Method for manufacturing a negative electrode for a lithium secondary battery

Abstract

Method for manufacturing a negative electrode (10) for an electrochemical cell of a lithium metal battery, the method comprising: Providing an electrically conductive metal substrate; Providing a non-aqueous, liquid electrolyte solution, including a lithium salt dissolved in a polar aprotic organic solvent; at least partial immersion of a surface of the metal substrate in the electrolyte solution; and Establishing an electrical potential between the metal substrate and a counter electrode (32) that is at least partially immersed in the electrolyte solution, so that lithium ions in the electrolyte solution are reduced to metallic lithium and deposited on the surface of the metal substrate in the form of a porous three-dimensional columnar lithium metal layer (18, 20) in order to increase an active surface area of ​​the lithium metal layer due to its porosity, wherein the lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) and the polar aprotic organic solvents fluoroethylene carbonate (FEC) and dimethyl dicarbonate (DMDC), and wherein the columnar lithium metal layer (18,20) comprises a plurality of polycrystalline or amorphous columns (22) of lithium metal with proximal ends (24) adjacent to the surface of the current collector (14,16) and distal ends (26) extending away from the current collector (12).

Description

Introduction

[0001] A battery is a device that converts chemical energy into electrical energy through electrochemical reduction-oxidation reactions (redox reactions). In secondary batteries or accumulators, these electrochemical reactions are reversible, allowing the accumulators to undergo multiple charge and discharge cycles.

[0002] Secondary lithium batteries generally comprise one or more electrochemical cells, including a negative electrode, a positive electrode, a porous separator, an electrolyte, a negative current collector, and a positive current collector. Such batteries are powered by the cooperative movement of lithium ions and electrons between the negative and positive electrodes of each electrochemical cell. The electrolyte is ionically conductive and provides a medium for the conduction of lithium ions through the electrochemical cell between the negative and positive electrodes. The current collectors are electrically conductive and allow electrons to move simultaneously from one electrode to another via an external circuit. The porous separator physically separates the electrodes and electrically insulates them while allowing free ion flow between them.

[0003] Lithium metal is a desirable negative electrode material for secondary lithium metal batteries due to its high specific capacity (3,860 mAh / g) and relatively low reduction potential (-3.04 V compared to a standard hydrogen electrode). When lithium metal is used as the negative electrode material in a battery, the lithium metal in the negative electrode oxidizes to lithium ions (Li). + During battery discharge, lithium ions migrate from the negative electrode through the electrolyte to the positive electrode, where they are stored. When the battery is recharged, the lithium ions are released from the positive electrode and migrate back through the electrolyte to the negative electrode, where they are reduced to lithium metal and deposited again.

[0004] The rate at which a lithium metal battery can be discharged and recharged (or cycled) depends on the rate at which lithium metal is oxidized to lithium ions at the negative electrode and the rate at which lithium ions are reduced to lithium metal and redeposited at the negative electrode. Additionally, the amount of lithium metal available to participate in the oxidation and reduction reactions during the discharge and recharge of the battery depends on the efficiency with which the lithium ions are released from and redeposited at the negative electrode without undergoing irreversible side reactions.

[0005] WO 2018 / 117547 A1 describes a lithium metal anode. The lithium metal anode comprises a current collector and a lithium metal thin film layer arranged on at least one surface of the current collector, with a thickness ranging from 0.1 to 200 µm. The lithium metal anode also includes a coating layer arranged on one surface of the lithium metal thin film layer, the coating layer comprising a Li-NCHO-based ionic compound.

[0006] US 2015 333 373 A1 describes a high-voltage electrolyte with an electrolyte solvent containing a mixture of a dinitrile solvent and a nitrile solvent, stable at a voltage of approximately 5 V or above. The dinitrile solvent contains at least one solvent from the group consisting of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, and sebaconitrile. The nitrile solvent comprises at least one solvent from the group consisting of acetonitrile, propionitrile, butyronitrile, pivalonitrile, and capronitrile.

[0007] US 2017 33 1 092 A1 describes electrochemical cells comprising a current collector with a negative electrode, a lithium metal negative electrode, an oxide electrolyte membrane, an adhesion promoter layer, a positive electrode, and a current collector with a positive electrode. The adhesion promoter layer advantageously reduces the interfacial impedance of the oxide electrolyte, at least at the positive electrode interface, and optionally also acts as an adhesive between the solid electrolyte separator and the positive electrode interface.

