Anode for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present invention relates to: a protective layer composition for forming a protective layer on an anode of a lithium secondary battery using lithium metal as the anode; an anode including a protective layer formed using same; and a lithium secondary battery, particularly a lithium-sulfur battery, using same. The lithium metal-protective composition according to one aspect of the present invention is used to form an organic-inorganic composite layer on a lithium metal layer, thus exhibiting an effect of improving the lifespan of a lithium secondary battery.

Description

Negative electrode for a lithium secondary battery and a lithium secondary battery including the same

[0001] The present invention relates to a negative electrode for use in a lithium secondary battery. In particular, it relates to a negative electrode usable in a lithium-sulfur battery.

[0002] This application claims priority based on Korean Patent Application No. 2024-0182935 filed with the Korean Intellectual Property Office on December 10, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] As the application range of lithium secondary batteries expands to include not only portable electronic devices but also electric vehicles (EVs) and electric storage systems (ESS), there is a growing demand for high-capacity, high-energy-density, and long-life lithium secondary batteries.

[0004] Among various lithium secondary batteries, the lithium-sulfur battery is a battery system that uses a sulfur-based material containing a sulfur-sulfur bond as the positive electrode active material, and uses lithium metal, a carbon-based material in which lithium ion insertion / extraction occurs, or silicon or tin that forms an alloy with lithium as the negative electrode active material.

[0005] A lithium-sulfur battery is formed by the conversion reaction of lithium ions and sulfur (S8+16Li) at the positive electrode. + +16e - -> The theoretical specific capacity from 8Li2S reaches 1,675 mAh / g, and when lithium metal is used as the anode, it exhibits a theoretical energy density of 2,600 Wh / kg. Since this is a very high value compared to the theoretical energy densities of other battery systems currently under study (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480 Wh / kg, Li-MnO2 battery: 1,000 Wh / kg, Na-S battery: 800 Wh / kg) and lithium-ion batteries (250 Wh / kg), it is attracting attention as a high-capacity, eco-friendly, and low-cost lithium secondary battery among the secondary batteries currently being developed.

[0006] However, in lithium-sulfur batteries, lithium ions can be reduced to lithium metal on the surface of the solid electrolyte interface (SEI) on the anode during the charging process, which leads to the formation of non-uniform structures on the anode surface and causes a problem of non-uniform resistance distribution. Consequently, as lithium accumulates unevenly due to repeated charging and discharging, structures such as dendrites and inactive lithium appear. Among these, dendrites are a major cause of separator destruction and short circuits, so research is ongoing to ensure uniform desorption of lithium ions and electrodeposition of lithium on the anode surface of lithium-sulfur batteries.

[0007] Furthermore, various attempts are being made to suppress the leaching of polysulfides and control the growth of lithium dendrites, such as protective layers and surface treatments of lithium anodes, but effective technology development that can be applied to produce batteries of a usable level is lacking.

[0008] The present invention aims to provide a protective layer composition capable of effectively protecting a lithium metal anode and an anode equipped with a protective layer to solve the aforementioned problem.

[0009] Specifically, the present invention aims to provide a cathode equipped with a protective layer that uniformly controls the desorption of lithium ions and the electrodeposition rate of lithium on the surface of the cathode during charging and discharging, and suppresses the dendrite growth of lithium ions.

[0010] Through this, the present invention aims to provide a lithium secondary battery with an improved lifespan, in particular a lithium-sulfur battery.

[0011] In order to achieve the above objective,

[0012] According to one aspect of the present invention, a composition for a protective layer of a lithium metal negative electrode of the following embodiments is provided.

[0013] The composition according to the first embodiment is,

[0014] It comprises inorganic particles and a binder, wherein the inorganic particles comprise oxide nanoparticles, and the binder comprises being free of hydroxy groups.

[0015] According to the second embodiment, in the first embodiment,

[0016] The above binder may include acrylate-based monomers, acrylic-based polymers, fluorine-based polymers, or mixtures thereof.

[0017] According to the third embodiment, in the first embodiment or the second embodiment,

[0018] The above fluorine-based polymer may include a polymer comprising vinylidene-derived repeating units and hexafluoropropylene (HFP)-derived repeating units.

[0019] According to the fourth embodiment, in any one of the first to third embodiments,

[0020] The polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit may have an HFP substitution rate of 3% to 20%.

[0021] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0022] The above acrylate-based monomer may include a photocrosslinkable monomer.

[0023] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0024] The oxide nanoparticles mentioned above may include silica, alumina, or a mixture thereof.

[0025] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0026] The particle size (D) of the above inorganic particle 50 ) can be 100 nm or less.

[0027] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0028] The weight ratio of the oxide nanoparticles and the binder may be 4:1 to 99:1 (oxide nanoparticles:binder).

[0029] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0030] The total solid content of the composition for the protective layer of the lithium metal anode may be 10 weight% or less.

[0031]

[0032] According to another aspect of the present invention, a negative electrode for a lithium secondary battery of the following embodiments is provided.

[0033] The cathode according to the 10th embodiment is,

[0034] lithium metal layer and

[0035] The above-mentioned lithium metal layer is formed on at least a portion of one surface and comprises an organic-inorganic composite layer including inorganic particles and a binder polymer, and

[0036] The above inorganic particles may include oxide nanoparticles, and the binder polymer may be free of hydroxyl groups.

[0037] According to the 11th embodiment, in the 10th embodiment,

[0038] The above binder polymer may include an acrylic polymer, a fluorine polymer, or a mixture thereof.

[0039] According to the 12th embodiment, in the 10th embodiment or the 11th embodiment,

[0040] The thickness of the above organic-inorganic composite layer may be 0.1 μm to 10 μm.

[0041] According to the 13th embodiment, in any one of the 10th to 12th embodiments,

[0042] The lithium metal layer may comprise a current collector and a lithium metal or lithium metal alloy formed on at least one surface of the current collector.

[0043]

[0044] According to another embodiment of the present invention, lithium secondary batteries of the following embodiments are provided.

[0045] A lithium secondary battery according to the 14th embodiment is,

[0046] According to any one of the 10th to 13th embodiments, the battery includes a cathode, an anode, a separator interposed between the cathode and the anode, an electrolyte, and a battery case, wherein an organic-inorganic composite layer within the cathode may be located on a surface facing the separator.

[0047] According to the 15th embodiment, in the 14th embodiment,

[0048] The above anode may include a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as an active material.

[0049] According to one aspect, it is possible to drastically reduce the rate of cell capacity reduction due to repeated charging and discharging of a lithium secondary battery, and thereby drastically improve the lifespan of the battery.

[0050] Specifically, by using a protective layer composition according to one aspect of the present invention, a stable protective layer can be formed on a lithium metal anode, thereby exhibiting the advantage of having an excellent effect of suppressing the degradation of the lithium metal anode.

[0051] In particular, a protective layer composition according to one aspect of the present invention can exhibit an excellent protective effect on a lithium metal anode by including oxide nanoparticles as inorganic particles and a hydroxyl-free binder as a binder. For example, using a hydroxyl-free binder can enhance the protective effect on the lithium metal anode by suppressing the hydration reaction on the surface of the oxide nanoparticles and suppressing ion exchange between the nanoparticles and lithium ions, but the mechanism of the present invention is not limited thereto. This effect can be further dramatically enhanced by using oxide nanoparticles with a size at the nanometer level and using a fluorine-based polymer as a hydroxyl-free binder, but the effect of the present invention is not limited thereto.

