Lithium secondary battery and method for manufacturing same

Abstract

The present disclosure provides a lithium secondary battery and a method for manufacturing a lithium secondary battery. The lithium secondary battery according to the present disclosure includes a negative electrode and an electrolyte, wherein the negative electrode includes a current collector and a porous structure disposed on the current collector, and the electrolyte may include a combination of a first solvent containing a cyanide and a second solvent containing an acetamide.

Description

Lithium secondary battery and method for manufacturing the same

[0001] The present disclosure relates to a lithium secondary battery and a method for manufacturing the same.

[0002]

[0003] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0004] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode.

[0005] Currently commercially available lithium secondary batteries mainly use carbon-based negative electrode active materials such as graphite. Carbon-based negative electrode active materials do not change in volume during charging and discharging, so the stability of lithium secondary batteries is high. The theoretical electric capacity of graphite is small, about 372 mAh / g.

[0006] Lithium metal can be used as a negative electrode active material. Lithium metal has a very large theoretical electric capacity of approximately 3860 mAh / g. During charging and discharging, dendrites can form on the surface of lithium metal due to side reactions with the electrolyte, and as these dendrites grow, they can cause a short circuit between the positive and negative electrodes. Consequently, the lifespan characteristics and thermal stability of lithium metal batteries containing lithium metal are degraded.

[0007] There is a need for methods to improve the lifespan characteristics and thermal stability of lithium metal batteries containing lithium metal. Furthermore, numerous studies are being conducted on lithium metal batteries without a negative electrode active material coating on the negative electrode current collector to achieve higher energy density compared to conventional lithium secondary batteries. However, it has been reported that lithium metal batteries without a negative electrode active material coating on the current collector inevitably suffer from volume changes due to the direct deposition of lithium on the current collector during repeated charge and discharge cycles.

[0008] The information described above disclosed in the background technology of this invention is intended only to enhance understanding of the background of the present invention and may therefore include information that does not constitute prior art.

[0009]

[0010] One embodiment provides a lithium secondary battery and a method for manufacturing the same to solve the above technical problem.

[0011]

[0012] A lithium secondary battery according to one embodiment of the present invention for solving the above technical problem comprises a negative electrode and an electrolyte, wherein the negative electrode comprises a current collector and a porous structure disposed on the current collector, and the electrolyte may comprise a combination of a first solvent comprising cyanide and a second solvent comprising acetamide.

[0013] A method for manufacturing a lithium secondary battery according to an embodiment of the present invention for solving the above technical problem comprises the steps of preparing a negative electrode by arranging a porous structure on a current collector and supplying an electrolyte, wherein the electrolyte may comprise a combination of a first solvent comprising cyanide and a second solvent comprising acetamide.

[0014]

[0015] According to some embodiments of the present disclosure, the utilization rate of internal pores of a porous structure disposed on a cathode current collector can be increased.

[0016] According to some embodiments of the present disclosure, by forming a lithium-affinity surface film, the influence of an electric field can be reduced to prevent the top deposition of lithium dendrites.

[0017] According to some embodiments of the present disclosure, dendrite formation is suppressed during the charging and discharging process, thereby enabling the production of a lithium metal battery with improved capacity retention rate, lifespan characteristics, and thermal stability.

[0018] According to some embodiments of the present disclosure, complex processes such as sputtering that previously existed in the process of manufacturing a negative electrode in a method for manufacturing a lithium secondary battery can be replaced.

[0019] According to some embodiments of the present disclosure, a lithium-affinity surface film can be easily formed on the surface of a porous structure disposed on a negative electrode current collector by only reacting with an electrolyte during the formation step after manufacturing a lithium secondary battery cell.

[0020] However, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by those skilled in the art from the description of the invention below.

[0021]

[0022] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0023] Figure 1 shows the appearance of a negative electrode for a lithium secondary battery before the formation process according to one embodiment.

[0024] Figure 2 shows the appearance of a negative electrode for a lithium secondary battery after the formation process according to one embodiment.

[0025] Figure 3 shows a cross-sectional SEM image of a porous structure before the formation process according to one embodiment.

[0026] Figure 4 shows a cross-sectional SEM image of a porous structure after a formation process according to one embodiment.

[0027] Figure 5 shows the appearance of a lithium secondary battery without a negative electrode active material layer before charging.

[0028] Figure 6 shows the appearance of a lithium secondary battery after charging, without a negative electrode active material layer.

[0029] FIG. 7 shows the appearance of a lithium secondary battery before the formation process according to one embodiment.

[0030] FIG. 8 shows the appearance of a lithium secondary battery after a formation process according to one embodiment.

[0031] FIG. 9 is a flowchart illustrating an example of a method for manufacturing a lithium secondary battery according to the present disclosure.

[0032] FIG. 10 is a schematic diagram illustrating a lithium secondary battery according to one embodiment.

[0033] FIG. 11 is a schematic diagram illustrating a lithium secondary battery according to one embodiment.

[0034] FIG. 12 is a schematic diagram illustrating a lithium secondary battery according to one embodiment.

[0035] FIG. 13 is a schematic diagram illustrating a lithium secondary battery according to one embodiment.

[0036]

[0037] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0038] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0039] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0040] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0041] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0042] Methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, but suitable methods and materials are described herein. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0043] In this specification, 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 excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof.

[0044] In this specification, the term “combination of these” means a mixture or combination with one or more of the described components, and may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0045] In this specification, the term “and / or” means any combination of one or more items described in relation and all combinations thereof. In this specification, the term “or” means “and / or”.

[0046] In this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is directly above the other part, but also cases where there is another part in between.

[0047] In this specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another.

[0048] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0049] In this specification, "alloy" means a mixture of two or more metals.

[0050] In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0051] In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0052] In this specification, "lithiation" and "to lithiate" refer to the process of adding lithium to a positive electrode active material or a negative electrode active material.

[0053] In this specification, "delithiation" and "to delithiate" refer to the process of removing lithium from a positive electrode active material or a negative electrode active material.

[0054] In this specification, "charge" and "to charge" refer to the process of providing electrochemical energy to a battery.

[0055] In this specification, "discharge" and "discharge" refer to the process of removing electrochemical energy from a battery.

[0056] In this specification, "anode" and "cathode" refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0057] In this specification, "cathode" and "anode" refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0058] The term alkyl used in the formulas in this specification refers to a fully saturated branched or unbranched (or straight-chain or linear) hydrocarbon.

[0059] In this specification, non-limiting examples of alkyls include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, isopentyl, neopentyl, iso-amyl, n-hexyl, 3-methylhexyl, 2,2-dimethylpentyl, 2,3-dimethylpentyl, n-heptyl, etc.

[0060] In this specification, one or more hydrogen atoms of the alkyl group are a halogen atom, a C1-C20 alkyl group substituted with a halogen atom (e.g., CCF3, CHCF2, CH2F, CCl3, etc.), a C1-C20 alkoxy, a C2-C20 alkoxyalkyl, a hydroxyl group, a nitro group, a cyano group, an amino group, an amidino group, a hydrazine, a hydrazone, a carboxyl group or its salt, a sulfonyl group, a sulfamoyl group, a sulfonic acid group or its salt, a phosphoric acid or its salt, or a C1-C20 alkyl group, a C2-C20 alkenyl group, a C2-C20 alkynyl group, a C1-C20 heteroalkyl group, a C6-C20 aryl group, a C6-C20 arylalkyl group, a C6-C20 heteroaryl group, a C7-C20 heteroarylalkyl group. It can be substituted with a C6-C20 heteroaryloxy group, a C6-C20 heteroaryloxyalkyl group, or a C6-C20 heteroarylalkyl group.

[0061] In this specification, the term halogen atom includes fluorine, bromine, chlorine, iodine, etc.

[0062] In this specification, the term C1-C20 alkyl group substituted with a halogen atom refers to a C1-C20 alkyl group substituted with one or more halo groups, and non-limiting examples include polyhaloalkyl containing monohaloalkyl, dihaloalkyl, or perhaloalkyl.

