Low temperature method of depositing a low impurity lithium fluoride containing layer

Abstract

This disclosure describes a plasma enhanced atomic layer deposition process for forming a Lithium Fluoride film or coating on a surface of a substrate using a vapor phase of a Lithium Fluoride precursor chemical having a general formula Li-O-C(Ri,2, and 3), wherein RI,2, and 3 are independently selected from H or a Ci to Cs alkyl, provided that at least one R group is the Ci to Cs alkyl and further provided that the at least one Ci to Cs alkyl group comprises one or more Fluorine atoms, such as CH2F, CHF2 or CF3. The resulting Lithium Fluoride film or coating on the surface has less than 5% atomic of carbon and less than 5% atomic of oxygen, preferably less than 1% atomic of Carbon and Oxygen.

Description

[0001] LOW TEMPERATURE METHOD OF DEPOSITING A LOW IMPURITY LITHIUM FLUORIDE CONTAINING LAYER

[0002] Cross Reference to Related Applications

[0003] This application claims priority to US Provisional Patent Application No. 63 / 728,921 , filed December 6, 2024, the entire contents of which are incorporated herein by reference.

[0004] Technical Field

[0005] The technical field is methods of forming films or coatings via vapor deposition processes, in particular Lithium Fluoride films or coatings.

[0006] Background Art

[0007] To improve the energy density and safety of lithium-ion batteries (LIBs), many studies have been conducted to identify and develop new types of cathode and / or anode active materials that make up LIBs. In particular, efforts have been made to replace the existing carbonaceous materials in the anode. Conventional LiBs use a carbon material (e.g., graphite) as the anode that enables the insertion / extraction of lithium ions; this is a key idea that enables the practical use of lithium-ion batteries. However, carbonaceous materials have reached the limit of their material specifically in terms of energy density. Instead of carbonaceous materials like graphite, the use of lithium metal and silicon, silicon oxide and silicon carbon composites as anode materials have been studied, but are still facing major obstacles such as safety problems and poor cycling characteristics.

[0008] The anode material of a battery must have a low discharge potential and a large amount of energy that can be extracted per unit weight or volume. From this point of view, lithium metal is suitable because of its very low reduction potential (-3.04 V against the standard hydrogen electrode) and high specific capacity by weight (3860 mA h g-1). However, when lithium metal is used as the anode material in a secondary (i.e. rechargeable) battery, lithium precipitates as dendrites during the charging process; these dendrites eventually grow large enough to penetrate the separator and come into contact with the cathode, causing a short circuit. In addition, the isolated lithium produced during the discharge process reduces cycling performance. Because of these problems, lithium metal has not been used as an anode material in lithium secondary batteries.

[0009] Silicon anodes are also considered as the next generation of anodes in lithium ion batteries, providing higher specific capacity (4200 mAh g-1) than graphite anodes (372 mAh g-1) with the same potential level (0.2 V vs Li+ / Li) as graphite anodes (0.05 V vs Li+ / Li). However, the silicon presents low electronic conductivity and suffers from large volume change in the discharge-charge process, which leads to the pulverization of silicon anode active materials and continuous formation of solid electrolyte interface layer (SEI). Consequently, the silicon anodes show poor cycle and rate performance.

[0010] Lastly, traditional cell types remain vulnerable to SEI formation owing to reaction with common battery electrolytes such as Li PF6and ethylene carbonate. This typically consumes significant amounts of Li, converting it to clusters of Li salts at the material interface. This contributes to eventual capacity fade, degradation of electrode binders, and uneven surface distribution of SEI layers that increase the risk of dendrite formation and thermal runaway events. Generally, it is highly desirable to coat electrode surfaces with exposure to electrolytes using barrier layers that are chemically inert, have high electrical conductivity and broad electrochemical stability. Unfortunately, very few materials display all of these properties simultaneously while maintaining high Li ionic conductivity, but this can often be overcome by even application of ultrathin coatings.

[0011] To overcome the problems described above, for various electrode types, surface modification with lithium fluoride (LiF) and lithium metal fluorides (LiMF) has been shown to have positive effects on the electrochemical performance of these materials. LiF has several advantages such as(1) a wide electrochemical window (high electrochemical stability), (2) and practical insolubility in most electrolytes. While the lithium ion diffusion coefficient for LiF is small, Li+ is sufficiently mobile to permeate the thin film when the LiF film is thin enough. As a result, the LiF passivated anode can be charged and discharged near its reversible lithiation potential (= no overpotential), and thus LiF is a promising coating material for lithium ion batteries. However, given the low mobility of Li ions in LiF, applying a thick coating can hinder, or block Li mobility, whereas low thickness, and / or totally uncoated / exposed surfaces can leave the substrate vulnerable to significant SEI formation during dis / charge. To prevent this, LiF must be applied evenly (conformal layers), and at a specific thickness on a given substrate to maximize performance, but many existing coating techniques are incapable of the required deposition control. In other words, a new coating technology is needed for LiF thin film that can provide exceptional control over film thickness down to the sub-nanometer level. Further, an acceptable deposition process on Li metal anode or silicon and carbon based anodes, that generally contain thermal sensitive organic components, should be performed at low temperatures, typically below 200°C or even below 170°C in the case of Li metal which melts at about 180°C.