[0008] US 2017 338 465 A1 describes a battery system and its operation. In one example, lithium material is deposited onto the anode region of a lithium secondary battery cell by a pulsed current. The pulsed current has both a positive and a negative polarity. One polarity causes lithium material to be deposited onto the anode region, and the opposite polarity causes lithium dendrites to be removed.

[0009] It is therefore the object of the invention to provide a method for improving the efficiency and rate at which lithium ions are repeatedly released from and deposited again from the negative electrode in order to improve the charging rate and Coulomb efficiency of secondary lithium metal batteries. Description of the invention

[0010] The problem is solved by a method according to the invention for manufacturing a negative electrode for an electrochemical cell of a lithium metal battery. In the method, an electrically conductive metal substrate and a non-aqueous, liquid electrolyte solution are provided. The electrolyte solution includes a lithium salt dissolved in a polar aprotic organic solvent. The lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), and the polar aprotic organic solvent comprises fluoroethylene carbonate (FEC) and dimethyl dicarbonate (DMDC). A surface of the metal substrate is at least partially immersed in the electrolyte solution. An electrical potential is established between the metal substrate and a counter electrode that is at least partially immersed in the electrolyte solution.Lithium ions in the electrolyte solution are reduced to metallic lithium and deposited on the surface of the metal substrate in the form of a porous, three-dimensional, columnar lithium metal layer. This porosity increases the active surface area of ​​the lithium metal layer. The columnar lithium metal layer comprises numerous polycrystalline or amorphous lithium metal columns with proximal ends adjacent to the surface of the current collector and distal ends extending away from the current collector.

[0011] The columnar lithium metal layer comprises more than 97% lithium by weight and is directly connected to the surface of the current collector.

[0012] The non-aqueous, liquid electrolyte solution has a lithium salt concentration in the range of 2 M to 6 M.

[0013] Lithium bis(fluorosulfonyl)imide constitutes, by weight, more than 70% of the lithium salt in the non-aqueous, liquid electrolyte solution. A mixture of fluoroethylene carbonate and dimethyl dicarbonate constitutes, by volume, more than 70% of the organic solvent in the non-aqueous, liquid electrolyte solution.

[0014] The columnar lithium metal layer has a thickness ranging from 10 micrometers to 100 micrometers.

[0015] Each of the lithium metal columns has a width ranging from 0.5 micrometers to 1.5 micrometers.

[0016] The columnar lithium metal layer has a porosity in the range of 3% to 4%.

[0017] The electrical potential between the metal substrate and the counter electrode is created by applying an electric charge to the counter electrode at an electric charging current density in the range of 0.5 mA / cm². 2 up to 5 mA / cm2 , manufactured.

[0018] In one form, the electrical potential between the metal substrate and the counter electrode is built up by applying a pulsed electrical charge to the counter electrode.

[0019] The metal substrate is non-porous and comprises a first main surface and an opposing second main surface. In such a case, the columnar lithium metal layer is formed on at least one of the first or second main surfaces of the metal substrate.

[0020] After the lithium metal layer has formed on the surface of the metal substrate, the metal substrate and the lithium metal layer are formed into a negative electrode of the desired size and shape. The negative electrode is then installed in an electrochemical cell of a secondary lithium metal battery. Brief description of the drawings Fig. 1 is a lateral cross-sectional view of a negative electrode, including a negative electrode current collector with a first lithium metal layer formed on a first main surface thereof, and a second lithium metal layer formed on a second main surface thereof; Fig. Figure 2 is an enlarged perspective view of a section of the negative electrode of Fig. 1, illustrating a three-dimensional columnar structure of one of the lithium metal layers; Fig. Figure 3 is a cross-sectional view of an embodiment of a device for forming a three-dimensional columnar lithium metal layer on a surface of an electrically conductive metal substrate by means of an electrochemical deposition process; Fig. Figure 4 is a scanning electron microscope (SEM) image of the upper surface of a three-dimensional columnar lithium metal layer formed on a copper substrate using an electrochemical deposition process; Fig. Figure 5 is a SEM image of a cross-section of the three-dimensional columnar lithium metal layer made of Fig. 4; Fig. Figure 6 is a SEM image of the upper surface of a planar lithium metal layer formed on a copper substrate using an electrochemical deposition process; and Fig. Figure 7 is a SEM image of a cross-section of the planar lithium metal layer made of Fig. 6. Detailed description

