Lithium metal battery

Abstract

The present invention relates to lithium metal battery comprising a cathode, a lithium metal anode, and a separator provided between the cathode and the lithium metal anode, wherein a coating layer including a polymer binder, a lithium salt, and inorganic particles in which a fluorine functional group is introduced onto the surface thereof is provided on at least one surface of the separator.

Description

lithium metal battery

[0001] The present invention relates to a lithium metal battery.

[0002] Conventional lithium secondary batteries utilize a carbon-based anode and operate by transporting lithium ions through a liquid electrolyte containing a lithium salt dissolved in an organic solvent. In contrast, lithium metal batteries utilize anodes consisting solely of a current collector or a layer of lithium metal deposited on the current collector. During charging, lithium ions are reduced and deposited from the anode to lithium metal, and during discharge, the lithium metal is oxidized to lithium ions.

[0003] Lithium metal, used in lithium metal batteries, has emerged as a material capable of producing high-capacity batteries due to its high electrical capacity per unit mass. However, lithium metal forms dendrites during the deposition and desorption of lithium ions, which can damage the separator and cause an electrical short between the anode and cathode.

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

[0005] [Prior Art Literature]

[0006] [Patent Document]

[0007] (Patent Document 1) Republic of Korea Patent Publication No. 10-2021-0009188

[0008] The present invention aims to provide a lithium metal battery capable of effectively suppressing the problem of battery performance degradation due to the occurrence of dendrites in a lithium metal battery.

[0009] One embodiment of the present invention provides 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, wherein a coating layer including a polymer binder, a lithium salt, and inorganic particles having a fluorine functional group introduced to the surface is provided on at least one surface of the separator.

[0010] The lithium metal battery according to the present invention can realize high stability and improved lifespan by having a coating layer capable of effectively preventing adverse effects due to dendrites on at least one side of the separator.

[0011] Figure 1 is a schematic cross-sectional view of a lithium metal battery according to one embodiment of the present invention.

[0012] Figure 2 shows the results of X-ray diffraction measurements of γ-Al2O3 particles before fluorination treatment and F-Al2O3 particles after fluorination treatment in a manufacturing example.

[0013] Figure 3 is a surface element analysis (EDS) image of fluorinated alumina (F-Al2O3) obtained according to a manufacturing example.

[0014] Figure 4 is an SEM image of a coated separator manufactured according to Example 1.

[0015] Figure 5 is a graph showing the life characteristics of coin cells to which a coating separator according to an example and a comparative example is applied.

[0016] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0017] In this specification, when it is said that a member is located "on" another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0018] In this specification, “%” and “part” indicating content are based on weight unless otherwise specified.

[0019] The lithium metal battery according to the present invention is distinguished from a lithium ion battery. Specifically, there is a significant difference in that a lithium metal battery uses lithium metal as an anode active material, while a lithium ion battery uses a non-lithium material (e.g., graphite) as an anode active material. Furthermore, an electrolyte suitable for a lithium metal battery has low reactivity with lithium metal and does not corrode lithium metal. On the other hand, an electrolyte suitable for a lithium ion battery can react with a non-lithium anode active material to form a solid-electrolyte interphase (SEI) layer. The SEI layer can play a positive role in controlling the thermodynamic chemical reactions occurring in a lithium ion battery. As mentioned above, lithium metal batteries and lithium ion batteries have significantly different operating characteristics due to the difference in anode active materials, and thus, the problems that need to be solved are bound to be different. Therefore, lithium metal batteries and lithium ion batteries cannot help but have different separator properties and electrolyte properties required for each, and in most cases, the same effect cannot be expected when applying components used in lithium ion batteries to lithium metal batteries. Therefore, it can be said that lithium metal batteries and lithium ion batteries are completely different technical fields.

[0020] Hereinafter, the present invention will be described in detail.

[0021] One embodiment of the present invention provides 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, wherein a coating layer including a polymer binder, a lithium salt, and inorganic particles having a fluorine functional group introduced to the surface is provided on at least one surface of the separator.

[0022] According to one embodiment of the present invention, the positive electrode may include a positive electrode active material including at least one selected from the group consisting 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 include a binder, the positive electrode active material, and a conductive material. However, the present invention is not limited thereto, and the composition and manufacturing method of the positive electrode may apply technical contents widely known in the art.