[0012] LiF also has attractive properties for other applications, such as optical applications; owing to its very low refractive index as well as its excellent UV transmittance properties (see the J. Phys. Soc. Jpn 27, (1969)). As such, a new, highly scalable and high productivity LiF ultra-thin film coating process could also be used for optical applications.

[0013] Another important application is the organic EL I LED applications. In the organic EL device, in order to lower the driving voltage of the device and improve the charge balance between electrons and holes, it is necessary to increase the efficiency of electron injection from the cathode to an organic layer, such as the electron transport layer. Methods for improving electron injection includes forming an electron injection layer containing an inorganic compound such as LiF, CsF, SrO or Li2O between a cathode and an organic layer to a thickness of < 20 nm as disclosed in U.S. Pat. Nos. 5,776,622 and Appl. Phys. 73, 1185 (1998)). The cathode material is aluminum metal and aluminum alloy, requiring the O2-free LiF deposition process. Additionally, alkali metal fluorides possess low refractive indexes, and low absorption in the UV-light range, making them ideal candidates as low refractive index coatings in optical interference stacks. Commonly these are applied to temperature and pressure sensitive materials, such as polycarbonate, that typically crystallize at higher temperature, and low pressure. Therefore a low temperature and high-pressure deposition process, utilizing plasma, is highly valuable.

[0014] Atomic layer deposition (ALD / CVD) techniques have been shown to be highly effective in fabricating various types of thin films with high conformality, uniformity, and selflimiting growth. However, the current LiF ALD / CVD processes reported have problems to be solved such as (1) the reliance on secondary fluorine-containing co-reactants which are hazardous, corrosive, and / or are known to significantly contribute to global warming, (2) low conformality, and poor stoichiometric control in LiF deposition while adding additional degrees of complexity owing to the use of a secondary co-reactant, (3) the use of very low volatility Li precursors which hinders throughput on an industrial scale, (4) the use of high temperature and primary vacuum conditions in conventional ALD conditions to access low impurity containing LiF thin layer. The high temperature requirements of existing LiF deposition process is particularly limiting. Finally, a LiF or lithium metal fluoride (LiMF) ALD process should ideally not contain an O containing co-reactant like previously reported for other metal fluorides at higher temperatures (WO2021257641A1) or undesired F-containing co-reactants in previously reported LiF plasma enhanced ALD processes.

[0015] For instance, Hornsveld et al. in Phys. Chem. Chem. Phys., 2021 , 23, 9304, report a LiF process at 150°C using Li(N(SiMe)3)2and SF6plasma with a low growth per cycle of 0.4 A per cycle. However, SF6is undesired for industrial application owing to its high global warming potential, as well as corrosion properties. In J. Vac. Sci. T echnol. A 38(5) Sep / Oct 2020, Kvalvik et al. reported Li F thermal ALD at 150-300°C using NH4F and Li(OtBu), but the resulted LiF contained oxygen and carbon in the range of 3-5% even at temperatures as high as 225°C, and while Oxygen and Carbon measurements at lower temperature are not reported. In addition, Li(OtBu) based process are notoriously unscalable owing to Li(OtBu) poor volatility, and the reactions also requiring a F containing co-reactant.

[0016] Summary of Invention

[0017] This disclosure reports the use of a single-source precursor, with self-contained Li and F components which, in combination with process conditions generally including an atmospheric nitrogen and / or argon plasma enhanced ALD process, manages to address each of the problems described above and result in a low temperature deposition (general less than 200 degrees C) of a high purity, conformal LiF film. The unexpected result of this process is a LiF film having less than 1 % Carbon and Oxygen, despite the low temperature in the deposition and the single-source precursor having both Carbon and Oxygen.

[0018] The invention may be understood in relation to the following embodiments presented as numbered SENTENCES:

[0019] 1 . A process for forming a Lithium Fluoride film or coating on a surface of an substrate, the process comprising a plasma enhanced atomic layer deposition comprising the following sequential steps: a) placing the substrate in a reactor capable of performing the atomic layer deposition process at a reactor and / or substrate temperature of from 50 degrees C to 200 degrees C, preferably from 75 degrees C to 175 degrees C, most preferably from 100 degrees C to 150 degrees C, b) exposing the surface to a vapor phase of a Lithium Fluoride precursor chemical having a general formula Li-O-C(Ri,2,and3), wherein Ri,2,and3 are independently selected from H or a Ci to Cs alkyl, provided that at least one R group is the Ci to Cs alkyl and further provided that the at least one Ci to C5 alkyl group comprises one or more Fluorine atoms, such as CH2F, CHF2or CF3, c) forming a plasma from a second reactant chemical, wherein said second reactant chemical, such as nitrogen or argon, does not contain fluorine or oxygen, d) exposing the surface after step c) to the plasma, such as a nitrogen plasma or an argon plasma, e) and repeating steps b), c) and d) at least once, thereby forming the Lithium Fluoride film or coating on the surface, at least a portion of the Lithium Fluoride film having less than 5% atomic of carbon and less than 5% atomic of oxygen, preferably less than 1 % atomic of Carbon and Oxygen, and more preferably less than 0.5% atomic of carbon and oxygen.

[0020] 2. The process of SENTENCE 1 , further comprising an inert gas purge step, such as nitrogen or argon, between steps b) and c) and between step c) of a first sequence and step b) of a subsequent second sequence.

