Solid secondary battery and method for manufacturing same

Abstract

Provided are a solid secondary battery and a method for manufacturing same. The solid secondary battery comprises: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on one surface or both surfaces of the positive electrode current collector, the positive electrode active material layer includes a composite positive electrode active material and a gel polymer electrolyte, the composite positive electrode active material includes a M2S composite, where M is an alkali metal and the alkali metal is Li or Na, and the gel polymer electrolyte contains a crosslinked polymer which is a polymerization product of a crosslinkable monomer having two or more crosslinking points.

Description

Solid secondary battery and manufacturing method thereof

[0001] It relates to a solid secondary battery and a method for manufacturing the same.

[0002] Recent industrial demands have led to the active development of batteries with high energy density and safety. Lithium batteries, for example, are used in a variety of applications, including information technology, communications devices, and automobiles. Because automobiles are life-threatening, safety is also crucial.

[0003] Lithium batteries using liquid electrolytes may have an increased risk of fire and / or explosion in the event of a short circuit. All-solid-state secondary batteries using solid electrolytes instead of liquid electrolytes are being proposed. Solid electrolytes are less likely to catch fire than liquid electrolytes.

[0004] All-solid-state secondary batteries can reduce the risk of fire or explosion and provide improved safety by using solid electrolytes instead of liquid electrolytes.

[0005] However, all-solid-state secondary batteries do not use solvents in the manufacture of the cathode, electrolyte, and anode, which can lead to reduced ionic conductivity and increased interfacial resistance, which can degrade capacity and high-rate characteristics. Furthermore, changes in cathode volume during charge / discharge can disrupt ion and electron networks, potentially resulting in unfavorable cycle life characteristics.

[0006] One aspect is the interaction between the solid electrolyte and the active material through the gel polymer electrolyte in the anode.

[0007] The aim is to provide a solid secondary battery with improved initial efficiency, specific capacity, energy density and lifespan by utilizing anodes that form an organic network.

[0008] According to another aspect, a method for manufacturing the above-described solid secondary battery is provided.

[0009] According to one embodiment, a solid secondary battery is provided, comprising: a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, wherein the positive electrode includes a positive electrode current collector; and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector, wherein the positive electrode active material layer includes a composite positive electrode active material and a gel polymer electrolyte, wherein the composite positive electrode active material includes an M2S complex, wherein M is an alkali metal, the alkali metal is Li or Na, and the gel polymer electrolyte contains a crosslinked polymer that is a polymerization product of a crosslinkable monomer having two or more crosslinking points.

[0010] The above M2S composite includes a composite of M2S, an alkali metal salt, and a carbon-based material, and the size of M2S crystallites obtained from an XRD spectrum of the composite is less than 9.9 nm, and the composite includes a solid solution of M2S and an alkali metal salt.

[0011] According to another aspect, a solid secondary battery is provided, which includes the above-described positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector.

[0012] The above M2S composite includes a composite of M2S, an alkali metal salt, and a carbon-based material, and the size of M2S crystallites obtained from an XRD spectrum of the composite is less than 9.9 nm, and the composite includes a solid solution of M2S and an alkali metal salt.

[0013] The above-mentioned positive electrode active material layer includes 40 to 80 parts by weight of a composite positive electrode active material and 20 to 60 parts by weight of a gel polymer electrolyte based on 100 parts by weight of the above-mentioned positive electrode active material layer. In addition, the gel polymer electrolyte includes a liquid electrolyte containing an organic solvent and a lithium salt, and the content of the liquid electrolyte is 40 to 95 parts by weight based on 100 parts by weight of the gel polymer electrolyte.

[0014] The above positive electrode active material layer further includes a solid electrolyte, and the content of the solid electrolyte is 10 to 20 parts by weight based on 100 parts by weight of the gel polymer electrolyte.

[0015] According to another aspect, a step of milling a composition including M2S and an alkali metal salt to obtain a milled product;

[0016] A method for manufacturing a solid secondary battery is provided, comprising: a step of manufacturing a positive electrode by adding and mixing a composition for forming a gel polymer electrolyte containing a crosslinking monomer for forming a gel polymer electrolyte to the above-mentioned milled product; a step of preparing an anode; and a step of arranging an electrolyte layer between the positive electrode and the negative electrode, wherein the composition for forming a gel polymer electrolyte contains a liquid electrolyte containing a lithium salt and an organic solvent and a crosslinking agent, wherein M is an alkali metal, and the alkali metal is Li or Na.

[0017] In the step of milling a composition including the M2S and a carbon-based material to obtain a milled product, an alkali metal salt is further added, and the step of milling the composition including the M2S and the carbon-based material to obtain a milled product includes a step of milling the M2S and the alkali metal salt to obtain an M2S-alkali metal salt complex; and a step of milling the composition including the M2S-alkali metal salt complex and the carbon-based material to obtain a milled product.

[0018] According to one aspect, a solid secondary battery having improved initial efficiency, energy density, and lifespan characteristics can be provided by improving the interfacial resistance between the cathode and the solid electrolyte and alleviating the expansion of the cathode volume by providing a cathode with an improved electronic conduction network.

[0019] Figure 1a is a schematic diagram of a positive electrode active material layer according to an embodiment.

[0020] Figure 1b is a schematic diagram of a positive electrode active material layer according to another embodiment.

[0021] Figures 2 to 6 are cross-sectional views of a solid secondary battery according to an exemplary embodiment.

[0022] <Brief explanation of the main symbols in the drawing>

[0023] 1: Li2S 2: Conductive material 3: Solid electrolyte (SE)

[0024] 4: GPE 10 positive electrode 11 positive electrode current collector

[0025] 12 Positive active material layer 20 Negative electrode 21 Negative current collector

[0026] 22 First negative electrode active material layer 30 Electrolyte layer 40 Inert member

[0027] Unless otherwise defined, all terms (including technical and scientific terms) used in this disclosure have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure pertains. Furthermore, terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning within the context of the relevant technology and this disclosure, and should not be interpreted in an idealized or overly formal sense.

[0028] Exemplary embodiments are described in this disclosure with reference to cross-sectional drawings that are schematic representations of idealized embodiments. As such, variations from the shapes depicted are to be expected, for example, as a result of manufacturing techniques and / or tolerances. Therefore, the embodiments described in this disclosure should not be construed as limited to the specific shapes of regions as depicted in this disclosure, but should encompass variations in shapes resulting from, for example, manufacturing. For example, regions depicted or described as flat may typically have rough and / or non-linear features. Moreover, angles depicted as sharp may be rounded. Therefore, the regions depicted in the drawings are schematic in nature, and their shapes are not intended to depict the precise shapes of the regions, nor are they intended to limit the scope of the claims.

[0029] This creative idea may be embodied in many different forms and should not be construed as limited to the embodiments described in this disclosure. These embodiments are provided so that this disclosure will be thorough and complete, and so that it will fully convey the scope of the creative idea to those skilled in the art. Like reference numerals in the drawings indicate like elements.

[0030] Unless otherwise specified herein, when a part such as a layer, film, region, or plate is said to be “on top of” another part, this includes not only cases where it is “directly on top of” the other part, but also cases where there is another part in between.

[0031] Unless otherwise specified herein, the singular may also include the plural. Furthermore, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0032] When a component is referred to as being "on" another component, it can be understood that it is either directly on top of the other component or that other components may be intervening between them. Conversely, when a component is referred to as being "directly on" another component, no intervening components are present.

[0033] Although terms such as "first," "second," "third," etc. may be used herein to describe various components, elements, regions, layers, and / or zones, these components, elements, regions, layers, and / or zones should not be limited by these terms. These terms are only used to distinguish one component, element, region, layer, or zone from another component, element, region, layer, or zone. Thus, a first component, element, region, layer, or zone described below may be referred to as a second component, element, region, layer, or zone without departing from the teachings of this disclosure.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms including "at least one," unless the content clearly dictates otherwise. "At least one" should not be construed as limiting to the singular. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The terms "comprises" and / or "comprising" as used in the detailed description specify the presence of stated features, regions, integers, steps, operations, components, and / or ingredients, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, components, ingredients, and / or groups thereof.

[0035] Spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used herein to readily describe the relationship of one component or feature to another. It will be understood that spatially relative terms are intended to encompass different orientations of the device when in use or operation in addition to the orientations depicted in the drawings. For example, if the device in the drawings were turned over, a component described as "below" or "below" another component or feature would then be oriented "above" the other component or feature. Thus, the exemplary term "below" can encompass both the above and below orientations. The device may be arranged in other orientations (rotated 90 degrees or otherwise rotated), and the spatially relative terms used herein may be interpreted accordingly.

[0036] "Group" means a group in the periodic table of elements according to the International Union of Pure and Applied Chemistry ("IUPAC") Group 1-18 classification system.

[0037] Unless otherwise defined herein, the particle size may be the average particle size. In addition, the particle size refers to the average particle size (D50), which means the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured by a method well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. Alternatively, the average particle size (D50) value can be obtained by measuring with a measuring device that utilizes dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. Alternatively, the average particle size (D50) value can be obtained by measuring with a laser diffraction method. When measuring by laser diffraction, more specifically, after the particles to be measured are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0038] In the present disclosure, “metal” includes both metals and metalloids such as silicon and germanium, in their elemental or ionic states, and “alloy” means a mixture of two or more metals.

[0039] In the present disclosure, “electrode active material” means an electrode material capable of undergoing lithiation and delithiation, “positive electrode active material” means a positive electrode material capable of undergoing lithiation and delithiation, and “negative electrode active material” means a negative electrode material capable of undergoing lithiation and delithiation.

[0040] In the present disclosure, “lithiation” and “lithiate” mean a process of adding lithium to an electrode active material, and “delithiation” and “delithiate” mean a process of removing lithium from an electrode active material.

[0041] In the present disclosure, “charging” and “charging” mean a process of providing electrochemical energy to a battery, and “discharging” and “discharging” mean a process of removing electrochemical energy from a battery.

[0042] In the present disclosure, “positive electrode” and “cathode” mean an electrode where electrochemical reduction and lithiation occur during a discharge process, and “negative electrode” and “anode” mean an electrode where electrochemical oxidation and delithiation occur during a discharge process.

[0043] As used herein, “combination thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0044] While specific implementations have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not currently anticipated or unforeseen may occur to the applicant or those skilled in the art. Accordingly, the appended claims, as filed and as amended, are intended to encompass all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0045] Hereinafter, composite cathode active materials according to exemplary embodiments, cathodes including the same, and solid secondary batteries having the same will be described in more detail.

[0046] A solid secondary battery according to an embodiment includes a positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode includes 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 positive electrode includes a positive electrode current collector; and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector, wherein the positive electrode active material layer includes a composite positive electrode active material and a gel polymer electrolyte, wherein the composite positive electrode active material includes an M2S complex, wherein M is an alkali metal, the alkali metal is Li or Na, and the gel polymer electrolyte contains a crosslinked polymer which is a polymerization product of a crosslinkable monomer having two or more crosslinking points.

[0047] In solid-state secondary batteries, solvents are not used in the anode, electrolyte, and cathode, which reduces ionic conductivity and increases interfacial resistance, potentially reducing capacity and high-rate characteristics. Furthermore, volume changes during charge and discharge can disrupt the ionic and electronic conducting network, potentially degrading the battery's lifespan.

[0048] In order to solve the above-described problem, a solid secondary battery according to one embodiment uses a composite cathode active material that can form an organic network between the cathode active material and the solid electrolyte through a gel polymer electrolyte in the cathode.

[0049] Figure 1a is a schematic diagram showing a positive electrode active material layer according to an embodiment.

[0050] Referring to this, the positive electrode active material layer contains Li2S (1), a carbon-based material as a conductive material (2), and a sulfide-based solid electrolyte (3), and an organic network is well formed through these components through a gel polymer electrolyte (4a) without the ion and electron networks being disconnected due to the change in positive electrode volume during the charge and discharge process. In addition, the gel polymer electrolyte (4a) contains a liquid electrolyte, so the ion conductivity is improved.

[0051] The positive electrode active material layer of Fig. 1b is different from the positive electrode active material layer of Fig. 1a only in the type of gel polymer electrolyte, and the gel polymer electrolyte (4b) contains a crosslinked polymer formed from a crosslinkable monomer having a larger crosslinking point compared to the gel polymer electrolyte (4a) of Fig. 1a, thereby forming a denser network structure and making the network of components of the positive electrode active material layer stronger.

[0052] The crosslinking points of the above crosslinking monomer are, for example, 2 to 4 or 2 to 3. Crosslinking monomers are, for example, ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol dimethacrylate, dipentaerythritol pentaacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, propoxylated(3) trimethylolpropane triacrylate, propoxylated(6) trimethylolpropane triacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, or combinations thereof.

[0053] The content of the gel polymer electrolyte in the positive electrode active material layer is 60 to 70 parts by weight, 61 to 69 parts by weight, 63 to 67 parts by weight, or 64 to 66.5 parts by weight based on 100 parts by weight of M2S. When the content of the gel polymer electrolyte is within the above range, the ion conductivity of the positive electrode active material layer is excellent.

[0054] The above gel polymer electrolyte includes a crosslinked polymer which is a polymerization product of a crosslinkable monomer, and a liquid electrolyte containing an organic solvent and a lithium salt, and the content of the liquid electrolyte is 40 to 95 parts by weight based on 100 parts by weight of the gel polymer electrolyte. The content of the crosslinked polymer in the gel polymer electrolyte is 5 to 60 parts by weight. When the content of the crosslinked polymer and the liquid electrolyte is within the above range, a solid secondary battery having an improved electron conducting network can be manufactured by providing a positive electrode, thereby improving the interfacial resistance between the positive electrode and the solid electrolyte and alleviating positive electrode volume expansion, thereby improving the initial efficiency, energy density, and lifespan characteristics.

[0055] Hereinafter, the composite anode active material constituting the anode and the anode including the same will be described in detail.

[0056] [Composite cathode active material]

[0057] According to one embodiment, the M2S composite includes a M2S composite, and the M2S composite includes, for example, a composite of M2S and a carbon-based material, a composite of M2S and a carbon-based material and a solid electrolyte, a composite of M2S and a solid electrolyte, a composite of M2S and a carbon-based material and an alkali metal salt, a composite of M2S and an alkali metal salt, a composite of M2S and a metal carbide, a composite of M2S and a carbon-based material and a metal carbide, a composite of M2S and a metal nitride, a composite of M2S and a carbon-based material and a metal nitride, or a combination thereof.

[0058] According to another embodiment, a composite cathode active material includes a composite of M2S and an alkali metal salt. The composite further includes a carbon-based material.

[0059] According to another embodiment, a composite cathode active material includes a composite of M2S, an alkali metal salt, and a carbon-based material. Wherein M is an alkali metal, and the alkali metal is Li or Na. M2S is, for example, Li2S or Na2S. The size of M2S crystallites obtained from an XRD spectrum of the composite is less than 9.9 nm, 9.85 nm or less, 9.83 nm or less, or 9.8 nm or less, 9.5 nm or less, 9.0 nm or less, or 8.5 nm or less. The composite includes a solid solution of M2S and an alkali metal salt. The size of the M2S crystallites obtained from the XRD spectrum of the complex is, for example, less than 1 to 9.9 nm, 1 to 9.8 nm, 2 to 9.8 nm, 2 to 9.5 nm, 2 to 9.0 nm, 2 to 8.5 nm or 3 to 8.5 nm. The complex comprises a solid solution of M2S and an alkali metal salt.

[0060] By forming a complex of M2S with an alkali metal salt and a carbon-based material, both the ionic conductivity and electronic conductivity of M2S can be improved simultaneously. Since the complex includes an alkali metal salt, the ionic conductivity of the composite cathode active material is improved, and since the complex includes a carbon-based material, the electronic conductivity of the composite cathode active material is improved, thereby reducing the internal resistance of a cathode and a lithium battery including the composite cathode active material.

[0061] The composite includes M2S crystallites, and as the size of the M2S crystallites is reduced to 21 nm or less, the volume change of the M2S crystallites during charge and discharge can be alleviated. For example, as the size of the M2S crystallites is reduced, the volume change due to a single M2S crystallite is reduced, so the overall volume change of the composite during charge and discharge can be alleviated. For example, as the size of the M2S crystallites is reduced, the grain boundaries between a plurality of M2S crystallites can more easily accommodate the volume change of the M2S crystallites during charge and discharge, so the volume change of the composite during charge and discharge is alleviated, and thus the possibility of defects such as cracks occurring can be reduced. When the composite cathode active material includes such a composite, the cycle characteristics and life characteristics of a solid secondary battery including the composite cathode active material are improved.

[0062] The composite includes M2S crystallites, and by reducing the size of the M2S crystallites to 21 nm or less, the contact area between the M2S crystallites and the alkali metal salt and / or carbon-based material can be further increased. As a result, the ionic conductivity and / or battery conductivity of the composite can be further improved. By including such a composite in the composite cathode active material, the reversibility of the electrode reaction in a secondary battery including the composite cathode active material can be improved. As a result, the specific capacity of the composite cathode active material can be increased.

[0063] The ionic conductivity of the composite can be increased by including a solid solution of M2S and an alkali metal salt. For example, since the solid solution of M2S and an alkali metal salt includes alkali metal ions arranged within the M2S crystallites, the ionic conductivity of the solid solution of M2S and an alkali metal salt can be improved compared to the ionic conductivity of M2S. Consequently, the ionic conductivity of the composite can be improved and the internal resistance of the composite can be reduced. By including such a composite in the composite cathode active material, the cycle characteristics and high-rate characteristics of a secondary battery including the composite cathode active material can be improved.