[0052] According to one aspect, a lithium metal negative electrode equipped with a protective layer using the protective layer composition according to the present invention can be used in a lithium-sulfur battery to suppress the leaching of lithium polysulfide and achieve the effect of improving the lifespan of the lithium-sulfur battery, but the effects of the present invention are not limited thereto.

[0053] The present invention will be described in more detail below.

[0054] As used in this specification, the term "composite" refers to a material in which two or more materials are combined to form physically and chemically different phases, thereby exhibiting more effective functions.

[0055] The term "(poly)sulfide" as used in this specification refers to "(poly)sulfide ion (S x 2- , 1≤x≤8” and "lithium (poly)sulfide (Li2S x or Li2S x - It is a concept that includes all of 1≤x≤8”.

[0056] The term "polysulfide" as used in this specification refers to "polysulfide ions (S x 2- , 1 <x≤8)" 및 "리튬폴리설파이드(Li2S x or Li2S x - 1 <x≤8)"를 모두 포함하는 개념이다.

[0057] Lithium secondary batteries have the characteristic that lithium ions are reduced on the surface of the negative electrode during charging and discharging, and lithium metal accumulates on the negative electrode through repeated charging and discharging.

[0058] According to one aspect of the present invention, a composition for forming a protective layer on a cathode to improve the lifespan of a lithium secondary battery by ensuring that the desorption and electrodeposition of lithium ions on the surface of the cathode occur at a uniform rate and suppressing the formation of dendrites of lithium ions on the surface of the cathode, a cathode with a protective layer formed using the same, and a lithium secondary battery using the same are provided.

[0059] In particular, when a negative electrode having a protective layer formed on a lithium metal using a composition for a protective layer according to one aspect of the present invention is applied to a lithium-sulfur battery, a lithium-sulfur battery is provided in which the problems of capacity retention rate degradation and lifespan reduction caused by the leaching of lithium polysulfide due to repeated charging and discharging are significantly improved.

[0060] A composition for a protective layer of a lithium metal anode according to one aspect of the present invention comprises inorganic particles and a binder. Specifically, the inorganic particles comprise oxide nanoparticles, and the binder comprises being free of hydroxyl groups.

[0061] In the present invention, the inorganic particles include oxide nanoparticles.

[0062] In this specification, oxide nanoparticles refer collectively to materials having a nano-sized particle size and represented by the chemical formula MxOy (where M is a non-metallic or metallic element).

[0063] In one embodiment of the present invention, the oxide nanoparticles have an average particle size (D 50 ) may be 1,000 μm or less, specifically 500 nm or less, preferably 100 nm or less. The average particle size (D) of the oxide nanoparticles is 50 ) may be, for example, 5 nm to 500 nm, specifically 5 nm to 200 nm, 10 nm to 100 nm, 10 nm to 50 nm, 20 nm to 45 nm, 25 nm to 45 nm, 30 nm to 45 nm, 35 nm to 45 nm, or 40 nm to 45 nm. The oxide nanoparticles may also exist in the form of secondary particles by aggregating multiple primary particles together. In this specification, the average particle size (D) of the oxide nanoparticles 50 ) is based on the size of the primary particle.

[0064] In this specification, the "average particle size Dn" refers to the particle size at the n% point of the cumulative volume distribution of particles according to particle size. That is, D 50Dn refers to the particle size at the 50% point of the cumulative volume distribution of particles according to particle size. The above Dn can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to calculate the particle size distribution by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam. Dn can be measured by calculating the particle diameter at the point that is n% of the cumulative volume distribution of particles according to particle size in the measuring device.

[0065] Various studies are being conducted on inorganic particles that can be used to form a protective layer for conventional lithium metal anodes. However, there are currently no satisfactory research results that have secured stability sufficient for commercializing batteries using lithium metal anodes and achieved charge-discharge cycle performance. In this invention, it was confirmed that by using a material having a nano-scale size and oxide properties of non-metal or metal elements as an inorganic particle to form a protective layer for a lithium metal anode, and a hydroxyl group-free binder together, the stability of the lithium metal anode can be improved and the cycle performance of a lithium secondary battery using a lithium metal anode can be dramatically improved.

[0066] In one embodiment of the present invention, the oxide nanoparticles may comprise, for example, silica, alumina, or a mixture thereof.

[0067] In one embodiment of the present invention, when the oxide nanoparticles include, for example, alumina, there is an advantage that the lifespan degradation phenomenon can be significantly improved even when the organic-inorganic composite layer is formed very thinly using the same, but the present invention is not limited thereto.

[0068] In one embodiment of the present invention, the oxide nanoparticles may be hollow particles or solid particles, but the present invention is not limited thereto.

[0069] According to one embodiment of the present invention, the binder may be included for, for example, to bind the inorganic particles together and to bind the inorganic particles together and the lithium metal layer together, although its use is not limited thereto. Accordingly, the binder may be used without limiting the types of binders used in the art as long as it is capable of achieving the above effects.

[0070] However, in the present invention, when using the oxide nanoparticles as inorganic particles, particularly by using a hydroxyl group-free binder, a protective layer can be stably formed, and the inhibition of degradation of the lithium metal anode by the protective layer and the improvement of the lifespan of the lithium secondary battery using the same can exhibit significant advantages. Specifically, when the hydroxyl group-free binder is composited with the oxide nanoparticles, the hydration reaction on the surface of the nanoparticles is inhibited, and the ion exchange between the nanoparticles and lithium ions is inhibited, thereby having the advantage of forming a stable protective layer of the lithium metal anode; however, the mechanism of the present invention is not limited thereto.

[0071] According to one embodiment of the present invention, when the composition for the protective layer of the lithium metal negative electrode uses a binder containing hydroxyl groups, a battery with a negative electrode having a protective layer formed therefrom may exhibit the characteristic of having a shorter lifespan than a battery with a negative electrode not having a protective layer, as the degradation of the negative electrode proceeds rapidly.

[0072] In this specification, the hydroxyl group-free binder preferably means a binder that does not contain any hydroxyl groups, but does not completely exclude cases where hydroxyl groups are incorporated into the structure by a series of chemical reactions while the binder is stored. However, if the binder contains trace amounts of hydroxyl groups, it is preferable that the content of the hydroxyl groups be 5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.1 wt% or less, or 0.01 wt% or less, based on the total weight of the binder, more specifically 0 wt% (i.e., not contained at all).

[0073] In one embodiment of the present invention, the binder may be used in a composition for forming a protective layer of a cathode, and may be used without limitation as long as it does not contain hydroxyl groups in its structure. For example, the binder may include an acrylate-based monomer, an acrylic-based polymer, a fluorine-based polymer, or a mixture thereof.

[0074] In one embodiment of the present invention, when the composition for forming a protective layer includes an acrylate-based monomer as a binder, a cross-linked acrylic polymer formed by performing a cross-linking process of the acrylate-based monomer after applying the composition for forming a protective layer onto a lithium metal layer may perform the function of a binder, but the mechanism of the present invention is not limited thereto.

[0075] In one embodiment of the present invention, the acrylate-based monomer is, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate. It may include dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octa(meth)acrylate, isoocta(meth)acrylate, nonadecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, n-tetradecyl (meth)acrylate, isobornyl (meth)acrylate, or a mixture of two or more of these, but the present invention is not limited thereto.

