Gel polymer electrolyte and lithium metal battery comprising same

Abstract

The present invention relates to a gel polymer electrolyte and a lithium metal battery comprising same, the gel polymer electrolyte comprising: a first lithium salt including a fluorine-based lithium salt; a second lithium salt including lithium difluoro(oxalato)borate (LiDFOB); a first organic solvent including a carbonate-based compound; a second organic solvent including a dinitrile-based compound and a mononitrile-based compound; and a crosslinked polymer including an ester-based compound, wherein the second organic solvent includes the dinitrile-based compound and the mononitrile-based compound in a weight ratio of 1:2.5 to 2.5:1.

Description

Gel polymer electrolyte, and lithium metal battery including the same

[0001] The present invention relates to a gel polymer electrolyte and a lithium metal battery containing the same.

[0002] Currently available lithium batteries primarily use carbon-based negative electrode active materials, such as graphite. While carbon-based negative electrode active materials offer high stability due to their lack of volume change during charging and discharging, their low capacity necessitates the use of negative electrode active materials with higher capacities.

[0003] Lithium metal, which has a much larger theoretical capacity compared to carbon-based negative electrode active materials, can be used as a negative electrode active material. 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 of a lithium metal battery containing lithium metal may be degraded.

[0004] The problem that the present invention aims to solve is to provide a gel polymer electrolyte that can suppress lithium dendrites by reducing side reactions between lithium and the electrolyte.

[0005] Another problem that the present invention aims to solve is to provide a gel polymer electrolyte that has excellent ion conductivity, high oxidation stability, and can prevent corrosion of lithium metal.

[0006] Another problem that the present invention aims to solve is to provide a lithium metal battery having high energy density and excellent lifespan comprising the gel polymer electrolyte.

[0007] Another problem that the present invention aims to solve is to provide a method for manufacturing a lithium metal battery having high energy density and excellent lifespan, comprising the gel polymer electrolyte.

[0008] A gel polymer electrolyte according to the concept of the present invention comprises: a first lithium salt comprising a fluorine-based lithium salt; a second lithium salt comprising lithium difluoro(oxalato)borate (LiDFOB); a first organic solvent comprising a carbonate-based compound; a second organic solvent comprising a dinitrile-based compound and a mononitrile-based compound; and a crosslinked polymer comprising an ester-based compound; wherein the second organic solvent may comprise the dinitrile-based compound and the mononitrile-based compound in a weight ratio of 1:2.5 to 2.5:1.

[0009] A lithium metal battery according to another concept of the present invention comprises a positive electrode layer; a negative electrode current collector; and an electrolyte layer disposed between the positive electrode layer and the negative electrode current collector, wherein the electrolyte layer may comprise the gel polymer electrolyte of claim 1.

[0010] A method for manufacturing a lithium metal battery according to another concept of the present invention may include: forming an electrode assembly by arranging a negative electrode current collector, a separator, and a positive electrode; housing the electrode assembly in a battery case, and then injecting a composition for forming a gel polymer electrolyte into the battery case; and curing the composition for forming a gel polymer electrolyte to form the gel polymer electrolyte.

[0011] The gel polymer electrolyte according to the present invention can suppress lithium dendrites by reducing side reactions between lithium and the electrolyte, has excellent ion conductivity and high oxidation stability, and can prevent corrosion of lithium metal. In addition, a lithium metal battery containing the gel polymer electrolyte according to the present invention can have high energy density and excellent lifespan.

[0012] FIG. 1 is a cross-sectional view of a lithium metal battery according to an exemplary embodiment.

[0013] FIG. 2 is a cross-sectional view of a lithium metal battery according to another exemplary embodiment.

[0014] FIGS. 3 and 4 are schematic perspective views of a lithium metal battery according to an exemplary embodiment.

[0015] In order to fully understand the structure and effects of the present invention, preferred embodiments of the present invention are described with reference to the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms and various modifications can be made. The description of these embodiments is provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention.

[0016] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the components are exaggerated for the effective description of the technical content. Throughout the specification, parts indicated by the same reference numeral represent the same components.

[0017] The embodiments described herein will be described with reference to cross-sectional and / or plan views, which are exemplary illustrations of the invention. In the drawings, the thicknesses of films and regions are exaggerated for effective description of the technical content. Accordingly, the regions illustrated in the drawings are schematic in nature, and the shapes of the regions illustrated in the drawings are intended to illustrate specific forms of regions of the device and are not intended to limit the scope of the invention. Although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. The embodiments described and illustrated herein also include their complementary embodiments.

[0018] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, 'comprises' and / or 'comprising' do not exclude the presence or addition of one or more other components to the mentioned components.

[0019] 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.

[0020] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0021] In this specification, “alloy” means a mixture of two or more metals.

[0022] In this specification, “electrode active material” refers to an electrode material capable of undergoing lithiation and delithiation.

[0023] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0024] In this specification, “anode active material” refers to an anode material capable of undergoing lithiation and delithiation.

[0025] In this specification, “lithiation” and “to lithiate” refer to the process of adding lithium to an electrode active material.

[0026] In this specification, “delithiation” and “to delithiate” refer to the process of removing lithium from an electrode active material.

[0027] In this specification, “charge” and “to charge” refer to the process of providing electrochemical energy to a battery.

[0028] In this specification, “discharge” and “discharge” refer to the process of removing electrochemical energy from a battery.

[0029] In this specification, “anode” and “cathode” refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0030] In this specification, “negative electrode” and “anode” refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process. Although specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or cannot be anticipated may arise to the applicant or those skilled in the art. Accordingly, the appended claims, which may be filed and modified, are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0031]

[0032] A lithium metal battery according to exemplary embodiments is described in more detail below.

[0033] A lithium metal battery (100) according to one embodiment may include an electrode assembly (40).