[0021] 3. The process of SENTENCES 1 or 2, wherein the process is performed at a pressure of 76 to 1000 T orr, preferably at about 760 T orr.

[0022] 4. The process of any one of SENTENCES 1 , 2, or 3, using a plasma source comprising:

[0023] - a plasma deposition head, comprising an aperture configured for delivering an atmospheric plasma from the deposition head to the substrate, and comprising a slotted cavity having parallel walls extending from opposing edges of the aperture;

[0024] - an electrode plate, mounted in the slotted cavity and extending from an interior of the deposition head towards the aperture; and

[0025] - a gas supply system, comprising a gas inlet, a gas supply chamber and gas outlets, wherein the gas supply chamber is arranged for receiving a mass flow of gas from the gas inlet and dividing the mass flow of gas between the gas outlets; wherein the gas outlets are provided on one side or opposing sides of the electrode plate, and wherein, in use, the mass flow of gas is divided for providing a flow of atmospheric plasma on one side or on the opposing sides of the electrode plate.

[0026] 5. The process of any one of SENTENCES 1 , 2, 3 or 4, wherein the Lithium Fluoride film or coating on the surface has a refractive index of from 1.30 to 1.5, preferable from 1.35 to 1.45.

[0027] 6. The process of any one of SENTENCES 1 , 2, 3, 4 or 5, wherein the Lithium Fluoride film or coating on the surface has a Lithium : Fluorine stoichiometry of Lii : Fo.7-1, as determined by X-ray Photoelectron Spectroscopy.

[0028] 7. The process of any one of SENTENCES 1 , 2, 3, 4, 5 or 6, wherein the Lithium Fluoride precursor chemical has the general formula Li-O-CH(Ri and 2).

[0029] 8. The process of SENTENCE 7, wherein at least one of R1 and 2 comprises at least one CF3group, preferably Li-O-CH(CF3)2 or Li-O-C(CF3)3.

[0030] 9. The process of any of the foregoing claims, wherein the substrate is selected from the group consisting of an anode or anode material for a secondary lithium ion battery, the anode or anode material comprising Lithium, Carbon, Silicon or mixtures thereof.

[0031] 10. The process of any of the foregoing SENTENCES, wherein the substrate is selected from the group consisting of an cathode or cathode material for a secondary lithium ion battery, the cathode or cathode material comprising oxides, phosphates or mixtures thereof

[0032] 11. The process of any of the foregoing SENTENCES, wherein the substrate is a sulfide, phosphate or oxide based solid-state-battery electrolyte or membrane.

[0033] 12. The process of SENTENCE 11 , wherein the electrolyte is selected from group consisting of Lithium Phosphorous oxynitride (LiPON), Lithium sulfide based glass ceramics, NASICON type phosphates, and garnet-type oxides.

[0034] 13. The process of any of the foregoing SENTENCES, wherein the substrate is an organic membrane, such as an electron injection layer for an organic electroluminescent (EL) device.

[0035] 14. The process of any of the foregoing SENTENCES, wherein the substrate is lithium metal.

[0036] 15. The process of any of the foregoing SENTENCES, further comprising a step of exposing the substrate to a vapor phase of an additional metal containing chemical precursor, preferably between steps b) and d), to thereby form a Lithium metal Fluoride (LiMF), wherein M is preferably selected from one or more of aluminum (Al), niobium (Nb), tantalum (Ta), zirconium (Zr), hafnium (Hf), magnesium (Mg), molybdenum (Mo), tungsten (W), or manganese (Mn).

[0037] Disclosure of Invention

[0038] This disclosure reports the use of a single-source precursor, with self-contained Li and F components for forming LiF films. The general formula for the genus of precursors is Li-O-C(Ri,2, and 3), wherein RI,2, and 3 are independently selected from H or a Ci to C5 alkyl, provided that at least one R group is the Ci to C5 alkyl and further provided that the at least one Ci to C5 alkyl group comprises one or more Fluorine atoms, such as CHF2or CF3. A preferred subgenus has the formula Li-O-CH(Ri and 2), further preferably having at least one CF3group on at least one R group (e.g. R = CF3, CH2-CF3, etc.). A specifically demonstrated, representative species is Li-O-CH(CF3)2. To ensure low Carbon content in the resulting films, smaller alkyl groups are general preferred such as Methyl or Ethyl and their partially fluorinated or perfluorinated analogs.

[0039] While the foregoing genus is not new, see WO2023248755A1 , these chemicals were selected and designed for LiOF film formation, which is why there is an oxygen atom in the molecule. It was thus wholly unexpected to discover that LiF, with undetectable levels of oxygen, could be vapor phase deposited, at all, much less at less than 200 degrees C. The expected low temperature films should have substantial oxygen content and unacceptable levels of carbon, making the layer unusable for the application. Under the conditions described herein, surprisingly, films having neither oxygen nor carbon, are formed even at 100 degrees C. This unexpected result will allow for coating objects such as battery electrodes with high purity LiF films, with an energy efficient, highly scalable process, including on thermal sensitive substrate such as Carbon based and Lithium metal based substrates.