[0064] Li2S-alkali metal salt-carbon material composites are distinguished from simple mixtures of Li2S, alkali metal salts, and carbon-based materials. Simple mixtures of Li2S, alkali metal salts, and carbon-based materials fail to maintain a dense interface between the Li2S, alkali metal salt, and carbon-based materials, resulting in high interfacial resistance and consequently degrading the lifespan characteristics of secondary batteries.

[0065] The composite includes M2S. Since M2S has a high theoretical capacity, a secondary battery having a high energy density can be provided. However, since M2S has low ionic conductivity and / or electronic conductivity, a composite is formed with an alkali metal salt and a carbon-based material to overcome this drawback. The content of M2S in the composite may be, for example, 10 to 80 wt%, 20 to 70 wt%, 30 to 60 wt%, or 40 to 60 wt% of the total weight of the composite. If the content of M2S is excessively increased, it may not be easy to improve the ionic conductivity and / or electronic conductivity of M2S. If the content of M2S is excessively low, the energy density of the secondary battery may be reduced.

[0066] The complex comprises an alkali metal salt. An alkali metal salt is, for example, a compound that does not contain sulfur (S). The alkali metal salt may be, for example, a binary compound or a ternary compound. The alkali metal salt may be, for example, a binary compound composed of an alkali metal and one element selected from Groups 13 to 17 of the Periodic Table of the Elements. The alkali metal salt may be, for example, a ternary compound composed of an alkali metal and two elements selected from Groups 13 to 17 of the Periodic Table of the Elements.

[0067] The alkali metal salt may be, for example, a lithium salt or a sodium salt. The lithium salt binary compound may include, for example, LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3, or a combination thereof. The lithium salt ternary compound may include, for example, Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or a combination thereof. The sodium salt binary compound may include, for example, NaI, NaBr, NaCl, NaF, Na2O, Na2Se, Na3N, Na3P, Na3As, Na3Sb, Na3Al2, NaB3, or a combination thereof. The sodium salt ternary compound may include, for example, Na3OCl, NaBF4, NaPF6, NaAsF6, NaClO4, NaNO3, NaAlO2, NaAlCl4, NaNO3, Na2CO3, NaBH4, Na2SO4, Na3BO3, Na3PO4, Na4NCl, Na5NCl2, Na3BN2, or a combination thereof. The ionic conductivity of the complex may be further improved by including the above-described lithium salt or sodium salt in the complex. Such a lithium salt or sodium salt can more easily form a solid solution with Na2S, for example, in the complex.

[0068] The content of the alkali metal salt in the composite may be 1 to 40 wt%, 5 to 35 wt%, 10 to 35 wt%, 15 to 35 wt%, 20 to 35 wt%, or 25 to 35 wt% of the total weight of the composite. If the content of the alkali metal salt is excessively increased, the energy density of the solid secondary battery may decrease. If the content of the alkali metal salt is excessively low, the ionic conductivity of the composite may decrease, which may increase the internal resistance of the composite positive electrode active material. As a result, the cycle characteristics of the solid secondary battery may deteriorate.

[0069] The molar ratio of M2S and the alkali metal salt in the composite may be, for example, 50:50 to 95:5, 60:40 to 95:5, 60:40 to 90:10, 65:35 to 90:10, 65:35 to 85:15, or 70:30 to 85:15. The molar ratio of M2S and the alkali metal salt in the composite may be, for example, 50:50 to 95:5, 50:50 to 90:10, 50:50 to 85:15, 50:50 to 80:20, 50:50 to 75:25, or 50:50 to 70:30. By having the molar ratio of M2S and the alkali metal salt in this range, the cycle characteristics of the solid secondary battery including the composite positive electrode active material can be further improved. If the molar ratio of M2S is excessively high, the ionic conductivity enhancement effect of the alkali metal salt may be minimal. If the molar ratio of M2S is excessively high, the energy density of the secondary battery containing the composite cathode active material may be reduced.

[0070] The composite includes a carbon-based material. The carbon-based material can be, for example, any material containing carbon atoms that is used as a conductive material in the art. The carbon-based material can be, for example, crystalline carbon, amorphous carbon, or a combination thereof. The carbon-based material can be, for example, a sintered product of a carbon precursor. The carbon-based material can be, for example, a carbon nanostructure. The carbon nanostructure can be, for example, a one-dimensional carbon nanostructure, a two-dimensional carbon nanostructure, a three-dimensional carbon nanostructure, or a combination thereof. The carbon nanostructure can be, for example, a carbon nanotube, a carbon nanofiber, a carbon nanobelt, a carbon nanorod, graphene, or a combination thereof. The carbon-based material can be, for example, a porous carbon-based material or a non-porous carbon-based material. The porous carbon-based material can include, for example, periodic and regular two-dimensional or three-dimensional pores. The porous carbon-based material may be, for example, carbon black such as Ketjen Black, acetylene black, Denka Black, thermal black, channel black, etc.; graphite, activated carbon, or a combination thereof. The form of the carbon-based material may be, but is not limited to, particle form, sheet form, flake form, etc., and any form used as a carbon-based material in the relevant technical field may be used.

[0071] The content of the carbon-based material included in the composite may be, for example, 1 to 20 wt%, 5 to 20 wt%, or 10 to 20 wt% of the total weight of the composite. If the content of the carbon-based material increases excessively, the energy density of the secondary battery may decrease. If the content of the carbon-based material decreases excessively, the electronic conductivity of the composite may decrease, which may increase the internal resistance of the composite cathode active material. As a result, the cycle characteristics of the secondary battery may deteriorate.

[0072] In the XRD spectrum of the composite, the first lattice constant (d1) derived from the first peak corresponding to the (111) crystal plane of M2S, for example, at a diffraction angle 2θ = 27° ± 2.0° may be larger than the second lattice constant (d2) derived from the second peak corresponding to the (111) crystal plane of M2S, at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectrum of M2S used in the manufacture of the composite. Since the M2S-alkali metal salt-carbon-based material composite has a larger lattice constant (d) than the M2S used in the manufacture of the composite, alkali metal ions can be more easily transported within the M2S crystal structure of the composite. The ionic conductivity of the composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved. The difference between the first lattice constant (d1) and the second lattice constant (d2) may be 0.05 Å or more, 0.15 Å or more, 0.2 Å or more, or 0.25 Å or more. The size of the first lattice constant (d1) may be, for example, 5.78 Å or more, 5.80 Å or more, 5.85 Å or more, 5.90 Å or more, or 6.0 Å or more. Since the composite has such a size of the first lattice constant (d1), the ionic conductivity of the composite cathode active material including the composite may be further improved. The internal resistance of a secondary battery including the composite cathode active material may be reduced and the cycle characteristics may be improved.

[0073] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a first diffraction angle, and in the XRD spectrum of M2S used in the preparation of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a second diffraction angle, and the first diffraction angle may be smaller than the second diffraction angle. For example, the position of the first peak may shift to a low angle compared to the position of the second peak. Therefore, the M2S-alkali metal salt-carbon-based material composite may have a reduced crystallite size compared to M2S used in the preparation of the composite. Since the M2S-alkali metal salt-carbon material composite has a reduced crystallite size, the volume change of the crystallites during charge and discharge is reduced, so the volume change of the composite containing multiple crystallites during charge and discharge can be alleviated. The occurrence of defects such as cracks during charge and discharge of the composite cathode active material containing such a composite can be suppressed. Consequently, the cycle characteristics of the secondary battery containing the composite cathode active material can be improved.

[0074] In the XRD spectrum of the composite, for example, a first peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a first full width at half maximum (FWHM1), and in the XRD spectrum of M2S used in the production of the composite, a second peak appearing at a diffraction angle 2θ = 27° ± 2.0° corresponding to the (111) crystal plane of M2S has a second full width at half maximum (FWHM2), and the first full width at half maximum may be larger than the second full width. Accordingly, the M2S-alkali metal salt-carbon-based material composite may have an increased lattice strain compared to the M2S used in the production of the composite. For example, the M2S-alkali metal salt-carbon-based material composite may have an increased lattice strain when M2S and an alkali metal salt form a solid solution. Since the M2S-alkali metal salt-carbon material composite has an increased full width at half maximum (FWHM) compared to the M2S used in the composite manufacturing, the ionic conductivity of a composite cathode active material including the composite can be further improved. The internal resistance of a secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0075] The first half-width (FWHM1) may be, for example, 1° or more, 1.05° or more, 1.10° or more, or 1.15° or more. When the composite has a first half-width (FWHM1) in this range, the ionic conductivity of the composite cathode active material including the composite can be further improved. The internal resistance of the solid secondary battery including the composite cathode active material can be reduced and the cycle characteristics can be improved.

[0076] The Mohs hardness of the alkali metal salt and carbon-based material may be greater than that of the M2S. The Mohs hardness of M2S is, for example, 0.6 or less. The Mohs hardness of Li2S is, for example, 0.6.

[0077] The Mohs hardness of the alkali metal salt may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, or 2.0 or more. When the alkali metal salt has a Mohs hardness within this range, the pulverization of M2S can be performed more easily during the milling process, and a solid solution of M2S and the alkali metal salt can be formed more easily. The Mohs hardness of LiI is, for example, 2.0. The Mohs hardness of NaI is, for example, 2.1.

[0078] The Mohs hardness of the carbon-based material may be 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.2 or more, or 1.5 or more, respectively. Since the carbon-based material has a Mohs hardness within this range, the pulverization of M2S can be performed more easily during the milling process, and the M2S-alkali metal salt-carbon-based material composite can be easily formed. The modal hardness of carbon nanofibers (CNF) is, for example, 1.5.

[0079] The particle size of the composite cathode active material, i.e., the size of the composite particles, may be, for example, 10 ㎛ or less, 8 ㎛ or less, 5 ㎛ or less, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The size of the composite particles may be, for example, 1 to 10 ㎛, 2 to 10 ㎛, 2 to 8 ㎛, or 3 to 8 ㎛. The size of the composite particles may be, for example, 0.1 to 10 ㎛, 0.1 to 8 ㎛, 0.1 to 5 ㎛, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛ or less. Since the composite particles have a size in this range, the volume change during charge and discharge is suppressed, and thus, deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the composite particles increases excessively, the volume change of the composite during charge / discharge cycles increases, which may accelerate the deterioration of the composite cathode active material containing the composite. Consequently, the cycle characteristics of the secondary battery containing such a composite cathode active material may deteriorate.

[0080] The size of the M2S particles included in the composite cathode active material, that is, the size of the M2S particles included in the composite, may be, for example, 2 ㎛ or less, 1.5 ㎛ or less, or 1 ㎛ or less. The size of the M2S particles may be, for example, 0.1 to 2 ㎛, 0.1 to 1.5 ㎛, or 0.1 to 1 ㎛ or less. Since the M2S particles have a size in this range, the volume change during charge and discharge is suppressed, and thus the deterioration of the composite cathode active material including the composite during charge and discharge can be suppressed. If the size of the M2S particles increases excessively, the volume change of the composite during charge and discharge may increase, which may accelerate the deterioration of the composite cathode active material including the composite. As a result, the cycle characteristics of a secondary battery including such a composite cathode active material may deteriorate.

[0081] Therefore, the cycle characteristics, such as life characteristics, of a secondary battery including a composite cathode active material can be improved. The size of the composite particles can be measured, for example, using laser diffraction, scanning electron microscopy, etc. The particle size of the composite particle is, for example, the arithmetic mean of the particle sizes of multiple particles measured using software from a scanning electron microscopy image.

[0082] In the present disclosure, "particle diameter" refers to the average diameter when the particle is spherical, and refers to the average major axis length when the particle is non-spherical. The particle diameter can be measured using a particle size analyzer (PSA). The "particle diameter" is, for example, the average particle diameter. The "average particle diameter" is, for example, the median particle diameter, D50. D50 is the size of particles corresponding to 50% of the cumulative volume when calculated from the side of particles having a small particle size in the size distribution of particles measured by laser diffraction, D90 is the size of particles corresponding to 90% of the cumulative volume when calculated from the side of particles having a small particle size in the size distribution of particles measured by laser diffraction, and D10 is the size of particles corresponding to 10% of the cumulative volume when calculated from the side of particles having a small particle size in the size distribution of particles measured by laser diffraction.

[0083] The composite includes a carbon-based material as described above, and the carbon-based material may include, for example, a fibrous carbon-based material. By including the fibrous carbon-based material in the composite, the electronic conductivity of the composite can be further improved. By including the fibrous carbon-based material in the composite, electronic conduction can be more easily performed from the surface to the interior of the composite. The internal resistance of a composite cathode active material including the composite can be reduced, and the cycle characteristics of a secondary battery including the composite cathode active material can be further improved.

[0084] The aspect ratio of the fibrous carbon-based material can be, for example, 2 or more, 3 or more, 4 or more, 5 or more, 10 or more, or 20 or more. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 3 to 30, 4 to 30, 5 to 30, 10 to 30, or 20 to 30. The aspect ratio of the fibrous carbon-based material can be, for example, 2 to 30, 2 to 20, 2 to 10, 2 to 8, 2 to 5, or 2 to 4. By having the fibrous carbon-based material having an aspect ratio in this range, the overall electronic conductivity of the composite is improved, and local electronic conductivity imbalances within the composite can be further alleviated.

[0085] The fibrous carbon-based material has the length and diameter ranges described above, facilitating the formation of a conductive network within the anode. The polygonal shape of the fibrous carbon-based material may include a circle, triangle, square, or other polygonal shape.

[0086] Furthermore, utilizing the aforementioned composite can secure a more extended ion conduction path in the cathode active material layer. Therefore, during charging and discharging of an all-solid-state secondary battery, the interruption of the ion conduction path due to volume changes in the cathode active material in the cathode active material layer can be more effectively prevented. Consequently, the initial efficiency, discharge capacity, high-rate characteristics, and / or cycle life characteristics of the all-solid-state secondary battery can be improved.

[0087] Furthermore, utilizing the aforementioned composite can improve the uniformity of ion conduction paths within the positive electrode active material layer. Consequently, the pressure required for manufacturing an all-solid-state secondary battery can be reduced. In other words, an all-solid-state secondary battery with excellent ion conduction paths can be realized even under reduced pressure. Furthermore, the formation of local overvoltages within the positive electrode active material layer during the charge / discharge process of an all-solid-state secondary battery can be effectively prevented.

[0088] The carbon nanofibers described above can be controlled to increase conductivity and reduce side reactions between the positive electrode active material and the sulfide-based solid electrolyte by nitrogen and fluorine doping.

[0089] By using a composite containing the above-described fibrous carbon-based material, the brittle nature of the positive electrode can be improved, enabling the manufacture of a positive electrode capable of thick film formation, thereby enabling the manufacture of a solid-state secondary battery with increased energy density. Furthermore, since the inclusion of the fibrous carbon-based material allows the volume change of the positive electrode active material during charge and discharge to be accommodated by dispersing it along the entire length, the volume change of the positive electrode active material can be accommodated more effectively than, for example, a carbon-based material in the form of spherical particles. Consequently, the disconnection between the positive electrode active material and the solid electrolyte due to the volume change of the positive electrode active material within the positive electrode active material layer can be suppressed, and the uniformity of the components within the positive electrode active material layer can be improved. Consequently, the cycle characteristics of the all-solid-state secondary battery can be improved.

[0090] The fibrous carbon-based material may include, for example, carbon nanostructures. The carbon nanostructures may include, for example, carbon nanofibers (CNFs), carbon nanotubes (CNTs), carbon nanobelts, carbon nanorods, or combinations thereof.

[0091] The carbon nanostructure can form a primary carbon nanostructure composed of a single carbon nanostructure and a secondary carbon nanostructure composed of a plurality of carbon nanostructures aggregated together.

[0092] The diameter of the primary carbon nanostructure can be, for example, 1 nm to 200 nm, 1 nm to 150 nm, 1 nm to 100 nm, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 20 nm. The length of the primary carbon nanostructure can be, for example, 10 nm to 2 μm, 10 nm to 1.5 μm, 10 nm to 1 μm, 10 nm to 500 nm, 10 nm to 400 nm, 10 nm to 300 nm, 10 nm to 200 nm, or 10 nm to 100 nm. The diameter and length of the primary carbon nanostructure can be measured from scanning electron microscope (SEM) or transmission electron microscope (TEM) images. Alternatively, the diameter and / or length of the primary carbon nanostructure can be measured by laser diffraction.

[0093] Secondary carbon nanostructures are, for example, structures formed by assembling primary carbon nanostructures in whole or in part to form bundles or bundle-type structures. The secondary carbon nanostructures may include, for example, bundle-type carbon nanostructures, rope-type carbon nanostructures, or combinations thereof. The diameter of the secondary carbon nanostructures may be, for example, 2 nm to 200 nm, 3 nm to 150 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 30 nm, or 5 nm to 20 nm. The length of the secondary carbon nanotube structure can be, for example, 20 nm to 2 ㎛, 30 nm to 1.5 ㎛, 50 nm to 1 ㎛, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 200 nm, or 50 nm to 100 nm or more. The diameter and length of the secondary carbon nanostructure can be measured from a scanning electron microscope (SEM) image or an optical microscope. Alternatively, the diameter and / or length of the secondary carbon nanostructure can be measured by laser diffraction. The secondary carbon nanostructure can be converted into the primary carbon nanostructure by, for example, dispersing it in a solvent or the like and then used in the preparation of a composite.

