Polymer protective layer comprising aromatic functional group, and negative electrode for lithium secondary battery comprising same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery comprising a protective layer. More specifically, the negative electrode comprises: a negative electrode current collector; and a protective layer on the negative electrode current collector, wherein the protective layer may include a first polymer. The first polymer includes a main chain comprising a chain-like hydrocarbon and a plurality of benzene derivatives connected to the main chain, wherein each of the plurality of benzene derivatives includes 2 to 4 benzene rings, and adjacent benzene rings may be connected by a single bond or may be fused by sharing carbon atoms.

Description

A polymer protective layer containing aromatic functional groups, and a negative electrode for a lithium secondary battery containing the same.

[0001] The present invention relates to a negative electrode protective layer for a lithium secondary battery, and more specifically, to a negative electrode-free battery comprising a polymer protective layer.

[0002] Currently available lithium-ion batteries primarily use carbon-based negative electrode active materials such as graphite. Recently, as the secondary battery industry expands into electric vehicles and energy storage devices, there is a demand for batteries with higher capacities.

[0003] Lithium metal, which has a higher theoretical capacity than carbon-based negative electrode active materials, can be used as a negative electrode active material. Furthermore, research is being conducted on negative electrode-free batteries in which only the negative current collector is used as the negative electrode, and lithium metal is used as the negative electrode active material by receiving lithium from the positive electrode through charging. Negative electrode-free batteries have an advantage in terms of high energy density as the negative electrode active material layer is omitted.

[0004] However, during the charging and discharging process of a negative electrode battery, a problem may occur where lithium transferred from the positive electrode is not uniformly deposited on the negative electrode current collector. Non-uniform deposition of lithium metal can form lithium dendrites, which can cause a short circuit between the positive and negative electrodes. As a result, the stability and lifespan characteristics of the battery may be degraded.

[0005]

[0006] The problem that the present invention aims to solve is to provide a negative electrode for a lithium secondary battery that suppresses lithium dendrites and induces uniform lithium electrodeposition.

[0007]

[0008] A negative electrode for a lithium secondary battery according to the concept of the present invention comprises a negative electrode current collector; and a protective layer on the negative electrode current collector, wherein the protective layer may comprise a first polymer. The first polymer comprises a main chain comprising a chain-type hydrocarbon and a plurality of benzene derivatives connected to the main chain, wherein each of the plurality of benzene derivatives comprises 2 to 4 benzene rings, and the benzene rings adjacent to each other may be connected by a single bond or fused by sharing carbon atoms. The thickness of the protective layer may be 0.5 μm to 10 μm.

[0009] A lithium secondary battery according to the concept of the present invention may include the negative electrode; the positive electrode; and an electrolyte layer interposed between the positive electrode and the negative electrode.

[0010]

[0011] The negative electrode for a lithium secondary battery according to the present invention comprises a polymer protective layer containing aromatic functional groups, thereby enabling lithium metal to be uniformly electrodeposited on the negative electrode current collector. By doing so, the present invention can suppress the formation of lithium dendrites and improve the lifespan characteristics of the battery.

[0012]

[0013] Figures 1 and 2 are schematic cross-sectional views of a lithium secondary battery.

[0014] FIGS. 3 and FIGS. 4 are cross-sectional views showing a lithium secondary battery according to embodiments of the present invention.

[0015] Figure 5 is an enlarged view of the M region of Figure 4.

[0016] FIGS. 6 and FIGS. 7 are cross-sectional views showing a lithium secondary battery according to a comparative example of the present invention.

[0017] Figure 8 is an enlarged view of the N region of Figure 7.

[0018] FIG. 9 is a cross-sectional view showing a cathode according to embodiments of the present invention.

[0019] FIGS. 10 to 12 are for illustrating a cathode according to embodiments of the present invention.

[0020] Figure 13 is an SEM image of a cathode according to a comparative example of the present invention.

[0021] FIG. 14 is an SEM image of a cathode according to one embodiment of the present invention.

[0022]

[0023] The present inventive concept described below is subject to various modifications and may have various embodiments, and 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, and it should be understood that it includes all modifications, equivalents, or substitutions that fall within the scope of the description of the present inventive concept.

[0024] The terms used below are used merely to describe specific embodiments and are not intended to limit the creative concept. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the following, terms such as "comprising" or "having" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, 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, components, materials, or combinations thereof. The " / " used below may be interpreted as "and" or "or" depending on the context.

[0025] In the drawings, thicknesses have been enlarged or reduced to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts. Throughout the specification, when a part such as a layer, film, region, or plate is described as being "on" or "above" another part, this includes not only cases where it is directly above another part but also cases where there is another part in between. Throughout the specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. Terms are used solely for the purpose of distinguishing one component from another. In this specification and drawings, components having substantially the same functional configuration are referred to by the same reference numerals to avoid redundant descriptions.

[0026] In the present disclosure, the "size" of a particle is, for example, the "particle diameter" of the particle. The "particle diameter" of the particle represents the average diameter when the particle is spherical and represents the average major axis length when the particle is non-spherical. The particle diameter of the particle can be measured using a particle size analyzer (PSA). The "particle diameter" of the particle is, 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 particle size corresponding to the 50% cumulative volume calculated from the side of the particle having a small particle size in the particle size distribution measured, for example, by laser diffraction.

[0027] In the present disclosure, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0028] In this disclosure, "alloy" means a mixture of two or more metals.

[0029] In the present disclosure, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0030] In the present disclosure, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0031] In the present disclosure, "lithiation" and "to lithiate" refer to the process of adding lithium to a positive electrode active material or a negative electrode active material.

