Lithium metal battery

Abstract

The present invention relates to a lithium metal battery comprising a positive electrode, a lithium metal negative electrode, and a separator provided between the positive electrode and the lithium metal negative electrode, at least one surface of the separator being provided with a coating layer comprising a polymer binder, a lithium salt, and inorganic particles having fluorine functional groups introduced on the surface.

Description

Technical Field

[0001] This invention relates to a lithium metal battery. Background Technology

[0002] Typical lithium-ion batteries use a carbon-based negative electrode and operate by moving lithium ions through a liquid electrolyte in which lithium salts are dissolved in an organic solvent. In contrast, lithium metal batteries use a negative electrode current collector alone, or a negative electrode with a lithium metal layer coated on it. They operate by reducing lithium ions to lithium metal at the negative electrode during charging and oxidizing the lithium metal back to lithium ions during discharging.

[0003] Lithium metal, used in lithium metal batteries, is a material that enables high-capacity batteries due to its high capacitance per unit mass. However, during the attachment / desorption of lithium ions, lithium metal forms dendrites, which can damage the separator and potentially cause a short circuit between the positive and negative electrodes.

[0004] Therefore, in order to effectively drive high-capacity lithium metal batteries, a technology is needed that can effectively prevent the side effects caused by dendrites in lithium metal batteries.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Korean Patent Publication No. 10-2021-0009188 Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to provide a lithium metal battery that can effectively suppress the performance degradation of the battery caused by the formation of dendrites in lithium metal batteries.

[0010] Technical solution

[0011] One embodiment of the present invention provides a lithium metal battery comprising: a positive electrode, a lithium metal negative electrode, and a separator disposed between the positive electrode and the lithium metal negative electrode, wherein at least one side of the separator is provided with a coating comprising a polymeric binder, a lithium salt, and inorganic particles with fluorine functional groups introduced onto the surface.

[0012] The effects of the invention

[0013] The lithium metal battery of the present invention has a coating on at least one side of the separator that can effectively prevent the side effects caused by dendrites, thereby achieving high stability and improved lifespan. Attached Figure Description

[0014] Figure 1A cross-sectional schematic diagram of a lithium metal battery according to an embodiment of the present invention is shown.

[0015] Figure 2 The results are X-ray diffraction measurements of γ-Al2O3 particles before fluorination and F-Al2O3 particles after fluorination in Manufacturing Example 2.

[0016] Figure 3 This is an image of surface elemental analysis (EDS) of fluorinated alumina (F-Al2O3) obtained according to a manufacturing example.

[0017] Figure 4 This is a SEM image of the coated diaphragm manufactured according to Example 1.

[0018] Figure 5 The graphs show the lifespan characteristics of coin batteries with coated separators applied to the embodiments and comparative examples. Detailed Implementation

[0019] In this specification, when a part is referred to as "containing" a certain element, unless otherwise stated, it means that other elements may be included, rather than excluded.

[0020] In this specification, when it is mentioned that a component is "above" another component, this includes not only the case where the component is in contact with the other component, but also the case where there is another component between the two components.

[0021] In this specification, unless otherwise specified, the terms “%” and “parts” indicating content are based on weight.

[0022] The lithium metal battery of this invention differs from lithium-ion batteries. Specifically, lithium metal batteries use lithium metal as the negative electrode active material, while lithium-ion batteries use non-lithium materials (e.g., graphite) as the negative electrode active material, resulting in significant differences. Furthermore, electrolytes suitable for lithium metal batteries exhibit low reactivity with lithium metal and do not corrode it. In contrast, electrolytes suitable for lithium-ion batteries can react with non-lithium negative electrode active materials to form an SEI (solid-electrolyte interphase) layer. This SEI layer plays a positive role in controlling the thermodynamic chemical reactions occurring in lithium-ion batteries. As mentioned earlier, due to the difference in negative electrode active materials, the operating characteristics of lithium metal batteries and lithium-ion batteries are significantly different, and therefore the problems that need to be solved are also necessarily different. Consequently, the required separator and electrolyte characteristics for lithium metal batteries and lithium-ion batteries are inevitably different. When the components used in lithium-ion batteries are applied to lithium metal batteries, the same results cannot be expected in most cases. Therefore, the technical fields of lithium metal batteries and lithium-ion batteries can be considered entirely different.

