Anode for anode-free battery and lithium secondary battery comprising same

Abstract

The present invention relates to an anode. More specifically, the anode comprises: an anode current collector; a coating layer on the anode current collector; and a lithium-resistant layer on the coating layer, wherein the coating layer comprises a carbon-based material and a lithiophilic metal, the lithium-resistant layer comprises a metal carbide, and the lithium-resistant layer may have a three-dimensional porous structure.

Description

Negative electrode for a non-negative electrode battery, and a lithium secondary battery including the same

[0001] This is about lithium secondary batteries.

[0002] Research is actively underway to improve the energy density of lithium-ion batteries. Recently, attempts to maximize energy density through cathode-free batteries, which omit or minimize the anode material, have been attracting attention. However, cathode-free batteries exhibit disadvantages in terms of stability and lifespan due to low initial efficiency caused by the absence of anode active material in the initial state and the problem of uneven lithium precipitation.

[0003] The problem that the present invention aims to solve is to induce uniform lithium deposition on the negative electrode current collector and to reduce dendrite formation. In addition, it aims to provide a negative electrode-free lithium secondary battery with improved stability and lifespan characteristics.

[0004] A cathode according to the concept of the present invention comprises a cathode current collector; a coating layer on the cathode current collector; and a lithium resistive layer on the coating layer, wherein the coating layer comprises a carbon-based material and a lithium-affinity metal, the lithium resistive layer comprises a metal carbide, and the lithium resistive layer may have a three-dimensional porous structure.

[0005] A cathode according to another concept of the present invention comprises a cathode current collector; a coating layer on the cathode current collector; and a lithium resistive layer on the coating layer, wherein the coating layer comprises a carbon-based material and a lithium-affinity metal, and the lithium resistive layer comprises a three-dimensional porous structure, and the three-dimensional porous structure may provide a path through which lithium ions can penetrate the lithium resistive layer.

[0006] A lithium secondary battery according to another concept of the present invention may include the negative electrode; a positive electrode and an electrolyte system between the positive electrode and the negative electrode.

[0007] According to one aspect, the lithium electrodeposition density and uniformity of the negative electrode can be improved, thereby preventing the formation of lithium dendrites. According to another aspect, the life characteristics of a negative electrode lithium secondary battery can be improved.

[0008] Figure 1 schematically illustrates a lithium secondary battery.

[0009] FIG. 2 is a cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

[0010] FIG. 3a is a cross-sectional view of a cathode according to one embodiment.

[0011] FIG. 3b is a cross-sectional view of a cathode according to one embodiment.

[0012] Figure 4a is an enlarged view of the M region of Figure 3a.

[0013] Figure 4b is an enlarged view of the M region of Figure 3b.

[0014] FIG. 5 is a cross-sectional view of a cathode according to one embodiment.

[0015] FIG. 6 is a plan view of a cathode according to one embodiment.

[0016]

[0017] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0018] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0019] The embodiments described herein will be described with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of the technical content. Accordingly, the regions illustrated in the drawings are schematic in nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific forms of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0020] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0021] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0022] In this specification, each of the phrases such as “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, and “at least one of A, B, or C” may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof.

[0023] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0024] In one embodiment, the average particle size in this specification may refer to the diameter measured by randomly selecting about 100 particles from an electron microscope image. Alternatively, the average particle size in this specification may refer to the diameter of a particle that has a cumulative volume of 50% in the particle size distribution, which can be measured by a particle size analyzer.

[0025] lithium secondary battery

[0026] FIG. 1 schematically illustrates a lithium secondary battery. A lithium secondary battery according to an embodiment of the present invention may include a positive electrode (CTH), a negative electrode (ANO), and an electrolyte system (ELS) between the positive electrode (CTH) and the negative electrode (ANO). As will be described below, in this specification, the electrolyte system (ELS) may refer to a system that mediates the exchange of electrochemical energy between the positive electrode (CTH) and the negative electrode (ANO). The electrolyte system (ELS) may include, for example, a solid electrolyte, a liquid electrolyte, etc., but is not limited thereto.

[0027] Cathode (CTH)

[0028] Referring to FIG. 2, the positive electrode (CTH) according to an embodiment of the present invention may include a positive electrode current collector (COL1) and a positive electrode active material layer (AML1) on the positive electrode current collector (COL1). The positive electrode active material layer (AML1) may include a positive electrode active material and may further include a solid electrolyte, a conductive material, a binder, etc.

[0029] The positive current collector (COL1) can provide a reference surface on which the positive active material layer (AML1) is placed. The positive current collector (COL1) may include, for example, a plate or foil comprising indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0030] Meanwhile, unlike as illustrated in FIG. 2, the positive current collector (COL1) may be omitted in one embodiment of the present invention. Although not illustrated, a carbon layer with a thickness of 0.1 μm to 4 μm may be further disposed between the positive current collector (COL1) and the positive active material layer (AML1) to increase the bonding strength between the positive current collector (COL1) and the positive active material layer (AML1).

[0031] The positive active material layer (AML1) according to an embodiment of the present invention may include a positive active material. The positive active material can store and release electrical / chemical energy by reversibly inserting and extracting lithium ions. The positive active material may be in the form of particles such as spherical or elliptical spheres, but is not limited thereto.

[0032] The positive active material may include positive active material particles. The positive active material may include positive active material particles in the form of a single particle. The positive active material may include positive active material particles in the form of secondary particles formed by the aggregation of multiple primary particles.

[0033] The positive electrode active material may include an oxide-based positive electrode active material, a sulfide-based positive electrode active material, or a combination thereof. In one embodiment, the positive electrode active material may include an oxide-based positive electrode active material. The oxide-based positive electrode active material may include, for example, a lithium transition metal oxide, a metal oxide, or a combination thereof. The lithium transition metal oxide includes, for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt mangense oxide, lithium manganate, lithium iron phosphate, or a combination thereof. The lithium oxide may include, for example, iron oxide, vanadium oxide, or a combination thereof. The oxide-based cathode active material can be, for example, single-crystal particles or polycrystalline particles.

[0034] In one embodiment, the positive electrode active material may include a sulfide-based positive electrode active material. The sulfide-based positive electrode active material may include, for example, nickel sulfide, copper sulfide, lithium sulfide, a lithium sulfide-containing composite, or a combination thereof.

[0035] The sulfide-based cathode active material may include, for example, Li2S or an oxidation / reduction reaction product of Li2S. Specifically, the sulfide-based cathode active material may include S8 or Li2S n It may include at least one lithium-sulfur compound among (1≤n≤8, where n is an integer).