[0023] According to one embodiment of the present invention, the lithium metal negative electrode may be a lithium metal thin film, and may be provided in a form in which a lithium metal layer is provided on the negative electrode current collector.

[0024] According to one embodiment of the present invention, the coating layer of the separator may be a polymer matrix composed of a polymer binder in which lithium salt and inorganic particles having a fluorine functional group introduced to the surface are dispersed.

[0025] According to one embodiment of the present invention, the inorganic particle having a fluorine functional group introduced onto the surface may have fluorine chemically bonded to the surface of the inorganic particle. Specifically, the fluorine functional group may be a fluorine group (-F). The inorganic particle having a fluorine functional group introduced onto the surface may have a fluorine group bonded to the surface of the inorganic particle, thereby increasing the Lewis acidity of the inorganic particle and restricting the movement of anions of lithium salts in an electrolyte. From this, the mobility and reaction uniformity of lithium ions at the interface between the lithium metal negative electrode and the electrolyte may be improved, thereby suppressing the growth of lithium dendrites on the surface of the lithium metal negative electrode.

[0026] According to one embodiment of the present invention, the inorganic particles may include 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 having a fluorine functional group introduced thereto may be Al2O3 having fluorine bonded to the surface (F-Al2O3). For example, the F-Al2O3 can be manufactured by contacting γ-Al2O3 with an aluminum fluoride aqueous solution and then heat-treating it at a temperature of about 500°C. However, the present invention is not limited thereto, and various methods known in the art for introducing fluorine groups to the surface of inorganic particles, specifically metal oxide particles, can be used.

[0027] According to one embodiment of the present invention, the fluorine functional group may be introduced in an amount of 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the inorganic particles. When the fluorine functional group is introduced within the above content range, the Lewis acidity of the inorganic particles is appropriately increased, thereby more strongly bonding with the anions of the lithium salt in the electrolyte, and the mobility and reaction uniformity of lithium ions are improved according to the movement of the limited anions, thereby effectively suppressing the growth of lithium dendrites in the lithium negative electrode.

[0028] According to one embodiment of the present invention, the content of the inorganic particles having a fluorine functional group introduced into the surface may be 10 parts by weight or more and 300 parts by weight or less, based on 100 parts by weight of the polymer binder. Specifically, the content of the inorganic particles having a fluorine functional group introduced into the surface may 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, based on 100 parts by weight of the polymer binder. Within the above content range, the inorganic particles having a fluorine functional group introduced into the surface can effectively suppress dendrite formation in the lithium metal negative electrode. If the content of the inorganic particles having a fluorine functional group introduced into the surface exceeds the above range, they may fall off from the binder, so that the shape of the coating layer may not be maintained, and may also cause the ionic conductivity of the separator to deteriorate. In addition, if the content of the inorganic particles having fluorine functional groups introduced to the surface is below the above range, the dendrites may not be effectively suppressed and / or the membrane may not be protected from dendrites.

[0029] According to one embodiment of the present invention, the particle size of the inorganic particles having a fluorine functional group introduced to the surface may be 10 nm to 100 nm, or 20 nm to 50 nm. The particle size of the inorganic particles having a fluorine functional group introduced to the surface is D 50 The particle size may be within the range of the above-mentioned inorganic particles, and the measurement method thereof may be measured using methods and devices widely known in the art. When the particle size of the above-mentioned inorganic particles is within the range, the uniform movement of lithium ions to the lithium metal negative electrode through the coating layer and the movement of lithium ions are improved during battery charging, thereby improving the battery life.

[0030] According to one embodiment of the present invention, the coating layer may be provided on one side of the separator facing the lithium metal negative electrode. The coating layer is provided on the side of the separator facing the lithium metal negative electrode, thereby effectively preventing damage to the separator due to dendrite formed at the lithium metal negative electrode, thereby improving the stability and lifespan of the lithium metal battery.

[0031] According to one embodiment of the present invention, the coating layer may further include 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 may play a role in facilitating the movement of lithium ions within the coating layer. Furthermore, Li, which is a cation of lithium salt in the coating layer + While the movement of lithium ions is facilitated, the movement of anions is restricted by the Lewis acidity increased by fluorination on the surface of the inorganic particles, so that lithium ions can be evenly deposited on the lithium metal negative electrode during charge and discharge of the battery, thereby suppressing the formation of dendrites. For this purpose, the lithium salt may be 50 to 150 parts by weight, or 70 to 120 parts by weight, based on 100 parts by weight of the total polymer binder.

