Lithium Metal Powder Anode Containing an Adhesive-Conductive Polymer and Method for Manufacturing Lithium Metal Battery

Abstract

One embodiment of the present invention provides a negative electrode for a lithium secondary battery. The embodiment according to the present invention introduces a polymer layer having adhesive and electrical conductivity to suppress the detachment of lithium metal particles and provides electrical connectivity, thereby enabling the battery to have excellent performance. In particular, the lithium metal particles have a core-shell structure, which has the effect of solving the problem of deactivation caused by volume change during the charging and discharging process.

Description

Technology Field

[0001] The present invention relates to a lithium metal powder cathode comprising an adhesive-electrically conductive polymer and a lithium metal battery comprising the same. Background Technology

[0002] With the rapid development of the electrical, electronic, telecommunications, and computer industries, the demand for high-performance and high-stability secondary batteries has gradually increased. In particular, driven by the trend toward miniaturization, lightweighting, and portability of precision electrical and electronic products, secondary batteries—which are key components in this field—are also required to be thinner and smaller. In response to these demands, one of the batteries currently receiving the most attention is the lithium secondary battery. Generally, a lithium secondary battery consists of a positive electrode, an electrolyte, and a negative electrode. These components are selected to satisfy various requirements of the secondary battery, such as battery life, charge / discharge capacity, temperature characteristics, and stability.

[0003] Carbon-based materials such as natural graphite, artificial graphite, and hard carbon, or lithium metal, are typically used as the negative electrode in lithium-ion batteries. The electrolyte consists of an organic solvent, a lithium salt, and a polymer separator.

[0004] To increase the capacity of lithium-ion batteries, the use of materials with high energy density or the expansion of battery surface area are required. In response to these demands, lithium metal is attracting attention as a next-generation anode material due to its high theoretical capacity, low potential, and larger capacity per unit mass or volume compared to graphite and hard carbon. Conventional lithium metal anodes have primarily been used in the form of lithium foil. However, lithium foil suffers from poor lithium ion electrodeposition and desorption performance due to its low specific surface area, and the formation of lithium dendrites on the anode surface during charging and discharging leads to uneven current density. Additionally, lithium foil, manufactured by rolling lithium ingots, has the disadvantage of being difficult to expand to a large surface area due to the inherent physical property limitations of lithium itself.

[0005] To address these issues, a method for manufacturing a lithium powder thin-film anode using lithium powder instead of lithium foil has been proposed. Lithium powder anodes have the advantage of improved battery characteristics due to an enhanced specific surface area compared to lithium foil. Furthermore, since universal coating technologies can be applied, it is easy to thin and expand the surface area of ​​the electrode.

[0006] However, cathodes using lithium metal powder have a problem in that the lithium metal powder composite layer detaches from the substrate (current collector) due to electrolyte penetration during the charging and discharging process. This detachment of the composite layer causes electrochemical deactivation of the lithium metal powder, resulting in a loss of lithium capable of participating in electrochemical reactions, and consequently leads to a rapid deterioration of the battery's lifespan characteristics.

[0007] Therefore, there is a need to develop a new technology that can improve the interfacial stability between the lithium metal powder composite layer and the substrate and maintain electrical connectivity. Meanwhile, the prior art Korean registered patent (KR 10-2329851) discloses a negative electrode using lithium powder, but uses a polyimide-based material as a binder for the lithium metal powder electrode. Since polyimide-based binders are representative insulating materials with very low electrical conductivity, there is a problem in that if the binder is present at the interface between the current collector and the lithium metal powder, electrical connectivity is reduced and the internal resistance of the battery increases, which can lead to a decrease in the battery's capacity and energy density. Prior art literature

[0008] Korean Registered Patent 10-2329851 The problem to be solved

[0009] The present invention provides a lithium metal battery having excellent performance by adopting a polymer layer having adhesiveness and electrical conductivity formed at the interface between a lithium metal powder composite layer and a substrate in a negative electrode using lithium metal particles as a method to solve the problems of the aforementioned prior art.

