FUNCTIONALIZED LITHIUM ANODE FOR BATTERIES

Abstract

A functionalized lithium anode for batteries, which is obtainable according to a specific process using diazonium salts. The embodiments also relate to the use of that lithium anode in cells, to a cell including that lithium anode, to the use of that cell in an electronic device, and to an electronic device including that cell.

Claims

1-15. (canceled)

16. A process for preparing a functionalized lithium anode, comprising contacting a lithium metal substrate with an aromatic diazonium salt in an organic solvent selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups.

17. The process according to claim 16, wherein the solvent is selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4 dioxane.

18. The process according to claim 16, wherein the lithium metal substrate is in the form of chips.

19. The process according to claim 16, wherein the diazonium salt is prepared from the corresponding aniline before the reaction with the lithium anode.

20. The process according to claim 16, wherein the diazonium salt is dissolved before the reaction with the lithium anode.

21. The process according to claim 19, wherein the diazonium salt is prepared or dissolved in a vessel and subsequently the lithium anode is introduced in that vessel to carry out the functionalization.

22. The process according to claim 16, wherein the diazonium salt is selected from a group of diazonium salts consisting of: 4-nitrobenzenediazonium tetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate, 3,5-dichlorophe-nyldiazonium tetrafluoroborate, and 4-propargyloxybenzenediazonium tetrafluoro-borate, and from a group of diazonium salts derived from a group of anilines comprising: 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol.

23. The process according to claim 16, wherein functionalization reaction is carried out electrochemically or chemically.

24. A functionalized lithium anode obtainable by the process according claim 16.

25. The functionalized lithium anode according to claim 24, wherein the functionalize lithium anode comprises an organic group derived from an aromatic diazonium salt attached to lithium, optionally substituted by functional groups.

26. The functionalized lithium anode according to claim 25, wherein the functionalize lithium anode comprises a substituted phenyl group attached to the lithium surface.

27. The use of the functionalized lithium anode according to claim 24 in Li—S cells, Li-ion cells, and Li—O.sub.2 cells.

28. A cell selected from Li—S cell, Li-ion cell or Li—O.sub.2 cell comprising a functionalized lithium anode according to claim 24.

29. The use of the cell of claim 28 in an electronic device.

30. An electronic device comprising the cell according to claim 28.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0030] The object of the present invention is a process for preparing a functionalized lithium anode for batteries, which comprises contacting a lithium metal substrate with an aromatic diazonium salt in an organic solvent selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups.

[0031] The inventors of the present invention have developed a process for preparing a functionalized lithium anode by reaction with a diazonium salt, which when incorporated into an electrochemical cell (from now on “cell”), in particular a Li—S cell, provides an improvement of both cycle life and coulombic efficiency. It has surprisingly found that the reduction of a diazonium salt on the surface of lithium metal grants to the lithium anode an enhanced physico-chemical stability that leads to a better battery efficacy and extended lifetime.

[0032] There are several advantages that the attachment of organic layers to lithium by reduction of diazonium salts have over other existing techniques/procedures proposed to protect Li anodes, from dendrite growth and other detrimental interaction processes (e.g. polysulfide's diffusion to the anode in Li—S batteries); one of them is undoubtedly the strong character of the (covalent) bond established between the immobilized organic layer and the lithium substrate, which constitutes a convenient mean to immobilize stable covalent films on lithium. It appears to be a method of choice for a strong covalent attachment of polymer chains to the surface forming ultrathin films (thickness can be varied from monolayers to microns). It confers to the organic modified lithium anode a chemical, mechanical and thermal stability, which overcomes those of other coatings casted via other methods. Hence, the result is a more resistant and durable protecting coating, which is able to resist to the often harsh conditions of the battery operation.

