Lithium metal battery

Abstract

The present invention relates to a lithium metal battery comprising: a positive electrode; a lithium metal negative electrode; the separator is arranged between the positive electrode and the lithium metal negative electrode, and at least one surface of the separator is provided with a coating containing a polymer binder, a lithium salt and a silicon dioxide-cellulose nanofiber composite.

Description

Lithium metal batteries 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 a silica-cellulose nanofiber composite.

[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 1 shows a schematic diagram of a coated separator suppressing dendrite formation in a lithium metal anode according to an embodiment of the present invention.

[0015] Figure 2 shows a schematic diagram of a coated separator suppressing dendrite formation in a lithium metal anode according to an embodiment of the present invention.

[0016] Figure 3 shows an SEM image of the diaphragm surface of Comparative Example 1.

[0017] Figure 4 shows an SEM image of the coated surface of the coated diaphragm of Example 1.

[0018] Figure 5 shows an SEM image of the coated surface of the coated diaphragm of Example 1.

[0019] Figure 6 shows the experimental results used to confirm the wettability of the diaphragms of the comparative and exemplary cases to water.

[0020] Figure 7 shows the experimental results used to confirm the wettability of the diaphragm of the comparative and exemplary examples to the electrolyte.

[0021] Figure 8 is a graph showing the lifespan characteristics of coin batteries with coated separators applied to the embodiments and comparative examples.

[0022] Figure 9 shows an image of the lithium metal anode of a lithium metal battery using the separator of Comparative Example 1 after 300 charge-discharge cycles.

[0023] Figure 10 shows an image of the lithium metal anode of a lithium metal battery using the coated separator of Example 1 after 300 charge-discharge cycles. Detailed Implementation

[0024] 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.

[0025] 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 are other components between the two components.

[0026] In this specification, unless otherwise specified, the terms “%” and “parts” indicating content are based on weight.

[0027] 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.

[0028] The present invention will now be described in detail.

[0029] 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 a silica-cellulose nanofiber composite.

[0030] 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.

[0031] 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.

[0032] According to one embodiment of the present invention, the coating of the diaphragm may contain lithium salt and silica-cellulose nanofiber composite dispersed in a polymer matrix composed of a polymeric adhesive.

[0033] According to one embodiment of the present invention, the silica-cellulose nanofiber composite can be formed by attaching silica particles to the surface of cellulose nanofibers. According to another embodiment of the present invention, the cellulose nanofibers can be cellulose fibers with an average diameter of nanometers, formed by cellulose chains of hexose glucose linked by β-1,4 bonds and bonded by interchain hydrogen bonds. The cellulose nanofibers are generally fibrous, with an average diameter ranging from several to tens of nm, specifically from 1 nm to 100 nm, specifically from 5 nm to 50 nm, and more specifically from 10 nm to 30 nm. Furthermore, the average length of the cellulose nanofibers can range from several to tens of μm, specifically from 1 μm to 100 μm, and more specifically from 5 μm to 30 μm. According to one embodiment of the present invention, the content of silica particles relative to 100 parts by weight of the cellulose nanofibers can be 10 parts by weight or more and 20 parts by weight or less. More detailed information and manufacturing methods of the silica-cellulose nanofiber composite can include all the contents disclosed in Korean Patent Publication No. 10-2020-0042220.

[0034] According to one embodiment of the present invention, the content of the silica-cellulose nanofiber composite material relative to 100 parts by weight of the polymeric adhesive can be 10 parts by weight or more and 300 parts by weight or less. Specifically, relative to 100 parts by weight of the polymeric adhesive, the content of the silica-cellulose nanofiber composite material 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 20 parts by weight or more and 40 parts by weight or less. Within the above content range, the silica-cellulose nanofiber composite material is uniformly dispersed within the coating to form a network of nanofibers, thereby appropriately imparting wettability to the coating and minimizing side effects caused by uneven distribution of the electrolyte. Furthermore, the silica-cellulose nanofiber composite material enables Li, as a cation of lithium salt in the coating, to... + While allowing ions to move freely, the movement of anions is restricted, thus enabling lithium ions to be uniformly deposited on the lithium metal anode during battery charging and discharging, thereby effectively suppressing dendrite formation.