[0021] The negative electrode described herein uses lithium metal as the active material of the negative electrode instead of a lithium intercalation material and can therefore be used to fabricate electrochemical cells with a relatively high energy density compared to electrochemical cells that contain other elements or compounds as the active material of the negative electrode. During the fabrication of the negative electrode, metallic lithium is deposited onto the surface of a metal substrate in the form of a porous, three-dimensional, columnar lithium metal layer consisting of a multitude of lithium metal columns.The porous three-dimensional columnar structure of the lithium metal layer increases the active surface area of ​​the layer without sacrificing capacity, which can help increase the charging rate and life cycle of the electrochemical cell compared to electrochemical cells that are essentially made with planar, non-porous layers of lithium metal as the active material of the negative electrode.

[0022] Fig. Figure 1 illustrates, in an idealized form, a side cross-sectional view of a negative electrode 10 for an electrochemical cell (not shown) of a secondary lithium metal battery (not shown). The negative electrode 10 encloses a negative electrode current collector 12 with a first main surface 14 and an opposing second main surface 16. A first lithium metal layer 18 is formed directly on the first main surface 14 of the current collector 12, and a second lithium metal layer 20 is formed directly on the second main surface 16 of the current collector 12.

[0023] During assembly, the negative electrode 10 can be electrically coupled to a positive electrode (not shown), which may contain a current collector of a positive metal electrode coated on one of its two sides with an active material layer of a positive electrode.A porous separator layer (not shown) can be present between one of the first or second lithium metal layers 18, 20 of the negative electrode current collector 12 and an opposite active material layer of the positive electrode of the positive electrode current collector, so that lithium ions can flow through the separator layer between the opposite lithium metal layer and the active material layer of the positive electrode, while electrons simultaneously migrate between the lithium metal layer and the active material layer of the positive electrode (and between the negative electrode current collector and the positive electrode current collector) through an external circuit.

[0024] The negative electrode current collector 12 can comprise any material capable of collecting and reversibly allowing free electrons to pass to and from the lithium metal layers 18, 20. For example, the negative electrode current collector 12 can comprise an electrically conductive metal or metal alloy, such as a transition metal or an alloy thereof. In some specific examples, the negative electrode current collector 12 can comprise copper (Cu), nickel (Ni), an iron alloy (Fe alloy) (e.g., stainless steel), or titanium (Ti). Other electrically conductive metals can, of course, be used if desired.

[0025] The negative electrode current collector 12 can be in the form of a thin and flexible, porous or non-porous, electrically conductive metal substrate. For example, the negative electrode current collector 12 can be in the form of a thin and flexible, non-porous metal foil, a porous metal mesh, a perforated metal sheet, or a porous open-cell metal foam. The specific configuration of the negative electrode current collector 12 can depend on its intended use. The negative electrode current collector 12 can have a thickness in the range of 8 micrometers to 150 micrometers. For example, in embodiments in which the negative electrode current collector 12 is in the form of a non-porous metal foil, a porous metal mesh, or a perforated metal sheet, the current collector 12 can have a thickness in the range of 8 micrometers to 20 micrometers.As another example, in embodiments in which the negative electrode current collector 12 is in the form of porous, open-cell metal foams, the current collector 12 can have a thickness in the range of 50 micrometers to 150 micrometers.

[0026] In Fig. In Figure 1, the first and second main surfaces 14, 16 of the current collector 12 are shown as substantially flat or planar, which may be the case in embodiments where the current collector 12 comprises a metal foil or a perforated metal sheet. However, in other embodiments, for example, where the current collector 12 comprises a metal mesh or an open-cell metal foam, the surfaces 14, 16 of the current collector 12 may be contoured, and the lithium metal layers 18, 20 may substantially conform to the contour thereof.

