

[0047] The present invention addresses this issue. By pre-lithiating the negative electrode before assembling the all-solid-state battery 1', and using the pre-lithiated negative electrode to manufacture the all-solid-state battery 1', the initial charge and discharge efficiency of the all-solid-state battery 1' can be increased. This will be described in more detail below.

[0048] Method for manufacturing pre-lithiation negative electrode

[0049] Figure 1A pressurized structure 1 configured to fabricate a pre-lithiated negative electrode 10 ′ and a pressing process for fabricating the pre-lithiated negative electrode 10 ′ are shown according to an embodiment of the present invention. Figure 2 The process of forming a Li-Ag alloy in a pre-lithiation process according to an embodiment of the present invention is shown. Figure 3 A manufacturing method according to an embodiment of the present invention is shown for manufacturing an all-solid-state battery 1 ′ including a pre-lithiated negative electrode 10 ′.

[0050] Reference Figure 1 and Figure 2 , a method for manufacturing a lithiated negative electrode 10' may include preparing a negative electrode assembly 10, the negative electrode assembly 10 including a negative electrode current collector 11 and an intermediate layer 12 disposed on at least one surface of the negative electrode current collector 11; coating an electrolyte 13 on the intermediate layer 12; manufacturing a pressurized structure 1 by stacking a lithium supply layer 14 in the intermediate layer 12 coated with the electrolyte 13, and performing pre-lithiation by applying pressure to the pressurized structure 1 along a stacking direction of the pressurized structure 1 to convert the intermediate layer 12 into a coating layer 12'.

[0051] First, the intermediate layer 12 may be stacked on at least one surface, preferably any one surface, of the negative electrode current collector 11. Here, the intermediate layer 12 may include silver (Ag) particles and a carbon material. The silver (Ag) particles may be understood as silver (Ag) in powder form and may form an alloy with lithium in a pre-lithiation operation to be described later.

[0052] Furthermore, the carbon material may include a carbon material selected from the group consisting of a particulate carbon material, a fibrous carbon material, and a combination thereof.

[0053] The particulate carbon material may include a carbon material selected from the group consisting of carbon black, easily graphitizable carbon (ie, soft carbon), non-graphitizable carbon (ie, hard carbon), and combinations thereof. The particle size of the particulate carbon material is not particularly limited and may be, for example, 10 nm to 200 nm.

[0054] Furthermore, the fibrous carbon material may include a carbon material selected from the group consisting of carbon nanofibers, carbon nanotubes, vapor-grown carbon fibers, and combinations thereof. The cross-sectional diameter of the fibers of the fibrous carbon material is not particularly limited and may be, for example, 10 nm to 200 nm.

[0055] In one embodiment, the method of stacking the intermediate layer 12 on the negative electrode current collector 11 can use conventional techniques used in the relevant technical field. For example, a slurry can be prepared by placing powders including silver particles and carbon materials in an organic solvent and mixing them. Thereafter, the intermediate layer 12 can be stacked on the negative electrode current collector 11 by applying the slurry to the negative electrode current collector 11 and then drying the slurry.

[0056] In one embodiment, the negative electrode current collector 11 may include a material that does not react with lithium. Specifically, the negative electrode current collector 11 may include at least a material selected from the group consisting of nickel (Ni), copper (Cu), stainless steel, and combinations thereof.

[0057] The thickness of the negative electrode current collector 11 is not particularly limited and may be, for example, 1 μm to 500 μm.

[0058] After the negative electrode assembly 10 including the intermediate layer 12 stacked on the negative electrode collector 11 is prepared through the above-described process, the electrolyte 13 may be applied to the intermediate layer 12 .

[0059] The electrolyte 13 may include a substance having high lithium-ion conductivity. For example, the electrolyte 13 may include a lithium salt and an organic solvent.

[0060] The lithium salt may be any compound that can provide lithium ions without particular limitation. For example, the lithium salt may include a compound selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI) and LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) and combinations thereof.

[0061] The concentration of the lithium salt may preferably be in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte 13 has appropriate conductivity and viscosity, and thus it may exhibit excellent electrolyte performance and enable efficient movement of lithium ions.

