Use of 1-allyl-2,3,4,5,6-pentafluorobenzene to treat a surface-deposited material of metallic lithium

Abstract

Use of 1-allyl-2,3,4,5,6-pentafluorobenzene to treat a surface-deposited material of metallic lithium The invention relates to the use of 1-allyl-2,3,4,5,6-pentafluorobenzene to treat a surface-deposited material of solid metallic lithium, said material comprising at least one compound selected from LiOH, Li2CO3, Li2O, Li3N and their mixtures. It also relates to a process for regenerating a solid metallic lithium surface, comprising at least the steps of: (1) having a substrate having at least one layer of solid metallic lithium coated, on at least one face of the substrate, with a deposit of a material comprising at least one compound selected from LiOH, Li2CO3, Li2O, Li3N and mixtures thereof, the thickness of the deposit being greater than or equal to 15 nm; and (2) contacting said deposit with at least 1-allyl-2,3,4,5,6-pentafluorobenzene. Figure for the abstract: None

Description

Title of the invention: Use of l-allyl-2,3,4,5,6-pentafluorobenzene for treating a material arranged on the surface of metallic lithium Technical field

[0001] The present invention relates to the field of lithium batteries, in particular third (liquid electrolyte batteries), fourth (all-solid-state batteries) or fifth generation (for example lithium-sulfur batteries or other emerging lithium metal technologies), and in this case any type of lithium batteries using liquid or solid electrolytes.

[0002] More specifically, the present invention relates to batteries using a negative electrode made of metallic lithium. It aims more particularly to overcome losses in electrochemical performance associated with the alteration, by formation of products of the LiOH, Li2CO3, Li2O and / or Li3N type, of the surface of metallic lithium electrodes. Prior art

[0003] Lithium batteries are increasingly used as autonomous energy sources, particularly in portable equipment, where they are gradually replacing nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) batteries. This development is explained by the continuous improvement in the performance of lithium batteries, thus giving them energy densities significantly higher than those offered by the NiCd and NiMH sectors. Lithium batteries find multiple applications, particularly in new information and communication technologies (NICT), medical devices, electric vehicles, the storage of energy from photovoltaic cells, etc.

[0004] Lithium ion batteries as energy storage devices require increased capacity. Regarding the selection of negative electrodes for lithium batteries, metallic lithium (Li metal) is theoretically one of the best candidates due to its high theoretical capacity and low redox potential.

[0005] However, lithium is highly reactive due to its electronic configuration, which involves the formation of a native passivation layer (native passivation layer), also called a native surface film, formed on the surface of the negative electrode (anode) during its production, transport and / or storage, and therefore hinders its performance as an anode for lithium batteries.

[0006] The thickness of the native passivation layer increases during storage of metallic lithium, as soon as it is stored in an atmosphere that can react with lithium. More precisely, as illustrated in [Fig.l], the presence of nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and / or water (H2O) in the storage atmosphere leads to the formation of LiOH, Li2CO3, Li2O and Li3N on the surface of the metallic lithium (Otto et al. [1]), resulting in the growth of the native passivation layer.

[0007] However, the diffusion coefficients of the compounds Li2CO3 and Li2O are much lower than those of metallic lithium, which has the consequence of considerably increasing the impedance of the metallic lithium electrodes. In addition, the non-uniformity of the native surface film creates privileged points for the growth of dendrites, which can lead to cycling defects and variable impedances between several metallic lithium electrodes.

[0008] Thus, the formation of LiOH, Li2CO3, Li2O and / or Li3N on the surface of metallic lithium can lead to an increase in ohmic resistance, also called high frequency resistance, and to a deterioration in the cycling characteristics of the metallic lithium anode such that the metallic lithium can become unusable as a negative electrode.

[0009] In order to overcome these drawbacks, treatments of the native passivation layer have been proposed in order to obtain metallic lithium electrodes having improved electrochemical performances, close to those of a new metallic lithium electrode.