[0094] The composite may contain, for example, 10 to 80 parts by weight of M2S, 1 to 40 parts by weight of an alkali metal salt, and 1 to 20 parts by weight of a carbon-based material, relative to 100 parts by weight of the composite. The M2S content contained in the composite may 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 M2S, relative to 100 parts by weight of the composite. The alkali metal salt content contained in the composite may 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 the alkali metal salt, relative to 100 parts by weight of the composite. The carbon-based material content contained in the composite may be, for example, 1 to 20 parts by weight, 5 to 20 parts by weight, or 5 to 15 parts by weight of the carbon-based material, relative to 100 parts by weight of the composite. Since the composite has a composition of M2S, alkali metal salt, and carbon-based material in this range, a composite cathode active material including the composite can provide excellent ionic conductivity and / or electronic conductivity.

[0095] The ionic conductivity of the complex is, for example, 1×10 at 25°C. -5 S / cm or more, 2×10 -5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. The ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy, DC polarization method, etc. Since the composite has an ionic conductivity in this range, the internal resistance of the composite cathode active material including the composite can be reduced. The cycle characteristics of the secondary battery including the composite cathode active material can be improved. The electronic conductivity of the composite can be, for example, 1×10 at 25°C. -5 S / cm or more, 2×10-5 S / cm or more, 4×10 -5 S / cm or more, 6×10 -5 S / cm or more, 8×10 -5 S / cm or more or 1×10 -4 It can be S / cm or more. The electronic conductivity can be measured using, for example, electrochemical impedance spectroscopy, DC polarization method, etc. Since the composite has an electronic conductivity in this range, the internal resistance of the composite cathode active material including the composite can be reduced. The cycle characteristics of the secondary battery including the composite cathode active material can be improved.

[0096] [anode]

[0097] [Cathode: Cathode active material]

[0098] According to one embodiment, a positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector, wherein the positive electrode active material layer comprises a composite positive electrode active material and a gel polymer electrolyte. The composite positive electrode active material comprises an M2S composite, wherein M is an alkali metal, the alkali metal is Li or Na, and the gel polymer electrolyte contains a crosslinked polymer which is a polymerization product of a crosslinkable monomer having two or more crosslinking points.

[0099] The above M2S composite comprises a composite of M2S and an alkali metal salt. The composite may further comprise a carbon-based material. The positive electrode active material layer comprises a composite positive electrode active material comprising a composite of M2S, an alkali metal salt, a carbon-based material, and a carbon-based material, and a gel polymer electrolyte. The gel polymer electrolyte may contain a crosslinked polymer of a crosslinkable monomer having two or more crosslinking points.

[0100] The positive electrode active material layer comprises 40 to 90 parts by weight of a composite positive electrode active material and 10 to 60 parts by weight of a gel polymer electrolyte relative to 100 parts by weight of the positive electrode active material layer. According to another embodiment, the positive electrode active material layer comprises 40 to 80 parts by weight, 70 to 90 parts by weight, or 70 to 80 parts by weight of a composite positive electrode active material and 20 to 60 parts by weight, 10 to 30 parts by weight, or 20 to 30 parts by weight of a gel polymer electrolyte relative to 100 parts by weight of the positive electrode active material layer.

[0101] The positive electrode contains a composite positive electrode active material and a gel polymer electrolyte, which enhances the ion-electron network and improves high-rate characteristics and life-cycle characteristics.

[0102] Referring to FIGS. 2 to 6, the positive electrode (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). The positive electrode active material layer (12) includes the composite positive electrode active material and the gel polymer electrolyte described above.

[0103] The positive electrode active material layer (12) may contain 40 to 90 parts by weight of a composite positive electrode active material and 10 to 60 parts by weight of a gel polymer electrolyte for 100 parts by weight of the positive electrode active material layer (12).

[0104] In the positive electrode active material layer, the composite positive electrode active material may be included in an amount of, for example, 40 to 80 parts by weight, 50 to 80 parts by weight, or 50 to 70 parts by weight. If the content of the composite positive electrode active material is excessively reduced, the energy density of the secondary battery is reduced. If the content of the composite positive electrode active material is excessively increased, the deterioration of the positive electrode may be accelerated due to volume changes of the positive electrode during charge and discharge. As a result, the cycle characteristics of the solid secondary battery (1) may be deteriorated.

[0105] The cathode active material layer (12) may additionally include other cathode active materials in addition to the composite cathode active material described above.

[0106] Other cathode active materials may include, for example, a Li2S-containing composite. The Li2S composite includes, for example, a composite of Li2S and a carbon-based material, a composite of Li2S and a carbon-based material and a solid electrolyte, a composite of Li2S and a solid electrolyte, a composite of Li2S and a lithium salt, a composite of Li2S and a metal carbide, a composite of Li2S and a carbon-based material and a metal carbide, a composite of Li2S and a metal nitride, a composite of Li2S and a carbon-based material and a metal nitride, or a combination thereof.

[0107] The composite of Li2S and a carbon-based material includes a carbon-based material. The carbon-based material refers to the carbon-based material of the composite cathode active material described above. The method for producing the composite of Li2S and a carbon-based material may be a dry method, a wet method, or a combination thereof, but is not limited thereto, and any method used in the art may be used. The method for producing the composite of Li2S and a carbon-based material includes, but is not limited to, milling, heat treatment, deposition, etc., and any method used in the art may be used.

[0108] 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, for example, any material used as an ion-conducting material in the relevant technical field. The solid electrolyte is, for example, an inorganic solid 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, a polymer solid electrolyte, or a combination thereof. The sulfide-based solid electrolyte includes, for example, Li, S, and P, and may optionally further include a halogen element. The sulfide-based solid electrolyte can be selected from among the sulfide-based solid electrolytes used in the electrolyte layer. The sulfide-based solid electrolyte has, for example, a molecular weight of 1×10 at room temperature. -5It can have an ionic conductivity of S / cm or more. The oxide-based solid electrolyte contains, for example, Li, O, and transition metal elements, and may optionally contain other elements. The oxide-based solid electrolyte has an ionic conductivity of, for example, 1×10 at room temperature. -5 It may be a solid electrolyte having an ionic conductivity of S / cm or more. The oxide-based solid electrolyte may be selected from among oxide-based solid electrolytes used in the electrolyte layer.

[0109] The composite of Li2S and a solid electrolyte includes a solid electrolyte. The solid electrolyte refers to the composite of Li2S, a carbon-based material, and a solid electrolyte described above.

[0110] The composite of Li2S and a lithium salt comprises Li2S and a lithium salt. The lithium salt refers to the lithium salt of the composite cathode active material described above. The lithium salt is particularly one or more lithium halide compounds selected from LiF, LiCl, LiBr, and LiI. The composite of Li2S and a lithium salt may be, for example, a composite of Li2 and a lithium halide. The composite of Li2 and a lithium salt may provide improved ionic conductivity by including a lithium halide compound. The composite of Li2S and a lithium salt 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 may provide high interfacial resistance by failing to maintain a dense interface between Li2S and a lithium salt, which may result in reduced cycle life characteristics of an all-solid-state secondary battery.

[0111] The composite of Li2S and metal carbide includes metal carbide. The metal carbide is, for example, a two-dimensional metal carbide. The two-dimensional metal carbide is, for example, M n+1 C n T x (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) is expressed as 2D metal carbides, for example, Ti2CT x , (Ti 0.5 , Nb0.5 )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 thereof. The surface of the two-dimensional metal carbide is terminated with O, OH and / or F.

[0112] A composite of Li2S, a carbon-based material, and a metal carbide includes a carbon-based material and a metal carbide. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal carbide described above.

[0113] The complex of Li2S and metal nitride includes 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 (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) is expressed as The surface of the two-dimensional metal nitride is terminated with O, OH and / or F.

[0114] A composite of Li2S, a carbon-based material, and a metal nitride includes a carbon-based material and a metal nitride. The carbon-based material refers to the composite of Li2S and a carbon-based material described above. The metal carbide refers to the composite of Li2S and a metal nitride described above.

[0115] The cathode active material layer (12) may additionally include, for example, a sulfide-based compound that is distinct from the cathode active material described above. The sulfide-based compound may be, for example, a compound containing a metal element other than Li and the element sulfur. The sulfide-based compound may be, for example, a compound containing a metal element belonging to Groups 1 to 14 of the Periodic Table of Elements having an atomic weight of 10 or more and the element sulfur. The sulfide-based compound may be, for example, FeS2, VS2, NaS, MnS, FeS, NiS, CuS, or a combination thereof. By the cathode active material layer additionally including a sulfide-based compound, the cycle characteristics of the all-solid-state secondary battery may be further improved. The content of the sulfide-based compound included in the cathode 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 cathode active material layer (12).

[0116] [Anode: Solid electrolyte]

[0117] The positive electrode active material layer (12) may further include, for example, a solid electrolyte. The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The solid electrolyte included in the positive electrode (10) may be the same as or different from the solid electrolyte included in the electrolyte layer (30). For more details on the solid electrolyte, refer to the electrolyte layer (30) section.

[0118] The solid electrolyte included in the positive electrode active material layer (12) may have a smaller average D50 particle diameter than the solid electrolyte included in the electrolyte layer (30). For example, the average D50 particle diameter of the solid electrolyte included in the positive electrode active material layer (12) may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less of the average D50 particle diameter of the solid electrolyte included in the electrolyte layer (30). The average D50 particle diameter is, for example, a median particle diameter (D50). The median particle diameter (D50) is the size of particles corresponding to 50% of the cumulative volume, calculated from the side of particles having a small particle size in a size distribution of particles measured by, for example, a laser diffraction method.

[0119] The solid electrolyte may be included in an amount of 10 to 60 parts by weight, 10 to 50 parts by weight, 20 to 50 parts by weight, or 30 to 50 parts by weight, based on 100 parts by weight of the positive electrode active material layer (12). If the content of the solid electrolyte is excessively reduced, the internal resistance of the positive electrode may increase, thereby deteriorating the cycle characteristics of the secondary battery. If the content of the sulfide-based solid electrolyte is excessively increased, the energy density of the secondary battery (1) may be reduced.

[0120] [Polar: Challenger]

[0121] The cathode active material layer (12) may further include a conductive material. The conductive material may be, for example, a carbon-based conductive material, a metal-based 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 thereto, and any material used as a carbon-based conductive material in the art may be used. The metal-based conductive material may be, for example, metal powder, metal fiber, or a combination thereof, but is not limited thereto, and any material used as a metal-based conductive material in the art may be used. The content of the conductive material included in the cathode 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 cathode active material layer (12).

[0122] The cathode active material layer (12) includes a carbon-based material, and the carbon-based material may be disposed only in the composite cathode active material. The cathode active material layer (12) may not additionally include a separate carbon-based material other than the composite cathode active material including the carbon-based material. Since the cathode active material layer does not include a separate carbon-based material, the energy density of the cathode and the secondary battery (1) can be improved and the manufacturing process can be simplified.

[0123] [Positive: Binder]

[0124] The positive electrode active material layer (12) may further include a binder. The binder may be, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., but is not limited thereto, and any binder used in the relevant technical field may be used. The binder content included in 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 may be omitted.

[0125] [Positive: Other additives]

[0126] The cathode active material layer (12) may further include additives such as fillers, coating agents, dispersants, and ion conductive aids in addition to the cathode active material, solid electrolyte, binder, and conductive agent described above.

[0127] As fillers, coating agents, dispersants, ion conductivity aids, etc. that the positive electrode active material layer (12) may include, known materials generally used in electrodes of all-solid-state secondary batteries may be used.

[0128] [Anode: Anode current collector]

[0129] The positive electrode collector (11) uses 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 collector (11) may be omitted. The thickness of the positive electrode collector (11) is, for example, 1 µm to 100 µm, 1 µm to 50 µm, 5 µm to 25 µm, or 10 µm to 20 µm.

[0130] The cathode 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 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 be, for example, an insulator. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film softens or liquefies, thereby blocking 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 an alloy thereof. The metal layer can act as an electrochemical fuse and be cut off in case of overcurrent to prevent a short circuit. The limit current and the maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer can be plated or deposited on the base film. As the thickness of the metal layer decreases, the limit current and / or the maximum current of the positive electrode current collector (11) decreases, thereby improving the stability of the lithium battery in case of a short circuit. A lead tab can be added on the metal layer for connection to the outside. 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 the metal layer melt, so that the metal layer can be electrically connected to the lead tab. In order to strengthen the welding of the metal layer and the lead tab, a metal chip can be added between the metal layer and the lead tab.The metal piece may be a thin piece of the same material as the metal of the metal layer. The metal piece may be, for example, a metal foil, a metal mesh, etc. The metal piece may be, for example, aluminum foil, copper foil, SUS foil, etc. After the metal piece is placed on the metal layer, the lead tab may be welded to the metal piece / metal layer laminate or the metal piece / metal layer / base film laminate. During welding, the base film, the metal layer, and / or the metal piece may melt, so that the metal layer or the metal layer / metal piece laminate may be electrically connected to the lead tab. A metal chip and / or a lead tab may be added to a portion of the metal layer. The base film may have a thickness of, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. When the base film has a thickness in this range, the weight of the electrode assembly can be more effectively reduced. The melting point of the base film may be, for example, 100 to 300°C, 100 to 250°C or less, or 100 to 200°C. Since the base film has a melting point within this range, the base film can be melted and easily bonded to the lead tab during the welding process of the lead tab. To improve the adhesion between the base film and the metal layer, a surface treatment such as corona treatment may be performed on the base film. The thickness of the metal layer may be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to μm. Since the metal layer has a thickness within this range, conductivity can be maintained while ensuring the stability of the electrode assembly. The thickness of the metal piece may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. Since the metal piece has a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having this structure, the positive electrode collector (11) can reduce the weight of the positive electrode and consequently improve the energy density of the positive electrode and lithium battery.

[0131] [Anode: Inert member]

[0132] Referring to FIGS. 5 and 6, the positive electrode (10) includes a positive electrode current collector (11) and a positive electrode active material layer (12) disposed on one side of the positive electrode current collector. An inactive member (40) is disposed on one side of the positive electrode (10). Referring to FIG. 5, the inactive member (40) is disposed on one side of the positive electrode active material layer (12) and the positive electrode current collector (11). Referring to FIG. 6,

[0133] The inert member (40) is disposed on one side of the positive electrode active material layer (12) and is disposed between the solid electrolyte layer (30) and the positive electrode current collector (11) facing the solid electrolyte layer (30). The inert member (40) is not disposed on one side of the positive electrode current collector (11).

[0134] By including an inert member (40), cracking of the electrolyte layer (30) is prevented during the manufacture and / or charging / discharging of the all-solid-state secondary battery (1), and as a result, the cycle characteristics of the all-solid-state secondary battery (2) are improved. In an all-solid-state secondary battery (1) that does not include an inert member (40), when the manufacture and / or charging / discharging of the all-solid-state secondary battery (1) is performed, uneven pressure is applied to the electrolyte layer (30) in contact with the positive electrode (10), which increases the possibility of cracking in the electrolyte layer (30), and thus, a short circuit may occur due to the growth of lithium metal through the crack.

[0135] In the all-solid-state secondary battery (1), the thickness of the inert member (40) is greater than or equal to the thickness of the positive electrode active material layer (12). Alternatively, in the all-solid-state secondary battery (1), the thickness of the inert member (40) is substantially equal to the thickness of the positive electrode (10). Since the thickness of the inert member (40) is equal to the thickness of the positive electrode (10), a uniform pressure is applied between the positive electrode (10) and the electrolyte layer (30), and the positive electrode (10) and the electrolyte layer (30) are sufficiently adhered to each other, so that the interfacial resistance between the positive electrode (10) and the electrolyte layer (30) can be reduced. In addition, since the electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0136] The inert member (40) surrounds the side surface of the positive electrode (10) and is in contact with the electrolyte layer (30). By the inert member (40) surrounding the side surface of the positive electrode (10) and being in contact with the electrolyte layer (30), cracks in the electrolyte layer (30) that occur due to a pressure difference during the pressing process in the electrolyte layer (30) that does not come into contact with the positive electrode (20) can be effectively suppressed. The inert member (40) surrounds the side surface of the positive electrode (10) and is separated from the negative electrode (20), more specifically, the first negative electrode active material layer (22). The inert member (40) surrounds the side surface of the positive electrode (10), is in contact with the electrolyte layer (30), and is separated from the negative electrode (20). Therefore, the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or a short circuit occurring due to overcharging of lithium, etc., is suppressed. For example, by placing an inert member (40) on one side of the positive electrode active material layer (12) and simultaneously on one side of the positive electrode current collector (11), the possibility of a short circuit occurring due to contact between the positive electrode current collector (11) and the negative electrode (20) is more effectively suppressed.

[0137] Referring to FIGS. 4 and 5, the inert member (40) extends from one side of the positive electrode (30) to the end of the electrolyte layer (30). By extending the inert member (40) to the end of the electrolyte layer (30), cracks occurring at the end of the electrolyte layer (30) can be suppressed. The end of the electrolyte layer (30) is the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) extends to the outermost part that is in contact with the side of the electrolyte layer (30). The inert member (40) is separated from the negative electrode (20), more specifically, from the first negative electrode active material layer (22). The inert member (40) extends to the end of the electrolyte layer (30), but does not contact the negative electrode (20). The inert member (40) fills a space extending from, for example, one side of the anode (30) to the end of the electrolyte layer (30).

[0138] Referring to FIGS. 4 and 5, the width of the inert member (40) extending from one side of the positive electrode (10) to the end of the electrolyte layer (30) is, for example, 1 to 30%, 1 to 25%, 1 to 20%, 1 to 15%, 1 to 10%, or 1 to 5% of the width between one side of the positive electrode (10) and the other side opposite to the one side. If the width of the inert member (40) is excessively large, the energy density of the all-solid-state secondary battery (1) is reduced. If the width of the inert member (40) is excessively small, the effect of arranging the inert member (40) is minimal.

