metallic layer comprising through-grains of lithium or lithium alloy

Abstract

The invention relates more particularly to a metallic layer comprising through-grains of lithium metal or lithium alloy, having improved electrochemical performance; a simple and easily industrializable manufacturing process for such a metallic layer; the use of such a metallic layer as a negative electrode to improve the lifespan of a lithium metal battery; and a lithium metal battery comprising such a metallic layer as a negative electrode. Figure to be published: Figure 1

Description

Title of the invention: metallic layer comprising through grains of lithium or lithium alloy

[0001] The present invention relates to the field of rechargeable lithium batteries, in particular used for the production of electric vehicles and / or the storage of intermittent energies of the solar and / or wind type.

[0002] The invention relates more particularly to a metal layer comprising through grains of lithium metal or lithium alloy having improved electrochemical performances, a simple and easily industrializable manufacturing method of such a metal layer, the use of such a metal layer as a negative electrode to improve the lifetime of a lithium metal battery, as well as a lithium metal battery comprising such a metal layer as a negative electrode.

[0003] Lithium Metal Polymer (or "LMP®") batteries currently on the market are "all-solid" batteries generally in the form of a thin film wound several times or several stacked thin films. This wound or stacked thin film generally comprises at least four functional films: a negative electrode (anode) ensuring the supply of lithium ions during discharge; a positive electrode (cathode) acting as a receptacle where the lithium ions are intercalated; a solid polymer electrolyte conducting lithium ions and located between the positive electrode and the negative electrode; and a current collector connected to the positive electrode to ensure the electrical connection.The negative electrode is generally made of a lithium metal foil or a lithium alloy; the solid polymer electrolyte is generally composed of a poly(ethylene oxide) (PEO)-based polymer and at least one lithium salt; the positive electrode comprises an electrode active material, usually based on a metal oxide (such as V2O5, LiV3O8, LiCoO2, LiNiO2, LiMn2O4 or LiNio.5Mno.5Ch) or based on a phosphate of the LiMPO4 type where M represents a metal cation selected from the group Fe, Mn, Co, Ni and Ti, and one of their combinations, and possibly carbon; and the current collector is generally made of a metal foil. The presence of a solid polymer electrolyte makes it possible in particular to overcome the problems of dendrites which quickly appear with a conventional separator soaked in liquid electrolyte such as those used for lithium-ion accumulators.In the case of a lithium metal battery, a fresh layer of lithium metal (Li°) is deposited during charging at the anode, then consumed during discharge.

[0004] Currently, the production of the lithium metal negative electrode for an all-solid-state battery comprises extruding a lithium metal ingot and rolling the extruded lithium to form a lithium metal sheet. In particular, a lithium metal ingot is extruded to obtain a coil with a thickness of about 250 μm; then the obtained extruded coil is placed in a rolling mill. The rolling may take place using a lubricant to obtain a laminate coil. The thickness of the laminate generally varies from 58 to 72 μm.Current processes for producing lithium metal negative electrode on a large scale have disadvantages due to the very nature of the laminated lithium metal which can react with the rolling rolls with which it is in contact, and / or deform and adhere to these rolls, and / or the extreme ductility of lithium or its alloys which reduces the tensile stress on the lithium film applicable at the exit of the rolling rolls to avoid rupture or tearing of the lithium film.

[0005] Furthermore, the solid lithium metal batteries currently on the market are not entirely satisfactory, due to their still high cost and their lifespan (or cyclability) which remains moderate. In particular, several problems related to the use of negative lithium metal electrodes have been raised: the process of plating and dissolution of the lithium from the negative electrode, then the reactivity of the lithium metal with the components of the battery, mainly the electrolyte. The lifespan of all-solid batteries is notably known to be, in large part, inherent to the degradation of the lithium metal anode.

[0006] Several solutions have been considered to overcome the problems associated with the use of lithium metal, such as the design of a solid electrolyte with improved mechanical and ionic conduction properties, the engineering of a new negative electrode structure, or the application of a protective layer to the surface of the lithium metal negative electrode.

[0007] For example, patent application US2021 / 265618 describes a layer positioned at the interface of the lithium metal anode and solid electrolyte layers, said layer comprising a porous carbon having a specific surface area greater than 500 m2 / g facing the solid electrolyte layer; and nanostructures facing the lithium metal anode layer and penetrating the porous carbon. Such an interface layer can be prepared by 3D printing techniques, and physical, chemical, or electrochemical deposition methods which are complex and expensive. Furthermore, adding an additional layer in a battery can prove to be a disadvantage when seeking to reduce the size of the batteries as much as possible.

[0008] The recent publication Storelli et al, J. Electrochem. Soc., 2021, 168, 040505 describes the use of two types of lithium foils with an oxide-based electrolyte. polyethylene (PEO) and shows that the lifespan of lithium batteries can be improved by reducing the surface roughness of a lithium sheet. Furthermore, a surface pre-treatment consisting of subjecting the lithium sheet to an initial cycle with a low current density, followed by a significant increase in the cycling current density, further improves the battery lifespan. However, this process appears difficult to industrialize.