[0062] Any substance can be used as the organic solvent without particular limitation, as long as it can serve as a medium that allows ions involved in the electrochemical reaction of the battery to move. For example, the organic solvent may include a solvent selected from the group consisting of ester-based solvents, ether-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, carbonate-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, dioxolane-based solvents, and sulfolane-based solvents, and combinations thereof.

[0063] Specifically, the organic solvent may include an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone or ε-caprolactone, an ether-based solvent such as dibutyl ether or tetrahydrofuran, a ketone-based solvent such as cyclohexanone, an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene, a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) or propylene carbonate (PC), an alcohol-based solvent such as ethanol or isopropanol, a nitrile-based solvent such as R-CN (R is a hydrocarbon group having a linear, branched or cyclic structure having 2 to 20 carbon atoms and including a double-bonded aromatic ring or an ether bond), an amide-based solvent such as dimethylformamide, a dioxolane-based solvent such as 1,3-dioxolane or a sulfolane-based solvent.

[0064] Among them, carbonate-based solvents are preferred, and more preferably a mixture of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and low-viscosity chain carbonates (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.). In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte 13 can be excellent.

[0065] The pressurized structure 1 can be manufactured by stacking a lithium supply layer 14 on the intermediate layer 12 coated with the electrolyte 13 after applying the electrolyte 13 to the intermediate layer 12. The lithium supply layer 14 supplies lithium ions to the intermediate layer 12 in a pre-lithiation operation to be described later, and the lithium supply layer 14 may include, for example, a lithium (Li) foil.

[0066] Here, the area of the lithium supply layer 14 may be greater than or equal to the area of the negative electrode assembly 10. Figure 1 and Figure 2 As shown, the area of the lithium supply layer 14 is greater than or equal to the area of the negative electrode assembly 10 to cover the entire area where the negative electrode assembly 10 is located, thereby allowing a more efficient pre-lithiation operation.

[0067] Thereafter, the intermediate layer 12 may be converted into the coating layer 12' by applying pressure to the pressurized structure 1 in its stacking direction. The meaning of "conversion" may refer to a series of processes in which a Li-Ag alloy is formed by a reaction between silver (Ag) particles in the intermediate layer 12 and lithium ions released from the lithium supply layer 14 or lithium ions moving through the electrolyte 13.

[0068] Thus, the coating 12 ′ may include a Li—Ag alloy formed by a reaction between silver (Ag) particles and lithium in a pre-lithiation operation.

[0069] This will be described in more detail with reference to the phase diagram of Li-Ag alloy. Figure 4 A phase diagram of Li-Ag alloy is shown.

[0070] Reference Figure 4 In the temperature range below about 124°C, the Li-Ag alloy can exist in the form of silver (Ag) phase, β phase, γ3 phase, γ2 phase, γ1 phase, and mixed states thereof. In addition, based on room temperature, when the lithium (Li) content is 0% to 35.0%, the silver (Ag) phase may appear; when the lithium (Li) content is 49% to 51%, the β phase may appear; when the lithium (Li) content is 66.5% to 69.1%, the γ3 phase may appear; when the lithium (Li) content is 78% to 83%, the γ2 phase may appear; and when the lithium (Li) content is 89% to 92%, the γ1 phase may appear.

[0071] Therefore, in Li-Ag alloys, as the content of lithium (Li) alloyed with silver (Ag) increases, the alloy may undergo a phase transformation of silver (Ag) phase → β phase → γ3 phase → γ2 phase → γ1 phase.

[0072] Here, the Li-Ag alloy according to an embodiment of the present invention preferably has a γ3 phase. In the coating layer 12' including the γ3-phase Li-Ag alloy and the pre-lithiated negative electrode 10' including the coating layer, the γ3-phase Li / Ag alloy may not revert to silver (Ag) particles even if the battery is repeatedly charged and discharged. In other words, the γ3-phase Li-Ag alloy in the coating layer 12' may be irreversibly formed.

[0073] In a conventional anode-free all-solid-state battery including a non-pre-lithiated coating (i.e., the intermediate layer 12), lithium is consumed due to the irreversible formation of a γ3-phase Li-Ag alloy during battery charging and discharging, thereby reducing the initial charge / discharge efficiency. According to an embodiment of the present invention, the γ3-phase Li-Ag alloy irreversibly formed as described above is pre-prepared by pre-lithiation before assembling the all-solid-state battery 1', and then the all-solid-state battery 1' is assembled, thereby minimizing the amount of lithium consumed during the initial charge and discharge.