[0032] In the present disclosure, "delithiation" and "to delithiate" refer to the process of removing lithium from a positive electrode active material or a negative electrode active material.

[0033] In this disclosure, "charge" and "to charge" refer to the process of providing electrochemical energy to a battery.

[0034] In this disclosure, "discharge" and "discharge" refer to the process of removing electrochemical energy from a battery.

[0035] In this disclosure, "anode" and "cathode" refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0036] In this disclosure, "cathode" and "anode" refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0037]

[0038] FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to one embodiment of the present invention. Referring to FIG. 1, a lithium secondary battery according to one embodiment includes a positive electrode layer (CTL), a negative electrode layer (ANL) facing the positive electrode layer (CTL), and an electrolyte layer (ELI) disposed between the positive electrode layer (CTL) and the negative electrode layer (ANL). However, the lithium secondary battery may further include an additional functional layer disposed between each layer, such as an adhesion enhancing layer.

[0039] FIG. 2 is a schematic cross-sectional view of a lithium secondary battery according to one embodiment of the present invention. As shown in FIG. 1, a lithium metal layer (LML) can be formed in a negative electrode structure in which the lithium metal layer (LML) is omitted, depending on the charging and discharging process.

[0040] In one embodiment, the positive layer (CTL) may include a positive current collector (COL1) and a positive active material layer (AML1) disposed on the positive current collector (COL1). The positive active material layer (AML1) may include a positive active material, a conductive material, and a binder.

[0041] The positive current collector (COL1) can provide a reference plane on which the positive active material layer (AML1) is placed. The positive current collector may include, for example, a plate or foil comprising indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0042] Meanwhile, unlike as illustrated in FIG. 1, the positive current collector (COL1) may be omitted in one embodiment of the present invention. Although not illustrated, a carbon layer with a thickness of 0.1 μm to 4 μm may be further disposed between the positive current collector (COL1) and the positive active material layer (AML1) to increase the bonding strength between the positive current collector (COL1) and the positive active material layer.

[0043] The positive electrode active material is a material capable of reversibly absorbing and desorbing lithium ions. The positive electrode active material may include, for example, 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, as well as nickel sulfide, copper sulfide, lithium sulfide, iron oxide, or vanadium oxide, but is not necessarily limited to these. The positive electrode active material may be a single material or a mixture of two or more materials.

[0044] Lithium transition metal oxides are, 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 Nor 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 Nor 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 Nor 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 b O2(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-fIt is a compound represented by any one of Fe2(PO4)3 (0≤f≤2) or LiFePO4. In such compounds, the uppercase “A” is Ni, Co, Mn, or a combination thereof; the uppercase “B” is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; the uppercase “D” is O, F, S, P, or a combination thereof; the uppercase “E” is Co, Mn, or a combination thereof; the uppercase “F” is F, S, P, or a combination thereof; the uppercase “G” is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; the uppercase “Q” is Ti, Mo, Mn, or a combination thereof; the uppercase “I” is Cr, V, Fe, Sc, Y, or a combination thereof; and the uppercase “J” is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

[0045] The positive electrode 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 and metal atomic layers are alternately and regularly arranged in a specific direction, thereby forming a two-dimensional plane for each atomic layer. The "cubic rock salt type structure" represents a sodium chloride (NaCl) type structure, which is a type of crystal structure; specifically, it exhibits a structure in which face-centered cubic lattices (fcc) formed by cations and anions, respectively, are offset from each other by half the ridge of the unit lattice. Lithium transition metal oxides having such a layered rock salt type structure are, for example, LiNi x Co y Al z O2(NCA) or LiNi x Co y Mn zO2(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.

[0046] The aforementioned compound contained 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 aforementioned compound and the compound to which the coating layer is added. Meanwhile, the coating layer added to the surface of the positive electrode active material may include, for example, oxides, hydroxides, oxyhydroxides, oxycarbonates, or hydroxycarbonates of the following coating elements. The compounds forming this coating layer are 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 is, for example, spray coating or immersion.

[0047] When the cathode active material is a ternary lithium transition metal oxide, such as NCA or NCM, containing nickel (Ni), it is possible to increase the capacity density of the battery and reduce metal leaching from the cathode active material during the charged state. Consequently, the cycle characteristics of the battery during the charged state are improved. Meanwhile, "cycle characteristics" refers to the degree of degradation of a battery due to charging and discharging; batteries with high cycle characteristics degrade less due to charging and discharging, while batteries with low cycle characteristics degrade more due to charging and discharging.

[0048] The shape of the positive electrode active material may include particle shapes such as spheres or ellipsoids. The particle size and content of the positive electrode active material are not particularly limited.

[0049] The positive active material layer (AML1) may include a conductive material. The conductive material can increase the conductivity of the positive active material by providing conductivity without causing chemical changes in the all-solid-state battery. The conductive material may include carbon-based materials. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0050] The positive active material layer (AML1) may further include a binder. The binder may include a material for binding the positive active material, conductive material, etc. contained in the positive active material layer (AML1) and for improving the bonding strength with the positive current collector (COL1). The binder serves to effectively bond the positive active material particles to each other and also to effectively bond the positive active material to the positive current collector (COL1). Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0051] An electrolyte layer (ELI) may be provided between the anode 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.