[0063] In this specification, monohaloalkyl refers to a case where one iodine, bromine, chlorine, or fluorine is present in the alkyl group, and dihaloalkyl and polyhaloalkyl refer to alkyl groups having two or more identical or different halo atoms.

[0064] In this specification, the term aryl group used in chemical formulas refers to an aromatic hydrocarbon comprising one or more rings, used alone or in combination.

[0065] In this specification, the term aryl also includes a group in which an aromatic ring is fused to one or more cycloalkyl rings.

[0066] In this specification, non-limiting examples of aryls include phenyl, naphthyl, tetrahydronaphthyl, etc.

[0067] In this specification, one or more hydrogen atoms of the aryl group may be substituted with substituents similar to those in the case of the alkyl group described above.

[0068] In this specification, one or more hydrogen atoms of the carbon ring can be substituted with a substituent similar to that of the alkyl group described above.

[0069] Exemplary embodiments will be described in more detail below.

[0070]

[0071] Cathode and Electrolyte

[0072] FIG. 1 shows the appearance (100) of a negative electrode for a lithium secondary battery before the formation process according to one embodiment. FIG. 2 also shows the appearance (101) of a negative electrode for a lithium secondary battery after the formation process according to one embodiment.

[0073] Referring to FIG. 1, a lithium secondary battery according to one embodiment of the present invention includes a negative electrode (110) and an electrolyte (120) surrounding the negative electrode (110), and the negative electrode (110) may include a current collector (112) and a porous structure (114) disposed on the current collector (112).

[0074] In one embodiment, the porous structure (114) may completely cover the surface of the current collector (112). Additionally, the porous structure (114) may include a plurality of pores for capturing lithium (or lithium ions). For example, on a volume basis, the porosity of the porous structure (114) may be 20% to 70%, 20% to 60%, or 30% to 60%.

[0075] During the charging and discharging of a lithium secondary battery according to one embodiment, lithium is captured in a porous structure (114) disposed on a current collector (112), thereby minimizing volume change of the lithium metal battery. Specifically, as the lithium secondary battery is charged, lithium ions contained in the electrolyte (120) can be electrodeposited on the porous structure (114).

[0076] The thickness of the porous structure (114) may be, for example, 0.1 μm to 100 μm, 0.1 μm to 80 μm, 1 μm to 80 μm, or 10 μm to 80 μm, but is not necessarily limited to these ranges and can be adjusted according to the required shape, capacity, etc. of the lithium secondary battery. If the thickness of the porous structure (114) increases excessively, the energy density of the lithium secondary battery may decrease.

[0077] In one embodiment, the porous structure (114) may be formed by coating the surface of a current collector (112) with a powder comprising carbon black, graphite, hard carbon, titanium dioxide (TiO2) oxide, molybdenum disulfide (MoS2), vanadium dioxide (VO2), vanadium pentoxide (V2O5), molybdenum dioxide (MoO2), titanium disulfide (TiS2), or a combination thereof, together with a polymer binder. For example, the porous structure (114) may be formed by slurry casting or slip casting a carbon black material onto the surface of a current collector (112) composed of copper foil.

[0078] In one embodiment, the electrolyte (120) surrounding the cathode (110) may comprise a combination of a first solvent comprising cyanide and a second solvent comprising acetamide. According to one embodiment, the mass ratio of the first solvent to the second solvent in the electrolyte (120) may be 5:95 to 40:60.

[0079] Specifically, the first solvent may include butyronitrile, acetonitrile, propionitrile, valeronitrile, isovaleronitrile, isobutyronitrile, hexanenitrile, heptanenitrile, 3-methoxypropionitrile, 5-ketohexanenitrile, methyl cyanoformate, ethyl cyanoformate, methyl cyanoacetate, ethyl cyanoacetate, or any combination thereof.

[0080] In addition, the second solvent may include any one of 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA), 2,2-difluoro-N,N-dimethylacetamide, 2-Fluoro-N,N-dimethylacetamide, 2,2,2-trifluoro-N,N-diethylacetamide (FDEA), 2,2-difluoro-N,N-diethylacetamide, 2-Fluoro-N,N-diethylacetamide, or any combination thereof.

[0081] In one embodiment, the second solvent may include at least one Fluoro group as a functional group. The second solvent including a Fluoro group as a functional group may facilitate a reduction decomposition reaction on the porous structure (114) compared to an acetamide-based solvent that does not include a Fluoro group as a functional group. Through this, an SEI film can be easily formed on the surface of the porous structure (114).

[0082] In one embodiment, the electrolyte (120) may further comprise a lithium salt containing boron. Here, the lithium salt may comprise any one of LiBF4, LiDFOB, LiBOB, or any combination thereof. For example, the concentration of the lithium salt may be 0.1 M to 2.0 M, 0.5 M to 1.5 M, or 0.1 M to 5.0 M.

[0083] The electrolyte (120) may include, for example, a liquid electrolyte, a solid electrolyte, a gel electrolyte, or any combination thereof.

[0084] In one embodiment, the liquid electrolyte may be prepared by dissolving a lithium salt containing boron in an organic solvent. The organic solvent may include the first solvent or the second solvent, and any organic solvent used in the art may be used.

[0085] In one embodiment, the solid electrolyte is, for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a polymeric solid electrolyte, or any combination thereof.

[0086] Solid electrolytes are, for example, oxide-based solid electrolytes. Oxide-based solid electrolytes are Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, 0≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(O≤x<1, O≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al yTi z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 It is one or more selected from (M = Te, Nb, or Zr, where x is an integer from 1 to 10). Solid electrolytes are produced by sintering methods, etc. For example, oxide-based solid electrolytes include Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a MaO 12 It is a garnet-type solid electrolyte selected from (M doped LLZO, M=Ga, W, Nb, Ta, or Al, x is an integer from 1 to 10).

[0087] Sulfide-based solid electrolytes may comprise, for example, lithium sulfide, silicon sulfide, phosphorus sulfide, boron sulfide, or any combination thereof. Sulfide-based solid electrolyte particles may comprise Li2S, P2S5, SiS2, GeS2, B2S3, or any combination thereof. Sulfide-based solid electrolyte particles may be Li2S or P2S5. Sulfide-based solid electrolyte particles are known to have high lithium ion conductivity compared to other inorganic compounds. For example, sulfide-based solid electrolytes comprise Li2S and P2S5. When the sulfide solid electrolyte material constituting the sulfide-based solid electrolyte comprises Li2S-P2S5, the mixed molar ratio of Li2S to P2S5 may be, for example, in the range of about 50:50 to about 90:10. Additionally, Li3PO4, halogens, halogen compounds, Li 2+2x Zn 1-x GeO4("LISICON", 0≤x<1), Li 3+y PO 4-x N x ("LIPON", 0 <x<4, 0<y<3), Li 3.25 Ge 0.25 P 0.75An inorganic solid electrolyte prepared by adding S4 ("ThioLISICON"), Li2O-Al2O3-TiO2-P2O5 ("LATP"), etc., to an inorganic solid electrolyte of Li2S-P2S5, SiS2, GeS2, B2S3, or a combination thereof can be used as a sulfide solid electrolyte. Non-limiting examples of sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiX (X = 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-ZmSn (0 <m<10, 0<n<10, Z=Ge, Zn 또는 Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, 및 Li2S-SiS2-Li p MO q (0 <p<10, 0<q<10, M=P, Si, Ge, B, Al, Ga 또는 In)을 포함한다. 이와 관련하여, 황화물계 고체전해질 재료는 황화물계 고체전해질 물질의 원료 시작 물질(예를 들면, Li2S, P2S5, 등)을 용융 담금질법(melt quenching method), 기계적 밀링법 등에 의해 처리함으로써 제조될 수 있다.

[0088] In addition, a calcination process may be performed after the above treatment. The sulfide-based solid electrolyte may be amorphous, crystalline, or a mixture thereof.