[0036] The sulfide-based cathode active material may include a composite of a lithium-sulfur compound and a conductive material. The sulfide-based cathode active material may include, for example, a composite of Li2S and carbon, a composite of Li2S, carbon, and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt, a composite of Li2S, a lithium salt, and carbon, a composite of Li2S, a lithium salt, a metal halide, and carbon, a composite of Li2S and a metal carbide, a composite of Li2S, carbon, and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S, carbon, and a metal nitride, or a combination thereof.

[0037] A sulfide-based cathode active material may include a sulfide-based composite and a conductive material. In one embodiment, the sulfide-based composite may have a particle shape such as a perfect spherical or elliptical sphere. The particle size of the sulfide-based composite is not particularly limited and may be within a range applicable to general cathode active materials. The size of the sulfide-based composite may be, for example, 0.1 to 50 μm, 0.5 to 30 μm, 0.5 to 20 μm, or 1 to 10 μm. The conductive material may coat the surface of the sulfide-based composite. The conductive material of the sulfide-based cathode active material can be used as a cathode active material by imparting electronic conductivity to the sulfide-based composite.

[0038] A sulfide-based cathode active material and a sulfide-based composite containing Li2S according to one embodiment of the present invention will be described in more detail. The sulfide-based cathode active material may comprise a composite of Li2S, a lithium salt, and carbon. More specifically, the sulfide-based cathode active material may comprise a composite of Li2S, a lithium halide, and carbon.

[0039] A sulfide-based composite according to one embodiment is Li2S-Li a X bIt may include a compound represented by (1≤a≤5, 1≤b≤5). X may be I, Br, Cl, F, H, O, Se, Te, N, P, As, Sb, Al, B, OCl, PF6, BF4, SbF6, AsF6, ClO4, AlO2, AlCl4, NO3, CO3, BH4, SO4, BO3, PO4, NCl, NCl2, BN2, or a combination thereof. a may be, for example, 1, 2, 3, 4, or 5. b may be, for example, 1, 2, 3, 4, or 5.

[0040] A sulfide-based composite according to one embodiment may further include a metal halide. In other words, the sulfide-based composite may include a composite of Li2S, a lithium salt, and a metal halide. The metal halide may contain a metal other than lithium.

[0041] Sulfide-based complexes are Li2S-Li a X1 b -MX2 c It may include a compound represented by . a may be an integer between 1 and 5, b may be an integer between 1 and 5, and c may be an integer between 1 and 5. M may be selected from the group consisting of aluminum (Al), silver (Ag), gold (Au), platinum (Pt), palladium (Pd), bismuth (Bi), tin (Sn), and zinc (Zn). X1 and X2 may each be selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0042] Since Li2S has relatively low ionic conductivity, a composite of Li2S and a lithium salt can be formed to improve ionic conductivity. The composite, which is a combination of Li2S and a lithium salt, can have improved ionic conductivity compared to Li2S alone. The content of Li2S in the composite can be 50 wt% to 95 wt%, 50 wt% to 90 wt%, 50 wt% to 80 wt%, or 50 wt% to 70 wt% of the total weight of the composite. By having a Li2S content within this range, the composite can simultaneously possess improved ionic conductivity and excellent ductility.

[0043] The content of lithium salt in the sulfide-based composite may be 5 wt% to 50 wt%, 10 wt% to 50 wt%, 20 wt% to 50 wt%, or 30 wt% to 50 wt% of the total weight of the composite. By having a lithium salt content within this range, the composite can simultaneously have improved ionic conductivity and excellent ductility.

[0044] The content of metal halides in the sulfide-based composite may be 5 wt% to 30 wt% or 5 wt% to 20 wt% of the total weight of the composite (CAM). By having a metal halide content within this range, the composite can simultaneously have improved ionic conductivity and excellent ductility.

[0045] In one embodiment, the content of Li2S in the sulfide-based composite may be greater than the content of the lithium salt. The content of Li2S in the sulfide-based composite may be greater than the content of the metal halide. For example, the molar ratio of Li2S to the lithium salt in the sulfide-based composite may be 51:49 to 95:5, 55:45 to 90:10, 60:40 to 90:10, or 70:30 to 90:10. By having such molar ratios, the composite can simultaneously possess enhanced ionic conductivity and excellent ductility.

[0046] The conductive material may include carbon. The conductive material may include, without limitation, materials containing carbon atoms that are used as conductive materials in the relevant art. For example, the conductive material may include crystalline carbon, amorphous carbon, or a combination thereof. The conductive material may include, for example, a sintered product of a carbon precursor. The conductive material may include, for example, carbon nanostructures.

[0047] The conductive material may include, for example, porous carbon or non-porous carbon. Porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbon may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black; graphite, activated carbon, or a combination thereof. The form of carbon within the conductive material may be, for example, particle form, sheet form, fibrous form, etc., but is not limited thereto and may be any form of carbon used in the relevant technical field.

[0048] In one embodiment of the present invention, the conductive material may include a fibrous carbon-based material. By including a fibrous carbon-based material in the conductive material, the electron conductivity of the positive electrode active material can be further improved. By including a fibrous carbon-based material in the conductive material, electron conduction from the surface to the interior of the positive electrode active material can be performed more easily. The internal resistance of the sulfide-based composite is reduced by the conductive material, and the cycle characteristics of the secondary battery can be further improved.

[0049] Fibrous carbon-based materials may include, for example, carbon nanostructures. Carbon nanostructures may include, for example, carbon nanofibers (CNF), carbon nanotubes (CNT), carbon nanobelts, carbon nanorods, or combinations thereof. Carbon nanostructures may form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure formed by the aggregation of multiple carbon nanostructures.

[0050] The method for manufacturing a sulfide-based cathode active material according to the embodiments may be a dry method, a wet method, or a combination thereof, but is not limited thereto. In the art, the method for manufacturing a cathode active material may be, for example, milling, heat treatment, deposition, etc., but is not necessarily limited thereto, and any method used in the art may be possible.

[0051] The positive active material layer (AML1) according to an embodiment of the present invention may include a solid electrolyte. As will be described later, when the electrolyte system (ELS) of a lithium secondary battery includes a solid electrolyte layer, the positive active material layer (AML1) may include a solid electrolyte to facilitate ion conduction. Any solid electrolyte used as an ion-conducting material in the relevant technical field may be used as the solid electrolyte within the positive active material layer. The solid electrolyte within the positive active material layer may be the same as or different from the solid electrolyte in the solid electrolyte layer.

