Dense lithium film deposition process on conductive substrates

Abstract

Dense lithium-coated conductive substrates are described, which are comprised of sheet metal or sheet carbonaceous material, and on at least one side of the substrate there is a 1-5000 nm thick lithiophilic interlayer comprising or consisting of at least one metal or semimetal element selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, and Mn. Also described are processes for producing such lithium-coated substrates.

Description

[Technical Field]

[0001] The present invention relates to a process for producing a lithiophilic interlayer on a conductive substrate and the subsequent deposition of a dense lithium film on such an interlayer. Thus, such a lithiophilic coated substrate has the composition Li(NH3) 4+x The intermediate layer can be used as a base structure for depositing a dense lithium layer on the intermediate layer during contact with a liquid lithium source (x=0-10). The present invention further relates to a lithiophilic intermediate layer and a correspondingly prepared substrate coated with dense lithium.

[0002] Currently, commercially available lithium batteries function according to the intercalation principle. Graphite materials (corresponding to the chemical formula LiC6) with a maximum capacity of 372 mAh / g are used as the anode. Higher capacities, and therefore energy densities, can be achieved by partial or complete replacement of graphite with alloy active materials such as silicon or tin ("alloy anode materials"), or by complete replacement of the graphite material with metallic lithium.

[0003] For the production of thin lithium electrodes with lithium thicknesses <30 μm required for future lithium metal accumulators, conventional extrusion processes are not applicable or are unfavourable, as one must resort to very costly processes such as a combination of extrusion and precision rolling, PVD techniques (plasma vapor deposition), or processes operating at higher temperatures (e.g., melt deposition of lithium onto current collectors at >180 °C).

[0004] Therefore, there is a need for a simplified, low-temperature, and easily scalable process for producing thin lithium foils or lithium coatings.

[0005] Metallic lithium in alkali metal solutions, especially in liquid ammonia, has long been known (e.g., W.C. Johnson, M.M. Piskur, J. Phys. Chem. 37 (1933) 93-99). When saturated lithium solutions are cooled to <-60 °C, phase separation occurs, forming a metallic bronze-colored liquid layer of composition (Li(NH3)4), called Li bronze, on top of a dilute blue solution (H. Jaffe, Z. Phys. 93, 1935, 741-761). The lithium / ammonia system is described in detail in R. Hoffmann et al., Angew. Chem. Int. Ed. 2009, 48, 8198-8232. These liquids belong to the group of electrides because they have high metal-like electrical conductivity due to the presence of free electrons.

[0006] J. Bronn ("Liquefied ammonia as a solvent", December 31, 1905, Julius Springer, Berlin, ISBN978-3-642-50511-9, DOI: 10.1087 / 978-3-642-50821-9, pp. 116-117) describes that ammonia can be removed from "lithium ammonium" under vacuum conditions at +50 to +60°C to produce crystallized lithium metal.

[0007] GB 642 034A describes an electrochemical process for the production of alkali and alkaline earth metals. In this process, lithium salts are electrolyzed, inter alia, in liquid ammonia, to obtain a liquid or paste-like lithium / ammonia adduct. In a second step, lithium metal can be obtained from this by evaporating the ammonia at low temperature. The metal is obtained in the form of a spongy mass (p. 7, lines 35-47).

[0008] WO 2021 / 245196 A1 describes a process for producing lithium metal and lithium alloy compacts from a solution of lithium metal in ammonia. In this process, the composition Li(NH3) 4+xA solution of metallic lithium in ammonia, with x=0-10, is brought into contact with a metallic or electronically conductive deposition substrate, and the ammonia is removed by flooding with an inert gas at a temperature of -100-100°C or a pressure of 0.001-700 mbar, so that the remaining lithium is deposited on the deposition substrate and / or doped with lithium or thereby alloyed.

[0009] the purpose The present invention aims to provide a scalable process for producing thin, uniform, and dense lithium coatings on substrates with good electronic conductivity, such as metal or carbon-based films, which can also be carried out at moderate temperatures. There is a further need to provide such substrates with thin, uniform, and dense lithium coatings. Description of the Invention

[0010] The lithium coated substrate according to the present invention has the composition Li(NH3) 4+x and x=0-10, with an electronically conductive substrate such as a metal or carbon-based foil, the lithium-coated metal or carbon-based substrate, usually a foil, is made readily wettable with elemental lithium in its lithiophilic form by application of a metal-containing interlayer.