[0040] The process that produces the above-described unexpected and surprising results is a plasma enhanced atomic layer deposition (“PEALD”) process. Unlike other LiF deposition processes, the fluorine component comes from the precursor instead of a fluorine containing co-reactant (e.g. an SF6plasma). Thus, the plasma of the process is a non-fluorine containing plasma, meaning there is no significant fluorine content is introduced or present in the plasma other than fluorine content that is derived from the precursor itself. That is to say, a non-fluorine containing plasma does not derive fluorine content from a second source used to generate a plasma. It is alternatively possible to dope the plasma with a small amount of second source fluorine content, generally less than 10% atomic, preferable less than 1% such as 0.5% or less, to adjust the F content in the LiF film. However, preferably, there is no detectable fluorine in the plasma derived from a second source (i.e. only from the precursor) and none of the plasma-forming second source chemicals introduced into the process contain fluorine. In addition, the plasma is a non-oxygen containing plasma, meaning generally less than 10% atomic oxygen, preferable less than 1% such as 0.2% or less, for the obvious reason that the desired film is LiF and not LiOF. As demonstrated below, the process can accommodate a small amount of intentionally introduced oxygen content in the plasma and still produce a high quality LiF film with undetectable levels of oxygen. This is especially surprising and means that the process is a robust one that can tolerate some levels of oxygen infiltration into the reaction, such as small amounts of air infiltration. This facilitates scale up and high volume industrial processes. The plasmas generally compatible with this process include plasmas of N2, H2, He, Ar and mixtures thereof. Ammonia and hydrazine plasmas are also compatible.

[0041] The PEALD process starts with the introduction of the above precursor into a PEALD reactor before, or subsequent to, introducing the target substrate(s). The PEALD reactor may be of any model or configuration capable of carrying out the steps of the process under the conditions of the process. Such reactors include spatial PEALD reactors suitable for coating large numbers or areas of 3D objects (e.g. battery electrodes). See, e.g., Chen, M., Nijboer, M. P., Kovalgin, A. Y., Nijmeijer, A., Roozeboom, F., & Luiten-Olieman, M. W. J. (2023). Atmospheric-pressure atomic layer deposition: recent applications and new emerging applications in high-porosity / 3D materials. Dalton Transactions, 52(30), 10254-10277. Many PEALD processes require high vacuum (e.g. 1-10 Torr) for the deposition process to occur at a commercially viable rate / speed. For spatial ALD processes, it is important that the process operates effectively at atmospheric pressure, with a sufficient deposition rate and film formation speed to enable commercial implementation.

[0042] The PEALD process may be performed in a Spatial ALD reactor using a plasma source based on a dielectric barrier discharge, similar to the one described in Y. Creyghton, A. Illiberi, A. Mione, W. van Boekel, N. Debernardi, M. Seitz, F. van den Bruele, P. Poodt & F. Roozeboom, (2016) Plasma-Enhanced Atmospheric-Pressure Spatial ALD of AI2O3 and ZrO2, ECS T ransactions 75(6), 11 .The PEALD process may be performed at a reactor and / or substrate temperature of 300 degrees C down to 50 degrees C, depending mainly on the user requirements of speed (generally higher temperature) versus thermal tolerance and thermal budget (generally lower temperature). For example, Li metal anode materials generally melt above 180 degrees C. Thus, many existing LiF film-forming processes cannot be used; and the process described herein should performed below this temperature such as at 150 degrees C. The process describe herein produces an unexpectedly high deposition rate or growth per cycle (“GPC”) at temperatures below 200 degrees C, as demonstrated below. This unexpectedly high GPC rate is sufficient to be commercially viable in a variety of industrial LiF coating processes, including battery anode coating.

[0043] A Lithium metal fluoride layer can be obtained by inserting a metal containing precursor pulse into the ALD sequence. The metal can be selected, without limitation, from the list consisting of aluminum (Al), niobium (Nb), tantalum (Ta), zirconium (Zr), hafnium (Hf), magnesium (Mg), molybdenum (Mo), tungsten (W), manganese (Mn), and their oxides and phosphate forms. The metal containing precursor can be for instance selected without limitation from the list consisting of AIMe3(TMA), AIMe2(OiPr), AI(tBu)Me2, AIMe2(OEt), Nb(OEt)5, Nb(=NtBu)(NMe2)3, Nb(=NtBu)(NEt2)3, Nb(=NtBu)Cp(NMe2)2, Nb(=NtBu)(MeCp)(NMe2)2, Nb(=NtBu)Cp(NEt2)2, Nb(=NtBu)Cp(OEt)2,