[0032] According to one embodiment of the present invention, the polymer binder may include at least one polymer selected from the group consisting of poly(ethylene oxide) (PEO), poly(acrylonitrile) (PAN), poly(vinylidene fluoride) (PVdF), poly(methyl metacrylate) (PMMA), poly(ethylene carbonate) (PEC), and poly(propylene carbonate) (PPC), and copolymers thereof. Specifically, the polymer binder may be PAN. As described above, the polymer binder may form a polymer matrix to disperse and fix the lithium salt and the inorganic particles within the coating layer.

[0033] According to one embodiment of the present invention, the coating layer may further include a plasticizer. The plasticizer may enable smoother movement of ions within the coating layer. The plasticizer may include at least one selected from the group consisting of gamma-Butyrolactone (GBL) and succinonitrile (SN).

[0034] According to one embodiment of the present invention, the thickness of the coating layer may be 1 μm to 20 μm. Specifically, the thickness of the coating layer may be 1 μm to 15 μm, or 2 μm to 10 μm. Within the above thickness range, the effect of the coating layer described above can be optimized and implemented.

[0035] According to one embodiment of the present invention, the separator may be a porous separator manufactured using a highly porous / permeable material such as felt, paper, or a microporous plastic film. The porous separator must be resistant to attack by the electrolyte and other battery components under a battery potential. For example, the porous separator may be a porous membrane made of glass, plastic, or ceramic. In addition, the porous separator may be a polymer separator having a porous or microporous network structure to confine the non-aqueous electrolyte. However, the present invention is not limited thereto, and any material commonly used in the art may be applied.

[0036] According to one embodiment of the present invention, the lithium metal battery may further include a lithium salt and an electrolyte provided between the positive electrode and the lithium metal negative electrode. The lithium salt included in the electrolyte may be the same as described above.

[0037] According to one embodiment of the present invention, the electrolyte may include a non-aqueous organic solvent. The non-aqueous organic solvent may be selected from the group consisting of glyme solvents and ether solvents. The glyme 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. In addition, 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.

[0038] According to one embodiment of the present invention, the electrolyte may include 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 alcohols, and polyvinylidene fluoride. In addition, 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. However, the organic solid electrolyte and the inorganic solid electrolyte are not limited thereto, and various materials applied in the art or newly developed materials may be applied without limitation.

[0039] Fig. 1 is a schematic cross-sectional view of a lithium metal battery according to one embodiment of the present invention. Specifically, Fig. 1 illustrates a lithium metal battery in which a porous separator (31) is provided between a positive electrode (20) and a lithium metal negative electrode (10), a coating layer is provided on one side of the separator facing the lithium metal negative electrode, in which inorganic particles (33) having fluorine functional groups introduced to the surface are dispersed within a polymer binder (32), and an electrolyte (40) is injected.

[0040] According to one embodiment of the present invention, the lithium metal battery may be a coin-shaped, square-shaped, pouch-shaped or thin-film-shaped battery.

[0041] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0042] [Manufacturing Example] Manufacturing of F-Al2O3

[0043] 2.0 g of gamma phase alumina (γ-Al2O3, 50 nm) was added to a 1 M NH4F (Ammonium fluoride) aqueous solution and stirred for 2 hours. Then, the mixture was dried at approximately 120°C for 12 hours to completely remove moisture. The dried powder was reacted in an electric furnace at approximately 500°C for 6 hours to obtain fluorinated alumina (F-Al2O3) particles.

[0044] Figure 2 shows the results of X-ray diffraction measurements of γ-Al2O3 particles before and after fluorination treatment in a manufacturing example. In Figure 2, it was confirmed that the crystal structure of the alumina particles did not change even after fluorination treatment.

[0045] Figure 3 is a surface element analysis (EDS) image of fluorinated alumina (F-Al2O3) obtained according to a manufacturing example. Referring to Figure 3, it was confirmed that fluorine was evenly distributed on the surface of the alumina particles.

[0046] [Example 1]

[0047] 1.0 g of PAN (Polyacrylonitrile, Mw 150,000) was added to 15.0 g of EC (Ethylene carbonate) and dissolved by stirring at a temperature of approximately 60°C for 4 hours. After PAN was completely dissolved, 1 g of LiPF6 (Lithium hexafluorophosphate) was added and completely dissolved to prepare a PAN solution.