[0052] The solid electrolyte may be, for example, an inorganic solid electrolyte. The solid electrolyte may be, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte may be, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The description of the solid electrolyte in the anode active material layer (AML1) may be applied in the same way to the solid electrolyte layer described below.

[0053] The positive active material layer (AML1) may include a conductive material. The conductive material may be, for example, a carbon-based material, a metal-based material, or a combination thereof. The metal-based material may be a metal powder, a metal fiber, or a combination thereof, but is not limited to these, and any metal-based material used as a conductive material in the relevant technical field is acceptable.

[0054] Carbon-based materials may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. The conductive material may include, for example, a calcined product of a carbon precursor. The conductive material may include, for example, porous carbon or non-porous carbon. Porous carbon may include, for example, periodic and regular two-dimensional or three-dimensional pores. Porous carbon may be, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black; graphite, activated carbon, or a combination thereof. The form of carbon within the conductive material may be, for example, particle form, sheet form, fibrous form, etc., but is not limited thereto and may be any form used as carbon in the relevant technical field.

[0055] The positive active material layer (AML1) may include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyethylene, etc., but is not limited to these, and any binder used in the relevant technical field may be possible.

[0056] The positive active material layer (AML1) may further include additives such as a coating agent, a dispersant, and an ion conductivity aid in addition to the positive active material, solid electrolyte, binder, and conductive material described above. The coating agent, dispersant, and ion conductivity aid that may be included in the positive active material layer (AML1) may be those generally used as electrode materials for lithium secondary batteries.

[0057]

[0058] Electrolyte System (ELS)

[0059] A lithium secondary battery according to an embodiment of the present invention may include an electrolyte system (ELS). The electrolyte system (ELS) may be disposed between a positive electrode (CTH) and a negative electrode (ANO). The electrolyte system (ELS) may include an electrolyte and provide a pathway for the movement of lithium ions between the positive electrode (CTH) and the negative electrode (ANO). Additionally, the electrolyte system (ELS) may prevent an electrical short circuit between the positive electrode (CTH) and the negative electrode (ANO) and physically separate the positive electrode (CTH) and the negative electrode (ANO).

[0060] In one embodiment, the electrolyte system (ELS) may include an electrolyte and a separator. The separator is located between the positive and negative electrodes and may separate the positive and negative electrodes. The electrolyte may be impregnated throughout the entire lithium secondary battery.

[0061] The electrolyte may include, for example, a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reactions of the battery can move. The non-aqueous organic solvent may be, for example, a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0062] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0063] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0064] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0065] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0066] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0067] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0068] In another embodiment, the electrolyte system (ELS) may further include crosslinkable polymers to form a crosslinked network. The crosslinkable polymers can form a crosslinked network to provide mechanical properties of the electrolyte system.

[0069] The separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, and a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc. may be used.

[0070] The separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate. The porous substrate may be a polymer membrane formed from any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0071] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0072] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0073] The above organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0074] In another embodiment, the electrolyte system (ELS) may include a solid electrolyte layer. The solid electrolyte layer may include a solid electrolyte to provide lithium ion conductivity while also serving as a separator that physically separates the anode and cathode. The solid electrolyte layer provides excellent thermal and chemical stability, thereby effectively preventing stability issues of the lithium secondary battery, such as electrical short circuits or electrolyte leakage.

[0075] In one embodiment, the solid electrolyte layer may include a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be produced by processing starting materials, such as Li2S or P2S5, by methods such as melt quenching or mechanical milling. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material comprising Li2S-P2S5 to form a solid electrolyte, the mixed molar ratio of Li2S and P2S5 may be, for example, in the range of Li2S : P2S5 = 20 : 80 to 90 : 10, 25 : 75 to 90 : 10, 30 : 70 to 70 : 30, and 40 : 60 to 60 : 40.

[0076] Sulfide-based solid electrolytes may include, for example, an argyrodite-type solid electrolyte represented by the following chemical formula 1:

[0077] <Chemical Formula 1>

[0078] Li + 12-n-x A n+ X 2- 6-x Y - x

[0079] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X is S, Se, or Te; Y is Cl, Br, I, F, CN, OCN, SCN, or N3; and 1≤n≤5, 0≤x≤2. Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Clx (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may be an argyrodite-type compound comprising one or more selected from (0≤x≤2). The sulfide-based solid electrolyte may be an argyrodite-type compound comprising, for example, one or more selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0080] Alternatively, sulfide-based solid electrolytes are Li 7-a-c M a PS 6-c X c It may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)). Here, X may be F, Br, Cl, or a combination thereof. M can be scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof. there is.

[0081] The density of the azirodite-type solid electrolyte may be 1.5 g / cc to 2.0 g / cc. Since the azirodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the lithium secondary battery containing the solid electrolyte layer is reduced, and the penetration and short-circuiting of the solid electrolyte layer due to the formation of lithium dendrites can be prevented.

[0082]

[0083] Cathode (ANO)

[0084] Referring again to FIG. 2, the cathode (ANO) according to an embodiment of the present invention may include a cathode current collector (COL2), a coating layer (CTL) on the cathode current collector (COL2), and a lithium resistive layer (PHL) on the coating layer (CTL).

[0085] The negative current collector (COL2) can provide a reference surface on which a coating layer is disposed. The negative current collector (COL2) may include, for example, a material that does not react with lithium, that is, does not form either an alloy or a compound with lithium. For example, the negative current collector (COL2) may include at least one of copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. The thickness of the negative current collector (COL2) may be 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0086] The negative current collector (COL2) may be composed of one of the metals described above, or may include an alloy of two or more metals or a coating material. The negative current collector (210) may, for example, have a plate-like or foil-like shape. Meanwhile, in one embodiment, the negative current collector (COL2) may be omitted.

[0087] Referring to FIGS. 3a and 3b, the negative electrode (ANO) may include a coating layer (CTL) on the negative electrode current collector (COL2). The coating layer (CTL) may allow lithium metal to grow between it and the negative electrode current collector (COL2) during charging of a lithium secondary battery with a negative electrode structure. The coating layer (CTL) acts as a protective layer for the lithium metal and simultaneously suppresses the precipitation and growth of lithium dendrites. After the charging process, a negative electrode active material layer (AML2) may be formed between the coating layer (CTL) and the negative electrode current collector (COL2). The negative electrode active material layer (AML2) may include a negative electrode active material. The negative electrode active material may include lithium metal or an alloy of lithium metal.