[0052] The separator (SEP) may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0053] The porous substrate may be a polymer membrane formed from any one of the following: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyacetal; polyamide; polyimide; polycarbonate; polyetherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene oxide; cyclic olefin copolymer; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0054] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0055] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include, but is not limited to, inorganic particles selected from SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0056] The above organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0057] In one embodiment, the electrolyte layer (ELI) may include a liquid electrolyte. The liquid electrolyte may include a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent may serve as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0058] The above-mentioned 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.

[0059] The above carbonate-based solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc.

[0060] Ester-based solvents such as methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, and caprolactone may be used.

[0061] As ether-based solvents, dibutyl ether, tetraglame, diglame, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. may be used. Additionally, as ketone-based solvents, cyclohexanone, etc. may be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. may be used, and as aprotic solvents, nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane; sulfolanes, etc. may be used.

[0062] The above-mentioned non-aqueous organic solvent can be used alone or in a mixture of two or more types.

[0063] In addition, when using a carbonate-based solvent, a mixture of cyclic carbonates and chain carbonates can be used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of 1:1 to 1:9.

[0064] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and facilitating the movement of lithium ions between the anode and cathode. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1It may include one or more selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0065] In one embodiment, the electrolyte layer (ELI) may comprise a gel polymer electrolyte. The gel polymer electrolyte may comprise a crosslinking polymer. A crosslinkable monomer may form a crosslinking network. The gel polymer electrolyte may further comprise a crosslinking agent, a photoinitiator, etc., to assist in the crosslinking of the crosslinkable monomer. The crosslinkable 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. The crosslinking polymer forms a crosslinking network, and a liquid electrolyte may be introduced into the formed crosslinking network. By introducing the liquid electrolyte into the crosslinking network, the exposure of the electrolyte to the electrode surface can be minimized, and a uniform lithium ion flow can be created throughout the electrode. The composition of the liquid electrolyte within the gel polymer electrolyte may be substantially the same as the liquid electrolyte described above. Stability may be improved by incorporating the liquid electrolyte into the crosslinking network. Stability can be improved by suppressing electrochemical side reactions and electrolyte decomposition reactions occurring at the anode and cathode.

[0066] In one embodiment, the electrolyte layer (ELI) may include a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x, 0≤x≤2, and one or more selected from. Sulfide-based solid electrolytes are produced by processing starting materials, such as Li2S or P2S5, by methods such as melt quenching or mechanical milling. Additionally, heat treatment may be performed after such processing. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. Furthermore, the solid electrolyte may include sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the sulfide-based solid electrolyte materials described above. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material comprising Li2S-P2S5 to form a solid electrolyte, the molar ratio of Li2S and P2S5 is, for example, in the range of Li2S : P2S5 = 20 : 80 to 90 : 10, 25 : 75 to 90 : 10, 30 : 70 to 70 : 30, and 40 : 60 to 60 : 40.

[0067] Sulfide-based solid electrolytes may include, for example, an argyrodite-type solid electrolyte represented by the following chemical formula A:

[0068] <Chemical Formula A>

[0069] Li + 12-n-x A n+ X 2- 6-x Y - x

[0070] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta; X is S, Se, or Te; Y is Cl, Br, I, F, CN, OCN, SCN, or N3; and 1≤n≤5, 0≤x≤2. Sulfide-based solid electrolytes are, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li7-x PS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x It may be an argyrodite-type compound containing one or more selected from 0≤x≤2. The sulfide-based solid electrolyte may be an argyrodite-type compound containing one or more selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0071] Alternatively, sulfide-based solid electrolytes are Li 7-a M a PS 6-c X c It may be an argyrodite-type compound containing (0≤a≤2, (0≤c≤2)). Here, X may be F, Br, Cl, or a combination thereof. M may be candium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), zinc (Zn), cadmium (Cd), mercury (Hg), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), arsenic (As), antimony (Sb), bismuth (Bi), or a combination thereof.

[0072] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or higher, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the solid electrolyte layer by Li can be effectively suppressed. The elastic modulus of the solid electrolyte may be, for example, 15 GPa to 35 GPa.

[0073]

[0074] Hereinafter, a negative electrode and a lithium secondary battery including a protective layer according to one embodiment will be described in detail. In this specification, a negative electrode lithium secondary battery may have substantially the same meaning as a lithium secondary battery, a lithium metal battery, or a negative electrode battery.

[0075] A lithium secondary battery according to embodiments of the present invention may be a negative electrode-free secondary battery in which a negative electrode active material layer is not present on a negative electrode current collector. For example, in a battery using lithium metal as a negative electrode material, the lithium metal layer on the negative electrode current collector may be omitted.

[0076] A negative electrode-free lithium secondary battery uses only a negative current collector without a negative active material layer. The battery operates through a process in which lithium ions transferred from the positive electrode are deposited on the surface of the negative current collector during charging, and the lithium deposited on the negative current collector is leached out and inserted into the positive electrode during discharging.

[0077] Anode-free batteries can maximize energy density per unit volume / weight of the battery because lithium metal, which is used as the anode active material, is omitted. However, lithium metal precipitated during operation can form lithium dendrites due to non-uniform current concentration during oxidation / reduction processes. Lithium dendrites cause losses in the lithium anode, which not only degrades the battery's capacity and lifespan but also cause short circuits between the anode and cathode, leading to stability issues.

[0078] By introducing a protective layer on the negative current collector, contact between lithium and the electrolyte can be minimized, thereby reducing side reactions or physically blocking dendrites. However, the protective layer may act as a resistive layer, potentially increasing the internal resistance of the cell. Furthermore, the chemical decomposition of functional groups within the polymer material contained in the protective layer can lead to the formation of Solid Electrolyte Interphase (SEI) and degrade functionality. Consequently, it becomes difficult to maintain performance during continuous charging and discharging processes, which may be disadvantageous in terms of long-term lifespan.