[0010] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0011] To achieve the above technical problem, one embodiment of the present invention provides a negative electrode for a lithium secondary battery.

[0012] A negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized by comprising: a substrate; a composite layer formed on the substrate and comprising lithium metal particles; and an adhesive conductive polymer interface layer formed between the lithium metal particles and the substrate.

[0013] In an embodiment of the present invention, the lithium metal particles may be a negative electrode for a lithium secondary battery, characterized by having a core-shell structure.

[0014] In an embodiment of the present invention, the negative electrode for a lithium secondary battery may be characterized in that, in the core-shell structure, the shell is composed of one or more selected from the group consisting of lithium salt, lithium oxide, lithium hydroxide, lithium nitride, and lithium fluoride, and the core comprises one or more selected from the group consisting of lithium metal and lithium alloy.

[0015] In an embodiment of the present invention, the composite layer may be a negative electrode for a lithium secondary battery, characterized by further including a conductive material or a binder.

[0016] In an embodiment of the present invention, the negative electrode for a lithium secondary battery may be characterized in that the thickness of the adhesive conductive polymer interface layer is 10 to 200 nm.

[0017] In an embodiment of the present invention, the adhesive conductive polymer interface layer may be a negative electrode for a lithium secondary battery, characterized by having both adhesiveness and electrical conductivity by including a conductive polymer having anionic functional groups.

[0018] In an embodiment of the present invention, the polymer may be a negative electrode for a lithium secondary battery characterized by comprising PEDOT:P(SS-co-AA).

[0019] In an embodiment of the present invention, the substrate may be a negative electrode for a lithium secondary battery, characterized in that it is a copper foil.

[0020] A lithium secondary battery according to another embodiment of the present invention for achieving the above technical problem comprises: a negative electrode for the lithium secondary battery; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

[0021] Another embodiment of the present invention for achieving the above technical problem provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0022] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises: a step of preparing a substrate; a step of forming a polymer interface layer by coating a polymer solution containing an adhesive conductive polymer on the substrate; and a step of forming a composite layer by applying a negative electrode slurry containing lithium metal particles on the polymer layer. Effects of the invention

[0023] According to an embodiment of the present invention, the adhesive-electron-conductive polymer interface layer simultaneously exhibits adhesion and electron conductivity, thereby simultaneously securing mechanical connectivity that suppresses the detachment of the lithium metal powder composite layer and electrical connectivity between the composite layer and the current collector. As a result, excellent battery performance can be maintained even after hundreds of charge-discharge cycles, and the battery operation stability can be improved.

[0024] In addition, according to an embodiment of the present invention, the polymer layer provides electrical connectivity without relying on conductive particles, thereby minimizing electron transfer resistance within the electrode and maintaining consistent electrical characteristics.

[0025] In addition, according to an embodiment of the present invention, by applying a lithium metal powder having a core-shell structure as a negative electrode active material, the problem of electrochemical deactivation caused by volume change during the charge-discharge process compared to existing technology is effectively resolved, thereby enabling stable performance in high-energy-density lithium metal batteries.

[0026] In addition, according to an embodiment of the present invention, since the adhesive conductive polymer corresponding to one component is introduced in a solution state and the lithium metal powder composite layer is introduced in a slurry state, it is suitable for manufacturing large-area electrodes through a roll-to-roll process, thereby enabling high-efficiency mass production and securing commercial productivity and scalability.