[0027] Now, referring to Fig. The first and second lithium metal layers 18, 20 are each physically connected to the first and second main surfaces 14, 16 of the current collector 12. The first and second lithium metal layers 18, 20 can be directly connected to the first and second main surfaces 14, 16 of the current collector 12, meaning that no intermediate material layers are formed on the first and second main surfaces 14, 16 of the current collector 12 prior to the formation of the first and second lithium metal layers 18, 20. The first and second lithium metal layers 18, 20 exhibit a three-dimensional columnar structure, with each layer 18, 20 comprising a plurality of polycrystalline or amorphous lithium metal columns or columns 22. Each of the columns 22 has a proximal end 24 adjacent to the first or second main surfaces 14, 16 of the pantograph 12 and a distal end 26 extending away from the pantograph 12.The columns 22 effectively increase the surface area of ​​layers 18 and 20, thereby increasing the rate at which lithium ions can be deposited onto and removed from the surfaces 14 and 16 of the current collector, compared to current collectors coated with solid, planar layers of lithium metal. For example, the columns 22 can provide layers 18 and 20 with a porosity in the range of 3% to 4%.

[0028] The columns 22 can be stochastically arranged on the first and second main surfaces 14, 16 of the pantograph 12. In Fig. Figure 2 shows the columns 22 as separated from each other on the surface 14, 16 of the current collector 12. However, in other embodiments, the columns 22 can be packed relatively closely together and can be adjacent to each other, with the columns 22 extending away from the current collector 12.

[0029] The columns 22, measured parallel to a plane defined by the first or second main surface 14, 16 of the current collector 12, can have widths in the range of 0.5 µm to 1.5 µm. The lithium metal columns 22 can have heights, measured perpendicular to the first or second main surface 14, 16 of the current collector 12, in the range of 10 µm to 100 µm, and the lithium metal layers 18, 20 can have thicknesses in the range of 10 µm to 100 µm. Therefore, the capacitance load of each of the lithium metal layers 18, 20 on the current collector 12 can be in the range of 2 mAh / cm². 2 up to 20 mAh / cm 2 lay.

[0030] The lithium metal columns 22 can consist essentially of lithium metal (Li-metal). For example, the lithium metal columns 22 can comprise more than 97% lithium by weight, or, more preferably, more than 99% lithium.

[0031] The lithium metal layers 18, 20 preferably do not comprise any other elements or compounds that undergo a reversible redox reaction with lithium during the operation of the electrochemical cell. For example, the lithium metal layers 18, 20 preferably do not comprise an intercalation support material formulated to undergo the reversible insertion or intercalation of lithium ions, or an alloying material capable of electrochemically alloying and forming compound phases with lithium. Furthermore, the lithium metal layers 18, 20 preferably do not comprise a conversion material or an alloying material capable of electrochemically alloying and forming compound phases with lithium. Some examples of materials preferably excluded from the lithium metal layers 18, 20 described herein 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 or iron, manganese, nickel, copper and / or cobalt). Furthermore, the lithium metal layers 18, 20 preferably do not comprise a polymeric binder. Some examples of polymeric binders, preferably excluding the lithium metal layers 18, 20 of the present description, include polyvinylidene fluoride (PVdF), ethylene propylene diene monomer rubber (EPDM rubber), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC) and polyacrylic acid.

[0032] Now, referring to Fig. 3. The first and second lithium metal layers 18, 20 can be formed on the first and second main surfaces 14, 16 of the current collector 12 using an electrochemical deposition process (also known as electroplating). In such a case, the current collector 12 can be arranged in an enclosed chamber 28 and be at least partially immersed in a non-aqueous, liquid electrolyte solution 30 together with a counter electrode 32. In some embodiments, the current collector 12 and the counter electrode 32 can be physically separated from each other in the electrolyte solution 30 by a porous separator 34.

[0033] The non-aqueous, liquid electrolyte solution 30 is ionically conductive and comprises a lithium salt dissolved in a polar aprotic organic solvent. The non-aqueous, liquid electrolyte solution 30 can have a lithium salt concentration in the range of 2 M to 6 M (molar) or, in particular, in the range of 3 M to 5 M. In a specific example, the non-aqueous, liquid electrolyte solution 30 can have a lithium salt concentration of about 4 M.

