Secondary batteries

Abstract

A secondary battery is presented comprising a positive electrode layer; a negative electrode layer; and a flexible electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the negative electrode layer comprises a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, and the initial charge capacity of the first negative electrode active material layer is less than 50% of the initial charge capacity of the positive electrode active material layer.

Description

[Technical Field]

[0001] This invention relates to a secondary battery. [Background technology]

[0002] Recently, industrial demands have led to active development of batteries with high energy density and safety. For example, lithium batteries are used in a variety of applications, including information equipment, communication equipment, and automobiles. Since automobiles are life-saving devices, safety is of paramount importance.

[0003] Lithium batteries using liquid electrolytes may have an increased risk of fire and / or explosion in the event of a short circuit. Secondary batteries using solid electrolytes instead of liquid electrolytes have been proposed. Solid electrolytes have a lower risk of ignition compared to liquid electrolytes.

[0004] By employing a solid electrolyte in rechargeable batteries, the possibility of fire and explosion can be reduced. Rechargeable batteries using solid electrolytes can offer improved safety. [Overview of the project] [Problems that the invention aims to solve]

[0005] The problem that this invention aims to solve is to provide a secondary battery having improved cycle characteristics by arranging a flexible electrolyte layer between the positive electrode layer and the negative electrode layer. [Means for solving the problem]

[0006] According to one embodiment, It includes a positive electrode layer; a negative electrode layer; and a flexible electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector. The negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector. A secondary battery is provided in which the initial charge capacity of the first negative electrode active material layer is less than 50% of the initial charge capacity of the positive electrode active material layer. [Effects of the Invention]

[0007] According to one embodiment, by arranging a flexible electrolyte layer between the positive electrode layer and the negative electrode layer, the interfacial resistance between the positive electrode layer and / or the negative electrode layer and the electrolyte layer is reduced, and cracks in the solid electrolyte layer during the charge and discharge process are suppressed, thereby providing a secondary battery with improved cycle characteristics. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view of a secondary battery according to one exemplary embodiment. [Figure 2] This is a cross-sectional view of a secondary battery according to one exemplary embodiment. [Figure 3] This is a cross-sectional view of a secondary battery according to one exemplary embodiment. [Figure 4] This is a cross-sectional view of a secondary battery according to one exemplary embodiment. [Figure 5] This is a schematic diagram of a secondary battery according to one exemplary embodiment. [Figure 6] This is a schematic diagram of a secondary battery according to one exemplary embodiment. [Figure 7] This is a schematic diagram of a secondary battery according to one exemplary embodiment. [Modes for carrying out the invention]

[0009] Unless otherwise specifically defined, all terms used in this invention (including technical and scientific terms) have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Furthermore, terms as defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the relevant art and in the context of this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0010] The present invention is described with reference to exemplary embodiments and cross-sectional views which are schematic diagrams of idealized embodiments. Thus, deformation from the illustrated shape must be expected as a result of, for example, manufacturing techniques and / or tolerances. Accordingly, embodiments described herein should not be construed as being limited to specific shapes of regions as illustrated herein, and should include, for example, deviations of shape caused by manufacturing. For example, a region illustrated or described as flat may typically be rough and / or have nonlinear features. Furthermore, corners that are sharply illustrated may also be rounded. Accordingly, regions illustrated in the drawings are essentially schematic, and their shapes are not intended to illustrate the exact shape of the region and are not intended to limit the scope of the claims.

[0011] This inventive idea can be realized in various other forms and should not be construed as being limited to the embodiments described herein. The embodiments are provided to ensure that the invention is thorough and complete, and to fully convey the scope of this inventive idea to those ordinary skill in the art. Same reference numerals refer to the same components.

[0012] When one component is said to be "on top of" another, one will understand that it is either directly above the other component or that the other component may be interposed between them. In contrast, when one component is said to be "directly on top of" another, there is no component interposed between them.

[0013] The terms "first," "second," "third," etc., may be used in the present invention to describe a variety of components, elements, regions, layers, and / or areas, but these components, elements, regions, layers, and / or areas should not be limited by these terms. These terms are used to distinguish one component, element, region, layer, or area from other elements, elements, regions, layers, or areas. Accordingly, the first component, element, region, layer, or area described below may be referred to as the second component, element, region, layer, or area without deviating from the teachings of the present invention.

[0014] The terminology used in this invention is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular form used in this application includes plural forms, including “at least one,” unless the content expressly indicates otherwise. “At least one” should not be construed as limiting to the singular. As used in this invention, the term “and / or” includes all any combination of one or more of the list items. The terms “including” and / or “including” used in the detailed description specify the presence of expressed features, regions, integers, stages, operations, components, and / or ingredients, and do not exclude the presence or addition of one or more other features, regions, integers, stages, operations, components, ingredients, and / or groups thereof.

[0015] Spatially relative terms such as “down,” “underside,” “bottom,” “up,” “top,” and “upper” may be used here to easily describe the relationship between one component or feature and other components or features. Spatially relative terms will be understood to be intended to include different orientations of the device when used or operated in addition to the orientation illustrated in the drawings. For example, if the device in the drawings is inverted, a component described as “below” or “below” another component or feature will be oriented “above” the other component or feature. Thus, the exemplary term “down” may encompass both upward and downward. The device may be positioned in other orientations (rotated 90° or in different directions), and the spatially relative terms used in this invention may be interpreted accordingly.

[0016] "Group" refers to a group of elements in the periodic table according to the International Union of Pure and Applied Chemistry ("IUPAC") classification system of groups 1-18.

[0017] In this invention, "particle size" refers to the average diameter when the particle is spherical, and to the average major axis length when the particle is non-spherical. The particle size can be measured using a particle size analyzer (PSA). "Particle size" is, for example, the average particle size. "Average particle size" is, for example, the median particle size, D50.

[0018] D50 is the particle size that corresponds to the 50% cumulative volume calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0019] D90 is the particle size that corresponds to the 90% cumulative volume calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0020] D10 is the particle size that corresponds to the 10% cumulative volume, calculated from the smallest particle size in the particle size distribution measured by laser diffraction.

[0021] In this invention, "viscosity" can be measured using a viscometer, such as a rotational viscometer like Brookfield's LV DV-II + Pro Viscometer (cone-plate type). Viscosity can be measured, for example, by dissolving an ionic liquid in dimethylformamide (DMF) at a concentration of 35 wt%, and then measuring at 1 atm and 25°C. For example, when measuring viscosity, the spindle is set to S40, rpm 15, and the sample loading volume is 1 mL.

[0022] In this invention, "weight-average molecular weight" may refer to a converted value relative to standard polystyrene measured by GPC (Gel Permeation Chromatography). The molecular weight is, for example, the weight-average molecular weight. For example, weight-average molecular weight measurement using GPC may be performed using an Agilent 1200 series, an Agilent PL mixed B column, and THF as the solvent.

[0023] In this invention, "metal" includes both metals and metalloids such as silicon and germanium, in either an elemental or ionic state.

[0024] In this invention, "alloy" means a mixture of two or more metals.

[0025] In this invention, "electrode active material" means an electrode material that can be lithium-treated and delithiated.

[0026] In this invention, "positive electrode active material" means a positive electrode material that can be lithium-ionized and delithiated.

[0027] In this invention, "negative electrode active material" means a negative electrode material that can be lithium-treated and delithiated.

[0028] In this invention, "lithification" and "lithification" refer to the process of adding lithium to the electrode active material.

[0029] In this invention, "desitization" and "to delithiate" refer to the process of removing lithium from the electrode active material.

[0030] In this invention, "charging" and "to charge" refer to the process of providing electrochemical energy to a battery.

[0031] In this invention, "discharge" and "to discharge" refer to the process of removing electrochemical energy from a battery.

[0032] In this invention, "positive electrode" and "cathode" refer to electrodes in which electrochemical reduction and lithiumization occur during the discharge process.

[0033] In this invention, "negative electrode" and "anode" refer to electrodes in which electrochemical oxidation and delithiation occur during the discharge process.

[0034] While specific embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or foreseeable may arise for the applicant or those skilled in the art. Accordingly, the claims of the filed and modifiable appendix are intended to include all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0035] The following describes a secondary battery according to an exemplary embodiment in more detail.

[0036] [Secondary battery] A secondary battery according to one embodiment includes a positive electrode layer; a negative electrode layer; and a flexible electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on one or both sides of the positive electrode current collector (e.g., at least one side of the positive electrode current collector), and the negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on one side of the negative electrode current collector, wherein the initial charge capacity of the first negative electrode active material layer is less than 50% of the initial charge capacity of the positive electrode active material layer.

[0037] By including a flexible electrolyte layer between the positive and negative electrode layers in a secondary battery, the interfacial resistance between the positive and / or negative electrode layers and the electrolyte layer is reduced, allowing the flexible electrolyte layer to more easily accommodate volume changes in the positive and / or negative electrode layers during charging and discharging of the secondary battery. The flexibility of the flexible electrolyte layer provides improved adhesion to the positive and / or negative electrode layers compared to a non-flexible electrolyte layer, which can prevent or reduce detachment of the positive and / or negative electrode layers from the electrolyte layer. A non-flexible electrolyte layer is, for example, an inorganic solid electrolyte layer. Since the flexibility of the electrolyte layer has a low possibility of cracking, it can suppress or reduce non-uniformity of ionic conductivity within the flexible electrolyte layer during the charging and discharging process of the secondary battery. On the other hand, with a non-flexible electrolyte layer, non-uniformity of ionic conductivity within the solid electrolyte layer may increase compared to localized cracks during charging and discharging of the secondary battery. Since the formation of defects such as pinholes within the electrolyte layer is suppressed in the flexible electrolyte layer, it can more effectively suppress or reduce the growth of lithium dendrites through such defects during the charging and discharging process of the secondary battery, and thereby short circuits in the secondary battery. A flexible electrolyte layer can suppress or reduce water-induced side reactions such as gas generation within a secondary battery by providing improved moisture stability compared to a non-flexible electrolyte layer. It can also more effectively suppress or reduce the decrease in ionic conductivity of the electrolyte layer within the secondary battery. Therefore, the cycle characteristics of the secondary battery can be further improved. For example, the efficiency and lifespan characteristics of the secondary battery can be improved.

[0038] Referring to Figures 1 to 4, the secondary battery 1 includes a positive electrode layer 10; a negative electrode layer 20; and a flexible electrolyte layer 30 disposed between the positive electrode layer 10 and the negative electrode layer 20. The positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one or both sides of the positive electrode current collector 11 (e.g., at least one side of the positive electrode current collector 11). The negative electrode layer 20 includes a negative electrode current collector 21 and a first negative electrode active material layer 22 disposed on one side of the negative electrode current collector 21. The initial charge capacity of the first negative electrode active material layer 22 is less than 50% of the initial charge capacity of the positive electrode active material layer 12.

[0039] [Electrolyte layer] [Electrolyte layer: organic electrolyte] Referring to Figures 1 to 4, the secondary battery 1 includes an electrolyte layer 30 positioned between the positive electrode layer 10 and the negative electrode layer 20. The electrolyte layer 30 is flexible. The electrolyte layer 30 may contain, for example, an organic electrolyte. The electrolyte layer 30 is also, for example, an organic electrolyte layer. The electrolyte layer 30 may not contain, or may exclude, an inorganic electrolyte. The electrolyte layer 30 may not contain, or may exclude, an inorganic electrolyte layer 30. The electrolyte layer 30 does not contain, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. The flexibility of the electrolyte layer 30 may be further improved by not including an inorganic solid electrolyte.

[0040] The electrolyte layer 30 may include, for example, a polymer electrolyte, a liquid electrolyte, or a combination thereof. The viscosity of the polymer electrolyte is, for example, even higher than that of the liquid electrolyte. The viscosity of the liquid electrolyte may also be, for example, 10 cps or more at 25°C and 1 atm. The liquid electrolyte may also be, for example, a high-viscosity liquid electrolyte having a viscosity of 10 cps or more at 25°C and 1 atm.

[0041] A polymer electrolyte is an electrolyte containing a polymer. Polymer electrolytes may include, for example, polymer solid electrolytes, polymer gel electrolytes, or combinations thereof. Polymer electrolytes can be classified into polymer solid electrolytes or polymer gel electrolytes, for example, depending on whether or not they contain a liquid. Alternatively, polymer electrolytes can be classified into polymer solid electrolytes or polymer gel electrolytes depending on their state at 25°C and 1 atm. Polymer solid electrolytes may, for example, contain a mixture of lithium salt and polymer, or a polymer having ion-conducting functional groups. Polymer solid electrolytes are also polymer electrolytes that are in a solid state at 25°C and 1 atm. Polymer solid electrolytes do not contain liquid.

[0042] Polymeric gel electrolytes may, for example, contain a liquid electrolyte and a polymer, or an organic solvent and a polymer having ionic conductive functional groups. Liquid electrolytes may also be, for example, ionic liquids, mixtures of lithium salts and ionic liquids, mixtures of lithium salts and organic solvents, mixtures of ionic liquids and organic solvents, or mixtures of lithium salts, ionic liquids, and organic solvents. Polymeric gel electrolytes may also be polymer electrolytes that are in a gel state at 25°C and 1 atm. Polymeric gel electrolytes may also, for example, contain no liquid, with the polymer itself being in a gel state.

[0043] Lithium salts used in polymer electrolytes and / or liquid electrolytes are not limited and any lithium salts that can be used as lithium salts for electrolytes in the art may be used. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (where x and y are 1 to 20, respectively), LiCl, LiI, or mixtures thereof, etc.

[0044] The polymer electrolyte may include, for example, a polymer containing repeating units having a thermopolymerizable functional group, a thermoset of the polymer, an oligomer containing repeating units having a thermopolymerizable functional group, a thermoset of the oligomer, a monomer having a thermopolymerizable functional group, a thermoset of the monomer, an oligomeric ionic liquid, a polymeric ionic liquid, or a combination thereof.

[0045] Polymers containing repeating units having thermopolymerizable functional groups, thermosets of such polymers, and oligomers containing repeating units having thermopolymerizable functional groups may further contain repeating units that do not have thermopolymerizable functional groups. The repeating units that do not have thermopolymerizable functional groups are not limited and any repeating units derived from unsaturated group-containing monomers used in the production of copolymers in the art may be used. The repeating units that do not have thermopolymerizable functional groups are, for example, acrylic monomers such as methyl acrylate and ethyl acrylate.

[0046] Thermally polymerizable functional groups may include, for example, cyano groups, hydroxyl groups, amino groups, amide groups, imide groups, carboxyl groups, acid anhydride groups, or combinations thereof.

[0047] Polymers and / or oligomers containing repeating units having a thermally polymerizable functional group may include, for example, repeating units derived from cyano group-containing monomers, repeating units derived from hydroxyl group-containing monomers, repeating units derived from acid anhydride group-containing monomers, repeating units derived from amino group-containing monomers, repeating units derived from amide group-containing monomers, repeating units derived from imide group-containing monomers, repeating units derived from carboxyl group-containing monomers, or combinations thereof. Monomers having a thermally polymerizable functional group may include, for example, cyano group-containing monomers, hydroxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, imide group-containing monomers, carboxyl group-containing monomers, acid anhydride group-containing monomers, or combinations thereof.

[0048] Cyano group-containing monomers include, for example, unsaturated carboxylic acid nitrile monomers such as acrylonitrile, methacrylonitrile, and vinylidene cyanide; cyanoalkyl ester monomers of unsaturated carboxylic acids such as 2-cyanoethyl (meth)acrylate, 2-cyanopropyl (meth)acrylate, and 3-cyanopropyl (meth)acrylate; and CH=CH-C(=O)-(OCH2CH2) n -CN(n=1~20), etc.