[0034] Referring to FIG. 1, an electrode assembly (40) according to one embodiment may include an anode (10) comprising an anode current collector (11) and an anode active material layer (12) on the anode current collector (11); a cathode (20) comprising a cathode current collector (21); a separator (30) disposed between the anode (10) and the cathode (20); and a gel polymer electrolyte (not shown). The anode (10), the cathode (20), and the separator (30) may be impregnated with a gel polymer electrolyte (not shown).

[0035] Referring to FIG. 2, the negative electrode (20) of a lithium metal battery (100) according to another embodiment may further include a lithium metal layer (22) disposed between a negative electrode current collector (21) and a separator (30). The lithium metal layer (22) may be a plated layer generated by charging the lithium metal battery (100).

[0036] A lithium metal battery (100) may use lithium metal as a negative electrode active material. During the charging and discharging process of the lithium metal battery, a lithium-containing metal layer may be precipitated and dissolved between the negative electrode current collector (21) and the separator (30). As the charging and discharging of the lithium metal battery is repeated, the lithium-containing metal layer may contain impurities remaining in the electrode, decomposition products of the electrolyte, etc.

[0037] The lithium-containing metal layer may have a rough and hard surface due to the inclusion of such impurities. Lithium dendrites may be deposited on the lithium-containing metal layer having such a rough surface. Lithium dendrites may continuously grow during the charging and discharging process and cause a short circuit between the positive electrode (10) and the negative electrode (20). Additionally, uneven growth of lithium dendrites on the negative electrode (20) during charging can easily cause damage within the cell, and the volume of the cell may expand significantly, making long-term operation difficult.

[0038] The positive electrode (10) and the negative electrode (20) may be spaced apart from each other with a separator (30) in between. The separator (30) may be placed between the positive electrode (10) and the negative electrode (20). The positive electrode (10), the negative electrode (20), and the separator (30) may come into contact with a gel polymer electrolyte (not shown).

[0039] A gel polymer electrolyte (not shown) may be a medium for transferring lithium ions between a positive electrode (10) and a negative electrode (20). Within the gel polymer electrolyte (not shown), the lithium ions may pass through a separator (30) and move toward the positive electrode (10) or the negative electrode (20).

[0040] Referring to FIGS. 3 and 4, the lithium metal battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is housed. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with a gel polymer electrolyte (not shown). Referring to FIGS. 3 and 4, the lithium metal battery (100) 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 electrode assembly (40) to the outside.

[0041]

[0042] positive electrode (10)

[0043] A positive electrode (10) for a lithium metal battery may include a positive electrode current collector (11) and a positive electrode active material layer (12) formed on the positive electrode current collector (11). The positive electrode active material layer (12) may include a positive electrode active material and may further include a binder and / or a conductive material. As an example, the positive electrode active material layer (12) may further include an additive that can serve as a sacrificial electrode.

[0044] The content of the positive active material in the positive active material layer (12) may be 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer (12). The content of each of the binder and the conductive material may be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer (12).

[0045] The above binder can perform the function of adhering the positive active material particles well to each other and also adhering the positive active material well to the positive current collector (11). Representative examples of binders include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including 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., but are not limited thereto.

[0046] The above conductive material can be used to impart conductivity to the electrode. Any electronically conductive material that does not cause chemical changes in the electrode can be used as the conductive material. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, 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.

[0047] The positive current collector (11) can provide a reference surface on which the positive active material layer (12) is placed. The positive current collector (11) may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive current collector (11) may include a plate or a foil.

[0048] Meanwhile, unlike as illustrated in FIG. 1, the positive current collector (11) may be omitted in one embodiment. 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 (11) and the positive active material layer (12) to increase the bonding strength between the positive current collector (11) and the positive active material layer (12).

[0049]

[0050] positive active material layer (12)

[0051] As the positive active material in the positive active material layer (12), a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more of the composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used.

[0052] The above 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.

[0053] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-bXb O2- c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li aMn 2-b X b About 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 About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); LiaNi 1-b-c Mn b X c About 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 b O2(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 Mn2G b O4(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).

[0054] In the above 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 L1 is Mn, Al, or a combination thereof.

[0055] A coating layer may be additionally added to the surface of the aforementioned compound. The coating layer may include, for example, an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, or a hydroxycarbonate of a coating element. The coating layer may be amorphous or crystalline. The coating element within the coating layer may be selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, and Zr. The method of forming the coating layer may be selected within a range that does not adversely affect the physical properties of the cathode active material. The coating method may include, for example, spray coating or immersion methods.

[0056] For example, the above-mentioned positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the 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 positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density lithium metal batteries.

[0057]

[0058] Negative electrode (20)

[0059] Referring to FIG. 1, a lithium metal battery (100) according to one embodiment may include a negative electrode (20) including a negative electrode current collector (21).

[0060] The negative electrode current collector (21) may include a material that does not react with lithium, for example, that is, does not form any alloys or compounds with lithium. The material constituting the negative electrode current collector (210) may include at least one metal selected from the group consisting of, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The thickness of the negative electrode current collector may be 1 to 20 μm, for example 5 to 15 μm, for example 7 to 10 μm.

[0061] The negative current collector (21) may be composed of one of the metals described above, or may include an alloy of two or more metals or a coating material. The negative current collector (21) is, for example, in the form of a plate or foil.

[0062] Referring to FIG. 2, the negative electrode (20) of a lithium metal battery (100) according to another embodiment may further include a lithium metal layer (22) disposed between a negative electrode current collector (21) and a separator (30). The lithium metal layer (22) may be a plated layer generated by charging the lithium metal battery (100).

[0063] The lithium metal layer (22) may include lithium or a lithium alloy. Since the lithium metal layer (22) 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 to these; any alloy used as a lithium alloy in the relevant technical field may be possible. The lithium metal layer (22) may be composed of one of these alloys or lithium, or may be composed of various types of alloys.