[0034] The electrolyte solution 30 is formulated such that during the electrochemical deposition process, metallic lithium is deposited on the current collector 12 in the form of a plurality of columns 22, as shown in Fig. 2, instead of being deposited in the form of a uniform planar layer. Therefore, lithium bis(fluorosulfonyl)imide, LiFSI, is preferably the predominant lithium salt in the electrolyte solution 30, meaning that LiFSI represents the largest volume fraction and / or the largest mass fraction of all lithium salts in the electrolyte solution 30. For example, LiFSI may constitute more than 50%, more than 70%, or more than 90% of all lithium salts in the electrolyte solution 30 by weight. In one form, the lithium salt in the electrolyte solution 30 may consist of lithium bis(fluorosulfonyl)imide. Additionally, the predominant organic solvents in the electrolyte solution 30 are carbonate esters, meaning that one or more carbonate esters represent the largest volume fraction and / or the largest mass fraction of all organic solvents in the electrolyte solution 30.In one formulation, the predominant organic solvents in electrolyte solution 30 comprise a mixture of a fluorinated cyclic carbonate (e.g., fluoroethylene carbonate, FEC) and a dialkyl carbonate (e.g., dimethyl dicarbonate, DMDC), meaning that a mixture of a fluorinated cyclic carbonate and a dialkyl carbonate constitutes the largest volume fraction and / or mass fraction of all organic solvents in electrolyte solution 30. For example, in one formulation, fluoroethylene carbonate and dimethyl dicarbonate may constitute more than 50%, more than 70%, or more than 90% of all organic solvents in electrolyte solution 30 by weight and / or volume. In another formulation, the organic solvent may consist of fluoroethylene carbonate and dimethyl dicarbonate (1:1 v / v).The electrolyte solution 30 is preferably formulated such that LiFSI is the predominant lithium salt in the electrolyte solution 30 and fluoroethylene carbonate and dimethyl dicarbonate are the predominant organic solvents in the electrolyte solution 30, since, without wishing to be bound to any theory, it is assumed that such a formulation is necessary for the development of a three-dimensional columnar structure in the lithium metal layers 18 during the electrochemical deposition process.

[0035] In some embodiments, the electrolyte solution 30 may include one or more additional lithium salts (referred to herein as "Co salts"), other than LiFSI. Some examples of Co salts that may be included in the electrolyte solution 30 in relatively small amounts are: LiClO4, LiAlCl4, Lil, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiN(SO2F)2, LiBOB, LiDFOB, LiPF6, LiNO3, Li2SO4, and / or LiCl. If present, the combined amount of the one or more Co salts included in the electrolyte solution 30, by weight and / or volume, may comprise less than 20%, less than 10%, or less than 5% of the total amount of lithium salts present in the electrolyte solution 30.

[0036] In some embodiments, the electrolyte solution 30 may include one or more additional organic solvents (hereinafter referred to as "co-solvents") besides fluoroethylene carbonate and dimethyl decarbonate. Some examples of co-solvents present in relatively small amounts in the electrolyte solution 30 include: acyclic ethers (e.g., 1,2-dimethoxyethane (DME), 1,2-diethoxyethane, ethoxymethoxyethane, tetraethylene glycol dimethyl ether, and / or poly(ethylene glycol) dimethyl ether), cyclic ethers (e.g., tetrahydrofuran and / or 2-methyltetrahydrofuran), carboxylic acid esters (e.g., methyl formate, methyl acetate, and / or methyl propionate), and / or gamma-lactones (e.g., gamma-butyrolactone and / or gamma-valerolactone).If present, the combined amount of one or more co-solvents contained in electrolyte solution 30, based on weight and / or volume, may comprise less than 20%, less than 10% or less than 5% of the total amount of organic solvents present in electrolyte solution 30.

[0037] The counter electrode 32 can be sacrificial or permanent. In embodiments where the counter electrode 32 is sacrificial, the electrode 32 can comprise any lithium-containing material capable of electrochemically releasing lithium ions when an electrical potential is established between the current collector 12 and the counter electrode 32. For example, in one embodiment, the counter electrode 32 can consist substantially of lithium (Li) metal; for instance, the counter electrode 32 can comprise more than 97% lithium by weight, or more preferably, more than 99% lithium. In other embodiments, the counter electrode 32 can be a support material with intercalated lithium ions or a lithium alloy. Examples of support materials that can be intercalated or alloyed with lithium include: carbon-based materials (e.g.,Graphite, activated carbon, carbon black and graphene), silicon, silicon-based alloys, tin oxide, aluminum, indium, zinc, germanium, silicon dioxide, titanium oxide, lithium titanate, transition metal oxides of the formula LiMeO2, LiMePO4 and / or LiMe2O4, where Me is a transition metal, and combinations thereof. In embodiments in which the counter electrode 32 is permanent, the electrode 32 may comprise an inert metal or an inert metal alloy.