[0027] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0028] FIG. 1 is a schematic diagram showing a negative electrode for a lithium secondary battery according to an embodiment of the present invention. FIG. 2 is a diagram showing a negative electrode for a lithium secondary battery and a comparative example according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing the manufacturing process of a lithium metal powder electrode according to the present invention. Figure 4 is a diagram showing the coating process in detail. FIG. 5 is an image showing a negative electrode for a lithium secondary battery manufactured according to an embodiment of the present invention. Figure 6 is a diagram showing a cross-sectional SEM image and height profile of a fabricated adhesive-conductive polymer interface layer. Figure 7 is a diagram showing the C 1s XPS spectra of the prepared conductive polymer and adhesive-conductive polymer. Figure 8 is a diagram showing the results of the interfacial adhesion analysis using SAICAS. FIG. 9 is a diagram showing the large-area manufacturing results of a lithium metal powder electrode according to the present invention. FIG. 10 is a drawing showing the thickness of a lithium metal powder composite layer (20 μm) formed on a substrate (10 μm). Figure 11 is a diagram showing the SEM image, EDS analysis results, and XPS spectrum of lithium metal particles. Figure 12 is a diagram showing the results of EDS analysis of oxygen elements in the cross-section of lithium metal particles. Figure 13 is a diagram showing the voltage profile of a lithium metal symmetric cell under certain conditions. Figure 14 is a diagram showing the lifespan characteristics of an NCM622 / Li battery. Fig. 15 is 3 mAh cm⁻¹ -2 This is a drawing showing SEM images of Comparative Example 1, Comparative Example 2, and the Example after lithium stripping. Specific details for implementing the invention

[0029] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0030] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0031] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0032] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0034] A negative electrode for a lithium secondary battery according to one embodiment of the present invention is described.

[0035] FIG. 1 is a schematic diagram showing a negative electrode for a lithium secondary battery according to an embodiment of the present invention.

[0036] A negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized by comprising, as shown in FIG. 1, a substrate (10); a composite layer (30) formed on the substrate and comprising lithium metal particles; and an adhesive conductive polymer interface layer (20) formed between the composite layer (30) and the substrate (10) and having electrical conductivity and adhesiveness.

[0037] A problem was raised regarding the limited thickness and width of lithium metal electrodes produced by conventional extrusion / pressing processes. To address this, a method was proposed to fabricate ultra-thin lithium electrodes by coating with lithium metal powder (LMP). However, coated LMP electrodes suffered from the problem that electrolyte penetration during the charge-discharge process weakened the adhesion between the LMP layer and the substrate, leading to reduced interfacial connectivity.

[0038] To solve this problem, the inventors of the present invention have proposed a secondary battery electrode having a novel structure in which a polymer interface layer having both electrical conductivity and adhesion is introduced between an LMP and a substrate.

[0039] The above-mentioned substrate (10) is a substrate composed of a material capable of serving as a current collector, and may be selected from the group consisting of, for example, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto and may use a substrate generally used in the industry.

[0040] The above composite layer (30) is a layer containing lithium metal particles (31). The lithium metal particles (31) are used as a negative electrode active material. In a lithium secondary battery using a conventional lithium metal negative electrode active material, applying lithium metal particles significantly increases the specific surface area of ​​the negative electrode active material compared to when lithium foil is used as the lithium metal, which is advantageous for battery characteristics. In particular, it has the characteristic of being able to suppress the growth of lithium dendrites by lowering the current density on the surface of the negative electrode. In addition, it has the advantage of having good reactivity of the negative electrode active material and being able to easily control the content.

[0041] At this time, the lithium metal particles (31) may have a core-cell structure.

[0042] Specifically, the core-cell structure may be composed of one or more selected from the group consisting of lithium salts, lithium oxides, lithium hydroxides, lithium nitrides, and lithium fluorides, wherein the cell on the surface of the particle is composed of lithium salts, lithium oxides, lithium hydroxides, lithium nitrides, and lithium fluorides. Additionally, the core inside the particle may be composed of one or more selected from the group consisting of lithium metals and lithium alloys.

[0043] In particular, the present invention can prevent an increase in internal resistance and a decrease in capacity of the battery by maintaining stable electrochemical performance of the lithium metal particles when lithium metal particles (31) having a core-shell structure are included in the composite layer (30). Through this, it has the feature of being usable in high-energy density batteries.

