Lithium metal battery negative electrode comprising polymer protective layer, and lithium metal battery comprising same

Abstract

The present invention relates to a lithium metal battery negative electrode that comprises a polymer protective layer. More specifically, the present invention comprises a polymer protective layer on a negative electrode current collector, wherein the polymer protective layer may comprise an ion conductive polymer and a zwitterionic salt.

Description

A negative electrode for a lithium metal battery including a polymer protective layer, and a lithium metal battery including the same

[0001] It relates to a polymer protective layer for a lithium metal battery and a lithium metal battery.

[0002]

[0003] Lithium-ion batteries currently on the market primarily use carbon-based anode active materials, such as graphite. Carbon-based anode active materials exhibit no volume change during charge and discharge, which enhances battery stability. However, their low capacity necessitates the use of anode active materials with higher capacities.

[0004] Lithium metal, which has a higher theoretical electric capacity than carbon-based negative electrode active materials, can be used as the negative electrode active material.

[0005] During the charge and discharge process of a lithium metal battery using lithium metal as the negative electrode active material, a lithium-containing metal layer may precipitate and dissolve between the negative electrode current collector and the electrolyte layer. As the lithium metal battery is repeatedly charged and discharged, the lithium-containing metal layer may contain impurities remaining in the electrode, electrolyte decomposition products, etc. Therefore, the surface of the lithium-containing metal layer becomes rough and hard due to the inclusion of these impurities. Lithium dendrites are precipitated on the lithium-containing metal layer with this rough surface. These lithium dendrites continuously grow during the charge and discharge process, which may cause a short circuit between the positive and negative electrodes.

[0006]

[0007] The problem to be solved by the present invention is to provide a lithium metal battery with improved life characteristics and stability by introducing a protective layer on the negative electrode.

[0008]

[0009] A negative electrode for a lithium metal battery according to the present invention may include a negative electrode current collector; and a polymer protective layer on the negative electrode current collector. The polymer protective layer may include an ion-conductive polymer and a zwitterionic salt.

[0010] A lithium secondary battery according to another concept of the present invention may include a positive electrode including a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector; an anode according to any one of claims 1 to 10; and an electrolyte layer interposed between the positive electrode and the negative electrode.

[0011] A method for manufacturing a lithium secondary battery according to another concept of the present invention may include manufacturing a positive electrode; manufacturing an anode; and manufacturing an electrolyte layer between the positive electrode and the anode. Manufacturing the negative electrode may include preparing a negative electrode current collector; and coating a mixed solution of an ion-conductive polymer and a zwitterionic salt on the negative electrode current collector to form a polymer protective layer.

[0012]

[0013] According to embodiments of the present invention, a polymer protective layer can be introduced to induce uniform lithium deposition on the negative electrode current collector and prevent lithium dendrite growth. Consequently, a lithium metal battery with improved lifespan and stability can be provided.

[0014]

[0015] Figures 1 and 2 are cross-sectional views schematically showing a lithium metal battery.

[0016] FIGS. 3 and 4 are cross-sectional views showing lithium metal batteries according to embodiments of the present invention.

[0017] Figure 5 is an enlarged view of area M of Figure 4.

[0018] Figures 6 and 7 are cross-sectional views showing a lithium metal battery according to a comparative example of the present invention.

[0019] Figure 8 is an enlarged view of area N of Figure 7.

[0020] Figure 9 is for explaining a cathode according to embodiments of the present invention.

[0021] Figure 10 is for explaining a cathode according to a comparative example of the present invention.

[0022] Figure 11 is for explaining a cathode according to embodiments of the present invention.

[0023]

[0024] The present inventive concept described below is capable of various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present inventive concept to specific embodiments, but rather to encompass all modifications, equivalents, or alternatives within the technical scope of the present inventive concept.

[0025] The terminology used below is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. Hereinafter, the terms "comprises" or "has" and the like are intended to indicate the presence of a feature, number, step, operation, component, part, ingredient, material, or combination thereof described in the specification, but should be understood to not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, ingredients, materials, or combinations thereof. The " / " used below may be interpreted as "and" or "or" depending on the context.

[0026] In order to clearly express various layers and regions in the drawings, the thickness is shown enlarged or reduced. Similar parts are designated by the same drawing reference numerals throughout the specification. When a part such as a layer, film, region, or plate is said to be "on" or "above" another part throughout the specification, this includes not only cases where it is directly above the other part, but also cases where there is another part in between. Terms such as first, second, etc. may be used throughout the specification to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. In this specification and the drawings, components having substantially the same functional configuration are referred to by the same reference numerals, and redundant descriptions are omitted.

[0027] In the present disclosure, the "size" of a particle refers to, for example, the "particle diameter" of the particle. The "particle diameter" of a particle refers to the average diameter when the particle is spherical, and refers to the average major axis length when the particle is non-spherical. The particle diameter of a particle can be measured using a particle size analyzer (PSA). The "particle diameter" of a particle refers to, for example, the average particle diameter. The average particle diameter is, for example, the median particle diameter (D50). The median particle diameter (D50) is the size of a particle corresponding to 50% of the cumulative volume, calculated from the side of particles having a small particle size in a size distribution of particles measured by, for example, laser diffraction.