[0023] The present invention will now be described in detail.

[0024] One embodiment of the present invention provides a lithium metal battery comprising: a positive electrode, a lithium metal negative electrode, and a separator disposed between the positive electrode and the lithium metal negative electrode, wherein at least one side of the separator is provided with a coating comprising a polymeric binder, a lithium salt, and inorganic particles with fluorine functional groups introduced onto the surface.

[0025] According to one embodiment of the present invention, the positive electrode may comprise a positive electrode active material selected from at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide. The positive electrode may comprise a binder, the positive electrode active material, and a conductive material. It should be noted that the present invention is not limited thereto, and the composition and manufacturing method of the positive electrode may employ techniques known in the art.

[0026] According to one embodiment of the present invention, the lithium metal anode may be a lithium metal thin film or may be provided in the form of a lithium metal layer disposed on the anode current collector.

[0027] According to one embodiment of the present invention, the coating of the diaphragm may have lithium salts and inorganic particles with fluorine functional groups introduced on the surface dispersed in a polymer matrix composed of a polymer adhesive.

[0028] According to one embodiment of the present invention, in the inorganic particles with fluorine functional groups introduced on their surface, fluorine can be chemically bonded to the surface of the inorganic particles. Specifically, the fluorine functional group can be a fluorine group (-F). In the inorganic particles with fluorine functional groups introduced on their surface, the fluorine group is bonded to the surface of the inorganic particles, thereby increasing the Lewis acidity of the inorganic particles, which can limit the movement of lithium salt anions in the electrolyte. This improves the lithium ion mobility and reaction uniformity at the interface between the lithium metal anode and the electrolyte, thus suppressing the growth of lithium dendrites on the surface of the lithium metal anode.

[0029] According to one embodiment of the present invention, the inorganic particles may comprise at least one selected from the group consisting of MgO, CaO, SrO, BaO, Sc2O3, Y2O3, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3, WO3, MnO2, Fe2O3, Co3O4, NiO, CuO, Ag2O, ZnO, Al2O3, Ga2O3, In2O3, SiO2, GeO2, SnO2, B2O3, and La2O3. Specifically, the inorganic particles may be Al2O3. More specifically, the inorganic particles incorporating fluorine functional groups may be surface-bonded Al2O3 (F-Al2O3). As an example, the F-Al2O3 may be manufactured by contacting γ-Al2O3 with an aqueous solution of aluminum fluoride and then heat-treating it at a temperature of approximately 500°C. It should be noted that the present invention is not limited thereto, and various methods known in the art that can introduce fluorine groups into inorganic particles, specifically into the surface of metal oxide particles, can be used.

[0030] According to one embodiment of the present invention, the content of the introduced fluorine functional group relative to 100 parts by weight of the inorganic particles can be more than 1 part by weight and less than 20 parts by weight. When the content of the introduced fluorine functional group is within the above-mentioned range, the Lewis acidity of the inorganic particles is appropriately increased, thereby forming a stronger bond with the lithium salt anions in the electrolyte. Furthermore, the restricted movement of the anions improves the lithium ion mobility and reaction uniformity, thereby effectively suppressing the growth of lithium dendrites in the lithium anode electrode.

[0031] According to one embodiment of the present invention, the content of the inorganic particles with fluorine functional groups introduced on the surface can be 10 parts by weight or more and 300 parts by weight or less, relative to 100 parts by weight of the polymeric adhesive. Specifically, the content of the inorganic particles with fluorine functional groups introduced on the surface can be 10 parts by weight or more and 200 parts by weight or less, 10 parts by weight or more and 100 parts by weight or less, 10 parts by weight or more and 50 parts by weight or less, 20 parts by weight or more and 50 parts by weight or less, or 30 parts by weight or more and 45 parts by weight or less, relative to 100 parts by weight of the polymeric adhesive. Within the above content range, the inorganic particles with fluorine functional groups introduced on the surface can effectively suppress dendrite formation in the lithium metal anode. When the content of the inorganic particles with fluorine functional groups introduced on the surface exceeds the above range, they may detach from the adhesive, resulting in the inability to maintain the shape of the coating, and may also become a cause of reduced ionic conductivity of the separator. Furthermore, when the content of inorganic particles with fluorine functional groups introduced into the surface is lower than the above range, it may not be able to effectively suppress dendrites and / or protect the diaphragm from the influence of dendrites.