[0074] In addition, it is preferred that the coating 12' does not include a γ1-phase Li-Ag alloy and a γ2-phase Li-Ag alloy. In the γ1-phase Li-Ag alloy and the γ2-phase Li-Ag alloy, Li and Ag form an alloy at a relatively high ratio. Therefore, when the coating 12' includes a γ1-phase Li-Ag alloy and a γ2-phase Li-Ag alloy, additional lithium alloy may not be formed when the all-solid-state battery 1' is charged after being assembled, and therefore, the all-solid-state battery 1' may be difficult to use as a negative electrode-free battery.

[0075] In one embodiment, the γ3 phase Li—Ag alloy may be represented by Li8Ag5 to Li9Ag4. Preferably, the γ3 phase Li—Ag alloy may be represented by the following Formula 1.

[0076] Formula 1:

[0077] Li x Ag (x is 1.98 to 2.25)

[0078] However, the value of x is based on Figure 4 As the technology develops, if the binary Li-Ag phase diagram becomes more complex, the value of x may be slightly different.

[0079] According to an embodiment of the present invention, the degree of phase transformation of the Li-Ag alloy can be adjusted by performing pre-lithiation while applying a specified pressure to the pressurized structure 1. In one embodiment, the pressure applied to the pressurized structure 1 can be 0.01 MPa to 0.1 MPa. When a pressure of 0.01 MPa to 0.1 MPa is applied to the pressurized structure 1, a γ3 phase Li-Ag alloy can be formed.

[0080] When a pressure of less than 0.01 MPa is applied to the pressurized structure 1, the Li-Ag alloying rate is relatively high, and the phase transformation of the Li-Ag alloy may exceed the γ3 phase and transform into the γ2 phase and the γ1 phase. On the other hand, when a pressure exceeding 0.1 MPa is applied to the pressurized structure 1, the Li-Ag alloying rate is too low, and therefore, the time required for pre-lithiation may increase, and the process efficiency may be reduced.

[0081] During the process of converting the intermediate layer 12 into the coating layer 12′ according to the manufacturing method of the embodiment of the present invention, the lithium (Li) content included in the Li—Ag alloy may increase due to the movement of lithium ions. Therefore, the Li—Ag alloy in the coating layer 12′ may undergo a phase transition from a silver (Ag) phase to a β phase to a γ3 phase.

[0082] In one embodiment, the pre-lithiation can be carried out for more than 5 hours but less than 10 hours. Preferably, the pre-lithiation can be carried out for 5 hours to 7 hours.

[0083] When the pre-lithiation is performed for less than 5 hours, the γ3 phase Li-Ag alloy in the coating 12' may not be fully formed. When the pre-lithiation time is more than 10 hours, the phase transformation of the Li-Ag alloy may exceed the γ3 phase and turn into the γ2 phase and the γ1 phase. When the pre-lithiation is performed for 5 to 7 hours, the initial cycle efficiency and coulombic efficiency of the all-solid-state battery 1' can be improved due to the pre-lithiation, and the process efficiency can be improved in a balanced manner.

[0084] In one embodiment, the pre-lithiation may be performed at room temperature. By performing the pre-lithiation at room temperature, costs may be reduced compared to cases where the pre-lithiation is performed at a temperature other than room temperature.

[0085] At the same time, there is no particular restriction on the method of applying pressure to the pressurized structure 1 in the stacking direction of the pressurized structure 1. For example, after attaching a pressure plate such as a glass plate to the upper and lower surfaces of the pressurized structure 1, pressure can be applied to the pressurized structure 1 by pressing the pressure plate.

[0086] In one embodiment, the pre-lithiation operation can be performed without applying a separate voltage. The intermediate layer 12 is converted into the coating layer 12 ′ comprising a γ3 phase Li—Ag alloy without applying a separate voltage, thereby reducing the energy input in the pre-lithiation process.

[0087] In addition, after pre-lithiation, the manufacturing method may further include collecting the pre-lithiated negative electrode 10' including the negative electrode current collector 11 and the coating 12', removing remaining impurities from the pre-lithiated negative electrode 10' with a washing solvent, and drying the pre-lithiated negative electrode 10' from which the impurities have been removed.