[0049] Examples of hydroxyl group-containing monomers include hydroxyalkyl ester monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0050] Examples of amino group-containing monomers include aminoalkyl ester monomers of unsaturated carboxylic acids such as aminomethyl (meth)acrylate, methylaminomethyl (meth)acrylate, dimethylaminomethyl (meth)acrylate, 2-aminoethyl (meth)acrylate, 2-methylaminoethyl (meth)acrylate, 2-ethylaminoethyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2-n-propylaminoethyl (meth)acrylate, 2-n-butylaminoethyl (meth)acrylate, 2-aminopropyl (meth)acrylate, 2-methylaminopropyl (meth)acrylate, 2-dimethylaminopropyl (meth)acrylate, 3-aminopropyl (meth)acrylate, 3-methylaminopropyl (meth)acrylate, and 3-dimethylaminopropyl (meth)acrylate.

[0051] Amide group-containing monomers include, for example, unsaturated carboxylic acid amide monomers such as (meth)acrylamide, α-chloroacrylamide, N,N'-methylenebis(meth)acrylamide, N,N'-ethylenebis(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, N-2-hydroxyethyl(meth)acrylamide, N-2-hydroxypropyl(meth)acrylamide, N-3-hydroxypropyl(meth)acrylamide, crotonamide, maleic acid diamide, fumaric acid diamide, and diacetone acrylamide; N-di These include unsaturated carboxylic acid amide monomers such as methylaminomethyl(meth)acrylamide, N-2-aminoethyl(meth)acrylamide, N-2-methylaminoethyl(meth)acrylamide, N-2-ethylaminoethyl(meth)acrylamide, N-2-dimethylaminoethyl(meth)acrylamide, N-2-diethylaminoethyl(meth)acrylamide, N-3-aminopropyl(meth)acrylamide, N-3-methylaminopropyl(meth)acrylamide, and N-3-dimethylaminopropyl(meth)acrylamide.

[0052] Examples of imide group-containing monomers include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.

[0053] Examples of carboxyl group-containing monomers include unsaturated monocarboxylic acid monomers such as (meth)acrylic acid and crotonic acid; unsaturated polycarboxylic acid monomers such as maleic acid, fumaric acid, itaconic acid, citraconic acid, and mesaconic acid; and alkyl ester monomers or amide monomers containing free carboxyl groups of the aforementioned unsaturated polycarboxylic acids.

[0054] Examples of monomers containing carboxylic acid anhydride groups include the acid anhydrides of the unsaturated polycarboxylic acids mentioned above.

[0055] Thermosetting products of polymers containing repeating units having thermopolymerizable functional groups, thermosetting products of oligomers containing repeating units having thermopolymerizable functional groups, and thermosetting products of monomers having thermopolymerizable functional groups are obtained by heat-treating the polymer containing repeating units having thermopolymerizable functional groups, the oligomer containing repeating units having thermopolymerizable functional groups, and the monomer having thermopolymerizable functional groups, respectively, at temperatures such as 50-200°C, 50-150°C, 50-100°C, or 50-70°C. The heat treatment time is, for example, 1-120 minutes, 5-100 minutes, 10-80 minutes, or 30-80 minutes.

[0056] Oligomeric ionic liquids and polymeric ionic liquids are, for example, the polymerization results of ionic liquid monomers.

[0057] Ionic liquid monomers include, 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-, SO4 2- The unsaturated monomers can be selected from among CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N-, which contain one or more anions selected from these. Such ionic liquid monomers can be polymerized to obtain oligomeric ionic liquids or polymeric ionic liquids.

[0058] A liquid electrolyte is, for example, an electrolyte that is in a liquid state at 25°C and 1 atm. The viscosity of a liquid electrolyte can also be, for example, 10 cps or more, 15 cps or more, 20 cps or more, 25 cps or more, or 30 cps at 25°C and 1 atm. The viscosity of a liquid electrolyte can also be, for example, 10-1000 cps, 15-500 cps, 20-300 cps, 25-200 cps, or 30-100 cps at 25°C and 1 atm. The viscosity of a liquid electrolyte can be measured using Brookfield's LV DV-II + Pro Viscometer (cone-plate type). Having a high viscosity within this range of liquid electrolytes can more effectively accommodate the volume changes of the positive electrode layer 10 and / or negative electrode layer 20 during charging and discharging, more effectively reduce the interfacial resistance at the interface between the positive electrode layer 10, the negative electrode layer 20, and / or the electrolyte layer 30, and provide improved bonding strength between the positive electrode layer 10, the negative electrode layer 20, and / or the electrolyte layer 30. As a result, the cycle characteristics of the secondary battery 1 can be improved. If the viscosity of the liquid electrolyte is excessively low, the above-mentioned effects will be negligible.

[0059] Liquid electrolytes may include, for example, ionic liquids.

[0060] Ionic liquids can be represented, for example, by one of the following chemical formulas 1 and 2. [ka]

[0061] In the above chemical formula 1, X1 is -N(R2)(R3)(R4) or -P(R2)(R3)(R4), R1, R2, R3, and R4 are each independently a halogen-substituted or unsubstituted C1-C30 alkyl group, a halogen-substituted or unsubstituted C1-C30 alkoxy group, a halogen-substituted or unsubstituted C6-C30 aryl group, a halogen-substituted or unsubstituted C6-C30 aryloxy group, a halogen-substituted or unsubstituted C3-C30 heteroaryl group, a halogen-substituted or unsubstituted C3-C30 heteroaryloxy group, a halogen-substituted or unsubstituted C4-C30 cycloalkyl group, a halogen-substituted or unsubstituted C3-C30 heterocycloalkyl group, or a halogen-substituted or unsubstituted C2-C100 alkylene oxide group. In the aforementioned chemical formula 2, [ka] X2 is a heterocycloalkyl or heteroaryl ring containing 1 to 3 heteroatoms and 2 to 30 carbon atoms, wherein the ring is substituted or unsubstituted, and X2 is =N(R5)(R6), -N(R5)=, =P(R5)(R6), or -P(R5)=. The substituents R5 and R6 substituted on the ring are, independently, hydrogen, a halogen-substituted or unsubstituted C1-C30 alkyl group, a halogen-substituted or unsubstituted C1-C30 alkoxy group, a halogen-substituted or unsubstituted C6-C30 aryl group, a halogen-substituted or unsubstituted C6-C30 aryloxy group, a halogen-substituted or unsubstituted C3-C30 heteroaryl group, a halogen-substituted or unsubstituted C3-C30 heteroaryloxy group, a halogen-substituted or unsubstituted C4-C30 cycloalkyl group, a halogen-substituted or unsubstituted C3-C30 heterocycloalkyl group, or a halogen-substituted or unsubstituted C2-C100 alkylene oxide group. - It is an anion.

[0062] Ionic liquids can be represented, for example, by one of the following chemical formulas 3 and 4. [ka]

Chem.

[0063] In the chemical formula 3, Z is N or P, R7, R8, R9 and R 10 are each independently a C1-C30 alkyl group substituted or unsubstituted with halogen, a C6-C30 aryl group substituted or unsubstituted with halogen, a C3-C30 heteroaryl group substituted or unsubstituted with halogen, a C4-C30 cycloalkyl group substituted or unsubstituted with halogen, or a C3-C30 heterocycloalkyl group substituted or unsubstituted with halogen, In the chemical formula 4, Z is N or P, R 11 、R 12 、R 13 、R 14 、R 15 、R 16 、and R 17 are each independently hydrogen, a C1-C30 alkyl group substituted or unsubstituted with halogen, a C6-C30 aryl group substituted or unsubstituted with halogen, a C3-C30 heteroaryl group substituted or unsubstituted with halogen, a C4-C30 cycloalkyl group substituted or unsubstituted with halogen, or a C3-C30 heterocycloalkyl group substituted or unsubstituted with halogen, and Y - is an anion.

[0064] The ionic liquid can be represented by, for example, one of the following chemical formulas 5 to 10. <l l>

Chem.

[0065] In the chemical formulas l0000553 to 10, R 18 、R 19 、R 20 and R 21Each of these is independently a halogen-substituted or unsubstituted C1-C30 alkyl group, a halogen-substituted or unsubstituted C6-C30 aryl group, a halogen-substituted or unsubstituted C3-C30 heteroaryl group, a halogen-substituted or unsubstituted C4-C30 cycloalkyl group, or a halogen-substituted or unsubstituted C3-C30 heterocycloalkyl group. R 22 , R 23 , R 24 , R 25 , R 26 , and R 27 Each of these is independently hydrogen, a halogen-substituted or unsubstituted C1-C30 alkyl group, a halogen-substituted or unsubstituted C6-C30 aryl group, a halogen-substituted or unsubstituted C3-C30 heteroaryl group, a halogen-substituted or unsubstituted C4-C30 cycloalkyl group, or a halogen-substituted or unsubstituted C3-C30 heterocycloalkyl group, Y - It is an anion.

[0066] Ionic liquids contain anions, and anions are, for example, BF4 - PF6 - AsF6 - SbF6 - AlCl4 - HSO4 - ClO4 - CH3SO3 - CF3CO2 - Cl - , Br - , I - SO4 2- PF6 - ClO4 - , BOB - (bis(oxalate)borate), CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - ,(C2F5SO2)(CF3SO2)N - (CF3SO2)2N - (CF3)3PF3 - (CF3)4PF2 -(CF3)5PF - (CF3)6P - , SF5CF2SO3 - , SF5CHFCF2SO3-, CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , C2N3 - (O(CF3)2C2(CF3)2O)2PO - , (FSO2)2N - (CF3SO2)2N - Or combinations thereof. The anions of the ionic liquids represented by chemical formulas 1 to 10 may also be selected from among the anions mentioned above.

[0067] Ionic liquids may include, for example, 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide, 1-methyl-1-butylpyrrolidinium bis(fluorosulfonyl)imide, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, 1-methyl-1-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide, or combinations thereof.

[0068] The molecular weight of ionic liquids is, for example, 1000 Daltons or less, 900 Daltons or less, 800 Daltons or less, or 500 Daltons or less. The molecular weight of ionic liquids is, for example, 50 to 1000 Daltons, 100 to 900 Daltons, 100 to 800 Daltons, or 100 to 500 Daltons.

[0069] The electrolyte layer 30 is, for example, a self-standing film. The electrolyte layer 30 is, for example, a flexible self-standing film. The fact that the electrolyte layer 30 is a self-standing film can further simplify the manufacturing process of secondary batteries and improve the process efficiency of secondary battery manufacturing.

[0070] [Electrolyte layer: porous membrane] The electrolyte layer 30 may further include a flexible porous membrane.

[0071] Flexible porous membranes may include, for example, polyolefins. Polyolefins have excellent short-circuit prevention effects and can improve the stability of secondary batteries through their shot-down effect. For example, flexible porous membranes are membranes made of resins such as polyethylene, polypropylene, polybutene, polyvinyl chloride, and mixtures thereof, or copolymers, but are not necessarily limited to these; any porous membrane that can be used in the relevant art is possible. For example, porous membranes made of polyolefin resins; porous membranes woven from polyolefin fibers; nonwoven fabrics containing polyolefins; aggregates of insulating material particles, etc., can be used. For example, porous membranes containing polyolefins have excellent applicability of binder solutions for manufacturing coating layers formed on the porous membrane, and the film thickness of the composite membrane can be reduced to increase the ratio of active material in the battery and increase the capacity per unit volume.

[0072] For example, polyolefins used as materials for porous membranes can be homopolymers, copolymers, or mixtures thereof, such as polyethylene and polypropylene. Polyethylene can be low-density, medium-density, or high-density polyethylene, and high-density polyethylene may be used from the viewpoint of mechanical strength. Also, two or more types of polyethylene may be mixed to impart flexibility. The polymerization catalyst used in the preparation of polyethylene is not limited, and catalysts such as Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts may be used. From the viewpoint of achieving both mechanical strength and high permeability, the weight-average molecular weight of polyethylene can be, for example, 100,000 to 12,000,000 Daltons, 100,000 to 8,000,000 Daltons, 100,000 to 5,000,000 Daltons, or 200,000 to 3,000,000 Daltons. Polypropylene can be homopolymers, random copolymers, or block copolymers, and these can be used alone or in mixtures of two or more. Furthermore, the polymerization catalyst is not limited, and catalysts such as Ziegler-Natta catalysts and metallocene catalysts can be used. The stereoregularity is also not limited, and isotactic, syndiotactic, or atactic polypropylene can be used, although inexpensive isotactic polypropylene may be used. Additives such as polyethylene or polyolefins other than polypropylene, and antioxidants may be added to the polyolefin.

[0073] For example, porous membranes may include polyolefins such as polyethylene and polypropylene, and multilayer membranes of two or more layers may be used. Mixed multilayer membranes such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators may be used, but are not limited to these. Any material and configuration that can be used as a porous substrate in the relevant art may be used.

[0074] For example, a porous membrane may include a diene polymer produced by polymerizing a monomer composition containing a diene monomer. The diene monomer may also be a conjugated diene monomer or a non-conjugated diene monomer. For example, the diene monomer may include one or more selected from the group consisting of 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, chloroprene, vinylpyridine, vinylnorbornene, dicyclopentadiene, and 1,4-hexadiene, but is not necessarily limited to these; any diene monomer usable in the art may be used.

[0075] The thickness of the porous film can be, for example, 1-100 μm, 1-30 μm, 5-20 μm, 5-15 μm, or 5-10 μm. If the porous film is too thin, it becomes difficult to maintain its mechanical properties, and if it is too thick, the internal resistance of the secondary battery may increase.

[0076] The porosity of a porous membrane can be, for example, 5–95 vol%, 10–90 vol%, 20–80 vol%, or 30–70 vol%. If the porosity is excessively low, the internal resistance of the electrolyte layer 30 may increase excessively. If the porosity of the porous membrane is excessively high, it will be difficult to maintain the mechanical properties of the porous membrane. The porosity of a porous membrane can be measured, for example, by nitrogen adsorption.

[0077] The pore size of the porous membrane can be, for example, 0.01-10 μm, 0.01-5 μm, 0.01-2 μm, 0.01-1 μm, 0.01-0.5 μm, or 0.1-0.5 μm. If the pore size of the porous membrane is excessively small, the internal resistance of the electrolyte layer 30 will increase excessively, and if the pore size of the porous substrate is excessively large, the possibility of a short circuit in the secondary battery may increase. The pore size of the porous membrane can be measured, for example, by the nitrogen adsorption method.

[0078] The electrolyte layer 30 may be included as a composite membrane. The composite membrane may further include a coating layer disposed on one or both sides (for example, at least one side of the porous membrane) of the porous membrane described above.

[0079] In a composite film, the coating layer may include, for example, a filler. The filler is not limited, and any filler that is usable in the art may be used.

[0080] In composite films, fillers can act as supports. When a porous film attempts to shrink at high temperatures, the fillers can support the porous film and suppress its shrinkage. The inclusion of fillers in the coating layer placed on the composite film ensures sufficient porosity, potentially improving mechanical properties. This can ensure improved structural stability in secondary batteries containing such composite films. The average particle size of the fillers in the coating layer can be 300 nm to 2 μm, 300 nm to 1.5 μm, or 300 nm to 1.0 μm. The average particle size of the fillers can be defined, for example, by the number-average particle size measured using a laser scattering particle size analyzer (e.g., HORIBA's LA-920). Using fillers with such average particle sizes allows for easy formation of a coating layer of appropriate thickness. Composite films containing such coating layers can have appropriate porosity. If the average particle size of the fillers is excessively small, the mechanical properties of the composite film may deteriorate.