[0038] The porous separator 34 can comprise any organic or inorganic material capable of physically separating and electrically insulating the current collector 12 from the counter electrode 32 while allowing the free flow of lithium ions between them. For example, the separator 34 can comprise a nonwoven material, such as a finished sheet, mesh, or mat of oriented or randomly oriented fibers. As another example, the separator 34 can comprise a microporous polymer material, such as a microporous polyolefin-based membrane or film. The separator layer 16 can comprise a single polyolefin or a combination of polyolefins, such as polyethylene (PE), polypropylene (PP), polyamide (PA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and / or polyvinyl chloride (PVC). In one form, the separator 34 can comprise a laminate of one or more polymer materials, such as a laminate of PE and PP.The separator 34 can have a thickness in the range of 10 µm to 30 µm.

[0039] The current collector 12 and the counter electrode 32 are electrically coupled to each other and, via an external circuit 38, to a power source 36. To initiate the electrochemical deposition process, an electrical potential is established between the current collector 12 and the counter electrode 32, for example, by applying an electric current from the power source 36 to the counter electrode 32 (electrons flow in the opposite direction to the current collector 12). Establishing this electrical potential between the current collector 12 and the counter electrode 32 initiates chemical oxidation and reduction reactions at the current collector 12 and the counter electrode 32. As a result, the lithium metal ions dissolved in the electrolyte solution 30 are reduced at the interface between the electrolyte solution 30 and the current collector 12, so that metallic lithium is deposited on the first and second main surfaces 14, 16 of the current collector 12.The electrolyte solution 30 is formulated such that during the electrochemical deposition process, metallic lithium is deposited on the current collector 12 in the form of a plurality of columns 22, as shown in . Fig. 2 shown, instead of being deposited in the form of a uniform planar layer.

[0040] In embodiments where the counter electrode 32 comprises lithium, lithium is oxidized from the counter electrode 12 and dissolves in the electrolyte solution 32 when an electrical potential is established between the current collector 32 and the counter electrode 30. The rate at which lithium dissolves from the counter electrode 32 into the electrolyte solution 30 is equal to the rate at which metallic lithium is coated or deposited on the first and second main surfaces 14, 16 of the current collector 12. In embodiments where the counter electrode 32 comprises an inert metal or an inert metal alloy, lithium ions must be periodically replenished in the electrolyte solution 30 to ensure a sufficient supply of lithium for deposition on the current collector 12.

[0041] The amount of metallic lithium deposited on the surfaces 14, 16 of the current collector 12 and the resulting thickness of the lithium metal layers 18, 20 can be controlled by controlling the electric current applied to the counter electrode 32 during the electrochemical deposition process and its duration. In some embodiments, a pulsed electric current can be applied to the counter electrode 32 during the electrochemical deposition process to allow the electrolyte solution 30 to reach an equilibrium state between the current pulses.

[0042] The electrical charging current density applied to the counter electrode 32 during the electrochemical deposition process can be in the range of one µA / cm². 2 up to an A / cm 2For example, in one form the electrical charging current density applied to the counter electrode 32 during the electrochemical deposition process can be in the range of 0.5 mA / cm². 2 up to 5 mA / cm 2 The electrical potential built up between the current collector 12 and the counter electrode 32 during the electrochemical deposition process can range from greater than 0 V to 1.0 V and can depend on the composition of the current collector 12, the counter electrode 32, and the electrolyte solution 30. The duration of the deposition process can depend on the desired thickness of the lithium metal layers 18, 20 and the electrical charge density applied to the counter electrode 32 during the electrochemical deposition process. For example, the electrical charge density applied to the counter electrode 32 during the electrochemical deposition process can be in the range of 0.5 mA / cm². 2up to 1 mA / cm 2 The deposition process can be carried out for a duration in the range of 4 hours to 8 hours in order to build up a thickness of the lithium metal layers 18, 20 of about 20 µm.