[0033] The reduction of aryl diazonium salts on lithium anodes constitutes also a versatile method: nearly an endless list of diazonium salts are available, commercially or by in-situ generation through the aniline derivative. This allows the grafting of a wide range of organic molecules, allowing simultaneously, tuning the Li surface properties. Adding to this, a large variety of solvents can be used to perform the grafting of these organic layers on lithium (e.g. toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine, 1,4-dioxane, or combinations thereof), which reinforces the flexibility of this method. Thus, by using a suitable solvent, the process of the invention allows grafting of diazonium precursors onto a lithium metal substrate without parasitic/secondary reactions between the solvent and lithium metal substrate.

[0034] Preferably, the solvent is non-polar. The solvent is selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups. In a preferred embodiment, the solvent is selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4-dioxane.

[0035] It is also a relatively simple and efficient technique to be performed: it can be achieved simply spontaneously or through electrochemical induction, by application of one potential step, in presence of non-cost reagents. This seriously rivals with more complexes set-ups and expensive techniques used today to perform the derivatization of the lithium surface, in order to reach the same purposes, i.e. to protect Li anodes from polysulfide's diffusion in Li—S batteries and other detrimental interaction processes (e.g. dendrite growth).

[0036] Throughout the present description and in the claims, the expressions in singular preceded by the articles “a” or “the” are understood to also include, in a broad manner, the reference to the plural, unless the context clearly indicates the contrary.

[0037] In the context of the present invention, it is understood that the term “approximately” referred to a determined value indicates that a certain variation for said value is accepted, generally of ±5%.

[0038] The description herein of any aspect or aspect of the invention using terms such as “comprising”, “having,” “including,” or “containing” with reference to an element or elements is intended to provide support for a similar aspect or aspect of the invention that “consists of”, “consists essentially of”, or “substantially comprises” that particular element or elements, unless otherwise stated or clearly contradicted by context.

[0039] The ranges disclosed in this description include both the lower and the upper limit thereof.

Lithium Metal Substrate

[0040] A lithium metal substrate, suitable for preparing lithium anodes is available in the form of chips, for example, from the company MTI. In a preferred embodiment, the lithium metal substrate is in the form of chips of high purity, usually 99,9%, and of variable shape, thickness and surface, depending of the type and architecture of the cell, wherein the anode is placed, for example, coin cell or pouch cell.

The Diazonium Salt

[0041] The lithium anode of the present invention is functionalized by means of a reaction with an aromatic diazonium salt in a solvent selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, preferably selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4-dioxane.

[0042] Generally, the diazonium salt is prepared from the corresponding aniline, or in some cases it is commercially available as such.

[0043] In a preferred embodiment, the diazonium salt is prepared from the corresponding aniline in the presence of a nitrosating reagent, for example, alkyl nitrites, such as methyl nitrite, isopropyl nitrite, tert-butyl nitrite, amyl nitrite or isoamyl nitrite, before the reaction with the lithium anode, without any need of isolation and purification

[0044] In another preferred embodiment, once synthesized, the diazonium salt may be isolated or it is used as a commercially available diazonium salt. In that embodiment, the diazonium salt is dissolved before the reaction with the lithium anode. In a more preferred embodiment, the diazonium salt is prepared or dissolved in a vessel and subsequently the lithium anode is introduced in that vessel to carry out the functionalization.

[0045] Diazonium salts suitable to be used in the process of the present patent application are not limited by the substituents present in the phenyl group, and may be, for example, 4-nitrobenzenediazonium tetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate, and 3,5-dichlorophenyldiazonium tetrafluoroborate, which are commercially available (Sigma-Aldrich), or 4-propargyloxybenzenediazonium tetrafluoroborate, disclosed in Jin et al., Click Chemistry on Solution-Dispersed Graphene and Monolayer CVD Graphene, Chem. Mat., 2011, 23 (14), 3362-3370. Halogenated diazonium salts may be used to post-functionalize the laminated separator by means of nucleophilic substitutions.

[0046] The 4-propargyloxybenzenediazonium tetrafluoroborate is suitable to post-functionalize the lithium anode by means of click chemistry as disclosed in Jin et al., op. cit.)

[0047] Anilines suitable to be used in the process of the present patent application are, for example, 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)-aniline, and 4-aminophenethyl alcohol, which are available commercially (Sigma-Aldrich).