[0032] According to one embodiment of the present invention, the particle size of the inorganic particles with fluorine functional groups introduced on the surface can be from 10 nm to 100 nm, or from 20 nm to 50 nm. The particle size of the inorganic particles with fluorine functional groups introduced on the surface can be D. 50 The particle size, in terms of its measurement method, can be measured using methods and equipment known in the art. When the particle size is within the aforementioned range of inorganic particles, during battery charging, the coating causes lithium ions to move uniformly towards the lithium metal anode and improves lithium ion movement, thereby further achieving excellent battery life.

[0033] According to one embodiment of the present invention, the coating may be disposed on one side of the separator facing the lithium metal anode. The coating being disposed on the side of the separator facing the lithium metal anode effectively prevents damage to the separator caused by dendrites formed in the lithium metal anode, thereby improving the stability and lifespan of the lithium metal battery.

[0034] According to one embodiment of the present invention, the coating may further comprise a lithium salt. The lithium salt may be selected from LiFSI (Lithium bis(fluorosulfonyl) imide), LiTFSI (Lithium bis(trifluoromethane sulfonyl) imide), LiPF6, LiBF4, LiAsF6, LiClO4, LiCsPF6, LiNO3, LiPO2F2, LiBr, LiBOB (Lithium bis(oxalato) borate), LiDFOB (Lithium difluoro(oxalate) borate), LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO3CF3)2, LiC4F9SO3, LiAlCl4, and LiTfl (Lithium trifluoromethanesulfonate). The lithium salt facilitates the smooth movement of lithium ions within the coating. Furthermore, Li, as the cation of the lithium salt in the coating... + This allows for the smooth movement of lithium ions, while the movement of anions is restricted by the increased Lewis acidity due to fluorination on the surface of inorganic particles. This enables lithium ions to be uniformly deposited on the lithium metal anode during battery charging and discharging, thus suppressing dendrite formation. Therefore, the lithium salt content can be 50 to 150 parts by weight, or 70 to 120 parts by weight, relative to 100 parts by weight of the overall polymer binder.

[0035] According to one embodiment of the present invention, the polymeric adhesive may comprise at least one polymer selected from the group consisting of poly(ethylene oxide) (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), poly(methyl methacrylate) (PMMA), poly(ethylene carbonate) (PEC), and poly(propylene carbonate) (PPC), and copolymers thereof. Specifically, the polymeric adhesive may be PAN. As previously described, the polymeric adhesive may form a polymeric matrix to disperse and fix the lithium salt and the inorganic particles in the coating.

[0036] According to one embodiment of the present invention, the coating may further comprise a plasticizer. The plasticizer enables ions in the coating to move more smoothly. The plasticizer may comprise at least one selected from the group consisting of gamma-butyrolactone (GBL) and succinonitrile (SN).

[0037] According to one embodiment of the present invention, the thickness of the coating can be from 1 μm to 20 μm. Specifically, the thickness of the coating can be from 1 μm to 15 μm, or from 2 μm to 10 μm. Within the above thickness range, the effect of the aforementioned coating can be optimized and achieved.

[0038] According to one embodiment of the present invention, the separator can be a porous separator made of a highly porous / permeable material such as felt, paper, or microporous plastic membrane. The porous separator must be resistant to corrosion by the electrolyte and other battery components at the battery potential. As an example, the porous separator can be a porous membrane made of glass, plastic, or ceramic. Furthermore, the porous separator can be a polymer separator with a porous or microporous network structure to encapsulate non-aqueous electrolytes. It should be noted that the present invention is not limited to these embodiments; any separator commonly used in the art can be applied.