[0088] The coating layer (CTL) may have a smaller thickness compared to the positive active material layer (AML1). The thickness of the coating layer (CTL) may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive active material layer (AML1). The thickness of the coating layer (CTL) may be, for example, 1 µm to 100 µm, 2 µm to 80 µm, 10 µm to 50 µm, 1 µm to 20 µm, 2 µm to 10 µm, or 3 µm to 7 µm. If the thickness of the coating layer (CTL) is excessively thin, lithium dendrites formed between the coating layer (CTL) and the negative current collector (COL2) may cause the coating layer (CTL) to collapse, thereby degrading the cycle characteristics of the lithium secondary battery. If the thickness of the coating layer (CTL) increases excessively, the energy density of the lithium secondary battery decreases, and the internal resistance of the battery due to the coating layer (CTL) increases, which may degrade the cycle characteristics of the cell.

[0089] Referring to FIGS. 4a and 4b, the coating layer (CTL) may include a carbon-based material (CCM) and metal particles (LPM). In one embodiment, the carbon-based material (CCM) may have a particle form. The average particle size (D50) of the carbon-based material (CCM) may be 100 nm to 10 µm. For example, the average particle size (D50) of the carbon-based material (CCM) may be 100 nm or more, 300 nm or more, 500 nm or more, or 1 µm. For example, the average particle size (D50) of the carbon-based material (CCM) may be 10 µm or less, 7 µm or less, 5 µm or less, 3 µm or less, or 2 µm or less.

[0090] If the average particle size (D50) of the carbon-based material (CCM) satisfies the range described above, the volume change of the lithium secondary battery during charging and discharging can be minimized, and a lithium secondary battery with a long lifespan can be provided.

[0091] In one embodiment, the carbonaceous material (CCM) may have a porous structure. For example, the BET specific surface area of ​​the carbonaceous material (CCM) is 5 m² 2 / g to 1000m 2 It can be / g. For example, the BET specific surface area of ​​a carbonaceous material (CCM) is 5m² 2 / g or more, 10m 2 / g or more, 20m 2 / g or more, 30m 2 / g or more, 40m 2 / g or more, 50m 2 / g or more, 60m 2 / g or more, 100m 2 / g or more, 200m 2 / g or more, 300m 2 / g or more, or 400m 2 It can be greater than / g. For example, the BET specific surface area of ​​a carbonaceous material (CCM) is 1000 m² 2 / g or less, 900m 2 / g or less, 800m 2 / g or less, 700m 2 / g or less, 600m2 / g or less, 500m 2 / g or less, 400m 2 / g or less, 300m 2 / g or less, 200m 2 / g or less, 100m 2 / g or less, 90m 2 / g or less, 80m 2 / g or less, or 70m 2 It may be less than / g.

[0092] If the BET specific surface area of ​​the carbon-based material (CCM) satisfies the range described above, the volume change of the lithium secondary battery during charging and discharging can be minimized, and a lithium secondary battery with a long lifespan can be provided.

[0093] For example, a carbon-based material (CCM) may include at least one of non-graphitizable carbons (hard carbon) or graphitizable carbons (soft carbons). For example, the carbon-based material (CCM) may include non-graphitizable carbons (hard carbon).

[0094] For example, a carbon-based material (CCM) may include at least one selected from the group consisting of carbon black, carbon nanotubes, acetylene black, furnace black, Kettjen black, and graphene. However, the carbon-based material (CCM) is not limited to the examples described above.

[0095] The shape of the carbonaceous material (CCM) may be at least one of spherical, elliptical, plate-like, or a combination thereof. However, the shape of the carbonaceous material (CCM) is not limited to the examples described above.

[0096] The coating layer may contain metal particles (LPM). The metal particles (LPM) can help lithium ions move toward the negative electrode current collector (COL2) during charging and discharging of the lithium secondary battery.

[0097] The metal particles (LPM) may include, for example, at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), magnesium (Mg), titanium (Ti), gallium (Ga), zinc oxide (ZnO), germanium (Ge), lead (Pb), antimony (Sb), or indium (In). For example, the metal particles (LPM) may include at least one of silver (Ag), magnesium (Mg), bismuth (Bi), gold (Au), platinum (Pt), or zinc (Zn).

[0098] Metal particles (LPM) can be composed of lithium-affinity metals. The characteristics of lithium-affinity metals can be represented by Equation 1 below.

[0099] [Equation 1]

[0100] △G=△H 523.15K -T△S 523.15K ≤ 0

[0101] In other words, the Gibbs free energy (△G) of the chemical reaction of a lithium-affinity metal with molten lithium at 250°C may be 0 kJ / mol or less. For example, the Gibbs free energy (△G) of the chemical reaction of a lithium-affinity metal with molten lithium at 250°C may be -1500 kJ / mol to 0 kJ / mol. Under the above conditions, the lithium-affinity metal may spontaneously form an alloy with lithium.

[0102] The metal particles (LPM) according to an embodiment of the present invention may be nanoparticles. The metal particles (LPM) may be single particles. The metal particles may be aggregates. Multiple single particles may aggregate to form a single particle, which can be defined as an aggregate. For example, the aggregate may be in the form of 10 or fewer single particles aggregated. In other words, the size of the aggregate may be nano-sized, similar to that of the single particles.

[0103] The average particle size of the metal particles (LPM) may be 5 nm to 300 nm. For example, the average particle size of the metal particles (LPM) may be 5 nm or more, or 10 nm or more. For example, the average particle size of the metal particles (LPM) may be 300 nm or less, 200 nm or less, or 100 nm or less. If the average particle size of the metal particles (LPM) satisfies the range described above, lithium ions can easily move toward the negative electrode current collector (COL2) during charging and discharging of the lithium secondary battery.

[0104] According to embodiments of the present invention, the average particle size of the metal particles (LPM) may be relatively small. The average particle size of the metal particles (LPM) may refer to the average size of the metal particles (LPM) present within the coating layer (CTL), namely single particles and aggregates. The average particle size may be defined as the average length of the major and minor axes measured by randomly selecting 100 metal particles (LPM) within the coating layer (CTL) in an electron microscope image. This average particle size may be calculated as a geometric average or an arithmetic average.