[0048] The transformation of an aniline into its diazonium salt is a well-known process disclosed in Organic Chemistry, such as, for example, M. B. Smith, J. March, March's Advanced Organic Chemistry (5.sup.th ed.), John Wiley & Sons, New York, 2001 (ISBN: 0-471-58589-0). In that reaction, the aniline is treated with nitrous acid, or the combination of sodium nitrite with hydrochloric acid, which yields nitrous acid, or an equivalent compound, such as alkyl nitrites, as disclosed in F. Csende, Alkyl Nitrites as Valuable Reagents in Organic Synthesis, Mini-Rev. Org. Chem., 2015, 12, 127-148, in an appropriate solvent, preferably a deoxygenated solvent.

[0049] The anion of the diazonium salt depends on the acid used in the diazotization reaction. Generally, the anion is hydrochloride, hydrobromide, or tetrafluoroborate.

[0050] In a preferred embodiment, the aniline is reacted with tert-butyl nitrite in a non-aqueous environment, such as a deoxygenated solvent selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4-dioxane.

[0051] In a preferred embodiment, the diazonium salt is selected from a group of diazonium salts comprising: 4-nitrobenzenediazonium tetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate, 3 ,5-dichlorophenyldiazonium tetrafluoroborate, and 4-propargyloxybenzenediazonium tetrafluoroborate, and from a group of diazonium salts derived from a group of anilines comprising: 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol. In a preferred embodiment, the lithium anode is functionalized using a diazonium salt derived from 3 ,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol, and more preferably from 3 ,5-bis (trifluoromethyl) aniline

The Functionalization Reaction

[0052] The process to functionalize the lithium anode comprises the reaction of the lithium anode with an aromatic diazonium salt.

[0053] The functionalization reaction is carried out electrochemically or chemically.

[0054] In a preferred embodiment, the reaction is carried out electrochemically.

[0055] In another preferred embodiment, the reaction is carried out chemically.

[0056] The reaction is performed usually at room temperature, but it can be carried out at other temperatures from 0° C. to 130° C., depending on the stability of the solvent and diazonium salt. Preferably, the reaction is performed at room temperature.

[0057] The electrochemical reaction of the diazonium salt can be carried out either by cyclic voltammetry or by using a potential step approach, in which a higher degree of control over the amount of materials deposited is provided. Very low reduction potentials are required, typically lower that 0 V (vs. Li/Li.sup.+), to achieve the diazonium electroreduction, preferably the reduction potential is −1 V (vs. Li/Li.sup.+). The generation of a radical only requires low potentials because of the electron withdrawing power of the diazonium group.

[0058] The chemical functionalization of the lithium anode is carried out in a solution of the diazonium salt, either prepared previously in situ from the corresponding aniline compound or simply dissolving a diazonium salt, which can be prepared and isolated, or commercially available, in a solvent selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, preferably selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4-dioxane. Preferably the solvent is selected from toluene, tetrahydrofuran, and 3,4-dihydro-2H-pyran. Generally, the reaction is finished after 30 min.

[0059] After the reaction, the process for preparing the functionalized lithium anode includes a washing step using the solvent used in the functionalization and additional solvents of different polarity, for example, acetonitrile and toluene, to reduce the adsorption of the diazonium salt on lithium surface.

[0060] The Functionalized Lithium Anode

[0061] Another aspect of the invention relates to the functionalized lithium anode obtainable by means of the process of the invention.

[0062] The functionalized lithium anode comprises an organic group derived from an aromatic diazonium salt attached to lithium, optionally substituted by functional groups such as substituted by from 1 to 5 functional groups independently selected from halo, —S—C.sub.1-C.sub.6 alkyl, —OH, fluoro (C.sub.1-C.sub.10) alkyl, C.sub.1-C.sub.5 alkyl, —(C.sub.1-C.sub.5 alkyl)—OH, NO.sub.2, CN, and propargyloxy.

