Lithium metal anode including protective layer

Abstract

The invention relates to a lithium metal anode (1, 10, 11) for a battery, comprising an anode active substrate (2) comprising an anode current collector (7) and a layer (8) consisting essentially of lithium metal arranged on a surface (4) of the anode current collector (7), and a first lithium metal anode protective layer (3) arranged on the layer (8) consisting essentially of lithium metal, characterized in that the first lithium metal anode protective layer (3) comprises lithium iodide (LiI) and lithium fluoride (LiF). The invention further relates to a method for manufacturing such a lithium metal anode.

Description

Technical Field

[0001] The present invention relates to a lithium metal anode for a lithium-ion battery pack, the anode comprising a protective layer. The present invention further relates to a lithium-ion battery pack comprising such a lithium metal anode and methods of manufacturing them. Background Art

[0002] In the past few decades, rechargeable battery packs have achieved significant success and commercialization as the most popular and reliable power sources for portable devices, electric vehicles, and energy storage stations. In particular, Li-ion battery packs outperform other battery pack systems on the market due to their high energy density and excellent cycle stability.

[0003] Due to the high theoretical capacity of lithium (3860 mAh / g), anodes containing lithium metal are well-known anodes for lithium-ion battery packs. However, high (electro)chemical reactivity and a strong tendency to form lithium dendrites have hindered their widespread application. Dendrites will grow on the surface of the anode and pose a safety risk by potentially causing short circuits and battery pack failures.

[0004] Dendrites and dead lithium (i.e., lithium that has become inactive and no longer participates in the electrochemical cycle) result from non-uniform lithium plating and stripping during the charge and discharge cycles, which can be caused by various reasons such as mechanical stress, surface energy, structural defects, (electro)chemical reactions. To reduce the risk of dendrite formation and dead lithium accumulation, and to improve the safety and lifespan of the battery pack, several solutions have been studied, including but not limited to introducing solid-state electrolytes, artificial lithium metal hosts, adding additives to the electrolyte, and organic / inorganic passivation layers for liquid electrolyte-based battery packs.

[0005] In particular, lithium-ion conducting passivation layers, i.e., protective layers, such as artificial solid electrolyte interface (SEI) coatings, have attracted great interest. Although natural SEI typically forms on the anode, it has been shown to generally be insufficient to prevent dendrite growth. The artificial SEI (a-SEI) layer acts as a barrier, inhibiting dendrite growth and providing a more stable surface for lithium deposition.

[0006] US2018 / 0294476 discloses a lithium secondary battery pack comprising a foil or coating of lithium or a lithium alloy on a current collector as the anode, and a 1 nm - 10 μm thin layer of a highly elastic ultra-high molecular weight (UHMW) polymer having a lithium ion conductivity of at least 10 -6 S / cm and a molecular weight of 0.5×10 6 to 9×10 6 g / mol.

[0007] The disadvantages of the above-mentioned UHMW polymer as a protective layer are that it is not chemically stable in all types of liquid electrolytes, especially in certain organic solvents used in liquid electrolytes, and is prone to swelling. Another disadvantage is that the ability of the UHMW polymer to repel solvents in the electrolyte results in unstable and variable ionic conductivity of lithium ions in the electrolyte. Summary of the Invention

[0008] The object of the present invention is to overcome one or more of the above disadvantages. One object of the present invention is to provide a lithium metal anode having excellent electrochemical properties. A further object is to provide a lithium metal anode which, when used in a battery pack, has an improved lifespan compared to lithium metal anodes of the prior art. Yet another object is to provide a lithium metal anode which is less prone to forming dendrites and / or accumulating dead lithium when used in a battery pack, thereby providing excellent performance in a secondary battery pack. A further object is to provide a chemically and electrochemically stable lithium metal anode.

[0009] Another object of the present invention is to provide a lithium ion battery pack which has an improved lifespan and can withstand a large number of charge / discharge cycles.

[0010] According to a first aspect of the present disclosure, there is provided a lithium metal anode for a battery pack as described in the appended claims. The lithium metal anode includes an anodic active substrate and a first lithium metal anode protective layer disposed on the surface of the anodic active substrate.

[0011] The anodic active substrate includes an anodic current collector and a layer disposed on the surface of the anodic current collector and consisting essentially of lithium metal.

[0012] "Consisting essentially of lithium metal" in the present disclosure means that the layer contains at least 50%, preferably at least 75%, more preferably at least 95% of lithium metal. In other words, the layer contains at most 50%, preferably at most 25%, more preferably at most 5% of components such as indium, magnesium, aluminum, zinc, silver, tin, silicon, antimony, bismuth, gold, sodium, copper, as well as carbonates, oxides, and hydroxides.

[0013] Advantageously, the first lithium metal anode protective layer is disposed on the layer of the anodic active substrate consisting essentially of lithium metal.