[0064] In another embodiment, the lithium metal layer (22) within the negative electrode (20) may be provided on the negative electrode current collector (21), for example, before assembly of the lithium metal battery (100). When the lithium metal layer (22) is placed on the negative electrode current collector (21) before assembly of the lithium metal battery (100), the lithium metal layer (22) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be placed on the negative electrode current collector (21) before assembly of the lithium metal battery (100).

[0065] When a lithium metal layer (22) is deposited by charging after assembly of the lithium metal battery (100), the energy density of the lithium metal battery (100) can be increased because the lithium metal layer (22) is not included during assembly of the lithium metal battery (100). The lithium metal layer (22) can be composed mainly of lithium (i.e., metallic lithium). During discharge, the lithium in the lithium metal layer (22) can be ionized and move to the positive electrode (10). In other words, lithium can be used as a negative electrode active material in the lithium metal battery (100). When a lithium metal layer (22) is formed by charging after assembly of the lithium metal battery (100), the negative electrode (20), that is, the region between the negative electrode current collector (21) and the separator (30), may be a Li-free region that does not contain lithium (Li) in the initial state or after complete discharge of the lithium metal battery (100).

[0066]

[0067] Separator (30)

[0068] The separator (30) separates the positive electrode (10) and the negative electrode (20) and provides a pathway for the movement of lithium ions; any separator commonly used in lithium-ion batteries can be used. That is, a separator with low resistance to the movement of ions in the electrolyte and excellent electrolyte moisture retention capacity can be used.

[0069] Depending on the type of lithium metal battery, a separator (30) (or separator) may be provided between the positive electrode (10) and the negative electrode (20). As for this separator (30), polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0070] The separator (30) 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.

[0071] 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.

[0072] The above organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0073] 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.

[0074] 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.

[0075]

[0076] Gel polymer electrolyte

[0077] The gel polymer electrolyte can be manufactured by a method in which it is poured into a battery case (50) into which an electrode assembly (40) is inserted and then cured, and thus has the advantage of being applicable to the existing non-aqueous electrolyte battery manufacturing process. The gel polymer electrolyte can maintain good processability by maintaining low viscosity when poured into the battery case (50). The gel polymer electrolyte can be easily cured by thermal curing or photocuring and thus can have a gel form.

[0078] The gel polymer electrolyte may comprise a first lithium salt, a second lithium salt, a first organic solvent, a second organic solvent, and a crosslinking polymer. The first lithium salt may comprise a fluorine-based lithium salt. The second lithium salt may comprise lithium difluoro(oxalato)borate (LiDFOB). The first organic solvent may comprise a carbonate-based compound. The second organic solvent may comprise a dinitrile-based compound and a mononitrile-based compound. The crosslinking polymer may comprise an ester-based compound.

[0079] The above gel polymer electrolyte can suppress lithium dendrites by reducing side reactions between lithium and the electrolyte, has excellent ion conductivity and high oxidation stability, and can prevent corrosion of lithium metal.

[0080] A gel polymer electrolyte can be formed by adding a cross-linking polymer to a liquid electrolyte containing a first lithium salt, a second lithium salt, a first organic solvent, and a second organic solvent.

[0081] The gel polymer electrolyte can effectively prevent the deterioration of the lithium battery by suppressing side reactions with the lithium metal layer (230) during charging and discharging of the lithium battery.

[0082] The first lithium salt may include a fluorinated lithium salt. The fluorinated lithium salt may be used without limitation as long as it is one that is commonly used in electrolytes for lithium secondary batteries. In addition, the fluorinated lithium salt may be used as a combination of one or more fluorinated lithium salts. For example, the above-mentioned fluorinated lithium salt may include lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrafluoroborate (LiBF4), lithium perfluorooxalatoborate (LiPFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoroethylene carbonate (LiFEC), or a combination thereof.

[0083] The second lithium salt may include lithium difluoro(oxalato)borate (LiDFOB).

[0084] The first lithium salt may be added at a concentration of, for example, 0.1 M to 2 M, 0.2 M to 2 M, 0.3 M to 1.8 M, 0.4 M to 1.5 M, 0.5 M to 1.2 M, or 0.5 M to 1 M, but is not limited thereto as long as the concentration range can be appropriately selected by a person skilled in the art.

[0085] The second lithium salt may be added at a concentration of, for example, 0.1 M to 1 M or less, 0.1 M to 1 M, 0.2 M to 1 M, 0.3 M to 0.9 M, 0.4 M to 0.8 M, 0.4 M to 0.7 M, or 0.5 M to 0.6 M, but is not limited thereto as long as the concentration range can be appropriately selected by a person skilled in the art.

[0086] The sum of the concentrations of the first lithium salt and the second lithium salt may be, for example, 0.5 M to 5 M, 0.5 M to 4 M, 0.5 M to 3 M, 0.6 M to 3 M, 0.6 M to 2 M, 0.8 M to 2 M, or 1 M to 2 M, but is not limited thereto as long as the sum of the concentrations of the first lithium salt and the second lithium salt is within a range that can be appropriately selected by a person skilled in the art.

[0087] The concentration ratio of the first lithium salt and the second lithium salt may be 0.5:1 to 3:1, 0.5:1 to 2.5:1, 0.5:1 to 2:1, or 1:1 to 2:1, but is not limited thereto as long as the concentration range of the first lithium salt and the second lithium salt can be appropriately selected by a person skilled in the art. The above concentration ratio may be based on molar concentration.

[0088] Excellent lithium conductivity can be achieved by using a mixture of the first lithium salt and the second lithium salt. By using the second lithium salt, dendrite growth at the cathode can be suppressed and oxidation stability can be increased.