[0010] As an example, we can cite the publication of Zhao et al. [2] which proposes to treat the native passivation layer with different plasmas. Five different gases were tested separately: Ar (physical attack due to ion bombardment without chemical reactions), H2, O2, N2 and NH3 (physical and also chemical attack between the plasma species and the lithium surface). Among the five plasmas studied, the Ar plasma proved to be the most effective in obtaining a "clean" lithium surface, i.e. almost free of impurities on the surface of the metallic lithium. It was also shown that after removing the native surface film, the metallic lithium reacts with the plasma to form a new surface layer of Li2O (O2 plasma) or Li3N (N2 and NH3 plasma). Although this method is effective in removing the native surface film of metallic lithium, it is complicated to implement and has a significant cost.

[0011] Thus, in general, the methods proposed until now for removing and / or modifying the native passivation layer are complex and / or expensive to implement. They are therefore difficult to transpose for implementation on an industrial scale.

[0012] There therefore remains a need for a new method, easy to implement and inexpensive, making it possible to have solid metallic lithium, dedicated to forming electrodes, which is certainly not coated on the surface with a native passivation layer detrimental to the electrochemical performance of the expected electrode, in particular in terms of cycling stability and / or ohmic resistance.

[0013] In particular, it would be advantageous if this method could be applied effectively to solid metallic lithium which has undergone prolonged storage, precisely favorable to the growth on the surface thereof of a material comprising LiOH, Li2CO3, Li2O, and / or Li3N, constituting the essential part of a native passivation layer. Statement of the invention

[0014] Thus, the invention relates, according to a first of its aspects, to the use of l-allyl-2,3,4,5,6-pentafluorobenzene, called “allylpentafluorobenzene”, for treating a material arranged on the surface of solid metallic lithium, said material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures.

[0015] As is apparent from the above, the material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, also called in the context of the invention “altering material”, is formed during aging, for example during prolonged storage, of a substrate having, at least on one of its faces, a layer of solid metallic lithium.

[0016] Surprisingly, the inventors have discovered that it is possible to significantly improve the electrochemical performances of a solid metallic lithium, altered by the formation of a surface deposit of LiOH, Li2CO3, Li2O and / or Li3N, in particular during the storage of this lithium, by bringing this surface deposit into contact with allylpentafluorobenzene.

[0017] As is clear from the examples below, this contacting makes it possible to effectively restore electrochemical performances very close to those observed with non-stored metallic lithium.

[0018] Thus, the invention also aims at the use of the l-allyl-2,3,4,5,6-pentafluorobenzene, in particular as defined above, for restoring the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of a metallic lithium electrode coated, in particular following storage, with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, said deposit having a thickness greater than or equal to 15 nm.

[0019] Finally, the present invention also relates to a method for regenerating a solid metallic lithium surface, comprising at least the steps of: (1) having a substrate comprising at least one layer of solid metallic lithium coated, at least on one of the faces of the substrate, with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, the thickness of the deposit being greater than or equal to 15 nm and; (2) contacting said deposit with at least l-allyl-2,3,4,5,6-pentafluorobenzene.

[0020] If necessary, the method according to the invention may comprise, subsequently to step (2), a step of eliminating the residual organic molecule(s) on the surface of said treated face, in particular by evaporation.

[0021] The regeneration of a solid metallic lithium surface can be characterized by an improvement in the electrochemical properties of the substrate, in particular the cycling stability and / or the ohmic resistance, to performance levels close to the electrochemical properties of the substrate at the end of its production.

[0022] In particular, the use according to the invention can implement one or more steps of the method according to the invention.

[0023] As detailed in the rest of the text, a metallic lithium electrode having a solid metallic lithium surface regenerated according to the method of the invention can find applications in various metallic lithium batteries, using any type of electrolyte, liquid or solid, in particular in the next generations of lithium-sulfur and lithium-air batteries.