[0044] In particular, the lithium metal particles (31) having a core-shell structure of the present invention have a shell portion formed as described above, so they can serve as a stable protective layer during the storage and delivery process of the lithium metal particles as well as during the electrode manufacturing process. In addition, by including the lithium metal particles with a core-shell structure in the composite layer (30), electrochemical stability is improved, thereby suppressing the increase in internal resistance and the decrease in capacity during the charging and discharging process. Through this, there is a feature that enables the realization of excellent performance required for high-energy density batteries.

[0045] The lithium metal particles may have various shapes, such as spherical, cylindrical, elliptical, one-dimensional linear, or two-dimensional tubular, and preferably may be spherical. In particular, spherical lithium metal particles can lower the effective current density by providing a large surface area compared to lithium foil or other shapes of lithium metal particles.

[0046] Here, effective current density refers to the value obtained by dividing the applied current density by the actual reaction surface area, and the lower this value, the more stably lithium can be electrodeposited on the electrode surface. The average particle size (D50) of the lithium metal particles can be selected within the range of 1 to 100 μm, preferably 5 to 60 μm, more preferably 10 to 40 μm, but is not limited thereto.

[0047] In addition, in the present invention, the composite layer (30) may further include a material corresponding to a negative electrode active material on the substrate in addition to the lithium metal particles (31). For example, the negative electrode active material may include, in addition to the lithium metal particles, a material capable of reversibly intercalating and deintercalating lithium ions, an alloy of lithium metal, a material capable of electrodepositing and dedepositing lithium, a transition metal oxide, or a combination thereof as the remainder.

[0048] The material capable of reversibly intercalating and deintercalating the lithium ions may be a carbon-based material, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include amorphous, plate-shaped, flake, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0049] As the alloy of the above lithium metal particles, an alloy of a metal selected from the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0050] Materials capable of doping and dedoping the above lithium include Si and SiO x(0 <x<2), Si-C 복합체, Si-Y 합금, Sn, SnO2, Sn-C 복합체, Sn-Y 합금 등을 들 수 있고, 또한 이들 중 적어도 하나와 SiO2를 혼합하여 사용할 수도 있다. 상기 원소Y로는 Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po 및 이들의 조합으로 이루어진 군에서 선택될 수 있다.

[0051] Examples of the above transition metal oxides include vanadium oxide and lithium vanadium oxide.

[0052] The negative active material may be included in an amount of 50 to 99 weight% relative to the total weight of the entire composite layer (30), and may be included in an amount of 85 to 99 weight%, 90 to 99 weight%, or 93 to 99 weight%.

[0053] Additionally, the composite layer (30) may optionally further include a binder and a conductive material. The binder or conductive material may be a material known in the art, and the present invention is not limited thereto.

[0054] For example, the binder may include one or more selected from the group consisting of polyimide-based polymers, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinylidene fluoride-trifluoroethylene (PVdF-TFE), styrene-butadiene rubber (SBR), polyimide (PI), polyisobutylene (PIB), polyacrylic acid (PAA), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyethylene (PE), and carboxymethylcellulose (CMC).

[0055] In addition, the binder is preferably included in an amount of 0.1 to 30 weight percent based on the total weight of the lithium powder.

[0056] The above conductive material can increase the conductivity of the electrode by being positioned in the empty space between the negative electrode active materials. It is not particularly limited as long as it is conductive without causing chemical changes in the battery; for example, graphite, carbon-based materials, conductive fibers, metal powders, conductive whiskey, conductive metal oxides, conductive polymers, etc., may be used.

[0057] The composite layer (30) may be formed, for example, by applying a cathode slurry on the substrate, and the cathode slurry may include a cathode active material and a solvent as described above, and may optionally include a conductive material and a binder.