[0089] The first organic solvent may include a carbonate-based compound. The carbonate-based compound may be used without limitation as long as it is one that is commonly used in electrolytes for lithium secondary batteries. For example, one or more carbonate-based compounds may be used as a mixture. For example, a mixture of a cyclic carbonate and a chain carbonate may be used as the carbonate-based compound.

[0090] Carbonate compounds may include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, propylene carbonate, ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, vinylene carbonate, or combinations thereof.

[0091] The first organic solvent may include a chain-type carbonate compound, a cyclic carbonate compound, or a combination thereof. The chain-type and cyclic carbonate compounds may be used without limitation as long as they are those commonly used in electrolytes for lithium secondary batteries.

[0092] The above-mentioned chain-type carbonate compounds may include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, or a combination thereof.

[0093] The above-mentioned cyclic carbonate compounds may include, for example, ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, vinylene carbonate, propylene carbonate, or a combination thereof.

[0094] Among the above carbonate compounds, if a cyclic carbonate compound with high viscosity and high dielectric constant and a chain carbonate compound with low viscosity and low dielectric constant are mixed in an appropriate ratio, an electrolyte with higher ionic conductivity can be produced.

[0095] The weight ratio of chain carbonate and ring carbonate when mixing the above carbonate-based compounds may be, for example, 0.5:1 to 5:1, 0.5:1 to 4:1, 0.5:1 to 3.5:1, or 0.8:1 to 3:1, but is not limited thereto as long as it is within a range that can be appropriately selected by a person skilled in the art.

[0096] The second organic solvent may include dinitrile-based compounds and mononitrile-based compounds. Dinitrile-based compounds and mononitrile-based compounds may be used without limitation as long as they are those commonly used in electrolytes for lithium secondary batteries.

[0097] Dainitrile-based compounds may include, for example, malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, or combinations thereof.

[0098] Mononitrile compounds may include, for example, acetonitrile, propionitrile, butyronitrile, pentanonitrile, hexanonitrile, heptanonitrile, or combinations thereof.

[0099] The above dinitrile-based compound and mononitrile-based compound may be mixed in a weight ratio of, for example, 1:2.5 to 2.5:1, 0.5:1 to 2.5:1, 0.5:1 to 2:1, 0.5:1 to 1.5:1, 0.6:1 to 1.2:1, 0.7:1 to 1.1:1, or 0.8:1 to 1:1. When the dinitrile-based compound and the mononitrile-based compound satisfy the above ranges, an electrolyte with excellent ionic conductivity and high oxidation stability can be prepared.

[0100] Dinitrile-based compounds possess high oxidation stability, but their high viscosity can impede ion conductivity. By mixing and using low-viscosity mononitrile-based compounds, it is possible to manufacture an electrolyte with high oxidation stability and excellent ion conductivity.

[0101] The content of the dinitrile-based compound may be 40% by weight or less of the total content of 100% by weight of the gel polymer electrolyte. For example, it may be greater than 0% and less than or equal to 40% by weight, 5% to 40% by weight, 10% to 40% by weight, or 15% to 35% by weight, but is not limited thereto.

[0102] The content of the mononitrile-based compound may be 40% by weight or less of the total content of 100% by weight of the gel polymer electrolyte. For example, it may be greater than 0% and less than or equal to 40% by weight, 5% to 40% by weight, 10% to 40% by weight, or 15% to 35% by weight, but is not limited thereto.

[0103] The first organic solvent and the second organic solvent may be mixed in a weight ratio of, for example, 3:7 to 7:3, 3.5:6.5 to 6.5:3.5, or 4:6 to 6:4, but are not limited thereto as long as they are within a range that can be appropriately selected by a person skilled in the art.

[0104] The gel polymer electrolyte may include a liquid electrolyte containing a first lithium salt, a second lithium salt, a first organic solvent, and a second organic solvent, and a cross-linked polymer. The cross-linked polymer is a polymerization product of a cross-linkable monomer.

[0105] The cross-linked polymer may include ester-based compounds. Ester-based compounds may be used without restriction as long as they are those commonly used in electrolytes for lithium secondary batteries.

[0106] Crosslinked polymers are polymerization products of crosslinkable monomers. Crosslinkable monomers include, for example, trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), ethylene glycol dimethacrylate (EGDMA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate (PO(3)TMPTA), propoxylated (6) trimethylolpropane triacrylate (PO(6)TMPTA), It may include propoxylated(6) trimethylolpropane triacrylate), ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate (PETA), propoxylated glyceryl triacrylate, dipentaerythritol pentaacrylate (DPEPA), or a combination thereof.

[0107] The content of the crosslinking polymer may be, for example, less than 60 wt%, 1 wt% to 50 wt%, 1 wt% to 45 wt%, 1 wt% to 40 wt%, 1 wt% to 35 wt%, 1 wt% to 30 wt%, 1 wt% to 25 wt%, 1 wt% to 20 wt%, 1 wt% to 15 wt%, 1 wt% to 10 wt%, 1 wt% to 9 wt%, 1 wt% to 8 wt%, 1 wt% to 7 wt%, 1 wt% to 6 wt%, or 1 wt% to 5 wt% based on the total weight of the gel polymer electrolyte, but is not limited thereto as long as it is an appropriate concentration that can form a gel polymer electrolyte by adding it to a liquid electrolyte.

[0108] The ionic conductivity of the gel polymer electrolyte at 25 ℃ and 1 atm may be 0.5 mS / cm, 1.0 mS / cm, 1.5 mS / cm, 2.0 mS / cm, 2.5 mS / cm, 3.0 mS / cm, 3.5 mS / cm, 4.0 mS / cm, or 4.5 mS / cm or higher. The ionic conductivity of the gel polymer electrolyte at 25°C and 1 atm may be 0.5 mS / cm to 10.0 mS / cm, 1.0 mS / cm to 10.0 mS / cm, 1.5 mS / cm to 10.0 mS / cm, 2.0 mS / cm to 10.0 mS / cm, 2.5 mS / cm to 10.0 mS / cm, 3.0 mS / cm to 10.0 mS / cm, 3.5 mS / cm to 10.0 mS / cm, 4.0 mS / cm to 10.0 mS / cm, or 4.5 mS / cm to 10.0 mS / cm.