[0011] The lithiophilic interlayer consists of a coating of 1-5000 nm, preferably 5-1000 nm, thick on a metallic or carbon-based substrate / foil containing at least one metal or semimetal element capable of forming an alloy with lithium. This element is selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, and Mn. Preferred elements are Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ga, In, and Mg. The elements Zn, Al, Au, Si, Sn, and Ga are particularly preferred. These elements are present either in pure form or as a mixture of at least two of the mentioned elements. The lithiophilic coating is applied to at least one, preferably all, or both sides of the substrate / foil.

[0012] The dense lithium-coated conductive substrate according to the present invention comprises a sheet metal or sheet carbon-based material having on at least one side of the substrate a 1 to 5000 nm thick lithiophilic interlayer comprising or consisting of at least one metal or semi-metal element selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, Mn.

[0013] On a conductive substrate made of a sheet metal or a sheet carbonaceous material, a film of the composition Li(NH3) 4+x The process according to the invention for depositing dense lithium films from liquid lithium / ammonia compositions having x=0-10 comprises the step of: a conductive substrate is lithiophilized and coated on at least one side with a 1-5000 nm thick intermediate layer comprising or consisting of at least one element selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, Mn; this construction has the composition Li(NH3) 4+x (x=0 to 10), and then the ammonia is completely removed.

[0014] According to the invention, the lithiophilic interlayer can be deposited by different processes, the most important of which are: 1. Physical vapor deposition (PVD). In this process, a substrate (e.g., a foil) is sputtered in a vacuum with at least one element that can be alloyed with lithium. If gold is used to construct the intermediate layer, it is preferable that the conductive substrate is pre-coated with a thin (1-50 nm thick) nickel layer, unless the substrate itself is made of nickel. The nickel layer acts as a diffusion barrier between the substrate and the gold layer. 2. Electrochemical thin film deposition ("plating"). In this galvanic process, a solution of an element capable of alloying with lithium is electrolyzed by a conductive substrate, usually in the form of a foil, which acts as a cathode, on which the element capable of alloying with lithium is deposited. Before the subsequent lithium coating step according to the invention, electrolyte residues must be removed by dripping, washing and, if necessary, drying. 3. Mechanical application of a thin foil containing the desired lithiophilized metal. This process is particularly applicable to gold, since gold foils with very thin layer thicknesses (i.e., <1 μm) are commercially available (e.g., from Nanjing Gold Foil Factory). In this case, improved contact and adhesion across the entire area of ​​the two layers / foils can be achieved by appropriate mechanical post-treatment processes, such as pressing, rolling, coiling, etc. In industrial applications, this is best achieved by an automated roll-to-roll process.

[0015] As a substrate with good electronic conductivity, a planar structure made of copper, nickel, or iron, or a film made of or containing carbon nanotubes (CNTs) or graphene is preferably used. Typically, such substrates are used as current-conducting films in lithium batteries.

[0016] According to the invention, the layer thickness is measured by the SEM method (SEM = Scanning Electron Microscopy). The measurements were carried out in accordance with DIN EN ISO 9220 (Metallic Coatings - Measurement of Coating Thickness - Scanning Electron Microscopy). Also, very thin (<100 nm) coating thicknesses can be measured using X-ray methods, in particular X-ray reflectivity techniques (XRR). This technique is described in Miho Yasaka, The Rigaku Journal, 26(2), 2010.

[0017] The substrate / foil, uniformly coated with the interlayer over its entire area, is then contacted with a solution of pure metallic lithium in ammonia, preferably pure liquid lithium bronze of composition Li(NH3)4, at temperatures ranging from -40 to +40°C, preferably from -10 to +30°C, even more preferably from +15 to +30°C, and particularly preferably at ambient temperatures of +20 to +30°C. To this end, the conductive substrate / foil with the lithiophilic interlayer is immersed in the liquid lithium / ammonia composition. This can be done piece by piece, for example, with tweezers, or continuously by a roll-to-roll process. Depending on the desired lithium layer thickness, temperature, and type of lithiophilic coating, the contact time ranges from 0.1 to 10,000 seconds, preferably from 1 to 2,000 seconds. During this process, part of the ammonia evaporates, and either an alloy consisting of lithium and the alloy-forming elements of the interlayer is formed in the contact area with the conductive lithiophilic substrate, or metallic lithium is deposited in pure form on the interlayer. Lithium alloy layers are often formed so that the concentrations of the alloying elements decrease outward.