[0039] According to one embodiment of the present invention, the lithium metal battery may further include a lithium salt and an electrolyte disposed between the positive electrode and the lithium metal negative electrode. The lithium salt contained in the electrolyte may be the same as described above.

[0040] According to one embodiment of the present invention, the electrolyte may contain a non-aqueous organic solvent. The non-aqueous organic solvent may be selected from the group consisting of glycol dimethyl ether solvents and ether solvents. The glycol dimethyl ether solvent may be selected from the group consisting of 1,2-dimethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dimethylene glycol dimethyl ether, trimethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and triethylene glycol diethyl ether. Furthermore, the ether solvent may be selected from the group consisting of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl ether, and dibutyl ether.

[0041] According to one embodiment of the present invention, the electrolyte may comprise an organic solid electrolyte and / or an inorganic solid electrolyte. The organic solid electrolyte may be selected from the group consisting of polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyester sulfides, polyvinyl alcohol, and polyvinylidene fluoride. Furthermore, the inorganic solid electrolyte may be selected from the group consisting of Li4SiO4, Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, Li2SiS3, Li4SiO4-LiILiOH, and Li3PO4-Li2S-SiS2. It should be noted that the organic and inorganic solid electrolytes are not limited thereto, and various substances used in the art or newly developed substances can be used without limitation.

[0042] Figure 1 A cross-sectional schematic diagram of a lithium metal battery according to an embodiment of the present invention is shown. Specifically, Figure 1 A lithium metal battery is shown, which has a porous separator 31 disposed between a positive electrode 20 and a lithium metal negative electrode 10. On one side of the separator facing the lithium metal negative electrode, there is a coating of inorganic particles 33 with fluorine functional groups dispersed in a polymer adhesive 32, and an electrolyte 40 is injected.

[0043] According to one embodiment of the present invention, the lithium metal battery may be a coin-shaped, square, pouch-type, or thin-film battery.

[0044] The present invention will be described in detail below through embodiments for specific purposes. However, the embodiments of the present invention can be modified in many different ways and should not be construed as limiting the scope of the invention to the embodiments described below. The embodiments in this specification are provided to illustrate the present invention more completely to those skilled in the art.

[0045] [Manufacturing Example] Manufacturing of F-Al2O3

[0046] 2.0 g of gamma-phase alumina (γ-Al₂O₃, 50 nm) was added to a 1 M aqueous solution of NH₄F (ammonium fluoride) and stirred for 2 hours. Then, it was dried at approximately 120 °C for 12 hours to completely remove moisture. The dried powder was then reacted in an electric furnace at approximately 500 °C for 6 hours to obtain fluorinated alumina (F-Al₂O₃) particles.

[0047] Figure 2 These are the X-ray diffraction results of γ-Al₂O₃ particles before and after fluorination in the manufacturing example. Figure 2 It can be confirmed that the crystal structure of the alumina particles did not change even after fluorination treatment.

[0048] Figure 3 This is an EDS image of fluorinated alumina (F-Al2O3) obtained according to a manufacturing example. (See reference) Figure 3 It can be confirmed that fluorine is uniformly distributed on the surface of the alumina particles.

[0049] [Example 1]

[0050] 1.0 g of PAN (polyacrylonitrile, Mw 150,000) was added to 15.0 g of EC (ethylene carbonate) and stirred at approximately 60°C for 4 hours to dissolve it. After the PAN was completely dissolved, 1 g of LiPF6 (lithium hexafluorophosphate) was added and dissolved completely to prepare the PAN solution.

[0051] Then, 0.4 g of fluorinated aluminum oxide (F-Al2O3) obtained according to the above manufacturing example was added to the PAN solution and stirred at a stirring speed of about 2,000 rpm for 30 minutes to produce a coating solution in which F-Al2O3 is uniformly dispersed.

[0052] The coated diaphragm is manufactured by casting the prepared coating solution to one side of a commercial diaphragm celgard2320 with a thickness of 10 μm using a doctor blade and then drying it in a vacuum oven at a temperature of about 60°C for 1 hour.