[0063] In a preferred embodiment, the lithium anode comprises a substituted phenyl group attached to the lithium surface, more preferably the phenyl group is derived from diazonium salts selected from the group comprising: 4-nitrobenzenediazonium tetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate, 3,5-dichlorophenyldiazonium tetrafluoroborate, and 4-propargyloxybenzenediazonium tetrafluoroborate, or from diazonium salts obtained from anilines selected from the group comprising: 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol.

[0064] Therefore, the phenyl group attached to the surface of the lithium anode is preferably selected from the group comprising: 4-nitrophenyl, 4-bromophenyl, 3,5-dichlorophenyl, 4-propargyloxyphenyl, 3,5-bis(trifluoromethyl)phenyl, 4-(heptadecafluorooctyl)phenyl, 4-phenethyl alcohol, and 3-(methylthio)phenyl. In a preferred embodiment, the substituted phenyl group is selected from 3,5-bis(trifluoromethyl)phenyl group, 4-(heptadecafluorooctyl) group and 4-phenethyl alcohol, and more preferably is 3,5-bis(trifluoromethyl)phenyl group.

[0065] X-ray photoelectron spectroscopy (XPS) confirms that functionalization takes place on the surface of the lithium anode. The functionalization is the result of a bonding of covalent character between the lithium surface and the phenyl group resulting from the homolytic dediazonation of the diazonium cation of the diazonium salt. This functionalization is maintained even after ultrasonic washing with different solvents, confirming the strength and the stability of the attachment.

Cells and Electronic Devices

[0066] Another aspect of the invention relates to the use of that functionalized lithium anode in Li—S cells, Li-ion cells, and Li—O.sub.2 cells.

[0067] The functionalized lithium anode is suitable to be incorporated to Li—S cells, Li-ion cells, and Li—O.sub.2 cells. In a preferred embodiment, it is used in Li—S cells. In another preferred embodiment it is suitable to be incorporated to Li—S coin cell, Li-ion coin cell and Li—O.sub.2 coin cell. In a more preferred embodiment it is used in Li—S coin cells.

[0068] A Li—S cell, such as, for example, CR2016-Type coin cell, contains usually the following elements: [0069] 1) Stainless steel cap [0070] 2) Lithium metal anode [0071] 3) Separator [0072] 4) Carbon-sulfur cathode [0073] 5) Stainless steel spacer [0074] 6) Stainless steel cap
as shown in FIG. 1.

[0075] In addition, the cell comprises an electrolyte. In a preferred embodiment the electrolyte consists of a combination of 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), bis(trifluoromethylsulfonylamine) lithium salt LiTFSI, and LiNO3.

[0076] Other electrolytes based on solutions of lithium salts such as lithium hexafluorophosphate (LiPF.sub.6), lithium perchlorate (LiClO.sub.4), LiCF.sub.3SO.sub.3 and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in nonaqueous solvents such as TEGDME, 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), diglyme (DG), ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), 2-ethoxyethyl ether (EEE), triglyme, poly(ethylene glycol) dimethyl ether (PEGDME), and mixtures thereof can also be used. The use of Room temperature Ionic Liquids (RTIL) electrolytes have been also reported e.g. bis(perfluoroethylsulfonyl)imide (EMImTFSI) or 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6), as an additive in liquid electrolytes, such as, for example, 0.5 M LiCF.sub.3SO.sub.3 or 0.5 M LiPF.sub.6 in DME/DOL solvent.

[0077] As shown in Example 10 and FIGS. 2 and 3, the functionalized lithium anode according to the invention shows an improvement of both cycle life and coulombic efficiency in cells due to lower electrolyte consumption, wherein the shuttle of polysulfides is retarded, which is the outcome of the enhanced stability of the lithium interface provided by the functionalization by means of a diazonium reduction.

[0078] Therefore, the advantages of the functionalized lithium anode of the present patent application over prior art lithium anodes are clear.

[0079] Another aspect of the invention relates to a Li—S cell, Li-ion cell or Li—O.sub.2 cell comprising that lithium anode, preferably a Li—S 1 cell.