[0024] Other characteristics, variants and advantages of the use and of the method according to the invention will emerge more clearly on reading the description, examples and figures which follow, given for illustrative and non-limiting purposes of the invention.

[0025] In the rest of the text, the expressions “between ... and ...”, “ranging from ... to ...” and “varying from ... to ...” are equivalent and are intended to mean that the limits are included, unless otherwise stated. Brief description of the drawings

[0026] [Fig.l] schematically presents the alteration mechanism of a solid metallic lithium surface. This figure is taken from Otto et al. [1].

[0027] [Fig.2] presents the Nyquist diagrams (hn(Z) as a function of Re(Z)), obtained by impedance spectroscopy for symmetrical Li° / electrolyte / Li° button cells manufactured from metallic lithium electrodes whose surface has been altered by growth of a deposit of the material considered according to the invention, having been subjected to the treatment according to the invention (“lithium stored for 12 months and treated with allylpentafluorobenzene”) and for symmetrical Li° / electrolyte / Li° buttons manufactured from metallic lithium electrodes whose surface has been altered or not by growth of a deposit of the material considered according to the invention and without treatment (respectively “lithium stored for 12 months” and “new / not stored lithium”) as described in the example;

[0028] [Fig.3] shows the evolution of the average potential of the charge / discharge plateaus in function of the number of cycles carried out for a symmetrical Li° / electrolyte / Li0 button cell manufactured from metallic lithium electrodes whose surface has been altered by growth of a deposit of the material considered according to the invention, having been subjected to the treatment according to the invention (“lithium stored for 12 months and treated with allylpentafluorobenzene”) and for symmetrical Li° / electrolyte / Li° buttons manufactured from metallic lithium electrodes whose surface has been altered or not by growth of a deposit of the material considered according to the invention and without treatment (respectively “lithium stored for 12 months” and “new / unstored lithium”), for cycling carried out with a current density of 0.2 mA / cm2 and an exchanged capacity of 2 mAh / cm2, as described in the example. Detailed description ALLYLPENTAFLUOROBENZENE

[0029] As indicated previously, the use and the method of the invention implement l-allyl-2,3,4,5,6-pentafluorobenzene (IUP name AC l,2,3,4,5-pentafluoro-6-prop-2-enylbenzene), more simply called allylpentafluo-robenzene.

[0030] Allypentafluorobenzene can be represented by the following formula (I):

[0031] [Chem.l]

[0032] Preferably, the allylpentafluorobenzene is used in the liquid state in individualized form. In particular, the allylpentafluorobenzene is not mixed with a solvent and / or is not inserted into a polymer network.

[0033] Allylpentafluorobenzene may be commercially available or prepared, prior to its use or implementation, by synthetic methods known to those skilled in the art.

[0034] In particular, allylpentafluorobenzene is not in a polymerized form. It is thus distinct from homopolymers or polymers.

[0035] In particular, allylpentafluorobenzene is in a non-ionic form. In particular, it is not a salt, in particular an ionic liquid. MATERIAL

[0036] As indicated previously, allylpentafluorobenzene proves to be particularly effective in ensuring that solid metallic lithium, dedicated to forming an electrode, does not have on its surface a material detrimental to the electrochemical properties of the electrode, in particular a so-called altering material, that is to say comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures.

[0037] In particular, the altering material consists of at least 50%, in particular at least 80%, more particularly at least 90%, in particular at least 95%, or even at least 99%, expressed as the number of lithium atoms constituting the compounds chosen from LiOH, Li2CO3, Li2O and Li3N, relative to the total number of lithium atoms in said altering material. The distribution of the compounds chosen from LiOH, Li2CO3, Li2O and Li3N may be inhomogeneous in the material placed on the surface of the solid metallic lithium.

[0038] The altering material may in particular comprise at least one compound chosen from LiOH, Li2CO3, Li2O and their mixtures, more particularly from Li2CO3, Li2O and their mixture.

[0039] The altering material is generally present in the form of a surface deposit of solid metallic lithium.