[0079] According to embodiments of the present invention, by introducing a polymer protective layer containing aromatic functional groups, it is possible to provide a negative electrode-free lithium secondary battery with improved performance and solve the above-mentioned problems.

[0080] FIGS. 3 and 4 are cross-sectional views of a lithium secondary battery including a negative electrode according to embodiments of the present invention. A lithium secondary battery according to the present invention may include a positive electrode layer (CTL), a negative electrode layer (ANL), and an electrolyte layer (ELI).

[0081] Referring to FIG. 3, the negative electrode (ANL) may include a protective layer (PTL) on a negative electrode current collector (COL2). The positive electrode (CTL) may include a positive 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).

[0082] 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 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 containing lithium, it may function as, for example, a lithium reservoir. The lithium alloy may be, for example, 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, but is not limited thereto; any alloy used as a lithium alloy in the art may be possible. The lithium metal layer (LML) may be composed of one of these alloys or lithium, or may be composed of various types of alloys. The lithium metal layer (LML) may be, for example, a plated layer. A lithium metal layer (LML) can be deposited on a negative current collector (COL2), for example, during the charging process of a secondary battery. If a protective layer (PTL) is included, the lithium metal layer (LML) can be deposited between the protective layer (PTL) and the negative current collector (COL2).

[0083] In one embodiment, the protective layer (PTL) may include a first surface facing the negative electrode current collector (COL2) and a second surface facing the electrolyte layer (ELI). The lithium concentration on the first surface may be greater than the lithium concentration on the second surface. Meanwhile, the lithium concentration may refer to the amount of lithium metal deposited per unit volume / area. That is, lithium metal may be deposited mainly between the protective layer (PTL) and the negative electrode current collector (COL2). In this way, lithium metal can be uniformly electrodeposited on the negative electrode current collector (COL2).

[0084] FIG. 5 is an enlarged view of the M region of FIG. 4. Referring to FIG. 5, a lithium metal layer (LML) may be formed between a current collector (COL2) and a 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 with respect to 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 excessively 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 actually deteriorate. The negative electrode (ANL) according to the embodiments of the present invention includes a protective layer (PTL), so that the lithium metal layer (LML) can be uniformly electrodeposited on the negative electrode current collector (COL2).

[0085] 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 protective layer (PTL) before the assembly of the battery. When the lithium metal layer (LML) is placed before the assembly of the battery, it acts as a lithium reservoir because the lithium metal layer (LML) is a metal layer containing lithium. For example, a lithium foil may be placed between the negative electrode current collector (COL2) and the protective layer (PTL) before the assembly of the secondary battery.

[0086] If a lithium metal layer (LML) is deposited by charging after the assembly of the battery, the energy density of the battery can be increased because the lithium metal layer (LML) is not included during the assembly of the battery. During the charging of the battery, lithium may be deposited, for example, between the protective layer (PTL) and the negative current collector (COL2). A lithium metal layer (LML) may be formed by the deposited lithium.

[0087] The lithium metal layer (LML) can be composed mainly 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 the negative electrode active material in a secondary battery. In addition, since the protective layer (PTL) covers the lithium metal layer (LML), the protective layer (PTL) can protect the lithium metal layer (LML) while simultaneously suppressing the precipitation growth of lithium dendrites. Therefore, the protective layer (PTL) can suppress short circuits and capacity degradation of the secondary battery and improve the cycle characteristics of the secondary battery. Furthermore, the protective layer (PTL) can protect the lithium metal layer (LML) while simultaneously improving the lithium electrodeposition density and ensuring that the lithium precipitation layer is uniformly electrodeposited.

[0088] FIGS. 6 and FIGS. 7 are cross-sectional views of a lithium secondary battery according to a comparative example of the present invention. Referring to FIG. 6, the negative electrode (ANL) according to the comparative example of the present invention has a protective layer (PTL) on the negative electrode current collector (COL2) omitted. That is, the negative electrode current collector (COL2) can come into 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). Thus, the lithium metal layer (LML) can come into direct contact with the electrolyte layer (ELI).

[0089] 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 current collector (COL2). Additionally, lithium dendrites (DRT) may be formed, which may degrade cell performance.

[0090] In addition, during the charging process of a non-anode battery, if the lithium ion concentration on the negative electrode surface is not uniform, a lithium metal layer (LML) may form mainly in areas with relatively short diffusion distances. When lithium ions are concentrated in areas with short diffusion distances, lithium dendrites may form. Consequently, long-term lifespan characteristics, such as short circuits, may be degraded.

[0091] FIG. 9 is a cross-sectional view showing a protective layer (PTL) according to embodiments of the present invention. Referring to FIG. 9, the protective layer (PTL) may include a first polymer (PLM) and an inorganic particle (IOG). Since the protective layer (PTL) has ion conductivity, it can form a channel for lithium ions to move through the electrolyte. By including the first polymer (PLM) in the protective layer (PTL), the mobility of lithium ions can be improved. The protective layer (PTL) may include a lithium salt. That is, the lithium salt in the electrolyte can move through the protective layer. Lithium ions can pass through the protective layer (PTL) and move to the negative electrode. As a result, lithium ions can be reduced and electrodeposited on the negative electrode current collector (COL2). In one embodiment, the ion conductivity of the protective layer may be 0.1 mS / cm to 10 mS / cm. This may be measured while the protective layer is impregnated in the electrolyte.