[0080] Another aspect of the invention relates to the use of that Li—S cell, Li-ion cell or Li—O.sub.2 cell in an electronic device, preferably the use of that Li—S cell.

[0081] Another aspect of the invention relates to an electronic device comprising that Li—S cell, Li-ion cell or Li—O.sub.2 cell, preferably a Li—S cell.

[0082] Common electronic devices containing such cells are, for example, electric wristwatches, both digital and analogic, backup power for personal computer real time clocks, laser pointers, small LED flashlights, solar/electric candles, LED bicycle head or tail lighting, pocket computers, hearing aids, electronic toys, heart rate monitors, digital thermometers, or digital altimeters.

[0083] The invention comprises the following embodiments: [0084] 1.—A process for preparing a functionalized lithium anode, characterized in that it comprises contacting a lithium metal substrate with an aromatic diazonium salt in a solvent selected from an ether, an enol ether, an aromatic hydrocarbon bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups, or a morpholine solvent bearing from 0 to 4 C.sub.1-C.sub.4 alkyl groups. [0085] 2.The process according to claim 1, characterized in that the solvent is selected from toluene, tetrahydrofuran, 3,4-dihydro-2H-pyran, 4-ethylmorpholine and 1,4 dioxane. [0086] 3.—The process according to embodiment 1, characterized in that the lithium metal substrate is in the form of chips. [0087] 4.—The process according to any of embodiments 1 to 3, characterized in that the diazonium salt is prepared from the corresponding aniline before the reaction with the lithium anode. [0088] 5.—The process according to any of embodiments 1 to 4, characterized in that the diazonium salt is dissolved before the reaction with the lithium anode. [0089] 6.—The process according to embodiment 4 or 5, characterized in that the diazonium salt is prepared or dissolved in a vessel and subsequently the lithium anode is introduced in that vessel to carry out the functionalization. [0090] 7.—The process according to any of embodiments 1 to 6, characterized in that the diazonium salt is selected from a group of diazonium salts comprising: 4-nitrobenzenediazonium tetrafluoroborate, 4-bromobenzenediazonium tetrafluoroborate, 3,5-dichlorophe-nyldiazonium tetrafluoroborate, and 4-propargyloxybenzenediazonium tetrafluoro-borate, and from a group of diazonium salts derived from a group of anilines comprising: 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol. [0091] 8.—The process according to embodiment 7, characterized in that the lithium anode is functionalized using a diazonium salt derived from 3,5-bis(trifluoromethyl)aniline, 4-(heptadecafluorooctyl)aniline, and 4-aminophenethyl alcohol. [0092] 9.—The process according to embodiment 8, characterized in that the lithium anode is functionalized using a diazonium salt derived from 3,5-bis(trifluoromethyl)aniline. [0093] 10.—The process according to any of embodiments 1 to 9, characterized in that functionalization reaction is carried out electrochemically or chemically. [0094] 11.—The process according to embodiment 10, characterized in that the reaction is carried out electrochemically. [0095] 12.—The process according to embodiment 10, characterized in that the reaction is carried out chemically. [0096] 13.—A functionalized lithium anode obtainable by means of the process according to any of embodiments 1 to 12. [0097] 14.—The functionalized lithium anode according to embodiment 13, characterized in that it comprises an organic group derived from an aromatic diazonium salt attached to lithium, optionally substituted by functional groups. [0098] 15.—The functionalized lithium anode according to embodiment 14, characterized in that it comprises a substituted phenyl group attached to the lithium surface. [0099] 16.—The functionalized lithium anode according to embodiment 15, characterized in that the phenyl group attached to the surface of the lithium anode is selected from the group comprising of: 4-nitrophenyl, 4-bromophenyl, 3,5-dichlorophenyl, 4-propargyloxyphenyl, 3,5-bis(trifluoromethyl)phenyl, 4-(heptadecafluorooctyl)phenyl, 4-phenethyl alcohol, and 3-(methylthio)phenyl. [0100] 17.—The functionalized lithium anode according to embodiment 16, characterized in that the phenyl group attached to the surface of the lithium anode is selected from 3,5-bis(trifluoromethyl)phenyl group, 4-(heptadecafluorooctyl) group and 4-phenethyl alcohol. [0101] 18.—The functionalized lithium anode according to embodiment 17, characterized in that the substituted phenyl group is 3,5-bis(trifluoromethyl)phenyl group. [0102] 19.—The use of the functionalized lithium anode according to any of embodiments 13 to 18 in Li—S cells, Li-ion cells, and Li-0.sub.2 cells. [0103] 20.—The use of the functionalized lithium anode according to embodiment 19 in Li—S cells. [0104] 21.—The use of the functionalized lithium anode according to any of embodiments 13 to 18 in Li—S coin cell, Li-ion coin cell and Li-O.sub.2 coin cell. [0105] 22—The use of the functionalized lithium anode according to embodiment 21 used in Li—S coin cells. [0106] 23.—A cell selected from Li—S cell, Li-ion cell or Li-O.sub.2 cell comprising a functionalized lithium anode according to any of embodiments 13 to 18. [0107] 24.—The cell according to embodiment 23, characterized in that the cell is a Li—S cell. [0108] 25.—The use of the cell of embodiment 23 or 24 in an electronic device. [0109] 26.—An electronic device comprising the cell according to embodiment 23 or 24.