[0014] The first lithium metal anode protective layer contains lithium iodide (LiI) and lithium fluoride (LiF) or consists essentially of lithium iodide (LiI) and lithium fluoride (LiF).

[0015] Advantageously, the weight ratio of fluoride ions to iodide ions in the first lithium metal anode protective layer is from 10:90 to 90:10, preferably from 30:70 to 70:30.

[0016] Advantageously, the first lithium metal anode protective layer has a thickness of 50 nm to 1000 nm, preferably 75 nm to 750 nm, more preferably 100 nm to 500 nm, such as 150 nm to 300 nm, for example 200 nm.

[0017] Advantageously, the lithium metal anode comprises a matrix. Advantageously, the matrix comprises LiF or consists essentially of LiF. Advantageously, at least a part (e.g., at least 50%, preferably at least 75%, more preferably at least 90%) and preferably all of LiI is dispersed (i.e., embedded) in the matrix.

[0018] Advantageously, the matrix comprising LiF or consisting essentially of LiF is porous, i.e., a porous matrix. Advantageously, at least a part and preferably all of LiI is present in the pores of the porous matrix. The term "present in the pores" is used to mean present at the wall surface of the pores and / or at least partially filling the pores.

[0019] Advantageously, the matrix comprises particles (i.e., grains). Advantageously, the particles (grains) comprise LiF or consist essentially of LiF. Advantageously, the particles have an average diameter of 10 nm to 500 nm, preferably 30 nm to 200 nm, more preferably 40 nm to 150 nm, such as 50 nm to 125 nm as measured by scanning electron microscopy (SEM).

[0020] Advantageously, when the matrix contains particles comprising LiF or consisting essentially of LiF, at least a part of LiI is present on a part of the particle surface (i.e., at least a part of LiI is present on the particle surface).

[0021] When the matrix is porous and comprises particles, LiI is advantageously present on a part of the particle surface and / or at least partially fills the pores between the particles, i.e., the pores of the porous matrix.

[0022] The lithium metal anode may include an additional lithium metal anode protective layer. Advantageously, the (optional) additional lithium metal anode protective layer comprises LiI and / or LiF or consists essentially of LiI and / or LiF.

[0023] Advantageously, such an additional lithium metal anode protective layer is provided on the first lithium metal anode protective layer. Alternatively or additionally, advantageously, such an additional lithium metal anode protective layer is provided between the first lithium metal anode protective layer and the anodic active substrate, in particular the layer consisting essentially of lithium metal of the anodic active substrate.

[0024] According to a second aspect of the present disclosure, a lithium ion battery pack as described in the appended claims is provided. Advantageously, the lithium ion battery pack includes the anode of the first aspect of the present invention. Advantageously, the battery pack is a secondary battery pack.

[0025] According to a third aspect of the present disclosure, there is provided a method of manufacturing a lithium metal anode as described in the appended claims. Advantageously, the lithium metal anode is the anode of a battery pack.

[0026] Advantageously, the lithium metal anode is as described in the first aspect of the present invention. In other words, the lithium metal anode advantageously comprises an anodic active substrate and a first lithium metal anode protective layer, wherein the anodic active substrate and the first lithium metal anode protective layer are as described above, that is, the first lithium metal anode protective layer contains LiI and LiF and is provided on the surface of a layer of the anodic active substrate consisting essentially of lithium metal.

[0027] The method comprises depositing a first lithium metal anode protective layer on a layer of the anodic active substrate consisting essentially of lithium metal. The first lithium metal anode protective layer is deposited by simultaneously thermally evaporating a first coating composition containing LiF or consisting essentially of LiF and a second coating composition containing LiI or consisting essentially of LiI.

[0028] Advantageously, the deposition rate ratio of the first coating composition to the second coating composition is from 1:10 to 20:1, preferably from 1:5 to 10:1, more preferably from 1:2 to 8:1, for example from 1:1 to 5:1.

[0029] The "deposition rate" of a coating composition in the present invention refers to the rate at which an evaporated substance or compound such as LiF or LiI condenses on a substrate to be coated, such as the anodic active substrate. According to the present invention, the deposition rate is the thickness in angstroms deposited in 1 second.

[0030] It can be seen therefrom that the deposition rate ratio of two substances (such as coating compositions) is the ratio of the deposition rate of one substance to the deposition rate of the other substance. In other words, a deposition rate ratio of 5:1 means that the thickness deposited by the first substance in 1 second is 5 times that of the second substance.

[0031] Advantageously, during the simultaneous thermal evaporation process, the first coating composition has a temperature of 600 °C to 800 °C, preferably 650 °C to 750 °C.

[0032] Advantageously, during the simultaneous thermal evaporation process, the second coating composition has a temperature of 150 °C to 300 °C, preferably 200 °C to 250 °C.