[0092] The inorganic particles (IOG) may include oxide-based or sulfide-based inorganic particles. By further including inorganic particles (IOG), the ion conductivity of the protective layer (PTL) can be improved.

[0093] For example, the inorganic particles (IOG) may include oxide-based solid electrolytes and / or sulfide-based solid electrolytes. More specifically, the oxide-based solid electrolyte is Li x La y Zr z A1 u O 12 (6≤x≤7, 1≤y≤5, 1≤z≤3, 0.1≤u≤1.0, and A1 is Ta, Al, Ga, or Nb), Li x Al y Ti z (PO4)3(1≤x≤2, 0.1≤y≤1, 1≤z≤2), Li x La y It may include at least one selected from TiO3 (0.1≤x≤1, 0.1≤y≤1). The sulfide-based solid electrolyte may include Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), and Li 7-x PS 6-x I x It may include at least one selected from a group consisting of (0≤x≤2).

[0094] Inorganic particles (IOGs) 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+1 It may include one or more lithium salts selected from SO2)(x and y are integers from 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0095] The thickness of the protective layer (PTL) may be 0.5 μm to 10 μm, 0.5 μm to 5 μm, 1 μm to 7 μm, or 1 μm to 3 μm. By having such a thickness, it is possible to physically suppress the non-uniform growth of the lithium metal layer while simultaneously satisfying high lithium ion conductivity.

[0096] As shown in FIG. 10, the first polymer (PLM) in the protective layer (PTL) is subjected to an electric field (E p It can be charged with a negative charge within. More specifically, the first polymer (PLM) can be charged as an anion in the charging environment of a lithium secondary battery. For example, the first polymer (PLM) can be charged as an anion within a voltage range of 2.0 to 3.5 V or 2.0 V to 2.5 V.

[0097] Figure 11 shows that lithium ions are uniformly distributed on the cathode interface. As shown in Figure 11, the first polymer (PLM) is negatively charged, which can maintain a uniform lithium ion concentration at the cathode interface.

[0098] FIG. 12 is a cross-sectional view showing the formation of a lithium metal layer (LML) on a negative electrode current collector (COL2). When lithium electrodeposition proceeds at the negative electrode, the lithium ions on the surface are consumed, and the lithium ion concentration on the surface may decrease. At this time, an anionic functional group can maintain a uniform lithium ion concentration at the negative electrode interface. As the lithium ion concentration is uniformly distributed on the negative electrode current collector (COL2), the lithium metal layer (LML) can be formed more uniformly. Consequently, in the charging environment of the battery, the first polymer (PLM) is negatively charged, which can improve the stability of the negative electrode interface.

[0099] Even if a polymer can maintain surface concentration by including anionic functional groups, the polymer may chemically decompose due to the strong reducing atmosphere of the charging environment. Due to the strong reactivity of lithium metal, functional groups within the polymer material may chemically decompose rather than become anionic. If the polymer within the protective layer (PTL) decomposes, it may form SEI or cause side reactions, acting as a type of resistance layer. Consequently, the protective layer (PTL) may not only fail to continuously maintain the performance originally required but may also exhibit adverse effects.

[0100] However, the cathode according to an embodiment of the present invention may include a first polymer (PLM). The first polymer (PLM) can induce reversible and uniform lithium electrodeposition even in a strong reducing atmosphere of the charging environment. That is, the first polymer (PLM) is configured to become anionic within the charging voltage range but not decompose, thereby improving the lifespan characteristics of the lithium secondary battery. Hereinafter, the structural features of the first polymer and the effects described above will be explained in more detail with reference to the chemical formula.

[0101] The first polymer (PLM) may include an aromatic group. For example, the first polymer (PLM) may be a polymer comprising a benzene derivative. The first polymer (PLM) may include a main chain comprising a chain-type hydrocarbon and a plurality of benzene derivatives connected to the main chain. More specifically, each of the benzene derivatives may include two to four benzene rings. The benzene rings adjacent to each other may be connected by a single bond or fused by sharing carbon atoms.

[0102] In this specification, benzene rings connected by a single bond may mean that two or more benzene rings are directly connected to each other through double or single bonds to form a ring assembly. For example, it may be a structure such as biphenyl, terphenyl, or quaterphenyl.

[0103] In this specification, the benzene rings being fused may mean that they are bonded by sharing two or more adjacent carbon atoms. For example, they may have structures such as naphthalene, anthracene, etc.

[0104] For example, the first polymer (PLM) can be expressed as shown in the following chemical formulas.

[0105] [Chemical Formula 1]

[0106]

[0107] [Chemical Formula 2]

[0108]

[0109] [Chemical Formula 3]

[0110]

[0111] In the above chemical formulas 1 to 3, n is an integer between 10 and 10,000, and R1 to R9 are each independently a hydrogen atom; a halogen atom; a C1-C6 alkyl group; a C6-C 30 aryl group; or C1-C 30 It can be a heterolink.

[0112] Number average molecular weight (M) of the first polymer (PLM) n ) may be in the range of 100,000 to 200,000 g / mol, 100,000 to 150,000 g / mol, or 140,000 to 180,000 g / mol.

[0113] Referring to Chemical Formulas 1 to 3 above, pi bonds within the benzene rings can be maintained through a structure in which adjacent benzene rings within the first polymer (PLM) are connected by single bonds or joined by sharing carbon atoms. Since the pi bonds within the benzene rings are maintained, aromatic functional groups may not decompose even in a strong reducing atmosphere. Aromatic functional groups may exist in a form that additionally stores electrons within the benzene rings. That is, in the charging environment of a lithium secondary battery, aromatic functional groups may become anionized but may not decompose. Consequently, they are maintained on the negative electrode surface without a decomposition reaction, thereby inducing reversible and uniform lithium electrodeposition.