[0088] Specifically, after pre-lithiation, the pressure plates attached to the upper and lower surfaces of the pressurized structure 1 may be removed, and the pre-lithiated negative electrode 10 ′ excluding the lithium supply layer 14 and the electrolyte 13 in the pressurized structure 1 may be collected.

[0089] Impurities such as electrolyte 13 may remain on the surface of pre-lithiated negative electrode 10', and these impurities can be removed using a washing solvent such as dimethyl carbonate. In addition to dimethyl carbonate, other substances that can dissolve and easily remove impurities can be used without particular limitation.

[0090] Thereafter, the washing solvent may be removed by drying the pre-lithiated negative electrode 10' under vacuum. Here, the drying may be performed at room temperature for about 1 hour, but the drying conditions are not particularly limited as long as the washing solvent can be removed.

[0091] Manufacturing method of all-solid-state battery

[0092] Figure 3 An all-solid-state battery 1' including a pre-lithiated negative electrode 10' according to an embodiment of the present invention is shown. Referring to the figure, the all-solid-state battery 1' according to an embodiment of the present invention may include a pre-lithiated negative electrode 10' manufactured by a manufacturing method according to an embodiment of the present invention, a solid electrolyte layer 20 provided on the pre-lithiated negative electrode 10' and including a solid electrolyte, and a positive electrode 30 including a positive electrode active material layer 32 containing a positive electrode active material and a positive electrode current collector 31.

[0093] The pre-lithiated negative electrode 10 ′ is substantially the same as the pre-lithiated negative electrode 10 ′ described in the above “Method for Manufacturing a Pre-lithiated Negative Electrode”, and thus redundant description thereof will be omitted.

[0094] In one embodiment, the solid electrolyte layer 20 may be located between the positive active material layer 32 and the coating layer 12 ′, and may include a solid electrolyte having lithium ion conductivity.

[0095] The solid electrolyte may include an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and the like. Preferably, a sulfide-based solid electrolyte having high lithium ion conductivity is used as the solid electrolyte. The sulfide-based solid electrolyte may include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (x and y are positive numbers, M is one of P, Si, Ge, B, Al, Ga and In), Li 10 GeP2S 12 etc. without particular limitation.

[0096] Oxide-based solid electrolytes may include perovskite-type LLTO (Li 3x La 2 / 3-x TiO3), phosphate-based NASICON-type LATP (Li 1+x Al x Ti 2-x (PO4)3) etc.

[0097] The positive electrode active material layer 32 may include a positive electrode active material, a solid electrolyte, a conductive material, a binder, etc. The positive electrode active material can allow lithium ions to be intercalated and deintercalated therein, and thus may include materials such as LiCoO2, LiMnO2, LiNiO2, LiVO2, or Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and other rock salt layer active materials, such as LiMn2O4 or Li(Ni0.5 Mn 1.5 ) O4 and other spinel-type active materials, such as inverse spinel-type active materials like LiNiVO4 or LiCoVO4, olivine-type active materials like LiFePO4, LiMnPO4, LiCoPO4 or LiNiPO4, silicon-containing active materials like Li2FeSiO4 or Li2MnSiO4, and rock salt-type active materials in which a part of the transition metal is substituted with different kinds of metals, such as LiNi 0.8 Co (0.2-x) Al x O2 (0 < x < 0.2), etc., and spinel-type active materials in which a part of the transition metal is substituted with different kinds of metals, such as Li 1+x Mn 2-x-y M y O4 (M is at least one of Al, Mg, Co, Fe, Ni or Zn, 0 < x + y < 2), etc., such as Li4Ti5O 12 and lithium titanates such as

[0098] The solid electrolyte may include oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. Sulfide-based solid electrolytes with high lithium ion conductivity can preferably be used as the solid electrolyte. Sulfide-based solid electrolytes may include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is one of Ge, Zn and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (x and y are positive numbers, M is one of P, Si, Ge, B, Al, Ga and In), Li 10 GeP2S 12 and so on without particular limitation. The solid electrolyte included in the positive electrode active material layer 32 may be the same as or different from the solid electrolyte included in the solid electrolyte layer 20.

[0099] The conductive material may include carbon black, conductive graphite, ethylene black, graphene, etc.

[0100] The binder may include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), and the like.