[0048] Then, 0.4 g of fluorinated alumina (F-Al2O3) obtained according to the above manufacturing example was added to the manufactured PAN solution, and stirred at a stirring speed of about 2,000 rpm for 30 minutes to prepare a coating solution in which F-Al2O3 was uniformly dispersed.

[0049] The manufactured coating solution was cast to a thickness of 10 ㎛ on one side of a commercial separator, Celgard 2320, using a doctor blade, and then dried in a vacuum oven at a temperature of approximately 60°C for 1 hour to manufacture a coated separator.

[0050] Figure 4 is an SEM image of a coated separator manufactured according to Example 1.

[0051] [Comparative Example 1]

[0052] A coated membrane was manufactured in the same manner as in Example 1, except that non-fluorinated Gamma phase alumina (γ-Al2O3, 50 nm) was used instead of fluorinated alumina (F-Al2O3).

[0053] [Comparative Example 2]

[0054] Only Cegard 2320, a commercial membrane, was used without a coating layer.

[0055] [Experimental Example]

[0056] Coin cells of the size of CR2032 (diameter 20 mm, thickness 32 mm) were manufactured and electrochemically evaluated. NCM811 was used as the positive electrode and Li metal foil was used as the negative electrode, and the coated separators according to the examples and comparative examples were applied, and the sizes of these were 14Φ, 16Φ, and 19Φ, respectively. 30㎕ of 1M LiPF6 (EC / DEC with 10% FEC) electrolyte was injected into each electrode to manufacture them. Then, the life characteristics of the manufactured coin cells were evaluated at a rate of 1 C charge and discharge.

[0057] FIG. 5 is a graph showing the life characteristics of coin cells to which coated separators according to Examples and Comparative Examples are applied. According to the results of FIG. 5, the performance difference between the Examples and Comparative Examples is not clearly evident up to about 50 cycles, but the coin cell to which the separator of Comparative Example 2 without a coating layer is applied shows that the capacity begins to decrease after about 50 cycles, and then rapidly decreases from about 75 cycles, converging to 0 at about 125 cycles. In addition, in the case of Comparative Example 1 using non-fluorinated alumina particles, it was confirmed that a gradual capacity decrease was observed up to about 110 cycles, and then rapidly decreased thereafter. In contrast, in the case of Example 1 using fluorinated alumina particles, it was confirmed that a capacity retention rate of more than 80% compared to the initial capacity was observed even after about 100 cycles, and that no rapid capacity decrease was observed even at about 150 cycles. Through this, it can be seen that the coated separator of Example 1 using fluorinated alumina particles effectively prevents dendrite formation in the lithium metal negative electrode, thereby contributing to improving battery life.

[0058] [Explanation of symbols]

[0059] 10: Lithium metal cathode

[0060] 20: Bipolar

[0061] 30: Membrane

[0062] 31: Porous membrane

[0063] 32: Polymer binder

[0064] 33: Inorganic particles with fluorine functional groups introduced to the surface

[0065] 40: Electrolyte

[0066] 100: Lithium metal battery

Claims

1. A positive electrode; a lithium metal negative electrode; and a separator provided between the positive electrode and the lithium metal negative electrode, A lithium metal battery, wherein a coating layer comprising a polymer binder, a lithium salt, and inorganic particles having a fluorine functional group introduced to the surface is provided on at least one surface of the separator.

2. In claim 1, A lithium metal battery, wherein the fluorine functional group is introduced in an amount of 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the inorganic particles.

3. In claim 1, A lithium metal battery, wherein the inorganic particles include 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. In claim 1, A lithium metal battery, wherein the content of inorganic particles having a fluorine functional group introduced to the surface is 10 parts by weight or more and 300 parts by weight or less with respect to 100 parts by weight of the polymer binder.

5. In claim 1, A lithium metal battery, wherein the coating layer is provided on one side of the separator facing the lithium metal negative electrode.

6. In claim 1, A lithium metal battery, wherein the polymer binder comprises at least one polymer selected from the group consisting of poly(ethylene oxide) (PEO), poly(acrylonitrile) (PAN), poly(vinylidene fluoride) (PVdF), poly(methyl metacrylate) (PMMA), poly(ethylene carbonate) (PEC), and poly(propylene carbonate) (PPC), and copolymers thereof.

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