[0139] The area of ​​the anode (10) is smaller than the area of ​​the electrolyte layer (30) in contact with the anode (10). An inert member (40) is arranged to surround the side of the anode (10) to compensate for the area difference between the anode (10) and the electrolyte layer (30). By compensating for the difference between the area of ​​the anode (10) and the area of ​​the electrolyte layer (30), cracks in the electrolyte layer (30) caused by the pressure difference during the pressing process are effectively suppressed. For example, the sum of the area of ​​the anode (10) and the area of ​​the inert member (40) is equal to the area of ​​the electrolyte layer (30). The electrolyte layer (30) may be, for example, a solid electrolyte layer.

[0140] The area of ​​the anode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area of ​​the electrolyte layer (30). The area of ​​the anode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area of ​​the electrolyte layer (30).

[0141] If the area of ​​the positive electrode (10) is equal to or larger than the area of ​​the electrolyte layer (30), the possibility of a short circuit occurring due to physical contact between the positive electrode (10) and the first negative electrode active material layer (22) or overcharging of lithium increases. The area of ​​the positive electrode (10) is, for example, equal to the area of ​​the positive electrode active material layer (12). The area of ​​the positive electrode (10) is, for example, equal to the area (11) of the positive electrode current collector.

[0142] The area of ​​the inert member (40) is, for example, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the area of ​​the anode (10). The area of ​​the inert member (40) is, for example, 1% to 50%, 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 15% of the area of ​​the anode (10).

[0143] The area (S1) of the positive electrode (10) is smaller than the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, less than 100%, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less of the area (S4) of the negative electrode current collector (21). The area (S1) of the positive electrode (10) is, for example, 50% to less than 100%, 50% to 99%, 55% to 98%, 60% to 97%, 70% to 96%, 80% to 95%, or 85% to 95% of the area (S4) of the negative electrode current collector (21). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the negative electrode (20). The area (S4) of the negative electrode current collector (21) is, for example, the same as the area of ​​the first negative electrode active material layer (22).

[0144] As used herein, “same” area, length, width, thickness, and / or shape includes all instances of having “substantially the same” area, length, width, thickness, and / or shape, except where the area, length, width, thickness, and / or shape are intentionally different from each other. “Same” area, length, width, and / or thickness includes a range where the unintentional difference in the area, length, width, and / or thickness of the compared objects is, for example, less than 3%, less than 2%, less than 1%, less than 0.5%, or less than 0.1%.

[0145] The thickness of the inert member (40) is, for example, greater than the thickness of the first negative electrode active material layer (22). 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, or 10% or less of the thickness of the 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 inert member (40).

[0146] The inert member (40) may be a gasket. By using a gasket as the inert member (40), cracks in the electrolyte layer (30) caused by a pressure difference during the pressing process can be effectively suppressed.

[0147] The inert member (40) has, for example, a single-layer structure. Alternatively, although not shown in the drawing, the inert member (40) may have a multi-layer structure. In the inert member (40) having a multi-layer structure, each layer may have a different composition. The inert member having a multi-layer structure may have, for example, a two-layer structure, a three-layer structure, a four-layer structure, or a five-layer structure. The inert member (40) having a multi-layer structure may include, for example, one or more adhesive layers and one or more support layers. The adhesive layer effectively prevents, for example, a separation between the positive electrode (10) and the electrolyte layer (30) due to a change in the volume of the positive electrode (10) that occurs during the charge / discharge process of the all-solid-state secondary battery (10), and improves the film strength of the inert member (40) by providing a bonding force between the support layer and other layers. The support layer provides support to the inert member (40), prevents unevenness of pressure applied to the electrolyte layer (30) during the pressurization process or the charge / discharge process, and prevents deformation of the all-solid-state secondary battery (1) being manufactured.

[0148] The inert member (40) is, for example, a flame-retardant inert member. The flame-retardant inert member prevents thermal runaway and ignition of the all-solid-state secondary battery (1) by providing flame retardancy. Consequently, the safety of the all-solid-state secondary battery (1) is further improved. The flame-retardant inert member prevents deterioration of the all-solid-state secondary battery (1) by absorbing residual moisture within the all-solid-state secondary battery (1), thereby improving the lifespan characteristics of the all-solid-state secondary battery (1).

[0149] The flame-retardant inert member includes, for example, a matrix and a filler. The matrix includes, for example, a substrate and a reinforcing material. The matrix includes, for example, a fibrous substrate and a fibrous reinforcing material. Since the matrix includes the substrate, the matrix can have elasticity. Therefore, the matrix can effectively accommodate volume changes during charge and discharge of the all-solid-state secondary battery (1) and can be arranged at various positions. The substrate included in the matrix includes, for example, a first fibrous material. Since the substrate includes the first fibrous material, the volume changes of the positive electrode (30) occurring during charge and discharge of the all-solid-state secondary battery (1) can be effectively accommodated and deformation of the inert member (40) due to the volume changes of the positive electrode (30) can be effectively suppressed. The first fibrous material is, for example, a material having an aspect ratio of 5 or more, 20 or more, or 50 or more. The first fibrous material is, for example, a material having an aspect ratio of 5 to 1000, 20 to 1000, or 50 to 1000. The first fibrous material is, for example, an insulating material. Since the first fibrous material is an insulating material, a short circuit between the positive electrode (30) and the negative electrode (20) caused by lithium dendrites, etc., generated during the charge and discharge process of the all-solid-state secondary battery (1) can be effectively prevented. The first fibrous material includes, for example, at least one selected from pulp fibers, insulating polymer fibers, and ion-conductive polymer fibers. The strength of the matrix is ​​improved by the inclusion of a reinforcing material in the matrix. Therefore, the matrix can prevent excessive volume change during charge and discharge of the all-solid-state secondary battery (1) and deformation of the all-solid-state secondary battery. The reinforcing material included in the matrix includes, for example, a second fibrous material. Since the reinforcing material includes the second fibrous material, the strength of the matrix can be increased more uniformly. The second fibrous material is, for example, a material having an aspect ratio of 3 or more, 5 or more, or 10 or more.The first fibrous material is, for example, a material having 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. Since the second fibrous material is a flame-retardant material, ignition due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or due to external impact can be effectively suppressed. The second fibrous material is, for example, glass fiber, metal oxide fiber, ceramic fiber, etc.

[0150] The flame-retardant inert member includes a filler in addition to a matrix. The filler may be disposed within the matrix, on the surface of the matrix, or on both the interior and the surface. The filler is, for example, an inorganic material. The filler included in the flame-retardant inert member is, for example, a moisture getter. The filler removes moisture remaining in the all-solid-state secondary battery (1) by adsorbing moisture, for example, at a temperature below 100°C, thereby preventing deterioration of the all-solid-state secondary battery (1). In addition, when the temperature of the all-solid-state secondary battery (1) increases to 150°C or higher due to thermal runaway occurring during the charge / discharge process of the all-solid-state secondary battery (1) or an external impact, the filler releases the adsorbed moisture, thereby effectively suppressing ignition of the all-solid-state secondary battery (1). That is, the filler is, for example, a flame retardant. The filler is, for example, a metal hydroxide having moisture adsorption properties. The metal hydroxide contained in the filler is, for example, Mg(OH)2, Fe(OH)3, Sb(OH)3, Sn(OH)4, TI(OH)3, Zr(OH)4, Al(OH)3, or a combination thereof. The content of the filler contained in the flame-retardant inert member is, for example, 10 to 80 parts by weight, 20 to 80 parts by weight, 30 to 80 parts by weight, 40 to 80 parts by weight, 50 to 80 parts by weight, 60 to 80 parts by weight, or 65 to 80 parts by weight, based on 100 parts by weight of the flame-retardant inert member (4).

[0151] The flame-retardant inert member may further comprise, for example, a binder. The binder may comprise, for example, a curable polymer or a non-curable polymer. A curable polymer is a polymer that cures by heat and / or pressure. A curable polymer is, for example, a solid at room temperature. The flame-retardant inert member (40) comprises, for example, a heat-pressure curable film and / or a cured product thereof. The heat-pressure curable polymer is, for example, TSA-66 from Toray.

[0152] The flame-retardant inert member may additionally include other materials in addition to the above-described substrate, reinforcing material, filler, and binder. The flame-retardant inert member may further include one or more selected from among paper, an insulating polymer, an ion-conducting polymer, an insulating inorganic material, an oxide-based solid electrolyte, and a sulfide-based solid electrolyte. The insulating polymer may be, for example, an olefin-based polymer such as polypropylene (PP) or polyethylene (PE).

[0153] The density of the substrate or the density of the reinforcing material included in the flame-retardant inert member may be, for example, 10% to 300%, 10% to 150%, 10% to 140%, 10% to 130%, or 10% to 120% of the density of the positive electrode active material included in the positive electrode active material layer (12).

[0154] The inert member (40) is a member that does not contain an electrochemically active material, for example, an electrode active material. The electrode active material is a material that absorbs / releases lithium. The inert member (40) is a member made of a material other than the electrode active material and used in the relevant technical field.

[0155] [All-solid-state secondary battery]

[0156] An all-solid-state secondary battery according to one embodiment includes the above-described positive electrode; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode. The negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector.

[0157] The negative electrode includes a negative electrode current collector and a lithium host layer disposed on one surface of the negative electrode current collector, the lithium host layer includes a lithium host structure, the lithium host structure includes one or more lithium hosts, the lithium hosts include a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, and includes a first inactive member disposed on one surface of the negative electrode.

[0158] A lithium precipitation layer may be formed inside and / or on the surface of the lithium host layer.

[0159] All-solid-state secondary batteries include lithium-containing sulfide-based cathode active materials as their cathode active materials. Therefore, the disruption of ion and / or electron transport pathways due to volume increase during initial discharge of non-lithium-containing sulfide-based cathode active materials, such as sulfur (S), is prevented. By preventing such disruption of ion and / or electron transport pathways, the cycle characteristics of all-solid-state secondary batteries are improved.

[0160] Since an all-solid-state secondary battery includes a lithium host layer on its anode, the lithium host acts as a support during the deposition of lithium metal on the anode, thereby suppressing the non-uniformity of lithium deposition. Furthermore, the formation and growth of lithium dendrites and / or isolated lithium (dead lithium) during the charge / discharge process of the all-solid-state secondary battery can be suppressed. Consequently, deterioration of the all-solid-state secondary battery is suppressed, and cycle characteristics are improved.

[0161] By including a lithium host layer in the anode of an all-solid-state secondary battery, rapid volume changes in the anode can be suppressed during the charge / discharge process of the all-solid-state secondary battery. By suppressing rapid volume changes in the anode, deterioration of the all-solid-state secondary battery due to volume changes during the charge / discharge process of the all-solid-state secondary battery is suppressed, and cycle characteristics are improved.

[0162] Since the all-solid-state secondary battery includes a solid electrolyte layer, the migration of polysulfides generated during charging and discharging of the lithium-containing sulfide-based positive electrode active material to the negative electrode is blocked. Consequently, side reactions between polysulfides and the negative electrode active material are suppressed.

[0163] By arranging an inert material on one side of the cathode, short-circuiting between lithium dendrites generated and grown during charging and discharging of an all-solid-state secondary battery and the anode and / or lithium metal melting at high temperatures is more effectively suppressed. Consequently, short-circuiting of the all-solid-state secondary battery is prevented and its lifespan characteristics are improved.

[0164] Referring to FIGS. 2 to 6, an all-solid-state secondary battery (1) includes a positive electrode (10); a negative electrode (20); and an electrolyte layer (30) disposed between the positive electrode (10) and the negative electrode (20). The negative electrode (20) includes a negative electrode current collector (21) and a first negative electrode active material layer (22) disposed on one surface of the negative electrode current collector.

[0165] [anode]

[0166] See the above mentioned polarities.

[0167] [cathode]

[0168] [Cathode: Cathode active material]

[0169] Referring to FIGS. 2 to 6, the negative electrode (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.

[0170] The negative electrode active material included in the first negative electrode active material layer (22) is, for example, a negative electrode material that can form an alloy or compound with lithium.

[0171] The negative electrode active material included in the first negative electrode active material layer (22) has, for example, a particle form. The average particle diameter of the negative electrode active material having a particle form is, for example, 4 ㎛ or less, 3 ㎛ or less, 2 ㎛ or less, 1 ㎛ or less, 500 nm or less, 300 nm or less, or 100 nm or less. The average particle diameter of the negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 3 ㎛, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 300 nm, or 10 nm to 100 nm. When the negative electrode active material has an average particle diameter in this range, reversible absorption and / or desorption of lithium can be facilitated during charge and discharge. The average particle size of the negative electrode active material is, for example, the median diameter (D50) measured using a laser particle size distribution meter.

[0172] The negative electrode active material included in the first negative electrode active material layer (22) includes, for example, at least one selected from among a carbon-based negative electrode active material and a metal or semi-metal negative electrode active material.

[0173] Carbon-based negative electrode materials include, for example, amorphous carbon, crystalline carbon, porous carbon, or a combination thereof.

[0174] The carbon-based negative electrode material is, in particular, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene, and any material classified as amorphous carbon in the relevant technical field is acceptable. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

[0175] The carbon-based negative electrode active material may be, for example, porous carbon. The porous carbon has a pore volume of, 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 porous carbon has an average pore diameter of, for example, 1 nm to 50 nm, 1 nm to 30 nm, or 1 nm to 10 nm. The porous carbon has a BET surface area of, for example, 100 m 2 / g to 3000 m 2 / g is.

[0176] The metal or metalloid negative electrode 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), and any metal or metalloid negative electrode active material that forms an alloy or compound with lithium in the relevant technical field may be used. For example, nickel (Ni) does not form an alloy with lithium and therefore is not a metal negative electrode active material.

[0177] The first negative electrode active material layer (22) includes a type of negative electrode active material among these negative electrode active materials, or includes a mixture of a plurality of different negative electrode active materials. For example, the first negative electrode active material layer (22) includes only amorphous carbon, or includes at least one 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) includes a mixture of amorphous carbon and at least one 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 the mixture of amorphous carbon and gold, etc., is a weight ratio, 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 this range and is selected according to the required characteristics of the all-solid-state secondary battery (1). When the negative electrode active material has this composition, the cycle characteristics of the all-solid-state secondary battery (1) are further improved.

[0178] The negative electrode active material included 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 a 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). Alternatively, the metalloid is a semiconductor. The content of the second particles is 1 to 99 wt%, 1 to 60 wt%, 8 to 60 wt%, 10 to 50 wt%, 15 to 40 wt%, or 20 to 30 wt% based on the total weight of the mixture. When the second particles have a content in this range, the cycle characteristics of, for example, a solid secondary battery (1) are further improved.

[0179] Alternatively, the first negative electrode active material layer (22) includes a composite negative electrode active material. The composite negative electrode active material may include, for example, a carbon-based support and a metal-based negative electrode active material supported on the carbon-based support. The composite negative electrode active material may have, for example, a structure in which silver (Ag) is supported on carbon particles. Since the composite negative electrode active material has such a structure, the uneven distribution of the metal-based negative electrode active material within the first negative electrode active material layer can be prevented and a uniform distribution can be obtained. As a result, the cycle characteristics of the all-solid-state secondary battery (1) including the first negative electrode active material layer (22) are further improved.

[0180] The metal-based negative electrode active material supported on the carbon-based support includes, for example, a metal, a metal oxide, a composite of a metal and a metal oxide, or a combination thereof. The metal includes, for example, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), tellurium (Te), and zinc (Zn). The metal oxide includes, 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. The metal oxide includes, for example, Au x O y (0 <x≤2, 0<y≤3), Pt x O y (0 <x≤1, 0<y≤2), Pd x O y (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 The y (0 <x≤1, 0<y≤3), Zn x The y (0 <x≤1, 0<y≤1) 또는 이들의 조합을 포함할 수 있다. 금속과 금속산화물의 복합체는 예를 들어 Au와 Au x The y (0 <x≤2, 0<y≤3)의 복합체, Pt와 Pt x The y (0 <x≤1, 0<y≤2)의 복합체, Pd와 Pd x The y (0 <x≤1, 0<y≤1)의 복합체, Si와 Si x The y (0 <x≤1, 0<y≤2)의 복합체, Ag 와 Ag x The y (0 <x≤2, 0<y≤1)의 복합체, Al과 Al x The y (0 <x≤2, 0<y≤3)의 복합체, Bi와 Bi x The y (0 <x≤2, 0<y≤3)의 복합체, Sn과 Sn x The y (0 <x≤1, 0<y≤2)의 복합체, Te과 Te x The y (0 <x≤1, 0<y≤3), Zn과 Zn x The y (0 <x≤1, 0<y≤1)의 복합체, 또는 이들의 조합을 포함할 수 있다.

[0181] The carbonaceous support is, for example, amorphous carbon. Amorphous carbon includes, but is not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), graphene, activated carbon, carbon nanofibers (CNF), carbon nanotubes (CNT), etc., and any material classified as amorphous carbon in the relevant technical field is possible. Amorphous carbon is carbon that has no crystallinity or very low crystallinity, and is distinguished from crystalline carbon or graphite carbon. Carbonaceous materials are, for example, carbonaceous negative electrode active materials.