[0109] As the gel polymer electrolyte has an ionic conductivity within this range, the internal resistance of the lithium battery equipped with the gel polymer electrolyte is reduced, and consequently, the reversibility of the electrode reaction of the lithium battery can be improved. Ionic conductivity can be measured, for example, using AC impedance analysis.

[0110] Gel polymer electrolytes can have high oxidation stability while possessing ionic conductivity as described above.

[0111] The oxidative stability of the gel polymer electrolyte can be verified, for example, by measuring the initial oxidative decomposition voltage. The initial oxidative decomposition voltage of the gel polymer electrolyte may be, for example, 4.0 V, 4.5 V, or 5.0 V or higher. The initial oxidative decomposition voltage of the gel polymer electrolyte may be 4.0 V to 8.0 V, 4.5 V to 8.0 V, or 5.0 V to 8.0 V.

[0112] Gel polymer electrolytes can have excellent lifespan characteristics by having high ionic conductivity and excellent oxidation stability.

[0113] A gel polymer electrolyte can be formed by crosslinking a composition for forming a gel polymer electrolyte. The method of crosslinking the composition for forming a gel polymer electrolyte is not particularly limited and may be crosslinked by, for example, heat, ultraviolet light, etc. Thermal crosslinking may be used from the perspective of manufacturing efficiency. The composition for forming a gel polymer may include, for example, a thermal initiator. The thermal initiator may be, for example, t-amyl peroxide, azobis-based, etc., but is not limited to these; any material used as a thermal initiator in the relevant technical field is acceptable. The content of the thermal initiator may be 0.1% by weight or less or 0.05% by weight or less of the total weight of the composition for forming a gel polymer electrolyte. The crosslinking product of the composition for forming a gel polymer electrolyte may be, for example, the result of heat treatment at 60 to 90°C for 1 to 3 hours. The heat treatment conditions may be adjusted according to the type of thermal initiator used.

[0114]

[0115] lithium metal battery (100)

[0116] Referring to FIGS. 1 and 2, a lithium metal battery (100) according to one embodiment may include an electrode assembly (40) comprising a positive electrode (10), a negative electrode (20), and a separator (30) disposed between the positive electrode (10) and the negative electrode (20). Although not illustrated, the positive electrode (10), the negative electrode (20), and the separator (30) of the electrode assembly (40) may be supported by a gel polymer electrolyte. Since the configuration of the positive electrode (10), the negative electrode (20), the gel polymer electrolyte, etc., can be applied as described above, a detailed description is omitted below.

[0117] According to one embodiment, referring to FIG. 1, the negative electrode (20) may include only a negative electrode current collector (21). According to another embodiment, referring to FIG. 2, the negative electrode (20) may include a negative electrode current collector (21) and a lithium metal layer (22) on the negative electrode current collector (21).

[0118] Referring to FIGS. 1 and 2, the positive electrode (10), the separator (30), and the negative electrode (20) may be wound, folded, or stacked to form an electrode assembly (40). Referring to FIGS. 3 and 4, the formed electrode assembly (40) may be housed in a battery case (50). The battery case (50) may contain a gel polymer electrolyte inside. In one embodiment, the battery case (50) may be of the pouch type.

[0119] The main body forming the pouch-type battery case according to one embodiment may be composed of a multilayer film, and the multilayer film may include an aluminum (Al) layer, a polymer film, and an adhesive layer. In this case, a pouch-type cell with a flexible and lightweight structure can be manufactured.

[0120]

[0121] Method for manufacturing a lithium metal battery

[0122] A lithium metal battery according to one embodiment may be manufactured by arranging a negative electrode current collector, a separator, and a positive electrode to form an electrode assembly; housing the electrode assembly in a battery case, and then injecting a composition for forming a gel polymer electrolyte into the battery case; and curing the composition for forming a gel polymer electrolyte to form the gel polymer electrolyte described above.

[0123] A composition for forming a gel polymer electrolyte may include a crosslinkable monomer, a first lithium salt, a second lithium salt, a first organic solvent, a second organic solvent, and a thermal initiator. Since the details regarding the crosslinkable monomer, the first lithium salt, the second lithium salt, the first organic solvent, and the second organic solvent can be applied as described above, a detailed description is omitted below.

[0124] The thermal initiator may include, for example, t-amyl peroxide, benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), dicumyl peroxide (DCP), tert-butyl peroxybenzoate (TBPB), lauroyl peroxide, or a combination thereof. The content of the thermal initiator may be 0.1 wt% or less or 0.05 wt% or less of the total weight of the composition for forming the gel polymer electrolyte.

[0125] Injecting the composition for forming a gel polymer electrolyte into the battery case can be performed under vacuum so that the composition can sufficiently penetrate the positive electrode, negative electrode, and separator.

[0126] Methods for curing a composition for forming a gel polymer electrolyte include curing using heat treatment, UV, or high-energy radiation (electron beam, γ-ray). The curing reaction using heat treatment can be carried out for 30 to 120 minutes at a temperature of 40 to 120 ℃, for example, 50 to 90 ℃.

[0127] The above heat treatment varies depending on the type of crosslinkable monomer, but can be performed, for example, at 40 to 120°C. When the heat treatment is performed within the above range, the electrolyte wettability of the separator is increased, thereby providing a lithium metal battery (100) with improved lifespan characteristics.

[0128]

[0129] The creative idea is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the creative idea and do not limit the scope of the creative idea to these examples alone.

