Lithium metal anode comprising rrotective layer

Abstract

To provide a lithium metal anode comprising a protective layer for lithium-ion battery.SOLUTION: The present invention relates to a lithium metal anode (1, 10, 11) for a battery, including: an anode active substrate 2 including an anode current collector 7 and a layer 8 substantially consisting of lithium metal provided on a surface 4 of the anode current collector 7, and a first lithium metal anode protective layer 3 provided on the layer 8 substantially consisting of lithium metal. The first lithium metal anode protective layer 3 comprises lithium iodide (LiI) and lithium fluoride (LiF). The present invention further relates to methods of producing such lithium metal anodes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lithium metal anode including a protective layer for a lithium-ion battery. The present invention further relates to a lithium-ion battery including the lithium metal anode, and a method for manufacturing the same.

Background Art

[0002] Rechargeable batteries have achieved remarkable success and commercialization in the past few decades as the most popular and reliable power sources for portable devices, electric vehicles, and energy storage stations. In particular, Li-ion batteries are superior to other battery systems in the market due to their high energy density and excellent cycle stability.

[0003] Anodes containing lithium metal are well-known as anodes for lithium-ion batteries because of the high theoretical capacity of lithium (3860 mAh / g). However, their high (electro)chemical reactivity and strong tendency to form lithium dendrites have hindered their widespread use. Dendrites grow on the anode surface, potentially causing short circuits and battery failures, thereby posing a safety risk.

[0004] Dendrites and dead lithium (i.e., lithium that has become inert and is no longer involved in the electrochemical cycle) can result in uneven lithium plating and stripping during charge-discharge cycles due to various reasons such as mechanical stress, surface energy, structural defects, and (electro)chemical reactions. To reduce the risk of dendrite formation and dead lithium accumulation, and to improve the safety and lifespan of the battery, several solutions have been investigated, including but not limited to the introduction of solid electrolytes, artificial lithium metal hosts, addition of additives to the electrolyte, and organic / inorganic passivation layers for liquid electrolyte-based batteries.

[0005] In particular, lithium-ion conductive passive layers such as artificial solid electrolyte interface (SEI) coatings, that is, protective layers, have attracted much attention. Natural SEI typically forms on the anode but has often been proven to be insufficient to prevent dendrite growth. The artificial SEI (aSEI) layer acts as a barrier, inhibits dendrite growth, and provides a more stable surface for lithium deposition.

[0006] U.S. Patent Application Publication No. 2018 / 0294476 discloses a lithium secondary battery including, as an anode, a foil or coating of lithium or a lithium alloy on a current collector and a highly elastic ultra-high molecular weight (UHMW) polymer having a lithium conductivity of at least 10 -6 S / cm, a molecular weight of 0.5×10 6 ~9×10 6 g / mol, and being a thin layer of 1 nm to 10 μm.

[0007] The demerits of the above-mentioned UHMW polymer as a protective layer are that it is not chemically stable and tends to swell in all types of liquid electrolytes, particularly in specific organic solvents used in liquid electrolytes. A further demerit is that due to the repulsive force of the UHMW polymer against the solvent of the electrolyte, the ionic conductivity of lithium ions in the electrolyte is unstable and prone to fluctuation.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The object of the present invention is to overcome one or more of the above-mentioned drawbacks. The object of the present invention is to provide a lithium metal anode having excellent electrochemical performance. A further object is to provide a lithium metal anode having an improved lifespan when used in a battery as compared to lithium metal anodes in the art. Yet another object is to provide a lithium metal anode that is less likely to cause dendrite formation and / or accumulation of dead lithium during use in a battery, thereby providing excellent performance in a secondary battery. A further object is to provide a chemically and electrochemically stable lithium metal anode.

[0010] A further object of the present invention is to provide a lithium-ion battery with an improved lifespan that can withstand a large number of charge / discharge cycles.

Means for Solving the Problems

[0011] According to a first aspect of the present disclosure, there is provided a lithium metal anode for a battery as shown in the appended claims. The lithium metal anode includes an anode active substrate and a first lithium metal anode protective layer provided on the surface of the anode active substrate.