[0081] The filler may be inorganic particles, organic particles, or a combination thereof. Inorganic particles may also be metal oxides, metalloid oxides, or a combination thereof. Specifically, the inorganic particles may be alumina, silica, boehmite, magnesia, or a combination thereof. Alumina, silica, etc., have small particle sizes and are easy to prepare dispersions of. For example, the inorganic particles may also be Al2O3, SiO2, TiO2, SnO2, CeO2, NiO, CaO, ZnO, MgO, ZrO2, Y2O3, SrTiO3, BaTiO3, MgF2, Mg(OH)2, or a combination thereof. Inorganic particles may also be spherical, plate-like, fibrous, etc., but are not limited to these, and any form usable in the art may be used. Organic particles may also be cross-linked polymers. The organic particles are also highly crosslinked polymers for which a glass transition temperature (Tg) is not specified. When highly crosslinked polymers are used, heat resistance is improved, and shrinkage of porous substrates at high temperatures can be effectively suppressed. The organic particles may include, but are not limited to, acrylate compounds and their derivatives, diallyl phthalate compounds and their derivatives, polyimide compounds and their derivatives, polyurethane compounds and their derivatives, copolymers thereof, or combinations thereof, and any that can be used as a filler in the art. For example, the filler may also be crosslinked polystyrene particles or crosslinked polymethyl methacrylate particles. The filler may also be a secondary particle formed by the aggregation of primary particles. In a separator containing a secondary particle filler, the porosity of the coating layer is increased, which can provide a lithium battery with excellent high-power characteristics. The glass transition temperature of organic particles can be measured, for example, by a DSC (Differential Scanning Calorimeter), DMA (Dynamic Mechanical Analyzer), TMA (Thermomechanical Analyzer), and / or TGA (Thermogravimetric Analyzer).

[0082] In a composite film, the coating layer may be arranged on both sides of a porous film, for example. The thickness of the coating layer may be 0.1 to 5 μm, 0.5 to 5 μm, or 0.5 to 3 μm, based on one side. When the thickness of the coating layer satisfies the above range, the composite film containing it may provide improved adhesion and breathability. Furthermore, by arranging the coating layer on both sides of the porous substrate, the adhesion between the composite binder and the electrode active material layer is further improved, and volume changes in the lithium battery may be suppressed. The coating layers arranged on both sides of the composite film may have the same composition. By arranging coating layers with the same composition on both sides of the composite film, the same adhesive force acts on the positive electrode layer and / or negative electrode layer on one side and the other side of the composite film, and volume changes in the secondary battery may be uniformly suppressed.

[0083] In a composite film, the coating layer may include, for example, a blend of binder and filler. The coating layer may include a binder and filler blend in which the binder and filler are uniformly mixed. By including a binder and filler blend in the coating layer, the adhesion between the porous substrate and the electrode active material layer can be further improved compared to a multilayer structure in which the binder and filler are arranged in separate layers. The binder:filler mixed weight ratio in the coating layer can also be 1:1 to 1:8. For example, the binder:filler ratio in the coating layer can be 1:1.5 to 1:7, 1:2 to 1:6, or 1:2 to 1:5. Improved adhesion and breathability can be obtained simultaneously within such a range of binder-filler ratios.

[0084] The binder contained in the coating layer is also a fluorinated polymer. The binder contained in the coating layer is also a fluorinated polymer in which some or all of the hydrogens linked to the carbons in the binder are replaced with fluorine. For example, a fluorinated polymer is also a polymer containing repeating units derived from one or more monomers selected from vinylidene fluoride monomer, tetrafluoroethylene monomer, and hexafluoropropylene. For example, the binder contained in the coating layer is also a fluorinated homopolymer. The binder contained in the coating layer is also a copolymer. The binder contained in the coating layer is also a fluorinated copolymer. A fluorinated copolymer contained in the coating layer is also a copolymer of tetrafluoroethylene monomer and other monomers. Other monomers used with tetrafluoroethylene monomer include one or more fluorine-containing monomers selected from the group consisting of vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, and perfluoroalkyl vinyl ethers. For example, the fluorine-based copolymer contained in the coating layer may also be tetrafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-chlorotrifluoroethylene copolymer, or tetrafluoroethylene-perfluoroalkyl vinyl ether. The fluorine-based copolymer contained in the coating layer may also be a copolymer of vinylidene fluoride monomer and other monomers. For example, the fluorine-based copolymer contained in the coating layer may also be a copolymer of vinylidene fluoride monomer and one or more fluorine-containing monomers selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, fluorovinyl, and perfluoroalkyl vinyl ether. Specifically, the vinylidene monomer may also be vinylidene fluoride homopolymer, vinylidene fluoride-hexafluoropropylene copolymer, or vinylidene fluoride-chlorotrifluoroethylene copolymer. The fluorine-based polymer contained in the coating layer may further contain hydrophilic functional groups. By further containing these hydrophilic functional groups, improved adhesion to the electrode active material layer can be obtained. Hydrophilic functional groups are polar functional groups.The fluorine polymer contained in the coating layer contains one or more hydrophilic functional groups selected from the group consisting of carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, acid anhydride groups, and hydroxyl groups and their salts, but is not necessarily limited to these; any hydrophilic functional group usable in the relevant art is acceptable. The weight-average molecular weight of the fluorine polymer contained in the coating layer is 100,000 Daltons or more. For example, the weight-average molecular weight of the fluorine polymer contained in the coating layer is 100,000 to 1,500,000 Daltons. For example, the weight-average molecular weight of the fluorine polymer contained in the coating layer is 300,000 to 1,500,000 Daltons. For example, the weight-average molecular weight of the fluorine polymer contained in the coating layer is 500,000 to 1,500,000 Daltons. For example, the weight-average molecular weight of the fluorine polymer contained in the coating layer is 1,000,000 to 1,500,000 Daltons. The aforementioned weight-average molecular weight is a polystyrene-converted value obtained by gel permeation chromatography. The adhesion to the positive electrode active material layer can be further improved within the weight-average molecular weight range of the fluorine-based polymer contained in the coating layer. If the weight-average molecular weight of the fluorine-based polymer contained in the coating layer is excessively small, the adhesion will decrease, and if the weight-average molecular weight is large, the manufacture of the binder composition will not be easy.

[0085] [Positive electrode layer] [Cathode layer: Cathode active material] Referring to Figures 1 to 4, the positive electrode layer 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on one or both sides of the positive electrode current collector 11 (for example, at least one side of the positive electrode current collector 11).

[0086] The positive electrode active material layer 12 may include, for example, an alkali metal-containing sulfide-based positive electrode active material or an alkali metal-containing oxide-based positive electrode active material. The alkali metal may include, for example, lithium or sodium. The positive electrode active material layer 12 may include, for example, a lithium-containing sulfide-based positive electrode active material, a lithium-containing oxide-based positive electrode active material, a sodium-containing sulfide-based positive electrode active material, or a sodium-containing oxide-based positive electrode active material.

[0087] The positive electrode active material layer 12 may include, for example, a Li2S-containing composite as an alkali metal-containing sulfide-based positive electrode active material.

[0088] The positive electrode active material layer 12 may contain 10-90 parts by weight, 30-90 parts by weight, 40-90 parts by weight, 40-80 parts by weight, 50-80 parts by weight, or 50-70 parts by weight of Li2S-containing composite per 100 parts by weight. If the content of Li2S-containing composite decreases excessively, the energy density of the secondary battery decreases. If the content of Li2S-containing composite increases excessively, the deterioration of the positive electrode layer may be accelerated due to volume changes in the positive electrode layer during charging and discharging. As a result, the cycle characteristics of the secondary battery 1 may deteriorate.

[0089] Li2S-containing composites include, for example, composites of Li2S and carbon-based materials, composites of Li2S, carbon-based materials and solid electrolytes, composites of Li2S and solid electrolytes, composites of Li2S, carbon-based materials and lithium salts, composites of Li2S and lithium salts, composites of Li2S and metal carbides, composites of Li2S, carbon-based materials and metal carbides, composites of Li2S and metal nitrides, composites of Li2S, carbon-based materials and metal nitrides, or combinations thereof.

[0090] Li2S-containing composites are distinguished from simple mixtures of Li2S and other materials. In simple mixtures of Li2S and other materials, the interfacial resistance between Li2S and the other materials is maintained, resulting in a high internal resistance of the positive electrode layer containing them. Therefore, the cycle characteristics of secondary battery 1 containing them may be reduced. On the other hand, in Li2S-containing composites, the interfacial resistance between Li2S and the other materials is reduced due to the mechanochemical or chemical compounding of Li2S and the other materials, thus reducing the internal resistance of the positive electrode layer containing them. Therefore, the cycle characteristics of secondary battery 1 containing a Li2S-containing composite may be improved.

[0091] Composites of Li2S and carbon-based materials include carbon-based materials. Carbon-based materials can be, for example, any material containing carbon atoms that is used as a conductive material in the art. Carbon-based materials can also be, for example, crystalline carbon, amorphous carbon, or a combination thereof. Carbon-based materials can also be, for example, calcined carbon precursors. Carbon-based materials can also be, for example, carbon nanostructures. Carbon nanostructures can be, for example, one-dimensional carbon nanostructures, two-dimensional carbon nanostructures, three-dimensional carbon nanostructures, or a combination thereof. Carbon nanostructures can also be, for example, carbon nanotubes, carbon nanofibers, carbon nanobelts, carbon nanorods, graphene, or a combination thereof. Carbon-based materials can also be, for example, porous carbon-based materials or non-porous carbon-based materials. Porous carbon-based materials may, for example, include periodic and regular two-dimensional or three-dimensional pores. Porous carbon-based materials include, for example, carbon blacks such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black; graphite, activated carbon, or combinations thereof. The form of carbon-based materials can be, for example, particulate, sheet-like, or flake-like; however, any form used as a carbon-based material in the relevant art is acceptable. Carbon-based materials may include, for example, fibrous carbon-based materials. The aspect ratio of fibrous carbon-based materials can be, for example, 2-30, 2-20, 2-10, 2-8, 2-5, or 2-4. Fibrous carbon-based materials may include fibrous carbon nanostructures. Fibrous carbon nanostructures may include, for example, carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or combinations thereof. The aspect ratio of fibrous carbon-based materials, i.e., the ratio of diameter to length, can be measured from SEM (Scanning Electron Microscopy) images.

[0092] The method for producing composites of Li2S and carbon-based materials may be a dry method, a wet method, or a combination thereof, but is not limited to these; any method used in the relevant art is acceptable. Examples of methods for producing composites of Li2S and carbon-based materials include milling, heat treatment, and vapor deposition, but is not necessarily limited to these; any method used in the relevant art is acceptable.

[0093] A composite of Li2S, a carbon-based material, and a solid electrolyte includes a carbon-based material and a solid electrolyte. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The solid electrolyte can be any material used as an ion-conducting material in the art, for example. The solid electrolyte is, for example, an inorganic electrolyte. The solid electrolyte is, for example, a crystalline solid electrolyte, an amorphous solid electrolyte, or a combination thereof. The solid electrolyte is, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof. A sulfide-based solid electrolyte contains, for example, Li, S, and P, and may further selectively contain halogen elements. The sulfide-based solid electrolyte can be selected from among sulfide-based solid electrolytes used in the positive electrode layer. A sulfide-based solid electrolyte has a capacity of, for example, 1 × 10⁻⁶ at room temperature. -5 It may have an ionic conductivity of S / cm or higher. Oxide-based solid electrolytes include, for example, Li, O, and transition metal elements, and may further selectively contain other elements. Oxide-based solid electrolytes have a conductivity of, for example, 1 × 10⁻⁶ at room temperature. -5 It is also a solid electrolyte having an ionic conductivity of S / cm or higher. Oxide-based solid electrolytes can be selected from among the oxide-based solid electrolytes used in the positive electrode layer.

[0094] The Li2S and solid electrolyte composite includes a solid electrolyte. The term "solid electrolyte" refers to the Li2S and carbon-based material and solid electrolyte composite described above.

[0095] A complex of Li2S and a lithium salt contains Li2S and a lithium salt. A lithium salt is, for example, a binary compound or a ternary compound. A lithium salt is a compound that does not contain sulfur (S). A lithium salt is also, for example, a binary compound consisting of lithium and one element selected from groups 13 to 17 of the periodic table. A lithium salt is also, for example, a ternary compound consisting of lithium and two elements selected from groups 13 to 17 of the periodic table. Binary compounds include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or combinations thereof. The ternary compounds include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or combinations thereof. The lithium salt is one or more lithium halide compounds selected in particular from LiF, LiCl, LiBr, and LiI. A Li2S-lithium salt composite is, for example, a Li2S-lithium halide composite. The Li2S-lithium salt composite may provide further improved ionic conductivity by including a lithium halide compound. The Li2S-lithium salt composite is distinguished from a simple mixture of Li2S, a carbon-based material, and a lithium salt. A simple mixture of Li2S and a lithium salt provides high interfacial resistance because it cannot maintain a dense interface between Li2S and the lithium salt, which may consequently reduce the lifespan characteristics of the secondary battery 1.

[0096] The composite of Li2S, carbon-based material, and lithium salt includes the carbon-based material and the lithium salt. The carbon-based material refers to the composite of Li2S and carbon-based material described above. The lithium salt refers to the composite of Li2S and lithium salt described above.

[0097] The Li2S-metal carbide composite contains a metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, Mn+1 C n T x It is expressed as (where M is a transition metal, T is a terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups). A two-dimensional metal carbide is, for example, Ti2CT. x , (Ti 0.5 Nb 0.5 )2CT x Nb2CT x V2CT x Ti3C2T x , (V 0.5 , Cr 0.5 )3C2T x Ti3CNT x Ta4C3T x Nb4C3T x Or a combination of these. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0098] The composite of Li2S, carbon-based material, and metal carbide includes the carbon-based material and the metal carbide. The carbon-based material refers to the composite of Li2S and carbon-based material described above. The metal carbide refers to the composite of Li2S and metal carbide described above.

[0099] The Li2S and metal nitride composite contains a metal nitride. The metal nitride is, for example, a two-dimensional metal nitride. The two-dimensional metal nitride is, for example, M n+1 N n T x It is expressed as (where M is the transition metal, T is the terminal group, T is O, OH and / or F, n=1, 2, or 3, and x is the number of terminal groups). The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0100] Li2S-containing composites are also composites of Li2S, lithium salts, and carbon-based materials. For example, Li2S-containing composites are also composites of Li2S, lithium salts, and fibrous carbon-based materials.

[0101] A composite of Li2S, lithium salt, and carbon-based material may contain, for example, 10 to 80 parts by weight of Li2S, 1 to 40 parts by weight of lithium salt, and 1 to 20 parts by weight of carbon-based material per 100 parts by weight of the composite. The Li2S content of the composite may also be, for example, 10 to 80 parts by weight, 20 to 70 parts by weight, 30 to 60 parts by weight, or 40 to 60 parts by weight of LiS per 100 parts by weight of the composite. The lithium salt content of the composite may also be, for example, 10 to 40 parts by weight, 15 to 40 parts by weight, 20 to 40 parts by weight, or 25 to 35 parts by weight of lithium salt per 100 parts by weight of the composite. The carbon-based material content of the composite may also be, for example, 1 to 20 parts by weight, 5 to 20 parts by weight, or 5 to 15 parts by weight of carbon-based material per 100 parts by weight of the composite. By having a composite with such a range of Li2S, lithium salt, and carbon-based material compositions, the secondary battery 1 containing the composite may provide further improved ionic conductivity and / or electronic conductivity.

[0102] The composite of Li2S, carbon-based material, and metal nitride includes the carbon-based material and the metal nitride. The carbon-based material refers to the composite of Li2S and carbon-based material described above. The metal nitride refers to the composite of Li2S and metal nitride described above.

[0103] The positive electrode active material layer 12 may further contain, for example, a sulfide-based compound, which is distinguished from the positive electrode active material described above. The sulfide-based compound may also contain, for example, a metal element other than Li and a sulfur element. The sulfide-based compound may also contain, for example, a metal element belonging to groups 1 to 14 of the periodic table with an atomic weight of 10 or more and a sulfur element. The sulfide-based compound may also be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. The further inclusion of a sulfide-based compound in the positive electrode active material layer 12 may further improve the cycle characteristics of the secondary battery 1. The content of such sulfide-based compounds in the positive electrode active material layer 12 may be 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less of the total weight of the positive electrode active material layer 12.

[0104] The positive electrode active material layer 12 may, for example, contain lithium metal oxide as an alkali metal-containing oxide-based positive electrode active material.