[0130]

[0131] Example 1

[0132] (Electrolyte manufacturing)

[0133] A liquid electrolyte was prepared by adding 0.6 M lithium hexafluorophosphate (LiPF6), 0.3 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 0.6 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed in a weight ratio of 15:25:15:20:25 with ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile.

[0134] A composition for forming a gel polymer electrolyte was prepared by adding the crosslinking monomer dipentaerythritol hexaacrylate (DPHA) to form a gel electrolyte.

[0135] At this time, the content of DPHA is 4% by weight relative to the total weight of the composition for forming the gel polymer electrolyte.

[0136] (Manufacture of cathode current collector)

[0137] A copper foil with a thickness of 10 μm was used as the cathode current collector.

[0138] (Anode manufacturing)

[0139] LiNi 0.8 Co 0.15 Al 0.05 O2 (NCA) powder and carbon conductive material (Super-P; Timcal Ltd.) were uniformly mixed in a weight ratio of 97:1.5, and then a PVDF (polyvinylidene fluoride) binder solution was added to prepare an anode active material slurry with a weight ratio of active material:carbon-based conductive material:binder = 97:1.5:1.5.

[0140] The prepared slurry was coated onto an aluminum substrate with a thickness of 20 μm using a doctor blade, dried under reduced pressure at 120 °C, and then rolled into a sheet shape using a roll press to manufacture an anode. The thickness of the anode active material layer was 80 μm.

[0141] (Lithium battery manufacturing)

[0142] A laminate was prepared by placing a polyethylene separator between the manufactured positive and negative current collectors. After injecting the gel polymer electrolyte forming composition prepared in Example 1 into the prepared laminate, a lithium battery containing a gel polymer electrolyte was manufactured by thermally crosslinking in a 70°C oven for 1 hour and 30 minutes.

[0143] The lithium battery had a structure of positive electrode / gel polymer electrolyte (separator) / negative electrode current collector.

[0144]

[0145] Example 2

[0146] In Example 2, a lithium metal battery was manufactured in the same manner as in Example 1 described above, except that the electrolyte composition was changed. The electrolyte of Example 2 was prepared as follows.

[0147] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4) and 0.6 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed with ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 15:25:15:20:25.

[0148] A composition for forming a gel polymer electrolyte was prepared by adding a crosslinkable monomer, dipentaerythritol hexaacrylate (DPHA), to form a gel electrolyte. At this time, the content of DPHA is 4% by weight of the total weight of the composition for forming the gel polymer electrolyte.

[0149]

[0150] Example 3

[0151] In Example 3, a lithium metal battery was manufactured in the same manner as in Example 1 described above, except that the electrolyte composition was changed. The electrolyte of Example 3 was prepared as follows.

[0152] A liquid electrolyte was prepared by adding 0.5 M lithium tetrafluoroborate (LiBF4), 0.5 M lithium bis(fluorosulfonyl)imide (LiFSI), and 0.5 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed with diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 30:10:30:30.

[0153] A composition for forming a gel polymer electrolyte was prepared by adding the crosslinkable monomer trimethylolpropane trimethacrylate (TMPTMA) to form a gel electrolyte. At this time, the content of TMPTMA is 4% by weight of the total weight of the composition for forming the gel polymer electrolyte.

[0154]

[0155] Example 4

[0156] In Example 4, a lithium metal battery was manufactured in the same manner as in Example 1 described above, except that the electrolyte composition was changed. The electrolyte of Example 4 was prepared as follows.

[0157] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4), 0.3 M lithium bis(fluorosulfonyl)imide (LiFSI), and 0.6 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed with diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 30:10:30:30.

[0158] A composition for forming a gel polymer electrolyte was prepared by adding the crosslinkable monomer trimethylolpropane trimethacrylate (TMPTMA) to form a gel electrolyte. At this time, the content of TMPTMA is 4% by weight of the total weight of the composition for forming the gel polymer electrolyte.

[0159]

[0160] Comparative Example 1: No LiDFOB added

[0161] In Comparative Example 1, a lithium metal battery was manufactured in the same manner as in Example 1 described above, except that the electrolyte composition was changed. The electrolyte of Comparative Example 1 was prepared as follows.

[0162] A liquid electrolyte was prepared by adding 0.6 M lithium hexafluorophosphate (LiPF6) and 0.3 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to a solvent mixed with ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 15:25:15:20:25.

[0163] A composition for forming a gel polymer electrolyte was prepared by adding a crosslinkable monomer, dipentaerythritol hexaacrylate (DPHA), to form a gel electrolyte. At this time, the content of DPHA is 4% by weight of the total weight of the composition for forming the gel polymer electrolyte.

[0164]

[0165] Comparative Example 2: No crosslinkable monomer added

[0166] Comparative Example 2 is a liquid electrolyte without added crosslinkable monomer, and a lithium metal battery was manufactured using the same method as the lithium metal battery manufacturing process of Example 1 described above, except for the thermal crosslinking step. The electrolyte of Comparative Example 2 was prepared as follows.

[0167] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4) and 0.6 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed with ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 45:35:15:2.5:2.5, without adding a crosslinking monomer.

[0168]

[0169] Comparative Example 3: Change in the ratio of dinitrile-based compounds and mononitrile-based compounds

[0170] In Comparative Example 3, a lithium metal battery was manufactured in the same manner as in Example 1 described above, except that the electrolyte composition was changed. The electrolyte of Comparative Example 3 was prepared as follows.

[0171] A liquid electrolyte was prepared by adding 0.6 M lithium tetrafluoroborate (LiBF4) and 0.6 M lithium difluoro(oxalato)borate (LiDFOB) to a solvent mixed with ethylene carbonate (EC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), glutaronitrile, and butytronitrile in a weight ratio of 15:20:10:40:15.