[0105] The content of metal particles (LPM) in the coating layer (CTL) may be 1% to 50% by weight relative to the total weight of the coating layer (CTL). For example, the content of metal particles (LPM) may be 3% or more by weight, 5% or more by weight, or 10% or more by weight relative to the total weight of the coating layer (CTL). For example, the content of metal particles (LPM) may be 50% or less by weight, 40% or less by weight, 30% or less by weight, 25% or less by weight, 20% or less by weight, or 15% or less by weight relative to the total weight of the coating layer (CTL). If the content of metal particles (LPM) satisfies the range described above, lithium ions can easily move toward the negative electrode current collector (COL2) during charging and discharging of the lithium secondary battery.

[0106] Referring to FIG. 4b, the negative electrode (ANO) according to an embodiment of the present invention may include a negative electrode active material (NAM). As in FIG. 4a, the negative electrode active material (NAM) may be omitted in the initial state of the negative electrode (ANO). Subsequently, the negative electrode active material (NAM) may be formed through a charging process. During the charging process, lithium ions may move toward the negative electrode current collector (COL2) through the coating layer (CTL). The lithium ions may be deposited as lithium metal on the negative electrode current collector (COL2).

[0107] The negative electrode active material (NAM) may be formed between the coating layer (CTL) and the negative electrode current collector (COL2) or within the coating layer (CTL). As lithium ions move through the coating layer (CTL) to the negative electrode current collector (COL2), a layer of negative electrode active material may be formed between the coating layer (CTL) and the negative electrode current collector (COL2). Additionally, some lithium ions may be reduced and exist as the negative electrode active material (NAM) within the coating layer (CTL). The negative electrode active material (NAM) may include lithium or an alloy of lithium metal. For example, the lithium alloy may be a Li-Al alloy, Li-Sn alloy, Li-In alloy, Li-Ag alloy, Li-Au alloy, Li-Zn alloy, Li-Ge alloy, Li-Si alloy, etc., but is not limited to these; any alloy used as a lithium alloy is acceptable. The negative electrode active material (NAM) may include one of these alloys or lithium. Alternatively, the negative electrode active material (NAM) may include various types of alloys.

[0108] The negative active material (NAM) within the coating layer (CTL) may exist throughout the coating layer (CTL), but the concentration of the negative active material (NAM) in the region adjacent to the negative current collector (COL2) may be greater. For example, the coating layer (CTL) may include a first surface (SF1) adjacent to the negative current collector (COL2) and a second surface (SF2) facing the first surface (SF1), wherein the concentration of the negative active material (NAM) in the first surface (SF1) may be greater than the concentration of the negative active material (NAM) in the second surface (SF2).

[0109] Specifically, the concentration of the negative active material (NAM) on the first surface (SF1) can be defined as the content of the negative active material (NAM) within an area extending up to about 10% of the thickness of the coating layer (CTL) in a direction away from the negative current collector (COL2) on the first surface (SF1). Additionally, the concentration of the negative active material (NAM) on the second surface (SF2) can be defined as the content of the negative active material (NAM) within an area extending up to about 10% of the thickness of the coating layer (CTL) in a direction toward the negative current collector (COL2) on the second surface (SF2). That is, the concentration of the negative active material (NAM) can be determined based on the content of the negative active material (NAM) up to a certain area extending toward the interior of the coating layer (CTL) with respect to each of the first surface (SF1) and the second surface (SF2).

[0110] The non-anode battery according to the embodiments of the present invention has been described in detail so far. The anode (ANO) according to the embodiments of the present invention is manufactured without including an initial anode active material layer, and then lithium metal precipitated through an initial formation process can be used as the anode active material. This allows not only the use of high-capacity lithium metal as the anode active material, but also significantly improves energy density per unit mass and per unit volume by introducing a structure that omits the initial anode.

[0111] However, there is a problem in that lithium dendrites are formed because lithium metal is not uniformly deposited during the charging / discharging process. In addition, there is a problem in that the long-term lifespan characteristics are disadvantageous due to irreversible loss of lithium, such as the absence of negative electrode active material in the beginning and the formation of dead lithium.

[0112] Accordingly, an embodiment of the present invention aims to provide a cathode-free lithium secondary battery with improved long-term life characteristics by inducing uniform lithium deposition through a cathode further comprising a lithium resistive layer and providing a cathode with a stable structure.

[0113] Referring again to FIG. 3a and FIG. 3b, the cathode (ANO) according to an embodiment of the present invention may include a lithium resistive layer (PHL). The lithium resistive layer (PHL) may be located on a coating layer (CTL). The lithium resistive layer (PHL) may be lithiophobic. By further including a lithium resistive layer (PHL) having lithium resistance on the coating layer (PHL), the lithium electrodeposition on the cathode current collector (COL2) can be made uniform.

[0114] The lithium resistive layer (PHL) is positioned on the coating layer (CTL) and can induce lithium ions delivered through the electrolyte system (ELS) during the charging process to be directed toward the coating layer (CTL) and the negative current collector (COL2). Since the lithium resistive layer (PHL) has lithium resistance, it can induce the lithium ion flow (LFX) to concentrate at the bottom of the negative electrode (ANO) rather than remaining at the top of the negative electrode (ANO). As shown in FIGS. 3a and 3b, the lithium ion flow (LFX) reaching the negative electrode (ANO) passes through the lithium resistive layer (PHL) and is guided to the bottom of the negative electrode (ANO), thereby allowing a uniform negative active material layer (AML2) to be formed between the coating layer (CTL) and the negative current collector (COL2).

[0115] In addition, the lithium resistive layer (PHL) can prevent lithium metal from being deposited on the upper surface of the anode (ANO). As the lithium resistive layer has lithium resistance, the lithium ion concentration on the upper surface of the anode can be lowered. This prevents the deposition of lithium metal on the upper surface of the anode (ANO), thereby reducing the growth of lithium dendrites and improving the lifespan and stability of the anode. Consequently, the lithium resistive layer (PHL) can improve the performance of the anode (ANO) by inducing the uniform deposition of lithium metal between the aforementioned coating layer (CTL) and the anode current collector (COL2).

[0116] Referring again to FIGS. 4a and 4b, a lithium resistive layer (PHL) according to one embodiment may include a metal carbide (TMC). The metal carbide (TMC) may have lithium resistivity. The metal carbide (TMC) may include a compound of carbon and a transition metal. The metal carbide (TMC) may have relatively high stiffness compared to the materials constituting the coating layer (CTL). As the metal carbide (TMC) has relatively high stiffness, it can provide structural stability to the anode (ANO). For example, the lithium resistive layer (PHL) can prevent short circuits by providing physical stability during lithium dendrite formation.