[0009] Thus, there is a need for new, less expensive technologies, easy to implement, particularly on an industrial level, which would make it possible to improve the lifespan of solid lithium metal batteries.

[0010] The aim of the invention is achieved by the metallic layer based on lithium metal or metal alloy which will be described below, as well as its manufacturing process.

[0011] The inventors of the present application have in fact surprisingly discovered that it is possible to provide a metal layer in which the lithium metal or the lithium alloy is in the form of through grains having particular dimensions so as to give said layer a microstructure suitable for improving the duration of a lithium battery.

[0012] The metal layer of the invention has a homogeneous microstructure, inducing better mechanical and electrochemical properties.

[0013] The invention therefore has as its first subject a metal layer comprising lithium or a lithium alloy, preferably for a lithium metal battery, said metal layer having a thickness e extending in a normal direction Dn, a width L extending in a transverse direction DT, and a length 1 extending in a rolling direction DL, the directions DN, DT, and DL being orthogonal to each other, characterized in that: * said metallic layer comprises through grains of lithium or lithium alloy, * each through grain is defined by at least one grain dimension dGN (in pm) extending in a direction parallel to the normal direction DN and by at least one grain surface SG (in mm2) on the plane defined by DT and DL, so that: * dGN = e (in pm), and * SG > 1.5 xnx [(2.9 xe) / 2]2, preferably SG > 2.0 xnx [(2.9 xe) / 2]2, particularly preferably SG > 2.5 xnx [(2.9 xe) / 2]2, and more particularly preferably SG > 3 xnx [(2.9 xe) / 2]2.

[0014] Thanks to a grain dimension dGN extending in a direction parallel to the normal direction DN and to a grain surface SG on the plane defined by DT and DL, the lithium or lithium alloy grains give the metal layer a particular microstructure, inducing better electrochemical properties.

[0015] In the invention, the grain dimension dGN extending in a direction parallel to the normal direction DN can be measured by microscopy, in particular by microscopy (in particular optical and / or electron microscopy), by tomography, or using a measuring probe, and preferably by microscopy (in particular optical and / or electron microscopy).

[0016] In the invention, the grain surface SG can be determined by microscopy, in particular by optical and / or electron microscopy, associated with the use of image processing software. The value of the grain surface SG corresponds to an average over 100 grains analyzed.

[0017] In the invention, SG > 1.5 xnx [(2.9 xe) / 2]2, preferably SG > 2.0 xnx [(2.9 xe) / 2]2, particularly preferably SG > 2.5 xnx [(2.9 xe) / 2]2, and more particularly preferably SG > 3 xnx [(2.9 xe) / 2]2.

[0018] According to a preferred embodiment of the invention, the metal layer of the invention is a self-supporting layer. This is also referred to as a self-supporting layer. In other words, it has sufficient mechanical strength to not require a support or substrate. According to this preferred embodiment of the invention, such a metal layer is therefore not deposited on a support or substrate. This also means that the metal layer of the invention has sufficient electrical conductivity to not require a current collector when manufacturing a battery comprising such a layer as a negative electrode. According to this preferred embodiment of the invention, such a metal layer is therefore not deposited on a current collector.

[0019] The metal layer comprising lithium or a lithium alloy of the invention may have a thickness e less than or equal to 100 μm, preferably less than or equal to 90 μm, particularly preferably less than or equal to 80 μm. Beyond 100 μm, the microstructure of the metal layer has a less significant impact on improving cyclability.

[0020] The metal layer preferably has a thickness greater than or equal to 1 μm, particularly preferably greater than or equal to 2 μm, and more particularly preferably greater than or equal to 5 μm.

[0021] In the metal layer, the lithium or the lithium alloy may represent at least approximately 90% by mass, relative to the total mass of the metal layer comprising lithium or a lithium alloy, preferably at least approximately 95% by mass, relative to the total mass of the metal layer comprising lithium or a lithium alloy, and particularly preferably from approximately 96 to 99% by mass, relative to the total mass of the metal layer comprising lithium or a lithium alloy.

[0022] According to a particularly preferred embodiment of the invention, the metal layer is made of lithium or a lithium alloy (i.e. it comprises Approximately 100% by mass of lithium or lithium alloy, relative to the total mass of the metal layer).

[0023] In the invention, the through grains are characterized by at least one grain dimension dGN (in pm) extending in a direction parallel to the normal direction DN with dGN = e (in pm), e being the thickness of the metal layer.

[0024] According to a preferred embodiment of the invention, said metal layer comprises at least 90% by mass, preferably at least 95% by mass, and particularly preferably only (i.e. 100%) of through grains of lithium or lithium alloy, relative to the total mass of the grains of lithium or lithium alloy present in said metal layer.

[0025] Lithium metal (or metallic lithium) corresponds to lithium with an oxidation state of zero (Li°).

[0026] The lithium alloy may be a lithium alloy such as, for example, an alloy of lithium and an element chosen from silicon (Si), tin (Sn), aluminum (Al), germanium (Ge), lead (Pb), bismuth (Bi), antimony (Sb), silver (Ag), zinc (Zn), indium (In), magnesium (Mg) and a mixture of at least two of the aforementioned elements.