EXAMPLES

Example 1: Chemical functionalization of a lithium anode

[0110] Inside a Glove Box, lithium chips (approx. 1.5 cm.sup.2, corresponding to 44 mg) were cleaned in n-pentane (3 min) and dried. Afterwards, a solution of 3,5-bis(trifluoromethyl) diazonium salt (10 mM) was prepared by dissolving 3,5-bis(trifluoromethyl)aniline in dry toluene. An excess of tert-butyl nitrite relatively to the diazonium salt (30 mM) was added and the solution was stirred during 30 mM. Then, lithium chips were introduced into the diazonium solution and stirred during 30 mM. Finally, chips were washed with toluene, solvent in which the functionalization was carried out, and acetonitrile, and dried.

[0111] X-ray photoelectron spectroscopy confirmed that the functionalization took place on lithium surface by the presence of a strong peak attributed to the F is binding energy. This peak was not observed in the spectrum corresponding to the non-functionalized lithium anode.

Examples 2-9: Chemical and electrochemical functionalization of a lithium anode

[0112] Functionalized anodes were prepared according to a 2.sup.3 factorial design, according to the factors shown in Table I:

TABLE-US-00001 TABLE I Factor Level− Level+ Diazonium 4-aminophenethyl (4-heptadecafluorooctyl)aniline precursor alcohol Process Chemical Electrochemical Temperature RT 50° C.

[0113] Experiments were carried according to the layout shown in Table II:

TABLE-US-00002 TABLE II Example Diazonium precursor Process Temperature 2 4-aminophenethyl alcohol Chemical RT 3 (4-heptadecafluoro- Chemical RT octyl)aniline 4 4-aminophenethyl alcohol Electrochemical RT 5 (4-heptadecafluoro- Electrochemical RT octyl)aniline 6 4-aminophenethyl alcohol Chemical 50° C. 7 (4-heptadecafluoro- Chemical 50° C. octyl)aniline 8 4-aminophenethyl alcohol Electrochemical 50° C 9 (4-heptadecafluoro- Electrochemical 50° C octyl)aniline

[0114] Reactions with 4-aminophenethyl alcohol (119 mg) as precursor of the diazonium salt were carried out using anhydrous tetrahydrofuran (THF) as solvent.

[0115] Reactions with (4-heptadecafluorooctyl)aniline (409 mg) as precursor of the diazonium salt and anhydrous 3,4-dihydro-2H-pyran as solvent.

[0116] Chemical functionalization was carried out following a substantially analogue procedure disclosed in Example 1.

[0117] Lithium chips were cleaned in n-pentane (3 min) and dried. Electrochemical functionalization took place by introducing the lithium chips into the diazonium salt solution (previously stirred for 30 min), and by applying a potential of −1 V (vs. Li/Li.sup.+) during 30 min. Lithium chips were the working electrode, Pt wire was the counter electrode and lithium wire was the reference electrode.