[0028] In this disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states.

[0029] In this disclosure, “alloy” means a mixture of two or more metals.

[0030] In the present disclosure, “positive electrode material” means a positive electrode material capable of undergoing lithiation and delithiation.

[0031] In the present disclosure, “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0032] In the present disclosure, “lithiation” and “lithiating” mean a process of adding lithium to a positive electrode active material or a negative electrode active material.

[0033] In the present disclosure, “delithiation” and “delithiate” mean a process of removing lithium from a positive electrode active material or a negative electrode active material.

[0034] In this disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery.

[0035] In this disclosure, “discharging” and “discharging” mean the process of removing electrochemical energy from a battery.

[0036] In the present disclosure, “positive electrode” and “cathode” mean an electrode at which electrochemical reduction and lithiation occur during a discharge process.

[0037] In the present disclosure, “cathode” and “anode” mean electrodes where electrochemical oxidation and delithiation occur during a discharge process.

[0038]

[0039] FIG. 1 is a cross-sectional view of a lithium metal battery according to one embodiment of the present invention. Referring to FIG. 1, the lithium metal battery according to one embodiment includes a cathode layer (CTL), an anode layer (ANL) facing the cathode layer (CTL), and an electrolyte layer (ELI) disposed between the cathode layer (CTL) and the anode layer (ANL). However, the present invention is not limited thereto, and the lithium metal battery may further include an additional functional layer, such as an adhesion enhancing layer, disposed between each layer.

[0040] Fig. 2 is a cross-sectional view of a lithium metal battery according to one embodiment of the present invention. As shown in Fig. 1, in a non-cathode structure in which a lithium metal layer (LML) is omitted from the cathode, a lithium metal layer (LML) can be formed according to a charge / discharge process.

[0041] In one embodiment, the cathode layer (CTL) may include a cathode current collector (COL1) and a cathode active material layer (AML1) disposed on the cathode current collector (COL1). The cathode active material layer (AML1) may include a cathode active material, a conductive material, and a binder.

[0042] The positive electrode current collector (COL1) can provide a reference surface on which the positive electrode active material layer (AML1) is disposed. The positive electrode current collector can include a plate or foil containing, for example, 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.

[0043] Meanwhile, unlike that illustrated in FIG. 1, in one embodiment of the present invention, the positive electrode current collector (COL1) may be omitted. Although not illustrated, a carbon layer having a thickness of 0.1 μm to 4 μm may be additionally disposed between the positive electrode current collector (COL1) and the positive electrode active material layer (AML1) to increase the bonding strength between the positive electrode current collector (COL1) and the positive electrode active material layer.

[0044] The cathode active material is a material that can reversibly absorb and desorb lithium ions. The cathode active material may include, but is not necessarily limited to, lithium transition metal oxides such as lithium cobalt oxide (LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), lithium manganate, and lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide. The cathode active materials may be used alone or as a mixture of two or more.

[0045] Lithium transition metal oxides include, for example, Li a A 1-b B b D2(0.90≤a≤1, 0≤b≤0.5), Li a E 1-b B b O 2-c D c (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05), LiE 2-b B b O 4-c D c (0≤b≤0.5, 0≤c≤0.05), Li a Ni 1-b-c Co b B c D α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Ni 1-b-c Co b B c O 2-α F α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Ni 1-b-c Mn b B c D α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α≤2), Li a Ni 1-b-c Mn b B c O 2-α F α (0.90≤a≤1, 0≤b≤0.5, 0≤c≤0.05, 0<α<2), Li a Ni b E c G d O2(0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1), Li a Ni b Co c Mn d GeO2(0.90≤a≤1, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0.001≤e≤0.1), Li a NiG bO2(0.9≤a≤1, 0.001≤b≤0.1), Li a CoG b O2(0.90≤a≤1, 0.001≤b≤0.1), Li a MnG b O2(0.90≤a≤1, 0.001≤b≤0.1), Li a Mn2GbO4(0.90≤a≤1, 0.001≤b≤0.1), QO2, QS2, LiQS2, V2O5, LiV2O5, LiIO2, LiNiVO4, Li 3-f J2(PO4)3(0≤f≤2), Li 3-f A compound represented by any one of Fe2(PO4)3(0≤f≤2), LiFePO4. In these compounds, the capital letter “A” is Ni, Co, Mn, or a combination thereof, the capital letter “B” is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof, the capital letter “D” is O, F, S, P, or a combination thereof, the capital letter “E” is Co, Mn, or a combination thereof, the capital letter “F” is F, S, P, or a combination thereof, the capital letter “G” is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof, the capital letter “Q” is Ti, Mo, Mn, or a combination thereof, the capital letter “I” is Cr, V, Fe, Sc, Y, or a combination thereof, and the capital letter “J” is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0046] The cathode active material may include, for example, a lithium salt of a transition metal oxide having a layered rock salt type structure among the lithium transition metal oxides described above. The "layered rock salt type structure" is, for example, a cubic rock salt type structure. <111> It is a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in a direction, and thereby each atomic layer forms a two-dimensional plane. The "cubic rock salt structure" refers to the sodium chloride type (NaCl type) structure, which is a type of crystal structure, and specifically refers to a structure in which the face-centered cubic lattice (fcc) formed by each cation and anion is arranged with a displacement of half of the ridge of the unit lattice. Lithium transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn z O2(NCM) (0 <x<1,0<y<1, 0<z<1, x+y+z=1) 등의 삼원계 리튬전이금속산화물일 수 있다. 양극 활물질이 층상암염형 구조를 갖는 삼원계 리튬전이금속산화물을 포함하는 경우, 전지의 에너지 밀도가 커지고 열안정성이 향상될 수 있다.