[0089] Polymer solid electrolytes are electrolytes that, for example, contain a mixture of a lithium salt and a polymer, or contain a polymer having ion-conducting functional groups. Polymer solid electrolytes are, for example, polymer electrolytes that do not contain a liquid electrolyte. The polymers included in the polymeric solid electrolyte are, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), poly(methylmethacrylate) (PMMA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), Polyaniline, Polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, Sulfonated poly, (ether ether ketone)(sulfonated poly(ether ether ketone), SPEEK), Sulfonated poly(arylene ether ketone sulfone)(sulfonated poly(aryl ether ketone, SPAEK), Poly[bis(benzimidazobenzisoquinolinones)](poly[bis(benzimidazobenzisoquinolinones)], SPBIBI), Poly(styrene sulfonate)(Poly(styrene sulfonate), PSS), Lithium 9,It may be 10-diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi+) or a combination thereof, but is not limited thereto; any that is used as a polymer electrolyte in the relevant technical field is acceptable. Any lithium salt that can be used as a lithium salt in the relevant technical field is acceptable. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C, x F 2x+1 SO2)(C y F 2y+1 SO2)(x and y are each 1 to 20), LiCl, LiI, LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide) or mixtures thereof, etc.

[0090] A gel electrolyte is, for example, a gel polymer electrolyte. A gel polymer electrolyte is an electrolyte that includes, for example, a liquid electrolyte and a polymer, or includes an organic solvent and a polymer having ion-conducting functional groups. The liquid electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent, a mixture of an ionic liquid and an organic solvent, or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt in a liquid state at room temperature or a room temperature molten salt that has a melting point below room temperature and consists solely of ions. The ionic liquid comprises, for example, a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF4 - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N -It may include one or more compounds selected from those containing one or more anions selected from among. A gel polymer electrolyte may be formed by impregnating the polymer solid electrolyte into the electrolyte in a lithium secondary battery. The gel electrolyte may further include inorganic particles.

[0091] Referring to FIG. 2, the electrolyte (120) can form a Solid Electrolyte Interphase Layer (SEI) (116) on a porous structure (114) through a lithium secondary battery formation process. The SEI layer (116) may refer to a thin chemical interface layer formed on the surface of the porous structure (114) of the negative electrode (110). The SEI layer (116) can be formed as the electrolyte (120) undergoes reduction decomposition on the surface of the porous structure (114) simultaneously with the movement of lithium ions to the negative electrode (110) during the charging process of the secondary battery.

[0092] The formed SEI layer (116) may have lithium-friendly properties. Therefore, the SEI layer (116) makes the surface of the porous structure (114) lithium-friendly, and allows lithium to be electrodeposited uniformly over the entire surface of the porous structure (114) without being locally electrodeposited during the subsequent charging process. Due to the increased lithium affinity caused by the SEI layer (116), the influence of the electric field described later is reduced, thereby preventing the electrodeposition of lithium on the upper surface of the porous structure (114).

[0093] In one embodiment, the SEI layer (116) may comprise a nitrogen (N)-containing film derived from a combination of a first solvent and a second solvent. Additionally, the SEI layer (116) may comprise a boron (B)-containing film derived from a lithium salt containing boron. Preferably, when the electrolyte (120) comprises a first solvent containing cyanide, a second solvent containing acetamide, and a lithium salt containing boron, the surface of the porous structure (114) may react with the electrolyte (120) during the formation process to form a stable SEI layer (116).

[0094] Here, the formation process can refer to the initial process undergone to activate the secondary battery by charging and discharging it for the first time, and to ensure the stable performance and lifespan of the secondary battery.

[0095] On the other hand, if a nitrogen (N)-containing film derived from a combination of a first solvent and a second solvent, or a boron (B)-containing film derived from a lithium salt containing boron, is not formed on the surface of a porous structure (114) composed of a conductive material having conductivity, the lithium affinity of the porous structure (114) decreases. Consequently, as the strongest electric field acts on the upper part of the porous structure (114) closest to the positive electrode, which is the opposite electrode, electrodeposition of lithium occurs starting from the upper part of the porous structure (114). That is, lithium ions may not be captured at the lower part of the porous structure (114), where the electric field is relatively weak.

[0096] For example, a porous structure (114) is formed by coating the surface of a current collector (112) with a powder containing carbon black, which is used as a commercial conductive material, but in the case where the combination of the first solvent and the second solvent is absent in the electrolyte (120), lithium electrodeposition occurs locally only on the upper part of the porous structure (114) or the surface layer of the porous structure (114) close to the anode, and thus lithium dendrites may occur.

[0097] In one embodiment, the porous structure (114) may further include a polymer binder. Here, the polymer binder may be the same material as the binder included in the interlayer described later. For example, the binder may be a fluorine-based binder such as polyvinylidene fluoride (PVDF).

[0098] According to one embodiment, a cross-sectional SEM image of a porous structure containing TiO2 before the formation process is shown in FIG. 3. Also, according to one embodiment, a cross-sectional SEM image of a porous structure containing TiO2 with an SEI layer formed on the surface after the formation process is shown in FIG. 4. According to one embodiment, the particle size of the powder forming the conductive material included in the porous structure (114) of FIG. 1 and FIG. 2 may be, for example, 0.5 μm to 2 μm, 2 μm to 4 μm, 4 μm to 8 μm, or 5 μm to 20 μm. By having the powder with a thickness within this range, the lifespan characteristics of the lithium secondary battery can be further improved.

[0099] According to some embodiments of the present disclosure, the utilization rate of internal pores of a porous structure disposed on a negative electrode current collector is increased, and by forming a lithium-affinity surface film, the influence of an electric field is reduced, thereby preventing the top deposition of lithium dendrites.

[0100] Specifically, according to some embodiments of the present disclosure, the porous structure of the cathode includes a lithium-affinity surface film through a formation process, thereby inducing lithium electrodeposition into the interior and surface of the porous structure, which suppresses the formation of lithium dendrites and suppresses lithium electrodeposition into the upper part, which minimizes the occurrence of a short circuit.

[0101] FIG. 5 shows the appearance (501) of a lithium secondary battery without a negative electrode active material layer before charging. FIG. 6 also shows the appearance (502) of a lithium secondary battery without a negative electrode active material layer after charging.

[0102] Referring to FIGS. 5 and 6, in a lithium secondary battery without a negative electrode active material layer, lithium ions can be reversibly electrodeposited or desorbed on the surface of a negative electrode current collector (510) during the charging and discharging process.

[0103] A lithium secondary battery without a negative electrode active material layer has the advantage of having a significantly higher energy density per unit weight compared to a conventional lithium-ion battery in which a thick negative electrode active material layer is coated on a negative electrode current collector. However, a lithium secondary battery without a negative electrode active material layer may inevitably undergo a change in volume as lithium metal (540) is directly deposited on the negative electrode current collector (510) during repeated charging and discharging. Specifically, while charging of a lithium secondary battery without a negative electrode active material layer is in progress, the volume of the positive electrode (530) and the separator (520) are the same, so the total volume of the lithium secondary battery may increase as the lithium metal (540) deposited on the negative electrode current collector (510) is newly formed.

[0104]

[0105] Lithium secondary battery and method for manufacturing a lithium secondary battery

[0106] FIG. 7 schematically illustrates the structure of a lithium secondary battery according to one embodiment. FIG. 8 also illustrates the appearance of a lithium secondary battery after charging according to one embodiment. Specifically, FIG. 7 and FIG. 8 illustrate the lithium secondary battery according to one embodiment by omitting the configuration other than the battery structure.

[0107] Referring to FIG. 7, a pre-charge lithium secondary battery (701) according to one embodiment of the present invention may include a positive electrode (730), a negative electrode current collector (710), a separator (720) disposed between the positive electrode (730) and the negative electrode current collector (710), a porous structure (740) disposed on the negative electrode current collector (710), an electrolyte (750) surrounding the negative electrode current collector (710) and the porous structure (740), and an SEI layer (742) formed on the porous structure (740). Specifically, the SEI layer (742) may be formed by the reaction between the porous structure (740) and the electrolyte (750) through a formation process of the lithium secondary battery (701).