[0033] Advantageously, during the simultaneous thermal evaporation process, the anodic active substrate has a temperature of 10 °C to 30 °C, preferably 15 °C to 25 °C, more preferably room temperature, for example 20 °C.

[0034] Advantageously, by techniques known in the art, particularly by one or more of pulsed laser deposition, chemical vapor deposition, and radio frequency (RF) sputtering, the anodic active substrate is provided by depositing a layer consisting essentially of lithium metal on the surface of the anode current collector.

[0035] Optionally, the method further includes depositing an additional lithium metal anode protective layer. Advantageously, the additional lithium metal anode protective layer is deposited by thermal evaporation of a third coating composition comprising LiI or LiF or consisting essentially of LiI or LiF. Optionally, the thermal evaporation is carried out simultaneously with the thermal evaporation of a fourth coating composition comprising LiF or LiI or consisting essentially of LiF or LiI.

[0036] In other words, when the additional lithium metal anode protective layer is deposited by thermal evaporation of only the third coating composition comprising LiI or LiF or consisting essentially of LiI or LiF, the obtained additional lithium metal anode protective layer comprises LiI or LiF or consists essentially of LiI or LiF. Alternatively, when the additional lithium metal anode protective layer is deposited by simultaneous thermal evaporation of the third coating composition comprising LiI or LiF or consisting essentially of LiI or LiF and the fourth coating composition comprising LiF or LiI or consisting essentially of LiF or LiI, the obtained additional lithium metal anode protective layer comprises LiI and LiF or consists essentially of LiI and LiF.

[0037] Advantageously, the optional additional lithium metal anode protective layer is deposited before depositing the first lithium metal anode protective layer. Alternatively or additionally, it is also advantageous to deposit the optional additional lithium metal anode protective layer after depositing the first lithium metal anode protective layer.

[0038] Advantageously, when the optional third and / or optional fourth coating composition comprises LiI or consists essentially of LiI, during their respective thermal evaporation processes, the respective coating compositions have a temperature of 250 °C to 400 °C, preferably 275 °C to 375 °C, more preferably 300 °C to 350 °C.

[0039] Advantageously, when the optional third and / or optional fourth coating composition comprises LiF or consists essentially of LiF, during their respective thermal evaporation processes, the respective coating compositions have a temperature of 500 °C to 900 °C, preferably 600 °C to 850 °C, more preferably 700 °C to 800 °C.

[0040] Advantageously, during the thermal evaporation of the optional third and / or optional fourth coating composition, the anodic active substrate has a temperature of 10 °C to 30 °C, preferably 15 °C to 25 °C, more preferably room temperature, such as 20 °C.

[0041] The advantage of the lithium metal anode protection layer containing LiI and LiF is more uniform lithium stripping and lithium plating, and battery cells with improved lifespan are obtained in use.

[0042] The advantage that LiF exists in a microstructure comprising particles having an average diameter of 10 nm to 150 nm is that the lithium ion conductivity of the protection layer is higher than that of LiF alone, thereby contributing to a more functional anode, i.e., an anode with better performance compared to lithium metal anodes of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Aspects of the present invention will now be described in more detail with reference to the accompanying drawings, in which like reference numerals denote like features and in which:

[0044] Figures 1-4 Schematically shows a lithium metal anode according to the present invention;

[0045] Figures 5-8 Shows scanning electron microscope (SEM) images of the surfaces of 4 anodes of the present invention;

[0046] Figure 9A 、 9B And 9C show SEM images of the surfaces of 3 anodes of the present invention after immersion in an organic solvent;

[0047] Figure 10A 、 10B And 10C show the particle size distributions of 3 anodes of the present invention after immersion in an organic solvent;

[0048] Figure 11 Shows the specific discharge capacity of 3 reference pouch cells and 1 pouch cell of the present invention as a function of the number of charge / discharge cycles; and

[0049] Figure 12 Shows the specific discharge capacity of 1 reference pouch cell and 6 pouch cells of the present invention as a function of the number of charge / discharge cycles. DETAILED DESCRIPTION OF THE INVENTION

[0051] Figure 1 Shows a schematic view of the lithium metal anode 1 of the present invention. The anode 1 includes an anodic active substrate 2. The anodic active substrate 2 includes an anode current collector 7 and a layer 8 substantially composed of lithium metal provided on the surface 4 of the anode current collector 7.

[0052] The anode current collector 7 can be any anode current collector known in the art, particularly an anode current collector for a lithium ion battery pack. The layer 8 substantially composed of lithium metal can be provided (e.g., deposited) on the anode current collector 7 by any technique in the art, preferably by pulsed laser deposition, vapor deposition, or RF sputtering.