[0058] At this time, the solvent is an organic solvent and comprises tetrahydrofuran (THF), tetramethylfuran (TMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylformamide (DMF), monomethylformamide (MMF), monomethylacetamide (MMA), dimethylacetamide (DMA), dimethylimidazolidinone, butyrolactone, diacetone alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, hexamethylphosphamide (HMPA), N-methyl-ε-carrolactam, tetramethylurea, chlorobenzene, dioxane, methyl It may include at least one selected from the group consisting of ethyl ketone (MEK), isobutyl methyl ketone, and sulforane.

[0059] The polymer interface layer (20) is formed at the interface between the substrate (10) and the composite layer (30). By using a dual-functional polymer material that possesses both adhesiveness and electrical conductivity, the polymer interface layer (20) can simultaneously secure mechanical connectivity that suppresses the detachment of lithium metal powder and electrical connectivity between the lithium metal powder and the substrate. Through this, excellent battery performance can be maintained even after hundreds of charge / discharge cycles. For example, the polymer interface layer (20) may be composed of a conductive polymer having anionic functional groups to provide both adhesiveness and electrical conductivity.

[0060] In particular, as a preferred example, the polymer interface layer (20) may include PEDOT:P(SS-co-AA).

[0061] The above PEDOT:P(SS-co-AA) corresponds to a material synthesized through the polymerization of electrically conductive PEDOT with adhesive poly(styrenesulfonate-co-acrylic acid) (hereinafter, P(SS-co-AA)). Specifically, P(SS-co-AA) is a copolymer in which vinyl styrenesulfonate and acrylic acid are randomly located within the polymer chain, and is composed of poly(styrenesulfonate) (PSS), which promotes the polymerization of 3,4-ethylenedioxythiophene 143 (EDOT), and poly(acrylic acid) (PAA), which provides adhesiveness.

[0062] The adhesive conductive polymer interface layer (20) may have a thickness in the range of 10 to 300 nm. If the thickness of the interface layer (20) is less than 10 nm, the expression of adhesive strength at the interface is limited, so the effect of preventing detachment of the lithium metal powder composite layer may be reduced. On the other hand, if the thickness of the interface layer (20) exceeds 300 nm, the energy density of the battery may be reduced. The interface layer (20) may preferably have a thickness of 20 to 200 nm, more preferably 100 nm or less, and within this range, adhesion and electrical conductivity are optimized to realize excellent battery characteristics. However, the thickness of the interface layer is not limited thereto.

[0064] Next, a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention will be described.

[0065] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention comprises: a step of preparing a substrate (S100); a step of forming a polymer layer by coating a polymer solution containing an adhesive conductive polymer onto the substrate (S200); and a step of forming a composite layer by applying a negative electrode slurry containing lithium metal particles onto the polymer layer (S300).

[0066] In the following method for manufacturing a negative electrode according to an embodiment of the present invention, redundant descriptions regarding parts identical to those previously described regarding a negative electrode for a lithium secondary battery are omitted.

[0067] First, prepare the equipment (S100).

[0068] The above-mentioned substrate (10) is a substrate composed of a material capable of serving as a current collector, and may be selected from the group consisting of, for example, copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto and may use a substrate generally used in the industry.

[0069] Next, a polymer solution is coated onto the substrate (S200).

[0070] A polymer solution can be prepared by dispersing an adhesive conductive polymer in a solvent. The polymer may include PEDOT:P(SS-co-AA) as previously described, and the solvent may be, for example, pure water (DI water). Additionally, dimethyl sulfoxide (DMSO) may be added before coating the polymer solution onto a substrate. Thus, a polymer interface layer is formed in this step.

[0071] Next, a negative electrode slurry containing lithium metal particles is applied onto the polymer interface layer (S300).

[0072] The above-mentioned cathode slurry comprises a cathode active material and a solvent. Additionally, it may optionally further comprise a conductive material and a binder. The above-mentioned cathode active material comprises lithium metal particles. Furthermore, as previously mentioned, the lithium metal particles may have a shell-core structure.