[0108] In one embodiment, before charging, the negative electrode of the lithium secondary battery (701) may include a negative current collector (710) in which the negative active material layer is free. The positive electrode (730) may include a positive current collector and a positive active material layer disposed on the positive current collector.

[0109] Referring to FIG. 8, a lithium secondary battery (702) after charging according to one embodiment of the present invention may further include lithium (760) electrodeposited in the pores of a porous structure (740). Specifically, the electrodeposited lithium (760) may be formed during the discharge process of the secondary battery by receiving electrons from lithium ions in the electrolyte (750) through the SEI layer (742) present on the pore surface of the porous structure (740) and being reduced. The SEI layer (742) has a lithium-friendly property, so even though the electric field is stronger on the upper part of the porous structure (740), it can reduce the relative influence of the electric field and prevent lithium dendrites from forming on the upper part of the porous structure (740).

[0110] According to some embodiments of the present disclosure, dendrite formation is suppressed during the charging and discharging process, thereby enabling the production of a lithium metal battery with improved capacity retention rate, lifespan characteristics, and thermal stability.

[0111] FIG. 9 is a flowchart illustrating an example of a method for manufacturing a lithium secondary battery according to the present disclosure.

[0112] A method (900) for manufacturing a lithium secondary battery according to one embodiment of the present invention may be initiated by preparing a negative electrode by placing a porous structure on a current collector (S910). The step of preparing the negative electrode (S910) may include the step of coating the surface of the current collector by applying a slurry in which titanium dioxide (TiO2) powder, having an average particle size (D50) of 0.5 μm to 20 μm, is dispersed in an NMP solvent with a polymer binder in a mass ratio of 98:2 to 90:10 with a solid content of 50 to 60%, and undergoing a vacuum drying process at 80°C to 130°C for 3 to 12 hours.

[0113] After this, an electrolyte may be provided (S920). For example, the cathode may be impregnated with the electrolyte. The electrolyte may comprise a combination of a first solvent containing cyanide and a second solvent containing acetamide. Additionally, the electrolyte may further comprise a lithium salt containing boron, and specifically, the lithium salt may comprise any one of LiBF4, LiDFOB, LiBOB, LiFMDFB (lithium fluoromalonato(difluoro)borate), or a combination thereof. Here, the first solvent and the second solvent are as described above.

[0114] In one embodiment, the method for manufacturing a lithium secondary battery (900) may further include the step of performing a formation process to impart electrical properties to the negative electrode. In the formation process, the electrolyte may form a Solid Electrolyte Interphase Layer (SEI layer) on a porous structure.

[0115] According to some embodiments of the present disclosure, in the process of manufacturing a negative electrode in a method for manufacturing a lithium secondary battery, complex processes such as sputtering that previously existed can be replaced, and a lithium-affinity surface film can be easily formed on the surface of a porous structure disposed on a negative electrode current collector by only reacting with an electrolyte during the formation stage after manufacturing a lithium secondary battery cell.

[0116] FIGS. 10 to 13 are schematic diagrams illustrating a lithium secondary battery according to one embodiment, where FIG. 10 is cylindrical, FIG. 11 is prismatic, and FIGS. 12 and 13 are pouch-type batteries. Referring to FIGS. 10 to 13, the lithium secondary battery (1) includes a battery structure (7, electrode assembly) having a separator (4, separator) interposed between a positive electrode (3) and a negative electrode (2), and a case (5) in which the battery structure (7) is housed. The positive electrode (3), the negative electrode (2), and the separator (4) may come into contact with an electrolyte (not shown). As shown in FIG. 10, the lithium secondary battery (1) may include an assembly (6, sealing member) that seals the case (5). Additionally, in FIG. 11, the lithium secondary battery (1) may include a positive lead tab (3') and a positive terminal (3"), a negative lead tab (2') and a negative terminal (2"). As shown in FIGS. 12 and 13, the lithium secondary battery (1) may include electrode tabs (70), namely a positive electrode tab (71) and a negative electrode tab (72), which serve as electrical passages for inducing current formed in the battery structure (7) to the outside.

[0117] Referring to FIG. 10, a lithium secondary battery (1) according to one embodiment includes the anode (3), the cathode (2), and the separator (4) described above. The anode (3), the cathode (2), and the separator (4) are wound or folded to form a battery structure (7). The formed battery structure (7) is housed in a case (5). An electrolyte is injected into the case (5) and sealed with a cap assembly (6) to complete the lithium secondary battery (1). The case (5) is cylindrical but is not necessarily limited to this shape and may be, for example, prismatic, thin film, etc.

[0118] Referring to FIG. 11, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), the aforementioned negative electrode (2), and a separator (4). The positive electrode (3), the negative electrode (2), and the separator (4) are wound, folded, or stacked to form a battery structure (7). The formed battery structure (7) is housed in a case (5). An electrolyte is injected into the case (5), cross-linked, and sealed to complete the lithium secondary battery (1). The case (5) is prismatic, but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc. A positive lead tab (3') and a positive terminal (3") are electrically connected to the positive electrode (3). A negative lead tab (2') and a negative terminal (2") are electrically connected to the negative electrode (2).

[0119] Referring to FIG. 12, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), the aforementioned negative electrode (2), and a separator (4). A separator (4) is disposed between the positive electrode (3) and the negative electrode (2), and the positive electrode (3), the negative electrode (2), and the separator (4) are wound or folded to form a battery structure (7). The formed battery structure (7) is housed in a case (5). It may include an electrode tab (70) that serves as an electrical path for inducing the current formed in the battery structure (7) to the outside. An electrolyte is injected into the case (5) and sealed to complete the lithium secondary battery (1). The case (5) is prismatic but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc.

[0120] Referring to FIG. 13, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), the aforementioned negative electrode (2), and a separator (4). An electrolyte containing the separator (4) is disposed between the positive electrode (3) and the negative electrode (2) to form a battery structure. For example, the battery structure (7) is stacked in a bicell structure and then housed in a case (5). It may include a positive electrode tab (71) and a negative electrode tab (72) that serve as electrical pathways for inducing the current formed in the battery structure (7) to the outside. The electrolyte is injected into the case (5) and sealed to complete the lithium secondary battery (1). The case (5) is prismatic but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc.

[0121] However, the present invention is not limited to this, and the case (5) may be configured in various shapes such as circular or pouch type. For example, the pouch-type lithium secondary battery corresponds to the lithium secondary battery (1) of FIGS. 10 to 13 in which a pouch is used as the case (5). The pouch-type lithium secondary battery includes one or more battery structures (7). A separator (4) is disposed between the positive electrode (3) and the negative electrode (2) to form the battery structure (7). After the battery structure (7) is stacked in a bicell structure, an electrolyte is supplied, and the battery is received and sealed in a pouch to complete the pouch-type lithium secondary battery.

[0122] Specifically, the battery structure (7) including the aforementioned positive electrode (3), negative electrode (2), and separator (4) is simply stacked and contained in a pouch, or wound into a jelly roll shape or folded and contained in a pouch. Subsequently, an electrolyte is injected into the pouch and sealed to complete the lithium secondary battery (1).

[0123] The case (5) may be made of metal such as aluminum, aluminum alloy, nickel-plated steel, or a laminate film or plastic that constitutes the pouch.

[0124] Lithium secondary battery (1) has excellent lifespan characteristics and high rate characteristics, so it is used in, for example, electric vehicles (EV). For example, it is used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEV). In addition, it is used in fields where a large amount of power storage is required. For example, it is used in electric bicycles, power tools, etc.

[0125] A plurality of lithium secondary batteries (1) are stacked to form a battery module, and a plurality of battery modules form a battery pack. Such a battery pack can be used in any device requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, etc. A battery module includes, for example, a plurality of batteries and a frame that holds them.

[0126] A battery pack includes, for example, a plurality of battery modules and a bus bar connecting them. The battery modules and / or battery pack may further include a cooling device. A plurality of battery packs are controlled by a battery management system. The battery management system includes a battery pack and a battery control device connected to the battery pack.