[0044] Nb(=NtBu)(MeCp)(OMe)2, Nb(=NtBu)(MeCp)(OEt)2, Ta(OEt)5, Ta(=NtBu)(NMe2)3, Ta(=NtBu)(NEt2)3, Ta(=NtBu)Cp(NMe2)2, Ta(=NtBu)(MeCp)(NMe2)2, Ta(=NtBu)Cp(NEt2)2, Ta(=NtBu)Cp(OEt)2, Ta(=NtBu)(MeCp)(OMe)2, Ta(=NtBu)(MeCp)(OEt)2, Zr(NMe2)4, Zr(NEtMe)4, Zr(NEt2)4, ZrCp(NMe2)3, Zr(nPrCp)(NMe2)3, Zr(nBuCp)(NMe2)3, Zr(tBuCp)(NMe2)3, Zr(sBuCp)(NMe2)3, ZrCI4, Zr(nPrCp)CI3, Zr(tBuCp)CI3, Zr(OtBu)4, ZrCp(OtBu)3, Zr(MeCp)(OtBu)3, Zr(MeCp)(OMe)3, Hf(NMe2)4, Hf(NEtMe)4, Hf(NEt2)4, HfCp(NMe2)3, Hf(nPrCp)(NMe2)3, Hf(nBuCp)(NMe2)3, Hf(tBuCp)(NMe2)3, Zr(sBuCp)(NMe2)3, HfCI4, Hf(nPrCp)CI3, Hf(tBuCp)CI3, Hf(OtBu)4, HfCp(OtBu)3, Hf(MeCp)(OtBu)3, Hf(MeCp)(OMe)3, W(=NtBu)2(NMe2)2, W(=NtBu)2(NtBu2)2, W(=NtBu)2(OtBu)2, W(CO)6, WF6, WCI5, WCI6, WOCI4WO2CI2, Mo(=NtBu)2(NMe2)2, Mo(=NtBu)2(NtBu2)2, Mo(=NtBu)2(OtBu)2, Mo(CO)e, MOF6, M0CI5, MOOCI4MOO2CI2, Mn(N(SiMe3)2)2, Mg(MeCp)2, Mg(EtCp)2, MgCp2, Mg(hfac)2, or mixture thereof.

[0045] Brief Description of the Drawings

[0046] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0047] - Figure 1 shows a first XPS depth profile for a Li F film growth on Si substrate;

[0048] - Figure 2 shows a precursor dose response curve;

[0049] - Figure 3 shows a second XPS depth profile for a Li F film growth on Si substrate;

[0050] - Figure 4 shows a comparison of the TGA curve between Li-O-CH(CF3)2(dashed line) and Li(hfac) (solid line);

[0051] - Figure 5 shows a third XPS depth profile for a Li F film growth on Si substrate;

[0052] - Figure 6 shows a fourth XPS depth profile for a Li F film growth on Si substrate;

[0053] - Figure 7 shows a fifth XPS depth profile for a Li F film growth on Si substrate.

[0054] Mode(s) for Carrying Out the Invention

[0055] The inventors selected Li-O-CH(CF3)2as a representative species for experimental demonstration and comparison to certain state of the art molecules and processes. Precursor synthesis has been previously described in WO2023248755A1 .

[0056] Examples

[0057] Example 1 : LiF film using N2Plasma

[0058] Li-O-CH(CF3)2was introduced into a stainless steel (“SUS”) container. Then, the temperature inside the container was set at 90 °C. The container is also connected to the PEALD reactor so that the gas in the container can be supplied to the PEALD reactor. Additional gas flow of 0.15 slm of N2gas was applied to the precursor container, afterwards diluted with 4.85 slm of N2gas, up to a total flow of 5 slm, leading to the PEALD reactor. At this time, the pressure in a SUS container is slightly above atmospheric pressure (operating near 760 T orr). Secondary co-reactant N2gas was separately delivered to the PEALD reactor at total flow rate of 60 slm, split over 2 plasma sources. In each plasma source, a 100 W plasma was ignited in the N2gas.

[0059] Next, a Si wafer substrate was introduced into the PEALD reactor. The temperature in the reactor was set at 150 degrees Celsius and is operated at near atmospheric pressure (760 Torr). The following PEALD deposition steps were repeated over 1500 cycles: (1) Li-O- CH(CF3)2precursor dose in N2carrier gas; (2) N2Purge; (3) N2plasma as a co-reactant dose; (4) N2Purge. The precursor- and plasma dose times were 0.1 s, both purge steps were 0.2 s. The total deposition time added up to 33 minutes, including start-up and shut-down.

[0060] The resulting film was 19.3 nm thick for a GPC average of about 0.13 A. The refractive index was 1.37 compared to a reference value of 1.392 at 0.6 pm. The deposited film was analyzed using an ellipsometer and x-ray photospectroscopy. The XPS depth profile shows LiF film growth on Si substrate (See Figure 1). The native SiO2layer was observed at the interface between Si substrate and deposited LiF film. At the reference 20 seconds etching point, the deposited film has no detectable carbon or oxygen (under 0.5% atomic). The Li to F ratio is not 1 to 1 using this analysis, but there is a known error in LiF ellipsometer and x- ray photospectroscopy analysis that causes the Li content to appear greater than it is. Brundle et al. in “Accuracy limitations for composition analysis by XPS using relative peak intensities: LiF as an example”, J. Vac. Sci. Technol. A 39, 013202 (2021). Thus, these films are in fact likely close to stoichiometric LiF but possibly, somewhat Li enriched. For most applications, this is nonconsequential. The key finding is that both Carbon and Oxygen are not present in detectable quantities. Despite using a nitrogen plasma, nitrogen was also undetectable in the film. Similar results were obtained at 200 degrees C and 100 degrees C.

[0061] Optimizing the flux of Nitrogen carrier gas and the pulse time, to increase precursor dose per cycle, produced a GPC of 0.4 A to 0.5 A at 100, 150 and 200 degrees C (Figure 2).

[0062] Example 2: LiF film using Argon Plasma

[0063] Experiment 2 used the same process as Experiment 1 , with the following modifications:

[0064] • Argon plasma using 150 ~ 300W plasma source.