[0101] The positive electrode current collector 31 may include a plate-type substrate having conductivity. The positive electrode current collector 31 may include aluminum foil.

[0102] The thickness of the positive electrode current collector 31 may be, for example, 1 μm to 500 μm without particular limitation.

[0103] Hereinafter, the embodiments of the present invention will be described in more detail through the following examples and comparative examples. The following examples and comparative examples are only used to exemplarily describe the embodiments of the present invention and are not intended to limit the scope and spirit of the present invention.

[0104] Preparation Example

[0105] (1) A slurry was prepared by placing silver (Ag) powder, Super C as a granular carbon material, and polyvinylidene fluoride (PVDF) as a binder in N-methyl-2-pyrrolidone (NMP) as an organic solvent. An intermediate layer was formed by coating the slurry onto a nickel thin film as a negative electrode current collector and drying the slurry. Here, the intermediate layer was circular, and its diameter was set to 10 mm.

[0106] (2) The electrolyte was applied to the negative electrode assembly including the negative electrode current collector and the intermediate layer. The electrolyte composition was 1.15M LiPF6 in EC / EMC (v:v=3:7) containing 10 wt% fluoroethylene carbonate (FEC).

[0107] (3) A lithium (Li) foil having an area larger than that of the negative electrode assembly is prepared as a lithium supply layer. The lithium foil is positioned to cover the entire intermediate layer of the negative electrode assembly.

[0108] (4) After placing a pressurized structure including the negative electrode assembly, electrolyte, and lithium supply layer on a glass plate, another glass plate is stacked on the upper surface of the pressurized structure as a pressure plate. Thereafter, pre-lithiation is performed by applying a specified pressure to the pressurized structure by pressing the lower and upper glass plates.

[0109] Here, the pressure applied to the pressurized structure was 0.05 MPa, and the pre-lithiation was performed at room temperature for 5 hours.

[0110] (5) The pressure applied to the pressurized structure was removed and the negative electrode assembly was collected. Thereafter, the negative electrode assembly was washed with dimethyl carbonate as a solvent, and then the solvent was removed by vacuum drying the negative electrode assembly at room temperature for 1 hour. Through this process, a pre-lithiated negative electrode was produced.

[0111] Comparative Preparation Example

[0112] A pre-lithiated negative electrode was manufactured by the same process as in the above Preparation Example, except that the pre-lithiation was performed without applying a separate pressure to the pressurizing structure.

[0113] Test Example 1

[0114] To confirm that the phase difference of the Li-Ag alloy depends on the pressure applied during pre-lithiation, the pre-lithiated anodes fabricated according to the Preparation Example and the Comparative Preparation Example were analyzed by in situ XRD while applying voltage and current.

[0115] Figure 5 The in-situ XRD results of the pre-lithiation negative electrode according to the comparative preparation example are shown. Figure 6 The in-situ XRD results of the pre-lithiation negative electrode according to the preparation example are shown. Here, the pre-lithiation by applying voltage and current is carried out at 0.5C (0.5mAcm -2 ) and 1 mAh cm -2 (or 0.15V) cut-off condition.

[0116] Referring to the in-situ XRD results of the negative electrode assembly including the pre-lithiated negative electrode according to the comparative preparation example Figure 5 During the pre-lithiation reaction, the silver (Ag) peak completely disappeared and the γ3 phase Li-Ag alloy peak appeared, which confirmed that all the silver (Ag) particles included in the intermediate layer participated in the alloying with lithium, and thus the intermediate layer was converted into a coating.

[0117] In addition, it was confirmed that the γ3 phase Li-Ag alloy peak disappeared and the γ2 phase Li-Ag alloy peak appeared. After that, a certain amount of the γ2 phase Li-Ag alloy underwent a phase transition to the γ1 phase, resulting in the observation of the γ1 phase Li-Ag alloy peak. Here, the vertical LPSCl peak is caused by the solid electrolyte.

[0118] Referring to the in-situ XRD results of the negative electrode assembly including the pre-lithiated negative electrode according to the preparation example Figure 6 During the pre-lithiation reaction, the silver (Ag) peak completely disappeared and the γ3 phase Li-Ag alloy peak appeared, confirming that all silver (Ag) particles included in the intermediate layer participated in the alloying with lithium, and thus the intermediate layer was converted into a coating.