[0105] Any lithium metal oxide can be used without limitation as long as it is commonly used in the art. The lithium metal oxide uses, for example, one or more of composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof with lithium. Specific examples thereof include Li a A 1-b B’ b D2 (in the above formula, 0.90 ≦ a ≦ 1 and 0 ≦ b ≦ 0.5); Li a E 1-b B’ b O 2-c D c (in the above formula, 0.90 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); LiE 2-b B’ b O 4-c D c (in the above formula, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b B’ c D α (in the above formula, 0.90 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α ≦ 2); Li a Ni 1-b-c Co b B’ c O 2-α ’F’ α (in the above formula, 0.90 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B’ c D α (in the above formula, 0.90 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α ≦ 2); Li a Ni 1-b-c Mn b B’ c O 2-α F’ α (in the above formula, 0.90 ≦ a ≦ 1, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05, 0 < α < 2); Li a Ni b E c G dO2(In the above formula, 0.90≦a≦1, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Ni b Co c Mn d GeO2 (In the above formula, 0.90 ≤ a ≤ 1, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (In the above formula, 0.90 ≤ a ≤ 1 and 0.001 ≤ b ≤ 0.1); QO2; V2O5; LiV2O5; LiI'O2; LiNiVO4; Li (3-f) J2(PO4)3(0≦f≦2);Li (3-f) Compounds represented by any one of the chemical formulas Fe2(PO4)3(0≦f≦2) or LiFePO4 may be used.

[0106] In the chemical formulas representing the compounds described above, A is Ni, Co, Mn, or a combination thereof; B' is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F' is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I' is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. It is also possible to use compounds with a coating layer attached to the surface of the compounds described above, and it is also possible to use mixtures of the compounds described above and compounds with a coating layer attached. The coating layer applied to the surface of the above-mentioned compound includes, for example, a coating element compound of an oxide, hydroxide, oxyhydroxy, oxycarbonate, or hydroxycarbonate of the coating element. The compound forming such a coating layer can be amorphous or crystalline. The coating elements included in the coating layer are Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer formation method is selected within a range that does not adversely affect the physical properties of the positive electrode active material. Coating methods include, for example, spray coating and immersion methods. Detailed explanations of specific coating methods are omitted as they are generally well understood by those engaged in this field.

[0107] The positive electrode active material layer 12 may, for example, contain lithium transition metal oxides represented by the following chemical formulas 11 to 18 as alkali metal-containing oxide-based positive electrode active materials. <Chemical formula 11> Li a Ni x Co y M z O 2-b A b

[0108] In the chemical formula 11, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.8 ≤ x < 1, 0 ≤ y ≤ 0.3, 0 < z ≤ 0.3, and x + y + z = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical formula 12> LiNi x Co y Mn z O2 <Chemical formula 13> LiNi x Co y Al z O2 In the chemical formulas 12 and 13, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2 and x + y + z = 1, <Chemical formula 14> LiNi x Co y Mn z Al w O2 In the chemical formula 14, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w ≤ 0.2, and x + y + z + w = 1, <Chemical formula 15> Li a Co x M y O 2-b A b In the chemical formula 15, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 0.1, and x + y = 1, M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical Formula 16> Li a Ni x Mn y M’zO 2-b A b In the Chemical Formula 16, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0 < x ≤ 0.3, 0.5 ≤ y < 1, 0 < z ≤ 0.3, and x + y + z = 1, M’ is cobalt (Co), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B) or a combination thereof, A is F, S, Cl, Br or a combination thereof, <Chemical Formula 17> Li a M1 x M2 y PO 4-b X b In the Chemical Formula 17, 0.90 ≤ a ≤ 1.1, 0 ≤ x ≤ 0.9, 0 ≤ y ≤ 0.5, 0.9 < x + y < 1.1, 0 ≤ b ≤ 2, M1 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr) or a combination thereof, M2 is magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zinc (Zn), boron (B), niobium (Nb), gallium (Ga), indium (In), molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si), chromium (Cr), vanadium (V), scandium (Sc), yttrium (Y), or a combination thereof. X is O, F, S, P, or a combination of these.

[0109] <Chemical formula 18> Li a M3 z PO4 In the aforementioned chemical formula 18, 0.90 ≤ a ≤ 1.1 and 0.9 ≤ z ≤ 1.1. M3 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), or a combination of these.

[0110] [Positive electrode layer: solid electrolyte] The positive electrode active material layer 12 may further include, for example, a solid electrolyte. The solid electrolyte may include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, or a combination thereof.

[0111] Solid electrolytes are, for example, sulfide-based solid electrolytes. Examples of sulfide-based solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiX (where X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n m and n are positive numbers, Z is one of Ge, Zn, or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO qp and q are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In, Li 7-x PS 6-x Cl x , 0≦x≦2, Li 7-x PS 6-x Br x , 0≦x≦2, and Li 7-x PS 6-x I x , one or more selected from 0 ≤ x ≤ 2. Sulfide-based solid electrolytes are produced by processing starting materials such as Li2S and P2S5 by methods such as melt-quenching or mechanical milling. After such processing, heat treatment can be performed. Solid electrolytes can be amorphous, crystalline, or a mixture of both. Solid electrolytes can also be, for example, those sulfide-based solid electrolyte materials mentioned above that contain at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements. For example, solid electrolytes can also be materials containing Li2S-P2S5. When utilizing Li2S-P2S5 as a sulfide-based solid electrolyte material to form a solid electrolyte, the molar ratio of Li2S to P2S5 is, for example, in the range of Li2S:P2S5 = 20:80~90:10, 25:75~90:10, 30:70~70:30, and 40:60~60:40.

[0112] Sulfide-based solid electrolytes may include, for example, argyrodite-type solid electrolytes represented by the following chemical formula 19. <Chemical formula 19> Li + 12-n-x A n+ X 2- 6-x Y - x

[0113] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X is S, Se, or Te, Y is Cl, Br, I, F, CN, OCN, SCN, or N3, and 1 ≤ n ≤ 5 and 0 ≤ x ≤ 2. A sulfide-based solid electrolyte is, for example, Li7-x PS 6-x Cl x , 0≦x≦2, Li 7-x PS 6-x Br x , 0≦x≦2, and Li 7-x PS 6-x I x It is also an argyrodite-type compound containing one or more values ​​selected from 0 ≤ x ≤ 2. Sulfide-based solid electrolytes are also argyrodite-type compounds containing one or more values ​​selected from, for example, Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0114] Oxide-based solid electrolytes include, for example, 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)(0≦x<1, 0≦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 y Ti 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 yTiO3(0 < x < 2, 0 < y < 3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0 ≤ x ≤ 10), or a combination thereof. The oxide - based solid electrolyte is produced, for example, by a sintering method or the like.

[0115] The oxide - based solid electrolyte is, for example, Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a M a O 12 (M - doped LLZO, M = Ga, W, Nb, Ta, or Al, 0 < a < 2, 0 ≤ x ≤ 10), which is a garnet - type solid electrolyte selected therefrom.

[0116] The positive electrode active material layer 12 may contain 10 - 60 parts by weight, 10 - 50 parts by weight, 20 - 50 parts by weight, or 30 - 50 parts by weight of the solid electrolyte with respect to 100 parts by weight. If the content of the solid electrolyte decreases excessively, the internal resistance of the positive electrode layer 10 increases, which may deteriorate the cycle characteristics of the secondary battery. If the content of the sulfide - based solid electrolyte increases excessively, the energy density of the secondary battery 1 may decrease.

[0117] [Positive electrode layer: Conductive material] The positive electrode active material layer 12 may further contain a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metallic conductive material, or a combination thereof. The carbon-based conductive material may be, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or a combination thereof, but is not limited to these; any material used as a carbon-based conductive material in the art may be used. The metallic conductive material may be, for example, metal powder, metal fiber, or a combination thereof; any material used as a metallic conductive material in the art may be used. The conductive material content in the positive electrode active material layer 12 may be, for example, 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% of the total weight of the positive electrode active material layer 12.

[0118] The positive electrode active material layer 12 contains a carbon-based material, and the carbon-based material may be present only in the composite positive electrode active material. The positive electrode active material layer 12 may not contain, or may exclude, any additional carbon-based material beyond the composite positive electrode active material containing the carbon-based material. By not including additional carbon-based material in the positive electrode active material layer 12, the energy density of the positive electrode and the secondary battery 1 can be improved, and the manufacturing process can be simplified.

[0119] [Positive electrode layer: Binder] The positive electrode active material layer 12 may further contain a binder. The binder may be, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited to these; any binder usable in the art may be used. The binder content of the positive electrode active material layer 12 may be, for example, 1 wt% to 10 wt% of the total weight of the positive electrode active material layer 12. The binder is optional.

[0120] [Positive electrode layer: Other additives] In addition to the positive electrode active material, solid electrolyte, binder, and conductive material described above, the positive electrode active material layer 12 may further contain additives such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0121] As fillers, coating agents, dispersants, ion conductivity enhancers, etc. that the positive electrode active material layer 12 may contain, known materials generally used for electrodes in secondary batteries 1 can be used.

[0122] [Positive electrode layer: Positive electrode current collector] The positive electrode current collector 11 may be a plate or foil made of, 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 electrode current collector 11 is optional. The thickness of the positive electrode current collector 11 may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 5 μm to 25 μm, or 10 μm to 20 μm.

[0123] The positive electrode current collector 11 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may also 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. The base film may also be, for example, an insulator. By including an insulating thermoplastic polymer in the base film, the base film may soften or liquefy when a short circuit occurs, interrupting battery operation and suppressing a rapid increase in current. The metal layer 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), or alloys thereof. The metal layer can act as an electrochemical fuse, disconnecting in the event of overcurrent to prevent short circuits. The limit current and maximum current can be adjusted by adjusting the thickness of the metal layer. The metal layer can be plated or deposited onto the base film. Reducing the thickness of the metal layer reduces the limit current and / or maximum current of the positive electrode current collector 11, thereby improving the stability of the lithium battery during short circuits. A lead tab can be added to the metal layer for external connection. The lead tab can be welded to the metal layer or the metal layer / base film laminate by ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer melt, while the metal layer is electrically connected to the lead tab. To make the weld between the metal layer and the lead tab stronger, a metal chip can be added between the metal layer and the lead tab. The metal chip is also a thin piece of the same material as the metal layer. Metal pieces can also be, for example, metal foil or metal mesh. Examples of metal pieces include aluminum foil, copper foil, and SUS foil.After placing a metal chip on a metal layer, the lead tab can be welded to a metal chip / metal layer laminate or a metal chip / metal layer / base film laminate by welding the lead tab to it. During welding, the base film, metal layer, and / or metal chip may melt, and the metal layer or metal layer / metal chip laminate may be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal layer. The thickness of the base film may be, for example, 1-50 μm, 1.5-50 μm, 1.5-40 μm, or 1-30 μm. Having the base film in such a thickness range can further effectively reduce the weight of the electrode assembly. The melting point of the base film may be, for example, 100-300°C, 100-250°C or lower, or 100-200°C. Having the base film in such a melting point range allows the base film to melt during the lead tab welding process and easily bond 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 layer. The thickness of the metal layer can be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to 1 μm. Having the metal layer in such a thickness range can ensure the stability of the electrode assembly while maintaining conductivity. The thickness of the metal piece can also be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Having the metal piece in such a thickness range can make it easier to connect the metal layer and the lead tab. Having such a structure in the positive electrode current collector 11 can reduce the weight of the positive electrode layer, and as a result, improve the energy density of the positive electrode and the lithium battery.

[0124] [Negative electrode layer] [Negative electrode layer: negative electrode active material] Referring to Figures 1 to 5, the negative electrode layer 20 includes a first negative electrode active material layer 22. The first negative electrode active material layer 22 includes, for example, a negative electrode active material and a binder.

[0125] The negative electrode active material contained in the first negative electrode active layer 22 is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0126] The negative electrode active material contained in the first negative electrode active material layer 22 has, for example, a particle form. The average particle size of the negative electrode active material having a particle form is, for example, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle size of the negative electrode active material having a particle form is, for example, 10 nm to 4 μm, 10 nm to 3 μm, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. Having an average particle size in such a range of negative electrode active material makes reversible absorption and / or desorbing of lithium during charging and discharging even easier. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size analyzer.

[0127] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, one or more selected from carbon-based negative electrode active materials and metal or semimetallic negative electrode active materials.

[0128] Carbon-based negative electrode active materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or combinations thereof.

[0129] Carbon-based negative electrode active materials are particularly amorphous carbon. Amorphous carbons include, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), and graphene, but are not necessarily limited to these; any material classified as amorphous carbon in the relevant technical field can be used. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0130] Carbon-based negative electrode active materials are, for example, porous carbon. The pore volume of porous carbon is, for example, 0.1 cc / g to 10.0 cc / g, 0.5 cc / g to 5 cc / g, or 0.1 cc / g to 1 cc / g. The average pore diameter of porous carbon is, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The BET specific surface area of ​​porous carbon is, for example, 100 m². 2 / g~3000m 2 It is / g.

[0131] The metallic or metalloid anode active material includes, but is not limited to, one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Any metallic or metalloid anode active material that can be used in the art to form an alloy or compound with lithium is acceptable. For example, nickel (Ni) does not form an alloy with lithium and is therefore not a metallic anode active material.

[0132] The first negative electrode active material layer 22 contains either one type of negative electrode active material or a mixture of multiple different negative electrode active materials. For example, the first negative electrode active material layer 22 contains only amorphous carbon, or one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). Alternatively, the first negative electrode active material layer 22 may contain a mixture of amorphous carbon and one or more selected from the group consisting of gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of amorphous carbon and gold, etc., is by weight and is, for example, 99:1 to 1:99, 10:1 to 1:2, 5:1 to 1:1, or 4:1 to 2:1, but is not necessarily limited to these ranges and is selected according to the required characteristics of the secondary battery 1. Having such a composition in the negative electrode active material further improves the cycle characteristics of the secondary battery 1.

[0133] The negative electrode active material contained in the first negative electrode active material layer 22 includes, for example, a mixture of first particles made of amorphous carbon and second particles made of a metal or metalloid. The metal or metalloid includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In other embodiments, the metalloid is a semiconductor. The content of the second particles is 1-99% by weight, 1-60% by weight, 8-60% by weight, 10-50% by weight, 15-40% by weight, or 20-30% by weight based on the total weight of the mixture. Having the second particles in such a range of content further improves the cycle characteristics of the secondary battery 1, for example.

[0134] On the other hand, the first negative electrode active material layer 22 contains a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metallic negative electrode active material supported on the carbon-based support. Having such a structure in the composite negative electrode active material prevents uneven distribution of the metallic negative electrode active material within the first negative electrode active material layer, resulting in a uniform distribution. As a result, the cycle characteristics of the secondary battery 1 including the first negative electrode active material layer 22 are further improved.

[0135] The metallic anode active material supported on a carbon-based support includes, for example, metals, metal oxides, composites of metals and metal oxides, or combinations thereof. Metals include, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), and zinc (Zn). Metal oxides include, for example, gold (Au) oxide, platinum (Pt) oxide, palladium (Pd) oxide, silicon (Si) oxide, silver (Ag) oxide, aluminum (Al) oxide, bismuth (Bi) oxide, tin (Sn) oxide, tellurium (Te) oxide, and zinc (Zn) oxide. Metal oxides include, for example, Au x O y (0 <x≦2、0<y≦3)、Pt x O y (0 <x≦1、0<y≦2)、Pd x Oy (0 < x ≤ 1, 0 < y ≤ 1), Si x O y (0 < x ≤ 1, 0 < y ≤ 2), Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), Al x O y (0 < x ≤ 2, 0 < y ≤ 3), Bi x O y (0 < x ≤ 2, 0 < y ≤ 3), Sn x O y (0 < x ≤ 1, 0 < y ≤ 2), Te x O y (0 < x ≤ 1, 0 < y ≤ 3), Zn x O y (0 < x ≤ 1, 0 < y ≤ 1) or combinations thereof may be included. The composite of metal and metal oxide is, for example, the composite of Au and Au x O y (0 < x ≤ 2, 0 < y ≤ 3), the composite of Pt and Pt x O y (0 < x ≤ 1, 0 < y ≤ 2), the composite of Pd and Pd x O y (0 < x ≤ 1, 0 < y ≤ 1), the composite of Si and Si x O y (0 < x ≤ 1, 0 < y ≤ 2), the composite of Ag and Ag x O y (0 < x ≤ 2, 0 < y ≤ 1), the composite of Al and Al x O y (0 < x ≤ 2, 0 < y ≤ 3), the composite of Bi and Bi x O y (0 < x ≤ 2, 0 < y ≤ 3), the composite of Sn and Sn x O y (0 < x ≤ 1, 0 < y ≤ 2), the composite of Te and Te x O y (0 < x ≤ 1, 0 < y ≤ 3), Zn and Zn x O y (0 < x ≤ 1, 0 < y ≤ 1) or combinations thereof may be included.