[0040] In particular, the deposit has a thickness greater than or equal to 15 nm, more particularly a thickness greater than or equal to 25 nm, in particular greater than or equal to 35 nm, or even greater than or equal to 50 nm. It should be noted that a deposit of such a thickness is generally only acquired following prolonged storage and that it is therefore clearly distinct from the native passivation film obtained just after the production of solid metallic lithium, and which has a thickness less than 15 nm (Otto et al. [1]).

[0041] The thickness of the deposit can be measured by secondary ion time-of-flight mass spectrometry (SIMS-TOF). Such a measurement method is described in particular in Otto et al. [1]. The thickness of the deposit can also be measured by scanning electron microscopy associated with a focused ion beam ("Focused Ion Beam-Scanning Electron Microscopy" in English terminology, or FIB-SEM), or by X-ray photoelectron spectrometry ("XPS" in English terminology, or XPS) in abrasion.

[0042] It is understood that the fractions of LiOH, Li2CO3, Li2O and Li3N in the material may vary with depth in the deposit, depending on the conditions under which the altering material was formed, such as the composition of the atmosphere and the duration of contact of the metallic lithium with this atmosphere. In particular, the composition may vary gradually between the altering material and the solid metallic lithium.

[0043] According to a particular embodiment, the altering material is present in the form of a continuous or discontinuous layer on the surface of solid metallic lithium.

[0044] This altering material is formed by reaction of metallic lithium with a storage atmosphere, contributing to the growth of the native passivation layer on the surface of the solid metallic lithium. Such an altering material is described in Otto et al., 2021 [1]. In particular, said material is arranged on the surface of solid metallic lithium having been stored for at least 1 month, in particular at least 6 months, or even at least 1 year. Generally, such storage is carried out in an anhydrous atmosphere, in particular at a temperature ranging from 15°C to 25°C, at a pressure ranging from 950 to 1050 mbar, and at a humidity level of less than 150 ppm of water, in particular at a temperature ranging from 18°C ​​to 23°C, at a pressure ranging from 990 to 1030 mbar, and at a humidity level of less than 100 ppm of water. SOLID METALLIC LITHIUM

[0045] Said material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures is arranged on the surface of solid metallic lithium.

[0046] The solid metallic lithium may consist of lithium metal or an alloy based on lithium metal, in particular chosen from alloys, in particular binary or ternary, comprising at least 90 atomic% of lithium, associated for example with zinc (Zn), aluminum (Al), magnesium (Mg), calcium (Ca), barium (Ba), indium (In), etc. or one of their mixtures.

[0047] This solid metallic lithium can be arranged in the form of at least one surface layer at at least one face of a substrate so as to form a metallic lithium electrode, in particular intended to be used as an anode in a lithium-metal battery, possibly attached to a current collector, in particular made of copper.

[0048] According to a particular embodiment, the substrate may be made of solid metallic lithium.

[0049] The substrate may have a thickness ranging from 10 μm to 1 mm, in particular from 15 μm to 500 μm, more particularly from 20 μm to 100 μm, in particular from 30 μm to 50 μm.

[0050] The altering material dedicated to be treated according to the invention can be arranged on both sides of said substrate. The treatment can be carried out on a single side of the substrate or on both sides of the substrate.

[0051] It is understood that the altering material dedicated to being treated is arranged at the level of the face of said substrate intended to be brought into contact, during its implementation as an electrode within a lithium-metal battery, with the electrolyte.

[0052] When the substrate is a metallic lithium electrode attached to a current collector, the altering material to be treated is arranged at the level of the face of the metallic lithium electrode opposite the current collector.

[0053] In particular, the subject of the invention makes it possible to improve the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of a metallic lithium electrode.

[0054] The electrochemical properties can be evaluated at the level of a symmetrical button cell composed of an electrolyte intercalated between two identical metallic lithium electrodes to be tested, the treated layer being positioned in contact with the electrolyte.