[0076] In one embodiment of the present invention, the acrylic polymer may be used without limitation as long as it is a homopolymer, copolymer, or conventional acrylic polymer of the acrylate monomer described above that does not contain hydroxyl groups.

[0077] In one embodiment of the present invention, the fluorine-based polymer may be used without limitation as long as it is a polymer that contains at least one fluorine atom and does not contain a hydroxyl group in its structure.

[0078] In one embodiment of the present invention, the fluorine-based polymer may include, for example, a polymer comprising vinylidene-derived repeating units.

[0079] According to one embodiment of the present invention, considering stability when used with the oxide nanoparticles, the binder polymer may comprise a fluorinated polymer comprising vinylidene-derived repeating units and hexafluoropropylene (HFP)-derived repeating units. The fluorinated polymer is known to have very low reactivity with other substances and has the advantage of maintaining the structure of the protective layer stably without reacting with lithium ions or electrolyte byproducts within the battery due to its electrochemical stability, but the present invention is not limited thereto.

[0080] In one embodiment of the present invention, when the fluorine-based polymer is used together with oxide nanoparticles, the fluorine-based polymer can be uniformly distributed between the oxide nanoparticles and / or on the surface of the nanoparticles, thereby exhibiting an advantageous effect in terms of making the entire protective layer hydrophobic. This has the advantage of lowering the polarity of the surface of the nanoparticles to block side reactions with lithium hydroxide, lithium ions, and electrolyte salts, thereby increasing the electrochemical stability of the protective layer, but the present invention is not limited thereto.

[0081] In one embodiment of the present invention, if the fluorine-based polymer does not include repeating units derived from hexafluoropropylene (HFP), the stability over time of the protective layer forming slurry for the fluorine-based polymer to react with the inorganic particles to form a protective layer may be reduced, the dispersibility of the inorganic particles and / or binder in the slurry may be reduced, or the color of the protective layer may change. Accordingly, the fluorine-based polymer includes repeating units derived from hexafluoropropylene (HFP), and it may be preferable to include repeating units derived from vinylidene in terms of improving the adhesion of the fluorine-based polymer.

[0082] Specifically, the fluorinated polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit comprises vinylidene compounds and hexafluoropropylene as monomers, and is a general term for polymers formed by polymerizing these monomers. At this time, the polymerization of the monomers is a general term for forms such as block polymerization, alternating polymerization, and random polymerization of two or more different monomers, but the present invention is not limited thereto.

[0083] In one embodiment of the present invention, the fluorinated polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit may include, for example, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0084] In one embodiment of the present invention, regarding the adhesiveness of the binder, the fluorinated polymer comprising the vinylidene-derived repeating unit and the hexafluoropropylene (HFP)-derived repeating unit preferably has an HFP substitution rate of 50% or less. Specifically, the HFP substitution rate may be 1% to 50%, 3% to 30%, 3% to 20%, specifically 5% to 15%, 8% to 15%, 8% to 12%, or 10% to 15%.

[0085] In this specification, the HFP substitution rate represents the ratio (%) of the number of hexafluoropropylene-derived repeating units to the total number of each monomer in the fluorinated polymer. That is, the HFP substitution rate of a polymer containing vinylidene-derived repeating units and hexafluoropropylene-derived repeating units refers to the ratio of the number of hexafluoropropylene-derived repeating units to the total number of vinylidene-derived repeating units and hexafluoropropylene-derived repeating units. This can be analyzed by conventional analytical methods for measuring the content of functional groups within a polymer.

[0086] In one embodiment of the present invention, the composition for the protective layer comprises inorganic particles and a binder for binding them as major components that exhibit a cathode degradation inhibition function. Specifically, it is preferable that the composition for the protective layer consists only of a suitable solvent, inorganic particles, and a binder; more specifically, it may be preferable that the solid content within the composition for the protective layer consists only of inorganic particles and a binder polymer.

[0087] In another embodiment of the present invention, as described below, the solid content of the composition for the protective layer may further include a crosslinking agent and / or an initiator in addition to inorganic particles and a binder polymer, but it is preferable that the total content of these be included in very small amounts.

[0088] In one embodiment of the present invention, the weight ratio of the oxide nanoparticles and the binder in the composition for the protective layer may be, for example, 4:1 to 99:1 (oxide nanoparticles:binder). Specifically, the weight ratio of the oxide nanoparticles and the binder may be 5:1 to 90:1, 6:1 to 60:1, 7:1 to 50:1, 8:1 to 40:1, 9:1 to 20:1, 9:1 to 15:1, or 9:1 to 10:1, but the present invention is not limited thereto. When the content of the oxide nanoparticles is within the range described above, it may exhibit advantageous effects in terms of suppressing the degradation of the negative electrode and improving the lifespan of the lithium secondary battery.

[0089] However, in one embodiment of the present invention, when the composition for the protective layer of the lithium metal anode comprises the acrylate-based monomer, the composition may further comprise a conventional crosslinking agent. Examples of the conventional crosslinking agent include photocuring initiators, thermal curing initiators, Type 1 initiators, Type 2 initiators, etc., but the present invention is not limited thereto. It is preferable that the crosslinking agent be added in an amount necessary for the crosslinking of the acrylate.

[0090] In one embodiment of the present invention, the total solid content of the composition for the protective layer is not particularly limited, but may be, for example, 15 weight% or less or 10 weight% or less in order to increase the phase stability of the composition for the protective layer, increase the ease of coating on the lithium metal layer, and form a protective layer of uniform thickness. Specifically, the total solid content of the composition for the protective layer may be 1 weight% to 15 weight%, 5 weight% to 10 weight%, 6 weight% to 9.5 weight%, or 8 weight% to 9.1 weight%, but the present invention is not limited thereto.

[0091] In one embodiment of the present invention, the solvent that can be used in the composition for the protective layer may be appropriately selected to improve the dispersion stability of the oxide nanoparticles and the binder depending on the type of oxide nanoparticles and the binder. In particular, since the slurry for the protective layer may be used to form a protective layer by directly applying and drying it on a lithium metal layer, it may be preferable to use a non-aqueous solvent, but the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the non-aqueous solvent that can be used in the composition for the protective layer may be, for example, tetrahydrofuran (THF), dimethoxyethane (DME), N-methyl-2-pyrrolidone (NMP), acetone, acetonitrile, dichloromethane, dimethylformamide, dimethyl sulfoxide, ethyl acetate, or a mixture of two or more of these, but the present invention is not limited thereto.

[0093] In one embodiment of the present invention, the solvent may be, for example, glycol ether, and may include, for example, dimethoxyethane (DME), but the present invention is not limited thereto.

[0094] According to one embodiment of the present invention, the composition for the protective layer can be prepared by adding inorganic particles and a binder polymer to a suitable solvent and stirring.

[0095] According to another embodiment of the present invention, the composition for the protective layer may be prepared by preparing an inorganic particle dispersion in which the inorganic particles are dispersed in a suitable solvent, preparing a binder polymer dispersion in which the binder polymer is dispersed in a suitable solvent, and mixing the prepared inorganic particle dispersion and the binder polymer dispersion, but the present invention is not limited thereto.

[0096]

[0097] According to another aspect of the present invention, a negative electrode for a lithium secondary battery having an organic-inorganic composite layer is provided.

[0098] The negative electrode for the lithium secondary battery described above specifically comprises a lithium metal layer and an organic-inorganic composite layer formed on at least a portion of one surface of the lithium metal layer, comprising inorganic particles and a binder polymer. In this case, the inorganic particles include oxide nanoparticles, and the binder polymer includes a hydroxyl group-free type.