[0182] The composite negative electrode active material may have, for example, a particle form. The particle size of the composite negative electrode active material having a particle form is, for example, 10 nm to 4 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. When the composite negative electrode active material has a particle size in this range, reversible absorption and / or desorption of lithium may be facilitated during charge and discharge. The metal-based negative electrode active material supported on the support may have, for example, a particle form. The particle size of the metal-based negative electrode active material may be, for example, 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 have, for example, a particle form. The particle size of the carbon-based support may be, for example, 10 nm to 2 ㎛, 10 nm to 1 ㎛, 10 nm to 500 nm, 10 nm to 200 nm, or 10 nm to 100 nm. By having a particle size in this range, the carbon-based support can be more uniformly arranged within the first negative electrode active material layer. The carbon-based support may be, for example, nanoparticles having a particle size of 500 nm or less. The particle sizes of the composite negative electrode active material, the particle sizes of the metal-based negative electrode active material, and the particle sizes 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 distribution analyzer. Alternatively, the average particle size may be determined automatically using software, for example, from an electron microscope image, or manually by a manual method.

[0183] [Cathode: Binder]

[0184] The binder included 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 thereto and any binder used in the relevant technical field may be used. The binder may be composed of a single binder or a plurality of different binders.

[0185] Since the first negative electrode active material layer (22) includes a binder, the first negative electrode active material layer (22) is stabilized on the negative electrode current collector (21). In addition, cracking of the first negative electrode active material layer (22) is suppressed despite changes in the volume and / or relative position of the first negative electrode active material layer (22) during the charge and discharge process. For example, if the first negative electrode active material layer (22) does not include a binder, the first negative electrode active material layer (22) can be easily separated from the negative electrode current collector (21). As the first negative electrode active material layer (22) is separated from the negative electrode current collector (21), the possibility of a short circuit occurring increases as the negative electrode current collector (21) comes into contact with the electrolyte layer (30) at the exposed portion of the negative electrode current collector (21). The first negative electrode active material layer (22) is manufactured by, for example, applying a slurry in which the material constituting the first negative electrode active material layer (22) is dispersed onto the negative electrode current collector (21) and drying the slurry. By including a binder in the first negative electrode active material layer (22), stable dispersion of the negative electrode active material in the slurry is possible. For example, when applying the slurry onto the negative electrode current collector (21) by screen printing, it is possible to suppress clogging of the screen (for example, clogging by aggregates of the negative electrode active material).

[0186] [Cathode: Other additives]

[0187] The first negative electrode active material layer (22) may further include additives used in a conventional all-solid-state secondary battery (1), such as fillers, coating agents, dispersants, and ion conductive aids.

[0188] [Cathode: Solid electrolyte]

[0189] The first negative electrode active material layer (22) may further include a solid electrolyte. The solid electrolyte may be, for example, a material selected from among the solid electrolytes included in the electrolyte layer (30). The solid electrolyte included in the first negative electrode active material layer (22) may act as a reaction site where lithium metal formation begins within the first negative electrode active material layer (22), a space where the formed lithium metal is stored, or a path for transferring lithium ions. The solid electrolyte may be omitted.

[0190] In the first negative electrode active material layer (22), the content of the solid electrolyte may be high, for example, in an area adjacent to the electrolyte layer (30), and low, for example, in an area adjacent to the negative electrode current collector (21). In the first negative electrode active material layer (22), the solid electrolyte may have a concentration gradient in which the concentration decreases, for example, from an area adjacent to the electrolyte layer (30) to an area adjacent to the negative electrode current collector (21).

[0191] [Cathode: First negative electrode active material layer]

[0192] The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is 0.005 to 0.45. The initial charge capacity of the positive electrode active material layer (12) is the first open circuit voltage (1 st Li / Li from open circuit voltage) + The initial charge capacity of the first negative electrode active material layer (22) is determined at the maximum charging voltage. The initial charge capacity of the first negative electrode active material layer (22) is determined at the second open circuit voltage (2 nd Li / Li from open circuit voltage) + It is determined at 0.01 V.

[0193] The maximum charging voltage is determined by the type of cathode active material. The maximum charging voltage can be, for example, 1.5 V, 2.0 V, 2.5 V, 3.0 V, 3.5 V, 4.0 V, 4.2 V, or 4.3 V. For example, the maximum charging voltage of Li2S or Li2S composite is Li / Li + can be 2.5 V for Li2S or Li2S complex. For example, the maximum charging voltage of Li / Li + It can be 3.0 V for. The ratio (B / A) of the initial charge capacity (B) of the first negative electrode active material layer (22) and the initial charge capacity (A) of the positive electrode active material layer is, for example, 0.01 to 0.3, 0.01 to 0.2, or 0.05 to 0.1. The initial charge capacity (mAh) of the positive electrode active material layer (12) is obtained by multiplying the charge capacity density (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 several types of positive electrode active materials are used, the charge capacity density × 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 also 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). When several 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 density of each of the positive electrode active material and the negative electrode active material can be measured using an all-solid-state half-cell using lithium metal as a counter electrode. The initial charge capacity of each of the positive electrode active material layer (12) and 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 value of the negative electrode active material in the first negative electrode active material layer (22). 2can be directly measured using an all-solid-state half-cell. For the positive electrode, the measurement is made from the first open circuit voltage (OCV) to the maximum charge voltage, for example, 3.0 V (vs. Li / Li + ) can be performed for an operating voltage of up to 0.01 V for the cathode, for example, lithium metal, from the second open circuit voltage (OCV). For example, an all-solid-state half-cell having a cathode active material layer can exhibit a current of 0.1 mA / cm from the first open circuit voltage to 3.0 V. 2 The all-solid-state half-cell having the first negative active material layer is charged with a constant current of 0.1 mA / cm from the second open circuit voltage 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 / cm 2 , or 0.5 mA / cm 2 The all-solid-state half-cell having the positive electrode active material layer can be charged from the first open circuit voltage to, for example, 2.5 V, 2.0 V, 3.5 V, or 4.0 V. The maximum charge voltage of the positive electrode active material layer can be determined by the maximum voltage of the battery that satisfies the safety conditions according to JISC8712:2015 of the Japanese Standards Association.

[0194] If the initial charge capacity of the first negative electrode active material layer (22) is too small, the thickness of the first negative electrode active material layer (22) becomes very thin, so that 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 collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the charge capacity of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1).

[0195] 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 to 50%, 1 to 40%, 1 to 30%, 1 to 20%, 1 to 10%, or 1 to 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 too thin, lithium dendrites formed between the first negative electrode active material layer (22) and the negative electrode current collector (21) collapse the first negative electrode active material layer (22), making it difficult to improve the cycle characteristics of the all-solid-state secondary battery (1). If the thickness of the first negative electrode active material layer (22) increases excessively, the energy density of the all-solid-state secondary battery (1) decreases and the internal resistance of the all-solid-state secondary battery (1) due to the first negative electrode active material layer (22) increases, making it difficult to improve the cycle characteristics of the all-solid-state 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.

[0196] [Cathode: Second negative electrode active material layer]

[0197] Referring to FIG. 5, the all-solid-state secondary battery (1) further includes, after being charged, a second negative electrode active material layer (24) disposed, 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 metal layer containing lithium or a lithium alloy. The metal layer contains lithium or a lithium alloy. Therefore, since the second negative electrode active material layer (24) is a metal layer containing lithium, it functions as, for example, a lithium reservoir. The lithium alloy is, but is not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, a Li-Si alloy, etc., and any lithium alloy used in the art may be used. The second negative electrode active material layer (24) may be made of one of these alloys or lithium, or may be made of several 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), for example, during the charging process of an all-solid-state secondary battery (1).

[0198] The thickness of the second negative electrode active material layer (24) is not particularly limited, but is, for example, 1 ㎛ to 500 ㎛, 1 ㎛ to 200 ㎛, 1 ㎛ to 150 ㎛, 1 ㎛ to 100 ㎛, or 1 ㎛ to 50 ㎛. If the thickness of the second negative electrode active material layer (24) is too thin, it is difficult for the second negative electrode active material layer (24) to perform the role of a lithium reservoir. If the thickness of the second negative electrode active material layer (24) is too thick, the mass and volume of the all-solid-state secondary battery (1) may increase, and the cycle characteristics of the all-solid-state secondary battery (1) may rather deteriorate.

[0199] Alternatively, in the all-solid-state secondary battery (1), the second negative electrode active material layer (24) may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22), for example, before assembling the all-solid-state secondary battery (1). When the second negative electrode active material layer (24) is disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1), the second negative electrode active material layer (24) acts as a lithium reservoir because it is a metal layer containing lithium. For example, a lithium foil may be disposed between the negative electrode current collector (21) and the first negative electrode active material layer (22) before assembling the all-solid-state secondary battery (1).

[0200] When the second negative electrode active material layer (24) is precipitated by charging after assembling the all-solid-state secondary battery (1), the energy density of the all-solid-state secondary battery (1) increases because the second negative electrode active material layer (24) is not included when assembling the all-solid-state secondary battery (1). When charging the all-solid-state secondary battery (1), the charging is performed in excess of the charging capacity of the first negative electrode active material layer (22). That is, the first negative electrode active material layer (22) is overcharged. At the initial stage of charging, lithium is absorbed into the first negative electrode active material layer (22). The negative electrode active material included in the first negative electrode active material layer (22) forms an alloy or compound with the lithium ions that have moved from the positive electrode (10). When charging exceeds the capacity of the first negative electrode active material layer (22), for example, lithium is deposited on the back surface of the first negative electrode active material layer (22), that is, between the negative electrode current collector (21) and the first negative electrode active material layer (22), and a metal layer corresponding to the second negative electrode active material layer (24) is formed by the deposited lithium. 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 the negative electrode active material included in the first negative electrode active material layer (22) including a material that forms an alloy or compound with lithium. During discharge, lithium in the first negative electrode active material layer (22) and the second negative electrode active material layer (24), that is, the metal layer, is ionized and moves toward the positive electrode (10). Therefore, it is possible to use lithium as the negative electrode active material in an all-solid-state secondary battery (1). In addition, 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 at the same time, it suppresses the precipitation and growth of lithium dendrites. Accordingly, it suppresses short circuits and capacity reduction of the all-solid-state secondary battery (1), and consequently improves the cycle characteristics of the all-solid-state secondary battery (1).In addition, when the second negative electrode active material layer (24) is disposed by charging after assembling the all-solid-state secondary battery (1), the negative electrode (20), i.e., the negative electrode current collector (21) and the first negative electrode active material layer (22) and the region between them are Li-free regions that do not contain lithium (Li) in the initial state or the state after complete discharge of the all-solid-state secondary battery (1).

[0201] [Cathode: Negative current collector]

[0202] The negative electrode current collector (21) is composed of, for example, a material that does not react with lithium, i.e., does not form an alloy or a compound. The material constituting the negative electrode current collector (21) is, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni), but is not necessarily limited thereto, and any material that can be used as an electrode current collector in the relevant technical field can be used. The negative electrode current collector (21) may be composed of one type of the above-described metal, or may be composed of an alloy or a coating material of two or more types of metals. The negative electrode current collector (21) is, for example, in the form of a plate or foil.

[0203] Referring to FIG. 4, the all-solid-state 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 disposed 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 element capable of forming an alloy with lithium includes, but is not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, bismuth, etc., and any element capable of forming an alloy with lithium in the art may be used. The thin film (23) is composed of one of these metals or an alloy of several types of metals. By placing the thin film (23) on one surface of the negative electrode current collector (21), for example, the deposition shape of the second negative electrode active material layer (24) deposited between the thin film (23) and the first negative electrode active material layer (22) becomes flatter, and the cycle characteristics of the all-solid-state secondary battery (1) can be further improved.

[0204] 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, it may be difficult for the function of the thin film (23) to be exerted. If the thickness of the thin film (23) is excessively thick, the thin film (23) itself absorbs lithium, which reduces the amount of lithium precipitated from the negative electrode, thereby lowering the energy density of the all-solid-state battery and deteriorating the cycle characteristics of the all-solid-state secondary battery (1). The thin film (23) may be disposed on the negative electrode current collector (21) by, for example, a vacuum deposition method, a sputtering method, a plating method, or the like, but is not necessarily limited to these methods, and any method capable of forming the thin film (23) in the relevant technical field may be used.

[0205] Although not shown in the drawing, 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 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 be an insulating polymer. Since the base film includes an insulating thermoplastic polymer, when a short circuit occurs, the base film may soften or liquefy, thereby blocking 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 an alloy thereof. The negative electrode current collector (21) may additionally include a metal piece and / or a lead tab. For more specific details regarding the base film, metal layer, metal chip, and lead tab of the negative electrode collector (21), refer to the positive electrode collector (11) described above. By having this structure, the negative electrode collector (21) can reduce the weight of the negative electrode, and consequently, improve the energy density of the negative electrode and lithium battery.

[0206] [Solid electrolyte layer]

[0207] [Solid electrolyte layer: solid electrolyte]

[0208] Referring to FIGS. 2 to 6, the solid electrolyte layer (30) includes a solid electrolyte disposed between the positive electrode (10) and the negative electrode (20). The solid electrolyte layer may include, for example, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0209] The solid electrolyte may include, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof.

[0210] The solid electrolyte is, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte is, for example, Li2S-P2S5, Li2S-P2S5-LiX, where X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p and q are positive numbers respectively, 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, at least one selected from 0≤x≤2. The sulfide-based solid electrolyte is manufactured by treating starting materials such as Li2S and P2S5 by a melting rapid cooling method or a mechanical milling method. In addition, heat treatment may be performed after the treatment. The solid electrolyte may be amorphous, crystalline, or a mixture thereof. In addition, the solid electrolyte may be, for example, one containing sulfur (S), phosphorus (P), and lithium (Li) as at least constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material containing Li2S-P2S5. When using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form a solid electrolyte, the mixing molar ratio of Li2S and P2S5 is, for example, in the range of Li2S:P2S5=20:80 to 90:10, 25:75 to 90:10, 30:70 to 70:30, 40:60 to 60:40.

[0211] The sulfide-based solid electrolyte may include, for example, an argyrodite type solid electrolyte represented by the following chemical formula 1.

[0212] <Chemical Formula 1>

[0213] Li + 12-n-x A n+ X 2- 6-x Y - x

[0214] In the above formula, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta, X is S, Se or Te, Y is Cl, Br, I, F, CN, OCN, SCN or N3, and 1≤n≤5, 0≤x≤2. The sulfide-based solid electrolyte is, for example, Li 7-x PS 6-x Cl x , 0≤x≤2, Li 7-xPS 6-x Br x , 0≤x≤2, and Li 7-x PS 6-x I x , may be an argyrodite-type compound including at least one selected from 0≤x≤2. The sulfide-based solid electrolyte may be, for example, an argyrodite-type compound including at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0215] The density of the argyrodite-type solid electrolyte may be 1.5 to 2.0 g / cc. Since the argyrodite-type solid electrolyte has a density of 1.5 g / cc or more, the internal resistance of the all-solid-state secondary battery is reduced, and penetration of the electrolyte layer by Li can be effectively suppressed.

[0216] Oxide 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), Li1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (0≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12 (M = Te, Nb, or Zr, 0≤x≤10), or a combination thereof. The oxide-based solid electrolyte is manufactured, for example, by a sintering method.

[0217] Oxide-based solid electrolytes include, 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) 중에서 선택된 가넷계(Garnet-type) 고체전해질이다.

[0218] The polymer solid electrolyte may, for example, comprise a mixture of a lithium salt and a polymer, or a polymer having ion-conducting functional groups. The polymer solid electrolyte may, for example, be a polymer electrolyte that is solid at 25°C and 1 atm. The polymer solid electrolyte may, for example, not comprise a liquid.The polymer solid electrolyte comprises a polymer, and the polymer is, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), polymethyl methacrylate (PMMA, poly(methylmethacrylate), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), Polyaniline, polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-Diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi. +) or a combination thereof, but is not limited thereto, and any lithium salt that can be used in polymer electrolytes in the relevant technical field is possible. The lithium salt can be any lithium salt that can be used in the relevant technical field. The lithium salt is, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are each 1 to 20), LiCl, LiI or a mixture thereof, etc. The polymer included in the polymer solid electrolyte may be, for example, a compound including 10 or more, 20 or more, 50 or more or 100 or more repeating units. The weight average molecular weight of the polymer included in the polymer solid electrolyte may be, for example, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more or 1,000,000 Dalton or more.

[0219] A gel electrolyte is, for example, a polymer gel electrolyte. A gel electrolyte can have a gel state without containing a polymer, for example.

[0220] A polymer gel electrolyte may include, for example, a liquid electrolyte and a polymer, or an organic solvent and a polymer having an ion-conducting functional group. The polymer gel electrolyte may be, for example, a polymer electrolyte that is in a gel state at 25°C and 1 atm. The polymer gel electrolyte may, for example, have a gel state without containing a liquid. The liquid electrolyte used in the polymer gel electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent; a mixture of a lithium salt and an organic solvent; a mixture of an ionic liquid and an organic solvent; or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer used in the polymer gel electrolyte may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt that has a melting point below room temperature, is composed solely of ions, and is liquid at room temperature or a molten salt at room temperature. Ionic liquids 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-, CF3SO3-, (FSO2)2N-, (C2F5SO2)2N-, (C2F5SO2)(CF3SO2)N-, and (CF3SO2)2N- may include at least one selected from compounds containing at least one anion selected from among. The polymer solid electrolyte may form a polymer gel electrolyte, for example, by being impregnated into a liquid electrolyte in a secondary battery. The polymer gel electrolyte may further include inorganic particles. The polymer included in the polymer gel electrolyte may be a compound including, for example, 10 or more, 20 or more, 50 or more, or 100 or more repeating units. The weight average molecular weight of the polymer included in the polymer gel electrolyte may be, for example, 500 Dalton or more, 1000 Dalton or more, 10,000 Dalton or more, 100,000 Dalton or more, or 1,000,000 Dalton or more.