[0035] Figure 1 illustrates a schematic diagram of a coated separator suppressing dendrite formation in a lithium metal anode according to an embodiment of the present invention. The left side of Figure 1 shows the dendrite formation process in a lithium metal battery without the coating of the present invention on the separator, and the right side shows the dendrite formation suppression process in a lithium metal battery with the coating of the present invention on the separator. Specifically, the silica-cellulose nanofiber composite in the coating of the present invention binds lithium salt anions during the charging and discharging of the lithium metal battery, allowing lithium ions to be uniformly deposited on the lithium metal anode, thereby suppressing the formation of lithium dendrites.

[0036] Figure 2 illustrates a schematic diagram of a coated separator suppressing dendrite formation in a lithium metal anode according to an embodiment of the present invention. The left side of Figure 2 shows the movement of lithium ions in a lithium metal battery without the coating of the present invention on the separator, and the right side shows the movement of lithium ions in a lithium metal battery with the coating of the present invention on the separator. Specifically, the silica-cellulose nanofiber composite in the coating of the present invention effectively improves the wettability of the coating to the electrolyte, thereby enabling lithium ions in the electrolyte to be uniformly deposited on the lithium metal anode during the charging and discharging of the lithium metal battery. That is, as mentioned above, the silica-cellulose nanofiber composite effectively suppresses the movement of lithium salt anions to the lithium metal anode, thereby imparting wettability to the separator to the electrolyte to induce the uniform movement of lithium salt lithium ions to the lithium metal anode, thereby suppressing the formation of lithium dendrites.

[0037] According to one embodiment of the present invention, the polymeric adhesive may comprise at least one non-fluorinated polymeric adhesive selected from the group consisting of poly(ethylene oxide), polyacrylonitrile, poly(methyl methacrylate), poly(ethylene carbonate), poly(PEC), poly(propylene carbonate), and PAN-co-PMMA copolymer. Specifically, according to one embodiment of the present invention, the polymeric adhesive of the coating may be a non-fluorinated polymeric adhesive. The coating does not use fluorinated polymeric adhesives, which generate hydrofluoric acid during battery operation and may lead to a decrease in battery performance; instead, it utilizes a non-fluorinated polymeric adhesive, thereby preventing the problems caused by fluorinated polymeric adhesives. Furthermore, the coating, by incorporating a non-fluorinated polymeric binder, enhances the adhesion between the separator and the lithium metal anode, and together with the silica-cellulose nanofiber composite, achieves high wettability to the electrolyte, enabling the uniform deposition of lithium ions onto the lithium metal anode during charging and discharging of the lithium metal battery. Additionally, as mentioned above, the polymeric binder can form a polymeric matrix to disperse and fix the lithium salt and the silica-cellulose nanofiber composite within the coating. Specifically, according to one embodiment of the invention, the polymeric binder may comprise a mixture of PAN and PAN-PMMA copolymer. More specifically, according to one embodiment of the invention, the weight ratio of PAN to PAN-PMMA copolymer (PAN-co-PMMA) contained in the polymeric binder may be from 3:1 to 5:1.

[0038] 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.

[0039] 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... + The silica-cellulose nanofiber composite allows for the smooth movement of lithium ions, while restricting the movement of anions. This enables lithium ions to be uniformly deposited on the lithium metal anode during battery charging and discharging, thus suppressing dendrite formation. Therefore, relative to 100 parts by weight of the polymer binder, the lithium salt content can be from 50 to 150 parts by weight, or from 70 to 120 parts by weight.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] According to one embodiment of the present invention, the lithium metal battery may be a coin-shaped, square, pouch-type, or thin-film battery.

[0047] 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 present 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.

[0048] [Example 1]

[0049] 0.8 g of PAN (polyacrylonitrile, Mw 150,000) and 0.2 g of PAN-co-PMMA (PAN-PMMA copolymer, Mw less than 100,000) were added to 11 g of EC (ethylene carbonate), and then 2 g of succinate (SN) was added as a plasticizer. The mixture was stirred at approximately 60°C for 4 hours to dissolve the PAN and PAN-co-PMMA. After the PAN and PAN-co-PMMA were completely dissolved, 1 g of LiPF6 was added and completely dissolved to prepare the polymer solution.

[0050] Then, 0.5g of the silica-cellulose nanofiber composite manufactured based on paragraph

[0052] of Korean Patent Publication No. 10-2020-0042220 was added to a polymer solution and dispersed using a ball mill for about 3 minutes to produce a coating solution.