[0047] The above-described compound included in the positive electrode active material may be covered by a coating layer (not shown). The positive electrode active material may also be a mixture of the above-described compound and a compound to which a coating layer is added. Meanwhile, the coating layer added to the surface of the positive electrode active material may include, for example, an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of the coating elements below. The compound forming the coating layer is amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer may include, for example, Li2O-ZrO2 (LZO). The method for forming the coating layer is selected within a range that does not adversely affect the physical properties of the positive electrode active material. The method for forming the coating layer includes, for example, spray coating, dipping, etc.

[0048] When the cathode active material is a ternary lithium transition metal oxide such as NCA or NCM that contains nickel (Ni), the capacity density of the battery can be increased, thereby reducing metal dissolution of the cathode active material in a charged state. As a result, the cycle characteristics of the battery in a charged state are improved. Meanwhile, the “cycle characteristics” are a characteristic indicating the degree to which the battery deteriorates due to charge / discharge of the battery. A battery with high cycle characteristics may deteriorate less due to charge / discharge, while a battery with low cycle characteristics may deteriorate more due to charge / discharge.

[0049] The shape of the positive electrode active material may include particle shapes such as a sphere or an ellipsoid, for example. The particle size and content of the positive electrode active material are not particularly limited.

[0050] The positive electrode active material layer (AML1) may include a conductive material. The conductive material can increase the conductivity of the positive electrode active material by providing conductivity without causing a chemical change in the all-solid-state battery. The conductive material may include a carbon-based material. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0051] The positive electrode active material layer (AML1) may further include a binder. The binder may include a material for binding the positive electrode active material, conductive material, etc. included in the positive electrode active material layer (AML1) and improving bonding strength with the positive electrode current collector (COL1). The binder serves to ensure that the positive electrode active material particles adhere well to each other and also to ensure that the positive electrode active material adheres well to the positive electrode current collector (COL1). Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0052] An electrolyte layer (ELI) may be provided between the cathode layer (CTL) and the cathode layer (ANL). Referring to FIG. 3, the electrolyte layer (ELI) may include a separator (SEP) and an electrolyte (ELL). In one embodiment, the electrolyte (ELL) may include at least one selected from a liquid electrolyte, a solid electrolyte, and a gel polymer electrolyte. In some cases, the separator (SEP) may be omitted.

[0053] A separator (SEP) may be present between the cathode layer (CTL) and the anode layer (ANL). The separator may be a multilayer film made of polyethylene, polypropylene, polyvinylidene fluoride, or two or more layers thereof. Furthermore, mixed multilayer films, such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator, may also be used.

[0054] A separator (SEP) may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0055] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, 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 thereof.

[0056] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0057] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0058] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0059] In one embodiment, the electrolyte (ELL) may be a liquid electrolyte. The liquid electrolyte may include a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0060] The above non-aqueous organic solvent may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0061] Examples of the above carbonate solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0062] Ester solvents that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0063] Examples of ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of ketone solvents that can be used include cyclohexanone. Examples of alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, 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 and 1,4-dioxolane; and sulfolanes.

[0064] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0065] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0066] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. 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+1SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium bis(oxalato)borate (LiBOB).

[0067] In one embodiment, the electrolyte (ELL) may be a gel polymer electrolyte. The gel polymer electrolyte may include a crosslinked polymer. The crosslinkable monomer may form a crosslinked network. The gel polymer electrolyte may further include a crosslinking agent, a photoinitiator, etc. to assist in crosslinking of the crosslinkable monomer. The crosslinking monomer, crosslinking agent, initiator, etc. are not particularly limited as long as they are commonly used in the art. Methods for forming the gel polymer electrolyte include curing using heat, UV, or high-energy radiation.

[0068] Cross-linked polymers form a cross-linked network, and a liquid electrolyte can be introduced into the formed cross-linked network. By introducing the liquid electrolyte into the cross-linked network, electrolyte exposure on the electrode surface can be minimized and lithium ion flow throughout the electrode can be ensured.

[0069] The composition of the electrolyte may be substantially identical to the liquid electrolyte described above. The liquid electrolyte can be incorporated into the cross-linked network of the gel polymer electrolyte, thereby enhancing stability. This can suppress electrochemical side reactions and electrolyte decomposition reactions occurring at the positive and negative electrodes, thereby enhancing stability.

[0070]

[0071] Hereinafter, a negative electrode and a lithium metal battery including a polymer protective layer according to one embodiment will be described in detail. The lithium metal battery according to embodiments of the present invention may be a non-negative lithium metal battery in which a lithium metal layer is omitted.