[0053] The anode 1 further includes a first lithium metal anode protective layer 3, which is disposed on the surface of the anode active substrate 2, in particular on the surface of the layer 8 substantially composed of lithium metal, opposite to the surface 4 adjacent to or in contact with the anode current collector 7.

[0054] The first lithium metal anode protective layer 3 contains lithium iodide (LiI) and lithium fluoride (LiF) or is substantially composed of lithium iodide (LiI) and lithium fluoride (LiF).

[0055] It is known that LiI and LiF have different lithium ion conductivities, approximately 10 -7 S / cm and approximately 10 -9 S / cm respectively. However, the inventors surprisingly found that the lithium ion conductivity of the first lithium metal anode protective layer 3 is higher than the lowest lithium ion conductivity, i.e., the lithium ion conductivity of LiF (approximately 10 -9 S / cm), which is contrary to expectations.

[0056] Therefore, as the inventors found, the current density on the anode is more uniform than that on an anode without such a protective layer or with another type of protective layer. The more uniform current density in turn leads to uniform lithium plating, and an anode that can withstand more lithium plating / stripping cycles is obtained. Therefore, a battery pack including this anode can withstand a higher number of charge / discharge cycles, resulting in improved lifespan.

[0057] A known phenomenon in lithium ion battery packs is the accumulation of dead lithium on the anode surface. Dead lithium is the lithium lost from the electrodes (initially from the anode and also from the cathode after a longer number of cycles), resulting in a smaller amount of lithium available for plating and stripping, i.e., for charging and discharging the battery pack. This reduces the number of charge / discharge cycles that the battery pack can withstand and thereby reduces the lifespan of the battery pack.

[0058] The inventors surprisingly found that when the protective layer contains LiI and LiF, LiI will leach out from the protective layer and dissolve in the electrolyte. It is believed that this leaching and dissolution is achieved because in organic solvents, especially in the organic solvents commonly used in the liquid electrolyte of lithium ion battery packs (such as ethers), the solubility of LiI is higher than that of LiF. Therefore, the dissolved LiI can replenish the lithium lost in the cathode. It is found that a triiodide / iodide (I3 - / I - ) redox pair is formed on the cathode side, thereby reducing the recycling of dead lithium. The dead lithium accumulated on the anode side during the cycling process is converted into soluble LiI, which diffuses into the cathode. I3 - is regenerated on the cathode side while the cathode returns to its lithiated state, thereby replenishing lithium ions from the dead lithium.

[0059] Such leaching and dissolution (of LiI) is particularly noted when the lithium metal anode comprises a matrix containing LiF or consisting essentially of LiF, and wherein LiI is dispersed (i.e., embedded or present) in the matrix.

[0060] In particular, when the matrix comprises particles or consists essentially of particles, the particles contain LiF or consist essentially of LiF, and LiI is at least partially present on the surface of the particles, significant leaching and dissolution of LiI occur. This makes the function of the battery pack even better. In other words, without wishing to be bound by any theory, there is a synergistic effect between the structure or morphology of the first lithium metal anode protective layer and the dissolution of LiI into the electrolyte, which provides an excellent lithium-ion battery pack.

[0061] Advantageously, when the matrix comprises particles containing LiF or consisting essentially of LiF, the particles have an average diameter of at least 1 nm, preferably at least 5 nm, more preferably at least 10 nm as measured by SEM. Advantageously, the particles have an average diameter of at most 750 nm, preferably at most 500 nm, more preferably at most 250 nm as measured by SEM.

[0062] Advantageously, the weight ratio of fluoride ions to iodide ions (F:I weight ratio) in the first lithium metal anode protective layer 3 is from 10:90 to 90:10, preferably from 20:80 to 80:20, more preferably from 30:70 to 70:30, most preferably from 40:60 to 60:40, such as from 45:55 to 55:45, for example 50:50.

[0063] Figure 2 The second anode 10 of the present invention is shown. Figure 2 The anode 10 differs from Figure 1 the anode 1 in that Figure 2 the anode 10 further comprises a second lithium metal anode protective layer 6. The second lithium metal anode protective layer 6 is present between the first lithium metal anode protective layer 3 and the anodic active substrate 2, particularly the layer 8 of the anodic active substrate 2 consisting essentially of lithium metal.

[0064] The second lithium metal anode protective layer 6 contains LiI and / or LiF or consists essentially of LiI and / or LiF.

[0065] When the second lithium metal anode protective layer 6 contains LiI and LiF or consists essentially of LiI and LiF, the layer is advantageously as described above for the first lithium metal anode protective layer 3. For example, the second lithium metal anode protective layer 6 may contain LiI and LiF or consist essentially of LiI and LiF, wherein the weight ratio of fluoride ions to iodide ions is different from the F:I weight ratio of the first lithium metal anode protective layer 3.