[0118] Finally, the Li chips were rinsed either with THF or 3,4-dihydro-2H-pyran, depending on the precursor of diazonium salt, and two further solvents of different polarity (toluene and acetonitrile) to reduce the adsorption of the diazonium salt on Li surface.

[0119] X-ray photoelectron spectroscopy confirmed that the functionalization took place on lithium surface in all four samples.

[0120] In the case of the functionalization with 4-aminophenethyl alcohol (Examples 2, 4, 6 and 8), main differences in comparison to the non-functionalized lithium anode were: [0121] An excess (at %) C1sII (BE=287 ev) attributed to C—O environments. [0122] An excess (at %) O1sII (BE=534 ev) (shoulder on the high biding energy side of the O1s peak) attributed to the presence of OH groups. [0123] A ratio C1sII (C—O)/O1sII (OH)≈1 (according to the C/OH ratio on the COH bond) in opposition to 3.8 on the pristine Li.

[0124] In the case of the functionalization with (4-heptadecafluorooctyl)aniline) (Examples 3, 5, 7 and 9), main differences in comparison to the non-functionalized lithium anode were: [0125] An excess (at %) of F1s (687 ev) and (690 eV) attributed to the F—C fluorocarbon bonding. [0126] An excess (at %) of C1s (293 eV) corresponding to C—F.

Example 10: Galvanostatic Test of the Li/S Battery Containing a Functionalized Lithium Anode

[0127] Galvanostatic testing of a functionalized lithium anode, prepared according to the procedure disclosed in Example 1, and non-functionalized lithium anode was carried out in a Li/S battery (CR2016-Type coin cell) containing the following elements: [0128] 1) Stainless steel cap (20 mm diameter, 1.6 mm thickness) [0129] 2) Lithium metal anode (Lithium 99.9% chip, 15.6 mm diameter, 0.25 mm thickness) [0130] 3) Separator (Celgard® 2500) [0131] 4) A 2.5 mAh.cm.sup.−2 sulfur/carbon-based cathode, containing 70% sulfur, 15% Ketjen Black carbon and 15% PEO. [0132] 5) Stainless steel spacer (2 discs: 16.7 mm diameter, 1 mm and 0.2 mm thickness respectively) [0133] 6) Stainless steel cap (20 mm diameter, 1.6 mm thickness) as shown in FIG. 1.

[0134] The separator was soaked in an ether-based electrolyte, that is 1:1 (v/v) dimethoxyethane:dioxolane, 1M LiTFSI, 0.2M LiNO.sub.3. [0135] Cells were cycled between 1.9-2.6 V at C/5, without any deep of discharge (DOD)/capacity limitation. 1300 mA/g was used as 1C.

[0136] The coulombic efficiency of both lithium anodes was recorded and represented versus the cycle number. The results are shown in FIG. 2. It was observed a better coulombic efficiency for the functionalized lithium anode (Δ) in comparison to the non-functionalized lithium anode (O). Actually, it can be seen that the coulombic efficiency remains higher for the cell containing the functionalized lithium anode indicating lower electrolyte consumption

[0137] The discharge capacity of both lithium anodes was recorded and represented versus the cycle number. The results are shown in FIG. 3. It was observed that the capacity values observed are very similar up to 120 cycles for both cells. After, though a progressive drop is observed for all the cases, it is clear the better performance of the cell containing the functionalized lithium anode (A), presenting higher values of discharge capacity as well as a better coulombic efficiency (FIG. 2). Thus, a better performance of the functionalized lithium anode (A) in comparison to the non-functionalized lithium anode (0) was observed when increasing the number of cycles.

[0138] Functionalized lithium anode according to the invention showed an improvement of both cycle life and coulombic efficiency in cells due to lower electrolyte consumption, wherein the shuttle of polysulfides is retarded, which is the outcome of the enhanced stability of the lithium interface provided by the functionalization by means of a diazonium reduction.