[0027] Lithium preferably represents at least approximately 40% by mass, particularly preferably at least approximately 80% by mass, and more particularly preferably at least approximately 90% by mass, relative to the total mass of the lithium alloy.

[0028] In a particular embodiment, the through grains have an average extrapolated diameter dG (in pm) > 3.5 xe, and preferably dG (in pm) > 5 x e. In the metal layer of the invention, the lithium or lithium alloy grains are larger than in prior art lithium-based metal layers. This gives the metal layer of the invention a particular microstructure conducive to better cyclability.

[0029] In the invention, the average extrapolated grain diameter dG can be determined from the grain area SG as defined above and by modeling the lithium or lithium alloy grains as circles. The average extrapolated grain diameter dG can then be obtained from the following relationship: SG = nx (dG / 2)2 [or dG = 2 x V(SG / n)].

[0030] Since the size of the through grains of lithium or lithium alloy and / or the surface area of ​​the through grains of lithium or lithium alloy is greater than in the metal layers of the prior art, the density of through grains can thus be reduced. The density of through grains depends on the thickness of the metal layer.

[0031] The metal layer according to the invention preferably has a density of through grains of lithium or lithium alloy in grains / mm2 < 151230 x (layer thickness in pm)2. Thus, for a given thickness, the metal layer according to the invention preferably has a density of through grains of lithium or lithium alloy lower than the grain density obtained according to Frost's law (power law vs. film thickness). Conversely, the metal layers of the prior art follow Frost's law.

[0032] More particularly, the density of through grains of lithium or lithium alloy in grains / mm2 < 101,786 x (thickness of the layer in pm)2, and even more particularly, the density of through grains of lithium or lithium alloy in grains / mm2 < 50,893 x (thickness of the layer in pm)2.

[0033] The metal layer according to the invention is preferably in the form of a film or a sheet.

[0034] The second subject of the invention is a method for manufacturing a metal layer conforming to the first subject, characterized in that it comprises at least the following steps: - a step i) of preparing a metal laminate containing at least three metal layers comprising lithium or a lithium alloy, each of the metal layers comprising through grains of lithium or lithium alloy and having an initial thickness eii, ei2, ei3, and - a step ii) of rolling said metal laminate to a final thickness of said laminate ef = e such that ef < eii, ef < ei2, and ef < ei3.

[0035] Step i)

[0036] The method of the invention is simple to implement, easily industrializable and it makes it possible in a few steps to obtain a metallic layer conforming to the first object of the invention, i.e. having a particular microstructure inducing better cyclability.

[0037] According to a preferred embodiment of the method of the invention, step i) comprises the extrusion of a lithium or lithium alloy ingot i-1) and the rolling i-2) to form the at least three metal layers comprising lithium or a lithium alloy, then the complexation of the metal layers i-3), preferably at a pressure ranging from 0.1 to 1.0 N / mm2, and a speed ranging from 0.5 to 50 m / min.

[0038] Extrusion i-1) is preferably carried out at a temperature ranging from 20 to 100°C.

[0039] The rolling of the extruded ingot i-2) can be carried out at a temperature ranging from 20 to 130°C.

[0040] The rolling of the extruded ingot i-2) can be carried out at a speed ranging from 1 to 70 m / min.

[0041] The rolling of the extruded ingot i-2) can be carried out with a force ranging from 5 to 35 kN.

[0042] Rolling i-2) during step i) is preferably carried out with a rolling mill comprising at least two working cylinders or rolls. The extruded ingot can thus pass between the two cylinders.

[0043] Preferably, the rolling i-2) of step i) is carried out with a lubricant and / or non-stick co-winding films.

[0044] This is preferably introduced at the entrance to the rolling mill, advantageously before the extruded ingot passes between the two rollers.

[0045] The lubricant may be chosen from volatile siloxanes such as methyl siloxanes, in particular chosen from polydimethylsiloxanes, hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane and dodecamethylhexasiloxane.

[0046] The complexation i-3) of the at least three metal layers can be carried out at a temperature ranging from 20 to 130°C.

[0047] The complexing can be carried out with a complexing machine, which is a machine known to the state of the art and to those skilled in the art.

[0048] At the end of the complexation, each of the metal layers of the metal laminate comprises through grains of lithium or lithium alloy and has an initial thickness eii, ei2, ei3.

[0049] Preferably, the at least three metal layers of the metal laminate have an initial thickness eib ei2, ei3 which is substantially identical, i.e. with a variation in thickness between them ranging from 0 to 10%.

[0050] At the end of step i), and in particular of complexation i-3), the metal laminate has a thickness less than or equal to 300 μm, preferably less than or equal to 250 μm, and particularly preferably less than or equal to 200 μm.

[0051] The metal laminate generally has a thickness greater than or equal to 30 μm.

[0052] Step ii)

[0053] The following step ii) implements a new rolling step to reduce the thickness of the laminate and form the metal layer of final thickness ef equal to the thickness e as defined in the first subject of the invention.