[0055] The cycling stability of the surface of a lithium electrode can be measured by applying charge / discharge cycles to the symmetrical button cell, and measuring the number of cycles before failure.

[0056] The ohmic resistance can be measured by impedance spectroscopy for a symmetrical button cell. The ohmic resistance can be determined from the Nyquist diagram, and corresponds to the intersection between the impedance curve and the abscissa axis at the highest frequency value.

[0057] As illustrated in the examples which follow, the treatment according to the invention makes it possible on the one hand to obtain an ohmic resistance of a metallic lithium electrode which has been stored at the same level as the ohmic resistance of a metallic lithium electrode which has not been stored ([Fig.2]), and on the other hand a significant increase in the number of cycles before failure compared to a metallic lithium electrode which has been stored but has not undergone treatment.

[0058] Thus, the cycling stability of a metallic lithium electrode comprising such a deposit can be significantly improved by the use according to the invention, in particular by at least 40%, more particularly by at least 50%, or even by at least 60% relative to the difference between the cycling stability before and after growth of said deposit.

[0059] As for the ohmic resistance of a metallic lithium electrode comprising said deposit, it can be significantly improved by the use according to the invention, in particular to an ohmic resistance less than 20%, in particular less than 10%, away from the ohmic resistance of the electrode before growth of the deposit.

[0060] Thus, allylpentafluorobenzene is also advantageous for restoring the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of a metallic lithium electrode coated, in particular following storage of metallic lithium, with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, said deposit having a thickness greater than or equal to 15 nm.

[0061] In particular, the storage conditions may be as described above. PROCESS

[0062] As indicated previously, the method of regenerating a solid metallic lithium surface can be carried out via at least the following steps: (1) having a substrate comprising at least one layer of solid metallic lithium coated, at least on one of the faces of the substrate, with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, the thickness of the deposit being greater than or equal to 15 nm and; (2) contacting said deposit with at least l-allyl-2,3,4,5,6-pentafluorobenzene.

[0063] In particular, the substrate, the deposit and the material may be as described above.

[0064] The method of the invention can advantageously be implemented directly at a metallic lithium electrode, in particular as described previously. In particular, the substrate in step (1) can be a metallic lithium electrode, possibly attached to a current collector, in particular made of copper. It is understood that the contacting is carried out at least at the face of said metallic lithium electrode intended to be brought into contact, within the lithium-metal battery, with the electrolyte. The method according to the invention is advantageously implemented before mounting the metallic lithium electrode within a battery.

[0065] In particular, the substrate used in step (1), preferably a metallic lithium electrode, comes from storage, in particular for at least 1 month, more particularly at least 6 months, or even at least 1 year, in particular in an anhydrous atmosphere.

[0066] The substrate coated with the deposit can optionally be obtained by one or more prior pre-treatment steps.

[0067] It is common to first flatten the substrate using a conventional rolling technique so that the reduction in the thickness of the substrate is less than or equal to 20%, in particular less than or equal to 15%, or even less than or equal to 12%. It is understood that the thickness of the substrate considered in step (1) is the thickness of the flattened substrate, if this pre-treatment step is considered.

[0068] The substrate coated with the deposit can also be obtained without a prior pre-treatment step.

[0069] During the contacting in step (2), the allylpentafluorobenzene may be in the form of a liquid comprising, or even consisting of, allylpentafluorobenzene. Preferably, the allylpentafluorobenzene is not in solution in a solvent or inserted into a polymer network.

[0070] Step (2) of contacting can be carried out by any technique known to those skilled in the art, in particular by depositing, on the surface of the deposit, a liquid comprising, or even consisting of, allylpentafluorobenzene, in particular by coating, for example using a doctor blade, by spraying or by vaporization ("spray coating"), or by dipping or immersing the substrate coated with the deposit in a bath comprising, or even consisting of allylpentafluorobenzene.