[0012] The anode active substrate includes an anode current collector and a layer substantially composed of lithium metal provided on the surface of the anode current collector.

[0013] In the present disclosure, "substantially composed of lithium metal" means that the layer contains at least 50%, preferably at least 75%, more preferably at least 95% 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, and carbonates, oxides, and hydroxides.

[0014] Advantageously, the first lithium metal anode protective layer is provided on a layer consisting essentially of lithium metal of the anode active substrate.

[0015] 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).

[0016] Advantageously, the weight ratio of fluoride to iodide in the first lithium metal anode protective layer is 10:90 to 90:10, preferably 30:70 to 70:30.

[0017] Advantageously, the thickness of the first lithium metal anode protective layer is 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.

[0018] Advantageously, the lithium metal anode contains a matrix. Advantageously, the matrix contains LiF or consists essentially of LiF. Advantageously, at least a part (for example at least 50%, preferably at least 75%, more preferably at least 90%) and preferably all of LiI are dispersed, that is, incorporated, in the matrix.

[0019] Advantageously, the matrix containing LiF or consisting essentially of LiF is porous, that is, a porous matrix. Advantageously, at least a part and preferably all of LiI are present in the pores of the porous matrix. The term "present in the pores" is used to mean present on the pore walls and / or filling the pores at least partially.

[0020] Advantageously, the matrix contains crystallites (i.e., particles). Advantageously, the crystallites (particles) contain LiF or consist essentially of LiF. Advantageously, the average diameter of the crystallites is 10 nm to 500 nm, preferably 30 nm to 200 nm, more preferably 50 nm to 125 nm, such as 40 nm to 150 nm, as measured by scanning electron microscopy (SEM).

[0021] Advantageously, when the matrix contains crystallites that contain LiF or consist essentially of LiF, LiI is at least partially present on a part of the surface of the crystallites (i.e., at least a part of LiI is present).

[0022] When the matrix is porous and contains crystallites, LiI is advantageously present on a part of the surface of the crystallites and / or is at least partially filled in the pores between the crystallites, i.e., the pores of the porous matrix.

[0023] The lithium metal anode can include a further lithium metal anode protective layer. Advantageously, the (optional) further lithium metal anode protective layer contains LiI and / or LiF or consists essentially of LiI and / or LiF.

[0024] Advantageously, this further lithium metal anode protective layer is provided on the first lithium metal anode protective layer. Alternatively or additionally, still advantageously, this further lithium metal anode protective layer is provided between the first lithium metal anode protective layer and the anode active substrate, particularly the layer of the anode active substrate that consists essentially of lithium metal.

[0025] According to a second aspect of the present disclosure, a lithium ion battery as shown in the appended claims is provided. Advantageously, the lithium ion battery includes the anode in the first aspect of the present invention. Advantageously, the battery is a secondary battery.

[0026] According to a third aspect of the present disclosure, there is provided a method for manufacturing a lithium metal anode as shown in the appended claims. Advantageously, the lithium metal anode is an anode for a battery.

[0027] Advantageously, this lithium metal anode conforms to the first aspect of the present invention. In other words, the lithium metal anode advantageously includes an anodic active substrate and a first lithium metal anode protective layer, and 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 substantially made of lithium metal of the anodic active substrate.

[0028] The method includes depositing a first lithium metal anode protective layer on a layer substantially made of lithium metal of the anodic active substrate. The first lithium metal anode protective layer is deposited by co-thermal evaporation of a first coating composition containing LiF or substantially consisting of LiF and a second coating composition containing LiI or substantially consisting of LiI.

[0029] 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.

[0030] In the present invention, the "deposition rate" of the coating composition means the rate at which an evaporated substance or compound, such as LiF or LiI, condenses on a substrate to be coated, such as an anodic active substrate. From the perspective of the present invention, the deposition rate is the thickness (angstroms) deposited in 1 second.

[0031] The deposition rate ratio of two substances (for example, coating compositions) means 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 first substance is 5 times greater than the second substance with respect to the thickness deposited in 1 second.

[0032] Advantageously, the temperature during co-thermal evaporation of the first coating composition is 600°C to 800°C, preferably 650°C to 750°C.