[0114] In one embodiment, the first polymer can be represented by the following chemical formula 4.

[0115] [Chemical Formula 4]

[0116]

[0117] (In the above Chemical Formula 4, n is an integer between 10 and 10,000.)

[0118] The first polymer can be negatively charged in the charging environment of a lithium secondary battery and reduced as shown in Chemical Formula 4-1 below.

[0119] [Chemical Formula 4-1]

[0120]

[0121] In one embodiment, the first polymer can be represented by the following chemical formula 5.

[0122] [Chemical Formula 5]

[0123]

[0124] (In the above chemical formula 5, n is an integer between 10 and 10,000.)

[0125] The first polymer can be negatively charged in the charging environment of a lithium secondary battery and reduced as shown in Chemical Formula 5-1 below.

[0126] [Chemical Formula 5-1]

[0127]

[0128] In one embodiment, the first polymer can be represented by the following chemical formula 6.

[0129] [Chemical Formula 6]

[0130]

[0131] (In the above chemical formula 6, n is an integer between 10 and 10,000.)

[0132] The first polymer can be negatively charged in the charging environment of a lithium secondary battery and reduced as shown in Chemical Formula 6-1 below.

[0133] [Chemical Formula 6-1]

[0134]

[0135] As shown in Chemical Formulas 4-1, 5-1, and 6-1 above, the aromatic functional group of the first polymer (PLM) can be anionized during the charging process of a lithium secondary battery. Since the reduced aromatic functional group has a structure in which electrons exist within the pi bond (π-bond), it can maintain an overall negative charge while simultaneously maintaining the structural stability of the functional group. In other words, the aromatic functional group of the first polymer may not decompose even in a strong reducing atmosphere. Therefore, the protective layer (PTL) can maintain reversible and uniform lithium electrodeposition performance even after the lithium secondary battery undergoes multiple charge-discharge cycles. Furthermore, the reduced protective layer (PTL) can maintain the cation concentration on the negative electrode surface above a certain level. Specifically, the negatively charged benzene ring can maintain the cation concentration on the negative electrode surface through electrostatic interactions. Consequently, it is possible to provide a lithium secondary battery that forms a uniform lithium metal layer while simultaneously improving long-term life characteristics.

[0136] The creative idea described herein will be explained in more detail below through examples and comparative examples. However, the examples are merely illustrative and do not limit the scope of the creative idea described herein.

[0137] For example, each of the plurality of benzene derivatives connected to the main chain containing a chain-type hydrocarbon in the first polymer is , , , , , , , , and It may include a structure such as.

[0138]

[0139] Manufacturing of lithium secondary batteries

[0140] LiNi as the positive active material 88 Co 10A cathode composition was obtained by mixing Al2O2 with Super-P (Timcal Ltd.) as a conductive material, PVdF (Solvay) as a binder, and N-methylpyrrolidone. In the cathode composition, the weight ratio of the cathode active material, conductive material, and binder was 97:1.5:1.5.

[0141] The above positive active material was coated onto an aluminum foil and dried at 50°C, and then the dried product was dried under vacuum at approximately 120°C to manufacture a positive electrode.

[0142] A cathode according to the examples and comparative examples described below was prepared, a PE separator with a thickness of 18 μm was placed between the manufactured anode and cathode, and a liquid electrolyte in which 0.6 M LiBF4 and 0.6 M LiDFOB were dissolved in a solvent in which FEC and DEC were mixed in a volume ratio of 1:2 was injected into the battery and sealed to manufacture a lithium secondary battery (pouch cell).

[0143]

[0144] Example 1

[0145] It has the structure of Chemical Formula 4 below, and has a number average molecular weight (M n A polymer solution was prepared by dissolving a polymer with a g / mol content of 118,000 g in an N-methylpyrrolidone organic solvent at a ratio of 10 wt%, and a cathode was prepared by coating it onto a copper current collector with a thickness of 10 μm using a casting method and then drying it in an oven at 80°C to form a protective layer with a thickness of about 1.5 μm.

[0146] [Chemical Formula 4]

[0147]

[0148]

[0149] Example 2

[0150] A protective layer approximately 1.5 μm thick was formed on a 10 μm thick copper (Cu) current collector and used as a cathode. It has the structure of Chemical Formula 5 below, and has a number average molecular weight (M nA cathode was prepared in the same manner as in Example 1 above, except that a polymer corresponding to 162,000 g / mol was used.

[0151] [Chemical Formula 5]

[0152]

[0153]

[0154] Example 3

[0155] A protective layer approximately 1.5 μm thick was formed on a 10 μm thick copper (Cu) current collector and used as a cathode. It has the structure of Chemical Formula 6 below, and has a number average molecular weight (M n A cathode was prepared in the same manner as in Example 1 above, except that a polymer corresponding to 167,000 g / mol was used.

[0156] [Chemical Formula 6]

[0157]

[0158]

[0159] Example 4

[0160] It has the structure of Chemical Formula 4 below, and has a number average molecular weight (M n 10 wt% of a polymer with a molecular weight of 118,000 g / mol, and LLZTO (Li) with an average particle size (D50) of 0.5 μm. 6.4 La3Zr 1.4 Ta 0.6 O 12 A slurry solution for coating a cathode protective layer was prepared by dissolving 10 wt% of the powder in an N-methylpyrrolidone organic solvent. The slurry solution was coated onto a 10 μm thick copper current collector by casting, and then dried in an oven at 80°C to produce a cathode with a protective layer approximately 1.5 μm thick.