[0071] In particular, the contacting of the deposit with the allylpentafluorobenzene can be maintained for a period of at least 30 seconds, more particularly between 30 seconds and 24 hours, in particular between 1 minute and 1 hour.

[0072] For example, said contacting step may be maintained until evaporation of the residual organic molecule(s) and, optionally, of the unreacted allylpentafluorobenzene, from the treated surface.

[0073] By “residual” molecules, we mean all the organic molecules resulting from possible reactions between the allylpentafluorobenzene and the substrate coated with the deposit, or even the molecules mixed with the allylpentafluorobenzene during contact.

[0074] The contacting of the allylpentafluorobenzene with the deposit can be carried out at atmospheric pressure, for example at a temperature between 10 and 50°C, in particular between 20°C and 30°C, advantageously at room temperature (25°C). Alternatively, it is possible to envisage higher temperatures, by carrying out this contacting in a closed system, therefore at higher pressures.

[0075] The contacting of the allylpentafluorobenzene with the deposit may optionally be accompanied by heating to a temperature strictly lower, under the pressure conditions used, than the boiling temperature of the allylpentafluorobenzene.

[0076] Preferably, the contacting of the allylpentafluorobenzene with the deposit is carried out under an anhydrous or neutral atmosphere, preferably under a neutral atmosphere, for example under a helium or argon atmosphere. For example, it is carried out under an argon atmosphere.

[0077] According to a particular embodiment, the step of bringing the allylpentafluorobenzene into contact with the deposit is repeated one or more times, in particular up to 20 times, in particular from 2 to 10 times, in particular from 3 to 5 times.

[0078] According to a particular embodiment, said step(s) (2) of contacting may be followed by a step of eliminating the residual organic molecule(s) on the surface of said treated face, in particular by evaporation.

[0079] This elimination can advantageously be carried out by heating to a temperature less than or equal to 150°C, in particular between 60 and 150°C; in particular between 70 and 90°C and more particularly around 80°C.

[0080] Preferably, this removal step is carried out under vacuum.

[0081] The duration of said elimination step may be between 30 minutes and 4 hours, in particular between 1 and 2 hours.

[0082] Advantageously, the method of the invention does not require any special equipment or heating at high temperatures. The method of the invention is thus easy to implement and proves advantageous in terms of cost, both in terms of equipment and implementation conditions.

[0083] Advantageously, the method of the invention can be easily transposed for industrial-scale production. It can be adapted, for example, via in-line dipping of a lithium strip, to large-scale processing.

[0084] As mentioned above, the method of the invention advantageously makes it possible to improve the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of the metallic lithium substrate, in particular of a metallic electrode. More particularly, the method of the invention makes it possible to recover electrochemical properties, in particular a cycling stability and / or an ohmic resistance, of the metallic lithium substrate close to those of the substrate before growth of the deposit. APPLICATIONS

[0085] As previously stated, a solid metallic lithium, whether supported or not, treated according to the invention is particularly advantageous as a metallic lithium electrode, in particular a negative electrode in a lithium battery.

[0086] Said metallic lithium electrode can more particularly be attached to a current collector, in particular made of copper.

[0087] Said electrode can be advantageously used as a negative electrode in a lithium battery, in particular a lithium-metal battery, the face treated according to the invention, in contact with the electrolyte, ensuring improved stability during cycling.

[0088] An electrochemical element, also called an electrochemical generator or accumulator, is described, comprising at least said metallic lithium electrode, in particular as a negative electrode.

[0089] As illustrated in the following examples, the treated face ensures satisfactory stability during cycling.

[0090] An electrochemical element conventionally comprises said negative lithium metal electrode, a positive electrode and an electrolyte film interposed between said positive and negative electrodes.

[0091] The positive electrode of a lithium electrochemical element generally comprises, as electrochemically active material, lamellar compounds, such as LiCoO2, LiNiO2 and mixed Li(Ni, Co, Mn, A1)O2, or compounds of spinel structure of compositions close to LiMn2O4, lithium phosphates, in particular LiMnFePO4 or LiFePO4.