[0033] Advantageously, the temperature during co-thermal evaporation of the second coating composition is 150°C to 300°C, preferably 200°C to 250°C.

[0034] Advantageously, the temperature of the anode active substrate during co-thermal evaporation is 10°C to 30°C, preferably 15°C to 25°C, more preferably room temperature, for example 20°C.

[0035] Advantageously, the anode active substrate is provided by depositing a layer consisting essentially of lithium metal on the surface of the anode current collector by techniques known in the art, in particular by one or more of pulsed laser deposition, evaporation, and radio frequency (RF) sputtering.

[0036] Optionally, the method further comprises depositing a further lithium metal anode protective layer. Advantageously, the further lithium metal anode protective layer is deposited by co-thermal evaporation of a third coating composition comprising or consisting essentially of LiI or LiF. Optionally, the co-thermal evaporation is carried out simultaneously with the co-thermal evaporation of a fourth coating composition comprising or consisting essentially of LiF or LiI.

[0037] In other words, when the deposition of the further lithium metal anode protective layer is carried out by co-thermal evaporation of only the third coating composition comprising or consisting essentially of LiI or LiF, the resulting further lithium metal anode protective layer comprises or consists essentially of LiI or LiF. Alternatively, when the deposition of the further lithium metal anode protective layer is carried out by co-thermal evaporation of the third coating composition comprising or consisting essentially of LiI or LiF and the fourth coating composition comprising or consisting essentially of LiF or LiI, the resulting further lithium metal anode protective layer comprises LiI and LiF or consists essentially of LiI and LiF.

[0038] Advantageously, any further lithium metal anode protective layer is deposited before depositing the first lithium metal anode protective layer. Alternatively or additionally, still advantageously, any further lithium metal anode protective layer is deposited after depositing the first lithium metal anode protective layer.

[0039] Advantageously, when any third and / or any fourth coating composition contains LiI or consists essentially of LiI, each coating composition has a temperature during each thermal evaporation of 250°C to 400°C, preferably 275°C to 375°C, more preferably 300°C to 350°C.

[0040] Advantageously, when any third and / or any fourth coating composition contains LiF or consists essentially of LiF, each coating composition has a temperature during each thermal evaporation of 500°C to 900°C, preferably 600°C to 850°C, more preferably 700°C to 800°C.

[0041] Advantageously, the anode active substrate has a temperature during the thermal evaporation of any third and / or any fourth coating composition of 10°C to 30°C, preferably 15°C to 25°C, more preferably room temperature, for example 20°C.

[0042] The advantages of the lithium metal anode protective layer containing LiI and LiF are more uniform lithium stripping and lithium plating, and a battery cell with improved life during use can be obtained.

[0043] LiF exists as a microstructure containing crystal grains with an average diameter of 10 nm to 150 nm. The advantage is that the lithium ion conductivity of the protective layer is higher than that of LiF alone, which contributes to a more functional anode, that is, an anode that functions better, compared to lithium metal anodes in the art.

[0044] Hereinafter, aspects of the present invention will be described in more detail with reference to the accompanying drawings. The same reference numerals describe the same features.

Brief Description of the Drawings

[0045]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9A

Figure 9B

Figure 9C

Figure 10A

Figure 10B

Figure 10C

Figure 11

Figure 12

DETAILED DESCRIPTION OF THE INVENTION

[0046] Figure 1 shows a schematic diagram of the lithium metal anode 1 of the present invention. The anode 1 includes an anode active substrate 2. The anode active substrate 2 includes an anode current collector 7 and a layer 8 made of substantially lithium metal provided on the surface 4 of the anode current collector 7.

[0047] The anode current collector 7 may be any anode current collector known in the art, particularly for lithium ion batteries. By any technique in the art, preferably pulsed laser deposition, evaporation or RF sputtering, a layer 8 made of substantially lithium metal can be provided, for example deposited, on the anode current collector 7.

[0048] The anode 1 further includes a first lithium metal anode protective layer 3, which is provided on the (surface of) the anode active substrate 2, particularly on the (surface of) the layer 8 made of substantially lithium metal. This surface is the surface opposite to the surface 4 adjacent to, i.e., in contact with, the anode current collector 7.