[0018] The quantitative removal of ammonia then completes the formation and deposition of lithium on the conductive substrate / foil with the lithiophilic interlayer. This step is carried out at temperatures between -40°C and +100°C, preferably between -10°C and +60°C, more preferably between +15°C and +30°C, and particularly preferably at ambient temperatures between +20°C and +30°C, preferably under reduced pressure, i.e., a pressure range of 0.001 to 700 mbar. Alternatively, ammonia can also be removed by passing a stream of inert gas through it. This process is generally less cost-effective than vacuum processes because the ammonia concentration is reduced by the stripping gas (inert gas stream), making ammonia recovery more difficult. After complete removal of the ammonia, elemental lithium metal remains on the lithiophilic deposition substrate in the form of a thin, uniform (coherent), area-like, and dense layer.

[0019] In the process according to the invention, metallic lithium is deposited on the lithiophilic interlayer in a layer thickness of 0.01 to 50 μm, preferably 0.1 to 30 μm, particularly preferably 0.5 to 25 μm, as determined by SEM.

[0020] Surprisingly, under these conditions, it was found that pure metallic lithium deposits in a thin, uniform, and dense form over the entire area on the surface lithiophilized according to the present invention. The density of the lithium can be characterized by measuring the specific surface area of ​​the lithium coating, measured by gas adsorption using the Brunauer, Emmett, and Teller (BET) method. These measurements were carried out using a Micromeritics ASAP2020 instrument. Due to the high reactivity of metallic lithium, noble gases such as argon / liquid argon were used as the metering gas. The measurements were carried out in accordance with ISO 9277 ("Determination of the specific surface area of ​​solids by gas adsorption - BET"). The lithium layer produced by the method according to the present invention has a surface area of ​​500 to 20,000 cm. 2 / g, preferably 1,000 to 10,000 cm 2 / g of Li.

[0021] Commercially available industrial lithium metal, or preferably purer battery or alloy-grade lithium, is used as the lithium source. Such metal grades are available, for example, from Sigma-Aldrich-Fluka (SAF). For example, there is a 99% "high sodium" technical grade with metallic impurities of 15,000 ppm or less, with sodium accounting for the overwhelmingly high percentage. Meanwhile, transition metals (especially Fe, Ag, Cu, and Zn) are present only in the low ppm range (1–20 ppm). The total of most transition metal impurities is in the 100 ppm or less range. Furthermore, lithium is available from SAF in battery quality, i.e., 99.9% Li content (based on metallic trace elements). These particularly pure battery grades contain up to 1500 ppm of extraneous metallic impurities, again dominated by sodium.

[0022] In the process according to the invention, metallic lithium is preferably used having a total content of transition metal impurities of 200 ppm or less, particularly preferably 100 ppm or less, and very particularly preferably 50 ppm or less. On the other hand, impurities including main group metals, in particular alkali metals and alkaline earth metals, as well as metals of the boron and carbon groups (groups 13 and 14), do not in principle interfere with the process. Therefore, they can also be present in higher contents, i.e., in the percentage range.

[0023] The thermal decomposition or dissociation of the lithium ammonia solution and compounds used, particularly the specified lithium bronzes, can occur either in the presence of additional organic solvents (e.g., hydrocarbons, ethers, or amines) or without such additives. In particular, saturated aliphatic hydrocarbons such as pentane, hexane, heptane, and octane, or common commercial mixtures of such compounds (industrial "petroleum ether," "white oil," and "benzine"), are suitable as organic solvents. Aromatic hydrocarbons can be used to a limited extent. The latter may promote undesirable decomposition with lithium amide formation. The use of ether-based compounds such as diethyl ether, dibutyl ether, methyl tert-butyl ether, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, and glymes is also possible, but is less preferred than the use of hydrocarbons.