[0066] When the second lithium metal anode protective layer 6 comprises LiI or consists essentially of LiI, i.e., does not contain any LiF, the second lithium metal anode protective layer 6 advantageously has a thickness of 5 nm to 800 nm, preferably 50 nm to 700 nm, more preferably 100 nm to 500 nm.

[0067] When the second lithium metal anode protective layer 6 comprises LiF or consists essentially of LiF, i.e., does not contain any LiI, the second lithium metal anode protective layer 6 advantageously has a thickness of 50 nm to 200 nm, preferably 75 nm to 175 nm, more preferably 100 nm to 150 nm.

[0068] Advantageously, the total thickness of the lithium metal anode protective layers 3, 6, i.e., the sum of the thicknesses of the first lithium metal anode protective layer 3 and the second lithium metal anode protective layer 6, is 5 nm to 2.5 μm, preferably 10 nm to 2 μm, more preferably 50 nm to 1.5 μm.

[0069] Figure 3 The third anode 11 of the present invention is shown. Figure 3 The anode 11 and Figure 1 The difference between the anode 1 and Figure 3 The anode 11 further includes a third lithium metal anode protective layer 5. The third lithium metal anode protective layer 5 is present on the first lithium metal anode protective layer 3.

[0070] The third lithium metal anode protective layer 5 comprises LiI and / or LiF or consists essentially of LiI and / or LiF.

[0071] Advantageously, the third lithium metal anode protective layer 5 is as described above for the second lithium metal anode protective layer 6, with the difference being the position of the lithium metal anode protective layer in the anode.

[0072] Figure 4 Another anode 12 of the present invention is shown. Figure 4 The anode 12 includes Figure 2 The second lithium metal anode protective layer 6 of the anode 10 and Figure 3 The third lithium metal anode protective layer 5 of the anode 11.

[0073] Advantageously, the total thickness of the lithium metal anode protective layers 3, 5, 6, i.e., the sum of the thicknesses of the first lithium metal anode protective layer 3, the second lithium metal anode protective layer 6, and the third lithium metal anode protective layer 5, is 5 nm to 2.5 μm, preferably 10 nm to 2 μm, more preferably 50 nm to 1.5 μm.

[0074] The present invention further relates to a battery pack, particularly a lithium-ion battery pack, including the anode of the present invention. Advantageously, the (lithium-ion) battery pack is a secondary (lithium-ion) battery pack.

[0075] The battery pack further includes a cathode. The cathode can be any cathode known in the art. Advantageously, the cathode includes a cathode current collector (which can be any cathode current collector known in the art) and a cathode active material. Non-limiting examples of the cathode active material include vanadates such as H2V3O8, NMC, and LiFePO4 (LFP).

[0076] The battery pack further includes an electrolyte. The electrolyte can be a liquid electrolyte or a solid electrolyte. The electrolyte can be any electrolyte known in the art, such as a liquid electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI) in dimethoxyethane (DME), for example, an electrolyte of 2M LiFSI in DME.

[0077] The battery pack may further include a separator, particularly when the electrolyte is a liquid electrolyte. The separator can be any separator known in the art.

[0078] The present invention further relates to a method of manufacturing the above anode. The method includes the operations of providing an anodic active substrate, optionally depositing a second lithium metal anode protective layer, depositing a first lithium metal anode protective layer, and optionally depositing a third lithium metal anode protective layer. The first, second, and third lithium metal anode protective layers are advantageously as described above.

[0079] First, an anodic active substrate is provided, where the anodic active substrate is as described above, for example and in particular includes an anode current collector and a layer consisting essentially of lithium metal.

[0080] The first lithium metal anode protective layer is deposited on the anodic active substrate or on the optional second lithium metal anode protective layer by simultaneously thermally evaporating a first coating composition and thermally evaporating a second coating composition. The first coating composition contains LiF or consists essentially of LiF. The second coating composition contains LiI or consists essentially of LiI.

[0081] Advantageously, the simultaneous thermal evaporation is carried out under vacuum. For this purpose, the anodic active substrate to be treated is placed in a reaction chamber, and then the pressure is reduced to below atmospheric pressure. Advantageously, the thermal evaporation is carried out under ultra-high vacuum, that is, at a working pressure in the reaction chamber of at most 10 -6 mbar.

[0082] Advantageously, after providing the anodic active substrate, the step of simultaneous thermal evaporation is carried out without exposing the anodic active substrate to the ambient atmosphere (for example, by maintaining a vacuum). This avoids the exposure of lithium to compounds such as oxygen and carbon dioxide, and avoids the formation of a natural layer of impurities on the layer consisting essentially of lithium metal, said impurities including one or more of carbonates, oxides, hydroxides, and nitrides.

[0083] Advantageously, during the simultaneous thermal evaporation process, the anodic active substrate is at room temperature.