[0049] The first lithium metal anode protective layer 3 contains lithium iodide (LiI) and lithium fluoride (LiF), or consists essentially of lithium iodide (LiI) and lithium fluoride (LiF).

[0050] LiI and LiF are about 10 -7 S / cm and about 10 -9It is known to have different lithium ion conductivities in S / cm. However, unexpectedly, contrary to expectations, the inventor has found that the lithium ion conductivity of the first lithium metal anode protective layer 3 is higher than the lowest lithium ion conductivity, that is, the lithium ion conductivity of LiF (about 10 -9 S / cm).

[0051] As a result, as the inventor has discovered, the current density of the anode is more uniform than that of an anode having no such protective layer or having another type of protective layer. Next, due to the more uniform current density, an anode can be obtained that can withstand uniform lithium plating and a greater number of lithium plating / stripping cycles. As a result, a battery including this anode can withstand a greater number of charge / discharge cycles and has an improved lifespan.

[0052] A known phenomenon in lithium ion batteries is the accumulation of dead lithium on the anode surface. This dead lithium is lithium that has detached from the electrode (initially from the anode and, after long cycles, also from the cathode), and the amount of lithium available for plating and stripping, that is, the amount of lithium for charging and discharging the battery, decreases. As a result, the number of charge / discharge cycles that the battery cell can withstand decreases, and thus the battery lifespan decreases.

[0053] Surprisingly, the inventor has found that when the protective layer contains LiI and LiF, LiI leaches out of the protective layer and dissolves in the electrolyte. This leaching and dissolution is thought to be realized because the solubility of LiI is higher than that of LiF in organic solvents, particularly the organic solvents typically used in the liquid electrolytes of lithium ion batteries (such as ethers). As a result, the dissolved LiI can replenish the lithium detached from the cathode. Triiodide / iodide (I 3- / I -) It has been found that a redox couple is formed on the cathode side, thereby alleviating the recovery of dead lithium. The dead lithium accumulated on the anode side during cycling is converted into soluble LiI and diffused to the cathode. While the cathode returns to its lithiated state, I 3- is regenerated on the cathode side, thereby replenishing lithium ions from dead lithium.

[0054] When the lithium metal anode contains LiF or a matrix substantially composed of LiF, this leaching and dissolution of (LiI) is particularly noted, and LiI is dispersed (i.e., incorporated or present) in the matrix.

[0055] In particular, when the matrix contains LiF or substantially consists of or substantially consists of crystallites of LiF and LiI is at least partially present on the surface of the crystallites, LiI leaches and dissolves considerably. This results in even better battery performance. 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, resulting in an excellent lithium-ion battery.

[0056] Advantageously, when the matrix contains LiF or substantially consists of crystallites of LiF, the average diameter of the crystallites is at least 1 nm, preferably at least 5 nm, more preferably at least 10 nm as measured by SEM. Advantageously, the average diameter of the crystallites is at most 750 nm, preferably at most 500 nm, more preferably at most 250 nm as measured by SEM.

[0057] Advantageously, the weight ratio of fluoride to iodide (F:I weight ratio) in the first lithium metal anode protective layer 3 is 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, most preferably 40:60 to 60:40 such as 45:55 to 55:45, for example 50:50.

[0058] Figure 2 shows the second anode 10 of the present invention. The difference between the anode 10 in Figure 2 and the anode 1 in Figure 1 is that the anode 10 in Figure 2 further includes 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 anode active substrate 2, particularly the layer 8 substantially made of lithium metal of the anode active substrate 2.

[0059] The second lithium metal anode protective layer 6 contains LiI and / or LiF, or consists essentially of LiI and / or LiF.

[0060] When the second lithium metal anode protective layer 6 contains LiI and LiF, or consists essentially of LiI and LiF, this layer is preferably as described for the first lithium metal anode protective layer 3. For example, the second lithium metal anode protective layer 6 can contain LiI and LiF, or consist essentially of LiI and LiF, and the weight ratio of fluoride to iodide is different from the F:I weight ratio of the first lithium metal anode protective layer 3.