[0054] Step ii) is preferably carried out with a force f ranging from 5 to 35 kN.

[0055] Step ii) is preferably carried out at a speed v ranging from 1 to 70 m / min.

[0056] Step ii) can be carried out at a temperature ranging from 20 to 130°C.

[0057] Step ii) is preferably carried out with a rolling mill comprising at least two working cylinders or rollers. The laminate can then pass between the two cylinders.

[0058] Preferably, step ii) is carried out with a lubricant and / or non-stick co-winding films.

[0059] The lubricant may be chosen from volatile siloxanes such as methyl siloxanes, in particular chosen from polydimethylsiloxanes, hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane and dodecamethylhexasiloxane.

[0060] This is preferably introduced at the entrance to the rolling mill, advantageously before the laminate passes between the two rollers.

[0061] According to a preferred embodiment of the invention, the final thickness ef is equal to the smallest of the initial thicknesses eib ei2, and ei3.

[0062] The third object of the invention is the use of a metal layer in accordance with the first object of the invention or as obtained according to a method in accordance with the second object of the invention, as a negative electrode, to improve the cyclability of a lithium metal battery.

[0063] As explained above, the metal layer of the invention has a particular microstructure of the lithium or lithium alloy grains which makes it possible to give it good electrochemical performance, in particular when it is used as a negative electrode or anode in a lithium metal battery.

[0064] The invention therefore has as its fourth object a lithium metal battery comprising: - at least one positive electrode, - at least one negative electrode, and - at least one solid or quasi-solid electrolyte interposed between the positive electrode and the negative electrode, characterized in that the negative electrode is a metal layer in accordance with the first subject of the invention or as obtained according to a process in accordance with the second subject of the invention.

[0065] The solid or quasi-solid electrolyte

[0066] In the present invention, the “solid or quasi-solid” electrolyte is in a solid form or in a gel form at room temperature (i.e. a temperature of 18-25°C), and preferably in a solid form.

[0067] The solid or quasi-solid electrolyte of the battery of the invention preferably comprises one or more polymeric materials.

[0068] The polymer material (or polymer materials when there are several) of the solid or quasi-solid electrolyte preferably represents at least approximately 30% by mass, and particularly preferably at least approximately 40% by mass, relative to the total mass of the solid or quasi-solid electrolyte.

[0069] The solid or quasi-solid electrolyte may be a polymer electrolyte comprising: - at least one lithium salt and at least one polymer material based on poly(ethylene oxide) (PEO), or - at least one polymer with cationic unipolar conduction.

[0070] The poly(ethylene oxide) (PEO)-based polymer material may be selected from a polystyrene-poly(ethylene oxide) block copolymer (PS-b-PEO), a polystyrene-poly(ethylene oxide)-polystyrene block copolymer (PS-b-PEO-b-PS), a poly(ethylene oxide-stat-propylene oxide) random copolymer (i.e. PEO-stat-PPO), a poly(ethylene oxide-stat-butylene oxide) random copolymer (i.e. PEO-stat-PBO), a poly(ethylene oxide), and a mixture thereof.

[0071] The lithium salt used in association with the poly(ethylene oxide)-based polymer material may be chosen from lithium fluorate (LiFO3), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium fluoroborate (LiBF4), lithium metaborate (LiBO2), lithium perchlorate (LiC104), lithium nitrate (LiNO3), lithium bis(fluorosulfonyl) imide (LiFSI), lithium bis(pentafluoroethylsulfonyl) imide (LiBETI), LiAsF6, LiCF3SO3, LiSbF6, LiSbCl6, Li2TiCl6, Li2SeCl6, Li2B10Cl10, Li2B12Cl12, lithium bis(oxalato)borate (LiBOB), and a mixture thereof.

[0072] The lithium salt preferably represents from 5 to 30% by mass, and even more preferably from 10 to 25% by mass, relative to the total mass of the polymer electrolyte.

[0073] Said polymer material based on poly(ethylene oxide) (PEO) can be combined with a reinforcing agent. This thus makes it possible to modulate the mechanical properties of the polymer material.

[0074] Said reinforcing agent is preferably chosen from cellulose nanofibrils, ceramic nanoparticles such as titanium oxide, aluminum oxide or silicon oxide nanoparticles, and fluorinated polymers and copolymers such as polyvinylidene fluoride (PVdF) or vinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP).

[0075] The unipolar conduction polymer may be a homopolymer or a copolymer comprising at least one organic polymer chain, organic anionic functions forming covalent bonds with the organic polymer chain, and metal cations associated (ionically) with the organic anionic functions.

[0076] In the invention, the term “polymer with cationic unipolar conduction” means a polymer (homopolymer or copolymer) comprising at least one organic polymer chain, organic anionic functions forming covalent bonds with the organic polymer chain, and metal cations associated with the organic anionic functions. Said metal cations are mobile species responsible for the ionic conduction of the polymer.

[0077] By organic polymer chain is meant a polymer chain free of metal and metalloid. In other words, the organic polymer chain does not comprise any metal or metalloid such as silicon, or is different from a polysiloxane chain, or does not include a Si-O bond.