[0099] In the above-described negative electrode for a lithium secondary battery, the inorganic particles and the binder polymer may be applied mutatis mutandis as described in the composition for the protective layer of the lithium metal negative electrode. Specifically, the description regarding the inorganic particles and the binder polymer shall be applied mutatis mutandis.

[0100] In one embodiment of the present invention, the organic-inorganic composite layer may have a thickness of 0.1 μm to 10 μm, for example, 0.4 μm to 10 μm, 0.6 μm to 9 μm, 0.7 μm to 8 μm, 0.8 μm to 7 μm, 0.9 μm to 6.9 μm, or 1.0 μm to 6.9 μm, but the present invention is not limited thereto.

[0101] In one embodiment of the present invention, when the oxide nanoparticles include a metallic oxide, for example, alumina, the thickness of the organic-inorganic composite layer may be 1 μm or less. For example, when the oxide nanoparticles include a metallic oxide, for example, alumina, the thickness of the organic-inorganic composite may be 0.1 μm to 0.8 μm, 0.3 μm to 0.6 μm, 0.4 μm to 0.6 μm, or 0.4 μm to 0.5 μm, but the present invention is not limited thereto.

[0102] In another embodiment of the present invention, when the oxide nanoparticles include a non-metallic oxide, for example, silica, the thickness of the organic-inorganic composite layer may be 5 μm to 10 μm. For example, when the oxide nanoparticles include a non-metallic oxide, for example, silica, the thickness of the organic-inorganic composite may be 6 μm to 8 μm, 6.5 μm to 7.5 μm, 6.9 μm to 7.4 μm, or 6.9 μm to 7 μm, but the present invention is not limited thereto.

[0103] In one embodiment of the present invention, the lithium metal layer may be provided as a free-standing film comprising lithium metal or a lithium metal alloy without a separate support.

[0104] In another embodiment of the present invention, the lithium metal layer may be provided in a form comprising lithium metal or a lithium metal alloy on a support.

[0105] At this time, the support may be a porous polymer support used as a current collector or separator in conventional lithium secondary battery electrodes, but is not limited thereto.

[0106] In one embodiment of the present invention, the negative electrode including the lithium metal layer and the protective layer may be (1) a current collector-free type consisting only of the lithium metal layer and the protective layer without including a current collector, (2) a form including a negative electrode current collector and a lithium metal layer / protective layer formed sequentially on at least one surface of the negative electrode current collector, or (3) a form including a negative electrode current collector but not including a lithium metal layer on the negative electrode current collector during the manufacture of the battery, and then forming a lithium metal layer on the negative electrode current collector when lithium ions supplied from the positive electrode and the electrolyte are reduced during the initial charging of the battery (anode-less type), but the present invention is not limited thereto.

[0107] In one embodiment of the present invention, the cathode may include a cathode current collector and a lithium metal layer provided on one or both sides of the cathode current collector. Alternatively, the cathode may not include a current collector and may be in a form comprising a self-supporting lithium metal plate and a protective layer.

[0108] In one embodiment of the present invention, when the negative electrode includes a current collector, the current collector supports the lithium metal layer and is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery using it. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., and aluminum-cadmium alloy may be used.

[0109] In one embodiment of the present invention, the lithium metal layer may comprise a current collector and a lithium metal or a lithium metal alloy formed on at least one surface of the current collector.

[0110] In one embodiment of the present invention, the lithium metal layer may be a thin film layer composed solely of lithium metal (Li).

[0111] In another embodiment of the present invention, the lithium metal layer may be a thin film layer composed of lithium and a lithium alloy alloyed with a material that forms an alloy with lithium, such as silicon, tin, indium, bromine, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, aluminum, or two or more of these materials.

[0112] In one embodiment of the present invention, the current collector supports the lithium metal layer and is not particularly limited as long as it has high conductivity without causing chemical changes in the lithium secondary battery using it. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, a surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used.

[0113] In one embodiment of the present invention, the current collector may be a copper foil with a thickness of, for example, 6 to 30 μm or, for example, 10 μm, but the present invention is not limited thereto.

[0114] In one embodiment of the present invention, the thickness of the lithium metal layer may be, for example, 20 μm or more. For example, the thickness of the lithium metal layer may be 20 μm to 100 μm, 20 μm to 80 μm, 20 μm to 70 μm, 20 μm to 60 μm, 20 μm to 55 μm, 25 μm to 55 μm, 25 μm to 50 μm, 25 μm to 45 μm, 30 μm to 45 μm, 25 μm to 40 μm, 25 μm to 35 μm, or 30 μm. When the thickness of the lithium metal layer is within the above-described range, it may exhibit advantageous effects in terms of the packing density of the battery and the energy density of the battery, but the present invention is not limited thereto.

[0115] In this specification, the thickness of each of the lithium metal layer and the organic-inorganic composite layer may be measured using a known thickness gauge. For example, the thickness of each of the lithium metal layer and the organic-inorganic composite layer may be measured using a U-Hite thickness gauge from TESA. Specifically, the thickness may be measured using the commercial thickness gauge under conditions of 0.6 N and a precision of 0.01 μm.

[0116] In one embodiment of the present invention, the organic-inorganic composite layer may be formed on at least a portion of one surface of the lithium metal layer. Specifically, the organic-inorganic composite layer may be formed to cover the entire surface of the lithium metal layer, or the organic-inorganic composite layer may be formed to cover a portion of one surface of the lithium metal layer such that a portion of the surface of the lithium metal layer is exposed to the outside. This may be achieved by intentionally applying and drying the composition for the protective layer only on a portion of the surface of the lithium metal layer, or by a hole formed on the surface of the protective layer due to the organic relationship between the weight ratio of the inorganic particles and the binder polymer and the thickness of the protective layer during the formation process of the protective layer. Both cases are possible.

[0117] At this time, the thickness of the organic-inorganic composite layer is measured based only on the area covering the surface of the lithium metal layer, and it is preferable to measure the thickness at at least 5 points and calculate the average value of these as the thickness of the organic-inorganic protective layer.

[0118] In one embodiment of the present invention, as described above, if the size of the inorganic particles is too large, the thickness uniformity of the organic-inorganic composite layer may be reduced when the organic-inorganic composite layer is formed thinly, and as a result, the effect of inhibiting the degradation of the cathode by the organic-inorganic composite layer may be negligible. Taking this into consideration, in one embodiment of the present invention, in order to control the thickness uniformity and thickness of the organic-inorganic composite layer, the average particle size (D) of the inorganic particles 50 ) may have a size of 50% or less of the thickness of the above organic-inorganic composite layer.

[0119] For example, the average particle size (D) of the above inorganic particles 50 Although the thickness of the organic-inorganic composite layer may be 1% to 50%, 1% to 30%, 1% to 20%, 5% to 20%, 1% to 10%, or 5% to 10%, which may have an advantageous effect in terms of improving the performance of the negative electrode and the performance of the lithium secondary battery by the organic-inorganic composite layer, the present invention is not limited thereto.

[0120] As described above, when the inorganic particle exists in the form of a secondary particle formed by the aggregation of a plurality of primary particles, the average particle size (D) of the inorganic particle 50 ) is based on the size of the primary particle.