[0072] A non-cathode lithium metal battery is a battery that uses only a cathode current collector without a cathode active material layer. When charging, lithium ions transferred from the cathode are deposited on the surface of the cathode current collector, and when discharging, the lithium deposited on the cathode current collector is eluted again and inserted into the cathode, thereby operating the battery.

[0073] Non-cathode lithium metal batteries can maximize energy density per volume / weight because they omit lithium metal, which is used as an anode active material. However, lithium metal precipitates during operation, and the resulting oxidation / reduction can lead to uneven current concentration, which can lead to the formation of lithium dendrites. Lithium dendrites not only cause lithium anode loss, reducing battery capacity and cycle life, but can also cause short circuits between the anode and cathode, posing safety concerns.

[0074] To address the aforementioned issues, various approaches have been proposed. For example, methods have been proposed to minimize contact between lithium and the electrolyte by introducing a protective film, thereby reducing side reactions or blocking dendrites.

[0075] However, even if a protective film is introduced, it only physically inhibits dendrite growth. Instead, it acts as a resistive layer, potentially increasing internal cell resistance. Consequently, it becomes difficult to maintain its shape during continuous charge / discharge, potentially negatively impacting long-term lifespan characteristics.

[0076] According to embodiments of the present invention, the performance of a lithium metal battery can be improved by introducing a polymer protective layer including an ion-conductive polymer and a zwitterionic salt.

[0077] Figures 3 and 4 are cross-sectional views of a lithium metal battery including a negative electrode according to embodiments of the present invention. The lithium metal battery according to the present invention may include a cathode layer (CTL), an negative electrode layer (ANL), and an electrolyte layer (ELI).

[0078] Referring to FIG. 3, the negative electrode (ANL) may include a polymer protective layer (PTL) on a negative electrode current collector (COL2). The positive electrode (CTL) may include a positive electrode active material layer (AML1) on a positive electrode current collector (COL1). In one embodiment, the electrolyte layer (ELI) may include a separator (SEP) and an electrolyte (ELL).

[0079] Referring to FIG. 4, the negative electrode (ANL) according to embodiments of the present invention may further include a lithium metal layer (LML) between the negative electrode current collector (COL2) and the polymer protective layer (PTL). The lithium metal layer (LML) may include lithium or a lithium alloy. Since the lithium metal layer (LML) is a metal layer including lithium, it may function as a lithium reservoir, for example. The lithium alloy may be, but is not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The lithium metal layer (LML) may be made of one of these alloys or lithium, or may be made of several types of alloys. The lithium metal layer (LML) may be, for example, a plated layer. A lithium metal layer (LML) may be deposited on a negative electrode current collector (COL2), for example, during the charging process of a secondary battery. When a polymer protective layer (PTL) is included, the lithium metal layer (LML) may be deposited between the polymer protective layer (PTL) and the negative electrode current collector (COL2).

[0080] In one embodiment, the polymer protective layer (PTL) may include a first side facing the negative current collector (COL2) and a second side facing the electrolyte layer (ELI). The lithium concentration of the first side may be greater than the lithium concentration of the second side. Meanwhile, the lithium concentration may refer to the amount of lithium metal deposited per unit volume / area. That is, the lithium metal may be mainly deposited between the polymer protective layer (PTL) and the negative current collector (COL2).

[0081] FIG. 5 is an enlarged view of area M of FIG. 4. Referring to FIG. 5, a lithium metal layer (LML) may be formed between a current collector (COL2) and a polymer protective layer (PTL). The lithium metal layer (LML) may have a first thickness (TK). The first thickness (TK) may be defined as the length from the negative current collector to the most protruding peak based on the second direction (D2). The first thickness (TK) is not particularly limited, but may be, for example, 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the first thickness (TK) of the lithium metal layer (LML) is too thin, it may be difficult for the lithium metal layer (LML) to perform the role of a lithium reservoir. If the first thickness (TK) of the lithium metal layer (LML) is excessively thick, the mass and volume of the secondary battery may increase, and the cycle characteristics of the secondary battery may rather deteriorate. The negative electrode (ANL) according to embodiments of the present invention includes a polymer protective layer (PTL), so that the lithium metal layer (LML) can be uniformly deposited on the negative electrode current collector (COL2).

[0082] In another embodiment of the present invention, a lithium metal layer (LML) within the negative electrode layer (ANL) may be provided between the negative electrode current collector (COL2) and the polymer protective layer (PTL) before assembling the battery. When the lithium metal layer (LML) is disposed before assembling the battery, the lithium metal layer (LML) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (COL2) and the polymer protective layer (PTL) before assembling the secondary battery.

[0083] When a lithium metal layer (LML) is deposited by charging after assembly of the battery, the energy density of the battery can be increased because the lithium metal layer (LML) is not included during battery assembly. When the battery is charged, lithium can be deposited, for example, between the polymer protective layer (PTL) and the negative electrode current collector (COL2). A lithium metal layer (LML) can be formed by the deposited lithium.