[0078] By organic anionic function is meant an anionic function free of metal and metalloid. In other words, the organic anionic function does not comprise a metal or metalloid such as silicon, or does not comprise a Si-O bond.

[0079] The cationic unipolar conduction polymer of the invention is a polymer comprising anionic organic recurring units (organic polymer chain and organic anionic functions covalently linked to said organic chain), said anionic organic recurring units being associated (ionically) with metal cations.

[0080] The cationic unipolar conduction polymer can be: - a homopolymer capable of being prepared from a) a monomer comprising at least one organic anionic function covalently grafted onto said monomer and at least one metal cation associated with the organic anionic function; or - a copolymer capable of being prepared from a) a monomer comprising at least one organic anionic function covalently grafted onto said monomer and at least one metal cation associated with the organic anionic function, and b) at least one other monomer different from monomer a) chosen from bl) monomers comprising at least one organic anionic function covalently grafted onto said monomer and at least one metal cation associated with the organic anionic function, and b2) organic monomers.

[0081] By organic monomer b2) is meant a monomer free of metal and metalloid. In other words, the organic monomer does not comprise a metal or metalloid such as silicon and / or is not a compound comprising Si-O bonds.

[0082] The metal cation (of the monomer) or the metal cations (of the polymer) associated with the organic anionic functions are preferably Li+ cations.

[0083] The monomer a) or b1), i.e. comprising at least one organic anionic function covalently grafted onto said monomer and at least one metal cation associated with the organic anionic function, may be chosen from aromatic and non-aromatic vinyl monomers, comprising at least one organic anionic function covalently grafted onto said organic monomer and at least one metal cation associated with the organic anionic function.

[0084] As an example of aromatic vinyl monomers, mention may be made of styrene and its derivatives.

[0085] Styrene derivatives are preferably derivatives in which the phenyl group of styrene is substituted with one or more groups selected from methyl, ethyl, and tert-butyl groups.

[0086] Examples of non-aromatic vinyl monomers include acrylate, methacrylate, acrylamide, methacrylamide, ethylene, propylene, dienes, or maleimide.

[0087] The organic monomer b2) may be a vinylidene fluoride, a phosphate, a phosphonate, an ether, a carbonate, a malonate, an amide, an acrylate, an anhydride, or an ester.

[0088] In this embodiment, the copolymer comprises, in addition to anionic organic recurring units associated with metal cations, recurring units of vinylidene fluoride, phosphate, phosphonate, ether, carbonate, malonate, amide, acrylate, anhydride, or ester.

[0089] The organic anionic function (of the monomer a) and b1)) or the organic anionic functions (of the polymer) can be chosen from sulfonate, borate and imide functions.

[0090] The organic anionic functions are preferably imides, particularly preferably bissulfonyl imides, more particularly preferably sulfonyl(trifluoromethylsulfonyl) imides (TFSI) or sulfonyl(fluorosulfonyl) (FSI) imides, and even more particularly preferably sulfonyl(trifluoromethylsulfonyl) imides (TFSI).

[0091] When the polymer electrolyte comprises a cationic unipolar conduction polymer, it then preferably does not comprise additional lithium salt(s).

[0092] The polymer electrolyte may further comprise at least one plasticizer or non-aqueous solvent. This thus makes it possible to form a gelled polymer electrolyte (i.e. in the form of a gel).

[0093] The non-aqueous solvent or plasticizer may be chosen from linear and cyclic carbonates such as propylene carbonate, ethylene carbonate or dimethyl carbonate; fluorinated carbonates such as fluoroethylene carbonate; nitriles such as succinonitrile; lactones such as γ-butyrolactone; liquid linear or cyclic polyethers; fluorinated polyethers; sulfur-containing solvents such as sulfolane and dimethyl sulfoxide; and a mixture thereof.

[0094] Among such non-aqueous solvents or plasticizers, mention may in particular be made of dimethyl ether, polyethylene glycol dimethyl ethers (or PEGDME) such as tetraethylene glycol dimethyl ether (TEGDME), dioxolane, ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl isopropyl carbonate (MiPC), ethyl acetate, ethyl butyrate (EB), or a mixture thereof.

[0095] Preferably, the non-aqueous solvent or plasticizer represents from 10% to 70% by mass approximately, even more preferably from 20% to 60% by mass approximately, relative to the total mass of the polymer electrolyte.

[0096] The solid or quasi-solid electrolyte is preferably in the form of a film.

[0097] Preferably, the solid or quasi-solid electrolyte film has a thickness of 5 to 45 μm, and preferably of 10 to 25 μm.

[0098] The solid or quasi-solid electrolyte can be prepared by any technique known to those skilled in the art, such as, for example, by coating, by extrusion or by pressing (cold or hot).

[0099] The positive electrode

[0100] The positive electrode may comprise a positive electrode active material, optionally an electronic conductivity generating agent, and optionally a polymer material.

[0101] The active material of the positive electrode is a reversible active material of lithium ions. In other words, it can reversibly insert or de-insert lithium ions.