[0121] According to one embodiment of the present invention, the organic-inorganic composite layer may be formed using a composition for a protective layer of lithium metal according to one aspect of the present invention described above, but the present invention is not limited thereto. For example, the organic-inorganic composite layer may be formed by applying the composition for a protective layer described above to one surface of a lithium metal layer and then drying it.

[0122] In one embodiment of the present invention, after applying a protective layer slurry to one surface of the lithium metal layer, a flattening process can be performed using a Meyer bar to ensure thickness uniformity.

[0123] In one embodiment of the present invention, to form the organic-inorganic composite layer, the method may include the step of drying in an oven at a temperature of 40°C to 60°C, for example at 50°C, after applying the slurry for the protective layer, but the method for manufacturing the organic-inorganic composite layer is not limited thereto.

[0124] In addition, the cathode according to one embodiment of the present invention may further include conventional configurations that can be used as a cathode for a lithium secondary battery, particularly a lithium-sulfur battery, and is not particularly limited to the configurations further included as long as they do not impede the purpose of the present invention.

[0125]

[0126] According to another aspect of the present invention, a lithium secondary battery comprising the above-described negative electrode is provided.

[0127] In one embodiment of the present invention, the lithium secondary battery may be a lithium-sulfur battery comprising a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as a positive electrode active material, but the present invention is not limited thereto.

[0128] The term "sulfur-based active material" applicable to the positive electrode of the above lithium-sulfur battery is a term encompassing, for example, inorganic sulfur (S8) and / or sulfur-containing compounds. The sulfur-containing compounds include, for example, Li2Sn (n≥1), disulfide compounds, organic sulfur compounds, and carbon-sulfur polymers ((C2S x ) n , x=2.5 to 50, n≥2) or a mixture thereof may be included, but the present invention is not limited thereto.

[0129] In one embodiment of the present invention, the positive electrode of the lithium sulfur battery comprises inorganic sulfur and / or a sulfur-containing compound as an active material, and may comprise a carbon material as a conductive material to ensure the electrical conductivity of sulfur. For example, the positive electrode may be provided in a form including a current collector and a positive electrode active material layer provided on at least one surface of the current collector, comprising inorganic sulfur (S8) and a carbon-based conductive material such as carbon black, but the present invention is not limited thereto.

[0130] In one embodiment of the present invention, the sulfur-based active material is an active material comprising sulfur and a carbon material, and may include, for example, a composite in which inorganic sulfur (S8) and / or a sulfur-containing compound is composited with a porous carbon material. For example, a sulfur-carbon composite prepared by mixing the inorganic sulfur (S8) and / or a sulfur-containing compound with a porous carbon material and then heat-treating it at a temperature at which sulfur melts to diffuse sulfur into the pores and / or outer surface of the porous carbon material may be used as an active material, but the present invention is not limited thereto.

[0131] In one embodiment of the present invention, the sulfur-based active material may include a material comprising a carbon-sulfur-carbon (C-Sn-C, n≥1) bond. Here, "carbon-sulfur-carbon (C-Sn-C, n≥1) bond" refers to a chemical bond between [carbon atom]-[n sulfur atoms]-[carbon atoms]. Here, the chemical bond may refer to a covalent bond.

[0132] In one embodiment of the present invention, the sulfur-based active material comprises carbon-sulfur-carbon (C-Sn-C, n≥1) bonds, and may include a material containing sulfur atoms that are covalently bonded to and fixed with carbon in a polymer matrix by, for example, mixing a polymer matrix and sulfur (S8) and heat-treating. The material containing carbon-sulfur-carbon (C-Sn-C, n≥1) bonds is a material characterized by not containing free sulfur and containing sulfur atoms fixed in a polymer matrix. For example, the active material may include a material known as sulfurized polyacrylonitrile (SPAN), but the present invention is not limited thereto.

[0133] In one embodiment of the present invention, the polyacrylonitrile sulfide is a material having a structure in which sulfur (S) is chemically bonded or inserted into an acrylonitrile polymer chain, and can generally be prepared by heat-treating an acrylonitrile polymer with sulfur (e.g., 300 to 600°C). During the heat treatment process, sulfur can form covalent or quasi-covalent bonds with the nitrogen and carbon skeletons within the polymer chain to form a stable composite structure. The acrylonitrile sulfide has the advantage of having sulfur fixed in the polymer matrix, which suppresses the leaching of sulfur or the dissolution of lithium polysulfide during the charging and discharging process, and provides excellent electrochemical stability.

[0134] More specifically, SPAN (polyacrylonitrile sulfide) can be a polymer composite in which sulfur is strongly covalently bonded to a polyacrylonitrile (PAN) polymer backbone in the form of oligos, or sulfide chains. It is formed by sulfur chemically bonding to the nitrogen atoms of the nitrile group or immediately adjacent carbon atoms of the PAN polymer, thereby covalently bonding sulfur chains in the form of oligos to the polymer chain. On average, the sulfur chain consists of about four sulfur atoms and is fixed in a form that docks to the carbon-nitrogen chain of the PAN polymer; it may include not only CSC bonds but also SS bonds, NS bonds, and NC-S bonds. In this way, within SPAN, sulfur is firmly bound to the polymer backbone through strong covalent bonds with some carbon atoms in the carbon chain or nitrogen atoms in the nitrile group. Consequently, when SPAN is used as an active material, free sulfur elements are not present in the active material, and since sulfur is stably fixed within the polymer, the leaching of polysulfides from the electrode can be effectively suppressed.

[0135] As such, since SPAN does not generate glassy sulfur or long-length, highly solid-soluble lithium polysulfides, polysulfide leaching from the electrode is significantly reduced. This can substantially mitigate the problems of capacity degradation and shortened lifespan in lithium secondary batteries (specifically, lithium-sulfur batteries) caused by the shuttle phenomenon. Consequently, it enables more stable and longer charge-discharge cycles and offers the advantage of greatly mitigating side reactions within the electrode and electrolyte caused by the dissolution of lithium polysulfides.

[0136] A lithium secondary battery according to one aspect of the present invention comprises the above-described negative electrode, positive electrode, a separator interposed between the negative electrode and the positive electrode, an electrolyte, and a battery case.

[0137] In one embodiment of the present invention, the lithium secondary battery may have a stacked structure such that the organic-inorganic composite layer of the negative electrode is formed on the surface facing the separator.

[0138] In one embodiment of the present invention, the anode may be used without particular limitation as long as it is used in a lithium secondary battery, and when used as a lithium-sulfur secondary battery, the anode may include a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as an active material.

[0139] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector.

[0140] The above positive current collector supports the positive active material and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, silver, etc., and aluminum-cadmium alloy may be used.

[0141] The above positive current collector can strengthen the bonding force with the positive active material by forming fine irregularities on its surface, and can be used in various forms such as film, sheet, foil, mesh, net, porous body, foam, nonwoven fabric, etc.

[0142] The above positive active material layer includes a positive active material and may further include a conductive material, a binder, and additives.

[0143] In one embodiment of the present invention, the positive active material may include a sulfur-carbon composite.

[0144] In one embodiment of the present invention, the sulfur-carbon composite may comprise a porous carbon material; and a sulfur-based compound supported on at least one of the outer surface and the interior of the pores of the porous carbon material. Since sulfur acting as the positive electrode active material does not have electrical conductivity on its own, it is used in a composite with a conductive material such as a carbon material, and a porous carbon material may be used to support the sulfur. Furthermore, the sulfur-based compound may be, for example, inorganic sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2Sx, 1 < x ≤ 8), disulfide compounds, carbon-sulfur polymers (C2S y ) n , y = 2.5 to 50, n ≥ 2), lithium sulfide (Li2S), or may contain two or more of these. Preferably, the sulfur compound may be inorganic sulfur (S8).