[0043] In some embodiments, the electrochemical deposition process described above can be used to deposit one or more three-dimensional columnar lithium metal layers onto one or more major surfaces of an electrically conductive metal substrate (not shown). The metal substrate, including the columnar lithium metal layer(s), can then be converted into a negative electrode of a desired size and shape. The resulting negative electrode can then be integrated into an electrochemical cell of a secondary lithium metal battery. In such a case, the three-dimensional columnar lithium metal layer(s) deposited on the major surface(s) of the metal substrate can comprise the active material of the negative electrode of the electrochemical cell. Examples

[0044] The negative electrode samples were fabricated in a laboratory setting by depositing layers of lithium metal onto copper substrates using an electrochemical deposition process. The morphology and porosity of the resulting lithium metal layers were analyzed using cryofocused ion beam scanning electron microscopy (cryoFIB SEM). Subsequently, each of the newly fabricated lithium metal negative electrode samples was combined with a positive electrode and a porous separator to form a complete electrochemical cell. The cycle performance of the newly fabricated electrochemical cells was evaluated at different charge rates. Example 1

[0045] A negative electrode, including a three-dimensional columnar lithium metal layer, was fabricated as described above (columnar Li-negative electrode) by immersing a copper substrate (10 µm thick) and a sacrificial lithium metal counter electrode (~500 µm thick) in a non-aqueous, liquid electrolyte solution. The copper substrate and the counter electrode were isolated from each other in the electrolyte solution by a multilayer porous polypropylene and polyethylene separator with a thickness of 25 µm. The electrolyte solution contained 4M lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in a mixture of fluoroethylene carbonate (FEC) and dimethyl decarbonate (DMDC) (1:1 v / v) (the LiFSI FEC:DMDC electrolyte solution). An electrical charge of 0.5 mA / cm² was applied to the counter electrode. 2The process was carried out for approximately 8 hours to deposit a columnar lithium metal layer with a thickness of 20 µm and a porosity of 3.3% on the copper substrate. The morphology of the resulting columnar lithium metal layer is shown in the Fig. 4 and Fig. 5 shown. The scale bar in Fig. 4 is 10 µm. The scale bar in Fig. 5 is 4 µm.

[0046] The cycle performance of the columnar Li-negative electrodes was evaluated using the newly fabricated columnar Li-negative electrodes to construct complete lithium battery cells. Each cell was housed in an Ar-filled glovebox and included a positive electrode and a porous separator positioned between the columnar Li-negative electrode and the positive electrode. The positive electrode comprised an 80 µm thick layer of lithium nickel manganese cobalt oxide (NMC) coated on a 16 µm thick aluminum foil. The porous separator was a 25 µm thick multilayer polypropylene and polyethylene separator. Each complete cell was filled with the LiFSI-FEC:DMDC electrolyte solution. The capacity of each complete cell was 5 mAh.

[0047] The cycle performance of the complete cells, including the column-shaped Li negative electrodes, was evaluated by discharging and recharging the cells at different charge rates: C / 10 (0.5 mA / cm²) 2 ) and C / 5 (1 mA / cm² 2 ) within a voltage window of 3.0 V to 4.3 V. The life cycle of each cell was fulfilled when the maximum charge capacity of the cell was reduced to 85% of its initial capacity (i.e., when the maximum charge capacity of each cell had fallen below 4 mAh). At a C / 10 charge rate, the life cycle of the complete cells, including the columnar Li-negative electrodes, was approximately 290. At a C / 5 charge rate, the life cycle of the complete cells, including the columnar Li-negative electrodes, was approximately 250. Example 2

[0048] For comparison, a negative electrode, including a planar lithium metal layer (planar Li-negative electrode), was fabricated by immersing a copper substrate (10 µm thick) and a sacrificial lithium metal counter electrode in a non-aqueous, liquid electrolyte solution. The copper substrate and the counter electrode were isolated from each other in the electrolyte solution by a multilayer porous polypropylene and polyethylene separator with a thickness of 25 µm. The electrolyte solution contained 4 M lithium bis(fluorosulfonyl)imide (LiFSI) dissolved in 1,2-dimethoxyethane (DME) (the LiFSI-DME electrolyte solution). An electrical charge of 0.5 mA / cm² was applied to the counter electrode. 2 The process was applied for approximately 8 hours to deposit a planar lithium metal layer with a thickness of 20 µm and a porosity of 2% on the copper substrate. The morphology of the resulting planar lithium metal layer is shown in the Fig. 6 and Fig. 7 shown. The scale bar in Fig. 6 is 10 µm. The scale bar in Fig. 7 is 4 µm.