[0161] [Chemical Formula 4]

[0162]

[0163]

[0164] Example 5

[0165] A protective layer approximately 1.5 μm thick was formed on a copper (Cu) current collector and used as a cathode. It has the structure of Chemical Formula 5 below, and has a number average molecular weight (M n A cathode was prepared in the same manner as in Example 4 above, except that a polymer with a molecular weight of 162,000 g / mol was used.

[0166] [Chemical Formula 5]

[0167]

[0168]

[0169] Example 6

[0170] A protective layer approximately 1.5 μm thick was formed on a copper (Cu) current collector and used as a cathode. It has the structure of Chemical Formula 6 below, and has a number average molecular weight (M n A cathode was prepared in the same manner as in Example 4 above, except that a polymer with a molecular weight of 167,000 g / mol was used.

[0171] [Chemical Formula 6]

[0172]

[0173]

[0174] Example 7

[0175] A protective layer approximately 1.5 μm thick was formed on a copper (Cu) current collector and used as a cathode. It has the structure of Chemical Formula 5 below, and has a number average molecular weight (M n A cathode was prepared in the same manner as in Example 4 above, except that a polymer with a molecular weight of 162,000 g / mol was used and Lithium bis(oxalato)borate (LiBOB) was used as an inorganic particle.

[0176] [Chemical Formula 5]

[0177]

[0178]

[0179] Comparative Example 1

[0180] Without a separate protective layer, only a copper (Cu) current collector was used as the cathode.

[0181]

[0182] Comparative Example 2

[0183] An NMP solution containing 10 wt% of PVdF was coated onto a copper (Cu) current collector by casting, and a protective layer of about 1.5 μm thickness was formed and used as a cathode.

[0184]

[0185] Comparative Example 3

[0186] A polymer of the following chemical formula 7 (Poly(lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate), Poly(MTFSI)) containing anionic functional groups was coated on a copper (Cu) current collector in the same manner as in Comparative Example 2 to form a protective layer with a thickness of about 1.5 μm and used as a cathode.

[0187] [Chemical Formula 7]

[0188]

[0189]

[0190] Comparative Example 4

[0191] A protective layer was formed by coating a polymer of the following chemical formula 4 to a thickness of about 0.4 μm on a copper (Cu) current collector in the same manner as in Example 1, and the polymer was used as a cathode.

[0192] [Chemical Formula 4]

[0193]

[0194]

[0195]

[0196] Comparative Example 5

[0197] A protective layer was formed by coating a polymer of the following chemical formula 4 to a thickness of about 20 μm on a copper (Cu) current collector in the same manner as in Example 1, and the polymer was used as a cathode.

[0198] [Chemical Formula 4]

[0199]

[0200] The embodiments and comparative examples of the present invention are summarized in Table 1 below.

[0201] Polymer Material Inorganic Particle Thickness Example 1 Poly(2-vinylnaphthalene)-1.5μm Example 2 Poly(4-vinylbiphenyl)-1.5μm Example 3 Poly(2-vinylanthracene)-1.5μm Example 4 Poly(2-vinylnaphthalene)Li 6.4 La3Zr 1.4 Ta 0.6 O 12 1.5μm Example 5 Poly(4-vinylbiphenyl)Li 6.4 La3Zr 1.4 Ta 0.6 O 12 1.5μm Example 6 Poly(2-vinylanthracene)Li 6.4 La3Zr 1.4 Ta 0.6 O 12 1.5 μm Example 7 Poly(4-vinylbiphenyl)LiBOB 1.5 μm Comparative Example 1 --- Comparative Example 2 Poly(vinylidene fluoride) 1.5 μm Comparative Example 3 Poly(MTFSI) 1.5 μm Comparative Example 4 Poly(2-vinylnaphthalene) 0.4 μm Comparative Example 5 Poly(2-vinylnaphthalene) 20 μm

[0202]

[0203] Evaluation Example 1: Life Characteristics Evaluation

[0204] The lifespan characteristics of a cathode-free lithium secondary battery including a cathode according to the above examples and comparative examples were measured and are shown in Table 2 below.

[0205] Cycle characteristics are evaluated based on the number of cycles until the battery capacity decreases to 80%, and capacity retention rate is evaluated based on the remaining battery capacity after 100 cycles.

[0206] Cycle Characteristics (@ 80%) Capacity Retention Rate (%, 100 cycle) Example 1 17388.6 Example 2 18189.0 Example 3 17788.6 Example 4 21191.7 Example 5 25293.3 Example 6 23592.4 Example 7 22291.0 Comparative Example 1 16087.5 Comparative Example 2 13383.3 Comparative Example 3 14981.2 Comparative Example 4 15887.5 Comparative Example 5 110.2

[0207] Referring to Table 2, it can be seen that the secondary battery according to the example has improved cycle characteristics and capacity retention rate compared to the comparative example.

[0208] Specifically, it can be seen that Comparative Example 2 includes a protective layer but does not include anionically charged functional groups, resulting in relatively low performance. Additionally, it can be seen that the polymer of Comparative Example 3 can be anionically charged but does not include a stable chemical structure like the embodiments of the present invention, which is disadvantageous in terms of long-term lifespan characteristics.

[0209] In addition, Comparative Examples 4 and 5 include the same protective layer as Example 1, but it can be seen that the lifespan characteristics are relatively inferior. As in Comparative Example 4, when the thickness of the protective layer is too thin, it indicates that the protective layer does not perform its role properly. Furthermore, as in Comparative Example 5, when the thickness increases beyond a certain level, it acts as a resistive layer, which means that the lifespan characteristics are significantly degraded.