[0102] The positive electrode active material may be: - a metal oxide such as, for example, a vanadium oxide VOX (2 < x < 2.5), LiV3O8, LiyNii xCoxO2 (0 < x < 1; 0 < y < 1), a manganese spinel LiyMni XMXO2 (M = Cr, Al, V, Ni, 0 < x < 0.5; 0 < y < 2), V2O5, LiCoO2, LiNiO2, LiMn2O4 and LiNi0 5 Mn0.5O2, Li(Nii_xyMnxCoy)O2, LiNixCoyAlzO2 (x + y + z= l) or - a metal phosphosilicate or phosphate, for example LiMPO4, where M represents a metal cation selected from the group Fe, Mn, Co, Ni and Ti, and a combination thereof, such as for example LiFePO4 or LiMnFePO4, or - a metal sulfate, for example iron sulfate Fe2(SO4)3.

[0103] The active material of the positive electrode is preferably chosen from iron phosphate and its derivatives, in particular LiFePO4.

[0104] The agent generating electronic conductivity may be chosen from carbon blacks, acetylene blacks, carbon fibers and nanofibers, carbon nanotubes, graphene, graphite, metal particles and fibers of at least one conductive metal such as aluminum, platinum, iron, cobalt and nickel, and one of their mixtures.

[0105] The active material of the positive electrode may represent from 60 to 95% by mass approximately, and preferably from 70 to 90% by mass approximately, relative to the total mass of the positive electrode.

[0106] The agent generating electronic conductivity may represent from 0.1 to 10% by mass approximately, and preferably from 0.3 to 5% by mass approximately, relative to the total mass of the positive electrode.

[0107] The polymer material may be a material chosen from homopolymers and copolymers of ethylene; homopolymers and copolymers of propylene; homopolymers and copolymers of ethylene oxide (eg POE, copolymer of POE), methylene oxide, propylene oxide, epichlorohydrin, allylglycidyl ether, and mixtures thereof; halogenated polymers such as homopolymers and copolymers of vinyl chloride, vinylidene fluoride (PVdF), vinylidene chloride, ethylene tetrafluoride, or chlorotrifluoroethylene, copolymers of vinylidene fluoride and hexafluoropropylene (PVdF-co-HFP) or mixtures thereof; electronically non-conductive polymers of anionic type such as poly(styrene sulfonate), poly(acrylic acid), poly(glutamate), alginate, pectin, gelatin or mixtures thereof;cationic polymers such as polyethyleneimine (PEI), polyaniline in the form of emeraldine salt (ES), quaternized poly(N-vinylimidazole), poly(acrylamide-co-diallyldimethyl ammonium chloride) (AMAC) or mixtures thereof; polyacrylates; anionic polymers substituted by an anion of a lithium salt; and a mixture thereof.

[0108] The anionic polymers substituted by an anion of a lithium salt are as defined in the invention.

[0109] The polymer material may in particular be a polymer material based on poly(ethylene oxide) (PEO) or an anionic polymer substituted by an anion of a lithium salt.

[0110] The polymer material may represent from 1 to 25% by mass approximately, and preferably from 5 to 20% by mass approximately, relative to the total mass of the positive electrode.

[0111] According to a particularly preferred embodiment of the invention, the active material of the positive electrode is coated with a carbon layer. The presence of the carbon layer makes it possible to improve the interface: active material - polymer material.

[0112] The carbon coating the active material preferably represents from 0.1 to 5% by mass approximately, relative to the mass of active material.

[0113] The carbon layer is preferably in the form of a layer with a thickness varying from approximately 1 to 4 nm.

[0114] The positive electrode may further comprise a lithium salt, preferably from 1 to 20% by mass of lithium salt, and more preferably from 1 to 10% by mass of lithium salt, relative to the total mass of the positive electrode.

[0115] The lithium salt may be as defined in the invention.

[0116] The current collector

[0117] The lithium battery may further comprise a current collector connected to the positive electrode.

[0118] The current collector is generally made of a metal sheet.

[0119] The current collector is preferably a stainless steel or aluminum, possibly coated with a carbon-based layer (anti-corrosion layer).

[0120] Preferably, the positive electrode film has a thickness of 20 to 100 μm, and preferably 40 to 50 μm.

[0121] The present invention is illustrated by the following exemplary embodiments, to which it is however not limited. Brief description of the drawings

[0122] The accompanying drawings illustrate the invention.

[0123] [Fig.l] represents a metal layer according to the invention of thickness e extending in a normal direction DN, of width L extending in a transverse direction DT, and of length 1 extending in a rolling direction DL, the directions Dn, Dt, and Dl being orthogonal to each other; and a through grain of lithium or of a lithium alloy within said metal layer defined by a grain dimension dGN (in pm) extending in a direction parallel to the normal direction DN and by a grain surface SG (in mm2) on the plane defined by DT and DL, so that dGN = e (in pm).

[0124] [Fig.2] represents a through grain of lithium or a lithium alloy having a surface SG, and its modeling in the form of a circle of average extrapolated diameter dG.