[0084] The simultaneous thermal evaporation of the first and second coating compositions includes heating the first coating composition to a first temperature to evaporate LiF, and heating the second coating composition to a second temperature to evaporate LiI. Advantageously, the coating compositions are continuously heated during the thermal evaporation process to maintain the evaporation of LiF and LiI. The evaporated LiF and LiI then condense on the anodic active substrate, thereby forming a first lithium metal anode protective layer. This first lithium metal anode protective layer thus comprises LiF and LiI or consists essentially of LiF and LiI.

[0085] Advantageously, during the simultaneous thermal evaporation process, the first coating composition has a temperature of 600 °C to 800 °C, preferably 650 °C to 750 °C.

[0086] Advantageously, during the simultaneous thermal evaporation process, the second coating composition has a temperature of 150 °C to 300 °C, preferably 200 °C to 250 °C.

[0087] Advantageously, the deposition rate ratio of the first coating composition to the second coating composition is from 1:10 to 20:1, preferably from 1:2 to 8:1.

[0088] The term "deposition rate" is used to denote the thickness (in angstroms per second) of the coating composition deposited per second on the substrate (such as the anodic active substrate 2) on which the coating composition is to be deposited. The term "deposition rate ratio" is used to denote the ratio of the deposition rate of the first coating composition to the deposition rate of the second coating composition.

[0089] The deposition rate of the coating composition depends on its temperature and the evaporation or sublimation temperature of the LiI and / or LiF it contains. As is to be understood, a higher temperature will result in a higher deposition rate. Thus, the temperatures of the first and second coating compositions are selected to match a predetermined deposition rate ratio.

[0090] Advantageously, the simultaneous thermal evaporation is carried out 1 to 50 times, preferably 5 to 30 times, more preferably 10 to 20 times. In particular, the thermal evaporation is carried out to obtain a predetermined thickness of the first lithium metal anode protective layer. It should be understood that the number of "passes" or the number of thermal evaporation cycles depends on the predetermined thickness to be obtained, as well as the thickness deposited per repetition.

[0091] Advantageously, when the anode is to include a second lithium metal anode protective layer comprising LiF or LiI or consisting essentially of LiF or LiI, the method further includes the step of separately thermally evaporating a third coating composition comprising LiF or LiI or consisting essentially of LiF or LiI before depositing the first protective layer 3.

[0092] Advantageously, the thermal evaporation is carried out under vacuum. For this purpose, the anodic active substrate to be treated is placed in the reaction chamber, and then the pressure is brought to below atmospheric pressure. Advantageously, the anodic active substrate is at room temperature during the thermal evaporation process.

[0093] When the third coating composition comprises LiF or consists essentially of LiF (i.e., does not contain LiI), it has a temperature of 500 °C to 900 °C during the thermal evaporation process. When the third coating composition comprises LiI or consists essentially of LiI (i.e., does not contain LiF), it has a temperature of 150 °C to 400 °C during the thermal evaporation process.

[0094] Alternatively, advantageously, when the anode is to include a second lithium metal anode protective layer comprising LiF and LiI or consisting essentially of LiF and LiI, the method further includes the step of simultaneously thermally evaporating a fourth coating composition comprising LiF or consisting essentially of LiF and a fifth coating composition comprising LiI or consisting essentially of LiI before depositing the first lithium metal anode protective layer 3.

[0095] The simultaneous thermal evaporation of the fourth and fifth coating compositions is advantageously as described above for the simultaneous thermal evaporation of the first and second coating compositions.

[0096] Advantageously, when the anode is to include a third lithium metal anode protective layer comprising LiF or LiI or consisting essentially of LiF or LiI, the method includes the step of thermally evaporating a sixth coating composition comprising LiF or LiI or consisting essentially of LiF or LiI separately after depositing the first lithium metal anode protective layer.

[0097] The thermal evaporation of the sixth coating composition comprising LiF or LiI or consisting essentially of LiF or LiI is advantageously as described above for the thermal evaporation of the third coating composition.

[0098] Alternatively, advantageously, when the anode is to include a third lithium metal anode protective layer comprising LiF and LiI or consisting essentially of LiF and LiI, the method includes the step of simultaneously thermally evaporating a seventh coating composition comprising LiF or consisting essentially of LiF and an eighth coating composition comprising LiI or consisting essentially of LiI after depositing the first lithium metal anode protective layer.

[0099] The simultaneous thermal evaporation of the seventh and eighth coating compositions is advantageously as described above for the simultaneous thermal evaporation of the first and second coating compositions. Detailed Description

[0100] Example 1

[0101] The anodic active substrate was prepared by cleaning the copper current collector with ethanol and drying it overnight under vacuum. Subsequently, a 25-μm-thick lithium metal layer was deposited on the copper current collector by physical vapor deposition (PVD). The PVD system (MBraun) was integrated into an Ar-glove box (MBraun) to avoid any contamination. The levels of H2O and O2 were maintained below 0.1 ppm. A quartz crystal controller (Inficon GmbH) and a quartz crystal microbalance sensor were used to control the lithium metal deposition. The copper current collector was fixed on a rotating glass substrate, and the chamber was evacuated to 10 -7 mbar. A lithium metal rod (Sigma Aldrich, 99.9% purity) was loaded into a stainless-steel source crucible to deposit a 25-μm-thick lithium metal layer.