[0073] The above solvent is an organic solvent comprising tetrahydrofuran (THF), tetramethylfuran (TMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylformamide (DMF), monomethylformamide (MMF), monomethylacetamide (MMA), dimethylacetamide (DMA), dimethylimidazolidinone, butyrolactone, diacetone alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, acetonitrile, hexamethylphosphamide (HMPA), N-methyl-ε-carrolactam, tetramethylurea, chlorobenzene, dioxane, and methyl It may include at least one selected from the group consisting of ethyl ketone (MEK), isobutyl methyl ketone, and sulforane.

[0074] The method of applying the above slurry can be selected from methods generally used in the technical field, for example, the slurry can be applied using a doctor blade.

[0076] Next, a lithium secondary battery including a negative electrode according to one embodiment of the present invention will be described.

[0077] A lithium secondary battery according to one embodiment of the present invention is characterized by comprising: a negative electrode for a lithium secondary battery according to one embodiment of the present invention; a positive electrode; and an electrolyte located between the negative electrode and the positive electrode.

[0078] The above-mentioned cathode includes the cathode for a lithium secondary battery described above.

[0079] The above anode comprises a substrate and an anode active material layer formed by applying an anode slurry containing an anode active material onto the substrate.

[0080] The above description may use the aforementioned cathode material, and it is acceptable to use materials known in the relevant technical field, but the present invention is not limited thereto.

[0081] The above-mentioned positive active material layer comprises a positive active material and may optionally further comprise a binder or a conductive material. The positive active material may be any positive active material known in the art, and, for example, it is preferable to use a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof, but the present invention is not limited thereto.

[0082] The above-mentioned binder and conductive material may use the cathode binder and cathode conductive material described above, and it is acceptable to use materials known in the relevant technical field, but the present invention is not limited thereto.

[0083] The above lithium secondary battery may further include a separator.

[0084] The above separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven or woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene may be primarily used in lithium secondary batteries, and separators coated with a composition containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength. Optionally, they may be used in a single-layer or multi-layer structure, and while it is acceptable to use separators known in the relevant art field, the present invention is not limited thereto.

[0085] The above electrolyte includes an organic solvent and a lithium salt.

[0086] The above organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used. The above organic solvent may be used alone or as a mixture of two or more types. When two or more types are mixed, the mixing ratio can be appropriately adjusted according to the desired battery performance. Meanwhile, it is acceptable to use organic solvents known in the relevant technical field, but the present invention is not limited thereto.

[0087] 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 operation of a basic lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Examples of the above lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiN(CF3SO2)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 Examples include SO2)(x and y are natural numbers), LiCl, LiI, LiB(C2O4)2, or combinations thereof, but the present invention is not limited thereto.

[0088] The concentration of the lithium salt can be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0089] In addition, the above electrolyte may additionally include pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc., as needed to improve charge / discharge characteristics and flame retardancy characteristics. In some cases, it may additionally include halogen-containing solvents such as carbon tetrachloride and trifluoroethylene to impart non-flammability, and may additionally include FEC (fluoro-ethylene carbonate), PRS (propene sulfone), FPC (fluoro-propylene carbonate), etc., to improve high-temperature storage characteristics.

[0091] The present invention will be explained in more detail below through manufacturing examples, comparative examples, and experimental examples. However, the present invention is not limited to the following manufacturing examples and experimental examples.

[0093] Example 1: Preparation of a lithium metal powder electrode comprising an adhesive conductive polymer interface layer

[0094] FIG. 2 is a diagram showing a negative electrode for a lithium secondary battery and a comparative example according to an embodiment of the present invention, showing the interface structure of a lithium metal powder electrode.

[0095] Referring to FIG. 2 above, a structure without an interface layer (Comparative Example 1), a structure including a conductive interface layer (Comparative Example 2), and a structure including an adhesive-conductive polymer interface layer (Example) are illustrated.