[0065] • 300 cycles

[0066] • 15 second cycle steps (i.e. 1 minute cycles and 300 minutes total)

[0067] The XPS depth profile shows LiF film growth on Si substrate (See Figure 3). The XPS depth profile shows LiF film growth on Si substrate. The native SiO2 layer was observed at the interface between Si substrate and deposited LiF film. The film thickness was 21.9 nm for a GPC average of about 0.74 A. The refractive index was 1 .40. Example 3 - TGA and ALD comparison to Lithium 1 ,1 ,1 ,5,5,5-hexafluoro-2,4-pentanedione (Li(hfac))

[0068] A recent published application, US20240047821A1 , proposes to address a similar problem to be solved, namely a low temperature LiF coating process for electrodes. The proposed precursor is (US20240047821A1):

[0069] The LiF precursor comprises a lithium- and fluorine-containing chemical compound. The LiF precursor is formulated to be the only source of lithium and fluorine atoms in the lithium fluoride layer 20. The LiF precursor may comprise a lithium- and fluorine- containing acetylacetonate (acac) compound. For example, the LiF precursor may comprise lithium hexafluoroacetylacetone Li(hfac).

[0070] In the reaction chamber 100, the LiF precursor may be heated to a temperature of greater than or equal to about 110 degrees Celsius to less than or equal to about 250 degrees Celsius, less than or equal to about 200 degrees Celsius, less than or equal to about 150° C., less than or equal to about 140° C., or less than or equal to about 110° C.

[0071] The inventors synthesized Li(hfac) and performed Thermogravimetric analysis (TGA) analysis. Figure 4 shows comparison of the TGA curve between Li-O-CH(CF3)2 (dashed line) and Li(hfac) (solid line). The Li-O-CH(CF3)2shows full evaporation at around 194 degrees C and the residual level in the TGA cup was below 1 wt% after TGA measurement up to 500 degrees C. Li(hfac) did not show full evaporation and 5 wt% residual was observed after TGA measurement. The step-isotherm measurement suggested that evaporation of the Li(hfac) compound begins at 244.5 degrees C. Li(hfac) thus is another example of the state of the art’s general inability to identify a viable low temperature process for LiF films.

[0072] Further, the inventors evaluated the ability to obtain low Oxygen content LiF layers using Li(hfac) and Ar plasma. Li(hfac) was introduced into a SUS container which was then heated at 90°C and similar conditions were applied as in Experiment 2 and a higher wafer temperature:

[0073] • Argon plasma using 150W plasma source.

[0074] • 300 cycles

[0075] • 15 second cycle steps (i.e. 1 minute cycles and 300 minutes total)

[0076] • Wafer temperature of 250°C

[0077] Despite the higher temperature used in this experiment, no film could be obtained. Example 4 - Thermal CVD

[0078] The Li-O-CH(CF3)2begins to thermally decompose beyond 225 degrees C. Therefore the inventors tested Li-O-CH(CF3)2 for thermal CVD at this temperature as a single source molecule with no plasma. As shown in Figure 5, the resulting films, while predominantly Li F, have approximately 5% Carbon and Oxygen. This is the expected result based on the molecular structure. This confirms the unexpected and surprising nature of the PEALD results.

[0079] Examples 5-6: Oxygen tolerance

[0080] Example 5 - ALD with water (H2O)

[0081] WO2023248755A1 describes ALD using Li-O-CH(CF3)2with oxidants, namely H2O, O3, and O3+ 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). In these tests, the films produced were LiOF films as described in WO2023248755A1 . Water, being a mild oxidant, produced films with approximately 15% atomic Oxygen whereas Ozone yielded approximately 35% Oxygen content.

[0082] Example 6 - ALD with dilute Oxygen gas (O2)

[0083] Based on the prior experiments with oxidizing co-reactants, the inventors hypothesized that the LiF PEALD process would be tolerant of some amount of Oxygen content in the reaction and still produce acceptable LiF films. To test this, the inventors replicated Experiment 1 , but included 0.2% O2(volume) in the N2plasma feed gas. Similar results were obtained, 19nm thickness and refractive index of 1.37. The Oxygen content was reduced to below the target 1 % limit (Figure 6). This indicates that the PEALD LiF film process described herein is sufficiently robust to tolerate small amounts of air infiltration that may occur in a high volume industrial scale manufacturing process.

[0084] Example 7 - LiF ALD using Li-O-C(CF3)3

[0085] Experiment 2 was reproduced with Li-O-C(CF3)3instead of Li-O-CH(CF3)2. The XPS depth profile shows LiF film growth on Si substrate (See Figure 7), with an Argon plasma and a temperature set at 150°C. The XPS depth profile shows LiF film growth on Si substrate. The native SiO2 layer was observed at the interface between Si substrate and deposited LiF film. The film thickness was 9.6 nm for a GPC average of about 0.32 A per cycle, lower than the GPC obtained with Li-O-CH(CF3)2. The refractive index was 1 .40. Industrial Applicability

[0086] The present invention is at least industrially applicable to coating secondary battery electrodes with Li F to improve their performance.

[0087] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0088] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

[0089] Notation and Nomenclature

[0090] The following detailed description and claims utilize a number of abbreviations, symbols, and terms, which are generally well known in the art, and include:

[0091] • The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

[0092] • "Comprising" in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms "consisting essentially of and “consisting of unless otherwise indicated herein.