[0084] The lithium metal layer (LML) can be mainly composed of lithium (i.e., metallic lithium). During discharge, lithium in the lithium metal layer (LML) can be ionized and move to the cathode layer (CTL). In other words, lithium can be used as an anode active material in a secondary battery. In addition, since the polymer protective layer (PTL) covers the lithium metal layer (LML), the polymer protective layer (PTL) can protect the lithium metal layer (LML) while suppressing the precipitation and growth of lithium dendrites. Therefore, the polymer protective layer (PTL) can suppress short-circuiting and capacity degradation of the secondary battery and improve the cycle characteristics of the secondary battery. In addition, the polymer protective layer (PTL) can protect the lithium metal layer (LML) while improving the lithium deposition density and ensuring that the lithium deposition layer is uniformly deposited.

[0085] Figures 6 and 7 are cross-sectional views of a lithium metal battery including a negative electrode according to a comparative example of the present invention.

[0086] Referring to Fig. 6, the negative electrode (ANL) according to the comparative example of the present invention omits the polymer protective layer on the negative electrode current collector (COL2). That is, the negative electrode current collector (COL2) can be in direct contact with the electrolyte layer (ELI). As shown in Fig. 7, a lithium metal layer (LML) can be formed between the electrolyte layer (ELI) and the negative electrode current collector (COL2). The lithium metal layer (LML) can be in direct contact with the electrolyte layer (ELI).

[0087] Figure 8 is an enlarged view of the N region of Figure 7. Referring to Figure 8, a lithium metal layer (LML) may be formed unevenly on the negative electrode current collector (COL2). That is, dendrites (DRT) may be formed, which may deteriorate cell performance.

[0088] Hereinafter, with reference to FIGS. 9 to 11, a polymer protective layer (PTL) according to an embodiment of the present invention will be described in detail.

[0089] The negative electrode according to embodiments of the present invention may include a polymer protective layer (PTL). The polymer protective layer (PTL) can physically suppress the uneven growth of a lithium metal layer (LML). The polymer protective layer (PTL) can ensure that the lithium metal layer (LML) is uniformly formed on the negative electrode current collector (COL2). Consequently, the lifespan characteristics of the battery can be improved.

[0090] Referring to FIG. 9, the polymer protective layer (PTL) may include an ion-conducting polymer (PLM). Since the polymer protective layer (PTL) includes the ion-conducting polymer (PLM), it can physically suppress the non-uniform growth of the lithium metal layer (LML). That is, the growth of lithium dendrites (DRT) can be reduced, thereby improving cell stability. In addition, since the ion-conducting polymer (PLM) has ion conductivity, it can provide a path for lithium salts in the electrolyte to move. The polymer protective layer has ion conductivity, which can generate a uniform lithium ion flow. In addition, it can maintain the lithium ion concentration on the negative electrode surface. As a result, lithium reduction can occur smoothly across the entire negative electrode surface, and the growth of lithium dendrites can be suppressed. The thickness of the polymer protective layer (PTL) may range from 0.5 μm to 10 μm, from 0.5 μm to 5 μm, from 1 μm to 7 μm, or from 1 μm to 3 μm. By having the above range, the polymer protective layer can physically inhibit dendrite growth without acting as an excessively resistant layer.

[0091] The ion conducting polymer (PLM) may be a polymer containing fluorine (F), nitrogen (N), oxygen (O), etc. More specifically, it may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene fluoride -co- hexafluoropropylene, PVdF-HFP), poly(diallyldimethylammonium bis(trufluoromethanesulfonyl)imide, PDDA-TFSI), poly(diallyldimethylammonium bis(fluorosulfonyl)imide, PDDA-FSI), polyacrylonitrile (PAN), and polyacrylic acid (PAA).

[0092] In one embodiment, the ion-conducting polymer (PLM) may include a copolymer of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP). The copolymerization ratio of PVdF and HFP may range from 6:4 to 8:2. As described above, when PVdF-HFP is used as the ion-conducting polymer (PLM), a polymer protective layer with improved physical and chemical stability and ionic conductivity can be provided. More specifically, polyvinylidene fluoride (PVdF) can provide mechanical properties, high chemical resistance, and electrochemical stability. In addition, when a hexafluoropropylene (HFP) copolymerization functional group is further included, a polymer protective layer (PTL) with improved ionic conductivity can be provided due to an increased free volume.

[0093] In one embodiment, the ion-conducting polymer may include poly(diallyldimethylammonium bis(trufluoromethanesulfonyl)imide, PDDA-TFSI. The electrostatic shielding effect of the ion-conducting polymer (PLM) can induce uniform deposition of lithium ions. In addition, the stability of the negative electrode interface can be improved through the SEI induced by anions. The mobility of cations can be improved by anion trapping. That is, the mobility of lithium ions can be improved.

[0094] Referring to Figure 9, the polymer protective layer may include a zwitterion salt (ZWI). Zwitterions are generally neutral, but may have different charges at different locations within the molecule, which may result in the formation of an electrical dipole. Zwitterion salts (ZWI) may include anionic and cationic functional groups.

[0095] In one embodiment, the cationic functional group is:

[0096] , , , and , and each of R1 to R6 is hydrogen (H), a C1-C6 alkyl group, or a C6-C 30 It can be an aryl group.

[0097] In one embodiment, the anionic functional group is sulfonate (SO3 - ), phosphate (PO4 - ), bis(fluorosulfonyl)imide (FSI) - ), and bis(trifluoromethanesulfonyl)imide (TFSI) - ) can be selected from.