[0096] Comparative Example 1 is a structure in which a lithium metal powder composite layer is formed directly on a current collector, and Comparative Example 2 is a structure in which a conductive polymer interface layer is formed between the current collector and the composite layer to provide an electron conduction path.

[0097] The example corresponds to a structure in which an adhesive-conductive polymer interface layer is formed between the current collector and the composite layer, providing both an electron conduction path and adhesive properties. The specific manufacturing process of Example 1 is as follows.

[0098] First, an adhesive-conductive current collector was prepared by coating an adhesive-conductive polymer solution, PEDOT:P(SS-co-AA), onto a copper foil. Subsequently, a slurry composed of lithium metal powder, a binder, and an organic solvent was applied onto the adhesive-conductive current collector.

[0100] Example 2 - Manufacturing process of lithium metal powder electrode

[0101] FIG. 3 is a schematic diagram showing the manufacturing process of a lithium metal powder electrode according to the present invention, illustrating a continuous coating process of an adhesive-conductive polymer interface layer and a lithium metal powder composite layer.

[0102] The above manufacturing process comprises continuous feeding of the substrate, solution coating, drying, and rolling processes.

[0103] Figure 4 shows the coating process of Figure 3 in detail, illustrating a process in which a lithium metal powder slurry is coated after the coating and drying of an adhesive-conductive polymer solution.

[0104] Figure 5 is an image showing an adhesive-conductive polymer coating layer formed on a substrate, and a lithium metal powder electrode for a secondary battery was manufactured according to the manufacturing process described above.

[0106] Experimental Example 1 - Analysis of the Structure of the Adhesive-Conductive Polymer Interfacial Layer

[0107] Figure 6 shows a cross-sectional SEM image and height profile of the adhesive-conductive polymer interface layer. The thickness of the interface layer was measured to be 92.4 nm.

[0108] Figure 7 shows the C 1s XPS spectra of a conductive polymer and an adhesive-conductive polymer. Referring to Figure 7, the OC=O peak observed in the spectrum of the adhesive-conductive polymer confirms the presence of an acrylic acid functional group.

[0110] Figure 8 shows the results of the interfacial adhesion analysis using SAICAS. Referring to Figure 8, it can be seen that the example in which an adhesive-conductive polymer is introduced as an interfacial layer exhibits superior adhesion compared to Comparative Examples 1 and 2.

[0112] FIG. 9 is a drawing showing the results of manufacturing a large-area lithium metal powder electrode according to the present invention. As shown in FIG. 9, according to the manufacturing process of the present invention, an electrode with a width of 300 mm was uniformly manufactured, which corresponds to a process characteristic made possible by using lithium metal powder.

[0113] FIG. 10 shows the thickness of a lithium metal powder composite layer (20 μm) formed on a substrate (10 μm).

[0115] Experimental Example 2: Analysis of Lithium Metal Particle Structure

[0116] Figure 11 is a diagram showing the SEM image, EDS analysis results, and XPS spectrum of lithium metal particles. It was confirmed that the particles have a core-shell structure, and the shell is composed of Li₂CO₃, LiOH, and Li₂O.

[0117] Figure 12 shows the results of EDS analysis of oxygen elements in the cross-section of a lithium metal particle. The oxygen element signal observed in the outer region of the particle shows that the structure is formed with Li₂CO₃, LiOH, and Li₂O constituting the shell surrounding the interior.

[0119] Experimental Example 3: Evaluation of Lithium Metal Symmetric Cells

[0120] Fig. 13 shows 0.5 mA cm -1 , 1 mAh cm -2This shows the voltage profile of a lithium metal symmetric cell under conditions. Referring to FIG. 13 above, it can be seen that the example exhibits stable voltage behavior compared to the comparative example.

[0121] Figure 14 shows the lifespan characteristics of an NCM622 / Li battery. Likewise, it can be seen that an embodiment of the present invention maintains a stable capacity for more than 200 cycles, as shown in Figure 14.