[0049] The cycle performance of the planar Li-negative electrodes was evaluated using the newly fabricated planar Li-negative electrodes to construct complete lithium battery cells. Each cell was housed in an Ar-filled glovebox and included a positive electrode and a porous separator positioned between the planar Li-negative electrode and the positive electrode. The positive electrode comprised an 80 µm thick layer of lithium nickel manganese cobalt oxide (NMC) coated on a 16 µm thick aluminum foil. The porous separator was a 25 µm thick multilayer polypropylene and polyethylene separator. Each complete cell was filled with the LiFSI-DME electrolyte solution. The capacity of each complete cell was 5 mAh.

[0050] The cycle performance of the complete cells, including the planar Li-negative electrodes, was evaluated by discharging and recharging the cells at different charge rates: C / 10 (0.5 mA / cm²) 2 ) and C / 5 (1 mA / cm² 2 ) within a voltage window of 3.0 V to 4.3 V. The life cycle of each cell was fulfilled when the maximum charge capacity of the cell was reduced to 85% of its initial capacity (i.e., when the maximum charge capacity of each cell had fallen below 4 mAh). At a C / 10 charge rate, the life cycle of the cells, including the planar Li-negative electrodes, was approximately 130. At a C / 5 charge rate, the life cycle of the cells, including the planar Li-negative electrodes, was approximately 65.

[0051] The total life cycle of complete cells prepared with planar lithium-negative electrodes was shorter than that of complete cells prepared with columnar lithium-negative electrodes. Furthermore, the life cycle of complete cells prepared with planar lithium-negative electrodes was significantly affected by an increase in the charging rate from C / 10 to C / 5 (life cycle reduced from 130 to 65). However, the life cycle of complete cells prepared with columnar lithium-negative electrodes was only weakly affected by an increase in the charging rate from C / 10 to C / 5 (life cycle reduced from 290 to 250).This shows that using Li-negative electrodes with a three-dimensional columnar structure, instead of a planar structure, can help increase the charging rate and life cycle of secondary lithium metal batteries without sacrificing capacity.

Claims

[1] Method for manufacturing a negative electrode (10) for an electrochemical cell of a lithium metal battery, the method comprising: Providing an electrically conductive metal substrate; Providing a non-aqueous, liquid electrolyte solution, including a lithium salt dissolved in a polar aprotic organic solvent; at least partial immersion of a surface of the metal substrate in the electrolyte solution; and Establishing an electrical potential between the metal substrate and a counter electrode (32) that is at least partially immersed in the electrolyte solution, so that lithium ions in the electrolyte solution are reduced to metallic lithium and deposited on the surface of the metal substrate in the form of a porous three-dimensional columnar lithium metal layer (18, 20) in order to increase an active surface area of ​​the lithium metal layer due to its porosity, wherein the lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) and the polar aprotic organic solvents fluoroethylene carbonate (FEC) and dimethyl dicarbonate (DMDC), and wherein the columnar lithium metal layer (18,20) comprises a plurality of polycrystalline or amorphous columns (22) of lithium metal with proximal ends (24) adjacent to the surface of the current collector (14,16) and distal ends (26) extending away from the current collector (12). [2] Method according to claim 1, wherein the columnar lithium metal layer (18,20) comprises more than 97% lithium by weight and is bonded directly to the surface of the current collector (14,16). [3] Method according to claim 1, wherein the non-aqueous liquid electrolyte solution has a lithium salt concentration in the range of 2 M to 6 M. [4] The method of claim 1, wherein lithium bis(fluorosulfonyl)imide constitutes more than 70% of the lithium salt in the non-aqueous liquid electrolyte solution by weight, and wherein a mixture of fluoroethylene carbonate and dimethyl dicarbonate constitutes more than 70% of the organic solvent in the non-aqueous liquid electrolyte solution by volume. [5] Method according to claim 1, wherein the columnar lithium metal layer (18,20) has a thickness in the range of 10 micrometers to 100 micrometers. [6] Method according to claim 1, wherein each of the lithium metal columns (22) has a width in the range of 0.5 micrometers to 1.5 micrometers. [7] Method according to claim 1, wherein the columnar lithium metal layer (18,20) has a porosity in the range of 3% to 4%. [8] Method according to claim 1, wherein the electrical potential between the metal substrate and the counter electrode (32) is increased by applying an electrical charge to the counter electrode (32) at an electrical charging current density in the range of 0.5 mA / cm² 2 up to 5 mA / cm 2 is being built. [9] Method according to claim 1, wherein the electrical potential between the metal substrate and the counter electrode (32) is established by applying a pulsed electrical charge to the counter electrode (32).

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