[0024] Due to the high reactivity of metallic lithium and the Li / (NH3) mixture, all process steps of the lithium coating operation are carried out either under an inert gas (preferably argon, helium) atmosphere, under a pure ammonia atmosphere, or under vacuum conditions.

[0025] Freshly deposited metallic lithium from lithium-NH3 compositions is highly reactive to air and moisture. To ensure its safe further processing in industrial applications, e.g., in the construction of battery cells, passivation of the metal surface, i.e., application of a thin protective layer, is a further preferred process step. Such a process step involves contact with a gaseous or liquid substance that forms stable polymers and / or salts upon contact with lithium. Such a process step is described, for example, in WO 2011 / 073324 A1.

[0026] In particular, elements or compounds selected from the group consisting of inorganic compounds: N2, CO2, CO, O2, NO2O, NO, NO2, HF, F2, PF3, PF5, BF3, POF3, and H3PO4; or liquid organic compounds / solvents / solutions (coating agents) selected from the group consisting of carbonate esters, chelated lithium borate solutions in organic solvents, organosulfur compounds, nitrogen-containing organic compounds, phosphorus-containing organic compounds, partially fluorinated hydrocarbons, and silicon-containing organic compounds. The organic solvents mentioned are preferably selected from the group consisting of oxygen-containing heterocycles, carbonate esters, nitriles, carboxylic acid esters, or ketones, and the organosulfur compounds are preferably selected from the group consisting of sulfites, sulfones, and sultones. As the chelated lithium borate, lithium bis(oxalato)borate (LiBOB) is preferably used. [Example]

[0027] Example 1: Application of an ultra-thin gold layer onto copper foil Both sides of an 8 μm thick copper foil with a diameter of 9 mm manufactured by Landt Instruments were coated with an ultra-thin (80 nm) gold foil manufactured by Nanjing Gold Foil Factory, and the metal foils were bonded together without bubbles by lightly pressing them with a soft stamp.

[0028] Example 2: Deposition of a lithium metal film on a copper sheet A 12 μm-thick copper sheet (10 × 10 mm) coated on both sides with an 80 nm-thick gold layer was inserted into an Ar-filled glove box. Here, it was contacted with (immersed in) lithium bronze for approximately 20 seconds at ambient temperature (25 °C). After this, the sheet was transferred to an Ar-filled desiccator, and the ammonia was completely removed, first at 500 mbar and then under full oil pump vacuum (0.01 mbar). After this treatment, the sheet appeared uniformly silvery. A lithium layer thickness of approximately 5 μm was measured by SEM examination of the cross-section of the sheet.

[0029] The specific surface area of ​​the lithium layer on top measured by BET is 1,800 cm 2 / g.

[0030] Example 3: Application of a gold layer using a sputtering process Gold was sputtered onto a 15 mm wide, 20 μm thick copper sheet in a Leica high-vacuum sputter coater (model EM ACE600). Argon was used as the sputtering gas, and the sputtering time was 15 min.

[0031] The 60 nm thickness of the gold layer was measured by high-resolution SEM examination of the cross section of the foil.

[0032] Example 4: Deposition of lithium metal film on Au-sputtered copper sheet A 20 μm thick copper sheet (15 × 10 mm), coated on one side with a 60 nm thick gold layer prepared according to Example 3, was placed in an Ar-filled glove box at ambient temperature (25 °C) in contact with (immersed in) lithium bronze for approximately 100 seconds. The sheet was then transferred to an Ar-filled desiccator, and the ammonia was completely removed, first at 500 mbar and then under full oil pump vacuum (0.01 mbar). After this treatment, the sheet appeared uniformly silvery. The lithium layer was measured to be approximately 8 μm thick by SEM examination.

[0033] The specific surface area of ​​the lithium layer on top, measured by BET, is 2,100 cm 2 / g.

Claims

1. On a conductive substrate made of a sheet metal or a sheet carbon-based material, a film of the composition Li(NH ３ ) ４＋ｘ A process for depositing dense lithium films from a liquid lithium-ammonia composition having (x=0-10), wherein the conductive substrate is coated on at least one side by applying an intermediate layer 1-5000 nm thick containing at least one metal or semi-metal element selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, Mn, or consisting of at least one such element, and the construction is then deposited on the substrate with a thickness of 1-5000 nm. ３ ) ４＋ｘ (x=0-10) and then completely removing the ammonia.