[0053] Figure 4 This is a SEM image of the coated diaphragm manufactured according to Example 1.

[0054] [Comparative Example 1]

[0055] The coated membrane was manufactured using the same method as in Example 1, except that unfluorinated gamma-phase alumina (γ-Al2O3, 50 nm) was used instead of fluorinated alumina (F-Al2O3).

[0056] [Comparative Example 2]

[0057] Without coating, only the commercially available diaphragm Celgard 2320 was used.

[0058] [Experimental Example]

[0059] A coin cell with a CR2032 diameter (20 mm in diameter, 32 mm in thickness) was fabricated for electrochemical evaluation. NCM811 was used as the positive electrode, Li metal foil as the negative electrode, and coated separators of the examples and comparative examples with dimensions of 14Φ, 16Φ, and 19Φ were applied. 30 μl of 1M LiPF6 electrolyte (EC / DEC containing 10% FEC) was injected into each electrode. The lifetime characteristics of the fabricated coin cell were then evaluated at a 1 C charge-discharge rate.

[0060] Figure 5 This is a graph showing the lifespan characteristics of coin batteries with coated separators applied to the embodiments and comparative examples. According to... Figure 5 As a result, up to approximately 50 cycles, the performance difference between the examples and the comparative examples was not significant. However, it was confirmed that the capacity of the coin cell using the uncoated separator of Comparative Example 2 began to decrease after approximately 50 cycles, then decreased sharply from approximately 75 cycles, and converged to 0 at approximately 125 cycles. Furthermore, in the case of Comparative Example 1 using unfluorinated alumina particles, it was confirmed that a gradual capacity decrease was observed up to approximately 110 cycles, after which the capacity began to decrease sharply. In contrast, in the case of Example 1 using fluorinated alumina particles, it was confirmed that a capacity retention rate of over 80% relative to the initial capacity was still observed even after approximately 100 cycles, and no sharp capacity decrease was observed even at approximately 150 cycles. Therefore, it can be concluded that the coated separator of Example 1 using fluorinated alumina particles effectively prevents dendrite formation in the lithium metal anode, thereby contributing to improved battery life.

[0061] Figure Labels

[0062] 10: Lithium metal anode, 20: Positive electrode, 30: Separator, 31: Porous separator, 32: Polymer binder, 33: Inorganic particles with fluorine functional groups introduced on the surface, 40: Electrolyte, 100: Lithium metal battery.

Claims

1. A lithium metal battery, comprising: a positive electrode, a lithium metal negative electrode, and a separator disposed between the positive electrode and the lithium metal negative electrode. The membrane has a coating comprising a polymeric adhesive, a lithium salt, and inorganic particles with fluorine functional groups introduced onto its surface on at least one side.

2. The lithium metal battery according to claim 1, wherein, The content of the introduced fluorine functional group is more than 1 part by weight and less than 20 parts by weight relative to 100 parts by weight of the inorganic particles.

3. The lithium metal battery according to claim 1, wherein, The inorganic particles comprise at least one selected from the group consisting of MgO, CaO, SrO, BaO, Sc2O3, Y2O3, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, Cr2O3, MoO3, WO3, MnO2, Fe2O3, Co3O4, NiO, CuO, Ag2O, ZnO, Al2O3, Ga2O3, In2O3, SiO2, GeO2, SnO2, B2O3, and La2O3.

4. The lithium metal battery according to claim 1, wherein, The content of inorganic particles with fluorine functional groups introduced on the surface is more than 10 parts by weight and less than 300 parts by weight, relative to 100 parts by weight of the polymer adhesive.

5. The lithium metal battery according to claim 1, wherein, The coating is applied to one side of the separator facing the lithium metal anode.

6. The lithium metal battery according to claim 1, wherein, The polymeric adhesive comprises at least one polymer selected from the group consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polymethyl methacrylate (PMMA), polyethylene carbonate (PEC), and polypropylene carbonate (PPC), and copolymers thereof.

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