[0172] A composition for forming a gel polymer electrolyte was prepared by adding a crosslinkable monomer, dipentaerythritol hexaacrylate (DPHA), to form a gel electrolyte. At this time, the content of DPHA is 4% by weight of the total weight of the composition for forming the gel polymer electrolyte.

[0173]

[0174] Table 1 below shows the compositions of the above-described Examples 1 to 4 and Comparative Examples 1 to 3.

[0175] Lithium Salt Organic Solvent Crosslinkable Monomer (WHg*) Lithium Salt 1 Lithium Salt 2 Example 1 LiPF6 0.6 M, LiTFSI 0.3 M LiDFOB 0.6 MEC:DEC:FEC:Glutaronitrile:Butytronitrile = 15:25:15:20:25 DPHA (4 WHg) Example 2 LiBF4 0.6 M LiDFOB 0.6 MEC:DEC:FEC:Glutaronitrile:Butytronitrile = 15:25:15:20:25 DPHA (4 WHg) Example 3 LiBF4 0.5 M, LiFSI 0.5 M LiDFOB 0.5 MEC:FEC:Glutaronitrile:Butytronitrile = 30:10:30:30 TMPTMA (4 WHg) Example 4 LiBF4 0.6 M, LiFSI 0.3 M LiDFOB 0.6 MDEC:FEC:Glutaronitrile:Butytronitrile = 30:10:30:30 TMPTMA (4 wt%) Comparative Example 1 LiPF6 0.6 M, LiTFSI 0.3 M - EC:DEC:FEC:Glutaronitrile:Butytronitrile = 15:25:15:20:25 DPHA (4 wt%) Comparative Example 2 LiBF 40.6 MLiDFOB 0.6 MEC:DEC:FEC:Glutaronitrile:Butytronitrile = 45:35:15:2.5:2.5 - Comparative Example 3 LiBF 40.6 MLiDFOB 0.6 MEC:DEC:FEC:Glutaronitrile:Butytronitrile = 15:20:10:40:15 DPHA (4 wt%)

[0176] * The content of the above-mentioned crosslinkable monomer refers to weight% relative to the total weight of the gel polymer electrolyte.

[0177] Evaluation Example 1: Ionic Conductivity and Oxidation Stability of Lithium Metal Battery

[0178] The ionic conductivity and oxidation stability of the gel polymer electrolytes used in the lithium metal batteries of Examples 1 to 4 and Comparative Examples 1 to 3 were measured.

[0179] In the case of ionic conductivity, it was measured using the AC impedance method. Specifically, ionic conductivity was measured by applying a voltage bias of 10 mV to the electrolyte in the frequency range of 0.1 Hz to 1 MHz, scanning the temperature, and measuring the resistance.

[0180] Oxidative stability was verified by measuring the initial oxidative decomposition voltage. Specifically, the initial oxidative decomposition voltage of the electrolyte was measured at room temperature (25 °C) using linear sweep voltammetry (LSV). For the measurement, a three-electrode electrochemical cell was used, with a Pt electrode as the working electrode and Li as the counter and reference electrodes. The voltage was scanned from 0 V to 7 V at a rate of 1 mV / sec. The initial oxidative decomposition voltage of the electrolyte refers to the voltage at which the current becomes 0.001 mA.

[0181] Looking at Table 2, it can be confirmed that the initial oxidative decomposition voltage of Examples 1 to 4 is higher than that of the Comparative Example, indicating stability against oxidative decomposition.

[0182]

[0183] Ionic Conductivity (mS / cm) Initial Oxidative Decomposition Voltage (V) Example 16.5 5.4 Example 24.9 5.3 Example 35.0 5.7 Example 4 4.8 5.6 Comparative Example 15.5 5.1 Comparative Example 25.3 4.3 Comparative Example 33.7 5.3

[0184] That is, it can be confirmed that the gel polymer electrolytes of Examples 1 to 4 have excellent ionic conductivity despite having higher oxidation stability compared to the comparative example.

[0185] Evaluation Example 2: Initial Charge / Discharge Efficiency and Lifetime Characteristics of a Lithium Metal Battery

[0186] The initial charge / discharge efficiency and lifespan characteristics of the lithium metal batteries of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated under the following conditions.

[0187] Constant current charging was performed at 25 ℃ with a current rate of 0.1 C until the voltage reached 4.2 V (vs. Li), and then cut-off was performed at a current rate of 0.05 C while maintaining 4.2 V in constant voltage mode. Subsequently, discharge was performed at a constant current rate of 0.1 C until the voltage reached 3.0 V (vs. Li) during discharge (formation cycle).

[0188] A lithium metal battery that has undergone a formation cycle was charged at 25°C at a current rate of 0.2 C until the voltage reached 4.2 V (vs. Li), and then cut off at a current rate of 0.05 C while maintaining 4.2 V in constant voltage mode. Subsequently, it was discharged at a constant current rate of 0.2 C until the voltage reached 3.0 V (vs. Li) during discharge (1st cycle). These cycles were repeated under the same conditions until the capacity retention rate reached 80%.

[0189] In all charge / discharge cycles, a 10-minute pause was taken after each charge / discharge cycle.

[0190] Initial charge / discharge efficiency (ICE) is defined by the following Equation 1:

[0191] <Mathematical Formula 1>

[0192] Initial charge / discharge efficiency [%] = [First cycle discharge capacity / First cycle charge capacity] × 100

[0193] Life characteristics are defined as the number of cycle repetitions until the capacity retention rate reaches 80%, and the capacity retention rate is defined by the following mathematical formula 2.

[0194] <Mathematical Formula 2>

[0195] Capacity Retention Rate [%] = [Discharge Capacity after n cycles / Discharge Capacity at 1st cycle] × 100 (%)

[0196] (where n is a natural number greater than or equal to 2)

[0197] The results of the room temperature charge / discharge experiment are shown in Table 3 below.