2. The lithiophilic conductive substrate has the composition Li(NH ３ ) ４＋ｘ 2. The process according to claim 1, characterized in that the lithium / ammonia composition, (x=0-10), is contacted with the lithium / ammonia composition at a temperature in the range of −40 to +40° C., preferably −10 to +30° C., even more preferably +15 to +30° C., particularly preferably at an ambient temperature of +20 to +30° C., for a period of 0.1 to 10,000 seconds, preferably 1 to 2,000 seconds.

3. 3. The process according to claim 1, wherein the ammonia is removed by flooding with an inert gas at a temperature of -40 to +100°C or at a reduced pressure in the range of 0.001 to 700 mbar within said temperature range, so that the remaining lithium is deposited on the deposition substrate in a uniform and area-dense manner.

4. 4. The process according to claim 1, wherein the ammonia is removed at a temperature of from -20 to +80°C.

5. The lithium / ammonia composition may have the composition Li(NH ３ ) ４ 5. The process according to claim 1, wherein a lithium bronze having the formula:

6. the lithiophilic intermediate layer (a) PVD film formation, b) electrochemical thin film deposition, or c) mechanical deposition; 6. The process according to claim 1, wherein the intermediate layer comprises or consists of at least one metal or semi-metal element selected from the group consisting of Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, Mn, preferably Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ga, In and Mg, more preferably Zn, Al, Au, Si, Sn, Ga and In.

7. The lithium coating, which is made of dense metallic lithium, has a viscosity of 500 to 20,000 cm as measured by the BET method using noble gases. ２ / g of Li, preferably 1,000 to 10,000 cm ２ 7. The process according to claim 1, characterized in that the catalyst has a specific surface area of ​​Li / g.

8. 8. The process according to claims 1 to 7, characterized in that the metallic lithium deposited on the lithiophilic interlayer has a layer thickness, measured by SEM, of 0.01 to 50 μm, preferably 0.1 to 30 μm, particularly preferably 0.5 to 25 μm.

9. 8. Process according to claims 1 to 7, characterized in that planar structures made of copper, nickel, iron or foils made of or containing carbon nanotubes (CNTs) or graphene are used as the conductive substrate.

10. The lithium coating or surface passivation of the lithium alloyed conductive substrate is ２ , CO ２ , CO, O ２ , N ２ O, NO, NO ２ , H.F., F. ２ , P.F. ３ , P.F. ５ , B.F. ３ , POF ３ , H ３ P.O. ４ or with a liquid organic coating agent selected from the group consisting of carbonate esters, chelated lithium borate solutions as solutions in organic solvents, organic sulfur compounds, N-containing organic compounds, phosphorus-containing organic compounds, partially fluorinated hydrocarbons, silicon-containing organic compounds.

11. 11. The process of claim 10, wherein the organic solvent is selected from the group consisting of an oxygen-containing heterocycle, a carbonate, a nitrile, a carboxylic acid ester, or a ketone, and the organic sulfur compound is selected from the group consisting of a sulfite, a sulfone, or a sultone.

12. 1. A dense lithium-coated conductive substrate, characterized in that said substrate consists of a sheet metal or sheet carbonaceous material and on at least one side of said substrate there is present a 1 to 5000 nm thick lithiophilic intermediate layer comprising or consisting of at least one metal or semi-metal element selected from the group Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ge, Ga, In, Mg, Cr, V, Mo, W, Zr, Mn.

13. 13. The substrate according to claim 12, characterized in that the metal or semi-metal element is selected from Zn, Al, B, Cd, Au, Ag, Si, Pb, Sn, Ga, In and Mg, more preferably Zn, Al, Au, Si, Sn, Ga and In.

14. The lithium coating of the dense lithium metal has a viscosity of 500 to 20,000 cm as measured by the BET method using noble gases. ２ / g of Li, preferably 1,000 to 10,000 cm ２ 14. The substrate according to claim 12 or 13, characterized in that it has a specific surface area of ​​Li / g.

15. 15. The substrate according to claim 12, wherein the metallic lithium deposited on the lithiophilic interlayer has a layer thickness, measured by SEM, of 0.01 to 50 μm, preferably 0.1 to 30 μm, particularly preferably 0.5 to 25 μm.

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