[0061] When the second lithium metal anode protective layer 6 contains LiI, or consists essentially of LiI, that is, does not contain any LiF, the second lithium metal anode protective layer 6 preferably has a thickness of 5 nm to 800 nm, preferably 50 nm to 700 nm, more preferably 100 nm to 500 nm.

[0062] When the second lithium metal anode protective layer 6 contains LiF, or consists essentially of LiF, that is, does not contain any LiI, the second lithium metal anode protective layer 6 preferably has a thickness of 50 nm to 200 nm, preferably 75 nm to 175 nm, more preferably 100 nm to 150 nm.

[0063] Preferably, the total thickness of the lithium metal anode protective layers 3 and 6, that is, 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.

[0064] Figure 3 shows the third anode 11 of the present invention. The difference between the anode 11 in Figure 3 and the anode 1 in Figure 1 is that the anode 11 in Figure 3 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.

[0065] The third lithium metal anode protective layer 5 contains LiI and / or LiF, or consists essentially of LiI and / or LiF.

[0066] Advantageously, the third lithium metal anode protective layer 5 is as described for the second lithium metal anode protective layer 6, and the difference is the position of the lithium metal anode protective layer in the anode.

[0067] Figure 4 shows a further anode 12 of the present invention. The anode 12 in Figure 4 includes both the second lithium metal anode protective layer 6 of the anode 10 in Figure 2 and the third lithium metal anode protective layer 5 of the anode 11 in Figure 3.

[0068] Advantageously, the total thickness of the lithium metal anode protective layers 3, 5, 6, that is, 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.

[0069] The present invention further relates to a battery including the anode of the present invention, particularly a lithium-ion battery. Advantageously, the (lithium-ion) battery is a secondary (lithium-ion) battery.

[0070] This battery further includes a cathode. The cathode can be any cathode known in the art. Advantageously, the cathode includes a cathode current collector that 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).

[0071] The battery further includes an electrolyte. The electrolyte may be a liquid electrolyte or a solid electrolyte. The electrolyte may 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 containing 2M LiFSI in DME.

[0072] In particular, when the electrolyte is a liquid electrolyte, the battery can further include a separator. The separator may be any separator known in the art.

[0073] The present invention further relates to a method for manufacturing the above anode. The method includes the operations of providing an anode active substrate, optionally depositing a third lithium metal anode protective layer, depositing a first lithium metal anode protective layer, and optionally depositing a second lithium metal anode protective layer. The first, second, and third lithium metal anode protective layers are preferably as described above.

[0074] First, an anode active substrate is provided, and the anode active substrate is as described above, for example, particularly including an anode current collector and a layer substantially made of lithium metal.

[0075] The first lithium metal anode protective layer is deposited on the anode active substrate or on any third lithium metal anode protective layer by co-thermal evaporation of a first coating composition and thermal evaporation of 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.

[0076] Advantageously, the co-thermal evaporation is carried out under vacuum. For this purpose, the anode active substrate to be treated is placed in a reaction chamber, and then the pressure is made below atmospheric pressure. Advantageously, the thermal evaporation is carried out in ultra-high vacuum, that is, the operating pressure in the reaction chamber is at most 10 -6 mbar.

[0077] Advantageously, the co-thermal evaporation process is carried out, for example, by maintaining a vacuum after providing the anode active substrate without exposing the anode active substrate to the ambient atmosphere. This avoids exposing lithium to compounds such as oxygen and carbon dioxide, and avoids forming a natural layer of impurities containing one or more of carbonate, oxide, hydroxide and nitride on a layer substantially composed of lithium metal.

[0078] Advantageously, the anode active substrate is at room temperature during co-thermal evaporation.

[0079] The co-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 composition is continuously heated during thermal evaporation, and the evaporation of LiF and LiI is continued. Then, the evaporated LiF and LiI condense on the anode active substrate, thereby forming a first lithium metal anode protective layer. Thus, the first lithium metal anode protective layer contains LiF and LiI or consists essentially of LiF and LiI.

[0080] Advantageously, the temperature of the first coating composition during co-thermal evaporation is 600°C to 800°C, preferably 650°C to 750°C.