[0119] However, in the negative electrode assembly including the pre-lithiated negative electrode according to the preparation example, after the γ3 phase Li-Ag alloy peak appeared, no γ2 phase Li-Ag alloy peak and γ1 phase Li-Ag alloy peak were observed. In addition, the section of the silver (Ag) peak was observed to be longer than that in the comparative preparation example, confirming that Li-Ag alloying occurred slowly.

[0120] The above results confirm that both Li-Ag alloying and Li electrodeposition occur in the negative electrode assemblies according to the preparation examples and the comparative preparation examples, wherein lithium (Li) metal is deposited on the negative electrode current collector. In the negative electrode assembly according to the preparation example, Li electrodeposition plays a more dominant role than Li-Ag alloying, while in the negative electrode assembly according to the comparative preparation example, Li-Ag alloying plays a more dominant role than Li electrodeposition.

[0121] Specifically, referring again to the phase diagram showing the Li-Ag binary alloy Figure 4 When the lithium (Li) content is about 66.5% to 69.1%, a γ3 phase Li-Ag alloy appears; when the lithium (Li) content is about 78% to 83%, a γ2 phase Li-Ag alloy appears; and when the lithium (Li) content is about 89% to 92%, a γ1 phase Li-Ag alloy appears.

[0122] That is, in the preparation example, the alloying reaction was carried out until the lithium (Li) content was about 69%, but in the comparative preparation example, the alloying reaction was carried out until the lithium (Li) content was about 92%, and a large amount of lithium participated in the alloying reaction. Therefore, it can be predicted that in the pre-lithiation process of the negative electrode assembly according to the preparation example, Li electrodeposition plays a more dominant role than Li-Ag alloying, while in the pre-lithiation process of the negative electrode assembly according to the comparative preparation example, Li-Ag alloying plays a more dominant role than Li electrodeposition.

[0123] Test Example 2

[0124] In order to confirm the effect of pre-lithiation time on the phase transition behavior of Li-Ag alloy, a negative electrode assembly including a pre-lithiation negative electrode was manufactured using the manufacturing method according to the preparation example by changing the time required to apply pressure to the pressurized structure. After the negative electrode assembly was manufactured by changing the pre-lithiation time, the pre-lithiation negative electrode was separated from the negative electrode assembly, and XRD analysis was performed on each pre-lithiation negative electrode. The XRD results of the pre-lithiation negative electrode are shown in FIG. Figure 7 shown.

[0125] Reference Figure 7When the pre-lithiation time is less than 5 hours, only the Ag phase and the β phase are observed. When the pre-lithiation time is continued for more than 5 hours, the γ3 phase is observed. In addition, the γ3 phase Li-Ag alloy peak becomes faint, and the γ2 phase Li-Ag alloy peak begins to be observed. It is expected that this is because the Li-Ag alloy in the γ3 phase transforms into the γ2 phase.

[0126] Example

[0127] (1) A solid electrolyte layer was prepared by placing 80 mg of lithium phosphorus sulfur chloride (LPSCl), a sulfide-based solid electrolyte, into a cylindrical mold and then applying a pressure of 70 MPa for 5 seconds. Here, the diameter of the solid electrolyte layer was about 10.1 mm.

[0128] (2) Compacted powder was prepared by placing the pre-lithiated negative electrode and the solid electrolyte layer prepared according to the Preparation Example into a coin cell mold and then applying a pressure of 500 MPa for 20 seconds.

[0129] (3) After the compacted powder is aligned with the center of the coin cell case, a gasket, lithium metal, a spacer, a plurality of springs, and a lid are assembled in sequence. The lithium metal has a diameter of 10 mm and a thickness of 300 μm, and the thickness of the spacer is 1 mm. Thereafter, a coin cell is manufactured by applying a stacking pressure of 0.6 MPa to the coin cell case. Although a stacking pressure of 0.6 MPa is applied in the embodiment, a pressure lower than this value may also be applied.

[0130] Comparative Example

[0131] (1) A slurry was prepared by placing silver (Ag) powder, Super C as a granular carbon material, and polyvinylidene fluoride (PVDF) as a binder in N-methyl-2-pyrrolidone (NMP) as an organic solvent. A negative electrode including an Ag / C layer formed on the negative electrode current collector was manufactured by coating the slurry on a nickel thin film as a negative electrode current collector and drying the slurry.