[0092] Advantageously, the positive electrode comprises, as electrochemically active material, LiNii / 3Mni / 3Coi / 3O2 or LiCoO2, preferably LiNii / 3 Mni / 3Coi / 3O2.

[0093] It also includes current collectors, generally made of copper for said negative electrode, or of aluminum for the positive electrode, which allow the circulation of electrons, and therefore electronic conduction, in the external circuit.

[0094] The metallic lithium electrode can be implemented in contact with any type of electrolyte, in particular in liquid, gelled or solid form.

[0095] The electrolyte in liquid form may more particularly be composed of a lithium salt dissolved in an organic or aqueous medium (conventionally in carbonate solvents, acetonitrile for lithium batteries), in the presence or absence of additives. Their implementation within a lithium electrochemical element is accompanied by the implementation of a separator to ensure electrical insulation between the positive and negative electrodes.

[0096] The electrolyte in solid form acts both as an ionic conductor and a separator between the positive and negative electrodes. It may, for example, be based on polyether(s), in particular based on poly(oxyethylene) (POE) and / or poly(oxypropylene) (PPO) in which a lithium salt is dissolved.

[0097] The electrochemical element may be more particularly intended for a lithium battery.

[0098] A lithium battery is also described, comprising at least said negative lithium electrode.

[0099] Advantageously, it may be a lithium-metal battery, in particular comprising at least said lithium metal electrode and an electrode comprising LiNii / 3Mni / 3Coi / 3O2 or LiCoO2, preferably LiNii / 3Mni / 3Coi / 3O2

[0100] It can also be a lithium-sulfur or lithium-air battery.

[0101] The invention will now be described by means of the following examples and figures, given of course for illustrative and non-limiting purposes of the invention. Examples

[0102] Treatment according to the invention of the material arranged on the surface of a metallic lithium electrode

[0103] A sample of metallic lithium with a thickness of 350 pm was taken at a date t o+i2mois from a roll of metallic lithium which had previously been stored for 12 months in an anhydrous atmosphere under the following conditions: - Dew point between -40 and -43°C; - Temperature of 20 + / - 2 °C; - Relative pressure to the outside (overpressure) of 40 + / - 5 Pa.

[0104] The metallic lithium sample is laminated between two strips of silicone film to reach a thickness of approximately 310 μm directly after its collection.

[0105] The allypentafluorobenzene is then poured onto the surface of the metallic lithium layer, in order to cover it entirely. The operation is carried out in an anhydrous room under a fume cupboard.

[0106] After 2 minutes of contact with the allylpentafluorobenzene, the metallic lithium sample is manually flattened between two strips of silicone film and placed for 1 hour at 80°C under vacuum in order to eliminate the remaining organic molecules and obtain a metallic lithium electrode.

[0107] Evaluation of the electrochemical properties of the metallic lithium electrodes treated according to the invention and comparison with comparative electrodes

[0108] The metallic lithium electrodes obtained at the end of the treatment described above, called “lithium stored for 12 months and treated with allylpentafluorobenzene”, or more simply “stored / treated lithium”, are mounted in three symmetrical button cells.

[0109] Symmetrical button cells are composed of an Osaka Soda membrane (POE PPO - LiTFSI) as electrolyte, intercalated between two identical metallic lithium electrodes, the treated layer being positioned in contact with the electrolyte.

[0110] For comparison, samples of metallic lithium with a thickness of 350 μm were taken from the same lithium roll to form metallic lithium electrodes:

[0111] - at a date t0 without storage for 12 months, then directly laminated between two silicone film strips to a thickness of about 310 μm, then mounted into symmetrical button cells as described previously. These electrodes are called "new / non-stored lithium".

[0112] - on date t0+i2moisS after storage of the roll for 12 months in an atmosphere anhydrous, then laminated between two strips of silicone film to achieve a thickness of approximately 310 μm, and then assembled into symmetrical button cells as described above. These electrodes are called "12-month stored lithium" or more simply "stored / untreated lithium".