[0081] Advantageously, the temperature of the second coating composition during co-thermal evaporation is 150°C to 300°C, preferably 200°C to 250°C.

[0082] Advantageously, the deposition rate ratio of the first coating composition to the second coating composition is 1:10 to 20:1, preferably 1:2 to 8:1.

[0083] The term "deposition rate" is used for the thickness of the coating composition deposited per second on a substrate on which the coating composition is deposited, for example, the anode active substrate 2 (unit: angstrom / second). The term "deposition rate ratio" is used for the ratio of the deposition rate of the first coating composition to the deposition rate of the second coating composition.

[0084] The deposition rate of the coating composition is determined by its temperature and the evaporation or sublimation temperature of LiI and / or LiF contained in the coating composition. Naturally, the higher the temperature, the faster the deposition rate. As a result, the temperatures of the first and second coating compositions are selected to match a predetermined deposition rate ratio.

[0085] Advantageously, the co-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 so that the first lithium metal anode protective layer obtains a predetermined thickness. It is understood that the number of "passes" or thermal evaporation cycles is determined by the predetermined thickness to be obtained and the thickness to be deposited in each repetition.

[0086] Advantageously, when the anode is planned to include LiF or LiI or consist essentially of LiF or LiI as the second lithium metal anode protective layer, the method further includes a step of thermally evaporating a third coating composition containing LiF or LiI or consisting essentially of LiF or LiI after the deposition of the first protective layer 3.

[0087] Advantageously, the thermal evaporation is carried out under vacuum. For this purpose, the anode active substrate to be treated is placed in a reaction chamber, and then the pressure is set to be less than atmospheric pressure. Advantageously, the anode active substrate is at room temperature during the thermal evaporation.

[0088] When the third coating composition contains LiF or consists essentially of LiF (i.e., does not contain LiI), the temperature during its thermal evaporation is 500°C to 900°C. When the third coating composition contains LiI or consists essentially of LiI (i.e., does not contain LiF), the temperature during its thermal evaporation is 150°C to 400°C.

[0089] Alternatively, and more preferably, when the anode is planned to include a second lithium metal anode protective layer that contains LiF and LiI or consists essentially of LiF and Li, the method further includes, after deposition of the first lithium metal anode protective layer 3, simultaneously thermally evaporating a fourth coating composition that contains LiF or consists essentially of LiF, and a fifth coating composition that contains LiI or consists essentially of LiI.

[0090] The simultaneous thermal evaporation of the fourth and fifth coating compositions is preferably as described for the simultaneous thermal evaporation of the first and second coating compositions.

[0091] Preferably, when the anode is planned to include a third lithium metal anode protective layer that contains LiF or LiI or consists essentially of LiF or LiI, the method includes thermally evaporating a sixth coating composition that contains LiF or LiI or consists essentially of LiF or LiI, respectively, before deposition of the first lithium metal anode protective layer.

[0092] Preferably, the thermal evaporation of the sixth coating composition that contains LiF or LiI or consists essentially of LiF or LiI is as described for the thermal evaporation of the third coating composition.

[0093] Alternatively, and more preferably, when the anode is planned to include a third lithium metal anode protective layer that contains LiF and LiI or consists essentially of LiF and LiI, the method includes, before deposition of the first lithium metal anode protective layer, simultaneously thermally evaporating a seventh coating composition that contains LiF or consists essentially of LiF, and an eighth coating composition that contains LiI or consists essentially of LiI.

[0094] The simultaneous thermal evaporation of the seventh and eighth coating compositions is preferably as described for the simultaneous thermal evaporation of the first and second coating compositions.

Examples

[0095] Example 1 The anode active substrate was prepared by cleaning the copper current collector with ethanol and drying it overnight under vacuum. Next, a 25-μm-thick lithium metal layer was deposited on the copper current collector by physical vapor deposition (PVD). To avoid any contamination, the PVD system (MBraun) was incorporated into an Ar glove box (MBraun). The H2O and O2 levels were kept below 0.1 ppm. A crystal oscillator controller (Inficon GmbH) and a crystal oscillator microbalance sensor were used to control the deposition of the lithium metal. 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, purity 99.9%) was filled into a stainless-steel source crucible to deposit a 25-μm-thick lithium metal layer.