[0102] Subsequently, six different anodes were prepared using this anodic active substrate, each anode having a 200-nm-thick lithium metal anode protective layer containing LiF and LiI. Each protective layer was deposited by simultaneously thermally evaporating a coating composition containing LiF (Sigma Aldrich, 99.99% purity, using an alumina crucible) and a coating composition containing LiI (Sigma Aldrich, 99.999% purity, using a stainless-steel crucible) at different deposition rate ratios. The deposition rate ratio was changed by varying the temperature of the coating compositions during thermal evaporation. Table 1 includes the LiF:LiI deposition rate ratios of the protective layers and the resulting weight ratios of fluoride ions to iodide ions.

[0103] Table 1: LiF:LiI deposition rate ratios and resulting F:I weight ratios

[0104]

[0105]

[0106] Figures 5 to 8 SEM images of the surfaces of the protective layers of Anode Nos. 1, 3, 5, and 6 are shown, respectively. It is clearly seen from the SEM images that the LiF-LiI co-deposited layer (i.e., obtained by simultaneous thermal evaporation of LiF and LiI) has a granular microstructure, where the grains (gray areas) are LiF and the brighter dots are LiI.

[0107] To further analyze the microstructure, Anode Nos. 3, 5, and 6 were immersed in 1,2-dimethoxyethane (DME), an organic solvent, at room temperature for 1 minute to 2 hours to simulate and evaluate the dissolution of LiI in the electrolyte and thereby simulate and evaluate its leaching from the protective layer. Figure 9A 、 9B and 9C show the SEM images of the surfaces of Anode Nos. 3, 6, and 5 after immersion in DME at room temperature for 20 minutes. A clear microstructure can be seen, showing at a ratio of 2:1 (Figure 9A ) and 5:1( Figure 9C The smaller particles of the anode obtained at a deposition rate ratio of). For anodes numbered 3, 5, and 6, the particle size distribution of LiF particles after immersion was also determined. Figure 10A 、 10B And 10C show the particle size distributions of anodes numbered 3, 5, and 6 respectively. Anode number 3 has an average particle size of 67 nm, while the average particle sizes of anodes numbered 4 and 5 are 52 nm and 82 nm respectively.

[0108] Example 2

[0109] Using anode number 4 of Example 1 as the anode (with a surface area of 7.56 cm 2 ), a soft-pack battery was assembled in a drying chamber with a dew point of -55 °C to -64 °C. As the cathode, a LiFePO4 (LFP) standard cathode with a loading of 13 mg / cm 2 , a battery capacity of 14 mAh, and a surface area of 6.40 cm 2 was used. An ether-based electrolyte containing lithium bis(fluorosulfonyl)imide (LiFSI) salt at 60 μn was used as the electrolyte. A 16-μm Teijin separator was also used in the soft-pack battery.

[0110] In addition, 3 reference soft-pack batteries were prepared, which had the anode active substrate of Example 1 as the anode, and the anode active substrate had no protective layer (Reference 1), had a 200-nm LiF protective layer (Reference 2), and had a 1000-nm LiI protective layer (Reference 3). The cathode, electrolyte, and separator were the same as those used in the soft-pack battery with anode number 4.

[0111] The repeated charge / discharge of all 4 soft-pack batteries was tested using a C / 3 charge and 1C discharge scheme. Using a NEWARE battery pack test system, the cycle test was carried out under ambient conditions and without applying external pressure.

[0112] Figure 11 Shows the specific discharge capacity as a function of the number of charge / discharge cycles. In the absence of any protective layer, the anode and thus the battery pack were stable up to almost 500 cycles (Reference 1), while Reference 2 (200 nm LiF) was stable up to 550 cycles, and Reference 3 (1000 nm LiI) was only stable up to 150 cycles. However, the soft-pack battery with anode number 4 of the present invention was stable for almost 650 cycles, significantly superior to all 3 reference battery packs.

[0113] Example 3

[0114] In addition to the pouch cells with the anode No. 4 of Example 1 and the pouch cells with an anode without any protective layer (Reference 1), pouch cells with the anodes No. 1, 2, 3, 5, and 6 of Example 1 were also prepared. They were prepared in the same manner as described in Example 2, having the same cathode, electrolyte, and pouch cells.