[0132] (2) A solid electrolyte layer was prepared by placing 80 mg of lithium phosphorus sulfur chloride (LPSCl) as a sulfide-based solid electrolyte into a cylindrical mold and then applying a pressure of 70 MPa for 5 seconds. Here, the diameter of the solid electrolyte layer was about 10.1 mm.

[0133] (3) Compacted powder was made by placing the fabricated negative electrode and solid electrolyte into a coin cell mold and then applying a pressure of 500 MPa for 20 seconds.

[0134] (4) After aligning the compacted powder to the center of the coin cell case, the gasket, lithium metal, spacer, two springs, and lid were assembled in sequence. The lithium metal had a diameter of 10 mm and a thickness of 300 μm, and the spacer had a thickness of 1 mm. The coin cell was then fabricated by applying a stacking pressure of 0.6 MPa to the coin cell case.

[0135] Test Example 3-Electrochemical Characteristics Analysis

[0136] In order to detect the initial cycle efficiency of the coin cells according to the embodiment and the comparative example, the coin cells were subjected to initial charge and discharge tests. 2 , 0.15 V and a current density of 0.1 mA / cm 2 Charge and discharge under the conditions of

[0137] Figure 8 The results of the coin cell according to the comparative example are shown. Figure 9 The results of the coin cell according to the embodiment are shown. In the case of the embodiment, in order to ensure repeatability, two coin cell samples were manufactured using the same manufacturing method.

[0138] Reference Figure 8 Coin cells including the negative electrode according to the comparative example (in which no pre-lithiation was performed) demonstrated very unstable behavior in the initial cycles and could not operate normally in a room temperature environment due to short circuits. This is expected to be because lithium was consumed during the initial charge and discharge process due to the irreversible formation of a γ3 phase Li-Ag alloy.

[0139] Reference Figure 9 , it was confirmed that Samples 1 and 2 including the pre-lithiated negative electrode according to the embodiment operated stably at room temperature. In addition, Figure 10 The coulombic efficiency of samples 1 and 2 depends on repeated charge and discharge cycles. Figure 10 , confirming that alloying and electrodeposition / desorption reactions occur simultaneously in the initial cycle, but as the cycles are repeated, the efficiency continues to improve and the sample behaves metallically. This is expected to be because the initial irreversible reaction is minimized by prelithiation.

[0140] It can be clearly seen from the above description that in the manufacturing method of the pre-lithiation negative electrode for an all-solid-state battery according to an embodiment of the present invention, a coating layer including a γ3 phase Li-Ag alloy is formed by pre-lithiating an intermediate layer including silver (Ag) particles and a carbon material.

[0141] In the manufacturing method according to an embodiment of the present invention, before assembling an all-solid-state battery, an irreversibly formed γ3-phase Li-Ag alloy is formed by pre-lithiation. Then, when assembling the all-solid-state battery, a coating layer comprising the γ3-phase Li-Ag alloy is placed between the negative electrode current collector and the solid electrolyte layer, thereby minimizing irreversible reactions during the initial charge and discharge cycles. As a result, the initial cycle efficiency and coulombic efficiency of the all-solid-state battery can be improved.

[0142] Specifically, applying a pressure of 0.01 MPa to 0.1 MPa while controlling the phase transition of Li-Ag alloy to the γ3 phase by performing pre-lithiation can improve the initial cycle efficiency and Coulombic efficiency of all-solid-state batteries.

[0143] The present invention has been described in detail with reference to the preferred embodiments of the present invention. However, it will be appreciated by those skilled in the art that these embodiments may be modified without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a pre-lithiation negative electrode, the method comprising: preparing a negative electrode assembly, the negative electrode assembly comprising a negative electrode current collector and an intermediate layer disposed on a surface of the negative electrode current collector, wherein the intermediate layer comprises silver particles and a carbon material; applying an electrolyte to the intermediate layer; manufacturing a pressurized structure by stacking a lithium supply layer on the intermediate layer coated with the electrolyte; as well as Pre-lithiation is performed by applying pressure to the pressurized structure along a stacking direction of the pressurized structure to convert the intermediate layer into a coating layer, thereby forming a pre-lithiated negative electrode, wherein the coating layer includes a γ3 phase Li-Ag alloy formed by reacting the silver particles with lithium during the pre-lithiation. 2 . The method according to claim 1 , wherein the electrolyte comprises a lithium salt and an organic solvent.