[0117] The metal carbide (TMC) may include, for example, at least one of titanium carbide (TiC), tungsten carbide (WC), niobium carbide (NbC), zirconium carbide (ZrC), hafnium carbide (HfC), boron carbide (B4C), or chromium carbide (Cr3C2). The above-described effect can be achieved by the lithium resistive layer (PHL) including a metal carbide (TMC) having lithium resistance.

[0118] A lithium resistive layer (PHL) according to an embodiment of the present invention may include a three-dimensional porous structure. A three-dimensional porous structure may refer to a structure that includes a plurality of voids inside. For example, a three-dimensional porous structure may include, but is not limited to, a mesh structure, a foam structure, or a perforated structure.

[0119] In a lithium secondary battery according to an embodiment of the present invention, the lithium resistive layer (PHL) includes a three-dimensional porous structure, so that the coating layer (CTL) and the electrolyte system (ELS) can be connected to each other through the lithium resistive layer (PHL). That is, as the lithium resistive layer (PHL) includes a three-dimensional porous structure, the inside and outside of the lithium resistive layer (PHL) can be connected.

[0120] In addition, as the lithium resistive layer (PHL) includes a three-dimensional porous structure, it can have lithium ion permeability. Specifically, the three-dimensional porous structure can provide a pathway for lithium ions to permeate the lithium resistive layer (PHL). As a result, lithium ion exchange between the electrolyte system (ELS) and the anode (ANO) can occur smoothly.

[0121] Specifically, referring to FIGS. 4a and 4b, the three-dimensional porous structure of the lithium resistive layer (PHL) may include a framework structure (STR) and a void space (VST) defined by the framework structure (STR). The framework structure (STR) is a region formed by the materials constituting the lithium resistive layer (PHL) and can provide lithium resistance. The void space (VST) is a region containing gaps or spaces between the framework structures (STR) and can provide a path for the movement of lithium ions; that is, lithium ion flow (LFX) can be delivered into the coating layer (CTL) through the void space (VST). Additionally, as the framework structure (VST) possesses lithium resistance, lithium ions are not concentrated inside the lithium resistive layer (PHL) but can move smoothly toward the coating layer (CTL).

[0122] As described above, even though the lithium resistive layer (PHL) has lithium resistance, the three-dimensional porous structure provides a lithium migration path to the lithium resistive layer (PHL), thereby preventing the lithium resistive layer (PHL) from acting as an excessive electrical resistive material at the cathode. Consequently, uniform lithium electrodeposition of the cathode active material layer (AML2) can be induced by utilizing lithium resistance within a range where the lithium resistive layer (PHL) does not act as an excessive resistor at the cathode (ANO).

[0123] According to an embodiment of the present invention, the thickness of the lithium resistive layer (PHL) may be smaller than the thickness of the coating layer (CTL). That is, in one embodiment, the coating layer (CTL) on the negative electrode current collector (COL2) in the negative electrode (ANO) occupies most of the thickness, and the lithium resistive layer (PHL) on the coating layer (CTL) may have a relatively thin thickness. The thickness of the lithium resistive layer (PHL) may be 0.5 μm or less, 1 μm or less, or 3 μm or less. Specifically, the thickness of the lithium resistive layer (PHL) may be 0.01 μm to 3 μm, 0.01 μm to 3 μm, or 0.01 μm to 1 μm. If the lithium resistive layer (PHL) exceeds the above range, the electrical resistance of the negative electrode (ANO) becomes relatively higher, and consequently, the performance of the battery may be degraded.

[0124] Hereinafter, the present invention will be described in detail through a cathode (ANO) of one embodiment with reference to FIGS. 5 and 6. In one embodiment, the cathode (ANO) may include a lithium resistive layer (PHL) having a perforated structure. Specifically, the perforated structure may include a plurality of through holes (THO) formed on the upper surface of the lithium resistive layer (PHL). At this time, each of the plurality of through holes (THO) may penetrate the lithium resistive layer (PHL). Each of the plurality of through holes (THO) may penetrate the lithium resistive layer (PHL) to expose a coating layer (CTL). In this way, by exposing the coating layer (CTL) through the plurality of through holes (THO) penetrating the lithium resistive layer (PHL), the lithium resistive layer (PHL) can provide a path for lithium ions to move. In particular, it provides a pathway for the movement of lithium ions between the electrolyte system (ELS) and the cathode (ANO), and can induce the flow of lithium ions toward the coating layer (CTL) and the cathode current collector (COL2).

[0125] In one embodiment, referring to FIG. 6, a plurality of through holes (THO) may be arranged regularly. For example, a plurality of through holes (THO) may be arranged along a first direction (D1) at a first pitch (PT1). Alternatively, a plurality of through holes (THO) may be arranged along a third direction (D3) at a first pitch (PT1). In this case, the first pitch (PT1) may refer to the distance between adjacent first through holes (THO1) and second through holes (THO2) among the plurality of through holes (THO). The distance between the first through hole (THO1) and the second through hole (THO2) may be defined as the distance between the center of the first through hole (THO1) and the center of the second through hole (THO2). That is, a plurality of through holes (THO) may be arranged spaced apart from each other by the first pitch (PT1).

[0126] As shown in FIG. 6, each of the plurality of through holes (THO) may be circular, but is not limited thereto, and may have various shapes such as elliptical, square, or hexagonal. Each of the plurality of through holes (THO) may have a first diameter (DI). The first diameter (DI) may be defined as the maximum distance between the outermost walls defining the through hole (THO). For example, if the through hole (THO) is circular, the first diameter (DI) may be the diameter of the through hole (THO).

[0127] In one embodiment, for a plurality of through holes (THO), the ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) may be in the range of 2 to 5. The ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) can be used as a measure of the density of the through holes (THO) of the lithium resistive layer (PHL). That is, as the ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) increases, the density of the through holes (THO) decreases, and as the ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) decreases, the density of the through holes (THO) increases.

[0128] In the present invention, the term “density of through holes (THO)” may refer to the number of through holes (THO) formed per unit area of ​​the lithium resistive layer (PHL). The density of through holes (THO) can be calculated by measuring the number of through holes (THO) existing within a certain area based on the surface of the lithium resistive layer (PHL). The density of through holes (THO) can be quantitatively verified using an optical microscope or an electron microscope.