[0098] A zwitterionic salt (ZWI) may have a cationic functional group and an anionic functional group linked to each other. The cationic and anionic functional groups may be linked by a hydrocarbon chain. Meanwhile, in the present specification, “ " can mean the location where it is connected.

[0099] For example, the zwitterionic salt may be N-methyl-N-(propane sulfonate)Pyrrolidinium (MPSP). Specifically, It can be displayed as follows.

[0100] The anionic functional group can maintain a uniform lithium ion concentration around the negative electrode interface. Conversely, when the lithium ion concentration is not uniform, the lithium metal layer (LML) may be formed primarily in areas with relatively short diffusion distances. In other words, the anionic functional group can maintain a uniform lithium ion concentration at the negative electrode interface, allowing the lithium metal layer (LML) to be formed more uniformly. In addition, the anionic functional group can bind relatively weakly to lithium ions. Since lithium ions can be easily separated, the mobility of lithium ions can be improved. Consequently, polarization phenomenon can be suppressed and lithium dendrite growth can be inhibited.

[0101] Referring to Fig. 10, when lithium metal is deposited on a portion of the negative electrode current collector (COL2), lithium ions may be concentrated around a localized area due to the electric field concentration. In other words, lithium metal may grow locally and form dendrites. The cationic functional group can disperse the area where lithium ions are deposited. As shown in Fig. 11, the polymer protective layer (PTL) can prevent the lithium metal layer (LML) from being concentrated in a localized area by including cationic functional groups.

[0102] The polymer protective layer (PTL) may include both an ion-conducting polymer (PLM) and a zwitterionic salt (ZWI). However, if an excessive amount of the zwitterionic salt (ZWI) is added to the polymer protective layer (PTL), aggregation may occur and resistance may increase. The weight ratio of the ion-conducting polymer (PLM) and the zwitterionic salt (ZWI) in the polymer protective layer (PTL) may be in the range of 10:1 to 1:3, 10:1 to 1:1, or 10:1 to 3:1. The content of the zwitterionic salt in the polymer protective layer may be 10 to 70 wt%, 10 to 50 wt%, or 10 to 30 wt%.

[0103] For example, using a polymer film as a protective layer on the negative electrode current collector can physically suppress lithium dendrites, but its effectiveness may be halved due to high resistance. Furthermore, adding a zwitterionic salt to the electrolyte can improve lithium ion concentration, but its effectiveness at the desired lithium deposition location may be halved.

[0104] In addition, when using an amphoteric polymer (poly zwitterion) containing an amphoteric functional group within the polymer repeating unit, it is difficult to expect the same level of effect as the embodiments of the present invention. For example, when using an amphoteric polymer (poly zwitterion) such as ammonium trifluoromethanesulfonylimide (Am-TFSI) as a polymer protective layer, the mechanical properties are low, making it impossible to exert a physical inhibition effect on lithium dendrites. Furthermore, the effect may be reduced because it overlaps with the role of the zwitterion salt (ZWI) contained in the polymer protective layer.

[0105] The polymer protective layer (PTL) according to embodiments of the present invention can achieve two effects simultaneously: physical inhibition of dendrites and uniform electrodeposition of lithium ions, including an ion-conducting polymer (PLM) and a zwitterionic salt (ZWI). More specifically, the polymer protective layer (PTL) can promote lithium salt dissociation. The polymer protective layer (PTL) can maintain a uniform lithium ion concentration at the negative electrode interface. The polymer protective layer (PTL) can disperse and electrodeposit lithium ions. As a result, a uniform lithium metal layer (LML) can be formed on the negative electrode current collector (COL2). The long-term life characteristics of a lithium metal battery can be improved.

[0106]

[0107] Hereinafter, a method for manufacturing a lithium metal battery of the present invention will be described. The method for manufacturing a lithium metal battery according to embodiments of the present invention may include manufacturing a positive electrode; manufacturing a negative electrode; and manufacturing an electrolyte layer between the positive electrode and the negative electrode.

[0108] More specifically, manufacturing the negative electrode may include preparing a negative electrode current collector; and coating a mixed solution of an ion-conductive polymer and a zwitterionic salt on the negative electrode current collector to form a polymer protective layer.

[0109] The description of ion-conducting polymers and zwitterionic salts can be applied equally to what has been described above.

[0110] To prepare a polymer protective layer, a mixed solution can be prepared by mixing an ion conductive polymer (PLM) and a zwitterionic salt (ZWI) in a certain weight ratio in an N-methyl-2-pyrrolidone (NMP) solvent. The weight ratio of the ion conductive polymer and the zwitterionic salt in the mixed solution can range from 10:1 to 1:3, from 10:1 to 1:1, or from 10:1 to 3:1. The content of the zwitterionic salt in the mixed solution can be from 10 to 70 wt%, from 10 to 50 wt%, or from 10 to 30 wt%.

[0111] The polymer protective layer can be formed on the negative electrode current collector by doctor blade casting. The thickness of the polymer protective layer can range from 0.5 μm to 10 μm, from 0.5 μm to 5 μm, from 1 μm to 7 μm, or from 1 μm to 3 μm. Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the examples are merely illustrative and the scope of the present invention is not limited thereto.