[0145] In one embodiment of the present invention, the porous carbon material supports a sulfur-based compound as an anode active material and provides a framework in which the sulfur-based compound can be uniformly and stably fixed, thereby improving the conductivity of the anode; any porous carbon material can be used without being particularly limited in type.

[0146] The above porous carbon material may be used in any form—spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk—as long as it is commonly used in lithium-sulfur batteries, without limitation. Any porous carbon material that has a porous structure or a high specific surface area and is commonly used in the industry may be acceptable.

[0147] For example, the porous carbon material may be one or more selected from the group consisting of graphite; graphene; carbon black such as Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermo Black; carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); carbon fibers such as graphite nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); graphite such as natural graphite, artificial graphite, and expanded graphite, and activated carbon, but is not limited thereto. Preferably, the porous carbon material may be a carbon nanotube.

[0148] In one embodiment of the present invention, the porous carbon material may include, for example, carbon nanotubes (CNT).

[0149] In one embodiment of the present invention, the sulfur-carbon composite may contain the sulfur-based compound in an amount of 65% by weight or more, for example, 65% to 90% by weight, 65% to 85% by weight, 70% to 80% by weight, or 70% to 75% by weight, based on the total weight of the sulfur-based compound and the porous carbon material.

[0150] When the content of sulfur-based compounds in the sulfur-carbon composite is within the range described above, it may be desirable in terms of the electron transfer surface area of ​​the sulfur-carbon composite and the wettability with the electrolyte of the anode; for example, it may be desirable to suppress the leaching of sulfur from the anode by increasing the usable surface area of ​​the sulfur-carbon composite, but the present invention is not limited thereto.

[0151] The method for manufacturing the above sulfur-carbon composite is not specifically limited in the present invention, and methods commonly used in the industry may be used. For example, a method of simply mixing the sulfur and porous carbon material and then heat-treating them to form a composite may be used.

[0152] In addition to the composition described above, the positive electrode active material may comprise one or more selected from transition metal elements, Group IIIA elements, Group IVA elements, sulfur compounds of these elements, and alloys of these elements and sulfur.

[0153] In one embodiment of the present invention, the conductive material, binder, and other components that can be used in the positive active material layer may utilize conventional technology and are not particularly limited to the present invention.

[0154] In one embodiment of the present invention, the lithium secondary battery comprises a separator. The separator separates or insulates the positive electrode and the negative electrode from each other and enables lithium ion transport between the positive electrode and the negative electrode. It may be made of a porous, non-conductive, or insulating material, and may be used without special limitations as long as it is a material commonly used as a separator in a lithium secondary battery. Such a separator may be an independent member, such as a film, or a coating layer added to the positive electrode and / or the negative electrode.

[0155] In one embodiment of the present invention, the electrolyte may comprise a non-aqueous solvent and a lithium salt as a medium through which ions involved in the electrochemical reaction of a lithium secondary battery, e.g., a lithium-sulfur battery, can move. The electrolyte is not particularly limited as long as it has a composition that can be used in a lithium secondary battery, specifically a lithium-sulfur battery.

[0156] In one embodiment of the present invention, the lithium-sulfur battery may have various shapes, for example, coin-type, pouch-type, or cylindrical shapes, but is not limited thereto.

[0157] As described above, when a negative electrode according to one embodiment of the present invention is applied to a lithium secondary battery, it can exhibit excellent effects in suppressing dendrite growth on the surface of the negative electrode through a physical blocking effect against dendrite growth by the protective layer and suppression of dendrite growth by improving ion conductivity, and accordingly, the battery life and Coulomb efficiency can be improved.

[0158] In particular, according to one embodiment of the present invention, a lithium-sulfur battery with improved lifespan and Coulomb efficiency can be provided.

[0159]

[0160] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0161] Evaluation Example 1.

[0162] The stability of the lithium metal anode according to whether the binder polymer in the protective layer contains hydroxyl groups was evaluated as follows.

[0163] After preparing a lithium foil with a thickness of 50 μm, a composition was prepared by mixing isobornyl acrylate (IBOA) or 2-carboxyethyl acrylate (CEA), which do not contain hydroxyl groups as acrylate-based monomers without solvent, with 2-hydroxy-2-methylpropiophenone (HMPP) as a photoinitiator in a weight ratio of 100:5, and then photocrosslinking was performed.

[0164] In subsequent experiments, the cathode without a protective layer formed as a reference (Evaluation Example 1-A), the cathode with a protective layer using isobornyl acrylate (Evaluation Example 1-B), and the cathode with a protective layer using 2-carboxyethyl acrylate (Evaluation Example 1-C) were named.

[0165] Measurement of the thickness of the protective layer

[0166] The average thickness was calculated by measuring the thickness at five locations where the organic-inorganic composite layer was coated on the manufactured cathode using a TESA U-Hite thickness gauge. The measuring pressure of the thickness gauge was 0.6 N, and the precision was 0.01 μm.

[0167] Evaluation Example 1-A Evaluation Example 1-B Evaluation Example 1-C Cross-sectional thickness of protective layer (㎛) - 1.5 3.3

[0168] Lifespan evaluation of lithium secondary batteries

[0169] A slurry prepared by mixing a sulfur-carbon composite (S8-CNT, S8:CNT=70:30 (wt% ratio)) and a binder in a weight ratio of 96:4 was applied and dried on a 10 µm aluminum current collector to obtain 2.71 mAhcm⁻¹. 2 An anode with a loading amount was prepared (anode porosity 77 vol%).

[0170] A separator (Cu 11-HS) was placed between the anode and the cathode of Evaluation Example 1-A, Evaluation Example 1-B, or Evaluation Example 1-C, respectively, and then placed in a pouch case. An electrolyte having a weight ratio of dimethoxyethane (DME):2-methylfuran (2-MeF):LiFSI:LiBETI:LiNO3 = 100:25:9:9:9 was injected in an amount of 2.5 g / g of El / S and sealed to produce a pouch battery.

[0171] The pouch battery manufactured as described above was activated by repeating 0.1C CC discharge followed by 0.1C CC charging three times at room temperature (30℃) in the range of 1.8 to 2.5 V. Subsequently, starting from the fourth cycle, 0.5C CC discharge and 0.2C CC charging were defined as one cycle, and charging and discharging were repeated until the capacity retention rate dropped to 80% based on the discharge capacity of the fourth cycle. The number of charge-discharge cycles (number of cycles) at which the capacity retention rate reached 80% was evaluated as the lifespan of the battery. The evaluation results are shown in Table 2 below.

[0172] Evaluation Example 1-A Evaluation Example 1-B Evaluation Example 1-C Cycle 16518656

[0173] From the above experiment, it was confirmed that applying a hydroxyl group-free binder to a lithium metal anode can suppress the degradation of the lithium metal anode and significantly improve the lifespan of the battery to which it is applied.

[0174] In particular, according to the results of Evaluation Example 1-C, it was confirmed that even though a protective layer was formed on the lithium metal anode, the battery life was inferior to that of a battery with an anode without a protective layer when a hydroxyl group-containing binder was applied. This was inferred to be because the hydroxyl groups of the binder within the protective layer reacted with lithium ions, causing a shortage of lithium required for the battery chemical reaction, which actually lowered the battery life.