[0115] The repeated charge / discharge of the reference pouch cells and the 6 pouch cells of the present invention was tested with a C / 2 charge and 1C discharge protocol. Using a NEWARE battery pack test system, the cycling test was carried out under ambient conditions and without applying external pressure.

[0116] Figure 12 The specific discharge capacity as a function of the number of charge / discharge cycles is shown. Without any protective layer, the anode and thus the battery pack were stable up to almost 320 cycles (Reference 1), while all the battery pack cells of the present invention were stable for at least 370 cycles (see anode No. 1), significantly superior to the reference battery pack cells. The pouch cell with the best performance was the pouch cell with anode No. 5 (deposition rate ratio of LiF:LiI of 5:1), which was stable up to almost 620 cycles.

[0117] Reference numerals

[0118] 1. Lithium metal anode

[0119] 2. Anode active substrate

[0120] 3. First lithium metal anode protective layer

[0121] 4. Surface of the anode current collector

[0122] 5. Third lithium metal anode protective layer

[0123] 6. Second lithium metal anode protective layer

[0124] 7. Anode current collector

[0125] 8. Layer containing lithium metal

[0126] 10. Lithium metal anode

[0127] 11. Lithium metal anode

[0128] 12. Lithium metal anode

Claims

1. A lithium metal anode (1, 10, 11, 12) for a battery, comprising an anode active substrate (2), the anode active substrate (2) comprising an anode current collector (7) and a layer (8) consisting essentially of lithium metal disposed on a surface (4) of the anode current collector (7), and a first lithium metal anode protective layer (3) disposed on the layer (8) consisting essentially of lithium metal, characterized in that The first lithium metal anode protection layer (3) comprises lithium iodide (LiI) and lithium fluoride (LiF).

2. The lithium metal anode (1, 10, 11, 12) according to claim 1, wherein the weight ratio of fluoride ions to iodide ions in the first lithium metal anode protective layer (3) is 10:90 to 90:

10.

3. The lithium metal anode (1, 10, 11, 12) according to any one of the preceding claims, wherein the thickness of the first lithium metal anode protective layer (3) is 50 nm to 1000 nm.

4. The lithium metal anode (1, 10, 11, 12) according to any one of claims 1 to 2, comprising a matrix comprising LiF, wherein at least a portion of LiI is dispersed in the matrix.

5. The lithium metal anode (1, 10, 11, 12) according to claim 4, wherein the matrix comprises particles containing LiF, wherein the particles have an average diameter of 10 nm to 500 nm as measured by scanning electron microscopy (SEM).

6. The lithium metal anode (1, 10, 11, 12) according to claim 5, wherein LiI is at least partially present on the surface of the LiF particles.

7. The lithium metal anode (10, 11, 12) according to any one of claims 1 to 2, wherein the lithium metal anode (10, 11, 12) comprises an additional lithium metal anode protection layer (5, 6) arranged on the first lithium metal anode protection layer (3) and / or between the first lithium metal anode protection layer (3) and the layer (8) essentially consisting of lithium metal, wherein the additional protection layer (5, 6) contains LiI and / or LiF.

8. Lithium-ion battery comprising a lithium metal anode (1, 10, 11, 12) according to any one of the preceding claims.

9. The lithium ion battery according to claim 8, which is a secondary battery.

10. A method for manufacturing a lithium metal anode (1, 10, 11, 12), comprising depositing a first lithium metal anode protective layer (3) on a layer (8) of an anode active substrate (2) by simultaneously thermally evaporating a first coating composition and a second coating composition, wherein the layer (8) consists essentially of lithium metal, thereby obtaining an anode (1, 10, 11, 12), characterized in that The first coating composition comprises LiF, and the second coating composition comprises LiI. 11 . The method according to claim 10 , wherein a deposition rate ratio of the first coating composition to the second coating composition is 1:10 to 20:

1.

12. The method according to any one of claims 10 to 11, wherein during the simultaneous thermal evaporation process, the first coating composition has a temperature of 600°C to 800°C.

13. The method according to any one of claims 10 to 11, wherein during the simultaneous thermal evaporation process, the second coating composition has a temperature of 150°C to 300°C.

14. A method according to any one of claims 10 to 11, wherein the anode active substrate (2) is provided by depositing a layer (8) consisting essentially of lithium metal on the surface (4) of the anode current collector (7) by one or more of pulsed laser deposition, vapor deposition and radio frequency sputtering.

15. The method according to any one of claims 10 to 11, further comprising depositing an additional lithium metal anode protective layer (5, 6) on the layer (8) essentially consisting of lithium metal before depositing the first lithium metal anode protective layer (3) and / or on the first lithium metal anode protective layer (3) after depositing the first lithium metal anode protective layer (3) by thermal evaporation of a third coating composition comprising LiI or LiF and optionally simultaneously thermally evaporating a fourth coating composition comprising LiF or LiI.

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