[0221] [Electrolyte layer: binder]

[0222] The electrolyte layer (30) may include, for example, a binder. The binder included in the electrolyte layer (30) is not limited to, but may include, for example, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc., and any binder used in the relevant technical field may be used. The binder of the electrolyte layer (30) may be the same as or different from the binder included in the positive electrode active material layer (12) and the negative electrode active material layer (22). The binder may be omitted.

[0223] The binder content included in the electrolyte layer (30) is 0.1 to 10 wt%, 0.1 to 5 wt%, 0.1 to 3 wt%, 0.1 to 1 wt%, 0 to 0.5 wt%, or 0 to 0.1 wt% with respect to the total weight of the electrolyte layer (30).

[0224] Referring to Fig. 6, the negative electrode (20) includes a negative electrode current collector (21) and a lithium host layer (22) disposed on one side of the negative electrode current collector (21). A first inactive member (42) is disposed on one side of the negative electrode (20).

[0225] The first inert member (42) is disposed on one side of the lithium host layer (22) and is disposed between the solid electrolyte layer (40) and the negative electrode current collector (21) facing the solid electrolyte layer (40). The second inert member (42) is not disposed on one side of the negative electrode current collector (21). The first inert member (42) is disposed on one side of the lithium host layer (22) and the negative electrode current collector (21). By including the first inert member (42), a short circuit between the lithium metal deposited on the lithium host layer (22) and the positive electrode (10) during charging and discharging of the all-solid-state secondary battery (1) is more effectively prevented, and cracking of the solid electrolyte layer (30) caused by uneven pressure applied to the solid electrolyte layer (30) in contact with the negative electrode (20) during manufacturing and / or charging and discharging of the all-solid-state secondary battery (1) is prevented, resulting in improved cycle characteristics of the all-solid-state secondary battery (2).

[0226] In the all-solid-state secondary battery (1), the thickness (T2) of the first inactive member (42) is substantially the same as the thickness (T1) of the lithium host layer (22). Since the sum of the thickness (T2) of the first inactive member (42) and the thickness (T4) of the negative electrode current collector (21) is substantially the same as the thickness (T3) of the negative electrode (20), a uniform pressure is applied between the negative electrode (20) and the solid electrolyte layer (30), and the negative electrode (20) and the solid electrolyte layer (30) are sufficiently in close contact, thereby reducing the interfacial resistance between the negative electrode (20) and the solid electrolyte layer (30). In addition, since the solid electrolyte layer (30) is sufficiently sintered during the pressurized manufacturing process of the all-solid-state secondary battery (1), the internal resistance of the solid electrolyte layer (30) and the all-solid-state secondary battery (1) including the same is reduced.

[0227] The manufacturing method of a solid secondary battery according to an embodiment is as follows.

[0228] A solid secondary battery according to one embodiment comprises: a step of milling a composition including M2S and an alkali metal salt to obtain a milled product; a step of adding and mixing a gel polymer electrolyte forming composition containing a crosslinking monomer for forming a gel polymer electrolyte to the milled product to prepare a positive electrode; a step of preparing a negative electrode; and a step of arranging an electrolyte between the positive electrode and the negative electrode, wherein the gel polymer electrolyte forming composition contains a liquid electrolyte containing a lithium salt and an organic solvent and a crosslinking agent.

[0229] In the step of milling the composition including the above M2S and alkali metal salt to obtain a milled product, a carbon-based material may be further added.

[0230] The step of milling the composition including the above M2S and an alkali metal salt to obtain a milled product includes the step of milling the M2S and an alkali metal salt to obtain an M2S-alkali metal salt complex; and the step of milling the composition including the M2S-alkali metal salt complex and a carbon-based material to obtain a milled product.

[0231] A crosslinking monomer for forming a gel polymer electrolyte is a substance having two or more crosslinking functional groups, for example, two to four. The crosslinking functional groups include, for example, polyfunctional (tri-substituted) methacrylates, and examples thereof include trimethylol propane triacrylate.

[0232] For example, diethylene glycol diacrylate (DEGDA), diethylene glycol dimethacrylate (DEGDMA), triethylene glycol diacrylate (TEGDA), triethylene glycol dimethacrylate (TEGDMA), tetraethylene glycol diacrylate (TTEGDA), glycidyl methacrylate, polyethylene glycol diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), polypropylene glycol diacrylate (PPGDA), dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), dianol diacrylate (DDA), dianol dimethacrylate (DDMA), ethoxylated trimethylolpropane triacrylate (ETPTA), acrylate-functionalized ethylene oxide, butanediol Dimethacrylate, ethoxylated neopentyl glycol diacrylate (NPEOGDA), propoxylated neopentyl glycol diacrylate (NPPOGDA), trimethylol propane triacrylate (TMPTA), trimethylol propane trimethacrylate (TMPTMA), pentaerythritol triacrylate (PETA), ethoxylated propoxylated trimethylolpropane triacrylate (TMPEOTA) / (TMPPOTA), propoxylated glyceryl triacrylate, tris(2-hydroxyethyl) isocyanurate triacrylate (THEICTA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPEPA), ditrimethylol propane Tetraacrylate (DTMPTTA); diglycidyl ester, diallyl suberate; acrylamide, divinylbenzene or combinations thereof.

[0233] The above crosslinking monomer may have a weight average molecular weight in the range of 200 to 2,000, and may be in the range of 200 to 1,000, for example, in the range of 200 to 500. If the weight average molecular weight is less than 200, the density of crosslinking points within the molecular structure of the polymer after crosslinking may be too high, preventing free movement of the lithium salt. On the other hand, if the weight average molecular weight is greater than 2,000, the density of crosslinking points within the molecular structure of the polymer after crosslinking may be too low, reducing the electrolyte blocking ability.

[0234] Based on the total weight of the crosslinking monomer and the liquid electrolyte, the content of the crosslinking monomer is 1 to 10 parts by weight, and the content of the liquid electrolyte is 90 to 99 parts by weight. If the content of the crosslinking monomer is less than 1 part by weight, the degree of crosslinking during crosslinking is too low, so that the crosslinking characteristics cannot be sufficiently expressed, and the electrolyte moisture absorption capacity and mechanical characteristics may be poor, and if it exceeds 10 parts by weight, the internal resistance within the electrode plate increases, which may act as a cause of capacity reduction during high-rate charge / discharge.

[0235] The composition for forming the above gel-type polymer electrolyte may further include a crosslinking agent, a photoinitiator, etc. to assist in crosslinking of the crosslinkable monomer. The crosslinking agent, initiator, etc. are not particularly limited as long as they are commonly used in the relevant technical field.

[0236] The initiator can be, for example, benzoin ethyl ether.

[0237] The content of the crosslinking agent, initiator, etc. may be within a conventional range. For example, the content of the initiator may be used in a range of 0.1 to 5 parts by weight, or 0.2 to 3 parts by weight, based on 100 parts by weight of the crosslinking monomer. Using the gel polymer electrolyte formed in this way, the ionic conductivity can be maintained at a value close to that of the liquid electrolyte, and the gel polymer electrolyte inside the positive and negative electrodes can play a role in preventing leakage of the liquid electrolyte. The electrolyte can be trapped in the polymer matrix of the gel polymer electrolyte and maintained within the polymer matrix, thereby helping the smooth movement of lithium ions. In addition, the excellent electrochemical properties of the polymer can suppress the electrolyte decomposition reaction within the range of -1 V to 5 V.

[0238] The electrolyte may be a solid electrolyte, a liquid electrolyte, or a combination thereof.

[0239] The liquid electrolyte may contain a lithium salt, an organic solvent, an ionic liquid, or a combination thereof. The solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a combination thereof.

[0240] Liquid electrolytes may be nonvolatile. Ionic liquids are salts or molten salts that are liquid at room temperature and are composed solely of ions and have a melting point below room temperature. Ionic liquids contain a) one or more cations selected from the group consisting of ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF4. - , PF6 - , AsF 6- , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br- , I - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - One selected from compounds containing at least one anion selected from. The ionic liquid is, for example, at least one selected from the group consisting of N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(3-trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The polymeric ionic liquid is a) one or more cations selected from ammonium series, pyrrolidinium series, pyridinium series, pyrimidinium series, imidazolium series, piperidinium series, pyrazolium series, oxazolium series, pyridazinium series, phosphonium series, sulfonium series, triazolium series, and mixtures thereof, and b) BF4 - , PF6 - , AsF6 - , SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , (CF3SO2)2N - , (FSO2)2N - , Cl - , Br - , I - , SO4 - , CF3SO3 - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , NO3 - , Al2Cl7 - , (CF3SO2)3C - , (CF3)2PF4 -, (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , SF5CF2SO3 - , SF5CHFCF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (O(CF3)2C2(CF3)2O)2PO - It may contain repeating units including one or more anions selected from. The lithium salt may be any lithium salt that can be used in the art. The lithium salt may be, for example, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, Li(FSO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein x and y are natural numbers), LiCl, LiI or a mixture thereof. The concentration of the lithium salt included in the liquid electrolyte may be 0.1 M to 5 M. The content of the liquid electrolyte impregnated in the positive electrode (10) is 0 to 100 parts by weight, 0 to 50 parts by weight, 0 to 30 parts by weight, 0 to 10 parts by weight or 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer (12) not including the liquid electrolyte.

[0241] According to one embodiment, the gel polymer electrolyte can be manufactured by a dry or wet process.

[0242] Mechanical milling can be used in the above milling. A ball mill, etc. can be used in the mechanical milling.

[0243] After the step of placing an electrolyte between the positive and negative electrodes, a step of obtaining a battery assembly and pressurizing it may be performed.

[0244] Pressurization is not limited to a roll press, a flat press, etc., but any pressurization method used in the relevant technical field may be used. The pressurization step may be omitted.

[0245] Pressurization is performed at a temperature of, for example, room temperature (20°C to 25°C) to 90°C. Alternatively, pressurization is performed at a high temperature of 100°C or higher. The pressurization time is, for example, 30 minutes or less, 20 minutes or less, 15 minutes or less, or 10 minutes or less. The pressurization time is 1 ms to 30 minutes, 1 ms to 20 minutes, 1 ms to 15 minutes, or 1 ms to 10 minutes. The pressurization method is, for example, isotactic press, roll press, flat press, etc., but is not necessarily limited to these methods and any pressurization method used in the art is possible. The pressure applied during pressurization is, for example, 500 MPa or less, for example, 400 MPa or less, 300 MPa or less, 200 MPa or less, or 100 MPa or less. The pressure applied during pressurization is, for example, 50 MPa to 500 MPa, 50 MPa to 400 MPa, 50 MPa to 300 MPa, 50 MPa to 200 MPa, 50 MPa to or 100 MPa. By this pressurization, for example, the solid electrolyte powder is sintered to form one solid electrolyte.

[0246] The pressurizing step is for example 40 to 100°C, for example 85 oPlate press treatment is performed at a pressure of 500 MPa for 30 min at C. This pressurization process sinteres the solid electrolyte layer, thereby improving battery characteristics. In addition, during this pressurization process, a polymerization reaction (crosslinking reaction) of the crosslinking monomer for forming a gel polymer electrolyte contained in the positive electrode active material layer occurs, thereby forming a gel polymer electrolyte.

[0247] Methods for forming a gel-type polymer electrolyte include curing using heat, UV, or high-energy radiation (electron beam, γ-ray). The curing reaction using heat can be carried out at a temperature of 40°C to 120°C, 45°C to 100°C, for example, 50°C to 90°C for 30 to 180 minutes.

[0248] According to one embodiment, a gel polymer electrolyte can be formed in the pressurizing step described above.

[0249] A composition for forming a gel polymer electrolyte comprises a crosslinking monomer, a lithium salt, an organic solvent, and an initiator. Depending on the type of crosslinking monomer, an additional heat treatment step may be performed in the above-described method for manufacturing a solid secondary battery. This heat treatment varies depending on the type of crosslinking monomer and is performed, for example, at 40°C to 120°C.

[0250] The gel polymer electrolyte manufactured according to the present invention has an ionic conductivity of 1x10 -4 It possesses a high ionic conductivity of over S / cm. This allows for increasing the relative content of lithium sulfide within the cathode, resulting in the manufacture of a cathode with improved energy density and capacity. Furthermore, the reduced volume change during charge / discharge facilitates thick film formation.

[0251] The ionic conductivity of the above gel polymer electrolyte is 1×10 -4 S / cm or more, 2×10 -4 S / cm or more, 4×10 -4 S / cm or more, 6×10 -4 S / cm or more, or 8×10-4 It can be S / cm or more. The ionic conductivity can be measured using, for example, electrochemical impedance spectroscopy, direct current polarization method, etc. Since the composite has an ionic conductivity in this range, the internal resistance of the positive electrode containing the gel polymer electrolyte can be reduced. The cycle characteristics of a secondary battery containing such a positive electrode can be improved.

[0252] When a gel polymer electrolyte is contained in the positive electrode active material layer, an organic network can be formed between the solid electrolyte and lithium sulfide through the gel polymer electrolyte in the positive electrode.

[0253] The positive electrode for a solid secondary battery according to the present invention can provide a positive electrode in which the resistance between the positive electrode and the solid electrolyte interface is improved and the network of the positive electrode active material and the solid electrolyte is strengthened and maintained.

[0254] The present invention is explained in more detail through the following examples and comparative examples. However, the examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0255] (Manufacturing of composite cathode active materials)

[0256] Manufacturing Example 1: Li2S-LiI-CNF, 2 steps, 10 hr, 600 rpm, 28G

[0257] (Stage 1)

[0258] Li2S and LiI were mixed in a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm for 10 h. The milling energy applied to the sample during milling was 28 G.

[0259] (Stage 2)

[0260] Li2S-LiI composite and carbon nanofiber (CNF) were mixed at a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm for 10 h. The milling energy applied to the sample during milling was 28 G. The Li2S-LiI-CNF composite was used as a composite cathode active material. The Mohs hardness of Li2S was 0.6, that of LiI was 2.0, and that of carbon nanofiber (CNF) was 1.5.

[0261] Manufacturing Example 2: Li2S-LiI-CNF, 2 steps, 8 hr, 600 rpm, 28G

[0262] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 1, except that the milling time in the first and second steps was changed to 8 hours.

[0263] Comparative Manufacturing Example 1: Li2S-LiI-CNF, 2 steps, 1 hr, 600 rpm, 28G

[0264] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 1, except that the milling time in the first and second steps was changed to 1 hour or 20 hours, respectively.

[0265] Comparative Manufacturing Example 2: Li2S-LiI-CNF, 2 steps, 20 hr, 600 rpm, 28G

[0266] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 1, except that the milling time in the first and second steps was changed to 20 hours.

[0267] Comparative Manufacturing Example 3: Li2S-LiI-CNF, 510 rpm, 10 hr, 2 steps, 20G

[0268] (Stage 1)

[0269] A first mixture was prepared by mixing Li2S and LiI in a weight ratio of 30:20. The first mixture was mechanically milled using a ball mill to prepare a Li2S-LiI complex. The milling conditions were 25°C, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G.

[0270] (Stage 2)

[0271] A second mixture was prepared by mixing the Li2S-LiI complex and carbon nanofibers (CNF) at a weight ratio of 50:10. The second mixture was mechanically milled using a ball mill to produce a Li2S-LiI-CNF complex.

[0272] The milling conditions were 25°C, 510 rpm for 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-LiI-CNF composite was used as the composite cathode active material.

[0273] Comparative Manufacturing Example 4-5: Li2S-LiI-CNF, 10 hr, 2 steps, 10 G or 30 G

[0274] A Li2S-LiI-CNF composite was manufactured in the same manner as in Manufacturing Example 1, except that the rotation speed was reduced in the first and second steps and the milling energy was changed to 10 G or 30 G, respectively.

[0275] Comparative Manufacturing Example 6: Simple mixture of Li2S and CNF

[0276] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was used as a cathode active material.

[0277] Comparative Manufacturing Example 7: Li2S-CNF, 600 rpm, 2 hr, 1 step, 20 G

[0278] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:30. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI composite. The milling conditions were 25°C, 600 rpm for 2 h. The milling energy applied to the sample during milling was 20 G. The Li2S-CNF composite was used as a composite cathode active material.

[0279] Comparative Manufacturing Example 8: Li2S-CNF, 600 rpm, 10 hr, 1 step, 20 G

[0280] A Li2S-CNF composite was manufactured using the same method as in Comparative Manufacturing Example 7, except that the milling time was changed to 10 hours.

[0281] Comparative Manufacturing Example 9: Li2S-CNF-LiI, 600 rpm, 10 hr, 2 stages, 20G

[0282] (Stage 1)

[0283] Li2S and carbon nanofibers (CNF) were mixed at a weight ratio of 30:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G.

[0284] (Stage 2)

[0285] Li2S-CNF composite and LiI were mixed at a weight ratio of 40:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-CNF-LiI composite. The milling conditions were 25°C, 600 rpm for 10 h. 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.

[0286] Comparative Manufacturing Example 10: Li2S-SE-CNF, 600 rpm, 10 hr, 2 steps, 20G

[0287] (Stage 1)

[0288] Li2S and Li6PS5Cl solid electrolyte (SE) were mixed at a weight ratio of 30:20. The mixture was mechanically milled using a ball mill to prepare a Li2S-SE composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G.

[0289] (Stage 2)

[0290] Li2S-SE composite and CNF were mixed at a weight ratio of 50:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-SE-CNF composite. The milling conditions were 25°C, 600 rpm, and 10 h. The milling energy applied to the sample during milling was 20 G. The Li2S-SE-CNF composite was used as a composite cathode active material.