[0123] Experimental Example 4: Surface Analysis of Lithium Metal Electrode After Stripping

[0124] Fig. 15 is 3 mAh cm⁻¹ -2 SEM images of Comparative Example 1, Comparative Example 2, and Example after lithium stripping are shown. Referring to FIG. 15, it can be seen that the Example exhibits a uniform surface in which the detachment of lithium metal powder is suppressed due to the adhesive-conductive polymer interface layer.

[0126] According to the above-described embodiment of the present invention, a polymer interface layer having adhesiveness and electrical conductivity is introduced between a substrate (current collector) and a lithium metal powder composite layer to suppress the detachment of lithium metal particles occurring during the charging and discharging process, thereby improving the interfacial stability of the electrode and preventing long-term performance degradation of the battery.

[0127] In addition, the polymer interface layer provides electrical connectivity without relying on conductive particles, thereby minimizing electron transfer resistance within the electrode and maintaining consistent electrical characteristics. This prevents an increase in internal battery resistance during charging and discharging, and enables the maintenance of stable capacity.

[0128] In addition, when lithium metal powder having a core-shell structure is applied as a negative electrode active material, the problem of electrochemical deactivation caused by volume change during the charge-discharge process observed in existing technologies can be effectively resolved, thereby enabling stable performance in high-energy-density lithium metal batteries.

[0129] In addition, since the adhesive conductive polymer of the present invention is introduced in a solution state and the lithium metal powder composite layer is introduced in a slurry state, it is suitable for manufacturing large-area electrodes through a roll-to-roll process, and through this, high-efficiency mass production is possible, thereby securing commercial productivity and scalability.

[0130] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0131] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention. Explanation of the symbols

[0133] 10 : Entry 20: Adhesive conductive polymer interface layer 30 : Combined layer 31: Lithium metal particles

Claims

Claim 1 A negative electrode for a lithium secondary battery, comprising: a substrate; a composite layer formed on the substrate and comprising lithium metal particles; and an adhesive conductive polymer interface layer formed between the lithium metal particles and the substrate; wherein the adhesive conductive polymer interface layer comprises a conductive polymer having anionic functional groups and simultaneously possesses adhesiveness and electrical conductivity, and the thickness of the adhesive conductive polymer interface layer is 10 to 300 nm. Claim 2 A negative electrode for a lithium secondary battery, characterized in that, in claim 1, the lithium metal particles have a core-shell structure. Claim 3 A negative electrode for a lithium secondary battery according to claim 2, wherein in the core-shell structure, the shell is composed of one or more selected from the group consisting of lithium salt, lithium oxide, lithium hydroxide, lithium nitride, and lithium fluoride, and the core comprises one or more selected from the group consisting of lithium metal and lithium alloy. Claim 4 A negative electrode for a lithium secondary battery according to claim 1, wherein the composite layer further comprises a binder. Claim 5 delete Claim 6 delete Claim 7 A negative electrode for a lithium secondary battery according to claim 1, wherein the polymer comprises PEDOT:P(SS-co-AA). Claim 8 A negative electrode for a lithium secondary battery according to claim 1, wherein the substrate is selected from the group consisting of copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof. Claim 9 A lithium secondary battery characterized by comprising: a negative electrode for a lithium secondary battery according to claim 1; a positive electrode; and an electrolyte interposed between the negative electrode and the positive electrode. Claim 10 A method for manufacturing a negative electrode for a lithium secondary battery, comprising: a step of preparing a substrate; a step of forming a polymer interface layer by coating a polymer solution containing an adhesive conductive polymer onto the substrate; and a step of forming a composite layer by applying a negative electrode slurry containing lithium metal particles onto the polymer interface layer, wherein the polymer interface layer simultaneously possesses adhesiveness and electrical conductivity and has a thickness of 10 to 300 nm. Claim 11 A method for manufacturing a negative electrode for a lithium secondary battery, wherein, in claim 10, the polymer solution comprises PEDOT:P(SS-co-AA).

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