[0112]

[0113] Example 1: Lithium metal battery including a polymer protective layer

[0114] PVdf-HFP was used as the ion-conducting polymer, and MPSP was used as the zwitterionic salt. The ion-conducting polymer and zwitterionic salt were mixed in an NMP solvent at a weight ratio of 8:2 to prepare an 8% concentration mixed solution. The mixed solution was coated on an anode current collector to prepare an anode including a polymer protective layer approximately 2 μm thick.

[0115] LiNi as positive electrode active material x Co y Al zA positive electrode composition was obtained by mixing O2(x + y + z = 1, x>0.6), Super-P (Timcal Ltd) as a conductive material, PVdf (Solvay) as a binder, and N-methylpyrrolidone. The mixing weight ratio of the positive electrode active material, conductive material, and binder in the positive electrode composition was 95:3:2.

[0116] The above positive electrode composition was coated on the top of aluminum foil, dried at about 50°C, and the dried resultant was dried in a vacuum at about 120°C to manufacture a positive electrode.

[0117] A separator (PE; 20 μm) was placed between the positive and negative electrodes manufactured above, and a liquid electrolyte was injected and sealed within the battery to manufacture a lithium secondary battery (pouch cell).

[0118]

[0119] Example 2: Lithium metal battery including a polymer protective layer

[0120] A negative electrode was manufactured in the same manner as in Example 1, except that the ion-conducting polymer and the zwitterionic salt were mixed in a weight ratio of 5:5.

[0121]

[0122] Example 3: Lithium metal battery including a polymer protective layer

[0123] A negative electrode was manufactured in the same manner as in Example 1, except that the thickness of the polymer protective layer was increased to approximately 10 μm.

[0124]

[0125] Example 4: Lithium metal battery including a polymer protective layer

[0126] A negative electrode was manufactured in the same manner as in Example 1, except that the ion-conducting polymer was changed to PVdF.

[0127]

[0128] Example 5: Lithium metal battery including a polymer protective layer

[0129] A negative electrode was manufactured in the same manner as in Example 1, except that the ion-conducting polymer was changed to PDDA-TFSI.

[0130]

[0131] Comparative Example 1

[0132] A cathode was manufactured with the polymer protective layer omitted.

[0133] Comparative Example 2

[0134] A polymer protective layer was formed using PVdF-HFP as an ion-conducting polymer, but omitting the zwitterionic salt. Only the ion-conducting polymer was added to NMP solvent to prepare an 8% concentration mixed solution. A cathode including the polymer protective layer was prepared.

[0135] Comparative Example 3

[0136] A 10% concentration solution was prepared using PEO as an ion-conducting polymer and Acetonitrile as a solvent. The mixed solution was coated on a negative electrode current collector to prepare a negative electrode including a polymer protective layer.

[0137] Comparative Example 4

[0138] An 8% mixed solution was prepared using Am-TFSI (Ammonium trifluoromethanesulfonylimide), a polymer containing an amphoteric functional group, and DMF as a solvent. The mixed solution was coated on a negative electrode current collector to prepare a negative electrode including a polymer protective layer.

[0139] Comparative Example 5

[0140] Am-TFSI, a polymer containing amphoteric functional groups, was used, and MPSP was used as a zwitterionic salt. The polymer and zwitterionic salt were mixed in a DMF solvent at a weight ratio of 8:2 to prepare a mixed solution with a concentration of 8%. The mixed solution was coated on a negative electrode current collector to prepare a negative electrode including a polymer protective layer.

[0141] Comparative Example 6

[0142] A lithium metal battery was manufactured using MPSP as an additive in the electrolyte.

[0143]

[0144] Examples and comparative examples of the present invention are shown in Table 1 below.

[0145] Ion-conductive polymer Zwitterionic salt Mixing ratio (weight ratio) Thickness Remarks Example 1 PVdF-HFP MPSP 8:22 μm Example 2 PVdF-HFP MPSP 5:52 μm Mixing ratio change Example 3 PVdF-HFP MPSP 8:210 μm Thickness change Example 4 PVDF MPSP 8:22 μm Polymer change Example 5 PDDA-TFSI MPSP 8:22 μm Polymer change Comparative Example 1----Comparative Example 2 PVdF-HFP--2 μm Comparative Example 3 PEO--2 μm Comparative Example 4 Am-TFSI PZI--2 μm Poly-zwitterion use Comparative Example 5 Am-TFSI PZI MPSP 8:22 μm Poly-zwitterion use Comparative Example 6-MPSP--Used as electrolyte additive

[0146]

[0147] Evaluation Example 1: Life Characteristics Evaluation

[0148] The life characteristics of lithium metal batteries according to the examples and comparative examples of the present invention were evaluated and are shown in Table 2 below. The number of cycles until 80% performance was reached and the average efficiency at 100 cycles were shown, respectively.

[0149] Life (@ 80%)100 CYCAverage Efficiency (%)RemarksExample 120599.6Example 219199.4Example 318399.5Example 418699.4Example 517999.3Comparative Example 116398.6Comparative Example 216599.0Comparative Example 313198.0Comparative Example 414898.9Comparative Example 511198.7Comparative Example 69497.1

[0150] Referring to Table 2, it can be seen that the life characteristics of the lithium secondary batteries according to the embodiments of the present invention are generally improved compared to the comparative examples.