[0175]

[0176] Evaluation Example 2.

[0177] [Preparation of composition for protective layer]

[0178] A slurry for the protective layer of a lithium metal anode was prepared by the following method.

[0179] Preparation Example 1

[0180] Particle size (D) in 1,2-dimethoxyethane (DME) 50 A dispersion of oxide nanoparticles with a concentration of 10 wt% was prepared by adding alumina (Al2O3) with a thickness of 40 nm.

[0181] A binder polymer solution was prepared by adding 5 g of HFP-PVDF polymer with an HFP substitution rate of 15% to 95 g of 1,2-dimethoxyethane (DME) and stirring.

[0182] A composition for a protective layer with a solid content of 9.1 wt% was prepared by sequentially adding an oxide nanoparticle dispersion and a binder polymer solution to a stirrer in a 5 / 1 v / v volume ratio so that the weight ratio of alumina to 15% HFP-PVDF polymer in the composition was 9:1, and stirring for 30 minutes.

[0183]

[0184] Preparation Example 2

[0185] Instead of alumina, particle size (D 50 A composition for a protective layer was prepared in the same manner as in Preparation Example 1, except that an oxide nanoparticle dispersion with a concentration of 10 wt% was prepared by adding silica (SiO2) with a thickness of 15 nm.

[0186] In the prepared protective layer composition, the weight ratio of silica to 15% HFP-PVDF polymer was 9:1, and the solid content was 9.1 wt%.

[0187]

[0188] Comparative Manufacturing Example 1

[0189] A composition for a protective layer was prepared in the same manner as in Preparation Example 1, except that 15% HFP-PVDF was changed as the binder polymer to a hydroxyl group-containing non-fluorinated binder polymer.

[0190] Specifically, the dispersion prepared in Preparation Example 1 was used as the oxide nanoparticle dispersion.

[0191] Next, as a binder polymer solution, a solution prepared by adding 10 g of cyano rubber (Shinetsu, CR-V, containing -OH) to 90 g of acetone and stirring was used.

[0192] A composition for a protective layer with a solid content of 10 wt% was prepared by sequentially adding an oxide nanoparticle dispersion and a binder polymer solution to a stirrer and stirring for 30 minutes so that the weight ratio of alumina to cyano rubber in the composition was 9:1.

[0193]

[0194] Comparative Manufacturing Example 2

[0195] A composition for a protective layer was prepared in the same manner as in Preparation Example 2, except that the binder polymer solution obtained in Comparative Preparation Example 1 was used.

[0196] In the prepared composition for the protective layer, the weight ratio of silica to cyano rubber was 9:1, and the solid content was 10 weight%.

[0197]

[0198] Comparative Manufacturing Example 3

[0199] A composition for a protective layer was prepared using silver nitrate (AgNO3) as an inorganic material and a fluorine-based polymer as a binder polymer.

[0200] First, 15% HFP-PVDF was added to tetrahydrofuran (THF) at 10% by weight based on the total weight of the solution, and the mixture was stirred to prepare a binder polymer solution.

[0201] Subsequently, 10 wt% of silver nitrate (AgNO3) was additionally added to the binder polymer solution, and 90 wt% of DME was added and stirred to prepare a composition for a protective layer in which the weight ratio of silver nitrate to 15% HFP-PVDF in the composition is 1:1 and the solid content is 10 wt%.

[0202]

[0203] Comparative Manufacturing Example 4

[0204] Average particle size (D as an organic particle) 50 A 5 wt% binder polymer dispersion was prepared by adding 2 μm poly(styrene-co-methacrylate) to anhydrous tetrahydrofuran, and then LiFSI was added to prepare a composition for a first protective layer. The composition for the first protective layer was prepared such that the solid content was 10 wt% and the weight ratio of LiFSI to organic particles was 3:10.

[0205] Next, a 30% by weight solution was prepared by dissolving diethylene glycol diacrylate (DEGDA) in THF. At this time, the concentration of DEGDA was prepared to be 30% by weight based on 100% by weight of organic particles in the composition for the first protective layer.

[0206]

[0207] [Manufacturing of the cathode]

[0208] Examples 1 to 3, Comparative Examples 1 to 6

[0209] A single-sided lithium foil was prepared by laminating a lithium foil approximately 30 μm thick onto one side of a copper foil 10 μm thick. Subsequently, the protective layer forming slurry prepared above was applied to the lithium side of the single-sided lithium foil and flattened to a uniform thickness using a Meyer bar. Then, depending on the amount of applied slurry, it was dried in a 50°C oven for 2 to 60 minutes to ensure complete drying of the slurry. Afterward, it was placed in a 25°C vacuum oven and vacuum dried for 15 hours. Through this process, an anode with an organic-inorganic composite layer formed on the surface of the lithium metal foil was manufactured.

[0210]

[0211] Comparative Example 7

[0212] A cathode was manufactured using the protective layer composition prepared in Comparative Manufacturing Example 4 in the following manner.

[0213] First, a single-sided lithium foil was prepared in which a lithium foil approximately 30 μm thick was laminated to one side of a copper foil 10 μm thick. A composition for a first protective layer was coated onto the lithium foil to a thickness of 3 μm using a doctor blade and then dried to form a lower protective layer first, after which a DEGDA solution was cast on top of the lower protective layer. After drying the cast product, UV was irradiated at 40°C to form a 4 μm thick upper protective layer containing a DEGDA crosslinking agent on the lithium metal layer.

[0214] After forming a protective layer, a solid electrolyte layer was formed on top of the protective layer. The composition for forming the solid electrolyte layer was prepared by mixing polyethylene oxide (PEO) and acetonitrile to obtain a 5 wt% PEO-acetonitrile solution, and then adding LiFSI to it. The LiFSI content was added at 30 parts by weight based on 100 parts by weight of PEO.

[0215]

[0216] Comparative Example 8

[0217] A cathode with a lower protective layer, an upper protective layer, and a solid electrolyte layer formed thereon was obtained in the same manner as Comparative Example 7, except that heat was applied instead of a UV irradiator during the crosslinking reaction to initiate the reaction.

[0218] At this time, the thickness of the lower protective layer was formed to be 3 μm, and the thickness of the upper protective layer was formed to be 7 μm.

[0219]

[0220] The characteristics of each manufactured cathode are summarized in Tables 3 to 5 below, and Comparative Example 1 represents a comparative example using a single-sided lithium foil that does not form an organic-inorganic composite layer as a cathode.

[0221]

[0222] Measurement of the thickness of the protective layer

[0223] The average thickness was calculated by measuring the thickness at five locations where the organic-inorganic composite layer was coated on the manufactured cathode using a TESA U-Hite thickness gauge. The measuring pressure of the thickness gauge was 0.6 N, and the precision was 0.01 μm.

[0224] Cathode Example 1 Example 2 Example 3 Composition for Protective Layer Preparation Example 1 Preparation Example 2 Total thickness of current collector and lithium metal layer (㎛) 38.4 38.4 39.5 Thickness of organic-inorganic composite layer (㎛) 0.4 0.67

[0225] Cathode Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Composition for protective layer - Comparative Preparation Example 1 Comparative Preparation Example 2 Total thickness of current collector and lithium metal layer (㎛) 39.5 39.1 39.5 39.5 38.4 Thickness of organic-inorganic composite layer (㎛) - 0.5 0.8 7.4 5.8

[0226] Cathode Comparative Example 6 Comparative Example 7 Comparative Example 8 Composition for Protective Layer Comparative Preparation Example 3 Comparative Preparation Example 4 Total thickness of current collector and lithium metal layer (㎛) 39.5 39.5 39.5 Thickness of organic-inorganic composite layer (㎛) 4 Bottom 3 Top 4 Bottom 3 Top 7

[0227] [Manufacturing of Lithium Secondary Batteries]

[0228] A coin cell was manufactured using each of the cathodes prepared above in the following manner.