[0125] [Fig.3] shows the capacity (in mAh / g) and the efficiency (in %) as a function of the number of cycles of a battery not in accordance with the invention.

[0126] [Fig.4] shows the internal resistance Ri (in Ohm.cm2) as a function of the number of cycles of a battery not in accordance with the invention.

[0127] [Fig.5] shows the capacity (in mAh / g) and the efficiency (in %) as a function of the number of cycles of a battery according to the invention.

[0128] [Fig.6] represents the evolution of the internal resistance Ri (in Ohm.cm2) as a function of the number of cycles, of a battery according to the invention. EXAMPLES

[0129] Unless otherwise indicated, all materials listed below were used as received from the manufacturers.

[0130] EXAMPLE 1: MANUFACTURE OF LITHIUM METAL FILMS

[0131] A thin film of lithium metal with a thickness of 18 μm in accordance with the invention was prepared according to the operating conditions detailed below.

[0132] Three layers of lithium metal with a thickness of approximately 18 μm were obtained by extrusion at a temperature of 30°C and rolling at a temperature of 20°C of a lithium ingot by applying a rolling speed of 50 m / min and a force of 5 kN.

[0133] Then these lithium metal layers were complexed at a pressure of 0.5 N / mm2, a temperature of 60°C, and a speed of 0.5 m / min to form a lithium metal laminate containing three lithium metal layers, each layer having a thickness of 18 pm.

[0134] Said metallic lithium metal laminate thus formed is rolled between two cylinders at a temperature of 30°C, in air (dew point of -40°C) by applying a rolling speed of 2 m / min and a force of 10 kN, to form a lithium metal film Fi with a thickness of 18 μm.

[0135] A comparative film of lithium metal with a thickness of 18 μm not in accordance with the invention was prepared according to the operating conditions detailed below.

[0136] A layer of lithium metal with a thickness of approximately 18 μm was obtained by extrusion at a temperature of 30°C and rolling at a temperature of 20°C of a lithium ingot by applying a rolling speed of 50 m / min and a force of 5 KN, to form a film of lithium metal Fc with a thickness of 18 μm.

[0137] Table 1 below lists the microstructural characteristics of the two films Fi and Fc thus formed.

[0138] [Tables 1] Fc Fi cIgn = thickness e (ym) 18 18 SG (mm2) 0.0022 0.0142 dG (jim) 52.2 134.5 grain density (number of grains / mm2) 467 70

[0139] From this Table 1, it can be seen that the comparative film Fc has a smaller surface area and a smaller average extrapolated grain diameter. More precisely, the film according to the invention Fi comprises through lithium grains having an average extrapolated diameter dG 2.5 times greater than that of the through lithium grains of the comparative film Fc. The film Fi has a microstructure different from that of the film Fc due to dynamic recrystallization occurring during steps i) and ii) of the method of the invention. This dynamic recrystallization can be observed by optical microscopy.

[0140] EXAMPLE 2: MANUFACTURE OF BATTERIES FROM LITHIUM METAL FILMS

[0141] A polymer electrolyte comprising 50% by mass of a copolymer of poly(vinylidene fluoride) and hexafluoropropylene sold under the reference “PVDF-HFP 21512” by the company Solvay, 48% by mass of poly(ethylene oxide) sold under the reference “POE IL” by the company Sumitomo Seika, and 12% by mass of LiTFSI sold by Solvay, was prepared by extrusion and lamination at 130°C between two silicone PET films. A polymer electrolyte film with a thickness of approximately 14 μm was obtained after lamination.

[0142] A positive electrode comprising 76% by mass of LiFePO4 (LFP) sold by Sumitomo Osaka Cernent, 1% by mass of carbon black sold under the reference “Ketjenblack EC600JD” by Akzo Nobel, 5.5% by mass of LiTFSI sold by Solvay, and 17.5% by mass of POE sold under the reference “POE IL” by Sumitomo Seika, was prepared by extrusion at 80°C. The mixture thus obtained was then rolled at 80°C onto a coated aluminum current collector sold by Armor to form a positive electrode film.

[0143] A first battery was then assembled by successive complexing of an assembly formed by:

[0144] - a negative electrode consisting of the Fc film as prepared in Example 1,

[0145] - the polymer electrolyte film as prepared above, and

[0146] - the positive electrode film as prepared above.

[0147] The complexing was carried out at a pressure of 5.103 Pa and at a temperature of 80°C in air (dew point of -40°C) in small cells (well known as "pouch cells") having a volume of approximately 10 cm3.

[0148] This first battery was then cycled at 80°C on a “Bitrode®” cycling bench with a charge / discharge regime equal to C / 10-D / 10 for the first cycle and C / 4-D / 2 for the following cycles in order to evaluate the electrochemical performances.

[0149] The results obtained are given in Figures 3 and 4.

[0150] [Fig.3] expresses the relative capacity (in mAh / g) and the efficiency (in %) as a function of the number of cycles. The gray curve (corresponding arrow) corresponds to the evolution of the capacity while the black curve (corresponding arrow) corresponds to the evolution of the efficiency. The evolution of the internal resistance (Ri in Ohm.cm2) as a function of the number of cycles is shown in [Fig.4].