[0113] Electrochemical impedance spectroscopy measurement

[0114] The impedance of the different batteries is measured at 60°C.

[0115] The impedance spectroscopy results for the different symmetrical button cells are presented in [Fig.2].

[0116] It is observed that the ohmic resistance of lithium stored for 12 months, untreated, can be significantly higher than the ohmic resistance of new / unstored lithium.

[0117] It is observed that the treatment according to the invention of lithium stored for 12 months makes it possible to find a low ohmic resistance, at the same level as new / unstored lithium. Cycling measurement

[0118] The cycling results, in charge and discharge at 60 °C, with a current density of 0.2 mA / cm2 and an exchanged capacity of 2 mAh / cm2 (charge and discharge step of 10 hours) are presented in [Fig.3]. The number of cycles before failure is reported in Table 2.

[0119] [T ables 2] New / not stored lithium Lithium stored for 12 months Lithium stored for 12 months and treated Number of cycles before defect 40 17 31

[0120] The results show that the storage of metallic lithium, and in particular the growth of the deposit of material altering the surface of the metallic lithium, leads to a significant degradation of the cyclability of a battery comprising a metallic lithium electrode stored for 12 months but not treated, with a number of cycles before failure which drops from 40 to 17. The treatment according to the invention makes it possible to significantly improve the cyclability of the metallic lithium electrode stored for 12 months, with a number of cycles before failure of 31. List of cited documents

[0121] [1] S.-K. Otto et al., ACS Appl. Energy Mater., vol. 4, no. 11, p. 12798-12807, 2021.

[0122] [2] B. Zhao et al., Journal of Energy Chemistry, vol. 66, p. 295-305, 2022.

Claims

Claims

1. Use of l-allyl-2,3,4,5,6-pentafluorobenzene, called “allylpentafluorobenzene”, for treating a material arranged on the surface of solid metallic lithium, said material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures.

2. Use according to the preceding claim, wherein said material is present in the form of a continuous or discontinuous layer on the surface of said solid metallic lithium.

3. Use according to claim 1 or 2, said material being arranged on the surface of solid metallic lithium having been stored for at least 1 month, in particular at least 6 months, or even at least 1 year, in particular in an anhydrous atmosphere.

4. Use according to any one of the preceding claims, in which the solid metallic lithium is arranged in the form of at least one surface layer at at least one face of a substrate so as to form a metallic lithium electrode, optionally attached to a current collector, in particular made of copper.

5. Use according to any one of the preceding claims, for improving the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of a metallic lithium electrode.

6. Use according to any one of claims 1 to 4, for restoring the electrochemical properties, in particular the cycling stability and / or the ohmic resistance, of a metallic lithium electrode coated with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, said deposit having a thickness greater than or equal to 15 nm.

7. Method for regenerating a solid metallic lithium surface, comprising at least the steps of: (1) providing a substrate comprising at least one layer of solid metallic lithium coated, at least on one of the faces of the substrate, with a deposit of a material comprising at least one compound chosen from LiOH, Li2CO3, Li2O, Li3N and their mixtures, the thickness of the deposit being greater than or equal to 15 nm and; (2) bringing said deposit into contact with at least l-allyl-2,3,4,5,6-pentafluorobenzene.

8. A method according to the preceding claim, wherein said deposit has a thickness greater than or equal to 25 nm, in particular greater than or equal to 35 nm, or even greater than or equal to 50 nm.

9. Method according to claim 7 or 8, wherein said substrate in step (1) is a metallic lithium electrode, optionally attached to a current collector, in particular made of copper.

10. Method according to any one of claims 7 to 9, in which said substrate implemented in step (1), preferably a metallic lithium electrode, comes from storage, in particular for at least 1 month, more particularly at least 6 months, or even at least 1 year, in particular in an anhydrous atmosphere.

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