[0291] Comparative Manufacturing Example 11: Li2S-LiI-CNF, 600 rpm, 2 hr, 1 step, 20 G

[0292] Li2S, LiI, and carbon nanofibers (CNF) were mixed in a weight ratio of 30:20:10. The mixture was mechanically milled using a ball mill to prepare a Li2S-LiI-CNF composite. The milling conditions were 25°C, 600 rpm for 2 h. 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.

[0293]

[0294] (Manufacturing of positive and solid secondary batteries)

[0295] Example 1: (Li2S-LiI-CNF)+GPE(TMPTA)+Binder-free containing cathode, Ag / C

[0296] Solid secondary battery containing a cathode and a sulfide-based solid electrolyte

[0297] A composition for forming a gel polymer electrolyte was added to the Li2S-LiI-CNF complex obtained according to Manufacturing Example 1, and the mixture was mixed for 20 minutes to prepare a positive electrode mixture.

[0298] The composition for forming the above gel polymer electrolyte was prepared by mixing trimethylolpropane triacrylate (TMPTA), a mixed solvent (weight ratio 1:1:0.5) of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in which 1.3 M LiPF6 was dissolved as a liquid electrolyte, and benzoin ethyl ether (Sigma-Aldrich, 240.30 g / mol) as an initiator. The composition for forming the gel polymer electrolyte contained 3 parts by weight of a crosslinking monomer and 97 parts by weight of a liquid electrolyte based on 100 parts by weight of the total weight of the composition, and the initiator was used in an amount of 3 parts by weight based on 100 parts by weight of the crosslinking monomer. The content of the above TMPTA was determined so that the content of the gel polymer electrolyte in the finally obtained positive electrode active material layer was 10 parts by weight based on 100 parts by weight of lithium sulfide.

[0299] The above-mentioned positive electrode mixture was obtained by dry mixing.

[0300] The positive electrode mixture was placed on one side of a positive electrode current collector made of aluminum foil coated on one side and plate pressed at a pressure of 200 MPa for 10 minutes to produce a positive electrode in the form of a sheet. The thickness of the positive electrode was approximately 120 μm and the loading level of the positive electrode mixture was approximately 8 mg / cm2. 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. The areas of the positive electrode active material layer and the positive electrode current collector were identical.

[0301] (Cathode manufacturing)

[0302] A 10 ㎛ thick SUS foil was prepared as a negative electrode collector. Carbon black (CB) with a primary particle diameter of approximately 30 nm and silver (Ag) particles with an average particle diameter of approximately 60 nm were prepared as negative electrode active materials.

[0303] A mixed powder of 4 g of carbon black (CB) and silver (Ag) particles in a weight ratio of 3:1 was placed in a container, and 4 g of an NMP solution containing 7 wt% of PVDF binder (Kureha #9300) was added thereto to prepare a mixed solution. A slurry was prepared by stirring the mixed solution while adding NMP little by little to the prepared mixed solution. The prepared slurry was applied to a SUS sheet using a bar coater, dried in air at 80°C for 10 minutes, and then vacuum-dried at 40°C for 10 hours to prepare a laminate. The prepared laminate was cold roll pressed to flatten the surface, thereby preparing a negative electrode having a first negative electrode active material layer / negative electrode current collector structure. The thickness of the first negative electrode active material layer was approximately 15 μm. The areas of the first negative electrode active material layer and the negative electrode current collector were the same.

[0304] (Manufacturing of solid electrolyte layer)

[0305] Li6PS5Cl solid electrolyte in the form of argyrodite crystals (D 50 =3.0 (m, crystalline), a mixture was prepared by adding 1.5 parts by weight of an acrylic binder to 98.5 parts by weight of a solid electrolyte. Octyl acetate was added to the prepared mixture and stirred to prepare 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 prepare a solid electrolyte layer.

[0306] (inert absence)

[0307] A flame-retardant inert member was manufactured by forming a slurry containing pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), an acrylic binder, and a solvent into a gasket shape and then removing the solvent.

[0308] The weight ratio of pulp fiber (cellulose fiber), glass fiber, aluminum hydroxide (Al(OH)3), and acrylic binder was 20:8:70:2. The thickness of the inert material was 120 ㎛.

[0309] Before placing the manufactured flame-retardant inert material on the solid electrolyte layer, moisture, etc. of the flame-retardant inert material was removed by vacuum heat treatment at 80°C for 5 hours.

[0310] (Manufacturing of all-solid-state secondary batteries)

[0311] A solid electrolyte layer was placed on the negative electrode such that the first negative electrode active material layer was in contact with the solid electrolyte layer, and a positive electrode was placed on the solid electrolyte layer. A laminate was prepared by placing a gasket surrounding the positive electrode and in contact with the solid electrolyte layer. The thickness of the gasket was approximately 120 ㎛. The above-mentioned flame-retardant inert material was used as the gasket. The gasket was placed so as to be in contact with the side surface of the positive electrode and the solid electrolyte layer. The positive electrode was placed at the center of the solid electrolyte layer, and the gasket was placed so as to surround the positive electrode and extend to the end of the solid electrolyte layer. The area of ​​the positive electrode was approximately 90% of the area of ​​the solid electrolyte layer, and the gasket was placed over the entire remaining 10% of the area of ​​the solid electrolyte layer where the positive electrode was not placed.

[0312] 85 prepared laminates oThe solid electrolyte layer was plate-pressed at 500 MPa for 30 min at C. This pressurization process sintered the solid electrolyte layer, thereby improving battery characteristics. The thickness of the sintered solid electrolyte layer was approximately 45 ㎛. The density of the Li6PS5Cl solid electrolyte, which was an argyrodite-type crystal contained in the sintered solid electrolyte layer, was 1.6 g / cc. The area of ​​the solid electrolyte layer was the same as that of the negative electrode.

[0313] The pressurized laminate was placed in a pouch and vacuum-sealed to manufacture an all-solid-state secondary battery. Portions of the positive and negative current collectors were extended outside the sealed battery to serve as positive and negative terminals.

[0314] The positive electrode active material layer of the above positive electrode contained Li2S, GPE, and CNF. GPE is a cross-linked product of TMPTA, and the content of GPE in the positive electrode active material layer is 30 parts by weight based on 100 parts by weight of the positive electrode active material layer, and the content of Li2S is 50 parts by weight based on 100 parts by weight of the positive electrode active material layer.

[0315] Example 2: (Li2S-LiI-CNF)+GPE(TMPTA)+Binder-free containing cathode, Ag / C

[0316] Solid secondary battery containing a cathode and a sulfide-based solid electrolyte

[0317] The content of GPE in the positive electrode active material layer is based on 100 parts by weight of the positive electrode active material layer.

[0318] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that the content of TMPTA, a monomer for forming GPE, was changed to 20 parts by weight. Then, the content of the crosslinking monomer in the composition for forming a gel-type polymer electrolyte was changed to 5 parts by weight based on 100 parts by weight of the composition so that the content of the crosslinking polymer in the GPE of the positive electrode was 5% by weight based on the total content of the gel-type polymer electrolyte.

[0319] Example 3: (Li2S-LiI-CNF)+GPE(TMPTA)+sulfide-based SE-containing cathode,

[0320] Solid secondary battery containing Ag / C cathode and sulfide-based solid electrolyte

[0321] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that a solid electrolyte was added during the manufacture of the positive electrode mixture.

[0322] The content of the above solid electrolyte is 10 parts by weight based on 100 parts by weight of the total weight of the positive electrode active material layer.

[0323] Li6PS5Cl (D50=3.0um, crystalline) in the form of argyrodite was prepared as a solid electrolyte.

[0324] Example 4: Solid secondary battery containing a cathode comprising (Li2S-LiI-CNF)+GPE(TMPTA)+binder, an Ag / C cathode, and a sulfide-based solid electrolyte.

[0325] When manufacturing the anode, PTFE, a binder, is added to the above mixture and mixed in a mortar.

[0326] A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode mixture was prepared by performing physical mixing. Here, the mixture and binder were controlled at a weight ratio of 60:1.2, and the positive electrode mixture was obtained by dry mixing.

[0327] Example 5: Solid secondary battery containing a cathode containing (Li2S-LiI-CNF)+GPE(ETPTA), an Ag / C cathode, and a sulfide-based solid electrolyte.

[0328] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that ethoxylated trimethylolpropane triacrylate (ETPTA) was used instead of trimethylolpropane triacrylate (TMPTA) when manufacturing a composition for forming a gel polymer electrolyte.

[0329] Example 6: Solid secondary battery containing a positive electrode containing (Li2S-LiI-CNF)+GPE(DEGDA), an Ag / C negative electrode, and a sulfide-based solid electrolyte.

[0330] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that diethylene glycol diacrylate (DEGDA) was used instead of trimethylolpropane triacrylate (TMPTA) when manufacturing a composition for forming a gel polymer electrolyte.

[0331] Example 7: Solid secondary battery containing (Li2S-LiI-CNF)+GPE(TEGDA) positive electrode, Ag / C negative electrode, and sulfide-based solid electrolyte

[0332] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that triethylene glycol diacrylate (TEGDA) was used instead of trimethylolpropane triacrylate (TMPTA) when manufacturing a composition for forming a gel polymer electrolyte.

[0333] Comparative Example 1: (Li2S+LiI-CNF composite)+sulfide-based SE+GPE-free containing cathode, Ag / C cathode and sulfide-based solid electrolyte containing electrode

[0334] When manufacturing the positive electrode active material layer, a composition for forming a gel polymer electrolyte is not added.

[0335] Except for this, the positive electrode and solid secondary battery were manufactured in the same manner as in Example 2.

[0336] Comparative Example 2: (Li2S+LiI-CNF composite)+GPE(HA)+sulfide-based SE-containing positive electrode, Ag / C negative electrode, and sulfide-based solid electrolyte-containing electrode

[0337] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that hexyl acrylate (HA), a crosslinking monomer with one crosslinking point, was used instead of trimethylolpropane triacrylate (TMPTA) when manufacturing a composition for forming a gel polymer electrolyte.

[0338] Comparative Example 3: (Li2S-CNF)+GPE free+binder containing cathode, Ag / C cathode and sulfide system

[0339] Anode containing solid electrolyte

[0340] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 4, except that the Li2S-CNF composite of Comparative Manufacturing Example 7 was used instead of the composite of Manufacturing Example 1 when manufacturing the positive electrode composite and GPE was not added.

[0341] Comparative Example 4: (Li2S-LiI+C complex)+GPE free+sulfide-based solid SE-containing cathode,

[0342] Electrode containing Ag / C cathode and sulfide-based solid electrolyte

[0343] A positive electrode and a solid secondary battery were manufactured in the same manner as in Example 1, except that a composition for forming a gel polymer electrolyte was not added during the manufacture of the positive electrode mixture.

[0344] Comparative Examples 5 to 14

[0345] A cathode and a solid secondary battery were manufactured according to Example 1, except that the composite or simple mixture obtained according to Comparative Manufacturing Examples 1 to 11 was used instead of the Li2S-LiI-CNF composite obtained according to Manufacturing Example 1 when manufacturing the cathode mixture.

[0346] Evaluation Example 1: XRD Analysis and Scanning Electron Microscopy Analysis

[0347] XRD spectra were measured using Cu Kα radiation for the raw material (bare) Li2S used in Example 1, the pulverized Li2S, the Li2S-LiI composite prepared in the first step in Example 1, and the Li2S-LiI-CNF composite prepared in Example 1. The measurement results are shown in Table 1 and Fig. 1 below. The Li2S crystallite size and lattice constant were derived from the first peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° in the XRD spectra.

[0348] The crushed Li2S was prepared by milling under the same conditions as in the first step of Example 1, except that the 30:20 weight ratio mixture of Li2S and LiI was changed to 50 parts by weight of Li2S. The second step was not performed.

[0349] The particle size (i.e., D50 particle diameter) of the composites was measured using a laser-assisted particle size analyzer (PSA) and a scanning electron microscope for the raw material Li2S used in Example 1, the pulverized Li2S, the Li2S-LiI composite prepared in the first step in Example 1, and the Li2S-LiI-CNF composite prepared in Example 1, and the Li2S particle size of the composites was measured using a scanning electron microscope. The measurement results are shown in Table 1 and FIGS. 2a to 2b below.

[0350] Distinction 2nd peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]bare Li2S 27.021 164.678 1st peak position [°]Li2S crystallite size [nm]Li2S particle size [㎛]crushed Li2S 26.9270 15.42 -Li2S-LiI complex (first stage) 26.60 748.831 less than Example 1 (Li2S-LiI-CNF complex) 26.70 20 less than 9.861

[0351] As shown in Table 1, the position of the first peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 shifted to a lower angle compared to the position of the second peak for the (111) crystal plane appearing at a diffraction angle 2θ = 27° ± 2.0° of bare Li2S. The first diffraction angle of the first peak of the Li2S-LiI-CNF composite of Example 1 was smaller than the second diffraction angle of the second peak of bare Li2S. Therefore, the crystallite size of the Li2S-LiI-CNF composite of Example 1 was significantly reduced compared to the crystallite size of bare Li2S. As shown in Table 1 and FIG. 1, the positions of the first peaks of the Li2S-LiI-CNF composite of Example 1 and the Li2S-LiI composite, which is an intermediate product of the first step of Example 1, were shifted to a low angle compared to the position of the first peak of the pulverized Li2S.

[0352] Although not shown in Table 1, the first lattice constant (d1) derived from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° of the Li2S-LiI-CNF composite of Example 1 was larger than the second lattice constant (d2) derived from the second peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° of bare Li2S. The first lattice constant (d1) was 5.78 Å or more.

[0353] It was determined that this was because LiI was dissolved within the Li2S crystal, increasing the lattice constant value. It was confirmed that the Li2S-LiI-CNF composite formed a solid solution.

[0354] Although not shown in Table 1, the first peak of the Li2S-LiI-CNF composite of Example 1 had a first full width at half maximum (FWHM1), and the second peak of bare Li2S had a second full width at half maximum (FWHM2), and the first full width was larger than the second full width. The first full width at half maximum (FWHM1) was 1° or greater.

[0355] Although not shown in Table 1, the particle size of the composite of Example 1 was approximately 5 μm.

[0356] Evaluation Example 2: XRD Analysis and Scanning Electron Microscopy Analysis

[0357] XRD spectra were measured using Cu Kα radiation for the composite cathode active materials (i.e., composites) manufactured in Manufacturing Examples 1 to 2 and Comparative Manufacturing Examples 1 to 11. The Li2S crystallite sizes calculated from the first peak for the (111) crystal plane appearing at a diffraction angle of 2θ = 27° ± 2.0° in the measured XRD spectra are shown in Table 2 below. The crystallite sizes were calculated using the Sherrer Equation.

[0358] The Li2S particle size (D50 particle size) of the composite cathode active materials manufactured in Manufacturing Examples 1 to 4 and Comparative Manufacturing Examples 1 to 11 was measured using a laser-based particle size analyzer (PSA) and a scanning electron microscope. The Li2S particle size of the composite cathode active material is the arithmetic mean of the particle sizes of multiple Li2S particles measured using software from scanning electron microscope images. The measurement results are shown in Table 2 below.

[0359]

[0360] Classification 1st stage milling 2nd stage milling Solid solution formation Li2S crystallite size [nm] Li2S particle size [㎛] Manufacturing example 1 (28 G, 10 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 10 hr 600 rpm, 28 G, 10 hr ○ Less than 9.81 Manufacturing example 2 (28 G, 8 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 8 hr 600 rpm, 28 G, 8 hr ○ Less than 7.21 Comparative manufacturing example 1 (28 G, 1 hr) (Li2S-LiI-CNF complex) 600 rpm, 28 G, 1 hr 600 rpm, 28 G, 1 hr ○ Less than 20.11 Comparative example 2 (28 G, 20 hr)(Li2S-LiI-CNF complex)600 rpm, 28 G, 20 hr600 rpm, 28 G, 20 hr△11.81 Less than Comparative Manufacturing Example 3 (Li2S-LiI-CNF complex)510 rpm, 20 G, 10 hr510 rpm, 20 G, 10 hr○9.91 Less than Comparative Manufacturing Example 4 (7 G, 10 hr)(Li2S-LiI-CNF complex)300 rpm, 7 G, 10 hr300 rpm, 7 G, 10 hr×27.23 Comparative Manufacturing Example 5 (38 G, 10 hr)(Li2S-LiI-CNF complex)700 rpm, 38 G, 10 hr700 rpm, 38 G, 10 hr△15.62 Comparative Manufacturing Example 6 (0 G)(Li2S+ CNF simple mixture)--×66.678Comparative manufacturing example 7 (28 G, 1 hr)(Li2S-CNF complex)600 rpm, 20 G, 2 hr-×24.073Comparative manufacturing example 8 (28 G, 10 hr)(Li2S-CNF complex)600 rpm, 20 G, 10 hr-×9.891Less thanComparative manufacturing example 9 (28 G, 10 hr)(Li2S-CNF-LiI complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr×15.22Comparative manufacturing example 10 (28 G, 10 hr)(Li2S-SE-CNF complex)600 rpm, 28 G, 10 hr600 rpm, 28 G, 10 hr×8.Comparative manufacturing example 11 (28 G, 2 hr) (Li2S-LiI-CNF complex) 600 rpm, 20 G, 2 hr - ○223.