[0136] Carbon-based supports include, for example, amorphous carbon. Amorphous carbon includes, for example, carbon black (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), and carbon nanotubes (CNT), but is not necessarily limited to these; any material classified as amorphous carbon in the relevant art can be used. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon. Carbon-based materials, such as carbonaceous materials, include, for example, carbon-based negative electrode active materials.

[0137] The composite anode active material may, for example, have a particulate form. The particle size of the composite anode active material having a particulate form is, for example, 10 nm to 4 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having a particle size in such a range for the composite anode active material makes the reversible absorption and / or desorbing of lithium during charging and discharging even easier. The metallic anode active material supported on a support may, for example, have a particulate form. The particle size of the metallic anode active material may, for example, be 1 nm to 200 nm, 1 nm to 150 nm, 5 nm to 100 nm, or 10 nm to 50 nm. The carbon-based support may, for example, have a particulate form. The particle size of the carbon-based support can be, for example, 10 nm to 2 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. Having particle sizes in this range allows the carbon-based support to be more uniformly distributed within the first anode active material layer. The carbon-based support can also be, for example, nanoparticles with a particle size of 500 nm or less. The particle size of the composite anode active material, the particle size of the metal-based anode active material, and the particle size of the carbon-based support are, for example, average particle sizes. The average particle size is, for example, the median diameter (D50) measured using a laser particle size analyzer. Alternatively, the average particle size can be automatically determined using software from electron microscope images, for example, or manually determined by hand.

[0138] [Negative electrode layer: Binder] The binder contained in the first negative electrode active material layer 22 is, for example, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride / hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, etc., but is not necessarily limited to these, and any binder that can be used in the art can be used. The binder may consist of one or more different binders.

[0139] The inclusion of a binder in the first negative electrode active material layer 22 stabilizes the first negative electrode active material layer 22 on the negative electrode current collector 21. Furthermore, cracking of the first negative electrode active material layer 22 is suppressed despite volume changes and / or relative positional changes of the first negative electrode active material layer 22 during the charge-discharge process. For example, if the first negative electrode active material layer 22 does not contain a binder, the first negative electrode active material layer 22 can be easily separated from the negative electrode current collector 21. When the first negative electrode active material layer 22 detaches from the negative electrode current collector 21, the exposed portion of the negative electrode current collector 21 comes into contact with the electrolyte layer 30, increasing the likelihood of a short circuit. The first negative electrode active material layer 22 is manufactured, for example, by coating a slurry in which the materials constituting the first negative electrode active material layer 22 are dispersed onto the negative electrode current collector 21 and drying it. By incorporating a binder into the first negative electrode active material layer 22, stable dispersion of the negative electrode active material in the slurry is possible. For example, when the slurry is applied onto the negative electrode current collector 21 by screen printing, screen clogging (e.g., clogging due to aggregates of the negative electrode active material) can be suppressed.

[0140] [Negative electrode layer: Other additives] The first negative electrode active material layer 22 may further contain additives used in conventional secondary batteries 1, such as fillers, coating agents, dispersants, and ion conductivity enhancers.

[0141] [Negative electrode layer: first negative electrode active material layer] The initial charge capacity of the first negative electrode active material layer may be, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the initial charge capacity of the positive electrode active material layer 12. The initial charge capacity of the first negative electrode active material layer may also be, for example, 0.1 to 50%, 0.5 to 45%, 1 to 40%, 1 to 30%, 1 to 20%, or 5 to 10% of the initial charge capacity of the positive electrode active material layer 12.

[0142] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer 12 is, for example, 0.005 to 0.5 or 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer 12 is Li / Li + For the first open circuit voltage (1st It is determined by charging from the open circuit voltage to the maximum charging voltage. The initial charging capacity of the first negative electrode active material layer 22 is Li / Li + For the second open circuit voltage (2 nd The maximum charging voltage is determined by the charging voltage from the open circuit voltage down to 0.01V. The maximum charging voltage is determined by the type of positive electrode active material. The maximum charging voltage can also be, for example, 1.5V, 2.0V, 2.5V, 3.0V, 3.5V, 4.0V, 4.2V, or 4.3V. For example, the maximum charging voltage for Li2S or Li2S composites is Li / Li + It is also 2.5V for this. For example, the maximum charging voltage for Li2S or Li2S composite is Li / Li + It is also 3.0V. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer 22 to the initial charge capacity (A) of the positive electrode active material layer 12 is, for example, 0.01~0.45, 0.01~0.4, 0.01~0.3, 0.01~0.2, or 0.05~0.1. The initial charge capacity (mAh) of the positive electrode active material layer 12 is obtained by multiplying the charge specific capacity (mAh / g) of the positive electrode active material by the mass (g) of the positive electrode active material in the positive electrode active material layer 12. When multiple types of positive electrode active materials are used, the charge specific capacity × mass value is calculated for each positive electrode active material, and the sum of these values ​​is the initial charge capacity of the positive electrode active material layer 12. The initial charge capacity of the first negative electrode active material layer 22 is calculated in the same way. The initial charge capacity of the first negative electrode active material layer 22 is obtained by multiplying the charge capacity density (mAh / g) of the negative electrode active material by the mass of the negative electrode active material in the first negative electrode active material layer 22. If multiple types of negative electrode active materials are used, the charge capacity density × mass value is calculated for each negative electrode active material, and the sum of these values ​​is the initial charge capacity of the first negative electrode active material layer 22. The charge capacity densities of the positive electrode active material and the negative electrode active material can be measured using a solid half-cell with lithium metal as the relative electrode. The initial charge capacities of the positive electrode active material layer 12 and the first negative electrode active material layer 22 are constant at a current density, for example, 0.1 mA / cm². 2This can be measured directly using a solid half-cell. For the positive electrode layer, the measurement is taken from the first open-circuit voltage (OCV) to the maximum charging voltage, for example, 3.0V (vs. Li / Li + The measurement can be performed for operating voltages up to 3.0V. For the negative electrode, the measurement can be performed for operating voltages from the second open-circuit voltage (OCV) up to 0.01V for the negative electrode, for example, lithium metal. For example, a solid half-cell having a positive electrode active material layer 12 can measure 0.1mA / cm² from the first open-circuit voltage up to 3.0V. 2 A solid half-cell, charged with a constant current and having a first negative electrode active material layer, draws 0.1 mA / cm² from the second open-circuit voltage up to 0.01 V. 2 It can be charged with a constant current. The current density during constant current charging is, for example, 0.2 mA / cm². 2 , or 0.5 mA / cm 2 Furthermore, a solid half-cell having a positive electrode active material layer 12 can be charged, for example, from a first open-circuit voltage to 2.5V, 2.0V, 3.5V, or 4.0V. The maximum charging voltage of the positive electrode active material layer 12 can be determined by the maximum voltage of a battery that satisfies the safety conditions according to JISC8712:2015 of the Japanese Industrial Standards Association.

[0143] If the initial charge capacity of the first negative electrode active material layer 22 is excessively small, the thickness of the first negative electrode active material layer 22 becomes very thin, so lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 during repeated charge and discharge processes cause the first negative electrode active material layer 22 to disintegrate, making it difficult to improve the cycle characteristics of the secondary battery 1. If the charge capacity of the first negative electrode active material layer 22 increases excessively, the energy density of the secondary battery 1 decreases, the internal resistance of the secondary battery 1 due to the first negative electrode active material layer 22 increases, making it difficult to improve the cycle characteristics of the secondary battery 1.

[0144] The thickness of the first negative electrode active material layer 22 is, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22 is, for example, 1-50%, 1-40%, 1-30%, 1-20%, 1-10%, or 1-5% of the thickness of the positive electrode active material layer 12. The thickness of the first negative electrode active material layer 22 is, for example, 1 μm to 20 μm, 2 μm to 15 μm, or 3 μm to 10 μm. If the thickness of the first negative electrode active material layer 22 is excessively thin, lithium dendrites formed between the first negative electrode active material layer 22 and the negative electrode current collector 21 will cause the first negative electrode active material layer 22 to disintegrate, making it difficult to improve the cycle characteristics of the secondary battery 1. If the thickness of the first negative electrode active material layer 22 increases excessively, the energy density of the secondary battery 1 decreases, and the internal resistance of the secondary battery 1 due to the first negative electrode active material layer 22 increases, making it difficult to improve the cycle characteristics of the secondary battery 1. If the thickness of the first negative electrode active material layer 22 decreases, for example, the initial charge capacity of the first negative electrode active material layer 22 also decreases.

[0145] [Negative electrode layer: second negative electrode active material layer] Referring to Figure 3, the secondary battery 1 further includes a second negative electrode active material layer 24 which, after being charged, is placed, for example, between the negative electrode current collector 21 and the first negative electrode active material layer 22. The second negative electrode active material layer 24 is a metallic layer containing lithium or a lithium alloy. The metallic layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer 24 is a metallic layer containing lithium, it acts, for example, as a lithium reservoir. Examples of lithium alloys include, but are not limited to, Li-Al alloys, Li-Sn alloys, Li-In alloys, Li-Ag alloys, Li-Au alloys, Li-Zn alloys, Li-Ge alloys, and Li-Si alloys; any alloy usable as a lithium alloy in the art can be used. The second negative electrode active material layer 24 may consist of one of these alloys or lithium, or of various types of alloys. The second negative electrode active material layer 24 is, for example, a plated layer. The second negative electrode active material layer 24 is deposited between the first negative electrode active material layer 22 and the negative electrode current collector 21 during the charging process of the secondary battery 1, for example.

[0146] The thickness of the second negative electrode active material layer 24 is not limited, but for example, it can be 1 μm to 500 μm, 1 μm to 200 μm, 1 μm to 150 μm, 1 μm to 100 μm, or 1 μm to 50 μm. If the thickness of the second negative electrode active material layer 24 is excessively thin, it will be difficult for the second negative electrode active material layer 24 to perform its role as a lithium reservoir. If the thickness of the second negative electrode active material layer 24 is excessively thick, the mass and volume of the secondary battery 1 will increase, which may actually worsen the cycle characteristics of the secondary battery 1.

[0147] On the other hand, in the secondary battery 1, the second negative electrode active material layer 24 may be placed, for example, between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the secondary battery 1. When the second negative electrode active material layer 24 is placed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the secondary battery 1, the second negative electrode active material layer 24 acts as a lithium reservoir because it is a lithium-containing metal layer. For example, lithium foil may be placed between the negative electrode current collector 21 and the first negative electrode active material layer 22 before the assembly of the secondary battery 1.

[0148] If the second negative electrode active material layer 24 is deposited by charging after the assembly of the secondary battery 1, the energy density of the secondary battery 1 increases because the second negative electrode active material layer 24 is not included at the time of assembly of the secondary battery 1. When the secondary battery 1 is charged, it is charged beyond the charging capacity of the first negative electrode active material layer 22. That is, the first negative electrode active material layer 22 is overcharged. In the initial stages of charging, lithium is absorbed into the first negative electrode active material layer 22. The negative electrode active material contained in the first negative electrode active material layer 22 forms an alloy or compound with lithium ions that have moved from the positive electrode layer 10. If the capacity of the first negative electrode active material layer 22 is exceeded during charging, for example, lithium is deposited on the back surface of the first negative electrode active material layer 22, i.e., between the negative electrode current collector 21 and the first negative electrode active material layer 22, and the deposited lithium forms a metal layer corresponding to the second negative electrode active material layer 24. The second negative electrode active material layer 24 is a metal layer mainly composed of lithium (i.e., metallic lithium). This result is obtained, for example, by including a substance in the negative electrode active material contained in the first negative electrode active material layer 22 that forms an alloy or compound with lithium. During discharge, the lithium in the first negative electrode active material layer 22, the second negative electrode active material layer 24, and the metal layer is ionized and moves toward the positive electrode layer 10. Therefore, lithium can be used as the negative electrode active material in the secondary battery 1. Furthermore, since the first negative electrode active material layer 22 covers the second negative electrode active material layer 24, it acts as a protective layer for the second negative electrode active material layer 24, i.e., the metal layer, and also plays a role in suppressing the deposition and growth of lithium dendrites. Therefore, short circuits and capacity degradation of the secondary battery 1 are suppressed, and as a result, the cycle characteristics of the secondary battery 1 are improved. Furthermore, when the second negative electrode active material layer 24 is positioned by charging after the assembly of the secondary battery 1, the negative electrode 20, that is, the negative electrode current collector 21, the first negative electrode active material layer 22, and the region between them, are lithium (Li)-free regions that do not contain lithium in the initial state or after complete discharge of the secondary battery 1.

[0149] [Negative electrode layer: negative electrode current collector] The negative electrode current collector 21 is made of a material that does not react with lithium, i.e., does not form any alloys or compounds. The materials constituting the negative electrode current collector 21 include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but are not necessarily limited to these; any material that can be used as an electrode current collector in the art can be used. The negative electrode current collector 21 may consist of one of the above-mentioned metals, or an alloy or coating material of two or more metals. The negative electrode current collector 21 may be in the form of a plate or foil, for example.

[0150] Referring to Figure 2, the secondary battery 1 may further include a thin film 23 containing an element capable of forming an alloy with lithium on one surface of the negative electrode current collector 21. The thin film 23 is placed between the negative electrode current collector 21 and the first negative electrode active material layer 22. The thin film 23 contains, for example, an element capable of forming an alloy with lithium. The elements capable of forming an alloy with lithium include, for example, gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth, but are not necessarily limited to these; any element capable of forming an alloy with lithium in the art can be used. The thin film 23 is composed of one of these metals or an alloy of several metals. By placing the thin film 23 on one surface of the negative electrode current collector 21, for example, the deposition morphology of the second negative electrode active material layer 24 deposited between the thin film 23 and the first negative electrode active material layer 22 can be further flattened, and the cycle characteristics of the secondary battery 1 can be further improved.

[0151] The thickness of the thin film 23 is, for example, 1 nm to 800 nm, 10 nm to 700 nm, 50 nm to 600 nm, or 100 nm to 500 nm. If the thickness of the thin film 23 is less than 1 nm, the function of the thin film 23 is difficult to achieve. If the thickness of the thin film 23 is excessively thick, the thin film 23 itself may absorb lithium, reducing the amount of lithium deposited at the negative electrode, lowering the energy density of the solid-state battery, and potentially degrading the cycle characteristics of the secondary battery 1. The thin film 23 can be disposed on the negative electrode current collector 21 by, for example, vacuum deposition, sputtering, or plating, but is not necessarily limited to these methods; any method that can form the thin film 23 in the relevant art can be used.

[0152] Although not shown in the drawings, the negative electrode current collector 21 may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The base film may include, for example, a polymer. The polymer may also 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. The polymer may also be an insulating polymer. By including an insulating thermoplastic polymer in the base film, the base film may soften or liquefy in the event of a short circuit, thereby interrupting battery operation and suppressing a rapid increase in current. The metal layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The negative electrode current collector 21 may further include metal pieces and / or lead tabs. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode current collector 21, please refer to the positive electrode current collector 11 described above. Having such a structure in the negative electrode current collector 21 reduces the weight of the negative electrode, and as a result, can improve the energy density of the negative electrode and the lithium battery.

[0153] [Negative electrode layer: First inert member] Referring to Figure 4, the secondary battery 1 further includes a first inert member 40 disposed on the other side of the negative electrode current collector 21. The first inert member 40 is, for example, a conductive flame-retardant inert member.