[0127]

[0128] cathode current collector

[0129] The negative electrode current collector may not include a negative electrode active material layer. In a negative electrode current collector that does not include a negative electrode active material layer, lithium metal may be plated onto the negative electrode current collector by charging. The plated metal layer may comprise plated lithium, lithium metal foil, lithium metal powder, lithium alloy foil, lithium alloy powder, an organic compound containing lithium, or a combination thereof. The metal layer may comprise non-fibrous lithium, non-needle lithium, plate lithium, or any combination thereof. The lithium alloy contains lithium and a first metal, and the first metal may include indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), zinc (Zn), nickel, iron, cobalt, chromium, cesium, sodium, potassium, calcium, yttrium, bismuth, tantalum, hafnium, barium, vanadium, strontium, lanthanum, or a combination thereof.

[0130] The material constituting the negative electrode current collector can be any material that does not react with lithium, that is, a material that does not form an alloy or compound with lithium and has conductivity. The metal substrate is, for example, a metal or an alloy. The metal substrate may be, for example, made of 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. The electrode current collector (200) may have a shape selected from, for example, a sheet, foil, film, plate, porous body, mesoporous body, through-hole containing body, polygonal ring body, mesh body, foam, and nonwoven body, but is not necessarily limited to these shapes and any shape used in the relevant technical field is possible.

[0131] The negative electrode current collector comprises, for example, a first metal substrate. The first metal substrate comprises the first metal as a main component or is composed of the first metal. The first metal substrate comprises the first metal as a main component or is composed of the first metal. The content of the first metal included in the first metal substrate is, for example, 90 weight% or more, 95 weight% or more, 99 weight% or more, or 99.9 weight% or more with respect to the total weight of the first metal substrate. The first metal substrate may be composed of, for example, a material that does not react with lithium, that is, does not form an alloy and / or compound with lithium.

[0132] The first metal may be, for example, copper (Cu), nickel (Ni), stainless steel (SUS), iron (Fe), and cobalt (Co), but is not necessarily limited to these; any metal used as a current collector in the relevant technical field may be used. The first metal substrate may be composed of, for example, one of the metals described above, or may be composed of an alloy of two or more metals. The first metal substrate is, for example, in the form of a sheet or foil.

[0133] The negative current collector may further include a coating layer (not shown) containing a second metal on a first metal substrate.

[0134] The cathode current collector may include, for example, a first metal substrate and a coating layer disposed on the first metal substrate and comprising a second metal. The second metal has a higher Mohs hardness than the first metal. That is, since the coating layer comprising the second metal is harder than the substrate comprising the first metal, deterioration of the first metal substrate can be prevented. The Mohs hardness of the material constituting the first metal substrate is, for example, 5.5 or less. The Mohs hardness of the first metal is, for example, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, or 3.0 or less. The Mohs hardness of the first metal may be, for example, 2.0 to 6.0. The coating layer comprises the second metal. The coating layer may, for example, comprise the second metal as a main component or be composed of the second metal. The content of the second metal included in the coating layer is, for example, 90% by weight or more, 95% by weight or more, 99% by weight or more, or 99.9% by weight or more with respect to the total weight of the coating layer. The coating layer may be composed of, for example, a material that does not react with lithium, that is, does not form an alloy and / or compound with lithium. The Mohs hardness of the material constituting the coating layer is, for example, 6.0 or more. For example, the Mohs hardness of the second metal is 6.0 or more, 6.5 or more, 7.0 or more, 7.5 or more, 8.0 or more, 8.5 or more, or 9.0 or more. The Mohs hardness of the second metal may be, for example, 6.0 to 12. If the Mohs hardness of the second metal is excessively low, it may be difficult to suppress the deterioration of the negative electrode current collector. If the Mohs hardness of the second metal is excessively high, processing may not be easy. The second metal is one or more selected from, for example, titanium (Ti), manganese (Mn), niobium (Nb), tantalum (Ta), iridium (Ir), vanadium (V), rhenium (Re), osmium (Os), tungsten (W), chromium (Cr), boron (B), ruthenium (Ru), and rhodium (Rh).The coating layer may be composed of, for example, one of the metals described above, or an alloy of two or more metals. The difference in Mohs hardness between the first metal included in the first metal substrate and the second metal included in the coating layer may be, for example, 2 or more, 2.5 or more, 3 or more, 3.5 or more, or 4 or more. By having such a difference in Mohs hardness between the first metal and the second metal, the deterioration of the negative current collector can be suppressed more effectively. The coating layer may have a single-layer structure or a multilayer structure of two or more layers. The coating layer may have a two-layer structure including, for example, a first coating layer and a second coating layer. The coating layer may have a three-layer structure including, for example, a first coating layer, a second coating layer, and a third coating layer. The thickness of the coating layer may be, for example, 10 nm to 1 μm, 50 nm to 500 nm, 50 nm to 200 nm, or 50 nm to 150 nm. The coating layer may be deposited on the first metal substrate by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods; any method capable of forming a coating layer in the relevant technical field is possible.

[0135] For example, the cathode current collector may have a reduced thickness compared to a conventional cathode current collector. Accordingly, the cathode according to the present disclosure is distinguished from a conventional electrode comprising a thick film current collector by including, for example, a thin film current collector.

[0136] As a result, the energy density of a lithium metal battery employing such an electrode is increased. The thickness of the negative electrode current collector may be, for example, less than 15 μm, 14.5 μm or less, or 14 μm or less. The thickness of the negative electrode current collector may be, for example, 0.1 μm to less than 15 μm, 1 μm to 14.5 μm, 2 μm to 14 μm, 3 μm to 14 μm, 5 μm to 14 μm, or 10 μm to 14 μm.

[0137] The cathode current collector may have a form selected from, for example, a sheet, foil, film, plate, porous body, mesoporous body, through-hole containing body, polygonal ring body, mesh body, foam, and nonwoven body, but is not necessarily limited to these forms, and any form used in the relevant technical field is possible.

[0138] The negative current collector may include, for example, a base film and a metal substrate layer disposed on one or both sides of the base film. The negative current collector may have a structure comprising a substrate, wherein the substrate may include, for example, a base film and a metal substrate layer disposed on one or both sides of the base film. An intermediate layer may be additionally disposed on the metal substrate layer.

[0139] For example, the base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. By including a thermoplastic polymer in the base film, the base film may melt upon the occurrence of a short circuit, thereby suppressing a sudden increase in current. The base film may be, for example, an insulator.

[0140] The metal substrate layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The metal substrate layer can act as an electrochemical fuse and cut off upon overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be controlled by adjusting the thickness of the metal substrate layer. The metal substrate layer may be plated or deposited on a base film. As the thickness of the metal substrate layer decreases, the limit current and / or maximum current of the negative electrode current collector decreases, thereby improving the stability of the lithium metal battery during a short circuit.

[0141] A lead tab may be added to the metal substrate layer for external connection. The lead tab may be welded to the metal substrate layer or the metal substrate layer / base film laminate by means of ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or the metal substrate layer may melt, thereby electrically connecting the metal substrate layer to the lead tab. To make the weld between the metal substrate layer and the lead tab more robust, a metal chip may be added between the metal substrate layer and the lead tab. The metal chip may be a thin sheet of the same material as the metal of the metal substrate layer. The metal chip may be, for example, metal foil, metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. The lead tab may be welded to the metal chip / metal substrate layer laminate or the metal chip / metal substrate layer / base film laminate by placing the metal chip on the metal substrate layer and then welding it to the lead tab. During welding, the base film, metal layer, and / or metal chip may melt, allowing the metal layer or the metal layer / metal chip laminate to be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal substrate layer. The thickness of the base film may be, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. By having the base film within this thickness range, the weight of the cathode assembly can be reduced more effectively. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C or lower, or 100 to 200 °C. By having the base film within this melting point range, the base film can melt during the welding process of the lead tab and be easily bonded to the lead tab. Surface treatments, such as corona treatment, may be performed on the base film to improve the adhesion between the base film and the metal substrate layer. The thickness of the metal substrate layer is, for example, 0.The thickness may be 0.1 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to 1 μm. By having a thickness within this range, the stability of the cathode can be ensured while maintaining conductivity. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. By having a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having the cathode current collector with this structure, the weight of the electrode can be reduced and, consequently, the energy density can be improved.