[0129] If the ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) is less than 2, the density of through holes increases excessively, which may reduce the structural stability of the lithium resistive layer (PHL). If the ratio of the first pitch (PT1) to the first diameter (DI) (PT1 / DI) exceeds 5, the density of through holes decreases, which increases the resistance of the negative electrode (ANO) and may reduce the performance of the battery.

[0130] Although not illustrated, the cathode (ANO) may further include a thin film provided between the cathode current collector (COL2) and the coating layer (CTL). The thin film may be provided on one side of the cathode current collector (COL2) to form an alloy with lithium. The thin film may include, for example, an element capable of forming an alloy with lithium. Elements capable of forming an alloy with lithium include, for example, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., but are not necessarily limited to these, and any element capable of forming an alloy with lithium in the art is possible. The thin film may be composed of one of these metals or may be composed of an alloy of various types of metals.

[0131] By placing the thin film on one side of the negative electrode current collector (COL2), the shape of the negative electrode active material layer (AML2) formed between the thin film and the coating layer (CTL) is further flattened, and the cycle characteristics of the lithium secondary battery can be improved. The thickness of the thin film may be, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film is less than 1 nm, it may be difficult to perform the function provided by the thin film. If the thickness of the thin film is excessively thick, the thin film itself absorbs lithium, which reduces the amount of lithium precipitated at the negative electrode (ANO), thereby lowering the energy density of the battery and degrading the cycle characteristics of the battery. The thin film may be formed on the negative electrode current collector (COL2) by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods; any method capable of forming a thin film in the relevant technical field may be possible.

[0132]

[0133] The present invention will be described in more detail below through specific embodiments. However, these embodiments are intended to illustrate the invention and the scope of the invention is not limited to these embodiments.

[0134] Manufacturing of lithium secondary batteries

[0135] (anode)

[0136] Li2S, LiI, and AlI3 were mixed. Specifically, Li2S, LiI, and AlI3 were mixed in a weight ratio of 40:15:5, and then mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3 composite. The prepared composite was mixed with carbon nanofiber (CNF) in a weight ratio of 60:10, and then mechanically milled using a ball mill to prepare a Li2S-LiI-AlI3-CNF cathode active material.

[0137] A cathode composition was prepared by mixing the above-mentioned cathode active material with azirodite-type Li6PS5Cl solid electrolyte particles and a PVdF-HFP binder. The cathode composition used was a mixture of cathode active material: solid electrolyte: binder in a weight ratio of 70:29:1. A cathode was prepared by coating the prepared cathode composition onto an aluminum cathode current collector.

[0138] (Solid electrolyte layer)

[0139] A mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of a solid electrolyte, which is an azirodite-type crystal, Li6PS5Cl. A slurry was prepared by stirring while adding octyl acetate to the prepared mixture. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and a laminate was prepared by drying in air at 80 °C for 10 minutes. A solid electrolyte layer was prepared by vacuum drying the prepared laminate at 80 °C for 2 hours.

[0140] (cathode)

[0141] A 10 μm thick SUS foil was prepared as the cathode current collector. Carbon black (CB) was prepared as the carbon-based material and silver (Ag) particles were prepared as the metal particles. The carbon black (CB) and silver (Ag) particles were mixed in a weight ratio of approximately 3:1.

[0142] A mixed solution was prepared by adding an NMP solution containing 7 wt% of a PVdF binder (Kureha #9300) to the above mixture. A cathode slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution.

[0143] The manufactured slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold-roll-pressed to flatten the surface, thereby preparing a cathode having a coating layer / cathode current collector structure. The thickness of the coating layer was approximately 15 μm.

[0144] A metal carbide composition was prepared to form a lithium resistive layer on a prepared coating layer. Specifically, the metal carbide composition comprises 98 parts by weight of titanium carbide particles and 2 parts by weight of a PVdF-HFP binder. The prepared composition was applied onto a coating layer and dried to form a lithium resistive layer. The thickness of the lithium resistive layer was approximately 1 μm.

[0145] Subsequently, holes were formed on the surface of the lithium resistive layer by performing a hole processing process using a punching machine. After undergoing a second drying process, a cathode of the final form was manufactured. In addition, the metal carbide in Example 1 was changed to tungsten carbide (WC) and prepared as the cathode of Example 2. Unlike the examples, a cathode having only a coating layer and no lithium resistive layer was prepared as the cathode of Comparative Example 1.

[0146] According to the above examples and comparative examples, a positive electrode, a solid electrolyte layer, and a negative electrode were sequentially stacked. Subsequently, a lithium secondary battery was manufactured by pressurizing the stacked structure.

[0147] Other lithium secondary batteries in the examples and comparative examples are summarized and shown in Table 1 below.

[0148] Coating Layer Lithium Resistant Layer (Metal Carbide) Thickness (Coating Layer / Protective Layer) Example 1 Ag / CO (TiC) 15 μm / 1 μm Example 2 Ag / CO (WC) 15 μm / 1 μm Comparative Example 1 Ag / CX 15 μm / -

[0149] Referring to Table 1, the cathodes of the examples and comparative examples both include a coating layer containing silver (Ag) particles and carbon (C), but Comparative Example 1 does not have a lithium resistive layer. Examples 1 and 2 have a lithium resistive layer of about 1 μm, and holes are processed so that the hole spacing / hole diameter (PT1 / DI) value is about 3.

[0150]

[0151] Evaluation Example 1: Life Characteristics Evaluation

[0152] The performance of a lithium secondary battery containing a negative electrode according to the above-described examples and comparative examples was evaluated. The capacity retention rate was measured and used as an indicator of lifespan characteristics.

[0153] Specifically, for the manufactured lithium secondary battery, the first cycle was charged at a constant current of 0.05C for 20 hours until the battery voltage reached approximately 2.8 V. Subsequently, the battery was cut off at a current of 0.05C while maintaining 2.8 V at all constant voltages. Then, the battery was discharged at a constant current of 0.1C for 10 hours until the battery voltage reached approximately 1.0 V. Through this process, the initial formation process was completed.

[0154] The lithium secondary battery that had undergone the formation phase was charged at a constant current of 0.1C for 10 hours until the battery voltage reached approximately 2.8 V. Subsequently, it was cut off at a current of 0.1C while maintaining 2.8 V in constant voltage mode. Afterward, it was discharged at a constant current of 0.1C for 10 hours until the battery voltage reached approximately 1.0 V.