[0051] The composition of the coating solution is shown in Table 1 below.

[0052] [Table 1]

[0053]

[0054] 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.

[0055] [Comparative Example 1]

[0056] Without coating, only the commercially available diaphragm Celgard 2320 was used.

[0057] [Comparative Example 2]

[0058] Alumina particles (Al2O3, 50 nm) were used instead of silica-cellulose nanofiber composites, and the coated membrane was otherwise manufactured using the same method as in Example 1.

[0059] Figure 3 shows an SEM image of the diaphragm surface of Comparative Example 1.

[0060] Figures 4 and 5 show SEM images of the coating surface of the coated diaphragm of Example 1. Specifically, Figure 5 is a magnified view of the results in Figure 4. Based on Figures 4 and 5, it can be confirmed that the coating of the coated diaphragm of Example 1 contains a silica-cellulose nanofiber composite dispersed within it.

[0061] Figure 6 shows the experimental results used to confirm the wettability of the membranes of the comparative examples and the embodiments for water. According to Figure 6, it can be confirmed that the surface wettability of Comparative Example 1, which does not have a separate coating, is low, while the coated membrane of Example 1, which uses a silica-cellulose nanofiber composite, has higher wettability for water than the coated membrane of Comparative Example 2, which uses alumina particles.

[0062] Figure 7 shows the experimental results used to confirm the wettability of the membranes of the comparative examples and embodiments to the electrolyte. According to Figure 7, it can be confirmed that the coated membrane of Example 1, which applied the silica-cellulose nanofiber composite, exhibits higher wettability to the electrolyte compared to Comparative Examples 1 and 2. In particular, the coated membrane of Example 1 absorbs the electrolyte immediately after it is dropped, demonstrating the best performance.

[0063] [Experimental Example]

[0064] A coin cell with a CR2032 diameter (20 mm in diameter, 32 mm in thickness) was fabricated for electrochemical evaluation. NCM622 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.

[0065] Figure 8 is a graph showing the lifespan characteristics of coin batteries using coated separators from Examples 1 and 2, and Comparative Examples 2. Based on the results in Figure 8, it can be confirmed that the lithium metal battery using the coated separator from Example 1 maintains a capacity similar to its initial performance even after 300 cycles. In contrast, the lithium metal batteries using separators from Comparative Examples 1 and 2 show a loss of approximately 10% of their initial capacity after 300 cycles, and exhibit a tendency for a sharp decrease in capacity compared to Example 1.

[0066] Figure 9 shows an image of the lithium metal anode of the lithium metal battery using the separator of Comparative Example 1 after 300 charge-discharge cycles. Figure 10 shows an image of the lithium metal anode of the lithium metal battery using the coated separator of Example 1 after 300 charge-discharge cycles. Referring to Figures 9 and 10, it can be confirmed that the lithium metal battery using the coated separator of Example 1 exhibits uniform lithium deposition on the lithium metal anode after charge-discharge, thereby significantly suppressing the formation of lithium dendrites. In contrast, the lithium metal battery using the separator of Comparative Example 1 exhibits uneven lithium deposition on the lithium metal anode after charge-discharge, and high-lithium dendrites are expected to partially form.

[0067] As shown in Figures 8 and 10, it can be seen that the lithium metal battery using the coated separator of Example 1 effectively suppresses dendrite formation by dispersing the lithium metal deposition on the lithium metal anode surface caused by repeated charging and discharging, thereby helping to improve the lifespan of the 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, wherein at least one side of the separator is provided with a coating comprising a polymeric binder, a lithium salt, and a silica-cellulose nanofiber composite.

2. The lithium metal battery according to claim 1, wherein, The silica-cellulose nanofiber composite is formed by silica particles being attached to the surface of cellulose nanofibers.

3. The lithium metal battery according to claim 2, wherein, The content of silica particles is 10 parts by weight or more and 20 parts by weight or less relative to 100 parts by weight of the cellulose nanofibers.

4. The lithium metal battery according to claim 1, wherein, The content of the silica-cellulose nanofiber composite 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 polymeric adhesive comprises at least one non-fluorinated polymeric adhesive selected from the group consisting of polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethylene carbonate (PEC), polypropylene carbonate (PPC), and PAN-PMMA copolymers.

6. The lithium metal battery according to claim 1, wherein, The polymeric adhesive comprises a mixture of PAN and PAN-PMMA copolymer.

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

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