[0142] According to one embodiment, a negative electrode active material layer may be free on the negative electrode current collector before charging and discharging. For example, a lithium metal layer may be free on the negative electrode current collector before charging and discharging.

[0143] According to one embodiment, a lithium metal layer including a plate-shaped lithium metal thin film may be disposed on a negative electrode current collector before performing charging and discharging.

[0144] According to one embodiment, the cathode may further include an interlayer disposed between the cathode current collector and the lithium metal layer.

[0145] According to one embodiment, the interlayer may be placed directly on, for example, one or both sides of the negative electrode current collector. Therefore, no other layer may be placed between the negative electrode current collector and the interlayer. By placing the interlayer directly on one or both sides of the negative electrode current collector, the bonding strength between the negative electrode current collector and the lithium metal layer may be further improved.

[0146] The thickness of the intermediate layer (not shown) may be, for example, 30% or less of the thickness of the negative current collector. The thickness of the intermediate layer (not shown) is, for example, 0.01 to 30%, 0.1 to 30%, 0.5 to 30%, 1 to 25%, 1 to 20%, 1 to 15%, 1 to 10%, 1 to 5%, or 1 to 3% of the thickness of the negative current collector. The thickness of the intermediate layer is, for example, 10 nm to 5 µm, 50 nm to 5 µm, 200 nm to 4 µm, 500 nm to 3 µm, 500 nm to 2 µm, 500 nm to 1.5 µm, or 700 nm to 1.3 µm.

[0147] By having the intermediate layer have a thickness within this range, the bonding strength between the cathode current collector and the metal layer is further improved, and the increase in interfacial resistance can be suppressed.

[0148] For example, the intermediate layer may include a binder. By including a binder in the intermediate layer, the bonding strength between the negative current collector and the lithium metal layer can be further improved. The binder included in the intermediate layer is, for example, a conductive binder or a non-conductive binder.

[0149] Conductive binders are, for example, ion-conducting binders and / or electronic-conducting binders. Binders that possess both ion conductivity and electronic conductivity may belong to both ion-conducting binders and electronic-conducting binders.

[0150] Ion-conducting binders are, for example, polystyrene sulfonate (PSS), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), poly(methylmethacrylate) (PMMA), polyethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, and polyacetylene. Ion-conducting binders may include polar functional groups. Ion-conducting binders containing polar functional groups are, for example, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi+ etc.The electronically conductive binder is, for example, polyacetylene, polythiophene, polypyrrole, poly(p-phenylene), poly(phenylenevinylene), poly(phenylenesulfide), polyaniline, etc. The intermediate layer may be, for example, a conductive layer containing a conductive polymer.

[0151] The binder included in the intermediate layer may be, for example, a fluorine-based binder. The fluorine-based binder included in the intermediate layer may be, for example, polyvinylidene fluoride (PVDF). The intermediate layer may be disposed on the negative current collector, for example, dry or wet. The intermediate layer may be, for example, a binding layer containing a binder.

[0152] The intermediate layer may additionally include, for example, a carbon-based conductive material. By including the carbon-based conductive material, the intermediate layer may be, for example, a conductive layer. The intermediate layer may be, for example, a conductive layer including a binder and a carbon-based conductive material.

[0153] The intermediate layer can be disposed on the cathode current collector in a dry manner by deposition, for example, CVD, PVD, etc. The intermediate layer can be disposed on the cathode current collector in a wet manner by, for example, spin coating, dip coating, etc. The intermediate layer can be disposed on the cathode current collector by, for example, depositing a carbon-based conductive material on the cathode current collector by deposition. The dry-coated intermediate layer consists of a carbon-based conductive material and may not contain a binder. Alternatively, the intermediate layer can be disposed on the cathode current collector by, for example, coating a composition comprising a carbon-based conductive material, a binder, and a solvent onto the surface of the cathode current collector and drying it. The intermediate layer may have a single-layer structure or a multilayer structure comprising multiple layers.

[0154]

[0155]

[0156] anode

[0157] A positive active material layer is disposed on a positive current collector to form a positive electrode. A positive active material layer is disposed on an electrolyte, and a positive current collector may be disposed on the positive active material layer.

[0158]

[0159] positive current collector

[0160] The positive electrode includes a positive electrode current collector. For example, a positive electrode can be prepared by forming a layer of positive electrode active material on the positive electrode current collector.

[0161] For example, the positive current collector may include 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.

[0162] According to one embodiment, the anode current collector may include aluminum (Al).

[0163] For example, the positive current collector may include a base film and a metal substrate layer disposed on one or both sides of the base film, in the same way as the negative current collector described above.

[0164]

[0165] positive active material layer

[0166] The positive active material layer may include a positive active material, a conductive material, and a binder.

[0167] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. The composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0168] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05), Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05), Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2), Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2), Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1), Li a NiG bO2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn2GbO4(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5), Li (3-f) Fe2(PO4)3(0≤f≤2), Li a FePO4(0.90≤a≤1.8).

[0169] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0170] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in a lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel cathode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0171] For example, the lithium transition metal oxide may be a compound represented by the following chemical formula 1:

[0172]

[0173] <Chemical Formula 1>

[0174] Li a Ni x Coy M z O 2-b A b

[0175]

[0176] In Chemical Formula 1, 1.0≤a≤1.2, 0≤b≤0.2, 0.6≤x<1, 0≤y≤0.3, 0 <z≤0.3, x+y+z=1, M은 망간(Mn), 바나듐(V), 마그네슘(Mg), 갈륨(Ga), 실리콘(Si), 텅스텐(W), 몰리브덴(Mo), 철(Fe), 크롬(Cr), 구리(Cu), 아연(Zn), 티타늄(Ti), 알루미늄(Al) 및 보론(B)으로 이루어진 군으로부터 선택된 하나 이상이고, A는 F, S, Cl, Br 또는 이들의 조합이다.

[0177] In Chemical Formula 1, for example, 0.7≤x<1, 0 <y≤0.3, 0<z≤0.3, 0.8≤x<1, 0<y≤0.2, 0<z≤0.2, 0.83≤x<0.97, 0<y≤0.15, 0<z≤0.15, 또는 0.85≤x<0.95, 0<y≤0.1, 0<z≤0.1일 수 있다.

[0178] For example, the lithium transition metal oxide may be at least one of the compounds represented by the following chemical formulas 2 and 3:

[0179]

[0180] <Chemical Formula 2>

[0181] LiNi x Co y Mn z O2

[0182]

[0183] In Chemical Formula 2, 0.6≤x≤0.95, 0 <y≤0.2, 0<z≤0.1이다. 예를 들어, 0.7≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다.

[0184]

[0185] <Chemical Formula 3>

[0186] LiNi x Co y Al z O2

[0187]

[0188] In Chemical Formula 3, 0.6≤x≤0.95, 0 <y≤0.2, 0<z≤0.1이다. 예를 들어, 0.7≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다. 예를 들어, 0.8≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다. 예를 들어, 0.82≤x≤0.95, 0<y≤0.15, 0<z≤0.15이다. 예를 들어, 0.85≤x≤0.95, 0<y≤0.1, 0<z≤0.1이다.

[0189] For example, lithium transition metal oxides are LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 0.04O2 , LiNi 0.8 Co 0.15 Mn 0.05O2 , LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02O2 , LiNi 0.8 Co 0.15 Al 0.05O2 , LiNi 0.8 Co 0.1 Mn 0.2O2 or LiNi 0.88 Co 0.1 Al 0.02O2 It could be.

[0190] For example, the positive electrode active material may be one having a coating layer on the surface of a lithium transition metal oxide, or a mixture of a lithium transition metal oxide and a lithium transition metal oxide having a coating layer may be used.

[0191] For example, the coating layer may include a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element.

[0192] For example, the compound forming the coating layer may be 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. For the coating layer formation process, any coating method may be used as long as the coating can be applied to the lithium transition metal oxide using the coating elements in a manner that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.).