[0096] Next, six different anodes with a lithium metal anode protective layer containing 200 nm of LiF and LiI were prepared using the anode active substrate. Coating compositions containing LiF (Sigma-Aldrich, purity 99.99%, using an alumina crucible) and coating compositions containing LiI (Sigma-Aldrich, purity 99.999%, using a stainless-steel crucible) were simultaneously thermally evaporated at different deposition rate ratios to deposit each protective layer. The deposition rate ratio was varied by changing the temperature of the coating composition during thermal evaporation. Table 1 summarizes the deposition rate ratio of LiF:LiI and the resulting weight ratio of fluoride and iodide in the protective layer.

[0097] Table 1: Deposition rate ratio of LiF:LiI and the resulting F:I weight ratio TIFF2025100408000002.tif72170

[0098] Figures 5 to 8 show SEM images of the surfaces of the protective layers of anode numbers 1, 3, 5, and 6, respectively. The LiF-LiI co-deposited layer (i.e., obtained by the simultaneous thermal evaporation of LiF and LiI) has a granular microstructure, and it is clear from the SEM images that these crystallites (gray regions) are LiF and the bright spots are LiI.

[0099] To further analyze the microstructure, Anodes Nos. 3, 5, and 6 were immersed in dimethoxyethane (DME) as an organic solvent at room temperature for 1 minute to 2 hours to simulate and evaluate the dissolution of LiI into the electrolyte and thus the leaching of LiI from the protective layer. Figures 9A, 9B, and 9C show SEM images of the surfaces of Anodes Nos. 3, 6, and 5 after immersion in DME for 20 minutes at room temperature. Distinct microstructures are visible, with smaller crystal grains shown for the anodes obtained at deposition rate ratios of 2:1 (Figure 9A) and 5:1 (Figure 9C). For Anodes Nos. 3, 5, and 6, the particle size distributions of the LiF crystal grains after immersion were also measured. Figures 10A, 10B, and 10C show the particle size distributions of Anodes Nos. 3, 5, and 6, respectively. Anode No. 3 had an average particle size of 67 nm, while the average particle sizes of Anodes Nos. 4 and 5 were 52 nm and 82 nm, respectively.

[0100] Example 2 As the anode, Anode No. 4 of Example 1 with a surface area of 7.56 cm 2 was used, and a pouch cell was assembled in a dry room having 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 cell capacity of 14 mAh, and a surface area of 6.40 cm 2 was used. An ether-based electrolyte of 60 μm containing lithium bis(fluorosulfonyl)imide (LiFSI) salt was used as the electrolyte. Teijin's 16 μm separator was also used in the pouch cell.

[0101] Furthermore, three reference pouch cells were also prepared using the anode active substrates of Example 1 without any protective layer (Reference 1), with a 200 nm LiF protective layer (Reference 2), and with a 1000 nm LiI protective layer (Reference 3) as the anode. The cathode, electrolyte, and separator were the same as those used in the pouch cell of Anode No. 4.

[0102] All four pouch cells were tested by repeating charging / discharging with a C / 3 charging and 1C discharging protocol. A NEWARE battery test system was used to conduct the cycle test without applying external pressure under environmental conditions.

[0103] Figure 11 shows the specific discharge capacity according to the number of charge / discharge cycles. The anode without any protective layer, and thus the battery, was stable up to approximately 500 cycles (Reference 1), while Reference 2 (200 nm of LiF) was up to 550 cycles and Reference 3 (1000 nm of LiI) was only up to 150 cycles. However, the pouch cell of the present invention having Anode No. 4 was stable up to approximately 650 cycles and was clearly superior to all three reference batteries.

[0104] Example 3 In addition to the pouch cell having Anode No. 4 of Example 1 and the pouch cell having an anode without any protective layer (Reference 1), pouch cells were prepared using Anode Nos. 1, 2, 3, 5, and 6 of Example 1. Using the same cathode, electrolyte, and pouch cell, the pouch cells were prepared in the same manner as in Example 2.