[0229] First, a sulfur-carbon composite (S870 wt%) was prepared by mixing inorganic sulfur (S8) and carbon nanotubes (CNT) as positive electrode active materials. A positive electrode slurry composition was then prepared using 96 wt% of the prepared sulfur-carbon composite and 4 wt% of a mixture of CMC and SBR (1:1 weight ratio) as a binder. The positive electrode slurry composition was applied to an aluminum current collector and dried to obtain a value of 3.4 mAh / cm² 2 After manufacturing an anode with a loading amount and a porosity of 75 vol%, it was stamped out to a size of 14 φ.

[0230] As a cathode, the cathode prepared above was punched to a size of 15 φ, and a polyethylene separator with a thickness of 12 μm and a porosity of 46 vol%, punched to a size of 19 φ, was interposed between the anode and the cathode.

[0231] After placing the anode / separator / cathode assembly into a coin-type case, 50 µL of electrolyte was injected and the lid was closed to seal it (El / S ratio = 11.1 g / g).

[0232] At this time, the electrolyte used was a mixture of 100 parts by weight of dimethoxyethane (DME), 9 parts by weight of LiFSI, 9 parts by weight of LiBETI, 9 parts by weight of LiNO3, and 25 parts by weight of 2-methyl furan (2-MeF).

[0233]

[0234] [Performance Evaluation of Lithium Secondary Batteries]

[0235] The lithium secondary battery prepared as described above was activated by repeating 0.1C CC discharge followed by 0.1C CC charging three times at room temperature (25℃) in the range of 1.8 to 2.5 V.

[0236] From the 4th cycle onwards, 0.5 C CC discharge and 0.2 C CC charge were defined as one cycle, and charging and discharging were repeated until the capacity retention rate dropped to 80% based on the discharge capacity of the 4th cycle. The number of charge-discharge cycles (number of cycles) at which the capacity retention rate reached 80% was evaluated as the lifespan of the battery. The evaluation results are shown in Tables 6 to 8 below.

[0237]

[0238] Example 1 Example 2 Example 3 Discharge capacity mAh / g_s1 st 1161113710434 th (Standard) 822837802100 th 899897846150 th 833850844Lifespan(Ret.80%)201200218Lifespan Decrease Rate(mAh / g_s) / cycle0.460.430.74

[0239] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Discharge capacity mAh / g_s1 st 108711461105109610924 th ( 기준 )796885822861851100 th 909472768867879150 th 789386244727762Lifespan(Ret.80%)16575106148158Lifespan Decrease Rate(mAh / g_s) / cycle0.852.050.980.830.79

[0240] Comparative Example 6 Comparative Example 7 Comparative Example 8 Discharge capacity mAh / g_s1 st 928388<104 th (Standard) 7261330100 th 805410150 th 680250 Lifespan (Ret. 80%) 13144 <5 Lifespan reduction rate (mAh / g_s) / cycle 1.44 0.63-

[0241] Referring to the evaluation results above, it was confirmed that in the case of Examples 1 to 3, which use oxide nanoparticles and a fluorine-based binder in the organic-inorganic composite layer of the cathode, the phenomenon of capacity degradation due to repeated charge-discharge cycles is improved and the battery life can be excellently improved.

[0242] On the other hand, it was confirmed that in the case of Comparative Examples 2 to 5, which use oxide nanoparticles in the organic-inorganic composite layer but use a non-fluorinated polymer and a hydroxyl group-containing polymer as the binder polymer, there is an inferior effect in that the lifespan is reduced compared to Comparative Example 1, which does not form an organic-inorganic composite layer.

[0243] Furthermore, in the case of Comparative Example 6, which uses silver nitrate as an inorganic particle, a decrease in capacity was observed, so the lifespan improvement effect could not be confirmed, and in the case of Comparative Examples 7 and 8, which form an organic-inorganic composite layer in a completely different way, it was confirmed that the battery capacity was significantly low and there was a problem of rapid capacity reduction.

[0244] Through the above experiments, it was confirmed that using the lithium metal protective composition according to one embodiment of the present invention can exhibit a significant lifespan improvement effect for lithium secondary batteries, particularly lithium-sulfur batteries.

Claims

1. Includes inorganic particles and a binder, The above inorganic particles include oxide nanoparticles, and The above binder is a composition for a protective layer of a lithium metal anode, which is free of a hydroxy group.

2. In Claim 1, The above binder comprises an acrylate-based monomer, an acrylic-based polymer, a fluorine-based polymer, or a mixture thereof, in a composition for a protective layer of a lithium metal anode.

3. In Claim 2, The above fluorine-based polymer is a composition for a protective layer of a lithium metal anode, comprising a polymer including vinylidene-derived repeating units and hexafluoropropylene (HFP)-derived repeating units.

4. In Claim 3, A polymer comprising the above vinylidene-derived repeating unit and hexafluoropropylene (HFP)-derived repeating unit, having an HFP substitution rate of 3% to 20%, for a composition for a protective layer of a lithium metal anode.

5. In Claim 2, The above acrylate-based monomer is a composition for a protective layer of a lithium metal anode comprising a photocrosslinkable monomer.

6. In Claim 1, The above oxide nanoparticles comprise silica, alumina, or a mixture thereof, a composition for a protective layer of a lithium metal anode.

7. In Claim 1, The particle size (D) of the above inorganic particle 50 A composition for a protective layer of a lithium metal anode, wherein the thickness is 100 nm or less.

8. In Claim 1, A composition for a protective layer of a lithium metal anode, wherein the weight ratio of the oxide nanoparticles and the binder is 4:1 to 99:1 (oxide nanoparticles:binder).

9. In Claim 1, A composition for a protective layer of a lithium metal anode, wherein the total solid content of the composition for the protective layer of the lithium metal anode is 10 weight% or less.

10. Lithium metal layer and The above-mentioned lithium metal layer is formed on at least a portion of one surface and comprises an organic-inorganic composite layer including inorganic particles and a binder polymer, and The above inorganic particles include oxide nanoparticles, and The above binder polymer is a negative electrode for a lithium secondary battery that is free of hydroxy groups.

11. In Claim 10, The above binder polymer comprises an acrylic polymer, a fluorine polymer, or a mixture thereof, for a negative electrode for a lithium secondary battery.

12. In Claim 10, A negative electrode for a lithium secondary battery, wherein the thickness of the above organic-inorganic composite layer is 0.1 μm to 10 μm.

13. In Claim 10, The above lithium metal layer is, A negative electrode for a lithium secondary battery comprising a current collector and a lithium metal or lithium metal alloy formed on at least one surface of the current collector.

14. A cathode, an anode, a separator interposed between the cathode and the anode, an electrolyte, and a battery case according to any one of claims 10 to 13, and A lithium secondary battery in which an organic-inorganic composite layer within the above-mentioned cathode is located on a surface facing the separator.

15. In Claim 14, A lithium secondary battery in which the above positive electrode comprises a sulfur-based compound containing a sulfur(S)-sulfur(S) bond as an active material.