[0154] The first inert member 40 includes, for example, a matrix, a filler, and a conductive material. The matrix includes, for example, a base material and a reinforcing material. The first inert member 40 may further include a filler, a binder, and the like.

[0155] The matrix includes, for example, a fibrous base material and a fibrous reinforcing material. The inclusion of a base material in the matrix allows the matrix to be elastic. Therefore, the matrix can effectively accommodate the volume changes during charging and discharging of the secondary battery 1 and can be positioned in various locations. The base material included in the matrix includes, for example, a first fibrous material. The inclusion of the first fibrous material in the base material allows for the effective accommodation of the volume changes of the secondary battery 1 that occur during the charging and discharging process, and effectively suppresses the deformation of the first inert member 40 due to the volume changes of the secondary battery 1. The first fibrous material is, for example, a material with an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material with an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material includes, for example, one or more selected from pulp fibers and polymer fibers. The inclusion of a reinforcing material in the matrix improves the strength of the matrix. Therefore, the matrix can prevent excessive volume changes during charging and discharging of the secondary battery 1, thereby preventing deformation of the secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. The inclusion of the second fibrous material in the reinforcing material can further uniformly increase the strength of the matrix. The second fibrous material is, for example, a material with an aspect ratio of 3 or more, 5 or more, or 10 or more. The first fibrous material is, for example, a material with an aspect ratio of 3 to 100, 5 to 100, or 10 to 100. The second fibrous material is, for example, a flame-retardant material. The fact that the second fibrous material is a flame-retardant material can effectively suppress ignition due to thermal runaway that occurs during the charging and discharging process of the secondary battery 1 or due to external impact. The second fibrous material is, for example, glass fiber, metal oxide fiber, ceramic fiber, etc.

[0156] The first inert member 40 includes a filler and a conductive material outside the matrix.

[0157] The filler may be placed inside the matrix, on the matrix surface, or both inside and on the surface. The filler is, for example, an inorganic material. The filler included in the conductive flame-retardant inert member is, for example, a moisture getter. The filler prevents the deterioration of the secondary battery 1 by removing moisture remaining inside the secondary battery 1 by adsorbing moisture at temperatures below 100°C. Furthermore, if the temperature of the secondary battery 1 rises above 150°C due to thermal runaway caused by the charging and discharging process or external shock, the filler can release the adsorbed moisture and effectively suppress ignition of the secondary battery 1. In other words, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide with moisture-adsorbing properties. The metal hydroxides contained in the filler are, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, Ti(OH)3, Zr(OH)4, Al(OH)3, or combinations thereof. The content of the filler in the conductive flame-retardant inert member is, for example, 10-80 parts by weight, 20-80 parts by weight, 30-80 parts by weight, 40-80 parts by weight, 50-80 parts by weight, 60-80 parts by weight, or 65-80 parts by weight per 100 parts by weight of the conductive flame-retardant inert member.

[0158] Examples of conductive materials include graphite, carbon black, acetylene black, Ketjen black, Denka black, carbon fiber, carbon nanotubes (CNTs), graphene, metal fibers, and metal powders. The 25°C electronic conductivity of the first inert member 50 is, for example, 100 times or more, 1000 times or more, or 10000 times or more, the 25°C electronic conductivity of the first inert member 40.

[0159] The first inert member 40 may further include, for example, a binder. The binder may include, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that is cured by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member includes, for example, a heat- and pressure-curable film and / or its cured product. A heat- and pressure-curable polymer is, for example, TSA-66 from Toray Industries, Inc.

[0160] The first inert member 40 may further contain other materials in addition to the above-described base material, reinforcing material, filler, conductive material, and binder. The conductive and flame-retardant inert member may further contain, for example, one or more selected from paper, insulating polymers, ion-conductive polymers, insulating inorganic substances, oxide-based solid electrolytes, and sulfide-based solid electrolytes. The insulating polymer is also, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0161] The density of the base material or the density of the reinforcing material included in the first inert member 40 is, for example, 10 to 300%, 10 to 150%, 10 to 140%, 10 to 130%, or 10 to 120% of the positive electrode active material density included in the positive electrode active material layer 12.

[0162] The first inert member 40 is a member that does not contain a substance having electrochemical activity, for example, an electrode active material. The electrode active material is a substance that occludes / releases lithium. The first inert member 40 is a member made of a substance other than the electrode active material and is made of a substance used in the relevant technical field.

[0163] The content of the conductive material included in the first inert member 40 is, for example, 1 to 30 parts by weight, 1 to 20 parts by weight, 1 to 15 parts by weight, 1 to 10 parts by weight, 5 to 40 parts by weight, 5 to 30 parts by weight, or 5 to 35 parts by weight with respect to 100 parts by weight of the first inert member 50.

[0164] The Young's modulus of the first inert member 40 is, for example, even smaller than the Young's modulus of the negative electrode current collector 21. The Young's modulus of the first inert member 40 is, for example, 50% or less, 30% or less, 10% or less, or 5% or less of the Young's modulus of the negative electrode current collector 21. The Young's modulus of the first inert member 50 is, for example, 0.01% to 50%, 0.1 to 30%, 0.1 to 10%, or 1 to 5% of the Young's modulus of the negative electrode current collector 21. The Young's modulus of the first inert member 40 is, for example, 100 MPa or less, 50 MPa or less, 30 MPa or less, 10 MPa or less, or 5 MPa or less. The elastic modulus of the first inert member 40 is, for example, 0.01 to 100 MPa, 0.1 to 50 MPa, 0.1 to 30 MPa, 0.1 to 10 MPa, or 1 to 5 MPa. The elastic modulus (Young's modulus) of the first inert member 40 and the negative electrode current collector 21 can be measured, for example, by the method according to ASTM D412.

[0165] Since the first inert member 40 is conductive, it can perform its role as a negative electrode current collector 50. Furthermore, since the first inert member 40 has a lower elastic modulus than the negative electrode current collector 50, it can more effectively accommodate the volume change of the negative electrode layer 20 during charging and discharging of the secondary battery 1. As a result, the first inert member 40 can effectively relieve the internal stress caused by the volume change of the secondary battery 1 during charging and discharging, thereby improving the cycle characteristics of the secondary battery 1.

[0166] The thickness of the first inert member 40 is, for example, greater than the thickness of the first negative electrode active material layer 22. Having a greater thickness for the first inert member 40 than the first negative electrode active material layer 22 allows for more effective accommodation of volume changes in the negative electrode layer 20 during charging and discharging. The thickness of the first negative electrode active material layer 22 is 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the thickness of the first inert member 40. The thickness of the first negative electrode active material layer 22 is, for example, 1% to 50%, 1% to 40%, 1% to 30%, 1% to 20%, or 1% to 10% of the thickness of the first inert member 50. The thickness of the first inert member 40 is, for example, 1 μm to 300 μm, 10 μm to 300 μm, 50 μm to 300 μm, or 100 μm to 200 μm. If the thickness of the first inert member 40 is excessively thin, it will be difficult to provide the desired effect, and if the thickness of the first inert member 40 is excessively thick, the energy density of the secondary battery 1 may decrease. The form of the first inert member 50 is not limited and can be selected depending on the form of the secondary battery 1. The first inert member 40 can also be, for example, in the form of a sheet, a rod, or a gasket. The first inert member 40 can be placed, for example, on one or both sides of a single secondary battery 1. The first inert member 40 can be placed, for example, between a plurality of stacked secondary batteries 1. The first inert member 40 can be placed, for example, between each of the stacked secondary batteries 1, on the top surface and / or the bottom surface.

[0167] The first inert member 40 has, for example, a single-layer structure. On the other hand, although not shown in the drawings, the first inert member 40 may have a multilayer structure. In the first inert member 40 having a multilayer structure, each layer may have a different composition from the others. The first inert member having a multilayer structure may have, for example, a two-layer, three-layer, four-layer, or five-layer structure. The first inert member 40 having a multilayer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer improves the film strength of the first inert member 40 by effectively absorbing the volume change of the negative electrode layer 20 that occurs during the charging and discharging process of the secondary battery 1 and by providing bonding force between the support layer and the other layers. The support layer provides support force to the first inert member 40, prevents non-uniformity of the pressure applied to the secondary battery 1 during the pressurizing process or charging and discharging process, and prevents deformation of the secondary battery 1.

[0168] [Secondary battery manufacturing] Referring to Figure 5, a secondary battery 1a according to one embodiment includes a positive electrode layer 10a, a negative electrode layer 20a, and a flexible electrolyte layer 30a. The positive electrode layer 10a, the negative electrode layer 20a, and the electrolyte layer 30a are wound or folded to form a battery structure 70a. The formed battery structure 70a is housed in a battery case 50a. The battery case 50a is sealed with a cap assembly 60a to complete the secondary battery 1a. The battery case 50a is cylindrical, but is not necessarily limited to this form, and can be, for example, rectangular or thin film. Alternatively, the positive electrode layer 10a, the negative electrode layer 20a, and the porous film 30a are wound or folded to form a battery structure 70a. The formed battery structure 70a is housed in a battery case 50a. A high-viscosity liquid electrolyte or a polymer electrolyte forming composition is injected into the battery case 50a and sealed with a cap assembly 60a to complete the secondary battery 1a. When a polymer electrolyte-forming composition is used, heat treatment is added. The secondary battery 1a is, for example, a lithium battery.

[0169] Referring to Figure 6, a secondary battery 1b according to one embodiment includes a positive electrode layer 10b, a negative electrode layer 20b, and a flexible electrolyte layer 30b. The electrolyte layer 30b is placed between the positive electrode layer 10b and the negative electrode layer 20b, and the positive electrode layer 10b, negative electrode layer 20b, and electrolyte layer 30b are wound or folded to form a battery structure 70b. The formed battery structure 70b is housed in a battery case 50b to complete the secondary battery 1b. It may include electrode tabs 80b that serve as electrical channels for guiding the current formed in the battery structure 70b to the outside. Alternatively, a high-viscosity liquid electrolyte or a polymer electrolyte forming composition is injected into the battery case 50a and sealed with a cap assembly 60a to complete the secondary battery 1a. If a polymer electrolyte forming composition is used, heat treatment is added. The secondary battery 1b is, for example, a lithium battery.

[0170] Referring to Figure 7, a secondary battery 1c according to one embodiment includes a positive electrode layer 10c, a negative electrode layer 20c, and a flexible electrolyte layer 30c. The electrolyte layer 30c is placed between the positive electrode layer 10c and the negative electrode layer 20c to form a battery structure 70c. After the battery structures 70c are stacked, they are housed in a battery case 50c to complete the secondary battery 1c. It may include electrode tabs 80c that serve as electrical channels for guiding the current formed in the battery structure 70c to the outside. The battery case 50c is rectangular, but is not necessarily limited to this form, and can be cylindrical, thin film, etc. Alternatively, a high-viscosity liquid electrolyte or a polymer electrolyte forming composition is injected into the battery case 50c and sealed with a cap assembly 60c to complete the secondary battery 1c. When a polymer electrolyte forming composition is used, heat treatment is added. The secondary battery 1c is, for example, a lithium battery.

[0171] Pouch-type lithium batteries correspond to the secondary batteries shown in Figures 5 to 7, which use a pouch as the battery case. A pouch-type secondary battery includes one or more battery structures. A separator is placed between the positive and negative electrodes to form the battery structure. After the battery structures are stacked in a bicell structure, they are impregnated with an electrolyte, housed in a pouch, and sealed to complete the pouch-type lithium battery. For example, although not shown in the drawings, the positive electrode, negative electrode, and separator described above may be simply stacked and housed in the pouch as an electrode assembly, or they may be wound up as a jelly roll electrode assembly, or folded and then housed in the pouch. Then, an organic electrolyte is injected into the pouch and sealed to complete the secondary battery.

[0172] Secondary batteries have excellent lifespan and high efficiency characteristics, and are therefore used in electric vehicles (EVs), for example. They are also used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). Furthermore, they are used in fields where large amounts of power storage are required, such as electric bicycles and power tools.

[0173] Secondary batteries are stacked in multiple layers to form battery modules, and multiple battery modules form a battery pack. Such battery packs can be used in all devices that require high capacity and high output. For example, they can be used in notebook computers, smartphones, electric vehicles, etc. A battery module includes, for example, multiple batteries and a frame that secures them. A battery pack includes, for example, multiple battery modules and bus bars that connect them. Battery modules and / or battery packs may further include cooling devices. Multiple battery packs are regulated by a battery management system. The battery management system includes battery packs and battery control devices connected to the battery packs.

[0174] The present invention will be explained in more detail through the following examples and comparative examples. However, these examples are for illustrative purposes only and do not limit the scope of the present invention.

[0175] Example 1: Li2S-LiI-CNF cathode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Ag-C anode layer, thermosetting after assembly of the laminate. (Manufacturing of composite cathode active materials) Li2S and LiI were mixed in a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G. Next, the Li2S-LiI composite and carbon nanofiber (CNF) were mixed in a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF composite. The milling conditions were 25°C and 600 rpm for 10 hours. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as a composite cathode active material.

[0176] (Manufacturing of the positive electrode layer) The Li2S-CNF composite described above was prepared as the positive electrode active material. Li6PS5Cl, an argyrodite-type crystalline material (D50 = 1.0 μm, crystalline), was prepared as the solid electrolyte. PTFE was prepared as the binder. These materials were mixed in a weight ratio of composite positive electrode active material:solid electrolyte:binder = 60:40:1.2 to prepare the positive electrode mixture. The positive electrode mixture was obtained by dry mixing using a ball mill.

[0177] A positive electrode was manufactured by placing a positive electrode mixture on one surface of a positive electrode current collector made of aluminum foil coated with carbon on one surface, and then plate pressing it at a pressure of 200 MPa for 10 minutes. The thickness of the positive electrode was approximately 120 μm. The thickness of the positive electrode active material layer 12 was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm.

[0178] The initial charge capacity of the positive electrode layer was measured using the half-cell described above. For Examples 1-3 and 7, the ratio (B / A) of the initial charge capacity (A) of the positive electrode active material layer to the initial charge capacity (B) of the first negative electrode active material layer was less than 30% (i.e., less than 0.3) in each case. The initial charge capacity of the positive electrode active material layer was calculated from the first open circuit voltage as Li / Li + The maximum charging voltage of 2.8V was determined by charging. Furthermore, the initial charging capacity of the first negative electrode active material layer was determined from the second open-circuit voltage as Li / Li + This was determined by charging to 0.01V.

[0179] (Manufacturing of the negative electrode layer) A 10 μm thick stainless steel (SUS) foil was prepared as the negative electrode current collector. Carbon black (CB) with a primary particle size of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as the negative electrode active material.

[0180] A mixed powder of carbon black (CB) and silver (Ag) particles in a 3:1 weight ratio was placed in a container. 4g of an NMP solution containing 7% by weight of PVDF binder (Kureha Corporation #9300) was added to prepare the mixed solution. Next, the NMP was gradually added to the mixed solution while stirring to produce a slurry. The prepared slurry was applied to a SUS sheet using a bar coater and dried in air at 80°C for 10 minutes. The resulting laminate was then vacuum-dried at 40°C for 10 hours. The dried laminate was subjected to a temperature of 5 ton·f / cm². 2 The surface of the first negative electrode active material layer of the laminate was flattened by cold roll pressing at a pressure of 5 m / sec. The negative electrode layer was fabricated by the above process. The thickness of the first negative electrode active material layer contained in the negative electrode layer was approximately 15 μm. The initial charge capacity of the negative electrode was measured using the half-cell described above.