[0193] For example, the anode may additionally include an additive that can serve as a sacrificial anode.

[0194] The content of the positive active material is 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0195] The binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. 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 (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0196] A conductive material is used to impart conductivity to an electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials 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 in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0197]

[0198] separator

[0199] A lithium secondary battery according to one embodiment may further include a separator (not shown).

[0200] As a separator, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof may be used, and of course, mixed multilayer films such as polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0201] The separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0202] 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.

[0203] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0204] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0205] 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.

[0206] This will be explained in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not limited thereto.

[0207]

[0208] Example 1: Preparation of a lithium secondary battery

[0209] A copper foil was prepared as a current collector. To coat a porous structure on the top of the copper foil, a slurry was first prepared by mixing titanium dioxide (TiO2) powder with a polymer binder (PVdF, Solef 5130) in a mass ratio of 98:2 and dispersing it in an NMP solvent at 1000 rpm for 10 minutes using a Thinky Mixer with a solid content of 57.1%. The slurry was applied onto the copper foil, and after drying in a vacuum oven at 100°C for 3 hours, a negative electrode with a porous structure thickness of 35 μm was manufactured. Here, the porosity of the porous structure is 56% by volume. Subsequently, a pouch cell was manufactured by laminating the manufactured negative electrode of the lithium secondary battery with a separator and a positive electrode. An electrolyte containing 1.2 M of LiTFSI lithium salt dissolved in a mixed solvent of butyronitrile (BN) and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) at a mass ratio of 1:9 was injected into the pouch cell.

[0210] In the case of the anode, Li 1.04 Ni 0.8 Co 0.1 Al 0.1 An anode slurry was prepared by dispersing an O2 anode active material and a PVDF binder together with a carbon black conductive material in an NMP solvent at a mass ratio of 97:1.5:1.5. The anode was prepared by coating the slurry onto a 12 μm aluminum substrate and then drying and rolling it in a vacuum oven at 120°C for 8 hours.

[0211] A polypropylene membrane with a thickness of 10 μm and an air permeability (JIS Gurley) value of 120 sec / 100 ml was used.

[0212]

[0213] Example 2: Preparation of a lithium secondary battery

[0214] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was injected in which 0.6 M of LiBF4 and 0.6 M of LiDFOB lithium salts were dissolved, respectively, in a mixed solvent of butyronitrile (BN), diethyl carbonate (DEC), and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) in a mass ratio of 10:23:67.

[0215]

[0216] Example 3: Preparation of a lithium secondary battery

[0217] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was injected in which 0.6 M of LiBF4 and 0.6 M of LiDFOB lithium salts were dissolved, respectively, in a mixed solvent of butyronitrile (BN) and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) in a mass ratio of 10:90.

[0218]

[0219] Example 4: Preparation of a lithium secondary battery

[0220] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was injected in which 0.6 M of LiBF4 and 0.6 M of LiDFOB lithium salts were dissolved, respectively, in a mixed solvent of butyronitrile (BN) and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) in a mass ratio of 25:75.

[0221]

[0222] Example 5: Preparation of a lithium secondary battery

[0223] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was injected in which lithium salts of LiBF4, LiDFOB, and LiFMDFB were dissolved at 0.6 M, 0.6 M, and 0.1 M, respectively, in a mixed solvent of butyronitrile (BN) and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) at a mass ratio of 25:75.

[0224]

[0225] Example 6: Preparation of a lithium secondary battery

[0226] A lithium secondary battery was prepared in the same manner as in Example 1, except that 0.6 M each of lithium salts LiBF4 and LiDFOB were dissolved in a mixed solvent of butyronitrile (BN), diethyl carbonate (DEC), and 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) in a mass ratio of 10:23:67 as the electrolyte, and a gel electrolyte (GPE) was injected by adding 4 wt% of dipentaerythritol hexaacrylate (DPHA) monomer and 1200 ppm of the polymerization initiator tert-butyl peroxypivalate. However, for the lithium secondary battery of Example 6, after injecting the electrolyte and performing vacuum pouch sealing, the internal gel electrolyte (GPE) was cured by leaving it at room temperature for 12 hours and then at 80°C for 3 hours.

[0227]

[0228]

[0229] Comparative Example 1: Manufacture of a lithium secondary battery

[0230] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte in which a 1.2 M LiTFSI salt was dissolved in a butyronitrile (BN) solvent was used as the electrolyte.

[0231]

[0232] Comparative Example 2: Manufacture of a lithium secondary battery

[0233] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte in which 1.2 M of LiTFSI salt was dissolved in 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) solvent was used as the electrolyte.

[0234]

[0235] Comparative Example 3: Manufacture of a lithium secondary battery

[0236] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was used in which LiBF4 and LiDFOB salts were dissolved at 0.6 M and 0.6 M, respectively, in a mixed solvent of FEC and DEC with a mass ratio of 42:58.

[0237]

[0238] Comparative Example 4: Manufacture of a lithium secondary battery

[0239] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte in which LiBF4 and LiDFOB salts were dissolved in a butyronitrile solvent at 0.6 M and 0.6 M, respectively, was used as the electrolyte.

[0240]

[0241] Comparative Example 5: Manufacture of a lithium secondary battery

[0242] A lithium secondary battery was prepared in the same manner as in Example 1, except that an electrolyte was used in which LiBF4 and LiDFOB salts were dissolved at 0.6 M and 0.6 M, respectively, in a 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA) solvent.

[0243]

[0244] Classification Porous Structure 1 Solvent 2 Solvent 3 Solvent Crosslinking Agent Lithium Salt Example 1 Copper Foil TiO2 + PVDF(98:2) Porosity 56% Thickness 35μm Butyronitrile FDMA--LiTFSI Example 2 Butyronitrile FDMA DEC-LiBF4, LiDFOB Example 3 Butyronitrile FDMA--LiBF4, LiDFOB Example 4 Butyronitrile FDMA--LiBF4, LiDFOB Example 5 Butyronitrile FDMA--LiBF4, LiDFOB, LiFMDFB Example 6 Butyronitrile FDMA DEC DPHALiBF4, LiDFOB Comparative Example 1 Butyronitrile---LiTFSI Comparative Example 2-FDMA--LiTFSI Comparative Example 3 FECDEC--LiBF4, LiDFOB 4Butyronitrile---LiBF4, LiDFOB Comparative Example 5-FDMA--LiBF4, LiDFOB

[0245] Evaluation Example 1: Measurement of capacity retention rate when charging and discharging n times. A lithium secondary battery composed of each negative electrode, positive electrode, separator, and electrolyte prepared according to Examples 1 to 6 and Comparative Examples 1 to 5 was manufactured, and a charge-discharge evaluation was performed.

[0246] Manufacturing of charge / discharge evaluation cells

[0247] A single-plate pouch cell was fabricated to perform the above charge-discharge evaluation. A single-plate pouch cell was fabricated by sequentially stacking a separator and an anode on top of the respective cathodes corresponding to Examples 1 to 6 and Comparative Examples 1 to 5 inside an aluminum pouch, injecting the electrolytes corresponding to Examples 1 to 6 and Comparative Examples 1 to 5 respectively, and then vacuum sealing the aluminum pouch. The cathodes and anodes were configured to be connected to tabs made of nickel and aluminum, respectively, so that they could be connected to external wires. In addition, in the case of the sealed pouch cell in which the gel electrolyte (GPE) of Example 6 was injected, it was left at room temperature for 12 hours to allow the electrolyte to fully impregnate the anode pores, and then left in an 80°C oven for 3 hours to cure the gel electrolyte (GPE) impregnated in all pores inside the pouch cell.

[0248] Charge / Discharge Evaluation in Progress

[0249] The pouch cell manufactured through the above process was charged with a constant current at a rate of 0.1C at 45℃ until the voltage reached 4.30V (vs. Li), and then cut off at a current rate of 0.05C while maintaining 4.30V in constant voltage mode. Subsequently, it was discharged with a constant current rate of 0.1C until the voltage reached 3.6V (vs. Li) during discharge (Formation Stage 1).