[0155] The charging and discharging process described above was repeated to perform a total of 200 charging and discharging cycles. Charging and discharging were performed with a rest period of approximately 5 minutes between each cycle.

[0156] At this time, the capacity retention rate in the nth cycle is defined by the following mathematical formula 1.

[0157] [Mathematical Formula 1]

[0158] Capacity Retention Rate (%) = (Capacity of Nth Cycle) / (Capacity of 1st Cycle) × 100

[0159] The capacity retention rate of the Nth cycle was evaluated based on the initial charge / discharge capacity.

[0160] The measurement results are shown in Table 2 below.

[0161] Capacity Retention Rate (%, @100 cycle) Capacity Retention Rate (%, @200 cycle) Example 1 93% 90% Example 2 92% 89% Comparative Example 189% 81%

[0162] Referring to the evaluation results above, it can be seen that the capacity retention rate of the lithium secondary battery according to the embodiment of the present invention is higher than that of the comparative example. Furthermore, it can be seen that as the number of cycles increases, the gap in capacity retention rates between the embodiment and the comparative example widens.

[0163] In the case of the lithium secondary battery according to the comparative example, the capacity retention rate decreases sharply when the number of cycles is increased to 200, but in the case of the examples, it can be seen that the decrease is relatively small. This means that the lithium secondary battery according to the embodiment of the present invention can improve long-term life characteristics through a negative electrode structure having a lithium resistive layer.

[0164] In addition, the evaluation results measured by changing the charge / discharge rate to 1.0C / 1.0C are shown in Table 3 below. The number of cycles was measured until the capacity retention rate reached approximately 50%.

[0165] cyc (@ 1.0C, 50% retention rate) Example 198 cyc Example 2103 cyc Comparative Example 110 cyc

[0166] Referring to Table 3, it can be indirectly confirmed that the capacity retention rate decreases when the charge / discharge speed is increased. In particular, in the comparative example, it can be seen that the lifespan characteristics dropped sharply after only 10 cycles. In contrast, in the example, it can be seen that the lifespan characteristics are maintained relatively even when the charge / discharge speed is increased.

Claims

1. Cathode current collector; A coating layer on the above-mentioned cathode current collector; and It includes a lithium resistant layer on the above coating layer, The above coating layer comprises a carbon-based material and a lithium-affinity metal, and The above lithium resistive layer includes metal carbide, and The above lithium resistive layer is a cathode having a three-dimensional porous structure.

2. In Paragraph 1, The above three-dimensional porous structure comprises at least one of a mesh structure, a foam structure, or a perforated structure, a cathode.

3. In Paragraph 1, The above three-dimensional porous structure comprises a skeletal structure including the metal carbide, and empty spaces defined by the skeletal structure, The above empty space is a cathode that provides a path for lithium ions to pass through the lithium resistive layer.

4. In Paragraph 1, The above metal carbide comprises at least one of titanium carbide (TiC), tungsten carbide (WC), niobium carbide (NbC), zirconium carbide (ZrC), hafnium carbide (HfC), boron carbide (B4C), or chromium carbide (Cr3C2), forming a cathode.

5. In Paragraph 1, The thickness of the lithium resistive layer is smaller than the thickness of the coating layer. cathode.

6. In Paragraph 1, The above carbon-based material comprises at least one of carbon black, carbon nanotube, acetylene black, furnace black, Kettjen black, or graphene, and The lithium-affinity metal comprises at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn). cathode.

7. In Paragraph 1, The above cathode further comprises a cathode active material provided between the coating layer and the cathode current collector or within the coating layer, and The above-mentioned negative electrode active material comprises lithium metal or an alloy of lithium metal, forming a negative electrode.

8. In Paragraph 7, The coating layer comprises a first surface facing the negative electrode current collector and a second surface facing the lithium resistive layer, A cathode in which the concentration of the cathode active material on the first surface is greater than the concentration of the cathode active material on the second surface.

9. Cathode current collector; A coating layer on the above-mentioned cathode current collector; and It includes a lithium resistant layer on the above coating layer, The above coating layer comprises a carbon-based material and a lithium-affinity metal, and The above lithium resistive layer includes a three-dimensional porous structure, and The above three-dimensional porous structure is a cathode that provides a path for lithium ions to penetrate the lithium resistive layer.

10. In Paragraph 9, The above three-dimensional porous structure includes a plurality of through holes, and Each of the above plurality of through holes penetrates the lithium resistive layer to expose the coating layer, forming a cathode.

11. In Paragraph 10, The above plurality of through holes are arranged at a first pitch along a first direction, and Each of the above plurality of through holes has a first diameter, and The ratio of the first pitch (PT1 / DI) to the first diameter is 2 to 5, cathode.

12. In Paragraph 9, The thickness of the lithium resistive layer is smaller than the thickness of the coating layer. cathode.

13. In Paragraph 9, The above lithium resistive layer comprises metal carbide, and The above metal carbide comprises at least one of titanium carbide (TiC), tungsten carbide (WC), niobium carbide (NbC), zirconium carbide (ZrC), hafnium carbide (HfC), boron carbide (B4C), or chromium carbide (Cr3C2), forming a cathode.

14. In Paragraph 9, The above carbon-based material comprises at least one of carbon black, carbon nanotube, acetylene black, furnace black, Kettjen black, or graphene, and The lithium-affinity metal comprises at least one of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn). cathode.

15. In Paragraph 9, The above cathode further comprises a cathode active material provided between the coating layer and the cathode current collector or within the coating layer, and The above-mentioned negative electrode active material comprises lithium metal or an alloy of lithium metal, forming a negative electrode.

16. In Paragraph 15, The coating layer comprises a first surface facing the negative electrode current collector and a second surface facing the lithium resistive layer, A cathode in which the concentration of the cathode active material on the first surface is greater than the concentration of the cathode active material on the second surface.

17. A cathode according to any one of paragraphs 1 to 16; Anode; and an electrolyte system between the anode and the cathode, Lithium secondary battery.

18. In Paragraph 17, The above electrolyte system comprises a solid electrolyte layer, Lithium secondary battery.

19. In Paragraph 18, The above solid electrolyte layer is Li 7-a-c M a PS 6-c X c It comprises an argyrodite-type sulfide-based solid electrolyte represented by (0≤a≤2, 0≤c≤2), and The above X is F, Br, Cl, or a combination thereof, and The above M is scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof, Lithium secondary battery.

20. In Paragraph 17, The above electrolyte system comprises a separator and an electrolyte, Lithium secondary battery.

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