[0210]

[0211] Evaluation Example 2: Lithium electrodeposition shape on negative current collector

[0212] Figures 13 and 14 are SEM images showing the lithium electrodeposition shape of the cathode according to Comparative Example 1 and Example 5, respectively. Lithium corresponding to a charge amount of 0.1 mAh / cm² per unit area was electrodeposited on a cathode current collector coated with a protective layer. Specifically, in the case of Figure 14, the lithium secondary battery of Example 5 was charged and discharged to electrodeposit lithium on the cathode, and then the battery was disassembled and observed. Comparing Figures 13 and 14, it can be seen that in the case of the cathode equipped with a protective layer according to Example 5 of the present invention, the lithium metal layer is formed uniformly in a rounder and larger shape. In contrast, it can be seen that on the cathode according to Comparative Example 1, the lithium metal layer is formed unevenly in the form of thin dendrites. This implies that the lithium metal layer is formed stably and uniformly from the nucleation stage.

Claims

1. Cathode current collector; and It includes a protective layer on the above-mentioned negative current collector, The above protective layer comprises a first polymer, and The first polymer comprises a main chain containing a chain-type hydrocarbon and a plurality of benzene derivatives connected to the main chain, and Each of the above plurality of benzene derivatives comprises 2 to 4 benzene rings, and the benzene rings adjacent to each other are connected by a single bond or are fused by sharing carbon atoms, The thickness of the protective layer is 0.5 μm to 10 μm, Negative electrode for lithium secondary batteries.

2. In Paragraph 1, A negative electrode for a lithium secondary battery, wherein the first polymer is configured to be charged with a negative charge in a voltage range of 2.0 to 3.5 V.

3. In Paragraph 1, A lithium metal layer further comprising between the above-mentioned negative current collector and the above-mentioned protective layer, Negative electrode for lithium secondary batteries.

4. In Paragraph 3, The thickness of the lithium metal layer is 0.1 μm to 100 μm, Negative electrode for lithium secondary batteries.

5. In Paragraph 1, The above protective layer further comprises a lithium salt, Negative electrode for lithium secondary batteries.

6. In Paragraph 1, The ionic conductivity of the protective layer is 0.1 mS / cm to 10 mS / cm, Negative electrode for lithium secondary batteries.

7. In Paragraph 1, The first polymer is at least one of a compound represented by the following chemical formula 1, a compound represented by the following chemical formula 2, or a compound represented by the following chemical formula 3. Negative electrode for lithium secondary batteries: [Chemical Formula 1] In the above chemical formula 1, n is an integer between 10 and 10,000, and R1 to R7 are each independently a hydrogen atom; a halogen atom; a C1-C6 alkyl group; a C6-C 30 aryl group; or C1-C 30 It is a heterocyclic ring, [Chemical Formula 2] In the above chemical formula 2, n is an integer between 10 and 10,000, and R1 to R9 are each independently a hydrogen atom; a halogen atom; a C1-C6 alkyl group; a C6-C 30 aryl group; or C1-C 30 It is a heterocyclic ring, [Chemical Formula 3] In the above chemical formula 3, n is an integer between 10 and 10,000, and R1 to R9 each independently a hydrogen atom; a halogen atom; a C1-C6 alkyl group; a C6-C 30 aryl group; or C1-C 30 It is a heterocyclic ring.

8. In Paragraph 1, The first polymer is at least one of a compound represented by the following chemical formula 4, a compound represented by the following chemical formula 5, or a compound represented by the following chemical formula 6. Negative electrode for lithium secondary batteries: [Chemical Formula 4] In the above chemical formula 4, n is an integer between 10 and 10,000, and [Chemical Formula 5] In the above chemical formula 5, n is an integer between 10 and 10,000, and [Chemical Formula 6] In the above chemical formula 6, n is an integer between 10 and 10,000.

9. In Paragraph 1, The above polymer protective layer further comprises inorganic particles, Negative electrode for lithium secondary batteries.

10. In Paragraph 9, The above-mentioned inorganic particles are one or more lithium salts selected from LiPF6, LiBF4, LiCl, LiI, lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB), or, Li x La y Zr z A1 u O 12 (6≤x≤7, 1≤y≤5, 1≤z≤3, 0.1≤u≤1.0, and A1 is Ta, Al, Ga, or Nb), Li x Al y Ti z (PO4)3(1≤x≤2, 0.1≤y≤1, 1≤z≤2), Li x La y A solid electrolyte comprising at least one oxide-based electrolyte selected from TiO3 (0.1≤x≤1, 0.1≤y≤1), Negative electrode for lithium secondary batteries.

11. Cathode according to paragraph 1; Anode; and A electrolyte layer interposed between the anode and the cathode, Lithium secondary battery.

12. In Paragraph 11, The above electrolyte layer comprises a liquid electrolyte, a gel polymer electrolyte, or a combination thereof. Lithium secondary battery.

13. In Paragraph 11, The above electrolyte layer comprises a solid electrolyte, Lithium secondary battery.

14. In Paragraph 13, The above-mentioned body electrolyte comprises a sulfide-based solid electrolyte, Lithium secondary battery.

15. In Paragraph 11, The protective layer comprises a first surface facing the negative electrode current collector; and a second surface facing the electrolyte layer, wherein The lithium concentration of the first surface is greater than the lithium concentration of the second surface. Lithium secondary battery.

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