[0198] Initial Charge / Discharge Efficiency (%) Lifespan Characteristics**(Number of Cycles) Example 188.6211 Example 289.4225 Example 388.2217 Example 488.3212 Comparative Example 187.5153 Comparative Example 287.4163 Comparative Example 388.1189

[0199] ** Life characteristics are defined as the number of cycle repetitions until the capacity retention rate reaches 80%.

[0200] Referring to Table 3, it can be confirmed that the lithium metal batteries according to Examples 1 to 4 have excellent initial efficiency and lifespan characteristics. In particular, it was confirmed that the lithium metal batteries according to Examples 1 to 4 stably maintain a capacity retention rate of 80% or more even after more than 200 cycles.

[0201]

[0202] Although exemplary embodiments have been described in detail with reference to the attached drawings, the present creative idea is not limited to such examples. It is obvious that a person skilled in the art to which the present creative idea belongs can derive various variations or modifications within the scope of the technical idea described in the patent claims, and these also naturally fall within the technical scope of the present creative idea.

Claims

1. A first lithium salt comprising a fluorine-based lithium salt; A second lithium salt comprising lithium difluoro(oxalato)borate (LiDFOB); A first organic solvent comprising a carbonate-based compound; A second organic solvent comprising a dinitrile-based compound and a mononitrile-based compound; and A cross-linked polymer comprising an ester-based compound; The second organic solvent comprises the dinitrile-based compound and the mononitrile-based compound in a weight ratio of 1:2.5 to 2.5:

1. Gel polymer electrolyte.

2. In Paragraph 1, The first lithium salt comprises lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium tetrafluoroborate (LiBF4), lithium perfluorooxalatoborate (LiPFOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium fluoroethylene carbonate (LiFEC), or a combination thereof. Gel polymer electrolyte.

3. In Paragraph 1, The concentration of the second lithium salt is 0.1 M to 1.0 M, Gel polymer electrolyte.

4. In Paragraph 1, The sum of the concentrations of the first lithium salt and the second lithium salt is 0.5 M to 5 M, Gel polymer electrolyte.

5. In Paragraph 1, The concentration ratio of the first lithium salt and the second lithium salt is 0.5:1 to 3:

1. Gel polymer electrolyte.

6. In Paragraph 1, The first organic solvent comprises dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, propylene carbonate, ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylene carbonate, vinylene carbonate, or a combination thereof. Gel polymer electrolyte.

7. In Paragraph 6, The first organic solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, or a combination thereof; and Fluoroethylene Carbonate (FEC), Ethylene Carbonate (EC), Butylene Carbonate, Vinylene Carbonate, Propylene Carbonate, or a combination thereof, comprising Gel polymer electrolyte.

8. In Paragraph 1, The above dinitrile-based compound comprises malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, or a combination thereof. Gel polymer electrolyte.

9. In Paragraph 1, The above dinitrile-based compound comprises malononitrile, succinonitrile, glutaronitrile, or a combination thereof. Gel polymer electrolyte.

10. In Paragraph 1, The above mononitrile-based compound comprises acetonitrile, propionitrile, butyronitrile, pentanonitrile, hexanonitrile, heptanonitrile, or a combination thereof. Gel polymer electrolyte.

11. In Paragraph 1, The above mononitrile-based compound comprises propionitrile, butyronitrile, pentanonitrile, or a combination thereof. Gel polymer electrolyte.

12. In Paragraph 1, The weight ratio of the first organic solvent and the second organic solvent is 3:7 to 7:3, Gel polymer electrolyte.

13. In Paragraph 1, The above-mentioned crosslinked polymer is a polymerization product of crosslinkable monomers, and The above-mentioned crosslinkable monomers are trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), ethylene glycol dimethacrylate (EGDMA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, trimethylolpropane triacrylate, propoxylated (3) trimethylolpropane triacrylate (PO(3)TMPTA), propoxylated (6) trimethylolpropane triacrylate (PO(6)TMPTA), Propoxylated(6) Trimethylolpropane Triacrylate), ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate (PETA), propoxylated glyceryl triacrylate, dipentaerythritol pentaacrylate (DPEPA), or a combination thereof, comprising Gel polymer electrolyte.

14. In Paragraph 1, The above-mentioned crosslinked polymer is a polymerization product of crosslinkable monomers, and The above-mentioned crosslinkable monomer comprises trimethylolpropane trimethacrylate (TMPTMA), dipentaerythritol hexaacrylate (DPHA), or a combination thereof, Gel polymer electrolyte.

15. In Paragraph 1, The content of the crosslinked polymer is 1% to 50% by weight based on the total weight of the gel polymer electrolyte, Gel polymer electrolyte.

16. A positive electrode comprising a positive current collector and a positive active material layer on the positive current collector; A cathode including a cathode current collector; A separator disposed between the anode and the cathode; and Comprising the gel polymer electrolyte of claim 1, Lithium metal battery.

17. In Paragraph 16, The above cathode further comprises a lithium metal layer disposed between the cathode current collector and the separator, Lithium metal battery.

18. In Paragraph 17, The above lithium metal layer comprises lithium or a lithium alloy, and The above lithium alloy comprises 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, or a combination thereof. Lithium metal battery.

19. Forming an electrode assembly by arranging a cathode current collector, a separator, and an anode; Housing the above electrode assembly in a battery case, and then injecting a composition for forming a gel polymer electrolyte into the battery case; and Comprising curing the above-mentioned composition for forming a gel polymer electrolyte to form the gel polymer electrolyte of claim 1, Method for manufacturing a lithium metal battery.

20. In Paragraph 19, The process of curing the above-mentioned composition for forming a gel polymer electrolyte to form a gel polymer electrolyte includes a curing reaction using heat treatment, and The above heat treatment is performed at 40 to 120 ℃, Method for manufacturing a lithium metal battery.

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