[0105] The reference pouch cell and six pouch cells of the present invention were tested by repeating charging / discharging with a C / 2 charging and 1C discharging protocol. A NEWARE battery test system was used to conduct the cycle test without applying external pressure under environmental conditions.

[0106] Figure 12 shows the specific discharge capacity according to the number of charge / discharge cycles. The anode without any protective layer, and thus the battery, was stable up to approximately 320 cycles (Reference 1), while all of the battery cells of the present invention were stable up to at least 370 cycles (refer to Anode No. 1) and were clearly superior to the reference battery cells. The most excellent pouch cell was the one having Anode No. 5 (deposition rate ratio LiF:LiI 5:1) and was stable up to approximately 620 cycles.

Explanation of Reference Signs

[0107] 1 Lithium metal anode 2 Anode active substrate 3 First lithium metal anode protective layer 4 Anode current collector surface 5 Second lithium metal anode protective layer 6 Third lithium metal anode protective layer 7 Anode current collector 8 Layer containing lithium metal 10 Lithium metal anode 11 Lithium metal anode 12 Lithium metal anode

Claims

1. A lithium metal anode (1, 10, 11, 12) comprising an anode current collector (7) and an anode active substrate (2) including a layer (8) substantially made of lithium metal provided on a surface (4) of the anode current collector (7), and a first lithium metal anode protective layer (3) provided on the layer (8) substantially made of lithium metal, wherein the first lithium metal anode protective layer (3) contains lithium iodide (LiI) and lithium fluoride (LiF).

2. The lithium metal anode (1, 10, 11, 12) according to Claim 1, wherein a weight ratio of fluoride to iodide in the first lithium metal anode protective layer (3) is 10:90 to 90:10, preferably 30:70 to 70:

30.

3. The lithium metal anode (1, 10, 11, 12) according to Claim 1, wherein a thickness of the first lithium metal anode protective layer (3) is 50 nm to 1000 nm, preferably 100 nm to 500 nm.

4. The lithium metal anode (1, 10, 11, 12) according to Claim 1, including a matrix containing LiF, and at least a part of LiI being dispersed in the matrix.

5. The lithium metal anode (1, 10, 11, 12) according to Claim 4, wherein the matrix contains crystal grains containing LiF, and an average diameter of the crystal grains is 10 nm to 500 nm, preferably 30 nm to 200 nm as measured by scanning electron microscopy (SEM).

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

7. The lithium metal anode (10, 11, 12) further includes additional lithium metal anode protective layers (5, 6) provided on the first lithium metal anode protective layer (3) and / or between the first lithium metal anode protective layer (3) and the layer (8) substantially made of lithium metal, and the additional protective layers (5, 6) contain LiI and / or LiF. The lithium metal anode (10, 11, 12) according to Claim 1.

8. A lithium ion battery including the lithium metal anode (1, 10, 11, 12) according to Claim 1.

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), wherein the layer (8) consists essentially of lithium metal by co-thermal evaporation of a first coating composition and a second coating composition, whereby the anode (1, 10, 11, 12) is obtained, characterized in that the first coating composition contains LiF and the second coating composition contains LiI.

11. The method according to claim 10, wherein the deposition rate ratio of the first coating composition to the second coating composition is 1:10 to 20:1, preferably 1:5 to 10:

1.

12. The method according to claim 10, wherein the temperature during the co-thermal evaporation of the first coating composition is 600°C to 800°C, preferably 650°C to 750°C.

13. The method according to claim 10, wherein the temperature during the co-thermal evaporation of the second coating composition is 150°C to 300°C, preferably 200°C to 250°C.

14. The method according to claim 10, wherein the anode active substrate (2) is provided by depositing a layer (8) consisting essentially of lithium metal on the surface (4) of an anode current collector (7) by one or more of pulsed laser deposition, evaporation, and high-frequency sputtering.

15. The method according to claim 10, further comprising depositing additional lithium metal anode protective layers (5, 6) by thermal evaporation of a third coating composition containing LiI or LiF, optionally simultaneously with a fourth coating composition containing LiF or LiI, on the layer (8) consisting essentially 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).

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