[0361] As shown in Table 2, the Li2S-LiI-CNF composites of Preparation Examples 1 and 2 included a Li2S-LiI solid solution, had a Li2S crystallite size of less than 9.9 nm, and had a Li2S particle size of 2 μm or less. In the Li2S-LiI-CNF composite of Comparative Preparation Example 1, the size of the Li2S crystallites was 9.9 nm or more due to a decrease in the milling energy during the preparation, and in the Li2S-LiI-CNF composite of Comparative Preparation Example 2, when the milling energy increased during the preparation, LiI was phase separated into a separate phase and a solid solution was not formed, and the size of the Li2S crystallites also increased. In addition, in the Li2S-LiI-CNF composite of Comparative Preparation Example 4, a Li2S-LiI solid solution was not formed due to an excessive decrease in the milling energy during the preparation. And in the Li2S-LiI-CNF complex of Comparative Manufacturing Example 5, the Li2S-LiI solid solution was not properly formed due to heat generation caused by increased milling energy during manufacturing.

[0362] The Li2S-LiI-CNF composite of Comparative Manufacturing Example 11 was manufactured in the first step, so it included a Li2S-LiI solid solution, but the Li2S crystallite size increased, and the Li2S particle size of the composite exceeded 2 μm.

[0363] The simple mixture of Li2S and CNF of Comparative Manufacturing Example 6, the Li2S-CNF complexes of Comparative Manufacturing Examples 5 to 6, and the Li2S-SE-LiI complex of Comparative Manufacturing Example 10 did not form a solid solution.

[0364] In the Li2S-CNF-LiI complex of Comparative Manufacturing Example 9, a Li2S-LiI solid solution was not properly formed because the Li2S-CNF complex was manufactured in the first step and then the Li2S-CNF-LiI complex was manufactured in the second step.

[0365] Evaluation Example 3: Charge / Discharge Test

[0366] The charge / discharge characteristics of the solid secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated by the following charge / discharge test.

[0367] Charge and discharge tests were performed by placing the all-solid-state secondary battery in a constant temperature chamber at 45°C.

[0368] The first cycle involved charging for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 2.5 V to 2.8 V. Subsequently, discharging was performed for 12.5 hours at a constant current of 0.1 C until the battery voltage reached 0.3 V.

[0369] The discharge capacity of the first cycle was taken as the standard capacity. The standard capacity is expressed as the specific capacity of Li2S in Table 2 below.

[0370] After the second cycle, charging and discharging were performed for up to 150 cycles under the same conditions as the first cycle. The measurement results are shown in Table 3 below. The initial efficiency is expressed by Equation 1 below.

[0371] <Formula 1>

[0372] Initial efficiency [%] = [1st cycle discharge capacity / 1st cycle charge capacity] × 100

[0373] The cycle count is the number of cycles required for the discharge capacity to decrease to 80% of the standard capacity after the second cycle. As the cycle count increases, the battery is considered to have better life characteristics.

[0374] Classification Anode capacity [mAh / g] Electrode density (mg / cm2) Electrode capacity (mAh / g) Initial efficiency [%] Number of cycles (times) Example 1 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder free 9001036083200 Example 2 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder free 8709.839183150 Example 3 (Li2S+LiI+CNF)+GPE(TMPTA)+Sulphide system SE 9201031781170 Example 4 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder Containing 82010.132082180 Example 5 (Li2S+LiI+CNF)+GPE(ETPTA) 9009.93608275 Example 6 (Li2S+LiI+CNF)+GPE(DEGDA) 91010.23648455 Example 7 (Li2S+LiI+CNF)+GPE(TEGDA) 9059.83628340 Comparative Example 1 (Li2S+LiI+CNF)+sulfide system SE1000104008230 Comparative Example 2 (Li2S+LiI+CNF)+GPE(monofunctional crosslinking monomer)+sulfide system SE9209.93688120 Comparative Example 3 (Li2S+CNF)+GPE free+binder Containing 50010.5250785 Comparative Example 4(Li2S+LiI+CNF)+sulfide system SE4009.92007810

[0375] As shown in Table 3, the solid secondary batteries of Examples 1 to 7 showed improved discharge capacity, initial efficiency, and life characteristics compared to Comparative Examples 1 to 4. The solid secondary battery of Example 1 showed the best electrode capacity, initial efficiency, and life characteristics, and the solid secondary battery of Example 2 showed a somewhat reduced life characteristics due to a decrease in the content of GPE compared to Example 1, which resulted in poor binding characteristics. And

[0376] The solid secondary battery of Example 3 contained more sulfide-based solid electrolyte than that of Example 1, so that the initial capacity increased, but the life characteristics decreased because the content of GPE decreased.

[0377] The solid secondary battery of Example 4 contained more binder than that of Example 1, so the initial resistance increased, the ionic conductivity decreased, the initial efficiency decreased somewhat, and the life characteristics were similar. The solid secondary battery of Example 5 had a reduced life characteristics because the chain length of ETPTA, a monomer for forming GPE, was longer than that of TMPTA, so the GPE was not formed densely, and the solid secondary batteries of Examples 6 and 7 had a somewhat reduced life compared to the solid secondary battery of Example 1, similar to that of Example 5.

[0378] The solid secondary battery of Comparative Example 1 showed a significantly reduced lifespan due to the presence of side reactions caused by the use of only a sulfide-based solid electrolyte. In addition, the solid secondary battery of Comparative Example 2 showed a significantly reduced lifespan due to the difficulty in forming GPE by using a GPE-forming monomer having one functional group. In addition, the solid secondary battery of Comparative Example 3 showed a reduced initial capacity and reduced lifespan due to the insufficient role of an ion conductor in the positive electrode, and the solid secondary battery of Comparative Example 4 showed a result in which it was difficult to develop an initial capacity due to the absence of LiI.

[0379] Evaluation Example 4: High-rate characteristics

[0380] The high-rate characteristics of the solid secondary batteries manufactured in Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated by the following charge-discharge test. The charge-discharge test was performed by placing the solid secondary batteries in a constant temperature bath at 45°C.

[0381] Each solid-state secondary battery was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.5 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 2.5 V in constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.05 C rate until the voltage reached 0.3 V (vs. Li) during discharge (formation cycle).

[0382] Each solid-state secondary battery was charged at a constant current of 0.1 C rate at 45°C until the voltage reached 2.5 V (vs. Li), and then cut-off at a current of 0.05 C rate while maintaining 2.5 V in constant voltage mode. Subsequently, the battery was discharged at a constant current of 0.1 C rate until the voltage reached 0.3 V (vs. Li) (first cycle).

[0383] The lithium battery that had undergone the Mars cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.2 C rate until the voltage reached 0.3 V (vs. Li) (second cycle).

[0384] The lithium battery that had undergone the first cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.33 C rate until the voltage reached 0.3 V (vs. Li) (second cycle).

[0385] The lithium battery that had undergone the second cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 0.5 C rate until the voltage reached 0.3 V (vs. Li) (third cycle).

[0386] The lithium battery that had undergone the third cycle was charged at a constant current of 0.2 C rate at 45°C until the voltage reached 2.5 V (vs. Li). Subsequently, it was discharged at a constant current of 1.0 C rate until the voltage reached 0.3 V (vs. Li) (4th cycle).

[0387] In all charge / discharge cycles, a 10-minute pause was observed after each charge / discharge cycle. Some of the results of the room-temperature charge / discharge experiments are shown in Table 4 below. The high-rate characteristics are defined by Equation 2 below.

[0388] <Formula 2>

[0389] High-rate characteristic [%] = [Discharge capacity in the 4th cycle / Discharge capacity in the 1st cycle] × 100

[0390] The cathode polarity characteristics (1C / 0.1C) [%] Example 1 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder-free 63 Example 2 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder-free 55 Example 3 (Li2S+LiI+CNF)+GPE(TMPTA)+Sulphide system SE 53 Example 4 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder containing 59 Example 5 (Li2S+LiI+CNF)+GPE(ETPTA) 57 Example 6 (Li2S+LiI+CNF)+GPE(DEGDA) 52 Example 7 (Li2S+LiI+CNF)+GPE(TEGDA) 51 Comparative Example 1 (Li2S+LiI+CNF)+Sulphide system SE55 Comparative Example 2 (Li2S+LiI+CNF)+GPE(monofunctional crosslinking monomer)+sulfide system SE52 Comparative Example 3 (Li2S+CNF)+binder-free 30 Comparative Example 4 (Li2S+LiI+CNF)+sulfide system SE45

[0391] As shown in Table 4, the solid secondary batteries of Examples 1 to 7 had improved high-rate characteristics compared to the solid secondary batteries of Comparative Examples 1 to 4.

[0392] Evaluation Example 5: Flexibility Evaluation

[0393] The flexibility of the solid secondary batteries of Examples 1 to 7 was evaluated by evaluating the time until fracture using a 3-point bending test, and the results are shown in Table 5 below.

[0394] Example 1 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder-free 54 Example 2 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder-free 48 Example 3 (Li2S+LiI+CNF)+GPE(TMPTA)+Sulphide-based SE 36 Example 4 (Li2S+LiI+CNF)+GPE(TMPTA)+Binder-containing 30 Example 5 (Li2S+LiI+CNF)+GPE(ETPTA) 35 Example 6 (Li2S+LiI+CNF)+GPE(DEGDA) 24 Example 7 (Li2S+LiI+CNF)+GPE(TEGDA) 29 Comparative Example 1 (Li2S+LiI+CNF)+Sulphide-based SE 15 Comparative Example 2(Li2S+LiI+CNF)+GPE(monofunctional crosslinking monomer)+sulfide-based SE21Comparative example 3(Li2S+CNF)+binder-free 11Comparative example 4(Li2S+LiI+CNF)+sulfide-based SE8

[0395] As a result of the evaluation, the solid secondary batteries of Examples 1 to 7 showed an increase in the time until rupture, as can be seen in Table 5, and thus, their flexibility was improved compared to the solid secondary batteries of Comparative Examples 1 to 4.

Claims

1. It comprises an anode; a cathode; and an electrolyte layer disposed between the anode and the cathode, The above negative electrode includes a negative electrode current collector and a first negative electrode active material layer disposed on one surface of the negative electrode current collector, The above positive electrode 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 above positive electrode active material layer includes a composite positive electrode active material and a gel polymer electrolyte, The above composite cathode active material comprises a M2S complex, wherein M is an alkali metal, and the alkali metal is Li or Na, A solid secondary battery containing a crosslinked polymer, wherein the gel polymer electrolyte is a polymerization product of a crosslinkable monomer having two or more crosslinking points.

2. In the first paragraph, the M2S complex is a solid secondary battery comprising a complex of M2S and a carbon-based material, a complex of M2S and a carbon-based material and a solid electrolyte, a complex of M2S and a solid electrolyte, a complex of M2S and a carbon-based material and an alkali metal salt, a complex of M2S and an alkali metal salt, a complex of M2S and a metal carbide, a complex of M2S and a carbon-based material and a metal carbide, a complex of M2S and a metal nitride, a complex of M2S and a carbon-based material and a metal nitride, or a combination thereof.

3. A solid secondary battery in the first paragraph, wherein the M2S complex includes a composite of M2S, an alkali metal salt, and a carbon-based material, the size of M2S crystallites obtained from the XRD spectrum of the complex is less than 9.9 nm, and the complex includes a solid solution of M2S and an alkali metal salt.

4. A solid secondary battery comprising 40 to 90 parts by weight of a composite positive electrode active material and 10 to 60 parts by weight of a gel polymer electrolyte per 100 parts by weight of the positive electrode active material layer in the first paragraph.

5. A solid secondary battery according to claim 1, wherein the crosslinking monomer is ethoxylated trimethylolpropane triacrylate, di(trimethylolpropane) tetraacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, dipropylene glycol diacrylate, dipropylene glycol dimethacrylate, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol dimethacrylate, dipentaerythritol pentaacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, propoxylated (3) trimethylolpropane triacrylate, propoxylated (6) trimethylolpropane triacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, or a combination thereof.

6. A solid secondary battery according to claim 1, wherein the gel polymer electrolyte comprises a liquid electrolyte containing an organic solvent and a lithium salt, and the content of the liquid electrolyte is 40 to 95 parts by weight based on 100 parts by weight of the gel polymer electrolyte.

7. In the second paragraph, the alkali metal salt is a lithium salt or a sodium salt, The molar ratio of the above M2S and alkali metal salt is 50:50 to 95:5, The above alkali metal salt is a binary compound or a ternary compound, The above binary compound comprises LiI, LiBr, LiCl, LiF, LiH, Li2O, Li2Se, Li2Te, Li3N, Li3P, Li3As, Li3Sb, Li3Al2, LiB3 or a combination thereof, or comprises NaI, NaBr, NaCl, NaF, Na2O, Na2Se, Na3N, Na3P, Na3As, Na3Sb, Na3Al2, NaB3 or a combination thereof, A solid secondary battery, wherein the ternary compound comprises Li3OCl, LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiNO3, Li2CO3, LiBH4, Li2SO4, Li3BO3, Li3PO4, Li4NCl, Li5NCl2, Li3BN2, or a combination thereof, or comprises Na3OCl, NaBF4, NaPF6, NaAsF6, NaClO4, NaNO3, NaAlO2, NaAlCl4, NaNO3, Na2CO3, NaBH4, Na2SO4, Na3BO3, Na3PO4, Na4NCl, Na5NCl2, Na3BN2, or a combination thereof.

8. In the second paragraph, the carbon-based material includes a fibrous carbon-based material, The above fibrous carbon material includes a carbon nanostructure, The above carbon nanostructure includes carbon nanofibers, carbon nanotubes, carbon nanobelts, carbon nanorods, or a combination thereof, A solid secondary battery, wherein the content of the carbon-based material is 1 to 10 wt% of the total weight of the positive electrode active material layer.

9. In the first paragraph, the positive electrode active material layer further includes a solid electrolyte, A solid secondary battery, wherein the content of the solid electrolyte is 1 to 10 parts by weight based on 100 parts by weight of the gel polymer electrolyte.

10. In the first paragraph, the negative electrode active material of the first negative electrode active material layer includes at least one selected from a carbon-based negative electrode active material and a metal-based negative electrode active material, The above carbon-based negative electrode active material includes amorphous carbon, crystalline carbon, porous carbon, or a combination thereof. A solid secondary battery, wherein the metal-based negative electrode active material comprises gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), or a combination thereof.

11. In the first paragraph, the negative electrode active material of the first negative electrode active material layer is a solid secondary battery having a structure in which a mixture of a metal-based negative electrode active material and a carbon-based material or a metal-based negative electrode active material is supported on a carbon-based material.

12. A solid secondary battery according to claim 1, wherein the negative electrode comprises a negative electrode current collector and a lithium host layer disposed on one surface of the negative electrode current collector, the lithium host layer comprises a lithium host structure, the lithium host structure comprises one or more lithium hosts, the lithium host comprises a carbon-based lithium host, a metal-based lithium host, a polymer-based lithium host, or a combination thereof, and comprises a first inactive member disposed on one surface of the negative electrode.

13. In the first paragraph, the negative electrode current collector is disposed between the negative electrode current collector and the first negative electrode active material layer. Further comprising a second negative electrode active material layer, The second negative electrode active material layer is a metal layer containing lithium or a lithium alloy, and the second negative electrode active material layer is a plated layer. A solid secondary battery, wherein the thickness of the first negative electrode active material layer is greater than the thickness of the second negative electrode active material layer.

14. An all-solid-state secondary battery according to claim 1, further comprising an inert elastic member disposed on one surface of the positive or negative electrode, or not comprising the inert elastic member.

15. An all-solid-state secondary battery according to claim 1, wherein the electrolyte layer comprises a solid electrolyte, a gel electrolyte, or a combination thereof, the solid electrolyte comprises a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, and the gel electrolyte comprises a polymer gel electrolyte.

16. In the 15th paragraph, the sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX, X is a halogen element, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n , m, n are positive numbers respectively, Z is one of Ge, Zn or Ga, Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , p and q are positive numbers respectively, 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 , at least one selected from 0≤x≤2, and the sulfide-based solid electrolyte comprises an argyrodite-type solid electrolyte, and the argyrodite-type solid electrolyte comprises at least one selected from Li6PS5Cl, Li6PS5Br, and Li6PS5I.

17. An all-solid-state secondary battery according to claim 1, wherein at least one of the positive electrode current collector and the negative electrode current collector comprises a base film and a metal layer disposed on one or both sides of the base film, wherein 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, and 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.

18. In the first paragraph, the electrolyte layer includes a solid electrolyte, a gel electrolyte, or a combination thereof, The above solid electrolyte includes a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a polymer solid electrolyte, or a combination thereof, A solid secondary battery, wherein the gel electrolyte comprises a polymer gel electrolyte.

19. A step of milling a composition including M2S and an alkali metal salt to obtain a milled product; A step of manufacturing a positive electrode by adding and mixing a composition for forming a gel polymer electrolyte containing a crosslinking monomer for forming a gel polymer electrolyte to the above-mentioned milled product; Step of preparing the cathode; and A step of placing an electrolyte layer between the anode and cathode, A method for manufacturing a solid secondary battery, wherein the composition for forming the gel polymer electrolyte comprises a liquid electrolyte containing a lithium salt and an organic solvent and a crosslinking agent, wherein M is an alkali metal and the alkali metal is Li or Na.

20. A method for manufacturing a solid secondary battery, wherein in the step of milling the composition including the M2S and an alkali metal salt to obtain a milled product in the step of claim 19, a carbon-based material is further added, and the step of milling the composition including the M2S and an alkali metal salt to obtain a milled product comprises the steps of milling the M2S and the alkali metal salt to obtain an M2S-alkali metal salt complex; and the step of milling the composition including the M2S-alkali metal salt complex and a carbon-based material to obtain a milled product.

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