[0151] The results presented in [Fig.3] demonstrate that the efficiency and relative capacity of the battery comprising the Fc film as the negative electrode are stable for approximately 520 cycles. The efficiency of the battery begins to decrease around the 400th cycle. In [Fig.4], a simultaneous increase in Ri is observed around the 400th cycle (an increase of 32%, which corresponds to an increase in Ri of 0.1% per cycle).

[0152] A second battery was then assembled using exactly the same method as that described above in example 2 by successive complexing of an assembly formed by:

[0153] - a negative electrode consisting of the film Fi as prepared in Example 1,

[0154] - the polymer electrolyte film as prepared above, and

[0155] - the positive electrode film as prepared above.

[0156] The performance of the second battery according to the present invention was compared with that of the first battery as prepared above.

[0157] The cycling conditions are identical to those used for the first battery.

[0158] The results obtained are given in Figures 5 and 6.

[0159] [Fig.5] expresses the relative capacity (in mAh / g) and the efficiency (in %) as a function of the number of cycles. The gray curve (corresponding arrow) corresponds to the evolution of the capacity while the black curve (corresponding arrow) corresponds to the evolution of the efficiency.

[0160] [Fig.6] represents the evolution of the internal resistance Ri (in Ohm.cm2) as a function of the number of cycles.

[0161] [Fig.5] shows a better cyclability of the second battery according to the present invention compared to that of the first battery. Indeed, the film Fi having a larger grain size allows a cyclability of approximately 770 cycles. The efficiency of the second battery according to the invention begins to decrease from the 650th cycle. In [Fig.6], we simultaneously observe around the 650th cycle an increase in Ri (increase of 24%, which corresponds to an increase in Ri of 0.05% per cycle).

[0162] The operation of the second battery according to the present invention is therefore improved compared to that of the first comparative battery.

Claims

Claims

1. A metal layer comprising lithium or a lithium alloy, preferably for a lithium metal battery, said metal layer having a thickness e extending in a normal direction DN, a width L extending in a transverse direction DT, and a length 1 extending in a rolling direction DL, the directions DN, DT, and Dl being orthogonal to each other, characterized in that: * said metal layer comprises through grains of lithium or lithium alloy, * each through grain is defined by at least one grain dimension dGN (in pm) extending in a direction parallel to the normal direction DN and by at least one grain surface SG (in mm2) on the plane defined by DT and DL, such that: * dGN = e (in pm), and * SG > 1.5 xnx [(2.9 xe) / 2]2, and preferably SG > 3 xnx [(2.9 xe) / 2] 2

2. Metal layer according to claim 1, characterized in that it is self-supporting.

3. Metal layer according to claim 1 or 2, characterized in that the through grains have an average extrapolated diameter dG (in pm) >3.5 V

4. A C. Metal layer according to any one of the preceding claims, characterized in that the thickness e is less than or equal to 100 μm.

5. A metal layer according to any preceding claim, characterized in that the metal layer has a through grain density (in grains / mm2) < 151230 x (layer thickness in pm)2.

6. A metal layer according to any one of the preceding claims, characterized in that said metal layer comprises at least 90% by mass of through grains of lithium or lithium alloy, relative to the total mass of lithium or lithium alloy grains present in said metal layer.

7. Metal layer according to any one of the preceding claims, characterized in that the lithium or the lithium alloy represents at least approximately 90% by mass, relative to the total mass of the metal layer comprising lithium or a lithium alloy.

8. A method of manufacturing a metal layer as defined in any one of the preceding claims, characterized in that it comprises at least the following steps: - a step i) of preparing a metal laminate containing at least three metal layers comprising lithium or a lithium alloy, each of the metal layers comprising through grains of lithium or lithium alloy and having an initial thickness eib ei2, ei3, and - a step ii) of rolling said metal laminate to a final thickness of said laminate ef = e such that ef < eib ef < ei2, and ef < ei3

9. Method according to claim 8, characterized in that step i) comprises the extrusion of a lithium or lithium alloy ingot i-1) and the rolling i-2) to form the at least three metal layers comprising lithium or a lithium alloy, then the complexation of the metal layers i-3), preferably at a pressure ranging from 0.1 to 1.0 N / mm2, and a speed ranging from 0.5 to 50 m / min.

10. Method according to claim 8 or 9, characterized in that step ii) is carried out at a speed v ranging from 1 to 70 m / min.

11. Method according to any one of claims 8 to 10, characterized in that step ii) is carried out with a force f ranging from 5 to 35 kN.

12. Method according to any one of claims 8 to 11, characterized in that the metal laminate has a thickness less than or equal to 300 μm.

13. Use of a metal layer as defined in any one of claims 1 to 7 as a negative electrode, for improving the cyclability of a lithium metal battery.

14. Lithium metal battery comprising: - at least one positive electrode, - at least one negative electrode, and - at least one solid or quasi-solid electrolyte interposed between the positive electrode and the negative electrode, characterized in that the negative electrode is a metal layer as defined in any one of claims 1 to 7.

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