[0181] (Thermosetting electrolyte composition) Into a 20 L four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, distilled water was introduced as a solvent, and 2-(N,N-dimethylamino)ethyl acrylate, methyl acrylate, and acrylonitrile were introduced in a certain molar ratio. A small amount of potassium persulfate was introduced as an initiator. The reaction was carried out for 18 hours while the temperature of the reaction solution was stably maintained between 65 °C and 70 °C. Then, after cooling to room temperature, the pH of the reaction solution was adjusted to 7-8 using a 25% aqueous ammonia solution to produce an acrylic polymer which is poly(2-(N,N-dimethylamino)ethyl acrylate-co-methyl acrylate-co-acrylonitrile) copolymer represented by the following chemical formula A. (The molar ratio of 2-(N,N-dimethylamino)ethyl acrylate, methyl acrylate, and acrylonitrile was 20:15:65. The weight average molecular weight of the acrylic binder was about 60,000 Dalton. The weight average molecular weight of the acrylic polymer was a relative value with respect to a polystyrene standard sample and was measured using gel permeation chromatography (GPC). [Chemical formula]

[0182] After dissolving 1.0 M of LiPF6 and 1.0 M of LiTFSI respectively in 94 g of a non-aqueous organic solvent in which ethylene carbonate (EC):dimethyl carbonate (DMC) was mixed at a volume ratio of 15:85, 5.0 g of the acrylic polymer represented by the above chemical formula A was added to produce a thermosetting electrolyte composition.

[0183] (Manufacture of secondary battery) A polypropylene separator (separator, celgard 3501) was prepared as a flexible porous separator. The separator was impregnated with the thermosetting electrolyte composition. Referring to FIG. 8, the separator was arranged such that a lithium metal layer contacted the separator on the negative electrode layer, and a positive electrode layer was arranged on the separator to prepare a laminate.

[0184] The prepared laminate was subjected to plate press and heat treatment at 85°C under a pressure of 0.5 MPa for 1 hour.

[0185] By simultaneously pressurizing and heat-treating the laminate, the thermosetting composition was thermally cured to form a polymer gel electrolyte. A polymer electrolyte layer was formed between the positive electrode layer and the negative electrode layer.

[0186] A pressurized laminate was placed in a pouch and vacuum-sealed to manufacture a secondary battery. Parts of the positive electrode current collector and the negative electrode current collector were extended to the outside of the sealed secondary battery and used as the positive electrode layer terminals and negative electrode layer terminals.

[0187] Example 2: Li2S-LiI-CNF cathode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Ag-C anode layer, thermosetting before assembly of laminate. A secondary battery was manufactured in the same manner as in Example 1, except that an electrolyte layer was prepared separately by impregnating a separation membrane with a polymer gel electrolyte, and then placed on the negative electrode layer, and the positive electrode layer was placed on the electrolyte layer.

[0188] The electrolyte layer was manufactured using the following method.

[0189] A polypropylene separator (Celgard 3501) was placed on the substrate as a flexible, porous separation membrane. A thermosetting electrolyte composition was applied to the separation membrane to impregnate it with the composition, and heat treatment was carried out at 85°C for 2 hours to prepare an electrolyte layer in which the separation membrane was impregnated with a polymer gel electrolyte.

[0190] Example 3: Li2S-LiI-CNF cathode layer / Flexible electrolyte layer (separation membrane + high viscosity liquid electrolyte) / Ag-C anode layer A secondary battery was manufactured in the same manner as in Example 1, except that a liquid electrolyte containing an ionic liquid was applied to the separation membrane instead of a thermosetting electrolyte composition, and the pressurized temperature was changed to 25°C.

[0191] The liquid electrolyte containing the ionic liquid was prepared as follows.

[0192] (High viscosity liquid electrolyte) A liquid electrolyte was prepared by dissolving 1.0 M LiPF6 and 1.0 M LiTFSI in 65 g of a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 15:85, and then adding 35 g of the ionic liquid shown in chemical formula B below.

[0193] As the ionic liquid, 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, represented by the following chemical formula B, was used. The viscosity of the liquid electrolyte was 22.5 cps at 1 atm and 25°C. [ka]

[0194] Example 4: NCM cathode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Ag-C anode layer, thermosetting after assembly of the laminate. Instead of a Li2S-LiI-CNF composite-containing cathode layer, a Li2O-ZrO2(LZO) coated LiNi layer manufactured as described below is used as the cathode layer. 0.8 Co 0.15 Mn 0.05 A lithium secondary battery was manufactured using the same method as in Example 1, except that an O2(NCM)-containing positive electrode layer was used.

[0195] (Manufacturing of the positive electrode layer) LiNi coated with Li2O-ZrO2 (LZO) as the positive electrode active material. 0.8 Co 0.15 Mn 0.05O2(NCM) was prepared. The LZO-coated positive electrode active material was manufactured by the method disclosed in Korean Published Patent No. 10-2016-0064942. Li6PS5Cl, an argyrodite-type crystalline material (D50=0.5μm, crystalline), was prepared as the solid electrolyte. A polytetrafluoroethylene (PTFE) binder was prepared as the binder. Carbon nanofibers (CNF) were prepared as the conductive material. These materials were mixed with xylene solvent in a weight ratio of positive electrode active material:solid electrolyte:conductive material:binder = 84:11.5:3:1.5. The slurry was formed into a sheet and then vacuum-dried at 40°C for 8 hours to produce a positive electrode sheet. The manufactured positive electrode sheet was placed on the carbon layer of a positive electrode current collector made of aluminum foil coated with a carbon layer on one side, and the positive electrode layer was manufactured by heated roll pressing at 85°C. The total thickness of the positive electrode layer was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 95 μm, and the thickness of the carbon-coated aluminum foil was approximately 25 μm.

[0196] The initial charge capacity of the positive electrode layer was measured using the half-cell described above. For Examples 4-6, the ratio (B / A) of the initial charge capacity of the first negative electrode active material layer to the initial charge capacity (A) of the positive electrode active material layer was less than 30% (e.g., less than 0.3). The initial charge capacity of the positive electrode active material layer was calculated from the first open circuit voltage as Li / Li + The maximum charging voltage of 4.25V was determined by charging. Furthermore, the initial charging capacity of the first negative electrode active material layer was determined by charging from the second open-circuit voltage down to 0.01V relative to Li / Li+.

[0197] Example 5: NCM cathode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Ag-C anode layer, thermosetting before assembly of laminate. A secondary battery was manufactured in the same manner as in Example 4, except that an electrolyte layer was prepared separately by impregnating a separation membrane with a polymer gel electrolyte, and then placed on the negative electrode layer, and the positive electrode layer was placed on the electrolyte layer.

[0198] The electrolyte layer was manufactured using the following method.

[0199] A polypropylene separator (Celgard 3501) was placed on a substrate as a flexible, porous separation membrane. A thermosetting electrolyte composition was applied to the separation membrane to impregnate it with the composition, and heat treatment was carried out at 85°C for 2 hours to prepare an electrolyte layer in which a polymer gel electrolyte was impregnated into the separation membrane.

[0200] Example 6: NCM cathode layer / Flexible electrolyte layer (separation membrane + high viscosity liquid electrolyte) / Ag-C anode layer Instead of the Li2S-LiI-CNF composite-containing cathode layer, the Li2O-ZrO2(LZO) coated LiNi prepared in Example 3 was used as the cathode layer. 0.8 Co 0.15 Mn 0.05 A lithium secondary battery was manufactured using the same method as in Example 3, except that an O2(NCM)-containing positive electrode layer was used.

[0201] Example 7: Li2S-LiI-CNF cathode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Ag-C anode layer / elastic sheet, thermosetting after assembly of laminate A secondary battery was manufactured in the same manner as in Example 1, except that a sheet-shaped conductive flame-retardant member having the same area and shape as the laminate was further placed on the outer surface of the negative electrode current collector of the pressurized laminate before placing the pressurized laminate into a pouch, and then the secondary battery was manufactured by vacuum sealing.

[0202] The conductive, flame-retardant, inert material sheet was prepared by the following method. The conductive, flame-retardant, inert material sheet can interact with the elastic sheet.

[0203] A slurry of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), acrylic binder, conductive material (Denka black), and solvent was mixed and formed into a sheet, which was then dried to produce a flame-retardant inert material. The weight ratio of cellulose fiber, glass fiber, aluminum hydroxide (Al(OH)3), acrylic binder, and conductive material was 20:8:50:2:20. The thickness of the conductive flame-retardant inert material was 120 μm. Before placing the manufactured conductive flame-retardant inert material on the negative electrode current collector, it was vacuum heat-treated at 80°C for 5 hours to remove moisture and other contaminants.

[0204] Comparative Example 1: Use of S-carbon (C) cathode layer / flexible electrolyte layer (separation membrane + low viscosity liquid electrolyte) / Li-metal anode layer and low viscosity liquid electrolyte. (Manufacturing of composite cathode active materials) Sulfur (S) and carbon-based material were mixed in a weight ratio of 70:30, and then heat-treated at 160°C to produce a sulfur-carbon composite. The carbon-based material had a specific surface area of ​​300 m². 2 The material was carbon nanotube (CNT) with a particle size of 30 μm and a weight of 30 μm / g.

[0205] (Manufacturing of the positive electrode layer) A slurry with a solid powder content of 25 wt% was prepared by mixing a sulfur-carbon composite, conductive material, and binder in a weight ratio of 90:5:5, then dissolving it in water. The slurry was bar-coated onto a carbon-coated aluminum foil current collector, dried at 50°C for 2 hours, and then rolled to prepare the positive electrode layer. Vapor-grown carbon fiber (VGCF) was used as the conductive material and polyvinylidene fluoride (PVDF) was used as the binder. The thickness of the positive electrode layer was approximately 120 μm. The thickness of the positive electrode active material layer was approximately 100 μm, and the thickness of the carbon-coated aluminum foil was approximately 20 μm.

[0206] (Manufacturing of the negative electrode layer) A negative electrode layer was prepared by placing a 20 μm thick lithium metal foil as the negative electrode active material layer on a 10 μm thick SUS foil as the negative electrode current collector.

[0207] (Low viscosity liquid electrolyte production)

[0208] A liquid electrolyte was prepared by dissolving 1.0 M LiPF6 in 100 g of a non-aqueous organic solvent mixture of ethylene carbonate (EC) and ethyl methyl carbonate (DEC) in a volume ratio of 30:70. The viscosity of the liquid electrolyte was less than 5 cps at 1 atm and 25°C.

[0209] (Secondary battery manufacturing) A polypropylene isolation membrane (separator, Celgard 3501) was prepared as a flexible, porous separation membrane.

[0210] A separation membrane was placed on the negative electrode layer so that the lithium metal layer was in contact with the separation membrane, and the positive electrode layer was placed on the separation membrane to prepare the laminate.

[0211] The prepared laminate was plate-pressed at 85°C and a pressure of 0.5 MPa for 1 hour.

[0212] The pressurized laminate was placed in a pouch, injected with a low-viscosity liquid electrolyte, and vacuum-sealed. Parts of the positive electrode current collector and negative electrode current collector were extended to the outside of the sealed battery and used as the positive electrode layer terminals and negative electrode layer terminals.

[0213] Comparative example 2: Li2S-LiI-CNT positive electrode layer / solid electrolyte layer (sulfide-based solid electrolyte) / Li-metal negative electrode layer, inorganic solid electrolyte layer (Manufacturing of composite cathode active materials) Li2S, LiI, and carbon nanotubes (CNTs) were mixed in a weight ratio of 70:20:10. The mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNT composite. The milling conditions were 25°C and 300 rpm for 12 hours.

[0214] A Li2S-LiI-CNT composite was used as the composite cathode active material.

[0215] (Manufacturing of the positive electrode layer) The cathode layer was prepared in the same manner as in Example 1, except that a Li2S-LiI-CNT composite was used.

[0216] (Manufacturing of the negative electrode layer) A negative electrode layer was prepared by placing a 20 μm thick lithium metal foil as the negative electrode active material layer on a 10 μm thick SUS foil as the negative electrode current collector.

[0217] (Manufacturing of solid electrolyte layer) A mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of an argyrodite-type crystalline Li6PS5Cl solid electrolyte (D50 = 3.0 mm, crystalline). Octyl acetate was added to the prepared mixture while stirring to produce a slurry. The prepared slurry was applied using a bar coater onto a 15 μm thick nonwoven fabric placed on a 75 μm thick PET substrate, and dried in air at 80°C for 10 minutes to prepare a laminate. The prepared laminate was vacuum dried at 80°C for 2 hours to produce a solid electrolyte layer.

[0218] (Manufacturing of secondary batteries) A laminate was prepared by placing a solid electrolyte layer on the negative electrode layer such that the lithium metal layer was in contact with the solid electrolyte layer, and then placing a positive electrode layer on the solid electrolyte layer.

[0219] The prepared laminate was subjected to plate press treatment at 85°C and a pressure of 500 MPa for 30 minutes.

[0220] A pressurized laminate was placed in a pouch and vacuum-sealed to manufacture a secondary battery. Parts of the positive electrode current collector and the negative electrode current collector were extended to the outside of the sealed battery and used as the positive and negative electrode terminals.

[0221] Comparative Example 3: Li2S-LiI-CNF positive electrode layer / flexible electrolyte layer (separation membrane + thermosetting polymer) / Cu current collector, thermosetting after assembly of laminate, negative electrode active material layer not used. A secondary battery was manufactured in the same manner as in Example 1, except that the first negative electrode active material layer containing carbon black (CB) and silver (Ag) particles was omitted. The negative electrode current collector was directly placed on the electrolyte layer.

[0222] Comparative example 4: NCM positive electrode layer / solid electrolyte layer (sulfide solid electrolyte) / Li-metal negative electrode layer, inorganic solid electrolyte layer Instead of the Li2S-LiI-CNT composite-containing cathode layer, the Li2O-ZrO2(LZO) coated LiNi prepared in Example 4 was used as the cathode layer. 0.8 Co 0.15 Mn 0.05 A lithium secondary battery was manufactured using the same method as in Comparative Example 2, except that an O2(NCM)-containing positive electrode layer was used.

[0223] Evaluation Example 1: Lifetime Characteristics Evaluation The charge-discharge characteristics of the secondary batteries manufactured in Examples 1-7, Comparative Examples 1-3, and Reference Example 1 were evaluated by the following charge-discharge tests. The charge-discharge tests were performed by placing the solid secondary batteries in a constant temperature bath at 45°C.

[0224] In the first cycle, the lithium battery was charged with a constant current of 0.05C rate at 45°C until the voltage reached 2.7V (vs.Li). Subsequently, it was discharged with a constant current of 0.05C rate until the voltage reached 1.0V (vs.Li).

[0225] Next, the lithium battery was charged at 45°C with a constant current of 0.1C rate until the voltage reached 2.7V (vs.Li). Then, the battery was discharged at a constant current of 0.1C rate until the voltage reached 1.0V (vs.Li), and this discharge cycle was repeated. The discharge capacity of the first cycle was defined as the standard capacity.

[0226] The charge-discharge characteristics of the secondary batteries manufactured in Examples 4-6 were evaluated by the following charge-discharge tests. The charge-discharge tests were performed by placing the all-solid-state secondary batteries in a constant temperature bath at 45°C.

[0227] In the first cycle, the lithium battery was charged with a constant current of 0.05C rate at 45°C until the voltage reached 4.2V (vs.Li). Subsequently, it was discharged with a constant current of 0.05C rate until the voltage reached 2.5V (vs.Li).

[0228] Next, the lithium battery was charged with a constant current at a rate of 0.1C at 45°C until the voltage reached 4.2V (vs.Li). Then, the battery was discharged with a constant current at a rate of 0.1C until the voltage reached 2.5V (vs.Li), and this discharge cycle was repeated.

[0229] The discharge capacity of the first cycle was set as the standard capacity.

[0230] From the second cycle onward, charging and discharging were performed under the same conditions as the first cycle for up to 150 cycles. The measurement results are shown in Table 1 below.

[0231] The cycle count refers to the number of cycles required for the discharge capacity to decrease to 80% of the standard capacity after the second cycle. A higher cycle count is considered to indicate better or more suitable lifespan characteristics. [Table 1]

[0232] As shown in Table 1, the secondary batteries of Examples 1 to 7 showed improved lifespan characteristics compared to the secondary batteries of Comparative Examples 1 to 3.

[0233] The secondary batteries of Examples 1 to 7 provided improved lifespan characteristics by including a flexible electrolyte, which reduced the interfacial resistance between the positive electrode layer, the negative electrode layer, and the electrolyte layer, and by effectively accommodating the volume changes of the positive electrode layer and the negative electrode layer during the charge and discharge process.