[0093] • “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0094] • Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0095] • Ranges may be expressed herein as from about one particular value, and / or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and / or to the other particular value, along with all combinations within said range.

[0096] • As used herein, “about” or “around” or “approximately” in the text or in a claim means±10% of the value stated.

[0097] • As used herein, “room temperature” in the text or in a claim means from approximately 20° C. to approximately 25° C.

[0098] • The term “ambient temperature” refers to an environment temperature approximately 20° C. to approximately 25° C.

[0099] • The term “substrate” refers to a material or materials on which a process is conducted. The substrate may be any secondary battery anode, cathode, electrolyte or membrane. The substrate may also have one or more layers of differing materials already deposited upon it from a previous manufacturing step. The substrate may contain materials which are used as battery electrode materials, such as Nickel, Cobalt, Manganese oxides, Lithium Iron Phosphate, Graphite, Silicon-Graphite composites, Silicon, Lithium metal and mixtures thereof. Examples of materials commonly used in the battery technology which may be included in the substrate include without limitation: Nickel Cobalt Manganese (NMC) Cathode with varying concentration of Ni, Co, Mn: NMCsn, NMC90.5.0.5, NMC622, NMC532, NMCm and derivatives, LFP (Li Iron Phosphate) and LMPF (Lithium Manganese Iron Phosphate), LMNO (Lithium Manganese Iron Phosphate), LCO (Lithium Cobalt Oxide), NCA (Nickel Cobalt Oxide), either polycrystalline or monocrystalline, Li metal, Silicon anodes grown by PECVD, Fluidised-bed CVD, wet coating or spray coating, natural or synthetic graphite, all of there with or without surface dopants or protective layers.

[0100] • Note that herein, the terms “film”, “coating” and “layer” may be used interchangeably. It is understood that a film may correspond to, or related to a layer, and that the layer may refer to the film. Furthermore, one of ordinary skill in the art will recognize that the terms “film” or “layer” used herein refer to a thickness of some material laid on or spread over a surface and that the surface may range from as large as the entire wafer to as small as a trench or a line.

[0101] • The standard abbreviations of the elements from the periodic table of elements are used herein. It should be understood that elements may be referred to by these abbreviation (e.g., Si refers to silicon, N refers to nitrogen, O refers to oxygen, C refers to carbon, H refers to hydrogen, F refers to fluorine, etc.).

[0102] • The unique CAS registry numbers (i.e., “CAS”) assigned by the Chemical Abstract Service are provided to identify the specific molecules disclosed.

[0103] • As used herein, the term “hydrocarbon” refers to a saturated or unsaturated function group containing exclusively carbon and hydrogen atoms. As used herein, the term “alkyl group” refers to saturated functional groups containing exclusively carbon and hydrogen atoms, An alkyl group is one type of hydrocarbon. Further, the term “alkyl group” refers to linear, branched, or cyclic alkyl groups. Examples of linear alkyl groups include without limitation, methyl groups, ethyl groups, propyl groups, butyl groups, etc. Examples of branched alkyls groups include without limitation, t-butyl. Examples of cyclic alkyl groups include without limitation, cyclopropyl groups, cyclopentyl groups, cyclohexyl groups, etc.

[0104] • As used herein, the abbreviation “Me” refers to a methyl group; the abbreviation “Et” refers to an ethyl group; the abbreviation “Pr” refers to any propyl group (i e., n-propyl or isopropyl); the abbreviation “iPr” refers to an isopropyl group; the abbreviation “Bu” refers to any butyl group (n-butyl, iso-butyl, tert-butyl, sec-butyl): the abbreviation “tBu” refers to a tert-butyl group; the abbreviation “sBu” refers to a sec-butyl group; the abbreviation “iBu” refers to an iso-butyl group; the abbreviation “Ph” refers to a phenyl group; the abbreviation “Am” refers to any amyl group (iso-amyl, sec-amyl, tert-amyl); the abbreviation “Cy” refers to a cyclic hydrocarbon group (cyclobutyl, cyclopentyl, cyclohexyl, etc.).

[0105] • Please note that the silicon-containing films, such as Si, SiN, SiO, SiOC, SiON, SiCON, are listed throughout the specification and claims without reference to their proper stoichiometry. The silicon-containing films may also include dopants, such as B, P, As, Ga and / or Ge. The fact that the film contains some residual hydrogen is also omitted from the film composition description. For instance, a SiOC film may contain residual H.

[0106] • Ranges may be expressed herein as from about one particular value, and / or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and / or to the other particular value, along with all combinations within said range. Any and all ranges recited herein are inclusive of their endpoints (i.e., x=1 to 4 or x ranges from 1 to 4 includes x=1 , x=4, and x=any number in between), irrespective of whether the term “inclusively” is used.

[0107] • Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”

[0108] • As used herein, the term “independently” when used in the context of describing R groups should be understood to denote that the subject R group is not only independently selected relative to other R groups bearing the same or different subscripts or superscripts, but is also independently selected relative to any additional species of that same R group. For example in the formula MR1 x (NR2R3)(4-x), where x is 2 or 3, the two or three R1 groups may, but need not be identical to each other or to R2 or to R3. Further, it should be understood that unless specifically stated otherwise, values of R groups are independent of each other when used in different formulas.