3. The method according to claim 2, wherein the lithium salt comprises a salt selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), and compounds in the group consisting of combinations thereof.

4. The method according to claim 2, wherein the organic solvent comprises a solvent selected from the group consisting of ester-based solvents, ether-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, carbonate-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, dioxolane-based solvents, sulfolane-based solvents, and combinations thereof. The method according to claim 1 , wherein an area of the lithium supply layer is larger than an area of the negative electrode assembly. The method according to claim 1 , wherein the pressure applied to the pressurizing structure is 0.01 MPa to 0.1 MPa. The method according to claim 1 , wherein the pre-lithiation is performed for more than 5 hours but less than 10 hours. The method according to claim 1 , wherein the pre-lithiation is performed for 5 to 7 hours.

9. The method of claim 1, wherein the pre-lithiation is performed at room temperature.

10. The method according to claim 1, wherein the γ3 phase Li-Ag alloy is composed of Li x Ag represents, wherein x is 1.98 to 2.

25. The method according to claim 1 , wherein the γ3 phase Li—Ag alloy is irreversibly formed. 12 . The method of claim 1 , wherein the coating does not include a γ2 phase Li—Ag alloy or a γ1 phase Li—Ag alloy.

13. The method of claim 1, wherein the carbon material comprises a material selected from the group consisting of a particulate carbon material, a fibrous carbon material, and combinations thereof.

14. The method according to claim 1, further comprising, after performing the pre-lithiation: collecting the pre-lithiated negative electrode including the negative electrode current collector and the coating; removing remaining impurities from the pre-lithiated negative electrode with a washing solvent; and The pre-lithiated negative electrode from which impurities have been removed is dried.

15. An all-solid-state battery, comprising: The pre-lithiation negative electrode prepared by the method according to claim 1; A solid electrolyte layer disposed on the pre-lithiated negative electrode, the solid electrolyte layer comprising a solid electrolyte; and A positive electrode is provided on the solid electrolyte layer, wherein the positive electrode comprises a positive electrode active material layer and a positive electrode current collector.

16. A method for manufacturing an all-solid-state battery, the method comprising: Manufacturing a pre-lithiated negative electrode, wherein manufacturing the pre-lithiated negative electrode comprises: preparing a negative electrode assembly, the negative electrode assembly comprising a negative electrode current collector and an intermediate layer disposed on a surface of the negative electrode current collector, wherein the intermediate layer comprises silver particles and a carbon material; applying an electrolyte to the intermediate layer; manufacturing a pressurized structure by stacking a lithium supply layer on the intermediate layer coated with the electrolyte; and performing pre-lithiation by applying pressure to the pressurized structure along a stacking direction of the pressurized structure to convert the intermediate layer into a coating layer, thereby forming a pre-lithiated negative electrode, wherein the coating layer includes a γ3-phase Li-Ag alloy formed by reacting the silver particles with lithium during the pre-lithiation; providing a solid electrolyte layer on the pre-lithiation negative electrode; and A positive electrode is provided on the solid electrolyte layer, and the positive electrode includes a positive electrode active material layer and a positive electrode current collector.

17. The method according to claim 16, wherein: The electrolyte includes a lithium salt and an organic solvent; the lithium salt includes a selected from the group consisting of LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10 , LiAlCl4, LiAlO4, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiN(SO2F)2(lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF2CF3)2(lithium bis(pentafluoroethanesulfonyl)imide, LiBETI), LiN(SO2CF3)2(lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), and combinations thereof; and The organic solvent includes a solvent selected from the group consisting of ester-based solvents, ether-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, carbonate-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, dioxolane-based solvents, sulfolane-based solvents, and combinations thereof.

18. The method of claim 16, wherein: The pressure applied to the pressurizing structure is 0.01 MPa to 0.1 MPa; and The pre-lithiation is performed at room temperature for more than 5 hours but less than 10 hours.

19. The method according to claim 16, wherein the γ3 phase Li-Ag alloy is composed of Li x Ag represents, wherein x is 1.98 to 2.

25.

20. The method of claim 16, wherein the coating does not include a γ2 phase Li-Ag alloy or a γ1 phase Li-Ag alloy.

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