[0250] A lithium secondary battery that has undergone the first stage of formation was charged at 45°C at a constant current of 0.2C in a voltage range of 3.6 to 4.3 V relative to lithium metal, and then cut off at a current rate of 0.05C while maintaining 4.30V in constant voltage mode. Subsequently, constant current discharge was performed at 0.2C until a cut-off voltage of 3.6V was reached (second stage of formation).

[0251] The Mars stage was completed by going through the above Mars 1 and 2 stages one cycle each.

[0252] A lithium secondary battery with a completed formation stage was charged at 45°C at a constant current of 0.33C in a voltage range of 3.6 to 4.3 V relative to lithium metal, and then cut off at a current rate of 0.05C while maintaining 4.30V in constant voltage mode. Subsequently, constant current discharge was performed at 1.0C until a cut-off voltage of 3.6V was reached.

[0253] The aforementioned charge / discharge process was repeated a total of 100 times. In all charge / discharge cycles, a 5-minute pause was observed after each charge / discharge cycle. Here, the capacity retention rate in the Nth cycle is defined by the following formula.

[0254] Capacity Retention Rate (%) = (Discharge Capacity at Nth Cycle / Discharge Capacity at 1st Cycle) × 100

[0255]

[0256] Evaluation Example 2: Confirmation of the volume change rate of a lithium secondary battery after n charge-discharge cycles

[0257] Using the same manufacturing and evaluation method as described in Evaluation Example 1 above, the thickness of the pouch cell of the lithium secondary battery manufactured according to Examples 1 to 6 and Comparative Examples 1 to 5 was measured using a digital micrometer before charge / discharge operation and after 50 cycles, and the volume change rate of the lithium secondary battery was confirmed according to the following equation.

[0258]

[0259] Volume change rate (%) = (Thickness of pouch cell after 50 cycles - Thickness of pouch cell before charge / discharge) / (Thickness of pouch cell before charge / discharge) × 100

[0260]

[0261] According to Evaluation Example 1 above, the cycles reaching a capacity retention rate of 80% were measured and listed in Table 2 below.

[0262]

[0263] According to Evaluation Example 2 above, the rate of change in volume of the lithium secondary battery after 50 cycles was measured and listed in Table 2 below.

[0264]

[0265] Volume change rate of lithium secondary battery after 50 cycles reaching a capacity retention rate of 80% Example 1: 1915.5 Example 2: 2112.1 Example 3: 2371.8 Example 4: 2452.4 Example 5: 2592.2 Example 6: 2541.7 Comparative Example 1: 13115.5 Comparative Example 2: 6113.1 Comparative Example 3: 1609.9 Comparative Example 4: 5710.4 Comparative Example 5: 1549.2

[0266]

[0267] Referring to Table 2, Examples 1 to 6 each exhibited superior capacity characteristics and capacity retention rate characteristics compared to Comparative Examples 1 to 5, as lithium metal was uniformly electrodeposited on the porous structure. Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. Cathode; and Contains electrolytes, The above cathode includes a current collector and a porous structure disposed on the current collector, and A lithium secondary battery comprising a combination of a first solvent containing cyanide and a second solvent containing acetamide, wherein the above electrolyte comprises a combination of the first solvent containing cyanide and the second solvent containing acetamide.

2. In Paragraph 1, A lithium secondary battery comprising the first solvent, which comprises butyronitrile, acetonitrile, propionitrile, valeronitrile, isovaleronitrile, isobutyronitrile, hexanenitrile, heptanenitrile, 3-methoxypropionitrile, 5-ketohexanenitrile, methyl cyanoformate, ethyl cyanoformate, methyl cyanoacetate, ethyl cyanoacetate, or any combination thereof.

3. In Paragraph 1, A lithium secondary battery comprising the second solvent, which comprises 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA), 2,2-difluoro-N,N-dimethylacetamide, 2-Fluoro-N,N-dimethylacetamide, 2,2,2-trifluoro-N,N-diethylacetamide (FDEA), 2,2-difluoro-N,N-diethylacetamide, 2-Fluoro-N,N-diethylacetamide, or any combination thereof.

4. In Paragraph 1, A lithium secondary battery in which the second solvent comprises at least one Fluoro group as a functional group.

5. In Paragraph 1, A lithium secondary battery in which the mass ratio of the first solvent to the second solvent in the above electrolyte is 5:95 to 40:

60.

6. In Paragraph 1, A lithium secondary battery, wherein the above electrolyte further comprises a lithium salt containing boron.

7. In Paragraph 6, A lithium secondary battery comprising any one of LiBF4, LiDFOB, LiBOB, LiFMDFB, or any combination thereof, wherein the above lithium salt comprises LiBF4, LiDFOB, LiBOB, LiFMDFB, or any combination thereof.

8. In Paragraph 1, A lithium secondary battery in which the above electrolyte forms a Solid Electrolyte Interphase Layer (SEI layer) on the porous structure during the formation process of the above lithium secondary battery.

9. In Paragraph 1, A lithium secondary battery in which the above porous structure completely covers the surface of the above current collector.

10. In Paragraph 9, A lithium secondary battery, wherein the porous structure is formed by coating the surface of the current collector with a powder comprising carbon black, graphite, hard carbon, titanium dioxide (TiO2) oxide, molybdenum disulfide (MoS2), vanadium dioxide (VO2), vanadium pentoxide (V2O5), molybdenum dioxide (MoO2), titanium disulfide (TiS2), or a combination thereof, together with a polymer binder.

11. In Paragraph 1, A lithium secondary battery having a porosity of 20% to 70% based on volume of the porous structure.

12. In Paragraph 1, The above-mentioned current collector is a lithium secondary battery comprising a foil structural layer containing copper (Cu).

13. In Paragraph 1, Before charging, the above negative electrode is a lithium secondary battery in which the negative electrode active material layer is absent (free).

14. A step of preparing a cathode by placing a porous structure on a current collector; and It includes a step of supplying electrolytes, A method for manufacturing a lithium secondary battery, wherein the above electrolyte comprises a combination of a first solvent comprising cyanide and a second solvent comprising acetamide.

15. In Paragraph 14, The method further includes the step of performing a formation process on the above cathode, and A method for manufacturing a lithium secondary battery, wherein in the above-described process, the electrolyte forms a Solid Electrolyte Interphase Layer (SEI layer) on the porous structure.

16. In Paragraph 14, The step of preparing the above cathode is, A method for manufacturing a lithium secondary battery, comprising the step of coating the surface of the above-mentioned current collector with a powder comprising carbon black, graphite, hard carbon, titanium dioxide (TiO2), molybdenum disulfide (MoS2), vanadium dioxide (VO2), vanadium pentoxide (V2O5), molybdenum dioxide (MoO2), titanium disulfide (TiS2), or a combination thereof, together with a polymer binder.

17. In Paragraph 14, A method for manufacturing a lithium secondary battery, wherein the first solvent comprises any one of butyronitrile, acetonitrile, propionitrile, valeronitrile, isovaleronitrile, isobutyronitrile, hexanenitrile, heptanenitrile, 3-methoxypropionitrile, 5-ketohexanenitrile, methyl cyanoformate, ethyl cyanoformate, methyl cyanoacetate, ethyl cyanoacetate, or any combination thereof.

18. In Paragraph 14, A method for manufacturing a lithium secondary battery, wherein the second solvent comprises any one of 2,2,2-trifluoro-N,N-dimethylacetamide (FDMA), 2,2-difluoro-N,N-dimethylacetamide, 2-Fluoro-N,N-dimethylacetamide, 2,2,2-trifluoro-N,N-diethylacetamide (FDEA), 2,2-difluoro-N,N-diethylacetamide, 2-Fluoro-N,N-diethylacetamide, or any combination thereof.

19. In Paragraph 14, A method for manufacturing a lithium secondary battery, wherein the above electrolyte further comprises a lithium salt containing boron.

20. In Paragraph 1, A lithium secondary battery, wherein the above electrolyte further comprises a lithium salt containing LiTFSI.

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