[0109] • As used in this application, the word “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion.

[0110] • Additionally, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0111] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step. The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

[0112] "Comprising" in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms "consisting essentially of and “consisting of unless otherwise indicated herein.

[0113] “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0114] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0115] Ranges may be expressed herein as from about one particular value, and / or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and / or to the other particular value, along with all combinations within said range.

[0116] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

Claims

What is claimed is:1 . A process for forming a Lithium Fluoride film or coating on a surface of an substrate, the process comprising a plasma enhanced atomic layer deposition comprising the following sequential steps: a) placing the substrate in a reactor capable of performing the atomic layer deposition process at a reactor and / or substrate temperature of from 50 degrees C to 200 degrees C, preferably from 50 degrees C to less than 110 degrees C or from 75 degrees C to 175 degrees C, most preferably from 100 degrees C to 150 degrees C, b) exposing the surface to a vapor phase of a Lithium Fluoride precursor chemical having a general formula Li-O-C(Ri,2, and 3), wherein Ri,2,and3 are independently selected from H or a Ci to C5 alkyl, provided that at least one R group is the Ci to C5 alkyl and further provided that the at least one Ci to C5alkyl group comprises one or more Fluorine atoms, such as CH2F, CHF2or CF3, c) forming a non-oxygen containing plasma from a second reactant chemical, wherein said second reactant chemical, such as nitrogen or argon, does not contain fluorine, d) exposing the surface after step c) to the plasma, such as a nitrogen plasma or an argon plasma, e) and repeating steps b), c) and d) at least once, thereby forming the Lithium Fluoride film or coating on the surface, at least a portion of the Lithium Fluoride film having less than 5% atomic of carbon and less than 5% atomic of oxygen, preferably less than 1 % atomic of Carbon and Oxygen, and more preferably less than 0.5% atomic of carbon and oxygen.

2. The process of claim 1 , further comprising an inert gas purge step, such as nitrogen or argon, between steps b) and c) and between step c) of a first sequence and step b) of a subsequent second sequence.

3. The process of claims 1 or 2, wherein the process is performed at a pressure of 76 to 1000 Torr, preferably 200 to 760 Torr and more preferably at about 760 Torr.

4. The process of any one of claims 1 , 2, or 3, using a plasma source comprising:- a plasma deposition head, comprising an aperture configured for delivering an atmospheric plasma from the deposition head to the substrate, and comprising aslotted cavity having parallel walls extending from opposing edges of the aperture;- an electrode plate, mounted in the slotted cavity and extending from an interior of the deposition head towards the aperture; and- a gas supply system, comprising a gas inlet, a gas supply chamber and gas outlets, wherein the gas supply chamber is arranged for receiving a mass flow of gas from the gas inlet and dividing the mass flow of gas between the gas outlets; wherein the gas outlets are provided on one side or opposing sides of the electrode plate, and wherein, in use, the mass flow of gas is divided for providing a flow of atmospheric plasma on one side or on the opposing sides of the electrode plate.

5. The process of any one of claims 1 , 2, 3 or 4, wherein the Lithium Fluoride film or coating on the surface has a refractive index of from 1 .30 to 1.5, preferable from 1 .35 to 1.45.

6. The process of any one of claims 1 , 2, 3, 4 or 5, wherein the Lithium Fluoride film or coating on the surface has a Lithium : Fluorine stoichiometry of Lii : Fo.7-1, as determined by X-ray Photoelectron Spectroscopy.

7. The process of any one of claims 1 , 2, 3, 4, 5 or 6, wherein the Lithium Fluoride precursor chemical has the general formula Li-O-CH(Ri and 2).

8. The process of claim 7, wherein at least one of R1 and 2 comprises at least one CF3group, preferably Li-O-CH(CF3)2 or Li-O-C(CF3)3.

9. The process of any of the foregoing claims, wherein the substrate is selected from the group consisting of an anode or anode material for a secondary lithium ion battery, the anode or anode material comprising Lithium, Carbon, Silicon or mixtures thereof.

10. The process of any of the foregoing claims, wherein the substrate is selected from the group consisting of an cathode or cathode material for a secondary lithium ion battery, the cathode or cathode material comprising oxides, phosphates or mixtures thereof.

11. The process of any of the foregoing claims, wherein the substrate is a sulfide, phosphate or oxide based solid-state-battery electrolyte or membrane.

12. The process of claim 11 , wherein the electrolyte is selected from group consisting of Lithium Phosphorous oxynitride (LiPON), Lithium sulfide based glass ceramics, NASICON type phosphates, and garnet-type oxides.

13. The process of any of the foregoing claims, wherein the substrate is an organic membrane, such as an electron injection layer for an organic electroluminescent (EL) device.

14. The process of any of the foregoing claims, wherein the substrate is lithium metal.

15. The process of any of the foregoing claims, further comprising a step of exposing the substrate to a vapor phase of an additional metal containing chemical precursor, preferably between steps b) and d), to thereby form a Lithium metal Fluoride (LiMF), wherein M is preferably selected from one or more of aluminum (Al), niobium (Nb), tantalum (Ta), zirconium (Zr), hafnium (Hf), magnesium (Mg), molybdenum (Mo), tungsten (W), or manganese (Mn).

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