[0151] More specifically, in the case of Examples 1 to 5, it can be seen that the life characteristics are improved by including more amphoteric ion salts, unlike in Comparative Examples 1 to 4.

[0152] In Comparative Example 4, it can be seen that the effect is lower than in the examples because the amphoteric polymer (poly-zwitterion) Am-TFSI was used. In addition, as in Comparative Example 5, when the amphoteric polymer (poly-zwitterion) further includes a zwitterion salt, it can be seen that the effect is further reduced compared to Comparative Example 4. This means that the mechanical properties of the Am-TFSI polymer are weaker than those of PVdF-HFP, and when mixed with a zwitterion salt, the properties are offset by the functional groups of the polymer, thereby lowering the performance.

[0153] In addition, compared to Comparative Example 6, which used a zwitterionic salt as an electrolyte additive, the zwitterionic salt can be introduced into the cathode protective layer to be concentrated on the cathode, and as a result, improved performance can be confirmed.

Claims

1. Negative current collector; and Including a polymer protective layer on the above negative electrode collector, The above polymer protective layer: Containing an ion-conducting polymer and a zwitterionic salt, Cathode for lithium metal batteries.

2. In paragraph 1, The above amphoteric ionic salt comprises a cationic functional group and an anionic functional group, The above cationic functional group is, , , , and , and each of R1 to R6 is hydrogen (H), a C1-C6 alkyl group, or a C6-C 30 is an aryl group, The above anionic functional group is, Sulfonate (SO3) - ), phosphate (PO4 - ), bis(fluorosulfonyl)imide (FSI) - ), and bis(trifluoromethanesulfonyl)imide (TFSI) - ) selected from, Cathode for lithium metal batteries.

3. In paragraph 1, The thickness of the polymer protective layer is 1 μm to 7 μm, Cathode for lithium metal batteries.

4. In paragraph 1, The weight ratio of the ion-conducting polymer and the zwitterionic salt in the polymer protective layer is 10:1 to 1:

3. Cathode for lithium metal batteries.

5. In paragraph 1, Further comprising a lithium metal layer between the negative electrode current collector and the polymer protective layer, Cathode for lithium metal batteries.

6. In paragraph 5, The thickness of the lithium metal layer is 1 μm to 500 μm, Cathode for lithium metal batteries.

7. In paragraph 1, The above ion conductive polymer comprises at least one selected from the group consisting of PVdF, PVdF-HFP, PDDA-TFSI, PDDA-FSI, PAN, Poly acrylic acid (PAA), and PEO. Cathode for lithium metal batteries.

8. In paragraph 1, The above amphoteric ion salt is N-methyl-N-(propane sulfonate)Pyrrolidinium (MPSP), a negative electrode for a lithium metal battery.

9. In paragraph 1, The polymer protective layer further comprises a lithium salt, Cathode for lithium metal batteries.

10. A lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer on the positive current collector; an anode according to any one of claims 1 to 9; and an electrolyte layer interposed between the positive electrode and the negative electrode.

11. In paragraph 10, The above electrolyte layer comprises a separator and a liquid electrolyte. Lithium secondary battery.

12. In paragraph 10, The above electrolyte layer comprises a gel polymer electrolyte, Lithium secondary battery.

13. In paragraph 10, The above electrolyte layer comprises a solid electrolyte, Lithium secondary battery.

14. In paragraph 10, The polymer protective layer includes a first surface facing the negative electrode current collector; and a second surface facing the electrolyte layer, The lithium concentration of the first side is greater than the lithium concentration of the second side, Lithium secondary battery.

15. Manufacturing the positive electrode; Manufacturing a cathode; and Including manufacturing an electrolyte layer between the positive electrode and the negative electrode, Manufacturing the above cathode: Preparing a negative electrode collector; and Comprising forming a polymer protective layer by coating a mixed solution of an ion-conductive polymer and a zwitterionic salt on the negative electrode current collector. Method for manufacturing lithium secondary batteries.

16. In paragraph 15, The thickness of the polymer protective layer is 1 μm to 7 μm, Method for manufacturing lithium secondary batteries.

17. In paragraph 15, The weight ratio of the ion-conducting polymer and the zwitterionic salt in the mixed solution is 10:1 to 1:

3. Method for manufacturing lithium secondary batteries.

18. In paragraph 15, The above amphoteric ionic salt comprises a cationic functional group and an anionic functional group, The above cationic functional group is, , , , and , and each of R1 to R6 is hydrogen (H), a C1-C6 alkyl group, or a C6-C 30 is an aryl group, The above anionic functional group is, Sulfonate (SO3) - ), phosphate (PO4 - ), bis(fluorosulfonyl)imide (FSI) - ), and bis(trifluoromethanesulfonyl)imide (TFSI) - ) selected from, Method for manufacturing lithium secondary batteries.

19. In paragraph 15, A method for manufacturing a lithium secondary battery, wherein the above amphoteric ion salt is N-methyl-N-(propane sulfonate)Pyrrolidinium (MPSP).

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