[0234] In the secondary battery of Comparative Example 1, polysulfide generated from sulfur (S) during the charge-discharge process dissolved in the liquid electrolyte, reducing the electrode capacity. The dissolved polysulfide then underwent a side reaction with the negative electrode layer, resulting in a decrease in battery life.

[0235] In the secondary battery of Comparative Example 2, defects such as cracks occurred in the solid electrolyte layer during the pressurized manufacturing process and the charging and discharging process of the secondary battery. Short circuits occurred due to the growth of lithium dendrites through these defects. As a result, the lifespan characteristics of the secondary battery were reduced.

[0236] In the secondary battery of Comparative Example 3, the polymer electrolyte layer was in direct contact with the negative electrode current collector, and during the charging and discharging process of the secondary battery, lithium metal was deposited and dissolved on the surface of the negative electrode current collector, resulting in dendrite formation and the generation of isolated lithium metal, which reduced the lifespan characteristics of the secondary battery.

[0237] Evaluation Example 2: High-Frequency Characteristic Evaluation After the life evaluation in Evaluation Example 1, the high efficiency characteristics of the secondary batteries manufactured in Examples 1-7 and Comparative Examples 1-4 were evaluated by the following charge-discharge tests. The charge-discharge tests were performed by placing the secondary batteries in a constant temperature bath at 45°C.

[0238] A lithium battery was charged at 45°C with a constant current of 0.1C rate until the voltage reached 2.7V (vs.Li). Subsequently, it was discharged at a constant current of 0.1C rate until the voltage reached 1.0V (vs.Li) (first cycle).

[0239] The lithium battery, after completing the first cycle, was charged at 45°C with a constant current of 0.1C rate until the voltage reached 2.7V (vs.Li). Subsequently, it was discharged at a constant current of 0.2C rate until the voltage reached 1.0V (vs.Li) (second cycle).

[0240] The lithium battery, after completing the second cycle, was charged with a constant current at 45°C at a rate of 0.12C until the voltage reached 2.7V (vs.Li). Subsequently, it was discharged at a constant current of 0.5C until the voltage reached 1.0V (vs.Li) (third cycle).

[0241] A lithium battery that had undergone the third cycle was charged with a constant current at 45°C at a rate of 0.1C until the voltage reached 2.7V (vs.Li). Subsequently, it was discharged at a constant current of 1.0C until the voltage reached 1.0V (vs.Li) (fourth cycle).

[0242] After the life evaluation in Evaluation Example 1, the lithium batteries manufactured in Examples 4-6 and Comparative Example 4 were charged at 45°C with a constant current of 0.1C rate until the voltage reached 2.5V (vs.Li). Subsequently, they were discharged with a constant current of 0.1C rate until the voltage reached 2.5V (vs.Li) (first cycle).

[0243] The lithium battery, after completing the first cycle, was charged at 45°C with a constant current at a rate of 0.1C until the voltage reached 2.5V (vs.Li). Subsequently, it was discharged at a constant current of 0.2C until the voltage reached 2.5V (vs.Li) (second cycle).

[0244] The lithium battery, after completing the second cycle, was charged at 45°C with a constant current of 0.1C rate until the voltage reached 2.5V (vs.Li). Subsequently, it was discharged at a constant current of 0.5C rate until the voltage reached 2.5V (vs.Li) (third cycle).

[0245] A lithium battery that had undergone the third cycle was charged with a constant current at 45°C at a rate of 0.1C until the voltage reached 2.5V (vs.Li). Subsequently, it was discharged at a constant current of 1.0C until the voltage reached 2.5V (vs.Li) (fourth cycle).

[0246] A 10-minute stop period was observed after each charge / discharge cycle in all charge / discharge cycles. Some of the results from the room-temperature charge / discharge experiments are shown in Table 2 below. The high-efficiency characteristic is defined by Equation 1 below. <Formula 1> High efficiency characteristic [%] = [Discharge capacity in the 4th cycle (1.0C) / Discharge capacity in the 1st cycle (0.1C)] × 100 [Table 2]

[0247] As shown in Table 2, the secondary batteries of Examples 1-3 and Example 7, which contain sulfide-based positive electrode active materials, showed improved high-efficiency characteristics compared to the secondary batteries of Comparative Examples 1-3, which contain sulfur-based or sulfide-based positive electrode active materials.

[0248] Furthermore, the secondary batteries of Examples 4 to 6, which included an oxide-based positive electrode active material, showed improved high-efficiency characteristics compared to the secondary battery of Comparative Example 4, which also included an oxide-based positive electrode active material. [Industrial applicability]

[0249] In one embodiment, by arranging a flexible electrolyte layer between the positive electrode layer and the negative electrode layer, the interfacial resistance between the positive electrode layer and / or the negative electrode layer and the electrolyte layer is reduced, and cracks in the solid electrolyte layer during the charge and discharge process are suppressed, thereby providing a secondary battery with improved cycle characteristics. [Explanation of Symbols]

[0250] 1, 1a, 1b, 1c secondary battery 10, 10a, 10b, 10c positive electrode layer 11 Positive electrode current collector 12 Cathode active material layer 20, 20a, 20b, 30a negative electrode layer 21 Negative electrode current collector 22 First negative electrode active material layer 30, 30a, 30b, 30c electrolyte layer 40 First inert member 50a, 50b, 50c battery case 60a, 60b, 60c Cap Assembly 70a, 70b, 70c battery assembly

Claims

1. The system includes a positive electrode layer; a negative electrode layer; and a flexible electrolyte layer disposed between the positive electrode layer and the negative electrode layer. The positive electrode layer includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, The negative electrode layer includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector. A secondary battery in which the initial charge capacity of the first negative electrode active material layer is less than 50% of the initial charge capacity of the positive electrode active material layer.

2. The secondary battery according to claim 1, wherein the electrolyte layer comprises a polymer electrolyte, a liquid electrolyte, or a combination thereof, and the viscosity of the liquid electrolyte is 10 cps or more at 25°C and 1 atm.

3. The secondary battery according to claim 2, wherein the polymer electrolyte comprises a polymer having repeating units having a thermopolymerizable functional group, a thermoset of the polymer, an oligomer having repeating units having a thermopolymerizable functional group, a thermoset of the oligomer, a monomer having a thermopolymerizable functional group, a thermoset of the monomer, an oligomeric ionic liquid, a polymeric ionic liquid, or a combination thereof.

4. The secondary battery according to claim 3, wherein the thermally polymerizable functional group comprises a cyano group, a hydroxyl group, an amino group, an amide group, an imide group, a carboxyl group, an acid anhydride group, or a combination thereof.

5. The secondary battery according to claim 2, wherein the liquid electrolyte comprises an ionic liquid, and the viscosity of the liquid electrolyte is 15 cps or more at 25°C and 1 atm.

6. The secondary battery according to claim 5, wherein the ionic liquid is represented by one of the following chemical formulas 1 and 2: 【Chemistry 1】 In the aforementioned chemical formula 1, X １ is -N(R ２ ) (Caution ３ ) (Caution ４ ) or -P(R ２ ) (Caution ３ ) (Caution ４ ) and R １ , R ２ , R ３ and R ４ are each independently a C1-C30 alkyl group substituted or unsubstituted with halogen, a C1-C30 alkoxy group substituted or unsubstituted with halogen, a C6-C30 aryl group substituted or unsubstituted with halogen, a C6-C30 aryloxy group substituted or unsubstituted with halogen, a C3-C30 heteroaryl group substituted or unsubstituted with halogen, a C3-C30 heteroaryloxy group substituted or unsubstituted with halogen, a C4-C30 cycloalkyl group substituted or unsubstituted with halogen, a C3-C30 heterocycloalkyl group substituted or unsubstituted with halogen, or a C2-C100 alkylene oxide group substituted or unsubstituted with halogen, In the aforementioned chemical formula 2, 【Chemistry 2】 This is a heterocycloalkyl ring or heteroaryl ring containing 1 to 3 heteroatoms and 2 to 30 carbon atoms, wherein the ring is substituted by substituents or is unsubstituted. X ２ is = N(R ５ ) (Caution ６ ), -N(R ５ ) =, = P(R ５ ) (Caution ６ ) or -P(R ５ ) = and The substituents substituted on the aforementioned ring, R ５ , and R ６ Each of these is independently hydrogen, a halogen-substituted or unsubstituted C1-C30 alkyl group, a halogen-substituted or unsubstituted C1-C30 alkoxy group, a halogen-substituted or unsubstituted C6-C30 aryl group, a halogen-substituted or unsubstituted C6-C30 aryloxy group, a halogen-substituted or unsubstituted C3-C30 heteroaryl group, a halogen-substituted or unsubstituted C3-C30 heteroaryloxy group, a halogen-substituted or unsubstituted C4-C30 cycloalkyl group, a halogen-substituted or unsubstituted C3-C30 heterocycloalkyl group, or a halogen-substituted or unsubstituted C2-C100 alkylene oxide group. Y- is an anion.

7. The electrolyte layer is a self-standing film. The secondary battery according to claim 1, wherein the electrolyte layer further comprises a flexible porous membrane.

8. The secondary battery according to claim 1, wherein the positive electrode active material layer comprises an alkali metal-containing sulfide-based positive electrode active material or an alkali metal-containing oxide-based positive electrode active material, and the alkali metal comprises lithium or sodium.

9. The alkali metal-containing sulfide-based cathode active material is Li ２ Contains S-containing complex, The Li ２ S-containing complex is Li ２ S and carbon-based composite, Li ２ A composite of S, carbon-based materials, and a solid electrolyte, Li ２ S and solid electrolyte complex, Li ２ A composite of S, carbon-based materials, and lithium salts, Li ２ A composite of S and lithium salt, Li ２ S and metal carbide composite, Li ２ S, carbon-based materials, and metal carbide composites, Li ２ Composite of S and metal nitride, Li ２ The secondary battery according to claim 8, comprising a composite of S, a carbon-based material, and a metal nitride, or a combination thereof.

10. The lithium salt is a binary compound or a ternary compound. The binary compound is LiI, LiBr, LiCl, LiF, LiH, Li ２ O, Li ２ Se, Li ２ Te, Li ３ N, Li ３ P, Li ３ As, Li ３ Sb, Li ３ Al ２ LiB ３ or a combination of these, The ternary compound is Li ３ OCl, LiPF ６ LiBF ４ LiSbF ６ LiAsF ６ LiClO ４ LiAlO ２ LiAlCl ４ LiNO ３ Li ２ CO ３ LiBH ４ Li ２ SO ４ Li ３ BO ３ Li ３ PO ４ Li ４ NCl, Li ５ NClin ２ Li ３ BN ２ The secondary battery according to claim 9, or a combination thereof.

11. The carbon-based material includes a fibrous carbon-based material, The secondary battery according to claim 9, wherein the fibrous carbon-based material includes a carbon nanostructure, and the carbon nanostructure includes carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof.

12. The Li ２ S-containing complex is Li ２ It contains a composite of S, lithium salt, and carbon-based material. The Li ２ Li per 100 parts by weight of S-containing composite ２ The mixture contains 10 to 80 parts by weight of S, 1 to 40 parts by weight of lithium salt, and 1 to 20 parts by weight of carbon-based material. The positive electrode active material layer further contains a sulfide-based solid electrolyte, In the positive electrode active material layer, the carbon-based material is Li ２ The secondary battery according to claim 9, wherein the sulfur is arranged only in the sulfur-containing composite.

13. The secondary battery according to claim 8, wherein the alkali metal-containing oxide positive electrode active material includes a lithium transition metal oxide represented by one of chemical formulas 11 to 18: <Chemical formula 11> Li ａ Ni ｘ Co ｙ M ｚ O ２－ｂ A ｂ In the aforementioned chemical formula 11, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.8 ≤ x < 1, 0 ≤ y ≤ 0.3, 0 < z ≤ 0.3, and x + y + z = 1. M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof. A is F, S, Cl, Br, or a combination thereof. <Chemical formula 12> L)) ｘ Co ｙ Mn ｚ O ２ <Chemical formula 13> L)) ｘ Co ｙ Al ｚ O ２ In the aforementioned chemical formulas 12 and 13, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, and x + y + z = 1. <Chemical formula 14> L)) ｘ Co ｙ Mn ｚ Al ｗ O ２ In the aforementioned chemical formula 14, 0.8 ≤ x ≤ 0.95, 0 ≤ y ≤ 0.2, 0 < z ≤ 0.2, 0 < w ≤ 0.2, and x + y + z + w = ​​1. <Chemical formula 15> Li ａ Co ｘ M ｙ O ２－ｂ A ｂ In the aforementioned chemical formula 15, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0.9 ≤ x ≤ 1, 0 ≤ y ≤ 0.1, and x + y = 1. M is manganese (Mn), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof. A is F, S, Cl, Br, or a combination thereof. <Chemical formula 16> Li ａ Ni ｘ Mn ｙ M' ｚ O ２－ｂ A ｂ In the aforementioned chemical formula 16, 1.0 ≤ a ≤ 1.2, 0 ≤ b ≤ 0.2, 0 < x ≤ 0.3, 0.5 ≤ y < 1, 0 < z ≤ 0.3, and x + y + z = 1. M' is cobalt (Co), niobium (Nb), vanadium (V), magnesium (Mg), gallium (Ga), silicon (Si), tungsten (W), molybdenum (Mo), iron (Fe), chromium (Cr), copper (Cu), zinc (Zn), titanium (Ti), aluminum (Al), boron (B), or a combination thereof. A is F, S, Cl, Br, or a combination thereof. <Chemical formula 17> Li ａ M1 ｘ M2 ｙ PO ４－ｂ X ｂ In the aforementioned chemical formula 17, 0.90 ≤ a ≤ 1.1, 0 ≤ x ≤ 0.9, 0 ≤ y ≤ 0.5, 0.9 < x + y < 1.1, and 0 ≤ b ≤ 2. M1 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), or a combination thereof. M2 is magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zinc (Zn), boron (B), niobium (Nb), gallium (Ga), indium (In), molybdenum (Mo), tungsten (W), aluminum (Al), silicon (Si), chromium (Cr), vanadium (V), scandium (Sc), yttrium (Y), or a combination thereof, and X is O, F, S, P, or a combination thereof. <Chemical formula 18> Li ａ M3 ｚ PO ４ In the above chemical formula 18, 0.90 ≤ a ≤ 1.1 and 0.9 ≤ z ≤ 1.

1. M3 is chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), or a combination of these.

14. The first negative electrode active material layer comprises a negative electrode active material and a binder. The secondary battery according to claim 1, wherein the negative electrode active material has a particle form and the average particle size of the negative electrode active material is 4 μm or less.

15. The anode active material comprises one or more selected from carbon-based anode active materials and metal or semimetallic anode active materials. The carbon-based anode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. The secondary battery according to claim 1, wherein the metal or metalloid anode active material includes gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

16. The negative electrode active material comprises a mixture of first particles containing amorphous carbon and second particles containing a metal or metalloid. The secondary battery according to claim 1, wherein the content of the second particles is 1 to 60 wt% based on the total weight of the mixture.

17. The secondary battery according to claim 1, wherein the initial charge capacity of the first negative electrode active material layer is 50% or less of the initial charge capacity of the positive electrode active material layer.

18. The second negative electrode active material layer further comprises, Between the negative electrode current collector and the first negative electrode active material layer and / or Displaced between the negative electrode current collector and the electrolyte layer, The secondary battery according to claim 1, wherein the second negative electrode active material layer is a metal layer, and the metal layer contains lithium or a lithium alloy.

19. One or more of the positive electrode current collector and the negative electrode current collector include a base film and a metal layer disposed on one or both sides of the base film. The base film comprises a polymer, and the polymer comprises polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. The secondary battery according to claim 1, wherein the metal layer comprises 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.

20. The secondary battery according to claim 1, further comprising a first inert member disposed on the other surface of the negative electrode current collector, wherein the first inert member includes a conductive flame-retardant inert member.

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